[ { "Question": "
\n
\n

\n The diagram illustrates some of the processes involved in DNA replication.\n

\n

\n \n

\n

\n [Source: Rohrmann, G., 2019.\n \n AcMNPV DNA replication\n \n . [diagram online] Available at:\n
\n https://www.ncbi.nlm.nih.gov/books/NBK543453/figure/ch05.F1/ [Accessed 26 October 2021].]\n

\n

\n

\n

\n What is shown in the diagram?\n

\n

\n A.  DNA polymerase bonding nucleotides in a 3’ to 5’ direction\n

\n

\n B.  Single-stranded DNA-binding proteins on the old strands\n

\n

\n C.  Gyrase reforming the double helix\n

\n

\n D.  DNA ligase joining Okazaki fragments in the leading strand\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "
\n

\n Despite the problems with question 25, many questions performed very well. Question 27 is an example. Candidates had to study a complex diagram of DNA replication and then decide which of four statements about replication was correct. Half of the candidates were successful and the discrimination index at 0.73 was exceptionally high, showing that the question was a very effective test.\n

\n
\n", "question_id": "22N.1A.HL.TZ0.27", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d1-2-protein-synthesis", "d1-2-17-initiation-of-translation" ] }, { "Question": "
\n
\n

\n Outline\n \n four\n \n types of membrane transport, including their use of energy.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n

\n a. simple diffusion is passive movement of molecules/ions along a concentration gradient ✔\n

\n

\n b. facilitated diffusion is passive movement of molecules/ions along a concentration gradient through a protein channel «without use of energy» ✔\n

\n

\n c. osmosis is the passage of water\n \n through a membrane\n \n from lower solute concentration to higher ✔\n \n OWTTE\n \n

\n

\n d. active transport is movement of molecules/ions\n \n against the concentration gradient\n \n «through membrane pumps» with the use of ATP/energy ✔\n \n Active transport requires mention of the use of energy.\n \n

\n

\n e. endocytosis is the infolding of membrane/formation of vesicles to bring molecules into cell with use of energy\n
\n \n \n OR\n \n \n
\n exocytosis is the infolding of membrane/formation of vesicles to release molecules from cell with use of energy ✔\n

\n

\n f. chemiosmosis occurs when protons diffuse through ATP synthase «in membrane» to produce ATP ✔\n

\n

\n \n The description of each type of transport should include the name and brief description.\n \n

\n

\n \n mpa, mpb and mpc require reference to concentration.\n \n

\n

\n

\n
\n", "Examiners report": "
\n

\n Membrane transport – In spite of the question asking about energy, many lost easy marks by forgetting to refer to it. Others did not mention the gradients. In osmosis, please stress to the students which concentration they are talking about. They should be talking clearly about water potential or solute concentration.\n

\n
\n", "question_id": "19M.2.SL.TZ2.A", "topics": [ "b-form-and-function" ], "subtopics": [ "b2-1-membranes-and-membrane-transport", "b2-1-5-movement-of-water-molecules-across-membranes-by-osmosis-and-the-role-of-aquaporins", "b2-1-6-channel-proteins-for-facilitated-diffusion", "b2-1-7-pump-proteins-for-active-transport", "b2-1-8-selectivity-in-membrane-permeability" ] }, { "Question": "
\n
\n

\n In the micrograph of a plant stem, which letter indicates the xylem?\n

\n

\n \n

\n

\n [Source: adapted from Kelvinsong/https://creativecommons.org/licenses/by/3.0/deed.en]\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "19N.1A.SL.TZ0.33", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-2-transport", "b3-2-9-distribution-of-tissues-in-a-transverse-section-of-the-stem-of-a-dicotyledonous-plant" ] }, { "Question": "
\n
\n

\n State the type of inheritance shown.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n «gene/autosomal» linkage ✔\n

\n

\n \n Reject sex linkage\n \n

\n
\n", "Examiners report": "None", "question_id": "19N.2.HL.TZ0.A", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-2-inheritance", "d3-2-17-punnett-grids-for-predicting-genotypic-and-phenotypic-ratios-in-dihybrid-crosses-involving-pairs-of-unlinked-autosomal-genes", "d3-2-18-loci-of-human-genes-and-their-polypeptide-products", "d3-2-19-autosomal-gene-linkage", "d3-2-20-recombinants-in-crosses-involving-two-linked-or-unlinked-genes" ] }, { "Question": "
\n
\n

\n The graph shows the incidence of trisomy resulting from non-disjunction in pregnancies at different maternal ages.\n

\n

\n \n

\n

\n [Source: Center for Disease Control]\n

\n

\n

\n

\n What can be inferred from the graph?\n

\n

\n A. The incidence of three copies of a chromosome increases directly in proportion with the age of the mother.\n

\n

\n B. The incidence of three sets of chromosomes increases from age 20.\n

\n

\n C. The incidence of three copies of a chromosome increases the most from age 35.\n

\n

\n D. The incidence of three sets of chromosomes increases the most from age 30.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "
\n

\n This question was in badly answered by the most capable candidates and therefore discriminated very badly. Unfortunately, candidates confused the words sets and copies. Some candidates believed the increase was proportionate, failing to realize a straight line should have been drawn if this was the case.\n

\n
\n", "question_id": "19M.1A.SL.TZ2.13", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-1-cell-and-nuclear-division", "d2-1-10-down-syndrome-and-non-disjunction" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Explain the change in heart rate during the period of hibernation.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n decreased/slower heart rate because bears less active/use less energy;\n
    2. \n
  2. \n less (cell) respiration / lower (rate of) metabolism;\n
    3. \n
  3. \n less oxygen/glucose required / less CO\n \n 2\n \n produced/needing to be removed;\n
    4. \n
  4. \n less muscle contraction/muscles require less blood;\n
    5. \n
  5. \n conserves energy;\n
    6. \n
\n
\n", "Examiners report": "
\n

\n Many candidates mentioned lack of activity as a reason for lower heart rate and some went on to mention reduced respiration rates or other aspects of physiology. Other candidates failed to offer an explanation and instead just described the data. A few claimed wrongly that bone porosity was directly proportional to age, in which case all those of a certain age would have the same degree of osteoporosis, which is plainly not the case.\n

\n
\n", "question_id": "22M.2.SL.TZ1.1C", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-3-homeostasis", "d3-3-1-homeostasis-as-maintenance-of-the-internal-environment-of-an-organism", "d3-3-2-negative-feedback-loops-in-homeostasis" ] }, { "Question": "
\n
\n

\n What happens during blood clotting?\n

\n

\n
\n A.  A chain reaction causes platelets to release antibodies to avoid infections.\n

\n

\n B.  Thrombin is converted into fibrinogen after a series of chemical reactions.\n

\n

\n C.  Sealing of wounds by fibrinogen makes platelets release antibodies for clotting.\n

\n

\n D.  Chemical reactions cause wounds to seal after platelets release clotting factors.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "23M.1A.SL.TZ1.26", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-2-defence-against-disease", "c3-2-3-sealing-of-cuts-in-skin-by-blood-clotting" ] }, { "Question": "
\n
\n

\n Suggest, with a reason, how the activity of the sloth varies with ambient temperature.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n the sloth will be more active at higher temperatures as it takes in more food for energy;\n
    2. \n
  2. \n as temperature rises, the sloth uncurls to dissipate/lose heat;\n
    3. \n
\n

\n \n Reason required\n \n .\n

\n
\n", "Examiners report": "
\n

\n Good reasoning was not seen often, best answers needed some of the elements in this linkage: higher temperature led to uncurling which led to movement which led to eating because of energy needs; \"sloth prefers staying curled up so cold does not affect them\" or \"sloth enjoys staying curled up\" were not acceptable\n

\n
\n", "question_id": "22M.2.SL.TZ1.H", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-3-homeostasis", "d3-3-1-homeostasis-as-maintenance-of-the-internal-environment-of-an-organism", "d3-3-2-negative-feedback-loops-in-homeostasis" ] }, { "Question": "
\n
\n (a.iii)\n
\n
\n

\n DNA has regions that do not code for proteins. State\n \n two\n \n functions of these regions.\n

\n

\n 1.\n

\n

\n 2.\n

\n

\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. promoters / operators / regulation of gene expression/transcription ✔\n

\n

\n b. telomeres/give protection to the end of chromosomes «during cell division» ✔\n

\n

\n c. genes for tRNA/rRNA production ✔\n

\n

\n d. other valid function for non-coding sequence ✔\n

\n

\n \n Do not accept stop codon, accept centromeres (connecting sister chromatids).\n \n

\n
\n", "Examiners report": "
\n

\n This question was well answered. The occasional answer made reference to processes associated with translation.\n

\n
\n", "question_id": "19M.2.HL.TZ2.2A.III", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d1-2-protein-synthesis", "d1-2-14-non-coding-sequences-in-dna-do-not-code-for-polypeptides" ] }, { "Question": "
\n
\n

\n Which plasma membrane is the least fluid at high temperatures?\n

\n

\n \n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "
\n

\n This question did not discriminate well with many candidates selecting option D which shows the membrane with no cholesterol.\n

\n
\n", "question_id": "22M.1A.HL.TZ2.3", "topics": [ "b-form-and-function" ], "subtopics": [ "b2-1-membranes-and-membrane-transport", "b2-1-10-fluid-mosaic-model-of-membrane-structure", "b2-1-12-cholesterol-and-membrane-fluidity-in-animal-cells" ] }, { "Question": "
\n
\n (d)\n
\n
\n

\n Outline\n \n two\n \n adaptations for water conservation in leaves of desert plants.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n \n Mark the first two answers only\n \n
\n (thick) wax layer/cuticle;\n
\n hairs on leaves/rolled leaves;\n
\n sunken stomata/stomata in pits/stomata opening at night/CAM physiology;\n
\n (leaves reduced to) spines/needles/no/few/small leaves/low surface area (to volume ratio) of leaves;\n
\n thick stems/water storage tissue/vertical stems (to avoid most intense sunlight);\n

\n
\n", "Examiners report": "
\n

\n A wide range of leaf adaptations were suggested and most candidates gave one or two that were accepted. Root adaptations were not accepted as the question asked for features of leaves.\n

\n
\n", "question_id": "22N.2.HL.TZ0.5D", "topics": [ "b-form-and-function" ], "subtopics": [ "b2-3-cell-specialization", "b2-3-7-adaptations-to-increase-surface-area-to-volume-ratios-of-cells" ] }, { "Question": "
\n
\n (c.i)\n
\n
\n

\n Identify, with a reason, the sex of this individual.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n male because «X and» Y chromosome present\n
\n \n \n OR\n \n \n
\n male because sex chromosomes/last two chromosomes/pair 21 are unpaired/different «from each other»/not homologous ✔\n

\n

\n \n The answer must include “male” and the reason.\n \n

\n
\n", "Examiners report": "
\n

\n 90 % of candidates correctly identified the individual as male, because the two sex chromosomes were different in size so must be an X and a Y. The other 10% mostly thought that there were two X chromosomes present, perhaps because pair 20 were X shaped.\n

\n
\n", "question_id": "19M.2.SL.TZ1.2C.I", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a3-1-diversity-of-organisms", "a3-1-7-karyotyping-and-karyograms" ] }, { "Question": "
\n
\n

\n Some scientists predict that, if humans continue to produce carbon dioxide at the current rate, the pH of the oceans will become more acidic. Suggest possible effects on the coral reefs.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n a. corals would not be able to maintain their skeletons;\n
\n b. (if coral reefs are lost) habitat will be lost;\n
\n c. some organisms/coral can decline if the water becomes too acidified;\n
\n d. coral bleaching could occur/become worse\n
\n OR\n
\n coral could expel their mutualistic alga/zooxanthellae;\n
\n e. enzymes could be denatured;\n

\n
\n", "Examiners report": "
\n

\n In 1d weaker students incorrectly wrote about the sea becoming acidic as the pH was increasing (sic). Indeed, it is becoming\n \n more\n \n acidic, as the pH is\n \n decreasing\n \n slightly, leading to more bleaching and the decrease in population of some creatures.\n

\n
\n", "question_id": "21N.2.SL.TZ0.D", "topics": [ "d-continuity-and-change", "b-form-and-function" ], "subtopics": [ "d4-3-climate-change", "d4-3-7-threats-to-coral-reefs-as-an-example-of-potential-ecosystem-collapse", "b4-1-adaptation-to-environment", "b4-1-5-conditions-required-for-coral-reef-formation" ] }, { "Question": "
\n
\n

\n Which products of the light-dependent reactions are used in the Calvin cycle?\n

\n

\n A. O\n \n 2\n \n and hydrogen ions\n

\n

\n B. ATP and CO\n \n 2\n \n

\n

\n C. Electrons and reduced NADP\n

\n

\n D. ATP and reduced NADP\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "22M.1A.HL.TZ1.31", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-3-photosynthesis", "c1-3-19-interdependence-of-the-light-dependent-and-light-independent-reactions" ] }, { "Question": "
\n
\n

\n Where can the entire genome of an organism be found?\n

\n

\n A. In the DNA present in plasmids of a bacterial cell\n

\n

\n B. In the DNA present in the nucleus of a eukaryotic cell\n

\n

\n C. In the DNA present in the nucleus and chloroplasts of a plant cell\n

\n

\n D. In the DNA present in the nucleus and mitochondria of an animal cell\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "
\n

\n This answer was not well answered by the candidates and did not discriminate well. Most candidates incorrectly answered B failing to include the mitochondrial DNA in the genome.\n

\n
\n", "question_id": "22M.1A.SL.TZ2.10", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a3-1-diversity-of-organisms", "a3-1-8-unity-and-diversity-of-genomes-within-species" ] }, { "Question": "
\n
\n

\n A dihybrid cross was carried out between two plants to determine whether the genes for seed shape and colour are linked. If the genes are unlinked, the expected ratio of 9:3:3:1 should occur. A chi-squared test was carried out on the observed results of the cross. The critical value for chi squared at the 5 % level of significance in this test was 7.82. The calculated value for chi squared was 6.25. What can be concluded from this data?\n

\n

\n A. The results prove that the genes are linked.\n

\n

\n B. The results prove that the genes are unlinked.\n

\n

\n C. There is significant evidence that the genes are linked.\n

\n

\n D. There is significant evidence that the genes are unlinked.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "
\n

\n Although slightly less than half of candidates answered correctly and the discrimination index was respectable rather than good, this was a relatively successful question on statistical hypothesis testing, which is typically a difficult area both for question setters and candidates. Performance seems to be improving in this part of the program.\n

\n
\n", "question_id": "21N.1A.HL.TZ1.35", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-2-inheritance", "d3-2-17-punnett-grids-for-predicting-genotypic-and-phenotypic-ratios-in-dihybrid-crosses-involving-pairs-of-unlinked-autosomal-genes" ] }, { "Question": "
\n
\n

\n Explain how natural selection could increase the prevalence of an antibiotic resistance gene in a species of soil bacterium.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n if antibiotic is in the environment/soil there is selection (pressure);\n
    2. \n
  2. \n bacteria without resistance (gene) die / converse;\n
    3. \n
  3. \n bacteria with resistance (gene) reproduce\n
    \n \n OR\n \n
    \n bacteria exchange/obtain resistance genes using plasmids/by conjugation;\n
    4. \n
  4. \n offspring inherit (the gene for) resistance/resistance passed on (to offspring);\n
    5. \n
\n

\n \n Do not award marks for general statements about natural selection – answers must refer to antibiotic resistance.\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.2.HL.TZ1.A", "topics": [ "d-continuity-and-change", "c-interaction-and-interdependence" ], "subtopics": [ "d4-1-natural-selection", "d4-1-15-artificial-selection-by-deliberate-choice-of-traits", "c3-2-defence-against-disease", "c3-2-14-evolution-of-resistance-to-several-antibiotics-in-strains-of-pathogenic-bacteria" ] }, { "Question": "
\n
\n

\n The graph shows the mitotic index in the roots of lentil plants at different distances from the end of the root.\n

\n

\n \n

\n

\n [Source:\n \n Physiologia Plantarum\n \n , Volume 105, Issue 1, January 1999, Pages 171–178, Effect of microgravity on the cell cycle\n
\n in the lentil root F. Yu, D. Driss-Ecole, J. Rembur, V. Legué, G. Perbal Wiley Online Library: https://onlinelibrary.wiley.\n
\n com/doi/abs/10.1034/j.1399-3054.1999.105125.x]\n

\n

\n

\n

\n What can be deduced from the graph?\n

\n

\n A. As the distance from the end of the root increases, more cells are undergoing mitosis.\n

\n

\n B. At 0.5 mm from the end of the root, most of the cells are in prophase.\n

\n

\n C. There were fewer cells observed at 1.5 mm than at 0.5 mm.\n

\n

\n D. As the distance from the end of the root increases, the percentage of cells in interphase increases.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "21N.1A.HL.TZ0.5", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-1-cell-and-nuclear-division", "d2-1-17-differences-between-tumours-in-rates-of-cell-division-and-growth-and-in-the-capacity-for-metastasis-and-invasion-of-neighbouring-tissue" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Outline energy flow through a community in a natural ecosystem.\n

\n
\n
\n

\n [5]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n communities are made up of populations of different species;\n
    2. \n
  2. \n plants receive energy from the sun/light;\n
    3. \n
  3. \n convert it to chemical energy through\n \n photosynthesis\n \n ;\n
    4. \n
  4. \n chemical energy is stored in organic/C-compounds;\n
    5. \n
  5. \n the energy is passed to other organisms through feeding / reference to food chain;\n
    6. \n
  6. \n respiration (of plants and animals) converts the chemical energy (of C-compounds) to other useful forms of energy;\n
    7. \n
  7. \n eventually the chemical energy is lost as heat energy;\n
    8. \n
  8. \n energy is non-recyclable/lost from a community/ecosystem;\n
    9. \n
  9. \n energy losses between trophic levels limit food chains/mass of top trophic levels/only about 10 % of energy is transferred;\n
    10. \n
\n
\n", "Examiners report": "
\n

\n This was well attempted with an average score of 3. The question was about energy, but weaker students also tended to include biomass. Fortunately, very few students failed to grasp the idea that the energy is lost from the ecosystem and not recycled.\n

\n
\n", "question_id": "22M.2.SL.TZ2.7A", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c4-2-transfers-of-energy-and-matter", "c4-2-3-flow-of-chemical-energy-through-food-chains", "c4-2-12-reductions-in-energy-availability-at-each-successive-stage-in-food-chains-due-to-large-energy-losses-between-trophic-levels" ] }, { "Question": "
\n
\n (f)\n
\n
\n

\n Compare and contrast the effect of clothianidin and thiacloprid treatments on the concentration of acetylcholine in royal jelly.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. both neonicotinoids reduce the concentration of acetylcholine in royal jelly (compared to control) ✔\n

\n

\n b. clothianidin reduces the concentration of acetylcholine in royal jelly more than thiacloprid (but perhaps not statistically different) ✔\n

\n

\n c. clothianidin is used in smaller concentrations (than thiacloprid) so no firm conclusion can be obtained ✔\n

\n

\n \n Need one similarity and one difference.\n \n

\n
\n", "Examiners report": "
\n

\n In general, the data analysis question was well attempted by the majority of students.\n

\n

\n A compare and contrast question, that required one similarity and one difference. Most were able to state that both treatments reduce the acetylcholine concentration in the royal jelly and that clothianidin reduced it more than thiacloprid. The more astute also commented on the differences in concentrations of the insecticides.\n

\n
\n", "question_id": "21M.2.HL.TZ2.1F", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c2-2-neural-signalling", "c2-2-12-effects-of-exogenous-chemicals-on-synaptic-transmission" ] }, { "Question": "
\n
\n

\n Compare and contrast the trends for\n \n O. rufipogon\n \n and\n \n O. sativa indica\n \n .\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n \n Similarities\n \n
\n both show diversity\n
\n \n \n OR\n \n \n
\n similar pattern/peaks and troughs in the first part of the chromosome / up to «approximately» 1.5 megabases\n
\n \n \n OR\n \n \n
\n similar diversity between 2.4 to 2.7 mb\n
\n \n \n OR\n \n \n
\n both highest at 0.7 mb ✔\n

\n

\n \n Differences\n \n
\n there are «two» major drops in diversity for\n \n O. sativa indica\n \n whereas none for\n \n O. rufipogon\n \n /much wider fluctuations in\n \n O. s. indica\n \n
\n \n \n OR\n \n \n
\n \n O.s. indica\n \n much lower at PROG1\n
\n \n \n OR\n \n \n
\n \n O.rufipogon\n \n does not drop < 2.5 whereas\n \n O. s. indica\n \n approaches 0\n
\n \n \n OR\n \n \n
\n \n O.rufipogon\n \n generally higher than\n \n O. s. indica\n \n after 1.4-1.5 ✔\n

\n

\n \n One answer from mpa and one from mpb required for 2 [max]\n \n .\n

\n

\n \n Accept a statement of where the drops occur.\n \n

\n
\n", "Examiners report": "None", "question_id": "19N.2.SL.TZ0.C", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a3-1-diversity-of-organisms" ] }, { "Question": "
\n
\n

\n The image shows a group of enveloped viral particles.\n

\n

\n \n

\n

\n \n [Source: Murphy, F. and Whitfield, S., n.d.\n \n Herpes virus image under the microscope\n \n . [image online] Available at: https://www.bbvaopenmind.com/en/science/research/virus-inspired-science/ [Accessed 3 July 2020].]\n \n

\n

\n
\n What is the most likely composition of the structure labelled X?\n

\n

\n
\n A.  Membrane derived from the host cell\n

\n

\n B.  Viral DNA\n

\n

\n C.  Viral cell walls\n

\n

\n D.  Viral enzymes\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "None", "question_id": "SPM.1A.HL.TZ0.14", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a2-3-viruses-(hl-only)", "a2-3-2-diversity-of-structure-in-viruses" ] }, { "Question": "
\n
\n

\n Draw labelled diagrams to show the structure of RNA nucleotides and how they are linked together to form a molecule of RNA.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n

\n a. ribose drawn as pentagon and labelled sugar/ribose;\n
\n b. base drawn with correct link to (C\n \n 1\n \n of) ribose and labelled base/nitrogenous base;\n
\n c. phosphate drawn with correct link to (C\n \n 5\n \n of) ribose and labelled P/phosphate;\n
\n d. two (or more) ribonucleotides drawn with correct link (C\n \n 3\n \n to C\n \n 5\n \n )\n

\n

\n \n

\n
\n", "Examiners report": "
\n

\n Many candidates were able to draw the structure of an RNA nucleotide and link it correctly by a 5’ to 3’ bond to another nucleotide. The commonest error was to show two strands of nucleotides linked by base pairing, indicating confusion between RNA and DNA.\n

\n
\n", "question_id": "21N.2.SL.TZ0.A", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a1-2-nucleic-acids", "a1-2-3-sugar-phosphate-bonding-and-the-sugar-phosphate-“backbone”-of-dna-and-rna", "a1-2-5-rna-as-a-polymer-formed-by-condensation-of-nucleotide-monomers" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Insulin is produced in β cells of the pancreas and not in other cells of the human body. Explain how differentiation of cells and regulation of gene expression allow proteins such as insulin to be produced in only certain types of body cell.\n

\n
\n
\n

\n [7]\n

\n
\n
\n", "Markscheme": "
\n

\n a. insulin production is determined by a gene ✔\n

\n

\n b. gene for insulin (is found in all cells), but only activated in (β cells of) pancreas ✔\n

\n

\n c. stem cells differentiate into specialized cells/(into pancreatic β) ✔\n

\n

\n d. during differentiation some genes are turned on and others off ✔\n

\n

\n e. insulin is a hormone that regulates the amount of glucose/sugar in blood ✔\n

\n

\n f. pancreatic β cells have sensors that detect glucose level in blood ✔\n

\n

\n g. an increase in glucose will increase transcription of mRNA of insulin ✔\n

\n

\n h. the site of transcription of insulin is in the pancreatic β cells ✔\n

\n

\n i. gene transcription is regulated by proteins that bind to specific base sequence in DNA/ enhancers/silencers/promoter proximal elements ✔\n

\n

\n j. regulatory sequences/proteins are specific to the gene they regulate / insulin regulator proteins are only found in in the pancreatic β cells ✔\n

\n

\n k. (DNA) methylation (usually) inhibits gene expression / (histone) acetylation promotes gene expression / tightness of coiling of DNA around histones affects gene expression ✔\n

\n

\n \n Accept sugar as equivalent to glucose\n \n .\n

\n
\n", "Examiners report": "
\n

\n In general, scores for this question were quite low. Candidates were too vague in their answers. Many failed to discuss chemical modification of DNA and the role of non-coding sequences in the regulation of gene expression.\n

\n
\n", "question_id": "21M.2.HL.TZ2.7C", "topics": [ "d-continuity-and-change", "a-unity-and-diversity" ], "subtopics": [ "d2-2-gene-expression-[hl-only]", "d2-2-4-epigenesis-as-the-development-of-patterns-of-differentiation-in-the-cells-of-a-multicellular-organism", "a2-2-cell-structure", "a2-2-13-cell-differentiation-as-the-process-for-developing-specialized-tissues-in-multicellular-organisms" ] }, { "Question": "
\n
\n

\n Which graph represents the action spectrum for a green plant receiving only blue light?\n

\n

\n \n

\n

\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "23M.1A.SL.TZ2.13", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-3-photosynthesis", "c1-3-6-similarities-and-differences-of-absorption-and-action-spectra" ] }, { "Question": "
\n
\n

\n Where in the nephron is most glucose reabsorbed?\n

\n

\n \n

\n

\n [Source: National Institute of Diabetes and Digestive and Kidney Diseases, n.d. [\n \n Nephron\n \n ]. [diagram online] Available at:\n
\n https://www.niddk.nih.gov/news/media-library/9164 [Accessed 23 March 2020].]\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "21N.1A.HL.TZ1.39", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-3-homeostasis", "d3-3-8-role-of-the-glomerulus-bowmans-capsule-and-proximal-convoluted-tubule-in-excretion" ] }, { "Question": "
\n
\n

\n What is always needed for seed germination?\n
\n
\n

\n

\n A.  Light\n

\n

\n B.  Oxygen\n

\n

\n C.  Carbon dioxide\n

\n

\n D.  Fertilizer\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "23M.1A.SL.TZ1.32", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-1-reproduction", "d3-1-12-dispersal-and-germination-of-seeds" ] }, { "Question": "
\n
\n

\n Explain the mechanism that prevents polyspermy during fertilization.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. cortical reaction (after first sperm nucleus enters the egg);\n
\n b. vesicles/cortical granules release their contents/enzymes (from the egg/zygote);\n
\n c. zona pellucida/glycoprotein coat/outer coat hardened / fertilization membrane formed;\n
\n d.\n \n enzymes\n \n of sperm/acrosome cannot digest (hardened coat)\n
\n \n OR\n \n
\n glycoproteins/ZP3 (in zona pellucida) altered so sperm cannot bind;\n

\n
\n", "Examiners report": "
\n

\n Answers were mixed. Most knew that there is a mechanism that prevents more sperm fusing with the egg after the first one and some gave accurate and detailed accounts of it.\n

\n
\n", "question_id": "21N.2.HL.TZ0.D", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-1-reproduction", "d3-1-15-mechanisms-to-prevent-polyspermy" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Y is the threshold potential. State what happens when the threshold potential is reached.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n sodium channels (start to) open\n
\n \n \n OR\n \n \n
\n depolarization/axon begins to depolarize\n
\n \n \n OR\n \n \n
\n action potential occurs;\n

\n

\n \n Reject pumping of ions\n \n .\n

\n
\n", "Examiners report": "
\n

\n Fundamental terms such as action potential or depolarization were not used in Q5(b) and (c). Some candidates failed to distinguish between elements and ions.\n

\n
\n", "question_id": "22M.2.HL.TZ1.5B", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c2-2-neural-signalling", "c2-2-3-nerve-impulses-as-action-potentials-that-are-propagated-along-nerve-fibres", "c2-2-8-depolarization-and-repolarization-during-action-potentials" ] }, { "Question": "
\n
\n (i)\n
\n
\n

\n State with a reason whether pangolins are autotrophic or heterotrophic.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n heterotrophic because it feeds on/eats food/other organisms /eats ants/termites/ doesn’t photosynthesise/does not produce its own food;\n

\n

\n \n Do not accept “it is not autotrophic” as it is part of the stem question.\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ2.4AI", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c4-2-transfers-of-energy-and-matter", "c4-2-6-autotrophs-as-organisms-that-use-external-energy-sources-to-synthesize-carbon-compounds-from-simple-inorganic-substances" ] }, { "Question": "
\n
\n

\n Explain the conclusion that can be drawn from Cross 1.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n allele/trait/gene for banded is dominant/allele for unbanded is recessive;\n
    2. \n
  2. \n because two banded spiders produced some unbanded offspring\n
    \n \n OR\n \n
    \n because there is a ratio of 3 banded:1 unbanded;\n
    3. \n
  3. \n both parents are heterozygous;\n
    4. \n
\n

\n \n Accept answers given in the form of Punnet squares.\n \n

\n

\n

\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ1.A", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-2-inheritance", "d3-2-5-effects-of-dominant-and-recessive-alleles-on-phenotype" ] }, { "Question": "
\n
\n

\n The diagram shows a section through a thylakoid. Electrons move from X to Y.\n

\n

\n \n

\n

\n [Source: Courtesy Alyse Da Quynh.]\n

\n

\n

\n

\n What do the letters X, Y and Z represent?\n

\n

\n \n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "20N.1A.HL.TZ0.30", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-3-photosynthesis", "c1-3-11-generation-of-oxygen-by-the-photolysis-of-water-in-photosystem-ii", "c1-3-12-atp-production-by-chemiosmosis-in-thylakoids" ] }, { "Question": "
\n
\n (d)\n
\n
\n

\n The data in the graph show a long-term trend in global LAI.\n

\n
\n
\n

\n

\n
\n
\n", "Markscheme": "
\n

\n Increase/increasing/upwards/rising (trend);\n

\n

\n \n Reject ‘positive’, ‘positive trend’ and ‘positive correlation’\n
\n \n \n Accept linear increase.\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ1.1D", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-3-climate-change", "d4-3-1-anthropogenic-causes-of-climate-change" ] }, { "Question": "
\n
\n

\n In the diagram, which of the processes labelled A to D transfers the largest mass of carbon per year in a woodland ecosystem?\n

\n

\n \n

\n

\n [Source: © International Baccalaureate Organization 2019]\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "19N.1A.SL.TZ0.19", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c4-2-transfers-of-energy-and-matter", "c4-2-17-constructing-carbon-cycle-diagrams", "c4-2-18-ecosystems-as-carbon-sinks-and-carbon-sources", "c4-2-19-release-of-carbon-dioxide-into-the-atmosphere-during-combustion-of-biomass-peat-coal-oil-and-natural-gas" ] }, { "Question": "
\n
\n (a.i)\n
\n
\n

\n Describe the structure of nucleosomes.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n a unit of DNA wound/coiled around 8 histone proteins / octamer;\n

\n
\n", "Examiners report": "
\n

\n The structure of a nucleosome was correctly described for many, but some did not mention the number of histones.\n

\n
\n", "question_id": "22M.2.HL.TZ2.5", "topics": [ "a-unity-and-diversity", "d-continuity-and-change" ], "subtopics": [ "a1-2-nucleic-acids", "a1-2-13-structure-of-a-nucleosome", "a1-2-6-dna-as-a-double-helix-made-of-two-antiparallel-strands-of-nucleotides-with-two-strands-linked-by-hydrogen-bonding-between-complementary-base-pairs", "d3-3-homeostasis", "d3-3-3-regulation-of-blood-glucose-as-an-example-of-the-role-of-hormones-in-homeostasis", "d3-3-4-physiological-changes-that-form-the-basis-of-type-1-and-type-2-diabetes" ] }, { "Question": "
\n
\n

\n Discuss whether natural selection would favour the transgenic EBF-producing thale cress plants if they were released into the wild.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. mutant aphids/varieties may be indifferent to/attracted to transgenic plants as these do not present a hazard «not favour» ✔\n
\n
\n b. initially/for limited time the plants would thrive as the aphids would be «largely»repelled and thus not eat the plants «so natural selection would favour them» ✔\n

\n

\n c. over time/in a few generations, the aphids population become more resistant/more attracted/less repelled to EBF and return to feed on the plants so long-term benefit very limited «so natural selection would not favour them» ✔\n

\n

\n d. the aphids resistant to EBF would not respond to other aphid alarms and «likely»be more readily eaten by predators «so the long-term benefit to plants could be supported by natural selection» ✔\n

\n

\n \n The answers must indicate whether natural selection would support or not for each statement.\n \n

\n
\n", "Examiners report": "
\n

\n There was some discussion in the G2 forms about the amount of reading before points h, I and j. Good candidates could be seen to have read it carefully, underling the key words. Weaker candidates not so. Very few candidates scored both marks in j as they just wrote about one possibility. Perhaps the answer box should have been larger.\n

\n
\n", "question_id": "19M.2.SL.TZ2.J", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-1-natural-selection", "d4-1-1-natural-selection-as-the-mechanism-driving-evolutionary-change" ] }, { "Question": "
\n
\n

\n Describe the processes that are carried out by enzymes that bind to DNA.\n

\n
\n
\n

\n [7]\n

\n
\n
\n", "Markscheme": "
\n

\n \n replication\n \n

\n

\n a. helicase unwinds the double helix/DNA;\n
\n b. helicase breaks hydrogen bonds between/separates/unzips DNA strands;\n
\n c. (DNA) gyrase/topoisomerase releases tensions in DNA as it unwinds;\n
\n d. (DNA) primase adds\n \n RNA\n \n primers (where DNA polymerase can bind);\n
\n e. DNA polymerase (III) replicates DNA/adds nucleotides (to make new strand);\n
\n f. DNA polymerase I replaces RNA (primers) with DNA;\n
\n g. DNA ligase seals nicks/joins sugar-phosphate backbones/joins (Okazaki)fragments;\n

\n

\n \n transcription\n \n

\n

\n h. RNA polymerase used for transcription;\n
\n i. RNA polymerase unwinds / separates DNA strands / binds to the promoter;\n
\n j. RNA polymerase copies DNA base sequence of a gene/makes mRNA;\n
\n k. restriction enzymes/endonucleases cut DNA at specific base sequences;\n
\n l. telomerase adds nucleotides to the ends of chromosomes/makes telomeres;\n

\n
\n", "Examiners report": "None", "question_id": "23M.2.HL.TZ1.B", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d1-1-dna-replication", "d1-1-3-role-of-helicase-and-dna-polymerase-in-dna-replication", "d1-1-8-functions-of-dna-primase-dna-polymerase-i-dna-polymerase-iii-and-dna-ligase-in-replication" ] }, { "Question": "
\n
\n

\n State\n

\n
\n
\n

\n

\n
\n
\n", "Markscheme": "
\n

\n from blood sample/hair/cheek/saliva/semen;\n

\n

\n \n Do not accept red blood cells\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.1B.SL.TZ1.A", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-3-photosynthesis", "c1-3-7-techniques-for-varying-concentrations-of-carbon-dioxide-light-intensity-or-temperature-experimentally-to-investigate-the-effects-of-limiting-factors-on-the-rate-of-photosynthesis" ] }, { "Question": "
\n
\n

\n State the role of cyclins in the cell cycle.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n (group of regulatory proteins that) control/regulate the cell cycle;\n
    2. \n
  2. \n activate cyclin-dependent kinases (which control cell cycle processes);\n
    3. \n
\n
\n", "Examiners report": "None", "question_id": "22M.2.HL.TZ2.A.III", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-1-cell-and-nuclear-division", "d2-1-15-control-of-the-cell-cycle-using-cyclins" ] }, { "Question": "
\n
\n

\n What occurs as a result of a cut in the skin of a finger?\n

\n

\n A. Prothrombin is transformed into thrombin.\n

\n

\n B. Fibrin is converted to insoluble fibrinogen.\n

\n

\n C. Platelets produce antibodies to prevent infection.\n

\n

\n D. Clotting factors are released from red blood cells.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "
\n

\n A high discrimination index and fewer than 30 % of candidates answering correctly show that only best-prepared candidates had studied this topic carefully enough.\n

\n
\n", "question_id": "21N.1A.SL.TZ0.25", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-2-defence-against-disease", "c3-2-3-sealing-of-cuts-in-skin-by-blood-clotting" ] }, { "Question": "
\n
\n (d)\n
\n
\n

\n Identify\n \n one\n \n adaptation of the leaf for the absorption of light visible in this micrograph.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n double layer of palisade cells;\n
    2. \n
  2. \n palisade layer on upper surface;\n
    3. \n
  3. \n dimensions of palisade cells maximize light absorption;\n
    4. \n
  4. \n thin/transparent epidermis/cuticle;\n
    5. \n
\n
\n", "Examiners report": "None", "question_id": "SPM.1B.SL.TZ0.2D", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-1-gas-exchange", "b3-1-7-adaptations-for-gas-exchange-in-leaves", "b3-1-8-distribution-of-tissues-in-a-leaf" ] }, { "Question": "
\n
\n

\n State\n \n one\n \n process that results in the loss of carbon dioxide from a marine organism such as a crustacean or a jellyfish.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n a. (aerobic/cellular) respiration ✔\n

\n

\n b. gas exchange / diffusion ✔\n

\n

\n \n Do not accept photosynthesis\n \n .\n

\n

\n \n Do not accept breathing\n \n

\n

\n \n Organism is taken to be a living thing\n \n .\n

\n
\n", "Examiners report": "
\n

\n In 4(a) most were able to state 'respiration' as the answer. 4(b) proved more difficult with fewer stating photosynthesis or absorption of dissolved CO\n \n 2\n \n or HCO\n \n 3\n \n from the seawater. Vague answers such as 'carbon in the water' were not credited. In 4(c) most knew that energy enters with sunlight, but did not state photosynthesis. They knew that it was transferred by feeding through the trophic levels and lost as heat due to respiration. A surprising number incorrectly stated that the energy was recycled and some drew diagrams of the energy flow showing this. In 4(d)(i) most were able to state that the crustacean was a richer source of carbon. An explanation using the data from the diagram was expected. In 4(d)(ii) most were able to present an argument for advantage or disadvantage.\n

\n
\n", "question_id": "21M.2.SL.TZ2.A", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c4-2-transfers-of-energy-and-matter", "c4-2-17-constructing-carbon-cycle-diagrams", "c4-2-18-ecosystems-as-carbon-sinks-and-carbon-sources" ] }, { "Question": "
\n
\n (i)\n
\n
\n

\n Suggest with a reason which P:L diet is closest to the normal diet of these bumblebees.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n 10:1 diet as this has the highest survival rate (after 7 days);\n

\n

\n \n Reason must be given.\n \n

\n
\n", "Examiners report": "None", "question_id": "22N.2.SL.TZ0.1I", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c4-2-transfers-of-energy-and-matter", "c4-2-15-primary-production-as-accumulation-of-carbon-compounds-in-biomass-by-autotrophs", "c4-2-16-secondary-production-as-accumulation-of-carbon-compounds-in-biomass-by-heterotrophs" ] }, { "Question": "
\n
\n

\n Outline the action taken by the diaphragm during inhalation.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n contracts/flattens/becomes less domed/increases volume of thorax;\n

\n
\n", "Examiners report": "None", "question_id": "21N.2.SL.TZ0.C", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-1-gas-exchange", "b3-1-5-ventilation-of-the-lungs" ] }, { "Question": "
\n
\n (b.ii)\n
\n
\n

\n Suggest reasons for this trend.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n less surface area is exposed when curled up\n
    \n \n \n OR\n \n \n
    \n more surface area is exposed when all limbs spread;\n
    2. \n
  2. \n curled position prevents heat loss/provides warmth\n
    \n \n \n OR\n \n \n
    \n stretched out position allows more heat loss/body cooled;\n
    3. \n
\n
\n", "Examiners report": "
\n

\n There were a few beautiful responses where surface area was specifically incorporated into the answer achieving maximum marks.\n

\n
\n", "question_id": "22M.2.SL.TZ1.1B.II", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-3-homeostasis", "d3-3-1-homeostasis-as-maintenance-of-the-internal-environment-of-an-organism", "d3-3-2-negative-feedback-loops-in-homeostasis" ] }, { "Question": "
\n
\n (ii)\n
\n
\n

\n how the DNA is amplified.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n PCR/polymerase chain reaction\n
\n \n \n OR\n \n \n
\n using Taq polymerase;\n

\n

\n

\n
\n", "Examiners report": "None", "question_id": "23M.1B.SL.TZ1.AII", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-3-photosynthesis", "c1-3-7-techniques-for-varying-concentrations-of-carbon-dioxide-light-intensity-or-temperature-experimentally-to-investigate-the-effects-of-limiting-factors-on-the-rate-of-photosynthesis" ] }, { "Question": "
\n
\n

\n The diagram shows the pressure changes in the left atrium, left ventricle and aorta during part of the cardiac cycle.\n

\n

\n \n

\n

\n Are the valves between the atria and the ventricles open or closed at time X and time Y?\n

\n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n
\n \n \n Time X\n \n \n \n Time Y\n \n
\n A.\n \n open\n \n open\n
\n B.\n \n open\n \n closed\n
\n C.\n \n closed\n \n open\n
\n D .\n \n closed\n \n closed\n
\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "23M.1A.HL.TZ2.27", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-2-transport", "b3-2-16-stages-in-the-cardiac-cycle" ] }, { "Question": "
\n
\n

\n What process best explains the formation of different pentadactyl limbs?\n

\n

\n A. Adaptive radiation\n

\n

\n B. Interbreeding\n

\n

\n C. Selective breeding\n

\n

\n D. Convergence\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "None", "question_id": "20N.1A.SL.TZ0.20", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a4-1-evolution-and-speciation", "a4-1-4-evidence-for-evolution-from-homologous-structures" ] }, { "Question": "
\n
\n (a.ii)\n
\n
\n

\n State the cumulative increase in the mass of control colonies at 7 weeks.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n 230 g;\n

\n

\n \n Accept range of 215 – 265. This takes into account the beginning and end of week 7.\n \n
\n \n Unit required.\n \n

\n
\n", "Examiners report": "None", "question_id": "22M.2.HL.TZ2.1A.II", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c2-2-neural-signalling", "c2-2-12-effects-of-exogenous-chemicals-on-synaptic-transmission" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Identify the structure labelled X.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n (Neurotransmitter) vesicle;\n

\n

\n \n Do not accept Vacuole.\n \n

\n
\n", "Examiners report": "
\n

\n The majority managed to label X as a vesicle in (a). In (b) weaker candidates tried to explain the propagation of the action potential, rather than the release of the neurotransmitter. Better candidates were able to give almost textbook answers to explain the actions of the pesticide. Many got tangled up trying to explain, with those who had never seen this part of the syllabus, just saying that pesticides kill insects.\n

\n
\n", "question_id": "22N.2.SL.TZ0.5", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c2-1-chemical-signalling-[hl-only]", "c2-1-3-hormones-neurotransmitters-cytokines-and-calcium-ions-as-examples-of-functional-categories-of-signalling-chemicals-in-animals", "c2-1-8-transmembrane-receptors-for-neurotransmitters-and-changes-to-membrane-potential", "c2-2-neural-signalling", "c2-2-12-effects-of-exogenous-chemicals-on-synaptic-transmission" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n The graph shows blood pressure changes on the left side of the heart during one heartbeat. Identify the\n \n two\n \n parts of the circulatory system that produce traces I and II on the graph.\n

\n

\n \n

\n

\n [Source: © International Baccalaureate Organization 2019]\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n I. aorta ✔\n

\n

\n II: «left» atrium ✔\n

\n
\n", "Examiners report": "
\n

\n This question was poorly answered with most students earning either one mark or no marks. It was more common for candidates to correctly identify the atrium rather than the aorta. ß\n

\n
\n", "question_id": "19M.2.HL.TZ2.3A", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-2-transport", "b3-2-16-stages-in-the-cardiac-cycle" ] }, { "Question": "
\n
\n (i)\n
\n
\n

\n Outline the conclusions that can be drawn from the data in the graph for the group of aphids fed for three generations on transgenic thale cress plants (T).\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. «over the generations» fewer are repelled by EBF ✔\n

\n

\n b. «over the generations» more are attracted to EBF ✔\n

\n

\n c. by G3 a «slight» increase in no choice ✔\n

\n

\n d. aphids respond less to EBF/alarm compound if they feed on plants that produce it/exposed to it constantly ✔\n

\n

\n e. mutant aphids with attraction to transgenic plants can arise from aphids with no attraction or repulsion to transgenic plants\n
\n \n \n OR\n \n \n
\n aphids with no attraction or repulsion to transgenic plants may produce new type of aphids with attraction to transgenic plants ✔\n

\n
\n", "Examiners report": "
\n

\n There was some discussion in the G2 forms about the amount of reading before points h, I and j. Good candidates could be seen to have read it carefully, underling the key words. Weaker candidates not so. In i. a large proportion gained both marks for stating that the percentage of attraction had increased and the percentage of repulsion had decreased.\n

\n
\n", "question_id": "19M.2.SL.TZ2.1I", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d1-1-dna-replication", "d1-1-5-applications-of-polymerase-chain-reaction-and-gel-electrophoresis" ] }, { "Question": "
\n
\n

\n Deduce, based on the data presented, whether the levels of neonicotinoids used in agriculture cause direct harm to\n \n B. terrestris\n \n .\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n yes, as even low/both doses (of first neonicotinoid) affect the (overall) development of colonies negatively; (\n \n From Graph 1\n \n )\n
    2. \n
  2. \n yes, as decreased numbers of queens (likely) affect reproductive capabilities; (\n \n From Graph 2\n \n )\n
    3. \n
  3. \n the second neonicotinoid (likely) had less/little/no effect on the bees as it had little effect on egg size; (\n \n From Graph 3\n \n )\n
    4. \n
\n

\n \n OWTTE\n \n

\n
\n", "Examiners report": "None", "question_id": "22M.2.HL.TZ2.D", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c2-2-neural-signalling", "c2-2-12-effects-of-exogenous-chemicals-on-synaptic-transmission" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n State how many chromosomes there would be in male or female gametes of\n \n L. purpureus\n \n .\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n 12;\n

\n

\n \n No alternative.\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ2.2", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-1-reproduction", "d3-1-8-sexual-reproduction-in-flowering-plants", "d3-2-inheritance", "d3-2-2-methods-for-conducting-genetic-crosses-in-flowering-plants" ] }, { "Question": "
\n
\n

\n Suggest\n \n two\n \n reasons, other than elevation, for the differences in nitrogen concentration in leaves of pitcher plants.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n pitcher plants consume more insects (at different sampling sites);\n
    2. \n
  2. \n larger insects contain more nitrogen;\n
    3. \n
  3. \n more nitrogen concentration in soil\n
    \n \n \n OR\n \n \n
    \n more nitrifying bacteria in the soil\n
    \n \n \n OR\n \n \n
    \n water-logged soil has less nitrogen;\n
    4. \n
  4. \n use of N/NPK fertilizers\n
    \n \n \n OR\n \n \n
    \n leaching of N in different sites;\n
    5. \n
\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ2.C", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-2-stability-and-change", "d4-2-8-eutrophication-of-aquatic-and-marine-ecosystems-due-to-leaching" ] }, { "Question": "
\n
\n

\n Explain whether these results fit the predicted Mendelian ratios for this cross.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n independent assortment predicts 1:1:1:1\n
    \n \n \n OR\n \n \n
    \n this (mendelian) ratio not seen / recombinants less frequent/parental types more frequent;\n
    2. \n
  2. \n suggests linkage\n
    \n \n \n OR\n \n \n
    \n small numbers so could be a result of differential survival;\n
    3. \n
\n
\n", "Examiners report": "None", "question_id": "SPM.2.HL.TZ0.B", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-2-inheritance", "d3-2-17-punnett-grids-for-predicting-genotypic-and-phenotypic-ratios-in-dihybrid-crosses-involving-pairs-of-unlinked-autosomal-genes" ] }, { "Question": "
\n
\n (a.iii)\n
\n
\n

\n Compare and contrast the cumulative increase in mass of the three groups of colonies once they were placed in the field.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n all increased in (cumulative) mass gain up to 5–6 weeks\n
    \n \n \n OR\n \n \n
    \n all decreased (in cumulative mass gain) after 6 weeks;\n
    2. \n
  2. \n both with neonicotinoids have significantly lower (cumulative) mass than the control colonies (at all periods)\n
    \n \n \n OR\n \n \n
    \n colonies exposed to high concentration always had the lowest (cumulative) mass gain;\n
    3. \n
\n

\n \n Accept vice versa\n \n .\n

\n
\n", "Examiners report": "None", "question_id": "22M.2.HL.TZ2.1A.III", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c2-2-neural-signalling", "c2-2-12-effects-of-exogenous-chemicals-on-synaptic-transmission" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Deduce, giving reasons, which brown pelican population decreased the most in the years following the study.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n California, as most eggs have a high level of DDE / most eggshells are thinning;\n
    2. \n
  2. \n (California as) less chicks hatching (results in smaller population size)\n
    \n \n \n OR\n \n \n
    \n (California as) birth rate less than death rate (so decrease in population);\n
    3. \n
\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ2.18B", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-2-stability-and-change", "d4-2-9-biomagnification-of-pollutants-in-natural-ecosystems" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Compare and contrast the effects of temperature on the biomass of autotrophs and heterotrophs with added nutrients.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. autotroph biomass decreases\n \n and\n \n heterotroph biomass increases with higher temperatures;\n
\n b. decrease in autotrophs is greater/larger/more than increase in heterotrophs\n
\n \n OR\n \n
\n little difference in biomass (between auto and heterotrophs) at highest temperature/27 °C;\n
\n c. autotrophs show smaller and smaller gains in biomass from initial as temperature rises/WTTE;\n
\n d. heterotrophs no gain in biomass at 21 °C then larger and larger gains as temperature rises;\n

\n
\n", "Examiners report": "
\n

\n Most candidates stated that autotroph biomass decreased and heterotroph biomass increased as temperature increased, but this contrast was only given one mark. Far fewer candidates gave a second worthwhile comparison or contrast. Very few candidates realised that at all temperatures the autotrophs had gained biomass from the initial level, but the gains were less as temperature rose. Similarly, few candidates stated that the heterotrophs had not gained mass at 21°C but gained increasing amounts of biomass as the temperature rose.\n

\n
\n", "question_id": "21N.2.SL.TZ0.1B", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-2-stability-and-change", "d4-2-4-use-of-a-model-to-investigate-the-effect-of-variables-on-ecosystem-stability" ] }, { "Question": "
\n
\n

\n Suggest reasons for the relationship shown in the graph.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n majority of individuals are active/walk to places if walkability is high;\n
    \n \n OR\n \n
    \n high walkability encourages the habit of walking so the coefficient ofactivity inequality would be low;\n
    2. \n
  2. \n with low walkability some individuals take exercise/go jogging and some do not;\n
    3. \n
  3. \n (with high walkability) people don’t need to drive increasing the incentive to walk;\n
    4. \n
\n

\n

\n

\n \n Accept reasonable answer.\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ1.D", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-3-muscle-and-motility-(hl-only)", "b3-3-9-reasons-for-locomotion" ] }, { "Question": "
\n
\n

\n The graph shows how the number of ant species found on isolated islands near New Guinea depends on the size of the island.\n

\n

\n \n

\n

\n [Source: University of Windsor,\n \n The Theory of Island Biogeography\n \n . Available at:\n
\n http://web2.uwindsor.ca/courses/biology/macisaac/55-437/lecture9.htm.]\n

\n

\n

\n

\n Explain the relationship between island size and number of ant species.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n (the larger islands contain) more species as there are more habitats;\n

\n
\n", "Examiners report": "
\n

\n The graph showing the number of ant species according to island size required an explanation of the graph. Many candidates simply stated the relationship with no explanation.\n

\n
\n", "question_id": "20N.2.SL.TZ0.C", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a4-2-conservation-of-biodiversity", "a4-2-5-evidence-for-a-biodiversity-crisis" ] }, { "Question": "
\n
\n (ii)\n
\n
\n

\n Explain what information is needed to find the trophic level of pangolins.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n what (prey) it eats/feeds on/ stomach content;\n
    2. \n
  2. \n the trophic level of what (prey) it eats/feeds on/the trophic level of ants/termites;\n
    3. \n
  3. \n trophic level is the position an organism occupies in the food chain/web;\n
    4. \n
\n

\n \n Do not award points for indicating that predator information is needed.\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ2.4AII", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c4-2-transfers-of-energy-and-matter", "c4-2-10-classification-of-organisms-into-trophic-levels" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Outline how these results indicate that blackberry distribution is limited by light intensity.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. as light level changes so does the percentage cover «of blackberry» ✔\n

\n

\n b. distribution is higher at intermediate/moderate light intensities ✔\n \n Accept appropriate numerical values\n \n

\n

\n c. little growth at low light intensities\n
\n \n OR\n \n
\n little growth at high light intensities ✔\n \n Accept appropriate numerical values\n \n

\n

\n d. distribution is bell shaped ✔\n

\n
\n", "Examiners report": "None", "question_id": "19N.2.SL.TZ0.12A", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-3-photosynthesis", "c1-3-7-techniques-for-varying-concentrations-of-carbon-dioxide-light-intensity-or-temperature-experimentally-to-investigate-the-effects-of-limiting-factors-on-the-rate-of-photosynthesis" ] }, { "Question": "
\n
\n

\n Distinguish between the processes of meiosis and mitosis.\n

\n
\n
\n

\n [5]\n

\n
\n
\n", "Markscheme": "
\n

\n \n

\n
\n", "Examiners report": "
\n

\n The best answers had clear comparative statements or were in a comparison table. The worst answers were continuous prose descriptions of the processes, as these all too often failed to be able to be pieced together to make full marking points.\n

\n

\n About half of the candidates did not mention cell divisions, but simply mentioned \"two cycles\" which was too vague and instead of writing haploid/diploid, many said 23/46, which only applies to human or certain organisms.\n

\n
\n", "question_id": "22M.2.SL.TZ1.B", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-1-cell-and-nuclear-division", "d2-1-4-roles-of-mitosis-and-meiosis-in-eukaryotes" ] }, { "Question": "
\n
\n

\n Outline the reason for the loss of dipterocarp forest ecosystems in South Asia.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n anthropogenic reasons / human activities / logging / removal of trees;\n
    2. \n
  2. \n to sell timber / grow crops / for plantations / agriculture;\n
    3. \n
\n
\n", "Examiners report": "None", "question_id": "None", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a4-2-conservation-of-biodiversity", "a4-2-4-causes-of-ecosystem-loss" ] }, { "Question": "
\n
\n

\n State the relationship between DDE concentration and eggshell thickness.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n the higher the DDE concentration, the lower the thickness/higher the thinning\n
\n \n \n OR\n \n \n
\n negative correlation/inverse relationship;\n

\n

\n \n Accept vice versa.\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ2.I", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-2-stability-and-change", "d4-2-9-biomagnification-of-pollutants-in-natural-ecosystems" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Suggest\n \n one\n \n reason that it is difficult to detect illegal use of HGH to enhance athletic performance.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n a. occurs naturally so hard to tell whether it has been injected ✔\n

\n

\n b. HGH has very short half life ✔\n

\n
\n", "Examiners report": "
\n

\n Students were unable to state that the detection of illegal use of HGH was due it already being naturally present in the body.\n

\n
\n", "question_id": "19M.2.HL.TZ1.20B", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c2-1-chemical-signalling-[hl-only]", "c2-1-10-mechanism-of-action-of-epinephrine-(adrenaline)-receptors" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Plasma cells secrete antibodies against specific antigens. Outline how plasma cells become activated.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n a. macrophages/phagocytes recognize/engulf pathogen and display antigens ✔\n

\n

\n b. antigen binds to T cell/helper T cell / antigen causes activation of T cell ✔\n

\n

\n c. antigen binds to antibodies in membrane of B cells ✔\n

\n

\n d. (activated) T cells activate B cells (that have the antigen bound to them) ✔\n

\n

\n e. activated B cells divide to produce a clone of cells ✔\n

\n

\n f. active plasma cells develop from the clone of cells/from activated B cells ✔\n

\n

\n \n Accept B-lymphocyte and Tlymphocyte instead of B cell and T cell throughout the answer.\n \n

\n
\n", "Examiners report": "
\n

\n Some explanations of the production of active plasma cells were excellent but weaker candidates were mostly very confused, with antigens and antibodies muddled up. Many candidates thought that plasma cells are already present and just need to be activated, rather than them being produced as a result of the activity of macrophages, T-cells and B-cells. There was too much focus on memory cells. The mean mark was low, 0.6 out of 3.\n

\n
\n", "question_id": "21M.2.SL.TZ1.4A", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-2-defence-against-disease", "c3-2-9-multiplication-of-activated-b-lymphocytes-to-form-clones-of-antibody-secreting-plasma-cells" ] }, { "Question": "
\n
\n (ii)\n
\n
\n

\n Outline the reasons for secretion of sweat in humans.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n cooling/removal of heat/lowering body temperature;\n
    2. \n
  2. \n to prevent overheating\n
    \n \n \n OR\n \n \n
    \n to help maintain body temperature/for temperature homeostasis/for thermoregulation\n
    \n \n \n OR\n \n \n
    \n to keep temperature at 37 °C;\n
    3. \n
\n

\n

\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ1.4BII", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a1-1-water", "a1-1-2-hydrogen-bonds-as-a-consequence-of-the-polar-covalent-bonds-within-water-molecules" ] }, { "Question": "
\n
\n

\n Data regarding the presence (+) or absence (–) of five traits in several different species are shown in the table.\n

\n

\n \n

\n

\n Which cladogram best represents the relationship between the five species?\n

\n

\n \n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "None", "question_id": "22M.1A.HL.TZ1.23", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a3-2-classification-and-cladistics-(hl-only)", "a3-2-7-analysing-cladograms" ] }, { "Question": "
\n
\n (f)\n
\n
\n

\n Deduce whether there is a correlation between the neural traces and the percentage of responding G1 neurons.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. there is a\n \n positive\n \n relationship/correlation between the size of neural traces and the percentage of responding G1 neurons\n \n Accept vice versa\n \n
\n \n \n OR\n \n \n
\n the chemicals that cause stronger/higher neural traces also cause the greatest percentage of responding G1 neurons ✔\n

\n

\n b. fox and stoat scents have «approximately» the same/similar neural traces and the same percentage of responding neurons/>75 % ✔\n

\n

\n c. mouse alarm compounds cause smaller neural traces and smaller percentage of responding neurons/25–75 % ✔\n

\n

\n d. control chemicals have\n \n no response\n \n in both cases\n
\n \n \n OR\n \n \n
\n \n no percentage\n \n of «G1 neurons» response and no action potential «in neural traces» ✔\n

\n
\n", "Examiners report": "
\n

\n Similarly, in 1f most could see the positive correlation, albeit not stating it, between the size of the trace and the percentage of responding G1 neurons.\n

\n
\n", "question_id": "19M.2.SL.TZ2.1F", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c2-2-neural-signalling" ] }, { "Question": "
\n
\n

\n How do greenhouse gases contribute to global warming?\n

\n

\n A. They destroy the ozone layer, allowing radiation to reach the Earth’s surface.\n

\n

\n B. They prevent radiation from the Earth escaping into space.\n

\n

\n C. They trap short wavelength radiation in the atmosphere.\n

\n

\n D. They are a product of combustion, which generates heat.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "
\n

\n The discrimination index was high, but only a third of candidates answered correctly. A popular misconception was that greenhouse gases trap short-wave radiation. If that was the case, visible light from the sun would be unable to penetrate the Earth’s atmosphere.\n

\n
\n", "question_id": "21N.1A.SL.TZ0.19", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-3-climate-change", "d4-3-2-positive-feedback-cycles-in-global-warming" ] }, { "Question": "
\n
\n

\n Compare and contrast the results for Hymenoptera and Lepidoptera.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n both show a decline in number;\n
    2. \n
  2. \n the mean decline for Hymenoptera is less than the mean for Lepidoptera\n
    \n \n \n OR\n \n \n
    \n there is a wider range of decline among the species of Lepidoptera;\n
    3. \n
\n
\n", "Examiners report": "None", "question_id": "22N.2.SL.TZ0.B", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c4-2-transfers-of-energy-and-matter", "c4-2-15-primary-production-as-accumulation-of-carbon-compounds-in-biomass-by-autotrophs", "c4-2-16-secondary-production-as-accumulation-of-carbon-compounds-in-biomass-by-heterotrophs" ] }, { "Question": "
\n
\n

\n What applies to DNA base sequences?\n

\n

\n I. Some genes do not code for proteins.\n

\n

\n II. Promoters are transcribed along with the gene.\n

\n

\n III. Introns are only found within genes coding for proteins.\n

\n

\n A. I only\n

\n

\n B. II only\n

\n

\n C. II and III only\n

\n

\n D. I, II and III\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "
\n

\n From Topic 7.1 candidates should know that introns are regions of DNA that do not code for proteins. This confused some candidates that failed to realize that introns are found within genes coding for proteins. In order to make this question more fair, the mark scheme was adapted and answers A and B were both accepted as correct.\n

\n
\n", "question_id": "19M.1A.HL.TZ2.14", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d1-2-protein-synthesis", "d1-2-13-initiation-of-transcription-at-the-promoter", "d1-2-14-non-coding-sequences-in-dna-do-not-code-for-polypeptides", "d1-2-15-post-transcriptional-modification-in-eukaryotic-cells" ] }, { "Question": "
\n
\n

\n The cladogram shows some of the groups in the three domains.\n

\n

\n \n

\n

\n [Source: Adapted from Eric Gaba (Sting, fr:Sting), Cherkash, Public domain, via Wikimedia Commons.\n
\n https://commons.wikimedia.org/wiki/File:Phylogenetic_tree.svg.]\n

\n

\n

\n

\n What domains do X, Y and Z represent?\n

\n

\n \n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "20N.1A.HL.TZ0.23", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a3-2-classification-and-cladistics-(hl-only)", "a3-2-7-analysing-cladograms", "a3-2-9-classification-of-all-organisms-into-three-domains-using-evidence-from-rrna-base-sequences" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Using the data in the graph, predict how the use of neonicotinoid pesticides will affect bumblebee populations.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n number of populations may/will decrease;\n
    2. \n
  2. \n both treatments decreased very significantly the number of queens;\n
    3. \n
  3. \n low treatment had (almost) the same effect as the high\n
    \n \n \n OR\n \n \n
    \n even low levels have as toxic/lethal effects as high levels;\n
    4. \n
  4. \n without new queens, new colonies cannot be founded;\n
    5. \n
  5. \n no/less/little reproduction (as only queens lay eggs);\n
    6. \n
  6. \n new colonies are essential to maintain bumblebee populations;\n
    7. \n
\n
\n", "Examiners report": "None", "question_id": "22M.2.HL.TZ2.1B", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c2-2-neural-signalling", "c2-2-12-effects-of-exogenous-chemicals-on-synaptic-transmission" ] }, { "Question": "
\n
\n

\n Which molecules are produced during the hydrolysis of a triglyceride molecule?\n

\n

\n
\n A.  Water and glycerol\n

\n

\n B.  Fatty acids and glycerol\n

\n

\n C.  Water and fatty acids\n

\n

\n D.  Water and lipids\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "SPM.1A.SL.TZ0.3", "topics": [], "subtopics": [] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Describe how plants transport organic compounds from where they are made to where they are stored.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n (overall) process is translocation / bidirectional / movement from source to sink;\n
    2. \n
  2. \n sugars/sucrose/organic compounds produced in leaves;\n
    3. \n
  3. \n (loaded by) active transport / passage by apoplast route;\n
    4. \n
  4. \n loaded into companion cells / transported in phloem / sieve tubes;\n
    5. \n
  5. \n high concentrations of solutes at the source cause uptake of water (by osmosis);\n
    6. \n
  6. \n water provides hydrostatic pressure for transport (from source to sink);\n
    7. \n
  7. \n unloaded / stored / used at\n \n sink\n \n ;\n
    8. \n
  8. \n lowers pressure at sink / creates pressure differential / water re-entry to xylem;\n
    9. \n
\n
\n", "Examiners report": "
\n

\n Question 6 was the least popular in section B.\n

\n

\n Most candidates provided correct and complete details of the process of translocation.\n

\n
\n", "question_id": "22M.2.SL.TZ2.6A", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-2-transport", "b3-2-18-adaptations-of-phloem-sieve-tubes-and-companion-cells-for-translocation-of-sap" ] }, { "Question": "
\n
\n

\n Explain how denaturation affects the activity of an enzyme.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n changes the shape of the (active site) of the enzyme;\n
    2. \n
  2. \n substrate would be unable to attach to the enzyme/active site;\n
    3. \n
  3. \n slows the enzyme activity / prevents reaction/catalysis from proceeding;\n
    4. \n
\n
\n", "Examiners report": "None", "question_id": "22M.2.SL.TZ1.C", "topics": [ "b-form-and-function" ], "subtopics": [ "b1-2-proteins", "b1-2-5-effect-of-ph-and-temperature-on-protein-structure" ] }, { "Question": "
\n
\n (d)\n
\n
\n

\n Distinguish between the effects of the mouse alarm compound and the effects of the control compound on the G1 neurons.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n mouse chemicals cause action potentials «in all six neurons» while control ones cause none «remain in resting potential»/mouse chemicals cause greater responses ✔\n

\n

\n \n OWTTE\n \n

\n
\n", "Examiners report": "
\n

\n Many missed the mark in d as they did not state that the control remained at zero.\n

\n
\n", "question_id": "19M.2.SL.TZ2.1D", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c2-2-neural-signalling" ] }, { "Question": "
\n
\n (a.i)\n
\n
\n

\n State how many water molecules are shown in the diagram.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n 10;\n

\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ1.4", "topics": [ "a-unity-and-diversity", "d-continuity-and-change" ], "subtopics": [ "a1-1-water", "a1-1-2-hydrogen-bonds-as-a-consequence-of-the-polar-covalent-bonds-within-water-molecules", "d3-3-homeostasis", "d3-3-6-thermoregulation-mechanisms-in-humans" ] }, { "Question": "
\n
\n

\n The dashed line shows the relationship between the activity of an enzyme and the concentration of its substrate. Which curve shows the effect of a non-competitive inhibitor on this relationship?\n

\n

\n \n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "21M.1A.HL.TZ2.29", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-1-enzymes-and-metabolism", "c1-1-15-competitive-inhibition-as-a-consequence-of-an-inhibitor-binding-reversibly-to-an-active-site" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n The map shows the widespread distribution of coral reef ecosystems (indicated by black dots) in the world’s oceans. Death of coral reefs is related to increasing atmospheric carbon dioxide concentrations.\n

\n

\n \n

\n

\n [Source: National Oceanic and Atmospheric Administration, 2021. Where Reef Building Corals Found. [map online] Available at: https://oceanservice.noaa.gov/education/tutorial_corals/media/supp_coral05a.html [Accessed 20 May 2021].]\n

\n

\n Explain how increased atmospheric carbon dioxide concentrations can lead to coral death.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. carbon dioxide dissolves in oceans/seawater ✔\n

\n

\n b. carbonic acid formed/equation/lowers pH/makes water acidic ✔\n

\n

\n c. prevents deposition of calcium carbonate/causes calcium carbonate to dissolve ✔\n

\n

\n d. skeleton of (hard) corals degraded ✔\n

\n

\n e. carbon dioxide is a greenhouse gas/causes warming/increases temperatures ✔\n

\n

\n f. warmer oceans cause corals to expel zooxanthellae ✔\n

\n

\n g. bleaching due to death/expulsion of mutualistic organisms/algae ✔\n

\n

\n \n Allow zooxanthellae instead of algae in mpf\n \n .\n

\n

\n \n Reject reacts and diffuses instead of dissolves in mpa\n \n .\n

\n
\n", "Examiners report": "
\n

\n Answers relating to global warming and therefore rising sea temperatures and also answers relating to ocean acidification were accepted. Many candidates knew that carbon dioxide causes acidification but fewer knew about the resulting problems with mineral deposition to form the skeleton in a hard coral.\n

\n
\n", "question_id": "21M.2.SL.TZ1.3A", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-3-climate-change", "d4-3-7-threats-to-coral-reefs-as-an-example-of-potential-ecosystem-collapse" ] }, { "Question": "
\n
\n (d)\n
\n
\n

\n Suggest reasons for the decreases in biomass of autotrophs as temperature rises, despite the increases in photosynthesis.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n \n biomass of autotrophs decreases as temperature rises because of\n \n :\n
\n a. more herbivory/grazing/feeding by (zooplankton/heterotrophs);\n
\n b. higher populations/numbers/biomass of zooplankton/heterotrophs;\n
\n c. more mortality/more decomposition/decay of autotrophs/phytoplankton;\n
\n d.\n \n respiration\n \n (rate higher than photosynthesis rate in autotrophs/phytoplankton);\n

\n
\n", "Examiners report": "
\n

\n Enzymes do not denature at the temperatures used in this experiment. Also, the autotrophs are phytoplankton living in seawater so transpiration cannot be the cause of biomass reductions at higher temperatures. The data in previous graphs showed higher biomasses of heterotrophs at higher temperatures and thus greater rates of herbivory were the obvious explanation for reduced autotroph biomass.\n

\n
\n", "question_id": "21N.2.SL.TZ0.1D", "topics": [ "d-continuity-and-change", "c-interaction-and-interdependence" ], "subtopics": [ "d4-2-stability-and-change", "d4-2-4-use-of-a-model-to-investigate-the-effect-of-variables-on-ecosystem-stability", "c1-3-photosynthesis", "c1-3-7-techniques-for-varying-concentrations-of-carbon-dioxide-light-intensity-or-temperature-experimentally-to-investigate-the-effects-of-limiting-factors-on-the-rate-of-photosynthesis" ] }, { "Question": "
\n
\n

\n The processes of photosynthesis and respiration have some factors in common and others differ. Compare and contrast both processes for specific factors.\n

\n
\n
\n

\n [7]\n

\n
\n
\n", "Markscheme": "
\n

\n \n

\n
\n", "Examiners report": "
\n

\n The comparison of the processes of cellular respiration and photosynthesis was done effectively. Some very good and well-organized answers were noted. It was common for students to use a table to organize their answers. Some correct answers contained full descriptions of the Calvin and the Krebs cycle, which was unnecessary.\n

\n
\n", "question_id": "22M.2.SL.TZ2.B", "topics": [ "c-interaction-and-interdependence", "b-form-and-function" ], "subtopics": [ "c1-2-cell-respiration", "c1-2-4-cell-respiration-as-a-system-for-producing-atp-within-the-cell-using-energy-released-from-carbon-compounds", "b4-2-ecological-niches", "b4-2-3-photosynthesis-as-the-mode-of-nutrition-in-plants-algae-and-several-groups-of-photosynthetic-prokaryotes" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Describe the control for this experiment.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. same apparatus with carbon dioxide present;\n

\n

\n b. (control has) no sodium hydroxide/alkali;\n

\n

\n c. control irrigated with untreated water/water with CO\n \n 2\n \n ;\n

\n

\n \n “Same apparatus” alone does not get the mark\n \n .\n

\n
\n", "Examiners report": "
\n

\n Many candidates had difficulty describing the control for this experiment. The question states that the experiment was to investigate whether carbon dioxide is required for photosynthesis therefore it seems straightforward that the plant would be in similar conditions with and without carbon dioxide. Some candidates assumed that the control plant would have similar conditions and no light.\n

\n
\n", "question_id": "20N.1B.SL.TZ0.3A", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-3-photosynthesis", "c1-3-7-techniques-for-varying-concentrations-of-carbon-dioxide-light-intensity-or-temperature-experimentally-to-investigate-the-effects-of-limiting-factors-on-the-rate-of-photosynthesis" ] }, { "Question": "
\n
\n

\n Explain the mechanisms involved in thermoregulation in humans.\n

\n
\n
\n

\n [7]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n normal body temperature is 37 ºC;\n
    2. \n
  2. \n peripheral thermoreceptors detect environmental temperature;\n
    3. \n
  3. \n supporting conscious behaviour to avoid temperature extremes, e.g. wearing more clothing;\n
    4. \n
  4. \n sends messages to hypothalamus/temperature control centre of the brain;\n
    5. \n
  5. \n the hypothalamus sends messages to pituitary gland;\n
    6. \n
  6. \n (pituitary) releases TSH;\n
    7. \n
  7. \n stimulating thyroxin release from thyroid;\n
    8. \n
  8. \n thyroxin controls metabolic rate / production of heat;\n
    9. \n
  9. \n muscle random contraction/shivering to generate heat;\n
    10. \n
  10. \n (brown) adipose tissue burns fat to generate waste heat;\n
    11. \n
  11. \n vasoconstriction to conserve heat / vasodilation to exchange heat with the environment;\n
    12. \n
\n
\n", "Examiners report": "None", "question_id": "SPM.2.SL.TZ0.A", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-3-homeostasis", "d3-3-5-thermoregulation-as-an-example-of-negative-feedback-control", "d3-3-6-thermoregulation-mechanisms-in-humans" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Outline the role of membrane proteins in the movement of specific ions at specific times in the transmission of nerve impulses.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n (during depolarization) Na\n \n +\n \n channels open;\n
    2. \n
  2. \n allowing Na\n \n +\n \n to flow into the axon;\n
    3. \n
  3. \n (during repolarization) K\n \n +\n \n channels open;\n
    4. \n
  4. \n allowing K\n \n +\n \n to flow out of the axon;\n
    5. \n
  5. \n the Na\n \n +\n \n /K\n \n +\n \n pump returns the (axon) membrane to the resting potential;\n
    6. \n
  6. \n by moving 3Na\n \n +\n \n out and 2K\n \n +\n \n in;\n
    7. \n
\n
\n", "Examiners report": "None", "question_id": "SPM.2.HL.TZ0.8B", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c2-2-neural-signalling", "c2-2-3-nerve-impulses-as-action-potentials-that-are-propagated-along-nerve-fibres" ] }, { "Question": "
\n
\n

\n The diagram shows a stage in cell division.\n

\n

\n \n

\n

\n [Source: © International Baccalaureate Organization 2019]\n

\n

\n

\n

\n What is the stage shown?\n

\n

\n A. Anaphase I of mitosis\n

\n

\n B. Anaphase II of mitosis\n

\n

\n C. Anaphase I of meiosis\n

\n

\n D. Anaphase II of meiosis\n

\n

\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "
\n

\n This proved to be a very easy question as 80% of the candidates recognized the cells were in anaphase II of meiosis.\n

\n
\n", "question_id": "19M.1A.SL.TZ2.17", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-1-cell-and-nuclear-division", "d2-1-8-identification-of-phases-of-mitosis" ] }, { "Question": "
\n
\n

\n Which process is common to photosynthesis and cell respiration?\n

\n

\n A. Photolysis\n

\n

\n B. The Calvin cycle\n

\n

\n C. The Krebs cycle\n

\n

\n D. Chemiosmosis\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "
\n

\n This wasn’t an exciting question but was the best discriminator on the exam, with nearly two thirds of candidates identifying chemiosmosis as a process that occurs in both photosynthesis and respiration.\n

\n
\n", "question_id": "19M.1A.HL.TZ1.31", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-2-cell-respiration", "c1-2-15-chemiosmosis-and-the-synthesis-of-atp-in-the-mitochondrion" ] }, { "Question": "
\n
\n

\n What is a universal characteristic of the genetic code?\n

\n

\n A. There are more than 64 different anticodons.\n

\n

\n B. There are more nucleotides than codons.\n

\n

\n C. There are more codons than amino acids.\n

\n

\n D. There are two or more amino acids for each codon.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "22M.1A.SL.TZ1.7", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d1-2-protein-synthesis", "d1-2-8-features-of-the-genetic-code" ] }, { "Question": "
\n
\n

\n What is/are required for facilitated diffusion?\n

\n

\n I. A concentration gradient\n

\n

\n II. ATP\n

\n

\n III. A channel protein\n

\n

\n A. I only\n

\n

\n B. I and III only\n

\n

\n C. II and III only\n

\n

\n D. I, II and III\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "22M.1A.SL.TZ1.3", "topics": [ "b-form-and-function" ], "subtopics": [ "b2-1-membranes-and-membrane-transport", "b2-1-6-channel-proteins-for-facilitated-diffusion", "b2-1-8-selectivity-in-membrane-permeability" ] }, { "Question": "
\n
\n (b.ii)\n
\n
\n

\n State how type I diabetes should be treated to avoid harmful health consequences of the condition.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n inject insulin / monitoring blood glucose / devices that release insulin;\n
    2. \n
  2. \n decrease consumption of sugars/CHO / diet modification;\n
    3. \n
  3. \n increase exercise;\n
    4. \n
  4. \n keep weight in healthy range;\n
    5. \n
\n
\n", "Examiners report": "None", "question_id": "22M.2.SL.TZ2.5B.II", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-3-homeostasis", "d3-3-4-physiological-changes-that-form-the-basis-of-type-1-and-type-2-diabetes" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Identify the recombinants.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n grey vestigial and black normal ✔\n

\n

\n \n Accept Ggvv and ggVv or alternative acceptable upper/lower case genotypes.\n \n

\n
\n", "Examiners report": "None", "question_id": "19N.2.HL.TZ0.2B", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-2-inheritance", "d3-2-17-punnett-grids-for-predicting-genotypic-and-phenotypic-ratios-in-dihybrid-crosses-involving-pairs-of-unlinked-autosomal-genes", "d3-2-18-loci-of-human-genes-and-their-polypeptide-products", "d3-2-19-autosomal-gene-linkage", "d3-2-20-recombinants-in-crosses-involving-two-linked-or-unlinked-genes" ] }, { "Question": "
\n
\n

\n Which process explains the observations shown in the images?\n

\n

\n A. Active transport\n

\n

\n B. Exocytosis\n

\n

\n C. Facilitated diffusion\n

\n

\n D. Osmosis\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "21M.1A.SL.TZ1.2", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-3-water-potential", "d2-3-3-water-movement-by-osmosis-into-or-out-of-cells" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Outline the cell theory.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. cells can only arise from preexisting cells ✔\n

\n

\n b. living organisms are composed of cells/smallest unit of life ✔\n

\n

\n c. organisms consisting of only one cell carry out all functions of life in that cell/cells perform life functions «at some point in their existence» ✔\n

\n

\n d. although most organisms conform to cell theory, there are exceptions ✔\n

\n
\n", "Examiners report": "None", "question_id": "19N.2.SL.TZ0.3", "topics": [ "a-unity-and-diversity", "c-interaction-and-interdependence" ], "subtopics": [ "a2-2-cell-structure", "a2-2-1-cells-as-the-basic-structural-unit-of-all-living-organisms", "a2-2-7-processes-of-life-in-unicellular-organisms", "a3-1-diversity-of-organisms", "a3-1-6-diversity-in-chromosome-numbers-of-plant-and-animal-species", "c1-2-cell-respiration", "c1-2-5-differences-between-anaerobic-and-aerobic-cell-respiration-in-humans", "c1-2-10-anaerobic-cell-respiration-in-yeast-and-its-use-in-brewing-and-baking" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Describe how plants are named and classified, including recognition features of plant phyla.\n

\n
\n
\n

\n [7]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n binomial naming\n
    \n \n \n OR\n \n \n
    \n genus and species name;\n
    2. \n
  2. \n plants constitute a kingdom\n
    3. \n
  3. \n plants are eukaryotes/belong to the domain eukaryota\n
    4. \n
  4. \n classified using a hierarchy of taxa\n
    \n \n \n OR\n \n \n
    \n kingdom, phylum, class, order, family, genus, species\n
    5. \n
  5. \n bryophyta/filicinophyta/coniferophyte/angiospermophyta is a\n \n phylum\n \n (of plants);\n
    6. \n
  6. \n bryophytes have only rhizoids/spores (produced in a capsule)/no roots/ no vascular tissue;\n
    7. \n
  7. \n filicinophytes have stems/roots/xylem-phloem/reproduce by spores/leaves that uncurl; but no seeds\n
    8. \n
  8. \n coniferophytes have seeds in cones/ vascular tissue/xylem-phloem/cambium/ but no flowers/no fruits\n
    9. \n
  9. \n angiospermophytes have flowers/produce seeds/produce fruits/vascular tissue/xylem-phloem;\n
    10. \n
  10. \n named example showing of the classification of a plant from species to domain or vice versa\n
    11. \n
  11. \n \n cladistics\n \n is used to reclassify groups of plants\n
    \n \n \n OR\n \n \n
    \n named example of a group of plants reclassified by\n \n cladistics\n \n ;\n
    12. \n
  12. \n use a dichotomous key to discriminate among plant features\n
    13. \n
\n

\n

\n

\n \n Each phylum of plants requires at least 2 features for the mark.\n \n

\n

\n \n Mp-e does not require all 4 phyla to be named.\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ1.7", "topics": [ "a-unity-and-diversity", "c-interaction-and-interdependence" ], "subtopics": [ "a3-2-classification-and-cladistics-(hl-only)", "a3-2-2-difficulties-classifying-organisms-into-the-traditional-hierarchy-of-taxa", "c4-2-transfers-of-energy-and-matter", "c4-2-17-constructing-carbon-cycle-diagrams" ] }, { "Question": "
\n
\n

\n Which molecular diagram shows part of a cellulose molecule?\n
\n
\n

\n

\n \n

\n

\n \n

\n

\n \n

\n

\n \n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "None", "question_id": "23M.1A.SL.TZ1.7", "topics": [ "b-form-and-function" ], "subtopics": [ "b1-1-carbohydrates-and-lipids", "b1-1-6-structure-of-cellulose-related-to-its-function-as-a-structural-polysaccharide-in-plants" ] }, { "Question": "
\n
\n (d)\n
\n
\n

\n The cladogram includes four marsupial (non-placental mammal) families.\n

\n

\n \n

\n

\n [Source: Koala image: Quartl, https://commons.wikimedia.org/wiki/Phascolarctos_cinereus#/media/\n
\n File:Friendly_Female_Koala.JPG; Wombat image: JJ Harrison, https://en.wikipedia.org/wiki/Wombat#/\n
\n media/File:Vombatus_ursinus_-Maria_Island_National_Park.jpg; Marsupial lion: Nobu Tamura,\n
\n https://en.wikipedia.org/wiki/Marsupial_lion#/media/File:Thylacoleo_BW.jpg;\n
\n Diprotodontoidea image: Anne Musser]\n

\n

\n

\n

\n Deduce the family that is most closely related to the Diprotodontoidea.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n Vombatidae/wombats ✔\n

\n
\n", "Examiners report": "
\n

\n Nearly everyone spotted the wombat correctly.\n

\n
\n", "question_id": "19M.2.SL.TZ2.4D", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a3-2-classification-and-cladistics-(hl-only)", "a3-2-7-analysing-cladograms" ] }, { "Question": "
\n
\n

\n How does the Miller-Urey experiment contribute to an explanation of the origin of life?\n

\n

\n
\n A.  It shows how phospholipids form protocells in specific laboratory conditions.\n

\n

\n B.  It explains how organic molecules arise from inorganic ones under certain environmental conditions.\n

\n

\n C.  It explains the synthesis of RNA, recreating deep sea vent conditions in the laboratory.\n

\n

\n D.  It shows how the last universal common ancestor (LUCA) evolved from vesicles.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "SPM.1A.HL.TZ0.13", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a2-1-origins-of-cells-(hl-only)", "a2-1-4-evidence-for-the-origin-of-carbon-compounds" ] }, { "Question": "
\n
\n

\n State the trophic level of the sea urchin.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n herbivore/primary consumer ✔\n

\n

\n \n Do not accept second trophic level\n \n

\n
\n", "Examiners report": "
\n

\n Primary consumer was frequently stated and second trophic level also seen, although not credited as the syllabus demands the former term.\n

\n
\n", "question_id": "19M.2.SL.TZ1.A", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c4-2-transfers-of-energy-and-matter", "c4-2-10-classification-of-organisms-into-trophic-levels" ] }, { "Question": "
\n
\n

\n Describe the movements in ions that occur during time\n \n t\n \n .\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n Na\n \n +\n \n /sodium ions diffuse into the axon (in the first part/half of\n \n t\n \n );\n
\n K\n \n +\n \n /potassium ions diffuse out of the axon (in the second half/part of\n \n t\n \n )\n

\n

\n \n Do not accept the name of the element without indication that it is an ion\n \n .\n

\n
\n", "Examiners report": "
\n

\n Some candidates talked about ion movement but with no reference to a specific ion; some described the Na\n \n +\n \n /K\n \n +\n \n pump here and received no marks.\n

\n
\n", "question_id": "22M.2.HL.TZ1.C", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c2-2-neural-signalling", "c2-2-3-nerve-impulses-as-action-potentials-that-are-propagated-along-nerve-fibres", "c2-2-8-depolarization-and-repolarization-during-action-potentials" ] }, { "Question": "
\n
\n

\n The cladogram shows one theory of how species of hominin evolved.\n

\n

\n \n

\n

\n What can be deduced using the information in the cladogram?\n

\n

\n A. The closest species to\n \n K. platyops\n \n is\n \n A. africanus\n \n .\n

\n

\n B.\n \n A. afarensis\n \n is extinct.\n

\n

\n C. The DNA of\n \n H. sapiens\n \n is the same as that of\n \n H. ergaster\n \n .\n

\n

\n D.\n \n H. sapiens\n \n and\n \n P. robustus\n \n shared a common ancestor.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "21N.1A.HL.TZ0.23", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a3-2-classification-and-cladistics-(hl-only)", "a3-2-7-analysing-cladograms" ] }, { "Question": "
\n
\n

\n State how type I diabetes should be treated to avoid harmful health consequences of the condition.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n inject insulin / monitoring blood glucose / devices that release insulin;\n
    2. \n
  2. \n decrease consumption of sugars/CHO / diet modification;\n
    3. \n
  3. \n increase exercise;\n
    4. \n
  4. \n keep weight in healthy range;\n
    5. \n
\n
\n", "Examiners report": "None", "question_id": "22M.2.SL.TZ2.B.II", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-3-homeostasis", "d3-3-4-physiological-changes-that-form-the-basis-of-type-1-and-type-2-diabetes" ] }, { "Question": "
\n
\n (d)\n
\n
\n

\n The proportion of banded and unbanded individuals in a population of\n \n D. plantarius\n \n can change. Suggest how such a change could occur.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n natural selection could favour one type over the other;\n
    2. \n
  2. \n greater survival of one type\n
    \n \n OR\n \n
    \n one type better camouflaged than the other type;\n
    3. \n
  3. \n one type more attractive during courtship/mate selection;\n
    4. \n
\n

\n

\n

\n \n Do not accept a list. Natural selection or sexual selections alone are not adequate.\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ1.5D", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-2-inheritance", "d3-2-5-effects-of-dominant-and-recessive-alleles-on-phenotype" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Using the graph, estimate isotonic sucrose solutions for potato tissue and carrot tissue.\n

\n

\n Potato:\n

\n

\n Carrot:\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n potato: 0.26 mol dm\n \n –3\n \n ✔\n \n Allow a range of 0.22–0.32\n \n
\n carrot: 0.50 mol dm\n \n –3\n \n ✔\n \n Allow a range of 0.45–0.55 (Allow 1 max if no units or either unit is omitted)\n \n

\n
\n", "Examiners report": "None", "question_id": "19N.1B.SL.TZ0.1A", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-3-water-potential", "d2-3-3-water-movement-by-osmosis-into-or-out-of-cells", "d2-3-4-changes-due-to-water-movement-in-plant-tissue-bathed-in-hypotonic-and-those-bathed-in-hypertonic-solutions" ] }, { "Question": "
\n
\n

\n The image shows a cell from the root tip of an onion (Allium cepa) (2n = 16) during late prophase of mitosis.\n

\n

\n \n

\n

\n \n [Source: Davidson, M.W. and Molecular Expressions at Florida State University, n.d.\n \n Late prophase\n \n . [image online]\n \n
\n \n Available at: https://micro.magnet.fsu.edu/micro/gallery/mitosis/mitosis.html [Accessed 5 October 2021].]\n \n

\n

\n

\n

\n How many chromatids are present in the cell?\n

\n

\n
\n A.  8\n

\n

\n B.  16\n

\n

\n C.  32\n

\n

\n D.  64\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "23M.1A.SL.TZ2.5", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-1-cell-and-nuclear-division", "d2-1-8-identification-of-phases-of-mitosis" ] }, { "Question": "
\n
\n

\n What feature of eukaryotic chromosomes distinguishes them from the chromosomes of prokaryotes?\n

\n

\n A. Histone proteins\n

\n

\n B. Circular DNA\n

\n

\n C. Double-stranded DNA molecules\n

\n

\n D. Multiple genes along the length of each chromosome\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "None", "question_id": "21M.1A.SL.TZ2.14", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a2-2-cell-structure", "a2-2-6-eukaryote-cell-structure" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Calculation of Simpson’s reciprocal diversity index for both rockpools gives the following results.\n

\n

\n \n

\n

\n Outline what conclusion can be drawn from the results.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B is more diverse/biodiverse than A;\n

\n

\n \n Accept vice-versa. Do not accept greater Simpson’s reciprocal diversity index\n \n .\n

\n
\n", "Examiners report": "
\n

\n The conclusion from the table showing values of Simpson’s reciprocal diversity index required mention of biodiversity, not simply that one pool is more diverse.\n

\n
\n", "question_id": "20N.2.SL.TZ0.14B", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a4-2-conservation-of-biodiversity", "a4-2-5-evidence-for-a-biodiversity-crisis" ] }, { "Question": "
\n
\n

\n Describe the overall effects of low and high doses of neonicotinoid on the egg lengths of all four species.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n low doses caused (slight) decrease in (average) egg lengths in 3 species/most species\n
    \n \n \n OR\n \n \n
    \n low doses caused a slight increase in 1 species/\n \n B. pascuorum\n \n ;\n
    2. \n
  2. \n high doses caused (slightly) lower (average) results in all 4 species (compared to control);\n
    3. \n
  3. \n in only one species/\n \n B. pratorum\n \n , the high doses caused larger lengths than the low doses;\n
    4. \n
\n

\n \n Accept any other valid comparison\n \n .\n

\n
\n", "Examiners report": "None", "question_id": "22M.2.HL.TZ2.C.II", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c2-2-neural-signalling", "c2-2-12-effects-of-exogenous-chemicals-on-synaptic-transmission" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n State the region of the kidney in which the loop of Henle is situated.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n medulla;\n

\n
\n", "Examiners report": "
\n

\n 70\n \n \n \n \n % of candidates knew that the loop of Henle is in the medulla.\n

\n
\n", "question_id": "22N.2.HL.TZ0.5B", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-3-homeostasis", "d3-3-9-role-of-the-loop-of-henle" ] }, { "Question": "
\n
\n (a.i)\n
\n
\n

\n Describe the effect of neonicotinoid pesticides on the nervous system of insects.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n blocks synaptic transmission at (cholinergic synapses);\n
    2. \n
  2. \n binds to (acetylcholine) receptors;\n
    3. \n
\n
\n", "Examiners report": "
\n

\n A pleasing number were able to correctly describe the effect of the pesticides on the synapses and state the cumulative increase correctly in ai and aii. However, in aiii, many did not see the similarity in pattern for the compare mark. In part b stronger candidates commented on the fact that even at low doses the pesticide had a great effect and that the difference between high and low doses was negligible. Many examiners were bemused by the answers to c(i) where about half of the candidates failed to identify\n \n B. lucorum\n \n as the most affected species.\n \n B. pascuorum\n \n and\n \n B. terrestris\n \n were often incorrectly given. In cii. Better candidates described the overall effects as asked, with weaker candidates just describing each species in turn. In 1d the top candidates looked at all of the data, but those who just stated that the effect was not noticeable as the egg length was not significantly smaller gained the mark.\n

\n
\n", "question_id": "22M.2.HL.TZ2.1A.I", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c2-2-neural-signalling", "c2-2-12-effects-of-exogenous-chemicals-on-synaptic-transmission" ] }, { "Question": "
\n
\n (d)\n
\n
\n

\n Apart from the ribosomes, explain the evidence for the endosymbiotic theory of the origin of eukaryotic cells.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n a. mitochondria/chloroplasts show features in common with\n \n prokaryotes\n \n /similar size;\n

\n

\n b. multiply by binary fission/in same manner;\n

\n

\n c. have naked loop of DNA/circular DNA/own DNA;\n

\n

\n d. surrounded by a double membrane;\n

\n
\n", "Examiners report": "None", "question_id": "20N.2.HL.TZ0.2D", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a2-2-cell-structure", "a2-2-12-origin-of-eukaryotic-cells-by-endosymbiosis" ] }, { "Question": "
\n
\n

\n The image shows a micrograph of a cell.\n

\n

\n \n

\n

\n [Source: © 2014, https://commons.wikimedia.org/wiki/File:Mitosis_(261_13)_Pressed;_root_meristem_of_onion_(cells_\n
\n in_prophase,_metaphase,_anaphase,_telophase).jpg by Doc. RNDr. Josef Reischig, CSc.]\n

\n

\n

\n

\n What explains the appearance of the cell in the micrograph?\n

\n

\n A. The cell is dying.\n

\n

\n B. The DNA is replicating.\n

\n

\n C. The cell is in metaphase.\n

\n

\n D. The cell is in telophase.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "
\n

\n Candidates also found this question easy, but it was a very good discriminator, this means that good candidates answered it well while weaker candidates did not. It therefore proved to be an effective question.\n

\n
\n", "question_id": "19M.1A.SL.TZ2.3", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-1-cell-and-nuclear-division", "d2-1-8-identification-of-phases-of-mitosis" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Draw\n \n one\n \n phospholipid molecule on the diagram to show a possible position in the membrane.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n phospholipid shown with circular head and 2 tails;\n
\n e.g.\n

\n

\n \n

\n

\n \n [Source: Material from: Stauch, B., Johansson, L.C., McCorvy, J.D.,\n \n
\n \n et al., Structural basis of ligand recognition at the human MT1\n \n
\n \n melatonin receptor, published 2019,\n \n Nature\n \n , reproduced with\n \n
\n \n permission of SNCSC.]\n \n

\n

\n phospholipid shown in either the upper or lower half of the membrane only with its head at the margin of the membrane and tails towards centre;\n

\n

\n \n Accept answers with two or more phospholipids shown, as long as all are correct.\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.2.HL.TZ1.2", "topics": [ "b-form-and-function", "c-interaction-and-interdependence" ], "subtopics": [ "b2-1-membranes-and-membrane-transport", "b2-1-14-gated-ion-channels-in-neurons", "b1-2-proteins", "b1-2-8-pleating-and-coiling-of-secondary-structure-of-proteins", "b1-2-6-chemical-diversity-in-the-r-groups-of-amino-acids-as-a-basis-for-the-immense-diversity-in-protein-form-and-function", "c3-1-integration-of-body-systems", "c3-1-11-modulation-of-sleep-patterns-by-melatonin-secretion-as-a-part-of-circadian-rhythms" ] }, { "Question": "
\n
\n

\n The graph shows the concentration of the lipid lecithin in the amniotic fluid surrounding the fetus during normal gestation. This lipid is produced in the lungs of the fetus and acts as a surfactant.\n

\n

\n \n

\n

\n [Source: Gluck, L. and Kulovich, M., n.d. [\n \n Concentrations of phospholipids\n \n ]. [graph online] Available at:\n
\n http://www.columbia.edu/itc/hs/medical/humandev/2004/Chpt12-LungDev.pdf [Accessed 28 October 2021].]\n

\n

\n

\n

\n What problem may occur in a baby born before 34 weeks gestation?\n

\n

\n A.  Type I pneumocytes do not produce sufficient surfactant for lungs to inflate.\n

\n

\n B.  There are no type II pneumocytes.\n

\n

\n C.  The alveolar walls stick together.\n

\n

\n D.  The alveoli are too large.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "
\n

\n This question concerned the production of a surfactant in the lungs. This question was the best discriminator on the paper. The most common incorrect response was A with candidates confusing the role of type I and type II pneumocytes.\n

\n
\n", "question_id": "22N.1A.SL.TZ0.28", "topics": [ "b-form-and-function" ], "subtopics": [ "b2-3-cell-specialization", "b2-3-8-adaptations-of-type-i-and-type-ii-pneumocytes-in-alveoli" ] }, { "Question": "
\n
\n

\n The electron micrograph shows a section through a plant cell.\n

\n

\n \n

\n

\n [Source: Photo © E. Newcomb.]\n

\n

\n In which structure(s) is the genome of the cell contained?\n

\n

\n A. Z only\n

\n

\n B. X, Y and Z only\n

\n

\n C. W and X only\n

\n

\n D. X and Y only\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "
\n

\n This question was difficult and did not discriminate well with most candidates opting for A, the nucleus alone rather than response B which included the chloroplast and mitochondrion. Section 3.1 (Genes) in the guide defines the genome as \"the whole of the genetic information of an organism\". Section 1.5 (The origin of cells) requires the candidates to have reviewed the evidence for the endosymbiotic theory so knowledge that some organelles also carry genetic material would be expected.\n

\n
\n", "question_id": "21M.1A.SL.TZ2.13", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a2-2-cell-structure", "a2-2-10-cell-types-and-cell-structures-viewed-in-light-and-electron-micrographs" ] }, { "Question": "
\n
\n (a.iv)\n
\n
\n

\n Suggest a reason for the changes in mass in the colonies between weeks 6 and 8.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n less production of honey/wax;\n
    2. \n
  2. \n fewer bees/dispersal of bees/queens;\n
    3. \n
  3. \n bad weather/environmental change/predators/disease/pests;\n
    4. \n
\n
\n", "Examiners report": "None", "question_id": "22M.2.HL.TZ2.1A.IV", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c2-2-neural-signalling", "c2-2-12-effects-of-exogenous-chemicals-on-synaptic-transmission" ] }, { "Question": "
\n
\n

\n Which event happens in meiosis II but not in meiosis I?\n

\n

\n A. Spindle microtubules attach to centromeres.\n

\n

\n B. Crossing over occurs.\n

\n

\n C. Sister chromatids move to opposite poles.\n

\n

\n D. Chromosomes become shorter and thicker by coiling.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "19N.1A.SL.TZ0.35", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-1-cell-and-nuclear-division", "d2-1-9-meiosis-as-a-reduction-division" ] }, { "Question": "
\n
\n (a.ii)\n
\n
\n

\n Explain how the two strands of the DNA double helix are held together.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n hydrogen bonding\n \n between\n \n nucleotides / bases;\n
    2. \n
  2. \n complementary base pairs;\n
    3. \n
  3. \n adenine-thymine and cytosine-guanine form base pairs (between the two strands with H-bonding);\n
    4. \n
  4. \n 2 bonds between A and T, while 3 bonds between C and G;\n
    5. \n
\n

\n \n OWTTE\n \n

\n

\n \n Full names required for c and d though use ecf.\n \n

\n
\n", "Examiners report": "None", "question_id": "22M.2.SL.TZ2.5A.II", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a1-2-nucleic-acids", "a1-2-6-dna-as-a-double-helix-made-of-two-antiparallel-strands-of-nucleotides-with-two-strands-linked-by-hydrogen-bonding-between-complementary-base-pairs" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Describe the structure of starch.\n

\n
\n
\n

\n [5]\n

\n
\n
\n", "Markscheme": "
\n

\n a. starch is a carbohydrate ✔\n

\n

\n b. starch is formed by carbon, hydrogen and oxygen ✔\n

\n

\n c. it is a polymer/chain/polysaccharide ✔\n

\n

\n d. formed from monosaccharides/simple sugars/glucose ✔\n

\n

\n e. linked together by condensation/dehydration ✔\n

\n

\n f. consists of amylose and amylopectin ✔\n

\n

\n g. amylose is a long chain/unbranched ✔\n

\n

\n h. amylopectin is branched ✔\n

\n
\n", "Examiners report": "
\n

\n (attempted by about 40 % of the cohort)\n

\n

\n The question was put in the context of the composition of pastry cream, rather than just diving in with questions. In part (a), the structure of starch was quite well known. The better answers included descriptions of polymers and monomers, amylose and amylopectin, and glucose. Part (b) was challenging to many, requiring a knowledge of the digestive system, enzyme action and the blood supply to the liver. It was possible to gain all of the marks by omitting the references to the blood stream. This was an example of where a clear 'essay plan' would have helped. Weaker candidates wrote at length about carbohydrate and fat digestion which was not required. Surprisingly the position of the pancreas was often confused, with pancreatic enzymes appearing in the stomach. The fundamental idea of the digestion of large molecules (proteins) to small soluble ones (amino acids) which can be absorbed into the blood stream at the villi was missed by many. Part (c) was a straightforward genetics cross, put into the context of lactose intolerance. In general, it was well answered. Although the question clearly stated that it was an autosomal recessive condition, many weaker students were determined to make it sex linked.\n

\n
\n", "question_id": "21M.2.HL.TZ2.5A", "topics": [ "b-form-and-function" ], "subtopics": [ "b1-1-carbohydrates-and-lipids", "b1-1-5-polysaccharides-as-energy-storage-compounds" ] }, { "Question": "
\n
\n (c.ii)\n
\n
\n

\n Describe the overall effects of low and high doses of neonicotinoid on the egg lengths of all four species.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n low doses caused (slight) decrease in (average) egg lengths in 3 species/most species\n
    \n \n \n OR\n \n \n
    \n low doses caused a slight increase in 1 species/\n \n B. pascuorum\n \n ;\n
    2. \n
  2. \n high doses caused (slightly) lower (average) results in all 4 species (compared to control);\n
    3. \n
  3. \n in only one species/\n \n B. pratorum\n \n , the high doses caused larger lengths than the low doses;\n
    4. \n
\n

\n \n Accept any other valid comparison\n \n .\n

\n
\n", "Examiners report": "None", "question_id": "22M.2.HL.TZ2.1C.II", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c2-2-neural-signalling", "c2-2-12-effects-of-exogenous-chemicals-on-synaptic-transmission" ] }, { "Question": "
\n
\n

\n Identify the molecule Z.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n glycerol /glycerin ✔\n

\n
\n", "Examiners report": "
\n

\n The diagram was generally confusing to candidates.\n

\n

\n This was generally missed.\n

\n

\n

\n
\n", "question_id": "21M.2.HL.TZ1.A.II", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-3-photosynthesis", "c1-3-18-synthesis-of-carbohydrates-amino-acids-and-other-carbon-compounds-using-the-products-of-the-calvin-cycle-and-mineral-nutrients" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Outline how two parents could have a child with any of the four ABO blood groups.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n

\n a. «first set of» gametes/parental genotype I\n \n A\n \n , i ✔\n

\n

\n b. «other set of» gametes/parental genotype I\n \n B\n \n , i ✔\n

\n

\n c. «genotypes of offspring are respectively» I\n \n A\n \n I\n \n B\n \n , I\n \n B\n \n i, I\n \n A\n \n i, ii ✔\n \n All four correct required\n \n .\n

\n

\n d. «phenotypes of offspring are respectively» AB, B, A, O ✔\n \n All four correct required linked to genotypes\n \n

\n

\n \n Award marks only for the first grid if more than one drawn;\n \n
\n \n e.g. of Punnett grid\n \n

\n

\n \n \n \n

\n

\n \n Answers can be given in a Punnett grid or in prose\n \n .\n

\n

\n \n Accept the four possible blood groups of the offspring anywhere in the answer\n \n .\n

\n
\n", "Examiners report": "None", "question_id": "19N.2.SL.TZ0.6B", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-2-inheritance", "d3-2-9-abo-blood-groups-as-an-example-of-multiple-alleles" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n State the name of the instrument used to make these traces.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n oscilloscope ✔\n

\n
\n", "Examiners report": "
\n

\n Fewer than 1 in 10 were able to name the oscilloscope. There were some G2 comments about this, but the students should have seen traces like this and should know how they were obtained.\n

\n
\n", "question_id": "19M.2.SL.TZ2.1C", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c2-2-neural-signalling" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Outline the role of tRNA in hemoglobin synthesis.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n decoding/translation (of the genetic code/RNA base sequence);\n
    2. \n
  2. \n carries/brings one amino acid/a specific amino acid/the amino acid (corresponding to codon/anticodon);\n
    3. \n
  3. \n tRNA has an\n \n anticodon\n \n which pairs with mRNA/is complementary to a\n \n codon\n \n (on mRNA);\n
    4. \n
\n
\n", "Examiners report": "
\n

\n There were varied answers to this question. The best made it clear that a tRNA molecule carries one specific amino acid corresponding to its anticodon and to the codon on mRNA to which it binds during translation.\n

\n
\n", "question_id": "22M.2.SL.TZ1.4C", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d1-2-protein-synthesis", "d1-2-6-roles-of-mrna-ribosomes-and-trna-in-translation" ] }, { "Question": "
\n
\n

\n Discuss the significance of the oxygen dissociation curves for adult hemoglobin and fetal hemoglobin.\n

\n
\n
\n

\n [6]\n

\n
\n
\n", "Markscheme": "
\n

\n a. oxyhemoglobin forms when partial pressure of oxygen is high\n
\n \n \n OR\n \n \n
\n oxyhemoglobin dissociates/breaks apart when partial pressure of oxygen is low ✔\n

\n

\n b. respiring tissues have low partial pressure of oxygen ✔\n

\n

\n c. sketch/statement of S-shaped «oxygen dissociation» curve ✔\n

\n

\n d. axes of graph labelled correctly as percentage oxygen saturation of hemoglobin on\n \n y\n \n -axis\n \n \n AND\n \n \n partial pressure of oxygen on\n \n x-\n \n axis ✔\n \n Both needed. Do not accept reverse axes.\n \n

\n

\n e. «small» decrease in oxygen partial pressure over steep part of curve results in dissociation of oxyhemoglobin/oxygen release to tissues ✔\n

\n

\n f. fetal hemoglobin is structurally different from adult/maternal hemoglobin ✔\n

\n

\n g. fetal dissociation curve to left of adult dissociation curve ✔\n

\n

\n h. fetal hemoglobin has greater affinity for oxygen than adult/maternal blood ✔\n

\n

\n i. fetus obtains its oxygen from mother’s blood «at placenta» ✔\n

\n

\n j. at any given partial pressure of oxygen fetus will take up oxygen from mother\n
\n \n \n OR\n \n \n
\n fetal hemoglobin always more saturated with oxygen than maternal blood ✔\n

\n

\n \n Some of these points may be present in annotated diagrams.\n \n

\n
\n", "Examiners report": "
\n

\n Most candidates generally provided good, and many complete, thorough explanations including well annotated diagrams, but there were also answers lacking sufficient details or containing diverse inaccuracies or incorrect terminology (\n \n e.g.\n \n concentration instead of partial pressure). Some candidates ventured sometimes in long explanations of hemoglobin structure or gas exchange at lung level in adults, or description of Bohr shift, all irrelevant for this question which differed slightly from questions in past papers on similar topics.\n

\n
\n", "question_id": "19M.2.HL.TZ2.23", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-1-gas-exchange", "b3-1-11-adaptations-of-foetal-and-adult-haemoglobin-for-the-transport-of-oxygen", "b3-1-13-oxygen-dissociation-curves-as-a-means-of-representing-the-affinity-of-haemoglobin-for-oxygen-at-different-oxygen-concentrations" ] }, { "Question": "
\n
\n

\n Which cell is a component of the innate immune system?\n

\n

\n
\n A.  T lymphocyte\n

\n

\n B.  Phagocyte\n

\n

\n C.  B lymphocyte\n

\n

\n D.  B memory cell\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "SPM.1A.HL.TZ0.29", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-2-defence-against-disease", "c3-2-4-differences-between-the-innate-immune-system-and-the-adaptive-immune-system" ] }, { "Question": "
\n
\n

\n A hummingbird is shown visiting a large flower.\n

\n

\n \n

\n

\n [Source: Nussbaumer, R./Naturepl.com, n.d. Black chinned hummingbird (\n \n Archilochus alexandri\n \n ). Available at:\n
\n https://www.naturepl.com/stock-photo/black-chinned-hummingbird-archilochus-alexandri-male-feeding-at-sageflower/search/detail-0_01140572.html.]\n

\n

\n

\n

\n What makes this a mutualistic relationship?\n

\n

\n A.  The bird feeds on nectar and transfers pollen to the stamen of a flower of the same species.\n

\n

\n B.  The bird obtains nutrients and the plant is assisted with pollination for sexual reproduction.\n

\n

\n C.  The bird requires pollen as a protein source and, while obtaining this, disperses seeds for the plant.\n

\n

\n D.  The bird transfers pollen to the stigma of flowers of a different species while feeding.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "22N.1A.HL.TZ0.34", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c4-1-populations-and-communities", "c4-1-11-herbivory-predation-interspecific-competition-mutualism-parasitism-and-pathogenicity-as-categories-of-interspecific-relationship-within-communities", "c4-1-12-mutualism-as-an-interspecific-relationship-that-benefits-both-species" ] }, { "Question": "
\n
\n

\n How do R group interactions contribute to protein structure?\n

\n

\n I. Determining the sequence of amino acids in the primary structure\n

\n

\n II. Stabilizing beta pleated sheets in the secondary structure\n

\n

\n III. Stabilizing further foldings of a polypeptide into a tertiary structure\n

\n

\n A. I only\n

\n

\n B. II and III only\n

\n

\n C. III only\n

\n

\n D. I, II and III\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "19N.1A.HL.TZ0.28", "topics": [ "b-form-and-function" ], "subtopics": [ "b1-2-proteins", "b1-2-1-generalized-structure-of-an-amino-acid", "b1-2-10-effect-of-polar-and-non-polar-amino-acids-on-tertiary-structure-of-proteins" ] }, { "Question": "
\n
\n

\n The micrograph shows two types of blood cell.\n

\n

\n \n

\n

\n What determines the differences between the two types of cell?\n

\n

\n
\n A.  Different number of mitotic cycles\n

\n

\n B.  Different expression of some genes\n

\n

\n C.  Reaction to oxygen of red blood cells\n

\n

\n D.  Reaction to antigens of white blood cells\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "23M.1A.SL.TZ1.1", "topics": [ "b-form-and-function" ], "subtopics": [ "b2-3-cell-specialization", "b2-3-5-cell-size-as-an-aspect-of-specialization" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Compare and contrast the changes in mean ambient and body temperatures during 2012.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n \n Accept one similarity\n \n :\n

\n
    \n
  1. \n both rise\n \n and\n \n then fall / both fall with hibernation\n \n and\n \n rise with activity\n
    2. \n
  2. \n both reach minimum during hibernation\n \n and\n \n maximum during activity;\n
    3. \n
  3. \n both lowest in January/February / both rise from January/February;\n
    \n \n
    \n Accept one difference\n     \n :\n
    \n
    \n
    4. \n
  4. \n one peak of ambient temp but body temp has two peaks / OWTTE;\n
    5. \n
  5. \n body temp remains maximal for longer/plateaus whereas ambient peaks;\n
    6. \n
  6. \n body temperature is always higher than ambient temperature;\n
    7. \n
  7. \n ambient range is greater than body temperature range / OWTTE;\n
    8. \n
\n
\n", "Examiners report": "
\n

\n Many candidates realized that they were expected to give similarities and differences between the curves, but most struggled to do this clearly. Rather than make eclectic statements about the data that may be correct but are not significant, the aim with a question such as this is to make comments that would allow someone who has not been shown the curves to sketch them. Some students confused maxima or minima with increases and decreases, so for example stating that ambient body temperature increased in July, when it reached a maximum in July and stopped increasing.\n

\n
\n", "question_id": "22M.2.SL.TZ1.1B", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-3-homeostasis", "d3-3-1-homeostasis-as-maintenance-of-the-internal-environment-of-an-organism", "d3-3-2-negative-feedback-loops-in-homeostasis" ] }, { "Question": "
\n
\n

\n Which structural feature enables saltatory conduction?\n

\n

\n A. Nodes of Ranvier between Schwann cells\n

\n

\n B. Na\n \n +\n \n channels under Schwann cells\n

\n

\n C. K\n \n +\n \n channels under Schwann cells\n

\n

\n D. Sodium–potassium pumps under Schwann cells\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "None", "question_id": "21M.1A.HL.TZ1.23", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c2-2-neural-signalling", "c2-2-11-saltatory-conduction-in-myelinated-fibres-to-achieve-faster-impulses" ] }, { "Question": "
\n
\n

\n The diagram shows mRNA codons.\n

\n

\n \n

\n

\n [Source: elementix / Alamy Stock Photo]\n

\n

\n

\n

\n The mRNA sequence UGGAACGUA codes for what amino acid sequence?\n

\n

\n A. Glycine-Glutamine-Methionine\n

\n

\n B. Methionine-Glutamine-Glycine\n

\n

\n C. Threonine-Valine-Histidine\n

\n

\n D. Tryptophan-Asparagine-Valine\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "19N.1A.SL.TZ0.7", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d1-2-protein-synthesis", "d1-2-9-using-the-genetic-code-expressed-as-a-table-of-mrna-codons" ] }, { "Question": "
\n
\n

\n The diagram shows the realized niches of the five species of warbler. Suggest how the fundamental niche of\n \n D. castanea\n \n might differ from its realized niche.\n

\n

\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. the realized is the actual niche and the fundamental is in the absence of competition;\n

\n

\n b. with no competition the\n \n D. castanea\n \n would have a larger habitat/more food\n
\n \n \n OR\n \n \n
\n \n D.castanea\n \n could occupy the niches currently occupied by the other warbler species;\n

\n

\n \n Accept named species\n \n .\n

\n
\n", "Examiners report": "
\n

\n Weaker candidates gave incomplete or confused suggestions in differentiating between the realised and fundamental niche.\n

\n
\n", "question_id": "20N.2.SL.TZ0.D", "topics": [ "b-form-and-function" ], "subtopics": [ "b4-2-ecological-niches", "b4-2-12-fundamental-and-realized-niches", "b4-2-13-competitive-exclusion-and-the-uniqueness-of-ecological-niches" ] }, { "Question": "
\n
\n

\n What is a function of luteinizing hormone (LH) in the female menstrual cycle?\n

\n

\n A. To promote secondary sexual characteristics\n

\n

\n B. To inhibit progesterone secretion\n

\n

\n C. To stimulate the follicle to release estrogen\n

\n

\n D. To trigger ovulation\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "21N.1A.SL.TZ0.30", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-1-reproduction", "d3-1-5-changes-during-the-ovarian-and-uterine-cycles-and-their-hormonal-regulation" ] }, { "Question": "
\n
\n (j)\n
\n
\n

\n Discuss whether natural selection would favour the transgenic EBF-producing thale cress plants if they were released into the wild.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. mutant aphids/varieties may be indifferent to/attracted to transgenic plants as these do not present a hazard «not favour» ✔\n
\n
\n b. initially/for limited time the plants would thrive as the aphids would be «largely»repelled and thus not eat the plants «so natural selection would favour them» ✔\n

\n

\n c. over time/in a few generations, the aphids population become more resistant/more attracted/less repelled to EBF and return to feed on the plants so long-term benefit very limited «so natural selection would not favour them» ✔\n

\n

\n d. the aphids resistant to EBF would not respond to other aphid alarms and «likely»be more readily eaten by predators «so the long-term benefit to plants could be supported by natural selection» ✔\n

\n

\n \n The answers must indicate whether natural selection would support or not for each statement.\n \n

\n
\n", "Examiners report": "
\n

\n There was some discussion in the G2 forms about the amount of reading before points h, I and j. Good candidates could be seen to have read it carefully, underling the key words. Weaker candidates not so. Very few candidates scored both marks in j as they just wrote about one possibility. Perhaps the answer box should have been larger.\n

\n
\n", "question_id": "19M.2.SL.TZ2.1J", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-1-natural-selection", "d4-1-1-natural-selection-as-the-mechanism-driving-evolutionary-change" ] }, { "Question": "
\n
\n

\n Using the graph, estimate isotonic sucrose solutions for potato tissue and carrot tissue.\n

\n

\n Potato:\n

\n

\n Carrot:\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n potato: 0.26 mol dm\n \n –3\n \n ✔\n \n Allow a range of 0.22–0.32\n \n
\n carrot: 0.50 mol dm\n \n –3\n \n ✔\n \n Allow a range of 0.45–0.55 (Allow 1 max if no units or either unit is omitted)\n \n

\n
\n", "Examiners report": "None", "question_id": "19N.1B.SL.TZ0.A", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-3-water-potential", "d2-3-3-water-movement-by-osmosis-into-or-out-of-cells", "d2-3-4-changes-due-to-water-movement-in-plant-tissue-bathed-in-hypotonic-and-those-bathed-in-hypertonic-solutions" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Explain how the amphipathic nature of phospholipids allows them to form bilayers.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. amphipathic means that they are both\n \n hydrophilic\n \n and\n \n hydrophobic\n \n ✔\n

\n

\n b. the outside hydrophilic parts are exposed to water ✔\n

\n

\n c. hydrophobic parts are away from water in the inside ✔\n

\n

\n \n Water or lack of needs to be mentioned for mpb\n \n

\n
\n", "Examiners report": "
\n

\n The terms hydrophilic and hydrophobic were commonly stated, although sometimes assigned to heads and tails incorrectly; however this was not penalised. Orientation towards or away from water was less often explained.\n

\n
\n", "question_id": "19M.1B.SL.TZ1.1C", "topics": [ "b-form-and-function" ], "subtopics": [ "b1-1-carbohydrates-and-lipids", "b1-1-12-formation-of-phospholipid-bilayers-as-a-consequence-of-the-hydrophobic-and-hydrophilic-regions" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n State how many different types of amino acid there are, which can become part of a polypeptide when mRNA is translated.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n 20;\n

\n
\n", "Examiners report": "
\n

\n Amazingly, most candidates missed gaining the mark for this question: a huge variety of incorrect numbers appeared, \"4\" was most frequent. Many candidates seemed to confuse the 4 nucleotide bases with the 20 amino acids.\n

\n
\n", "question_id": "22M.2.SL.TZ1.2", "topics": [ "b-form-and-function" ], "subtopics": [ "b1-2-proteins", "b1-2-4-infinite-variety-of-possible-peptide-chains", "b1-2-5-effect-of-ph-and-temperature-on-protein-structure" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Explain the mechanisms involved in thermoregulation in humans.\n

\n
\n
\n

\n [7]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n normal body temperature is 37 ºC;\n
    2. \n
  2. \n peripheral thermoreceptors detect environmental temperature;\n
    3. \n
  3. \n supporting conscious behaviour to avoid temperature extremes, e.g. wearing more clothing;\n
    4. \n
  4. \n sends messages to hypothalamus/temperature control centre of the brain;\n
    5. \n
  5. \n the hypothalamus sends messages to pituitary gland;\n
    6. \n
  6. \n (pituitary) releases TSH;\n
    7. \n
  7. \n stimulating thyroxin release from thyroid;\n
    8. \n
  8. \n thyroxin controls metabolic rate / production of heat;\n
    9. \n
  9. \n muscle random contraction/shivering to generate heat;\n
    10. \n
  10. \n (brown) adipose tissue burns fat to generate waste heat;\n
    11. \n
  11. \n vasoconstriction to conserve heat / vasodilation to exchange heat with the environment;\n
    12. \n
\n
\n", "Examiners report": "None", "question_id": "SPM.2.SL.TZ0.8A", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-3-homeostasis", "d3-3-5-thermoregulation-as-an-example-of-negative-feedback-control", "d3-3-6-thermoregulation-mechanisms-in-humans" ] }, { "Question": "
\n
\n

\n Absorption spectra of two photosynthetic pigments are shown. Phycoerythrin is a red pigment found in many marine red algae, while chlorophyll a is the major pigment in green plants and algae.\n

\n

\n \n

\n

\n What do the absorption spectra show about the pigments?\n

\n

\n A.  Phycoerythrin absorbs mostly red light.\n

\n

\n B.  Chlorophyll a reflects more green light than phycoerythrin.\n

\n

\n C.  Chlorophyll a photosynthesizes more at 550 nm than phycoerythrin.\n

\n

\n D.  Phycoerythrin does not absorb blue light.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "22N.1A.SL.TZ0.12", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-3-photosynthesis", "c1-3-5-absorption-of-specific-wavelengths-of-light-by-photosynthetic-pigments" ] }, { "Question": "
\n
\n

\n What is a feature of phagocytic white blood cells?\n

\n

\n A. Stimulate blood clotting\n

\n

\n B. Found only in the circulatory system\n

\n

\n C. Form part of non-specific immunity\n

\n

\n D. Produce antibodies\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "20N.1A.SL.TZ0.26", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-2-defence-against-disease", "c3-2-5-infection-control-by-phagocytes" ] }, { "Question": "
\n
\n (g)\n
\n
\n

\n Describe what is happening to the bone during hibernation.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n resorption/breaking down occurs\n \n and\n \n formation/rebuilding occurs;\n
    2. \n
  2. \n at similar rates / more resorption at most times;\n
    3. \n
  3. \n no/little (overall) change (in bone mass);\n
    4. \n
  4. \n lag between bone resorption rising and formation rising / OWTTE;\n
    5. \n
  5. \n bone resorption rising towards end as formation dropping / OWTTE;\n
    6. \n
\n
\n", "Examiners report": "
\n

\n In this question candidates were expected to deduce the changes to bone from the concentrations of the markers. Given that neither of them reaches zero, we can assume that bone formation and resorption both continue throughout the hibernation period. Few candidates made this point clearly. The other 'best' answer was to comment on relative overall amounts of formation and resorption, either by stating that they are approximately equal or that there is slightly more resorption.\n

\n
\n", "question_id": "22M.2.SL.TZ1.1G", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-3-homeostasis", "d3-3-1-homeostasis-as-maintenance-of-the-internal-environment-of-an-organism", "d3-3-2-negative-feedback-loops-in-homeostasis" ] }, { "Question": "
\n
\n

\n Discuss the relationship between atmospheric carbon dioxide concentration and global temperatures.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n

\n a. greenhouse effect keeps Earth warm ✔\n

\n

\n b. (over-time) earth’s temperature has fluctuated naturally ✔\n

\n

\n c. changes in human activities have led to increases in CO\n \n 2\n \n concentration ✔\n

\n

\n d. CO\n \n 2\n \n absorbs infrared/long wave radiation / trapping heat ✔\n

\n

\n e. increase in atmospheric CO\n \n 2\n \n (concentration) correlates with/causes increased global average temperature ✔\n

\n

\n f. use of fossil fuels increases atmospheric CO\n \n 2\n \n ✔\n

\n

\n g. deforestation removes a carbon sink / less CO\n \n 2\n \n absorbed ✔\n

\n

\n h. loss of polar ice causes less reflection of surface light/ more reradiation as heat contributing to (global) warming ✔\n

\n

\n i. CO\n \n 2\n \n is not the only greenhouse gas/ there are other greenhouse gases ✔\n

\n
\n", "Examiners report": "
\n

\n This question was attempted by approximately 56 % of candidates.\n

\n

\n This question was actually quite narrow as reflected in the number of marks it could earn. Some candidates understood which part of the global warming topic was being asked of them and stuck to the topic. Good applications to the carbon cycle were given. Strong responses avoided deviations into consequences and how humans should behave. Several misunderstandings surfaced. For example that CO\n \n 2\n \n was responsible for the breakdown of the ozone layer. Many seemed to tie ozone layer destruction and global warming information together in their explanation. Atmospheric carbon dioxide and the ozone layer were confused. Some thought that the ozone layer traps heat.\n

\n
\n", "question_id": "21M.2.SL.TZ1.C", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-3-climate-change", "d4-3-1-anthropogenic-causes-of-climate-change" ] }, { "Question": "
\n
\n

\n Which organic molecules may contain the element sulphur?\n

\n

\n A. Proteins\n

\n

\n B. Carbohydrates\n

\n

\n C. Phospholipids\n

\n

\n D. Nucleic acids\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "None", "question_id": "21M.1A.HL.TZ2.7", "topics": [ "b-form-and-function" ], "subtopics": [ "b1-2-proteins", "b1-2-9-dependence-of-tertiary-structure-on-hydrogen-bonds-ionic-bonds-disulfide-covalent-bonds-and-hydrophobic-interactions" ] }, { "Question": "
\n
\n (d)\n
\n
\n

\n Sketch the pattern seen in a typical electrocardiogram (ECG) trace for one complete cardiac cycle, including labels of the main features.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n a. sketch with the correct shape ✔\n

\n

\n b. P, Q, R, S and T indicated ✔\n

\n

\n c. atrial contraction/systole/depolarisation labelled ✔\n

\n

\n d. ventricular contraction/systole/depolarisation labelled ✔\n

\n

\n e. ventricular relaxation/diastole/repolarization labelled ✔\n

\n

\n \n Correct shape should show peaks at P R and T and dips at Q and S\n \n

\n

\n \n

\n
\n", "Examiners report": "
\n

\n In part (d) the better candidates could sketch the pattern seen in a typical electrocardiogram. Some made errors in the shape or letters but could still achieve marks for showing the areas of contraction or relaxation.\n

\n
\n", "question_id": "19M.2.HL.TZ2.18D", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-2-transport", "b3-2-16-stages-in-the-cardiac-cycle" ] }, { "Question": "
\n
\n

\n Promoters are non-coding regions in DNA. What is the role of a promoter?\n

\n

\n A. It starts translation.\n

\n

\n B. It starts mRNA splicing.\n

\n

\n C. It is a binding site for DNA polymerase during DNA replication.\n

\n

\n D. It is a binding site for RNA polymerase during transcription.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "22M.1A.HL.TZ2.27", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d1-2-protein-synthesis", "d1-2-13-initiation-of-transcription-at-the-promoter" ] }, { "Question": "
\n
\n

\n \n Chlorella\n \n and\n \n Paramecium\n \n are both unicellular eukaryotic organisms living in freshwater.\n \n Chlorella\n \n is photosynthetic and has a cell wall. Which organelle will be found in\n \n Paramecium\n \n but not in\n \n Chlorella\n \n ?\n

\n

\n A. Chloroplast\n

\n

\n B. Contractile vacuole\n

\n

\n C. Rough endoplasmic reticulum\n

\n

\n D. Mitochondrion\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "
\n

\n Only about half of candidates chose the contractile vacuole for a structure in the cells of\n \n Paramecium\n \n but not\n \n Chlorella\n \n . The expected reasoning was that the cell wall of Chlorella protects it against bursting due to excessive entry of water by osmosis, so a contractile vacuole is not needed. The commonest other answer was rough endoplasmic reticulum. While a photosynthetic cell is not likely to secrete much protein and so will not have an extensive rough ER, generally eukaryotic cells have at least some. This question was thought by the examining team to be just about acceptable, though the issue of whether unicellular algae have contractile vacuoles is complicated by their presence in some species. If there is a flagellum, there is a gap in the cell wall, and the flagellum itself is not protected by cell wall, so as with animal cells there is a danger of bursting and a contractile vacuole is generally needed.\n

\n
\n", "question_id": "20N.1A.SL.TZ0.1", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a2-2-cell-structure", "a2-2-6-eukaryote-cell-structure", "a2-2-8-differences-in-eukaryotic-cell-structure-between-animals-fungi-and-plants" ] }, { "Question": "
\n
\n

\n The diagram shows the elements present in two organic molecules, W and X.\n
\n Which molecules could W and X be?\n

\n

\n \n

\n

\n \n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "SPM.1A.HL.TZ0.2", "topics": [ "a-unity-and-diversity", "b-form-and-function" ], "subtopics": [ "b1-2-proteins", "b1-2-1-generalized-structure-of-an-amino-acid", "b1-1-carbohydrates-and-lipids", "b1-1-9-formation-of-triglycerides-and-phospholipids-by-condensation-reactions", "a1-2-nucleic-acids", "a1-2-4-bases-in-each-nucleic-acid-that-form-the-basis-of-a-code" ] }, { "Question": "
\n
\n

\n The graph shows the changing membrane potential during a nerve impulse. Which letter indicates when the potassium channels open?\n

\n

\n \n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "20N.1A.HL.TZ0.25", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c2-2-neural-signalling", "c2-2-9-propagation-of-an-action-potential-along-a-nerve-fibre/axon-as-a-result-of-local-currents", "c2-2-10-oscilloscope-traces-showing-resting-potentials-and-action-potentials" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Calculate the increase in mean global temperature between 1880 and 2010.\n

\n

\n .......... °C\n

\n

\n

\n

\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n 0.87; (\n \n accept values between 0.8 and 0.9\n \n )\n

\n
\n", "Examiners report": "
\n

\n Many candidates got the calculations right.\n

\n
\n", "question_id": "22M.2.SL.TZ1.3A", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-3-climate-change", "d4-3-1-anthropogenic-causes-of-climate-change" ] }, { "Question": "
\n
\n

\n What is a difference between eukaryotic and prokaryotic cells?\n

\n

\n
\n A.  Cell walls are found only in prokaryotes.\n

\n

\n B.  Naked DNA with histones is found only in prokaryotes.\n

\n

\n C.  Compartmentalization is found only in eukaryotes.\n

\n

\n D.  Cilia and flagella are found only in prokaryotes.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "23M.1A.SL.TZ1.2", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a2-2-cell-structure", "a2-2-5-prokaryote-cell-structure", "a2-2-6-eukaryote-cell-structure" ] }, { "Question": "
\n
\n

\n The cycle shows part of the light-independent reactions in photosynthesis.\n

\n

\n \n

\n

\n What occurs in Step 1?\n
\n
\n

\n

\n A.  ATP is formed for Step 2.\n

\n

\n B.  Rubisco catalyses the hydrolysis of ribulose bisphosphate.\n

\n

\n C.  A carboxylase catalyses the carboxylation of ribulose bisphosphate.\n

\n

\n D.  NADP is converted to reduced NADP.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "23M.1A.HL.TZ1.30", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-3-photosynthesis", "c1-3-19-interdependence-of-the-light-dependent-and-light-independent-reactions" ] }, { "Question": "
\n
\n

\n An electron micrograph of a mitochondrion is shown.\n

\n

\n \n

\n

\n The distance between the inner and outer membranes, which are shown by the box, is always very small. What is the advantage of this small distance?\n

\n

\n A.  Enables a high concentration of electrons to build up quickly\n

\n

\n B.  Enables a high concentration of protons to build up quickly\n

\n

\n C.  Allows fast diffusion of glucose into the mitochondrion\n

\n

\n D.  Allows fast diffusion of reduced NAD out of the mitochondrion\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "
\n

\n This question had an even higher discrimination index of 0.75 and as in question 27 about half of candidates answered it correctly. The discrimination index shows that it tended to be the better-prepared candidates who could identify the advantage of the small space between the inner and outer membrane of the mitochondrion. Teachers sometimes comment that images included in questions are not necessary. Interestingly both questions 27 and 30 had a diagram or micrograph that arguably was not needed, but both questions proved highly effective.\n

\n
\n", "question_id": "22N.1A.HL.TZ0.30", "topics": [ "b-form-and-function" ], "subtopics": [ "b2-2-organelles-and-compartmentalization", "b2-2-4-adaptations-of-the-mitochondrion-for-production-of-atp-by-aerobic-cell-respiration" ] }, { "Question": "
\n
\n

\n Which process is an example of catabolism?\n

\n

\n A. Translation of mRNA\n

\n

\n B. Replication of DNA\n

\n

\n C. Hydrolysis of protein\n

\n

\n D. Synthesis of a disaccharide\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "21M.1A.SL.TZ2.6", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-1-enzymes-and-metabolism", "c1-1-3-anabolic-and-catabolic-reactions" ] }, { "Question": "
\n
\n (a.i)\n
\n
\n

\n Deduce the concentration of ZDV that would cause a 50 % reduction in root growth compared to the control.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n 75 μmol ✔\n

\n

\n \n Allow answers in the range of 70 µmol–80 µmol\n \n .\n

\n
\n", "Examiners report": "
\n

\n Part (ii) was better answered than part (i) as many answers provided were outside the acceptable range of answers.\n

\n
\n", "question_id": "21M.2.HL.TZ1.1A.I", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a2-3-viruses-(hl-only)", "a2-3-6-rapid-evolution-in-viruses" ] }, { "Question": "
\n
\n

\n The diagram shows the structure of the protein CXCL12.\n

\n

\n \n

\n

\n [Source: Lu, J., Chatterjee, M., Schmid, H. et al. CXCL14 as an emerging immune and inflammatory modulator.\n
\n \n J Inflamm\n \n 13, 1 (2016).\n \n https://doi.org/10.1186/s12950-015-0109-9\n \n Distributed under the terms of the\n
\n Creative Commons Attribution 4.0 International License (\n \n http://creativecommons.org/licenses/by/4.0/\n \n ).]\n

\n

\n

\n

\n Which chemical group is found at X?\n

\n

\n A. NH\n \n 2\n \n

\n

\n B. NOH\n

\n

\n C. COH\n

\n

\n D. COOH\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "22M.1A.SL.TZ2.6", "topics": [ "b-form-and-function" ], "subtopics": [ "b1-2-proteins", "b1-2-1-generalized-structure-of-an-amino-acid" ] }, { "Question": "
\n
\n (a.i)\n
\n
\n

\n Based on their structure, the insect and bat wings are analogous. Outline what is meant by an analogous trait.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. analogous traits have a different evolutionary history/ancestry ✔\n

\n

\n b. different structures are adaptations for flight ✔\n

\n

\n c. selective pressure leads to a similar solution to the problem of flying ✔\n

\n
\n", "Examiners report": "
\n

\n Candidates found it hard to express themselves without contradiction.\n

\n

\n In both parts the key to successful answers was in using the organisms given in the example. Contradictions were thus avoided.\n

\n
\n", "question_id": "21M.2.SL.TZ1.5A.I", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a4-1-evolution-and-speciation", "a4-1-5-convergent-evolution-as-the-origin-of-analogous-structures" ] }, { "Question": "
\n
\n

\n State the name of the instrument used to make these traces.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n oscilloscope ✔\n

\n
\n", "Examiners report": "
\n

\n Fewer than 1 in 10 were able to name the oscilloscope. There were some G2 comments about this, but the students should have seen traces like this and should know how they were obtained.\n

\n
\n", "question_id": "19M.2.SL.TZ2.C", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c2-2-neural-signalling" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n State\n \n one\n \n function of Rubisco.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n a. enzyme involved in\n \n photosynthesis\n \n /\n \n carbon fixation\n \n /\n \n Calvin cycle\n \n
\n \n \n OR\n \n \n
\n speeds up chemical reactions in\n \n photosynthesis\n \n ✔\n

\n

\n b. carboxylation of RuBP ✔\n

\n

\n c. production of carbohydrate in photosynthesis ✔\n

\n

\n d. addition of carbon dioxide to form glucose (in Calvin cycle) ✔\n

\n

\n \n Either photosynthesis or carbon fixation must be mentioned\n \n .\n

\n
\n", "Examiners report": "
\n

\n There were some G2 comments about the function of Rubisco. It is mentioned in 2.4. and the stem did say that it was an enzyme. Simply stating that it was an enzyme involved in photosynthesis was sufficient for the mark. A detailed function was not required. Most could state the role of the active site and that the genus was\n \n Pisume.\n \n The word genus in this context confused some French candidates who answered 'male or female'. 3(d) was simply testing the factors controlling enzyme action. Weaker students just listed several factors. When it says one factor, only the first is considered. The difference between heat and temperature was occasionally confused. The examiners were looking for the effect of increasing and decreasing the factor. Many students seemed to be obsessed with denaturing. For example the answer 'temperature' (first mark): as the temperature is too high the enzyme denatures (no second mark as no mention of decreasing temperature). Few used the collision theory idea which was expected.\n

\n
\n", "question_id": "21M.2.HL.TZ2.3A", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-3-photosynthesis", "c1-3-15-carbon-fixation-by-rubisco" ] }, { "Question": "
\n
\n (e)\n
\n
\n

\n Suggest reasons for the difference between the data for\n \n S. pneumoniae\n \n and\n \n H. influenzae\n \n .\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n Hib vaccination program started earlier/PCV vaccination program started later\n
    \n \n \n OR\n \n \n
    \n Hib vaccine developed before PCV vaccine;\n
    2. \n
  2. \n deaths due to\n \n H. influenzae\n \n drop earlier than deaths due to\n \n S. pneumoniae\n \n because of earlier vaccination;\n
    3. \n
  3. \n more deaths due to\n \n S. pneumoniae\n \n than\n \n H. influenzae\n \n (in any year) as lower % of children vaccinated against\n \n S. pneumoniae\n \n (compared\n \n H. influenzae\n \n );\n
    4. \n
\n

\n \n Mp a to c: accept vice versa.\n \n

\n

\n \n Comparative terms expected (do not award mp for just stating values).\n \n

\n

\n \n Mpa and mpb: there must be a clear reference to time.\n \n

\n

\n \n Mpc: there must be clear indication to vaccination.\n \n

\n

\n \n Allow no points for bacterial virulence / disease severity, etc., as bacterial pathogenicity is not addressed on graphs.\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ2.1E", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-2-defence-against-disease", "c3-2-16-vaccines-and-immunization" ] }, { "Question": "
\n
\n (b.ii)\n
\n
\n

\n Explain how evolution by natural selection depends on mutations.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n

\n a. mutations cause variation among organisms of same species/population;\n

\n

\n b. some variations/mutations make individual more suited to its environment/way of life;\n

\n

\n c. individuals that are better adapted survive and produce offspring;\n

\n

\n d. individuals pass on genetic characteristics/mutation/variation to offspring;\n

\n

\n e. natural selection increases frequency of characteristics/alleles that make individuals better adapted;\n

\n
\n", "Examiners report": "None", "question_id": "20N.2.SL.TZ0.4B.II", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-1-natural-selection", "d4-1-2-roles-of-mutation-and-sexual-reproduction-in-generating-the-variation-on-which-natural-selection-acts" ] }, { "Question": "
\n
\n

\n Some strains of the pathogenic bacterium\n \n Staphylococcus aureus\n \n have developed mechanisms that protect them against foreign DNA. What effect does this have on the evolution of antibiotic resistance in these strains of\n \n S. aureus\n \n ?\n

\n

\n A. Slower evolution, as bacteria with the antibiotic resistance gene will not reproduce\n

\n

\n B. Slower evolution, as the antibiotic resistance gene from other species will not be accepted\n

\n

\n C. Faster evolution, as mutations within a population are less likely to occur\n

\n

\n D. Faster evolution, as antibiotic resistance genes can only be passed to individuals of the same species\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "
\n

\n Answered correctly by 50 % of the candidates that understood that by not accepting the antibiotic resistance gene,\n \n Staphylococcus aureus\n \n will be slow to develop resistance to the antibiotic.\n

\n
\n", "question_id": "22M.1A.HL.TZ2.19", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-1-natural-selection", "d4-1-15-artificial-selection-by-deliberate-choice-of-traits" ] }, { "Question": "
\n
\n (a.iii)\n
\n
\n

\n State the role of cyclins in the cell cycle.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n (group of regulatory proteins that) control/regulate the cell cycle;\n
    2. \n
  2. \n activate cyclin-dependent kinases (which control cell cycle processes);\n
    3. \n
\n
\n", "Examiners report": "None", "question_id": "22M.2.HL.TZ2.2A.III", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-1-cell-and-nuclear-division", "d2-1-15-control-of-the-cell-cycle-using-cyclins" ] }, { "Question": "
\n
\n

\n Explain how water is used in photosynthesis.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n a. water is split/broken «up»/lysed/undergoes photolysis ✔\n \n For mpa, reject “water is cut in half”. For mpa, accept photolysis only if the context shows that water is being split\n \n .\n

\n

\n b. producing/providing electrons ✔\n

\n

\n c. replaces electrons lost by Photosystem II / PSII / P680 / chlorophyll a ✔\n \n For mpc, do not accept just chlorophyll\n \n .\n

\n

\n d. allows electrons «to continue» to pass along the electron transport chain ✔\n

\n

\n e. provides protons/H+ «inside thylakoid» to help generate a «proton» gradient/maintain high concentration inside thylakoid ✔\n \n For mpe, reject pumping of protons into the thylakoid as photolysis produces them inside the thylakoid\n \n .\n

\n
\n", "Examiners report": "None", "question_id": "19N.2.SL.TZ0.B.II", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-3-photosynthesis", "c1-3-2-conversion-of-carbon-dioxide-to-glucose-in-photosynthesis-using-hydrogen-obtained-by-splitting-water" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n The graph shows how the number of ant species found on isolated islands near New Guinea depends on the size of the island.\n

\n

\n \n

\n

\n [Source: University of Windsor,\n \n The Theory of Island Biogeography\n \n . Available at:\n
\n http://web2.uwindsor.ca/courses/biology/macisaac/55-437/lecture9.htm.]\n

\n

\n

\n

\n Explain the relationship between island size and number of ant species.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n (the larger islands contain) more species as there are more habitats;\n

\n
\n", "Examiners report": "
\n

\n The graph showing the number of ant species according to island size required an explanation of the graph. Many candidates simply stated the relationship with no explanation.\n

\n
\n", "question_id": "20N.2.SL.TZ0.14C", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a4-2-conservation-of-biodiversity", "a4-2-5-evidence-for-a-biodiversity-crisis" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Outline the types of evidence that can be used to place a species in a particular clade.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n a. a clade is a group of organisms that have evolved from a common ancestor ✔\n

\n

\n b. identify the base sequences of a gene ✔\n

\n

\n c. identify amino acid sequence of a protein ✔\n

\n

\n d. comparing homologous structures ✔\n

\n

\n e. the fewer the differences, the closer they diverged in time from a common ancestor ✔\n \n Accept vice versa.\n \n

\n
\n", "Examiners report": "
\n

\n Those who had been taught it gained at least two marks for evidence and clades, with comparing base sequences of genes and amino acid sequences of proteins amongst the most common correct answers.\n

\n
\n", "question_id": "19M.2.HL.TZ2.4C", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a3-2-classification-and-cladistics-(hl-only)", "a3-2-4-clades-as-groups-of-organisms-with-common-ancestry-and-shared-characteristics" ] }, { "Question": "
\n
\n

\n The diagram represents transcription and translation.\n

\n

\n \n

\n

\n [Source: © International Baccalaureate Organization 2020.]\n

\n

\n

\n

\n What structures do the letters X and Y represent?\n

\n

\n \n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "20N.1A.SL.TZ0.9", "topics": [ "d-continuity-and-change", "b-form-and-function" ], "subtopics": [ "d1-2-protein-synthesis", "d1-2-7-complementary-base-pairing-between-trna-and-mrna", "b2-2-organelles-and-compartmentalization", "b2-2-2-advantage-of-the-separation-of-the-nucleus-and-cytoplasm-into-separate-compartments" ] }, { "Question": "
\n
\n

\n What occurs during inhalation?\n

\n

\n \n

\n

\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "21N.1A.SL.TZ0.27", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-1-gas-exchange", "b3-1-5-ventilation-of-the-lungs" ] }, { "Question": "
\n
\n

\n John Cairns used the technique of autoradiography to produce photographs of DNA from the bacterium\n \n E. coli\n \n .\n

\n

\n \n

\n

\n [Source: © Cold Spring Harbor Laboratory Press. Autoradiography of bacterium E. coli DNA - micrograph, The Chromosome of\n
\n Escherichia coli Cairns, J.P., 1963. Cold Spring Harbor Symposia,\n \n Quantitative Biology\n \n , 28(44).]\n

\n

\n

\n

\n Which conclusion was drawn from his experiments?\n

\n

\n A. The DNA in all organisms is circular.\n

\n

\n B. DNA in\n \n E. coli\n \n naturally contains thymidine.\n

\n

\n C. DNA replication is conservative.\n

\n

\n D. The DNA in\n \n E. coli\n \n is 900 μm in length.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "
\n

\n The technique developed by Cairns is part of the program in sub-topic 3.2, but answers to this question showed that relatively few candidates were familiar with it.\n

\n
\n", "question_id": "21N.1A.SL.TZ0.13", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a2-2-cell-structure", "a2-2-5-prokaryote-cell-structure" ] }, { "Question": "
\n
\n (b.ii)\n
\n
\n

\n Explain the reasons for food chains rarely containing more than four or five trophic levels.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n a. energy is lost between the trophic levels;\n
\n b. transfer between levels is only usually 10% efficient\n
\n OR\n
\n energy transformations take place in living organisms / the process is never 100% efficient;\n
\n c. energy is lost by the organism/used in respiration / released as heat/movement;\n
\n d. energy is lost as waste/feces/urine/undigested food/uneaten parts;\n
\n e. as energy is lost between trophic levels and so (higher ones) have less biomass / less biomass available for next level;\n

\n
\n", "Examiners report": "
\n

\n Most were able to gain at least two marks for the explanation of energy loss through the trophic levels.\n

\n
\n", "question_id": "21N.2.SL.TZ0.3B.II", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c4-2-transfers-of-energy-and-matter", "c4-2-3-flow-of-chemical-energy-through-food-chains" ] }, { "Question": "
\n
\n (d)\n
\n
\n

\n All of the leaves in the image are from\n \n Solanum\n \n , a wild genus of tomato.\n

\n

\n \n

\n

\n [Source: Courtesy: National Science Foundation, Credit Leonie Moyle.]\n

\n

\n

\n

\n State\n \n one\n \n cause of variation in a plant such as the tomato.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n a. mutations;\n
\n b. meiosis/crossing over/random assortment of homologous pairs;\n
\n c. sexual reproduction/recombination/random fertilisation;\n

\n
\n", "Examiners report": "
\n

\n In 3d there was a great deal of variety in the leaf shape, so an answer in terms of sexual reproduction was looked for.\n

\n
\n", "question_id": "21N.2.SL.TZ0.3D", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d1-3-mutations-and-gene-editing", "d1-3-7-mutation-as-a-source-of-genetic-variation" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Outline how hydrogen bonds form in water.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n a. water (molecules) are polar/dipolar/have partially positive and negative poles/have δ+ and δ-;\n

\n

\n b. attraction/bonding between positive and negative (poles);\n

\n

\n c. hydrogen bond formed between hydrogen and oxygen;\n \n Reject if H and O in same molecule.\n \n

\n

\n d. bond/attraction between different water molecules/intermolecular;\n

\n

\n \n Marks can be awarded in an annotated diagram.\n \n

\n

\n \n Reject answers stating or implying that there are whole positive or negative charges for mpa\n \n .\n

\n
\n", "Examiners report": "
\n

\n Answers were mostly good here, with many candidates scoring full marks. A very common misconception was that hydrogen bonds are strong – a single hydrogen bond is a weak interaction and it is only because there are many hydrogen bonds in water that they collectively exert large cohesive forces. A few candidates thought that hydrogen bonds were within rather than between water molecules.\n

\n
\n", "question_id": "20N.2.HL.TZ0.7", "topics": [ "a-unity-and-diversity", "b-form-and-function", "d-continuity-and-change" ], "subtopics": [ "a1-1-water", "a1-1-2-hydrogen-bonds-as-a-consequence-of-the-polar-covalent-bonds-within-water-molecules", "b3-2-transport", "b3-2-7-transport-of-water-from-roots-to-leaves-during-transpiration", "d3-3-homeostasis", "d3-3-7-role-of-the-kidney-in-osmoregulation-and-excretion" ] }, { "Question": "
\n
\n

\n Which row of the table describes a type of nutrition?\n

\n

\n
\n \n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "SPM.1A.SL.TZ0.26", "topics": [ "b-form-and-function" ], "subtopics": [ "b4-2-ecological-niches", "b4-2-4-holozoic-nutrition-in-animals", "b4-2-6-saprotrophic-nutrition-in-some-fungi-and-bacteria" ] }, { "Question": "
\n
\n

\n Explain the production of antibodies in humans.\n

\n
\n
\n

\n [7]\n

\n
\n
\n", "Markscheme": "
\n

\n a. antigens stimulate antibody production;\n
\n b. antibodies produced by lymphocytes;\n
\n c. macrophages/phagocytes ingest/engulf pathogens and display antigens from them;\n
\n d. T-cells activated by binding antigen/by macrophage displaying antigen;\n
\n e. activated T-cells cause activation of B-cells;\n
\n f. mitosis/division of (activated) B-cells (to produce a clone of cells)\n
\n g. plasma cells formed from divided/activated/growing/differentiating B-cells;\n
\n h. plasma cells/plasma B-cells secrete antibodies;\n
\n i. clonal selection / plasma cells make same type of antibody/antibody specific to same antigen;\n
\n j. some activated B-cells become memory cells;\n

\n
\n", "Examiners report": "
\n

\n This was another question giving scope to candidates to show the breadth of their biological understanding. The best answers were impressive but given the challenging nature of the topic it isn’t surprising that there were also some very muddled accounts. The weakest candidates struggled to remember the differences between antigens, antibodies and lymphocytes.\n

\n
\n", "question_id": "21N.2.HL.TZ0.B", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-2-defence-against-disease", "c3-2-6-lymphocytes-as-cells-in-the-adaptive-immune-system-that-cooperate-to-produce-antibodies", "c3-2-8-activation-of-b-lymphocytes-by-helper-t-lymphocytes", "c3-2-10-immunity-as-a-consequence-of-retaining-memory-cells" ] }, { "Question": "
\n
\n (b.i)\n
\n
\n

\n Determine the sequence of amino acids that could be translated from the sequence of mRNA.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n met-ser-arg-arg\n
\n \n \n OR\n \n \n
\n start-ser-arg-arg\n
\n \n \n OR\n \n \n
\n met-ser-arg-arg-stop\n
\n \n \n OR\n \n \n
\n start-ser-arg-arg-stop ✔\n

\n

\n \n Do not accept peptides containing an amino acid/leu for the last codon\n \n .\n

\n
\n", "Examiners report": "None", "question_id": "19N.2.SL.TZ0.2B.I", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d1-2-protein-synthesis", "d1-2-9-using-the-genetic-code-expressed-as-a-table-of-mrna-codons" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Compare and contrast hormonal and nervous communication.\n

\n
\n
\n

\n [7]\n

\n
\n
\n", "Markscheme": "
\n

\n \n Similarities\n \n

\n

\n a. both used for communication between cells/tissues/organs/parts of the body / WTTE ✔\n

\n

\n b. both cause a response/change in specific/target cells\n
\n \n \n OR\n \n \n
\n both use chemicals that bind to receptors / hormones and neurotransmitters are both chemicals ✔\n

\n

\n c. both can stimulate or inhibit (processes in target cells) / WTTE ✔\n

\n

\n d. both can work over long distances/between widely separated parts of the body / WTTE ✔\n

\n

\n e. both under (overall) control of the brain/CNS / brain (has role in) sending hormones and nerve impulses ✔\n

\n

\n f. both use feedback mechanisms/negative feedback / both used in homeostasis ✔\n

\n

\n \n Differences\n \n

\n

\n \n \n \n

\n

\n m. example of use of hormonal and use of nervous communication\n \n ✔\n \n

\n
\n", "Examiners report": "
\n

\n Weaker candidates found this a real challenge as it was necessary to understand the nature of the nervous and endocrine systems well enough to be able to point out similarities and differences. Often there was no obvious comparing or contrasting in the answers.\n

\n
\n", "question_id": "21M.2.SL.TZ1.6C", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-1-integration-of-body-systems", "c3-1-3-integration-of-organs-in-animal-bodies-by-hormonal-and-nervous-signalling-and-by-transport-of-materials-and-energy" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Explain the function of the left ventricle.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n contracts to generate high pressure / pumps blood at high pressure;\n
    2. \n
  2. \n pump blood (through the aorta) to all parts of the body (apart from the lungs);\n
    3. \n
  3. \n receives blood from the left atrium;\n
    4. \n
  4. \n contraction is stimulated by the AV node;\n
    5. \n
\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ1.3C", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-2-transport", "b3-2-15-adaptations-of-the-mammalian-heart-for-delivering-pressurized-blood-to-the-arteries" ] }, { "Question": "
\n
\n

\n What is the function of the loop of Henle?\n

\n

\n A. To reabsorb salt\n

\n

\n B. To maintain a hypertonic solution in the medulla\n

\n

\n C. To transport liquid from the collecting ducts to the convoluted tubules\n

\n

\n D. To reabsorb glucose\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "19M.1A.HL.TZ2.33", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-3-homeostasis", "d3-3-9-role-of-the-loop-of-henle" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Outline how the properties of water make it an ideal transport medium in plants.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n

\n a. polarity of water;\n
\n b. hydrogen bonds between water molecules;\n
\n c. cohesion between water molecules/water molecules stick together;\n
\n d. cohesion allows tensions/low pressures/transpiration pull/movement upward/against gravity;\n
\n e. adhesion to cellulose/cell walls generates tensions/pull (in xylem)\n
\n \n OR\n \n
\n adhesion to xylem walls/vessel walls causes capillary rise/upward movement;\n
\n f. solvent for many substances / many substances dissolve;\n
\n g. liquid at most temperatures experienced by plants / liquid so can flow;\n

\n

\n \n Polarity of water and/or hydrogen bonding can be shown in an annotated diagram\n \n .\n

\n
\n", "Examiners report": "
\n

\n Most candidates knew at least some properties of water that make it useful as a medium for transport in plants. As in previous papers, cohesion and adhesion are often treated as the same process or were confused. Another common error is to refer to hydrogen bonds as strong – their effects are strong because so many hydrogen bonds are formed in water but, thinking of them individually, they are weak interactions.\n

\n
\n", "question_id": "21N.2.HL.TZ0.7", "topics": [ "a-unity-and-diversity", "b-form-and-function", "c-interaction-and-interdependence" ], "subtopics": [ "a1-1-water", "a1-1-5-solvent-properties-of-water-linked-to-its-role-as-a-medium-for-metabolism-and-for-transport-in-plants-and-animals", "b3-2-transport", "b3-2-7-transport-of-water-from-roots-to-leaves-during-transpiration", "b3-2-9-distribution-of-tissues-in-a-transverse-section-of-the-stem-of-a-dicotyledonous-plant", "b3-2-10-distribution-of-tissues-in-a-transverse-section-of-the-root-of-a-dicotyledonous-plant", "c1-3-photosynthesis", "c1-3-19-interdependence-of-the-light-dependent-and-light-independent-reactions" ] }, { "Question": "
\n
\n

\n The diagram shows the link reaction between glycolysis and the Krebs cycle.\n

\n

\n \n

\n

\n [Source: © International Baccalaureate Organization 2019]\n

\n

\n

\n

\n Which type of reaction is occurring?\n

\n

\n A. Pyruvate is carboxylated.\n

\n

\n B. CO2 is oxidized.\n

\n

\n C. NAD+ is reduced.\n

\n

\n D. Pyruvate is phosphorylated.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "19N.1A.HL.TZ0.30", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-2-cell-respiration", "c1-2-11-oxidation-and-decarboxylation-of-pyruvate-as-a-link-reaction-in-aerobic-cell-respiration" ] }, { "Question": "
\n
\n

\n A woman with blood type A has three children with a man who has blood type AB. The first child has blood type B. What is the probability that the second child born to the couple will have blood type AB?\n

\n

\n A. 0.75\n

\n

\n B. 0.50\n

\n

\n C. 0.25\n

\n

\n D. 0.00\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "21M.1A.SL.TZ2.15", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-2-inheritance", "d3-2-9-abo-blood-groups-as-an-example-of-multiple-alleles" ] }, { "Question": "
\n
\n (d)\n
\n
\n

\n Explain how a nerve impulse is passed on to other neurons.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n impulses pass to another neuron at a\n \n synapse\n \n /\n \n across synaptic gap\n \n /\n \n cleft\n \n ;\n
    2. \n
  2. \n (depolarization causes) Ca\n \n 2+\n \n /calcium ions to diffuse into the (presynaptic) neuron/axon;\n
    3. \n
  3. \n depolarization (of presynaptic neuron) causes release of a neurotransmitter\n
    \n \n \n OR\n \n \n
    \n neurotransmitters diffuse across the synapse;\n
    4. \n
  4. \n (neurotransmitters) bind to receptors on postsynaptic neuron/membrane;\n
    5. \n
  5. \n (if the threshold potential is reached) an action potential occurs/sodium gates open (in the postsynaptic neuron);\n
    6. \n
\n
\n", "Examiners report": "
\n

\n Use of term \"synapse\" was often missing; involvement of the brain was sometimes built into the passage of a nerve impulse to another neuron.\n

\n
\n", "question_id": "22M.2.SL.TZ1.5D", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c2-2-neural-signalling", "c2-2-6-release-of-neurotransmitters-from-a-presynaptic-membrane" ] }, { "Question": "
\n
\n

\n Which statement applies to the tertiary structure of enzymes?\n

\n

\n A. Tertiary structure is the sequence of amino acids in an enzyme.\n

\n

\n B. Some enzymes do not have a tertiary structure.\n

\n

\n C. An example of tertiary structure in an enzyme is the alpha helix.\n

\n

\n D. A change in the tertiary structure of an enzyme may result in a change in the structure of the active site.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "21M.1A.HL.TZ1.28", "topics": [ "b-form-and-function" ], "subtopics": [ "b1-2-proteins", "b1-2-9-dependence-of-tertiary-structure-on-hydrogen-bonds-ionic-bonds-disulfide-covalent-bonds-and-hydrophobic-interactions", "b1-2-10-effect-of-polar-and-non-polar-amino-acids-on-tertiary-structure-of-proteins" ] }, { "Question": "
\n
\n

\n Yeast cells,\n \n Saccharomyces cerevisiae\n \n , were incubated with and without glucose at three different temperatures for a period of four minutes, during which the rate of CO\n \n 2\n \n production was measured with a CO\n \n 2\n \n sensor.\n \n

\n

\n [Source: © International Baccalaureate Organization 2019]\n

\n

\n

\n

\n What conclusion can be drawn from the results of this experiment?\n

\n

\n A. Yeast uses lipids rather than glucose in respiration at low temperatures.\n

\n

\n B. Addition of glucose has a greater impact on rates of cell respiration at lower temperatures.\n

\n

\n C. Rates of cell respiration increase with temperature.\n

\n

\n D. More glucose is produced at higher temperatures.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "19M.2.SL.TZ1.11", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-2-cell-respiration", "c1-2-6-variables-affecting-the-rate-of-cell-respiration" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Describe the major characteristics of a eutrophic lake.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. normally shallow ✔\n

\n

\n b. low water visibility\n
\n \n \n OR\n \n \n
\n high levels of nutrients/phosphates/potassium\n
\n \n \n OR\n \n \n
\n low oxygen concentration\n
\n \n \n OR\n \n \n
\n high BOD ✔\n

\n

\n c. high net primary productivity\n
\n \n \n OR\n \n \n
\n algal bloom\n
\n \n \n OR\n \n \n
\n low biodiversity ✔\n

\n
\n", "Examiners report": "None", "question_id": "19N.2.SL.TZ0.17C", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-2-stability-and-change", "d4-2-8-eutrophication-of-aquatic-and-marine-ecosystems-due-to-leaching" ] }, { "Question": "
\n
\n

\n Describe anaerobic respiration in humans and in yeast.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n (in both) anaerobic respiration gives a small amount of ATP/2 ATP/energy from glucose;\n
    2. \n
  2. \n anaerobic respiration occurs when there is no oxygen;\n
    3. \n
  3. \n anaerobic respiration in\n \n yeast\n \n produces ethanol and carbon dioxide/alcoholic fermentation;\n
    4. \n
  4. \n anaerobic respiration in\n \n humans\n \n (in muscle) produces lactate/lactic acid/lactic acid fermentation;\n
    5. \n
  5. \n both undergo glycolysis;\n
    6. \n
\n

\n \n Do not accept mpd if CO\n \n 2\n \n also included\n \n .\n

\n
\n", "Examiners report": "
\n

\n In 3a. the top candidates scored all three marks with ease, but many, especially in Spanish scored zero. A common mistake was to say that humans produce lactic acid and CO\n \n 2\n \n . In bi, many were confused by the term ‘thermal properties’, but most were able to gain at least one point for comparing their boiling/freezing temperatures, specific heat capacities and latent heat of fusion. The best candidates also explained the differences in terms of hydrogen bonds between the water molecules. In bii, few got past stating that methane is a greenhouse gas/causes an increase in temperature of the atmosphere. The better candidates stated that it was a powerful greenhouse gas, but it had a relatively short life span compared to CO\n \n 2\n \n . A surprising number thought that methane’s main danger was that it destroyed the ozone layer.\n

\n
\n", "question_id": "22M.2.HL.TZ2.A", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-2-cell-respiration", "c1-2-5-differences-between-anaerobic-and-aerobic-cell-respiration-in-humans", "c1-2-10-anaerobic-cell-respiration-in-yeast-and-its-use-in-brewing-and-baking" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Suggest reasons for the differences in LAI between the boreal and equatorial zones.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n climate/temperature/light consistent throughout year in equatorial but seasonal variation in boreal;\n
    2. \n
  2. \n conditions suitable for photosynthesis throughout the year in equatorial but not in boreal;\n
    3. \n
  3. \n temperatures higher/growing season longer in equatorial versus lower/shorter in boreal;\n
    4. \n
  4. \n water frozen/unavailable in boreal during winter whereas always available in equatorial;\n
    5. \n
  5. \n shorter daylengths in winter in boreal (than those months in equatorial so lower LAI);\n
    6. \n
  6. \n boreal LAI higher (than equatorial) in July due to longer daylengths;\n
    7. \n
  7. \n equatorial trees/plants are evergreen / boreal trees/plants are deciduous/have less/no leaves in winter;\n
    8. \n
  8. \n variation in angle of light rays (between different latitudes);\n
    9. \n
\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ1.1B", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-3-climate-change", "d4-3-1-anthropogenic-causes-of-climate-change" ] }, { "Question": "
\n
\n

\n Using the data in the graph, predict how the use of neonicotinoid pesticides will affect bumblebee populations.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n number of populations may/will decrease;\n
    2. \n
  2. \n both treatments decreased very significantly the number of queens;\n
    3. \n
  3. \n low treatment had (almost) the same effect as the high\n
    \n \n \n OR\n \n \n
    \n even low levels have as toxic/lethal effects as high levels;\n
    4. \n
  4. \n without new queens, new colonies cannot be founded;\n
    5. \n
  5. \n no/less/little reproduction (as only queens lay eggs);\n
    6. \n
  6. \n new colonies are essential to maintain bumblebee populations;\n
    7. \n
\n
\n", "Examiners report": "None", "question_id": "22M.2.HL.TZ2.B", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c2-2-neural-signalling", "c2-2-12-effects-of-exogenous-chemicals-on-synaptic-transmission" ] }, { "Question": "
\n
\n

\n State\n \n one\n \n reason for having a control group.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n any reference to comparison ✔\n

\n
\n", "Examiners report": "None", "question_id": "19N.2.HL.TZ0.F", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a3-2-classification-and-cladistics-(hl-only)", "a3-2-7-analysing-cladograms" ] }, { "Question": "
\n
\n (d)\n
\n
\n

\n Deduce, based on the data presented, whether the levels of neonicotinoids used in agriculture cause direct harm to\n \n B. terrestris\n \n .\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n yes, as even low/both doses (of first neonicotinoid) affect the (overall) development of colonies negatively; (\n \n From Graph 1\n \n )\n
    2. \n
  2. \n yes, as decreased numbers of queens (likely) affect reproductive capabilities; (\n \n From Graph 2\n \n )\n
    3. \n
  3. \n the second neonicotinoid (likely) had less/little/no effect on the bees as it had little effect on egg size; (\n \n From Graph 3\n \n )\n
    4. \n
\n

\n \n OWTTE\n \n

\n
\n", "Examiners report": "None", "question_id": "22M.2.HL.TZ2.1D", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c2-2-neural-signalling", "c2-2-12-effects-of-exogenous-chemicals-on-synaptic-transmission" ] }, { "Question": "
\n
\n

\n Evaluate the effect of salt on blood pressure using the data in the graph.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. systolic pressure increases with salt in diet during treatment;\n

\n

\n b. diastolic pressure is slightly higher/no change with salt during treatment\n
\n \n \n OR\n \n \n
\n diastolic pressure only changes towards the end of the period;\n

\n

\n c. (blood) pressure goes back to normal after treatment\n
\n \n \n OR\n \n \n
\n salt causes increased (blood) pressure;\n

\n

\n d. standard deviation values overlap therefore not statistically significant;\n

\n
\n", "Examiners report": "
\n

\n The majority could evaluate that salt increased blood pressure, most comparing the effect on systolic and diastolic blood pressure.\n

\n
\n", "question_id": "20N.2.SL.TZ0.A", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-2-transport", "b3-2-3-adaptations-of-arteries-for-the-transport-of-blood-away-from-the-heart" ] }, { "Question": "
\n
\n

\n Distinguish between the different phases of the cardiac cycle in the atria and in the ventricular muscle.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. action potential of atrium precedes the ventricle\n
\n \n \n OR\n \n \n
\n the phases happen later in ventricle\n
\n \n \n OR\n \n \n
\n atrium contracts before the ventricle ✔\n

\n

\n b. atrium has a shorter phase 2/longer phase 2 in ventricle\n
\n \n \n OR\n \n \n
\n atrium falls abruptly in phase 2/ventricle shows a plateau in phase 2 ✔\n

\n

\n c. phase 3 is more distinct/falls more abruptly in ventricular action potential ✔\n

\n

\n d. ventricular phase is overall longer than atrial phase ✔\n

\n
\n", "Examiners report": "
\n

\n Part (c) confused many candidates and they did not realise they had to refer to the graphs in their answers. Most scored one mark for stating ventricular contraction occurs after atrial contraction.\n

\n
\n", "question_id": "19M.2.HL.TZ2.C", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-2-transport", "b3-2-16-stages-in-the-cardiac-cycle" ] }, { "Question": "
\n
\n

\n State the region of the kidney in which the loop of Henle is situated.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n medulla;\n

\n
\n", "Examiners report": "
\n

\n 70\n \n \n \n \n % of candidates knew that the loop of Henle is in the medulla.\n

\n
\n", "question_id": "22N.2.HL.TZ0.B", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-3-homeostasis", "d3-3-9-role-of-the-loop-of-henle" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Estimate the resting potential for this axon.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n −65\n \n mV\n \n ✔\n

\n

\n \n Unit required; minus sign required. Accept answers from −62mV to −65mV\n \n .\n

\n
\n", "Examiners report": "None", "question_id": "21M.2.HL.TZ1.4A", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c2-2-neural-signalling", "c2-2-10-oscilloscope-traces-showing-resting-potentials-and-action-potentials" ] }, { "Question": "
\n
\n

\n The image shows a human karyogram.\n

\n

\n \n

\n

\n \n National Cancer Institute, 1997. Karyotype. [diagram online]\n \n
\n \n Available at: https://commons.wikimedia.org/wiki/\n \n
\n \n File:Karyotype_(normal).jpg [Accessed 14 February 2022]. Public domain.\n \n

\n

\n

\n

\n From which person was the karyogram obtained?\n

\n

\n
\n A.  A female with Down syndrome\n

\n

\n B.  A female without Down syndrome\n

\n

\n C.  A male with Down syndrome\n

\n

\n D.  A male without Down syndrome\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "23M.1A.SL.TZ2.15", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a3-1-diversity-of-organisms", "a3-1-7-karyotyping-and-karyograms" ] }, { "Question": "
\n
\n

\n The pedigree chart shows the inheritance of hemophilia in some of the descendants of Queen Victoria. Which letter points to a family member certain to be heterozygous?\n

\n

\n \n

\n

\n [Source: © International Baccalaureate Organization 2019]\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "None", "question_id": "19N.1A.HL.TZ0.12", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-2-inheritance", "d3-2-12-haemophilia-as-an-example-of-a-sex-linked-genetic-disorder", "d3-2-13-pedigree-charts-to-deduce-patterns-of-inheritance-of-genetic-disorders" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Outline how cuts in the skin are sealed to prevent blood loss.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n

\n a. platelets respond to/detect skin/blood vessel damage ✔\n

\n

\n b. platelets release clotting factors ✔\n

\n

\n c. clotting factors trigger a chain/cascade of reactions ✔\n

\n

\n d. «leading to» formation of thrombin ✔\n

\n

\n e. thrombin causes fibrinogen conversion into fibrin ✔\n

\n

\n f. blood clot seals the wound due to fibrin network of fibres ✔\n

\n

\n \n Accept answers presented as a flow chart\n \n .\n

\n
\n", "Examiners report": "None", "question_id": "19N.2.SL.TZ0.6", "topics": [ "c-interaction-and-interdependence", "d-continuity-and-change", "b-form-and-function" ], "subtopics": [ "c3-2-defence-against-disease", "c3-2-3-sealing-of-cuts-in-skin-by-blood-clotting", "d3-2-inheritance", "d3-2-9-abo-blood-groups-as-an-example-of-multiple-alleles", "b3-1-gas-exchange", "b3-1-4-adaptations-of-mammalian-lungs-for-gas-exchange" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Suggest\n \n two\n \n reasons for the overall decline in the epidemic after week 51.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. «overall decline due to» fewer cases in rural areas ✔\n

\n

\n \n Answers relating to people who died from the disease or develop immunity to it\n \n :\n
\n b. fewer cases due to deaths of people who had the disease/people recovering\n
\n \n \n OR\n \n \n
\n more people vaccinated/became immune/made antibodies/were not vulnerable to infection ✔\n

\n

\n \n Answers relating to health care workers or availability of resources\n \n :\n
\n c. more doctors/nurses/medical equipment/treatment centers/hospitals/spending/aid/NGOs ✔\n

\n

\n \n Answers relating to medical techniques used to tackle the epidemic\n \n :\n
\n d. better treatments/infection control/hygiene/quarantine/new vaccine/new antiviral drugs ✔\n

\n

\n \n Answers relating to the public and patients\n \n :\n
\n e. education/better awareness/avoidance of infection/taking precautions/vaccination accepted ✔\n

\n

\n \n Answers relating to reservoirs of infection\n \n :\n
\n f. fewer infected people «who could spread infection»/fewer bats/less contact with bats ✔\n

\n
\n", "Examiners report": "
\n

\n This was a timely question with Ebola epidemics again causing great problems in parts of Africa. Students were expected to have had some practice at analysing data relating to an epidemic because of this Skill in the programme: Analysis of epidemiological data related to vaccination programmes. It was assumed that candidates would understand terms such as ‘case’, ‘fatal case’, ‘infect’ and ‘treat’.\n

\n

\n A wide range of possible reasons for the decline in the epidemic was accepted here and most candidates scored both marks. The commonest type of misunderstanding was that there might be few people left to become infected. Given that the total number of cases was only in the thousands and the population of Guinea must be in the millions, that explanation for the decline was implausible. As this was a suggest question and candidates are not required to have specific knowledge of the Ebola epidemic, any reasonable answer was accepted even if it was not historically true.\n

\n
\n", "question_id": "19M.2.SL.TZ1.1C", "topics": [ "c-interaction-and-interdependence", "a-unity-and-diversity" ], "subtopics": [ "c3-2-defence-against-disease", "a2-3-viruses-(hl-only)" ] }, { "Question": "
\n
\n

\n State\n \n one\n \n other gas that contributes to global warming.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n methane/nitrous oxide/water vapour/ozone/CFCs/other halogenated gases;\n

\n
\n", "Examiners report": "
\n

\n Nearly all candidates could name another greenhouse gas that is contributing to global warming. Methane was the commonest answer. Water vapour was also allowed as it is increasing in the atmosphere.\n

\n
\n", "question_id": "22N.2.SL.TZ0.C", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-3-climate-change", "d4-3-1-anthropogenic-causes-of-climate-change" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Outline how the neuron is stimulated to release the neurotransmitter.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n the arrival of a nerve impulse/action potential/depolarization (stimulates the release of a neurotransmitter);\n
    2. \n
  2. \n depolarization stimulates calcium ion channels to open;\n
    \n \n \n OR\n \n \n
    \n calcium ions enter the presynaptic knob/button\n
    3. \n
  3. \n (calcium ions) cause the vesicle to fuse with / move to the membrane\n
    \n \n \n OR\n \n \n
    \n vesicles release neurotransmitter by\n \n exocytosis\n \n ;\n
    4. \n
\n
\n", "Examiners report": "None", "question_id": "22N.2.SL.TZ0.5B", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c2-1-chemical-signalling-[hl-only]", "c2-1-8-transmembrane-receptors-for-neurotransmitters-and-changes-to-membrane-potential" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Explain how ATP is generated in mitochondria by chemiosmosis.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n

\n a. protons pumped across inner membrane of mitochondria/into intermembrane space;\n

\n

\n b. using energy released by flow of electrons/by electron transport/by electron carriers;\n

\n

\n c. proton gradient established/maintained / proton motive force generated;\n

\n

\n d. protons pass/diffuse back through inner membrane/membrane of cristae/to matrix;\n

\n

\n e. through\n \n ATP synthase\n \n ;\n

\n

\n f. ATP production coupled to flow of protons / ATP from ADP and Pi using energy from protons;\n

\n

\n \n Marks can be awarded in an annotated diagram\n \n .\n

\n
\n", "Examiners report": "
\n

\n This was answered more successfully by most candidates and there were some impressively detailed and accurate answers.\n

\n
\n", "question_id": "20N.2.HL.TZ0.3B", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-2-cell-respiration", "c1-2-15-chemiosmosis-and-the-synthesis-of-atp-in-the-mitochondrion" ] }, { "Question": "
\n
\n

\n What are common features of holozoic nutrition and saprotrophic nutrition?\n

\n

\n
\n \n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "SPM.1A.HL.TZ0.35", "topics": [ "b-form-and-function" ], "subtopics": [ "b4-2-ecological-niches", "b4-2-4-holozoic-nutrition-in-animals", "b4-2-6-saprotrophic-nutrition-in-some-fungi-and-bacteria" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Explain how carbohydrates are transported from plant leaves.\n

\n
\n
\n

\n [7]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n translocation/movement by mass flow;\n
    2. \n
  2. \n in\n \n phloem sieve tubes\n \n ;\n
    3. \n
  3. \n sieve plates/pores in end walls/lack of organelles allows flow (of sap);\n
    4. \n
  4. \n carbohydrates (principally) transported as sucrose;\n
    5. \n
  5. \n (sucrose/glucose/sugar/carbohydrate) loaded (into phloem) by active transport;\n
    6. \n
  6. \n loading/pumping in (of sugars) by companion cells;\n
    7. \n
  7. \n high solute concentration generated (at the source);\n
    8. \n
  8. \n water enters by osmosis (due to the high solute concentration);\n
    9. \n
  9. \n hydrostatic pressure increased/high hydrostatic pressure generated;\n
    10. \n
  10. \n pressure gradient causes flow (from source to sink);\n
    11. \n
  11. \n leaves are a source because carbohydrates are made there;\n
    12. \n
  12. \n transport to the sink where carbohydrates are used/stored;\n
    13. \n
\n
\n", "Examiners report": "
\n

\n This was answered well by many candidates, with correct use of terminology. Some answers gave considerable detail about methods used to load assimilate into phloem. The specific structures used for transport (sieve tubes) were not always named and their adaptations were rarely included. Many candidates stated that phloem transport is bidirectional and that xylem transport is not — a hypothesis that has been falsified! Transport in a single phloem sieve tube can only be in one direction at one time, though the direction can be reversed if the hydrostatic pressure gradient switches, for example when a growing leaf changes from being a sink to a source. Xylem transport can also be bidirectional over time, as xylem sap sinks down to the roots of deciduous trees when leaves are lost in the fall and some plants allow xylem sap to sink to the roots every night when transpiration stops.\n

\n
\n", "question_id": "22N.2.HL.TZ0.7C", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-2-transport", "b3-2-18-adaptations-of-phloem-sieve-tubes-and-companion-cells-for-translocation-of-sap" ] }, { "Question": "
\n
\n

\n Evaluate the evidence from the bar chart that increases in carbon dioxide cause increases in carbon storage in young, developing forests.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n more carbon stored/allocated (by the tree as a whole) with elevated carbon dioxide;\n
    2. \n
  2. \n evidence (from the bar chart) is strong (for the trend/hypothesis);\n
    3. \n
  3. \n all elevated plots have more carbon stored than all ambient plots in all sites/no overlap;\n
    4. \n
  4. \n more/most carbon allocated to\n \n wood\n \n (in stems and roots) with elevated carbon dioxide;\n
    5. \n
  5. \n more carbon allocated to narrow roots/leaves with elevated carbon dioxide;\n
    6. \n
  6. \n narrow roots increase most in Oak Ridge;\n
    7. \n
  7. \n most increase in wood (in stems and roots) in Rhinelander and Duke;\n
    8. \n
  8. \n much/more variation between plots at Oak Ridge (than at Rhinelander and Duke);\n
    9. \n
  9. \n no error bars so significance of differences is uncertain;\n
    10. \n
\n

\n \n Accept mpd and mpe if the answer refers only to Rhinelander and Duke.\n \n

\n

\n \n Allow mph if the answer describes an anomaly at Oak Ridge that does not follow the trend seen in Rhinelander and Duke.\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ1.G", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-3-climate-change", "d4-3-1-anthropogenic-causes-of-climate-change" ] }, { "Question": "
\n
\n

\n On the graph, which curve represents the change in FSH levels during the menstrual cycle?\n

\n

\n \n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "19N.1A.SL.TZ0.30", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-1-reproduction", "d3-1-5-changes-during-the-ovarian-and-uterine-cycles-and-their-hormonal-regulation" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Explain how natural selection can cause mate selection behaviour patterns to develop in a species such as eastern bluebirds.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n a. natural selection favours specific types of mate selection/behaviour;\n

\n

\n b. (behaviour/mate selection) increases the chances of survival/reproduction;\n

\n

\n c. chosen organisms/males will leave more offspring;\n

\n

\n d. pass on gene(s) for behavior to offspring;\n

\n

\n e. (behaviour/allele) will become more prevalent/frequent in a population;\n

\n
\n", "Examiners report": "
\n

\n It was difficult for many to provide focused answers for this question, although most candidates could provide valid partial explanations.\n

\n
\n", "question_id": "20N.2.SL.TZ0.8B", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-1-natural-selection", "d4-1-7-sexual-selection-as-a-selection-pressure-in-animal-species" ] }, { "Question": "
\n
\n

\n Which hormone helps control levels of glucose in blood?\n

\n

\n
\n A.  Insulin secreted by the liver cells\n

\n

\n B.  Thyroxin secreted by the thyroid gland\n

\n

\n C.  Glucagon secreted by the α cells of the pancreas\n

\n

\n D.  Melatonin secreted by the β cells of the pancreas\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "23M.1A.SL.TZ1.30", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-3-homeostasis", "d3-3-3-regulation-of-blood-glucose-as-an-example-of-the-role-of-hormones-in-homeostasis" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Analyse the data shown in the graph for evidence of a relationship between LAI and El Niño events.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n decreases in LAI during El Niño\n
    \n \n OR\n \n
    \n increases in LAI between El Niño events;\n
    2. \n
  2. \n 1983-4/other example of a decrease during El Niño\n
    \n \n OR\n \n
    \n 1984-6/other example of increase between El Niño events;\n
    \n OR\n
    \n 94-95/2009 anomalous as LAI rises during El Niño event;\n
    \n \n OR\n \n
    \n 99-2000 anomalous as LAI decreases between El Niño events;\n
    3. \n
  3. \n larger decrease (in LAI) with more intense/longer El Niño events\n
    \n \n OR\n \n
    \n no/less decrease during less intense/briefer El Niño events;\n
    4. \n
\n

\n \n Mpa refers to changes in LAI, not whether levels were high or low.\n \n

\n

\n \n The example given for mpb must correspond with the trend given in mpa. The graph does not show the years clearly so we must show some lenience in mpb – award this mark if it is clear which period the candidate was referring to.\n \n

\n

\n \n For mpa, do not accept answers implying that decreases in LAI cause El Niño or increases in LAI prevent El Niño.\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ1.1C", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-3-climate-change", "d4-3-1-anthropogenic-causes-of-climate-change" ] }, { "Question": "
\n
\n (c.i)\n
\n
\n

\n Identify the species whose eggs are most affected by a high dose of neonicotinoid.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n \n B. lucorum\n \n ;\n

\n
\n", "Examiners report": "None", "question_id": "22M.2.HL.TZ2.1C.I", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c2-2-neural-signalling", "c2-2-12-effects-of-exogenous-chemicals-on-synaptic-transmission" ] }, { "Question": "
\n
\n

\n The image shows part of a section through the stem of a non-woody plant. Where does transport of sucrose occur?\n

\n

\n \n

\n

\n [Source: Courtesy of Kelly Cude, PhD, Professor Biological Sciences, College of the Canyons.]\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "21M.1A.SL.TZ2.33", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-2-transport", "b3-2-9-distribution-of-tissues-in-a-transverse-section-of-the-stem-of-a-dicotyledonous-plant" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Rotenone is a naturally occurring toxin that blocks the electron transport chain in insects and fish. Outline the consequences of exposure to a toxin like rotenone for cell respiration.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n lower rate of\n \n aerobic\n \n respiration / inhibits\n \n aerobic\n \n respiration;\n
    2. \n
  2. \n reduced NAD (not oxidised) accumulates;\n
    3. \n
  3. \n fewer/no electrons (from reduced NAD and FADH) to be transported by carriers;\n
    4. \n
  4. \n less/no energy to transfer protons (from matrix to intermembrane space);\n
    5. \n
  5. \n proton gradient cannot be maintained;\n
    6. \n
  6. \n less/no diffusion of protons through ATP synthase;\n
    7. \n
  7. \n ADP is not phosphorylated / less ATP produced / no energy to produce ATP;\n
    8. \n
  8. \n oxygen not binding to protons / accepting electrons / no water formed;\n
    9. \n
\n
\n", "Examiners report": "None", "question_id": "SPM.2.HL.TZ0.9C", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-2-cell-respiration", "c1-2-16-role-of-oxygen-as-terminal-electron-acceptor-in-aerobic-cell-respiration" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Draw a fully labelled graph of the action spectrum for photosynthesis.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n a. axes correctly labelled «wavelength and\n \n rate\n \n of photosynthesis» ✔\n \n Accept\n \n \n rate\n \n \n of oxygen production for\n \n \n rate\n \n \n of photosynthesis.\n \n

\n

\n b. 400 and 700\n \n nm\n \n as limits ✔\n

\n

\n c. correct shape of curve involving two peaks at the correct places, broader in the blue-violet range not starting at zero and a narrower peak in the orange-red range with the trough in the green range that does not reach zero ✔\n

