-
· Why are QBv6 (2025 sciences) questions split by parts?
+
· The 2025 science questionbanks have very few questions. Will you merge the previous questionbank into it?
-
Ask IB ¯\_(ツ)_/¯ Full combined version coming soon!
+
Soon™... it requires huge manual work because the syllabus changes are big.
· I tried to save all the questions as PDF, and my computer got frozen!
diff --git a/app/index.js b/app/index.js
index 8402f09..6de3506 100644
--- a/app/index.js
+++ b/app/index.js
@@ -11,6 +11,21 @@ function toggleMS(){document.getElementById("markscheme").classList.toggle("hidd
function toggleR(){document.getElementById("report").classList.toggle("hidden")}
function toggleHelp(){document.getElementById("helpmenu").classList.toggle("hidden")}
function toggleDownAllQs(){document.getElementById("addalltoPDFbtn").classList.remove('hidden');document.getElementById("generatePDFbtn").classList.remove('hidden')}
+function toggleFilters(){document.querySelector(".selectables").classList.remove('hidden')};
+
+
+function checkWidth() {
+ const btn1 = document.getElementById('generatePDFbtn');
+ const btn2 = document.getElementById('addalltoPDFbtn');
+ if (window.innerWidth <= 480) {
+ btn1.style.display = 'none';
+ btn2.style.display = 'none';
+ } else {
+ btn1.style.display = '';
+ btn2.style.display = '';
+ }
+}
+window.addEventListener('resize', checkWidth);
function toggleDarkMode() {
@@ -56,7 +71,7 @@ document.addEventListener("DOMContentLoaded", () => {
}
});
-function startRandomTimerLoop() {
+/*function startRandomTimerLoop() {
var randomTime = Math.floor(11 * Math.random()) + 20;
setTimeout(() => {
alert("Provided by pirateIB\nhttps://pirateib.xyz");
@@ -67,7 +82,7 @@ window.onload = function() {
setTimeout(() => {
startRandomTimerLoop();
}, 300000);
-};
+};*/
/*function generatePDF() {
const selectedQuestionIds = JSON.parse(sessionStorage.getItem("selectedQuestionIds")) || [];
@@ -94,7 +109,6 @@ function generatePDF() {
const selectedQuestionIds = JSON.parse(sessionStorage.getItem("selectedQuestionIds")) || [];
if (0 === selectedQuestionIds.length) return alert("Select some questions first!");
- // Prompt the user for including markschemes
let includeMarkschemes = null;
while (includeMarkschemes !== "yes" && includeMarkschemes !== "no") {
includeMarkschemes = prompt("Do you want to include markschemes? (yes/no)").toLowerCase();
@@ -177,10 +191,12 @@ if (event.key === 'Escape') {
const fileNameMap = {
'bioqb': 'Biology QB.json',
'bioqb25-split': 'Biology 2025 QB split.json',
+ 'bioqb25-merged': 'Biology 2025 QB merged.json',
'bioqb25-full': 'Biology 2025 QB full.json',
'bmqb': 'Business Management QB.json',
'chemqb': 'Chemistry QB.json',
'chemqb25-split': 'Chemistry 2025 QB split.json',
+ 'chemqb25-merged': 'Chemistry 2025 QB merged.json',
'chemqb25-full': 'Chemistry 2025 QB full.json',
'compsciqb': 'Computer Science QB.json',
'destechqb': 'Design Technology QB.json',
@@ -193,6 +209,7 @@ const fileNameMap = {
'mathaiqb': 'Math AI QB.json',
'phyqb': 'Physics QB.json',
'phyqb25-split': 'Physics 2025 QB split.json',
+ 'phyqb25-merged': 'Physics 2025 QB merged.json',
'phyqb25-full': 'Physics 2025 QB full.json',
'psychqb': 'Psychology QB.json',
'sehsqb': 'SEHS QB.json'
@@ -278,7 +295,8 @@ async function loadJSON(filename) {
}
try {
- const response = await fetch(`../assets/jsonqb/${filename}`);
+ const response = await fetch(`https://pub-59370068cd854c158959e7ca4578e5bd.r2.dev/${filename}`); // ../assets/jsonqb/
+
if (!response.ok) {
throw new Error('Network response was not ok');
}
@@ -298,17 +316,20 @@ async function loadJSON(filename) {
};
});
sessionStorage.setItem('selectedQuestionIds', '[]');
+ sessionStorage.setItem('visibleIDs', '[]');
setTimeout(() => {
processData(data, filename);
hideLoading();
sessionStorage.setItem('selectedQuestionIds', '[]');
+ sessionStorage.setItem('visibleIDs', '[]');
}, 0);
} catch (error) {
console.error('Error fetching JSON:', error);
hideLoading();
sessionStorage.setItem('selectedQuestionIds', '[]');
+ sessionStorage.setItem('visibleIDs', '[]');
}
}
@@ -318,9 +339,12 @@ function processData(data, filename) {
jsonDataFetched = true;
currentFileName = filename;
+ jsonData = data;
+
topics = [...new Set(data.flatMap(item => item.topics))].sort();
subtopics = [...new Set(data.flatMap(item => item.subtopics))].sort();
renderTopics();
+ renderSubtopics();
const fragment = document.createDocumentFragment();
@@ -379,7 +403,7 @@ function processData(data, filename) {
const content = `
${questionid}
Topics: ${topics.join(', ')}
-
Subtopics: ${subtopics.join(', ')}
+
Subtopics
${subtopics.join(', ')}
${question}
`;
@@ -453,6 +477,7 @@ function processData(data, filename) {
domCache.rightCol.appendChild(fragment);
updateSquareContainers();
toggleDownAllQs();
+ toggleFilters();
}
@@ -511,7 +536,29 @@ function createContainer(type, questionid, filename, content, parent) {
parent.appendChild(container);
}
+function renderSubtopics() {
+ const subtopicListContainer = document.getElementById('subtopic-select');
+ subtopicListContainer.innerHTML = '
';
+ const fragment = document.createDocumentFragment();
+
+ subtopics.forEach(subtopic => {
+ const option = document.createElement('option');
+ option.innerText = subtopic;
+ option.value = subtopic;
+ fragment.appendChild(option);
+ });
+
+ subtopicListContainer.appendChild(fragment);
+}
+
function renderTopics() {
+ currentFilters.level = currentFilters.paper = currentFilters.subtopic = null;
+ document.getElementById('level-select').value = '';
+ document.getElementById('paper-select').value = '';
+ document.getElementById('subtopic-select').value = '';
+
+ const topicListContainer = document.getElementById('topic-list');
+ topicListContainer.innerHTML = '';
const fragment = document.createDocumentFragment();
topics.forEach(topic => {
@@ -519,22 +566,127 @@ function renderTopics() {
label.classList.add('topic-label');
const checkbox = document.createElement('input');
- checkbox.type = 'checkbox';
- checkbox.name = 'topic';
+ checkbox.type = 'checkbox';
+ checkbox.name = 'topic';
checkbox.value = topic;
- checkbox.addEventListener('change', () => {
- document.querySelectorAll(`div[class*="${topic}"]`)
- .forEach(div => div.classList.toggle('hidden'));
- });
+checkbox.addEventListener('change', () => {
+ document.getElementById('level-select').value = '';
+ document.getElementById('paper-select').value = '';
+ document.getElementById('subtopic-select').value = '';
- label.append(checkbox, topic);
- fragment.appendChild(label);
+ currentFilters.level = null;
+ currentFilters.paper = null;
+ currentFilters.subtopic = null;
+
+ const checkedTopics = Array.from(
+ document.querySelectorAll('input[name="topic"]:checked')
+ ).map(cb => cb.value);
+
+ applyAllFilters('topic', checkedTopics);
+ applyAllFilters('level', null);
+ applyAllFilters('paper', null);
+ applyAllFilters('subtopic', null);
+
+ const visibleIds = Array.from(
+ document.querySelectorAll('#right-col > div:not(.hidden)')
+ ).map(div => div.id);
+ sessionStorage.setItem('visibleIDs', JSON.stringify(visibleIds));
+});
+
+ label.append(checkbox, document.createTextNode(topic));
+ fragment.append(label);
});
- domCache.leftCol.appendChild(fragment);
+ topicListContainer.appendChild(fragment);
}
+function findRecordById(qid) {
+ return jsonData.find(item => item.question_id === qid) || {};
+}
+
+
+const currentFilters = {
+ level: null,
+ paper: null,
+ topic: null,
+ subtopic: null
+};
+
+function applyAllFilters(type, value) {
+if (type === 'topic' || type === 'subtopic') {
+ const arr = Array.isArray(value) ? value.filter(Boolean) : [];
+ currentFilters[type] = arr.length > 0 ? arr : null;
+}
+else {
+ currentFilters[type] = value || null;
+}
+ document.querySelectorAll('#right-col > div').forEach(div => {
+ const qid = div.id;
+ const record = findRecordById(qid);
+ let hide = false;
+
+ // 1) Level
+ if (currentFilters.level) {
+ const ok = currentFilters.level === 'standard'
+ ? qid.includes('.SL.')
+ : (qid.includes('.HL.') || qid.includes('.AHL.'));
+ hide ||= !ok;
+ }
+
+ if (currentFilters.paper) {
+ const pap = currentFilters.paper;
+ const regex = pap === '1'
+ ? /\.1(?:[ABC])?\./
+ : new RegExp(`\\.${pap}\\.`);
+ hide ||= !regex.test(qid);
+ }
+
+ if (!currentFilters.topic) {
+ hide ||= true;
+ } else {
+ const ok = (record.topics || []).some(t =>
+ currentFilters.topic.includes(t)
+ );
+ hide ||= !ok;
+ }
+
+ if (currentFilters.subtopic) {
+ const ok = (record.subtopics||[])
+ .some(st => currentFilters.subtopic.includes(st));
+ hide ||= !ok;
+ }
+
+ div.classList.toggle('hidden', hide);
+ });
+ }
+
+
+
+document.addEventListener('DOMContentLoaded', () => {
+ document.getElementById('paper-select')
+ .addEventListener('change', e => {
+ applyAllFilters('paper', e.target.value);
+ });
+ document.getElementById('level-select')
+ .addEventListener('change', e => {
+ applyAllFilters('level', e.target.value);
+ });
+
+ document
+ .getElementById('subtopic-select')
+ .addEventListener('change', e => {
+ const vals = Array.from(e.target.selectedOptions)
+ .map(opt => opt.value)
+ .filter(v => v !== ''); // ← remove the "" entry
+
+ applyAllFilters('subtopic', vals);
+ });
+
+});
+
+
+
function updateSquareContainers() {
document.querySelectorAll('.square-container').forEach(container => {
const firstChild = container.children[0];
@@ -565,4 +717,6 @@ function resetState() {
domCache.rightCol.innerHTML = '';
document.querySelectorAll('.topic-label').forEach(label => label.remove());
sessionStorage.setItem('selectedQuestionIds', '[]');
-}
\ No newline at end of file
+ sessionStorage.setItem('visibleIDs', '[]');
+ checkWidth()
+}
diff --git a/assets/jsonqb/Biology 2025 QB merged.json b/assets/jsonqb/Biology 2025 QB merged.json
new file mode 100644
index 0000000..1c92ebf
--- /dev/null
+++ b/assets/jsonqb/Biology 2025 QB merged.json
@@ -0,0 +1,3455 @@
+[
+ {
+ "question_id": "19M.3.SL.TZ1.1",
+ "Question": "
\n
Membrane structure can be investigated using a technique known as freeze fracture.
Cells are frozen and then split. Fracturing often occurs between the two phospholipid layers of membranes in the cell. An electron micrograph of such a fractured membrane is shown.
\n

\n
[Source: © Science Photo Library]
\n
\n
Using the scale bar, calculate the magnification of the image.
\n
[2]
\n
a.
\n
\n
Explain how electron micrographs such as this helped to falsify the Davson–Danielli model of membrane structure.
\n
[2]
\n
b.
\n
\n
Explain how the amphipathic nature of phospholipids allows them to form bilayers.
\n
[2]
\n
c.
\n
",
+ "Markscheme": "
\n
✔
\n
a.
\n
\n
a. the Davson–Danielli model proposed two layers of protein on either side of a lipid bilayer ✔ OWTTE
b. micrographs illustrate proteins in and/or crossing the membrane ✔
\n
b.
\n
\n
a. amphipathic means that they are both hydrophilic and hydrophobic ✔
\n
b. the outside hydrophilic parts are exposed to water ✔
\n
c. hydrophobic parts are away from water in the inside ✔
\n
Water or lack of needs to be mentioned for mpb
\n
c.
\n
",
+ "Examiners report": "
\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
a.
\n
\n
Descriptions of protein layers either side of the phospholipid bilayer in the Davson-Danielli model were unclear. Embedded or integral proteins were frequently stated for the second marking point.
\n
b.
\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
c.
\n
",
+ "topics": [
+ "a-unity-and-diversity",
+ "b-form-and-function",
+ "c-interaction-and-interdependence"
+ ],
+ "subtopics": [
+ "a2-2-2-microscopy-skills",
+ "a2-2-cell-structure",
+ "b1-1-12-formation-of-phospholipid-bilayers-as-a-consequence-of-the-hydrophobic-and-hydrophilic-regions",
+ "b1-1-carbohydrates-and-lipids",
+ "c1-1-8-effects-of-temperature-ph-and-substrate-concentration-on-the-rate-of-enzyme-activity",
+ "c1-1-enzymes-and-metabolism"
+ ]
+ },
+ {
+ "question_id": "19M.3.SL.TZ1.2",
+ "Question": "
\n
When feed for animals is stored, moisture levels need to be kept low to prevent the growth of fungi. Feed was exposed to 15 % moisture and placed into a respirometer. O2 consumption was monitored using the respirometer over a period of six days.
\n

\n
[Source: © International Baccalaureate Organization 2019]
\n
\n
Outline how O2 consumption is measured using a respirometer.
\n
[2]
\n
a.i.
\n
\n
Suggest one conclusion that can be drawn from the results shown in the graph.
\n
[1]
\n
a.ii.
\n
\n
Other than humidity, suggest a variable that would need to be controlled in this experiment.
\n
[1]
\n
a.iii.
\n
\n
Outline the role of fungi in nutrient cycling.
\n
[2]
\n
b.
\n
",
+ "Markscheme": "
\n
a. a CO2 absorber/KOH is added ✔
\n
b. a bubble/starting water level is measured ✔
\n
c. «the rate of» movement of the bubble/pressure reduction is a measure of O2 consumption ✔
\n
a.i.
\n
\n
a. as fungus grows, the rate of oxygen consumption increases ✔
\n
b. around day 4/5 fungus begins to grow/no growth in days 1–3 ✔
\n
c. the rate of fungus growth/rate of respiration is highest after 5 days ✔
\n
a.ii.
\n
\n
temperature/amount or type of feed «in the respirometer»/amount of CO2 absorber
OR
other reasonable suggestion ✔
\n
Do not accept light
\n
a.iii.
\n
\n
a. act as saprotrophs/decomposers ✔
\n
b. rot/feed on/break down organic matter/food/organisms
OR
return nutrients trapped in organic matter to the cycle/soil ✔
\n
Do not accept detritivores
\n
b.
\n
",
+ "Examiners report": "
\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
a.i.
\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
a.ii.
\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
a.iii.
\n
",
+ "topics": [
+ "b-form-and-function",
+ "c-interaction-and-interdependence"
+ ],
+ "subtopics": [
+ "b3-1-9-transpiration-as-a-consequence-of-gas-exchange-in-a-leaf",
+ "b3-1-gas-exchange",
+ "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-transport",
+ "b4-2-6-saprotrophic-nutrition-in-some-fungi-and-bacteria",
+ "b4-2-ecological-niches",
+ "c1-2-6-variables-affecting-the-rate-of-cell-respiration",
+ "c1-2-cell-respiration"
+ ]
+ },
+ {
+ "question_id": "19M.3.SL.TZ2.1",
+ "Question": "
\n
Two models of plasma membrane structure are shown.
\n

\n
[Source: diagram from article published in The American Journal of Pathology, 65, J Singer and G Nicolson,
The structure and chemistry of mammalian cell membranes, 427–437, Copyright Elsevier (1971)]
\n
\n
Phospholipase C is an enzyme that digests the polar heads of phospholipids. Scientists used phospholipase C to test these models of membrane structure. They found that the enzyme could digest the heads of phospholipids in the plasma membranes of red blood cells.
\n
\n
State the scientists who proposed model A.
\n
[1]
\n
a.
\n
\n
Label the model A diagram to show a region of protein.
\n
[1]
\n
b.i.
\n
\n
Label the model B diagram to show a phospholipid.
\n
[1]
\n
b.ii.
\n
\n
Deduce one conclusion about the structure of the plasma membrane reached by the scientists from their results.
\n
[1]
\n
c.i.
\n
\n
Suggest one reason for maintaining a pH of 7.5 throughout the experiment.
\n
[2]
\n
c.ii.
\n
\n
State one technological improvement, other than enzymatic digestion, that led to the falsification of previous models to determine the current model of membrane structure.
\n
[1]
\n
d.
\n
",
+ "Markscheme": "
\n
Davson–Danielli ✔
\n
a.
\n
\n

\n
[Source: diagram from article published in The American Journal of Pathology, 65, J Singer and G Nicolson, The structure and chemistry of mammalian cell membranes, 427–437, Copyright Elsevier (1971)]
\n
Accept label to top protein.
\n
b.i.
\n
\n

\n
[Source: diagram from article published in The American Journal of Pathology, 65, J Singer and G Nicolson, The structure and chemistry of mammalian cell membranes, 427–437, Copyright Elsevier (1971)]
\n
Accept a label to any part of any phospholipid
Accept different form of labelling that clearly indicate the phospholipids.
\n
b.ii.
\n
\n
a. phospholipids on outside/exposed ✔
\n
b. impossibility of continuous protein layer «of Davson–Danielli/model A» ✔
\n
c. supports idea of mosaic pattern of membrane
OR
supports model B ✔
\n
Award any other valid conclusion.
\n
Do not accept \"membrane is made of phospholipids\".
\n
c.i.
\n
\n
a. pH values away from optimum pH affect enzyme
OR
so enzyme can function properly
OR
pH 7.5 is the optimum pH for the enzyme ✔
b. sketch of enzyme activity versus pH ✔ Sketch of enzyme activity needs labels.
\n
c. change in pH affects 3D structure of protein/active site
OR
change in pH denatures the enzyme / protein ✔
\n
d. substrate does not fit in active site
OR
interaction of substrate and active site affected ✔
\n
c.ii.
\n
\n
a. scanning electronmicrography / SEM ✔
\n
b. freeze fracture/etching ✔
\n
c. X-ray diffraction
OR
crystallography ✔
\n
d. fluorescent antibody / marker tagging ✔
\n
Do not accept electron microscope
\n
Accept description of process
\n
d.
\n
",
+ "Examiners report": "
\n
There were a variety of suggestions for the names of the scientists with Singer and Nicolson, as given in the question paper, being a common incorrect answer.
\n
a.
\n
\n
Most students could label the areas with protein and phospholipid.
\n
b.i.
\n
\n
Most students could label the areas with protein and phospholipid.
\n
b.ii.
\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
c.i.
\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
c.ii.
\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
d.
\n
",
+ "topics": [
+ "b-form-and-function",
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "b2-1-10-fluid-mosaic-model-of-membrane-structure",
+ "b2-1-membranes-and-membrane-transport",
+ "d3-1-8-sexual-reproduction-in-flowering-plants",
+ "d3-1-reproduction"
+ ]
+ },
+ {
+ "question_id": "19M.3.SL.TZ2.12",
+ "Question": "
\n
A survey was made of the intertidal zone at Butter Lump Bay, Great Cumbrae, Scotland. The three species of barnacle found were Elminius modestus (EM), Chthamalus montagui (CM) and Semibalanus balanoides (SB). The kite diagram shows the vertical distribution of these three species from the low tide mark at 0 m to 2.25 m above low tide.
\n

\n
[Source: reprinted from Estuarine Coastal and Shelf Science, 152, M C Gallagher, et al., The invasive barnacle species,
Austrominius modestus: Its status and competition with indigenous barnacles on the Isle of Cumbrae, Scotland,
pages 134–141, 2014 with permission from Elsevier]
\n
\n
Outline how the data could have been obtained.
\n
[2]
\n
a.
\n
\n
Describe the distribution of C. montagui and S. balanoides barnacles in Butter Lump Bay.
\n
[2]
\n
b.
\n
\n
E. modestus is an invasive barnacle while the others are native species. Analyse the data to show how it supports this statement.
\n
[2]
\n
c.
\n
\n
State one abiotic factor that could have determined the distribution of barnacles.
\n
[1]
\n
d.
\n
\n
Barnacles are sensitive to pollution. Outline how it might be possible to use these organisms as indicator species.
\n
[2]
\n
e.
\n
",
+ "Markscheme": "
\n
a. transect across area to be studied ✔
\n
b. count/record barnacles «per species» in quadrats at regular intervals ✔
\n
a.
\n
\n
a. both species present throughout the range ✔
\n
b. C. montagui has small number of individuals «throughout»
OR
C.montagui occupies «mostly» upper shore/intertidal zone
\n
c. S. balanoides «mostly» occupies low tide area ✔
OR
S.balanoides has large number of individuals «throughout» ✔
\n
OWTTE referring to maximum numbers at specific heights.
\n
b.
\n
\n
a. native species/C. montagui and S. balanoides have niches that don’t overlap much / are distinct
OR
range of E. modestus overlaps with both native species ✔
\n
b. niches of native species «which don’t overlap much» shows competition between native species
OR
E.modestus invades habitats of C. montagui/S. balanoides resulting in competition with «both» native species ✔
\n
c. EM has a wide niche/higher tolerance/covers entire «intertidal» range making it easier to invade the habitat ✔
\n
c.
\n
\n
a. exposure/tides/waves ✔
\n
b. temperature ✔
\n
c. surfaces «of attachment» ✔
\n
d. resource availability/nutrients ✔
\n
e. pH ✔
\n
f. light ✔
\n
g. salinity ✔
\n
Do not accept biotic factors eg: “competition or predation”
\n
d.
\n
\n
a. indicator species need particular environmental conditions
OR
indicator species tolerate only certain environmental conditions ✔
\n
b. increase/decrease in population size «over time» shows effect of environmental conditions ✔
\n
c. used to calculate biotic index/index of cleanliness ✔
\n
d. index of 10/high index number indicates totally unpolluted
OR
index of 2 or 1/low index number indicates severe pollution ✔
\n
e.
\n
",
+ "Examiners report": "
\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
a.
\n
\n
Candidates were able to describe the distributions of the barnacles very well in part (b).
\n
b.
\n
\n
Candidates had difficulty finding data to support E.modestus being aninvasive barnacle in part (c).
\n
c.
\n
\n
In part (e) some candidates chose to describe invasive species in general (without using the data) and others described the data but were not able to attach this to the idea of an invasive species. Many repeated the information given in the question.
\n
e.
\n
",
+ "topics": [
+ "b-form-and-function",
+ "c-interaction-and-interdependence",
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "b4-1-4-range-of-tolerance-of-a-limiting-factor",
+ "b4-1-adaptation-to-environment",
+ "c4-1-13-resource-competition-between-endemic-and-invasive-species",
+ "c4-1-populations-and-communities",
+ "d4-1-4-abiotic-factors-as-selection-pressures",
+ "d4-1-natural-selection"
+ ]
+ },
+ {
+ "question_id": "19M.3.SL.TZ2.3",
+ "Question": "
\n
A study was conducted on 25 healthy, non-smoking males to look at the effect of exercise and altitude on ventilation rate. Subjects were first asked to rest in a sitting position for six minutes. They then pedalled for three periods of six minutes at increasing exercise intensity: at 20 %, 30 % and 40 % of their maximal aerobic power. The entire study was conducted either in normal sea level oxygen conditions or in lower oxygen conditions simulating an altitude of 4000 m. The results are shown in the bar chart.
\n

\n
[Source: E Hermand, et al., (2015), Periodic breathing in healthy humans at exercise in hypoxia,
Journal of Applied Physiology, 118, pages 115–123. https://doi.org/10.1152/japplphysiol.00832.2014]
\n
\n
State one other variable that should have been controlled in this study.
\n
\n
[1]
\n
a.
\n
\n
Compare and contrast the effect of increasing exercise intensity at sea level and at an altitude of 4000 m.
\n
[2]
\n
b.
\n
\n
Outline how ventilation rate could have been monitored in this study.
\n
[2]
\n
c.
\n
",
+ "Markscheme": "
\n
age/height/fitness level/weight/room temperature/rest in between tests/model or type of bike ✔
\n
Other valid factor. Only mark first factor listed.
\n
Do not accept sex, health, smoking, oxygen level or altitude as this already listed.
\n
a.
\n
\n
a. in both sea level and 4000m ventilation rate while exercising «at all intensities» is «significantly» more than at rest
OR
both sea level and 4000m show an increase in ventilation rate «dm3 min–1» as exercise intensity increased ✔
\n
b. ventilation rate at 4000m «slightly» higher than at sea level for all conditions
OR
higher ventilation rate at 4000m not «significantly» different as error bars overlap ✔
\n
Accept positive correlation.
\n
b.
\n
\n
a. «data logging» with spirometer
OR
chest belt ✔
\n
b. «tidal» volume recorded for a given period of time
OR
average «tidal» volume found and multiplied by number breaths per minute ✔
\n
Do not accept confusion with respirometer (measuring oxygen consumption or CO2 release).
\n
Must include a reference to time.
\n
c.
\n
",
+ "Examiners report": "
\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
a.
\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
b.
\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
c.
\n
",
+ "topics": [
+ "b-form-and-function"
+ ],
+ "subtopics": [
+ "b3-1-5-ventilation-of-the-lungs",
+ "b3-1-gas-exchange"
+ ]
+ },
+ {
+ "question_id": "19M.3.SL.TZ2.5",
+ "Question": "
\n
Scientists investigated how relative brain mass varied in primate evolution. The graph shows the relative brain mass for species belonging to different primate groups against time of divergence from the common ancestor of modern humans in million years ago (Mya), 0 being the present era.
\n

\n
[Source: S Herculano-Houzel and J H Kaas, (2011), Brain, Behavior and Evolution, 77, pages 33–44.
© 2011 Karger Publishers, Basel, Switzerland]
\n
\n
State the trend in relative brain mass in primates other than humans according to their time of divergence from humans.
\n
[1]
\n
a.
\n
\n
Suggest one reason that the relative brain mass of Homo is different from Parapithecus and Australopithecus.
\n
[1]
\n
b.
\n
\n
Deduce, with a reason, whether the relative brain mass is a good indicator of brain development.
\n
[1]
\n
c.
\n
\n
Primates belong to the phylum chordata. The neural tube of chordates is formed by the infolding of the ectoderm followed by the elongation of the tube. Outline the process of formation of neurons from this neural tube in primates.
\n
[2]
\n
d.
\n
",
+ "Markscheme": "
\n
the longer ago they diverged from humans, the greater the relative brain mass ✔
\n
Accept inverse.
\n
Do not accept negative correlation.
\n
a.
\n
\n
a. human cerebral cortex has extensive folding producing a greater mass ✔
\n
b. better diet/more protein allowed increase in «relative» brain mass in humans ✔
\n
c. others had larger body to protect them from predators «without increase in brain mass» ✔
\n
b.
\n
\n
a. not a good indicator because it depends on body mass ✔
\n
b. not a good indicator as less developed organisms show a larger relative brain mass ✔
\n
Accept answers referring to specific organisms shown
\n
c.
\n
\n
a. neurons formed by a process called neurulation ✔
\n
b. neurons are «initially» produced by differentiation «in the neural tube» ✔
\n
c. immature neurons migrate to a final location ✔
\n
d. an axon grows from each immature neuron in response to chemical stimuli ✔
\n
e. some axons extend beyond the neural tube to reach other parts of the body ✔
\n
f. a developing neuron forms multiple synapses ✔
\n
d.
\n
",
+ "Examiners report": "
\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
a.
\n
\n
In parts (b) and (c) few candidates referred to ‘relative’ brain mass thereby providing incorrect responses.
\n
b.
\n
\n
In parts (b) and (c) few candidates referred to ‘relative’ brain mass thereby providing incorrect responses.
\n
c.
\n
\n
In Part (d) many candidates were familiar with the process of neuron formation in primates though some may have been confused by the introduction to the question.
\n
d.
\n
",
+ "topics": [
+ "c-interaction-and-interdependence"
+ ],
+ "subtopics": [
+ "c3-1-4-the-brain-as-a-central-information-integration-organ",
+ "c3-1-integration-of-body-systems"
+ ]
+ },
+ {
+ "question_id": "19M.2.HL.TZ1.1",
+ "Question": "
\n
Ebola virus disease (EVD) is the disease in humans and other primates that is caused by the Ebola virus. Fruit bats are the reservoir for the virus and are able to spread the disease without being affected. Humans can become infected by contact with fruit bats or with people infected by the virus, their body fluids or equipment used to treat them.
\n
The stacked bar graph shows the epidemiological data for the EVD cases in Conakry, the capital city of Guinea, surrounding suburbs and rural areas in Guinea from the beginning of January 2014 to the end of March 2015.
\n

\n
[Source: Adriana Rico, et al. “Epidemiology of Epidemic Ebola Virus Disease in Conakry and Surrounding Prefectures,
Guinea, 2014–2015.” Emerging Infectious Diseases 22.2 (2016): 178–183. PMC. Web. 23 Mar. 2017.
https://wwwnc.cdc.gov/eid/article/22/2/15-1304_article]
\n
\n
The table summarizes epidemiological data from Guinea during the Ebola outbreak in 2014. The data are based on figures supplied by Ebola treatment centres. The last column refers to people who died in places other than Ebola treatment centres.
\n

\n
[Source: Adriana Rico, et al. “Epidemiology of Epidemic Ebola Virus Disease in Conakry and Surrounding Prefectures,
Guinea, 2014–2015.” Emerging Infectious Diseases 22.2 (2016): 178–183. PMC. Web. 23 Mar. 2017.
https://wwwnc.cdc.gov/eid/article/22/2/15-1304_article]
\n
\n
An antiviral drug, T-705, was tested in order to establish whether it has potential to treat EVD. The graph shows the data from an in vitro trial of T-705 on cells that had been infected with Ebola virus five days previously. Virus concentration and live cells are shown as a percentage of the control.
\n

\n
[Source: Oestereich, Lisa & Rieger, Toni & Neumann, Melanie & Bernreuther, Christian & Lehmann, Maria & Krasemann,
Susanne & Wurr, Stephanie & Emmerich, Petra & de Lamballerie, Xavier & Ölschläger, Stephan & Günther, Stephan. (2014).
Evaluation of Antiviral Efficacy of Ribavirin, Arbidol, and T-705 (Favipiravir) in a Mouse Model for Crimean-Congo
Hemorrhagic Fever. PLoS neglected tropical diseases. 8. e2804. 10.1371/journal.pntd.0002804.]
\n
\n
In 2015, an experimental vaccine was trialled in Guinea in an area where new Ebola cases continue to develop. Among the nearly 6000 people who accepted the vaccine, no cases were recorded after vaccination. In comparison, there were 23 cases among those who did not accept the vaccine.
\n
\n
Identify the week and year in which the first cases were recorded in the suburbs.
\n
Week:
\n
Year:
\n
[1]
\n
a.
\n
\n
Based on the graph, compare and contrast the progress of the epidemic in the suburbs and rural areas.
\n
[3]
\n
b.
\n
\n
Suggest two reasons for the overall decline in the epidemic after week 51.
\n
[2]
\n
c.
\n
\n
Compare and contrast the data for Conakry with the data for the three suburbs.
\n
[2]
\n
d.
\n
\n
Suggest reasons for the high percentage of fatal cases at Ebola treatment centres.
\n
[3]
\n
e.
\n
\n
Based on these data, outline the evidence that T-705 has potential to be used as a treatment for EVD.
\n
[2]
\n
f.
\n
\n
Explain how vaccination can lead to the production of B cells specific to the Ebola virus.
\n
[3]
\n
g.
\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
[2]
\n
h.
\n
",
+ "Markscheme": "
\n
week 34 AND 2014 ✔
\n
both needed
\n
a.
\n
\n
a. start of epidemic/first cases in rural areas
OR
epidemic spread to suburbs later ✔
\n
b. higher maximum number of cases/greater increase in rural areas
OR
converse for suburbs ✔
\n
c. increase came earlier in rural areas «than suburbs»
OR
number of cases peaked earlier in rural areas
OR
more cases in rural areas «than suburbs» in 2014 ✔
\n
d. decrease came earlier in rural areas «than suburbs»
OR
decreasing in rural areas but not in suburbs in 2015/by end of study period
OR
more cases in suburbs than rural areas in 2015 ✔
\n
e. «large» fluctuations in both ✔
\n
b.
\n
\n
a. «overall decline due to» fewer cases in rural areas ✔
\n
Answers relating to people who died from the disease or develop immunity to it:
b. fewer cases due to deaths of people who had the disease/people recovering
OR
more people vaccinated/became immune/made antibodies/were not vulnerable to infection ✔
\n
Answers relating to health care workers or availability of resources:
c. more doctors/nurses/medical equipment/treatment centers/hospitals/spending/aid/NGOs ✔
\n
Answers relating to medical techniques used to tackle the epidemic:
d. better treatments/infection control/hygiene/quarantine/new vaccine/new antiviral drugs ✔
\n
Answers relating to the public and patients:
e. education/better awareness/avoidance of infection/taking precautions/vaccination accepted ✔
\n
Answers relating to reservoirs of infection:
f. fewer infected people «who could spread infection»/fewer bats/less contact with bats ✔
\n
c.
\n
\n
differences:
a. Conakry has more cases than any of the suburbs
OR
more cases in total in the suburbs than in Conakry ✔
\n
b. more male cases in Conakry whereas more female cases in suburbs ✔
\n
c. higher «% of» fatal cases at Ebola treatment centers in suburbs than in Conakry ✔
\n
similarity:
d. in both Conakry and suburbs «% of» fatal cases in treatment centers is higher than outside ✔
\n
d.
\n
\n
a. most serious cases are in/are taken to treatment centers
OR
treatment centers are set up where there are most cases/most serious cases ✔
\n
b. long time/distance to travel between contracting disease and arrival at treatment center
OR
travel to treatment center weakens/upsets/harms the patient ✔
\n
c. Ebola is a virulent disease/Ebola virus mutated «to become virulent»
OR
little known about Ebola/new disease so treatments not yet developed ✔
\n
d. no/not enough vaccine/antiviral drug available «in 2014/15»
OR
antibiotics do not work against viral diseases ✔
\n
e. secondary infections/Ebola patients infected with other diseases/other Ebola strains
OR
ineffective hygiene/cleaning/sterilization/use of contaminated equipment/disposal of corpses ✔
\n
f. small number of staff relative to patients/treatment centers overcrowded/swamped with patients
OR
insufficient equipment/supplies for large number of patients/with the rapid rise in patients ✔
\n
g. better reporting at Ebola centers/deaths due to Ebola not reported in rural areas ✔
\n
e.
\n
\n
a. cells not killed/few cells killed «even at high concentrations» ✔
\n
b. «T-705» effective/viruses reduced/viruses killed at 100 μM
OR
«T-705» very effective/viruses much reduced/nearly all viruses killed at 1000 μM ✔
\n
c. virus concentration decreases as T-705 concentration increases ✔
\n
d. drug has «high» potential for treatment «at high enough concentration» ✔
\n
f.
\n
\n
a. vaccine contains Ebola antigens ✔
\n
b. vaccine «could» contain weakened/attenuated/dead/killed form of «Ebola» virus/virus genetically modified to express an Ebola/viral protein ✔
\n
c. phagocyte/macrophage engulfs the antigen/presents the antigen to T cell ✔
\n
d. antigen recognized by «specific» T cells/binds to T cells ✔
\n
e. «activated» T cells activate «specific) B cells ✔
\n
f. «activated» B cells make the antibodies «against Ebola» ✔
\n
g. B cells divide forming «clone of» plasma cells/producing more B cells specific to Ebola ✔
\n
g.
\n
\n
a. poor transport infrastructure/poor communication/bad roads/difficult access/no maps/support slow arriving/scattered population ✔
\n
b. poor education/understanding of disease amongst health workers/local population
OR
continued contact with infected people / other example of unsafe actions ✔
\n
c. more sources of infection such as bats/difficult to find sources of infection ✔
\n
d. lack of/limited access to medical care/doctors/health care workers ✔
\n
e. lack of/no access to/unaffordability of treatment centers/medicalsupplies/equipment/antivirals/drugs/vaccine/treatments ✔
\n
f. refusal/reluctance in local population to be vaccinated
OR
difficult to find/reach everyone to vaccinate them/repeat the vaccination ✔
\n
g. migration of people spreads the infection ✔
\n
h.poor sanitation/lack of clean water ✔
\n
h.
\n
",
+ "Examiners report": "
\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
Nearly all candidates read from the graph the week and year in which the first cases were recorded in the suburbs.
\n
a.
\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
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
b.
\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
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
c.
\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
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
d.
\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
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
e.
\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
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
f.
\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
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
g.
\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
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
h.
\n
",
+ "topics": [
+ "a-unity-and-diversity",
+ "c-interaction-and-interdependence"
+ ],
+ "subtopics": [
+ "a2-3-viruses-(hl-only)",
+ "c3-2-defence-against-disease"
+ ]
+ },
+ {
+ "question_id": "19M.2.HL.TZ1.2",
+ "Question": "
\n
The karyogram shown is for the African marsh rat (Dasymys incomtus). In this species, sex is determined by X and Y chromosomes. Females are XX and males are XY.
\n

\n
[Source: adapted from https://embryology.med.unsw.edu.au]
\n
\n
Thomas Hunt Morgan established that genes for body colour and wing size in Drosophila are autosomally linked. The allele for grey body (b+) is dominant over that for black body (b) and the allele for normal wing size (vg+) is dominant over that for vestigial wing (vg).
\n
\n
Distinguish between the structure of the chromosomes of prokaryotes and eukaryotes.
\n
[2]
\n
a.
\n
\n
Outline the causes of sickle cell anemia.
\n
[2]
\n
b.
\n
\n
Identify, with a reason, the sex of this individual.
\n
[1]
\n
c.i.
\n
\n
State the haploid number for this nucleus.
\n
[1]
\n
c.ii.
\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
[2]
\n
d.i.
\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
Explain these results, based on the knowledge that the genes for body colour and wing size are autosomally linked.
\n
[2]
\n
d.ii.
\n
",
+ "Markscheme": "
\n
a. prokaryotes have circular DNA/chromosome but eukaryote chromosomes linear/OWTTE ✔
OR
eukaryotes have telomeres/centromeres whereas prokaryotes do not ✔
\n
b. some prokaryotes have plasmids whereas eukaryotes do not ✔
\n
c. eukaryotes have multiple chromosomes whereas prokaryotes «typically» have only one ✔
\n
d. histones/nucleosomes/proteins associated with DNA in eukaryotes but not in prokaryotes/naked DNA in prokaryotes
OR
eukaryote DNA can coil/supercoil/condense «due to histones» but not prokaryote DNA ✔
\n
a.
\n
\n
a. genetic disease/caused by a gene
OR
inherited «from parents»
OR
caused by mutation «of a gene» ✔
\n
b. base substitution
OR
GAG → GTG ✔
\n
c. hemoglobin gene mutated / different allele/form/version of hemoglobin gene
OR
HbA → HbS ✔
\n
d. leads to change in amino acid sequence «in hemoglobin»
OR
glutamic acid → valine ✔
\n
e. only homozygotes have full disease/sickled cells / heterozygote has milder form
OR
hemoglobin crystallizes at low oxygen concentration ✔
\n
f. «selected for/spreads in population» as it gives resistance to malaria ✔
\n
b.
\n
\n
male because «X and» Y chromosome present
OR
male because sex chromosomes/last two chromosomes/pair 21 are unpaired/different «from each other»/not homologous ✔
\n
The answer must include “male” and the reason.
\n
c.i.
\n
\n

\n
d.i.
\n
\n
a. not a 1:1:1:1 ratio «because of linkage»
OR
not independent assortment
OR
grey normal and black vestigial types/parental combinations/double dominant and double recessive were commoner than 25 %/commoner than expected ✔
b. «linked genes» so were on the same chromosome ✔
\n
c. grey body vestigial wing and black body normal wing are recombinants
OR
2 % plus 3 % of the offspring are recombinants ✔
\n
d. recombinants due to crossing over/exchange of genes between «non-sister» chromatids
OR
2 % and 3 % of offspring were due to crossing over
OR
genes inherited together unless separated by crossing over ✔
\n
e. crossing over between the two loci/between the two genes on the chromosomes ✔
\n
f. few recombinants/not much crossing over because genes/gene loci close together ✔
\n
Accept any of these points from an annotated diagram.
\n
d.ii.
\n
",
+ "Examiners report": "
\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
a.
\n
\n
This question also elicited a wide range of answers. Some were accurate and detailed but some showed no knowledge of this genetic disease. There was lack of clarity in many answers, for example the disease was described as the mutation and sickling of cells was known but not linked to haemoglobin. The weakest answers tended to describe anemia in general, with iron deficiency sometimes given as the cause.
\n
b.
\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
c.i.
\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
c.ii.
\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
d.i.
\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
d.ii.
\n
",
+ "topics": [
+ "a-unity-and-diversity",
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "a2-2-12-origin-of-eukaryotic-cells-by-endosymbiosis",
+ "a2-2-5-prokaryote-cell-structure",
+ "a2-2-6-eukaryote-cell-structure",
+ "a2-2-cell-structure",
+ "a3-1-7-karyotyping-and-karyograms",
+ "a3-1-diversity-of-organisms",
+ "d2-1-9-meiosis-as-a-reduction-division",
+ "d2-1-cell-and-nuclear-division",
+ "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",
+ "d3-2-inheritance"
+ ]
+ },
+ {
+ "question_id": "19M.2.HL.TZ1.20",
+ "Question": "
\n
\n (a)\n
\n
\n
\n Deduce from the results of the study whether HGH improves strength.\n
\n
\n
\n
\n
\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",
+ "Markscheme": "
\n (a)\n
\n
\n the drug does not appear to improve strength as less mass can be lifted «by arms and legs» ✔\n
\n
\n
\n (b)\n
\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 (a)\n
\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
\n (b)\n
\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",
+ "topics": [
+ "c-interaction-and-interdependence"
+ ],
+ "subtopics": [
+ "c2-1-10-mechanism-of-action-of-epinephrine-(adrenaline)-receptors",
+ "c2-1-chemical-signalling-[hl-only]"
+ ]
+ },
+ {
+ "question_id": "19M.2.HL.TZ1.21",
+ "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
\n
\n (a.ii)\n
\n
\n
\n Describe briefly how an artificial pacemaker works.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a.i)\n
\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
\n (a.ii)\n
\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 (a.i)\n
\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
\n (a.ii)\n
\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",
+ "topics": [
+ "b-form-and-function"
+ ],
+ "subtopics": [
+ "b3-2-15-adaptations-of-the-mammalian-heart-for-delivering-pressurized-blood-to-the-arteries",
+ "b3-2-16-stages-in-the-cardiac-cycle",
+ "b3-2-transport"
+ ]
+ },
+ {
+ "question_id": "19M.2.HL.TZ1.3",
+ "Question": "
\n
The electron micrographs show a typical prokaryote and a mitochondrion.
\n

\n
\n
Compare and contrast the structure of a typical prokaryotic cell with that of a mitochondrion.
\n
[4]
\n
a.
\n
\n
Explain how mitochondria could have been formed from free living prokaryotes.
\n
[2]
\n
b.
\n
",
+ "Markscheme": "
\n
differences
\n
a. prokaryote has cell wall but mitochondrion does not ✔
\n
b. mitochondrion has double membrane whereas prokaryote has single membrane
OR
«Gram negative» bacteria have cell wall between two membranes whereas mitochondria has intermembrane space between two membranes ✔
\n
c. mitochondrion has cristae/invaginations of inner membrane but prokaryote does not
OR
prokaryote «may have» flagella/pili/«slime» capsule which mitochondria do not have ✔
\n
similarities
\n
d. 70S ribosomes in both ✔
\n
e. DNA in both / loop of DNA in both / naked DNA in both ✔
\n
f. shape similar/both rod shaped/OWTTE
OR
size of both is similar/both about 3 μm long ✔
\n
g. both are membrane-bound/OWTTE ✔
\n
a.
\n
\n
a. endocytosis/engulfing of prokaryote by a larger/another/anaerobic prokaryote/cell ✔
\n
b. double membrane of the mitochondrion is the result of endocytosis
OR
inner membrane of mitochondrion from engulfed cell and outer from food vacuole ✔
\n
c. «engulfed prokaryotic cell» was aerobic/respired aerobically/consumed oxygen
OR
«engulfed prokaryotic cell» provided energy/ATP ✔
\n
d. «engulfed prokaryotic cell» not destroyed/not digested
OR
«endo»symbiotic/mutualistic relationship developed ✔
\n
e. «engulfed prokaryotic cell» had its own DNA/own «70S» ribosomes ✔
\n
Do not award mpc for “mitochondrion makes ATP”.
\n
b.
\n
",
+ "Examiners report": "
\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
a.
\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
b.
\n
",
+ "topics": [
+ "a-unity-and-diversity",
+ "b-form-and-function"
+ ],
+ "subtopics": [
+ "a2-2-12-origin-of-eukaryotic-cells-by-endosymbiosis",
+ "a2-2-cell-structure",
+ "b3-2-15-adaptations-of-the-mammalian-heart-for-delivering-pressurized-blood-to-the-arteries",
+ "b3-2-transport"
+ ]
+ },
+ {
+ "question_id": "19M.2.HL.TZ1.4",
+ "Question": "
\n
The micrograph shows a vascular bundle from the stem of a barley plant.
\n

\n
[Source: Copyright Carolina Biological Supply Company. Used by permission only.]
\n
\n
Xylem and phloem contain structures that are adapted for transport. Outline the differences between these structures in xylem and phloem.
\n
[2]
\n
a.
\n
\n
Explain how the properties of water allow it to move through xylem vessels.
\n
[2]
\n
b.
\n
\n
Outline how the structure of cellulose makes it suitable as a component of cell walls.
\n
[2]
\n
c.
\n
",
+ "Markscheme": "
\n
a. plasma membrane in phloem/sieve tubes but not in xylem/vessels
OR
xylem/vessels dead/acellular and phloem/sieve tubes alive ✔
\n
b. xylem vessels have thicker walls «than phloem» ✔
\n
c. xylem «vessel» walls are lignified «but phloem walls are not» ✔
\n
d. phloem vessels have sieve plates «whereas xylem vessels have no cross walls» ✔
\n
e. xylem/vessels are wider/larger than phloem/sieve tubes ✔
\n
f. companion cells in phloem «but not in xylem» ✔
\n
a.
\n
\n
a. water is polar/a dipole/oxygen slightly negative and hydrogen slightly positive ✔
\n
b. polarity results in hydrogen bonds/attraction between water molecules ✔
\n
c. hydrogen bonding/polarity causes cohesion of water «molecules» ✔
\n
d. cohesion/hydrogen bonding allows water to withstand tension/withstand low pressure/be pulled «upwards»/moved against gravity ✔
\n
e. cohesion/hydrogen bonding prevents column of water «in xylem» from breaking/column of water is maintained ✔
\n
f. adhesion of water to xylem/vessel walls «due to hydrogen bonds» ✔
\n
b.
\n
\n
a. chains of glucose/1-4 glycosidic linkages/covalent bonding between glucose ✔
\n
b. beta glucose so alternating orientation of glucose units
OR
beta glucose forms straight chains ✔
\n
c. forms microfibrils/long and thin/thin fibres/parallel bundles of cellulose molecules
OR
hydrogen bonding/cross linkage between cellulose molecules holds them together ✔
\n
d. high tensile strength/rigid/doesn’t stretch so provides support/allows turgidity ✔
\n
c.
\n
",
+ "Examiners report": "
\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
a.
\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
b.
\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
c.
\n
",
+ "topics": [
+ "a-unity-and-diversity",
+ "b-form-and-function"
+ ],
+ "subtopics": [
+ "a1-1-3-cohesion-of-water-molecules-due-to-hydrogen-bonding-and-consequences-for-organisms",
+ "a1-1-water",
+ "b1-1-6-structure-of-cellulose-related-to-its-function-as-a-structural-polysaccharide-in-plants",
+ "b1-1-carbohydrates-and-lipids",
+ "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",
+ "b3-2-9-distribution-of-tissues-in-a-transverse-section-of-the-stem-of-a-dicotyledonous-plant",
+ "b3-2-transport"
+ ]
+ },
+ {
+ "question_id": "19M.2.HL.TZ1.5",
+ "Question": "
\n
Outline the functions of rough endoplasmic reticulum and Golgi apparatus.
\n
[3]
\n
a.
\n
\n
Outline the control of metabolism by end-product inhibition.
\n
[5]
\n
b.
\n
\n
Explain how hydrophobic and hydrophilic properties contribute to the arrangement of molecules in a membrane.
\n
[7]
\n
c.
\n
",
+ "Markscheme": "
\n
a. ribosomes on RER synthesize/produce polypeptides/proteins ✔
\n
b. proteins from RER for secretion/export/use outside cell/for lysosomes ✔
\n
c. Golgi alters/modifies proteins/example of modification ✔
\n
d. vesicles budded off Golgi transport proteins «to plasma membrane»
OR
exocytosis/secretion of proteins in vesicles from the Golgi ✔
\n
Accept “for use inside and outside the cell” for mpb.
\n
a.
\n
\n
a. metabolism is chains/web of enzyme-catalyzed reactions
OR
metabolic pathway is a chain of enzyme-catalyzed reactions ✔
\n
b. end product/inhibitor is final product of chain/pathway ✔
\n
c. inhibits/binds to/blocks the first enzyme in chain/pathway ✔
\n
d. non-competitive inhibition ✔
\n
e. end-product/inhibitor binds to an allosteric site/site away from the active site ✔
\n
f. changes the shape of the active site/affinity of the active site «for the substrate» ✔
\n
g. prevents intermediates from building up
OR
prevents formation of excess «end» product/stops production when there is enough
OR
whole metabolic pathway can be switched off ✔
\n
h. negative feedback ✔
\n
i. binding of the end product/inhibitor is reversible
OR
pathway restarts if end product/inhibitor detaches/if end product concentration is low ✔
\n
j. isoleucine inhibits/slows «activity of first enzyme in» threonine to isoleucine pathway ✔
\n
Allow mark points shown in clearly annotated diagrams.
\n
To gain mpd, mpe and mpf the answer must be in the context of end-product inhibition, not enzyme inhibition generally.
\n
b.
\n
\n
a. hydrophilic is attracted to/soluble in water and hydrophobic not attracted/insoluble ✔
\n
b. hydrophilic phosphate/head and hydrophobic hydrocarbon/tail in phospholipids ✔
\n
c. phospholipid bilayer in water/in membranes ✔
\n
d. hydrophilic heads «of phospholipids» face outwards/are on surface ✔
\n
e. hydrophobic tails «of phospholipids» face inwards/are inside/are in core ✔
\n
f. cholesterol is «mainly» hydrophobic/amphipathic so is located among phospholipids/in hydrophobic region of membrane ✔
\n
g. some amino acids are hydrophilic and some are hydrophobic ✔
\n
h. hydrophobic «amino acids/regions of» proteins in phospholipid bilayer «core» ✔
\n
i. hydrophilic «amino acids/regions of» proteins are on the membrane surface ✔
\n
j. integral proteins are embedded in membranes due to hydrophobic properties/region
OR
transmembrane proteins have a hydrophobic middle region and hydrophilic ends ✔
\n
k. peripheral proteins on are on the membrane surface/among phosphate heads due to being «entirely» hydrophilic
OR
«carbohydrate» part of glycoproteins is hydrophilic so is outside the membrane ✔
\n
l. pore of channel proteins is hydrophilic ✔
\n
Allow mark points shown in clearly annotated diagram.
\n
In any part of the answer, accept polar instead of hydrophilic and non-polar or apolar instead of hydrophobic.
\n
c.
\n
",
+ "Examiners report": "
\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
a.
\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
b.
\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
c.
\n
",
+ "topics": [
+ "b-form-and-function",
+ "c-interaction-and-interdependence"
+ ],
+ "subtopics": [
+ "b2-1-10-fluid-mosaic-model-of-membrane-structure",
+ "b2-1-membranes-and-membrane-transport",
+ "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",
+ "b2-2-organelles-and-compartmentalization",
+ "c1-1-16-regulation-of-metabolic-pathways-by-feedback-inhibition",
+ "c1-1-enzymes-and-metabolism",
+ "c2-1-6-differences-between-transmembrane-receptors-in-a-plasma-membrane-and-intracellular-receptors-in-the-cytoplasm-or-nucleus",
+ "c2-1-chemical-signalling-[hl-only]"
+ ]
+ },
+ {
+ "question_id": "19M.2.HL.TZ1.6",
+ "Question": "
\n
Outline the process of inspiration in humans.
\n
[4]
\n
a.
\n
\n
Describe the functions of valves in the mammalian heart.
\n
[4]
\n
b.
\n
\n
Explain how blood solute concentrations are kept within narrow limits in the human body.
\n
[7]
\n
c.
\n
",
+ "Markscheme": "
\n
a. diaphragm and external intercostal muscles contract ✔
\n
b. diaphragm moves down/becomes flatter
OR
external intercostals raise the ribcage/move the ribcage up/out ✔
\n
c. muscles/diaphragm/intercostals increase volume of thorax/expand the thorax
OR
muscles/diaphragm/intercostals decrease pressure in the thorax ✔
\n
d. as volume «of thorax/lungs» increases the pressure decreases ✔
\n
e. air enters «lungs» due to decreased pressure/higher pressure outside body ✔
\n
f. air flows to lungs through trachea and bronchi/bronchioles ✔
\n
Accept thoracic cavity or chest cavity in place of thorax in any part of the answer.
\n
Do not allow “oxygen” instead of air in mpe or mpf.
\n
a.
\n
\n
a. prevents backflow/ensures one-way flow/controls direction of flow ✔
\n
b. open valves allow blood to flow through
OR
opening and closing of valves controls timing of blood flow «during cardiac cycle» ✔
\n
c. closed «semilunar» valves allow ventricles/chambers to fill with blood
OR
closed «semilunar» valves allow pressure in ventricles to rise «rapidly» ✔
\n
d. valves open when pressure is higher upstream/OWTTE/converse for closed valves ✔
\n
e. AV/bicuspid/tricuspid/mitral valves prevent backflow from ventricle to atrium
OR
AV/bicuspid/tricuspid/mitral valves open when pressure in atrium is higher «than in the ventricle»/when atrium is pumping/contracting ✔
\n
f. semilunar/aortic/pulmonary valves prevent backflow from artery to ventricle
OR
semilunar/aortic/pulmonary valves open when pressure in ventricle is higher «than in the artery»/when ventricle is pumping/contracting ✔
\n
Allow mpa, mpb, mpc or mpd if the point is made through the example of one specific valve.
\n
b.
\n
\n
a. solute concentration of blood monitored by the brain/hypothalamus ✔
\n
b. pituitary gland secretes ADH ✔
\n
c. ADH secreted when solute concentration/osmolarity is too high/a person is dehydrated/OWTTE ✔
\n
d. collecting duct more permeable to water ✔
\n
e. «more» aquaporins/opens aquaporins «in the plasma membrane of collecting duct cells» ✔
\n
f. «more» water reabsorbed «into the medulla» ✔
\n
g. medulla is hypertonic/hyperosmotic «so water can be reabsorbed from filtrate» ✔
\n
h. small volume of urine/concentrated urine produced «with ADH» ✔
\n
i. no/little/less ADH secreted if «blood» solute concentration is too low ✔
\n
j. collecting duct less permeable to water/less water reabsorbed/large volume of urine produced/dilute urine produced «with low/no ADH» ✔
\n
k. insulin causes blood glucose «concentration» to be reduced ✔
\n
l. glucose stored as glycogen in the liver ✔
\n
m. glucagon causes blood glucose «concentration» to be increased ✔
\n
n. negative feedback ✔
\n
Accept hypertonic for solute concentration too high and hypotonic for too low.
\n
c.
\n
",
+ "Examiners report": "
\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
a.
\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
b.
\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
c.
\n
",
+ "topics": [
+ "b-form-and-function",
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "b3-1-5-ventilation-of-the-lungs",
+ "b3-1-gas-exchange",
+ "b3-2-15-adaptations-of-the-mammalian-heart-for-delivering-pressurized-blood-to-the-arteries",
+ "b3-2-transport",
+ "d3-3-7-role-of-the-kidney-in-osmoregulation-and-excretion",
+ "d3-3-homeostasis"
+ ]
+ },
+ {
+ "question_id": "19M.2.HL.TZ2.15",
+ "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
\n
\n (a.iii)\n
\n
\n
\n Using the climograph, outline the pattern of rainfall.\n
\n
\n
\n
\n
\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",
+ "Markscheme": "
\n (a.ii)\n
\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
\n (a.iii)\n
\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
\n (b)\n
\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 (a.iii)\n
\n
\n Most outlined correctly the pattern of rainfall, but irrelevant answers were seen.\n
\n
\n
\n (b)\n
\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",
+ "topics": [
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "d4-2-14-cyclical-succession-in-ecosystems",
+ "d4-2-stability-and-change"
+ ]
+ },
+ {
+ "question_id": "19M.2.HL.TZ2.18",
+ "Question": "
\n
\n (a)\n
\n
\n
\n Describe the structure of cardiac muscle cells.\n
\n
\n
\n
\n
\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
\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
\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",
+ "Markscheme": "
\n (a)\n
\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
\n (b)\n
\n
\n semilunar / sigmoid / pulmonary\n \n and\n \n aortic valve ✔\n
\n
\n
\n (c)\n
\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
\n (d)\n
\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 (a)\n
\n
\n The stronger candidates could describe the structure of cardiac muscle cells.\n
\n
\n
\n (b)\n
\n
\n Most could name the semilunar valves.\n
\n
\n
\n (c)\n
\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
\n (d)\n
\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",
+ "topics": [
+ "b-form-and-function"
+ ],
+ "subtopics": [
+ "b2-3-9-adaptations-of-cardiac-muscle-cells-and-striated-muscle-fibres",
+ "b2-3-cell-specialization",
+ "b3-2-15-adaptations-of-the-mammalian-heart-for-delivering-pressurized-blood-to-the-arteries",
+ "b3-2-16-stages-in-the-cardiac-cycle",
+ "b3-2-transport"
+ ]
+ },
+ {
+ "question_id": "19M.2.HL.TZ2.2",
+ "Question": "
\n
DNA methylation has a critical role in gene regulation by affecting transcription. Samples were taken from two colon cancer tumours (T1 and T2) and two normal colon samples (N1 and N2). A particular gene was implicated as a possible cause of cancer. The promoter of this gene was cloned (A–J). The data show the DNA methylation patterns from these samples. The numbers (32–269) represent different markers in the promoter.
\n

\n
[Source: Philipp Schatz, Dimo Dietrich & Matthias Schuster. Rapid analysis of CpG methylation patterns using RNase T1
cleavage and MALDI-TOF. Nucleic Acids Research (2004) 32 (21): e167, doi:10.1093/nar/gnh165.
Reproduced by permission of Oxford University Press]
\n
\n
Identify the stage of mitosis labelled X in the image, giving a reason.
\n

\n
[Source: Copyright 2002, The Trustees of Indiana University]
\n
[1]
\n
a.i.
\n
\n
Outline what is indicated by the mitotic index of tissue taken from a tumour.
\n
[2]
\n
a.ii.
\n
\n
DNA has regions that do not code for proteins. State two functions of these regions.
\n
1.
\n
2.
\n
\n
[2]
\n
a.iii.
\n
\n
Outline the difference in methylation pattern between tumorous and normal tissue samples.
\n
\n
[2]
\n
b.i.
\n
\n
Suggest a way methylation may affect tumour cell genes.
\n
[1]
\n
b.ii.
\n
",
+ "Markscheme": "
\n
telophase because the chromosomes/chromatids have reached the poles
OR
«late» anaphase as some chromosomes/chromatids are still moving/tails visible ✔
\n
OWTTE
\n
a.i.
\n
\n
a. mitotic index is an indication of the ratio/percentage of cells undergoing mitosis/cell division ✔
\n
b. cancer cells «generally» divide much more than normal «somatic» cells ✔
\n
c. a high/elevated mitotic index in tumours / possible diagnosis of cancer /measure of how aggressive/fast growing the tumour is ✔
\n
a.ii.
\n
\n
a. promoters / operators / regulation of gene expression/transcription ✔
\n
b. telomeres/give protection to the end of chromosomes «during cell division» ✔
\n
c. genes for tRNA/rRNA production ✔
\n
d. other valid function for non-coding sequence ✔
\n
Do not accept stop codon, accept centromeres (connecting sister chromatids).
\n
a.iii.
\n
\n
a. «overall» much more methylation in the colon tumour samples than normal ✔
\n
b. tumour and normal samples the markers 258 and 269 similar degree of methylation/fewer differences ✔
\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 eg marker 32 ✔
\n
b.i.
\n
\n
a. «DNA» methylation may inhibit transcription of genes that would prevent cancer/tumor formation ✔
\n
b. «DNA» methylation may increase mitosis/cell division leading to tumor formation ✔
\n
Do not accept discussion of histone methylation.
\n
b.ii.
\n
",
+ "Examiners report": "
\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
a.i.
\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
a.ii.
\n
\n
This question was well answered. The occasional answer made reference to processes associated with translation.
\n
a.iii.
\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
b.i.
\n
\n
Students lacked the understanding of epigenetics necessary to make reasonable suggestions.
\n
b.ii.
\n
",
+ "topics": [
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "d1-2-14-non-coding-sequences-in-dna-do-not-code-for-polypeptides",
+ "d1-2-protein-synthesis",
+ "d2-1-17-differences-between-tumours-in-rates-of-cell-division-and-growth-and-in-the-capacity-for-metastasis-and-invasion-of-neighbouring-tissue",
+ "d2-1-8-identification-of-phases-of-mitosis",
+ "d2-1-cell-and-nuclear-division",
+ "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",
+ "d2-2-gene-expression-[hl-only]"
+ ]
+ },
+ {
+ "question_id": "19M.2.HL.TZ2.22",
+ "Question": "
\n
\n (a)\n
\n
\n
\n State\n \n one\n \n function of the atrioventricular node.\n
\n
\n
\n
\n
\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",
+ "Markscheme": "
\n (a)\n
\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
\n (b)\n
\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 (a)\n
\n
\n A large number could state one correct function of the atrioventricular node, mainly that it causes ventricular systole.\n
\n
\n
\n (b)\n
\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",
+ "topics": [
+ "b-form-and-function"
+ ],
+ "subtopics": [
+ "b2-3-9-adaptations-of-cardiac-muscle-cells-and-striated-muscle-fibres",
+ "b2-3-cell-specialization",
+ "b3-2-15-adaptations-of-the-mammalian-heart-for-delivering-pressurized-blood-to-the-arteries",
+ "b3-2-transport"
+ ]
+ },
+ {
+ "question_id": "19M.2.HL.TZ2.3",
+ "Question": "
\n
The graph shows blood pressure changes on the left side of the heart during one heartbeat. Identify the two parts of the circulatory system that produce traces I and II on the graph.
\n

\n
[Source: © International Baccalaureate Organization 2019]
\n
[2]
\n
a.
\n
\n
Outline the actions taken by the body to avoid infection when the skin is cut.
\n
[3]
\n
b.
\n
\n
Hormones are distributed throughout the body by the blood. Outline the roles of two reproductive hormones during the menstrual cycle in women.
\n
[2]
\n
c.
\n
",
+ "Markscheme": "
\n
I. aorta ✔
\n
II: «left» atrium ✔
\n
a.
\n
\n
a. platelets/cut tissues release clotting factors ✔ Mp a requires student to identify source of clotting factors.
\n
b. «clotting factors» activate thrombin «from prothrombin» ✔
\n
c. thrombin converts fibrinogen to fibrin ✔
\n
d. «fibrin» forms a clot/scab/mesh that seals the cut ✔
\n
e. phagocytic white blood cells ingest pathogens ✔
\n
b.
\n
\n
a. FSH/follicle stimulating hormone stimulates the development of follicles/follicle cell division in the ovary «to produce eggs» ✔ Two different hormones must be identified.
\n
b. LH/luteinizing hormone triggers ovulation/development of the corpus luteum ✔
\n
c. estrogen stimulates development of the uterine lining/endometrium ✔ Description of role required as well as name of hormone.
\n
d. progesterone maintains the uterine lining/endometrium
OR
inhibits other hormones by negative feedback eg, FSH ✔
\n
e. HCG stimulates ovary to produce progesterone «in early pregnancy» ✔
\n
f. other verifiable hormone and roles relevant to the menstrual cycle ✔
\n
c.
\n
",
+ "Examiners report": "
\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
a.
\n
\n
This question about clotting was well answered with most being able to correctly identify the roles of clotting factors, fibrinogen and thrombin, though in a number of cases, specific details were lacking.
\n
b.
\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
c.
\n
",
+ "topics": [
+ "b-form-and-function",
+ "c-interaction-and-interdependence",
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "b3-2-16-stages-in-the-cardiac-cycle",
+ "b3-2-transport",
+ "c3-2-3-sealing-of-cuts-in-skin-by-blood-clotting",
+ "c3-2-defence-against-disease",
+ "d3-1-5-changes-during-the-ovarian-and-uterine-cycles-and-their-hormonal-regulation",
+ "d3-1-reproduction",
+ "d4-3-12-evolution-as-a-consequence-of-climate-change",
+ "d4-3-climate-change"
+ ]
+ },
+ {
+ "question_id": "19M.2.HL.TZ2.4",
+ "Question": "
\n
The images show parts of plants belonging to two different phyla.
\n

\n
State the phylum of plant X and of plant Y.
\n
X:
\n
Y:
\n
[2]
\n
a.
\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
[3]
\n
b.
\n
\n
Successful sexual reproduction in flowering plants depends on several essential processes. Outline the role of pollination and seed dispersal.
\n
Pollination:
\n
\n
Seed dispersal:
\n
\n
\n
[2]
\n
c.
\n
",
+ "Markscheme": "
\n
X: Filicinophyta ✔
\n
Y: Coniferophyta/Conifera/Gymnosperms ✔
\n
a.
\n
\n
a. «previous» classification used to be based on the appearance/structures of the plant/leaves/flowers/seeds/analogy/phenotype ✔
\n
b. «modern cladistics uses» RNA/DNA nucleotide/base sequencing/amino acid sequencing/homology ✔
\n
c. DNA mutation occurs at a relatively constant rate allowing estimation of when species diverged ✔
\n
d. a shared/common derived characteristic places organisms in the same clade ✔
\n
e. the number of changes in sequences indicates distance from common ancestor
OR
the fewer the differences «in sequences» means the closer the relationship ✔
\n
b.
\n
\n
pollination:
transfer/dispersal/movement of pollen from anther/stamen to stigma
OR
transfer/dispersal/movement of pollen between plants/flowers prior to/allowing fertilization ✔
\n
seed dispersal:
«strategy of» distribution of seeds so that new plants have space/nutrients to develop/avoid competition/colonize new habitats ✔
\n
Accept any other valid role.
\n
Accept OWTTE. Answers must be about the role.
\n
c.
\n
",
+ "Examiners report": "
\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
a.
\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
b.
\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
c.
\n
",
+ "topics": [
+ "a-unity-and-diversity",
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "a3-2-4-clades-as-groups-of-organisms-with-common-ancestry-and-shared-characteristics",
+ "a3-2-8-using-cladistics-to-investigate-whether-the-classification-of-groups-corresponds-to-evolutionary-relationships",
+ "a3-2-classification-and-cladistics-(hl-only)",
+ "d3-1-12-dispersal-and-germination-of-seeds",
+ "d3-1-8-sexual-reproduction-in-flowering-plants",
+ "d3-1-reproduction"
+ ]
+ },
+ {
+ "question_id": "19M.2.HL.TZ2.8",
+ "Question": "
\n
Outline energy flow through a food chain.
\n
[4]
\n
a.
\n
\n
Draw a fully labelled graph of the action spectrum for photosynthesis.
\n
[3]
\n
b.
\n
\n
Explain Calvin’s experiment and what was discovered about photosynthesis through his work.
\n
[8]
\n
c.
\n
",
+ "Markscheme": "
\n
a. energy from the sun/light energy is converted to chemical energy by photosynthesis ✔
\n
b. «chemical» energy flows through the food chains by feeding ✔
\n
c. energy is released «from carbon compounds» by respiration
OR
energy from respiration is used by living organisms and converted to heat ✔
\n
d. heat is not recyclable / heat is lost from food chains
OR
heat cannot be converted to other forms of energy ✔
\n
e. energy is lost in excretion/uneaten material/egestion/feces ✔
\n
f. energy losses between trophic levels limits the length of food chains
OR
energy transfer is only 10 % between trophic levels ✔
\n
a.
\n
\n
a. axes correctly labelled «wavelength and rate of photosynthesis» ✔ Accept rate of oxygen production for rate of photosynthesis.
\n
b. 400 and 700 nm as limits ✔
\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
d. peaks of activity at 430 nm AND at 660 nm ✔
\n
e. peaks indicated as «violet» blue light AND peak indicated as «orange» red light ✔
\n
\n
b.
\n
\n
a. Calvin cycle is light-independent ✔
\n
b. carbon fixation
OR
carboxylation of ribulose bisphosphate/RuBP occurs ✔
\n
c. algae placed in thin glass container/“lollipop” apparatus ✔
\n
d. given plenty of light and bicarbonate/ CO2 ✔
\n
e. at start of experiment algae supplied radioactive carbon/HCO3-/14C ✔
\n
f. samples taken at intervals / heat/alcohol killed samples ✔
\n
g. C-compounds separated by chromatography ✔
\n
h. 14C/radioactive-compounds identified by autoradiography ✔
\n
i. showed that RuBP was phosphorylated ✔
\n
j. after five seconds/immediately more glycerate-3-phosphate/3-PGA labelled than any other compound ✔
\n
k. shows glycerate-3-phosphate/3-PGA first «carboxylated» compound/the first stable product ✔
\n
l. next compound to be detected containing radioactive carbon was triose phosphate/G3P/glyceraldehyde 3 phosphate ✔
\n
m. showed that a wide range of carbon compounds was quickly made in sequence ✔
\n
n. showed that a cycle of reactions was used to regenerate RuBP ✔
\n
c.
\n
",
+ "Examiners report": "
\n
Was well answered with most students being knowledgeable about ecology.
\n
a.
\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
b.
\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
c.
\n
",
+ "topics": [
+ "c-interaction-and-interdependence"
+ ],
+ "subtopics": [
+ "c1-1-13-cyclical-and-linear-pathways-in-metabolism",
+ "c1-1-enzymes-and-metabolism",
+ "c1-3-6-similarities-and-differences-of-absorption-and-action-spectra",
+ "c1-3-photosynthesis",
+ "c4-2-3-flow-of-chemical-energy-through-food-chains",
+ "c4-2-transfers-of-energy-and-matter"
+ ]
+ },
+ {
+ "question_id": "19M.2.SL.TZ1.1",
+ "Question": "
\n
Ebola virus disease (EVD) is the disease in humans and other primates that is caused by the Ebola virus. Fruit bats are the reservoir for the virus and are able to spread the disease without being affected. Humans can become infected by contact with fruit bats or with people infected by the virus, their body fluids or equipment used to treat them.
\n
The table shows data for four African countries that were affected by the 2014–2015 Ebola outbreak.
\n

\n
[Source: adapted with permission, from Ebola Situation Report, figure 1, http://apps.who.int/ebola/current-situation/ebolasituation-
report-2-march-2016, March 2016, and from Successful treatment of advanced Ebola virus infection with T-705
(favipiravir) in a small animal model, Oestereich, L. et al, 2014, under CC BY 3.0]
\n
\n
The graphs show the progress of the EVD epidemic in Guinea and Liberia for the period April 2014 to May 2015.
\n

\n
[Source: Ebola Situation Report 2 March 2016 and data from International Journal of Infectious Diseases, 38,
Ligui Wang et al, Epidemiological features and trends of Ebola virus disease in West Africa, 52-53.,
Copyright 2015, with permission from Elsevier]
\n
\n
An antiviral drug, T-705, was tested in order to establish whether it has potential to treat EVD. The graph shows the data from an in vitro trial of T-705 on cells that had been infected with Ebola virus five days previously. Virus concentration and live cells are shown as percentage of the control.
\n

\n
[Source: Oestereich, Lisa & Rieger, Toni & Neumann, Melanie & Bernreuther, Christian & Lehmann, Maria & Krasemann,
Susanne & Wurr, Stephanie & Emmerich, Petra & de Lamballerie, Xavier & Ölschläger, Stephan & Günther, Stephan. (2014).
Evaluation of Antiviral Efficacy of Ribavirin, Arbidol, and T-705 (Favipiravir) in a Mouse Model for Crimean-Congo
Hemorrhagic Fever. PLoS neglected tropical diseases. 8. e2804. 10.1371/journal.pntd.0002804.]
\n
\n
Identify the country with the largest number of Ebola cases.
\n
[1]
\n
a.i.
\n
\n
Identify the country with the largest number of deaths.
\n
[1]
\n
a.ii.
\n
\n
Analysis of the data suggests that the number of deaths from EVD is not related to the total population size. State one piece of evidence from the data that would support this analysis.
\n
[1]
\n
b.
\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
[1]
\n
c.
\n
\n
Based on the data, compare and contrast the progress of the epidemic in Liberia and Guinea.
\n
[3]
\n
d.
\n
\n
Suggest two possible reasons for the drop in the daily numbers of newly infected cases after October 2014 in Liberia.
\n
[2]
\n
e.
\n
\n
Based on these data, outline the evidence that T-705 has potential to be used as a treatment for EVD.
\n
[2]
\n
f.
\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 one other way in which international organizations can assist with combatting an epidemic of Ebola.
\n
[1]
\n
g.
\n
",
+ "Markscheme": "
\n
country with biggest population/Mali has lowest number of deaths
OR
country with smallest population/Liberia has biggest number of deaths ✔
\n
OWTTE
\n
b.
\n
\n
greater density means more frequent contact with infected people/animals ✔
\n
Need both greater density and frequency of contact
\n
c.
\n
\n
a. overall pattern similar in both/both show a rise and a fall in the infections ✔
b. both countries show an increase during 2014
OR
neither country shows an increase in 2015 ✔
\n
c. both show a sudden drop at one point
OR
sudden drop earlier «Oct–Nov 14» in Liberia than in Guinea «Dec 14, Jan 15» ✔
\n
d. Guinea fluctuates whereas Liberia rises to a peak and then decreases/no fluctuations ✔
\n
e. epidemic starts earlier «in April 14» in Guinea than in Liberia «in June 14» ✔
\n
f. epidemic peaks earlier «Sept 14» in Liberia than in Guinea «Dec 14» ✔
\n
g. epidemic lasts longer in Guinea than it does in Liberia
OR
last case recorded in Liberia Feb 15 while cases continue «at least» until May 15 in Guinea ✔
\n
h. numbers of cases in Guinea generally lower than in Liberia
OR
number of cases higher in Liberia than in Guinea ✔
\n
d.
\n
\n
a. improved medical care/support/supplies/equipment/training of staff/hygiene/distribution of vaccine ✔
b. improved understanding of how to avoid infection «amongst public»/greater awareness in society/better education✔
\n
c. rise in number of deaths means fewer infectious individuals ✔
\n
d. impact of disease control measures/control policies/quarantine/isolation ✔
\n
e. drop in the number of fruit bats ✔
\n
f. maybe seasonal changes/weather changes ✔
\n
g. people may have left the area ✔
\n
h. international aid arrives ✔
\n
OWTTE
\n
e.
\n
\n
a. cells not killed/few cells killed «even at high concentrations» ✔
\n
b. «T-705» effective/viruses reduced/viruses killed at 100 μM
OR
«T-705» very effective/viruses much reduced/nearly all viruses killed at 1000 μM ✔
\n
c. virus concentration decreases as T-705 concentration increases ✔
\n
d. drug has «high» potential for treatment «at high enough concentration» ✔
\n
f.
\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
g.
\n
",
+ "Examiners report": "
\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
a.i.
\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
c.
\n
\n
Data is described rather than interpreted e.g. epidemic starts in April for Guinea and in June for Liberia instead of epidemic starts earlier in Guinea than in Liberia
\n
d.
\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
e.
\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
f.
\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
g.
\n
",
+ "topics": [
+ "a-unity-and-diversity",
+ "c-interaction-and-interdependence"
+ ],
+ "subtopics": [
+ "a2-3-viruses-(hl-only)",
+ "c3-2-defence-against-disease"
+ ]
+ },
+ {
+ "question_id": "19M.2.SL.TZ1.10",
+ "Question": "
\n
\n (a)\n
\n
\n
\n State the trophic level of the sea urchin.\n
\n
\n
\n
\n
\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",
+ "Markscheme": "
\n (a)\n
\n
\n herbivore/primary consumer ✔\n
\n
\n \n Do not accept second trophic level\n \n
\n
\n
\n (c)\n
\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 (a)\n
\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
\n (c)\n
\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",
+ "topics": [
+ "c-interaction-and-interdependence",
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "c4-2-10-classification-of-organisms-into-trophic-levels",
+ "c4-2-transfers-of-energy-and-matter",
+ "d4-2-5-role-of-keystone-species-in-the-stability-of-ecosystems",
+ "d4-2-stability-and-change"
+ ]
+ },
+ {
+ "question_id": "19M.2.SL.TZ1.11",
+ "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
\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
\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
\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",
+ "Markscheme": "
\n
\n (a)\n
\n
\n 6.5 m ✔\n
\n
\n \n Unit required\n \n
\n
\n
\n (b)\n
\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
\n (c)\n
\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 (a)\n
\n
\n Richness appeared well understood but the depth unit was sometimes omitted.\n
\n
\n
\n (b)\n
\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
\n (c)\n
\n
\n The reduction in light or temperature with greater depth was recognized but not often linked to growth or photosynthesis.\n
\n
\n",
+ "topics": [
+ "b-form-and-function",
+ "c-interaction-and-interdependence"
+ ],
+ "subtopics": [
+ "b4-1-4-range-of-tolerance-of-a-limiting-factor",
+ "b4-1-5-conditions-required-for-coral-reef-formation",
+ "b4-1-adaptation-to-environment",
+ "c1-2-6-variables-affecting-the-rate-of-cell-respiration",
+ "c1-2-cell-respiration",
+ "c4-1-12-mutualism-as-an-interspecific-relationship-that-benefits-both-species",
+ "c4-1-populations-and-communities"
+ ]
+ },
+ {
+ "question_id": "19M.2.SL.TZ1.14",
+ "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
\n
\n (a)\n
\n
\n
\n Describe the relationship between rock phosphate production and world population.\n
\n
\n
\n
\n
\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
\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",
+ "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
\n (a)\n
\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
\n (b)\n
\n
\n leaching/soil erosion, run-off/removed by the harvesting of agricultural crops ✔\n
\n
\n
\n (c)\n
\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 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
\n (a)\n
\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
\n (b)\n
\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
\n (c)\n
\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",
+ "topics": [
+ "c-interaction-and-interdependence",
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "c4-1-13-resource-competition-between-endemic-and-invasive-species",
+ "c4-1-populations-and-communities",
+ "d4-2-2-requirements-for-stability-in-ecosystems",
+ "d4-2-6-assessing-sustainability-of-resource-harvesting-from-natural-ecosystems",
+ "d4-2-stability-and-change"
+ ]
+ },
+ {
+ "question_id": "19M.2.SL.TZ1.16",
+ "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
\n
\n (a.ii)\n
\n
\n
\n Suggest reasons for the differences in predation.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a.i)\n
\n
\n predation was greater in those born in captivity ✔\n
\n
\n
\n (a.ii)\n
\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 (a.i)\n
\n
\n This question was generally well answered.\n
\n
\n
\n (a.ii)\n
\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",
+ "topics": [
+ "b-form-and-function"
+ ],
+ "subtopics": [
+ "b4-2-10-adaptations-of-predators-for-finding-catching-and-killing-prey-and-of-prey-animals-for-resisting-predation",
+ "b4-2-ecological-niches"
+ ]
+ },
+ {
+ "question_id": "19M.2.SL.TZ1.17",
+ "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
\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
\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",
+ "Markscheme": "
\n (a.i)\n
\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
\n (a.ii)\n
\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
\n (b)\n
\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 (a.i)\n
\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
\n (a.ii)\n
\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
\n (b)\n
\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",
+ "topics": [
+ "b-form-and-function"
+ ],
+ "subtopics": [
+ "b4-2-1-ecological-niche-as-the-role-of-a-species-in-an-ecosystem",
+ "b4-2-13-competitive-exclusion-and-the-uniqueness-of-ecological-niches",
+ "b4-2-ecological-niches"
+ ]
+ },
+ {
+ "question_id": "19M.2.SL.TZ1.2",
+ "Question": "
\n
Identify which electron micrograph shows a mitochondrion, providing one observation to support your choice.
\n

\n
[1]
\n
a.
\n
\n
Discuss the evidence for the theory that mitochondria may have evolved from free-living prokaryotes by endosymbiosis.
\n
[3]
\n
b.
\n
",
+ "Markscheme": "
\n
«micrograph» C cristae/double membrane is visible/«folds of» membranes inside ✔
\n
Must state observation
\n
a.
\n
\n
a. «double» membrane may have formed when engulfed ✔
\n
b. replicate by binary fission like free-living prokaryotes
OR
reproduce separate from «host» cell replication ✔
\n
c. they have their own «circular» DNA AND reproduce on their own ✔
\n
d. they have «70s» ribosomes AND can manufacture «their own» proteins ✔
\n
e. have organelle«s» similar to free-living prokaryotes ✔
\n
f. similar in size to free-living prokaryotes ✔
\n
g. mitochondrial inner membranes manufacture ATP like bacterial membranes ✔
\n
h. currently there is no free-living prokaryote like a mitochondrion ✔
\n
b.
\n
",
+ "Examiners report": "
\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
a.
\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
b.
\n
",
+ "topics": [
+ "a-unity-and-diversity",
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "a2-2-10-cell-types-and-cell-structures-viewed-in-light-and-electron-micrographs",
+ "a2-2-12-origin-of-eukaryotic-cells-by-endosymbiosis",
+ "a2-2-5-prokaryote-cell-structure",
+ "a2-2-6-eukaryote-cell-structure",
+ "a2-2-cell-structure",
+ "a3-1-7-karyotyping-and-karyograms",
+ "a3-1-diversity-of-organisms",
+ "d2-1-9-meiosis-as-a-reduction-division",
+ "d2-1-cell-and-nuclear-division"
+ ]
+ },
+ {
+ "question_id": "19M.2.SL.TZ1.3",
+ "Question": "
\n
The diagram shows the human heart.
\n