\n

\n d. peaks of activity at 430 nm\n \n \n AND\n \n \n at 660 nm ✔\n

\n

\n e. peaks indicated as «violet» blue light AND peak indicated as «orange» red light ✔\n

\n

\n

\n
\n", "Examiners report": "
\n

\n A number of students made errors in their sketches. Axes were commonly mis-labelled. The colors were commonly presented in the reverse order with red at the left end and blue at the right end. Showing red as a higher peak was another common error. The overall shape was often correctly drawn.\n

\n
\n", "question_id": "19M.2.SL.TZ2.8B", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-3-photosynthesis", "c1-3-6-similarities-and-differences-of-absorption-and-action-spectra" ] }, { "Question": "
\n
\n

\n Explain how hydrophobic and hydrophilic properties contribute to the arrangement of molecules in a membrane.\n

\n
\n
\n

\n [7]\n

\n
\n
\n", "Markscheme": "
\n

\n a. hydrophilic is attracted to/soluble in water and hydrophobic not attracted/insoluble ✔\n

\n

\n b. hydrophilic phosphate/head and hydrophobic hydrocarbon/tail in\n \n phospholipids\n \n ✔\n

\n

\n c.\n \n phospholipid bilayer\n \n in water/in membranes ✔\n

\n

\n d. hydrophilic heads «of phospholipids» face outwards/are on surface ✔\n

\n

\n e. hydrophobic tails «of phospholipids» face inwards/are inside/are in core ✔\n

\n

\n f. cholesterol is «mainly» hydrophobic/amphipathic so is located among phospholipids/in hydrophobic region of membrane ✔\n

\n

\n g. some amino acids are hydrophilic and some are hydrophobic ✔\n

\n

\n h. hydrophobic «amino acids/regions of» proteins in phospholipid bilayer «core» ✔\n

\n

\n i. hydrophilic «amino acids/regions of» proteins are on the membrane surface ✔\n

\n

\n j.\n \n integral proteins\n \n are embedded in membranes due to hydrophobic properties/region\n
\n \n \n OR\n \n \n
\n \n transmembrane\n \n proteins have a hydrophobic middle region and hydrophilic ends ✔\n

\n

\n k.\n \n peripheral proteins\n \n on are on the membrane surface/among phosphate heads due to being «entirely» hydrophilic\n
\n \n \n OR\n \n \n
\n «carbohydrate» part of\n \n glycoproteins\n \n is hydrophilic so is outside the membrane ✔\n

\n

\n l. pore of\n \n channel proteins\n \n is hydrophilic ✔\n

\n

\n \n Allow mark points shown in clearly annotated diagram.\n \n

\n

\n \n In any part of the answer, accept polar instead of hydrophilic and non-polar or apolar instead of hydrophobic.\n \n

\n
\n", "Examiners report": "
\n

\n Candidates struggled to explain the meaning of the term hydrophobic. Many stated the literal meaning – water-fearing, hence repelled by water. This was not accepted as hydrophobic molecules aren’t repelled by water. They appear to be, because water is more attracted to polar or ionic substances than to apolar/hydrophobic substances, but there is no chemical mechanism for repulsion and of course molecules do not fear each other. Many focused only on phospholipids, but stronger answers also included information on proteins and how the positions they occupy within the membrane depend on their hydrophobic and hydrophilic properties.\n

\n
\n", "question_id": "19M.2.SL.TZ1.C", "topics": [ "c-interaction-and-interdependence", "b-form-and-function" ], "subtopics": [ "c2-1-chemical-signalling-[hl-only]", "c2-1-6-differences-between-transmembrane-receptors-in-a-plasma-membrane-and-intracellular-receptors-in-the-cytoplasm-or-nucleus", "b2-1-membranes-and-membrane-transport", "b2-1-10-fluid-mosaic-model-of-membrane-structure" ] }, { "Question": "
\n
\n

\n What is a proteome?\n

\n

\n A. The genes that code for all the proteins in the ribosome\n

\n

\n B. The group of proteins that generate a proton gradient in mitochondria\n

\n

\n C. The entire genome of a prokaryote\n

\n

\n D. The entire set of proteins expressed by an organism at a certain time\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "19N.1A.HL.TZ0.6", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-2-gene-expression-[hl-only]", "d2-2-5-differences-between-the-genome-transcriptome-and-proteome-of-individual-cells" ] }, { "Question": "
\n
\n (e)\n
\n
\n

\n State\n \n one\n \n reason that identical twins may show different methylation patterns as they grow older.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n (different) environment/illness/disease/diet;\n

\n

\n \n Not mutation\n \n

\n
\n", "Examiners report": "
\n

\n Most candidates knew that differences in environmental factors can cause differences in methylation pattern.\n

\n
\n", "question_id": "22N.2.HL.TZ0.4E", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-2-gene-expression-[hl-only]", "d2-2-7-epigenetic-inheritance-through-heritable-changes-to-gene-expression" ] }, { "Question": "
\n
\n

\n Suggest reasons for the difference between the fraction attributed to\n \n S. pneumoniae\n \n in all cases of ARI and in cases where antibiotics were used to treat the infection.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n highest attributed fraction (in both age groups) is in cases where antibiotic used;\n
    2. \n
  2. \n ARI cases due to\n \n S. pneumoniae\n \n can be severe so antibiotics are often prescribed;\n
    3. \n
  3. \n all cases include other causes / viral ARI which may not require antibiotics;\n
    4. \n
  4. \n antibiotics administered without prescription or physician consultation/to reduce symptoms;\n
    5. \n
\n

\n \n Mpa: Comparative terms expected (do not award mp for just stating values).\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ2.G", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-2-defence-against-disease", "c3-2-16-vaccines-and-immunization" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Suggest a reason for the F\n \n 2\n \n generation not corresponding exactly to the expected ratio of purple-flowered and white-flowered plants.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n chance /\n \n \n OWWTE\n \n \n ;\n

\n

\n \n (any of the usual mechanisms causing recombination of alleles) NOT mutation.\n \n

\n

\n \n Any wording that implies the bigger the sample size, the closer to 3:1.\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ2.2C", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-2-inheritance", "d3-2-2-methods-for-conducting-genetic-crosses-in-flowering-plants" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Identify the month when small birds had the greatest chance of being infected by\n \n B. burgdorferi\n \n bacteria in the year 2000\n \n and\n \n the month when they would be most likely to become infected according to the 2080 predictions.\n

\n

\n 2000:\n

\n

\n 2080:\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n «2000» August AND «2080» July ✔\n

\n

\n \n Both required\n \n .\n

\n
\n", "Examiners report": "None", "question_id": "19N.2.SL.TZ0.1C", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a4-2-conservation-of-biodiversity" ] }, { "Question": "
\n
\n

\n The gene that codes for a particular polypeptide includes the base sequence shown.\n

\n

\n GAGTACCCT\n

\n

\n What is the base sequence of the mRNA molecule which is complementary to this sequence?\n

\n

\n A. GAGTACCCT\n

\n

\n B. CTCATGGGA\n

\n

\n C. GUGTUCCCT\n

\n

\n D. CUCAUGGGA\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "19M.1A.SL.TZ1.10", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d1-2-protein-synthesis", "d1-2-5-translation-as-the-synthesis-of-polypeptides-from-mrna", "d1-2-6-roles-of-mrna-ribosomes-and-trna-in-translation", "d1-2-7-complementary-base-pairing-between-trna-and-mrna" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Explain how natural selection could increase the prevalence of an antibiotic resistance gene in a species of soil bacterium.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n if antibiotic is in the environment/soil there is selection (pressure);\n
    2. \n
  2. \n bacteria without resistance (gene) die / converse;\n
    3. \n
  3. \n bacteria with resistance (gene) reproduce\n
    \n \n OR\n \n
    \n bacteria exchange/obtain resistance genes using plasmids/by conjugation;\n
    4. \n
  4. \n offspring inherit (the gene for) resistance/resistance passed on (to offspring);\n
    5. \n
\n

\n \n Do not award marks for general statements about natural selection – answers must refer to antibiotic resistance.\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.2.HL.TZ1.3", "topics": [ "d-continuity-and-change", "c-interaction-and-interdependence" ], "subtopics": [ "d4-1-natural-selection", "d4-1-15-artificial-selection-by-deliberate-choice-of-traits", "c3-2-defence-against-disease", "c3-2-14-evolution-of-resistance-to-several-antibiotics-in-strains-of-pathogenic-bacteria", "c3-2-13-antibiotics-as-chemicals-that-block-processes-occurring-in-bacteria-but-not-in-eukaryotic-cells" ] }, { "Question": "
\n
\n

\n The graph of the effect of pH on immobilized lipase activity does not allow for the determination of optimum pH precisely. Explain how a more exact value for the optimum pH could be determined.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. the experiment is repeated with smaller increments of pH ✔\n

\n

\n b. «repeated» within the range of the optimum pH\n
\n \n \n OR\n \n \n
\n between pH 6/7 and 8 ✔\n

\n

\n c. the pH that gives the highest enzyme activity is optimum ✔\n

\n
\n", "Examiners report": "
\n

\n Candidates found this question to be challenging. Students were asked to “explain how a more exact value for the optimum pH could be determined.” Students who completed practical 3 and were also taught the second skill listed in the subject guide in topic 2.5 (Design of experiments to test the effect of temperature, pH and substrate concentration on the activity of enzymes) should have been able to achieve the marks. Common incorrect answers suggested using better graphs or different calculation methods. Students should be instructed to understand the difference between experimental methods and data-processing tools.\n

\n
\n", "question_id": "19M.1B.SL.TZ1.B", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-1-enzymes-and-metabolism", "c1-1-8-effects-of-temperature-ph-and-substrate-concentration-on-the-rate-of-enzyme-activity" ] }, { "Question": "
\n
\n

\n The graph shows the effect of methylation on the expression of MT1E, a gene involved in the control of prostate cancer development. Patients with a reduced expression of this gene are more likely to develop prostate cancer.\n

\n

\n \n

\n

\n \n [Source: © 2017 Demidenko et al. 2017. Decreased expression of MT1E is a potential biomarker of\n
\n prostate cancer progression.\n \n Oncotarget\n \n , 8, pp. 61709–61718. Distributed under the terms of the Creative Commons Attribution License 3.0 (CC BY 3.0). Image redrawn and reannotated.]\n \n

\n

\n
\n What are effects of MT1E methylation?\n

\n

\n
\n A.  It reduces transcription of MT1E, increasing the risk of prostate cancer.\n

\n

\n B.  It increases translation of MT1E, reducing the risk of prostate cancer.\n

\n

\n C.  It reduces replication of MT1E, reducing the risk of prostate cancer.\n

\n

\n D.  It increases the chances of mutation in proto-oncogenes, increasing the risk of prostate cancer.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "None", "question_id": "SPM.1A.HL.TZ0.19", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-2-gene-expression-[hl-only]", "d2-2-6-methylation-of-the-promoter-and-histones-in-nucleosomes-as-examples-of-epigenetic-tags", "d2-2-7-epigenetic-inheritance-through-heritable-changes-to-gene-expression" ] }, { "Question": "
\n
\n

\n What is required for natural selection to occur?\n

\n

\n I. Acquired characteristics\n

\n

\n II. Advantageous characteristics\n

\n

\n III. Genetic variation\n

\n

\n A. I only\n

\n

\n B. I and III only\n

\n

\n C. II and III only\n

\n

\n D. I, II and III\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "
\n

\n The answers to this question show poor knowledge of the requirements for natural selection, as many candidates believed acquired characteristics are needed.\n

\n
\n", "question_id": "19M.1A.SL.TZ2.20", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-1-natural-selection", "d4-1-2-roles-of-mutation-and-sexual-reproduction-in-generating-the-variation-on-which-natural-selection-acts" ] }, { "Question": "
\n
\n

\n Which reaction occurs in blood clotting?\n

\n

\n \n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "None", "question_id": "21M.1A.SL.TZ1.30", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-2-defence-against-disease", "c3-2-3-sealing-of-cuts-in-skin-by-blood-clotting" ] }, { "Question": "
\n
\n

\n Non-disjunction of chromosome 21 causes trisomy. What can be said about the incidence of non-disjunction in chromosome 21?\n

\n

\n
\n A.  It increases greatly with maternal age after 30 years.\n

\n

\n B.  Chromosome 21 always suffers non-disjunction.\n

\n

\n C.  Very young mothers have no chance of non-disjunction.\n

\n

\n D.  There is no relation between age and the probability of non-disjunction.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "None", "question_id": "23M.1A.SL.TZ1.15", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-1-cell-and-nuclear-division", "d2-1-10-down-syndrome-and-non-disjunction" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Suggest one advantage of using a mesocosm in this type of research.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n environmentally safe/cheaper/control of variables easier;\n

\n
\n", "Examiners report": "None", "question_id": "23M.1B.SL.TZ2.3B", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-2-stability-and-change", "d4-2-4-use-of-a-model-to-investigate-the-effect-of-variables-on-ecosystem-stability" ] }, { "Question": "
\n
\n

\n The diagrams show how monosaccharide molecules are joined to form chains in two polysaccharides.\n

\n

\n \n

\n

\n [Source: Amelse, J. Achieving Net Zero Carbon Dioxide by Sequestering Biomass Carbon.\n \n Preprints\n \n 2020, 2020070576\n
\n (doi:\n \n 10.20944/preprints202007.0576.v1\n \n ). Fig SI9. Distributed under a Creative Commons CC BY license Attribution\n
\n 4.0 International (CC BY 4.0),\n \n https://creativecommons.org/licenses/by/4.0/\n \n .]\n

\n

\n Using the diagram and the table, which diagram and monosaccharide represent glycogen?\n

\n

\n \n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "21N.1A.SL.TZ1.9", "topics": [ "b-form-and-function" ], "subtopics": [ "b1-1-carbohydrates-and-lipids", "b1-1-5-polysaccharides-as-energy-storage-compounds" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Using evidence from the chart, identify, giving a reason, which group of neurons responded most to the chemicals.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n G1 always respond more than 25% «except control», while G2 and G3 always respond 25% or less ✔\n

\n

\n G1 always responds more than G2 and G3/all of the others ✔\n

\n

\n \n OWTTE\n \n

\n
\n", "Examiners report": "
\n

\n many lost the mark by not stating the reason that the G1 responses were higher than the others (G2 and G3)\n

\n
\n", "question_id": "19M.2.SL.TZ2.1B", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c2-2-neural-signalling" ] }, { "Question": "
\n
\n (c.i)\n
\n
\n

\n Identify X, the enzyme which copies a DNA sequence.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n \n RNA polymerase\n \n ;\n

\n
\n", "Examiners report": "
\n

\n About half of candidates knew that X must be RNA polymerase. Some candidates thought that it was DNA polymerase, perhaps because the question referred to copying a DNA sequence. This answer was not accepted as the diagram did not show replication.\n

\n
\n", "question_id": "22N.2.HL.TZ0.4C.I", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d1-1-dna-replication", "d1-1-3-role-of-helicase-and-dna-polymerase-in-dna-replication" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Explain\n \n one\n \n cause of mutation.\n

\n

\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n \n

\n

\n \n Not chromosomal\n \n .\n

\n
\n", "Examiners report": "
\n

\n Many were confused by a relatively simple question, but a large proportion gained both marks by linking radiation or carcinogens to changes in the DNA base sequence.\n

\n
\n", "question_id": "19M.2.SL.TZ2.4B", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d1-3-mutations-and-gene-editing", "d1-3-4-causes-of-gene-mutation" ] }, { "Question": "
\n
\n (e)\n
\n
\n

\n The life expectancy of a human at the time of the study was 80 years. Estimate the porosity of the bones of the individual who was approximately 32 years old.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n 6 %;\n

\n

\n \n Accept answers in the range 6.0 to 6.5 %.\n \n
\n \n Percentage sign required.\n \n

\n
\n", "Examiners report": "
\n

\n This question was very unusual in that the discrimination index was negative — stronger candidates were slightly less likely to answer correctly than weaker candidates, for reasons that are not obvious! Only a minority gave the expected answer of 6 %. A very common answer was 7 %, which is reached by calculating the age proportion correctly as 0.4 but using the trend line rather than the data point for the individual who was 32 years old. Careful reading of the question was needed to avoid this mistake.\n

\n
\n", "question_id": "22M.2.SL.TZ1.1E", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-3-homeostasis", "d3-3-1-homeostasis-as-maintenance-of-the-internal-environment-of-an-organism", "d3-3-2-negative-feedback-loops-in-homeostasis" ] }, { "Question": "
\n
\n

\n A cell from the lungs, observed under the microscope, contains a large number of secretory organelles. Which conclusion can be drawn about the cell?\n

\n

\n A. It is a type I pneumocyte.\n

\n

\n B. It is a type II pneumocyte.\n

\n

\n C. It could be either a type I or type II pneumocyte.\n

\n

\n D. It is a red blood cell.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "22M.1A.HL.TZ1.27", "topics": [ "b-form-and-function" ], "subtopics": [ "b2-3-cell-specialization", "b2-3-8-adaptations-of-type-i-and-type-ii-pneumocytes-in-alveoli" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Suggest with a reason which system best reproduces the conditions of the natural environment.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n a. horizontal flow/«figure» B because it is larger\n
\n \n \n OR\n \n \n
\n horizontal flow/«figure» B contains more/several plants ✔\n

\n

\n b. horizontal flow/«figure» B because it works by natural flow\n
\n \n \n OR\n \n \n
\n horizontal flow/«figure» B because it works without a pump ✔\n \n Do not accept river instead of flow\n \n .\n

\n
\n", "Examiners report": "None", "question_id": "19N.1B.SL.TZ0.1B", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-2-stability-and-change", "d4-2-4-use-of-a-model-to-investigate-the-effect-of-variables-on-ecosystem-stability" ] }, { "Question": "
\n
\n

\n The graph shows the effect of increasing light intensity on the rate of CO\n \n 2\n \n uptake by a species of green plant maintained in conditions of constant temperature and CO\n \n 2\n \n concentration.\n

\n

\n \n

\n

\n [Source: © International Baccalaureate Organization 2019]\n

\n

\n

\n

\n Which statement is consistent with the graph?\n

\n

\n A. Photosynthesis stops at high light intensity.\n

\n

\n B. Rates of photosynthesis increase with temperature.\n

\n

\n C. Cell respiration leads to net production of CO\n \n 2\n \n at low light intensity.\n

\n

\n D. There is a negative correlation between CO\n \n 2\n \n uptake and light intensity.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "
\n

\n Many candidates (and some teachers commenting in feedback forms) chose answer A, but this is to confuse a plateau on the graph with a decrease to zero. Perhaps the term ‘rate’ was not understood and it was thought that the graph showed cumulative absorption of carbon dioxide. This is another question where more than straight factual recall is required.\n

\n
\n", "question_id": "19M.1A.SL.TZ1.12", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-3-photosynthesis", "c1-3-7-techniques-for-varying-concentrations-of-carbon-dioxide-light-intensity-or-temperature-experimentally-to-investigate-the-effects-of-limiting-factors-on-the-rate-of-photosynthesis" ] }, { "Question": "
\n
\n

\n Which feature of the cell in the micrograph is consistent with the endosymbiotic theory?\n

\n

\n A. X has a single membrane.\n

\n

\n B. Y has a double membrane.\n

\n

\n C. X contains 70S ribosomes.\n

\n

\n D. Y contains 80S ribosomes.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "20N.1A.HL.TZ0.2", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a2-2-cell-structure", "a2-2-12-origin-of-eukaryotic-cells-by-endosymbiosis" ] }, { "Question": "
\n
\n

\n Which are two proteins that assist in the unwinding and separation of DNA strands during replication?\n

\n

\n A. Helicase and DNA polymerase III\n

\n

\n B. DNA gyrase and DNA polymerase I\n

\n

\n C. Helicase and DNA primase\n

\n

\n D. Single-strand binding protein and DNA gyrase\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "
\n

\n For reasons that are hard to explain, this question had one of the highest ever discrimination indices at 0.72, with about half of candidates answering correctly.\n

\n
\n", "question_id": "20N.1A.SL.TZ0.27", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d1-1-dna-replication", "d1-1-3-role-of-helicase-and-dna-polymerase-in-dna-replication" ] }, { "Question": "
\n
\n

\n What is a consequence of anaerobic cell respiration in muscles?\n

\n

\n
\n A.  Large yield of readily available ATP and ethanol production\n

\n

\n B.  Small yield of readily available ATP and lactate accumulation\n

\n

\n C.  Large yield of ATP and production of carbon dioxide and lactic acid\n

\n

\n D.  Small yield of ATP that is not readily available and carbon dioxide production\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "23M.1A.SL.TZ1.13", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-2-cell-respiration", "c1-2-9-conversion-of-pyruvate-to-lactate-as-a-means-of-regenerating-nad-in-anaerobic-cell-respiration" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Identify in which continent the fewest types of neonicotinoid were detected in honey samples.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n Oceania ✔\n

\n
\n", "Examiners report": "
\n

\n In general, the data analysis question was well attempted by the majority of students.\n

\n

\n Almost all were able to name Oceania.\n

\n
\n", "question_id": "21M.2.HL.TZ2.1A", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c2-2-neural-signalling", "c2-2-12-effects-of-exogenous-chemicals-on-synaptic-transmission" ] }, { "Question": "
\n
\n

\n Scientists studied differences in the base sequences of a gene found in five animal species in order to determine their evolutionary relationships. A cladogram was constructed based on these differences.\n

\n

\n \n

\n

\n
\n What can be deduced from the cladogram?\n

\n

\n
\n A.  There are only three clades shown.\n

\n

\n B.  Morphological differences between V and Z increase with time.\n

\n

\n C.  There is only one difference between the amino acid sequences of X and Y.\n

\n

\n D.  Y and Z have a more recent common ancestor than W and X.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "SPM.1A.HL.TZ0.25", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a3-2-classification-and-cladistics-(hl-only)", "a3-2-7-analysing-cladograms" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Outline how the hormone auxin controls phototropism in plant shoots.\n

\n
\n
\n

\n [5]\n

\n
\n
\n", "Markscheme": "
\n

\n a. grows/bends towards (brightest) light/sun ✔\n

\n

\n b. auxin moved from lighter to shadier side (of shoot/stem tip/apex) ✔\n

\n

\n c. moved by auxin efflux pumps ✔\n

\n

\n d. auxin promotes cell elongation/cell growth / auxin causes cell wall acidification/loosening ✔\n

\n

\n e. more growth on shady side of stem (due to auxin concentration gradient) ✔\n

\n

\n f. binds to auxin receptors (in target cells) ✔\n

\n

\n g. auxin/auxin receptors promote expression of genes (for growth)/for H\n \n +\n \n secretion into wall ✔\n

\n
\n", "Examiners report": "
\n

\n Candidates tended either to know the mechanism of phototropism very well, or not at all. It wasn't always clear that the terms shoot, stem and leaf were correctly distinguished in some candidates' minds.\n

\n
\n", "question_id": "21M.2.HL.TZ1.6B", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-1-integration-of-body-systems", "c3-1-21-promotion-of-cell-growth-by-auxin", "c3-1-22-interactions-between-auxin-and-cytokinin-as-a-means-of-regulating-root-and-shoot-growth" ] }, { "Question": "
\n
\n

\n In 1882, Engelmann investigated photosynthesis by shining light of varying wavelength on a green alga. He observed where aerobic bacteria accumulated.\n

\n

\n \n

\n

\n [Source: Republished with permission of Oxford University Press, from\n \n Plant Physiology and Development\n \n ,\n \n Sixth Edition\n \n by\n
\n Lincoln Taiz, Eduardo Zeiger, Ian M. Møller, and Angus Murphy, 2015. Permission conveyed through Copyright\n
\n Clearance Center, Inc.]\n

\n

\n

\n

\n What can be deduced from this experiment?\n

\n

\n A. Only parts of the chloroplast contained chlorophyll.\n

\n

\n B. The distribution of bacteria indicates the action spectrum of photosynthesis.\n

\n

\n C. Most oxygen is released from the algae in green light.\n

\n

\n D. Chloroplasts reflect blue and red light.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "
\n

\n A G2 comment suggested that this question would take too long to answer, but the statistics showed that students did not find it difficult.\n

\n
\n", "question_id": "21N.1A.SL.TZ1.8", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-3-photosynthesis", "c1-3-5-absorption-of-specific-wavelengths-of-light-by-photosynthetic-pigments" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Outline how the properties of water make it an effective coolant for the body.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n hydrogen bonds hold water molecules together/make water molecules cohere;\n
    2. \n
  2. \n evaporation requires breaking of hydrogen bonds / heat needed to break hydrogen bonds\n
    3. \n
  3. \n water has a high heat of vaporization/high latent heat;\n
    4. \n
  4. \n evaporation of water/sweat removes heat from/cools the skin/body;\n
    5. \n
\n
\n", "Examiners report": "
\n

\n This question revealed widespread misunderstanding of the properties of water and changes of state. Most candidates though that water's high specific heat capacity explains its role as a coolant and that sweat cools the body by taking heat from it to raise its temperature. Few candidates referred to the requirement for heat to break hydrogen bonds as water evaporates. To be able to understand biological processes properly, a firm grounding in physics and chemistry is needed, but all too often it was lacking.\n

\n
\n", "question_id": "22M.2.SL.TZ1.6A", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a1-1-water", "a1-1-6-physical-properties-of-water-and-the-consequences-for-animals-in-aquatic-habitats" ] }, { "Question": "
\n
\n

\n Which process occurs in meiosis but not in mitosis?\n

\n

\n A. Attachment of spindle fibres to the centromeres of each chromosome\n

\n

\n B. Movement of homologous chromosomes to opposite ends\n

\n

\n C. Replication of DNA prior to the start of cell division\n

\n

\n D. Separation of sister chromatids during anaphase\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "22M.1A.SL.TZ1.12", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-1-cell-and-nuclear-division", "d2-1-4-roles-of-mitosis-and-meiosis-in-eukaryotes", "d2-1-9-meiosis-as-a-reduction-division" ] }, { "Question": "
\n
\n

\n The grey line in each of the graphs below represents the rate of reaction catalysed by an uninhibited enzyme as substrate concentration is increased.\n

\n

\n Which graph shows expected results if a competitive inhibitor was added to the reaction?\n

\n

\n \n

\n

\n [Source: © International Baccalaureate Organization 2019]\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "19N.1A.HL.TZ0.29", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-1-enzymes-and-metabolism", "c1-1-15-competitive-inhibition-as-a-consequence-of-an-inhibitor-binding-reversibly-to-an-active-site" ] }, { "Question": "
\n
\n

\n Calculate the length of the entire cell labelled Y, showing your working.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n 50 μm = 27/28/29 mm,\n \n Y\n \n = 8/9/10 mm\n
\n \n \n OR\n \n \n
\n 50 x 9 /27\n
\n \n \n OR\n \n \n
\n 16.7 μm (accept answers in the range of 14.8 μm to 17.2 μm)\n

\n

\n \n Award\n \n [1]\n \n for correct ratios not precise measurements in the work or\n \n [1]\n \n for correct answer with correct unit\n \n .\n

\n
\n", "Examiners report": "
\n

\n Most answers were correct, but some calculations were difficult to follow; some errors in unit conversions led to incorrect decimal places.\n

\n
\n", "question_id": "22M.2.SL.TZ2.A.II", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a2-2-cell-structure", "a2-2-2-microscopy-skills" ] }, { "Question": "
\n
\n (e)\n
\n
\n

\n Compare and contrast the data in the chart for males and females.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n Similarities (Compare)\n

\n

\n a. lower percentage of obesity with more steps per day in both males and females\n
\n \n \n OR\n \n \n
\n percentage obesity is most similar at 1000 steps\n
\n \n \n OR\n \n \n
\n correlation of steps to percent obesity plateaus after 8000 steps for both males and females;\n

\n

\n
\n Differences (Contrast)\n

\n

\n b. the range difference of obesity percentage among different steps is bigger in females (9% - 31% versus 18% to 30%)\n
\n \n \n OR\n \n \n
\n walking has a greater impact on lowering obesity rates in females than males\n
\n \n \n OR\n \n \n
\n men show a greater percentage of obesity\n
\n \n \n OR\n \n \n
\n at 1000 steps per day there are more obese women than men;\n

\n

\n

\n

\n \n One similarity and one difference required for two marks.\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ1.1E", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-3-muscle-and-motility-(hl-only)", "b3-3-9-reasons-for-locomotion" ] }, { "Question": "
\n
\n

\n The image shows the result of DNA profiling of a mother, a child and four men. Which man is most probably the father of the child?\n

\n

\n \n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "21N.1A.SL.TZ0.16", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d1-1-dna-replication", "d1-1-5-applications-of-polymerase-chain-reaction-and-gel-electrophoresis" ] }, { "Question": "
\n
\n

\n With reference to the diagram, explain how water in sweat evaporates.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n heat increases molecular motion/vibration;\n
    2. \n
  2. \n (hydrogen) bonds break/bonds between water molecules break;\n
    3. \n
  3. \n water evaporation is separation of water molecules/water changes from liquid to gas/vapour;\n
    4. \n
  4. \n heat removed from skin surface/body;\n
    5. \n
\n

\n

\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ1.I", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-3-homeostasis", "d3-3-6-thermoregulation-mechanisms-in-humans" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Outline the biomagnification of DDE in brown pelicans.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n DDE accumulates in (fat tissues of) organisms/bioaccumulation;\n
    2. \n
  2. \n (brown) pelicans/birds feed on fish/organisms (that have accumulated DDE);\n
    3. \n
  3. \n (DDE) is not excreted;\n
    4. \n
  4. \n (DDE) concentration\n \n increases\n \n as trophic level increases;\n
    5. \n
  5. \n (brown) pelicans are in a high trophic level (so have a high accumulation);\n
    6. \n
\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ2.18C", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-2-stability-and-change", "d4-2-9-biomagnification-of-pollutants-in-natural-ecosystems" ] }, { "Question": "
\n
\n (a.i)\n
\n
\n

\n On the diagrams, label with a letter H the hydrophilic end of a phospholipid.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n hydrophilic end of phospholipid shown ✔\n

\n

\n \n For 2a, i, ii and iii, accept letters written on the structure even if a line is not drawn.\n \n

\n

\n \n Award the mark if the full word is used to label the structure. Labels must be unambiguous.\n \n

\n
\n", "Examiners report": "
\n

\n There were numerous examples of ambiguous labels, for example, an H without an arrow placed beside the membrane making it unclear whether the student was indicating the hydrophobic or hydrophilic part of the membrane.\n

\n
\n", "question_id": "21M.2.SL.TZ2.2A.I", "topics": [ "b-form-and-function" ], "subtopics": [ "b1-1-carbohydrates-and-lipids", "b1-1-12-formation-of-phospholipid-bilayers-as-a-consequence-of-the-hydrophobic-and-hydrophilic-regions" ] }, { "Question": "
\n
\n

\n Which pedigree chart is consistent with the inheritance of red-green colour blindness?\n

\n

\n \n

\n

\n [Source: © International Baccalaureate Organization 2019]\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "None", "question_id": "19M.1A.SL.TZ1.16", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-2-inheritance", "d3-2-11-sex-determination-in-humans-and-inheritance-of-genes-on-sex-chromosomes" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Suggest\n \n one\n \n reason that the relative brain mass of\n \n Homo\n \n is different from\n \n Parapithecus\n \n and\n \n Australopithecus\n \n .\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n a. human cerebral cortex has extensive folding producing a greater mass ✔\n

\n

\n b. better diet/more protein allowed increase in «relative» brain mass in humans ✔\n

\n

\n c. others had larger body to protect them from predators «without increase in brain mass» ✔\n

\n
\n", "Examiners report": "
\n

\n In parts (b) and (c) few candidates referred to ‘relative’ brain mass thereby providing incorrect responses.\n

\n
\n", "question_id": "19M.1B.SL.TZ2.5B", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-1-integration-of-body-systems", "c3-1-4-the-brain-as-a-central-information-integration-organ" ] }, { "Question": "
\n
\n

\n The structure of monomers affects the structure and function of the polymers they form. Which row\n
\n describes the structural features of polysaccharides made from alpha-glucose and beta-glucose?\n

\n

\n \n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "SPM.1A.HL.TZ0.5", "topics": [ "b-form-and-function" ], "subtopics": [ "b1-1-carbohydrates-and-lipids", "b1-1-6-structure-of-cellulose-related-to-its-function-as-a-structural-polysaccharide-in-plants" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Explain the conclusion that can be drawn from Cross 1.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n allele/trait/gene for banded is dominant/allele for unbanded is recessive;\n
    2. \n
  2. \n because two banded spiders produced some unbanded offspring\n
    \n \n OR\n \n
    \n because there is a ratio of 3 banded:1 unbanded;\n
    3. \n
  3. \n both parents are heterozygous;\n
    4. \n
\n

\n \n Accept answers given in the form of Punnet squares.\n \n

\n

\n

\n
\n", "Examiners report": "None", "question_id": "23M.2.HL.TZ1.5", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-2-inheritance", "d3-2-5-effects-of-dominant-and-recessive-alleles-on-phenotype" ] }, { "Question": "
\n
\n

\n If seeds of an unknown species of plant are discovered, what assumption can be made about the species?\n

\n

\n A. Its male gametes are contained within pollen.\n

\n

\n B. Its seeds are contained within fruits.\n

\n

\n C. It is in the domain archaea.\n

\n

\n D. It is in the phylum angiospermophyta.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "
\n

\n Candidates showed poor knowledge on conifers, as many assumed that only angiosperms produce seeds. This topic is found in 5.3 of the guide.\n

\n
\n", "question_id": "19M.1A.SL.TZ2.21", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-1-reproduction", "d3-1-8-sexual-reproduction-in-flowering-plants" ] }, { "Question": "
\n
\n

\n Distinguish between the structure of chromosomes in prokaryotes and eukaryotes.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n prokaryotes (usually) have one chromosome while eukaryotes have numerous chromosomes;\n
    2. \n
  2. \n prokaryotes have a circular chromosome while eukaryotes have linear ones;\n
    3. \n
  3. \n eukaryotes’ chromosomes are associated with histones/proteins but prokaryotes/Eubacteria have naked DNA vs eukaryote DNA associated to proteins/histones;\n
    4. \n
\n

\n \n Accept only differences.\n \n

\n

\n \n Differentiating terms expected;\n \n

\n
\n", "Examiners report": "
\n

\n This question led to a large number of correct answers. Some answers focused on the difference between prokaryotes and eukaryotes instead of their chromosomes.\n

\n
\n", "question_id": "22M.2.SL.TZ2.B.I", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a2-2-cell-structure", "a2-2-5-prokaryote-cell-structure", "a2-2-6-eukaryote-cell-structure" ] }, { "Question": "
\n
\n

\n Explain how cladistics can be used to investigate evolutionary relationships.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. (cladistics) shows evolutionary relationships through a common ancestor ✔\n

\n

\n b. cladistics uses DNA/protein/derived/shared anatomical characteristics/traits ✔\n

\n

\n c. time of divergence is related to the number of differences in DNA (base sequence) / protein (sequence of amino acids) ✔\n

\n

\n d. homologous (versus analogous) traits are used to place an organism in a clade ✔\n

\n

\n e. more shared characteristics mean a more recent common ancestor ✔\n

\n
\n", "Examiners report": "
\n

\n Candidates found it hard to express themselves without contradiction.\n

\n

\n Carrying examples into part (b) made for the most successful answers. Very few gained marks for providing answers that included molecular level cladistic evidence, e.g. DNA, protein sequencing, etc.\n

\n
\n", "question_id": "21M.2.HL.TZ1.B", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a3-2-classification-and-cladistics-(hl-only)", "a3-2-2-difficulties-classifying-organisms-into-the-traditional-hierarchy-of-taxa", "a3-2-8-using-cladistics-to-investigate-whether-the-classification-of-groups-corresponds-to-evolutionary-relationships" ] }, { "Question": "
\n
\n

\n What would happen if the unicellular organism was placed in a solution slightly less concentrated than the cytoplasm of the cell, rather than in distilled water?\n

\n

\n A.  The cell would become larger.\n

\n

\n B.  More water would be expelled from the cell.\n

\n

\n C.  X would fill more slowly.\n

\n

\n D.  X would not appear.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "
\n

\n Question 3 caused much more difficulty for the candidates and discriminated very poorly with both the incorrect responses A and B being very common. The question may have been poorly worded as the concept is straightforward. If the cell is removed from the distilled water and placed in a solution that is more concentrated than the distilled water, but less concentrated than the cell, water will still enter the cell, but more slowly than previously. This would cause structure X to fill more slowly.\n

\n
\n", "question_id": "22N.1A.SL.TZ0.3", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-3-water-potential", "d2-3-3-water-movement-by-osmosis-into-or-out-of-cells" ] }, { "Question": "
\n
\n

\n What is a reason that Taq polymerase is a suitable enzyme for use in the polymerase chain reaction (PCR)?\n

\n

\n
\n A.  It can work at a wide range of pH.\n

\n

\n B.  It works at higher temperatures than most enzymes.\n

\n

\n C.  It can separate two strands of DNA.\n

\n

\n D.  It allows DNA to be replicated without the use of primers.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "SPM.1A.HL.TZ0.9", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d1-1-dna-replication", "d1-1-4-polymerase-chain-reaction-and-gel-electrophoresis-as-tools-for-amplifying-and-separating-dna" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n The process X uses oxygen and produces ATP. Identify the process X.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n \n aerobic\n \n respiration ✔\n

\n
\n", "Examiners report": "
\n

\n The diagram was generally confusing to candidates.\n

\n

\n Although many answered cell respiration, aerobic respiration was expected since the question defined aerobic respiration.\n

\n
\n", "question_id": "21M.2.SL.TZ1.2C", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-2-cell-respiration", "c1-2-4-cell-respiration-as-a-system-for-producing-atp-within-the-cell-using-energy-released-from-carbon-compounds" ] }, { "Question": "
\n
\n

\n The diagram shows the elements present in two organic molecules, W and X.\n
\n Which molecules could W and X be?\n

\n

\n \n

\n

\n
\n \n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "SPM.1A.SL.TZ0.1", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a1-1-water", "a1-1-2-hydrogen-bonds-as-a-consequence-of-the-polar-covalent-bonds-within-water-molecules" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Explain how natural selection can cause traits such as drought resistance to develop in wild plants.\n

\n
\n
\n

\n [7]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n (natural selection occurs if) there is variation in degree of drought resistance among members of a population/same species;\n
    2. \n
  2. \n variation is caused by mutations (when changes occur in the DNA/nucleic bases/chromosomes);\n
    3. \n
  3. \n variation during meiosis occurs (with separation of chromosomes);\n
    4. \n
  4. \n variation occurs during sexual reproduction (as different alleles combine);\n
    5. \n
  5. \n some variations make some plants more drought-resistant;\n
    6. \n
  6. \n example of variations: deeper roots/more storage tissue for water/thicker cuticles/less opening of stomata/other verifiable variations;\n
    7. \n
  7. \n these variations let some survive and reproduce better/have more offspring\n
    \n \n \n OR\n \n \n
    \n (these variations) confer selective advantage;\n
    8. \n
  8. \n these variations/characteristics are passed onto offspring which survive better;\n
    9. \n
  9. \n natural selection increases the frequency of these characteristics;\n
    10. \n
  10. \n eventually leads to changes/evolution in the species / more drought-resistant plants;\n
    11. \n
\n
\n", "Examiners report": "
\n

\n The inclusion of ‘drought resistance’ in the stem of the question should have been a suggestion to include it, but many answers were far to general with a vague attempt to explain Natural Selection in general without explaining how the initial variation in the population came about. There were quite a few ‘Lamarckian’ answers with claims of individuals adapting to cope with the change. The average for this question was only 2.8, putting it as one of the most poorly answered.\n

\n
\n", "question_id": "22M.2.SL.TZ2.7B", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-1-natural-selection", "d4-1-1-natural-selection-as-the-mechanism-driving-evolutionary-change", "d4-1-2-roles-of-mutation-and-sexual-reproduction-in-generating-the-variation-on-which-natural-selection-acts" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Explain how increased levels of atmospheric carbon dioxide contribute to global warming.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n carbon dioxide absorbs/traps long wavelength/infra-red radiation;\n
    2. \n
  2. \n \n more heat\n \n trapped in/\n \n less heat\n \n escapes from atmosphere with more carbon dioxide;\n
    3. \n
  3. \n short wave/UV radiation from the sun passes through the atmosphere/reaches the Earth’s surface;\n
    4. \n
  4. \n radiation from the sun/sunlight warms the (surface of the) Earth;\n
    5. \n
  5. \n long wavelength/infra-red radiated from the (warmed) Earth’s surface;\n
    6. \n
\n

\n \n Do not accept answers relating to ozone in the atmosphere because the question refers to carbon dioxide.\n \n
\n \n For mpa do not accept heat instead of LW/IR radiation.\n \n

\n
\n", "Examiners report": "
\n

\n Understanding of the greenhouse effect is very patchy and in some cases is lamentably weak. Some candidates still think that 'increased CO\n \n 2\n \n burns a hole through the ozone layer' or that the greenhouse effect is due to carbon dioxide being reflected back to the Earth's atmosphere. Nearly all answers included errors of understanding. Global warming will have a major impacts on all IB students' future lives so we owe it to them to make sure they understand how it is happening. Perhaps they should memorise these elements:\n

\n \n
\n", "question_id": "22N.2.SL.TZ0.3B", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-3-climate-change", "d4-3-1-anthropogenic-causes-of-climate-change", "d4-3-2-positive-feedback-cycles-in-global-warming" ] }, { "Question": "
\n
\n

\n How do both mitochondria and chloroplasts provide evidence for the endosymbiotic theory?\n

\n

\n A. They have double membranes.\n

\n

\n B. They have 80S ribosomes similar to prokaryotes.\n

\n

\n C. They contain the same DNA as the nucleus of the cell.\n

\n

\n D. They exist together in eukaryote cells for their mutual benefit.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "None", "question_id": "21N.1A.HL.TZ0.4", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a2-2-cell-structure", "a2-2-12-origin-of-eukaryotic-cells-by-endosymbiosis" ] }, { "Question": "
\n
\n

\n The researchers assessed age as a proportion of normal life span, rather than in years. Suggest\n \n one\n \n reason for this.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n to allow comparison of bears and humans;\n
    2. \n
  2. \n bears have a different life span to humans / bears do not live to 80 years;\n
    3. \n
  3. \n because they age at different rates;\n
    4. \n
\n
\n", "Examiners report": "
\n

\n Most candidates were successful here, using the argument that humans and bears have different life spans.\n

\n
\n", "question_id": "22M.2.SL.TZ1.F", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-3-homeostasis", "d3-3-1-homeostasis-as-maintenance-of-the-internal-environment-of-an-organism", "d3-3-2-negative-feedback-loops-in-homeostasis" ] }, { "Question": "
\n
\n

\n The graph shows results of an experiment by Hershey and Chase in 1952 in which bacteria were infected with a mixture of virus particles labelled with either\n \n 32\n \n P or\n \n 35\n \n S. A suspension of the infected bacteria was agitated with a blender, and samples collected from the suspension were centrifuged to record the percentage of isotope remaining on the outside of the cells.\n

\n

\n \n

\n

\n [Source: Republished with permission of ROCKEFELLER UNIVERSITY PRESS, from Independent functions of protein and nucleic acid in growth of bacteriophage. Hershey, A.D. and Chase, M., 1952. (\n \n Journal of General Physiology\n \n , 36(1), p.47). Society of General Physiologists, Rockefeller Institute for Medical Research, Rockefeller Institute; permission conveyed through Copyright Clearance Center, Inc.]\n

\n

\n

\n

\n What do curves X and Y represent?\n

\n

\n \n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "
\n

\n The statistics show that the candidates found this question difficult, and it did not discriminate well. The graph in the stem of the question was taken from the original Hersey and Chase 1952 publication. The G2 forms suggest two reasons why the candidates found this question difficult.\n

\n

\n First, they may not have remembered what is meant by supernatant and sediment. However, these terms are important in understanding the Hershey and Chase experiment and should have been known.\n

\n

\n Secondly, 'the percentage of isotope remaining on the outside of the cells' was possibly misleading. This may have led candidates to think that some of the isotopes were still attached to the outside of the bacterial cell when the intended meaning was the amount of isotope apart from the bacterial cells which would therefore be in the supernatant.\n

\n

\n As the question is only considering the percentage of the isotope in the supernatant the 35S from the protein shell of the bacteriophage would be found in the highest percentage as it does not enter the bacterial cell as shown by line X. As some of the 32P from the phage genetic material would have entered the bacterial cell, a lower percentage would be found in the supernatant which corresponds to line Y. This gives correct answer B.\n

\n
\n", "question_id": "21M.1A.HL.TZ2.26", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a1-2-nucleic-acids", "a1-2-14-evidence-from-the-hershey-chase-experiment-for-dna-as-the-genetic-material" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Describe how the structure of the chloroplast is adapted to its function in photosynthesis.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n

\n a. thylakoids have a small internal volume to maximize hydrogen gradient / quickly increase concentration gradient ✔\n

\n

\n b. many grana / thylakoids give large surface area ✔\n

\n

\n c. (grana) contain (photosynthetic) pigments/electron carriers/ATP synthase enzymes ✔\n

\n

\n d. (photosynthetic) pigments/chlorophyll arranged into photosystems allowing maximum absorption of light energy ✔\n

\n

\n e. stroma has suitable pH/ enzymes of Calvin/light independent cycle ✔\n

\n

\n f. lamellae connect/separate grana maximizing photosynthetic efficiency ✔\n

\n

\n \n Accept diagram showing the disposition in space\n \n .\n

\n
\n", "Examiners report": "
\n

\n Question 6 was a popular question.\n

\n

\n Well answered.\n

\n
\n", "question_id": "21M.2.HL.TZ2.6B", "topics": [ "b-form-and-function" ], "subtopics": [ "b2-2-organelles-and-compartmentalization", "b2-2-5-adaptations-of-the-chloroplast-for-photosynthesis" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Structure III is the ovary. Outline the processes that occur in the ovary.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n \n female\n \n gamete/ovule is produced/meiosis to produce ovules/ovule develops;\n
    2. \n
  2. \n Fertilisation occurs\n
    \n \n \n OR\n \n \n
    \n fusion/union of male and female gametes/nuclei;\n
    3. \n
  3. \n development of seed (from fertilised ovule);\n
    4. \n
  4. \n development of fruit (from the whole ovary);\n
    5. \n
\n

\n \n Mpb: Do not accept union of pollen and ovule (Too vague).\n \n

\n

\n \n Do not accept carpel/pistil as equivalent of ovary\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ2.3B", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-1-reproduction", "d3-1-8-sexual-reproduction-in-flowering-plants" ] }, { "Question": "
\n
\n

\n What is used in a pregnancy test kit?\n
\n
\n

\n

\n A.  Monoclonal antibodies against hybridoma cells\n

\n

\n B.  Antibodies against monoclonal hybridoma cells\n

\n

\n C.  HCG produced by plasma cells fused with tumour cells\n

\n

\n D.  Monoclonal antibodies produced by hybridoma cells against HCG\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "23M.1A.HL.TZ1.37", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-1-reproduction", "d3-1-17-pregnancy-testing-by-detection-of-human-chorionic-gonadotropin-secretion" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Annotate the diagram by adding arrows to show how deoxygenated blood enters the heart.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n arrows added to the diagram to show how deoxygenated blood enters the heart;\n

\n

\n \n

\n

\n \n [Source: CC BY-SA 3.0, https://commons.wikimedia.org/\n \n \n w/index.php?curid=606903. Open access.]\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ1.3A", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-2-transport", "b3-2-15-adaptations-of-the-mammalian-heart-for-delivering-pressurized-blood-to-the-arteries" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n State the percentage of G2 neurons in the mice that respond to the fox scent.\n

\n

\n . . . . . . . . . . . . . . . . . . . .%\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n 10–25 «%» ✔\n

\n
\n", "Examiners report": "
\n

\n Nearly all were able to state the answer of 10-25%.\n

\n
\n", "question_id": "19M.2.SL.TZ2.1A", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c2-2-neural-signalling" ] }, { "Question": "
\n
\n

\n Describe how toxins such as DDT might concentrate in the bodies of birds.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n some toxins/DDT are persistent/degrade slowly (once released into the environment);\n
    2. \n
  2. \n (some toxins/DDT) enter the food chain through producers/lower trophic levels;\n
    3. \n
  3. \n (some toxins/DDT) are passed on to higher trophic levels in the food chain;\n
    4. \n
  4. \n (they are) difficult to excrete / are not excreted;\n
    5. \n
  5. \n (they) accumulate in fatty tissues of animals;\n
    6. \n
  6. \n higher trophic levels/top consumers have higher/the highest concentration of pesticides in their bodies;\n
    7. \n
  7. \n they bioaccumulate/biomagnify;\n
    8. \n
\n
\n", "Examiners report": "None", "question_id": "SPM.2.HL.TZ0.A", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-2-stability-and-change", "d4-2-9-biomagnification-of-pollutants-in-natural-ecosystems" ] }, { "Question": "
\n
\n

\n The diagram shows some of the intermediate compounds produced during the Calvin cycle. At what stage does carboxylation take place?\n
\n
\n

\n

\n \n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "21N.1A.SL.TZ1.31", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-3-photosynthesis", "c1-3-17-regeneration-of-rubp-in-the-calvin-cycle-using-atp" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Distinguish between the processes of meiosis and mitosis.\n

\n
\n
\n

\n [5]\n

\n
\n
\n", "Markscheme": "
\n

\n \n

\n
\n", "Examiners report": "
\n

\n The best answers had clear comparative statements or were in a comparison table. The worst answers were continuous prose descriptions of the processes, as these all too often failed to be able to be pieced together to make full marking points.\n

\n

\n About half of the candidates did not mention cell divisions, but simply mentioned \"two cycles\" which was too vague and instead of writing haploid/diploid, many said 23/46, which only applies to human or certain organisms.\n

\n
\n", "question_id": "22M.2.SL.TZ1.7B", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-1-cell-and-nuclear-division", "d2-1-4-roles-of-mitosis-and-meiosis-in-eukaryotes" ] }, { "Question": "
\n
\n

\n What would show that a person has developed metastatic cancer?\n

\n

\n A. Alveolus cells forming a tumour in the lungs\n

\n

\n B. Cancer cells producing the skin pigment melanin in the liver\n

\n

\n C. A tumour in the prostate gland increasing levels of prostate-specific antigen\n

\n

\n D. Cancerous lymphocytes in blood plasma\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "
\n

\n This also had a low discrimination index, but for the opposite reason – most candidates struggled with it. Metastasis is included in sub-topic 1.6 of the program, so candidates could be expected to know that it is the spread of cancer to form secondary tumours. Three of the four answers were describing primary tumours, so were not correct. The expected answer was that cancer cells in the liver producing the skin pigment melanin indicate metastasis. Perhaps candidates did not realise that cells producing melanin must have originated from skin cells.\n

\n
\n", "question_id": "20N.1A.HL.TZ0.4", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-1-cell-and-nuclear-division", "d2-1-17-differences-between-tumours-in-rates-of-cell-division-and-growth-and-in-the-capacity-for-metastasis-and-invasion-of-neighbouring-tissue" ] }, { "Question": "
\n
\n

\n Distinguish between the changes in porosity of the bones in humans and bears as age increases.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n porosity increased in humans\n \n and\n \n decreased in bears;\n

\n

\n \n Both needed\n \n .\n

\n
\n", "Examiners report": "
\n

\n Well answered with most candidates referring to the positive and negative correlations.\n

\n
\n", "question_id": "22M.2.SL.TZ1.D", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-3-homeostasis", "d3-3-1-homeostasis-as-maintenance-of-the-internal-environment-of-an-organism", "d3-3-2-negative-feedback-loops-in-homeostasis" ] }, { "Question": "
\n
\n (a.ii)\n
\n
\n

\n Outline what is indicated by the mitotic index of tissue taken from a tumour.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. mitotic index is an indication of the ratio/percentage of cells undergoing mitosis/cell division ✔\n

\n

\n b. cancer cells «generally» divide much more than normal «somatic» cells ✔\n

\n

\n c. a\n \n high/elevated\n \n mitotic index in tumours / possible diagnosis of cancer /measure of how aggressive/fast growing the tumour is ✔\n

\n
\n", "Examiners report": "
\n

\n Many students could accurately define the term mitotic index. An area of misunderstanding was to categorize the mitotic index as a rate rather than a ratio.\n

\n
\n", "question_id": "19M.2.SL.TZ2.2A.II", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-1-cell-and-nuclear-division", "d2-1-17-differences-between-tumours-in-rates-of-cell-division-and-growth-and-in-the-capacity-for-metastasis-and-invasion-of-neighbouring-tissue" ] }, { "Question": "
\n
\n

\n State processes occurring during interphase.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. DNA replication ✔\n

\n

\n b. cell growth ✔\n

\n

\n c. duplication of organelles/mitochondria / production of microtubules/protein synthesis ✔\n

\n

\n \n Accept first two answers only\n \n .\n

\n
\n", "Examiners report": "
\n

\n There were several G2 comments about Q2a, as it could be said that several processes were occurring. Perhaps it should have been more specific. Two out of DNA replication, cell growth and duplication of organelles were expected for the two marks. A surprising number of candidates in all languages, confused 'processes' with 'phases' and stated that interphase consisted of G1, S and G2. Most managed to label prophase and anaphase correctly on the diagram as required in part (b). The answers to part (b) were generally clear, but some lost marks for not comparing the same point. For example 'Mitosis produces diploid cells, but meiosis produces gametes' did not score a mark. The mitotic index was well known.\n

\n
\n", "question_id": "21M.2.HL.TZ2.A", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-1-cell-and-nuclear-division", "d2-1-13-phases-of-the-cell-cycle" ] }, { "Question": "
\n
\n

\n Which property of DNA explains how genetic information can be replicated accurately?\n

\n

\n
\n A.  Complementary base pairing\n

\n

\n B.  The double helical shape\n

\n

\n C.  5’ – 3’ bonding in the sugar-phosphate backbone\n

\n

\n D.  The ability of DNA to bind to histones\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "None", "question_id": "SPM.1A.HL.TZ0.3", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a1-2-nucleic-acids", "a1-2-8-role-of-complementary-base-pairing-in-allowing-genetic-information-to-be-replicated-and-expressed" ] }, { "Question": "
\n
\n

\n State\n \n two\n \n variables measured by the probes.\n

\n

\n 1:\n

\n

\n 2:\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n temperature;\n
    2. \n
  2. \n pH;\n
    3. \n
  3. \n minerals / salt concentration / conductivity;\n
    4. \n
  4. \n O\n \n 2\n \n (concentration);\n
    5. \n
  5. \n CO\n \n 2\n \n (concentration);\n
    6. \n
\n
\n", "Examiners report": "None", "question_id": "23M.1B.SL.TZ2.A", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-2-stability-and-change", "d4-2-4-use-of-a-model-to-investigate-the-effect-of-variables-on-ecosystem-stability" ] }, { "Question": "
\n
\n

\n What distinguishes cellulose from glycogen and starch?\n

\n

\n A. Only cellulose is found in plants.\n

\n

\n B. Only cellulose is made up of glucose monomers.\n

\n

\n C. Cellulose is far more branched than starch and glycogen.\n

\n

\n D. Cellulose has a structural role whereas starch and glycogen function in energy storage.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "21M.1A.SL.TZ1.8", "topics": [ "b-form-and-function" ], "subtopics": [ "b1-1-carbohydrates-and-lipids", "b1-1-5-polysaccharides-as-energy-storage-compounds" ] }, { "Question": "
\n
\n (b.ii)\n
\n
\n

\n Explain the scientific reasoning for your hypothesis.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n a. high light (intensity) increases photosynthesis;\n

\n

\n b. photosynthesis consumes CO\n \n 2\n \n ;\n

\n

\n c. (more photosynthesis/less CO\n \n 2\n \n ) increases pH/decreases acidity;\n

\n

\n d. less light means more respiration (than photosynthesis);\n

\n

\n e. respiration produces CO\n \n 2\n \n \n \n AND\n \n \n lowers pH/increases acidity;\n

\n

\n \n Allow inverse for all answers\n \n .\n

\n

\n \n Do not accept reference to colour only instead of pH\n \n .\n

\n
\n", "Examiners report": "
\n

\n Most candidates realised that increased light intensity leads to an increase rate of photosynthesis, which consumes CO\n \n 2\n \n , or vice versa. Most related the change in colour to a change in CO\n \n 2\n \n concentration, but didn't link it to a change in pH, for which the indicator is specific. Stronger candidates understood the experiment and were able to analyse its results effectively, adding that the effect of respiration increased over that of photosynthesis as light intensity decreased, thus a lower pH.\n

\n
\n", "question_id": "20N.1B.SL.TZ0.3B.II", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-3-photosynthesis", "c1-3-7-techniques-for-varying-concentrations-of-carbon-dioxide-light-intensity-or-temperature-experimentally-to-investigate-the-effects-of-limiting-factors-on-the-rate-of-photosynthesis" ] }, { "Question": "
\n
\n

\n Outline\n \n three\n \n ways in which a\n \n named\n \n environmental disturbance can impact an ecosystem.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n a. numbers of species ✔\n

\n

\n b. types of species ✔\n

\n

\n c. impacts on food chains/webs ✔\n

\n

\n d. food production/availability ✔\n

\n

\n e. habitat/ecosystem alteration ✔\n

\n

\n f. biochemical processes «photosynthesis/respiration/decomposition» ✔\n

\n

\n g. biogeochemical processes «erosion/nutrient cycles» ✔\n

\n

\n h. first example of abiotic environmental factor ✔\n

\n

\n i. second example of abiotic environmental factor ✔\n

\n

\n \n Award\n \n [2 max]\n \n if the environmental disturbance is not named.\n \n

\n

\n \n The environmental disturbance may be a factor such as fire, farming, construction, extreme weather, introduction of an alien species/other human intervention.\n \n

\n

\n \n Explanations are not required.\n \n

\n
\n", "Examiners report": "
\n

\n Many candidates listed three environmental disturbances and could gain only one mark if there was a correctly assigned impact. Deforestation, flooding and forest fires were most often cited, with impacts including species number, habitats, biodiversity, food chains and an abiotic factor.\n

\n
\n", "question_id": "19M.2.SL.TZ1.13", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a4-2-conservation-of-biodiversity", "a4-2-3-causes-of-anthropogenic-species-extinction", "a4-2-4-causes-of-ecosystem-loss" ] }, { "Question": "
\n
\n

\n The life expectancy of a human at the time of the study was 80 years. Estimate the porosity of the bones of the individual who was approximately 32 years old.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n 6 %;\n

\n

\n \n Accept answers in the range 6.0 to 6.5 %.\n \n
\n \n Percentage sign required.\n \n

\n
\n", "Examiners report": "
\n

\n This question was very unusual in that the discrimination index was negative — stronger candidates were slightly less likely to answer correctly than weaker candidates, for reasons that are not obvious! Only a minority gave the expected answer of 6 %. A very common answer was 7 %, which is reached by calculating the age proportion correctly as 0.4 but using the trend line rather than the data point for the individual who was 32 years old. Careful reading of the question was needed to avoid this mistake.\n

\n
\n", "question_id": "22M.2.SL.TZ1.E", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-3-homeostasis", "d3-3-1-homeostasis-as-maintenance-of-the-internal-environment-of-an-organism", "d3-3-2-negative-feedback-loops-in-homeostasis" ] }, { "Question": "
\n
\n

\n Using a Punnett grid, explain the results of this cross.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n male and female gamete genotypes/alleles shown as P and p (or others following convention with a suitable key)\n \n in a punnet grid\n \n ;\n
    2. \n
  2. \n F\n \n 2\n \n genotypes shown as PP, Pp, pP and pp;\n
    3. \n
  3. \n F\n \n 2\n \n phenotypes indicated for each genotype on the Punnett grid / 3 purple to 1 white ratio indicated;\n
    4. \n
\n

\n

\n

\n \n Accept other upper-case and lower-case letters for the alleles.\n \n
\n \n \n \n
\n \n No punnet grid = 2 MAX.\n \n

\n

\n \n Allow ECF if alleles incorrect.\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ2.B", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-2-inheritance", "d3-2-2-methods-for-conducting-genetic-crosses-in-flowering-plants" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Describe the functions of proteins in cell membranes.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n

\n a. facilitated diffusion by channel proteins ✔\n

\n

\n b. active transport by protein pumps\n
\n \n \n OR\n \n \n
\n protein pumps\n \n eg\n \n sodium-potassium ✔\n

\n

\n c. cell recognition by glycoproteins/protein receptors ✔\n

\n

\n d. communication/receptors for hormones/signal molecules ✔\n

\n

\n e. cell adhesion ✔\n

\n

\n f. allow up to one additional mark for AHL material ✔\n

\n
\n", "Examiners report": "
\n

\n A wide variety of fairly well-developed answers. Often, they did not couple a type of protein with its function or missed marks by being too general. Saying “transport proteins” was not enough. Often the terms integral and peripheral proteins were mentioned without going beyond that. Channel proteins and facilitated diffusion was most commonly given. The mistaken idea that proteins offer structural support or strengthen the cell membrane was seen repeatedly.\n

\n
\n", "question_id": "19M.2.SL.TZ1.7B", "topics": [ "b-form-and-function" ], "subtopics": [ "b2-1-membranes-and-membrane-transport", "b2-1-4-integral-and-peripheral-proteins-in-membranes" ] }, { "Question": "
\n
\n

\n What is a feature of the human genome?\n

\n

\n A. Plasmids\n

\n

\n B. Messenger RNA\n

\n

\n C. Transfer RNA\n

\n

\n D. Mitochondrial DNA\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "
\n

\n The statistics suggest that this question was not too difficult. As commented on some G2 forms, 'components' of the human genome would have been a better word than 'features'. Other G2 forms indicated that mRMA and tRNA should be included but this is incorrect as only DNA in chromosomes and in mitochondria are considered part of the human genome.\n

\n
\n", "question_id": "21M.1A.SL.TZ2.10", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a3-1-diversity-of-organisms", "a3-1-8-unity-and-diversity-of-genomes-within-species" ] }, { "Question": "
\n
\n

\n Draw a plan diagram in the right-hand box with labels to show the distribution of tissues in this transverse section of a leaf.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n palisade mesophyll;\n
    2. \n
  2. \n spongy mesophyll;\n
    3. \n
  3. \n lower epidermis;\n
    4. \n
  4. \n upper epidermis;\n
    5. \n
  5. \n xylem/phloem/vascular bundle;\n
    6. \n
\n

\n \n 1 mark for each correctly labelled tissue shown as a layer in proportion.\n \n

\n
\n", "Examiners report": "None", "question_id": "SPM.1B.SL.TZ0.A", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a2-2-cell-structure", "a2-2-10-cell-types-and-cell-structures-viewed-in-light-and-electron-micrographs", "a2-2-11-drawing-and-annotation-based-on-electron-micrographs" ] }, { "Question": "
\n
\n

\n What is a function of histones?\n

\n

\n
\n A.  Supercoiling of DNA during binary fission in prokaryotes\n

\n

\n B.  Synthesis of proteins\n

\n

\n C.  Formation of microtubules during mitosis\n

\n

\n D.  Condensation of DNA\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "SPM.1A.SL.TZ0.14", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-1-cell-and-nuclear-division", "d2-1-6-condensation-and-movement-of-chromosomes-as-shared-features-of-mitosis-and-meiosis" ] }, { "Question": "
\n
\n

\n An individual was presented with a stimulus resulting in the release of epinephrine. What was the most likely nature of the stimulus?\n

\n

\n A. Sunset and the onset of darkness\n

\n

\n B. An image of a close friend\n

\n

\n C. The intake of glucose\n

\n

\n D. A coach shouting to begin physical activity\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "21M.1A.SL.TZ1.19", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-1-integration-of-body-systems", "c3-1-12-epinephrine-(adrenaline)-secretion-by-the-adrenal-glands-to-prepare-the-body-for-vigorous-activity" ] }, { "Question": "
\n
\n

\n The graph shows atmospheric oxygen levels over time.\n

\n

\n \n

\n

\n About 2.5 billion years ago, a significant rise in atmospheric oxygen occurred. What was the cause of this rise?\n

\n

\n A. Photosynthesis by non-vascular land plants\n

\n

\n B. Photosynthesis by vascular land plants\n

\n

\n C. Oxygen produced by photosynthetic bacteria being released from the ocean into the atmosphere\n

\n

\n D. Volcanic activity\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "
\n

\n This question was based on the first Application in 2.9 (Photosynthesis) which requires a study of changes to the Earth's atmosphere due to photosynthesis. The graph shows the oxygenation of the atmosphere happening between 2.5 and 2 billion years ago. To answer the question correctly candidates had to choose which group of photosynthesizers were most likely to have caused this. Over 55 % correctly chose photosynthetic bacteria in the oceans, but large numbers also chose vascular land plants, including some of the stronger candidates. This group appeared less than 0.5 billion years ago. Detailed knowledge of the timings of plant evolution are not expected but students are expected to appreciate that the Great Oxygenation Event was due to prokaryotes photosynthesizing in the oceans.\n

\n
\n", "question_id": "21M.1A.HL.TZ1.10", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-3-photosynthesis", "c1-3-11-generation-of-oxygen-by-the-photolysis-of-water-in-photosystem-ii" ] }, { "Question": "
\n
\n (a.i)\n
\n
\n

\n Calculate the number of species of grebe with problems due to entanglement.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n 2;\n

\n
\n", "Examiners report": "
\n

\n This question outlining how plastic pollution affects marine birds was straightforward for all candidates.\n

\n
\n", "question_id": "20N.2.SL.TZ0.13A.I", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-2-stability-and-change", "d4-2-10-effects-of-microplastic-and-macroplastic-pollution-of-the-oceans" ] }, { "Question": "
\n
\n

\n The table shows features of greenhouse gases in the atmosphere.\n

\n

\n \n

\n

\n According to the data in the table, which greenhouse gas contributes the most to climate change?\n

\n

\n A. Carbon dioxide because it is the most abundant greenhouse gas\n

\n

\n B. Methane because it has the shortest lifespan\n

\n

\n C. Nitrous oxides because they absorb the greatest amount of shortwave radiation\n

\n

\n D. CFCs because they destroy the ozone layer\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "
\n

\n Very easy question with 93 % of candidates answering correctly.\n

\n
\n", "question_id": "22M.1A.SL.TZ2.15", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-3-climate-change", "d4-3-1-anthropogenic-causes-of-climate-change" ] }, { "Question": "
\n
\n

\n Identify the structure labelled X.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n (Neurotransmitter) vesicle;\n

\n

\n \n Do not accept Vacuole.\n \n

\n
\n", "Examiners report": "
\n

\n The majority managed to label X as a vesicle in (a). In (b) weaker candidates tried to explain the propagation of the action potential, rather than the release of the neurotransmitter. Better candidates were able to give almost textbook answers to explain the actions of the pesticide. Many got tangled up trying to explain, with those who had never seen this part of the syllabus, just saying that pesticides kill insects.\n

\n
\n", "question_id": "22N.2.SL.TZ0.A", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c2-1-chemical-signalling-[hl-only]", "c2-1-3-hormones-neurotransmitters-cytokines-and-calcium-ions-as-examples-of-functional-categories-of-signalling-chemicals-in-animals" ] }, { "Question": "
\n
\n

\n Onion (\n \n Allium cepa\n \n ) epidermis was placed in pure water and observed with a light microscope using high magnification.\n

\n

\n \n

\n

\n What would happen to these cells if they were transferred to a hypertonic solution?\n

\n

\n
\n A.  Cells would gain mass.\n

\n

\n B.  Cells would take in water by osmosis and swell.\n

\n

\n C.  Cells would burst open, releasing their content.\n

\n

\n D.  Cell membranes would detach from walls at some points.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "23M.1A.SL.TZ1.4", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-3-water-potential", "d2-3-2-water-movement-from-less-concentrated-to-more-concentrated-solutions" ] }, { "Question": "
\n
\n (a.i)\n
\n
\n

\n State\n \n two\n \n causes of the decrease of biomass along food chains in terrestrial ecosystems.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. «cell» respiration/loss of CO\n \n 2\n \n /biomass consumed to provide/as a source of energy ✔\n

\n

\n b. loss of energy «as heat» between trophic levels means less energy available for building biomass ✔\n

\n

\n c. waste products «other than CO\n \n 2\n \n »/loss of urea/feces/egesta ✔\n

\n

\n d. material used/CO\n \n 2\n \n released by saprotrophs ✔\n

\n

\n e. undigested/uneaten material «teeth, bones,\n \n etc\n \n »/detritus buried/not consumed\n
\n \n \n OR\n \n \n
\n formation of peat/fossils/limestone ✔\n

\n
\n", "Examiners report": "
\n

\n A large proportion of students looked at this question and immediately reeled off an answer in terms of energy (as in many previous years). Few made the connection between biomass and energy, for example in respiration CO\n \n 2\n \n is lost from the food chain during respiration, or that urea has mass\n \n etc\n \n .\n

\n
\n", "question_id": "19M.2.SL.TZ2.3", "topics": [ "c-interaction-and-interdependence", "d-continuity-and-change" ], "subtopics": [ "c4-2-transfers-of-energy-and-matter", "c4-2-14-restrictions-on-the-number-of-trophic-levels-in-ecosystems-due-to-energy-losses", "c4-2-18-ecosystems-as-carbon-sinks-and-carbon-sources", "d4-3-climate-change", "d4-3-12-evolution-as-a-consequence-of-climate-change" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Explain the decrease in activity of the enzyme on either side of the optimum temperature.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n as temperature rises/is higher (than optimal temperature), the enzyme is denatured;\n
    2. \n
  2. \n as the temperature drops the enzyme molecules have less kinetic energy\n
    \n \n \n OR\n \n \n
    \n fewer successful collisions;\n
    3. \n
\n

\n \n OWTTE\n \n

\n
\n", "Examiners report": "
\n

\n In a. many incorrectly stated that the enzyme was denatured either side of the optimum. Denaturation was reasonably well known, but the explanation for increased activity with rising temperature was not. Surprisingly some candidates missed the obvious references to temperature and wrote about pH instead. Knowledge of the enzymes involved in gene transfer was very patchy, with over a quarter of candidates leaving it blank. This was the worst scoring question on the paper.\n

\n
\n", "question_id": "22M.2.SL.TZ2.5", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-1-enzymes-and-metabolism", "c1-1-8-effects-of-temperature-ph-and-substrate-concentration-on-the-rate-of-enzyme-activity" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Phosphate can be lost from agricultural land in several different ways. State\n \n one\n \n of these.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n leaching/soil erosion, run-off/removed by the harvesting of agricultural crops ✔\n

\n
\n", "Examiners report": "
\n

\n Most students obtained the mark here, possibly because the mark scheme allowed for a variety of answers for the mark.\n

\n
\n", "question_id": "19M.2.SL.TZ1.14B", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-2-stability-and-change", "d4-2-2-requirements-for-stability-in-ecosystems" ] }, { "Question": "
\n
\n

\n A self-sustaining system is set up in a sterile, sealed, transparent glass bottle with damp, sterilized soil and a small garden plant. If the system remains sterile, what could be the reason that the plant fails to grow and dies?\n

\n

\n A.  Lack of soil nutrients\n

\n

\n B.  Lack of oxygen\n

\n

\n C.  Lack of space\n

\n

\n D.  Lack of water\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "None", "question_id": "22N.1A.SL.TZ0.18", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a2-1-origins-of-cells-(hl-only)", "a2-1-2-cells-as-the-smallest-units-of-self-sustaining-life" ] }, { "Question": "
\n
\n (e)\n
\n
\n

\n Compare and contrast the effects of the mouse alarm compound and stoat scent on the G1 neurons.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. both chemicals cause action potentials\n
\n \n \n OR\n \n \n
\n both chemicals respond in the majority of/five/most neurons ✔\n

\n

\n b. stoat scent causes a higher action potential/longer/bigger response than mouse alarm compound «in each neuron»\n
\n \n \n OR\n \n \n
\n neuron 2 reacts strongly to the stoat scent but has a minimal/no response to the mouse alarm compound ✔\n

\n
\n", "Examiners report": "
\n

\n Answers to e were encouraging as most were able to give both the similarity and the difference.\n

\n
\n", "question_id": "19M.2.SL.TZ2.1E", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c2-2-neural-signalling" ] }, { "Question": "
\n
\n

\n The diagrams show the structure of leucine, an essential amino acid. Which diagram highlights the part of leucine that distinguishes it from other amino acids?\n

\n

\n
\n \n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "SPM.1A.SL.TZ0.4", "topics": [ "b-form-and-function" ], "subtopics": [ "b1-2-proteins", "b1-2-6-chemical-diversity-in-the-r-groups-of-amino-acids-as-a-basis-for-the-immense-diversity-in-protein-form-and-function" ] }, { "Question": "
\n
\n

\n What distinguishes aerobic respiration from anaerobic respiration in humans?\n

\n

\n
\n A.  Mitochondria are only used in anaerobic respiration.\n

\n

\n B.  Aerobic respiration yields lower quantities of ATP.\n

\n

\n C.  Only aerobic respiration can use glucose as a starting substrate.\n

\n

\n D.  Only aerobic respiration produces carbon dioxide.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "SPM.1A.SL.TZ0.6", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-2-cell-respiration", "c1-2-5-differences-between-anaerobic-and-aerobic-cell-respiration-in-humans" ] }, { "Question": "
\n
\n

\n Outline how ventilation rate could have been monitored in this study.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. «data logging» with spirometer\n
\n \n \n OR\n \n \n
\n chest belt ✔\n

\n

\n b. «tidal» volume recorded for a given period of time\n
\n \n \n OR\n \n \n
\n average «tidal» volume found and multiplied by number breaths per minute ✔\n

\n

\n \n Do not accept confusion with respirometer (measuring oxygen consumption or CO\n \n 2\n \n release).\n \n

\n

\n \n Must include a reference to time.\n \n

\n
\n", "Examiners report": "
\n

\n Question (c) was poorly answered. Many candidates thought a respirometer would be used to measure ventilation rate while other candidates gave a description of how to measure the number of breaths per minute. This was considered inadequate as the Y axis of the graph indicated that ventilation rate was volume per minute, so reference to volume and time were required in the response.\n

\n
\n", "question_id": "19M.1B.SL.TZ2.C", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-1-gas-exchange", "b3-1-5-ventilation-of-the-lungs" ] }, { "Question": "
\n
\n

\n Outline the conclusions that can be drawn from the data in the graph for the group of aphids fed for three generations on transgenic thale cress plants (T).\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. «over the generations» fewer are repelled by EBF ✔\n

\n

\n b. «over the generations» more are attracted to EBF ✔\n

\n

\n c. by G3 a «slight» increase in no choice ✔\n

\n

\n d. aphids respond less to EBF/alarm compound if they feed on plants that produce it/exposed to it constantly ✔\n

\n

\n e. mutant aphids with attraction to transgenic plants can arise from aphids with no attraction or repulsion to transgenic plants\n
\n \n \n OR\n \n \n
\n aphids with no attraction or repulsion to transgenic plants may produce new type of aphids with attraction to transgenic plants ✔\n

\n
\n", "Examiners report": "
\n

\n There was some discussion in the G2 forms about the amount of reading before points h, I and j. Good candidates could be seen to have read it carefully, underling the key words. Weaker candidates not so. In i. a large proportion gained both marks for stating that the percentage of attraction had increased and the percentage of repulsion had decreased.\n

\n
\n", "question_id": "19M.2.SL.TZ2.I", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d1-1-dna-replication", "d1-1-5-applications-of-polymerase-chain-reaction-and-gel-electrophoresis" ] }, { "Question": "
\n
\n

\n What is a method of transmission of HIV and its effect on the immune system?\n

\n

\n \n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "None", "question_id": "22M.1A.SL.TZ1.26", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-2-defence-against-disease", "c3-2-11-transmission-of-hiv-in-body-fluids" ] }, { "Question": "
\n
\n

\n Which statement applies to cholesterol?\n

\n

\n A. It is hydrophobic and found on the outside of the phospholipid bilayer.\n

\n

\n B. It is hydrophilic and found inside the phospholipid bilayer.\n

\n

\n C. It impacts membrane fluidity.\n

\n

\n D. It is transported in association with glucose in the blood.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "21M.1A.HL.TZ1.6", "topics": [ "b-form-and-function" ], "subtopics": [ "b2-1-membranes-and-membrane-transport", "b2-1-12-cholesterol-and-membrane-fluidity-in-animal-cells" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n State the mean annual decline in insect biomass.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n 2.5\n \n \n \n \n %;\n

\n

\n \n % required\n \n

\n
\n", "Examiners report": "
\n

\n In general, the Data based question was well answered. In (a) all but a handful of candidates failed to state 2.5, but unfortunately many failed to also include the unit. In (b) Most gave a difference, but similarities were rarer. The statement that both show a decline would have earned the mark. A surprising number were confused by the arithmetic involved in (c), with most calculating that the decrease was 8000, but either forgetting to subtract this from the 400,000, or doing it incorrectly. In (d) almost everyone counted 5 correctly and in (e) a large proportion gained both marks for a comparison and a contrast. The calculation in (f) involved the use of ratios. There was a G2 comment that this was not common knowledge. However, as all IB students continue to study mathematics at some level, it was not considered beyond their capabilities. 40\n \n \n \n \n % of the students gained the mark. A similar number gained the mark in (g), usually for an correct answer, but many answered in terms of the actual ratios, which did not gain the mark. In (h) 80\n \n \n \n \n % were able to spot that there was an inverse relationship between high lipid content and survivability, but in (i) fewer were able to cite the 10:1 diet as closest to the normal diet, some failing to state the reason. The answers t (j) were very varied, with most gaining marks for the possible loss of natural food sources or\n
\n the bees having to look for others. Better candidates noted that there was no control where the bees were fed their normal diet as it was a simulation, not using pollen. There was a G2 comment that the graph was somewhat crowded and should have been bigger. This is perhaps true.\n

\n
\n", "question_id": "22N.2.SL.TZ0.1A", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c4-2-transfers-of-energy-and-matter", "c4-2-15-primary-production-as-accumulation-of-carbon-compounds-in-biomass-by-autotrophs", "c4-2-16-secondary-production-as-accumulation-of-carbon-compounds-in-biomass-by-heterotrophs" ] }, { "Question": "
\n
\n

\n Models are used as representations of the real world. Evaluate the use of food webs to represent ecological communities.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n \n Advantages\n \n :\n
\n a. food webs summarize all possible food chains «in the community» ✔\n \n OWTTE\n \n

\n

\n b. realistic representation ✔\n

\n

\n \n Limitations\n \n :\n
\n c. some communities/ecosystems are too complex to represent ✔\n

\n

\n d. only shows qualitative information/not quantitative data\n
\n \n \n OR\n \n \n
\n saprotrophs/abiotic factors not taken into account ✔\n

\n

\n \n Needs one advantage and one limitation to obtain\n \n [2]\n \n .\n \n
\n \n Do not accept mentions of trophic levels\n \n .\n

\n
\n", "Examiners report": "None", "question_id": "19N.2.SL.TZ0.B", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c4-2-transfers-of-energy-and-matter", "c4-2-4-construction-of-food-chains-and-food-webs-to-represent-feeding-relationships-in-a-community" ] }, { "Question": "
\n
\n

\n Black walnut (\n \n Juglans nigra\n \n ) secretes the chemical juglone into the soil surrounding its roots. Juglone inhibits cell respiration in other species of plants. What does this example illustrate?\n

\n

\n
\n A.  Mutualism\n

\n

\n B.  Intraspecific competition\n

\n

\n C.  Allelopathy\n

\n

\n D.  Parasitism\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "SPM.1A.SL.TZ0.28", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c4-1-populations-and-communities", "c4-1-6-negative-feedback-control-of-population-size-by-density-dependent-factors", "c4-1-12-mutualism-as-an-interspecific-relationship-that-benefits-both-species" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Draw\n \n one\n \n phospholipid molecule on the diagram to show a possible position in the membrane.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n phospholipid shown with circular head and 2 tails;\n
\n e.g.\n

\n

\n \n

\n

\n \n [Source: Material from: Stauch, B., Johansson, L.C., McCorvy, J.D.,\n \n
\n \n et al., Structural basis of ligand recognition at the human MT1\n \n
\n \n melatonin receptor, published 2019,\n \n Nature\n \n , reproduced with\n \n
\n \n permission of SNCSC.]\n \n

\n

\n phospholipid shown in either the upper or lower half of the membrane only with its head at the margin of the membrane and tails towards centre;\n

\n

\n \n Accept answers with two or more phospholipids shown, as long as all are correct.\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.2.HL.TZ1.2A", "topics": [ "b-form-and-function" ], "subtopics": [ "b2-1-membranes-and-membrane-transport", "b2-1-14-gated-ion-channels-in-neurons" ] }, { "Question": "
\n
\n

\n Outline how O\n \n 2\n \n consumption is measured using a respirometer.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. a CO\n \n 2\n \n absorber/KOH is added ✔\n

\n

\n b. a bubble/starting water level is measured ✔\n

\n

\n c. «the rate of» movement of the bubble/pressure reduction is a measure of O\n \n 2\n \n consumption ✔\n

\n
\n", "Examiners report": "
\n

\n Very few candidates achieved a mark. Some confused a respirometer with a spirometer; others mentioned data logging probes. Credit was given for mention of a water column. Only the highest scoring candidates understood that a carbon dioxide absorber is required to allow pressure changes to be measured.\n

\n
\n", "question_id": "19M.1B.SL.TZ1.A.I", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-2-cell-respiration", "c1-2-6-variables-affecting-the-rate-of-cell-respiration" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Suggest a reason for high total serum cholesterol not always being an indicator of CHD risk.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n depends on the type of cholesterol/ratio of HDL to LDL/some types of cholesterol do not increase the chance of CHD;\n
    2. \n
  2. \n may not indicate CHD if lack other risk factors for CHD;\n
    3. \n
\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ1.20B", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-2-transport", "b3-2-6-causes-and-consequences-of-occlusion-of-the-coronary-arteries" ] }, { "Question": "
\n
\n (d.iii)\n
\n
\n

\n Outline the reason for plasma insulin levels changing in the first 30 minutes of the test.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n as blood glucose rises,\n \n insulin\n \n \n rises\n \n /\n \n increases\n \n to reduce the level/\n \n OWTTE\n \n ;\n

\n

\n \n Blood glucose must be mentioned as well as a rise in insulin\n \n .\n

\n
\n", "Examiners report": "None", "question_id": "20N.1B.SL.TZ0.1D.III", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-3-homeostasis", "d3-3-3-regulation-of-blood-glucose-as-an-example-of-the-role-of-hormones-in-homeostasis" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Explain how changes to the cell cycle can result in tumour formation.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n cell cycle is (repeated) sequence of cytokinesis/cell division, (then) interphase(then) mitosis / cell cycle includes the sequence of interphase, mitosis and cytokinesis/cell division (to form new cells which repeat the cycle)\n
    2. \n
  2. \n \n cyclins\n \n control/regulate this cycle / ensure the cell moves on to the next stage of the cycle when it is appropriate\n
    3. \n
  3. \n extra cells produced when they are needed\n
    4. \n
  4. \n tumour formation is the result of uncontrolled cell division/ cells growing and dividing endlessly\n
    5. \n
  5. \n repeated mitoses/high mitotic index\n
    6. \n
  6. \n due to mutations in\n \n oncogenes\n \n /\n \n oncogenes\n \n may become active and contribute to the development of a cancer cell\n
    7. \n
  7. \n carcinogens/radiation/mutagenic chemicals/mutagens/smoking cause mutations/tumours;\n
    8. \n
\n

\n

\n
\n", "Examiners report": "None", "question_id": "23M.2.HL.TZ2.6A", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-1-cell-and-nuclear-division", "d2-1-15-control-of-the-cell-cycle-using-cyclins" ] }, { "Question": "
\n
\n (a.i)\n
\n
\n

\n State the relationship between sloth body temperature and ambient temperature.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n body temperature increases with ambient temperature / positive correlation;\n

\n

\n \n Since direct can be either –/+, no credit for direct correlation alone.\n \n

\n
\n", "Examiners report": "None", "question_id": "22M.2.SL.TZ1.1A.I", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-3-homeostasis", "d3-3-1-homeostasis-as-maintenance-of-the-internal-environment-of-an-organism", "d3-3-2-negative-feedback-loops-in-homeostasis" ] }, { "Question": "
\n
\n

\n Describe the mechanism by which the heartbeat is initiated.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. sinoatrial node/SAN initiates contraction of atria;\n

\n

\n b. SAN sends messages to the atrioventricular/AV node;\n

\n

\n c. AV node initiates ventricular contraction;\n

\n

\n d. through conducting fibres;\n

\n
\n", "Examiners report": "
\n

\n Most candidates did well in this question, strongest candidates distinguishing themselves by complete and very detailed answers.\n

\n
\n", "question_id": "20N.2.HL.TZ0.C", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-2-transport", "b3-2-16-stages-in-the-cardiac-cycle" ] }, { "Question": "
\n
\n

\n Which is an adaptation to increase rates of gas exchange in the lung?\n

\n

\n A. Small surface area\n

\n

\n B. Dry surface\n

\n

\n C. High vascularization\n

\n

\n D. Muscular alveoli\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "
\n

\n Some centres expressed concern that the term vascularization might be difficult for the candidates. However, they may have heard the term when referring to the cardiovascular system. Although it is not the recommended way to arrive at correct responses, the candidates could have arrived at the correct solution by eliminating the other three responses which are obviously incorrect.\n

\n
\n", "question_id": "21M.1A.SL.TZ2.27", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-1-gas-exchange", "b3-1-4-adaptations-of-mammalian-lungs-for-gas-exchange" ] }, { "Question": "
\n
\n

\n Scientists sequenced the genes in each chromosome of chimpanzees (\n \n Pan troglodytes\n \n ) and humans (Homo sapiens). The graph shows the mean divergence between the genes of these species by chromosome.\n

\n

\n \n

\n

\n \n [Source: Material from: Mikkelsen, T.S. et al, Initial sequence of the chimpanzee genome and\n \n
\n \n comparison with the human genome, 2005\n \n Nature\n \n , reproduced with permission of SNCSC.]\n \n

\n

\n
\n What can be deduced from this data?\n

\n

\n
\n A.  Autosomes are more similar than Y chromosomes.\n

\n

\n B.  There is the same number of chromosomes in humans and chimpanzees.\n

\n

\n C.  Humans are more closely related to chimpanzees than to other species.\n

\n

\n D.  Smaller chromosomes are more similar than larger chromosomes.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "None", "question_id": "23M.1A.SL.TZ1.14", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-2-inheritance", "d3-2-1-production-of-haploid-gametes-in-parents-and-their-fusion-to-form-a-diploid-zygote-as-the-means-of-inheritance" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Explain how changes to the cell cycle can result in tumour formation.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n cell cycle is (repeated) sequence of cytokinesis/cell division, (then) interphase(then) mitosis / cell cycle includes the sequence of interphase, mitosis and cytokinesis/cell division (to form new cells which repeat the cycle)\n
    2. \n
  2. \n \n cyclins\n \n control/regulate this cycle / ensure the cell moves on to the next stage of the cycle when it is appropriate\n
    3. \n
  3. \n extra cells produced when they are needed\n
    4. \n
  4. \n tumour formation is the result of uncontrolled cell division/ cells growing and dividing endlessly\n
    5. \n
  5. \n repeated mitoses/high mitotic index\n
    6. \n
  6. \n due to mutations in\n \n oncogenes\n \n /\n \n oncogenes\n \n may become active and contribute to the development of a cancer cell\n
    7. \n
  7. \n carcinogens/radiation/mutagenic chemicals/mutagens/smoking cause mutations/tumours;\n
    8. \n
\n

\n

\n
\n", "Examiners report": "None", "question_id": "23M.2.HL.TZ2.6", "topics": [ "d-continuity-and-change", "b-form-and-function", "c-interaction-and-interdependence" ], "subtopics": [ "d2-1-cell-and-nuclear-division", "d2-1-15-control-of-the-cell-cycle-using-cyclins", "b3-2-transport", "b3-2-16-stages-in-the-cardiac-cycle", "c4-2-transfers-of-energy-and-matter", "c4-2-17-constructing-carbon-cycle-diagrams", "c4-2-19-release-of-carbon-dioxide-into-the-atmosphere-during-combustion-of-biomass-peat-coal-oil-and-natural-gas" ] }, { "Question": "
\n
\n

\n With reference to the diagram, identify\n \n one\n \n example of catabolism.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n a. (letter X) breakdown of monosaccharides/respiration ✔\n

\n

\n b. (letter Y) hydrolysis/photolysis in photosynthesis/oxidation of water ✔\n

\n

\n \n Answer must come from the diagram\n \n .\n

\n
\n", "Examiners report": "
\n

\n The diagram was generally confusing to candidates.\n

\n

\n Too often candidates did not make reference to the diagram when giving an example of catabolism. Some thought that ADP changing to ATP was catabolism. This probably comes from a failure to understand paired reactions.\n

\n
\n", "question_id": "21M.2.SL.TZ1.E", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-1-enzymes-and-metabolism", "c1-1-3-anabolic-and-catabolic-reactions" ] }, { "Question": "
\n
\n

\n Which is a feature of phloem sieve tube cells?\n

\n

\n
\n A.  Numerous chloroplasts\n

\n

\n B.  No nucleus\n

\n

\n C.  Lignified walls\n

\n

\n D.  No cytoplasm\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "SPM.1A.HL.TZ0.12", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-2-transport", "b3-2-18-adaptations-of-phloem-sieve-tubes-and-companion-cells-for-translocation-of-sap" ] }, { "Question": "
\n
\n

\n Which statements are characteristics of alleles?\n

\n

\n I. Alleles differ significantly in number of base pairs.\n

\n

\n II. Alleles are specific forms of a gene.\n

\n

\n III. New alleles are formed by mutation.\n

\n

\n A. I and II only\n

\n

\n B. I and III only\n

\n

\n C. II and III only\n

\n

\n D. I, II and III\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "19N.1A.SL.TZ0.10", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-2-inheritance", "d3-2-3-genotype-as-the-combination-of-alleles-inherited-by-an-organism", "d3-2-5-effects-of-dominant-and-recessive-alleles-on-phenotype", "d3-2-8-single-nucleotide-polymorphisms-and-multiple-alleles-in-gene-pools" ] }, { "Question": "
\n
\n

\n Glucose moves from the filtrate in the nephron into the bloodstream during normal kidney function. Which location and method describe this movement of glucose?\n

\n

\n \n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "22M.1A.SL.TZ1.39", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-3-homeostasis", "d3-3-8-role-of-the-glomerulus-bowmans-capsule-and-proximal-convoluted-tubule-in-excretion" ] }, { "Question": "
\n
\n

\n Discuss briefly whether amino acids on the surface of the protein are likely to be polar or non-polar.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n polar/hydrophilic where exposed to the cytoplasm/to fluid outside cell/to polar phospholipid heads;\n
\n non-polar/hydrophobic where exposed to the (core of the) membrane/hydrophobic tails (of phospholipids);\n

\n
\n", "Examiners report": "None", "question_id": "23M.2.HL.TZ1.C", "topics": [ "b-form-and-function" ], "subtopics": [ "b1-2-proteins", "b1-2-6-chemical-diversity-in-the-r-groups-of-amino-acids-as-a-basis-for-the-immense-diversity-in-protein-form-and-function" ] }, { "Question": "
\n
\n

\n What is evidence for the endosymbiotic theory?\n
\n
\n

\n

\n A.  Eukaryote mitochondria contain DNA.\n

\n

\n B.  Prokaryotes evolved before eukaryotes.\n

\n

\n C.  Unicellular organisms exist as both prokaryotes and eukaryotes.\n

\n

\n D.  Prokaryote cells have no double membranes.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "None", "question_id": "23M.1A.HL.TZ2.4", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a2-2-cell-structure", "a2-2-12-origin-of-eukaryotic-cells-by-endosymbiosis" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Explain Calvin’s experiment and what was discovered about photosynthesis through his work.\n

\n
\n
\n

\n [8]\n

\n
\n
\n", "Markscheme": "
\n

\n a. Calvin cycle is light-independent ✔\n

\n

\n b. carbon fixation\n
\n \n \n OR\n \n \n
\n carboxylation of ribulose bisphosphate/RuBP occurs ✔\n

\n

\n c. algae placed in thin glass container/“lollipop” apparatus ✔\n

\n

\n d. given plenty of light and bicarbonate/ CO\n \n 2\n \n ✔\n

\n

\n e. at start of experiment algae supplied radioactive carbon/HCO\n \n 3\n \n -/\n \n 14\n \n C ✔\n

\n

\n f. samples taken at intervals / heat/alcohol killed samples ✔\n

\n

\n g. C-compounds separated by chromatography ✔\n

\n

\n h.\n \n 14\n \n C/radioactive-compounds identified by autoradiography ✔\n

\n

\n i. showed that RuBP was phosphorylated ✔\n

\n

\n j. after five seconds/immediately more glycerate-3-phosphate/3-PGA labelled than any other compound ✔\n

\n

\n k. shows glycerate-3-phosphate/3-PGA first «carboxylated» compound/the first stable product ✔\n

\n

\n l. next compound to be detected containing radioactive carbon was triose phosphate/G3P/glyceraldehyde 3 phosphate ✔\n

\n

\n m. showed that a wide range of carbon compounds was quickly made in sequence ✔\n

\n

\n n. showed that a cycle of reactions was used to regenerate RuBP ✔\n

\n
\n", "Examiners report": "
\n

\n This question was commonly answered poorly with students showing a lack of knowledge of both the Calvin cycle as well as the Calving experiment.\n

\n
\n", "question_id": "19M.2.HL.TZ2.8C", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-1-enzymes-and-metabolism", "c1-1-13-cyclical-and-linear-pathways-in-metabolism" ] }, { "Question": "
\n
\n (a.ii)\n
\n
\n

\n The table shows the global carbon budget over two decades; the years 1990 to 1999 and 2000 to 2009.\n

\n

\n \n

\n

\n [Source: © International Baccalaureate Organization 2019]\n

\n

\n

\n

\n Using the table, explain causes of the changes in carbon flux over the two decades.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n a. increased CO\n \n 2\n \n flux to the atmosphere due to increased burning of fossil fuels by industry/transportation / cement production ✔\n

\n

\n b. «land use change leading to» decreased rate of forest burning\n
\n \n \n OR\n \n \n
\n better fire suppression leading to decrease in CO\n \n 2\n \n release\n
\n \n \n OR\n \n \n
\n example of land use changes that uses less fossil fuel\n
\n \n \n OR\n \n \n
\n increase in land covered by forests/plants / forests recovering from historical forestry\n
\n \n \n OR\n \n \n
\n any other reasonable explanation of land use change that would lead to decreased rate of carbon flow to atmosphere ✔\n

\n

\n c. carbon storage in land decreased as less photosynthesis due to fewer forests/more construction\n
\n \n \n OR\n \n \n
\n release of methane due to «drying of» wetlands/sealing of land with concrete/buildings/roads ✔\n

\n

\n d. carbon storage in ocean increased due to more photosynthesis/algae/greater concentration of CO\n \n 2\n \n in the atmosphere\n
\n \n \n OR\n \n \n
\n increased diffusion/rate of dissolving of CO\n \n 2\n \n into ocean from the atmosphere\n
\n \n \n OR\n \n \n
\n limestone/carbonate accumulation «more snails» ✔\n

\n
\n", "Examiners report": "
\n

\n 3a(ii) was the question most discussed on the G2 comments. The expectation was that the students would address each of the four arrows, with an explanation for each. Good candidates did this. Others just combined everything into a general essay on climate change. Weaker candidates just restated the figures without any explanation of them at all. Whilst it is appreciated that none of the candidates was around between 1990 and 1999, references to the Industrial revolution were out by well over a century. This question would have benefitted from a larger answer box.\n

\n
\n", "question_id": "19M.2.SL.TZ2.3A.II", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c4-2-transfers-of-energy-and-matter", "c4-2-18-ecosystems-as-carbon-sinks-and-carbon-sources" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Outline the processes occurring during interphase in the cell cycle.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n growth/increase in cell size;\n
    2. \n
  2. \n division of mitochondria/chloroplasts/production of more organelles/number of organelles doubled;\n
    3. \n
  3. \n replication of DNA/amount of DNA is doubled;\n
    4. \n
  4. \n transcription of genes/production of mRNA;\n
    5. \n
  5. \n protein synthesis;\n
    6. \n
  6. \n cell respiration/production of ATP;\n
    7. \n
\n

\n \n Allow organelles ‘replicated’ for mpb.\n \n

\n
\n", "Examiners report": "
\n

\n Many candidates included growth and DNA replication in their answers. Other processes such as protein synthesis and cell respiration were mentioned less often.\n

\n
\n", "question_id": "22N.2.HL.TZ0.6", "topics": [ "d-continuity-and-change", "c-interaction-and-interdependence" ], "subtopics": [ "d2-1-cell-and-nuclear-division", "d2-1-13-phases-of-the-cell-cycle", "d2-1-14-cell-growth-during-interphase", "c2-2-neural-signalling", "c2-2-8-depolarization-and-repolarization-during-action-potentials", "c2-2-9-propagation-of-an-action-potential-along-a-nerve-fibre/axon-as-a-result-of-local-currents", "c3-2-defence-against-disease", "c3-2-6-lymphocytes-as-cells-in-the-adaptive-immune-system-that-cooperate-to-produce-antibodies" ] }, { "Question": "
\n
\n

\n What is a community?\n

\n

\n A. A group of individuals of the same species in a given area\n

\n

\n B. A group of animals that interact socially\n

\n

\n C. A group of organisms interacting with the abiotic environment\n

\n

\n D. A group of populations interacting with each other within a given area\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "22M.1A.SL.TZ1.17", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c4-1-populations-and-communities", "c4-1-10-a-community-as-all-of-the-interacting-organisms-in-an-ecosystem" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Explain how blood solute concentrations are kept within narrow limits in the human body.\n

\n
\n
\n

\n [7]\n

\n
\n
\n", "Markscheme": "
\n

\n a. solute concentration of blood monitored by the brain/hypothalamus ✔\n

\n

\n b. pituitary gland secretes ADH ✔\n

\n

\n c. ADH secreted when solute concentration/osmolarity is too high/a person is dehydrated/\n \n OWTTE\n \n ✔\n

\n

\n d. collecting duct more permeable to water ✔\n

\n

\n e. «more»\n \n aquaporins\n \n /opens\n \n aquaporins\n \n «in the plasma membrane of collecting duct cells» ✔\n

\n

\n f. «more» water reabsorbed «into the medulla» ✔\n

\n

\n g. medulla is hypertonic/hyperosmotic «so water can be reabsorbed from filtrate» ✔\n

\n

\n h. small volume of urine/concentrated urine produced «with ADH» ✔\n

\n

\n i. no/little/less ADH secreted if «blood» solute concentration is too low ✔\n

\n

\n j. collecting duct less permeable to water/less water reabsorbed/large volume of urine produced/dilute urine produced «with low/no ADH» ✔\n

\n

\n k. insulin causes blood glucose «concentration» to be reduced ✔\n

\n

\n l. glucose stored as glycogen in the\n \n liver\n \n ✔\n

\n

\n m. glucagon causes blood glucose «concentration» to be increased ✔\n

\n

\n n. negative feedback ✔\n

\n

\n \n Accept hypertonic for solute concentration too high and hypotonic for too low.\n \n

\n
\n", "Examiners report": "
\n

\n This was another question where many candidates struggled. Sub-topic 11.3 of the programme is titled ‘The kidney and osmoregulation’ but perhaps the connection was not made. A significant minority wrote only about regulation of blood sugar levels Others gave an exhaustive account of kidney function, but mostly did not have time left to write enough about osmoregulation. A small proportion of candidates gave a convincing account of the negative feedback mechanisms that keep blood solute concentrations within narrow limits.\n

\n
\n", "question_id": "19M.2.HL.TZ1.6C", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-3-homeostasis", "d3-3-7-role-of-the-kidney-in-osmoregulation-and-excretion" ] }, { "Question": "
\n
\n

\n The image shows a replication fork.\n

\n

\n \n

\n

\n Which row identifies X, Y and Z in the diagram?\n

\n

\n \n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "22M.1A.HL.TZ1.26", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d1-1-dna-replication", "d1-1-7-differences-between-replication-on-the-leading-strand-and-the-lagging-strand" ] }, { "Question": "
\n
\n

\n The graph shows the effect of increasing substrate concentration on the rate of an enzyme-catalysed reaction.\n

\n

\n \n

\n

\n

\n

\n Which type of inhibition corresponds to the labelled curves?\n

\n

\n \n

\n

\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "
\n

\n This was another relatively hard question with a low discrimination index. Surprisingly, some of the stronger candidates seem to have muddled up the effect of substrate concentration on competitive and non-competitive inhibitors.\n

\n
\n", "question_id": "22M.1A.HL.TZ1.29", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-1-enzymes-and-metabolism", "c1-1-15-competitive-inhibition-as-a-consequence-of-an-inhibitor-binding-reversibly-to-an-active-site" ] }, { "Question": "
\n
\n

\n Natural selection can operate in different ways. What is the effect of disruptive selection?\n

\n

\n A. It eliminates individuals with intermediate forms of a characteristic.\n

\n

\n B. It eliminates individuals at random regardless of their characteristics.\n

\n

\n C. It favours individuals with intermediate forms of a characteristic.\n

\n

\n D. It favours individuals at one extreme of the range of variation in a characteristic.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "None", "question_id": "19M.1A.HL.TZ1.35", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-1-natural-selection", "d4-1-12-differences-between-directional-disruptive-and-stabilizing-selection" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Distinguish between the transfers of energy and inorganic nutrients in ecosystems.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n energy is lost (between trophic levels) / not all passed on / not reused / must be supplied;\n

\n

\n nutrients are recycled/reused;\n

\n
\n", "Examiners report": "
\n

\n A sizeable number of candidates seemed to miss the point here, in what was intended to be an easy question. The command term ‘distinguish’ is an instruction to give the key differences. In this case, the distinction was that energy flows through an ecosystem and is ultimately lost whereas inorganic nutrients can be recycled.\n

\n
\n", "question_id": "20N.2.HL.TZ0.4", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c4-2-transfers-of-energy-and-matter", "c4-2-3-flow-of-chemical-energy-through-food-chains", "c4-2-22-recycling-of-all-chemical-elements-required-by-living-organisms-in-ecosystems", "c4-2-6-autotrophs-as-organisms-that-use-external-energy-sources-to-synthesize-carbon-compounds-from-simple-inorganic-substances", "c4-2-7-use-of-light-as-the-external-energy-source-in-photoautotrophs-and-oxidation-reactions-as-the-energy-source-in-chemoautotrophs" ] }, { "Question": "
\n
\n

\n The base sequences of a short section of DNA are shown, together with mRNA that has been transcribed from it and one of the tRNA anticodons that could be used to translate the mRNA.\n

\n

\n \n

\n

\n

\n

\n

\n

\n

\n

\n Which strand of DNA is transcribed and to which codon in the mRNA would the tRNA anticodon bind during translation?\n

\n

\n \n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "
\n

\n This question was too long to answer in one minute, but this is compensated by other easy questions. It discriminated very well and was not too difficult.\n

\n
\n", "question_id": "19M.1A.HL.TZ2.9", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d1-2-protein-synthesis", "d1-2-12-directionality-of-transcription-and-translation" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Xylem and phloem contain structures that are adapted for transport. Outline the differences between these structures in xylem and phloem.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. plasma membrane in phloem/sieve tubes but not in xylem/vessels\n
\n \n \n OR\n \n \n
\n xylem/vessels dead/acellular and phloem/sieve tubes alive ✔\n

\n

\n b. xylem vessels have thicker walls «than phloem» ✔\n

\n

\n c. xylem «vessel» walls are lignified «but phloem walls are not» ✔\n

\n

\n d. phloem vessels have sieve plates «whereas xylem vessels have no cross walls» ✔\n

\n

\n e. xylem/vessels are wider/larger than phloem/sieve tubes ✔\n

\n

\n f. companion cells in phloem «but not in xylem» ✔\n

\n
\n", "Examiners report": "
\n

\n Many candidates knew nothing about the structure of the conducting tissues of plants and instead gave some rudimentary information on their functions. A common misconception is that phloem sieve tubes are wider than xylem vessels. This may have come from a failure to identify correctly the xylem and phloem tissue correctly in the micrograph. The most commonly known feature of xylem was the lignified wall and if phloem was the presence of companion cells.\n

\n
\n", "question_id": "19M.2.HL.TZ1.4A", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-2-transport", "b3-2-9-distribution-of-tissues-in-a-transverse-section-of-the-stem-of-a-dicotyledonous-plant", "b3-2-18-adaptations-of-phloem-sieve-tubes-and-companion-cells-for-translocation-of-sap" ] }, { "Question": "
\n
\n (i)\n
\n
\n

\n State how many water molecules are shown in the diagram.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n 10;\n

\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ1.4AI", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a1-1-water", "a1-1-2-hydrogen-bonds-as-a-consequence-of-the-polar-covalent-bonds-within-water-molecules" ] }, { "Question": "
\n
\n

\n What is the order of increasing size of muscle structures?\n

\n

\n A. muscle, muscle fibre, myofibril, sarcomere\n

\n

\n B. myofibril, muscle fibre, sarcomere, muscle\n

\n

\n C. sarcomere, myofibril, muscle fibre, muscle\n

\n

\n D. muscle fibre, sarcomere, myofibril, muscle\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "19M.1A.HL.TZ2.37", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-3-muscle-and-motility-(hl-only)", "b3-3-2-sliding-filament-model-of-muscle-contraction", "b3-3-3-role-of-the-protein-titin-and-antagonistic-muscles-in-muscle-relaxation", "b3-3-4-structure-and-function-of-motor-units-in-skeletal-muscle" ] }, { "Question": "
\n
\n

\n The image shows a cross-section of a flower.\n

\n

\n \n

\n

\n [Source: © International Baccalaureate Organization 2019]\n

\n

\n

\n

\n Where does production of haploid gametes occur?\n

\n

\n A. I and II only\n

\n

\n B. III and IV only\n

\n

\n C. I and III only\n

\n

\n D. II and IV only\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "19M.1A.SL.TZ1.32", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-1-reproduction", "d3-1-8-sexual-reproduction-in-flowering-plants" ] }, { "Question": "
\n
\n

\n Explain gene linkage and its effects on inheritance.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. located on the same chromosome;\n
\n b. genes/gene loci close together (on the same chromosome);\n
\n c. do not follow (the law of) independent assortment;\n
\n d. more chance of recombination if genes are further apart;\n
\n e. inherited together unless crossing over/recombination occurs;\n
\n f. ratios of offspring in dihybrid crosses are different from expected/non-Mendelian\n
\n \n OR\n \n
\n more offspring with parental phenotype combinations than expected;\n

\n
\n", "Examiners report": "
\n

\n The was some confusion between autosomal and sex linkage. Candidates tended either to have a secure understanding of the mechanisms at work in autosomal gene linkage, or none. This question and (d) correlated closely with candidates’ overall score on the paper, so distinguished particularly effectively between stronger and weaker candidates.\n

\n
\n", "question_id": "21N.2.HL.TZ0.C", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-2-inheritance", "d3-2-19-autosomal-gene-linkage" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Mendel found the same pattern of inheritance in all the crosses that he performed. Outline, with examples, different types of inheritance that produce non-Mendelian ratios.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n

\n a. some traits may involve many genes/be polygenic\n \n eg\n \n : height, skin colour «correct example required» ✔\n \n Accept any verifiable examples of these types of inheritance.\n \n

\n

\n b. linked genes/alleles of different genes on same chromosome ✔\n

\n

\n c. «small numbers of» recombinant phenotypes due to crossing over «between linked genes» ✔\n

\n

\n d. co-dominance of specific alleles/intermediate forms\n \n eg\n \n : pink flowers «from red and white ones»/blood groups «correct example required» ✔\n

\n

\n e. sex-linked effects\n \n eg\n \n : colour blindness «correct example required» ✔\n

\n

\n f. environmental influence on inheritance/epigenetics/methylation ✔\n

\n

\n g. any other example of non-Mendelien inheritance with a specific example ✔\n

\n

\n

\n
\n", "Examiners report": "
\n

\n This question was less well answered. Students commonly indicated linked genes and sex-lined genes as examples of non-Mendelian inheritance. Accurate discussion of co-dominance was less frequent.\n

\n
\n", "question_id": "19M.2.SL.TZ2.7B", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-2-inheritance", "d3-2-9-abo-blood-groups-as-an-example-of-multiple-alleles", "d3-2-10-incomplete-dominance-and-codominance", "d3-2-11-sex-determination-in-humans-and-inheritance-of-genes-on-sex-chromosomes" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Estimate the median number of bacterial cells per gram of feces in the R enterotype.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n 1.9 × 10\n \n 11\n \n / 190000 million / 190 billion (cells per gram);\n

\n

\n \n Cells per gram not needed as in stem. Accept 1.80 × 10\n \n 11\n \n to 1.95 × 10\n \n 11\n \n .\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ2.1B", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-2-defence-against-disease", "c3-2-1-pathogens-as-the-cause-of-infectious-diseases" ] }, { "Question": "
\n
\n

\n How do DNA and messenger RNA (mRNA) molecules differ in eukaryotes?\n

\n

\n
\n A.  mRNA is twice the size of DNA and is formed from four different bases.\n

\n

\n B.  DNA contains ribose while mRNA contains deoxyribose.\n

\n

\n C.  mRNA has the same bases as DNA but contains ribose.\n

\n

\n D.  DNA has two strands while mRNA has only one.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "23M.1A.SL.TZ1.11", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a1-2-nucleic-acids", "a1-2-7-differences-between-dna-and-rna" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Distinguish between the thermal properties of air and water as they relate to the habitat of animals.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n water has a (much) higher specific heat capacity (than air);\n
    2. \n
  2. \n water requires more energy gain/loss to change temperature;\n
    3. \n
  3. \n (water) provides more stable thermal habitats than air / temperature of water bodies remains more constant than air temperature;\n
    4. \n
  4. \n water has a higher thermal conductivity than air;\n
    5. \n
  5. \n more heat is transferred from organisms to water than to air;\n
    6. \n
  6. \n water is a good evaporative coolant and air is not;\n
    7. \n
  7. \n aquatic mammals have (proportionally) more body fat as insulation;\n
    8. \n
\n
\n", "Examiners report": "None", "question_id": "SPM.2.SL.TZ0.8C", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a1-1-water", "a1-1-6-physical-properties-of-water-and-the-consequences-for-animals-in-aquatic-habitats" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n State the main characteristic of stem cells.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n undifferentiated/pluripotent/ability to divide/differentiate into any types of cells/differentiate along different pathways;\n

\n
\n", "Examiners report": "
\n

\n In a. most were able to say the stem cells were undifferentiated. Many put ‘unspecialised’ instead, which was not credited. There were several, justified G2 comments about the size of the micrograph, which made it difficult to measure the diameter accurately. However, this was generally very poorly answered, with over half failing to get the mark for either the correct answer or the correct calculation. In 1d the better candidates stated that the person could now live a normal life, but as it was not in the genome the progeny could still be affected. The word ‘progeny’ was commented on by several teachers, who pointed out that ‘children’, or ‘offspring’ would have been clearer for those working in an additional language.\n

\n
\n", "question_id": "22M.2.SL.TZ2.2A", "topics": [ "b-form-and-function" ], "subtopics": [ "b2-3-cell-specialization", "b2-3-2-properties-of-stem-cells" ] }, { "Question": "
\n
\n

\n Which graph represents the effect of humidity on the transpiration rate in plants?\n

\n

\n \n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "None", "question_id": "22M.1A.SL.TZ1.32", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-1-gas-exchange", "b3-1-9-transpiration-as-a-consequence-of-gas-exchange-in-a-leaf" ] }, { "Question": "
\n
\n

\n In mammals, mature red blood cells are specialized in that they lack nuclei, mitochondria or ribosomes. Which statement applies to red blood cells?\n

\n

\n A. No chemical reactions take place within their cytoplasm.\n

\n

\n B. They cannot produce new enzymes.\n

\n

\n C. Materials cannot enter red blood cells.\n

\n

\n D. Materials cannot exit red blood cells.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "21M.1A.SL.TZ1.1", "topics": [ "b-form-and-function" ], "subtopics": [ "b2-3-cell-specialization", "b2-3-5-cell-size-as-an-aspect-of-specialization" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n State another independent variable that would affect the activity of this enzyme.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n temperature\n
\n \n \n OR\n \n \n
\n lactose/substrate concentration\n
\n \n \n OR\n \n \n
\n Inhibitors / cofactors ✔\n

\n

\n \n Do not accept pH or acidity\n \n .\n

\n
\n", "Examiners report": "None", "question_id": "19N.1B.SL.TZ0.2A", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-1-enzymes-and-metabolism", "c1-1-8-effects-of-temperature-ph-and-substrate-concentration-on-the-rate-of-enzyme-activity" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Outline energy flow through a food chain.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n

\n a. energy from the sun/light energy is converted to chemical energy by photosynthesis ✔\n

\n

\n b. «chemical» energy flows through the food chains by feeding ✔\n

\n

\n c. energy is released «from carbon compounds» by respiration\n
\n \n \n OR\n \n \n
\n energy from respiration is used by living organisms and converted to heat ✔\n

\n

\n d. heat is not recyclable / heat is lost from food chains\n
\n \n \n OR\n \n \n
\n heat cannot be converted to other forms of energy ✔\n

\n

\n e. energy is lost in excretion/uneaten material/egestion/feces ✔\n

\n

\n f. energy losses between trophic levels limits the length of food chains\n
\n \n \n OR\n \n \n
\n energy transfer is only 10 % between trophic levels ✔\n

\n
\n", "Examiners report": "
\n

\n Was well answered with most students being knowledgeable about ecology.\n

\n
\n", "question_id": "19M.2.SL.TZ2.8A", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c4-2-transfers-of-energy-and-matter", "c4-2-3-flow-of-chemical-energy-through-food-chains" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Outline the sequence of events that occurs during mitosis.\n

\n
\n
\n

\n [5]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n supercoiling/condensation of\n \n chromosomes\n \n ;\n
    2. \n
  2. \n breakup of nuclear membrane;\n
    3. \n
  3. \n growth of spindle/microtubules;\n
    4. \n
  4. \n attachment of spindle/microtubules to chromosomes/centromeres;\n
    5. \n
  5. \n chromosomes line up at the equator/middle\n
    6. \n
  6. \n division of centromeres;\n
    7. \n
  7. \n separation of sister chromatids/chromosomes\n
    \n \n OR\n \n
    \n sister chromatids/chromosomes move to opposite poles;\n
    8. \n
  8. \n reformation of nuclear membranes around chromosomes at each pole;\n
    9. \n
\n

\n

\n

\n \n If events are not in the correct order, then award a maximum of 4 marks.\n \n

\n

\n \n Names of phases of mitosis not required.\n \n

\n

\n \n Award a max of 1 mark for listing the phases in the correct order when the list constitutes the entire response.\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ1.6A", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-1-cell-and-nuclear-division", "d2-1-7-phases-of-mitosis" ] }, { "Question": "
\n
\n

\n What happens during blood clotting?\n
\n
\n

\n

\n A.  A chain reaction causes platelets to release antibodies to avoid infections.\n

\n

\n B.  Thrombin is converted into fibrinogen after a series of chemical reactions.\n

\n

\n C.  Sealing of wounds by fibrinogen makes platelets release antibodies for clotting.\n

\n

\n D.  Chemical reactions cause wounds to seal after platelets release clotting factors.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "23M.1A.SL.TZ1.21", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-2-defence-against-disease", "c3-2-3-sealing-of-cuts-in-skin-by-blood-clotting" ] }, { "Question": "
\n
\n

\n Which event occurs in the first division of meiosis?\n

\n

\n A.  Synthesis of DNA\n

\n

\n B.  Pulling apart of sister chromatids\n

\n

\n C.  Halving of the chromosome number\n

\n

\n D.  Division of centromeres\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "22N.1A.SL.TZ0.14", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-1-cell-and-nuclear-division", "d2-1-9-meiosis-as-a-reduction-division" ] }, { "Question": "
\n
\n (ii)\n
\n
\n

\n Suggest\n \n one\n \n reason for a decline in the brown pelican population with the most eggshell thinning.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n more risk of predation/ eggs break more easily/fewer chicks hatch;\n

\n

\n \n \n OWTTE\n \n \n

\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ2.18AII", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-2-stability-and-change", "d4-2-9-biomagnification-of-pollutants-in-natural-ecosystems" ] }, { "Question": "
\n
\n

\n What is the role of HCG in early pregnancy?\n

\n

\n A. It prevents the degeneration of the corpus luteum in the ovary.\n

\n

\n B. It initiates the development of the uterus lining.\n

\n

\n C. It inhibits the production of estrogen.\n

\n

\n D. It stimulates uterine contractions.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "None", "question_id": "22M.1A.HL.TZ1.40", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-1-reproduction", "d3-1-17-pregnancy-testing-by-detection-of-human-chorionic-gonadotropin-secretion" ] }, { "Question": "
\n
\n

\n Other than humidity, suggest a variable that would need to be controlled in this experiment.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n temperature/amount or type of feed «in the respirometer»/amount of CO\n \n 2\n \n absorber\n
\n \n \n OR\n \n \n
\n other reasonable suggestion ✔\n

\n

\n \n Do not accept light\n \n

\n
\n", "Examiners report": "
\n

\n Often more than one answer was given but only the first was marked. Temperature and amount of feed were the most common answers.\n

\n
\n", "question_id": "19M.1B.SL.TZ1.A.III", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-2-cell-respiration", "c1-2-6-variables-affecting-the-rate-of-cell-respiration" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Calculate how long all the heart chambers are in diastole at the same time.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n 0.4 s;\n

\n
\n", "Examiners report": "None", "question_id": "23M.2.HL.TZ1.22A", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-2-transport", "b3-2-16-stages-in-the-cardiac-cycle" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Outline the roles of helicase and ligase in DNA replication.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n

\n \n helicase\n \n :\n

\n

\n a. unwinds/uncoils the DNA «double helix» ✔\n

\n

\n b. breaks hydrogen bonds «between bases» ✔\n

\n

\n c. separates the «two» strands/unzips the DNA/creates replication fork ✔\n

\n

\n \n ligase\n \n :\n

\n

\n d. seals nicks/forms a continuous «sugar-phosphate» backbone/strand ✔\n

\n

\n e. makes sugar-phosphate bonds/covalent bonds between adjacent nucleotides ✔\n

\n

\n f. after «RNA» primers are removed/where an «RNA» primer was replaced by DNA ✔\n

\n

\n g. «helps to» join Okazaki fragments ✔\n

\n
\n", "Examiners report": "
\n

\n This was generally well answered, with most candidates knowing at least something of the roles of these two enzymes. Most candidates knew that ligase connects Okazaki fragments but some claimed that it creates hydrogen bonds between nucleotides on template and the new strand. Many candidates did not distinguish between unwinding of DNA and separating the strands. Two details that should be more widely known are that helicase separates the two strands of a DNA molecule by encouraging the breakage of hydrogen bonds between bases and that ligase seals nicks by making sugar phosphate bonds.\n

\n
\n", "question_id": "19M.2.SL.TZ1.7A", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d1-1-dna-replication", "d1-1-3-role-of-helicase-and-dna-polymerase-in-dna-replication" ] }, { "Question": "
\n
\n

\n Identify\n \n one\n \n variable that should be kept constant while measuring enzyme activity at all temperatures.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n pH/concentration of enzyme/concentration of substrate;\n

\n

\n \n Do not accept temperature\n
\n \n

\n

\n \n Do not accept “amount”\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.1B.SL.TZ1.B", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-1-enzymes-and-metabolism", "c1-1-8-effects-of-temperature-ph-and-substrate-concentration-on-the-rate-of-enzyme-activity" ] }, { "Question": "
\n
\n (d)\n
\n
\n

\n Outline the conclusions that can be drawn from the graph showing data for PCV and\n \n S. pneumoniae\n \n .\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n number of deaths (due to\n \n S. pneumoniae\n \n ) and percentage of children not vaccinated (with PCV) both fall (along the years)\n
    \n \n \n OR\n \n \n
    \n number of deaths (due to\n \n S. pneumoniae\n \n ) decreases while percentage of vaccinated children (with PCV) increases (along the years);\n
    2. \n
  2. \n \n positive\n \n correlation between number of deaths and percentage of children not vaccinated /\n
    \n \n \n OR\n \n \n
    \n \n negative\n \n correlation between number of deaths and percentage of children vaccinated / vaccination reduces the number of deaths;\n
    3. \n
  3. \n increased reduction in the number of deaths from 2010 onwards;\n
    4. \n
  4. \n still large number of deaths/large number of children unvaccinated in 2015;\n
    5. \n
\n

\n \n Comparative terms expected (do not award mp for just stating values).\n \n

\n

\n \n Mpb: do not allow “directly or inversely proportional”.\n \n

\n

\n \n Mpb: Do not just accept “positive correlation” or “negative correlation” without a clear indication of the variables being correlated\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ2.1D", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-2-defence-against-disease", "c3-2-16-vaccines-and-immunization" ] }, { "Question": "
\n
\n

\n Evaluate the reliability of the results.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n only 3 readings at each temperature may be insufficient;\n
    2. \n
  2. \n reliable as error bars are small;\n
    3. \n
\n
\n", "Examiners report": "None", "question_id": "23M.1B.SL.TZ1.C", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-1-enzymes-and-metabolism", "c1-1-8-effects-of-temperature-ph-and-substrate-concentration-on-the-rate-of-enzyme-activity" ] }, { "Question": "
\n
\n (a.ii)\n
\n
\n

\n Identify structure Y.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n glomerulus/Bowman’s capsule;\n

\n
\n", "Examiners report": "
\n

\n 80% of candidates identified the structure as the glomerulus or Bowman's capsule.\n

\n
\n", "question_id": "22N.2.HL.TZ0.5A.II", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-3-homeostasis", "d3-3-8-role-of-the-glomerulus-bowmans-capsule-and-proximal-convoluted-tubule-in-excretion" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Calculate, showing your working, the percentage change in mean cholesterol level after\n \n one week\n \n on the study diet.\n

\n

\n

\n

\n . . . . . . . . . . . . . . . . . . . .%\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n ((165–150) ÷ 150) × 100;\n

\n

\n (=) 10 (%);\n

\n

\n \n Allow up to 167 = 11.3 %\n \n

\n

\n \n 1 mark for correct working if above 167\n \n .\n

\n
\n", "Examiners report": "None", "question_id": "20N.1B.SL.TZ0.1C", "topics": [ "b-form-and-function" ], "subtopics": [ "b1-2-proteins", "b1-2-3-dietary-requirements-for-amino-acids", "b1-1-carbohydrates-and-lipids", "b1-1-10-difference-between-saturated-monounsaturated-and-polyunsaturated-fatty-acids" ] }, { "Question": "
\n
\n (a.i)\n
\n
\n

\n Identify, with a reason, the stage shown at X.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n anaphase;\n
    2. \n
  2. \n the (replicated) chromosomes/chromatids are separating/moving to opposite poles of the cell;\n
    3. \n
\n

\n \n OWTTE\n \n

\n
\n", "Examiners report": "
\n

\n This question was generally well done; a few identified the incorrect phase of mitosis, but the observations about cellular events being observed was often correct.\n

\n
\n", "question_id": "22M.2.HL.TZ2.2", "topics": [ "d-continuity-and-change", "a-unity-and-diversity" ], "subtopics": [ "d2-1-cell-and-nuclear-division", "d2-1-8-identification-of-phases-of-mitosis", "a2-2-cell-structure", "a2-2-2-microscopy-skills", "d2-1-15-control-of-the-cell-cycle-using-cyclins", "a2-2-5-prokaryote-cell-structure", "a2-2-6-eukaryote-cell-structure" ] }, { "Question": "
\n
\n

\n The image shows part of a myofibril from a relaxed muscle fibre.\n

\n

\n \n

\n

\n [Source: Sarcomere. Sameerb. Available at https://commons.wikimedia.org/wiki/File:Sarcomere.gif\n
\n [Accessed 30 November 2021].]\n

\n

\n

\n

\n What occurs during muscle contraction?\n

\n

\n A. Myosin binding sites are blocked.\n

\n

\n B. The bands labelled Y get shorter.\n

\n

\n C. The bands labelled X get shorter.\n

\n

\n D. Calcium ions bind to myosin.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "21N.1A.HL.TZ1.38", "topics": [ "b-form-and-function" ], "subtopics": [ "b2-3-cell-specialization", "b2-3-9-adaptations-of-cardiac-muscle-cells-and-striated-muscle-fibres" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Identify the chromosome that is affected by a trisomy in this individual, naming the condition that this trisomy gives rise to.\n

\n

\n Chromosome number:\n

\n

\n Name of condition:\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n 21\n \n \n AND\n \n \n Down syndrome/trisomy 21 ✔\n

\n

\n \n Both needed\n \n

\n
\n", "Examiners report": "
\n

\n The idea of 21 trisomy and Down Syndrome was very common. Rarely students made references to autism or other conditions after correctly identifying 21 trisomy. Rarely other chromosome numbers with incorrect conditions were referred to\n

\n
\n", "question_id": "19M.2.SL.TZ1.6B", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-1-cell-and-nuclear-division", "d2-1-10-down-syndrome-and-non-disjunction" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n State the name and function of structures I and II.\n

\n

\n Structure I name and function: ..............................................................................................................\n

\n

\n ..........................................................................................................................................................\n

\n

\n Structure II name and function: .............................................................................................................\n

\n

\n ..........................................................................................................................................................\n

\n

\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n I is the stigma which receives the\n \n pollen\n \n /where\n \n pollen\n \n lands/is captured (during pollination);\n
    2. \n
  2. \n II is the anther and produces/contains/releases\n \n pollen\n \n ;\n
    3. \n
\n

\n \n Both name and function must be included in each marking point.\n \n

\n

\n \n The role in pollination should be stated. Do not accept “pollination” on its own.\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ2.3A", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-1-reproduction", "d3-1-9-features-of-an-insect-pollinated-flower" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Discuss whether the data supports the hypothesis that the gradient in cyanogenesis is due to its benefits against herbivory in rural areas.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. (hypothesis) not supported;\n

\n

\n b. large overlap/little difference between cyanogenic and non-cyanogenic (in herbivory);\n

\n

\n c. smaller difference between cyanogenic and non-cyanogenic in rural areas;\n

\n

\n d. both show negative correlation between herbivory and distance from city center/same trend;\n

\n

\n e. some support/hypothesis partly supported by lower herbivory in cyanogenic (at all distances).\n

\n

\n \n Do not accept ‘No’ unqualified as an answer\n \n .\n

\n

\n \n Do not award mpe if the answer states that the hypothesis is supported without doubt/fully\n \n .\n

\n
\n", "Examiners report": "
\n

\n This was possibly the hardest part of the data-based question. Candidates were spread approximately equally between 0, 1 and 2 marks. Many candidates did not realise that the differences between herbivory in cyanogenic and non-cyanogenic plants were unlikely to be significant, especially in the rural areas that were furthest from the city. The hypothesis stated in the question was therefore not supported. Candidates should be encouraged to consider both the closeness of means and also the spread, when analysing data.\n

\n
\n", "question_id": "20N.2.SL.TZ0.1C", "topics": [ "b-form-and-function" ], "subtopics": [ "b4-2-ecological-niches", "b4-2-9-adaptations-of-herbivores-for-feeding-on-plants-and-of-plants-for-resisting-herbivory" ] }, { "Question": "
\n
\n

\n What is always a consequence of the evaporation of water from mesophyll cells in leaves of a healthy plant?\n

\n

\n
\n A.  Plasmolysis occurs in mesophyll cells.\n

\n

\n B.  Photosynthesis stops.\n

\n

\n C.  Stomata close to reduce transpiration.\n

\n

\n D.  Water moves up the stem in the xylem.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "SPM.1A.SL.TZ0.18", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-1-gas-exchange", "b3-1-7-adaptations-for-gas-exchange-in-leaves" ] }, { "Question": "
\n
\n

\n The diagram shows the structure of insulin.\n

\n

\n \n

\n

\n
\n From the diagram, what can be concluded about the structure of insulin?\n

\n

\n
\n A.  It is composed of two polypeptide chains stabilized by disulfide bonds.\n

\n

\n B.  It is a simple protein composed of one continuous polypeptide chain.\n

\n

\n C.  It is a fibrous protein.\n

\n

\n D.  Its molecules do not display quaternary structure.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "None", "question_id": "SPM.1A.HL.TZ0.6", "topics": [ "b-form-and-function" ], "subtopics": [ "b1-2-proteins", "b1-2-12-relationship-of-form-and-function-in-globular-and-fibrous-proteins" ] }, { "Question": "
\n
\n

\n The diagram represents transmission across a cholinergic synapse. Where would a neonicotinoid pesticide act to prevent synaptic transmission?\n

\n

\n \n

\n

\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "23M.1A.HL.TZ2.29", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c2-2-neural-signalling", "c2-2-12-effects-of-exogenous-chemicals-on-synaptic-transmission" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Explain how speciation occurs, including the different processes of isolation and selection.\n

\n
\n
\n

\n [7]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n Species is a group of organisms that interbreeds (normally in the wild) and produce fertile offspring;\n
    2. \n
  2. \n within an interbreeding population there is variety / variation exists;\n
    3. \n
  3. \n some adaptations favour survival to reproductive age /survival of the fittest / natural selection;\n
    4. \n
  4. \n alleles for these adaptations become more frequent/are inherited in the population /change with time;\n
    5. \n
  5. \n speciation is the formation of new species;\n
    6. \n
  6. \n (speciation) occurs because populations have become reproductively isolated / no longer able to interbreed / exposed to different selection pressures;\n
    7. \n
  7. \n behavioural isolation involves differences in courtship or mating behaviours;\n
    8. \n
  8. \n temporal isolation involves differences in the timing of courtship or mating behaviours;\n
    9. \n
  9. \n geographical isolation / allopatric refers to the physical barriers that exist that keep two populations from mating;\n
    10. \n
  10. \n polyploidy can lead to reproductive isolation;\n
    11. \n
  11. \n stabilizing selection is when the two extremes of a trait have lower reproductive fitness (OWTTE) / favours average phenotype;\n
    12. \n
  12. \n directional selection is when one extreme of the trait has lower reproductive fitness (OWTTE);\n
    13. \n
  13. \n disruptive/diversifying selection favours both extreme phenotypes / intermediate phenotype has lower fitness;\n
    14. \n
\n
\n", "Examiners report": "
\n

\n Many had a \"good idea\" of speciation and knew about the different types of isolation and selection. Very few discussed the role of polyploidy.\n

\n
\n", "question_id": "22M.2.SL.TZ2.7C", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a4-1-evolution-and-speciation", "a4-1-7-roles-of-reproductive-isolation-and-differential-selection-in-speciation" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Outline how adaptive radiation provides evidence for evolution.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n diversification/ different species produced from a common/shared ancestor;\n
    2. \n
  2. \n homologous features have similarities of structure\n
    3. \n
  3. \n despite different functions;\n
    4. \n
  4. \n (different) adaptation to different environments/different selective pressures;\n
    5. \n
  5. \n pentadactyl limbs/Darwin’s finches/other example of adaptive radiation described correctly;\n
    6. \n
\n

\n \n Allow any of the marking points with reference to a named example e.g. Darwin’s finches or pentadactyl limb.\n \n

\n
\n", "Examiners report": "
\n

\n Some candidates misread the question and wrote about radiation causing mutations. Other answers described how a species changes over time due to natural selection. A few answers gave a convincing account of how structures such as the pentadactyl limb give evidence for evolution because similarities of structure despite differences of function indicate common ancestry.\n

\n
\n", "question_id": "22N.2.HL.TZ0.8A", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a4-1-evolution-and-speciation", "a4-1-9-adaptive-radiation-as-a-source-of-biodiversity" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Explain the need for halving the chromosome number during a sexual life cycle and how this is done.\n

\n
\n
\n

\n [7]\n

\n
\n
\n", "Markscheme": "
\n

\n a. chromosome number is halved so the zygote/offspring has same number as the parent / so that chromosome number is not doubled;\n
\n b. process is meiosis;\n
\n c. DNA/chromosomes replicate (so each chromosome consists of two chromatids);\n
\n d. homologous chromosomes pair in prophase I;\n
\n e. (these) separate in anaphase I into two cells;\n
\n f. (after meiosis I) cells are haploid;\n
\n g. in meiosis II chromatids are separated;\n
\n h. result is\n \n four\n \n haploid cells/gametes;\n
\n i. each gamete is genetically unique;\n
\n j. (uniqueness) is due to crossing over/independent assortment/random alignment of chromosomes;\n
\n k. fertilization results in the formation of a diploid zygote;\n
\n l. (fertilization) results in variation in a population\n

\n
\n", "Examiners report": "
\n

\n This provided a departure from the usual questions requiring a straight recall of meiosis. In general, it was well attempted, with all but a few students failing to state that meiosis was at the heart of the question. Despite the question stating\n \n halving\n \n of the chromosome number, many insisted on writing about chromosomal errors such as Down syndrome, which was not pertinent to the question.\n

\n
\n", "question_id": "21N.2.SL.TZ0.6B", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-1-cell-and-nuclear-division", "d2-1-4-roles-of-mitosis-and-meiosis-in-eukaryotes" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Outline the cell theory.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. cells can only arise from preexisting cells ✔\n

\n

\n b. living organisms are composed of cells/smallest unit of life ✔\n

\n

\n c. organisms consisting of only one cell carry out all functions of life in that cell/cells perform life functions «at some point in their existence» ✔\n

\n

\n d. although most organisms conform to cell theory, there are exceptions ✔\n

\n
\n", "Examiners report": "None", "question_id": "19N.2.SL.TZ0.3A", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a2-2-cell-structure", "a2-2-1-cells-as-the-basic-structural-unit-of-all-living-organisms" ] }, { "Question": "
\n
\n

\n Suggest a reason that the mass of protein and lipid mixture eaten at 25:1 is lower than at 50:1.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n the mixture was closer to what the bees ate naturally;\n
    2. \n
  2. \n the bees like the taste better/prefer sucrose;\n
    3. \n
  3. \n there was more lipid in the 25:1 mixture so they achieved their daily lipid/energy requirement with less mass of food;\n
    4. \n
  4. \n the bees eating 50:1 diet ate more to reach their daily lipid requirement;\n
    5. \n
  5. \n prefer the higher proportion of protein (in the 50:1)\n
    6. \n
\n
\n", "Examiners report": "None", "question_id": "22N.2.SL.TZ0.G", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c4-2-transfers-of-energy-and-matter", "c4-2-14-restrictions-on-the-number-of-trophic-levels-in-ecosystems-due-to-energy-losses", "c4-2-15-primary-production-as-accumulation-of-carbon-compounds-in-biomass-by-autotrophs" ] }, { "Question": "
\n
\n (d)\n
\n
\n

\n Distinguish between the changes in porosity of the bones in humans and bears as age increases.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n porosity increased in humans\n \n and\n \n decreased in bears;\n

\n

\n \n Both needed\n \n .\n

\n
\n", "Examiners report": "
\n

\n Well answered with most candidates referring to the positive and negative correlations.\n

\n
\n", "question_id": "22M.2.SL.TZ1.1D", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-3-homeostasis", "d3-3-1-homeostasis-as-maintenance-of-the-internal-environment-of-an-organism", "d3-3-2-negative-feedback-loops-in-homeostasis" ] }, { "Question": "
\n
\n

\n A pollen tube grows down the style to an egg inside the ovary of a flower. What is the next process that occurs?\n

\n

\n A. Dispersal\n

\n

\n B. Fertilization\n

\n

\n C. Germination\n

\n

\n D. Pollination\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "19N.1A.SL.TZ0.34", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-1-reproduction", "d3-1-8-sexual-reproduction-in-flowering-plants" ] }, { "Question": "
\n
\n

\n Outline the control of metabolism by end-product inhibition.\n

\n
\n
\n

\n [5]\n

\n
\n
\n", "Markscheme": "
\n

\n a. metabolism is chains/web of\n \n enzyme\n \n -catalyzed reactions\n
\n \n \n OR\n \n \n
\n metabolic pathway is a chain of\n \n enzyme\n \n -catalyzed reactions ✔\n

\n

\n b. end product/inhibitor is final product of chain/pathway ✔\n

\n

\n c. inhibits/binds to/blocks the first enzyme in chain/pathway ✔\n

\n

\n d. non-competitive inhibition ✔\n

\n

\n e. end-product/inhibitor binds to an allosteric site/site away from the active site ✔\n

\n

\n f. changes the shape of the\n \n active site\n \n /affinity of the\n \n active site\n \n «for the substrate» ✔\n

\n

\n g. prevents intermediates from building up\n
\n \n \n OR\n \n \n
\n prevents formation of excess «end» product/stops production when there is enough\n
\n \n \n OR\n \n \n
\n whole metabolic pathway can be switched off ✔\n

\n

\n h. negative feedback ✔\n

\n

\n i. binding of the end product/inhibitor is reversible\n
\n \n \n OR\n \n \n
\n pathway restarts if end product/inhibitor detaches/if end product concentration is low ✔\n

\n

\n j. isoleucine inhibits/slows «activity of first enzyme in» threonine to isoleucine pathway ✔\n

\n

\n \n Allow mark points shown in clearly annotated diagrams.\n \n

\n

\n \n To gain mpd, mpe and mpf the answer must be in the context of end-product inhibition, not enzyme inhibition generally.\n \n

\n
\n", "Examiners report": "
\n

\n Answers to this question were rather polarised. Candidates who had studied this topic and understood it had no difficulty in scoring high marks but other candidates struggled to include any useful ideas in their answers. Weaker answers tended to exclude the ideas of enzyme catalysis, pathways of reactions and the mechanisms involved in non-competitive enzyme inhibition. Diagrams to illustrate the process were a valuable part of some answers.\n

\n
\n", "question_id": "19M.2.HL.TZ1.B", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-1-enzymes-and-metabolism", "c1-1-16-regulation-of-metabolic-pathways-by-feedback-inhibition" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Explain how polypeptides are produced by the process of translation.\n

\n
\n
\n

\n [8]\n

\n
\n
\n", "Markscheme": "
\n

\n a. mRNA is translated;\n

\n

\n b. mRNA binds with ribosome/with small subunit of ribosome;\n

\n

\n c. tRNA-activating enzymes/aminoacyl tRNA synthetases attach specific amino acid to tRNA;\n

\n

\n d.\n \n anticodon\n \n of 3 bases/nucleotides on tRNA;\n

\n

\n e. start codon/AUG on mRNA;\n

\n

\n f. tRNA carrying first amino acid/methionine binds to P/peptidyl site (when large subunit binds);\n

\n

\n g. anticodon (on tRNA) binds to codon (on mRNA);\n

\n

\n h.\n \n complementary\n \n \n base\n \n \n pairing\n \n (between codon and anticodon);\n

\n

\n i. tRNA for next codon binds to A site/amino acyl site;\n

\n

\n j. peptide bond forms between amino acids (on tRNAs) at P and A sites;\n

\n

\n k. ribosome moves along mRNA to next codon/by three bases/in 5’ to 3’ direction;\n

\n

\n l. tRNA released from E/exit site;\n

\n

\n m. process/cycle repeats to elongate the polypeptide/until stop codon is reached;\n

\n

\n n. release of polypeptide and mRNA/disassembly of ribosome complex at\n \n stop codon\n \n ;\n

\n

\n \n Marks can be awarded in an annotated diagram\n \n .\n

\n

\n \n Accept UAA, UAG or UGA instead of stop codon in mpm or mpn but do not accept terminator sequence\n \n .\n

\n

\n \n Do not award mpk for the ribosome moving to the start codon in a 5’ to 3’ direction\n \n .\n

\n
\n", "Examiners report": "
\n

\n Explanations of translation were generally good, with many of the significant events included. Fewer candidates than in the past included unnecessary information about transcription. A common omission was the presence of a three-base (or nucleotide) anticodon on tRNA and a frequent small error was the idea that during initiation the first tRNA binds to the A site and then moves to the P site, rather than binding to the P site immediately.\n

\n
\n", "question_id": "20N.2.HL.TZ0.6C", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d1-2-protein-synthesis", "d1-2-5-translation-as-the-synthesis-of-polypeptides-from-mrna", "d1-2-10-stepwise-movement-of-the-ribosome-along-mrna-and-linkage-of-amino-acids-by-peptide-bonding-to-the-growing-polypeptide-chain", "d1-2-14-non-coding-sequences-in-dna-do-not-code-for-polypeptides" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Draw the symbol for individual X on the diagram.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n \n

\n
\n", "Examiners report": "
\n

\n The majority of candidates managed to draw the correct symbol for a heterozygous female in the correct place in (a). However, there were a few who thought that X was male. Just over a half correctly gave 50\n \n \n \n \n % for (b). There were a large number of very pleasing answers in (c) to explain why the gene is not sex linked including that if it were sex linked, then you could not have a heterozygous male, and if it were sex linked, the daughter would have been heterozygous. The explanations in (d ) were not of such a high quality, with a large proportion failing to note that it hinges on the coding for a different amino acid, thus producing a different protein. Students should be careful about restating the stem as the 'protein changes' did not score as that was in the stem.\n

\n
\n", "question_id": "22N.2.SL.TZ0.4A", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-2-inheritance", "d3-2-13-pedigree-charts-to-deduce-patterns-of-inheritance-of-genetic-disorders" ] }, { "Question": "
\n
\n

\n Which process is most responsible for movement of water from roots to leaves of a plant on a hot sunny day?\n

\n

\n A. Active translocation of mineral ions in roots\n

\n

\n B. Active transport of organic compounds into sieve tubes\n

\n

\n C. Raised hydrostatic pressure gradients\n

\n

\n D. Evaporation of water from mesophyll cell walls\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "19N.1A.SL.TZ0.32", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-2-transport", "b3-2-7-transport-of-water-from-roots-to-leaves-during-transpiration" ] }, { "Question": "
\n
\n

\n Outline the conclusions that can be drawn from the graph showing data for PCV and\n \n S. pneumoniae\n \n .\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n number of deaths (due to\n \n S. pneumoniae\n \n ) and percentage of children not vaccinated (with PCV) both fall (along the years)\n
    \n \n \n OR\n \n \n
    \n number of deaths (due to\n \n S. pneumoniae\n \n ) decreases while percentage of vaccinated children (with PCV) increases (along the years);\n
    2. \n
  2. \n \n positive\n \n correlation between number of deaths and percentage of children not vaccinated /\n
    \n \n \n OR\n \n \n
    \n \n negative\n \n correlation between number of deaths and percentage of children vaccinated / vaccination reduces the number of deaths;\n
    3. \n
  3. \n increased reduction in the number of deaths from 2010 onwards;\n
    4. \n
  4. \n still large number of deaths/large number of children unvaccinated in 2015;\n
    5. \n
\n

\n \n Comparative terms expected (do not award mp for just stating values).\n \n

\n

\n \n Mpb: do not allow “directly or inversely proportional”.\n \n

\n

\n \n Mpb: Do not just accept “positive correlation” or “negative correlation” without a clear indication of the variables being correlated\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ2.D", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-2-defence-against-disease", "c3-2-16-vaccines-and-immunization" ] }, { "Question": "
\n
\n

\n Compare and contrast the effects of the mouse alarm compound and stoat scent on the G1 neurons.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. both chemicals cause action potentials\n
\n \n \n OR\n \n \n
\n both chemicals respond in the majority of/five/most neurons ✔\n

\n

\n b. stoat scent causes a higher action potential/longer/bigger response than mouse alarm compound «in each neuron»\n
\n \n \n OR\n \n \n
\n neuron 2 reacts strongly to the stoat scent but has a minimal/no response to the mouse alarm compound ✔\n

\n
\n", "Examiners report": "
\n

\n Answers to e were encouraging as most were able to give both the similarity and the difference.\n

\n
\n", "question_id": "19M.2.SL.TZ2.E", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c2-2-neural-signalling" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Outline the process of protein denaturation.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n

\n a. change to conformation/shape/tertiary structure/3-D shape;\n
\n b. bonds within the protein/intramolecular bonds broken/changed;\n
\n c. pH and temperature (outside tolerated ranges) can cause denaturation;\n
\n d. vibrations/heat at high temperatures breaks bonds;\n
\n e. high pH/low pH/extreme pH alters ionization/charges (of amino acids and breaks ionic bonds);\n
\n f. protein cannot carry out its function\n
\n \n OR\n \n
\n \n active site\n \n of\n \n enzymes\n \n cannot bind substrates/catalyze reaction/no enzyme-substate complex;\n
\n g. permanent/irreversible change (usually)\n
\n \n OR\n \n
\n soluble proteins become insoluble/precipitate;\n

\n

\n \n Allow any mark points if made clearly on an annotated graph or diagram\n \n .\n

\n
\n", "Examiners report": "
\n

\n Most candidates knew that denaturation can be caused by excessive temperatures or extreme pH. Fewer candidates mentioned how bonds within a protein are broken by heat or kinetic energy. Even fewer explained how R-group ionization in acidic and basic amino acids can be altered by pH changes, breaking the ionic bonds within protein molecules that help to stabilize tertiary structure.\n

\n
\n", "question_id": "21N.2.HL.TZ0.8", "topics": [ "b-form-and-function", "c-interaction-and-interdependence" ], "subtopics": [ "b1-2-proteins", "b1-2-5-effect-of-ph-and-temperature-on-protein-structure", "c3-2-defence-against-disease", "c3-2-6-lymphocytes-as-cells-in-the-adaptive-immune-system-that-cooperate-to-produce-antibodies", "c3-2-8-activation-of-b-lymphocytes-by-helper-t-lymphocytes", "c3-2-10-immunity-as-a-consequence-of-retaining-memory-cells", "c1-1-enzymes-and-metabolism", "c1-1-15-competitive-inhibition-as-a-consequence-of-an-inhibitor-binding-reversibly-to-an-active-site", "c1-1-16-regulation-of-metabolic-pathways-by-feedback-inhibition", "c1-1-17-mechanism-based-inhibition-as-a-consequence-of-chemical-changes-to-the-active-site-caused-by-the-irreversible-binding-of-an-inhibitor" ] }, { "Question": "
\n
\n (a.ii)\n
\n
\n

\n Describe briefly how an artificial pacemaker works.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. a pacemaker contains a battery and pulse generator\n
\n \n \n OR\n \n \n
\n it is connected to the heart by wires/cables ✔\n

\n

\n b. it detects that the heart’s natural rhythm is incorrect ✔\n

\n

\n c. it sends electrical impulses to correct the heartbeat/it replaces sinoatrial node ✔\n

\n

\n d. provide a regular impulse/constant rhythm ✔\n

\n
\n", "Examiners report": "
\n

\n A majority of the candidates stated that the pacemaker sends electrical impulses or replaces the SA node, and they achieved 1 mark. Few were able to state that the pacemaker is connected to the heart by wires or that it monitors the heart rate itself.\n

\n
\n", "question_id": "19M.2.HL.TZ1.21A.II", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-2-transport", "b3-2-15-adaptations-of-the-mammalian-heart-for-delivering-pressurized-blood-to-the-arteries", "b3-2-16-stages-in-the-cardiac-cycle" ] }, { "Question": "
\n
\n

\n Which is a density-independent limiting factor for a kangaroo?\n

\n

\n
\n A.  A forest fire\n

\n

\n B.  Predation\n

\n

\n C.  Climate change\n

\n

\n D.  Eutrophication\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "None", "question_id": "SPM.1A.HL.TZ0.37", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c4-1-populations-and-communities", "c4-1-6-negative-feedback-control-of-population-size-by-density-dependent-factors", "c4-1-14-tests-for-interspecific-competition" ] }, { "Question": "
\n
\n

\n The diagram shows the human male reproductive system.\n

\n

\n \n

\n

\n [Source: logika600/Shutterstock]\n

\n

\n

\n

\n Which numbers indicate a gland providing fluid for sperm and a tube that transports sperm only?\n

\n

\n \n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "19M.1A.SL.TZ2.31", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-1-reproduction", "d3-1-4-anatomy-of-the-human-male-and-female-reproductive-systems" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Outline the functions of type I and type II pneumocytes.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n \n type I\n \n :\n

\n

\n a. carry out gas exchange\n
\n \n \n OR\n \n \n
\n diffusion of gases/CO\n \n 2\n \n /O\n \n 2\n \n ✔\n

\n

\n \n type II\n \n :\n

\n

\n b. secrete fluid/surfactant ✔\n

\n
\n", "Examiners report": "
\n

\n Weak knowledge of pneumocytes from many candidates and whilst many showed an understanding of gas exchange they failed to articulate it properly using the correct phrasing and terminology.\n

\n
\n", "question_id": "19M.2.SL.TZ1.4", "topics": [ "b-form-and-function" ], "subtopics": [ "b2-3-cell-specialization", "b2-3-8-adaptations-of-type-i-and-type-ii-pneumocytes-in-alveoli", "b3-1-gas-exchange", "b3-1-4-adaptations-of-mammalian-lungs-for-gas-exchange" ] }, { "Question": "
\n
\n (d.i)\n
\n
\n

\n Annotate the diagram to show a peptide bond between two amino acids.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n any annotation between a C=O and the next NH ✔\n

\n

\n \n e.g.\n \n

\n

\n \n \n \n

\n
\n", "Examiners report": "None", "question_id": "19N.2.SL.TZ0.2D.I", "topics": [ "b-form-and-function" ], "subtopics": [ "b1-2-proteins", "b1-2-2-condensation-reactions-forming-dipeptides-and-longer-chains-of-amino-acids" ] }, { "Question": "
\n
\n

\n Distinguish between the outcomes of a cell dividing either by mitosis or meiosis.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. mitosis produces two daughter cells while meiosis four ✔\n

\n

\n b. mitosis produces cells with same number of chromosomes (2n) while in meiosis they are halved (n) ✔\n

\n

\n c. mitosis produces body cells but meiosis produces gametes\n
\n \n \n OR\n \n \n
\n mitosis produces genetically identical cells but meiosis does not ✔\n

\n

\n \n Allow answers in a table\n \n .\n

\n

\n \n Reference to both has to be present for the\n \n mark.\n

\n
\n", "Examiners report": "
\n

\n There were several G2 comments about Q2a, as it could be said that several processes were occurring. Perhaps it should have been more specific. Two out of DNA replication, cell growth and duplication of organelles were expected for the two marks. A surprising number of candidates in all languages, confused 'processes' with 'phases' and stated that interphase consisted of G1, S and G2. Most managed to label prophase and anaphase correctly on the diagram as required in part (b). The answers to part (b) were generally clear, but some lost marks for not comparing the same point. For example 'Mitosis produces diploid cells, but meiosis produces gametes' did not score a mark. The mitotic index was well known.\n

\n
\n", "question_id": "21M.2.HL.TZ2.C", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-1-cell-and-nuclear-division", "d2-1-4-roles-of-mitosis-and-meiosis-in-eukaryotes" ] }, { "Question": "
\n
\n

\n The diagram shows compounds in the Krebs cycle labelled as X, Y and Z.\n

\n

\n \n

\n

\n [Source: © International Baccalaureate Organization 2019]\n

\n

\n How many carbon atoms are there in Y and in the acetyl group of acetyl CoA?\n

\n

\n \n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "
\n

\n This question was easy and discriminated very well.\n

\n
\n", "question_id": "19M.1A.HL.TZ2.15", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-2-cell-respiration", "c1-2-12-oxidation-and-decarboxylation-of-acetyl-groups-in-the-krebs-cycle-with-a-yield-of-atp-and-reduced-nad" ] }, { "Question": "
\n
\n

\n A nucleotide containing dideoxyribose is shown.\n

\n

\n \n

\n

\n

\n

\n What is the reason for the use of dideoxyribonucleotides to terminate sequences in base sequencing?\n

\n

\n A. Nucleotides cannot form 5′ to 3′ linkages with dideoxyribonucleotides.\n

\n

\n B. Nucleotides cannot form base pairs with dideoxyribonucleotides.\n

\n

\n C. Dideoxyribonucleotides cannot form hydrogen bonds with deoxyribose.\n

\n

\n D. Dideoxyribonucleotides do not have all four nitrogenous bases.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "
\n

\n This question discriminated well. In Topic 7.1 it states that candidates should be able to understand the use of nucleotides containing dideoxyribonucleic acid to stop DNA replication in preparation of samples for base sequencing. Some candidates believed dideoxynucleotides failed to form base pairs with nucleotides, showing lack of understanding of the sequencing process.\n

\n
\n", "question_id": "19M.1A.HL.TZ2.13", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d1-1-dna-replication", "d1-1-7-differences-between-replication-on-the-leading-strand-and-the-lagging-strand" ] }, { "Question": "
\n
\n (d.i)\n
\n
\n

\n Compare the data for plasma insulin levels before and after the study diet.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. both show same pattern of rise, level and then decrease / show same trend;\n

\n

\n b. both show same/similar levels of insulin (at all times) due to overlapping error bars;\n

\n

\n c. both rise for 30/45 minutes;\n

\n

\n \n Do not give credit for contrasts\n \n .\n

\n
\n", "Examiners report": "None", "question_id": "20N.1B.SL.TZ0.1D.I", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-3-homeostasis", "d3-3-3-regulation-of-blood-glucose-as-an-example-of-the-role-of-hormones-in-homeostasis" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Outline\n \n four\n \n different processes,\n \n with examples\n \n , that allow substances to pass through the plasma membrane.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n simple/passive diffusion\n \n down a concentration gradient\n \n /\n \n from high concentration to low concentration\n \n (without the use of channels/proteins); (\n \n e.g., CO\n \n 2\n \n / O\n \n 2\n \n / H\n \n 2\n \n O / steroid hormones\n \n )\n
    2. \n
  2. \n osmosis is the diffusion of\n \n water\n \n from an area of high water potential / low solute concentration to low water potential / high solute concentration;\n
    3. \n
  3. \n facilitated diffusion is passive transport/diffusion through a protein channel; (\n \n e.g., glucose\n \n )\n
    4. \n
  4. \n active transport requires energy/ATP to move the molecules through a protein channel (\n \n e.g., Na-K pump / sodium potassium pump\n \n )\n \n against a concentration gradient\n \n /\n \n from low solute concentration to high concentration\n \n ;\n
    5. \n
  5. \n endocytosis is the infolding of membranes to form a vesicle and take in a large molecule; (\n \n e.g., macrophages engulfing pathogens\n \n )\n
    6. \n
  6. \n exocytosis is the fusion of vesicles with membranes to release a large molecule; (\n \n e.g. neurotransmitters\n \n )\n
    7. \n
\n
\n", "Examiners report": "
\n

\n This question in section B was the second most commonly selected, but in performance, tended to do more poorly than the other questions.\n

\n

\n Most candidates could list the processes that allow passage across the plasma membrane, but many answers lacked some of the necessary elements, most commonly leaving out examples (e.g. an example for gradient).\n

\n
\n", "question_id": "22M.2.SL.TZ2.8A", "topics": [ "b-form-and-function" ], "subtopics": [ "b2-1-membranes-and-membrane-transport", "b2-1-3-simple-diffusion-across-membranes", "b2-1-4-integral-and-peripheral-proteins-in-membranes", "b2-1-5-movement-of-water-molecules-across-membranes-by-osmosis-and-the-role-of-aquaporins", "b2-1-6-channel-proteins-for-facilitated-diffusion", "b2-1-7-pump-proteins-for-active-transport", "b2-1-8-selectivity-in-membrane-permeability" ] }, { "Question": "
\n
\n

\n There were 79 progeny in Cross 4. Predict the expected results by completing the table.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n \n \n \n \n \n \n \n \n
\n 0\n \n 79\n \n 0.000/0\n
\n

\n \n All three parts of the answer must be correct for the mark to be awarded.\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ1.C", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-2-inheritance", "d3-2-5-effects-of-dominant-and-recessive-alleles-on-phenotype" ] }, { "Question": "
\n
\n

\n Cladistics and other evolutionary evidence suggest that mammals and birds have a more recent common ancestor than mammals and amphibians. Draw a cladogram to show the relationships between mammals, birds and amphibians.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n \n

\n

\n \n What is important is that the proper relationships are shown not the style used\n \n .\n

\n
\n", "Examiners report": "
\n

\n Candidates found it hard to express themselves without contradiction.\n

\n

\n Examiners accepted a wide variety of diagrams and orientations as long as the relationships among amphibians, birds and mammals were appropriate. Nevertheless, there was poor performance on this question. It was the question most often left blank in Section A.\n

\n
\n", "question_id": "21M.2.HL.TZ1.C", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a3-2-classification-and-cladistics-(hl-only)", "a3-2-7-analysing-cladograms" ] }, { "Question": "
\n
\n

\n The diagram shows the movement of ions that can occur across the membrane of a neuron.\n

\n

\n \n

\n

\n
\n From the diagram, what can be deduced about the movement of sodium ions?\n

\n

\n
\n A.  They are actively pumped out and some re-enter by facilitated diffusion.\n

\n

\n B.  They are actively pumped out and some re-enter by simple diffusion.\n

\n

\n C.  They diffuse out of the cell along with potassium ions.\n

\n

\n D.  There is a net movement of sodium ions into the cell.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "None", "question_id": "SPM.1A.HL.TZ0.15", "topics": [ "b-form-and-function", "c-interaction-and-interdependence" ], "subtopics": [ "c2-2-neural-signalling", "c2-2-9-propagation-of-an-action-potential-along-a-nerve-fibre/axon-as-a-result-of-local-currents", "b2-1-membranes-and-membrane-transport", "b2-1-15-sodium-potassium-pumps-as-an-example-of-exchange-transporters" ] }, { "Question": "
\n
\n

\n The image shows a transverse section through a collecting duct in a vertebrate kidney.\n

\n

\n \n

\n

\n [Source: Professor Peter Takizawa, Yale University]\n

\n

\n How is the movement of materials across the wall of the collecting duct affected by the release of ADH from the pituitary gland?\n

\n

\n A. There is increased movement of water in the direction of arrow I.\n

\n

\n B. There is increased movement of sodium in the direction of arrow I.\n

\n

\n C. There is increased movement of water in the direction of arrow II.\n

\n

\n D. There is increased movement of sodium in the direction of arrow II.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "None", "question_id": "19M.1A.HL.TZ1.39", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-3-homeostasis", "d3-3-10-osmoregulation-by-water-reabsorption-in-the-collecting-ducts" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Outline the processes occurring during interphase in the cell cycle.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n growth/increase in cell size;\n
    2. \n
  2. \n division of mitochondria/chloroplasts/production of more organelles/number of organelles doubled;\n
    3. \n
  3. \n replication of DNA/amount of DNA is doubled;\n
    4. \n
  4. \n transcription of genes/production of mRNA;\n
    5. \n
  5. \n protein synthesis;\n
    6. \n
  6. \n cell respiration/production of ATP;\n
    7. \n
\n

\n \n Allow organelles ‘replicated’ for mpb.\n \n

\n
\n", "Examiners report": "
\n

\n Many candidates included growth and DNA replication in their answers. Other processes such as protein synthesis and cell respiration were mentioned less often.\n

\n
\n", "question_id": "22N.2.HL.TZ0.6A", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-1-cell-and-nuclear-division", "d2-1-13-phases-of-the-cell-cycle", "d2-1-14-cell-growth-during-interphase" ] }, { "Question": "
\n
\n (a.i)\n
\n
\n

\n Based on their structure, the insect and bat wings are analogous. Outline what is meant by an analogous trait.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. analogous traits have a different evolutionary history/ancestry ✔\n

\n

\n b. different structures are adaptations for flight ✔\n

\n

\n c. selective pressure leads to a similar solution to the problem of flying ✔\n

\n
\n", "Examiners report": "
\n

\n Candidates found it hard to express themselves without contradiction.\n

\n

\n In both parts the key to successful answers was in using the organisms given in the example. Contradictions were thus avoided.\n

\n
\n", "question_id": "21M.2.SL.TZ1.5", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a4-1-evolution-and-speciation", "a4-1-5-convergent-evolution-as-the-origin-of-analogous-structures", "a4-1-4-evidence-for-evolution-from-homologous-structures", "a3-2-classification-and-cladistics-(hl-only)", "a3-2-2-difficulties-classifying-organisms-into-the-traditional-hierarchy-of-taxa", "a3-2-8-using-cladistics-to-investigate-whether-the-classification-of-groups-corresponds-to-evolutionary-relationships", "a3-2-7-analysing-cladograms" ] }, { "Question": "
\n
\n

\n State the relationship between BCH and brain mass of shrews.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n positive correlation/the greater the BCH the greater the brain mass;\n

\n

\n \n No mark for ‘positive relationship’ or for directly proportional\n \n

\n
\n", "Examiners report": "
\n

\n Most candidate described the relationship shown on the graph as a positive correlation. Some referred to it incorrectly as directly proportional, but that would be revealed by data points along a straight line on the graph. The term 'positive relationship' is vague and should be discouraged.\n

\n
\n", "question_id": "22N.2.HL.TZ0.A", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-1-integration-of-body-systems", "c3-1-4-the-brain-as-a-central-information-integration-organ" ] }, { "Question": "
\n
\n

\n What is a difference between aerobic respiration and anaerobic respiration in yeast?\n

\n

\n A. Anaerobic respiration requires enzymes, aerobic respiration does not.\n

\n

\n B. Anaerobic respiration requires glucose, aerobic respiration does not.\n

\n

\n C. Anaerobic respiration produces ethanol, aerobic respiration does not.\n

\n

\n D. Anaerobic respiration does not produce oxygen, aerobic respiration does.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "21M.1A.SL.TZ1.11", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-2-cell-respiration", "c1-2-10-anaerobic-cell-respiration-in-yeast-and-its-use-in-brewing-and-baking" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Describe\n \n two\n \n pieces of evidence that show that eukaryotic cells originated by endosymbiosis.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n mitochondria/chloroplasts have their own DNA;\n
    2. \n
  2. \n mitochondria can self-replicate/undergo a process like binary fission;\n
    3. \n
  3. \n mitochondria/chloroplasts have double membranes;\n
    4. \n
  4. \n mitochondria/chloroplasts have(\n \n 70s\n \n ) ribosomes;\n
    5. \n
  5. \n mitochondria/chloroplasts are sensitive to antibiotics;\n
    6. \n
  6. \n similar in size to bacteria\n
    7. \n
\n
\n", "Examiners report": "None", "question_id": "22N.2.SL.TZ0.2C", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a2-2-cell-structure", "a2-2-12-origin-of-eukaryotic-cells-by-endosymbiosis" ] }, { "Question": "
\n
\n

\n The anticodons of three tRNAs and the amino acids they carry are shown in the table.\n

\n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n
\n \n tRNA anticodon\n \n \n \n Amino acid\n \n
\n GCA\n \n Arginine\n
\n AAU\n \n Leucine\n
\n CAG\n \n Valine\n
\n

\n

\n

\n Which base sequence of an mRNA molecule would code for an arginine–leucine–valine tripeptide?\n
\n
\n

\n

\n A.  GCA AAU CAG\n

\n

\n B.  GCA AAT CAG\n

\n

\n C.  CGT TTA GTC\n

\n

\n D.  CGU UUA GUC\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "23M.1A.SL.TZ2.9", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d1-2-protein-synthesis", "d1-2-5-translation-as-the-synthesis-of-polypeptides-from-mrna" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Using the data in the stacked column graph, describe the features that characterize the B2 enterotype.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n nearly half is\n \n Bacteroides\n \n / more\n \n Bacteroides\n \n (than other enterotypes);\n
    2. \n
  2. \n few\n \n Prevotella\n \n /fewer\n \n Prevotella\n \n than in P and R\n
    \n \n \n OR\n \n \n
    \n less\n \n Faecalibacterium\n \n than other enterotypes\n
    \n \n \n OR\n \n \n
    \n \n Ruminococcus\n \n is the lowest in B2;\n
    3. \n
  3. \n only 40 % other taxa / fewer other taxa (than other enterotypes) / less overall diversity (of taxa);\n
    4. \n
\n

\n

\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ2.1A", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a2-2-cell-structure", "a2-2-5-prokaryote-cell-structure" ] }, { "Question": "
\n
\n (h)\n
\n
\n

\n Suggest how the graph would differ for a human during a long period of inactivity.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n more\n \n resorption\n \n than\n \n formation\n \n ;\n
    2. \n
  2. \n PICP/bone formation (always) lower (than in bears);\n
    3. \n
  3. \n ICTP/bone resorption (always) higher (than in bears);\n
    4. \n
  4. \n ICTP above PICP by a greater amount in humans (than in bears);\n
    5. \n
\n
\n", "Examiners report": "
\n

\n Candidates were expected to suggest a difference between the bears and humans in the concentration of one or both of the markers, that would result in loss of bone mass. A common fault was to predict changes in the markers during a period of inactivity in humans, but changes over time were not the issue — it was differences between humans and bears that were relevant to the question.\n

\n
\n", "question_id": "22M.2.SL.TZ1.1H", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-3-homeostasis", "d3-3-1-homeostasis-as-maintenance-of-the-internal-environment-of-an-organism", "d3-3-2-negative-feedback-loops-in-homeostasis" ] }, { "Question": "
\n
\n (a.ii)\n
\n
\n

\n The bird and bat wings share homologous bone structures whereas the insect wing does not. Outline the conclusion that can be drawn about the evolution of these wings, based on homologous structures.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n a. bird and bat share a more recent common ancestor (than the insect) ✔\n

\n

\n b. bird and bat are more closely related than insect and bat / insect and bird ✔\n

\n

\n c. bird and bat wings evolved from a common ancestor (by natural selection) ✔\n

\n
\n", "Examiners report": "
\n

\n Candidates found it hard to express themselves without contradiction.\n

\n

\n In both parts the key to successful answers was in using the organisms given in the example. Contradictions were thus avoided.\n

\n
\n", "question_id": "21M.2.SL.TZ1.5A.II", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a4-1-evolution-and-speciation", "a4-1-4-evidence-for-evolution-from-homologous-structures" ] }, { "Question": "
\n
\n

\n Which mechanism prevents polyspermy?\n

\n

\n A. Polar body formation\n

\n

\n B. The acrosome reaction\n

\n

\n C. Spermatogenesis\n

\n

\n D. The cortical reaction\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "22M.1A.HL.TZ1.37", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-1-reproduction", "d3-1-15-mechanisms-to-prevent-polyspermy" ] }, { "Question": "
\n
\n

\n What material is formed when organic matter is not fully decomposed in acidic waterlogged soils?\n

\n

\n A. Coal\n

\n

\n B. Hydrogen\n

\n

\n C. Oil\n

\n

\n D. Peat\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "19N.1A.SL.TZ0.20", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-3-climate-change", "d4-3-8-afforestation-forest-regeneration-and-restoration-of-peat-forming-wetlands-as-approaches-to-carbon-sequestration" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Outline the role of the sodium–potassium pump in maintaining the resting potential.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. sodium/potassium pump pumps sodium ions Na\n \n +\n \n out of axon and pumps potassium ions/K\n \n +\n \n in ✔\n

\n

\n b. requires energy/ATP/against concentration gradients/active transport ✔\n

\n

\n c. three sodium ions pumped out for every two potassium ions pumped in ✔\n

\n

\n d. results in charge difference between inside and outside where outside is positive relative to inside ✔\n

\n
\n", "Examiners report": "
\n

\n Strong students answered this question showing clear understanding of the process. However, most students showed poor understanding with errors: correct direction of ions being pumped not known; the direction of ions during repolarization was mixed up with resting state. Few wrote about the charge difference between inside and outside of the axon during the resting potential.\n

\n
\n", "question_id": "21M.2.HL.TZ1.4B", "topics": [ "b-form-and-function" ], "subtopics": [ "b2-1-membranes-and-membrane-transport", "b2-1-15-sodium-potassium-pumps-as-an-example-of-exchange-transporters" ] }, { "Question": "
\n
\n

\n Which characteristic of the subclavian vein distinguishes it from the subclavian artery?\n
\n
\n

\n

\n A.  Larger lumen\n

\n

\n B.  Absence of valves\n

\n

\n C.  Presence of pores\n

\n

\n D.  Two layers of muscle\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "None", "question_id": "23M.1A.SL.TZ1.20", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-2-transport", "b3-2-2-structure-of-arteries-and-veins", "b3-2-5-adaptations-of-veins-for-the-return-of-blood-to-the-heart" ] }, { "Question": "
\n
\n (f)\n
\n
\n

\n The mean daily food intake fluctuated from day to day. State the month that contains the day on which the mean intake of food was highest.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n May;\n

\n
\n", "Examiners report": "None", "question_id": "22M.2.SL.TZ1.1F", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-3-homeostasis", "d3-3-1-homeostasis-as-maintenance-of-the-internal-environment-of-an-organism", "d3-3-2-negative-feedback-loops-in-homeostasis" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Suggest\n \n one\n \n other factor that has to be kept constant in all the jars during the experiment.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n temperature/volume of indicator/identical jars/number of beads/size of beads / density of\n \n Chlorella\n \n / other reasonable answer\n

\n

\n \n Do not accept light/pH/humidity\n \n .\n

\n
\n", "Examiners report": "
\n

\n A very large number of candidates suggested a valid factor that should be kept constant.\n

\n
\n", "question_id": "20N.1B.SL.TZ0.3C", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-3-photosynthesis", "c1-3-7-techniques-for-varying-concentrations-of-carbon-dioxide-light-intensity-or-temperature-experimentally-to-investigate-the-effects-of-limiting-factors-on-the-rate-of-photosynthesis" ] }, { "Question": "
\n
\n (e)\n
\n
\n

\n Compare and contrast the results for winter and spring.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n \n Compare part of answer = similarity\n \n :\n

\n
    \n
  1. \n both have low BCH (compared with summer);\n
    \n
    \n \n Contrast part of answer\n \n :\n
    \n
    \n
    2. \n
  2. \n greater body mass in spring than winter;\n \n \n
    \n OR\n     \n     \n
    \n overall/mean/average BCH higher in spring than in winter;\n \n \n
    \n OR\n     \n     \n
    \n more variation\n \n in body mass\n \n in spring than winter;\n
    3. \n
\n

\n \n For the second alternative in mpb, the answer must not state simply that BCH is higher in spring as there is much overlap. Do not accept quoted figures without the similarity or difference being stated.\n \n

\n
\n", "Examiners report": "
\n

\n This was a 'compare and contrast' question, so similarities and differences were expected in the answer. There were plenty of choices for differences between winter and spring but only one acceptable similarity — that BCH was lower in both winter and spring than in summer. Some answers failed to discriminate between BCH and brain mass — the trends were not the same so these terms were not interchangeable. Some candidates gave a comparison and then repeated it as the converse statement — for example 'sample mass is higher in spring than winter and is lower in winter than spring'. Clearly this is not necessary.\n

\n
\n", "question_id": "22N.2.HL.TZ0.1E", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-1-integration-of-body-systems", "c3-1-4-the-brain-as-a-central-information-integration-organ" ] }, { "Question": "
\n
\n

\n Explain what information is needed to find the trophic level of pangolins.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n what (prey) it eats/feeds on/ stomach content;\n
    2. \n
  2. \n the trophic level of what (prey) it eats/feeds on/the trophic level of ants/termites;\n
    3. \n
  3. \n trophic level is the position an organism occupies in the food chain/web;\n
    4. \n
\n

\n \n Do not award points for indicating that predator information is needed.\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ2.II", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c4-2-transfers-of-energy-and-matter", "c4-2-10-classification-of-organisms-into-trophic-levels" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Discuss the relationship between atmospheric carbon dioxide concentration and global temperatures.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n

\n a. greenhouse effect keeps Earth warm ✔\n

\n

\n b. (over-time) earth’s temperature has fluctuated naturally ✔\n

\n

\n c. changes in human activities have led to increases in CO\n \n 2\n \n concentration ✔\n

\n

\n d. CO\n \n 2\n \n absorbs infrared/long wave radiation / trapping heat ✔\n

\n

\n e. increase in atmospheric CO\n \n 2\n \n (concentration) correlates with/causes increased global average temperature ✔\n

\n

\n f. use of fossil fuels increases atmospheric CO\n \n 2\n \n ✔\n

\n

\n g. deforestation removes a carbon sink / less CO\n \n 2\n \n absorbed ✔\n

\n

\n h. loss of polar ice causes less reflection of surface light/ more reradiation as heat contributing to (global) warming ✔\n

\n

\n i. CO\n \n 2\n \n is not the only greenhouse gas/ there are other greenhouse gases ✔\n

\n
\n", "Examiners report": "
\n

\n This question was attempted by approximately 56 % of candidates.\n

\n

\n This question was actually quite narrow as reflected in the number of marks it could earn. Some candidates understood which part of the global warming topic was being asked of them and stuck to the topic. Good applications to the carbon cycle were given. Strong responses avoided deviations into consequences and how humans should behave. Several misunderstandings surfaced. For example that CO\n \n 2\n \n was responsible for the breakdown of the ozone layer. Many seemed to tie ozone layer destruction and global warming information together in their explanation. Atmospheric carbon dioxide and the ozone layer were confused. Some thought that the ozone layer traps heat.\n

\n
\n", "question_id": "21M.2.SL.TZ1.7C", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-3-climate-change", "d4-3-1-anthropogenic-causes-of-climate-change" ] }, { "Question": "
\n
\n

\n Determine, with a reason, the nucleotide base that was marked with radioactivity.\n

\n

\n Base:\n

\n

\n Reason:\n

\n

\n

\n

\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. thymine / T ✔\n

\n

\n b. because only in DNA / not in RNA ✔\n

\n
\n", "Examiners report": "
\n

\n Few were able to name thymine as the base or give a reason it was used in the experiment.\n

\n
\n", "question_id": "19M.2.SL.TZ2.B", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a1-2-nucleic-acids", "a1-2-4-bases-in-each-nucleic-acid-that-form-the-basis-of-a-code" ] }, { "Question": "
\n
\n

\n The diagram shows structures involved in contraction of a sarcomere.\n

\n

\n \n

\n

\n [Source: Anatomy & Physiology by Lindsay M. Biga, Sierra Dawson, Amy Harwell, Robin Hopkins, Joel Kaufmann, Mike LeMaster, Philip Matern, Katie Morrison-Graham, Devon Quick & Jon Runyeon is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License (\n \n https://creativecommons.org/licenses/by-sa/4.0/\n \n ), except where otherwise noted.]\n

\n

\n

\n

\n What is X?\n

\n

\n A. Myosin filament\n

\n

\n B. Sarcomere\n

\n

\n C. Actin filament\n

\n

\n D. Myofibril\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "21M.1A.HL.TZ2.38", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-3-muscle-and-motility-(hl-only)", "b3-3-2-sliding-filament-model-of-muscle-contraction" ] }, { "Question": "
\n
\n (ii)\n
\n
\n

\n Global ecosystem modelling suggests that most of the change in LAI is due to increases in atmospheric carbon dioxide. Explain how rising atmospheric carbon dioxide (CO\n \n 2\n \n ) concentration could cause the observed change in LAI.\n

\n
\n
\n

\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n more\n \n photosynthesis\n \n (with higher carbon dioxide concentration);\n
    2. \n
  2. \n more plant growth/more (plant) biomass/more leaves/more plants;\n
    3. \n
\n

\n \n If the answer focuses on greenhouse effect or global warming, do not award mpa, but mpb can be awarded if one of the alternatives is included in the answer.\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ1.1DII", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-3-climate-change", "d4-3-1-anthropogenic-causes-of-climate-change" ] }, { "Question": "
\n
\n

\n Identify the species whose eggs are most affected by a high dose of neonicotinoid.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n \n B. lucorum\n \n ;\n

\n
\n", "Examiners report": "None", "question_id": "22M.2.HL.TZ2.C.I", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c2-2-neural-signalling", "c2-2-12-effects-of-exogenous-chemicals-on-synaptic-transmission" ] }, { "Question": "
\n
\n

\n Based on the graph, compare and contrast the progress of the epidemic in the suburbs and rural areas.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n a. start of epidemic/first cases in rural areas\n
\n \n \n OR\n \n \n
\n epidemic spread to suburbs later ✔\n

\n

\n b. higher maximum number of cases/greater increase in rural areas\n
\n \n \n OR\n \n \n
\n converse for suburbs ✔\n

\n

\n c. increase came earlier in rural areas «than suburbs»\n
\n \n \n OR\n \n \n
\n number of cases peaked earlier in rural areas\n
\n \n \n OR\n \n \n
\n more cases in rural areas «than suburbs» in 2014 ✔\n

\n

\n d. decrease came earlier in rural areas «than suburbs»\n
\n \n \n OR\n \n \n
\n decreasing in rural areas but not in suburbs in 2015/by end of study period\n
\n \n \n OR\n \n \n
\n more cases in suburbs than rural areas in 2015 ✔\n

\n

\n e. «large» fluctuations in both ✔\n

\n
\n", "Examiners report": "
\n

\n This was a timely question with Ebola epidemics again causing great problems in parts of Africa. Students were expected to have had some practice at analysing data relating to an epidemic because of this Skill in the programme: Analysis of epidemiological data related to vaccination programmes. It was assumed that candidates would understand terms such as ‘case’, ‘fatal case’, ‘infect’ and ‘treat’.\n

\n

\n The skill required in this question was picking significant trends out of data with a great deal of noise. Only one similarity was accepted – the large week-to-week fluctuation in number of cases. The differences between the rural areas and the suburbs were that Ebola epidemic started earlier in rural areas, rose to higher peaks and started declining earlier.\n

\n
\n", "question_id": "19M.2.SL.TZ1.B", "topics": [ "c-interaction-and-interdependence", "a-unity-and-diversity" ], "subtopics": [ "c3-2-defence-against-disease", "a2-3-viruses-(hl-only)" ] }, { "Question": "
\n
\n

\n Two cells have the following characteristics.\n

\n

\n \n

\n

\n Which deduction is supported by this information?\n

\n

\n A. Both cells are from plants.\n

\n

\n B. Cell I is more complex than cell II.\n

\n

\n C. Cell II is an animal cell.\n

\n

\n D. Cell I is prokaryotic.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "22M.1A.SL.TZ1.1", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a2-2-cell-structure", "a2-2-10-cell-types-and-cell-structures-viewed-in-light-and-electron-micrographs" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Explain whether these results fit the predicted Mendelian ratios for this cross.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n independent assortment predicts 1:1:1:1\n
    \n \n \n OR\n \n \n
    \n this (mendelian) ratio not seen / recombinants less frequent/parental types more frequent;\n
    2. \n
  2. \n suggests linkage\n
    \n \n \n OR\n \n \n
    \n small numbers so could be a result of differential survival;\n
    3. \n
\n
\n", "Examiners report": "None", "question_id": "SPM.2.HL.TZ0.7B", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-2-inheritance", "d3-2-17-punnett-grids-for-predicting-genotypic-and-phenotypic-ratios-in-dihybrid-crosses-involving-pairs-of-unlinked-autosomal-genes" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Each measurement was repeated several times. Explain the need for replicates of each treatment.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n more reliable results;\n
    2. \n
  2. \n to identify outliers/anomalous results\n
    \n \n \n OR\n
    \n     \n     \n reduce random errors;\n
    3. \n
  3. \n assess the variability of the data\n
    \n \n \n OR\n
    \n     \n     \n allows statistical tests/calculation of mean/standard deviation/correlation;\n
    4. \n
\n

\n \n Mp a: do not accept “accurate”.\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.1B.SL.TZ2.2C", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-1-enzymes-and-metabolism", "c1-1-8-effects-of-temperature-ph-and-substrate-concentration-on-the-rate-of-enzyme-activity" ] }, { "Question": "
\n
\n

\n Two reactions of the Krebs cycle are shown.\n

\n

\n \n

\n

\n What type of reactions are isocitrate and oxalosuccinate undergoing?\n

\n

\n \n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "
\n

\n Nearly all candidates knew that one type of reaction was decarboxylation and, from the answers offered, the other had to be either oxidation or reduction. More candidates than expected got this wrong and thought that removal of hydrogen from a Krebs cycle intermediate is reduction.\n

\n
\n", "question_id": "20N.1A.HL.TZ0.31", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-2-cell-respiration", "c1-2-12-oxidation-and-decarboxylation-of-acetyl-groups-in-the-krebs-cycle-with-a-yield-of-atp-and-reduced-nad" ] }, { "Question": "
\n
\n

\n How does auxin exert its effect on plant cells?\n

\n

\n A. Acts directly on the cell wall, causing expansion\n

\n

\n B. Binds to a receptor resulting in expression of genes\n

\n

\n C. Causes the vacuole to absorb water and expand the cell\n

\n

\n D. Causes the cell to undergo cell division\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "
\n

\n Only 42 % of candidates were able to pick out how auxin exerts its effects on plant cells and all the four answers attracted significant numbers of candidates, suggesting a widespread lack of knowledge of this aspect of plant physiology.\n

\n
\n", "question_id": "20N.1A.HL.TZ0.33", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-1-integration-of-body-systems", "c3-1-20-auxin-efflux-carriers-as-an-example-of-maintaining-concentration-gradients-of-phytohormones" ] }, { "Question": "
\n
\n

\n What is the correct arrangement for the components of one strand in a DNA molecule?\n

\n

\n \n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "21N.1A.SL.TZ0.10", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a1-2-nucleic-acids", "a1-2-3-sugar-phosphate-bonding-and-the-sugar-phosphate-“backbone”-of-dna-and-rna" ] }, { "Question": "
\n
\n

\n Testing the chromosomes of a girl with Turner syndrome produced the following karyogram.\n

\n

\n \n

\n

\n [Source: Turner’s syndrome karyotype 45,XO. This female lacks the second X chromosome present in the\n
\n normal karyotype. Symptoms include short stature, neck webbing, elbow deformity, widely spaced nipples with shield chest, primary amenorrhea, sexual infantilism and sterility. The ovaries are reduced to fibrous streaks. Also known as XO syndrome or ovarian short-stature syndrome. Credit: Wessex Reg. Genetics Centre. Attribution 4.0 International (CC BY 4.0).]\n