\n
\n
On the diagram, label the aorta.
\n
[1]
\n
a.i.
\n
\n
On the diagram, label the right atrium.
\n
[1]
\n
a.ii.
\n
\n
Explain how valves control the flow of blood through the heart.
\n
[2]
\n
b.
\n
\n
Outline the causes and consequences of blood clot formation in coronary arteries.
\n
[2]
\n
c.
\n
\n
Outline the role of lymphocytes in defence against disease.
\n
[2]
\n
d.
\n
",
+ "Markscheme": "
\n
both labelled clearly as in diagram ✔
\n

\n
[Source: BlueRingMedia/Shutterstock]
\n
a.i.
\n
\n
both labelled clearly as in diagram ✔
\n

\n
[Source: BlueRingMedia/Shutterstock]
\n
a.ii.
\n
\n
a. valves open and close in response to changes in blood pressure/heart contraction/pumping ✔
\n
b. valve prevents backflow/maintains direction of blood flow ✔
\n
c. valves allow heart chambers to fill/to empty ✔
\n
b.
\n
\n
a. coronary heart disease/CHD/coronary artery disease/CAD occurs when there is reduction of oxygen to the heart muscle ✔
\n
b. high ratio of LDL to HDL/fatty diet leads to plaque formation in arteries ✔
\n
c. plaque breaks off causing damage that activates blood clot formation ✔
\n
d. clots «in the bloodstream» may block a coronary artery/coronary thrombosis reducing blood flow/oxygen
OR
clots can cause heart attack/muscle death ✔
\n
e. sickle cell anemia «crisis» produces blood clots «that can cause coronary/arterial blockage» ✔
\n
c.
\n
\n
a. produce antibodies ✔
\n
b. memory cells confer immunity ✔
\n
c. specific immunity results from production of antibodies specific to a particular antigen ✔
\n
d. recognize pathogens ✔
\n
e. destroy foreign cells/cancer cells ✔
\n
d.
\n
",
+ "Examiners report": "
\n
Labelling the heart was generally ok, though the rest of this question was weakly answered.
\n
a.i.
\n
\n
Labelling the heart was generally ok, though the rest of this question was weakly answered.
\n
a.ii.
\n
\n
Most candidates knew that heart valves prevent backflow of blood but that was all. There were a variety of misconceptions such as that valves pump blood or that the SA node sends signals to the valves to make them open/close.
\n
b.
\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
c.
\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
d.
\n
",
+ "topics": [
+ "b-form-and-function",
+ "c-interaction-and-interdependence"
+ ],
+ "subtopics": [
+ "b3-2-15-adaptations-of-the-mammalian-heart-for-delivering-pressurized-blood-to-the-arteries",
+ "b3-2-transport",
+ "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",
+ "c3-2-defence-against-disease"
+ ]
+ },
+ {
+ "question_id": "19M.2.SL.TZ1.4",
+ "Question": "
\n
The diagram shows the structure of an alveolus and an adjacent capillary.
\n

\n
[Source: © International Baccalaureate Organization 2019]
\n
\n
Outline the functions of type I and type II pneumocytes.
\n
[2]
\n
a.
\n
\n
Explain how gases are exchanged between the air in the alveolus and the blood in the capillaries.
\n
[3]
\n
b.
\n
",
+ "Markscheme": "
\n
type I:
\n
a. carry out gas exchange
OR
diffusion of gases/CO2/O2 ✔
\n
type II:
\n
b. secrete fluid/surfactant ✔
\n
a.
\n
\n
a. O2 concentration in alveolar air greater than in capillary/blood «prior to gas exchange»
OR
hemoglobin in blood binds oxygen maintaining the concentration gradient ✔
\n
b. O2 gas dissolves in water lining the alveolus ✔
\n
c. O2 diffuses through wall of alveolus and capillary into blood ✔
\n
d. CO2 concentration in blood greater than in alveolar air «prior to gas exchange» ✔
\n
e. CO2 diffuses through wall of capillary and alveolus into alveolar airspace ✔
\n
b.
\n
",
+ "Examiners report": "
\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
a.
\n
\n
The command term was “explain”. Only a few candidates actually explained the process. Candidates gave very general responses without reference to diffusion or the correct concentration gradients. Very often diffusion was referred to in general for gas exchange and it was not linked to concentration gradients. Some students got max 2 for correct references to diffusion with reference to both gases. Students getting max 3 were able to include references to correct concentration gradients as well.
\n
b.
\n
",
+ "topics": [
+ "a-unity-and-diversity",
+ "b-form-and-function"
+ ],
+ "subtopics": [
+ "a1-1-3-cohesion-of-water-molecules-due-to-hydrogen-bonding-and-consequences-for-organisms",
+ "a1-1-water",
+ "b1-1-6-structure-of-cellulose-related-to-its-function-as-a-structural-polysaccharide-in-plants",
+ "b1-1-carbohydrates-and-lipids",
+ "b2-3-8-adaptations-of-type-i-and-type-ii-pneumocytes-in-alveoli",
+ "b2-3-cell-specialization",
+ "b3-1-4-adaptations-of-mammalian-lungs-for-gas-exchange",
+ "b3-1-gas-exchange",
+ "b3-2-7-transport-of-water-from-roots-to-leaves-during-transpiration",
+ "b3-2-transport"
+ ]
+ },
+ {
+ "question_id": "19M.2.SL.TZ1.5",
+ "Question": "
\n
The table gives common names and binomial names for some mammals.
\n

\n
\n
State one feature that characterizes these species as mammals.
\n
[1]
\n
a.
\n
\n
Identify the two species most closely related.
\n
1.
\n
2.
\n
\n
[1]
\n
b.
\n
\n
Identify two species from the list that are classified in different genera.
\n
1.
\n
2.
\n
\n
[1]
\n
c.
\n
",
+ "Markscheme": "
\n
fur/hair/mammary glands/feed young with milk/three inner-ear bones/lungs ventilated by diaphragm/lungs contain alveoli ✔
\n
a.
\n
\n
Canis aureus/golden jackal AND Canis lupus/grey wolf ✔
\n
Both needed
\n
b.
\n
\n
Hapalemur aureus/Golden bamboo lemur AND Canis aureus/golden jackel/Canis lupus/grey wolf/Vulpes vulpes/red fox
OR
Vulpes vulpes/red fox AND Canis aureus/golden jackal/Canis lupus/grey wolf/Hapalemur aureus/golden bamboo lemur ✔
\n
c.
\n
",
+ "Examiners report": "
\n
The most common correct answers were having fur/hair or providing milk. Warm-blood or live birth were often given but were not accepted as other classes of animals exhibit these characteristics.
\n
a.
\n
\n
Well done but some thought the species aureus meant they were similar rather than choosing the genus name.
\n
b.
\n
",
+ "topics": [
+ "b-form-and-function",
+ "c-interaction-and-interdependence"
+ ],
+ "subtopics": [
+ "b2-1-10-fluid-mosaic-model-of-membrane-structure",
+ "b2-1-membranes-and-membrane-transport",
+ "c2-1-6-differences-between-transmembrane-receptors-in-a-plasma-membrane-and-intracellular-receptors-in-the-cytoplasm-or-nucleus",
+ "c2-1-chemical-signalling-[hl-only]",
+ "c3-1-16-control-of-peristalsis-in-the-digestive-system-by-the-central-nervous-system-and-enteric-nervous-system",
+ "c3-1-integration-of-body-systems"
+ ]
+ },
+ {
+ "question_id": "19M.2.SL.TZ1.6",
+ "Question": "
\n
The image shows the chromosomes from a body cell of an adult human.
\n

\n
[Source: http://www.ornl.gov/sci/techresources/Human_Genome/graphics/slides/elsikaryotype.shtml,
U.S. Department of Energy Human Genome Program.]
\n
\n
Identify, with a reason, the sex of this individual.
\n
\n
[1]
\n
a.
\n
\n
Identify the chromosome that is affected by a trisomy in this individual, naming the condition that this trisomy gives rise to.
\n
Chromosome number:
\n
Name of condition:
\n
[1]
\n
b.
\n
",
+ "Markscheme": "
\n
male because Y chromosome present
OR
male because sex chromosomes/last two chromosomes/pair 23 are unpaired/different «from each other»/not homologous ✔
\n
a.
\n
\n
21 AND Down syndrome/trisomy 21 ✔
\n
Both needed
\n
b.
\n
",
+ "Examiners report": "
\n
Candidates knew this!
\n
a.
\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
b.
\n
",
+ "topics": [
+ "a-unity-and-diversity",
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "a3-1-7-karyotyping-and-karyograms",
+ "a3-1-diversity-of-organisms",
+ "d2-1-10-down-syndrome-and-non-disjunction",
+ "d2-1-cell-and-nuclear-division"
+ ]
+ },
+ {
+ "question_id": "19M.2.SL.TZ1.7",
+ "Question": "
\n
Outline the stages in the production of mRNA by transcription.
\n
[4]
\n
a.
\n
\n
Describe the functions of proteins in cell membranes.
\n
[4]
\n
b.
\n
\n
Explain how natural selection can lead to speciation.
\n
[7]
\n
c.
\n
",
+ "Markscheme": "
\n
a. DNA is unwound/strands are separated «by RNA polymerase» ✔
\n
b. new nucleotides attached to template strand «by RNA polymerase» ✔
\n
c. complementary base pairing/base pairing with an example
OR
adenine with thymine/uracil with adenine/cytosine with guanine/guanine with cytosine ✔
\n
d. mRNA detaches from template ✔
\n
e. DNA rewinds ✔
\n
a.
\n
\n
a. facilitated diffusion by channel proteins ✔
\n
b. active transport by protein pumps
OR
protein pumps eg sodium-potassium ✔
\n
c. cell recognition by glycoproteins/protein receptors ✔
\n
d. communication/receptors for hormones/signal molecules ✔
\n
e. cell adhesion ✔
\n
f. allow up to one additional mark for AHL material ✔
\n
b.
\n
\n
a. natural selection is caused by selection pressures in the environment
OR
example of a selection pressure ✔
\n
b. natural selection requires that variation exists within a species ✔
\n
c. variation arises randomly due to mutation
OR
variation is enhanced by meiosis/sexual reproduction ✔
\n
d. over-production of offspring promotes selection
OR
natural selection occurs when there is competition/overpopulation/predators/environmental changes/changes in selection pressures ✔
\n
e. well adapted individuals/individuals with best variations survive to reproduce/survival of fittest ✔
\n
f. «frequency of» genes/alleles conferring an advantage are selected for
OR
genes/alleles conferring a disadvantage are selected against ✔
\n
g. genetic divergence/difference increases
OR
natural selection «genetically» isolates members of a species so eventually they can no longer produce fertile offspring ✔
\n
h. genetic divergence» leads to reproductive isolation ✔
\n
i. geographical/behavioural/ecological factors may lead to «reproductive» isolation ✔
\n
j. prolonged «reproductive» isolation leads to speciation ✔
\n
k. up to one additional mark for AHL information ✔
\n
c.
\n
",
+ "Examiners report": "
\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
a.
\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
b.
\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
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
c.
\n
",
+ "topics": [
+ "a-unity-and-diversity",
+ "b-form-and-function",
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "a4-1-6-speciation-by-splitting-of-pre-existing-species",
+ "a4-1-evolution-and-speciation",
+ "b2-1-4-integral-and-peripheral-proteins-in-membranes",
+ "b2-1-membranes-and-membrane-transport",
+ "d1-1-3-role-of-helicase-and-dna-polymerase-in-dna-replication",
+ "d1-1-dna-replication",
+ "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",
+ "d1-2-protein-synthesis"
+ ]
+ },
+ {
+ "question_id": "19M.2.SL.TZ1.8",
+ "Question": "
\n
Describe how detritivores obtain nutrition and the effects they have in ecosystems.
\n
[4]
\n
a.
\n
\n
Outline the role of amylase in digestion in humans.
\n
[4]
\n
b.
\n
\n
Explain how plants capture and use light in photosynthesis.
\n
[7]
\n
c.
\n
",
+ "Markscheme": "
\n
a. «detritivores» obtain nutrition from detritus/waste/dead bodies ✔
\n
b. are heterotrophic ✔
\n
c. removes large waste/cleans up the ecosystem
OR
helps control spread of disease ✔
\n
d. facilitates further decomposition ✔
\n
e. contribute to the supply of «inorganic» nutrients for autotrophs/nutrient cycling
OR
improve soil conditions/aeration ✔
\n
a.
\n
\n
a. amylase is an enzyme ✔
\n
b. secreted by salivary glands/pancreas ✔
\n
c. active/released into the mouth/small intestine ✔
\n
d. acts on starch/polysaccharides ✔
\n
e. breaks «glycosidic» bond by hydrolysis/adding water ✔
\n
f. converts insoluble/large molecule to soluble/small molecules ✔
\n
g. product is maltose/disaccharide/sugar molecule ✔
\n
b.
\n
\n
a. plants convert light energy into chemical energy by photosynthesis ✔
\n
b. photosynthesis takes place in chloroplasts ✔
\n
c. chloroplasts «are organelles that» contain the pigment chlorophyll ✔
\n
d. chloroplasts/chlorophyll «in plants» absorb sunlight ✔
\n
e. «chlorophyll» absorbs red AND blue light most effectively ✔
\n
f. light causes photolysis/splits water molecule ✔
\n
g. carbon dioxide AND water are reactants «in photosynthesis» ✔
\n
h. glucose AND oxygen are products «of photosynthesis» ✔
\n
i. light intensity is a limiting factor for the rate of photosynthesis ✔
\n
j. organic/carbon compounds/glucose provide food/stored energy «for plant itself, animals,food chains» ✔
\n
k. up to one additional mark for an accurate detail from AHL ✔
\n
c.
\n
",
+ "Examiners report": "
\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
a.
\n
\n
The name, location and correct function of the enzyme was very common making 3 max the most common marks. Students who got fewer marks gave generic explanations of the process of digestion. Some students made incorrect references to amylase digesting proteins. A few candidates ignored amylase and discussed digestion in general.
\n
b.
\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
c.
\n
",
+ "topics": [
+ "c-interaction-and-interdependence"
+ ],
+ "subtopics": [
+ "c1-3-5-absorption-of-specific-wavelengths-of-light-by-photosynthetic-pigments",
+ "c1-3-photosynthesis"
+ ]
+ },
+ {
+ "question_id": "19M.2.SL.TZ2.1",
+ "Question": "
\n
Mice (Mus musculus) have various defence systems against predators such as foxes (Vulpus vulpus) or stoats (Mustela erminea). The mice release specific alarm compounds when under threat that serve as danger signals for other mice. Predators also release scents that the mice can detect.
\n
In one study, mice were exposed to paper soaked in compounds taken from other mice, foxes or stoats in a test chamber. The scientists then measured the reaction of three different groups of neurons used in smelling: G1, G2 and G3, as shown in the diagram.
\n

\n
The percentage of G1, G2 and G3 neurons responding to the mouse, fox and stoat compounds, as well as a control compound, are shown in the chart.
\n

\n
Percentage of response of neurons in mice
\n
[Source: Julien Brechbühl, et al., (2013), PNAS, 110 (12), pages 4762–4767]
\n
\n
The scientists recorded the neural traces (action and resting potentials) of six G1 neurons exposed to the compounds from the different animals. The horizontal bar beneath each trace corresponds to the time of exposure to the test compound.
\n

\n
[Source: adapted from J Brechbühl, et al., (2013), PNAS, 110 (12), pages 4762–4767]
\n
\n
Another study was carried out on the defence systems in aphids (Myzus persicae) which feed on thale cress plants (Arabidopsis thaliana). Individual aphids release an alarm compound containing the chemical (E)-β-farnesene (EBF) when attacked by a predator. Other aphids are repelled and leave the thale cress plant or hide.
\n
The gene for EBF was inserted to produce transgenic (T) thale cress plants to test aphid reaction to EBF over several generations. Aphids were raised on wild type (W) thale cress and then allowed to feed for three generations on either W or T thale cress. Aphids were tested in each generation for their reaction when EBF was added to a choice chamber. The percentages of aphids attracted to or repelled by EBF and those which made no choice were recorded.
\n

\n
[Source: M De Vos, et al., (2010), PNAS, 107 (33), pages 14673–14678]
\n
\n
State the percentage of G2 neurons in the mice that respond to the fox scent.
\n
. . . . . . . . . . . . . . . . . . . .%
\n
[1]
\n
a.
\n
\n
Using evidence from the chart, identify, giving a reason, which group of neurons responded most to the chemicals.
\n
[1]
\n
b.
\n
\n
State the name of the instrument used to make these traces.
\n
[1]
\n
c.
\n
\n
Distinguish between the effects of the mouse alarm compound and the effects of the control compound on the G1 neurons.
\n
[1]
\n
d.
\n
\n
Compare and contrast the effects of the mouse alarm compound and stoat scent on the G1 neurons.
\n
[2]
\n
e.
\n
\n
Deduce whether there is a correlation between the neural traces and the percentage of responding G1 neurons.
\n
[2]
\n
f.
\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
[1]
\n
g.
\n
\n
Identify, with a reason, the aphids that were most strongly repelled by EBF.
\n
[1]
\n
h.
\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
[2]
\n
i.
\n
\n
Discuss whether natural selection would favour the transgenic EBF-producing thale cress plants if they were released into the wild.
\n
[2]
\n
j.
\n
",
+ "Markscheme": "
\n
G1 always respond more than 25% «except control», while G2 and G3 always respond 25% or less ✔
\n
G1 always responds more than G2 and G3/all of the others ✔
\n
OWTTE
\n
b.
\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
OWTTE
\n
d.
\n
\n
a. both chemicals cause action potentials
OR
both chemicals respond in the majority of/five/most neurons ✔
\n
b. stoat scent causes a higher action potential/longer/bigger response than mouse alarm compound «in each neuron»
OR
neuron 2 reacts strongly to the stoat scent but has a minimal/no response to the mouse alarm compound ✔
\n
e.
\n
\n
a. there is a positive relationship/correlation between the size of neural traces and the percentage of responding G1 neurons Accept vice versa
OR
the chemicals that cause stronger/higher neural traces also cause the greatest percentage of responding G1 neurons ✔
\n
b. fox and stoat scents have «approximately» the same/similar neural traces and the same percentage of responding neurons/>75 % ✔
\n
c. mouse alarm compounds cause smaller neural traces and smaller percentage of responding neurons/25–75 % ✔
\n
d. control chemicals have no response in both cases
OR
no percentage of «G1 neurons» response and no action potential «in neural traces» ✔
\n
f.
\n
\n
the mice would have the same response to another mouse’s danger signal as to the actual presence of the predator/fox
OR
adaptation to fool predator by producing a scent similar to predator’s own scent
OR
allows a group response to a predator/fox/danger when just one mouse detects the danger ✔
\n
Accept any other feasible answer.
\n
g.
\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
OR
the aphids that fed on wild-type thale cress plants/W of G3 as they had «about» 85 % repelled/had the higher % response ✔
\n
Answer should refer to a percentage.
\n
h.
\n
\n
a. «over the generations» fewer are repelled by EBF ✔
\n
b. «over the generations» more are attracted to EBF ✔
\n
c. by G3 a «slight» increase in no choice ✔
\n
d. aphids respond less to EBF/alarm compound if they feed on plants that produce it/exposed to it constantly ✔
\n
e. mutant aphids with attraction to transgenic plants can arise from aphids with no attraction or repulsion to transgenic plants
OR
aphids with no attraction or repulsion to transgenic plants may produce new type of aphids with attraction to transgenic plants ✔
\n
i.
\n
\n
a. mutant aphids/varieties may be indifferent to/attracted to transgenic plants as these do not present a hazard «not favour» ✔
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
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
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
The answers must indicate whether natural selection would support or not for each statement.
\n
j.
\n
",
+ "Examiners report": "
\n
Nearly all were able to state the answer of 10-25%.
\n
a.
\n
\n
many lost the mark by not stating the reason that the G1 responses were higher than the others (G2 and G3)
\n
b.
\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
c.
\n
\n
Many missed the mark in d as they did not state that the control remained at zero.
\n
d.
\n
\n
Answers to e were encouraging as most were able to give both the similarity and the difference.
\n
e.
\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
f.
\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
g.
\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
h.
\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
i.
\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
j.
\n
",
+ "topics": [
+ "c-interaction-and-interdependence",
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "c2-2-neural-signalling",
+ "d1-1-5-applications-of-polymerase-chain-reaction-and-gel-electrophoresis",
+ "d1-1-dna-replication",
+ "d3-1-9-features-of-an-insect-pollinated-flower",
+ "d3-1-reproduction",
+ "d4-1-1-natural-selection-as-the-mechanism-driving-evolutionary-change",
+ "d4-1-natural-selection"
+ ]
+ },
+ {
+ "question_id": "19M.2.SL.TZ2.16",
+ "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
\n
\n (b)\n
\n
\n
\n Outline the effect of carrying capacity on the growth of a population.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\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
\n (b)\n
\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 (a)\n
\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
\n (b)\n
\n
\n Most candidates had an idea about carrying capacity, but there was only one element in the outline of many.\n
\n
\n",
+ "topics": [
+ "c-interaction-and-interdependence"
+ ],
+ "subtopics": [
+ "c4-1-5-carrying-capacity-and-competition-for-limited-resources",
+ "c4-1-7-population-growth-curves",
+ "c4-1-8-modelling-of-the-sigmoid-population-growth-curve",
+ "c4-1-populations-and-communities"
+ ]
+ },
+ {
+ "question_id": "19M.2.SL.TZ2.2",
+ "Question": "
\n
Identify the stage of mitosis labelled X in the image, giving a reason.
\n

\n
[Source: Copyright 2002, The Trustees of Indiana University]
\n
[1]
\n
a.
\n
\n
Outline the use of a karyogram during pregnancy.
\n
[3]
\n
b.
\n
",
+ "Markscheme": "
\n
telophase because the chromosomes/chromatids have reached the poles
OR
«late» anaphase as some chromosomes/chromatids are still moving/tails visible ✔
\n
OWTTE
\n
a.
\n
\n
a. is a photograph/diagram of homologous pairs of chromosomes that can be analysed ✔
b. information may be used to determine other chromosome abnormalities/changes in chromosome numbers/possible birth defects ✔
\n
c. Down syndrome/trisomy can be detected if there are three copies of a chromosome Not just “Down syndrome”.
OR
accept any other valid example ✔
\n
d. other missing or extra pieces of chromosomes can be detected ✔
\n
e. sex can be determined as the Y chromosome is shorter than the X ✔ Or correct ref to X and Y.
\n
b.
\n
",
+ "Examiners report": "
\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
a.
\n
\n
Most knew what a karyogram was. However, the question was about use, which does not involve a detailed description, taking up half the space about how the sample was obtained and the risks involved. Most knew that it was to do with the chromosomes, few stated that it was a diagram or a picture of the homologous pairs. An explanation of how it is used to confirm sex was needed.
\n
b.
\n
",
+ "topics": [
+ "a-unity-and-diversity",
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "a1-2-4-bases-in-each-nucleic-acid-that-form-the-basis-of-a-code",
+ "a1-2-nucleic-acids",
+ "d2-1-17-differences-between-tumours-in-rates-of-cell-division-and-growth-and-in-the-capacity-for-metastasis-and-invasion-of-neighbouring-tissue",
+ "d2-1-8-identification-of-phases-of-mitosis",
+ "d2-1-cell-and-nuclear-division"
+ ]
+ },
+ {
+ "question_id": "19M.2.SL.TZ2.3",
+ "Question": "
\n
State two causes of the decrease of biomass along food chains in terrestrial ecosystems.
\n
[2]
\n
a.i.
\n
\n
The table shows the global carbon budget over two decades; the years 1990 to 1999 and 2000 to 2009.
\n

\n
[Source: © International Baccalaureate Organization 2019]
\n
\n
Using the table, explain causes of the changes in carbon flux over the two decades.
\n
[3]
\n
a.ii.
\n
\n
Suggest how climate change can influence the natural selection of organisms that live in the Arctic oceans.
\n
[3]
\n
b.
\n
",
+ "Markscheme": "
\n
a. «cell» respiration/loss of CO2/biomass consumed to provide/as a source of energy ✔
\n
b. loss of energy «as heat» between trophic levels means less energy available for building biomass ✔
\n
c. waste products «other than CO2»/loss of urea/feces/egesta ✔
\n
d. material used/CO2 released by saprotrophs ✔
\n
e. undigested/uneaten material «teeth, bones, etc»/detritus buried/not consumed
OR
formation of peat/fossils/limestone ✔
\n
a.i.
\n
\n
a. increased CO2 flux to the atmosphere due to increased burning of fossil fuels by industry/transportation / cement production ✔
\n
b. «land use change leading to» decreased rate of forest burning
OR
better fire suppression leading to decrease in CO2 release
OR
example of land use changes that uses less fossil fuel
OR
increase in land covered by forests/plants / forests recovering from historical forestry
OR
any other reasonable explanation of land use change that would lead to decreased rate of carbon flow to atmosphere ✔
\n
c. carbon storage in land decreased as less photosynthesis due to fewer forests/more construction
OR
release of methane due to «drying of» wetlands/sealing of land with concrete/buildings/roads ✔
\n
d. carbon storage in ocean increased due to more photosynthesis/algae/greater concentration of CO2 in the atmosphere
OR
increased diffusion/rate of dissolving of CO2 into ocean from the atmosphere
OR
limestone/carbonate accumulation «more snails» ✔
\n
a.ii.
\n
\n
a. individuals in a population will show a variation of adaptations to climate change ✔
b. organisms that resist temperature changes
OR
current changes of the ocean/melting ice/more acidity/changes in food chains will survive better ✔
\n
c. reproduce more and pass on their characteristics ✔
\n
d. organisms with less adaptation will disappear with time ✔
\n
e. example «eg 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» OWTTE ✔
\n
f. changes will occur within species
OR
new species may appear «over time» ✔
\n
Accept any valid example of an Arctic ocean organism.
\n
b.
\n
",
+ "Examiners report": "
\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 CO2 is lost from the food chain during respiration, or that urea has mass etc.
\n
a.i.
\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
a.ii.
\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
b.
\n
",
+ "topics": [
+ "c-interaction-and-interdependence",
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "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",
+ "c4-2-19-release-of-carbon-dioxide-into-the-atmosphere-during-combustion-of-biomass-peat-coal-oil-and-natural-gas",
+ "c4-2-transfers-of-energy-and-matter",
+ "d3-1-5-changes-during-the-ovarian-and-uterine-cycles-and-their-hormonal-regulation",
+ "d3-1-reproduction",
+ "d4-3-12-evolution-as-a-consequence-of-climate-change",
+ "d4-3-climate-change"
+ ]
+ },
+ {
+ "question_id": "19M.2.SL.TZ2.4",
+ "Question": "
\n
The images show parts of plants belonging to two different phyla.
\n

\n
State the phylum of plant X and of plant Y.
\n
X:
\n
Y:
\n
\n
[2]
\n
a.
\n
\n
Explain one cause of mutation.
\n
\n
[2]
\n
b.
\n
\n
Outline the types of evidence that can be used to place a species in a particular clade.
\n
[3]
\n
c.
\n
\n
The cladogram includes four marsupial (non-placental mammal) families.
\n

\n
[Source: Koala image: Quartl, https://commons.wikimedia.org/wiki/Phascolarctos_cinereus#/media/
File:Friendly_Female_Koala.JPG; Wombat image: JJ Harrison, https://en.wikipedia.org/wiki/Wombat#/
media/File:Vombatus_ursinus_-Maria_Island_National_Park.jpg; Marsupial lion: Nobu Tamura,
https://en.wikipedia.org/wiki/Marsupial_lion#/media/File:Thylacoleo_BW.jpg;
Diprotodontoidea image: Anne Musser]
\n
\n
Deduce the family that is most closely related to the Diprotodontoidea.
\n
[1]
\n
d.
\n
",
+ "Markscheme": "
\n
X: Filicinophyta ✔
\n
Y: Coniferophyta/Conifera/Gymnosperms ✔
\n
a.
\n
\n

\n
Not chromosomal.
\n
b.
\n
\n
a. a clade is a group of organisms that have evolved from a common ancestor ✔
\n
b. identify the base sequences of a gene ✔
\n
c. identify amino acid sequence of a protein ✔
\n
d. comparing homologous structures ✔
\n
e. the fewer the differences, the closer they diverged in time from a common ancestor ✔ Accept vice versa.
\n
c.
\n
\n
Vombatidae/wombats ✔
\n
d.
\n
",
+ "Examiners report": "
\n
Those who had been taught it could identify the filicinophyte and the coniferophyte, albeit with a variety of spellings.
\n
a.
\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
b.
\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
c.
\n
\n
Nearly everyone spotted the wombat correctly.
\n
d.
\n
",
+ "topics": [
+ "a-unity-and-diversity",
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "a3-2-4-clades-as-groups-of-organisms-with-common-ancestry-and-shared-characteristics",
+ "a3-2-7-analysing-cladograms",
+ "a3-2-classification-and-cladistics-(hl-only)",
+ "d1-3-4-causes-of-gene-mutation",
+ "d1-3-mutations-and-gene-editing",
+ "d3-1-12-dispersal-and-germination-of-seeds",
+ "d3-1-8-sexual-reproduction-in-flowering-plants",
+ "d3-1-reproduction"
+ ]
+ },
+ {
+ "question_id": "19M.2.SL.TZ2.5",
+ "Question": "
\n
Outline four types of membrane transport, including their use of energy.
\n
[4]
\n
a.
\n
\n
Draw the structure of a dipeptide.
\n
[3]
\n
b.
\n
\n
Explain the action of enzymes in digestion and the different roles of at least two named enzymes that are produced in the pancreas.
\n
[8]
\n
c.
\n
",
+ "Markscheme": "
\n
a. simple diffusion is passive movement of molecules/ions along a concentration gradient ✔
\n
b. facilitated diffusion is passive movement of molecules/ions along a concentration gradient through a protein channel «without use of energy» ✔
\n
c. osmosis is the passage of water through a membrane from lower solute concentration to higher ✔ OWTTE
\n
d. active transport is movement of molecules/ions against the concentration gradient«through membrane pumps» with the use of ATP/energy ✔ Active transport requires mention of the use of energy.
\n
e. endocytosis is the infolding of membrane/formation of vesicles to bring molecules into cell with use of energy
OR
exocytosis is the infolding of membrane/formation of vesicles to release molecules from cell with use of energy ✔
\n
f. chemiosmosis occurs when protons diffuse through ATP synthase «in membrane» to produce ATP ✔
\n
The description of each type of transport should include the name and brief description.
\n
mpa, mpb and mpc require reference to concentration.
\n
\n
a.
\n
\n
a. two amino acids, one with NH2/NH3+end and one with COOH/COO– end ✔
\n
b. peptide bond between C=0 and N—H correctly drawn ✔
\n
c. «chiral» C with H and R group on each amino acid ✔
\n
d. peptide bond labelled/clearly indicated between C terminal of one amino acid and N terminal of the second amino acid ✔
\n

\n
Labels not required for amino group and carboxyl group.
\n
b.
\n
\n
a. enzymes catalyse/speed up chemical reactions/lower the energy needed ✔ OWTTE
\n
b. have specific active sites to which specific substrates bind ✔
\n
c. enzyme catalysis involves molecular motion and the collision of substrates with the active site ✔ OWTTE
\n
d. enzymes break macromolecules into monomers/smaller molecules indigestion ✔
\n
e. smaller molecules/monomers more readily absorbed ✔
\n
f. <<pancreas>> secretes enzymes into the «lumen of» small intestine ✔
\n
g. the small intestine has an alkaline pH ✔
\n
h. enzymes have maximum action at specific pHs
OR
enzymes can be denatured at other pHs ✔
\n
i. amylase breaks down starch into sugars/disaccharides ✔
\n
j. lipase breaks lipids/triglycerides into monoglycerides/fatty acids and glycerol ✔
\n
k. endopeptidase/protease breaks «peptide» bonds in proteins/polypeptides ✔
\n
l. accept any other valid pancreatic enzyme, substrate and product ✔
\n
Award [6 max] if there is no mention of two specific groups of enzymes.
\n
c.
\n
",
+ "Examiners report": "
\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
a.
\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
b.
\n
\n
Enzymes in digestion. A disturbing number of candidates saw the word pancreas and wrote about insulin and glucagon. These are hormones, produced by ENdocrine glands not enzymes produced by EXocrine glands. Better candidates scored nearly full marks, by describing enzyme action and correctly describing the three main enzymes from the pancreas. Weaker candidates could not string the correct sequence together and scored very few marks. Better candidates wrote some sort of plan before starting, using the space below the instructions for Section B. This should be encouraged.
\n
c.
\n
",
+ "topics": [
+ "b-form-and-function"
+ ],
+ "subtopics": [
+ "b1-2-2-condensation-reactions-forming-dipeptides-and-longer-chains-of-amino-acids",
+ "b1-2-proteins",
+ "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",
+ "b2-1-membranes-and-membrane-transport"
+ ]
+ },
+ {
+ "question_id": "19M.2.SL.TZ2.6",
+ "Question": "
\n
Describe briefly the endosymbiotic theory.
\n
[3]
\n
a.
\n
\n
Outline how photosynthesis produces glucose.
\n
[4]
\n
b.
\n
\n
Discuss the control of blood glucose levels and the consequences if they are not maintained.
\n
[8]
\n
c.
\n
",
+ "Markscheme": "
\n
a. eukaryotes evolved from prokaryotes ✔
\n
b. prokaryotes engulfed other prokaryotes without digesting them ✔
\n
c. engulfed aerobic cell/prokaryote became mitochondria ✔
\n
d. engulfed photosynthetic cell/ prokaryotes became chloroplasts ✔
\n
e. these organelles have a double membrane «due to the engulfing process» ✔
\n
f. mitochondria/chloroplasts contain DNA/small ribosomes/70S ribosomes ✔
\n
a.
\n
\n
a. solar/light energy is converted to chemical energy ✔
\n
b. energy needed to produce glucose ✔
\n
c. only specific wavelengths are absorbed by chlorophyll
OR
red and blue absorbed most strongly.
OR
chlorophyll is the pigment that absorbs light energy ✔
d. H(+)/electrons from water are used to reduce compounds ✔
\n
e. CO2 is absorbed/used/reduced to produce carbohydrates ✔
\n
f. correct word/balanced symbol equation of photosynthesis ✔
\n
Accept correct reference to NADPH/ATP from AHL.
\n
b.
\n
\n
control: [6 max]
a. homeostasis is the maintenance of a constant internal environment ✔
\n
b. the pancreas produces hormones that control the levels of glucose ✔
\n
c. if glucose levels in blood are high, beta-cells «of the pancreas» produce insulin ✔
\n
d. «insulin» causes the cells to take up /absorb glucose ✔
\n
e. liver stores excess glucose as glycogen ✔
\n
f. if glucose levels in blood are low, alpha-cells «of the pancreas» produce glucagon ✔
\n
g. «glucagon» causes the liver to break down glycogen into glucose ✔
\n
h. «glucagon» increase levels of glucose in the blood ✔
\n
i. negative feedback controls the glucose levels ✔ OWTTE
\n
consequences:
\n
j. if the pancreas produces little/no insulin a person can develop type I diabetes ✔
\n
k. a person with type I diabetes «usually» needs/is dependent on injections of insulin ✔
\n
l. type II diabetes occurs when the body becomes resistant to insulin/cells do not respond to insulin ✔
\n
m. type II diabetes can «sometimes» be controlled by diet and exercise ✔
\n
n. named consequence of having diabetes «eg: eye damage» ✔
\n
Award [6 max] if no consequences are given.
\n
c.
\n
",
+ "Examiners report": "
\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
a.
\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
b.
\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
c.
\n
",
+ "topics": [
+ "a-unity-and-diversity",
+ "b-form-and-function",
+ "c-interaction-and-interdependence",
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "a2-2-12-origin-of-eukaryotic-cells-by-endosymbiosis",
+ "a2-2-cell-structure",
+ "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",
+ "b2-1-membranes-and-membrane-transport",
+ "c1-3-1-transformation-of-light-energy-to-chemical-energy-when-carbon-compounds-are-produced-in-photosynthesis",
+ "c1-3-photosynthesis",
+ "d3-3-3-regulation-of-blood-glucose-as-an-example-of-the-role-of-hormones-in-homeostasis",
+ "d3-3-homeostasis"
+ ]
+ },
+ {
+ "question_id": "19M.2.SL.TZ2.7",
+ "Question": "
\n
\n (a)\n
\n
\n
\n Distinguish between the structures of DNA and RNA.\n
\n
\n
\n
\n
\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
\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",
+ "Markscheme": "
\n (a)\n
\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
\n (b)\n
\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
\n (c)\n
\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 (a)\n
\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
\n (b)\n
\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
\n (c)\n
\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",
+ "topics": [
+ "a-unity-and-diversity",
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "a1-2-7-differences-between-dna-and-rna",
+ "a1-2-nucleic-acids",
+ "d1-3-2-consequences-of-base-substitutions",
+ "d1-3-mutations-and-gene-editing",
+ "d3-2-10-incomplete-dominance-and-codominance",
+ "d3-2-11-sex-determination-in-humans-and-inheritance-of-genes-on-sex-chromosomes",
+ "d3-2-9-abo-blood-groups-as-an-example-of-multiple-alleles",
+ "d3-2-inheritance"
+ ]
+ },
+ {
+ "question_id": "19M.2.SL.TZ2.8",
+ "Question": "
\n
\n (a)\n
\n
\n
\n Outline energy flow through a food chain.\n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n
\n Draw a fully labelled graph of the action spectrum for photosynthesis.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\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
\n (b)\n
\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 (a)\n
\n
\n Was well answered with most students being knowledgeable about ecology.\n
\n
\n
\n (b)\n
\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",
+ "topics": [
+ "c-interaction-and-interdependence"
+ ],
+ "subtopics": [
+ "c1-3-6-similarities-and-differences-of-absorption-and-action-spectra",
+ "c1-3-photosynthesis",
+ "c4-2-3-flow-of-chemical-energy-through-food-chains",
+ "c4-2-transfers-of-energy-and-matter"
+ ]
+ },
+ {
+ "question_id": "19N.3.SL.TZ0.1",
+ "Question": "
\n
An experiment was carried out on osmosis in carrot (Daucus carota) root tissue and potato (Solanum tuberosum) tuber tissue. Similar sized pieces of tissue were cut and soaked in different sucrose solutions for 24 hours. The results are shown in the graph below.
\n

\n
\n
Using the graph, estimate isotonic sucrose solutions for potato tissue and carrot tissue.
\n
Potato:
\n
Carrot:
\n
[2]
\n
a.
\n
\n
Suggest a reason for the difference in the isotonic points for the potato and the carrot tissues.
\n
[1]
\n
b.
\n
\n
From the evidence provided by the graph, evaluate the reliability of these data.
\n
[2]
\n
c.
\n
\n
Explain one reason for calculating the percentage change in mass.
\n
[2]
\n
d.
\n
",
+ "Markscheme": "
\n
potato: 0.26 mol dm–3 ✔ Allow a range of 0.22–0.32
carrot: 0.50 mol dm–3 ✔ Allow a range of 0.45–0.55 (Allow 1 max if no units or either unit is omitted)
\n
a.
\n
\n
different dissolved solutes/sugars/sucrose/salts/molarities ✔
OR
may have been grown in different soils giving their tissues different contents ✔
OR
may have been stored under different conditions ✔
OR
may be more dehydrated / different water content ✔
OR
different types of tissue / different age ✔
\n
Do not accept starch.
\n
b.
\n
\n
a. the data show clear trends
OR
a trend line could be drawn through these data
OR
there are no outliers ✔
\n
b. the error bars/standard deviations shown
OR
the error bars/standard deviations vary with concentration ✔
\n
c. sample size is unknown ✔
\n
c.
\n
\n
a. the change in mass indicates whether the tissue has gained/lost water ✔
\n
b. the pieces of tissue will not be the same mass «at the beginning of the experiment» ✔
\n
c. to compare the relative changes in mass ✔
\n
d.
\n
",
+ "Examiners report": "
",
+ "topics": [
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "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",
+ "d2-3-water-potential",
+ "d4-2-4-use-of-a-model-to-investigate-the-effect-of-variables-on-ecosystem-stability",
+ "d4-2-stability-and-change"
+ ]
+ },
+ {
+ "question_id": "19N.3.SL.TZ0.2",
+ "Question": "
\n
The enzyme beta-galactosidase hydrolyses lactose to release glucose and fructose. A study was carried out to determine how acidity affects the activity of a beta-galactosidase enzyme, extracted from the fungus Penicillium simplicissimum.
\n

\n
[Source: Cruz R, et al. Properties of a new fungal β-galactosidase with potential application in the dairy industry.
Revista de Microbiologia 30: 265–271, 1999]
\n
\n
State another independent variable that would affect the activity of this enzyme.
\n
[1]
\n
a.
\n
\n
Outline the measurements which would need to be taken to determine the activity of the beta-galactosidase at different pH values.
\n
[2]
\n
b.
\n
",
+ "Markscheme": "
\n
temperature
OR
lactose/substrate concentration
OR
Inhibitors / cofactors ✔
\n
Do not accept pH or acidity.
\n
a.
\n
\n
a. test samples for the concentration/amount of products/glucose/fructose/substrate/lactose ✔ Accept use Benedict/Fehling to see change in amount of reducing sugar
\n
b. take samples of the reaction mixture at regular/timed intervals ✔ Must indicate that samples are taken at timed intervals
\n
c. repeated measurements «at the different pH values» ✔
\n
d. measure independent/controlled/standardised/variables / temperature ✔
\n
b.
\n
",
+ "Examiners report": "
",
+ "topics": [
+ "b-form-and-function",
+ "c-interaction-and-interdependence"
+ ],
+ "subtopics": [
+ "b3-1-9-transpiration-as-a-consequence-of-gas-exchange-in-a-leaf",
+ "b3-1-gas-exchange",
+ "c1-1-8-effects-of-temperature-ph-and-substrate-concentration-on-the-rate-of-enzyme-activity",
+ "c1-1-enzymes-and-metabolism"
+ ]
+ },
+ {
+ "question_id": "19N.1B.SL.TZ0.3",
+ "Question": "
\n
\n (a)\n
\n
\n
\n Estimate the solute concentration of the zucchini cells.\n
\n
\n
\n
\n
\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
\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
\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",
+ "Markscheme": "
\n (a)\n
\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
\n (b)\n
\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
\n (c)\n
\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
\n (d)\n
\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",
+ "topics": [
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "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",
+ "d2-3-water-potential"
+ ]
+ },
+ {
+ "question_id": "19N.2.HL.TZ0.1",
+ "Question": "
\n
The black-legged tick (Ixodes scapularis) is an arthropod which sucks blood from humans and other mammals. It is encountered mainly in wooded and semi-wooded areas. Some ticks can be infected by the bacterium Borrelia burgdorferi. When a tick bites a human, the bacterium is often introduced, causing Lyme disease. Lyme disease is a public health problem in North America and, if left untreated, can cause important neurological impairment. The diagram represents the two-year life cycle of a tick.
\n

\n
[Source: Cary Institute of Ecosystem Studies / Leslie Tumblety]
\n
\n
Scientists fear that global warming will change the distribution range of ticks.
\n
The graphs show the developmental stages of ticks throughout seasons in a densely human-populated area of south-eastern Canada, surrounded by woods (circled on the map). Values are already established for 2000 and are predicted for 2080.
\n

\n
[Source: reprinted from International Journal for Parasitology, 36(1), N.H. Ogden, A. Maarouf, I.K. Barker, M. Bigras-Poulin,
L.R. Lindsay, M.G. Morshed, C.J. O’Callaghan, F. Ramay, D. Waltner-Toews, D.F. Charron, Climate change
and the potential for range expansion of the Lyme disease vector Ixodes scapularis in Canada,
63–70, Copyright (2006), with permission from Elsevier]
\n
\n
White-footed mice (Peromyscus leucopus) in eastern North America’s wooded areas often host B. burgdorferi bacteria. To determine whether bacterial transmission from mice to tick nymphs could be prevented, mice were vaccinated with antigens from Lyme disease-causing B. burgdorferi. Scientists captured wild mice at two different sites in the woods once a month, over 4 months. Each time, they measured the levels of antibodies to B. burgdorferi present in the captured and re-captured mice, inoculated all of them, and released them into the woods. The control group was not vaccinated with B. burgdorferi antigen.
\n

\n
[Source: Copyright (2004) National Academy of Sciences, U.S.A. An ecological approach to preventing human infection:
Vaccinating wild mouse reservoirs intervenes in the Lyme disease cycle, Jean I. Tsao, J. Timothy Wootton, Jonas Bunikis,
Maria Gabriela Luna, Durland Fish, Alan G. Barbour, Proceedings of the National Academy of Sciences
Dec 2004, 101 (52) 18159–18164; DOI: 10.1073/pnas.0405763102]
\n
\n
The summer after vaccination, the prevalence of B. burgdorferi infection in tick nymphs collected on mice from the two sites was measured.
\n

\n
[Source: Copyright (2004) National Academy of Sciences, U.S.A. An ecological approach to preventing human infection:
Vaccinating wild mouse reservoirs intervenes in the Lyme disease cycle, Jean I. Tsao, J. Timothy Wootton, Jonas Bunikis,
Maria Gabriela Luna, Durland Fish, Alan G. Barbour, Proceedings of the National Academy of Sciences
Dec 2004, 101 (52) 18159–18164; DOI: 10.1073/pnas.0405763102]
\n
\n
State the domain into which ticks are classified.
\n
[1]
\n
a.
\n
\n
Using information from the text, identify one possible simple treatment for Lyme disease.
\n
[1]
\n
b.
\n
\n
Identify the month when small birds had the greatest chance of being infected by B. burgdorferi bacteria in the year 2000 and the month when they would be most likely to become infected according to the 2080 predictions.
\n
2000:
\n
2080:
\n
[1]
\n
c.
\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
[2]
\n
d.
\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
[3]
\n
e.
\n
\n
State the reason for performing the experiment in the months of May to August.
\n
[1]
\n
f.i.
\n
\n
Suggest possible reasons for the observed pattern of presence of antibodies in vaccinated mice.
\n
[3]
\n
f.ii.
\n
\n
Analyse the data on the state of infection of tick nymphs with B. burgdorferi in control and vaccinated mice.
\n
[2]
\n
g.
\n
\n
Using all the data, discuss whether inoculating mice with the antigen to B. burgdorferi could be an effective method of controlling the spread of Lyme disease.
\n
[3]
\n
h.
\n
",
+ "Markscheme": "
\n
eukaryote ✔
\n
Accept eukaryotes.
\n
a.
\n
\n
antibiotics / named antibiotics ✔
\n
b.
\n
\n
«2000» August AND «2080» July ✔
\n
Both required.
\n
c.
\n
\n
a. adults present through autumn and winter «according to the life cycle diagram»
OR
some adults «must» survive winter «despite graph suggesting zero» ✔
\n
b. adults peak in October «& November»/in autumn/between September and December ✔
\n
c. adults die after laying eggs in winter/beginning of spring ✔
\n
d. smaller peak/10 % versus 55 % peak/smaller numbers of adults in April/spring ✔
\n
e. adults absent from June to September/summer ✔
\n
Each mark point, requires month or season.
Jan - Mar = winter
Apr - Jun = spring
Jul - Sep = summer
Oct - Dec = autumn = fall
\n
Do not accept that there are the lowest number or no adults in winter.
\n
d.
\n
\n
a. nymphs present through most of year/longer period/from March to November/through spring and summer «so more risk of infection» ✔
\n
b. more adults in winter/in January/February so more risk of infection then ✔
\n
c. infection will be possible through more/most months of/throughout the year ✔
\n
d. Lyme disease likely to/will increase ✔
\n
e.
\n
\n
because nymphs are present/numbers of nymphs rise «in these months»
OR
build up immunity/antibodies in mice before nymphs «peak» ✔
\n
Ignore references to larvae.
\n
f.i.
\n
\n
a. low antibody level initially as mice not previously exposed to antigen/bacteria ✔
\n
b. vaccination causes antibody production/development of immunity ✔
\n
c. increased proportion of mice have been vaccinated in each successive month ✔
\n
d. second vaccination/booster shot increases antibody level/speeds up antibody production ✔
\n
e. memory cells produced so greater/faster antibody production ✔
\n
f. many/rising numbers of nymphs which may spread the bacteria/antigens to mice ✔
\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
f.ii.
\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
b. at Site 2 the proportion of infected nymphs is lower in those collected from vaccinated than control mice
OR
at Site 2 «significantly» more nymphs are not infected from vaccinated than control mice ✔ For mpb and mpd, accept converse answers that give the proportions/percentages of uninfected nymphs rather than infected.
\n
c. at both sites there are fewer infected than uninfected nymphs in those collected from both vaccinated and control mice ✔
\n
d. proportion of infected nymphs is lower at Site 1 than Site 2 in nymphs collected from both control and vaccinated mice
OR
22 % of control mice and 23 % of vaccinated mice with infected nymphs at Site 1 AND 39 % of control mice and 29 % of vaccinated mice with infected nymphs at Site 2 ✔ Percentages are required for the second alternative of mpd.
\n
Accept “ticks” instead of “tick nymphs” or “nymphs”
\n
Do not accept quoting of untransformed numerical data.
\n
g.
\n
\n
a. Site 2 suggests that vaccination could reduce «nymph» infection rate «so method might be effective» ✔
\n
b. Site 1 suggests that vaccination does not reduce «nymph» infection rate «so method probably not effective» ✔
\n
c. effective «to some extent» as vaccination increases antibodies/immunity in mice ✔
\n
d. high antibody levels needed/ many mice need to be vaccinated «for the method to be effective» ✔
\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
f. there are other hosts/mammals/birds ✔
\n
g. difficult/expensive «to vaccinate many small mammals/mice»
OR
cheaper to use protective clothing/tick repellant/avoid wooded areas/other method ✔
\n
h.
\n
",
+ "Examiners report": "
",
+ "topics": [
+ "a-unity-and-diversity",
+ "c-interaction-and-interdependence"
+ ],
+ "subtopics": [
+ "a3-2-7-analysing-cladograms",
+ "a3-2-9-classification-of-all-organisms-into-three-domains-using-evidence-from-rrna-base-sequences",
+ "a3-2-classification-and-cladistics-(hl-only)",
+ "a4-2-conservation-of-biodiversity",
+ "c3-2-10-immunity-as-a-consequence-of-retaining-memory-cells",
+ "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-defence-against-disease"
+ ]
+ },
+ {
+ "question_id": "19N.2.HL.TZ0.2",
+ "Question": "
\n
The diagram shows one of Thomas Hunt Morgan’s crosses of Drosophila in the early 20th century.
\n

\n
\n
State the type of inheritance shown.
\n
[1]
\n
a.
\n
\n
Identify the recombinants.
\n
[1]
\n
b.
\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
[2]
\n
c.
\n
",
+ "Markscheme": "
\n
«gene/autosomal» linkage ✔
\n
Reject sex linkage
\n
a.
\n
\n
grey vestigial and black normal ✔
\n
Accept Ggvv and ggVv or alternative acceptable upper/lower case genotypes.
\n
b.
\n
\n
a. yes/observed ratio did differ significantly «from the expected Mendelian ratio»
OR
expected ratio is 1:1:1:1 / 575 of each type / 25 % of each type ✔ Correct ratio not needed in first alternative of mpa
\n
b. 3 degrees of freedom ✔
\n
c. critical value is 7.815 «at the 5 % level / 11.345 «at the 1 % level» ✔ Accept mpc if candidates indicate the critical value of chi squared by circling it.
\n
d. chi-squared value «of 1002.6» exceeds the critical value ✔
\n
Allow other levels of significance as long as the critical value is correctly stated for the chosen level.
\n
c.
\n
",
+ "Examiners report": "
",
+ "topics": [
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "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",
+ "d3-2-inheritance"
+ ]
+ },
+ {
+ "question_id": "19N.2.HL.TZ0.3",
+ "Question": "
\n
Describe what is shown in a cladogram.
\n
[2]
\n
a.
\n
\n
Outline how variation in organisms of the same species could lead to natural selection.
\n
[3]
\n
b.
\n
",
+ "Markscheme": "
\n
a. similarities/differences between organisms/species/clades ✔ mpa and mpd concern actual characteristics, not evolutionary relationships.
\n
b. «probable» evolutionary relationships/closeness/common ancestry/phylogeny ✔ mpb concerns such relationships
\n
c. divergence/splits/speciation/branches/nodes ✔ mpc concerns the structure branching of the cladogram
\n
d. relative similarity/differences between base sequence/amino acid sequence ✔
\n
a.
\n
\n
a. survival of the better adapted/fittest ✔
\n
b. more reproduction of better adapted/fittest/individuals with favorable variations ✔
\n
c. genes for favorable variations/adaptations passed on to offspring ✔ Accept answers in the converse.
\n
d. competition for resources/more offspring produced than the environment can support/a struggle for existence ✔ Accept answers in the converse.
\n
b.
\n
",
+ "Examiners report": "
",
+ "topics": [
+ "a-unity-and-diversity",
+ "c-interaction-and-interdependence"
+ ],
+ "subtopics": [
+ "a3-2-7-analysing-cladograms",
+ "a3-2-classification-and-cladistics-(hl-only)",
+ "a4-1-1-evolution-as-change-in-the-heritable-characteristics-of-a-population",
+ "a4-1-evolution-and-speciation",
+ "c1-2-10-anaerobic-cell-respiration-in-yeast-and-its-use-in-brewing-and-baking",
+ "c1-2-5-differences-between-anaerobic-and-aerobic-cell-respiration-in-humans",
+ "c1-2-cell-respiration"
+ ]
+ },
+ {
+ "question_id": "19N.2.HL.TZ0.6",
+ "Question": "
\n
Draw the structure of a section of DNA showing all possible bases.
\n
[4]
\n
a.
\n
\n
Outline the structural and genetic characteristics of eukaryotic chromosomes.
\n
[4]
\n
b.
\n
\n
Explain how a polypeptide chain is synthesized in a eukaryotic cell.
\n
[7]
\n
c.
\n
",
+ "Markscheme": "
\n
a. sugar, phosphate and base linked correctly to form at least one nucleotide ✔ 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
b. deoxyribose, phosphate and base/named base labelled at least once ✔
\n
c. adenine paired with thymine and cytosine paired with guanine ✔ For mpc, full names of all four bases are required, but not relative sizes of the purine and pyrimidine bases.
\n
d. two antiparallel chains of nucleotides linked by hydrogen bonds with all sugar-phosphate bonds in correct position ✔ 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
a.
\n
\n
a. linear/not circular DNA molecule
OR
one chromosome is one molecule of DNA/one chromosome is two DNA molecules «after replication» ✔
\n
b. associated with histone proteins/nucleosomes ✔
\n
c. centromere joins sister chromatids «after DNA replication» ✔
\n
d. telomeres at the end «of the chromosome/chromatid» ✔
\n
e. carries a sequence of genes / each gene occupies a specific locus ✔ Do not accept ‘sequence of bases’ for mpe.
\n
f. alternative alleles of genes / homologous chromosomes carry same sequence of genes ✔
\n
g. chromosomes in pairs / two «homologous chromosomes» of each type «in a diploid cell» ✔
\n
h. non-coding sequences/example of a non-coding sequence ✔ Do not allow mph if the response states that chromosomes are always condensed.
\n
i. supercoiled/condensed «during mitosis/meiosis» ✔
\n
b.
\n
\n
a. translation occurs on ribosomes ✔
\n
b. tRNA-activating enzymes attach amino acids to tRNAs ✔
\n
c. small and large ribosome units assemble on mRNA
OR
translation/polypeptide synthesis starts at a start codon ✔
\n
d. each tRNA arriving at the ribosome binds to the A site ✔
\n
e. anticodon «on tRNA» binds to codon «on mRNA» ✔
\n
f. according to complementary base pairing/A with U and G with C ✔
\n
g. ribosome moves along the mRNA / mRNA moves over ribosome ✔
\n
h. t-RNA shifts from the A site to P site/from the P to the E site ✔
\n
i. peptide bond between amino acids «on tRNAs at A and P sites» ✔
\n
j. tRNA released from ribosome at E site ✔
\n
k. cycle repeats with other tRNAs / polypeptide grows as tRNAs bring more amino acids ✔
\n
l. until stop codon on mRNA is reached ✔
\n
m. components are disassembled / polypeptide leaves the ribosome ✔
\n
Accept these points in an annotated diagram.
Do not award any marks for events in transcription.
\n
c.
\n
",
+ "Examiners report": "
",
+ "topics": [
+ "a-unity-and-diversity",
+ "b-form-and-function",
+ "c-interaction-and-interdependence",
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "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",
+ "a1-2-nucleic-acids",
+ "a2-2-6-eukaryote-cell-structure",
+ "a2-2-cell-structure",
+ "b1-1-2-production-of-macromolecules-by-condensation-reactions-that-link-monomers-to-form-a-polymer",
+ "b1-1-carbohydrates-and-lipids",
+ "b1-2-4-infinite-variety-of-possible-peptide-chains",
+ "b1-2-proteins",
+ "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",
+ "c2-1-chemical-signalling-[hl-only]",
+ "d1-2-5-translation-as-the-synthesis-of-polypeptides-from-mrna",
+ "d1-2-protein-synthesis"
+ ]
+ },
+ {
+ "question_id": "19N.2.HL.TZ0.7",
+ "Question": "
\n
Outline the reasons for the differences in blood concentrations between the renal artery and the renal vein.
\n
[4]
\n
a.
\n
\n
Outline how two parents could have a child with any of the four ABO blood groups.
\n
[4]
\n
b.
\n
\n
Explain the control mechanism of the heart rate.
\n
[7]
\n
c.
\n
",
+ "Markscheme": "
\n
a. urea/waste products lower in vein due to excretion «in urine»/ultrafiltration but not reabsorption ✔
\n
b. oxygen lower in vein due to use in cell respiration/in kidney tissue ✔
\n
c. carbon dioxide higher in vein due to production by cell respiration/excretion by kidney cells ✔
\n
d. glucose lower in vein due to use in cell respiration «by kidney tissue» ✔
\n
e. sodium/chloride/ion concentrations changed due to production of hypertonic/hypotonic urine
OR
sodium/chloride/ion concentrations lower due to removal of excess ✔
\n
f. ion/solute concentrations lower in vein than artery if ADH has been secreted
OR
ion/solute concentrations in vein vary depending on amount of water reabsorbed in the collecting duct ✔
\n
g. drug/toxin concentrations lower in vein due to excretion in urine ✔
\n
Accept any point given as the converse.
\n
Each mark point includes a difference and reason for it.
\n
a.
\n
\n
a. IA, i for one set of gametes/parental genotype ✔
\n
b. IB, i for the other set of gametes/parental genotype ✔
\n
c. «genotypes of offspring are» IAIB, IAi, IBi, ii ✔
\n
d. «phenotypes of offspring are» AB, A, B, O ✔
\n
Answers can be given in a Punnett grid or in prose.
\n
Accept the four possible blood groups of the offspring anywhere in the answer.
\n
b.
\n
\n
a. sinoatrial node/SAN is a specialized group of muscle cells
OR
sinoatrial node/SAN is located in the right atrium ✔
\n
b. acts as a pacemaker/controls the heart rate
OR
initiates/generates the heart beat/starts the cardiac cycle ✔
\n
c. sends out electrical signal/impulses/depolarisations ✔
\n
d. electrical signal stimulates contraction «of heart muscle» ✔
\n
e. signal passes through walls of atria/passes to AV node ✔
\n
f. then through walls of the ventricles ✔
\n
g. medulla «oblongata of brain» can change/increase/decrease the rate ✔
\n
h. through nerves/named example of nerve/autonomic/sympathetic/ parasympathetic nervous system ✔ In mph, only accept vagus nerve for slowing heart rate and sympathetic nerve for accelerating it.
\n
i. one nerve increases the rate and the other decreases it ✔
\n
j. epinephrine/adrenaline increases heart rate/force of contraction ✔
\n
k. epinephrine/adrenaline prepares the body for vigorous activity/is part of fight or flight response ✔
\n
c.
\n
",
+ "Examiners report": "
",
+ "topics": [
+ "c-interaction-and-interdependence",
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "c3-1-14-feedback-control-of-heart-rate-following-sensory-input-from-baroreceptors-and-chemoreceptors",
+ "c3-1-integration-of-body-systems",
+ "d3-2-9-abo-blood-groups-as-an-example-of-multiple-alleles",
+ "d3-2-inheritance",
+ "d3-3-8-role-of-the-glomerulus-bowmans-capsule-and-proximal-convoluted-tubule-in-excretion",
+ "d3-3-homeostasis"
+ ]
+ },
+ {
+ "question_id": "19N.2.SL.TZ0.1",
+ "Question": "
\n
Cultivated rice, Oryza sativa, is one of the most important human foods. The two main sub-species of cultivated rice are O. sativa indica and O. sativa japonica. O. rufipogon is a wild species from which they probably evolved.
\n
\n
To investigate whether the sub-species of cultivated rice evolved independently from the wild species, scientists analysed their chromosomes to find areas with similar DNA base sequences. Wild species tend to have many different alleles of genes present on each chromosome, but during the development of a crop plant by artificial selection from a wild species, this diversity drops considerably, increasing the base sequence similarity.
The number of different alleles of the genes on a chromosome can be represented by a diversity index. The following graph of part of chromosome 7 shows the diversity index of O. rufipogon and two varieties of cultivated rice, O. sativa indica and O. sativa japonica. The gene PROG1 allows the plant to stand upright, which is typical of cultivated rice. Its position is indicated by the vertical arrow on the graph.
\n

\n
[Source: He Z, Zhai W, Wen H, Tang T, Wang Y, Lu X, et al. (2011) Two Evolutionary Histories in the Genome of Rice:
the Roles of Domestication Genes. PLoS Genet 7(6): e1002100. https://doi.org/10.1371/journal.pgen.1002100]
\n
\n
In another experiment, scientists retrieved genome sequences of the wild rice O. rufipogon taken from a wide range of geographical sites (I, II and III) and those of the two sub-species of O. sativa from gene banks.
\n
The pie charts, presented along with a cladogram, show the proportion of alleles for three genes which confer specific characteristics to O. sativa. Mutations can produce derived alleles that are different from the original ancestral alleles. The control group represents wild rice species other than O. rufipogon.
\n

\n
[Source: reprinted by permission from Springer Nature: Nature, Huang, X., Kurata, N., Wei, X. et al. A map of rice
genome variation reveals the origin of cultivated rice. Nature 490, 497–501 (2012) doi:10.1038/nature11532]
\n
\n
State the reason that O. sativa and O. rufipogon are classified as different species.
\n
[1]
\n
a.
\n
\n
Determine which type of rice has the lowest overall diversity index.
\n
[1]
\n
b.
\n
\n
Compare and contrast the trends for O. rufipogon and O. sativa indica.
\n
[2]
\n
c.
\n
\n
State the proportion of the ancestral allele for the gene GS3 in the O. rufipogon-III population.
\n
[1]
\n
d.
\n
\n
Distinguish between the proportion of ancestral and derived alleles for all three genes in O. sativa indica and O. sativa japonica.
\n
[2]
\n
e.
\n
\n
State one reason for having a control group.
\n
[1]
\n
f.
\n
\n
Using all of the data, discuss whether there is evidence that the two sub-species of O. sativa might have evolved independently from O. rufipogon.
\n
[4]
\n
g.
\n
",
+ "Markscheme": "
\n
cannot interbreed to produce fertile offspring ✔
\n
Accept converse or a good explanation.
\n
a.
\n
\n
«O. sativa» japonica ✔
\n
b.
\n
\n
Similarities
both show diversity
OR
similar pattern/peaks and troughs in the first part of the chromosome / up to «approximately» 1.5 megabases
OR
similar diversity between 2.4 to 2.7 mb
OR
both highest at 0.7 mb ✔
\n
Differences
there are «two» major drops in diversity for O. sativa indica whereas none for O. rufipogon/much wider fluctuations in O. s. indica
OR
O.s. indica much lower at PROG1
OR
O.rufipogon does not drop < 2.5 whereas O. s. indica approaches 0
OR
O.rufipogon generally higher than O. s. indica after 1.4-1.5 ✔
\n
One answer from mpa and one from mpb required for 2 [max].
\n
Accept a statement of where the drops occur.
\n
c.
\n
\n
/0.75/75% ✔
\n
Do not accept 0.75% or 75 or ratios
\n
d.
\n
\n
a. O.s. indica has more of the ancestral allele «for all three genes» ✔ Accept converse.
\n
b. lower/higher values for ancestral/derived are not for the same genes ✔ Allow specific gene examples.
\n
c. for O. s. indica the highest proportion is for DPL2 ancestral, but for O. s. japonica is GS3 derived allele ✔ Allow converse for smallest derived.
\n
e.
\n
\n
any reference to comparison ✔
\n
f.
\n
\n
a. large difference in diversity index between O. s. indica and O. s. japonica «suggests independent evolution» ✔
\n
b. «some of the» peaks/troughs for O. s. indica and O. s. japonica in different positions «suggests independent evolution» ✔
\n
c. O.s. indica has a similar diversity index to O. rufipogon «which suggests closer relationship/recent divergence» ✔
Allow converse for japonica
\n
d. O.s. japonica has very different proportions of ancestral and derived alleles compared to O. s. indica ✔
\n
e. O.s. indica has similar large number of ancestral alleles to O. rufipogon I/II ✔ Allow converse for derived
\n
f. O.s. japonica has a large number of derived alleles similar to O. rufipogon III
OR
«but» the number of derived alleles is greater in O. s. japonica than in O.rufipogon III ✔ Allow converse for ancestral
\n
g. O.s. indica and O. s. japonica are in different clades ✔
OR
O.s. indica and O. rufipogon I are in the same clade ✔
\n
h. evidence from one chromosome/3 genes/2 studies is not sufficient to form a conclusion ✔
\n
g.
\n
",
+ "Examiners report": "
",
+ "topics": [
+ "a-unity-and-diversity",
+ "c-interaction-and-interdependence"
+ ],
+ "subtopics": [
+ "a3-1-diversity-of-organisms",
+ "a3-2-7-analysing-cladograms",
+ "a3-2-classification-and-cladistics-(hl-only)",
+ "a4-2-conservation-of-biodiversity",
+ "c3-2-10-immunity-as-a-consequence-of-retaining-memory-cells",
+ "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-defence-against-disease"
+ ]
+ },
+ {
+ "question_id": "19N.2.SL.TZ0.12",
+ "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
\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",
+ "Markscheme": "
\n (a)\n
\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
\n (c)\n
\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",
+ "topics": [
+ "c-interaction-and-interdependence"
+ ],
+ "subtopics": [
+ "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",
+ "c1-3-photosynthesis",
+ "c4-2-11-construction-of-energy-pyramids",
+ "c4-2-transfers-of-energy-and-matter"
+ ]
+ },
+ {
+ "question_id": "19N.2.SL.TZ0.13",
+ "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
\n
\n (b)\n
\n
\n
\n Compare and contrast fundamental and realized niche of a species.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\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
\n (b)\n
\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",
+ "topics": [
+ "b-form-and-function",
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "b4-2-12-fundamental-and-realized-niches",
+ "b4-2-ecological-niches",
+ "d4-2-5-role-of-keystone-species-in-the-stability-of-ecosystems",
+ "d4-2-stability-and-change"
+ ]
+ },
+ {
+ "question_id": "19N.2.SL.TZ0.14",
+ "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
\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",
+ "Markscheme": "
\n (b)\n
\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
\n (c)\n
\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",
+ "topics": [
+ "c-interaction-and-interdependence",
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "c4-2-4-construction-of-food-chains-and-food-webs-to-represent-feeding-relationships-in-a-community",
+ "c4-2-transfers-of-energy-and-matter",
+ "d4-2-5-role-of-keystone-species-in-the-stability-of-ecosystems",
+ "d4-2-stability-and-change"
+ ]
+ },
+ {
+ "question_id": "19N.2.SL.TZ0.15",
+ "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
\n
\n (b)\n
\n
\n
\n Outline how plastic ingestion may lead to biomagnification in these marine species.\n
\n
\n
\n
\n
\n
\n (b.i)\n
\n
\n
\n State an example of an alien species.\n
\n
\n
\n
\n
\n
\n (b.ii)\n
\n
\n
\n Outline the impact of alien species on endemic species in ecosystems.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\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
\n (b)\n
\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
\n (b.i)\n
\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
\n (b.ii)\n
\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",
+ "topics": [
+ "a-unity-and-diversity",
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "a4-2-6-causes-of-the-current-biodiversity-crisis",
+ "a4-2-conservation-of-biodiversity",
+ "d4-2-9-biomagnification-of-pollutants-in-natural-ecosystems",
+ "d4-2-stability-and-change"
+ ]
+ },
+ {
+ "question_id": "19N.2.SL.TZ0.2",
+ "Question": "
\n
A short base sequence of mRNA and a table of the genetic code are shown below.
\n
Sequence of mRNA
\n

\n
Table of the genetic code
\n

\n
\n
The diagram shows a section of a polypeptide.
\n

\n
\n
Outline the function of codons.
\n
[1]
\n
a.
\n
\n
Determine the sequence of amino acids that could be translated from the sequence of mRNA.
\n
[1]
\n
b.i.
\n
\n
Determine the DNA base sequence transcribed to form this sequence of mRNA.
\n
[1]
\n
b.ii.
\n
\n
Suggest a hypothesis that accounts for the slightly different meaning of some codons in a very limited number of organisms.
\n
[1]
\n
c.
\n
\n
Annotate the diagram to show a peptide bond between two amino acids.
\n
[1]
\n
d.i.
\n
\n
State the type of reaction that removes water while linking amino acids together to form polypeptides.
\n
[1]
\n
d.ii.
\n
\n
Outline the function of Rubisco and of spider silk in relation to their three-dimensional conformation.
\n

\n
[2]
\n
e.
\n
",
+ "Markscheme": "
\n
«three bases on mRNA» coding for one amino acid «in a polypeptide» ✔
\n
a.
\n
\n
met-ser-arg-arg
OR
start-ser-arg-arg
OR
met-ser-arg-arg-stop
OR
start-ser-arg-arg-stop ✔
\n
Do not accept peptides containing an amino acid/leu for the last codon.
\n
b.i.
\n
\n
TAC TCG GCT TCC ATC GAC ✔
\n
b.ii.
\n
\n
they occurred after the common origin of life OWTTE
OR
the genetic code is not «in fact» universal ✔
\n
Look for alternatives.
\n
c.
\n
\n
any annotation between a C=O and the next NH ✔
\n
e.g.
\n

\n
d.i.
\n
\n
condensation ✔
\n
Do not accept anabolism alone.
\n
d.ii.
\n
\n

\n
Award [1] per correct row or correct column.
\n
e.
\n
",
+ "Examiners report": "
",
+ "topics": [
+ "b-form-and-function",
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "b1-2-2-condensation-reactions-forming-dipeptides-and-longer-chains-of-amino-acids",
+ "b1-2-proteins",
+ "d1-2-10-stepwise-movement-of-the-ribosome-along-mrna-and-linkage-of-amino-acids-by-peptide-bonding-to-the-growing-polypeptide-chain",
+ "d1-2-11-mutations-that-change-protein-structure",
+ "d1-2-7-complementary-base-pairing-between-trna-and-mrna",
+ "d1-2-8-features-of-the-genetic-code",
+ "d1-2-9-using-the-genetic-code-expressed-as-a-table-of-mrna-codons",
+ "d1-2-protein-synthesis"
+ ]
+ },
+ {
+ "question_id": "19N.2.SL.TZ0.3",
+ "Question": "
\n
Outline the cell theory.
\n
[2]
\n
a.
\n
\n
State two functions of life.
\n
[2]
\n
b.
\n
\n
List three characteristics of eukaryotic homologous chromosomes.
\n
[3]
\n
c.
\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
[3]
\n
d.
\n
",
+ "Markscheme": "
\n
a. cells can only arise from preexisting cells ✔
\n
b. living organisms are composed of cells/smallest unit of life ✔
\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
d. although most organisms conform to cell theory, there are exceptions ✔
\n
a.
\n
\n
a. nutrition ✔
\n
b. metabolism/respiration ✔
\n
c. growth ✔
\n
d. response/irritability ✔
\n
e. excretion ✔
\n
f. homeostasis ✔
\n
g. reproduction ✔
\n
Do not allow “feeding”, plants do not “feed”.
\n
Mark the first two answers only.
\n
b.
\n
\n
a. linear DNA molecules
OR
DNA associated with histone «proteins» ✔
\n
b. carry the same sequence of genes ✔
\n
c. «but» not necessarily the same alleles «of those genes» ✔
\n
d. both are present when nucleus is in diploid state ✔
OR
occur in pairs ✔
\n
e. have same size/length/banding patterns ✔
\n
f. centromeres are in the same position ✔
\n
c.
\n
\n

\n
Award [1] per correct row.
\n
d.
\n
",
+ "Examiners report": "
",
+ "topics": [
+ "a-unity-and-diversity",
+ "c-interaction-and-interdependence"
+ ],
+ "subtopics": [
+ "a2-2-1-cells-as-the-basic-structural-unit-of-all-living-organisms",
+ "a2-2-7-processes-of-life-in-unicellular-organisms",
+ "a2-2-cell-structure",
+ "a3-1-6-diversity-in-chromosome-numbers-of-plant-and-animal-species",
+ "a3-1-diversity-of-organisms",
+ "a4-1-1-evolution-as-change-in-the-heritable-characteristics-of-a-population",
+ "a4-1-evolution-and-speciation",
+ "c1-2-10-anaerobic-cell-respiration-in-yeast-and-its-use-in-brewing-and-baking",
+ "c1-2-5-differences-between-anaerobic-and-aerobic-cell-respiration-in-humans",
+ "c1-2-cell-respiration"
+ ]
+ },
+ {
+ "question_id": "19N.2.SL.TZ0.4",
+ "Question": "
\n
State the immediate consequence of a species producing more offspring than the environment can support.
\n
[1]
\n
a.
\n
\n
Explain the consequence of overpopulation on the survival and reproduction of better adapted individuals within a population.
\n
[3]
\n
b.
\n
",
+ "Markscheme": "
\n
competition/lack of resources/death/exceeding carrying capacity ✔
\n
Allow a description of it.
Do not allow “overpopulation” or “natural selection”.
\n
a.
\n
\n
a. «better adapted» tend to survive more ✔
\n
b. «better adapted» reproduce/produce more offspring ✔
\n
c. pass on characteristics to their offspring «when they reproduce» ✔
\n
d. their frequency increases «within the population» due to natural selection ✔
\n
e. leading to evolution ✔
\n
b.
\n
",
+ "Examiners report": "
",
+ "topics": [
+ "b-form-and-function",
+ "c-interaction-and-interdependence",
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "b1-1-12-formation-of-phospholipid-bilayers-as-a-consequence-of-the-hydrophobic-and-hydrophilic-regions",
+ "b1-1-carbohydrates-and-lipids",
+ "c1-3-2-conversion-of-carbon-dioxide-to-glucose-in-photosynthesis-using-hydrogen-obtained-by-splitting-water",
+ "c1-3-photosynthesis",
+ "d4-1-3-overproduction-of-offspring-and-competition-for-resources-as-factors-that-promote-natural-selection",
+ "d4-1-natural-selection"
+ ]
+ },
+ {
+ "question_id": "19N.2.SL.TZ0.5",
+ "Question": "
\n
Draw a section of the Singer-Nicolson model of an animal cell membrane.
\n
[4]
\n
a.
\n
\n
Outline the principles used by scientists to classify organisms.
\n
[4]
\n
b.
\n
\n
Explain the movement of energy and inorganic nutrients in an ecosystem.
\n
[7]
\n
c.
\n
",
+ "Markscheme": "
\n
a. bilayer of phospholipids with both “tails” towards the inside «of the bilayer» ✔ This can be taken unlabeled from diagram.
\n
b. hydrophilic/polar and hydrophobic/non-polar annotation ✔
\n
c. cholesterol between phospholipid tails ✔
\n
d. glycoprotein ✔
\n
e. integral proteins/channel proteins ✔
\n
f. peripheral proteins ✔ Allow this if it does not extend across the membrane
\n
Elements should be clearly drawn, correctly positioned and annotated.
\n
a.
\n
\n
a. use of the binomial system ✔
\n
b. agreed/developed by scientists / OWTTE ✔
\n
c. hierarchy of taxa used ✔ Names of the seven taxa not required.
\n
d. three domains used/three domain names ✔ OWTTE
\n
e. genome/DNA sequence similarities
OR
amino acid sequence of specific proteins ✔
\n
f. species from a common ancestor are grouped together
OR
included in the same clade/branch in cladogram ✔
\n
g. use evidence of evolutionary origin ✔ Allow example e.g. fossil record comparison
\n
h. shared characteristics within a group
OR
similar embryonic development ✔
\n
b.
\n
\n
a. autotrophs/producers/plants obtain inorganic nutrients from the «abiotic» environment ✔
\n
b. energy provided «mainly» by sunlight ✔
\n
c. light energy converted «to chemical energy» through photosynthesis ✔
\n
d. photosynthesis/producers/autotrophs convert inorganic carbon/carbon dioxide and water into carbon/organic compounds ✔
\n
e. «these» carbon compounds/foods contain/are a source of «useable» energy «for life» ✔
\n
f. carbon compounds/energy are transferred along food chains when eaten by consumers/heterotrophs ✔ Allow OWTTE for mpf for passed up trophic levels.
\n
g. respiration returns carbon «dioxide» to the environment ✔
\n
h. respiration releases stored/chemical energy as ATP/heat ✔
\n
i. energy/ATP is used to carry out life functions/synthesis/growth/movement ✔
\n
j. energy is lost/not recycled ✔
\n
k. nutrients are recycled / example of recycled nutrient e.g. carbon ✔
\n
l. decomposers recycle minerals/inorganic nutrients ✔
\n
c.
\n
",
+ "Examiners report": "
",
+ "topics": [
+ "a-unity-and-diversity",
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "a3-2-1-need-for-classification-of-organisms",
+ "a3-2-2-difficulties-classifying-organisms-into-the-traditional-hierarchy-of-taxa",
+ "a3-2-classification-and-cladistics-(hl-only)",
+ "d4-2-2-requirements-for-stability-in-ecosystems",
+ "d4-2-stability-and-change"
+ ]
+ },
+ {
+ "question_id": "19N.2.SL.TZ0.6",
+ "Question": "
\n
Outline how cuts in the skin are sealed to prevent blood loss.
\n
[4]
\n
a.
\n
\n
Outline how two parents could have a child with any of the four ABO blood groups.
\n
[4]
\n
b.
\n
\n
Explain how ventilation and lung structure contribute to passive gas exchange.
\n
[7]
\n
c.
\n
",
+ "Markscheme": "
\n
a. platelets respond to/detect skin/blood vessel damage ✔
\n
b. platelets release clotting factors ✔
\n
c. clotting factors trigger a chain/cascade of reactions ✔
\n
d. «leading to» formation of thrombin ✔
\n
e. thrombin causes fibrinogen conversion into fibrin ✔
\n
f. blood clot seals the wound due to fibrin network of fibres ✔
\n
Accept answers presented as a flow chart.
\n
a.
\n
\n
a. «first set of» gametes/parental genotype IA, i ✔
\n
b. «other set of» gametes/parental genotype IB, i ✔
\n
c. «genotypes of offspring are respectively» IAIB, IBi, IAi, ii ✔ All four correct required.
\n
d. «phenotypes of offspring are respectively» AB, B, A, O ✔ All four correct required linked to genotypes
\n
Award marks only for the first grid if more than one drawn;
e.g. of Punnett grid
\n

\n
Answers can be given in a Punnett grid or in prose.
\n
Accept the four possible blood groups of the offspring anywhere in the answer.
\n
b.
\n
\n
a. air carried through trachea AND bronchi/bronchioles AND alveoli ✔ All three required in correct order.
\n
b. alveoli increase the surface area/thin walled for gas exchange ✔
\n
c. gas exchange carried out through type I pneumocytes ✔
\n
d. type II pneumocytes secrete surfactant to reduce surface tension ✔
\n
e. moist surface/surfactant allows gases to diffuse in solution ✔
\n
f. ventilation/moving blood maintains concentration gradients of oxygen and carbon dioxide ✔
\n
g. between air in alveoli and blood in «adjacent» capillaries
OR
oxygen diffuses from alveoli to capillaries and carbon dioxide from capillaries to alveoli ✔ OWTTE
\n
h. external intercostal muscles/diaphragm contract during inspiration ✔
\n
i. lowering air pressure «in lungs»/increasing thorax volume ✔
\n
j. relaxation of external intercostal muscles/diaphragm enable «passive» expiration ✔
\n
k. internal intercostal «and abdominal muscles» contract «to force» expiration ✔
\n
l. expiration due to increasing air pressure «in lungs»/decreasing thorax volume ✔
\n
Accept correctly annotated diagram.
\n
c.
\n
",
+ "Examiners report": "
",
+ "topics": [
+ "b-form-and-function",
+ "c-interaction-and-interdependence",
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "b3-1-4-adaptations-of-mammalian-lungs-for-gas-exchange",
+ "b3-1-gas-exchange",
+ "c3-2-3-sealing-of-cuts-in-skin-by-blood-clotting",
+ "c3-2-defence-against-disease",
+ "d3-2-9-abo-blood-groups-as-an-example-of-multiple-alleles",
+ "d3-2-inheritance"
+ ]
+ },
+ {
+ "question_id": "19N.2.SL.TZ0.7",
+ "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
\n
\n (c)\n
\n
\n
\n Explain the control mechanism of the heart rate.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (b)\n
\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
\n (c)\n
\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",
+ "topics": [
+ "c-interaction-and-interdependence",
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "c3-1-14-feedback-control-of-heart-rate-following-sensory-input-from-baroreceptors-and-chemoreceptors",
+ "c3-1-integration-of-body-systems",
+ "d3-2-9-abo-blood-groups-as-an-example-of-multiple-alleles",
+ "d3-2-inheritance"
+ ]
+ },
+ {
+ "question_id": "19N.2.SL.TZ0.8",
+ "Question": "
\n
\n (a)\n
\n
\n
\n Draw a half-view of an animal-pollinated flower.\n
\n
\n
\n
\n
\n
\n (c)\n
\n
\n
\n Explain the movement of energy and inorganic nutrients in an ecosystem.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\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
\n (c)\n
\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",
+ "topics": [
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "d3-1-9-features-of-an-insect-pollinated-flower",
+ "d3-1-reproduction",
+ "d4-2-2-requirements-for-stability-in-ecosystems",
+ "d4-2-stability-and-change"
+ ]
+ },
+ {
+ "question_id": "20N.3.SL.TZ0.1",
+ "Question": "
\n
A nomogram can be used to determine the body mass index (BMI) of an individual.
\n