\n

\n

\n

\n The condition can result from non-disjunction occurring in anaphase I of meiosis in an egg cell. Two cells result from the first division, one of which would lead to Turner syndrome. Which chromosomes will be in the other cell (polar body) at the end of meiosis I?\n

\n

\n A. 44 autosomes and X\n

\n

\n B. 44 autosomes and XX\n

\n

\n C. 22 autosomes and X\n

\n

\n D. 22 autosomes and XX\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "
\n

\n This was also a question where the answer could only be reached by careful deduction. It was necessary to understand that the chromosome number is halved in the first division of meiosis, so the two daughter cells produced will normally have 22 autosomes and one sex chromosome each. The karyogram shows that Turner’s syndrome is due to having only one X chromosome and no Y. One of the two gametes that fuse to produce a cell with this karyotype must have no sex chromosome. This is due to non-disjunction, where both sex chromosomes pass into one cell, rather than segregating. The answer to the question is therefore D.\n

\n
\n", "question_id": "20N.1A.SL.TZ0.13", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-1-cell-and-nuclear-division", "d2-1-9-meiosis-as-a-reduction-division" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Describe the structure of the DNA molecule.\n

\n
\n
\n

\n [5]\n

\n
\n
\n", "Markscheme": "
\n

\n a. two stranded/double\n \n helix\n \n ✔\n

\n

\n b. antiparallel / strands running in opposite directions\n
\n \n \n OR\n \n \n
\n one strand organized 5’ to 3’ and the other 3’ to 5’ ✔\n

\n

\n c. sugar-phosphate backbone ✔\n

\n

\n d. each strand formed by chains of nucleotides ✔\n

\n

\n e. each nucleotide is formed by a phosphate, a deoxyribose and a base / annotated diagram of a nucleotide clearly indicated as a nucleotide ✔\n

\n

\n f. the bases are adenine, guanine, cytosine and thymine ✔\n

\n

\n g. strands held together by hydrogen bonds (between complementary base pairs)\n
\n \n \n OR\n \n \n
\n A pairs with T and C pairs with G ✔\n

\n

\n \n Both helix and two strands needed for mp a. Double helix is sufficient for the mark\n \n .\n

\n

\n \n Points can be awarded to annotated diagrams\n \n .\n

\n

\n \n For mp c, the explicit label sugar phosphate backbone is required\n \n .\n

\n

\n \n To award mp d from a diagram, at least three pairs of nucleotides should be shown\n \n .\n

\n

\n \n For mp e, the diagram would need to be labelled as a nucleotide\n \n .\n

\n

\n \n For mp e, expect deoxyribose not just sugar\n \n .\n

\n

\n \n The written names of the bases are required for mp f\n \n .\n

\n

\n \n Do not penalize twice for mp f and g for using letters\n \n .\n

\n

\n \n If they only ever use the symbols A,T,C and G they are ineligible for mp f. If however, they say A pairs with T and C pairs with G, then they would get mp g. If they wrote adenine pairs with thymine and cytosine pairs with guanine, then they would obtain both mp f and mp g\n \n .\n

\n
\n", "Examiners report": "
\n

\n A surprising number of students failed to discuss nucleotides explicitly.\n

\n
\n", "question_id": "21M.2.SL.TZ2.7A", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a1-2-nucleic-acids", "a1-2-6-dna-as-a-double-helix-made-of-two-antiparallel-strands-of-nucleotides-with-two-strands-linked-by-hydrogen-bonding-between-complementary-base-pairs" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Arginine and ornithine are in the same group of biochemicals. Identify this group.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n amino acids;\n

\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ2.2A", "topics": [ "b-form-and-function" ], "subtopics": [ "b1-2-proteins", "b1-2-1-generalized-structure-of-an-amino-acid" ] }, { "Question": "
\n
\n

\n How is involuntary peristalsis in the intestine directly controlled in humans?\n

\n

\n
\n A.  By the endocrine system\n

\n

\n B.  By the central nervous system (CNS)\n

\n

\n C.  By the sympathetic nervous system\n

\n

\n D.  By the enteric nervous system (ENS)\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "SPM.1A.HL.TZ0.28", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-1-integration-of-body-systems", "c3-1-16-control-of-peristalsis-in-the-digestive-system-by-the-central-nervous-system-and-enteric-nervous-system" ] }, { "Question": "
\n
\n (i)\n
\n
\n

\n Calculate the percentage increase in the mean concentration of osteocalcin from pre-hibernation to hibernation.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n 250 % (\n \n Allow 240 to 260 %\n \n )\n

\n
\n", "Examiners report": "
\n

\n A very small proportion of candidates correctly calculated the percentage difference. There were many different incorrect answers, with 350 % being the most popular, which is the amount of osteocalcin during hibernation as a percentage of the amount pre-hibernation.\n

\n
\n", "question_id": "22M.2.SL.TZ1.1I", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-3-homeostasis", "d3-3-1-homeostasis-as-maintenance-of-the-internal-environment-of-an-organism", "d3-3-2-negative-feedback-loops-in-homeostasis" ] }, { "Question": "
\n
\n (d)\n
\n
\n

\n State the season when shrew brain mass is greatest.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n Summer;\n

\n
\n", "Examiners report": "
\n

\n 90\n \n \n \n \n % of candidates correctly identified summer as the season when brain mass was greatest.\n

\n
\n", "question_id": "22N.2.HL.TZ0.1D", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-1-integration-of-body-systems", "c3-1-4-the-brain-as-a-central-information-integration-organ" ] }, { "Question": "
\n
\n

\n Many blood-feeding insects inject an anticoagulant into their host in order to prevent blood from clotting. Female mosquitoes of the genus\n \n Anopheles\n \n inject the anticoagulant anophelin, which inhibits the action of the enzyme thrombin. Which statement explains how anophelin prevents blood clotting?\n

\n

\n A. Platelets are no longer produced.\n

\n

\n B. Platelets cannot produce fibrin.\n

\n

\n C. Fibrinogen is not converted to fibrin.\n

\n

\n D. Prothrombin is not converted to thrombin.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "22M.1A.SL.TZ2.25", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-2-defence-against-disease", "c3-2-3-sealing-of-cuts-in-skin-by-blood-clotting" ] }, { "Question": "
\n
\n

\n Outline likely health benefits of universal PCV vaccination of children, other than reducing the incidence of ARI.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n less use of antibiotics;\n
    2. \n
  2. \n less antibiotic resistance (in pathogens) / antibiotics more successful at treating infectious/bacterial diseases;\n
    3. \n
  3. \n decrease in health care costs / less money spent on antibiotics;\n
    4. \n
  4. \n decreased mortality / protection of immune-deficient patients/non-vaccinated population/ achieve herd immunity;\n
    5. \n
\n

\n \n Since the question already states “other than reducing the incidence of ARI”, this reason should not be accepted.\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ2.J", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-2-defence-against-disease", "c3-2-16-vaccines-and-immunization" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Suggest a reason that researchers use BCH rather than brain mass to indicate brain size.\n

\n

\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n easier to measure/doesn’t require dissection/non-invasive / shrew not harmed/killed/more ethical;\n

\n

\n \n The mark can be awarded for one of these reasons even if it is not the first reason given in the answer\n \n .\n

\n
\n", "Examiners report": "
\n

\n Many candidates came up with unlikely reasons for using BCH as a measure, rather than that it was easier to measure and less harmful to the shrew. A common misconception was that brain mass was an inaccurate measure of brain size because brain density might be variable. It was surprising that so many candidates thought the height of the brain case would give a better measure of brain size, especially as the scatter graph showed that BCH is not directly proportional to brain mass.\n

\n
\n", "question_id": "22N.2.HL.TZ0.1C", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-1-integration-of-body-systems", "c3-1-4-the-brain-as-a-central-information-integration-organ" ] }, { "Question": "
\n
\n (a.ii)\n
\n
\n

\n Identify the molecule Z.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n glycerol /glycerin ✔\n

\n
\n", "Examiners report": "
\n

\n The diagram was generally confusing to candidates.\n

\n

\n This was generally missed.\n

\n

\n

\n
\n", "question_id": "21M.2.HL.TZ1.2A.II", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-3-photosynthesis", "c1-3-18-synthesis-of-carbohydrates-amino-acids-and-other-carbon-compounds-using-the-products-of-the-calvin-cycle-and-mineral-nutrients" ] }, { "Question": "
\n
\n

\n Despite continuous scientific research into the control of pathogens, it has proved very difficult to eliminate them. What is/are the reason(s) for this?\n

\n

\n I.   Development of antibiotic resistance in viruses\n

\n

\n II.  Development of antibiotic resistance in bacteria\n

\n

\n III. Mutations of pathogens\n

\n

\n A.  II only\n

\n

\n B.  I and II only\n

\n

\n C.  II and III only\n

\n

\n D.  I, II and III\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "22N.1A.SL.TZ0.27", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-2-defence-against-disease", "c3-2-1-pathogens-as-the-cause-of-infectious-diseases" ] }, { "Question": "
\n
\n

\n Outline the relationship between ambient daily temperature and food intake in March.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n food intake rises as daily temperature increases / positive correlation;\n
    2. \n
  2. \n the lowest food intake corresponds to the lowest temperature;\n
    3. \n
\n
\n", "Examiners report": "None", "question_id": "22M.2.SL.TZ1.G", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-3-homeostasis", "d3-3-1-homeostasis-as-maintenance-of-the-internal-environment-of-an-organism", "d3-3-2-negative-feedback-loops-in-homeostasis" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Outline the structures in\n \n M. tuberculosis\n \n that are not present in a human cell.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n a. cell wall ✔\n

\n

\n b. pili/flagella ✔\n

\n

\n c. 70S ribosomes ✔\n

\n

\n d. nucleoid / circular DNA\n
\n \n \n OR\n \n \n
\n naked DNA ✔\n

\n

\n e. plasmids ✔\n

\n

\n \n As candidates do not need to know the structure of Mycobacterium tuberculosis, all prokaryotic structures are accepted\n \n .\n

\n

\n \n Ignore references to membrane bound\n \n \n organelles\n \n .\n

\n
\n", "Examiners report": "
\n

\n (attempted by about 60 % of the cohort)\n

\n

\n Part (a) was a departure from the 'draw a prokaryote' type of question that has appeared numerous times. In general, it was well answered. There were some good diagrams as answers which clearly showed only the prokaryotic characteristics. Part (b) asked for an explanation of the production of antibodies. Many weaker students wrote at length about non-specific phagocytosis which was not credited. Weaker students confused antibodies and antigens and even talked about antibiotics. This question was designed to be answered by the Standard Level students using Standard Level material. Some tried to include HL material and became very confused. Part (c) was really a question about Darwin's theory of evolution set in context. Many of the answers were very Lamarckian with the antibiotic causing the mutation, instead of some bacteria already having resistance. Better students opened with comments and an explanation that antibiotics only kill bacteria.\n

\n
\n", "question_id": "21M.2.SL.TZ2.6A", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a2-2-cell-structure", "a2-2-5-prokaryote-cell-structure", "a2-2-10-cell-types-and-cell-structures-viewed-in-light-and-electron-micrographs" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Describe the organelles and other structures in animal cells that are visible in electron micrographs.\n

\n
\n
\n

\n [7]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n plasma membrane is thin layer forming outer boundary;\n
    2. \n
  2. \n cytoplasm fills space between membrane and nucleus;\n
    3. \n
  3. \n nucleus enclosed in nuclear membrane / nuclear membrane enclosing nucleus;\n
    4. \n
  4. \n chromosomes inside the nucleus/ visible during mitosis/ as rods (of condensed DNA);\n
    5. \n
  5. \n mitochondria with cristae/double membranes;\n
    6. \n
  6. \n (80S) ribosomes seen as dots free in cytoplasm/attached to rough ER;\n
    7. \n
  7. \n endoplasmic reticulum is a network interconnected tubes/ membranes /rough ER has ribosomes/ smooth ER does not;\n
    8. \n
  8. \n Golgi apparatus with stack of sacs/cisternae/curved or folded membranes/vesicles budding off;\n
    9. \n
  9. \n vesicles which are small membrane sacs;\n
    10. \n
  10. \n lysosome which contains enzymes/which is densely staining;\n
    11. \n
  11. \n any other organelle that would be visible correctly described;\n
    12. \n
\n

\n \n Allow any point made on an annotated diagram.\n \n

\n

\n \n Do not award any marks for just labels. Descriptions are needed.\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ2.7A", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a2-2-cell-structure", "a2-2-10-cell-types-and-cell-structures-viewed-in-light-and-electron-micrographs" ] }, { "Question": "
\n
\n

\n Which statement applies to transfers in an ecosystem?\n
\n
\n

\n

\n A.  Green plants can transfer heat energy from the sun into chemical energy.\n

\n

\n B.  The greatest loss of energy occurs towards the end of a food chain.\n

\n

\n C.  Production of carbon dioxide by respiration results in loss of biomass in a food chain.\n

\n

\n D.  Both energy and nutrients are finite and must be recycled.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "23M.1A.SL.TZ2.19", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c4-2-transfers-of-energy-and-matter", "c4-2-3-flow-of-chemical-energy-through-food-chains" ] }, { "Question": "
\n
\n (h)\n
\n
\n

\n Using only evidence from the data in Question 1, suggest\n \n two\n \n strategies for reducing obesity in countries where this health problem is most prevalent.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n use public education to encourage people to walk more/become more active;\n
    2. \n
  2. \n improve city design to improve walkability;\n
    3. \n
  3. \n reduce distances between homes / shops / workplaces / parks;\n
    4. \n
  4. \n more sidewalks / make it easier for pedestrians to cross roads / other specific measure;\n
    5. \n
\n

\n

\n

\n \n Do not accept answers that involve diet as that is beyond the scope of the data given.\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ1.1H", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-3-muscle-and-motility-(hl-only)", "b3-3-9-reasons-for-locomotion" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Outline the process of inhalation.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n

\n a. diaphragm contracts / moves downwards/flattens ✔\n

\n

\n b.\n \n external\n \n intercostal muscles contract ✔\n

\n

\n c. (muscle contraction) moves the rib cage upwards and outwards ✔\n

\n

\n d. increases volume of the thorax / lungs ✔\n

\n

\n e. difference in pressure/decreasing pressure causes air to flow into lungs / lungs inflate ✔\n

\n
\n", "Examiners report": "
\n

\n This question was attempted by approximately 56 % of candidates.\n

\n

\n Done well by many. Diaphragm contraction and external intercostal muscle contraction was commonly known along with the idea that the rib cage moves upwards and outwards. Further understanding of the consequent pressure changes in the thorax was not clear.\n

\n
\n", "question_id": "21M.2.SL.TZ1.7A", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-1-gas-exchange", "b3-1-5-ventilation-of-the-lungs" ] }, { "Question": "
\n
\n

\n The images of the radiolarian, a single-celled marine organism, were produced using a light microscope (left) and a scanning electron microscope (right).\n

\n

\n \n

\n

\n [Source: Munir,S.;Sun,J.;Morton, S.L. The First Record and Classification of Planktonic Radiolarian\n
\n (\n \n Phylum Retaria\n \n ) and Phaeodarian (\n \n Phylum Cercozoa\n \n ) in the Eastern Indian Ocean.\n \n Biology\n \n 2021, 10, 202.\n
\n \n https://doi.org/10.3390/\n \n \n biology10030202\n \n Copyright: © 2021 by the authors. This article is an open access\n
\n article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (\n \n https://creativecommons.org/licenses/by/4.0/\n \n ).]\n

\n

\n

\n

\n What is a reason for the difference in quality of these images?\n

\n

\n A. Light cannot pass through the specimen.\n

\n

\n B. Higher magnification can be achieved with the electron microscope.\n

\n

\n C. The resolution of the electron microscope is higher.\n

\n

\n D. Samples are stained with methylene blue when viewed with the light microscope.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "
\n

\n The majority of students answered this correctly. The most common mistake was to answer that a higher magnification can be achieved with the electron microscope. This could not be determined from the images as both were at the same scale.\n

\n
\n", "question_id": "22M.1A.SL.TZ2.2", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a2-2-cell-structure", "a2-2-3-developments-in-microscopy" ] }, { "Question": "
\n
\n

\n State the type of reaction that removes water while linking amino acids together to form polypeptides.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n condensation ✔\n

\n

\n \n Do not accept anabolism alone\n \n .\n

\n
\n", "Examiners report": "None", "question_id": "19N.2.SL.TZ0.D.II", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d1-2-protein-synthesis", "d1-2-10-stepwise-movement-of-the-ribosome-along-mrna-and-linkage-of-amino-acids-by-peptide-bonding-to-the-growing-polypeptide-chain" ] }, { "Question": "
\n
\n

\n What is the difference between the DNA of adult identical (monozygotic) twins?\n

\n

\n A. Order of genes\n

\n

\n B. Sequence of nucleotides\n

\n

\n C. Methylation pattern\n

\n

\n D. Ratio of complementary base pairs\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "21N.1A.HL.TZ1.27", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-2-gene-expression-[hl-only]", "d2-2-10-monozygotic-twin-studies" ] }, { "Question": "
\n
\n

\n The diagram shows the three-dimensional structure of tRNA.\n

\n

\n \n

\n

\n [Source: Structure reproduced with the kind permission of N.R. Voss.]\n

\n

\n

\n

\n What can attach to the region marked X?\n

\n

\n A. mRNA\n

\n

\n B. An amino acid\n

\n

\n C. An anticodon\n

\n

\n D. The P site of the ribosome\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "20N.1A.SL.TZ0.28", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d1-2-protein-synthesis", "d1-2-7-complementary-base-pairing-between-trna-and-mrna" ] }, { "Question": "
\n
\n (i)\n
\n
\n

\n Identify the relationship between migration distance and plumage colouration.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n the longer the migration, the lighter the colour /\n \n vice versa\n \n ;\n
    2. \n
  2. \n too much variation so it is not possible to see a relationship;\n
    3. \n
\n
\n", "Examiners report": "None", "question_id": "23M.1A.SL.TZ2.8AI", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-1-natural-selection", "d4-1-7-sexual-selection-as-a-selection-pressure-in-animal-species" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n The amount of food passing into food chains can be affected by the rate of photosynthesis. Explain the effect of\n \n one\n \n limiting factor on photosynthesis.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n a. the rate of reaction will be limited by the limiting factor that is nearest to its minimum value;\n

\n

\n \n temperature\n \n :\n
\n b. enzymes that control photosynthesis are influenced by temperature;\n
\n c. as temperature increases, reaction rate will increase;\n
\n d. above a certain temperature, the rate of photosynthesis will decrease;\n
\n e. (where temperature is limiting) essential enzymes begin to denature/not working to optimum;\n

\n

\n \n light intensity\n \n :\n
\n f. light is source of energy / converted into chemical energy;\n
\n g. as light intensity increases reaction rate will increase;\n
\n h. at a certain light intensity, rate of photosynthesis will plateau;\n
\n i. another factor becomes limiting;\n

\n

\n \n CO\n \n 2\n \n concentration\n \n :\n
\n j. CO\n \n 2\n \n is fixed to form organic molecules;\n
\n k. as CO\n \n 2\n \n concentration increases, reaction rate will increase;\n
\n l. at a certain concentration of CO\n \n 2\n \n , rate of photosynthesis will plateau;\n
\n m. another factor becomes limiting;\n

\n

\n \n Accept answers using an\n \n annotated\n \n graph to explain\n \n

\n

\n \n Only accept the first factor described\n \n

\n

\n \n Do not accept pH as a limiting factor\n \n

\n
\n", "Examiners report": "
\n

\n In 3c, most knew that temperature/CO\n \n 2\n \n concentration/light affect photosynthesis but could not explain the idea of acting as a limiting factor. Only the better students gained all 3 marks.\n

\n
\n", "question_id": "21N.2.SL.TZ0.3C", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-3-photosynthesis", "c1-3-7-techniques-for-varying-concentrations-of-carbon-dioxide-light-intensity-or-temperature-experimentally-to-investigate-the-effects-of-limiting-factors-on-the-rate-of-photosynthesis" ] }, { "Question": "
\n
\n (b.i)\n
\n
\n

\n Outline the difference in methylation pattern between tumorous and normal tissue samples.\n

\n

\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. «overall» much more methylation in the colon tumour samples than normal ✔\n

\n

\n b. tumour and normal samples the markers 258 and 269 similar degree of methylation/fewer differences ✔\n

\n

\n c. degree of methylation on certain markers may correlate with the presence of cancer / correct example of a marker only methylated in tumour cells\n \n eg\n \n marker 32 ✔\n

\n
\n", "Examiners report": "
\n

\n Many students detected that greater degrees of methylation in tumour samples. Fewer could accurately summarize the specific differences between methylation in the two samples.\n

\n
\n", "question_id": "19M.2.HL.TZ2.2B.I", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-2-gene-expression-[hl-only]", "d2-2-6-methylation-of-the-promoter-and-histones-in-nucleosomes-as-examples-of-epigenetic-tags", "d2-2-7-epigenetic-inheritance-through-heritable-changes-to-gene-expression" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Describe how toxins such as DDT might concentrate in the bodies of birds.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n some toxins/DDT are persistent/degrade slowly (once released into the environment);\n
    2. \n
  2. \n (some toxins/DDT) enter the food chain through producers/lower trophic levels;\n
    3. \n
  3. \n (some toxins/DDT) are passed on to higher trophic levels in the food chain;\n
    4. \n
  4. \n (they are) difficult to excrete / are not excreted;\n
    5. \n
  5. \n (they) accumulate in fatty tissues of animals;\n
    6. \n
  6. \n higher trophic levels/top consumers have higher/the highest concentration of pesticides in their bodies;\n
    7. \n
  7. \n they bioaccumulate/biomagnify;\n
    8. \n
\n
\n", "Examiners report": "None", "question_id": "SPM.2.HL.TZ0.9", "topics": [ "d-continuity-and-change", "c-interaction-and-interdependence" ], "subtopics": [ "d4-2-stability-and-change", "d4-2-9-biomagnification-of-pollutants-in-natural-ecosystems", "c1-1-enzymes-and-metabolism", "c1-1-14-allosteric-sites-and-non-competitive-inhibition", "c1-2-cell-respiration", "c1-2-16-role-of-oxygen-as-terminal-electron-acceptor-in-aerobic-cell-respiration" ] }, { "Question": "
\n
\n

\n The image shows tetrads in the anther of a lily. A tetrad is a group of four cells, produced when one mother cell divides by meiosis. The tetrad indicated by the arrow contains a total of 48 chromosomes.\n

\n

\n \n

\n

\n [Source: [Tetrad], 2012. [image online] Available at: https://www.iasprr.org/old/iasprr-pix/lily/tetrad.jpg [accessed: 4 April 2019]. Photo courtesy of Professor Scott D. Russell.]\n

\n

\n

\n

\n What is the diploid number of the plant?\n

\n

\n A. 12\n

\n

\n B. 24\n

\n

\n C. 48\n

\n

\n D. 96\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "21M.1A.SL.TZ2.12", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-1-cell-and-nuclear-division", "d2-1-9-meiosis-as-a-reduction-division" ] }, { "Question": "
\n
\n

\n State the relationship between sloth body temperature and ambient temperature.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n body temperature increases with ambient temperature / positive correlation;\n

\n

\n \n Since direct can be either –/+, no credit for direct correlation alone.\n \n

\n
\n", "Examiners report": "None", "question_id": "22M.2.SL.TZ1.A.I", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-3-homeostasis", "d3-3-1-homeostasis-as-maintenance-of-the-internal-environment-of-an-organism", "d3-3-2-negative-feedback-loops-in-homeostasis" ] }, { "Question": "
\n
\n (a.ii)\n
\n
\n

\n Identify the country with the largest number of deaths.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n Liberia ✔\n

\n
\n", "Examiners report": "None", "question_id": "19M.2.HL.TZ1.1A.II", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a2-3-viruses-(hl-only)" ] }, { "Question": "
\n
\n

\n Under certain conditions, living organisms on Earth produce and release methane. What favours the production of methane?\n

\n

\n A. Forest fires\n

\n

\n B. High light intensity\n

\n

\n C. Anaerobic conditions\n

\n

\n D. Dry conditions\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "20N.1A.SL.TZ0.18", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-3-climate-change", "d4-3-2-positive-feedback-cycles-in-global-warming" ] }, { "Question": "
\n
\n

\n What are the type of reaction and the product(s) shown in this reaction?\n

\n

\n \n

\n

\n \n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "20N.1A.SL.TZ0.6", "topics": [ "b-form-and-function" ], "subtopics": [ "b1-1-carbohydrates-and-lipids", "b1-1-2-production-of-macromolecules-by-condensation-reactions-that-link-monomers-to-form-a-polymer" ] }, { "Question": "
\n
\n

\n State the cumulative increase in the mass of control colonies at 7 weeks.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n 230 g;\n

\n

\n \n Accept range of 215 – 265. This takes into account the beginning and end of week 7.\n \n
\n \n Unit required.\n \n

\n
\n", "Examiners report": "None", "question_id": "22M.2.HL.TZ2.A.II", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c2-2-neural-signalling", "c2-2-12-effects-of-exogenous-chemicals-on-synaptic-transmission" ] }, { "Question": "
\n
\n

\n Identify the process Y and state the name of the organelle where it takes place in a plant cell.\n

\n

\n Process Y:\n

\n

\n Name of the organelle:\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n process Y: photosynthesis ✔\n

\n

\n organelle: chloroplast ✔\n

\n

\n \n Both needed\n \n .\n

\n
\n", "Examiners report": "
\n

\n The diagram was generally confusing to candidates.\n

\n

\n This was generally answered correctly.\n

\n
\n", "question_id": "21M.2.SL.TZ1.A.I", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c4-2-transfers-of-energy-and-matter", "c4-2-18-ecosystems-as-carbon-sinks-and-carbon-sources" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n State processes occurring during interphase.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. DNA replication ✔\n

\n

\n b. cell growth ✔\n

\n

\n c. duplication of organelles/mitochondria / production of microtubules/protein synthesis ✔\n

\n

\n \n Accept first two answers only\n \n .\n

\n
\n", "Examiners report": "
\n

\n There were several G2 comments about Q2a, as it could be said that several processes were occurring. Perhaps it should have been more specific. Two out of DNA replication, cell growth and duplication of organelles were expected for the two marks. A surprising number of candidates in all languages, confused 'processes' with 'phases' and stated that interphase consisted of G1, S and G2. Most managed to label prophase and anaphase correctly on the diagram as required in part (b). The answers to part (b) were generally clear, but some lost marks for not comparing the same point. For example 'Mitosis produces diploid cells, but meiosis produces gametes' did not score a mark. The mitotic index was well known.\n

\n
\n", "question_id": "21M.2.SL.TZ2.2", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-1-cell-and-nuclear-division", "d2-1-13-phases-of-the-cell-cycle", "d2-1-7-phases-of-mitosis", "d2-1-4-roles-of-mitosis-and-meiosis-in-eukaryotes", "d2-1-17-differences-between-tumours-in-rates-of-cell-division-and-growth-and-in-the-capacity-for-metastasis-and-invasion-of-neighbouring-tissue" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Describe the genetic and hormonal control of male sexual characteristics in a human.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n a. male if (X and) Y chromosomes present ✔\n

\n

\n b. gene on Y chromosome/SRY promotes development of testes (from embryonic gonads) ✔\n

\n

\n c. testes secrete testosterone ✔\n

\n

\n d. testosterone stimulates sperm production/spermatogenesis ✔\n

\n

\n e. testosterone stimulates development (in fetus) of male genitals/primary sexual characteristics ✔\n

\n

\n f. testosterone stimulates development of male\n \n secondary\n \n sexual characteristics\n
\n \n \n OR\n \n \n
\n testosterone causes changes to become adult male during puberty ✔\n

\n

\n \n Allow first alternative for mpf if two secondary sexual characteristics are named instead of the general term ‘secondary sexual characteristics’\n \n .\n

\n
\n", "Examiners report": "
\n

\n There were some excellent answers that easily scored the three marks, but also many poorer ones, sometimes with no mention of genetic control or testosterone.\n

\n
\n", "question_id": "21M.2.HL.TZ1.6", "topics": [ "d-continuity-and-change", "c-interaction-and-interdependence" ], "subtopics": [ "d3-1-reproduction", "d3-1-3-differences-between-male-and-female-sexes-in-sexual-reproduction", "c3-1-integration-of-body-systems", "c3-1-21-promotion-of-cell-growth-by-auxin", "c3-1-22-interactions-between-auxin-and-cytokinin-as-a-means-of-regulating-root-and-shoot-growth", "c3-1-3-integration-of-organs-in-animal-bodies-by-hormonal-and-nervous-signalling-and-by-transport-of-materials-and-energy" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n State the\n \n mode\n \n for the number of steps per day in Japan and USA, rounding your answers up or down to the nearest 1000 steps.\n
\n
\n

\n

\n Japan: ..................................................................................................\n

\n

\n
\n USA:  ....................................................................................................\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n Japan: 6000\n \n and\n \n USA: 4000;\n \n (both needed)\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ1.1A", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-3-muscle-and-motility-(hl-only)", "b3-3-9-reasons-for-locomotion" ] }, { "Question": "
\n
\n

\n What can lead to the emergence of analogous structures?\n

\n

\n
\n A.  Divergent evolution from a recent common ancestor\n

\n

\n B.  Convergent evolution of unrelated species\n

\n

\n C.  Splits in the fundamental niche of a species\n

\n

\n D.  Splits in the realized niche of a species\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "SPM.1A.SL.TZ0.23", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a4-1-evolution-and-speciation", "a4-1-5-convergent-evolution-as-the-origin-of-analogous-structures" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Draw a labelled diagram to show the structure of a single nucleotide of RNA.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n ribose drawn as a pentagon and labelled;\n
    2. \n
  2. \n base linked correctly (to C1) of ribose and labelled;\n
    3. \n
  3. \n phosphate linked correctly (to C5) of ribose and labelled;\n
    4. \n
\n

\n \n

\n

\n \n Award\n \n [2 max]\n \n if more than one nucleotide drawn.\n \n

\n

\n \n “Sugar” alone is insufficient.\n \n

\n
\n", "Examiners report": "
\n

\n Occasionally, deoxyribose was seen rather ribose; sometimes more than one nucleotide was shown limiting maximum marks.\n

\n
\n", "question_id": "22M.2.SL.TZ1.7A", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a1-2-nucleic-acids", "a1-2-5-rna-as-a-polymer-formed-by-condensation-of-nucleotide-monomers" ] }, { "Question": "
\n
\n

\n State\n \n one\n \n feature of the sloth that would indicate it is a mammal.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n mammals have mammary glands;\n
    2. \n
  2. \n produce milk for their offspring;\n
    3. \n
  3. \n bodies covered in hair/fur;\n
    4. \n
\n

\n \n Characteristic must be exclusive to mammals.\n \n

\n

\n \n If more than one answer, use the first one given.\n \n

\n
\n", "Examiners report": "
\n

\n Have hair/fur or feed young with milk were the best answers. Many students wrote \"give birth to live young;\" While this is true of most mammals, monotremes lay eggs. Furthermore, some other animals give birth to live young (ovoviviparous) such as some reptiles and some groups of fish. We credited only characteristics exclusive to all mammals.\n

\n
\n", "question_id": "22M.2.SL.TZ1.I", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-3-homeostasis", "d3-3-1-homeostasis-as-maintenance-of-the-internal-environment-of-an-organism", "d3-3-2-negative-feedback-loops-in-homeostasis" ] }, { "Question": "
\n
\n

\n Using a Punnett square, determine how a smooth-haired puppy could be produced in the offspring.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n WK Wk wK and wk for male gamete genotypes and wk for female;\n

\n

\n wwKk shown in Punnett square and identified as smooth;\n

\n

\n \n

\n
\n", "Examiners report": "
\n

\n There were some complaints from teachers that epistasis is not included in the program. It was not expected that candidates would have studied ratios derived from interaction between genes and instead it was intended that they work out the pattern of inheritance themselves from the information provided. About a third of candidates successfully did this. The Punnett squares drawn up by other candidates often revealed fundamental misunderstandings of dihybrid inheritance.\n

\n
\n", "question_id": "20N.2.SL.TZ0.B", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-2-inheritance", "d3-2-10-incomplete-dominance-and-codominance" ] }, { "Question": "
\n
\n (b.i)\n
\n
\n

\n Define mutation.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n change in genetic makeup/DNA/nucleotide/base sequence\n

\n
\n", "Examiners report": "None", "question_id": "20N.2.SL.TZ0.4B.I", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d1-3-mutations-and-gene-editing", "d1-3-4-causes-of-gene-mutation" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n State the approximate value of the membrane potential at X.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n 0 mV; (\n \n accept answers in the range of – 10 mV to +10 mV\n \n ) (\n \n Units required\n \n )\n

\n
\n", "Examiners report": "
\n

\n There were some truly brilliant answers to Question 5. However, the weakest answers in the examination were also found here. Of the questions, these were the most commonly left blank.\n

\n

\n Candidates were often unable to approximate X. Missing units resulted in no marks awarded.\n

\n
\n", "question_id": "22M.2.SL.TZ1.5", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c2-2-neural-signalling", "c2-2-10-oscilloscope-traces-showing-resting-potentials-and-action-potentials", "c2-2-3-nerve-impulses-as-action-potentials-that-are-propagated-along-nerve-fibres", "c2-2-8-depolarization-and-repolarization-during-action-potentials", "c2-2-6-release-of-neurotransmitters-from-a-presynaptic-membrane" ] }, { "Question": "
\n
\n

\n A pregnant woman had fetal cells removed by chorionic villus sampling and tested. The following karyogram was produced.\n

\n

\n \n

\n

\n [Source: Mediscan / Alamy Stock Photo]\n

\n

\n

\n

\n What does this show?\n

\n

\n A. The child is female with Down syndrome.\n

\n

\n B. The child is female without Down syndrome.\n

\n

\n C. The child is male with Down syndrome.\n

\n

\n D. The child is male without Down syndrome.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "19N.1A.SL.TZ0.14", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a3-1-diversity-of-organisms", "a3-1-7-karyotyping-and-karyograms" ] }, { "Question": "
\n
\n (i)\n
\n
\n

\n With reference to the diagram, explain how water in sweat evaporates.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n heat increases molecular motion/vibration;\n
    2. \n
  2. \n (hydrogen) bonds break/bonds between water molecules break;\n
    3. \n
  3. \n water evaporation is separation of water molecules/water changes from liquid to gas/vapour;\n
    4. \n
  4. \n heat removed from skin surface/body;\n
    5. \n
\n

\n

\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ1.4BI", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-3-homeostasis", "d3-3-6-thermoregulation-mechanisms-in-humans" ] }, { "Question": "
\n
\n

\n Some vaccinations, such as the smallpox vaccine, provide lifelong immunity against the disease. For others, such as tetanus, this immunity lasts for a shorter period of time. Why is a tetanus booster vaccination recommended every 10 years?\n

\n

\n A.  Antibodies that formed after the first vaccination persist in the blood for up to 10 years.\n

\n

\n B.  Memory cells are not produced after the first vaccination.\n

\n

\n C.  Only non-specific immunity is stimulated after the first vaccination.\n

\n

\n D.  Memory cells gradually decline over 10 years.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "22N.1A.HL.TZ0.23", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-2-defence-against-disease", "c3-2-10-immunity-as-a-consequence-of-retaining-memory-cells", "c3-2-16-vaccines-and-immunization" ] }, { "Question": "
\n
\n (a.ii)\n
\n
\n

\n Calculate the length of the entire cell labelled Y, showing your working.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n 50 μm = 27/28/29 mm,\n \n Y\n \n = 8/9/10 mm\n
\n \n \n OR\n \n \n
\n 50 x 9 /27\n
\n \n \n OR\n \n \n
\n 16.7 μm (accept answers in the range of 14.8 μm to 17.2 μm)\n

\n

\n \n Award\n \n [1]\n \n for correct ratios not precise measurements in the work or\n \n [1]\n \n for correct answer with correct unit\n \n .\n

\n
\n", "Examiners report": "
\n

\n Most answers were correct, but some calculations were difficult to follow; some errors in unit conversions led to incorrect decimal places.\n

\n
\n", "question_id": "22M.2.SL.TZ2.2A.II", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a2-2-cell-structure", "a2-2-2-microscopy-skills" ] }, { "Question": "
\n
\n (d)\n
\n
\n

\n The concentration of urea in blood plasma is typically about 30 mg per 100 ml. In urine it can be as high as 1800 mg per 100 ml. Explain how this increase in concentration is achieved.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n urea is toxic/ a (excretory) waste product removed from the body/ blood (plasma) by the kidneys/in the urine (to be excreted in the urine);\n
    2. \n
  2. \n urea filtered out from blood in glomerulus/Bowman’s capsule;\n
    3. \n
  3. \n water reabsorbed from filtrate (by osmosis);\n
    4. \n
  4. \n in proximal convoluted tubule/\n \n descending\n \n loop of Henle/collecting duct;\n
    5. \n
  5. \n loop of Henle maintains hypertonic conditions in the medulla;\n
    6. \n
  6. \n little/no urea reabsorbed from filtrate;\n
    7. \n
\n

\n

\n
\n", "Examiners report": "None", "question_id": "23M.2.HL.TZ2.2D", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-3-homeostasis", "d3-3-7-role-of-the-kidney-in-osmoregulation-and-excretion" ] }, { "Question": "
\n
\n (d.i)\n
\n
\n

\n Identify with a reason the city where the plants were more insulated from freezing temperatures.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n Montreal because it has the lowest number of days below 0 °C without snow cover;\n

\n

\n \n Do not award the mark for Montreal if the reason is not given\n \n .\n

\n
\n", "Examiners report": "
\n

\n 90 % of candidates identified Montreal as the city where plants were more insulated because it was where there were fewer freezing days without snow cover.\n

\n
\n", "question_id": "20N.2.SL.TZ0.1D.I", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-2-stability-and-change", "d4-2-4-use-of-a-model-to-investigate-the-effect-of-variables-on-ecosystem-stability" ] }, { "Question": "
\n
\n

\n A female is overweight, feels cold and tired, and often fails to ovulate during the menstrual cycle. Which two hormones are probably secreted at insufficient levels?\n

\n

\n A. Estrogen and FSH\n

\n

\n B. LH and thyroxin\n

\n

\n C. Insulin and glucagon\n

\n

\n D. Epinephrine and leptin\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "20N.1A.SL.TZ0.30", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-1-reproduction", "d3-1-5-changes-during-the-ovarian-and-uterine-cycles-and-their-hormonal-regulation" ] }, { "Question": "
\n
\n (g)\n
\n
\n

\n State the activity and season that occupied the greatest mean percentage of observation time.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n \n rest\n \n ing in\n \n spring\n \n ;\n

\n
\n", "Examiners report": "
\n

\n 80\n \n \n \n \n % of candidates identified the season and activity correctly.\n

\n
\n", "question_id": "22N.2.HL.TZ0.1G", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-1-integration-of-body-systems", "c3-1-4-the-brain-as-a-central-information-integration-organ" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Explain gene linkage and its effects on inheritance.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. located on the same chromosome;\n
\n b. genes/gene loci close together (on the same chromosome);\n
\n c. do not follow (the law of) independent assortment;\n
\n d. more chance of recombination if genes are further apart;\n
\n e. inherited together unless crossing over/recombination occurs;\n
\n f. ratios of offspring in dihybrid crosses are different from expected/non-Mendelian\n
\n \n OR\n \n
\n more offspring with parental phenotype combinations than expected;\n

\n
\n", "Examiners report": "
\n

\n The was some confusion between autosomal and sex linkage. Candidates tended either to have a secure understanding of the mechanisms at work in autosomal gene linkage, or none. This question and (d) correlated closely with candidates’ overall score on the paper, so distinguished particularly effectively between stronger and weaker candidates.\n

\n
\n", "question_id": "21N.2.HL.TZ0.2C", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-2-inheritance", "d3-2-19-autosomal-gene-linkage" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n A pyramid of energy represents the amount of energy taken in by each trophic level per unit time and per unit area. Discuss the advantages and disadvantages of the use of pyramids of energy as models of energy flow in an ecosystem.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n

\n \n Advantages\n \n :\n
\n a. can show the energy loss/transfer between trophic levels ✔\n

\n

\n b. permits a ‹quantitative› comparison between ecosystems ✔\n

\n

\n c. shows change over time ✔\n

\n

\n \n Disadvantages\n \n :\n
\n d. are difficult to produce accurately ✔\n

\n

\n e. require destructive methods to obtain the data ✔\n

\n

\n f. do not show all the interactions/food chains/feeding relationships «between different members of the community» ✔\n

\n

\n g. cannot represent organisms that feed at different trophic levels ✔\n

\n

\n \n Award\n \n [3 max]\n \n if only one side of the argument is given\n \n .\n

\n
\n", "Examiners report": "None", "question_id": "19N.2.SL.TZ0.12C", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c4-2-transfers-of-energy-and-matter", "c4-2-11-construction-of-energy-pyramids" ] }, { "Question": "
\n
\n (d)\n
\n
\n

\n Outline the role of melatonin in humans.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n control/maintain/regulate circadian rhythms;\n
    2. \n
  2. \n secreted/released late evening/end of day/in dark/night time/dim light/absence of blue light;\n
    3. \n
  3. \n helps to induce sleep/sleepiness/influences timing of sleeping/waking/control sleep cycle;\n
    4. \n
\n

\n \n Do not award mpb unless the answer is referring to secretion, not just correlations.\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.2.HL.TZ1.2D", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-1-integration-of-body-systems", "c3-1-11-modulation-of-sleep-patterns-by-melatonin-secretion-as-a-part-of-circadian-rhythms" ] }, { "Question": "
\n
\n

\n Which cell component arose first during the formation of the earliest cells?\n

\n

\n A. Chloroplast\n

\n

\n B. Plasma membrane\n

\n

\n C. Mitochondria\n

\n

\n D. Cell wall\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "22M.1A.SL.TZ1.4", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a2-2-cell-structure", "a2-2-12-origin-of-eukaryotic-cells-by-endosymbiosis" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Explain the control mechanism of the heart rate.\n

\n
\n
\n

\n [7]\n

\n
\n
\n", "Markscheme": "
\n

\n a.\n \n sinoatrial node/SAN\n \n is a specialized group of muscle cells\n
\n \n \n OR\n \n \n
\n \n sinoatrial node/SAN\n \n is located in the right atrium ✔\n

\n

\n b. acts as a pacemaker/controls the heart rate\n
\n \n \n OR\n \n \n
\n initiates/generates the heart beat/starts the cardiac cycle ✔\n

\n

\n c. sends out electrical signal/impulses/depolarisations ✔\n

\n

\n d. electrical signal stimulates contraction «of heart muscle» ✔\n

\n

\n e. signal passes through walls of atria/passes to AV node ✔\n

\n

\n f. then through walls of the ventricles ✔\n

\n

\n g. medulla «oblongata of brain» can change/increase/decrease the rate ✔\n

\n

\n h. through nerves/named example of nerve/autonomic/sympathetic/ parasympathetic nervous system ✔\n \n In mph, only accept vagus nerve for slowing heart rate and sympathetic nerve for accelerating it\n \n .\n

\n

\n i. one nerve increases the rate and the other decreases it ✔\n

\n

\n j. epinephrine/adrenaline increases heart rate/force of contraction ✔\n

\n

\n k. epinephrine/adrenaline prepares the body for vigorous activity/is part of fight or flight response ✔\n

\n
\n", "Examiners report": "None", "question_id": "19N.2.SL.TZ0.7C", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-1-integration-of-body-systems", "c3-1-14-feedback-control-of-heart-rate-following-sensory-input-from-baroreceptors-and-chemoreceptors" ] }, { "Question": "
\n
\n

\n The micrograph shows tissues in a plant stem.\n

\n

\n \n

\n

\n What is the reason that no nucleus is visible in Z?\n
\n
\n

\n

\n A.  Xylem vessels are formed from dead lignified cells.\n

\n

\n B.  Staining of cells destroys their nucleus.\n

\n

\n C.  Phloem companion cells lack a nucleus.\n

\n

\n D.  The nucleus is too small to be seen in a light microscope slide preparation.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "None", "question_id": "23M.1A.SL.TZ1.33", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-2-transport", "b3-2-9-distribution-of-tissues-in-a-transverse-section-of-the-stem-of-a-dicotyledonous-plant" ] }, { "Question": "
\n
\n

\n What is the main contribution of greenhouse gases to global warming?\n

\n

\n
\n A.  Absorbing long wave radiation, therefore retaining atmospheric heat\n

\n

\n B.  Converting long wave radiation to short wave radiation\n

\n

\n C.  Producing a hole in the ozone layer, therefore allowing more heat into atmosphere\n

\n

\n D.  Reflecting short wave radiation, therefore increasing the atmospheric temperature\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "None", "question_id": "23M.1A.SL.TZ1.19", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-3-photosynthesis", "c1-3-8-carbon-dioxide-enrichment-experiments-as-a-means-of-predicting-future-rates-of-photosynthesis-and-plant-growth" ] }, { "Question": "
\n
\n

\n State the domain into which ticks are classified.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n eukaryote ✔\n

\n

\n \n Accept eukaryotes\n \n .\n

\n
\n", "Examiners report": "None", "question_id": "19N.2.SL.TZ0.A", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a3-2-classification-and-cladistics-(hl-only)", "a3-2-9-classification-of-all-organisms-into-three-domains-using-evidence-from-rrna-base-sequences", "a4-2-conservation-of-biodiversity" ] }, { "Question": "
\n
\n

\n Distinguish between levels of predation in marmots born in the wild and those born in captivity.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n predation was greater in those born in captivity ✔\n

\n
\n", "Examiners report": "
\n

\n This question was generally well answered.\n

\n
\n", "question_id": "19M.2.SL.TZ1.A.I", "topics": [ "b-form-and-function" ], "subtopics": [ "b4-2-ecological-niches", "b4-2-10-adaptations-of-predators-for-finding-catching-and-killing-prey-and-of-prey-animals-for-resisting-predation" ] }, { "Question": "
\n
\n

\n The mean stomatal density for the lower epidermis of\n \n P. decandrum\n \n was around 600 per mm\n \n 2\n \n . Predict how the stomatal density for the upper epidermis would compare.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n (upper surface/epidermis usually has) fewer stomata/lower stomatal density/no stomata/OWTTE\n

\n

\n \n Do not accept a numerical value only\n \n .\n

\n
\n", "Examiners report": "
\n

\n Most predicted that the upper epidermis would have a lower density, although some stated the reverse.\n

\n
\n", "question_id": "20N.1B.SL.TZ0.B", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-1-gas-exchange", "b3-1-10-stomatal-density" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Describe the movements in ions that occur during time\n \n t\n \n .\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n Na\n \n +\n \n /sodium ions diffuse into the axon (in the first part/half of\n \n t\n \n );\n
\n K\n \n +\n \n /potassium ions diffuse out of the axon (in the second half/part of\n \n t\n \n )\n

\n

\n \n Do not accept the name of the element without indication that it is an ion\n \n .\n

\n
\n", "Examiners report": "
\n

\n Some candidates talked about ion movement but with no reference to a specific ion; some described the Na\n \n +\n \n /K\n \n +\n \n pump here and received no marks.\n

\n
\n", "question_id": "22M.2.HL.TZ1.5C", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c2-2-neural-signalling", "c2-2-3-nerve-impulses-as-action-potentials-that-are-propagated-along-nerve-fibres", "c2-2-8-depolarization-and-repolarization-during-action-potentials" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Explain transcription.\n

\n
\n
\n

\n [7]\n

\n
\n
\n", "Markscheme": "
\n

\n a. synthesis of RNA/mRNA / transcription of DNA to RNA;\n
\n b. RNA nucleotides linked together to form a strand/chain;\n
\n c. RNA strand assembled on DNA template/antisense strand / copy made of sense strand;\n
\n d.\n \n RNA polymerase\n \n carries out transcription/links RNA nucleotides;\n
\n e. uncoiling/separation of DNA strands;\n
\n f.  5’ end of nucleotides linked to 3’ end of (growing RNA) strand;\n
\n g.\n \n complementary base pairing\n \n (is the basis of copying the base sequence);\n
\n h.\n \n uracil\n \n instead of\n \n thymine\n \n in RNA;\n
\n i. starts at/RNA polymerase binds to a promoter;\n
\n j. regulated by transcription factors/DNA binding proteins/nucleosomes;\n

\n

\n \n Annotated diagrams can be used\n \n .\n

\n
\n", "Examiners report": "
\n

\n Answers were mixed. Strong candidates had no difficulty in describing transcription in detail but weaker ones tended to get confused with replication and/or translation. Helicase was often stated as the enzyme that uncoils and splits the double helix, rather than RNA polymerase. Marks were not awarded merely for stating that transcription is 5’ to 3’ unless it was clear that the candidate understood that the 5’ terminal of a free nucleotide is linked to the 3’ terminal of the chain of nucleotides already linked up. Candidates are expected to show understanding in their answers, rather than just state memorized phrases.\n

\n
\n", "question_id": "21N.2.HL.TZ0.6B", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d1-2-protein-synthesis", "d1-2-1-transcription-as-the-synthesis-of-rna-using-a-dna-template", "d1-2-13-initiation-of-transcription-at-the-promoter" ] }, { "Question": "
\n
\n

\n Using the life cycle diagram and the graph for the year 2000, analyse the distribution of adult ticks throughout the different seasons.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. adults present through autumn and winter «according to the life cycle diagram»\n
\n \n \n OR\n \n \n
\n some adults «must» survive winter «despite graph suggesting zero» ✔\n

\n

\n b. adults peak in October «& November»/in autumn/between September and December ✔\n

\n

\n c. adults die after laying eggs in winter/beginning of spring ✔\n

\n

\n d. smaller peak/10 % versus 55 % peak/smaller numbers of adults in April/spring ✔\n

\n

\n e. adults absent from June to September/summer ✔\n

\n

\n \n Each mark point, requires month or season.\n \n
\n \n Jan - Mar = winter\n \n
\n \n Apr - Jun = spring\n \n
\n \n Jul - Sep = summer\n \n
\n \n Oct - Dec = autumn = fall\n \n

\n

\n \n Do not accept that there are the lowest number or no adults in winter.\n \n

\n
\n", "Examiners report": "None", "question_id": "19N.2.SL.TZ0.D", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a4-2-conservation-of-biodiversity" ] }, { "Question": "
\n
\n

\n Which pentadactyl limb is adapted for flight?\n

\n

\n \n

\n

\n [Source: adapted from Volkov Vladislav Petrovich, https://en.wikipedia.org/wiki/Homology_(biology)#/media/File:Homology_\n
\n vertebrates-en.svg and Zebra.element, https://en.wikipedia.org/wiki/File:Bat_mouse_forelimbs.png]\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "19N.1A.SL.TZ0.21", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a4-1-evolution-and-speciation", "a4-1-4-evidence-for-evolution-from-homologous-structures" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n A family has a history of hemophilia that is caused by a sex-linked recessive allele. A woman from this family is a carrier and marries a man who does not have the allele. Showing your working, determine the probability of their children having the disease.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n alleles clearly labelled for both parents (in a Punnett square or other format);\n
    2. \n
  2. \n correct genotypes for all four possibilities for children;\n
    \n \n
    3. \n
  3. \n phenotypes of the children: the sons would have a 50 % chance of having hemophilia and the daughters would have 0 % chance of having hemophilia/50 % chance of being a carrier;\n
    4. \n
\n

\n \n Sex needs to be mentioned for mpc but info can be taken from the Punnett square\n \n .\n

\n
\n", "Examiners report": "
\n

\n A standard sex -linked genetics question. It was expected that an indication that half of the boys would suffer from haemophilia, not just a ‘25 % possibility’.\n

\n
\n", "question_id": "22M.2.SL.TZ2.6B", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-2-inheritance", "d3-2-11-sex-determination-in-humans-and-inheritance-of-genes-on-sex-chromosomes", "d3-2-12-haemophilia-as-an-example-of-a-sex-linked-genetic-disorder" ] }, { "Question": "
\n
\n

\n Outline the stages of the carbon cycle that involve plants or materials made by plants.\n

\n
\n
\n

\n [5]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n absorption/diffusion of carbon dioxide from the atmosphere/water by plants;\n
    2. \n
  2. \n \n photosynthesis\n \n fixes/converts carbon (dioxide) to carbohydrates/carbon compounds;\n
    3. \n
  3. \n respiration in plants converts carbohydrates/carbon compounds to carbon dioxide;\n
    4. \n
  4. \n saprotrophs/detritivores digest dead plants/plant matter releasing carbon/carbon dioxide;\n
    \n \n \n OR\n \n \n
    \n decomposition returns carbon to the soil/releases CO\n \n 2\n \n to atmosphere/water/environment\n
    5. \n
  5. \n peat forms when decomposition of dead plant matter is incomplete storing carbon/ creating a reservoir;\n
    \n \n \n OR\n \n \n
    \n fossilization of carbon stores carbon as coal/oil/natural gas;\n
    6. \n
  6. \n forest fires/combustion of plants converts (carbohydrates/carbon compounds) to carbon dioxide;\n
    7. \n
  7. \n plants are eaten by consumers (moving carbon in the food chain)\n
    8. \n
  8. \n humans use plant products for making cloth/household items/building/arts creating a reservoir for carbon\n
    \n \n \n OR\n \n \n
    \n Humans burn fossil fuels releasing CO\n \n 2\n \n ;\n
    9. \n
  9. \n Plants act as carbon sinks/reservoirs\n
    10. \n
\n

\n

\n

\n \n Carbon may be used in place CO\n \n 2\n \n an carbohydrates\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ1.B", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c4-2-transfers-of-energy-and-matter", "c4-2-17-constructing-carbon-cycle-diagrams" ] }, { "Question": "
\n
\n

\n The diagram shows the carbon flux in gigatonnes per year between some of the Earth’s global reservoirs.\n

\n

\n \n

\n

\n [Source: Figure 7.3 and Table 7.1 from Denman, K.L., G. Brasseur, A. Chidthaisong, P. Ciais, P.M. Cox, R.E. Dickinson, D.\n
\n Hauglustaine, C. Heinze, E. Holland, D. Jacob, U. Lohmann, S Ramachandran, P.L. da Silva Dias, S.C. Wofsy and\n
\n X. Zhang, 2007: Couplings Between Changes in the Climate System and Biogeochemistry. In:\n \n Climate Change\n \n
\n \n 2007: The Physical Science Basis\n \n . Contribution of Working Group I to the Fourth Assessment Report of the\n
\n Intergovernmental Panel on Climate Change [Solomon, S., D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt,\n
\n M. Tignor and H.L. Miller (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.]\n

\n

\n

\n

\n What can be deduced from the information in the diagram?\n

\n

\n A. Arrows S are mainly due to respiration of marine plants and animals.\n

\n

\n B. Photosynthesis is a component of both arrows Q and S.\n

\n

\n C. Every day, more carbon is removed from the ocean than is added.\n

\n

\n D. Ocean carbon is stored as dissolved calcium carbonate.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "21N.1A.SL.TZ1.16", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c4-2-transfers-of-energy-and-matter", "c4-2-17-constructing-carbon-cycle-diagrams", "c4-2-18-ecosystems-as-carbon-sinks-and-carbon-sources" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Explain the development of antibiotic resistance in terms of natural selection.\n

\n
\n
\n

\n [7]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n antibiotics can (generally) kill/destroy bacteria;\n
    2. \n
  2. \n some bacteria show variation/antibiotic resistance;\n
    3. \n
  3. \n variation/resistance is due to a random mutation;\n
    4. \n
  4. \n resistant bacteria are not killed/destroyed by the antibiotic\n
    \n \n \n OR\n \n \n
    \n bacteria without the mutation die;\n
    5. \n
  5. \n (resistant) bacteria have a selective advantage / unequal success;\n
    6. \n
  6. \n the bacteria with this variation/resistance reproduces/multiplies;\n
    7. \n
  7. \n mutation/gene is passed on to the offspring / the offspring will be resistant to the antibiotic;\n
    8. \n
  8. \n resistant bacteria become more common;\n
    9. \n
  9. \n bacteria have evolved to be resistant to the antibiotic;\n
    10. \n
\n

\n \n Award\n \n [6 max]\n \n if pathogen is used instead of bacteria throughout the answer with no mention of bacteria\n \n .\n

\n
\n", "Examiners report": "
\n

\n This natural selection question had better responses than in previous years. There seems to be a widespread misconception that bacteria can mutate after exposure to an antibiotic rather than surviving because of a genetic variation. Some confusion was demonstrated concerning the use of antibiotics: some candidates did not understand that antibiotics are used against bacteria (not viruses). There was lots of confusion in the use of different but similar words — antibiotics / antibody / antigen\n

\n
\n", "question_id": "22M.2.SL.TZ1.7C", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-2-defence-against-disease", "c3-2-14-evolution-of-resistance-to-several-antibiotics-in-strains-of-pathogenic-bacteria" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n State one cause of lung cancer.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n smoking/tobacco;\n
    2. \n
  2. \n passive smoking;\n
    3. \n
  3. \n Radon/other radiation;\n
    4. \n
  4. \n exposure to arsenic/asbestos/smoke from coal burning/fires/silica/rock dust/vehicle exhaust fumes/nitrogen oxides;\n
    5. \n
\n

\n

\n
\n", "Examiners report": "None", "question_id": "23M.2.HL.TZ2.3A", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-1-cell-and-nuclear-division", "d2-1-17-differences-between-tumours-in-rates-of-cell-division-and-growth-and-in-the-capacity-for-metastasis-and-invasion-of-neighbouring-tissue" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Outline the role of UV radiation as a mutagen.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n affects/damages/causes change in oncogenes/errors in DNA repair;\n
    2. \n
  2. \n UV radiation might alter complementary base pairing/break hydrogen bonds/fuse bases;\n
    3. \n
  3. \n double helix may uncoil;\n
    4. \n
  4. \n strands may separate/break;\n
    5. \n
  5. \n DNA sequence may be altered/DNA bases may re-connect to different bases after separating;\n
    6. \n
  6. \n DNA strand may break into pieces / fragments of DNA may be lost;\n
    7. \n
\n
\n", "Examiners report": "None", "question_id": "SPM.2.HL.TZ0.10A", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d1-3-mutations-and-gene-editing", "d1-3-4-causes-of-gene-mutation" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Identify, with a reason, the sex of this individual.\n

\n

\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n male because Y chromosome present\n
\n \n \n OR\n \n \n
\n male because sex chromosomes/last two chromosomes/pair 23 are unpaired/different «from each other»/not homologous ✔\n

\n
\n", "Examiners report": "
\n

\n Candidates knew this!\n

\n
\n", "question_id": "19M.2.SL.TZ1.6A", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a3-1-diversity-of-organisms", "a3-1-7-karyotyping-and-karyograms" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Determine which type of rice has the lowest overall diversity index.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n «\n \n O. sativa\n \n »\n \n japonica\n \n ✔\n

\n
\n", "Examiners report": "None", "question_id": "19N.2.SL.TZ0.1B", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a3-1-diversity-of-organisms" ] }, { "Question": "
\n
\n

\n Using all of the data so far, suggest whether exposure to freezing temperatures in the four cities is supported as a reason for the differences in HCN production in\n \n T. repens\n \n .\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. cities with more days without snow cover have positive correlation between distance from city center and HCN / vice versa for Montreal;\n

\n

\n b. fewer plants with HCN within cities that have more days without snow cover/have more exposure to freezing temperatures / converse for\n \n Montreal\n \n which has fewer days without snow cover;\n

\n

\n c. HCN is 0.2 (or less) HCN in cities that have more days without snow cover proportion whereas city with fewer days/Montreal it is 0.5/more than 0.4;\n

\n

\n d. in Toronto cyanogenic and non-cyanogenic plants show little difference in herbivory;\n

\n

\n e. support for hypothesis/exposure to freezing temperatures as reason.\n

\n

\n \n Do not accept ‘Yes’ unqualified as an answer, but accept it if supported by reasoning\n \n .\n

\n
\n", "Examiners report": "
\n

\n Many candidates found this to be another difficult question. There was a lot of data to consider and as in (c) it was necessary to take into account whether differences were likely to have been significant. In the histogram showing the amount of cold experienced, the large error bars show that only differences between Montreal and the other three cities are great enough to be considered reliable. When combined with data for the proportion of plants with HCN in each city, it was clear that there was support for exposure to cold as a reason.\n

\n
\n", "question_id": "20N.2.SL.TZ0.D.II", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-2-stability-and-change", "d4-2-4-use-of-a-model-to-investigate-the-effect-of-variables-on-ecosystem-stability" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n State\n \n one\n \n function of the atrioventricular node.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n a. relays signal from SAN to ventricles ✔\n

\n

\n b. causes ventricular systole ✔\n

\n

\n c. delays signal enabling both ventricles to contract simultaneously\n
\n \n \n OR\n \n \n
\n delays signal so the atria empty before ventricular systole ✔\n

\n
\n", "Examiners report": "
\n

\n A large number could state one correct function of the atrioventricular node, mainly that it causes ventricular systole.\n

\n
\n", "question_id": "19M.2.HL.TZ2.22A", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-2-transport", "b3-2-15-adaptations-of-the-mammalian-heart-for-delivering-pressurized-blood-to-the-arteries" ] }, { "Question": "
\n
\n

\n Black walnut (\n \n Juglans nigra\n \n ) secretes the chemical juglone into the soil surrounding its roots. Juglone inhibits cell respiration in other species of plants. What does this example illustrate?\n

\n

\n
\n A.  Mutualism\n

\n

\n B.  Intraspecific competition\n

\n

\n C.  Allelopathy\n

\n

\n D.  Parasitism\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "SPM.1A.HL.TZ0.38", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c4-1-populations-and-communities", "c4-1-11-herbivory-predation-interspecific-competition-mutualism-parasitism-and-pathogenicity-as-categories-of-interspecific-relationship-within-communities", "c4-1-12-mutualism-as-an-interspecific-relationship-that-benefits-both-species" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Draw a section of the Singer-Nicolson model of an animal cell membrane.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n

\n a. bilayer of phospholipids with both “tails” towards the inside «of the bilayer» ✔\n \n This can be taken unlabeled from diagram\n \n .\n

\n

\n b. hydrophilic/polar\n \n and\n \n hydrophobic/non-polar annotation ✔\n

\n

\n c. cholesterol between phospholipid tails ✔\n

\n

\n d. glycoprotein ✔\n

\n

\n e. integral proteins/channel proteins ✔\n

\n

\n f. peripheral proteins ✔\n \n Allow this if it does not extend across the membrane\n \n

\n

\n \n Elements should be clearly drawn, correctly positioned and annotated.\n \n

\n
\n", "Examiners report": "None", "question_id": "19N.2.SL.TZ0.5", "topics": [ "a-unity-and-diversity", "d-continuity-and-change" ], "subtopics": [ "a3-2-classification-and-cladistics-(hl-only)", "a3-2-1-need-for-classification-of-organisms", "a3-2-2-difficulties-classifying-organisms-into-the-traditional-hierarchy-of-taxa", "d4-2-stability-and-change", "d4-2-2-requirements-for-stability-in-ecosystems" ] }, { "Question": "
\n
\n

\n Suggest\n \n one\n \n conclusion that can be drawn from the results shown in the graph.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n a. as fungus grows, the rate of oxygen consumption increases ✔\n

\n

\n b. around day 4/5 fungus begins to grow/no growth in days 1–3 ✔\n

\n

\n c. the rate of fungus growth/rate of respiration is highest after 5 days ✔\n

\n
\n", "Examiners report": "
\n

\n Many candidates described what was shown by the graph rather than making a conclusion related to the growth of fungi. Thus “oxygen consumption increased after day 4” or references to the feed respiring were common answers.\n

\n
\n", "question_id": "19M.1B.SL.TZ1.A.II", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-2-cell-respiration", "c1-2-6-variables-affecting-the-rate-of-cell-respiration" ] }, { "Question": "
\n
\n (e)\n
\n
\n

\n Deduce the change in mitotic index after 72 hours compared to the control.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n 0.3 / 100 % increase / doubling ✔\n

\n

\n \n Do not penalize errors in significant figures. For example, 0.34 would be acceptable\n \n .\n

\n
\n", "Examiners report": "
\n

\n Those who had experience calculating mitotic index did well with this question.\n

\n
\n", "question_id": "21M.2.HL.TZ1.1E", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-1-cell-and-nuclear-division", "d2-1-17-differences-between-tumours-in-rates-of-cell-division-and-growth-and-in-the-capacity-for-metastasis-and-invasion-of-neighbouring-tissue" ] }, { "Question": "
\n
\n (d)\n
\n
\n

\n Based on the data, compare and contrast the progress of the epidemic in Liberia and Guinea.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n a. overall pattern similar in both/both show a rise and a fall in the infections ✔\n
\n
\n b. both countries show an increase during 2014\n
\n \n \n OR\n \n \n
\n neither country shows an increase in 2015 ✔\n

\n

\n c. both show a sudden drop at one point\n
\n \n \n OR\n \n \n
\n sudden drop earlier «Oct–Nov 14» in Liberia than in Guinea «Dec 14, Jan 15» ✔\n

\n

\n d. Guinea fluctuates whereas Liberia rises to a peak and then decreases/no fluctuations ✔\n

\n

\n e. epidemic starts earlier «in April 14» in Guinea than in Liberia «in June 14» ✔\n

\n

\n f. epidemic peaks earlier «Sept 14» in Liberia than in Guinea «Dec 14» ✔\n

\n

\n g. epidemic lasts longer in Guinea than it does in Liberia\n
\n \n \n OR\n \n \n
\n last case recorded in Liberia Feb 15 while cases continue «at least» until May 15 in Guinea ✔\n

\n

\n h. numbers of cases in Guinea generally lower than in Liberia\n
\n \n \n OR\n \n \n
\n number of cases higher in Liberia than in Guinea ✔\n

\n
\n", "Examiners report": "
\n

\n Data is described rather than interpreted\n \n e.g.\n \n epidemic starts in April for Guinea and in June for Liberia instead of epidemic starts earlier in Guinea than in Liberia\n

\n
\n", "question_id": "19M.2.HL.TZ1.1D", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a2-3-viruses-(hl-only)" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Outline the specific functions of\n \n three named\n \n proteins.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n a. Rubisco fixes CO\n \n 2\n \n from atmosphere during photosynthesis;\n
\n b. insulin controls blood glucose levels;\n
\n c. collagen forms connective tissue/ligaments;\n
\n d. spider silk forms the spider web;\n
\n e. rhodopsin involved in photoreceptor;\n
\n f. immunoglobulins/antibodies attach to antigens/pathogens;\n
\n g. actin/myosin performs muscle contraction;\n
\n h. hemoglobin carries oxygen in red blood cells;\n

\n

\n \n Accept any other correct\n \n three named\n \n proteins\n \n

\n

\n \n If an enzyme is named, the correct substrate must be stated\n \n

\n
\n", "Examiners report": "None", "question_id": "21N.2.HL.TZ0.2B", "topics": [ "b-form-and-function" ], "subtopics": [ "b1-2-proteins", "b1-2-11-quaternary-structure-of-non-conjugated-and-conjugated-proteins" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Explain how the properties of water allow it to move through xylem vessels.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. water is polar/a dipole/oxygen slightly negative and hydrogen slightly positive ✔\n

\n

\n b. polarity results in hydrogen bonds/attraction between water molecules ✔\n

\n

\n c. hydrogen bonding/polarity causes cohesion of water «molecules» ✔\n

\n

\n d. cohesion/hydrogen bonding allows water to withstand tension/withstand low pressure/be pulled «upwards»/moved against gravity ✔\n

\n

\n e. cohesion/hydrogen bonding prevents column of water «in xylem» from breaking/column of water is maintained ✔\n

\n

\n f. adhesion of water to xylem/vessel walls «due to hydrogen bonds» ✔\n

\n
\n", "Examiners report": "
\n

\n This was better known, but many candidates still confuse adhesion with cohesion, or do not distinguish between them. Cohesion is far more significant in xylem transport because it explains how tensions can be resisted. Adhesion of water to the wall of xylem vessels is only significant when air-filled xylem vessels are refilling with aqueous sap under positive pressures. If this happens at all in a plant, it will generally only be once per year and yet adhesion to the xylem was the most common answer given. In some answers cause and effect had been confused so cohesion was given as the cause of hydrogen bonding rather than the effect.\n

\n
\n", "question_id": "19M.2.SL.TZ1.4B", "topics": [ "b-form-and-function", "a-unity-and-diversity" ], "subtopics": [ "b3-2-transport", "b3-2-7-transport-of-water-from-roots-to-leaves-during-transpiration", "a1-1-water", "a1-1-3-cohesion-of-water-molecules-due-to-hydrogen-bonding-and-consequences-for-organisms" ] }, { "Question": "
\n
\n

\n In multicellular animals, embryonic stem cells have the ability to differentiate into a range of cells with different functions. What is the term used to describe cells with this property?\n

\n

\n
\n A.  Pluripotent\n

\n

\n B.  Multipotent\n

\n

\n C.  Totipotent\n

\n

\n D.  Specialized\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "None", "question_id": "SPM.1A.HL.TZ0.16", "topics": [ "b-form-and-function" ], "subtopics": [ "b2-3-cell-specialization", "b2-3-4-differences-between-totipotent-pluripotent-and-multipotent-stem-cells" ] }, { "Question": "
\n
\n

\n What are linked by hydrogen bonds?\n

\n

\n A. Hydrogen and oxygen within a water molecule\n

\n

\n B. Phosphate and sugar within a DNA molecule\n

\n

\n C. Base and sugar between DNA nucleotides\n

\n

\n D. Hydrogen and oxygen in different water molecules\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "
\n

\n Only 40 % of candidates answered this question correctly. A common misunderstanding was to think that hydrogen bonds are within water molecules (intramolecular) rather than between water molecules (intermolecular).\n

\n
\n", "question_id": "22M.1A.SL.TZ1.6", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a1-2-nucleic-acids", "a1-2-6-dna-as-a-double-helix-made-of-two-antiparallel-strands-of-nucleotides-with-two-strands-linked-by-hydrogen-bonding-between-complementary-base-pairs", "a1-1-water", "a1-1-2-hydrogen-bonds-as-a-consequence-of-the-polar-covalent-bonds-within-water-molecules" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n The figure shows a tripeptide.\n

\n

\n \n

\n

\n Label\n \n one\n \n peptide bond in this molecule.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n circle/bracket around peptide bond / arrow pointing to peptide bond / peptide bond labelled;\n

\n

\n \n

\n

\n \n Allow either peptide bond\n \n

\n

\n \n Allow if adjacent C=O and NH groups are included in the circle/bracket, but do not allow if other parts of the molecule are included\n \n .\n

\n
\n", "Examiners report": "
\n

\n 80 % of candidates indicated one of the two peptide bonds in the diagram correctly.\n

\n
\n", "question_id": "21N.2.HL.TZ0.4A", "topics": [ "b-form-and-function" ], "subtopics": [ "b1-2-proteins", "b1-2-2-condensation-reactions-forming-dipeptides-and-longer-chains-of-amino-acids" ] }, { "Question": "
\n
\n

\n With reference to all the data, suggest a reason for the difference in standardized mean path length for summer and winter.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n in winter shrews have smaller brains/smaller BCH / converse for summer;\n
    2. \n
  2. \n lower/poorer memory/thinking/cognitive skills/learning/intelligence/senses/sense of smell/ability to find food in winter/converse for summer;\n
    3. \n
\n
\n", "Examiners report": "
\n

\n The instruction to refer to all the data does not indicate that conclusions from each graph should be restated, but rather than the research findings should be combined to produce a hypothesis. The expected reasoning here was that the lower BCH of shrews in winter showed brain mass was on average lower, so cognitive ability was reduced and shrews were slower to find food.\n

\n
\n", "question_id": "22N.2.HL.TZ0.L", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-1-integration-of-body-systems", "c3-1-4-the-brain-as-a-central-information-integration-organ" ] }, { "Question": "
\n
\n (c.i)\n
\n
\n

\n Using the graph, identify the percentage who had received the tuberculosis vaccine in 2012.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n 89%;\n

\n

\n \n Allow 88 to 91 %.\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.2.HL.TZ2.1", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-2-defence-against-disease", "c3-2-16-vaccines-and-immunization" ] }, { "Question": "
\n
\n

\n Which structure in the chloroplast diagram is adapted to carry out chemiosmosis?\n

\n

\n \n

\n

\n [Source: © International Baccalaureate Organization 2019]\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "None", "question_id": "19N.1A.HL.TZ0.31", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-3-photosynthesis", "c1-3-12-atp-production-by-chemiosmosis-in-thylakoids" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n The images show parts of plants belonging to two different phyla.\n

\n

\n \n

\n

\n State the phylum of plant X and of plant Y.\n

\n

\n X:\n

\n

\n Y:\n

\n

\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n X: Filicinophyta ✔\n

\n

\n Y: Coniferophyta/Conifera/Gymnosperms ✔\n

\n
\n", "Examiners report": "
\n

\n Those who had been taught it could identify the filicinophyte and the coniferophyte, albeit with a variety of spellings.\n

\n
\n", "question_id": "19M.2.SL.TZ2.4", "topics": [ "d-continuity-and-change", "a-unity-and-diversity" ], "subtopics": [ "d1-3-mutations-and-gene-editing", "d1-3-4-causes-of-gene-mutation", "a3-2-classification-and-cladistics-(hl-only)", "a3-2-4-clades-as-groups-of-organisms-with-common-ancestry-and-shared-characteristics", "a3-2-7-analysing-cladograms" ] }, { "Question": "
\n
\n

\n X indicates the movement of a structure in the neuron. Explain what events trigger this movement and what happens next.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n a. depolarization of pre-synaptic membrane / action potential/nerve impulse arrives;\n

\n

\n b. uptake of calcium / calcium ions diffuse in / calcium channels open;\n

\n

\n c. structures containing neurotransmitter/vesicles move to/fuse with membrane;\n

\n

\n d.\n \n neurotransmitter\n \n /\n \n acetylcholine\n \n released by\n \n exocytosis\n \n into cleft/binds to postsynaptic membrane/receptors;\n

\n

\n \n Must see exocytosis\n \n .\n

\n
\n", "Examiners report": "
\n

\n This was generally well answered. Some suggested that the vesicle is released into the synaptic cleft, instead of neurotransmitter being released by exocytosis.\n

\n
\n", "question_id": "20N.2.SL.TZ0.C.II", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c2-2-neural-signalling", "c2-2-6-release-of-neurotransmitters-from-a-presynaptic-membrane", "c2-2-7-generation-of-an-excitatory-postsynaptic-potential" ] }, { "Question": "
\n
\n

\n Deduce whether there is a correlation between the neural traces and the percentage of responding G1 neurons.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. there is a\n \n positive\n \n relationship/correlation between the size of neural traces and the percentage of responding G1 neurons\n \n Accept vice versa\n \n
\n \n \n OR\n \n \n
\n the chemicals that cause stronger/higher neural traces also cause the greatest percentage of responding G1 neurons ✔\n

\n

\n b. fox and stoat scents have «approximately» the same/similar neural traces and the same percentage of responding neurons/>75 % ✔\n

\n

\n c. mouse alarm compounds cause smaller neural traces and smaller percentage of responding neurons/25–75 % ✔\n

\n

\n d. control chemicals have\n \n no response\n \n in both cases\n
\n \n \n OR\n \n \n
\n \n no percentage\n \n of «G1 neurons» response and no action potential «in neural traces» ✔\n

\n
\n", "Examiners report": "
\n

\n Similarly, in 1f most could see the positive correlation, albeit not stating it, between the size of the trace and the percentage of responding G1 neurons.\n

\n
\n", "question_id": "19M.2.SL.TZ2.F", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c2-2-neural-signalling" ] }, { "Question": "
\n
\n

\n Which role does positive feedback play in fruit ripening?\n

\n

\n
\n A.  The production of ethylene leads to fruit ripening, which stops the production of ethylene.\n

\n

\n B.  The production of ethylene leads to fruit ripening, which causes more ethylene production.\n

\n

\n C.  The production of RuBP leads to fruit ripening, which stops the production of RuBP.\n

\n

\n D.  The production of RuBP leads to fruit ripening, which causes more RuBP production.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "SPM.1A.HL.TZ0.22", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-1-integration-of-body-systems", "c3-1-23-positive-feedback-in-fruit-ripening-and-ethylene-production" ] }, { "Question": "
\n
\n

\n Three cell types are shown in the micrographs.\n

\n

\n \n

\n

\n [Source: left: UCSF School of Medicine, Courtesy of Prof. D Schmucker. middle: Professor Roger Meicenheimer, Miami University, Department of Botany. right: Courtesy of visualhistology.com.]\n

\n

\n

\n

\n What feature distinguishes striated muscle fibres from the three cell types shown in the images?\n

\n

\n A. Mitochondria\n

\n

\n B. Nucleoid regions\n

\n

\n C. Multinucleate structure\n

\n

\n D. Membrane-bound organelles\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "21M.1A.HL.TZ2.2", "topics": [ "b-form-and-function" ], "subtopics": [ "b2-3-cell-specialization", "b2-3-9-adaptations-of-cardiac-muscle-cells-and-striated-muscle-fibres" ] }, { "Question": "
\n
\n

\n Describe the structure of cardiac muscle cells.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. cardiac muscle cells are branched ✔\n

\n

\n b. rich in mitochondria ✔\n

\n

\n c. rich in glycogen granules ✔\n

\n

\n d. formed by short cylindrical cells ✔\n

\n

\n e. contains\n \n intercalated\n \n discs ✔\n

\n

\n f. has gap junctions ✔\n

\n

\n g. «intercalated discs are» transverse cross-bands which represent the attachment site between adjacent cells ✔\n

\n

\n \n Do not accept myogenic as it is not a structure.\n \n

\n
\n", "Examiners report": "
\n

\n The stronger candidates could describe the structure of cardiac muscle cells.\n

\n
\n", "question_id": "19M.2.HL.TZ2.A", "topics": [ "b-form-and-function" ], "subtopics": [ "b2-3-cell-specialization", "b2-3-9-adaptations-of-cardiac-muscle-cells-and-striated-muscle-fibres" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Outline\n \n one\n \n example of a human disease caused by an autosomal recessive allele.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n name of condition e.g. PKU / other example;\n
    2. \n
  2. \n mutation in the gene for (the enzyme) phenylalanine hydroxylase (PAH) / if other example used name of gene that is mutated;\n
    3. \n
  3. \n outline of inheritance pattern, e.g. both parents need to carry the recessive allele;\n
    4. \n
  4. \n (without dietary modification, result is) toxic build-up of phenylalanine in the blood / low levels of tyrosine / symptoms if other example used;\n
    5. \n
  5. \n phenylalanine is not converted to tyrosine (by the enzyme) / effect of the mutation on the protein/enzyme/metabolism if other example used;\n
    6. \n
  6. \n requires dietary modification (as treatment) / treatment for other example used;\n
    7. \n
\n
\n", "Examiners report": "None", "question_id": "SPM.2.SL.TZ0.7B", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-2-inheritance", "d3-2-7-phenylketonuria-as-an-example-of-a-human-disease-due-to-a-recessive-allele" ] }, { "Question": "
\n
\n

\n Describe transport across cell membranes by osmosis.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n

\n a. form of diffusion;\n
\n b. osmosis is the movement of water molecules;\n
\n c. (movement) across a\n \n selectively\n \n /\n \n semi\n \n /\n \n partially permeable\n \n membrane/cell membrane;\n
\n d. from a region of low\n \n solute\n \n concentration to a region of high\n \n solute\n \n concentration (until equilibrium is reached)\n
\n OR\n
\n movement of\n \n water\n \n molecules from a high concentration of\n \n water\n \n to a low concentration of water molecules;\n
\n e. it is a passive transport mechanism/does not use ATP;\n
\n f. channel proteins/aquaporins are used;\n

\n
\n", "Examiners report": "
\n

\n Most gained at least 2 marks describing osmosis. Common mistakes were not making it clear whether the concentration was referring to water or to the solute. A surprising number of students did not refer to water at all.\n

\n
\n", "question_id": "21N.2.SL.TZ0.B", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-3-water-potential", "d2-3-3-water-movement-by-osmosis-into-or-out-of-cells" ] }, { "Question": "
\n
\n

\n By which process do potassium ions move through potassium channels in axons?\n

\n

\n A. Active transport\n

\n

\n B. Exocytosis\n

\n

\n C. Facilitated diffusion\n

\n

\n D. Simple diffusion\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "19N.1A.HL.TZ0.2", "topics": [ "b-form-and-function" ], "subtopics": [ "b2-1-membranes-and-membrane-transport", "b2-1-15-sodium-potassium-pumps-as-an-example-of-exchange-transporters" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Describe how plants are named and classified, including recognition features of plant phyla.\n

\n
\n
\n

\n [7]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n binomial naming\n
    \n \n \n OR\n \n \n
    \n genus and species name;\n
    2. \n
  2. \n plants constitute a kingdom\n
    3. \n
  3. \n plants are eukaryotes/belong to the domain eukaryota\n
    4. \n
  4. \n classified using a hierarchy of taxa\n
    \n \n \n OR\n \n \n
    \n kingdom, phylum, class, order, family, genus, species\n
    5. \n
  5. \n bryophyta/filicinophyta/coniferophyte/angiospermophyta is a\n \n phylum\n \n (of plants);\n
    6. \n
  6. \n bryophytes have only rhizoids/spores (produced in a capsule)/no roots/ no vascular tissue;\n
    7. \n
  7. \n filicinophytes have stems/roots/xylem-phloem/reproduce by spores/leaves that uncurl; but no seeds\n
    8. \n
  8. \n coniferophytes have seeds in cones/ vascular tissue/xylem-phloem/cambium/ but no flowers/no fruits\n
    9. \n
  9. \n angiospermophytes have flowers/produce seeds/produce fruits/vascular tissue/xylem-phloem;\n
    10. \n
  10. \n named example showing of the classification of a plant from species to domain or vice versa\n
    11. \n
  11. \n \n cladistics\n \n is used to reclassify groups of plants\n
    \n \n \n OR\n \n \n
    \n named example of a group of plants reclassified by\n \n cladistics\n \n ;\n
    12. \n
  12. \n use a dichotomous key to discriminate among plant features\n
    13. \n
\n

\n

\n

\n \n Each phylum of plants requires at least 2 features for the mark.\n \n

\n

\n \n Mp-e does not require all 4 phyla to be named.\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.2.HL.TZ1.7A", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a3-2-classification-and-cladistics-(hl-only)", "a3-2-2-difficulties-classifying-organisms-into-the-traditional-hierarchy-of-taxa" ] }, { "Question": "
\n
\n

\n In fruit flies (\n \n Drosophila melanogaster\n \n ), grey bodies (b\n \n +\n \n ) are dominant to black bodies (b) and normal wings (vg\n \n +\n \n ) are dominant to vestigial wings (vg). Homozygous vestigial winged, black bodied flies were crossed with individuals that were heterozygous for both traits. 2300 individuals were counted and the phenotypes observed were recorded as shown.\n

\n

\n 965 normal wings, grey bodies\n
\n 944 vestigial wings, black bodies\n
\n 206 vestigial wings, grey bodies\n
\n 185 normal wings, black bodies\n

\n

\n

\n

\n Which statement is valid?\n

\n

\n A. The predicted phenotypic ratio was 9:3:3: 1.\n

\n

\n B. There is independent assortment of wings but not body colour.\n

\n

\n C. The expected number of vestigial winged, grey bodied flies was 575.\n

\n

\n D. The traits are on different chromosomes.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "
\n

\n This proved to be the third most difficult question, with all of the four choices attracting some candidates. Perhaps the 1:1:1:1 ratio from a dihybrid test cross was unfamiliar. It was not a quick question to answer and was close to the end of the exam, but the number of questions left unanswered by candidates (blanks) did not rise with the last few questions, suggesting that lack of time was not the problem.\n

\n
\n", "question_id": "21M.1A.HL.TZ1.36", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-2-inheritance", "d3-2-17-punnett-grids-for-predicting-genotypic-and-phenotypic-ratios-in-dihybrid-crosses-involving-pairs-of-unlinked-autosomal-genes" ] }, { "Question": "
\n
\n

\n How does auxin contribute to phototropism?\n

\n

\n A. It increases production of light-sensitive proteins.\n

\n

\n B. It increases growth of cells on the shaded side of the stem.\n

\n

\n C. It inhibits growth of axillary buds.\n

\n

\n D. It inhibits stem elongation.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "21M.1A.HL.TZ2.34", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-1-integration-of-body-systems", "c3-1-21-promotion-of-cell-growth-by-auxin" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Outline how sex is determined in humans.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n genetically determined/determined by (pair of) sex chromosomes/X and Y chromosomes;\n
    2. \n
  2. \n sperm carry either an X or a Y chromosome;\n
    3. \n
  3. \n egg is X and if fertilized by X sperm leads to a female child / XX female\n
    \n \n \n OR\n \n \n
    \n egg is X and if fertilized by Y sperm leads to a male child / XY male;\n
    4. \n
\n
\n", "Examiners report": "None", "question_id": "SPM.2.SL.TZ0.6A", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a3-1-diversity-of-organisms", "a3-1-7-karyotyping-and-karyograms" ] }, { "Question": "
\n
\n (d)\n
\n
\n

\n Deduce the conclusions that can be drawn from the data in the graph.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. reduced acetylcholine does not affect larval survival in the first two days ✔\n

\n

\n b. reduced acetylcholine causes increased mortality from day 3 onwards ✔\n

\n

\n c. 90 % versus 40 % survival/other valid numerical comparison by day 5\n
\n \n \n OR\n \n \n
\n (much) greater decrease in survival occurs between days 4 and 5/by day 5 for the reduced group ✔\n

\n

\n \n Do not accept answers without times/ days\n \n .\n

\n
\n", "Examiners report": "
\n

\n In general, the data analysis question was well attempted by the majority of students.\n

\n

\n An answer comparing the survival as the days progressed was expected. Answers tended to be too general.\n

\n
\n", "question_id": "21M.2.HL.TZ2.1D", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c2-2-neural-signalling", "c2-2-12-effects-of-exogenous-chemicals-on-synaptic-transmission" ] }, { "Question": "
\n
\n

\n What cell component is found in eukaryotic cells but not in prokaryotic cells?\n
\n
\n

\n

\n A.  Mitochondria for respiration\n

\n

\n B.  DNA containing genetic information\n

\n

\n C.  Ribosomes for protein synthesis\n

\n

\n D.  Cell wall to maintain shape\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "None", "question_id": "23M.1A.SL.TZ2.2", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a2-2-cell-structure", "a2-2-5-prokaryote-cell-structure" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Explain the shape of the polypeptide chain at X.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n \n alpha helix\n \n /\n \n \n \n α\n \n \n helix\n \n
    2. \n
  2. \n type of secondary structure / second level of protein structure;\n
    3. \n
  3. \n maintained by hydrogen bonds;\n
    4. \n
  4. \n between C=O group and an N–H group;\n
    5. \n
\n
\n", "Examiners report": "
\n

\n This was one of the most successfully answered of questions, with better prepared candidates recognizing the alpha helix and explaining it in terms of hydrogen bonding.\n

\n
\n", "question_id": "22M.2.HL.TZ1.4B", "topics": [ "b-form-and-function" ], "subtopics": [ "b1-2-proteins", "b1-2-8-pleating-and-coiling-of-secondary-structure-of-proteins" ] }, { "Question": "
\n
\n

\n Describe the effect of neonicotinoid pesticides on the nervous system of insects.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n blocks synaptic transmission at (cholinergic synapses);\n
    2. \n
  2. \n binds to (acetylcholine) receptors;\n
    3. \n
\n
\n", "Examiners report": "
\n

\n A pleasing number were able to correctly describe the effect of the pesticides on the synapses and state the cumulative increase correctly in ai and aii. However, in aiii, many did not see the similarity in pattern for the compare mark. In part b stronger candidates commented on the fact that even at low doses the pesticide had a great effect and that the difference between high and low doses was negligible. Many examiners were bemused by the answers to c(i) where about half of the candidates failed to identify\n \n B. lucorum\n \n as the most affected species.\n \n B. pascuorum\n \n and\n \n B. terrestris\n \n were often incorrectly given. In cii. Better candidates described the overall effects as asked, with weaker candidates just describing each species in turn. In 1d the top candidates looked at all of the data, but those who just stated that the effect was not noticeable as the egg length was not significantly smaller gained the mark.\n

\n
\n", "question_id": "22M.2.HL.TZ2.A.I", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c2-2-neural-signalling", "c2-2-12-effects-of-exogenous-chemicals-on-synaptic-transmission" ] }, { "Question": "
\n
\n

\n Which is an example of evolution by selective breeding?\n
\n
\n

\n

\n A.  Selection of prey animals that can run faster than their predators\n

\n

\n B.  The variation in the size of different breeds of dogs\n

\n

\n C.  The tendency, during breeding, for birds to produce more offspring than will survive\n

\n

\n D.  Some female spiders only breeding with males which make the right signals\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "23M.1A.SL.TZ2.17", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a4-1-evolution-and-speciation", "a4-1-3-evidence-for-evolution-from-selective-breeding-of-domesticated-animals-and-crop-plants" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Outline how the structure of cellulose makes it suitable as a component of cell walls.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. chains of glucose/1-4 glycosidic linkages/covalent bonding between glucose ✔\n

\n

\n b. beta glucose so alternating orientation of glucose units\n
\n \n \n OR\n \n \n
\n beta glucose forms straight chains ✔\n

\n

\n c. forms microfibrils/long and thin/thin fibres/parallel bundles of cellulose molecules\n
\n \n \n OR\n \n \n
\n hydrogen bonding/cross linkage between cellulose molecules holds them together ✔\n

\n

\n d. high tensile strength/rigid/doesn’t stretch so provides support/allows turgidity ✔\n

\n
\n", "Examiners report": "
\n

\n Many candidates found this question the hardest in Section A. There were a few knowledgeable accounts that easily scored the two marks, but far more revealed little or no understanding of the structure of cellulose. It might be thought to be an obscure topic, but cellulose may be the most abundant biochemical on Earth. It is the key to how plants support themselves and grow. The paper that candidates wrote their answers on was mostly cellulose and nearly all candidates will have been wearing clothes composed largely of it. One misunderstanding that was often evident was that cellulose is freely permeable. The cell wall as a whole has this property, but it is due to the gaps between cellulose microfibrils, not to the cellulose itself. Another common mistake was to state that cellulose is made of starch, so contrasts between these two polysaccharides should be emphasised more widely.\n

\n
\n", "question_id": "19M.2.SL.TZ1.4C", "topics": [ "b-form-and-function" ], "subtopics": [ "b1-1-carbohydrates-and-lipids", "b1-1-6-structure-of-cellulose-related-to-its-function-as-a-structural-polysaccharide-in-plants" ] }, { "Question": "
\n
\n

\n What is a role of activated B cells?\n

\n

\n A. Secrete antibiotics in response to specific antigens\n

\n

\n B. Activate T cells in the immune response\n

\n

\n C. Release histamine in response to allergens\n

\n

\n D. Multiply to form clones of plasma cells\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "19N.1A.SL.TZ0.37", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-2-defence-against-disease", "c3-2-8-activation-of-b-lymphocytes-by-helper-t-lymphocytes", "c3-2-9-multiplication-of-activated-b-lymphocytes-to-form-clones-of-antibody-secreting-plasma-cells" ] }, { "Question": "
\n
\n

\n Identify the country with the largest number of Ebola cases.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n Sierra Leone ✔\n

\n
\n", "Examiners report": "
\n

\n This set of data-based questions produced the best showing among candidates. Teachers are to be commended for developing these skills in their students. Many candidates showed confidence in looking at unfamiliar data and formulating answers. Some weaknesses included not being careful with what they were writing when there were similar aspects in the data set (total population size and population density), comparing and contrasting - many students finding this difficult and simply writing descriptions of the data set rather than focussing on similarities and differences. Also giving information on part of a data set where some aspects of the data set may be similar in name but fundamentally different (e.g. Total population and population density) – Some candidates used incorrect parts of data sets rather than those that had been asked about - for example, talking about Ebola cases rather than Ebola deaths, total population size rather than population density.\n

\n
\n", "question_id": "19M.2.HL.TZ1.A.I", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a2-3-viruses-(hl-only)" ] }, { "Question": "
\n
\n

\n What is the reason for Taq DNA polymerase being used in the polymerase chain reaction (PCR)?\n

\n

\n A. It does not denature at high temperatures.\n

\n

\n B. It produces Okazaki fragments more rapidly.\n

\n

\n C. It allows translation to proceed rapidly.\n

\n

\n D. It works efficiently with helicase in PCR.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "None", "question_id": "20N.1A.SL.TZ0.10", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d1-1-dna-replication", "d1-1-4-polymerase-chain-reaction-and-gel-electrophoresis-as-tools-for-amplifying-and-separating-dna" ] }, { "Question": "
\n
\n (a.ii)\n
\n
\n

\n Deduce the genotype of Queen Victoria’s daughter Alice.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n X\n \n H\n \n X\n \n h\n \n ;\n

\n
\n", "Examiners report": "
\n

\n Any symbols were accepted for the alleles, as long as they were shown superscript to X and the genotype was heterozygous. 70 % of candidates answered correctly.\n

\n
\n", "question_id": "21N.2.SL.TZ0.2A.II", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-2-inheritance", "d3-2-12-haemophilia-as-an-example-of-a-sex-linked-genetic-disorder" ] }, { "Question": "
\n
\n

\n Which process(es) occur(s) by osmosis?\n

\n

\n I. Uptake of water by cells in the wall of the intestine\n

\n

\n II. Loss of water from a plant cell in a hypertonic environment\n

\n

\n III. Evaporation of water from sweat on the skin surface\n

\n

\n A. I only\n

\n

\n B. I and II only\n

\n

\n C. II and III only\n

\n

\n D. I, II and III\n

\n

\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "19M.1A.SL.TZ1.4", "topics": [ "d-continuity-and-change", "b-form-and-function" ], "subtopics": [ "d2-3-water-potential", "d2-3-3-water-movement-by-osmosis-into-or-out-of-cells", "b2-1-membranes-and-membrane-transport", "b2-1-5-movement-of-water-molecules-across-membranes-by-osmosis-and-the-role-of-aquaporins" ] }, { "Question": "
\n
\n

\n Explain how this relationship differs from that in humans.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n humans maintain/regulate a constant body temperature at different ambient temperatures/maintained by homeostasis;\n

\n
\n", "Examiners report": "
\n

\n Often steady or constant body temperatures for humans was given rather than homeostasis. Some candidates erroneously described humans as warming up in response to cold ambient temperatures.\n

\n
\n", "question_id": "22M.2.SL.TZ1.A.II", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-3-homeostasis", "d3-3-1-homeostasis-as-maintenance-of-the-internal-environment-of-an-organism", "d3-3-2-negative-feedback-loops-in-homeostasis" ] }, { "Question": "
\n
\n (b.i)\n
\n
\n

\n Label the model A diagram to show a region of protein.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n \n

\n

\n [Source: diagram from article published in\n \n The American Journal of Pathology\n \n ,\n \n 65\n \n , J Singer and G Nicolson, The structure and chemistry of mammalian cell membranes, 427–437, Copyright Elsevier (1971)]\n

\n

\n \n Accept label to top protein.\n \n

\n
\n", "Examiners report": "
\n

\n Most students could label the areas with protein and phospholipid.\n

\n
\n", "question_id": "19M.1B.SL.TZ2.1B.I", "topics": [ "b-form-and-function" ], "subtopics": [ "b2-1-membranes-and-membrane-transport", "b2-1-10-fluid-mosaic-model-of-membrane-structure" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Draw a molecular diagram of alpha-D-glucose.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n a. hexagonal ring structure with O at one point (between C1 and C5);\n

\n

\n b. correct orientation of OH groups (on carbons 1 to 4);\n \n Hydrogens not required\n \n

\n

\n c. CH\n \n 2\n \n OH group shown on fifth carbon with correct orientation;\n
\n \n \n OR\n \n \n
\n d. 6 carbon chain with oxygen on first C;\n

\n

\n e. H and OH groups correctly orientated;\n

\n

\n \n Carbons do not need to be numbered\n \n .\n

\n

\n \n Allow boat or chair diagrams\n \n .\n

\n

\n \n

\n

\n \n Allow\n \n [2 max]\n \n if linear structure drawn\n \n .\n

\n
\n", "Examiners report": "
\n

\n This was the less favourite option question, generally attempted by the better candidates. In part (a) the candidates tended to gain either 3 for a correct structure or zero. A G2 comment asked whether the different forms of glucose were needed; knowledge of the structure of alpha-glucose is stated in the syllabus.\n

\n

\n Most gained some marks for what was really a description of photosynthesis in part (b), and the transformations of carbon compounds in the carbon cycle was quite well known. Some students lost marks by continuing to use the term ‘carbon compounds’ instead of carbon dioxide and the specific compounds. Many went off on a tangent to write about carbon dioxide and climate change\n \n etc\n \n . Many drew some quite detailed flow charts of the carbon cycle from which some marks could be gleaned or ambiguous statements clarified.\n

\n
\n", "question_id": "20N.2.SL.TZ0.5", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-3-photosynthesis", "c1-3-1-transformation-of-light-energy-to-chemical-energy-when-carbon-compounds-are-produced-in-photosynthesis", "c4-2-transfers-of-energy-and-matter", "c4-2-18-ecosystems-as-carbon-sinks-and-carbon-sources", "c4-2-22-recycling-of-all-chemical-elements-required-by-living-organisms-in-ecosystems" ] }, { "Question": "
\n
\n

\n Huntington’s disease can develop in middle age and leads to death of brain cells. It is carried by an autosomal dominant gene. What can be deduced about a man who has the disease?\n

\n

\n A. Half of his children will get the disease.\n

\n

\n B. Neither of his parents had the disease, but one must have been a carrier.\n

\n

\n C. At least one of his grandparents must have had the disease.\n

\n

\n D. His sons are more likely to have the disease than his daughters.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "21N.1A.SL.TZ1.12", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-2-inheritance", "d3-2-5-effects-of-dominant-and-recessive-alleles-on-phenotype" ] }, { "Question": "
\n
\n

\n More than 90 % of cellular cholesterol is located in the cell’s plasma membrane. What is the main role of cholesterol in the plasma membranes of mammalian cells?\n

\n

\n A. To regulate membrane fluidity\n

\n

\n B. To increase membrane solubility\n

\n

\n C. To increase membrane permeability\n

\n

\n D. To regulate membrane temperature\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "None", "question_id": "22M.1A.HL.TZ1.2", "topics": [ "b-form-and-function" ], "subtopics": [ "b2-1-membranes-and-membrane-transport", "b2-1-12-cholesterol-and-membrane-fluidity-in-animal-cells" ] }, { "Question": "
\n
\n

\n Compare and contrast the results for winter and spring.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n \n Compare part of answer = similarity\n \n :\n

\n
    \n
  1. \n both have low BCH (compared with summer);\n
    \n
    \n \n Contrast part of answer\n \n :\n
    \n
    \n
    2. \n
  2. \n greater body mass in spring than winter;\n \n \n
    \n OR\n     \n     \n
    \n overall/mean/average BCH higher in spring than in winter;\n \n \n
    \n OR\n     \n     \n
    \n more variation\n \n in body mass\n \n in spring than winter;\n
    3. \n
\n

\n \n For the second alternative in mpb, the answer must not state simply that BCH is higher in spring as there is much overlap. Do not accept quoted figures without the similarity or difference being stated.\n \n

\n
\n", "Examiners report": "
\n

\n This was a 'compare and contrast' question, so similarities and differences were expected in the answer. There were plenty of choices for differences between winter and spring but only one acceptable similarity — that BCH was lower in both winter and spring than in summer. Some answers failed to discriminate between BCH and brain mass — the trends were not the same so these terms were not interchangeable. Some candidates gave a comparison and then repeated it as the converse statement — for example 'sample mass is higher in spring than winter and is lower in winter than spring'. Clearly this is not necessary.\n

\n
\n", "question_id": "22N.2.HL.TZ0.E", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-1-integration-of-body-systems", "c3-1-4-the-brain-as-a-central-information-integration-organ" ] }, { "Question": "
\n
\n

\n Compare and contrast the structure of a typical prokaryotic cell with that of a mitochondrion.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n

\n \n differences\n \n

\n

\n a. prokaryote has cell wall but mitochondrion does not ✔\n

\n

\n b. mitochondrion has double membrane whereas prokaryote has single membrane\n
\n \n \n OR\n \n \n
\n «Gram negative» bacteria have cell wall between two membranes whereas mitochondria has intermembrane space between two membranes ✔\n

\n

\n c. mitochondrion has cristae/invaginations of inner membrane but prokaryote does not\n
\n \n \n OR\n \n \n
\n prokaryote «may have» flagella/pili/«slime» capsule which mitochondria do not have ✔\n

\n

\n \n similarities\n \n

\n

\n d.\n \n 70S\n \n ribosomes in both ✔\n

\n

\n e.\n \n DNA\n \n in both / loop of\n \n DNA\n \n in both / naked\n \n DNA\n \n in both ✔\n

\n

\n f. shape similar/both rod shaped/\n \n OWTTE\n \n
\n \n \n OR\n \n \n
\n size of both is similar/both about 3 μm long ✔\n

\n

\n g. both are membrane-bound/\n \n OWTTE\n \n ✔\n

\n
\n", "Examiners report": "
\n

\n Answers were spread over the whole of the four-mark range. The scale bars allowed the sizes of both to be calculated – they were close, but even so a substantial number of candidates claimed that one or other was significantly larger.\n

\n
\n", "question_id": "19M.2.HL.TZ1.A", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a2-2-cell-structure", "a2-2-12-origin-of-eukaryotic-cells-by-endosymbiosis" ] }, { "Question": "
\n
\n

\n Domestic dogs (\n \n Canis familiaris\n \n ) have evolved from grey wolves (\n \n Canis lupus\n \n ). Evidence suggests that the domestication of dogs first occurred around 30 000 years ago. Which best describes the evolution giving rise to the domestic dog?\n

\n

\n
\n A.  The wolf produced offspring in large numbers which underwent natural selection.\n

\n

\n B.  Variations in the wolf population that resembled modern dogs favoured wolf survival.\n

\n

\n C.  Wolves showing favourable traits were selected for breeding.\n

\n

\n D.  Dogs were better suited to changes in the natural environment than wolves.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "SPM.1A.HL.TZ0.40", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-1-natural-selection", "d4-1-15-artificial-selection-by-deliberate-choice-of-traits" ] }, { "Question": "
\n
\n

\n The garden snail,\n \n Helix aspersa\n \n , is a herbivore.\n
\n
\n

\n

\n \n

\n

\n [Source: Sinan Önder /https://www.pexels.com/photo/animal-close-up-crawling-garden-243128/]\n

\n

\n

\n

\n Explain how the population of snails in an ecosystem could be estimated by capture-mark-release-recapture, identifying the limitations in the method.\n

\n
\n
\n

\n [6]\n

\n
\n
\n", "Markscheme": "
\n

\n a. snails in the ecosystem are captured and marked ✔\n

\n

\n b. they are released back in to the ecosystem and allowed to mix ✔\n

\n

\n c. a second sample of snails are captured in the ecosystem and those that are marked are counted ✔\n

\n

\n d. sufficient time given between first and second sample to allow for mixing ✔\n

\n

\n e. the ratio of the first sample size to those recaptured marked = the ratio of the number in the second sample to the population/formula ✔\n

\n

\n f. area of habitat determined ✔\n

\n

\n g. assumes sample size is large enough to be significant ✔\n

\n

\n h. assumes there is no emigration/immigration/death of snails ✔\n

\n

\n i. assumes the marking of the snail does not affect their survival ✔\n

\n

\n j. assumes no misidentification of species ✔\n

\n

\n k. assumes marked snails do not lose their marks ✔\n

\n
\n", "Examiners report": "
\n

\n This longer response question was also well answered, and stronger candidates often scored full marks. Only very weak students were not able to provide some outline of the method used, although fewer students achieved the marks that rewarded knowledge about the assumptions of the method. Many felt that the time required was a drawback, and very few were able to achieve the marking point available for correct use of the Lincoln index. For all experimental skills in the subject guide, students should be taught to outline how the method is carried out and how the data collected can be processed; and to evaluate errors, limitations and assumptions.\n

\n
\n", "question_id": "19M.2.SL.TZ1.19", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c4-1-populations-and-communities", "c4-1-4-capture-mark-release-recapture-and-the-lincoln-index-to-estimate-population-size-for-motile-organisms" ] }, { "Question": "
\n
\n

\n Which regions of DNA code for the production of specific proteins?\n

\n

\n A. Telomeres\n

\n

\n B. Genes for ribosomal RNA\n

\n

\n C. Exons\n

\n

\n D. Regulators of gene expression\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "21M.1A.HL.TZ1.26", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d1-2-protein-synthesis", "d1-2-15-post-transcriptional-modification-in-eukaryotic-cells" ] }, { "Question": "
\n
\n

\n The graph shows changes in the concentration of an antibody in the blood of an individual subjected to two separate infections at time X and time Y.\n

\n

\n \n

\n

\n [Source: Illustration from Anatomy & Physiology, Connexions Web site.\n \n http://cnx.org/content/col11496/1.6/\n \n , Jun 19, 2013 OpenStax College © 1999-2021, Rice University. Except where otherwise noted, textbooks on this site are licensed under a Creative Commons Attribution 4.0 International License (\n \n https://creativecommons.org/licenses/by/4.0/\n \n ).]\n

\n

\n

\n

\n What distinguishes the events occurring at Y from those occurring at X?\n

\n

\n A. The individual was infected with different pathogens at X and Y.\n

\n

\n B. Memory B cells are involved in antibody production at Y but not at X.\n

\n

\n C. There is no clonal selection involved.\n

\n

\n D. There are no T lymphocytes involved.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "
\n

\n This question was the easiest on the paper for the candidates with 89 % selecting the correct response.\n

\n
\n", "question_id": "21M.1A.SL.TZ2.37", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-2-defence-against-disease", "c3-2-10-immunity-as-a-consequence-of-retaining-memory-cells" ] }, { "Question": "
\n
\n

\n Suggest a way methylation may affect tumour cell genes.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n a. «DNA» methylation may inhibit transcription of genes that would prevent cancer/tumor formation ✔\n

\n

\n b. «DNA» methylation may increase mitosis/cell division leading to tumor formation ✔\n

\n

\n \n Do not accept discussion of histone methylation.\n \n

\n
\n", "Examiners report": "
\n

\n Students lacked the understanding of epigenetics necessary to make reasonable suggestions.\n

\n
\n", "question_id": "19M.2.HL.TZ2.B.II", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-2-gene-expression-[hl-only]", "d2-2-6-methylation-of-the-promoter-and-histones-in-nucleosomes-as-examples-of-epigenetic-tags", "d2-2-7-epigenetic-inheritance-through-heritable-changes-to-gene-expression" ] }, { "Question": "
\n
\n

\n The magnification of the micrograph is 2000×.\n

\n

\n \n

\n

\n [Source: https://upload.wikimedia.org/wikipedia/commons/6/6c/HeLa_cells_stained_with_Hoechst_33258.jpg\n
\n by TenOfAllTrades.]\n

\n

\n

\n

\n What is the maximum diameter of the nucleus in the cell labelled X?\n

\n

\n A. 10 μm\n

\n

\n B. 10 nm\n

\n

\n C. 20 μm\n

\n

\n D. 20 nm\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "
\n

\n Many students found it difficult to calculate the maximum diameter of the nucleus without a calculator.\n

\n
\n", "question_id": "19M.1A.SL.TZ2.2", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a2-2-cell-structure", "a2-2-2-microscopy-skills" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Describe how detritivores obtain nutrition and the effects they have in ecosystems.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n

\n a. «detritivores» obtain nutrition from detritus/waste/dead bodies ✔\n

\n

\n b. are heterotrophic ✔\n

\n

\n c. removes large waste/cleans up the ecosystem\n
\n \n \n OR\n \n \n
\n helps control spread of disease ✔\n

\n

\n d. facilitates further decomposition ✔\n

\n

\n e. contribute to the supply of «inorganic» nutrients for autotrophs/nutrient cycling\n
\n \n \n OR\n \n \n
\n improve soil conditions/aeration ✔\n

\n
\n", "Examiners report": "
\n

\n Most candidates got max 2 for mp a (nutrition of detritivores) and mp e (recycling of nutrients). Candidates getting high marks were able to provide correct examples of detritivores and correctly link to their role in enriching the soil and remove dead material. The biggest problem was the notion that detritivores recycle energy.\n

\n
\n", "question_id": "19M.2.SL.TZ1.8", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-3-photosynthesis", "c1-3-5-absorption-of-specific-wavelengths-of-light-by-photosynthetic-pigments" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Outline how the properties of water make it an effective coolant for the body.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n hydrogen bonds hold water molecules together/make water molecules cohere;\n
    2. \n
  2. \n evaporation requires breaking of hydrogen bonds / heat needed to break hydrogen bonds\n
    3. \n
  3. \n water has a high heat of vaporization/high latent heat;\n
    4. \n
  4. \n evaporation of water/sweat removes heat from/cools the skin/body;\n
    5. \n
\n
\n", "Examiners report": "
\n

\n This question revealed widespread misunderstanding of the properties of water and changes of state. Most candidates though that water's high specific heat capacity explains its role as a coolant and that sweat cools the body by taking heat from it to raise its temperature. Few candidates referred to the requirement for heat to break hydrogen bonds as water evaporates. To be able to understand biological processes properly, a firm grounding in physics and chemistry is needed, but all too often it was lacking.\n

\n
\n", "question_id": "22M.2.HL.TZ1.6", "topics": [ "a-unity-and-diversity", "b-form-and-function", "d-continuity-and-change" ], "subtopics": [ "a1-1-water", "a1-1-6-physical-properties-of-water-and-the-consequences-for-animals-in-aquatic-habitats", "b3-1-gas-exchange", "b3-1-9-transpiration-as-a-consequence-of-gas-exchange-in-a-leaf", "d3-3-homeostasis", "d3-3-7-role-of-the-kidney-in-osmoregulation-and-excretion" ] }, { "Question": "
\n
\n

\n William Bateson and Reginald Punnett used the sweet pea (\n \n Lathyrus odoratus\n \n ) in genetics studies in the early 20\n \n th\n \n century. Pure-breeding plants that produced purple flowers and long pollen grains were crossed with pure-breeding plants that produced red flowers and round pollen grains. The resulting offspring all produced purple flowers and long pollen grains. Two of the F\n \n 1\n \n generation plants were crossed. The table shows the ratio of phenotypes in the F\n \n 2\n \n generation.\n

\n

\n \n

\n

\n What is an explanation for these experimental results?\n

\n

\n A. Purple flowers and long pollen grains are dominant and the alleles have assorted independently.\n

\n

\n B. The genes for flower colour and pollen shape are linked and all plants producing long pollen grains are recombinants.\n

\n

\n C. The genes for flower colour and pollen shape are linked and all plants producing red flowers are recombinants.\n

\n

\n D. Plants producing purple flowers and round pollen grains arose through crossing over.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "
\n

\n This was a wordy question that turned out to be quite time consuming. Many candidates failed to realize that if the alleles had assorted independently the ratios would have been 9:3:3:1. The only way the results shown could have been obtained was through genetic linkage between purple and long and red and round. Purple and round are formed by recombination of alleles through crossing over.\n

\n
\n", "question_id": "19M.1A.HL.TZ2.20", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-2-inheritance", "d3-2-17-punnett-grids-for-predicting-genotypic-and-phenotypic-ratios-in-dihybrid-crosses-involving-pairs-of-unlinked-autosomal-genes" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n State the approximate value of the membrane potential at X.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n 0 mV; (\n \n accept answers in the range of – 10 mV to +10 mV\n \n ) (\n \n Units required\n \n )\n

\n
\n", "Examiners report": "
\n

\n There were some truly brilliant answers to Question 5. However, the weakest answers in the examination were also found here. Of the questions, these were the most commonly left blank.\n

\n

\n Candidates were often unable to approximate X. Missing units resulted in no marks awarded.\n

\n
\n", "question_id": "22M.2.HL.TZ1.5A", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c2-2-neural-signalling", "c2-2-10-oscilloscope-traces-showing-resting-potentials-and-action-potentials" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n The enzyme Rubisco is used in carbon fixation during photosynthesis. Identify\n \n four\n \n other examples of proteins that illustrate the wide range of functions of this group of biochemicals in living organisms.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n

\n a. insulin receptors start the cellular signalling pathway/other receptor\n

\n

\n b. leptin is a hormone / other protein hormone ✔\n

\n

\n c. immunoglobulins/antibodies defend body from disease ✔\n

\n

\n d. rhodopsin/photosystems convert light energy to electrical impulses ✔\n

\n

\n e. keratin/collagen/other example is a structural protein ✔\n

\n

\n f. tubulin/microtubules part of cytoskeleton/ involved in cell division\n

\n

\n g. ATP synthase is an enzyme that catalyzes the formation of ATP / other enzyme and function ✔\n

\n

\n h. fibrin/fibrinogen is a protein involved in clotting ✔\n

\n

\n i. hemoglobin/sodium potassium pump/other example is a transport protein ✔\n

\n

\n j. actin/myosin/other example is involved in muscle contraction ✔\n

\n

\n k. any other named example and function ✔\n

\n

\n l. a second other named example and function ✔\n

\n

\n m. spider silk is used to form spider webs/capture prey ✔\n

\n

\n \n Accept only one example of each protein type for example only one enzyme or only one hormone etc\n \n .\n

\n

\n \n Mp k can be awarded only once\n \n .\n

\n

\n \n Mp I can be awarded only once\n \n .\n

\n
\n", "Examiners report": "
\n

\n Question 6 was a popular question.\n

\n

\n Well answered by most except for when students gave multiple examples of proteins of the same functional type; for example, four examples of enzymes when the question asked for an illustration of the wide range of functions of proteins.\n

\n
\n", "question_id": "21M.2.HL.TZ2.6C", "topics": [ "b-form-and-function" ], "subtopics": [ "b1-2-proteins", "b1-2-6-chemical-diversity-in-the-r-groups-of-amino-acids-as-a-basis-for-the-immense-diversity-in-protein-form-and-function", "b1-2-12-relationship-of-form-and-function-in-globular-and-fibrous-proteins" ] }, { "Question": "
\n
\n (f)\n
\n
\n

\n Suggest\n \n two\n \n hypotheses to account for the relationship between the mean number of steps per day and the proportion of people who are obese.\n

\n

\n

\n

\n Hypothesis 1: ...........................................................................................................\n

\n

\n ...............................................................................................................................\n

\n

\n

\n

\n Hypothesis 2: ...........................................................................................................\n

\n

\n ...............................................................................................................................\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n \n (any order)\n \n

\n
    \n
  1. \n obesity causes people to be less active/take fewer steps;\n
    2. \n
  2. \n people who are less active/take fewer steps (are more likely to) become obese;\n
    3. \n
  3. \n People who are not obese tend to have healthier habits, including walking more;\n
    4. \n
\n

\n

\n

\n \n Accept hypothesis and a null hypothesis for the two.\n \n \n
\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ1.1F", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-3-muscle-and-motility-(hl-only)", "b3-3-9-reasons-for-locomotion" ] }, { "Question": "
\n
\n (a.i)\n
\n
\n

\n Describe the structure of nucleosomes.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n a unit of DNA wound/coiled around 8 histone proteins / octamer;\n

\n
\n", "Examiners report": "
\n

\n The structure of a nucleosome was correctly described for many, but some did not mention the number of histones.\n

\n
\n", "question_id": "22M.2.HL.TZ2.5A.I", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a1-2-nucleic-acids", "a1-2-13-structure-of-a-nucleosome" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Xylem and phloem contain structures that are adapted for transport. Outline the differences between these structures in xylem and phloem.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. plasma membrane in phloem/sieve tubes but not in xylem/vessels\n
\n \n \n OR\n \n \n
\n xylem/vessels dead/acellular and phloem/sieve tubes alive ✔\n

\n

\n b. xylem vessels have thicker walls «than phloem» ✔\n

\n

\n c. xylem «vessel» walls are lignified «but phloem walls are not» ✔\n

\n

\n d. phloem vessels have sieve plates «whereas xylem vessels have no cross walls» ✔\n

\n

\n e. xylem/vessels are wider/larger than phloem/sieve tubes ✔\n

\n

\n f. companion cells in phloem «but not in xylem» ✔\n

\n
\n", "Examiners report": "
\n

\n Many candidates knew nothing about the structure of the conducting tissues of plants and instead gave some rudimentary information on their functions. A common misconception is that phloem sieve tubes are wider than xylem vessels. This may have come from a failure to identify correctly the xylem and phloem tissue correctly in the micrograph. The most commonly known feature of xylem was the lignified wall and if phloem was the presence of companion cells.\n

\n
\n", "question_id": "19M.2.HL.TZ1.4", "topics": [ "b-form-and-function", "a-unity-and-diversity" ], "subtopics": [ "b3-2-transport", "b3-2-9-distribution-of-tissues-in-a-transverse-section-of-the-stem-of-a-dicotyledonous-plant", "b3-2-18-adaptations-of-phloem-sieve-tubes-and-companion-cells-for-translocation-of-sap", "b3-2-7-transport-of-water-from-roots-to-leaves-during-transpiration", "a1-1-water", "a1-1-3-cohesion-of-water-molecules-due-to-hydrogen-bonding-and-consequences-for-organisms", "b1-1-carbohydrates-and-lipids", "b1-1-6-structure-of-cellulose-related-to-its-function-as-a-structural-polysaccharide-in-plants" ] }, { "Question": "
\n
\n (c.i)\n
\n
\n

\n Compare and contrast the data for 1998–1999 and 2002–2003.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n \n \n Similarities\n \n \n
\n a. similar range of cover in both periods\n
\n OR\n
\n weak correlation/no correlation in either;\n

\n

\n \n \n Differences\n \n \n
\n b. higher WSSTA range/more WSSTA in 1998–1999 than 2002–2003\n
\n OR\n
\n positive (2002–2003) versus negative correlation (98–99)\n
\n OR\n
\n more coral reefs with very low % of coral cover (0–20 %) in 2002–2003;\n

\n

\n \n Must respond with one similarity and one difference for full marks\n \n .\n

\n
\n", "Examiners report": "
\n

\n In 1c contrasts were common, but few gained the comparison mark as well.\n

\n
\n", "question_id": "21N.2.SL.TZ0.1C.I", "topics": [ "d-continuity-and-change", "b-form-and-function" ], "subtopics": [ "d4-3-climate-change", "d4-3-7-threats-to-coral-reefs-as-an-example-of-potential-ecosystem-collapse", "b4-1-adaptation-to-environment", "b4-1-5-conditions-required-for-coral-reef-formation" ] }, { "Question": "
\n
\n (j)\n
\n
\n

\n A hypothesis has been proposed that an increase in parathyroid hormone concentration causes an increase in osteocalcin in bears. Evaluate the evidence for this hypothesis provided by the data.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n (hypothesis supported by)\n
    \n positive/direct correlation/direct relationship (between parathyroid hormone and osteocalcin)\n
    \n \n \n OR\n \n \n
    \n osteocalcin rises as parathyroid hormone rises/vice versa;\n
    2. \n
  2. \n no evidence for causal link / causal link cannot be assumed / correlation does not prove causation;\n
    \n \n \n OR\n \n \n
    \n no evidence that parathyroid hormone causes change in osteocalcin;\n
    \n \n \n OR\n \n \n
    \n other factors may cause change in osteocalcin;\n
    3. \n
\n
\n", "Examiners report": "
\n

\n This type of question is increasingly well answered with more candidates understanding that two variables being positively correlated does not prove a causation. The situation would have been different if an experiment had been done with the levels of parathyroid hormone as the independent variable controlled by the researchers.\n

\n
\n", "question_id": "22M.2.SL.TZ1.1J", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-3-homeostasis", "d3-3-1-homeostasis-as-maintenance-of-the-internal-environment-of-an-organism", "d3-3-2-negative-feedback-loops-in-homeostasis" ] }, { "Question": "
\n
\n

\n In which processes are macromolecules broken down into monomers?\n

\n

\n A. Anabolism and catabolism\n

\n

\n B. Catabolism and hydrolysis\n

\n

\n C. Hydrolysis and reduction\n

\n

\n D. Reduction and anabolism\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "19N.1A.SL.TZ0.6", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-1-enzymes-and-metabolism", "c1-1-3-anabolic-and-catabolic-reactions" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Explain how temperature affects enzymes.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n speed of reaction/catalysis increases as temperature rises;\n
    2. \n
  2. \n faster molecular motion so more collisions between substrate and active site;\n
    3. \n
  3. \n denaturation at higher temperatures;\n
    4. \n
  4. \n (denaturation causes) shape/conformation/structure of enzyme/active site altered/damaged;\n
    5. \n
  5. \n an enzyme works fastest at its optimum temperature;\n
    6. \n
  6. \n inactivation at lower temperatures (due to very few collisions);\n
    7. \n
  7. \n sketch graph to model the effect of temperature on enzyme activity;\n
    8. \n
\n

\n \n Graphs would need to be well annotated.\n \n

\n

\n \n Must not be bell shaped.\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ2.6A", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-1-enzymes-and-metabolism", "c1-1-8-effects-of-temperature-ph-and-substrate-concentration-on-the-rate-of-enzyme-activity" ] }, { "Question": "
\n
\n

\n What are the evolutionary origins and functions of homologous structures?\n

\n

\n \n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "21M.1A.SL.TZ1.15", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a4-1-evolution-and-speciation", "a4-1-4-evidence-for-evolution-from-homologous-structures" ] }, { "Question": "
\n
\n

\n The diagram shows the longitudinal section of phloem tissue at a plant source.\n

\n

\n \n

\n

\n

\n

\n What is a function of the structures labelled X?\n

\n

\n A. To provide the companion cell with carbon dioxide\n

\n

\n B. To provide the companion cell with glucose\n

\n

\n C. To allow movement of sucrose into the sieve tube\n

\n

\n D. To allow movement of starch into the sieve tube\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "22M.1A.HL.TZ2.32", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-2-transport", "b3-2-18-adaptations-of-phloem-sieve-tubes-and-companion-cells-for-translocation-of-sap" ] }, { "Question": "
\n
\n

\n An individual is heterozygous for two linked genes\n \n .\n

\n

\n To investigate the frequency of crossing over, a test cross is carried out between the individual and another that is homozygous recessive for both genes. What are the possible recombinants in the offspring of this cross?\n

\n

\n \n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "22M.1A.HL.TZ1.36", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-2-inheritance", "d3-2-16-segregation-and-independent-assortment-of-unlinked-genes-in-meiosis", "d3-2-20-recombinants-in-crosses-involving-two-linked-or-unlinked-genes" ] }, { "Question": "
\n
\n

\n Which molecule is depicted in the diagram?\n

\n

\n \n

\n

\n A. A saturated fatty acid\n

\n

\n B. An unsaturated fatty acid\n

\n

\n C. A trans fat\n

\n

\n D. A vegetable oil\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "
\n

\n About two thirds of candidates answered this question correctly, but the discrimination index was surprisingly low. Some of the stronger candidates thought that the molecule depicted was an unsaturated fatty acid, perhaps because of the double bond in the carboxyl group. It is only in the hydrocarbon chain that a double bond indicates an unsaturated fatty acid.\n

\n
\n", "question_id": "21M.1A.SL.TZ1.10", "topics": [ "b-form-and-function" ], "subtopics": [ "b1-1-carbohydrates-and-lipids", "b1-1-10-difference-between-saturated-monounsaturated-and-polyunsaturated-fatty-acids" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Comment on the total energy content of the two diets.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n a. energy is not changed (between the two diets);\n

\n

\n b. study diet\n \n slightly\n \n lower in energy than habitual diet (but means/SD overlap);\n

\n

\n c. spread of values show more variation for habitual diet / higher SD in habitual;\n

\n
\n", "Examiners report": "
\n

\n Considering that all students must complete an Individual investigation as part of their Biology course, few understood the significance of the uncertainties shown in the first table or the overlap of the standard deviations in the graph in part d. Only the better candidates were able to say that the energy was extremely similar in both diets. A surprising number could not calculate a percentage change in part c.\n

\n

\n In part b, the command term was ‘distinguish’ which means that only differences were looked for. Similarly in d(i), ‘compare’ means that only similarities were needed. If both were required, the command term is ‘compare and contrast’.\n

\n

\n In d, few could state that there was no significant difference in the two curves due to the overlap of the error bars. Most knew that the beta cells of the pancreas secrete insulin, although a surprising number thought that they were produced by the red blood cells. In e, many gained two marks for linking saturated fats to cholesterol and its consequence.\n

\n

\n

\n
\n", "question_id": "20N.1B.SL.TZ0.1A", "topics": [ "b-form-and-function" ], "subtopics": [ "b1-2-proteins", "b1-2-3-dietary-requirements-for-amino-acids", "b1-1-carbohydrates-and-lipids", "b1-1-10-difference-between-saturated-monounsaturated-and-polyunsaturated-fatty-acids" ] }, { "Question": "
\n
\n

\n The diagram shows the food web for an aquatic ecosystem in which letters R–Z represent individual species.\n

\n

\n \n

\n

\n [Source: © International Baccalaureate Organization 2019]\n

\n

\n

\n

\n Which organism is a tertiary consumer?\n

\n

\n A. Organism T\n

\n

\n B. Organism U\n

\n

\n C. Organism W\n

\n

\n D. Organism Y\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "19M.1A.SL.TZ1.18", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c4-2-transfers-of-energy-and-matter", "c4-2-3-flow-of-chemical-energy-through-food-chains" ] }, { "Question": "
\n
\n

\n In which stage of the cell cycle are chromosomes duplicated?\n

\n

\n \n

\n

\n [Source: M1llx, 2019. Cell cycle simple pl. [online] Available at:\n \n https://commons.wikimedia.org/wiki/File:Cell_cycle_simple_\n \n \n pl.png\n \n This file is licensed\n
\n under the Creative Commons Attribution-Share Alike 4.0 International license.\n
\n \n https://creativecommons.org/licenses/by-sa/4.0/deed.en\n \n [Accessed 1 August 2019].]\n

\n

\n

\n

\n A. G1 phase\n

\n

\n B. G2 phase\n

\n

\n C. S phase\n

\n

\n D. Mitosis\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "22M.1A.HL.TZ1.4", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-1-cell-and-nuclear-division", "d2-1-13-phases-of-the-cell-cycle" ] }, { "Question": "
\n
\n

\n When does DNA replication occur?\n

\n

\n A. S phase of interphase\n

\n

\n B. Early prophase\n

\n

\n C. G phase of interphase\n

\n

\n D. Late prophase\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "None", "question_id": "21M.1A.SL.TZ2.4", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-1-cell-and-nuclear-division", "d2-1-5-dna-replication-as-a-prerequisite-for-both-mitosis-and-meiosis" ] }, { "Question": "
\n
\n (l)\n
\n
\n

\n With reference to all the data, suggest a reason for the difference in standardized mean path length for summer and winter.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n in winter shrews have smaller brains/smaller BCH / converse for summer;\n
    2. \n
  2. \n lower/poorer memory/thinking/cognitive skills/learning/intelligence/senses/sense of smell/ability to find food in winter/converse for summer;\n
    3. \n
\n
\n", "Examiners report": "
\n

\n The instruction to refer to all the data does not indicate that conclusions from each graph should be restated, but rather than the research findings should be combined to produce a hypothesis. The expected reasoning here was that the lower BCH of shrews in winter showed brain mass was on average lower, so cognitive ability was reduced and shrews were slower to find food.\n

\n
\n", "question_id": "22N.2.HL.TZ0.1L", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-1-integration-of-body-systems", "c3-1-4-the-brain-as-a-central-information-integration-organ" ] }, { "Question": "
\n
\n

\n Deduce the change in mitotic index after 72 hours compared to the control.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n 0.3 / 100 % increase / doubling ✔\n

\n

\n \n Do not penalize errors in significant figures. For example, 0.34 would be acceptable\n \n .\n

\n
\n", "Examiners report": "
\n

\n Those who had experience calculating mitotic index did well with this question.\n

\n
\n", "question_id": "21M.2.HL.TZ1.E", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-1-cell-and-nuclear-division", "d2-1-17-differences-between-tumours-in-rates-of-cell-division-and-growth-and-in-the-capacity-for-metastasis-and-invasion-of-neighbouring-tissue" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n State the probability that Edward had hemophilia.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n 0.5/50 %;\n

\n
\n", "Examiners report": "
\n

\n Approximately 50 % of the candidates were correct with their answer of 50 %. It was expected that candidates would recognize that Edward is male because he has a box rather than circle in the pedigree. Then from there, they would calculate the 50 %.\n

\n
\n", "question_id": "22M.2.SL.TZ1.4A", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-2-inheritance", "d3-2-12-haemophilia-as-an-example-of-a-sex-linked-genetic-disorder", "d3-2-13-pedigree-charts-to-deduce-patterns-of-inheritance-of-genetic-disorders" ] }, { "Question": "
\n
\n

\n Using\n \n all\n \n of the data, discuss whether there is evidence that the two sub-species of\n \n O. sativa\n \n might have evolved independently from\n \n O. rufipogon\n \n .\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n

\n a. large difference in diversity index between\n \n O. s. indica\n \n and\n \n O. s. japonica\n \n «suggests independent evolution» ✔\n

\n

\n b. «some of the» peaks/troughs for\n \n O. s. indica\n \n and\n \n O. s. japonica\n \n in different positions «suggests independent evolution» ✔\n

\n

\n c.\n \n O.s. indica\n \n has a similar diversity index to\n \n O. rufipogon\n \n «which suggests closer relationship/recent divergence» ✔\n
\n \n Allow converse for japonica\n \n

\n

\n d.\n \n O.s. japonica\n \n has very different proportions of ancestral and derived alleles compared to\n \n O. s. indica\n \n ✔\n

\n

\n e.\n \n O.s. indica\n \n has similar large number of ancestral alleles to\n \n O. rufipogon I/II\n \n ✔\n \n Allow converse for derived\n \n

\n

\n f.\n \n O.s. japonica\n \n has a large number of derived alleles similar to\n \n O. rufipogon III\n \n
\n \n \n OR\n \n \n
\n «but» the number of derived alleles is greater in\n \n O. s. japonica\n \n than in\n \n O.rufipogon III\n \n ✔\n \n Allow converse for ancestral\n \n

\n

\n g.\n \n O.s. indica\n \n and\n \n O. s. japonica\n \n are in different clades ✔\n
\n \n \n OR\n \n \n
\n \n O.s. indica\n \n and\n \n O. rufipogon\n \n I are in the same clade ✔\n

\n

\n h. evidence from one chromosome/3 genes/2 studies is not sufficient to form a conclusion ✔\n

\n
\n", "Examiners report": "None", "question_id": "19N.2.SL.TZ0.G", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a3-2-classification-and-cladistics-(hl-only)", "a3-2-7-analysing-cladograms", "a3-1-diversity-of-organisms" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Outline how nucleosomes affect the transcription of DNA.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n (nucleosomes can) promote AND inhibit transcription of genes/expression of genes;\n
    2. \n
  2. \n (nucleosomes can) prevent transcription by (tight) condensation/supercoiling/packing of DNA;\n
    3. \n
  3. \n (nucleosomes can) allow/prevent binding of RNA polymerase/transcription factors;\n
    4. \n
  4. \n tagging/acetylation/methylation of nucleosomes/histones can promote/inhibit transcription;\n
    5. \n
  5. \n movement of histones/nucleosomes (along DNA) can affect which genes are transcribed;\n
    6. \n
\n

\n \n ‘Affects transcription’ is in the question — no mark.\n \n

\n
\n", "Examiners report": "
\n

\n Many candidates knew something of the role of nucleosomes in regulating DNA transcription. A wide range of answers was accepted for the single mark.\n

\n
\n", "question_id": "22N.2.HL.TZ0.4B", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-2-gene-expression-[hl-only]", "d2-2-6-methylation-of-the-promoter-and-histones-in-nucleosomes-as-examples-of-epigenetic-tags" ] }, { "Question": "
\n
\n

\n The diagram shows the carbon cycle.\n

\n

\n \n

\n

\n

\n

\n Which letters represent respiration?\n

\n

\n
\n A.  R and T\n

\n

\n B.  P and V\n

\n

\n C.  Q and R\n

\n

\n D.  R and V\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "23M.1A.SL.TZ2.20", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c4-2-transfers-of-energy-and-matter", "c4-2-17-constructing-carbon-cycle-diagrams" ] }, { "Question": "
\n
\n

\n The diagrams represent cross sections of the stem and root of a plant.\n

\n

\n \n

\n

\n Which tissues transport water in the stem and the root?\n

\n

\n \n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "22M.1A.SL.TZ1.33", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-2-transport", "b3-2-10-distribution-of-tissues-in-a-transverse-section-of-the-root-of-a-dicotyledonous-plant" ] }, { "Question": "
\n
\n

\n The picture shows lentils sprouts growing towards a light source from the left.\n

\n

\n \n

\n

\n [Source: Russell Neches, Lentil sprouts reaching for the sun [image online] Available at\n \n https://www.flickr.com/photos/rneches/2081938105/\n \n This file is licensed under\n
\n the Creative Commons Attribution 2.0 Generic (CC BY 2.0)\n
\n \n https://creativecommons.org/licenses/by/2.0/\n \n .]\n

\n

\n

\n

\n How has this response been brought about?\n

\n

\n A. A higher concentration of auxins on the light side caused faster photosynthesis.\n

\n

\n B. A higher concentration of auxins on the shaded side caused faster meiosis.\n

\n

\n C. A higher concentration of auxins on the shaded side caused faster cell elongation.\n

\n

\n D. A higher concentration of chloroplasts on the light side allowed for more photosynthesis.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "22M.1A.HL.TZ2.33", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-1-integration-of-body-systems", "c3-1-21-promotion-of-cell-growth-by-auxin" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Compare and contrast the results for Hymenoptera and Lepidoptera.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n both show a decline in number;\n
    2. \n
  2. \n the mean decline for Hymenoptera is less than the mean for Lepidoptera\n
    \n \n \n OR\n \n \n
    \n there is a wider range of decline among the species of Lepidoptera;\n
    3. \n
\n
\n", "Examiners report": "None", "question_id": "22N.2.SL.TZ0.1B", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c4-2-transfers-of-energy-and-matter", "c4-2-15-primary-production-as-accumulation-of-carbon-compounds-in-biomass-by-autotrophs", "c4-2-16-secondary-production-as-accumulation-of-carbon-compounds-in-biomass-by-heterotrophs" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Outline how depolarization of the membrane of an axon occurs.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. (local depolarization) causes ion / sodium / voltage gated channels to open ✔\n

\n

\n b. altering membrane permeability to sodium ions/Na\n \n +\n \n /positive ions / Na\n \n +\n \n diffuses into the cytoplasm ✔\n

\n

\n c. membrane potential (of the axon) changes from negative to positive ✔\n

\n

\n d. a threshold potential is reached\n \n and\n \n an action potential is generated ✔\n

\n

\n \n Do not accept sodium pumps\n \n .\n

\n

\n \n Mp b requires evidence that the student recognizes sodium is an ion\n \n .\n

\n

\n \n Numerical values indicating change from −70 to +30/+40/+55 can be accepted\n \n .\n

\n
\n", "Examiners report": "
\n

\n In many exams, candidates seemed to confuse the voltage gated ion channels with sodium-potassium pumps.\n

\n
\n", "question_id": "21M.2.SL.TZ2.2B", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c2-2-neural-signalling", "c2-2-6-release-of-neurotransmitters-from-a-presynaptic-membrane" ] }, { "Question": "
\n
\n

\n What allows the movement of water under tension in the xylem?\n

\n

\n
\n A.  Adhesion of water molecules to dissolved mineral salts\n

\n

\n B.  Cohesion of water molecules due to hydrogen bonding\n

\n

\n C.  Adhesion between water molecules due to uneven sharing of charges\n

\n

\n D.  Cohesion between water molecules and other polar substances\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "SPM.1A.HL.TZ0.1", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a1-1-water", "a1-1-3-cohesion-of-water-molecules-due-to-hydrogen-bonding-and-consequences-for-organisms" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Describe the structure of the DNA molecule.\n

\n
\n
\n

\n [5]\n

\n
\n
\n", "Markscheme": "
\n

\n a. two stranded/double\n \n helix\n \n ✔\n

\n

\n b. antiparallel / strands running in opposite directions\n
\n \n \n OR\n \n \n
\n one strand organized 5’ to 3’ and the other 3’ to 5’ ✔\n

\n

\n c. sugar-phosphate backbone ✔\n

\n

\n d. each strand formed by chains of nucleotides ✔\n

\n

\n e. each nucleotide is formed by a phosphate, a deoxyribose and a base / annotated diagram of a nucleotide clearly indicated as a nucleotide ✔\n

\n

\n f. the bases are adenine, guanine, cytosine and thymine ✔\n

\n

\n g. strands held together by hydrogen bonds (between complementary base pairs)\n
\n \n \n OR\n \n \n
\n A pairs with T and C pairs with G ✔\n

\n

\n \n Both helix and two strands needed for mp a. Double helix is sufficient for the mark\n \n .\n

\n

\n \n Points can be awarded to annotated diagrams\n \n .\n

\n

\n \n For mp c, the explicit label sugar phosphate backbone is required\n \n .\n

\n

\n \n To award mp d from a diagram, at least three pairs of nucleotides should be shown\n \n .\n

\n

\n \n For mp e, the diagram would need to be labelled as a nucleotide\n \n .\n

\n

\n \n For mp e, expect deoxyribose not just sugar\n \n .\n

\n

\n \n The written names of the bases are required for mp f\n \n .\n

\n

\n \n Do not penalize twice for mp f and g for using letters\n \n .\n

\n

\n \n If they only ever use the symbols A,T,C and G they are ineligible for mp f. If however, they say A pairs with T and C pairs with G, then they would get mp g. If they wrote adenine pairs with thymine and cytosine pairs with guanine, then they would obtain both mp f and mp g\n \n .\n

\n
\n", "Examiners report": "
\n

\n A surprising number of students failed to discuss nucleotides explicitly.\n

\n
\n", "question_id": "21M.2.HL.TZ2.7", "topics": [ "a-unity-and-diversity", "d-continuity-and-change" ], "subtopics": [ "a1-2-nucleic-acids", "a1-2-6-dna-as-a-double-helix-made-of-two-antiparallel-strands-of-nucleotides-with-two-strands-linked-by-hydrogen-bonding-between-complementary-base-pairs", "d1-1-dna-replication", "d1-1-3-role-of-helicase-and-dna-polymerase-in-dna-replication", "d1-1-8-functions-of-dna-primase-dna-polymerase-i-dna-polymerase-iii-and-dna-ligase-in-replication", "d2-2-gene-expression-[hl-only]", "d2-2-4-epigenesis-as-the-development-of-patterns-of-differentiation-in-the-cells-of-a-multicellular-organism", "a2-2-cell-structure", "a2-2-13-cell-differentiation-as-the-process-for-developing-specialized-tissues-in-multicellular-organisms" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n State\n \n one\n \n use of monoclonal antibodies.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n a. pregnancy testing kits/detection of hCG (to diagnose pregnancy) ✔\n

\n

\n b. produce antibodies for treating arthritis/\n \n C.difficile\n \n /anthrax/psoriasis/ulcerative colitis/asthma/ankylosing spondylitis/Crohn’s disease/multiple sclerosis/HIV/other named disease if verified / targeting tumor cells in treatment of cancer\n
\n \n \n OR\n \n \n
\n gives artificial/passive\n \n immunity\n \n (if injected) ✔\n

\n

\n c. blood typing/testing urine for drugs/other verified specific use of monoclonal antibodies ✔\n

\n

\n \n \n Mark only the first answer\n \n \n .\n

\n
\n", "Examiners report": "None", "question_id": "21M.2.HL.TZ1.4C", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-1-reproduction", "d3-1-17-pregnancy-testing-by-detection-of-human-chorionic-gonadotropin-secretion" ] }, { "Question": "
\n
\n

\n Suggest possible reasons for the difficulty of preventing or controlling a viral epidemic such as the 2014 EVD epidemic in a remote rural region.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. poor transport infrastructure/poor communication/bad roads/difficult access/no maps/support slow arriving/scattered population ✔\n

\n

\n b. poor education/understanding of disease amongst health workers/local population\n
\n \n \n OR\n \n \n
\n continued contact with infected people / other example of unsafe actions ✔\n

\n

\n c. more sources of infection such as bats/difficult to find sources of infection ✔\n

\n

\n d. lack of/limited access to medical care/doctors/health care workers ✔\n

\n

\n e. lack of/no access to/unaffordability of treatment centers/medicalsupplies/equipment/antivirals/drugs/vaccine/treatments ✔\n

\n

\n f. refusal/reluctance in local population to be vaccinated\n
\n \n \n OR\n \n \n
\n difficult to find/reach everyone to vaccinate them/repeat the vaccination ✔\n

\n

\n g. migration of people spreads the infection ✔\n

\n

\n h.poor sanitation/lack of clean water ✔\n

\n
\n", "Examiners report": "
\n

\n This was a timely question with Ebola epidemics again causing great problems in parts of Africa. Students were expected to have had some practice at analysing data relating to an epidemic because of this Skill in the programme: Analysis of epidemiological data related to vaccination programmes. It was assumed that candidates would understand terms such as ‘case’, ‘fatal case’, ‘infect’ and ‘treat’.\n

\n

\n This was a third question where a very wide range of answers were accepted. Even so, not all candidates scored both marks. The commonest weakness was vague answers such as “shortage of resources”. The best answers gave common-sense reasons for special difficulties in controlling an epidemic in the population of a remote rural region.\n

\n
\n", "question_id": "19M.2.SL.TZ1.H", "topics": [ "c-interaction-and-interdependence", "a-unity-and-diversity" ], "subtopics": [ "c3-2-defence-against-disease", "a2-3-viruses-(hl-only)" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Draw labelled diagrams to show the structure of RNA nucleotides and how they are linked together to form a molecule of RNA.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n

\n a. ribose drawn as pentagon and labelled sugar/ribose;\n
\n b. base drawn with correct link to (C\n \n 1\n \n of) ribose and labelled base/nitrogenous base;\n
\n c. phosphate drawn with correct link to (C\n \n 5\n \n of) ribose and labelled P/phosphate;\n
\n d. two (or more) ribonucleotides drawn with correct link (C\n \n 3\n \n to C\n \n 5\n \n )\n

\n

\n \n

\n
\n", "Examiners report": "
\n

\n Many candidates were able to draw the structure of an RNA nucleotide and link it correctly by a 5’ to 3’ bond to another nucleotide. The commonest error was to show two strands of nucleotides linked by base pairing, indicating confusion between RNA and DNA.\n

\n
\n", "question_id": "21N.2.SL.TZ0.6A", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a1-2-nucleic-acids", "a1-2-3-sugar-phosphate-bonding-and-the-sugar-phosphate-“backbone”-of-dna-and-rna", "a1-2-5-rna-as-a-polymer-formed-by-condensation-of-nucleotide-monomers" ] }, { "Question": "
\n
\n

\n Transpiration continued after the fifth leaf had been removed. Suggest what can be concluded.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n transpiration does not only occur in the leaves\n
\n \n \n OR\n \n \n
\n transpiration through stem/shoot ✔\n

\n
\n", "Examiners report": "None", "question_id": "19N.1B.SL.TZ0.A.II", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-1-gas-exchange", "b3-1-9-transpiration-as-a-consequence-of-gas-exchange-in-a-leaf" ] }, { "Question": "
\n
\n (a.ii)\n
\n
\n

\n Explain how this relationship differs from that in humans.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n humans maintain/regulate a constant body temperature at different ambient temperatures/maintained by homeostasis;\n

\n
\n", "Examiners report": "
\n

\n Often steady or constant body temperatures for humans was given rather than homeostasis. Some candidates erroneously described humans as warming up in response to cold ambient temperatures.\n

\n
\n", "question_id": "22M.2.SL.TZ1.1A.II", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-3-homeostasis", "d3-3-1-homeostasis-as-maintenance-of-the-internal-environment-of-an-organism", "d3-3-2-negative-feedback-loops-in-homeostasis" ] }, { "Question": "
\n
\n

\n The mitotic index is an important prognostic tool for predicting the response of cancer cells to chemotherapy. Outline how the mitotic index is calculated.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n number of cells (seen under the microscope) undergoing mitosis divided by the total number of cells (observed in sample area) ✔\n

\n

\n \n Can be given as a %\n \n .\n

\n
\n", "Examiners report": "
\n

\n There were several G2 comments about Q2a, as it could be said that several processes were occurring. Perhaps it should have been more specific. Two out of DNA replication, cell growth and duplication of organelles were expected for the two marks. A surprising number of candidates in all languages, confused 'processes' with 'phases' and stated that interphase consisted of G1, S and G2. Most managed to label prophase and anaphase correctly on the diagram as required in part (b). The answers to part (b) were generally clear, but some lost marks for not comparing the same point. For example 'Mitosis produces diploid cells, but meiosis produces gametes' did not score a mark. The mitotic index was well known.\n

\n
\n", "question_id": "21M.2.HL.TZ2.D", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-1-cell-and-nuclear-division", "d2-1-17-differences-between-tumours-in-rates-of-cell-division-and-growth-and-in-the-capacity-for-metastasis-and-invasion-of-neighbouring-tissue" ] }, { "Question": "
\n
\n

\n Compare and contrast the effect of clothianidin and thiacloprid treatments on the concentration of acetylcholine in royal jelly.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. both neonicotinoids reduce the concentration of acetylcholine in royal jelly (compared to control) ✔\n

\n

\n b. clothianidin reduces the concentration of acetylcholine in royal jelly more than thiacloprid (but perhaps not statistically different) ✔\n

\n

\n c. clothianidin is used in smaller concentrations (than thiacloprid) so no firm conclusion can be obtained ✔\n

\n

\n \n Need one similarity and one difference.\n \n

\n
\n", "Examiners report": "
\n

\n In general, the data analysis question was well attempted by the majority of students.\n

\n

\n A compare and contrast question, that required one similarity and one difference. Most were able to state that both treatments reduce the acetylcholine concentration in the royal jelly and that clothianidin reduced it more than thiacloprid. The more astute also commented on the differences in concentrations of the insecticides.\n

\n
\n", "question_id": "21M.2.HL.TZ2.F", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c2-2-neural-signalling", "c2-2-12-effects-of-exogenous-chemicals-on-synaptic-transmission" ] }, { "Question": "
\n
\n

\n Identify the country with the largest number of deaths.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n Liberia ✔\n

\n
\n", "Examiners report": "None", "question_id": "19M.2.HL.TZ1.A.II", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a2-3-viruses-(hl-only)" ] }, { "Question": "
\n
\n (d)\n
\n
\n

\n The mitotic index is an important prognostic tool for predicting the response of cancer cells to chemotherapy. Outline how the mitotic index is calculated.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n number of cells (seen under the microscope) undergoing mitosis divided by the total number of cells (observed in sample area) ✔\n

\n

\n \n Can be given as a %\n \n .\n

\n
\n", "Examiners report": "
\n

\n There were several G2 comments about Q2a, as it could be said that several processes were occurring. Perhaps it should have been more specific. Two out of DNA replication, cell growth and duplication of organelles were expected for the two marks. A surprising number of candidates in all languages, confused 'processes' with 'phases' and stated that interphase consisted of G1, S and G2. Most managed to label prophase and anaphase correctly on the diagram as required in part (b). The answers to part (b) were generally clear, but some lost marks for not comparing the same point. For example 'Mitosis produces diploid cells, but meiosis produces gametes' did not score a mark. The mitotic index was well known.\n

\n
\n", "question_id": "21M.2.HL.TZ2.2D", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-1-cell-and-nuclear-division", "d2-1-17-differences-between-tumours-in-rates-of-cell-division-and-growth-and-in-the-capacity-for-metastasis-and-invasion-of-neighbouring-tissue" ] }, { "Question": "
\n
\n (a.i)\n
\n
\n

\n Identify the stage of mitosis labelled X in the image, giving a reason.\n

\n

\n \n

\n

\n [Source: Copyright 2002, The Trustees of Indiana University]\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n telophase because the chromosomes/chromatids have reached the poles\n
\n \n \n OR\n \n \n
\n «late» anaphase as some chromosomes/chromatids are still moving/tails visible ✔\n

\n

\n \n OWTTE\n \n

\n
\n", "Examiners report": "
\n

\n Both anaphase and telophase were accepted as answers, but students had difficulty providing a reason that was an appropriate justification; for example, students might say telophase and then support this with the statement because chromatids are seen moving to opposite poles. Students sometimes referred to chromatids as homologous chromosomes. As this is an image of plant cells, students would be mistaken by referring to a cleavage furrow. The mechanism of cytokinesis involves the formation of a cell plate.\n

\n
\n", "question_id": "19M.2.SL.TZ2.2A.I", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-1-cell-and-nuclear-division", "d2-1-8-identification-of-phases-of-mitosis" ] }, { "Question": "
\n
\n

\n What is a function of histones?\n

\n

\n
\n A.  Supercoiling of DNA during binary fission in prokaryotes\n

\n

\n B.  Synthesis of proteins\n

\n

\n C.  Formation of microtubules during mitosis\n

\n

\n D.  Condensation of DNA\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "SPM.1A.HL.TZ0.20", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-1-cell-and-nuclear-division", "d2-1-6-condensation-and-movement-of-chromosomes-as-shared-features-of-mitosis-and-meiosis" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Outline the process of protein denaturation.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n

\n a. change to conformation/shape/tertiary structure/3-D shape;\n
\n b. bonds within the protein/intramolecular bonds broken/changed;\n
\n c. pH and temperature (outside tolerated ranges) can cause denaturation;\n
\n d. vibrations/heat at high temperatures breaks bonds;\n
\n e. high pH/low pH/extreme pH alters ionization/charges (of amino acids and breaks ionic bonds);\n
\n f. protein cannot carry out its function\n
\n \n OR\n \n
\n \n active site\n \n of\n \n enzymes\n \n cannot bind substrates/catalyze reaction/no enzyme-substate complex;\n
\n g. permanent/irreversible change (usually)\n
\n \n OR\n \n
\n soluble proteins become insoluble/precipitate;\n

\n

\n \n Allow any mark points if made clearly on an annotated graph or diagram\n \n .\n

\n
\n", "Examiners report": "
\n

\n Most candidates knew that denaturation can be caused by excessive temperatures or extreme pH. Fewer candidates mentioned how bonds within a protein are broken by heat or kinetic energy. Even fewer explained how R-group ionization in acidic and basic amino acids can be altered by pH changes, breaking the ionic bonds within protein molecules that help to stabilize tertiary structure.\n

\n
\n", "question_id": "21N.2.SL.TZ0.8A", "topics": [ "b-form-and-function" ], "subtopics": [ "b1-2-proteins", "b1-2-5-effect-of-ph-and-temperature-on-protein-structure" ] }, { "Question": "
\n
\n (d)\n
\n
\n

\n Explain how a single base substitution mutation in DNA can cause a change to a protein.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n sequence of DNA bases determines the amino acid sequence of a protein;\n
    2. \n
  2. \n changing one base (on the DNA) can cause the triplet /mRNA to code for a different\n \n amino acid\n \n ;\n
    3. \n
  3. \n changing one base (on the DNA) causes a different protein to be made (during translation);\n
    4. \n
\n
\n", "Examiners report": "None", "question_id": "22N.2.SL.TZ0.4D", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d1-2-protein-synthesis", "d1-2-11-mutations-that-change-protein-structure" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Explain how the function of DNA is linked to its molecular structure.\n

\n
\n
\n

\n [7]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n DNA base sequence provides information;\n
    2. \n
  2. \n gene expression / genes provides a template for the construction of a protein;\n
    3. \n
  3. \n transcription occurs / mRNA is built using DNA as a template;\n
    4. \n
  4. \n DNA nucleotide structure described/sugar and phosphate and base;\n
    5. \n
  5. \n polymer of nucleotides makes a DNA strand;\n
    6. \n
  6. \n DNA has two anti-parallel strands;\n
    7. \n
  7. \n complementary base pairs/A pairs with T and C with G;\n
    8. \n
  8. \n strands linked by hydrogen bonding between bases;\n
    9. \n
  9. \n double helix shape / helix held by hydrogen bonds;\n
    10. \n
\n

\n \n Accept points in clearly labelled diagram\n \n

\n
\n", "Examiners report": "None", "question_id": "SPM.2.HL.TZ0.10B", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a1-2-nucleic-acids", "a1-2-6-dna-as-a-double-helix-made-of-two-antiparallel-strands-of-nucleotides-with-two-strands-linked-by-hydrogen-bonding-between-complementary-base-pairs" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Explain the role of mutations in evolution.\n

\n
\n
\n

\n [7]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n new phenotypes/traits may result from mutations;\n
    2. \n
  2. \n mutations increase variation/differences between individuals in a population/species;\n
    3. \n
  3. \n individuals with new phenotype/trait may have more chances of survival;\n
    4. \n
  4. \n (more chances of survival) in a changing environment / presence of selection pressures;\n
    5. \n
  5. \n (selection pressure can be) intraspecific competition/abiotic factor;\n
    6. \n
  6. \n natural selection occurs;\n
    7. \n
  7. \n individuals with (advantageous) mutation have longer life spans/live longer;\n
    8. \n
  8. \n (so) more chances of reproduction;\n
    9. \n
  9. \n mutated gene passed on to new generations;\n
    10. \n
  10. \n allele frequencies change in the population over time;\n
    11. \n
  11. \n evolution is a consequence of natural selection;\n
    12. \n
\n
\n", "Examiners report": "None", "question_id": "SPM.2.SL.TZ0.7C", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d1-3-mutations-and-gene-editing", "d1-3-7-mutation-as-a-source-of-genetic-variation" ] }, { "Question": "
\n
\n (i)\n
\n
\n

\n There are viruses in soils that are pathogens of animals. Outline a reason for antibiotics in soil not eliminating these viruses.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n viruses lack metabolism/plasma membranes/cell walls / viruses are not livingorganisms;\n
    2. \n
  2. \n antibiotics kill/target bacteria/prokaryotes but not viruses;\n
    3. \n
  3. \n viral pathogens of animals use animal metabolism (which is not affected by antibiotics);\n
    4. \n
\n

\n

\n
\n", "Examiners report": "None", "question_id": "23M.2.HL.TZ1.3BI", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-2-defence-against-disease", "c3-2-14-evolution-of-resistance-to-several-antibiotics-in-strains-of-pathogenic-bacteria" ] }, { "Question": "
\n
\n (a.i)\n
\n
\n

\n State the property of amphipathic phospholipids that enables them to form a bilayer.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n have both a hydrophilic and a hydrophobic region\n
\n \n \n OR\n \n \n
\n have both a polar and a non-polar region ✔\n

\n
\n", "Examiners report": "None", "question_id": "19N.2.HL.TZ0.4", "topics": [ "b-form-and-function", "c-interaction-and-interdependence" ], "subtopics": [ "b1-1-carbohydrates-and-lipids", "b1-1-12-formation-of-phospholipid-bilayers-as-a-consequence-of-the-hydrophobic-and-hydrophilic-regions", "c1-3-photosynthesis", "c1-3-2-conversion-of-carbon-dioxide-to-glucose-in-photosynthesis-using-hydrogen-obtained-by-splitting-water" ] }, { "Question": "
\n
\n

\n The table shows the results of blood type tests on samples from four individuals. Which row represents an individual who can accept transfusions from people with blood type AB?\n

\n

\n \n

\n

\n [Source: © International Baccalaureate Organization 2019]\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "
\n

\n This was the most debated question among the examining team and no doubt also in schools. It was another question where the majority of candidates chose one incorrect answer, in this case B. The blood of that individual clumped with both Anti-A and Anti-B serum so must have been in blood group AB. They were therefore able to accept blood of any type.\n

\n

\n The individual we are looking for cannot accept blood of group A or AB. This suggests that they are in group B and answer A is therefore correct, as that individual’s blood clotted with Anti-B serum. Ironically this was the least popular answer.\n

\n

\n However, we are not told in the question whether the person could accept blood of group B. If they could not, they would have been in blood group O rather than B, giving answer C. This was the second least popular answer! Because of this ambiguity in the question, both answers A and C were accepted. Even then, less than 20 % of candidates got one of the allowed answers and the discrimination index was very low.\n

\n

\n Questions on blood groups are usually too easy, so it is something of a rarity to have constructed such a difficult question. It was based on this statement in 11.1 of the AHL: ‘Antigens on the surface of red blood cells stimulate antibody production in a person with a different blood group’ but it proved to be much too complicated.\n

\n
\n", "question_id": "19M.1A.SL.TZ1.37", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-2-defence-against-disease", "c3-2-7-antigens-as-recognition-molecules-that-trigger-antibody-production" ] }, { "Question": "
\n
\n

\n Identify, with a reason, the aphids that were most strongly repelled by EBF.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n the aphids that were fed on wild-type thale cress/W as they had 80 % «or more» repelled each generation/ always had the higher % response\n
\n \n \n OR\n \n \n
\n the aphids that fed on wild-type thale cress plants/W of G3 as they had «about» 85 % repelled/had the higher % response ✔\n

\n

\n \n Answer should refer to a percentage.\n \n

\n
\n", "Examiners report": "
\n

\n There was some discussion in the G2 forms about the amount of reading before points h, I and j. Good candidates could be seen to have read it carefully, underling the key words. Weaker candidates not so. In 1h a reason in terms of the highest percentage was looked for and was missed by weaker candidates.\n

\n
\n", "question_id": "19M.2.SL.TZ2.H", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d1-1-dna-replication", "d1-1-5-applications-of-polymerase-chain-reaction-and-gel-electrophoresis" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n There were 79 progeny in Cross 4. Predict the expected results by completing the table.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n \n \n \n \n \n \n \n \n
\n 0\n \n 79\n \n 0.000/0\n
\n

\n \n All three parts of the answer must be correct for the mark to be awarded.\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ1.5C", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-2-inheritance", "d3-2-5-effects-of-dominant-and-recessive-alleles-on-phenotype" ] }, { "Question": "
\n
\n (d.ii)\n
\n
\n

\n Using all of the data so far, suggest whether exposure to freezing temperatures in the four cities is supported as a reason for the differences in HCN production in\n \n T. repens\n \n .\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. cities with more days without snow cover have positive correlation between distance from city center and HCN / vice versa for Montreal;\n

\n

\n b. fewer plants with HCN within cities that have more days without snow cover/have more exposure to freezing temperatures / converse for\n \n Montreal\n \n which has fewer days without snow cover;\n

\n

\n c. HCN is 0.2 (or less) HCN in cities that have more days without snow cover proportion whereas city with fewer days/Montreal it is 0.5/more than 0.4;\n

\n

\n d. in Toronto cyanogenic and non-cyanogenic plants show little difference in herbivory;\n

\n

\n e. support for hypothesis/exposure to freezing temperatures as reason.\n

\n

\n \n Do not accept ‘Yes’ unqualified as an answer, but accept it if supported by reasoning\n \n .\n

\n
\n", "Examiners report": "
\n

\n Many candidates found this to be another difficult question. There was a lot of data to consider and as in (c) it was necessary to take into account whether differences were likely to have been significant. In the histogram showing the amount of cold experienced, the large error bars show that only differences between Montreal and the other three cities are great enough to be considered reliable. When combined with data for the proportion of plants with HCN in each city, it was clear that there was support for exposure to cold as a reason.\n

\n
\n", "question_id": "20N.2.SL.TZ0.1D.II", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-2-stability-and-change", "d4-2-4-use-of-a-model-to-investigate-the-effect-of-variables-on-ecosystem-stability" ] }, { "Question": "
\n
\n

\n Congenital lactase deficiency is a type of lactose intolerance that occurs in infants. It is inherited in an autosomal recessive pattern. Calculate the chance of congenital lactose intolerance in a child whose parents are both carriers for the disorder, showing fully how you reached your answer.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n a. gametes of both parents shown as a capital and small letter (e.g. L and l) ✔\n

\n

\n b. possible F1 genotypes ✔\n

\n

\n c. 25 % lactose intolerant, 50 % carriers, 25 % lactose tolerant\n
\n \n \n OR\n \n \n
\n 75 % tolerant and 25 % intolerant\n
\n \n \n OR\n \n \n
\n child has 25 %/1:4/\n \n \n \n 1\n \n \n 4\n \n \n \n chances of inheritance of intolerance ✔\n

\n

\n \n

\n
\n", "Examiners report": "
\n

\n (attempted by about 40 % of the cohort)\n

\n

\n The question was put in the context of the composition of pastry cream, rather than just diving in with questions. In part (a), the structure of starch was quite well known. The better answers included descriptions of polymers and monomers, amylose and amylopectin, and glucose. Part (b) was challenging to many, requiring a knowledge of the digestive system, enzyme action and the blood supply to the liver. It was possible to gain all of the marks by omitting the references to the blood stream. This was an example of where a clear 'essay plan' would have helped. Weaker candidates wrote at length about carbohydrate and fat digestion which was not required. Surprisingly the position of the pancreas was often confused, with pancreatic enzymes appearing in the stomach. The fundamental idea of the digestion of large molecules (proteins) to small soluble ones (amino acids) which can be absorbed into the blood stream at the villi was missed by many. Part (c) was a straightforward genetics cross, put into the context of lactose intolerance. In general, it was well answered. Although the question clearly stated that it was an autosomal recessive condition, many weaker students were determined to make it sex linked.\n

\n
\n", "question_id": "21M.2.SL.TZ2.C", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-2-inheritance", "d3-2-4-phenotype-as-the-observable-traits-of-an-organism-resulting-from-genotype-and-environmental-factors" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Describe two limiting factors on this ecosystem.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n light limits photosynthesis\n
    \n \n \n OR\n \n \n
    \n daylength limits growth season;\n
    2. \n
  2. \n (low) temperature limits growth/slows metabolism\n
    \n \n \n OR\n \n \n
    \n (low) temperature slows activity of decomposers;\n
    3. \n
  3. \n (lack of) water due to frozen water/permafrost\n
    \n \n \n OR\n \n \n
    \n (lack of) water/rain limits photosynthesis/productivity;\n
    4. \n
  4. \n nutrients (in permafrost)/quality/depth of soil limit production of organic molecules /\n \n \n OWTTE\n \n \n
    \n \n \n OR\n \n \n
    \n insufficient soil / permafrost for tree growth;\n
    5. \n
\n

\n \n Award marks only for factors accompanied by a description.\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ2.17B", "topics": [ "b-form-and-function" ], "subtopics": [ "b4-1-adaptation-to-environment", "b4-1-4-range-of-tolerance-of-a-limiting-factor" ] }, { "Question": "
\n
\n (e)\n
\n
\n

\n Suggest a reason for the effect of a diet reduced in acetylcholine on the larval survival rate.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n (larvae lacking acetylcholine/with reduced AcH cannot survive because) acetylcholine is a neurotransmitter taking message from one neuron to another in synapses of nervous tissues\n
\n \n \n OR\n \n \n
\n messages would not pass from one neuron to the other\n
\n \n \n OR\n \n \n
\n (larvae) unable to synthesise/produce AcH, so need it from their diet ✔\n

\n

\n \n OWTTE\n \n .\n

\n
\n", "Examiners report": "
\n

\n In general, the data analysis question was well attempted by the majority of students.\n

\n

\n At least half of the candidates did not know that acetylcholine is a neurotransmitter (section 6.5).\n

\n
\n", "question_id": "21M.2.HL.TZ2.1E", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c2-2-neural-signalling", "c2-2-12-effects-of-exogenous-chemicals-on-synaptic-transmission" ] }, { "Question": "
\n
\n

\n Describe the trend in body posture as ambient temperature rises from 22 to 34 °C.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n As ambient temperature increases, the sloth spends more time with limbs spread\n
\n \n \n OR\n \n \n
\n as ambient temperature increases the sloth spends less time curled in a ball\n
\n \n \n OR\n \n \n
\n as ambient temperature rises, the posture changes from 1 to 6;\n

\n
\n", "Examiners report": "None", "question_id": "22M.2.SL.TZ1.B.I", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-3-homeostasis", "d3-3-1-homeostasis-as-maintenance-of-the-internal-environment-of-an-organism", "d3-3-2-negative-feedback-loops-in-homeostasis" ] }, { "Question": "
\n
\n

\n District administrators combatting the 2014 Ebola epidemic in West Africa were assisted by international organizations such as the World Health Organization, who provided data on the progress of the epidemic. Suggest\n \n one\n \n other way in which international organizations can assist with combatting an epidemic of Ebola.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n raise awareness/provide information for local population/supply health workers/equipment/ train local staff/share expertise/provide financial support/provide vaccine/travel ban alert to affected country ✔\n

\n
\n", "Examiners report": "
\n

\n Again, most students got a mark here for correct reasoning. Those who lost a mark made references to research. Research was not accepted as it might have future benefits, but not likely to help in the immediate epidemic.\n

\n
\n", "question_id": "19M.2.HL.TZ1.G", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a2-3-viruses-(hl-only)" ] }, { "Question": "
\n
\n

\n State the main characteristic of stem cells.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n undifferentiated/pluripotent/ability to divide/differentiate into any types of cells/differentiate along different pathways;\n

\n
\n", "Examiners report": "
\n

\n In a. most were able to say the stem cells were undifferentiated. Many put ‘unspecialised’ instead, which was not credited. There were several, justified G2 comments about the size of the micrograph, which made it difficult to measure the diameter accurately. However, this was generally very poorly answered, with over half failing to get the mark for either the correct answer or the correct calculation. In 1d the better candidates stated that the person could now live a normal life, but as it was not in the genome the progeny could still be affected. The word ‘progeny’ was commented on by several teachers, who pointed out that ‘children’, or ‘offspring’ would have been clearer for those working in an additional language.\n

\n
\n", "question_id": "22M.2.SL.TZ2.A", "topics": [ "b-form-and-function" ], "subtopics": [ "b2-3-cell-specialization", "b2-3-2-properties-of-stem-cells" ] }, { "Question": "
\n
\n

\n The table shows concentrations of potassium ions and sodium ions inside and outside human cells.\n

\n

\n \n

\n

\n [Source: © International Baccalaureate Organization 2019]\n

\n

\n

\n

\n What explains these concentrations?\n

\n

\n A. Potassium ions diffuse in and sodium ions diffuse out.\n

\n

\n B. Sodium ions diffuse in and potassium ions diffuse out.\n

\n

\n C. Active transport pumps sodium ions in and potassium ions out.\n

\n

\n D. Active transport pumps sodium ions out and potassium ions in.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "19M.1A.HL.TZ2.5", "topics": [ "b-form-and-function" ], "subtopics": [ "b2-1-membranes-and-membrane-transport", "b2-1-15-sodium-potassium-pumps-as-an-example-of-exchange-transporters" ] }, { "Question": "
\n
\n

\n Outline the steps to produce a 10 % egg white solution.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n measure 10 g/parts egg whites;\n
    2. \n
  2. \n add to 90 g/parts of water;\n
    3. \n
\n

\n \n Accept use of volume instead of mass.\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.1B.SL.TZ2.B", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-1-enzymes-and-metabolism", "c1-1-8-effects-of-temperature-ph-and-substrate-concentration-on-the-rate-of-enzyme-activity" ] }, { "Question": "
\n
\n

\n Which compound is a waste product of anaerobic respiration in humans?\n

\n

\n A. Carbon dioxide\n

\n

\n B. Ethanol\n

\n

\n C. Lactate\n

\n

\n D. Pyruvate\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "19N.1A.SL.TZ0.12", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-2-cell-respiration", "c1-2-5-differences-between-anaerobic-and-aerobic-cell-respiration-in-humans" ] }, { "Question": "
\n
\n (f)\n
\n
\n

\n Suggest\n \n two\n \n abiotic factors, other than temperature and nutrient supply, that may affect the production of biomass of the grasslands.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. water availability/rainfall/humidity;\n
\n b. light/sunlight (intensity) / daylength;\n
\n c. salinity of\n \n soil\n \n / high/low\n \n soil\n \n pH;\n
\n d. chemical pollution/herbicides/allelopathy/parasitic weeds;\n

\n

\n \n Mark the first two answers only\n \n .\n
\n \n Do not accept carbon dioxide or weather conditions\n \n .\n

\n
\n", "Examiners report": "
\n

\n About half of answers given were accepted. Carbon dioxide concentration was unlikely to vary enough to affect grassland biomass production. Vague answers such as ‘pH’ were not accepted but soil pH was.\n

\n
\n", "question_id": "21N.2.SL.TZ0.1F", "topics": [ "d-continuity-and-change", "c-interaction-and-interdependence" ], "subtopics": [ "d4-2-stability-and-change", "d4-2-4-use-of-a-model-to-investigate-the-effect-of-variables-on-ecosystem-stability", "c1-3-photosynthesis", "c1-3-7-techniques-for-varying-concentrations-of-carbon-dioxide-light-intensity-or-temperature-experimentally-to-investigate-the-effects-of-limiting-factors-on-the-rate-of-photosynthesis" ] }, { "Question": "
\n
\n

\n What is a similarity between the testes of males and the ovaries of females in humans?\n

\n

\n A. They produce gametes throughout the life of the individual.\n

\n

\n B. They secrete hormones into the blood stream.\n

\n

\n C. Their development is controlled by a gene on the Y chromosome.\n

\n

\n D. They release products to the outside of the body directly through the urethra.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "21M.1A.SL.TZ2.30", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-1-reproduction", "d3-1-4-anatomy-of-the-human-male-and-female-reproductive-systems" ] }, { "Question": "
\n
\n

\n State the approximate value of the membrane potential at X.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n 0 mV; (\n \n accept answers in the range of – 10 mV to +10 mV\n \n ) (\n \n Units required\n \n )\n

\n
\n", "Examiners report": "
\n

\n There were some truly brilliant answers to Question 5. However, the weakest answers in the examination were also found here. Of the questions, these were the most commonly left blank.\n

\n

\n Candidates were often unable to approximate X. Missing units resulted in no marks awarded.\n

\n
\n", "question_id": "22M.2.HL.TZ1.A", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c2-2-neural-signalling", "c2-2-10-oscilloscope-traces-showing-resting-potentials-and-action-potentials" ] }, { "Question": "
\n
\n

\n The children in a family have blood groups A, B and O. What are the genotypes of their parents?\n

\n

\n A. I\n \n A\n \n I\n \n A\n \n and I\n \n B\n \n i\n

\n

\n B. I\n \n A\n \n i and I\n \n B\n \n i\n

\n

\n C. I\n \n A\n \n I\n \n B\n \n and ii\n

\n

\n D. I\n \n A\n \n I\n \n B\n \n and I\n \n B\n \n i\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "19M.1A.SL.TZ2.15", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-2-inheritance", "d3-2-10-incomplete-dominance-and-codominance" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Outline the binomial system of classification.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n

\n a. the binomial system of names for species is universal among biologists\n
\n OR\n
\n named according to a globally recognized scheme;\n
\n b. allows to classify organisms into groups based on similar characteristics/common ancestry/DNA;\n
\n c. every species is given a binomial name;\n
\n d. members of the same species can mate and reproduce fertile offspring\n
\n e. genus is written first, followed by species;\n
\n f. genus is capitalized, (followed by) species is lower case\n
\n OR\n
\n an\n \n underlined\n \n correct example/stated that it must be underlined or italicized;\n

\n
\n", "Examiners report": "
\n

\n This part was about the use of the binomial system for naming organisms. Weaker students insisted on describing the complete classification starting from kingdom, which was not required and put themselves in danger of losing the clarity mark for including superfluous material. Most were able to gain 2 marks for saying that the genus was written before species and about the use of capital/lower case or underlining or italicising.\n

\n
\n", "question_id": "21N.2.SL.TZ0.6C", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a3-1-diversity-of-organisms", "a3-1-3-binomial-system-for-naming-organisms" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Draw labelled diagrams to show the structure of RNA nucleotides and how they are linked together to form a molecule of RNA.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n

\n a. ribose drawn as pentagon and labelled sugar/ribose;\n
\n b. base drawn with correct link to (C\n \n 1\n \n of) ribose and labelled base/nitrogenous base;\n
\n c. phosphate drawn with correct link to (C\n \n 5\n \n of) ribose and labelled P/phosphate;\n
\n d. two (or more) ribonucleotides drawn with correct link (C\n \n 3\n \n to C\n \n 5\n \n )\n

\n

\n \n

\n
\n", "Examiners report": "
\n

\n Many candidates were able to draw the structure of an RNA nucleotide and link it correctly by a 5’ to 3’ bond to another nucleotide. The commonest error was to show two strands of nucleotides linked by base pairing, indicating confusion between RNA and DNA.\n

\n
\n", "question_id": "21N.2.HL.TZ0.6", "topics": [ "a-unity-and-diversity", "d-continuity-and-change" ], "subtopics": [ "a1-2-nucleic-acids", "a1-2-3-sugar-phosphate-bonding-and-the-sugar-phosphate-“backbone”-of-dna-and-rna", "a1-2-5-rna-as-a-polymer-formed-by-condensation-of-nucleotide-monomers", "d1-2-protein-synthesis", "d1-2-1-transcription-as-the-synthesis-of-rna-using-a-dna-template", "d1-2-13-initiation-of-transcription-at-the-promoter", "d4-1-natural-selection", "d4-1-2-roles-of-mutation-and-sexual-reproduction-in-generating-the-variation-on-which-natural-selection-acts", "d3-2-inheritance", "d3-2-14-continuous-variation-due-to-polygenic-inheritance-and/or-environmental-factors" ] }, { "Question": "
\n
\n (b.i)\n
\n
\n

\n Identify the group with the greatest number of species with problems due to ingestion of plastics.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C / albatrosses, petrels and shearwaters;\n

\n
\n", "Examiners report": "None", "question_id": "20N.2.SL.TZ0.13B.I", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-2-stability-and-change", "d4-2-10-effects-of-microplastic-and-macroplastic-pollution-of-the-oceans" ] }, { "Question": "
\n
\n

\n State how many chromosomes there would be in male or female gametes of\n \n L. purpureus\n \n .\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n 12;\n

\n

\n \n No alternative.\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ2.A", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-1-reproduction", "d3-1-8-sexual-reproduction-in-flowering-plants" ] }, { "Question": "
\n
\n

\n A pair of alleles controls the secretion of antigens corresponding to blood group in saliva. Examine the pedigree chart.\n

\n

\n \n

\n

\n [Source: © International Baccalaureate Organization 2019]\n

\n

\n

\n

\n Based on this pedigree chart, which best describes the allele conferring antigen secretion in saliva?\n

\n

\n A. Dominant\n

\n

\n B. Recessive\n

\n

\n C. Sex-linked\n

\n

\n D. Co-dominant\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "None", "question_id": "19N.1A.SL.TZ0.16", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-2-inheritance", "d3-2-11-sex-determination-in-humans-and-inheritance-of-genes-on-sex-chromosomes" ] }, { "Question": "
\n
\n (b.i)\n
\n
\n

\n Describe the trend in body posture as ambient temperature rises from 22 to 34 °C.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n As ambient temperature increases, the sloth spends more time with limbs spread\n
\n \n \n OR\n \n \n
\n as ambient temperature increases the sloth spends less time curled in a ball\n
\n \n \n OR\n \n \n
\n as ambient temperature rises, the posture changes from 1 to 6;\n

\n
\n", "Examiners report": "None", "question_id": "22M.2.SL.TZ1.1B.I", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-3-homeostasis", "d3-3-1-homeostasis-as-maintenance-of-the-internal-environment-of-an-organism", "d3-3-2-negative-feedback-loops-in-homeostasis" ] }, { "Question": "
\n
\n

\n Outline the process of inhalation.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n

\n a. diaphragm contracts / moves downwards/flattens ✔\n

\n

\n b.\n \n external\n \n intercostal muscles contract ✔\n

\n

\n c. (muscle contraction) moves the rib cage upwards and outwards ✔\n

\n

\n d. increases volume of the thorax / lungs ✔\n

\n

\n e. difference in pressure/decreasing pressure causes air to flow into lungs / lungs inflate ✔\n

\n
\n", "Examiners report": "
\n

\n This question was attempted by approximately 56 % of candidates.\n

\n

\n Done well by many. Diaphragm contraction and external intercostal muscle contraction was commonly known along with the idea that the rib cage moves upwards and outwards. Further understanding of the consequent pressure changes in the thorax was not clear.\n

\n
\n", "question_id": "21M.2.SL.TZ1.A", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-1-gas-exchange", "b3-1-5-ventilation-of-the-lungs" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Explain the factors that can contribute to the exponential growth phase in a sigmoid population curve.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n a. ideal environment/unlimited resources/below carrying capacity ✔\n

\n

\n b. little disease/few predators ✔\n

\n

\n c. high natality/birth rate\n \n \n AND\n \n \n immigration ✔\n \n Both needed.\n \n

\n

\n d. natality and immigration\n \n greater\n \n than mortality and emigration ✔\n

\n
\n", "Examiners report": "
\n

\n The vast majority of candidates could provide part of an explanation; most mentioned resources, but for many the effect of natality, mortality, immigration and emigration (both not well distinguished for some) was obscure.\n

\n
\n", "question_id": "19M.2.SL.TZ2.16A", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c4-1-populations-and-communities", "c4-1-7-population-growth-curves", "c4-1-8-modelling-of-the-sigmoid-population-growth-curve" ] }, { "Question": "
\n
\n (b.ii)\n
\n
\n

\n Explain how water is used in photosynthesis.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n a. water is split/broken «up»/lysed/undergoes photolysis ✔\n \n For mpa, reject “water is cut in half”. For mpa, accept photolysis only if the context shows that water is being split\n \n .\n

\n

\n b. producing/providing electrons ✔\n

\n

\n c. replaces electrons lost by Photosystem II / PSII / P680 / chlorophyll a ✔\n \n For mpc, do not accept just chlorophyll\n \n .\n

\n

\n d. allows electrons «to continue» to pass along the electron transport chain ✔\n

\n

\n e. provides protons/H+ «inside thylakoid» to help generate a «proton» gradient/maintain high concentration inside thylakoid ✔\n \n For mpe, reject pumping of protons into the thylakoid as photolysis produces them inside the thylakoid\n \n .\n

\n
\n", "Examiners report": "None", "question_id": "19N.2.SL.TZ0.4B.II", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-3-photosynthesis", "c1-3-2-conversion-of-carbon-dioxide-to-glucose-in-photosynthesis-using-hydrogen-obtained-by-splitting-water" ] }, { "Question": "
\n
\n

\n Polyploidy has been a cause of rapid speciation in some plant genera, such as\n \n Helianthus\n \n . Which observation is evidence that speciation has occurred?\n

\n

\n
\n A.  A polyploid plant reproduces asexually.\n

\n

\n B.  A polyploid plant produces male and female gametes.\n

\n

\n C.  Fertile offspring are produced when a polyploid plant crosses with a diploid plant.\n

\n

\n D.  Fertilization can occur between polyploid individuals.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "SPM.1A.HL.TZ0.33", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a4-1-evolution-and-speciation", "a4-1-11-abrupt-speciation-in-plants-by-hybridization-and-polyploidy" ] }, { "Question": "
\n
\n

\n Suggest a reason for the difference in the time observed eating and drinking.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n more food/energy eaten/required in winter/cold;\n
    2. \n
  2. \n food needed to maintain temperature/stay warm/generate heat;\n
    3. \n
  3. \n more loss of body heat in cold conditions;\n
    4. \n
  4. \n more energy used hunting for food;\n
    5. \n
  5. \n food less available in winter/harder to find enough food;\n
    6. \n
\n
\n", "Examiners report": "
\n

\n This was generally well answered, with candidates mostly focussing on food being harder to find in winter and more energy being needed to maintain body heat.\n

\n
\n", "question_id": "22N.2.HL.TZ0.H", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-1-integration-of-body-systems", "c3-1-4-the-brain-as-a-central-information-integration-organ" ] }, { "Question": "
\n
\n

\n The image shows leucyl-tRNA synthetase from Thermus thermophilus complexed with a tRNA. This tRNA-activating enzyme joins the amino acid leucine to tRNA using ATP.\n

\n

\n \n

\n

\n Why is leucyl-tRNA synthetase not used to join the amino acid valine to tRNA?\n
\n
\n

\n

\n A.  Phosphorylation of valine occurs at a later stage.\n

\n

\n B.  Valine does not need to be activated to attach to tRNA.\n

\n

\n C.  Leucyl-tRNA synthetase is substrate-specific.\n

\n

\n D.  Valine has a different anticodon from leucine.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "23M.1A.SL.TZ1.27", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d1-2-protein-synthesis", "d1-2-7-complementary-base-pairing-between-trna-and-mrna" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Calculate the actual thickness of the leaf, from upper to lower surface along the line a–b, showing your working.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n correct measurement of the line on the image (\n \n \n +\n \n \n /\n \n \n -\n \n \n 1mm);\n
    2. \n
  2. \n correct calculation and including units;\n
    3. \n
\n

\n \n Allow ECF – ruler measurements\n \n \n +\n \n \n /\n \n \n -\n \n \n 1mm\n \n

\n
\n", "Examiners report": "None", "question_id": "SPM.1B.SL.TZ0.2B", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a2-2-cell-structure", "a2-2-2-microscopy-skills" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Explain how water balance is restored in mammals when they are dehydrated.\n

\n
\n
\n

\n [7]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n thirst;\n
    2. \n
  2. \n more water drunk / more water reabsorbed from feces (in the colon/large intestine);\n
    3. \n
  3. \n osmoreceptors in the hypothalamus detect dehydration/high solute concentration in blood;\n
    4. \n
  4. \n ADH secreted;\n
    5. \n
  5. \n by the pituitary gland;\n
    6. \n
  6. \n ADH signals to collecting duct/DCT (cells) to increase permeability to water;\n
    7. \n
  7. \n more aquaporins (in plasma membranes of collecting duct/distal convoluted tubule cells);\n
    8. \n
  8. \n more water reabsorbed from filtrate (in collecting ducts/distal convoluted tubules);\n
    9. \n
  9. \n reabsorption by osmosis / reabsorption due to medulla being hypertonic;\n
    10. \n
  10. \n reabsorbed water passes into the blood/reduces the solute concentration of blood;\n
    11. \n
  11. \n smaller volume/more concentrated/hypertonic urine formed;\n
    12. \n
  12. \n less sweating;\n
    13. \n
\n
\n", "Examiners report": "
\n