\n
\n
State the BMI of a person of mass 80 kg and 1.80 m in height.
\n
[1]
\n
a.
\n
\n
Explain how measurement of BMI could help to assess whether a person has an increased risk of type II diabetes.
\n
[2]
\n
b.
\n
",
+ "Markscheme": "
\n
25
\n
Accept 24.5 to 26.
\n
Units not required.
\n
a.
\n
\n
a. BMI could indicate if a person is overweight/obese/too heavy for their height;
\n
b. overweight/obesity increases the probability of developing type II diabetes;
\n
Do not accept “High BMI increases the risk of diabetes.”
\n
b.
\n
",
+ "Examiners report": "
\n
Most candidates correctly stated the BMI of the individual. Some did it by reading from the nomogram, and others by calculation.
\n
a.
\n
\n
In (b) many candidates stated that a high BMI leads to obesity without explaining that a high BMI is only a possible indicator of obesity.
\n
b.
\n
",
+ "topics": [
+ "b-form-and-function",
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "b1-1-10-difference-between-saturated-monounsaturated-and-polyunsaturated-fatty-acids",
+ "b1-1-carbohydrates-and-lipids",
+ "b1-2-3-dietary-requirements-for-amino-acids",
+ "b1-2-proteins",
+ "d3-3-3-regulation-of-blood-glucose-as-an-example-of-the-role-of-hormones-in-homeostasis",
+ "d3-3-homeostasis"
+ ]
+ },
+ {
+ "question_id": "20N.3.SL.TZ0.2",
+ "Question": "
\n
In an investigation to compare the elasticity of arteries and veins, rings of the same diameter (20 mm) of artery and vein tissue were cut from blood vessels obtained from a mammal.
\n

\n
[Source: © International Baccalaureate Organization 2020.]
\n
Each ring was attached to a clamp. Multiple masses of 10 g were added and removed. The vertical diameter of the artery and the vein was measured, both with the mass and once the mass had been removed.
\n

\n
The results are shown in the table.
\n

\n
\n
State the independent and dependent variables in this experiment.
\n
Independent:
\n
Dependent:
\n
[2]
\n
a.
\n
\n
State one feature of the rings that has to be kept constant apart from their initial diameter.
\n
[1]
\n
b.
\n
\n
Explain the differences between the results shown for vein and artery.
\n
[3]
\n
c.
\n
",
+ "Markscheme": "
\n
a. Independent: mass;
\n
b. Dependent: (vertical) diameter/length;
\n
Do not accept elasticity
\n
a.
\n
\n
a. width/section depth/slice of the ring;
\n
b. same animal/age/freshness/temperature;
\n
Don’t accept thickness or diameter.
\n

\n
b.
\n
\n
a. veins have thinner walls (than arteries);
\n
b. veins sustain lower (blood) pressure (than arteries);
\n
c. when stretched, veins become longer (than arteries);
\n
d. veins have less muscle/elastic (fibre in their) walls (than arteries);
\n
e. veins have lower elasticity/recover less/remain more stretched (than arteries after weights removed);
\n
Accept inverse for arteries in all cases.
\n
Do not accept a listing of numerical values without explanation.
\n
c.
\n
",
+ "Examiners report": "
\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
a.
\n
\n
In part (b) many candidates suggested that the samples should be of the same thickness.
\n
b.
\n
\n
In part (b) many candidates suggested that the samples should be of the same thickness.
\n
c.
\n
",
+ "topics": [
+ "b-form-and-function"
+ ],
+ "subtopics": [
+ "b3-2-2-structure-of-arteries-and-veins",
+ "b3-2-transport"
+ ]
+ },
+ {
+ "question_id": "20N.3.SL.TZ0.3",
+ "Question": "
\n
To investigate whether carbon dioxide is required for photosynthesis, a plant was irrigated using water from which carbon dioxide had been removed and was then placed in the apparatus shown in the diagram. The apparatus was left in darkness for 24 hours to destarch the leaves. Then, after several hours in light, a leaf was removed from the plant and found to contain no starch when tested. A control was performed using a second plant. A leaf from this plant tested positive for starch.
\n

\n
[Source: © International Baccalaureate Organization 2020.]
\n
\n
Describe the control for this experiment.
\n
[2]
\n
a.
\n
\n
Outline how the carbon dioxide could be removed from the water used to irrigate the plant.
\n
[1]
\n
b.
\n
\n
Suggest how a plastic bag placed around the plant pot prevents carbon dioxide from reaching the plant’s leaves.
\n
[1]
\n
c.
\n
\n
A chromatograph was made of the photosynthetic pigments of a leaf of the plant.
\n

\n
[Source: Adapted from “Diversity of Photosynthetic Pigments” by Alexander F. Motten in Tested Studies for
Laboratory Teaching, Volume 16 of the Association for Biology Laboratory Education and used by permission of the
author.]
\n
\n
Outline what measurements would be taken to identify pigment X.
\n
[2]
\n
d.
\n
",
+ "Markscheme": "
\n
a. same apparatus with carbon dioxide present;
\n
b. (control has) no sodium hydroxide/alkali;
\n
c. control irrigated with untreated water/water with CO2;
\n
“Same apparatus” alone does not get the mark.
\n
a.
\n
\n
a. boiling (and cooling) the water;
\n
b. expose the water to a vacuum;
\n
Allow distillation of water.
\n
b.
\n
\n
a. to prevent CO2 from (organisms in) the soil affecting the experiment;
\n
b. the plastic bag is impermeable to gases;
\n
c.
\n
\n
a. the distance travelled from the origin/O to the solvent front;
\n
b. the distance travelled by the pigment (from the origin O to X);
\n
Accept X to solvent front if the candidate indicates that this allows O to X to be calculated.
\n
d.
\n
",
+ "Examiners report": "
\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
a.
\n
\n
There were many suggestions on how carbon dioxide could be removed from water despite boiling the water being an assessment statement.
\n
b.
\n
\n
The plastic bag caused considerable confusion with many candidates stating that it was to prevent carbon dioxide reaching the roots and being taken up the stem to the leaves for photosynthesis.
\n
c.
\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
d.
\n
",
+ "topics": [
+ "c-interaction-and-interdependence"
+ ],
+ "subtopics": [
+ "c1-3-4-separation-and-identification-of-photosynthetic-pigments-by-chromatography",
+ "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",
+ "c1-3-photosynthesis"
+ ]
+ },
+ {
+ "question_id": "20N.2.HL.TZ0.2",
+ "Question": "
\n
The diagram shows part of two neurons.
\n

\n
[Source: © International Baccalaureate Organization 2020.]
\n
\n
Outline how the amphipathic properties of phospholipids play a role in membrane structure.
\n
[2]
\n
a.i.
\n
\n
State the role of cholesterol in animal cell membranes.
\n
[1]
\n
a.ii.
\n
\n
Describe what happens to the membranes of an animal cell during mitosis.
\n
[2]
\n
b.
\n
\n
State the name of the structure shown.
\n
[1]
\n
c.i.
\n
\n
X indicates the movement of a structure in the neuron. Explain what events trigger this movement and what happens next.
\n
[3]
\n
c.ii.
\n
",
+ "Markscheme": "
\n
a. part hydrophobic/not attracted to water/non-polar AND part hydrophilic/attracted to water/polar;
\n
b. bilayer formed (formed naturally by phospholipids in water);
\n
c. hydrophilic heads/parts face outwards and hydrophobic tails/parts face inwards.
\n
Do not allow water loving/hating in mpa or mpc.
\n
a.i.
\n
\n
a. controls/regulates/reduces fluidity of membrane / prevents crystallization of phospholipids;
\n
b. reduces permeability to some substances.
\n
Do not accept ‘stabilizes membrane’.
\n
a.ii.
\n
\n
a. nuclear membrane breaks down/disappears (in prophase/at start of mitosis);
\n
b. nuclear membrane reforms around two new nuclei (in telophase/at end of mitosis);
\n
c. plasma membrane pulled inwards at equator / cleavage furrow formed;
\n
d. membrane pinches apart to form two cells / cytoplasm divided / cytokinesis.
\n
b.
\n
\n
synapse/synaptic
\n
Allow any answer including either of these terms unless out of context.
\n
c.i.
\n
\n
a. depolarization of pre-synaptic membrane / action potential/nerve impulse arrives;
\n
b. uptake of calcium / calcium ions diffuse in / calcium channels open;
\n
c. structures containing neurotransmitter/vesicles move to/fuse with membrane;
\n
d. neurotransmitter/acetylcholine released by exocytosis into cleft/binds to postsynaptic membrane/receptors;
\n
Must see exocytosis.
\n
c.ii.
\n
",
+ "Examiners report": "
\n
Knowledge of the amphipathic properties of phospholipids was generally good.
\n
a.i.
\n
\n
Half of candidates were able to state the role of cholesterol in animal cell membranes.
\n
a.ii.
\n
\n
The mark scheme allowed candidates to score marks either for describing changes to the nuclear membrane or the role that the plasma membrane plays in cytokinesis. The best answers referred to both. Many of the candidates who wrote about the nuclear membrane had rather sketchy understanding of how it breaks up into small vesicles at the end of prophase and then reforms around both daughter nuclei in telophase.
\n
b.
\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
c.i.
\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
c.ii.
\n
",
+ "topics": [
+ "a-unity-and-diversity",
+ "b-form-and-function",
+ "c-interaction-and-interdependence"
+ ],
+ "subtopics": [
+ "a2-2-12-origin-of-eukaryotic-cells-by-endosymbiosis",
+ "a2-2-cell-structure",
+ "b1-1-12-formation-of-phospholipid-bilayers-as-a-consequence-of-the-hydrophobic-and-hydrophilic-regions",
+ "b1-1-carbohydrates-and-lipids",
+ "b2-1-10-fluid-mosaic-model-of-membrane-structure",
+ "b2-1-membranes-and-membrane-transport",
+ "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",
+ "c2-2-neural-signalling"
+ ]
+ },
+ {
+ "question_id": "20N.2.HL.TZ0.3",
+ "Question": "
\n
The electron micrograph shows part of a cell including a mitochondrion.
\n

\n
[Source: Used with permission of McGraw-Hill Education, from Harrison’s Principles of Internal Medicine,
J L Jameson et al., 16th edition, 2004; permission conveyed through Copyright Clearance Center, Inc.]
\n
\n
Outline how the structures labelled X and Y are adapted to carry out the function of the mitochondrion.
\n
X:
\n
\n
Y:
\n
[2]
\n
a.
\n
\n
Explain how ATP is generated in mitochondria by chemiosmosis.
\n
[4]
\n
b.
\n
",
+ "Markscheme": "
\n
X: large/increased SA area for ATP production/electron transport/oxidative phosphorylation/proton pumping
OR
X: small/narrow intermembrane space for generating proton gradient (rapidly/steeply);
\n
Y: contains enzymes for Krebs cycle/link reaction;
\n
a.
\n
\n
a. protons pumped across inner membrane of mitochondria/into intermembrane space;
\n
b. using energy released by flow of electrons/by electron transport/by electron carriers;
\n
c. proton gradient established/maintained / proton motive force generated;
\n
d. protons pass/diffuse back through inner membrane/membrane of cristae/to matrix;
\n
e. through ATP synthase;
\n
f. ATP production coupled to flow of protons / ATP from ADP and Pi using energy from protons;
\n
Marks can be awarded in an annotated diagram.
\n
b.
\n
",
+ "Examiners report": "
\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
a.
\n
\n
This was answered more successfully by most candidates and there were some impressively detailed and accurate answers.
\n
b.
\n
",
+ "topics": [
+ "a-unity-and-diversity",
+ "b-form-and-function",
+ "c-interaction-and-interdependence"
+ ],
+ "subtopics": [
+ "a2-2-10-cell-types-and-cell-structures-viewed-in-light-and-electron-micrographs",
+ "a2-2-cell-structure",
+ "b2-2-4-adaptations-of-the-mitochondrion-for-production-of-atp-by-aerobic-cell-respiration",
+ "b2-2-organelles-and-compartmentalization",
+ "c1-2-15-chemiosmosis-and-the-synthesis-of-atp-in-the-mitochondrion",
+ "c1-2-cell-respiration",
+ "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",
+ "c2-1-chemical-signalling-[hl-only]"
+ ]
+ },
+ {
+ "question_id": "20N.2.HL.TZ0.6",
+ "Question": "
\n
Proteins are an important group of chemicals found in all living organisms.
\n
\n
Draw a molecular diagram to show the formation of a peptide bond.
\n
[3]
\n
a.
\n
\n
Outline how proteins are digested and the products of protein digestion absorbed in humans.
\n
[4]
\n
b.
\n
\n
Explain how polypeptides are produced by the process of translation.
\n
[8]
\n
c.
\n
",
+ "Markscheme": "
\n
a. two amino acids correctly drawn;
\n
b. removal/production of H2O molecule shown;
\n
c. peptide bond labelled between C of C=O and N of N-H;
\n

\n
Accept specific examples of amino acids correctly drawn for example glycine with H instead of R.
\n
mpc can be awarded if the peptide bond is shown as in the dipeptide diagram but there are errors elsewhere.
\n
a.
\n
\n
a. digested by peptidases/proteases;
\n
b. pepsin/pepsinogen/endopeptidase secreted by stomach (lining)/digests proteins in stomach;
\n
c. pancreas secretes/pancreatic juice contains endopeptidase/trypsin/peptidase;
\n
d. endopeptidase digest proteins/polypeptides to shorter chains of amino acids/shorter peptides;
\n
e. amino acids absorbed by active uptake/transport;
\n
f. in small intestine/ileum;
\n
g. villi increase the surface area for absorption;
\n
h. absorbed into bloodstream/into capillaries;
\n
Peptidase can be accepted instead of endopeptidase in mpc, but not in mpb or mpd.
\n
b.
\n
\n
a. mRNA is translated;
\n
b. mRNA binds with ribosome/with small subunit of ribosome;
\n
c. tRNA-activating enzymes/aminoacyl tRNA synthetases attach specific amino acid to tRNA;
\n
d. anticodon of 3 bases/nucleotides on tRNA;
\n
e. start codon/AUG on mRNA;
\n
f. tRNA carrying first amino acid/methionine binds to P/peptidyl site (when large subunit binds);
\n
g. anticodon (on tRNA) binds to codon (on mRNA);
\n
h. complementary base pairing (between codon and anticodon);
\n
i. tRNA for next codon binds to A site/amino acyl site;
\n
j. peptide bond forms between amino acids (on tRNAs) at P and A sites;
\n
k. ribosome moves along mRNA to next codon/by three bases/in 5’ to 3’ direction;
\n
l. tRNA released from E/exit site;
\n
m. process/cycle repeats to elongate the polypeptide/until stop codon is reached;
\n
n. release of polypeptide and mRNA/disassembly of ribosome complex at stop codon;
\n
Marks can be awarded in an annotated diagram.
\n
Accept UAA, UAG or UGA instead of stop codon in mpm or mpn but do not accept terminator sequence.
\n
Do not award mpk for the ribosome moving to the start codon in a 5’ to 3’ direction.
\n
c.
\n
",
+ "Examiners report": "
\n
Mostly full marks were gained although some had the correct diagrams but failed to label the peptide bond.
\n
a.
\n
\n
Nearly all candidates had some knowledge of protein digestion and many scored 3 or 4 of the 4-mark total. The relatively low mark allocation reflects that the program does not require detailed study of protein digestion or absorption. Few students referred to endopeptidases, which are stipulated in guidance for sub-topic 6.1 and also few stated that villi in the small intestine increase the surface area for absorption.
\n
b.
\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
c.
\n
",
+ "topics": [
+ "b-form-and-function",
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "b1-2-2-condensation-reactions-forming-dipeptides-and-longer-chains-of-amino-acids",
+ "b1-2-proteins",
+ "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",
+ "d1-2-5-translation-as-the-synthesis-of-polypeptides-from-mrna",
+ "d1-2-protein-synthesis"
+ ]
+ },
+ {
+ "question_id": "20N.2.HL.TZ0.7",
+ "Question": "
\n
Water is the medium of life.
\n
\n
Outline how hydrogen bonds form in water.
\n
[3]
\n
a.
\n
\n
Describe the processes that cause water to move from the roots of plants to their leaves.
\n
[4]
\n
b.
\n
\n
Explain the role of the kidney in osmoregulation.
\n
[8]
\n
c.
\n
",
+ "Markscheme": "
\n
a. water (molecules) are polar/dipolar/have partially positive and negative poles/have δ+ and δ-;
\n
b. attraction/bonding between positive and negative (poles);
\n
c. hydrogen bond formed between hydrogen and oxygen; Reject if H and O in same molecule.
\n
d. bond/attraction between different water molecules/intermolecular;
\n
Marks can be awarded in an annotated diagram.
\n
Reject answers stating or implying that there are whole positive or negative charges for mpa.
\n
a.
\n
\n
a. water moved/transported in xylem vessels;
\n
b. transported under tension/suction/pulled up (in xylem vessels);
\n
c. transpiration/loss of water (vapour) generates pulling forces/low pressure/tension;
\n
d. tension/pull generated when water evaporates from cell walls (in mesophyll);
\n
e. transpiration is loss of water vapour from leaf (surface)/stomata;
\n
f. cohesivity/cohesion in water due to hydrogen bonding/attractions between water molecules;
\n
g. cohesion/WTTE so chain/column of water (molecules) doesn’t break/remains continuous;
\n
h. transpiration stream is a column of/flow of water in xylem from roots to leaves;
\n
Do not award marks for absorption of water by roots.
\n
b.
\n
\n
a. osmoregulation is regulation of water and solute/salt balance/solute concentrations;
\n
b. nephron (is the functional unit of the kidney/osmoregulates);
\n
c. ultrafiltration in glomerulus / glomerular filtrate collected by Bowman’s capsule;
\n
d. loop of Henle establishes/maintains hypertonic conditions in medulla;
\n
e. osmosis/reabsorption of water (from filtrate) in the collecting duct;
\n
f. brain/hypothalamus monitors blood solute concentration / pituitary secretes ADH;
\n
g. ADH secreted when solute concentration of blood is too high/hypertonic/when dehydrated;
\n
h. ADH increases permeability of collecting duct to water;
\n
i. ADH causes more aquaporins (in membranes of collecting duct wall cells);
\n
j. more water reabsorbed resulting in more concentrated/hypertonic urine/less volume of urine;
\n
k. less/no ADH secreted when solute concentration (of blood) is too low/hypotonic;
\n
l. less water reabsorbed resulting in dilute/hypotonic urine/large volume of urine;
\n
Reject ‘water balance’ and ‘water concentration’ for mpa.
\n
c.
\n
",
+ "Examiners report": "
\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
a.
\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
b.
\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
c.
\n
",
+ "topics": [
+ "a-unity-and-diversity",
+ "b-form-and-function",
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "a1-1-2-hydrogen-bonds-as-a-consequence-of-the-polar-covalent-bonds-within-water-molecules",
+ "a1-1-water",
+ "b3-2-7-transport-of-water-from-roots-to-leaves-during-transpiration",
+ "b3-2-transport",
+ "d3-3-7-role-of-the-kidney-in-osmoregulation-and-excretion",
+ "d3-3-homeostasis"
+ ]
+ },
+ {
+ "question_id": "20N.2.SL.TZ0.1",
+ "Question": "
\n
A study was conducted to look at the short-term effects of a change in diet on the risk of disease in young adults. The table shows data on the habitual diet of the participants as well as the study diet followed for two weeks.
\n

\n
[Source: Horowitz, J.F., Ortega, J.F., Hinko, A., Li, M., Nelson, R.K. and Mora-Rodriguez, R.,
2018. Changes in markers for cardio-metabolic disease risk after only 1-2 weeks of a high saturated fat diet in
overweight adults. PLoS ONE, 13(6), e0198372.]
\n
\n
Total blood plasma cholesterol levels were measured before the study began and once a week after starting the study diet. Mean results are shown in the bar chart, including the standard deviation.
\n

\n
[Source: Horowitz, J.F., Ortega, J.F., Hinko, A., Li, M., Nelson, R.K. and Mora-Rodriguez, R.,
2018. Changes in markers for cardio-metabolic disease risk after only 1-2 weeks of a high saturated fat diet in
overweight adults. PLoS ONE, 13(6), e0198372.]
\n
\n
Control of blood glucose concentration was investigated using an oral glucose tolerance test. For this test, the person was given a concentrated glucose drink (at time zero) and then blood samples were taken every 15 minutes to determine the plasma insulin level. This test was done before the study diet and after two weeks on the study diet. Mean results are shown in the graph, including the standard deviation.
\n

\n
[Source: Horowitz, J.F., Ortega, J.F., Hinko, A., Li, M., Nelson, R.K. and Mora-Rodriguez, R.,
2018. Changes in markers for cardio-metabolic disease risk after only 1-2 weeks of a high saturated fat diet in
overweight adults. PLoS ONE, 13(6), e0198372.]
\n
\n
Comment on the total energy content of the two diets.
\n
[1]
\n
a.
\n
\n
Distinguish between the two diets.
\n
[2]
\n
b.
\n
\n
Calculate, showing your working, the percentage change in mean cholesterol level after one week on the study diet.
\n
\n
. . . . . . . . . . . . . . . . . . . .%
\n
[2]
\n
c.
\n
\n
Compare the data for plasma insulin levels before and after the study diet.
\n
[2]
\n
d.i.
\n
\n
State which cells secrete insulin.
\n
[1]
\n
d.ii.
\n
\n
Outline the reason for plasma insulin levels changing in the first 30 minutes of the test.
\n
[1]
\n
d.iii.
\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
[3]
\n
e.
\n
",
+ "Markscheme": "
\n
a. energy is not changed (between the two diets);
\n
b. study diet slightly lower in energy than habitual diet (but means/SD overlap);
\n
c. spread of values show more variation for habitual diet / higher SD in habitual;
\n
a.
\n
\n
a. they differ in percent of saturated and unsaturated fats (but not total fat);
\n
b. percent of saturated fats is higher in study diet / lower in habitual diet;
\n
c. (mono/poly) unsaturated fats decreased in study diet compared to habitual diet/more in habitual diet
OR
polyunsaturated fats in study diet only half of what they were in habitual diet;
\n
d. (slightly) less carbohydrate in study;
\n
Allow numerical points if they are a valid comparison using distinguishing terms.
\n
b.
\n
\n
((165–150) ÷ 150) × 100;
\n
(=) 10 (%);
\n
Allow up to 167 = 11.3 %
\n
1 mark for correct working if above 167.
\n
c.
\n
\n
a. both show same pattern of rise, level and then decrease / show same trend;
\n
b. both show same/similar levels of insulin (at all times) due to overlapping error bars;
\n
c. both rise for 30/45 minutes;
\n
Do not give credit for contrasts.
\n
d.i.
\n
\n
β cells of pancreas/islets (of Langerhans);
\n
d.ii.
\n
\n
as blood glucose rises, insulin rises/increases to reduce the level/OWTTE;
\n
Blood glucose must be mentioned as well as a rise in insulin.
\n
d.iii.
\n
\n
Hypothesis is partially supported
a. Increased saturated fats in study diet resulted in increase in cholesterol levels;
\n
b. cholesterol level is risk for blockage of coronary arteries;
\n
Hypothesis is not supported
c. high insulin levels are sign of (Type II) diabetes;
\n
d. insulin levels were the same in both diets so no increased risk;
\n
e. study only 2 weeks long;
\n
e.
\n
",
+ "Examiners report": "
\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
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
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
a.
\n
",
+ "topics": [
+ "b-form-and-function",
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "b1-1-10-difference-between-saturated-monounsaturated-and-polyunsaturated-fatty-acids",
+ "b1-1-carbohydrates-and-lipids",
+ "b1-2-3-dietary-requirements-for-amino-acids",
+ "b1-2-proteins",
+ "b4-2-9-adaptations-of-herbivores-for-feeding-on-plants-and-of-plants-for-resisting-herbivory",
+ "b4-2-ecological-niches",
+ "d3-3-3-regulation-of-blood-glucose-as-an-example-of-the-role-of-hormones-in-homeostasis",
+ "d3-3-homeostasis",
+ "d4-2-4-use-of-a-model-to-investigate-the-effect-of-variables-on-ecosystem-stability",
+ "d4-2-stability-and-change"
+ ]
+ },
+ {
+ "question_id": "20N.2.SL.TZ0.12",
+ "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
\n
\n (b)\n
\n
\n
\n Outline the principle of competitive exclusion.\n
\n
\n
\n
\n
\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
\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",
+ "Markscheme": "
\n (a)\n
\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
\n (b)\n
\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
\n (c)\n
\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
\n (d)\n
\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 (a)\n
\n
\n Overall, well answered.\n
\n
\n
\n (b)\n
\n
\n When describing competitive exclusion many candidates simply described competition. Some mentioned habitat rather than niche.\n
\n
\n
\n (d)\n
\n
\n Weaker candidates gave incomplete or confused suggestions in differentiating between the realised and fundamental niche.\n
\n
\n",
+ "topics": [
+ "b-form-and-function"
+ ],
+ "subtopics": [
+ "b4-2-12-fundamental-and-realized-niches",
+ "b4-2-13-competitive-exclusion-and-the-uniqueness-of-ecological-niches",
+ "b4-2-ecological-niches"
+ ]
+ },
+ {
+ "question_id": "20N.2.SL.TZ0.13",
+ "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
\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
\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
\n
\n (b.ii)\n
\n
\n
\n Describe how ingested plastics can cause problems to marine birds.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a.i)\n
\n
\n (a.ii)\n
\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
\n (b.i)\n
\n
\n C / albatrosses, petrels and shearwaters;\n
\n
\n
\n (b.ii)\n
\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": "
\n (a.i)\n
\n
\n This question outlining how plastic pollution affects marine birds was straightforward for all candidates.\n
\n
\n",
+ "topics": [
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "d4-2-10-effects-of-microplastic-and-macroplastic-pollution-of-the-oceans",
+ "d4-2-stability-and-change"
+ ]
+ },
+ {
+ "question_id": "20N.2.SL.TZ0.14",
+ "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
\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
\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
\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",
+ "Markscheme": "
\n (a.i)\n
\n
\n (a.ii)\n
\n
\n (b)\n
\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
\n (c)\n
\n
\n (the larger islands contain) more species as there are more habitats;\n
\n
\n",
+ "Examiners report": "
\n (a.i)\n
\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
\n (b)\n
\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
\n (c)\n
\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",
+ "topics": [
+ "a-unity-and-diversity"
+ ],
+ "subtopics": [
+ "a4-2-5-evidence-for-a-biodiversity-crisis",
+ "a4-2-conservation-of-biodiversity"
+ ]
+ },
+ {
+ "question_id": "20N.2.SL.TZ0.15",
+ "Question": "
\n
\n
\n Explain what information a pyramid of energy provides about an ecological community.\n
\n
\n
\n
\n
\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
\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
\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",
+ "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
\n (a)\n
\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
\n (b)\n
\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
\n (c)\n
\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 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
\n (a)\n
\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
\n (b)\n
\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
\n (c)\n
\n
\n Many suggested that sea urchins' predators were not present, but too many irrelevant or blank answers were seen.\n
\n
\n",
+ "topics": [
+ "a-unity-and-diversity",
+ "c-interaction-and-interdependence",
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "a4-2-6-causes-of-the-current-biodiversity-crisis",
+ "a4-2-conservation-of-biodiversity",
+ "c4-1-3-random-quadrat-sampling-to-estimate-population-size-for-sessile-organisms",
+ "c4-1-populations-and-communities",
+ "c4-2-11-construction-of-energy-pyramids",
+ "c4-2-transfers-of-energy-and-matter",
+ "d4-2-5-role-of-keystone-species-in-the-stability-of-ecosystems",
+ "d4-2-stability-and-change"
+ ]
+ },
+ {
+ "question_id": "20N.2.SL.TZ0.2",
+ "Question": "
\n
The photomicrograph below shows the protozoan Paramecium caudatum.
\n

\n
[Source: Deuterostome, CC BY-SA 3.0
https://creativecommons.org/licenses/by-sa/3.0, via Wikimedia Commons.]
\n
\n
State the genus of this organism.
\n
[1]
\n
a.i.
\n
\n
State the domain in which it is classified.
\n
[1]
\n
a.ii.
\n
\n
Outline the method of nutrition carried out by P. caudatum.
\n
[1]
\n
b.
\n
\n
Outline one aspect of how P. caudatum carries out homeostasis.
\n
[2]
\n
c.
\n
\n
Apart from the ribosomes, explain the evidence for the endosymbiotic theory of the origin of eukaryotic cells.
\n
[3]
\n
d.
\n
",
+ "Markscheme": "
\n
heterotroph/consumer as it feeds on bacteria/algae/yeast/smaller single celled organisms
OR
heterotroph/consumer as it does not have chloroplasts
\n
Heterotrophic must be qualified.
\n
b.
\n
\n
a. lives in fresh water so water enters cell (by osmosis);
\n
b. contractile vacuoles collect and expel water;
\n
c. homeostasis is keeping internal conditions within limit/constant / involves osmoregulation/regulating water content/potential;
\n
c.
\n
\n
a. mitochondria/chloroplasts show features in common with prokaryotes/similar size;
\n
b. multiply by binary fission/in same manner;
\n
c. have naked loop of DNA/circular DNA/own DNA;
\n
d. surrounded by a double membrane;
\n
d.
\n
",
+ "Examiners report": "
\n
In a about half of the candidates named the genus correctly (Paramaecium), 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
a.i.
\n
",
+ "topics": [
+ "a-unity-and-diversity",
+ "b-form-and-function",
+ "c-interaction-and-interdependence"
+ ],
+ "subtopics": [
+ "a2-2-12-origin-of-eukaryotic-cells-by-endosymbiosis",
+ "a2-2-cell-structure",
+ "b1-1-12-formation-of-phospholipid-bilayers-as-a-consequence-of-the-hydrophobic-and-hydrophilic-regions",
+ "b1-1-carbohydrates-and-lipids",
+ "b2-1-10-fluid-mosaic-model-of-membrane-structure",
+ "b2-1-membranes-and-membrane-transport",
+ "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",
+ "c2-2-neural-signalling"
+ ]
+ },
+ {
+ "question_id": "20N.2.SL.TZ0.3",
+ "Question": "
\n
The diagram shows part of two neurons.
\n

\n
[Source: © International Baccalaureate Organization 2020.]
\n
\n
Outline how the amphipathic properties of phospholipids play a role in membrane structure.
\n
[2]
\n
a.
\n
\n
State the name of the structure shown.
\n
[1]
\n
b.i.
\n
\n
X indicates the movement of a structure in the neuron. Explain what events trigger this movement and what happens next.
\n
[3]
\n
b.ii.
\n
",
+ "Markscheme": "
\n
a. part hydrophobic/not attracted to water/non-polar AND part hydrophilic/attracted to water/polar; Both needed.
\n
b. bilayer formed (formed naturally by phospholipids in water);
\n
c. hydrophilic heads/parts face outwards AND hydrophobic tails/parts face inwards;
\n
Do not allow water loving/hating in mpa or mpc.
\n
a.
\n
\n
synapse/synaptic
\n
b.i.
\n
\n
a. depolarization of pre-synaptic membrane / action potential/nerve impulse arrives;
\n
b. uptake of calcium / calcium ions diffuse in / calcium channels open;
\n
c. structures containing neurotransmitter/vesicles move to/fuse with membrane;
\n
d. neurotransmitter/acetylcholine released by exocytosis into cleft/binds to postsynaptic membrane/receptors;
\n
b.ii.
\n
",
+ "Examiners report": "
\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
a.
\n
",
+ "topics": [
+ "b-form-and-function",
+ "c-interaction-and-interdependence"
+ ],
+ "subtopics": [
+ "b1-1-12-formation-of-phospholipid-bilayers-as-a-consequence-of-the-hydrophobic-and-hydrophilic-regions",
+ "b1-1-carbohydrates-and-lipids",
+ "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",
+ "c2-1-chemical-signalling-[hl-only]"
+ ]
+ },
+ {
+ "question_id": "20N.2.SL.TZ0.4",
+ "Question": "
\n
Sketch the complementary strand to complete the section of a DNA diagram.
\n

\n
[3]
\n
a.
\n
\n
Define mutation.
\n
[1]
\n
b.i.
\n
\n
Explain how evolution by natural selection depends on mutations.
\n
[4]
\n
b.ii.
\n
",
+ "Markscheme": "
\n
a. correct base sequence: T, G, A;
\n
b. strand drawn anti-parallel;
\n
c. correct shapes used;
\n

\n
Award [2 max] if bonds are not from the correct carbon or if the nucleotides are not joined.
\n
a.
\n
\n
change in genetic makeup/DNA/nucleotide/base sequence
\n
b.i.
\n
\n
a. mutations cause variation among organisms of same species/population;
\n
b. some variations/mutations make individual more suited to its environment/way of life;
\n
c. individuals that are better adapted survive and produce offspring;
\n
d. individuals pass on genetic characteristics/mutation/variation to offspring;
\n
e. natural selection increases frequency of characteristics/alleles that make individuals better adapted;
\n
b.ii.
\n
",
+ "Examiners report": "
\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 etc.
\n
a.
\n
",
+ "topics": [
+ "a-unity-and-diversity",
+ "c-interaction-and-interdependence",
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "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",
+ "a1-2-nucleic-acids",
+ "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",
+ "c4-2-transfers-of-energy-and-matter",
+ "d1-3-4-causes-of-gene-mutation",
+ "d1-3-mutations-and-gene-editing",
+ "d4-1-2-roles-of-mutation-and-sexual-reproduction-in-generating-the-variation-on-which-natural-selection-acts",
+ "d4-1-natural-selection"
+ ]
+ },
+ {
+ "question_id": "20N.2.SL.TZ0.5",
+ "Question": "
\n
Life is based on carbon compounds.
\n
\n
Draw a molecular diagram of alpha-D-glucose.
\n
[3]
\n
a.
\n
\n
Outline how carbon compounds are produced in cells using light energy.
\n
[5]
\n
b.
\n
\n
Explain the transformations of carbon compounds in the carbon cycle.
\n
[7]
\n
c.
\n
",
+ "Markscheme": "
\n
a. hexagonal ring structure with O at one point (between C1 and C5);
\n
b. correct orientation of OH groups (on carbons 1 to 4); Hydrogens not required
\n
c. CH2OH group shown on fifth carbon with correct orientation;
OR
d. 6 carbon chain with oxygen on first C;
\n
e. H and OH groups correctly orientated;
\n
Carbons do not need to be numbered.
\n
Allow boat or chair diagrams.
\n

\n
Allow [2 max] if linear structure drawn.
\n
a.
\n
\n
a. occurs by the process of photosynthesis;
\n
b. occurs in chloroplasts of plant cells/using chlorophyll;
\n
c. chlorophyll absorbs red/blue light AND reflects green light; Both needed for marking point.
\n
d. raw materials/starting products are carbon dioxide and water/shown in an equation;
\n
e. water is split by photolysis;
\n
f. oxygen is produced as waste/by-product/lost;
\n
g. glucose formed/shown in an equation;
\n
h. glucose molecules combine to form starch for storage;
\n
i. light energy transformed to chemical;
\n
b.
\n
\n
a. autotrophs/producers convert carbon dioxide into carbohydrates/carbon compounds in photosynthesis;
\n
b. carbon dioxide diffuses/moves from the atmosphere /water into autotrophs/plants;
\n
c. carbon compounds are transferred through food chains/OWTTE;
\n
d. carbon dioxide produced by respiration diffuses out of organisms into water/atmosphere;
\n
e. decomposers release carbon dioxide during decay/putrefaction;
\n
f. methane is produced from organic matter in anaerobic conditions (by methanogens);
\n
g. some methane diffuses into the atmosphere/accumulates in the ground;
\n
h. methane is oxidized to carbon dioxide (and water) in the atmosphere;
\n
i. peat forms when organic matter is not fully decomposed because of acidic/anaerobic conditions in waterlogged soils;
\n
j. partially decomposed organic matter from past geological eras/fossils was converted into coal/oil/gas that accumulated in rocks;
\n
k. carbon dioxide is produced by the combustion of biomass/fossilized organic matter/fuels;
\n
i. hard parts of some animals/corals/molluscs are composed of calcium carbonate
\n
m. can become fossilized in limestone;
\n
As this is an “explain” question, simply drawing a labelled diagram is not enough for [7]. Diagram would need sufficient annotations to meet the command term.
\n
If carbon compounds are referred to instead of carbon dioxide, penalise once then ecf.
\n
c.
\n
",
+ "Examiners report": "
\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
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 etc. Many drew some quite detailed flow charts of the carbon cycle from which some marks could be gleaned or ambiguous statements clarified.
\n
a.
\n
",
+ "topics": [
+ "c-interaction-and-interdependence",
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "c1-3-1-transformation-of-light-energy-to-chemical-energy-when-carbon-compounds-are-produced-in-photosynthesis",
+ "c1-3-photosynthesis",
+ "c4-2-18-ecosystems-as-carbon-sinks-and-carbon-sources",
+ "c4-2-22-recycling-of-all-chemical-elements-required-by-living-organisms-in-ecosystems",
+ "c4-2-transfers-of-energy-and-matter",
+ "d3-2-10-incomplete-dominance-and-codominance",
+ "d3-2-inheritance"
+ ]
+ },
+ {
+ "question_id": "20N.2.SL.TZ0.6",
+ "Question": "
\n
According to the cell theory, living organisms are composed of cells.
\n
\n
Draw the ultrastructure of a prokaryotic cell based on electron micrographs.
\n
[3]
\n
a.
\n
\n
Outline what occurs in cells in the first division of meiosis.
\n
[5]
\n
b.
\n
\n
Explain the role of cells in the defence against infectious disease.
\n
[7]
\n
c.
\n
",
+ "Markscheme": "
\n
a. cell wall;
\n
b. plasma membrane; Clearly shown as a separate line under the cell wall or the inner line
\n
c. cytoplasm AND 70S ribosomes; Do not allow (small) circles
\n
d. nucleoid/naked DNA;
\n
e. plasmid
OR
pili
OR
flagella/flagellum;
\n
Structures correctly drawn and labelled.
\n
Award [2 max] if any exclusively eukaryotic structures are shown.
\n
Do not allow cilia as they are not found in prokaryotes.
\n
a.
\n
\n
a. halves the chromosome number/produces haploid cells;
\n
b. at start of meiosis each chromosome consists of two sister chromatids attached by a centromere;
\n
c. prophase (I): pairing of homologous chromosomes;
\n
d. crossing over occurs;
\n
e. chromosomes condense by supercoiling;
\n
f. metaphase (I): pairs of homologous chromosomes/bivalents move to equator of spindle
OR
metaphase (I): orientation of pairs of homologous chromosomes (prior to separation) is random;
\n
g. anaphase (I): centromeres do not divide
OR
anaphase (I): spindle fibre pulls chromosome/whole centromere with two sister chromatids to opposite poles;
\n
h. telophase (I): arrival of centromere with sister chromatids at opposite poles;
\n
Some of these can be awarded for correctly annotated diagrams.
\n
No credit for events in meiosis II.
\n
b.
\n
\n
a. cells of skin provide a physical barrier/produce fatty acids/lactic acid/lysozyme which stops entry of microbes
OR
mucous membranes produce mucus to trap pathogens
OR
stomach cells produce hydrochloric acid which kills microbes;
\n
b. platelets start the clotting process preventing access of pathogens;
\n
c. (two types of) white blood cells fight infections in the body;
\n
d. phagocytes ingest pathogens (by endocytosis/phagocytosis);
\n
e. gives non-specific immunity to diseases / ingest any type of pathogen;
\n
f. production of antibodies by lymphocytes/B cells;
\n
g. in response to particular pathogens/antigens;
\n
h. gives specific immunity;
\n
i. lymphocyte/B cell makes only one type of antibody;
\n
j. plasma cells produce large quantity of (one type of) antibody;
\n
k. some lymphocytes act/remain as memory cells;
\n
l. can quickly reproduce to form a clone of plasma cells if a pathogen carrying a specific antigen is re-encountered;
\n
m. results in faster defence against second exposure to specific antigen/pathogen/disease;
\n
c.
\n
",
+ "Examiners report": "
\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
a.
\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
b.
\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
c.
\n
",
+ "topics": [
+ "a-unity-and-diversity",
+ "b-form-and-function",
+ "c-interaction-and-interdependence",
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "a2-2-11-drawing-and-annotation-based-on-electron-micrographs",
+ "a2-2-cell-structure",
+ "b1-2-2-condensation-reactions-forming-dipeptides-and-longer-chains-of-amino-acids",
+ "b1-2-proteins",
+ "c3-2-6-lymphocytes-as-cells-in-the-adaptive-immune-system-that-cooperate-to-produce-antibodies",
+ "c3-2-defence-against-disease",
+ "d2-1-9-meiosis-as-a-reduction-division",
+ "d2-1-cell-and-nuclear-division"
+ ]
+ },
+ {
+ "question_id": "20N.2.SL.TZ0.7",
+ "Question": "
\n
\n (a)\n
\n
\n
\n Outline how hydrogen bonds form in water.\n
\n
\n
\n
\n
\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",
+ "Markscheme": "
\n (a)\n
\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
\n (b)\n
\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 (a)\n
\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
\n (b)\n
\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",
+ "topics": [
+ "a-unity-and-diversity",
+ "b-form-and-function"
+ ],
+ "subtopics": [
+ "a1-1-2-hydrogen-bonds-as-a-consequence-of-the-polar-covalent-bonds-within-water-molecules",
+ "a1-1-water",
+ "b3-2-7-transport-of-water-from-roots-to-leaves-during-transpiration",
+ "b3-2-transport"
+ ]
+ },
+ {
+ "question_id": "21M.2.HL.TZ1.1",
+ "Question": "
\n
The mechanism of action of vinblastine, an anticancer drug, was investigated over a range of concentrations. Vinblastine is an alkaloid isolated from the periwinkle plant (Catharansus roseus). The percentage of cells in mitosis and ratio of anaphase to metaphase in cells exposed to this drug in vitro for a fixed time were recorded. The data are displayed in two graphs.
\n

\n
[Source: Republished with permission of American Society for Pharmacology and Experimental Therapeutics, from Mechanism of Mitotic Block and Inhibition of Cell Proliferation by the Semisynthetic Vinca Alkaloids Vinorelbine and Its Newer Derivative Vinflunine, Molecular Pharmacology, Vivian K. Ngan, Krista Bellman, Bridget T. Hill, Leslie Wilson and Mary Ann Jordan, Volume 60 , Issue 1, 2001; permission conveyed through Copyright Clearance Center, Inc.]
\n
\n
By referring to both graphs, evaluate the hypothesis that vinblastine targets cells in mitosis and prevents them from completing the process.
\n
[3]
\n
e.
\n
\n
Some anticancer drugs inhibit mitosis by blocking the formation of the spindle. Suggest one other way in which vinblastine could block mitosis.
\n
[1]
\n
f.
\n
\n
Discuss one advantage and one disadvantage of using plant tissue to investigate drugs intended to treat cancer in humans.
\n
Advantage:
\n
\n
Disadvantage:
\n
[2]
\n
g.
\n
",
+ "Markscheme": "
\n
Evaluation of evidence in graph on left
\n
a. increase in (percentage of) cells in mitosis (as vinblastine concentration rises) ✔
\n
b. supports hypothesis that cells get stuck in/cannot complete mitosis ✔
\n
Evaluation of evidence in graph on right
\n
c. drop in anaphase-metaphase ratio due to fewer cells in anaphase/more cells in metaphase ✔
\n
d. cells not progressing from metaphase to anaphase/get stuck in metaphase ✔
\n
Do not allow mpa if the candidate is arguing that the hypothesis is not supported.
\n
e.
\n
\n
a. causes microtubules/spindle fibres to break up / tubulin molecules to depolymerize ✔
\n
b. prevents contraction of spindle microtubules/fibres ✔
\n
c. disrupts/damages kinetochores/centromeres/microtubule motors/centrioles/centrosomes ✔
\n
d. prevents separation/pulling apart of (sister) chromatids/chromosomes/centromeres ✔
\n
e. prevents microtubules/spindle binding to chromatids/chromosomes/centromeres/DNA ✔
\n
Mark the first suggestion only in the answer.
\n
Do not allow answers about DNA replication or other processes that precede mitosis.
\n
f.
\n
\n
Advantage:
\n
avoids risks for humans/harm to humans / more ethical (than with human patients/volunteers) ✔
\n
Disadvantage:
\n
differences between plant and human cells so humans may not respond in same way
OR
plants have cell wall/no centrioles/other relevant difference between plant and human cells ✔
\n
Not enough for mpa to say ‘not using humans’.
\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
g.
\n
",
+ "Examiners report": "
\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
e.
\n
\n
A wide range of possible ways in which mitosis could be blocked was accepted and about a third of candidates suggested one of these. Methods of blocking DNA replication or cytokinesis were not accepted as the question specifically referred to mitosis.
\n
f.
\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
g.
\n
",
+ "topics": [
+ "a-unity-and-diversity",
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "a2-3-6-rapid-evolution-in-viruses",
+ "a2-3-viruses-(hl-only)",
+ "d2-1-1-generation-of-new-cells-in-living-organisms-by-cell-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",
+ "d2-1-cell-and-nuclear-division"
+ ]
+ },
+ {
+ "question_id": "21M.2.HL.TZ1.2",
+ "Question": "
\n
The image shows part of a plant cell with a chloroplast in close proximity to mitochondria.
\n

\n
[Source: Photo © E. Newcomb.]
\n
\n
State two structural similarities between mitochondria and chloroplasts.
\n
1.
\n
2.
\n
\n
[2]
\n
a.
\n
\n
Compare and contrast mitochondria and chloroplasts in terms of the substrates they use and the products they produce.
\n
[2]
\n
b.
\n
\n
Outline how the compounds produced by chloroplasts are distributed throughout the plant.
\n
[3]
\n
c.
\n
",
+ "Markscheme": "
\n
a. (a loop of) DNA ✔
\n
b. 70S ribosomes ✔
\n
c. double membrane ✔
\n
d. electron transport chains/enzyme complexes in (internal) membranes ✔
\n
e. enzymes in a region of fluid/in stroma and matrix ✔
\n
f. large area of (internal) membrane/cristae and thylakoids ✔
\n
Only two answers should be marked – the first on each line.
\n
Do not award marks for functions rather than structures, for example ATP production.
\n
Allow spaces inside cristae and thylakoids for mpf.
\n
a.
\n
\n
a. ATP produced by both / ADP used by both ✔
\n
b. oxygen produced by chloroplasts and used by mitochondria ✔
\n
c. carbon dioxide produced by mitochondria and used by chloroplasts ✔
\n
d. carbon/organic compounds built up in chloroplasts/anabolism and broken down in mitochondria/catabolism ✔
\n
Do not award mpd for statements about carbohydrates or glucose (because the pyruvate used by mitochondria is not a carbohydrate).
\n
b.
\n
\n
a. in phloem ✔
\n
b. loading into sieve tubes/by active transport/by cotransport/by companion cells ✔
\n
c. entry of water (to phloem) by osmosis/because of high solute concentration ✔
\n
d. causes high/hydrostatic pressure ✔
\n
e. flow from high pressure to lower pressure down pressure gradient ✔ from source to sink ✔
\n
Do not award mpa if xylem included with phloem.
\n
Do not award a mark solely for mentioning the term ‘translocation'.
\n
c.
\n
",
+ "Examiners report": "
\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
a.
\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
b.
\n
\n
This question also required a link to be made, after which marks were relatively easily earned. The phase 'distributed throughout the plant' indicated that it was carbon compounds, not oxygen, that were the issue, so phloem transport was the distribution method expected. Transport of oxygen out through stomata and transport within leaf cells were not relevant to the question as asked. The average score was only 0.6 out of 3.
\n
c.
\n
",
+ "topics": [
+ "a-unity-and-diversity",
+ "b-form-and-function",
+ "c-interaction-and-interdependence"
+ ],
+ "subtopics": [
+ "a2-2-6-eukaryote-cell-structure",
+ "a2-2-cell-structure",
+ "b2-2-4-adaptations-of-the-mitochondrion-for-production-of-atp-by-aerobic-cell-respiration",
+ "b2-2-5-adaptations-of-the-chloroplast-for-photosynthesis",
+ "b2-2-organelles-and-compartmentalization",
+ "b3-2-18-adaptations-of-phloem-sieve-tubes-and-companion-cells-for-translocation-of-sap",
+ "b3-2-transport",
+ "c1-3-18-synthesis-of-carbohydrates-amino-acids-and-other-carbon-compounds-using-the-products-of-the-calvin-cycle-and-mineral-nutrients",
+ "c1-3-photosynthesis"
+ ]
+ },
+ {
+ "question_id": "21M.2.HL.TZ1.4",
+ "Question": "
\n
Plasma cells secrete antibodies against specific antigens. Outline how plasma cells become activated.
\n
[3]
\n
a.
\n
\n
A hybridoma is a cell produced by the fusion of a plasma cell with a tumour cell. Explain the advantages of using hybridoma cells in the production of monoclonal antibodies.
\n
[2]
\n
b.
\n
\n
State one use of monoclonal antibodies.
\n
[1]
\n
c.
\n
",
+ "Markscheme": "
\n
a. macrophages/phagocytes recognize/engulf pathogen and display antigens ✔
\n
b. antigen binds to T cell/helper T cell / antigen causes activation of T cell ✔
\n
c. antigen binds to antibodies in membrane of B cells ✔
\n
d. (activated) T cells activate B cells (that have the antigen bound to them) ✔
\n
e. activated B cells divide to produce a clone of cells ✔
\n
f. active plasma cells develop from the clone of cells/from activated B cells ✔
\n
Accept B-lymphocyte and Tlymphocyte instead of B cell and T cell throughout the answer.
\n
a.
\n
\n
a. endless cell divisions/unregulated mitosis (in hybridoma cells) ✔
\n
b. large clone/population of identical cells produced ✔
\n
c. all cells (in clone) produce same type of antibody ✔
\n
d. large amount of (chosen) antibody can be produced ✔
\n
For mpa it must be clear that it is the hybridoma cells not tumour cells that divide endlessly and that division is more than just rapid.
\n
b.
\n
\n
a. pregnancy testing kits/detection of hCG (to diagnose pregnancy) ✔
\n
b. produce antibodies for treating arthritis/C.difficile/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
OR
gives artificial/passive immunity (if injected) ✔
\n
c. blood typing/testing urine for drugs/other verified specific use of monoclonal antibodies ✔
\n
Mark only the first answer.
\n
c.
\n
",
+ "Examiners report": "
\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
a.
\n
\n
This was another low-scoring question for most candidates. Many did not understand well enough how hybridoma cells are produced. There was also a lack of distinction between rapid proliferation of cells and proliferation that continues indefinitely.
\n
b.
\n
",
+ "topics": [
+ "b-form-and-function",
+ "c-interaction-and-interdependence",
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "b2-1-15-sodium-potassium-pumps-as-an-example-of-exchange-transporters",
+ "b2-1-membranes-and-membrane-transport",
+ "c2-2-10-oscilloscope-traces-showing-resting-potentials-and-action-potentials",
+ "c2-2-neural-signalling",
+ "c3-2-9-multiplication-of-activated-b-lymphocytes-to-form-clones-of-antibody-secreting-plasma-cells",
+ "c3-2-defence-against-disease",
+ "d3-1-17-pregnancy-testing-by-detection-of-human-chorionic-gonadotropin-secretion",
+ "d3-1-reproduction"
+ ]
+ },
+ {
+ "question_id": "21M.2.HL.TZ1.5",
+ "Question": "
\n
\n (b)\n
\n
\n
\n Explain how cladistics can be used to investigate evolutionary relationships.\n
\n
\n
\n
\n
\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",
+ "Markscheme": "
\n (b)\n
\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
\n (c)\n
\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 (b)\n
\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
\n (c)\n
\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",
+ "topics": [
+ "a-unity-and-diversity"
+ ],
+ "subtopics": [
+ "a3-2-2-difficulties-classifying-organisms-into-the-traditional-hierarchy-of-taxa",
+ "a3-2-7-analysing-cladograms",
+ "a3-2-8-using-cladistics-to-investigate-whether-the-classification-of-groups-corresponds-to-evolutionary-relationships",
+ "a3-2-classification-and-cladistics-(hl-only)"
+ ]
+ },
+ {
+ "question_id": "21M.2.HL.TZ1.6",
+ "Question": "
\n
Hormones are produced by one tissue in an organism and have their effect on a target tissue.
\n
\n
Describe the genetic and hormonal control of male sexual characteristics in a human.
\n
[3]
\n
a.
\n
\n
Outline how the hormone auxin controls phototropism in plant shoots.
\n
[5]
\n
b.
\n
\n
Compare and contrast hormonal and nervous communication.
\n
[7]
\n
c.
\n
",
+ "Markscheme": "
\n
a. male if (X and) Y chromosomes present ✔
\n
b. gene on Y chromosome/SRY promotes development of testes (from embryonic gonads) ✔
\n
c. testes secrete testosterone ✔
\n
d. testosterone stimulates sperm production/spermatogenesis ✔
\n
e. testosterone stimulates development (in fetus) of male genitals/primary sexual characteristics ✔
\n
f. testosterone stimulates development of male secondary sexual characteristics
OR
testosterone causes changes to become adult male during puberty ✔
\n
Allow first alternative for mpf if two secondary sexual characteristics are named instead of the general term ‘secondary sexual characteristics’.
\n
a.
\n
\n
a. grows/bends towards (brightest) light/sun ✔
\n
b. auxin moved from lighter to shadier side (of shoot/stem tip/apex) ✔
\n
c. moved by auxin efflux pumps ✔
\n
d. auxin promotes cell elongation/cell growth / auxin causes cell wall acidification/loosening ✔
\n
e. more growth on shady side of stem (due to auxin concentration gradient) ✔
\n
f. binds to auxin receptors (in target cells) ✔
\n
g. auxin/auxin receptors promote expression of genes (for growth)/for H+ secretion into wall ✔
\n
b.
\n
\n
Similarities
\n
a. both used for communication between cells/tissues/organs/parts of the body / WTTE ✔
\n
b. both cause a response/change in specific/target cells
OR
both use chemicals that bind to receptors / hormones and neurotransmitters are both chemicals ✔
\n
c. both can stimulate or inhibit (processes in target cells) / WTTE ✔
\n
d. both can work over long distances/between widely separated parts of the body / WTTE ✔
\n
e. both under (overall) control of the brain/CNS / brain (has role in) sending hormones and nerve impulses ✔
\n
f. both use feedback mechanisms/negative feedback / both used in homeostasis ✔
\n
Differences
\n

\n
m. example of use of hormonal and use of nervous communication ✔
\n
c.
\n
",
+ "Examiners report": "
\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
a.
\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
b.
\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
c.
\n
",
+ "topics": [
+ "c-interaction-and-interdependence",
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "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",
+ "c3-1-integration-of-body-systems",
+ "d3-1-3-differences-between-male-and-female-sexes-in-sexual-reproduction",
+ "d3-1-reproduction"
+ ]
+ },
+ {
+ "question_id": "21M.2.HL.TZ1.8",
+ "Question": "
\n
Cellular processes at the molecular level are regulated by enzymes.
\n
\n
Outline the process of DNA profiling.
\n
[4]
\n
a.
\n
\n
Outline the role of DNA polymerase III in DNA replication.
\n
[4]
\n
b.
\n
\n
Explain the factors that affect the rate of enzyme-controlled reactions in cells.
\n
[7]
\n
c.
\n
",
+ "Markscheme": "
\n
a. sample of DNA obtained from person/hair/blood/mouth/crime scene ✔
\n
b. PCR used to amplify/make copies of DNA (in sample) ✔
\n
c. using Taq DNA polymerase / using DNA polymerase from thermophilic bacteria ✔
\n
d. tandem repeats amplified/used ✔
\n
e. gel electrophoresis used to separate DNA (into bands) ✔
\n
f. separation according to length of fragments/number of repeats
OR
fragments of same length/number of repeats travel same distance ✔
\n
g. pattern of bands/numbers of repeats is the profile/is unique to the individual ✔
\n
h. example of application/forensics/crime investigation/paternity ✔
\n
Do not accept ‘determine ancestry’ for mph. Other genes/chromosomes are more often used for that.
\n
Accept STR for (short) tandem repeat in mpd.
\n
a.
\n
\n
a. binds to template strand adjacent to a primer/at the primer ✔
\n
b. adds nucleotides to template strand/to single stranded DNA ✔
\n
c. using complementary base pairing ✔
\n
d. links nucleotides with sugar-phosphate/phosphodiester bonds ✔
\n
e. adds nucleotides/builds new strand in 5' 3' direction ✔
\n
f. lagging strand is built in short segments/Okazaki fragments/synthesis is discontinuous ✔
\n
Accept A to T and G to C instead of ‘complementary’ in mpc.
\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
b.
\n
\n
a. temperature increases rate up to optimum and higher temperatures decrease rate / graph ✔
\n
b. faster molecular movement as temperature rises (so more substrate-active site collisions) ✔
\n
c. high temperature/heat causes denaturation/irreversible change to active site (so rate reduces) ✔
\n
d. rate decreased if pH is above and below optimum/if pH is too high or low / graph ✔
\n
e. pH affects shape/structure of enzyme/active site /affects ionization (of amino acids) ✔
\n
f. increases in substrate concentration cause rate to rise towards a plateau/WTTE / graph ✔
\n
g. greater chance of substrate-active site collisions with higher substrate concentration
OR
active sites saturated/all full at high substrate concentrations ✔
\n
h. higher enzyme concentration increases rate (as there are more active sites) ✔
\n
i. enzyme inhibitors/competitive inhibitors/non-competitive inhibitors reduce the rate ✔
\n
j. end-product inhibitors switch off metabolic pathway / act on enzyme at start of pathway rate ✔
OR
allosteric site used to control enzyme activity by binding of (non-competitive) inhibitor
\n
Graphs can be used for mpa, mpd mpf and mph but x-axis must have the variable indicated.
\n
For mpa there must be exponential rise to optimum then faster drop.
\n
For mpd there must be a bellshaped curve but it need not be exactly symmetrical.
\n
For mpf and mph there must be decreasing increases in rate towards a plateau.
\n
c.
\n
",
+ "Examiners report": "
\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
a.
\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
b.
\n
\n
This was expected to be high-scoring, because it is such a standard topic, but candidates may have been running out of steam by the time they reached it and many answers were too brief, with significant points omitted.
\n
c.
\n
",
+ "topics": [
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "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",
+ "d1-1-dna-replication"
+ ]
+ },
+ {
+ "question_id": "21M.2.HL.TZ2.1",
+ "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
\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
\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
\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
\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
\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
\n
\n (g)\n
\n
\n
\n Explain how neonicotinoids affect synaptic transmission in insects.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n (b)\n
\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
\n (c)\n
\n
\n 57 (%) ✔\n
\n
\n \n Allow range 56 % to 58 %\n \n .\n
\n
\n
\n (d)\n
\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
\n (e)\n
\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
\n (f)\n
\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
\n (g)\n
\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 (a)\n
\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
\n (b)\n
\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
\n (c)\n
\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
\n (d)\n
\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
\n (e)\n
\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
\n (f)\n
\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
\n (g)\n
\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",
+ "topics": [
+ "c-interaction-and-interdependence"
+ ],
+ "subtopics": [
+ "c2-2-12-effects-of-exogenous-chemicals-on-synaptic-transmission",
+ "c2-2-neural-signalling"
+ ]
+ },
+ {
+ "question_id": "21M.2.HL.TZ2.2",
+ "Question": "
\n
Cholinergic synapses use acetylcholine as their neurotransmitter. They are widespread in the body, passing on signals to muscle cells. These synapses are affected by neonicotinoid pesticides.
\n
The diagrams, which are not drawn to scale, show the synapse between two neurons and a detail of the synaptic cleft.
\n

\n
\n
On the diagrams, label with a letter H the hydrophilic end of a phospholipid.
\n
[1]
\n
a.i.
\n
\n
On the diagrams, label with a letter E a vesicle involved in exocytosis.
\n
[1]
\n
a.ii.
\n
\n
On the diagrams, label with a letter P a location where a neonicotinoid pesticide could bind.
\n
[1]
\n
a.iii.
\n
\n
Outline how depolarization of the membrane of an axon occurs.
\n
[2]
\n
b.
\n
\n
Explain how acetylcholine initiates an action potential in a postsynaptic membrane.
\n
[2]
\n
c.
\n
\n
State the action of the enzyme acetylcholinesterase.
\n
[1]
\n
d.i.
\n
\n
Explain what happens to an enzyme if there is a change of pH.
\n
[3]
\n
d.ii.
\n
",
+ "Markscheme": "
\n
hydrophilic end of phospholipid shown ✔
\n
For 2a, i, ii and iii, accept letters written on the structure even if a line is not drawn.
\n
Award the mark if the full word is used to label the structure. Labels must be unambiguous.
\n
a.i.
\n
\n
an exocytic vesicle shown ✔
\n
For 2 a, i, ii and iii, accept letters written on the structure even if a line is not drawn.
\n
Award the mark if the full word is used to label the structure. Labels must be unambiguous.
\n
Accept any of the three intact circles or the exocytosis shown within the box.
\n
a.ii.
\n
\n
any receptor protein on post synaptic membrane marked ✔
\n
For 2 a, i, ii and iii, accept letters written on the structure even if a line is not drawn.
\n
Award the mark if the full word is used to label the structure.
\n
Must unambiguously be pointed to a receptor on the synapse side. Accept labels of acetylcholinesterase.
\n
a.iii.
\n
\n
a. (local depolarization) causes ion / sodium / voltage gated channels to open ✔
\n
b. altering membrane permeability to sodium ions/Na+/positive ions / Na+ diffuses into the cytoplasm ✔
\n
c. membrane potential (of the axon) changes from negative to positive ✔
\n
d. a threshold potential is reached and an action potential is generated ✔
\n
Do not accept sodium pumps.
\n
Mp b requires evidence that the student recognizes sodium is an ion.
\n
Numerical values indicating change from −70 to +30/+40/+55 can be accepted.
\n
b.
\n
\n
a. acetylcholine binds to the receptor protein ✔
\n
b. (causing a) change in tertiary structure / conformation of protein ✔
\n
c. diffusion/entry of ions / Na+ through the receptor/channel protein allowed ✔
\n
c.
\n
\n
breaks down acetylcholine (to acetyl and choline) ✔
\n
d.i.
\n
\n
a. change in pH can cause a change in the tertiary structure of the enzyme
OR
enzyme denatured ✔
\n
b. causing a change in the active site / substrate not able to bind ✔
\n
c. the enzyme will not work as efficiently / decreased rate of reaction ✔
\n
d. (may no longer be) the optimum/optimal pH for enzyme activity ✔
\n
Allow answer in the form of a graph.
\n
d.ii.
\n
",
+ "Examiners report": "
\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
a.i.
\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
a.iii.
\n
\n
In many exams, candidates seemed to confuse the voltage gated ion channels with sodium-potassium pumps.
\n
b.
\n
",
+ "topics": [
+ "b-form-and-function",
+ "c-interaction-and-interdependence",
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "b1-1-12-formation-of-phospholipid-bilayers-as-a-consequence-of-the-hydrophobic-and-hydrophilic-regions",
+ "b1-1-carbohydrates-and-lipids",
+ "b1-2-5-effect-of-ph-and-temperature-on-protein-structure",
+ "b1-2-proteins",
+ "b2-1-13-membrane-fluidity-and-the-fusion-and-formation-of-vesicles",
+ "b2-1-membranes-and-membrane-transport",
+ "c2-1-5-localized-and-distant-effects-of-signalling-molecules",
+ "c2-1-chemical-signalling-[hl-only]",
+ "c2-2-6-release-of-neurotransmitters-from-a-presynaptic-membrane",
+ "c2-2-7-generation-of-an-excitatory-postsynaptic-potential",
+ "c2-2-neural-signalling",
+ "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",
+ "d2-1-4-roles-of-mitosis-and-meiosis-in-eukaryotes",
+ "d2-1-7-phases-of-mitosis",
+ "d2-1-cell-and-nuclear-division"
+ ]
+ },
+ {
+ "question_id": "21M.2.HL.TZ2.3",
+ "Question": "
\n
A broad bean is the seed of a species, Vicia faba, in the Fabaceae, a family of flowering plants. This family contains many species that are used as sources of food.
\n

\n
\n
On the diagram, label the testa and the radicle.
\n
[2]
\n
a.
\n
\n
An experiment was done to test the hypothesis that temperature affects the rate of germination of the broad bean. Outline two factors apart from temperature that should be controlled in this experiment.
\n
[2]
\n
b.
\n
\n
State the genus of the broad bean.
\n
[1]
\n
c.
\n
\n
Broad beans are rich in starch and cellulose. Compare and contrast the structure of starch and cellulose.
\n
[2]
\n
d.
\n
\n
Once the germinated bean grows above the ground, state the process used by the bean in the production of starch.
\n
[1]
\n
e.
\n
",
+ "Markscheme": "
\n
a. testa labelled ✔
\n
b. radicle labelled ✔ (must point to the bottom half of the embryo or the tip).
\n

\n
a.
\n
\n
a. same amount/type of soil/substrate / pH of soil ✔ e.g.: heater
\n
b. same amount of water / humidity ✔
\n
c. oxygen/aeration ✔
\n
d. same measurement of germination / time ✔ e.g.: emergence of radicle
\n
e. same number/source/age of seeds ✔
\n
Accept discussion of light only in as much as it relates to temperature.
\n
b.
\n
\n
Vicia ✔
\n
No mark if the species name is included.
\n
Mark can be awarded if the genus is not capitalized.
\n
c.
\n
\n
a. both polymers of glucose molecules / polysaccharides
OR
both form 1,4 glycosidic bond ✔
\n
b. starch is formed by alpha glucose while cellulose is formed by beta glucose
OR
in starch C1 hydroxyl groups are found in same plane while in cellulose on different planes
OR
in cellulose, alternatively the beta glucose needs to be placed upside-down in order to have C1 hydroxyl groups on the same plane
OR
two types of starch (amylose and amylopectin) but one type of cellulose ✔
\n
One similarity and one difference.
\n
Comparison to cellulose needed.
\n
d.
\n
\n
photosynthesis
\n
Do not accept condensation or polymerization; if list of processes given, mark the first answer.
\n
e.
\n
",
+ "Examiners report": "
\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
a.
\n
\n
Several answers considered how light is needed for germination without any reference to its relationship to temperature.
\n
b.
\n
\n
This question presented some confusion to Spanish speaking candidates since the word \"género\" is the same for \"genus\" and \"gender\", so some candidates write \"male/female\" in their answers.
\n
c.
\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
d.
\n
",
+ "topics": [
+ "b-form-and-function",
+ "c-interaction-and-interdependence"
+ ],
+ "subtopics": [
+ "b1-1-5-polysaccharides-as-energy-storage-compounds",
+ "b1-1-carbohydrates-and-lipids",
+ "c1-3-15-carbon-fixation-by-rubisco",
+ "c1-3-photosynthesis"
+ ]
+ },
+ {
+ "question_id": "21M.2.HL.TZ2.5",
+ "Question": "
\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 two types of inheritance, using the example of parents that are heterozygous for two genes A and B.
\n
[7]
\n
a.
\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
[4]
\n
b.
\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
[4]
\n
c.
\n
",
+ "Markscheme": "
\n
a. unlinked genes are on different chromosomes / vice versa ✔
\n
b. unlinked alleles migrate/segregate/are inherited independently (during meiosis) / vice versa ✔
\n
c. (In unlinked inheritance) there is an equal chance for all 4 options to occur / AB, Ab, aB, ab / vice versa ✔
\n
d. (dihybrid crosses involving) linked genes do not produce Mendelian ratios ✔
\n
e. (excluding recombinants) there is a 1:1 chance of inheriting the different options/AB or ab ✔
\n
f. in linked characteristics alleles might not migrate together if there is crossing over/ recombinants are formed ✔
\n
g. crossing over occurs in prophase I of meiosis ✔
\n
h. when the sister chromatids migrate in meiosis II the characteristics forming gametes are different/Ab, aB ✔
\n
i. formation of recombinants causes changes in ratio/probability of inheritance/genetic variation ✔
\n
j. correct named example of inheritance of linked/unlinked characteristics ✔
\n
k. Punnett/paired diagrams of both unlinked and linked characteristics ✔
\n
l. genes which are linked but are far apart on the chromosome can display independent assortment ✔
\n
Mp a could be awarded from an annotated diagram.
\n
Allow annotated diagram of inheritance / could be shown in a Punnett square.
\n
Allow annotated diagram of linked inheritance for mp f.
\n
For mp K, accept sex linked examples involving two genes.
\n
If the student interprets the question as sex-linked and autosomal inheritance, look for WTTE marks from the scheme.
\n
a.
\n
\n
a. germinal epithelium divide endlessly (by mitosis giving rise to spermatagonia)
\n
b. spermatogonia are diploid/2n ✔
\n
c. spermatogonia divide by mitosis / provide a continuous supply throughout adult life ✔
\n
d. (some) spermatogonia enlarge forming primary spermatocytes ✔
\n
e. primary spermatocytes undergo the first division of meiosis/meiosis I ✔
\n
f. secondary spermatocytes produced are haploid/n ✔
\n
g. secondary spermatocytes undergo the second division of meiosis (to produce spermatids) ✔
\n
h. spermatids develop tails
OR
spermatids differentiate into spermatozoa / spermatids associate with Sertoli cells ✔
\n
Marks can be awarded to an annotated diagram.
\n
Do not accept sperm or spermatozoa as equivalent to spermatagonia or spermatocytes.
\n
b.
\n
\n
a. nucleus/nuclear membrane ✔
\n
b. membrane bound organelles ✔
\n
c. mitochondria ✔
\n
d. rough ER/smooth ER/golgi apparatus ✔
\n
e. lysosomes / centrioles ✔
\n
f. large/80S ribosomes / ribosomes attached to a membrane ✔
\n
g. linear chromosomes / histones ✔
\n
c.
\n
",
+ "Examiners report": "
\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
a.
\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
b.
\n
",
+ "topics": [
+ "a-unity-and-diversity",
+ "b-form-and-function",
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "a2-2-5-prokaryote-cell-structure",
+ "a2-2-6-eukaryote-cell-structure",
+ "a2-2-cell-structure",
+ "b1-1-5-polysaccharides-as-energy-storage-compounds",
+ "b1-1-carbohydrates-and-lipids",
+ "d3-1-14-spermatogenesis-and-oogenesis-in-humans",
+ "d3-1-reproduction",
+ "d3-2-10-incomplete-dominance-and-codominance",
+ "d3-2-3-genotype-as-the-combination-of-alleles-inherited-by-an-organism",
+ "d3-2-inheritance"
+ ]
+ },
+ {
+ "question_id": "21M.2.HL.TZ2.6",
+ "Question": "
\n
Explain the role of hydrogen ions used in photosynthesis.
\n
[7]
\n
a.
\n
\n
Describe how the structure of the chloroplast is adapted to its function in photosynthesis.
\n
[4]
\n
b.
\n
\n
The enzyme Rubisco is used in carbon fixation during photosynthesis. Identify four other examples of proteins that illustrate the wide range of functions of this group of biochemicals in living organisms.
\n
[4]
\n
c.
\n
",
+ "Markscheme": "
\n
a. hydrogen ions (and oxygen) are obtained from photolysis of water ✔
\n
b. (excited) electrons (from Photosystem II) contribute to generate a hydrogen ion/proton gradient
OR
protons build up in the thylakoid space/inside the thylakoid ✔
\n
c. ATP synthase generates ATP by chemiosmosis/using the proton gradient/by movement of protons from the thylakoid space to the stroma ✔
\n
d. (two) high energy/excited electrons (from Photosystem II) are passed through an electron transport chain ✔
\n
e. NADP accepts H+ (from the stroma) / electrons to produce NADPH+/reduced NADP ✔
\n
f. ATP/reduced NADP/NADPH+ are used by light-independent reactions/Calvin cycle in the stroma ✔
\n
g. (in Calvin cycle) carbon fixation to ribulose bisphosphate/RuBP produces G3P ✔
\n
h. ATP is used to transform G3P to TP ✔
\n
i. reduced NADP/NADPH+ is used to transform G3P to TP ✔
\n
Accept answers in an annotated diagram.
\n
Accept NADPH2/NADPH/NADPH + H+ in place of NADPH+.
\n
a.
\n
\n
a. thylakoids have a small internal volume to maximize hydrogen gradient / quickly increase concentration gradient ✔
\n
b. many grana / thylakoids give large surface area ✔
\n
c. (grana) contain (photosynthetic) pigments/electron carriers/ATP synthase enzymes ✔
\n
d. (photosynthetic) pigments/chlorophyll arranged into photosystems allowing maximum absorption of light energy ✔
\n
e. stroma has suitable pH/ enzymes of Calvin/light independent cycle ✔
\n
f. lamellae connect/separate grana maximizing photosynthetic efficiency ✔
\n
Accept diagram showing the disposition in space.
\n
b.
\n
\n
a. insulin receptors start the cellular signalling pathway/other receptor
\n
b. leptin is a hormone / other protein hormone ✔
\n
c. immunoglobulins/antibodies defend body from disease ✔
\n
d. rhodopsin/photosystems convert light energy to electrical impulses ✔
\n
e. keratin/collagen/other example is a structural protein ✔
\n
f. tubulin/microtubules part of cytoskeleton/ involved in cell division
\n
g. ATP synthase is an enzyme that catalyzes the formation of ATP / other enzyme and function ✔
\n
h. fibrin/fibrinogen is a protein involved in clotting ✔
\n
i. hemoglobin/sodium potassium pump/other example is a transport protein ✔
\n
j. actin/myosin/other example is involved in muscle contraction ✔
\n
k. any other named example and function ✔
\n
l. a second other named example and function ✔
\n
m. spider silk is used to form spider webs/capture prey ✔
\n
Accept only one example of each protein type for example only one enzyme or only one hormone etc.
\n
Mp k can be awarded only once.
\n
Mp I can be awarded only once.
\n
c.
\n
",
+ "Examiners report": "
\n
Question 6 was a popular question.
\n
A relatively high scoring section, though many students failed to discuss the role of hydrogen in the light independent reactions.
\n
a.
\n
\n
Question 6 was a popular question.
\n
Well answered.
\n
b.
\n
\n
Question 6 was a popular question.
\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
c.
\n
",
+ "topics": [
+ "b-form-and-function",
+ "c-interaction-and-interdependence"
+ ],
+ "subtopics": [
+ "b1-2-12-relationship-of-form-and-function-in-globular-and-fibrous-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-proteins",
+ "b2-2-5-adaptations-of-the-chloroplast-for-photosynthesis",
+ "b2-2-organelles-and-compartmentalization",
+ "c1-3-13-reduction-of-nadp-by-photosystem-i",
+ "c1-3-photosynthesis"
+ ]
+ },
+ {
+ "question_id": "21M.2.HL.TZ2.7",
+ "Question": "
\n
Describe the structure of the DNA molecule.
\n
[5]
\n
a.
\n
\n
Outline the role of three enzymes used in the replication of DNA.
\n
[3]
\n
b.
\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
[7]
\n
c.
\n
",
+ "Markscheme": "
\n
a. two stranded/double helix ✔
\n
b. antiparallel / strands running in opposite directions
OR
one strand organized 5’ to 3’ and the other 3’ to 5’ ✔
\n
c. sugar-phosphate backbone ✔
\n
d. each strand formed by chains of nucleotides ✔
\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
f. the bases are adenine, guanine, cytosine and thymine ✔
\n
g. strands held together by hydrogen bonds (between complementary base pairs)
OR
A pairs with T and C pairs with G ✔
\n
Both helix and two strands needed for mp a. Double helix is sufficient for the mark.
\n
Points can be awarded to annotated diagrams.
\n
For mp c, the explicit label sugar phosphate backbone is required.
\n
To award mp d from a diagram, at least three pairs of nucleotides should be shown.
\n
For mp e, the diagram would need to be labelled as a nucleotide.
\n
For mp e, expect deoxyribose not just sugar.
\n
The written names of the bases are required for mp f.
\n
Do not penalize twice for mp f and g for using letters.
\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
a.
\n
\n
a. helicase to separate/unwind DNA strands ✔
\n
b. gyrase / toposiomerase to relax the tension as bacterial DNA is being uncoiled / prevent supercoiling ✔
\n
c. primase to synthesise primers ✔
\n
d. polymerase (I) removes primers and replaces with nucleotide ✔
\n
e. polymerase (III) adds nucleotides (in a 5' to 3' direction) ✔
\n
f. ligase joins (Okazaki) fragments together ✔
\n
Accept the enzyme name without ‘DNA’ included; e.g. ‘DNA ligase’ or ‘ligase’ can both be accepted.
\n
b.
\n
\n
a. insulin production is determined by a gene ✔
\n
b. gene for insulin (is found in all cells), but only activated in (β cells of) pancreas ✔
\n
c. stem cells differentiate into specialized cells/(into pancreatic β) ✔
\n
d. during differentiation some genes are turned on and others off ✔
\n
e. insulin is a hormone that regulates the amount of glucose/sugar in blood ✔
\n
f. pancreatic β cells have sensors that detect glucose level in blood ✔
\n
g. an increase in glucose will increase transcription of mRNA of insulin ✔
\n
h. the site of transcription of insulin is in the pancreatic β cells ✔
\n
i. gene transcription is regulated by proteins that bind to specific base sequence in DNA/ enhancers/silencers/promoter proximal elements ✔
\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
k. (DNA) methylation (usually) inhibits gene expression / (histone) acetylation promotes gene expression / tightness of coiling of DNA around histones affects gene expression ✔
\n
Accept sugar as equivalent to glucose.
\n
c.
\n
",
+ "Examiners report": "
\n
A surprising number of students failed to discuss nucleotides explicitly.
\n
a.
\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
c.
\n
",
+ "topics": [
+ "a-unity-and-diversity",
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "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",
+ "a1-2-nucleic-acids",
+ "a2-2-13-cell-differentiation-as-the-process-for-developing-specialized-tissues-in-multicellular-organisms",
+ "a2-2-cell-structure",
+ "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",
+ "d1-1-dna-replication",
+ "d2-2-4-epigenesis-as-the-development-of-patterns-of-differentiation-in-the-cells-of-a-multicellular-organism",
+ "d2-2-gene-expression-[hl-only]"
+ ]
+ },
+ {
+ "question_id": "21M.2.SL.TZ1.2",
+ "Question": "
\n
The diagram shows some of the metabolic processes taking place in a plant cell.
\n

\n
\n
Identify the process Y and state the name of the organelle where it takes place in a plant cell.
\n
Process Y:
\n
Name of the organelle:
\n
[1]
\n
a.i.
\n
\n
Identify the molecule Z.
\n
[1]
\n
a.ii.
\n
\n
State the type of reaction which converts excess monosaccharides to polysaccharides.
\n
[1]
\n
b.
\n
\n
The process X uses oxygen and produces ATP. Identify the process X.
\n
[1]
\n
c.
\n
\n
Outline the uses of ATP in plant cells.
\n
[2]
\n
d.
\n
\n
With reference to the diagram, identify one example of catabolism.
\n
[1]
\n
e.
\n
",
+ "Markscheme": "
\n
process Y: photosynthesis ✔
\n
organelle: chloroplast ✔
\n
Both needed.
\n
a.i.
\n
\n
glycerol /glycerin ✔
\n
a.ii.
\n
\n
condensation/dehydration/synthesis/anabolic/anabolism ✔
\n
b.
\n
\n
aerobic respiration ✔
\n
c.
\n
\n
a. used as an energy source ✔
\n
b. supplies/releases energy for biochemical reactions ✔
\n
c. photosynthesis/active transport/other verifiable example of reaction or process ✔
\n
d.
\n
\n
a. (letter X) breakdown of monosaccharides/respiration ✔
\n
b. (letter Y) hydrolysis/photolysis in photosynthesis/oxidation of water ✔
\n
Answer must come from the diagram.
\n
e.
\n
",
+ "Examiners report": "
\n
The diagram was generally confusing to candidates.
\n
This was generally answered correctly.
\n
a.i.
\n
\n
The diagram was generally confusing to candidates.
\n
This was generally missed.
\n
\n
a.ii.
\n
\n
The diagram was generally confusing to candidates.
\n
This was often answered correctly.
\n
b.
\n
\n
The diagram was generally confusing to candidates.
\n
Although many answered cell respiration, aerobic respiration was expected since the question defined aerobic respiration.
\n
c.
\n
\n
The diagram was generally confusing to candidates.
\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
d.
\n
\n
The diagram was generally confusing to candidates.
\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
e.
\n
",
+ "topics": [
+ "a-unity-and-diversity",
+ "b-form-and-function",
+ "c-interaction-and-interdependence"
+ ],
+ "subtopics": [
+ "a2-2-6-eukaryote-cell-structure",
+ "a2-2-cell-structure",
+ "b1-1-2-production-of-macromolecules-by-condensation-reactions-that-link-monomers-to-form-a-polymer",
+ "b1-1-carbohydrates-and-lipids",
+ "c1-1-3-anabolic-and-catabolic-reactions",
+ "c1-1-enzymes-and-metabolism",
+ "c1-2-4-cell-respiration-as-a-system-for-producing-atp-within-the-cell-using-energy-released-from-carbon-compounds",
+ "c1-2-cell-respiration",
+ "c1-3-18-synthesis-of-carbohydrates-amino-acids-and-other-carbon-compounds-using-the-products-of-the-calvin-cycle-and-mineral-nutrients",
+ "c1-3-2-conversion-of-carbon-dioxide-to-glucose-in-photosynthesis-using-hydrogen-obtained-by-splitting-water",
+ "c1-3-photosynthesis",
+ "c4-2-18-ecosystems-as-carbon-sinks-and-carbon-sources",
+ "c4-2-transfers-of-energy-and-matter"
+ ]
+ },
+ {
+ "question_id": "21M.2.SL.TZ1.4",
+ "Question": "
\n
Squid have been used for research on nerve impulses. The mechanism of nerve transmission in these animals is the same as that in humans. The image shows an oscilloscope trace from a nerve impulse in a squid’s giant axon.
\n

\n
[squid] Pixabay.
\n
\n
Estimate the resting potential for this axon.
\n
[1]
\n
a.
\n
\n
Outline the role of the sodium–potassium pump in maintaining the resting potential.
\n
[2]
\n
b.
\n
",
+ "Markscheme": "
\n
−65 mV ✔
\n
Unit required; minus sign required. Accept answers from −62mV to −65mV.
\n
a.
\n
\n
a. sodium/potassium pump pumps sodium ions Na+ out of axon and pumps potassium ions/K+ in ✔
\n
b. requires energy/ATP/against concentration gradients/active transport ✔
\n
c. three sodium ions pumped out for every two potassium ions pumped in ✔
\n
d. results in charge difference between inside and outside where outside is positive relative to inside ✔
\n
b.
\n
",
+ "Examiners report": "
\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
b.
\n
",
+ "topics": [
+ "b-form-and-function",
+ "c-interaction-and-interdependence"
+ ],
+ "subtopics": [
+ "b2-1-15-sodium-potassium-pumps-as-an-example-of-exchange-transporters",
+ "b2-1-membranes-and-membrane-transport",
+ "c2-2-10-oscilloscope-traces-showing-resting-potentials-and-action-potentials",
+ "c2-2-neural-signalling",
+ "c3-2-9-multiplication-of-activated-b-lymphocytes-to-form-clones-of-antibody-secreting-plasma-cells",
+ "c3-2-defence-against-disease"
+ ]
+ },
+ {
+ "question_id": "21M.2.SL.TZ1.5",
+ "Question": "
\n
The image shows the wings of an insect, bird and bat.
\n