\n This was poorly answered by many candidates. The discrimination index was very high but the mean mark was only 1.5 out of 7. Often candidates did not get beyond the basic ideas of thirst and drinking water to rehydrate. The best candidates gave concise but detailed accounts of the roles of the hypothalamus, pituitary gland, collecting duct and aquaporins.\n

\n
\n", "question_id": "22M.2.HL.TZ1.6C", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-3-homeostasis", "d3-3-7-role-of-the-kidney-in-osmoregulation-and-excretion" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Explain how genetic variation between the individuals in a species can be generated.\n

\n
\n
\n

\n [7]\n

\n
\n
\n", "Markscheme": "
\n

\n a.\n \n mutation\n \n (in genes/DNA generates variation)\n

\n

\n b. base substitution / change to base sequence of gene / makes single nucleotide polymorphisms /SNPs ✔\n

\n

\n c. new\n \n alleles\n \n formed / different\n \n alleles\n \n of gene / multiple\n \n alleles\n \n ✔\n

\n

\n d. radiation/mutagenic chemicals/mutagens cause/increase the chance of mutation ✔\n

\n

\n e.\n \n meiosis\n \n (generates variation) ✔\n

\n

\n f. recombination/new combinations of genes/alleles produced by\n \n crossing over\n \n ✔\n

\n

\n g. independent assortment/random orientation of (pairs of homologous) chromosomes/bivalents ✔\n

\n

\n h. gametes/chromosomes/DNA/genes from two parents combined (in sexual reproduction)\n

\n

\n i. random fertilization (increases genetic variation) ✔\n

\n

\n j. in reproductively/geographically isolated populations natural selection may differ ✔\n

\n

\n k. in small/isolated populations gene pools change/evolution occurs due to natural selection/genetic drift ✔\n

\n

\n l. disruptive selection can cause different varieties/variants/types/phenotypes to diverge ✔ transfer of genes (between bacteria) in plasmids ✔\n

\n

\n \n For mpf it is not enough just to state ‘crossing over’\n \n .\n

\n

\n \n Do not accept types of mutation other than substitution for mpb\n \n .\n

\n
\n", "Examiners report": "
\n

\n More marks were scored here, with most candidates at least mentioning mutation and some of the events of meiosis. As this was an explain question it was not enough merely to name a process, such as crossing over, some indication of how it generates variation was expected. A common misunderstanding was to think that geographic isolation in itself generates variation.\n

\n
\n", "question_id": "21M.2.SL.TZ1.7B", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d1-3-mutations-and-gene-editing", "d1-3-7-mutation-as-a-source-of-genetic-variation" ] }, { "Question": "
\n
\n (e)\n
\n
\n

\n Suggest\n \n two\n \n possible reasons for the drop in the daily numbers of newly infected cases after October 2014 in Liberia.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. improved medical care/support/supplies/equipment/training of staff/hygiene/distribution of vaccine ✔\n
\n
\n b. improved understanding of how to avoid infection «amongst public»/greater awareness in society/better education✔\n

\n

\n c. rise in number of deaths means fewer infectious individuals ✔\n

\n

\n d. impact of disease control measures/control policies/quarantine/isolation ✔\n

\n

\n e. drop in the number of fruit bats ✔\n

\n

\n f. maybe seasonal changes/weather changes ✔\n

\n

\n g. people may have left the area ✔\n

\n

\n h. international aid arrives ✔\n

\n

\n \n OWTTE\n \n

\n
\n", "Examiners report": "
\n

\n This was a well answered response where almost all students got full marks. Students were able to identify more than three marking points here mp a, b, c and d were most common. Some students provided mp e and f. Few used mp g and h.\n

\n
\n", "question_id": "19M.2.HL.TZ1.1E", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a2-3-viruses-(hl-only)" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n The image shows human red blood cells.\n

\n

\n \n

\n

\n [Source: someoneice/123rf.com.]\n

\n

\n

\n

\n Outline what will happen to human red blood cells if transferred to distilled water.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n cells absorb water by\n \n osmosis\n \n and swell/increase in volume\n
\n \n OR\n \n
\n cells burst/lyse;\n

\n
\n", "Examiners report": "
\n

\n This was mostly well answered with candidates realising that water entry due to osmosis would cause the cells to burst.\n

\n
\n", "question_id": "21N.2.HL.TZ0.3", "topics": [ "d-continuity-and-change", "c-interaction-and-interdependence" ], "subtopics": [ "d2-3-water-potential", "d2-3-3-water-movement-by-osmosis-into-or-out-of-cells", "c2-2-neural-signalling", "c2-2-9-propagation-of-an-action-potential-along-a-nerve-fibre/axon-as-a-result-of-local-currents" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Explain how the presence of a Y chromosome in the cells of a human embryo causes it to develop as a male.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n gene/genetic information on Y chromosome causes embryo to develop testes;\n
    2. \n
  2. \n (developing) testes in embryo secrete testosterone;\n
    3. \n
  3. \n testosterone causes male genitalia/penis to develop;\n
    4. \n
\n

\n

\n

\n \n Accept SRY gene in mp-a\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ1.6C", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-2-inheritance", "d3-2-11-sex-determination-in-humans-and-inheritance-of-genes-on-sex-chromosomes" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Describe the mechanism by which the heartbeat is initiated.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. sinoatrial node/SAN initiates contraction of atria;\n

\n

\n b. SAN sends messages to the atrioventricular/AV node;\n

\n

\n c. AV node initiates ventricular contraction;\n

\n

\n d. through conducting fibres;\n

\n
\n", "Examiners report": "
\n

\n Most candidates did well in this question, strongest candidates distinguishing themselves by complete and very detailed answers.\n

\n
\n", "question_id": "20N.2.HL.TZ0.22C", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-2-transport", "b3-2-16-stages-in-the-cardiac-cycle" ] }, { "Question": "
\n
\n

\n State the trend in relative brain mass in primates other than humans according to their time of divergence from humans.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n the longer ago they diverged from humans, the greater the relative brain mass ✔\n

\n

\n \n Accept inverse.\n \n

\n

\n \n Do not accept negative correlation.\n \n

\n
\n", "Examiners report": "
\n

\n This question concerned how relative brain mass varied in primate evolution. Overall it was not well answered. The decreasing scale on the X-axis caused confusion for a lot of candidates in part (a).\n

\n
\n", "question_id": "19M.1B.SL.TZ2.A", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-1-integration-of-body-systems", "c3-1-4-the-brain-as-a-central-information-integration-organ" ] }, { "Question": "
\n
\n

\n How would the body respond to a rise above normal body temperature?\n

\n

\n
\n \n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "SPM.1A.SL.TZ0.21", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-3-homeostasis", "d3-3-1-homeostasis-as-maintenance-of-the-internal-environment-of-an-organism" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Calculate the maximum diameter of the stem cell cluster on the micrograph, showing your working and giving the units.\n

\n

\n

\n

\n

\n

\n

\n

\n ..........\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n correct formula: 1.1cm = 500 μm, 2.7cm = length,\n \n \n \n \n 2\n \n \n .\n \n \n 7\n \n \n ×\n \n \n 500\n \n \n \n \n 1\n \n \n .\n \n \n 1\n \n \n \n \n =\n \n \n Xμm\n \n \n ;\n
    2. \n
  2. \n correct answer\n \n with unit\n \n : 1227μm;\n
    3. \n
\n

\n \n Allow answer in range of 1150 μm to 1350 μm\n \n .\n
\n
\n

\n
\n", "Examiners report": "None", "question_id": "22M.2.SL.TZ2.2B", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a2-2-cell-structure", "a2-2-2-microscopy-skills" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Describe what occurs in a neuron when an action potential is propagated along the axon.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n sodium\n \n ions\n \n /\n \n Na\n \n +\n \n \n enter/diffuse in;\n
    2. \n
  2. \n depolarization/membrane potential/voltage changes from negative to positive;\n
    3. \n
  3. \n potassium channels open AND potassium ions/K+ exit/diffuse out;\n
    4. \n
  4. \n repolarization/membrane potential/voltage changes back from positive to negative;\n
    5. \n
  5. \n local current due to diffusion of sodium ions along the neuron;\n
    6. \n
  6. \n (local currents) cause next sodium channels to open/next part of axon to depolarize;\n
    7. \n
  7. \n opening of sodium channels triggered when threshold potential/-50mV reached;\n
    8. \n
\n

\n \n Do not award mpa for sodium being pumped in (rather than diffusing).\n \n
\n \n Allow mpc with ECF if direction of both sodium and potassium is wrong, or if both movements are described as pumping.\n \n

\n
\n", "Examiners report": "
\n

\n Answers were very varied and some were excellent. A few missed the point and described synaptic transmission. In some weaker answers there was confusion about the role of the sodium-potassium pump and what makes sodium and potassium ions move across the membrane during depolarisation and repolarisation. The mechanism of propagation by the formation of local currents was sometime attempted but rarely expressed clearly.\n

\n
\n", "question_id": "22N.2.HL.TZ0.6B", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c2-2-neural-signalling", "c2-2-8-depolarization-and-repolarization-during-action-potentials", "c2-2-9-propagation-of-an-action-potential-along-a-nerve-fibre/axon-as-a-result-of-local-currents" ] }, { "Question": "
\n
\n

\n Suggest reasons for this trend.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n less surface area is exposed when curled up\n
    \n \n \n OR\n \n \n
    \n more surface area is exposed when all limbs spread;\n
    2. \n
  2. \n curled position prevents heat loss/provides warmth\n
    \n \n \n OR\n \n \n
    \n stretched out position allows more heat loss/body cooled;\n
    3. \n
\n
\n", "Examiners report": "
\n

\n There were a few beautiful responses where surface area was specifically incorporated into the answer achieving maximum marks.\n

\n
\n", "question_id": "22M.2.SL.TZ1.B.II", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-3-homeostasis", "d3-3-1-homeostasis-as-maintenance-of-the-internal-environment-of-an-organism", "d3-3-2-negative-feedback-loops-in-homeostasis" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n State the level of protein structure at which the polypeptide chains of hemoglobin are combined.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n quaternary / fourth level;\n

\n
\n", "Examiners report": "
\n

\n Many candidates knew that association of polypeptide chains is quaternary structure. Any spelling of this term was accepted — only a minority got it correct.\n

\n
\n", "question_id": "22M.2.HL.TZ1.4A", "topics": [ "b-form-and-function" ], "subtopics": [ "b1-2-proteins", "b1-2-11-quaternary-structure-of-non-conjugated-and-conjugated-proteins" ] }, { "Question": "
\n
\n (a.i)\n
\n
\n

\n State the distance from the city centre at which the highest proportion of plants sampled contained HCN.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n 32 (km);\n

\n

\n \n Accept answers in the range of 31 to 33 (km)\n \n .\n

\n
\n", "Examiners report": "
\n

\n This was intended to be an easy first mark but only 70 %  answered it correctly, with others mostly giving the maximum distance rather than the distance with the highest proportion of plants containing cyanide.\n

\n
\n", "question_id": "20N.2.SL.TZ0.1A.I", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-2-stability-and-change", "d4-2-4-use-of-a-model-to-investigate-the-effect-of-variables-on-ecosystem-stability" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n It has been argued that variation in the global mean surface temperature has been caused by variation in energy from the Sun. Analyse whether evidence from the graphs supports this argument.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n (\n \n Evidence does not support this argument because\n \n :)\n

\n
    \n
  1. \n overall increase in surface temperature but no overall increase/slight decrease in solar irradiance;\n
    2. \n
  2. \n peaks and troughs in solar irradiance do not correspond with fluctuations in surface temperature;\n
    3. \n
\n

\n \n Do not award marks for claims that the evidence supports the argument, for example, claims that the fluctuations coincide.\n \n

\n
\n", "Examiners report": "
\n

\n Most candidates earned one of the two marks for the idea that the long-term trend in global mean surface temperature is an increase whereas there has if anything been an overall decrease in energy from the Sun between 1980 and 2020. Few answers pointed out that ten-year cycles in Sun's energy that are seen do not correspond to fluctuations in surface mean temperature. Weaker answers tended to pick out single instances of a rise in Sun's energy corresponding with a rise in surface temperature. Very few answers included any comments on the small variation in Sun's energy — only ranging from 1360.2 to 1362.2 W m-2 which is less than 0.15\n \n \n \n \n % fluctuation, with no overall increase, whereas surface temperature has increased by more than a degree Celsius in the 40 years from 1978 to 2018.\n

\n
\n", "question_id": "22N.2.SL.TZ0.3A", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-3-climate-change", "d4-3-1-anthropogenic-causes-of-climate-change", "d4-3-2-positive-feedback-cycles-in-global-warming" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Explain how cladistics can be used to investigate evolutionary relationships.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. (cladistics) shows evolutionary relationships through a common ancestor ✔\n

\n

\n b. cladistics uses DNA/protein/derived/shared anatomical characteristics/traits ✔\n

\n

\n c. time of divergence is related to the number of differences in DNA (base sequence) / protein (sequence of amino acids) ✔\n

\n

\n d. homologous (versus analogous) traits are used to place an organism in a clade ✔\n

\n

\n e. more shared characteristics mean a more recent common ancestor ✔\n

\n
\n", "Examiners report": "
\n

\n Candidates found it hard to express themselves without contradiction.\n

\n

\n Carrying examples into part (b) made for the most successful answers. Very few gained marks for providing answers that included molecular level cladistic evidence, e.g. DNA, protein sequencing, etc.\n

\n
\n", "question_id": "21M.2.HL.TZ1.5B", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a3-2-classification-and-cladistics-(hl-only)", "a3-2-2-difficulties-classifying-organisms-into-the-traditional-hierarchy-of-taxa", "a3-2-8-using-cladistics-to-investigate-whether-the-classification-of-groups-corresponds-to-evolutionary-relationships" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Outline how mutation can lead to cancer.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n mutations are random changes in the sequences of genes/DNA;\n
    2. \n
  2. \n (mutation) may involve addition/deletion/substitution/inversion of DNA bases;\n
    3. \n
  3. \n (mutations) in tumour suppressor genes/oncogenes;\n
    4. \n
  4. \n uncontrolled cell division/mitosis occurs;\n
    5. \n
  5. \n abnormal cells cannot perform their function;\n
    6. \n
  6. \n they divide repeatedly to form tumours;\n
    7. \n
\n
\n", "Examiners report": "None", "question_id": "SPM.2.SL.TZ0.7A", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d1-3-mutations-and-gene-editing", "d1-3-6-consequences-of-mutation-in-germ-cells-and-somatic-cells" ] }, { "Question": "
\n
\n

\n The diagram shows the energy flow between five “sinks” in a terrestrial ecosystem.\n

\n

\n \n

\n

\n In a typical terrestrial ecosystem, which trophic level would have the highest biomass?\n

\n

\n A. Autotrophs\n

\n

\n B. Primary consumers\n

\n

\n C. Secondary consumers\n

\n

\n D. Detritus feeders\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "None", "question_id": "21M.1A.SL.TZ1.21", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c4-2-transfers-of-energy-and-matter", "c4-2-6-autotrophs-as-organisms-that-use-external-energy-sources-to-synthesize-carbon-compounds-from-simple-inorganic-substances", "c4-2-12-reductions-in-energy-availability-at-each-successive-stage-in-food-chains-due-to-large-energy-losses-between-trophic-levels" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Describe the transport of carbon compounds such as sucrose and amino acids in phloem.\n

\n
\n
\n

\n [7]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n transport/translocation in (phloem)\n \n sieve tubes\n \n ;\n
    2. \n
  2. \n flow of sap through pores in end walls/sieve plates;\n
    3. \n
  3. \n sugar/amino acids are transported dissolved in water/sap;\n
    4. \n
  4. \n loaded into phloem (companion cells/sieve tubes) by active transport;\n
    5. \n
  5. \n protons pumped out and sucrose then enters by cotransport;\n
    6. \n
  6. \n high solute concentration created in phloem/sieve tube;\n
    7. \n
  7. \n water enters (sieve tube) by osmosis;\n
    8. \n
  8. \n hydrostatic pressure in sieve tube increases;\n
    9. \n
  9. \n unloading from sieve tubes in sink/in roots;\n
    10. \n
  10. \n water leaves by osmosis lowering the hydrostatic pressure;\n
    11. \n
  11. \n sap movement (in phloem) from higher to lower pressure;\n
    12. \n
  12. \n movement from source/leaves to sink/roots;\n
    13. \n
\n
\n", "Examiners report": "None", "question_id": "23M.2.HL.TZ1.8B", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-2-transport", "b3-2-18-adaptations-of-phloem-sieve-tubes-and-companion-cells-for-translocation-of-sap" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n State the mean annual decline in insect biomass.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n 2.5\n \n \n \n \n %;\n

\n

\n \n % required\n \n

\n
\n", "Examiners report": "
\n

\n In general, the Data based question was well answered. In (a) all but a handful of candidates failed to state 2.5, but unfortunately many failed to also include the unit. In (b) Most gave a difference, but similarities were rarer. The statement that both show a decline would have earned the mark. A surprising number were confused by the arithmetic involved in (c), with most calculating that the decrease was 8000, but either forgetting to subtract this from the 400,000, or doing it incorrectly. In (d) almost everyone counted 5 correctly and in (e) a large proportion gained both marks for a comparison and a contrast. The calculation in (f) involved the use of ratios. There was a G2 comment that this was not common knowledge. However, as all IB students continue to study mathematics at some level, it was not considered beyond their capabilities. 40\n \n \n \n \n % of the students gained the mark. A similar number gained the mark in (g), usually for an correct answer, but many answered in terms of the actual ratios, which did not gain the mark. In (h) 80\n \n \n \n \n % were able to spot that there was an inverse relationship between high lipid content and survivability, but in (i) fewer were able to cite the 10:1 diet as closest to the normal diet, some failing to state the reason. The answers t (j) were very varied, with most gaining marks for the possible loss of natural food sources or\n
\n the bees having to look for others. Better candidates noted that there was no control where the bees were fed their normal diet as it was a simulation, not using pollen. There was a G2 comment that the graph was somewhat crowded and should have been bigger. This is perhaps true.\n

\n
\n", "question_id": "22N.2.SL.TZ0.1", "topics": [ "c-interaction-and-interdependence", "b-form-and-function" ], "subtopics": [ "c4-2-transfers-of-energy-and-matter", "c4-2-15-primary-production-as-accumulation-of-carbon-compounds-in-biomass-by-autotrophs", "c4-2-16-secondary-production-as-accumulation-of-carbon-compounds-in-biomass-by-heterotrophs", "c4-2-14-restrictions-on-the-number-of-trophic-levels-in-ecosystems-due-to-energy-losses", "b4-1-adaptation-to-environment", "b4-1-2-adaptations-of-organisms-to-the-abiotic-environment-of-their-habitat" ] }, { "Question": "
\n
\n

\n The genetic code is shown.\n

\n

\n \n

\n

\n In a coding gene, the DNA triplet in the transcribed strand is changed from AGG to TCG.\n
\n What would be the result of this change in the genome?\n

\n

\n A. A non-functional protein\n

\n

\n B. A different but functional protein\n

\n

\n C. No change in the protein\n

\n

\n D. Termination of the polypeptide\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "
\n

\n This was another poorly answered question with only slightly more than 25 % answering correctly - the expected success rate with guessing. However, the discrimination index was high, showing that well-prepared candidates tended to get it right and weaker candidates mostly chose one of the distractors, with B proving particularly popular. It was necessary to realise from the presence of U rather than T that the chart gave the genetic code in terms of mRNA base sequences, not DNA. The DNA base sequence of the transcribed strand given in the question therefore had to be converted to the complementary RNA base sequence that results from transcription. Then the amino acid coded for before and after the base change had to be deduced from the chart. This gave the result of serine both before and after the base change, leading to answer C – no change in the protein. If candidates thought that the mRNA triplet was the same as the DNA triplet apart from U instead of T, they would have expected the amino acid to be different, directing them to one of the three distractors.\n

\n
\n", "question_id": "20N.1A.SL.TZ0.8", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d1-2-protein-synthesis", "d1-2-9-using-the-genetic-code-expressed-as-a-table-of-mrna-codons" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n The lung tumour in the light micrograph was slow-growing. Predict with a reason what would have been visible in the micrograph if the tumour was growing rapidly.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n \n See\n \n

\n

\n a. more mitosis\n
\n \n \n OR\n \n \n
\n cells in prophase/metaphase/anaphase/telophase;\n

\n

\n \n Why\n \n

\n

\n b. more dividing cells/tumour cell divide uncontrollably\n
\n \n \n OR\n \n \n
\n a higher mitotic index;\n

\n

\n

\n
\n", "Examiners report": "None", "question_id": "23M.2.HL.TZ2.3C", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-1-cell-and-nuclear-division", "d2-1-17-differences-between-tumours-in-rates-of-cell-division-and-growth-and-in-the-capacity-for-metastasis-and-invasion-of-neighbouring-tissue" ] }, { "Question": "
\n
\n

\n State the probability that Edward had hemophilia.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n 0.5/50 %;\n

\n
\n", "Examiners report": "
\n

\n Approximately 50 % of the candidates were correct with their answer of 50 %. It was expected that candidates would recognize that Edward is male because he has a box rather than circle in the pedigree. Then from there, they would calculate the 50 %.\n

\n
\n", "question_id": "22M.2.SL.TZ1.A", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-2-inheritance", "d3-2-12-haemophilia-as-an-example-of-a-sex-linked-genetic-disorder", "d3-2-13-pedigree-charts-to-deduce-patterns-of-inheritance-of-genetic-disorders" ] }, { "Question": "
\n
\n

\n The light micrograph shows two blood vessels, an artery and a vein, in transverse section.\n

\n

\n \n

\n

\n [Source: Columbia Center for New Media Teaching and Learning, n.d. Epithelium: Simple Squamous Epithelium. [image online] Available at: http://www.columbia.edu/itc/hs/medical/sbpm_histology_old/lab/lab02_squamous.html [Accessed 29 November 2019].]\n

\n

\n

\n

\n What explains the different shapes of these blood vessels?\n

\n

\n A. Arteries do not have valves.\n

\n

\n B. Muscle cells are found only in the walls of veins.\n

\n

\n C. Arteries have a larger lumen-to-wall thickness ratio.\n

\n

\n D. There are fewer elastic fibres in the walls of veins.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "
\n

\n Very few candidates answered this correctly with many incorrectly answering C, that arteries have a larger lumen-to-wall thickness ratio than veins. The question was taken from 6.2 Identification of blood vessels as arteries, capillaries or veins from the structure of their walls.\n

\n
\n", "question_id": "22M.1A.SL.TZ2.26", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-2-transport", "b3-2-2-structure-of-arteries-and-veins" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Compare and contrast mitochondria and chloroplasts in terms of the substrates they use and the products they produce.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. ATP produced by both / ADP used by both ✔\n

\n

\n b. oxygen produced by chloroplasts and used by mitochondria ✔\n

\n

\n c. carbon dioxide produced by mitochondria and used by chloroplasts ✔\n

\n

\n d. carbon/organic compounds built up in chloroplasts/anabolism and broken down in mitochondria/catabolism ✔\n

\n

\n \n Do not award mpd for statements about carbohydrates or glucose (because the pyruvate used by mitochondria is not a carbohydrate)\n \n .\n

\n
\n", "Examiners report": "
\n

\n To answer this question, candidates had to know that chloroplasts photosynthesize and mitochondria respire aerobically. They then had to compare or contrast the substrates or products of these two processes. The mean mark was 0.6 out of 2, showing that many candidates failed to do this. Well-prepared candidates had no difficulty.\n

\n
\n", "question_id": "21M.2.HL.TZ1.2B", "topics": [ "b-form-and-function" ], "subtopics": [ "b2-2-organelles-and-compartmentalization", "b2-2-4-adaptations-of-the-mitochondrion-for-production-of-atp-by-aerobic-cell-respiration", "b2-2-5-adaptations-of-the-chloroplast-for-photosynthesis" ] }, { "Question": "
\n
\n (b.i)\n
\n
\n

\n Explain what happens in a person when they develop type I diabetes.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n insulin is necessary to control/regulate blood glucose concentrations\n
    \n \n \n OR\n \n \n
    \n insulin is necessary for the cells to take up glucose (for energy);\n
    2. \n
  2. \n insufficient insulin is made by the pancreas\n
    \n \n \n OR\n \n \n
    \n \n autoimmune response\n \n /\n \n antibodies\n \n destroy the (β) cells of the pancreas that make insulin;\n
    3. \n
  3. \n reduced uptake of glucose from the blood / glucose accumulates in the blood / elevated blood glucose levels;\n
    4. \n
\n

\n \n “sugar” is NOT accepted in place of glucose. However, this should only be penalized once; i.e., utiltize ECF.\n \n

\n
\n", "Examiners report": "
\n

\n This question about blood sugar regulation was well done by most. This was a question where the use of general terms rather than specific terms led to lost marks. For example, sugars instead of glucose and ‘the body’ instead of ‘the pancreas’\n

\n
\n", "question_id": "22M.2.SL.TZ2.5B.I", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-3-homeostasis", "d3-3-3-regulation-of-blood-glucose-as-an-example-of-the-role-of-hormones-in-homeostasis", "d3-3-4-physiological-changes-that-form-the-basis-of-type-1-and-type-2-diabetes" ] }, { "Question": "
\n
\n

\n What is a reason that Taq polymerase is a suitable enzyme for use in the polymerase chain reaction (PCR)?\n

\n

\n
\n A.  It can work at a wide range of pH.\n

\n

\n B.  It works at higher temperatures than most enzymes.\n

\n

\n C.  It can separate two strands of DNA.\n

\n

\n D.  It allows DNA to be replicated without the use of primers.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "SPM.1A.SL.TZ0.7", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d1-1-dna-replication", "d1-1-4-polymerase-chain-reaction-and-gel-electrophoresis-as-tools-for-amplifying-and-separating-dna" ] }, { "Question": "
\n
\n (a.i)\n
\n
\n

\n Identify, with a reason, the stage shown at X.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n anaphase;\n
    2. \n
  2. \n the (replicated) chromosomes/chromatids are separating/moving to opposite poles of the cell;\n
    3. \n
\n

\n \n OWTTE\n \n

\n
\n", "Examiners report": "
\n

\n This question was generally well done; a few identified the incorrect phase of mitosis, but the observations about cellular events being observed was often correct.\n

\n
\n", "question_id": "22M.2.SL.TZ2.2A.I", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-1-cell-and-nuclear-division", "d2-1-8-identification-of-phases-of-mitosis" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n One criticism of the experiment is that it only measured the rate of transpiration indirectly. Explain how the experiment is an indirect measurement of transpiration.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. transpiration is water evaporating from «the leaves of» a plant ✔\n

\n

\n b. what is being measured is water uptake to the plant ✔\n

\n

\n c. assumes no water used for other processes/photosynthesis ✔\n

\n

\n \n This is not about water loss from apparatus\n \n

\n
\n", "Examiners report": "
\n

\n This item was rarely answered well, with many candidates simply describing what would happen in a potometer. An ability to outline limitations, assumptions and possible errors shows the ability to evaluate, and is one of the objectives of the DP Biology course. A similar question on the limitations of the potometer last year was also answered poorly.\n

\n
\n", "question_id": "19M.1B.SL.TZ1.2C", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-1-gas-exchange", "b3-1-9-transpiration-as-a-consequence-of-gas-exchange-in-a-leaf" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Draw a half-view of an animal-pollinated flower.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n

\n a.\n \n sepals\n \n as outermost part of flower ✔\n

\n

\n b.\n \n petals\n \n as largest part of flower ✔\n

\n

\n c.\n \n stamen\n \n drawn with recognizable anther and filament\n
\n \n \n OR\n \n \n
\n \n anther\n \n and\n \n filament\n \n shown as parts of the stamen ✔\n

\n

\n d.\n \n carpel/pistil\n \n drawn with recognizable stigma, style and ovary\n
\n \n \n OR\n \n \n
\n \n stigma\n \n ,\n \n style\n \n and\n \n ovary\n \n shown as parts of the carpel ✔\n

\n

\n e.\n \n nectary\n \n at base of the ovary ✔\n

\n

\n f.\n \n ovule\n \n inside the ovary ✔\n

\n

\n \n As the question does not specify a labelled half-view, allow some marks for unlabeled structures: award one mark for any two of the six structures in the mark scheme (mpa to mpf). It must be clear what each unlabeled part is. The maximum mark is therefore 3 for an unlabeled half-view.\n \n

\n
\n", "Examiners report": "None", "question_id": "19N.2.SL.TZ0.8A", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-1-reproduction", "d3-1-9-features-of-an-insect-pollinated-flower" ] }, { "Question": "
\n
\n (f)\n
\n
\n

\n Calculate the mass of lipid eaten when the bumblebees were presented with the 5:1 diet.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n 0.025g;\n

\n

\n \n Unit needed\n \n

\n
\n", "Examiners report": "None", "question_id": "22N.2.SL.TZ0.1F", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c4-2-transfers-of-energy-and-matter", "c4-2-15-primary-production-as-accumulation-of-carbon-compounds-in-biomass-by-autotrophs", "c4-2-16-secondary-production-as-accumulation-of-carbon-compounds-in-biomass-by-heterotrophs" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Outline the process of DNA profiling.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n

\n a. sample of DNA obtained from person/hair/blood/mouth/crime scene ✔\n

\n

\n b. PCR used to amplify/make copies of DNA (in sample) ✔\n

\n

\n c. using\n \n Taq\n \n DNA polymerase / using DNA polymerase from thermophilic bacteria ✔\n

\n

\n d. tandem repeats amplified/used ✔\n

\n

\n e. gel electrophoresis used to separate DNA (into bands) ✔\n

\n

\n f. separation according to length of fragments/number of repeats\n
\n \n \n OR\n \n \n
\n fragments of same length/number of repeats travel same distance ✔\n

\n

\n g. pattern of bands/numbers of repeats is the profile/is unique to the individual ✔\n

\n

\n h. example of application/forensics/crime investigation/paternity ✔\n

\n

\n \n Do not accept ‘determine ancestry’ for mph\n \n .\n \n Other genes/chromosomes are more often used for that\n \n .\n

\n

\n \n Accept STR for (short) tandem repeat in mpd\n \n .\n

\n
\n", "Examiners report": "
\n

\n There were some good outlines of DNA profiling. Most knew at least one application of the process. There was some confusion between profiling and sequencing and the use of tandem repeats was often missed.\n

\n
\n", "question_id": "21M.2.SL.TZ1.8A", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d1-1-dna-replication", "d1-1-5-applications-of-polymerase-chain-reaction-and-gel-electrophoresis" ] }, { "Question": "
\n
\n (c.i)\n
\n
\n

\n Deduce\n \n one\n \n conclusion about the structure of the plasma membrane reached by the scientists from their results.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n a. phospholipids on outside/exposed ✔\n

\n

\n b. impossibility of continuous protein layer «of Davson–Danielli/model A» ✔\n

\n

\n c. supports idea of mosaic pattern of membrane\n
\n \n \n OR\n \n \n
\n supports model B ✔\n

\n

\n \n Award any other valid conclusion.\n \n

\n

\n \n Do not accept \"membrane is made of phospholipids\".\n \n

\n
\n", "Examiners report": "
\n

\n Many candidates answered that the enzyme acted on the phospholipids but failed to make a deduction about the structure of the membrane.\n

\n
\n", "question_id": "19M.1B.SL.TZ2.1C.I", "topics": [ "b-form-and-function" ], "subtopics": [ "b2-1-membranes-and-membrane-transport", "b2-1-10-fluid-mosaic-model-of-membrane-structure" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n The figure shows a tripeptide.\n

\n

\n \n

\n

\n Label\n \n one\n \n peptide bond in this molecule.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n circle/bracket around peptide bond / arrow pointing to peptide bond / peptide bond labelled;\n

\n

\n \n

\n

\n \n Allow either peptide bond\n \n

\n

\n \n Allow if adjacent C=O and NH groups are included in the circle/bracket, but do not allow if other parts of the molecule are included\n \n

\n
\n", "Examiners report": "
\n

\n However, in part 2b, many did not describe the functions of the named proteins correctly. Common mistakes were assuming that all hormones are proteins, with many incorrectly giving oestrogen, testosterone and thyroxin for example. Examples were anticipated from the list of proteins found in section 2.4 of the guide.\n

\n
\n", "question_id": "21N.2.SL.TZ0.2A", "topics": [ "b-form-and-function" ], "subtopics": [ "b1-2-proteins", "b1-2-2-condensation-reactions-forming-dipeptides-and-longer-chains-of-amino-acids" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Outline\n \n one\n \n cause of denaturation in proteins.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n increase in temperature/heat;\n
    2. \n
  2. \n change of pH;\n
    3. \n
  3. \n salt;\n
    4. \n
  4. \n heavy metals;\n
    5. \n
\n
\n", "Examiners report": "
\n

\n Most candidates answered these questions about enzymes either really well or very poorly. Some erroneous answers mistook the active site as being separate to the enzyme or part of the substrate. Another problem had to do with temperature as a denaturant. Lowering the temperature does not denature the enzyme, though it may slow the reaction down. The candidate needed to say increased or hot temperature to gain a mark.\n

\n
\n", "question_id": "22M.2.SL.TZ1.2B", "topics": [ "b-form-and-function" ], "subtopics": [ "b1-2-proteins", "b1-2-5-effect-of-ph-and-temperature-on-protein-structure" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Describe the effect of temperature on the total biomass.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. negative correlation/decrease (in biomass) as temperature rises in added-nutrients (mesocosms);\n
\n b. little/no (significant) change in biomass as temperature increases in control (mesocosms);\n

\n
\n", "Examiners report": "
\n

\n The word ‘total’ confused some candidates who tried to write about both the control and added-nutrients without distinguishing between them. Of those candidates who realised that ‘total’ must mean the total biomass within a mesocosm, almost all got the decrease in ‘with nutrients’ mesocosms as temperature increased, but many were not discerning enough with the control mesocosms. The differences were less than the error bars, so were clearly insignificant and should have been ignored Question 2.\n

\n
\n", "question_id": "21N.2.SL.TZ0.1A", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-2-stability-and-change", "d4-2-4-use-of-a-model-to-investigate-the-effect-of-variables-on-ecosystem-stability" ] }, { "Question": "
\n
\n

\n Discuss\n \n one\n \n advantage and\n \n one\n \n disadvantage of using plant tissue to investigate drugs intended to treat cancer in humans.\n

\n

\n Advantage:\n

\n

\n

\n

\n Disadvantage:\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n \n Advantage\n \n :\n

\n

\n avoids risks for humans/harm to humans / more ethical (than with human patients/volunteers) ✔\n

\n

\n \n Disadvantage\n \n :\n

\n

\n differences between plant and human cells so humans may not respond in same way\n
\n \n \n OR\n \n \n
\n plants have cell wall/no centrioles/other relevant difference between plant and human cells ✔\n

\n

\n \n Not enough for mpa to say ‘not using humans’.\n \n

\n

\n \n For mpb there must be either a statement that differences between cells may cause a different response, or a specific example of a cell difference\n \n .\n

\n
\n", "Examiners report": "
\n

\n Most candidates were able to suggest an advantage of using plant tissue and any reasonable answer was accepted. Fewer gave a disadvantage that was credited. Vague answers such as plants are different from humans were not rewarded with a mark.\n

\n
\n", "question_id": "21M.2.HL.TZ1.G", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-1-cell-and-nuclear-division", "d2-1-17-differences-between-tumours-in-rates-of-cell-division-and-growth-and-in-the-capacity-for-metastasis-and-invasion-of-neighbouring-tissue" ] }, { "Question": "
\n
\n

\n The table compares ribosomal RNA (rRNA) sequences of two organisms from each of the three domains by showing an association coefficient. The more similar the rRNA sequences of the organisms, the larger the coefficient.\n

\n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n
\n \n \n \n S. cerevisiae\n \n \n \n \n \n L. minor\n \n \n \n \n \n E. Coli\n \n \n \n \n \n B. firmus\n \n \n \n \n \n M. ruminantium\n \n \n \n \n \n M. barkeri\n \n \n
\n \n \n S. cerevisiae\n \n \n \n —\n \n 0.29\n \n 0.05\n \n 0.08\n \n 0.11\n \n 0.08\n
\n \n \n L. minor\n \n \n \n \n —\n \n 0.10\n \n 0.06\n \n 0.10\n \n 0.07\n
\n \n \n E. Coli\n \n \n \n \n \n —\n \n 0.25\n \n 0.12\n \n 0.12\n
\n \n \n B. firmus\n \n \n \n \n \n \n —\n \n 0.13\n \n 0.12\n
\n \n \n M. ruminantium\n \n \n \n \n \n \n \n —\n \n 0.24\n
\n \n \n M. barkeri\n \n \n \n \n \n \n \n \n —\n
\n

\n \n [Source: Woese, C.R. and Fox, G.E., 1977. Phylogenetic structure of the prokaryotic domain:\n \n
\n \n The primary kingdoms.\n \n Proc. Natl.\n \n Acad Sci. USA, 74(11), pp. 5088–5090.]\n \n

\n

\n What can be concluded from the data?\n
\n
\n

\n

\n A.\n \n L. minor\n \n and\n \n E. coli\n \n are both eubacteria.\n

\n

\n B.\n \n S. cerevisiae\n \n and\n \n M. barkeri\n \n are in the same domain.\n

\n

\n C.\n \n M. ruminantium\n \n is an archaean, therefore so is\n \n B. firmus\n \n .\n

\n

\n D.\n \n E. coli\n \n and\n \n B. firmus\n \n are in the same domain.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "23M.1A.HL.TZ1.17", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a3-2-classification-and-cladistics-(hl-only)", "a3-2-9-classification-of-all-organisms-into-three-domains-using-evidence-from-rrna-base-sequences" ] }, { "Question": "
\n
\n

\n The apparatus shown was used to investigate the effect of varying carbon dioxide concentration on the rate of photosynthesis. Carbon dioxide concentrations were varied by adding different amounts of sodium hydrogen carbonate (NaHCO\n \n 3\n \n ) to water.\n

\n

\n \n

\n

\n

\n

\n What is the dependent variable in this investigation?\n

\n

\n A. Temperature\n

\n

\n B. Light intensity\n

\n

\n C. Amount of NaHCO\n \n 3\n \n added\n

\n

\n D. Volume of oxygen produced\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "22M.1A.SL.TZ2.12", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-3-photosynthesis", "c1-3-7-techniques-for-varying-concentrations-of-carbon-dioxide-light-intensity-or-temperature-experimentally-to-investigate-the-effects-of-limiting-factors-on-the-rate-of-photosynthesis" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n State\n \n one\n \n process that results in the loss of carbon dioxide from a marine organism such as a crustacean or a jellyfish.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n a. (aerobic/cellular) respiration ✔\n

\n

\n b. gas exchange / diffusion ✔\n

\n

\n \n Do not accept photosynthesis\n \n .\n

\n

\n \n Do not accept breathing\n \n

\n

\n \n Organism is taken to be a living thing\n \n .\n

\n
\n", "Examiners report": "
\n

\n In 4(a) most were able to state 'respiration' as the answer. 4(b) proved more difficult with fewer stating photosynthesis or absorption of dissolved CO\n \n 2\n \n or HCO\n \n 3\n \n from the seawater. Vague answers such as 'carbon in the water' were not credited. In 4(c) most knew that energy enters with sunlight, but did not state photosynthesis. They knew that it was transferred by feeding through the trophic levels and lost as heat due to respiration. A surprising number incorrectly stated that the energy was recycled and some drew diagrams of the energy flow showing this. In 4(d)(i) most were able to state that the crustacean was a richer source of carbon. An explanation using the data from the diagram was expected. In 4(d)(ii) most were able to present an argument for advantage or disadvantage.\n

\n
\n", "question_id": "21M.2.SL.TZ2.4A", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c4-2-transfers-of-energy-and-matter", "c4-2-17-constructing-carbon-cycle-diagrams", "c4-2-18-ecosystems-as-carbon-sinks-and-carbon-sources" ] }, { "Question": "
\n
\n

\n In the grass plant\n \n Halopyrum mucronatum\n \n , the enzyme amylase breaks bonds in polysaccharides during germination. The graph shows how the activity of the enzyme varies with the concentration of polysaccharide.\n

\n

\n \n

\n

\n \n [Source: Material from: Siddiqui, Z.S. and Khan, M.A., The role of enzyme amylase in two germinating seed morphs of\n \n
\n \n \n Halopyrum mucronatum\n \n (L.) Stapf. in saline and non-saline environment, published 2011,\n \n Acta Physiologiae\n \n \n
\n \n \n Plantarum\n \n , reproduced with permission of SNCSC.]\n \n

\n

\n

\n

\n What is the reason for the curve levelling off?\n
\n
\n

\n

\n A.  There is insufficient substrate for the enzyme to act on.\n

\n

\n B.  The product acts as an enzyme inhibitor.\n

\n

\n C.  The enzymes have all been consumed in the reaction.\n

\n

\n D.  All the enzyme active sites are occupied by substrate.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "23M.1A.SL.TZ2.8", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-1-enzymes-and-metabolism", "c1-1-8-effects-of-temperature-ph-and-substrate-concentration-on-the-rate-of-enzyme-activity" ] }, { "Question": "
\n
\n

\n Distinguish between the thermal properties of air and water as they relate to the habitat of animals.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n water has a (much) higher specific heat capacity (than air);\n
    2. \n
  2. \n water requires more energy gain/loss to change temperature;\n
    3. \n
  3. \n (water) provides more stable thermal habitats than air / temperature of water bodies remains more constant than air temperature;\n
    4. \n
  4. \n water has a higher thermal conductivity than air;\n
    5. \n
  5. \n more heat is transferred from organisms to water than to air;\n
    6. \n
  6. \n water is a good evaporative coolant and air is not;\n
    7. \n
  7. \n aquatic mammals have (proportionally) more body fat as insulation;\n
    8. \n
\n
\n", "Examiners report": "None", "question_id": "SPM.2.SL.TZ0.C", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a1-1-water", "a1-1-6-physical-properties-of-water-and-the-consequences-for-animals-in-aquatic-habitats" ] }, { "Question": "
\n
\n

\n The diagram shows a graph of an action potential.\n

\n

\n \n

\n

\n [Source: https://www.ncbi.nlm.nih.gov/books/NBK538143/figure/article-17127.image.f1/?report=objectonly\n
\n \n Physiology, Action Potential\n \n by Michael H. Grider and Carolyn S. Glaubensklee.\n
\n Copyright © 2019, StatPearls Publishing LLC\n
\n \n https://creativecommons.org/licenses/by/4.0/]\n \n

\n

\n

\n

\n What is happening at X?\n

\n

\n A. Sodium channels close.\n

\n

\n B. Calcium channels open.\n

\n

\n C. Sodium channels open.\n

\n

\n D. Potassium channels close.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "None", "question_id": "19M.1A.SL.TZ1.29", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c2-2-neural-signalling", "c2-2-3-nerve-impulses-as-action-potentials-that-are-propagated-along-nerve-fibres" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Outline the reason that the curve for fetal hemoglobin is to the left of normal adult hemoglobin.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n fetal hemoglobin has a higher affinity for oxygen then normal hemoglobin;\n
    2. \n
  2. \n oxygen will pass from normal/maternal/mother’s hemoglobin to fetal hemoglobin (in the placenta);\n
    3. \n
\n
\n", "Examiners report": "None", "question_id": "23M.2.HL.TZ1.23B", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-1-gas-exchange", "b3-1-13-oxygen-dissociation-curves-as-a-means-of-representing-the-affinity-of-haemoglobin-for-oxygen-at-different-oxygen-concentrations" ] }, { "Question": "
\n
\n

\n The table shows the approximate energy stores in a man with an average mass.\n

\n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n
\n \n \n Available energy / kJ\n \n
\n \n Organ or tissue\n \n \n \n Carbohydrates\n \n \n \n Lipids\n \n \n \n Proteins\n \n
\n Brain\n \n 30\n \n 0\n \n 0\n
\n Liver\n \n 1700\n \n 2000\n \n 1700\n
\n Adipose tissue\n \n 330\n \n 560 000\n \n 170  ​\n
\n

\n \n [Source: Reprinted from\n \n Clinics in Endocrinology and Metabolism\n \n , 5(2),\n
\n Cahill Jr., G.F., Starvation in Man, Copyright (1976), with permission from Elsevier.]\n \n

\n

\n
\n What can be concluded from the data?\n

\n

\n
\n A.  The brain contains no short-term stored energy.\n

\n

\n B.  The liver contains less long-term than short-term stored energy.\n

\n

\n C.  The adipose tissue provides for most of the long-term energy storage.\n

\n

\n D.  Carbohydrates provide more energy per gram than lipids or proteins.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "23M.1A.SL.TZ1.8", "topics": [ "b-form-and-function" ], "subtopics": [ "b1-1-carbohydrates-and-lipids", "b1-1-11-triglycerides-in-adipose-tissues-for-energy-storage-and-thermal-insulation" ] }, { "Question": "
\n
\n

\n Calculate, showing your working, the percentage change in mean cholesterol level after\n \n one week\n \n on the study diet.\n

\n

\n

\n

\n . . . . . . . . . . . . . . . . . . . .%\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n ((165–150) ÷ 150) × 100;\n

\n

\n (=) 10 (%);\n

\n

\n \n Allow up to 167 = 11.3 %\n \n

\n

\n \n 1 mark for correct working if above 167\n \n .\n

\n
\n", "Examiners report": "None", "question_id": "20N.1B.SL.TZ0.C", "topics": [ "b-form-and-function" ], "subtopics": [ "b1-2-proteins", "b1-2-3-dietary-requirements-for-amino-acids", "b1-1-carbohydrates-and-lipids", "b1-1-10-difference-between-saturated-monounsaturated-and-polyunsaturated-fatty-acids" ] }, { "Question": "
\n
\n

\n Suggest reasons for the difference between the data for\n \n S. pneumoniae\n \n and\n \n H. influenzae\n \n .\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n Hib vaccination program started earlier/PCV vaccination program started later\n
    \n \n \n OR\n \n \n
    \n Hib vaccine developed before PCV vaccine;\n
    2. \n
  2. \n deaths due to\n \n H. influenzae\n \n drop earlier than deaths due to\n \n S. pneumoniae\n \n because of earlier vaccination;\n
    3. \n
  3. \n more deaths due to\n \n S. pneumoniae\n \n than\n \n H. influenzae\n \n (in any year) as lower % of children vaccinated against\n \n S. pneumoniae\n \n (compared\n \n H. influenzae\n \n );\n
    4. \n
\n

\n \n Mp a to c: accept vice versa.\n \n

\n

\n \n Comparative terms expected (do not award mp for just stating values).\n \n

\n

\n \n Mpa and mpb: there must be a clear reference to time.\n \n

\n

\n \n Mpc: there must be clear indication to vaccination.\n \n

\n

\n \n Allow no points for bacterial virulence / disease severity, etc., as bacterial pathogenicity is not addressed on graphs.\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ2.E", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-2-defence-against-disease", "c3-2-16-vaccines-and-immunization" ] }, { "Question": "
\n
\n

\n What is a consequence of anaerobic cell respiration in muscles?\n

\n

\n
\n A.  Large yield of readily available ATP and ethanol production\n

\n

\n B.  Small yield of readily available ATP and lactate accumulation\n

\n

\n C.  Large yield of ATP and production of carbon dioxide and lactic acid\n

\n

\n D.  Small yield of ATP that is not readily available and carbon dioxide production\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "23M.1A.SL.TZ1.9", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-2-cell-respiration", "c1-2-9-conversion-of-pyruvate-to-lactate-as-a-means-of-regenerating-nad-in-anaerobic-cell-respiration" ] }, { "Question": "
\n
\n (a.i)\n
\n
\n

\n Outline how the amphipathic properties of phospholipids play a role in membrane structure.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. part hydrophobic/not attracted to water/non-polar\n \n \n AND\n \n \n part hydrophilic/attracted to water/polar;\n

\n

\n b.\n \n bilayer\n \n formed (formed naturally by phospholipids in water);\n

\n

\n c.\n \n hydrophilic\n \n heads/parts face outwards and\n \n hydrophobic\n \n tails/parts face inwards.\n

\n

\n \n Do not allow water loving/hating in mpa or mpc\n \n .\n

\n
\n", "Examiners report": "
\n

\n Knowledge of the amphipathic properties of phospholipids was generally good.\n

\n
\n", "question_id": "20N.2.SL.TZ0.2A.I", "topics": [ "b-form-and-function" ], "subtopics": [ "b1-1-carbohydrates-and-lipids", "b1-1-12-formation-of-phospholipid-bilayers-as-a-consequence-of-the-hydrophobic-and-hydrophilic-regions" ] }, { "Question": "
\n
\n

\n The diagram shows part of the carbon cycle involving methane.\n

\n

\n \n

\n

\n [Source: NASA GISS, n.d.\n \n Rough schematic of methane sources and sinks\n \n . [diagram online] Available at:\n
\n https://www.giss.nasa.gov/research/features/200409_methane/ [Accessed 26 October 2021].]\n

\n

\n

\n

\n Which conditions favour methane production in W, X and Y?\n

\n

\n A.  Presence of eubacteria and organic matter\n

\n

\n B.  Presence of archaeans and waterlogged soil\n

\n

\n C.  Presence of eubacteria and waterlogged soil\n

\n

\n D.  Presence of archaeans and oxygen\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "22N.1A.HL.TZ0.16", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c4-2-transfers-of-energy-and-matter", "c4-2-17-constructing-carbon-cycle-diagrams" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Describe how ATP is produced by Photosystem II in the light-dependent stage of photosynthesis.\n

\n
\n
\n

\n [5]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n light (energy) absorbed by pigments/chlorophyll/photosystems;\n
    2. \n
  2. \n excited electrons passed to electron carriers/electron transport chain;\n
    3. \n
  3. \n protons/hydrogen ions pumped into thylakoid (space);\n
    4. \n
  4. \n proton gradient/high proton concentration generated;\n
    5. \n
  5. \n protons pass via ATP synthase to the stroma;\n
    6. \n
  6. \n ATP synthase phosphorylates ADP/ATP synthase converts ADP to ATP;\n
    7. \n
  7. \n photophosphorylation/chemiosmosis;\n
    8. \n
  8. \n ATP synthase/electron carriers/proton pumps/photosystems/pigment are in the thylakoid membrane;\n
    9. \n
\n
\n", "Examiners report": "
\n

\n There was evidence that many candidates had prepared carefully for this topic and were fully familiar with the sequence of events in the light-dependent reactions that result in ATP production. In some of the weaker answers the protons were moving in the wrong direction and some candidates were confused about the differences in structure between chloroplasts and mitochondria and therefore the nature of the proton gradient.\n

\n
\n", "question_id": "22N.2.HL.TZ0.7B", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-3-photosynthesis", "c1-3-14-thylakoids-as-systems-for-performing-the-light-dependent-reactions-of-photosynthesis" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Outline\n \n four\n \n types of membrane transport, including their use of energy.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n

\n a. simple diffusion is passive movement of molecules/ions along a concentration gradient ✔\n

\n

\n b. facilitated diffusion is passive movement of molecules/ions along a concentration gradient through a protein channel «without use of energy» ✔\n

\n

\n c. osmosis is the passage of water\n \n through a membrane\n \n from lower solute concentration to higher ✔\n \n OWTTE\n \n

\n

\n d. active transport is movement of molecules/ions\n \n against the concentration gradient\n \n «through membrane pumps» with the use of ATP/energy ✔\n \n Active transport requires mention of the use of energy.\n \n

\n

\n e. endocytosis is the infolding of membrane/formation of vesicles to bring molecules into cell with use of energy\n
\n \n \n OR\n \n \n
\n exocytosis is the infolding of membrane/formation of vesicles to release molecules from cell with use of energy ✔\n

\n

\n f. chemiosmosis occurs when protons diffuse through ATP synthase «in membrane» to produce ATP ✔\n

\n

\n \n The description of each type of transport should include the name and brief description.\n \n

\n

\n \n mpa, mpb and mpc require reference to concentration.\n \n

\n

\n

\n
\n", "Examiners report": "
\n

\n Membrane transport – In spite of the question asking about energy, many lost easy marks by forgetting to refer to it. Others did not mention the gradients. In osmosis, please stress to the students which concentration they are talking about. They should be talking clearly about water potential or solute concentration.\n

\n
\n", "question_id": "19M.2.SL.TZ2.5A", "topics": [ "b-form-and-function" ], "subtopics": [ "b2-1-membranes-and-membrane-transport", "b2-1-5-movement-of-water-molecules-across-membranes-by-osmosis-and-the-role-of-aquaporins", "b2-1-6-channel-proteins-for-facilitated-diffusion", "b2-1-7-pump-proteins-for-active-transport", "b2-1-8-selectivity-in-membrane-permeability" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Annotate the diagram by adding arrows to show how deoxygenated blood enters the heart.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n arrows added to the diagram to show how deoxygenated blood enters the heart;\n

\n

\n \n

\n

\n \n [Source: CC BY-SA 3.0, https://commons.wikimedia.org/\n \n \n w/index.php?curid=606903. Open access.]\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ1.3", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-2-transport", "b3-2-15-adaptations-of-the-mammalian-heart-for-delivering-pressurized-blood-to-the-arteries" ] }, { "Question": "
\n
\n

\n The diagram shows the chromosomes derived from a single homologous pair following meiosis in a diploid cell.\n

\n

\n \n

\n

\n Which diagram represents the homologous pair from which these chromosomes were derived?\n

\n

\n \n

\n

\n [Source: © International Baccalaureate Organization 2019]\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "
\n

\n Perhaps surprisingly this proved to be the easiest question on the exam, with 86 % answering correctly. This is pleasing as it shows widespread understanding of recombination in meiosis.\n

\n
\n", "question_id": "19M.1A.SL.TZ1.36", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-1-cell-and-nuclear-division", "d2-1-11-meiosis-as-a-source-of-variation" ] }, { "Question": "
\n
\n (d)\n
\n
\n

\n \n Allium\n \n root tips continue to show some growth even at high concentrations of NVP. Suggest a possible reason for the growth seen in root tips with 800μmol NVP.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n a. still some mitosis ✔\n

\n

\n b. individual cells grow/elongate (expand by absorbing water) ✔\n

\n

\n c. NVP is not 100 % effective / does not enter all of the cells / not all cells have come in contact with NVP ✔\n

\n

\n d. roots have reached maximum saturation of NVP and are no longer functionally affected ✔\n

\n

\n e. some cells are resistant to the drug ✔\n

\n

\n \n Accept reasonable suggestions\n \n .\n

\n
\n", "Examiners report": "
\n

\n Most candidates earned this mark; some gave imaginative answers.\n

\n
\n", "question_id": "21M.2.HL.TZ1.1D", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-1-cell-and-nuclear-division", "d2-1-13-phases-of-the-cell-cycle" ] }, { "Question": "
\n
\n (e)\n
\n
\n

\n Describe the effects of temperature and nitrate concentration on biomass.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n a. increased temperature raises biomass;\n
\n b. increased nitrate raises biomass more than increased temperature;\n
\n c. increased nitrate and temperature raises biomass by same amount as nitrate alone;\n

\n
\n", "Examiners report": "
\n

\n This was another question where many candidates’ answers lacked discernment. The increase in biomass with nitrate was clearly greater than that with temperature alone, but the increase with nitrate and temperature combined was not significantly different from nitrate alone. A useful way of thinking about answering questions such as this is ‘If I read out my answer to someone over the phone, would they correctly sketch the relative size of the bars without seeing the actual bar chart?’ With many candidates the answer to this would have been no.\n

\n
\n", "question_id": "21N.2.SL.TZ0.1E", "topics": [ "d-continuity-and-change", "c-interaction-and-interdependence" ], "subtopics": [ "d4-2-stability-and-change", "d4-2-4-use-of-a-model-to-investigate-the-effect-of-variables-on-ecosystem-stability", "c1-3-photosynthesis", "c1-3-7-techniques-for-varying-concentrations-of-carbon-dioxide-light-intensity-or-temperature-experimentally-to-investigate-the-effects-of-limiting-factors-on-the-rate-of-photosynthesis" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Outline how two parents could have a child with any of the four ABO blood groups.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n

\n a. I\n \n A\n \n , i for one set of gametes/parental genotype ✔\n

\n

\n b. I\n \n B\n \n , i for the other set of gametes/parental genotype ✔\n

\n

\n c. «genotypes of offspring are» I\n \n A\n \n I\n \n B\n \n , I\n \n A\n \n i, I\n \n B\n \n i, ii ✔\n

\n

\n d. «phenotypes of offspring are» AB, A, B, O ✔\n

\n

\n \n Answers can be given in a Punnett grid or in prose.\n \n

\n

\n \n Accept the four possible blood groups of the offspring anywhere in the answer.\n \n

\n
\n", "Examiners report": "None", "question_id": "19N.2.SL.TZ0.7B", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-2-inheritance", "d3-2-9-abo-blood-groups-as-an-example-of-multiple-alleles" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Explain how cells and cell components in the blood defend the body against infectious disease.\n

\n
\n
\n

\n [7]\n

\n
\n
\n", "Markscheme": "
\n

\n \n Platelets\n \n :\n \n \n [3 max]\n \n \n

\n
    \n
  1. \n damage/cuts to blood vessels causes platelets to be activated;\n
    2. \n
  2. \n the platelets release clotting factors;\n
    3. \n
  3. \n initiates cascade of reactions\n
    \n \n \n OR\n \n \n
    \n fibrinogen is converted to fibrin;\n
    4. \n
  4. \n forms a mesh over the damaged area;\n
    5. \n
  5. \n prevents pathogens from entering the body;\n
    \n
    \n \n Phagocytes\n \n :\n \n \n [3 max]\n
    \n     \n     \n
    6. \n
  6. \n phagocytes/phagocytic white blood cells in the blood travel to the site of infection;\n
    7. \n
  7. \n (phagocytes) squeeze between the capillary cells;\n
    8. \n
  8. \n (phagocytes) engulf/ingest/take in pathogens;\n
    9. \n
  9. \n the pathogen is digested/broken down by/within the phagocyte;\n
    \n
    \n \n Lymphocytes\n \n :\n \n \n [3 max]\n \n \n
    10. \n
  10. \n lymphocytes recognize a particular fragment/antigen of a pathogen;\n
    11. \n
  11. \n (lymphocytes) release antibodies;\n
    12. \n
  12. \n (antibodies) provide specific immunity;\n
    13. \n
  13. \n memory cells provide rapid response giving long-term immunity (to pathogens previously recognized);\n
    14. \n
  14. \n antibodies destroy pathogens;\n
    15. \n
\n

\n \n ECF may be applied when candidates use white blood cells in place of specific terms\n \n .\n

\n
\n", "Examiners report": "
\n

\n Among all candidates, there was knowledge of how each of the blood components (platelets, phagocytes, lymphocytes) can defend against infectious disease; each of the marking points in the mark scheme was eventually awarded; popular ideas were that fibrin is formed, phagocytes engulf pathogens and antibodies provide specific immunity.\n

\n

\n Correct terminology was confused or was not employed in too many answers.\n

\n
\n", "question_id": "22M.2.SL.TZ1.6C", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-2-defence-against-disease", "c3-2-10-immunity-as-a-consequence-of-retaining-memory-cells" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Describe how plants affect the amount of carbon dioxide in the atmosphere.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n plants reduce the amount of carbon dioxide in the atmosphere by\n \n photosynthesis\n \n ;\n
    2. \n
  2. \n carbon dioxide is fixed/converted into organic substances/sugars/ OWTTE;\n
    3. \n
  3. \n plants respire which releases carbon dioxide into the atmosphere;\n
    4. \n
  4. \n plant decomposition may release CO\n \n 2\n \n
    5. \n
  5. \n carbon in dead plants is trapped/ stored in fossil fuels / peat\n
    6. \n
  6. \n combustion of plants/wood/ fossil fuels adds to the amount of carbon dioxide in the atmosphere;\n
    7. \n
\n

\n \n \n OR\n \n Shows correct equation\n \n

\n
\n", "Examiners report": "
\n

\n In (b) many saw the words 'Carbon Dioxide' and immediately treated it as a long answer on greenhouse gases, thus putting their quality mark in jeopardy for superfluous content. Most were aware of photosynthesis removing CO\n \n 2\n \n from the atmosphere by fixing it into organic compounds and many mentioned plant respiration as increasing it. However, there were some disturbing answers where students mixed up photosynthesis and respiration. The question was about plants, but many answered in terms of animals.\n

\n
\n", "question_id": "22N.2.SL.TZ0.6B", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c4-2-transfers-of-energy-and-matter", "c4-2-18-ecosystems-as-carbon-sinks-and-carbon-sources", "c4-2-19-release-of-carbon-dioxide-into-the-atmosphere-during-combustion-of-biomass-peat-coal-oil-and-natural-gas" ] }, { "Question": "
\n
\n (e)\n
\n
\n

\n Compare and contrast the results for the 1:1 and the 1:10 P:L diets.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n in both a greater mass of sucrose was eaten (than of the P:L mixture)\n
    \n \n \n OR\n \n \n
    \n the total mass eaten by both groups is the same/very similar;\n
    2. \n
  2. \n the mass of sucrose eaten in the 1:10 mixture diet is greater than in the 1:1 diet\n
    \n \n \n OR\n \n \n
    \n the mass of the P:L mixture eaten in the 1:10 is less than in the 1:1;\n
    3. \n
\n

\n \n Accept vice versa for all answers.\n \n

\n
\n", "Examiners report": "None", "question_id": "22N.2.SL.TZ0.1E", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c4-2-transfers-of-energy-and-matter", "c4-2-15-primary-production-as-accumulation-of-carbon-compounds-in-biomass-by-autotrophs", "c4-2-16-secondary-production-as-accumulation-of-carbon-compounds-in-biomass-by-heterotrophs" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Outline a reason for the muscles being described as antagonistic.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n cause opposite movements / pull in opposite directions / when one\n \n contracts\n \n the other\n \n relaxes\n \n ;\n

\n
\n", "Examiners report": "
\n

\n Most candidates were able to outline what antagonistic muscles are. The term 'extended' was sometimes used instead of 'relax' which is the preferred term as it indicates passivity.\n

\n
\n", "question_id": "22M.2.HL.TZ1.5", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-3-muscle-and-motility-(hl-only)", "b3-3-3-role-of-the-protein-titin-and-antagonistic-muscles-in-muscle-relaxation", "b3-3-8-internal-and-external-intercostal-muscles-as-an-example-of-antagonistic-muscle-action-to-facilitate-internal-body-movements", "b3-3-2-sliding-filament-model-of-muscle-contraction" ] }, { "Question": "
\n
\n

\n Describe the use of gene knockout technology in research.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n gene knockout technology is a genetic engineering technique/intentional alteration in the sequence of a  gene;\n
    2. \n
  2. \n making a gene inactive;\n
    3. \n
  3. \n using site specific nucleases / CRISPR;\n
    4. \n
  4. \n researcher observes changes in phenotype of organism;\n
    5. \n
  5. \n allows researcher to determine function of the gene;\n
    6. \n
  6. \n entire library of knockout organisms exists;\n
    7. \n
  7. \n made available to researchers;\n
    8. \n
\n
\n", "Examiners report": "None", "question_id": "SPM.2.HL.TZ0.C", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d1-3-mutations-and-gene-editing", "d1-3-8-gene-knockout-as-a-technique-for-investigating-the-function-of-a-gene-by-changing-it-to-make-it-inoperative" ] }, { "Question": "
\n
\n (d)\n
\n
\n

\n Explain how cardiac muscle is adapted to its function.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n many mitochondria for aerobic respiration;\n
    2. \n
  2. \n cells are branched allowing for faster transmission/allow impulse to spread;\n
    3. \n
  3. \n cardiac muscle is myogenic so does not require the CNS to initiate contraction;\n
    4. \n
  4. \n cells are not fused together/are connected by gap junctions/intercalated discs (which) allows easier transmission between cells;\n
    5. \n
\n
\n", "Examiners report": "None", "question_id": "23M.2.HL.TZ1.22D", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-2-transport", "b3-2-15-adaptations-of-the-mammalian-heart-for-delivering-pressurized-blood-to-the-arteries" ] }, { "Question": "
\n
\n

\n Which is an example of natural selection?\n

\n

\n A. A giraffe stretching its neck to reach higher leaves\n

\n

\n B. A juvenile bird learning to sing\n

\n

\n C. Development of antibiotic resistance in bacteria\n

\n

\n D. Selective breeding of tail-less cats\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "19M.1A.SL.TZ1.21", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-1-natural-selection", "d4-1-1-natural-selection-as-the-mechanism-driving-evolutionary-change", "d4-1-5-differences-between-individuals-in-adaptation-survival-and-reproduction-as-the-basis-for-natural-selection" ] }, { "Question": "
\n
\n (d)\n
\n
\n

\n When the data in the table were used to calculate chi-squared, the calculated value was 0.056. The critical value is 3.84. Explain the conclusion that can be drawn from the calculated and critical values for chi-squared.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n (when the calculated value is smaller than the critical value) there is no significant association between the two species / H\n \n 0\n \n /null hypothesis accepted;\n
    2. \n
  2. \n it is random chance if both species are either present or absent in most quadrats;\n
    3. \n
\n
\n", "Examiners report": "None", "question_id": "22M.2.SL.TZ2.3D", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c4-1-populations-and-communities", "c4-1-15-use-of-the-chi-squared-test-for-association-between-two-species" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Explain the regulation of metabolic pathways by end-product inhibition.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n final product in pathway acts as an inhibitor/blocks (reaction)/slows (reaction);\n
    2. \n
  2. \n first/early/earlier enzyme (in pathway is inhibited);\n
    3. \n
  3. \n non-competitive / binds at allosteric site / causes active site to change;\n
    4. \n
  4. \n production of end-product reduced/paused when there is an excess;\n
    5. \n
  5. \n isoleucine inhibits enzyme using threonine as substrate at start of pathway to isoleucine;\n
    6. \n
  6. \n negative feedback / production restarts when end-product used up/concentration drops;\n
    7. \n
\n

\n \n For mpe accept other examples of end-product inhibition if verified. Please add a note in such cases.\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.2.HL.TZ1.6B", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-1-enzymes-and-metabolism", "c1-1-16-regulation-of-metabolic-pathways-by-feedback-inhibition" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Describe the state of the heart valves at 0.3 s.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n atrioventricular/AV valves closed;\n
    2. \n
  2. \n semi-lunar valves open;\n
    3. \n
\n
\n", "Examiners report": "None", "question_id": "23M.2.HL.TZ1.22C", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-2-transport", "b3-2-16-stages-in-the-cardiac-cycle" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Outline how variation in organisms of the same species could lead to natural selection.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n a. survival of the better adapted/fittest ✔\n

\n

\n b. more reproduction of better adapted/fittest/individuals with favorable variations ✔\n

\n

\n c. genes for favorable variations/adaptations passed on to offspring ✔\n \n Accept answers in the converse\n \n .\n

\n

\n d. competition for resources/more offspring produced than the environment can support/a struggle for existence ✔\n \n Accept answers in the converse\n \n .\n

\n
\n", "Examiners report": "None", "question_id": "19N.2.SL.TZ0.3B", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a4-1-evolution-and-speciation", "a4-1-1-evolution-as-change-in-the-heritable-characteristics-of-a-population" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Explain how the information in the box labelled B indicates that the gene is\n \n not\n \n sex-linked.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n if it was sex-linked it would be on the x chromosome;\n
    2. \n
  2. \n there cannot be a heterozygous male if the trait is sex-linked\n
    3. \n
  3. \n males would pass the allele to their daughter;\n
    4. \n
  4. \n daughter is not shown as heterozygous so it is not sex-linked;\n
    5. \n
\n
\n", "Examiners report": "None", "question_id": "22N.2.SL.TZ0.4C", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-2-inheritance", "d3-2-12-haemophilia-as-an-example-of-a-sex-linked-genetic-disorder", "d3-2-13-pedigree-charts-to-deduce-patterns-of-inheritance-of-genetic-disorders" ] }, { "Question": "
\n
\n

\n What is a function of the enzyme helicase?\n

\n

\n A. It coils DNA up into a double helical shape.\n

\n

\n B. It links DNA nucleotides in a new DNA strand.\n

\n

\n C. It breaks hydrogen bonds between the DNA strands.\n

\n

\n D. It forms temporary hydrogen bonds to produce messenger RNA.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "22M.1A.SL.TZ2.11", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d1-1-dna-replication", "d1-1-3-role-of-helicase-and-dna-polymerase-in-dna-replication" ] }, { "Question": "
\n
\n

\n State the name of the valves that prevent blood flowing from the arteries back into the heart.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n semilunar / sigmoid / pulmonary\n \n and\n \n aortic valve ✔\n

\n
\n", "Examiners report": "
\n

\n Most could name the semilunar valves.\n

\n
\n", "question_id": "19M.2.HL.TZ2.B", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-2-transport", "b3-2-15-adaptations-of-the-mammalian-heart-for-delivering-pressurized-blood-to-the-arteries" ] }, { "Question": "
\n
\n (g)\n
\n
\n

\n State the relationship between activity inequality and obesity shown in the scattergraph.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n as activity inequality rises percentage obesity rises\n
\n \n OR\n \n
\n Positive/direct correlation/relationship;\n

\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ1.1G", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-3-muscle-and-motility-(hl-only)", "b3-3-9-reasons-for-locomotion" ] }, { "Question": "
\n
\n

\n Which equation represents a process in yeast that causes bread to rise?\n

\n

\n
\n A.  Glucose + oxygen → ethanol + carbon dioxide\n

\n

\n B.  Glucose → carbon dioxide + water\n

\n

\n C.  Glucose + oxygen → carbon dioxide + water\n

\n

\n D.  Glucose → ethanol + carbon dioxide\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "23M.1A.SL.TZ2.12", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-2-cell-respiration", "c1-2-10-anaerobic-cell-respiration-in-yeast-and-its-use-in-brewing-and-baking" ] }, { "Question": "
\n
\n

\n The diagram shows a section through a membrane. What are the modes of transport in the diagram?\n

\n

\n \n \n \n

\n

\n [Source: © International Baccalaureate Organization 2020.]\n

\n

\n \n \n \n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "20N.1A.SL.TZ0.4", "topics": [ "b-form-and-function" ], "subtopics": [ "b2-1-membranes-and-membrane-transport", "b2-1-3-simple-diffusion-across-membranes", "b2-1-6-channel-proteins-for-facilitated-diffusion", "b2-1-7-pump-proteins-for-active-transport", "b2-1-8-selectivity-in-membrane-permeability" ] }, { "Question": "
\n
\n

\n Outline the use of ATP.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n source of energy (for use in the cell)\n
\n OR\n
\n example of use of ATP\n
\n OR\n
\n when ATP is converted to ADP + Pi (is hydrolyzed) the energy stored in the phosphate bond is released to be used by the cell;\n

\n
\n", "Examiners report": "None", "question_id": "21N.2.SL.TZ0.B.II", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-2-cell-respiration", "c1-2-3-energy-transfers-during-interconversions-between-atp-and-adp" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Outline the principle of competitive exclusion.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. no two species can occupy the same niche;\n

\n

\n b. competition between them would cause one species to drive the other out\n
\n \n \n OR\n \n \n
\n one of the two species would need to adapt and evolve accordingly;\n

\n
\n", "Examiners report": "
\n

\n When describing competitive exclusion many candidates simply described competition. Some mentioned habitat rather than niche.\n

\n
\n", "question_id": "20N.2.SL.TZ0.12B", "topics": [ "b-form-and-function" ], "subtopics": [ "b4-2-ecological-niches", "b4-2-13-competitive-exclusion-and-the-uniqueness-of-ecological-niches" ] }, { "Question": "
\n
\n

\n Onion (\n \n Allium cepa\n \n ) epidermis was placed in pure water and observed with a light microscope using high magnification.\n

\n

\n \n

\n

\n What would happen to these cells if they were transferred to a hypertonic solution?\n

\n

\n
\n A.  Cells would gain mass.\n

\n

\n B.  Cells would take in water by osmosis and swell.\n

\n

\n C.  Cells would burst open, releasing their content.\n

\n

\n D.  Cell membranes would detach from walls at some points.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "23M.1A.SL.TZ1.3", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-3-water-potential", "d2-3-2-water-movement-from-less-concentrated-to-more-concentrated-solutions" ] }, { "Question": "
\n
\n (ii)\n
\n
\n

\n Calculate the difference in time between 40 % of children receiving the hepatitis B vaccine and 40 % receiving the pneumococcal vaccine.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n 13\n \n years\n \n ;\n

\n

\n \n Allow any value between 13 and 14 years inclusive.\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ2.1CII", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-2-defence-against-disease", "c3-2-16-vaccines-and-immunization" ] }, { "Question": "
\n
\n

\n Which is a feature of phloem sieve tube cells?\n

\n

\n
\n A.  Numerous chloroplasts\n

\n

\n B.  No nucleus\n

\n

\n C.  Lignified walls\n

\n

\n D.  No cytoplasm\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "SPM.1A.SL.TZ0.10", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-2-transport", "b3-2-18-adaptations-of-phloem-sieve-tubes-and-companion-cells-for-translocation-of-sap" ] }, { "Question": "
\n
\n (b.i)\n
\n
\n

\n Describe the evidence that is provided by the data in the table for the harmful effects of rising sea temperatures on corals.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. effects (generally) increase with temperature anomalies/WSSTA;\n
\n b. effects increase for all different coral covers\n
\n OR\n
\n in the 25-49 cover there is an anomaly/is not an increasing trend;\n
\n c. harmful effect is higher in coral covers between1 50-75 % / vice versa;\n

\n
\n", "Examiners report": "
\n

\n In 1b many just described the incidence at various points, instead of stating that there was no clear trend. There were a few G2 comments that the map did not include compass points, which, perhaps, has some justification. However, by convention maps are usually shown with North at the top.\n

\n

\n The expression ‘coral cover’ did confuse some of the weaker students who imagined that the corals somehow has a sort of cover over them. Most students gained at least 1 mark in 1b (i), despite the criticism from the G2 forms that it was very complex.\n

\n
\n", "question_id": "21N.2.SL.TZ0.1B.I", "topics": [ "d-continuity-and-change", "b-form-and-function" ], "subtopics": [ "d4-3-climate-change", "d4-3-7-threats-to-coral-reefs-as-an-example-of-potential-ecosystem-collapse", "b4-1-adaptation-to-environment", "b4-1-5-conditions-required-for-coral-reef-formation" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n The images show parts of plants belonging to two different phyla.\n

\n

\n \n

\n

\n State the phylum of plant X and of plant Y.\n

\n

\n X:\n

\n

\n Y:\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n X: Filicinophyta ✔\n

\n

\n Y: Coniferophyta/Conifera/Gymnosperms ✔\n

\n
\n", "Examiners report": "
\n

\n This question requiring students to identify plant phyla from images was successfully answered by most. It was more common for students to correctly identify Plant Y as a member of the Coniferophyta phylum with a greater number being unable to identify Plant X as a member of the Filicinophyta phylum.\n

\n
\n", "question_id": "19M.2.HL.TZ2.4", "topics": [ "a-unity-and-diversity", "d-continuity-and-change" ], "subtopics": [ "a3-2-classification-and-cladistics-(hl-only)", "a3-2-8-using-cladistics-to-investigate-whether-the-classification-of-groups-corresponds-to-evolutionary-relationships", "d3-1-reproduction", "d3-1-8-sexual-reproduction-in-flowering-plants", "d3-1-12-dispersal-and-germination-of-seeds" ] }, { "Question": "
\n
\n

\n The graph shows the percentage of stomata that are open in two different species of plants over a 24-hour period.\n

\n

\n \n

\n

\n What does this graph show about plants X and Y?\n

\n

\n A. Plant X absorbs most carbon dioxide at night.\n

\n

\n B. Plant Y is adapted to desert conditions.\n

\n

\n C. Plant X photosynthesises most at midday.\n

\n

\n D. Plant Y only respires during the day.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "None", "question_id": "20N.1A.SL.TZ0.32", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-1-gas-exchange", "b3-1-7-adaptations-for-gas-exchange-in-leaves" ] }, { "Question": "
\n
\n

\n Suggest\n \n two\n \n hypotheses to account for the relationship between the mean number of steps per day and the proportion of people who are obese.\n

\n

\n

\n

\n Hypothesis 1: ...........................................................................................................\n

\n

\n ...............................................................................................................................\n

\n

\n

\n

\n Hypothesis 2: ...........................................................................................................\n

\n

\n ...............................................................................................................................\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n \n (any order)\n \n

\n
    \n
  1. \n obesity causes people to be less active/take fewer steps;\n
    2. \n
  2. \n people who are less active/take fewer steps (are more likely to) become obese;\n
    3. \n
  3. \n People who are not obese tend to have healthier habits, including walking more;\n
    4. \n
\n

\n

\n

\n \n Accept hypothesis and a null hypothesis for the two.\n \n \n
\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ1.F", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-3-muscle-and-motility-(hl-only)", "b3-3-9-reasons-for-locomotion" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Explain why some biologists think protecting keystone species would help preserve biological diversity in an ecosystem.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n a large effect on the ecosystem/community structure/environment«relative to abundance»\n
\n \n \n OR\n \n \n
\n influence the balance of other populations in the ecosystem\n
\n \n \n OR\n \n \n
\n other species in the habitat would also disappear\n
\n \n \n OR\n \n \n
\n many other species dependent on them for survival ✔\n

\n
\n", "Examiners report": "None", "question_id": "19N.2.SL.TZ0.13A", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-2-stability-and-change", "d4-2-5-role-of-keystone-species-in-the-stability-of-ecosystems" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Explain the heart sounds.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n a. «heart sounds» produced by the closing of the valves ✔\n

\n

\n b. first sound «lub» is due to «closure of» the atrioventricular valves ✔\n \n Accept bicuspid/mitral and tricuspid\n \n .\n

\n

\n c. second sound «dub» is due to «closure of» the semilunar valves ✔\n \n Accept pulmonary/aortic valves\n \n .\n

\n

\n d. sequence of sounds from a healthy heart is lub dub «pause lub dub pause» ✔\n \n OWTTE\n \n

\n
\n", "Examiners report": "None", "question_id": "19N.1B.HL.TZ0.21C", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-2-transport", "b3-2-16-stages-in-the-cardiac-cycle" ] }, { "Question": "
\n
\n (a.ii)\n
\n
\n

\n Outline the relationship shown in the graph.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n \n positive correlation\n \n / (proportion with) HCN increases as distance increases;\n

\n
\n", "Examiners report": "
\n

\n This was answered more successfully with 90 % of candidates gaining the mark. The answer ‘positive relationship’ was not enough and either ‘positive correlation’ or description of it were required.\n

\n
\n", "question_id": "20N.2.SL.TZ0.1A.II", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-2-stability-and-change", "d4-2-4-use-of-a-model-to-investigate-the-effect-of-variables-on-ecosystem-stability" ] }, { "Question": "
\n
\n

\n The graph shows the results of an investigation into the activity of turnip peroxidase. The accumulation of the product of the reaction catalysed by the enzyme is shown at different pH values.\n

\n

\n \n

\n

\n [Source: © International Baccalaureate Organization 2019]\n

\n

\n

\n

\n Based on the data in the graph, what is most probably the optimum pH for turnip peroxidase?\n

\n

\n A. Between 3 and 5\n

\n

\n B. Between 10 and 11\n

\n

\n C. Between 7 and 8\n

\n

\n D. Between 9 and 10\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "19M.1A.SL.TZ1.9", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-1-enzymes-and-metabolism", "c1-1-8-effects-of-temperature-ph-and-substrate-concentration-on-the-rate-of-enzyme-activity" ] }, { "Question": "
\n
\n

\n Ethylene glycol is used as an antifreeze chemical. If a person ingests it accidentally, ethylene glycol is rapidly converted by a series of enzyme-catalysed reactions in the liver to oxalic acid, which is toxic. The diagram summarizes the steps and enzymes involved in the conversion of ethylene glycol to oxalic acid.\n

\n

\n \n

\n

\n

\n

\n The production of oxalic acid can be prevented if the person drinks ethanol, a competitive inhibitor of the enzyme alcohol dehydrogenase I. Which statement explains the mode of action of ethanol on the reaction?\n

\n

\n A. It causes end product inhibition.\n

\n

\n B. It disrupts the shape of the active site by binding to another site on alcohol dehydrogenase I.\n

\n

\n C. It occupies the active site of alcohol dehydrogenase I, preventing ethylene glycol from binding.\n

\n

\n D. It binds to ethylene glycol, preventing it from fitting into the active site of alcohol dehydrogenase I.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "
\n

\n Despite having a lot of text in the question stem this question was correctly answered by 85 % of the candidates.\n

\n
\n", "question_id": "22M.1A.HL.TZ2.29", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-1-enzymes-and-metabolism", "c1-1-15-competitive-inhibition-as-a-consequence-of-an-inhibitor-binding-reversibly-to-an-active-site" ] }, { "Question": "
\n
\n

\n The diagrams represent cells with the same concentration of dissolved substances in their cytoplasm. If all the cells were placed in the same hypertonic sucrose solution, which cell would show the greatest rate of change in the concentration of its cytoplasm?\n

\n

\n \n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "
\n

\n This question was taken from 1.1 (Introduction of cells) and required knowledge that the rate of change in the concentration of the cytoplasm would occur in the cell with the greatest surface area to volume ratio. The question did not discriminate well; many candidates chose the cell with the biggest volume and surface area (answer D) rather than the one with the largest surface area to volume ratio which would give the greatest rate of change.\n

\n
\n", "question_id": "21M.1A.SL.TZ2.1", "topics": [ "b-form-and-function" ], "subtopics": [ "b2-3-cell-specialization", "b2-3-6-surface-area-to-volume-ratios-and-constraints-on-cell-size" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Describe how leaf cells make use of light energy.\n

\n
\n
\n

\n [5]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n leaf cells contain chloroplasts;\n
    2. \n
  2. \n light is absorbed by chlorophyll (in chloroplasts);\n
    3. \n
  3. \n other pigments absorb different wavelengths;\n
    4. \n
  4. \n light energy is used in photosynthesis;\n
    5. \n
  5. \n (light is needed) to combine water and carbon dioxide/fix carbon dioxide;\n
    6. \n
  6. \n carbon compounds/organic compounds/glucose/starch/carbohydrate are produced;\n
    7. \n
  7. \n blue\n \n \n and\n \n \n red light is absorbed;\n
    8. \n
  8. \n perform photolysis\n
    \n \n \n OR\n \n \n
    \n split water molecules;\n
    9. \n
\n

\n \n Wavelengths accepted for mpg\n \n .\n

\n
\n", "Examiners report": "
\n

\n Generally speaking, students know how leaf cells make use of light energy; at least three marks were usually gained. Some candidates made the answer too complex and involved, when a simple straight-forward answer would have been better.\n

\n
\n", "question_id": "22M.2.SL.TZ1.6B", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-3-photosynthesis", "c1-3-1-transformation-of-light-energy-to-chemical-energy-when-carbon-compounds-are-produced-in-photosynthesis", "c1-3-5-absorption-of-specific-wavelengths-of-light-by-photosynthetic-pigments" ] }, { "Question": "
\n
\n (g)\n
\n
\n

\n Explain how neonicotinoids affect synaptic transmission in insects.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n a. neonicotinoids bind to the (acetylcholine) receptor (in insects) ✔\n

\n

\n b. (binding happens) in (cholinergic) synapses/at motor end plate/between motor neuron and muscles ✔\n

\n

\n c. neonicotinoids bind irreversibly (to receptors)\n
\n \n \n OR\n \n \n
\n (receptors are blocked so) acetylcholine is unable to bind ✔\n

\n

\n d. acetylcholinesterase/enzymes cannot break down neonicotinoids ✔\n

\n

\n e. (synaptic) transmission prevented ✔\n

\n

\n f. (causing) insect paralysis/death ✔\n

\n
\n", "Examiners report": "
\n

\n In general, the data analysis question was well attempted by the majority of students.\n

\n

\n Those students who had studied synaptic transmission scored well. However, many knew the role of acetylcholine here, but not in Q(1)(e).\n

\n
\n", "question_id": "21M.2.HL.TZ2.1G", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c2-2-neural-signalling", "c2-2-12-effects-of-exogenous-chemicals-on-synaptic-transmission" ] }, { "Question": "
\n
\n

\n A plant is allowed to photosynthesize in an atmosphere containing radioactive\n \n 14\n \n C. Where in the plant stem would radioactive sugars be found?\n

\n

\n \n

\n

\n [Source: sinhyu/123rf.com.]\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "
\n

\n This question required candidates to know that phloem transports sugars and then also either recognise phloem tissue in a micrograph or know its relative position in a vascular bundle. Of the tissues labelled, A and D were not part of the vascular bundle and C was easily recognizable as xylem. To a well-prepared candidate, the small, thin-walled cells labelled B were clearly phloem, with the characteristic pattern of larger sieve tubes and smaller companion cells just about visible. Areas of sclerenchyma and cambium in the micrograph were not labelled as they would have been more confusable with phloem. A G2 comment was made that all living tissue would eventually have received radioactive sugars in this experiment, but the candidate’s task is always to choose the best answer, and phloem would become radioactive first and reach the highest levels.\n

\n
\n", "question_id": "21N.1A.SL.TZ1.32", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-1-gas-exchange", "b3-1-8-distribution-of-tissues-in-a-leaf" ] }, { "Question": "
\n
\n

\n The diagram represents a sarcomere. Which structure is myosin?\n

\n

\n \n

\n

\n [Source: MPI of Molecular Plant Physiology. [\n \n Sarcomere\n \n ]. [diagram online] Available at: http://www.macroevolution.net/sarcomere.html [accessed 4 April 2019]. Source adapted.]\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "21M.1A.HL.TZ1.37", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-3-muscle-and-motility-(hl-only)", "b3-3-2-sliding-filament-model-of-muscle-contraction" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Outline the causes and consequences of blood clot formation in coronary arteries.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. coronary heart disease/CHD/coronary artery disease/CAD occurs when there is reduction of oxygen to the heart muscle ✔\n

\n

\n b. high ratio of LDL to HDL/fatty diet leads to plaque formation in arteries ✔\n

\n

\n c. plaque breaks off causing damage that activates blood clot formation ✔\n

\n

\n d. clots «in the bloodstream» may block a coronary artery/coronary thrombosis reducing blood flow/oxygen\n
\n \n \n OR\n \n \n
\n clots can cause heart attack/muscle death ✔\n

\n

\n e. sickle cell anemia «crisis» produces blood clots «that can cause coronary/arterial blockage» ✔\n

\n
\n", "Examiners report": "
\n

\n Clots were related to a fatty diet or cholesterol but rarely to plaque build-up. The idea that plaque breaking could activate clot formation was seldom mentioned. Without really giving any accurate information, candidates got a mark just by linking blood clots to heart attack. There were many misconceptions and confusion. The first confusion was that blood clots lead to strokes. Quite a few responses focused on seizures and strokes as a possible consequence. In fairness to candidates, there is ambiguity in the way we use terminology in the common parlance. Cardiac arrest, cardiac failure, CHD and heart attack are technically not synonyms, though they are often used interchangeably. A student of biology is expected to understand the differences.\n

\n
\n", "question_id": "19M.2.SL.TZ1.3C", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-2-defence-against-disease", "c3-2-3-sealing-of-cuts-in-skin-by-blood-clotting" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Identify the protein labelled in the diagram.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n histone;\n

\n
\n", "Examiners report": "
\n

\n Nearly all candidates know that the proteins in nucleosomes are histones.\n

\n
\n", "question_id": "22N.2.HL.TZ0.4", "topics": [ "a-unity-and-diversity", "d-continuity-and-change", "c-interaction-and-interdependence" ], "subtopics": [ "a1-2-nucleic-acids", "a1-2-13-structure-of-a-nucleosome", "d2-2-gene-expression-[hl-only]", "d2-2-6-methylation-of-the-promoter-and-histones-in-nucleosomes-as-examples-of-epigenetic-tags", "d1-1-dna-replication", "d1-1-3-role-of-helicase-and-dna-polymerase-in-dna-replication", "d1-2-protein-synthesis", "d1-2-14-non-coding-sequences-in-dna-do-not-code-for-polypeptides", "c1-1-enzymes-and-metabolism", "c1-1-14-allosteric-sites-and-non-competitive-inhibition", "d2-2-7-epigenetic-inheritance-through-heritable-changes-to-gene-expression" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Explain the role of the kidney in osmoregulation.\n

\n
\n
\n

\n [8]\n

\n
\n
\n", "Markscheme": "
\n

\n a. osmoregulation is regulation of water and solute/salt balance/solute concentrations;\n

\n

\n b.\n \n nephron\n \n (is the functional unit of the kidney/osmoregulates);\n

\n

\n c. ultrafiltration in glomerulus / glomerular filtrate collected by Bowman’s capsule;\n

\n

\n d. loop of Henle establishes/maintains hypertonic conditions in medulla;\n

\n

\n e. osmosis/reabsorption of water (from filtrate) in the collecting duct;\n

\n

\n f. brain/hypothalamus monitors blood solute concentration / pituitary secretes ADH;\n

\n

\n g. ADH secreted when solute concentration of blood is too high/hypertonic/when dehydrated;\n

\n

\n h. ADH increases permeability of collecting duct to water;\n

\n

\n i. ADH causes more aquaporins (in membranes of collecting duct wall cells);\n

\n

\n j. more water reabsorbed resulting in more concentrated/hypertonic urine/less volume of urine;\n

\n

\n k. less/no ADH secreted when solute concentration (of blood) is too low/hypotonic;\n

\n

\n l. less water reabsorbed resulting in dilute/hypotonic urine/large volume of urine;\n

\n

\n \n Reject ‘water balance’ and ‘water concentration’ for mpa\n \n .\n

\n
\n", "Examiners report": "
\n

\n There was some excellent knowledge of kidney function, frequently going way beyond the question’s requirements. In some cases, candidates just described all processes occurring in the kidney instead of actually answering the question. This generally led to the loss of the extra clarity mark.\n

\n
\n", "question_id": "20N.2.HL.TZ0.7C", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-3-homeostasis", "d3-3-7-role-of-the-kidney-in-osmoregulation-and-excretion" ] }, { "Question": "
\n
\n

\n A hypothesis has been proposed that an increase in parathyroid hormone concentration causes an increase in osteocalcin in bears. Evaluate the evidence for this hypothesis provided by the data.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n (hypothesis supported by)\n
    \n positive/direct correlation/direct relationship (between parathyroid hormone and osteocalcin)\n
    \n \n \n OR\n \n \n
    \n osteocalcin rises as parathyroid hormone rises/vice versa;\n
    2. \n
  2. \n no evidence for causal link / causal link cannot be assumed / correlation does not prove causation;\n
    \n \n \n OR\n \n \n
    \n no evidence that parathyroid hormone causes change in osteocalcin;\n
    \n \n \n OR\n \n \n
    \n other factors may cause change in osteocalcin;\n
    3. \n
\n
\n", "Examiners report": "
\n

\n This type of question is increasingly well answered with more candidates understanding that two variables being positively correlated does not prove a causation. The situation would have been different if an experiment had been done with the levels of parathyroid hormone as the independent variable controlled by the researchers.\n

\n
\n", "question_id": "22M.2.SL.TZ1.J", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-3-homeostasis", "d3-3-1-homeostasis-as-maintenance-of-the-internal-environment-of-an-organism", "d3-3-2-negative-feedback-loops-in-homeostasis" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Outline the changes to chromosomes that occur during prophase in the first division of meiosis.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n pairing/synapsis of homologous chromosomes / homologous chromosomes form bivalents;\n
    2. \n
  2. \n crossing over / chromatid breaks then rejoins to non-sister chromatid;\n
    3. \n
  3. \n exchange of DNA/alleles/genetic information between chromatids/chromosomes;\n
    4. \n
  4. \n recombination / new combinations of alleles/genes generated;\n
    5. \n
  5. \n condensation/shortening/thickening/supercoiling of chromatids/chromosomes;\n
    6. \n
  6. \n formation of a chiasma where crossing over occurred;\n
    7. \n
\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ1.7A", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-1-cell-and-nuclear-division", "d2-1-16-consequences-of-mutations-in-genes-that-control-the-cell-cycle" ] }, { "Question": "
\n
\n (ii)\n
\n
\n

\n Identify the interactions that are shown between the water molecules.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n hydrogen bonds/H bond;\n

\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ1.4AII", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a1-1-water", "a1-1-2-hydrogen-bonds-as-a-consequence-of-the-polar-covalent-bonds-within-water-molecules" ] }, { "Question": "
\n
\n

\n The table shows the estimated total number of genes in several organisms.\n

\n

\n \n

\n

\n What can be deduced from the information in this table?\n

\n

\n A. Throughout evolution, the number of genes increases.\n

\n

\n B. The domestic dog is more closely genetically related to the fruit fly than to the human.\n

\n

\n C. The number of genes does not determine evolutionary success.\n

\n

\n D. Humans produce about half as many proteins as rice.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "
\n

\n Most candidates chose the anticipated answer — that the number of genes an organism has does not determine whether or not it is evolutionarily successful. Candidates were expected to regard all of organisms in the table as successful, because they still exist today.\n

\n
\n", "question_id": "22M.1A.SL.TZ1.13", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-1-natural-selection", "d4-1-9-concept-of-the-gene-pool" ] }, { "Question": "
\n
\n

\n The first day of the menstrual cycle is when menstruation begins. What occurs around day 15 of the cycle?\n

\n

\n
\n A.  Formation of a corpus luteum\n

\n

\n B.  The placenta starts to secrete progesterone\n

\n

\n C.  The end of menstruation\n

\n

\n D.  Blood progesterone concentration reaches its maximum\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "None", "question_id": "SPM.1A.SL.TZ0.22", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-1-reproduction", "d3-1-5-changes-during-the-ovarian-and-uterine-cycles-and-their-hormonal-regulation" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Compare and contrast the effect on men and women of an increase in serum cholesterol.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n both have increased CHD with increasing cholesterol;\n
    2. \n
  2. \n men always higher incidence CHD than women at each level (of cholesterol);\n
    3. \n
\n

\n \n Accept vice versa\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ1.20A", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-2-transport", "b3-2-6-causes-and-consequences-of-occlusion-of-the-coronary-arteries" ] }, { "Question": "
\n
\n

\n What is always a consequence of the evaporation of water from mesophyll cells in leaves of a healthy plant?\n

\n

\n
\n A.  Plasmolysis occurs in mesophyll cells.\n

\n

\n B.  Photosynthesis stops.\n

\n

\n C.  Stomata close to reduce transpiration.\n

\n

\n D.  Water moves up the stem in the xylem.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "SPM.1A.HL.TZ0.26", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-1-gas-exchange", "b3-1-7-adaptations-for-gas-exchange-in-leaves" ] }, { "Question": "
\n
\n (a.i)\n
\n
\n

\n State with a reason whether pangolins are autotrophic or heterotrophic.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n heterotrophic because it feeds on/eats food/other organisms /eats ants/termites/ doesn’t photosynthesise/does not produce its own food;\n

\n

\n \n Do not accept “it is not autotrophic” as it is part of the stem question.\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ2.4", "topics": [ "c-interaction-and-interdependence", "a-unity-and-diversity" ], "subtopics": [ "c4-2-transfers-of-energy-and-matter", "c4-2-6-autotrophs-as-organisms-that-use-external-energy-sources-to-synthesize-carbon-compounds-from-simple-inorganic-substances", "c4-2-10-classification-of-organisms-into-trophic-levels", "a4-1-evolution-and-speciation", "a4-1-4-evidence-for-evolution-from-homologous-structures" ] }, { "Question": "
\n
\n

\n The diagram shows changes in pressure in the left atrium, left ventricle and aorta during a single cardiac cycle. At what point during the cycle does the atrioventricular valve close?\n

\n

\n \n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "None", "question_id": "21M.1A.HL.TZ2.25", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-2-transport", "b3-2-16-stages-in-the-cardiac-cycle" ] }, { "Question": "
\n
\n

\n What happens in the first division of meiosis?\n
\n
\n

\n

\n A.  Formation of chiasmata where two sister chromatids join\n

\n

\n B.  Exchange of chromatids between homologous chromosomes\n

\n

\n C.  Exchange of DNA between non-sister chromatids of homologous chromosomes\n

\n

\n D.  Formation of chiasmata between non-homologous chromosomes\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "23M.1A.SL.TZ1.36", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-1-cell-and-nuclear-division", "d2-1-9-meiosis-as-a-reduction-division" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Identify the structure labelled X.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n (Neurotransmitter) vesicle;\n

\n

\n \n Do not accept Vacuole.\n \n

\n
\n", "Examiners report": "
\n

\n The majority managed to label X as a vesicle in (a). In (b) weaker candidates tried to explain the propagation of the action potential, rather than the release of the neurotransmitter. Better candidates were able to give almost textbook answers to explain the actions of the pesticide. Many got tangled up trying to explain, with those who had never seen this part of the syllabus, just saying that pesticides kill insects.\n

\n
\n", "question_id": "22N.2.SL.TZ0.5A", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c2-1-chemical-signalling-[hl-only]", "c2-1-3-hormones-neurotransmitters-cytokines-and-calcium-ions-as-examples-of-functional-categories-of-signalling-chemicals-in-animals" ] }, { "Question": "
\n
\n

\n The graph shows the proportion of a bacterial population of\n \n Neisseria gonorrhoeae\n \n , displaying resistance to the antibiotic tetracycline.\n

\n

\n \n

\n

\n [Source: © All rights reserved.\n \n Canadian Antimicrobial Resistance Surveillance System Report, 2016\n \n . Public Health Agency of Canada. Adapted and reproduced with permission from the Minister of Health, 2022.]\n

\n

\n

\n

\n What can be deduced from this graph?\n

\n

\n A. Bacteria with beneficial adaptations survive and pass on their genes.\n

\n

\n B. Immunity to tetracycline is triggered by over-use of the antibiotic.\n

\n

\n C. Genetic variation in this bacterial population is increasing.\n

\n

\n D. Use of tetracycline inhibits the growth of antibiotic-resistant\n \n N. gonorrhoeae\n \n .\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "
\n

\n This question attracted the most criticism from teachers on G2 forms. The graph showed fluctuating levels of antibiotic resistance, with an overall trend of increasing resistance. Candidates were expected to understand that antibiotic resistance is a heritable trait, so a change in antibiotic resistance levels is evolution. The explanation of increasing resistance levels is therefore based in natural selection: bacteria with genes for resistance have an advantage so survive, reproduce and pass on their genes. After careful scrutiny of the question, it was decided that there was a second acceptable answer. Although the graph does not provide information on antibiotic use, it was not unreasonable to deduce that using the antibiotic causes evolution by acting as a selective agent. Both answers A and D were therefore marked as correct in order to award the benefit of the doubt. The question has been altered for the published version for the examinations CD, with A being the correct option.\n

\n
\n", "question_id": "22M.1A.HL.TZ1.21", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-1-natural-selection", "d4-1-15-artificial-selection-by-deliberate-choice-of-traits" ] }, { "Question": "
\n
\n

\n Which part of aerobic respiration directly involves oxygen molecules?\n
\n
\n

\n

\n A.  Conversion of glucose to pyruvate\n

\n

\n B.  Accepting electrons from the electron transport chain\n

\n

\n C.  Oxidizing acetyl groups in the Krebs cycle\n

\n

\n D.  Production of NAD from reduced NAD\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "23M.1A.HL.TZ2.26", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-2-cell-respiration", "c1-2-16-role-of-oxygen-as-terminal-electron-acceptor-in-aerobic-cell-respiration" ] }, { "Question": "
\n
\n

\n Carbon sinks are any reservoirs that absorb and store carbon dioxide from the atmosphere. Which process increases the size of the carbon sink in oceans?\n

\n

\n A.  Photosynthesis\n

\n

\n B.  Respiration\n

\n

\n C.  Ocean acidification\n

\n

\n D.  Decomposition\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "
\n

\n This question asked the candidates to identify which process would increase the size of carbon sinks in oceans. The question performed badly with only 14\n \n \n \n \n % of candidates answering correctly. In retrospect, the question should have been reworded to make the correct response less ambiguous.\n

\n
\n", "question_id": "22N.1A.SL.TZ0.19", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c4-2-transfers-of-energy-and-matter", "c4-2-18-ecosystems-as-carbon-sinks-and-carbon-sources", "c4-2-19-release-of-carbon-dioxide-into-the-atmosphere-during-combustion-of-biomass-peat-coal-oil-and-natural-gas" ] }, { "Question": "
\n
\n

\n Which are examples of non-coding DNA?\n

\n

\n
\n A.  Dominant and recessive alleles\n

\n

\n B.  Promoters and telomeres\n

\n

\n C.  Oncogenes and tumour suppressor genes\n

\n

\n D.  Introns and exons\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "SPM.1A.HL.TZ0.10", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d1-2-protein-synthesis", "d1-2-14-non-coding-sequences-in-dna-do-not-code-for-polypeptides" ] }, { "Question": "
\n
\n

\n A DNA triplet on the strand that is transcribed has the bases TAG. Which anticodon on tRNA is used in translation?\n

\n

\n A.  AUC\n

\n

\n B.  UAG\n

\n

\n C.  TAG\n

\n

\n D.  ATC\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "
\n

\n In question 10, candidates were asked to state which bases would be found on a tRNA anticodon transcribed from DNA. The question discriminated poorly with most candidates opting for response A which corresponded to the bases that would be found on the mRNA strand. It was commented that there might be confusion with the use of \"the strand that is transcribed\" and perhaps using the words coding or template strands would be less ambiguous. Another commented that a diagram may have made the question clearer.\n

\n
\n", "question_id": "22N.1A.SL.TZ0.10", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d1-2-protein-synthesis", "d1-2-7-complementary-base-pairing-between-trna-and-mrna" ] }, { "Question": "
\n
\n (d)\n
\n
\n

\n Outline the role of lymphocytes in defence against disease.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. produce antibodies ✔\n

\n

\n b. memory cells confer immunity ✔\n

\n

\n c. specific immunity results from production of antibodies specific to a particular antigen ✔\n

\n

\n d. recognize pathogens ✔\n

\n

\n e. destroy foreign cells/cancer cells ✔\n

\n
\n", "Examiners report": "
\n

\n Many candidates correctly stated that lymphocytes produce antibodies. Lymphocytes were often mistaken for phagocytes and lengthy descriptions of engulfing of diseases were given.\n

\n
\n", "question_id": "19M.2.SL.TZ1.3D", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-2-defence-against-disease", "c3-2-6-lymphocytes-as-cells-in-the-adaptive-immune-system-that-cooperate-to-produce-antibodies" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Explain the effects that the environment can have on DNA in living organisms.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n

\n \n Mutation\n \n

\n

\n a. (environment can cause)\n \n mutation\n \n ;\n
\n b. mutations are base sequence changes;\n
\n c. radiation/UV/gamma rays can cause mutations/changes to base sequences;\n
\n d. mutagenic/carcinogenic chemicals can cause mutations / mustard gas/another example;\n

\n

\n \n Epigenetics\n \n

\n

\n e. (environment) can cause changes to\n \n gene expression\n \n ;\n
\n f. methylation (patterns) in DNA changed (in response to environmental factors);\n
\n g. methylation inhibits (gene transcription) / acetylation promotes (gene transcription);\n
\n h. body temperature/stress/diet (can affect gene expression);\n

\n

\n \n For mpd do not allow ‘mutagen’ instead of ‘mutagenic chemical’ as it includes forms of radiation as well as chemicals.\n \n

\n

\n \n Allow smoking and asbestos as examples of mutagens /carcinogens in mpd.\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.2.HL.TZ1.7C", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d1-3-mutations-and-gene-editing", "d1-3-5-randomness-in-mutation" ] }, { "Question": "
\n
\n

\n Sorbitol is oxidized to sorbose by the enzyme sorbitol dehydrogenase. The conversion rate was measured by monitoring sorbose concentrations. The graph shows the activity of sorbitol dehydrogenase at different pH values.\n

\n

\n \n

\n

\n \n [Source: Tae-Su Kim, Gao Hui, Jinglin Li, Vipin C. Kalia, Karthikeyan Muthusamy,\n
\n Jae Kyung Sohng, In-Won Kim and Jung-Kul\n \n \n Lee, 2019.\n
\n Overcoming NADPH product inhibition improves D-sorbitol conversion to L-sorbose.\n
\n \n Scientific Reports\n \n , 9,\n \n \n p. 815. https://doi.org/10.1038/s41598-018-37401-0. Open Access.]\n \n

\n

\n
\n What can be deduced from these results?\n

\n

\n

\n

\n A.  There is no conversion of sorbitol to sorbose at a pH of 10.\n

\n

\n B.  At least 10 % of the product is transformed to substrate at a pH of 9.\n

\n

\n C.  The pH affects the rate of activity of the enzyme sorbitol dehydrogenase.\n

\n

\n D.  The amount of sorbose produced is not affected by the substrate concentration.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "23M.1A.SL.TZ1.10", "topics": [], "subtopics": [] }, { "Question": "
\n
\n

\n The diagram shows protein channels involved in the passive movement of a substance into the cell across the cell membrane.\n

\n

\n \n

\n

\n

\n

\n

\n

\n What describes this movement?\n
\n
\n

\n

\n A.  Energy of ATP is used to transport substances into the cell.\n

\n

\n B.  Substances can move from areas of low to areas of high concentration.\n

\n

\n C.  The proteins ensure that movement of substances is only in one direction.\n

\n

\n D.  Net movement occurs until the concentrations in and out of the cell are equal.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "23M.1A.SL.TZ2.3", "topics": [ "b-form-and-function" ], "subtopics": [ "b2-1-membranes-and-membrane-transport", "b2-1-4-integral-and-peripheral-proteins-in-membranes" ] }, { "Question": "
\n
\n (d.ii)\n
\n
\n

\n State which cells secrete insulin.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n \n β cells\n \n of pancreas/islets (of Langerhans);\n

\n
\n", "Examiners report": "None", "question_id": "20N.1B.SL.TZ0.1D.II", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-3-homeostasis", "d3-3-3-regulation-of-blood-glucose-as-an-example-of-the-role-of-hormones-in-homeostasis" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Based on the mode of transmission of the Ebola virus, suggest a possible reason for the relationship between population density and the number of Ebola cases in these four countries.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n greater density means more frequent contact with infected people/animals ✔\n

\n

\n \n Need both greater density and frequency of contact\n \n

\n
\n", "Examiners report": "
\n

\n Most candidates correctly used high density and frequency of contact to describe the relationship. Very few responses discussed high density but did not relate it to the frequency of contact. Others focused on modes of transmission alone and did not relate it to density.\n

\n
\n", "question_id": "19M.2.HL.TZ1.1C", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a2-3-viruses-(hl-only)" ] }, { "Question": "
\n
\n

\n State\n \n one\n \n technological improvement, other than enzymatic digestion, that led to the falsification of previous models to determine the current model of membrane structure.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n a. scanning electronmicrography / SEM ✔\n

\n

\n b. freeze fracture/etching ✔\n

\n

\n c. X-ray diffraction\n
\n \n \n OR\n \n \n
\n crystallography ✔\n

\n

\n d. fluorescent antibody / marker tagging ✔\n

\n

\n \n Do not accept electron microscope\n \n

\n

\n \n Accept description of process\n \n

\n
\n", "Examiners report": "
\n

\n Stating a technological improvement that led to the currently accepted model of the cell membrane proved more challenging and only the better candidates answered correctly.\n

\n
\n", "question_id": "19M.1B.SL.TZ2.D", "topics": [ "b-form-and-function" ], "subtopics": [ "b2-1-membranes-and-membrane-transport", "b2-1-10-fluid-mosaic-model-of-membrane-structure" ] }, { "Question": "
\n
\n (b.i)\n
\n
\n

\n State\n \n one\n \n process that produces ATP.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n (cell) respiration/photosynthesis;\n

\n
\n", "Examiners report": "
\n

\n The production of ATP and its use was well known. Although respiration was expected in b(i), photosynthesis was allowed, as ATP is produced in the light-dependent reactions.\n

\n
\n", "question_id": "21N.2.SL.TZ0.4B.I", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-2-cell-respiration", "c1-2-4-cell-respiration-as-a-system-for-producing-atp-within-the-cell-using-energy-released-from-carbon-compounds" ] }, { "Question": "
\n
\n

\n The action spectra for two different types of photosynthetic organisms are shown.\n \n Ulva\n \n , or sea lettuce, is a green marine alga composed of two layers of cells. The action spectrum for crop plants was plotted from an average of 22 species of plants.\n

\n

\n \n

\n

\n What describes photosynthesis in these organisms?\n

\n

\n A.\n \n Ulva\n \n photosynthesizes more than crop plants at red wavelengths.\n

\n

\n B.  Crop plants photosynthesize more than\n \n Ulva\n \n in green light.\n

\n

\n C.  Photosynthesis by\n \n Ulva\n \n is highest in red light while that of crop plants is highest in blue.\n

\n

\n D.  Both have zero photosynthesis at 750 nm.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "22N.1A.HL.TZ0.8", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-3-photosynthesis", "c1-3-6-similarities-and-differences-of-absorption-and-action-spectra" ] }, { "Question": "
\n
\n

\n Explain how biogeographic factors affect the richness and evenness of biodiversity.\n

\n
\n
\n

\n [6]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n biogeographic features are combinations of species, habitats and physical features;\n
    2. \n
  2. \n richness is the number of different species present (in an area);\n
    3. \n
  3. \n evenness refers to relative abundance of the different species (in an area) /\n \n \n OWTTE\n \n \n ;\n
    4. \n
  4. \n large nature reserves/large islands (potentially) have greater biodiversity /richness / evenness;\n
    5. \n
  5. \n large areas (tend to) have more species/populations/habitats/richness\n
    \n \n \n OR\n \n \n
    \n large areas have more stability/higher biodiversity index\n
    \n \n \n OR\n \n \n
    \n have less chances of loss of a species;\n
    6. \n
  6. \n connected areas/nature reserves have more diversity than isolated ones\n
    \n \n \n OR\n \n \n
    \n corridors between (small) areas/ reserves increases richness/biodiversity;\n
    7. \n
  7. \n the greater the surface:perimeter ratio, the greater the biodiversity;\n
    8. \n
  8. \n edges are transition areas\n
    \n \n \n OR\n \n \n
    \n have greater richness/lower evenness\n
    \n \n \n OR\n \n \n
    \n are less stable;\n
    9. \n
  9. \n circular shape has more biodiversity than rectangular shape;\n
    10. \n
  10. \n biodiversity measured by Simpson’s / diversity index;\n
    11. \n
  11. \n one additional abiotic factor affecting biodiversity;\n
    12. \n
\n

\n \n e.g. precipitation, soil quality/content, temperature, etc.\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ2.21", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a4-2-conservation-of-biodiversity", "a4-2-6-causes-of-the-current-biodiversity-crisis", "a4-1-evolution-and-speciation", "a4-1-9-adaptive-radiation-as-a-source-of-biodiversity" ] }, { "Question": "
\n
\n

\n The lung tumour in the light micrograph was slow-growing. Predict with a reason what would have been visible in the micrograph if the tumour was growing rapidly.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n \n See\n \n

\n

\n a. more mitosis\n
\n \n \n OR\n \n \n
\n cells in prophase/metaphase/anaphase/telophase;\n

\n

\n \n Why\n \n

\n

\n b. more dividing cells/tumour cell divide uncontrollably\n
\n \n \n OR\n \n \n
\n a higher mitotic index;\n

\n

\n

\n
\n", "Examiners report": "None", "question_id": "23M.2.HL.TZ2.C", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-1-cell-and-nuclear-division", "d2-1-17-differences-between-tumours-in-rates-of-cell-division-and-growth-and-in-the-capacity-for-metastasis-and-invasion-of-neighbouring-tissue" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Explain how a newly discovered plant species would be classified and named.\n

\n
\n
\n

\n [7]\n

\n
\n
\n", "Markscheme": "
\n

\n \n Naming\n \n :\n

\n
    \n
  1. \n binomial nomenclature / (plant is) given a binomial/double name;\n
    2. \n
  2. \n first name is the genus and second name is the species / genus initial upper case and species lower case;\n
    3. \n
  3. \n names (of plant species) are international/are universally understood/are published in journals;\n
    \n
    \n \n Classification\n \n :\n
    4. \n
  4. \n study the characteristics/structure/reproduction/chemical properties/DNA (of the plant);\n
    5. \n
  5. \n put/classify (the plant) in a group/genus with other similar species;\n
    6. \n
  6. \n natural classification corresponds with evolution / natural classification is based on many features;\n
    7. \n
  7. \n analogous features/features due to convergent evolution should not be used;\n
    8. \n
  8. \n hierarchy of groups/taxa (in traditional classification / 3 or more taxa in correct sequence (kingdom-phylum-class);\n
    9. \n
  9. \n two or more of bryophyta, filicinophyta, coniferophyta and angiospermophyta named;\n
    10. \n
  10. \n a clade is a group of organisms evolved from a common ancestor;\n
    11. \n
  11. \n base sequences/amino acid sequences used to group organisms into clades/deduce evolutionary relationships;\n
    12. \n
  12. \n cladograms show the relationships between clades/likely evolutionary divergence of clades;\n
    13. \n
  13. \n each branch point/node represents where species are formed via divergent evolution;\n
    14. \n
  14. \n species are now classified into a sequence of clades (rather than a rigid hierarchy of taxa);\n
    15. \n
\n

\n \n Mpi accept common names, mosses, ferns etc\n \n .\n

\n
\n", "Examiners report": "
\n

\n There were a few G2 comments that part (c) on classification was above the level expected at Standard Level. This part was in common with Higher Level, but did only contain material from the Core (cladistics appears in section 5.4). There were a large number of marking points to score on. The naming was well known, as was classification into taxa and the different plant phyla. Some weaker students tried to go all the way back to eukaryotes and prokaryotes and animalia and plantae, giving far too much superfluous information. Good explanations of the use of clades were seen by better candidates.\n

\n
\n", "question_id": "22N.2.SL.TZ0.6C", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a3-2-classification-and-cladistics-(hl-only)", "a3-2-1-need-for-classification-of-organisms", "a3-2-9-classification-of-all-organisms-into-three-domains-using-evidence-from-rrna-base-sequences" ] }, { "Question": "
\n
\n

\n The diagram shows the food web for an aquatic ecosystem in which letters R–Z represent individual species.\n

\n

\n \n

\n

\n [Source: © International Baccalaureate Organization 2019]\n

\n

\n

\n

\n Which organism is a tertiary consumer?\n

\n

\n A. Organism T\n

\n

\n B. Organism U\n

\n

\n C. Organism W\n

\n

\n D. Organism Y\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "19M.1A.SL.TZ1.14", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c4-2-transfers-of-energy-and-matter", "c4-2-3-flow-of-chemical-energy-through-food-chains" ] }, { "Question": "
\n
\n (g)\n
\n
\n

\n District administrators combatting the 2014 Ebola epidemic in West Africa were assisted by international organizations such as the World Health Organization, who provided data on the progress of the epidemic. Suggest\n \n one\n \n other way in which international organizations can assist with combatting an epidemic of Ebola.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n raise awareness/provide information for local population/supply health workers/equipment/ train local staff/share expertise/provide financial support/provide vaccine/travel ban alert to affected country ✔\n

\n
\n", "Examiners report": "
\n

\n Again, most students got a mark here for correct reasoning. Those who lost a mark made references to research. Research was not accepted as it might have future benefits, but not likely to help in the immediate epidemic.\n

\n
\n", "question_id": "19M.2.HL.TZ1.1G", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a2-3-viruses-(hl-only)" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Distinguish between the structure of the chromosomes of prokaryotes and eukaryotes.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. prokaryotes have circular DNA/chromosome but eukaryote chromosomes linear/\n \n OWTTE\n \n ✔\n
\n \n \n OR\n \n \n
\n eukaryotes have telomeres/centromeres whereas prokaryotes do not ✔\n

\n

\n b. some prokaryotes have plasmids whereas eukaryotes do not ✔\n

\n

\n c. eukaryotes have multiple chromosomes whereas prokaryotes «typically» have only one ✔\n

\n

\n d. histones/nucleosomes/proteins associated with DNA in eukaryotes but not in prokaryotes/naked DNA in prokaryotes\n
\n \n \n OR\n \n \n
\n eukaryote DNA can coil/supercoil/condense «due to histones» but not prokaryote DNA ✔\n

\n
\n", "Examiners report": "
\n

\n Answers to this question were variable. Some candidates wrote about cell structure rather than chromosome and many wrote about the location of chromosomes in the cell rather than their structure. Weaker candidates did not know the difference between prokaryotes and eukaryotes and some think that prokaryotes are plants and eukaryotes are animals. The term ‘naked’ was often used for DNA not enclosed in a nuclear membrane, when in this context it should be reserved for DNA that is not associated with histone proteins.\n

\n
\n", "question_id": "19M.2.SL.TZ1.2A", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a2-2-cell-structure", "a2-2-5-prokaryote-cell-structure", "a2-2-6-eukaryote-cell-structure" ] }, { "Question": "
\n
\n (f)\n
\n
\n

\n Using the data in the violin plots, deduce the age range at which children are most likely to develop ARI due to\n \n S. pneumoniae\n \n .\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n 2 – 5\n \n years\n \n ;\n
    2. \n
  2. \n higher number/value/percentage/attributable fraction for 2 – 5 years (than 0 – 5years);\n
    3. \n
\n

\n

\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ2.1F", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-2-defence-against-disease", "c3-2-16-vaccines-and-immunization" ] }, { "Question": "
\n
\n

\n Pressure changes inside the thorax cause the movement of air in and out of the lung alveoli during ventilation. Alveolar pressure correlates to thoracic pressure. The diagram shows pressure changes in lung alveoli during ventilation in relation to normal atmospheric pressure. What causes forced movement of air out of the lungs at T?\n

\n

\n \n

\n

\n \n

\n

\n

\n

\n

\n

\n

\n

\n

\n

\n

\n

\n

\n

\n

\n

\n

\n

\n

\n

\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "22M.1A.SL.TZ2.27", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-1-gas-exchange", "b3-1-5-ventilation-of-the-lungs" ] }, { "Question": "
\n
\n

\n In a woodland ecosystem, each tree provides food for numerous aphids which feed on the sap of the tree. The aphids are eaten by carnivorous beetles, as shown in the food chain.\n

\n

\n Oak Tree → Aphids → Beetles\n

\n

\n Which pyramid of energy represents this relationship?\n

\n

\n \n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "21N.1A.SL.TZ0.18", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c4-2-transfers-of-energy-and-matter", "c4-2-11-construction-of-energy-pyramids" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Compare and contrast the information provided for baleen whales and sea turtles.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. both show cases of entanglement/ingestion ✔\n

\n

\n b. sea turtles similar number of species affected by entanglement/ ingestion while baleen whales more species affected by entanglement than ingestion\n
\n \n \n OR\n \n \n
\n higher percentage of sea turtles species affected by entanglement/ ingestion than baleen whales\n
\n \n \n OR\n \n \n
\n higher number of species of «baleen» whales than species of sea turtles ✔\n

\n

\n \n Do not accept answers quoting numerical values only\n \n .\n

\n
\n", "Examiners report": "None", "question_id": "19N.2.SL.TZ0.15A", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-2-stability-and-change", "d4-2-9-biomagnification-of-pollutants-in-natural-ecosystems" ] }, { "Question": "
\n
\n

\n The diagram shows a staggered transverse section (cut across rather than down) through the heart.\n

\n

\n \n

\n

\n [Source: Oregon State University, n.d.\n \n Heart Anatomy\n \n . [diagram online] Available at:\n
\n https://open.oregonstate.education/aandp/chapter/19-1-heart-anatomy/ [Accessed 28 October 2021].]\n

\n

\n

\n

\n In what state are the valves when the ventricles are contracting?\n

\n

\n \n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "
\n

\n It was commented that the diagram of the heart seen from above may be more challenging compared to the usual images depicted in books and examinations and this was intended. One centre commented that it is difficult to distinguish between the R and L semilunar valves, but this is not necessary to answer the question. Statistically the question discriminated well.\n

\n
\n", "question_id": "22N.1A.SL.TZ0.26", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-2-transport", "b3-2-15-adaptations-of-the-mammalian-heart-for-delivering-pressurized-blood-to-the-arteries" ] }, { "Question": "
\n
\n (j)\n
\n
\n

\n Outline likely health benefits of universal PCV vaccination of children, other than reducing the incidence of ARI.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n less use of antibiotics;\n
    2. \n
  2. \n less antibiotic resistance (in pathogens) / antibiotics more successful at treating infectious/bacterial diseases;\n
    3. \n
  3. \n decrease in health care costs / less money spent on antibiotics;\n
    4. \n
  4. \n decreased mortality / protection of immune-deficient patients/non-vaccinated population/ achieve herd immunity;\n
    5. \n
\n

\n \n Since the question already states “other than reducing the incidence of ARI”, this reason should not be accepted.\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ2.1J", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-2-defence-against-disease", "c3-2-16-vaccines-and-immunization" ] }, { "Question": "
\n
\n

\n The image shows an electron micrograph of virus particles known to infect the bacterium\n \n Vibrio parahaemolyticus\n \n , which is associated with gastroenteritis, wound infections and septicemia in humans and animals.\n

\n

\n \n

\n

\n [Source: Lin, Y. and Lin, C., 2012. Transmission electron micrograph of phage ϕpp2 particles with several structural proteins. [micrograph] (\n \n BMC Genomics\n \n , 13:224).]\n

\n

\n

\n

\n What does a virus have in common with a living cell?\n

\n

\n A. 70S ribosomes\n

\n

\n B. Genetic material\n

\n

\n C. Reproduction by binary fission\n

\n

\n D. Anaerobic respiration\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "21M.1A.HL.TZ2.1", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a2-3-viruses-(hl-only)", "a2-3-1-structural-features-common-to-viruses" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Identify in which continent the fewest types of neonicotinoid were detected in honey samples.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n Oceania ✔\n

\n
\n", "Examiners report": "
\n

\n In general, the data analysis question was well attempted by the majority of students.\n

\n

\n Almost all were able to name Oceania.\n

\n
\n", "question_id": "21M.2.SL.TZ2.1", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c2-2-neural-signalling", "c2-2-12-effects-of-exogenous-chemicals-on-synaptic-transmission" ] }, { "Question": "
\n
\n

\n \n Yersinia pestis\n \n is a bacterium that caused an outbreak of bubonic plague in the 14th century. It normally produces ATP in the presence of oxygen but can still produce ATP if oxygen is absent.\n
\n Which term describes this characteristic?\n

\n

\n
\n A.  Facultative respiration\n

\n

\n B.  Facultative anaerobe\n

\n

\n C.  Obligate anaerobe\n

\n

\n D.  Obligate aerobe\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "SPM.1A.HL.TZ0.34", "topics": [ "b-form-and-function" ], "subtopics": [ "b4-2-ecological-niches", "b4-2-2-differences-between-organisms-that-are-obligate-anaerobes-facultative-anaerobes-and-obligate-aerobes" ] }, { "Question": "
\n
\n (ii)\n
\n
\n

\n Global ecosystem modelling suggests that most of the change in LAI is due to increases in atmospheric carbon dioxide. Explain how rising atmospheric carbon dioxide (CO\n \n 2\n \n ) concentration could cause the observed change in LAI.\n

\n
\n
\n

\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n more\n \n photosynthesis\n \n (with higher carbon dioxide concentration);\n
    2. \n
  2. \n more plant growth/more (plant) biomass/more leaves/more plants;\n
    3. \n
\n

\n \n If the answer focuses on greenhouse effect or global warming, do not award mpa, but mpb can be awarded if one of the alternatives is included in the answer.\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ1.DII", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-3-climate-change", "d4-3-1-anthropogenic-causes-of-climate-change" ] }, { "Question": "
\n
\n

\n The diagram shows a neural synapse in the central nervous system of a honey bee (\n \n Apis mellifera\n \n ).\n

\n

\n \n

\n

\n [Source: © International Baccalaureate Organization 2019]\n

\n

\n

\n

\n How do neonicotinoid pesticides cause paralysis and death of honey bees?\n

\n

\n A. They destroy I.\n

\n

\n B. They bind to II.\n

\n

\n C. They inhibit the release of III.\n

\n

\n D. They block the activity of IV.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "19M.1A.SL.TZ1.24", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c2-2-neural-signalling", "c2-2-12-effects-of-exogenous-chemicals-on-synaptic-transmission" ] }, { "Question": "
\n
\n

\n Which cells are subject to attack by HIV?\n

\n

\n A. Lymphocytes\n

\n

\n B. Erythrocytes\n

\n

\n C. Platelets\n

\n

\n D. Phagocytes\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "None", "question_id": "21M.1A.SL.TZ2.26", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-2-defence-against-disease", "c3-2-12-infection-of-lymphocytes-by-hiv-with-aids-as-a-consequence" ] }, { "Question": "
\n
\n (ii)\n
\n
\n

\n Sex is determined in the same way in pangolins as in humans. State how many autosomes there are in somatic cells of\n \n M. pentadactyla\n \n .\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n 38\n
\n \n \n OR\n \n \n
\n 19\n \n pairs\n \n ;\n

\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ2.4CII", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-2-inheritance", "d3-2-1-production-of-haploid-gametes-in-parents-and-their-fusion-to-form-a-diploid-zygote-as-the-means-of-inheritance" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Outline how energy flows in an ecosystem.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n energy from the sun is captured by plants/autotrophs;\n
    2. \n
  2. \n light energy is converted to chemical energy by\n \n photosynthesis\n \n ;\n
    3. \n
  3. \n energy is passed to animals/consumers/along the food chain;\n
    4. \n
  4. \n at each stage in the food chain energy is lost by respiration/as heat;\n
    5. \n
  5. \n \n much\n \n less energy/only about 10\n \n \n \n \n % is available at each stage/trophic level of the food chain;\n
    6. \n
  6. \n some energy is made available to decomposers when organisms die/parts fall to the ground;\n
    7. \n
  7. \n energy cannot be recycled;\n
    8. \n
\n
\n", "Examiners report": "
\n

\n Explaining the energy flow in part (a), was one of the best answered questions on the paper. However, the\n
\n conversion of light energy to chemical energy was missed by many. Some weaker candidates are still confusing energy with biomass, and lost marks due to contradictory statements such as saying that in the end the energy goes into the soil and is taken up by the plants again.\n

\n

\n In both (a) and (b) many students drew diagrams, Carbon cycles etc. Some of these aided the explanation, but the majority contributed nothing.\n

\n
\n", "question_id": "22N.2.SL.TZ0.6A", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c4-2-transfers-of-energy-and-matter", "c4-2-3-flow-of-chemical-energy-through-food-chains" ] }, { "Question": "
\n
\n

\n The mitochondrion in the electron micrograph shows some features that make it efficient for its function. Which labelled feature allows a rapid build-up of proton concentration for chemiosmosis?\n

\n

\n \n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "22M.1A.HL.TZ2.30", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-3-photosynthesis", "c1-3-12-atp-production-by-chemiosmosis-in-thylakoids", "c1-2-cell-respiration", "c1-2-15-chemiosmosis-and-the-synthesis-of-atp-in-the-mitochondrion" ] }, { "Question": "
\n
\n

\n Outline\n \n two\n \n adaptations for water conservation in leaves of desert plants.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n \n Mark the first two answers only\n \n
\n (thick) wax layer/cuticle;\n
\n hairs on leaves/rolled leaves;\n
\n sunken stomata/stomata in pits/stomata opening at night/CAM physiology;\n
\n (leaves reduced to) spines/needles/no/few/small leaves/low surface area (to volume ratio) of leaves;\n
\n thick stems/water storage tissue/vertical stems (to avoid most intense sunlight);\n

\n
\n", "Examiners report": "
\n

\n A wide range of leaf adaptations were suggested and most candidates gave one or two that were accepted. Root adaptations were not accepted as the question asked for features of leaves.\n

\n
\n", "question_id": "22N.2.HL.TZ0.D", "topics": [ "b-form-and-function" ], "subtopics": [ "b2-3-cell-specialization", "b2-3-7-adaptations-to-increase-surface-area-to-volume-ratios-of-cells" ] }, { "Question": "
\n
\n

\n The cladogram includes four marsupial (non-placental mammal) families.\n

\n

\n \n

\n

\n [Source: Koala image: Quartl, https://commons.wikimedia.org/wiki/Phascolarctos_cinereus#/media/\n
\n File:Friendly_Female_Koala.JPG; Wombat image: JJ Harrison, https://en.wikipedia.org/wiki/Wombat#/\n
\n media/File:Vombatus_ursinus_-Maria_Island_National_Park.jpg; Marsupial lion: Nobu Tamura,\n
\n https://en.wikipedia.org/wiki/Marsupial_lion#/media/File:Thylacoleo_BW.jpg;\n
\n Diprotodontoidea image: Anne Musser]\n

\n

\n

\n

\n Deduce the family that is most closely related to the Diprotodontoidea.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n Vombatidae/wombats ✔\n

\n
\n", "Examiners report": "
\n

\n Nearly everyone spotted the wombat correctly.\n

\n
\n", "question_id": "19M.2.SL.TZ2.D", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a3-2-classification-and-cladistics-(hl-only)", "a3-2-7-analysing-cladograms" ] }, { "Question": "
\n
\n

\n A human organ is being prepared for transplant. In what type of solution must it be bathed?\n

\n

\n A. A hypertonic solution\n

\n

\n B. A hypotonic solution\n

\n

\n C. Pure water containing no solutes\n

\n

\n D. A solution with the same osmolarity as the organ tissue\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "21M.1A.SL.TZ1.4", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-3-water-potential", "d2-3-7-medical-applications-of-isotonic-solutions" ] }, { "Question": "
\n
\n

\n State the reason for performing the experiment in the months of May to August.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n because nymphs are present/numbers of nymphs rise «in these months»\n
\n \n \n OR\n \n \n
\n build up immunity/antibodies in mice before nymphs «peak» ✔\n

\n

\n \n Ignore references to larvae\n \n .\n

\n
\n", "Examiners report": "None", "question_id": "19N.2.SL.TZ0.F.I", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-2-defence-against-disease", "c3-2-7-antigens-as-recognition-molecules-that-trigger-antibody-production" ] }, { "Question": "
\n
\n (b.ii)\n
\n
\n

\n Determine the DNA base sequence transcribed to form this sequence of mRNA.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n TAC TCG GCT TCC ATC GAC ✔\n

\n
\n", "Examiners report": "None", "question_id": "19N.2.SL.TZ0.2B.II", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d1-2-protein-synthesis", "d1-2-7-complementary-base-pairing-between-trna-and-mrna" ] }, { "Question": "
\n
\n

\n The molecular structures of the mouse alarm compound and fox scent are very similar. Suggest an evolutionary advantage for this chemical similarity.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n the mice would have the same response to another mouse’s danger signal as to the actual presence of the predator/fox\n
\n \n \n OR\n \n \n
\n adaptation to fool predator by producing a scent similar to predator’s own scent\n
\n \n \n OR\n \n \n
\n allows a group response to a predator/fox/danger when just one mouse detects the danger ✔\n

\n

\n \n Accept any other feasible answer\n \n .\n

\n
\n", "Examiners report": "
\n

\n In g, better candidates were able to suggest an evolutionary advantage either from the point of view of one mouse being able to bring about a group response, or from the point of view that the fox could not distinguish between mice and other foxes.\n

\n
\n", "question_id": "19M.2.SL.TZ2.G", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c2-2-neural-signalling" ] }, { "Question": "
\n
\n (a.i)\n
\n
\n

\n Describe the trend in the data.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n negative correlation between the number of leaves\n \n removed\n \n and transpiration rate\n \n Do not accept type of correlation alone, as a description is required\n \n .\n
\n \n \n OR\n \n \n
\n as more leaves are removed the transpiration rate drops ✔\n \n OWTTE\n \n

\n
\n", "Examiners report": "None", "question_id": "19N.1B.SL.TZ0.2A.I", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-1-gas-exchange", "b3-1-9-transpiration-as-a-consequence-of-gas-exchange-in-a-leaf" ] }, { "Question": "
\n
\n

\n Which diagram represents blood flow through the mammalian heart?\n

\n

\n \n

\n

\n [Source: © International Baccalaureate Organization 2019]\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "
\n

\n Teachers expected this question to be too easy, but only two thirds of candidates answered it correctly, showing some weak understanding of blood flow through the heart.\n

\n
\n", "question_id": "19M.1A.SL.TZ1.20", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-2-transport", "b3-2-15-adaptations-of-the-mammalian-heart-for-delivering-pressurized-blood-to-the-arteries" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Explain how vesicles are used by cells to move materials.\n

\n
\n
\n

\n [5]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n fluidity of membranes allows vesicles to bud off membranes/fuse with membranes;\n
    2. \n
  2. \n materials taken into cells by endocytosis/vesicle formation;\n
    3. \n
  3. \n \n Paramecium\n \n takes in food / phagocytes engulf pathogens / another example;\n
    4. \n
  4. \n materials released from cells by exocytosis/by vesicle fusing with plasma membrane;\n
    5. \n
  5. \n neurotransmitter released at synapses / protein secretion / secretion from gland cell / another example;\n
    6. \n
  6. \n movement/transport of materials (inside vesicles) within cells/through the cytoplasm/between organelles/from an organelle to the (plasma)membrane/from the (plasma) membrane to an organelle;\n
    7. \n
  7. \n movement of proteins from the rough ER to the Golgi / another example;\n
    8. \n
\n
\n", "Examiners report": "None", "question_id": "23M.2.HL.TZ1.8A", "topics": [ "b-form-and-function" ], "subtopics": [ "b2-2-organelles-and-compartmentalization", "b2-2-9-structure-and-function-of-vesicles-in-cells" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Identify the genotype of the male wire-haired dog.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n WwKk\n

\n
\n", "Examiners report": "
\n

\n Only 40 % of candidates answered this correctly. A surprisingly high number of candidates gave a genotype with only one allele for each gene, suggesting that they were not familiar with dihybrid crosses. In many cases it was hard to distinguish between upper and lower case letters -W/w and K/k. Candidates should be encouraged to make letters used for alleles as clear as possible.\n

\n
\n", "question_id": "20N.2.SL.TZ0.5A", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-2-inheritance", "d3-2-10-incomplete-dominance-and-codominance" ] }, { "Question": "
\n
\n (d)\n
\n
\n

\n Using the following table, compare and contrast anaerobic cell respiration in yeasts and in humans. The first row has been completed as an example.\n

\n

\n \n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n \n

\n

\n \n Award\n \n [1]\n \n per correct row\n \n .\n

\n
\n", "Examiners report": "None", "question_id": "19N.2.HL.TZ0.3D", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-2-cell-respiration", "c1-2-5-differences-between-anaerobic-and-aerobic-cell-respiration-in-humans", "c1-2-10-anaerobic-cell-respiration-in-yeast-and-its-use-in-brewing-and-baking" ] }, { "Question": "
\n
\n

\n Explain how communication between neurons during synaptic transmission is achieved through neurotransmitters.\n

\n
\n
\n

\n [6]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n neurotransmitters are (chemicals) released by exocytosis/vesicles (in the pre-synaptic neuron) after the arrival of a nerve impulse;\n
    2. \n
  2. \n neurotransmitters leave the presynaptic neuron;\n
    3. \n
  3. \n (neurotransmitters) attach to receptors in the postsynaptic neuron;\n
    4. \n
  4. \n neurotransmitters (in the synaptic cleft) are broken down/reabsorbed;\n
    5. \n
  5. \n fast-acting neurotransmitters attach to protein-ion channels (in postsynaptic membrane);\n
    6. \n
  6. \n slow-acting neurotransmitters activate second messengers (in postsynaptic membrane);\n
    7. \n
  7. \n slow-acting neurotransmitters affect more than one neuron;\n
    8. \n
  8. \n some neurotransmitters excite nerve impulses (in postsynaptic neuron) while others inhibit them;\n
    9. \n
  9. \n excitatory neurotransmitter causes generation of action potential;\n
    10. \n
  10. \n inhibitory neurotransmitter prevents threshold being reached (preventing action potential);\n
    11. \n
  11. \n summation of all excitatory / inhibitory neurotransmitters received in postsynaptic neuron;\n
    12. \n
\n

\n \n Mp e and f: accept correct named example of fast-acting or slow-acting neurotransmitters.\n
\n \n

\n

\n \n Mp i and j: Accept correct named examples of excitatory/inhibitory neurotransmitters.\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ2.9", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c2-2-neural-signalling", "c2-2-5-synapses-as-junctions-between-neurons-and-between-neurons-and-effector-cells", "c2-2-6-release-of-neurotransmitters-from-a-presynaptic-membrane", "c2-2-7-generation-of-an-excitatory-postsynaptic-potential" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Deduce reasons for the difference between the results of Cross 2 and Cross 3.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n (1:1 ratio) in cross 2 as banded parent is heterozygous/has one copy of each allele;\n
    2. \n
  2. \n (no unbanded offspring) in cross 3 as banded parent is homozygous/has two alleles for banded;\n
    3. \n
  3. \n (in crosses 2 and 3) banded parental phenotypes are the same but their genotypes are different;\n
    4. \n
\n

\n

\n

\n

\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ1.5B", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-2-inheritance", "d3-2-5-effects-of-dominant-and-recessive-alleles-on-phenotype" ] }, { "Question": "
\n
\n (a.i)\n
\n
\n

\n Identify structure X.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n \n proximal\n \n convoluted tubule/PCT;\n

\n
\n", "Examiners report": "
\n

\n 60null% of candidates identified the proximal convoluted tubule.\n

\n
\n", "question_id": "22N.2.HL.TZ0.5A.I", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-3-homeostasis", "d3-3-8-role-of-the-glomerulus-bowmans-capsule-and-proximal-convoluted-tubule-in-excretion" ] }, { "Question": "
\n
\n

\n Where do hydrogen bonds form?\n

\n

\n A. Between the slight negative charge of hydrogen and slight positive charge of oxygen within a water molecule\n

\n

\n B. Between the slight positive charge of hydrogen and slight negative charge of oxygen within a water molecule\n

\n

\n C. Between the slight positive charge of hydrogen and slight negative charge of oxygen in different water molecules\n

\n

\n D. Between the slight negative charge of hydrogen and slight positive charge of oxygen in different water molecules\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "
\n

\n Many candidates realized that hydrogen bonds are formed with other water molecules, not within the molecules themselves.\n

\n
\n", "question_id": "19M.1A.SL.TZ2.6", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a1-1-water", "a1-1-2-hydrogen-bonds-as-a-consequence-of-the-polar-covalent-bonds-within-water-molecules" ] }, { "Question": "
\n
\n

\n Photolysis and carboxylation of RuBP occur during photosynthesis. Where in the chloroplast do these reactions occur?\n

\n

\n \n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "22M.1A.HL.TZ2.31", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-3-photosynthesis", "c1-3-11-generation-of-oxygen-by-the-photolysis-of-water-in-photosystem-ii", "c1-3-15-carbon-fixation-by-rubisco" ] }, { "Question": "
\n
\n

\n Explain the shape of the polypeptide chain at X.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n \n alpha helix\n \n /\n \n \n \n α\n \n \n helix\n \n
    2. \n
  2. \n type of secondary structure / second level of protein structure;\n
    3. \n
  3. \n maintained by hydrogen bonds;\n
    4. \n
  4. \n between C=O group and an N–H group;\n
    5. \n
\n
\n", "Examiners report": "
\n

\n This was one of the most successfully answered of questions, with better prepared candidates recognizing the alpha helix and explaining it in terms of hydrogen bonding.\n

\n
\n", "question_id": "22M.2.HL.TZ1.B", "topics": [ "b-form-and-function" ], "subtopics": [ "b1-2-proteins", "b1-2-8-pleating-and-coiling-of-secondary-structure-of-proteins" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Describe the secondary structure of proteins.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. polypeptide wound into a helical structure / alpha/α helix\n
\n \n OR\n \n
\n polypeptide folded back on itself forming a pleated sheet / beta/β pleated sheet;\n
\n b. stabilized/held in shape by/due to hydrogen bonds (between C=O and N-H groups);\n
\n c. secondary structures are regular/unvarying (within polypeptides/proteins);\n

\n

\n \n Allow annotated diagrams\n \n

\n
\n", "Examiners report": "
\n

\n There were some good answers here describing secondary structures and the role of hydrogen bonding.\n

\n
\n", "question_id": "21N.2.HL.TZ0.4B", "topics": [ "b-form-and-function" ], "subtopics": [ "b1-2-proteins", "b1-2-8-pleating-and-coiling-of-secondary-structure-of-proteins" ] }, { "Question": "
\n
\n

\n The apparatus in the diagram was used to assess the effects of factors on transpiration rates.\n

\n

\n \n

\n

\n [Source: Republished with permission of Springer-Verlag from E\n \n xperimentelle Pflanzenphysiologie: Band 2\n \n , Peter Schopfer, 1st edition, 1st Jan 1989; permission conveyed through Copyright Clearance Center, Inc.]\n

\n

\n

\n

\n Which factor would be a controlled variable in an experiment designed to assess the effects of temperature on transpiration rate?\n

\n

\n A. The opening and closing of stomata\n

\n

\n B. The intensity of light striking the plant\n

\n

\n C. The height of the water in the reservoir\n

\n

\n D. The evaporation of water from the leaves\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "21M.1A.SL.TZ2.32", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-1-gas-exchange", "b3-1-9-transpiration-as-a-consequence-of-gas-exchange-in-a-leaf" ] }, { "Question": "
\n
\n (f)\n
\n
\n

\n Based on these data, outline the evidence that T-705 has potential to be used as a treatment for EVD.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. cells not killed/few cells killed «even at high concentrations» ✔\n

\n

\n b. «T-705» effective/viruses reduced/viruses killed at 100 μM\n
\n \n \n OR\n \n \n
\n «T-705» very effective/viruses much reduced/nearly all viruses killed at 1000 μM ✔\n

\n

\n c. virus concentration decreases as T-705 concentration increases ✔\n

\n

\n d. drug has «high» potential for treatment «at high enough concentration» ✔\n

\n
\n", "Examiners report": "
\n

\n This was a timely question with Ebola epidemics again causing great problems in parts of Africa. Students were expected to have had some practice at analysing data relating to an epidemic because of this Skill in the programme: Analysis of epidemiological data related to vaccination programmes. It was assumed that candidates would understand terms such as ‘case’, ‘fatal case’, ‘infect’ and ‘treat’.\n

\n

\n This was generally very well answered, with candidates correctly concluding that the drug had potential as a treatment because at a high enough dose it reduced the number of viruses without harming a significant number of cells.\n

\n
\n", "question_id": "19M.2.SL.TZ1.1F", "topics": [ "c-interaction-and-interdependence", "a-unity-and-diversity" ], "subtopics": [ "c3-2-defence-against-disease", "a2-3-viruses-(hl-only)" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Cladistics and other evolutionary evidence suggest that mammals and birds have a more recent common ancestor than mammals and amphibians. Draw a cladogram to show the relationships between mammals, birds and amphibians.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n \n

\n

\n \n What is important is that the proper relationships are shown not the style used\n \n .\n

\n
\n", "Examiners report": "
\n

\n Candidates found it hard to express themselves without contradiction.\n

\n

\n Examiners accepted a wide variety of diagrams and orientations as long as the relationships among amphibians, birds and mammals were appropriate. Nevertheless, there was poor performance on this question. It was the question most often left blank in Section A.\n

\n
\n", "question_id": "21M.2.HL.TZ1.5C", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a3-2-classification-and-cladistics-(hl-only)", "a3-2-7-analysing-cladograms" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Estimate the difference between the highest and lowest mean body temperatures.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n 5 °C;\n

\n

\n \n Units required. Accept answers in the range 4.5 to 5.5 °C\n \n .\n

\n
\n", "Examiners report": "
\n

\n 70 % of candidates were able to read two temperatures from the graph and subtract the higher from the lower correctly.\n

\n
\n", "question_id": "22M.2.SL.TZ1.1A", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-3-homeostasis", "d3-3-1-homeostasis-as-maintenance-of-the-internal-environment-of-an-organism", "d3-3-2-negative-feedback-loops-in-homeostasis" ] }, { "Question": "
\n
\n

\n The diagram shows the arrangement of introns and exons in a segment of pre-mRNA. Pre-mRNA is immature mRNA containing introns and exons.\n

\n

\n \n

\n

\n Which is a mature mRNA molecule derived from the pre-mRNA by splicing?\n

\n

\n \n

\n

\n [Source: © International Baccalaureate Organization 2019]\n

\n

\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "None", "question_id": "19M.1A.SL.TZ1.27", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d1-2-protein-synthesis", "d1-2-16-alternative-splicing-of-exons-to-produce-variants-of-a-protein-from-a-single-gene" ] }, { "Question": "
\n
\n

\n What prevents plants from converting carbon dioxide into glucose in the dark?\n

\n

\n A. They do not have a source of energy.\n

\n

\n B. It is too cold.\n

\n

\n C. They do not require glucose during the night.\n

\n

\n D. Their enzymes are inhibited.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "None", "question_id": "21N.1A.SL.TZ0.8", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-3-photosynthesis", "c1-3-1-transformation-of-light-energy-to-chemical-energy-when-carbon-compounds-are-produced-in-photosynthesis" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Toxins often act as inhibitors. Compare and contrast competitive and non-competitive enzyme inhibition.\n

\n
\n
\n

\n [7]\n

\n
\n
\n", "Markscheme": "
\n

\n \n

\n

\n a valid example of each;\n

\n

\n \n Answers must have at least one similarity for 7 max\n \n .\n

\n
\n", "Examiners report": "None", "question_id": "SPM.2.HL.TZ0.9B", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-1-enzymes-and-metabolism", "c1-1-14-allosteric-sites-and-non-competitive-inhibition" ] }, { "Question": "
\n
\n

\n Sulfanilamide inhibits an enzyme that catalyses a reaction involving PABA, an intermediate in the synthesis of folate in bacteria. The structures of sulfanilamide and PABA are shown.\n

\n

\n \n

\n

\n The graph shows the rate of reaction with increasing substrate concentration and with fixed low concentration of different types of inhibitors. Which line on the graph represents the effect of sulfanilamide?\n

\n

\n \n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "20N.1A.HL.TZ0.29", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-1-enzymes-and-metabolism", "c1-1-15-competitive-inhibition-as-a-consequence-of-an-inhibitor-binding-reversibly-to-an-active-site" ] }, { "Question": "
\n
\n

\n State the role of cholesterol in animal cell membranes.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n a. controls/regulates/reduces fluidity of membrane / prevents crystallization of phospholipids;\n

\n

\n b. reduces permeability to some substances.\n

\n

\n \n Do not accept ‘stabilizes membrane’\n \n .\n

\n
\n", "Examiners report": "
\n

\n Half of candidates were able to state the role of cholesterol in animal cell membranes.\n

\n
\n", "question_id": "20N.2.SL.TZ0.A.II", "topics": [ "b-form-and-function" ], "subtopics": [ "b2-1-membranes-and-membrane-transport", "b2-1-10-fluid-mosaic-model-of-membrane-structure" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Outline the functions of rough endoplasmic reticulum and Golgi apparatus.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n a.\n \n ribosomes\n \n on RER synthesize/produce polypeptides/proteins ✔\n

\n

\n b. proteins from RER for secretion/export/use outside cell/for lysosomes ✔\n

\n

\n c. Golgi alters/modifies proteins/example of modification ✔\n

\n

\n d.\n \n vesicles\n \n budded off Golgi transport proteins «to plasma membrane»\n
\n \n \n OR\n \n \n
\n exocytosis/secretion of proteins in\n \n vesicles\n \n from the Golgi ✔\n

\n

\n \n Accept “for use inside and outside the cell” for mpb.\n \n

\n
\n", "Examiners report": "
\n

\n Most candidates had some knowledge and some had broad understanding of this topic. A common mistake was to think that the rough endoplasmic reticulum makes ribosomes. Many candidates stated that the Golgi apparatus packages proteins but they did not always mention that the packages are vesicles. If this was all that the Golgi did, vesicles from the rough ER could be used to secrete proteins. The role of the Golgi apparatus therefore involved processing or modification of proteins rather than just packaging of them.\n

\n
\n", "question_id": "19M.2.HL.TZ1.5", "topics": [ "b-form-and-function", "c-interaction-and-interdependence" ], "subtopics": [ "b2-2-organelles-and-compartmentalization", "b2-2-7-structure-and-function-of-free-ribosomes-and-of-the-rough-endoplasmic-reticulum", "b2-2-8-structure-and-function-of-the-golgi-apparatus", "c1-1-enzymes-and-metabolism", "c1-1-16-regulation-of-metabolic-pathways-by-feedback-inhibition", "c2-1-chemical-signalling-[hl-only]", "c2-1-6-differences-between-transmembrane-receptors-in-a-plasma-membrane-and-intracellular-receptors-in-the-cytoplasm-or-nucleus", "b2-1-membranes-and-membrane-transport", "b2-1-10-fluid-mosaic-model-of-membrane-structure" ] }, { "Question": "
\n
\n

\n Andalusian fowl have varied colours and types of feathers. The allele for black feathers is codominant with the allele for white, producing blue feathers in the heterozygote. The texture of feathers is controlled by another gene, with silky feathers recessive to normal. Blue silky birds are crossed with black silky birds. What is the expected proportion of blue silky offspring?\n

\n

\n A. 0%\n

\n

\n B. 25%\n

\n

\n C. 50%\n

\n

\n D. 100%\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "20N.1A.SL.TZ0.35", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-2-inheritance", "d3-2-10-incomplete-dominance-and-codominance" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Describe the genetic and hormonal control of male sexual characteristics in a human.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n a. male if (X and) Y chromosomes present ✔\n

\n

\n b. gene on Y chromosome/SRY promotes development of testes (from embryonic gonads) ✔\n

\n

\n c. testes secrete testosterone ✔\n

\n

\n d. testosterone stimulates sperm production/spermatogenesis ✔\n

\n

\n e. testosterone stimulates development (in fetus) of male genitals/primary sexual characteristics ✔\n

\n

\n f. testosterone stimulates development of male\n \n secondary\n \n sexual characteristics\n
\n \n \n OR\n \n \n
\n testosterone causes changes to become adult male during puberty ✔\n

\n

\n \n Allow first alternative for mpf if two secondary sexual characteristics are named instead of the general term ‘secondary sexual characteristics’\n \n .\n

\n
\n", "Examiners report": "
\n

\n There were some excellent answers that easily scored the three marks, but also many poorer ones, sometimes with no mention of genetic control or testosterone.\n

\n
\n", "question_id": "21M.2.SL.TZ1.6A", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-1-reproduction", "d3-1-3-differences-between-male-and-female-sexes-in-sexual-reproduction" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Outline how changes in temperature over short time periods could give a misleading impression of changes to the Earth’s climate.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n short-term reading could show global temperatures falling while the trend is rising\n
\n \n \n OR\n \n \n
\n fluctuations from year to year may not show long-term trend;\n

\n
\n", "Examiners report": "
\n

\n Answers to this question suffered due to poor expression of an answer. Other candidates answers were succinct and to the point as they used the data to make the point clear.\n

\n
\n", "question_id": "22M.2.SL.TZ1.3B", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-3-climate-change", "d4-3-1-anthropogenic-causes-of-climate-change" ] }, { "Question": "
\n
\n

\n Which features of phospholipids give them their amphipathic properties?\n

\n

\n A. Basic phosphate groups and acidic lipids\n

\n

\n B. Acidic phosphate groups and basic lipids\n

\n

\n C. Hydrophobic phosphate groups and hydrophilic fatty acids\n

\n

\n D. Hydrophilic phosphate groups and hydrophobic fatty acids\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "
\n

\n A G2 comment was made that the terms acidic and basic are not part of the program, but they are commonly used terms in biochemistry and in this question were only used in distractors, so candidates could identify the correct answer without being sure about them.\n

\n
\n", "question_id": "21N.1A.SL.TZ0.2", "topics": [ "b-form-and-function" ], "subtopics": [ "b1-1-carbohydrates-and-lipids", "b1-1-12-formation-of-phospholipid-bilayers-as-a-consequence-of-the-hydrophobic-and-hydrophilic-regions" ] }, { "Question": "
\n
\n

\n What blood flow does the right semilunar valve prevent?\n

\n

\n A. Backflow of blood to the right atrium during ventricular contraction\n

\n

\n B. Blood flowing from the aorta back into the heart when the ventricle is filling\n

\n

\n C. Blood flowing from the pulmonary artery to the right ventricle when the heart is relaxing\n

\n

\n D. Blood flowing from the right atrium to the vena cava when the right atrium contracts\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "
\n

\n Knowledge of the structure and functioning of the heart is normally strong so it was surprising that this proved to be the second most difficult question on the paper. All four possible answers attracted substantial numbers of candidates, suggesting that many were guessing. The percentage answering correctly was only a little above the 25 % guess-level. Many candidates were confused about whether arteries always carry oxygenated blood or where the right semilunar valve is located.\n

\n
\n", "question_id": "21M.1A.HL.TZ1.29", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-2-transport", "b3-2-15-adaptations-of-the-mammalian-heart-for-delivering-pressurized-blood-to-the-arteries" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Suggest how climate change can influence the natural selection of organisms that live in the Arctic oceans.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n a. individuals in a population will show a variation of adaptations to climate change ✔\n
\n
\n b. organisms that resist temperature changes\n
\n \n \n OR\n \n \n
\n current changes of the ocean/melting ice/more acidity/changes in food chains will survive better ✔\n

\n

\n c. reproduce more and pass on their characteristics ✔\n

\n

\n d. organisms with less adaptation will disappear with time ✔\n

\n

\n e. example «\n \n eg\n \n polar bears have less ice to be able to catch prey/seals and are starving the ones that manage to find other food sources will survive»\n \n OWTTE\n \n ✔\n

\n

\n f. changes will occur within species\n
\n \n \n OR\n \n \n
\n new species may appear «over time» ✔\n

\n

\n \n Accept any valid example of an Arctic ocean organism.\n \n

\n
\n", "Examiners report": "
\n

\n In 3b weaker candidates seemed to think that they needed to give a detailed description of climate change and filled up most of the box with it. Better candidates were able to state that animals who could cope with warmer surroundings, would survive to breed and pass on their characteristics, while those who could not would perish, and give an example such as the polar bear. There were some G2 comments that Arctic foodwebs were not on the syllabus. It is doubted that any IB student does not know that it is cold in the Arctic, but because of climate change it is warming up slowly.\n

\n
\n", "question_id": "19M.2.HL.TZ2.3B", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-3-climate-change", "d4-3-12-evolution-as-a-consequence-of-climate-change" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Describe briefly the endosymbiotic theory.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n a. eukaryotes evolved from prokaryotes ✔\n

\n

\n b. prokaryotes engulfed other prokaryotes without digesting them ✔\n

\n

\n c. engulfed aerobic cell/prokaryote became mitochondria ✔\n

\n

\n d. engulfed photosynthetic cell/ prokaryotes became chloroplasts ✔\n

\n

\n e. these organelles have a double membrane «due to the engulfing process» ✔\n

\n

\n f. mitochondria/chloroplasts contain DNA/small ribosomes/70S ribosomes ✔\n

\n
\n", "Examiners report": "
\n

\n Endosymbiotic theory. Those who had been taught it gained at least one mark. Few mentioned that the cell that became the mitochondrion was aerobic, and that the one that became the chloroplast was photosynthetic.\n

\n
\n", "question_id": "19M.2.SL.TZ2.6", "topics": [ "a-unity-and-diversity", "c-interaction-and-interdependence", "d-continuity-and-change" ], "subtopics": [ "a2-2-cell-structure", "a2-2-12-origin-of-eukaryotic-cells-by-endosymbiosis", "c1-3-photosynthesis", "c1-3-1-transformation-of-light-energy-to-chemical-energy-when-carbon-compounds-are-produced-in-photosynthesis", "d3-3-homeostasis", "d3-3-3-regulation-of-blood-glucose-as-an-example-of-the-role-of-hormones-in-homeostasis" ] }, { "Question": "
\n
\n

\n What is polyploidy?\n

\n

\n A. Having an extra set of chromosomes\n

\n

\n B. Having an extra sex chromosome\n

\n

\n C. Having an extra autosome\n

\n

\n D. Having two or more nuclei\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "None", "question_id": "22M.1A.HL.TZ1.35", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a4-1-evolution-and-speciation", "a4-1-11-abrupt-speciation-in-plants-by-hybridization-and-polyploidy" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Describe the hormone feedback mechanisms that help to prepare a woman’s body for pregnancy, sustain the pregnancy and then give birth.\n

\n
\n
\n

\n [7]\n

\n
\n
\n", "Markscheme": "
\n

\n \n Preparing the woman’s body for pregnancy\n \n

\n

\n a. FSH stimulates estrogen secretion (by the developing follicle);\n
\n b. estrogen increases FSH receptors so boosting estrogen production/so causing positive feedback;\n
\n c. estrogen stimulates repair/thickening of the endometrium/uterus lining;\n
\n d.\n \n high levels of estrogen\n \n stimulate LH production/inhibit FSH secretion (negative feedback);\n
\n e. LH (surge/peak) stimulates ovulation;\n

\n

\n \n Sustaining pregnancy\n \n

\n

\n f. LH stimulates the development of corpus luteum / corpus luteum secretes progesterone;\n
\n g. progesterone inhibits FSH/LH secretion (negative feedback);\n
\n h. progesterone maintains lining of uterus/endometrium (for pregnancy/implant of embryo);\n
\n i. progesterone inhibits uterine contractions;\n
\n j. HCG (secreted by embryo) stimulates maintenance of corpus luteum;\n

\n

\n \n Childbirth\n \n

\n

\n k. oxytocin stimulates uterine/myometrial contractions which stimulate oxytocin secretion;\n
\n l. positive feedback (mechanism used to stimulate childbirth);\n

\n
\n", "Examiners report": "None", "question_id": "23M.2.HL.TZ1.6C", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-1-reproduction", "d3-1-19-hormonal-control-of-pregnancy-and-childbirth" ] }, { "Question": "
\n
\n

\n The first enzyme in the metabolic pathway that produces isoleucine is threonine deaminase. Which graph illustrates the relationship between threonine deaminase activity and threonine concentration?\n

\n

\n \n

\n

\n [Source: © International Baccalaureate Organization 2019]\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "
\n

\n The programme specifies the threonine to isoleucine pathway as the example of end-product inhibition that should be studied (8.1 of AHL). Candidates were therefore expected to know that threonine is the substrate for the enzyme threonine deaminase, but they could also have also deduced this from the name of the enzyme. It was expected that candidates would recognise the curve for the effect of increasing substrate concentration on enzyme activity and choose answer B. Two thirds of candidates successfully did this, but the discrimination index was rather low, showing that some candidates chose another answer. Perhaps they remembered that this enzyme can be affected by an end product inhibitor and therefore chose a curve where enzyme activity decreased with increased threonine concentration.\n

\n
\n", "question_id": "19M.1A.HL.TZ1.29", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-1-enzymes-and-metabolism", "c1-1-13-cyclical-and-linear-pathways-in-metabolism" ] }, { "Question": "
\n
\n (b.i)\n
\n
\n

\n Distinguish between the structure of chromosomes in prokaryotes and eukaryotes.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n prokaryotes (usually) have one chromosome while eukaryotes have numerous chromosomes;\n
    2. \n
  2. \n prokaryotes have a circular chromosome while eukaryotes have linear ones;\n
    3. \n
  3. \n eukaryotes’ chromosomes are associated with histones/proteins but prokaryotes/Eubacteria have naked DNA vs eukaryote DNA associated to proteins/histones;\n
    4. \n
\n

\n \n Accept only differences.\n \n

\n

\n \n Differentiating terms expected;\n \n

\n
\n", "Examiners report": "
\n

\n This question led to a large number of correct answers. Some answers focused on the difference between prokaryotes and eukaryotes instead of their chromosomes.\n

\n
\n", "question_id": "22M.2.SL.TZ2.2B.I", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a2-2-cell-structure", "a2-2-5-prokaryote-cell-structure", "a2-2-6-eukaryote-cell-structure" ] }, { "Question": "
\n
\n

\n Suggest\n \n one\n \n reason for maintaining a pH of 7.5 throughout the experiment.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. pH values away from optimum pH affect enzyme\n
\n \n \n OR\n \n \n
\n so enzyme can function properly\n
\n \n \n OR\n \n \n
\n pH 7.5 is the optimum pH for the enzyme ✔\n
\n
\n b. sketch of enzyme activity versus pH ✔\n \n Sketch of enzyme activity needs labels.\n \n

\n

\n c. change in pH affects 3D structure of protein/active site\n
\n \n \n OR\n \n \n
\n change in pH denatures the enzyme / protein ✔\n

\n

\n d. substrate does not fit in active site\n
\n \n \n OR\n \n \n
\n interaction of substrate and active site affected ✔\n

\n
\n", "Examiners report": "
\n

\n Most candidates answered correctly that a specific pH was necessary for the enzyme to function properly and that deviation from this pH could denature the enzyme.\n

\n
\n", "question_id": "19M.1B.SL.TZ2.C.II", "topics": [ "b-form-and-function" ], "subtopics": [ "b2-1-membranes-and-membrane-transport", "b2-1-10-fluid-mosaic-model-of-membrane-structure" ] }, { "Question": "
\n
\n

\n DNA has regions that do not code for proteins. State\n \n two\n \n functions of these regions.\n

\n

\n 1.\n

\n

\n 2.\n

\n

\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. promoters / operators / regulation of gene expression/transcription ✔\n

\n

\n b. telomeres/give protection to the end of chromosomes «during cell division» ✔\n

\n

\n c. genes for tRNA/rRNA production ✔\n

\n

\n d. other valid function for non-coding sequence ✔\n

\n

\n \n Do not accept stop codon, accept centromeres (connecting sister chromatids).\n \n

\n
\n", "Examiners report": "
\n

\n This question was well answered. The occasional answer made reference to processes associated with translation.\n

\n
\n", "question_id": "19M.2.HL.TZ2.A.III", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d1-2-protein-synthesis", "d1-2-14-non-coding-sequences-in-dna-do-not-code-for-polypeptides" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Outline\n \n four\n \n types of membrane transport, including their use of energy.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n

\n a. simple diffusion is passive movement of molecules/ions along a concentration gradient ✔\n

\n

\n b. facilitated diffusion is passive movement of molecules/ions along a concentration gradient through a protein channel «without use of energy» ✔\n

\n

\n c. osmosis is the passage of water\n \n through a membrane\n \n from lower solute concentration to higher ✔\n \n OWTTE\n \n

\n

\n d. active transport is movement of molecules/ions\n \n against the concentration gradient\n \n «through membrane pumps» with the use of ATP/energy ✔\n

\n

\n e. endocytosis is the infolding of membrane/formation of vesicles to bring molecules into cell with use of energy\n
\n \n \n OR\n \n \n
\n exocytosis is the infolding of membrane/formation of vesicles to release molecules from cell with use of energy ✔\n

\n

\n f. chemiosmosis occurs when protons diffuse through ATP synthase «in membrane» to produce ATP ✔\n

\n

\n \n mpa, mpb and mpc require reference to concentration.\n \n

\n

\n \n Active transport requires mention of the use of energy.\n \n

\n
\n", "Examiners report": "
\n

\n Question 6 was the most popular extended response question. It was less common for students to correctly describe endocytosis and exocytosis. A common misconception was for students to describe both types of bulk transport as passive processes when they both require energy. Students also commonly failed to make reference to concentration gradients in their discussions of active and passive transport.\n

\n
\n", "question_id": "19M.2.SL.TZ2.6A", "topics": [ "b-form-and-function" ], "subtopics": [ "b2-1-membranes-and-membrane-transport", "b2-1-5-movement-of-water-molecules-across-membranes-by-osmosis-and-the-role-of-aquaporins", "b2-1-6-channel-proteins-for-facilitated-diffusion", "b2-1-7-pump-proteins-for-active-transport", "b2-1-8-selectivity-in-membrane-permeability" ] }, { "Question": "
\n
\n

\n Which statement applies to enzymes?\n

\n

\n A. Enzyme function depends on collisions between substrate and active sites.\n

\n

\n B. One active site typically binds to a broad range of substrates.\n

\n

\n C. The active site on the substrate is specific to one enzyme.\n

\n

\n D. When enzymes are immobilized they stop working.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "
\n

\n This was expected to be a relatively easy question but fewer than 40 % of candidates answered it correctly. The most popular answer was incorrect substrates do not have active sites. This is a common error of understanding. The expected answer was that enzyme function depends on collisions between substrate and active site.\n

\n
\n", "question_id": "21M.1A.SL.TZ1.14", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-1-enzymes-and-metabolism", "c1-1-1-enzymes-as-catalysts", "c1-1-2-role-of-enzymes-in-metabolism" ] }, { "Question": "
\n
\n

\n What is the arrangement of the components of nucleotides in a single DNA strand?\n

\n

\n \n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "None", "question_id": "22N.1A.HL.TZ0.7", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a1-2-nucleic-acids", "a1-2-6-dna-as-a-double-helix-made-of-two-antiparallel-strands-of-nucleotides-with-two-strands-linked-by-hydrogen-bonding-between-complementary-base-pairs" ] }, { "Question": "
\n
\n

\n Draw the same chromosomes to show their structure at the same stage of meiosis if there had been one chiasma between two gene loci.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n all four upper arms with one A and both chromosomes with one B and one b on the lower arms;\n

\n

\n \n

\n

\n \n The chromatids can be shown as single lines rather than the wider versions in the question\n \n .\n

\n
\n", "Examiners report": "
\n

\n This was mostly well answered but some candidates showed one chromatid flopped over a non-sister chromatid, like crossed legs of a seated person, without any recombination having occurred. This showed a misunderstanding of the process of crossing over and chiasma formation. There were also a wide range of other answers showing confusion about events in meiosis.\n

\n
\n", "question_id": "21N.2.SL.TZ0.B.I", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-1-cell-and-nuclear-division", "d2-1-9-meiosis-as-a-reduction-division", "d2-1-11-meiosis-as-a-source-of-variation" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Explain the role of the hormone ADH in osmoregulation.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n ADH secreted if blood is hypertonic/solute concentration too high/water content too low/dehydrated;\n
    2. \n
  2. \n aquaporins open/more aquaporins in (plasma membranes of cells in DCT/collecting duct) with ADH;\n
    3. \n
  3. \n DCT/collecting duct becomes more permeable to water/reabsorbs more water (from filtrate);\n
    4. \n
\n
\n", "Examiners report": "
\n

\n This was generally well answered. A few candidates thought that ADH could both increase and decrease water reabsorption in the nephron. The commonest omission was hypertonic conditions being the signal that results in ADH secretion.\n

\n
\n", "question_id": "22N.2.HL.TZ0.5C", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-3-homeostasis", "d3-3-10-osmoregulation-by-water-reabsorption-in-the-collecting-ducts" ] }, { "Question": "
\n
\n

\n The diagram shows a prokaryotic cell.\n

\n

\n \n

\n

\n [Source: © Rice University. 1999–2023\n \n Figure 4.5 Prokaryotic cell\n \n . [image online] Available at: https://openstax.org/apps/archive/20220815.182343/resources/50163f8ff80f335574f41bfc10cc49a1e87cf9df [Accessed 13 January 2023].]\n

\n

\n

\n

\n What are the structures labelled Y and Z?\n

\n

\n \n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "22N.1A.SL.TZ0.1", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a2-2-cell-structure", "a2-2-5-prokaryote-cell-structure" ] }, { "Question": "
\n
\n

\n Describe the effects of temperature and nitrate concentration on biomass.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n a. increased temperature raises biomass;\n
\n b. increased nitrate raises biomass more than increased temperature;\n
\n c. increased nitrate and temperature raises biomass by same amount as nitrate alone;\n

\n
\n", "Examiners report": "
\n

\n This was another question where many candidates’ answers lacked discernment. The increase in biomass with nitrate was clearly greater than that with temperature alone, but the increase with nitrate and temperature combined was not significantly different from nitrate alone. A useful way of thinking about answering questions such as this is ‘If I read out my answer to someone over the phone, would they correctly sketch the relative size of the bars without seeing the actual bar chart?’ With many candidates the answer to this would have been no.\n

\n
\n", "question_id": "21N.2.SL.TZ0.E", "topics": [ "d-continuity-and-change", "c-interaction-and-interdependence" ], "subtopics": [ "d4-2-stability-and-change", "d4-2-4-use-of-a-model-to-investigate-the-effect-of-variables-on-ecosystem-stability", "c1-3-photosynthesis", "c1-3-7-techniques-for-varying-concentrations-of-carbon-dioxide-light-intensity-or-temperature-experimentally-to-investigate-the-effects-of-limiting-factors-on-the-rate-of-photosynthesis" ] }, { "Question": "
\n
\n

\n The diagram shows a plant shoot and the direction of the light which the shoot received.\n

\n

\n \n

\n

\n [Source: USDA-NRCS PLANTS Database. Available at: https://commons.wikimedia.org/wiki/File:Alnus_seedling_drawing.png\n
\n [Accessed 30 November 2021].]\n

\n

\n

\n

\n What are the direction of movement and the effect of auxin in the tip of a plant shoot when receiving light from one side?\n

\n

\n \n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "21N.1A.HL.TZ1.33", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-1-integration-of-body-systems", "c3-1-21-promotion-of-cell-growth-by-auxin" ] }, { "Question": "
\n
\n

\n Suggest with a reason which P:L diet is closest to the normal diet of these bumblebees.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n 10:1 diet as this has the highest survival rate (after 7 days);\n

\n

\n \n Reason must be given.\n \n

\n
\n", "Examiners report": "None", "question_id": "22N.2.SL.TZ0.I", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c4-2-transfers-of-energy-and-matter", "c4-2-15-primary-production-as-accumulation-of-carbon-compounds-in-biomass-by-autotrophs", "c4-2-16-secondary-production-as-accumulation-of-carbon-compounds-in-biomass-by-heterotrophs" ] }, { "Question": "
\n
\n (g)\n
\n
\n

\n The molecular structures of the mouse alarm compound and fox scent are very similar. Suggest an evolutionary advantage for this chemical similarity.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n the mice would have the same response to another mouse’s danger signal as to the actual presence of the predator/fox\n
\n \n \n OR\n \n \n
\n adaptation to fool predator by producing a scent similar to predator’s own scent\n
\n \n \n OR\n \n \n
\n allows a group response to a predator/fox/danger when just one mouse detects the danger ✔\n

\n

\n \n Accept any other feasible answer\n \n .\n

\n
\n", "Examiners report": "
\n

\n In g, better candidates were able to suggest an evolutionary advantage either from the point of view of one mouse being able to bring about a group response, or from the point of view that the fox could not distinguish between mice and other foxes.\n

\n
\n", "question_id": "19M.2.SL.TZ2.1G", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c2-2-neural-signalling" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Describe the distribution of\n \n C. montagui\n \n and\n \n S. balanoides\n \n barnacles in Butter Lump Bay.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. both species present throughout the range ✔\n

\n

\n b.\n \n C. montagui\n \n has small number of individuals «throughout»\n
\n \n \n OR\n \n \n \n
\n C.montagui\n \n occupies «mostly» upper shore/intertidal zone\n

\n

\n c.\n \n S. balanoides\n \n «mostly» occupies low tide area ✔\n
\n \n \n OR\n \n \n
\n \n S.balanoides\n \n has large number of individuals «throughout» ✔\n

\n

\n \n OWTTE referring to maximum numbers at specific heights.\n \n

\n
\n", "Examiners report": "
\n

\n Candidates were able to describe the distributions of the barnacles very well in part (b).\n

\n
\n", "question_id": "19M.1B.SL.TZ2.12B", "topics": [ "b-form-and-function" ], "subtopics": [ "b4-1-adaptation-to-environment", "b4-1-4-range-of-tolerance-of-a-limiting-factor" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n State the alternative hypothesis for this study.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n there is a positive / negative association between the two species;\n
\n they tend to grow together / they tend to grow apart;\n

\n

\n \n OWTTE\n \n

\n
\n", "Examiners report": "
\n

\n There were many correct answers, but a number confused the alternate and null hypotheses.\n

\n
\n", "question_id": "22M.2.SL.TZ2.3A", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c4-1-populations-and-communities", "c4-1-15-use-of-the-chi-squared-test-for-association-between-two-species" ] }, { "Question": "
\n
\n (a.iii)\n
\n
\n

\n On the diagrams, label with a letter P a location where a neonicotinoid pesticide could bind.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n any receptor protein on post synaptic membrane marked ✔\n

\n

\n \n For 2 a, i, ii and iii, accept letters written on the structure even if a line is not drawn.\n \n

\n

\n \n Award the mark if the full word is used to label the structure.\n \n

\n

\n \n Must unambiguously be pointed to a receptor on the synapse side. Accept labels of acetylcholinesterase\n \n .\n

\n
\n", "Examiners report": "
\n

\n Both receptor proteins and acetylcholinesterase were accepted as proteins to which acetylcholine can bind. The markscheme did not accept locations other than on the synaptic side.\n

\n
\n", "question_id": "21M.2.HL.TZ2.2A.III", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c2-1-chemical-signalling-[hl-only]", "c2-1-5-localized-and-distant-effects-of-signalling-molecules" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Outline the role of DNA polymerase III in DNA replication.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n

\n a. binds to template strand adjacent to a primer/at the primer ✔\n

\n

\n b. adds nucleotides to template strand/to single stranded DNA ✔\n

\n

\n c. using complementary base pairing ✔\n

\n

\n d. links nucleotides with sugar-phosphate/phosphodiester bonds ✔\n

\n

\n e. adds nucleotides/builds new strand in 5'\n \n \n →\n \n \n 3' direction ✔\n

\n

\n f. lagging strand is built in short segments/Okazaki fragments/synthesis is discontinuous ✔\n

\n

\n \n Accept A to T and G to C instead of ‘complementary’ in mpc\n \n .\n

\n

\n \n For mpb it must be clear that nucleotides, not bases, are added to an existing strand of DNA. Do not accept ‘to replication fork’ for this\n \n .\n

\n
\n", "Examiners report": "
\n

\n For the well-prepared candidate, this posed no problems and the four marks were easily earned. At the other end of the performance range almost all candidates mentioned Okazaki fragments — a benefit of giving something a distinctive name.\n

\n
\n", "question_id": "21M.2.HL.TZ1.8B", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d1-1-dna-replication", "d1-1-8-functions-of-dna-primase-dna-polymerase-i-dna-polymerase-iii-and-dna-ligase-in-replication" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n It has been argued that variation in the global mean surface temperature has been caused by variation in energy from the Sun. Analyse whether evidence from the graphs supports this argument.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n (\n \n Evidence does not support this argument because\n \n :)\n

\n
    \n
  1. \n overall increase in surface temperature but no overall increase/slight decrease in solar irradiance;\n
    2. \n
  2. \n peaks and troughs in solar irradiance do not correspond with fluctuations in surface temperature;\n
    3. \n
\n

\n \n Do not award marks for claims that the evidence supports the argument, for example, claims that the fluctuations coincide.\n \n

\n
\n", "Examiners report": "
\n

\n Most candidates earned one of the two marks for the idea that the long-term trend in global mean surface temperature is an increase whereas there has if anything been an overall decrease in energy from the Sun between 1980 and 2020. Few answers pointed out that ten-year cycles in Sun's energy that are seen do not correspond to fluctuations in surface mean temperature. Weaker answers tended to pick out single instances of a rise in Sun's energy corresponding with a rise in surface temperature. Very few answers included any comments on the small variation in Sun's energy — only ranging from 1360.2 to 1362.2 W m-2 which is less than 0.15\n \n \n \n \n % fluctuation, with no overall increase, whereas surface temperature has increased by more than a degree Celsius in the 40 years from 1978 to 2018.\n

\n
\n", "question_id": "22N.2.HL.TZ0.3", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-3-climate-change", "d4-3-1-anthropogenic-causes-of-climate-change", "d4-3-2-positive-feedback-cycles-in-global-warming" ] }, { "Question": "
\n
\n

\n Based on the mode of transmission of the Ebola virus, suggest a possible reason for the relationship between population density and the number of Ebola cases in these four countries.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n greater density means more frequent contact with infected people/animals ✔\n

\n

\n \n Need both greater density and frequency of contact\n \n

\n
\n", "Examiners report": "
\n

\n Most candidates correctly used high density and frequency of contact to describe the relationship. Very few responses discussed high density but did not relate it to the frequency of contact. Others focused on modes of transmission alone and did not relate it to density.\n

\n
\n", "question_id": "19M.2.HL.TZ1.C", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a2-3-viruses-(hl-only)" ] }, { "Question": "
\n
\n

\n Hershey and Chase used a bacteriophage (a virus that infects bacteria) to investigate the chemical nature of genes. The diagram shows a bacteriophage.\n

\n

\n \n

\n

\n [Source: Graham Knott and Christel Genoud, ‘Commentary: is EM dead?’,\n \n Journal of Cell Science\n \n (2013),\n
\n \n 126\n \n : 4545–4552, reproduced with permission. http://jcs.biologists.org/content/126/20/4545.figures-only\n
\n doi: 10.1242/jcs.124123\n \n http://www.biologists.com/journal-of-cell-science]\n \n

\n

\n

\n

\n The sulphur in the protein and the phosphorus in the DNA of the bacteriophage were radioactively labelled. The data obtained after bacterial infection and centrifugation are shown in the table.\n

\n

\n \n

\n

\n What did Hershey and Chase conclude from their experiment?\n

\n

\n A. DNA was mainly outside the bacterial cells.\n

\n

\n B. Viruses infect bacterial cells with proteins.\n

\n

\n C. Viral DNA was found within the bacterial cells.\n

\n

\n D. Neither protein nor DNA were chemicals making up genes in viruses.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "
\n

\n This was a good question, it discriminated very well and was not too difficult.\n

\n
\n", "question_id": "19M.1A.HL.TZ2.11", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a1-2-nucleic-acids", "a1-2-14-evidence-from-the-hershey-chase-experiment-for-dna-as-the-genetic-material" ] }, { "Question": "
\n
\n

\n Compare and contrast the results for trials 2 and 9.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n \n Similarity between 2 and 9\n \n :\n

\n
    \n
  1. \n winter path length longer (than spring and summer) in both (trials 2 and 9/from entrances B and C);\n
    \n \n
    \n Contrast between 2 and 9\n     \n :\n
    \n
    \n
    2. \n
  2. \n path length longer in trial 2 than 9/from entrance B than entrance C (in all seasons);\n
    \n \n \n OR\n \n \n
    \n error/bar/standard deviation/variation in data greater in trial 2 than 9/from entrance B than entrance C (in all seasons);\n
    3. \n
\n
\n", "Examiners report": "
\n

\n As in part (e), a similarity and a difference were required. When analysing data, candidates should try to keep in mind whether aspects are of interest and lead to conclusions significant conclusions or not. Here the two interesting findings were that the path length was highest in winter in both trials and that the shrews' performance between trial 2 and 90 had improved in all seasons, so they found the food with a shorter path length.\n

\n
\n", "question_id": "22N.2.HL.TZ0.K", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-1-integration-of-body-systems", "c3-1-4-the-brain-as-a-central-information-integration-organ" ] }, { "Question": "
\n
\n

\n In transcription, which enzyme has a role similar to that of helicase in replication?\n

\n

\n A.  DNA polymerase III\n

\n

\n B.  Ligase\n

\n

\n C.  RNA polymerase\n

\n

\n D.  DNA polymerase I\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "22N.1A.HL.TZ0.26", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d1-2-protein-synthesis", "d1-2-1-transcription-as-the-synthesis-of-rna-using-a-dna-template" ] }, { "Question": "
\n
\n

\n The electron micrograph shows sarcomeres in myofibrils of striated muscle during muscle contraction. The lines P–Q and R–S show two regions of one sarcomere.\n \n

\n

\n [Source: Republished with permission of Elsevier - Health Sciences Division from\n \n Cell\n \n by Don W. Fawcett 1981 ; permission conveyed through Copyright Clearance Center, Inc.]\n

\n

\n

\n

\n How would regions P–Q and R–S change when the muscle relaxes?\n

\n

\n \n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "
\n

\n This question was answered correctly by only 33 % of the candidates. Incorrect responses were distributed fairly evenly among the options. The question discriminated well showing the better candidates were answering correctly.\n

\n
\n", "question_id": "22M.1A.HL.TZ2.38", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-3-muscle-and-motility-(hl-only)", "b3-3-2-sliding-filament-model-of-muscle-contraction", "b3-3-3-role-of-the-protein-titin-and-antagonistic-muscles-in-muscle-relaxation" ] }, { "Question": "
\n
\n

\n Two components of biodiversity are richness and evenness. Deduce which of the two pools was higher in richness.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A;\n

\n
\n", "Examiners report": "
\n

\n Candidates could deduce the richness and evenness of the pools but gave incomplete answers to the other two parts of this question.\n

\n
\n", "question_id": "20N.2.SL.TZ0.A.I", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a4-2-conservation-of-biodiversity", "a4-2-5-evidence-for-a-biodiversity-crisis" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Suggest a reason for using a lower power objective lens when first focusing on a slide under the microscope.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n it is easier to find the specimen using a low power objective lens\n
    \n \n \n OR\n \n \n
    \n there is a larger field of view/depth of focus;\n
    2. \n
  2. \n it is easier to locate the most interesting part of the specimen with a low power objective lens;\n
    3. \n
  3. \n most microscopes are calibrated so that once in focus using the low power objective lens they will be close    to focus using the higher power, so this helps focusing;\n
    4. \n
  4. \n reduced risk of cracking the slide;\n
    5. \n
\n
\n", "Examiners report": "None", "question_id": "SPM.1B.SL.TZ0.2C", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a2-2-cell-structure", "a2-2-2-microscopy-skills" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Outline how ventilation rate could have been monitored in this study.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. «data logging» with spirometer\n
\n \n \n OR\n \n \n
\n chest belt ✔\n

\n

\n b. «tidal» volume recorded for a given period of time\n
\n \n \n OR\n \n \n
\n average «tidal» volume found and multiplied by number breaths per minute ✔\n

\n

\n \n Do not accept confusion with respirometer (measuring oxygen consumption or CO\n \n 2\n \n release).\n \n

\n

\n \n Must include a reference to time.\n \n

\n
\n", "Examiners report": "
\n

\n Question (c) was poorly answered. Many candidates thought a respirometer would be used to measure ventilation rate while other candidates gave a description of how to measure the number of breaths per minute. This was considered inadequate as the Y axis of the graph indicated that ventilation rate was volume per minute, so reference to volume and time were required in the response.\n

\n
\n", "question_id": "19M.1B.SL.TZ2.3C", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-1-gas-exchange", "b3-1-5-ventilation-of-the-lungs" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Describe the processes that are carried out by enzymes that bind to DNA.\n

\n
\n
\n

\n [7]\n

\n
\n
\n", "Markscheme": "
\n

\n \n replication\n \n

\n

\n a. helicase unwinds the double helix/DNA;\n
\n b. helicase breaks hydrogen bonds between/separates/unzips DNA strands;\n
\n c. (DNA) gyrase/topoisomerase releases tensions in DNA as it unwinds;\n
\n d. (DNA) primase adds\n \n RNA\n \n primers (where DNA polymerase can bind);\n
\n e. DNA polymerase (III) replicates DNA/adds nucleotides (to make new strand);\n
\n f. DNA polymerase I replaces RNA (primers) with DNA;\n
\n g. DNA ligase seals nicks/joins sugar-phosphate backbones/joins (Okazaki)fragments;\n

\n

\n \n transcription\n \n

\n

\n h. RNA polymerase used for transcription;\n
\n i. RNA polymerase unwinds / separates DNA strands / binds to the promoter;\n
\n j. RNA polymerase copies DNA base sequence of a gene/makes mRNA;\n
\n k. restriction enzymes/endonucleases cut DNA at specific base sequences;\n
\n l. telomerase adds nucleotides to the ends of chromosomes/makes telomeres;\n

\n
\n", "Examiners report": "None", "question_id": "23M.2.HL.TZ1.7B", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d1-1-dna-replication", "d1-1-3-role-of-helicase-and-dna-polymerase-in-dna-replication", "d1-1-8-functions-of-dna-primase-dna-polymerase-i-dna-polymerase-iii-and-dna-ligase-in-replication" ] }, { "Question": "
\n
\n

\n State the function of the tap and reservoir.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n to reset the potometer\n
\n \n \n OR\n \n \n
\n move the air column to the right/end\n
\n \n \n OR\n \n \n
\n to replace/replenish water in tube ✔\n

\n

\n \n Accept meniscus or air bubble as alternatives to column in all parts of question\n \n

\n
\n", "Examiners report": "
\n

\n All sections of this question revealed that students were unfamiliar with use and set-up of the potometer. This question was also commented on frequently by teachers in the G2 form who noted the absence of reservoirs in some of the potometers used in student labs. However, it was felt that students familiar with the working of any potometer could have used the information in the diagram to answer this question correctly.\n

\n
\n", "question_id": "19M.1B.SL.TZ1.A", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-1-gas-exchange", "b3-1-9-transpiration-as-a-consequence-of-gas-exchange-in-a-leaf" ] }, { "Question": "
\n
\n

\n How can a chi-squared test be used in ecological research?\n

\n

\n A. To test the effect of an abiotic factor on one plant species\n

\n

\n B. To test whether two species tend to live together\n

\n

\n C. To test whether one population of plants is taller than another\n

\n

\n D. To test whether one species is more tolerant to heavy metals than another\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "20N.1A.SL.TZ0.17", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c4-1-populations-and-communities", "c4-1-15-use-of-the-chi-squared-test-for-association-between-two-species" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Discuss the evidence for the theory that mitochondria may have evolved from free-living prokaryotes by endosymbiosis.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n a. «double» membrane may have formed when engulfed ✔\n

\n

\n b. replicate by binary fission like free-living prokaryotes\n
\n \n \n OR\n \n \n
\n reproduce separate from «host» cell replication ✔\n

\n

\n c. they have their own «circular» DNA\n \n \n AND\n \n \n reproduce on their own ✔\n

\n

\n d. they have «70s» ribosomes\n \n \n AND\n \n \n can manufacture «their own» proteins ✔\n

\n

\n e. have organelle«s» similar to free-living prokaryotes ✔\n

\n

\n f. similar in size to free-living prokaryotes ✔\n

\n

\n g. mitochondrial inner membranes manufacture ATP like bacterial membranes ✔\n

\n

\n h. currently there is no free-living prokaryote like a mitochondrion ✔\n

\n
\n", "Examiners report": "
\n

\n The command term for this question was “discuss”. Connections were not made as many candidates just gave a list of features of mitochondria with no attempt at explanation or discussion. There was some confusion between the words endocytosis and endosymbiosis. In spite of the many shortcomings, there were a few brilliant responses\n

\n
\n", "question_id": "19M.2.HL.TZ1.2B", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a2-2-cell-structure", "a2-2-12-origin-of-eukaryotic-cells-by-endosymbiosis" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Outline how the amphipathic properties of phospholipids play a role in membrane structure.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. part hydrophobic/not attracted to water/non-polar\n \n \n AND\n \n \n part hydrophilic/attracted to water/polar;\n \n Both needed\n \n .\n

\n

\n b. bilayer formed (formed naturally by phospholipids in water);\n

\n

\n c.\n \n hydrophilic\n \n heads/parts face outwards\n \n \n AND\n \n \n \n hydrophobic\n \n tails/parts face inwards;\n

\n

\n \n Do not allow water loving/hating in mpa or mpc\n \n .\n

\n
\n", "Examiners report": "
\n

\n Knowledge of amphipathic properties in part a was good. In b, most could state that the diagram shows a synapse. A variety of spelling is usually allowed, but in this case ‘synapsis’ was not allowed in English as this refers to the pairing of homologous chromosomes. There were some G2 comments that the X could be taken as the structure. However X clearly points to an arrow, not a structure. Most were able to gain some marks by describing the events, but some lost marks by not clearly indicating that it is the vesicle containing the neurotransmitter that moves.\n

\n
\n", "question_id": "20N.2.SL.TZ0.3", "topics": [ "b-form-and-function", "c-interaction-and-interdependence" ], "subtopics": [ "b1-1-carbohydrates-and-lipids", "b1-1-12-formation-of-phospholipid-bilayers-as-a-consequence-of-the-hydrophobic-and-hydrophilic-regions", "c2-1-chemical-signalling-[hl-only]", "c2-1-5-localized-and-distant-effects-of-signalling-molecules", "c2-1-7-initiation-of-signal-transduction-pathways-by-receptors", "c2-1-8-transmembrane-receptors-for-neurotransmitters-and-changes-to-membrane-potential", "c2-1-9-transmembrane-receptors-that-activate-g-proteins" ] }, { "Question": "
\n
\n

\n What happens in the acrosome reaction?\n
\n
\n

\n

\n A.  Enzymes digest the zona pellucida around an ovum, allowing a sperm to enter.\n

\n

\n B.  Enzymes digest the binding proteins of the zona pellucida so that no more sperm enter.\n

\n

\n C.  Acrosomes release binding proteins to the zona pellucida for sperm entrance.\n

\n

\n D.  Acrosomes react with the cortical granules to allow fertilization.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "None", "question_id": "23M.1A.HL.TZ1.40", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-1-reproduction", "d3-1-15-mechanisms-to-prevent-polyspermy" ] }, { "Question": "
\n
\n

\n DNA methylation profiles in zebrafish (Danio rerio) gametes were determined. The methylated areas were divided into three groups according to the amount of methylation: high, medium and low methylation.\n

\n

\n \n

\n

\n \n [Source: Potok, M.E., Nix, D.A., Parnell, T.J. and Cairns, B.R., 2013.\n \n
\n \n Reprogramming the Maternal Zebrafish Genome afterFertilization to\n \n
\n \n Match the Paternal Methylation Pattern.\n \n
\n \n \n Cell\n \n , [e-journal] 153(4), pp. 759–772. http://dx.doi.org/10.1016/j.\n \n
\n \n cell.2013.04.030.]\n \n

\n

\n Methylation of DNA in sperm and egg is removed immediately after fertilization. What is the reason for this?\n

\n

\n
\n A.  Methylation allows RNA polymerase to join the promoter.\n

\n

\n B.  It is needed to form homologous pairs of chromosomes.\n

\n

\n C.  It allows expression of genes linked to early development.\n

\n

\n D.  Transcription of promoters only occurs in methylated genes.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "23M.1A.HL.TZ1.26", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-2-gene-expression-[hl-only]", "d2-2-6-methylation-of-the-promoter-and-histones-in-nucleosomes-as-examples-of-epigenetic-tags", "d2-2-7-epigenetic-inheritance-through-heritable-changes-to-gene-expression" ] }, { "Question": "
\n
\n

\n Which is a density-independent limiting factor for a kangaroo?\n

\n

\n
\n A.  A forest fire\n

\n

\n B.  Predation\n

\n

\n C.  Climate change\n

\n

\n D.  Eutrophication\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "None", "question_id": "SPM.1A.SL.TZ0.29", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c4-1-populations-and-communities", "c4-1-6-negative-feedback-control-of-population-size-by-density-dependent-factors", "c4-1-12-mutualism-as-an-interspecific-relationship-that-benefits-both-species" ] }, { "Question": "
\n
\n

\n Suggest a reason for a larger percentage of corals being infected with white syndrome on reefs with a higher cover of corals.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n a. the closer the corals are (to each other) the easier the transmission;\n
\n b. other organisms in the community may act as vectors/carriers / OWTTE;\n

\n
\n", "Examiners report": "
\n

\n In 1b (iii) the better students realised that it was to do with higher density of corals, not just the more vague ‘higher cover’ given in the stem.\n

\n
\n", "question_id": "21N.2.SL.TZ0.B.III", "topics": [ "d-continuity-and-change", "b-form-and-function" ], "subtopics": [ "d4-3-climate-change", "d4-3-7-threats-to-coral-reefs-as-an-example-of-potential-ecosystem-collapse", "b4-1-adaptation-to-environment", "b4-1-5-conditions-required-for-coral-reef-formation" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Outline the process of DNA profiling.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n

\n a. sample of DNA obtained from person/hair/blood/mouth/crime scene ✔\n

\n

\n b. PCR used to amplify/make copies of DNA (in sample) ✔\n

\n

\n c. using\n \n Taq\n \n DNA polymerase / using DNA polymerase from thermophilic bacteria ✔\n

\n

\n d. tandem repeats amplified/used ✔\n

\n

\n e. gel electrophoresis used to separate DNA (into bands) ✔\n

\n

\n f. separation according to length of fragments/number of repeats\n
\n \n \n OR\n \n \n
\n fragments of same length/number of repeats travel same distance ✔\n

\n

\n g. pattern of bands/numbers of repeats is the profile/is unique to the individual ✔\n

\n

\n h. example of application/forensics/crime investigation/paternity ✔\n

\n

\n \n Do not accept ‘determine ancestry’ for mph\n \n .\n \n Other genes/chromosomes are more often used for that\n \n .\n

\n

\n \n Accept STR for (short) tandem repeat in mpd\n \n .\n

\n
\n", "Examiners report": "
\n

\n There were some good outlines of DNA profiling. Most knew at least one application of the process. There was some confusion between profiling and sequencing and the use of tandem repeats was often missed.\n

\n
\n", "question_id": "21M.2.HL.TZ1.8", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d1-1-dna-replication", "d1-1-5-applications-of-polymerase-chain-reaction-and-gel-electrophoresis", "d1-1-8-functions-of-dna-primase-dna-polymerase-i-dna-polymerase-iii-and-dna-ligase-in-replication" ] }, { "Question": "
\n
\n

\n The diagram shows where the exchange of substances between blood and tissue fluid occurs in a capillary bed.\n

\n

\n \n

\n

\n
\n What explains the movement of solutes between blood and tissue fluid at region X?\n

\n

\n
\n A.  Blood plasma has a higher concentration of solutes than tissue fluid.\n

\n

\n B.  Tissue fluid has a more negative water potential than blood plasma.\n

\n

\n C.  Hydrostatic pressure is higher in blood than in tissue fluid.\n

\n

\n D.  The permeability of capillary walls is highest at region X.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "SPM.1A.HL.TZ0.27", "topics": [ "b-form-and-function" ], "subtopics": [ "b2-1-membranes-and-membrane-transport", "b2-1-5-movement-of-water-molecules-across-membranes-by-osmosis-and-the-role-of-aquaporins" ] }, { "Question": "
\n
\n

\n Which adaptation would allow plants to live in saline irrigated soil?\n
\n
\n

\n

\n A.  Small, shallow roots\n

\n

\n B.  Active uptake and compartmentalization of mineral ions to maintain homeostasis\n

\n

\n C.  Increased transpiration to replace water in stems\n

\n

\n D.  Leaves with a large surface area for increased photosynthesis\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "23M.1A.HL.TZ1.31", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-2-transport", "b3-2-17-generation-of-root-pressure-in-xylem-vessels-by-active-transport-of-mineral-ions" ] }, { "Question": "
\n
\n

\n Black, short-haired guinea pigs, heterozygous for both characteristics, were crossed. They produced offspring with the phenotypes black short-haired, black long-haired, white short-haired and white long-haired in the ratio 9:3:3:1. A different cross produced offspring with phenotypes in the ratio 1:1:1:1. What were the genotypes of the parents in the second cross?\n

\n

\n A.  BbSs × BbSs\n

\n

\n B.  BBSs × BbSS\n

\n

\n C.  BbSs × bbss\n

\n

\n D.  bbSS × BBss\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "22N.1A.HL.TZ0.35", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-2-inheritance", "d3-2-17-punnett-grids-for-predicting-genotypic-and-phenotypic-ratios-in-dihybrid-crosses-involving-pairs-of-unlinked-autosomal-genes" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Explain the role of the electron transport chain in the generation of ATP by cell respiration.\n

\n
\n
\n

\n [7]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n electron transport chain performs chemiosmosis / chemiosmosis generates ATP;\n
    2. \n
  2. \n receives energy/electrons from oxidation reactions/from Krebs cycle/glycolysis;\n
    3. \n
  3. \n receives electrons from reduced NAD/NADH/reduced FAD/FADH;\n
    4. \n
  4. \n energy released as electrons pass from carrier to carrier (in the chain);\n
    5. \n
  5. \n release of energy (from electron flow) coupled to proton pumping;\n
    6. \n
  6. \n protons pumped into intermembrane space;\n
    7. \n
  7. \n creates proton gradient;\n
    8. \n
  8. \n protons diffuse back/move down the concentration gradient (across membrane);\n
    9. \n
  9. \n protons pass through ATP synthase;\n
    10. \n
  10. \n protons return to the matrix;\n
    11. \n
  11. \n flow of protons provides energy for generating ATP;\n
    12. \n
  12. \n electrons transferred to oxygen at end of electron transport chain;\n
    13. \n
\n
\n", "Examiners report": "
\n

\n For well-prepared candidates this question posed no difficulty and there were some excellent detailed accounts of chemiosmosis. The discrimination index was the highest for any question on the paper, indicating that there was no room for lucky guesses about the biology here!\n

\n
\n", "question_id": "22M.2.HL.TZ1.7C", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-2-cell-respiration", "c1-2-14-generation-of-a-proton-gradient-by-flow-of-electrons-along-the-electron-transport-chain" ] }, { "Question": "
\n
\n

\n Explain how a single base substitution mutation in DNA can cause a change to a protein.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n sequence of DNA bases determines the amino acid sequence of a protein;\n
    2. \n
  2. \n changing one base (on the DNA) can cause the triplet /mRNA to code for a different\n \n amino acid\n \n ;\n
    3. \n
  3. \n changing one base (on the DNA) causes a different protein to be made (during translation);\n
    4. \n
\n
\n", "Examiners report": "None", "question_id": "22N.2.SL.TZ0.D", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d1-2-protein-synthesis", "d1-2-11-mutations-that-change-protein-structure" ] }, { "Question": "
\n
\n

\n Outline the requirements for sustainability within a sealed mesocosm.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n photosynthetic organisms/autotrophs/plants as producers;\n
    2. \n
  2. \n \n light\n \n (as energy source) for photosynthesis;\n
    3. \n
  3. \n nutrient/water recycling (by saprotrophs);\n
    4. \n
  4. \n decomposers/saprotrophs to breakdown (toxic) wastes;\n
    5. \n
\n

\n \n The question is “outline”, so do not accept only a list of variables without a brief account.\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.1B.SL.TZ2.C", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-2-stability-and-change", "d4-2-4-use-of-a-model-to-investigate-the-effect-of-variables-on-ecosystem-stability" ] }, { "Question": "
\n
\n

\n What is an example of anabolism?\n
\n
\n

\n

\n A.  Formation of peptides after protein digestion\n

\n

\n B.  Formation of glucose and fructose from sucrose\n

\n

\n C.  Formation of maltose from two glucose molecules\n

\n

\n D.  Formation of glycerol and fatty acids from triglycerides\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "23M.1A.SL.TZ1.6", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-1-enzymes-and-metabolism", "c1-1-3-anabolic-and-catabolic-reactions" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Outline how the shrew labelled P differs from the normal relationship between BCH and brain mass.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n high BCH but brain mass is low/lower than expected/lower than others with similar BCH;\n
    2. \n
  2. \n (fairly) low brain mass but BCH is high/higher than expected/higher than others with similar brain mass;\n
    3. \n
\n
\n", "Examiners report": "
\n

\n Almost all candidates understood what made P an outlier, but not all could express lucidly how it deviated from the trend.\n

\n
\n", "question_id": "22N.2.HL.TZ0.1B", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-1-integration-of-body-systems", "c3-1-4-the-brain-as-a-central-information-integration-organ" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Explain how acetylcholine initiates an action potential in a postsynaptic membrane.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. acetylcholine binds to the receptor protein ✔\n

\n

\n b. (causing a) change in\n \n tertiary\n \n structure / conformation of protein ✔\n

\n

\n c. diffusion/entry of ions / Na\n \n +\n \n through the receptor/channel protein allowed ✔\n

\n
\n", "Examiners report": "None", "question_id": "21M.2.SL.TZ2.2C", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c2-2-neural-signalling", "c2-2-7-generation-of-an-excitatory-postsynaptic-potential" ] }, { "Question": "
\n
\n

\n What is evidence for the endosymbiotic theory in eukaryotic cells?\n

\n

\n
\n A.  Mitochondrion with DNA\n

\n

\n B.  Golgi complex in cytoplasm\n

\n

\n C.  Single nuclear membrane\n

\n

\n D.  Ribosomes in cytoplasm\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "None", "question_id": "23M.1A.HL.TZ1.4", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a2-2-cell-structure", "a2-2-12-origin-of-eukaryotic-cells-by-endosymbiosis" ] }, { "Question": "
\n
\n (f.i)\n
\n
\n

\n State the reason for performing the experiment in the months of May to August.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n because nymphs are present/numbers of nymphs rise «in these months»\n
\n \n \n OR\n \n \n
\n build up immunity/antibodies in mice before nymphs «peak» ✔\n

\n

\n \n Ignore references to larvae\n \n .\n

\n
\n", "Examiners report": "None", "question_id": "19N.2.SL.TZ0.1F.I", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-2-defence-against-disease", "c3-2-7-antigens-as-recognition-molecules-that-trigger-antibody-production" ] }, { "Question": "
\n
\n

\n Explain the technique used to estimate the population size of a\n \n named\n \n species of organism that is able to move.\n

\n
\n
\n

\n [6]\n

\n
\n
\n", "Markscheme": "
\n

\n a. named species ✔\n \n Do not award marks for group of animals eg birds.\n \n \n Do not award the mark for this point if the method doesn’t apply for the species\n \n .\n

\n

\n b. capture and count a sample of the population ✔\n

\n

\n c. example of method of capture ✔\n

\n

\n d. apply a mark that will not affect the survival of the animal «\n \n e.g.\n \n non-toxic paint spot/ear tag/leg ring/radio transmitter» ✔\n \n OWTTE\n \n

\n

\n e. release the organism into the environment ✔\n

\n

\n f. allow time to become randomly dispersed ✔\n \n OWTTE\n \n

\n

\n g. capture «a second sample» and count the complete sample ✔\n

\n

\n h. count the marked individuals in the second sample ✔\n

\n

\n i. define formula to estimate the population size ✔\n \n \n \n N\n \n \n =\n \n \n \n \n \n \n \n n\n \n \n \n 1\n \n \n \n \n ×\n \n \n \n \n \n n\n \n \n \n 2\n \n \n \n \n \n \n \n \n \n n\n \n \n \n 3\n \n \n \n \n \n \n \n \n where n\n \n 1\n \n = first capture, n\n \n 2\n \n = second capture, n\n \n 3\n \n = number marked in second capture.\n \n
\n \n Accept alternative displays of formula, e.g. different variables, wording displayed in a formula, etc\n \n .\n

\n

\n j. only estimates could be obtained ✔\n

\n
\n", "Examiners report": "None", "question_id": "19N.2.SL.TZ0.18", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c4-1-populations-and-communities", "c4-1-4-capture-mark-release-recapture-and-the-lincoln-index-to-estimate-population-size-for-motile-organisms" ] }, { "Question": "
\n
\n

\n Which is\n \n not\n \n essential in a viable mesocosm?\n

\n

\n A. Light source\n

\n

\n B. Autotroph\n

\n

\n C. Saprotroph\n

\n

\n D. Herbivore\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "19M.1A.SL.TZ2.19", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-2-stability-and-change", "d4-2-4-use-of-a-model-to-investigate-the-effect-of-variables-on-ecosystem-stability" ] }, { "Question": "
\n
\n

\n Which step occurs in\n \n both\n \n spermatogenesis and oogenesis?\n

\n

\n A.  First division of meiosis is stopped in prophase I until puberty begins.\n

\n

\n B.  Germinal epithelium cells divide by mitosis.\n

\n

\n C.  At the end of the first division in meiosis, the cytoplasm is divided equally between daughter cells.\n

\n

\n D.  Four haploid gametes are produced at the end of meiosis II.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "22N.1A.HL.TZ0.39", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-1-reproduction", "d3-1-4-anatomy-of-the-human-male-and-female-reproductive-systems" ] }, { "Question": "
\n
\n (a.ii)\n
\n
\n

\n Suggest\n \n two\n \n possible reasons for the change in distribution.\n

\n

\n 1.\n

\n

\n 2.\n

\n

\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. no predators ✔\n

\n

\n b. ample food supply/habitats ✔\n

\n

\n c. few competitors ✔\n

\n

\n d. resistant to disease ✔\n

\n

\n e. high reproductive rate ✔\n

\n

\n f. no physical barrier to prevent spread of grey squirrels on mainland ✔\n

\n
\n", "Examiners report": "
\n

\n This was answered well by only a few students even though the mark scheme allowed for a wide range of answers.\n

\n
\n", "question_id": "19M.2.SL.TZ1.17A.II", "topics": [ "b-form-and-function" ], "subtopics": [ "b4-2-ecological-niches", "b4-2-1-ecological-niche-as-the-role-of-a-species-in-an-ecosystem" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Outline a method that could have been used in this study to measure the numbers of sea urchins per 0.25 m\n \n 2\n \n .\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. with\n \n quadrats\n \n (of 0.5 m side / 0.25m\n \n 2\n \n );\n

\n

\n b. (quadrats) position determined at fixed distance by transects\n
\n \n \n OR\n \n \n
\n (quadrats) position determined at random;\n

\n

\n c. random sampling / capture-recapture;\n

\n

\n d. average number calculated;\n

\n
\n", "Examiners report": "
\n

\n Most candidates did well on this question, especially strong ones, although there was evidence that many candidates are not familiar with population evaluation skills. Candidates should be aware that writing \"quadrants\" (with a \"n\") is questionable, and that although it may not be assumed that they knew what echinoderms or sea urchins were, the capture-mark-release-recapture method was not really appropriate to evaluate their numbers, given the very limited areas of 0.25 m\n \n 2\n \n .\n

\n
\n", "question_id": "20N.2.SL.TZ0.15A", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c4-1-populations-and-communities", "c4-1-3-random-quadrat-sampling-to-estimate-population-size-for-sessile-organisms" ] }, { "Question": "
\n
\n (h)\n
\n
\n

\n Suggest a reason for the difference in the time observed eating and drinking.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n more food/energy eaten/required in winter/cold;\n
    2. \n
  2. \n food needed to maintain temperature/stay warm/generate heat;\n
    3. \n
  3. \n more loss of body heat in cold conditions;\n
    4. \n
  4. \n more energy used hunting for food;\n
    5. \n
  5. \n food less available in winter/harder to find enough food;\n
    6. \n
\n
\n", "Examiners report": "
\n

\n This was generally well answered, with candidates mostly focussing on food being harder to find in winter and more energy being needed to maintain body heat.\n

\n
\n", "question_id": "22N.2.HL.TZ0.1H", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-1-integration-of-body-systems", "c3-1-4-the-brain-as-a-central-information-integration-organ" ] }, { "Question": "
\n
\n

\n On the diagrams, label with a letter E a vesicle involved in exocytosis.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n an exocytic vesicle shown ✔\n

\n

\n \n For 2 a, i, ii and iii, accept letters written on the structure even if a line is not drawn.\n \n

\n

\n \n Award the mark if the full word is used to label the structure. Labels must be unambiguous.\n \n

\n

\n \n Accept any of the three intact circles or the exocytosis shown within the box.\n \n

\n
\n", "Examiners report": "None", "question_id": "21M.2.HL.TZ2.A.II", "topics": [ "b-form-and-function" ], "subtopics": [ "b2-1-membranes-and-membrane-transport", "b2-1-13-membrane-fluidity-and-the-fusion-and-formation-of-vesicles" ] }, { "Question": "
\n
\n

\n The graph shows the activity of an enzyme at various temperatures. The pH of the experiment was kept constant at pH 8.\n

\n

\n \n

\n

\n Based on the data, what would the result be if the experiment was repeated at pH 9?\n

\n

\n A. The enzyme activity would be higher.\n

\n

\n B. The results of the enzyme activity would be almost the same.\n

\n

\n C. The enzyme activity would be lower.\n

\n

\n D. There is not enough information to make a reliable prediction.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "22M.1A.SL.TZ1.5", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-1-enzymes-and-metabolism", "c1-1-8-effects-of-temperature-ph-and-substrate-concentration-on-the-rate-of-enzyme-activity" ] }, { "Question": "
\n
\n

\n Suggest a reason for the changes in mass in the colonies between weeks 6 and 8.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n less production of honey/wax;\n
    2. \n
  2. \n fewer bees/dispersal of bees/queens;\n
    3. \n
  3. \n bad weather/environmental change/predators/disease/pests;\n
    4. \n
\n
\n", "Examiners report": "None", "question_id": "22M.2.HL.TZ2.A.IV", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c2-2-neural-signalling", "c2-2-12-effects-of-exogenous-chemicals-on-synaptic-transmission" ] }, { "Question": "
\n
\n

\n The number of protein-coding genes in the human genome is estimated to be about 20 000, which is much less than the size of the proteome. What is one reason for this?\n

\n

\n A. Exons are removed from RNA before translation.\n

\n

\n B. There are more types of amino acids than nucleotides.\n

\n

\n C. mRNA can be spliced after transcription.\n

\n

\n D. Base substitutions occur during transcription.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "20N.1A.HL.TZ0.26", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-2-gene-expression-[hl-only]", "d2-2-5-differences-between-the-genome-transcriptome-and-proteome-of-individual-cells" ] }, { "Question": "
\n
\n

\n By referring to both graphs, evaluate the hypothesis that vinblastine targets cells in mitosis and prevents them from completing the process.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n \n Evaluation of evidence in graph on left\n \n

\n

\n a. increase in (percentage of) cells in mitosis (as vinblastine concentration rises) ✔\n

\n

\n b. supports hypothesis that cells get stuck in/cannot complete mitosis ✔\n

\n

\n \n Evaluation of evidence in graph on right\n \n

\n

\n c. drop in anaphase-metaphase ratio due to fewer cells in anaphase/more cells in metaphase ✔\n

\n

\n d. cells not progressing from metaphase to anaphase/get stuck in metaphase ✔\n

\n

\n \n Do not allow mpa if the candidate is arguing that the hypothesis is not supported\n \n .\n

\n
\n", "Examiners report": "
\n

\n This was another challenging data-analysis task with marks spread across the whole range, but full marks were rarely awarded. Many candidates thought that a rise in mitotic index had to mean that more cells were entering mitosis and they failed to deduce from the drop to zero of the anaphase-metaphase ratio that cells were getting stuck in metaphase. As in (d), it was necessary both to understand how cells progress through the cell cycle and be able to make deductions from trends in quantitative data.\n

\n
\n", "question_id": "21M.1B.SL.TZ1.E", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-1-cell-and-nuclear-division", "d2-1-1-generation-of-new-cells-in-living-organisms-by-cell-division" ] }, { "Question": "
\n
\n (f.ii)\n
\n
\n

\n Suggest possible reasons for the observed pattern of presence of antibodies in vaccinated mice.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n a. low antibody level initially as mice not previously exposed to antigen/bacteria ✔\n

\n

\n b. vaccination causes antibody production/development of immunity ✔\n

\n

\n c. increased proportion of mice have been vaccinated in each successive month ✔\n

\n

\n d. second vaccination/booster shot increases antibody level/speeds up antibody production ✔\n

\n

\n e.\n \n memory cells\n \n produced so greater/faster antibody production ✔\n

\n

\n f. many/rising numbers of nymphs which may spread the bacteria/antigens to mice ✔\n

\n

\n \n Ignore any references to non-vaccinated/control mice – this means that no marks are awarded for them because the question is about vaccinated mice, but there is no penalty for including this information in an answer\n \n .\n

\n
\n", "Examiners report": "None", "question_id": "19N.2.SL.TZ0.1F.II", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-2-defence-against-disease", "c3-2-8-activation-of-b-lymphocytes-by-helper-t-lymphocytes" ] }, { "Question": "
\n
\n

\n Scientists studying ground finches (\n \n Geospiza fortis\n \n ) on the island of Daphne Major in Galapagos found great differences in the shapes of the beaks.\n

\n

\n \n

\n

\n [Source: Public domain.]\n

\n

\n What is the explanation for this variation in beak shape between the birds?\n

\n

\n A. Ground finches grow larger beaks if there is competition for food.\n

\n

\n B. They belong to different species.\n

\n

\n C. They are adapted for different diets.\n

\n

\n D. The more a beak is used by a ground finch, the larger it becomes.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "21N.1A.SL.TZ0.21", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a4-1-evolution-and-speciation", "a4-1-1-evolution-as-change-in-the-heritable-characteristics-of-a-population" ] }, { "Question": "
\n
\n

\n Which gases have made the most significant contributions to global warming?\n

\n

\n A. Water and carbon dioxide\n

\n

\n B. Carbon dioxide and methane\n

\n

\n C. Methane and nitrous oxide\n

\n

\n D. Carbon dioxide and ozone\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "
\n

\n Though most candidates opted for answer B (carbon dioxide and methane), the question discriminated well with the better students correctly giving response A (water and carbon dioxide). This should have been one of the easier questions as the required knowledge came directly from 4.4 in the guide (Climate change):\n

\n

\n Carbon dioxide and water vapour are the most significant greenhouse gases.\n

\n

\n Other gases including methane and nitrogen oxides have less impact.\n

\n

\n The use of the term water rather than water vapour may have confused some candidates.\n

\n
\n", "question_id": "21M.1A.SL.TZ2.19", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-3-climate-change", "d4-3-1-anthropogenic-causes-of-climate-change" ] }, { "Question": "
\n
\n

\n Explain how cardiac muscle is adapted to its function.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n many mitochondria for aerobic respiration;\n
    2. \n
  2. \n cells are branched allowing for faster transmission/allow impulse to spread;\n
    3. \n
  3. \n cardiac muscle is myogenic so does not require the CNS to initiate contraction;\n
    4. \n
  4. \n cells are not fused together/are connected by gap junctions/intercalated discs (which) allows easier transmission between cells;\n
    5. \n
\n
\n", "Examiners report": "None", "question_id": "23M.2.HL.TZ1.D", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-2-transport", "b3-2-15-adaptations-of-the-mammalian-heart-for-delivering-pressurized-blood-to-the-arteries" ] }, { "Question": "
\n
\n (a.ii)\n
\n
\n

\n Identify the root length, as a percentage of the control, resulting from a ZDV concentration of\n \n \n 400\n \n \n \n \n μmol\n \n \n .\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n 24 % ✔\n

\n

\n \n Allow answers in the range 23 %–25 %\n \n .\n

\n
\n", "Examiners report": "
\n

\n Part (ii) was better answered than part (i) as many answers provided were outside the acceptable range of answers.\n

\n
\n", "question_id": "21M.2.HL.TZ1.1A.II", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a2-3-viruses-(hl-only)", "a2-3-6-rapid-evolution-in-viruses" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Explain how hydrophobic and hydrophilic properties contribute to the arrangement of molecules in a membrane.\n

\n
\n
\n

\n [7]\n

\n
\n
\n", "Markscheme": "
\n

\n a. hydrophilic is attracted to/soluble in water and hydrophobic not attracted/insoluble ✔\n

\n

\n b. hydrophilic phosphate/head and hydrophobic hydrocarbon/tail in\n \n phospholipids\n \n ✔\n

\n

\n c.\n \n phospholipid bilayer\n \n in water/in membranes ✔\n

\n

\n d. hydrophilic heads «of phospholipids» face outwards/are on surface ✔\n

\n

\n e. hydrophobic tails «of phospholipids» face inwards/are inside/are in core ✔\n

\n

\n f. cholesterol is «mainly» hydrophobic/amphipathic so is located among phospholipids/in hydrophobic region of membrane ✔\n

\n

\n g. some amino acids are hydrophilic and some are hydrophobic ✔\n

\n

\n h. hydrophobic «amino acids/regions of» proteins in phospholipid bilayer «core» ✔\n

\n

\n i. hydrophilic «amino acids/regions of» proteins are on the membrane surface ✔\n

\n

\n j.\n \n integral proteins\n \n are embedded in membranes due to hydrophobic properties/region\n
\n \n \n OR\n \n \n
\n \n transmembrane\n \n proteins have a hydrophobic middle region and hydrophilic ends ✔\n

\n

\n k.\n \n peripheral proteins\n \n on are on the membrane surface/among phosphate heads due to being «entirely» hydrophilic\n
\n \n \n OR\n \n \n
\n «carbohydrate» part of\n \n glycoproteins\n \n is hydrophilic so is outside the membrane ✔\n

\n

\n l. pore of\n \n channel proteins\n \n is hydrophilic ✔\n

\n

\n \n Allow mark points shown in clearly annotated diagram.\n \n

\n

\n \n In any part of the answer, accept polar instead of hydrophilic and non-polar or apolar instead of hydrophobic.\n \n

\n
\n", "Examiners report": "
\n

\n Candidates struggled to explain the meaning of the term hydrophobic. Many stated the literal meaning – water-fearing, hence repelled by water. This was not accepted as hydrophobic molecules aren’t repelled by water. They appear to be, because water is more attracted to polar or ionic substances than to apolar/hydrophobic substances, but there is no chemical mechanism for repulsion and of course molecules do not fear each other. Many focused only on phospholipids, but stronger answers also included information on proteins and how the positions they occupy within the membrane depend on their hydrophobic and hydrophilic properties.\n

\n
\n", "question_id": "19M.2.SL.TZ1.5C", "topics": [ "c-interaction-and-interdependence", "b-form-and-function" ], "subtopics": [ "c2-1-chemical-signalling-[hl-only]", "c2-1-6-differences-between-transmembrane-receptors-in-a-plasma-membrane-and-intracellular-receptors-in-the-cytoplasm-or-nucleus", "b2-1-membranes-and-membrane-transport", "b2-1-10-fluid-mosaic-model-of-membrane-structure" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Describe how human activities have caused average surface air temperatures on Earth to increase.\n

\n
\n
\n

\n [7]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n release of carbon dioxide;\n
    2. \n
  2. \n combustion of fossil fuels produces carbon dioxide;\n
    3. \n
  3. \n forest fires (caused by humans) produce carbon dioxide;\n
    4. \n
  4. \n deforestation reduces carbon dioxide uptake by photosynthesis;\n
    5. \n
  5. \n release of methane;\n
    6. \n
  6. \n from cattle/sheep/ruminant digestive systems / other verified source of anthropogenic methane;\n
    7. \n
  7. \n greenhouse effect / carbon dioxide/methane is a greenhouse gas;\n
    8. \n
  8. \n carbon dioxide/methane allow short wave radiation in sunlight to pass through the atmosphere;\n
    9. \n
  9. \n longer wave/infra-red radiation emitted by the warmed Earth’s surface;\n
    10. \n
  10. \n carbon dioxide/methane absorbs/reflects back longer wave/infra-red radiation;\n
    11. \n
\n

\n

\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ2.6C", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-3-climate-change", "d4-3-1-anthropogenic-causes-of-climate-change" ] }, { "Question": "
\n
\n

\n How does HIV affect the immune system adversely?\n

\n

\n A. Progressive reduction in number of active lymphocytes\n

\n

\n B. Continuous overproduction of antibodies\n

\n

\n C. Rapid production of clone of plasma cells\n

\n

\n D. Immediate development of AIDS\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "None", "question_id": "19N.1A.SL.TZ0.22", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-2-defence-against-disease", "c3-2-12-infection-of-lymphocytes-by-hiv-with-aids-as-a-consequence" ] }, { "Question": "
\n
\n

\n What are the functions of DNA primase and DNA polymerase I in DNA replication?\n

\n

\n \n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "
\n

\n In Topic 7.1 it says that the proteins and enzymes involved in DNA replication should include helicase, DNA gyrase, single strand binding proteins, DNA primase and DNA polymerases I and III. There was a complaint in the G2s mentioning that DNA primase is really RNA primase. This is a misunderstanding, as it is really an RNA polymerase. This question showed the highest discrimination index.\n

\n
\n", "question_id": "19M.1A.HL.TZ2.12", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d1-1-dna-replication", "d1-1-8-functions-of-dna-primase-dna-polymerase-i-dna-polymerase-iii-and-dna-ligase-in-replication" ] }, { "Question": "
\n
\n

\n The diagram shows two polysaccharides, formed from condensation of many glucose molecules.\n

\n

\n \n

\n

\n [Source: © International Baccalaureate Organization 2019]\n

\n

\n

\n

\n What are the names of X and Y?\n

\n

\n \n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "
\n

\n Many candidates wrongly believed the diagram of X could easily be amylopectin (instead of glycogen) whilst Y has to be amylose, this led to students spending more time on the question. Some candidates confused amylose with the enzyme amylase, but the question clearly stated that two carbohydrates were shown.\n

\n
\n", "question_id": "19M.1A.SL.TZ2.7", "topics": [ "b-form-and-function" ], "subtopics": [ "b1-1-carbohydrates-and-lipids", "b1-1-2-production-of-macromolecules-by-condensation-reactions-that-link-monomers-to-form-a-polymer" ] }, { "Question": "
\n
\n

\n Identify the stage of mitosis labelled X in the image, giving a reason.\n

\n

\n \n

\n

\n [Source: Copyright 2002, The Trustees of Indiana University]\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n telophase because the chromosomes/chromatids have reached the poles\n
\n \n \n OR\n \n \n
\n «late» anaphase as some chromosomes/chromatids are still moving/tails visible ✔\n

\n

\n \n OWTTE\n \n

\n
\n", "Examiners report": "
\n

\n Both anaphase and telophase were accepted as answers, but students had difficulty providing a reason that was an appropriate justification; for example, students might say telophase and then support this with the statement because chromatids are seen moving to opposite poles. Students sometimes referred to chromatids as homologous chromosomes. As this is an image of plant cells, students would be mistaken by referring to a cleavage furrow. The mechanism of cytokinesis involves the formation of a cell plate.\n

\n
\n", "question_id": "19M.2.SL.TZ2.A.I", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-1-cell-and-nuclear-division", "d2-1-8-identification-of-phases-of-mitosis" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Explain how natural selection could increase the prevalence of an antibiotic resistance gene in a species of soil bacterium.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n if antibiotic is in the environment/soil there is selection (pressure);\n
    2. \n
  2. \n bacteria without resistance (gene) die / converse;\n
    3. \n
  3. \n bacteria with resistance (gene) reproduce\n
    \n \n OR\n \n
    \n bacteria exchange/obtain resistance genes using plasmids/by conjugation;\n
    4. \n
  4. \n offspring inherit (the gene for) resistance/resistance passed on (to offspring);\n
    5. \n
\n

\n \n Do not award marks for general statements about natural selection – answers must refer to antibiotic resistance.\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.2.HL.TZ1.3A", "topics": [ "d-continuity-and-change", "c-interaction-and-interdependence" ], "subtopics": [ "d4-1-natural-selection", "d4-1-15-artificial-selection-by-deliberate-choice-of-traits", "c3-2-defence-against-disease", "c3-2-14-evolution-of-resistance-to-several-antibiotics-in-strains-of-pathogenic-bacteria" ] }, { "Question": "
\n
\n

\n What are all the possible phenotypes of children born to a mother with blood group AB and a father with blood group A?\n

\n

\n A. AB only\n

\n

\n B. A and B\n

\n

\n C. AB, A and B\n

\n

\n D. AB, A and O\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "20N.1A.SL.TZ0.15", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-2-inheritance", "d3-2-9-abo-blood-groups-as-an-example-of-multiple-alleles" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Deduce from the results of the study whether HGH improves strength.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n the drug does not appear to improve strength as less mass can be lifted «by arms and legs» ✔\n

\n
\n", "Examiners report": "
\n

\n While this was generally done well, those who missed this mark chose to write about muscle growth rather than the mass being lifted.\n

\n
\n", "question_id": "19M.2.HL.TZ1.20A", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c2-1-chemical-signalling-[hl-only]", "c2-1-10-mechanism-of-action-of-epinephrine-(adrenaline)-receptors" ] }, { "Question": "
\n
\n

\n The electron micrograph shows a transverse section through a myelinated neuron.\n

\n

\n \n

\n

\n [Source: Transmission electron micrograph of a myelinated axon.\n \n https://commons.wikimedia.org/wiki/File:Myelinated_neuron.jpg\n \n . This file is licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license (\n \n https://creativecommons.org/licenses/by-sa/3.0/deed.en\n \n ).]\n

\n

\n What process is facilitated by the presence of the structure labelled X?\n

\n

\n A. Repolarization of the nerve cell membrane\n

\n

\n B. Generation of an action potential\n

\n

\n C. Saltatory conduction\n

\n

\n D. Synaptic transmission\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "
\n

\n This question discriminated well with the stronger candidates answering correctly and the weaker candidates selecting response D Synaptic transmission.\n

\n
\n", "question_id": "21M.1A.SL.TZ2.24", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c2-2-neural-signalling", "c2-2-4-variation-in-the-speed-of-nerve-impulses" ] }, { "Question": "
\n
\n

\n Identify, with a reason, the stage shown at X.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n anaphase;\n
    2. \n
  2. \n the (replicated) chromosomes/chromatids are separating/moving to opposite poles of the cell;\n
    3. \n
\n

\n \n OWTTE\n \n

\n
\n", "Examiners report": "
\n

\n This question was generally well done; a few identified the incorrect phase of mitosis, but the observations about cellular events being observed was often correct.\n

\n
\n", "question_id": "22M.2.SL.TZ2.A.I", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-1-cell-and-nuclear-division", "d2-1-8-identification-of-phases-of-mitosis" ] }, { "Question": "
\n
\n

\n The micrograph shows part of a human sperm cell. Which region of the cell is responsible for the greatest production of ATP?\n

\n

\n \n

\n

\n [Source: Oliveira, J.B.A., Petersen, C.G., Massaro, F.C. et al. Motile sperm organelle morphology examination (MSOME):\n
\n intervariation study of normal sperm and sperm with large nuclear vacuoles.\n \n Reprod Biol Endocrinol\n \n 8, 56 (2010).\n
\n https://doi.org/10.1186/1477-7827-8-56.\n \n https://embryology.med.unsw.edu.au/embryology/index.php/File:Single_\n \n
\n \n human_spermatozoa.jpg\n \n Creative Commons Attribution License (CC BY 2.0) (\n \n http://creativecommons.org/licenses/\n \n
\n \n by/2.0\n \n ).]\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "21N.1A.HL.TZ1.40", "topics": [ "b-form-and-function" ], "subtopics": [ "b2-3-cell-specialization", "b2-3-10-adaptations-of-sperm-and-egg-cells" ] }, { "Question": "
\n
\n

\n The pregnancy test for humans is based on detection of the hormone HCG. What is the reason for detection of this hormone indicating pregnancy?\n

\n

\n A. HCG is involved in milk production.\n

\n

\n B. HCG production is blocked by negative feedback during menstruation.\n

\n

\n C. HCG is produced by an embryo.\n

\n

\n D. HCG is released during the acrosome reaction.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "
\n

\n The basis for this question was an Application in 11.1 (Antibody production and vaccination). Even if candidates did not know that it is the embryo that secretes HCG, they should have been able to eliminate the three distractors and then realise that HCG production by embryos must be the answer.\n

\n
\n", "question_id": "21M.1A.HL.TZ1.39", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-1-reproduction", "d3-1-17-pregnancy-testing-by-detection-of-human-chorionic-gonadotropin-secretion" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Describe how autotrophs absorb light energy\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n a. light absorbed by (photosynthetic)\n \n pigments\n \n ;\n

\n

\n b. chlorophyll absorbs blue and red / drawing of absorption spectrum for chlorophyll;\n

\n

\n c. photosystems are groups of pigment molecules/are light harvesting complexes;\n

\n

\n d. photosystems are located in thylakoid membranes;\n

\n

\n e. electrons excited/raised to higher energy level;\n

\n
\n", "Examiners report": "
\n

\n As this question was near the end of Section A, the mark scheme was constructed so as to reward stronger answers, rather than simple ideas such as ‘light is absorbed by chlorophyll’. Answers were very varied. Few candidates including any ideas about photosystems.\n

\n
\n", "question_id": "20N.2.SL.TZ0.4C", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c4-2-transfers-of-energy-and-matter", "c4-2-6-autotrophs-as-organisms-that-use-external-energy-sources-to-synthesize-carbon-compounds-from-simple-inorganic-substances", "c4-2-7-use-of-light-as-the-external-energy-source-in-photoautotrophs-and-oxidation-reactions-as-the-energy-source-in-chemoautotrophs" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Explain how vesicles are used by cells to move materials.\n

\n
\n
\n

\n [5]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n fluidity of membranes allows vesicles to bud off membranes/fuse with membranes;\n
    2. \n
  2. \n materials taken into cells by endocytosis/vesicle formation;\n
    3. \n
  3. \n \n Paramecium\n \n takes in food / phagocytes engulf pathogens / another example;\n
    4. \n
  4. \n materials released from cells by exocytosis/by vesicle fusing with plasma membrane;\n
    5. \n
  5. \n neurotransmitter released at synapses / protein secretion / secretion from gland cell / another example;\n
    6. \n
  6. \n movement/transport of materials (inside vesicles) within cells/through the cytoplasm/between organelles/from an organelle to the (plasma)membrane/from the (plasma) membrane to an organelle;\n
    7. \n
  7. \n movement of proteins from the rough ER to the Golgi / another example;\n
    8. \n
\n
\n", "Examiners report": "None", "question_id": "23M.2.HL.TZ1.8", "topics": [ "b-form-and-function" ], "subtopics": [ "b2-2-organelles-and-compartmentalization", "b2-2-9-structure-and-function-of-vesicles-in-cells", "b3-2-transport", "b3-2-18-adaptations-of-phloem-sieve-tubes-and-companion-cells-for-translocation-of-sap" ] }, { "Question": "
\n
\n

\n What occurs at gas exchange surfaces in the lungs of mammals?\n

\n

\n
\n I.  Gases diffuse across a moist surface.\n
\n II.  Concentration gradients are maintained by ventilation.\n
\n III.  Water is lost.\n

\n

\n
\n A.  I and II only\n

\n

\n B.  I and III only\n

\n

\n C.  II and III only\n

\n

\n D.  I, II and III\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "SPM.1A.SL.TZ0.17", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-1-gas-exchange", "b3-1-2-properties-of-gas-exchange-surfaces", "b3-1-4-adaptations-of-mammalian-lungs-for-gas-exchange" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Explain how a newly discovered plant species would be classified and named.\n

\n
\n
\n

\n [7]\n

\n
\n
\n", "Markscheme": "
\n

\n Naming:\n

\n
    \n
  1. \n binomial nomenclature/(plant is) given a binomial/double name;\n
    2. \n
  2. \n first name is the genus and second name is the species/genus initial uppercase and species lower case;\n
    3. \n
  3. \n names (of plant species) are international/are universally understood/are published in journals;\n
    \n
    \n Classification:\n
    \n
    \n
    4. \n
  4. \n study the characteristics/structure/reproduction/chemical properties/DNA (of the plant);\n
    5. \n
  5. \n put/classify (the plant) in a group/genus with other similar species;\n
    6. \n
  6. \n natural classification corresponds with evolution/natural classification is based on many features;\n
    7. \n
  7. \n analogous features/features due to convergent evolution should not be used;\n
    8. \n
  8. \n hierarchy of groups/taxa (in traditional classification/3 or more taxa in correct sequence (kingdom-phylum-class);\n
    9. \n
  9. \n two or more of bryophyta, filicinophyta, coniferophyta and angiospermophyta named;\n
    10. \n
  10. \n a clade is a group of organisms evolved from a common ancestor;\n
    11. \n
  11. \n base sequences/amino acid sequences used to group organisms into clades/deduce evolutionary relationships;\n
    12. \n
  12. \n cladograms show the relationships between clades/likely evolutionary divergence of clades;\n
    13. \n
  13. \n each branch point/node represents where species are formed via divergent evolution;\n
    14. \n
  14. \n species are now classified into a sequence of clades (rather than a rigid hierarchy of taxa);\n
    15. \n
\n

\n \n For mpi, common names such as ‘mosses’ are acceptable\n \n .\n

\n
\n", "Examiners report": "
\n

\n A very wide range of ideas was credited with marks in this question. Most candidates knew that plants are either classified according to their observable traits or the base sequences of their DNA. Many answers also included the hierarchy of taxa used in traditional classification and traits of plant phyla. At least some features of binomial nomenclature were included in most answers. The best answers included changes to plant classification that have resulted from sequence analysis and cladistics.\n

\n
\n", "question_id": "22N.2.HL.TZ0.8C", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a3-2-classification-and-cladistics-(hl-only)", "a3-2-1-need-for-classification-of-organisms", "a3-2-9-classification-of-all-organisms-into-three-domains-using-evidence-from-rrna-base-sequences" ] }, { "Question": "
\n
\n

\n The diagram shows the structure of a nucleosome.\n

\n

\n \n

\n

\n [Source: Zephyris. Nucleosome 1KX5 colour coded. Available at\n \n https://en.wikipedia.org/wiki/Nucleosome#/media/File:Nucleosome_1KX5_colour_coded.png\n \n
\n This file is licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license (\n \n https://creativecommons.org/licenses/by-sa/3.0/deed.en\n \n ).]\n

\n

\n

\n

\n What is the structure labelled T?\n

\n

\n A. 5' end of RNA\n

\n

\n B. 5' end of uncoiled DNA\n

\n

\n C. N-terminal tail of one DNA strand\n

\n

\n D. N-terminal tail of one histone\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "
\n

\n This question received some criticism in the comments on the G2 forms. It was suggested that this question was too difficult for IB level students, the diagram was not clear and the term ‘N terminal tail’ was out of the scope of the IB guide. The question related to 7.1 in the biology guide “Utilization of molecular visualization software to analyse the association between protein and DNA within a nucleosome”. Despite criticism, the question did discriminate well, possibly because the more able students were able to eliminate the incorrect responses by looking at the diagram leaving response D as the correct response. It is understood that questions on multiple choice tests would not normally be expected to be answered by this means.\n

\n
\n", "question_id": "22M.1A.HL.TZ2.26", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a1-2-nucleic-acids", "a1-2-13-structure-of-a-nucleosome" ] }, { "Question": "
\n
\n

\n Explain how evolution by natural selection depends on mutations.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n

\n a. mutations cause variation among organisms of same species/population;\n

\n

\n b. some variations/mutations make individual more suited to its environment/way of life;\n

\n

\n c. individuals that are better adapted survive and produce offspring;\n

\n

\n d. individuals pass on genetic characteristics/mutation/variation to offspring;\n

\n

\n e. natural selection increases frequency of characteristics/alleles that make individuals better adapted;\n

\n
\n", "Examiners report": "None", "question_id": "20N.2.SL.TZ0.B.II", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-1-natural-selection", "d4-1-2-roles-of-mutation-and-sexual-reproduction-in-generating-the-variation-on-which-natural-selection-acts" ] }, { "Question": "
\n
\n

\n Humans have been improving crop species for thousands of years by cross-breeding plants with desirable characteristics. The photograph shows the changes in dry cobs of corn (\n \n Zea mays\n \n ) over 10 000 years.\n

\n

\n \n

\n

\n [Source: Evolution of Maize Cobs © Robert S. Peabody Institute of Archaeology,\n
\n Phillips Academy, Andover, Massachusetts. All Rights Reserved.]\n

\n

\n

\n

\n What is the name of the process that was used to produce modern corn?\n

\n

\n A. Selective breeding\n

\n

\n B. Adaptive radiation\n

\n

\n C. Discontinuous variation\n

\n

\n D. Natural selection\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "None", "question_id": "22M.1A.SL.TZ2.20", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a4-1-evolution-and-speciation", "a4-1-3-evidence-for-evolution-from-selective-breeding-of-domesticated-animals-and-crop-plants" ] }, { "Question": "
\n
\n

\n What is a consequence of the ability of water to form many intermolecular hydrogen bonds?\n

\n

\n
\n A.  Ice has a higher density than water and floats, providing habitats for fish-eating mammals.\n

\n

\n B.  Light can pass through water, so algae can photosynthesise.\n

\n

\n C.  Some small invertebrates can walk on water surfaces.\n

\n

\n D.  Small amounts of energy are needed to change water from one state to another, so that evaporation rates and  condensation rates are rapid.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "SPM.1A.SL.TZ0.2", "topics": [ "b-form-and-function" ], "subtopics": [ "b1-1-carbohydrates-and-lipids", "b1-1-9-formation-of-triglycerides-and-phospholipids-by-condensation-reactions" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n State\n \n one\n \n other variable that should have been controlled in this study.\n

\n

\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n age/height/fitness level/weight/room temperature/rest in between tests/model or type of bike ✔\n

\n

\n \n Other valid factor. Only mark first factor listed.\n \n

\n

\n \n Do not accept sex, health, smoking, oxygen level or altitude as this already listed.\n \n

\n
\n", "Examiners report": "
\n

\n In this question the candidates were asked to look at data on the effect of exercise and altitude on ventilation rate. Most candidates could state one other variable that should have been controlled in this study.\n

\n
\n", "question_id": "19M.1B.SL.TZ2.3A", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-1-gas-exchange", "b3-1-5-ventilation-of-the-lungs" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Outline\n \n four\n \n different processes,\n \n with examples\n \n , that allow substances to pass through the plasma membrane.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n simple/passive diffusion\n \n down a concentration gradient\n \n /\n \n from high concentration to low concentration\n \n (without the use of channels/proteins); (\n \n e.g., CO\n \n 2\n \n / O\n \n 2\n \n / H\n \n 2\n \n O / steroid hormones\n \n )\n
    2. \n
  2. \n osmosis is the diffusion of\n \n water\n \n from an area of high water potential / low solute concentration to low water potential / high solute concentration;\n
    3. \n
  3. \n facilitated diffusion is passive transport/diffusion through a protein channel; (\n \n e.g., glucose\n \n )\n
    4. \n
  4. \n active transport requires energy/ATP to move the molecules through a protein channel (\n \n e.g., Na-K pump / sodium potassium pump\n \n )\n \n against a concentration gradient\n \n /\n \n from low solute concentration to high concentration\n \n ;\n
    5. \n
  5. \n endocytosis is the infolding of membranes to form a vesicle and take in a large molecule; (\n \n e.g., macrophages engulfing pathogens\n \n )\n
    6. \n
  6. \n exocytosis is the fusion of vesicles with membranes to release a large molecule; (\n \n e.g. neurotransmitters\n \n )\n
    7. \n
\n
\n", "Examiners report": "
\n

\n This question in section B was the second most commonly selected, but in performance, tended to do more poorly than the other questions.\n

\n

\n Most candidates could list the processes that allow passage across the plasma membrane, but many answers lacked some of the necessary elements, most commonly leaving out examples (e.g. an example for gradient).\n

\n
\n", "question_id": "22M.2.HL.TZ2.8", "topics": [ "b-form-and-function", "d-continuity-and-change" ], "subtopics": [ "b2-1-membranes-and-membrane-transport", "b2-1-3-simple-diffusion-across-membranes", "b2-1-4-integral-and-peripheral-proteins-in-membranes", "b2-1-5-movement-of-water-molecules-across-membranes-by-osmosis-and-the-role-of-aquaporins", "b2-1-6-channel-proteins-for-facilitated-diffusion", "b2-1-7-pump-proteins-for-active-transport", "b2-1-8-selectivity-in-membrane-permeability", "d3-3-homeostasis", "d3-3-7-role-of-the-kidney-in-osmoregulation-and-excretion", "b4-1-adaptation-to-environment", "b4-1-8-adaptations-to-life-in-hot-deserts-and-tropical-rainforest" ] }, { "Question": "
\n
\n (h)\n
\n
\n

\n State the relationship between high lipid content and survivability on day 7.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n the higher the lipid content, the fewer bees survived/negative correlation;\n

\n
\n", "Examiners report": "None", "question_id": "22N.2.SL.TZ0.1H", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c4-2-transfers-of-energy-and-matter", "c4-2-15-primary-production-as-accumulation-of-carbon-compounds-in-biomass-by-autotrophs", "c4-2-16-secondary-production-as-accumulation-of-carbon-compounds-in-biomass-by-heterotrophs" ] }, { "Question": "
\n
\n

\n Explain how sexual reproduction gives rise to genetic variation.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n recombination of parental alleles during fertilization;\n
    2. \n
  2. \n fertilized egg contains a mixture of paternal and maternal chromosomes;\n
    3. \n
  3. \n crossing over/meiosis gives rise to new combinations of alleles;\n
    4. \n
\n
\n", "Examiners report": "None", "question_id": "SPM.2.SL.TZ0.B", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-1-natural-selection", "d4-1-2-roles-of-mutation-and-sexual-reproduction-in-generating-the-variation-on-which-natural-selection-acts", "d1-3-mutations-and-gene-editing", "d1-3-7-mutation-as-a-source-of-genetic-variation" ] }, { "Question": "
\n
\n

\n Which term describes the whole of the genetic information of an organism?\n

\n

\n
\n A.  Genome\n

\n

\n B.  DNA\n

\n

\n C.  Gene pool\n

\n

\n D.  Allele frequency\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "None", "question_id": "SPM.1A.SL.TZ0.16", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a3-1-diversity-of-organisms", "a3-1-8-unity-and-diversity-of-genomes-within-species" ] }, { "Question": "
\n
\n

\n The table shows the mRNA codons for three amino acids.\n

\n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n
\n \n Valine\n \n \n \n Threonine\n \n \n \n Proline\n \n
\n GUU\n \n ACU\n \n CCU\n
\n GCC\n \n ACC\n \n CCC\n
\n GCA\n \n ACA\n \n CGA\n
\n GCG\n \n ACG\n \n CCG\n
\n

\n Which substitution mutation of a base triplet on a DNA strand will lead to the same polypeptide being formed at translation?\n

\n

\n
\n A.  TGA to TCA\n

\n

\n B.  CGT to CTA\n

\n

\n C.  CAA to CGA\n

\n

\n D.  GCT to GGA\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "SPM.1A.HL.TZ0.11", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d1-3-mutations-and-gene-editing", "d1-3-1-gene-mutations-as-structural-changes-to-genes-at-the-molecular-level", "d1-3-2-consequences-of-base-substitutions" ] }, { "Question": "
\n
\n

\n A molecule of DNA is found to contain 200 guanine bases, representing 25 % of the total number of bases. How many phosphate groups does this molecule of DNA contain?\n

\n

\n A. 50\n

\n

\n B. 200\n

\n

\n C. 800\n

\n

\n D. 1000\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "22M.1A.SL.TZ1.9", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a1-2-nucleic-acids", "a1-2-3-sugar-phosphate-bonding-and-the-sugar-phosphate-“backbone”-of-dna-and-rna" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Distinguish between species richness and evenness as components of biodiversity.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n richness is how many species are in an area, evenness considers the relative number of each species;\n

\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ1.17C", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a4-1-evolution-and-speciation", "a4-1-9-adaptive-radiation-as-a-source-of-biodiversity" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Outline the reasons for the differences in blood concentrations between the renal artery and the renal vein.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n

\n a. urea/waste products lower in vein due to excretion «in urine»/ultrafiltration but not reabsorption ✔\n

\n

\n b. oxygen lower in vein due to use in cell respiration/in kidney tissue ✔\n

\n

\n c. carbon dioxide higher in vein due to production by cell respiration/excretion by kidney cells ✔\n

\n

\n d. glucose lower in vein due to use in cell respiration «by kidney tissue» ✔\n

\n

\n e. sodium/chloride/ion concentrations changed due to production of hypertonic/hypotonic urine\n
\n \n \n OR\n \n \n
\n sodium/chloride/ion concentrations lower due to removal of excess ✔\n

\n

\n f. ion/solute concentrations lower in vein than artery if ADH has been secreted\n
\n \n \n OR\n \n \n
\n ion/solute concentrations in vein vary depending on amount of water reabsorbed in the collecting duct ✔\n

\n

\n g. drug/toxin concentrations lower in vein due to excretion in urine ✔\n

\n

\n \n Accept any point given as the converse.\n \n

\n

\n \n Each mark point includes a difference and reason for it.\n \n

\n
\n", "Examiners report": "None", "question_id": "19N.2.HL.TZ0.7A", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-3-homeostasis", "d3-3-8-role-of-the-glomerulus-bowmans-capsule-and-proximal-convoluted-tubule-in-excretion" ] }, { "Question": "
\n
\n

\n Which statement applies to HIV?\n

\n

\n A. HIV infects red blood cells resulting in decreased production of hemoglobin.\n

\n

\n B. HIV can be effectively treated using antibiotics.\n

\n

\n C. HIV can only be transmitted by sexual intercourse.\n

\n

\n D. HIV causes a reduction in production of antibodies.\n

\n

\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "19M.1A.SL.TZ1.28", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-2-defence-against-disease", "c3-2-11-transmission-of-hiv-in-body-fluids", "c3-2-12-infection-of-lymphocytes-by-hiv-with-aids-as-a-consequence" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Explain the propagation of nerve impulses along the membrane of a neuron.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n a. depolarization of part of axon/membrane triggers/causes depolarization of next part;\n
\n b. local currents;\n
\n c. diffusion of sodium ions between depolarized part and next/polarized part (of axon);\n
\n d. resting potential reduced/polarization of membrane becomes less /change from -70 to -50mV;\n
\n e. sodium channels open when -50mV/threshold potential reached;\n
\n f. entry of sodium ions causes depolarization;\n
\n g. saltatory conduction in myelinated neurons/axons;\n

\n

\n \n Allow answers in an annotated diagram\n \n

\n
\n", "Examiners report": "
\n

\n This was a more difficult question with a much higher correlation coefficient. Many candidates did not understand what is meant by propagation of an impulse along the membrane of a neuron and answers tended to include accounts of the whole sequence of events in an action potential or in synaptic transmission. The mark most frequently awarded was for the mechanism of saltatory conduction.\n

\n
\n", "question_id": "21N.2.HL.TZ0.3C", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c2-2-neural-signalling", "c2-2-9-propagation-of-an-action-potential-along-a-nerve-fibre/axon-as-a-result-of-local-currents" ] }, { "Question": "
\n
\n

\n Cisplatin is an anti-cancer drug that prevents tumour cells from dividing by mitosis as it inhibits cell processes at stage S of interphase. How does cisplatin prevent cancer cells from dividing?\n

\n

\n A. It inhibits the replication of DNA.\n

\n

\n B. It inhibits the growth of the spindle fibres.\n

\n

\n C. It prevents the breakdown of the nuclear membrane.\n

\n

\n D. It prevents the condensation of chromosomes.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "None", "question_id": "22M.1A.HL.TZ2.5", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-1-cell-and-nuclear-division", "d2-1-13-phases-of-the-cell-cycle" ] }, { "Question": "
\n
\n (a.i)\n
\n
\n

\n Identify the site with the highest incidence of diseased colonies.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n Capricorn and Bunkers group;\n

\n
\n", "Examiners report": "
\n

\n In general, the data analysis question was well attempted by the majority of students. In 1a almost all were able to correctly name the Capricorn and Bunkers Group.\n

\n
\n", "question_id": "21N.2.SL.TZ0.1A.I", "topics": [ "d-continuity-and-change", "b-form-and-function" ], "subtopics": [ "d4-3-climate-change", "d4-3-7-threats-to-coral-reefs-as-an-example-of-potential-ecosystem-collapse", "b4-1-adaptation-to-environment", "b4-1-5-conditions-required-for-coral-reef-formation" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Outline the role of fungi in nutrient cycling.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. act as saprotrophs/decomposers ✔\n

\n

\n b. rot/feed on/break down organic matter/food/organisms\n
\n \n \n OR\n \n \n
\n return nutrients trapped in organic matter to the cycle/soil ✔\n

\n

\n \n Do not accept detritivores\n \n

\n
\n", "Examiners report": "None", "question_id": "19M.1B.SL.TZ1.2B", "topics": [ "b-form-and-function" ], "subtopics": [ "b4-2-ecological-niches", "b4-2-6-saprotrophic-nutrition-in-some-fungi-and-bacteria" ] }, { "Question": "
\n
\n

\n What is a property of arteries?\n

\n

\n A. Arteries have elastic walls.\n

\n

\n B. Arteries have valves.\n

\n

\n C. All arteries carry oxygenated blood.\n

\n

\n D. Arteries receive blood from the atria.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "None", "question_id": "21M.1A.SL.TZ1.27", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-2-transport", "b3-2-3-adaptations-of-arteries-for-the-transport-of-blood-away-from-the-heart" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Draw the structure of a dipeptide.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n a. two amino acids, one with NH\n \n 2\n \n /NH\n \n 3\n \n +end and one with COOH/COO– end ✔\n

\n

\n b. peptide bond between C=0 and N—H correctly drawn ✔\n

\n

\n c. «chiral» C with H and R group on each amino acid ✔\n

\n

\n d. peptide bond labelled/clearly indicated between C terminal of one amino acid and N terminal of the second amino acid ✔\n

\n

\n \n

\n

\n \n Labels not required for amino group and carboxyl group.\n \n

\n
\n", "Examiners report": "
\n

\n Structure of the dipeptide – candidates who also do chemistry were at an advantage here. Diagrams went from the superb to something Picasso might have produced.\n

\n
\n", "question_id": "19M.2.SL.TZ2.5B", "topics": [ "b-form-and-function" ], "subtopics": [ "b1-2-proteins", "b1-2-2-condensation-reactions-forming-dipeptides-and-longer-chains-of-amino-acids" ] }, { "Question": "
\n
\n (c.i)\n
\n
\n

\n State the name of the structure shown.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n synapse/synaptic\n

\n

\n \n Allow any answer including either of these terms unless out of context\n \n .\n

\n
\n", "Examiners report": "
\n

\n As pointed out on some G2 forms, the question here was rather ambiguous as it wasn’t 100 % clear what structure was referred to, so any answer indicating that the candidate knew the diagram showed a synapse was accepted.\n

\n
\n", "question_id": "20N.2.SL.TZ0.2C.I", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c2-2-neural-signalling", "c2-2-5-synapses-as-junctions-between-neurons-and-between-neurons-and-effector-cells" ] }, { "Question": "
\n
\n

\n State the property of amphipathic phospholipids that enables them to form a bilayer.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n have both a hydrophilic and a hydrophobic region\n
\n \n \n OR\n \n \n
\n have both a polar and a non-polar region ✔\n

\n
\n", "Examiners report": "None", "question_id": "19N.2.SL.TZ0.A.I", "topics": [ "b-form-and-function" ], "subtopics": [ "b1-1-carbohydrates-and-lipids", "b1-1-12-formation-of-phospholipid-bilayers-as-a-consequence-of-the-hydrophobic-and-hydrophilic-regions" ] }, { "Question": "
\n
\n (c.i)\n
\n
\n

\n \n B. subtilis\n \n colonies form biofilms through quorum sensing. Define quorum sensing.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n «a system of» behaviours triggered as a function of population density ✔\n

\n
\n", "Examiners report": "
\n

\n This question was a good discriminator, as weaker students were unable to use correct terminology such as “population density,” instead resorting to vague phrases like “when the bacteria sense something.”\n

\n
\n", "question_id": "19M.2.HL.TZ1.9C.I", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c2-1-chemical-signalling-[hl-only]", "c2-1-2-cell-signalling-by-bacteria-in-quorum-sensing" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Outline how cuts in the skin are sealed to prevent blood loss.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n

\n a. platelets respond to/detect skin/blood vessel damage ✔\n

\n

\n b. platelets release clotting factors ✔\n

\n

\n c. clotting factors trigger a chain/cascade of reactions ✔\n

\n

\n d. «leading to» formation of thrombin ✔\n

\n

\n e. thrombin causes fibrinogen conversion into fibrin ✔\n

\n

\n f. blood clot seals the wound due to fibrin network of fibres ✔\n

\n

\n \n Accept answers presented as a flow chart\n \n .\n

\n
\n", "Examiners report": "None", "question_id": "19N.2.SL.TZ0.6A", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-2-defence-against-disease", "c3-2-3-sealing-of-cuts-in-skin-by-blood-clotting" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Suggest\n \n one\n \n way in which depth may act as a limiting factor for coral.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n low light levels/lower temperatures cannot support growth/metabolism ✔\n

\n

\n \n Requires the explanation for the mark\n \n

\n
\n", "Examiners report": "
\n

\n The reduction in light or temperature with greater depth was recognized but not often linked to growth or photosynthesis.\n

\n
\n", "question_id": "19M.2.SL.TZ1.11C", "topics": [ "b-form-and-function" ], "subtopics": [ "b4-1-adaptation-to-environment", "b4-1-5-conditions-required-for-coral-reef-formation" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Outline a reason that the orca whale would be difficult to represent in a pyramid of energy.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n orca is in different trophic levels depending on its food source;\n

\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ1.15C", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c4-2-transfers-of-energy-and-matter", "c4-2-12-reductions-in-energy-availability-at-each-successive-stage-in-food-chains-due-to-large-energy-losses-between-trophic-levels" ] }, { "Question": "
\n
\n

\n What is the benefit to living organisms that water has a high specific heat capacity?\n

\n

\n A. Heat can be lost from the skin when sweat evaporates.\n

\n

\n B. Aquatic environments do not have a great fluctuation in their temperature.\n

\n

\n C. The amount of heat stored by water is highly predictable.\n

\n

\n D. It allows water to be a solvent for chemical reactions at body temperature.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "
\n

\n This was another question that few candidates were able to cope with, and two of the discriminators were more popular than the correct answer. One of the distractors revealed confusion between latent heat of vaporization and specific heat capacity, which is understandable. The other indicated faulty reasoning, probably due to insecure understanding of the consequences of water’s high specific heat capacity.\n

\n
\n", "question_id": "21N.1A.SL.TZ0.7", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a1-1-water", "a1-1-6-physical-properties-of-water-and-the-consequences-for-animals-in-aquatic-habitats" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Outline a function of cholesterol in cell membranes.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n reduces fluidity of membrane / reduces permeability of membrane (to some molecules);\n

\n

\n \n Accept ‘controls’ or ‘maintains ‘ as a BOD.\n \n

\n
\n", "Examiners report": "None", "question_id": "22N.2.SL.TZ0.2B", "topics": [ "b-form-and-function" ], "subtopics": [ "b1-1-carbohydrates-and-lipids", "b1-1-10-difference-between-saturated-monounsaturated-and-polyunsaturated-fatty-acids" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n The graph shows blood pressure changes on the left side of the heart during one heartbeat. Identify the\n \n two\n \n parts of the circulatory system that produce traces I and II on the graph.\n

\n

\n \n

\n

\n [Source: © International Baccalaureate Organization 2019]\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n I. aorta ✔\n

\n

\n II: «left» atrium ✔\n

\n
\n", "Examiners report": "
\n

\n This question was poorly answered with most students earning either one mark or no marks. It was more common for candidates to correctly identify the atrium rather than the aorta. ß\n

\n
\n", "question_id": "19M.2.HL.TZ2.3", "topics": [ "b-form-and-function", "c-interaction-and-interdependence", "d-continuity-and-change" ], "subtopics": [ "b3-2-transport", "b3-2-16-stages-in-the-cardiac-cycle", "c3-2-defence-against-disease", "c3-2-3-sealing-of-cuts-in-skin-by-blood-clotting", "d3-1-reproduction", "d3-1-5-changes-during-the-ovarian-and-uterine-cycles-and-their-hormonal-regulation" ] }, { "Question": "
\n
\n

\n The graphs show how the frequency (f) of a trait within a population changes when subjected to selection pressures. Which graph shows stabilizing selection?\n

\n

\n \n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "23M.1A.HL.TZ2.33", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-1-natural-selection", "d4-1-12-differences-between-directional-disruptive-and-stabilizing-selection" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Outline the requirements for sustainability within a sealed mesocosm.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n photosynthetic organisms/autotrophs/plants as producers;\n
    2. \n
  2. \n \n light\n \n (as energy source) for photosynthesis;\n
    3. \n
  3. \n nutrient/water recycling (by saprotrophs);\n
    4. \n
  4. \n decomposers/saprotrophs to breakdown (toxic) wastes;\n
    5. \n
\n

\n \n The question is “outline”, so do not accept only a list of variables without a brief account.\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.1B.SL.TZ2.3C", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-2-stability-and-change", "d4-2-4-use-of-a-model-to-investigate-the-effect-of-variables-on-ecosystem-stability" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n State the percentage of G2 neurons in the mice that respond to the fox scent.\n

\n

\n . . . . . . . . . . . . . . . . . . . .%\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n 10–25 «%» ✔\n

\n
\n", "Examiners report": "
\n

\n Nearly all were able to state the answer of 10-25%.\n

\n
\n", "question_id": "19M.2.SL.TZ2.1", "topics": [ "c-interaction-and-interdependence", "d-continuity-and-change" ], "subtopics": [ "c2-2-neural-signalling", "d1-1-dna-replication", "d1-1-5-applications-of-polymerase-chain-reaction-and-gel-electrophoresis", "d4-1-natural-selection", "d4-1-1-natural-selection-as-the-mechanism-driving-evolutionary-change" ] }, { "Question": "
\n
\n (k)\n
\n
\n

\n Compare and contrast the results for trials 2 and 9.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n \n Similarity between 2 and 9\n \n :\n

\n
    \n
  1. \n winter path length longer (than spring and summer) in both (trials 2 and 9/from entrances B and C);\n
    \n \n
    \n Contrast between 2 and 9\n     \n :\n
    \n
    \n
    2. \n
  2. \n path length longer in trial 2 than 9/from entrance B than entrance C (in all seasons);\n
    \n \n \n OR\n \n \n
    \n error/bar/standard deviation/variation in data greater in trial 2 than 9/from entrance B than entrance C (in all seasons);\n
    3. \n
\n
\n", "Examiners report": "
\n

\n As in part (e), a similarity and a difference were required. When analysing data, candidates should try to keep in mind whether aspects are of interest and lead to conclusions significant conclusions or not. Here the two interesting findings were that the path length was highest in winter in both trials and that the shrews' performance between trial 2 and 90 had improved in all seasons, so they found the food with a shorter path length.\n

\n
\n", "question_id": "22N.2.HL.TZ0.1K", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-1-integration-of-body-systems", "c3-1-4-the-brain-as-a-central-information-integration-organ" ] }, { "Question": "
\n
\n (d)\n
\n
\n

\n Explain the mechanism that prevents polyspermy during fertilization.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. cortical reaction (after first sperm nucleus enters the egg);\n
\n b. vesicles/cortical granules release their contents/enzymes (from the egg/zygote);\n
\n c. zona pellucida/glycoprotein coat/outer coat hardened / fertilization membrane formed;\n
\n d.\n \n enzymes\n \n of sperm/acrosome cannot digest (hardened coat)\n
\n \n OR\n \n
\n glycoproteins/ZP3 (in zona pellucida) altered so sperm cannot bind;\n

\n
\n", "Examiners report": "
\n

\n Answers were mixed. Most knew that there is a mechanism that prevents more sperm fusing with the egg after the first one and some gave accurate and detailed accounts of it.\n

\n
\n", "question_id": "21N.2.HL.TZ0.2D", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-1-reproduction", "d3-1-15-mechanisms-to-prevent-polyspermy" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Outline the principles used by scientists to classify organisms.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n

\n a. use of the binomial system ✔\n

\n

\n b. agreed/developed by scientists /\n \n OWTTE\n \n ✔\n

\n

\n c. hierarchy of taxa used ✔\n \n Names of the seven taxa not required\n \n .\n

\n

\n d. three domains used/three domain names ✔\n \n OWTTE\n \n

\n

\n e. genome/DNA sequence similarities\n
\n \n \n OR\n \n \n
\n amino acid sequence of specific proteins ✔\n

\n

\n f. species from a common ancestor are grouped together\n
\n \n \n OR\n \n \n
\n included in the same clade/branch in cladogram ✔\n

\n

\n g. use evidence of evolutionary origin ✔ Allow example\n \n e.g.\n \n fossil record comparison\n

\n

\n h. shared characteristics within a group\n
\n \n \n OR\n \n \n
\n similar embryonic development ✔\n

\n
\n", "Examiners report": "None", "question_id": "19N.2.HL.TZ0.5B", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a3-2-classification-and-cladistics-(hl-only)", "a3-2-1-need-for-classification-of-organisms", "a3-2-2-difficulties-classifying-organisms-into-the-traditional-hierarchy-of-taxa" ] }, { "Question": "
\n
\n

\n The micrograph of a section through a plant stem shows at least ten different types of cells.\n

\n

\n \n

\n

\n [Source: Joan Carles Juarez / Shutterstock.com.]\n

\n

\n

\n

\n What explains the differences between these cells?\n

\n

\n A. Only one gene is expressed in each cell type.\n

\n

\n B. Different genes are expressed in each cell type.\n

\n

\n C. Only useful genes remain in the DNA of each cell type.\n

\n

\n D. Changes in the DNA sequence take place when these cells develop.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "
\n

\n It was commented that the use of plant material was an unnecessary distractor but that did not show in the student responses with over 70 % of students answering correctly and the question discriminating well.\n

\n
\n", "question_id": "22M.1A.HL.TZ2.6", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-2-gene-expression-[hl-only]", "d2-2-5-differences-between-the-genome-transcriptome-and-proteome-of-individual-cells" ] }, { "Question": "
\n
\n

\n The pedigree chart shows a family affected by cystic fibrosis.\n

\n

\n \n

\n

\n [Source: © International Baccalaureate Organization 2019]\n

\n

\n

\n

\n What is the genotype of the affected boy’s father?\n

\n

\n A. AA only\n

\n

\n B. Either AA or Aa\n

\n

\n C. Aa only\n

\n

\n D. aa only\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "
\n

\n This was a good question, it discriminated very well and was not too difficult.\n

\n
\n", "question_id": "19M.1A.SL.TZ2.14", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-2-inheritance", "d3-2-13-pedigree-charts-to-deduce-patterns-of-inheritance-of-genetic-disorders" ] }, { "Question": "
\n
\n (a.i)\n
\n
\n

\n Draw a Punnett square to show all the possible genotypes of Queen Victoria’s children.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. parental alleles shown as X\n \n H\n \n and X\n \n h\n \n (female) and X\n \n H\n \n and Y (male);\n
\n b. Punnett square with genotypes of offspring shown as X\n \n H\n \n X\n \n H\n \n and X\n \n H\n \n Y and X\n \n H\n \n X\n \n h\n \n and X\n \n h\n \n Y;\n

\n

\n \n

\n
\n", "Examiners report": "
\n

\n Generally this was well answered. Common errors were to omit X and or Y chromosomes, show alleles on both X and Y chromosomes, or show the male X chromosome with a recessive h allele.\n

\n
\n", "question_id": "21N.2.SL.TZ0.2A.I", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-2-inheritance", "d3-2-12-haemophilia-as-an-example-of-a-sex-linked-genetic-disorder" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Draw a plan diagram in the right-hand box with labels to show the distribution of tissues in this transverse section of a leaf.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n palisade mesophyll;\n
    2. \n
  2. \n spongy mesophyll;\n
    3. \n
  3. \n lower epidermis;\n
    4. \n
  4. \n upper epidermis;\n
    5. \n
  5. \n xylem/phloem/vascular bundle;\n
    6. \n
\n

\n \n 1 mark for each correctly labelled tissue shown as a layer in proportion.\n \n

\n
\n", "Examiners report": "None", "question_id": "SPM.1B.SL.TZ0.2", "topics": [ "a-unity-and-diversity", "b-form-and-function" ], "subtopics": [ "a2-2-cell-structure", "a2-2-10-cell-types-and-cell-structures-viewed-in-light-and-electron-micrographs", "a2-2-11-drawing-and-annotation-based-on-electron-micrographs", "a2-2-2-microscopy-skills", "b3-1-gas-exchange", "b3-1-7-adaptations-for-gas-exchange-in-leaves", "b3-1-8-distribution-of-tissues-in-a-leaf" ] }, { "Question": "
\n
\n (j)\n
\n
\n

\n Discuss whether these studies show that habitat destruction can affect global bumblebee numbers.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n habitat destruction removes the plants/flowers/natural food source of the bees;\n
    2. \n
  2. \n bees have to look for other food sources;\n
    3. \n
  3. \n many of these alternative sources of food are not suitable for bee survival\n
    \n \n \n OR\n \n \n
    \n pollen with a different proportion of protein to lipid would reduce survival;\n
    4. \n
  4. \n no control where bees are fed their normal diet is included;\n
    5. \n
  5. \n simulation is not using natural pollen / habitat;\n
    \n \n \n OR\n \n \n
    \n sample size is too small to make conclusions;\n
    6. \n
\n

\n \n Accept other reasonable discussion using the data.\n \n

\n
\n", "Examiners report": "None", "question_id": "22N.2.SL.TZ0.1J", "topics": [ "b-form-and-function" ], "subtopics": [ "b4-1-adaptation-to-environment", "b4-1-2-adaptations-of-organisms-to-the-abiotic-environment-of-their-habitat" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n State the immediate consequence of a species producing more offspring than the environment can support.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n competition/lack of resources/death/exceeding carrying capacity ✔\n

\n

\n \n Allow a description of it.\n \n
\n \n Do not allow “overpopulation” or “natural selection”\n \n .\n

\n
\n", "Examiners report": "None", "question_id": "19N.2.SL.TZ0.4", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-1-natural-selection", "d4-1-3-overproduction-of-offspring-and-competition-for-resources-as-factors-that-promote-natural-selection" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Testis cells are eukaryotic cells. Identify the structures seen under the electron microscope in testis cells that are not present in prokaryotic cells.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n

\n a. nucleus/nuclear membrane ✔\n

\n

\n b. membrane bound organelles ✔\n

\n

\n c. mitochondria ✔\n

\n

\n d. rough ER/smooth ER/golgi apparatus ✔\n

\n

\n e. lysosomes / centrioles ✔\n

\n

\n f. large/80S ribosomes / ribosomes attached to a membrane ✔\n

\n

\n g. linear chromosomes / histones ✔\n

\n
\n", "Examiners report": "None", "question_id": "21M.2.SL.TZ2.5C", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a2-2-cell-structure", "a2-2-5-prokaryote-cell-structure", "a2-2-6-eukaryote-cell-structure" ] }, { "Question": "
\n
\n

\n Suggest with a reason which system best reproduces the conditions of the natural environment.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n a. horizontal flow/«figure» B because it is larger\n
\n \n \n OR\n \n \n
\n horizontal flow/«figure» B contains more/several plants ✔\n

\n

\n b. horizontal flow/«figure» B because it works by natural flow\n
\n \n \n OR\n \n \n
\n horizontal flow/«figure» B because it works without a pump ✔\n \n Do not accept river instead of flow\n \n .\n

\n
\n", "Examiners report": "None", "question_id": "19N.1B.SL.TZ0.B", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-2-stability-and-change", "d4-2-4-use-of-a-model-to-investigate-the-effect-of-variables-on-ecosystem-stability" ] }, { "Question": "
\n
\n (ii)\n
\n
\n

\n Explain the reasons for antibiotics secreted into soil not harming insects or other animals in the soil.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n antibiotics (only) affect/kill/block processes in bacteria/prokaryotes / do not affect eukaryotes;\n
    2. \n
  2. \n metabolism/protein synthesis/ribosomes/cell walls not targeted in insects/animals/eukaryotes;\n
    3. \n
  3. \n no cell walls in animals (so antibiotics cannot attack cell walls);\n
    4. \n
  4. \n antibiotics are secreted (by microbes/fungi) to prevent competition (with other microbes);\n
    5. \n
\n

\n

\n
\n", "Examiners report": "None", "question_id": "23M.2.HL.TZ1.3BII", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-2-defence-against-disease", "c3-2-13-antibiotics-as-chemicals-that-block-processes-occurring-in-bacteria-but-not-in-eukaryotic-cells" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Annotate the diagram to illustrate the amphipathic nature of phospholipids.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n line to circle labelled phosphate (head)\n \n and\n \n (tail) labelled fatty acid/hydrocarbon/lipid (tail);\n
    2. \n
  2. \n label hydrophilic/polar/attracted to water/\n \n and\n \n hydrophobic/non polar/not attracted to water;\n
    3. \n
\n
\n", "Examiners report": "
\n

\n Part (a) was a variation on a classic Section B question on the phospholipid bilayer. Approximately 1 in 10 students left it blank, suggesting that many did not think that they had to reply to it as there was no answer box. Cholesterol's function in reducing fluidity and permeability was not well known in (b). In (c) poorer candidates described endosymbiosis, rather than answering the question. Many knew about double membranes, own DNA and 70s ribosomes, but did not score any marks as they failed to say that they were in mitochondria and/or chloroplasts. This is perhaps a case where planning the answer was lacking, rather than rushing in.\n

\n
\n", "question_id": "22N.2.SL.TZ0.2A", "topics": [ "b-form-and-function" ], "subtopics": [ "b1-1-carbohydrates-and-lipids", "b1-1-12-formation-of-phospholipid-bilayers-as-a-consequence-of-the-hydrophobic-and-hydrophilic-regions" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Explain the reasons for none of the females in the pedigree chart having hemophilia.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n hemophilia is X-linked/sex-linked/carried on the X chromosome;\n
    2. \n
  2. \n females have two X chromosomes\n
    \n \n \n OR\n \n \n
    \n males only have one X chromosome;\n
    3. \n
  3. \n hemophilia is caused by a recessive allele;\n
    4. \n
  4. \n (trait) must be on both alleles to be expressed\n
    \n \n \n OR\n \n \n
    \n females would require the allele on both X chromosomes to have the disease\n
    \n \n \n OR\n \n \n
    \n females can be carriers when allele is only on one chromosome;\n
    5. \n
\n
\n", "Examiners report": "
\n

\n There were many good answers for this question showing understanding of haemophilia being sex linked and recessive Quite a number then failed to get the third mark by being too vague in their explanations. Some candidates thought that hemophilia is carried on Y chromosome; many understand that females have two X chromosomes; talk about females as carriers was often seen, but without any details to expand the answer; or that males are most likely to have hemophilia but, again, no details; for the most part answers showed shallow understanding.\n

\n
\n", "question_id": "22M.2.SL.TZ1.4B", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-2-inheritance", "d3-2-12-haemophilia-as-an-example-of-a-sex-linked-genetic-disorder", "d3-2-13-pedigree-charts-to-deduce-patterns-of-inheritance-of-genetic-disorders" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Sketch the complementary strand to complete the section of a DNA diagram.\n

\n

\n \n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n a. correct base sequence: T, G, A;\n

\n

\n b. strand drawn anti-parallel;\n

\n

\n c. correct shapes used;\n

\n

\n \n

\n

\n \n Award\n \n [2 max]\n \n if bonds are not from the correct carbon or if the nucleotides are not joined\n \n .\n

\n
\n", "Examiners report": "
\n

\n In part (a) most could gain marks for the correct shapes and sequence but did not gain the third mark as it was not shown as antiparallel. Some lost marks as a 2MAX was awarded if the bonds were not from the correct carbons. In part (b) the definition of mutation was quite well known, and most gained some marks in the explanation. Weaker students just wrote about evolution without relating it to mutations as asked. They also tended to give unnecessary examples, involving finches and moths\n \n etc\n \n .\n

\n
\n", "question_id": "20N.2.SL.TZ0.4A", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a1-2-nucleic-acids", "a1-2-6-dna-as-a-double-helix-made-of-two-antiparallel-strands-of-nucleotides-with-two-strands-linked-by-hydrogen-bonding-between-complementary-base-pairs" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Draw a plan diagram in the right-hand box with labels to show the distribution of tissues in this transverse section of a leaf.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n palisade mesophyll;\n
    2. \n
  2. \n spongy mesophyll;\n
    3. \n
  3. \n lower epidermis;\n
    4. \n
  4. \n upper epidermis;\n
    5. \n
  5. \n xylem/phloem/vascular bundle;\n
    6. \n
\n

\n \n 1 mark for each correctly labelled tissue shown as a layer in proportion.\n \n

\n
\n", "Examiners report": "None", "question_id": "SPM.1B.SL.TZ0.2A", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a2-2-cell-structure", "a2-2-10-cell-types-and-cell-structures-viewed-in-light-and-electron-micrographs", "a2-2-11-drawing-and-annotation-based-on-electron-micrographs" ] }, { "Question": "
\n
\n (d)\n
\n
\n

\n Explain the role of calcium ions in muscle contraction.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n calcium released from sarcoplasmic reticulum;\n
    2. \n
  2. \n calcium binds to troponin;\n
    3. \n
  3. \n causes tropomyosin to move;\n
    4. \n
  4. \n uncovers binding sites;\n
    5. \n
  5. \n myosin heads bind to the actin forming cross bridges;\n
    6. \n
\n
\n", "Examiners report": "
\n

\n Well prepared candidates had no difficulty in describing the role of calcium in muscle contraction but they were in the minority. The discrimination index was very high.\n

\n
\n", "question_id": "22M.2.HL.TZ1.5D", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-3-muscle-and-motility-(hl-only)", "b3-3-2-sliding-filament-model-of-muscle-contraction" ] }, { "Question": "
\n
\n (a.i)\n
\n
\n

\n Identify the country with the largest number of Ebola cases.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n Sierra Leone ✔\n

\n
\n", "Examiners report": "
\n

\n This set of data-based questions produced the best showing among candidates. Teachers are to be commended for developing these skills in their students. Many candidates showed confidence in looking at unfamiliar data and formulating answers. Some weaknesses included not being careful with what they were writing when there were similar aspects in the data set (total population size and population density), comparing and contrasting - many students finding this difficult and simply writing descriptions of the data set rather than focussing on similarities and differences. Also giving information on part of a data set where some aspects of the data set may be similar in name but fundamentally different (e.g. Total population and population density) – Some candidates used incorrect parts of data sets rather than those that had been asked about - for example, talking about Ebola cases rather than Ebola deaths, total population size rather than population density.\n

\n
\n", "question_id": "19M.2.SL.TZ1.1", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a2-3-viruses-(hl-only)" ] }, { "Question": "
\n
\n

\n The light micrograph shows the structure of blood vessels in a muscle.\n

\n

\n \n

\n

\n \n [Source: Calvo, J.L., n.d. [image online] Available at: https://www.shutterstock.com/image-photo/muscular-artery-veinnervebundles-\n \n
\n \n surrounded-785176687 [Accessed 12 January 2022].]\n \n

\n

\n
\n Which blood vessel is shown by X?\n

\n

\n
\n A.  A vein\n

\n

\n B.  An artery\n

\n

\n C.  An arteriole\n

\n

\n D.  A capillary\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "None", "question_id": "23M.1A.SL.TZ1.25", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-2-transport", "b3-2-2-structure-of-arteries-and-veins" ] }, { "Question": "
\n
\n

\n Calculate the magnification of the image, showing your working.\n

\n

\n

\n

\n . . . . . . . . . . . . . . . . . . . . x\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n \n Calculation\n \n : size of bar ÷ 15 μm (1.5 cm ÷ 15 μm or 15 000 μm ÷ 15 μm);\n

\n

\n \n Answer\n \n : 1000 x;\n

\n

\n \n First marking point is for division by 15 μm\n \n ;\n

\n

\n \n Second marking point is for the correct answer; accept 930 and 1070 x\n \n .\n

\n
\n", "Examiners report": "
\n

\n Most candidates managed to calculate the magnification correctly by dividing their scale bar measurement by the provided scale, others inverted the division or displayed incomprehensible calculations; some calculations were difficult to follow, with no apparent methodology or structure; there were too many unit conversion errors, sometimes because candidates did not use units within their calculation (\n \n e.g.\n \n measuring in centimetres, but calculating as millimetres); a limited number measured the complete image width but didn't adjust the scale bar proportionally.\n

\n
\n", "question_id": "20N.1B.SL.TZ0.A", "topics": [ "b-form-and-function", "a-unity-and-diversity" ], "subtopics": [ "b3-1-gas-exchange", "b3-1-10-stomatal-density", "a2-2-cell-structure", "a2-2-2-microscopy-skills" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n State the relationship between BCH and brain mass of shrews.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n positive correlation/the greater the BCH the greater the brain mass;\n

\n

\n \n No mark for ‘positive relationship’ or for directly proportional\n \n

\n
\n", "Examiners report": "
\n

\n Most candidate described the relationship shown on the graph as a positive correlation. Some referred to it incorrectly as directly proportional, but that would be revealed by data points along a straight line on the graph. The term 'positive relationship' is vague and should be discouraged.\n

\n
\n", "question_id": "22N.2.HL.TZ0.1A", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-1-integration-of-body-systems", "c3-1-4-the-brain-as-a-central-information-integration-organ" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Deduce whether the pattern of cyanogenesis was the same in all of the areas around all four cities.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a.\n \n Toronto,\n \n \n NYC\n \n and\n \n Boston\n \n show same pattern/all show positive correlation/relationship/WTTE;\n

\n

\n b.\n \n Montreal\n \n shows negative correlation/negative relationship/WTTE so is different;\n

\n
\n", "Examiners report": "
\n

\n Here candidates were expected to state that the four cities did not all show the same pattern, as three have a positive correlation, but the fourth city (Montreal) has a weak negative correlation. A few failed to include Toronto among the cities with a positive correlation and instead singled it out for showing a stronger correlation than the others.\n

\n
\n", "question_id": "20N.2.SL.TZ0.1B", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-2-stability-and-change", "d4-2-4-use-of-a-model-to-investigate-the-effect-of-variables-on-ecosystem-stability" ] }, { "Question": "
\n
\n

\n How is the Na/K ion ratio established during the resting potential phase of neuron activity?\n

\n

\n
\n \n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "SPM.1A.SL.TZ0.13", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c2-2-neural-signalling", "c2-2-2-generation-of-the-resting-potential-by-pumping-to-establish-and-maintain-concentration-gradients-of-sodium-and-potassium-ions" ] }, { "Question": "
\n
\n (a.i)\n
\n
\n

\n State the property of amphipathic phospholipids that enables them to form a bilayer.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n have both a hydrophilic and a hydrophobic region\n
\n \n \n OR\n \n \n
\n have both a polar and a non-polar region ✔\n

\n
\n", "Examiners report": "None", "question_id": "19N.2.SL.TZ0.4A.I", "topics": [ "b-form-and-function" ], "subtopics": [ "b1-1-carbohydrates-and-lipids", "b1-1-12-formation-of-phospholipid-bilayers-as-a-consequence-of-the-hydrophobic-and-hydrophilic-regions" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Outline the function of codons.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n «three bases on mRNA» coding for one amino acid «in a polypeptide» ✔\n

\n
\n", "Examiners report": "None", "question_id": "19N.2.SL.TZ0.2A", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d1-2-protein-synthesis", "d1-2-8-features-of-the-genetic-code" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Explain how blood clotting occurs and the consequence for a person who has hemophilia.\n

\n
\n
\n

\n [7]\n

\n
\n
\n", "Markscheme": "
\n

\n \n Clotting process\n \n :\n

\n
    \n
  1. \n blood clotting seals cuts in the skin;\n
    2. \n
  2. \n clotting factors are released (from platelets);\n
    3. \n
  3. \n thrombin is activated;\n
    4. \n
  4. \n a cascade reaction occurs (with thrombin);\n
    5. \n
  5. \n (thrombin causes) fibrinogen is converted to fibrin;\n
    6. \n
  6. \n fibrin forms a clot/blocks the cut/prevents blood from being lost;\n
    \n \n Consequences of hemophilia\n \n :\n
    7. \n
  7. \n if a person does not have enough clotting factors/hemophilia, the clot will not form;\n
    8. \n
  8. \n pathogens can enter the body more easily;\n
    9. \n
  9. \n (in hemophiliacs) blood will be lost from a cut which affects blood pressure/bleeding to death;\n
    10. \n
  10. \n loss of blood affects amount of hemoglobin/O\n \n 2\n \n carried around the body;\n
    11. \n
  11. \n reference to lifestyle / menstrual/birth problems\n
    12. \n
\n

\n \n e.g. surgery, contact sports\n \n

\n
\n", "Examiners report": "
\n

\n The formation of a clot by the final formation of fibrin was reasonably well known, although many implied that the thrombin directly converted the fibrinogen and did not mention the cascade of reactions. In the consequences for haemophiliacs the fact that the clot would not form and they risked bleeding to death and were more susceptible to infections were well known. There were some G2 comments that 7 marks seemed difficult to attain, this did not seem to be the case with an average of 4.1 marks for the question.\n

\n
\n", "question_id": "22M.2.SL.TZ2.6C", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-2-defence-against-disease", "c3-2-3-sealing-of-cuts-in-skin-by-blood-clotting" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Cells produce a large variety of proteins with different sequences of amino acids. Explain how this is done.\n

\n
\n
\n

\n [7]\n

\n
\n
\n", "Markscheme": "
\n

\n a. protein is produced when a gene is expressed / switched on ✔\n

\n

\n b. genetic code/codons consists of three nucleotides/bases/base triplet ✔\n

\n

\n c. genetic code in DNA is\n \n transcribed\n \n /\n \n transcription\n \n (to mRNA) ✔\n

\n

\n d. mRNA exits the nucleus ✔\n

\n

\n e. mRNA (code) is\n \n translated\n \n /\n \n translation\n \n into a polypeptide/protein ✔\n

\n

\n f. amino acid sequence/polypeptide formation occurs at a ribosome ✔\n

\n

\n g. one codon translates to one amino acid ✔\n

\n

\n h. tRNA carries code for specific amino acids ✔\n

\n

\n i. tRNA anticodon matches with specific codon in mRNA ✔\n

\n

\n j. amino acids joined (by peptide bonds) to form polypeptide ✔\n

\n

\n k. sequence of amino acids determined by order of bases/nucleotides/codons in DNA/mRNA ✔\n

\n

\n l. proteins vary based on which amino acids are used\n \n and\n \n their order\n
\n \n \n OR\n \n \n
\n protein variety increases by mutations to DNA ✔\n

\n
\n", "Examiners report": "
\n

\n This question was attempted by about 42 % of candidates.\n

\n

\n Some brilliant, clear answers were given earning the maximum marks. However, coherent essays explaining protein synthesis were rare. Some students dwelled on transcription without ever mentioning translation. Codons, anticodons and their locations were not clearly understood. Valid information did appear but it was frequently mixed up or incomplete.\n

\n
\n", "question_id": "21M.2.SL.TZ1.6B", "topics": [ "b-form-and-function" ], "subtopics": [ "b1-2-proteins", "b1-2-4-infinite-variety-of-possible-peptide-chains" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Based on the graph, compare and contrast the progress of the epidemic in the suburbs and rural areas.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n a. start of epidemic/first cases in rural areas\n
\n \n \n OR\n \n \n
\n epidemic spread to suburbs later ✔\n

\n

\n b. higher maximum number of cases/greater increase in rural areas\n
\n \n \n OR\n \n \n
\n converse for suburbs ✔\n

\n

\n c. increase came earlier in rural areas «than suburbs»\n
\n \n \n OR\n \n \n
\n number of cases peaked earlier in rural areas\n
\n \n \n OR\n \n \n
\n more cases in rural areas «than suburbs» in 2014 ✔\n

\n

\n d. decrease came earlier in rural areas «than suburbs»\n
\n \n \n OR\n \n \n
\n decreasing in rural areas but not in suburbs in 2015/by end of study period\n
\n \n \n OR\n \n \n
\n more cases in suburbs than rural areas in 2015 ✔\n

\n

\n e. «large» fluctuations in both ✔\n

\n
\n", "Examiners report": "
\n

\n This was a timely question with Ebola epidemics again causing great problems in parts of Africa. Students were expected to have had some practice at analysing data relating to an epidemic because of this Skill in the programme: Analysis of epidemiological data related to vaccination programmes. It was assumed that candidates would understand terms such as ‘case’, ‘fatal case’, ‘infect’ and ‘treat’.\n

\n

\n The skill required in this question was picking significant trends out of data with a great deal of noise. Only one similarity was accepted – the large week-to-week fluctuation in number of cases. The differences between the rural areas and the suburbs were that Ebola epidemic started earlier in rural areas, rose to higher peaks and started declining earlier.\n

\n
\n", "question_id": "19M.2.SL.TZ1.1B", "topics": [ "c-interaction-and-interdependence", "a-unity-and-diversity" ], "subtopics": [ "c3-2-defence-against-disease", "a2-3-viruses-(hl-only)" ] }, { "Question": "
\n
\n

\n Changes in heart rate occur during and after a period of exercise.\n

\n

\n \n

\n

\n

\n

\n Which structure sends messages to the sinoatrial node of the heart to cause changes in heart rate?\n

\n

\n A. Adipose tissue\n

\n

\n B. Medulla of the brain\n

\n

\n C. Pineal gland\n

\n

\n D. Thyroid gland\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "22M.1A.HL.TZ2.25", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-2-transport", "b3-2-16-stages-in-the-cardiac-cycle" ] }, { "Question": "
\n
\n

\n Compare and contrast the data for Conakry with the data for the three suburbs.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n \n differences\n \n :\n
\n a. Conakry has more cases than any of the suburbs\n
\n \n \n OR\n \n \n
\n more cases in total in the suburbs than in Conakry ✔\n

\n

\n b. more male cases in Conakry whereas more female cases in suburbs ✔\n

\n

\n c. higher «% of»\n \n fatal\n \n cases at Ebola\n \n treatment centers\n \n in suburbs than in Conakry ✔\n

\n

\n \n similarity\n \n :\n
\n d. in both Conakry and suburbs «% of»\n \n fatal\n \n cases in\n \n treatment centers\n \n is higher than outside ✔\n

\n
\n", "Examiners report": "
\n

\n This was a timely question with Ebola epidemics again causing great problems in parts of Africa. Students were expected to have had some practice at analysing data relating to an epidemic because of this Skill in the programme: Analysis of epidemiological data related to vaccination programmes. It was assumed that candidates would understand terms such as ‘case’, ‘fatal case’, ‘infect’ and ‘treat’.\n

\n

\n This was another question where the skill was in picking out significant trends. Differences between individual suburbs were not significant so all the answers accepted were either similarities or differences between the capital city and the suburbs generally. Most but not all candidates made two or more statements about the data that were significant enough to score marks. Some students treated percentages as though they were absolute numbers and for example added the percentage of fatal cases in and outside treatment centres together, which does not give a meaningful total.\n

\n
\n", "question_id": "19M.2.SL.TZ1.D", "topics": [ "c-interaction-and-interdependence", "a-unity-and-diversity" ], "subtopics": [ "c3-2-defence-against-disease", "a2-3-viruses-(hl-only)" ] }, { "Question": "
\n
\n

\n Which protein is identified with its function?\n

\n

\n \n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "None", "question_id": "19M.1A.HL.TZ2.16", "topics": [ "b-form-and-function" ], "subtopics": [ "b1-2-proteins", "b1-2-11-quaternary-structure-of-non-conjugated-and-conjugated-proteins", "b1-2-12-relationship-of-form-and-function-in-globular-and-fibrous-proteins" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Identify the total percentage of honey samples contaminated with neonicotinoid pesticides in the continent with the lowest overall levels of contamination.\n

\n

\n

\n

\n . . . . . . . . . . . . %\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n 57 (%) ✔\n

\n

\n \n Allow range 56 % to 58 %\n \n .\n

\n
\n", "Examiners report": "
\n

\n In general, the data analysis question was well attempted by the majority of students.\n

\n

\n Most read the graphs correctly, stating between 56 and 58 %.\n

\n
\n", "question_id": "21M.2.HL.TZ2.1C", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c2-2-neural-signalling", "c2-2-12-effects-of-exogenous-chemicals-on-synaptic-transmission" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Explain how natural selection can lead to speciation.\n

\n
\n
\n

\n [7]\n

\n
\n
\n", "Markscheme": "
\n

\n a. natural selection is caused by selection pressures in the environment\n
\n \n \n OR\n \n \n
\n example of a selection pressure ✔\n

\n

\n b. natural selection requires that variation exists within a species ✔\n

\n

\n c. variation arises randomly due to mutation\n
\n \n \n OR\n \n \n
\n variation is enhanced by meiosis/sexual reproduction ✔\n

\n

\n d. over-production of offspring promotes selection\n
\n \n \n OR\n \n \n
\n natural selection occurs when there is competition/overpopulation/predators/environmental changes/changes in selection pressures ✔\n

\n

\n e. well adapted individuals/individuals with best variations survive to reproduce/survival of fittest ✔\n

\n

\n f. «frequency of» genes/alleles conferring an advantage are selected for\n
\n \n \n OR\n \n \n
\n genes/alleles conferring a disadvantage are selected against ✔\n

\n

\n g. genetic divergence/difference increases\n
\n \n \n OR\n \n \n
\n natural selection «genetically» isolates members of a species so eventually they can no longer produce fertile offspring ✔\n

\n

\n h. genetic divergence» leads to reproductive isolation ✔\n

\n

\n i. geographical/behavioural/ecological factors may lead to «reproductive» isolation ✔\n

\n

\n j. prolonged «reproductive» isolation leads to speciation ✔\n

\n

\n k. up to one additional mark for AHL information ✔\n

\n
\n", "Examiners report": "
\n

\n There were some excellent explanations given in well-structured responses. Many candidates avoided talking about natural selection in genetics terms, losing marks in the process. Darwin’s finches, industrial melanism and the giraffe were common examples. Some students invented their own creative examples.\n

\n

\n The idea that natural selection limits biodiversity appeared a few times. The flawed case of the peppered moth was given to exemplify speciation, however Darwin's finches were the most frequent example.\n

\n
\n", "question_id": "19M.2.SL.TZ1.7C", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a4-1-evolution-and-speciation", "a4-1-6-speciation-by-splitting-of-pre-existing-species" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Deduce with a reason the identity of the father.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n male 2;\n
    2. \n
  2. \n each band in the child’s DNA must be the same as a band in either the mother or the father\n
    \n \n \n OR\n \n \n
    \n any band in the child’s profile that is not present in the mother’s profile must be present in the father’s;\n
    3. \n
\n

\n \n Must mention both the mother and father\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.1B.SL.TZ1.3B", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-3-photosynthesis", "c1-3-7-techniques-for-varying-concentrations-of-carbon-dioxide-light-intensity-or-temperature-experimentally-to-investigate-the-effects-of-limiting-factors-on-the-rate-of-photosynthesis" ] }, { "Question": "
\n
\n

\n The image shows an electron micrograph of part of a cell.\n

\n

\n \n

\n

\n [Source: Dr. Eldon Newcomb – Emeritis Professor at The University of Wisconsin – Madison.]\n

\n

\n

\n

\n Which features do the two structures labelled X and Y have in common?\n

\n

\n A. They are surrounded by a double membrane.\n

\n

\n B. They contain 70S ribosomes.\n

\n

\n C. They contain naked DNA.\n

\n

\n D. They are only found in leaf cells.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "
\n

\n There was criticism that the resolution of the micrograph wasn’t high enough, but it was typical for electron micrographs of plant cells and the internal structure of chloroplasts and the nucleus was clear. This skill from 1.2 of the Core was being tested: Interpretation of electron micrographs to identify organelles and deduce the function of specialized cells. The nucleus and chloroplasts both had a typical appearance, so well-prepared candidates should have been able to identify them. Answer A could then be chosen either by eliminating the incorrect answers, or by knowing that both nucleus and chloroplast are double membraned. The endosymbiotic theory for the origin of chloroplasts should have helped inform candidates about the two membranes of chloroplasts.\n

\n
\n", "question_id": "19M.1A.SL.TZ1.2", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a2-2-cell-structure", "a2-2-10-cell-types-and-cell-structures-viewed-in-light-and-electron-micrographs" ] }, { "Question": "
\n
\n

\n Duckweed (\n \n Lemna gibba\n \n ) is a plant that grows on the surface of water. It was grown in cultures and the percentage increase in total area covered per day was obtained. The graph shows the specific growth rates per day for duckweed measured over 22 days.\n

\n

\n \n

\n

\n \n Material from: Mkandawire, M. and Dudel, E.G., Assignment of Lemna gibba L. (duckweed) bioassay for in situ\n \n
\n \n ecotoxicity assessment, published 2005,\n \n Aquatic Ecology\n \n , reproduced with permission of SNCSC.\n \n

\n

\n Suggest reasons for the slowing down of duckweed population growth after day 6.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n high growth rate (before day 6) depleted nutrients;\n
    2. \n
  2. \n overcrowding/competition for resources;\n
    3. \n
  3. \n (intraspecific)\n \n competition\n \n slows growth rate;\n
    4. \n
  4. \n carrying capacity has been reached/stabilized;\n
    5. \n
  5. \n intoxication from excretion limits growth;\n
    6. \n
\n

\n \n mp b: Accept resources examples such as CO2, nutrients, light, space, etc.\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ2.19", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-2-stability-and-change", "d4-2-8-eutrophication-of-aquatic-and-marine-ecosystems-due-to-leaching" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Distinguish between competitive and non-competitive enzyme inhibition.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n

\n \n

\n

\n \n Accept mpd in a graph\n \n .\n

\n

\n \n Accept mpa, mpb or mpc on an annotated diagram\n \n .\n

\n

\n \n

\n

\n [Source: Enzyme inhibition curves,\n
\n ImranKhan1992, Available at:\n \n https://\n \n
\n \n commons.wikimedia.org/wiki/\n \n
\n \n File:Enzyme_kinetics_curve.png#/media/\n \n
\n \n File:Enzyme_kinetics_curve.png\n \n CC0 1.0\n
\n Universal (CC0 1.0) Public Domain Dedication\n
\n \n https://creativecommons.org/publicdomain/\n \n
\n \n zero/1.0/deed.en\n \n Source adapted.]\n

\n
\n", "Examiners report": "
\n

\n In a parallel way to 6(c) and 7(b), there was a tendency for candidates to write about the two types of enzyme inhibition separately and as a result not to distinguish between them fully. For example. many candidates stated that competitive inhibitors show some chemical similarity to the substrate but did not then state that non-competitive inhibitors are typically dissimilar. An error which is repeatedly seen in enzyme questions is for candidates to state that the active site is on the substrate rather than the enzyme. Some candidates drew sketch graphs to show the difference between competitive and non-competitive inhibitors in the effect of substrate concentration, but either did not label the x-axis or labelled it ‘time’ rather than ‘substrate concentration’.\n

\n
\n", "question_id": "21N.2.HL.TZ0.8C", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-1-enzymes-and-metabolism", "c1-1-15-competitive-inhibition-as-a-consequence-of-an-inhibitor-binding-reversibly-to-an-active-site", "c1-1-16-regulation-of-metabolic-pathways-by-feedback-inhibition", "c1-1-17-mechanism-based-inhibition-as-a-consequence-of-chemical-changes-to-the-active-site-caused-by-the-irreversible-binding-of-an-inhibitor" ] }, { "Question": "
\n
\n (b.ii)\n
\n
\n

\n The researchers concluded that there was a threshold coral cover percentage, below which infection rates tended to remain fairly low. Using the data in the table, identify this threshold level.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n 50 % / 25 % / 49 %\n
\n OR\n
\n 25–49 % (coral cover);\n

\n
\n", "Examiners report": "
\n

\n Most were able to able to gain the mark in 1b (ii) for saying that the threshold level was 25 – 49 %.\n

\n
\n", "question_id": "21N.2.SL.TZ0.1B.II", "topics": [ "d-continuity-and-change", "b-form-and-function" ], "subtopics": [ "d4-3-climate-change", "d4-3-7-threats-to-coral-reefs-as-an-example-of-potential-ecosystem-collapse", "b4-1-adaptation-to-environment", "b4-1-5-conditions-required-for-coral-reef-formation" ] }, { "Question": "
\n
\n

\n A dichotomous key can be used to distinguish four types of plant. Which of the plants could be a bryophyte?\n

\n

\n \n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "
\n

\n This was the third most difficult question on the paper in terms of the percentage of candidates answering it correctly. To find the correct answer the only required knowledge was that bryophytes do not have vascular tissue.\n

\n
\n", "question_id": "21M.1A.HL.TZ1.24", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a3-1-diversity-of-organisms", "a3-1-14-engagement-with-local-plant-or-animal-species-to-develop-a-dichotomous-key" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Calculate the number of Coleoptera species that would be expected to exist after one year from a starting number of 400\n \n \n \n \n 000 species, assuming the mean rate of decline.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n 392\n \n \n \n \n 000 (species);\n

\n
\n", "Examiners report": "None", "question_id": "22N.2.SL.TZ0.1C", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c4-2-transfers-of-energy-and-matter", "c4-2-15-primary-production-as-accumulation-of-carbon-compounds-in-biomass-by-autotrophs", "c4-2-16-secondary-production-as-accumulation-of-carbon-compounds-in-biomass-by-heterotrophs" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Describe anaerobic respiration in humans and in yeast.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n (in both) anaerobic respiration gives a small amount of ATP/2 ATP/energy from glucose;\n
    2. \n
  2. \n anaerobic respiration occurs when there is no oxygen;\n
    3. \n
  3. \n anaerobic respiration in\n \n yeast\n \n produces ethanol and carbon dioxide/alcoholic fermentation;\n
    4. \n
  4. \n anaerobic respiration in\n \n humans\n \n (in muscle) produces lactate/lactic acid/lactic acid fermentation;\n
    5. \n
  5. \n both undergo glycolysis;\n
    6. \n
\n

\n \n Do not accept mpd if CO\n \n 2\n \n also included\n \n .\n

\n
\n", "Examiners report": "
\n

\n In 3a. the top candidates scored all three marks with ease, but many, especially in Spanish scored zero. A common mistake was to say that humans produce lactic acid and CO\n \n 2\n \n . In bi, many were confused by the term ‘thermal properties’, but most were able to gain at least one point for comparing their boiling/freezing temperatures, specific heat capacities and latent heat of fusion. The best candidates also explained the differences in terms of hydrogen bonds between the water molecules. In bii, few got past stating that methane is a greenhouse gas/causes an increase in temperature of the atmosphere. The better candidates stated that it was a powerful greenhouse gas, but it had a relatively short life span compared to CO\n \n 2\n \n . A surprising number thought that methane’s main danger was that it destroyed the ozone layer.\n

\n
\n", "question_id": "22M.2.HL.TZ2.3A", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-2-cell-respiration", "c1-2-5-differences-between-anaerobic-and-aerobic-cell-respiration-in-humans", "c1-2-10-anaerobic-cell-respiration-in-yeast-and-its-use-in-brewing-and-baking" ] }, { "Question": "
\n
\n

\n Explain what happens to an enzyme if there is a change of pH.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n a. change in pH can cause a change in the tertiary structure of the enzyme\n
\n \n \n OR\n \n \n
\n enzyme denatured ✔\n

\n

\n b. causing a change in the active site / substrate not able to bind ✔\n

\n

\n c. the enzyme will not work as efficiently / decreased rate of reaction ✔\n

\n

\n d. (may no longer be) the\n \n optimum\n \n /\n \n optimal\n \n pH for enzyme activity ✔\n

\n

\n \n Allow answer in the form of a graph\n \n .\n

\n
\n", "Examiners report": "None", "question_id": "21M.2.SL.TZ2.D.II", "topics": [ "b-form-and-function" ], "subtopics": [ "b1-2-proteins", "b1-2-5-effect-of-ph-and-temperature-on-protein-structure" ] }, { "Question": "
\n
\n

\n What cell component is found in eukaryotic cells but not in prokaryotic cells?\n
\n
\n

\n

\n A.  Mitochondria for respiration\n

\n

\n B.  DNA containing genetic information\n

\n

\n C.  Ribosomes for protein synthesis\n

\n

\n D.  Cell wall to maintain shape\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "None", "question_id": "23M.1A.SL.TZ2.1", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a2-2-cell-structure", "a2-2-5-prokaryote-cell-structure" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Outline the sequence of events that occurs during mitosis.\n

\n
\n
\n

\n [5]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n supercoiling/condensation of\n \n chromosomes\n \n ;\n
    2. \n
  2. \n breakup of nuclear membrane;\n
    3. \n
  3. \n growth of spindle/microtubules;\n
    4. \n
  4. \n attachment of spindle/microtubules to chromosomes/centromeres;\n
    5. \n
  5. \n chromosomes line up at the equator/middle\n
    6. \n
  6. \n division of centromeres;\n
    7. \n
  7. \n separation of sister chromatids/chromosomes\n
    \n \n OR\n \n
    \n sister chromatids/chromosomes move to opposite poles;\n
    8. \n
  8. \n reformation of nuclear membranes around chromosomes at each pole;\n
    9. \n
\n

\n

\n

\n \n If events are not in the correct order, then award a maximum of 4 marks.\n \n

\n

\n \n Names of phases of mitosis not required.\n \n

\n

\n \n Award a max of 1 mark for listing the phases in the correct order when the list constitutes the entire response.\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ1.6", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-1-cell-and-nuclear-division", "d2-1-7-phases-of-mitosis", "d3-2-inheritance", "d3-2-11-sex-determination-in-humans-and-inheritance-of-genes-on-sex-chromosomes" ] }, { "Question": "
\n
\n

\n The graph shows the absorption spectra of chlorophyll a and chlorophyll b.\n

\n

\n \n

\n

\n [Source: adapted from F. P. Zscheile and C. L. Comar, 'Influence of Preparative Procedure on the Purity of Chlorophyll\n
\n Components as Shown by Absorption Spectra.'\n \n Int. J. Plant Sciences\n \n , Volume 102, Number\n \n 3\n \n , Mar., 1941, pp. 463–481.\n
\n Used with the kind permission of University of Chicago Press.]\n

\n

\n

\n

\n What can be concluded from the graph?\n

\n

\n A. Both chlorophyll a and chlorophyll b absorb a large amount of green light\n

\n

\n B. Chlorophyll b absorbs red light more efficiently than blue light\n

\n

\n C. Other pigments must absorb light between blue and red in the spectrum\n

\n

\n D. Chlorophyll a and chlorophyll b have different absorption peaks\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "
\n

\n This question discriminated very well, as most candidates realized that chlorophylls a and b have different absorption peaks. Some candidates confused the wavelengths for red and blue light therefore choosing B.\n

\n
\n", "question_id": "19M.1A.SL.TZ2.11", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-3-photosynthesis", "c1-3-5-absorption-of-specific-wavelengths-of-light-by-photosynthetic-pigments" ] }, { "Question": "
\n
\n

\n Through a series of enzymatic reactions, the amino acid threonine is converted to isoleucine. The graph shows the rate of reaction of threonine deaminase according to the concentration of its substrate threonine, with and without the presence of isoleucine.\n

\n

\n \n

\n

\n \n [Source: Calhoun, D.H., Rimernian, R.A. and Hatfield, G.W., 1973.\n \n
\n \n Threonine Deaminase from Escherichia coli.\n \n
\n \n I. Purification and Properties.\n \n The Journal Of Biological Chemistry\n \n ,\n \n
\n \n 248(10), pp. 3511–3516. Open Access.]\n \n

\n

\n What can be seen from these results?\n
\n
\n

\n

\n A.  Threonine deaminase only works in the presence of isoleucine.\n

\n

\n B.  Isoleucine inhibits threonine deaminase at low concentrations of threonine.\n

\n

\n C.  Production of isoleucine is inhibited at high concentration of threonine.\n

\n

\n D.  End-product inhibition controls the production of threonine deaminase.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "23M.1A.HL.TZ1.28", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-1-enzymes-and-metabolism", "c1-1-16-regulation-of-metabolic-pathways-by-feedback-inhibition" ] }, { "Question": "
\n
\n

\n What molecule functions as the final electron acceptor in the mitochondrial electron transport chain?\n

\n

\n A. Oxygen\n

\n

\n B. ATP\n

\n

\n C. Reduced NAD\n

\n

\n D. Reduced FAD\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "
\n

\n According to the statistics, this question had the highest discrimination index with response C being the most popular incorrect response.\n

\n
\n", "question_id": "21M.1A.HL.TZ2.30", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-2-cell-respiration", "c1-2-13-transfer-of-energy-by-reduced-nad-to-the-electron-transport-chain-in-the-mitochondrion" ] }, { "Question": "
\n
\n

\n In humans, male pattern baldness is caused by a recessive sex-linked gene found only on the X chromosome.\n

\n

\n \n

\n

\n If a father who does not have male pattern baldness and a mother who is a carrier for it have a child, what is the probability that the child will develop male pattern baldness in adulthood?\n

\n

\n A. 0 %\n

\n

\n B. 25 %\n

\n

\n C. 50 %\n

\n

\n D. 75 %\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "21N.1A.SL.TZ0.15", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-2-inheritance", "d3-2-13-pedigree-charts-to-deduce-patterns-of-inheritance-of-genetic-disorders" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Distinguish between the structures of DNA and RNA.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n \n

\n

\n \n A table format is not required but clear distinctions must be apparent.\n \n

\n

\n \n The full names of the bases must be given.\n \n

\n
\n", "Examiners report": "
\n

\n This question was well answered by most. Students are cautioned against representing bases with letter symbols such as A,C,T,G and U. The expectation of the mark scheme is that students write out the full names.\n

\n
\n", "question_id": "19M.2.HL.TZ2.7", "topics": [ "a-unity-and-diversity", "d-continuity-and-change" ], "subtopics": [ "a1-2-nucleic-acids", "a1-2-7-differences-between-dna-and-rna", "d3-2-inheritance", "d3-2-9-abo-blood-groups-as-an-example-of-multiple-alleles", "d3-2-10-incomplete-dominance-and-codominance", "d3-2-11-sex-determination-in-humans-and-inheritance-of-genes-on-sex-chromosomes", "d1-3-mutations-and-gene-editing", "d1-3-2-consequences-of-base-substitutions" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Outline the role of UV radiation as a mutagen.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n affects/damages/causes change in oncogenes/errors in DNA repair;\n
    2. \n
  2. \n UV radiation might alter complementary base pairing/break hydrogen bonds/fuse bases;\n
    3. \n
  3. \n double helix may uncoil;\n
    4. \n
  4. \n strands may separate/break;\n
    5. \n
  5. \n DNA sequence may be altered/DNA bases may re-connect to different bases after separating;\n
    6. \n
  6. \n DNA strand may break into pieces / fragments of DNA may be lost;\n
    7. \n
\n
\n", "Examiners report": "None", "question_id": "SPM.2.HL.TZ0.10", "topics": [ "d-continuity-and-change", "a-unity-and-diversity" ], "subtopics": [ "d1-3-mutations-and-gene-editing", "d1-3-4-causes-of-gene-mutation", "a1-2-nucleic-acids", "a1-2-6-dna-as-a-double-helix-made-of-two-antiparallel-strands-of-nucleotides-with-two-strands-linked-by-hydrogen-bonding-between-complementary-base-pairs", "d1-3-8-gene-knockout-as-a-technique-for-investigating-the-function-of-a-gene-by-changing-it-to-make-it-inoperative" ] }, { "Question": "
\n
\n

\n The graph shows human body temperature variation in a daily rhythm of 24 hours.\n

\n

\n \n

\n

\n

\n

\n Which hormone controls this variation?\n

\n

\n A. Progesterone\n

\n

\n B.  Insulin\n

\n

\n C.  Glucagon\n

\n

\n D.  Thyroxin\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "22N.1A.SL.TZ0.29", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-3-homeostasis", "d3-3-5-thermoregulation-as-an-example-of-negative-feedback-control" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n State\n \n two\n \n structural similarities between mitochondria and chloroplasts.\n

\n

\n 1.\n

\n

\n 2.\n

\n

\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. (a loop of) DNA ✔\n

\n

\n b.\n \n 70S\n \n ribosomes ✔\n

\n

\n c.\n \n double\n \n membrane ✔\n

\n

\n d. electron transport chains/enzyme complexes in (internal) membranes ✔\n

\n

\n e. enzymes in a region of fluid/in stroma and matrix ✔\n

\n

\n f. large area of (internal) membrane/cristae and thylakoids ✔\n

\n

\n \n \n Only two answers should be marked – the first on each line\n \n \n .\n

\n

\n \n Do not award marks for functions rather than structures, for example ATP production\n \n .\n

\n

\n \n Allow spaces inside cristae and thylakoids for mpf\n \n .\n

\n
\n", "Examiners report": "
\n

\n Surprisingly few candidates achieved two marks for this question, with many thinking that these organelles were cells with cell membranes, cell walls or even nuclei.\n

\n
\n", "question_id": "21M.2.SL.TZ1.2A", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a2-2-cell-structure", "a2-2-6-eukaryote-cell-structure" ] }, { "Question": "
\n
\n

\n What assumption is made when using the Hardy-Weinberg equation for calculating changes in allele frequencies in a population?\n

\n

\n
\n A.  The population size is large.\n

\n

\n B.  Natural selection is taking place.\n

\n

\n C.  Mutations are occurring in the population.\n

\n

\n D.  There is variation among the phenotypes of the population.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "None", "question_id": "SPM.1A.HL.TZ0.39", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-1-natural-selection", "d4-1-13-hardy-weinberg-equation-and-calculations-of-allele-or-genotype-frequencies" ] }, { "Question": "
\n
\n

\n What function is maintained as a result of the release of HCG?\n

\n

\n A. Production of milk by the mammary glands\n

\n

\n B. Release of oxytocin by the posterior pituitary gland\n

\n

\n C. Production of FSH by the anterior pituitary gland\n

\n

\n D. Production of progesterone by the ovary\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "
\n

\n Some G2 forms commented that the distinction between anterior and posterior pituitary gland appears only in the Options. However, the distinction between the anterior and posterior pituitary was not necessary to answer the question. In Section 6.5 (Hormones, homeostasis and reproduction), the candidates are required to understand that 'The menstrual cycle is controlled by negative and positive feedback mechanisms involving ovarian and pituitary hormones'. This should have been sufficient knowledge to answer the question correctly.\n

\n
\n", "question_id": "21M.1A.HL.TZ2.40", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-1-reproduction", "d3-1-17-pregnancy-testing-by-detection-of-human-chorionic-gonadotropin-secretion" ] }, { "Question": "
\n
\n

\n The diagram shows some reactions occurring during respiration in the mitochondrion.\n

\n

\n \n

\n

\n Energy that is released by oxidation reactions in the mitochondrial matrix is carried to the cristae of the mitochondria. How is this energy carried?\n
\n
\n

\n

\n A.  As ATP\n

\n

\n B.  As glucose\n

\n

\n C.  In lysed water\n

\n

\n D.  As reduced NAD\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "23M.1A.HL.TZ1.29", "topics": [ "b-form-and-function" ], "subtopics": [ "b2-2-organelles-and-compartmentalization", "b2-2-4-adaptations-of-the-mitochondrion-for-production-of-atp-by-aerobic-cell-respiration" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Outline the effect of carrying capacity on the growth of a population.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. carrying capacity is maximum population size/number of individuals that environment can support\n
\n \n \n OR\n \n \n
\n carrying capacity varies with abundance of limiting resources ✔\n

\n

\n b. population growth slows/fluctuates as the carrying capacity of environment reached ✔\n

\n
\n", "Examiners report": "
\n

\n Most candidates had an idea about carrying capacity, but there was only one element in the outline of many.\n

\n
\n", "question_id": "19M.2.SL.TZ2.16B", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c4-1-populations-and-communities", "c4-1-5-carrying-capacity-and-competition-for-limited-resources" ] }, { "Question": "
\n
\n

\n Which feature is common to both mRNA and DNA?\n

\n

\n A. Covalent bonds between adjacent nucleotides\n

\n

\n B. Hydrogen bonds between guanine and cytosine\n

\n

\n C. Ribose sugar attached to phosphate\n

\n

\n D. Antiparallel arrangement of polynucleotide strands\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "None", "question_id": "21M.1A.SL.TZ2.9", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a1-2-nucleic-acids", "a1-2-3-sugar-phosphate-bonding-and-the-sugar-phosphate-“backbone”-of-dna-and-rna" ] }, { "Question": "
\n
\n

\n The crustacean and the jellyfish obtain carbon compounds by feeding. State\n \n one\n \n source of carbon for marine organisms, other than feeding.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n a. photosynthesis ✔\n

\n

\n b. absorption of (dissolved) carbon dioxide / (hydrogen)carbonate directly from the oceans ✔\n

\n

\n \n Accept reference to carbonate or hydrogencarbonate ions\n \n .\n

\n
\n", "Examiners report": "
\n

\n In 4(a) most were able to state 'respiration' as the answer. 4(b) proved more difficult with fewer stating photosynthesis or absorption of dissolved CO\n \n 2\n \n or HCO\n \n 3\n \n from the seawater. Vague answers such as 'carbon in the water' were not credited. In 4(c) most knew that energy enters with sunlight, but did not state photosynthesis. They knew that it was transferred by feeding through the trophic levels and lost as heat due to respiration. A surprising number incorrectly stated that the energy was recycled and some drew diagrams of the energy flow showing this. In 4(d)(i) most were able to state that the crustacean was a richer source of carbon. An explanation using the data from the diagram was expected. In 4(d)(ii) most were able to present an argument for advantage or disadvantage.\n

\n
\n", "question_id": "21M.2.SL.TZ2.B", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c4-2-transfers-of-energy-and-matter", "c4-2-17-constructing-carbon-cycle-diagrams", "c4-2-18-ecosystems-as-carbon-sinks-and-carbon-sources" ] }, { "Question": "
\n
\n

\n Which factor(s) would favour evolution by natural selection?\n

\n

\n I. Long lifespans\n

\n

\n II. Favourable characteristics acquired by individuals during their lifetime\n

\n

\n III. Variation within a species\n

\n

\n A. II only\n

\n

\n B. III only\n

\n

\n C. I and II\n

\n

\n D. I and III\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "
\n

\n The question did discriminate well. It was commented that the word ‘lifespans’ may be difficult for non-native English speakers.\n

\n
\n", "question_id": "22M.1A.SL.TZ2.23", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a4-1-evolution-and-speciation", "a4-1-1-evolution-as-change-in-the-heritable-characteristics-of-a-population" ] }, { "Question": "
\n
\n

\n Cell metabolism involves anabolic and catabolic reactions. Which process directly involves anabolism?\n

\n

\n A. Active transport of ions\n

\n

\n B. Release of energy from glucose\n

\n

\n C. Production of intracellular enzymes\n

\n

\n D. Breakdown of worn-out cell organelles by lysosomes\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "22M.1A.SL.TZ2.1", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-1-enzymes-and-metabolism", "c1-1-3-anabolic-and-catabolic-reactions" ] }, { "Question": "
\n
\n (g)\n
\n
\n

\n Suggest reasons for the difference between the fraction attributed to\n \n S. pneumoniae\n \n in all cases of ARI and in cases where antibiotics were used to treat the infection.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n highest attributed fraction (in both age groups) is in cases where antibiotic used;\n
    2. \n
  2. \n ARI cases due to\n \n S. pneumoniae\n \n can be severe so antibiotics are often prescribed;\n
    3. \n
  3. \n all cases include other causes / viral ARI which may not require antibiotics;\n
    4. \n
  4. \n antibiotics administered without prescription or physician consultation/to reduce symptoms;\n
    5. \n
\n

\n \n Mpa: Comparative terms expected (do not award mp for just stating values).\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ2.1G", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-2-defence-against-disease", "c3-2-16-vaccines-and-immunization" ] }, { "Question": "
\n
\n (h)\n
\n
\n

\n Using\n \n all\n \n the data, discuss whether inoculating mice with the antigen to\n \n B. burgdorferi\n \n could be an effective method of controlling the spread of Lyme disease.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n a.\n \n Site 2\n \n suggests that vaccination could reduce «nymph» infection rate «so method might be effective» ✔\n

\n

\n b.\n \n Site 1\n \n suggests that vaccination does not reduce «nymph» infection rate «so method probably not effective» ✔\n

\n

\n c. effective «to some extent» as vaccination increases antibodies/immunity in mice ✔\n

\n

\n d. high antibody levels needed/ many mice need to be vaccinated «for the method to be effective» ✔\n

\n

\n e. some nymphs are still infected / «absolute» numbers «rather than proportions» of infected nymphs are similar in those collected from control and vaccinated mice ✔\n

\n

\n f. there are other hosts/mammals/birds ✔\n

\n

\n g. difficult/expensive «to vaccinate many small mammals/mice»\n
\n \n \n OR\n \n \n
\n cheaper to use protective clothing/tick repellant/avoid wooded areas/other method ✔\n

\n
\n", "Examiners report": "None", "question_id": "19N.2.SL.TZ0.1H", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-2-defence-against-disease", "c3-2-10-immunity-as-a-consequence-of-retaining-memory-cells" ] }, { "Question": "
\n
\n

\n Apart from the ribosomes, explain the evidence for the endosymbiotic theory of the origin of eukaryotic cells.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n a. mitochondria/chloroplasts show features in common with\n \n prokaryotes\n \n /similar size;\n

\n

\n b. multiply by binary fission/in same manner;\n

\n

\n c. have naked loop of DNA/circular DNA/own DNA;\n

\n

\n d. surrounded by a double membrane;\n

\n
\n", "Examiners report": "None", "question_id": "20N.2.HL.TZ0.D", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a2-2-cell-structure", "a2-2-12-origin-of-eukaryotic-cells-by-endosymbiosis" ] }, { "Question": "
\n
\n

\n Over time, the hull of a sunken ship may become colonized by a wide range of marine organisms. What term is used to describe all of the organisms living in and on a sunken ship?\n

\n

\n A. A community\n

\n

\n B. An ecological niche\n

\n

\n C. A population\n

\n

\n D. An ecosystem\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "
\n

\n This question was criticised on G2 forms for being confusingly worded, but it had a good discrimination index and nearly 60 % of candidates answered correctly. The question asked about the animals around the sunken ship and not the ship as well, so the answer was community rather than ecosystem.\n

\n
\n", "question_id": "21M.1A.SL.TZ1.20", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c4-1-populations-and-communities", "c4-1-10-a-community-as-all-of-the-interacting-organisms-in-an-ecosystem" ] }, { "Question": "
\n
\n (g)\n
\n
\n

\n Explain how vaccination can lead to the production of B cells specific to the Ebola virus.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n a.\n \n vaccine\n \n contains Ebola\n \n antigens\n \n ✔\n

\n

\n b. vaccine «could» contain weakened/attenuated/dead/killed form of «Ebola» virus/virus genetically modified to express an Ebola/viral protein ✔\n

\n

\n c. phagocyte/macrophage engulfs the antigen/presents the antigen to T cell ✔\n

\n

\n d. antigen recognized by «specific» T cells/binds to T cells ✔\n

\n

\n e. «activated» T cells activate «specific) B cells ✔\n

\n

\n f. «activated» B cells make the\n \n antibodies\n \n «against Ebola» ✔\n

\n

\n g. B cells divide forming «clone of» plasma cells/producing more B cells specific to Ebola ✔\n

\n
\n", "Examiners report": "
\n

\n This was a timely question with Ebola epidemics again causing great problems in parts of Africa. Students were expected to have had some practice at analysing data relating to an epidemic because of this Skill in the programme: Analysis of epidemiological data related to vaccination programmes. It was assumed that candidates would understand terms such as ‘case’, ‘fatal case’, ‘infect’ and ‘treat’.\n

\n

\n Vaccination is a major focus on 11.1 of the programme so it was perhaps surprising that answers here were not better. Given the current outbreaks of measles and other diseases that can be prevented by vaccination, this topic should be given greater prominence in some schools. There were a few impressive answers giving the details of the steps that lead up to production of antibodies against a specific pathogen, but less than a quarter of candidates scored all three marks. There were many misconceptions. The terms ‘resistant’ and ‘immune’ have different meanings in biology, which should be carefully distinguished. Some candidates think that a vaccine contains a small amount of the pathogen. Would those candidates be happy to be infected with Ebola viruses as long as it was only a few? There was too much talk of cells ‘remembering’ the antigen or the virus. Memory cell is perhaps an unfortunate term. They are only memory cells in the sense that if an antigen binds to the antibodies they display, after cell multiplication more of those antibodies are produced and they will bind to the same antigens on the surface of an invading pathogen. This is just a series of molecular processes, not true memory.\n

\n
\n", "question_id": "19M.2.SL.TZ1.1G", "topics": [ "c-interaction-and-interdependence", "a-unity-and-diversity" ], "subtopics": [ "c3-2-defence-against-disease", "a2-3-viruses-(hl-only)" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Distinguish between the two diets.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. they differ in percent of saturated and unsaturated fats (but not total fat);\n

\n

\n b. percent of saturated fats is higher in study diet / lower in habitual diet;\n

\n

\n c. (mono/poly) unsaturated fats decreased in study diet compared to habitual diet/more in habitual diet\n
\n \n \n OR\n \n \n
\n polyunsaturated fats in study diet only half of what they were in habitual diet;\n

\n

\n d. (slightly) less carbohydrate in study;\n

\n

\n \n Allow numerical points if they are a valid comparison using distinguishing terms\n \n .\n

\n
\n", "Examiners report": "None", "question_id": "20N.1B.SL.TZ0.1B", "topics": [ "b-form-and-function" ], "subtopics": [ "b1-2-proteins", "b1-2-3-dietary-requirements-for-amino-acids", "b1-1-carbohydrates-and-lipids", "b1-1-10-difference-between-saturated-monounsaturated-and-polyunsaturated-fatty-acids" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Describe the barriers that exist to hybridization between species.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n courtship behaviour is often complex and unique to a species;\n
    2. \n
  2. \n (at several stages in courtship ritual) rejection occurs if characteristic behaviour not exhibited;\n
    3. \n
  3. \n species-specific egg fertilization;\n
    4. \n
  4. \n compatibility of acrosome with vitelline layer;\n
    5. \n
  5. \n inability of successfully attached wrong species sperm to develop continuity with egg membrane;\n
    6. \n
  6. \n sterility of interspecific hybrids;\n
    7. \n
  7. \n due to differences in chromosome number;\n
    8. \n
\n
\n", "Examiners report": "None", "question_id": "SPM.2.HL.TZ0.8C", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a4-1-evolution-and-speciation", "a4-1-10-barriers-to-hybridization-and-sterility-of-interspecific-hybrids-as-mechanisms-for-of-preventing-the-mixing-of-alleles-between-species" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Other than position in the tree, suggest\n \n two\n \n ways in which the niches of the warblers in the ecosystem may differ.\n

\n

\n 1.\n

\n

\n 2.\n

\n

\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. different food/prey;\n

\n

\n b. different predators;\n

\n

\n c. active at different times of the day;\n

\n

\n d. present at different times of the year;\n

\n

\n e. different nest sites;\n

\n

\n f. different temperatures;\n

\n

\n \n Do not accept “different habitats\n \n ”.\n

\n
\n", "Examiners report": "None", "question_id": "20N.2.SL.TZ0.12C", "topics": [ "b-form-and-function" ], "subtopics": [ "b4-2-ecological-niches", "b4-2-12-fundamental-and-realized-niches", "b4-2-13-competitive-exclusion-and-the-uniqueness-of-ecological-niches" ] }, { "Question": "
\n
\n

\n Some bacteria can synthesize the amino acid isoleucine from threonine, a process involving five enzymes (E\n \n 1\n \n to E\n \n 5\n \n ) and four intermediary products (P, Q, R and S). The production of isoleucine is controlled by end-product inhibition.\n

\n

\n \n

\n

\n

\n

\n

\n

\n

\n

\n

\n

\n

\n

\n

\n

\n

\n

\n

\n

\n Which statement describes this end-product inhibition?\n

\n

\n A. If isoleucine accumulates, it inhibits the production of P.\n

\n

\n B. End-product inhibition causes a build-up of intermediary products.\n

\n

\n C. Isoleucine inhibits E\n \n 5\n \n , so no more isoleucine is produced.\n

\n

\n D. Isoleucine affects the structure of threonine.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "None", "question_id": "21N.1A.HL.TZ1.29", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-1-enzymes-and-metabolism", "c1-1-16-regulation-of-metabolic-pathways-by-feedback-inhibition" ] }, { "Question": "
\n
\n (e)\n
\n
\n

\n With reference to the diagram, identify\n \n one\n \n example of catabolism.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n a. (letter X) breakdown of monosaccharides/respiration ✔\n

\n

\n b. (letter Y) hydrolysis/photolysis in photosynthesis/oxidation of water ✔\n

\n

\n \n Answer must come from the diagram\n \n .\n

\n
\n", "Examiners report": "
\n

\n The diagram was generally confusing to candidates.\n

\n

\n Too often candidates did not make reference to the diagram when giving an example of catabolism. Some thought that ADP changing to ATP was catabolism. This probably comes from a failure to understand paired reactions.\n

\n
\n", "question_id": "21M.2.SL.TZ1.2E", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-1-enzymes-and-metabolism", "c1-1-3-anabolic-and-catabolic-reactions" ] }, { "Question": "
\n
\n

\n There are viruses in soils that are pathogens of animals. Outline a reason for antibiotics in soil not eliminating these viruses.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n viruses lack metabolism/plasma membranes/cell walls / viruses are not livingorganisms;\n
    2. \n
  2. \n antibiotics kill/target bacteria/prokaryotes but not viruses;\n
    3. \n
  3. \n viral pathogens of animals use animal metabolism (which is not affected by antibiotics);\n
    4. \n
\n

\n

\n
\n", "Examiners report": "None", "question_id": "23M.2.HL.TZ1.I", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-2-defence-against-disease", "c3-2-14-evolution-of-resistance-to-several-antibiotics-in-strains-of-pathogenic-bacteria" ] }, { "Question": "
\n
\n

\n Which graph represents the action spectrum for a green plant receiving only blue light?\n

\n

\n \n

\n

\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "23M.1A.SL.TZ2.10", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-3-photosynthesis", "c1-3-6-similarities-and-differences-of-absorption-and-action-spectra" ] }, { "Question": "
\n
\n

\n The same apparatus was used in another experiment, but the potted plant was exposed to light. Predict with a reason the results for lime water in flask C after one hour.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n no change/limewater stays clear\n
\n \n \n OR\n \n \n
\n because plant takes in carbon dioxide by photosynthesis;\n

\n

\n \n Do not accept references to oxygen produced by photosynthesis\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.1B.SL.TZ1.D", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-1-enzymes-and-metabolism", "c1-1-8-effects-of-temperature-ph-and-substrate-concentration-on-the-rate-of-enzyme-activity" ] }, { "Question": "
\n
\n (d)\n
\n
\n

\n Using the information in the graph, describe how the experiment could be extended to determine the optimum temperature for immobilized HRP.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n the graph shows the optimum temperature to be near 40 °C;\n
    2. \n
  2. \n choose smaller range of temperature (between 30 and 50 °C);\n
    3. \n
  3. \n smaller increments of temperature\n
    4. \n
\n

\n \n c. Accept numbers such as 1 or 5 degrees.\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.1B.SL.TZ1.1D", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-1-enzymes-and-metabolism", "c1-1-8-effects-of-temperature-ph-and-substrate-concentration-on-the-rate-of-enzyme-activity" ] }, { "Question": "
\n
\n (d)\n
\n
\n

\n Outline\n \n one\n \n factor that could affect the activity of Rubisco.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. name of factor ✔\n

\n

\n b. how it affects rate of reaction ✔\n

\n

\n \n Example answer\n \n :\n

\n

\n \n temperature\n \n ✔\n

\n

\n \n as the temperature increases the rate of reaction increases until it reaches a maximum and then decreases rapidly\n \n ✔\n

\n

\n \n Accept answers in a graph\n \n .\n

\n
\n", "Examiners report": "
\n

\n There were some G2 comments about the function of Rubisco. It is mentioned in 2.4. and the stem did say that it was an enzyme. Simply stating that it was an enzyme involved in photosynthesis was sufficient for the mark. A detailed function was not required. Most could state the role of the active site and that the genus was\n \n Pisume.\n \n The word genus in this context confused some French candidates who answered 'male or female'. 3(d) was simply testing the factors controlling enzyme action. Weaker students just listed several factors. When it says one factor, only the first is considered. The difference between heat and temperature was occasionally confused. The examiners were looking for the effect of increasing and decreasing the factor. Many students seemed to be obsessed with denaturing. For example the answer 'temperature' (first mark): as the temperature is too high the enzyme denatures (no second mark as no mention of decreasing temperature). Few used the collision theory idea which was expected.\n

\n
\n", "question_id": "21M.2.SL.TZ2.3D", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-1-enzymes-and-metabolism", "c1-1-8-effects-of-temperature-ph-and-substrate-concentration-on-the-rate-of-enzyme-activity" ] }, { "Question": "
\n
\n (a.i)\n
\n
\n

\n Identify the process Y and state the name of the organelle where it takes place in a plant cell.\n

\n

\n Process Y:\n

\n

\n Name of the organelle:\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n process Y: photosynthesis ✔\n

\n

\n organelle: chloroplast ✔\n

\n

\n \n Both needed\n \n .\n

\n
\n", "Examiners report": "
\n

\n The diagram was generally confusing to candidates.\n

\n

\n This was generally answered correctly.\n

\n
\n", "question_id": "21M.2.SL.TZ1.2A.I", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c4-2-transfers-of-energy-and-matter", "c4-2-18-ecosystems-as-carbon-sinks-and-carbon-sources" ] }, { "Question": "
\n
\n (g)\n
\n
\n

\n The first study used mesocosms and the second study was carried out in natural grassland. Discuss the use of mesocosms as opposed to a study in a natural environment.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n \n advantages of mesocosms/converse problems with studies in natural environments\n \n
\n a. easier to manipulate/control variables/conditions / less susceptible to outside influences\n
\n \n OR\n \n
\n easier to replicate\n
\n \n OR\n \n
\n take up less space;\n

\n

\n \n disadvantages of mesocosms/converse opportunities with studies in natural environments\n \n
\n b. some trophic levels missing/incomplete food chains in mesocosms\n
\n \n OR\n \n
\n large animals cannot be included / ethical concerns about enclosing animals in mesocosms\n
\n \n OR\n \n
\n some variables lacking in mesocosms / doesn’t show what happens in natural ecosystems;\n

\n

\n \n Allow only one mark for an advantage and one mark for a disadvantage as this is a discuss question\n \n .\n

\n
\n", "Examiners report": "
\n

\n Because this was a ‘discuss’ question, one mark was awarded for arguments in favour or mesocosms and one mark for counter arguments. The best answers weighed up the relative advantage of these two approaches, rather than just singing the praises of one of them.\n

\n
\n", "question_id": "21N.2.SL.TZ0.1G", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-2-stability-and-change", "d4-2-4-use-of-a-model-to-investigate-the-effect-of-variables-on-ecosystem-stability" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n State how many different types of amino acid there are, which can become part of a polypeptide when mRNA is translated.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n 20;\n

\n
\n", "Examiners report": "
\n

\n Amazingly, most candidates missed gaining the mark for this question: a huge variety of incorrect numbers appeared, \"4\" was most frequent. Many candidates seemed to confuse the 4 nucleotide bases with the 20 amino acids.\n

\n
\n", "question_id": "22M.2.SL.TZ1.2A", "topics": [ "b-form-and-function" ], "subtopics": [ "b1-2-proteins", "b1-2-4-infinite-variety-of-possible-peptide-chains" ] }, { "Question": "
\n
\n

\n Blood clotting involves a cascade of reactions. Which statement describes the blood-clotting process?\n

\n

\n A. Red blood cells release clotting factors that result in the production of fibrin.\n

\n

\n B. Clotting factors trigger the conversion of the inactive thrombin to prothrombin.\n

\n

\n C. Insoluble fibrinogen is converted into soluble fibrin.\n

\n

\n D. Fibrin forms a mesh that traps platelets and blood cells.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "
\n

\n About half of candidates answered this question correctly, but the discrimination index was rather low. Answer D was clearly correct, but many candidates chose A or B instead. A was incorrect because red blood cells do not release clotting factors. B was incorrect because thrombin is not converted to prothrombin. As ever, candidates are advised to read all the possible choices.\n

\n
\n", "question_id": "22M.1A.SL.TZ1.22", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-2-defence-against-disease", "c3-2-3-sealing-of-cuts-in-skin-by-blood-clotting" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Explain how plants capture and use light in photosynthesis.\n

\n
\n
\n

\n [7]\n

\n
\n
\n", "Markscheme": "
\n

\n a. plants convert light energy into chemical energy by photosynthesis ✔\n

\n

\n b. photosynthesis takes place in chloroplasts ✔\n

\n

\n c. chloroplasts «are organelles that» contain the pigment chlorophyll ✔\n

\n

\n d. chloroplasts/chlorophyll «in plants» absorb sunlight ✔\n

\n

\n e. «chlorophyll» absorbs red\n \n \n AND\n \n \n blue light most effectively ✔\n

\n

\n f. light causes photolysis/splits water molecule ✔\n

\n

\n g. carbon dioxide\n \n \n AND\n \n \n water are reactants «in photosynthesis» ✔\n

\n

\n h. glucose\n \n \n AND\n \n \n oxygen are products «of photosynthesis» ✔\n

\n

\n i. light\n \n intensity\n \n is a limiting factor for the\n \n rate\n \n of photosynthesis ✔\n

\n

\n j. organic/carbon compounds/glucose provide food/stored energy «for plant itself, animals,food chains» ✔\n

\n

\n k. up to one additional mark for an accurate detail from AHL ✔\n

\n
\n", "Examiners report": "
\n

\n Generally well done with some very knowledgeable answers from the Higher Level programme sometimes to the detriment of the more basic answers required by the standard level examination. Many candidates who attempted this response got more than 4 marks for mp b, d, g and h which were the most common. Students getting higher marks were able to focus on correct conversion of energy, efficiency of red and blue light absorption, and photolysis. Some egregious misconceptions exist among candidates such as plants are green because they absorb green light. The idea that during photosynthesis light energy is converted to chemical energy was frequently neglected.\n

\n
\n", "question_id": "19M.2.SL.TZ1.8C", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-3-photosynthesis", "c1-3-5-absorption-of-specific-wavelengths-of-light-by-photosynthetic-pigments" ] }, { "Question": "
\n
\n

\n Broad beans are rich in starch and cellulose. Compare and contrast the structure of starch and cellulose.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. both polymers of glucose molecules / polysaccharides\n
\n \n \n OR\n \n \n
\n both form 1,4 glycosidic bond ✔\n

\n

\n b. starch is formed by alpha glucose while cellulose is formed by beta glucose\n
\n \n \n OR\n \n \n
\n in starch C1 hydroxyl groups are found in same plane while in cellulose on different planes\n
\n \n \n OR\n \n \n
\n in cellulose, alternatively the beta glucose needs to be placed upside-down in order to have C1 hydroxyl groups on the same plane\n
\n \n \n OR\n \n \n
\n two types of starch (amylose and amylopectin) but one type of cellulose ✔\n

\n

\n \n One similarity and one difference\n \n .\n

\n

\n \n Comparison to cellulose needed\n \n .\n

\n
\n", "Examiners report": "
\n

\n Candidates seemed to find it difficult to find similarities and differences in structure between starch and cellulose, and many wrote about their functions, or simply mentioned that both were made of \"glucose\" without referencing that they are both polymers. There was limited recognition that there are two forms of starch: amylose and amylopectin that differ in their degree of branching.\n

\n
\n", "question_id": "21M.2.SL.TZ2.D", "topics": [ "b-form-and-function" ], "subtopics": [ "b1-1-carbohydrates-and-lipids", "b1-1-5-polysaccharides-as-energy-storage-compounds" ] }, { "Question": "
\n
\n

\n Huntington’s disease is an autosomal dominant genetic disease. What are the chances of two parents that are heterozygous for the gene having a child with Huntington’s disease?\n

\n

\n A. 25 %\n

\n

\n B. 50 %\n

\n

\n C. 75 %\n

\n

\n D. 100 %\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "22M.1A.SL.TZ1.16", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-2-inheritance", "d3-2-5-effects-of-dominant-and-recessive-alleles-on-phenotype" ] }, { "Question": "
\n
\n

\n Two kinds of wolf spider rub specialized body parts together in order to produce distinct sounds to attract females. Females of both groups will only allow a male of the same kind to mate with them. It has been found through experimentation, however, that offspring can be produced from crossings between the two groups. What can be hypothesized?\n

\n

\n I.   The groups are reproductively isolated.\n

\n

\n II.  They could be the same species.\n

\n

\n III. This is an example of behavioural isolation.\n

\n

\n A.  I only\n

\n

\n B.  II only\n

\n

\n C.  I and II only\n

\n

\n D.  I, II and III\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "22N.1A.HL.TZ0.36", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a4-1-evolution-and-speciation", "a4-1-7-roles-of-reproductive-isolation-and-differential-selection-in-speciation" ] }, { "Question": "
\n
\n

\n Suggest\n \n two\n \n possible reasons for the drop in the daily numbers of newly infected cases after October 2014 in Liberia.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. improved medical care/support/supplies/equipment/training of staff/hygiene/distribution of vaccine ✔\n
\n
\n b. improved understanding of how to avoid infection «amongst public»/greater awareness in society/better education✔\n

\n

\n c. rise in number of deaths means fewer infectious individuals ✔\n

\n

\n d. impact of disease control measures/control policies/quarantine/isolation ✔\n

\n

\n e. drop in the number of fruit bats ✔\n

\n

\n f. maybe seasonal changes/weather changes ✔\n

\n

\n g. people may have left the area ✔\n

\n

\n h. international aid arrives ✔\n

\n

\n \n OWTTE\n \n

\n
\n", "Examiners report": "
\n

\n This was a well answered response where almost all students got full marks. Students were able to identify more than three marking points here mp a, b, c and d were most common. Some students provided mp e and f. Few used mp g and h.\n

\n
\n", "question_id": "19M.2.HL.TZ1.E", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a2-3-viruses-(hl-only)" ] }, { "Question": "
\n
\n

\n Compare and contrast the data in the chart for males and females.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n Similarities (Compare)\n

\n

\n a. lower percentage of obesity with more steps per day in both males and females\n
\n \n \n OR\n \n \n
\n percentage obesity is most similar at 1000 steps\n
\n \n \n OR\n \n \n
\n correlation of steps to percent obesity plateaus after 8000 steps for both males and females;\n

\n

\n
\n Differences (Contrast)\n

\n

\n b. the range difference of obesity percentage among different steps is bigger in females (9% - 31% versus 18% to 30%)\n
\n \n \n OR\n \n \n
\n walking has a greater impact on lowering obesity rates in females than males\n
\n \n \n OR\n \n \n
\n men show a greater percentage of obesity\n
\n \n \n OR\n \n \n
\n at 1000 steps per day there are more obese women than men;\n

\n

\n

\n

\n \n One similarity and one difference required for two marks.\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ1.E", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-3-muscle-and-motility-(hl-only)", "b3-3-9-reasons-for-locomotion" ] }, { "Question": "
\n
\n

\n Based on these data, outline the evidence that T-705 has potential to be used as a treatment for EVD.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. cells not killed/few cells killed «even at high concentrations» ✔\n

\n

\n b. «T-705» effective/viruses reduced/viruses killed at 100 μM\n
\n \n \n OR\n \n \n
\n «T-705» very effective/viruses much reduced/nearly all viruses killed at 1000 μM ✔\n

\n

\n c. virus concentration decreases as T-705 concentration increases ✔\n

\n

\n d. drug has «high» potential for treatment «at high enough concentration» ✔\n

\n
\n", "Examiners report": "
\n

\n Graph was well read and understood by most. The question was answered with more insight than expected, especially when alluding to the implications of live cells at high drug concentrations\n

\n
\n", "question_id": "19M.2.HL.TZ1.F", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a2-3-viruses-(hl-only)" ] }, { "Question": "
\n
\n

\n What is a difference between two alleles of a gene?\n

\n

\n A.  Their positions on homologous chromosomes\n

\n

\n B.  Their amino acid sequence\n

\n

\n C.  The characteristic they influence\n

\n

\n D.  Their base sequence\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "
\n

\n The candidates were asked for the differences between two alleles of a gene. The question performed quite well statistically. It was suggested that response B should be considered as a suitable answer at SL but this was considered wrong as a gene consists of nucleotides.\n

\n
\n", "question_id": "22N.1A.SL.TZ0.13", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-2-inheritance", "d3-2-3-genotype-as-the-combination-of-alleles-inherited-by-an-organism" ] }, { "Question": "
\n
\n

\n Identify X, the enzyme which copies a DNA sequence.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n \n RNA polymerase\n \n ;\n

\n
\n", "Examiners report": "
\n

\n About half of candidates knew that X must be RNA polymerase. Some candidates thought that it was DNA polymerase, perhaps because the question referred to copying a DNA sequence. This answer was not accepted as the diagram did not show replication.\n

\n
\n", "question_id": "22N.2.HL.TZ0.C.I", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d1-1-dna-replication", "d1-1-3-role-of-helicase-and-dna-polymerase-in-dna-replication" ] }, { "Question": "
\n
\n

\n The diagram shows the product of a polymerization reaction.\n

\n

\n \n

\n

\n What is formed in this polymerization reaction?\n

\n

\n A.  A dipeptide formed by the hydrolysis of two nucleotides\n

\n

\n B.  A tripeptide formed by the hydrolysis of three amino acids\n

\n

\n C.  A dipeptide formed by the condensation of two amino acids\n

\n

\n D.  A tripeptide formed by the condensation of three amino acids\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "22N.1A.SL.TZ0.7", "topics": [ "b-form-and-function" ], "subtopics": [ "b1-1-carbohydrates-and-lipids", "b1-1-5-polysaccharides-as-energy-storage-compounds" ] }, { "Question": "
\n
\n

\n What is the reason for antibiotics not damaging human cells?\n

\n

\n A. The dose is too small to be harmful.\n

\n

\n B. The dose is taken for only a short time.\n

\n

\n C. Antibiotics occur naturally in humans.\n

\n

\n D. Human metabolism is different from bacterial metabolism.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "19M.1A.SL.TZ2.27", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-2-defence-against-disease", "c3-2-13-antibiotics-as-chemicals-that-block-processes-occurring-in-bacteria-but-not-in-eukaryotic-cells" ] }, { "Question": "
\n
\n

\n The image shows an organism belonging to the Kingdom Animalia.\n

\n

\n \n

\n

\n [Source: Titan beetle male. Locality: “RK4,5 route Cacao”, French Guiana\n
\n © 2011, Didier Descouens\n \n https://creativecommons.org/licenses/by-sa/4.0/]\n \n

\n

\n

\n

\n What feature does this organism have in common with all members of the phylum chordata?\n

\n

\n A. Legs and wings\n

\n

\n B. Mouth but no anus\n

\n

\n C. Bilateral symmetry\n

\n

\n D. Chitinous exoskeleton\n

\n

\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "19M.1A.HL.TZ1.22", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a3-2-classification-and-cladistics-(hl-only)" ] }, { "Question": "
\n
\n

\n The graph shows the energy changes during a chemical reaction. The horizontal lines represent the original energy values.\n

\n

\n \n

\n

\n Which graph represents the energy changes once a suitable enzyme has been added?\n

\n

\n \n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "23M.1A.SL.TZ2.25", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d1-2-protein-synthesis", "d1-2-15-post-transcriptional-modification-in-eukaryotic-cells" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Outline the role of\n \n three\n \n enzymes used in the replication of DNA.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n a. helicase to separate/unwind DNA strands ✔\n

\n

\n b. gyrase / toposiomerase to relax the tension as bacterial DNA is being uncoiled / prevent supercoiling ✔\n

\n

\n c. primase to synthesise primers ✔\n

\n

\n d. polymerase (I) removes primers and replaces with nucleotide ✔\n

\n

\n e. polymerase (III) adds nucleotides (in a 5' to 3' direction) ✔\n

\n

\n f. ligase joins (Okazaki) fragments together ✔\n

\n

\n \n Accept the enzyme name without ‘DNA’ included; e.g. ‘DNA ligase’ or ‘ligase’ can both be accepted\n \n .\n

\n
\n", "Examiners report": "
\n

\n Well answered.\n

\n
\n", "question_id": "21M.2.HL.TZ2.7B", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d1-1-dna-replication", "d1-1-3-role-of-helicase-and-dna-polymerase-in-dna-replication", "d1-1-8-functions-of-dna-primase-dna-polymerase-i-dna-polymerase-iii-and-dna-ligase-in-replication" ] }, { "Question": "
\n
\n

\n The table shows the number of cells in various stages of the cell cycle in four samples of ovarian tissue from different patients. Which tissue sample A, B, C or D has the highest mitotic index?\n

\n

\n \n

\n

\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "19M.1A.HL.TZ1.5", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-1-cell-and-nuclear-division", "d2-1-17-differences-between-tumours-in-rates-of-cell-division-and-growth-and-in-the-capacity-for-metastasis-and-invasion-of-neighbouring-tissue" ] }, { "Question": "
\n
\n

\n The diagram shows a cladogram for part of the animal kingdom.\n

\n

\n \n

\n

\n \n [Source: Semmens, D.C., Mirabeau, O., Moghul, I., Pancholi, M.R., Wurm, Y. and Elphick, M.R., 2016. Transcriptomic\n \n \n identification of starfish neuropeptide precursors yields new insights into neuropeptide evolution.\n \n Open Biology\n \n ,\n \n \n [e-journal] 6(2). https://doi.org/10.1098/rsob.150224. Source adapted. Public domain.]\n \n

\n

\n

\n

\n Which group does\n \n not\n \n represent a clade?\n

\n

\n
\n A.  1 to 3\n

\n

\n B.  1 to 5\n

\n

\n C.  4 to 7\n

\n

\n D.  1 to 10\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "23M.1A.HL.TZ2.25", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a3-2-classification-and-cladistics-(hl-only)", "a3-2-2-difficulties-classifying-organisms-into-the-traditional-hierarchy-of-taxa" ] }, { "Question": "
\n
\n (ii)\n
\n
\n

\n Suggest\n \n two\n \n reasons, other than mate selection, for variation in plumage colouration in red knots.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n camouflage to avoid predators (in different migratory routes);\n
    2. \n
  2. \n different diets (in different migratory routes);\n
    3. \n
  3. \n less migratory distance leaves more energy to produce pigments (in plumage);\n
    4. \n
  4. \n geographic isolation (due to different migratory routes) leads to different gene pools;\n
    5. \n
\n
\n", "Examiners report": "None", "question_id": "23M.1A.SL.TZ2.8AII", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-1-natural-selection", "d4-1-7-sexual-selection-as-a-selection-pressure-in-animal-species" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n State\n \n two\n \n structural similarities between mitochondria and chloroplasts.\n

\n

\n 1.\n

\n

\n 2.\n

\n

\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. (a loop of) DNA ✔\n

\n

\n b.\n \n 70S\n \n ribosomes ✔\n

\n

\n c.\n \n double\n \n membrane ✔\n

\n

\n d. electron transport chains/enzyme complexes in (internal) membranes ✔\n

\n

\n e. enzymes in a region of fluid/in stroma and matrix ✔\n

\n

\n f. large area of (internal) membrane/cristae and thylakoids ✔\n

\n

\n \n \n Only two answers should be marked – the first on each line\n \n \n .\n

\n

\n \n Do not award marks for functions rather than structures, for example ATP production\n \n .\n

\n

\n \n Allow spaces inside cristae and thylakoids for mpf\n \n .\n

\n
\n", "Examiners report": "
\n

\n Surprisingly few candidates achieved two marks for this question, with many thinking that these organelles were cells with cell membranes, cell walls or even nuclei.\n

\n
\n", "question_id": "21M.2.HL.TZ1.2", "topics": [ "a-unity-and-diversity", "b-form-and-function" ], "subtopics": [ "a2-2-cell-structure", "a2-2-6-eukaryote-cell-structure", "b2-2-organelles-and-compartmentalization", "b2-2-4-adaptations-of-the-mitochondrion-for-production-of-atp-by-aerobic-cell-respiration", "b2-2-5-adaptations-of-the-chloroplast-for-photosynthesis", "b3-2-transport", "b3-2-18-adaptations-of-phloem-sieve-tubes-and-companion-cells-for-translocation-of-sap" ] }, { "Question": "
\n
\n

\n The activity of amylase from two bacterial species and a fungus was measured at different pH levels and constant temperature. The results are shown in the graph.\n

\n

\n \n

\n

\n [Source: Held, P., 2012.\n \n Enzymatic Digestion of Polysaccharides. Part II: Optimization of Polymer Digestion and Glucose\n \n \n Production in Microplates\n \n . Available at: https://www.agilent.com/cs/library/applications/enzymatic-digestion-of-polysaccharides-part-II-5994-3304EN-agilent.pdf.]\n

\n

\n

\n

\n Which statement about the effect of pH on amylase can be concluded?\n

\n

\n A.\n \n A. oryzae\n \n amylase has the highest optimum pH.\n

\n

\n B.  A change in pH affects amylase most in\n \n B. licheniformis\n \n .\n

\n

\n C.  The optimum pH is 6 in\n \n B. subtilis\n \n .\n

\n

\n D.  Amylase activity at pH 8 is the lowest in\n \n B. licheniformis\n \n .\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "22N.1A.SL.TZ0.9", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-1-enzymes-and-metabolism", "c1-1-8-effects-of-temperature-ph-and-substrate-concentration-on-the-rate-of-enzyme-activity" ] }, { "Question": "
\n
\n

\n Which statement is valid regarding chromatids?\n

\n

\n A. Sister chromatids separate during meiosis I.\n

\n

\n B. Chiasmata form between non-sister chromatids.\n

\n

\n C. Crossing over is the exchange of DNA between sister chromatids only.\n

\n

\n D. Non-sister chromatids have the same combination of alleles.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "21M.1A.SL.TZ1.35", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-1-cell-and-nuclear-division", "d2-1-5-dna-replication-as-a-prerequisite-for-both-mitosis-and-meiosis" ] }, { "Question": "
\n
\n

\n What feature of eukaryotic chromosomes distinguishes them from the chromosomes of prokaryotes?\n

\n

\n A. Histone proteins\n

\n

\n B. Circular DNA\n

\n

\n C. Double-stranded DNA molecules\n

\n

\n D. Multiple genes along the length of each chromosome\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "None", "question_id": "21M.1A.SL.TZ2.11", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a2-2-cell-structure", "a2-2-5-prokaryote-cell-structure", "a2-2-6-eukaryote-cell-structure" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n On the diagram, label the testa and the radicle.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. testa labelled ✔\n

\n

\n b. radicle labelled ✔ (\n \n must point to the bottom half of the embryo or the tip\n \n ).\n

\n

\n \n

\n
\n", "Examiners report": "
\n

\n Many candidates did not correctly label the testa and in many cases the radicle was labelled too high up, pointing at the hypocotyl.\n

\n
\n", "question_id": "21M.2.HL.TZ2.3", "topics": [ "b-form-and-function" ], "subtopics": [ "b1-1-carbohydrates-and-lipids", "b1-1-5-polysaccharides-as-energy-storage-compounds" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Outline the functions of rough endoplasmic reticulum and Golgi apparatus.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n a.\n \n ribosomes\n \n on RER synthesize/produce polypeptides/proteins ✔\n

\n

\n b. proteins from RER for secretion/export/use outside cell/for lysosomes ✔\n

\n

\n c. Golgi alters/modifies proteins/example of modification ✔\n

\n

\n d.\n \n vesicles\n \n budded off Golgi transport proteins «to plasma membrane»\n
\n \n \n OR\n \n \n
\n exocytosis/secretion of proteins in\n \n vesicles\n \n from the Golgi ✔\n

\n

\n \n Accept “for use inside and outside the cell” for mpb.\n \n

\n
\n", "Examiners report": "
\n

\n Most candidates had some knowledge and some had broad understanding of this topic. A common mistake was to think that the rough endoplasmic reticulum makes ribosomes. Many candidates stated that the Golgi apparatus packages proteins but they did not always mention that the packages are vesicles. If this was all that the Golgi did, vesicles from the rough ER could be used to secrete proteins. The role of the Golgi apparatus therefore involved processing or modification of proteins rather than just packaging of them.\n

\n
\n", "question_id": "19M.2.HL.TZ1.5A", "topics": [ "b-form-and-function" ], "subtopics": [ "b2-2-organelles-and-compartmentalization", "b2-2-7-structure-and-function-of-free-ribosomes-and-of-the-rough-endoplasmic-reticulum", "b2-2-8-structure-and-function-of-the-golgi-apparatus" ] }, { "Question": "
\n
\n

\n What is exchanged between a sealed mesocosm and the surrounding external environment?\n

\n

\n A. Energy\n

\n

\n B. Water\n

\n

\n C. Air\n

\n

\n D. Nothing can pass\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "
\n

\n This question had the lowest discrimination index on the paper so some well-prepared candidates must have answered it incorrectly. More than half of candidates thought that nothing can pass in or out of a sealed mesocosm, forgetting that energy will almost certainly be able to pass in or out in the form of heat and probably also in as light. In terms of thermodynamics, a closed system exchanges energy but not matter with its environment.\n

\n
\n", "question_id": "21N.1A.SL.TZ0.17", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-2-stability-and-change", "d4-2-4-use-of-a-model-to-investigate-the-effect-of-variables-on-ecosystem-stability" ] }, { "Question": "
\n
\n

\n Based on these data, outline the evidence that T-705 has potential to be used as a treatment for EVD.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. cells not killed/few cells killed «even at high concentrations» ✔\n

\n

\n b. «T-705» effective/viruses reduced/viruses killed at 100 μM\n
\n \n \n OR\n \n \n
\n «T-705» very effective/viruses much reduced/nearly all viruses killed at 1000 μM ✔\n

\n

\n c. virus concentration decreases as T-705 concentration increases ✔\n

\n

\n d. drug has «high» potential for treatment «at high enough concentration» ✔\n

\n
\n", "Examiners report": "
\n

\n This was a timely question with Ebola epidemics again causing great problems in parts of Africa. Students were expected to have had some practice at analysing data relating to an epidemic because of this Skill in the programme: Analysis of epidemiological data related to vaccination programmes. It was assumed that candidates would understand terms such as ‘case’, ‘fatal case’, ‘infect’ and ‘treat’.\n

\n

\n This was generally very well answered, with candidates correctly concluding that the drug had potential as a treatment because at a high enough dose it reduced the number of viruses without harming a significant number of cells.\n

\n
\n", "question_id": "19M.2.SL.TZ1.F", "topics": [ "c-interaction-and-interdependence", "a-unity-and-diversity" ], "subtopics": [ "c3-2-defence-against-disease", "a2-3-viruses-(hl-only)" ] }, { "Question": "
\n
\n

\n Which is the hierarchy of taxa in order of decreasing numbers of species?\n

\n

\n A. domain, phylum, order, family\n

\n

\n B. phylum, order, family, class\n

\n

\n C. domain, phylum, order, class\n

\n

\n D. phylum, class, family, order\n

\n

\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "None", "question_id": "19M.1A.HL.TZ2.23", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a3-2-classification-and-cladistics-(hl-only)", "a3-2-1-need-for-classification-of-organisms" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n The chi-squared value was calculated as shown. Deduce, with reasons, whether the observed ratio differed significantly from the expected Mendelian ratio.\n

\n

\n \n \n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. yes/observed ratio did differ significantly «from the expected Mendelian ratio»\n
\n \n \n OR\n \n \n
\n expected ratio is 1:1:1:1 / 575 of each type / 25 % of each type ✔\n \n Correct ratio not needed in first alternative of mpa\n \n

\n

\n b. 3 degrees of freedom ✔\n

\n

\n c. critical value is 7.815 «at the 5 % level / 11.345 «at the 1 % level» ✔\n \n Accept mpc if candidates indicate the critical value of chi squared by circling it.\n \n

\n

\n d. chi-squared value «of 1002.6» exceeds the critical value ✔\n

\n

\n \n Allow other levels of significance as long as the critical value is correctly stated for the chosen level\n \n .\n

\n
\n", "Examiners report": "None", "question_id": "19N.2.HL.TZ0.2C", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-2-inheritance", "d3-2-21-use-of-a-chi-squared-test-on-data-from-dihybrid-crosses" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n State\n

\n
\n
\n

\n

\n
\n
\n", "Markscheme": "
\n

\n from blood sample/hair/cheek/saliva/semen;\n

\n

\n \n Do not accept red blood cells\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.1B.SL.TZ1.3A", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-3-photosynthesis", "c1-3-7-techniques-for-varying-concentrations-of-carbon-dioxide-light-intensity-or-temperature-experimentally-to-investigate-the-effects-of-limiting-factors-on-the-rate-of-photosynthesis" ] }, { "Question": "
\n
\n (h)\n
\n
\n

\n Identify, with a reason, the aphids that were most strongly repelled by EBF.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n the aphids that were fed on wild-type thale cress/W as they had 80 % «or more» repelled each generation/ always had the higher % response\n
\n \n \n OR\n \n \n
\n the aphids that fed on wild-type thale cress plants/W of G3 as they had «about» 85 % repelled/had the higher % response ✔\n

\n

\n \n Answer should refer to a percentage.\n \n

\n
\n", "Examiners report": "
\n

\n There was some discussion in the G2 forms about the amount of reading before points h, I and j. Good candidates could be seen to have read it carefully, underling the key words. Weaker candidates not so. In 1h a reason in terms of the highest percentage was looked for and was missed by weaker candidates.\n

\n
\n", "question_id": "19M.2.SL.TZ2.1H", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d1-1-dna-replication", "d1-1-5-applications-of-polymerase-chain-reaction-and-gel-electrophoresis" ] }, { "Question": "
\n
\n (h)\n
\n
\n

\n Suggest possible reasons for the difficulty of preventing or controlling a viral epidemic such as the 2014 EVD epidemic in a remote rural region.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. poor transport infrastructure/poor communication/bad roads/difficult access/no maps/support slow arriving/scattered population ✔\n

\n

\n b. poor education/understanding of disease amongst health workers/local population\n
\n \n \n OR\n \n \n
\n continued contact with infected people / other example of unsafe actions ✔\n

\n

\n c. more sources of infection such as bats/difficult to find sources of infection ✔\n

\n

\n d. lack of/limited access to medical care/doctors/health care workers ✔\n

\n

\n e. lack of/no access to/unaffordability of treatment centers/medicalsupplies/equipment/antivirals/drugs/vaccine/treatments ✔\n

\n

\n f. refusal/reluctance in local population to be vaccinated\n
\n \n \n OR\n \n \n
\n difficult to find/reach everyone to vaccinate them/repeat the vaccination ✔\n

\n

\n g. migration of people spreads the infection ✔\n

\n

\n h.poor sanitation/lack of clean water ✔\n

\n
\n", "Examiners report": "
\n

\n This was a timely question with Ebola epidemics again causing great problems in parts of Africa. Students were expected to have had some practice at analysing data relating to an epidemic because of this Skill in the programme: Analysis of epidemiological data related to vaccination programmes. It was assumed that candidates would understand terms such as ‘case’, ‘fatal case’, ‘infect’ and ‘treat’.\n

\n

\n This was a third question where a very wide range of answers were accepted. Even so, not all candidates scored both marks. The commonest weakness was vague answers such as “shortage of resources”. The best answers gave common-sense reasons for special difficulties in controlling an epidemic in the population of a remote rural region.\n

\n
\n", "question_id": "19M.2.SL.TZ1.1H", "topics": [ "c-interaction-and-interdependence", "a-unity-and-diversity" ], "subtopics": [ "c3-2-defence-against-disease", "a2-3-viruses-(hl-only)" ] }, { "Question": "
\n
\n

\n The diagram shows the structure of\n \n E. coli\n \n ribonuclease HI, a bacterial protein consisting of\n \n one\n \n polypeptide chain.\n

\n

\n \n

\n

\n [Source: RCSB PDB. 1JL1 D10A E. coli ribonuclease HI. PDB DOI: 10.2210/pdb1JL1/pdb Mol* (Goedken, E.R., Marqusee, S. Native-state energetics of a thermostabilized variant of ribonuclease HI. (2001)\n \n J Mol Biol\n \n 314:\n
\n 863–871 DOI:10.1006/jmbi.2001.5184) [image online] Available at:\n \n https://www.rcsb.org/structure/1jl1\n \n
\n [Accessed 25 November 2019]. This file is licensed under the Creative Commons CC0 1.0 Universal (\n \n https://creativecommons.org/\n \n \n publicdomain/zero/1.0/\n \n ).]\n

\n

\n

\n

\n Which level(s) of protein structure is/are shown?\n

\n

\n A. Alpha helix only\n

\n

\n B. Quaternary only\n

\n

\n C. Primary and secondary\n

\n

\n D. Secondary and tertiary\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "
\n

\n This question did not discriminate well, as many students answered that both primary and secondary structures are shown in the diagram. The diagram clearly shows secondary and tertiary structure. The stem of the question indicates the protein had only one polypeptide ruling out quaternary structure. The sequence of amino acids is not shown in the diagram making D the only correct response.\n

\n
\n", "question_id": "22M.1A.HL.TZ2.28", "topics": [ "b-form-and-function" ], "subtopics": [ "b1-2-proteins", "b1-2-11-quaternary-structure-of-non-conjugated-and-conjugated-proteins" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Using the graph, explain the Bohr shift.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n a. respiring tissues produce CO\n \n 2\n \n ;\n

\n

\n b. CO\n \n 2\n \n leads to an increase in H\n \n +\n \n /decrease in blood pH;\n

\n

\n c. increased acidity/decreased pH shifts the oxygen dissociation curve to the right;\n

\n

\n d. affinity of the hemoglobin for oxygen is reduced;\n

\n

\n e. greater release of oxygen from hemoglobin (at the same partial pressure of oxygen) in tissues;\n

\n
\n", "Examiners report": "
\n

\n Most candidates did well in this question, but strongest candidates distinguished themselves with complete and very detailed answers. Although candidates did well, there were many inaccuracies in some answers. Bohr shift is the shift to the right of the oxygen dissociation curve in respiring tissues; it does not refer to the reverse process at lung level.\n

\n
\n", "question_id": "20N.2.HL.TZ0.23A", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-1-gas-exchange", "b3-1-12-bohr-shift" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Describe how toxins such as DDT might concentrate in the bodies of birds.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n some toxins/DDT are persistent/degrade slowly (once released into the environment);\n
    2. \n
  2. \n (some toxins/DDT) enter the food chain through producers/lower trophic levels;\n
    3. \n
  3. \n (some toxins/DDT) are passed on to higher trophic levels in the food chain;\n
    4. \n
  4. \n (they are) difficult to excrete / are not excreted;\n
    5. \n
  5. \n (they) accumulate in fatty tissues of animals;\n
    6. \n
  6. \n higher trophic levels/top consumers have higher/the highest concentration of pesticides in their bodies;\n
    7. \n
  7. \n they bioaccumulate/biomagnify;\n
    8. \n
\n
\n", "Examiners report": "None", "question_id": "SPM.2.HL.TZ0.9A", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-2-stability-and-change", "d4-2-9-biomagnification-of-pollutants-in-natural-ecosystems" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Describe the use of gene knockout technology in research.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n gene knockout technology is a genetic engineering technique/intentional alteration in the sequence of a  gene;\n
    2. \n
  2. \n making a gene inactive;\n
    3. \n
  3. \n using site specific nucleases / CRISPR;\n
    4. \n
  4. \n researcher observes changes in phenotype of organism;\n
    5. \n
  5. \n allows researcher to determine function of the gene;\n
    6. \n
  6. \n entire library of knockout organisms exists;\n
    7. \n
  7. \n made available to researchers;\n
    8. \n
\n
\n", "Examiners report": "None", "question_id": "SPM.2.HL.TZ0.10C", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d1-3-mutations-and-gene-editing", "d1-3-8-gene-knockout-as-a-technique-for-investigating-the-function-of-a-gene-by-changing-it-to-make-it-inoperative" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Describe the risk to the human population of indiscriminate use of antibiotics.\n

\n
\n
\n

\n [5]\n

\n
\n
\n", "Markscheme": "
\n

\n a. antibiotics block bacterial processes ✔\n

\n

\n b. example of bacterial process ✔ e.g.\n \n cell wall formation\n \n

\n

\n c. variations exist naturally in a population / some are naturally resistant to the antibiotic ✔\n

\n

\n d. bacteria that are not resistant to this antibiotic will die / only resistant will survive (when antibiotic given) ✔\n

\n

\n e. this characteristic could be passed to next generation ✔\n

\n

\n f. (natural selection) leads to changes in the proportions/frequency in the population ✔\n