\n
[Source: [insect wing] Halvard Hatlen https://upload.wikimedia.org/wikipedia/commons/0/0f/Dip-trichoceridae-wing.png. [bird wing] University of Maryland, Department of Geology. [bat wing] University of Maryland, Department of Geology.]
\n
\n
Based on their structure, the insect and bat wings are analogous. Outline what is meant by an analogous trait.
\n
[2]
\n
a.i.
\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
[1]
\n
a.ii.
\n
\n
Explain how cladistics can be used to investigate evolutionary relationships.
\n
[2]
\n
b.
\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
[1]
\n
c.
\n
",
+ "Markscheme": "
\n
a. analogous traits have a different evolutionary history/ancestry ✔
\n
b. different structures are adaptations for flight ✔
\n
c. selective pressure leads to a similar solution to the problem of flying ✔
\n
a.i.
\n
\n
a. bird and bat share a more recent common ancestor (than the insect) ✔
\n
b. bird and bat are more closely related than insect and bat / insect and bird ✔
\n
c. bird and bat wings evolved from a common ancestor (by natural selection) ✔
\n
a.ii.
\n
\n
a. (cladistics) shows evolutionary relationships through a common ancestor ✔
\n
b. cladistics uses DNA/protein/derived/shared anatomical characteristics/traits ✔
\n
c. time of divergence is related to the number of differences in DNA (base sequence) / protein (sequence of amino acids) ✔
\n
d. homologous (versus analogous) traits are used to place an organism in a clade ✔
\n
e. more shared characteristics mean a more recent common ancestor ✔
\n
b.
\n
\n

\n
What is important is that the proper relationships are shown not the style used.
\n
c.
\n
",
+ "Examiners report": "
\n
Candidates found it hard to express themselves without contradiction.
\n
In both parts the key to successful answers was in using the organisms given in the example. Contradictions were thus avoided.
\n
a.i.
\n
\n
Candidates found it hard to express themselves without contradiction.
\n
In both parts the key to successful answers was in using the organisms given in the example. Contradictions were thus avoided.
\n
a.ii.
\n
\n
Candidates found it hard to express themselves without contradiction.
\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
b.
\n
\n
Candidates found it hard to express themselves without contradiction.
\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
c.
\n
",
+ "topics": [
+ "a-unity-and-diversity"
+ ],
+ "subtopics": [
+ "a3-2-2-difficulties-classifying-organisms-into-the-traditional-hierarchy-of-taxa",
+ "a3-2-7-analysing-cladograms",
+ "a3-2-8-using-cladistics-to-investigate-whether-the-classification-of-groups-corresponds-to-evolutionary-relationships",
+ "a3-2-classification-and-cladistics-(hl-only)",
+ "a4-1-4-evidence-for-evolution-from-homologous-structures",
+ "a4-1-5-convergent-evolution-as-the-origin-of-analogous-structures",
+ "a4-1-evolution-and-speciation"
+ ]
+ },
+ {
+ "question_id": "21M.2.SL.TZ1.6",
+ "Question": "
\n
Outline the structure of proteins.
\n
[3]
\n
a.
\n
\n
Cells produce a large variety of proteins with different sequences of amino acids. Explain how this is done.
\n
[7]
\n
b.
\n
\n
Outline the range of functions of proteins in cells.
\n
[5]
\n
c.
\n
",
+ "Markscheme": "
\n
a. protein formed from amino acids
OR
20 different amino acids ✔
\n
b. linked together by peptide bonds ✔
\n
c. may consist of one or more polypeptides linked together ✔
\n
d. have a specific shape/conformation/folding ✔
\n
e. shape determines function ✔
\n
a.
\n
\n
a. protein is produced when a gene is expressed / switched on ✔
\n
b. genetic code/codons consists of three nucleotides/bases/base triplet ✔
\n
c. genetic code in DNA is transcribed/transcription (to mRNA) ✔
\n
d. mRNA exits the nucleus ✔
\n
e. mRNA (code) is translated/translation into a polypeptide/protein ✔
\n
f. amino acid sequence/polypeptide formation occurs at a ribosome ✔
\n
g. one codon translates to one amino acid ✔
\n
h. tRNA carries code for specific amino acids ✔
\n
i. tRNA anticodon matches with specific codon in mRNA ✔
\n
j. amino acids joined (by peptide bonds) to form polypeptide ✔
\n
k. sequence of amino acids determined by order of bases/nucleotides/codons in DNA/mRNA ✔
\n
l. proteins vary based on which amino acids are used and their order
OR
protein variety increases by mutations to DNA ✔
\n
b.
\n
\n
a. enzymes that catalyse/speed up/control (the rate and direction of) metabolic reactions ✔
\n
b. proteins can be hormones which are chemical messengers to cells ✔
\n
c. proteins that transport through the membrane such as channel/carrier/pumps / that regulate what enters/leaves the cell ✔
\n
d. hemoglobin in red blood cells that transports/ binds oxygen ✔
\n
e. membrane proteins for cell/tissue recognition/cell adhesion/communication ✔
\n
f. structural elements of muscle fibre/actin/myosin for movement
OR
spindle fibres move chromosomes ✔
\n
g. histones condense DNA into chromosomes ✔
\n
The question requires answer that the function is in cells.
\n
c.
\n
",
+ "Examiners report": "
\n
This question was attempted by about 42 % of candidates.
\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
a.
\n
\n
This question was attempted by about 42 % of candidates.
\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
b.
\n
\n
This question was attempted by about 42 % of candidates.
\n
Generally good answers were received for those who read the question correctly, i.e. protein function within cells.
\n
c.
\n
",
+ "topics": [
+ "b-form-and-function",
+ "c-interaction-and-interdependence",
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "b1-2-4-infinite-variety-of-possible-peptide-chains",
+ "b1-2-5-effect-of-ph-and-temperature-on-protein-structure",
+ "b1-2-proteins",
+ "c3-1-3-integration-of-organs-in-animal-bodies-by-hormonal-and-nervous-signalling-and-by-transport-of-materials-and-energy",
+ "c3-1-integration-of-body-systems",
+ "d3-1-3-differences-between-male-and-female-sexes-in-sexual-reproduction",
+ "d3-1-reproduction"
+ ]
+ },
+ {
+ "question_id": "21M.2.SL.TZ1.7",
+ "Question": "
\n
Outline the process of inhalation.
\n
[4]
\n
a.
\n
\n
Explain the process of gas exchange taking place in the alveoli.
\n
[7]
\n
b.
\n
\n
Discuss the relationship between atmospheric carbon dioxide concentration and global temperatures.
\n
[4]
\n
c.
\n
",
+ "Markscheme": "
\n
a. diaphragm contracts / moves downwards/flattens ✔
\n
b. external intercostal muscles contract ✔
\n
c. (muscle contraction) moves the rib cage upwards and outwards ✔
\n
d. increases volume of the thorax / lungs ✔
\n
e. difference in pressure/decreasing pressure causes air to flow into lungs / lungs inflate ✔
\n
a.
\n
\n
a. O2 diffuses into blood and CO2 diffuses out from blood ✔
\n
b. blood entering the alveoli is high in CO2/low in O2 ✔
OR
air in alveolus is high in O2/low in CO2 ✔
\n
c. diffusion (in either direction) take place due to concentration gradients ✔
\n
d. concentration gradients maintained by ventilation/blood flow ✔
\n
e. large surface area created by many alveoli/spherical shape of alveoli for more efficient diffusion ✔
\n
f. rich supply of capillaries (around alveoli) allows efficient exchange ✔
\n
g. type I pneumocytes are thin to allow easy diffusion/short distances ✔
\n
h. gases must dissolve in liquid lining of alveolus in order to be exchanged ✔
\n
i. type II pneumocytes secrete surfactants to reduce surface tension/prevent lungs sticking together ✔
\n
j. type II pneumocytes create moist conditions in alveoli ✔
\n
b.
\n
\n
a. greenhouse effect keeps Earth warm ✔
\n
b. (over-time) earth’s temperature has fluctuated naturally ✔
\n
c. changes in human activities have led to increases in CO2 concentration ✔
\n
d. CO2 absorbs infrared/long wave radiation / trapping heat ✔
\n
e. increase in atmospheric CO2 (concentration) correlates with/causes increased global average temperature ✔
\n
f. use of fossil fuels increases atmospheric CO2 ✔
\n
g. deforestation removes a carbon sink / less CO2 absorbed ✔
\n
h. loss of polar ice causes less reflection of surface light/ more reradiation as heat contributing to (global) warming ✔
\n
i. CO2 is not the only greenhouse gas/ there are other greenhouse gases ✔
\n
c.
\n
",
+ "Examiners report": "
\n
This question was attempted by approximately 56 % of candidates.
\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
a.
\n
\n
This question was attempted by approximately 56 % of candidates.
\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
b.
\n
\n
This question was attempted by approximately 56 % of candidates.
\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 CO2 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
c.
\n
",
+ "topics": [
+ "b-form-and-function",
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "b3-1-4-adaptations-of-mammalian-lungs-for-gas-exchange",
+ "b3-1-5-ventilation-of-the-lungs",
+ "b3-1-gas-exchange",
+ "d1-3-7-mutation-as-a-source-of-genetic-variation",
+ "d1-3-mutations-and-gene-editing",
+ "d4-3-1-anthropogenic-causes-of-climate-change",
+ "d4-3-climate-change"
+ ]
+ },
+ {
+ "question_id": "21M.2.SL.TZ2.2",
+ "Question": "
\n
The diagram shows the stages in the cell cycle.
\n

\n
\n
State processes occurring during interphase.
\n
[2]
\n
a.
\n
\n
Using the letter C, label the stage on the diagram where chromosome supercoiling occurs.
\n
[1]
\n
b.i.
\n
\n
Using the letter M, label the stage on the diagram where sister chromatids migrate to opposite poles.
\n
[1]
\n
b.ii.
\n
\n
Distinguish between the outcomes of a cell dividing either by mitosis or meiosis.
\n
[2]
\n
c.
\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
[1]
\n
d.
\n
",
+ "Markscheme": "
\n
a. DNA replication ✔
\n
b. cell growth ✔
\n
c. duplication of organelles/mitochondria / production of microtubules/protein synthesis ✔
\n
Accept first two answers only.
\n
a.
\n
\n
prophase ✔
\n
The stage should be clearly labelled.
\n
If more than one stage is shown the candidate does not receive a mark.
\n
b.i.
\n
\n
anaphase ✔
\n
The stage should be clearly labelled.
\n
If more than one stage is shown the candidate does not receive a mark.
\n
b.ii.
\n
\n
a. mitosis produces two daughter cells while meiosis four ✔
\n
b. mitosis produces cells with same number of chromosomes (2n) while in meiosis they are halved (n) ✔
\n
c. mitosis produces body cells but meiosis produces gametes
OR
mitosis produces genetically identical cells but meiosis does not ✔
\n
Allow answers in a table.
\n
Reference to both has to be present for the mark.
\n
c.
\n
\n
number of cells (seen under the microscope) undergoing mitosis divided by the total number of cells (observed in sample area) ✔
\n
Can be given as a %.
\n
d.
\n
",
+ "Examiners report": "
\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
a.
\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
b.i.
\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
b.ii.
\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
c.
\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
d.
\n
",
+ "topics": [
+ "b-form-and-function",
+ "c-interaction-and-interdependence",
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "b1-1-12-formation-of-phospholipid-bilayers-as-a-consequence-of-the-hydrophobic-and-hydrophilic-regions",
+ "b1-1-carbohydrates-and-lipids",
+ "b1-2-5-effect-of-ph-and-temperature-on-protein-structure",
+ "b1-2-proteins",
+ "c2-2-6-release-of-neurotransmitters-from-a-presynaptic-membrane",
+ "c2-2-7-generation-of-an-excitatory-postsynaptic-potential",
+ "c2-2-neural-signalling",
+ "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",
+ "d2-1-4-roles-of-mitosis-and-meiosis-in-eukaryotes",
+ "d2-1-7-phases-of-mitosis",
+ "d2-1-cell-and-nuclear-division"
+ ]
+ },
+ {
+ "question_id": "21M.2.SL.TZ2.3",
+ "Question": "
\n
The image represents the structure of the enzyme Rubisco from common pea (Pisum sativum).
\n

\n
\n
State one function of Rubisco.
\n
[1]
\n
a.
\n
\n
State a role of the active site of an enzyme.
\n
[1]
\n
b.
\n
\n
State the genus of the plant where this Rubisco is found.
\n
[1]
\n
c.
\n
\n
Outline one factor that could affect the activity of Rubisco.
\n
[2]
\n
d.
\n
",
+ "Markscheme": "
\n
a. enzyme involved in photosynthesis/carbon fixation/Calvin cycle
OR
speeds up chemical reactions in photosynthesis ✔
\n
b. carboxylation of RuBP ✔
\n
c. production of carbohydrate in photosynthesis ✔
\n
d. addition of carbon dioxide to form glucose (in Calvin cycle) ✔
\n
Either photosynthesis or carbon fixation must be mentioned.
\n
a.
\n
\n
site to which substrate binds
OR
catalytic site ✔
\n
Give credit for the lock and key analogy.
\n
b.
\n
\n
a. name of factor ✔
\n
b. how it affects rate of reaction ✔
\n
Example answer:
\n
temperature ✔
\n
as the temperature increases the rate of reaction increases until it reaches a maximum and then decreases rapidly ✔
\n
Accept answers in a graph.
\n
d.
\n
",
+ "Examiners report": "
\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 Pisume. 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
a.
\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 Pisume. 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
b.
\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 Pisume. 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
c.
\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 Pisume. 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
d.
\n
",
+ "topics": [
+ "b-form-and-function",
+ "c-interaction-and-interdependence"
+ ],
+ "subtopics": [
+ "b1-1-5-polysaccharides-as-energy-storage-compounds",
+ "b1-1-carbohydrates-and-lipids",
+ "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",
+ "c1-1-enzymes-and-metabolism",
+ "c1-3-15-carbon-fixation-by-rubisco",
+ "c1-3-photosynthesis"
+ ]
+ },
+ {
+ "question_id": "21M.2.SL.TZ2.4",
+ "Question": "
\n
The mass of an individual organism can affect its physiology and feeding ecology. The diagram shows the relative mass of carbon (black) and total wet mass (grey) of a marine crustacean, Calanus hyperboreus and a jellyfish, Bathocyroe fosteri.
\n

\n
[Source: Kristian McConville, Angus Atkinson, Elaine S. Fileman, John I. Spicer, Andrew G. Hirst. Disentangling the counteracting effects of water content and carbon mass on zooplankton growth. Journal of Plankton Research. 2017, Volume 39, Issue 2, Pages 246–256. https://doi.org/10.1093/plankt/fbw094. Adapted (and translated) by permission of Oxford University Press.]
\n
\n
State one process that results in the loss of carbon dioxide from a marine organism such as a crustacean or a jellyfish.
\n
[1]
\n
a.
\n
\n
The crustacean and the jellyfish obtain carbon compounds by feeding. State one source of carbon for marine organisms, other than feeding.
\n
[1]
\n
b.
\n
\n
Explain how energy enters, flows through and is lost from marine food chains.
\n
[3]
\n
c.
\n
\n
Deduce whether jellyfish or crustacea are a richer source of carbon in a food chain.
\n
[1]
\n
d.i.
\n
\n
Suggest with a reason whether having a large body mass is an advantage or disadvantage for jellyfish.
\n
[1]
\n
d.ii.
\n
",
+ "Markscheme": "
\n
a. (aerobic/cellular) respiration ✔
\n
b. gas exchange / diffusion ✔
\n
Do not accept photosynthesis.
\n
Do not accept breathing
\n
Organism is taken to be a living thing.
\n
a.
\n
\n
a. photosynthesis ✔
\n
b. absorption of (dissolved) carbon dioxide / (hydrogen)carbonate directly from the oceans ✔
\n
Accept reference to carbonate or hydrogencarbonate ions.
\n
b.
\n
\n
a. light energy is converted to chemical energy (in carbon compounds/sugars) by photosynthesis ✔
\n
b. (chemical) energy (in carbon compounds) flows by means of feeding/through food chains/webs ✔
\n
c. only (approximately) 10 % of energy is passed to the next trophic level ✔
\n
d. energy released as heat (by respiration) ✔
\n
e. energy is not recycled ✔
\n
f. after death, energy may remain trapped as undigested detritus/fossils/fossil fuels ✔
\n
c.
\n
\n
crustacean as they have more carbon per unit volume
OR
crustacean as jellyfish has little carbon per total body size ✔
\n
OWTTE.
\n
The conclusion must be supported from the information given.
\n
d.i.
\n
\n
a. advantage of large size is ability to eat /catch large prey ✔
\n
b. (advantage as) lower rates of predation of large jellyfish ✔
\n
c. (advantage as) can produce more reproductive cells ✔
\n
d. (disadvantage as) can move slower to escape from predators/capture prey ✔
\n
e. (disadvantage as) needs more energy/nutrients to maintain structure/move/grow ✔
\n
f. (disadvantage as) low surface area to volume ratio and thus possibly difficulty with materials/gas/nutrient exchange ✔
\n
g. (disadvantage as) more prone to mechanical damage during storms ✔
\n
Accept other reasonable answer.
\n
Must say advantage or disadvantage.
\n
d.ii.
\n
",
+ "Examiners report": "
\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 CO2 or HCO3 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
a.
\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 CO2 or HCO3 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
b.
\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 CO2 or HCO3 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
c.
\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 CO2 or HCO3 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
d.i.
\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 CO2 or HCO3 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
d.ii.
\n
",
+ "topics": [
+ "c-interaction-and-interdependence",
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "c4-2-17-constructing-carbon-cycle-diagrams",
+ "c4-2-18-ecosystems-as-carbon-sinks-and-carbon-sources",
+ "c4-2-transfers-of-energy-and-matter",
+ "d4-3-5-changes-in-ocean-currents-altering-the-timing-and-extent-of-nutrient-upwelling",
+ "d4-3-climate-change"
+ ]
+ },
+ {
+ "question_id": "21M.2.SL.TZ2.5",
+ "Question": "
\n
Pastry cream or confectioners’ custard is made with a combination of milk (rich in casein and lactose), egg yolks, sugar, starch and a flavouring such as vanilla.
\n
\n
Describe the structure of starch.
\n
[5]
\n
a.
\n
\n
Explain how amino acids in casein could reach the liver, starting from the moment when the person takes a bite of pastry cream pie.
\n
[7]
\n
b.
\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
[3]
\n
c.
\n
",
+ "Markscheme": "
\n
a. starch is a carbohydrate ✔
\n
b. starch is formed by carbon, hydrogen and oxygen ✔
\n
c. it is a polymer/chain/polysaccharide ✔
\n
d. formed from monosaccharides/simple sugars/glucose ✔
\n
e. linked together by condensation/dehydration ✔
\n
f. consists of amylose and amylopectin ✔
\n
g. amylose is a long chain/unbranched ✔
\n
h. amylopectin is branched ✔
\n
a.
\n
\n
a. food is mechanically/physically digested in the mouth through mastication/chewing ✔
\n
b. mixed with saliva (to form the bolus) in mouth ✔
\n
c. moved through esophagus/peristalsis ✔
\n
d. proteins digested in the stomach (pepsin) ✔
\n
e. pancreas secretes enzymes into lumen of small intestine
OR
(endo)peptidases/trypsin) are secreted by pancreas ✔
\n
f. enzymes digest macromolecules to monomers
OR
endopeptidases digest polypeptides to peptides/amino acids ✔
\n
g. villi of small intestine absorb amino acids ✔ Allow pepsin.
\n
h. amino acids carried to blood capillaries ✔
\n
i. blood (capillaries) carry amino acids to (hepatic portal) vein/blood vessel going to liver ✔
\n
j. amino acids absorbed by active transport/protein pumps in the villi ✔
\n
b.
\n
\n
a. gametes of both parents shown as a capital and small letter (e.g. L and l) ✔
\n
b. possible F1 genotypes ✔
\n
c. 25 % lactose intolerant, 50 % carriers, 25 % lactose tolerant
OR
75 % tolerant and 25 % intolerant
OR
child has 25 %/1:4/ chances of inheritance of intolerance ✔
\n

\n
c.
\n
",
+ "Examiners report": "
\n
(attempted by about 40 % of the cohort)
\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
a.
\n
\n
(attempted by about 40 % of the cohort)
\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
b.
\n
\n
(attempted by about 40 % of the cohort)
\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
c.
\n
",
+ "topics": [
+ "a-unity-and-diversity",
+ "b-form-and-function",
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "a2-2-5-prokaryote-cell-structure",
+ "a2-2-6-eukaryote-cell-structure",
+ "a2-2-cell-structure",
+ "b1-1-5-polysaccharides-as-energy-storage-compounds",
+ "b1-1-carbohydrates-and-lipids",
+ "d3-2-10-incomplete-dominance-and-codominance",
+ "d3-2-3-genotype-as-the-combination-of-alleles-inherited-by-an-organism",
+ "d3-2-4-phenotype-as-the-observable-traits-of-an-organism-resulting-from-genotype-and-environmental-factors",
+ "d3-2-inheritance"
+ ]
+ },
+ {
+ "question_id": "21M.2.SL.TZ2.6",
+ "Question": "
\n
Tuberculosis (TB) is an infectious disease caused by the bacterium Mycobacterium tuberculosis.
\n
\n
Outline the structures in M. tuberculosis that are not present in a human cell.
\n
[3]
\n
a.
\n
\n
Explain the production of antibodies when a patient is infected with the TB bacterium.
\n
[7]
\n
b.
\n
\n
Describe the risk to the human population of indiscriminate use of antibiotics.
\n
[5]
\n
c.
\n
",
+ "Markscheme": "
\n
a. cell wall ✔
\n
b. pili/flagella ✔
\n
c. 70S ribosomes ✔
\n
d. nucleoid / circular DNA
OR
naked DNA ✔
\n
e. plasmids ✔
\n
As candidates do not need to know the structure of Mycobacterium tuberculosis, all prokaryotic structures are accepted.
\n
Ignore references to membrane bound organelles.
\n
a.
\n
\n
a. phagocytes/lymphocytes are white blood cells ✔
\n
b. TB bacterium has a specific antigen ✔
\n
c. this antigen is recognised by white blood cells ✔
\n
d. a clone of lymphocytes/plasma cells/B cells are produced ✔
\n
e. antibodies are produced by lymphocytes ✔
\n
f. each lymphocyte produces just one type of antibody ✔
\n
g. (this is) specific immunity ✔
\n
h. (part of the) antibody/immunoglobulin binds to the antigen / specific antibody binds to the specific antigen ✔
\n
i. antibodies are proteins/immunoglobulins ✔
\n
j. (some) plasma cells become memory cells ✔
\n
k. memory cells reproduce quickly ✔
\n
l. memory cells prevent infection in the future ✔
\n
Allow annotated diagrams to explain the process.
\n
b.
\n
\n
a. antibiotics block bacterial processes ✔
\n
b. example of bacterial process ✔ e.g. cell wall formation
\n
c. variations exist naturally in a population / some are naturally resistant to the antibiotic ✔
\n
d. bacteria that are not resistant to this antibiotic will die / only resistant will survive (when antibiotic given) ✔
\n
e. this characteristic could be passed to next generation ✔
\n
f. (natural selection) leads to changes in the proportions/frequency in the population ✔
\n
g. human population will be exposed to antibiotic resistant bacteria and will not have antibiotic to kill them ✔
\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
c.
\n
",
+ "Examiners report": "
\n
(attempted by about 60 % of the cohort)
\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
a.
\n
\n
(attempted by about 60 % of the cohort)
\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
b.
\n
\n
(attempted by about 60 % of the cohort)
\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
c.
\n
",
+ "topics": [
+ "a-unity-and-diversity",
+ "c-interaction-and-interdependence"
+ ],
+ "subtopics": [
+ "a2-2-10-cell-types-and-cell-structures-viewed-in-light-and-electron-micrographs",
+ "a2-2-5-prokaryote-cell-structure",
+ "a2-2-cell-structure",
+ "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",
+ "c3-2-6-lymphocytes-as-cells-in-the-adaptive-immune-system-that-cooperate-to-produce-antibodies",
+ "c3-2-defence-against-disease"
+ ]
+ },
+ {
+ "question_id": "21N.2.HL.TZ0.2",
+ "Question": "
\n
Hemophilia is a sex-linked disease that affected some members of royal families in Europe during the 19th and 20th centuries.
\n

\n
\n
The diagram shows the structure of two chromosomes after the first division of meiosis, assuming that there was no crossing over or chiasmata formation.
\n

\n
\n
Draw a Punnett square to show all the possible genotypes of Queen Victoria’s children.
\n
[2]
\n
a.i.
\n
\n
Deduce the genotype of Queen Victoria’s daughter Alice.
\n
[1]
\n
a.ii.
\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
[1]
\n
b.i.
\n
\n
State the stage of meiosis where chiasmata formation may occur.
\n
[1]
\n
b.ii.
\n
\n
Explain gene linkage and its effects on inheritance.
\n
[2]
\n
c.
\n
\n
Explain the mechanism that prevents polyspermy during fertilization.
\n
[2]
\n
d.
\n
",
+ "Markscheme": "
\n
a. parental alleles shown as XH and Xh (female) and XH and Y (male);
b. Punnett square with genotypes of offspring shown as XHXH and XHY and XHXh and XhY;
\n

\n
a.i.
\n
\n
all four upper arms with one A and both chromosomes with one B and one b on the lower arms;
\n

\n
The chromatids can be shown as single lines rather than the wider versions in the question.
\n
b.i.
\n
\n
a. located on the same chromosome;
b. genes/gene loci close together (on the same chromosome);
c. do not follow (the law of) independent assortment;
d. more chance of recombination if genes are further apart;
e. inherited together unless crossing over/recombination occurs;
f. ratios of offspring in dihybrid crosses are different from expected/non-Mendelian
OR
more offspring with parental phenotype combinations than expected;
\n
c.
\n
\n
a. cortical reaction (after first sperm nucleus enters the egg);
b. vesicles/cortical granules release their contents/enzymes (from the egg/zygote);
c. zona pellucida/glycoprotein coat/outer coat hardened / fertilization membrane formed;
d. enzymes of sperm/acrosome cannot digest (hardened coat)
OR
glycoproteins/ZP3 (in zona pellucida) altered so sperm cannot bind;
\n
d.
\n
",
+ "Examiners report": "
\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
a.i.
\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
a.ii.
\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
b.i.
\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
b.ii.
\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
c.
\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
d.
\n
",
+ "topics": [
+ "b-form-and-function",
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "b1-2-11-quaternary-structure-of-non-conjugated-and-conjugated-proteins",
+ "b1-2-proteins",
+ "d2-1-11-meiosis-as-a-source-of-variation",
+ "d2-1-9-meiosis-as-a-reduction-division",
+ "d2-1-cell-and-nuclear-division",
+ "d3-1-15-mechanisms-to-prevent-polyspermy",
+ "d3-1-reproduction",
+ "d3-2-12-haemophilia-as-an-example-of-a-sex-linked-genetic-disorder",
+ "d3-2-19-autosomal-gene-linkage",
+ "d3-2-inheritance"
+ ]
+ },
+ {
+ "question_id": "21N.2.HL.TZ0.3",
+ "Question": "
\n
The image shows human red blood cells.
\n

\n
[Source: someoneice/123rf.com.]
\n
\n
Outline what will happen to human red blood cells if transferred to distilled water.
\n
[1]
\n
a.
\n
\n
Stem cells can be used to treat Stargardt’s disease. State one other condition treated using stem cells.
\n
[1]
\n
b.
\n
\n
Explain the propagation of nerve impulses along the membrane of a neuron.
\n
[3]
\n
c.
\n
",
+ "Markscheme": "
\n
cells absorb water by osmosis and swell/increase in volume
OR
cells burst/lyse;
\n
a.
\n
\n
leukemia/other diseases of the hematopoietic system / skin burns;
\n
b.
\n
\n
a. depolarization of part of axon/membrane triggers/causes depolarization of next part;
b. local currents;
c. diffusion of sodium ions between depolarized part and next/polarized part (of axon);
d. resting potential reduced/polarization of membrane becomes less /change from -70 to -50mV;
e. sodium channels open when -50mV/threshold potential reached;
f. entry of sodium ions causes depolarization;
g. saltatory conduction in myelinated neurons/axons;
\n
Allow answers in an annotated diagram
\n
c.
\n
",
+ "Examiners report": "
\n
This was mostly well answered with candidates realising that water entry due to osmosis would cause the cells to burst.
\n
a.
\n
\n
A range of conditions were suggested, most of which are not currently treatable using stem cells. Diabetes and neurological diseases were not accepted. 60 % of candidates gave an acceptable answer, with leukaemia much the commonest. The correlation between the mark on this question and overall scores was fairly low, which may suggest that inappropriate examples have been learned in some schools. It is important not to raise hopes of stem cell treatment for specific diseases when research is still continuing and regulatory approval is unlikely for many years.
\n
b.
\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
c.
\n
",
+ "topics": [
+ "c-interaction-and-interdependence",
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "c2-2-9-propagation-of-an-action-potential-along-a-nerve-fibre/axon-as-a-result-of-local-currents",
+ "c2-2-neural-signalling",
+ "d2-3-3-water-movement-by-osmosis-into-or-out-of-cells",
+ "d2-3-water-potential"
+ ]
+ },
+ {
+ "question_id": "21N.2.HL.TZ0.4",
+ "Question": "
\n
The figure shows a tripeptide.
\n

\n
Label one peptide bond in this molecule.
\n
[1]
\n
a.
\n
\n
Describe the secondary structure of proteins.
\n
[2]
\n
b.
\n
\n
Outline the action taken by the diaphragm during inhalation.
\n
[1]
\n
c.
\n
",
+ "Markscheme": "
\n
circle/bracket around peptide bond / arrow pointing to peptide bond / peptide bond labelled;
\n

\n
Allow either peptide bond
\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
a.
\n
\n
a. polypeptide wound into a helical structure / alpha/α helix
OR
polypeptide folded back on itself forming a pleated sheet / beta/β pleated sheet;
b. stabilized/held in shape by/due to hydrogen bonds (between C=O and N-H groups);
c. secondary structures are regular/unvarying (within polypeptides/proteins);
\n
Allow annotated diagrams
\n
b.
\n
\n
contracts/flattens/becomes less domed/increases volume of thorax;
\n
c.
\n
",
+ "Examiners report": "
\n
80 % of candidates indicated one of the two peptide bonds in the diagram correctly.
\n
a.
\n
\n
There were some good answers here describing secondary structures and the role of hydrogen bonding.
\n
b.
\n
\n
80 % of candidates knew that the diaphragm contracts than relaxes during inhalation, or stated that it flattens rather than moves upwards.
\n
c.
\n
",
+ "topics": [
+ "b-form-and-function",
+ "c-interaction-and-interdependence"
+ ],
+ "subtopics": [
+ "b1-2-2-condensation-reactions-forming-dipeptides-and-longer-chains-of-amino-acids",
+ "b1-2-8-pleating-and-coiling-of-secondary-structure-of-proteins",
+ "b1-2-proteins",
+ "b3-1-5-ventilation-of-the-lungs",
+ "b3-1-gas-exchange",
+ "c2-1-10-mechanism-of-action-of-epinephrine-(adrenaline)-receptors",
+ "c2-1-chemical-signalling-[hl-only]"
+ ]
+ },
+ {
+ "question_id": "21N.2.HL.TZ0.5",
+ "Question": "
\n
Compare and contrast the mode of nutrition of detritivores and saprotrophs.
\n

\n
[2]
\n
a.
\n
\n
Explain how some plant species are able to respond to changes in their abiotic environment and flower at a precise time of the year.
\n
[3]
\n
b.
\n
\n
Outline the extension of the stem in plants.
\n
[2]
\n
c.
\n
",
+ "Markscheme": "
\n

\n
Accept not autotrophic/not photosynthetic instead of heterotrophic.
\n
Do not accept that both groups are decomposers or consumers for the similarity.
\n
a.
\n
\n
a. genes for flowering are activated/gene activation/changes to gene expression;
b. shoot apex changes from producing leaves/stem to producing flowers;
c. daylength/duration of the day/night length/photoperiod measured/detected/responded to;
d. short day plants flower when they have a long night/period of darkness
OR
long day plants only flower when they have a short night/period of darkness;
e. so short day plants/SDPs flower in late summer/fall/autumn/winter
OR
so long day plants/LDPs flower in spring/(early) summer;
\n
b.
\n
\n
a. apical meristem (of shoot/stem) produces cells/elongates the stem
OR
cell division/mitosis in tip/apex of shoot/stem;
b. auxin stimulates cell/stem growth/extension/enlargement;
c. elongation of cells causes stem to grow (in length);
\n
c.
\n
",
+ "Examiners report": "
\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
a.
\n
\n
The only relevant changes in the abiotic environment were night length variation over the seasons of the year, which determines when flowering should occur. There were many complicated answers describing the interconversion of the forms of phytochrome, but according to the syllabus this level of detail is not expected and often the simpler ideas that plants can measure night length and respond by the timing of flowering in the year were omitted. Also mostly missing, were the idea of changes to gene expression in the shoot apex, so floral organs start to develop instead of leaves. The average score for this question was only slightly higher than one mark, but the correlation coefficient was high.
\n
b.
\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
c.
\n
",
+ "topics": [
+ "c-interaction-and-interdependence"
+ ],
+ "subtopics": [
+ "c3-1-21-promotion-of-cell-growth-by-auxin",
+ "c3-1-integration-of-body-systems"
+ ]
+ },
+ {
+ "question_id": "21N.2.HL.TZ0.6",
+ "Question": "
\n
RNA molecules play numerous roles in gene expression and so contribute to variation.
\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
[4]
\n
a.
\n
\n
Explain transcription.
\n
[7]
\n
b.
\n
\n
Distinguish between continuous and discrete variation, using examples.
\n
[4]
\n
c.
\n
",
+ "Markscheme": "
\n
a. ribose drawn as pentagon and labelled sugar/ribose;
b. base drawn with correct link to (C1 of) ribose and labelled base/nitrogenous base;
c. phosphate drawn with correct link to (C5 of) ribose and labelled P/phosphate;
d. two (or more) ribonucleotides drawn with correct link (C3 to C5)
\n

\n
a.
\n
\n
a. synthesis of RNA/mRNA / transcription of DNA to RNA;
b. RNA nucleotides linked together to form a strand/chain;
c. RNA strand assembled on DNA template/antisense strand / copy made of sense strand;
d. RNA polymerase carries out transcription/links RNA nucleotides;
e. uncoiling/separation of DNA strands;
f. 5’ end of nucleotides linked to 3’ end of (growing RNA) strand;
g. complementary base pairing (is the basis of copying the base sequence);
h. uracil instead of thymine in RNA;
i. starts at/RNA polymerase binds to a promoter;
j. regulated by transcription factors/DNA binding proteins/nucleosomes;
\n
Annotated diagrams can be used.
\n
b.
\n
\n

\n
c.
\n
",
+ "Examiners report": "
\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
a.
\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
b.
\n
\n
Differences between continuous and discrete variation were not well known and the average performance for this question was the lowest for any part of Section B. A general fault was to describe the two types of variation separately and in consequence forget to include both sides of a distinction. For example, some candidates stated that the environment can cause continuous variation, but most did not then also state that discrete variation is generally unaffected by environment. A mark was awarded for examples of the two types of variation, but in some cases an inappropriate example was chosen, such as hair colour for discrete variation or eye colour for continuous variation. The latter example was best avoided entirely as there are aspects of both continuous and discrete variation in the pigmentation of the iris.
\n
c.
\n
",
+ "topics": [
+ "a-unity-and-diversity",
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "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",
+ "a1-2-nucleic-acids",
+ "a2-2-12-origin-of-eukaryotic-cells-by-endosymbiosis",
+ "a2-2-cell-structure",
+ "d1-2-1-transcription-as-the-synthesis-of-rna-using-a-dna-template",
+ "d1-2-13-initiation-of-transcription-at-the-promoter",
+ "d1-2-protein-synthesis",
+ "d3-2-14-continuous-variation-due-to-polygenic-inheritance-and/or-environmental-factors",
+ "d3-2-inheritance",
+ "d4-1-2-roles-of-mutation-and-sexual-reproduction-in-generating-the-variation-on-which-natural-selection-acts",
+ "d4-1-natural-selection"
+ ]
+ },
+ {
+ "question_id": "21N.2.HL.TZ0.7",
+ "Question": "
\n
Plants have developed efficient methods for transport and for synthesis of foods.
\n
\n
Outline how the properties of water make it an ideal transport medium in plants.
\n
[4]
\n
a.
\n
\n
Distinguish between the xylem and phloem of plants.
\n
[4]
\n
b.
\n
\n
Explain how the light-independent reactions of photosynthesis rely on the light-dependent reactions.
\n
[7]
\n
c.
\n
",
+ "Markscheme": "
\n
a. polarity of water;
b. hydrogen bonds between water molecules;
c. cohesion between water molecules/water molecules stick together;
d. cohesion allows tensions/low pressures/transpiration pull/movement upward/against gravity;
e. adhesion to cellulose/cell walls generates tensions/pull (in xylem)
OR
adhesion to xylem walls/vessel walls causes capillary rise/upward movement;
f. solvent for many substances / many substances dissolve;
g. liquid at most temperatures experienced by plants / liquid so can flow;
\n
Polarity of water and/or hydrogen bonding can be shown in an annotated diagram.
\n
a.
\n
\n

\n
b.
\n
\n
a. light-dependent reactions produce ATP/reduced NADP;
b. ATP generated by chemiosmosis/by photophosphorylation/by ATP synthase;
c. reduced NADP produced by/using electrons from Photosystem I;
d. RuBP + CO2 to glycerate 3-phosphate (in light independent reactions);
e. glycerate 3-phosphate reduced to triose phosphate (in light independent reactions);
f. ATP/reduced NADP used in the light-independent reactions;
g. reduced NADP provides electrons/hydrogen / to reduce (glycerate 3-phosphate)
OR
reduced NADP used to convert glycerate 3-phosphate to triose phosphate;
h. ATP provides energy (for reduction of glycerate 3-phosphate);
i. ATP needed to regenerate RuBP
j. ATP/reduced NADP run out in darkness
k. Calvin cycle only possible with light/in the day/is indirectly dependent on light;
\n
c.
\n
",
+ "Examiners report": "
\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
a.
\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
b.
\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
c.
\n
",
+ "topics": [
+ "a-unity-and-diversity",
+ "b-form-and-function",
+ "c-interaction-and-interdependence"
+ ],
+ "subtopics": [
+ "a1-1-5-solvent-properties-of-water-linked-to-its-role-as-a-medium-for-metabolism-and-for-transport-in-plants-and-animals",
+ "a1-1-water",
+ "b3-2-10-distribution-of-tissues-in-a-transverse-section-of-the-root-of-a-dicotyledonous-plant",
+ "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-transport",
+ "c1-3-19-interdependence-of-the-light-dependent-and-light-independent-reactions",
+ "c1-3-photosynthesis"
+ ]
+ },
+ {
+ "question_id": "21N.2.HL.TZ0.8",
+ "Question": "
\n
Proteins carry out many important functions in cells and in organisms.
\n
\n
Outline the process of protein denaturation.
\n
[4]
\n
a.
\n
\n
Explain the production of antibodies in humans.
\n
[7]
\n
b.
\n
\n
Distinguish between competitive and non-competitive enzyme inhibition.
\n
[4]
\n
c.
\n
",
+ "Markscheme": "
\n
a. change to conformation/shape/tertiary structure/3-D shape;
b. bonds within the protein/intramolecular bonds broken/changed;
c. pH and temperature (outside tolerated ranges) can cause denaturation;
d. vibrations/heat at high temperatures breaks bonds;
e. high pH/low pH/extreme pH alters ionization/charges (of amino acids and breaks ionic bonds);
f. protein cannot carry out its function
OR
active site of enzymes cannot bind substrates/catalyze reaction/no enzyme-substate complex;
g. permanent/irreversible change (usually)
OR
soluble proteins become insoluble/precipitate;
\n
Allow any mark points if made clearly on an annotated graph or diagram.
\n
a.
\n
\n
a. antigens stimulate antibody production;
b. antibodies produced by lymphocytes;
c. macrophages/phagocytes ingest/engulf pathogens and display antigens from them;
d. T-cells activated by binding antigen/by macrophage displaying antigen;
e. activated T-cells cause activation of B-cells;
f. mitosis/division of (activated) B-cells (to produce a clone of cells)
g. plasma cells formed from divided/activated/growing/differentiating B-cells;
h. plasma cells/plasma B-cells secrete antibodies;
i. clonal selection / plasma cells make same type of antibody/antibody specific to same antigen;
j. some activated B-cells become memory cells;
\n
b.
\n
",
+ "Examiners report": "
\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
a.
\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
b.
\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
c.
\n
",
+ "topics": [
+ "b-form-and-function",
+ "c-interaction-and-interdependence"
+ ],
+ "subtopics": [
+ "b1-2-5-effect-of-ph-and-temperature-on-protein-structure",
+ "b1-2-proteins",
+ "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",
+ "c1-1-enzymes-and-metabolism",
+ "c3-2-10-immunity-as-a-consequence-of-retaining-memory-cells",
+ "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-defence-against-disease"
+ ]
+ },
+ {
+ "question_id": "21N.2.SL.TZ0.1",
+ "Question": "
\n
The incidence of white syndrome, an infectious disease of coral, was investigated in a six-year study on Australia’s Great Barrier Reef. The map shows disease conditions on coral reefs at six study sites.
\n

\n
[Source: adapted from Bruno, J.F., Selig, E.R., Casey, K.S., Page, C.A., Willis, B.L., Harvell, C.D., Sweatman,
H. and Melendy, A.M., 2007. PLOS Biology, [e-journal] 5(6), e124. https://doi.org/10.1371/journal.pbio.0050124.]
\n
\n
Satellites were used to record sea surface temperatures. The temperatures each week above a reef were compared with mean temperatures for that week between 1985 and 2004. If the sea surface temperature was 1 °C or more above the mean, this was recorded as a weekly sea surface temperature anomaly (WSSTA). The number of WSSTAs was calculated for the twelve months preceding the date on which a reef was surveyed for white syndrome.
\n
On each reef, the number of cases of white syndrome in a 1500 m2 sample area was surveyed once per year. The table shows these cases in relation to numbers of WSSTAs and coral cover on the reef. Low coral cover was 0–24 % and high coral cover was 50–75 %.
\n

\n
[Source: adapted from Bruno, J.F., Selig, E.R., Casey, K.S., Page, C.A., Willis, B.L., Harvell, C.D., Sweatman,
H. and Melendy, A.M., 2007. PLOS Biology, [e-journal] 5(6), e124. https://doi.org/10.1371/journal.pbio.0050124.]
\n
\n
The graphs show the relationship between the weekly sea surface temperature anomalies (WSSTA) and coral cover during two twelve-month periods (1998–99 and 2002–03), which were the warmest in the six-year study. Each dot represents one studied reef.
\n

\n
[Source: adapted from Bruno, J.F., Selig, E.R., Casey, K.S., Page, C.A., Willis, B.L., Harvell, C.D., Sweatman,
H. and Melendy, A.M., 2007. PLOS Biology, [e-journal] 5(6), e124. https://doi.org/10.1371/journal.pbio.0050124.]
\n
\n
Identify the site with the highest incidence of diseased colonies.
\n
[1]
\n
a.i.
\n
\n
Deduce whether there is a trend in the incidence of white syndrome over the north-south range of latitude.
\n
[1]
\n
a.ii.
\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
[2]
\n
b.i.
\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
[1]
\n
b.ii.
\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
[1]
\n
b.iii.
\n
\n
Compare and contrast the data for 1998–1999 and 2002–2003.
\n
[2]
\n
c.i.
\n
\n
Suggest a reason for the correlation between coral cover and WSSTA in 1998–1999.
\n
[1]
\n
c.ii.
\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
[3]
\n
d.
\n
\n
This study was carried out over six years on the Australian Great Barrier Reef. State one advantage of field investigations compared with mesocosm experiments to study ecological processes.
\n
[1]
\n
e.
\n
",
+ "Markscheme": "
\n
Capricorn and Bunkers group;
\n
a.i.
\n
\n
there is no clear trend;
\n
a.ii.
\n
\n
a. effects (generally) increase with temperature anomalies/WSSTA;
b. effects increase for all different coral covers
OR
in the 25-49 cover there is an anomaly/is not an increasing trend;
c. harmful effect is higher in coral covers between1 50-75 % / vice versa;
\n
b.i.
\n
\n
50 % / 25 % / 49 %
OR
25–49 % (coral cover);
\n
b.ii.
\n
\n
a. the closer the corals are (to each other) the easier the transmission;
b. other organisms in the community may act as vectors/carriers / OWTTE;
\n
b.iii.
\n
\n
Similarities
a. similar range of cover in both periods
OR
weak correlation/no correlation in either;
\n
Differences
b. higher WSSTA range/more WSSTA in 1998–1999 than 2002–2003
OR
positive (2002–2003) versus negative correlation (98–99)
OR
more coral reefs with very low % of coral cover (0–20 %) in 2002–2003;
\n
Must respond with one similarity and one difference for full marks.
\n
c.i.
\n
\n
coral cover lower on reefs with higher temperature;
\n
c.ii.
\n
\n
a. corals would not be able to maintain their skeletons;
b. (if coral reefs are lost) habitat will be lost;
c. some organisms/coral can decline if the water becomes too acidified;
d. coral bleaching could occur/become worse
OR
coral could expel their mutualistic alga/zooxanthellae;
e. enzymes could be denatured;
\n
d.
\n
\n
real environmental conditions / larger scale investigations / more variables studied;
\n
e.
\n
",
+ "Examiners report": "
\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
a.i.
\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
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
b.i.
\n
\n
Most were able to able to gain the mark in 1b (ii) for saying that the threshold level was 25 – 49 %.
\n
b.ii.
\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
b.iii.
\n
\n
In 1c contrasts were common, but few gained the comparison mark as well.
\n
c.i.
\n
\n
In 1d weaker students incorrectly wrote about the sea becoming acidic as the pH was increasing (sic). Indeed, it is becoming more acidic, as the pH is decreasing slightly, leading to more bleaching and the decrease in population of some creatures.
\n
d.
\n
\n
In 1e most were able to give a reason why the study was better than a mesocosm.
\n
e.
\n
",
+ "topics": [
+ "b-form-and-function",
+ "c-interaction-and-interdependence",
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "b4-1-5-conditions-required-for-coral-reef-formation",
+ "b4-1-adaptation-to-environment",
+ "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",
+ "c1-3-photosynthesis",
+ "d4-2-4-use-of-a-model-to-investigate-the-effect-of-variables-on-ecosystem-stability",
+ "d4-2-stability-and-change",
+ "d4-3-7-threats-to-coral-reefs-as-an-example-of-potential-ecosystem-collapse",
+ "d4-3-climate-change"
+ ]
+ },
+ {
+ "question_id": "21N.2.SL.TZ0.2",
+ "Question": "
\n
The figure shows a tripeptide.
\n

\n
Label one peptide bond in this molecule.
\n
[1]
\n
a.
\n
\n
Outline the specific functions of three named proteins.
\n
[3]
\n
b.
\n
\n
Outline the action taken by the diaphragm during inhalation.
\n
[1]
\n
c.
\n
",
+ "Markscheme": "
\n
circle/bracket around peptide bond / arrow pointing to peptide bond / peptide bond labelled;
\n

\n
Allow either peptide bond
\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
a.
\n
\n
a. Rubisco fixes CO2 from atmosphere during photosynthesis;
b. insulin controls blood glucose levels;
c. collagen forms connective tissue/ligaments;
d. spider silk forms the spider web;
e. rhodopsin involved in photoreceptor;
f. immunoglobulins/antibodies attach to antigens/pathogens;
g. actin/myosin performs muscle contraction;
h. hemoglobin carries oxygen in red blood cells;
\n
Accept any other correct three named proteins
\n
If an enzyme is named, the correct substrate must be stated
\n
b.
\n
\n
contracts/flattens/becomes less domed/increases volume of thorax;
\n
c.
\n
",
+ "Examiners report": "
\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
a.
\n
",
+ "topics": [
+ "b-form-and-function",
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "b1-2-11-quaternary-structure-of-non-conjugated-and-conjugated-proteins",
+ "b1-2-2-condensation-reactions-forming-dipeptides-and-longer-chains-of-amino-acids",
+ "b1-2-proteins",
+ "b3-1-5-ventilation-of-the-lungs",
+ "b3-1-gas-exchange",
+ "d2-1-11-meiosis-as-a-source-of-variation",
+ "d2-1-9-meiosis-as-a-reduction-division",
+ "d2-1-cell-and-nuclear-division",
+ "d3-2-12-haemophilia-as-an-example-of-a-sex-linked-genetic-disorder",
+ "d3-2-inheritance"
+ ]
+ },
+ {
+ "question_id": "21N.2.SL.TZ0.3",
+ "Question": "
\n
Compare and contrast the mode of nutrition of detritivores and saprotrophs.
\n

\n
[2]
\n
a.
\n
\n
The image shows an example of a soil food web.
\n

\n
[Source: Anon., n.d. The Soil Food Web. [image online] Available at: https://www.nrcs.usda.gov/wps/portal/nrcs/
photogallery/soils/health/biology/gallery/?cid=1788&position=Promo [Accessed 11 March 2020].]
\n
\n
Draw a food chain from this food web, showing at least three organisms.
\n
[1]
\n
b.i.
\n
\n
Explain the reasons for food chains rarely containing more than four or five trophic levels.
\n
[3]
\n
b.ii.
\n
\n
The amount of food passing into food chains can be affected by the rate of photosynthesis. Explain the effect of one limiting factor on photosynthesis.
\n
[3]
\n
c.
\n
\n
All of the leaves in the image are from Solanum, a wild genus of tomato.
\n

\n
[Source: Courtesy: National Science Foundation, Credit Leonie Moyle.]
\n
\n
State one cause of variation in a plant such as the tomato.
\n
[1]
\n
d.
\n
",
+ "Markscheme": "
\n

\n
Accept not autotrophic/not photosynthetic instead of heterotrophic.
\n
Do not accept that both groups are decomposers or consumers for the similarity.
\n
a.
\n
\n
food chain of three or more organisms starting with plants;
\n
b.i.
\n
\n
a. energy is lost between the trophic levels;
b. transfer between levels is only usually 10% efficient
OR
energy transformations take place in living organisms / the process is never 100% efficient;
c. energy is lost by the organism/used in respiration / released as heat/movement;
d. energy is lost as waste/feces/urine/undigested food/uneaten parts;
e. as energy is lost between trophic levels and so (higher ones) have less biomass / less biomass available for next level;
\n
b.ii.
\n
\n
a. the rate of reaction will be limited by the limiting factor that is nearest to its minimum value;
\n
temperature:
b. enzymes that control photosynthesis are influenced by temperature;
c. as temperature increases, reaction rate will increase;
d. above a certain temperature, the rate of photosynthesis will decrease;
e. (where temperature is limiting) essential enzymes begin to denature/not working to optimum;
\n
light intensity:
f. light is source of energy / converted into chemical energy;
g. as light intensity increases reaction rate will increase;
h. at a certain light intensity, rate of photosynthesis will plateau;
i. another factor becomes limiting;
\n
CO2 concentration:
j. CO2 is fixed to form organic molecules;
k. as CO2 concentration increases, reaction rate will increase;
l. at a certain concentration of CO2, rate of photosynthesis will plateau;
m. another factor becomes limiting;
\n
Accept answers using an annotated graph to explain
\n
Only accept the first factor described
\n
Do not accept pH as a limiting factor
\n
c.
\n
\n
a. mutations;
b. meiosis/crossing over/random assortment of homologous pairs;
c. sexual reproduction/recombination/random fertilisation;
\n
d.
\n
",
+ "Examiners report": "
\n
Knowledge of detritivores and saprotrophs was good in 3a, with many of the poorer answers describing them as feeding on inorganic material.
\n
a.
\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
b.i.
\n
\n
Most were able to gain at least two marks for the explanation of energy loss through the trophic levels.
\n
b.ii.
\n
\n
In 3c, most knew that temperature/CO2 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
c.
\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
d.
\n
",
+ "topics": [
+ "c-interaction-and-interdependence",
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "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",
+ "c1-3-photosynthesis",
+ "c4-2-3-flow-of-chemical-energy-through-food-chains",
+ "c4-2-4-construction-of-food-chains-and-food-webs-to-represent-feeding-relationships-in-a-community",
+ "c4-2-transfers-of-energy-and-matter",
+ "d1-3-7-mutation-as-a-source-of-genetic-variation",
+ "d1-3-mutations-and-gene-editing",
+ "d2-3-3-water-movement-by-osmosis-into-or-out-of-cells",
+ "d2-3-water-potential"
+ ]
+ },
+ {
+ "question_id": "21N.2.SL.TZ0.4",
+ "Question": "
\n
State one process that produces ATP.
\n
[1]
\n
b.i.
\n
\n
Outline the use of ATP.
\n
[1]
\n
b.ii.
\n
\n
State one function of epinephrine in the human body.
\n
[1]
\n
c.
\n
",
+ "Markscheme": "
\n
a. arteries carry blood at high pressure;
b. rupture of arteries is prevented by thick muscular/elastic walls;
c. narrow lumen to maintain a high blood pressure;
d. elastic tissue allows artery to stretch and recoil (to even out pressures);
e. arteries have muscle layers which contract to increase/control the blood flow;
f. folding in the endothelium allows stretching
OR
smooth endothelium reduces friction;
\n
a.
\n
\n
(cell) respiration/photosynthesis;
\n
b.i.
\n
\n
source of energy (for use in the cell)
OR
example of use of ATP
OR
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
b.ii.
\n
\n
increases heart rate
OR
prepares the body for action;
\n
c.
\n
",
+ "Examiners report": "
\n
Most could state that the arteries carry blood at high pressure, but had difficulty getting the other two marks.
\n
a.
\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
b.i.
\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
c.
\n
",
+ "topics": [
+ "b-form-and-function",
+ "c-interaction-and-interdependence"
+ ],
+ "subtopics": [
+ "b3-1-5-ventilation-of-the-lungs",
+ "b3-1-gas-exchange",
+ "b3-2-2-structure-of-arteries-and-veins",
+ "b3-2-3-adaptations-of-arteries-for-the-transport-of-blood-away-from-the-heart",
+ "b3-2-transport",
+ "c1-2-3-energy-transfers-during-interconversions-between-atp-and-adp",
+ "c1-2-4-cell-respiration-as-a-system-for-producing-atp-within-the-cell-using-energy-released-from-carbon-compounds",
+ "c1-2-cell-respiration",
+ "c2-1-10-mechanism-of-action-of-epinephrine-(adrenaline)-receptors",
+ "c2-1-chemical-signalling-[hl-only]"
+ ]
+ },
+ {
+ "question_id": "21N.2.SL.TZ0.5",
+ "Question": "
\n
Substances can move into and out of cells through the cell membrane.
\n
\n
Outline the significance of surface area to volume ratio in the limitation of cell size.
\n
[4]
\n
a.
\n
\n
Describe transport across cell membranes by osmosis.
\n
[4]
\n
b.
\n
\n
Explain the adaptations of the small intestine to its function.
\n
[7]
\n
c.
\n
",
+ "Markscheme": "
\n
a. surface area of the cell affects the rate of material exchange;
b. when the cell increases in size, so does its chemical activity/metabolism;
c. (when the cell increases in size/grows) more substances need to be taken in / more waste products need to be excreted;
d. as the volume of the cell increases, so does the surface area, however not to the same extent
OR
when the cell gets bigger, its surface area to volume ratio gets smaller;
e. substances will not be able enter the cell fast enough/cell volume will not be supplied
\n
OR
metabolic rate will exceed the rate of exchange
OR
when the surface area: volume ratio is higher, the diffusion rate increases;
f. some cells have adaptations to increase their surface area/flatten/microvilli/shape of red blood cells;
g. cells in growth areas tend to divide and remain small
OR
cells divide when maximum size is reached;
\n
a.
\n
\n
a. form of diffusion;
b. osmosis is the movement of water molecules;
c. (movement) across a selectively/semi/partially permeable membrane/cell membrane;
d. from a region of low solute concentration to a region of high solute concentration (until equilibrium is reached)
OR
movement of water molecules from a high concentration of water to a low concentration of water molecules;
e. it is a passive transport mechanism/does not use ATP;
f. channel proteins/aquaporins are used;
\n
b.
\n
\n
a. small intestine is where nutrients are absorbed into the bloodstream;
b. very long to maximize absorption;
c. (the small intestine) is lined with (smooth) muscle to allow for the mixing/ and moving of digested food;
d. muscles are circular and longitudinal;
e. that perform peristalsis;
f. the pancreas (and gall bladder) secretes substances into the small intestine to aid digestion;
g. contain villi, to increase surface area;
h. villi have microvilli to increase surface area even more;
i. villi absorb products of digestion/mineral ions/vitamins/glucose;
j. dense capillary network rapidly transports absorbed products;
k. lacteal absorbs lipids from the intestine (into the lymphatic system);
l. (most of the) chemical digestion (into monomers) occurs in small intestine/description of specific enzyme action;
\n
Accept annotated diagrams as part of the explanation.
\n

\n
[Source: © 1999–2022, Rice University. Except
where otherwise noted, textbooks on this site are
licensed under a Creative Commons Attribution 4.0
International License https://creativecommons.org/
licenses/by/4.0/. Image available at https://
openstax.org/books/anatomy-and-physiology/
pages/23-5-the-small-and-large-intestines?
query=villus&target=%7B%22type%22%3A%
22search%22%2C%22index%22%3A0%7D#fsid1272744]
\n
c.
\n
",
+ "Examiners report": "
\n
Most knew that as the cell increases in size, the SA:volume ratio decreases but had difficulty explaining its significance.
\n
a.
\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
b.
\n
\n
The structure and function of the small intestine was quite well known. Many missed a mark for omitting to say that the products of digestion are absorbed into the blood. Some of the descriptions of microvilli were not clear, not making it evident that they were on the epithelial cells of the villi. The presence and functions of the muscle layers were well known.
\n
c.
\n
",
+ "topics": [
+ "b-form-and-function",
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "b2-3-6-surface-area-to-volume-ratios-and-constraints-on-cell-size",
+ "b2-3-cell-specialization",
+ "d2-3-3-water-movement-by-osmosis-into-or-out-of-cells",
+ "d2-3-water-potential"
+ ]
+ },
+ {
+ "question_id": "21N.2.SL.TZ0.6",
+ "Question": "
\n
Organisms have evolved a great diversity of cell types.
\n
\n
Describe the endosymbiotic theory.
\n
[4]
\n
a.
\n
\n
Explain the need for halving the chromosome number during a sexual life cycle and how this is done.
\n
[7]
\n
b.
\n
\n
Outline the binomial system of classification.
\n
[4]
\n
c.
\n
",
+ "Markscheme": "
\n
a. theory that eukaryotic cells evolved from prokaryotes
OR
origin of eukaryotic organisms based on some organisms living inside/engulfed by other organisms
OR
prokaryotic cell engulfed another prokaryote including it in cytoplasm without digesting it;
b. mitochondria/chloroplasts have double membranes;
c. mitochondria/chloroplasts have their own DNA/loop of DNA/naked DNA;
d. mitochondria/chloroplasts have similar size to prokaryotes;
e. mitochondria/chloroplasts can reproduce by binary fission;
f. mitochondria/chloroplasts have 70S ribosomes (same as prokaryotes);
\n
a.
\n
\n
a. chromosome number is halved so the zygote/offspring has same number as the parent / so that chromosome number is not doubled;
b. process is meiosis;
c. DNA/chromosomes replicate (so each chromosome consists of two chromatids);
d. homologous chromosomes pair in prophase I;
e. (these) separate in anaphase I into two cells;
f. (after meiosis I) cells are haploid;
g. in meiosis II chromatids are separated;
h. result is four haploid cells/gametes;
i. each gamete is genetically unique;
j. (uniqueness) is due to crossing over/independent assortment/random alignment of chromosomes;
k. fertilization results in the formation of a diploid zygote;
l. (fertilization) results in variation in a population
\n
b.
\n
\n
a. the binomial system of names for species is universal among biologists
OR
named according to a globally recognized scheme;
b. allows to classify organisms into groups based on similar characteristics/common ancestry/DNA;
c. every species is given a binomial name;
d. members of the same species can mate and reproduce fertile offspring
e. genus is written first, followed by species;
f. genus is capitalized, (followed by) species is lower case
OR
an underlined correct example/stated that it must be underlined or italicized;
\n
c.
\n
",
+ "Examiners report": "
\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
a.
\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 halving of the chromosome number, many insisted on writing about chromosomal errors such as Down syndrome, which was not pertinent to the question.
\n
b.
\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
c.
\n
",
+ "topics": [
+ "a-unity-and-diversity",
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "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",
+ "a1-2-nucleic-acids",
+ "a2-2-12-origin-of-eukaryotic-cells-by-endosymbiosis",
+ "a2-2-cell-structure",
+ "a3-1-3-binomial-system-for-naming-organisms",
+ "a3-1-diversity-of-organisms",
+ "d2-1-4-roles-of-mitosis-and-meiosis-in-eukaryotes",
+ "d2-1-cell-and-nuclear-division"
+ ]
+ },
+ {
+ "question_id": "21N.2.SL.TZ0.7",
+ "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
\n
\n (b)\n
\n
\n
\n Distinguish between the xylem and phloem of plants.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\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
\n (b)\n
\n
\n
\n
\n
\n",
+ "Examiners report": "
\n (a)\n
\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
\n (b)\n
\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",
+ "topics": [
+ "a-unity-and-diversity",
+ "b-form-and-function"
+ ],
+ "subtopics": [
+ "a1-1-5-solvent-properties-of-water-linked-to-its-role-as-a-medium-for-metabolism-and-for-transport-in-plants-and-animals",
+ "a1-1-water",
+ "b3-2-10-distribution-of-tissues-in-a-transverse-section-of-the-root-of-a-dicotyledonous-plant",
+ "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-transport"
+ ]
+ },
+ {
+ "question_id": "22M.2.HL.TZ1.4",
+ "Question": "
\n
Hemoglobin is a conjugated protein consisting of four polypeptide chains with attached heme groups.
\n

\n
[Source: LAGUNA DESIGN/Science Photo Library via Getty Images.]
\n
\n
State the level of protein structure at which the polypeptide chains of hemoglobin are combined.
\n
[1]
\n
a.
\n
\n
Explain the shape of the polypeptide chain at X.
\n
[2]
\n
b.
\n
\n
Outline the role of tRNA in hemoglobin synthesis.
\n
[2]
\n
c.
\n
",
+ "Markscheme": "
\n
quaternary / fourth level;
\n
a.
\n
\n
\n- \nalpha helix / helix\n
\n- type of secondary structure / second level of protein structure;
\n- maintained by hydrogen bonds;
\n- between C=O group and an N–H group;
\n
\n
b.
\n
\n
\n- decoding/translation (of the genetic code/RNA base sequence);
\n- carries/brings one amino acid/a specific amino acid/the amino acid (corresponding to codon/anticodon);
\n- tRNA has an anticodon which pairs with mRNA/is complementary to a codon (on mRNA);
\n
\n
c.
\n
",
+ "Examiners report": "
\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
a.
\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
b.
\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
c.
\n
",
+ "topics": [
+ "b-form-and-function",
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "b1-2-11-quaternary-structure-of-non-conjugated-and-conjugated-proteins",
+ "b1-2-8-pleating-and-coiling-of-secondary-structure-of-proteins",
+ "b1-2-proteins",
+ "d1-2-6-roles-of-mrna-ribosomes-and-trna-in-translation",
+ "d1-2-protein-synthesis"
+ ]
+ },
+ {
+ "question_id": "22M.2.HL.TZ1.5",
+ "Question": "
\n
The diagram shows a section through part of the leg of an insect and antagonistic muscles X and Y. The tibia moves in the direction shown by the arrow when the muscle is flexing.
\n

\n
[Source: D G Mackean www.biology-resources.com.]
\n
\n
Outline a reason for the muscles being described as antagonistic.
\n
[1]
\n
a.
\n
\n
Describe the role of muscle Y.
\n
[2]
\n
b.
\n
\n
Outline how the muscle attachment of insects differs from humans.
\n
[1]
\n
c.
\n
\n
Explain the role of calcium ions in muscle contraction.
\n
[3]
\n
d.
\n
",
+ "Markscheme": "
\n
cause opposite movements / pull in opposite directions / when one contracts the other relaxes;
\n
a.
\n
\n
\n- flexor/flexion;
\n- bends/flexes the leg/limb/joint;
\n
\n
b.
\n
\n
insect muscle is attached inside (the skeleton) and human muscle outside (the skeleton);
insect muscle is attached to exoskeleton and human to endoskeleton/bones;
\n
c.
\n
\n
\n- calcium released from sarcoplasmic reticulum;
\n- calcium binds to troponin;
\n- causes tropomyosin to move;
\n- uncovers binding sites;
\n- myosin heads bind to the actin forming cross bridges;
\n
\n
d.
\n
",
+ "Examiners report": "
\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
a.
\n
\n
The mark scheme here was rather too demanding and very few candidates were awarded both marks. The biological distinctions between flexors and flexion were too fine and marks should have been awarded for other relevant ideas. A flexor is a muscle that causes flexion. Although we may speak colloquially of 'flexing our muscles' it is not a muscle that flexes but a limb at a joint.
\n
b.
\n
\n
This question probed whether candidates understood the difference between the skeletons of mammals and insects and thus where muscles are attached. Although the diagram shows tendon-like attachment of insect muscles, many candidates claimed that the lack of tendons was the prime difference.
\n
c.
\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
d.
\n
",
+ "topics": [
+ "b-form-and-function",
+ "c-interaction-and-interdependence"
+ ],
+ "subtopics": [
+ "b3-3-2-sliding-filament-model-of-muscle-contraction",
+ "b3-3-3-role-of-the-protein-titin-and-antagonistic-muscles-in-muscle-relaxation",
+ "b3-3-8-internal-and-external-intercostal-muscles-as-an-example-of-antagonistic-muscle-action-to-facilitate-internal-body-movements",
+ "b3-3-muscle-and-motility-(hl-only)",
+ "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-neural-signalling"
+ ]
+ },
+ {
+ "question_id": "22M.2.HL.TZ1.6",
+ "Question": "
\n
Outline how the properties of water make it an effective coolant for the body.
\n
[3]
\n
a.
\n
\n
Describe how changes in weather conditions affect the transport and loss of water in plants.
\n
[5]
\n
b.
\n
\n
Explain how water balance is restored in mammals when they are dehydrated.
\n
[7]
\n
c.
\n
",
+ "Markscheme": "
\n
\n- hydrogen bonds hold water molecules together/make water molecules cohere;
\n- evaporation requires breaking of hydrogen bonds / heat needed to break hydrogen bonds
\n- water has a high heat of vaporization/high latent heat;
\n- evaporation of water/sweat removes heat from/cools the skin/body;
\n
\n
a.
\n
\n
\n- water (vapor) lost by transpiration/through stomata;
\n- transpiration/loss of water from leaves causes transport of water (in xylem);
Temperature: \n- faster/more water loss/transpiration/transport in hotter weather;
\n- more heat for evaporation;
Humidity: \n- slower/less water loss/transpiration/transport in more humid weather;
\n- faster diffusion of water (vapor) out of the leaf/through the stomata with low humidity outside;
OR
no evaporation if air is saturated with water vapor/with 100 % humidity;
Wind:\n \n- faster/more water loss/transpiration/transport in windy/windier weather;
\n- wind/air movement carries away water vapor from around the leaf/stomata;
\n- high winds can cause stomatal closure and so reduce transpiration;
Drought:\n \n- drought causes stomata to close so reduces loss/transport;
\n
\n
b.
\n
\n
\n- thirst;
\n- more water drunk / more water reabsorbed from feces (in the colon/large intestine);
\n- osmoreceptors in the hypothalamus detect dehydration/high solute concentration in blood;
\n- ADH secreted;
\n- by the pituitary gland;
\n- ADH signals to collecting duct/DCT (cells) to increase permeability to water;
\n- more aquaporins (in plasma membranes of collecting duct/distal convoluted tubule cells);
\n- more water reabsorbed from filtrate (in collecting ducts/distal convoluted tubules);
\n- reabsorption by osmosis / reabsorption due to medulla being hypertonic;
\n- reabsorbed water passes into the blood/reduces the solute concentration of blood;
\n- smaller volume/more concentrated/hypertonic urine formed;
\n- less sweating;
\n
\n
c.
\n
",
+ "Examiners report": "
\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
a.
\n
\n
More marks were scored here, but again there was widespread misunderstanding of the forces that cause water to evaporate and diffuse out of leaves, and of how conditions such as humidity, temperature and wind can influence the process. Few candidates mentioned concentration gradients between air spaces in the leaf and the atmosphere outside the leaf. There was a tendency to get trends the wrong way round, for example by suggesting that transpiration increases during rainfall because plants have plenty of water and therefore choose to open their stomata more widely.
\n
b.
\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
c.
\n
",
+ "topics": [
+ "a-unity-and-diversity",
+ "b-form-and-function",
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "a1-1-6-physical-properties-of-water-and-the-consequences-for-animals-in-aquatic-habitats",
+ "a1-1-water",
+ "b3-1-9-transpiration-as-a-consequence-of-gas-exchange-in-a-leaf",
+ "b3-1-gas-exchange",
+ "d3-3-7-role-of-the-kidney-in-osmoregulation-and-excretion",
+ "d3-3-homeostasis"
+ ]
+ },
+ {
+ "question_id": "22M.2.HL.TZ1.7",
+ "Question": "
\n
Outline reasons for the therapeutic use of stem cells.
\n
[3]
\n
a.
\n
\n
Describe how monoclonal antibodies are produced.
\n
[5]
\n
b.
\n
\n
Explain the role of the electron transport chain in the generation of ATP by cell respiration.
\n
[7]
\n
c.
\n
",
+ "Markscheme": "
\n
\n- unspecialized/undifferentiated stem cells can divide/differentiate along different pathways;
\n- (stem cells are accessible as they) come from embryos/bone marrow/umbilical cord blood/adult tissue;
\n- (stem cells) can regenerate/repair/regrow diseased/damaged tissues in people;
\n- valid specific example;
\n- drugs can be tested on stem cells (in laboratories to see if they are harmful);
\n
\n
a.
\n
\n
\n- mice/rabbit/small mammal injected with one type of antigen;
\n- cells from the spleen/antibody-producing cells are removed;
\n- plasma cells that produce antibodies (are used);
\n- myeloma/tumor cells that divide endlessly (are used);
\n- fusion of plasma cells with tumor/myeloma cells / fusion produces hybridoma cells;
\n- selection of hybridoma cells / medium used that only allows growth of hybridoma cells;
\n- fused cells/hybridoma cells are cultured/grown in tissue culture/grown in a fermenter;
\n- (hybridoma) cells divide endlessly and produce the desired antibodies;
\n
\n
b.
\n
\n
\n- electron transport chain performs chemiosmosis / chemiosmosis generates ATP;
\n- receives energy/electrons from oxidation reactions/from Krebs cycle/glycolysis;
\n- receives electrons from reduced NAD/NADH/reduced FAD/FADH;
\n- energy released as electrons pass from carrier to carrier (in the chain);
\n- release of energy (from electron flow) coupled to proton pumping;
\n- protons pumped into intermembrane space;
\n- creates proton gradient;
\n- protons diffuse back/move down the concentration gradient (across membrane);
\n- protons pass through ATP synthase;
\n- protons return to the matrix;
\n- flow of protons provides energy for generating ATP;
\n- electrons transferred to oxygen at end of electron transport chain;
\n
\n
c.
\n
",
+ "Examiners report": "
\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
a.
\n
\n
Production of monoclonal antibodies was not widely understood and the mean mark was below 1 (out of 5). Many answers described the normal immune response by the body that results in production of antibodies, rather than the production of hybridoma cells that allow large-scale antibody manufacture.
\n
b.
\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
c.
\n
",
+ "topics": [
+ "c-interaction-and-interdependence"
+ ],
+ "subtopics": [
+ "c1-2-14-generation-of-a-proton-gradient-by-flow-of-electrons-along-the-electron-transport-chain",
+ "c1-2-cell-respiration"
+ ]
+ },
+ {
+ "question_id": "22M.2.HL.TZ2.1",
+ "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
\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
\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
\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
\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
\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
\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
\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",
+ "Markscheme": "
\n (a.i)\n
\n
\n - \n blocks synaptic transmission at (cholinergic synapses);\n
\n - \n binds to (acetylcholine) receptors;\n
\n
\n
\n
\n (a.ii)\n
\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
\n (a.iii)\n
\n
\n - \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 \n - \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 \n
\n
\n \n Accept vice versa\n \n .\n
\n
\n
\n (a.iv)\n
\n
\n - \n less production of honey/wax;\n
\n - \n fewer bees/dispersal of bees/queens;\n
\n - \n bad weather/environmental change/predators/disease/pests;\n
\n
\n
\n
\n (b)\n
\n
\n - \n number of populations may/will decrease;\n
\n - \n both treatments decreased very significantly the number of queens;\n
\n - \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 \n - \n without new queens, new colonies cannot be founded;\n
\n - \n no/less/little reproduction (as only queens lay eggs);\n
\n - \n new colonies are essential to maintain bumblebee populations;\n
\n
\n
\n
\n (c.i)\n
\n
\n \n B. lucorum\n \n ;\n
\n
\n
\n (c.ii)\n
\n
\n - \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 \n - \n high doses caused (slightly) lower (average) results in all 4 species (compared to control);\n
\n - \n in only one species/\n \n B. pratorum\n \n , the high doses caused larger lengths than the low doses;\n
\n
\n
\n \n Accept any other valid comparison\n \n .\n
\n
\n
\n (d)\n
\n
\n - \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
\n - \n yes, as decreased numbers of queens (likely) affect reproductive capabilities; (\n \n From Graph 2\n \n )\n
\n - \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
\n
\n
\n \n OWTTE\n \n
\n
\n",
+ "Examiners report": "
\n (a.i)\n
\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",
+ "topics": [
+ "c-interaction-and-interdependence"
+ ],
+ "subtopics": [
+ "c2-2-12-effects-of-exogenous-chemicals-on-synaptic-transmission",
+ "c2-2-neural-signalling"
+ ]
+ },
+ {
+ "question_id": "22M.2.HL.TZ2.2",
+ "Question": "
\n
Identify, with a reason, the stage shown at X.
\n
[2]
\n
a.i.
\n
\n
Calculate the length of the entire cell labelled Y, showing your working.
\n
[1]
\n
a.ii.
\n
\n
State the role of cyclins in the cell cycle.
\n
[1]
\n
a.iii.
\n
\n
Distinguish between the structure of chromosomes in prokaryotes and eukaryotes.
\n
[2]
\n
b.i.
\n
\n
Explain Cairns’s technique to measure the length of the DNA molecule.
\n
[2]
\n
b.ii.
\n
",
+ "Markscheme": "
\n
\n- anaphase;
\n- the (replicated) chromosomes/chromatids are separating/moving to opposite poles of the cell;
\n
\n
OWTTE
\n
a.i.
\n
\n
50 μm = 27/28/29 mm, Y = 8/9/10 mm
OR
50 x 9 /27
OR
16.7 μm (accept answers in the range of 14.8 μm to 17.2 μm)
\n
Award [1] for correct ratios not precise measurements in the work or [1] for correct answer with correct unit.
\n
a.ii.
\n
\n
\n- (group of regulatory proteins that) control/regulate the cell cycle;
\n- activate cyclin-dependent kinases (which control cell cycle processes);
\n
\n
a.iii.
\n
\n
\n- prokaryotes (usually) have one chromosome while eukaryotes have numerous chromosomes;
\n- prokaryotes have a circular chromosome while eukaryotes have linear ones;
\n- eukaryotes’ chromosomes are associated with histones/proteins but prokaryotes/Eubacteria have naked DNA vs eukaryote DNA associated to proteins/histones;
\n
\n
Accept only differences.
\n
Differentiating terms expected;
\n
b.i.
\n
\n
\n- Cairns grew prokaryotes/E. coli in radioactive thymidine/thymine/thymine containing tritium;
\n- contents of cell put on photographic film/surface (for several weeks) / used autoradiography and electron microscopes;
\n- measured the length of the DNA molecule and photographed it / produced image of DNA;
\n- could show the new strands were all labelled with thymidine/thymine;
\n
\n
b.ii.
\n
",
+ "Examiners report": "
\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
a.i.
\n
\n
Most answers were correct, but some calculations were difficult to follow; some errors in unit conversions led to incorrect decimal places.
\n
a.ii.
\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
b.i.
\n
\n
Asking students to outline Cairn’s technique led to a number of blank answers. That there was a role for autoradiography was better known than how this was used to obtain the length estimate.
\n
b.ii.
\n
",
+ "topics": [
+ "a-unity-and-diversity",
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "a2-2-2-microscopy-skills",
+ "a2-2-5-prokaryote-cell-structure",
+ "a2-2-6-eukaryote-cell-structure",
+ "a2-2-cell-structure",
+ "d2-1-15-control-of-the-cell-cycle-using-cyclins",
+ "d2-1-8-identification-of-phases-of-mitosis",
+ "d2-1-cell-and-nuclear-division"
+ ]
+ },
+ {
+ "question_id": "22M.2.HL.TZ2.3",
+ "Question": "
\n
A group of students used quadrat sampling and the chi-squared test to find out whether the distributions of two plant species were associated with each other or not. These two species were found in the ground vegetation in a woodland ecosystem.
\n

\n
[Source: (left) Pixabay.
(right) Topic, J., n.d. Veronica montana 2. [image online] Available at: http://www.freenatureimages.eu/Plants/
Flora%20S-Z/Veronica%20montana/#Veronica%2520montana%25202%252C%2520Bosereprijs%252C%2520Saxifr
aga-Jasenka%2520Topic.jpg [Accessed 3 December 2019].
\n
The numbers of quadrats with one, both or neither species present were counted and recorded. The observed frequencies from 150 quadrats are shown in the following contingency table.
\n

\n
\n
State the alternative hypothesis for this study.
\n
[1]
\n
a.
\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
[1]
\n
b.
\n
\n
State the number of degrees of freedom for this test to determine the critical value of chi-squared.
\n
[1]
\n
c.
\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
[1]
\n
d.
\n
",
+ "Markscheme": "
\n
there is a positive / negative association between the two species;
they tend to grow together / they tend to grow apart;
\n
OWTTE
\n
a.
\n
\n
\n- \n ;
\n- 25.7;
\n
\n
Award [1] for proper values chosen/equation or [1] for answer.
\n
b.
\n
\n
1 (df)
OR
(r-1) (c-1);
\n
c.
\n
\n
\n- (when the calculated value is smaller than the critical value) there is no significant association between the two species / H0/null hypothesis accepted;
\n- it is random chance if both species are either present or absent in most quadrats;
\n
\n
d.
\n
",
+ "Examiners report": "
\n
There were many correct answers, but a number confused the alternate and null hypotheses.
\n
a.
\n
\n
Calculating the degrees of freedom proved problematic for many.
\n
c.
\n
",
+ "topics": [
+ "c-interaction-and-interdependence"
+ ],
+ "subtopics": [
+ "c1-2-10-anaerobic-cell-respiration-in-yeast-and-its-use-in-brewing-and-baking",
+ "c1-2-5-differences-between-anaerobic-and-aerobic-cell-respiration-in-humans",
+ "c1-2-cell-respiration",
+ "c4-1-15-use-of-the-chi-squared-test-for-association-between-two-species",
+ "c4-1-populations-and-communities"
+ ]
+ },
+ {
+ "question_id": "22M.2.HL.TZ2.5",
+ "Question": "
\n
DNA forms chromosomes, but much of eukaryote DNA is non-coding.
\n

\n
[Source: Pixabay.]
\n
\n
People can be analysed genetically for risks of specific diseases before they actually develop. One of these is type I diabetes.
\n
\n
Describe the structure of nucleosomes.
\n
[1]
\n
a.i.
\n
\n
Explain how the two strands of the DNA double helix are held together.
\n
[2]
\n
a.ii.
\n
\n
There are multiple tandem repeats of nucleotide segments of DNA found in the non-coding DNA between genes. Outline how tandem repeats are used for DNA profiling.
\n
[3]
\n
a.iii.
\n
\n
Explain what happens in a person when they develop type I diabetes.
\n
[2]
\n
b.i.
\n
\n
State how type I diabetes should be treated to avoid harmful health consequences of the condition.
\n
[1]
\n
b.ii.
\n
",
+ "Markscheme": "
\n
a unit of DNA wound/coiled around 8 histone proteins / octamer;
\n
a.i.
\n
\n
\n- hydrogen bonding between nucleotides / bases;
\n- complementary base pairs;
\n- adenine-thymine and cytosine-guanine form base pairs (between the two strands with H-bonding);
\n- 2 bonds between A and T, while 3 bonds between C and G;
\n
\n
OWTTE
\n
Full names required for c and d though use ecf.
\n
a.ii.
\n
\n
\n- tandem repeats (at one locus) vary in number of times sequence repeats / represent different alleles for one locus;
\n- DNA sample cut by restriction enzymes into fragments;
\n- samples of DNA are amplified at specific genetic sites with PCR;
\n- the fragments are separated by their size/number of repeats with gel electrophoresis;
\n- fluorescent/radioactive label attached to different tandem repeats;
\n- data from several loci at one time uniquely identify individuals / like a fingerprint, combinations of alleles are specific to an individual;
\n- \ncomparisons/similarities between fragment patterns to determine paternity/evidence match to a suspect’s profile / other example of comparison/similarity;
\n
\n
OWTTE
\n
a.iii.
\n
\n
\n- insulin is necessary to control/regulate blood glucose concentrations
OR
insulin is necessary for the cells to take up glucose (for energy); \n- insufficient insulin is made by the pancreas
OR
autoimmune response/antibodies destroy the (β) cells of the pancreas that make insulin; \n- reduced uptake of glucose from the blood / glucose accumulates in the blood / elevated blood glucose levels;
\n
\n
“sugar” is NOT accepted in place of glucose. However, this should only be penalized once; i.e., utiltize ECF.
\n
b.i.
\n
\n
\n- inject insulin / monitoring blood glucose / devices that release insulin;
\n- decrease consumption of sugars/CHO / diet modification;
\n- increase exercise;
\n- keep weight in healthy range;
\n
\n
b.ii.
\n
",
+ "Examiners report": "
\n
The structure of a nucleosome was correctly described for many, but some did not mention the number of histones.
\n
a.i.
\n
\n
There was a noticeable number of blank answers with respect to this question about using tandem repeats as the foundation of DNA profiling. Others had a good idea about PCR and gel electrophoresis, but many didn't mention restriction enzymes and did not clearly understand that patterns are compared.
\n
a.iii.
\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
b.i.
\n
",
+ "topics": [
+ "a-unity-and-diversity",
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "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",
+ "a1-2-nucleic-acids",
+ "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",
+ "d3-3-homeostasis"
+ ]
+ },
+ {
+ "question_id": "22M.2.SL.TZ1.1",
+ "Question": "
\n
Three-toed sloths (Bradypus variegatus) are placental mammals that live in trees in Central and South America. They eat leaves and fruit and get almost all their water from succulent plants.
\n