\n

\n g. human population will be exposed to antibiotic resistant bacteria and will not have antibiotic to kill them ✔\n

\n

\n h. (antibiotic resistant bacteria) may pass resistance to other bacteria species/types by means of plasmids (so other bacteria species turn resistant too) ✔\n

\n
\n", "Examiners report": "
\n

\n (attempted by about 60 % of the cohort)\n

\n

\n Part (a) was a departure from the 'draw a prokaryote' type of question that has appeared numerous times. In general, it was well answered. There were some good diagrams as answers which clearly showed only the prokaryotic characteristics. Part (b) asked for an explanation of the production of antibodies. Many weaker students wrote at length about non-specific phagocytosis which was not credited. Weaker students confused antibodies and antigens and even talked about antibiotics. This question was designed to be answered by the Standard Level students using Standard Level material. Some tried to include HL material and became very confused. Part (c) was really a question about Darwin's theory of evolution set in context. Many of the answers were very Lamarckian with the antibiotic causing the mutation, instead of some bacteria already having resistance. Better students opened with comments and an explanation that antibiotics only kill bacteria.\n

\n
\n", "question_id": "21M.2.SL.TZ2.6C", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-2-defence-against-disease", "c3-2-14-evolution-of-resistance-to-several-antibiotics-in-strains-of-pathogenic-bacteria" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n State a role of the active site of an enzyme.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n site to which\n \n substrate\n \n binds\n
\n \n \n OR\n \n \n
\n catalytic site ✔\n

\n

\n \n Give credit for the lock and key analogy\n \n .\n

\n
\n", "Examiners report": "
\n

\n There were some G2 comments about the function of Rubisco. It is mentioned in 2.4. and the stem did say that it was an enzyme. Simply stating that it was an enzyme involved in photosynthesis was sufficient for the mark. A detailed function was not required. Most could state the role of the active site and that the genus was\n \n Pisume.\n \n The word genus in this context confused some French candidates who answered 'male or female'. 3(d) was simply testing the factors controlling enzyme action. Weaker students just listed several factors. When it says one factor, only the first is considered. The difference between heat and temperature was occasionally confused. The examiners were looking for the effect of increasing and decreasing the factor. Many students seemed to be obsessed with denaturing. For example the answer 'temperature' (first mark): as the temperature is too high the enzyme denatures (no second mark as no mention of decreasing temperature). Few used the collision theory idea which was expected.\n

\n
\n", "question_id": "21M.2.SL.TZ2.3B", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-1-enzymes-and-metabolism", "c1-1-4-enzymes-as-globular-proteins-with-an-active-site-for-catalysis", "c1-1-5-interactions-between-substrate-and-active-site-to-allow-induced-fit-binding", "c1-1-6-role-of-molecular-motion-and-substrate-active-site-collisions-in-enzyme-catalysis", "c1-1-7-relationships-between-the-structure-of-the-active-site-enzyme-substrate-specificity-and-denaturation" ] }, { "Question": "
\n
\n

\n A total of 271 164 people were tested for blood groups in Mexico. The pie chart summarizes the ABO blood group distribution.\n

\n

\n \n

\n

\n \n [Source: Canizalez-Román, A. et al., 2018. Blood Groups Distribution and Gene Diversity\n \n
\n \n of the ABO and Rh (D) Loci in the Mexican Population.\n \n
\n \n \n BioMed Research International\n \n , (Article ID 1925619).\n \n
\n \n http://dx.doi.org/10.1155/2018/1925619. Public domain.]\n \n

\n

\n What can be concluded from the ABO blood group distribution in Mexico?\n
\n
\n

\n

\n A.  Allele frequencies are not the same for all blood group alleles.\n

\n

\n B.  The majority of the Mexican population shows a co-dominant phenotype.\n

\n

\n C.  Most of the Mexican population can receive blood from all blood groups.\n

\n

\n D.  Only 2 % of the Mexican population have a heterozygous genotype for blood groups.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "None", "question_id": "23M.1A.SL.TZ1.34", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-2-inheritance", "d3-2-14-continuous-variation-due-to-polygenic-inheritance-and/or-environmental-factors" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Identify the recombinant phenotypes amongst the offspring.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n brown body vestigial wings\n \n \n AND\n \n \n black body, normal wings\n

\n
\n", "Examiners report": "None", "question_id": "SPM.2.HL.TZ0.7", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-2-inheritance", "d3-2-20-recombinants-in-crosses-involving-two-linked-or-unlinked-genes", "d3-2-17-punnett-grids-for-predicting-genotypic-and-phenotypic-ratios-in-dihybrid-crosses-involving-pairs-of-unlinked-autosomal-genes" ] }, { "Question": "
\n
\n

\n What is a common feature of enzymes?\n

\n

\n
\n A.  They all react with substrates.\n

\n

\n B.  They all decrease the rate of reaction.\n

\n

\n C.  They are all secreted from cells in vesicles.\n

\n

\n D.  They all bind to the active site of their substrate.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "None", "question_id": "SPM.1A.HL.TZ0.8", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-1-enzymes-and-metabolism", "c1-1-1-enzymes-as-catalysts", "c1-1-2-role-of-enzymes-in-metabolism" ] }, { "Question": "
\n
\n

\n Explain how carbohydrates are transported from plant leaves.\n

\n
\n
\n

\n [7]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n translocation/movement by mass flow;\n
    2. \n
  2. \n in\n \n phloem sieve tubes\n \n ;\n
    3. \n
  3. \n sieve plates/pores in end walls/lack of organelles allows flow (of sap);\n
    4. \n
  4. \n carbohydrates (principally) transported as sucrose;\n
    5. \n
  5. \n (sucrose/glucose/sugar/carbohydrate) loaded (into phloem) by active transport;\n
    6. \n
  6. \n loading/pumping in (of sugars) by companion cells;\n
    7. \n
  7. \n high solute concentration generated (at the source);\n
    8. \n
  8. \n water enters by osmosis (due to the high solute concentration);\n
    9. \n
  9. \n hydrostatic pressure increased/high hydrostatic pressure generated;\n
    10. \n
  10. \n pressure gradient causes flow (from source to sink);\n
    11. \n
  11. \n leaves are a source because carbohydrates are made there;\n
    12. \n
  12. \n transport to the sink where carbohydrates are used/stored;\n
    13. \n
\n
\n", "Examiners report": "
\n

\n This was answered well by many candidates, with correct use of terminology. Some answers gave considerable detail about methods used to load assimilate into phloem. The specific structures used for transport (sieve tubes) were not always named and their adaptations were rarely included. Many candidates stated that phloem transport is bidirectional and that xylem transport is not — a hypothesis that has been falsified! Transport in a single phloem sieve tube can only be in one direction at one time, though the direction can be reversed if the hydrostatic pressure gradient switches, for example when a growing leaf changes from being a sink to a source. Xylem transport can also be bidirectional over time, as xylem sap sinks down to the roots of deciduous trees when leaves are lost in the fall and some plants allow xylem sap to sink to the roots every night when transpiration stops.\n

\n
\n", "question_id": "22N.2.HL.TZ0.C", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-2-transport", "b3-2-18-adaptations-of-phloem-sieve-tubes-and-companion-cells-for-translocation-of-sap" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n State\n \n two\n \n variables measured by the probes.\n

\n

\n 1:\n

\n

\n 2:\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n temperature;\n
    2. \n
  2. \n pH;\n
    3. \n
  3. \n minerals / salt concentration / conductivity;\n
    4. \n
  4. \n O\n \n 2\n \n (concentration);\n
    5. \n
  5. \n CO\n \n 2\n \n (concentration);\n
    6. \n
\n
\n", "Examiners report": "None", "question_id": "23M.1B.SL.TZ2.3A", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-2-stability-and-change", "d4-2-4-use-of-a-model-to-investigate-the-effect-of-variables-on-ecosystem-stability" ] }, { "Question": "
\n
\n (ii)\n
\n
\n

\n how the DNA is amplified.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n PCR/polymerase chain reaction\n
\n \n \n OR\n \n \n
\n using Taq polymerase;\n

\n

\n

\n
\n", "Examiners report": "None", "question_id": "23M.1B.SL.TZ1.3AII", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-3-photosynthesis", "c1-3-7-techniques-for-varying-concentrations-of-carbon-dioxide-light-intensity-or-temperature-experimentally-to-investigate-the-effects-of-limiting-factors-on-the-rate-of-photosynthesis" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Distinguish between the distribution of\n \n D. tigrina\n \n and that of\n \n D. coronata\n \n .\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n a.\n \n D. tigrina\n \n lives higher in the tree than\n \n D. coronata\n \n ;\n

\n

\n b.\n \n D. coronata\n \n occupies a greater area/height range than\n \n D. tigrina\n \n ;\n

\n

\n c.\n \n D. tigrina\n \n found in the outer regions and\n \n D. coronata\n \n found on the inside;\n

\n

\n \n Accept vice-versa\n \n .\n

\n
\n", "Examiners report": "
\n

\n Overall, well answered.\n

\n
\n", "question_id": "20N.2.SL.TZ0.12A", "topics": [ "b-form-and-function" ], "subtopics": [ "b4-2-ecological-niches", "b4-2-12-fundamental-and-realized-niches", "b4-2-13-competitive-exclusion-and-the-uniqueness-of-ecological-niches" ] }, { "Question": "
\n
\n

\n What is a common feature of enzymes?\n

\n

\n
\n A.  They all react with substrates.\n

\n

\n B.  They all decrease the rate of reaction.\n

\n

\n C.  They are all secreted from cells in vesicles.\n

\n

\n D.  They all bind to the active site of their substrate.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "None", "question_id": "SPM.1A.SL.TZ0.5", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-1-enzymes-and-metabolism", "c1-1-1-enzymes-as-catalysts", "c1-1-2-role-of-enzymes-in-metabolism" ] }, { "Question": "
\n
\n

\n \n B. subtilis\n \n colonies form biofilms through quorum sensing. Define quorum sensing.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n «a system of» behaviours triggered as a function of population density ✔\n

\n
\n", "Examiners report": "
\n

\n This question was a good discriminator, as weaker students were unable to use correct terminology such as “population density,” instead resorting to vague phrases like “when the bacteria sense something.”\n

\n
\n", "question_id": "19M.2.HL.TZ1.C.I", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c2-1-chemical-signalling-[hl-only]", "c2-1-2-cell-signalling-by-bacteria-in-quorum-sensing" ] }, { "Question": "
\n
\n (a.i)\n
\n
\n

\n State the genus of this organism.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n \n Paramecium\n \n

\n
\n", "Examiners report": "
\n

\n In a about half of the candidates named the genus correctly (\n \n \n Paramaecium\n \n \n ), but significantly fewer could state the correct domain (eukaryota). The most common wrong answers were prokaryote and eubacteria. Only the better candidates were able to outline the method of nutrition (heterotrophy) in b and describe how homeostasis is carried out, in spite of being specifically stated in the syllabus. The endosymbiotic theory was quite well known.\n

\n
\n", "question_id": "20N.2.SL.TZ0.2", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a2-2-cell-structure", "a2-2-12-origin-of-eukaryotic-cells-by-endosymbiosis" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Explain the decrease in activity of the enzyme on either side of the optimum temperature.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n as temperature rises/is higher (than optimal temperature), the enzyme is denatured;\n
    2. \n
  2. \n as the temperature drops the enzyme molecules have less kinetic energy\n
    \n \n \n OR\n \n \n
    \n fewer successful collisions;\n
    3. \n
\n

\n \n OWTTE\n \n

\n
\n", "Examiners report": "
\n

\n In a. many incorrectly stated that the enzyme was denatured either side of the optimum. Denaturation was reasonably well known, but the explanation for increased activity with rising temperature was not. Surprisingly some candidates missed the obvious references to temperature and wrote about pH instead. Knowledge of the enzymes involved in gene transfer was very patchy, with over a quarter of candidates leaving it blank. This was the worst scoring question on the paper.\n

\n
\n", "question_id": "22M.2.SL.TZ2.5A", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-1-enzymes-and-metabolism", "c1-1-8-effects-of-temperature-ph-and-substrate-concentration-on-the-rate-of-enzyme-activity" ] }, { "Question": "
\n
\n

\n What is an outcome of natural selection?\n

\n

\n
\n A.  Evolution\n

\n

\n B.  Mutations\n

\n

\n C.  Reproductive isolation\n

\n

\n D.  Variation\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "None", "question_id": "SPM.1A.SL.TZ0.30", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-1-natural-selection", "d4-1-5-differences-between-individuals-in-adaptation-survival-and-reproduction-as-the-basis-for-natural-selection" ] }, { "Question": "
\n
\n

\n A two-cell sea urchin (\n \n Echinoidea\n \n ) embryo was physically separated by scientists into two cells. Each cell, through further embryonic development, became an adult sea urchin.\n

\n

\n \n

\n

\n [Source: Clker-Free-Vector-Images/Pixabay.]\n

\n

\n

\n

\n What is the relationship between the two adult sea urchins?\n

\n

\n A. They are equivalent to non-identical twins.\n

\n

\n B. Half of the genes would be the same.\n

\n

\n C. Both adults would have haploid cells.\n

\n

\n D. They are clones.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "21M.1A.SL.TZ1.17", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-1-cell-and-nuclear-division", "d2-1-1-generation-of-new-cells-in-living-organisms-by-cell-division" ] }, { "Question": "
\n
\n

\n The pedigree chart shows the inheritance of three generations of Duane syndrome, a condition caused by a dominant allele that affects alignment of the eyes.\n

\n

\n \n

\n

\n \n [Source: Yang, M.-M., Ho, M. et al., 2013.\n \n Pedigree of a Chinese family with Duane retraction syndrome\n \n . [diagram online]\n \n
\n \n Available at: https://www.researchgate.net/figure/Pedigree-of-a-Chinese-family-with-Duane-retraction-syndrome-\n \n
\n \n Squares-men-circles_fig1_236921765 [Accessed 5 October 2021]. Public domain.]\n \n

\n

\n

\n

\n If individuals II:1 and II:2 had a third child, what is the probability that the child would have Duane syndrome?\n
\n
\n

\n

\n A.  25 %\n

\n

\n B.  50 %\n

\n

\n C.  75 %\n

\n

\n D.  100 %\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "23M.1A.SL.TZ2.16", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-2-inheritance", "d3-2-2-methods-for-conducting-genetic-crosses-in-flowering-plants", "d3-2-5-effects-of-dominant-and-recessive-alleles-on-phenotype" ] }, { "Question": "
\n
\n

\n Which processes are involved in the development of cancer?\n

\n

\n I. Mutations occur in oncogenes.\n

\n

\n II. Oncogenes prevent cancer.\n

\n

\n III. Oncogenes affect cell cycle regulatory proteins.\n

\n

\n A. I and II only\n

\n

\n B. I and III only\n

\n

\n C. II and III only\n

\n

\n D. I, II and III\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "
\n

\n This question was too easy, as answer II was too obviously wrong. This question did not discriminate well because most candidates had it right. Candidates did not seem to be put off by the fact that in I it said that mutations occur in oncogenes instead of saying that oncogenes are the result of a mutation in protooncogenes.\n

\n
\n", "question_id": "19M.1A.HL.TZ2.4", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-1-cell-and-nuclear-division", "d2-1-16-consequences-of-mutations-in-genes-that-control-the-cell-cycle", "d1-3-mutations-and-gene-editing", "d1-3-6-consequences-of-mutation-in-germ-cells-and-somatic-cells" ] }, { "Question": "
\n
\n

\n What is the primary function of the free ribosomes shown in the electron micrograph?\n

\n

\n \n

\n

\n [Source: J Gordon Betts, et al.\n \n Anatomy and Physiology\n \n . Houston Texas: OpenStax, 2013. https://openstax.org/books/\n
\n anatomy-and-physiology/pages/3-2-the-cytoplasm-and-cellular-organelles. Image file available at\n \n https://commons.\n \n
\n \n wikimedia.org/wiki/File:0313_Endoplasmic_Reticulum.jpg#/media/File:0313_Endoplasmic_Reticulum_b_labeled.\n \n
\n \n png\n \n . This file is licensed under the Creative Commons Attribution 3.0 Unported license.\n \n https://creativecommons.org/\n \n
\n \n licenses/by/3.0/deed.en\n \n .]\n

\n

\n

\n

\n A. Synthesize proteins to be used within the cell\n

\n

\n B. Synthesize proteins for use in lysosomes\n

\n

\n C. Carry amino acids to mRNA for protein synthesis\n

\n

\n D. Synthesize proteins for secretion\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "None", "question_id": "21N.1A.HL.TZ1.28", "topics": [ "b-form-and-function" ], "subtopics": [ "b2-2-organelles-and-compartmentalization", "b2-2-7-structure-and-function-of-free-ribosomes-and-of-the-rough-endoplasmic-reticulum" ] }, { "Question": "
\n
\n

\n What is produced by meiosis in a cell of a male animal?\n

\n

\n A. Four gametes, each with the same number of chromosomes\n

\n

\n B. Two gametes, each with the same number of chromosomes\n

\n

\n C. Four gametes, each with different numbers of chromosomes\n

\n

\n D. Two gametes, each with different numbers of chromosomes\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "None", "question_id": "22M.1A.SL.TZ1.15", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-1-cell-and-nuclear-division", "d2-1-4-roles-of-mitosis-and-meiosis-in-eukaryotes" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Humans need to balance water and solute concentrations and also excrete nitrogenous wastes. Explain how the different parts of the kidney carry out these processes.\n

\n
\n
\n

\n [7]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n humans are osmoregulators/maintain the internal concentrations of the blood/osmolarity within specific/ limited range / OWTTE;\n
    2. \n
  2. \n glomerulus / Bowman’s capsule (in the nephron) carry out ultrafiltration;\n
    3. \n
  3. \n proximal convoluted tubule selectively reabsorbs glucose/solute/salts/amino acids;\n
    4. \n
  4. \n loop of Henle maintains hypertonic conditions in the medulla/absorbs salts (by active transport);\n
    5. \n
  5. \n loop of Henle reabsorbs water (by osmosis);\n
    6. \n
  6. \n (osmoreceptors in the hypothalamus) cause production of ADH if the blood is too concentrated / person is dehydrated / OWTTE;\n
    7. \n
  7. \n ADH causes more uptake of water/increases permeability in the collecting duct;\n
    8. \n
  8. \n resulting in a more concentrated urine / lower volume of urine;\n
    9. \n
  9. \n excess amino acids are broken down producing nitrogenous waste / ammonia / urea as a result;\n
    10. \n
  10. \n ammonia is toxic and is converted into non-toxic urea;\n
    11. \n
  11. \n urea is eliminated in the urine;\n
    12. \n
\n

\n \n Marks can be awarded to clearly annotated diagrams\n \n .\n

\n
\n", "Examiners report": "
\n

\n Generally, there were good accounts of the functioning of the nephron, but some elements were missing such as which substances are reabsorbed in the proximal tubule and which are absorbed in the loop of Henle, although permeability was mentioned. Discussion about the role of ADH was well done. The discussion of the management of nitrogenous wastes was least well done in this question.\n

\n
\n", "question_id": "22M.2.SL.TZ2.8B", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-3-homeostasis", "d3-3-7-role-of-the-kidney-in-osmoregulation-and-excretion" ] }, { "Question": "
\n
\n

\n What is a benefit of having xylem vessels close to phloem sieve tubes in plants?\n
\n
\n

\n

\n A.  Sugars can flow in both xylem vessels and phloem.\n

\n

\n B.  Water can be supplied more easily to the phloem.\n

\n

\n C.  A high concentration of solutes can be established at the source.\n

\n

\n D.  Hydrostatic pressure can be established to move sugars to the source.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "23M.1A.SL.TZ2.29", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-2-transport", "b3-2-7-transport-of-water-from-roots-to-leaves-during-transpiration" ] }, { "Question": "
\n
\n

\n Compare and contrast the results for the 1:1 and the 1:10 P:L diets.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n in both a greater mass of sucrose was eaten (than of the P:L mixture)\n
    \n \n \n OR\n \n \n
    \n the total mass eaten by both groups is the same/very similar;\n
    2. \n
  2. \n the mass of sucrose eaten in the 1:10 mixture diet is greater than in the 1:1 diet\n
    \n \n \n OR\n \n \n
    \n the mass of the P:L mixture eaten in the 1:10 is less than in the 1:1;\n
    3. \n
\n

\n \n Accept vice versa for all answers.\n \n

\n
\n", "Examiners report": "None", "question_id": "22N.2.SL.TZ0.E", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c4-2-transfers-of-energy-and-matter", "c4-2-15-primary-production-as-accumulation-of-carbon-compounds-in-biomass-by-autotrophs", "c4-2-16-secondary-production-as-accumulation-of-carbon-compounds-in-biomass-by-heterotrophs" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Suggest a reason that it is difficult to keep global commercial sea fishing activity at a sustainable level.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n requires agreements/policies/enforcement between countries;\n
    2. \n
  2. \n commercial companies compete to increase profit;\n
    3. \n
\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ1.18C", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-2-stability-and-change", "d4-2-6-assessing-sustainability-of-resource-harvesting-from-natural-ecosystems" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Suggest a reason for the loss of bird habitats.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n deforestation/forest fires;\n
    2. \n
  2. \n clearing land for houses/farming/growth of cities;\n
    3. \n
\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ1.17A", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a4-2-conservation-of-biodiversity", "a4-2-7-need-for-several-approaches-to-conservation-of-biodiversity" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Discuss briefly whether amino acids on the surface of the protein are likely to be polar or non-polar.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n polar/hydrophilic where exposed to the cytoplasm/to fluid outside cell/to polar phospholipid heads;\n
\n non-polar/hydrophobic where exposed to the (core of the) membrane/hydrophobic tails (of phospholipids);\n

\n
\n", "Examiners report": "None", "question_id": "23M.2.HL.TZ1.2C", "topics": [ "b-form-and-function" ], "subtopics": [ "b1-2-proteins", "b1-2-6-chemical-diversity-in-the-r-groups-of-amino-acids-as-a-basis-for-the-immense-diversity-in-protein-form-and-function" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Using the data, outline the different use of thiamethoxam in North and South America.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n thiamethoxam is the most used in North America (but not in South America) / CONVERSE\n
\n \n \n OR\n \n \n
\n in South America they use different neonicotinoids to thiamethoxam ✔\n

\n

\n \n OWTTE\n \n .\n

\n

\n \n Allow numerical comparison\n \n .\n

\n
\n", "Examiners report": "
\n

\n In general, the data analysis question was well attempted by the majority of students.\n

\n

\n Most identified that the proportion of the pesticide was greater in North than South America. This does not actually mean that a greater mass was used as these were relative frequency graphs.\n

\n
\n", "question_id": "21M.2.HL.TZ2.1B", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c2-2-neural-signalling", "c2-2-12-effects-of-exogenous-chemicals-on-synaptic-transmission" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Arginine and ornithine are in the same group of biochemicals. Identify this group.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n amino acids;\n

\n
\n", "Examiners report": "None", "question_id": "23M.2.HL.TZ2.2", "topics": [ "b-form-and-function", "c-interaction-and-interdependence", "d-continuity-and-change" ], "subtopics": [ "b1-2-proteins", "b1-2-1-generalized-structure-of-an-amino-acid", "c1-1-enzymes-and-metabolism", "c1-1-13-cyclical-and-linear-pathways-in-metabolism", "c1-1-10-effect-of-enzymes-on-activation-energy", "d3-3-homeostasis", "d3-3-7-role-of-the-kidney-in-osmoregulation-and-excretion" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Calculate the probability of male Y having an allele for the disorder.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n 50\n \n \n \n \n %/ 0.5/ 1/2;\n

\n
\n", "Examiners report": "None", "question_id": "22N.2.SL.TZ0.4B", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-2-inheritance", "d3-2-13-pedigree-charts-to-deduce-patterns-of-inheritance-of-genetic-disorders" ] }, { "Question": "
\n
\n (i)\n
\n
\n

\n Using the graph, identify the percentage who had received the tuberculosis vaccine in 2012.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n 89%;\n

\n

\n \n Allow 88 to 91 %.\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ2.1CI", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-2-defence-against-disease", "c3-2-16-vaccines-and-immunization" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Explain how increased carbon dioxide in the air leads to the greenhouse effect.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n short wave radiation from sun passes through atmosphere / is not absorbed by CO\n \n 2\n \n ;\n
    2. \n
  2. \n infrared/long wave (radiation) / heat emitted from/released from (surface of) Earth;\n
    3. \n
  3. \n CO\n \n 2\n \n in the atmosphere absorbs infrared/long wave (radiation)/heat / cannot pass through the greenhouse gases;\n
    4. \n
  4. \n this results in warm/increased temperatures on Earth/global warming;\n
    5. \n
\n

\n \n Do not accept “reflected” for mpb\n \n .\n

\n
\n", "Examiners report": "
\n

\n There were elegant answers to this question demonstrating a high level of understanding. Many other candidates mixed up all sorts of ideas here, including the idea of ozone being a cause of global warming and stating as a \"fact\" that heat travels from the sun to the earth. Among the confused ideas was the notion that carbon dioxide is a toxic pollutant.\n

\n
\n", "question_id": "22M.2.SL.TZ1.3C", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-3-climate-change", "d4-3-1-anthropogenic-causes-of-climate-change", "d4-3-2-positive-feedback-cycles-in-global-warming" ] }, { "Question": "
\n
\n (b.i)\n
\n
\n

\n The image shows an example of a soil food web.\n

\n

\n \n

\n

\n [Source: Anon., n.d. The Soil Food Web. [image online] Available at: https://www.nrcs.usda.gov/wps/portal/nrcs/\n
\n photogallery/soils/health/biology/gallery/?cid=1788&position=Promo [Accessed 11 March 2020].]\n

\n

\n

\n

\n Draw a food chain from this food web, showing at least three organisms.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n food chain of three or more organisms\n \n starting with plants\n \n ;\n

\n
\n", "Examiners report": "
\n

\n Many took the word ‘draw’ literally in the food chain, and the drawings of the nematodes and fungi amused the examiners. A food chain must start with a plant. The stem did say “three organisms”. Detritus was not taken as an organism, so negated the mark.\n

\n
\n", "question_id": "21N.2.SL.TZ0.3B.I", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c4-2-transfers-of-energy-and-matter", "c4-2-4-construction-of-food-chains-and-food-webs-to-represent-feeding-relationships-in-a-community" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Suggest one difference between tissue taken from a lung cancer tumour and normal lung tissue that might be seen in micrographs.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n fewer/smaller/lack of alveoli/air spaces;\n
    2. \n
  2. \n many cells/nuclei per area / much denser tissue;\n
    3. \n
  3. \n more cells undergoing mitosis (in the tumour);\n
    4. \n
\n

\n

\n
\n", "Examiners report": "None", "question_id": "23M.2.HL.TZ2.3B", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-1-cell-and-nuclear-division", "d2-1-17-differences-between-tumours-in-rates-of-cell-division-and-growth-and-in-the-capacity-for-metastasis-and-invasion-of-neighbouring-tissue" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Explain how temperature affects enzymes.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n speed of reaction/catalysis increases as temperature rises;\n
    2. \n
  2. \n faster molecular motion so more collisions between substrate and active site;\n
    3. \n
  3. \n denaturation at higher temperatures;\n
    4. \n
  4. \n (denaturation causes) shape/conformation/structure of enzyme/active site altered/damaged;\n
    5. \n
  5. \n an enzyme works fastest at its optimum temperature;\n
    6. \n
  6. \n inactivation at lower temperatures (due to very few collisions);\n
    7. \n
  7. \n sketch graph to model the effect of temperature on enzyme activity;\n
    8. \n
\n

\n \n Graphs would need to be well annotated.\n \n

\n

\n \n Must not be bell shaped.\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ2.6", "topics": [ "c-interaction-and-interdependence", "d-continuity-and-change" ], "subtopics": [ "c1-1-enzymes-and-metabolism", "c1-1-8-effects-of-temperature-ph-and-substrate-concentration-on-the-rate-of-enzyme-activity", "d4-3-climate-change", "d4-3-1-anthropogenic-causes-of-climate-change" ] }, { "Question": "
\n
\n (d)\n
\n
\n

\n Explain the role of lactose in the expression of the gene for lactase production.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n lactose binds to\n \n repressor\n \n protein;\n
    2. \n
  2. \n repressor protein (with lactose bound) cannot block/bind to the\n \n promoter\n \n /\n \n Y\n \n ;\n
    3. \n
  3. \n \n RNA polymerase\n \n /\n \n X\n \n binds to the promoter/transcribes the gene;\n
    4. \n
  4. \n \n lactase\n \n produced (if lactose present)/\n \n lactase\n \n production inhibited if lactose absent;\n
    5. \n
\n

\n \n Accept the converse of mpa to mpd with lactose absent.\n \n

\n
\n", "Examiners report": "
\n

\n Many candidates realised from the diagram that lactose binds to the repressor. Fewer could explain convincingly that this removes the repressor from the promoter, so RNA polymerase can bind and transcribe the gene for lactase. Many candidates earned a mark by giving the last idea on the mark scheme, which is that presence of lactose results in lactase production. It should be emphasized that the lac operon does not need to be taught to future students — the expectation here was that answers would be based on general understanding of transcription and on the information provided in the question. These was no expectation that candidates would already be familiar with the lac operon.\n

\n
\n", "question_id": "22N.2.HL.TZ0.4D", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-1-enzymes-and-metabolism", "c1-1-14-allosteric-sites-and-non-competitive-inhibition" ] }, { "Question": "
\n
\n

\n What is the term for the attraction of water molecules to other water molecules?\n

\n

\n A. Surface tension\n

\n

\n B. Capillary action\n

\n

\n C. Cohesion\n

\n

\n D. Adhesion\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "
\n

\n It was pleasing to see that three quarters of candidates knew that attraction between water molecules causes cohesion and far fewer incorrectly chose adhesion. These two terms are sometimes treated by candidates as though their meanings are interchangeable, but cohesion is attraction between water molecules and adhesion is attraction to a surface.\n

\n
\n", "question_id": "21M.1A.SL.TZ1.12", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a1-1-water", "a1-1-3-cohesion-of-water-molecules-due-to-hydrogen-bonding-and-consequences-for-organisms" ] }, { "Question": "
\n
\n

\n Which structures are found only in prokaryotic cells?\n

\n

\n A. Ribosomes\n

\n

\n B. Pili\n

\n

\n C. Cell walls\n

\n

\n D. Flagella\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "
\n

\n This was not an easy first question. In the SL Bio guide section 1.2 the guidance states that pili and flagella should be shown on diagrams of prokaryotic cells. There is a note that cell walls can be found on both but does not mention that flagella can also be found on eukaryotic cells. An example where flagella can be found is in sperm cell tails. It is obvious from the answers that candidates did not know this, as many answered question D instead of B.\n

\n
\n", "question_id": "19M.1A.SL.TZ2.1", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a2-2-cell-structure", "a2-2-5-prokaryote-cell-structure", "a2-2-6-eukaryote-cell-structure" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Hormones are distributed throughout the body by the blood. Outline the roles of\n \n two\n \n reproductive hormones during the menstrual cycle in women.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. FSH/follicle stimulating hormone stimulates the development of follicles/follicle cell division in the ovary «to produce eggs» ✔\n \n Two different hormones must be identified.\n \n

\n

\n b. LH/luteinizing hormone triggers ovulation/development of the corpus luteum ✔\n

\n

\n c. estrogen stimulates development of the uterine lining/endometrium ✔\n \n Description of role required as well as name of hormone.\n \n

\n

\n d. progesterone maintains the uterine lining/endometrium\n
\n \n \n OR\n \n \n
\n inhibits other hormones by negative feedback\n \n eg\n \n , FSH ✔\n

\n

\n e. HCG stimulates ovary to produce progesterone «in early pregnancy» ✔\n

\n

\n f. other verifiable hormone and roles relevant to the menstrual cycle ✔\n

\n
\n", "Examiners report": "
\n

\n Students were able to correctly identify hormones that played a role in the menstrual cycle and were often successful in outlining their function. A common problem was distinguishing the role of progesterone from that of estrogen.\n

\n
\n", "question_id": "19M.2.SL.TZ2.3C", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-1-reproduction", "d3-1-5-changes-during-the-ovarian-and-uterine-cycles-and-their-hormonal-regulation" ] }, { "Question": "
\n
\n

\n The hydrolysis of a pure sample of an organic molecule produces a pentose sugar, thymine, guanine and cytosine. What other substances could be expected to be present in the hydrolysed sample?\n

\n

\n A. RNA\n

\n

\n B. Uracil\n

\n

\n C. Phosphate\n

\n

\n D. ATP\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "21M.1A.SL.TZ1.9", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a1-2-nucleic-acids", "a1-2-2-components-of-a-nucleotide" ] }, { "Question": "
\n
\n (b.ii)\n
\n
\n

\n Suggest a way methylation may affect tumour cell genes.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n a. «DNA» methylation may inhibit transcription of genes that would prevent cancer/tumor formation ✔\n

\n

\n b. «DNA» methylation may increase mitosis/cell division leading to tumor formation ✔\n

\n

\n \n Do not accept discussion of histone methylation.\n \n

\n
\n", "Examiners report": "
\n

\n Students lacked the understanding of epigenetics necessary to make reasonable suggestions.\n

\n
\n", "question_id": "19M.2.HL.TZ2.2B.II", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-2-gene-expression-[hl-only]", "d2-2-6-methylation-of-the-promoter-and-histones-in-nucleosomes-as-examples-of-epigenetic-tags", "d2-2-7-epigenetic-inheritance-through-heritable-changes-to-gene-expression" ] }, { "Question": "
\n
\n

\n Lipids are more efficient energy stores than carbohydrates. What is a reason for this?\n

\n

\n A. Lipids are bigger molecules than carbohydrates.\n

\n

\n B. Lipids release more energy per gram than carbohydrates.\n

\n

\n C. Lipids can be more easily mobilized than carbohydrates when needed.\n

\n

\n D. Lipids can be used in aerobic and anaerobic respiration when needed.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "22M.1A.HL.TZ2.8", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-2-cell-respiration", "c1-2-17-differences-between-lipids-and-carbohydrates-as-respiratory-substrates" ] }, { "Question": "
\n
\n (b.ii)\n
\n
\n

\n Using the letter M, label the stage on the diagram where sister chromatids migrate to opposite poles.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n anaphase ✔\n

\n

\n \n The stage should be clearly labelled\n \n .\n

\n

\n \n If more than one stage is shown the candidate does not receive a mark\n \n .\n

\n
\n", "Examiners report": "
\n

\n There were several G2 comments about Q2a, as it could be said that several processes were occurring. Perhaps it should have been more specific. Two out of DNA replication, cell growth and duplication of organelles were expected for the two marks. A surprising number of candidates in all languages, confused 'processes' with 'phases' and stated that interphase consisted of G1, S and G2. Most managed to label prophase and anaphase correctly on the diagram as required in part (b). The answers to part (b) were generally clear, but some lost marks for not comparing the same point. For example 'Mitosis produces diploid cells, but meiosis produces gametes' did not score a mark. The mitotic index was well known.\n

\n
\n", "question_id": "21M.2.HL.TZ2.2B.II", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-1-cell-and-nuclear-division", "d2-1-7-phases-of-mitosis", "d2-1-13-phases-of-the-cell-cycle" ] }, { "Question": "
\n
\n

\n The blood of two men was tested and the results are shown. Anti-D refers to the rhesus blood group. Clotting indicates that antigens associated with a particular factor or blood group are present in a blood sample.\n

\n

\n \n

\n

\n [Source: © International Baccalaureate Organization 2019]\n

\n

\n The man who tested positive for anti-D was then tested for ABO blood group. These results were obtained.\n

\n

\n \n

\n

\n [Source: © International Baccalaureate Organization 2019]\n

\n

\n

\n

\n What ABO blood group does the man testing positive for anti-D have?\n

\n

\n A. A\n

\n

\n B. B\n

\n

\n C. AB\n

\n

\n D. O\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "
\n

\n Many candidates failed to realize that a negative reaction meant the antigens for A and for B were not present in the blood of the man tested.\n

\n
\n", "question_id": "19M.1A.SL.TZ2.36", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-2-defence-against-disease", "c3-2-7-antigens-as-recognition-molecules-that-trigger-antibody-production" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Describe briefly the endosymbiotic theory.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n a. eukaryotes evolved from prokaryotes ✔\n

\n

\n b. prokaryotes engulfed other prokaryotes without digesting them ✔\n

\n

\n c. engulfed aerobic cell/prokaryote became mitochondria ✔\n

\n

\n d. engulfed photosynthetic cell/ prokaryotes became chloroplasts ✔\n

\n

\n e. these organelles have a double membrane «due to the engulfing process» ✔\n

\n

\n f. mitochondria/chloroplasts contain DNA/small ribosomes/70S ribosomes ✔\n

\n
\n", "Examiners report": "
\n

\n Endosymbiotic theory. Those who had been taught it gained at least one mark. Few mentioned that the cell that became the mitochondrion was aerobic, and that the one that became the chloroplast was photosynthetic.\n

\n
\n", "question_id": "19M.2.HL.TZ2.6A", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a2-2-cell-structure", "a2-2-12-origin-of-eukaryotic-cells-by-endosymbiosis" ] }, { "Question": "
\n
\n

\n Where are protons pumped, to allow chemiosmosis in aerobic respiration to occur?\n

\n

\n A. From outside the mitochondrion through the double membranes\n

\n

\n B. From carrier to carrier in the inner mitochondrial membrane\n

\n

\n C. From the matrix of the mitochondrion to the space between the membranes\n

\n

\n D. From the space between the membranes to the cytoplasm outside the mitochondrion\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "21N.1A.HL.TZ1.30", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-2-cell-respiration", "c1-2-15-chemiosmosis-and-the-synthesis-of-atp-in-the-mitochondrion" ] }, { "Question": "
\n
\n

\n What is the cause of positive phototropism?\n

\n

\n
\n A.  Increased concentration of auxin on the side of the stem closest to the light\n

\n

\n B.  Degradation of auxin on the side of the stem closest to the light\n

\n

\n C.  Increased concentration of auxin on the side of the stem furthest from the light\n

\n

\n D.  Degradation of auxin on the side of the stem furthest from the light\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "SPM.1A.HL.TZ0.21", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-1-integration-of-body-systems", "c3-1-18-positive-phototropism-as-a-directional-growth-response-to-lateral-light-in-plant-shoots" ] }, { "Question": "
\n
\n

\n The diagram represents transmission across a cholinergic synapse. Where would a neonicotinoid pesticide act to prevent synaptic transmission?\n

\n

\n \n

\n

\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "23M.1A.HL.TZ2.20", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c2-2-neural-signalling", "c2-2-12-effects-of-exogenous-chemicals-on-synaptic-transmission" ] }, { "Question": "
\n
\n

\n Which hormone is part of a negative feedback control system and acts on cells in the hypothalamus?\n

\n

\n A. Insulin\n

\n

\n B. Glucagon\n

\n

\n C. Melatonin\n

\n

\n D. Leptin\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "19M.1A.SL.TZ2.29", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-3-homeostasis", "d3-3-2-negative-feedback-loops-in-homeostasis", "d3-3-3-regulation-of-blood-glucose-as-an-example-of-the-role-of-hormones-in-homeostasis" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Explain the conclusion that can be drawn from Cross 1.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n allele/trait/gene for banded is dominant/allele for unbanded is recessive;\n
    2. \n
  2. \n because two banded spiders produced some unbanded offspring\n
    \n \n OR\n \n
    \n because there is a ratio of 3 banded:1 unbanded;\n
    3. \n
  3. \n both parents are heterozygous;\n
    4. \n
\n

\n \n Accept answers given in the form of Punnet squares.\n \n

\n

\n

\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ1.5A", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-2-inheritance", "d3-2-5-effects-of-dominant-and-recessive-alleles-on-phenotype" ] }, { "Question": "
\n
\n

\n Identify structure Y.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n glomerulus/Bowman’s capsule;\n

\n
\n", "Examiners report": "
\n

\n 80% of candidates identified the structure as the glomerulus or Bowman's capsule.\n

\n
\n", "question_id": "22N.2.HL.TZ0.A.II", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-3-homeostasis", "d3-3-8-role-of-the-glomerulus-bowmans-capsule-and-proximal-convoluted-tubule-in-excretion" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Using a Punnett grid, explain the results of this cross.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n male and female gamete genotypes/alleles shown as P and p (or others following convention with a suitable key)\n \n in a punnet grid\n \n ;\n
    2. \n
  2. \n F\n \n 2\n \n genotypes shown as PP, Pp, pP and pp;\n
    3. \n
  3. \n F\n \n 2\n \n phenotypes indicated for each genotype on the Punnett grid / 3 purple to 1 white ratio indicated;\n
    4. \n
\n

\n

\n

\n \n Accept other upper-case and lower-case letters for the alleles.\n \n
\n \n \n \n
\n \n No punnet grid = 2 MAX.\n \n

\n

\n \n Allow ECF if alleles incorrect.\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ2.2B", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-2-inheritance", "d3-2-2-methods-for-conducting-genetic-crosses-in-flowering-plants" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Outline energy flow through a food chain.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n

\n a. energy from the sun/light energy is converted to chemical energy by photosynthesis ✔\n

\n

\n b. «chemical» energy flows through the food chains by feeding ✔\n

\n

\n c. energy is released «from carbon compounds» by respiration\n
\n \n \n OR\n \n \n
\n energy from respiration is used by living organisms and converted to heat ✔\n

\n

\n d. heat is not recyclable / heat is lost from food chains\n
\n \n \n OR\n \n \n
\n heat cannot be converted to other forms of energy ✔\n

\n

\n e. energy is lost in excretion/uneaten material/egestion/feces ✔\n

\n

\n f. energy losses between trophic levels limits the length of food chains\n
\n \n \n OR\n \n \n
\n energy transfer is only 10 % between trophic levels ✔\n

\n
\n", "Examiners report": "
\n

\n Was well answered with most students being knowledgeable about ecology.\n

\n
\n", "question_id": "19M.2.HL.TZ2.8", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c4-2-transfers-of-energy-and-matter", "c4-2-3-flow-of-chemical-energy-through-food-chains", "c1-3-photosynthesis", "c1-3-6-similarities-and-differences-of-absorption-and-action-spectra", "c1-1-enzymes-and-metabolism", "c1-1-13-cyclical-and-linear-pathways-in-metabolism" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Explain how animal cells produce the ATP that they need.\n

\n
\n
\n

\n [5]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n respiration/cell respiration;\n
    2. \n
  2. \n energy released from glucose/lipids/organic compounds;\n
    3. \n
  3. \n anaerobic respiration does not require oxygen;\n
    4. \n
  4. \n lactate is produced in anaerobic respiration/word equation for anaerobic respiration;\n
    5. \n
  5. \n oxygen used in aerobic respiration;\n
    6. \n
  6. \n carbon dioxide and water produced in aerobic respiration/word equation for aerobic respiration;\n
    7. \n
  7. \n mitochondria used for aerobic respiration;\n
    8. \n
  8. \n larger yield of ATP from aerobic than anaerobic respiration;\n
    9. \n
\n

\n

\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ2.7B", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-2-cell-respiration", "c1-2-4-cell-respiration-as-a-system-for-producing-atp-within-the-cell-using-energy-released-from-carbon-compounds" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n List\n \n three\n \n characteristics of eukaryotic homologous chromosomes.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n a. linear DNA molecules\n
\n \n \n OR\n \n \n
\n DNA associated with histone «proteins» ✔\n

\n

\n b. carry the same sequence of\n \n genes\n \n ✔\n

\n

\n c. «but» not necessarily the same\n \n alleles\n \n «of those genes» ✔\n

\n

\n d. both are present when nucleus is in diploid state ✔\n
\n \n \n OR\n \n \n
\n occur in pairs ✔\n

\n

\n e. have\n \n same\n \n size/length/banding patterns ✔\n

\n

\n f. centromeres are in the same position ✔\n

\n
\n", "Examiners report": "None", "question_id": "19N.2.SL.TZ0.3C", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a3-1-diversity-of-organisms", "a3-1-6-diversity-in-chromosome-numbers-of-plant-and-animal-species" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n State\n \n one\n \n function of epinephrine in the human body.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n increases heart rate\n
\n OR\n
\n prepares the body for action;\n

\n
\n", "Examiners report": "
\n

\n In part 4c, many students would have benefitted from the inclusion of (adrenaline) after epinephrine as they seemed to not know of the latter. Epinephrine is the term used in the syllabus (section 6.2), so it was expected that the students were familiar with it.\n

\n
\n", "question_id": "21N.2.HL.TZ0.4C", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c2-1-chemical-signalling-[hl-only]", "c2-1-10-mechanism-of-action-of-epinephrine-(adrenaline)-receptors" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Outline the criteria that should be used to assess whether a group of organisms is a species.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n a. organisms can potentially interbreed;\n

\n

\n b. to produce fertile offspring;\n

\n

\n c. same sequence of genes (on chromosomes) / same types of chromosomes;\n

\n

\n d. similar traits/phenotype/WTTE;\n

\n

\n e. same chromosome number/karyotype;\n

\n
\n", "Examiners report": "
\n

\n This was the most successfully answered part of Question 8. Many knew that members of a species can interbreed and produce fertile offspring. Surprisingly few mentioned that similarities in characteristics or phenotype are found in species.\n

\n
\n", "question_id": "20N.2.HL.TZ0.8", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a3-1-diversity-of-organisms", "a3-1-5-difficulties-distinguishing-between-populations-and-species-due-to-divergence-of-noninterbreeding-populations-during-speciation" ] }, { "Question": "
\n
\n (i)\n
\n
\n

\n State a variable that should be kept constant.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n enzyme/substrate/egg white concentration/volume/pH/temperature;\n

\n

\n \n Accept another reasonable variable.\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.1B.SL.TZ2.2AI", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-1-enzymes-and-metabolism", "c1-1-8-effects-of-temperature-ph-and-substrate-concentration-on-the-rate-of-enzyme-activity" ] }, { "Question": "
\n
\n

\n Succinate dehydrogenase is an enzyme that catalyses the oxidation of succinic acid. If malonic acid is added to the mixture, the rate of reaction is reduced. An increase in succinic acid will increase the rate of reaction again. For this system, which term best describes malonic acid?\n

\n

\n A. Substrate\n

\n

\n B. End product\n

\n

\n C. Non-competitive inhibitor\n

\n

\n D. Competitive inhibitor\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "21M.1A.HL.TZ1.30", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-1-enzymes-and-metabolism", "c1-1-16-regulation-of-metabolic-pathways-by-feedback-inhibition" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Outline the role of ADH in osmoregulation.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n ADH (secreted by pituitary) if body/blood is dehydrated/hypertonic/has high solute concentration;\n
    2. \n
  2. \n more aquaporins / aquaporins open (in collecting duct);\n
    3. \n
  3. \n collecting duct more permeable to water/reabsorbs more water (from filtrate/urine);\n
    4. \n
  4. \n water reabsorbed by osmosis/water reabsorbed because medulla is hypertonic;\n
    5. \n
  5. \n (reabsorbed) water passes (from filtrate) to blood / blood solute concentration reduced;\n
    6. \n
  6. \n less water lost in urine / smaller volume of (more concentrated) urine;\n
    7. \n
  7. \n negative feedback / less/no ADH secreted when blood solute concentration returns to normal;\n
    8. \n
\n

\n \n Do not accept answers suggesting that ADH has a different effect when body fluids are hypotonic.\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.2.HL.TZ1.6A", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-3-homeostasis", "d3-3-7-role-of-the-kidney-in-osmoregulation-and-excretion", "d3-3-10-osmoregulation-by-water-reabsorption-in-the-collecting-ducts" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Compare and contrast the effect of ZDV and NVP on the growth of\n \n Allium\n \n roots.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n \n Similarities\n \n :\n

\n

\n a. reduce root length (compared to the control) ✔\n

\n

\n b. (ZDV and NVP) have greatest change (in growth) at lowest concentrations (of ZDV and NVP) ✔\n

\n

\n c. same effect at 200 μmol ✔\n

\n

\n d. above/at about 400 μmol effect levels off ✔\n

\n

\n \n Differences\n \n :\n

\n

\n e. the change/differences become significant after 200 μmol ✔\n

\n

\n f. ZDV has a (slightly) larger effect / NVP has a (slightly) smaller effect / WTTE\n
\n \n \n OR\n \n \n
\n above 400 μmol effect of ZDV remains higher / NVP remains lower ✔\n

\n

\n \n Answer must contain one similarity and one difference\n \n .\n

\n

\n \n Credit may be given for numeric differences when accurately stated\n \n .\n

\n
\n", "Examiners report": "
\n

\n There was a tendency to describe data rather than interpreting it. Instead of writing that root length was reduced, students simply compared numbers. Commonly either a comparison or a contrast was missing.\n

\n
\n", "question_id": "21M.2.HL.TZ1.1B", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a2-3-viruses-(hl-only)", "a2-3-6-rapid-evolution-in-viruses" ] }, { "Question": "
\n
\n

\n Which cell is a component of the innate immune system?\n

\n

\n
\n A.  T lymphocyte\n

\n

\n B.  Phagocyte\n

\n

\n C.  B lymphocyte\n

\n

\n D.  B memory cell\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "SPM.1A.SL.TZ0.20", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-2-defence-against-disease", "c3-2-4-differences-between-the-innate-immune-system-and-the-adaptive-immune-system" ] }, { "Question": "
\n
\n

\n Based on these experimental results, suggest\n \n one\n \n advantage of immobilizing lipase.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n a. it increases the range of temperature/pH that give high activity ✔\n

\n

\n b. allows for commercial use in detergents ✔\n

\n
\n", "Examiners report": "
\n

\n Most candidates saw that the enzymes could work at a higher temperature and a broader range of temperature and pH values and were therefore able to achieve 1 mark. Few students could connect this to the industrial uses for enzymes. This was one of many instances in the paper where students’ inability to use precise language affected their scores. Specifically, students should be reminded that terms like “affect” and “change” do not communicate differences in data as well as words like “increase” and “decrease.”\n

\n
\n", "question_id": "19M.1B.SL.TZ1.C", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-1-enzymes-and-metabolism", "c1-1-8-effects-of-temperature-ph-and-substrate-concentration-on-the-rate-of-enzyme-activity" ] }, { "Question": "
\n
\n

\n Explain the heart sounds.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n a. «heart sounds» produced by the closing of the valves ✔\n

\n

\n b. first sound «lub» is due to «closure of» the atrioventricular valves ✔\n \n Accept bicuspid/mitral and tricuspid\n \n .\n

\n

\n c. second sound «dup» is due to «closure of» the semilunar valves ✔\n \n Accept pulmonary/aortic valves\n \n .\n

\n

\n d. sequence of sounds is lub dup ✔\n \n OWTTE\n \n

\n
\n", "Examiners report": "None", "question_id": "19N.1B.HL.TZ0.19", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-2-transport", "b3-2-16-stages-in-the-cardiac-cycle" ] }, { "Question": "
\n
\n

\n State the number of degrees of freedom for this test to determine the critical value of chi-squared.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n 1 (df)\n
\n \n \n OR\n \n \n
\n (r-1) (c-1);\n

\n
\n", "Examiners report": "
\n

\n Calculating the degrees of freedom proved problematic for many.\n

\n
\n", "question_id": "22M.2.SL.TZ2.C", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c4-1-populations-and-communities", "c4-1-15-use-of-the-chi-squared-test-for-association-between-two-species" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Explain how denaturation affects the activity of an enzyme.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n changes the shape of the (active site) of the enzyme;\n
    2. \n
  2. \n substrate would be unable to attach to the enzyme/active site;\n
    3. \n
  3. \n slows the enzyme activity / prevents reaction/catalysis from proceeding;\n
    4. \n
\n
\n", "Examiners report": "None", "question_id": "22M.2.SL.TZ1.2C", "topics": [ "b-form-and-function" ], "subtopics": [ "b1-2-proteins", "b1-2-5-effect-of-ph-and-temperature-on-protein-structure" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n From the evidence provided by the graph, evaluate the reliability of these data.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. the data show clear trends\n
\n \n \n OR\n \n \n
\n a trend line could be drawn through these data\n
\n \n \n OR\n \n \n
\n there are no outliers ✔\n

\n

\n b. the error bars/standard deviations shown\n
\n \n \n OR\n \n \n
\n the error bars/standard deviations vary with concentration ✔\n

\n

\n c. sample size is unknown ✔\n

\n
\n", "Examiners report": "None", "question_id": "19N.1B.SL.TZ0.1C", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-3-water-potential", "d2-3-3-water-movement-by-osmosis-into-or-out-of-cells", "d2-3-4-changes-due-to-water-movement-in-plant-tissue-bathed-in-hypotonic-and-those-bathed-in-hypertonic-solutions" ] }, { "Question": "
\n
\n (d)\n
\n
\n

\n A standard potometer only measures water uptake. Explain how this apparatus measures the amount of water lost by the shoot as well as uptake.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n water uptake by shoot causes a decrease in reading for balance 2;\n
    2. \n
  2. \n water lost by the shoot would be total loss from the system;\n
    3. \n
\n

\n \n OWTTE\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.1B.SL.TZ1.3D", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-3-photosynthesis", "c1-3-7-techniques-for-varying-concentrations-of-carbon-dioxide-light-intensity-or-temperature-experimentally-to-investigate-the-effects-of-limiting-factors-on-the-rate-of-photosynthesis" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n With respect to this food chain, outline what is meant by a keystone species.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n a. keystone species have a disproportionate effect on the biological community ✔\n

\n

\n b. removal of the sea bream «due to fishing» ✔\n

\n

\n c. results in more sea urchins ✔\n

\n

\n d. which significantly reduce the producers/seagrass ✔\n

\n

\n \n Do not accept first trophic level for mpd\n \n

\n
\n", "Examiners report": "
\n

\n The syllabus definition of a keystone species was not often given, so alternative wording had to be judged on merit. The keystone species was not always recognized as the sea bream, but if it was, three marks were easily achieved.\n

\n
\n", "question_id": "19M.2.SL.TZ1.10C", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-2-stability-and-change", "d4-2-5-role-of-keystone-species-in-the-stability-of-ecosystems" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Describe the structure of cardiac muscle cells.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. cardiac muscle cells are branched ✔\n

\n

\n b. rich in mitochondria ✔\n

\n

\n c. rich in glycogen granules ✔\n

\n

\n d. formed by short cylindrical cells ✔\n

\n

\n e. contains\n \n intercalated\n \n discs ✔\n

\n

\n f. has gap junctions ✔\n

\n

\n g. «intercalated discs are» transverse cross-bands which represent the attachment site between adjacent cells ✔\n

\n

\n \n Do not accept myogenic as it is not a structure.\n \n

\n
\n", "Examiners report": "
\n

\n The stronger candidates could describe the structure of cardiac muscle cells.\n

\n
\n", "question_id": "19M.2.HL.TZ2.18A", "topics": [ "b-form-and-function" ], "subtopics": [ "b2-3-cell-specialization", "b2-3-9-adaptations-of-cardiac-muscle-cells-and-striated-muscle-fibres" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Explain the cause of sickle cell anemia and how this disease affects humans.\n

\n
\n
\n

\n [8]\n

\n
\n
\n", "Markscheme": "
\n

\n a. caused by a single nucleotide/base substitution mutation/GAG to GTG ✔\n

\n

\n b. «mutation of» a gene of β-globin/a subunit of hemoglobin ✔\n

\n

\n c. mRNA copies the mutation of DNA and substitutes an amino acid in hemoglobin «subunit» ✔\n

\n

\n d. glutamic acid is substituted by valine ✔\n

\n

\n e. sickle cell anemia involves distorted hemoglobin protein/HbS ✔\n

\n

\n f. «distorted HbS causes» distortion/sickling/shape change of red blood cells ✔\n

\n

\n g. «distorted/sickled red blood cells» block capillaries/blood flow ✔\n

\n

\n h. HbS/sickled red blood cells cannot carry enough oxygen «for the body»/leads to fatigue ✔\n

\n

\n i. low oxygen concentration seriously affects structure of HbS ✔\n

\n

\n j. homozygous «HbS/HbS» state causes severe anemia/death at low oxygen concentrations ✔\n

\n

\n k. heterozygous state has less anemia/minor effects/less effect of structure of hemoglobin\n
\n \n \n OR\n \n \n
\n heterozygous state only affected at high altitude/extreme exercise/low levels of oxygen ✔\n

\n

\n l. «heterozygous state» provides protection against malaria parasite/selective advantage in malaria areas ✔\n

\n

\n \n OWTTE\n \n

\n
\n", "Examiners report": "
\n

\n This question was well answered. The mutation and its impact was well understood by most. The genetic causes were less frequently discussed.\n

\n
\n", "question_id": "19M.2.SL.TZ2.7C", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d1-3-mutations-and-gene-editing", "d1-3-2-consequences-of-base-substitutions" ] }, { "Question": "
\n
\n

\n Label the model A diagram to show a region of protein.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n \n

\n

\n [Source: diagram from article published in\n \n The American Journal of Pathology\n \n ,\n \n 65\n \n , J Singer and G Nicolson, The structure and chemistry of mammalian cell membranes, 427–437, Copyright Elsevier (1971)]\n

\n

\n \n Accept label to top protein.\n \n

\n
\n", "Examiners report": "
\n

\n Most students could label the areas with protein and phospholipid.\n

\n
\n", "question_id": "19M.1B.SL.TZ2.B.I", "topics": [ "b-form-and-function" ], "subtopics": [ "b2-1-membranes-and-membrane-transport", "b2-1-10-fluid-mosaic-model-of-membrane-structure" ] }, { "Question": "
\n
\n

\n A tissue sample was examined under the microscope in order to determine a mitotic index. The number of cells in each stage of the cell cycle was determined and the data were entered into a table.\n

\n

\n \n

\n

\n What is the mitotic index?\n

\n

\n A. 0.125\n

\n

\n B. 0.25\n

\n

\n C. 0.75\n

\n

\n D. 1.00\n

\n

\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "21M.1A.HL.TZ1.7", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-1-cell-and-nuclear-division", "d2-1-17-differences-between-tumours-in-rates-of-cell-division-and-growth-and-in-the-capacity-for-metastasis-and-invasion-of-neighbouring-tissue" ] }, { "Question": "
\n
\n (b.iii)\n
\n
\n

\n Suggest a reason for a larger percentage of corals being infected with white syndrome on reefs with a higher cover of corals.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n a. the closer the corals are (to each other) the easier the transmission;\n
\n b. other organisms in the community may act as vectors/carriers / OWTTE;\n

\n
\n", "Examiners report": "
\n

\n In 1b (iii) the better students realised that it was to do with higher density of corals, not just the more vague ‘higher cover’ given in the stem.\n

\n
\n", "question_id": "21N.2.SL.TZ0.1B.III", "topics": [ "d-continuity-and-change", "b-form-and-function" ], "subtopics": [ "d4-3-climate-change", "d4-3-7-threats-to-coral-reefs-as-an-example-of-potential-ecosystem-collapse", "b4-1-adaptation-to-environment", "b4-1-5-conditions-required-for-coral-reef-formation" ] }, { "Question": "
\n
\n

\n What function is performed by the part of the cell shown in the electron micrograph?\n

\n

\n \n

\n

\n [Source: George E. Palade Electron Microscopy Slide Collection Harvey Cushing/John Hay Whitney Medical Library Yale University Library.]\n

\n

\n

\n

\n A. Locomotion\n

\n

\n B. Synthesis of proteins\n

\n

\n C. Movement of chromosomes\n

\n

\n D. Breakdown of cellular organelles\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "21M.1A.SL.TZ2.2", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a2-2-cell-structure", "a2-2-10-cell-types-and-cell-structures-viewed-in-light-and-electron-micrographs" ] }, { "Question": "
\n
\n

\n Draw a Punnett square to show all the possible genotypes of Queen Victoria’s children.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. parental alleles shown as X\n \n H\n \n and X\n \n h\n \n (female) and X\n \n H\n \n and Y (male);\n
\n b. Punnett square with genotypes of offspring shown as X\n \n H\n \n X\n \n H\n \n and X\n \n H\n \n Y and X\n \n H\n \n X\n \n h\n \n and X\n \n h\n \n Y;\n

\n

\n \n

\n
\n", "Examiners report": "
\n

\n Generally this was well answered. Common errors were to omit X and or Y chromosomes, show alleles on both X and Y chromosomes, or show the male X chromosome with a recessive h allele.\n

\n
\n", "question_id": "21N.2.SL.TZ0.A.I", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-2-inheritance", "d3-2-12-haemophilia-as-an-example-of-a-sex-linked-genetic-disorder" ] }, { "Question": "
\n
\n

\n Using the data, deduce whether pretreatment with ultrasound is effective for hydrolysing proteins.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n it is not, as hydrolysis is higher without ultrasound pretreatment\n
\n \n \n OR\n \n \n
\n it is not, as hydrolysis is lower with ultrasound pretreatment;\n

\n

\n \n Do not accept numerical values only with no attempt to evaluate their importance.\n
\n \n

\n

\n \n Do not accept increase/decrease instead of lower/higher.\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.1B.SL.TZ2.D", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-1-enzymes-and-metabolism", "c1-1-8-effects-of-temperature-ph-and-substrate-concentration-on-the-rate-of-enzyme-activity" ] }, { "Question": "
\n
\n

\n What are functions of type I and type II alveolar pneumocytes?\n
\n
\n

\n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n
\n \n \n Type I\n \n \n \n Type II\n \n
\n A.\n \n Produce surfactant\n \n Exchange CO\n \n 2\n \n
\n B.\n \n Exchange CO\n \n 2\n \n \n Exchange CO\n \n 2\n \n
\n C.\n \n Phagocytic cells\n \n Protective epithelial cells\n
\n D.\n \n Carry out gas exchange\n \n Produce surfactant\n
\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "23M.1A.HL.TZ1.22", "topics": [ "b-form-and-function" ], "subtopics": [ "b2-3-cell-specialization", "b2-3-8-adaptations-of-type-i-and-type-ii-pneumocytes-in-alveoli" ] }, { "Question": "
\n
\n (a.ii)\n
\n
\n

\n Transpiration continued after the fifth leaf had been removed. Suggest what can be concluded.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n transpiration does not only occur in the leaves\n
\n \n \n OR\n \n \n
\n transpiration through stem/shoot ✔\n

\n
\n", "Examiners report": "None", "question_id": "19N.1B.SL.TZ0.2A.II", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-1-gas-exchange", "b3-1-9-transpiration-as-a-consequence-of-gas-exchange-in-a-leaf" ] }, { "Question": "
\n
\n

\n What occurs during the establishment of a resting membrane potential of a neuron?\n

\n

\n
\n A.  Both sodium and potassium ions are pumped outside the neuron.\n

\n

\n B.  Sodium ions are pumped out while potassium ions are pumped into the neuron.\n

\n

\n C.  Both sodium and potassium ions are at rest inside the membrane of the neuron.\n

\n

\n D.  Sodium ions leave by diffusion and potassium ions enter the neuron by active transport.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "23M.1A.SL.TZ1.23", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c2-2-neural-signalling", "c2-2-2-generation-of-the-resting-potential-by-pumping-to-establish-and-maintain-concentration-gradients-of-sodium-and-potassium-ions" ] }, { "Question": "
\n
\n (a.i)\n
\n
\n

\n Outline the changes of distribution of the grey squirrel from 1945 to 2010.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. overall the grey squirrel distribution has increased «and the red squirrel decreased» ✔\n

\n

\n b. in 2010 the grey squirrel was found in areas where it was previously not found ✔\n

\n

\n c. grey squirrel has dominated/red squirrel virtually eliminated ✔\n

\n

\n \n OWTTE\n \n

\n
\n", "Examiners report": "
\n

\n While most candidates were able to achieve a mark by noting that the grey squirrel “dominated” in the second map, students again lost marks due to an inability to communicate concepts clearly. A large number of students confused distribution with population size, an idea not addressed in the maps.\n

\n
\n", "question_id": "19M.2.SL.TZ1.17A.I", "topics": [ "b-form-and-function" ], "subtopics": [ "b4-2-ecological-niches", "b4-2-1-ecological-niche-as-the-role-of-a-species-in-an-ecosystem" ] }, { "Question": "
\n
\n

\n Which activity directly contributes the most to recent increases in atmospheric CO\n \n 2\n \n concentrations?\n

\n

\n A. Landfills\n

\n

\n B. Planting trees\n

\n

\n C. Cattle rearing\n

\n

\n D. Burning of fossil fuels\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "
\n

\n This was an easy question for most candidates with 89 % answering correctly.\n

\n
\n", "question_id": "22M.1A.SL.TZ2.19", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c4-2-transfers-of-energy-and-matter", "c4-2-18-ecosystems-as-carbon-sinks-and-carbon-sources" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Explain the neural control of swallowing.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n a. voluntary passage of food through the mouth ✔\n

\n

\n b. «bolus of» food touches the walls of the pharynx ✔\n

\n

\n c. nerve sends message/impulse to brain ✔\n

\n

\n d. swallowing centre in the medulla «oblongata» ✔\n

\n

\n e. now involuntary/unconscious/autonomic responses/reflexes ✔\n

\n

\n f. triggers closing of epiglottis «to prevent choking» ✔\n

\n

\n g. leading to contraction of muscles/peristalsis «in the pharynx and esophagus» ✔\n

\n
\n", "Examiners report": "
\n

\n Very few candidates recognized the voluntary aspect of swallowing. The role of the medulla and consequent involuntary action were most often described, although answers were frequently quite muddled.\n

\n
\n", "question_id": "19M.2.SL.TZ1.5A", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-1-integration-of-body-systems", "c3-1-16-control-of-peristalsis-in-the-digestive-system-by-the-central-nervous-system-and-enteric-nervous-system" ] }, { "Question": "
\n
\n (f)\n
\n
\n

\n Based on these data, outline the evidence that T-705 has potential to be used as a treatment for EVD.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. cells not killed/few cells killed «even at high concentrations» ✔\n

\n

\n b. «T-705» effective/viruses reduced/viruses killed at 100 μM\n
\n \n \n OR\n \n \n
\n «T-705» very effective/viruses much reduced/nearly all viruses killed at 1000 μM ✔\n

\n

\n c. virus concentration decreases as T-705 concentration increases ✔\n

\n

\n d. drug has «high» potential for treatment «at high enough concentration» ✔\n

\n
\n", "Examiners report": "
\n

\n Graph was well read and understood by most. The question was answered with more insight than expected, especially when alluding to the implications of live cells at high drug concentrations\n

\n
\n", "question_id": "19M.2.HL.TZ1.1F", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a2-3-viruses-(hl-only)" ] }, { "Question": "
\n
\n

\n Suggest\n \n two\n \n reasons, other than mate selection, for variation in plumage colouration in red knots.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n camouflage to avoid predators (in different migratory routes);\n
    2. \n
  2. \n different diets (in different migratory routes);\n
    3. \n
  3. \n less migratory distance leaves more energy to produce pigments (in plumage);\n
    4. \n
  4. \n geographic isolation (due to different migratory routes) leads to different gene pools;\n
    5. \n
\n
\n", "Examiners report": "None", "question_id": "23M.1A.SL.TZ2.II", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-1-natural-selection", "d4-1-7-sexual-selection-as-a-selection-pressure-in-animal-species" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n The figure shows a tripeptide.\n

\n

\n \n

\n

\n Label\n \n one\n \n peptide bond in this molecule.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n circle/bracket around peptide bond / arrow pointing to peptide bond / peptide bond labelled;\n

\n

\n \n

\n

\n \n Allow either peptide bond\n \n

\n

\n \n Allow if adjacent C=O and NH groups are included in the circle/bracket, but do not allow if other parts of the molecule are included\n \n .\n

\n
\n", "Examiners report": "
\n

\n 80 % of candidates indicated one of the two peptide bonds in the diagram correctly.\n

\n
\n", "question_id": "21N.2.HL.TZ0.4", "topics": [ "b-form-and-function" ], "subtopics": [ "b1-2-proteins", "b1-2-2-condensation-reactions-forming-dipeptides-and-longer-chains-of-amino-acids", "b1-2-8-pleating-and-coiling-of-secondary-structure-of-proteins", "b3-1-gas-exchange", "b3-1-5-ventilation-of-the-lungs" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Outline the control of metabolism by end-product inhibition.\n

\n
\n
\n

\n [5]\n

\n
\n
\n", "Markscheme": "
\n

\n a. metabolism is chains/web of\n \n enzyme\n \n -catalyzed reactions\n
\n \n \n OR\n \n \n
\n metabolic pathway is a chain of\n \n enzyme\n \n -catalyzed reactions ✔\n

\n

\n b. end product/inhibitor is final product of chain/pathway ✔\n

\n

\n c. inhibits/binds to/blocks the first enzyme in chain/pathway ✔\n

\n

\n d. non-competitive inhibition ✔\n

\n

\n e. end-product/inhibitor binds to an allosteric site/site away from the active site ✔\n

\n

\n f. changes the shape of the\n \n active site\n \n /affinity of the\n \n active site\n \n «for the substrate» ✔\n

\n

\n g. prevents intermediates from building up\n
\n \n \n OR\n \n \n
\n prevents formation of excess «end» product/stops production when there is enough\n
\n \n \n OR\n \n \n
\n whole metabolic pathway can be switched off ✔\n

\n

\n h. negative feedback ✔\n

\n

\n i. binding of the end product/inhibitor is reversible\n
\n \n \n OR\n \n \n
\n pathway restarts if end product/inhibitor detaches/if end product concentration is low ✔\n

\n

\n j. isoleucine inhibits/slows «activity of first enzyme in» threonine to isoleucine pathway ✔\n

\n

\n \n Allow mark points shown in clearly annotated diagrams.\n \n

\n

\n \n To gain mpd, mpe and mpf the answer must be in the context of end-product inhibition, not enzyme inhibition generally.\n \n

\n
\n", "Examiners report": "
\n

\n Answers to this question were rather polarised. Candidates who had studied this topic and understood it had no difficulty in scoring high marks but other candidates struggled to include any useful ideas in their answers. Weaker answers tended to exclude the ideas of enzyme catalysis, pathways of reactions and the mechanisms involved in non-competitive enzyme inhibition. Diagrams to illustrate the process were a valuable part of some answers.\n

\n
\n", "question_id": "19M.2.HL.TZ1.5B", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-1-enzymes-and-metabolism", "c1-1-16-regulation-of-metabolic-pathways-by-feedback-inhibition" ] }, { "Question": "
\n
\n

\n Explain the process of gas exchange taking place in the alveoli.\n

\n
\n
\n

\n [7]\n

\n
\n
\n", "Markscheme": "
\n

\n a. O\n \n 2\n \n diffuses into blood and CO\n \n 2\n \n diffuses out from blood ✔\n

\n

\n b. blood entering the alveoli is high in CO\n \n 2\n \n /low in O\n \n 2\n \n ✔\n
\n \n \n OR\n \n \n
\n air in alveolus is high in O\n \n 2\n \n /low in CO\n \n 2\n \n ✔\n

\n

\n c. diffusion (in either direction) take place due to concentration gradients ✔\n

\n

\n d. concentration gradients maintained by ventilation/blood flow ✔\n

\n

\n e. large surface area created by many alveoli/spherical shape of alveoli for more efficient diffusion ✔\n

\n

\n f. rich supply of capillaries (around alveoli) allows efficient exchange ✔\n

\n

\n g. type I pneumocytes are thin to allow easy diffusion/short distances ✔\n

\n

\n h. gases must dissolve in liquid lining of alveolus in order to be exchanged ✔\n

\n

\n i. type II pneumocytes secrete surfactants to reduce surface tension/prevent lungs sticking together ✔\n

\n

\n j. type II pneumocytes create moist conditions in alveoli ✔\n

\n
\n", "Examiners report": "
\n

\n This question was attempted by approximately 56 % of candidates.\n

\n

\n Some coherent, clear answers were given earning the maximum marks. However, commonly, valid ideas were given but were jumbled. Coherent writing was usually missing. The term diffusion was missing in many answers. The idea that alveoli are surrounded by capillaries to enable exchange of gases between the air in alveolus and the blood did not seem to be a mental picture for many. Concentration gradients as a reason for diffusion of oxygen or carbon dioxide between the alveoli and the blood was rarely explained. However, it seemed that everyone knew about surfactants from type II pneumocytes.\n

\n
\n", "question_id": "21M.2.SL.TZ1.B", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-1-gas-exchange", "b3-1-4-adaptations-of-mammalian-lungs-for-gas-exchange" ] }, { "Question": "
\n
\n

\n When the data in the table were used to calculate chi-squared, the calculated value was 0.056. The critical value is 3.84. Explain the conclusion that can be drawn from the calculated and critical values for chi-squared.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n (when the calculated value is smaller than the critical value) there is no significant association between the two species / H\n \n 0\n \n /null hypothesis accepted;\n
    2. \n
  2. \n it is random chance if both species are either present or absent in most quadrats;\n
    3. \n
\n
\n", "Examiners report": "None", "question_id": "22M.2.SL.TZ2.D", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c4-1-populations-and-communities", "c4-1-15-use-of-the-chi-squared-test-for-association-between-two-species" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n State the name of the valves that prevent blood flowing from the arteries back into the heart.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n semilunar / sigmoid / pulmonary\n \n and\n \n aortic valve ✔\n

\n
\n", "Examiners report": "
\n

\n Most could name the semilunar valves.\n

\n
\n", "question_id": "19M.2.HL.TZ2.18B", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-2-transport", "b3-2-15-adaptations-of-the-mammalian-heart-for-delivering-pressurized-blood-to-the-arteries" ] }, { "Question": "
\n
\n (a.ii)\n
\n
\n

\n Two components of biodiversity are richness and evenness. Deduce which of the two pools was higher in evenness.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B;\n

\n
\n", "Examiners report": "None", "question_id": "20N.2.SL.TZ0.14A.II", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a4-2-conservation-of-biodiversity", "a4-2-5-evidence-for-a-biodiversity-crisis" ] }, { "Question": "
\n
\n

\n How many chromosomes are there in a cell during anaphase of mitosis, if the diploid number of the cell is 20?\n

\n

\n A. 10\n

\n

\n B. 20\n

\n

\n C. 40\n

\n

\n D. 80\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "
\n

\n Some candidates were caught out by this question, either because their understanding of mitosis had weaknesses or because they did not think carefully enough. In anaphase, the two sister chromatids that have made up each chromosome in prophase and metaphase have separated. Guidance in sub-topic 1.6 of the program indicates that they should be referred to as chromosomes as soon as separation has occurred, rather than as chromatids. In anaphase there are therefore double the diploid number of chromosomes in a cell. Cytokinesis will subsequently halve the number, so the daughter cells are diploid.\n

\n
\n", "question_id": "20N.1A.SL.TZ0.5", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-1-cell-and-nuclear-division", "d2-1-4-roles-of-mitosis-and-meiosis-in-eukaryotes" ] }, { "Question": "
\n
\n (d)\n
\n
\n

\n Using the life cycle diagram and the graph for the year 2000, analyse the distribution of adult ticks throughout the different seasons.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. adults present through autumn and winter «according to the life cycle diagram»\n
\n \n \n OR\n \n \n
\n some adults «must» survive winter «despite graph suggesting zero» ✔\n

\n

\n b. adults peak in October «& November»/in autumn/between September and December ✔\n

\n

\n c. adults die after laying eggs in winter/beginning of spring ✔\n

\n

\n d. smaller peak/10 % versus 55 % peak/smaller numbers of adults in April/spring ✔\n

\n

\n e. adults absent from June to September/summer ✔\n

\n

\n \n Each mark point, requires month or season.\n \n
\n \n Jan - Mar = winter\n \n
\n \n Apr - Jun = spring\n \n
\n \n Jul - Sep = summer\n \n
\n \n Oct - Dec = autumn = fall\n \n

\n

\n \n Do not accept that there are the lowest number or no adults in winter.\n \n

\n
\n", "Examiners report": "None", "question_id": "19N.2.SL.TZ0.1D", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a4-2-conservation-of-biodiversity" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n This micrograph shows a transverse section of an artery.\n

\n

\n \n

\n

\n [Source: OpenStax College, 2013. Comparison of artery and vein. [image online] Available at:\n
\n \n https://en.wikipedia.org/wiki/File:2102_Comparison_of_Artery_and_Vein.jpg\n \n Attribution 3.0 Unported\n
\n (CC BY 3.0)\n \n https:/creativecommons.org/licenses/by/3.0/deed.en\n \n [Accessed 11 March 2020].]\n

\n

\n

\n

\n Explain how the specialized structures of arteries help them to achieve their functions.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n a. arteries carry blood at high pressure;\n
\n b. rupture of arteries is prevented by thick muscular/elastic walls;\n
\n c. narrow lumen to maintain a high blood pressure;\n
\n d. elastic tissue allows artery to stretch and recoil (to even out pressures);\n
\n e. arteries have muscle layers which contract to increase/control the blood flow;\n
\n f. folding in the endothelium allows stretching\n
\n OR\n
\n smooth endothelium reduces friction;\n

\n
\n", "Examiners report": "
\n

\n Most could state that the arteries carry blood at high pressure, but had difficulty getting the other two marks.\n

\n
\n", "question_id": "21N.2.SL.TZ0.4A", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-2-transport", "b3-2-2-structure-of-arteries-and-veins", "b3-2-3-adaptations-of-arteries-for-the-transport-of-blood-away-from-the-heart" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Using a Punnett square, determine how a smooth-haired puppy could be produced in the offspring.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n WK Wk wK and wk for male gamete genotypes and wk for female;\n

\n

\n wwKk shown in Punnett square and identified as smooth;\n

\n

\n \n

\n
\n", "Examiners report": "
\n

\n There were some complaints from teachers that epistasis is not included in the program. It was not expected that candidates would have studied ratios derived from interaction between genes and instead it was intended that they work out the pattern of inheritance themselves from the information provided. About a third of candidates successfully did this. The Punnett squares drawn up by other candidates often revealed fundamental misunderstandings of dihybrid inheritance.\n

\n
\n", "question_id": "20N.2.SL.TZ0.5B", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-2-inheritance", "d3-2-10-incomplete-dominance-and-codominance" ] }, { "Question": "
\n
\n

\n Explain how breathing is controlled by the brain.\n

\n
\n
\n

\n [6]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n breathing is an automatic process/can occur without conscious intervention/is involuntary/ autonomic;\n
    2. \n
  2. \n voluntary/conscious factors can override automatic functions (for a limited time);\n
    3. \n
  3. \n control of the breathing comes from the respiratory centre;\n
    4. \n
  4. \n (respiratory centre) located in the medulla of the brain;\n
    5. \n
  5. \n exercise results in higher CO2 levels in blood;\n
    6. \n
  6. \n breathing rate changes in response changes to blood pH/acidity/CO2 level;\n
    7. \n
  7. \n medulla contains chemoreceptors\n
    \n \n \n OR\n \n \n
    \n chemoreptors in aortic/carotid bodies send signals to medulla;\n
    8. \n
  8. \n respiratory centre/medulla sends nerve impulses to diaphragm/intercostal muscles;\n
    9. \n
  9. \n stimulates (the intercostal muscles/diaphragm) to control breathing rate/depth of inspiration/contraction;\n
    10. \n
\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ1.8", "topics": [ "c-interaction-and-interdependence", "b-form-and-function" ], "subtopics": [ "c3-1-integration-of-body-systems", "c3-1-15-feedback-control-of-ventilation-rate-following-sensory-input-from-chemoreceptors", "b3-1-gas-exchange", "b3-1-5-ventilation-of-the-lungs" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Draw a molecular diagram to show the formation of a peptide bond.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n a.\n \n two\n \n amino acids correctly drawn;\n

\n

\n b. removal/production of H\n \n 2\n \n O molecule shown;\n

\n

\n c. peptide bond labelled between C of C=O and N of N-H;\n

\n

\n \n

\n

\n \n Accept specific examples of amino acids correctly drawn for example glycine with H instead of R.\n \n

\n

\n \n mpc can be awarded if the peptide bond is shown as in the dipeptide diagram but there are errors elsewhere\n \n .\n

\n
\n", "Examiners report": "
\n

\n Mostly full marks were gained although some had the correct diagrams but failed to label the peptide bond.\n

\n
\n", "question_id": "20N.2.HL.TZ0.6", "topics": [ "b-form-and-function", "d-continuity-and-change" ], "subtopics": [ "b1-2-proteins", "b1-2-2-condensation-reactions-forming-dipeptides-and-longer-chains-of-amino-acids", "d1-2-protein-synthesis", "d1-2-5-translation-as-the-synthesis-of-polypeptides-from-mrna", "d1-2-10-stepwise-movement-of-the-ribosome-along-mrna-and-linkage-of-amino-acids-by-peptide-bonding-to-the-growing-polypeptide-chain", "d1-2-14-non-coding-sequences-in-dna-do-not-code-for-polypeptides" ] }, { "Question": "
\n
\n

\n The pentadactyl limbs of mammals, birds, reptiles and amphibians are examples of which kind of structures?\n

\n

\n A. Homologous\n

\n

\n B. Analogous\n

\n

\n C. Vestigial\n

\n

\n D. Convergent\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "None", "question_id": "21N.1A.SL.TZ0.20", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a4-1-evolution-and-speciation", "a4-1-4-evidence-for-evolution-from-homologous-structures" ] }, { "Question": "
\n
\n (a.i)\n
\n
\n

\n Two components of biodiversity are richness and evenness. Deduce which of the two pools was higher in richness.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A;\n

\n
\n", "Examiners report": "
\n

\n Candidates could deduce the richness and evenness of the pools but gave incomplete answers to the other two parts of this question.\n

\n
\n", "question_id": "20N.2.SL.TZ0.14A.I", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a4-2-conservation-of-biodiversity", "a4-2-5-evidence-for-a-biodiversity-crisis" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Identify the stage of mitosis labelled X in the image, giving a reason.\n

\n

\n \n

\n

\n [Source: Copyright 2002, The Trustees of Indiana University]\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n telophase because the chromosomes/chromatids have reached the poles\n
\n \n \n OR\n \n \n
\n «late» anaphase as some chromosomes/chromatids are still moving/tails visible ✔\n

\n

\n \n OWTTE\n \n

\n
\n", "Examiners report": "
\n

\n Most were able to correctly state (late) anaphase or telophase but did not give a reason as clearly asked. Many students seem to have excellent eyesight as they claimed to see that the chromosomes were unwinding and that the nuclear membranes had formed. Please encourage the students not to go beyond what can be seen.\n

\n
\n", "question_id": "19M.2.SL.TZ2.2A", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-1-cell-and-nuclear-division", "d2-1-8-identification-of-phases-of-mitosis" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Suggest\n \n two\n \n reasons, other than elevation, for the differences in nitrogen concentration in leaves of pitcher plants.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n pitcher plants consume more insects (at different sampling sites);\n
    2. \n
  2. \n larger insects contain more nitrogen;\n
    3. \n
  3. \n more nitrogen concentration in soil\n
    \n \n \n OR\n \n \n
    \n more nitrifying bacteria in the soil\n
    \n \n \n OR\n \n \n
    \n water-logged soil has less nitrogen;\n
    4. \n
  4. \n use of N/NPK fertilizers\n
    \n \n \n OR\n \n \n
    \n leaching of N in different sites;\n
    5. \n
\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ2.20C", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-2-stability-and-change", "d4-2-8-eutrophication-of-aquatic-and-marine-ecosystems-due-to-leaching" ] }, { "Question": "
\n
\n (a.ii)\n
\n
\n

\n Suggest\n \n one\n \n conclusion that can be drawn from the results shown in the graph.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n a. as fungus grows, the rate of oxygen consumption increases ✔\n

\n

\n b. around day 4/5 fungus begins to grow/no growth in days 1–3 ✔\n

\n

\n c. the rate of fungus growth/rate of respiration is highest after 5 days ✔\n

\n
\n", "Examiners report": "
\n

\n Many candidates described what was shown by the graph rather than making a conclusion related to the growth of fungi. Thus “oxygen consumption increased after day 4” or references to the feed respiring were common answers.\n

\n
\n", "question_id": "19M.1B.SL.TZ1.2A.II", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-2-cell-respiration", "c1-2-6-variables-affecting-the-rate-of-cell-respiration" ] }, { "Question": "
\n
\n

\n where the DNA of each individual could be taken from.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n from blood sample/hair/cheek/saliva/semen;\n

\n

\n \n Do not accept red blood cells\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.1B.SL.TZ1.I", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-3-photosynthesis", "c1-3-7-techniques-for-varying-concentrations-of-carbon-dioxide-light-intensity-or-temperature-experimentally-to-investigate-the-effects-of-limiting-factors-on-the-rate-of-photosynthesis" ] }, { "Question": "
\n
\n

\n What is a function of DNA polymerase I?\n

\n

\n A. Adds nucleotides in a 5’ to 3’ direction to elongate the chain\n

\n

\n B. Uncoils the DNA double helix and splits it into two template strands\n

\n

\n C. Removes RNA primer and replaces it with DNA\n

\n

\n D. Produces sugar-phosphate bonds to link Okazaki fragments\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "19N.1A.SL.TZ0.26", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d1-1-dna-replication", "d1-1-3-role-of-helicase-and-dna-polymerase-in-dna-replication", "d1-1-8-functions-of-dna-primase-dna-polymerase-i-dna-polymerase-iii-and-dna-ligase-in-replication" ] }, { "Question": "
\n
\n

\n What is contained in skeletal muscle?\n
\n
\n

\n

\n A.  Cross bridges between muscle fibres\n

\n

\n B.  Sarcomeres formed of contractile myofibrils\n

\n

\n C.  Myosin filaments forming cross bridges with troponin and tropomyosin\n

\n

\n D.  Multinucleate cells with numerous microfibrils made of contractile sarcomeres\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "23M.1A.HL.TZ1.38", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-3-muscle-and-motility-(hl-only)", "b3-3-2-sliding-filament-model-of-muscle-contraction" ] }, { "Question": "
\n
\n (i)\n
\n
\n

\n Calculate the percentage of containers that contained food.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n 4(%);\n

\n
\n", "Examiners report": "
\n

\n Percentage calculations often cause widespread difficulties but most candidates found this one easy. The only common mistake was to divide 4 by a hundred, and then forget to multiply by a hundred to turn the proportion into a percentage.\n

\n
\n", "question_id": "22N.2.HL.TZ0.1I", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-1-integration-of-body-systems", "c3-1-4-the-brain-as-a-central-information-integration-organ" ] }, { "Question": "
\n
\n

\n The stem of a young plant is cut through and the cut end is immersed in water containing a red dye. The plant continues to transpire as normal. In what region of the stem would the red colour be visible soon after immersion?\n

\n

\n \n

\n

\n \n [Source: Berkshire Community College Bioscience Image Library, 2014. Herbaceous Dicot Stem: Vascular Bundles Young\n \n
\n \n Helianthus. [image online] Available at: https://www.flickr.com/photos/146824358@N03/36834307513 [Accessed\n \n
\n \n 4 October 2021]. Public domain.]\n \n

\n

\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "23M.1A.SL.TZ2.28", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-2-transport", "b3-2-7-transport-of-water-from-roots-to-leaves-during-transpiration" ] }, { "Question": "
\n
\n

\n Explain how the results in the graph could have been obtained.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. using a potometer ✔\n \n Accept transpirometer but not respirometer\n \n .\n

\n

\n b. leafy shoot attached to a reservoir and a graduated «capillary» tube ✔\n

\n

\n c. as transpiration increases water uptake «by roots» also increases ✔\n

\n

\n d. distance/time for bubble «in capillary tube» to travel is used to measure transpiration rate ✔\n

\n
\n", "Examiners report": "None", "question_id": "19N.1B.SL.TZ0.C", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-1-gas-exchange", "b3-1-9-transpiration-as-a-consequence-of-gas-exchange-in-a-leaf" ] }, { "Question": "
\n
\n (a.i)\n
\n
\n

\n Distinguish between levels of predation in marmots born in the wild and those born in captivity.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n predation was greater in those born in captivity ✔\n

\n
\n", "Examiners report": "
\n

\n This question was generally well answered.\n

\n
\n", "question_id": "19M.2.SL.TZ1.16A.I", "topics": [ "b-form-and-function" ], "subtopics": [ "b4-2-ecological-niches", "b4-2-10-adaptations-of-predators-for-finding-catching-and-killing-prey-and-of-prey-animals-for-resisting-predation" ] }, { "Question": "
\n
\n

\n What is the minimum number of nucleotides needed to code for a polypeptide composed of 210 amino acids?\n

\n

\n A. 70\n

\n

\n B. 210\n

\n

\n C. 420\n

\n

\n D. 630\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "22M.1A.SL.TZ1.10", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d1-2-protein-synthesis", "d1-2-9-using-the-genetic-code-expressed-as-a-table-of-mrna-codons" ] }, { "Question": "
\n
\n (a.iii)\n
\n
\n

\n Using the climograph, outline the pattern of rainfall.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n rainfall concentrated between April to December/peaks in June-August «followed by months with little/no rainfall» ✔\n

\n

\n \n OWTTE\n \n

\n
\n", "Examiners report": "
\n

\n Most outlined correctly the pattern of rainfall, but irrelevant answers were seen.\n

\n
\n", "question_id": "19M.2.HL.TZ2.15A.III", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-2-stability-and-change", "d4-2-14-cyclical-succession-in-ecosystems" ] }, { "Question": "
\n
\n

\n Explain how ventilation rate is changed during vigorous physical exercise.\n

\n
\n
\n

\n [6]\n

\n
\n
\n", "Markscheme": "
\n

\n a. exercise increases the rate of cellular respiration ✔\n

\n

\n b. increases production of CO\n \n 2\n \n ✔\n

\n

\n c.  increased CO\n \n 2\n \n causes increased acidity in blood\n
\n \n \n OR\n \n \n
\n decrease pH ✔\n

\n

\n d. chemoreceptors in aorta/carotid artery/medulla oblongata detect change in pH ✔\n

\n

\n e. impulse/signal/message to breathing centre\n
\n \n \n OR\n \n \n
\n impulse/signal/message to medulla oblongata ✔\n

\n

\n f. impulse/signal/message to to diaphragm for more frequent contraction\n
\n \n \n OR\n \n \n
\n impulse/signal/message to intercostal muscles for more frequent contraction ✔\n

\n

\n g. increase ventilation rate for more gas exchange ✔\n

\n

\n h. long term effects of increased lung surface area\n
\n \n \n OR\n \n \n
\n vital capacity ✔\n

\n

\n i. training decreases ventilation rate over time ✔\n

\n
\n", "Examiners report": "None", "question_id": "19N.1B.SL.TZ0.23", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-1-integration-of-body-systems", "c3-1-14-feedback-control-of-heart-rate-following-sensory-input-from-baroreceptors-and-chemoreceptors", "c3-1-15-feedback-control-of-ventilation-rate-following-sensory-input-from-chemoreceptors" ] }, { "Question": "
\n
\n (a.i)\n
\n
\n

\n State\n \n two\n \n causes of the decrease of biomass along food chains in terrestrial ecosystems.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. «cell» respiration/loss of CO\n \n 2\n \n /biomass consumed to provide/as a source of energy ✔\n

\n

\n b. loss of energy «as heat» between trophic levels means less energy available for building biomass ✔\n

\n

\n c. waste products «other than CO\n \n 2\n \n »/loss of urea/feces/egesta ✔\n

\n

\n d. material used/CO\n \n 2\n \n released by saprotrophs ✔\n

\n

\n e. undigested/uneaten material «teeth, bones,\n \n etc\n \n »/detritus buried/not consumed\n
\n \n \n OR\n \n \n
\n formation of peat/fossils/limestone ✔\n

\n
\n", "Examiners report": "
\n

\n A large proportion of students looked at this question and immediately reeled off an answer in terms of energy (as in many previous years). Few made the connection between biomass and energy, for example in respiration CO\n \n 2\n \n is lost from the food chain during respiration, or that urea has mass\n \n etc\n \n .\n

\n
\n", "question_id": "19M.2.SL.TZ2.3A.I", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c4-2-transfers-of-energy-and-matter", "c4-2-14-restrictions-on-the-number-of-trophic-levels-in-ecosystems-due-to-energy-losses" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Outline how the prickly pear cactus may become an ecological problem in Kruger National Park.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n they can become an invasive species because they lack predators\n
    \n \n \n OR\n \n \n
    \n uncontrolled population growth due to lack of predators;\n
    2. \n
  2. \n compete with local/endemic species for nutrients/habitat;\n
    3. \n
  3. \n may cause (endemic) species to become extinct/reduction in numbers;\n
    4. \n
\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ1.16A", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-2-stability-and-change", "d4-2-11-restoration-of-natural-processes-in-ecosystems-by-rewilding" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Outline the stages in the production of mRNA by transcription.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n

\n a. DNA is unwound/strands are separated «by RNA polymerase» ✔\n

\n

\n b. new nucleotides attached to template strand «by RNA polymerase» ✔\n

\n

\n c.\n \n complementary\n \n base pairing/base pairing with an example\n
\n \n \n OR\n \n \n
\n adenine with thymine/uracil with adenine/cytosine with guanine/guanine with cytosine ✔\n

\n

\n d. mRNA detaches from template ✔\n

\n

\n e. DNA rewinds ✔\n

\n
\n", "Examiners report": "
\n

\n Almost all students had a clear idea of complementary base pairing and that A pairs with U in RNA. However, this question revealed weakness in the understanding of transcription and the ability to distinguish transcription from DNA replication and RNA translation. Often times candidates had hybrid answers containing information from at least two, but sometimes all three processes. Many candidates were able to gain a couple of the easier marks in 7a on transcription despite having a poor understanding of the process.\n

\n
\n", "question_id": "19M.2.SL.TZ1.7", "topics": [ "d-continuity-and-change", "b-form-and-function", "a-unity-and-diversity" ], "subtopics": [ "d1-2-protein-synthesis", "d1-2-1-transcription-as-the-synthesis-of-rna-using-a-dna-template", "d1-2-2-role-of-hydrogen-bonding-and-complementary-base-pairing-in-transcription", "d1-2-4-transcription-as-a-process-required-for-the-expression-of-genes", "b2-1-membranes-and-membrane-transport", "b2-1-4-integral-and-peripheral-proteins-in-membranes", "a4-1-evolution-and-speciation", "a4-1-6-speciation-by-splitting-of-pre-existing-species" ] }, { "Question": "
\n
\n (d)\n
\n
\n

\n Compare and contrast the data for Conakry with the data for the three suburbs.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n \n differences\n \n :\n
\n a. Conakry has more cases than any of the suburbs\n
\n \n \n OR\n \n \n
\n more cases in total in the suburbs than in Conakry ✔\n

\n

\n b. more male cases in Conakry whereas more female cases in suburbs ✔\n

\n

\n c. higher «% of»\n \n fatal\n \n cases at Ebola\n \n treatment centers\n \n in suburbs than in Conakry ✔\n

\n

\n \n similarity\n \n :\n
\n d. in both Conakry and suburbs «% of»\n \n fatal\n \n cases in\n \n treatment centers\n \n is higher than outside ✔\n

\n
\n", "Examiners report": "
\n

\n This was a timely question with Ebola epidemics again causing great problems in parts of Africa. Students were expected to have had some practice at analysing data relating to an epidemic because of this Skill in the programme: Analysis of epidemiological data related to vaccination programmes. It was assumed that candidates would understand terms such as ‘case’, ‘fatal case’, ‘infect’ and ‘treat’.\n

\n

\n This was another question where the skill was in picking out significant trends. Differences between individual suburbs were not significant so all the answers accepted were either similarities or differences between the capital city and the suburbs generally. Most but not all candidates made two or more statements about the data that were significant enough to score marks. Some students treated percentages as though they were absolute numbers and for example added the percentage of fatal cases in and outside treatment centres together, which does not give a meaningful total.\n

\n
\n", "question_id": "19M.2.SL.TZ1.1D", "topics": [ "c-interaction-and-interdependence", "a-unity-and-diversity" ], "subtopics": [ "c3-2-defence-against-disease", "a2-3-viruses-(hl-only)" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Estimate the resting potential for this axon.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n −65\n \n mV\n \n ✔\n

\n

\n \n Unit required; minus sign required. Accept answers from −62mV to −65mV\n \n .\n

\n
\n", "Examiners report": "
\n

\n Strong students answered this question showing clear understanding of the process. However, most students showed poor understanding with errors: correct direction of ions being pumped not known; the direction of ions during repolarization was mixed up with resting state. Few wrote about the charge difference between inside and outside of the axon during the resting potential.\n

\n
\n", "question_id": "21M.2.SL.TZ1.4", "topics": [ "c-interaction-and-interdependence", "b-form-and-function" ], "subtopics": [ "c2-2-neural-signalling", "c2-2-10-oscilloscope-traces-showing-resting-potentials-and-action-potentials", "b2-1-membranes-and-membrane-transport", "b2-1-15-sodium-potassium-pumps-as-an-example-of-exchange-transporters" ] }, { "Question": "
\n
\n

\n State the activity and season that occupied the greatest mean percentage of observation time.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n \n rest\n \n ing in\n \n spring\n \n ;\n

\n
\n", "Examiners report": "
\n

\n 80\n \n \n \n \n % of candidates identified the season and activity correctly.\n

\n
\n", "question_id": "22N.2.HL.TZ0.G", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-1-integration-of-body-systems", "c3-1-4-the-brain-as-a-central-information-integration-organ" ] }, { "Question": "
\n
\n

\n Identify the group with the greatest number of species with problems due to ingestion of plastics.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C / albatrosses, petrels and shearwaters;\n

\n
\n", "Examiners report": "None", "question_id": "20N.2.SL.TZ0.B.I", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-2-stability-and-change", "d4-2-10-effects-of-microplastic-and-macroplastic-pollution-of-the-oceans" ] }, { "Question": "
\n
\n

\n Cell metabolism involves anabolic and catabolic reactions. Which process directly involves anabolism?\n

\n

\n A. Active transport of ions\n

\n

\n B. Release of energy from glucose\n

\n

\n C. Production of intracellular enzymes\n

\n

\n D. Breakdown of worn-out cell organelles by lysosomes\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "22M.1A.SL.TZ2.8", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-1-enzymes-and-metabolism", "c1-1-3-anabolic-and-catabolic-reactions" ] }, { "Question": "
\n
\n

\n The electron micrograph shows a section through part of an animal cell.\n

\n

\n \n

\n

\n [Source: https://en.wikipedia.org/wiki/Mitochondrion#/media/File:Mitochondria,mammalian_lung_-TEM.jpg,\n
\n by Louisa Howard.]\n

\n

\n

\n

\n Which process is occurring on the structures labelled X?\n

\n

\n A. The Krebs cycle\n

\n

\n B. The link reaction\n

\n

\n C. Glycolysis\n

\n

\n D. Phosphorylation of ADP\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "19M.1A.HL.TZ1.30", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-2-cell-respiration", "c1-2-11-oxidation-and-decarboxylation-of-pyruvate-as-a-link-reaction-in-aerobic-cell-respiration", "c1-2-12-oxidation-and-decarboxylation-of-acetyl-groups-in-the-krebs-cycle-with-a-yield-of-atp-and-reduced-nad", "c1-2-13-transfer-of-energy-by-reduced-nad-to-the-electron-transport-chain-in-the-mitochondrion" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n \n E. modestus\n \n is an invasive barnacle while the others are native species. Analyse the data to show how it supports this statement.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. native species/\n \n C. montagui\n \n and\n \n S. balanoides\n \n have niches that don’t overlap much / are distinct\n
\n \n \n OR\n \n \n
\n range of\n \n E. modestus\n \n overlaps with both native species ✔\n

\n

\n b. niches of native species «which don’t overlap much» shows competition between native species\n
\n \n \n OR\n \n \n
\n \n E.modestus\n \n invades habitats of\n \n C. montagui\n \n /\n \n S. balanoides\n \n resulting in competition with «both» native species ✔\n

\n

\n c. EM has a wide niche/higher tolerance/covers entire «intertidal» range making it easier to invade the habitat ✔\n

\n
\n", "Examiners report": "
\n

\n Candidates had difficulty finding data to support\n \n E.modestus\n \n being aninvasive barnacle in part (c).\n

\n
\n", "question_id": "19M.1B.SL.TZ2.12C", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c4-1-populations-and-communities", "c4-1-13-resource-competition-between-endemic-and-invasive-species" ] }, { "Question": "
\n
\n

\n Explain what is meant by competitive exclusion, with respect to a\n \n named\n \n example of an invasive species.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n

\n a. when two species with similar niches occupy the same habitat ✔\n

\n

\n b. the competition increases\n
\n \n \n OR\n \n \n
\n reduction in resources ✔\n

\n

\n c. the population of one species will die/be excluded ✔\n

\n

\n d. an invasive species «often» lacks predators ✔\n

\n

\n e. the endemic species is usually the one that cannot compete ✔\n

\n

\n f.\n \n eg\n \n : grey squirrel/Japanese knot weed/cane toad ✔\n

\n

\n \n \n [3 max]\n \n \n \n if the invasive species is not named.\n \n

\n

\n \n Do not allow humans.\n \n

\n
\n", "Examiners report": "
\n

\n This was generally well answered. There were a wide variety of verifiable invasive species and only a few confused examples. The most common example was the cane toad introduced into Australia. Candidates understood increased competition and lack of predation.\n

\n
\n", "question_id": "19M.2.SL.TZ1.14", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c4-1-populations-and-communities", "c4-1-13-resource-competition-between-endemic-and-invasive-species" ] }, { "Question": "
\n
\n (e)\n
\n
\n

\n Evaluate the effect of the change in distribution of the different life stages of ticks on the spread of Lyme disease in south-eastern Canada.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n a.\n \n nymphs\n \n present through most of year/longer period/from March to November/through spring and summer «so more risk of infection» ✔\n

\n

\n b. more\n \n adults\n \n in winter/in January/February so more risk of infection then ✔\n

\n

\n c. infection will be possible through more/most months of/throughout the year ✔\n

\n

\n d. Lyme disease likely to/will increase ✔\n

\n
\n", "Examiners report": "None", "question_id": "19N.2.SL.TZ0.1E", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a4-2-conservation-of-biodiversity" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n State\n \n one\n \n process that results in the loss of carbon dioxide from a marine organism such as a crustacean or a jellyfish.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n a. (aerobic/cellular) respiration ✔\n

\n

\n b. gas exchange / diffusion ✔\n

\n

\n \n Do not accept photosynthesis\n \n .\n

\n

\n \n Do not accept breathing\n \n

\n

\n \n Organism is taken to be a living thing\n \n .\n

\n
\n", "Examiners report": "
\n

\n In 4(a) most were able to state 'respiration' as the answer. 4(b) proved more difficult with fewer stating photosynthesis or absorption of dissolved CO\n \n 2\n \n or HCO\n \n 3\n \n from the seawater. Vague answers such as 'carbon in the water' were not credited. In 4(c) most knew that energy enters with sunlight, but did not state photosynthesis. They knew that it was transferred by feeding through the trophic levels and lost as heat due to respiration. A surprising number incorrectly stated that the energy was recycled and some drew diagrams of the energy flow showing this. In 4(d)(i) most were able to state that the crustacean was a richer source of carbon. An explanation using the data from the diagram was expected. In 4(d)(ii) most were able to present an argument for advantage or disadvantage.\n

\n
\n", "question_id": "21M.2.SL.TZ2.4", "topics": [ "c-interaction-and-interdependence", "d-continuity-and-change" ], "subtopics": [ "c4-2-transfers-of-energy-and-matter", "c4-2-17-constructing-carbon-cycle-diagrams", "c4-2-18-ecosystems-as-carbon-sinks-and-carbon-sources", "d4-3-climate-change", "d4-3-5-changes-in-ocean-currents-altering-the-timing-and-extent-of-nutrient-upwelling" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n The crustacean and the jellyfish obtain carbon compounds by feeding. State\n \n one\n \n source of carbon for marine organisms, other than feeding.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n a. photosynthesis ✔\n

\n

\n b. absorption of (dissolved) carbon dioxide / (hydrogen)carbonate directly from the oceans ✔\n

\n

\n \n Accept reference to carbonate or hydrogencarbonate ions\n \n .\n

\n
\n", "Examiners report": "
\n

\n In 4(a) most were able to state 'respiration' as the answer. 4(b) proved more difficult with fewer stating photosynthesis or absorption of dissolved CO\n \n 2\n \n or HCO\n \n 3\n \n from the seawater. Vague answers such as 'carbon in the water' were not credited. In 4(c) most knew that energy enters with sunlight, but did not state photosynthesis. They knew that it was transferred by feeding through the trophic levels and lost as heat due to respiration. A surprising number incorrectly stated that the energy was recycled and some drew diagrams of the energy flow showing this. In 4(d)(i) most were able to state that the crustacean was a richer source of carbon. An explanation using the data from the diagram was expected. In 4(d)(ii) most were able to present an argument for advantage or disadvantage.\n

\n
\n", "question_id": "21M.2.SL.TZ2.4B", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c4-2-transfers-of-energy-and-matter", "c4-2-17-constructing-carbon-cycle-diagrams", "c4-2-18-ecosystems-as-carbon-sinks-and-carbon-sources" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Explain the mechanisms involved in thermoregulation in humans.\n

\n
\n
\n

\n [7]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n normal body temperature is 37 ºC;\n
    2. \n
  2. \n peripheral thermoreceptors detect environmental temperature;\n
    3. \n
  3. \n supporting conscious behaviour to avoid temperature extremes, e.g. wearing more clothing;\n
    4. \n
  4. \n sends messages to hypothalamus/temperature control centre of the brain;\n
    5. \n
  5. \n the hypothalamus sends messages to pituitary gland;\n
    6. \n
  6. \n (pituitary) releases TSH;\n
    7. \n
  7. \n stimulating thyroxin release from thyroid;\n
    8. \n
  8. \n thyroxin controls metabolic rate / production of heat;\n
    9. \n
  9. \n muscle random contraction/shivering to generate heat;\n
    10. \n
  10. \n (brown) adipose tissue burns fat to generate waste heat;\n
    11. \n
  11. \n vasoconstriction to conserve heat / vasodilation to exchange heat with the environment;\n
    12. \n
\n
\n", "Examiners report": "None", "question_id": "SPM.2.SL.TZ0.8", "topics": [ "d-continuity-and-change", "c-interaction-and-interdependence", "a-unity-and-diversity" ], "subtopics": [ "d3-3-homeostasis", "d3-3-5-thermoregulation-as-an-example-of-negative-feedback-control", "d3-3-6-thermoregulation-mechanisms-in-humans", "c1-1-enzymes-and-metabolism", "c1-1-8-effects-of-temperature-ph-and-substrate-concentration-on-the-rate-of-enzyme-activity", "a1-1-water", "a1-1-6-physical-properties-of-water-and-the-consequences-for-animals-in-aquatic-habitats" ] }, { "Question": "
\n
\n

\n The electron micrograph shows a thin section through a plant mesophyll cell.\n

\n

\n \n

\n

\n [Source: https://commons.wikimedia.org/wiki/File:Euglena_sp.jpg, by Deuterostome\n
\n \n https://creativecommons.org/licenses/by-sa/3.0/legalcode]\n \n

\n

\n

\n

\n What is the magnification of the image?\n

\n

\n A. × 75\n

\n

\n B. × 300\n

\n

\n C. × 3000\n

\n

\n D. × 7500\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "19N.1A.SL.TZ0.1", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a2-2-cell-structure", "a2-2-2-microscopy-skills" ] }, { "Question": "
\n
\n

\n The image shows the structure of the protein hemoglobin\n

\n

\n \n

\n

\n [Source: Hemoglobin molecule, Microbiology ID: e42bd376-624b-4c0f-972f-e0c57998e765@4.4 OpenStax Microbiology\n
\n https://cnx.org/contents/5CvTdmJL@4.4 and\n \n https://commons.wikimedia.org/wiki/File:OSC_Microbio_07_04_\n \n
\n \n hemoglobin.jpg\n \n Licensed under a Creative Commons Attribution 4.0 International License,\n
\n \n https://creativecommons.org/licenses/by/4.0\n \n .]\n

\n

\n

\n

\n What level of protein structure bonds the α and β chains together?\n

\n

\n A. Primary\n

\n

\n B. Secondary\n

\n

\n C. Tertiary\n

\n

\n D. Quaternary\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "
\n

\n This question proved surprisingly challenging. The linking together of polypeptides in a hemoglobin molecule is quaternary structure. A misreading of the question might have led to the answer ‘primary structure’ as that is the bonding together within polypeptides, but few candidates chose that answer and many more chose secondary or tertiary structure. Perhaps ‘binds’ rather than ‘bonds’ in the question would have helped avoid misunderstandings.\n

\n
\n", "question_id": "21N.1A.HL.TZ1.6", "topics": [ "b-form-and-function" ], "subtopics": [ "b1-2-proteins", "b1-2-8-pleating-and-coiling-of-secondary-structure-of-proteins" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Explain how mitochondria could have been formed from free living prokaryotes.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. endocytosis/engulfing of prokaryote by a larger/another/anaerobic prokaryote/cell ✔\n

\n

\n b. double membrane of the mitochondrion is the result of endocytosis\n
\n \n \n OR\n \n \n
\n inner membrane of mitochondrion from engulfed cell and outer from food vacuole ✔\n

\n

\n c. «engulfed prokaryotic cell» was aerobic/respired aerobically/consumed oxygen\n
\n \n \n OR\n \n \n
\n «engulfed prokaryotic cell» provided energy/ATP ✔\n

\n

\n d. «engulfed prokaryotic cell» not destroyed/not digested\n
\n \n \n OR\n \n \n
\n «endo»symbiotic/mutualistic relationship developed ✔\n

\n

\n e. «engulfed prokaryotic cell» had its own DNA/own «70S» ribosomes ✔\n

\n

\n \n Do not award mpc for “mitochondrion makes ATP”.\n \n

\n
\n", "Examiners report": "
\n

\n This was generally well answered with candidates explaining how endocytosis would have got a free-living prokaryote into a larger cell and because it made itself useful, there was a selective advantage in developing a mutualistic relationship rather than digesting the engulfed cell. Some candidates gave valid evidence for endosymbiosis – presence of DNA, 70S ribosomes or the double membrane.\n

\n
\n", "question_id": "19M.2.HL.TZ1.3B", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a2-2-cell-structure", "a2-2-12-origin-of-eukaryotic-cells-by-endosymbiosis" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Outline how\n \n in situ\n \n conservation may help preserve populations of amphibians.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n the amphibians are kept in their natural habitat;\n
    \n \n \n OR\n \n \n
    \n preserves habitat/resources for amphibians;\n
    2. \n
  2. \n area can be actively managed\n
    \n \n \n OR\n \n \n
    \n pollution/predators/alien species can be controlled in the area;\n
    3. \n
\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ1.17B", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a4-2-conservation-of-biodiversity", "a4-2-6-causes-of-the-current-biodiversity-crisis" ] }, { "Question": "
\n
\n

\n State the name of the structure shown.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n synapse/synaptic\n

\n
\n", "Examiners report": "None", "question_id": "20N.2.HL.TZ0.B.I", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c2-1-chemical-signalling-[hl-only]", "c2-1-5-localized-and-distant-effects-of-signalling-molecules" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Describe adaptations in mammals living in desert ecosystems to maintain osmolarity in their bodies.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n behavioural adaptations to avoid over-heating / hiding in burrows/out of sun during hot period of day / active at cooler times of the day/nocturnal animals / panting;\n
    2. \n
  2. \n adaptations for heat exchange such as large ears;\n
    3. \n
  3. \n may have longer loop of Henle (to reabsorb more water);\n
    4. \n
  4. \n may produce more ADH (according to osmotic concentrations of the blood) / produce concentrated urine / lower volume of urine;\n
    5. \n
  5. \n camel humps that store fat that releases (metabolic) water when broken down;\n
    6. \n
  6. \n reduced sweat;\n
    7. \n
  7. \n any other valid adaptation; (e.g., light coloured coats)\n
    8. \n
\n
\n", "Examiners report": "
\n

\n Long loops of Henle was the most common desert adaptation discussed. There were common misconceptions about camels’ humps being water storage organs rather than the production of metabolic water.\n

\n
\n", "question_id": "22M.2.SL.TZ2.8C", "topics": [ "b-form-and-function" ], "subtopics": [ "b4-1-adaptation-to-environment", "b4-1-8-adaptations-to-life-in-hot-deserts-and-tropical-rainforest" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Explain how sexual reproduction gives rise to genetic variation.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n recombination of parental alleles during fertilization;\n
    2. \n
  2. \n fertilized egg contains a mixture of paternal and maternal chromosomes;\n
    3. \n
  3. \n crossing over/meiosis gives rise to new combinations of alleles;\n
    4. \n
\n
\n", "Examiners report": "None", "question_id": "SPM.2.SL.TZ0.6B", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-1-natural-selection", "d4-1-2-roles-of-mutation-and-sexual-reproduction-in-generating-the-variation-on-which-natural-selection-acts", "d1-3-mutations-and-gene-editing", "d1-3-7-mutation-as-a-source-of-genetic-variation" ] }, { "Question": "
\n
\n

\n Outline the role of the right atrium in the cardiac cycle.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n right atrium collects (deoxygenated) blood from the body;\n
    2. \n
  2. \n blood drains into atrium through/from the vena cava;\n
    3. \n
  3. \n deoxygenated blood present in vena cava/right atrium/right ventricle;\n
    4. \n
  4. \n right atrium pumps blood into the right ventricle;\n
    5. \n
  5. \n during atrial systole/ventricular diastole/at the start of the cardiac cycle;\n
    6. \n
  6. \n sinoatrial node is in the right atrium/sinoatrial node acts as the (natural) pacemaker / sinoatrial node initiates the heartbeat;\n
    7. \n
  7. \n SA node sends out electrical signal to stimulate contraction in the (walls of the) atria/then propagated to the AV node / (walls of the) ventricles;\n
    8. \n
\n

\n

\n
\n", "Examiners report": "None", "question_id": "23M.2.HL.TZ2.B", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-2-transport", "b3-2-16-stages-in-the-cardiac-cycle" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Outline the significance of surface area to volume ratio in the limitation of cell size.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n

\n a. surface area of the cell affects the rate of material exchange;\n
\n b. when the cell increases in size, so does its chemical activity/metabolism;\n
\n c. (when the cell increases in size/grows) more substances need to be taken in / more waste products need to be excreted;\n
\n d. as the volume of the cell increases, so does the surface area, however not to the same extent\n
\n OR\n
\n when the cell gets bigger, its surface area to volume ratio gets smaller;\n
\n e. substances will not be able enter the cell fast enough/cell volume will not be supplied\n

\n

\n OR\n
\n metabolic rate will exceed the rate of exchange\n
\n OR\n
\n when the surface area: volume ratio is higher, the diffusion rate increases;\n
\n f. some cells have adaptations to increase their surface area/flatten/microvilli/shape of red blood cells;\n
\n g. cells in growth areas tend to divide and remain small\n
\n OR\n
\n cells divide when maximum size is reached;\n

\n
\n", "Examiners report": "
\n

\n Most knew that as the cell increases in size, the SA:volume ratio decreases but had difficulty explaining its significance.\n

\n
\n", "question_id": "21N.2.SL.TZ0.5A", "topics": [ "b-form-and-function" ], "subtopics": [ "b2-3-cell-specialization", "b2-3-6-surface-area-to-volume-ratios-and-constraints-on-cell-size" ] }, { "Question": "
\n
\n

\n The Silver Springs feed into the Silver River in Florida. The diagram shows a pyramid of energy for the Silver Springs ecosystem. The units are kJ m\n \n –2\n \n y\n \n –1\n \n .\n

\n

\n \n

\n

\n [Source: © International Baccalaureate Organization 2019]\n

\n

\n

\n

\n What do level I and level III represent in the pyramid of energy?\n

\n

\n \n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "
\n

\n This question was easy, most candidates recognized that I was the producer and only a few believed II was a tertiary consumer instead of a secondary consumer.\n

\n
\n", "question_id": "19M.1A.SL.TZ2.18", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c4-2-transfers-of-energy-and-matter", "c4-2-3-flow-of-chemical-energy-through-food-chains" ] }, { "Question": "
\n
\n

\n A strand of DNA containing four codons with base sequence ACT GTA CTC TAC mutates, changing the base sequence to ACT ATG CTC TAC. What type of mutation has occurred?\n

\n

\n
\n A.  Insertion\n

\n

\n B.  Substitution\n

\n

\n C.  Deletion\n

\n

\n D.  Degeneracy\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "SPM.1A.SL.TZ0.8", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d1-3-mutations-and-gene-editing", "d1-3-1-gene-mutations-as-structural-changes-to-genes-at-the-molecular-level" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n State the level of protein structure at which the polypeptide chains of hemoglobin are combined.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n quaternary / fourth level;\n

\n
\n", "Examiners report": "
\n

\n Many candidates knew that association of polypeptide chains is quaternary structure. Any spelling of this term was accepted — only a minority got it correct.\n

\n
\n", "question_id": "22M.2.HL.TZ1.4", "topics": [ "b-form-and-function", "d-continuity-and-change" ], "subtopics": [ "b1-2-proteins", "b1-2-11-quaternary-structure-of-non-conjugated-and-conjugated-proteins", "b1-2-8-pleating-and-coiling-of-secondary-structure-of-proteins", "d1-2-protein-synthesis", "d1-2-6-roles-of-mrna-ribosomes-and-trna-in-translation" ] }, { "Question": "
\n
\n

\n Which molecules are produced during the hydrolysis of a triglyceride molecule?\n

\n

\n
\n A.  Water and glycerol\n

\n

\n B.  Fatty acids and glycerol\n

\n

\n C.  Water and fatty acids\n

\n

\n D.  Water and lipids\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "SPM.1A.HL.TZ0.4", "topics": [ "b-form-and-function" ], "subtopics": [ "b1-1-carbohydrates-and-lipids", "b1-1-9-formation-of-triglycerides-and-phospholipids-by-condensation-reactions" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Outline\n \n four\n \n types of membrane transport, including their use of energy.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n

\n a. simple diffusion is passive movement of molecules/ions along a concentration gradient ✔\n

\n

\n b. facilitated diffusion is passive movement of molecules/ions along a concentration gradient through a protein channel «without use of energy» ✔\n

\n

\n c. osmosis is the passage of water\n \n through a membrane\n \n from lower solute concentration to higher ✔\n \n OWTTE\n \n

\n

\n d. active transport is movement of molecules/ions\n \n against the concentration gradient\n \n «through membrane pumps» with the use of ATP/energy ✔\n \n Active transport requires mention of the use of energy.\n \n

\n

\n e. endocytosis is the infolding of membrane/formation of vesicles to bring molecules into cell with use of energy\n
\n \n \n OR\n \n \n
\n exocytosis is the infolding of membrane/formation of vesicles to release molecules from cell with use of energy ✔\n

\n

\n f. chemiosmosis occurs when protons diffuse through ATP synthase «in membrane» to produce ATP ✔\n

\n

\n \n The description of each type of transport should include the name and brief description.\n \n

\n

\n \n mpa, mpb and mpc require reference to concentration.\n \n

\n

\n

\n
\n", "Examiners report": "
\n

\n Membrane transport – In spite of the question asking about energy, many lost easy marks by forgetting to refer to it. Others did not mention the gradients. In osmosis, please stress to the students which concentration they are talking about. They should be talking clearly about water potential or solute concentration.\n

\n
\n", "question_id": "19M.2.SL.TZ2.5", "topics": [ "b-form-and-function" ], "subtopics": [ "b2-1-membranes-and-membrane-transport", "b2-1-5-movement-of-water-molecules-across-membranes-by-osmosis-and-the-role-of-aquaporins", "b2-1-6-channel-proteins-for-facilitated-diffusion", "b2-1-7-pump-proteins-for-active-transport", "b2-1-8-selectivity-in-membrane-permeability", "b1-2-proteins", "b1-2-2-condensation-reactions-forming-dipeptides-and-longer-chains-of-amino-acids" ] }, { "Question": "
\n
\n

\n Which statement provides evidence for endosymbiosis?\n

\n

\n A. Early prokaryotes contributed to a large increase in oxygen in the atmosphere.\n

\n

\n B. Eukaryotic mitochondria and chloroplasts have their own circular DNA.\n

\n

\n C. Certain groups of ancient prokaryotes developed mechanisms to carry out aerobic respiration.\n

\n

\n D. Experiments by Miller and Urey produced simple organic molecules in abiotic conditions.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "19N.1A.HL.TZ0.3", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a2-2-cell-structure", "a2-2-12-origin-of-eukaryotic-cells-by-endosymbiosis" ] }, { "Question": "
\n
\n

\n The graph shows changes in the membrane potential in an action potential.\n \n

\n

\n What is the approximate value of the threshold potential?\n

\n

\n A. −88 mV\n

\n

\n B. −70 mV\n

\n

\n C. −50 mV\n

\n

\n D. +45 mV\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "21N.1A.HL.TZ0.28", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c2-2-neural-signalling", "c2-2-10-oscilloscope-traces-showing-resting-potentials-and-action-potentials" ] }, { "Question": "
\n
\n

\n What is the role of HCG in pregnancy?\n

\n

\n A.  It is secreted by the embryo to stimulate progesterone secretion by the ovary during early pregnancy.\n

\n

\n B.  Together with oxytocin, it is involved in the positive feedback required for uterine contractions during birth.\n

\n

\n C.  It sustains the secretion of progesterone by the placenta throughout pregnancy.\n

\n

\n D.  It stimulates the ovary to maintain secretion of estrogen in early pregnancy.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "
\n

\n This question was answered correctly by less than half of candidates and the discrimination index was relatively low. The expected answer was A because embryos do secrete HCG, and because HCG does stimulate progesterone secretion by the ovary. The answer is a direct restatement of one of the understandings in sub-topic 11.4 of the program. Some of the better-prepared candidates must have rejected this answer and chosen another instead. Answers B and C were undoubtedly incorrect. Answer D stated that HCG stimulates the ovary to maintain secretion of estrogen during early pregnancy. Estrogen levels are low during the months when HCG from the embryo is sustaining pregnancy and they are lower than progesterone levels until about week 24 of a pregnancy, when the placenta has become responsible for HCG secretion. Answer A was therefore a better answer than D, though in retrospect a more obviously incorrect distractor should have been used for D.\n

\n
\n", "question_id": "22N.1A.HL.TZ0.40", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-1-reproduction", "d3-1-17-pregnancy-testing-by-detection-of-human-chorionic-gonadotropin-secretion" ] }, { "Question": "
\n
\n (g)\n
\n
\n

\n Analyse the data on the state of infection of tick nymphs with\n \n B. burgdorferi\n \n in control and vaccinated mice.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. at Site 1 there is little/no significant difference in the proportion of infected nymphs/numbers of infected and uninfected nymphs collected from both control and vaccinated mice ✔\n

\n

\n b. at Site 2 the proportion of infected nymphs is lower in those collected from vaccinated than control mice\n
\n \n \n OR\n \n \n
\n at Site 2 «significantly» more nymphs are not infected from vaccinated than control mice ✔\n \n For mpb and mpd, accept converse answers that give the proportions/percentages of uninfected nymphs rather than infected\n \n .\n

\n

\n c. at both sites there are fewer infected than uninfected nymphs in those collected from both vaccinated and control mice ✔\n

\n

\n d. proportion of infected nymphs is lower at Site 1 than Site 2 in nymphs collected from both control and vaccinated mice\n
\n \n \n OR\n \n \n
\n 22 % of control mice and 23 % of vaccinated mice with infected nymphs at Site 1\n \n \n AND\n \n \n 39 % of control mice and 29 % of vaccinated mice with infected nymphs at Site 2 ✔\n \n Percentages are required for the second alternative of mpd\n \n .\n

\n

\n \n Accept “ticks” instead of “tick nymphs” or “nymphs”\n \n

\n

\n \n Do not accept quoting of untransformed numerical data\n \n .\n

\n
\n", "Examiners report": "None", "question_id": "19N.2.SL.TZ0.1G", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-2-defence-against-disease", "c3-2-9-multiplication-of-activated-b-lymphocytes-to-form-clones-of-antibody-secreting-plasma-cells" ] }, { "Question": "
\n
\n (d)\n
\n
\n

\n Predict what would happen to a red blood cell placed in distilled water.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n a. water would move into the red blood cells ✔\n

\n

\n b. it would lyse\n
\n \n \n OR\n \n \n
\n swell\n
\n \n \n OR\n \n \n
\n burst ✔\n

\n
\n", "Examiners report": "None", "question_id": "19N.1B.SL.TZ0.3D", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-3-water-potential", "d2-3-3-water-movement-by-osmosis-into-or-out-of-cells", "d2-3-4-changes-due-to-water-movement-in-plant-tissue-bathed-in-hypotonic-and-those-bathed-in-hypertonic-solutions" ] }, { "Question": "
\n
\n

\n Using the following table, compare and contrast anaerobic cell respiration in yeasts and in humans. The first row has been completed as an example.\n

\n

\n \n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n \n

\n

\n \n Award\n \n [1]\n \n per correct row\n \n .\n

\n
\n", "Examiners report": "None", "question_id": "19N.2.HL.TZ0.D", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-2-cell-respiration", "c1-2-5-differences-between-anaerobic-and-aerobic-cell-respiration-in-humans", "c1-2-10-anaerobic-cell-respiration-in-yeast-and-its-use-in-brewing-and-baking" ] }, { "Question": "
\n
\n (b.i)\n
\n
\n

\n Draw the same chromosomes to show their structure at the same stage of meiosis if there had been one chiasma between two gene loci.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n all four upper arms with one A and both chromosomes with one B and one b on the lower arms;\n

\n

\n \n

\n

\n \n The chromatids can be shown as single lines rather than the wider versions in the question\n \n .\n

\n
\n", "Examiners report": "
\n

\n This was mostly well answered but some candidates showed one chromatid flopped over a non-sister chromatid, like crossed legs of a seated person, without any recombination having occurred. This showed a misunderstanding of the process of crossing over and chiasma formation. There were also a wide range of other answers showing confusion about events in meiosis.\n

\n
\n", "question_id": "21N.2.SL.TZ0.2B.I", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-1-cell-and-nuclear-division", "d2-1-9-meiosis-as-a-reduction-division", "d2-1-11-meiosis-as-a-source-of-variation" ] }, { "Question": "
\n
\n

\n Which graph represents the change in cell surface area to volume ratio with increasing cell diameter?\n

\n

\n \n

\n

\n [Source: © International Baccalaureate Organization 2019]\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "
\n

\n Contrary to the trend of the first question being easy, this proved to be the most difficult in the paper with fewer than 30 % of candidates answering it correctly. Most missed that the graph showed the ratio of surface area to volume, not simply surface area, or perhaps they did not understand that this ratio gets smaller as cell size increases, choosing instead answers showing it getting larger. A and B both showed the ratio getting smaller, but A could be rejected because the line intercepted both x- and y-axes, which isn’t possible if we assume the origin of the axes is zero. A more time-consuming method of identifying B as the correct answer was to do a few sample calculations with cubes of different diameter. For example, the surface area/volume ratios of cubes of diameter 1, 2 and 3 are 6, 3 and 2 respectively, so equal increases in diameter give decreasing decreases in ratio. The line on the graph is therefore curved as in B. Given the significant consequences to living organisms of surface area to volume ratios, this is an area of the programme that deserves more emphasis, if it has previously been neglected.\n

\n
\n", "question_id": "19M.1A.SL.TZ1.1", "topics": [ "b-form-and-function" ], "subtopics": [ "b2-3-cell-specialization", "b2-3-6-surface-area-to-volume-ratios-and-constraints-on-cell-size" ] }, { "Question": "
\n
\n (b.i)\n
\n
\n

\n State an example of an alien species.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n name of species and where it is invasive\n \n e.g.\n \n introduction of cane toads in Australia ✔\n

\n

\n \n Accept common name of species but not general groups e.g. toads\n \n .\n

\n
\n", "Examiners report": "None", "question_id": "19N.2.SL.TZ0.15B.I", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a4-2-conservation-of-biodiversity", "a4-2-6-causes-of-the-current-biodiversity-crisis" ] }, { "Question": "
\n
\n

\n Where in the mitochondrion does the formation of acetyl CoA occur?\n

\n

\n \n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "
\n

\n The discrimination index for this question was the lowest on the paper. Some of the better-prepared candidates thought that acetyl CoA is produced on the inner mitochondrial membrane, rather than in the matrix.\n

\n
\n", "question_id": "22M.1A.HL.TZ1.30", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-3-photosynthesis", "c1-3-14-thylakoids-as-systems-for-performing-the-light-dependent-reactions-of-photosynthesis" ] }, { "Question": "
\n
\n

\n Estimate the resting potential for this axon.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n −65\n \n mV\n \n ✔\n

\n

\n \n Unit required; minus sign required. Accept answers from −62mV to −65mV\n \n .\n

\n
\n", "Examiners report": "None", "question_id": "21M.2.HL.TZ1.A", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c2-2-neural-signalling", "c2-2-10-oscilloscope-traces-showing-resting-potentials-and-action-potentials" ] }, { "Question": "
\n
\n

\n Outline the reasons for secretion of sweat in humans.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n cooling/removal of heat/lowering body temperature;\n
    2. \n
  2. \n to prevent overheating\n
    \n \n \n OR\n \n \n
    \n to help maintain body temperature/for temperature homeostasis/for thermoregulation\n
    \n \n \n OR\n \n \n
    \n to keep temperature at 37 °C;\n
    3. \n
\n

\n

\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ1.II", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a1-1-water", "a1-1-2-hydrogen-bonds-as-a-consequence-of-the-polar-covalent-bonds-within-water-molecules" ] }, { "Question": "
\n
\n

\n A person was infected with a pathogen and then later in life they were re-infected with the same pathogen. The graph shows the concentration of antibodies found in the blood that were produced in response to these two infections.\n

\n

\n \n

\n

\n What is the reason for the faster rise in antibody concentration after the second infection?\n

\n

\n A. The patient had previously been vaccinated with the antibody.\n

\n

\n B. Antibodies had been stored after the first exposure.\n

\n

\n C. Lymphocytes rapidly reproduced to form plasma cells.\n

\n

\n D. The second exposure was more infectious.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "
\n

\n This question proved to be the hardest on the paper, with fewer candidates answering correctly than the ‘guess’ level of 25 %. The low discrimination index showed that even well-prepared candidates struggled. Most candidates thought that antibodies could be stored in the body. Although antibodies do persist for a time after an infection, the question referred to a second infection ‘later in life’, implying too long a delay for antibodies to persist. Guidance in sub-topic 6.3 states that students are expected to know that memory cells persist after an infection and can quickly reproduce to form a clone of plasma cells that produce antibodies. The expected answer to the question was therefore that lymphocytes can rapidly reproduce to form plasma cells. Perhaps candidates did not appreciate that memory cells are lymphocytes.\n

\n
\n", "question_id": "21N.1A.SL.TZ0.26", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-2-defence-against-disease", "c3-2-7-antigens-as-recognition-molecules-that-trigger-antibody-production" ] }, { "Question": "
\n
\n (b.i)\n
\n
\n

\n Using the letter C, label the stage on the diagram where chromosome supercoiling occurs.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n prophase ✔\n

\n

\n \n The stage should be clearly labelled\n \n .\n

\n

\n \n If more than one stage is shown the candidate does not receive a mark\n \n .\n

\n
\n", "Examiners report": "
\n

\n There were several G2 comments about Q2a, as it could be said that several processes were occurring. Perhaps it should have been more specific. Two out of DNA replication, cell growth and duplication of organelles were expected for the two marks. A surprising number of candidates in all languages, confused 'processes' with 'phases' and stated that interphase consisted of G1, S and G2. Most managed to label prophase and anaphase correctly on the diagram as required in part (b). The answers to part (b) were generally clear, but some lost marks for not comparing the same point. For example 'Mitosis produces diploid cells, but meiosis produces gametes' did not score a mark. The mitotic index was well known.\n

\n
\n", "question_id": "21M.2.HL.TZ2.2B.I", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-1-cell-and-nuclear-division", "d2-1-7-phases-of-mitosis", "d2-1-13-phases-of-the-cell-cycle" ] }, { "Question": "
\n
\n (a.i)\n
\n
\n

\n On the diagram, label the aorta.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n both labelled clearly as in diagram ✔\n

\n

\n \n

\n

\n [Source: BlueRingMedia/Shutterstock]\n

\n
\n", "Examiners report": "
\n

\n Labelling the heart was generally ok, though the rest of this question was weakly answered.\n

\n
\n", "question_id": "19M.2.HL.TZ1.3A.I", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-2-transport", "b3-2-15-adaptations-of-the-mammalian-heart-for-delivering-pressurized-blood-to-the-arteries" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Describe the structure of starch.\n

\n
\n
\n

\n [5]\n

\n
\n
\n", "Markscheme": "
\n

\n a. starch is a carbohydrate ✔\n

\n

\n b. starch is formed by carbon, hydrogen and oxygen ✔\n

\n

\n c. it is a polymer/chain/polysaccharide ✔\n

\n

\n d. formed from monosaccharides/simple sugars/glucose ✔\n

\n

\n e. linked together by condensation/dehydration ✔\n

\n

\n f. consists of amylose and amylopectin ✔\n

\n

\n g. amylose is a long chain/unbranched ✔\n

\n

\n h. amylopectin is branched ✔\n

\n
\n", "Examiners report": "
\n

\n (attempted by about 40 % of the cohort)\n

\n

\n The question was put in the context of the composition of pastry cream, rather than just diving in with questions. In part (a), the structure of starch was quite well known. The better answers included descriptions of polymers and monomers, amylose and amylopectin, and glucose. Part (b) was challenging to many, requiring a knowledge of the digestive system, enzyme action and the blood supply to the liver. It was possible to gain all of the marks by omitting the references to the blood stream. This was an example of where a clear 'essay plan' would have helped. Weaker candidates wrote at length about carbohydrate and fat digestion which was not required. Surprisingly the position of the pancreas was often confused, with pancreatic enzymes appearing in the stomach. The fundamental idea of the digestion of large molecules (proteins) to small soluble ones (amino acids) which can be absorbed into the blood stream at the villi was missed by many. Part (c) was a straightforward genetics cross, put into the context of lactose intolerance. In general, it was well answered. Although the question clearly stated that it was an autosomal recessive condition, many weaker students were determined to make it sex linked.\n

\n
\n", "question_id": "21M.2.SL.TZ2.5", "topics": [ "b-form-and-function", "d-continuity-and-change" ], "subtopics": [ "b1-1-carbohydrates-and-lipids", "b1-1-5-polysaccharides-as-energy-storage-compounds", "d3-2-inheritance", "d3-2-4-phenotype-as-the-observable-traits-of-an-organism-resulting-from-genotype-and-environmental-factors" ] }, { "Question": "
\n
\n

\n How would the body respond to a rise above normal body temperature?\n

\n

\n
\n \n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "SPM.1A.HL.TZ0.30", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-3-homeostasis", "d3-3-1-homeostasis-as-maintenance-of-the-internal-environment-of-an-organism" ] }, { "Question": "
\n
\n

\n Which genotype would be normally found in a gamete?\n

\n

\n A. Rr\n

\n

\n B. RS\n

\n

\n C. rStt\n

\n

\n D. TUt\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "
\n

\n This question proved to be too difficult, with fewer candidates answering it correctly than at the guess-rate of 25 %. To answer correctly, candidates had to appreciate that upper- and lower-case letters are used for dominant and recessive alleles of a gene and that in a haploid gamete there is only one allele of each gene. The only possible answer was therefore RS. Nearly four times as many candidates chose Rr instead. This was the first of the four answers so perhaps some candidates did not read beyond it. The advice is always to read all four answers, even if the first one seems beguilingly attractive.\n

\n
\n", "question_id": "21M.1A.SL.TZ1.18", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-2-inheritance", "d3-2-1-production-of-haploid-gametes-in-parents-and-their-fusion-to-form-a-diploid-zygote-as-the-means-of-inheritance" ] }, { "Question": "
\n
\n

\n What is a property of water?\n

\n

\n A. Water has a low specific heat capacity so large increases in heat energy cause a small temperature change.\n

\n

\n B. Water is an excellent solvent for non-polar substances.\n

\n

\n C. Covalent bonds between adjacent water molecules are responsible for its unique properties.\n

\n

\n D. Water molecules are highly cohesive which is important for transport in xylem.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "19N.1A.SL.TZ0.8", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a1-1-water" ] }, { "Question": "
\n
\n (a.ii)\n
\n
\n

\n Deduce whether there is a trend in the incidence of white syndrome over the north-south range of latitude.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n there is no clear trend;\n

\n
\n", "Examiners report": "None", "question_id": "21N.2.SL.TZ0.1A.II", "topics": [ "d-continuity-and-change", "b-form-and-function" ], "subtopics": [ "d4-3-climate-change", "d4-3-7-threats-to-coral-reefs-as-an-example-of-potential-ecosystem-collapse", "b4-1-adaptation-to-environment", "b4-1-5-conditions-required-for-coral-reef-formation" ] }, { "Question": "
\n
\n

\n Outline the difference in methylation pattern between tumorous and normal tissue samples.\n

\n

\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. «overall» much more methylation in the colon tumour samples than normal ✔\n

\n

\n b. tumour and normal samples the markers 258 and 269 similar degree of methylation/fewer differences ✔\n

\n

\n c. degree of methylation on certain markers may correlate with the presence of cancer / correct example of a marker only methylated in tumour cells\n \n eg\n \n marker 32 ✔\n

\n
\n", "Examiners report": "
\n

\n Many students detected that greater degrees of methylation in tumour samples. Fewer could accurately summarize the specific differences between methylation in the two samples.\n

\n
\n", "question_id": "19M.2.HL.TZ2.B.I", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-2-gene-expression-[hl-only]", "d2-2-6-methylation-of-the-promoter-and-histones-in-nucleosomes-as-examples-of-epigenetic-tags", "d2-2-7-epigenetic-inheritance-through-heritable-changes-to-gene-expression" ] }, { "Question": "
\n
\n

\n What conveys messages from the central nervous system to an endocrine gland?\n

\n

\n
\n A.  Sensory neurons\n

\n

\n B.  Hormones\n

\n

\n C.  Interneurons\n

\n

\n D.  Motor neurons\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "SPM.1A.SL.TZ0.19", "topics": [ "c-interaction-and-interdependence", "d-continuity-and-change" ], "subtopics": [ "d3-3-homeostasis", "d3-3-3-regulation-of-blood-glucose-as-an-example-of-the-role-of-hormones-in-homeostasis", "d3-1-reproduction", "d3-1-13-control-of-the-developmental-changes-of-puberty-by-gonadotropin-releasing-hormone-and-steroid-sex-hormones", "c2-1-chemical-signalling-[hl-only]", "c2-1-3-hormones-neurotransmitters-cytokines-and-calcium-ions-as-examples-of-functional-categories-of-signalling-chemicals-in-animals" ] }, { "Question": "
\n
\n

\n Students examined micrographs and counted cells in the different stages of mitosis as well as those cells with no visible chromosomes. The table shows their results.\n

\n

\n \n

\n

\n What is the mitotic index?\n

\n

\n A. 0.2\n

\n

\n B. 0.4\n

\n

\n C. 0.6\n

\n

\n D. 0.7\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "19N.1A.HL.TZ0.5", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-1-cell-and-nuclear-division", "d2-1-17-differences-between-tumours-in-rates-of-cell-division-and-growth-and-in-the-capacity-for-metastasis-and-invasion-of-neighbouring-tissue" ] }, { "Question": "
\n
\n

\n The pie chart shows the modes of nutrition of fungi in Huahu Lake wetland in China.\n

\n

\n \n

\n

\n \n [Source: Fei Xie, Anzhou Ma, Hanchang Zhou, Yu Liang, Jun Yin, Ke Ma, Xuliang Zhuang and Guoqiang Zhuang, 2020.\n \n
\n \n Revealing Fungal Communities in Alpine Wetlands through Species Diversity, Functional Diversity and Ecological\n \n
\n \n Network Diversity.\n \n Microorganisms\n \n , 8, p. 632. Open Access.]\n \n

\n

\n
\n What is the most common mode of nutrition of fungi in this wetland?\n

\n

\n
\n A.  Heterotrophic fungi that feed on living organisms by ingestion\n

\n

\n B.  Autotrophic fungi that obtain organic nutrients from detritus by internal digestion\n

\n

\n C.  Fungi that have either an autotrophic or heterotrophic method of nutrition\n

\n

\n D.  Heterotrophic fungi obtaining nutrients from dead organisms by external digestion\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "23M.1A.SL.TZ1.18", "topics": [ "b-form-and-function" ], "subtopics": [ "b4-2-ecological-niches", "b4-2-6-saprotrophic-nutrition-in-some-fungi-and-bacteria" ] }, { "Question": "
\n
\n

\n Describe the endosymbiotic theory.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n

\n a. theory that eukaryotic cells evolved from prokaryotes\n
\n OR\n
\n origin of eukaryotic organisms based on some organisms living inside/engulfed by other organisms\n
\n OR\n
\n prokaryotic cell engulfed another prokaryote including it in cytoplasm without digesting it;\n
\n b. mitochondria/chloroplasts have double membranes;\n
\n c. mitochondria/chloroplasts have their own DNA/loop of DNA/naked DNA;\n
\n d. mitochondria/chloroplasts have similar size to prokaryotes;\n
\n e. mitochondria/chloroplasts can reproduce by binary fission;\n
\n f. mitochondria/chloroplasts have 70S ribosomes (same as prokaryotes);\n

\n
\n", "Examiners report": "
\n

\n The theory of endosymbiosis was quite well known. Common errors included the original engulfing process being carried out by a eukaryote, rather than a prokaryote.\n

\n
\n", "question_id": "21N.2.HL.TZ0.A", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a2-2-cell-structure", "a2-2-12-origin-of-eukaryotic-cells-by-endosymbiosis" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n State the number of degrees of freedom for this test to determine the critical value of chi-squared.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n 1 (df)\n
\n \n \n OR\n \n \n
\n (r-1) (c-1);\n

\n
\n", "Examiners report": "
\n

\n Calculating the degrees of freedom proved problematic for many.\n

\n
\n", "question_id": "22M.2.SL.TZ2.3C", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c4-1-populations-and-communities", "c4-1-15-use-of-the-chi-squared-test-for-association-between-two-species" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Outline energy flow through a community in a natural ecosystem.\n

\n
\n
\n

\n [5]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n communities are made up of populations of different species;\n
    2. \n
  2. \n plants receive energy from the sun/light;\n
    3. \n
  3. \n convert it to chemical energy through\n \n photosynthesis\n \n ;\n
    4. \n
  4. \n chemical energy is stored in organic/C-compounds;\n
    5. \n
  5. \n the energy is passed to other organisms through feeding / reference to food chain;\n
    6. \n
  6. \n respiration (of plants and animals) converts the chemical energy (of C-compounds) to other useful forms of energy;\n
    7. \n
  7. \n eventually the chemical energy is lost as heat energy;\n
    8. \n
  8. \n energy is non-recyclable/lost from a community/ecosystem;\n
    9. \n
  9. \n energy losses between trophic levels limit food chains/mass of top trophic levels/only about 10 % of energy is transferred;\n
    10. \n
\n
\n", "Examiners report": "
\n

\n This was well attempted with an average score of 3. The question was about energy, but weaker students also tended to include biomass. Fortunately, very few students failed to grasp the idea that the energy is lost from the ecosystem and not recycled.\n

\n
\n", "question_id": "22M.2.SL.TZ2.7", "topics": [ "c-interaction-and-interdependence", "d-continuity-and-change" ], "subtopics": [ "c4-2-transfers-of-energy-and-matter", "c4-2-3-flow-of-chemical-energy-through-food-chains", "c4-2-12-reductions-in-energy-availability-at-each-successive-stage-in-food-chains-due-to-large-energy-losses-between-trophic-levels", "d4-1-natural-selection", "d4-1-1-natural-selection-as-the-mechanism-driving-evolutionary-change", "d4-1-2-roles-of-mutation-and-sexual-reproduction-in-generating-the-variation-on-which-natural-selection-acts" ] }, { "Question": "
\n
\n (b.ii)\n
\n
\n

\n Outline the impact of alien species on endemic species in ecosystems.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. ‹interspecific› competition with endemic/native species ✔\n \n May be outlined using a specific example\n \n

\n

\n b. may cause the extinction/reduction of endemic/native species\n
\n \n \n OR\n \n \n
\n reduces biodiversity\n
\n \n \n OR\n \n \n
\n becomes invasive ✔\n

\n

\n c. does not have endemic / natural predators so may increase in numbers ✔\n

\n

\n d. upsets the balance between predators and prey\n
\n \n \n OR\n \n \n
\n disrupts food chains ✔\n

\n
\n", "Examiners report": "None", "question_id": "19N.2.SL.TZ0.15B.II", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a4-2-conservation-of-biodiversity", "a4-2-6-causes-of-the-current-biodiversity-crisis" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Natural forests in the area around Mangalore contain hardwood trees such as teak,\n \n Tectona grandis\n \n , which are deciduous, shedding their leaves once a year. Suggest, with a reason, when this might happen.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. dry season/Jan/Feb ✔\n

\n

\n b. «drop leaves» to prevent water loss/transpiration «since no rainfall for almost four months» ✔\n

\n
\n", "Examiners report": "
\n

\n Many provided correct answers, but also an important number could not relate the process to prevention of water loss during the dry months.\n

\n
\n", "question_id": "19M.2.HL.TZ2.15B", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-2-stability-and-change", "d4-2-14-cyclical-succession-in-ecosystems" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Explain the reasons for variation in human height.\n

\n
\n
\n

\n [7]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n environment affects height;\n
    2. \n
  2. \n nutrition/malnutrition affects growth rate / other example of environmental factor affecting height;\n
    3. \n
  3. \n genes/alleles affect height / height is partly heritable;\n
    4. \n
  4. \n polygenic / many genes influence height;\n
    5. \n
  5. \n continuous variation;\n
    6. \n
  6. \n normal/bell-shaped distribution of height;\n
    7. \n
  7. \n some alleles (of these genes) increase height and some reduce it;\n
    8. \n
  8. \n many possible combinations of alleles of these genes;\n
    9. \n
  9. \n specific gene mutations/alleles cause dwarfism/extreme height;\n
    10. \n
  10. \n meiosis generates variation (in height);\n
    11. \n
  11. \n mutations generate variation (in height);\n
    12. \n
  12. \n males tend to be/are on average taller than females;\n
    13. \n
  13. \n loss of height during aging;\n
    14. \n
\n
\n", "Examiners report": "
\n

\n This was a relatively high scoring question, with a mean mark of 2.4 (out of 7). Teachers expressed surprise in G2 forms that their students were being expected to make 7 valid points in their answer, but the wide-ranging mark scheme ensured that this was possible. There was some confusion between polygenic inheritance and multiple alleles. Weaker candidates tended to think that dominant alleles make us taller and recessive alleles cause shortness. Another fault in many answers was to focus on natural selection and evolution of height — if anything natural selection will reduce variation in human height rather than cause it.\n

\n
\n", "question_id": "22M.2.SL.TZ1.8C", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-2-inheritance", "d3-2-14-continuous-variation-due-to-polygenic-inheritance-and/or-environmental-factors" ] }, { "Question": "
\n
\n

\n The offspring, which were all heterozygous for grey body and normal wings, were crossed with flies that were homozygous recessive for both genes. The table shows the percentages of offspring produced.\n

\n

\n \n

\n

\n Explain these results, based on the knowledge that the genes for body colour and wing size are autosomally linked.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. not a 1:1:1:1 ratio «because of linkage»\n
\n \n \n OR\n \n \n
\n not independent assortment\n
\n \n \n OR\n \n \n
\n grey normal and black vestigial types/parental combinations/double dominant and double recessive were commoner than 25 %/commoner than expected ✔\n
\n
\n b. «linked genes» so were on the same chromosome ✔\n

\n

\n c. grey body vestigial wing and black body normal wing are recombinants\n
\n \n \n OR\n \n \n
\n 2 % plus 3 % of the offspring are recombinants ✔\n

\n

\n d. recombinants due to crossing over/exchange of genes between «non-sister» chromatids\n
\n \n \n OR\n \n \n
\n 2 % and 3 % of offspring were due to crossing over\n
\n \n \n OR\n \n \n
\n genes inherited together unless separated by crossing over ✔\n

\n

\n e. crossing over between the two loci/between the two genes on the chromosomes ✔\n

\n

\n f. few recombinants/not much crossing over because genes/gene loci close together ✔\n

\n

\n \n Accept any of these points from an annotated diagram.\n \n

\n
\n", "Examiners report": "
\n

\n Most candidates found it very hard to explain the non-Mendelian ratio. A good start would have been to state the expected Mendelian ratio for unlinked genes in this type of cross and then compare this with the actual percentages. Answers tended to state which traits tended to be inherited together rather than explain the mechanism. An obvious answer was that that the two genes are located on the same chromosome but only a minority of candidates stated this and even fewer made the point that crossing over between the two gene loci results in the small percentage of recombinants. Many students referred to the 9:3:3:1 ratio, even though the cross performed in this case would not have given this ratio, even if there had not been gene linkage. Also many candidates claimed that more individuals showed dominant phenotypes than recessive, which was not supported by the percentages.\n

\n
\n", "question_id": "19M.2.HL.TZ1.D.II", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-2-inheritance", "d3-2-16-segregation-and-independent-assortment-of-unlinked-genes-in-meiosis" ] }, { "Question": "
\n
\n (a.ii)\n
\n
\n

\n On the diagrams, label with a letter E a vesicle involved in exocytosis.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n an exocytic vesicle shown ✔\n

\n

\n \n For 2 a, i, ii and iii, accept letters written on the structure even if a line is not drawn.\n \n

\n

\n \n Award the mark if the full word is used to label the structure. Labels must be unambiguous.\n \n

\n

\n \n Accept any of the three intact circles or the exocytosis shown within the box.\n \n

\n
\n", "Examiners report": "None", "question_id": "21M.2.HL.TZ2.2A.II", "topics": [ "b-form-and-function" ], "subtopics": [ "b2-1-membranes-and-membrane-transport", "b2-1-13-membrane-fluidity-and-the-fusion-and-formation-of-vesicles" ] }, { "Question": "
\n
\n

\n What special property of phospholipid molecules explains their ability to spontaneously assemble into a lipid bilayer?\n

\n

\n A. They are hydrophobic.\n

\n

\n B. They are amphipathic.\n

\n

\n C. They are saturated.\n

\n

\n D. They are hydrophilic\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "21M.1A.SL.TZ2.3", "topics": [ "b-form-and-function" ], "subtopics": [ "b1-1-carbohydrates-and-lipids", "b1-1-12-formation-of-phospholipid-bilayers-as-a-consequence-of-the-hydrophobic-and-hydrophilic-regions" ] }, { "Question": "
\n
\n (g)\n
\n
\n

\n Suggest a reason that the mass of protein and lipid mixture eaten at 25:1 is lower than at 50:1.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n the mixture was closer to what the bees ate naturally;\n
    2. \n
  2. \n the bees like the taste better/prefer sucrose;\n
    3. \n
  3. \n there was more lipid in the 25:1 mixture so they achieved their daily lipid/energy requirement with less mass of food;\n
    4. \n
  4. \n the bees eating 50:1 diet ate more to reach their daily lipid requirement;\n
    5. \n
  5. \n prefer the higher proportion of protein (in the 50:1)\n
    6. \n
\n
\n", "Examiners report": "None", "question_id": "22N.2.SL.TZ0.1G", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c4-2-transfers-of-energy-and-matter", "c4-2-14-restrictions-on-the-number-of-trophic-levels-in-ecosystems-due-to-energy-losses", "c4-2-15-primary-production-as-accumulation-of-carbon-compounds-in-biomass-by-autotrophs" ] }, { "Question": "
\n
\n

\n What is the role of calcium ions in muscle contraction?\n

\n

\n A. To enable actin to expose binding sites on myosin\n

\n

\n B. To bind to troponin, exposing binding sites on actin\n

\n

\n C. To prevent an action potential in the muscle membrane\n

\n

\n D. To bind to tropomyosin, blocking binding sites on actin\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "20N.1A.HL.TZ0.38", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-3-muscle-and-motility-(hl-only)", "b3-3-2-sliding-filament-model-of-muscle-contraction" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n State processes occurring during interphase.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. DNA replication ✔\n

\n

\n b. cell growth ✔\n

\n

\n c. duplication of organelles/mitochondria / production of microtubules/protein synthesis ✔\n

\n

\n \n Accept first two answers only\n \n .\n

\n
\n", "Examiners report": "
\n

\n There were several G2 comments about Q2a, as it could be said that several processes were occurring. Perhaps it should have been more specific. Two out of DNA replication, cell growth and duplication of organelles were expected for the two marks. A surprising number of candidates in all languages, confused 'processes' with 'phases' and stated that interphase consisted of G1, S and G2. Most managed to label prophase and anaphase correctly on the diagram as required in part (b). The answers to part (b) were generally clear, but some lost marks for not comparing the same point. For example 'Mitosis produces diploid cells, but meiosis produces gametes' did not score a mark. The mitotic index was well known.\n

\n
\n", "question_id": "21M.2.HL.TZ2.2A", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-1-cell-and-nuclear-division", "d2-1-13-phases-of-the-cell-cycle" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Explain how vaccination can result in specific immunity to a viral disease.\n

\n
\n
\n

\n [7]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n vaccinations are specific to a specific disease;\n
    2. \n
  2. \n vaccines contain non-self antigens/antigens from pathogens;\n
    3. \n
  3. \n can be live relative/attenuated version of the virus;\n
    4. \n
  4. \n trigger a primary immune response (without causing the disease);\n
    5. \n
  5. \n lymphocytes with specific receptors (are activated and) produce memory cells;\n
    6. \n
  6. \n (memory cells) cause a faster production of antibodies on a second exposure/exposure to the disease;\n
    7. \n
  7. \n (memory cells) provide long term immunity;\n
    8. \n
\n
\n", "Examiners report": "None", "question_id": "SPM.2.HL.TZ0.8", "topics": [ "c-interaction-and-interdependence", "a-unity-and-diversity" ], "subtopics": [ "c2-2-neural-signalling", "c2-2-3-nerve-impulses-as-action-potentials-that-are-propagated-along-nerve-fibres", "a4-1-evolution-and-speciation", "a4-1-10-barriers-to-hybridization-and-sterility-of-interspecific-hybrids-as-mechanisms-for-of-preventing-the-mixing-of-alleles-between-species" ] }, { "Question": "
\n
\n

\n Where is the greatest quantity of water reabsorbed from the nephron?\n
\n
\n

\n

\n A.  Bowman’s capsule\n

\n

\n B.  Proximal convoluted tubule\n

\n

\n C.  Loop of Henle\n

\n

\n D.  Collecting duct\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "23M.1A.HL.TZ2.38", "topics": [ "b-form-and-function" ], "subtopics": [ "b2-3-cell-specialization", "b2-3-7-adaptations-to-increase-surface-area-to-volume-ratios-of-cells" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Some plant families, such as the figwort family, have been reclassified on the basis of evidence from cladistics. Explain the methods that have been used recently to reclassify groups of plants.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n a. «previous» classification used to be based on the appearance/structures of the plant/leaves/flowers/seeds/analogy/phenotype ✔\n

\n

\n b. «modern cladistics uses» RNA/DNA nucleotide/base sequencing/amino acid sequencing/homology ✔\n

\n

\n c. DNA mutation occurs at a relatively constant rate allowing estimation of when species diverged ✔\n

\n

\n d. a shared/common derived characteristic places organisms in the same clade ✔\n

\n

\n e. the number of changes in sequences indicates distance from common ancestor\n
\n \n \n OR\n \n \n
\n the fewer the differences «in sequences» means the closer the relationship ✔\n

\n
\n", "Examiners report": "
\n

\n Many students were able to identify molecular sequencing as a method used to re-classify plants. Fewer were clear on the notion of original classification being mistakenly based on analogous features.\n

\n
\n", "question_id": "19M.2.HL.TZ2.4B", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a3-2-classification-and-cladistics-(hl-only)", "a3-2-8-using-cladistics-to-investigate-whether-the-classification-of-groups-corresponds-to-evolutionary-relationships" ] }, { "Question": "
\n
\n

\n The first study used mesocosms and the second study was carried out in natural grassland. Discuss the use of mesocosms as opposed to a study in a natural environment.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n \n advantages of mesocosms/converse problems with studies in natural environments\n \n
\n a. easier to manipulate/control variables/conditions / less susceptible to outside influences\n
\n \n OR\n \n
\n easier to replicate\n
\n \n OR\n \n
\n take up less space;\n

\n

\n \n disadvantages of mesocosms/converse opportunities with studies in natural environments\n \n
\n b. some trophic levels missing/incomplete food chains in mesocosms\n
\n \n OR\n \n
\n large animals cannot be included / ethical concerns about enclosing animals in mesocosms\n
\n \n OR\n \n
\n some variables lacking in mesocosms / doesn’t show what happens in natural ecosystems;\n

\n

\n \n Allow only one mark for an advantage and one mark for a disadvantage as this is a discuss question\n \n .\n

\n
\n", "Examiners report": "
\n

\n Because this was a ‘discuss’ question, one mark was awarded for arguments in favour or mesocosms and one mark for counter arguments. The best answers weighed up the relative advantage of these two approaches, rather than just singing the praises of one of them.\n

\n
\n", "question_id": "21N.2.SL.TZ0.G", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-2-stability-and-change", "d4-2-4-use-of-a-model-to-investigate-the-effect-of-variables-on-ecosystem-stability" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Using the scale bar, calculate the magnification of the image.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n \n \n \n \n \n \n scale bar length\n \n \n \n \n \n \n image size\n \n \n \n \n \n =\n \n \n ×\n \n \n 660\n \n \n \n ✔\n

\n
\n", "Examiners report": "
\n

\n Two marks were awarded for an answer within the given range, since many candidates did not show working, and the question did not request it. Many candidates measured the whole diagram for the numerator instead of the scale bar, and others inverted the formula. A formula in words that appeared correct was not credited if the numbers then negated this. Errors in unit conversion were frequent, but credit was given for working.\n

\n
\n", "question_id": "19M.1B.SL.TZ1.1A", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a2-2-cell-structure", "a2-2-2-microscopy-skills" ] }, { "Question": "
\n
\n

\n Creeper in chickens is a condition in which the chickens are born with very short legs. The creeper allele (C) is dominant over the normal allele (c). Embryos which are homozygous for the dominant allele fail to develop into viable chickens and die before they hatch. What phenotypic ratio would you expect in the live offspring of a cross between two creeper chickens?\n

\n

\n A. All creeper\n

\n

\n B. 1 creeper; 2 normal\n

\n

\n C. 2 creeper; 1 normal\n

\n

\n D. 3 creeper; 1 normal\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "19M.1A.SL.TZ1.15", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-2-inheritance", "d3-2-5-effects-of-dominant-and-recessive-alleles-on-phenotype" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Identify the recombinant phenotypes amongst the offspring.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n brown body vestigial wings\n \n \n AND\n \n \n black body, normal wings\n

\n
\n", "Examiners report": "None", "question_id": "SPM.2.HL.TZ0.7A", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-2-inheritance", "d3-2-20-recombinants-in-crosses-involving-two-linked-or-unlinked-genes" ] }, { "Question": "
\n
\n

\n Discuss whether these studies show that habitat destruction can affect global bumblebee numbers.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n habitat destruction removes the plants/flowers/natural food source of the bees;\n
    2. \n
  2. \n bees have to look for other food sources;\n
    3. \n
  3. \n many of these alternative sources of food are not suitable for bee survival\n
    \n \n \n OR\n \n \n
    \n pollen with a different proportion of protein to lipid would reduce survival;\n
    4. \n
  4. \n no control where bees are fed their normal diet is included;\n
    5. \n
  5. \n simulation is not using natural pollen / habitat;\n
    \n \n \n OR\n \n \n
    \n sample size is too small to make conclusions;\n
    6. \n
\n

\n \n Accept other reasonable discussion using the data.\n \n

\n
\n", "Examiners report": "None", "question_id": "22N.2.SL.TZ0.J", "topics": [ "b-form-and-function" ], "subtopics": [ "b4-1-adaptation-to-environment", "b4-1-2-adaptations-of-organisms-to-the-abiotic-environment-of-their-habitat" ] }, { "Question": "
\n
\n (b.ii)\n
\n
\n

\n Explain the role of methane in climate change.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n methane is a greenhouse gas\n
    \n \n \n OR\n \n \n
    \n methane causes an increase in temperature of the atmosphere;\n
    2. \n
  2. \n methane is one of the most powerful greenhouse gases / more powerful than CO\n \n 2\n \n ;\n
    3. \n
  3. \n methane has a relatively short lifespan compared to CO\n \n 2\n \n /decomposes to CO\n \n 2\n \n ;\n
    4. \n
\n

\n \n Other verifiable sources\n \n .\n

\n
\n", "Examiners report": "None", "question_id": "22M.2.SL.TZ2.3B.II", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-3-climate-change", "d4-3-1-anthropogenic-causes-of-climate-change" ] }, { "Question": "
\n
\n

\n What happens to an RNA molecule in eukaryotes after transcription in order to process it into mRNA?\n
\n
\n

\n

\n A.  Introns are added.\n

\n

\n B.  Exons are removed.\n

\n

\n C.  Adenine nucleotides are added at the 3’ end.\n

\n

\n D.  Adenine nucleotides are removed from the 5’ end.\n

\n
\n
\n

\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "23M.1A.HL.TZ2.23", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d1-2-protein-synthesis", "d1-2-14-non-coding-sequences-in-dna-do-not-code-for-polypeptides", "d1-2-15-post-transcriptional-modification-in-eukaryotic-cells" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n This micrograph shows a transverse section of an artery.\n

\n

\n \n

\n

\n [Source: OpenStax College, 2013. Comparison of artery and vein. [image online] Available at:\n
\n \n https://en.wikipedia.org/wiki/File:2102_Comparison_of_Artery_and_Vein.jpg\n \n Attribution 3.0 Unported\n
\n (CC BY 3.0)\n \n https:/creativecommons.org/licenses/by/3.0/deed.en\n \n [Accessed 11 March 2020].]\n

\n

\n

\n

\n Explain how the specialized structures of arteries help them to achieve their functions.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n a. arteries carry blood at high pressure;\n
\n b. rupture of arteries is prevented by thick muscular/elastic walls;\n
\n c. narrow lumen to maintain a high blood pressure;\n
\n d. elastic tissue allows artery to stretch and recoil (to even out pressures);\n
\n e. arteries have muscle layers which contract to increase/control the blood flow;\n
\n f. folding in the endothelium allows stretching\n
\n OR\n
\n smooth endothelium reduces friction;\n

\n
\n", "Examiners report": "
\n

\n Most could state that the arteries carry blood at high pressure, but had difficulty getting the other two marks.\n

\n
\n", "question_id": "21N.2.SL.TZ0.4", "topics": [ "b-form-and-function", "c-interaction-and-interdependence" ], "subtopics": [ "b3-2-transport", "b3-2-2-structure-of-arteries-and-veins", "b3-2-3-adaptations-of-arteries-for-the-transport-of-blood-away-from-the-heart", "c1-2-cell-respiration", "c1-2-4-cell-respiration-as-a-system-for-producing-atp-within-the-cell-using-energy-released-from-carbon-compounds", "c1-2-3-energy-transfers-during-interconversions-between-atp-and-adp", "c2-1-chemical-signalling-[hl-only]", "c2-1-10-mechanism-of-action-of-epinephrine-(adrenaline)-receptors" ] }, { "Question": "
\n
\n

\n Label with a C the tissue where organic compounds are transported.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n \n \n \n

\n

\n [Source: Nbnidhi, https:// commons.wikimedia.org/wiki/ File:Transverse_section_of_dicot _stem.jpg]\n

\n

\n \n Award\n \n [1]\n \n for correct labeling of C\n \n

\n
\n", "Examiners report": "
\n

\n This was another question that was difficult for students. This question again required students to understand one of the skills from the subject guide, this time in topic 9.2 (Identification of xylem and phloem in microscope images of stem and root). Student responses to this question, however, suggested that few students could identify phloem and xylem under a microscope.\n

\n
\n", "question_id": "19M.1B.SL.TZ1.D.II", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-2-transport", "b3-2-9-distribution-of-tissues-in-a-transverse-section-of-the-stem-of-a-dicotyledonous-plant" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Comment on the total energy content of the two diets.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n a. energy is not changed (between the two diets);\n

\n

\n b. study diet\n \n slightly\n \n lower in energy than habitual diet (but means/SD overlap);\n

\n

\n c. spread of values show more variation for habitual diet / higher SD in habitual;\n

\n
\n", "Examiners report": "
\n

\n Considering that all students must complete an Individual investigation as part of their Biology course, few understood the significance of the uncertainties shown in the first table or the overlap of the standard deviations in the graph in part d. Only the better candidates were able to say that the energy was extremely similar in both diets. A surprising number could not calculate a percentage change in part c.\n

\n

\n In part b, the command term was ‘distinguish’ which means that only differences were looked for. Similarly in d(i), ‘compare’ means that only similarities were needed. If both were required, the command term is ‘compare and contrast’.\n

\n

\n In d, few could state that there was no significant difference in the two curves due to the overlap of the error bars. Most knew that the beta cells of the pancreas secrete insulin, although a surprising number thought that they were produced by the red blood cells. In e, many gained two marks for linking saturated fats to cholesterol and its consequence.\n

\n

\n

\n
\n", "question_id": "20N.2.SL.TZ0.1", "topics": [ "b-form-and-function", "d-continuity-and-change" ], "subtopics": [ "b1-2-proteins", "b1-2-3-dietary-requirements-for-amino-acids", "b1-1-carbohydrates-and-lipids", "b1-1-10-difference-between-saturated-monounsaturated-and-polyunsaturated-fatty-acids", "d3-3-homeostasis", "d3-3-3-regulation-of-blood-glucose-as-an-example-of-the-role-of-hormones-in-homeostasis" ] }, { "Question": "
\n
\n

\n In premature babies born earlier than the 30\n \n th\n \n week of pregnancy, type II pneumocytes are usually not fully developed, so they do not carry out their function normally. What is a possible consequence of this?\n

\n

\n A. The number of alveoli reduces.\n

\n

\n B. The size of the alveoli increases.\n

\n

\n C. Capillary networks do not develop fully and oxygen is not absorbed.\n

\n

\n D. Surface tension between alveoli does not decrease and the alveoli stick together.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "19M.1A.HL.TZ2.26", "topics": [ "b-form-and-function" ], "subtopics": [ "b2-3-cell-specialization", "b2-3-8-adaptations-of-type-i-and-type-ii-pneumocytes-in-alveoli" ] }, { "Question": "
\n
\n (e)\n
\n
\n

\n Suggest reasons for the high percentage of fatal cases at Ebola treatment centres.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n a. most serious cases are in/are taken to treatment centers\n
\n \n \n OR\n \n \n
\n treatment centers are set up where there are most cases/most serious cases ✔\n

\n

\n b. long time/distance to travel between contracting disease and arrival at treatment center\n
\n \n \n OR\n \n \n
\n travel to treatment center weakens/upsets/harms the patient ✔\n

\n

\n c. Ebola is a virulent disease/Ebola virus mutated «to become virulent»\n
\n \n \n OR\n \n \n
\n little known about Ebola/new disease so treatments not yet developed ✔\n

\n

\n d. no/not enough vaccine/antiviral drug available «in 2014/15»\n
\n \n \n OR\n \n \n
\n antibiotics do not work against viral diseases ✔\n

\n

\n e. secondary infections/Ebola patients infected with other diseases/other Ebola strains\n
\n \n \n OR\n \n \n
\n ineffective hygiene/cleaning/sterilization/use of contaminated equipment/disposal of corpses ✔\n

\n

\n f. small number of staff relative to patients/treatment centers overcrowded/swamped with patients\n
\n \n \n OR\n \n \n
\n insufficient equipment/supplies for large number of patients/with the rapid rise in patients ✔\n

\n

\n g. better reporting at Ebola centers/deaths due to Ebola not reported in rural areas ✔\n

\n
\n", "Examiners report": "
\n

\n This was a timely question with Ebola epidemics again causing great problems in parts of Africa. Students were expected to have had some practice at analysing data relating to an epidemic because of this Skill in the programme: Analysis of epidemiological data related to vaccination programmes. It was assumed that candidates would understand terms such as ‘case’, ‘fatal case’, ‘infect’ and ‘treat’.\n

\n

\n This was a more difficult question. We might expect fewer fatalities in percentage terms at treatment centres than elsewhere, but the data showed that there were more. Not all candidates realised that the figures given indicated the percentage of people diagnosed with Ebola that died, not the percentage of the population as a whole. As in 1(c) a wide variety of answers was accepted. Some of the answers related to Ebola having a high mortality rate generally, but to score three marks it was necessary to find reasons for treatment centres in particular having high rates of death. One suggestion commonly given but not accepted was that patients became infected after arrival at treatment centres – this would not necessarily give a high fatality rate or percentage and also uninfected people are unlikely to be brought to treatment centres. Some students thought that the more infected people a patient came into contact with, the more infected they would be. This ignores the potential for the Ebola virus to multiply exponentially once inside a patient. Material shortages were only accepted as a reason if this was combined with the idea that treatment centres were swamped with patients.\n

\n
\n", "question_id": "19M.2.SL.TZ1.1E", "topics": [ "c-interaction-and-interdependence", "a-unity-and-diversity" ], "subtopics": [ "c3-2-defence-against-disease", "a2-3-viruses-(hl-only)" ] }, { "Question": "
\n
\n

\n The image shows a molecule of oleic acid.\n

\n

\n \n

\n

\n

\n

\n What describes oleic acid?\n

\n

\n
\n A.  Cis polyunsaturated\n

\n

\n B.  Cis monounsaturated\n

\n

\n C.  Trans polyunsaturated\n

\n

\n D.  Trans monounsaturated\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "23M.1A.SL.TZ2.7", "topics": [ "b-form-and-function" ], "subtopics": [ "b1-1-carbohydrates-and-lipids", "b1-1-10-difference-between-saturated-monounsaturated-and-polyunsaturated-fatty-acids" ] }, { "Question": "
\n
\n

\n What type of molecule is formed by the chemical reaction shown in the diagram?\n

\n

\n \n

\n

\n

\n

\n A. Dipeptide\n

\n

\n B. Disaccharide\n

\n

\n C. Diglyceride\n

\n

\n D. Cellulose\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "19M.1A.SL.TZ1.6", "topics": [ "b-form-and-function" ], "subtopics": [ "b1-1-carbohydrates-and-lipids", "b1-1-2-production-of-macromolecules-by-condensation-reactions-that-link-monomers-to-form-a-polymer" ] }, { "Question": "
\n
\n

\n Which drawing represents beta-D-glucose?\n

\n

\n \n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "23M.1A.SL.TZ2.6", "topics": [ "b-form-and-function" ], "subtopics": [ "b1-1-carbohydrates-and-lipids", "b1-1-5-polysaccharides-as-energy-storage-compounds" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n State the type of inheritance shown.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n «gene/autosomal» linkage ✔\n

\n

\n \n Reject sex linkage\n \n

\n
\n", "Examiners report": "None", "question_id": "19N.2.HL.TZ0.2A", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-2-inheritance", "d3-2-17-punnett-grids-for-predicting-genotypic-and-phenotypic-ratios-in-dihybrid-crosses-involving-pairs-of-unlinked-autosomal-genes", "d3-2-18-loci-of-human-genes-and-their-polypeptide-products", "d3-2-19-autosomal-gene-linkage", "d3-2-20-recombinants-in-crosses-involving-two-linked-or-unlinked-genes" ] }, { "Question": "
\n
\n (b.i)\n
\n
\n

\n Identify the structure labelled X.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n ovule ✔\n

\n
\n", "Examiners report": "
\n

\n This question was derived from the skill of drawing half-views of animal pollinated flowers and the understanding of mutualistic relationships involved in plant reproduction. A large number could identify the ovule, but many incorrect answers, such as ovary, were also seen, as well as totally irrelevant answers.\n

\n
\n", "question_id": "19M.2.SL.TZ2.1B.I", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-1-reproduction", "d3-1-9-features-of-an-insect-pollinated-flower" ] }, { "Question": "
\n
\n

\n The global carbon cycle involves sinks where carbon is stored, and fluxes where carbon is transferred. What are the largest sink and flux?\n

\n

\n \n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "
\n

\n In Topic 4.3 candidates had to estimate carbon fluxes due to processes in the carbon cycle. Candidates should have known that respiration and combustion return carbon dioxide to the atmosphere while photosynthesis uses this carbon dioxide. The total amount for the carbon dioxide released to the atmosphere is equal or smaller than the carbon dioxide absorbed, therefore eliminating answers A and B. Unfortunately, many capable candidates chose these options, making this question a bad discriminator. The ocean is by far the largest sink.\n

\n
\n", "question_id": "19M.1A.SL.TZ2.23", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c4-2-transfers-of-energy-and-matter", "c4-2-18-ecosystems-as-carbon-sinks-and-carbon-sources", "c4-2-19-release-of-carbon-dioxide-into-the-atmosphere-during-combustion-of-biomass-peat-coal-oil-and-natural-gas" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Pangolins are unique among mammals in having evolved scales, which are a recognition feature of reptiles. Explain which features you expect pangolins to have, which would show that they are mammals, not reptiles.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n hair;\n
    2. \n
  2. \n mammary glands/milk secretion;\n
    3. \n
  3. \n alveoli in lungs;\n
    4. \n
  4. \n lower mandible/jaw consisting of just one bone;\n
    5. \n
  5. \n giving birth to live young/are placental (apart from duck-billed platypus/echidna);\n
    6. \n
  6. \n external ears/ pinna;\n
    7. \n
  7. \n warm-blooded/endothermic/constant body temperature;\n
    8. \n
\n

\n \n Mpa: pangolin underside may be covered with sparse fur.\n \n

\n

\n \n Do not accept double circulation. Mpe: accept “do not lay eggs” as WTTE Do not accept internal fertilization.\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.2.HL.TZ2.4B", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-1-reproduction", "d3-1-18-role-of-the-placenta-in-foetal-development-inside-the-uterus" ] }, { "Question": "
\n
\n

\n What does an action spectrum for photosynthesis show?\n

\n

\n A. The range of conditions over which photosynthesis can occur in a plant\n

\n

\n B. The percentage of light absorbed at each wavelength by photosynthetic pigments\n

\n

\n C. The percentage of light absorbed at each energy level by a plant\n

\n

\n D. The relative amount of photosynthesis at each wavelength of light\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "22M.1A.SL.TZ2.7", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-3-photosynthesis", "c1-3-6-similarities-and-differences-of-absorption-and-action-spectra" ] }, { "Question": "
\n
\n

\n Explain the production of antibodies when a patient is infected with the TB bacterium.\n

\n
\n
\n

\n [7]\n

\n
\n
\n", "Markscheme": "
\n

\n a. phagocytes/lymphocytes are white blood cells ✔\n

\n

\n b. TB bacterium has a specific antigen ✔\n

\n

\n c. this antigen is recognised by white blood cells ✔\n

\n

\n d. a clone of lymphocytes/plasma cells/B cells are produced ✔\n

\n

\n e. antibodies are produced by lymphocytes ✔\n

\n

\n f. each lymphocyte produces just one type of antibody ✔\n

\n

\n g. (this is) specific immunity ✔\n

\n

\n h. (part of the) antibody/immunoglobulin binds to the antigen / specific antibody binds to the specific antigen ✔\n

\n

\n i. antibodies are proteins/immunoglobulins ✔\n

\n

\n j. (some) plasma cells become memory cells ✔\n

\n

\n k. memory cells reproduce quickly ✔\n

\n

\n l. memory cells prevent infection in the future ✔\n

\n

\n \n Allow annotated diagrams to explain the process\n \n .\n

\n
\n", "Examiners report": "
\n

\n (attempted by about 60 % of the cohort)\n

\n

\n Part (a) was a departure from the 'draw a prokaryote' type of question that has appeared numerous times. In general, it was well answered. There were some good diagrams as answers which clearly showed only the prokaryotic characteristics. Part (b) asked for an explanation of the production of antibodies. Many weaker students wrote at length about non-specific phagocytosis which was not credited. Weaker students confused antibodies and antigens and even talked about antibiotics. This question was designed to be answered by the Standard Level students using Standard Level material. Some tried to include HL material and became very confused. Part (c) was really a question about Darwin's theory of evolution set in context. Many of the answers were very Lamarckian with the antibiotic causing the mutation, instead of some bacteria already having resistance. Better students opened with comments and an explanation that antibiotics only kill bacteria.\n

\n
\n", "question_id": "21M.2.HL.TZ2.B", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-2-defence-against-disease", "c3-2-6-lymphocytes-as-cells-in-the-adaptive-immune-system-that-cooperate-to-produce-antibodies", "c3-2-10-immunity-as-a-consequence-of-retaining-memory-cells" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Successful sexual reproduction in flowering plants depends on several essential processes. Outline the role of pollination and seed dispersal.\n

\n

\n Pollination:\n

\n

\n

\n

\n Seed dispersal:\n

\n

\n

\n

\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n \n pollination\n \n :\n
\n transfer/dispersal/movement of\n \n pollen\n \n from anther/stamen to\n \n stigma\n \n
\n \n \n OR\n \n \n
\n transfer/dispersal/movement of\n \n pollen\n \n between plants/flowers prior to/allowing\n \n fertilization\n \n ✔\n

\n

\n \n seed dispersal\n \n :\n
\n «strategy of» distribution of seeds so that new plants have space/nutrients to develop/avoid competition/colonize new habitats ✔\n

\n

\n \n Accept any other valid role.\n \n

\n

\n \n Accept OWTTE. Answers must be about the role.\n \n

\n
\n", "Examiners report": "
\n

\n Most students were able to outline the role of seed dispersal in minimizing competition between parent and offspring. Slightly fewer were successful in correctly outlining the role of pollination in sexual reproduction with a number being unable to correctly draw upon the necessary vocabulary.\n

\n
\n", "question_id": "19M.2.SL.TZ2.4C", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-1-reproduction", "d3-1-8-sexual-reproduction-in-flowering-plants", "d3-1-12-dispersal-and-germination-of-seeds" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Explain the effect of temperature on the rate of photosynthesis in this mesocosm.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n \n rate of photosynthesis increases as temperature rises because\n \n :\n
\n a. temperature is the limiting factor for photosynthesis;\n
\n b. higher temperatures increase enzyme activity;\n
\n c. faster molecular motion/more molecular kinetic energy/more frequent enzyme-substrate collisions;\n
\n d. Calvin cycle/light independent reactions (of photosynthesis) speed up;\n

\n
\n", "Examiners report": "
\n

\n About half candidates merely stated the relationship shown in the graph, rather than actually explaining it. An explanation based on enzyme activity were expected. Performance in this question and in (d) correlated well with the overall performance of each candidate on the paper, probably because biological understanding was required. Other parts of question 1 were less well correlated, as is typical for data analysis questions.\n

\n
\n", "question_id": "21N.2.SL.TZ0.1C", "topics": [ "d-continuity-and-change", "c-interaction-and-interdependence" ], "subtopics": [ "d4-2-stability-and-change", "d4-2-4-use-of-a-model-to-investigate-the-effect-of-variables-on-ecosystem-stability", "c1-3-photosynthesis", "c1-3-7-techniques-for-varying-concentrations-of-carbon-dioxide-light-intensity-or-temperature-experimentally-to-investigate-the-effects-of-limiting-factors-on-the-rate-of-photosynthesis" ] }, { "Question": "
\n
\n (a.ii)\n
\n
\n

\n On the diagram, label the right atrium.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n both labelled clearly as in diagram ✔\n

\n

\n \n

\n

\n [Source: BlueRingMedia/Shutterstock]\n

\n
\n", "Examiners report": "
\n

\n Labelling the heart was generally ok, though the rest of this question was weakly answered.\n

\n
\n", "question_id": "19M.2.HL.TZ1.3A.II", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-2-transport", "b3-2-15-adaptations-of-the-mammalian-heart-for-delivering-pressurized-blood-to-the-arteries" ] }, { "Question": "
\n
\n (a.i)\n
\n
\n

\n Outline how O\n \n 2\n \n consumption is measured using a respirometer.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. a CO\n \n 2\n \n absorber/KOH is added ✔\n

\n

\n b. a bubble/starting water level is measured ✔\n

\n

\n c. «the rate of» movement of the bubble/pressure reduction is a measure of O\n \n 2\n \n consumption ✔\n

\n
\n", "Examiners report": "
\n

\n Very few candidates achieved a mark. Some confused a respirometer with a spirometer; others mentioned data logging probes. Credit was given for mention of a water column. Only the highest scoring candidates understood that a carbon dioxide absorber is required to allow pressure changes to be measured.\n

\n
\n", "question_id": "19M.1B.SL.TZ1.2A.I", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-2-cell-respiration", "c1-2-6-variables-affecting-the-rate-of-cell-respiration" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Explain the action of neonicotinoid pesticides in insects.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n prevents synaptic/nerve transmission\n
    2. \n
  2. \n is /acts like /has similar structure to a neurotransmitter/acetylcholine\n
    3. \n
  3. \n (neonicotinoid pesticides) bind to acetylcholine receptors in the post synaptic membrane;\n
    4. \n
  4. \n neonicotinoid pesticides are not broken down (as acetylcholine would be) by acetylcholinesterase/enzyme;\n
    5. \n
  5. \n the receptors are overstimulated\n
    6. \n
  6. \n paralyses/kills the insects;\n
    7. \n
\n
\n", "Examiners report": "None", "question_id": "22N.2.SL.TZ0.5C", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c2-2-neural-signalling", "c2-2-12-effects-of-exogenous-chemicals-on-synaptic-transmission" ] }, { "Question": "
\n
\n

\n Annotate the diagram to show a peptide bond between two amino acids.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n any annotation between a C=O and the next NH ✔\n