\n
[Source: Adapted from Laube, S., 2003. Three-toed-sloth (Bradypus variegatus), Lake Gatun, Republic of Panama. [image online] Available at: https://meta.wikimedia.org/wiki/User:Bradipus#/media/File:Bradypus.jpg]
\n
\n
Three-toed sloths change their body posture in response to the temperature of their environment (ambient temperature). Researchers assessed posture on a scale from 1 to 6, with 1 being when the sloth was curled into a tight ball and 6 when it had all limbs spread. The percentage of time the sloths were observed in each position was recorded at ambient temperatures from 22 °C to 34 °C. The researchers also measured the body temperature of the sloths over the same range of ambient temperatures.
\n

\n
[Source: Adapted from Cliffe, R.N., Scantlebury, D.M., Kennedy, S.J., Avey-Arroyo, J., Mindich, D. and Wilson, R.P., 2018. The metabolic response of the Bradypus sloth to temperature. PeerJ, [e-journal] 6: e5600. http://dx.doi.org/10.7717/peerj.5600. Licensed under a Creative Commons Attribution 4.0 International License https://creativecommons.org/licenses/by/4.0/.]
\n
\n
The daily food intake of three-toed sloths and daily ambient temperatures were monitored over a 160-day period from February to early July. The graphs show the mean results.
\n

\n
[Source: Cliffe et al. (2015), Sloths like it hot: ambient temperature modulates food intake in the brown-throated sloth (Bradypus variegatus). PeerJ 3:e875; DOI 10.7717/peerj.875 Licensed under a Creative Commons Attribution 4.0 International License https://creativecommons.org/licenses/by/4.0/.]
\n
\n
State the relationship between sloth body temperature and ambient temperature.
\n
[1]
\n
a.i.
\n
\n
Explain how this relationship differs from that in humans.
\n
[1]
\n
a.ii.
\n
\n
Describe the trend in body posture as ambient temperature rises from 22 to 34 °C.
\n
[1]
\n
b.i.
\n
\n
Suggest reasons for this trend.
\n
[2]
\n
b.ii.
\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
[1]
\n
f.
\n
\n
Outline the relationship between ambient daily temperature and food intake in March.
\n
[2]
\n
g.
\n
\n
Suggest, with a reason, how the activity of the sloth varies with ambient temperature.
\n
[1]
\n
h.
\n
\n
State one feature of the sloth that would indicate it is a mammal.
\n
[1]
\n
i.
\n
",
+ "Markscheme": "
\n
body temperature increases with ambient temperature / positive correlation;
\n
Since direct can be either –/+, no credit for direct correlation alone.
\n
a.i.
\n
\n
humans maintain/regulate a constant body temperature at different ambient temperatures/maintained by homeostasis;
\n
a.ii.
\n
\n
As ambient temperature increases, the sloth spends more time with limbs spread
OR
as ambient temperature increases the sloth spends less time curled in a ball
OR
as ambient temperature rises, the posture changes from 1 to 6;
\n
b.i.
\n
\n
\n- less surface area is exposed when curled up
OR
more surface area is exposed when all limbs spread; \n- curled position prevents heat loss/provides warmth
OR
stretched out position allows more heat loss/body cooled; \n
\n
b.ii.
\n
\n
\n- food intake rises as daily temperature increases / positive correlation;
\n- the lowest food intake corresponds to the lowest temperature;
\n
\n
g.
\n
\n
\n- the sloth will be more active at higher temperatures as it takes in more food for energy;
\n- as temperature rises, the sloth uncurls to dissipate/lose heat;
\n
\n
Reason required.
\n
h.
\n
\n
\n- mammals have mammary glands;
\n- produce milk for their offspring;
\n- bodies covered in hair/fur;
\n
\n
Characteristic must be exclusive to mammals.
\n
If more than one answer, use the first one given.
\n
i.
\n
",
+ "Examiners report": "
\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
a.ii.
\n
\n
There were a few beautiful responses where surface area was specifically incorporated into the answer achieving maximum marks.
\n
b.ii.
\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
h.
\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
i.
\n
",
+ "topics": [
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "d3-3-1-homeostasis-as-maintenance-of-the-internal-environment-of-an-organism",
+ "d3-3-2-negative-feedback-loops-in-homeostasis",
+ "d3-3-homeostasis"
+ ]
+ },
+ {
+ "question_id": "22M.2.SL.TZ1.2",
+ "Question": "
\n
The diagrams represent the structure of a protein before and after it has become denatured.
\n

\n
[Source: Dean Williams, L., 2019. Molecular Interactions. [online] Available at: https://ww2.chemistry.gatech.edu/~lw26/
structure/molecular_interactions/mol_int.html [Accessed 20 August 2019].]
\n
\n
State how many different types of amino acid there are, which can become part of a polypeptide when mRNA is translated.
\n
[1]
\n
a.
\n
\n
Outline one cause of denaturation in proteins.
\n
[1]
\n
b.
\n
\n
Explain how denaturation affects the activity of an enzyme.
\n
[2]
\n
c.
\n
",
+ "Markscheme": "
\n
\n- increase in temperature/heat;
\n- change of pH;
\n- salt;
\n- heavy metals;
\n
\n
b.
\n
\n
\n- changes the shape of the (active site) of the enzyme;
\n- substrate would be unable to attach to the enzyme/active site;
\n- slows the enzyme activity / prevents reaction/catalysis from proceeding;
\n
\n
c.
\n
",
+ "Examiners report": "
\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
a.
\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
b.
\n
",
+ "topics": [
+ "b-form-and-function"
+ ],
+ "subtopics": [
+ "b1-2-4-infinite-variety-of-possible-peptide-chains",
+ "b1-2-5-effect-of-ph-and-temperature-on-protein-structure",
+ "b1-2-proteins"
+ ]
+ },
+ {
+ "question_id": "22M.2.SL.TZ1.3",
+ "Question": "
\n
The graph shows the mean annual changes in global temperatures between 1880 and 2014. The mean temperature from 1951 to 1980 was used as the value of zero change in temperature.
\n

\n
[Source: National Aeronautics and Space Administration, n.d. GISS Surface Temperature Analysis (v3). [online]
Available at: https://data.giss.nasa.gov/gistemp/graphs_v3/ [Accessed 20 August 2019].]
\n
\n
Calculate the increase in mean global temperature between 1880 and 2010.
\n
.......... °C
\n
\n
\n
[1]
\n
a.
\n
\n
Outline how changes in temperature over short time periods could give a misleading impression of changes to the Earth’s climate.
\n
[1]
\n
b.
\n
\n
Explain how increased carbon dioxide in the air leads to the greenhouse effect.
\n
[3]
\n
c.
\n
",
+ "Markscheme": "
\n
0.87; (accept values between 0.8 and 0.9)
\n
a.
\n
\n
short-term reading could show global temperatures falling while the trend is rising
OR
fluctuations from year to year may not show long-term trend;
\n
b.
\n
\n
\n- short wave radiation from sun passes through atmosphere / is not absorbed by CO2;
\n- infrared/long wave (radiation) / heat emitted from/released from (surface of) Earth;
\n- CO2 in the atmosphere absorbs infrared/long wave (radiation)/heat / cannot pass through the greenhouse gases;
\n- this results in warm/increased temperatures on Earth/global warming;
\n
\n
Do not accept “reflected” for mpb.
\n
c.
\n
",
+ "Examiners report": "
\n
Many candidates got the calculations right.
\n
a.
\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
b.
\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
c.
\n
",
+ "topics": [
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "d4-3-1-anthropogenic-causes-of-climate-change",
+ "d4-3-2-positive-feedback-cycles-in-global-warming",
+ "d4-3-climate-change"
+ ]
+ },
+ {
+ "question_id": "22M.2.SL.TZ1.4",
+ "Question": "
\n
The pedigree chart shows the incidence of hemophilia in some of the descendants of Queen Victoria.
\n

\n
\n
State the probability that Edward had hemophilia.
\n
[1]
\n
a.
\n
\n
Explain the reasons for none of the females in the pedigree chart having hemophilia.
\n
[3]
\n
b.
\n
",
+ "Markscheme": "
\n
\n- hemophilia is X-linked/sex-linked/carried on the X chromosome;
\n- females have two X chromosomes
OR
males only have one X chromosome; \n- hemophilia is caused by a recessive allele;
\n- (trait) must be on both alleles to be expressed
OR
females would require the allele on both X chromosomes to have the disease
OR
females can be carriers when allele is only on one chromosome; \n
\n
b.
\n
",
+ "Examiners report": "
\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
a.
\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
b.
\n
",
+ "topics": [
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "d1-2-6-roles-of-mrna-ribosomes-and-trna-in-translation",
+ "d1-2-protein-synthesis",
+ "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",
+ "d3-2-inheritance"
+ ]
+ },
+ {
+ "question_id": "22M.2.SL.TZ1.5",
+ "Question": "
\n
The graph shows the change in the membrane potential of an axon during an action potential.
\n

\n
\n
State the approximate value of the membrane potential at X.
\n
[1]
\n
a.
\n
\n
Y is the threshold potential. State what happens when the threshold potential is reached.
\n
[1]
\n
b.
\n
\n
Describe the movements in ions that occur during time t.
\n
[2]
\n
c.
\n
\n
Explain how a nerve impulse is passed on to other neurons.
\n
[3]
\n
d.
\n
",
+ "Markscheme": "
\n
0 mV; (accept answers in the range of – 10 mV to +10 mV) (Units required)
\n
a.
\n
\n
sodium channels (start to) open
OR
depolarization/axon begins to depolarize
OR
action potential occurs;
\n
Reject pumping of ions.
\n
b.
\n
\n
Na+/sodium ions diffuse into the axon (in the first part/half of t);
K+ /potassium ions diffuse out of the axon (in the second half/part of t)
\n
Do not accept the name of the element without indication that it is an ion.
\n
c.
\n
\n
\n- impulses pass to another neuron at a synapse/across synaptic gap/cleft;
\n- (depolarization causes) Ca2+/calcium ions to diffuse into the (presynaptic) neuron/axon;
\n- depolarization (of presynaptic neuron) causes release of a neurotransmitter
OR
neurotransmitters diffuse across the synapse; \n- (neurotransmitters) bind to receptors on postsynaptic neuron/membrane;
\n- (if the threshold potential is reached) an action potential occurs/sodium gates open (in the postsynaptic neuron);
\n
\n
d.
\n
",
+ "Examiners report": "
\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
Candidates were often unable to approximate X. Missing units resulted in no marks awarded.
\n
a.
\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
b.
\n
\n
Some candidates talked about ion movement but with no reference to a specific ion; some described the Na+/K+ pump here and received no marks.
\n
c.
\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
d.
\n
",
+ "topics": [
+ "c-interaction-and-interdependence"
+ ],
+ "subtopics": [
+ "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",
+ "c2-2-6-release-of-neurotransmitters-from-a-presynaptic-membrane",
+ "c2-2-8-depolarization-and-repolarization-during-action-potentials",
+ "c2-2-neural-signalling"
+ ]
+ },
+ {
+ "question_id": "22M.2.SL.TZ1.6",
+ "Question": "
\n
Outline reasons for the therapeutic use of stem cells.
\n
[3]
\n
a.
\n
\n
Describe how leaf cells make use of light energy.
\n
[5]
\n
b.
\n
\n
Explain how cells and cell components in the blood defend the body against infectious disease.
\n
[7]
\n
c.
\n
",
+ "Markscheme": "
\n
\n- unspecialized/undifferentiated stem cells can divide / differentiate along different pathways;
\n- (stem cells are accessible as they) come from embryos/bone marrow/umbilical cord blood/adult tissue;
\n- (stem cells) can regenerate/repair diseased/damaged tissues in people;
\n- valid specific example;
\n- drugs can be tested on stem cells (in laboratories to see if they are harmful);
\n
\n
a.
\n
\n
\n- leaf cells contain chloroplasts;
\n- light is absorbed by chlorophyll (in chloroplasts);
\n- other pigments absorb different wavelengths;
\n- light energy is used in photosynthesis;
\n- (light is needed) to combine water and carbon dioxide/fix carbon dioxide;
\n- carbon compounds/organic compounds/glucose/starch/carbohydrate are produced;
\n- blue and red light is absorbed;
\n- perform photolysis
OR
split water molecules; \n
\n
Wavelengths accepted for mpg.
\n
b.
\n
\n
Platelets: [3 max]
\n
\n- damage/cuts to blood vessels causes platelets to be activated;
\n- the platelets release clotting factors;
\n- initiates cascade of reactions
OR
fibrinogen is converted to fibrin; \n- forms a mesh over the damaged area;
\n- prevents pathogens from entering the body;
Phagocytes: [3 max]
\n \n- phagocytes/phagocytic white blood cells in the blood travel to the site of infection;
\n- (phagocytes) squeeze between the capillary cells;
\n- (phagocytes) engulf/ingest/take in pathogens;
\n- the pathogen is digested/broken down by/within the phagocyte;
Lymphocytes: [3 max]\n \n- lymphocytes recognize a particular fragment/antigen of a pathogen;
\n- (lymphocytes) release antibodies;
\n- (antibodies) provide specific immunity;
\n- memory cells provide rapid response giving long-term immunity (to pathogens previously recognized);
\n- antibodies destroy pathogens;
\n
\n
ECF may be applied when candidates use white blood cells in place of specific terms.
\n
c.
\n
",
+ "Examiners report": "
\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
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
a.
\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
b.
\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
Correct terminology was confused or was not employed in too many answers.
\n
c.
\n
",
+ "topics": [
+ "a-unity-and-diversity",
+ "c-interaction-and-interdependence"
+ ],
+ "subtopics": [
+ "a1-1-6-physical-properties-of-water-and-the-consequences-for-animals-in-aquatic-habitats",
+ "a1-1-water",
+ "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",
+ "c1-3-photosynthesis",
+ "c3-2-10-immunity-as-a-consequence-of-retaining-memory-cells",
+ "c3-2-defence-against-disease"
+ ]
+ },
+ {
+ "question_id": "22M.2.SL.TZ1.7",
+ "Question": "
\n
Draw a labelled diagram to show the structure of a single nucleotide of RNA.
\n
[3]
\n
a.
\n
\n
Distinguish between the processes of meiosis and mitosis.
\n
[5]
\n
b.
\n
\n
Explain the development of antibiotic resistance in terms of natural selection.
\n
[7]
\n
c.
\n
",
+ "Markscheme": "
\n
\n- ribose drawn as a pentagon and labelled;
\n- base linked correctly (to C1) of ribose and labelled;
\n- phosphate linked correctly (to C5) of ribose and labelled;
\n
\n

\n
Award [2 max] if more than one nucleotide drawn.
\n
“Sugar” alone is insufficient.
\n
a.
\n
\n

\n
b.
\n
\n
\n- antibiotics can (generally) kill/destroy bacteria;
\n- some bacteria show variation/antibiotic resistance;
\n- variation/resistance is due to a random mutation;
\n- resistant bacteria are not killed/destroyed by the antibiotic
OR
bacteria without the mutation die; \n- (resistant) bacteria have a selective advantage / unequal success;
\n- the bacteria with this variation/resistance reproduces/multiplies;
\n- mutation/gene is passed on to the offspring / the offspring will be resistant to the antibiotic;
\n- resistant bacteria become more common;
\n- bacteria have evolved to be resistant to the antibiotic;
\n
\n
Award [6 max] if pathogen is used instead of bacteria throughout the answer with no mention of bacteria.
\n
c.
\n
",
+ "Examiners report": "
\n
Occasionally, deoxyribose was seen rather ribose; sometimes more than one nucleotide was shown limiting maximum marks.
\n
a.
\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
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
b.
\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
c.
\n
",
+ "topics": [
+ "a-unity-and-diversity",
+ "c-interaction-and-interdependence",
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "a1-2-5-rna-as-a-polymer-formed-by-condensation-of-nucleotide-monomers",
+ "a1-2-nucleic-acids",
+ "c3-2-14-evolution-of-resistance-to-several-antibiotics-in-strains-of-pathogenic-bacteria",
+ "c3-2-defence-against-disease",
+ "d2-1-4-roles-of-mitosis-and-meiosis-in-eukaryotes",
+ "d2-1-cell-and-nuclear-division"
+ ]
+ },
+ {
+ "question_id": "22M.2.SL.TZ1.8",
+ "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
\n
\n (b)\n
\n
\n
\n Describe how DNA profiling can be used to establish paternity.\n
\n
\n
\n
\n
\n
\n (c)\n
\n
\n
\n Explain the reasons for variation in human height.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n
\n
\n
\n - \n \n ribose\n \n drawn as a pentagon and labelled;\n
\n - \n \n base\n \n linked correctly (to C\n \n 1\n \n ) of ribose and labelled;\n
\n - \n \n phosphate\n \n linked correctly (to C\n \n 5\n \n ) of ribose and labelled;\n
\n
\n
\n
\n (b)\n
\n
\n - \n DNA sample is collected from the child and its (potential) parents;\n
\n - \n from saliva/mouth swab/blood/other body cells;\n
\n - \n PCR used to amplify/produce more copies of the DNA;\n
\n - \n short tandem repeats/genes consisting of a repeating sequence of bases repeats copied/used;\n
\n - \n number of repeats varies between individuals;\n
\n - \n unlikely that two individuals have same number of repeats for every gene included;\n
\n - \n gel electrophoresis used to separate DNA fragments according to length/number of repeats;\n
\n - \n gel electrophoresis generates a unique pattern of bands\n
\n - \n DNA profile is the pattern of bands / diagram showing pattern of bands as in a DNA profile;\n
\n - \n all bands in the child’s profile must be in one of the parents’ profiles / OWTTE;\n
\n
\n
\n
\n (c)\n
\n
\n - \n environment affects height;\n
\n - \n nutrition/malnutrition affects growth rate / other example of environmental factor affecting height;\n
\n - \n genes/alleles affect height / height is partly heritable;\n
\n - \n polygenic / many genes influence height;\n
\n - \n continuous variation;\n
\n - \n normal/bell-shaped distribution of height;\n
\n - \n some alleles (of these genes) increase height and some reduce it;\n
\n - \n many possible combinations of alleles of these genes;\n
\n - \n specific gene mutations/alleles cause dwarfism/extreme height;\n
\n - \n meiosis generates variation (in height);\n
\n - \n mutations generate variation (in height);\n
\n - \n males tend to be/are on average taller than females;\n
\n - \n loss of height during aging;\n
\n
\n
\n",
+ "Examiners report": "
\n (a)\n
\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
\n (b)\n
\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
\n (c)\n
\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",
+ "topics": [
+ "a-unity-and-diversity",
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "a1-2-5-rna-as-a-polymer-formed-by-condensation-of-nucleotide-monomers",
+ "a1-2-nucleic-acids",
+ "d1-1-5-applications-of-polymerase-chain-reaction-and-gel-electrophoresis",
+ "d1-1-dna-replication",
+ "d3-2-14-continuous-variation-due-to-polygenic-inheritance-and/or-environmental-factors",
+ "d3-2-inheritance"
+ ]
+ },
+ {
+ "question_id": "22M.2.SL.TZ2.2",
+ "Question": "
\n
An oval-shaped stem cell cluster is shown in the micrograph.
\n

\n
[Source: Sontag, S., Förster, M., Seré, K. and Zenke, M., 2017. [online] Available at: https://bio-protocol.org/e2419 [Accessed
6 December 2019]. Source adapted.]
\n
\n
State the main characteristic of stem cells.
\n
[1]
\n
a.
\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
[1]
\n
b.
\n
\n
State one therapeutic role of stem cells.
\n
[1]
\n
c.
\n
\n
Discuss how the use of stem cells to treat hereditary diseases could affect the person who received the treatment and their progeny.
\n
[2]
\n
d.
\n
",
+ "Markscheme": "
\n
undifferentiated/pluripotent/ability to divide/differentiate into any types of cells/differentiate along different pathways;
\n
a.
\n
\n
\n- correct formula: 1.1cm = 500 μm, 2.7cm = length, ;
\n- correct answer with unit: 1227μm;
\n
\n
Allow answer in range of 1150 μm to 1350 μm.
\n
b.
\n
\n
treatment of Stargardt’s disease/leukemia/diabetes/heart disease/Parkinson’s disease;
\n
Any other verifiable condition.
\n
c.
\n
\n
\n- could improve quality/length of life of the treated person;
\n- disease could still be passed on to progeny if defective gene/allele in gametes is not replaced/changed;
\n
\n
d.
\n
",
+ "Examiners report": "
\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
a.
\n
",
+ "topics": [
+ "a-unity-and-diversity",
+ "b-form-and-function",
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "a2-2-2-microscopy-skills",
+ "a2-2-5-prokaryote-cell-structure",
+ "a2-2-6-eukaryote-cell-structure",
+ "a2-2-cell-structure",
+ "b2-3-2-properties-of-stem-cells",
+ "b2-3-cell-specialization",
+ "d2-1-8-identification-of-phases-of-mitosis",
+ "d2-1-cell-and-nuclear-division"
+ ]
+ },
+ {
+ "question_id": "22M.2.SL.TZ2.3",
+ "Question": "
\n
Methane can be the product of anaerobic respiration in some organisms.
\n
\n
Describe anaerobic respiration in humans and in yeast.
\n
[3]
\n
a.
\n
\n
Distinguish between the thermal properties of water and methane.
\n
[2]
\n
b.i.
\n
\n
Explain the role of methane in climate change.
\n
[2]
\n
b.ii.
\n
",
+ "Markscheme": "
\n
\n- (in both) anaerobic respiration gives a small amount of ATP/2 ATP/energy from glucose;
\n- anaerobic respiration occurs when there is no oxygen;
\n- anaerobic respiration in yeast produces ethanol and carbon dioxide/alcoholic fermentation;
\n- anaerobic respiration in humans (in muscle) produces lactate/lactic acid/lactic acid fermentation;
\n- both undergo glycolysis;
\n
\n
Do not accept mpd if CO2 also included.
\n
a.
\n
\n
\n- water has higher boiling/melting point;
\n- water has a higher specific heat capacity;
\n- water has a higher latent heat of vaporization;
\n- differences due to water having many H-bonds/polarity between the molecules while methane has no H-bonds/polarity;
\n
\n
b.i.
\n
\n
\n- methane is a greenhouse gas
OR
methane causes an increase in temperature of the atmosphere; \n- methane is one of the most powerful greenhouse gases / more powerful than CO2;
\n- methane has a relatively short lifespan compared to CO2/decomposes to CO2;
\n
\n
Other verifiable sources.
\n
b.ii.
\n
",
+ "Examiners report": "
\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 CO2. 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 CO2. A surprising number thought that methane’s main danger was that it destroyed the ozone layer.
\n
a.
\n
",
+ "topics": [
+ "c-interaction-and-interdependence",
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "c1-2-10-anaerobic-cell-respiration-in-yeast-and-its-use-in-brewing-and-baking",
+ "c1-2-5-differences-between-anaerobic-and-aerobic-cell-respiration-in-humans",
+ "c1-2-cell-respiration",
+ "c4-1-15-use-of-the-chi-squared-test-for-association-between-two-species",
+ "c4-1-populations-and-communities",
+ "d4-3-1-anthropogenic-causes-of-climate-change",
+ "d4-3-climate-change"
+ ]
+ },
+ {
+ "question_id": "22M.2.SL.TZ2.5",
+ "Question": "
\n
Enzyme activity is affected by temperature and pH.
\n

\n
\n
Explain the decrease in activity of the enzyme on either side of the optimum temperature.
\n
[2]
\n
a.
\n
\n
In biotechnology, enzymes are used to transfer genes to bacteria. Outline how two specific enzymes are used for the transfer.
\n
[2]
\n
b.
\n
",
+ "Markscheme": "
\n
\n- as temperature rises/is higher (than optimal temperature), the enzyme is denatured;
\n- as the temperature drops the enzyme molecules have less kinetic energy
OR
fewer successful collisions; \n
\n
OWTTE
\n
a.
\n
\n
\n- restriction enzymes/(restriction) endonucleases cut the gene and the bacterial/plasmid/vector DNA in the same/specific restriction sites
OR
(restriction) endonucleases work by targeting a specific sequence of base pairs in DNA causing both strands of the DNA to break apart; \n- (DNA) ligase attaches/inserts the gene to the bacterial/plasmid/vector DNA
OR
(DNA) ligase joins the vector and gene by fusing their sugar-phosphate backbones together (with a covalent phosphodiester bond); \n- correct reference to reverse transcriptase;
\n
\n
Accept correct mention of reverse transcriptase.
\n
b.
\n
",
+ "Examiners report": "
\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
a.
\n
",
+ "topics": [
+ "a-unity-and-diversity",
+ "c-interaction-and-interdependence",
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "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",
+ "a1-2-nucleic-acids",
+ "c1-1-8-effects-of-temperature-ph-and-substrate-concentration-on-the-rate-of-enzyme-activity",
+ "c1-1-enzymes-and-metabolism",
+ "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",
+ "d3-3-homeostasis"
+ ]
+ },
+ {
+ "question_id": "22M.2.SL.TZ2.6",
+ "Question": "
\n
People with the inherited disease hemophilia have a deficiency in one of the proteins that act as clotting factors in blood.
\n
\n
Outline how a protein is made in a cell by the process of translation.
\n
[5]
\n
a.
\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
[3]
\n
b.
\n
\n
Explain how blood clotting occurs and the consequence for a person who has hemophilia.
\n
[7]
\n
c.
\n
",
+ "Markscheme": "
\n
\n- translation occurs on ribosomes when proteins/polypeptides are synthesized;
\n- amino acid sequence of a protein is determined by the mRNA;
\n- mRNA is determined by the order of bases of DNA/order of bases sequence in a gene;
\n- codons (of 3 bases) on mRNA correspond to one amino acid in a polypeptide;
\n- codons are on mRNA and anticodons on tRNA;
\n- mRNA binds to ribosome/(during initiation) small ribosomal subunit binds to the start of the mRNA sequence;
\n- tRNA transfers an amino acid to large ribosomal subunit/to the ribosome;
\n- reference to start or stop codon;
\n- tRNA moves to the next mRNA codon to continue the process, creating an amino acid chain;
\n- peptide bond formed between amino acids
\n- translation/order of amino acids depends on complementary base pairing between codons and anticodons;
\n
\n
a.
\n
\n
\n- alleles clearly labelled for both parents (in a Punnett square or other format);
\n- correct genotypes for all four possibilities for children;
\n \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
\n
Sex needs to be mentioned for mpc but info can be taken from the Punnett square.
\n
b.
\n
\n
Clotting process:
\n
\n- blood clotting seals cuts in the skin;
\n- clotting factors are released (from platelets);
\n- thrombin is activated;
\n- a cascade reaction occurs (with thrombin);
\n- (thrombin causes) fibrinogen is converted to fibrin;
\n- fibrin forms a clot/blocks the cut/prevents blood from being lost;
Consequences of hemophilia: \n- if a person does not have enough clotting factors/hemophilia, the clot will not form;
\n- pathogens can enter the body more easily;
\n- (in hemophiliacs) blood will be lost from a cut which affects blood pressure/bleeding to death;
\n- loss of blood affects amount of hemoglobin/O2 carried around the body;
\n- reference to lifestyle / menstrual/birth problems
\n
\n
e.g. surgery, contact sports
\n
c.
\n
",
+ "Examiners report": "
\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
a.
\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
b.
\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
c.
\n
",
+ "topics": [
+ "b-form-and-function",
+ "c-interaction-and-interdependence",
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "b3-2-18-adaptations-of-phloem-sieve-tubes-and-companion-cells-for-translocation-of-sap",
+ "b3-2-transport",
+ "c3-2-3-sealing-of-cuts-in-skin-by-blood-clotting",
+ "c3-2-defence-against-disease",
+ "d1-2-5-translation-as-the-synthesis-of-polypeptides-from-mrna",
+ "d1-2-protein-synthesis",
+ "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",
+ "d3-2-inheritance"
+ ]
+ },
+ {
+ "question_id": "22M.2.SL.TZ2.7",
+ "Question": "
\n
The growing human population has an increasing demand for energy derived from crop plants. At the same time, increasing droughts that are part of climate change make it difficult to grow crops in some parts of the world.
\n
\n
Outline energy flow through a community in a natural ecosystem.
\n
[5]
\n
a.
\n
\n
Explain how natural selection can cause traits such as drought resistance to develop in wild plants.
\n
[7]
\n
b.
\n
\n
Suggest possible benefits and risks of using genetic modification to develop varieties of crop plant with traits such as drought resistance.
\n
[3]
\n
c.
\n
",
+ "Markscheme": "
\n
\n- communities are made up of populations of different species;
\n- plants receive energy from the sun/light;
\n- convert it to chemical energy through photosynthesis;
\n- chemical energy is stored in organic/C-compounds;
\n- the energy is passed to other organisms through feeding / reference to food chain;
\n- respiration (of plants and animals) converts the chemical energy (of C-compounds) to other useful forms of energy;
\n- eventually the chemical energy is lost as heat energy;
\n- energy is non-recyclable/lost from a community/ecosystem;
\n- energy losses between trophic levels limit food chains/mass of top trophic levels/only about 10 % of energy is transferred;
\n
\n
a.
\n
\n
\n- (natural selection occurs if) there is variation in degree of drought resistance among members of a population/same species;
\n- variation is caused by mutations (when changes occur in the DNA/nucleic bases/chromosomes);
\n- variation during meiosis occurs (with separation of chromosomes);
\n- variation occurs during sexual reproduction (as different alleles combine);
\n- some variations make some plants more drought-resistant;
\n- example of variations: deeper roots/more storage tissue for water/thicker cuticles/less opening of stomata/other verifiable variations;
\n- these variations let some survive and reproduce better/have more offspring
OR
(these variations) confer selective advantage; \n- these variations/characteristics are passed onto offspring which survive better;
\n- natural selection increases the frequency of these characteristics;
\n- eventually leads to changes/evolution in the species / more drought-resistant plants;
\n
\n
b.
\n
\n
Benefits:
\n
\n- increase crop growth/food productivity;
\n- with limited water/ less water is used;
\n- increase amount of land available for food production in dry areas;
Risks: \n- these plants may out-compete other species in the community/may cause extinction of some species/affect the food chains in the community;
\n- the modified gene/recombinant DNA may pass to other organisms;
\n- more grain requires more nutrients from the soil so its quality may diminish/monoculture issues;
\n- GMO may have health effects in consumers / OWTTE;
\n
\n
Must include at least one benefit and one risk for [3 max].
\n
c.
\n
",
+ "Examiners report": "
\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
a.
\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
b.
\n
\n
Again, drought resistance was in the stem, but not always used. There were many general ‘rants’ about GMO crops without setting out the facts.
\n
c.
\n
",
+ "topics": [
+ "a-unity-and-diversity",
+ "c-interaction-and-interdependence",
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "a4-1-7-roles-of-reproductive-isolation-and-differential-selection-in-speciation",
+ "a4-1-evolution-and-speciation",
+ "c4-2-12-reductions-in-energy-availability-at-each-successive-stage-in-food-chains-due-to-large-energy-losses-between-trophic-levels",
+ "c4-2-3-flow-of-chemical-energy-through-food-chains",
+ "c4-2-transfers-of-energy-and-matter",
+ "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",
+ "d4-1-natural-selection"
+ ]
+ },
+ {
+ "question_id": "22M.2.SL.TZ2.8",
+ "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
\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
\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",
+ "Markscheme": "
\n (a)\n
\n
\n - \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
\n - \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
\n - \n facilitated diffusion is passive transport/diffusion through a protein channel; (\n \n e.g., glucose\n \n )\n
\n - \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
\n - \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
\n - \n exocytosis is the fusion of vesicles with membranes to release a large molecule; (\n \n e.g. neurotransmitters\n \n )\n
\n
\n
\n
\n (b)\n
\n
\n - \n humans are osmoregulators/maintain the internal concentrations of the blood/osmolarity within specific/ limited range / OWTTE;\n
\n - \n glomerulus / Bowman’s capsule (in the nephron) carry out ultrafiltration;\n
\n - \n proximal convoluted tubule selectively reabsorbs glucose/solute/salts/amino acids;\n
\n - \n loop of Henle maintains hypertonic conditions in the medulla/absorbs salts (by active transport);\n
\n - \n loop of Henle reabsorbs water (by osmosis);\n
\n - \n (osmoreceptors in the hypothalamus) cause production of ADH if the blood is too concentrated / person is dehydrated / OWTTE;\n
\n - \n ADH causes more uptake of water/increases permeability in the collecting duct;\n
\n - \n resulting in a more concentrated urine / lower volume of urine;\n
\n - \n excess amino acids are broken down producing nitrogenous waste / ammonia / urea as a result;\n
\n - \n ammonia is toxic and is converted into non-toxic urea;\n
\n - \n urea is eliminated in the urine;\n
\n
\n
\n \n Marks can be awarded to clearly annotated diagrams\n \n .\n
\n
\n
\n (c)\n
\n
\n - \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
\n - \n adaptations for heat exchange such as large ears;\n
\n - \n may have longer loop of Henle (to reabsorb more water);\n
\n - \n may produce more ADH (according to osmotic concentrations of the blood) / produce concentrated urine / lower volume of urine;\n
\n - \n camel humps that store fat that releases (metabolic) water when broken down;\n
\n - \n reduced sweat;\n
\n - \n any other valid adaptation; (e.g., light coloured coats)\n
\n
\n
\n",
+ "Examiners report": "
\n (a)\n
\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
\n (b)\n
\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
\n (c)\n
\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",
+ "topics": [
+ "b-form-and-function",
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "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",
+ "b2-1-membranes-and-membrane-transport",
+ "b4-1-8-adaptations-to-life-in-hot-deserts-and-tropical-rainforest",
+ "b4-1-adaptation-to-environment",
+ "d3-3-7-role-of-the-kidney-in-osmoregulation-and-excretion",
+ "d3-3-homeostasis"
+ ]
+ },
+ {
+ "question_id": "22N.2.HL.TZ0.1",
+ "Question": "
\n
\n (a)\n
\n
\n
\n State the relationship between BCH and brain mass of shrews.\n
\n
\n
\n
\n
\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
\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
\n
\n (d)\n
\n
\n
\n State the season when shrew brain mass is greatest.\n
\n
\n
\n
\n
\n
\n (e)\n
\n
\n
\n Compare and contrast the results for winter and spring.\n
\n
\n
\n
\n
\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
\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
\n
\n (i)\n
\n
\n
\n Calculate the percentage of containers that contained food.\n
\n
\n
\n
\n
\n
\n (j)\n
\n
\n
\n Outline a reason that the path length was standardized.\n
\n
\n
\n
\n
\n
\n (k)\n
\n
\n
\n Compare and contrast the results for trials 2 and 9.\n
\n
\n
\n
\n
\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",
+ "Markscheme": "
\n (a)\n
\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
\n (a)\n
\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
\n (b)\n
\n
\n - \n high BCH but brain mass is low/lower than expected/lower than others with similar BCH;\n
\n - \n (fairly) low brain mass but BCH is high/higher than expected/higher than others with similar brain mass;\n
\n
\n
\n
\n (c)\n
\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
\n (d)\n
\n
\n (e)\n
\n
\n \n Compare part of answer = similarity\n \n :\n
\n
\n - \n both have low BCH (compared with summer);\n
\n
\n \n Contrast part of answer\n \n :\n
\n
\n \n - \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 \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
\n (g)\n
\n
\n \n rest\n \n ing in\n \n spring\n \n ;\n
\n
\n
\n (h)\n
\n
\n - \n more food/energy eaten/required in winter/cold;\n
\n - \n food needed to maintain temperature/stay warm/generate heat;\n
\n - \n more loss of body heat in cold conditions;\n
\n - \n more energy used hunting for food;\n
\n - \n food less available in winter/harder to find enough food;\n
\n
\n
\n
\n (i)\n
\n
\n (j)\n
\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
\n (k)\n
\n
\n \n Similarity between 2 and 9\n \n :\n
\n
\n - \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 \n - \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 \n
\n
\n
\n (l)\n
\n
\n - \n in winter shrews have smaller brains/smaller BCH / converse for summer;\n
\n - \n lower/poorer memory/thinking/cognitive skills/learning/intelligence/senses/sense of smell/ability to find food in winter/converse for summer;\n
\n
\n
\n",
+ "Examiners report": "
\n (a)\n
\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
\n (a)\n
\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
\n (b)\n
\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
\n (c)\n
\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
\n (d)\n
\n
\n 90\n \n % of candidates correctly identified summer as the season when brain mass was greatest.\n
\n
\n
\n (e)\n
\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
\n (g)\n
\n
\n 80\n \n % of candidates identified the season and activity correctly.\n
\n
\n
\n (h)\n
\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
\n (i)\n
\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
\n (j)\n
\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
\n (k)\n
\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
\n (l)\n
\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",
+ "topics": [
+ "c-interaction-and-interdependence"
+ ],
+ "subtopics": [
+ "c3-1-4-the-brain-as-a-central-information-integration-organ",
+ "c3-1-integration-of-body-systems"
+ ]
+ },
+ {
+ "question_id": "22N.2.HL.TZ0.4",
+ "Question": "
\n
\n (a)\n
\n
\n
\n Identify the protein labelled in the diagram.\n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n
\n Outline how nucleosomes affect the transcription of DNA.\n
\n
\n
\n
\n
\n
\n (c.i)\n
\n
\n
\n Identify X, the enzyme which copies a DNA sequence.\n
\n
\n
\n
\n
\n
\n (c.ii)\n
\n
\n
\n Identify Y, non-coding DNA at the start of a gene.\n
\n
\n
\n
\n
\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
\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",
+ "Markscheme": "
\n (a)\n
\n
\n (b)\n
\n
\n - \n (nucleosomes can) promote AND inhibit transcription of genes/expression of genes;\n
\n - \n (nucleosomes can) prevent transcription by (tight) condensation/supercoiling/packing of DNA;\n
\n - \n (nucleosomes can) allow/prevent binding of RNA polymerase/transcription factors;\n
\n - \n tagging/acetylation/methylation of nucleosomes/histones can promote/inhibit transcription;\n
\n - \n movement of histones/nucleosomes (along DNA) can affect which genes are transcribed;\n
\n
\n
\n \n ‘Affects transcription’ is in the question — no mark.\n \n
\n
\n
\n (c.i)\n
\n
\n \n RNA polymerase\n \n ;\n
\n
\n
\n (c.ii)\n
\n
\n (d)\n
\n
\n - \n lactose binds to\n \n repressor\n \n protein;\n
\n - \n repressor protein (with lactose bound) cannot block/bind to the\n \n promoter\n \n /\n \n Y\n \n ;\n
\n - \n \n RNA polymerase\n \n /\n \n X\n \n binds to the promoter/transcribes the gene;\n
\n - \n \n lactase\n \n produced (if lactose present)/\n \n lactase\n \n production inhibited if lactose absent;\n
\n
\n
\n \n Accept the converse of mpa to mpd with lactose absent.\n \n
\n
\n
\n (e)\n
\n
\n (different) environment/illness/disease/diet;\n
\n
\n \n Not mutation\n \n
\n
\n",
+ "Examiners report": "
\n (a)\n
\n
\n Nearly all candidates know that the proteins in nucleosomes are histones.\n
\n
\n
\n (b)\n
\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
\n (c.i)\n
\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
\n (c.ii)\n
\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
\n (d)\n
\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
\n (e)\n
\n
\n Most candidates knew that differences in environmental factors can cause differences in methylation pattern.\n
\n
\n",
+ "topics": [
+ "a-unity-and-diversity",
+ "c-interaction-and-interdependence",
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "a1-2-13-structure-of-a-nucleosome",
+ "a1-2-nucleic-acids",
+ "c1-1-14-allosteric-sites-and-non-competitive-inhibition",
+ "c1-1-enzymes-and-metabolism",
+ "d1-1-3-role-of-helicase-and-dna-polymerase-in-dna-replication",
+ "d1-1-dna-replication",
+ "d1-2-14-non-coding-sequences-in-dna-do-not-code-for-polypeptides",
+ "d1-2-protein-synthesis",
+ "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",
+ "d2-2-gene-expression-[hl-only]"
+ ]
+ },
+ {
+ "question_id": "22N.2.HL.TZ0.5",
+ "Question": "
\n
\n (a.i)\n
\n
\n
\n Identify structure X.\n
\n
\n
\n
\n
\n
\n (a.ii)\n
\n
\n
\n Identify structure Y.\n
\n
\n
\n
\n
\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
\n
\n (c)\n
\n
\n
\n Explain the role of the hormone ADH in osmoregulation.\n
\n
\n
\n
\n
\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",
+ "Markscheme": "
\n (a.i)\n
\n
\n \n proximal\n \n convoluted tubule/PCT;\n
\n
\n
\n (a.i)\n
\n
\n \n proximal\n \n convoluted tubule/PCT;\n
\n
\n
\n (a.ii)\n
\n
\n glomerulus/Bowman’s capsule;\n
\n
\n
\n (b)\n
\n
\n (c)\n
\n
\n - \n ADH secreted if blood is hypertonic/solute concentration too high/water content too low/dehydrated;\n
\n - \n aquaporins open/more aquaporins in (plasma membranes of cells in DCT/collecting duct) with ADH;\n
\n - \n DCT/collecting duct becomes more permeable to water/reabsorbs more water (from filtrate);\n
\n
\n
\n
\n (d)\n
\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 (a.i)\n
\n
\n 60null% of candidates identified the proximal convoluted tubule.\n
\n
\n
\n (a.i)\n
\n
\n 60null% of candidates identified the proximal convoluted tubule.\n
\n
\n
\n (a.ii)\n
\n
\n 80% of candidates identified the structure as the glomerulus or Bowman's capsule.\n
\n
\n
\n (b)\n
\n
\n 70\n \n % of candidates knew that the loop of Henle is in the medulla.\n
\n
\n
\n (c)\n
\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
\n (d)\n
\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",
+ "topics": [
+ "b-form-and-function",
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "b2-3-7-adaptations-to-increase-surface-area-to-volume-ratios-of-cells",
+ "b2-3-cell-specialization",
+ "d3-3-10-osmoregulation-by-water-reabsorption-in-the-collecting-ducts",
+ "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-homeostasis"
+ ]
+ },
+ {
+ "question_id": "22N.2.HL.TZ0.6",
+ "Question": "
\n
\n (a)\n
\n
\n
\n Outline the processes occurring during interphase in the cell cycle.\n
\n
\n
\n
\n
\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
\n
\n (c)\n
\n
\n
\n Explain how cells in the bloodstream cause a specific immune response.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n - \n growth/increase in cell size;\n
\n - \n division of mitochondria/chloroplasts/production of more organelles/number of organelles doubled;\n
\n - \n replication of DNA/amount of DNA is doubled;\n
\n - \n transcription of genes/production of mRNA;\n
\n - \n protein synthesis;\n
\n - \n cell respiration/production of ATP;\n
\n
\n
\n \n Allow organelles ‘replicated’ for mpb.\n \n
\n
\n
\n (a)\n
\n
\n - \n growth/increase in cell size;\n
\n - \n division of mitochondria/chloroplasts/production of more organelles/number of organelles doubled;\n
\n - \n replication of DNA/amount of DNA is doubled;\n
\n - \n transcription of genes/production of mRNA;\n
\n - \n protein synthesis;\n
\n - \n cell respiration/production of ATP;\n
\n
\n
\n \n Allow organelles ‘replicated’ for mpb.\n \n
\n
\n
\n (b)\n
\n
\n - \n sodium\n \n ions\n \n /\n \n Na\n \n +\n \n \n enter/diffuse in;\n
\n - \n depolarization/membrane potential/voltage changes from negative to positive;\n
\n - \n potassium channels open AND potassium ions/K+ exit/diffuse out;\n
\n - \n repolarization/membrane potential/voltage changes back from positive to negative;\n
\n - \n local current due to diffusion of sodium ions along the neuron;\n
\n - \n (local currents) cause next sodium channels to open/next part of axon to depolarize;\n
\n - \n opening of sodium channels triggered when threshold potential/-50mV reached;\n
\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
\n (c)\n
\n
\n - \n (specific immune response is) production of antibodies in response to a particular pathogen;\n
\n - \n antibody is specific to/binds to a specific\n \n antigen\n \n ;\n
\n - \n macrophages/phagocytes engulf/present antigens from pathogens/viruses/bacteria;\n
\n - \n T lymphocytes activated by antigens/antigen presentation/antigens presented by macrophage;\n
\n - \n (activated) T lymphocytes activate B lymphocytes;\n
\n - \n only B lymphocytes that produce antibodies against the antigen/pathogen are activated;\n
\n - \n (activated) B lymphocytes clone/divide by mitosis to form\n \n plasma cells\n \n ;\n
\n - \n plasma cells then secrete (large quantity) of an antibody/secrete antibodies of same type;\n
\n - \n some B lymphocytes/plasma cells form memory cells;\n
\n - \n memory cells give long-lasting immunity/faster response to a disease/pathogen;\n
\n
\n
\n \n Accept B and T cells instead of B and T lymphocytes.\n \n
\n
\n",
+ "Examiners report": "
\n (a)\n
\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
\n (a)\n
\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
\n (b)\n
\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
\n (c)\n
\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",
+ "topics": [
+ "c-interaction-and-interdependence",
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "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",
+ "c2-2-neural-signalling",
+ "c3-2-6-lymphocytes-as-cells-in-the-adaptive-immune-system-that-cooperate-to-produce-antibodies",
+ "c3-2-defence-against-disease",
+ "d2-1-13-phases-of-the-cell-cycle",
+ "d2-1-14-cell-growth-during-interphase",
+ "d2-1-cell-and-nuclear-division"
+ ]
+ },
+ {
+ "question_id": "22N.2.HL.TZ0.7",
+ "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
\n
\n (c)\n
\n
\n
\n Explain how carbohydrates are transported from plant leaves.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (b)\n
\n
\n - \n light (energy) absorbed by pigments/chlorophyll/photosystems;\n
\n - \n excited electrons passed to electron carriers/electron transport chain;\n
\n - \n protons/hydrogen ions pumped into thylakoid (space);\n
\n - \n proton gradient/high proton concentration generated;\n
\n - \n protons pass via ATP synthase to the stroma;\n
\n - \n ATP synthase phosphorylates ADP/ATP synthase converts ADP to ATP;\n
\n - \n photophosphorylation/chemiosmosis;\n
\n - \n ATP synthase/electron carriers/proton pumps/photosystems/pigment are in the thylakoid membrane;\n
\n
\n
\n
\n (c)\n
\n
\n - \n translocation/movement by mass flow;\n
\n - \n in\n \n phloem sieve tubes\n \n ;\n
\n - \n sieve plates/pores in end walls/lack of organelles allows flow (of sap);\n
\n - \n carbohydrates (principally) transported as sucrose;\n
\n - \n (sucrose/glucose/sugar/carbohydrate) loaded (into phloem) by active transport;\n
\n - \n loading/pumping in (of sugars) by companion cells;\n
\n - \n high solute concentration generated (at the source);\n
\n - \n water enters by osmosis (due to the high solute concentration);\n
\n - \n hydrostatic pressure increased/high hydrostatic pressure generated;\n
\n - \n pressure gradient causes flow (from source to sink);\n
\n - \n leaves are a source because carbohydrates are made there;\n
\n - \n transport to the sink where carbohydrates are used/stored;\n
\n
\n
\n",
+ "Examiners report": "
\n (b)\n
\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
\n (c)\n
\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",
+ "topics": [
+ "b-form-and-function",
+ "c-interaction-and-interdependence"
+ ],
+ "subtopics": [
+ "b3-2-18-adaptations-of-phloem-sieve-tubes-and-companion-cells-for-translocation-of-sap",
+ "b3-2-transport",
+ "c1-3-14-thylakoids-as-systems-for-performing-the-light-dependent-reactions-of-photosynthesis",
+ "c1-3-photosynthesis"
+ ]
+ },
+ {
+ "question_id": "22N.2.HL.TZ0.8",
+ "Question": "
\n
\n (a)\n
\n
\n
\n Outline how adaptive radiation provides evidence for evolution.\n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n
\n Describe polyploidy and how it can lead to speciation.\n
\n
\n
\n
\n
\n
\n (c)\n
\n
\n
\n Explain how a newly discovered plant species would be classified and named.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n - \n diversification/ different species produced from a common/shared ancestor;\n
\n - \n homologous features have similarities of structure\n
\n - \n despite different functions;\n
\n - \n (different) adaptation to different environments/different selective pressures;\n
\n - \n pentadactyl limbs/Darwin’s finches/other example of adaptive radiation described correctly;\n
\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
\n (a)\n
\n
\n - \n diversification/ different species produced from a common/shared ancestor;\n
\n - \n homologous features have similarities of structure\n
\n - \n despite different functions;\n
\n - \n (different) adaptation to different environments/different selective pressures;\n
\n - \n pentadactyl limbs/Darwin’s finches/other example of adaptive radiation described correctly;\n
\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
\n (b)\n
\n
\n - \n polyploidy is having more than two (complete) sets of chromosomes/3n/4n/other specific example of polyploidy;\n
\n - \n can be due to errors in meiosis/production of diploid gametes;\n
\n - \n can be due to DNA replication without mitosis/cytokinesis;\n
\n - \n polyploidy causes reproductive isolation;\n
\n - \n diploids crossed with tetraploids produce infertile (triploid) offspring / triploid offspring are infertile;\n
\n - \n tetraploids are therefore a new species/failure to interbreed/reproductive isolation leads to speciation;\n
\n - \n (many) examples in the onion family/Allium/other valid example of speciation by polyploidy;\n
\n - \n infertile interspecific hybrids can become fertile by becoming polyploid;\n
\n
\n
\n \n Reject non-disjunction as a cause of polyploidy as it usually applies to a single bivalent.\n \n
\n
\n
\n (c)\n
\n
\n Naming:\n
\n
\n - \n binomial nomenclature/(plant is) given a binomial/double name;\n
\n - \n first name is the genus and second name is the species/genus initial uppercase and species lower case;\n
\n - \n names (of plant species) are international/are universally understood/are published in journals;\n
\n
\n Classification:\n
\n
\n \n - \n study the characteristics/structure/reproduction/chemical properties/DNA (of the plant);\n
\n - \n put/classify (the plant) in a group/genus with other similar species;\n
\n - \n natural classification corresponds with evolution/natural classification is based on many features;\n
\n - \n analogous features/features due to convergent evolution should not be used;\n
\n - \n hierarchy of groups/taxa (in traditional classification/3 or more taxa in correct sequence (kingdom-phylum-class);\n
\n - \n two or more of bryophyta, filicinophyta, coniferophyta and angiospermophyta named;\n
\n - \n a clade is a group of organisms evolved from a common ancestor;\n
\n - \n base sequences/amino acid sequences used to group organisms into clades/deduce evolutionary relationships;\n
\n - \n cladograms show the relationships between clades/likely evolutionary divergence of clades;\n
\n - \n each branch point/node represents where species are formed via divergent evolution;\n
\n - \n species are now classified into a sequence of clades (rather than a rigid hierarchy of taxa);\n
\n
\n
\n \n For mpi, common names such as ‘mosses’ are acceptable\n \n .\n
\n
\n",
+ "Examiners report": "
\n (a)\n
\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
\n (a)\n
\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
\n (b)\n
\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
\n (c)\n
\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",
+ "topics": [
+ "a-unity-and-diversity"
+ ],
+ "subtopics": [
+ "a3-2-1-need-for-classification-of-organisms",
+ "a3-2-9-classification-of-all-organisms-into-three-domains-using-evidence-from-rrna-base-sequences",
+ "a3-2-classification-and-cladistics-(hl-only)",
+ "a4-1-11-abrupt-speciation-in-plants-by-hybridization-and-polyploidy",
+ "a4-1-9-adaptive-radiation-as-a-source-of-biodiversity",
+ "a4-1-evolution-and-speciation"
+ ]
+ },
+ {
+ "question_id": "22N.2.SL.TZ0.1",
+ "Question": "
\n
\n (a)\n
\n
\n
\n State the mean annual decline in insect biomass.\n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n
\n Compare and contrast the results for Hymenoptera and Lepidoptera.\n
\n
\n
\n
\n
\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 000 species, assuming the mean rate of decline.\n
\n
\n
\n
\n
\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
\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
\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
\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
\n
\n (h)\n
\n
\n
\n State the relationship between high lipid content and survivability on day 7.\n
\n
\n
\n
\n
\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
\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",
+ "Markscheme": "
\n (a)\n
\n
\n 2.5\n \n %;\n
\n
\n \n % required\n \n
\n
\n
\n (a)\n
\n
\n 2.5\n \n %;\n
\n
\n \n % required\n \n
\n
\n
\n (b)\n
\n
\n - \n both show a decline in number;\n
\n - \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 \n
\n
\n
\n (c)\n
\n
\n 392\n \n 000 (species);\n
\n
\n
\n (d)\n
\n
\n (e)\n
\n
\n - \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 \n - \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 \n
\n
\n \n Accept vice versa for all answers.\n \n
\n
\n
\n (f)\n
\n
\n 0.025g;\n
\n
\n \n Unit needed\n \n
\n
\n
\n (g)\n
\n
\n - \n the mixture was closer to what the bees ate naturally;\n
\n - \n the bees like the taste better/prefer sucrose;\n
\n - \n there was more lipid in the 25:1 mixture so they achieved their daily lipid/energy requirement with less mass of food;\n
\n - \n the bees eating 50:1 diet ate more to reach their daily lipid requirement;\n
\n - \n prefer the higher proportion of protein (in the 50:1)\n
\n
\n
\n
\n (h)\n
\n
\n the higher the lipid content, the fewer bees survived/negative correlation;\n
\n
\n
\n (i)\n
\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
\n (j)\n
\n
\n - \n habitat destruction removes the plants/flowers/natural food source of the bees;\n
\n - \n bees have to look for other food sources;\n
\n - \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 \n - \n no control where bees are fed their normal diet is included;\n
\n - \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 \n
\n
\n \n Accept other reasonable discussion using the data.\n \n
\n
\n",
+ "Examiners report": "
\n (a)\n
\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 % 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 % 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
\n (a)\n
\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 % 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 % 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",
+ "topics": [
+ "b-form-and-function",
+ "c-interaction-and-interdependence"
+ ],
+ "subtopics": [
+ "b4-1-2-adaptations-of-organisms-to-the-abiotic-environment-of-their-habitat",
+ "b4-1-adaptation-to-environment",
+ "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",
+ "c4-2-16-secondary-production-as-accumulation-of-carbon-compounds-in-biomass-by-heterotrophs",
+ "c4-2-transfers-of-energy-and-matter"
+ ]
+ },
+ {
+ "question_id": "22N.2.SL.TZ0.2",
+ "Question": "
\n
\n (a)\n
\n
\n
\n Annotate the diagram to illustrate the amphipathic nature of phospholipids.\n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n
\n Outline a function of cholesterol in cell membranes.\n
\n
\n
\n
\n
\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",
+ "Markscheme": "
\n (a)\n
\n
\n - \n line to circle labelled phosphate (head)\n \n and\n \n (tail) labelled fatty acid/hydrocarbon/lipid (tail);\n
\n - \n label hydrophilic/polar/attracted to water/\n \n and\n \n hydrophobic/non polar/not attracted to water;\n
\n
\n
\n
\n (a)\n
\n
\n - \n line to circle labelled phosphate (head)\n \n and\n \n (tail) labelled fatty acid/hydrocarbon/lipid (tail);\n
\n - \n label hydrophilic/polar/attracted to water/\n \n and\n \n hydrophobic/non polar/not attracted to water;\n
\n
\n
\n
\n (b)\n
\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
\n (c)\n
\n
\n - \n mitochondria/chloroplasts have their own DNA;\n
\n - \n mitochondria can self-replicate/undergo a process like binary fission;\n
\n - \n mitochondria/chloroplasts have double membranes;\n
\n - \n mitochondria/chloroplasts have(\n \n 70s\n \n ) ribosomes;\n
\n - \n mitochondria/chloroplasts are sensitive to antibiotics;\n
\n - \n similar in size to bacteria\n
\n
\n
\n",
+ "Examiners report": "
\n (a)\n
\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
\n (a)\n
\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",
+ "topics": [
+ "a-unity-and-diversity",
+ "b-form-and-function"
+ ],
+ "subtopics": [
+ "a2-2-12-origin-of-eukaryotic-cells-by-endosymbiosis",
+ "a2-2-cell-structure",
+ "b1-1-10-difference-between-saturated-monounsaturated-and-polyunsaturated-fatty-acids",
+ "b1-1-12-formation-of-phospholipid-bilayers-as-a-consequence-of-the-hydrophobic-and-hydrophilic-regions",
+ "b1-1-carbohydrates-and-lipids"
+ ]
+ },
+ {
+ "question_id": "22N.2.SL.TZ0.3",
+ "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
\n
\n (b)\n
\n
\n
\n Explain how increased levels of atmospheric carbon dioxide contribute to global warming.\n
\n
\n
\n
\n
\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",
+ "Markscheme": "
\n (a)\n
\n
\n (\n \n Evidence does not support this argument because\n \n :)\n
\n
\n - \n overall increase in surface temperature but no overall increase/slight decrease in solar irradiance;\n
\n - \n peaks and troughs in solar irradiance do not correspond with fluctuations in surface temperature;\n
\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
\n (b)\n
\n
\n - \n carbon dioxide absorbs/traps long wavelength/infra-red radiation;\n
\n - \n \n more heat\n \n trapped in/\n \n less heat\n \n escapes from atmosphere with more carbon dioxide;\n
\n - \n short wave/UV radiation from the sun passes through the atmosphere/reaches the Earth’s surface;\n
\n - \n radiation from the sun/sunlight warms the (surface of the) Earth;\n
\n - \n long wavelength/infra-red radiated from the (warmed) Earth’s surface;\n
\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
\n (c)\n
\n
\n methane/nitrous oxide/water vapour/ozone/CFCs/other halogenated gases;\n
\n
\n",
+ "Examiners report": "
\n (a)\n
\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 % 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
\n (b)\n
\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 Short wave radiation from the sun causes the Earth's surface to warm up.\n
\n - \n The warmed surface of the Earth emits long wave radiation.\n
\n - \n Greenhouse gases such as carbon dioxide absorb some of this long-wave radiation, which becomes\n
\n heat.\n \n - \n If the concentration of carbon dioxide or other greenhouse gases in the atmosphere rises, more heat is\n
\n trapped and the Earth becomes warmer.\n \n - \n Burning of fossil fuels causes the atmospheric carbon dioxide concentration to rise.\n
\n
\n
\n
\n (c)\n
\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",
+ "topics": [
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "d4-3-1-anthropogenic-causes-of-climate-change",
+ "d4-3-2-positive-feedback-cycles-in-global-warming",
+ "d4-3-climate-change"
+ ]
+ },
+ {
+ "question_id": "22N.2.SL.TZ0.4",
+ "Question": "
\n
\n (a)\n
\n
\n
\n Draw the symbol for individual X on the diagram.\n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n
\n Calculate the probability of male Y having an allele for the disorder.\n
\n
\n
\n
\n
\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
\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",
+ "Markscheme": "
\n (a)\n
\n
\n
\n
\n
\n
\n (a)\n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n 50\n \n %/ 0.5/ 1/2;\n
\n
\n
\n (c)\n
\n
\n - \n if it was sex-linked it would be on the x chromosome;\n
\n - \n there cannot be a heterozygous male if the trait is sex-linked\n
\n - \n males would pass the allele to their daughter;\n
\n - \n daughter is not shown as heterozygous so it is not sex-linked;\n
\n
\n
\n
\n (d)\n
\n
\n - \n sequence of DNA bases determines the amino acid sequence of a protein;\n
\n - \n changing one base (on the DNA) can cause the triplet /mRNA to code for a different\n \n amino acid\n \n ;\n
\n - \n changing one base (on the DNA) causes a different protein to be made (during translation);\n
\n
\n
\n",
+ "Examiners report": "
\n (a)\n
\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 % 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
\n (a)\n
\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 % 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",
+ "topics": [
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "d1-2-11-mutations-that-change-protein-structure",
+ "d1-2-protein-synthesis",
+ "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",
+ "d3-2-inheritance"
+ ]
+ },
+ {
+ "question_id": "22N.2.SL.TZ0.5",
+ "Question": "
\n
\n (a)\n
\n
\n
\n Identify the structure labelled X.\n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n
\n Outline how the neuron is stimulated to release the neurotransmitter.\n
\n
\n
\n
\n
\n
\n (c)\n
\n
\n
\n Explain the action of neonicotinoid pesticides in insects.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n (Neurotransmitter) vesicle;\n
\n
\n \n Do not accept Vacuole.\n \n
\n
\n
\n (a)\n
\n
\n (Neurotransmitter) vesicle;\n
\n
\n \n Do not accept Vacuole.\n \n
\n
\n
\n (b)\n
\n
\n - \n the arrival of a nerve impulse/action potential/depolarization (stimulates the release of a neurotransmitter);\n
\n - \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 \n - \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 \n
\n
\n
\n (c)\n
\n
\n - \n prevents synaptic/nerve transmission\n
\n - \n is /acts like /has similar structure to a neurotransmitter/acetylcholine\n
\n - \n (neonicotinoid pesticides) bind to acetylcholine receptors in the post synaptic membrane;\n
\n - \n neonicotinoid pesticides are not broken down (as acetylcholine would be) by acetylcholinesterase/enzyme;\n
\n - \n the receptors are overstimulated\n
\n - \n paralyses/kills the insects;\n
\n
\n
\n",
+ "Examiners report": "
\n (a)\n
\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
\n (a)\n
\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",
+ "topics": [
+ "c-interaction-and-interdependence"
+ ],
+ "subtopics": [
+ "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",
+ "c2-1-chemical-signalling-[hl-only]",
+ "c2-2-12-effects-of-exogenous-chemicals-on-synaptic-transmission",
+ "c2-2-neural-signalling"
+ ]
+ },
+ {
+ "question_id": "22N.2.SL.TZ0.6",
+ "Question": "
\n
\n (a)\n
\n
\n
\n Outline how energy flows in an ecosystem.\n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n
\n Describe how plants affect the amount of carbon dioxide in the atmosphere.\n
\n
\n
\n
\n
\n
\n (c)\n
\n
\n
\n Explain how a newly discovered plant species would be classified and named.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n - \n energy from the sun is captured by plants/autotrophs;\n
\n - \n light energy is converted to chemical energy by\n \n photosynthesis\n \n ;\n
\n - \n energy is passed to animals/consumers/along the food chain;\n
\n - \n at each stage in the food chain energy is lost by respiration/as heat;\n
\n - \n \n much\n \n less energy/only about 10\n \n % is available at each stage/trophic level of the food chain;\n
\n - \n some energy is made available to decomposers when organisms die/parts fall to the ground;\n
\n - \n energy cannot be recycled;\n
\n
\n
\n
\n (a)\n
\n
\n - \n energy from the sun is captured by plants/autotrophs;\n
\n - \n light energy is converted to chemical energy by\n \n photosynthesis\n \n ;\n
\n - \n energy is passed to animals/consumers/along the food chain;\n
\n - \n at each stage in the food chain energy is lost by respiration/as heat;\n
\n - \n \n much\n \n less energy/only about 10\n \n % is available at each stage/trophic level of the food chain;\n
\n - \n some energy is made available to decomposers when organisms die/parts fall to the ground;\n
\n - \n energy cannot be recycled;\n
\n
\n
\n
\n (b)\n
\n
\n - \n plants reduce the amount of carbon dioxide in the atmosphere by\n \n photosynthesis\n \n ;\n
\n - \n carbon dioxide is fixed/converted into organic substances/sugars/ OWTTE;\n
\n - \n plants respire which releases carbon dioxide into the atmosphere;\n
\n - \n plant decomposition may release CO\n \n 2\n \n
\n - \n carbon in dead plants is trapped/ stored in fossil fuels / peat\n
\n - \n combustion of plants/wood/ fossil fuels adds to the amount of carbon dioxide in the atmosphere;\n
\n
\n
\n \n \n OR\n \n Shows correct equation\n \n
\n
\n
\n (c)\n
\n
\n \n Naming\n \n :\n
\n
\n - \n binomial nomenclature / (plant is) given a binomial/double name;\n
\n - \n first name is the genus and second name is the species / genus initial upper case and species lower case;\n
\n - \n names (of plant species) are international/are universally understood/are published in journals;\n
\n
\n \n Classification\n \n :\n \n - \n study the characteristics/structure/reproduction/chemical properties/DNA (of the plant);\n
\n - \n put/classify (the plant) in a group/genus with other similar species;\n
\n - \n natural classification corresponds with evolution / natural classification is based on many features;\n
\n - \n analogous features/features due to convergent evolution should not be used;\n
\n - \n hierarchy of groups/taxa (in traditional classification / 3 or more taxa in correct sequence (kingdom-phylum-class);\n
\n - \n two or more of bryophyta, filicinophyta, coniferophyta and angiospermophyta named;\n
\n - \n a clade is a group of organisms evolved from a common ancestor;\n
\n - \n base sequences/amino acid sequences used to group organisms into clades/deduce evolutionary relationships;\n
\n - \n cladograms show the relationships between clades/likely evolutionary divergence of clades;\n
\n - \n each branch point/node represents where species are formed via divergent evolution;\n
\n - \n species are now classified into a sequence of clades (rather than a rigid hierarchy of taxa);\n
\n
\n
\n \n Mpi accept common names, mosses, ferns etc\n \n .\n
\n
\n",
+ "Examiners report": "
\n (a)\n
\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
\n (a)\n
\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
\n (b)\n
\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
\n (c)\n
\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",
+ "topics": [
+ "a-unity-and-diversity",
+ "c-interaction-and-interdependence"
+ ],
+ "subtopics": [
+ "a3-2-1-need-for-classification-of-organisms",
+ "a3-2-9-classification-of-all-organisms-into-three-domains-using-evidence-from-rrna-base-sequences",
+ "a3-2-classification-and-cladistics-(hl-only)",
+ "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",
+ "c4-2-3-flow-of-chemical-energy-through-food-chains",
+ "c4-2-transfers-of-energy-and-matter"
+ ]
+ },
+ {
+ "question_id": "23M.1A.SL.TZ2.8",
+ "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
\n
\n (i)\n
\n
\n
\n Identify the relationship between migration distance and plumage colouration.\n
\n
\n
\n
\n
\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",
+ "Markscheme": "
\n
\n (i)\n
\n
\n - \n the longer the migration, the lighter the colour /\n \n vice versa\n \n ;\n
\n - \n too much variation so it is not possible to see a relationship;\n
\n
\n
\n
\n (ii)\n
\n
\n - \n camouflage to avoid predators (in different migratory routes);\n
\n - \n different diets (in different migratory routes);\n
\n - \n less migratory distance leaves more energy to produce pigments (in plumage);\n
\n - \n geographic isolation (due to different migratory routes) leads to different gene pools;\n
\n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "c-interaction-and-interdependence",
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "c1-1-8-effects-of-temperature-ph-and-substrate-concentration-on-the-rate-of-enzyme-activity",
+ "c1-1-enzymes-and-metabolism",
+ "d4-1-7-sexual-selection-as-a-selection-pressure-in-animal-species",
+ "d4-1-natural-selection"
+ ]
+ },
+ {
+ "question_id": "23M.1B.SL.TZ1.1",
+ "Question": "
\n
\n (a)\n
\n
\n
\n State the purpose of lime water in flask B.\n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n
\n Suggest a reason that the pot was covered with a plastic bag.\n
\n
\n
\n
\n
\n
\n (c)\n
\n
\n
\n Suggest a suitable control for this experiment.\n
\n
\n
\n
\n
\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",
+ "Markscheme": "
\n (a)\n
\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
\n (b)\n
\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
\n (c)\n
\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
\n (d)\n
\n
\n - \n the graph shows the optimum temperature to be near 40 °C;\n
\n - \n choose smaller range of temperature (between 30 and 50 °C);\n
\n - \n smaller increments of temperature\n
\n
\n
\n \n c. Accept numbers such as 1 or 5 degrees.\n \n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "c-interaction-and-interdependence"
+ ],
+ "subtopics": [
+ "c1-1-8-effects-of-temperature-ph-and-substrate-concentration-on-the-rate-of-enzyme-activity",
+ "c1-1-enzymes-and-metabolism"
+ ]
+ },
+ {
+ "question_id": "23M.1B.SL.TZ1.3",
+ "Question": "
\n
\n
\n (i)\n
\n
\n
\n where the DNA of each individual could be taken from.\n
\n
\n
\n
\n
\n
\n (ii)\n
\n
\n
\n how the DNA is amplified.\n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n
\n Deduce with a reason the identity of the father.\n
\n
\n
\n
\n
\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
\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",
+ "Markscheme": "
\n (a)\n
\n
\n from blood sample/hair/cheek/saliva/semen;\n
\n
\n \n Do not accept red blood cells\n \n
\n
\n
\n (i)\n
\n
\n from blood sample/hair/cheek/saliva/semen;\n
\n
\n \n Do not accept red blood cells\n \n
\n
\n
\n (ii)\n
\n
\n PCR/polymerase chain reaction\n
\n \n \n OR\n \n \n
\n using Taq polymerase;\n
\n
\n
\n
\n
\n (b)\n
\n
\n - \n male 2;\n
\n - \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 \n
\n
\n \n Must mention both the mother and father\n \n
\n
\n
\n (c)\n
\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
\n (d)\n
\n
\n - \n water uptake by shoot causes a decrease in reading for balance 2;\n
\n - \n water lost by the shoot would be total loss from the system;\n
\n
\n
\n \n OWTTE\n \n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "c-interaction-and-interdependence"
+ ],
+ "subtopics": [
+ "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",
+ "c1-3-photosynthesis"
+ ]
+ },
+ {
+ "question_id": "23M.1B.SL.TZ2.2",
+ "Question": "
\n
\n (i)\n
\n
\n
\n State a variable that should be kept constant.\n
\n
\n
\n
\n
\n
\n (ii)\n
\n
\n
\n Identify the independent variable.\n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n
\n Outline the steps to produce a 10 % egg white solution.\n
\n
\n
\n
\n
\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
\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",
+ "Markscheme": "
\n (i)\n
\n
\n enzyme/substrate/egg white concentration/volume/pH/temperature;\n
\n
\n \n Accept another reasonable variable.\n \n
\n
\n
\n (ii)\n
\n
\n (with/without) ultrasound pretreatment / time;\n
\n
\n
\n (b)\n
\n
\n - \n measure 10 g/parts egg whites;\n
\n - \n add to 90 g/parts of water;\n
\n
\n
\n \n Accept use of volume instead of mass.\n \n
\n
\n
\n (c)\n
\n
\n - \n more reliable results;\n
\n - \n to identify outliers/anomalous results\n
\n \n \n OR\n
\n \n \n reduce random errors;\n \n - \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 \n
\n
\n \n Mp a: do not accept “accurate”.\n \n
\n
\n
\n (d)\n
\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",
+ "topics": [
+ "c-interaction-and-interdependence"
+ ],
+ "subtopics": [
+ "c1-1-8-effects-of-temperature-ph-and-substrate-concentration-on-the-rate-of-enzyme-activity",
+ "c1-1-enzymes-and-metabolism"
+ ]
+ },
+ {
+ "question_id": "23M.1B.SL.TZ2.3",
+ "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
\n
\n (b)\n
\n
\n
\n Suggest one advantage of using a mesocosm in this type of research.\n
\n
\n
\n
\n
\n
\n (c)\n
\n
\n
\n Outline the requirements for sustainability within a sealed mesocosm.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n - \n temperature;\n
\n - \n pH;\n
\n - \n minerals / salt concentration / conductivity;\n
\n - \n O\n \n 2\n \n (concentration);\n
\n - \n CO\n \n 2\n \n (concentration);\n
\n
\n
\n
\n (b)\n
\n
\n environmentally safe/cheaper/control of variables easier;\n
\n
\n
\n (c)\n
\n
\n - \n photosynthetic organisms/autotrophs/plants as producers;\n
\n - \n \n light\n \n (as energy source) for photosynthesis;\n
\n - \n nutrient/water recycling (by saprotrophs);\n
\n - \n decomposers/saprotrophs to breakdown (toxic) wastes;\n
\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",
+ "topics": [
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "d4-2-4-use-of-a-model-to-investigate-the-effect-of-variables-on-ecosystem-stability",
+ "d4-2-stability-and-change"
+ ]
+ },
+ {
+ "question_id": "23M.2.HL.TZ1.2",
+ "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
\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
\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
\n
\n (d)\n
\n
\n
\n Outline the role of melatonin in humans.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\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
\n (a)\n
\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
\n (b)\n
\n
\n beta pleated sheet/beta-loop/beta strands;\n
\n
\n \n Reject ‘beta helix’\n \n
\n
\n
\n (c)\n
\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
\n (d)\n
\n
\n - \n control/maintain/regulate circadian rhythms;\n
\n - \n secreted/released late evening/end of day/in dark/night time/dim light/absence of blue light;\n
\n - \n helps to induce sleep/sleepiness/influences timing of sleeping/waking/control sleep cycle;\n
\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",
+ "topics": [
+ "b-form-and-function",
+ "c-interaction-and-interdependence"
+ ],
+ "subtopics": [
+ "b1-2-6-chemical-diversity-in-the-r-groups-of-amino-acids-as-a-basis-for-the-immense-diversity-in-protein-form-and-function",
+ "b1-2-8-pleating-and-coiling-of-secondary-structure-of-proteins",
+ "b1-2-proteins",
+ "b2-1-14-gated-ion-channels-in-neurons",
+ "b2-1-membranes-and-membrane-transport",
+ "c3-1-11-modulation-of-sleep-patterns-by-melatonin-secretion-as-a-part-of-circadian-rhythms",
+ "c3-1-integration-of-body-systems"
+ ]
+ },
+ {
+ "question_id": "23M.2.HL.TZ1.22",
+ "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
\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
\n
\n (c)\n
\n
\n
\n Describe the state of the heart valves at 0.3 s.\n
\n
\n
\n
\n
\n
\n (d)\n
\n
\n
\n Explain how cardiac muscle is adapted to its function.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n (b)\n
\n
\n (c)\n
\n
\n - \n atrioventricular/AV valves closed;\n
\n - \n semi-lunar valves open;\n
\n
\n
\n
\n (d)\n
\n
\n - \n many mitochondria for aerobic respiration;\n
\n - \n cells are branched allowing for faster transmission/allow impulse to spread;\n
\n - \n cardiac muscle is myogenic so does not require the CNS to initiate contraction;\n
\n - \n cells are not fused together/are connected by gap junctions/intercalated discs (which) allows easier transmission between cells;\n
\n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "b-form-and-function"
+ ],
+ "subtopics": [
+ "b3-2-15-adaptations-of-the-mammalian-heart-for-delivering-pressurized-blood-to-the-arteries",
+ "b3-2-16-stages-in-the-cardiac-cycle",
+ "b3-2-transport"
+ ]
+ },
+ {
+ "question_id": "23M.2.HL.TZ1.23",
+ "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
\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",
+ "Markscheme": "
\n (a)\n
\n
\n lungs/alveoli;\n
\n
\n
\n (b)\n
\n
\n - \n fetal hemoglobin has a higher affinity for oxygen then normal hemoglobin;\n
\n - \n oxygen will pass from normal/maternal/mother’s hemoglobin to fetal hemoglobin (in the placenta);\n
\n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "b-form-and-function"
+ ],
+ "subtopics": [
+ "b3-1-12-bohr-shift",
+ "b3-1-13-oxygen-dissociation-curves-as-a-means-of-representing-the-affinity-of-haemoglobin-for-oxygen-at-different-oxygen-concentrations",
+ "b3-1-gas-exchange"
+ ]
+ },
+ {
+ "question_id": "23M.2.HL.TZ1.3",
+ "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
\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
\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",
+ "Markscheme": "
\n (a)\n
\n
\n - \n if antibiotic is in the environment/soil there is selection (pressure);\n
\n - \n bacteria without resistance (gene) die / converse;\n
\n - \n bacteria with resistance (gene) reproduce\n
\n \n OR\n \n
\n bacteria exchange/obtain resistance genes using plasmids/by conjugation;\n \n - \n offspring inherit (the gene for) resistance/resistance passed on (to offspring);\n
\n
\n
\n \n Do not award marks for general statements about natural selection – answers must refer to antibiotic resistance.\n \n
\n
\n
\n (a)\n
\n
\n - \n if antibiotic is in the environment/soil there is selection (pressure);\n
\n - \n bacteria without resistance (gene) die / converse;\n
\n - \n bacteria with resistance (gene) reproduce\n
\n \n OR\n \n
\n bacteria exchange/obtain resistance genes using plasmids/by conjugation;\n \n - \n offspring inherit (the gene for) resistance/resistance passed on (to offspring);\n
\n
\n
\n \n Do not award marks for general statements about natural selection – answers must refer to antibiotic resistance.\n \n
\n
\n
\n (i)\n
\n
\n - \n viruses lack metabolism/plasma membranes/cell walls / viruses are not livingorganisms;\n
\n - \n antibiotics kill/target bacteria/prokaryotes but not viruses;\n
\n - \n viral pathogens of animals use animal metabolism (which is not affected by antibiotics);\n
\n
\n
\n
\n
\n
\n (ii)\n
\n
\n - \n antibiotics (only) affect/kill/block processes in bacteria/prokaryotes / do not affect eukaryotes;\n
\n - \n metabolism/protein synthesis/ribosomes/cell walls not targeted in insects/animals/eukaryotes;\n
\n - \n no cell walls in animals (so antibiotics cannot attack cell walls);\n
\n - \n antibiotics are secreted (by microbes/fungi) to prevent competition (with other microbes);\n
\n
\n
\n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "c-interaction-and-interdependence",
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "c3-2-13-antibiotics-as-chemicals-that-block-processes-occurring-in-bacteria-but-not-in-eukaryotic-cells",
+ "c3-2-14-evolution-of-resistance-to-several-antibiotics-in-strains-of-pathogenic-bacteria",
+ "c3-2-defence-against-disease",
+ "d4-1-15-artificial-selection-by-deliberate-choice-of-traits",
+ "d4-1-natural-selection"
+ ]
+ },
+ {
+ "question_id": "23M.2.HL.TZ1.6",
+ "Question": "
\n
\n (a)\n
\n
\n
\n Outline the role of ADH in osmoregulation.\n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n
\n Explain the regulation of metabolic pathways by end-product inhibition.\n
\n
\n
\n
\n
\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",
+ "Markscheme": "
\n (a)\n
\n
\n - \n ADH (secreted by pituitary) if body/blood is dehydrated/hypertonic/has high solute concentration;\n
\n - \n more aquaporins / aquaporins open (in collecting duct);\n
\n - \n collecting duct more permeable to water/reabsorbs more water (from filtrate/urine);\n
\n - \n water reabsorbed by osmosis/water reabsorbed because medulla is hypertonic;\n
\n - \n (reabsorbed) water passes (from filtrate) to blood / blood solute concentration reduced;\n
\n - \n less water lost in urine / smaller volume of (more concentrated) urine;\n
\n - \n negative feedback / less/no ADH secreted when blood solute concentration returns to normal;\n
\n
\n
\n \n Do not accept answers suggesting that ADH has a different effect when body fluids are hypotonic.\n \n
\n
\n
\n (a)\n
\n
\n - \n ADH (secreted by pituitary) if body/blood is dehydrated/hypertonic/has high solute concentration;\n
\n - \n more aquaporins / aquaporins open (in collecting duct);\n
\n - \n collecting duct more permeable to water/reabsorbs more water (from filtrate/urine);\n
\n - \n water reabsorbed by osmosis/water reabsorbed because medulla is hypertonic;\n
\n - \n (reabsorbed) water passes (from filtrate) to blood / blood solute concentration reduced;\n
\n - \n less water lost in urine / smaller volume of (more concentrated) urine;\n
\n - \n negative feedback / less/no ADH secreted when blood solute concentration returns to normal;\n
\n
\n
\n \n Do not accept answers suggesting that ADH has a different effect when body fluids are hypotonic.\n \n
\n
\n
\n (b)\n
\n
\n - \n final product in pathway acts as an inhibitor/blocks (reaction)/slows (reaction);\n
\n - \n first/early/earlier enzyme (in pathway is inhibited);\n
\n - \n non-competitive / binds at allosteric site / causes active site to change;\n
\n - \n production of end-product reduced/paused when there is an excess;\n
\n - \n isoleucine inhibits enzyme using threonine as substrate at start of pathway to isoleucine;\n
\n - \n negative feedback / production restarts when end-product used up/concentration drops;\n
\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
\n (c)\n
\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",
+ "topics": [
+ "c-interaction-and-interdependence",
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "c1-1-16-regulation-of-metabolic-pathways-by-feedback-inhibition",
+ "c1-1-enzymes-and-metabolism",
+ "d3-1-19-hormonal-control-of-pregnancy-and-childbirth",
+ "d3-1-reproduction",
+ "d3-3-10-osmoregulation-by-water-reabsorption-in-the-collecting-ducts",
+ "d3-3-7-role-of-the-kidney-in-osmoregulation-and-excretion",
+ "d3-3-homeostasis"
+ ]
+ },
+ {
+ "question_id": "23M.2.HL.TZ1.7",
+ "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
\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
\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
\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",
+ "Markscheme": "
\n (a)\n
\n
\n - \n pairing/synapsis of homologous chromosomes / homologous chromosomes form bivalents;\n
\n - \n crossing over / chromatid breaks then rejoins to non-sister chromatid;\n
\n - \n exchange of DNA/alleles/genetic information between chromatids/chromosomes;\n
\n - \n recombination / new combinations of alleles/genes generated;\n
\n - \n condensation/shortening/thickening/supercoiling of chromatids/chromosomes;\n
\n - \n formation of a chiasma where crossing over occurred;\n
\n
\n
\n
\n (a)\n
\n
\n - \n binomial naming\n
\n \n \n OR\n \n \n
\n genus and species name;\n \n - \n plants constitute a kingdom\n
\n - \n plants are eukaryotes/belong to the domain eukaryota\n
\n - \n classified using a hierarchy of taxa\n
\n \n \n OR\n \n \n
\n kingdom, phylum, class, order, family, genus, species\n \n - \n bryophyta/filicinophyta/coniferophyte/angiospermophyta is a\n \n phylum\n \n (of plants);\n
\n - \n bryophytes have only rhizoids/spores (produced in a capsule)/no roots/ no vascular tissue;\n
\n - \n filicinophytes have stems/roots/xylem-phloem/reproduce by spores/leaves that uncurl; but no seeds\n
\n - \n coniferophytes have seeds in cones/ vascular tissue/xylem-phloem/cambium/ but no flowers/no fruits\n
\n - \n angiospermophytes have flowers/produce seeds/produce fruits/vascular tissue/xylem-phloem;\n
\n - \n named example showing of the classification of a plant from species to domain or vice versa\n
\n - \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 \n - \n use a dichotomous key to discriminate among plant features\n
\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
\n (b)\n
\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
\n (c)\n
\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",
+ "topics": [
+ "a-unity-and-diversity",
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "a3-2-2-difficulties-classifying-organisms-into-the-traditional-hierarchy-of-taxa",
+ "a3-2-classification-and-cladistics-(hl-only)",
+ "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",
+ "d1-1-dna-replication",
+ "d1-3-5-randomness-in-mutation",
+ "d1-3-mutations-and-gene-editing",
+ "d2-1-16-consequences-of-mutations-in-genes-that-control-the-cell-cycle",
+ "d2-1-cell-and-nuclear-division"
+ ]
+ },
+ {
+ "question_id": "23M.2.HL.TZ1.8",
+ "Question": "
\n
\n (a)\n
\n
\n
\n Explain how vesicles are used by cells to move materials.\n
\n
\n
\n
\n
\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",
+ "Markscheme": "
\n (a)\n
\n
\n - \n fluidity of membranes allows vesicles to bud off membranes/fuse with membranes;\n
\n - \n materials taken into cells by endocytosis/vesicle formation;\n
\n - \n \n Paramecium\n \n takes in food / phagocytes engulf pathogens / another example;\n
\n - \n materials released from cells by exocytosis/by vesicle fusing with plasma membrane;\n
\n - \n neurotransmitter released at synapses / protein secretion / secretion from gland cell / another example;\n
\n - \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
\n - \n movement of proteins from the rough ER to the Golgi / another example;\n
\n
\n
\n
\n (a)\n
\n
\n - \n fluidity of membranes allows vesicles to bud off membranes/fuse with membranes;\n
\n - \n materials taken into cells by endocytosis/vesicle formation;\n
\n - \n \n Paramecium\n \n takes in food / phagocytes engulf pathogens / another example;\n
\n - \n materials released from cells by exocytosis/by vesicle fusing with plasma membrane;\n
\n - \n neurotransmitter released at synapses / protein secretion / secretion from gland cell / another example;\n
\n - \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
\n - \n movement of proteins from the rough ER to the Golgi / another example;\n
\n
\n
\n
\n (b)\n
\n
\n - \n transport/translocation in (phloem)\n \n sieve tubes\n \n ;\n
\n - \n flow of sap through pores in end walls/sieve plates;\n
\n - \n sugar/amino acids are transported dissolved in water/sap;\n
\n - \n loaded into phloem (companion cells/sieve tubes) by active transport;\n
\n - \n protons pumped out and sucrose then enters by cotransport;\n
\n - \n high solute concentration created in phloem/sieve tube;\n
\n - \n water enters (sieve tube) by osmosis;\n
\n - \n hydrostatic pressure in sieve tube increases;\n
\n - \n unloading from sieve tubes in sink/in roots;\n
\n - \n water leaves by osmosis lowering the hydrostatic pressure;\n
\n - \n sap movement (in phloem) from higher to lower pressure;\n
\n - \n movement from source/leaves to sink/roots;\n
\n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "b-form-and-function"
+ ],
+ "subtopics": [
+ "b2-2-9-structure-and-function-of-vesicles-in-cells",
+ "b2-2-organelles-and-compartmentalization",
+ "b3-2-18-adaptations-of-phloem-sieve-tubes-and-companion-cells-for-translocation-of-sap",
+ "b3-2-transport"
+ ]
+ },
+ {
+ "question_id": "23M.2.HL.TZ2.2",
+ "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
\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",
+ "Markscheme": "
\n (a)\n
\n
\n (d)\n
\n
\n - \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
\n - \n urea filtered out from blood in glomerulus/Bowman’s capsule;\n
\n - \n water reabsorbed from filtrate (by osmosis);\n
\n - \n in proximal convoluted tubule/\n \n descending\n \n loop of Henle/collecting duct;\n
\n - \n loop of Henle maintains hypertonic conditions in the medulla;\n
\n - \n little/no urea reabsorbed from filtrate;\n
\n
\n
\n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "b-form-and-function",
+ "c-interaction-and-interdependence",
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "b1-2-1-generalized-structure-of-an-amino-acid",
+ "b1-2-proteins",
+ "c1-1-10-effect-of-enzymes-on-activation-energy",
+ "c1-1-13-cyclical-and-linear-pathways-in-metabolism",
+ "c1-1-enzymes-and-metabolism",
+ "d3-3-7-role-of-the-kidney-in-osmoregulation-and-excretion",
+ "d3-3-homeostasis"
+ ]
+ },
+ {
+ "question_id": "23M.2.HL.TZ2.3",
+ "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
\n
\n (a)\n
\n
\n
\n State one cause of lung cancer.\n
\n
\n
\n
\n
\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
\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",
+ "Markscheme": "
\n (a)\n
\n
\n - \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
\n - \n II is the anther and produces/contains/releases\n \n pollen\n \n ;\n
\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
\n (a)\n
\n
\n - \n smoking/tobacco;\n
\n - \n passive smoking;\n
\n - \n Radon/other radiation;\n
\n - \n exposure to arsenic/asbestos/smoke from coal burning/fires/silica/rock dust/vehicle exhaust fumes/nitrogen oxides;\n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n - \n fewer/smaller/lack of alveoli/air spaces;\n
\n - \n many cells/nuclei per area / much denser tissue;\n
\n - \n more cells undergoing mitosis (in the tumour);\n
\n
\n
\n
\n
\n
\n (c)\n
\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",
+ "topics": [
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "d2-1-17-differences-between-tumours-in-rates-of-cell-division-and-growth-and-in-the-capacity-for-metastasis-and-invasion-of-neighbouring-tissue",
+ "d2-1-cell-and-nuclear-division",
+ "d3-1-8-sexual-reproduction-in-flowering-plants",
+ "d3-1-9-features-of-an-insect-pollinated-flower",
+ "d3-1-reproduction"
+ ]
+ },
+ {
+ "question_id": "23M.2.HL.TZ2.4",
+ "Question": "
\n
\n (a.i)\n
\n
\n
\n State with a reason whether pangolins are autotrophic or heterotrophic.\n
\n
\n
\n
\n
\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",
+ "Markscheme": "
\n (a.i)\n
\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
\n (b)\n
\n
\n - \n hair;\n
\n - \n mammary glands/milk secretion;\n
\n - \n alveoli in lungs;\n
\n - \n lower mandible/jaw consisting of just one bone;\n
\n - \n giving birth to live young/are placental (apart from duck-billed platypus/echidna);\n
\n - \n external ears/ pinna;\n
\n - \n warm-blooded/endothermic/constant body temperature;\n
\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",
+ "topics": [
+ "c-interaction-and-interdependence",
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "c4-2-10-classification-of-organisms-into-trophic-levels",
+ "c4-2-6-autotrophs-as-organisms-that-use-external-energy-sources-to-synthesize-carbon-compounds-from-simple-inorganic-substances",
+ "c4-2-transfers-of-energy-and-matter",
+ "d3-1-18-role-of-the-placenta-in-foetal-development-inside-the-uterus",
+ "d3-1-reproduction",
+ "d3-2-1-production-of-haploid-gametes-in-parents-and-their-fusion-to-form-a-diploid-zygote-as-the-means-of-inheritance",
+ "d3-2-inheritance"
+ ]
+ },
+ {
+ "question_id": "23M.2.HL.TZ2.6",
+ "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
\n
\n (b)\n
\n
\n
\n Outline the role of the right atrium in the cardiac cycle.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n - \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
\n - \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
\n - \n extra cells produced when they are needed\n
\n - \n tumour formation is the result of uncontrolled cell division/ cells growing and dividing endlessly\n
\n - \n repeated mitoses/high mitotic index\n
\n - \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
\n - \n carcinogens/radiation/mutagenic chemicals/mutagens/smoking cause mutations/tumours;\n
\n
\n
\n
\n
\n
\n (a)\n
\n
\n - \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
\n - \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
\n - \n extra cells produced when they are needed\n
\n - \n tumour formation is the result of uncontrolled cell division/ cells growing and dividing endlessly\n
\n - \n repeated mitoses/high mitotic index\n
\n - \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
\n - \n carcinogens/radiation/mutagenic chemicals/mutagens/smoking cause mutations/tumours;\n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n - \n right atrium collects (deoxygenated) blood from the body;\n
\n - \n blood drains into atrium through/from the vena cava;\n
\n - \n deoxygenated blood present in vena cava/right atrium/right ventricle;\n
\n - \n right atrium pumps blood into the right ventricle;\n
\n - \n during atrial systole/ventricular diastole/at the start of the cardiac cycle;\n
\n - \n sinoatrial node is in the right atrium/sinoatrial node acts as the (natural) pacemaker / sinoatrial node initiates the heartbeat;\n
\n - \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
\n
\n
\n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "b-form-and-function",
+ "c-interaction-and-interdependence",
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "b3-2-16-stages-in-the-cardiac-cycle",
+ "b3-2-transport",
+ "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",
+ "c4-2-transfers-of-energy-and-matter",
+ "d2-1-15-control-of-the-cell-cycle-using-cyclins",
+ "d2-1-cell-and-nuclear-division"
+ ]
+ },
+ {
+ "question_id": "23M.2.SL.TZ1.1",
+ "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
\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
\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
\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 (i)\n
\n
\n
\n State the trend.\n
\n
\n
\n
\n
\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 (e)\n
\n
\n
\n Compare and contrast the data in the chart for males and females.\n
\n
\n
\n
\n
\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
\n
\n (g)\n
\n
\n
\n State the relationship between activity inequality and obesity shown in the scattergraph.\n
\n
\n
\n
\n
\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",
+ "Markscheme": "
\n (a)\n
\n
\n Japan: 6000\n \n and\n \n USA: 4000;\n \n (both needed)\n \n
\n
\n
\n (a)\n
\n
\n Japan: 6000\n \n and\n \n USA: 4000;\n \n (both needed)\n \n
\n
\n
\n (b)\n
\n
\n - \n climate/temperature/light consistent throughout year in equatorial but seasonal variation in boreal;\n
\n - \n conditions suitable for photosynthesis throughout the year in equatorial but not in boreal;\n
\n - \n temperatures higher/growing season longer in equatorial versus lower/shorter in boreal;\n
\n - \n water frozen/unavailable in boreal during winter whereas always available in equatorial;\n
\n - \n shorter daylengths in winter in boreal (than those months in equatorial so lower LAI);\n
\n - \n boreal LAI higher (than equatorial) in July due to longer daylengths;\n
\n - \n equatorial trees/plants are evergreen / boreal trees/plants are deciduous/have less/no leaves in winter;\n
\n - \n variation in angle of light rays (between different latitudes);\n
\n
\n
\n
\n (c)\n
\n
\n - \n decreases in LAI during El Niño\n
\n \n OR\n \n
\n increases in LAI between El Niño events;\n \n - \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 \n - \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 \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
\n (d)\n
\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
\n (i)\n
\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
\n (ii)\n
\n
\n - \n more\n \n photosynthesis\n \n (with higher carbon dioxide concentration);\n
\n - \n more plant growth/more (plant) biomass/more leaves/more plants;\n
\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
\n (e)\n
\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
\n (f)\n
\n
\n \n (any order)\n \n
\n
\n - \n obesity causes people to be less active/take fewer steps;\n
\n - \n people who are less active/take fewer steps (are more likely to) become obese;\n
\n - \n People who are not obese tend to have healthier habits, including walking more;\n
\n
\n
\n
\n
\n \n Accept hypothesis and a null hypothesis for the two.\n \n \n
\n \n
\n
\n
\n (g)\n
\n
\n as activity inequality rises percentage obesity rises\n
\n \n OR\n \n
\n Positive/direct correlation/relationship;\n
\n
\n
\n (h)\n
\n
\n - \n use public education to encourage people to walk more/become more active;\n
\n - \n improve city design to improve walkability;\n
\n - \n reduce distances between homes / shops / workplaces / parks;\n
\n - \n more sidewalks / make it easier for pedestrians to cross roads / other specific measure;\n
\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",
+ "topics": [
+ "b-form-and-function",
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "b3-3-9-reasons-for-locomotion",
+ "b3-3-muscle-and-motility-(hl-only)",
+ "d4-3-1-anthropogenic-causes-of-climate-change",
+ "d4-3-climate-change"
+ ]
+ },
+ {
+ "question_id": "23M.2.SL.TZ1.15",
+ "Question": "
\n
\n (a)\n
\n
\n
\n Identify the trophic level of sea lions. [\n
\n
\n
\n
\n
\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
\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",
+ "Markscheme": "
\n (a)\n
\n
\n secondary consumer / third trophic level/ trophic level 3 / 3;\n
\n
\n
\n (b)\n
\n
\n - \n energy content in biomass/all organisms of each trophic level;\n
\n - \n size of study area included;\n
\n - \n over period of time / per year;\n
\n
\n
\n
\n (c)\n
\n
\n orca is in different trophic levels depending on its food source;\n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "c-interaction-and-interdependence"
+ ],
+ "subtopics": [
+ "c4-2-10-classification-of-organisms-into-trophic-levels",
+ "c4-2-11-construction-of-energy-pyramids",
+ "c4-2-12-reductions-in-energy-availability-at-each-successive-stage-in-food-chains-due-to-large-energy-losses-between-trophic-levels",
+ "c4-2-transfers-of-energy-and-matter"
+ ]
+ },
+ {
+ "question_id": "23M.2.SL.TZ1.16",
+ "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
\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",
+ "Markscheme": "
\n (a)\n
\n
\n - \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 \n - \n compete with local/endemic species for nutrients/habitat;\n
\n - \n may cause (endemic) species to become extinct/reduction in numbers;\n
\n
\n
\n
\n (b)\n
\n
\n - \n (before 2002) the cactus moth had abundant food so the population grew exponentially;\n
\n - \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 \n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "b-form-and-function",
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "b4-2-10-adaptations-of-predators-for-finding-catching-and-killing-prey-and-of-prey-animals-for-resisting-predation",
+ "b4-2-ecological-niches",
+ "d4-2-11-restoration-of-natural-processes-in-ecosystems-by-rewilding",
+ "d4-2-stability-and-change"
+ ]
+ },
+ {
+ "question_id": "23M.2.SL.TZ1.17",
+ "Question": "
\n
\n (a)\n
\n
\n
\n Suggest a reason for the loss of bird habitats.\n
\n
\n
\n
\n
\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
\n
\n (c)\n
\n
\n
\n Distinguish between species richness and evenness as components of biodiversity.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n - \n deforestation/forest fires;\n
\n - \n clearing land for houses/farming/growth of cities;\n
\n
\n
\n
\n (b)\n
\n
\n - \n the amphibians are kept in their natural habitat;\n
\n \n \n OR\n \n \n
\n preserves habitat/resources for amphibians;\n \n - \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 \n
\n
\n
\n (c)\n
\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",
+ "topics": [
+ "a-unity-and-diversity"
+ ],
+ "subtopics": [
+ "a4-1-9-adaptive-radiation-as-a-source-of-biodiversity",
+ "a4-1-evolution-and-speciation",
+ "a4-2-6-causes-of-the-current-biodiversity-crisis",
+ "a4-2-7-need-for-several-approaches-to-conservation-of-biodiversity",
+ "a4-2-conservation-of-biodiversity"
+ ]
+ },
+ {
+ "question_id": "23M.2.SL.TZ1.18",
+ "Question": "
\n
\n (a)\n
\n
\n
\n Label with a P on the\n \n -axis the level of commercial sea fishing activity that would result in maximum sustainability.\n
\n
\n
\n
\n
\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
\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
\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",
+ "Markscheme": "
\n (a)\n
\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
\n (b)\n
\n
\n fish are being caught faster than they can reproduce;\n
\n
\n
\n (c)\n
\n
\n - \n requires agreements/policies/enforcement between countries;\n
\n - \n commercial companies compete to increase profit;\n
\n
\n
\n
\n (d)\n
\n
\n - \n random sample is captured and marked/tagged (in a manner that will not harm fish);\n
\n - \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 \n - \n second sample is captured and both the total number and the number of marked fish counted;\n
\n - \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 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 \n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "c-interaction-and-interdependence",
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "c4-1-4-capture-mark-release-recapture-and-the-lincoln-index-to-estimate-population-size-for-motile-organisms",
+ "c4-1-populations-and-communities",
+ "d4-2-6-assessing-sustainability-of-resource-harvesting-from-natural-ecosystems",
+ "d4-2-stability-and-change"
+ ]
+ },
+ {
+ "question_id": "23M.2.SL.TZ1.20",
+ "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
\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",
+ "Markscheme": "
\n (a)\n
\n
\n - \n both have increased CHD with increasing cholesterol;\n
\n - \n men always higher incidence CHD than women at each level (of cholesterol);\n
\n
\n
\n \n Accept vice versa\n \n
\n
\n
\n (b)\n
\n
\n - \n depends on the type of cholesterol/ratio of HDL to LDL/some types of cholesterol do not increase the chance of CHD;\n
\n - \n may not indicate CHD if lack other risk factors for CHD;\n
\n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "b-form-and-function"
+ ],
+ "subtopics": [
+ "b3-2-6-causes-and-consequences-of-occlusion-of-the-coronary-arteries",
+ "b3-2-transport"
+ ]
+ },
+ {
+ "question_id": "23M.2.SL.TZ1.3",
+ "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
\n
\n (c)\n
\n
\n
\n Explain the function of the left ventricle.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\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
\n (a)\n
\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
\n (c)\n
\n
\n - \n contracts to generate high pressure / pumps blood at high pressure;\n
\n - \n pump blood (through the aorta) to all parts of the body (apart from the lungs);\n
\n - \n receives blood from the left atrium;\n
\n - \n contraction is stimulated by the AV node;\n
\n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "b-form-and-function"
+ ],
+ "subtopics": [
+ "b3-2-15-adaptations-of-the-mammalian-heart-for-delivering-pressurized-blood-to-the-arteries",
+ "b3-2-transport"
+ ]
+ },
+ {
+ "question_id": "23M.2.SL.TZ1.4",
+ "Question": "
\n
\n (a.i)\n
\n
\n
\n State how many water molecules are shown in the diagram.\n
\n
\n
\n
\n
\n
\n (i)\n
\n
\n
\n State how many water molecules are shown in the diagram.\n
\n
\n
\n
\n
\n
\n (ii)\n
\n
\n
\n Identify the interactions that are shown between the water molecules.\n
\n
\n
\n
\n
\n
\n (i)\n
\n
\n
\n With reference to the diagram, explain how water in sweat evaporates.\n
\n
\n
\n
\n
\n
\n (ii)\n
\n
\n
\n Outline the reasons for secretion of sweat in humans.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a.i)\n
\n
\n (i)\n
\n
\n (ii)\n
\n
\n hydrogen bonds/H bond;\n
\n
\n
\n (i)\n
\n
\n - \n heat increases molecular motion/vibration;\n
\n - \n (hydrogen) bonds break/bonds between water molecules break;\n
\n - \n water evaporation is separation of water molecules/water changes from liquid to gas/vapour;\n
\n - \n heat removed from skin surface/body;\n
\n
\n
\n
\n
\n
\n (ii)\n
\n
\n - \n cooling/removal of heat/lowering body temperature;\n
\n - \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 \n
\n
\n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "a-unity-and-diversity",
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "a1-1-2-hydrogen-bonds-as-a-consequence-of-the-polar-covalent-bonds-within-water-molecules",
+ "a1-1-water",
+ "d3-3-6-thermoregulation-mechanisms-in-humans",
+ "d3-3-homeostasis"
+ ]
+ },
+ {
+ "question_id": "23M.2.SL.TZ1.5",
+ "Question": "
\n
\n (a)\n
\n
\n
\n Explain the conclusion that can be drawn from Cross 1.\n
\n
\n
\n
\n
\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
\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
\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",
+ "Markscheme": "
\n (a)\n
\n
\n - \n allele/trait/gene for banded is dominant/allele for unbanded is recessive;\n
\n - \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 \n - \n both parents are heterozygous;\n
\n
\n
\n \n Accept answers given in the form of Punnet squares.\n \n
\n
\n
\n
\n
\n (b)\n
\n
\n - \n (1:1 ratio) in cross 2 as banded parent is heterozygous/has one copy of each allele;\n
\n - \n (no unbanded offspring) in cross 3 as banded parent is homozygous/has two alleles for banded;\n
\n - \n (in crosses 2 and 3) banded parental phenotypes are the same but their genotypes are different;\n
\n
\n
\n
\n
\n
\n
\n
\n (c)\n
\n
\n \n \n \n 0\n | \n \n 79\n | \n \n 0.000/0\n | \n
\n \n
\n
\n \n All three parts of the answer must be correct for the mark to be awarded.\n \n
\n
\n
\n (d)\n
\n
\n - \n natural selection could favour one type over the other;\n
\n - \n greater survival of one type\n
\n \n OR\n \n
\n one type better camouflaged than the other type;\n \n - \n one type more attractive during courtship/mate selection;\n
\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",
+ "topics": [
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "d3-2-5-effects-of-dominant-and-recessive-alleles-on-phenotype",
+ "d3-2-inheritance"
+ ]
+ },
+ {
+ "question_id": "23M.2.SL.TZ1.6",
+ "Question": "
\n
\n (a)\n
\n
\n
\n Outline the sequence of events that occurs during mitosis.\n
\n
\n
\n
\n
\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",
+ "Markscheme": "
\n (a)\n
\n
\n - \n supercoiling/condensation of\n \n chromosomes\n \n ;\n
\n - \n breakup of nuclear membrane;\n
\n - \n growth of spindle/microtubules;\n
\n - \n attachment of spindle/microtubules to chromosomes/centromeres;\n
\n - \n chromosomes line up at the equator/middle\n
\n - \n division of centromeres;\n
\n - \n separation of sister chromatids/chromosomes\n
\n \n OR\n \n
\n sister chromatids/chromosomes move to opposite poles;\n \n - \n reformation of nuclear membranes around chromosomes at each pole;\n
\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
\n (a)\n
\n
\n - \n supercoiling/condensation of\n \n chromosomes\n \n ;\n
\n - \n breakup of nuclear membrane;\n
\n - \n growth of spindle/microtubules;\n
\n - \n attachment of spindle/microtubules to chromosomes/centromeres;\n
\n - \n chromosomes line up at the equator/middle\n
\n - \n division of centromeres;\n
\n - \n separation of sister chromatids/chromosomes\n
\n \n OR\n \n
\n sister chromatids/chromosomes move to opposite poles;\n \n - \n reformation of nuclear membranes around chromosomes at each pole;\n
\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
\n (c)\n
\n
\n - \n gene/genetic information on Y chromosome causes embryo to develop testes;\n
\n - \n (developing) testes in embryo secrete testosterone;\n
\n - \n testosterone causes male genitalia/penis to develop;\n
\n
\n
\n
\n
\n \n Accept SRY gene in mp-a\n \n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "d2-1-7-phases-of-mitosis",
+ "d2-1-cell-and-nuclear-division",
+ "d3-2-11-sex-determination-in-humans-and-inheritance-of-genes-on-sex-chromosomes",
+ "d3-2-inheritance"
+ ]
+ },
+ {
+ "question_id": "23M.2.SL.TZ1.7",
+ "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
\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
\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",
+ "Markscheme": "
\n (a)\n
\n
\n - \n binomial naming\n
\n \n \n OR\n \n \n
\n genus and species name;\n \n - \n plants constitute a kingdom\n
\n - \n plants are eukaryotes/belong to the domain eukaryota\n
\n - \n classified using a hierarchy of taxa\n
\n \n \n OR\n \n \n
\n kingdom, phylum, class, order, family, genus, species\n \n - \n bryophyta/filicinophyta/coniferophyte/angiospermophyta is a\n \n phylum\n \n (of plants);\n
\n - \n bryophytes have only rhizoids/spores (produced in a capsule)/no roots/ no vascular tissue;\n
\n - \n filicinophytes have stems/roots/xylem-phloem/reproduce by spores/leaves that uncurl; but no seeds\n
\n - \n coniferophytes have seeds in cones/ vascular tissue/xylem-phloem/cambium/ but no flowers/no fruits\n
\n - \n angiospermophytes have flowers/produce seeds/produce fruits/vascular tissue/xylem-phloem;\n
\n - \n named example showing of the classification of a plant from species to domain or vice versa\n
\n - \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 \n - \n use a dichotomous key to discriminate among plant features\n
\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
\n (a)\n
\n
\n - \n pairing/synapsis of homologous chromosomes / homologous chromosomes form bivalents;\n
\n - \n crossing over / chromatid breaks then rejoins to non-sister chromatid;\n
\n - \n exchange of DNA/alleles/genetic information between chromatids/chromosomes;\n
\n - \n recombination / new combinations of alleles/genes generated;\n
\n - \n condensation/shortening/thickening/supercoiling of chromatids/chromosomes;\n
\n - \n formation of a chiasma where crossing over occurred;\n
\n
\n
\n
\n (b)\n
\n
\n - \n absorption/diffusion of carbon dioxide from the atmosphere/water by plants;\n
\n - \n \n photosynthesis\n \n fixes/converts carbon (dioxide) to carbohydrates/carbon compounds;\n
\n - \n respiration in plants converts carbohydrates/carbon compounds to carbon dioxide;\n
\n - \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 \n - \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 \n - \n forest fires/combustion of plants converts (carbohydrates/carbon compounds) to carbon dioxide;\n
\n - \n plants are eaten by consumers (moving carbon in the food chain)\n
\n - \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 \n - \n Plants act as carbon sinks/reservoirs\n
\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",
+ "topics": [
+ "a-unity-and-diversity",
+ "c-interaction-and-interdependence",
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "a3-2-2-difficulties-classifying-organisms-into-the-traditional-hierarchy-of-taxa",
+ "a3-2-classification-and-cladistics-(hl-only)",
+ "c4-2-17-constructing-carbon-cycle-diagrams",
+ "c4-2-transfers-of-energy-and-matter",
+ "d2-1-16-consequences-of-mutations-in-genes-that-control-the-cell-cycle",
+ "d2-1-cell-and-nuclear-division"
+ ]
+ },
+ {
+ "question_id": "23M.2.SL.TZ2.1",
+ "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
\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
\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
\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
\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
\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
\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
\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
\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
\n
\n (i)\n
\n
\n
\n Using the data, predict the effect of universal PCV vaccination in LMICs.\n
\n
\n
\n
\n
\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",
+ "Markscheme": "
\n (a)\n
\n
\n - \n nearly half is\n \n Bacteroides\n \n / more\n \n Bacteroides\n \n (than other enterotypes);\n
\n - \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 \n - \n only 40 % other taxa / fewer other taxa (than other enterotypes) / less overall diversity (of taxa);\n
\n
\n
\n
\n
\n
\n (a)\n
\n
\n - \n nearly half is\n \n Bacteroides\n \n / more\n \n Bacteroides\n \n (than other enterotypes);\n
\n - \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 \n - \n only 40 % other taxa / fewer other taxa (than other enterotypes) / less overall diversity (of taxa);\n
\n
\n
\n
\n
\n
\n (b)\n
\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
\n (i)\n
\n
\n 89%;\n
\n
\n \n Allow 88 to 91 %.\n \n
\n
\n
\n (ii)\n
\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
\n (d)\n
\n
\n - \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 \n - \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 \n - \n increased reduction in the number of deaths from 2010 onwards;\n
\n - \n still large number of deaths/large number of children unvaccinated in 2015;\n
\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
\n (e)\n
\n
\n - \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 \n - \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
\n - \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
\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
\n (f)\n
\n
\n - \n 2 – 5\n \n years\n \n ;\n
\n - \n higher number/value/percentage/attributable fraction for 2 – 5 years (than 0 – 5years);\n
\n
\n
\n
\n
\n
\n (g)\n
\n
\n - \n highest attributed fraction (in both age groups) is in cases where antibiotic used;\n
\n - \n ARI cases due to\n \n S. pneumoniae\n \n can be severe so antibiotics are often prescribed;\n
\n - \n all cases include other causes / viral ARI which may not require antibiotics;\n
\n - \n antibiotics administered without prescription or physician consultation/to reduce symptoms;\n
\n
\n
\n \n Mpa: Comparative terms expected (do not award mp for just stating values).\n \n
\n
\n
\n (h)\n
\n
\n - \n higher population in lower-middle income countries/subgroup (compared to the other 2 subgroups);\n
\n - \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 \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
\n (i)\n
\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
\n (j)\n
\n
\n - \n less use of antibiotics;\n
\n - \n less antibiotic resistance (in pathogens) / antibiotics more successful at treating infectious/bacterial diseases;\n
\n - \n decrease in health care costs / less money spent on antibiotics;\n
\n - \n decreased mortality / protection of immune-deficient patients/non-vaccinated population/ achieve herd immunity;\n
\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",
+ "topics": [
+ "a-unity-and-diversity",
+ "c-interaction-and-interdependence"
+ ],
+ "subtopics": [
+ "a2-2-5-prokaryote-cell-structure",
+ "a2-2-cell-structure",
+ "c3-2-1-pathogens-as-the-cause-of-infectious-diseases",
+ "c3-2-16-vaccines-and-immunization",
+ "c3-2-defence-against-disease"
+ ]
+ },
+ {
+ "question_id": "23M.2.SL.TZ2.18",
+ "Question": "
\n
\n (i)\n
\n
\n
\n State the relationship between DDE concentration and eggshell thickness.\n
\n
\n
\n
\n
\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
\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
\n
\n (c)\n
\n
\n
\n Outline the biomagnification of DDE in brown pelicans.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (i)\n
\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
\n (ii)\n
\n
\n more risk of predation/ eggs break more easily/fewer chicks hatch;\n
\n
\n \n \n OWTTE\n \n \n
\n
\n
\n (b)\n
\n
\n - \n California, as most eggs have a high level of DDE / most eggshells are thinning;\n
\n - \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 \n
\n
\n
\n (c)\n
\n
\n - \n DDE accumulates in (fat tissues of) organisms/bioaccumulation;\n
\n - \n (brown) pelicans/birds feed on fish/organisms (that have accumulated DDE);\n
\n - \n (DDE) is not excreted;\n
\n - \n (DDE) concentration\n \n increases\n \n as trophic level increases;\n
\n - \n (brown) pelicans are in a high trophic level (so have a high accumulation);\n
\n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "d4-2-9-biomagnification-of-pollutants-in-natural-ecosystems",
+ "d4-2-stability-and-change"
+ ]
+ },
+ {
+ "question_id": "23M.2.SL.TZ2.2",
+ "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
\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
\n
\n (b)\n
\n
\n
\n Using a Punnett grid, explain the results of this cross.\n
\n
\n
\n
\n
\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",
+ "Markscheme": "
\n (a)\n
\n
\n 12;\n
\n
\n \n No alternative.\n \n
\n
\n
\n (a)\n
\n
\n (b)\n
\n
\n - \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
\n - \n F\n \n 2\n \n genotypes shown as PP, Pp, pP and pp;\n
\n - \n F\n \n 2\n \n phenotypes indicated for each genotype on the Punnett grid / 3 purple to 1 white ratio indicated;\n
\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
\n (c)\n
\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",
+ "topics": [
+ "b-form-and-function",
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "b1-2-1-generalized-structure-of-an-amino-acid",
+ "b1-2-proteins",
+ "d3-1-8-sexual-reproduction-in-flowering-plants",
+ "d3-1-reproduction",
+ "d3-2-2-methods-for-conducting-genetic-crosses-in-flowering-plants",
+ "d3-2-inheritance"
+ ]
+ },
+ {
+ "question_id": "23M.2.SL.TZ2.20",
+ "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
\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
\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",
+ "Markscheme": "
\n (a)\n
\n
\n - \n excess nutrients/eutrophication;\n
\n - \n excessive growth of algae/algal blooms;\n
\n - \n blocking of sun prevents photosynthesis;\n
\n - \n increased decomposition of algae/organisms;\n
\n - \n increased biochemical oxygen demand/BOD;\n
\n - \n other organisms/fish die due to lack of oxygen;\n
\n
\n
\n
\n (b)\n
\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
\n (c)\n
\n
\n - \n pitcher plants consume more insects (at different sampling sites);\n
\n - \n larger insects contain more nitrogen;\n
\n - \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 \n - \n use of N/NPK fertilizers\n
\n \n \n OR\n \n \n
\n leaching of N in different sites;\n \n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "d4-2-8-eutrophication-of-aquatic-and-marine-ecosystems-due-to-leaching",
+ "d4-2-stability-and-change"
+ ]
+ },
+ {
+ "question_id": "23M.2.SL.TZ2.3",
+ "Question": "
\n
\n (a)\n
\n
\n
\n State one cause of lung cancer.\n
\n
\n
\n
\n
\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
\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
\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",
+ "Markscheme": "
\n (a)\n
\n
\n - \n smoking/tobacco;\n
\n - \n passive smoking;\n
\n - \n Radon/other radiation;\n
\n - \n exposure to arsenic/asbestos/smoke from coal burning/fires/silica/rock dust/vehicle exhaust fumes/nitrogen oxides;\n
\n
\n
\n
\n
\n
\n (a)\n
\n
\n - \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
\n - \n II is the anther and produces/contains/releases\n \n pollen\n \n ;\n
\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
\n (b)\n
\n
\n - \n \n female\n \n gamete/ovule is produced/meiosis to produce ovules/ovule develops;\n
\n - \n Fertilisation occurs\n
\n \n \n OR\n \n \n
\n fusion/union of male and female gametes/nuclei;\n \n - \n development of seed (from fertilised ovule);\n
\n - \n development of fruit (from the whole ovary);\n
\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
\n (c)\n
\n
\n - \n attracts an insect/animal/which pollinates the flower;\n
\n - \n attracts a pollinator;\n
\n
\n
\n \n Mpa: Both parts of the sentence are needed to award the point.\n \n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "d2-1-17-differences-between-tumours-in-rates-of-cell-division-and-growth-and-in-the-capacity-for-metastasis-and-invasion-of-neighbouring-tissue",
+ "d2-1-cell-and-nuclear-division",
+ "d3-1-8-sexual-reproduction-in-flowering-plants",
+ "d3-1-9-features-of-an-insect-pollinated-flower",
+ "d3-1-reproduction"
+ ]
+ },
+ {
+ "question_id": "23M.2.SL.TZ2.4",
+ "Question": "
\n
\n (a.i)\n
\n
\n
\n State with a reason whether pangolins are autotrophic or heterotrophic.\n
\n
\n
\n
\n
\n
\n (i)\n
\n
\n
\n State with a reason whether pangolins are autotrophic or heterotrophic.\n
\n
\n
\n
\n
\n
\n (ii)\n
\n
\n
\n Explain what information is needed to find the trophic level of pangolins.\n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n
\n Outline evidence for evolution from the limbs of mammals such as pangolins.\n
\n
\n
\n
\n
\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",
+ "Markscheme": "
\n (a.i)\n
\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
\n (i)\n
\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
\n (ii)\n
\n
\n - \n what (prey) it eats/feeds on/ stomach content;\n
\n - \n the trophic level of what (prey) it eats/feeds on/the trophic level of ants/termites;\n
\n - \n trophic level is the position an organism occupies in the food chain/web;\n
\n
\n
\n \n Do not award points for indicating that predator information is needed.\n \n
\n
\n
\n (b)\n
\n
\n - \n pentadactyl;\n
\n - \n homologous with limbs of other vertebrates;\n
\n - \n due to common ancestry;\n
\n - \n adaptation;\n
\n
\n
\n
\n
\n
\n (ii)\n
\n
\n 38\n
\n \n \n OR\n \n \n
\n 19\n \n pairs\n \n ;\n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "a-unity-and-diversity",
+ "c-interaction-and-interdependence",
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "a4-1-4-evidence-for-evolution-from-homologous-structures",
+ "a4-1-evolution-and-speciation",
+ "c4-2-10-classification-of-organisms-into-trophic-levels",
+ "c4-2-6-autotrophs-as-organisms-that-use-external-energy-sources-to-synthesize-carbon-compounds-from-simple-inorganic-substances",
+ "c4-2-transfers-of-energy-and-matter",
+ "d3-2-1-production-of-haploid-gametes-in-parents-and-their-fusion-to-form-a-diploid-zygote-as-the-means-of-inheritance",
+ "d3-2-inheritance"
+ ]
+ },
+ {
+ "question_id": "23M.2.SL.TZ2.6",
+ "Question": "
\n
\n (a)\n
\n
\n
\n Explain how temperature affects enzymes.\n
\n
\n
\n
\n
\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",
+ "Markscheme": "
\n (a)\n
\n
\n - \n speed of reaction/catalysis increases as temperature rises;\n
\n - \n faster molecular motion so more collisions between substrate and active site;\n
\n - \n denaturation at higher temperatures;\n
\n - \n (denaturation causes) shape/conformation/structure of enzyme/active site altered/damaged;\n
\n - \n an enzyme works fastest at its optimum temperature;\n
\n - \n inactivation at lower temperatures (due to very few collisions);\n
\n - \n sketch graph to model the effect of temperature on enzyme activity;\n
\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
\n (a)\n
\n
\n - \n speed of reaction/catalysis increases as temperature rises;\n
\n - \n faster molecular motion so more collisions between substrate and active site;\n
\n - \n denaturation at higher temperatures;\n
\n - \n (denaturation causes) shape/conformation/structure of enzyme/active site altered/damaged;\n
\n - \n an enzyme works fastest at its optimum temperature;\n
\n - \n inactivation at lower temperatures (due to very few collisions);\n
\n - \n sketch graph to model the effect of temperature on enzyme activity;\n
\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
\n (c)\n
\n
\n - \n release of carbon dioxide;\n
\n - \n combustion of fossil fuels produces carbon dioxide;\n
\n - \n forest fires (caused by humans) produce carbon dioxide;\n
\n - \n deforestation reduces carbon dioxide uptake by photosynthesis;\n
\n - \n release of methane;\n
\n - \n from cattle/sheep/ruminant digestive systems / other verified source of anthropogenic methane;\n
\n - \n greenhouse effect / carbon dioxide/methane is a greenhouse gas;\n
\n - \n carbon dioxide/methane allow short wave radiation in sunlight to pass through the atmosphere;\n
\n - \n longer wave/infra-red radiation emitted by the warmed Earth’s surface;\n
\n - \n carbon dioxide/methane absorbs/reflects back longer wave/infra-red radiation;\n
\n
\n
\n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "c-interaction-and-interdependence",
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "c1-1-8-effects-of-temperature-ph-and-substrate-concentration-on-the-rate-of-enzyme-activity",
+ "c1-1-enzymes-and-metabolism",
+ "d4-3-1-anthropogenic-causes-of-climate-change",
+ "d4-3-climate-change"
+ ]
+ },
+ {
+ "question_id": "23M.2.SL.TZ2.7",
+ "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
\n
\n (b)\n
\n
\n
\n Explain how animal cells produce the ATP that they need.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n - \n plasma membrane is thin layer forming outer boundary;\n
\n - \n cytoplasm fills space between membrane and nucleus;\n
\n - \n nucleus enclosed in nuclear membrane / nuclear membrane enclosing nucleus;\n
\n - \n chromosomes inside the nucleus/ visible during mitosis/ as rods (of condensed DNA);\n
\n - \n mitochondria with cristae/double membranes;\n
\n - \n (80S) ribosomes seen as dots free in cytoplasm/attached to rough ER;\n
\n - \n endoplasmic reticulum is a network interconnected tubes/ membranes /rough ER has ribosomes/ smooth ER does not;\n
\n - \n Golgi apparatus with stack of sacs/cisternae/curved or folded membranes/vesicles budding off;\n
\n - \n vesicles which are small membrane sacs;\n
\n - \n lysosome which contains enzymes/which is densely staining;\n
\n - \n any other organelle that would be visible correctly described;\n
\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
\n (a)\n
\n
\n - \n plasma membrane is thin layer forming outer boundary;\n
\n - \n cytoplasm fills space between membrane and nucleus;\n
\n - \n nucleus enclosed in nuclear membrane / nuclear membrane enclosing nucleus;\n
\n - \n chromosomes inside the nucleus/ visible during mitosis/ as rods (of condensed DNA);\n
\n - \n mitochondria with cristae/double membranes;\n
\n - \n (80S) ribosomes seen as dots free in cytoplasm/attached to rough ER;\n
\n - \n endoplasmic reticulum is a network interconnected tubes/ membranes /rough ER has ribosomes/ smooth ER does not;\n
\n - \n Golgi apparatus with stack of sacs/cisternae/curved or folded membranes/vesicles budding off;\n
\n - \n vesicles which are small membrane sacs;\n
\n - \n lysosome which contains enzymes/which is densely staining;\n
\n - \n any other organelle that would be visible correctly described;\n
\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
\n (b)\n
\n
\n - \n respiration/cell respiration;\n
\n - \n energy released from glucose/lipids/organic compounds;\n
\n - \n anaerobic respiration does not require oxygen;\n
\n - \n lactate is produced in anaerobic respiration/word equation for anaerobic respiration;\n
\n - \n oxygen used in aerobic respiration;\n
\n - \n carbon dioxide and water produced in aerobic respiration/word equation for aerobic respiration;\n
\n - \n mitochondria used for aerobic respiration;\n
\n - \n larger yield of ATP from aerobic than anaerobic respiration;\n
\n
\n
\n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "a-unity-and-diversity",
+ "c-interaction-and-interdependence"
+ ],
+ "subtopics": [
+ "a2-2-10-cell-types-and-cell-structures-viewed-in-light-and-electron-micrographs",
+ "a2-2-cell-structure",
+ "c1-2-4-cell-respiration-as-a-system-for-producing-atp-within-the-cell-using-energy-released-from-carbon-compounds",
+ "c1-2-cell-respiration"
+ ]
+ },
+ {
+ "question_id": "SPM.1B.SL.TZ0.2",
+ "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
\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
\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
\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",
+ "Markscheme": "
\n (a)\n
\n
\n - \n palisade mesophyll;\n
\n - \n spongy mesophyll;\n
\n - \n lower epidermis;\n
\n - \n upper epidermis;\n
\n - \n xylem/phloem/vascular bundle;\n
\n
\n
\n \n 1 mark for each correctly labelled tissue shown as a layer in proportion.\n \n
\n
\n
\n (a)\n
\n
\n - \n palisade mesophyll;\n
\n - \n spongy mesophyll;\n
\n - \n lower epidermis;\n
\n - \n upper epidermis;\n
\n - \n xylem/phloem/vascular bundle;\n
\n
\n
\n \n 1 mark for each correctly labelled tissue shown as a layer in proportion.\n \n
\n
\n
\n (b)\n
\n
\n - \n correct measurement of the line on the image (\n \n /\n \n 1mm);\n
\n - \n correct calculation and including units;\n
\n
\n
\n \n Allow ECF – ruler measurements\n \n /\n \n 1mm\n \n
\n
\n
\n (c)\n
\n
\n - \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 \n - \n it is easier to locate the most interesting part of the specimen with a low power objective lens;\n
\n - \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
\n - \n reduced risk of cracking the slide;\n
\n
\n
\n
\n (d)\n
\n
\n - \n double layer of palisade cells;\n
\n - \n palisade layer on upper surface;\n
\n - \n dimensions of palisade cells maximize light absorption;\n
\n - \n thin/transparent epidermis/cuticle;\n
\n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "a-unity-and-diversity",
+ "b-form-and-function"
+ ],
+ "subtopics": [
+ "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",
+ "a2-2-cell-structure",
+ "b3-1-7-adaptations-for-gas-exchange-in-leaves",
+ "b3-1-8-distribution-of-tissues-in-a-leaf",
+ "b3-1-gas-exchange"
+ ]
+ },
+ {
+ "question_id": "SPM.2.HL.TZ0.10",
+ "Question": "
\n
\n (a)\n
\n
\n
\n Outline the role of UV radiation as a mutagen.\n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n
\n Explain how the function of DNA is linked to its molecular structure.\n
\n
\n
\n
\n
\n
\n (c)\n
\n
\n
\n Describe the use of gene knockout technology in research.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n - \n affects/damages/causes change in oncogenes/errors in DNA repair;\n
\n - \n UV radiation might alter complementary base pairing/break hydrogen bonds/fuse bases;\n
\n - \n double helix may uncoil;\n
\n - \n strands may separate/break;\n
\n - \n DNA sequence may be altered/DNA bases may re-connect to different bases after separating;\n
\n - \n DNA strand may break into pieces / fragments of DNA may be lost;\n
\n
\n
\n
\n (a)\n
\n
\n - \n affects/damages/causes change in oncogenes/errors in DNA repair;\n
\n - \n UV radiation might alter complementary base pairing/break hydrogen bonds/fuse bases;\n
\n - \n double helix may uncoil;\n
\n - \n strands may separate/break;\n
\n - \n DNA sequence may be altered/DNA bases may re-connect to different bases after separating;\n
\n - \n DNA strand may break into pieces / fragments of DNA may be lost;\n
\n
\n
\n
\n (b)\n
\n
\n - \n DNA base sequence provides information;\n
\n - \n gene expression / genes provides a template for the construction of a protein;\n
\n - \n transcription occurs / mRNA is built using DNA as a template;\n
\n - \n DNA nucleotide structure described/sugar and phosphate and base;\n
\n - \n polymer of nucleotides makes a DNA strand;\n
\n - \n DNA has two anti-parallel strands;\n
\n - \n complementary base pairs/A pairs with T and C with G;\n
\n - \n strands linked by hydrogen bonding between bases;\n
\n - \n double helix shape / helix held by hydrogen bonds;\n
\n
\n
\n \n Accept points in clearly labelled diagram\n \n
\n
\n
\n (c)\n
\n
\n - \n gene knockout technology is a genetic engineering technique/intentional alteration in the sequence of a gene;\n
\n - \n making a gene inactive;\n
\n - \n using site specific nucleases / CRISPR;\n
\n - \n researcher observes changes in phenotype of organism;\n
\n - \n allows researcher to determine function of the gene;\n
\n - \n entire library of knockout organisms exists;\n
\n - \n made available to researchers;\n
\n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "a-unity-and-diversity",
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "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",
+ "a1-2-nucleic-acids",
+ "d1-3-4-causes-of-gene-mutation",
+ "d1-3-8-gene-knockout-as-a-technique-for-investigating-the-function-of-a-gene-by-changing-it-to-make-it-inoperative",
+ "d1-3-mutations-and-gene-editing"
+ ]
+ },
+ {
+ "question_id": "SPM.2.HL.TZ0.7",
+ "Question": "
\n
\n (a)\n
\n
\n
\n Identify the recombinant phenotypes amongst the offspring.\n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n
\n Explain whether these results fit the predicted Mendelian ratios for this cross.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n brown body vestigial wings\n \n \n AND\n \n \n black body, normal wings\n
\n
\n
\n (a)\n
\n
\n brown body vestigial wings\n \n \n AND\n \n \n black body, normal wings\n
\n
\n
\n (b)\n
\n
\n - \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 \n - \n suggests linkage\n
\n \n \n OR\n \n \n
\n small numbers so could be a result of differential survival;\n \n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "d3-2-17-punnett-grids-for-predicting-genotypic-and-phenotypic-ratios-in-dihybrid-crosses-involving-pairs-of-unlinked-autosomal-genes",
+ "d3-2-20-recombinants-in-crosses-involving-two-linked-or-unlinked-genes",
+ "d3-2-inheritance"
+ ]
+ },
+ {
+ "question_id": "SPM.2.HL.TZ0.8",
+ "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
\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
\n
\n (c)\n
\n
\n
\n Describe the barriers that exist to hybridization between species.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n - \n vaccinations are specific to a specific disease;\n
\n - \n vaccines contain non-self antigens/antigens from pathogens;\n
\n - \n can be live relative/attenuated version of the virus;\n
\n - \n trigger a primary immune response (without causing the disease);\n
\n - \n lymphocytes with specific receptors (are activated and) produce memory cells;\n
\n - \n (memory cells) cause a faster production of antibodies on a second exposure/exposure to the disease;\n
\n - \n (memory cells) provide long term immunity;\n
\n
\n
\n
\n (b)\n
\n
\n - \n (during depolarization) Na\n \n +\n \n channels open;\n
\n - \n allowing Na\n \n +\n \n to flow into the axon;\n
\n - \n (during repolarization) K\n \n +\n \n channels open;\n
\n - \n allowing K\n \n +\n \n to flow out of the axon;\n
\n - \n the Na\n \n +\n \n /K\n \n +\n \n pump returns the (axon) membrane to the resting potential;\n
\n - \n by moving 3Na\n \n +\n \n out and 2K\n \n +\n \n in;\n
\n
\n
\n
\n (c)\n
\n
\n - \n courtship behaviour is often complex and unique to a species;\n
\n - \n (at several stages in courtship ritual) rejection occurs if characteristic behaviour not exhibited;\n
\n - \n species-specific egg fertilization;\n
\n - \n compatibility of acrosome with vitelline layer;\n
\n - \n inability of successfully attached wrong species sperm to develop continuity with egg membrane;\n
\n - \n sterility of interspecific hybrids;\n
\n - \n due to differences in chromosome number;\n
\n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "a-unity-and-diversity",
+ "c-interaction-and-interdependence"
+ ],
+ "subtopics": [
+ "a4-1-10-barriers-to-hybridization-and-sterility-of-interspecific-hybrids-as-mechanisms-for-of-preventing-the-mixing-of-alleles-between-species",
+ "a4-1-evolution-and-speciation",
+ "c2-2-3-nerve-impulses-as-action-potentials-that-are-propagated-along-nerve-fibres",
+ "c2-2-neural-signalling"
+ ]
+ },
+ {
+ "question_id": "SPM.2.HL.TZ0.9",
+ "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
\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
\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",
+ "Markscheme": "
\n (a)\n
\n
\n - \n some toxins/DDT are persistent/degrade slowly (once released into the environment);\n
\n - \n (some toxins/DDT) enter the food chain through producers/lower trophic levels;\n
\n - \n (some toxins/DDT) are passed on to higher trophic levels in the food chain;\n
\n - \n (they are) difficult to excrete / are not excreted;\n
\n - \n (they) accumulate in fatty tissues of animals;\n
\n - \n higher trophic levels/top consumers have higher/the highest concentration of pesticides in their bodies;\n
\n - \n they bioaccumulate/biomagnify;\n
\n
\n
\n
\n (a)\n
\n
\n - \n some toxins/DDT are persistent/degrade slowly (once released into the environment);\n
\n - \n (some toxins/DDT) enter the food chain through producers/lower trophic levels;\n
\n - \n (some toxins/DDT) are passed on to higher trophic levels in the food chain;\n
\n - \n (they are) difficult to excrete / are not excreted;\n
\n - \n (they) accumulate in fatty tissues of animals;\n
\n - \n higher trophic levels/top consumers have higher/the highest concentration of pesticides in their bodies;\n
\n - \n they bioaccumulate/biomagnify;\n
\n
\n
\n
\n (b)\n
\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
\n (c)\n
\n
\n - \n lower rate of\n \n aerobic\n \n respiration / inhibits\n \n aerobic\n \n respiration;\n
\n - \n reduced NAD (not oxidised) accumulates;\n
\n - \n fewer/no electrons (from reduced NAD and FADH) to be transported by carriers;\n
\n - \n less/no energy to transfer protons (from matrix to intermembrane space);\n
\n - \n proton gradient cannot be maintained;\n
\n - \n less/no diffusion of protons through ATP synthase;\n
\n - \n ADP is not phosphorylated / less ATP produced / no energy to produce ATP;\n
\n - \n oxygen not binding to protons / accepting electrons / no water formed;\n
\n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "c-interaction-and-interdependence",
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "c1-1-14-allosteric-sites-and-non-competitive-inhibition",
+ "c1-1-enzymes-and-metabolism",
+ "c1-2-16-role-of-oxygen-as-terminal-electron-acceptor-in-aerobic-cell-respiration",
+ "c1-2-cell-respiration",
+ "d4-2-9-biomagnification-of-pollutants-in-natural-ecosystems",
+ "d4-2-stability-and-change"
+ ]
+ },
+ {
+ "question_id": "SPM.2.SL.TZ0.6",
+ "Question": "
\n
\n (a)\n
\n
\n
\n Outline how sex is determined in humans.\n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n
\n Explain how sexual reproduction gives rise to genetic variation.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n - \n genetically determined/determined by (pair of) sex chromosomes/X and Y chromosomes;\n
\n - \n sperm carry either an X or a Y chromosome;\n
\n - \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 \n
\n
\n
\n (a)\n
\n
\n - \n genetically determined/determined by (pair of) sex chromosomes/X and Y chromosomes;\n
\n - \n sperm carry either an X or a Y chromosome;\n
\n - \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 \n
\n
\n
\n (b)\n
\n
\n - \n recombination of parental alleles during fertilization;\n
\n - \n fertilized egg contains a mixture of paternal and maternal chromosomes;\n
\n - \n crossing over/meiosis gives rise to new combinations of alleles;\n
\n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "a-unity-and-diversity",
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "a3-1-7-karyotyping-and-karyograms",
+ "a3-1-diversity-of-organisms",
+ "d1-3-7-mutation-as-a-source-of-genetic-variation",
+ "d1-3-mutations-and-gene-editing",
+ "d4-1-2-roles-of-mutation-and-sexual-reproduction-in-generating-the-variation-on-which-natural-selection-acts",
+ "d4-1-natural-selection"
+ ]
+ },
+ {
+ "question_id": "SPM.2.SL.TZ0.7",
+ "Question": "
\n
\n (a)\n
\n
\n
\n Outline how mutation can lead to cancer.\n
\n
\n
\n
\n
\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
\n
\n (c)\n
\n
\n
\n Explain the role of mutations in evolution.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n - \n mutations are random changes in the sequences of genes/DNA;\n
\n - \n (mutation) may involve addition/deletion/substitution/inversion of DNA bases;\n
\n - \n (mutations) in tumour suppressor genes/oncogenes;\n
\n - \n uncontrolled cell division/mitosis occurs;\n
\n - \n abnormal cells cannot perform their function;\n
\n - \n they divide repeatedly to form tumours;\n
\n
\n
\n
\n (a)\n
\n
\n - \n mutations are random changes in the sequences of genes/DNA;\n
\n - \n (mutation) may involve addition/deletion/substitution/inversion of DNA bases;\n
\n - \n (mutations) in tumour suppressor genes/oncogenes;\n
\n - \n uncontrolled cell division/mitosis occurs;\n
\n - \n abnormal cells cannot perform their function;\n
\n - \n they divide repeatedly to form tumours;\n
\n
\n
\n
\n (b)\n
\n
\n - \n name of condition e.g. PKU / other example;\n
\n - \n mutation in the gene for (the enzyme) phenylalanine hydroxylase (PAH) / if other example used name of gene that is mutated;\n
\n - \n outline of inheritance pattern, e.g. both parents need to carry the recessive allele;\n
\n - \n (without dietary modification, result is) toxic build-up of phenylalanine in the blood / low levels of tyrosine / symptoms if other example used;\n
\n - \n phenylalanine is not converted to tyrosine (by the enzyme) / effect of the mutation on the protein/enzyme/metabolism if other example used;\n
\n - \n requires dietary modification (as treatment) / treatment for other example used;\n
\n
\n
\n
\n (c)\n
\n
\n - \n new phenotypes/traits may result from mutations;\n
\n - \n mutations increase variation/differences between individuals in a population/species;\n
\n - \n individuals with new phenotype/trait may have more chances of survival;\n
\n - \n (more chances of survival) in a changing environment / presence of selection pressures;\n
\n - \n (selection pressure can be) intraspecific competition/abiotic factor;\n
\n - \n natural selection occurs;\n
\n - \n individuals with (advantageous) mutation have longer life spans/live longer;\n
\n - \n (so) more chances of reproduction;\n
\n - \n mutated gene passed on to new generations;\n
\n - \n allele frequencies change in the population over time;\n
\n - \n evolution is a consequence of natural selection;\n
\n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "d1-3-6-consequences-of-mutation-in-germ-cells-and-somatic-cells",
+ "d1-3-7-mutation-as-a-source-of-genetic-variation",
+ "d1-3-mutations-and-gene-editing",
+ "d3-2-7-phenylketonuria-as-an-example-of-a-human-disease-due-to-a-recessive-allele",
+ "d3-2-inheritance"
+ ]
+ },
+ {
+ "question_id": "SPM.2.SL.TZ0.8",
+ "Question": "
\n
\n (a)\n
\n
\n
\n Explain the mechanisms involved in thermoregulation in humans.\n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n
\n Explain the relationship between temperature and the activity of enzymes.\n
\n
\n
\n
\n
\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",
+ "Markscheme": "
\n (a)\n
\n
\n - \n normal body temperature is 37 ºC;\n
\n - \n peripheral thermoreceptors detect environmental temperature;\n
\n - \n supporting conscious behaviour to avoid temperature extremes, e.g. wearing more clothing;\n
\n - \n sends messages to hypothalamus/temperature control centre of the brain;\n
\n - \n the hypothalamus sends messages to pituitary gland;\n
\n - \n (pituitary) releases TSH;\n
\n - \n stimulating thyroxin release from thyroid;\n
\n - \n thyroxin controls metabolic rate / production of heat;\n
\n - \n muscle random contraction/shivering to generate heat;\n
\n - \n (brown) adipose tissue burns fat to generate waste heat;\n
\n - \n vasoconstriction to conserve heat / vasodilation to exchange heat with the environment;\n
\n
\n
\n
\n (a)\n
\n
\n - \n normal body temperature is 37 ºC;\n
\n - \n peripheral thermoreceptors detect environmental temperature;\n
\n - \n supporting conscious behaviour to avoid temperature extremes, e.g. wearing more clothing;\n
\n - \n sends messages to hypothalamus/temperature control centre of the brain;\n
\n - \n the hypothalamus sends messages to pituitary gland;\n
\n - \n (pituitary) releases TSH;\n
\n - \n stimulating thyroxin release from thyroid;\n
\n - \n thyroxin controls metabolic rate / production of heat;\n
\n - \n muscle random contraction/shivering to generate heat;\n
\n - \n (brown) adipose tissue burns fat to generate waste heat;\n
\n - \n vasoconstriction to conserve heat / vasodilation to exchange heat with the environment;\n
\n
\n
\n
\n (b)\n
\n
\n - \n as temperature increases, the rate of molecular motion increases;\n
\n - \n increasing the frequency of collision between enzyme and substrate;\n
\n - \n increasing the rate of reaction;\n
\n - \n until an optimum temperature is reached;\n
\n - \n with further increase in temperature, enzymes denature;\n
\n
\n
\n
\n (c)\n
\n
\n - \n water has a (much) higher specific heat capacity (than air);\n
\n - \n water requires more energy gain/loss to change temperature;\n
\n - \n (water) provides more stable thermal habitats than air / temperature of water bodies remains more constant than air temperature;\n
\n - \n water has a higher thermal conductivity than air;\n
\n - \n more heat is transferred from organisms to water than to air;\n
\n - \n water is a good evaporative coolant and air is not;\n
\n - \n aquatic mammals have (proportionally) more body fat as insulation;\n
\n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "a-unity-and-diversity",
+ "c-interaction-and-interdependence",
+ "d-continuity-and-change"
+ ],
+ "subtopics": [
+ "a1-1-6-physical-properties-of-water-and-the-consequences-for-animals-in-aquatic-habitats",
+ "a1-1-water",
+ "c1-1-8-effects-of-temperature-ph-and-substrate-concentration-on-the-rate-of-enzyme-activity",
+ "c1-1-enzymes-and-metabolism",
+ "d3-3-5-thermoregulation-as-an-example-of-negative-feedback-control",
+ "d3-3-6-thermoregulation-mechanisms-in-humans",
+ "d3-3-homeostasis"
+ ]
+ }
+]
\ No newline at end of file
diff --git a/assets/jsonqb/Chemistry 2025 QB merged.json b/assets/jsonqb/Chemistry 2025 QB merged.json
new file mode 100644
index 0000000..6653bf5
--- /dev/null
+++ b/assets/jsonqb/Chemistry 2025 QB merged.json
@@ -0,0 +1,1785 @@
+[
+ {
+ "question_id": "19M.3.SL.TZ1.2",
+ "Question": "
\n
Powdered zinc was reacted with 25.00 cm3 of 1.000 mol dm−3 copper(II) sulfate solution in an insulated beaker. Temperature was plotted against time.
\n

\n
\n
Estimate the time at which the powdered zinc was placed in the beaker.
\n
[1]
\n
a(i).
\n
\n
State what point Y on the graph represents.
\n
[1]
\n
a(ii).
\n
\n
The maximum temperature used to calculate the enthalpy of reaction was chosen at a point on the extrapolated (dotted) line.
\n
State the maximum temperature which should be used and outline one assumption made in choosing this temperature on the extrapolated line.
\n
\n
Maximum temperature:
\n
Assumption:
\n
[2]
\n
b(i).
\n
\n
To determine the enthalpy of reaction the experiment was carried out five times. The same volume and concentration of copper(II) sulfate was used but the mass of zinc was different each time. Suggest, with a reason, if zinc or copper(II) sulfate should be in excess for each trial.
\n
[1]
\n
b(ii).
\n
\n
The formula q = mcΔT was used to calculate the energy released. The values used in the calculation were m = 25.00 g, c = 4.18 J g−1 K−1.
\n
State an assumption made when using these values for m and c.
\n

\n
[2]
\n
b(iii).
\n
\n
Predict, giving a reason, how the final enthalpy of reaction calculated from this experiment would compare with the theoretical value.
\n
[1]
\n
b(iv).
\n
",
+ "Markscheme": "
\n
100 «s» [✔]
\n
\n
Note: Accept 90 to 100 s.
\n
a(i).
\n
\n
highest recorded temperature
OR
when rate of heat production equals rate of heat loss [✔]
\n
\n
Note: Accept “maximum temperature”.
\n
Accept “completion/end point of reaction”.
\n
a(ii).
\n
\n
Maximum temperature:
73 «°C» [✔]
\n
Assumption:
«temperature reached if» reaction instantaneous
OR
«temperature reached if reaction occurred» without heat loss [✔]
\n
\n
Note: Accept “rate of heat loss is constant” OR “rate of temperature decrease is constant”.
\n
b(i).
\n
\n
Any one of:
copper(II) sulfate AND mass/amount of zinc is independent variable/being changed.
OR
copper(II) sulfate AND with zinc in excess there is no independent variable «as amount of copper(II) sulfate is fixed» [✔]
\n
copper(II) sulfate AND having excess zinc will not yield different results in each trial [✔]
\n
zinc AND results can be used to see if amount of zinc affects temperature rise «so this can be allowed for» [✔]
\n
zinc AND reduces variables/keeps the amount reacting constant [✔]
\n
b(ii).
\n
\n

\n
\n
Note: Accept “copper(II) sulfate/zinc sulfate” for “solution”.
\n
b(iii).
\n
\n
lower/less exothermic/less negative AND heat loss/some heat not accounted for
OR
lower/less exothermic/less negative AND mass of reaction mixture greater than 25.00 g
OR
greater/more exothermic /more negative AND specific heat of solution less than water [✔]
\n
\n
Note: Accept “temperature is lower” instead of “heat loss”.
\n
Accept “similar to theoretical value AND heat losses have been compensated for”.
\n
Accept “greater/more exothermic/more negative AND linear extrapolation overestimates heat loss”.
\n
b(iv).
\n
",
+ "Examiners report": "
\n
Almost all candidates identified 100 s as the time at which the reaction was initiated.
\n
a(i).
\n
\n
Many students gained this mark through stating this was the highest temperature recorded, though even more took advantage of the acceptance of the completion of the reaction, expressed in many different ways. Very few answered that it was when heat loss equalled heat production.
\n
a(ii).
\n
\n
Even though almost all students recognised 100 seconds as the start time of the reaction less than 50% chose the extrapolated temperature at this time. Predictably the most common answer was the maximum of the graph, followed closely by the intercept with the y-axis. With regard to reasons, again relatively few gained the mark, though most who did wrote “no loss of heat”, even though it was rare to find this preceded by “the temperature that would have been attained if …”.
\n
b(i).
\n
\n
The correct answer depended on whether students considered the object of the additional trials was to investigate the effect of a new independent variable (excess copper(II) sulphate) or to obtain additional values of the same enthalpy change so they could be averaged (excess zinc). Answers that gave adequate reasons were rare.
\n
b(ii).
\n
\n
Again relatively few gained these marks for stating that it was assumed the density and specific heat of the solution were the same as water.
\n
b(iii).
\n
\n
Only about a third of the students correctly deduced that loss of heat to the environment means that the experimental value is lower than the theoretical one, though other answers, such as “higher because linear extrapolation over-compensates for the heat losses” were also accepted.
\n
b(iv).
\n
",
+ "topics": [
+ "tools"
+ ],
+ "subtopics": [
+ "tool-2-technology",
+ "tool-3-mathematics"
+ ]
+ },
+ {
+ "question_id": "19M.2.HL.TZ1.1",
+ "Question": "
\n
Xylene is a derivative of benzene. One isomer is 1,4-dimethylbenzene.
\n

\n
\n
Xylene, like benzene, can be nitrated.
\n
\n
Bromine reacts with alkanes.
\n
\n
State the number of 1H NMR signals for this isomer of xylene and the ratio in which they appear.
\n
\n
[2]
\n
a.
\n
\n
Draw the structure of one other isomer of xylene which retains the benzene ring.
\n
[1]
\n
b.
\n
\n
Write the equation for the production of the active nitrating agent from concentrated sulfuric and nitric acids.
\n
[1]
\n
c(i).
\n
\n
Explain the mechanism for the nitration of benzene, using curly arrows to indicate the movement of electron pairs.
\n
[4]
\n
c(ii).
\n
\n
Identify the initiation step of the reaction and its conditions.
\n
[2]
\n
d(i).
\n
\n
1,4-dimethylbenzene reacts as a substituted alkane. Draw the structures of the two products of the overall reaction when one molecule of bromine reacts with one molecule of 1,4-dimethylbenzene.
\n
[2]
\n
d(ii).
\n
\n
The organic product is not optically active. Discuss whether or not the organic product is a racemic mixture.
\n
[1]
\n
e.
\n
",
+ "Markscheme": "
\n
Number of signals: 2 [✔]
\n
Ratio:
\n
3 : 2
\n
OR
\n
6 : 4 [✔]
\n
Note: Accept any correct integer or fractional ratio. Accept ratios in reverse order.
\n
a.
\n
\n
[✔]
\n
b.
\n
\n
2H2SO4 + HNO3 ⇌ NO2+ + 2HSO4− + H3O+ [✔]
\n
Note: Accept a single arrow instead of an equilibrium sign.
Accept “H2SO4 + HNO3 ⇌ NO2+ + HSO4− + H2O”.
Accept “H2SO4 + HNO3 ⇌ H2NO3+ + HSO4−”.
Accept equivalent two step reactions in which sulfuric acid first behaves as a strong acid and protonates the nitric acid, before behaving as a dehydrating agent removing water from it.
\n
c(i).
\n
\n

\n
curly arrow going from benzene ring to N «of +NO2/NO2+» [✔]
carbocation with correct formula and positive charge on ring [✔]
curly arrow going from C–H bond to benzene ring of cation [✔]
formation of organic product nitrobenzene AND H+ [✔]
\n
\n
Note: Accept mechanism with corresponding Kekulé structures.
Do not accept a circle in M2 or M3.
Accept first arrow starting either inside the circle or on the circle.
If Kekulé structure used, first arrow must start on the double bond.
M2 may be awarded from correct diagram for M3.
M4: Accept “C6H5NO2 + H2SO4” if HSO4− used in M3.
\n
c(ii).
\n
\n
Br2 2Br• [✔]
\n
«sun»light/UV/hv
OR
high temperature [✔]
\n
Note: Do not penalize missing radical symbol on Br.
Accept “homolytic fission of bromine” for M1.
\n
d(i).
\n
\n
[✔]
\n
HBr [✔]
\n
\n
Note: Accept condensed formulae, such as CH3C6H4CH2Br.
\n
d(ii).
\n
\n
no AND there is no chiral carbon
\n
OR
\n
no AND there is no carbon with four different substituents/groups [✔]
\n
\n
Note: Accept “no AND no asymmetric carbon
atom”.
\n
e.
\n
",
+ "Examiners report": "
\n
Many identified two correct peaks but quite a few less the correct ratio.
\n
a.
\n
\n
Generally well done, although some candidates repeated the formula of the 1,4-isomer structure or drew the wrong bond, e.g. benzene ring to H rather than C on CH3.
\n
b.
\n
\n
The production of NO3− was a common answer.
\n
c(i).
\n
\n
Performance was fairly good by schools covering the topic while others had no idea. There were many careless steps, such as omission or misplacement of + sign.
\n
c(ii).
\n
\n
Very well done, with a few making reference to a catalyst.
\n
d(i).
\n
\n
Some candidates lost one mark for the bond originated from H in CH3 instead of C. Some teachers thought the use of the word “substituted alkane” made the question more difficult than it should have been.
\n
d(ii).
\n
\n
One of the most poorly answered questions on the exam with only 10 % of candidates earning this mark. Some candidates just answered ‘yes’ or ‘no’ on whether the organic product is a racemic mix and very few mentioned the absence of a chiral carbon. One teacher though the use of benzene in this question made it unnecessarily tough, stating “the optical activity of benzene has not been covered due to the limited chemistry of benzene included in the specification. An aliphatic compound here would test the understanding of enantiomers without the confusion of adding benzene”. Candidates should recognize that carbon in benzene cannot be the centre of optical activity and look for chiral carbons in the substitution chains.
\n
e.
\n
",
+ "topics": [
+ "reactivity-3-what-are-the-mechanisms-of-chemical-change",
+ "structure-2-models-of-bonding-and-structure",
+ "structure-3-classification-of-matter"
+ ],
+ "subtopics": [
+ "reactivity-3-3-electron-sharing-reactions",
+ "reactivity-3-4-electron-pair-sharing-reactions",
+ "structure-2-2-the-covalent-model",
+ "structure-3-2-functional-groups-classification-of-organic-compounds"
+ ]
+ },
+ {
+ "question_id": "19M.2.HL.TZ1.2",
+ "Question": "
\n
Benzoic acid, C6H5COOH, is another derivative of benzene.
\n
\n
Identify the wavenumber of one peak in the IR spectrum of benzoic acid, using section 26 of the data booklet.
\n
[1]
\n
a.
\n
\n
Identify the spectroscopic technique that is used to measure the bond lengths in solid benzoic acid.
\n
[1]
\n
b.
\n
\n
Outline one piece of physical evidence for the structure of the benzene ring.
\n
[1]
\n
c.
\n
\n
Draw the structure of the conjugate base of benzoic acid showing all the atoms and all the bonds.
\n
[1]
\n
d.
\n
\n
Outline why both C to O bonds in the conjugate base are the same length and suggest a value for them. Use section 10 of the data booklet.
\n
[2]
\n
e.
\n
\n
The pH of an aqueous solution of benzoic acid at 298 K is 2.95. Determine the concentration of hydroxide ions in the solution, using section 2 of the data booklet.
\n
[2]
\n
f(i).
\n
\n
Formulate the equation for the complete combustion of benzoic acid in oxygen using only integer coefficients.
\n
[2]
\n
f(ii).
\n
\n
The combustion reaction in (f)(ii) can also be classed as redox. Identify the atom that is oxidized and the atom that is reduced.
\n
[1]
\n
g.
\n
\n
Suggest how benzoic acid, Mr = 122.13, forms an apparent dimer, Mr = 244.26, when dissolved in a non-polar solvent such as hexane.
\n
[1]
\n
h.
\n
\n
State the reagent used to convert benzoic acid to phenylmethanol (benzyl alcohol), C6H5CH2OH.
\n
[1]
\n
i.
\n
",
+ "Markscheme": "
\n
Any wavenumber in the following ranges:
2500−3000 «cm−1» [✔]
1700−1750 «cm−1» [✔]
2850−3090 «cm−1» [✔]
\n
a.
\n
\n
X-ray «crystallography/spectroscopy» [✔]
\n
b.
\n
\n
Any one of:
\n
«regular» hexagon
\n
OR
\n
all «H–C–C/C-C-C» angles equal/120º [✔]
all C–C bond lengths equal/intermediate between double and single
\n
OR
\n
bond order 1.5 [✔]
\n
c.
\n
\n
[✔]
\n
\n
Note: Accept Kekulé structures.
Negative sign must be shown in correct position.
\n
d.
\n
\n
electrons delocalized «across the O–C–O system»
\n
OR
\n
resonance occurs [✔]
\n
122 «pm» < C–O < 143 «pm» [✔]
\n
\n
Note: Accept “delocalized π-bond”.
Accept “bond intermediate between single and double bond” or “bond order 1.5” for M1.
Accept any answer in range 123 to 142 pm.
\n
e.
\n
\n
ALTERNATIVE 1:
[H+] «= 10−2.95» = 1.122 × 10−3 «mol dm−3» [✔]
\n
«[OH−] = =» 8.91 × 10−12 «mol dm−3» [✔]
\n
\n
ALTERNATIVE 2:
pOH = «14 − 2.95 =» 11.05 [✔]
«[OH−] = 10−11.05 =» 8.91 × 10−12 «mol dm−3» [✔]
\n
\n
Note: Award [2] for correct final answer.
Accept other methods.
\n
f(i).
\n
\n
2C6H5COOH (s) + 15O2 (g) → 14CO2 (g) + 6H2O (l)
correct products [✔]
correct balancing [✔]
\n
f(ii).
\n
\n
Oxidized:
\n
C/carbon «in C6H5COOH»
\n
AND
\n
Reduced:
\n
O/oxygen «in O2» [✔]
\n
g.
\n
\n
«intermolecular» hydrogen bonding [✔]
\n
\n
Note: Accept diagram showing hydrogen bonding.
\n
h.
\n
\n
lithium aluminium hydride/LiAlH4 [✔]
\n
i.
\n
",
+ "Examiners report": "
\n
Most candidates could identify a wavenumber or range of wavenumbers in the IR spectrum of benzoic acid.
\n
a.
\n
\n
Less than half the candidates identified x-ray crystallography as a technique used to measure bond lengths. There were many stating IR spectroscopy and quite a few random guesses.
\n
b.
\n
\n
Again less than half the candidates could accurately give a physical piece of evidence for the structure of benzene. Many missed the mark by not being specific, stating ‘all bonds in benzene with same length’ rather than ‘all C-C bonds in benzene have the same length’.
\n
c.
\n
\n
Very poorly answered with only 1 in 5 getting this question correct. Many did not show all the bonds and all the atoms or either forgot or misplaced the negative sign on the conjugate base.
\n
d.
\n
\n
This question was a challenge. Candidates were not able to explain the intermediate bond length and the majority suggested the value of either the bond length of C to O single bond or double bond.
\n
e.
\n
\n
Generally well done with a few calculating the pOH rather than the concentration of hydroxide ion asked for.
\n
f(i).
\n
\n
Most earned at least one mark by correctly stating the products of the reaction.
\n
f(ii).
\n
\n
Another question where not reading correctly was a concern. Instead of identifying the atom that is oxidized and the atom that is reduced, answers included formulas of molecules or the atoms were reversed for the redox processes.
\n
g.
\n
\n
The other question where only 10 % of the candidates earned a mark. Few identified hydrogen bonding as the reason for carboxylic acids forming dimers. There were many G2 forms stating that the use of the word “dimer” is not in the syllabus, however the candidates were given that a dimer has double the molar mass and the majority seemed to understand that the two molecules joined together somehow but could not identify hydrogen bonding as the cause.
\n
h.
\n
\n
Very few candidates answered this part correctly and scored the mark. Common answers were H2SO4, HCl & Sn, H2O2. In general, strongest candidates gained the mark.
\n
i.
\n
",
+ "topics": [
+ "reactivity-1-what-drives-chemical-reactions",
+ "reactivity-3-what-are-the-mechanisms-of-chemical-change",
+ "structure-2-models-of-bonding-and-structure"
+ ],
+ "subtopics": [
+ "reactivity-1-3-energy-from-fuels",
+ "reactivity-3-1-proton-transfer-reactions",
+ "structure-2-2-the-covalent-model"
+ ]
+ },
+ {
+ "question_id": "19M.2.HL.TZ1.25",
+ "Question": "
\n
\n (a)\n
\n
\n
\n \n Identify the chiral carbon atom using an asterisk, *.\n \n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n
\n \n Enantiomers can be identified using a polarimeter. Outline how this instrument differentiates the enantiomers.\n \n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n
\n \n [\n \n ✔]\n \n \n
\n
\n
\n (b)\n
\n
\n \n «plane-»polarized light passed through sample\n \n [✔]\n \n \n
\n
\n \n
\n analyser/second polarizer determines angle of rotation of plane of plane-polarized light\n
\n \n \n OR\n \n \n
\n each enantiomer rotates plane «of plane-polarized light» in opposite directions «by the same angle»\n \n [✔]\n \n \n
\n
\n",
+ "Examiners report": "
\n (a)\n
\n
\n Some candidates had difficulty identifying the chiral carbon in a methadone structure, with quite a few varied answers. However, many managed to mark the correct carbon.\n
\n
\n
\n (b)\n
\n
\n Very poorly answered. Few scored any marks at all when outlining how a polarimeter can be used to differentiate between enantiomers. Many referred to the light or the enantiomers themselves being rotated.\n
\n
\n",
+ "topics": [
+ "structure-3-classification-of-matter"
+ ],
+ "subtopics": [
+ "structure-3-2-functional-groups-classification-of-organic-compounds"
+ ]
+ },
+ {
+ "question_id": "19M.2.HL.TZ1.4",
+ "Question": "
\n
This question is about the decomposition of hydrogen peroxide.
\n
\n
Hydrogen peroxide decomposes to water and oxygen when a catalyst such as potassium iodide, KI, is added.
\n
2H2O2 (aq) O2 (g) + 2H2O (l)
\n
\n
Suggest why many chemicals, including hydrogen peroxide, are kept in brown bottles instead of clear colourless bottles.
\n
[1]
\n
a.
\n
\n
In a laboratory experiment solutions of potassium iodide and hydrogen peroxide were mixed and the volume of oxygen generated was recorded. The volume was adjusted to 0 at t = 0.
\n

\n
The data for the first trial is given below.
\n

\n
Plot a graph on the axes below and from it determine the average rate of
formation of oxygen gas in cm3 O2 (g) s−1.
\n

\n
Average rate of reaction:
\n
[3]
\n
b(i).
\n
\n
Two more trials (2 and 3) were carried out. The results are given below.
\n

\n
Determine the rate equation for the reaction and its overall order, using your answer from (b)(i).
\n
Rate equation:
\n
Overall order:
\n
[2]
\n
b(ii).
\n
\n
Additional experiments were carried out at an elevated temperature. On the axes below, sketch Maxwell–Boltzmann energy distribution curves at two temperatures T1 and T2, where T2 > T1.
\n

\n
[2]
\n
b(iii).
\n
\n
Apart from a greater frequency of collisions, explain, by annotating your graphs in (b)(iii), why an increased temperature causes the rate of reaction to increase.
\n
[2]
\n
b(iv).
\n
\n
MnO2 is another possible catalyst for the reaction. State the IUPAC name for MnO2.
\n
[1]
\n
b(v).
\n
\n
Comment on why peracetic acid, CH3COOOH, is always sold in solution with ethanoic acid and hydrogen peroxide.
\n
H2O2 (aq) + CH3COOH (aq) ⇌ CH3COOOH (aq) + H2O (l)
\n
[1]
\n
c.
\n
\n
Sodium percarbonate, 2Na2CO3•3H2O2, is an adduct of sodium carbonate and hydrogen peroxide and is used as a cleaning agent.
\n
Mr (2Na2CO3•3H2O2) = 314.04
\n
Calculate the percentage by mass of hydrogen peroxide in sodium percarbonate, giving your answer to two decimal places.
\n
[2]
\n
d.
\n
",
+ "Markscheme": "
\n
decomposes in light [✔]
\n
\n
Note: Accept “sensitive to light”.
\n
a.
\n
\n

\n
points correctly plotted [✔]
\n
best fit line AND extended through (to) the origin [✔]
\n
Average rate of reaction:
«slope (gradient) of line =» 0.022 «cm3 O2 (g) s−1» [✔]
\n
\n
Note: Accept range 0.020–0.024cm3 O2 (g) s−1.
\n
b(i).
\n
\n
Rate equation:
Rate = k[H2O2] × [KI] [✔]
\n
Overall order:
2 [✔]
\n
\n
Note: Rate constant must be included.
\n
b(ii).
\n
\n