\n

\n \n e.g.\n \n

\n

\n \n \n \n

\n
\n", "Examiners report": "None", "question_id": "19N.2.SL.TZ0.D.I", "topics": [ "b-form-and-function" ], "subtopics": [ "b1-2-proteins", "b1-2-2-condensation-reactions-forming-dipeptides-and-longer-chains-of-amino-acids" ] }, { "Question": "
\n
\n (c.ii)\n
\n
\n

\n Suggest a reason for the correlation between coral cover and WSSTA in 1998–1999.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n coral cover lower on reefs with higher temperature;\n

\n
\n", "Examiners report": "None", "question_id": "21N.2.SL.TZ0.1C.II", "topics": [ "d-continuity-and-change", "b-form-and-function" ], "subtopics": [ "d4-3-climate-change", "d4-3-7-threats-to-coral-reefs-as-an-example-of-potential-ecosystem-collapse", "b4-1-adaptation-to-environment", "b4-1-5-conditions-required-for-coral-reef-formation" ] }, { "Question": "
\n
\n

\n The bird and bat wings share homologous bone structures whereas the insect wing does not. Outline the conclusion that can be drawn about the evolution of these wings, based on homologous structures.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n a. bird and bat share a more recent common ancestor (than the insect) ✔\n

\n

\n b. bird and bat are more closely related than insect and bat / insect and bird ✔\n

\n

\n c. bird and bat wings evolved from a common ancestor (by natural selection) ✔\n

\n
\n", "Examiners report": "
\n

\n Candidates found it hard to express themselves without contradiction.\n

\n

\n In both parts the key to successful answers was in using the organisms given in the example. Contradictions were thus avoided.\n

\n
\n", "question_id": "21M.2.SL.TZ1.A.II", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a4-1-evolution-and-speciation", "a4-1-4-evidence-for-evolution-from-homologous-structures" ] }, { "Question": "
\n
\n

\n In the fruit fly\n \n Drosophila\n \n , the alleles for red eyes and brown bodies are dominant to the alleles for white eyes and yellow bodies. Which cross would be suitable to determine whether the genes are linked?\n
\n
\n

\n

\n A.  Heterozygous red-eyed flies crossed with yellow-bodied flies\n

\n

\n B.  White-eyed flies crossed with homozygous brown-bodied flies\n

\n

\n C.  Homozygous red-eyed, brown-bodied flies crossed with white-eyed, yellow-bodied flies\n

\n

\n D.  Heterozygous red-eyed, brown-bodied flies crossed with white-eyed, yellow-bodied flies\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "23M.1A.SL.TZ2.32", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-2-inheritance", "d3-2-19-autosomal-gene-linkage", "d3-2-20-recombinants-in-crosses-involving-two-linked-or-unlinked-genes" ] }, { "Question": "
\n
\n

\n Outline what is indicated by the mitotic index of tissue taken from a tumour.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. mitotic index is an indication of the ratio/percentage of cells undergoing mitosis/cell division ✔\n

\n

\n b. cancer cells «generally» divide much more than normal «somatic» cells ✔\n

\n

\n c. a\n \n high/elevated\n \n mitotic index in tumours / possible diagnosis of cancer /measure of how aggressive/fast growing the tumour is ✔\n

\n
\n", "Examiners report": "
\n

\n Many students could accurately define the term mitotic index. An area of misunderstanding was to categorize the mitotic index as a rate rather than a ratio.\n

\n
\n", "question_id": "19M.2.SL.TZ2.A.II", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-1-cell-and-nuclear-division", "d2-1-17-differences-between-tumours-in-rates-of-cell-division-and-growth-and-in-the-capacity-for-metastasis-and-invasion-of-neighbouring-tissue" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n To calculate chi-squared, expected values must first be calculated. Assuming that there is no association between the two species, calculate the expected number of quadrats in which both species would be present, showing your working.\n

\n

\n

\n

\n

\n

\n

\n

\n

\n

\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n \n \n \n \n 70\n \n \n \n \n ×\n \n \n \n \n 55\n \n \n \n 150\n \n \n \n ;\n
    2. \n
  2. \n 25.7;\n
    3. \n
\n

\n \n Award\n \n [1]\n \n for proper values chosen/equation or\n \n [1]\n \n for answer\n \n .\n

\n
\n", "Examiners report": "None", "question_id": "22M.2.SL.TZ2.3B", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c4-1-populations-and-communities", "c4-1-15-use-of-the-chi-squared-test-for-association-between-two-species" ] }, { "Question": "
\n
\n

\n Merriam’s kangaroo rat (\n \n Dipodomys merriami\n \n ) is a small mammal found in desert biomes in the southwestern USA and Mexico. What would help these kangaroo rats to conserve water in order to survive high temperatures in desert biomes?\n
\n
\n

\n

\n A.  Increased sweating\n

\n

\n B.  A long loop of Henle\n

\n

\n C.  Decreased secretion of ADH\n

\n

\n D.  Decreased reabsorption from the collecting duct\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "23M.1A.HL.TZ1.39", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-3-homeostasis", "d3-3-9-role-of-the-loop-of-henle" ] }, { "Question": "
\n
\n (d)\n
\n
\n

\n Outline what is meant by the niche concept.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. the role of an organism in its environment\n
\n \n \n OR\n \n \n
\n functional position of an organism in its environment ✔\n
\n
\n b. includes «spatial» habitat AND feeding activities AND interactions with other species in the community ✔\n \n All required\n \n .\n

\n

\n c. no two species can occupy the same niche ✔\n

\n

\n d. a niche can be fundamental or realized ✔\n \n OWTTE\n \n

\n
\n", "Examiners report": "None", "question_id": "19N.2.HL.TZ0.14D", "topics": [ "b-form-and-function" ], "subtopics": [ "b4-2-ecological-niches", "b4-2-1-ecological-niche-as-the-role-of-a-species-in-an-ecosystem", "b4-2-12-fundamental-and-realized-niches", "b4-2-13-competitive-exclusion-and-the-uniqueness-of-ecological-niches" ] }, { "Question": "
\n
\n (d.ii)\n
\n
\n

\n The offspring, which were all heterozygous for grey body and normal wings, were crossed with flies that were homozygous recessive for both genes. The table shows the percentages of offspring produced.\n

\n

\n \n

\n

\n Explain these results, based on the knowledge that the genes for body colour and wing size are autosomally linked.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. not a 1:1:1:1 ratio «because of linkage»\n
\n \n \n OR\n \n \n
\n not independent assortment\n
\n \n \n OR\n \n \n
\n grey normal and black vestigial types/parental combinations/double dominant and double recessive were commoner than 25 %/commoner than expected ✔\n
\n
\n b. «linked genes» so were on the same chromosome ✔\n

\n

\n c. grey body vestigial wing and black body normal wing are recombinants\n
\n \n \n OR\n \n \n
\n 2 % plus 3 % of the offspring are recombinants ✔\n

\n

\n d. recombinants due to crossing over/exchange of genes between «non-sister» chromatids\n
\n \n \n OR\n \n \n
\n 2 % and 3 % of offspring were due to crossing over\n
\n \n \n OR\n \n \n
\n genes inherited together unless separated by crossing over ✔\n

\n

\n e. crossing over between the two loci/between the two genes on the chromosomes ✔\n

\n

\n f. few recombinants/not much crossing over because genes/gene loci close together ✔\n

\n

\n \n Accept any of these points from an annotated diagram.\n \n

\n
\n", "Examiners report": "
\n

\n Most candidates found it very hard to explain the non-Mendelian ratio. A good start would have been to state the expected Mendelian ratio for unlinked genes in this type of cross and then compare this with the actual percentages. Answers tended to state which traits tended to be inherited together rather than explain the mechanism. An obvious answer was that that the two genes are located on the same chromosome but only a minority of candidates stated this and even fewer made the point that crossing over between the two gene loci results in the small percentage of recombinants. Many students referred to the 9:3:3:1 ratio, even though the cross performed in this case would not have given this ratio, even if there had not been gene linkage. Also many candidates claimed that more individuals showed dominant phenotypes than recessive, which was not supported by the percentages.\n

\n
\n", "question_id": "19M.2.HL.TZ1.2D.II", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-2-inheritance", "d3-2-16-segregation-and-independent-assortment-of-unlinked-genes-in-meiosis" ] }, { "Question": "
\n
\n

\n What feature of arteries is most important in maintaining sufficiently high blood pressure?\n

\n

\n A. A wide lumen\n

\n

\n B. Elastic fibres in the wall\n

\n

\n C. Valves at intervals\n

\n

\n D. A thin wall\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "20N.1A.SL.TZ0.25", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-2-transport", "b3-2-2-structure-of-arteries-and-veins", "b3-2-3-adaptations-of-arteries-for-the-transport-of-blood-away-from-the-heart" ] }, { "Question": "
\n
\n

\n State which cells secrete insulin.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n \n β cells\n \n of pancreas/islets (of Langerhans);\n

\n
\n", "Examiners report": "None", "question_id": "20N.1B.SL.TZ0.D.II", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-3-homeostasis", "d3-3-3-regulation-of-blood-glucose-as-an-example-of-the-role-of-hormones-in-homeostasis" ] }, { "Question": "
\n
\n

\n The diagram shows a ribosome and associated mRNA\n

\n

\n \n

\n

\n

\n

\n Which of these events occurs first in translation?\n

\n

\n A.  Small ribosomal subunit binds to mRNA.\n

\n

\n B.  Large ribosomal subunit binds to mRNA.\n

\n

\n C.  Initiator tRNA enters E site.\n

\n

\n D.  Initiator tRNA enters A site.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "None", "question_id": "22N.1A.HL.TZ0.28", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d1-2-protein-synthesis", "d1-2-17-initiation-of-translation" ] }, { "Question": "
\n
\n

\n What is a result of crossing over in meiosis?\n
\n
\n

\n

\n A.  Gene linkage\n

\n

\n B.  Non-disjunction\n

\n

\n C.  Haploid cells\n

\n

\n D.  Variation in gametes\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "23M.1A.SL.TZ2.31", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-1-cell-and-nuclear-division", "d2-1-11-meiosis-as-a-source-of-variation" ] }, { "Question": "
\n
\n

\n The diagram shows the human female reproductive system\n

\n

\n \n

\n

\n [Source: © International Baccalaureate Organization 2019]\n

\n

\n

\n

\n Which labels indicate where fertilization occurs and where luteinizing hormone (LH) acts?\n

\n

\n \n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "
\n

\n Although fertilization can occur in the uterus it is more usual that this occurs in the oviducts.\n

\n
\n", "question_id": "19M.1A.SL.TZ2.30", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-1-reproduction", "d3-1-5-changes-during-the-ovarian-and-uterine-cycles-and-their-hormonal-regulation" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n State\n \n one\n \n feature of the rings that has to be kept constant apart from their initial diameter.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n a. width/section depth/slice of the ring;\n

\n

\n b. same animal/age/freshness/temperature;\n

\n

\n \n Don’t accept thickness or diameter\n \n .\n

\n

\n \n

\n
\n", "Examiners report": "
\n

\n In part (b) many candidates suggested that the samples should be of the same thickness.\n

\n
\n", "question_id": "20N.1B.SL.TZ0.2B", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-2-transport", "b3-2-2-structure-of-arteries-and-veins" ] }, { "Question": "
\n
\n (i)\n
\n
\n

\n State the relationship between DDE concentration and eggshell thickness.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n the higher the DDE concentration, the lower the thickness/higher the thinning\n
\n \n \n OR\n \n \n
\n negative correlation/inverse relationship;\n

\n

\n \n Accept vice versa.\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ2.18AI", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-2-stability-and-change", "d4-2-9-biomagnification-of-pollutants-in-natural-ecosystems" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Compare and contrast the mode of nutrition of detritivores and saprotrophs.\n

\n

\n \n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n \n

\n

\n \n Accept not autotrophic/not photosynthetic instead of heterotrophic\n \n .\n

\n

\n \n Do not accept that both groups are decomposers or consumers for the similarity\n \n .\n

\n
\n", "Examiners report": "
\n

\n About half of candidates answered correctly and there were some well-informed answers, but also many that showed a lack of familiarity with nutrition in detritivores and saprotrophs.\n

\n
\n", "question_id": "21N.2.HL.TZ0.5", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-1-integration-of-body-systems", "c3-1-21-promotion-of-cell-growth-by-auxin" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Structure IV contains a gland that secretes a sugary liquid. Suggest a benefit to the plant of secreting this liquid.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n attracts an insect/animal/which pollinates the flower;\n
    2. \n
  2. \n attracts a pollinator;\n
    3. \n
\n

\n \n Mpa: Both parts of the sentence are needed to award the point.\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ2.3C", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-1-reproduction", "d3-1-9-features-of-an-insect-pollinated-flower" ] }, { "Question": "
\n
\n

\n Atropine drops are used by opticians to dilate the pupil, so that a thorough examination of the retina can be performed. Atropine binds to acetylcholine receptors in synapses.\n

\n

\n \n

\n

\n

\n

\n What is the effect of atropine binding in synapses?\n

\n

\n A.  Inhibits the binding of acetylcholine at the presynaptic membrane\n

\n

\n B.  Inhibits the release of acetylcholine from the presynaptic neuron\n

\n

\n C.  Prevents binding of acetylcholine at the postsynaptic membrane\n

\n

\n D.  Prevents transport of acetylcholine through the postsynaptic membrane\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "22N.1A.HL.TZ0.24", "topics": [ "b-form-and-function", "c-interaction-and-interdependence" ], "subtopics": [ "c2-2-neural-signalling", "c2-2-6-release-of-neurotransmitters-from-a-presynaptic-membrane", "b2-1-membranes-and-membrane-transport", "b2-1-14-gated-ion-channels-in-neurons" ] }, { "Question": "
\n
\n

\n Which structures are part of the walls of both capillaries and veins?\n

\n

\n I. Cells\n

\n

\n II. Pores\n

\n

\n III. Elastic fibres\n

\n

\n A. I only\n

\n

\n B. I and II\n

\n

\n C. I and III\n

\n

\n D. I, II and III\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "
\n

\n This was another question where fewer candidates answered correctly than the guess-level of 25%. The most popular choice had elastic fibres as a feature of both capillaries and veins. This indicates that many candidates' knowledge of the structure of blood vessels was weak.\n

\n
\n", "question_id": "22M.1A.SL.TZ1.25", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-2-transport", "b3-2-1-adaptations-of-capillaries-for-exchange-of-materials-between-blood-and-the-internal-or-external-environment", "b3-2-5-adaptations-of-veins-for-the-return-of-blood-to-the-heart" ] }, { "Question": "
\n
\n

\n Suggest possible reasons for the observed pattern of presence of antibodies in vaccinated mice.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n a. low antibody level initially as mice not previously exposed to antigen/bacteria ✔\n

\n

\n b. vaccination causes antibody production/development of immunity ✔\n

\n

\n c. increased proportion of mice have been vaccinated in each successive month ✔\n

\n

\n d. second vaccination/booster shot increases antibody level/speeds up antibody production ✔\n

\n

\n e.\n \n memory cells\n \n produced so greater/faster antibody production ✔\n

\n

\n f. many/rising numbers of nymphs which may spread the bacteria/antigens to mice ✔\n

\n

\n \n Ignore any references to non-vaccinated/control mice – this means that no marks are awarded for them because the question is about vaccinated mice, but there is no penalty for including this information in an answer\n \n .\n

\n
\n", "Examiners report": "None", "question_id": "19N.2.SL.TZ0.F.II", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-2-defence-against-disease", "c3-2-8-activation-of-b-lymphocytes-by-helper-t-lymphocytes" ] }, { "Question": "
\n
\n

\n The image shows the four chambers of the mammalian heart viewed from the ventral side. The sinoatrial node is located in the wall of one of these chambers. Which chamber is it?\n

\n

\n \n

\n

\n [Source: Anatomy Corner, n.d. [\n \n Elk heart\n \n ]. [image online] Available at:\n \n http://anatomycorner.com/main/image-gallery/elk-heart/\n \n
\n [Accessed 23 March 2020].]\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "
\n

\n The last skill in sub-topic 6.2 was the basis for this question. Students are expected to identify chambers and blood vessels of the heart from dissected hearts, images of photographs of hearts or diagrams of heart structure. A G2 comment was made that the term ‘ventral’ may have been unfamiliar to students and that ‘front view’ would have been better. This wasn’t a human heart so the term ‘front view’ would be ambiguous. What is the front view of a sheep? The terms dorsal and ventral are useful when studying bilaterians and ideally students should become familiar with them. Also identifying parts of the heart in a photo of a heart or a real specimen is a much more useful skill than identifying them in a diagram, where they are very likely already to be labelled.\n

\n
\n", "question_id": "21N.1A.HL.TZ1.24", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-2-transport", "b3-2-15-adaptations-of-the-mammalian-heart-for-delivering-pressurized-blood-to-the-arteries" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Compare and contrast the structure of a typical prokaryotic cell with that of a mitochondrion.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n

\n \n differences\n \n

\n

\n a. prokaryote has cell wall but mitochondrion does not ✔\n

\n

\n b. mitochondrion has double membrane whereas prokaryote has single membrane\n
\n \n \n OR\n \n \n
\n «Gram negative» bacteria have cell wall between two membranes whereas mitochondria has intermembrane space between two membranes ✔\n

\n

\n c. mitochondrion has cristae/invaginations of inner membrane but prokaryote does not\n
\n \n \n OR\n \n \n
\n prokaryote «may have» flagella/pili/«slime» capsule which mitochondria do not have ✔\n

\n

\n \n similarities\n \n

\n

\n d.\n \n 70S\n \n ribosomes in both ✔\n

\n

\n e.\n \n DNA\n \n in both / loop of\n \n DNA\n \n in both / naked\n \n DNA\n \n in both ✔\n

\n

\n f. shape similar/both rod shaped/\n \n OWTTE\n \n
\n \n \n OR\n \n \n
\n size of both is similar/both about 3 μm long ✔\n

\n

\n g. both are membrane-bound/\n \n OWTTE\n \n ✔\n

\n
\n", "Examiners report": "
\n

\n Answers were spread over the whole of the four-mark range. The scale bars allowed the sizes of both to be calculated – they were close, but even so a substantial number of candidates claimed that one or other was significantly larger.\n

\n
\n", "question_id": "19M.2.HL.TZ1.3", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a2-2-cell-structure", "a2-2-12-origin-of-eukaryotic-cells-by-endosymbiosis" ] }, { "Question": "
\n
\n

\n Identify the independent variable.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n (with/without) ultrasound pretreatment / time;\n

\n
\n", "Examiners report": "None", "question_id": "23M.1B.SL.TZ2.II", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-1-enzymes-and-metabolism", "c1-1-8-effects-of-temperature-ph-and-substrate-concentration-on-the-rate-of-enzyme-activity" ] }, { "Question": "
\n
\n (e)\n
\n
\n

\n Once the germinated bean grows above the ground, state the process used by the bean in the production of starch.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n photosynthesis\n

\n

\n \n Do not accept condensation or polymerization; if list of processes given, mark the first answer\n \n .\n

\n
\n", "Examiners report": "None", "question_id": "21M.2.SL.TZ2.3E", "topics": [ "b-form-and-function" ], "subtopics": [ "b1-1-carbohydrates-and-lipids", "b1-1-5-polysaccharides-as-energy-storage-compounds" ] }, { "Question": "
\n
\n

\n A group of students used quadrat sampling to gather data on the presence of two plant species in an area. They performed a chi-squared test to assess whether the distribution of the two species was associated. The calculated value of the chi-squared test was below the critical value. What can be deduced from the results of the chi-squared test?\n

\n

\n A. The alternative hypothesis is accepted.\n

\n

\n B. The distribution of one species is independent from the other.\n

\n

\n C. Both species are evenly distributed in the grassland ecosystem.\n

\n

\n D. The distribution of both species is correlated with abiotic factors.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "
\n

\n This apparently straightforward question did not discriminate as well as expected with many candidates opting for response A.\n

\n
\n", "question_id": "22M.1A.SL.TZ2.17", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-2-inheritance", "d3-2-21-use-of-a-chi-squared-test-on-data-from-dihybrid-crosses" ] }, { "Question": "
\n
\n

\n Outline a reason that the path length was standardized.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n compensates for the different distances between entrances and food/OWTTE;\n
\n \n \n OR\n \n \n
\n to enable (fair/valid) comparison/OWTTE;\n

\n

\n \n Do not accept unspecific answers such as ‘to be consistent’.\n \n

\n
\n", "Examiners report": "
\n

\n This was another question that tested candidates' ability to express a relatively simple idea clearly, rather than having to understand a more complicated idea. The key part of the answer was that standardizing path lengths allowed results to be compared to find the effect of the intended independent variable, by cancelling out another variable.\n

\n
\n", "question_id": "22N.2.HL.TZ0.J", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-1-integration-of-body-systems", "c3-1-4-the-brain-as-a-central-information-integration-organ" ] }, { "Question": "
\n
\n

\n Which statement applies to the placenta?\n
\n
\n

\n

\n A.  Carbon dioxide diffuses from fetus to mother across the placenta.\n

\n

\n B.  Maternal and fetal blood mix at the placenta.\n

\n

\n C.  If an ovum is not fertilized the placenta is lost during menstruation.\n

\n

\n D.  The umbilical cord connects the placenta to the mother’s abdomen.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "None", "question_id": "23M.1A.HL.TZ2.40", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-1-reproduction", "d3-1-18-role-of-the-placenta-in-foetal-development-inside-the-uterus" ] }, { "Question": "
\n
\n

\n The system of sex determination in chimpanzees (\n \n Pan troglodytes\n \n ) is the same as in other mammals. A chimpanzee has 48 chromosomes in the nuclei of its body cells.\n

\n

\n What can be deduced from this information?\n

\n

\n A. The sex of the chimpanzee\n

\n

\n B. The number of genes in each chromosome\n

\n

\n C. Whether non-disjunction has occurred\n

\n

\n D. The number of autosomes in a diploid cell\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "
\n

\n There were claims by some teachers that both C and D could be correct answers. The instruction to students should always be to choose the best of the available answers. This necessitates reading all four answers and not stopping after reaching an answer that on the surface looks correct. Here answer D is undoubtedly correct – if we know that chimpanzees have two sex chromosomes and that there are 48 chromosomes in the nuclei of a chimpanzee’s body cells, we can deduce the number of autosomes. 40 % of candidates chose this answer and the high discrimination index shows that it was favoured by the stronger candidates. Answer C is much less convincing than D – the stage at which non-disjunction might or might not have occurred isn’t specified so the deduction would be vague. Also, non-disjunction is diagnosed by looking at the chromosome types, not just the overall chromosome number.\n

\n
\n", "question_id": "19M.1A.SL.TZ1.13", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-2-inheritance", "d3-2-11-sex-determination-in-humans-and-inheritance-of-genes-on-sex-chromosomes" ] }, { "Question": "
\n
\n

\n The table contains information about the diet of some animals.\n

\n

\n \n

\n

\n Which pyramid of energy represents this information?\n

\n

\n \n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "22M.1A.SL.TZ1.18", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c4-2-transfers-of-energy-and-matter", "c4-2-11-construction-of-energy-pyramids" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Estimate the solute concentration of the zucchini cells.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n 0.36 mol dm\n \n -3\n \n /M ✔\n

\n

\n \n Units required\n \n
\n \n Allow a range of 0.35–0.37 mol dm\n \n -3\n \n /M\n \n .\n

\n
\n", "Examiners report": "None", "question_id": "19N.1B.SL.TZ0.3A", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-3-water-potential", "d2-3-3-water-movement-by-osmosis-into-or-out-of-cells", "d2-3-4-changes-due-to-water-movement-in-plant-tissue-bathed-in-hypotonic-and-those-bathed-in-hypertonic-solutions" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n State the effect of carbon dioxide in blood on the rate of ventilation.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n increased carbon dioxide in blood increases the rate of ventilation\n
\n \n \n OR\n \n \n
\n positive correlation/relationship;\n

\n
\n", "Examiners report": "
\n

\n Most candidates knew that CO\n \n 2\n \n affects the rate of ventilation, but some did not specify that an increase in CO\n \n 2\n \n caused an increase in ventilation rate, or vice versa.\n

\n
\n", "question_id": "20N.2.SL.TZ0.23C", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-1-integration-of-body-systems", "c3-1-15-feedback-control-of-ventilation-rate-following-sensory-input-from-chemoreceptors" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Draw the symbol for individual X on the diagram.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n \n

\n
\n", "Examiners report": "
\n

\n The majority of candidates managed to draw the correct symbol for a heterozygous female in the correct place in (a). However, there were a few who thought that X was male. Just over a half correctly gave 50\n \n \n \n \n % for (b). There were a large number of very pleasing answers in (c) to explain why the gene is not sex linked including that if it were sex linked, then you could not have a heterozygous male, and if it were sex linked, the daughter would have been heterozygous. The explanations in (d ) were not of such a high quality, with a large proportion failing to note that it hinges on the coding for a different amino acid, thus producing a different protein. Students should be careful about restating the stem as the 'protein changes' did not score as that was in the stem.\n

\n
\n", "question_id": "22N.2.SL.TZ0.4", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-2-inheritance", "d3-2-13-pedigree-charts-to-deduce-patterns-of-inheritance-of-genetic-disorders", "d3-2-12-haemophilia-as-an-example-of-a-sex-linked-genetic-disorder", "d1-2-protein-synthesis", "d1-2-11-mutations-that-change-protein-structure" ] }, { "Question": "
\n
\n

\n This DNA sequence was used to synthesize a polypeptide.\n

\n

\n DNA (sense strand): 3′ T A C T G A 5′\n

\n

\n DNA (template strand): 5′ A T G A C T 3′\n

\n

\n Which are the bases of the tRNA (anticodons)?\n

\n

\n A. T A C   T G A\n

\n

\n B. U A C   U G A\n

\n

\n C. A U G   A C U\n

\n

\n D. A T G   A C T\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "
\n

\n The discrimination index for this question was low, and as only 44 % answered correctly, the explanation was not that it was too easy. The question asked for the bases of the anticodons used to produce a polypeptide. They will be complementary to the DNA sense strand, because it will have the same base sequence (apart from T/U) as the codons of the mRNA that is translated into the polypeptide. B was almost as popular as the correct answer, but gives the codons, rather than the anticodons.\n

\n
\n", "question_id": "22M.1A.HL.TZ1.28", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d1-2-protein-synthesis", "d1-2-7-complementary-base-pairing-between-trna-and-mrna", "d1-1-dna-replication", "d1-1-6-directionality-of-dna-polymerases" ] }, { "Question": "
\n
\n

\n The ability to digest lactose in adulthood appeared due to a mutation in the lactase gene. The frequency of the lactase persistence allele was recorded as 0.8 in present-day European populations and as 0.05 in fossils from populations of their prehistoric ancestors.\n

\n

\n What could have caused the change in the allele frequency?\n

\n

\n
\n A.  Drinking more milk caused the mutation to occur.\n

\n

\n B.  There was a strong positive selection for the lactase persistence allele.\n

\n

\n C.  Lactase persistence was transferred to humans from cows.\n

\n

\n D.  Prehistoric milk did not contain lactose.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "23M.1A.HL.TZ1.16", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c4-2-transfers-of-energy-and-matter", "c4-2-4-construction-of-food-chains-and-food-webs-to-represent-feeding-relationships-in-a-community" ] }, { "Question": "
\n
\n

\n The image shows part of a section through the stem of a non-woody plant.\n

\n

\n \n

\n

\n [Source: © Ross Koning. Image used with the kind permission of the author.\n \n http://plantphys.info.]\n \n

\n

\n

\n

\n Which feature distinguishes the transport of materials in the tissue labelled I from that in the tissue labelled II?\n

\n

\n A. In II, active transport is used.\n

\n

\n B. In II, products of photosynthesis are transported.\n

\n

\n C. In I, movement of materials is the result of transpiration.\n

\n

\n D. In I, there is a higher solute concentration.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "19M.1A.HL.TZ1.33", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-2-transport", "b3-2-18-adaptations-of-phloem-sieve-tubes-and-companion-cells-for-translocation-of-sap" ] }, { "Question": "
\n
\n (a.i)\n
\n
\n

\n State\n \n one\n \n condition which would require the use of an artificial pacemaker.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n a. heartbeat too slow/fast/irregular/tachycardia/fibrillations ✔\n

\n

\n b. sinoatrial node is malfunctioning ✔\n

\n

\n c. pathway that conducts electrical impulses generated by the sinoatrial node is impaired ✔\n

\n

\n \n Do not accept heart attack\n \n

\n
\n", "Examiners report": "
\n

\n This was generally well answered, with a few students identifying generic (and incorrect) medical problems such as heart attacks and hypertension.\n

\n
\n", "question_id": "19M.2.HL.TZ1.21A.I", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-2-transport", "b3-2-15-adaptations-of-the-mammalian-heart-for-delivering-pressurized-blood-to-the-arteries", "b3-2-16-stages-in-the-cardiac-cycle" ] }, { "Question": "
\n
\n

\n \n Allium\n \n root tips continue to show some growth even at high concentrations of NVP. Suggest a possible reason for the growth seen in root tips with 800μmol NVP.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n a. still some mitosis ✔\n

\n

\n b. individual cells grow/elongate (expand by absorbing water) ✔\n

\n

\n c. NVP is not 100 % effective / does not enter all of the cells / not all cells have come in contact with NVP ✔\n

\n

\n d. roots have reached maximum saturation of NVP and are no longer functionally affected ✔\n

\n

\n e. some cells are resistant to the drug ✔\n

\n

\n \n Accept reasonable suggestions\n \n .\n

\n
\n", "Examiners report": "
\n

\n Most candidates earned this mark; some gave imaginative answers.\n

\n
\n", "question_id": "21M.2.HL.TZ1.D", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-1-cell-and-nuclear-division", "d2-1-13-phases-of-the-cell-cycle" ] }, { "Question": "
\n
\n

\n Chromosome numbers vary between species. Which statement refers to humans?\n

\n

\n A. An egg cell has 22 autosomes.\n

\n

\n B. A sperm cell has 23 autosomes.\n

\n

\n C. An egg cell has two X chromosomes.\n

\n

\n D. A zygote has two autosomes.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "
\n

\n This was another question that many candidates found too hard; less than 20 % answered correctly. The term autosome is included in sub-topic 3.2 of the program and an understanding of it was required in this question. That was not the only source of confusion though, as the most popular choice of answer - that a human egg cell has two X chromosomes — was clearly incorrect.\n

\n
\n", "question_id": "22M.1A.SL.TZ1.14", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-2-inheritance", "d3-2-1-production-of-haploid-gametes-in-parents-and-their-fusion-to-form-a-diploid-zygote-as-the-means-of-inheritance" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Explain the role of cells in the defence against infectious disease.\n

\n
\n
\n

\n [7]\n

\n
\n
\n", "Markscheme": "
\n

\n a. cells of skin provide a physical barrier/produce fatty acids/lactic acid/lysozyme which stops entry of microbes\n
\n \n \n OR\n \n \n
\n mucous membranes produce mucus to trap pathogens\n
\n \n \n OR\n \n \n
\n stomach cells produce hydrochloric acid which kills microbes;\n

\n

\n b. platelets start the clotting process preventing access of pathogens;\n

\n

\n c. (two types of) white blood cells fight infections in the body;\n

\n

\n d. phagocytes ingest pathogens (by endocytosis/phagocytosis);\n

\n

\n e. gives non-specific immunity to diseases / ingest any type of pathogen;\n

\n

\n f. production of antibodies by lymphocytes/B cells;\n

\n

\n g. in response to particular pathogens/antigens;\n

\n

\n h. gives specific immunity;\n

\n

\n i. lymphocyte/B cell makes only one type of antibody;\n

\n

\n j. plasma cells produce large quantity of (one type of) antibody;\n

\n

\n k. some lymphocytes act/remain as memory cells;\n

\n

\n l. can quickly reproduce to form a clone of plasma cells if a pathogen carrying a specific antigen is re-encountered;\n

\n

\n m. results in faster defence against second exposure to specific antigen/pathogen/disease;\n

\n
\n", "Examiners report": "
\n

\n In part (c), defence against infection was well known. Poor candidates lost marks by using loose, non-biological expressions such as the ‘white blood cells eat the infection/disease’. However, most had a fair idea of the cellular response to infection.\n

\n
\n", "question_id": "20N.2.SL.TZ0.6C", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-2-defence-against-disease", "c3-2-6-lymphocytes-as-cells-in-the-adaptive-immune-system-that-cooperate-to-produce-antibodies" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Suggest a suitable control for this experiment.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n using the same apparatus without a plant\n
\n \n \n OR\n \n \n
\n cover the whole plant with a plastic bag;\n

\n

\n \n Do not accept a controlled variable\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.1B.SL.TZ1.1C", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-1-enzymes-and-metabolism", "c1-1-8-effects-of-temperature-ph-and-substrate-concentration-on-the-rate-of-enzyme-activity" ] }, { "Question": "
\n
\n

\n The colours of the indicator in the jars ranged from yellow to purple after five hours.\n

\n

\n Predict the distribution of indicator colours in jars 1 to 9.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n the jars closer to the light had more purple colours\n
\n \n \n OR\n \n \n
\n the jar the furthest from the light was yellow\n
\n \n \n OR\n \n \n
\n purple to yellow\n

\n

\n \n Allow for answers indicating colours for each jar within this range\n \n .\n

\n
\n", "Examiners report": "
\n

\n Most candidates predicted the colour range accurately from purple to yellow; weaker candidates either inverted the range or did not include the extremes (\n \n e.g.\n \n purple to magenta), which were stated in the question stem.\n

\n
\n", "question_id": "20N.1B.SL.TZ0.B.I", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-3-photosynthesis", "c1-3-7-techniques-for-varying-concentrations-of-carbon-dioxide-light-intensity-or-temperature-experimentally-to-investigate-the-effects-of-limiting-factors-on-the-rate-of-photosynthesis" ] }, { "Question": "
\n
\n

\n Which feature of capillaries distinguishes them from arteries and veins?\n

\n

\n A. Narrow diameter\n

\n

\n B. Valves to prevent backflow\n

\n

\n C. Thick muscular walls\n

\n

\n D. Elastic tissue\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "None", "question_id": "19M.1A.SL.TZ1.26", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-2-transport", "b3-2-1-adaptations-of-capillaries-for-exchange-of-materials-between-blood-and-the-internal-or-external-environment", "b3-2-2-structure-of-arteries-and-veins" ] }, { "Question": "
\n
\n

\n What is an advantage of capillary walls being one cell thick in the systemic circulation?\n

\n

\n A. To allow carbon dioxide to diffuse into tissues\n

\n

\n B. To allow oxygen to diffuse out of tissues\n

\n

\n C. To allow glucose to diffuse into tissues\n

\n

\n D. To allow urea to diffuse into tissues\n

\n

\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "19M.1A.SL.TZ2.24", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-2-transport", "b3-2-1-adaptations-of-capillaries-for-exchange-of-materials-between-blood-and-the-internal-or-external-environment" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Calculate the percentage increase in the use of liquid fuels from 1950 to 1975.\n

\n

\n %\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n «\n \n \n \n \n \n (\n \n \n 2250\n \n \n −\n \n \n 300\n \n \n )\n \n \n ×\n \n \n 100\n \n \n \n 300\n \n \n \n \n = » 650 «%» ✔\n

\n
\n", "Examiners report": "
\n

\n A certain number provided reasonable answers considering the y-axis graduations, but too many had totally incorrect and unrealistic answers, showing that they could not calculate a percentage increase.\n

\n
\n", "question_id": "19M.2.SL.TZ2.3A", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c4-2-transfers-of-energy-and-matter", "c4-2-19-release-of-carbon-dioxide-into-the-atmosphere-during-combustion-of-biomass-peat-coal-oil-and-natural-gas" ] }, { "Question": "
\n
\n (a.i)\n
\n
\n

\n State the relationship between sloth body temperature and ambient temperature.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n body temperature increases with ambient temperature / positive correlation;\n

\n

\n \n Since direct can be either –/+, no credit for direct correlation alone.\n \n

\n
\n", "Examiners report": "
\n

\n Often steady or constant body temperatures for humans was given rather than homeostasis. Some candidates erroneously described humans as warming up in response to cold ambient temperatures.\n

\n
\n", "question_id": "22M.2.SL.TZ1.1", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-3-homeostasis", "d3-3-1-homeostasis-as-maintenance-of-the-internal-environment-of-an-organism", "d3-3-2-negative-feedback-loops-in-homeostasis" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n State the immediate consequence of a species producing more offspring than the environment can support.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n competition/lack of resources/death/exceeding carrying capacity ✔\n

\n

\n \n Allow a description of it.\n \n
\n \n Do not allow “overpopulation” or “natural selection”\n \n .\n

\n
\n", "Examiners report": "None", "question_id": "19N.2.SL.TZ0.4A", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-1-natural-selection", "d4-1-3-overproduction-of-offspring-and-competition-for-resources-as-factors-that-promote-natural-selection" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Identify the week and year in which the first cases were recorded in the suburbs.\n

\n

\n Week:\n

\n

\n Year:\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n week 34\n \n \n AND\n \n \n 2014 ✔\n

\n

\n \n both needed\n \n

\n
\n", "Examiners report": "
\n

\n This was a timely question with Ebola epidemics again causing great problems in parts of Africa. Students were expected to have had some practice at analysing data relating to an epidemic because of this Skill in the programme: Analysis of epidemiological data related to vaccination programmes. It was assumed that candidates would understand terms such as ‘case’, ‘fatal case’, ‘infect’ and ‘treat’.\n

\n

\n Nearly all candidates read from the graph the week and year in which the first cases were recorded in the suburbs.\n

\n
\n", "question_id": "19M.2.HL.TZ1.1A", "topics": [ "c-interaction-and-interdependence", "a-unity-and-diversity" ], "subtopics": [ "c3-2-defence-against-disease", "a2-3-viruses-(hl-only)" ] }, { "Question": "
\n
\n

\n By the end of the 19th century in England, the dark form of the moth\n \n Biston betularia\n \n formed up to 98\n \n \n \n \n % of the total population in industrial areas. From 1970, the percentage of dark forms decreased significantly. What is an explanation for the decrease?\n

\n

\n A.  An increase in environmental pollution killed the dark forms more than the light forms.\n

\n

\n B.  Reduction of pollution resulted in greater camouflage for light forms of the moth.\n

\n

\n C.  Dark forms could no longer find mates.\n

\n

\n D.  Light forms had superior feeding mechanisms.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "22N.1A.SL.TZ0.20", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-1-natural-selection", "d4-1-5-differences-between-individuals-in-adaptation-survival-and-reproduction-as-the-basis-for-natural-selection" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n State the trend in relative brain mass in primates other than humans according to their time of divergence from humans.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n the longer ago they diverged from humans, the greater the relative brain mass ✔\n

\n

\n \n Accept inverse.\n \n

\n

\n \n Do not accept negative correlation.\n \n

\n
\n", "Examiners report": "
\n

\n This question concerned how relative brain mass varied in primate evolution. Overall it was not well answered. The decreasing scale on the X-axis caused confusion for a lot of candidates in part (a).\n

\n
\n", "question_id": "19M.1B.SL.TZ2.5A", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-1-integration-of-body-systems", "c3-1-4-the-brain-as-a-central-information-integration-organ" ] }, { "Question": "
\n
\n (a.i)\n
\n
\n

\n On the diagrams, label with a letter H the hydrophilic end of a phospholipid.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n hydrophilic end of phospholipid shown ✔\n

\n

\n \n For 2a, i, ii and iii, accept letters written on the structure even if a line is not drawn.\n \n

\n

\n \n Award the mark if the full word is used to label the structure. Labels must be unambiguous.\n \n

\n
\n", "Examiners report": "
\n

\n There were numerous examples of ambiguous labels, for example, an H without an arrow placed beside the membrane making it unclear whether the student was indicating the hydrophobic or hydrophilic part of the membrane.\n

\n
\n", "question_id": "21M.2.HL.TZ2.2", "topics": [ "b-form-and-function", "c-interaction-and-interdependence" ], "subtopics": [ "b1-1-carbohydrates-and-lipids", "b1-1-12-formation-of-phospholipid-bilayers-as-a-consequence-of-the-hydrophobic-and-hydrophilic-regions", "b2-1-membranes-and-membrane-transport", "b2-1-13-membrane-fluidity-and-the-fusion-and-formation-of-vesicles", "c2-1-chemical-signalling-[hl-only]", "c2-1-5-localized-and-distant-effects-of-signalling-molecules", "c2-2-neural-signalling", "c2-2-6-release-of-neurotransmitters-from-a-presynaptic-membrane", "c2-2-7-generation-of-an-excitatory-postsynaptic-potential", "b1-2-proteins", "b1-2-5-effect-of-ph-and-temperature-on-protein-structure" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Outline how a protein is made in a cell by the process of translation.\n

\n
\n
\n

\n [5]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n translation occurs on ribosomes when proteins/polypeptides are synthesized;\n
    2. \n
  2. \n amino acid sequence of a protein is determined by the mRNA;\n
    3. \n
  3. \n mRNA is determined by the order of bases of DNA/order of bases sequence in a gene;\n
    4. \n
  4. \n codons (of 3 bases) on mRNA correspond to one amino acid in a polypeptide;\n
    5. \n
  5. \n codons are on mRNA and anticodons on tRNA;\n
    6. \n
  6. \n mRNA binds to ribosome/(during initiation) small ribosomal subunit binds to the start of the mRNA sequence;\n
    7. \n
  7. \n tRNA transfers an amino acid to large ribosomal subunit/to the ribosome;\n
    8. \n
  8. \n reference to start or stop codon;\n
    9. \n
  9. \n tRNA moves to the next mRNA codon to continue the process, creating an amino acid chain;\n
    10. \n
  10. \n peptide bond formed between amino acids\n
    11. \n
  11. \n translation/order of amino acids depends on complementary base pairing between codons and anticodons;\n
    12. \n
\n
\n", "Examiners report": "
\n

\n Well prepared candidates were able to clearly explain the production of a protein by translation. Weak candidates usually scored a few points. Many started with a very detailed description of transcription, which was not necessary and put them in danger of losing the quality mark.\n

\n
\n", "question_id": "22M.2.SL.TZ2.6", "topics": [ "d-continuity-and-change", "c-interaction-and-interdependence" ], "subtopics": [ "d1-2-protein-synthesis", "d1-2-5-translation-as-the-synthesis-of-polypeptides-from-mrna", "d3-2-inheritance", "d3-2-11-sex-determination-in-humans-and-inheritance-of-genes-on-sex-chromosomes", "d3-2-12-haemophilia-as-an-example-of-a-sex-linked-genetic-disorder", "c3-2-defence-against-disease", "c3-2-3-sealing-of-cuts-in-skin-by-blood-clotting" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Explain the consequence of overpopulation on the survival and reproduction of better adapted individuals within a population.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n a. «better adapted» tend to survive more ✔\n

\n

\n b. «better adapted» reproduce/produce more offspring ✔\n

\n

\n c. pass on characteristics to their offspring «when they reproduce» ✔\n

\n

\n d. their frequency increases «within the population» due to natural selection ✔\n

\n

\n e. leading to evolution ✔\n

\n
\n", "Examiners report": "None", "question_id": "19N.2.SL.TZ0.4B", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-1-natural-selection", "d4-1-3-overproduction-of-offspring-and-competition-for-resources-as-factors-that-promote-natural-selection" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Describe the functions of valves in the mammalian heart.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n

\n a. prevents backflow/ensures one-way flow/controls direction of flow ✔\n

\n

\n b.\n \n open\n \n valves allow blood to flow through\n
\n \n \n OR\n \n \n
\n opening and closing of valves controls timing of blood flow «during cardiac cycle» ✔\n

\n

\n c.\n \n closed\n \n «semilunar» valves allow ventricles/chambers to fill with blood\n
\n \n \n OR\n \n \n
\n \n closed\n \n «semilunar» valves allow pressure in ventricles to rise «rapidly» ✔\n

\n

\n d. valves open when\n \n pressure\n \n is higher upstream/\n \n OWTTE\n \n /converse for closed valves ✔\n

\n

\n e. AV/bicuspid/tricuspid/mitral valves prevent backflow from ventricle to atrium\n
\n \n \n OR\n \n \n
\n AV/bicuspid/tricuspid/mitral valves open when pressure in atrium is higher «than in the ventricle»/when atrium is pumping/contracting ✔\n

\n

\n f. semilunar/aortic/pulmonary valves prevent backflow from artery to ventricle\n
\n \n \n OR\n \n \n
\n semilunar/aortic/pulmonary valves open when pressure in ventricle is higher «than in the artery»/when ventricle is pumping/contracting ✔\n

\n

\n \n Allow mpa, mpb, mpc or mpd if the point is made through the example of one specific valve.\n \n

\n
\n", "Examiners report": "
\n

\n Most candidates got the general idea of valves in the heart preventing backflow, but many did not make any other valid points. A clear statement of what is achieved by valves opening and by valves closing was expected and then comments on the specific roles of the atrio-ventricular and the semi-lunar valves.\n

\n
\n", "question_id": "19M.2.HL.TZ1.6B", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-2-transport", "b3-2-15-adaptations-of-the-mammalian-heart-for-delivering-pressurized-blood-to-the-arteries" ] }, { "Question": "
\n
\n (d)\n
\n
\n

\n Using the data, deduce whether pretreatment with ultrasound is effective for hydrolysing proteins.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n it is not, as hydrolysis is higher without ultrasound pretreatment\n
\n \n \n OR\n \n \n
\n it is not, as hydrolysis is lower with ultrasound pretreatment;\n

\n

\n \n Do not accept numerical values only with no attempt to evaluate their importance.\n
\n \n

\n

\n \n Do not accept increase/decrease instead of lower/higher.\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.1B.SL.TZ2.2D", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-1-enzymes-and-metabolism", "c1-1-8-effects-of-temperature-ph-and-substrate-concentration-on-the-rate-of-enzyme-activity" ] }, { "Question": "
\n
\n

\n Which organism can best be described as a saprotroph?\n

\n

\n A. A fungus that digests its food externally and absorbs the products of digestion\n

\n

\n B. A beetle that feeds by ingesting the dung of other animal species and digesting its food internally\n

\n

\n C. A single-celled eukaryote that is able to photosynthesize and consumes smaller organisms by endocytosis\n

\n

\n D. A giraffe that feeds by ingesting leaves from an acacia tree\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "None", "question_id": "19M.1A.SL.TZ1.17", "topics": [ "b-form-and-function" ], "subtopics": [ "b4-2-ecological-niches", "b4-2-6-saprotrophic-nutrition-in-some-fungi-and-bacteria" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Sea urchins are destroying the giant kelp alga (\n \n Macrocystis pyrifera\n \n ) marine forests of South East Australia. Suggest a reason that sea urchins might be an invasive species in this environment.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n the sea urchins’ limiting factors in their original habitat are missing\n
\n \n \n OR\n \n \n
\n lack of (natural) predators for sea urchins\n

\n
\n", "Examiners report": "
\n

\n Many suggested that sea urchins' predators were not present, but too many irrelevant or blank answers were seen.\n

\n
\n", "question_id": "20N.2.SL.TZ0.15C", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a4-2-conservation-of-biodiversity", "a4-2-6-causes-of-the-current-biodiversity-crisis" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n The image shows human red blood cells.\n

\n

\n \n

\n

\n [Source: someoneice/123rf.com.]\n

\n

\n

\n

\n Outline what will happen to human red blood cells if transferred to distilled water.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n cells absorb water by\n \n osmosis\n \n and swell/increase in volume\n
\n \n OR\n \n
\n cells burst/lyse;\n

\n
\n", "Examiners report": "
\n

\n This was mostly well answered with candidates realising that water entry due to osmosis would cause the cells to burst.\n

\n
\n", "question_id": "21N.2.SL.TZ0.3A", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-3-water-potential", "d2-3-3-water-movement-by-osmosis-into-or-out-of-cells" ] }, { "Question": "
\n
\n (a.i)\n
\n
\n

\n State with a reason whether pangolins are autotrophic or heterotrophic.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n heterotrophic because it feeds on/eats food/other organisms /eats ants/termites/ doesn’t photosynthesise/does not produce its own food;\n

\n

\n \n Do not accept “it is not autotrophic” as it is part of the stem question.\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.2.HL.TZ2.4", "topics": [ "c-interaction-and-interdependence", "d-continuity-and-change" ], "subtopics": [ "c4-2-transfers-of-energy-and-matter", "c4-2-6-autotrophs-as-organisms-that-use-external-energy-sources-to-synthesize-carbon-compounds-from-simple-inorganic-substances", "c4-2-10-classification-of-organisms-into-trophic-levels", "d3-1-reproduction", "d3-1-18-role-of-the-placenta-in-foetal-development-inside-the-uterus", "d3-2-inheritance", "d3-2-1-production-of-haploid-gametes-in-parents-and-their-fusion-to-form-a-diploid-zygote-as-the-means-of-inheritance" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Outline the changes to chromosomes that occur during prophase in the first division of meiosis.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n pairing/synapsis of homologous chromosomes / homologous chromosomes form bivalents;\n
    2. \n
  2. \n crossing over / chromatid breaks then rejoins to non-sister chromatid;\n
    3. \n
  3. \n exchange of DNA/alleles/genetic information between chromatids/chromosomes;\n
    4. \n
  4. \n recombination / new combinations of alleles/genes generated;\n
    5. \n
  5. \n condensation/shortening/thickening/supercoiling of chromatids/chromosomes;\n
    6. \n
  6. \n formation of a chiasma where crossing over occurred;\n
    7. \n
\n
\n", "Examiners report": "None", "question_id": "23M.2.HL.TZ1.7", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-1-cell-and-nuclear-division", "d2-1-16-consequences-of-mutations-in-genes-that-control-the-cell-cycle", "d1-1-dna-replication", "d1-1-3-role-of-helicase-and-dna-polymerase-in-dna-replication", "d1-1-8-functions-of-dna-primase-dna-polymerase-i-dna-polymerase-iii-and-dna-ligase-in-replication", "d1-3-mutations-and-gene-editing", "d1-3-5-randomness-in-mutation" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Outline how the structures labelled X and Y are adapted to carry out the function of the mitochondrion.\n

\n

\n X:\n

\n

\n

\n

\n Y:\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n X: large/increased SA area for ATP production/electron transport/oxidative phosphorylation/proton pumping\n
\n \n \n OR\n \n \n
\n X: small/narrow intermembrane space for generating proton gradient (rapidly/steeply);\n

\n

\n Y: contains enzymes for Krebs cycle/link reaction;\n

\n
\n", "Examiners report": "
\n

\n The mean mark for this question was only 0.6 – less than half marks. Many students did not recognise they had to describe adaptations so, for example, the large surface area of the cristae or the small volume of the intermembrane space had to be included together with the function carried out. Weaker candidates had forgotten basic ideas of what happens in the mitochondrion.\n

\n
\n", "question_id": "20N.2.HL.TZ0.3", "topics": [ "b-form-and-function", "a-unity-and-diversity", "c-interaction-and-interdependence" ], "subtopics": [ "b2-2-organelles-and-compartmentalization", "b2-2-4-adaptations-of-the-mitochondrion-for-production-of-atp-by-aerobic-cell-respiration", "a2-2-cell-structure", "a2-2-10-cell-types-and-cell-structures-viewed-in-light-and-electron-micrographs", "c1-2-cell-respiration", "c1-2-15-chemiosmosis-and-the-synthesis-of-atp-in-the-mitochondrion" ] }, { "Question": "
\n
\n

\n Tall heterozygous pea plants were crossed and the resulting seeds grown. Out of 360 plants, 270 were tall and 90 dwarf. What describes the expected genotypes resulting from the cross?\n

\n

\n A. All 270 tall plants were heterozygous.\n

\n

\n B. All 270 tall plants were homozygous.\n

\n

\n C. Only 90 plants were homozygous.\n

\n

\n D. All dwarf plants were homozygous.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "20N.1A.SL.TZ0.14", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-2-inheritance", "d3-2-5-effects-of-dominant-and-recessive-alleles-on-phenotype" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Outline the extension of the stem in plants.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. apical meristem (of shoot/stem) produces cells/elongates the stem\n
\n \n OR\n \n
\n cell division/mitosis in tip/apex of shoot/stem;\n
\n b. auxin stimulates cell/stem growth/extension/enlargement;\n
\n c. elongation of cells causes stem to grow (in length);\n

\n
\n", "Examiners report": "
\n

\n Again, accounts were varied, with stronger ones clearly explaining how the shoot apical meristem generates cells by mitosis and how elongation of these cells, stimulated by auxin, causes stem elongation. Some candidates were side-tracked by phototropism but were able to score some marks from among irrelevant ideas.\n

\n
\n", "question_id": "21N.2.HL.TZ0.5C", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-1-integration-of-body-systems", "c3-1-21-promotion-of-cell-growth-by-auxin" ] }, { "Question": "
\n
\n

\n Evaluate the effect of the change in distribution of the different life stages of ticks on the spread of Lyme disease in south-eastern Canada.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n a.\n \n nymphs\n \n present through most of year/longer period/from March to November/through spring and summer «so more risk of infection» ✔\n

\n

\n b. more\n \n adults\n \n in winter/in January/February so more risk of infection then ✔\n

\n

\n c. infection will be possible through more/most months of/throughout the year ✔\n

\n

\n d. Lyme disease likely to/will increase ✔\n

\n
\n", "Examiners report": "None", "question_id": "19N.2.SL.TZ0.E", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a4-2-conservation-of-biodiversity" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n State the function of the tap and reservoir.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n to reset the potometer\n
\n \n \n OR\n \n \n
\n move the air column to the right/end\n
\n \n \n OR\n \n \n
\n to replace/replenish water in tube ✔\n

\n

\n \n Accept meniscus or air bubble as alternatives to column in all parts of question\n \n

\n
\n", "Examiners report": "
\n

\n All sections of this question revealed that students were unfamiliar with use and set-up of the potometer. This question was also commented on frequently by teachers in the G2 form who noted the absence of reservoirs in some of the potometers used in student labs. However, it was felt that students familiar with the working of any potometer could have used the information in the diagram to answer this question correctly.\n

\n
\n", "question_id": "19M.1B.SL.TZ1.2A", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-1-gas-exchange", "b3-1-9-transpiration-as-a-consequence-of-gas-exchange-in-a-leaf" ] }, { "Question": "
\n
\n

\n The chi-squared value was calculated as shown. Deduce, with reasons, whether the observed ratio differed significantly from the expected Mendelian ratio.\n

\n

\n \n \n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. yes/observed ratio did differ significantly «from the expected Mendelian ratio»\n
\n \n \n OR\n \n \n
\n expected ratio is 1:1:1:1 / 575 of each type / 25 % of each type ✔\n \n Correct ratio not needed in first alternative of mpa\n \n

\n

\n b. 3 degrees of freedom ✔\n

\n

\n c. critical value is 7.815 «at the 5 % level / 11.345 «at the 1 % level» ✔\n \n Accept mpc if candidates indicate the critical value of chi squared by circling it.\n \n

\n

\n d. chi-squared value «of 1002.6» exceeds the critical value ✔\n

\n

\n \n Allow other levels of significance as long as the critical value is correctly stated for the chosen level\n \n .\n

\n
\n", "Examiners report": "None", "question_id": "19N.2.HL.TZ0.C", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-2-inheritance", "d3-2-21-use-of-a-chi-squared-test-on-data-from-dihybrid-crosses" ] }, { "Question": "
\n
\n

\n The foxglove,\n \n Digitalis purpurea\n \n , was once classified in the figwort family. The figwort family has been reclassified and is now much smaller.\n

\n

\n \n

\n

\n [Source: Shiva A., 2008 [image online] Available at: https://en.wikipedia.org/wiki/File:Purple_Foxglove_(Digitalis_\n
\n purpurea)_2008_02.jpg [Accessed 14 January 2023] CC BY SA 4.0.\n

\n

\n Funhoff, D., 2017.\n \n Figwort (Scrophularia canina)\n \n flowers,\n \n Theisbergstegen, Pfalz, Germany\n \n . [image online]\n
\n Available at: https://www.naturepl.com/stock-photo/figwort-(scrophularia-canina)-flowers-theisbergstegen-pfalzgermany-june/search/detail-0_01550655.html [Accessed 28 October 2021].]\n

\n

\n

\n

\n Why were species such as the foxglove moved into other families?\n

\n

\n A.  The appearance was too dissimilar.\n

\n

\n B.  The plants are found in different locations.\n

\n

\n C.  The genera were different.\n

\n

\n D.  The DNA sequences indicated different ancestry.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "22N.1A.SL.TZ0.22", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a3-2-classification-and-cladistics-(hl-only)", "a3-2-8-using-cladistics-to-investigate-whether-the-classification-of-groups-corresponds-to-evolutionary-relationships" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Explain the relationship between temperature and the activity of enzymes.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n as temperature increases, the rate of molecular motion increases;\n
    2. \n
  2. \n increasing the frequency of collision between enzyme and substrate;\n
    3. \n
  3. \n increasing the rate of reaction;\n
    4. \n
  4. \n until an optimum temperature is reached;\n
    5. \n
  5. \n with further increase in temperature, enzymes denature;\n
    6. \n
\n
\n", "Examiners report": "None", "question_id": "SPM.2.SL.TZ0.8B", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-1-enzymes-and-metabolism", "c1-1-8-effects-of-temperature-ph-and-substrate-concentration-on-the-rate-of-enzyme-activity" ] }, { "Question": "
\n
\n (c.ii)\n
\n
\n

\n State the haploid number for this nucleus.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n 21\n

\n
\n", "Examiners report": "
\n

\n Slightly more than 50 % of candidates got this right. A common wrong answer was 42 – diploid number. There were a variety of other answers, some of which must have been guesses from candidates who did not understand the term haploid.\n

\n
\n", "question_id": "19M.2.SL.TZ1.2C.II", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-1-cell-and-nuclear-division", "d2-1-9-meiosis-as-a-reduction-division" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Explain how energy enters, flows through and is lost from marine food chains.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n a. light energy is converted to chemical energy (in carbon compounds/sugars) by\n \n photosynthesis\n \n ✔\n

\n

\n b. (chemical) energy (in carbon compounds) flows by means of feeding/through food chains/webs ✔\n

\n

\n c. only (approximately) 10 % of energy is passed to the next trophic level ✔\n

\n

\n d. energy released as heat (by respiration) ✔\n

\n

\n e. energy is not recycled ✔\n

\n

\n f. after death, energy may remain trapped as undigested detritus/fossils/fossil fuels ✔\n

\n
\n", "Examiners report": "
\n

\n In 4(a) most were able to state 'respiration' as the answer. 4(b) proved more difficult with fewer stating photosynthesis or absorption of dissolved CO\n \n 2\n \n or HCO\n \n 3\n \n from the seawater. Vague answers such as 'carbon in the water' were not credited. In 4(c) most knew that energy enters with sunlight, but did not state photosynthesis. They knew that it was transferred by feeding through the trophic levels and lost as heat due to respiration. A surprising number incorrectly stated that the energy was recycled and some drew diagrams of the energy flow showing this. In 4(d)(i) most were able to state that the crustacean was a richer source of carbon. An explanation using the data from the diagram was expected. In 4(d)(ii) most were able to present an argument for advantage or disadvantage.\n

\n
\n", "question_id": "21M.2.SL.TZ2.4C", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-3-climate-change", "d4-3-5-changes-in-ocean-currents-altering-the-timing-and-extent-of-nutrient-upwelling" ] }, { "Question": "
\n
\n

\n Determine the sequence of amino acids that could be translated from the sequence of mRNA.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n met-ser-arg-arg\n
\n \n \n OR\n \n \n
\n start-ser-arg-arg\n
\n \n \n OR\n \n \n
\n met-ser-arg-arg-stop\n
\n \n \n OR\n \n \n
\n start-ser-arg-arg-stop ✔\n

\n

\n \n Do not accept peptides containing an amino acid/leu for the last codon\n \n .\n

\n
\n", "Examiners report": "None", "question_id": "19N.2.SL.TZ0.B.I", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d1-2-protein-synthesis", "d1-2-9-using-the-genetic-code-expressed-as-a-table-of-mrna-codons" ] }, { "Question": "
\n
\n

\n The concentration of urea in blood plasma is typically about 30 mg per 100 ml. In urine it can be as high as 1800 mg per 100 ml. Explain how this increase in concentration is achieved.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n urea is toxic/ a (excretory) waste product removed from the body/ blood (plasma) by the kidneys/in the urine (to be excreted in the urine);\n
    2. \n
  2. \n urea filtered out from blood in glomerulus/Bowman’s capsule;\n
    3. \n
  3. \n water reabsorbed from filtrate (by osmosis);\n
    4. \n
  4. \n in proximal convoluted tubule/\n \n descending\n \n loop of Henle/collecting duct;\n
    5. \n
  5. \n loop of Henle maintains hypertonic conditions in the medulla;\n
    6. \n
  6. \n little/no urea reabsorbed from filtrate;\n
    7. \n
\n

\n

\n
\n", "Examiners report": "None", "question_id": "23M.2.HL.TZ2.D", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-3-homeostasis", "d3-3-7-role-of-the-kidney-in-osmoregulation-and-excretion" ] }, { "Question": "
\n
\n

\n Deduce the genotype of Queen Victoria’s daughter Alice.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n X\n \n H\n \n X\n \n h\n \n ;\n

\n
\n", "Examiners report": "
\n

\n Any symbols were accepted for the alleles, as long as they were shown superscript to X and the genotype was heterozygous. 70 % of candidates answered correctly.\n

\n
\n", "question_id": "21N.2.SL.TZ0.A.II", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-2-inheritance", "d3-2-12-haemophilia-as-an-example-of-a-sex-linked-genetic-disorder" ] }, { "Question": "
\n
\n

\n Identify the structure labelled X.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n ovule ✔\n

\n
\n", "Examiners report": "
\n

\n This question was derived from the skill of drawing half-views of animal pollinated flowers and the understanding of mutualistic relationships involved in plant reproduction. A large number could identify the ovule, but many incorrect answers, such as ovary, were also seen, as well as totally irrelevant answers.\n

\n
\n", "question_id": "19M.2.SL.TZ2.B.I", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-1-reproduction", "d3-1-9-features-of-an-insect-pollinated-flower" ] }, { "Question": "
\n
\n

\n Describe the distribution of\n \n C. montagui\n \n and\n \n S. balanoides\n \n barnacles in Butter Lump Bay.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. both species present throughout the range ✔\n

\n

\n b.\n \n C. montagui\n \n has small number of individuals «throughout»\n
\n \n \n OR\n \n \n \n
\n C.montagui\n \n occupies «mostly» upper shore/intertidal zone\n

\n

\n c.\n \n S. balanoides\n \n «mostly» occupies low tide area ✔\n
\n \n \n OR\n \n \n
\n \n S.balanoides\n \n has large number of individuals «throughout» ✔\n

\n

\n \n OWTTE referring to maximum numbers at specific heights.\n \n

\n
\n", "Examiners report": "
\n

\n Candidates were able to describe the distributions of the barnacles very well in part (b).\n

\n
\n", "question_id": "19M.1B.SL.TZ2.B", "topics": [ "b-form-and-function" ], "subtopics": [ "b4-1-adaptation-to-environment", "b4-1-4-range-of-tolerance-of-a-limiting-factor" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Evaluate the effect of salt on blood pressure using the data in the graph.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. systolic pressure increases with salt in diet during treatment;\n

\n

\n b. diastolic pressure is slightly higher/no change with salt during treatment\n
\n \n \n OR\n \n \n
\n diastolic pressure only changes towards the end of the period;\n

\n

\n c. (blood) pressure goes back to normal after treatment\n
\n \n \n OR\n \n \n
\n salt causes increased (blood) pressure;\n

\n

\n d. standard deviation values overlap therefore not statistically significant;\n

\n
\n", "Examiners report": "
\n

\n The majority could evaluate that salt increased blood pressure, most comparing the effect on systolic and diastolic blood pressure.\n

\n
\n", "question_id": "20N.2.SL.TZ0.22A", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-2-transport", "b3-2-3-adaptations-of-arteries-for-the-transport-of-blood-away-from-the-heart" ] }, { "Question": "
\n
\n

\n Suggest reasons for the differences in predation.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. the marmots have experience with/recognize predators ✔\n

\n

\n b. parents shield them from predators\n
\n \n \n OR\n \n \n
\n parents teach them about predators ✔\n

\n

\n c. those born in the wild are favoured in\n \n natural selection\n \n ✔\n

\n
\n", "Examiners report": "
\n

\n Most candidates were able to score at least 1 mark here by commenting on either the greater experience with predators for marmots in the wild, or the role of learning. However, some examiners noted that students tended to use anthropomorphisms when discussing animals in this option. Also, it was surprising that very few students were able to achieve the marking point that those born in the wild were favoured by natural selection, as natural selection is one of the central ideas in biology.\n

\n
\n", "question_id": "19M.2.SL.TZ1.A.II", "topics": [ "b-form-and-function" ], "subtopics": [ "b4-2-ecological-niches", "b4-2-10-adaptations-of-predators-for-finding-catching-and-killing-prey-and-of-prey-animals-for-resisting-predation" ] }, { "Question": "
\n
\n

\n The graph shows the blood levels of hormones associated with the menstrual cycle.\n

\n

\n \n

\n

\n [Source: By OpenStax College - Anatomy & Physiology, Connexions Web site.\n \n http://cnx.org/content/col11496/1.6/\n \n , Jun 19, 2013., CC BY 3.0 (\n \n https://creativecommons.org/licenses/by/3.0/\n \n ),\n \n https://commons.wikimedia.org/w/index.php?curid=30148641\n \n .]\n

\n

\n

\n

\n Which line on the graph represents progesterone?\n

\n

\n A. Line A\n

\n

\n B. Line B\n

\n

\n C. Line C\n

\n

\n D. Line D\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "21M.1A.SL.TZ1.28", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-1-reproduction", "d3-1-5-changes-during-the-ovarian-and-uterine-cycles-and-their-hormonal-regulation" ] }, { "Question": "
\n
\n

\n Based on the data, compare and contrast the progress of the epidemic in Liberia and Guinea.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n a. overall pattern similar in both/both show a rise and a fall in the infections ✔\n
\n
\n b. both countries show an increase during 2014\n
\n \n \n OR\n \n \n
\n neither country shows an increase in 2015 ✔\n

\n

\n c. both show a sudden drop at one point\n
\n \n \n OR\n \n \n
\n sudden drop earlier «Oct–Nov 14» in Liberia than in Guinea «Dec 14, Jan 15» ✔\n

\n

\n d. Guinea fluctuates whereas Liberia rises to a peak and then decreases/no fluctuations ✔\n

\n

\n e. epidemic starts earlier «in April 14» in Guinea than in Liberia «in June 14» ✔\n

\n

\n f. epidemic peaks earlier «Sept 14» in Liberia than in Guinea «Dec 14» ✔\n

\n

\n g. epidemic lasts longer in Guinea than it does in Liberia\n
\n \n \n OR\n \n \n
\n last case recorded in Liberia Feb 15 while cases continue «at least» until May 15 in Guinea ✔\n

\n

\n h. numbers of cases in Guinea generally lower than in Liberia\n
\n \n \n OR\n \n \n
\n number of cases higher in Liberia than in Guinea ✔\n

\n
\n", "Examiners report": "
\n

\n Data is described rather than interpreted\n \n e.g.\n \n epidemic starts in April for Guinea and in June for Liberia instead of epidemic starts earlier in Guinea than in Liberia\n

\n
\n", "question_id": "19M.2.HL.TZ1.D", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a2-3-viruses-(hl-only)" ] }, { "Question": "
\n
\n

\n Suggest\n \n two\n \n abiotic factors, other than temperature and nutrient supply, that may affect the production of biomass of the grasslands.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. water availability/rainfall/humidity;\n
\n b. light/sunlight (intensity) / daylength;\n
\n c. salinity of\n \n soil\n \n / high/low\n \n soil\n \n pH;\n
\n d. chemical pollution/herbicides/allelopathy/parasitic weeds;\n

\n

\n \n Mark the first two answers only\n \n .\n
\n \n Do not accept carbon dioxide or weather conditions\n \n .\n

\n
\n", "Examiners report": "
\n

\n About half of answers given were accepted. Carbon dioxide concentration was unlikely to vary enough to affect grassland biomass production. Vague answers such as ‘pH’ were not accepted but soil pH was.\n

\n
\n", "question_id": "21N.2.SL.TZ0.F", "topics": [ "d-continuity-and-change", "c-interaction-and-interdependence" ], "subtopics": [ "d4-2-stability-and-change", "d4-2-4-use-of-a-model-to-investigate-the-effect-of-variables-on-ecosystem-stability", "c1-3-photosynthesis", "c1-3-7-techniques-for-varying-concentrations-of-carbon-dioxide-light-intensity-or-temperature-experimentally-to-investigate-the-effects-of-limiting-factors-on-the-rate-of-photosynthesis" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Referring to the data, compare and contrast the changes in the use of the different fuels between 1950 and 1975.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n \n

\n

\n \n

\n

\n [Source: Boden T ; Marland G ; Andres R J (1999): Global, Regional, and National Fossil-Fuel CO2 Emissions (1751 - 2014) (V. 2017). Carbon Dioxide Information Analysis Center (CDIAC), Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States). doi:10.3334/ CDIAC/00001_V2017]\n

\n
\n", "Examiners report": "
\n

\n Most interpreted the graph correctly, but it was more difficult for some to include similarities, only focusing on differences. A certain number ignored to take only 1950 to 1975 into account, as specified in the question.\n

\n
\n", "question_id": "19M.2.SL.TZ2.3B", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c4-2-transfers-of-energy-and-matter", "c4-2-19-release-of-carbon-dioxide-into-the-atmosphere-during-combustion-of-biomass-peat-coal-oil-and-natural-gas" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Explain how ventilation and lung structure contribute to passive gas exchange.\n

\n
\n
\n

\n [7]\n

\n
\n
\n", "Markscheme": "
\n

\n a. air carried through trachea\n \n \n AND\n \n \n bronchi/bronchioles\n \n \n AND\n \n \n alveoli ✔\n \n All three required in correct order.\n \n

\n

\n b. alveoli increase the surface area/thin walled for gas exchange ✔\n

\n

\n c. gas exchange carried out through type I pneumocytes ✔\n

\n

\n d. type II pneumocytes secrete surfactant to reduce surface tension ✔\n

\n

\n e. moist surface/surfactant allows gases to diffuse in solution ✔\n

\n

\n f. ventilation/moving blood maintains concentration gradients of oxygen and carbon dioxide ✔\n

\n

\n g. between air in alveoli and blood in «adjacent» capillaries\n
\n \n \n OR\n \n \n
\n oxygen diffuses from alveoli to capillaries and carbon dioxide from capillaries to alveoli ✔\n \n OWTTE\n \n

\n

\n h.\n \n external\n \n intercostal muscles/\n \n diaphragm\n \n contract during inspiration ✔\n

\n

\n i. lowering air pressure «in lungs»/increasing thorax volume ✔\n

\n

\n j. relaxation of external intercostal muscles/diaphragm enable «passive» expiration ✔\n

\n

\n k.\n \n internal\n \n intercostal «and abdominal muscles» contract «to force» expiration ✔\n

\n

\n l. expiration due to increasing air pressure «in lungs»/decreasing thorax volume ✔\n

\n

\n \n Accept correctly annotated diagram\n \n .\n

\n
\n", "Examiners report": "None", "question_id": "19N.2.SL.TZ0.6C", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-1-gas-exchange", "b3-1-4-adaptations-of-mammalian-lungs-for-gas-exchange" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Describe how the changes in world rock phosphate production after 1985 may have affected world food supplies.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. phosphorus is important as a fertilizer ✔\n

\n

\n b. a drop in phosphate could lead to less agricultural output ✔\n

\n

\n c. «this could mean» less food available for increasing population ✔\n

\n
\n", "Examiners report": "
\n

\n Students who struggled to read the graph correctly had problems with this question. Very few scored the full marks here, as only a small number of students clearly stated that rock phosphates were used as fertilisers to increase plant growth. Few students composed coherent answers that tied together fertiliser use, agricultural output and food.\n

\n
\n", "question_id": "19M.2.SL.TZ1.14C", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-2-stability-and-change", "d4-2-6-assessing-sustainability-of-resource-harvesting-from-natural-ecosystems" ] }, { "Question": "
\n
\n

\n Suggest a reason for using a lower power objective lens when first focusing on a slide under the microscope.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n it is easier to find the specimen using a low power objective lens\n
    \n \n \n OR\n \n \n
    \n there is a larger field of view/depth of focus;\n
    2. \n
  2. \n it is easier to locate the most interesting part of the specimen with a low power objective lens;\n
    3. \n
  3. \n most microscopes are calibrated so that once in focus using the low power objective lens they will be close    to focus using the higher power, so this helps focusing;\n
    4. \n
  4. \n reduced risk of cracking the slide;\n
    5. \n
\n
\n", "Examiners report": "None", "question_id": "SPM.1B.SL.TZ0.C", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a2-2-cell-structure", "a2-2-2-microscopy-skills" ] }, { "Question": "
\n
\n

\n Explain the heart sounds.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n a. «heart sounds» produced by the closing of the valves ✔\n

\n

\n b. first sound «lub» is due to «closure of» the atrioventricular valves ✔\n \n Accept bicuspid/mitral and tricuspid\n \n .\n

\n

\n c. second sound «dub» is due to «closure of» the semilunar valves ✔\n \n Accept pulmonary/aortic valves\n \n .\n

\n

\n d. sequence of sounds from a healthy heart is lub dub «pause lub dub pause» ✔\n \n OWTTE\n \n

\n
\n", "Examiners report": "None", "question_id": "19N.1B.HL.TZ0.C", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-2-transport", "b3-2-16-stages-in-the-cardiac-cycle" ] }, { "Question": "
\n
\n

\n Explain how ATP is generated in mitochondria by chemiosmosis.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n

\n a. protons pumped across inner membrane of mitochondria/into intermembrane space;\n

\n

\n b. using energy released by flow of electrons/by electron transport/by electron carriers;\n

\n

\n c. proton gradient established/maintained / proton motive force generated;\n

\n

\n d. protons pass/diffuse back through inner membrane/membrane of cristae/to matrix;\n

\n

\n e. through\n \n ATP synthase\n \n ;\n

\n

\n f. ATP production coupled to flow of protons / ATP from ADP and Pi using energy from protons;\n

\n

\n \n Marks can be awarded in an annotated diagram\n \n .\n

\n
\n", "Examiners report": "
\n

\n This was answered more successfully by most candidates and there were some impressively detailed and accurate answers.\n

\n
\n", "question_id": "20N.2.HL.TZ0.B", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-2-cell-respiration", "c1-2-15-chemiosmosis-and-the-synthesis-of-atp-in-the-mitochondrion" ] }, { "Question": "
\n
\n

\n Using the data in the violin plots, deduce the age range at which children are most likely to develop ARI due to\n \n S. pneumoniae\n \n .\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n 2 – 5\n \n years\n \n ;\n
    2. \n
  2. \n higher number/value/percentage/attributable fraction for 2 – 5 years (than 0 – 5years);\n
    3. \n
\n

\n

\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ2.F", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-2-defence-against-disease", "c3-2-16-vaccines-and-immunization" ] }, { "Question": "
\n
\n (g)\n
\n
\n

\n Discuss\n \n one\n \n advantage and\n \n one\n \n disadvantage of using plant tissue to investigate drugs intended to treat cancer in humans.\n

\n

\n Advantage:\n

\n

\n

\n

\n Disadvantage:\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n \n Advantage\n \n :\n

\n

\n avoids risks for humans/harm to humans / more ethical (than with human patients/volunteers) ✔\n

\n

\n \n Disadvantage\n \n :\n

\n

\n differences between plant and human cells so humans may not respond in same way\n
\n \n \n OR\n \n \n
\n plants have cell wall/no centrioles/other relevant difference between plant and human cells ✔\n

\n

\n \n Not enough for mpa to say ‘not using humans’.\n \n

\n

\n \n For mpb there must be either a statement that differences between cells may cause a different response, or a specific example of a cell difference\n \n .\n

\n
\n", "Examiners report": "
\n

\n Most candidates were able to suggest an advantage of using plant tissue and any reasonable answer was accepted. Fewer gave a disadvantage that was credited. Vague answers such as plants are different from humans were not rewarded with a mark.\n

\n
\n", "question_id": "21M.2.HL.TZ1.1G", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-1-cell-and-nuclear-division", "d2-1-17-differences-between-tumours-in-rates-of-cell-division-and-growth-and-in-the-capacity-for-metastasis-and-invasion-of-neighbouring-tissue" ] }, { "Question": "
\n
\n

\n Explain\n \n one\n \n reason for calculating the percentage change in mass.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. the change in mass indicates whether the tissue has gained/lost water ✔\n

\n

\n b. the pieces of tissue will not be the same mass «at the beginning of the experiment» ✔\n

\n

\n c. to compare the relative changes in mass ✔\n

\n
\n", "Examiners report": "None", "question_id": "19N.1B.SL.TZ0.D", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-3-water-potential", "d2-3-3-water-movement-by-osmosis-into-or-out-of-cells", "d2-3-4-changes-due-to-water-movement-in-plant-tissue-bathed-in-hypotonic-and-those-bathed-in-hypertonic-solutions" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Outline the steps to produce a 10 % egg white solution.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n measure 10 g/parts egg whites;\n
    2. \n
  2. \n add to 90 g/parts of water;\n
    3. \n
\n

\n \n Accept use of volume instead of mass.\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.1B.SL.TZ2.2B", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-1-enzymes-and-metabolism", "c1-1-8-effects-of-temperature-ph-and-substrate-concentration-on-the-rate-of-enzyme-activity" ] }, { "Question": "
\n
\n

\n Female grasshoppers have XX sex chromosomes and males have XO, signifying a single X chromosome. An X chromosome will be present in only half of the male gametes. A recessive mutation is induced by radiation in the X chromosome of a male. In which generation will the effect of this radiation appear?\n

\n

\n
\n A.  F1 females\n

\n

\n B.  F1 males\n

\n

\n C.  F2 females\n

\n

\n D.  F2 males\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "SPM.1A.HL.TZ0.31", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-2-inheritance", "d3-2-2-methods-for-conducting-genetic-crosses-in-flowering-plants" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Identify, with a reason, the sex of this individual.\n

\n

\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n male because Y chromosome present\n
\n \n \n OR\n \n \n
\n male because sex chromosomes/last two chromosomes/pair 23 are unpaired/different «from each other»/not homologous ✔\n

\n
\n", "Examiners report": "
\n

\n Candidates knew this!\n

\n
\n", "question_id": "19M.2.SL.TZ1.6", "topics": [ "a-unity-and-diversity", "d-continuity-and-change" ], "subtopics": [ "a3-1-diversity-of-organisms", "a3-1-7-karyotyping-and-karyograms", "d2-1-cell-and-nuclear-division", "d2-1-10-down-syndrome-and-non-disjunction" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Describe how DNA profiling can be used to establish paternity.\n

\n
\n
\n

\n [5]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n DNA sample is collected from the child and its (potential) parents;\n
    2. \n
  2. \n from saliva/mouth swab/blood/other body cells;\n
    3. \n
  3. \n PCR used to amplify/produce more copies of the DNA;\n
    4. \n
  4. \n short tandem repeats/genes consisting of a repeating sequence of bases repeats copied/used;\n
    5. \n
  5. \n number of repeats varies between individuals;\n
    6. \n
  6. \n unlikely that two individuals have same number of repeats for every gene included;\n
    7. \n
  7. \n gel electrophoresis used to separate DNA fragments according to length/number of repeats;\n
    8. \n
  8. \n gel electrophoresis generates a unique pattern of bands\n
    9. \n
  9. \n DNA profile is the pattern of bands / diagram showing pattern of bands as in a DNA profile;\n
    10. \n
  10. \n all bands in the child’s profile must be in one of the parents’ profiles / OWTTE;\n
    11. \n
\n
\n", "Examiners report": "
\n

\n Answers to this question were very variable, with some very well-informed accounts including the use of genes containing of tandem repeats and details of the collection of DNA samples from both parents and the child. There were also many accounts with errors of understanding. A common misconception is that paternity is established by finding the male whose profile has most similarities to that of the child. This does not prove that a man is the father of the child and instead the father's profile must contain all bands in the child's profile that do not occur in that of the mother.\n

\n
\n", "question_id": "22M.2.SL.TZ1.8B", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d1-1-dna-replication", "d1-1-5-applications-of-polymerase-chain-reaction-and-gel-electrophoresis" ] }, { "Question": "
\n
\n (e)\n
\n
\n

\n By referring to both graphs, evaluate the hypothesis that vinblastine targets cells in mitosis and prevents them from completing the process.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n \n Evaluation of evidence in graph on left\n \n

\n

\n a. increase in (percentage of) cells in mitosis (as vinblastine concentration rises) ✔\n

\n

\n b. supports hypothesis that cells get stuck in/cannot complete mitosis ✔\n

\n

\n \n Evaluation of evidence in graph on right\n \n

\n

\n c. drop in anaphase-metaphase ratio due to fewer cells in anaphase/more cells in metaphase ✔\n

\n

\n d. cells not progressing from metaphase to anaphase/get stuck in metaphase ✔\n

\n

\n \n Do not allow mpa if the candidate is arguing that the hypothesis is not supported\n \n .\n

\n
\n", "Examiners report": "
\n

\n This was another challenging data-analysis task with marks spread across the whole range, but full marks were rarely awarded. Many candidates thought that a rise in mitotic index had to mean that more cells were entering mitosis and they failed to deduce from the drop to zero of the anaphase-metaphase ratio that cells were getting stuck in metaphase. As in (d), it was necessary both to understand how cells progress through the cell cycle and be able to make deductions from trends in quantitative data.\n

\n
\n", "question_id": "21M.1B.SL.TZ1.1E", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-1-cell-and-nuclear-division", "d2-1-1-generation-of-new-cells-in-living-organisms-by-cell-division" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n State the reason that\n \n O. sativa\n \n and\n \n O. rufipogon\n \n are classified as different species.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n cannot interbreed to produce\n \n fertile\n \n offspring ✔\n

\n

\n \n Accept converse or a good explanation\n \n .\n

\n
\n", "Examiners report": "None", "question_id": "19N.2.SL.TZ0.1A", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a3-1-diversity-of-organisms" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Autosomal genes are located in chromosomes that are not sex chromosomes. The inheritance of autosomal genes is affected by whether the genes are linked or unlinked. Explain the\n \n two\n \n types of inheritance, using the example of parents that are heterozygous for two genes A and B.\n

\n
\n
\n

\n [7]\n

\n
\n
\n", "Markscheme": "
\n

\n a. unlinked genes are on different chromosomes / vice versa ✔\n

\n

\n b. unlinked alleles migrate/segregate/are inherited independently (during meiosis) / vice versa ✔\n

\n

\n c. (In unlinked inheritance) there is an equal chance for all 4 options to occur / AB, Ab, aB, ab / vice versa ✔\n

\n

\n d. (dihybrid crosses involving) linked genes do not produce Mendelian ratios ✔\n

\n

\n e. (excluding recombinants) there is a 1:1 chance of inheriting the different options/AB or ab ✔\n

\n

\n f. in linked characteristics alleles might not migrate together if there is crossing over/ recombinants are formed ✔\n

\n

\n g. crossing over occurs in prophase I of meiosis ✔\n

\n

\n h. when the sister chromatids migrate in meiosis II the characteristics forming gametes are different/Ab, aB ✔\n

\n

\n i. formation of recombinants causes changes in ratio/probability of inheritance/genetic variation ✔\n

\n

\n j. correct named example of inheritance of linked/unlinked characteristics ✔\n

\n

\n k. Punnett/paired diagrams of both unlinked and linked characteristics ✔\n

\n

\n l. genes which are linked but are far apart on the chromosome can display independent assortment ✔\n

\n

\n \n Mp a could be awarded from an annotated diagram\n \n .\n

\n

\n \n Allow annotated diagram of inheritance / could be shown in a Punnett square\n \n .\n

\n

\n \n Allow annotated diagram of linked inheritance for mp f\n \n .\n

\n

\n \n For mp K, accept sex linked examples involving two genes\n \n .\n

\n

\n \n If the student interprets the question as sex-linked and autosomal inheritance, look for WTTE marks from the scheme\n \n .\n

\n
\n", "Examiners report": "
\n

\n Question 5 was not a popular question choice. Few candidates performed well on this question overall. Many students wrote vaguely about dominant and recessive alleles or confused gene linkage with \"sex-linkage\" or even multiple alleles and blood groups.\n

\n
\n", "question_id": "21M.2.HL.TZ2.5", "topics": [ "d-continuity-and-change", "a-unity-and-diversity" ], "subtopics": [ "d3-2-inheritance", "d3-2-3-genotype-as-the-combination-of-alleles-inherited-by-an-organism", "d3-2-10-incomplete-dominance-and-codominance", "d3-1-reproduction", "d3-1-14-spermatogenesis-and-oogenesis-in-humans", "a2-2-cell-structure", "a2-2-5-prokaryote-cell-structure", "a2-2-6-eukaryote-cell-structure" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Draw a molecular diagram to show the formation of a peptide bond.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n a.\n \n two\n \n amino acids correctly drawn;\n

\n

\n b. removal/production of H\n \n 2\n \n O molecule shown;\n

\n

\n c. peptide bond labelled between C of C=O and N of N-H;\n

\n

\n \n

\n

\n \n Accept specific examples of amino acids correctly drawn for example glycine with H instead of R.\n \n

\n

\n \n mpc can be awarded if the peptide bond is shown as in the dipeptide diagram but there are errors elsewhere\n \n .\n

\n
\n", "Examiners report": "
\n

\n Mostly full marks were gained although some had the correct diagrams but failed to label the peptide bond.\n

\n
\n", "question_id": "20N.2.SL.TZ0.6A", "topics": [ "b-form-and-function" ], "subtopics": [ "b1-2-proteins", "b1-2-2-condensation-reactions-forming-dipeptides-and-longer-chains-of-amino-acids" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Outline the structures in\n \n M. tuberculosis\n \n that are not present in a human cell.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n a. cell wall ✔\n

\n

\n b. pili/flagella ✔\n

\n

\n c. 70S ribosomes ✔\n

\n

\n d. nucleoid / circular DNA\n
\n \n \n OR\n \n \n
\n naked DNA ✔\n

\n

\n e. plasmids ✔\n

\n

\n \n As candidates do not need to know the structure of Mycobacterium tuberculosis, all prokaryotic structures are accepted\n \n .\n

\n

\n \n Ignore references to membrane bound\n \n \n organelles\n \n .\n

\n
\n", "Examiners report": "
\n

\n (attempted by about 60 % of the cohort)\n

\n

\n Part (a) was a departure from the 'draw a prokaryote' type of question that has appeared numerous times. In general, it was well answered. There were some good diagrams as answers which clearly showed only the prokaryotic characteristics. Part (b) asked for an explanation of the production of antibodies. Many weaker students wrote at length about non-specific phagocytosis which was not credited. Weaker students confused antibodies and antigens and even talked about antibiotics. This question was designed to be answered by the Standard Level students using Standard Level material. Some tried to include HL material and became very confused. Part (c) was really a question about Darwin's theory of evolution set in context. Many of the answers were very Lamarckian with the antibiotic causing the mutation, instead of some bacteria already having resistance. Better students opened with comments and an explanation that antibiotics only kill bacteria.\n

\n
\n", "question_id": "21M.2.SL.TZ2.6", "topics": [ "a-unity-and-diversity", "c-interaction-and-interdependence" ], "subtopics": [ "a2-2-cell-structure", "a2-2-5-prokaryote-cell-structure", "a2-2-10-cell-types-and-cell-structures-viewed-in-light-and-electron-micrographs", "c3-2-defence-against-disease", "c3-2-6-lymphocytes-as-cells-in-the-adaptive-immune-system-that-cooperate-to-produce-antibodies", "c3-2-10-immunity-as-a-consequence-of-retaining-memory-cells", "c3-2-14-evolution-of-resistance-to-several-antibiotics-in-strains-of-pathogenic-bacteria" ] }, { "Question": "
\n
\n (a.i)\n
\n
\n

\n Identify the country with the largest number of Ebola cases.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n Sierra Leone ✔\n

\n
\n", "Examiners report": "
\n

\n This set of data-based questions produced the best showing among candidates. Teachers are to be commended for developing these skills in their students. Many candidates showed confidence in looking at unfamiliar data and formulating answers. Some weaknesses included not being careful with what they were writing when there were similar aspects in the data set (total population size and population density), comparing and contrasting - many students finding this difficult and simply writing descriptions of the data set rather than focussing on similarities and differences. Also giving information on part of a data set where some aspects of the data set may be similar in name but fundamentally different (e.g. Total population and population density) – Some candidates used incorrect parts of data sets rather than those that had been asked about - for example, talking about Ebola cases rather than Ebola deaths, total population size rather than population density.\n

\n
\n", "question_id": "19M.2.HL.TZ1.1A.I", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a2-3-viruses-(hl-only)" ] }, { "Question": "
\n
\n

\n The diagram shows protein channels involved in the passive movement of a substance into the cell across the cell membrane.\n

\n

\n \n

\n

\n

\n

\n

\n

\n What describes this movement?\n
\n
\n

\n

\n A.  Energy of ATP is used to transport substances into the cell.\n

\n

\n B.  Substances can move from areas of low to areas of high concentration.\n

\n

\n C.  The proteins ensure that movement of substances is only in one direction.\n

\n

\n D.  Net movement occurs until the concentrations in and out of the cell are equal.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "23M.1A.SL.TZ2.4", "topics": [ "b-form-and-function" ], "subtopics": [ "b2-1-membranes-and-membrane-transport", "b2-1-4-integral-and-peripheral-proteins-in-membranes" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Outline the process of inspiration in humans.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n

\n a.\n \n diaphragm\n \n and\n \n external intercostal\n \n muscles\n \n contract\n \n ✔\n

\n

\n b.\n \n diaphragm\n \n moves down/becomes flatter\n
\n \n \n OR\n \n \n
\n \n external intercostals\n \n raise the ribcage/move the ribcage up/out ✔\n

\n

\n c. muscles/diaphragm/intercostals increase volume of thorax/expand the thorax\n
\n \n \n OR\n \n \n
\n muscles/diaphragm/intercostals decrease pressure in the thorax ✔\n

\n

\n d. as volume «of thorax/lungs» increases the pressure decreases ✔\n

\n

\n e. air enters «lungs» due to decreased pressure/higher pressure outside body ✔\n

\n

\n f.\n \n air\n \n flows to lungs through trachea and bronchi/bronchioles ✔\n

\n

\n \n Accept thoracic cavity or chest cavity in place of thorax in any part of the answer.\n \n

\n

\n \n Do not allow “oxygen” instead of air in mpe or mpf.\n \n

\n
\n", "Examiners report": "
\n

\n The mechanisms used to cause ventilation of the lungs are poorly understood by many candidates, despite them being used throughout our lives. Cause and effect are often confused – air rushes in to cause a volume increase in the lungs for example.\n

\n
\n", "question_id": "19M.2.HL.TZ1.6", "topics": [ "b-form-and-function", "d-continuity-and-change" ], "subtopics": [ "b3-1-gas-exchange", "b3-1-5-ventilation-of-the-lungs", "b3-2-transport", "b3-2-15-adaptations-of-the-mammalian-heart-for-delivering-pressurized-blood-to-the-arteries", "d3-3-homeostasis", "d3-3-7-role-of-the-kidney-in-osmoregulation-and-excretion" ] }, { "Question": "
\n
\n

\n Which is the hierarchy of taxa in order of increasing numbers of species?\n

\n

\n A. genus, family, order, class\n

\n

\n B. class, order, genus, family\n

\n

\n C. genus, family, class, order\n

\n

\n D. class, order, family, genus\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "None", "question_id": "19M.1A.HL.TZ2.28", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a3-2-classification-and-cladistics-(hl-only)", "a3-2-1-need-for-classification-of-organisms" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Analysis of the data suggests that the number of deaths from EVD is not related to the total population size. State\n \n one\n \n piece of evidence from the data that would support this analysis.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n country with biggest population/Mali has lowest number of deaths\n
\n \n \n OR\n \n \n
\n country with smallest population/Liberia has biggest number of deaths ✔\n

\n

\n \n OWTTE\n \n

\n
\n", "Examiners report": "None", "question_id": "19M.2.HL.TZ1.1B", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a2-3-viruses-(hl-only)" ] }, { "Question": "
\n
\n

\n In 1925, Gorter and Grendel carried out an experiment to study the structure of cell membranes in different mammals. The total surface area of red blood cells was measured in a sample and compared to the surface area formed by a single layer of lipid extracted from cell membranes and floated on water.\n

\n

\n \n

\n

\n Which diagram best illustrates Gorter and Grendel’s conclusion drawn from this experiment?\n

\n

\n \n

\n

\n [Source: Gorter, E. and Grendel, F., 1925. On bimolecular layers of lipoids on the chromocytes of the blood.\n \n Journal of Experimental Medicine\n \n 41(4), pp. 439–443.]\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "
\n

\n This question was on the work of Gorter and Grendel in determining the structure of the cell membrane. The data shows that the surface area of membrane in red blood cells is half the surface area of extracted lipids suggesting there is a lipid bilayer making response C correct. It was commented that this was beyond the scope of the syllabus but in setting the question it was considered that there was enough evidence in the data for students to conclude a bilayer was present. No conclusion could be drawn from the data about proteins, ruling out answers A and D. The question discriminated rather poorly with most students opting for response A.\n

\n
\n", "question_id": "22N.1A.SL.TZ0.5", "topics": [], "subtopics": [] }, { "Question": "
\n
\n

\n Which process results in the exchange of gases across the membrane of pneumocytes?\n

\n

\n A. Active transport\n

\n

\n B. Simple diffusion\n

\n

\n C. Facilitated diffusion\n

\n

\n D. Mass flow\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "21M.1A.HL.TZ1.21", "topics": [ "b-form-and-function" ], "subtopics": [ "b2-3-cell-specialization", "b2-3-8-adaptations-of-type-i-and-type-ii-pneumocytes-in-alveoli" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Outline the roles of helicase and ligase in DNA replication.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n

\n \n helicase\n \n :\n

\n

\n a. unwinds/uncoils the DNA «double helix» ✔\n

\n

\n b. breaks hydrogen bonds «between bases» ✔\n

\n

\n c. separates the «two» strands/unzips the DNA/creates replication fork ✔\n

\n

\n \n ligase\n \n :\n

\n

\n d. seals nicks/forms a continuous «sugar-phosphate» backbone/strand ✔\n

\n

\n e. makes sugar-phosphate bonds/covalent bonds between adjacent nucleotides ✔\n

\n

\n f. after «RNA» primers are removed/where an «RNA» primer was replaced by DNA ✔\n

\n

\n g. «helps to» join Okazaki fragments ✔\n

\n
\n", "Examiners report": "
\n

\n This was generally well answered, with most candidates knowing at least something of the roles of these two enzymes. Most candidates knew that ligase connects Okazaki fragments but some claimed that it creates hydrogen bonds between nucleotides on template and the new strand. Many candidates did not distinguish between unwinding of DNA and separating the strands. Two details that should be more widely known are that helicase separates the two strands of a DNA molecule by encouraging the breakage of hydrogen bonds between bases and that ligase seals nicks by making sugar phosphate bonds.\n

\n
\n", "question_id": "19M.2.HL.TZ1.7", "topics": [ "d-continuity-and-change", "a-unity-and-diversity" ], "subtopics": [ "d1-1-dna-replication", "d1-1-3-role-of-helicase-and-dna-polymerase-in-dna-replication", "a4-1-evolution-and-speciation", "a4-1-6-speciation-by-splitting-of-pre-existing-species" ] }, { "Question": "
\n
\n

\n Suggest a reason for the effect of a diet reduced in acetylcholine on the larval survival rate.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n (larvae lacking acetylcholine/with reduced AcH cannot survive because) acetylcholine is a neurotransmitter taking message from one neuron to another in synapses of nervous tissues\n
\n \n \n OR\n \n \n
\n messages would not pass from one neuron to the other\n
\n \n \n OR\n \n \n
\n (larvae) unable to synthesise/produce AcH, so need it from their diet ✔\n

\n

\n \n OWTTE\n \n .\n

\n
\n", "Examiners report": "
\n

\n In general, the data analysis question was well attempted by the majority of students.\n

\n

\n At least half of the candidates did not know that acetylcholine is a neurotransmitter (section 6.5).\n

\n
\n", "question_id": "21M.2.HL.TZ2.E", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c2-2-neural-signalling", "c2-2-12-effects-of-exogenous-chemicals-on-synaptic-transmission" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Autosomal genes are located in chromosomes that are not sex chromosomes. The inheritance of autosomal genes is affected by whether the genes are linked or unlinked. Explain the\n \n two\n \n types of inheritance, using the example of parents that are heterozygous for two genes A and B.\n

\n
\n
\n

\n [7]\n

\n
\n
\n", "Markscheme": "
\n

\n a. unlinked genes are on different chromosomes / vice versa ✔\n

\n

\n b. unlinked alleles migrate/segregate/are inherited independently (during meiosis) / vice versa ✔\n

\n

\n c. (In unlinked inheritance) there is an equal chance for all 4 options to occur / AB, Ab, aB, ab / vice versa ✔\n

\n

\n d. (dihybrid crosses involving) linked genes do not produce Mendelian ratios ✔\n

\n

\n e. (excluding recombinants) there is a 1:1 chance of inheriting the different options/AB or ab ✔\n

\n

\n f. in linked characteristics alleles might not migrate together if there is crossing over/ recombinants are formed ✔\n

\n

\n g. crossing over occurs in prophase I of meiosis ✔\n

\n

\n h. when the sister chromatids migrate in meiosis II the characteristics forming gametes are different/Ab, aB ✔\n

\n

\n i. formation of recombinants causes changes in ratio/probability of inheritance/genetic variation ✔\n

\n

\n j. correct named example of inheritance of linked/unlinked characteristics ✔\n

\n

\n k. Punnett/paired diagrams of both unlinked and linked characteristics ✔\n

\n

\n l. genes which are linked but are far apart on the chromosome can display independent assortment ✔\n

\n

\n \n Mp a could be awarded from an annotated diagram\n \n .\n

\n

\n \n Allow annotated diagram of inheritance / could be shown in a Punnett square\n \n .\n

\n

\n \n Allow annotated diagram of linked inheritance for mp f\n \n .\n

\n

\n \n For mp K, accept sex linked examples involving two genes\n \n .\n

\n

\n \n If the student interprets the question as sex-linked and autosomal inheritance, look for WTTE marks from the scheme\n \n .\n

\n
\n", "Examiners report": "
\n

\n Question 5 was not a popular question choice. Few candidates performed well on this question overall. Many students wrote vaguely about dominant and recessive alleles or confused gene linkage with \"sex-linkage\" or even multiple alleles and blood groups.\n

\n
\n", "question_id": "21M.2.SL.TZ2.5A", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-2-inheritance", "d3-2-3-genotype-as-the-combination-of-alleles-inherited-by-an-organism", "d3-2-10-incomplete-dominance-and-codominance" ] }, { "Question": "
\n
\n

\n The image shows the changes in heart rate of an athlete during exercise.\n

\n

\n \n

\n

\n [Source: Liddle, P.F., 2010. Heart Rate Variability (HRV) during exercise. [online] Available at: https://canute1.wordpress.com/2010/07/ [Accessed 1 August 2019].]\n

\n

\n

\n

\n What is likely to have occurred between 0 and 4 minutes and between 24 and 28 minutes?\n

\n

\n \n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "22M.1A.SL.TZ1.21", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-1-integration-of-body-systems", "c3-1-12-epinephrine-(adrenaline)-secretion-by-the-adrenal-glands-to-prepare-the-body-for-vigorous-activity", "c3-1-14-feedback-control-of-heart-rate-following-sensory-input-from-baroreceptors-and-chemoreceptors" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Suggest a reason that the pot was covered with a plastic bag.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n soil releases CO\n \n 2\n \n from microorganisms/decomposers/bacteria/fungi\n
\n \n \n OR\n \n \n
\n respiration by microorganisms may affect the result;\n

\n
\n", "Examiners report": "None", "question_id": "23M.1B.SL.TZ1.1B", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-1-enzymes-and-metabolism", "c1-1-8-effects-of-temperature-ph-and-substrate-concentration-on-the-rate-of-enzyme-activity" ] }, { "Question": "
\n
\n

\n What causes the atrioventricular valves to close during a heartbeat?\n

\n

\n A. Pressure in the atria is higher than in the ventricles.\n

\n

\n B. Pressure in the atria is lower than in the ventricles.\n

\n

\n C. Pressure in the arteries is higher than in the ventricles.\n

\n

\n D. Pressure in the arteries is lower than in the ventricles.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "19M.1A.HL.TZ2.25", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-2-transport", "b3-2-16-stages-in-the-cardiac-cycle" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Explain the differences between the results shown for vein and artery.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n a. veins have thinner walls (than arteries);\n

\n

\n b. veins sustain lower (blood) pressure (than arteries);\n

\n

\n c. when stretched, veins become longer (than arteries);\n

\n

\n d. veins have less muscle/elastic (fibre in their) walls (than arteries);\n

\n

\n e. veins have lower elasticity/recover less/remain more stretched (than arteries after weights removed);\n

\n

\n \n Accept inverse for arteries in all cases\n \n .\n

\n

\n \n Do not accept a listing of numerical values without explanation\n \n .\n

\n
\n", "Examiners report": "
\n

\n In part (b) many candidates suggested that the samples should be of the same thickness.\n

\n
\n", "question_id": "20N.1B.SL.TZ0.2C", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-2-transport", "b3-2-2-structure-of-arteries-and-veins" ] }, { "Question": "
\n
\n

\n How is facilitated diffusion in axons similar to active transport?\n

\n

\n A. They both require the energy of ATP.\n

\n

\n B. They both move substances against a concentration gradient.\n

\n

\n C. They both use sodium–potassium pumps.\n

\n

\n D. They are both carried out by proteins embedded in the axon membrane.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "21N.1A.SL.TZ0.3", "topics": [ "b-form-and-function" ], "subtopics": [ "b2-1-membranes-and-membrane-transport", "b2-1-6-channel-proteins-for-facilitated-diffusion" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Explain how cells in the bloodstream cause a specific immune response.\n

\n
\n
\n

\n [7]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n (specific immune response is) production of antibodies in response to a particular pathogen;\n
    2. \n
  2. \n antibody is specific to/binds to a specific\n \n antigen\n \n ;\n
    3. \n
  3. \n macrophages/phagocytes engulf/present antigens from pathogens/viruses/bacteria;\n
    4. \n
  4. \n T lymphocytes activated by antigens/antigen presentation/antigens presented by macrophage;\n
    5. \n
  5. \n (activated) T lymphocytes activate B lymphocytes;\n
    6. \n
  6. \n only B lymphocytes that produce antibodies against the antigen/pathogen are activated;\n
    7. \n
  7. \n (activated) B lymphocytes clone/divide by mitosis to form\n \n plasma cells\n \n ;\n
    8. \n
  8. \n plasma cells then secrete (large quantity) of an antibody/secrete antibodies of same type;\n
    9. \n
  9. \n some B lymphocytes/plasma cells form memory cells;\n
    10. \n
  10. \n memory cells give long-lasting immunity/faster response to a disease/pathogen;\n
    11. \n
\n

\n \n Accept B and T cells instead of B and T lymphocytes.\n \n

\n
\n", "Examiners report": "
\n

\n Here again there was a wide range of answers. The best focussed throughout on how specificity in immune responses is achieved. The weakest were very muddled, with confusion between antigens and pathogens and between antigens and antibodies. Nearly all candidates mentioned memory cells and their role in long term immunity.\n

\n
\n", "question_id": "22N.2.HL.TZ0.6C", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-2-defence-against-disease", "c3-2-6-lymphocytes-as-cells-in-the-adaptive-immune-system-that-cooperate-to-produce-antibodies" ] }, { "Question": "
\n
\n (c.ii)\n
\n
\n

\n Identify Y, non-coding DNA at the start of a gene.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n promoter;\n

\n
\n", "Examiners report": "
\n

\n Fewer candidates knew that Y must be the promoter. This could be deduced from the diagram which showed that Y is the site to which RNA polymerase first binds. Other incorrect suggestions were primer, intron, start codon and telomere.\n

\n
\n", "question_id": "22N.2.HL.TZ0.4C.II", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d1-2-protein-synthesis", "d1-2-14-non-coding-sequences-in-dna-do-not-code-for-polypeptides" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Outline how the properties of water make it an ideal transport medium in plants.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n

\n a. polarity of water;\n
\n b. hydrogen bonds between water molecules;\n
\n c. cohesion between water molecules/water molecules stick together;\n
\n d. cohesion allows tensions/low pressures/transpiration pull/movement upward/against gravity;\n
\n e. adhesion to cellulose/cell walls generates tensions/pull (in xylem)\n
\n \n OR\n \n
\n adhesion to xylem walls/vessel walls causes capillary rise/upward movement;\n
\n f. solvent for many substances / many substances dissolve;\n
\n g. liquid at most temperatures experienced by plants / liquid so can flow;\n

\n

\n \n Polarity of water and/or hydrogen bonding can be shown in an annotated diagram\n \n .\n

\n
\n", "Examiners report": "
\n

\n Most candidates knew at least some properties of water that make it useful as a medium for transport in plants. As in previous papers, cohesion and adhesion are often treated as the same process or were confused. Another common error is to refer to hydrogen bonds as strong – their effects are strong because so many hydrogen bonds are formed in water but, thinking of them individually, they are weak interactions.\n

\n
\n", "question_id": "21N.2.SL.TZ0.7A", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a1-1-water", "a1-1-5-solvent-properties-of-water-linked-to-its-role-as-a-medium-for-metabolism-and-for-transport-in-plants-and-animals" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Outline the relationship between\n \n Zooxanthellae\n \n and reef-building coral reef species.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. a symbiotic/mutualistic relationship ✔\n

\n

\n b.\n \n Zooxanthellae\n \n obtain shelter/habitat/exposure to light ✔\n

\n

\n c. coral obtains energy/food through photosynthesis of the\n \n Zooxanthellae\n \n ✔\n

\n
\n", "Examiners report": "
\n

\n This was a well-answered question with many candidates knowing the term symbiosis or mutualism. Protection provided by coral was often stated but the role of\n \n Zooxanthellae\n \n in providing nutrients from photosynthesis was less often seen.\n

\n
\n", "question_id": "19M.2.SL.TZ1.11B", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c4-1-populations-and-communities", "c4-1-12-mutualism-as-an-interspecific-relationship-that-benefits-both-species" ] }, { "Question": "
\n
\n

\n Explain how neonicotinoids affect synaptic transmission in insects.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n a. neonicotinoids bind to the (acetylcholine) receptor (in insects) ✔\n

\n

\n b. (binding happens) in (cholinergic) synapses/at motor end plate/between motor neuron and muscles ✔\n

\n

\n c. neonicotinoids bind irreversibly (to receptors)\n
\n \n \n OR\n \n \n
\n (receptors are blocked so) acetylcholine is unable to bind ✔\n

\n

\n d. acetylcholinesterase/enzymes cannot break down neonicotinoids ✔\n

\n

\n e. (synaptic) transmission prevented ✔\n

\n

\n f. (causing) insect paralysis/death ✔\n

\n
\n", "Examiners report": "
\n

\n In general, the data analysis question was well attempted by the majority of students.\n

\n

\n Those students who had studied synaptic transmission scored well. However, many knew the role of acetylcholine here, but not in Q(1)(e).\n

\n
\n", "question_id": "21M.2.HL.TZ2.G", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c2-2-neural-signalling", "c2-2-12-effects-of-exogenous-chemicals-on-synaptic-transmission" ] }, { "Question": "
\n
\n

\n Identify the relationship between migration distance and plumage colouration.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n the longer the migration, the lighter the colour /\n \n vice versa\n \n ;\n
    2. \n
  2. \n too much variation so it is not possible to see a relationship;\n
    3. \n
\n
\n", "Examiners report": "None", "question_id": "23M.1A.SL.TZ2.I", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-1-natural-selection", "d4-1-7-sexual-selection-as-a-selection-pressure-in-animal-species" ] }, { "Question": "
\n
\n

\n The graph shows enzyme activity plotted against temperature.\n

\n

\n \n

\n

\n

\n

\n What is the reason for the drop in enzyme activity above 40 °C?\n

\n

\n A. A decrease in the enzyme concentration\n

\n

\n B. Reaction is saturated because active sites are occupied\n

\n

\n C. Insufficient activation energy for the reaction to proceed\n

\n

\n D. Changes to the conformation of the enzyme\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "22M.1A.SL.TZ1.8", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-1-enzymes-and-metabolism", "c1-1-8-effects-of-temperature-ph-and-substrate-concentration-on-the-rate-of-enzyme-activity" ] }, { "Question": "
\n
\n

\n A variety of\n \n Pelargonium\n \n has yellow leaves. When plants of this variety are crossed, the resulting seeds produce green, yellow and white seedlings in the ratio 1 : 2 : 1. If plants with yellow leaves are crossed with plants with green leaves, what would the expected ratio of phenotypes in the offspring be?\n

\n

\n \n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "19N.1A.SL.TZ0.15", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-2-inheritance", "d3-2-10-incomplete-dominance-and-codominance" ] }, { "Question": "
\n
\n

\n The diagram shows the human female reproductive system.\n

\n

\n \n

\n

\n [Source: © International Baccalaureate Organization 2019]\n

\n

\n

\n

\n What is produced by structure X?\n

\n

\n A. FSH\n

\n

\n B. X chromosomes\n

\n

\n C. Fertilized eggs\n

\n

\n D. Estrogen and progesterone\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "19M.1A.SL.TZ1.30", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-1-reproduction", "d3-1-5-changes-during-the-ovarian-and-uterine-cycles-and-their-hormonal-regulation" ] }, { "Question": "
\n
\n (c.ii)\n
\n
\n

\n Suggest\n \n one\n \n reason for maintaining a pH of 7.5 throughout the experiment.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. pH values away from optimum pH affect enzyme\n
\n \n \n OR\n \n \n
\n so enzyme can function properly\n
\n \n \n OR\n \n \n
\n pH 7.5 is the optimum pH for the enzyme ✔\n
\n
\n b. sketch of enzyme activity versus pH ✔\n \n Sketch of enzyme activity needs labels.\n \n

\n

\n c. change in pH affects 3D structure of protein/active site\n
\n \n \n OR\n \n \n
\n change in pH denatures the enzyme / protein ✔\n

\n

\n d. substrate does not fit in active site\n
\n \n \n OR\n \n \n
\n interaction of substrate and active site affected ✔\n

\n
\n", "Examiners report": "
\n

\n Most candidates answered correctly that a specific pH was necessary for the enzyme to function properly and that deviation from this pH could denature the enzyme.\n

\n
\n", "question_id": "19M.1B.SL.TZ2.1C.II", "topics": [ "b-form-and-function" ], "subtopics": [ "b2-1-membranes-and-membrane-transport", "b2-1-10-fluid-mosaic-model-of-membrane-structure" ] }, { "Question": "
\n
\n

\n At what stage of spermatogenesis does the first division of meiosis occur?\n
\n
\n

\n

\n A.  Spermatogonium to primary spermatocyte\n

\n

\n B.  Primary spermatocyte to secondary spermatocyte\n

\n

\n C.  Secondary spermatocyte to spermatid\n

\n

\n D.  Spermatid to mature sperm cell\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "23M.1A.HL.TZ2.39", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-1-reproduction", "d3-1-14-spermatogenesis-and-oogenesis-in-humans" ] }, { "Question": "
\n
\n

\n State a variable that should be kept constant.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n enzyme/substrate/egg white concentration/volume/pH/temperature;\n

\n

\n \n Accept another reasonable variable.\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.1B.SL.TZ2.I", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-1-enzymes-and-metabolism", "c1-1-8-effects-of-temperature-ph-and-substrate-concentration-on-the-rate-of-enzyme-activity" ] }, { "Question": "
\n
\n

\n Which process results in decreased variation?\n

\n

\n A. Meiosis\n

\n

\n B. Mutation\n

\n

\n C. Sexual reproduction\n

\n

\n D. Natural selection\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "
\n

\n There was some concern among teachers that this question might be misinterpreted, but three quarters of candidates answered correctly and the discrimination index was high. Natural selection can decrease variation by eliminating alleles that reduce fitness.\n

\n
\n", "question_id": "21M.1A.SL.TZ1.22", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-1-natural-selection", "d4-1-2-roles-of-mutation-and-sexual-reproduction-in-generating-the-variation-on-which-natural-selection-acts" ] }, { "Question": "
\n
\n

\n Melatonin controls circadian rhythms and is involved in the sleep-wake cycle. The pineal gland, which secretes melatonin, is inhibited by light. The graph shows a normal cycle where bedtime is around 10pm.\n

\n

\n \n

\n

\n

\n

\n Using data from the graph, what might be the effect(s) of screen light from a laptop, tablet or phone at bedtime?\n

\n

\n I.   Delay in melatonin production\n

\n

\n II.  Lower peak concentration of melatonin\n

\n

\n III. Peak of melatonin earlier in the evening\n

\n

\n A.  I only\n

\n

\n B.  III only\n

\n

\n C.  II and III only\n

\n

\n D.  I, II and III\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "
\n

\n This was the most problematic question on the paper. For multiple-completion questions to work satisfactorily, each of the possibilities must be unequivocally right or wrong. Here it was clear that use of a bright screen at bedtime is likely to delay melatonin production because the pineal gland would be inhibited. It was also clear that the peak of melatonin production would not be earlier in the evening. It was not clear whether there would be a lower peak of melatonin in the night. Given that a plateau in melatonin concentration is reached during the night, it seems more likely that the peak would not be lower, even if the rise took place later, leading to answer A. However, more candidates chose answer B, showing that they expected a lower peak. This is not unequivocally wrong, so the examining team decided to accept both answers A and B. Over 90\n \n \n \n \n % of candidates gained the mark and inevitably the discrimination index was low.\n

\n
\n", "question_id": "22N.1A.HL.TZ0.25", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-2-defence-against-disease", "c3-2-1-pathogens-as-the-cause-of-infectious-diseases" ] }, { "Question": "
\n
\n

\n What is produced by type II pneumocytes?\n

\n

\n A. Epinephrine\n

\n

\n B. Elastase\n

\n

\n C. Pulmonary surfactant\n

\n

\n D. Alpha 1-antitrypsin\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "19M.1A.SL.TZ1.23", "topics": [ "b-form-and-function" ], "subtopics": [ "b2-3-cell-specialization", "b2-3-8-adaptations-of-type-i-and-type-ii-pneumocytes-in-alveoli" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n State the\n \n mode\n \n for the number of steps per day in Japan and USA, rounding your answers up or down to the nearest 1000 steps.\n
\n
\n

\n

\n Japan: ..................................................................................................\n

\n

\n
\n USA:  ....................................................................................................\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n Japan: 6000\n \n and\n \n USA: 4000;\n \n (both needed)\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ1.1", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-3-muscle-and-motility-(hl-only)", "b3-3-9-reasons-for-locomotion" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Discuss the control of blood glucose levels and the consequences if they are not maintained.\n

\n
\n
\n

\n [8]\n

\n
\n
\n", "Markscheme": "
\n

\n \n control\n \n :\n \n \n [6 max]\n \n \n
\n
\n a. homeostasis is the maintenance of a constant internal environment ✔\n

\n

\n b. the pancreas produces hormones that control the levels of glucose ✔\n

\n

\n c. if glucose levels in blood are high, beta-cells «of the pancreas» produce insulin ✔\n

\n

\n d. «insulin» causes the cells to take up /absorb glucose ✔\n

\n

\n e. liver stores excess glucose as glycogen ✔\n

\n

\n f. if glucose levels in blood are low, alpha-cells «of the pancreas» produce glucagon ✔\n

\n

\n g. «glucagon» causes the liver to break down glycogen into glucose ✔\n

\n

\n h. «glucagon» increase levels of glucose in the blood ✔\n

\n

\n i. negative feedback controls the glucose levels ✔\n \n OWTTE\n \n

\n

\n \n consequences\n \n :\n

\n

\n j. if the pancreas produces little/no insulin a person can develop\n \n type I\n \n diabetes ✔\n

\n

\n k. a person with\n \n type I\n \n diabetes «usually» needs/is dependent on injections of insulin ✔\n

\n

\n l.\n \n type II\n \n diabetes occurs when the body becomes resistant to insulin/cells do not respond to insulin ✔\n

\n

\n m.\n \n type II\n \n diabetes can «sometimes» be controlled by diet and exercise ✔\n

\n

\n n. named consequence of having diabetes «\n \n eg\n \n : eye damage» ✔\n

\n

\n \n Award\n \n [6 max]\n \n if no consequences are given.\n \n
\n
\n

\n
\n", "Examiners report": "
\n

\n Control of blood glucose levels. Weaker candidates tied themselves in knots trying to explain. Weak candidates also described insulin and glucagon as enzymes, not hormones. Other common mistakes were Alpha cells and Beta cells do not move, they just produce the hormones and glucagon and insulin do not have any direct effect on the glycogen molecules. The causes and treatment of type 2 diabetes were quite well known. A large number of students used the word ‘digest’ incorrectly, stating that glucose was ‘digested’ to glycogen.\n

\n
\n", "question_id": "19M.2.SL.TZ2.6C", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-3-homeostasis", "d3-3-3-regulation-of-blood-glucose-as-an-example-of-the-role-of-hormones-in-homeostasis" ] }, { "Question": "
\n
\n

\n The diagram shows the flow of energy through an ecosystem in\n \n \n \n kJ m\n \n \n \n –\n \n \n 2\n \n \n \n \n \n y\n \n \n \n –\n \n \n 1\n \n \n \n \n .\n \n \n

\n

\n \n

\n

\n [Source: “Energy flow: Figure 3,” (\n \n https://cnx.org/contents/24nI-KJ8@24.18:fbNheNoN@8/Energy-Flow\n \n ) by OpenStax College, Biology CC BY 4.0 (\n \n https://creativecommons.org/licenses/by/4.0/\n \n ).]\n

\n

\n What percentage of the energy passed from primary producers to primary consumers is lost to cellular respiration by tertiary consumers?\n

\n

\n A. 0.001%\n

\n

\n B. 0.08%\n

\n

\n C. 0.2%\n

\n

\n D. 0.4%\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "
\n

\n The candidates found this question difficult, possibly because the arrow coming from the primary producers shows 40 000 kJ m\n \n −2\n \n y\n \n −1\n \n leaving but only half of that is taken up by primary consumers, the remainder being lost to saprotrophs and detritivores. Some G2 forms suggested that the calculation was too difficult without the aid of a calculator but if the candidates had chosen the correct values from the diagram the calculation would have been straightforward (\n \n \n 80\n \n \n \n \n ×\n \n \n \n 100\n \n \n \n 20\n \n \n \n \n 000\n \n \n \n \n =\n \n \n 0\n \n \n .\n \n \n 4\n \n \n \n \n %\n \n \n ).\n

\n
\n", "question_id": "21M.1A.SL.TZ2.18", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c4-2-transfers-of-energy-and-matter", "c4-2-11-construction-of-energy-pyramids" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Compare and contrast the community structure within and outside the marine protected area.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n \n compare\n \n :\n

\n

\n a. all three species present in both\n
\n \n \n OR\n \n \n
\n richness is the same ✔\n

\n

\n b. sea urchin numbers highest in both\n
\n \n \n OR\n \n \n
\n sea bream density less than sea urchin density in both ✔\n \n Allow converse answer\n \n

\n

\n c. all species numbers are affected by fishing ✔\n

\n

\n \n contrast\n \n :\n

\n

\n d. sea urchin population is greater outside the marine protected area ✔\n

\n

\n e. reduction in sea bream/sea grass percent cover outside the marine protected area ✔\n

\n

\n f. less species evenness outside the marine protected area ✔\n

\n
\n", "Examiners report": "
\n

\n There were nearly always at least two differences between the areas described but much less often a comparison, so three marks were not often awarded. Some candidates gave explanations rather than following the command term.\n

\n
\n", "question_id": "19M.2.HL.TZ1.10B", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-2-stability-and-change", "d4-2-15-climax-communities-and-arrested-succession" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Outline how the amphipathic properties of phospholipids play a role in membrane structure.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. part hydrophobic/not attracted to water/non-polar\n \n \n AND\n \n \n part hydrophilic/attracted to water/polar;\n \n Both needed\n \n .\n

\n

\n b. bilayer formed (formed naturally by phospholipids in water);\n

\n

\n c.\n \n hydrophilic\n \n heads/parts face outwards\n \n \n AND\n \n \n \n hydrophobic\n \n tails/parts face inwards;\n

\n

\n \n Do not allow water loving/hating in mpa or mpc\n \n .\n

\n
\n", "Examiners report": "
\n

\n Knowledge of amphipathic properties in part a was good. In b, most could state that the diagram shows a synapse. A variety of spelling is usually allowed, but in this case ‘synapsis’ was not allowed in English as this refers to the pairing of homologous chromosomes. There were some G2 comments that the X could be taken as the structure. However X clearly points to an arrow, not a structure. Most were able to gain some marks by describing the events, but some lost marks by not clearly indicating that it is the vesicle containing the neurotransmitter that moves.\n

\n
\n", "question_id": "20N.2.SL.TZ0.3A", "topics": [ "b-form-and-function" ], "subtopics": [ "b1-1-carbohydrates-and-lipids", "b1-1-12-formation-of-phospholipid-bilayers-as-a-consequence-of-the-hydrophobic-and-hydrophilic-regions" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Calculate the increase in mean global temperature between 1880 and 2010.\n

\n

\n .......... °C\n

\n

\n

\n

\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n 0.87; (\n \n accept values between 0.8 and 0.9\n \n )\n

\n
\n", "Examiners report": "
\n

\n Many candidates got the calculations right.\n

\n
\n", "question_id": "22M.2.SL.TZ1.3", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-3-climate-change", "d4-3-1-anthropogenic-causes-of-climate-change", "d4-3-2-positive-feedback-cycles-in-global-warming" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n The map shows the widespread distribution of coral reef ecosystems (indicated by black dots) in the world’s oceans. Death of coral reefs is related to increasing atmospheric carbon dioxide concentrations.\n

\n

\n \n

\n

\n [Source: National Oceanic and Atmospheric Administration, 2021. Where Reef Building Corals Found. [map online] Available at: https://oceanservice.noaa.gov/education/tutorial_corals/media/supp_coral05a.html [Accessed 20 May 2021].]\n

\n

\n Explain how increased atmospheric carbon dioxide concentrations can lead to coral death.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. carbon dioxide dissolves in oceans/seawater ✔\n

\n

\n b. carbonic acid formed/equation/lowers pH/makes water acidic ✔\n

\n

\n c. prevents deposition of calcium carbonate/causes calcium carbonate to dissolve ✔\n

\n

\n d. skeleton of (hard) corals degraded ✔\n

\n

\n e. carbon dioxide is a greenhouse gas/causes warming/increases temperatures ✔\n

\n

\n f. warmer oceans cause corals to expel zooxanthellae ✔\n

\n

\n g. bleaching due to death/expulsion of mutualistic organisms/algae ✔\n

\n

\n \n Allow zooxanthellae instead of algae in mpf\n \n .\n

\n

\n \n Reject reacts and diffuses instead of dissolves in mpa\n \n .\n

\n
\n", "Examiners report": "
\n

\n Answers relating to global warming and therefore rising sea temperatures and also answers relating to ocean acidification were accepted. Many candidates knew that carbon dioxide causes acidification but fewer knew about the resulting problems with mineral deposition to form the skeleton in a hard coral.\n

\n
\n", "question_id": "21M.2.HL.TZ1.3", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-3-climate-change", "d4-3-7-threats-to-coral-reefs-as-an-example-of-potential-ecosystem-collapse" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n State the purpose of lime water in flask B.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n to check there is no carbon dioxide (left in the air)/show any carbon dioxide present;\n

\n

\n \n Do not accept absorb carbon dioxide\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.1B.SL.TZ1.1A", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-1-enzymes-and-metabolism", "c1-1-8-effects-of-temperature-ph-and-substrate-concentration-on-the-rate-of-enzyme-activity" ] }, { "Question": "
\n
\n

\n What process occurs in both mitosis and meiosis?\n

\n

\n A. Formation of chiasmata\n

\n

\n B. Reduction division\n

\n

\n C. Separation of chromatids\n

\n

\n D. Exchange of alleles between non-sister chromatids\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "21M.1A.SL.TZ2.35", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-1-cell-and-nuclear-division", "d2-1-5-dna-replication-as-a-prerequisite-for-both-mitosis-and-meiosis" ] }, { "Question": "
\n
\n

\n The micrograph shows a glomerulus and Bowman’s capsule, where ultrafiltration takes place in the kidney.\n

\n

\n \n

\n

\n [Source: MICROSCAPE/SCIENCE PHOTO LIBRARY.]\n

\n

\n

\n

\n What facilitates the formation of glomerular filtrate?\n

\n

\n A. Many fenestrations in walls of capillaries in the glomerulus\n

\n

\n B. High pressure in the Bowman’s capsule\n

\n

\n C. ADH secreted by the pituitary gland\n

\n

\n D. Osmosis caused by a high concentration of urea in the blood\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "None", "question_id": "22M.1A.HL.TZ2.39", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-3-homeostasis", "d3-3-8-role-of-the-glomerulus-bowmans-capsule-and-proximal-convoluted-tubule-in-excretion" ] }, { "Question": "
\n
\n

\n Suggest a reason for the correlation between coral cover and WSSTA in 1998–1999.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n coral cover lower on reefs with higher temperature;\n

\n
\n", "Examiners report": "None", "question_id": "21N.2.SL.TZ0.C.II", "topics": [ "d-continuity-and-change", "b-form-and-function" ], "subtopics": [ "d4-3-climate-change", "d4-3-7-threats-to-coral-reefs-as-an-example-of-potential-ecosystem-collapse", "b4-1-adaptation-to-environment", "b4-1-5-conditions-required-for-coral-reef-formation" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Label with a P on the\n \n \n x\n \n \n -axis the level of commercial sea fishing activity that would result in maximum sustainability.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n label P on\n \n x\n \n -axis below the peak yield;\n
\n \n Dotted line for guidance, not required in answer.\n \n

\n

\n \n

\n

\n \n Do not accept if P is\n \n only\n \n on the curve\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ1.18A", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-2-stability-and-change", "d4-2-6-assessing-sustainability-of-resource-harvesting-from-natural-ecosystems" ] }, { "Question": "
\n
\n

\n A couple have four children whose blood groups are A, B and AB. What is the likely combination of the parents’ genotypes?\n

\n

\n A.  I\n \n A\n \n i and I\n \n B\n \n i\n

\n

\n B.  I\n \n A\n \n i and I\n \n B\n \n I\n \n B\n \n

\n

\n C.  I\n \n A\n \n I\n \n B\n \n and ii\n

\n

\n D.  I\n \n A\n \n I\n \n A\n \n and I\n \n B\n \n I\n \n B\n \n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "
\n

\n The candidates were asked to identify the likely combination of the parents' genotypes given the blood groups of their four children. Once centre queried the lack of any children with blood group O. However, four children do not represent a statistically significant sample and it is very likely that one of the possible blood groups is not present. The question was answered correctly by 61\n \n \n \n \n % of the students and was a good discriminator.\n

\n
\n", "question_id": "22N.1A.SL.TZ0.15", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-2-inheritance", "d3-2-10-incomplete-dominance-and-codominance" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Explain the production of antibodies in humans.\n

\n
\n
\n

\n [7]\n

\n
\n
\n", "Markscheme": "
\n

\n a. antigens stimulate antibody production;\n
\n b. antibodies produced by lymphocytes;\n
\n c. macrophages/phagocytes ingest/engulf pathogens and display antigens from them;\n
\n d. T-cells activated by binding antigen/by macrophage displaying antigen;\n
\n e. activated T-cells cause activation of B-cells;\n
\n f. mitosis/division of (activated) B-cells (to produce a clone of cells)\n
\n g. plasma cells formed from divided/activated/growing/differentiating B-cells;\n
\n h. plasma cells/plasma B-cells secrete antibodies;\n
\n i. clonal selection / plasma cells make same type of antibody/antibody specific to same antigen;\n
\n j. some activated B-cells become memory cells;\n

\n
\n", "Examiners report": "
\n

\n This was another question giving scope to candidates to show the breadth of their biological understanding. The best answers were impressive but given the challenging nature of the topic it isn’t surprising that there were also some very muddled accounts. The weakest candidates struggled to remember the differences between antigens, antibodies and lymphocytes.\n

\n
\n", "question_id": "21N.2.HL.TZ0.8B", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-2-defence-against-disease", "c3-2-6-lymphocytes-as-cells-in-the-adaptive-immune-system-that-cooperate-to-produce-antibodies", "c3-2-8-activation-of-b-lymphocytes-by-helper-t-lymphocytes", "c3-2-10-immunity-as-a-consequence-of-retaining-memory-cells" ] }, { "Question": "
\n
\n (b.ii)\n
\n
\n

\n X indicates the movement of a structure in the neuron. Explain what events trigger this movement and what happens next.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n a. depolarization of pre-synaptic membrane / action potential/nerve impulse arrives;\n

\n

\n b. uptake of calcium / calcium ions diffuse in / calcium channels open;\n

\n

\n c. structures containing neurotransmitter/vesicles move to/fuse with membrane;\n

\n

\n d.\n \n neurotransmitter\n \n /\n \n acetylcholine\n \n released by exocytosis into cleft/binds to postsynaptic membrane/receptors;\n

\n
\n", "Examiners report": "None", "question_id": "20N.2.HL.TZ0.3B.II", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c2-1-chemical-signalling-[hl-only]", "c2-1-7-initiation-of-signal-transduction-pathways-by-receptors", "c2-1-8-transmembrane-receptors-for-neurotransmitters-and-changes-to-membrane-potential", "c2-1-9-transmembrane-receptors-that-activate-g-proteins" ] }, { "Question": "
\n
\n

\n The graph shows the results of an experimental investigation that compared the rates at which lactose, glucose and galactose are broken down in the process of anaerobic cellular respiration by the yeast\n \n Torulopsis cremoris\n \n .\n

\n

\n \n

\n

\n [Source: Rogosa, M., 1948 Mechanism of the Fermentation of Lactose by Yeasts.\n \n Journal of Biological Chemistry\n \n , 175, p.418. (CC BY 4.0)\n \n https://creativecommons.org/licenses/by/4.0/\n \n .]\n

\n

\n

\n

\n What can be concluded from these results?\n

\n

\n A. Cellular respiration of lactose involves the production of glucose and galactose.\n

\n

\n B. The breakdown of glucose and galactose occurs more slowly in the presence of lactose.\n

\n

\n C. The rate of cellular respiration is greater for glucose than for lactose and galactose.\n

\n

\n D. The percentage of sugar remaining after 42 hours is greater for galactose than glucose.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "
\n

\n Some teachers commented that this question would be difficult for the students as they were unable to carry out experiments in class. However, the statistics show that the question performed well in terms of difficulty and discrimination. The theory of anaerobic respiration is required in 2.8 (Cell respiration). This question can be answered simply by looking at the graphs.\n

\n
\n", "question_id": "21M.1A.HL.TZ2.11", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-2-cell-respiration", "c1-2-10-anaerobic-cell-respiration-in-yeast-and-its-use-in-brewing-and-baking" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Outline how the data could have been obtained.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a.\n \n transect\n \n across area to be studied ✔\n

\n

\n b. count/record barnacles «per species» in\n \n quadrats\n \n at regular intervals ✔\n

\n
\n", "Examiners report": "
\n

\n The data in this question was a kite diagram showing the distribution of three barnacle species. In part (a) most strong candidates could outline how the data was obtained though many failed to use specific vocabulary and did not mention transects or quadrats.\n

\n
\n", "question_id": "19M.1B.SL.TZ2.12A", "topics": [ "b-form-and-function" ], "subtopics": [ "b4-1-adaptation-to-environment", "b4-1-4-range-of-tolerance-of-a-limiting-factor" ] }, { "Question": "
\n
\n

\n Outline primary succession.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n colonization of areas that were barren/not previously inhabited/not occupied by organisms;\n

\n
\n", "Examiners report": "None", "question_id": "23M.2.HL.TZ2.A", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-2-stability-and-change", "d4-2-13-changes-occurring-during-primary-succession" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Draw a labelled diagram to show the structure of a single nucleotide of RNA.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n ribose drawn as a pentagon and labelled;\n
    2. \n
  2. \n base linked correctly (to C1) of ribose and labelled;\n
    3. \n
  3. \n phosphate linked correctly (to C5) of ribose and labelled;\n
    4. \n
\n

\n \n

\n

\n \n Award\n \n [2 max]\n \n if more than one nucleotide drawn.\n \n

\n

\n \n “Sugar” alone is insufficient.\n \n

\n
\n", "Examiners report": "
\n

\n Occasionally, deoxyribose was seen rather ribose; sometimes more than one nucleotide was shown limiting maximum marks.\n

\n
\n", "question_id": "22M.2.SL.TZ1.7", "topics": [ "a-unity-and-diversity", "d-continuity-and-change", "c-interaction-and-interdependence" ], "subtopics": [ "a1-2-nucleic-acids", "a1-2-5-rna-as-a-polymer-formed-by-condensation-of-nucleotide-monomers", "d2-1-cell-and-nuclear-division", "d2-1-4-roles-of-mitosis-and-meiosis-in-eukaryotes", "c3-2-defence-against-disease", "c3-2-14-evolution-of-resistance-to-several-antibiotics-in-strains-of-pathogenic-bacteria" ] }, { "Question": "
\n
\n

\n The diagram shows a simplified carbon cycle.\n

\n

\n \n

\n

\n Which processes are taking place at X and Y?\n

\n

\n \n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "22M.1A.SL.TZ1.19", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c4-2-transfers-of-energy-and-matter", "c4-2-17-constructing-carbon-cycle-diagrams" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Explain the movement of energy and inorganic nutrients in an ecosystem.\n

\n
\n
\n

\n [7]\n

\n
\n
\n", "Markscheme": "
\n

\n a. autotrophs/producers/plants obtain inorganic nutrients from the «abiotic» environment ✔\n

\n

\n b. energy provided «mainly» by sunlight ✔\n

\n

\n c. light energy converted «to chemical energy» through photosynthesis ✔\n

\n

\n d. photosynthesis/producers/autotrophs convert inorganic carbon/carbon dioxide and water into carbon/organic compounds ✔\n

\n

\n e. «these» carbon compounds/foods contain/are a source of «useable» energy «for life» ✔\n

\n

\n f. carbon compounds/energy are transferred along food chains when eaten by consumers/heterotrophs ✔\n \n Allow OWTTE for mpf for passed up trophic levels\n \n .\n

\n

\n g. respiration returns carbon «dioxide» to the environment ✔\n

\n

\n h. respiration releases stored/chemical energy as ATP/heat ✔\n

\n

\n i. energy/ATP is used to carry out life functions/synthesis/growth/movement ✔\n

\n

\n j. energy is lost/not recycled ✔\n

\n

\n k. nutrients are recycled / example of recycled nutrient\n \n e.g.\n \n carbon ✔\n

\n

\n l. decomposers recycle minerals/inorganic nutrients ✔\n

\n
\n", "Examiners report": "None", "question_id": "19N.2.SL.TZ0.5C", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-2-stability-and-change", "d4-2-2-requirements-for-stability-in-ecosystems" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Outline how plastic ingestion may lead to biomagnification in these marine species.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n a. plastic broken down into microplastics to be able to enter the food chain ✔\n

\n

\n b. plastic/microplastics become more concentrated at each trophic level ✔\n

\n

\n \n Accept descriptions of biomagnification involving any of the species in the table\n \n .\n

\n
\n", "Examiners report": "None", "question_id": "19N.2.SL.TZ0.15B", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-2-stability-and-change", "d4-2-9-biomagnification-of-pollutants-in-natural-ecosystems" ] }, { "Question": "
\n
\n

\n Label with an R the tissue where the red dye would appear.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n \n \n \n

\n

\n [Source: Nbnidhi, https:// commons.wikimedia.org/wiki/ File:Transverse_section_of_dicot _stem.jpg]\n

\n

\n \n Award\n \n [1]\n \n for correct labeling of R\n \n

\n
\n", "Examiners report": "
\n

\n This was another question that was difficult for students. This question again required students to understand one of the skills from the subject guide, this time in topic 9.2 (Identification of xylem and phloem in microscope images of stem and root). Student responses to this question, however, suggested that few students could identify phloem and xylem under a microscope.\n

\n
\n", "question_id": "19M.1B.SL.TZ1.D.I", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-2-transport", "b3-2-7-transport-of-water-from-roots-to-leaves-during-transpiration" ] }, { "Question": "
\n
\n

\n The data shows part of the genetic code for mRNA. Which anticodon could be found on a tRNA molecule bonded to lysine?\n

\n

\n \n

\n

\n A. AAG\n

\n

\n B. UUC\n

\n

\n C. TTT\n

\n

\n D. GAA\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "21N.1A.SL.TZ0.11", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d1-2-protein-synthesis", "d1-2-7-complementary-base-pairing-between-trna-and-mrna" ] }, { "Question": "
\n
\n

\n What is PCR used for?\n

\n

\n A. Separate fragments of DNA by size\n

\n

\n B. Amplify small amounts of DNA\n

\n

\n C. Compare DNA samples\n

\n

\n D. Genetically modify organisms’ DNA\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "19N.1A.SL.TZ0.17", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d1-1-dna-replication", "d1-1-4-polymerase-chain-reaction-and-gel-electrophoresis-as-tools-for-amplifying-and-separating-dna", "d1-1-5-applications-of-polymerase-chain-reaction-and-gel-electrophoresis" ] }, { "Question": "
\n
\n

\n Explain what information a pyramid of energy provides about an ecological community.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n

\n a. shows the amount of energy at each trophic level (of a food chain/web);\n

\n

\n b. (energy) measured over a period of time/year\n
\n \n \n OR\n \n \n
\n units are energy per area per time/kJ m\n \n –2\n \n year\n \n –1\n \n ;\n

\n

\n c. the width/size of each bar represents the amount of energy;\n

\n

\n d. the bottom level represent the producers;\n

\n

\n e. subsequent levels represent consumers;\n

\n

\n f. each level should be roughly one tenth of the size/10 % of the preceding level;\n
\n \n \n OR\n \n \n
\n organisms at the top of the food chain are shown to have much less energy available to them;\n

\n

\n g. the energy that enters a community is ultimately lost as heat/in respiration\n

\n

\n \n Some answers may be displayed in a diagram\n \n .\n

\n
\n", "Examiners report": "
\n

\n The better candidates performed well in this question while weaker candidates are still confused by pyramids of energy. Many referred to numbers, or biomass at each trophic level. Very few candidates stated that the measurements were taken over a period of time.\n

\n
\n", "question_id": "20N.2.SL.TZ0.15", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c4-2-transfers-of-energy-and-matter", "c4-2-11-construction-of-energy-pyramids" ] }, { "Question": "
\n
\n

\n Movement of insects requires muscles in antagonistic pairs. The diagram shows an insect leg with muscles labelled X and Y.\n

\n

\n \n

\n

\n [Source: Johnson, S.K., n.d. [\n \n Insect leg\n \n ]. [diagram online] Available at: http://www.susankjohnson.com/portfolio.shtml\n
\n [Accessed 26 October 2021].]\n

\n

\n

\n

\n What actions in the human arm are equivalent to muscle X contracting and muscle Y relaxing?\n

\n

\n A.  triceps contracts, biceps relaxes, arm extends\n

\n

\n B.  biceps contracts, triceps relaxes, arm flexes\n

\n

\n C.  triceps contracts, biceps relaxes, arm flexes\n

\n

\n D.  biceps contracts, triceps relaxes, arm extends\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "None", "question_id": "22N.1A.HL.TZ0.37", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-3-muscle-and-motility-(hl-only)", "b3-3-3-role-of-the-protein-titin-and-antagonistic-muscles-in-muscle-relaxation" ] }, { "Question": "
\n
\n (b.i)\n
\n
\n

\n State the name of the structure shown.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n synapse/synaptic\n

\n
\n", "Examiners report": "None", "question_id": "20N.2.HL.TZ0.3B.I", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c2-1-chemical-signalling-[hl-only]", "c2-1-5-localized-and-distant-effects-of-signalling-molecules" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Identify which electron micrograph shows a mitochondrion, providing\n \n one\n \n observation to support your choice.\n

\n

\n \n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n «micrograph»\n \n C\n \n cristae/double membrane is visible/«folds of» membranes inside ✔\n

\n

\n \n Must state observation\n \n

\n
\n", "Examiners report": "
\n

\n Most candidates identified the correct micrograph but for the wrong reason such as 70S ribosomes visible, has a matrix, or correct shape. Only starch granules were visible in the image, not ribosomes.\n

\n
\n", "question_id": "19M.2.SL.TZ1.2", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a2-2-cell-structure", "a2-2-10-cell-types-and-cell-structures-viewed-in-light-and-electron-micrographs", "a2-2-12-origin-of-eukaryotic-cells-by-endosymbiosis" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Outline what occurs in cells in the first division of meiosis.\n

\n
\n
\n

\n [5]\n

\n
\n
\n", "Markscheme": "
\n

\n a. halves the chromosome number/produces haploid cells;\n

\n

\n b. at start of meiosis each chromosome consists of two sister chromatids attached by a centromere;\n

\n

\n c. prophase (I): pairing of homologous chromosomes;\n

\n

\n d. crossing over occurs;\n

\n

\n e. chromosomes condense by supercoiling;\n

\n

\n f. metaphase (I): pairs of homologous chromosomes/bivalents move to equator of spindle\n
\n \n \n OR\n \n \n
\n metaphase (I): orientation of pairs of homologous chromosomes (prior to separation) is random;\n

\n

\n g. anaphase (I): centromeres do not divide\n
\n \n \n OR\n \n \n
\n anaphase (I): spindle fibre pulls chromosome/whole centromere with two sister chromatids to opposite poles;\n

\n

\n h. telophase (I): arrival of centromere with sister chromatids at opposite poles;\n

\n

\n \n Some of these can be awarded for correctly annotated diagrams\n \n .\n

\n

\n \n No credit for events in meiosis II\n \n .\n

\n
\n", "Examiners report": "
\n

\n In part (b), those who had been well prepared easily gained the 5 marks, but there was a significant proportion who did not know the difference between mitosis and meiosis.\n

\n
\n", "question_id": "20N.2.SL.TZ0.6B", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-1-cell-and-nuclear-division", "d2-1-9-meiosis-as-a-reduction-division" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Outline the inheritance of blood types in the ABO blood system in humans.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n

\n a. i and I\n \n A\n \n and I\n \n B\n \n are\n \n alleles\n \n (of the blood group gene) ✔\n

\n

\n b. I\n \n A\n \n is dominant and i is recessive / I\n \n B\n \n is dominant and i is recessive ✔\n

\n

\n c. Group O (only) with ii\n \n and\n \n Group A with I\n \n A\n \n i or I\n \n A\n \n I\n \n A\n \n / Group B with I\n \n B\n \n i or I\n \n B\n \n I\n \n B\n \n

\n

\n d. I\n \n A\n \n and I\n \n B\n \n are\n \n co-dominant\n \n so Group AB with I\n \n A\n \n I\n \n B\n \n ✔\n

\n

\n e. one allele/copy of the gene inherited from each parent/Punnett square showing this ✔\n

\n

\n \n Disallow mpa if allele notation is incorrect (such as using different letters for different alleles) but allow other mps\n \n .\n

\n

\n \n The notation I\n \n i\n \n can be accepted instead of i\n \n .\n

\n

\n \n Reject blood groups or types being dominant/recessive – it should be alleles\n \n .\n

\n
\n", "Examiners report": "
\n

\n For a well-prepared candidate this was a very routine exercise, but many candidates were not so prepared. A common fault was to confuse blood groups with the alleles that determine the groups, either in notation for alleles, or overall. Commonly, answers did not distinguish between gene and allele. Some candidates focused too much on the consequences of blood groups (including rhesus +ve/−ve) for blood transfusion which was not relevant to the question.\n

\n
\n", "question_id": "21M.2.HL.TZ1.7", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-2-inheritance", "d3-2-9-abo-blood-groups-as-an-example-of-multiple-alleles", "d1-3-mutations-and-gene-editing", "d1-3-7-mutation-as-a-source-of-genetic-variation" ] }, { "Question": "
\n
\n

\n The karyogram shown belongs to a human being.\n

\n

\n \n

\n

\n [Source: Reproduced from Tennakoon J, Kandasamy Y, Alcock G, Koh TH. Edwards syndrome with double trisomy.\n \n Singapore\n \n \n Med J\n \n . 2008 Jul;49(7):e190-1. PMID: 18695855.]\n

\n

\n

\n

\n What can be deduced from this karyogram?\n

\n

\n A. The person is a male with Down syndrome.\n

\n

\n B. The person is a female with Down syndrome.\n

\n

\n C. The person is a male with a genetic disorder.\n

\n

\n D. The person is a female with a missing chromosome.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n

\n

\n

\n \n NOTE FOR TEACHERS: The credit line under the image may give students an indication of the correct answer. Teachers may wish to adjust their quizzes/exams accordingly.\n \n

\n
\n", "Examiners report": "None", "question_id": "22M.1A.SL.TZ2.14", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-1-cell-and-nuclear-division", "d2-1-10-down-syndrome-and-non-disjunction" ] }, { "Question": "
\n
\n (d)\n
\n
\n

\n Explain\n \n one\n \n reason for calculating the percentage change in mass.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. the change in mass indicates whether the tissue has gained/lost water ✔\n

\n

\n b. the pieces of tissue will not be the same mass «at the beginning of the experiment» ✔\n

\n

\n c. to compare the relative changes in mass ✔\n

\n
\n", "Examiners report": "None", "question_id": "19N.1B.SL.TZ0.1D", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-3-water-potential", "d2-3-3-water-movement-by-osmosis-into-or-out-of-cells", "d2-3-4-changes-due-to-water-movement-in-plant-tissue-bathed-in-hypotonic-and-those-bathed-in-hypertonic-solutions" ] }, { "Question": "
\n
\n

\n On the diagrams, label with a letter H the hydrophilic end of a phospholipid.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n hydrophilic end of phospholipid shown ✔\n

\n

\n \n For 2a, i, ii and iii, accept letters written on the structure even if a line is not drawn.\n \n

\n

\n \n Award the mark if the full word is used to label the structure. Labels must be unambiguous.\n \n

\n
\n", "Examiners report": "
\n

\n There were numerous examples of ambiguous labels, for example, an H without an arrow placed beside the membrane making it unclear whether the student was indicating the hydrophobic or hydrophilic part of the membrane.\n

\n
\n", "question_id": "21M.2.SL.TZ2.A.I", "topics": [ "b-form-and-function" ], "subtopics": [ "b1-1-carbohydrates-and-lipids", "b1-1-12-formation-of-phospholipid-bilayers-as-a-consequence-of-the-hydrophobic-and-hydrophilic-regions" ] }, { "Question": "
\n
\n

\n Calculate the actual thickness of the leaf, from upper to lower surface along the line a–b, showing your working.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n correct measurement of the line on the image (\n \n \n +\n \n \n /\n \n \n -\n \n \n 1mm);\n
    2. \n
  2. \n correct calculation and including units;\n
    3. \n
\n

\n \n Allow ECF – ruler measurements\n \n \n +\n \n \n /\n \n \n -\n \n \n 1mm\n \n

\n
\n", "Examiners report": "None", "question_id": "SPM.1B.SL.TZ0.B", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a2-2-cell-structure", "a2-2-2-microscopy-skills" ] }, { "Question": "
\n
\n

\n Which evolutionary pathway is most likely to result in the evolution of analogous structures in Species W and Z?\n

\n

\n \n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "
\n

\n This question performed well in terms both in terms of difficulty and having the highest discrimination on the paper.\n

\n
\n", "question_id": "21M.1A.SL.TZ2.21", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a4-1-evolution-and-speciation", "a4-1-5-convergent-evolution-as-the-origin-of-analogous-structures" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Describe polyploidy and how it can lead to speciation.\n

\n
\n
\n

\n [5]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n polyploidy is having more than two (complete) sets of chromosomes/3n/4n/other specific example of polyploidy;\n
    2. \n
  2. \n can be due to errors in meiosis/production of diploid gametes;\n
    3. \n
  3. \n can be due to DNA replication without mitosis/cytokinesis;\n
    4. \n
  4. \n polyploidy causes reproductive isolation;\n
    5. \n
  5. \n diploids crossed with tetraploids produce infertile (triploid) offspring / triploid offspring are infertile;\n
    6. \n
  6. \n tetraploids are therefore a new species/failure to interbreed/reproductive isolation leads to speciation;\n
    7. \n
  7. \n (many) examples in the onion family/Allium/other valid example of speciation by polyploidy;\n
    8. \n
  8. \n infertile interspecific hybrids can become fertile by becoming polyploid;\n
    9. \n
\n

\n \n Reject non-disjunction as a cause of polyploidy as it usually applies to a single bivalent.\n \n

\n
\n", "Examiners report": "
\n

\n A minority of answers defined polyploidy correctly and then explained how it results in speciation through reproductive isolation. Weaker responses muddled up aneuploidy with polyploidy so claimed that non-disjunction of a pair of chromosomes causes polyploidy. The average score for this question was low, because it tended to be weaker candidates who were answering it, and also because it is a relatively difficult part of the program.\n

\n
\n", "question_id": "22N.2.HL.TZ0.8B", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a4-1-evolution-and-speciation", "a4-1-11-abrupt-speciation-in-plants-by-hybridization-and-polyploidy" ] }, { "Question": "
\n
\n

\n Once the germinated bean grows above the ground, state the process used by the bean in the production of starch.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n photosynthesis\n

\n

\n \n Do not accept condensation or polymerization; if list of processes given, mark the first answer\n \n .\n

\n
\n", "Examiners report": "None", "question_id": "21M.2.SL.TZ2.E", "topics": [ "b-form-and-function" ], "subtopics": [ "b1-1-carbohydrates-and-lipids", "b1-1-5-polysaccharides-as-energy-storage-compounds" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Explain how the results in the graph could have been obtained.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. using a potometer ✔\n \n Accept transpirometer but not respirometer\n \n .\n

\n

\n b. leafy shoot attached to a reservoir and a graduated «capillary» tube ✔\n

\n

\n c. as transpiration increases water uptake «by roots» also increases ✔\n

\n

\n d. distance/time for bubble «in capillary tube» to travel is used to measure transpiration rate ✔\n

\n
\n", "Examiners report": "None", "question_id": "19N.1B.SL.TZ0.2C", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-1-gas-exchange", "b3-1-9-transpiration-as-a-consequence-of-gas-exchange-in-a-leaf" ] }, { "Question": "
\n
\n

\n Which statement defines alleles?\n

\n

\n A. They are the different forms of a gene that have the same effect on the phenotype.\n

\n

\n B. They are the similar forms of a gene in different positions of a chromosome.\n

\n

\n C. They are the various forms of a gene with slight differences in their base sequences.\n

\n

\n D. They are the different forms of a gene coding for identical polypeptide chains.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "22M.1A.SL.TZ2.13", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-2-inheritance", "d3-2-3-genotype-as-the-combination-of-alleles-inherited-by-an-organism" ] }, { "Question": "
\n
\n

\n Which is an example of speciation?\n

\n

\n A. Selective breeding to produce new varieties of the wheat\n \n Triticum aestivum\n \n with higher crop yield\n

\n

\n B. Evolution of different courtship behaviours in separate populations of the cricket\n \n Gryllus rubens\n \n

\n

\n C. Natural selection leading to an increase in the frequency of darker individuals of\n \n Biston betularia\n \n

\n

\n D. Selective feeding by koalas (\n \n Phascolarctos cinereus\n \n ) on\n \n Eucalyptus\n \n species\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "
\n

\n Some G2 forms pointed out that speciation is not part of the SL material and only occurs in HL. Although there may be some justification in the comments, it was assumed that candidates would deduce what was required from their study of Topic 5.1 (Evidence for evolution) — populations of a species can gradually diverge into separate species by evolution. The question performed well according to difficulty and discrimination statistics.\n

\n
\n", "question_id": "21M.1A.SL.TZ2.20", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a4-1-evolution-and-speciation", "a4-1-6-speciation-by-splitting-of-pre-existing-species", "a4-1-7-roles-of-reproductive-isolation-and-differential-selection-in-speciation" ] }, { "Question": "
\n
\n (i)\n
\n
\n

\n where the DNA of each individual could be taken from.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n from blood sample/hair/cheek/saliva/semen;\n

\n

\n \n Do not accept red blood cells\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.1B.SL.TZ1.3AI", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-3-photosynthesis", "c1-3-7-techniques-for-varying-concentrations-of-carbon-dioxide-light-intensity-or-temperature-experimentally-to-investigate-the-effects-of-limiting-factors-on-the-rate-of-photosynthesis" ] }, { "Question": "
\n
\n

\n Which statement correctly describes genome and proteome?\n

\n

\n A. Only the genome but not the proteome can be analysed using gel electrophoresis.\n

\n

\n B. The genome and the proteome are the same in all tissues in an organism.\n

\n

\n C. In cells of different tissues, the genome is the same while the proteome varies.\n

\n

\n D. Only mutations in the proteome but not in the genome cause any variability.\n

\n

\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "
\n

\n This question showed some weakness of understanding among better candidates. In section 3.1 it states that the genome is the whole of the genetic information of an organism while in the protein section 2.1 it mentions the fact that every individual has a unique proteome. In 3.5 it clearly states that gel electrophoresis is used to separate proteins or fragments of DNA according to size, therefore excluding A as an answer. Answer B is incorrect, as it is mentioning tissues (unicellular organisms do not have tissues) and the proteome differs in different tissues. Answer D is too obviously wrong so hardly any candidate chose it.\n

\n
\n", "question_id": "19M.1A.HL.TZ2.8", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-2-gene-expression-[hl-only]", "d2-2-5-differences-between-the-genome-transcriptome-and-proteome-of-individual-cells" ] }, { "Question": "
\n
\n

\n What activates a tyrosine kinase pathway in a cell following binding to a receptor?\n

\n

\n
\n A.  Odorant molecules\n

\n

\n B.  Epinephrine\n

\n

\n C.  Taste molecules\n

\n

\n D.  Insulin\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "SPM.1A.HL.TZ0.18", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c2-1-chemical-signalling-[hl-only]", "c2-1-11-transmembrane-receptors-with-tyrosine-kinase-activity" ] }, { "Question": "
\n
\n

\n Which process does\n \n not\n \n take place in the stroma of chloroplasts?\n

\n

\n A. Synthesis of carbohydrates\n

\n

\n B. Fixation of carbon\n

\n

\n C. Reduction of NADP\n

\n

\n D. Synthesis of ribulose bisphosphate\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "
\n

\n Answers were divided almost equally between the four possible answers in this question suggesting a lot of guesswork but the discrimination index shows that better-prepared candidates tended to answer correctly. Arguably none of the answers is completely correct. Shrewd candidates could eliminate answers A and D, because if D, was correct, A was also, and both could not be correct. Reduction of NADP was the expected answer but arguably it occurs in the stroma, as the reaction takes place adjacent to the outer surface of the thylakoid membrane. Even so, this was the best answer.\n

\n
\n", "question_id": "21M.1A.HL.TZ1.32", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-3-photosynthesis", "c1-3-12-atp-production-by-chemiosmosis-in-thylakoids" ] }, { "Question": "
\n
\n

\n Explain the role of calcium ions in muscle contraction.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n calcium released from sarcoplasmic reticulum;\n
    2. \n
  2. \n calcium binds to troponin;\n
    3. \n
  3. \n causes tropomyosin to move;\n
    4. \n
  4. \n uncovers binding sites;\n
    5. \n
  5. \n myosin heads bind to the actin forming cross bridges;\n
    6. \n
\n
\n", "Examiners report": "
\n

\n Well prepared candidates had no difficulty in describing the role of calcium in muscle contraction but they were in the minority. The discrimination index was very high.\n

\n
\n", "question_id": "22M.2.HL.TZ1.D", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-3-muscle-and-motility-(hl-only)", "b3-3-2-sliding-filament-model-of-muscle-contraction" ] }, { "Question": "
\n
\n (j)\n
\n
\n

\n Outline a reason that the path length was standardized.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n compensates for the different distances between entrances and food/OWTTE;\n
\n \n \n OR\n \n \n
\n to enable (fair/valid) comparison/OWTTE;\n

\n

\n \n Do not accept unspecific answers such as ‘to be consistent’.\n \n

\n
\n", "Examiners report": "
\n

\n This was another question that tested candidates' ability to express a relatively simple idea clearly, rather than having to understand a more complicated idea. The key part of the answer was that standardizing path lengths allowed results to be compared to find the effect of the intended independent variable, by cancelling out another variable.\n

\n
\n", "question_id": "22N.2.HL.TZ0.1J", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-1-integration-of-body-systems", "c3-1-4-the-brain-as-a-central-information-integration-organ" ] }, { "Question": "
\n
\n (d.ii)\n
\n
\n

\n Explain what happens to an enzyme if there is a change of pH.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n a. change in pH can cause a change in the tertiary structure of the enzyme\n
\n \n \n OR\n \n \n
\n enzyme denatured ✔\n

\n

\n b. causing a change in the active site / substrate not able to bind ✔\n

\n

\n c. the enzyme will not work as efficiently / decreased rate of reaction ✔\n

\n

\n d. (may no longer be) the\n \n optimum\n \n /\n \n optimal\n \n pH for enzyme activity ✔\n

\n

\n \n Allow answer in the form of a graph\n \n .\n

\n
\n", "Examiners report": "None", "question_id": "21M.2.SL.TZ2.2D.II", "topics": [ "b-form-and-function" ], "subtopics": [ "b1-2-proteins", "b1-2-5-effect-of-ph-and-temperature-on-protein-structure" ] }, { "Question": "
\n
\n (d)\n
\n
\n

\n The diagram shows the realized niches of the five species of warbler. Suggest how the fundamental niche of\n \n D. castanea\n \n might differ from its realized niche.\n

\n

\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. the realized is the actual niche and the fundamental is in the absence of competition;\n

\n

\n b. with no competition the\n \n D. castanea\n \n would have a larger habitat/more food\n
\n \n \n OR\n \n \n
\n \n D.castanea\n \n could occupy the niches currently occupied by the other warbler species;\n

\n

\n \n Accept named species\n \n .\n

\n
\n", "Examiners report": "
\n

\n Weaker candidates gave incomplete or confused suggestions in differentiating between the realised and fundamental niche.\n

\n
\n", "question_id": "20N.2.SL.TZ0.12D", "topics": [ "b-form-and-function" ], "subtopics": [ "b4-2-ecological-niches", "b4-2-12-fundamental-and-realized-niches", "b4-2-13-competitive-exclusion-and-the-uniqueness-of-ecological-niches" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n If a zucchini is allowed to dry in the open air, predict how the osmolarity of the zucchini cells would change.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n osmolarity will increase «because the cells become dehydrated»\n
\n \n \n OR\n \n \n
\n the cells become hypertonic ✔\n

\n

\n \n Accept water potential of the tissue decreases.\n \n
\n \n Do not accept \"change\" instead of \"increase\".\n \n

\n
\n", "Examiners report": "None", "question_id": "19N.1B.SL.TZ0.3B", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-3-water-potential", "d2-3-3-water-movement-by-osmosis-into-or-out-of-cells", "d2-3-4-changes-due-to-water-movement-in-plant-tissue-bathed-in-hypotonic-and-those-bathed-in-hypertonic-solutions" ] }, { "Question": "
\n
\n

\n What life function is illustrated?\n

\n

\n A.  Nutrition\n

\n

\n B.  Homeostasis\n

\n

\n C.  Endocytosis\n

\n

\n D.  Response\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "
\n

\n Both these questions 2 and 3 referred to a diagram of a unicellular organism that had been placed in distilled water. Question 2 asked the candidates to identify the life function illustrated and more than 50\n \n \n \n \n % of the candidates correctly identified the process as homeostasis.\n
\n
\n

\n
\n", "question_id": "22N.1A.SL.TZ0.2", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-3-homeostasis", "d3-3-1-homeostasis-as-maintenance-of-the-internal-environment-of-an-organism" ] }, { "Question": "
\n
\n

\n Outline the uses of ATP in plant cells.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. used as an energy source ✔\n

\n

\n b. supplies/releases energy for biochemical reactions ✔\n

\n

\n c. photosynthesis/active transport/other verifiable example of reaction or process ✔\n

\n
\n", "Examiners report": "
\n

\n The diagram was generally confusing to candidates.\n

\n

\n Expressing the nature of ATP in an outline of its use to plants was problematic for many students. Rather than a source of energy it was thought to be energy itself. Many processes use ATP in one part of the pathway or another, so a wide variety of seemingly contradictory answers received credit. For example, ATP is used in cell respiration during glycolysis. Credit was given for glycolysis as well as for respiration.\n

\n
\n", "question_id": "21M.2.SL.TZ1.D", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-3-photosynthesis", "c1-3-2-conversion-of-carbon-dioxide-to-glucose-in-photosynthesis-using-hydrogen-obtained-by-splitting-water" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Outline how sex is determined in humans.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n genetically determined/determined by (pair of) sex chromosomes/X and Y chromosomes;\n
    2. \n
  2. \n sperm carry either an X or a Y chromosome;\n
    3. \n
  3. \n egg is X and if fertilized by X sperm leads to a female child / XX female\n
    \n \n \n OR\n \n \n
    \n egg is X and if fertilized by Y sperm leads to a male child / XY male;\n
    4. \n
\n
\n", "Examiners report": "None", "question_id": "SPM.2.SL.TZ0.6", "topics": [ "a-unity-and-diversity", "d-continuity-and-change" ], "subtopics": [ "a3-1-diversity-of-organisms", "a3-1-7-karyotyping-and-karyograms", "d4-1-natural-selection", "d4-1-2-roles-of-mutation-and-sexual-reproduction-in-generating-the-variation-on-which-natural-selection-acts", "d1-3-mutations-and-gene-editing", "d1-3-7-mutation-as-a-source-of-genetic-variation" ] }, { "Question": "
\n
\n

\n Which organism would be classified as a saprotroph?\n

\n

\n A. A single-celled eukaryote that obtains its carbon compounds by photosynthesis and ingestion of other single-celled organisms\n

\n

\n B. A jellyfish that uses the stinging cells in its tentacles to paralyse its prey, which is passed to an internal gastric cavity through a single opening\n

\n

\n C. A fungus that feeds by secretion of digestive enzymes onto its food and absorption of digested material\n

\n

\n D. A dung beetle that feeds on the fecal material left behind by other animals\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "21M.1A.SL.TZ2.17", "topics": [ "b-form-and-function" ], "subtopics": [ "b4-2-ecological-niches", "b4-2-6-saprotrophic-nutrition-in-some-fungi-and-bacteria" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Describe how the structure of cardiac muscle cells allows them to carry out their function.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n \n

\n

\n \n Not necessary to present answer in a table.\n \n

\n

\n \n Award\n \n [1]\n \n for each set of corresponding structure and function.\n \n

\n
\n", "Examiners report": "
\n

\n Many could provide a correct description including many elements, but many discussed the structure of the heart as a whole, rather than the cellular structure of cardiac muscle cells or discussed at length the myogenic nature of cardiac tissue.\n

\n
\n", "question_id": "19M.2.HL.TZ2.22B", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-2-transport", "b3-2-15-adaptations-of-the-mammalian-heart-for-delivering-pressurized-blood-to-the-arteries", "b2-3-cell-specialization", "b2-3-9-adaptations-of-cardiac-muscle-cells-and-striated-muscle-fibres" ] }, { "Question": "
\n
\n

\n The mRNA codon UAC codes for the amino acid tyrosine. Which tRNA carries tyrosine?\n

\n

\n \n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "
\n

\n The G2 forms raised two concerns with this question.\n

\n

\n Firstly, the use of the term codon to describe a DNA sequence of 3 bases when this term is normally used for sequences of bases on mRNA. It is normal to use the term triplet referring to bases on a strand of DNA though codon is an accepted but infrequently used alternative.\n

\n

\n Secondly, the question does not make it clear if it is referring to the sense or antisense strand, both of which would give different responses.\n

\n

\n Both answers C and D were accepted as correct, and the question will be changed before the paper is published.\n

\n
\n", "question_id": "21M.1A.HL.TZ2.28", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d1-2-protein-synthesis", "d1-2-17-initiation-of-translation" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Distinguish between the outcomes of a cell dividing either by mitosis or meiosis.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. mitosis produces two daughter cells while meiosis four ✔\n

\n

\n b. mitosis produces cells with same number of chromosomes (2n) while in meiosis they are halved (n) ✔\n

\n

\n c. mitosis produces body cells but meiosis produces gametes\n
\n \n \n OR\n \n \n
\n mitosis produces genetically identical cells but meiosis does not ✔\n

\n

\n \n Allow answers in a table\n \n .\n

\n

\n \n Reference to both has to be present for the\n \n mark.\n

\n
\n", "Examiners report": "
\n

\n There were several G2 comments about Q2a, as it could be said that several processes were occurring. Perhaps it should have been more specific. Two out of DNA replication, cell growth and duplication of organelles were expected for the two marks. A surprising number of candidates in all languages, confused 'processes' with 'phases' and stated that interphase consisted of G1, S and G2. Most managed to label prophase and anaphase correctly on the diagram as required in part (b). The answers to part (b) were generally clear, but some lost marks for not comparing the same point. For example 'Mitosis produces diploid cells, but meiosis produces gametes' did not score a mark. The mitotic index was well known.\n

\n
\n", "question_id": "21M.2.HL.TZ2.2C", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-1-cell-and-nuclear-division", "d2-1-4-roles-of-mitosis-and-meiosis-in-eukaryotes" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n The niches of the red and grey squirrels overlap. Explain the concept of competitive exclusion with respect to the changes in squirrel distribution shown in the maps.\n

\n

\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n a. competitive exclusion states two species that occupy a similar niche in the same location cannot coexist ✔\n

\n

\n b. one of the two competitors will always have an advantage over the other ✔\n

\n

\n c. leads to extinction/displacement/evolution of the second competitor ✔\n

\n

\n d. grey squirrels have replaced/occupied niches formerly occupied by red squirrels\n
\n \n \n OR\n \n \n
\n habitats favour the grey squirrel in competition for the niche ✔\n

\n

\n e. the niche of one competitor/both competitors becomes narrower ✔\n

\n
\n", "Examiners report": "
\n

\n This question was yet another instance where weaker students were disadvantaged by their inability to access the appropriate subject-specific vocabulary. They tended not to use the term “niche” with this question, and too frequently “niche” and “habitat” were confused.\n

\n
\n", "question_id": "19M.2.SL.TZ1.17B", "topics": [ "b-form-and-function" ], "subtopics": [ "b4-2-ecological-niches", "b4-2-13-competitive-exclusion-and-the-uniqueness-of-ecological-niches" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Outline the reasons for the differences in blood concentrations between the renal artery and the renal vein.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n

\n a. urea/waste products lower in vein due to excretion «in urine»/ultrafiltration but not reabsorption ✔\n

\n

\n b. oxygen lower in vein due to use in cell respiration/in kidney tissue ✔\n

\n

\n c. carbon dioxide higher in vein due to production by cell respiration/excretion by kidney cells ✔\n

\n

\n d. glucose lower in vein due to use in cell respiration «by kidney tissue» ✔\n

\n

\n e. sodium/chloride/ion concentrations changed due to production of hypertonic/hypotonic urine\n
\n \n \n OR\n \n \n
\n sodium/chloride/ion concentrations lower due to removal of excess ✔\n

\n

\n f. ion/solute concentrations lower in vein than artery if ADH has been secreted\n
\n \n \n OR\n \n \n
\n ion/solute concentrations in vein vary depending on amount of water reabsorbed in the collecting duct ✔\n

\n

\n g. drug/toxin concentrations lower in vein due to excretion in urine ✔\n

\n

\n \n Accept any point given as the converse.\n \n

\n

\n \n Each mark point includes a difference and reason for it.\n \n

\n
\n", "Examiners report": "None", "question_id": "19N.2.HL.TZ0.7", "topics": [ "d-continuity-and-change", "c-interaction-and-interdependence" ], "subtopics": [ "d3-3-homeostasis", "d3-3-8-role-of-the-glomerulus-bowmans-capsule-and-proximal-convoluted-tubule-in-excretion", "d3-2-inheritance", "d3-2-9-abo-blood-groups-as-an-example-of-multiple-alleles", "c3-1-integration-of-body-systems", "c3-1-14-feedback-control-of-heart-rate-following-sensory-input-from-baroreceptors-and-chemoreceptors" ] }, { "Question": "
\n
\n

\n The diagram shows a type of fatty acid.\n

\n

\n \n

\n

\n What type of fatty acid is shown?\n

\n

\n A. Trans unsaturated\n

\n

\n B. Cis unsaturated\n

\n

\n C. Trans saturated\n

\n

\n D. Cis saturated\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "
\n

\n A very good discriminator question, showing lack of knowledge in the weaker candidates.\n

\n
\n", "question_id": "19M.1A.SL.TZ2.12", "topics": [ "b-form-and-function" ], "subtopics": [ "b1-1-carbohydrates-and-lipids", "b1-1-10-difference-between-saturated-monounsaturated-and-polyunsaturated-fatty-acids" ] }, { "Question": "
\n
\n (a.i)\n
\n
\n

\n Identify the process Y and state the name of the organelle where it takes place in a plant cell.\n

\n

\n Process Y:\n

\n

\n Name of the organelle:\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n process Y: photosynthesis ✔\n

\n

\n organelle: chloroplast ✔\n

\n

\n \n Both needed\n \n .\n

\n
\n", "Examiners report": "
\n

\n The diagram was generally confusing to candidates.\n

\n

\n This was generally answered correctly.\n

\n
\n", "question_id": "21M.2.SL.TZ1.2", "topics": [ "c-interaction-and-interdependence", "b-form-and-function" ], "subtopics": [ "c4-2-transfers-of-energy-and-matter", "c4-2-18-ecosystems-as-carbon-sinks-and-carbon-sources", "c1-3-photosynthesis", "c1-3-18-synthesis-of-carbohydrates-amino-acids-and-other-carbon-compounds-using-the-products-of-the-calvin-cycle-and-mineral-nutrients", "b1-1-carbohydrates-and-lipids", "b1-1-2-production-of-macromolecules-by-condensation-reactions-that-link-monomers-to-form-a-polymer", "c1-2-cell-respiration", "c1-2-4-cell-respiration-as-a-system-for-producing-atp-within-the-cell-using-energy-released-from-carbon-compounds", "c1-3-2-conversion-of-carbon-dioxide-to-glucose-in-photosynthesis-using-hydrogen-obtained-by-splitting-water", "c1-1-enzymes-and-metabolism", "c1-1-3-anabolic-and-catabolic-reactions" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Outline the action taken by the diaphragm during inhalation.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n contracts/flattens/becomes less domed/increases volume of thorax;\n

\n
\n", "Examiners report": "None", "question_id": "21N.2.SL.TZ0.2C", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-1-gas-exchange", "b3-1-5-ventilation-of-the-lungs" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Outline how mutation can lead to cancer.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n mutations are random changes in the sequences of genes/DNA;\n
    2. \n
  2. \n (mutation) may involve addition/deletion/substitution/inversion of DNA bases;\n
    3. \n
  3. \n (mutations) in tumour suppressor genes/oncogenes;\n
    4. \n
  4. \n uncontrolled cell division/mitosis occurs;\n
    5. \n
  5. \n abnormal cells cannot perform their function;\n
    6. \n
  6. \n they divide repeatedly to form tumours;\n
    7. \n
\n
\n", "Examiners report": "None", "question_id": "SPM.2.SL.TZ0.7", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d1-3-mutations-and-gene-editing", "d1-3-6-consequences-of-mutation-in-germ-cells-and-somatic-cells", "d3-2-inheritance", "d3-2-7-phenylketonuria-as-an-example-of-a-human-disease-due-to-a-recessive-allele", "d1-3-7-mutation-as-a-source-of-genetic-variation" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Describe what is shown in a cladogram.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. similarities/differences between organisms/species/clades ✔\n \n mpa and mpd concern actual characteristics, not evolutionary relationships\n \n .\n

\n

\n b. «probable» evolutionary relationships/closeness/common ancestry/phylogeny ✔\n \n mpb concerns such relationships\n \n

\n

\n c. divergence/splits/speciation/branches/nodes ✔\n \n mpc concerns the structure branching of the cladogram\n \n

\n

\n d. relative similarity/differences between base sequence/amino acid sequence ✔\n

\n
\n", "Examiners report": "None", "question_id": "19N.2.HL.TZ0.3A", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a3-2-classification-and-cladistics-(hl-only)", "a3-2-7-analysing-cladograms" ] }, { "Question": "
\n
\n

\n Using the climograph, identify the relationship between maximum temperature and rainfall.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n maximum temperature occurs just when rainfall begins/at the onset of the rainy season/monsoon\n
\n \n \n OR\n \n \n
\n negative relationship «as maximum temperature drops, rainfall increases» ✔\n

\n

\n \n OWTTE\n \n

\n
\n", "Examiners report": "None", "question_id": "19M.2.HL.TZ2.A.II", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-2-stability-and-change", "d4-2-14-cyclical-succession-in-ecosystems" ] }, { "Question": "
\n
\n

\n What is the arrangement of subunits in a DNA nucleotide?\n

\n

\n A.  sugar – base – phosphate\n

\n

\n B.  sugar – phosphate – base\n

\n

\n C.  phosphate – sugar – base\n

\n

\n D.  sugar – phosphate – base – base – phosphate – sugar\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "
\n

\n This question required the students to identify the arrangement of the subunits of a DNA nucleotide. This question discriminated well and was statistically the second-best performing question on the paper.\n

\n
\n", "question_id": "22N.1A.SL.TZ0.6", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a1-2-nucleic-acids", "a1-2-6-dna-as-a-double-helix-made-of-two-antiparallel-strands-of-nucleotides-with-two-strands-linked-by-hydrogen-bonding-between-complementary-base-pairs" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Based on the information, suggest with a reason which of the labelled cell types will become more common in\n \n Allium\n \n root tips treated with ZDV.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. Y (will become more common) ✔\n

\n

\n b. spindle not formed yet\n
\n \n \n OR\n \n \n
\n cells x and z have spindles ✔\n

\n

\n c. cells in Y cannot progress (into Z/into metaphase) ✔\n

\n
\n", "Examiners report": "
\n

\n Many students correctly identified cell type Y but reasoning was less accurate.\n

\n
\n", "question_id": "21M.2.HL.TZ1.1C", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-1-cell-and-nuclear-division", "d2-1-13-phases-of-the-cell-cycle" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Draw a labelled diagram to show the structure of a single nucleotide of RNA.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n \n

\n
    \n
  1. \n \n ribose\n \n drawn as a pentagon and labelled;\n
    2. \n
  2. \n \n base\n \n linked correctly (to C\n \n 1\n \n ) of ribose and labelled;\n
    3. \n
  3. \n \n phosphate\n \n linked correctly (to C\n \n 5\n \n ) of ribose and labelled;\n
    4. \n
\n
\n", "Examiners report": "
\n

\n Many candidates were able to draw a nucleotide and label the subunits correctly. Weaker candidates did not know what a nucleotide was, so often drew a diagram of either a DNA or RNA polynucleotide.\n

\n
\n", "question_id": "22M.2.SL.TZ1.8A", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a1-2-nucleic-acids", "a1-2-5-rna-as-a-polymer-formed-by-condensation-of-nucleotide-monomers" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n State the reason that\n \n O. sativa\n \n and\n \n O. rufipogon\n \n are classified as different species.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n cannot interbreed to produce\n \n fertile\n \n offspring ✔\n

\n

\n \n Accept converse or a good explanation\n \n .\n

\n
\n", "Examiners report": "None", "question_id": "19N.2.SL.TZ0.1", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a3-1-diversity-of-organisms", "a3-2-classification-and-cladistics-(hl-only)", "a3-2-7-analysing-cladograms" ] }, { "Question": "
\n
\n (e)\n
\n
\n

\n Distinguish between the proportion of ancestral and derived alleles for all three genes in\n \n O. sativa indica\n \n and\n \n O. sativa japonica\n \n .\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a.\n \n O.s. indica\n \n has more of the ancestral allele «for all three genes» ✔\n \n Accept converse\n \n .\n

\n

\n b. lower/higher values for ancestral/derived are not for the same genes ✔\n \n Allow specific gene examples\n \n .\n

\n

\n c. for\n \n O. s. indica\n \n the highest proportion is for\n \n DPL2\n \n \n ancestral\n \n , but for\n \n O. s. japonica\n \n is\n \n GS3\n \n \n derived\n \n allele ✔\n \n Allow converse for smallest derived.\n \n

\n
\n", "Examiners report": "None", "question_id": "19N.2.HL.TZ0.1E", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a3-2-classification-and-cladistics-(hl-only)", "a3-2-7-analysing-cladograms" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n The graph of the effect of pH on immobilized lipase activity does not allow for the determination of optimum pH precisely. Explain how a more exact value for the optimum pH could be determined.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. the experiment is repeated with smaller increments of pH ✔\n

\n

\n b. «repeated» within the range of the optimum pH\n
\n \n \n OR\n \n \n
\n between pH 6/7 and 8 ✔\n

\n

\n c. the pH that gives the highest enzyme activity is optimum ✔\n

\n
\n", "Examiners report": "
\n

\n Candidates found this question to be challenging. Students were asked to “explain how a more exact value for the optimum pH could be determined.” Students who completed practical 3 and were also taught the second skill listed in the subject guide in topic 2.5 (Design of experiments to test the effect of temperature, pH and substrate concentration on the activity of enzymes) should have been able to achieve the marks. Common incorrect answers suggested using better graphs or different calculation methods. Students should be instructed to understand the difference between experimental methods and data-processing tools.\n

\n
\n", "question_id": "19M.1B.SL.TZ1.1B", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-1-enzymes-and-metabolism", "c1-1-8-effects-of-temperature-ph-and-substrate-concentration-on-the-rate-of-enzyme-activity" ] }, { "Question": "
\n
\n

\n In an experiment on osmosis, red blood cells were immersed in a salt solution for two hours. The micrographs show the appearance of these cells before and after immersion in the salt solution.\n

\n

\n \n

\n

\n [Source: Ed Uthman, Acanthocytes, from peripheral blood [image online] Available at:\n
\n \n https://en.wikipedia.org/wiki/\n \n \n Acanthocyte#/media/File:Acanthocytes,_Peripheral_Blood_(3884092551).jpg\n
\n \n This file is licensed under the Creative Commons Attribution 2.0 Generic (CC BY 2.0)\n \n https://creativecommons.org/licenses/by/2.0/\n \n Source adapted.]\n

\n

\n

\n

\n What explains the observed changes?\n

\n

\n A. The salt solution was hypertonic and entered the red blood cells.\n

\n

\n B. The salt solution was hypotonic and disrupted the membranes of the red blood cells.\n

\n

\n C. The salt solution was hypertonic and water moved into it from the red blood cells.\n

\n

\n D. The salt solution was hypotonic and mineral salts were lost from the red blood cells.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "
\n

\n This question performed well in terms in terms of difficulty and in having the highest discrimination index on the paper.\n

\n
\n", "question_id": "22M.1A.SL.TZ2.3", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-3-water-potential", "d2-3-3-water-movement-by-osmosis-into-or-out-of-cells" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n From the data, identify the depth along the transect where the greatest species richness is observed.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n 6.5 m ✔\n

\n

\n \n Unit required\n \n

\n
\n", "Examiners report": "
\n

\n Richness appeared well understood but the depth unit was sometimes omitted.\n

\n
\n", "question_id": "19M.2.SL.TZ1.11A", "topics": [ "b-form-and-function" ], "subtopics": [ "b4-1-adaptation-to-environment", "b4-1-4-range-of-tolerance-of-a-limiting-factor" ] }, { "Question": "
\n
\n (d)\n
\n
\n

\n State the proportion of the ancestral allele for the gene GS3 in the\n \n O. rufipogon-III\n \n population.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n \n \n \n \n 3\n \n \n 4\n \n \n \n \n /0.75/75% ✔\n

\n

\n \n Do not accept 0.75% or 75 or ratios\n \n

\n
\n", "Examiners report": "None", "question_id": "19N.2.HL.TZ0.1D", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a3-2-classification-and-cladistics-(hl-only)", "a3-2-7-analysing-cladograms" ] }, { "Question": "
\n
\n (b.ii)\n
\n
\n

\n Describe how ingested plastics can cause problems to marine birds.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. fill up the stomachs (of young birds) so they feel full / starve to death;\n

\n

\n b. damage the digestive system / cut the gut/stomach/oesophagus/intestines (leading to internal bleeding);\n

\n

\n c. block passage of food (causing starvation);\n

\n

\n d. cause choking (so cannot breathe);\n

\n

\n e. contain/decompose to toxic chemicals (poisoning birds)\n
\n \n \n OR\n \n \n
\n toxins/microplastics in seawater build up/biomagnify (and poison wildlife);\n

\n
\n", "Examiners report": "None", "question_id": "20N.2.SL.TZ0.13B.II", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-2-stability-and-change", "d4-2-10-effects-of-microplastic-and-macroplastic-pollution-of-the-oceans" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Outline the measurements which would need to be taken to determine the activity of the beta-galactosidase at different pH values.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. test samples for the concentration/amount of products/glucose/fructose/substrate/lactose ✔\n \n Accept use Benedict/Fehling to see change in amount of reducing sugar\n \n

\n

\n b. take samples of the reaction mixture at regular/timed intervals ✔\n \n Must indicate that samples are taken at timed intervals\n \n

\n

\n c. repeated measurements «at the different pH values» ✔\n

\n

\n d. measure independent/controlled/standardised/variables / temperature ✔\n

\n
\n", "Examiners report": "None", "question_id": "19N.1B.SL.TZ0.2B", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-1-enzymes-and-metabolism", "c1-1-8-effects-of-temperature-ph-and-substrate-concentration-on-the-rate-of-enzyme-activity" ] }, { "Question": "
\n
\n