\n
peak of T2 to right of AND lower than T1 [✔]
\n
lines begin at origin AND T2 must finish above T1 [✔]
\n
b(iii).
\n
\n
Ea marked on graph [✔]
\n
explanation in terms of more “particles” with E ≥ Ea
\n
OR
\n
greater area under curve to the right of Ea in T2 [✔]
\n
b(iv).
\n
\n
manganese(IV) oxide
\n
OR
\n
manganese dioxide [✔]
\n
\n
Note: Accept “manganese(IV) dioxide”.
\n
b(v).
\n
\n
moves «position of» equilibrium to right/products [✔]
\n
\n
Note: Accept “reactants are always present as the reaction is in equilibrium”.
\n
c.
\n
\n
M( H2O2) «= 2 × 1.01 + 2 × 16.00» = 34.02 «g» [✔]
\n
«% H2O2 = 3 × × 100 =» 32.50 «%» [✔]
\n
\n
Note: Award [2] for correct final answer.
\n
d.
\n
",
+ "Examiners report": "
\n
There were a couple of comments claiming that this NOS question on “why to store hydrogen peroxide in brown bottles” is not the syllabus. Most candidates were quite capable of reasoning this out.
\n
a.
\n
\n
Most candidates could plot a best fit line and find the slope to calculate an average rate of reaction.
\n
b(i).
\n
\n
Good performance but with answers that either typically included only [H2O2] with first or second order equation or even suggesting zero order rate equation.
\n
b(ii).
\n
\n
Fair performance; errors including not starting the two curves at the origin, drawing peak for T2 above T1, T2 finishing below T1 or curves crossing the x-axis.
\n
b(iii).
\n
\n
The majority of candidates earned at least one mark, many both marks. Errors included not annotating the graph with Ea and referring to increase of kinetic energy as reason for higher rate at T2.
\n
b(iv).
\n
\n
A well answered question. Very few candidates had problem with nomenclature.
\n
b(v).
\n
\n
One teacher suggested that “stored” would have been better than “sold” for this question. There were a lot of irrelevant answers with many believing the back reaction was an acid dissociation.
\n
c.
\n
\n
It is recommended that candidates use the relative atomic masses given in the periodic table.
\n
d.
\n
",
+ "topics": [
+ "reactivity-2-how-much-how-fast-and-how-far",
+ "structure-1-models-of-the-particulate-nature-of-matter",
+ "structure-2-models-of-bonding-and-structure",
+ "structure-3-classification-of-matter",
+ "tools"
+ ],
+ "subtopics": [
+ "reactivity-2-2-how-fast-the-rate-of-chemical-change",
+ "reactivity-2-3-how-far-the-extent-of-chemical-change",
+ "structure-1-4-counting-particles-by-mass-the-mole",
+ "structure-2-4-from-models-to-materials",
+ "structure-3-2-functional-groups-classification-of-organic-compounds",
+ "tool-1-experimental-techniques",
+ "tool-3-mathematics"
+ ]
+ },
+ {
+ "question_id": "19M.2.HL.TZ1.7",
+ "Question": "
\n
An aqueous solution of silver nitrate, AgNO3 (aq), can be electrolysed using platinum electrodes.
\n
Formulate the half-equations for the reaction at each electrode during electrolysis.
\n
Cathode (negative electrode):
\n
Anode (positive electrode):
\n
",
+ "Markscheme": "
\n
Cathode (negative electrode):
Ag+ (aq) + e− → Ag (s) [✔]
\n
Anode (positive electrode):
2H2O(l) → O2 (g) + 4H+ (aq) + 4e− [✔]
\n
\n
Note: Accept 4OH− (aq) → O2 (g) + 2H2O(l) + 4e−
\n
Accept multiple or fractional coefficients in both half-equations.
\n
",
+ "Examiners report": "
\n
Very few answers were correct, even for stronger candidates. Many failed to formulate the correct half equation for the reaction at the anode and used the nitrate ion instead of oxidation of H2O. Some candidates lost one of the marks for using equilibrium arrows in an electrolysis equation.
\n
",
+ "topics": [
+ "reactivity-1-what-drives-chemical-reactions",
+ "reactivity-3-what-are-the-mechanisms-of-chemical-change",
+ "structure-2-models-of-bonding-and-structure"
+ ],
+ "subtopics": [
+ "reactivity-1-4-entropy-and-spontaneity",
+ "reactivity-3-2-electron-transfer-reactions",
+ "structure-2-4-from-models-to-materials"
+ ]
+ },
+ {
+ "question_id": "19M.2.HL.TZ1.8",
+ "Question": "
\n
\n (a)\n
\n
\n
\n \n Draw the structure of the repeating unit of starch and state the type of linkage formed between these units.\n \n
\n
\n \n
\n \n
\n
\n \n Type of linkage:\n \n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n
\n \n Formulate the equation for the complete hydrolysis of a starch molecule, (C\n \n 6\n \n H\n \n 10\n \n O\n \n 5\n \n )\n \n n\n \n .\n \n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n
\n
\n
\n \n continuation bonds\n \n \n AND\n \n \n −O attached to just one end\n \n \n AND\n \n \n both H atoms on end carbons must be on the same side\n \n [✔]\n \n \n
\n
\n \n
\n \n Type of linkage:\n \n
\n glycosidic\n \n [✔]\n \n \n
\n
\n
\n
\n \n \n \n Note:\n \n Square brackets not required.\n \n \n
\n
\n \n \n Ignore “n” if given.\n \n \n
\n
\n \n \n Mark may be awarded if a polymer is shown but with the repeating unit clearly identified.\n \n \n
\n
\n \n \n Accept “ether”.\n \n \n
\n
\n
\n
\n
\n (b)\n
\n
\n \n (C\n \n \n 6\n \n \n H\n \n \n 10\n \n \n O\n \n \n 5\n \n \n )\n \n \n n\n \n \n (s) +\n \n n\n \n H\n \n 2\n \n O (l) →\n \n n\n \n C\n \n 6\n \n H\n \n 12\n \n O\n \n 6\n \n (aq)\n \n [✔]\n \n \n
\n
\n
\n
\n \n \n Note:\n \n Accept “(n-1)H\n \n 2\n \n O”.\n \n
\n
\n \n Do\n \n not\n \n award mark if “n” not included.\n \n
\n
\n",
+ "Examiners report": "
\n (a)\n
\n
\n Candidates were required to draw the structure of the repeating unit of starch given the ring structure as a starting point. This proved extremely difficult with very few candidates scoring a mark. Commonly, the structure of\n \n \n \n -glucose was given, or an attempt was made to draw a polymer. Naming the type of linkage formed was answered well.\n
\n
\n
\n (b)\n
\n
\n Also proved challenging, with many candidates unable to write an equation for the hydrolysis of a starch molecule (C\n \n 6\n \n H\n \n 10\n \n O\n \n 5\n \n )\n \n n\n \n . The n was often omitted from otherwise correct equations or the product was incorrectly given as (C\n \n 6\n \n H\n \n 12\n \n O\n \n 6\n \n )\n \n n\n \n .\n
\n
\n",
+ "topics": [
+ "structure-2-models-of-bonding-and-structure"
+ ],
+ "subtopics": [
+ "structure-2-4-from-models-to-materials"
+ ]
+ },
+ {
+ "question_id": "19M.2.HL.TZ2.2",
+ "Question": "
\n
The thermal decomposition of dinitrogen monoxide occurs according to the equation:
\n
2N2O (g) → 2N2 (g) + O2 (g)
\n
The reaction can be followed by measuring the change in total pressure, at constant temperature, with time.
\n
The x-axis and y-axis are shown with arbitrary units.
\n

\n
\n
This decomposition obeys the rate expression:
\n
= k[N2O]
\n
\n
Explain why, as the reaction proceeds, the pressure increases by the amount shown.
\n
[2]
\n
a.
\n
\n
Outline, in terms of collision theory, how a decrease in pressure would affect the rate of reaction.
\n
[2]
\n
b.
\n
\n
Deduce how the rate of reaction at t = 2 would compare to the initial rate.
\n
[1]
\n
c(i).
\n
\n
It has been suggested that the reaction occurs as a two-step process:
\n
Step 1: N2O (g) → N2 (g) + O (g)
\n
Step 2: N2O (g) + O (g) → N2 (g) + O2 (g)
\n
Explain how this could support the observed rate expression.
\n
[2]
\n
c(ii).
\n
\n
The experiment is repeated using the same amount of dinitrogen monoxide in the same apparatus, but at a lower temperature.
\n
Sketch, on the axes in question 2, the graph that you would expect.
\n
[2]
\n
d.
\n
\n
The experiment gave an error in the rate because the pressure gauge was inaccurate.
\n
Outline whether repeating the experiment, using the same apparatus, and averaging the results would reduce the error.
\n
[1]
\n
e.
\n
\n
The graph below shows the Maxwell–Boltzmann distribution of molecular energies at a particular temperature.
\n

\n
The rate at which dinitrogen monoxide decomposes is significantly increased by a metal oxide catalyst.
\n
Annotate and use the graph to outline why a catalyst has this effect.
\n
[2]
\n
f.
\n
\n
Determine the standard entropy change, in J K−1, for the decomposition of dinitrogen monoxide.
\n
2N2O (g) → 2N2 (g) + O2 (g)
\n

\n
[2]
\n
g(i).
\n
\n
Dinitrogen monoxide has a positive standard enthalpy of formation, ΔHfθ.
\n
Deduce, giving reasons, whether altering the temperature would change the spontaneity of the decomposition reaction.
\n
[3]
\n
g(ii).
\n
",
+ "Markscheme": "
\n
increase in the amount/number of moles/molecules «of gas» [✔]
\n
from 2 to 3/by 50 % [✔]
\n
a.
\n
\n
«rate of reaction decreases»
concentration/number of molecules in a given volume decreases
OR
more space between molecules [✔]
\n
collision rate/frequency decreases
OR
fewer collisions per unit time [✔]
\n
\n
Note: Do not accept just “larger space/volume” for M1.
\n
b.
\n
\n
half «of the initial rate» [✔]
\n
\n
Note: Accept “lower/slower «than initial rate»”.
\n
c(i).
\n
\n
1 slower than 2
OR
1 rate determinant step/RDS [✔]
\n
\n
1 is unimolecular/involves just one molecule so it must be first order
OR
if 1 faster/2 RDS, second order in N2O
OR
if 1 faster/2 RDS, first order in O [✔]
\n
c(ii).
\n
\n

\n
smaller initial gradient [✔]
\n
initial pressure is lower AND final pressure of gas lower «by similar factor» [✔]
\n
d.
\n
\n
no AND it is a systematic error/not a random error
\n
OR
\n
no AND «a similar magnitude» error would occur every time [✔]
\n
e.
\n
\n

\n
catalysed and uncatalysed Ea marked on graph AND with the catalysed being at lower energy [✔]
\n
\n
«for catalysed reaction» greater proportion of/more molecules have E ≥ Ea / E > Ea
OR
«for catalysed reaction» greater area under curve to the right of the Ea [✔]
\n
\n
Note: Accept “more molecules have the activation energy”.
\n
f.
\n
\n
ΔSθ = 2(Sθ(N2)) + Sθ(O2) – 2(Sθ(N2O))
OR
ΔSθ = 2 × 193 «J mol-1 K-1» + 205 «J mol-1 K-1» – 2 × 220 «J mol-1 K-1» [✔]
\n
«ΔSθ = +»151 «J K-1» [✔]
\n
\n
Note: Award [2] for correct final answer.
\n
g(i).
\n
\n
exothermic decomposition
OR
ΔH(decomposition) < 0 [✔]
\n
TΔSθ > ΔHθ
OR
ΔGθ «= ΔHθ – TΔSθ» < 0 «at all temperatures» [✔]
\n
reaction spontaneous at all temperatures [✔]
\n
g(ii).
\n
",
+ "Examiners report": "
\n
Students were able in general to relate more moles of gas to increase in pressure.
\n
a.
\n
\n
Few students were able to relate the effect of reduced pressure at constant volume with a decrease in concentration of gas molecules and mostly did not even refer to this, but rather concentrated on lower rate of reaction and frequency of collisions. Many candidates lost a mark by failing to explain rate as collisions per unit time, frequency, etc.
\n
b.
\n
\n
Though the differential equation was considered to be misleading by teachers, most candidates attempted to answer this question, and more than half did so correctly, considering they had the graph to visualize the gradient.
\n
c(i).
\n
\n
Most students were able to identity step 1 as the RDS/slow but few mentioned unimolecularity or referred vaguely to NO2 as the only reagent (which was obvious) and got only 1 mark.
\n
c(ii).
\n
\n
Many students drew a lower initial gradient, but most did not reflect the effect of lower temperature on pressure at constant volume and started and finished the curve at the same pressure as the original one.
\n
\n
d.
\n
\n
Almost all candidates identified the inaccurate pressure gauge as a systematic error, thus relating accuracy to this type of error.
\n
e.
\n
\n
The graph was generally well done, but in quite a few cases, candidates did not mention that increase of rate in the catalyzed reaction was due to E (particles) > Ea or did so too vaguely.
\n
f.
\n
\n
Candidates were able to calculate the ΔS of the reaction, though in some cases they failed to multiply by the number of moles.
\n
g(i).
\n
\n
Though the question asked for decomposition (in bold), most candidates ignored this and worked on the basis of a the ΔH of formation. However, many did write a sound explanation for that situation. On the other hand, in quite a number of cases, they did not state the sign of the ΔH (probably taking it for granted) nor explicitly relate ΔG and spontaneity, which left the examiner with no possibility of evaluating their reasoning.
\n
g(ii).
\n
",
+ "topics": [
+ "reactivity-1-what-drives-chemical-reactions",
+ "reactivity-2-how-much-how-fast-and-how-far",
+ "structure-1-models-of-the-particulate-nature-of-matter",
+ "tools"
+ ],
+ "subtopics": [
+ "reactivity-1-4-entropy-and-spontaneity",
+ "reactivity-2-2-how-fast-the-rate-of-chemical-change",
+ "structure-1-5-ideal-gases",
+ "tool-2-technology",
+ "tool-3-mathematics"
+ ]
+ },
+ {
+ "question_id": "19M.2.HL.TZ2.3",
+ "Question": "
\n
Dinitrogen monoxide, N2O, causes depletion of ozone in the stratosphere.
\n
\n
Different sources of N2O have different ratios of 14N : 15N.
\n
\n
The Lewis (electron dot) structure of the dinitrogen monoxide molecule can be represented as:
\n

\n
\n
Outline why ozone in the stratosphere is important.
\n
[1]
\n
a(i).
\n
\n
Dinitrogen monoxide in the stratosphere is converted to nitrogen monoxide, NO (g).
\n
Write two equations to show how NO (g) catalyses the decomposition of ozone.
\n
[2]
\n
a(ii).
\n
\n
State one analytical technique that could be used to determine the ratio of 14N : 15N.
\n
[1]
\n
b(i).
\n
\n
A sample of gas was enriched to contain 2 % by mass of 15N with the remainder being 14N.
\n
Calculate the relative molecular mass of the resulting N2O.
\n
[2]
\n
b(ii).
\n
\n
Predict, giving two reasons, how the first ionization energy of 15N compares with that of 14N.
\n
[2]
\n
b(iii).
\n
\n
Explain why the first ionization energy of nitrogen is greater than both carbon and oxygen.
\n
Nitrogen and carbon:
\n
Nitrogen and oxygen:
\n
[2]
\n
c.
\n
\n
State what the presence of alternative Lewis structures shows about the nature of the bonding in the molecule.
\n
[1]
\n
d(i).
\n
\n
State, giving a reason, the shape of the dinitrogen monoxide molecule.
\n
[1]
\n
d(ii).
\n
\n
Deduce the hybridization of the central nitrogen atom in the molecule.
\n
[1]
\n
d(iii).
\n
",
+ "Markscheme": "
\n
absorbs UV/ultraviolet light «of longer wavelength than absorbed by O2» [✔]
\n
a(i).
\n
\n
NO (g) + O3 (g) → NO2 (g) + O2 (g) [✔]
NO2 (g) + O3 (g) → NO (g) + 2O2 (g) [✔]
\n
\n
Note: Ignore radical signs.
\n
Accept equilibrium arrows.
\n
Award [1 max] for NO2 (g) + O (g) → NO (g) + O2 (g).
\n
a(ii).
\n
\n
mass spectrometry/MS [✔]
\n
b(i).
\n
\n
« =» 14.02 [✔]
\n
«Mr = (14.02 × 2) + 16.00 =» 44.04 [✔]
\n
b(ii).
\n
\n
Any two:
\n
same AND have same nuclear charge /number of protons/Zeff [✔]
\n
same AND neutrons do not affect attraction/ionization energy/Zeff
OR
same AND neutrons have no charge [✔]
\n
same AND same attraction for «outer» electrons [✔]
\n
same AND have same electronic configuration/shielding [✔]
\n
\n
Note: Accept “almost the same”.
\n
“Same” only needs to be stated once.
\n
b(iii).
\n
\n
Nitrogen and carbon:
\n
N has greater nuclear charge/«one» more proton «and electrons both lost from singly filled p-orbitals» [✔]
\n
\n
Nitrogen and oxygen:
\n
O has a doubly filled «p-»orbital
OR
N has only singly occupied «p-»orbitals [✔]
\n
\n
Note: Accept “greater e– - e- repulsion in O” or “lower e– - e- repulsion in N”.
\n
Accept box annotation of electrons for M2.
\n
c.
\n
\n
delocalization
\n
OR
\n
delocalized π-electrons [✔]
\n
\n
Note: Accept “resonance”.
\n
d(i).
\n
\n
linear AND 2 electron domains
\n
OR
\n
linear AND 2 regions of electron density [✔]
\n
\n
Note: Accept “two bonds AND no lone pairs” for reason.
\n
d(ii).
\n
",
+ "Examiners report": "
\n
Candidates sometimes failed to identify how ozone works in chemical terms, referring to protects/deflects, i.e., the consequence rather than the mechanism.
\n
a(i).
\n
\n
Many candidates recalled the first equation for NO catalyzed decomposition of ozone only. Some considered other radical species.
\n
a(ii).
\n
\n
All candidates, with very few exceptions, answered this correctly.
\n
b(i).
\n
\n
Most candidates were able to calculate the accurate mass of N2O, though quite a few candidates just calculated the mass of N and didn’t apply it to N2O, losing an accessible mark.
\n
b(ii).
\n
\n
Many students realized that neutrons had no charge and could not affect IE significantly, but many others struggled a lot with this question since they considered that 15N would have a higher IE because they considered the greater mass of the nucleus would result in an increase of attraction of the electrons.
\n
b(iii).
\n
\n
Mixed responses here; the explanation of higher IE for N with respect to C was less well explained, though it should have been the easiest. It was good to see that most candidates could explain the difference in IE of N and O, either mentioning paired/unpaired electrons or drawing box diagrams.
\n
c.
\n
\n
Most candidates identified resonance for this given Lewis representation.
\n
d(i).
\n
\n
Though quite a number of candidates suggested a linear shape correctly, they often failed to give a complete correct explanation, just mentioning the absence of lone pairs but not two bonds, instead of referring to electron domains.
\n
d(ii).
\n
\n
Hybridisation of the N atom was correct in most cases.
\n
d(iii).
\n
",
+ "topics": [
+ "reactivity-1-what-drives-chemical-reactions",
+ "structure-1-models-of-the-particulate-nature-of-matter",
+ "structure-2-models-of-bonding-and-structure",
+ "structure-3-classification-of-matter"
+ ],
+ "subtopics": [
+ "reactivity-1-4-entropy-and-spontaneity",
+ "structure-1-2-the-nuclear-atom",
+ "structure-1-3-electron-configurations",
+ "structure-2-2-the-covalent-model",
+ "structure-3-1-the-periodic-table-classification-of-elements",
+ "structure-3-2-functional-groups-classification-of-organic-compounds"
+ ]
+ },
+ {
+ "question_id": "19M.2.HL.TZ2.4",
+ "Question": "
\n
Rhenium, Re, was the last element with a stable isotope to be isolated.
\n
\n
Before its isolation, scientists predicted the existence of rhenium and some of its properties.
\n
\n
One chloride of rhenium has the empirical formula ReCl3.
\n
\n
Rhenium forms salts containing the perrhenate(VII) ion, ReO4−.
\n
\n
The stable isotope of rhenium contains 110 neutrons.
\n
State the nuclear symbol notation for this isotope.
\n
[1]
\n
a.
\n
\n
Suggest the basis of these predictions.
\n
[2]
\n
b(i).
\n
\n
A scientist wants to investigate the catalytic properties of a thin layer of rhenium metal on a graphite surface.
\n
Describe an electrochemical process to produce a layer of rhenium on graphite.
\n
[2]
\n
b(ii).
\n
\n
Predict two other chemical properties you would expect rhenium to have, given its position in the periodic table.
\n
[2]
\n
b(iii).
\n
\n
Describe how the relative reactivity of rhenium, compared to silver, zinc, and copper, can be established using pieces of rhenium and solutions of these metal sulfates.
\n
[2]
\n
c.
\n
\n
State the name of this compound, applying IUPAC rules.
\n
[1]
\n
d(i).
\n
\n
Calculate the percentage, by mass, of rhenium in ReCl3.
\n
[2]
\n
d(ii).
\n
\n
Suggest why the existence of salts containing an ion with this formula could be predicted. Refer to section 6 of the data booklet.
\n
[1]
\n
e(i).
\n
\n
Deduce the coefficients required to complete the half-equation.
\n
ReO4− (aq) + ____H+ (aq) + ____e− ⇌ [Re(OH)2]2+ (aq) + ____H2O (l) Eθ = +0.36 V
\n
[1]
\n
e(ii).
\n
\n
Predict, giving a reason, whether the reduction of ReO4− to [Re(OH)2]2+ would oxidize Fe2+ to Fe3+ in aqueous solution. Use section 24 of the data booklet.
\n
[1]
\n
e(iii).
\n
",
+ "Markscheme": "
\n
[✔]
\n
a.
\n
\n
gap in the periodic table
OR
element with atomic number «75» unknown
OR
break/irregularity in periodic trends [✔]
\n
«periodic table shows» regular/periodic trends «in properties» [✔]
\n
b(i).
\n
\n
electrolyze «a solution of /molten» rhenium salt/Ren+ [✔]
\n
graphite as cathode/negative electrode
OR
rhenium forms at cathode/negative electrode [✔]
\n
\n
Note: Accept “using rhenium anode” for M1.
\n
b(ii).
\n
\n
Any two of:
variable oxidation states [✔]
\n
forms complex ions/compounds [✔]
\n
coloured compounds/ions [✔]
\n
«para»magnetic compounds/ions [✔]
\n
\n
Note: Accept other valid responses related to its chemical metallic properties.
\n
Do not accept “catalytic properties”.
\n
b(iii).
\n
\n
place «pieces of» Re into each solution [✔]
\n
if Re reacts/is coated with metal, that metal is less reactive «than Re» [✔]
\n
\n
Note: Accept other valid observations such as “colour of solution fades” or “solid/metal appears” for “reacts”.
\n
c.
\n
\n
rhenium(III) chloride
OR
rhenium trichloride [✔]
\n
d(i).
\n
\n
«Mr ReCl3 = 186.21 + (3 × 35.45) =» 292.56 [✔]
«100 × =» 63.648 «%» [✔]
\n
d(ii).
\n
\n
same group as Mn «which forms MnO4-»
OR
in group 7/has 7 valence electrons, so its «highest» oxidation state is +7 [✔]
\n
e(i).
\n
\n
ReO4− (aq) + 6H+ (aq) + 3e− ⇌ [Re(OH)2]2+ (aq) + 2H2O (l) [✔]
\n
e(ii).
\n
\n
no AND ReO4− is a weaker oxidizing agent than Fe3+
OR
no AND Fe3+ is a stronger oxidizing agent than ReO4−
OR
no AND Fe2+ is a weaker reducing agent than [Re(OH)2]2+
OR
no AND [Re(OH)2]2+ is a stronger reducing agent than Fe2+
OR
no AND cell emf would be negative/–0.41 V [✔]
\n
e(iii).
\n
",
+ "Examiners report": "
\n
It was expected that this question would be answered correctly by all HL candidates. However, many confused the A-Z positions or calculated very unusual numbers for A, sometimes even with decimals.
\n
a.
\n
\n
This is a NOS question which required some reflection on the full meaning of the periodic table and the wealth of information contained in it. But very few candidates understood that they were being asked to explain periodicity and the concept behind the periodic table, which they actually apply all the time. Some were able to explain the “gap” idea and other based predictions on properties of nearby elements instead of thinking of periodic trends. A fair number of students listed properties of transition metals in general.
\n
b(i).
\n
\n
Generally well done; most described the cell identifying the two electrodes correctly and a few did mention the need for Re salt/ion electrolyte.
\n
b(ii).
\n
\n
Generally well answered though some students suggested physical properties rather than chemical ones.
\n
b(iii).
\n
\n
Many candidates chose to set up voltaic cells and in other cases failed to explain the actual experimental set up of Re being placed in solutions of other metal salts or the reaction they could expect to see.
\n
c.
\n
\n
Almost all candidates were able to name the compound according to IUPAC.
\n
d(i).
\n
\n
Most candidates were able to answer this stoichiometric question correctly.
\n
d(ii).
\n
\n
This should have been a relatively easy question but many candidates sometimes failed to see the connection with Mn or the amount of electrons in its outer shell.
\n
e(i).
\n
\n
Surprisingly, a great number of students were unable to balance this simple half-equation that was given to them to avoid difficulties in recall of reactants/products.
\n
e(ii).
\n
\n
Many students understood that the oxidation of Fe2+ was not viable but were unable to explain why in terms of oxidizing and reducing power; many students simply gave numerical values for EΘ often failing to realise that the oxidation of Fe2+ would have the inverse sign to the reduction reaction.
\n
e(iii).
\n
",
+ "topics": [
+ "reactivity-3-what-are-the-mechanisms-of-chemical-change",
+ "structure-1-models-of-the-particulate-nature-of-matter",
+ "structure-3-classification-of-matter",
+ "tools"
+ ],
+ "subtopics": [
+ "reactivity-3-2-electron-transfer-reactions",
+ "structure-1-2-the-nuclear-atom",
+ "structure-1-4-counting-particles-by-mass-the-mole",
+ "structure-3-1-the-periodic-table-classification-of-elements",
+ "structure-3-2-functional-groups-classification-of-organic-compounds",
+ "tool-1-experimental-techniques"
+ ]
+ },
+ {
+ "question_id": "19M.2.HL.TZ2.5",
+ "Question": "
\n
Carbonated water is produced when carbon dioxide is dissolved in water under pressure. The following equilibria are established.
\n
Equilibrium (1) CO2 (g)
CO2 (aq)
\n
Equilibrium (2) CO2 (aq) + H2O (l)
H+ (aq) + HCO3− (aq)
\n
\n
Carbon dioxide acts as a weak acid.
\n
\n
Soda water has sodium hydrogencarbonate, NaHCO3, dissolved in the carbonated water.
\n
\n
Distinguish between a weak and strong acid.
\n
Weak acid:
\n
Strong acid:
\n
[1]
\n
a(i).
\n
\n
The hydrogencarbonate ion, produced in Equilibrium (2), can also act as an acid.
\n
State the formula of its conjugate base.
\n
[1]
\n
a(ii).
\n
\n
When a bottle of carbonated water is opened, these equilibria are disturbed.
\n
State, giving a reason, how a decrease in pressure affects the position of Equilibrium (1).
\n
[1]
\n
b.
\n
\n
At 298 K the concentration of aqueous carbon dioxide in carbonated water is 0.200 mol dm−3 and the pKa for Equilibrium (2) is 6.36.
\n
Calculate the pH of carbonated water.
\n
[3]
\n
c.
\n
\n
Identify the type of bonding in sodium hydrogencarbonate.
\n
Between sodium and hydrogencarbonate:
\n
Between hydrogen and oxygen in hydrogencarbonate:
\n
[2]
\n
d(i).
\n
\n
Predict, referring to Equilibrium (2), how the added sodium hydrogencarbonate affects the pH.(Assume pressure and temperature remain constant.)
\n
[2]
\n
d(ii).
\n
\n
100.0cm3 of soda water contains 3.0 × 10−2g NaHCO3.
\n
Calculate the concentration of NaHCO3 in mol dm−3.
\n
[2]
\n
d(iii).
\n
\n
The uncertainty of the 100.0cm3 volumetric flask used to make the solution was ±0.6cm3.
\n
Calculate the maximum percentage uncertainty in the mass of NaHCO3 so that the concentration of the solution is correct to ±1.0 %.
\n
[1]
\n
d(iv).
\n
\n
The reaction of the hydroxide ion with carbon dioxide and with the hydrogencarbonate ion can be represented by Equations 3 and 4.
\n
Equation (3) OH− (aq) + CO2 (g) → HCO3− (aq)
Equation (4) OH− (aq) + HCO3− (aq) → H2O (l) + CO32− (aq)
\n
Discuss how these equations show the difference between a Lewis base and a Brønsted–Lowry base.
\n
\n
Equation (3):
\n
Equation (4):
\n
[2]
\n
e.
\n
\n
Aqueous sodium hydrogencarbonate has a pH of approximately 7 at 298 K.
\n
Sketch a graph of pH against volume when 25.0cm3 of 0.100 mol dm−3 NaOH (aq) is gradually added to 10.0cm3 of 0.0500 mol dm−3 NaHCO3 (aq).
\n

\n
[2]
\n
f.
\n
",
+ "Markscheme": "
\n
Weak acid: partially dissociated/ionized «in aqueous solution/water»
AND
Strong acid: «assumed to be almost» completely/100 % dissociated/ionized «in aqueous solution/water» [✔]
\n
a(i).
\n
\n
shifts to left/reactants AND to increase amount/number of moles/molecules of gas/CO2 (g) [✔]
\n
\n
Note: Accept “shifts to left/reactants AND to increase pressure”.
\n
b.
\n
\n
«Ka =» 10–6.36/4.37 × 10–7 =
OR
«Ka =» 10–6.36/4.37 × 10–7 = [✔]
\n
\n
[H+] « » = 2.95 × 10–4 «mol dm–3» [✔]
«pH =» 3.53 [✔]
\n
\n
Note: Award [3] for correct final answer.
\n
c.
\n
\n
Between sodium and hydrogencarbonate:
ionic [✔]
\n
Between hydrogen and oxygen in hydrogencarbonate:
«polar» covalent [✔]
\n
d(i).
\n
\n
«additional HCO3-» shifts position of equilibrium to left [✔]
\n
pH increases [✔]
\n
\n
Note: Do not award M2 without any justification in terms of equilibrium shift in M1.
\n
d(ii).
\n
\n
«molar mass of NaHCO3 =» 84.01 «g mol-1» [✔]
\n
«concentration = =» 3.6 × 10–3 «mol dm-3» [✔]
\n
\n
Note: Award [2] for correct final answer.
\n
d(iii).
\n
\n
«1.0 – 0.6 = ± » 0.4 «%» [✔]
\n
d(iv).
\n
\n
Equation (3):
OH- donates an electron pair AND acts as a Lewis base [✔]
\n
Equation (4):
OH- accepts a proton/H+/hydrogen ion AND acts as a Brønsted–Lowry base [✔]
\n
e.
\n
\n

\n
S-shaped curve from ~7 to between 12 and 14 [✔]
\n
equivalence point at 5 cm3 [✔]
\n
\n
Note: Accept starting point >6~7.
\n
f.
\n
",
+ "Examiners report": "
\n
As expected, many candidates were able to distinguish between strong and weak acids; some candidates referred to “dissolve” rather than dissociate.
\n
a(i).
\n
\n
More than half the candidates were able to deduce that carbonate was the conjugate base but a significant proportion of those that did, wrote the carbonate ion with an incorrect charge.
\n
a(ii).
\n
\n
Many students gave generic responses referring to a correct shift without conveying the idea of compensation or restoration of pressure or moles of gas. This generic reply reflects the difficulty in applying a theoretical concept to the practical situation described in the question.
\n
b.
\n
\n
Most candidates calculated the pH of the aqueous CO2. Some candidates attempted to use the Henderson-Hasselback equation and others used the quadratic expression to calculate [H+] (these two options were very common in the Spanish scripts) getting incorrect solutions. These answers usually ended in pH of approx. 1 which candidates should realize cannot be correct for soda water.
\n
c.
\n
\n
This was an easy question, especially the identification of the type of bond between H and O, yet some candidates interpreted that the question referred to intermolecular bonding.
\n
d(i).
\n
\n
A significant number of candidates omitted the “equilibrium” involved in the dissolution of a weak base.
\n
d(ii).
\n
\n
This is another stoichiometry question that most candidates were able to solve well, with occasional errors when calculating Mr of hydrogen carbonate.
\n
d(iii).
\n
\n
Mixed responses, more attention should be given to this simple calculation which is straightforward and should be easy as required for IA reports.
\n
d(iv).
\n
\n
This was a good way to test this topic because answers showed that, while candidates usually knew the topic in theory, they could not apply this to identify the Lewis and Bronsted-Lowry bases in the context of a reaction that was given to them. In some cases, they failed to specify the base, OH- or also lost marks referring just to electrons, an electron or H instead of hydrogen ions or H+ for example.
\n
e.
\n
\n
Most students that got 1mark for this titration curve was for the general shape, because few realized they had the data to calculate the equivalence point. There were also some difficulties in establishing the starting point even if it was specified in the stem.
\n
f.
\n
",
+ "topics": [
+ "reactivity-2-how-much-how-fast-and-how-far",
+ "reactivity-3-what-are-the-mechanisms-of-chemical-change",
+ "structure-1-models-of-the-particulate-nature-of-matter",
+ "structure-2-models-of-bonding-and-structure",
+ "tools"
+ ],
+ "subtopics": [
+ "reactivity-2-3-how-far-the-extent-of-chemical-change",
+ "reactivity-3-1-proton-transfer-reactions",
+ "reactivity-3-4-electron-pair-sharing-reactions",
+ "structure-1-4-counting-particles-by-mass-the-mole",
+ "structure-2-1-the-ionic-model",
+ "structure-2-2-the-covalent-model",
+ "tool-2-technology",
+ "tool-3-mathematics"
+ ]
+ },
+ {
+ "question_id": "19M.2.HL.TZ2.6",
+ "Question": "
\n
Phenylethene can be polymerized to form polyphenylethene (polystyrene, PS).
\n

\n
\n
The major product of the reaction with hydrogen bromide is C6H5–CHBr–CH3 and the minor product is C6H5–CH2–CH2Br.
\n
\n
Draw the repeating unit of polyphenylethene.
\n
[1]
\n
a.
\n
\n
Phenylethene is manufactured from benzene and ethene in a two-stage process. The overall reaction can be represented as follows with ΔGθ = +10.0 kJ mol−1 at 298 K.
\n

\n
Calculate the equilibrium constant for the overall conversion at 298 K, using section 1 of the data booklet.
\n
[2]
\n
b.
\n
\n
The benzene ring of phenylethene reacts with the nitronium ion, NO2+, and the C=C double bond reacts with hydrogen bromide, HBr.
\n
Compare and contrast these two reactions in terms of their reaction mechanisms.
\n
\n
Similarity:
\n
Difference:
\n
[2]
\n
c.
\n
\n
Outline why the major product, C6H5–CHBr–CH3, can exist in two forms and state the relationship between these forms.
\n
\n
Two forms:
\n
Relationship:
\n
[2]
\n
d(i).
\n
\n
The minor product, C6H5–CH2–CH2Br, can exist in different conformational forms (isomers).
\n
Outline what this means.
\n
[1]
\n
d(ii).
\n
\n
The minor product, C6H5–CH2–CH2Br, can be directly converted to an intermediate compound, X, which can then be directly converted to the acid C6H5–CH2–COOH.
\n
C6H5–CH2–CH2Br → X → C6H5–CH2–COOH
\n
Identify X.
\n
[1]
\n
e.
\n
",
+ "Markscheme": "
\n
[✔]
\n
\n
Note: Do not penalize the use of brackets and “n”.
\n
Do not award the mark if the continuation bonds are missing.
\n
a.
\n
\n
ln k «= » = –4.04 [✔]
\n
k = 0.0176 [✔]
\n
\n
Note: Award [2] for correct final answer.
\n
b.
\n
\n
Similarity:
«both» involve an electrophile
OR
«both» electrophilic [✔]
\n
\n
Difference:
first/reaction of ring/with NO2+ is substitution/S«E» AND second/reaction of C=C/with HBr is addition/A«E» [✔]
\n
\n
Note: Answer must state which is substitution and which is addition for M2.
\n
c.
\n
\n
Two forms:
chiral/asymmetric carbon
OR
carbon atom attached to 4 different groups [✔]
\n
\n
Relationship:
mirror images
OR
enantiomers/optical isomers [✔]
\n
\n
Note: Accept appropriate diagrams for either or both marking points.
\n
d(i).
\n
\n
benzene ring «of the C6H5–CH2» and the bromine «on the CH2–Br» can take up different relative positions by rotating about the «C–C, σ–»bond [✔]
\n
\n
Note: Accept “different parts of the molecule can rotate relative to each other”.
\n
Accept “rotation around σ–bond”.
\n
d(ii).
\n
\n
C6H5–CH2–CH2OH [✔]
\n
e.
\n
",
+ "Examiners report": "
\n
Most candidates were able to draw the monomer correctly. Some candidates made careless mistakes writing C6H6.
\n
a.
\n
\n
Another calculation which most candidates were able to work out, though some failed to convert ΔG given value in kJ mol-1 to J mol-1 or forgot the negative sign. Some used an inappropriate expression of R.
\n
b.
\n
\n
The strong candidates were generally able to see the similarity between the two reactions but unexpectedly some could not identify “electrophilic” as a similarity even if they referred to the differences as electrophilic substitution/addition, so probably were unable to understand what was being asked.
\n
c.
\n
\n
Candidates were given the products of the addition reaction and asked about the major product. Perhaps they were put off by the term “forms” and thus failed to “see” the chiral C that allowed the existence of enantiomers. There was some confusion with the type of isomerism and some even suggested cis/trans isomers.
\n
d(i).
\n
\n
If candidates seemed rather confused in the previous question, they seemed more so in this one. Most simply referred to isomers in general, not seeming to be slightly aware of what conformational isomerism is, even if it is in the curriculum.
\n
d(ii).
\n
\n
Quite well answered though some candidates suggested an aldehyde rather than the alcohol, or forgot that C has two hydrogens apart from the -OH. In other cases, they left a Br there.
\n
e.
\n
",
+ "topics": [
+ "reactivity-2-how-much-how-fast-and-how-far",
+ "reactivity-3-what-are-the-mechanisms-of-chemical-change",
+ "structure-2-models-of-bonding-and-structure",
+ "structure-3-classification-of-matter"
+ ],
+ "subtopics": [
+ "reactivity-2-3-how-far-the-extent-of-chemical-change",
+ "reactivity-3-2-electron-transfer-reactions",
+ "reactivity-3-4-electron-pair-sharing-reactions",
+ "structure-2-2-the-covalent-model",
+ "structure-2-4-from-models-to-materials",
+ "structure-3-2-functional-groups-classification-of-organic-compounds"
+ ]
+ },
+ {
+ "question_id": "19M.2.SL.TZ1.1",
+ "Question": "
\n
Xylene is a derivative of benzene. One isomer is 1,4-dimethylbenzene.
\n

\n
\n
Bromine reacts with alkanes.
\n
\n
State the number of 1H NMR signals for this isomer of xylene and the ratio in which they appear.
\n
Number of signals:
\n
Ratio:
\n
[2]
\n
a.
\n
\n
Draw the structure of one other isomer of xylene which retains the benzene ring.
\n
[1]
\n
b.
\n
\n
Identify the initiation step of the reaction and its conditions.
\n
[2]
\n
c(i).
\n
\n
1,4-dimethylbenzene reacts as a substituted alkane. Draw the structures of the two products of the overall reaction when one molecule of bromine reacts with one molecule of 1,4-dimethylbenzene.
\n
[2]
\n
c(ii).
\n
",
+ "Markscheme": "
\n
Number of signals:
2 [✔]
\n
Ratio:
3 : 2
OR
6 : 4 [✔]
\n
\n
Note: Accept any correct integer or fractional ratio.
\n
Accept ratios in reverse order.
\n
a.
\n
\n
[✔]
\n
b.
\n
\n
Br2 → 2Br• [✔]
\n
«sun»light/UV/hv
OR
high temperature [✔]
\n
\n
Note: Do not penalize missing radical symbol on Br.
\n
Accept “homolytic fission of bromine” for M1.
\n
c(i).
\n
\n
[✔]
\n
HBr [✔]
\n
\n
Note: Accept condensed formulae, such as CH3C6H4CH2Br.
\n
Accept skeletal structures.
\n
c(ii).
\n
",
+ "Examiners report": "
\n
Most students gained M1 but very few gained M2, suggesting that the correct answer of 2 signals may have been a guess.
\n
a.
\n
\n
Another isomer of xylene was generally correctly drawn, but some candidates drew the original compound.
\n
b.
\n
\n
Drawing or describing the homolytic fission of bromine was generally done well.
\n
c(i).
\n
\n
Very few students gained 2 marks finding hard to apply their knowledge of free radical substitution to a benzene containing compound. Many thought that the bromine will attach to the benzene ring or would substitute the alkyl group twice and not produce HBr.
\n
c(ii).
\n
",
+ "topics": [
+ "reactivity-3-what-are-the-mechanisms-of-chemical-change",
+ "structure-2-models-of-bonding-and-structure",
+ "structure-3-classification-of-matter"
+ ],
+ "subtopics": [
+ "reactivity-3-3-electron-sharing-reactions",
+ "reactivity-3-4-electron-pair-sharing-reactions",
+ "structure-2-2-the-covalent-model",
+ "structure-3-2-functional-groups-classification-of-organic-compounds"
+ ]
+ },
+ {
+ "question_id": "19M.2.SL.TZ1.10",
+ "Question": "
\n
\n
\n \n Ascorbic acid and retinol are two important vitamins.\n \n
\n
\n \n Explain why ascorbic acid is soluble in water and retinol is not. Use section 35 of the data booklet.\n \n
\n
\n
\n
\n
\n
\n (a)\n
\n
\n
\n \n The melting points of cocoa butter and coconut oil are 34 °C and 25 °C respectively.\n \n
\n
\n \n Explain this in terms of their saturated fatty acid composition.\n \n
\n
\n
\n
\n",
+ "Markscheme": "
\n
\n \n \n ascorbic acid:\n \n many hydroxyl/OH groups\n \n \n AND\n \n retinol\n \n : few/one hydroxyl/OH group\n
\n \n \n OR\n \n \n
\n \n ascorbic acid\n \n : many hydroxyl/OH groups\n \n \n AND\n \n retinol\n \n : long hydrocarbon chain\n \n [✔]\n \n \n
\n
\n \n \n ascorbic acid\n \n : «many» H-bond with water\n
\n \n \n OR\n \n \n
\n \n retinol\n \n : cannot «sufficiently» H-bond with water\n \n [✔]\n \n \n
\n
\n
\n
\n \n \n \n Note:\n \n Do\n \n not\n \n accept “OH\n \n −\n \n /hydroxide”.\n \n \n
\n
\n
\n (a)\n
\n
\n \n coconut oil has higher content of lauric/short-chain «saturated» fatty acids\n
\n \n \n OR\n \n \n
\n cocoa butter has higher content of stearic/palmitic/longer chain «saturated» fatty acids\n \n [\n \n ✔\n \n ]\n \n \n
\n
\n \n longer chain fatty acids have greater surface area/larger electron cloud\n \n [✔]\n \n \n
\n
\n \n stronger London/dispersion/instantaneous dipole-induced dipole forces «between triglycerides of longer chain saturated fatty acids»\n \n [✔]\n \n \n
\n
\n
\n
\n \n \n \n Note:\n \n Do\n \n not\n \n accept arguments that relate to melting points of saturated and unsaturated fats.\n \n \n
\n
\n",
+ "Examiners report": "
\n
\n Another instance where candidates insist on discussing water solubility in terms of polarity or hydrophilicity rather than its fundamental dependence on the presence of sufficient groups that can form hydrogen bonds to water. A few however gained a mark through pointing out the significance of the –OH groups in ascorbic acid and the long hydrocarbon chain in retinol.\n
\n
\n
\n (a)\n
\n
\n Candidates had difficulty explaining the melting points of fats in terms of length of carbon chain, and referred instead to an explanation of saturated and unsaturated fat structures.\n
\n
\n",
+ "topics": [
+ "structure-2-models-of-bonding-and-structure",
+ "structure-3-classification-of-matter"
+ ],
+ "subtopics": [
+ "structure-2-2-the-covalent-model",
+ "structure-3-2-functional-groups-classification-of-organic-compounds"
+ ]
+ },
+ {
+ "question_id": "19M.2.SL.TZ1.13",
+ "Question": "
\n
\n (b)\n
\n
\n
\n \n Show that, for combustion of equal masses of fuel, ethanol (\n \n M\n \n r\n \n \n = 46 g mol\n \n −1\n \n ) has a lower carbon footprint than octane (\n \n M\n \n \n r\n \n = 114 g mol\n \n −1\n \n ).\n \n
\n
\n
\n
\n
\n
\n (c)\n
\n
\n
\n \n Biodiesel containing ethanol can be made from renewable resources.\n \n
\n
\n \n Suggest\n \n one\n \n environmental disadvantage of producing biodiesel from renewable resources.\n \n
\n
\n
\n
\n",
+ "Markscheme": "
\n (b)\n
\n
\n \n \n \n Alternative 1\n \n \n
\n C\n \n 2\n \n H\n \n 5\n \n OH (l) + 3O\n \n 2\n \n (g) → 2CO\n \n 2\n \n (g) + 3H\n \n 2\n \n O (l) / 1 mol ethanol produces 2 mol CO\n \n 2\n \n
\n \n \n OR\n \n \n
\n C\n \n 8\n \n H18 (l) + 12.5O\n \n 2\n \n (g) → 8CO\n \n 2\n \n (g) + 9H\n \n 2\n \n O (l) / 1 mol octane produces 8 mol CO\n \n 2\n \n \n [✔]\n \n \n
\n
\n \n
\n For 1 g of fuel:\n
\n «\n \n \n \n × 2 mol CO\n \n 2\n \n (g) =» 0.04 «mol CO\n \n 2\n \n (g)» from ethanol\n \n [✔]\n \n \n
\n
\n \n «\n \n \n \n × 8 mol CO\n \n 2\n \n (g) =» 0.07 «mol CO\n \n 2\n \n (g)» from octane\n \n [✔]\n \n \n
\n
\n
\n
\n \n \n \n Alternative 2\n \n \n
\n ratio of C in ethanol:octane is 2:8, so ratio in carbon dioxide produced per mole will be 1:4\n \n [✔]\n \n \n
\n
\n \n ratio amount of fuel in 1 g =\n \n \n \n = 2.5:1\n \n [✔]\n \n \n
\n
\n \n 4 > 2.5 so octane produces more carbon dioxide\n
\n \n \n OR\n \n \n
\n ratio of amount of carbon dioxide = 2.5:4 = 1:1.61 so octane produces more «for combustion of same mass»\n \n [✔]\n \n \n
\n
\n
\n (c)\n
\n
\n \n use of «farm» land «for production»\n
\n \n \n OR\n \n \n
\n deforestation «for crop production for fuel»\n
\n \n \n OR\n \n \n
\n can release more NO\n \n x\n \n «than normal fuel on combustion»\n \n [✔]\n \n \n
\n
\n
\n
\n \n \n \n Note:\n \n Ignore any reference to cost.\n \n \n
\n
\n",
+ "Examiners report": "
\n (b)\n
\n
\n A question that gave the opportunity for a variety of different approaches. This challenge was beyond all but the best students, though there were a number of well argued responses.\n
\n
\n
\n (c)\n
\n
\n Many students did not take into account “production from renewable resources” and answered in terms of the combustion of biodiesel, though about a third correctly identified the area of land biofuel crops require.\n
\n
\n",
+ "topics": [
+ "reactivity-1-what-drives-chemical-reactions"
+ ],
+ "subtopics": [
+ "reactivity-1-3-energy-from-fuels"
+ ]
+ },
+ {
+ "question_id": "19M.2.SL.TZ1.4",
+ "Question": "
\n
This question is about peroxides.
\n
\n
Hydrogen peroxide decomposes to water and oxygen when a catalyst such as potassium iodide, KI, is added.
\n
2H2O2 (aq) O2 (g) + 2H2O (l)
\n
\n
Suggest why many chemicals, including hydrogen peroxide, are kept in brown bottles instead of clear colourless bottles.
\n
[1]
\n
a.
\n
\n
In a laboratory experiment solutions of potassium iodide and hydrogen peroxide were mixed and the volume of oxygen generated was recorded. The volume was adjusted to 0 at t = 0.
\n

\n
The data for the first trial is given below.
\n

\n
Plot a graph on the axes below and from it determine the average rate of formation of oxygen gas in cm3 O2 (g) s−1.
\n

\n
Average rate of reaction:
\n
[3]
\n
b(i).
\n
\n
Additional experiments were carried out at an elevated temperature. On the axes below, sketch Maxwell–Boltzmann energy distribution curves at two temperatures T1 and T2, where T2 > T1.
\n

\n
[2]
\n
b(ii).
\n
\n
Apart from a greater frequency of collisions, explain, by annotating your graphs in (b)(ii), why an increased temperature causes the rate of reaction to increase.
\n
[2]
\n
b(iii).
\n
\n
MnO2 is another possible catalyst for the reaction. State the IUPAC name for MnO2.
\n
[1]
\n
b(iv).
\n
\n
Comment on why peracetic acid, CH3COOOH, is always sold in solution with ethanoic acid and hydrogen peroxide.
\n
H2O2 (aq) + CH3COOH (aq) CH3COOOH (aq) + H2O (l)
\n
[1]
\n
c.
\n
\n
Sodium percarbonate, 2Na2CO3•3H2O2, is an adduct of sodium carbonate and hydrogen peroxide and is used as a cleaning agent.
\n
Mr (2Na2CO3•3H2O2) = 314.04
\n
Calculate the percentage by mass of hydrogen peroxide in sodium percarbonate, giving your answer to two decimal places.
\n
[2]
\n
d.
\n
",
+ "Markscheme": "
\n
decomposes in light [✔]
\n
\n
Note: Accept “sensitive to light”.
\n
a.
\n
\n

\n
points correctly plotted [✔]
\n
best fit line AND extended through (to) the origin [✔]
\n
Average rate of reaction:
«slope (gradient) of line =» 0.022 «cm3 O2 (g) s−1» [✔]
\n
\n
Note: Accept range 0.020–0.024cm3 O2 (g) s−1.
\n
b(i).
\n
\n

\n
peak of T2 to right of AND lower than T1 [✔]
\n
lines begin at origin AND T2 must finish above T1 [✔]
\n
b(ii).
\n
\n
Ea marked on graph [✔]
\n
explanation in terms of more “particles” with E ≥ Ea
OR
greater area under curve to the right of Ea in T2 [✔]
\n
b(iii).
\n
\n
manganese(IV) oxide
OR
manganese dioxide [✔]
\n
\n
Note: Accept “manganese(IV) dioxide”.
\n
b(iv).
\n
\n
move «position of» equilibrium to right/products [✔]
\n
\n
Note: Accept “reactants are always present as the reaction is in equilibrium”.
\n
c.
\n
\n
M (H2O2) «= 2 × 1.01 + 2 × 16.00» = 34.02 «g» [✔]
\n
«% H2O2 = 3 × × 100 =» 32.50 «%» [✔]
\n
\n
Note: Award [2] for correct final answer.
\n
d.
\n
",
+ "Examiners report": "
\n
The explanation that the brown bottle prevented light causing a decomposition of the chemical was well answered but some incorrectly suggested it helped to stop mixing up of chemicals e.g. acid/water/peroxide.
\n
a.
\n
\n
The graphing was disappointing with a surprising number of students missing at least one mark for failing to draw a straight line or for failing to draw the line passing through the origin. Also some were unable to calculate the gradient.
\n
b(i).
\n
\n
The drawing of the two curves at T1 and T2 was generally poorly done.
\n
b(ii).
\n
\n
Explaining why temperature increase caused an increase in reaction rate was generally incorrectly answered with most students failing to mention “activation energy” in their answer or failing to annotate the graph.
\n
b(iii).
\n
\n
Many could correctly name manganese(IV)oxide, but there were answers of magnesium(IV) oxide or manganese(II) oxide.
\n
b(iv).
\n
\n
Suggesting why peractic acid was sold in solution was very poorly answered and only a few students mentioned equilibrium and, if they did, they thought it would move to the left to restore equilibrium.
\n
c.
\n
\n
Calculating the % by mass was generally well answered although some candidates started by using rounded values of atomic masses which made their final answer unprecise.
\n
d.
\n
",
+ "topics": [
+ "reactivity-2-how-much-how-fast-and-how-far",
+ "structure-1-models-of-the-particulate-nature-of-matter",
+ "structure-2-models-of-bonding-and-structure",
+ "structure-3-classification-of-matter",
+ "tools"
+ ],
+ "subtopics": [
+ "reactivity-2-1-how-much-the-amount-of-chemical-change",
+ "reactivity-2-2-how-fast-the-rate-of-chemical-change",
+ "reactivity-2-3-how-far-the-extent-of-chemical-change",
+ "structure-1-4-counting-particles-by-mass-the-mole",
+ "structure-2-4-from-models-to-materials",
+ "structure-3-2-functional-groups-classification-of-organic-compounds",
+ "tool-1-experimental-techniques",
+ "tool-3-mathematics"
+ ]
+ },
+ {
+ "question_id": "19M.2.SL.TZ1.5",
+ "Question": "
\n
Both vinegar (a dilute aqueous solution of ethanoic acid) and bleach are used as cleaning agents.
\n
\n
Bleach reacts with ammonia, also used as a cleaning agent, to produce the poisonous compound chloramine, NH2Cl.
\n
\n
Outline why ethanoic acid is classified as a weak acid.
\n
[1]
\n
a.
\n
\n
A solution of bleach can be made by reacting chlorine gas with a sodium hydroxide solution.
\n
Cl2 (g) + 2NaOH (aq) NaOCl (aq) + NaCl (aq) + H2O (l)
\n
Suggest, with reference to Le Châtelier’s principle, why it is dangerous to mix vinegar and bleach together as cleaners.
\n
[3]
\n
b.
\n
\n
Draw a Lewis (electron dot) structure of chloramine.
\n
[1]
\n
c(i).
\n
\n
Deduce the molecular geometry of chloramine and estimate its H–N–H bond angle.
\n
\n
Molecular geometry:
\n
H–N–H bond angle:
\n
[2]
\n
c(ii).
\n
",
+ "Markscheme": "
\n
partial dissociation «in aqueous solution» [✔]
\n
a.
\n
\n
ethanoic acid/vinegar reacts with NaOH [✔]
\n
moves equilibrium to left/reactant side [✔]
\n
releases Cl2 (g)/chlorine gas
OR
Cl2 (g)/chlorine gas is toxic [✔]
\n
\n
Note: Accept “ethanoic acid produces H+ ions”.
\n
Accept “ethanoic acid/vinegar reacts with NaOCl”.
\n
Do not accept “2CH3COOH + NaOCl + NaCl → 2CH3COONa + Cl2 + H2O” as it does not refer to equilibrium.
\n
Accept suitable molecular or ionic equations for M1 and M3.
\n
b.
\n
\n
[✔]
\n
\n
Note: Accept any combination of dots/crosses or lines to represent electron pairs.
\n
c(i).
\n
\n
Molecular geometry:
«trigonal» pyramidal [✔]
\n
H–N–H bond angle:
107° [✔]
\n
\n
Note: Accept angles in the range of 100–109.
\n
c(ii).
\n
",
+ "Examiners report": "
\n
The definition of a weak acid was generally correct.
\n
a.
\n
\n
Explaining why it was dangerous to mix chlorine with vinegar was not well answered but most students gained at least one mark for stating that “chlorine gas will be produced”, but couldn’t link it to equilibrium ideas.
\n
b.
\n
\n
The Lewis structure of chloramine was correct for strong candidates, but many made the mistake of omitting electron pairs on N and Cl.
\n
c(i).
\n
\n
The molecular geometry and bond angles often did not correspond to each other with quite a few candidates stating trigonal planar and then 107 for the angle.
\n
c(ii).
\n
",
+ "topics": [
+ "reactivity-2-how-much-how-fast-and-how-far",
+ "reactivity-3-what-are-the-mechanisms-of-chemical-change",
+ "structure-2-models-of-bonding-and-structure"
+ ],
+ "subtopics": [
+ "reactivity-2-3-how-far-the-extent-of-chemical-change",
+ "reactivity-3-1-proton-transfer-reactions",
+ "structure-2-2-the-covalent-model"
+ ]
+ },
+ {
+ "question_id": "19M.2.SL.TZ1.6",
+ "Question": "
\n
This question is about iron.
\n
\n
State the nuclear symbol notation, , for iron-54.
\n
[1]
\n
a.
\n
\n
Mass spectrometry analysis of a sample of iron gave the following results:
\n

\n
Calculate the relative atomic mass, Ar, of this sample of iron to two decimal places.
\n
[2]
\n
b.
\n
\n
An iron nail and a copper nail are inserted into a lemon.
\n

\n
Explain why a potential is detected when the nails are connected through a voltmeter.
\n
[2]
\n
c.
\n
",
+ "Markscheme": "
\n
[✔]
\n
a.
\n
\n
«Ar =» 54 × 0.0584 + 56 × 0.9168 + 57 × 0.0217 + 58 × 0.0031
OR
«Ar =» 55.9111 [✔]
\n
«Ar =» 55.91 [✔]
\n
Notes:
\n
Award [2] for correct final answer.
Do not accept data booklet value (55.85).
\n
b.
\n
\n
lemon juice is the electrolyte
OR
lemon juice allows flow of ions
OR
each nail/metal forms a half-cell with the lemon juice [✔]
\n
Note: Accept “lemon juice acts as a salt bridge”.
\n
Any one of:
iron is higher than copper in the activity series
OR
each half-cell/metal has a different redox/electrode potential [✔]
\n
Note: Accept “iron is more reactive than copper”.
\n
iron is oxidized
OR
Fe → Fe2+ + 2e–
OR
Fe → Fe3+ + 3e−
OR
iron is anode/negative electrode of cell [✔]
\n
copper is cathode/positive electrode of cell
OR
reduction occurs at the cathode
OR
2H+ + 2e− → H2 [✔]
\n
electrons flow from iron to copper [✔]
\n
\n
Notes:
Accept “lemon juice acts as a salt bridge”.
Accept “iron is more reactive than copper”.
\n
c.
\n
",
+ "Examiners report": "
\n
The nuclear symbol notation was generally correct. However, some students swapped atomic and mass numbers and hence lost the mark.
\n
a.
\n
\n
Calculation of RAM was generally correctly calculated, but some candidates did not give their answer to two decimal places while they should use the provided periodic table.
\n
b.
\n
\n
Very few students gained the 2 marks available for explaining the potential generated in the lemon as they didn’t realise it was the lemon that acted as the electrolyte and allowed ions to flow. Some were able to gain a mark for explaining that electrons moved from iron to copper as iron is more reactive.
\n
c.
\n
",
+ "topics": [
+ "reactivity-3-what-are-the-mechanisms-of-chemical-change",
+ "structure-1-models-of-the-particulate-nature-of-matter"
+ ],
+ "subtopics": [
+ "reactivity-3-2-electron-transfer-reactions",
+ "structure-1-2-the-nuclear-atom"
+ ]
+ },
+ {
+ "question_id": "19M.2.SL.TZ1.8",
+ "Question": "
\n
\n (a)\n
\n
\n
\n \n Draw a circle around the functional group formed between the amino acids and state its name.\n \n
\n
\n \n
\n \n
\n
\n \n Name:\n \n
\n
\n
\n
\n
\n
\n (c)\n
\n
\n
\n \n Calculate the energy released, in kJ g\n \n −1\n \n , when 3.49 g of starch are completely combusted in a calorimeter, increasing the temperature of 975 g of water from 21.0 °C to 36.0 °C. Use section 1 of the data booklet.\n \n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n
\n
\n
\n \n \n Name\n \n :\n
\n amide/amido/carboxamide\n \n [✔]\n \n \n
\n
\n
\n
\n \n \n \n Note:\n \n Accept “peptide bond/linkage”.\n \n \n
\n
\n
\n (c)\n
\n
\n \n \n q\n \n = «\n \n mc\n \n ΔT = 975 g × 4.18 J g\n \n –1\n \n K\n \n –1\n \n × 15.0 K =» 61 100 «J» / 61.1 «kJ»\n \n [✔]\n \n \n
\n
\n \n «heat per gram =\n \n \n \n \n =\n \n » 17.5 «kJ g\n \n –1\n \n »\n \n [✔]\n \n \n
\n
\n
\n
\n \n \n \n Note:\n \n Award\n \n [2]\n \n for correct final answer.\n \n \n
\n
\n",
+ "Examiners report": "
\n (a)\n
\n
\n Many candidates correctly circled the bond between the amino acid residues, though in some cases their circle missed out key atoms. Many correctly identified it as a peptide or amide linkage.\n
\n
\n
\n (c)\n
\n
\n The incorrect mass was frequently used when calculating energy released from combustion of starch in a calorimeter. Those who used the mass of water correctly frequently stopped when energy in kJ or J was calculated, and did not seem to notice that the question asked for the energy to be calculated in kJg\n \n −1\n \n so a further calculation was required.\n
\n
\n",
+ "topics": [
+ "reactivity-1-what-drives-chemical-reactions",
+ "structure-3-classification-of-matter",
+ "tools"
+ ],
+ "subtopics": [
+ "reactivity-1-1-measuring-enthalpy-changes",
+ "structure-3-2-functional-groups-classification-of-organic-compounds",
+ "tool-1-experimental-techniques"
+ ]
+ },
+ {
+ "question_id": "19M.2.SL.TZ2.13",
+ "Question": "
\n
\n (a)\n
\n
\n
\n \n State\n \n one\n \n greenhouse gas, other than carbon dioxide.\n \n
\n
\n
\n
\n
\n
\n (c)\n
\n
\n
\n \n Outline\n \n one\n \n approach to controlling industrial emissions of carbon dioxide.\n \n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n \n \n Any one of:\n \n
\n methane, water, nitrous oxide/nitrogen(I) oxide, ozone, CFCs, sulfur hexafluoride\n \n [✔]\n \n \n
\n
\n
\n
\n \n \n \n Note:\n \n Accept formulas.\n \n \n
\n
\n \n \n Do\n \n not\n \n accept “NO\n \n 2\n \n ”, “NO\n \n x\n \n ”, “oxides of sulfur”.\n \n \n
\n
\n
\n (c)\n
\n
\n \n \n Any one of:\n \n
\n capture where produced «and stored»\n \n [✔]\n \n \n
\n
\n \n use scrubbers to remove\n \n [✔]\n \n \n
\n
\n \n use as feedstock for synthesizing other chemicals\n \n [✔]\n \n \n
\n
\n \n carbon credit/tax/economic incentive/fines/country specific action\n \n [✔]\n \n
\n \n
\n
\n \n use alternative energy\n
\n \n \n OR\n \n \n
\n stop/reduce use of fossil fuels for producing energy\n \n [✔]\n \n \n
\n
\n \n use carbon reduced fuels «such as methane»\n \n [✔]\n \n \n
\n
\n \n increase efficiency/reduce energy use\n \n [✔]\n \n \n
\n
\n",
+ "Examiners report": "
\n (a)\n
\n
\n This question was well answered.\n
\n
\n
\n (c)\n
\n
\n This question was reasonably answered although there were many students who gave vague answers that did not receive marks. Carbon cannot be “filtered out” and the process of “carbon capture or scrubbing” is different from filtering.\n
\n
\n",
+ "topics": [
+ "reactivity-1-what-drives-chemical-reactions"
+ ],
+ "subtopics": [
+ "reactivity-1-3-energy-from-fuels"
+ ]
+ },
+ {
+ "question_id": "19M.2.SL.TZ2.2",
+ "Question": "
\n
The thermal decomposition of dinitrogen monoxide occurs according to the equation:
\n
2N2O (g) → 2N2 (g) + O2 (g)
\n
The reaction can be followed by measuring the change in total pressure, at constant temperature, with time.
\n
The x-axis and y-axis are shown with arbitrary units.
\n

\n
\n
Explain why, as the reaction proceeds, the pressure increases by the amount shown.
\n
[2]
\n
a.
\n
\n
Outline, in terms of collision theory, how a decrease in pressure would affect the rate of reaction.
\n
[2]
\n
b.
\n
\n
The experiment is repeated using the same amount of dinitrogen monoxide in the same apparatus, but at a lower temperature.
\n
Sketch, on the axes in question 2, the graph that you would expect.
\n
[2]
\n
c.
\n
\n
The experiment gave an error in the rate because the pressure gauge was inaccurate. Outline whether repeating the experiment, using the same apparatus, and averaging the results would reduce the error.
\n
[1]
\n
d.
\n
\n
The graph below shows the Maxwell–Boltzmann distribution of molecular energies at a particular temperature.
\n

\n
The rate at which dinitrogen monoxide decomposes is significantly increased by a metal oxide catalyst.
\n
Annotate and use the graph to outline why a catalyst has this effect.
\n
[2]
\n
e.
\n
",
+ "Markscheme": "
\n
increase in the amount/number of moles/molecules «of gas» [✔]
\n
from 2 to 3/by 50 % [✔]
\n
a.
\n
\n
«rate of reaction decreases»
concentration/number of molecules in a given volume decreases
OR
more space between molecules [✔]
\n
collision rate/frequency decreases
OR
fewer collisions per second/unit time [✔]
\n
\n
Note: Do not accept just “larger space/volume” for M1.
\n
b.
\n
\n

\n
smaller initial gradient [✔]
\n
initial pressure is lower AND final pressure of gas lower «by similar factor» [✔]
\n
\n
c.
\n
\n
no AND it is a systematic error/not a random error
OR
no AND «a similar magnitude» error would occur every time [✔]
\n
d.
\n
\n

\n
catalysed and uncatalysed Ea marked on graph AND with the catalysed being at lower energy [✔]
\n
«for catalysed reaction» greater proportion of/more molecules have E ≥ Ea / E > Ea
OR
«for catalysed reaction» greater area under curve to the right of the Ea [✔]
\n
Note: Accept “more molecules have the activation energy”.
\n
e.
\n
",
+ "Examiners report": "
\n
About a quarter of the candidates gave the full answer. Some only gained the first marking point (M1) by recognizing the increase in the number of moles of gas. Some candidates wrote vague answers that did not receive credit such as “pressure increases as more gaseous products form” without explicitly recognizing that the reactants have fewer moles of gas than the products. Some candidates mistook it for a system at equilibrium when the pressure stops changing (although a straight arrow is shown in the equation). A teacher commented that the wording of the question was rather vague “not clear if question is asking about stoichiometry (i.e. how 200 & 300 connect to coefficients) or rates (i.e. explain graph shape)”. We did not see a discussion of the slope of the graph with time and most candidates understood the question as it was intended.
\n
a.
\n
\n
More than half of the candidates obtained the mark allocated for “less frequent collisions” at lower pressure, but only strong candidates explained that this was due to the lower concentration or increased spacing between molecules. Some candidates talked about a decrease in kinetic energy and they did not show a good understanding of collision theory. Some candidates lost M1 for stating “fewer collisions” without reference to time or probability.
\n
b.
\n
\n
This was a challenging question. Candidates usually obtained only one of the two marks allocated for the answer. Most of them scored the mark for a lower initial slope at low temperature, while others scored a mark for sketching their curve below the original curve as all pressures (initial and final) will be lower at the lower temperature. A teacher commented that the wording was unclear “sketch on the axes in question 2”, and it would have been better to label the graph instead.
\n
c.
\n
\n
This question was well answered by nearly 70 % of the candidates reflecting a good understanding of the impact of systematic errors. Some students did not gain the mark because of an incomplete answer. The question raised much debate among teachers. They worried if the error was clearly a systematic one. However, a high proportion of candidates had very clear and definite answers. In Spanish and French, the wording was a bit ambiguous which caused the markscheme in these languages to be more opened.
\n
d.
\n
\n
This question discriminated very well between high-scoring and low-scoring candidates. About half of the candidates annotated the Maxwell-Boltzmann distribution to show the effect of the catalyst. Some left it blank and some sketched a new distribution that would be obtained at a higher temperature instead. The majority of candidates knew that the catalyst provided an alternative route with lower Ea but only stronger candidates related it to the annotation of the graph and used the accurate language needed to score M2. A common mistake was stating that molecules have higher kinetic energy when a catalyst is added.
\n
e.
\n
",
+ "topics": [
+ "reactivity-2-how-much-how-fast-and-how-far",
+ "structure-1-models-of-the-particulate-nature-of-matter",
+ "tools"
+ ],
+ "subtopics": [
+ "reactivity-2-2-how-fast-the-rate-of-chemical-change",
+ "structure-1-5-ideal-gases",
+ "tool-1-experimental-techniques",
+ "tool-2-technology",
+ "tool-3-mathematics"
+ ]
+ },
+ {
+ "question_id": "19M.2.SL.TZ2.3",
+ "Question": "
\n
Dinitrogen monoxide, N2O, causes depletion of ozone in the stratosphere.
\n
\n
Different sources of N2O have different ratios of 14N:15N.
\n
\n
Outline why ozone in the stratosphere is important.
\n
[1]
\n
a.
\n
\n
State one analytical technique that could be used to determine the ratio of 14N:15N.
\n
[1]
\n
b(i).
\n
\n
A sample of gas was enriched to contain 2 % by mass of 15N with the remainder being 14N.
\n
Calculate the relative molecular mass of the resulting N2O.
\n
[2]
\n
b(ii).
\n
\n
Predict, giving two reasons, how the first ionization energy of 15N compares with that of 14N.
\n
[2]
\n
b(iii).
\n
\n
Suggest why it is surprising that dinitrogen monoxide dissolves in water to give a neutral solution.
\n
[1]
\n
c.
\n
",
+ "Markscheme": "
\n
absorbs UV/ultraviolet light «of longer wavelength than absorbed by O2» [✔]
\n
a.
\n
\n
mass spectrometry/MS [✔]
\n
b(i).
\n
\n
« » 14.02 [✔]
\n
«Mr = (14.02 × 2) + 16.00 =» 44.04 [✔]
\n
b(ii).
\n
\n
Any two:
same AND have same nuclear charge/number of protons/Zeff [✔]
\n
same AND neutrons do not affect attraction/ionization energy/Zeff
OR
same AND neutrons have no charge [✔]
\n
same AND same attraction for «outer» electrons [✔]
\n
same AND have same electronic configuration/shielding [✔]
\n
\n
Note: Accept “almost the same”.
“same” only needs to be stated once.
\n
b(iii).
\n
\n
oxides of nitrogen/non-metals are «usually» acidic [✔]
\n
c.
\n
",
+ "Examiners report": "
\n
60 % of the candidates were aware that ozone in the atmosphere absorbs UV light. Some candidates did not gain the mark for not specifying the type of radiation absorbed.
\n
a.
\n
\n
Well answered. More than half of the candidates stated mass spectrometry is used to determine the ratio of the isotopes.
\n
b(i).
\n
\n
Many candidates successfully calculated the relative atomic mass of nitrogen in the sample. M2 was awarded independently of M1, so candidates who calculated the relative molecular mass using the Ar of nitrogen in the data booklet (14.01) were awarded M2. Many candidates scored both marks.
\n
b(ii).
\n
\n
This was a challenging question for many candidates, while stronger candidates often showed clarity of thinking and were able to conclude that the ionization energies of the two isotopes must be the same and to provide two different reasons for this. Some candidates did realize that the ionization energies are similar but did not give the best reasons to support their answer. Many candidates thought the ionization energies would be different because the size of the nucleus was different. Some teachers commented that the question was difficult while others liked it because it made students apply their knowledge in an unfamiliar situation. The question had a good discrimination index.
\n
b(iii).
\n
\n
Only a quarter of the candidates answered correctly. Some simply stated that N2O forms HNO3 with water which did not gain the mark.
\n
c.
\n
",
+ "topics": [
+ "structure-1-models-of-the-particulate-nature-of-matter",
+ "structure-2-models-of-bonding-and-structure",
+ "structure-3-classification-of-matter"
+ ],
+ "subtopics": [
+ "structure-1-2-the-nuclear-atom",
+ "structure-2-2-the-covalent-model",
+ "structure-3-1-the-periodic-table-classification-of-elements",
+ "structure-3-2-functional-groups-classification-of-organic-compounds"
+ ]
+ },
+ {
+ "question_id": "19M.2.SL.TZ2.4",
+ "Question": "
\n
Rhenium, Re, was the last element with a stable isotope to be isolated.
\n
\n
One chloride of rhenium has the empirical formula ReCl3.
\n
\n
Before its isolation, scientists predicted the existence of rhenium and some of its properties.
\n
Suggest the basis of these predictions.
\n
[2]
\n
a.
\n
\n
Describe how the relative reactivity of rhenium, compared to silver, zinc, and copper, can be established using pieces of rhenium and solutions of these metal sulfates.
\n
[2]
\n
b.
\n
\n
State the name of this compound, applying IUPAC rules.
\n
[1]
\n
c(i).
\n
\n
Calculate the percentage, by mass, of rhenium in ReCl3.
\n
[2]
\n
c(ii).
\n
",
+ "Markscheme": "
\n
gap in the periodic table
OR
element with atomic number «75» unknown
OR
break/irregularity in periodic trends [✔]
\n
«periodic table shows» regular/periodic trends «in properties» [✔]
\n
a.
\n
\n
place «pieces of» Re into each solution [✔]
\n
if Re reacts/is coated with metal, that metal is less reactive «than Re» [✔]
\n
\n
Note: Accept other valid observations such as “colour of solution fades” or “solid/metal appears” for “reacts”.
\n
b.
\n
\n
rhenium(III) chloride
OR
rhenium trichloride [✔]
\n
c(i).
\n
\n
«Mr ReCl3 = 186.21 + (3 × 35.45) =» 292.56 [✔]
\n
«100 × =» 63.648 «%» [✔]
\n
c(ii).
\n
",
+ "Examiners report": "
\n
This nature of science question generated a lot of discussion among teachers. Some in support of such questions and others concerned that it takes a lot of time for candidates to know how to answer. Some teachers thought it was unclear what the question was asking. It is pleasing that about a quarter of the candidates answered both parts successfully and many candidates gained one mark usually for “periodic trends”. However, some candidates only focused on one part of the question. Quite a few candidates discussed isotopes, probably thrown off by the stem. A teacher was concerned that since transition metals are not part of the SL syllabus that Re was a bad choice, however, the question did not really require any transition metal chemistry to be answered.
\n
a.
\n
\n
This question was a good discriminator between high-scoring and low-scoring candidates. It was well answered by more than half of the candidates who had obviously carried out such displacement reactions and interpreted the outcomes during the course. Some candidates did not state the obvious of dipping the metal into the sulfates.
\n
b.
\n
\n
More than half of the candidates named ReCl3 correctly. Common mistakes included “rhenium chloride” and “trichlororhenium”.
\n
c(i).
\n
\n
The majority of candidates calculated the percentage, by mass, of rhenium in ReCl3 correctly. Some rounding errors were seen that students should be more careful with.
\n
c(ii).
\n
",
+ "topics": [
+ "reactivity-3-what-are-the-mechanisms-of-chemical-change",
+ "structure-1-models-of-the-particulate-nature-of-matter",
+ "structure-2-models-of-bonding-and-structure",
+ "structure-3-classification-of-matter",
+ "tools"
+ ],
+ "subtopics": [
+ "reactivity-3-2-electron-transfer-reactions",
+ "structure-1-2-the-nuclear-atom",
+ "structure-1-4-counting-particles-by-mass-the-mole",
+ "structure-2-4-from-models-to-materials",
+ "structure-3-1-the-periodic-table-classification-of-elements",
+ "structure-3-2-functional-groups-classification-of-organic-compounds",
+ "tool-1-experimental-techniques"
+ ]
+ },
+ {
+ "question_id": "19M.2.SL.TZ2.5",
+ "Question": "
\n
Carbonated water is produced when carbon dioxide is dissolved in water under pressure.
\n
The following equilibria are established.
\n

\n
\n
Carbon dioxide acts as a weak acid.
\n
\n
Soda water has sodium hydrogencarbonate, NaHCO3, dissolved in the carbonated water.
\n
\n
Distinguish between a weak and strong acid.
\n
\n
Weak acid:
\n
Strong acid:
\n
[1]
\n
a(i).
\n
\n
The hydrogencarbonate ion, produced in Equilibrium (2), can also act as an acid.
\n
State the formula of its conjugate base.
\n
[1]
\n
a(ii).
\n
\n
When a bottle of carbonated water is opened, these equilibria are disturbed.
\n
State, giving a reason, how a decrease in pressure affects the position of Equilibrium (1).
\n
[1]
\n
a(iii).
\n
\n
Predict, referring to Equilibrium (2), how the added sodium hydrogencarbonate affects the pH.(Assume pressure and temperature remain constant.)
\n
[2]
\n
b(i).
\n
\n
100.0 cm3 of soda water contains 3.0 × 10−2 g NaHCO3.
\n
Calculate the concentration of NaHCO3 in mol dm−3.
\n
[2]
\n
b(ii).
\n
\n
Identify the type of bonding in sodium hydrogencarbonate.
\n
\n
Between sodium and hydrogencarbonate:
\n
Between hydrogen and oxygen in hydrogencarbonate:
\n
[2]
\n
b(iii).
\n
",
+ "Markscheme": "
\n
Weak acid: partially dissociated/ionized «in solution/water»
AND
Strong acid: «assumed to be almost» completely/100 % dissociated/ionized «in solution/water» [✔]
\n
a(i).
\n
\n
shifts to left/reactants AND to increase amount/number of moles/molecules of gas/CO2 (g) [✔]
\n
a(iii).
\n
\n
«additional HCO3–» shifts position of equilibrium to left [✔]
\n
pH increases [✔]
\n
\n
Note: Do not award M2 without any justification in terms of equilibrium shift in M1.
\n
b(i).
\n
\n
«molar mass of NaHCO3 =» 84.01 «g mol–1» [✔]
\n
«concentration = » 3.6 × 10–3 «mol dm–3» [✔]
\n
\n
Note: Award [2] for correct final answer.
\n
b(ii).
\n
\n
Between sodium and hydrogencarbonate:
ionic [✔]
\n
Between hydrogen and oxygen in hydrogencarbonate:
«polar» covalent [✔]
\n
b(iii).
\n
",
+ "Examiners report": "
\n
It was rather disappointing that less than 70 % of the candidates could distinguish between weak and strong acids. Many candidates referred to pH differences.
\n
a(i).
\n
\n
A poorly answered question, though it discriminated very well between high-scoring and low-scoring candidates. Less than 40 % of the candidates were able to deduce the formula of the conjugate base of HCO3-. Wrong answers included water, the hydroxide ion and carbon dioxide.
\n
a(ii).
\n
\n
This was a relatively challenging question. Only about a quarter of the candidates explained how a decrease in pressure affected the equilibrium. Some candidates stated there was no shift in the equilibrium as the number of moles is the same on both sides of the equation, not acknowledging that only gaseous substances need to be considered when deciding the direction of shift in equilibrium due to a change in pressure. Some candidates wrote that the equilibrium shifts right because the gas escapes.
\n
a(iii).
\n
\n
This was one of the most challenging questions on the paper that required application of Le Chatelier’s Principle in an unfamiliar situation. Most candidates did not refer to equilibrium (2), as directed by the question, and hence could not gain any marks. Some candidates stated that NaHCO3 was an acid and decreased pH. Some answers had contradictions that showed poor understanding of the pH concept.
\n
b(i).
\n
\n
Very well answered. Most candidates calculated the molar concentration correctly.
\n
b(ii).
\n
\n
Many candidates identified the bonding between sodium and hydrogencarbonate as ionic. A much smaller proportion of candidates identified the bonding between hydrogen and oxygen in hydrogencarbonate as covalent. The most common mistake was “hydrogen bonding”.
\n
b(iii).
\n
",
+ "topics": [
+ "reactivity-2-how-much-how-fast-and-how-far",
+ "reactivity-3-what-are-the-mechanisms-of-chemical-change",
+ "structure-1-models-of-the-particulate-nature-of-matter",
+ "structure-2-models-of-bonding-and-structure",
+ "tools"
+ ],
+ "subtopics": [
+ "reactivity-2-3-how-far-the-extent-of-chemical-change",
+ "reactivity-3-1-proton-transfer-reactions",
+ "structure-1-4-counting-particles-by-mass-the-mole",
+ "structure-2-1-the-ionic-model",
+ "structure-2-2-the-covalent-model",
+ "tool-2-technology",
+ "tool-3-mathematics"
+ ]
+ },
+ {
+ "question_id": "19M.2.SL.TZ2.6",
+ "Question": "
\n
\n (a)\n
\n
\n
\n \n Draw the repeating unit of polyphenylethene.\n \n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n
\n \n Determine the density of calcium, in g cm\n \n −3\n \n , using section 2 of the data booklet.\n \n
\n
\n \n Ar = 40.08; metallic radius (r) = 1.97 × 10\n \n −10\n \n m\n \n
\n
\n
\n
\n
\n
\n (c(i))\n
\n
\n
\n \n Suggest\n \n two\n \n reasons why oil decomposes faster at the surface of the ocean than at greater depth.\n \n
\n
\n
\n
\n
\n
\n (c(ii))\n
\n
\n
\n \n Oil spills can be treated with an enzyme mixture to speed up decomposition.\n \n
\n
\n \n Outline\n \n one\n \n factor to be considered when assessing the greenness of an enzyme mixture.\n \n
\n
\n
\n
\n
\n
\n (e)\n
\n
\n
\n \n The minor product, C\n \n 6\n \n H\n \n 5\n \n –CH\n \n 2\n \n –CH\n \n 2\n \n Br, can be directly converted to an intermediate compound,\n \n X\n \n , which can then be directly converted to the acid C\n \n 6\n \n H\n \n 5\n \n –CH\n \n 2\n \n –COOH.\n \n
\n
\n \n C\n \n 6\n \n H\n \n 5\n \n –CH\n \n 2\n \n –CH\n \n 2\n \n Br →\n \n X\n \n → C\n \n 6\n \n H\n \n 5\n \n –CH\n \n 2\n \n –COOH\n \n
\n
\n \n Identify\n \n X\n \n .\n \n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n
\n \n [\n \n ✔]\n \n \n
\n
\n
\n
\n \n \n \n Note:\n \n \n \n Do\n \n not\n \n penalize the use of brackets and “n”.\n \n \n
\n
\n \n \n Do\n \n not\n \n award the mark if the continuation bonds are missing.\n \n \n
\n
\n
\n (b)\n
\n
\n \n \n a\n \n = «\n \n \n \n =» 5.572 × 10\n \n –10\n \n «m»\n
\n \n \n OR\n \n \n
\n volume of unit cell = «(5.572 × 10\n \n –10\n \n m)\n \n 3\n \n × 10\n \n 6\n \n =» 1.73 × 10\n \n –22\n \n «cm\n \n 3\n \n »\n \n [✔]\n \n \n
\n
\n \n mass of unit cell =«\n \n \n \n =» 2.66 × 10\n \n –22\n \n «g»\n \n [✔]\n \n \n
\n
\n \n density = «\n \n \n \n » 1.54 «g cm\n \n –3\n \n »\n \n [✔]\n \n \n
\n
\n
\n
\n \n \n \n Note:\n \n Award\n \n [3]\n \n for correct final answer.\n \n \n
\n
\n
\n (c(i))\n
\n
\n \n \n Any two of:\n \n
\n surface water is warmer «so faster reaction rate»/more light/energy from the sun\n \n [✔]\n \n \n
\n
\n \n more oxygen «for aerobic bacteria/oxidation of oil»\n \n [✔]\n \n \n
\n
\n \n greater surface area\n \n [✔]\n \n \n
\n
\n
\n (c(ii))\n
\n
\n \n \n Any one of:\n \n
\n non-hazardous/toxic to the environment/living organisms\n \n [✔]\n \n \n
\n
\n \n energy requirements «during production»\n \n [✔]\n \n \n
\n
\n \n quantity/type of waste produced «during production»\n
\n \n \n OR\n \n \n
\n atom economy\n \n [✔]\n \n \n
\n
\n \n safety of process\n \n [✔]\n \n \n
\n
\n
\n
\n \n \n \n Note:\n \n Accept “use of solvents/toxic materials «during production»”.\n \n \n
\n
\n \n \n Do\n \n not\n \n accept “more steps involved”.\n \n \n
\n
\n
\n (e)\n
\n
\n \n C\n \n 6\n \n H\n \n 5\n \n –CH\n \n 2\n \n –CH\n \n 2\n \n OH\n \n [✔]\n \n \n
\n
\n",
+ "Examiners report": "
\n (a)\n
\n
\n Most candidates were able to draw the monomer correctly. Some candidates made careless mistakes writing C\n \n 6\n \n H\n \n 6\n \n .\n
\n
\n
\n (b)\n
\n
\n Majority of the candidates managed to get three marks in determining the density of the calcium.\n
\n
\n
\n (c(i))\n
\n
\n While many candidates did receive two marks for this question some candidates only suggested one reason or repeated the same reason (for example - heat and energy from the sun) even though the question clearly asked for two reasons.\n
\n
\n
\n (c(ii))\n
\n
\n Students tend to struggle with these questions and end up giving journalistic or vague answers that cannot be awarded marks. It is important for teachers to instruct students to give more specific answers directly related to the topics presented.\n
\n
\n
\n (e)\n
\n
\n Quite well answered though some candidates suggested an aldehyde rather than the alcohol, or forgot that C has two hydrogens apart from the -OH. In other cases, they left a Br there.\n
\n
\n",
+ "topics": [
+ "reactivity-2-how-much-how-fast-and-how-far",
+ "reactivity-3-what-are-the-mechanisms-of-chemical-change",
+ "structure-2-models-of-bonding-and-structure",
+ "tools"
+ ],
+ "subtopics": [
+ "reactivity-2-1-how-much-the-amount-of-chemical-change",
+ "reactivity-2-2-how-fast-the-rate-of-chemical-change",
+ "reactivity-3-2-electron-transfer-reactions",
+ "reactivity-3-4-electron-pair-sharing-reactions",
+ "structure-2-3-the-metallic-model",
+ "structure-2-4-from-models-to-materials",
+ "tool-3-mathematics"
+ ]
+ },
+ {
+ "question_id": "19M.2.SL.TZ2.9",
+ "Question": "
\n
\n
\n \n The regular rise and fall of sea levels, known as tides, can be used to generate energy.\n \n
\n
\n \n State\n \n one\n \n advantage, other than limiting greenhouse gas emissions, and one disadvantage of tidal power.\n \n
\n
\n
\n
\n \n Advantage:\n \n
\n
\n \n Disadvantage:\n \n
\n
\n
\n
\n
\n
\n (d(i))\n
\n
\n
\n \n Suggest\n \n two\n \n reasons why oil decomposes faster at the surface of the ocean than at greater depth.\n \n
\n
\n
\n
\n
\n
\n (d(ii))\n
\n
\n
\n \n Oil spills can be treated with an enzyme mixture to speed up decomposition.\n \n
\n
\n \n Outline\n \n one\n \n factor to be considered when assessing the greenness of an enzyme mixture.\n \n
\n
\n
\n
\n",
+ "Markscheme": "
\n
\n \n \n \n Advantage\n \n \n
\n \n Any one of:\n \n
\n renewable\n \n [✔]\n \n
\n predictable supply\n \n [✔]\n \n
\n tidal barrage may prevent flooding\n \n [✔]\n \n
\n effective at low speeds\n \n [✔]\n \n
\n long life-span\n \n [✔]\n \n
\n low cost to run\n \n [✔]\n \n \n
\n
\n \n
\n \n \n Disadvantage\n \n \n
\n \n Any one of:\n \n
\n cost of construction\n \n [✔]\n \n
\n changes/unknown effects on marine life\n \n [✔]\n \n
\n changes circulation of tides in the area\n \n [✔]\n \n
\n power output is variable\n \n [✔]\n \n
\n limited locations where feasible\n \n [✔]\n \n
\n equipment maintenance can be challenging\n \n [✔]\n \n
\n difficult to store energy\n \n [✔]\n \n \n
\n
\n
\n
\n \n \n \n Note\n \n : Do\n \n not\n \n accept vague generalizations.\n \n \n
\n
\n \n \n Do\n \n not\n \n accept economic issues for both advantage and disadvantage.\n \n \n
\n
\n \n \n Do\n \n not\n \n accept sustainable.\n \n \n
\n
\n \n \n Accept “energy” or “electricity” for “power”.\n \n \n
\n
\n
\n (d(i))\n
\n
\n \n \n Any two of:\n \n
\n surface water is warmer «so faster reaction rate»/more light/energy from the sun\n \n [✔]\n \n \n
\n
\n \n more oxygen «for aerobic bacteria/oxidation of oil»\n \n [✔]\n \n \n
\n
\n \n greater surface area\n \n [✔]\n \n \n
\n
\n
\n (d(ii))\n
\n
\n \n \n Any one of:\n \n
\n non-hazardous/toxic to the environment/living organisms\n \n [✔]\n \n \n
\n
\n \n energy requirements «during production»\n \n [✔]\n \n \n
\n
\n \n quantity/type of waste produced «during production»\n
\n \n \n OR\n \n \n
\n atom economy\n \n [✔]\n \n \n
\n
\n \n safety of process\n \n [✔]\n \n \n
\n
\n
\n
\n \n \n \n Note\n \n : Accept “use of solvents/toxic materials «during production»”.\n \n \n
\n
\n \n \n Do\n \n not\n \n accept “more steps involved”.\n \n \n
\n
\n",
+ "Examiners report": "
\n
\n Many candidates performed well on this question especially when identifying an advantage of tidal power. The students who struggled tended to either give vague or journalistic answers especially for the disadvantage of tidal power.\n
\n
\n
\n (d(i))\n
\n
\n Many candidates received two marks for this part while some candidates only suggested one reason or repeated the same reason (for example - heat and energy from the sun) even though the question clearly asked for two reasons.\n
\n
\n
\n (d(ii))\n
\n
\n The candidates struggled with this part and gave journalistic or vague answers that cannot be awarded marks. Atom economy was mentioned correctly by a few candidates.\n
\n
\n",
+ "topics": [
+ "reactivity-1-what-drives-chemical-reactions",
+ "reactivity-2-how-much-how-fast-and-how-far"
+ ],
+ "subtopics": [
+ "reactivity-1-3-energy-from-fuels",
+ "reactivity-2-1-how-much-the-amount-of-chemical-change",
+ "reactivity-2-2-how-fast-the-rate-of-chemical-change"
+ ]
+ },
+ {
+ "question_id": "19N.3.SL.TZ0.1",
+ "Question": "
\n
A student investigated how the type of acid in acid deposition affects limestone, a building material mainly composed of calcium carbonate.
\n