\n X indicates the movement of a structure in the neuron. Explain what events trigger this movement and what happens next.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n a. depolarization of pre-synaptic membrane / action potential/nerve impulse arrives;\n

\n

\n b. uptake of calcium / calcium ions diffuse in / calcium channels open;\n

\n

\n c. structures containing neurotransmitter/vesicles move to/fuse with membrane;\n

\n

\n d.\n \n neurotransmitter\n \n /\n \n acetylcholine\n \n released by exocytosis into cleft/binds to postsynaptic membrane/receptors;\n

\n
\n", "Examiners report": "None", "question_id": "20N.2.HL.TZ0.B.II", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c2-1-chemical-signalling-[hl-only]", "c2-1-7-initiation-of-signal-transduction-pathways-by-receptors", "c2-1-8-transmembrane-receptors-for-neurotransmitters-and-changes-to-membrane-potential", "c2-1-9-transmembrane-receptors-that-activate-g-proteins" ] }, { "Question": "
\n
\n

\n Outline the principles used by scientists to classify organisms.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n

\n a. use of the binomial system ✔\n

\n

\n b. agreed/developed by scientists /\n \n OWTTE\n \n ✔\n

\n

\n c. hierarchy of taxa used ✔\n \n Names of the seven taxa not required\n \n .\n

\n

\n d. three domains used/three domain names ✔\n \n OWTTE\n \n

\n

\n e. genome/DNA sequence similarities\n
\n \n \n OR\n \n \n
\n amino acid sequence of specific proteins ✔\n

\n

\n f. species from a common ancestor are grouped together\n
\n \n \n OR\n \n \n
\n included in the same clade/branch in cladogram ✔\n

\n

\n g. use evidence of evolutionary origin ✔ Allow example\n \n e.g.\n \n fossil record comparison\n

\n

\n h. shared characteristics within a group\n
\n \n \n OR\n \n \n
\n similar embryonic development ✔\n

\n
\n", "Examiners report": "None", "question_id": "19N.2.HL.TZ0.B", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a3-2-classification-and-cladistics-(hl-only)", "a3-2-1-need-for-classification-of-organisms", "a3-2-2-difficulties-classifying-organisms-into-the-traditional-hierarchy-of-taxa" ] }, { "Question": "
\n
\n

\n What property of water accounts for its usefulness as a coolant in sweat?\n

\n

\n A. High specific heat capacity\n

\n

\n B. High latent heat of vaporization\n

\n

\n C. High boiling point\n

\n

\n D. High melting point\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "21M.1A.SL.TZ2.7", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-3-homeostasis", "d3-3-6-thermoregulation-mechanisms-in-humans" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n State the relationship between elevation and nitrogen concentration in leaves of pitcher plants.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n the higher the elevation, the greater the nitrogen content\n
\n \n \n OR\n \n \n
\n positive relationship;\n

\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ2.20B", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-2-stability-and-change", "d4-2-8-eutrophication-of-aquatic-and-marine-ecosystems-due-to-leaching" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Plasma cells secrete antibodies against specific antigens. Outline how plasma cells become activated.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n a. macrophages/phagocytes recognize/engulf pathogen and display antigens ✔\n

\n

\n b. antigen binds to T cell/helper T cell / antigen causes activation of T cell ✔\n

\n

\n c. antigen binds to antibodies in membrane of B cells ✔\n

\n

\n d. (activated) T cells activate B cells (that have the antigen bound to them) ✔\n

\n

\n e. activated B cells divide to produce a clone of cells ✔\n

\n

\n f. active plasma cells develop from the clone of cells/from activated B cells ✔\n

\n

\n \n Accept B-lymphocyte and Tlymphocyte instead of B cell and T cell throughout the answer.\n \n

\n
\n", "Examiners report": "
\n

\n Some explanations of the production of active plasma cells were excellent but weaker candidates were mostly very confused, with antigens and antibodies muddled up. Many candidates thought that plasma cells are already present and just need to be activated, rather than them being produced as a result of the activity of macrophages, T-cells and B-cells. There was too much focus on memory cells. The mean mark was low, 0.6 out of 3.\n

\n
\n", "question_id": "21M.2.HL.TZ1.4", "topics": [ "c-interaction-and-interdependence", "d-continuity-and-change" ], "subtopics": [ "c3-2-defence-against-disease", "c3-2-9-multiplication-of-activated-b-lymphocytes-to-form-clones-of-antibody-secreting-plasma-cells", "d3-1-reproduction", "d3-1-17-pregnancy-testing-by-detection-of-human-chorionic-gonadotropin-secretion" ] }, { "Question": "
\n
\n (d)\n
\n
\n

\n A chromatograph was made of the photosynthetic pigments of a leaf of the plant.\n

\n

\n \n

\n

\n [Source: Adapted from “Diversity of Photosynthetic Pigments” by Alexander F. Motten in Tested Studies for\n
\n Laboratory Teaching, Volume 16 of the Association for Biology Laboratory Education and used by permission of the\n
\n author.]\n

\n

\n

\n

\n Outline what measurements would be taken to identify pigment X.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. the distance travelled from the origin/O to the solvent front;\n

\n

\n b. the distance travelled by the pigment (from the origin O to X);\n

\n

\n \n Accept X to solvent front if the candidate indicates that this allows O to X to be calculated\n \n .\n

\n
\n", "Examiners report": "
\n

\n Most candidates managed to outline what measurements would be taken to identify the pigment on the chromatogram with many identifying the pigment although this was not required.\n

\n
\n", "question_id": "20N.1B.SL.TZ0.3D", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-3-photosynthesis", "c1-3-4-separation-and-identification-of-photosynthetic-pigments-by-chromatography" ] }, { "Question": "
\n
\n

\n Using the letter C, label the stage on the diagram where chromosome supercoiling occurs.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n prophase ✔\n

\n

\n \n The stage should be clearly labelled\n \n .\n

\n

\n \n If more than one stage is shown the candidate does not receive a mark\n \n .\n

\n
\n", "Examiners report": "
\n

\n There were several G2 comments about Q2a, as it could be said that several processes were occurring. Perhaps it should have been more specific. Two out of DNA replication, cell growth and duplication of organelles were expected for the two marks. A surprising number of candidates in all languages, confused 'processes' with 'phases' and stated that interphase consisted of G1, S and G2. Most managed to label prophase and anaphase correctly on the diagram as required in part (b). The answers to part (b) were generally clear, but some lost marks for not comparing the same point. For example 'Mitosis produces diploid cells, but meiosis produces gametes' did not score a mark. The mitotic index was well known.\n

\n
\n", "question_id": "21M.2.HL.TZ2.B.I", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-1-cell-and-nuclear-division", "d2-1-7-phases-of-mitosis", "d2-1-13-phases-of-the-cell-cycle" ] }, { "Question": "
\n
\n (a.i)\n
\n
\n

\n Using the climograph, calculate the range of temperature.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n «30 − 26 =» 4 «°C» ✔\n

\n

\n \n Accept answers between 3 to 5 «°C».\n \n

\n
\n", "Examiners report": "
\n

\n Many could provide correct answers, but there were some who stated the range extremes instead of calculating the difference between them. Some also saw a correlation where there is none.\n

\n
\n", "question_id": "19M.2.SL.TZ2.15A.I", "topics": [ "c-interaction-and-interdependence", "a-unity-and-diversity" ], "subtopics": [ "c4-1-populations-and-communities", "c4-1-13-resource-competition-between-endemic-and-invasive-species", "a4-2-conservation-of-biodiversity", "a4-2-6-causes-of-the-current-biodiversity-crisis" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Suggest a hypothesis that accounts for the slightly different meaning of some codons in a very limited number of organisms.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n they occurred after the common origin of life\n \n OWTTE\n \n
\n \n \n OR\n \n \n
\n the genetic code is not «in fact» universal ✔\n

\n

\n \n Look for alternatives\n \n .\n
\n
\n

\n
\n", "Examiners report": "None", "question_id": "19N.2.SL.TZ0.2C", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d1-2-protein-synthesis", "d1-2-11-mutations-that-change-protein-structure" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n State the relationship between BCH and brain mass of shrews.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n positive correlation/the greater the BCH the greater the brain mass;\n

\n

\n \n No mark for ‘positive relationship’ or for directly proportional\n \n

\n
\n", "Examiners report": "
\n

\n Most candidate described the relationship shown on the graph as a positive correlation. Some referred to it incorrectly as directly proportional, but that would be revealed by data points along a straight line on the graph. The term 'positive relationship' is vague and should be discouraged.\n

\n
\n", "question_id": "22N.2.HL.TZ0.1", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-1-integration-of-body-systems", "c3-1-4-the-brain-as-a-central-information-integration-organ" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Outline the action taken by the diaphragm during inhalation.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n contracts/flattens/becomes less domed/increases volume of thorax;\n

\n
\n", "Examiners report": "
\n

\n 80 % of candidates knew that the diaphragm contracts than relaxes during inhalation, or stated that it flattens rather than moves upwards.\n

\n
\n", "question_id": "21N.2.SL.TZ0.4C", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-1-gas-exchange", "b3-1-5-ventilation-of-the-lungs" ] }, { "Question": "
\n
\n (a.i)\n
\n
\n

\n State how many water molecules are shown in the diagram.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n 10;\n

\n
\n", "Examiners report": "None", "question_id": "23M.2.HL.TZ1.4", "topics": [ "a-unity-and-diversity", "d-continuity-and-change" ], "subtopics": [ "a1-1-water", "a1-1-2-hydrogen-bonds-as-a-consequence-of-the-polar-covalent-bonds-within-water-molecules", "d3-3-homeostasis", "d3-3-6-thermoregulation-mechanisms-in-humans" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Describe what is shown in a cladogram.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. similarities/differences between organisms/species/clades ✔\n \n mpa and mpd concern actual characteristics, not evolutionary relationships\n \n .\n

\n

\n b. «probable» evolutionary relationships/closeness/common ancestry/phylogeny ✔\n \n mpb concerns such relationships\n \n

\n

\n c. divergence/splits/speciation/branches/nodes ✔\n \n mpc concerns the structure branching of the cladogram\n \n

\n

\n d. relative similarity/differences between base sequence/amino acid sequence ✔\n

\n
\n", "Examiners report": "None", "question_id": "19N.2.HL.TZ0.3", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a3-2-classification-and-cladistics-(hl-only)", "a3-2-7-analysing-cladograms", "a4-1-evolution-and-speciation", "a4-1-1-evolution-as-change-in-the-heritable-characteristics-of-a-population" ] }, { "Question": "
\n
\n (a.i)\n
\n
\n

\n Identify structure X.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n \n proximal\n \n convoluted tubule/PCT;\n

\n
\n", "Examiners report": "
\n

\n 60null% of candidates identified the proximal convoluted tubule.\n

\n
\n", "question_id": "22N.2.HL.TZ0.5", "topics": [ "d-continuity-and-change", "b-form-and-function" ], "subtopics": [ "d3-3-homeostasis", "d3-3-8-role-of-the-glomerulus-bowmans-capsule-and-proximal-convoluted-tubule-in-excretion", "d3-3-9-role-of-the-loop-of-henle", "d3-3-10-osmoregulation-by-water-reabsorption-in-the-collecting-ducts", "b2-3-cell-specialization", "b2-3-7-adaptations-to-increase-surface-area-to-volume-ratios-of-cells" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Outline how the carbon dioxide could be removed from the water used to irrigate the plant.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n a. boiling (and cooling) the water;\n

\n

\n b. expose the water to a vacuum;\n

\n

\n \n Allow distillation of water\n \n .\n

\n
\n", "Examiners report": "
\n

\n There were many suggestions on how carbon dioxide could be removed from water despite boiling the water being an assessment statement.\n

\n
\n", "question_id": "20N.1B.SL.TZ0.3B", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-3-photosynthesis", "c1-3-7-techniques-for-varying-concentrations-of-carbon-dioxide-light-intensity-or-temperature-experimentally-to-investigate-the-effects-of-limiting-factors-on-the-rate-of-photosynthesis" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Outline evidence for evolution from the limbs of mammals such as pangolins.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n pentadactyl;\n
    2. \n
  2. \n homologous with limbs of other vertebrates;\n
    3. \n
  3. \n due to common ancestry;\n
    4. \n
  4. \n adaptation;\n
    5. \n
\n

\n

\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ2.4B", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a4-1-evolution-and-speciation", "a4-1-4-evidence-for-evolution-from-homologous-structures" ] }, { "Question": "
\n
\n

\n What is the proteome of an individual?\n

\n

\n
\n A.  The amino acids unique to an individual making up the proteins in cells\n

\n

\n B.  The way in which an individual’s polypeptides are folded into a three-dimensional structure\n

\n

\n C.  The proteins synthesized as an expression of an individual’s genes\n

\n

\n D.  All possible combinations of amino acids an individual contains\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "23M.1A.HL.TZ2.8", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-2-gene-expression-[hl-only]", "d2-2-5-differences-between-the-genome-transcriptome-and-proteome-of-individual-cells" ] }, { "Question": "
\n
\n (d)\n
\n
\n

\n Identify in how many of the diets sucrose was the greatest mass of food consumed.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n 5;\n

\n
\n", "Examiners report": "None", "question_id": "22N.2.SL.TZ0.1D", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c4-2-transfers-of-energy-and-matter", "c4-2-15-primary-production-as-accumulation-of-carbon-compounds-in-biomass-by-autotrophs", "c4-2-16-secondary-production-as-accumulation-of-carbon-compounds-in-biomass-by-heterotrophs" ] }, { "Question": "
\n
\n

\n The graph shows the activity of an enzyme at different temperatures.\n

\n

\n \n

\n

\n [Source: © International Baccalaureate Organization 2019]\n

\n

\n

\n

\n What does the dashed line in the graph represent?\n

\n

\n A. Increasing temperature increases substrate concentration.\n

\n

\n B. Increasing temperature affects the active site.\n

\n

\n C. Increasing temperature increases the rate of reaction.\n

\n

\n D. Increasing temperature decreases the movement of particles.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "
\n

\n This question discriminated very well and was easy. The graph does not have values for temperature, therefore it is not showing that temperature starts at 0 ºC. An increase in temperature with modify the tertiary structure of the protein, affecting the active site. At the same time the increase in temperature increases Brownian movement, increasing the chances of collision between enzyme and substrate.\n

\n
\n", "question_id": "19M.1A.SL.TZ2.9", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-1-enzymes-and-metabolism", "c1-1-1-enzymes-as-catalysts" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Draw a labelled diagram to show the structure of a single nucleotide of RNA.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n \n

\n
    \n
  1. \n \n ribose\n \n drawn as a pentagon and labelled;\n
    2. \n
  2. \n \n base\n \n linked correctly (to C\n \n 1\n \n ) of ribose and labelled;\n
    3. \n
  3. \n \n phosphate\n \n linked correctly (to C\n \n 5\n \n ) of ribose and labelled;\n
    4. \n
\n
\n", "Examiners report": "
\n

\n Many candidates were able to draw a nucleotide and label the subunits correctly. Weaker candidates did not know what a nucleotide was, so often drew a diagram of either a DNA or RNA polynucleotide.\n

\n
\n", "question_id": "22M.2.HL.TZ1.8", "topics": [ "a-unity-and-diversity", "d-continuity-and-change" ], "subtopics": [ "a1-2-nucleic-acids", "a1-2-5-rna-as-a-polymer-formed-by-condensation-of-nucleotide-monomers", "d1-1-dna-replication", "d1-1-5-applications-of-polymerase-chain-reaction-and-gel-electrophoresis", "d3-2-inheritance", "d3-2-14-continuous-variation-due-to-polygenic-inheritance-and/or-environmental-factors" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Outline the role of ADH in osmoregulation.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n ADH (secreted by pituitary) if body/blood is dehydrated/hypertonic/has high solute concentration;\n
    2. \n
  2. \n more aquaporins / aquaporins open (in collecting duct);\n
    3. \n
  3. \n collecting duct more permeable to water/reabsorbs more water (from filtrate/urine);\n
    4. \n
  4. \n water reabsorbed by osmosis/water reabsorbed because medulla is hypertonic;\n
    5. \n
  5. \n (reabsorbed) water passes (from filtrate) to blood / blood solute concentration reduced;\n
    6. \n
  6. \n less water lost in urine / smaller volume of (more concentrated) urine;\n
    7. \n
  7. \n negative feedback / less/no ADH secreted when blood solute concentration returns to normal;\n
    8. \n
\n

\n \n Do not accept answers suggesting that ADH has a different effect when body fluids are hypotonic.\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.2.HL.TZ1.6", "topics": [ "d-continuity-and-change", "c-interaction-and-interdependence" ], "subtopics": [ "d3-3-homeostasis", "d3-3-7-role-of-the-kidney-in-osmoregulation-and-excretion", "d3-3-10-osmoregulation-by-water-reabsorption-in-the-collecting-ducts", "c1-1-enzymes-and-metabolism", "c1-1-16-regulation-of-metabolic-pathways-by-feedback-inhibition", "d3-1-reproduction", "d3-1-19-hormonal-control-of-pregnancy-and-childbirth" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Describe the endosymbiotic theory.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n

\n a. theory that eukaryotic cells evolved from prokaryotes\n
\n OR\n
\n origin of eukaryotic organisms based on some organisms living inside/engulfed by other organisms\n
\n OR\n
\n prokaryotic cell engulfed another prokaryote including it in cytoplasm without digesting it;\n
\n b. mitochondria/chloroplasts have double membranes;\n
\n c. mitochondria/chloroplasts have their own DNA/loop of DNA/naked DNA;\n
\n d. mitochondria/chloroplasts have similar size to prokaryotes;\n
\n e. mitochondria/chloroplasts can reproduce by binary fission;\n
\n f. mitochondria/chloroplasts have 70S ribosomes (same as prokaryotes);\n

\n
\n", "Examiners report": "
\n

\n The theory of endosymbiosis was quite well known. Common errors included the original engulfing process being carried out by a eukaryote, rather than a prokaryote.\n

\n
\n", "question_id": "21N.2.HL.TZ0.6A", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a2-2-cell-structure", "a2-2-12-origin-of-eukaryotic-cells-by-endosymbiosis" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n State the trophic level of the sea urchin.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n herbivore/primary consumer ✔\n

\n

\n \n Do not accept second trophic level\n \n

\n
\n", "Examiners report": "
\n

\n Primary consumer was frequently stated and second trophic level also seen, although not credited as the syllabus demands the former term.\n

\n
\n", "question_id": "19M.2.SL.TZ1.10A", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c4-2-transfers-of-energy-and-matter", "c4-2-10-classification-of-organisms-into-trophic-levels" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Using the data in the stacked column graph, describe the features that characterize the B2 enterotype.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n nearly half is\n \n Bacteroides\n \n / more\n \n Bacteroides\n \n (than other enterotypes);\n
    2. \n
  2. \n few\n \n Prevotella\n \n /fewer\n \n Prevotella\n \n than in P and R\n
    \n \n \n OR\n \n \n
    \n less\n \n Faecalibacterium\n \n than other enterotypes\n
    \n \n \n OR\n \n \n
    \n \n Ruminococcus\n \n is the lowest in B2;\n
    3. \n
  3. \n only 40 % other taxa / fewer other taxa (than other enterotypes) / less overall diversity (of taxa);\n
    4. \n
\n

\n

\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ2.1", "topics": [ "a-unity-and-diversity", "c-interaction-and-interdependence" ], "subtopics": [ "a2-2-cell-structure", "a2-2-5-prokaryote-cell-structure", "c3-2-defence-against-disease", "c3-2-1-pathogens-as-the-cause-of-infectious-diseases" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Identify the week and year in which the first cases were recorded in the suburbs.\n

\n

\n Week:\n

\n

\n Year:\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n week 34\n \n \n AND\n \n \n 2014 ✔\n

\n

\n \n both needed\n \n

\n
\n", "Examiners report": "
\n

\n This was a timely question with Ebola epidemics again causing great problems in parts of Africa. Students were expected to have had some practice at analysing data relating to an epidemic because of this Skill in the programme: Analysis of epidemiological data related to vaccination programmes. It was assumed that candidates would understand terms such as ‘case’, ‘fatal case’, ‘infect’ and ‘treat’.\n

\n

\n Nearly all candidates read from the graph the week and year in which the first cases were recorded in the suburbs.\n

\n
\n", "question_id": "19M.2.HL.TZ1.1", "topics": [ "c-interaction-and-interdependence", "a-unity-and-diversity" ], "subtopics": [ "c3-2-defence-against-disease", "a2-3-viruses-(hl-only)" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Deduce, with a reason, whether the relative brain mass is a good indicator of brain development.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n a. not a good indicator because it depends on body mass ✔\n

\n

\n b. not a good indicator as less developed organisms show a larger relative brain mass ✔\n

\n

\n \n Accept answers referring to specific organisms shown\n \n

\n
\n", "Examiners report": "
\n

\n In parts (b) and (c) few candidates referred to ‘relative’ brain mass thereby providing incorrect responses.\n

\n
\n", "question_id": "19M.1B.SL.TZ2.5C", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-1-integration-of-body-systems", "c3-1-4-the-brain-as-a-central-information-integration-organ" ] }, { "Question": "
\n
\n

\n For what reason do gametes contain only one allele of each gene?\n

\n

\n
\n A.  To prevent inbreeding in a population\n

\n

\n B.  Haploid cells contain only one set of chromosomes\n

\n

\n C.  The two alleles of a gene are separated during mitosis\n

\n

\n D.  Crossing over will always produce one allele of a gene\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "23M.1A.SL.TZ1.16", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-1-cell-and-nuclear-division", "d2-1-7-phases-of-mitosis" ] }, { "Question": "
\n
\n

\n Which statement best describes how evolution occurs?\n
\n
\n

\n

\n A.  Species which produce the most offspring are favoured by natural selection.\n

\n

\n B.  Mutations in somatic cells are passed on to offspring.\n

\n

\n C.  Natural selection decreases the frequency of unfavourable characteristics.\n

\n

\n D.  Changes in species lead towards greater complexity over time.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "23M.1A.SL.TZ2.18", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a4-1-evolution-and-speciation", "a4-1-1-evolution-as-change-in-the-heritable-characteristics-of-a-population" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Describe the endosymbiotic theory.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n

\n a. theory that eukaryotic cells evolved from prokaryotes\n
\n OR\n
\n origin of eukaryotic organisms based on some organisms living inside/engulfed by other organisms\n
\n OR\n
\n prokaryotic cell engulfed another prokaryote including it in cytoplasm without digesting it;\n
\n b. mitochondria/chloroplasts have double membranes;\n
\n c. mitochondria/chloroplasts have their own DNA/loop of DNA/naked DNA;\n
\n d. mitochondria/chloroplasts have similar size to prokaryotes;\n
\n e. mitochondria/chloroplasts can reproduce by binary fission;\n
\n f. mitochondria/chloroplasts have 70S ribosomes (same as prokaryotes);\n

\n
\n", "Examiners report": "
\n

\n The theory of endosymbiosis was quite well known. Common errors included the original engulfing process being carried out by a eukaryote, rather than a prokaryote.\n

\n
\n", "question_id": "21N.2.SL.TZ0.6", "topics": [ "a-unity-and-diversity", "d-continuity-and-change" ], "subtopics": [ "a2-2-cell-structure", "a2-2-12-origin-of-eukaryotic-cells-by-endosymbiosis", "d2-1-cell-and-nuclear-division", "d2-1-4-roles-of-mitosis-and-meiosis-in-eukaryotes", "a3-1-diversity-of-organisms", "a3-1-3-binomial-system-for-naming-organisms" ] }, { "Question": "
\n
\n

\n Identify with a reason the city where the plants were more insulated from freezing temperatures.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n Montreal because it has the lowest number of days below 0 °C without snow cover;\n

\n

\n \n Do not award the mark for Montreal if the reason is not given\n \n .\n

\n
\n", "Examiners report": "
\n

\n 90 % of candidates identified Montreal as the city where plants were more insulated because it was where there were fewer freezing days without snow cover.\n

\n
\n", "question_id": "20N.2.SL.TZ0.D.I", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-2-stability-and-change", "d4-2-4-use-of-a-model-to-investigate-the-effect-of-variables-on-ecosystem-stability" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Sketch the complementary strand to complete the section of a DNA diagram.\n

\n

\n \n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n a. correct base sequence: T, G, A;\n

\n

\n b. strand drawn anti-parallel;\n

\n

\n c. correct shapes used;\n

\n

\n \n

\n

\n \n Award\n \n [2 max]\n \n if bonds are not from the correct carbon or if the nucleotides are not joined\n \n .\n

\n
\n", "Examiners report": "
\n

\n In part (a) most could gain marks for the correct shapes and sequence but did not gain the third mark as it was not shown as antiparallel. Some lost marks as a 2MAX was awarded if the bonds were not from the correct carbons. In part (b) the definition of mutation was quite well known, and most gained some marks in the explanation. Weaker students just wrote about evolution without relating it to mutations as asked. They also tended to give unnecessary examples, involving finches and moths\n \n etc\n \n .\n

\n
\n", "question_id": "20N.2.SL.TZ0.4", "topics": [ "a-unity-and-diversity", "d-continuity-and-change" ], "subtopics": [ "a1-2-nucleic-acids", "a1-2-6-dna-as-a-double-helix-made-of-two-antiparallel-strands-of-nucleotides-with-two-strands-linked-by-hydrogen-bonding-between-complementary-base-pairs", "d1-3-mutations-and-gene-editing", "d1-3-4-causes-of-gene-mutation", "d4-1-natural-selection", "d4-1-2-roles-of-mutation-and-sexual-reproduction-in-generating-the-variation-on-which-natural-selection-acts" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Outline how sperm are produced from diploid cells in the testis and how this production can be sustained over many decades of adult life.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n

\n a. germinal epithelium divide endlessly (by mitosis giving rise to spermatagonia)\n

\n

\n b. spermatogonia are diploid/2n ✔\n

\n

\n c. spermatogonia divide by mitosis / provide a continuous supply throughout adult life ✔\n

\n

\n d. (some) spermatogonia enlarge forming primary spermatocytes ✔\n

\n

\n e. primary spermatocytes undergo the first division of meiosis/meiosis I ✔\n

\n

\n f. secondary spermatocytes produced are haploid/n ✔\n

\n

\n g. secondary spermatocytes undergo the second division of meiosis (to produce spermatids) ✔\n

\n

\n h. spermatids develop tails\n
\n \n \n OR\n \n \n
\n spermatids differentiate into spermatozoa / spermatids associate with Sertoli cells ✔\n

\n

\n \n Marks can be awarded to an annotated diagram\n \n .\n

\n

\n \n Do not accept sperm or spermatozoa as equivalent to spermatagonia or spermatocytes\n \n .\n

\n
\n", "Examiners report": "
\n

\n Although many candidates performed very well, many answers were vague and simply stated that sperm cells were made by meiosis without any further details. Commonly, the stages where meiosis occurs and where mitosis occurs were muddled as well as whether primary or secondary spermatocytes were diploid or haploid. The terms spermatozoa and spermatids were commonly used interchangeably.\n

\n
\n", "question_id": "21M.2.HL.TZ2.5B", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-1-reproduction", "d3-1-14-spermatogenesis-and-oogenesis-in-humans" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Distinguish between the xylem and phloem of plants.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n

\n \n

\n
\n", "Examiners report": "
\n

\n The average mark was 2/4 for the differences between xylem and phloem. As in 6(c) marks were often lost because only one side of a distinction was given in the answer. A common misconception is that transport in xylem is unidirectional whereas in phloem it is bidirectional. Simultaneous bidirectional transport in individual sieve tubes was hypothesized at one time but this has been falsified. Sap can move in either direction at different times in both phloem sieve tubes and xylem vessels and recent research shows that xylem sap drops back down to the roots as often as every night in some herbaceous plants, making the ascent of sap in air-filled vessels a daily task. Adhesion to cellulose (not lignin) in xylem walls and capillary action is therefore more important for water transport in plants than previously realized.\n

\n
\n", "question_id": "21N.2.SL.TZ0.7B", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-2-transport", "b3-2-7-transport-of-water-from-roots-to-leaves-during-transpiration", "b3-2-9-distribution-of-tissues-in-a-transverse-section-of-the-stem-of-a-dicotyledonous-plant", "b3-2-10-distribution-of-tissues-in-a-transverse-section-of-the-root-of-a-dicotyledonous-plant" ] }, { "Question": "
\n
\n (b.i)\n
\n
\n

\n The colours of the indicator in the jars ranged from yellow to purple after five hours.\n

\n

\n Predict the distribution of indicator colours in jars 1 to 9.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n the jars closer to the light had more purple colours\n
\n \n \n OR\n \n \n
\n the jar the furthest from the light was yellow\n
\n \n \n OR\n \n \n
\n purple to yellow\n

\n

\n \n Allow for answers indicating colours for each jar within this range\n \n .\n

\n
\n", "Examiners report": "
\n

\n Most candidates predicted the colour range accurately from purple to yellow; weaker candidates either inverted the range or did not include the extremes (\n \n e.g.\n \n purple to magenta), which were stated in the question stem.\n

\n
\n", "question_id": "20N.1B.SL.TZ0.3B.I", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-3-photosynthesis", "c1-3-7-techniques-for-varying-concentrations-of-carbon-dioxide-light-intensity-or-temperature-experimentally-to-investigate-the-effects-of-limiting-factors-on-the-rate-of-photosynthesis" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Describe transport across cell membranes by osmosis.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n

\n a. form of diffusion;\n
\n b. osmosis is the movement of water molecules;\n
\n c. (movement) across a\n \n selectively\n \n /\n \n semi\n \n /\n \n partially permeable\n \n membrane/cell membrane;\n
\n d. from a region of low\n \n solute\n \n concentration to a region of high\n \n solute\n \n concentration (until equilibrium is reached)\n
\n OR\n
\n movement of\n \n water\n \n molecules from a high concentration of\n \n water\n \n to a low concentration of water molecules;\n
\n e. it is a passive transport mechanism/does not use ATP;\n
\n f. channel proteins/aquaporins are used;\n

\n
\n", "Examiners report": "
\n

\n Most gained at least 2 marks describing osmosis. Common mistakes were not making it clear whether the concentration was referring to water or to the solute. A surprising number of students did not refer to water at all.\n

\n
\n", "question_id": "21N.2.SL.TZ0.5B", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-3-water-potential", "d2-3-3-water-movement-by-osmosis-into-or-out-of-cells" ] }, { "Question": "
\n
\n

\n State the haploid number for this nucleus.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n 21\n

\n
\n", "Examiners report": "
\n

\n Slightly more than 50 % of candidates got this right. A common wrong answer was 42 – diploid number. There were a variety of other answers, some of which must have been guesses from candidates who did not understand the term haploid.\n

\n
\n", "question_id": "19M.2.SL.TZ1.C.II", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-1-cell-and-nuclear-division", "d2-1-9-meiosis-as-a-reduction-division" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Identify the genotype of the male wire-haired dog.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n WwKk\n

\n
\n", "Examiners report": "
\n

\n Only 40 % of candidates answered this correctly. A surprisingly high number of candidates gave a genotype with only one allele for each gene, suggesting that they were not familiar with dihybrid crosses. In many cases it was hard to distinguish between upper and lower case letters -W/w and K/k. Candidates should be encouraged to make letters used for alleles as clear as possible.\n

\n
\n", "question_id": "20N.2.HL.TZ0.5", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-2-inheritance", "d3-2-10-incomplete-dominance-and-codominance" ] }, { "Question": "
\n
\n

\n Identify structure X.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n \n proximal\n \n convoluted tubule/PCT;\n

\n
\n", "Examiners report": "
\n

\n 60null% of candidates identified the proximal convoluted tubule.\n

\n
\n", "question_id": "22N.2.HL.TZ0.A.I", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-3-homeostasis", "d3-3-8-role-of-the-glomerulus-bowmans-capsule-and-proximal-convoluted-tubule-in-excretion" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Outline the reason for the change in yield in region III of the diagram.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n fish are being caught faster than they can reproduce;\n

\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ1.18B", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-2-stability-and-change", "d4-2-6-assessing-sustainability-of-resource-harvesting-from-natural-ecosystems" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Outline primary succession.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n colonization of areas that were barren/not previously inhabited/not occupied by organisms;\n

\n
\n", "Examiners report": "None", "question_id": "23M.2.HL.TZ2.17A", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-2-stability-and-change", "d4-2-13-changes-occurring-during-primary-succession" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Compare and contrast the mode of nutrition of detritivores and saprotrophs.\n

\n

\n \n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n \n

\n

\n \n Accept not autotrophic/not photosynthetic instead of heterotrophic.\n \n

\n

\n \n Do not accept that both groups are decomposers or consumers for the similarity\n \n .\n

\n
\n", "Examiners report": "
\n

\n Knowledge of detritivores and saprotrophs was good in 3a, with many of the poorer answers describing them as feeding on inorganic material.\n

\n
\n", "question_id": "21N.2.SL.TZ0.3", "topics": [ "c-interaction-and-interdependence", "d-continuity-and-change" ], "subtopics": [ "c4-2-transfers-of-energy-and-matter", "c4-2-4-construction-of-food-chains-and-food-webs-to-represent-feeding-relationships-in-a-community", "c4-2-3-flow-of-chemical-energy-through-food-chains", "c1-3-photosynthesis", "c1-3-7-techniques-for-varying-concentrations-of-carbon-dioxide-light-intensity-or-temperature-experimentally-to-investigate-the-effects-of-limiting-factors-on-the-rate-of-photosynthesis", "d1-3-mutations-and-gene-editing", "d1-3-7-mutation-as-a-source-of-genetic-variation" ] }, { "Question": "
\n
\n (a.i)\n
\n
\n

\n Describe the effect of neonicotinoid pesticides on the nervous system of insects.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n blocks synaptic transmission at (cholinergic synapses);\n
    2. \n
  2. \n binds to (acetylcholine) receptors;\n
    3. \n
\n
\n", "Examiners report": "
\n

\n A pleasing number were able to correctly describe the effect of the pesticides on the synapses and state the cumulative increase correctly in ai and aii. However, in aiii, many did not see the similarity in pattern for the compare mark. In part b stronger candidates commented on the fact that even at low doses the pesticide had a great effect and that the difference between high and low doses was negligible. Many examiners were bemused by the answers to c(i) where about half of the candidates failed to identify\n \n B. lucorum\n \n as the most affected species.\n \n B. pascuorum\n \n and\n \n B. terrestris\n \n were often incorrectly given. In cii. Better candidates described the overall effects as asked, with weaker candidates just describing each species in turn. In 1d the top candidates looked at all of the data, but those who just stated that the effect was not noticeable as the egg length was not significantly smaller gained the mark.\n

\n
\n", "question_id": "22M.2.SL.TZ2.1", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c2-2-neural-signalling", "c2-2-12-effects-of-exogenous-chemicals-on-synaptic-transmission" ] }, { "Question": "
\n
\n

\n Which statement is evidence for the endosymbiotic theory?\n

\n

\n A. Chloroplasts contain 70S ribosomes.\n

\n

\n B. Protein synthesis occurs in the cytoplasm.\n

\n

\n C. Organic molecules can be synthesised abiotically.\n

\n

\n D. RNA is self-replicating.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "None", "question_id": "21M.1A.HL.TZ2.5", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a2-2-cell-structure", "a2-2-12-origin-of-eukaryotic-cells-by-endosymbiosis" ] }, { "Question": "
\n
\n

\n Suggest reasons for the high percentage of fatal cases at Ebola treatment centres.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n a. most serious cases are in/are taken to treatment centers\n
\n \n \n OR\n \n \n
\n treatment centers are set up where there are most cases/most serious cases ✔\n

\n

\n b. long time/distance to travel between contracting disease and arrival at treatment center\n
\n \n \n OR\n \n \n
\n travel to treatment center weakens/upsets/harms the patient ✔\n

\n

\n c. Ebola is a virulent disease/Ebola virus mutated «to become virulent»\n
\n \n \n OR\n \n \n
\n little known about Ebola/new disease so treatments not yet developed ✔\n

\n

\n d. no/not enough vaccine/antiviral drug available «in 2014/15»\n
\n \n \n OR\n \n \n
\n antibiotics do not work against viral diseases ✔\n

\n

\n e. secondary infections/Ebola patients infected with other diseases/other Ebola strains\n
\n \n \n OR\n \n \n
\n ineffective hygiene/cleaning/sterilization/use of contaminated equipment/disposal of corpses ✔\n

\n

\n f. small number of staff relative to patients/treatment centers overcrowded/swamped with patients\n
\n \n \n OR\n \n \n
\n insufficient equipment/supplies for large number of patients/with the rapid rise in patients ✔\n

\n

\n g. better reporting at Ebola centers/deaths due to Ebola not reported in rural areas ✔\n

\n
\n", "Examiners report": "
\n

\n This was a timely question with Ebola epidemics again causing great problems in parts of Africa. Students were expected to have had some practice at analysing data relating to an epidemic because of this Skill in the programme: Analysis of epidemiological data related to vaccination programmes. It was assumed that candidates would understand terms such as ‘case’, ‘fatal case’, ‘infect’ and ‘treat’.\n

\n

\n This was a more difficult question. We might expect fewer fatalities in percentage terms at treatment centres than elsewhere, but the data showed that there were more. Not all candidates realised that the figures given indicated the percentage of people diagnosed with Ebola that died, not the percentage of the population as a whole. As in 1(c) a wide variety of answers was accepted. Some of the answers related to Ebola having a high mortality rate generally, but to score three marks it was necessary to find reasons for treatment centres in particular having high rates of death. One suggestion commonly given but not accepted was that patients became infected after arrival at treatment centres – this would not necessarily give a high fatality rate or percentage and also uninfected people are unlikely to be brought to treatment centres. Some students thought that the more infected people a patient came into contact with, the more infected they would be. This ignores the potential for the Ebola virus to multiply exponentially once inside a patient. Material shortages were only accepted as a reason if this was combined with the idea that treatment centres were swamped with patients.\n

\n
\n", "question_id": "19M.2.SL.TZ1.E", "topics": [ "c-interaction-and-interdependence", "a-unity-and-diversity" ], "subtopics": [ "c3-2-defence-against-disease", "a2-3-viruses-(hl-only)" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Explain the conclusion that can be drawn from Cross 1.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n allele/trait/gene for banded is dominant/allele for unbanded is recessive;\n
    2. \n
  2. \n because two banded spiders produced some unbanded offspring\n
    \n \n OR\n \n
    \n because there is a ratio of 3 banded:1 unbanded;\n
    3. \n
  3. \n both parents are heterozygous;\n
    4. \n
\n

\n \n Accept answers given in the form of Punnet squares.\n \n

\n

\n

\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ1.5", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-2-inheritance", "d3-2-5-effects-of-dominant-and-recessive-alleles-on-phenotype" ] }, { "Question": "
\n
\n

\n The diagram shows water molecules.\n

\n

\n \n

\n

\n

\n

\n Which property of water is\n \n not\n \n illustrated?\n

\n

\n A.  Cohesion\n

\n

\n B.  Dipolarity\n

\n

\n C.  Hydrogen bonding\n

\n

\n D.  Adhesion\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "22N.1A.SL.TZ0.8", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a1-1-water", "a1-1-2-hydrogen-bonds-as-a-consequence-of-the-polar-covalent-bonds-within-water-molecules" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Identify the stage of mitosis labelled X in the image, giving a reason.\n

\n

\n \n

\n

\n [Source: Copyright 2002, The Trustees of Indiana University]\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n telophase because the chromosomes/chromatids have reached the poles\n
\n \n \n OR\n \n \n
\n «late» anaphase as some chromosomes/chromatids are still moving/tails visible ✔\n

\n

\n \n OWTTE\n \n

\n
\n", "Examiners report": "
\n

\n Most were able to correctly state (late) anaphase or telophase but did not give a reason as clearly asked. Many students seem to have excellent eyesight as they claimed to see that the chromosomes were unwinding and that the nuclear membranes had formed. Please encourage the students not to go beyond what can be seen.\n

\n
\n", "question_id": "19M.2.SL.TZ2.2", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-1-cell-and-nuclear-division", "d2-1-8-identification-of-phases-of-mitosis" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n HGH is a peptide hormone. Describe the mode of action of peptide hormones on target cells.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n a. peptide hormones do not enter the cell ✔\n

\n

\n b. they bind to receptors/proteins in the plasma membrane of the target cell ✔\n

\n

\n c. a secondary messenger initiates the cell response ✔\n

\n

\n d. causes a cascade of actions that changes the cell’s physiology ✔\n

\n

\n e. cAMP is a common secondary messenger ✔\n

\n
\n", "Examiners report": "
\n

\n Although a few students still confused peptide and steroid hormones, many were able to score 2 or 3 marks here. Most of these students stated that peptide hormones do not enter the cell due to their hydrophilic nature, that they do bind to receptors on the cell membrane, and that this binding initiates a secondary messenger and causes a cascade of reactions. This level of detailed knowledge was not seen elsewhere in the paper. One possible reason for this is that peptide and steroid hormones have appeared frequently on recent exam papers, and that the use of past papers remains the most common way for students to prepare for these exams.\n

\n
\n", "question_id": "19M.2.SL.TZ1.20C", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-3-homeostasis", "d3-3-3-regulation-of-blood-glucose-as-an-example-of-the-role-of-hormones-in-homeostasis" ] }, { "Question": "
\n
\n

\n Calculate the mass of lipid eaten when the bumblebees were presented with the 5:1 diet.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n 0.025g;\n

\n

\n \n Unit needed\n \n

\n
\n", "Examiners report": "None", "question_id": "22N.2.SL.TZ0.F", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c4-2-transfers-of-energy-and-matter", "c4-2-15-primary-production-as-accumulation-of-carbon-compounds-in-biomass-by-autotrophs", "c4-2-16-secondary-production-as-accumulation-of-carbon-compounds-in-biomass-by-heterotrophs" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Outline how hydrogen bonds form in water.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n a. water (molecules) are polar/dipolar/have partially positive and negative poles/have δ+ and δ-;\n

\n

\n b. attraction/bonding between positive and negative (poles);\n

\n

\n c. hydrogen bond formed between hydrogen and oxygen;\n \n Reject if H and O in same molecule.\n \n

\n

\n d. bond/attraction between different water molecules/intermolecular;\n

\n

\n \n Marks can be awarded in an annotated diagram.\n \n

\n

\n \n Reject answers stating or implying that there are whole positive or negative charges for mpa\n \n .\n

\n
\n", "Examiners report": "
\n

\n Answers were mostly good here, with many candidates scoring full marks. A very common misconception was that hydrogen bonds are strong – a single hydrogen bond is a weak interaction and it is only because there are many hydrogen bonds in water that they collectively exert large cohesive forces. A few candidates thought that hydrogen bonds were within rather than between water molecules.\n

\n
\n", "question_id": "20N.2.SL.TZ0.7A", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a1-1-water", "a1-1-2-hydrogen-bonds-as-a-consequence-of-the-polar-covalent-bonds-within-water-molecules" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Describe anaerobic respiration in humans and in yeast.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n (in both) anaerobic respiration gives a small amount of ATP/2 ATP/energy from glucose;\n
    2. \n
  2. \n anaerobic respiration occurs when there is no oxygen;\n
    3. \n
  3. \n anaerobic respiration in\n \n yeast\n \n produces ethanol and carbon dioxide/alcoholic fermentation;\n
    4. \n
  4. \n anaerobic respiration in\n \n humans\n \n (in muscle) produces lactate/lactic acid/lactic acid fermentation;\n
    5. \n
  5. \n both undergo glycolysis;\n
    6. \n
\n

\n \n Do not accept mpd if CO\n \n 2\n \n also included\n \n .\n

\n
\n", "Examiners report": "
\n

\n In 3a. the top candidates scored all three marks with ease, but many, especially in Spanish scored zero. A common mistake was to say that humans produce lactic acid and CO\n \n 2\n \n . In bi, many were confused by the term ‘thermal properties’, but most were able to gain at least one point for comparing their boiling/freezing temperatures, specific heat capacities and latent heat of fusion. The best candidates also explained the differences in terms of hydrogen bonds between the water molecules. In bii, few got past stating that methane is a greenhouse gas/causes an increase in temperature of the atmosphere. The better candidates stated that it was a powerful greenhouse gas, but it had a relatively short life span compared to CO\n \n 2\n \n . A surprising number thought that methane’s main danger was that it destroyed the ozone layer.\n

\n
\n", "question_id": "22M.2.SL.TZ2.3", "topics": [ "c-interaction-and-interdependence", "d-continuity-and-change" ], "subtopics": [ "c1-2-cell-respiration", "c1-2-5-differences-between-anaerobic-and-aerobic-cell-respiration-in-humans", "c1-2-10-anaerobic-cell-respiration-in-yeast-and-its-use-in-brewing-and-baking", "d4-3-climate-change", "d4-3-1-anthropogenic-causes-of-climate-change" ] }, { "Question": "
\n
\n

\n On the diagrams, label with a letter P a location where a neonicotinoid pesticide could bind.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n any receptor protein on post synaptic membrane marked ✔\n

\n

\n \n For 2 a, i, ii and iii, accept letters written on the structure even if a line is not drawn.\n \n

\n

\n \n Award the mark if the full word is used to label the structure.\n \n

\n

\n \n Must unambiguously be pointed to a receptor on the synapse side. Accept labels of acetylcholinesterase\n \n .\n

\n
\n", "Examiners report": "
\n

\n Both receptor proteins and acetylcholinesterase were accepted as proteins to which acetylcholine can bind. The markscheme did not accept locations other than on the synaptic side.\n

\n
\n", "question_id": "21M.2.HL.TZ2.A.III", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c2-1-chemical-signalling-[hl-only]", "c2-1-5-localized-and-distant-effects-of-signalling-molecules" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Draw the structure of a section of DNA showing all possible bases.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n

\n a. sugar, phosphate and base linked correctly to form at least one nucleotide ✔\n \n For mpa, ignore labelling of the subunits of the nucleotide. Carbon atoms in deoxyribose do not have to be numbered but the phosphate should be linked to C5 and the base to C1. Shapes other than circles and rectangles could be used for the phosphate and base\n \n .\n

\n

\n b.\n \n deoxyribose\n \n ,\n \n phosphate\n \n and base/named base labelled at least once ✔\n

\n

\n c.\n \n adenine\n \n paired with\n \n thymine\n \n and\n \n cytosine\n \n paired with\n \n guanine\n \n ✔\n \n For mpc, full names of all four bases are required, but not relative sizes of the purine and pyrimidine bases\n \n .\n

\n

\n d. two antiparallel chains of nucleotides linked by\n \n hydrogen bonds\n \n with all sugar-phosphate bonds in correct position ✔\n \n For mpd, a bond should connect the C3 of deoxyribose on one nucleotide to the phosphate on the adjacent nucleotide. Two nucleotides in each strand is sufficient\n \n .\n

\n
\n", "Examiners report": "None", "question_id": "19N.2.HL.TZ0.6", "topics": [ "a-unity-and-diversity", "d-continuity-and-change", "b-form-and-function" ], "subtopics": [ "a1-2-nucleic-acids", "a1-2-6-dna-as-a-double-helix-made-of-two-antiparallel-strands-of-nucleotides-with-two-strands-linked-by-hydrogen-bonding-between-complementary-base-pairs", "a2-2-cell-structure", "a2-2-6-eukaryote-cell-structure", "d1-2-protein-synthesis", "d1-2-5-translation-as-the-synthesis-of-polypeptides-from-mrna", "b1-2-proteins", "b1-2-4-infinite-variety-of-possible-peptide-chains", "b1-1-carbohydrates-and-lipids", "b1-1-2-production-of-macromolecules-by-condensation-reactions-that-link-monomers-to-form-a-polymer" ] }, { "Question": "
\n
\n

\n Identify, with a reason, the sex of this individual.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n male because «X and» Y chromosome present\n
\n \n \n OR\n \n \n
\n male because sex chromosomes/last two chromosomes/pair 21 are unpaired/different «from each other»/not homologous ✔\n

\n

\n \n The answer must include “male” and the reason.\n \n

\n
\n", "Examiners report": "
\n

\n 90 % of candidates correctly identified the individual as male, because the two sex chromosomes were different in size so must be an X and a Y. The other 10% mostly thought that there were two X chromosomes present, perhaps because pair 20 were X shaped.\n

\n
\n", "question_id": "19M.2.SL.TZ1.C.I", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a3-1-diversity-of-organisms", "a3-1-7-karyotyping-and-karyograms" ] }, { "Question": "
\n
\n

\n The oceans absorb much of the carbon dioxide in the atmosphere. The combustion of fossil fuels has increased carbon dioxide ocean concentrations. What adverse effect does this have on marine life?\n

\n

\n A. Heterotrophs consume more phytoplankton.\n

\n

\n B. Phytoplankton have increased rates of photosynthesis.\n

\n

\n C. Corals deposit less calcium carbonate to form skeletons.\n

\n

\n D. Increased pH reduces enzyme activity in marine organisms.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "20N.1A.SL.TZ0.19", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-3-climate-change", "d4-3-1-anthropogenic-causes-of-climate-change" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Describe the relationship between rock phosphate production and world population.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. as population increases so does phosphate production/positive correlation ✔\n

\n

\n b. since 1985 phosphate production has not risen while population has continued to increase ✔\n

\n
\n", "Examiners report": "
\n

\n Many candidates were able to score 1 mark here for seeing the positive correlation. However, students continue to have problems determining when changes shown on graphs are significant. Although the final mark scheme allowed for credit to be given if a student wrote that the phosphate levels off/fluctuates/drops and rises while population has continued to increase, many candidates were still unable to draw correct conclusions about the final years shown on the graph.\n

\n
\n", "question_id": "19M.2.SL.TZ1.14A", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-2-stability-and-change", "d4-2-6-assessing-sustainability-of-resource-harvesting-from-natural-ecosystems" ] }, { "Question": "
\n
\n (e)\n
\n
\n

\n The hypothesis made before the study was that saturated fats in the diet affected the risk of coronary artery blockage and diabetes. Using all the data in question 1, evaluate whether this hypothesis is supported by the study.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n \n Hypothesis is partially supported\n \n
\n a. Increased saturated fats in study diet resulted in increase in cholesterol levels;\n

\n

\n b. cholesterol level is risk for blockage of coronary arteries;\n

\n

\n \n Hypothesis is not supported\n \n
\n c. high insulin levels are sign of (Type II) diabetes;\n

\n

\n d. insulin levels were the same in both diets so no increased risk;\n

\n

\n e. study only 2 weeks long;\n

\n
\n", "Examiners report": "None", "question_id": "20N.1B.SL.TZ0.1E", "topics": [ "d-continuity-and-change", "b-form-and-function" ], "subtopics": [ "d3-3-homeostasis", "d3-3-3-regulation-of-blood-glucose-as-an-example-of-the-role-of-hormones-in-homeostasis", "b1-2-proteins", "b1-2-3-dietary-requirements-for-amino-acids", "b1-1-carbohydrates-and-lipids", "b1-1-10-difference-between-saturated-monounsaturated-and-polyunsaturated-fatty-acids" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Outline how photosynthesis produces glucose.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n

\n a. solar/light energy is converted to chemical energy ✔\n

\n

\n b. energy needed to produce glucose ✔\n

\n

\n c. only specific wavelengths are absorbed by chlorophyll\n
\n \n \n OR\n \n \n
\n red and blue absorbed most strongly.\n
\n \n \n OR\n \n \n
\n chlorophyll is the pigment that absorbs light energy ✔\n
\n
\n d. H\n \n (+)\n \n /electrons from water are used to reduce compounds ✔\n

\n

\n e. CO\n \n 2\n \n is absorbed/used/reduced to produce carbohydrates ✔\n

\n

\n f. correct word/\n \n balanced\n \n symbol equation of photosynthesis ✔\n

\n

\n \n Accept correct reference to NADPH/ATP from AHL.\n \n

\n
\n", "Examiners report": "
\n

\n Glucose and photosynthesis. Again, this was an example of leaping into an answer without planning. Despite G2 protestations, HL material was not expected. Better candidates were able to gain full marks by stating that the light was trapped by chloroplasts, processes converted this into chemical energy and energy was needed to make glucose and included a correct equation ( if a symbol equation, it needed to be balanced).\n

\n
\n", "question_id": "19M.2.SL.TZ2.6B", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-3-photosynthesis", "c1-3-1-transformation-of-light-energy-to-chemical-energy-when-carbon-compounds-are-produced-in-photosynthesis" ] }, { "Question": "
\n
\n

\n Scientific evidence demonstrates that reducing total cardiovascular risk results in the prevention of coronary heart disease. The chart shows attributable deaths in global population (in thousands) due to six leading cardiovascular risk factors.\n

\n

\n \n

\n
\n Mendis, Shanthi, Puska, Pekka, Norrving, B, World Health Organization, World Heart Federation et al. (2011).\n \n Global\n \n
\n \n atlas on cardiovascular disease prevention and control\n \n / edited by: Shanthi Mendis ... [et al.]. World Health Organization.\n
\n Graph of attributable deaths due to selected risk factors.\n
\n

\n Describe how\n \n two\n \n named risk factors shown in the graph can lead to coronary heart disease.\n

\n

\n 1.\n

\n

\n

\n

\n 2.\n

\n

\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n raised blood pressure damages arteries/coronary/cerebral blood vessels (manifesting as heart attacks and strokes);\n
    2. \n
  2. \n smoking tobacco causes greater platelet aggregation (increases risk of thrombosis/CHD due to atherosclerosis)\n
    \n \n \n OR\n \n \n
    \n smoking tobacco lowers oxygen supply / greater oxygen demand (so heart works more)\n
    \n \n \n OR\n \n \n
    \n \n nicotine\n \n (in smoking tobacco) causes vasoconstriction/raises blood pressure (that can damage arteries);\n
    3. \n
  3. \n high glucose causes stronger contraction of blood vessels/raised bloodpressure (causing damage to arteries/ coronary/cerebral blood vessels);\n
    4. \n
  4. \n physical inactivity prevents return of venous blood from the extremities;\n
    5. \n
  5. \n overweight and obesity causes greater risk of clot/plaque formation\n
    \n \n \n OR\n \n \n
    \n overweight and obesity raises blood pressure/vasoconstriction;\n
    6. \n
  6. \n high cholesterol promotes plaque formation/blockage of arteries (which increases risk of thrombosis/CHD due to atherosclerosis);\n
    7. \n
\n

\n \n If more than two factors written, mark only the first two descriptions.\n
\n \n

\n

\n \n Award only if descriptions are included.\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ2.24", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-2-transport", "b3-2-6-causes-and-consequences-of-occlusion-of-the-coronary-arteries" ] }, { "Question": "
\n
\n

\n The image shows a neuron.\n

\n

\n \n

\n

\n

\n

\n What is the function of X?\n

\n

\n A. Increases the speed of transmission along the axon\n

\n

\n B. Increases the rate of exchange of sodium and potassium ions\n

\n

\n C. Holds bundles of neurons together to form a nerve\n

\n

\n D. Determines the direction of the action potential\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "None", "question_id": "22M.1A.SL.TZ1.28", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c2-2-neural-signalling", "c2-2-4-variation-in-the-speed-of-nerve-impulses" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Draw the ultrastructure of a prokaryotic cell based on electron micrographs.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n a. cell wall;\n

\n

\n b. plasma membrane;\n \n Clearly shown as a separate line under the cell wall or the inner line\n \n

\n

\n c. cytoplasm\n \n \n AND\n \n \n \n 70S\n \n ribosomes;\n \n Do not allow (small) circles\n \n

\n

\n d. nucleoid/naked DNA;\n

\n

\n e. plasmid\n
\n \n \n OR\n \n \n
\n pili\n
\n \n \n OR\n \n \n
\n flagella/flagellum;\n

\n

\n \n Structures correctly drawn and labelled\n \n .\n

\n

\n \n Award\n \n [2 max]\n \n if any exclusively eukaryotic structures are shown\n \n .\n

\n

\n \n Do not allow cilia as they are not found in prokaryotes\n \n .\n

\n
\n", "Examiners report": "
\n

\n In part (a) many candidates were penalised for drawing clear eukaryotic structures such as mitochondria. The general level of the drawings was better than in the past. However a prokaryote should not be represented as a square. Ribosomes must be shown as dots, not circles.\n

\n

\n

\n
\n", "question_id": "20N.2.SL.TZ0.6", "topics": [ "a-unity-and-diversity", "d-continuity-and-change", "c-interaction-and-interdependence" ], "subtopics": [ "a2-2-cell-structure", "a2-2-11-drawing-and-annotation-based-on-electron-micrographs", "d2-1-cell-and-nuclear-division", "d2-1-9-meiosis-as-a-reduction-division", "c3-2-defence-against-disease", "c3-2-6-lymphocytes-as-cells-in-the-adaptive-immune-system-that-cooperate-to-produce-antibodies" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Identify the trophic level of sea lions. [\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n secondary consumer / third trophic level/ trophic level 3 / 3;\n

\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ1.15A", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c4-2-transfers-of-energy-and-matter", "c4-2-10-classification-of-organisms-into-trophic-levels" ] }, { "Question": "
\n
\n (c.ii)\n
\n
\n

\n X indicates the movement of a structure in the neuron. Explain what events trigger this movement and what happens next.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n a. depolarization of pre-synaptic membrane / action potential/nerve impulse arrives;\n

\n

\n b. uptake of calcium / calcium ions diffuse in / calcium channels open;\n

\n

\n c. structures containing neurotransmitter/vesicles move to/fuse with membrane;\n

\n

\n d.\n \n neurotransmitter\n \n /\n \n acetylcholine\n \n released by\n \n exocytosis\n \n into cleft/binds to postsynaptic membrane/receptors;\n

\n

\n \n Must see exocytosis\n \n .\n

\n
\n", "Examiners report": "
\n

\n This was generally well answered. Some suggested that the vesicle is released into the synaptic cleft, instead of neurotransmitter being released by exocytosis.\n

\n
\n", "question_id": "20N.2.SL.TZ0.2C.II", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c2-2-neural-signalling", "c2-2-6-release-of-neurotransmitters-from-a-presynaptic-membrane", "c2-2-7-generation-of-an-excitatory-postsynaptic-potential" ] }, { "Question": "
\n
\n (a.i)\n
\n
\n

\n Deduce the concentration of ZDV that would cause a 50 % reduction in root growth compared to the control.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n 75 μmol ✔\n

\n

\n \n Allow answers in the range of 70 µmol–80 µmol\n \n .\n

\n
\n", "Examiners report": "
\n

\n Part (ii) was better answered than part (i) as many answers provided were outside the acceptable range of answers.\n

\n
\n", "question_id": "21M.2.SL.TZ1.1", "topics": [ "a-unity-and-diversity", "d-continuity-and-change" ], "subtopics": [ "a2-3-viruses-(hl-only)", "a2-3-6-rapid-evolution-in-viruses", "d2-1-cell-and-nuclear-division", "d2-1-13-phases-of-the-cell-cycle", "d2-1-17-differences-between-tumours-in-rates-of-cell-division-and-growth-and-in-the-capacity-for-metastasis-and-invasion-of-neighbouring-tissue" ] }, { "Question": "
\n
\n

\n Testosterone is a hormone that is important for male reproductive development.\n

\n

\n \n

\n

\n

\n

\n To which group of compounds does testosterone belong?\n

\n

\n A. Nucleotides\n

\n

\n B. Carbohydrates\n

\n

\n C. Lipids\n

\n

\n D. Amino acids\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "
\n

\n The guidance for sub-topic 2.1 of the program states that candidates should be able to identify steroids as lipids from molecular diagrams. The task of identifying a testosterone molecule as a lipid was therefore reasonable, but fewer than 30 % of SL candidates answered correctly and the low discrimination index shows that some of the stronger candidates were unsuccessful. Substantial numbers of candidates chose each of the distractors, showing that they thought the molecule was a nucleotide, carbohydrate or amino acid.\n

\n
\n", "question_id": "21N.1A.SL.TZ0.6", "topics": [ "b-form-and-function" ], "subtopics": [ "b1-1-carbohydrates-and-lipids", "b1-1-13-ability-of-non-polar-steroids-to-pass-through-the-phospholipid-bilayer" ] }, { "Question": "
\n
\n

\n The diagram shows a section through an alveolus.\n

\n

\n \n

\n

\n [Source: Bergman, Ronald A., Ph.D., and D'Alessandro, Michael P., M.D. Pulmonary alveoli, “Anatomy Atlases”. Available online: http://www.anatomyatlases.org/ [Accessed 02/01/2023].]\n

\n

\n

\n

\n What are the functions of the following labelled structures?\n

\n

\n \n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "22N.1A.HL.TZ0.22", "topics": [ "b-form-and-function" ], "subtopics": [ "b2-3-cell-specialization", "b2-3-8-adaptations-of-type-i-and-type-ii-pneumocytes-in-alveoli" ] }, { "Question": "
\n
\n (a.i)\n
\n
\n

\n Identify the stage of mitosis labelled X in the image, giving a reason.\n

\n

\n \n

\n

\n [Source: Copyright 2002, The Trustees of Indiana University]\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n telophase because the chromosomes/chromatids have reached the poles\n
\n \n \n OR\n \n \n
\n «late» anaphase as some chromosomes/chromatids are still moving/tails visible ✔\n

\n

\n \n OWTTE\n \n

\n
\n", "Examiners report": "
\n

\n Both anaphase and telophase were accepted as answers, but students had difficulty providing a reason that was an appropriate justification; for example, students might say telophase and then support this with the statement because chromatids are seen moving to opposite poles. Students sometimes referred to chromatids as homologous chromosomes. As this is an image of plant cells, students would be mistaken by referring to a cleavage furrow. The mechanism of cytokinesis involves the formation of a cell plate.\n

\n
\n", "question_id": "19M.2.HL.TZ2.2", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-1-cell-and-nuclear-division", "d2-1-8-identification-of-phases-of-mitosis", "d2-1-17-differences-between-tumours-in-rates-of-cell-division-and-growth-and-in-the-capacity-for-metastasis-and-invasion-of-neighbouring-tissue", "d1-2-protein-synthesis", "d1-2-14-non-coding-sequences-in-dna-do-not-code-for-polypeptides", "d2-2-gene-expression-[hl-only]", "d2-2-6-methylation-of-the-promoter-and-histones-in-nucleosomes-as-examples-of-epigenetic-tags", "d2-2-7-epigenetic-inheritance-through-heritable-changes-to-gene-expression" ] }, { "Question": "
\n
\n (a.ii)\n
\n
\n

\n State the role of cholesterol in animal cell membranes.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n a. controls/regulates/reduces fluidity of membrane / prevents crystallization of phospholipids;\n

\n

\n b. reduces permeability to some substances.\n

\n

\n \n Do not accept ‘stabilizes membrane’\n \n .\n

\n
\n", "Examiners report": "
\n

\n Half of candidates were able to state the role of cholesterol in animal cell membranes.\n

\n
\n", "question_id": "20N.2.SL.TZ0.2A.II", "topics": [ "b-form-and-function" ], "subtopics": [ "b2-1-membranes-and-membrane-transport", "b2-1-10-fluid-mosaic-model-of-membrane-structure" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n The figure shows a tripeptide.\n

\n

\n \n

\n

\n Label\n \n one\n \n peptide bond in this molecule.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n circle/bracket around peptide bond / arrow pointing to peptide bond / peptide bond labelled;\n

\n

\n \n

\n

\n \n Allow either peptide bond\n \n

\n

\n \n Allow if adjacent C=O and NH groups are included in the circle/bracket, but do not allow if other parts of the molecule are included\n \n

\n
\n", "Examiners report": "
\n

\n However, in part 2b, many did not describe the functions of the named proteins correctly. Common mistakes were assuming that all hormones are proteins, with many incorrectly giving oestrogen, testosterone and thyroxin for example. Examples were anticipated from the list of proteins found in section 2.4 of the guide.\n

\n
\n", "question_id": "21N.2.SL.TZ0.2", "topics": [ "b-form-and-function" ], "subtopics": [ "b1-2-proteins", "b1-2-2-condensation-reactions-forming-dipeptides-and-longer-chains-of-amino-acids", "b1-2-11-quaternary-structure-of-non-conjugated-and-conjugated-proteins", "b3-1-gas-exchange", "b3-1-5-ventilation-of-the-lungs" ] }, { "Question": "
\n
\n (d)\n
\n
\n

\n Outline the uses of ATP in plant cells.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. used as an energy source ✔\n

\n

\n b. supplies/releases energy for biochemical reactions ✔\n

\n

\n c. photosynthesis/active transport/other verifiable example of reaction or process ✔\n

\n
\n", "Examiners report": "
\n

\n The diagram was generally confusing to candidates.\n

\n

\n Expressing the nature of ATP in an outline of its use to plants was problematic for many students. Rather than a source of energy it was thought to be energy itself. Many processes use ATP in one part of the pathway or another, so a wide variety of seemingly contradictory answers received credit. For example, ATP is used in cell respiration during glycolysis. Credit was given for glycolysis as well as for respiration.\n

\n
\n", "question_id": "21M.2.SL.TZ1.2D", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-3-photosynthesis", "c1-3-2-conversion-of-carbon-dioxide-to-glucose-in-photosynthesis-using-hydrogen-obtained-by-splitting-water" ] }, { "Question": "
\n
\n

\n What is an example of negative feedback in the menstrual cycle?\n

\n

\n A. High levels of estrogen inhibit FSH secretion.\n

\n

\n B. High levels of LH stop progesterone secretion.\n

\n

\n C. High levels of FSH delay ovulation.\n

\n

\n D. High levels of progesterone make follicles less receptive to FSH.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "None", "question_id": "22M.1A.SL.TZ2.29", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-1-reproduction", "d3-1-5-changes-during-the-ovarian-and-uterine-cycles-and-their-hormonal-regulation" ] }, { "Question": "
\n
\n

\n Compare and contrast the data for 1998–1999 and 2002–2003.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n \n \n Similarities\n \n \n
\n a. similar range of cover in both periods\n
\n OR\n
\n weak correlation/no correlation in either;\n

\n

\n \n \n Differences\n \n \n
\n b. higher WSSTA range/more WSSTA in 1998–1999 than 2002–2003\n
\n OR\n
\n positive (2002–2003) versus negative correlation (98–99)\n
\n OR\n
\n more coral reefs with very low % of coral cover (0–20 %) in 2002–2003;\n

\n

\n \n Must respond with one similarity and one difference for full marks\n \n .\n

\n
\n", "Examiners report": "
\n

\n In 1c contrasts were common, but few gained the comparison mark as well.\n

\n
\n", "question_id": "21N.2.SL.TZ0.C.I", "topics": [ "d-continuity-and-change", "b-form-and-function" ], "subtopics": [ "d4-3-climate-change", "d4-3-7-threats-to-coral-reefs-as-an-example-of-potential-ecosystem-collapse", "b4-1-adaptation-to-environment", "b4-1-5-conditions-required-for-coral-reef-formation" ] }, { "Question": "
\n
\n

\n What occurs in the light-independent reactions of photosynthesis?\n

\n

\n A.  Glycerate 3-phosphate is reduced to triose phosphate.\n

\n

\n B.  Ribulose bisphosphate is regenerated using reduced NADP.\n

\n

\n C.  Ribulose bisphosphate is oxidized to two molecules of glycerate 3-phosphate.\n

\n

\n D.  Both ATP and NADP are used to produce triose phosphate.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "
\n

\n Both questions 31 and 32 were answered correctly by fewer than 40\n \n \n \n \n % of candidates. In question 31 this either indicates poor understanding of the Calvin cycle or careless reading of the possible answers, in which each word matters. In question 32 the poor performance suggests unfamiliarity with the use of potometers - a prescribed practical for Higher Level students. Many candidates thought that the volume of water in the reservoir had to be controlled, when in fact the reservoir is used to control the position of the air bubble in the capillary tube at the start of each measurement period.\n

\n

\n The discrimination index in question 31 was high suggesting that the better-prepared candidates answered it correctly, but in question 32 it was relatively low. This suggests that much of the variance was between schools rather than between candidates, emphasizing the need for all prescribed practicals to be included in the teaching program.\n

\n
\n", "question_id": "22N.1A.HL.TZ0.31", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-3-photosynthesis", "c1-3-19-interdependence-of-the-light-dependent-and-light-independent-reactions" ] }, { "Question": "
\n
\n (a.i)\n
\n
\n

\n Draw a Punnett square to show all the possible genotypes of Queen Victoria’s children.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. parental alleles shown as X\n \n H\n \n and X\n \n h\n \n (female) and X\n \n H\n \n and Y (male);\n
\n b. Punnett square with genotypes of offspring shown as X\n \n H\n \n X\n \n H\n \n and X\n \n H\n \n Y and X\n \n H\n \n X\n \n h\n \n and X\n \n h\n \n Y;\n

\n

\n \n

\n
\n", "Examiners report": "
\n

\n Generally this was well answered. Common errors were to omit X and or Y chromosomes, show alleles on both X and Y chromosomes, or show the male X chromosome with a recessive h allele.\n

\n
\n", "question_id": "21N.2.HL.TZ0.2", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-2-inheritance", "d3-2-12-haemophilia-as-an-example-of-a-sex-linked-genetic-disorder", "d2-1-cell-and-nuclear-division", "d2-1-9-meiosis-as-a-reduction-division", "d2-1-11-meiosis-as-a-source-of-variation", "d3-2-19-autosomal-gene-linkage", "d3-1-reproduction", "d3-1-15-mechanisms-to-prevent-polyspermy" ] }, { "Question": "
\n
\n (b.ii)\n
\n
\n

\n State the stage of meiosis where chiasmata formation may occur.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n prophase I;\n

\n
\n", "Examiners report": "
\n

\n Mostly Prophase I was given as the answer but all other phases of Meiosis I were given by some candidates and others failed to specify 1st or 2nd division of meiosis.\n

\n
\n", "question_id": "21N.2.SL.TZ0.2B.II", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-1-cell-and-nuclear-division", "d2-1-9-meiosis-as-a-reduction-division", "d2-1-11-meiosis-as-a-source-of-variation" ] }, { "Question": "
\n
\n

\n When there is no vaccination, the estimated number of cases for lower-middle income countries is larger than in either low income or upper-middle income countries. Suggest\n \n one\n \n reason for this.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n higher population in lower-middle income countries/subgroup (compared to the other 2 subgroups);\n
    2. \n
  2. \n low income population may not have/have less access to medicine/antibiotics/vaccination (compared to lower-middle income population)/ low-income populations may not report data\n
    \n \n \n OR\n \n \n
    \n upper-middle population may have better living conditions/more adequate medical diagnoses (compared to lower-middle income population);\n
    3. \n
\n

\n \n Lower-middle income subgroup is not the same as LMIC (includes all 3 subgroups).\n \n LMIC should not be used as equivalent.\n \n \n

\n

\n \n Mpb: accept vice versa.\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ2.H", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-2-defence-against-disease", "c3-2-16-vaccines-and-immunization" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Explain how the light-independent reactions of photosynthesis rely on the light-dependent reactions.\n

\n
\n
\n

\n [7]\n

\n
\n
\n", "Markscheme": "
\n

\n a. light-dependent reactions produce ATP/reduced NADP;\n
\n b. ATP generated by chemiosmosis/by photophosphorylation/by ATP synthase;\n
\n c. reduced NADP produced by/using electrons from Photosystem I;\n
\n d. RuBP + CO\n \n 2\n \n to glycerate 3-phosphate (in light independent reactions);\n
\n e. glycerate 3-phosphate reduced to triose phosphate (in light independent reactions);\n
\n f. ATP/reduced NADP used in the light-independent reactions;\n
\n g. reduced NADP provides electrons/hydrogen / to reduce (glycerate 3-phosphate)\n
\n \n OR\n \n
\n reduced NADP used to convert glycerate 3-phosphate to triose phosphate;\n
\n h. ATP provides energy (for reduction of glycerate 3-phosphate);\n
\n i. ATP needed to regenerate RuBP\n
\n j. ATP/reduced NADP run out in darkness\n
\n k.\n \n Calvin cycle\n \n only possible with light/in the day/is indirectly dependent on light;\n

\n
\n", "Examiners report": "
\n

\n This was a fair but challenging question and it yielded the highest correlation coefficient on the paper. Answers covered the whole gamut from the thoroughly confused to the masterly. Full names of intermediates in the Calvin cycle are preferred because abbreviations such as GP are often ambiguous. Weak points in some answers were the need for reduced NADP in the reduction of glycerate 3-phosphate to triose phosphate and the need also for energy from ATP both for this reduction reaction and for phosphorylation reactions in the regeneration of ribulose bisphosphate.\n

\n
\n", "question_id": "21N.2.HL.TZ0.7C", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-3-photosynthesis", "c1-3-19-interdependence-of-the-light-dependent-and-light-independent-reactions" ] }, { "Question": "
\n
\n

\n Deduce\n \n one\n \n conclusion about the structure of the plasma membrane reached by the scientists from their results.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n a. phospholipids on outside/exposed ✔\n

\n

\n b. impossibility of continuous protein layer «of Davson–Danielli/model A» ✔\n

\n

\n c. supports idea of mosaic pattern of membrane\n
\n \n \n OR\n \n \n
\n supports model B ✔\n

\n

\n \n Award any other valid conclusion.\n \n

\n

\n \n Do not accept \"membrane is made of phospholipids\".\n \n

\n
\n", "Examiners report": "
\n

\n Many candidates answered that the enzyme acted on the phospholipids but failed to make a deduction about the structure of the membrane.\n

\n
\n", "question_id": "19M.1B.SL.TZ2.C.I", "topics": [ "b-form-and-function" ], "subtopics": [ "b2-1-membranes-and-membrane-transport", "b2-1-10-fluid-mosaic-model-of-membrane-structure" ] }, { "Question": "
\n
\n

\n State the relationship between high lipid content and survivability on day 7.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n the higher the lipid content, the fewer bees survived/negative correlation;\n

\n
\n", "Examiners report": "None", "question_id": "22N.2.SL.TZ0.H", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c4-2-transfers-of-energy-and-matter", "c4-2-15-primary-production-as-accumulation-of-carbon-compounds-in-biomass-by-autotrophs", "c4-2-16-secondary-production-as-accumulation-of-carbon-compounds-in-biomass-by-heterotrophs" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Distinguish between the different phases of the cardiac cycle in the atria and in the ventricular muscle.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. action potential of atrium precedes the ventricle\n
\n \n \n OR\n \n \n
\n the phases happen later in ventricle\n
\n \n \n OR\n \n \n
\n atrium contracts before the ventricle ✔\n

\n

\n b. atrium has a shorter phase 2/longer phase 2 in ventricle\n
\n \n \n OR\n \n \n
\n atrium falls abruptly in phase 2/ventricle shows a plateau in phase 2 ✔\n

\n

\n c. phase 3 is more distinct/falls more abruptly in ventricular action potential ✔\n

\n

\n d. ventricular phase is overall longer than atrial phase ✔\n

\n
\n", "Examiners report": "
\n

\n Part (c) confused many candidates and they did not realise they had to refer to the graphs in their answers. Most scored one mark for stating ventricular contraction occurs after atrial contraction.\n

\n
\n", "question_id": "19M.2.HL.TZ2.18C", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-2-transport", "b3-2-16-stages-in-the-cardiac-cycle" ] }, { "Question": "
\n
\n (i)\n
\n
\n

\n State the trend.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n Increase/increasing/upwards/rising (trend);\n

\n

\n \n Reject ‘positive’, ‘positive trend’ and ‘positive correlation’\n
\n \n \n Accept linear increase.\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ1.1DI", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-3-climate-change", "d4-3-1-anthropogenic-causes-of-climate-change" ] }, { "Question": "
\n
\n

\n Outline the reason for plasma insulin levels changing in the first 30 minutes of the test.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n as blood glucose rises,\n \n insulin\n \n \n rises\n \n /\n \n increases\n \n to reduce the level/\n \n OWTTE\n \n ;\n

\n

\n \n Blood glucose must be mentioned as well as a rise in insulin\n \n .\n

\n
\n", "Examiners report": "None", "question_id": "20N.1B.SL.TZ0.D.III", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-3-homeostasis", "d3-3-3-regulation-of-blood-glucose-as-an-example-of-the-role-of-hormones-in-homeostasis" ] }, { "Question": "
\n
\n

\n What happens in the heart when epinephrine is secreted into the blood?\n

\n

\n I. Pressure in the heart falls.\n

\n

\n II. The pulmonary artery transports oxygenated blood at a faster rate.\n

\n

\n III. The sinoatrial node increases the rate of electrical signals.\n

\n

\n A. I only\n

\n

\n B. I and II only\n

\n

\n C. II and III only\n

\n

\n D. III only\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "
\n

\n The discrimination index for this question was high, but only about a third of candidates answered it correctly. It was essential to read the question carefully and not jump to hasty conclusions. Of the three statements offered, II was not correct because the pulmonary artery does not carry oxygenated blood.\n

\n
\n", "question_id": "20N.1A.HL.TZ0.21", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-1-integration-of-body-systems", "c3-1-12-epinephrine-(adrenaline)-secretion-by-the-adrenal-glands-to-prepare-the-body-for-vigorous-activity", "c2-1-chemical-signalling-[hl-only]", "c2-1-10-mechanism-of-action-of-epinephrine-(adrenaline)-receptors" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Describe the effect of temperature on the total biomass.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. negative correlation/decrease (in biomass) as temperature rises in added-nutrients (mesocosms);\n
\n b. little/no (significant) change in biomass as temperature increases in control (mesocosms);\n

\n
\n", "Examiners report": "
\n

\n The word ‘total’ confused some candidates who tried to write about both the control and added-nutrients without distinguishing between them. Of those candidates who realised that ‘total’ must mean the total biomass within a mesocosm, almost all got the decrease in ‘with nutrients’ mesocosms as temperature increased, but many were not discerning enough with the control mesocosms. The differences were less than the error bars, so were clearly insignificant and should have been ignored Question 2.\n

\n
\n", "question_id": "21N.2.HL.TZ0.1", "topics": [ "d-continuity-and-change", "c-interaction-and-interdependence" ], "subtopics": [ "d4-2-stability-and-change", "d4-2-4-use-of-a-model-to-investigate-the-effect-of-variables-on-ecosystem-stability", "c1-3-photosynthesis", "c1-3-7-techniques-for-varying-concentrations-of-carbon-dioxide-light-intensity-or-temperature-experimentally-to-investigate-the-effects-of-limiting-factors-on-the-rate-of-photosynthesis" ] }, { "Question": "
\n
\n

\n Which encircled area shows a clade?\n

\n

\n \n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "None", "question_id": "22M.1A.SL.TZ2.21", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a3-2-classification-and-cladistics-(hl-only)", "a3-2-4-clades-as-groups-of-organisms-with-common-ancestry-and-shared-characteristics", "a3-2-7-analysing-cladograms" ] }, { "Question": "
\n
\n

\n Which is an example of evolution by selective breeding?\n
\n
\n

\n

\n A.  Selection of prey animals that can run faster than their predators\n

\n

\n B.  The variation in the size of different breeds of dogs\n

\n

\n C.  The tendency, during breeding, for birds to produce more offspring than will survive\n

\n

\n D.  Some female spiders only breeding with males which make the right signals\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "23M.1A.SL.TZ2.22", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a4-1-evolution-and-speciation", "a4-1-3-evidence-for-evolution-from-selective-breeding-of-domesticated-animals-and-crop-plants" ] }, { "Question": "
\n
\n

\n What occurs during the establishment of a resting membrane potential of a neuron?\n

\n

\n
\n A.  Both sodium and potassium ions are pumped outside the neuron.\n

\n

\n B.  Sodium ions are pumped out while potassium ions are pumped into the neuron.\n

\n

\n C.  Both sodium and potassium ions are at rest inside the membrane of the neuron.\n

\n

\n D.  Sodium ions leave by diffusion and potassium ions enter the neuron by active transport.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "23M.1A.SL.TZ1.29", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c2-2-neural-signalling", "c2-2-2-generation-of-the-resting-potential-by-pumping-to-establish-and-maintain-concentration-gradients-of-sodium-and-potassium-ions" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Outline the role of the right atrium in the cardiac cycle.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n right atrium collects (deoxygenated) blood from the body;\n
    2. \n
  2. \n blood drains into atrium through/from the vena cava;\n
    3. \n
  3. \n deoxygenated blood present in vena cava/right atrium/right ventricle;\n
    4. \n
  4. \n right atrium pumps blood into the right ventricle;\n
    5. \n
  5. \n during atrial systole/ventricular diastole/at the start of the cardiac cycle;\n
    6. \n
  6. \n sinoatrial node is in the right atrium/sinoatrial node acts as the (natural) pacemaker / sinoatrial node initiates the heartbeat;\n
    7. \n
  7. \n SA node sends out electrical signal to stimulate contraction in the (walls of the) atria/then propagated to the AV node / (walls of the) ventricles;\n
    8. \n
\n

\n

\n
\n", "Examiners report": "None", "question_id": "23M.2.HL.TZ2.6B", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-2-transport", "b3-2-16-stages-in-the-cardiac-cycle" ] }, { "Question": "
\n
\n

\n Distinguish between the proportion of ancestral and derived alleles for all three genes in\n \n O. sativa indica\n \n and\n \n O. sativa japonica\n \n .\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a.\n \n O.s. indica\n \n has more of the ancestral allele «for all three genes» ✔\n \n Accept converse\n \n .\n

\n

\n b. lower/higher values for ancestral/derived are not for the same genes ✔\n \n Allow specific gene examples\n \n .\n

\n

\n c. for\n \n O. s. indica\n \n the highest proportion is for\n \n DPL2\n \n \n ancestral\n \n , but for\n \n O. s. japonica\n \n is\n \n GS3\n \n \n derived\n \n allele ✔\n \n Allow converse for smallest derived.\n \n

\n
\n", "Examiners report": "None", "question_id": "19N.2.HL.TZ0.E", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a3-2-classification-and-cladistics-(hl-only)", "a3-2-7-analysing-cladograms" ] }, { "Question": "
\n
\n

\n What is most likely to increase in the presence of insulin?\n

\n

\n A. The rate of anaerobic respiration\n

\n

\n B. The chances of Type I diabetes\n

\n

\n C. The uptake of glucose by muscles\n

\n

\n D. The concentration of glucagon\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "
\n

\n The two terms glucagon and glycogen are easily confused and it was clear that some candidates had done this here, so chose answer D — that the concentration of glucagon rises in the presence of insulin. Special attention should be given where two terms are close in spelling but different in meaning.\n

\n
\n", "question_id": "22M.1A.SL.TZ1.30", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-3-homeostasis", "d3-3-3-regulation-of-blood-glucose-as-an-example-of-the-role-of-hormones-in-homeostasis" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Distinguish between the structure of the chromosomes of prokaryotes and eukaryotes.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. prokaryotes have circular DNA/chromosome but eukaryote chromosomes linear/\n \n OWTTE\n \n ✔\n
\n \n \n OR\n \n \n
\n eukaryotes have telomeres/centromeres whereas prokaryotes do not ✔\n

\n

\n b. some prokaryotes have plasmids whereas eukaryotes do not ✔\n

\n

\n c. eukaryotes have multiple chromosomes whereas prokaryotes «typically» have only one ✔\n

\n

\n d. histones/nucleosomes/proteins associated with DNA in eukaryotes but not in prokaryotes/naked DNA in prokaryotes\n
\n \n \n OR\n \n \n
\n eukaryote DNA can coil/supercoil/condense «due to histones» but not prokaryote DNA ✔\n

\n
\n", "Examiners report": "
\n

\n Answers to this question were variable. Some candidates wrote about cell structure rather than chromosome and many wrote about the location of chromosomes in the cell rather than their structure. Weaker candidates did not know the difference between prokaryotes and eukaryotes and some think that prokaryotes are plants and eukaryotes are animals. The term ‘naked’ was often used for DNA not enclosed in a nuclear membrane, when in this context it should be reserved for DNA that is not associated with histone proteins.\n

\n
\n", "question_id": "19M.2.HL.TZ1.2", "topics": [ "a-unity-and-diversity", "d-continuity-and-change" ], "subtopics": [ "a2-2-cell-structure", "a2-2-5-prokaryote-cell-structure", "a2-2-6-eukaryote-cell-structure", "a3-1-diversity-of-organisms", "a3-1-7-karyotyping-and-karyograms", "d2-1-cell-and-nuclear-division", "d2-1-9-meiosis-as-a-reduction-division", "d3-2-inheritance", "d3-2-16-segregation-and-independent-assortment-of-unlinked-genes-in-meiosis", "d3-2-17-punnett-grids-for-predicting-genotypic-and-phenotypic-ratios-in-dihybrid-crosses-involving-pairs-of-unlinked-autosomal-genes" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Determine, with a reason, the nucleotide base that was marked with radioactivity.\n

\n

\n Base:\n

\n

\n Reason:\n

\n

\n

\n

\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. thymine / T ✔\n

\n

\n b. because only in DNA / not in RNA ✔\n

\n
\n", "Examiners report": "
\n

\n Few were able to name thymine as the base or give a reason it was used in the experiment.\n

\n
\n", "question_id": "19M.2.SL.TZ2.2B", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a1-2-nucleic-acids", "a1-2-4-bases-in-each-nucleic-acid-that-form-the-basis-of-a-code" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Explain\n \n one\n \n reason for calculating the percentage changes in mass.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. the change in mass indicates whether the tissue has gained/lost water ✔\n

\n

\n b. the pieces of tissue will not all be the same mass «at the beginning of the experiment» ✔\n

\n

\n c. to compare the relative changes in mass ✔\n

\n
\n", "Examiners report": "None", "question_id": "19N.1B.SL.TZ0.3C", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-3-water-potential", "d2-3-3-water-movement-by-osmosis-into-or-out-of-cells", "d2-3-4-changes-due-to-water-movement-in-plant-tissue-bathed-in-hypotonic-and-those-bathed-in-hypertonic-solutions" ] }, { "Question": "
\n
\n

\n What is evidence for the endosymbiotic theory in eukaryotic cells?\n

\n

\n
\n A.  Mitochondrion with DNA\n

\n

\n B.  Golgi complex in cytoplasm\n

\n

\n C.  Single nuclear membrane\n

\n

\n D.  Ribosomes in cytoplasm\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "None", "question_id": "23M.1A.HL.TZ1.5", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a2-2-cell-structure", "a2-2-12-origin-of-eukaryotic-cells-by-endosymbiosis" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Outline how energy flows in an ecosystem.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n energy from the sun is captured by plants/autotrophs;\n
    2. \n
  2. \n light energy is converted to chemical energy by\n \n photosynthesis\n \n ;\n
    3. \n
  3. \n energy is passed to animals/consumers/along the food chain;\n
    4. \n
  4. \n at each stage in the food chain energy is lost by respiration/as heat;\n
    5. \n
  5. \n \n much\n \n less energy/only about 10\n \n \n \n \n % is available at each stage/trophic level of the food chain;\n
    6. \n
  6. \n some energy is made available to decomposers when organisms die/parts fall to the ground;\n
    7. \n
  7. \n energy cannot be recycled;\n
    8. \n
\n
\n", "Examiners report": "
\n

\n Explaining the energy flow in part (a), was one of the best answered questions on the paper. However, the\n
\n conversion of light energy to chemical energy was missed by many. Some weaker candidates are still confusing energy with biomass, and lost marks due to contradictory statements such as saying that in the end the energy goes into the soil and is taken up by the plants again.\n

\n

\n In both (a) and (b) many students drew diagrams, Carbon cycles etc. Some of these aided the explanation, but the majority contributed nothing.\n

\n
\n", "question_id": "22N.2.SL.TZ0.6", "topics": [ "c-interaction-and-interdependence", "a-unity-and-diversity" ], "subtopics": [ "c4-2-transfers-of-energy-and-matter", "c4-2-3-flow-of-chemical-energy-through-food-chains", "c4-2-18-ecosystems-as-carbon-sinks-and-carbon-sources", "c4-2-19-release-of-carbon-dioxide-into-the-atmosphere-during-combustion-of-biomass-peat-coal-oil-and-natural-gas", "a3-2-classification-and-cladistics-(hl-only)", "a3-2-1-need-for-classification-of-organisms", "a3-2-9-classification-of-all-organisms-into-three-domains-using-evidence-from-rrna-base-sequences" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Compare and contrast the structure of a typical prokaryotic cell with that of a mitochondrion.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n

\n \n differences\n \n

\n

\n a. prokaryote has cell wall but mitochondrion does not ✔\n

\n

\n b. mitochondrion has double membrane whereas prokaryote has single membrane\n
\n \n \n OR\n \n \n
\n «Gram negative» bacteria have cell wall between two membranes whereas mitochondria has intermembrane space between two membranes ✔\n

\n

\n c. mitochondrion has cristae/invaginations of inner membrane but prokaryote does not\n
\n \n \n OR\n \n \n
\n prokaryote «may have» flagella/pili/«slime» capsule which mitochondria do not have ✔\n

\n

\n \n similarities\n \n

\n

\n d.\n \n 70S\n \n ribosomes in both ✔\n

\n

\n e.\n \n DNA\n \n in both / loop of\n \n DNA\n \n in both / naked\n \n DNA\n \n in both ✔\n

\n

\n f. shape similar/both rod shaped/\n \n OWTTE\n \n
\n \n \n OR\n \n \n
\n size of both is similar/both about 3 μm long ✔\n

\n

\n g. both are membrane-bound/\n \n OWTTE\n \n ✔\n

\n
\n", "Examiners report": "
\n

\n Answers were spread over the whole of the four-mark range. The scale bars allowed the sizes of both to be calculated – they were close, but even so a substantial number of candidates claimed that one or other was significantly larger.\n

\n
\n", "question_id": "19M.2.HL.TZ1.3A", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a2-2-cell-structure", "a2-2-12-origin-of-eukaryotic-cells-by-endosymbiosis" ] }, { "Question": "
\n
\n (f)\n
\n
\n

\n State\n \n one\n \n reason for having a control group.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n any reference to comparison ✔\n

\n
\n", "Examiners report": "None", "question_id": "19N.2.HL.TZ0.1F", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a3-2-classification-and-cladistics-(hl-only)", "a3-2-7-analysing-cladograms" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Explain why some biologists think protecting keystone species would help preserve biological diversity in an ecosystem.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n a. «research demonstrates that keystone species» have a «disproportionately» large effect on their environment relative to abundance\n
\n \n \n OR\n \n \n
\n «keystone species» maintain a balance in the «stable» numbers of each species within a community\n
\n \n \n OR\n \n \n
\n «keystone species» have a large impact in preserving and stabilizing the biodiversity by preventing overpopulation/monopoly/out competition ✔\n

\n

\n b. a keystone species’ disappearance would start a domino effect/other species in the habitat would also disappear\n
\n \n \n OR\n \n \n
\n their loss leads to an imbalance in the food web\n
\n \n \n OR\n \n \n
\n their loss leads to a decrease in biodiversity ✔\n

\n

\n \n Do not accept protecting keystone species prevents disappearance of other species since it repeats the question\n \n .\n

\n
\n", "Examiners report": "None", "question_id": "19N.2.SL.TZ0.14C", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-2-stability-and-change", "d4-2-5-role-of-keystone-species-in-the-stability-of-ecosystems" ] }, { "Question": "
\n
\n (a.i)\n
\n
\n

\n On the diagram, label the aorta.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n both labelled clearly as in diagram ✔\n

\n

\n \n

\n

\n [Source: BlueRingMedia/Shutterstock]\n

\n
\n", "Examiners report": "
\n

\n Labelling the heart was generally ok, though the rest of this question was weakly answered.\n

\n
\n", "question_id": "19M.2.SL.TZ1.3", "topics": [ "b-form-and-function", "c-interaction-and-interdependence" ], "subtopics": [ "b3-2-transport", "b3-2-15-adaptations-of-the-mammalian-heart-for-delivering-pressurized-blood-to-the-arteries", "c3-2-defence-against-disease", "c3-2-3-sealing-of-cuts-in-skin-by-blood-clotting", "c3-2-6-lymphocytes-as-cells-in-the-adaptive-immune-system-that-cooperate-to-produce-antibodies" ] }, { "Question": "
\n
\n (b.ii)\n
\n
\n

\n Outline the use of ATP.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n source of energy (for use in the cell)\n
\n OR\n
\n example of use of ATP\n
\n OR\n
\n when ATP is converted to ADP + Pi (is hydrolyzed) the energy stored in the phosphate bond is released to be used by the cell;\n

\n
\n", "Examiners report": "None", "question_id": "21N.2.SL.TZ0.4B.II", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-2-cell-respiration", "c1-2-3-energy-transfers-during-interconversions-between-atp-and-adp" ] }, { "Question": "
\n
\n

\n What are features of both endoskeletons of mammals and exoskeletons of insects?\n

\n

\n A. They are both made of bone.\n

\n

\n B. They both have cartilage.\n

\n

\n C. They are both moved by antagonistic sets of muscles.\n

\n

\n D. Both consist of dead tissue.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "
\n

\n This was an easy question. One comment mentions that not all bones or parts of the insect exoskeleton are moved. The question focuses on common features; the fact that they are moved by muscles does not imply that they are all moved.\n

\n
\n", "question_id": "19M.1A.HL.TZ2.35", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-3-muscle-and-motility-(hl-only)", "b3-3-5-roles-of-skeletons-as-anchorage-for-muscles-and-as-levers" ] }, { "Question": "
\n
\n

\n The graph shows three hormones circulating during pregnancy in the rat, with birth occurring at 22 days.\n

\n

\n \n

\n

\n [Source: Dr Paul Kenyon University of Plymouth (retired).]\n

\n

\n

\n

\n What are hormones X and Z?\n

\n

\n \n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "20N.1A.SL.TZ0.40", "topics": [], "subtopics": [] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Sea otters are considered keystone species in this environment. Suggest how the presence of sea otters could affect the algae population.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n a. sea otters (feeding on sea urchins) limit sea urchin population;\n

\n

\n b. the largest sea urchins are eaten;\n

\n

\n c. shown by low biomass/small size (of sea urchins);\n

\n

\n d. fewer/smaller sea urchins allow for increase in algae population;\n

\n

\n e. sea otters have a top down effect;\n

\n

\n \n Allow converse reasoning\n \n .\n

\n
\n", "Examiners report": "
\n

\n The majority of candidates could suggest that the sea algae population could be affected by sea otters feeding on sea urchins; most nevertheless did not use the graphs or mention that a top down effect was present.\n

\n
\n", "question_id": "20N.2.SL.TZ0.15B", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-2-stability-and-change", "d4-2-5-role-of-keystone-species-in-the-stability-of-ecosystems" ] }, { "Question": "
\n
\n

\n how the DNA is amplified.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n PCR/polymerase chain reaction\n
\n \n \n OR\n \n \n
\n using Taq polymerase;\n

\n

\n

\n
\n", "Examiners report": "None", "question_id": "23M.1B.SL.TZ1.II", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-3-photosynthesis", "c1-3-7-techniques-for-varying-concentrations-of-carbon-dioxide-light-intensity-or-temperature-experimentally-to-investigate-the-effects-of-limiting-factors-on-the-rate-of-photosynthesis" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n After fertilization, seeds of\n \n T. grandiflora\n \n form in a small pod. If you were provided with Petri dishes, absorbent cotton balls and seeds, suggest how\n \n one\n \n variable affecting germination of these seeds could be investigated.\n

\n

\n \n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n a. different values for the named independent variable ✔\n \n Name of the independent variable must be included, eg temperature.\n \n

\n

\n b. large / equal number of seeds in each Petri dish ✔\n

\n

\n c. control of other variables «than seeds» ✔\n

\n

\n d. mentions how germination will be determined\n \n eg appearance of radicle.\n \n
\n \n \n OR\n \n \n
\n how germination rate/percentage will be measured ✔\n \n eg\n \n \n number germinated over time/in a set time.\n \n \n Do not accept measurement of growth of stem/number of leaves.\n \n

\n

\n e. includes a control giving seeds all factors needed ✔\n

\n

\n \n Possible factors include water, oxygen, temperature, pH, light, salt concentration.\n \n

\n

\n

\n
\n", "Examiners report": "
\n

\n This question was an open opportunity for candidates to display their understanding of experimental processes. Although a certain number of well-structured answers were seen, this was probably the most poorly handled question of this paper. Although most had understood that only one variable could be changed at a time, it was expected they should have the basic knowledge that water is essential for germination and would go beyond experiments involving one seed with water and one with no water, as too many suggested. The majority could not understand that, to draw valid conclusions, many seeds should be used in many repeats and that controls should be used. They also had much difficulty at suggesting how results could be gathered, often confusing germination with seedling growth. One can therefore wonder about how the practical programme is delivered in many schools.\n

\n
\n", "question_id": "19M.1B.SL.TZ2.1C", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-1-reproduction", "d3-1-8-sexual-reproduction-in-flowering-plants" ] }, { "Question": "
\n
\n

\n The scattergraph shows the genome sizes of four Enterococcus species.\n

\n

\n \n

\n

\n \n [Source: Lebreton, F., Manson, A.L., Saavedra, J.T., Straub, T.J., Earl, A.M. and Gilmore, M.S., 2017.\n \n
\n \n Tracing the Enterococci from Paleozoic Origins to the Hospital (Figure 1A).\n \n
\n \n \n Cell\n \n , [e-journal] 169(5), pp. 849–861. http://dx.doi.org/10.1016/j. cell.2017.04.027.]\n \n

\n

\n What can be concluded about the genomes in Enterococcus?\n
\n
\n

\n

\n A.\n \n E. pallens\n \n has the greatest number of genes.\n

\n

\n B.\n \n E. faecalis\n \n and\n \n E. faecium\n \n have the same mean number of genes.\n

\n

\n C.  The total genetic information in\n \n Enterococcus\n \n is constant within each species.\n

\n

\n D.\n \n E. columbae\n \n has more DNA than\n \n E. faecium\n \n .\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n A\n

\n
\n", "Examiners report": "None", "question_id": "23M.1A.SL.TZ1.12", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a3-1-diversity-of-organisms", "a3-1-9-diversity-of-eukaryote-genomes" ] }, { "Question": "
\n
\n

\n Using the letter M, label the stage on the diagram where sister chromatids migrate to opposite poles.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n anaphase ✔\n

\n

\n \n The stage should be clearly labelled\n \n .\n

\n

\n \n If more than one stage is shown the candidate does not receive a mark\n \n .\n

\n
\n", "Examiners report": "
\n

\n There were several G2 comments about Q2a, as it could be said that several processes were occurring. Perhaps it should have been more specific. Two out of DNA replication, cell growth and duplication of organelles were expected for the two marks. A surprising number of candidates in all languages, confused 'processes' with 'phases' and stated that interphase consisted of G1, S and G2. Most managed to label prophase and anaphase correctly on the diagram as required in part (b). The answers to part (b) were generally clear, but some lost marks for not comparing the same point. For example 'Mitosis produces diploid cells, but meiosis produces gametes' did not score a mark. The mitotic index was well known.\n

\n
\n", "question_id": "21M.2.HL.TZ2.B.II", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-1-cell-and-nuclear-division", "d2-1-7-phases-of-mitosis", "d2-1-13-phases-of-the-cell-cycle" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Outline the effect of nitrogen compounds from agricultural land leaching into a lake.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n excess nutrients/eutrophication;\n
    2. \n
  2. \n excessive growth of algae/algal blooms;\n
    3. \n
  3. \n blocking of sun prevents photosynthesis;\n
    4. \n
  4. \n increased decomposition of algae/organisms;\n
    5. \n
  5. \n increased biochemical oxygen demand/BOD;\n
    6. \n
  6. \n other organisms/fish die due to lack of oxygen;\n
    7. \n
\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ2.20A", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-2-stability-and-change", "d4-2-8-eutrophication-of-aquatic-and-marine-ecosystems-due-to-leaching" ] }, { "Question": "
\n
\n (i)\n
\n
\n

\n Using the data, predict the effect of universal PCV vaccination in LMICs.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n (worldwide) drastic/huge/important/significant decrease/decrease of 42 million ARI cases (treated with antibiotics);\n

\n

\n \n There must be an indication of magnitude of decrease in the answer for the mark to be awarded.\n \n

\n

\n \n Accept 30 to 50 million for the decrease.\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ2.1I", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-2-defence-against-disease", "c3-2-16-vaccines-and-immunization" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n State the type of reaction which converts excess monosaccharides to polysaccharides.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n condensation/dehydration/synthesis/anabolic/anabolism ✔\n

\n
\n", "Examiners report": "
\n

\n The diagram was generally confusing to candidates.\n

\n

\n This was often answered correctly.\n

\n
\n", "question_id": "21M.2.SL.TZ1.2B", "topics": [ "b-form-and-function" ], "subtopics": [ "b1-1-carbohydrates-and-lipids", "b1-1-2-production-of-macromolecules-by-condensation-reactions-that-link-monomers-to-form-a-polymer" ] }, { "Question": "
\n
\n

\n Explain how vaccination can lead to the production of B cells specific to the Ebola virus.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n a.\n \n vaccine\n \n contains Ebola\n \n antigens\n \n ✔\n

\n

\n b. vaccine «could» contain weakened/attenuated/dead/killed form of «Ebola» virus/virus genetically modified to express an Ebola/viral protein ✔\n

\n

\n c. phagocyte/macrophage engulfs the antigen/presents the antigen to T cell ✔\n

\n

\n d. antigen recognized by «specific» T cells/binds to T cells ✔\n

\n

\n e. «activated» T cells activate «specific) B cells ✔\n

\n

\n f. «activated» B cells make the\n \n antibodies\n \n «against Ebola» ✔\n

\n

\n g. B cells divide forming «clone of» plasma cells/producing more B cells specific to Ebola ✔\n

\n
\n", "Examiners report": "
\n

\n This was a timely question with Ebola epidemics again causing great problems in parts of Africa. Students were expected to have had some practice at analysing data relating to an epidemic because of this Skill in the programme: Analysis of epidemiological data related to vaccination programmes. It was assumed that candidates would understand terms such as ‘case’, ‘fatal case’, ‘infect’ and ‘treat’.\n

\n

\n Vaccination is a major focus on 11.1 of the programme so it was perhaps surprising that answers here were not better. Given the current outbreaks of measles and other diseases that can be prevented by vaccination, this topic should be given greater prominence in some schools. There were a few impressive answers giving the details of the steps that lead up to production of antibodies against a specific pathogen, but less than a quarter of candidates scored all three marks. There were many misconceptions. The terms ‘resistant’ and ‘immune’ have different meanings in biology, which should be carefully distinguished. Some candidates think that a vaccine contains a small amount of the pathogen. Would those candidates be happy to be infected with Ebola viruses as long as it was only a few? There was too much talk of cells ‘remembering’ the antigen or the virus. Memory cell is perhaps an unfortunate term. They are only memory cells in the sense that if an antigen binds to the antibodies they display, after cell multiplication more of those antibodies are produced and they will bind to the same antigens on the surface of an invading pathogen. This is just a series of molecular processes, not true memory.\n

\n
\n", "question_id": "19M.2.SL.TZ1.G", "topics": [ "c-interaction-and-interdependence", "a-unity-and-diversity" ], "subtopics": [ "c3-2-defence-against-disease", "a2-3-viruses-(hl-only)" ] }, { "Question": "
\n
\n

\n If a plant is exposed to light, which colour of light would lead to the lowest rate of oxygen release by a green plant?\n

\n

\n A. Blue\n

\n

\n B. Red\n

\n

\n C. Green\n

\n

\n D. White\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "21M.1A.SL.TZ1.16", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-3-photosynthesis", "c1-3-5-absorption-of-specific-wavelengths-of-light-by-photosynthetic-pigments" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Explain the role of hydrogen ions used in photosynthesis.\n

\n
\n
\n

\n [7]\n

\n
\n
\n", "Markscheme": "
\n

\n a. hydrogen ions (and oxygen) are obtained from\n \n photolysis\n \n of water ✔\n

\n

\n b. (excited) electrons (from Photosystem II) contribute to generate a hydrogen ion/proton gradient\n
\n \n \n OR\n \n \n
\n protons build up in the thylakoid space/inside the thylakoid ✔\n

\n

\n c. ATP synthase generates ATP by chemiosmosis/using the proton gradient/by movement of protons from the thylakoid space to the stroma ✔\n

\n

\n d. (two) high energy/excited electrons (from Photosystem II) are passed through an electron transport chain ✔\n

\n

\n e. NADP accepts H\n \n +\n \n (from the stroma) / electrons to produce NADPH\n \n +\n \n /reduced NADP ✔\n

\n

\n f. ATP/reduced NADP/NADPH\n \n +\n \n are used by light-independent reactions/Calvin cycle in the stroma ✔\n

\n

\n g. (in Calvin cycle) carbon fixation to ribulose bisphosphate/RuBP produces G3P ✔\n

\n

\n h. ATP is used to transform G3P to TP ✔\n

\n

\n i. reduced NADP/NADPH\n \n +\n \n is used to transform G3P to TP ✔\n

\n

\n \n Accept answers in an annotated diagram\n \n .\n

\n

\n \n Accept NADPH\n \n 2\n \n /NADPH/NADPH + H\n \n +\n \n in place of NADPH\n \n +\n \n \n .\n

\n
\n", "Examiners report": "
\n

\n Question 6 was a popular question.\n

\n

\n A relatively high scoring section, though many students failed to discuss the role of hydrogen in the light independent reactions.\n

\n
\n", "question_id": "21M.2.HL.TZ2.6A", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-3-photosynthesis", "c1-3-13-reduction-of-nadp-by-photosystem-i" ] }, { "Question": "
\n
\n

\n Using the graph, explain the Bohr shift.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n a. respiring tissues produce CO\n \n 2\n \n ;\n

\n

\n b. CO\n \n 2\n \n leads to an increase in H\n \n +\n \n /decrease in blood pH;\n

\n

\n c. increased acidity/decreased pH shifts the oxygen dissociation curve to the right;\n

\n

\n d. affinity of the hemoglobin for oxygen is reduced;\n

\n

\n e. greater release of oxygen from hemoglobin (at the same partial pressure of oxygen) in tissues;\n

\n
\n", "Examiners report": "
\n

\n Most candidates did well in this question, but strongest candidates distinguished themselves with complete and very detailed answers. Although candidates did well, there were many inaccuracies in some answers. Bohr shift is the shift to the right of the oxygen dissociation curve in respiring tissues; it does not refer to the reverse process at lung level.\n

\n
\n", "question_id": "20N.2.HL.TZ0.A", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-1-gas-exchange", "b3-1-12-bohr-shift" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Distinguish between the structures of DNA and RNA.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n \n

\n

\n \n A table format is not required but clear distinctions must be apparent.\n \n

\n

\n \n The full names of the bases must be given.\n \n

\n
\n", "Examiners report": "
\n

\n This question was well answered by most. Students are cautioned against representing bases with letter symbols such as A,C,T,G and U. The expectation of the mark scheme is that students write out the full names.\n

\n
\n", "question_id": "19M.2.SL.TZ2.7A", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a1-2-nucleic-acids", "a1-2-7-differences-between-dna-and-rna" ] }, { "Question": "
\n
\n (d)\n
\n
\n

\n State\n \n one\n \n abiotic factor that could have determined the distribution of barnacles.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n a. exposure/tides/waves ✔\n

\n

\n b. temperature ✔\n

\n

\n c. surfaces «of attachment» ✔\n

\n

\n d. resource availability/nutrients ✔\n

\n

\n e. pH ✔\n

\n

\n f. light ✔\n

\n

\n g. salinity ✔\n

\n

\n \n Do not accept biotic factors eg: “competition or predation”\n \n

\n
\n", "Examiners report": "None", "question_id": "19M.1B.SL.TZ2.12D", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-1-natural-selection", "d4-1-4-abiotic-factors-as-selection-pressures" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Describe the processes that cause water to move from the roots of plants to their leaves.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n

\n a. water moved/transported in\n \n xylem\n \n \n vessels\n \n ;\n

\n

\n b. transported under tension/suction/pulled up (in xylem vessels);\n

\n

\n c. transpiration/loss of water (vapour) generates pulling forces/low pressure/tension;\n

\n

\n d. tension/pull generated when water evaporates from cell walls (in mesophyll);\n

\n

\n e. transpiration is loss of water\n \n vapour\n \n from leaf (surface)/stomata;\n

\n

\n f.\n \n cohesivity\n \n /\n \n cohesion\n \n in water due to hydrogen bonding/attractions between water molecules;\n

\n

\n g. cohesion/WTTE so chain/column of water (molecules) doesn’t break/remains continuous;\n

\n

\n h. transpiration stream is a column of/flow of water in xylem from roots to leaves;\n

\n

\n \n Do not award marks for absorption of water by roots\n \n .\n

\n
\n", "Examiners report": "
\n

\n This was answered quite well. There were some traditional areas of confusion, with cohesion and adhesion either muddled up or treated as the same thing. Some candidates thought high pressure caused by roots and low pressure caused by leaves could exist at the same time in xylem. Few responses referred to water being transported in the vessels of xylem. In some answers water was said to evaporate from stomata, instead of the moist, blotting-paper-like cells walls of the mesophyll. Some answers included details of how water is absorbed into roots, which was outside the scope of the question. Despite these common faults, many candidates described clearly how tension is generated in xylem and how cohesive columns of water can be pulled up to leaves.\n

\n
\n", "question_id": "20N.2.SL.TZ0.7B", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-2-transport", "b3-2-7-transport-of-water-from-roots-to-leaves-during-transpiration" ] }, { "Question": "
\n
\n

\n A chromatograph was made of the photosynthetic pigments of a leaf of the plant.\n

\n

\n \n

\n

\n [Source: Adapted from “Diversity of Photosynthetic Pigments” by Alexander F. Motten in Tested Studies for\n
\n Laboratory Teaching, Volume 16 of the Association for Biology Laboratory Education and used by permission of the\n
\n author.]\n

\n

\n

\n

\n Outline what measurements would be taken to identify pigment X.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. the distance travelled from the origin/O to the solvent front;\n

\n

\n b. the distance travelled by the pigment (from the origin O to X);\n

\n

\n \n Accept X to solvent front if the candidate indicates that this allows O to X to be calculated\n \n .\n

\n
\n", "Examiners report": "
\n

\n Most candidates managed to outline what measurements would be taken to identify the pigment on the chromatogram with many identifying the pigment although this was not required.\n

\n
\n", "question_id": "20N.1B.SL.TZ0.D", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-3-photosynthesis", "c1-3-4-separation-and-identification-of-photosynthetic-pigments-by-chromatography" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n State the main characteristic of stem cells.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n undifferentiated/pluripotent/ability to divide/differentiate into any types of cells/differentiate along different pathways;\n

\n
\n", "Examiners report": "
\n

\n In a. most were able to say the stem cells were undifferentiated. Many put ‘unspecialised’ instead, which was not credited. There were several, justified G2 comments about the size of the micrograph, which made it difficult to measure the diameter accurately. However, this was generally very poorly answered, with over half failing to get the mark for either the correct answer or the correct calculation. In 1d the better candidates stated that the person could now live a normal life, but as it was not in the genome the progeny could still be affected. The word ‘progeny’ was commented on by several teachers, who pointed out that ‘children’, or ‘offspring’ would have been clearer for those working in an additional language.\n

\n
\n", "question_id": "22M.2.SL.TZ2.2", "topics": [ "b-form-and-function", "a-unity-and-diversity" ], "subtopics": [ "b2-3-cell-specialization", "b2-3-2-properties-of-stem-cells", "a2-2-cell-structure", "a2-2-2-microscopy-skills" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Outline the additional information that would be required to convert the food web into a pyramid of energy.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n energy content in biomass/all organisms of each trophic level;\n
    2. \n
  2. \n size of study area included;\n
    3. \n
  3. \n over period of time / per year;\n
    4. \n
\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ1.15B", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c4-2-transfers-of-energy-and-matter", "c4-2-11-construction-of-energy-pyramids" ] }, { "Question": "
\n
\n

\n What information can be deduced from the sequence of nodes in a cladogram?\n

\n

\n A. The geological period in which the species in the clade diverged from their common ancestor\n

\n

\n B. The probable sequence of divergence among the species in the clade\n

\n

\n C. The number of characteristics the species have in common\n

\n

\n D. The number of mutations that have occurred since the species shared a common ancestor\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "21M.1A.HL.TZ2.23", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a3-2-classification-and-cladistics-(hl-only)", "a3-2-7-analysing-cladograms" ] }, { "Question": "
\n
\n (a.ii)\n
\n
\n

\n Suggest reasons for the differences in predation.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. the marmots have experience with/recognize predators ✔\n

\n

\n b. parents shield them from predators\n
\n \n \n OR\n \n \n
\n parents teach them about predators ✔\n

\n

\n c. those born in the wild are favoured in\n \n natural selection\n \n ✔\n

\n
\n", "Examiners report": "
\n

\n Most candidates were able to score at least 1 mark here by commenting on either the greater experience with predators for marmots in the wild, or the role of learning. However, some examiners noted that students tended to use anthropomorphisms when discussing animals in this option. Also, it was surprising that very few students were able to achieve the marking point that those born in the wild were favoured by natural selection, as natural selection is one of the central ideas in biology.\n

\n
\n", "question_id": "19M.2.SL.TZ1.16A.II", "topics": [ "b-form-and-function" ], "subtopics": [ "b4-2-ecological-niches", "b4-2-10-adaptations-of-predators-for-finding-catching-and-killing-prey-and-of-prey-animals-for-resisting-predation" ] }, { "Question": "
\n
\n

\n State the name of the structure shown.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n synapse/synaptic\n

\n

\n \n Allow any answer including either of these terms unless out of context\n \n .\n

\n
\n", "Examiners report": "
\n

\n As pointed out on some G2 forms, the question here was rather ambiguous as it wasn’t 100 % clear what structure was referred to, so any answer indicating that the candidate knew the diagram showed a synapse was accepted.\n

\n
\n", "question_id": "20N.2.SL.TZ0.C.I", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c2-2-neural-signalling", "c2-2-5-synapses-as-junctions-between-neurons-and-between-neurons-and-effector-cells" ] }, { "Question": "
\n
\n

\n Deduce the concentration of ZDV that would cause a 50 % reduction in root growth compared to the control.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n 75 μmol ✔\n

\n

\n \n Allow answers in the range of 70 µmol–80 µmol\n \n .\n

\n
\n", "Examiners report": "
\n

\n Part (ii) was better answered than part (i) as many answers provided were outside the acceptable range of answers.\n

\n
\n", "question_id": "21M.2.HL.TZ1.A.I", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a2-3-viruses-(hl-only)", "a2-3-6-rapid-evolution-in-viruses" ] }, { "Question": "
\n
\n

\n The apparatus is set up to measure the rate of transpiration. As transpiration occurs from the leafy shoot, water is drawn through the apparatus and is measured by timing the movement of the air bubble along the capillary tube.\n

\n

\n \n

\n

\n Which variable(s) must be controlled if transpiration rates are compared in different plant species?\n

\n

\n I.   Total leaf surface area\n

\n

\n II.  Volume of water in the reservoir\n

\n

\n III. Room temperature\n

\n

\n A.  I only\n

\n

\n B.  III only\n

\n

\n C.  I and III only\n

\n

\n D.  I, II and III\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "22N.1A.HL.TZ0.32", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-1-gas-exchange", "b3-1-9-transpiration-as-a-consequence-of-gas-exchange-in-a-leaf" ] }, { "Question": "
\n
\n

\n Identify\n \n one\n \n adaptation of the leaf for the absorption of light visible in this micrograph.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n double layer of palisade cells;\n
    2. \n
  2. \n palisade layer on upper surface;\n
    3. \n
  3. \n dimensions of palisade cells maximize light absorption;\n
    4. \n
  4. \n thin/transparent epidermis/cuticle;\n
    5. \n
\n
\n", "Examiners report": "None", "question_id": "SPM.1B.SL.TZ0.D", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-1-gas-exchange", "b3-1-7-adaptations-for-gas-exchange-in-leaves", "b3-1-8-distribution-of-tissues-in-a-leaf" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n State the type of inheritance shown.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n «gene/autosomal» linkage ✔\n

\n

\n \n Reject sex linkage\n \n

\n
\n", "Examiners report": "None", "question_id": "19N.2.HL.TZ0.2", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-2-inheritance", "d3-2-17-punnett-grids-for-predicting-genotypic-and-phenotypic-ratios-in-dihybrid-crosses-involving-pairs-of-unlinked-autosomal-genes", "d3-2-18-loci-of-human-genes-and-their-polypeptide-products", "d3-2-19-autosomal-gene-linkage", "d3-2-20-recombinants-in-crosses-involving-two-linked-or-unlinked-genes", "d3-2-21-use-of-a-chi-squared-test-on-data-from-dihybrid-crosses" ] }, { "Question": "
\n
\n

\n The diagram shows a motor neuron.\n

\n

\n \n

\n

\n [Source: © International Baccalaureate Organization 2019]\n

\n

\n

\n

\n What are the biochemical nature and function of the myelin sheath?\n

\n

\n A. The myelin sheath is mainly protein which allows growth of the axon.\n

\n

\n B. The myelin sheath is mainly protein which acts as membrane carriers.\n

\n

\n C. The myelin sheath is mainly lipid which allows saltatory conduction.\n

\n

\n D. The myelin sheath is mainly lipid which provides an energy source.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "
\n

\n This question had a very high discrimination index, showing only the most capable candidates were able to answer the question.\n

\n
\n", "question_id": "19M.1A.SL.TZ2.28", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c2-2-neural-signalling", "c2-2-1-neurons-as-cells-within-the-nervous-system-that-carry-electrical-impulses", "c2-2-4-variation-in-the-speed-of-nerve-impulses" ] }, { "Question": "
\n
\n

\n Which statement applies to an axon at rest?\n

\n

\n A. There is no electric potential difference between the external and internal surfaces of the plasma membrane.\n

\n

\n B. The external surface of the plasma membrane is positive relative to the internal surface.\n

\n

\n C. The external surface of the plasma membrane is negative relative to the internal surface.\n

\n

\n D. The internal surface of the plasma membrane has a much higher concentration of sodium ions.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "21M.1A.HL.TZ1.22", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c2-2-neural-signalling", "c2-2-9-propagation-of-an-action-potential-along-a-nerve-fibre/axon-as-a-result-of-local-currents" ] }, { "Question": "
\n
\n

\n In the micrograph, which letter points to a cell in anaphase?\n

\n

\n \n

\n

\n [Source: Berkshire Community College Bioscience Image Library,\n
\n https://commons.wikimedia.org/wiki/File:Mitotic_Stages_in_Apical_Meristem_of_Allium_Root_Tip_(36762516673).jpg,\n
\n licensed under Creative Commons CC0 1.0 Universal Public Domain Dedication]\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "None", "question_id": "19N.1A.SL.TZ0.4", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-1-cell-and-nuclear-division", "d2-1-8-identification-of-phases-of-mitosis" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Outline how adaptive radiation provides evidence for evolution.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n diversification/ different species produced from a common/shared ancestor;\n
    2. \n
  2. \n homologous features have similarities of structure\n
    3. \n
  3. \n despite different functions;\n
    4. \n
  4. \n (different) adaptation to different environments/different selective pressures;\n
    5. \n
  5. \n pentadactyl limbs/Darwin’s finches/other example of adaptive radiation described correctly;\n
    6. \n
\n

\n \n Allow any of the marking points with reference to a named example e.g. Darwin’s finches or pentadactyl limb.\n \n

\n
\n", "Examiners report": "
\n

\n Some candidates misread the question and wrote about radiation causing mutations. Other answers described how a species changes over time due to natural selection. A few answers gave a convincing account of how structures such as the pentadactyl limb give evidence for evolution because similarities of structure despite differences of function indicate common ancestry.\n

\n
\n", "question_id": "22N.2.HL.TZ0.8", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a4-1-evolution-and-speciation", "a4-1-9-adaptive-radiation-as-a-source-of-biodiversity", "a4-1-11-abrupt-speciation-in-plants-by-hybridization-and-polyploidy", "a3-2-classification-and-cladistics-(hl-only)", "a3-2-1-need-for-classification-of-organisms", "a3-2-9-classification-of-all-organisms-into-three-domains-using-evidence-from-rrna-base-sequences" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n State one cause of lung cancer.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n smoking/tobacco;\n
    2. \n
  2. \n passive smoking;\n
    3. \n
  3. \n Radon/other radiation;\n
    4. \n
  4. \n exposure to arsenic/asbestos/smoke from coal burning/fires/silica/rock dust/vehicle exhaust fumes/nitrogen oxides;\n
    5. \n
\n

\n

\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ2.3", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-1-cell-and-nuclear-division", "d2-1-17-differences-between-tumours-in-rates-of-cell-division-and-growth-and-in-the-capacity-for-metastasis-and-invasion-of-neighbouring-tissue" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n The receptor contains seven alpha helices and one other secondary structure. Deduce what this other secondary structure is.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n beta pleated sheet/beta-loop/beta strands;\n

\n

\n \n Reject ‘beta helix’\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.2.HL.TZ1.2B", "topics": [ "b-form-and-function" ], "subtopics": [ "b1-2-proteins", "b1-2-8-pleating-and-coiling-of-secondary-structure-of-proteins" ] }, { "Question": "
\n
\n (d)\n
\n
\n

\n Explain how the population of fish in a pond could be estimated using the capture-mark-release-recapture method.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n random sample is captured and marked/tagged (in a manner that will not harm fish);\n
    2. \n
  2. \n captured sample is released and allowed to mix with general population\n
    \n \n \n OR\n \n \n
    \n captured sample is released then wait a few days/weeks;\n
    3. \n
  3. \n second sample is captured and both the total number and the number of marked fish counted;\n
    4. \n
  4. \n ratio of recaptured marked fish to number in second sample = the ratio of the number in the first sample marked and released to the population size\n
    \n \n \n OR\n \n \n
    \n Population Size =\n \n \n \n \n \n n\n \n \n 1\n \n \n \n ×\n \n \n \n n\n \n \n 2\n \n \n \n \n \n n\n \n \n 2\n \n \n \n \n
    \n n\n \n 1\n \n = number in first sample marked\n
    \n n\n \n 2\n \n = number in second sample\n
    \n n\n \n 3\n \n = number of recaptured individuals marked\n
    5. \n
\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ1.18D", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c4-1-populations-and-communities", "c4-1-4-capture-mark-release-recapture-and-the-lincoln-index-to-estimate-population-size-for-motile-organisms" ] }, { "Question": "
\n
\n (d.ii)\n
\n
\n

\n Label with a C the tissue where organic compounds are transported.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n \n \n \n

\n

\n [Source: Nbnidhi, https:// commons.wikimedia.org/wiki/ File:Transverse_section_of_dicot _stem.jpg]\n

\n

\n \n Award\n \n [1]\n \n for correct labeling of C\n \n

\n
\n", "Examiners report": "
\n

\n This was another question that was difficult for students. This question again required students to understand one of the skills from the subject guide, this time in topic 9.2 (Identification of xylem and phloem in microscope images of stem and root). Student responses to this question, however, suggested that few students could identify phloem and xylem under a microscope.\n

\n
\n", "question_id": "19M.1B.SL.TZ1.2D.II", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-2-transport", "b3-2-9-distribution-of-tissues-in-a-transverse-section-of-the-stem-of-a-dicotyledonous-plant" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Outline reasons for the therapeutic use of stem cells.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n unspecialized/undifferentiated stem cells can divide/differentiate along different pathways;\n
    2. \n
  2. \n (stem cells are accessible as they) come from embryos/bone marrow/umbilical cord blood/adult tissue;\n
    3. \n
  3. \n (stem cells) can regenerate/repair/regrow diseased/damaged tissues in people;\n
    4. \n
  4. \n valid specific example;\n
    5. \n
  5. \n drugs can be tested on stem cells (in laboratories to see if they are harmful);\n
    6. \n
\n
\n", "Examiners report": "
\n

\n Most candidates knew something of the therapeutic uses of stem cells, including differentiation for specific roles. There was a tendency for over-optimism over what can be fixed using stem cells. For example, stem cells are not a treatment for most cancers. The best answers stuck to well-established procedures such as the treatments for leukaemia using stem cells from bone marrow.\n

\n
\n", "question_id": "22M.2.HL.TZ1.7", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-2-cell-respiration", "c1-2-14-generation-of-a-proton-gradient-by-flow-of-electrons-along-the-electron-transport-chain" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Outline reasons for the therapeutic use of stem cells.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n unspecialized/undifferentiated stem cells can divide / differentiate along different pathways;\n
    2. \n
  2. \n (stem cells are accessible as they) come from embryos/bone marrow/umbilical cord blood/adult tissue;\n
    3. \n
  3. \n (stem cells) can regenerate/repair diseased/damaged tissues in people;\n
    4. \n
  4. \n valid specific example;\n
    5. \n
  5. \n drugs can be tested on stem cells (in laboratories to see if they are harmful);\n
    6. \n
\n
\n", "Examiners report": "
\n

\n Some excellent answers; stem cells was usually well answered, leaf cells was often more complex than necessary but marks were usually able to be gained, though many answers were missing the obvious, for example leaf cells contain chloroplasts. Defence against disease; far too often over-complicated and confused answers. It is important that students are aware of the level they need to know. There is no need to over-complicate and risk loss of understanding, which was evident across many answers and which was so confused across the roles of macrophages, B cells and T cells. Equally, for cell components, more often than not this was ignored or mistakenly discussed as skin and mucus over platelets.\n

\n

\n Mostly well done. Appropriate examples provided for stem cell therapies. It seems that many candidates think that all stem cells can differentiate into \"any\" type of cells, which is not correct. Other candidates showed understanding of the discrimination between the source and the potential of the cells. Occasionally candidate showed confusion about the term \"stem\" in that \"stem cells show the way plants grow\"; sometimes therapeutic use of stem cells was confused with gene editing.\n

\n
\n", "question_id": "22M.2.SL.TZ1.6", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-3-photosynthesis", "c1-3-1-transformation-of-light-energy-to-chemical-energy-when-carbon-compounds-are-produced-in-photosynthesis", "c1-3-5-absorption-of-specific-wavelengths-of-light-by-photosynthetic-pigments", "c3-2-defence-against-disease", "c3-2-10-immunity-as-a-consequence-of-retaining-memory-cells" ] }, { "Question": "
\n
\n

\n Using\n \n all\n \n the data, discuss whether inoculating mice with the antigen to\n \n B. burgdorferi\n \n could be an effective method of controlling the spread of Lyme disease.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n a.\n \n Site 2\n \n suggests that vaccination could reduce «nymph» infection rate «so method might be effective» ✔\n

\n

\n b.\n \n Site 1\n \n suggests that vaccination does not reduce «nymph» infection rate «so method probably not effective» ✔\n

\n

\n c. effective «to some extent» as vaccination increases antibodies/immunity in mice ✔\n

\n

\n d. high antibody levels needed/ many mice need to be vaccinated «for the method to be effective» ✔\n

\n

\n e. some nymphs are still infected / «absolute» numbers «rather than proportions» of infected nymphs are similar in those collected from control and vaccinated mice ✔\n

\n

\n f. there are other hosts/mammals/birds ✔\n

\n

\n g. difficult/expensive «to vaccinate many small mammals/mice»\n
\n \n \n OR\n \n \n
\n cheaper to use protective clothing/tick repellant/avoid wooded areas/other method ✔\n

\n
\n", "Examiners report": "None", "question_id": "19N.2.SL.TZ0.H", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-2-defence-against-disease", "c3-2-10-immunity-as-a-consequence-of-retaining-memory-cells" ] }, { "Question": "
\n
\n (d.ii)\n
\n
\n

\n State the type of reaction that removes water while linking amino acids together to form polypeptides.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n condensation ✔\n

\n

\n \n Do not accept anabolism alone\n \n .\n

\n
\n", "Examiners report": "None", "question_id": "19N.2.SL.TZ0.2D.II", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d1-2-protein-synthesis", "d1-2-10-stepwise-movement-of-the-ribosome-along-mrna-and-linkage-of-amino-acids-by-peptide-bonding-to-the-growing-polypeptide-chain" ] }, { "Question": "
\n
\n (a.i)\n
\n
\n

\n Outline how the amphipathic properties of phospholipids play a role in membrane structure.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. part hydrophobic/not attracted to water/non-polar\n \n \n AND\n \n \n part hydrophilic/attracted to water/polar;\n

\n

\n b.\n \n bilayer\n \n formed (formed naturally by phospholipids in water);\n

\n

\n c.\n \n hydrophilic\n \n heads/parts face outwards and\n \n hydrophobic\n \n tails/parts face inwards.\n

\n

\n \n Do not allow water loving/hating in mpa or mpc\n \n .\n

\n
\n", "Examiners report": "
\n

\n Knowledge of the amphipathic properties of phospholipids was generally good.\n

\n
\n", "question_id": "20N.2.HL.TZ0.2", "topics": [ "b-form-and-function", "c-interaction-and-interdependence" ], "subtopics": [ "b1-1-carbohydrates-and-lipids", "b1-1-12-formation-of-phospholipid-bilayers-as-a-consequence-of-the-hydrophobic-and-hydrophilic-regions", "b2-1-membranes-and-membrane-transport", "b2-1-10-fluid-mosaic-model-of-membrane-structure", "c2-2-neural-signalling", "c2-2-5-synapses-as-junctions-between-neurons-and-between-neurons-and-effector-cells", "c2-2-6-release-of-neurotransmitters-from-a-presynaptic-membrane", "c2-2-7-generation-of-an-excitatory-postsynaptic-potential" ] }, { "Question": "
\n
\n

\n Which statement best describes how evolution occurs?\n
\n
\n

\n

\n A.  Species which produce the most offspring are favoured by natural selection.\n

\n

\n B.  Mutations in somatic cells are passed on to offspring.\n

\n

\n C.  Natural selection decreases the frequency of unfavourable characteristics.\n

\n

\n D.  Changes in species lead towards greater complexity over time.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "23M.1A.SL.TZ2.23", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a4-1-evolution-and-speciation", "a4-1-1-evolution-as-change-in-the-heritable-characteristics-of-a-population" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Models are used as representations of the real world. Evaluate the use of food webs to represent ecological communities.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n \n Advantages\n \n :\n
\n a. food webs summarize all possible food chains «in the community» ✔\n \n OWTTE\n \n

\n

\n b. realistic representation ✔\n

\n

\n \n Limitations\n \n :\n
\n c. some communities/ecosystems are too complex to represent ✔\n

\n

\n d. only shows qualitative information/not quantitative data\n
\n \n \n OR\n \n \n
\n saprotrophs/abiotic factors not taken into account ✔\n

\n

\n \n Needs one advantage and one limitation to obtain\n \n [2]\n \n .\n \n
\n \n Do not accept mentions of trophic levels\n \n .\n

\n
\n", "Examiners report": "None", "question_id": "19N.2.SL.TZ0.14B", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c4-2-transfers-of-energy-and-matter", "c4-2-4-construction-of-food-chains-and-food-webs-to-represent-feeding-relationships-in-a-community" ] }, { "Question": "
\n
\n

\n The hypothesis made before the study was that saturated fats in the diet affected the risk of coronary artery blockage and diabetes. Using all the data in question 1, evaluate whether this hypothesis is supported by the study.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n \n Hypothesis is partially supported\n \n
\n a. Increased saturated fats in study diet resulted in increase in cholesterol levels;\n

\n

\n b. cholesterol level is risk for blockage of coronary arteries;\n

\n

\n \n Hypothesis is not supported\n \n
\n c. high insulin levels are sign of (Type II) diabetes;\n

\n

\n d. insulin levels were the same in both diets so no increased risk;\n

\n

\n e. study only 2 weeks long;\n

\n
\n", "Examiners report": "None", "question_id": "20N.1B.SL.TZ0.E", "topics": [ "d-continuity-and-change", "b-form-and-function" ], "subtopics": [ "d3-3-homeostasis", "d3-3-3-regulation-of-blood-glucose-as-an-example-of-the-role-of-hormones-in-homeostasis", "b1-2-proteins", "b1-2-3-dietary-requirements-for-amino-acids", "b1-1-carbohydrates-and-lipids", "b1-1-10-difference-between-saturated-monounsaturated-and-polyunsaturated-fatty-acids" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n State the probability that Edward had hemophilia.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n 0.5/50 %;\n

\n
\n", "Examiners report": "
\n

\n Approximately 50 % of the candidates were correct with their answer of 50 %. It was expected that candidates would recognize that Edward is male because he has a box rather than circle in the pedigree. Then from there, they would calculate the 50 %.\n

\n
\n", "question_id": "22M.2.SL.TZ1.4", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-2-inheritance", "d3-2-12-haemophilia-as-an-example-of-a-sex-linked-genetic-disorder", "d3-2-13-pedigree-charts-to-deduce-patterns-of-inheritance-of-genetic-disorders" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Outline the process of inhalation.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n

\n a. diaphragm contracts / moves downwards/flattens ✔\n

\n

\n b.\n \n external\n \n intercostal muscles contract ✔\n

\n

\n c. (muscle contraction) moves the rib cage upwards and outwards ✔\n

\n

\n d. increases volume of the thorax / lungs ✔\n

\n

\n e. difference in pressure/decreasing pressure causes air to flow into lungs / lungs inflate ✔\n

\n
\n", "Examiners report": "
\n

\n This question was attempted by approximately 56 % of candidates.\n

\n

\n Done well by many. Diaphragm contraction and external intercostal muscle contraction was commonly known along with the idea that the rib cage moves upwards and outwards. Further understanding of the consequent pressure changes in the thorax was not clear.\n

\n
\n", "question_id": "21M.2.SL.TZ1.7", "topics": [ "b-form-and-function", "d-continuity-and-change" ], "subtopics": [ "b3-1-gas-exchange", "b3-1-5-ventilation-of-the-lungs", "b3-1-4-adaptations-of-mammalian-lungs-for-gas-exchange", "d4-3-climate-change", "d4-3-1-anthropogenic-causes-of-climate-change" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n State the alternative hypothesis for this study.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n there is a positive / negative association between the two species;\n
\n they tend to grow together / they tend to grow apart;\n

\n

\n \n OWTTE\n \n

\n
\n", "Examiners report": "
\n

\n There were many correct answers, but a number confused the alternate and null hypotheses.\n

\n
\n", "question_id": "22M.2.HL.TZ2.3", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c4-1-populations-and-communities", "c4-1-15-use-of-the-chi-squared-test-for-association-between-two-species" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n State where in the body the blood would be flowing at point X on the graph.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n lungs/alveoli;\n

\n
\n", "Examiners report": "None", "question_id": "23M.2.HL.TZ1.23A", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-1-gas-exchange", "b3-1-12-bohr-shift" ] }, { "Question": "
\n
\n

\n What is an example of anabolism?\n
\n
\n

\n

\n A.  Formation of peptides after protein digestion\n

\n

\n B.  Formation of glucose and fructose from sucrose\n

\n

\n C.  Formation of maltose from two glucose molecules\n

\n

\n D.  Formation of glycerol and fatty acids from triglycerides\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n C\n

\n
\n", "Examiners report": "None", "question_id": "23M.1A.SL.TZ1.5", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-1-enzymes-and-metabolism", "c1-1-3-anabolic-and-catabolic-reactions" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Explain the role of hydrogen ions used in photosynthesis.\n

\n
\n
\n

\n [7]\n

\n
\n
\n", "Markscheme": "
\n

\n a. hydrogen ions (and oxygen) are obtained from\n \n photolysis\n \n of water ✔\n

\n

\n b. (excited) electrons (from Photosystem II) contribute to generate a hydrogen ion/proton gradient\n
\n \n \n OR\n \n \n
\n protons build up in the thylakoid space/inside the thylakoid ✔\n

\n

\n c. ATP synthase generates ATP by chemiosmosis/using the proton gradient/by movement of protons from the thylakoid space to the stroma ✔\n

\n

\n d. (two) high energy/excited electrons (from Photosystem II) are passed through an electron transport chain ✔\n

\n

\n e. NADP accepts H\n \n +\n \n (from the stroma) / electrons to produce NADPH\n \n +\n \n /reduced NADP ✔\n

\n

\n f. ATP/reduced NADP/NADPH\n \n +\n \n are used by light-independent reactions/Calvin cycle in the stroma ✔\n

\n

\n g. (in Calvin cycle) carbon fixation to ribulose bisphosphate/RuBP produces G3P ✔\n

\n

\n h. ATP is used to transform G3P to TP ✔\n

\n

\n i. reduced NADP/NADPH\n \n +\n \n is used to transform G3P to TP ✔\n

\n

\n \n Accept answers in an annotated diagram\n \n .\n

\n

\n \n Accept NADPH\n \n 2\n \n /NADPH/NADPH + H\n \n +\n \n in place of NADPH\n \n +\n \n \n .\n

\n
\n", "Examiners report": "
\n

\n Question 6 was a popular question.\n

\n

\n A relatively high scoring section, though many students failed to discuss the role of hydrogen in the light independent reactions.\n

\n
\n", "question_id": "21M.2.HL.TZ2.6", "topics": [ "c-interaction-and-interdependence", "b-form-and-function" ], "subtopics": [ "c1-3-photosynthesis", "c1-3-13-reduction-of-nadp-by-photosystem-i", "b2-2-organelles-and-compartmentalization", "b2-2-5-adaptations-of-the-chloroplast-for-photosynthesis", "b1-2-proteins", "b1-2-6-chemical-diversity-in-the-r-groups-of-amino-acids-as-a-basis-for-the-immense-diversity-in-protein-form-and-function", "b1-2-12-relationship-of-form-and-function-in-globular-and-fibrous-proteins" ] }, { "Question": "
\n
\n (h)\n
\n
\n

\n When there is no vaccination, the estimated number of cases for lower-middle income countries is larger than in either low income or upper-middle income countries. Suggest\n \n one\n \n reason for this.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n higher population in lower-middle income countries/subgroup (compared to the other 2 subgroups);\n
    2. \n
  2. \n low income population may not have/have less access to medicine/antibiotics/vaccination (compared to lower-middle income population)/ low-income populations may not report data\n
    \n \n \n OR\n \n \n
    \n upper-middle population may have better living conditions/more adequate medical diagnoses (compared to lower-middle income population);\n
    3. \n
\n

\n \n Lower-middle income subgroup is not the same as LMIC (includes all 3 subgroups).\n \n LMIC should not be used as equivalent.\n \n \n

\n

\n \n Mpb: accept vice versa.\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ2.1H", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-2-defence-against-disease", "c3-2-16-vaccines-and-immunization" ] }, { "Question": "
\n
\n

\n Using only evidence from the data in Question 1, suggest\n \n two\n \n strategies for reducing obesity in countries where this health problem is most prevalent.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n use public education to encourage people to walk more/become more active;\n
    2. \n
  2. \n improve city design to improve walkability;\n
    3. \n
  3. \n reduce distances between homes / shops / workplaces / parks;\n
    4. \n
  4. \n more sidewalks / make it easier for pedestrians to cross roads / other specific measure;\n
    5. \n
\n

\n

\n

\n \n Do not accept answers that involve diet as that is beyond the scope of the data given.\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ1.H", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-3-muscle-and-motility-(hl-only)", "b3-3-9-reasons-for-locomotion" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n State the domain into which ticks are classified.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n eukaryote ✔\n

\n

\n \n Accept eukaryotes\n \n .\n

\n
\n", "Examiners report": "None", "question_id": "19N.2.HL.TZ0.1", "topics": [ "a-unity-and-diversity", "c-interaction-and-interdependence" ], "subtopics": [ "a3-2-classification-and-cladistics-(hl-only)", "a3-2-9-classification-of-all-organisms-into-three-domains-using-evidence-from-rrna-base-sequences", "a4-2-conservation-of-biodiversity", "c3-2-defence-against-disease", "c3-2-7-antigens-as-recognition-molecules-that-trigger-antibody-production", "c3-2-8-activation-of-b-lymphocytes-by-helper-t-lymphocytes", "c3-2-9-multiplication-of-activated-b-lymphocytes-to-form-clones-of-antibody-secreting-plasma-cells", "c3-2-10-immunity-as-a-consequence-of-retaining-memory-cells" ] }, { "Question": "
\n
\n (a.ii)\n
\n
\n

\n Using the climograph, identify the relationship between maximum temperature and rainfall.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n maximum temperature occurs just when rainfall begins/at the onset of the rainy season/monsoon\n
\n \n \n OR\n \n \n
\n negative relationship «as maximum temperature drops, rainfall increases» ✔\n

\n

\n \n OWTTE\n \n

\n
\n", "Examiners report": "None", "question_id": "19M.2.HL.TZ2.15A.II", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-2-stability-and-change", "d4-2-14-cyclical-succession-in-ecosystems" ] }, { "Question": "
\n
\n (i)\n
\n
\n

\n where the DNA of each individual could be taken from.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n from blood sample/hair/cheek/saliva/semen;\n

\n

\n \n Do not accept red blood cells\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.1B.SL.TZ1.AI", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-3-photosynthesis", "c1-3-7-techniques-for-varying-concentrations-of-carbon-dioxide-light-intensity-or-temperature-experimentally-to-investigate-the-effects-of-limiting-factors-on-the-rate-of-photosynthesis" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Compare and contrast the effect of increasing exercise intensity at sea level and at an altitude of 4000 m.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. in both sea level and 4000m ventilation rate while exercising «at all intensities» is «significantly» more than at rest\n
\n \n \n OR\n \n \n
\n both sea level and 4000m show an increase in ventilation rate «dm\n \n 3\n \n min\n \n –1\n \n » as exercise intensity increased ✔\n

\n

\n b. ventilation rate at 4000m «slightly» higher than at sea level for all conditions\n
\n \n \n OR\n \n \n
\n higher ventilation rate at 4000m not «significantly» different as error bars overlap ✔\n

\n

\n \n Accept positive correlation.\n \n

\n
\n", "Examiners report": "
\n

\n In this question the candidates were asked to look at data on the effect of exercise and altitude on ventilation rate. Most candidates could state one other variable that should have been controlled in this study and could compare and contrast the effect of increasing exercise intensity in the two groups.\n

\n
\n", "question_id": "19M.1B.SL.TZ2.3B", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-1-gas-exchange", "b3-1-5-ventilation-of-the-lungs" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Outline the structure of proteins.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n a. protein formed from amino acids\n
\n \n \n OR\n \n \n
\n 20 different amino acids ✔\n

\n

\n b. linked together by peptide bonds ✔\n

\n

\n c. may consist of one or more polypeptides linked together ✔\n

\n

\n d. have a specific shape/conformation/folding ✔\n

\n

\n e. shape determines function ✔\n

\n
\n", "Examiners report": "
\n

\n This question was attempted by about 42 % of candidates.\n

\n

\n Many candidates used the terms primary, secondary, tertiary and quaternary as their basic outline. These terms occur in AHL but not in the core. Therefore, without an outline of the meaning of these terms few marks could be earned.\n

\n
\n", "question_id": "21M.2.SL.TZ1.6", "topics": [ "b-form-and-function" ], "subtopics": [ "b1-2-proteins", "b1-2-4-infinite-variety-of-possible-peptide-chains", "b1-2-5-effect-of-ph-and-temperature-on-protein-structure" ] }, { "Question": "
\n
\n (d.i)\n
\n
\n

\n A fly that is homozygous dominant for both body colour and wing size mates with a fly that is recessive for both characteristics. In the table, draw the arrangement of alleles for the offspring of this mating and for the homozygous recessive parent.\n

\n

\n \n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n \n

\n
\n", "Examiners report": "
\n

\n This was generally well answered, with more than two thirds of candidates getting at least one of the genotypes correct. The best answers gave the alleles on lines that symbolised linked genes on a chromosome, but there was a potential pitfall here. If the alleles were arranged in a way that was impossible, given the nature of the cross, one mark was deducted. For example, each chromosome must have one of each gene, not two copies of one gene.\n

\n
\n", "question_id": "19M.2.HL.TZ1.2D.I", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-2-inheritance", "d3-2-16-segregation-and-independent-assortment-of-unlinked-genes-in-meiosis", "d3-2-17-punnett-grids-for-predicting-genotypic-and-phenotypic-ratios-in-dihybrid-crosses-involving-pairs-of-unlinked-autosomal-genes" ] }, { "Question": "
\n
\n

\n The anticodons of three tRNAs and the amino acids they carry are shown in the table.\n

\n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n
\n \n tRNA anticodon\n \n \n \n Amino acid\n \n
\n GCA\n \n Arginine\n
\n AAU\n \n Leucine\n
\n CAG\n \n Valine\n
\n

\n

\n

\n Which base sequence of an mRNA molecule would code for an arginine–leucine–valine tripeptide?\n
\n
\n

\n

\n A.  GCA AAU CAG\n

\n

\n B.  GCA AAT CAG\n

\n

\n C.  CGT TTA GTC\n

\n

\n D.  CGU UUA GUC\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "23M.1A.SL.TZ2.11", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d1-2-protein-synthesis", "d1-2-5-translation-as-the-synthesis-of-polypeptides-from-mrna" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Explain the transformations of carbon compounds in the carbon cycle.\n

\n
\n
\n

\n [7]\n

\n
\n
\n", "Markscheme": "
\n

\n a. autotrophs/producers convert carbon dioxide into carbohydrates/carbon compounds in photosynthesis;\n

\n

\n b. carbon dioxide diffuses/moves from the atmosphere /water into autotrophs/plants;\n

\n

\n c. carbon compounds are transferred through food chains/\n \n OWTTE\n \n ;\n

\n

\n d. carbon dioxide produced by respiration diffuses out of organisms into water/atmosphere;\n

\n

\n e. decomposers release carbon dioxide during decay/putrefaction;\n

\n

\n f. methane is produced from organic matter\n \n in anaerobic conditions\n \n (by methanogens);\n

\n

\n g. some methane diffuses into the atmosphere/accumulates in the ground;\n

\n

\n h. methane is oxidized to carbon dioxide (and water) in the atmosphere;\n

\n

\n i. peat forms when organic matter is not fully decomposed because of acidic/anaerobic conditions in waterlogged soils;\n

\n

\n j. partially decomposed organic matter from past geological eras/fossils was converted into coal/oil/gas that accumulated in rocks;\n

\n

\n k. carbon dioxide is produced by the combustion of biomass/fossilized organic matter/fuels;\n

\n

\n i. hard parts of some animals/corals/molluscs are composed of calcium carbonate\n

\n

\n m. can become fossilized in limestone;\n

\n

\n \n As this is an “explain” question, simply drawing a labelled diagram is not enough for\n \n [7]\n \n . Diagram would need sufficient annotations to meet the command term\n \n .\n

\n

\n \n If carbon compounds are referred to instead of carbon dioxide, penalise once then ecf\n \n .\n

\n
\n", "Examiners report": "None", "question_id": "20N.2.SL.TZ0.5C", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c4-2-transfers-of-energy-and-matter", "c4-2-18-ecosystems-as-carbon-sinks-and-carbon-sources", "c4-2-22-recycling-of-all-chemical-elements-required-by-living-organisms-in-ecosystems" ] }, { "Question": "
\n
\n (a.i)\n
\n
\n

\n State the distance from the city centre at which the highest proportion of plants sampled contained HCN.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n 32 (km);\n

\n

\n \n Accept answers in the range of 31 to 33 (km)\n \n .\n

\n
\n", "Examiners report": "
\n

\n This was intended to be an easy first mark but only 70 %  answered it correctly, with others mostly giving the maximum distance rather than the distance with the highest proportion of plants containing cyanide.\n

\n
\n", "question_id": "20N.2.HL.TZ0.1", "topics": [ "d-continuity-and-change", "b-form-and-function" ], "subtopics": [ "d4-2-stability-and-change", "d4-2-4-use-of-a-model-to-investigate-the-effect-of-variables-on-ecosystem-stability", "b4-2-ecological-niches", "b4-2-9-adaptations-of-herbivores-for-feeding-on-plants-and-of-plants-for-resisting-herbivory" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Estimate the difference between the highest and lowest mean body temperatures.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n 5 °C;\n

\n

\n \n Units required. Accept answers in the range 4.5 to 5.5 °C\n \n .\n

\n
\n", "Examiners report": "
\n

\n 70 % of candidates were able to read two temperatures from the graph and subtract the higher from the lower correctly.\n

\n
\n", "question_id": "22M.2.HL.TZ1.1", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-3-homeostasis", "d3-3-1-homeostasis-as-maintenance-of-the-internal-environment-of-an-organism", "d3-3-2-negative-feedback-loops-in-homeostasis" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n State the letter on an ECG corresponding with the events from 0.0 to 0.1 s.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n P;\n

\n
\n", "Examiners report": "None", "question_id": "23M.2.HL.TZ1.22B", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-2-transport", "b3-2-16-stages-in-the-cardiac-cycle" ] }, { "Question": "
\n
\n (ii)\n
\n
\n

\n Identify the independent variable.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n (with/without) ultrasound pretreatment / time;\n

\n
\n", "Examiners report": "None", "question_id": "23M.1B.SL.TZ2.2AII", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-1-enzymes-and-metabolism", "c1-1-8-effects-of-temperature-ph-and-substrate-concentration-on-the-rate-of-enzyme-activity" ] }, { "Question": "
\n
\n (a.iii)\n
\n
\n

\n Other than humidity, suggest a variable that would need to be controlled in this experiment.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n temperature/amount or type of feed «in the respirometer»/amount of CO\n \n 2\n \n absorber\n
\n \n \n OR\n \n \n
\n other reasonable suggestion ✔\n

\n

\n \n Do not accept light\n \n

\n
\n", "Examiners report": "
\n

\n Often more than one answer was given but only the first was marked. Temperature and amount of feed were the most common answers.\n

\n
\n", "question_id": "19M.1B.SL.TZ1.2A.III", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-2-cell-respiration", "c1-2-6-variables-affecting-the-rate-of-cell-respiration" ] }, { "Question": "
\n
\n (i)\n
\n
\n

\n State the trend.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n Increase/increasing/upwards/rising (trend);\n

\n

\n \n Reject ‘positive’, ‘positive trend’ and ‘positive correlation’\n
\n \n \n Accept linear increase.\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ1.DI", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-3-climate-change", "d4-3-1-anthropogenic-causes-of-climate-change" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Compare and contrast fundamental and realized niche of a species.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. both describe the habitat/role/relationship occupied by a species ✔\n

\n

\n b. the fundamental niche is the potential role of a species in its ecosystem and realized niche is the actual role\n
\n \n \n OR\n \n \n
\n the fundamental niche depends on the adaptations of a species whereas the realized niche is limited by competition/predation\n
\n \n \n OR\n \n \n
\n realized niche is ‹usually› smaller than fundamental niche ✔\n

\n
\n", "Examiners report": "None", "question_id": "19N.2.SL.TZ0.13B", "topics": [ "b-form-and-function" ], "subtopics": [ "b4-2-ecological-niches", "b4-2-12-fundamental-and-realized-niches" ] }, { "Question": "
\n
\n

\n Plants produce carbon dioxide in respiration and use carbon dioxide in photosynthesis. The graph shows the volume of carbon dioxide exchanged in a plant at different light intensities.\n

\n

\n \n

\n

\n

\n

\n What is shown by the graph?\n

\n

\n A. There is no photosynthesis between W and X.\n

\n

\n B. There is no photosynthesis between Y and Z.\n

\n

\n C. There is more respiration than photosynthesis between Y and Z.\n

\n

\n D. There is more respiration than photosynthesis between W and X.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n D\n

\n
\n", "Examiners report": "None", "question_id": "20N.1A.SL.TZ0.12", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-3-photosynthesis", "c1-3-7-techniques-for-varying-concentrations-of-carbon-dioxide-light-intensity-or-temperature-experimentally-to-investigate-the-effects-of-limiting-factors-on-the-rate-of-photosynthesis" ] }, { "Question": "
\n
\n

\n Sketch the pattern seen in a typical electrocardiogram (ECG) trace for one complete cardiac cycle, including labels of the main features.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n a. sketch with the correct shape ✔\n

\n

\n b. P, Q, R, S and T indicated ✔\n

\n

\n c. atrial contraction/systole/depolarisation labelled ✔\n

\n

\n d. ventricular contraction/systole/depolarisation labelled ✔\n

\n

\n e. ventricular relaxation/diastole/repolarization labelled ✔\n

\n

\n \n Correct shape should show peaks at P R and T and dips at Q and S\n \n

\n

\n \n

\n
\n", "Examiners report": "
\n

\n In part (d) the better candidates could sketch the pattern seen in a typical electrocardiogram. Some made errors in the shape or letters but could still achieve marks for showing the areas of contraction or relaxation.\n

\n
\n", "question_id": "19M.2.HL.TZ2.D", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-2-transport", "b3-2-16-stages-in-the-cardiac-cycle" ] }, { "Question": "
\n
\n (d.i)\n
\n
\n

\n Label with an R the tissue where the red dye would appear.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n \n \n \n

\n

\n [Source: Nbnidhi, https:// commons.wikimedia.org/wiki/ File:Transverse_section_of_dicot _stem.jpg]\n

\n

\n \n Award\n \n [1]\n \n for correct labeling of R\n \n

\n
\n", "Examiners report": "
\n

\n This was another question that was difficult for students. This question again required students to understand one of the skills from the subject guide, this time in topic 9.2 (Identification of xylem and phloem in microscope images of stem and root). Student responses to this question, however, suggested that few students could identify phloem and xylem under a microscope.\n

\n
\n", "question_id": "19M.1B.SL.TZ1.2D.I", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-2-transport", "b3-2-7-transport-of-water-from-roots-to-leaves-during-transpiration" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Describe how plants transport organic compounds from where they are made to where they are stored.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n (overall) process is translocation / bidirectional / movement from source to sink;\n
    2. \n
  2. \n sugars/sucrose/organic compounds produced in leaves;\n
    3. \n
  3. \n (loaded by) active transport / passage by apoplast route;\n
    4. \n
  4. \n loaded into companion cells / transported in phloem / sieve tubes;\n
    5. \n
  5. \n high concentrations of solutes at the source cause uptake of water (by osmosis);\n
    6. \n
  6. \n water provides hydrostatic pressure for transport (from source to sink);\n
    7. \n
  7. \n unloaded / stored / used at\n \n sink\n \n ;\n
    8. \n
  8. \n lowers pressure at sink / creates pressure differential / water re-entry to xylem;\n
    9. \n
\n
\n", "Examiners report": "
\n

\n Question 6 was the least popular in section B.\n

\n

\n Most candidates provided correct and complete details of the process of translocation.\n

\n
\n", "question_id": "22M.2.HL.TZ2.6", "topics": [ "b-form-and-function", "c-interaction-and-interdependence" ], "subtopics": [ "b3-2-transport", "b3-2-18-adaptations-of-phloem-sieve-tubes-and-companion-cells-for-translocation-of-sap", "c1-2-cell-respiration", "c1-2-4-cell-respiration-as-a-system-for-producing-atp-within-the-cell-using-energy-released-from-carbon-compounds", "b4-2-ecological-niches", "b4-2-3-photosynthesis-as-the-mode-of-nutrition-in-plants-algae-and-several-groups-of-photosynthetic-prokaryotes" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Explain the change in numbers of the cactus moth throughout the study period.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n (before 2002) the cactus moth had abundant food so the population grew exponentially;\n
    2. \n
  2. \n (after 2002) the population size fell as the amount of cactus plants decreased\n
    \n \n \n OR\n \n \n
    \n from 2003 low population of moths corresponds with low number of cladodes/cactus plants;\n
    3. \n
\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ1.16B", "topics": [ "b-form-and-function" ], "subtopics": [ "b4-2-ecological-niches", "b4-2-10-adaptations-of-predators-for-finding-catching-and-killing-prey-and-of-prey-animals-for-resisting-predation" ] }, { "Question": "
\n
\n

\n What is common to RNA and DNA?\n

\n

\n A. Thymine\n

\n

\n B. Nitrogenous bases\n

\n

\n C. Histones\n

\n

\n D. Deoxyribose\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n B\n

\n
\n", "Examiners report": "
\n

\n Question 7 was the third easiest in the exam, and several teachers commented that it was too easy, but on the other hand we can be pleased that more than 80% of candidates knew that both RNA and DNA contain nitrogenous bases.\n

\n
\n", "question_id": "19M.1A.SL.TZ1.7", "topics": [ "a-unity-and-diversity" ], "subtopics": [ "a1-2-nucleic-acids", "a1-2-7-differences-between-dna-and-rna" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n State\n \n one\n \n other gas that contributes to global warming.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n methane/nitrous oxide/water vapour/ozone/CFCs/other halogenated gases;\n

\n
\n", "Examiners report": "
\n

\n Nearly all candidates could name another greenhouse gas that is contributing to global warming. Methane was the commonest answer. Water vapour was also allowed as it is increasing in the atmosphere.\n

\n
\n", "question_id": "22N.2.SL.TZ0.3C", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-3-climate-change", "d4-3-1-anthropogenic-causes-of-climate-change" ] }, { "Question": "
\n
\n (d)\n
\n
\n

\n State\n \n one\n \n technological improvement, other than enzymatic digestion, that led to the falsification of previous models to determine the current model of membrane structure.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n a. scanning electronmicrography / SEM ✔\n

\n

\n b. freeze fracture/etching ✔\n

\n

\n c. X-ray diffraction\n
\n \n \n OR\n \n \n
\n crystallography ✔\n

\n

\n d. fluorescent antibody / marker tagging ✔\n

\n

\n \n Do not accept electron microscope\n \n

\n

\n \n Accept description of process\n \n

\n
\n", "Examiners report": "
\n

\n Stating a technological improvement that led to the currently accepted model of the cell membrane proved more challenging and only the better candidates answered correctly.\n

\n
\n", "question_id": "19M.1B.SL.TZ2.1D", "topics": [ "b-form-and-function" ], "subtopics": [ "b2-1-membranes-and-membrane-transport", "b2-1-10-fluid-mosaic-model-of-membrane-structure" ] }, { "Question": "
\n
\n (b)\n
\n
\n

\n Outline the stages of the carbon cycle that involve plants or materials made by plants.\n

\n
\n
\n

\n [5]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n absorption/diffusion of carbon dioxide from the atmosphere/water by plants;\n
    2. \n
  2. \n \n photosynthesis\n \n fixes/converts carbon (dioxide) to carbohydrates/carbon compounds;\n
    3. \n
  3. \n respiration in plants converts carbohydrates/carbon compounds to carbon dioxide;\n
    4. \n
  4. \n saprotrophs/detritivores digest dead plants/plant matter releasing carbon/carbon dioxide;\n
    \n \n \n OR\n \n \n
    \n decomposition returns carbon to the soil/releases CO\n \n 2\n \n to atmosphere/water/environment\n
    5. \n
  5. \n peat forms when decomposition of dead plant matter is incomplete storing carbon/ creating a reservoir;\n
    \n \n \n OR\n \n \n
    \n fossilization of carbon stores carbon as coal/oil/natural gas;\n
    6. \n
  6. \n forest fires/combustion of plants converts (carbohydrates/carbon compounds) to carbon dioxide;\n
    7. \n
  7. \n plants are eaten by consumers (moving carbon in the food chain)\n
    8. \n
  8. \n humans use plant products for making cloth/household items/building/arts creating a reservoir for carbon\n
    \n \n \n OR\n \n \n
    \n Humans burn fossil fuels releasing CO\n \n 2\n \n ;\n
    9. \n
  9. \n Plants act as carbon sinks/reservoirs\n
    10. \n
\n

\n

\n

\n \n Carbon may be used in place CO\n \n 2\n \n an carbohydrates\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ1.7B", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c4-2-transfers-of-energy-and-matter", "c4-2-17-constructing-carbon-cycle-diagrams" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Annotate the diagram to illustrate the amphipathic nature of phospholipids.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n line to circle labelled phosphate (head)\n \n and\n \n (tail) labelled fatty acid/hydrocarbon/lipid (tail);\n
    2. \n
  2. \n label hydrophilic/polar/attracted to water/\n \n and\n \n hydrophobic/non polar/not attracted to water;\n
    3. \n
\n
\n", "Examiners report": "
\n

\n Part (a) was a variation on a classic Section B question on the phospholipid bilayer. Approximately 1 in 10 students left it blank, suggesting that many did not think that they had to reply to it as there was no answer box. Cholesterol's function in reducing fluidity and permeability was not well known in (b). In (c) poorer candidates described endosymbiosis, rather than answering the question. Many knew about double membranes, own DNA and 70s ribosomes, but did not score any marks as they failed to say that they were in mitochondria and/or chloroplasts. This is perhaps a case where planning the answer was lacking, rather than rushing in.\n

\n
\n", "question_id": "22N.2.SL.TZ0.2", "topics": [ "b-form-and-function", "a-unity-and-diversity" ], "subtopics": [ "b1-1-carbohydrates-and-lipids", "b1-1-12-formation-of-phospholipid-bilayers-as-a-consequence-of-the-hydrophobic-and-hydrophilic-regions", "b1-1-10-difference-between-saturated-monounsaturated-and-polyunsaturated-fatty-acids", "a2-2-cell-structure", "a2-2-12-origin-of-eukaryotic-cells-by-endosymbiosis" ] }, { "Question": "
\n
\n (e)\n
\n
\n

\n By referring to both graphs, evaluate the hypothesis that vinblastine targets cells in mitosis and prevents them from completing the process.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n \n Evaluation of evidence in graph on left\n \n

\n

\n a. increase in (percentage of) cells in mitosis (as vinblastine concentration rises) ✔\n

\n

\n b. supports hypothesis that cells get stuck in/cannot complete mitosis ✔\n

\n

\n \n Evaluation of evidence in graph on right\n \n

\n

\n c. drop in anaphase-metaphase ratio due to fewer cells in anaphase/more cells in metaphase ✔\n

\n

\n d. cells not progressing from metaphase to anaphase/get stuck in metaphase ✔\n

\n

\n \n Do not allow mpa if the candidate is arguing that the hypothesis is not supported\n \n .\n

\n
\n", "Examiners report": "
\n

\n This was another challenging data-analysis task with marks spread across the whole range, but full marks were rarely awarded. Many candidates thought that a rise in mitotic index had to mean that more cells were entering mitosis and they failed to deduce from the drop to zero of the anaphase-metaphase ratio that cells were getting stuck in metaphase. As in (d), it was necessary both to understand how cells progress through the cell cycle and be able to make deductions from trends in quantitative data.\n

\n
\n", "question_id": "21M.2.HL.TZ1.1", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d2-1-cell-and-nuclear-division", "d2-1-1-generation-of-new-cells-in-living-organisms-by-cell-division", "d2-1-17-differences-between-tumours-in-rates-of-cell-division-and-growth-and-in-the-capacity-for-metastasis-and-invasion-of-neighbouring-tissue" ] }, { "Question": "
\n
\n

\n A fly that is homozygous dominant for both body colour and wing size mates with a fly that is recessive for both characteristics. In the table, draw the arrangement of alleles for the offspring of this mating and for the homozygous recessive parent.\n

\n

\n \n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n \n

\n
\n", "Examiners report": "
\n

\n This was generally well answered, with more than two thirds of candidates getting at least one of the genotypes correct. The best answers gave the alleles on lines that symbolised linked genes on a chromosome, but there was a potential pitfall here. If the alleles were arranged in a way that was impossible, given the nature of the cross, one mark was deducted. For example, each chromosome must have one of each gene, not two copies of one gene.\n

\n
\n", "question_id": "19M.2.HL.TZ1.D.I", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-2-inheritance", "d3-2-16-segregation-and-independent-assortment-of-unlinked-genes-in-meiosis", "d3-2-17-punnett-grids-for-predicting-genotypic-and-phenotypic-ratios-in-dihybrid-crosses-involving-pairs-of-unlinked-autosomal-genes" ] }, { "Question": "
\n
\n

\n Compare the data for plasma insulin levels before and after the study diet.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. both show same pattern of rise, level and then decrease / show same trend;\n

\n

\n b. both show same/similar levels of insulin (at all times) due to overlapping error bars;\n

\n

\n c. both rise for 30/45 minutes;\n

\n

\n \n Do not give credit for contrasts\n \n .\n

\n
\n", "Examiners report": "None", "question_id": "20N.1B.SL.TZ0.D.I", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-3-homeostasis", "d3-3-3-regulation-of-blood-glucose-as-an-example-of-the-role-of-hormones-in-homeostasis" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Describe the organelles and other structures in animal cells that are visible in electron micrographs.\n

\n
\n
\n

\n [7]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n plasma membrane is thin layer forming outer boundary;\n
    2. \n
  2. \n cytoplasm fills space between membrane and nucleus;\n
    3. \n
  3. \n nucleus enclosed in nuclear membrane / nuclear membrane enclosing nucleus;\n
    4. \n
  4. \n chromosomes inside the nucleus/ visible during mitosis/ as rods (of condensed DNA);\n
    5. \n
  5. \n mitochondria with cristae/double membranes;\n
    6. \n
  6. \n (80S) ribosomes seen as dots free in cytoplasm/attached to rough ER;\n
    7. \n
  7. \n endoplasmic reticulum is a network interconnected tubes/ membranes /rough ER has ribosomes/ smooth ER does not;\n
    8. \n
  8. \n Golgi apparatus with stack of sacs/cisternae/curved or folded membranes/vesicles budding off;\n
    9. \n
  9. \n vesicles which are small membrane sacs;\n
    10. \n
  10. \n lysosome which contains enzymes/which is densely staining;\n
    11. \n
  11. \n any other organelle that would be visible correctly described;\n
    12. \n
\n

\n \n Allow any point made on an annotated diagram.\n \n

\n

\n \n Do not award any marks for just labels. Descriptions are needed.\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.2.SL.TZ2.7", "topics": [ "a-unity-and-diversity", "c-interaction-and-interdependence" ], "subtopics": [ "a2-2-cell-structure", "a2-2-10-cell-types-and-cell-structures-viewed-in-light-and-electron-micrographs", "c1-2-cell-respiration", "c1-2-4-cell-respiration-as-a-system-for-producing-atp-within-the-cell-using-energy-released-from-carbon-compounds" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Describe how the rose shoot could be treated to show what part of the plant loses water.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n parts of the shoot/leaves are removed/covered in petroleum jelly/Vaseline;\n

\n

\n \n Accept part wrapped in plastic\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.1B.SL.TZ1.3C", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-3-photosynthesis", "c1-3-7-techniques-for-varying-concentrations-of-carbon-dioxide-light-intensity-or-temperature-experimentally-to-investigate-the-effects-of-limiting-factors-on-the-rate-of-photosynthesis" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n State the independent and dependent variables in this experiment.\n

\n

\n Independent:\n

\n

\n Dependent:\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n

\n a. Independent: mass;\n

\n

\n b. Dependent: (vertical) diameter/length;\n

\n

\n \n Do not accept elasticity\n \n

\n
\n", "Examiners report": "
\n

\n The experiment described an investigation to compare the elasticity of arteries and veins. In (a) the most common error was to reverse the correct responses of mass and diameter.\n

\n
\n", "question_id": "20N.1B.SL.TZ0.2A", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-2-transport", "b3-2-2-structure-of-arteries-and-veins" ] }, { "Question": "
\n
\n

\n Calculate the percentage of containers that contained food.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n 4(%);\n

\n
\n", "Examiners report": "
\n

\n Percentage calculations often cause widespread difficulties but most candidates found this one easy. The only common mistake was to divide 4 by a hundred, and then forget to multiply by a hundred to turn the proportion into a percentage.\n

\n
\n", "question_id": "22N.2.HL.TZ0.I", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-1-integration-of-body-systems", "c3-1-4-the-brain-as-a-central-information-integration-organ" ] }, { "Question": "
\n
\n (c)\n
\n
\n

\n Explain the movement of energy and inorganic nutrients in an ecosystem.\n

\n
\n
\n

\n [7]\n

\n
\n
\n", "Markscheme": "
\n

\n a. autotrophs/producers/plants obtain inorganic nutrients from the «abiotic» environment ✔\n

\n

\n b. energy is provided «mainly» by sunlight ✔\n

\n

\n c. light energy is converted «to chemical energy» through photosynthesis✔\n

\n

\n d. photosynthesis/producers/autotrophs convert inorganic carbon/carbon dioxide and water into carbon/organic compounds ✔\n

\n

\n e. carbon compounds/foods contain/are a source of «usable» energy «for life» ✔\n

\n

\n f. carbon compounds/energy are transferred along food chains when eaten by consumers/heterotrophs ✔\n

\n

\n g. respiration returns carbon «dioxide» to the environment ✔\n

\n

\n h. respiration releases stored/chemical energy as heat/ATP ✔\n

\n

\n i. energy/ATP is used to carry out life functions/synthesis/growth/movement ✔\n

\n

\n j. energy is lost/is not recycled ✔\n \n Both related by “or” required\n \n .\n

\n

\n k. nutrients are recycled / example of recycled nutrient e.g. carbon ✔\n

\n

\n l. decomposers recycle minerals/inorganic nutrients ✔\n

\n

\n \n Award\n \n [5 max]\n \n if only energy is mentioned\n \n .\n

\n
\n", "Examiners report": "None", "question_id": "19N.2.SL.TZ0.8C", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-2-stability-and-change", "d4-2-2-requirements-for-stability-in-ecosystems" ] }, { "Question": "
\n
\n (a.i)\n
\n
\n

\n Identify the site with the highest incidence of diseased colonies.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n Capricorn and Bunkers group;\n

\n
\n", "Examiners report": "
\n

\n In general, the data analysis question was well attempted by the majority of students. In 1a almost all were able to correctly name the Capricorn and Bunkers Group.\n

\n
\n", "question_id": "21N.2.SL.TZ0.1", "topics": [ "d-continuity-and-change", "b-form-and-function" ], "subtopics": [ "d4-3-climate-change", "d4-3-7-threats-to-coral-reefs-as-an-example-of-potential-ecosystem-collapse", "b4-1-adaptation-to-environment", "b4-1-5-conditions-required-for-coral-reef-formation" ] }, { "Question": "
\n
\n

\n Identify Y, non-coding DNA at the start of a gene.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n promoter;\n

\n
\n", "Examiners report": "
\n

\n Fewer candidates knew that Y must be the promoter. This could be deduced from the diagram which showed that Y is the site to which RNA polymerase first binds. Other incorrect suggestions were primer, intron, start codon and telomere.\n

\n
\n", "question_id": "22N.2.HL.TZ0.C.II", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d1-2-protein-synthesis", "d1-2-14-non-coding-sequences-in-dna-do-not-code-for-polypeptides" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n State the name and function of structures I and II.\n

\n

\n Structure I name and function: ..............................................................................................................\n

\n

\n ..........................................................................................................................................................\n

\n

\n Structure II name and function: .............................................................................................................\n

\n

\n ..........................................................................................................................................................\n

\n

\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n I is the stigma which receives the\n \n pollen\n \n /where\n \n pollen\n \n lands/is captured (during pollination);\n
    2. \n
  2. \n II is the anther and produces/contains/releases\n \n pollen\n \n ;\n
    3. \n
\n

\n \n Both name and function must be included in each marking point.\n \n

\n

\n \n The role in pollination should be stated. Do not accept “pollination” on its own.\n \n

\n
\n", "Examiners report": "None", "question_id": "23M.2.HL.TZ2.3", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d3-1-reproduction", "d3-1-9-features-of-an-insect-pollinated-flower", "d3-1-8-sexual-reproduction-in-flowering-plants" ] }, { "Question": "
\n
\n

\n Explain the reasons for antibiotics secreted into soil not harming insects or other animals in the soil.\n

\n
\n
\n

\n [2]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n antibiotics (only) affect/kill/block processes in bacteria/prokaryotes / do not affect eukaryotes;\n
    2. \n
  2. \n metabolism/protein synthesis/ribosomes/cell walls not targeted in insects/animals/eukaryotes;\n
    3. \n
  3. \n no cell walls in animals (so antibiotics cannot attack cell walls);\n
    4. \n
  4. \n antibiotics are secreted (by microbes/fungi) to prevent competition (with other microbes);\n
    5. \n
\n

\n

\n
\n", "Examiners report": "None", "question_id": "23M.2.HL.TZ1.II", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c3-2-defence-against-disease", "c3-2-13-antibiotics-as-chemicals-that-block-processes-occurring-in-bacteria-but-not-in-eukaryotic-cells" ] }, { "Question": "
\n
\n

\n Describe the trend in the data.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n negative correlation between the number of leaves\n \n removed\n \n and transpiration rate\n \n Do not accept type of correlation alone, as a description is required\n \n .\n
\n \n \n OR\n \n \n
\n as more leaves are removed the transpiration rate drops ✔\n \n OWTTE\n \n

\n
\n", "Examiners report": "None", "question_id": "19N.1B.SL.TZ0.A.I", "topics": [ "b-form-and-function" ], "subtopics": [ "b3-1-gas-exchange", "b3-1-9-transpiration-as-a-consequence-of-gas-exchange-in-a-leaf" ] }, { "Question": "
\n
\n (a.ii)\n
\n
\n

\n Suggest how entanglement in plastics can lead to the death of marine birds.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n a. birds are unable to fly/swim for food;\n

\n

\n b. unable to escape predators;\n

\n

\n c. birds drown;\n

\n

\n d. birds suffocate / are strangled;\n

\n
\n", "Examiners report": "None", "question_id": "20N.2.SL.TZ0.13A.II", "topics": [ "d-continuity-and-change" ], "subtopics": [ "d4-2-stability-and-change", "d4-2-10-effects-of-microplastic-and-macroplastic-pollution-of-the-oceans" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Outline, using graphs, the effect of different factors that influence enzyme activity.\n

\n
\n
\n

\n [5]\n

\n
\n
\n", "Markscheme": "
\n
    \n
  1. \n enzymes have active sites that bind specific substrates;\n
    2. \n
  2. \n act as catalysts to speed up reactions\n
    \n \n \n OR\n \n \n
    \n lower activation energy;\n
    3. \n
  3. \n rate/activity increases with temperature;\n
    4. \n
  4. \n up to an\n \n optimum temperature\n \n ;\n
    5. \n
  5. \n sharp decline in activity above (optimum temperature);\n
    \n (\n \n Graph has to be clearly asymmetrical for mpe\n \n )\n
    \n (\n \n Graph shown would earn mpc, mpd and mpe\n \n )\n
    \n \n ;\n
    6. \n
  6. \n rate/activity declines at a pH above and below the\n \n optimum pH\n \n
    \n (\n \n Graph shown would earn mpf\n \n )\n
    \n \n ;\n
    7. \n
  7. \n rate/activity increases sharply as substrate concentration goes up;\n
    8. \n
  8. \n above a certain concentration, the rate reaches a maximum/plateau;\n
    \n (\n \n Graph shown would earn mpg and mph\n \n )\n
    \n \n ;\n
    9. \n
  9. \n competitive inhibitor present, as substrate concentration increases, enzyme requires higher concentration to achieve maximum rate / graph showing this with and without inhibitor;\n
    10. \n
  10. \n non-competitive inhibitor present, as substrate concentration rises, enzyme activity is lower at all substrate concentrations / graph showing shape with and without inhibitor;\n
    11. \n
\n

\n \n Award\n \n [3 max]\n \n if there are no graphs.\n \n

\n

\n \n For each graph, axes must be correctly labelled, the shape must be correctly drawn.\n \n

\n

\n \n Marks can be awarded to a correctly annotated graph.\n \n

\n
\n", "Examiners report": "
\n

\n This question was the most popular choice of essay as well as the most successful.\n

\n

\n Many earned full marks, but many others contained errors. Some of these errors included inverted axes, no abrupt curve drop for high temperatures, an asymmetric graph shown for pH, the optimum temperature or pH not mentioned or labelled.\n

\n
\n", "question_id": "22M.2.HL.TZ2.7", "topics": [ "c-interaction-and-interdependence", "d-continuity-and-change", "a-unity-and-diversity" ], "subtopics": [ "c1-1-enzymes-and-metabolism", "c1-1-8-effects-of-temperature-ph-and-substrate-concentration-on-the-rate-of-enzyme-activity", "d1-1-dna-replication", "d1-1-8-functions-of-dna-primase-dna-polymerase-i-dna-polymerase-iii-and-dna-ligase-in-replication", "a4-1-evolution-and-speciation", "a4-1-7-roles-of-reproductive-isolation-and-differential-selection-in-speciation" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Outline the significance of surface area to volume ratio in the limitation of cell size.\n

\n
\n
\n

\n [4]\n

\n
\n
\n", "Markscheme": "
\n

\n a. surface area of the cell affects the rate of material exchange;\n
\n b. when the cell increases in size, so does its chemical activity/metabolism;\n
\n c. (when the cell increases in size/grows) more substances need to be taken in / more waste products need to be excreted;\n
\n d. as the volume of the cell increases, so does the surface area, however not to the same extent\n
\n OR\n
\n when the cell gets bigger, its surface area to volume ratio gets smaller;\n
\n e. substances will not be able enter the cell fast enough/cell volume will not be supplied\n

\n

\n OR\n
\n metabolic rate will exceed the rate of exchange\n
\n OR\n
\n when the surface area: volume ratio is higher, the diffusion rate increases;\n
\n f. some cells have adaptations to increase their surface area/flatten/microvilli/shape of red blood cells;\n
\n g. cells in growth areas tend to divide and remain small\n
\n OR\n
\n cells divide when maximum size is reached;\n

\n
\n", "Examiners report": "
\n

\n Most knew that as the cell increases in size, the SA:volume ratio decreases but had difficulty explaining its significance.\n

\n
\n", "question_id": "21N.2.SL.TZ0.5", "topics": [ "b-form-and-function", "d-continuity-and-change" ], "subtopics": [ "b2-3-cell-specialization", "b2-3-6-surface-area-to-volume-ratios-and-constraints-on-cell-size", "d2-3-water-potential", "d2-3-3-water-movement-by-osmosis-into-or-out-of-cells" ] }, { "Question": "
\n
\n

\n Explain the scientific reasoning for your hypothesis.\n

\n
\n
\n

\n [3]\n

\n
\n
\n", "Markscheme": "
\n

\n a. high light (intensity) increases photosynthesis;\n

\n

\n b. photosynthesis consumes CO\n \n 2\n \n ;\n

\n

\n c. (more photosynthesis/less CO\n \n 2\n \n ) increases pH/decreases acidity;\n

\n

\n d. less light means more respiration (than photosynthesis);\n

\n

\n e. respiration produces CO\n \n 2\n \n \n \n AND\n \n \n lowers pH/increases acidity;\n

\n

\n \n Allow inverse for all answers\n \n .\n

\n

\n \n Do not accept reference to colour only instead of pH\n \n .\n

\n
\n", "Examiners report": "
\n

\n Most candidates realised that increased light intensity leads to an increase rate of photosynthesis, which consumes CO\n \n 2\n \n , or vice versa. Most related the change in colour to a change in CO\n \n 2\n \n concentration, but didn't link it to a change in pH, for which the indicator is specific. Stronger candidates understood the experiment and were able to analyse its results effectively, adding that the effect of respiration increased over that of photosynthesis as light intensity decreased, thus a lower pH.\n

\n
\n", "question_id": "20N.1B.SL.TZ0.B.II", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-3-photosynthesis", "c1-3-7-techniques-for-varying-concentrations-of-carbon-dioxide-light-intensity-or-temperature-experimentally-to-investigate-the-effects-of-limiting-factors-on-the-rate-of-photosynthesis" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n Define neurotransmitter.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n chemical substance that transmits message across synapses/from one cell to another ✔\n

\n

\n \n OWTTE\n \n
\n \n Do not accept \"connection\" instead of \"synapse\"\n \n .\n

\n
\n", "Examiners report": "None", "question_id": "19N.2.HL.TZ0.6A", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c2-1-chemical-signalling-[hl-only]", "c2-1-3-hormones-neurotransmitters-cytokines-and-calcium-ions-as-examples-of-functional-categories-of-signalling-chemicals-in-animals", "c2-1-4-chemical-diversity-of-hormones-and-neurotransmitters" ] }, { "Question": "
\n
\n (a)\n
\n
\n

\n State\n \n one\n \n function of Rubisco.\n

\n
\n
\n

\n [1]\n

\n
\n
\n", "Markscheme": "
\n

\n a. enzyme involved in\n \n photosynthesis\n \n /\n \n carbon fixation\n \n /\n \n Calvin cycle\n \n
\n \n \n OR\n \n \n
\n speeds up chemical reactions in\n \n photosynthesis\n \n ✔\n

\n

\n b. carboxylation of RuBP ✔\n

\n

\n c. production of carbohydrate in photosynthesis ✔\n

\n

\n d. addition of carbon dioxide to form glucose (in Calvin cycle) ✔\n

\n

\n \n Either photosynthesis or carbon fixation must be mentioned\n \n .\n

\n
\n", "Examiners report": "
\n

\n There were some G2 comments about the function of Rubisco. It is mentioned in 2.4. and the stem did say that it was an enzyme. Simply stating that it was an enzyme involved in photosynthesis was sufficient for the mark. A detailed function was not required. Most could state the role of the active site and that the genus was\n \n Pisume.\n \n The word genus in this context confused some French candidates who answered 'male or female'. 3(d) was simply testing the factors controlling enzyme action. Weaker students just listed several factors. When it says one factor, only the first is considered. The difference between heat and temperature was occasionally confused. The examiners were looking for the effect of increasing and decreasing the factor. Many students seemed to be obsessed with denaturing. For example the answer 'temperature' (first mark): as the temperature is too high the enzyme denatures (no second mark as no mention of decreasing temperature). Few used the collision theory idea which was expected.\n

\n
\n", "question_id": "21M.2.SL.TZ2.3", "topics": [ "c-interaction-and-interdependence" ], "subtopics": [ "c1-3-photosynthesis", "c1-3-15-carbon-fixation-by-rubisco", "c1-1-enzymes-and-metabolism", "c1-1-4-enzymes-as-globular-proteins-with-an-active-site-for-catalysis", "c1-1-5-interactions-between-substrate-and-active-site-to-allow-induced-fit-binding", "c1-1-6-role-of-molecular-motion-and-substrate-active-site-collisions-in-enzyme-catalysis", "c1-1-7-relationships-between-the-structure-of-the-active-site-enzyme-substrate-specificity-and-denaturation", "c1-1-8-effects-of-temperature-ph-and-substrate-concentration-on-the-rate-of-enzyme-activity" ] } ]