\n
The student monitored the mass of six similarly sized pieces of limestone. Three were placed in beakers containing 200.0 cm3 of 0.100 mol dm−3 nitric acid, HNO3 (aq), and the other three in 200.0 cm3 of 0.100 mol dm−3 sulfuric acid, H2SO4 (aq).
\n

\n
The limestone was removed from the acid, washed, dried with a paper towel and weighed every day at the same time and then replaced in the beakers.
\n
The student plotted the mass of one of the pieces of limestone placed in nitric acid against time.
\n

\n
[Source: © International Baccalaureate Organization 2019]
\n
\n
The student hypothesized that sulfuric acid would cause a larger mass loss than nitric acid.
\n
\n
Draw a best-fit line on the graph.
\n
[1]
\n
a.
\n
\n
Determine the initial rate of reaction of limestone with nitric acid from the graph.
\n
Show your working on the graph and include the units of the initial rate.
\n
[3]
\n
b(i).
\n
\n
Explain why the rate of reaction of limestone with nitric acid decreases and reaches zero over the period of five days.
\n
[2]
\n
b(ii).
\n
\n
Suggest a source of error in the procedure, assuming no human errors occurred and the balance was accurate.
\n
[1]
\n
b(iii).
\n
\n
Justify this hypothesis.
\n
[1]
\n
c(i).
\n
\n
The student obtained the following total mass losses.
\n

\n
She concluded that nitric acid caused more mass loss than sulfuric acid, which did not support her hypothesis.
\n
Suggest an explanation for the data, assuming that no errors were made by the student.
\n
[1]
\n
c(ii).
\n
",
+ "Markscheme": "
\n
best-fit smooth curve ✔
\n
NOTE: Do not accept a series of connected lines that pass through all points OR any straight line representation.
\n
a.
\n
\n
tangent drawn at time zero ✔
g day−1 ✔
0.16 ✔
\n
\n
NOTE: Accept other reasonable units for initial rate eg, mol dm−3 s−1, mol dm−3 min−1, g s−1 OR g min−1.
\n
M3 can only be awarded if the value corresponds to the correct unit given in M2.
Accept values for the initial rate for M3 in the range: 0.13 − 0.20 g day−1 OR 1.5 × 10−6 g s−1 − 2.3 × 10−6 g s−1 OR 7.5 × 10−8 − 1.2 × 10−7 mol dm−3 s−1 OR 4.5 × 10−6 − 6.9 × 10−6 mol dm−3 min−1 OR 9.0 × 10−5 − 1.4 × 10−4 g min−1 OR a range based on any other reasonable unit for rate.
\n
Ignore any negative rate value.
Award [2 max] for answers such as 0.12/0.11 g day−1, incorrectly obtained by using the first two points on the graph (the average rate between t = 0 and 1 day).
Award [1 max] for correctly calculating any other average rate.
\n
b(i).
\n
\n
acid used up
OR
acid is the limiting reactant ✔
\n
concentration of acid decreases
OR
less frequent collisions ✔
\n
NOTE: Award [1 max] for \"surface area decreases\" if the idea that CaCO3 is used up/acts as the limiting reactant” is conveyed for M1.
\n
Do not accept “reaction reaches equilibrium” for M2.
\n
b(ii).
\n
\n
surface area not uniform
NOTE: Accept “acids impure.
\n
OR
limestone pieces do not have same composition/source
NOTE: Accept “«limestone» contains impurities”.
\n
OR
limestone absorbed water «which increased mass»
\n
OR
acid removed from solution when limestone removed
NOTE: Accept “loss of limestone when dried\" OR \"loss of limestone due to crumbling when removed from beaker”.
\n
OR
«some» calcium sulfate deposited on limestone lost
\n
OR
pieces of paper towel may have stuck to limestone
\n
OR
beakers not covered/evaporation
\n
OR
temperature was not controlled ✔
\n
b(iii).
\n
\n
sulfuric acid is diprotic/contains two H+ «while nitric acid contains one H+»/releases more H+ «so reacts with more limestone»
OR
higher concentration of protons/H+ ✔
\n
NOTE: Ignore any reference to the relative strengths of sulfuric acid and nitric acid.
Accept “sulfuric acid has two hydrogens «whereas nitric has one»”.
Accept \"dibasic\" for \"diprotic\".
\n
c(i).
\n
\n
calcium sulfate remained/deposited on limestone «in sulfuric acid»
OR
reaction prevented/stopped by slightly soluble/deposited/layer of calcium sulfate ✔
\n
NOTE: Answer must refer to calcium sulfate.
\n
c(ii).
\n
",
+ "Examiners report": "
",
+ "topics": [
+ "empty-topic",
+ "reactivity-2-how-much-how-fast-and-how-far",
+ "tools"
+ ],
+ "subtopics": [
+ "reactivity-2-2-how-fast-the-rate-of-chemical-change",
+ "tool-1-experimental-techniques",
+ "tool-3-mathematics"
+ ]
+ },
+ {
+ "question_id": "19N.3.SL.TZ0.2",
+ "Question": "
\n
Ethanol was electrolysed at different voltages. The products at the anode, ethanoic acid, ethanal and carbon dioxide, were collected and analysed.
\n
The percentages of products obtained using three different catalysts mounted on a carbon anode, platinum (Pt/C), platinum and ruthenium alloy (PtRu/C) and platinum and tin alloy (PtSn/C) are shown.
\n

\n
Chemical yields of ethanoic acid, ethanal and carbon dioxide as a function of voltage for
oxidation of 0.100 mol dm−3 ethanol at Pt/C, PtRu/C and PtSn/C anodes at 80°C.
\n
[Source: Product Distributions and Efficiencies for Ethanol Oxidation in a Proton Exchange Membrane Electrolysis Cell, Rakan M. Altarawneh and Peter G. Pickup, Journal of the Electrochemical Society, 2017, volume 164, issue 7, http://jes.ecsdl.org/. Distributed under the terms of the Creative Commons Attribution 4.0 License (CC BY, http://creativecommons.org/licenses/by/4.0/)]
\n
\n
Describe the effect of increasing the voltage on the chemical yield of:
\n
Ethanal using Pt/C:
\n
Carbon dioxide using PtRu/C:
\n
[2]
\n
a(i).
\n
\n
Determine the change in the average oxidation state of carbon.
\n
From ethanol to ethanal:
\n
From ethanol to carbon dioxide:
\n
[2]
\n
a(ii).
\n
\n
List the three products at the anode from the least to the most oxidized.
\n
[1]
\n
a(iii).
\n
\n
Deduce, giving your reason, which catalyst is most effective at fully oxidizing ethanol.
\n
[1]
\n
b.
\n
",
+ "Markscheme": "
\n
Ethanal using Pt/C:
decreases ✔
\n
Carbon dioxide using PtRu/C:
«generally» increases AND then decreases ✔
\n
NOTE: Accept “no clear trend/pattern” OR “increases and decreases” OR “increases, reaches a plateau and «then» decreases” for M2.
\n
a(i).
\n
\n
From ethanol to ethanal:
−2 to −1
OR
+1/increases by 1 ✔
\n
NOTE: Do not accept “2− to 1−”.
\n
From ethanol to carbon dioxide:
−2 to +4
OR
+6/increases by 6 ✔
\n
NOTE: Do not accept “2− to 4+”.
\n
Do not penalize incorrect notation twice.
\n
Penalize incorrect oxidation state value of carbon in ethanol once only.
\n
a(ii).
\n
\n
ethanal < ethanoic acid < carbon dioxide ✔
\n
NOTE: Accept formulas.
No ECF from 2aii calculations.
\n
a(iii).
\n
\n
Pt/platinum/PtC AND highest yield of CO2 «at all voltages» ✔
\n
NOTE: ECF from 2aiii.
\n
b.
\n
",
+ "Examiners report": "
",
+ "topics": [
+ "empty-topic",
+ "reactivity-1-what-drives-chemical-reactions",
+ "structure-3-classification-of-matter"
+ ],
+ "subtopics": [
+ "reactivity-1-3-energy-from-fuels",
+ "structure-3-1-the-periodic-table-classification-of-elements"
+ ]
+ },
+ {
+ "question_id": "19N.2.HL.TZ0.4",
+ "Question": "
\n
A molecule of citric acid, C6H8O7, is shown.
\n

\n
The equation for the first dissociation of citric acid in water is
\n
C6H8O7 (aq) + H2O (l) C6H7O7− (aq) + H3O+ (aq)
\n
\n
Identify a conjugate acid–base pair in the equation.
\n
[1]
\n
a(i).
\n
\n
The value of Ka at 298 K for the first dissociation is 5.01 × 10−4.
\n
State, giving a reason, the strength of citric acid.
\n
[1]
\n
a(ii).
\n
\n
The dissociation of citric acid is an endothermic process. State the effect on the hydrogen ion concentration, [H+], and on Ka, of increasing the temperature.
\n

\n
[2]
\n
a(iii).
\n
\n
Calculate the standard Gibbs free energy change, , in kJ mol−1, for the first dissociation of citric acid at 298 K, using section 1 of the data booklet.
\n
[1]
\n
a(iv).
\n
\n
Comment on the spontaneity of the reaction at 298 K.
\n
[1]
\n
a(v).
\n
\n
Outline two laboratory methods of distinguishing between solutions of citric acid and hydrochloric acid of equal concentration, stating the expected observations.
\n
[2]
\n
b.
\n
",
+ "Markscheme": "
\n
C6H8O7 AND C6H7O7−
OR
H2O AND H3O+ ✔
\n
a(i).
\n
\n
weak acid AND partially dissociated
OR
weak acid AND equilibrium lies to left
OR
weak acid AND Ka < 1 ✔
\n
a(ii).
\n
\n

\n
a(iii).
\n
\n
« = −RT ln K = −8.31 J K–1 mol–1 × 298 K × ln(5.01 × 10–4) ÷ 1000 =» 18.8 «kJ mol–1» ✔
\n
a(iv).
\n
\n
non-spontaneous AND positive ✔
\n
a(v).
\n
\n
Any two of:
\n
«electrical» conductivity AND HCl greater ✔
\n
pH AND citric acid higher ✔
\n
titrate with strong base AND pH at equivalence higher for citric acid ✔
\n
add reactive metal/carbonate/hydrogen carbonate AND stronger effervescence/faster reaction with HCl ✔
\n
titration AND volume of alkali for complete neutralisation greater for citric acid ✔
\n
titrate with strong base AND more than one equivalence point for complete neutralisation of citric acid ✔
\n
titrate with strong base AND buffer zone with citric acid ✔
\n
\n
NOTE: Accept “add universal indicator AND HCl more red/pink” for M2.
\n
Accept any acid reaction AND HCl greater rise in temperature.
\n
Accept specific examples throughout.
\n
Do not accept “smell” or “taste”.
\n
b.
\n
",
+ "Examiners report": "
",
+ "topics": [
+ "reactivity-1-what-drives-chemical-reactions",
+ "reactivity-2-how-much-how-fast-and-how-far",
+ "reactivity-3-what-are-the-mechanisms-of-chemical-change",
+ "tools"
+ ],
+ "subtopics": [
+ "reactivity-1-4-entropy-and-spontaneity",
+ "reactivity-2-3-how-far-the-extent-of-chemical-change",
+ "reactivity-3-1-proton-transfer-reactions",
+ "tool-2-technology"
+ ]
+ },
+ {
+ "question_id": "19N.2.HL.TZ0.5",
+ "Question": "
\n
Another common acid found in food is ethanoic acid.
\n
\n
A sample of ethanoic acid was titrated with sodium hydroxide solution, and the following pH curve obtained.
\n

\n
Annotate the graph to show the buffer region and the volume of sodium hydroxide at the equivalence point.
\n
[2]
\n
a.
\n
\n
Identify the most suitable indicator for the titration using section 22 of the data booklet.
\n
[1]
\n
b(i).
\n
\n
Describe, using a suitable equation, how the buffer solution formed during the titration resists pH changes when a small amount of acid is added.
\n
[2]
\n
b(ii).
\n
",
+ "Markscheme": "
\n

\n
buffer region on graph ✔
equivalence point/Veq on graph ✔
\n
NOTE: Construction lines not required.
\n
a.
\n
\n
phenolphthalein ✔
\n
NOTE: Accept phenol red.
\n
b(i).
\n
\n
ALTERNATIVE 1:
H+ (aq) + CH3COO– (aq) → CH3COOH (aq) ✔
\n
added acid neutralised by ethanoate ions
OR
«weak» CH3COOH (aq)/ethanoic acid replaces H+ (aq)
OR
CH3COOH/CH3COO– ratio virtually/mostly unchanged ✔
\n
ALTERNATIVE 2:
CH3COOH (aq) H+ (aq) + CH3COO– (aq) ✔
\n
equilibrium shifts to the ethanoic acid side
OR
CH3COOH/CH3COO− ratio virtually/mostly unchanged ✔
\n
b(ii).
\n
",
+ "Examiners report": "
",
+ "topics": [
+ "reactivity-3-what-are-the-mechanisms-of-chemical-change"
+ ],
+ "subtopics": [
+ "reactivity-3-1-proton-transfer-reactions"
+ ]
+ },
+ {
+ "question_id": "19N.2.SL.TZ0.1",
+ "Question": "
\n
The equations show steps in the formation and decomposition of ozone in the stratosphere, some of which absorb ultraviolet light.
\n
Step 1 O2 → 2O•
\n
Step 2 O• + O2 → O3
\n
Step 3 O3 → O• + O2
\n
Step 4 O• + O3 → 2O2
\n
\n
Draw the Lewis structures of oxygen, O2, and ozone, O3.
\n
[2]
\n
a.
\n
\n
Outline why both bonds in the ozone molecule are the same length and predict the bond length in the ozone molecule. Refer to section 10 of the data booklet.
\n
Reason:
\n
Length:
\n
[2]
\n
b.
\n
\n
Distinguish ultraviolet light from visible light in terms of wavelength and energy.
\n
[1]
\n
c.
\n
\n
Discuss how the different bond strengths between the oxygen atoms in O2 and O3 in the ozone layer affect radiation reaching the Earth’s surface.
\n
[2]
\n
d.
\n
",
+ "Markscheme": "
\n

\n
NOTES: Coordinate bond may be represented by an arrow.
\n
Do not accept delocalized structure for ozone.
\n
a.
\n
\n
resonance «structures»
OR
delocalization of «the double/pi bond» electrons ✔
121 «pm» < length < 148 «pm» ✔
\n
NOTE: Accept any length between these two values.
\n
b.
\n
\n
«UV» shorter wavelength AND higher energy «than visible» ✔
\n
c.
\n
\n
«bond» in O2 stronger than in O3 ✔
\n
ozone absorbs lower frequency/energy «radiation than oxygen»
OR
ozone absorbs longer wavelength «radiation than oxygen» ✔
\n
\n
NOTE: Accept ozone «layer» absorbs a range of frequencies.
\n
d.
\n
",
+ "Examiners report": "
",
+ "topics": [
+ "structure-1-models-of-the-particulate-nature-of-matter",
+ "structure-2-models-of-bonding-and-structure"
+ ],
+ "subtopics": [
+ "structure-1-3-electron-configurations",
+ "structure-2-2-the-covalent-model"
+ ]
+ },
+ {
+ "question_id": "19N.2.SL.TZ0.16",
+ "Question": "
\n
\n (a)\n
\n
\n
\n \n Discuss the data.\n \n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n
\n \n Outline what is meant by the degradation of energy.\n \n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n \n «similar specific energy and» pentane has «much» larger energy density ✔\n \n
\n
\n \n \n Any two for\n \n [2 max]\n \n :\n \n
\n similar number of bonds/«C and H» atoms in 1 kg «leading to similar specific energy»\n
\n \n \n OR\n
\n \n \n only one carbon difference in structure «leading to similar specific energy» ✔\n
\n \n NOTE:\n \n \n Accept “both are alkanes” for M2.\n \n
\n \n
\n
\n \n pentane is a liquid\n \n \n AND\n \n \n butane is a gas «at STP» ✔\n
\n \n NOTE: Accept “pentane would be easier to transport”.\n \n
\n \n
\n
\n \n 1 m\n \n 3\n \n of pentane contains greater amount/mass than 1 m\n \n 3\n \n of butane ✔\n
\n \n NOTE: Accept “same volume” for “1 m\n \n 3\n \n ” and “more moles” for “greater amount” for M4.\n \n
\n \n
\n
\n
\n (b)\n
\n
\n \n energy converted to heat\n
\n \n \n OR\n \n \n
\n energy converted to less useful/dispersed forms\n
\n \n \n OR\n \n \n
\n energy converted to forms that have lower potential to do work\n
\n \n \n OR\n \n \n
\n heat transferred to the surroundings ✔\n \n
\n
\n \n \n NOTE: Reference to energy conversion/transfer required. Do\n \n not\n \n accept reference to loss of energy.\n \n \n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "reactivity-1-what-drives-chemical-reactions"
+ ],
+ "subtopics": [
+ "reactivity-1-3-energy-from-fuels"
+ ]
+ },
+ {
+ "question_id": "19N.2.SL.TZ0.2",
+ "Question": "
\n
The biochemical oxygen demand of a water sample can be determined by the following series of reactions. The final step is titration of the sample with sodium thiosulfate solution, Na2S2O3 (aq).
\n
2Mn2+ (aq) + O2 (aq) + 4OH− (aq) → 2MnO2 (s) + 2H2O (l)
\n
MnO2 (s) + 2I− (aq) + 4H+ (aq) → Mn2+ (aq) + I2 (aq) + 2H2O (l)
\n
2S2O32− (aq) + I2 (aq) → 2I− (aq) + S4O62− (aq)
\n
A student analysed two 300.0 cm3 samples of water taken from the school pond: one immediately (day 0), and the other after leaving it sealed in a dark cupboard for five days (day 5). The following results were obtained for the titration of the samples with 0.0100 mol dm−3 Na2S2O3 (aq).
\n

\n
\n
Determine the mole ratio of S2O32− to O2, using the balanced equations.
\n
[1]
\n
a(i).
\n
\n
Calculate the number of moles of oxygen in the day 0 sample.
\n
[2]
\n
a(ii).
\n
\n
The day 5 sample contained 5.03 × 10−5 moles of oxygen.
\n
Determine the 5-day biochemical oxygen demand of the pond, in mg dm−3 (“parts per million”, ppm).
\n
[2]
\n
a(iii).
\n
\n
Calculate the percentage uncertainty of the day 5 titre.
\n
[1]
\n
b(i).
\n
\n
Suggest a modification to the procedure that would make the results more reliable.
\n
[1]
\n
b(ii).
\n
",
+ "Markscheme": "
\n
✔
\n
« ✔
\n
NOTE: Award [2] for correct final answer.
\n
a(ii).
\n
\n
«difference in moles per dm3 = (6.45 × 10−5 − 5.03 × 10−5) × =»
\n
4.73 × 10−5 «mol dm−3» ✔
\n
«convert to mg per dm3: 4.73 × 10−5 mol dm−3 × 32.00 g mol−1 × 1000 mg g–1 = » 1.51 «ppm/mg dm−3» ✔
\n
NOTE: Award [2] for correct final answer.
\n
a(iii).
\n
\n
« «%»✔
\n
b(i).
\n
\n
repetition / take several samples «and average» ✔
\n
b(ii).
\n
",
+ "Examiners report": "
",
+ "topics": [
+ "reactivity-2-how-much-how-fast-and-how-far",
+ "tools"
+ ],
+ "subtopics": [
+ "reactivity-2-1-how-much-the-amount-of-chemical-change",
+ "tool-1-experimental-techniques",
+ "tool-3-mathematics"
+ ]
+ },
+ {
+ "question_id": "19N.2.SL.TZ0.4",
+ "Question": "
\n
A molecule of citric acid, C6H8O7, is shown.
\n

\n
The equation for the first dissociation of citric acid in water is
\n
C6H8O7 (aq) + H2O (l) C6H7O7− (aq) + H3O+ (aq)
\n
\n
Identify a conjugate acid–base pair in the equation.
\n
[1]
\n
a(i).
\n
\n
The value of the equilibrium constant for the first dissociation at 298 K is 5.01 × 10−4.
\n
State, giving a reason, the strength of citric acid.
\n
[1]
\n
a(ii).
\n
\n
The dissociation of citric acid is an endothermic process. State the effect on the hydrogen ion concentration, [H+], and on the equilibrium constant, of increasing the temperature.
\n

\n
[2]
\n
a(iii).
\n
\n
Outline one laboratory methods of distinguishing between solutions of citric acid and hydrochloric acid of equal concentration, stating the expected observations.
\n
[1]
\n
b.
\n
",
+ "Markscheme": "
\n
C6H8O7 AND C6H7O7−
OR
H2O AND H3O+ ✔
\n
a(i).
\n
\n
weak acid AND partially dissociated
OR
weak acid AND equilibrium lies to left
OR
weak acid AND Kc/Ka<1 ✔
\n
a(ii).
\n
\n

\n
a(iii).
\n
\n
Any one of:
«electrical» conductivity AND HCl greater ✔
pH AND citric acid higher ✔
titrate with strong base AND pH at equivalence higher for citric acid ✔
add reactive metal/carbonate/hydrogen carbonate AND stronger effervescence/faster reaction with HCl ✔
titration AND volume of alkali for complete neutralisation greater for citric acid ✔
titrate with strong base AND more than one equivalence point for complete neutralisation of citric acid ✔
titrate with strong base AND buffer zone with citric acid ✔
\n
\n
NOTE: Accept “add universal indicator AND HCl more red/pink” for M2.
\n
Accept any acid reaction AND HCl greater rise in temperature.
\n
Accept specific examples throughout.
\n
Do not accept “smell” or “taste”.
\n
b.
\n
",
+ "Examiners report": "
",
+ "topics": [
+ "reactivity-2-how-much-how-fast-and-how-far",
+ "reactivity-3-what-are-the-mechanisms-of-chemical-change",
+ "tools"
+ ],
+ "subtopics": [
+ "reactivity-2-3-how-far-the-extent-of-chemical-change",
+ "reactivity-3-1-proton-transfer-reactions",
+ "tool-2-technology"
+ ]
+ },
+ {
+ "question_id": "19N.2.SL.TZ0.6",
+ "Question": "
\n
Automobile air bags inflate by a rapid decomposition reaction. One typical compound used is guanidinium nitrate, C(NH2)3NO3, which decomposes very rapidly to form nitrogen, water vapour and carbon.
\n
\n
Deduce the equation for the decomposition of guanidinium nitrate.
\n
[1]
\n
a(i).
\n
\n
Calculate the total number of moles of gas produced from the decomposition of 10.0 g of guanidinium nitrate.
\n
[1]
\n
a(ii).
\n
\n
Calculate the pressure, in kPa, of this gas in a 10.0 dm3 air bag at 127°C, assuming no gas escapes.
\n
[1]
\n
a(iii).
\n
\n
Suggest why water vapour deviates significantly from ideal behaviour when the gases are cooled, while nitrogen does not.
\n
[2]
\n
a(iv).
\n
\n
Another airbag reactant produces nitrogen gas and sodium.
\n
Suggest, including an equation, why the products of this reactant present a safety hazard.
\n
[2]
\n
b.
\n
",
+ "Markscheme": "
\n
C(NH2)3NO3 (s) → 2N2 (g) + 3H2O (g) + C (s) ✔
\n
a(i).
\n
\n
moles of gas = « » 0.409 «mol» ✔
\n
a(ii).
\n
\n
«» = 136 «kPa» ✔
\n
a(iii).
\n
\n
Any two of:
nitrogen non-polar/London/dispersion forces AND water polar/H-bonding ✔
water has «much» stronger intermolecular forces ✔
water molecules attract/condense/occupy smaller volume «and therefore deviate from ideal behaviour» ✔
\n
a(iv).
\n
\n
2Na (s) + 2H2O (l) → 2NaOH (aq) + H2 (g) ✔
\n
hydrogen explosive
OR
highly exothermic reaction
OR
sodium reacts violently with water
OR
forms strong alkali ✔
\n
NOTE: Accept the equation of combustion of hydrogen.
Do not accept just “sodium is reactive/dangerous”.
\n
b.
\n
",
+ "Examiners report": "
",
+ "topics": [
+ "reactivity-2-how-much-how-fast-and-how-far",
+ "structure-1-models-of-the-particulate-nature-of-matter",
+ "structure-3-classification-of-matter",
+ "tools"
+ ],
+ "subtopics": [
+ "reactivity-2-1-how-much-the-amount-of-chemical-change",
+ "structure-1-5-ideal-gases",
+ "structure-3-1-the-periodic-table-classification-of-elements",
+ "tool-1-experimental-techniques"
+ ]
+ },
+ {
+ "question_id": "20N.3.SL.TZ0.1",
+ "Question": "
\n
In order to determine the oil content of different types of potato crisps (chips), a student weighed of crushed crisps and mixed them with of non-polar solvent.
\n
She assumed all the oil in the crisps dissolved in the solvent.
\n
The student then filtered the mixture to remove any solids, and gently heated the solution on a hot plate to evaporate the solvent.
\n
She measured the mass of the oil that remained from each type of crisps
\n
\n
Suggest why a non-polar solvent was needed.
\n
[1]
\n
a.
\n
\n
State one reason why the mixture was not heated strongly.
\n
[1]
\n
b.
\n
\n
Non-polar solvents can be toxic. Suggest a modification to the experiment which allows the evaporated solvent to be collected.
\n
[1]
\n
c.
\n
\n
Suggest one source of error in the experiment, excluding faulty apparatus and human error, that would lead to the following:
\n

\n
[2]
\n
d.
\n
",
+ "Markscheme": "
\n
oil is non-polar «and dissolves best in non-polar solvents»
OR
oil does not dissolve in polar solvents ✔
\n
Do not accept “like dissolves like” only.
\n
a.
\n
\n
solvent/oil is flammable
OR
solvent/oil must be kept below its flash point
OR
oxidation/decomposition of oil
OR
mixture has a low boiling point ✔
\n
Accept “to prevent evaporation of oil”.
\n
b.
\n
\n
distillation «instead of evaporation» ✔
\n
Accept “pass vapour through a condenser and collect liquid”.
\n
Do not accept “condensation” without experimental details.
\n
c.
\n
\n
Experimental mass greater than actual mass of oil in crisps:
other substances «in the crisps» are soluble in the solvent
OR
not all the solvent evaporates ✔
\n
Experimental mass less than actual mass of oil in crisps:
not all oil dissolved/extracted ✔
\n
Accept “oil evaporated” OR “oil burned/decomposed” OR “oil absorbed by the filter” OR “assumption «all oil dissolved» was wrong” for M2.
\n
Do not accept examples of human errors OR faulty apparatus.
\n
d.
\n
",
+ "Examiners report": "
\n
A well answered question where replies used all the alternatives provided. Very few candidates limited their answer to \"like dissolves like\" and while this expression was used most student elaborated with higher quality answer. Some common incorrect responses included students talking about dissolving the crisps (chips) or indicating the oil was a polar compound.
\n
a.
\n
\n
Another correctly answered question. As accepted by notes many candidates scored by stating \"to prevent evaporation of oil\". This resulted in the same argument scoring twice as often used for 1d as well. Some students incorrectly indicated the problem was to prevent the evaporation of the solvent which was the point of this step in the experiment. This could indicate a general lack of understanding of experimental methods.
\n
b.
\n
\n
A bit disappointing as the number of correct answers were substantially lower than expected. Many students responded using a fume hood or other method to remove the solvent. Once again this indicates a general misunderstanding about experimental methods.
\n
c.
\n
\n
Even weak candidates scored at least one point and often both. One common pitfall was to invert the arguments or provide answers excluded by the stem. A frequent incorrect answer was identification of faulty apparatus and human error which was specifically excluded in the question.
\n
d.
\n
",
+ "topics": [
+ "tools"
+ ],
+ "subtopics": [
+ "tool-1-experimental-techniques",
+ "tool-3-mathematics"
+ ]
+ },
+ {
+ "question_id": "20N.1B.SL.TZ0.18",
+ "Question": "
\n
\n (a(ii))\n
\n
\n
\n \n The vapour pressure of pure ethanal at\n \n \n \n is\n \n .\n \n
\n
\n \n Calculate the vapour pressure of ethanal above the liquid mixture at\n \n \n \n .\n \n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n
\n \n Describe how this mixture is separated by fractional distillation.\n \n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a(ii))\n
\n
\n \n ✔\n
\n
\n
\n (b)\n
\n
\n \n Any two of:\n \n
\n continuous evaporation and condensation\n
\n \n \n OR\n \n \n
\n increased surface area in column helps condensation ✔\n
\n \n Accept “glass «beads» aid condensation «in fractionating column»”.\n \n
\n
\n temperature decreases up the fractionating column ✔\n
\n
\n liquids condense at different heights\n
\n \n \n OR\n \n \n
\n liquid of lowest boiling point collected first\n
\n \n \n OR\n \n \n
\n liquid with weakest intermolecular forces collected first\n
\n \n \n OR\n \n \n
\n most volatile component collected first\n
\n \n \n OR\n \n \n
\n fractions/liquids collected in order of boiling point/volatility ✔\n
\n \n Accept “liquids collected in order of molar mass”.\n \n
\n
\n",
+ "Examiners report": "
\n (a(ii))\n
\n
\n This question involving Raoult's Law was very well answered and most were able to calculate the mole fraction of ethanal in the mixture (0.250) and the corresponding vapour pressure of ethanal above the liquid mixture at 20 °C (25.3 kPa). There was one G2 comment on this question. One teacher stated that the diagram shows four fractions but the stem of the question specifically states only three components and hence the fourth test tube is not required. The teacher commented that some students may have been distracted by this.\n
\n
\n
\n (b)\n
\n
\n In this question candidates were required to describe how the mixture can be separated by fractional distillation. Only the better candidates scored both marks, though most gained at least one mark, usually for stating that the most volatile component is collected first. Many did not convey the idea that there is continuous evaporation and condensation in the process or the fact that the temperature decreases up the fractionating column.\n
\n
\n",
+ "topics": [
+ "structure-1-models-of-the-particulate-nature-of-matter",
+ "tools"
+ ],
+ "subtopics": [
+ "structure-1-5-ideal-gases",
+ "tool-1-experimental-techniques"
+ ]
+ },
+ {
+ "question_id": "20N.3.SL.TZ0.2",
+ "Question": "
\n
An investigation was carried out to determine the effect of chain length of the alcohol on the equilibrium constant, , for the reversible reaction:
\n
\n
The reactants, products and the catalyst form a homogeneous mixture.
\n
Fixed volumes of each alcohol, the ethanoic acid and the sulfuric acid catalyst were placed in sealed conical flasks.
\n
At equilibrium, the flasks were placed in an ice bath, and samples of each flask titrated with to determine the ethanoic acid concentration present in the equilibrium mixture.
\n
The following processed results were obtained.
\n

\n
© International Baccalaureate Organization 2020
\n
\n
Identify the independent and dependent variables in this experiment.
\n

\n
[1]
\n
a.
\n
\n
The ice bath is used at equilibrium to slow down the forward and reverse reactions. Explain why adding a large amount of water to the reaction mixture would also slow down both reactions.
\n
[2]
\n
b.
\n
\n
Suggest why the titration must be conducted quickly even though a low temperature is maintained.
\n
[1]
\n
c.
\n
\n
An additional experiment was conducted in which only the sulfuric acid catalyst was titrated with . Outline why this experiment was necessary.
\n
[1]
\n
d.
\n
\n
Calculate the percentage uncertainty and percentage error in the experimentally determined value of for methanol.
\n

\n
[2]
\n
e.
\n
\n
Comment on the magnitudes of random and systematic errors in this experiment using the answers in (e).
\n
[2]
\n
f.
\n
\n
Suggest a risk of using sulfuric acid as the catalyst.
\n
[1]
\n
g.
\n
",
+ "Markscheme": "
\n
Independent variable:
chain length OR number of carbon «atoms in alcohol»
AND
Dependent variable:
volume of OR /equilibrium constant OR equilibrium concentration/moles of ✔
\n
a.
\n
\n
dilution/lower concentrations ✔
\n
less frequent collisions «per unit volume» ✔
\n
Accept “lowers concentration of acid catalyst” for M1. M2 must refer to increase in activation energy or different pathway.
\n
Do not accept responses referring to equilibrium.
\n
b.
\n
\n
equilibrium shifts to left
OR
more ethanoic acid is produced «as ethanoic acid is neutralized»
OR
prevents/slows down ester hydrolysis ✔
\n
Accept “prevents equilibrium shift” if described correctly without direction.
\n
c.
\n
\n
to determine volume/moles of used up by the catalyst/sulfuric acid «in the titration»
OR
to eliminate/reduce «systematic» error caused by acid catalyst ✔
\n
Do not accept “control” OR “standard” alone.
\n
d.
\n
\n
Percentage uncertainty:
✔
\n
Percentage error:
✔
\n
Award [1 max] if calculations are reversed OR if incorrect alcohol is used.
\n
e.
\n
\n
Any two:
\n
large percentage error means large systematic error «in procedure» ✔
\n
small percentage uncertainty means small random errors ✔
\n
random errors smaller than systematic error ✔
\n
Award [2] for “both random and systematic errors are significant.”
\n
f.
\n
\n
corrosive/burns/irritant/strong oxidizing agent/carcinogenic
OR
disposal is an environmental issue
OR
causes other side reactions/dehydration/decomposition ✔
\n
Do not accept just “risk of accidents” OR “health risks” OR “hazardous”.
\n
g.
\n
",
+ "Examiners report": "",
+ "topics": [
+ "reactivity-2-how-much-how-fast-and-how-far",
+ "reactivity-3-what-are-the-mechanisms-of-chemical-change",
+ "tools"
+ ],
+ "subtopics": [
+ "reactivity-2-3-how-far-the-extent-of-chemical-change",
+ "reactivity-3-1-proton-transfer-reactions",
+ "tool-1-experimental-techniques",
+ "tool-3-mathematics"
+ ]
+ },
+ {
+ "question_id": "20N.2.HL.TZ0.7",
+ "Question": "
\n
Nitrogen monoxide reacts with oxygen gas to form nitrogen dioxide.
\n
The following experimental data was obtained.
\n

\n
Deduce the partial order of reaction with respect to nitrogen monoxide and oxygen.
\n

\n
\n
\n
[2]
\n
a.
\n
\n
Nitrogen monoxide reacts with oxygen gas to form nitrogen dioxide.
\n
Deduce, giving a reason, whether the following mechanism is possible.
\n

\n
\n
[1]
\n
b.
\n
",
+ "Markscheme": "
\n
: second ✔
: first ✔
\n
a.
\n
\n
not possible AND «proposed» mechanism does not match experimental rate law
OR
not possible AND «proposed» mechanism shows zero/not first order with respect to oxygen ✔
\n
b.
\n
",
+ "Examiners report": "
\n
Most candidates could correctly deduce the order of each reactant from rate experimental rate data.
\n
a.
\n
\n
60% of candidates could explain why the proposed reaction mechanism was inconsistent with the empirical data given.
\n
b.
\n
",
+ "topics": [
+ "reactivity-2-how-much-how-fast-and-how-far"
+ ],
+ "subtopics": [
+ "reactivity-2-2-how-fast-the-rate-of-chemical-change"
+ ]
+ },
+ {
+ "question_id": "20N.2.SL.TZ0.11",
+ "Question": "
\n
\n (a)\n
\n
\n
\n \n Calculate the energy released, in\n \n , from the complete combustion of\n \n \n \n \n \n of ethanol.\n \n
\n
\n
\n
\n
\n
\n (c)\n
\n
\n
\n \n Outline the advantages and disadvantages of using biodiesel instead of gasoline as fuel for a car. Exclude any discussion of cost.\n \n
\n
\n \n
\n \n
\n
\n
\n
\n
\n
\n (d)\n
\n
\n
\n \n A mixture of gasoline and ethanol is often used as a fuel. Suggest an advantage of such a mixture over the use of pure gasoline. Exclude any discussion of cost.\n \n
\n
\n
\n
\n
\n
\n
\n
\n (e(ii))\n
\n
\n
\n \n Methane is another greenhouse gas. Contrast the reasons why methane and carbon dioxide are considered significant greenhouse gases.\n \n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n \n ✔\n
\n
\n
\n (c)\n
\n
\n \n Advantages:\n \n [2 max]\n \n \n
\n
\n renewable ✔\n
\n
\n uses up waste «such as used cooking oil» ✔\n
\n
\n lower carbon footprint/carbon neutral ✔\n
\n
\n higher flashpoint ✔\n
\n
\n produces less\n \n /\n \n
\n \n \n OR\n \n \n
\n less polluting emissions ✔\n
\n
\n has lubricating properties\n
\n \n \n OR\n \n \n
\n preserves/increases lifespan of engine ✔\n
\n
\n increases the life of the catalytic converter ✔\n
\n
\n eliminates dependence on foreign suppliers ✔\n
\n
\n does not require pipelines/infrastructure «to produce» ✔\n
\n
\n relatively less destruction of habitat compared to obtaining petrochemicals ✔\n
\n
\n
\n
\n \n Accept “higher energy density” OR “biodegradable” for advantage.\n \n
\n
\n
\n \n Disadvantages:\n \n [2 max]\n \n \n
\n
\n needs conversion/transesterification ✔\n
\n
\n takes time to produce/grow plants ✔\n
\n
\n takes up land\n
\n \n \n OR\n \n \n
\n deforestation ✔\n
\n
\n fertilizers/pesticides/phosphates/nitrates «used in production of crops» have negative environmental effects ✔\n
\n
\n biodiversity affected\n
\n \n \n OR\n \n \n
\n loss of habitats «due to energy crop plantations» ✔\n
\n
\n cannot be used at low temperatures ✔\n
\n
\n variable quality «in production» ✔\n
\n
\n high viscosity/can clog/damage engines ✔\n
\n
\n
\n \n Accept “lower specific energy” as disadvantage.\n \n
\n
\n \n Do\n \n not\n \n accept “lower octane number” as disadvantage”.\n \n
\n
\n
\n (d)\n
\n
\n \n Any one:\n \n
\n
\n uses up fossil fuels more slowly ✔\n
\n
\n lower carbon footprint/CO2 emissions ✔\n
\n
\n undergoes more complete combustion ✔\n
\n
\n produces fewer particulates ✔\n
\n
\n higher octane number/rating\n
\n \n \n OR\n \n \n
\n less knocking ✔\n
\n
\n prevents fuel injection system build up\n
\n \n \n OR\n \n \n
\n helps keep engine clean ✔\n
\n
\n
\n \n Accept an example of a suitable advantage even if repeated from 11c.\n \n
\n
\n
\n (e(ii))\n
\n
\n carbon dioxide is highly/more abundant «in the atmosphere» ✔\n
\n
\n methane is more effective/potent «as a greenhouse gas»\n
\n \n \n OR\n \n \n
\n methane/better/more effective at absorbing\n \n «radiation»\n
\n \n \n OR\n \n \n
\n methane has greater greenhouse factor\n
\n \n \n OR\n \n \n
\n methane has greater global warming potential/GWP✔\n
\n
\n
\n \n Accept “carbon dioxide contributes more to global warming” for M1.\n \n
\n
\n",
+ "Examiners report": "
\n (a)\n
\n
\n Almost all were able to calculate the energy released from the complete combustion of ethanol.\n
\n
\n
\n (c)\n
\n
\n Most gained at least one mark for an advantage of using biodiesel instead of gasoline as fuel for a car and most scored one mark at least for a disadvantage of biodiesel. Many conveyed solid understanding, though the disadvantages were not as well articulated as the advantages. Some incorrectly based their responses on cost factors which were excluded as outlined in the stem of the question.\n
\n
\n
\n (d)\n
\n
\n Most scored the one mark for this question, with \"less knocking or higher octane number/rating\" the most common correct answer seen.\n
\n
\n
\n (e(ii))\n
\n
\n This was another \"Contrast-type\" question, which was better answered compared to (e)(i). Many scored both marks by stating that carbon dioxide is more abundant in the atmosphere whereas methane is more effective at absorbing IR radiation.\n
\n
\n",
+ "topics": [
+ "reactivity-1-what-drives-chemical-reactions"
+ ],
+ "subtopics": [
+ "reactivity-1-3-energy-from-fuels"
+ ]
+ },
+ {
+ "question_id": "20N.2.SL.TZ0.9",
+ "Question": "
\n
\n (a)\n
\n
\n
\n \n Calculate the energy released, in\n \n , from the complete combustion of\n \n \n \n \n \n of ethanol.\n \n
\n
\n
\n
\n
\n
\n (c)\n
\n
\n
\n \n Outline the advantages and disadvantages of using biodiesel instead of gasoline as fuel for a car. Exclude any discussion of cost.\n \n
\n
\n \n
\n \n
\n
\n
\n
\n
\n
\n (d)\n
\n
\n
\n \n A mixture of gasoline and ethanol is often used as a fuel. Suggest an advantage of such a mixture over the use of pure gasoline. Exclude any discussion of cost.\n \n
\n
\n
\n
\n
\n
\n
\n
\n (f(ii))\n
\n
\n
\n \n Methane is another greenhouse gas. Contrast the reasons why methane and carbon dioxide are considered significant greenhouse gases.\n \n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n \n ✔\n
\n
\n
\n (c)\n
\n
\n \n Advantages:\n \n [2 max]\n \n \n
\n
\n renewable ✔\n
\n
\n uses up waste «such as used cooking oil» ✔\n
\n
\n lower carbon footprint/carbon neutral ✔\n
\n
\n higher flashpoint ✔\n
\n
\n produces less\n \n /\n \n
\n \n \n OR\n \n \n
\n less polluting emissions ✔\n
\n
\n has lubricating properties\n
\n \n \n OR\n \n \n
\n preserves/increases lifespan of engine ✔\n
\n
\n increases the life of the catalytic converter ✔\n
\n
\n eliminates dependence on foreign suppliers ✔\n
\n
\n does not require pipelines/infrastructure «to produce» ✔\n
\n
\n relatively less destruction of habitat compared to obtaining petrochemicals ✔\n
\n
\n
\n
\n \n Accept “higher energy density” OR “biodegradable” for advantage.\n \n
\n
\n
\n \n Disadvantages:\n \n [2 max]\n \n \n
\n
\n needs conversion/transesterification ✔\n
\n
\n takes time to produce/grow plants ✔\n
\n
\n takes up land\n
\n \n \n OR\n \n \n
\n deforestation ✔\n
\n
\n fertilizers/pesticides/phosphates/nitrates «used in production of crops» have negative environmental effects ✔\n
\n
\n biodiversity affected\n
\n \n \n OR\n \n \n
\n loss of habitats «due to energy crop plantations» ✔\n
\n
\n cannot be used at low temperatures ✔\n
\n
\n variable quality «in production» ✔\n
\n
\n high viscosity/can clog/damage engines ✔\n
\n
\n
\n \n Accept “lower specific energy” as disadvantage.\n \n
\n
\n \n Do\n \n not\n \n accept “lower octane number” as disadvantage”.\n \n
\n
\n
\n (d)\n
\n
\n \n Any one:\n \n
\n
\n uses up fossil fuels more slowly ✔\n
\n
\n lower carbon footprint/CO2 emissions ✔\n
\n
\n undergoes more complete combustion ✔\n
\n
\n produces fewer particulates ✔\n
\n
\n higher octane number/rating\n
\n \n \n OR\n \n \n
\n less knocking ✔\n
\n
\n prevents fuel injection system build up\n
\n \n \n OR\n \n \n
\n helps keep engine clean ✔\n
\n
\n
\n \n Accept an example of a suitable advantage even if repeated from 9c.\n \n
\n
\n
\n (f(ii))\n
\n
\n carbon dioxide is highly/more abundant «in the atmosphere» ✔\n
\n
\n methane is more effective/potent «as a greenhouse gas»\n
\n \n \n OR\n \n \n
\n methane/better/more effective at absorbing\n \n «radiation»\n
\n \n \n OR\n \n \n
\n methane has greater greenhouse factor\n
\n \n \n OR\n \n \n
\n methane has greater global warming potential/GWP✔\n
\n
\n
\n \n Accept “carbon dioxide contributes more to global warming” for M1.\n \n
\n
\n",
+ "Examiners report": "
\n (a)\n
\n
\n Even rather weak candidates answered this one correctly.\n
\n
\n
\n (c)\n
\n
\n There were many good answers, but few candidates fully scored. Higher energy density and lower specific energy were quite common, and so references to damaging engines. Many students spent more time explaining each advantage rather than simply outlining. There were fewer journalistic and generic answers for this type of question than in the past.\n
\n
\n
\n (d)\n
\n
\n Another question where many candidates obtained the mark. In quite a few cases students repeated the argument for (c) and this allowed them to get two points for the same answer.\n
\n
\n
\n (f(ii))\n
\n
\n We received many good answers, but it was worrying the number of students that still provided general and shallow comments. Of the 3 contrast question this had the best response.\n
\n
\n",
+ "topics": [
+ "reactivity-1-what-drives-chemical-reactions"
+ ],
+ "subtopics": [
+ "reactivity-1-3-energy-from-fuels"
+ ]
+ },
+ {
+ "question_id": "21M.2.HL.TZ1.1",
+ "Question": "
\n
Iron may be extracted from iron (II) sulfide, FeS.
\n
\n
Iron (II) sulfide, FeS, is ionically bonded.
\n
\n
The first step in the extraction of iron from iron (II) sulfide is to roast it in air to form iron (III) oxide and sulfur dioxide.
\n
\n
Outline why metals, like iron, can conduct electricity.
\n
[1]
\n
a.
\n
\n
Justify why sulfur is classified as a non-metal by giving two of its chemical properties.
\n
[2]
\n
b.
\n
\n
Sketch the first eight successive ionisation energies of sulfur.
\n

\n
[2]
\n
c.
\n
\n
Describe the bonding in this type of solid.
\n
[2]
\n
d(i).
\n
\n
State a technique that could be used to determine the crystal structure of the solid compound.
\n
[1]
\n
d(ii).
\n
\n
State the full electron configuration of the sulfide ion.
\n
[1]
\n
d(iii).
\n
\n
Outline, in terms of their electronic structures, why the ionic radius of the sulfide ion is greater than that of the oxide ion.
\n
[1]
\n
d(iv).
\n
\n
Suggest why chemists find it convenient to classify bonding into ionic, covalent and metallic.
\n
[1]
\n
d(v).
\n
\n
Write the equation for this reaction.
\n
[1]
\n
e(i).
\n
\n
Deduce the change in the oxidation state of sulfur.
\n
[1]
\n
e(ii).
\n
\n
Suggest why this process might raise environmental concerns.
\n
[1]
\n
e(iii).
\n
\n
Explain why the addition of small amounts of carbon to iron makes the metal harder.
\n
[2]
\n
f.
\n
",
+ "Markscheme": "
\n
mobile/delocalized «sea of» electrons
\n
a.
\n
\n
Any two of:
\n
forms acidic oxides «rather than basic oxides» ✔
\n
forms covalent/bonds compounds «with other non-metals» ✔
\n
forms anions «rather than cations» ✔
\n
behaves as an oxidizing agent «rather than a reducing agent» ✔
\n
Award [1 max] for 2 correct non-chemical properties such as non-conductor, high ionisation energy, high electronegativity, low electron affinity if no marks for chemical properties are awarded.
\n
b.
\n
\n

\n
two regions of small increases AND a large increase between them✔
\n
large increase from 6th to 7th ✔
\n
Accept line/curve showing these trends.
\n
c.
\n
\n
electrostatic attraction ✔
\n
between oppositely charged ions/between Fe2+ and S2− ✔
\n
d(i).
\n
\n
X-ray crystallography ✔
\n
d(ii).
\n
\n
1s2 2s2 2p6 3s2 3p6 ✔
\n
Do not accept “[Ne] 3s2 3p6”.
\n
d(iii).
\n
\n
«valence» electrons further from nucleus/extra electron shell/ electrons in third/3s/3p level «not second/2s/2p»✔
\n
Accept 2,8 (for O2–) and 2,8,8 (for S2–)
\n
d(iv).
\n
\n
allows them to explain the properties of different compounds/substances
OR
enables them to generalise about substances
OR
enables them to make predictions ✔
\n
Accept other valid answers.
\n
d(v).
\n
\n
4FeS(s) + 7O2(g) → 2Fe2O3(s) + 4SO2(g) ✔
\n
Accept any correct ratio.
\n
e(i).
\n
\n
+6
OR
−2 to +4 ✔
\n
Accept “6/VI”.
Accept “−II, 4//IV”.
Do not accept 2- to 4+.
\n
e(ii).
\n
\n
sulfur dioxide/SO2 causes acid rain ✔
\n
Accept sulfur dioxide/SO2/dust causes respiratory problems
Do not accept just “causes respiratory problems” or “causes acid rain”.
\n
e(iii).
\n
\n
disrupts the regular arrangement «of iron atoms/ions»
OR
carbon different size «to iron atoms/ions» ✔
\n
prevents layers/atoms sliding over each other ✔
\n
f.
\n
",
+ "Examiners report": "
",
+ "topics": [
+ "reactivity-2-how-much-how-fast-and-how-far",
+ "reactivity-3-what-are-the-mechanisms-of-chemical-change",
+ "structure-1-models-of-the-particulate-nature-of-matter",
+ "structure-2-models-of-bonding-and-structure",
+ "structure-3-classification-of-matter"
+ ],
+ "subtopics": [
+ "reactivity-2-1-how-much-the-amount-of-chemical-change",
+ "reactivity-3-2-electron-transfer-reactions",
+ "structure-1-3-electron-configurations",
+ "structure-2-1-the-ionic-model",
+ "structure-2-2-the-covalent-model",
+ "structure-2-3-the-metallic-model",
+ "structure-2-4-from-models-to-materials",
+ "structure-3-1-the-periodic-table-classification-of-elements"
+ ]
+ },
+ {
+ "question_id": "21M.2.HL.TZ1.6",
+ "Question": "
\n
When dinitrogen pentoxide, N2O5, is heated the colourless gas undergoes thermal decomposition to produce brown nitrogen dioxide:
\n
N2O5 (g) → 2NO2 (g) + O2 (g)
\n
\n
Data for the decomposition at constant temperature is given.
\n

\n
\n
Suggest how the extent of decomposition could be measured.
\n
[1]
\n
a.
\n
\n
Plot the missing point on the graph and draw the best-fit line.
\n

\n
[2]
\n
b(i).
\n
\n
Outline why increasing the concentration of N2O5 increases the rate of reaction.
\n
[1]
\n
b(ii).
\n
\n
Write the rate expression for this reaction.
\n
[1]
\n
b(iii).
\n
\n
Calculate the value of the rate constant, k, giving its units.
\n
[3]
\n
b(iv).
\n
",
+ "Markscheme": "
\n
use colorimeter
OR
change in colour
OR
change in volume
OR
change in pressure ✔
\n
Accept suitable instruments, e.g. pressure probe/oxygen sensor.
\n
a.
\n
\n

\n
point correct ✔
\n
straight line passing close to all points AND through origin ✔
\n
Accept free hand drawn line as long as attempt to be linear and meets criteria for M2.
\n
b(i).
\n
\n
greater frequency of collisions «as concentration increases»
OR
more collisions per unit time «as concentration increases» ✔
\n
Accept “rate/chance/probability/likelihood” instead of “frequency”.
\n
Do not accept just “more collisions”.
\n
b(ii).
\n
\n
rate = k[N2O5] ✔
\n
b(iii).
\n
\n
k = ✔
\n
«k = = » 0.030 «min–1» ✔
\n
min–1 ✔
\n
M1 can be awarded from correct M2 if not explicitly stated.
\n
Accept k = gradient.
\n
Accept values in the range 0.028–0.032.
\n
Award [3] for correct final answer.
\n
b(iv).
\n
",
+ "Examiners report": "
",
+ "topics": [
+ "reactivity-2-how-much-how-fast-and-how-far",
+ "tools"
+ ],
+ "subtopics": [
+ "reactivity-2-2-how-fast-the-rate-of-chemical-change",
+ "reactivity-2-3-how-far-the-extent-of-chemical-change",
+ "tool-1-experimental-techniques",
+ "tool-3-mathematics"
+ ]
+ },
+ {
+ "question_id": "21M.2.HL.TZ1.7",
+ "Question": "
\n
Oxygen exists as two allotropes, diatomic oxygen, O2, and ozone, O3.
\n
\n
Draw a Lewis (electron dot) structure for ozone.
\n
[1]
\n
a(i).
\n
\n
Discuss the relative length of the two O−O bonds in ozone.
\n
[2]
\n
a(ii).
\n
\n
Explain why there are frequencies of UV light that will dissociate O3 but not O2.
\n
[2]
\n
b.
\n
\n
Explain, using equations, how the presence of results in a chain reaction that decreases the concentration of ozone in the stratosphere.
\n
[2]
\n
c.
\n
",
+ "Markscheme": "
\n
✔
\n
Accept any combination of lines, dots or crosses to represent electrons.
\n
Do not accept structures that represent 1.5 bonds.
\n
a(i).
\n
\n
both equal ✔
\n
delocalization/resonance ✔
\n
Accept bond length between 121 and 148 pm/ that of single O−O bond and double O=O bond for M1.
\n
a(ii).
\n
\n
bond in O3 is weaker
OR
O3 bond order 1.5/< 2 ✔
\n
Do not accept bond in O3 is longer for M1.
\n
lower frequency/longer wavelength «UV light» has enough energy to break the O–O bond in O3 «but not that in O2» ✔
\n
Accept “lower frequency/longer wavelength «UV light» has lower energy”.
\n
b.
\n
\n
✔
\n
AND
✔
\n
Do not penalize missing radical.
\n
Accept:for M2:
AND
\n
c.
\n
",
+ "Examiners report": "
",
+ "topics": [
+ "structure-2-models-of-bonding-and-structure"
+ ],
+ "subtopics": [
+ "structure-2-2-the-covalent-model"
+ ]
+ },
+ {
+ "question_id": "21M.2.HL.TZ2.1",
+ "Question": "
\n
Limestone can be converted into a variety of useful commercial products through the lime cycle. Limestone contains high percentages of calcium carbonate, CaCO3.
\n

\n
\n
Thermodynamic data for the decomposition of calcium carbonate is given.
\n

\n
\n
The second step of the lime cycle produces calcium hydroxide, Ca(OH)2.
\n
\n
Calcium hydroxide reacts with carbon dioxide to reform calcium carbonate.
\n
Ca(OH)2 (aq) + CO2 (g) → CaCO3 (s) + H2O (l)
\n
\n
Calcium carbonate is heated to produce calcium oxide, CaO.
\n
CaCO3 (s) → CaO (s) + CO2 (g)
\n
Calculate the volume of carbon dioxide produced at STP when 555 g of calcium carbonate decomposes. Use sections 2 and 6 of the data booklet.
\n
[2]
\n
a.
\n
\n
Calculate the enthalpy change of reaction, ΔH, in kJ, for the decomposition of calcium carbonate.
\n
[2]
\n
b(i).
\n
\n
Calculate the change in entropy, ΔS, in J K−1, for the decomposition of calcium carbonate.
\n
[1]
\n
b(ii).
\n
\n
Determine the temperature, in K, at which the decomposition of calcium carbonate becomes spontaneous, using b(i), b(ii) and section 1 of the data booklet.
\n
(If you do not have answers for b(i) and b(ii), use ΔH = 190 kJ and ΔS = 180 J K−1, but these are not the correct answers.)
\n
[2]
\n
b(iii).
\n
\n
Sketch an energy profile for the decomposition of calcium carbonate based on your answer to b(i), labelling the axes and activation energy, Ea.
\n

\n
[3]
\n
b(iv).
\n
\n
State how adding a catalyst to the reaction would impact the enthalpy change of reaction, ΔH, and the activation energy, Ea.
\n

\n
[1]
\n
b(v).
\n
\n
Write the equation for the reaction of Ca(OH)2 (aq) with hydrochloric acid, HCl (aq).
\n
[1]
\n
c(i).
\n
\n
Determine the volume, in dm3, of 0.015 mol dm−3 calcium hydroxide solution needed to neutralize 35.0 cm3 of 0.025 mol dm−3 HCl (aq).
\n
[2]
\n
c(ii).
\n
\n
Saturated calcium hydroxide solution is used to test for carbon dioxide. Calculate the pH of a 2.33 × 10−2 mol dm−3 solution of calcium hydroxide, a strong base.
\n
[2]
\n
c(iii).
\n
\n
Determine the mass, in g, of CaCO3 (s) produced by reacting 2.41 dm3 of 2.33 × 10−2 mol dm−3 of Ca(OH)2 (aq) with 0.750 dm3 of CO2 (g) at STP.
\n
[2]
\n
d(i).
\n
\n
2.85 g of CaCO3 was collected in the experiment in d(i). Calculate the percentage yield of CaCO3.
\n
(If you did not obtain an answer to d(i), use 4.00 g, but this is not the correct value.)
\n
[1]
\n
d(ii).
\n
\n
Outline how one calcium compound in the lime cycle can reduce a problem caused by acid deposition.
\n
[1]
\n
e.
\n
",
+ "Markscheme": "
\n
«nCaCO3 = =» 5.55 «mol» ✓
\n
«V = 5.55 mol × 22.7 dm3 mol−1 =» 126 «dm3» ✓
\n
Award [2] for correct final answer.
\n
Accept method using pV = nRT to obtain the volume with p as either 100 kPa (126 dm3) or 101.3 kPa (125 dm3).
\n
Do not penalize use of 22.4 dm3 mol–1 to obtain the volume (124 dm3).
\n
a.
\n
\n
«ΔH =» (−635 «kJ» – 393.5 «kJ») – (−1207 «kJ») ✓
\n
«ΔH = + » 179 «kJ» ✓
\n
Award [2] for correct final answer.
\n
Award [1 max] for −179 kJ.
\n
Ignore an extra step to determine total enthalpy change in kJ: 179 kJ mol-1 x 5.55 mol = 993 kJ.
\n
Award [2] for an answer in the range 990 - 993« kJ».
\n
b(i).
\n
\n
«ΔS = (40 J K−1 + 214 J K−1) − (93 J K−1) =» 161 «J K−1» ✓
\n
Ignore an extra step to determine total entropy change in JK–1: 161 J mol–1K–1 x 5.55 mol = 894 «J mol–1K–1»
\n
Award [1] for 894 «J mol–1K–1».
\n
b(ii).
\n
\n
«spontaneous» if ΔG = ΔH − TΔS < 0
OR
ΔH < TΔS ✓
\n
«T >=» 1112 «K» ✓
\n
Award [2] for correct final answer.
\n
Accept “1056 K” if both of the incorrect values are used to solve the problem.
\n
Do not award M2 for any negative T value.
\n
b(iii).
\n
\n
endothermic sketch ✓
\n
x-axis labelled “extent of reaction/progress of reaction/reaction coordinate/reaction pathway” AND y-axis labelled “potential energy/energy/enthalpy✓
\n
activation energy/Ea ✓
\n

\n
Do not accept “time” for x-axis.
\n
b(iv).
\n
\n
ΔH same AND lower Ea ✓
\n
b(v).
\n
\n
Ca(OH)2 (aq) + 2HCl (aq) → 2H2O (l) + CaCl2 (aq) ✓
\n
c(i).
\n
\n
«nHCl = 0.0350 dm3 × 0.025 mol dm−3 =» 0.00088 «mol»
\n
OR
nCa(OH)2 = nHCl/0.00044 «mol» ✓
\n
«V = =» 0.029 «dm3» ✓
\n
Award [2] for correct final answer.
\n
Award [1 max] for 0.058 «dm3».
\n
c(ii).
\n
\n
Alternative 1:
\n
[OH−] = « 2 × 2.33 × 10−2 mol dm−3 =» 0.0466 «mol dm−3» ✓
\n
«[H+] = = 2.15 × 10−13 mol dm−3»
\n
pH = « −log (2.15 × 10−13) =» 12.668 ✓
\n
\n
Alternative 2:
\n
[OH−] =« 2 × 2.33 × 10−2 mol dm−3 =» 0.0466 «mol dm−3» ✓
\n
«pOH = −log (0.0466) = 1.332»
\n
pH = «14.000 – pOH = 14.000 – 1.332 =» 12.668 ✓
\n
\n
Award [2] for correct final answer.
\n
Award [1 max] for pH =12.367.
\n
c(iii).
\n
\n
«nCa(OH)2 = 2.41 dm3 × 2.33 × 10−2 mol dm−3 =» 0.0562 «mol» AND
\n
«nCO2 ==» 0.0330 «mol» ✓
\n
«CO2 is the limiting reactant»
\n
«mCaCO3 = 0.0330 mol × 100.09 g mol−1 =» 3.30 «g» ✓
\n
\n
Only award ECF for M2 if limiting reagent is used.
\n
Accept answers in the range 3.30 - 3.35 «g».
\n
d(i).
\n
\n
« × 100 =» 86.4 «%» ✓
\n
\n
Accept answers in the range 86.1-86.4 «%».
\n
Accept “71.3 %” for using the incorrect given value of 4.00 g.
\n
d(ii).
\n
\n
«add» Ca(OH)2/CaCO3/CaO AND to «acidic» water/river/lake/soil
OR
«use» Ca(OH)2/CaCO3/CaO in scrubbers «to prevent release of acidic pollution» ✓
\n
\n
Accept any correct name for any of the calcium compounds listed.
\n
e.
\n
",
+ "Examiners report": "
",
+ "topics": [
+ "reactivity-1-what-drives-chemical-reactions",
+ "reactivity-2-how-much-how-fast-and-how-far",
+ "reactivity-3-what-are-the-mechanisms-of-chemical-change",
+ "structure-1-models-of-the-particulate-nature-of-matter",
+ "structure-3-classification-of-matter"
+ ],
+ "subtopics": [
+ "reactivity-1-2-energy-cycles-in-reactions",
+ "reactivity-1-4-entropy-and-spontaneity",
+ "reactivity-2-1-how-much-the-amount-of-chemical-change",
+ "reactivity-2-2-how-fast-the-rate-of-chemical-change",
+ "reactivity-3-1-proton-transfer-reactions",
+ "structure-1-5-ideal-gases",
+ "structure-3-1-the-periodic-table-classification-of-elements"
+ ]
+ },
+ {
+ "question_id": "21M.2.HL.TZ2.6",
+ "Question": "
\n
Bromate and bromide ions react in acidic aqueous solution.
\n
BrO3− (aq) + 5Br− (aq) + 6H+ (aq) → 3Br2 (l) + 3H2O (l)
\n
The following rate data was collected.
\n

\n
\n
Determine the rate expression for the reaction.
\n

\n
[2]
\n
a.
\n
\n
Determine the value and unit of the rate constant using the rate expression in (a).
\n
[2]
\n
b.
\n
",
+ "Markscheme": "
\n
BrO3–: 1/first AND Br–: 1/first AND H+: 2/second ✓
\n
«Rate =» k[BrO3−][Br−][H+]2 ✓
\n
M2: Square brackets required for the mark.
\n
a.
\n
\n
«k ==» 8.0 ✓
\n
mol−3 dm9 s−1 ✓
\n
b.
\n
",
+ "Examiners report": "
",
+ "topics": [
+ "reactivity-2-how-much-how-fast-and-how-far"
+ ],
+ "subtopics": [
+ "reactivity-2-2-how-fast-the-rate-of-chemical-change"
+ ]
+ },
+ {
+ "question_id": "21M.2.HL.TZ2.7",
+ "Question": "
\n
Consider the following equilibrium reaction:
\n
2SO2 (g) + O2 (g) 2SO3 (g)
\n
\n
State the equilibrium constant expression, Kc, for the reaction above.
\n
[1]
\n
a.
\n
\n
State and explain how the equilibrium would be affected by increasing the volume of the reaction container at a constant temperature.
\n
[3]
\n
b.
\n
\n
SO2 (g), O2 (g) and SO3 (g) are mixed and allowed to reach equilibrium at 600 °C.
\n

\n
Determine the value of Kc at 600 °C.
\n
[2]
\n
c.
\n
",
+ "Markscheme": "
\n
«Kc = » ✓
\n
Square brackets required for the mark.
\n
a.
\n
\n
pressure decrease «due to larger volume» ✓
\n
reaction shifts to side with more moles/molecules «of gas» ✓
\n
reaction shifts left/towards reactants ✓
\n
Award M3 only if M1 OR M2 awarded.
\n
b.
\n
\n
[O2] = 1.25 «mol dm−3» AND [SO3] = 3.50 «mol dm−3» ✓
\n
«Kc ==» 4.36 ✓
\n
\n
Award [2] for correct final answer
\n
c.
\n
",
+ "Examiners report": "
",
+ "topics": [
+ "reactivity-2-how-much-how-fast-and-how-far"
+ ],
+ "subtopics": [
+ "reactivity-2-3-how-far-the-extent-of-chemical-change"
+ ]
+ },
+ {
+ "question_id": "21M.2.SL.TZ1.1",
+ "Question": "
\n
Iron may be extracted from iron (II) sulfide, FeS.
\n
\n
Iron (II) sulfide, FeS, is ionically bonded.
\n
\n
The first step in the extraction of iron from iron (II) sulfide is to roast it in air to form iron (III) oxide and sulfur dioxide.
\n
\n
Outline why metals, like iron, can conduct electricity.
\n
[1]
\n
a.
\n
\n
Justify why sulfur is classified as a non-metal by giving two of its chemical properties.
\n
[2]
\n
b.
\n
\n
Describe the bonding in this type of solid.
\n
[2]
\n
c(i).
\n
\n
State the full electron configuration of the sulfide ion.
\n
[1]
\n
c(ii).
\n
\n
Outline, in terms of their electronic structures, why the ionic radius of the sulfide ion is greater than that of the oxide ion.
\n
[1]
\n
c(iii).
\n
\n
Suggest why chemists find it convenient to classify bonding into ionic, covalent and metallic.
\n
[1]
\n
c(iv).
\n
\n
Write the equation for this reaction.
\n
[1]
\n
d(i).
\n
\n
Deduce the change in the oxidation state of sulfur.
\n
[1]
\n
d(ii).
\n
\n
Suggest why this process might raise environmental concerns.
\n
[1]
\n
d(iii).
\n
\n
Explain why the addition of small amounts of carbon to iron makes the metal harder.
\n
[2]
\n
e.
\n
",
+ "Markscheme": "
\n
mobile/delocalized «sea of» electrons
\n
a.
\n
\n
Any two of:
\n
forms acidic oxides «rather than basic oxides» ✔
\n
forms covalent/bonds compounds «with other non-metals» ✔
\n
forms anions «rather than cations» ✔
\n
behaves as an oxidizing agent «rather than a reducing agent» ✔
\n
Award [1 max] for 2 correct non-chemical properties such as non-conductor, high ionisation energy, high electronegativity, low electron affinity if no marks for chemical properties are awarded.
\n
b.
\n
\n
electrostatic attraction ✔
\n
between oppositely charged ions/between Fe2+ and S2− ✔
\n
c(i).
\n
\n
1s2 2s2 2p6 3s2 3p6 ✔
\n
Do not accept “[Ne] 3s2 3p6”.
\n
c(ii).
\n
\n
«valence» electrons further from nucleus/extra electron shell/ electrons in third/3s/3p level «not second/2s/2p»✔
\n
Accept 2,8 (for O2–) and 2,8,8 (for S2–)
\n
c(iii).
\n
\n
allows them to explain the properties of different compounds/substances
OR
enables them to generalise about substances
OR
enables them to make predictions ✔
\n
Accept other valid answers.
\n
c(iv).
\n
\n
4FeS(s) + 7O2(g) → 2Fe2O3(s) + 4SO2(g) ✔
\n
Accept any correct ratio.
\n
d(i).
\n
\n
+6
OR
−2 to +4 ✔
\n
Accept “6/VI”.
Accept “−II, 4//IV”.
Do not accept 2− to 4+.
\n
d(ii).
\n
\n
sulfur dioxide/SO2 causes acid rain ✔
\n
Accept sulfur dioxide/SO2/dust causes respiratory problems
Do not accept just “causes respiratory problems” or “causes acid rain”.
\n
d(iii).
\n
\n
disrupts the regular arrangement «of iron atoms/ions»
OR
carbon different size «to iron atoms/ions» ✔
\n
prevents layers/atoms sliding over each other ✔
\n
e.
\n
",
+ "Examiners report": "
",
+ "topics": [
+ "reactivity-2-how-much-how-fast-and-how-far",
+ "reactivity-3-what-are-the-mechanisms-of-chemical-change",
+ "structure-1-models-of-the-particulate-nature-of-matter",
+ "structure-2-models-of-bonding-and-structure",
+ "structure-3-classification-of-matter"
+ ],
+ "subtopics": [
+ "reactivity-2-1-how-much-the-amount-of-chemical-change",
+ "reactivity-3-2-electron-transfer-reactions",
+ "structure-1-3-electron-configurations",
+ "structure-2-1-the-ionic-model",
+ "structure-2-2-the-covalent-model",
+ "structure-2-3-the-metallic-model",
+ "structure-2-4-from-models-to-materials",
+ "structure-3-1-the-periodic-table-classification-of-elements"
+ ]
+ },
+ {
+ "question_id": "21M.2.SL.TZ1.2",
+ "Question": "
\n
Iron (II) sulfide reacts with hydrochloric acid to form hydrogen sulfide, H2S.
\n
\n
In aqueous solution, hydrogen sulfide acts as an acid.
\n
\n
Draw the Lewis (electron dot) structure of hydrogen sulfide.
\n
[1]
\n
a(i).
\n
\n
Predict the shape of the hydrogen sulfide molecule.
\n
[1]
\n
a(ii).
\n
\n
State the formula of its conjugate base.
\n
[1]
\n
b(i).
\n
\n
Saturated aqueous hydrogen sulfide has a concentration of 0.10 mol dm−3 and a pH of 4.0. Demonstrate whether it is a strong or weak acid.
\n
[1]
\n
b(ii).
\n
\n
Calculate the hydroxide ion concentration in saturated aqueous hydrogen sulfide.
\n
[1]
\n
b(iii).
\n
\n
A gaseous sample of nitrogen, contaminated only with hydrogen sulfide, was reacted with excess sodium hydroxide solution at constant temperature. The volume of the gas changed from 550 cm3 to 525 cm3.
\n
Determine the mole percentage of hydrogen sulfide in the sample, stating one assumption you made.
\n

\n
[3]
\n
c.
\n
",
+ "Markscheme": "
\n
OR
✔
\n
Accept any combination of lines, dots or crosses to represent electrons.
\n
a(i).
\n
\n
bent/non-linear/angular/v-shaped✔
\n
a(ii).
\n
\n
weak AND strong acid of this concentration/[H+] = 0.1 mol dm−3 would have pH = 1
OR
weak AND [H+] = 10−4 < 0.1 «therefore only fraction of acid dissociated» ✔
\n
b(ii).
\n
\n
10−10 «mol dm−3» ✔
\n
b(iii).
\n
\n
Mole percentage H2S:
volume of H2S = «550 − 525 = » 25 «cm3» ✔
mol % H2S = « = » 4.5 «%» ✔
\n
Award [2] for correct final answer of 4.5 «%»
\n
\n
Assumption:
«both» gases behave as ideal gases ✔
Accept “volume of gas mol of gas”.
Accept “reaction goes to completion”.
Accept “nitrogen is insoluble/does not react with NaOH/only H2S reacts with NaOH”.
\n
c.
\n
",
+ "Examiners report": "
",
+ "topics": [
+ "reactivity-3-what-are-the-mechanisms-of-chemical-change",
+ "structure-1-models-of-the-particulate-nature-of-matter",
+ "structure-2-models-of-bonding-and-structure"
+ ],
+ "subtopics": [
+ "reactivity-3-1-proton-transfer-reactions",
+ "structure-1-5-ideal-gases",
+ "structure-2-2-the-covalent-model"
+ ]
+ },
+ {
+ "question_id": "21M.2.SL.TZ1.3",
+ "Question": "
\n
Magnetite, Fe3O4, is another ore of iron that contains both Fe2+ and Fe3+.
\n
\n
Iron exists as several isotopes.
\n
\n
In acidic solution, hydrogen peroxide, H2O2, will oxidize Fe2+.
\n
Fe2+ (aq) → Fe3+ (aq) + e−
\n
\n
Deduce the ratio of Fe2+:Fe3+ in Fe3O4.
\n
[1]
\n
a.
\n
\n
State the type of spectroscopy that could be used to determine their relative abundances.
\n
[1]
\n
b(i).
\n
\n
State the number of protons, neutrons and electrons in each species.
\n

\n
[2]
\n
b(ii).
\n
\n
Iron has a relatively small specific heat capacity; the temperature of a 50 g sample rises by 44.4°C when it absorbs 1 kJ of heat energy.
\n
Determine the specific heat capacity of iron, in J g−1 K−1. Use section 1 of the data booklet.
\n
[1]
\n
c.
\n
\n
Write the half-equation for the reduction of hydrogen peroxide to water in acidic solution.
\n
[1]
\n
d(i).
\n
\n
Deduce a balanced equation for the oxidation of Fe2+ by acidified hydrogen peroxide.
\n
[1]
\n
d(ii).
\n
",
+ "Markscheme": "
\n
1:2 ✔
\n
Accept 2 Fe3+: 1 Fe2+
Do not accept 2:1 only
\n
a.
\n
\n
mass «spectroscopy»/MS ✔
\n
b(i).
\n
\n

\n
Award [1 max] for 4 correct values.
\n
b(ii).
\n
\n
specific heat capacity « = » = 0.45 «J g−1 K−1» ✔
\n
c.
\n
\n
H2O2(aq) + 2H+(aq) + 2e−→ 2H2O(l) ✔
\n
d(i).
\n
\n
H2O2(aq) + 2H+(aq) + 2Fe2+(aq) → 2H2O(l) + 2Fe3+(aq) ✔
\n
d(ii).
\n
",
+ "Examiners report": "
",
+ "topics": [
+ "reactivity-1-what-drives-chemical-reactions",
+ "reactivity-3-what-are-the-mechanisms-of-chemical-change",
+ "structure-1-models-of-the-particulate-nature-of-matter",
+ "tools"
+ ],
+ "subtopics": [
+ "reactivity-1-1-measuring-enthalpy-changes",
+ "reactivity-3-2-electron-transfer-reactions",
+ "structure-1-2-the-nuclear-atom",
+ "structure-1-4-counting-particles-by-mass-the-mole",
+ "tool-1-experimental-techniques"
+ ]
+ },
+ {
+ "question_id": "21M.2.SL.TZ1.5",
+ "Question": "
\n
Ethanol is obtained by the hydration of ethene, C2H4.
\n
\n
State the class of compound to which ethene belongs.
\n
[1]
\n
a(i).
\n
\n
State the molecular formula of the next member of the homologous series to which ethene belongs.
\n
[1]
\n
a(ii).
\n
\n
Justify why ethene has only a single signal in its 1H NMR spectrum.
\n
[1]
\n
b.
\n
\n
Suggest two possible products of the incomplete combustion of ethene that would not be formed by complete combustion.
\n
[1]
\n
c.
\n
\n
A white solid was formed when ethene was subjected to high pressure.
\n
Deduce the type of reaction that occurred.
\n
[1]
\n
d.
\n
",
+ "Markscheme": "
\n
C3H6 ✔
\n
Accept structural formula.
\n
a(ii).
\n
\n
hydrogen atoms/protons in same chemical environment ✔
\n
Accept “all H atoms/protons are equivalent”.
Accept “symmetrical”
\n
b.
\n
\n
carbon monoxide/CO AND carbon/C/soot ✔
\n
c.
\n
\n
«addition» polymerization ✔
\n
d.
\n
",
+ "Examiners report": "
",
+ "topics": [
+ "reactivity-1-what-drives-chemical-reactions",
+ "structure-2-models-of-bonding-and-structure",
+ "structure-3-classification-of-matter"
+ ],
+ "subtopics": [
+ "reactivity-1-3-energy-from-fuels",
+ "structure-2-4-from-models-to-materials",
+ "structure-3-2-functional-groups-classification-of-organic-compounds"
+ ]
+ },
+ {
+ "question_id": "21M.2.SL.TZ1.6",
+ "Question": "
\n
When dinitrogen pentoxide, N2O5, is heated the colourless gas undergoes thermal decomposition to produce brown nitrogen dioxide:
\n
N2O5 (g) → 2NO2 (g) + O2 (g)
\n
\n
Data for the decomposition at constant temperature is given.
\n

\n
\n
Suggest how the extent of decomposition could be measured.
\n
[1]
\n
a.
\n
\n
Plot the missing point on the graph and draw the best-fit line.
\n

\n
[2]
\n
b(i).
\n
\n
Deduce the relationship between the concentration of N2O5 and the rate of reaction.
\n
[1]
\n
b(ii).
\n
\n
Outline why increasing the concentration of N2O5 increases the rate of reaction.
\n
[1]
\n
b(iii).
\n
",
+ "Markscheme": "
\n
use colorimeter
OR
change in colour
OR
change in volume
OR
change in pressure ✔
\n
Accept suitable instruments, e.g. pressure probe/oxygen sensor.
\n
a.
\n
\n

\n
point correct ✔
\n
straight line passing close to all points AND through origin ✔
\n
Accept free hand drawn line as long as attempt to be linear and meets criteria for M2.
\n
b(i).
\n
\n
« rate of reaction is directly» proportional to/∝[N2O5]
OR
doubling concentration doubles rate ✔
\n
Do not accept “rate increases as concentration increases”/ positive correlation
\n
Accept linear
\n
b(ii).
\n
\n
greater frequency of collisions «as concentration increases»
OR
more collisions per unit time «as concentration increases» ✔
\n
Accept “rate/chance/probability/likelihood” instead of “frequency”.
\n
Do not accept just “more collisions”.
\n
b(iii).
\n
",
+ "Examiners report": "
",
+ "topics": [
+ "reactivity-2-how-much-how-fast-and-how-far",
+ "tools"
+ ],
+ "subtopics": [
+ "reactivity-2-2-how-fast-the-rate-of-chemical-change",
+ "reactivity-2-3-how-far-the-extent-of-chemical-change",
+ "tool-1-experimental-techniques",
+ "tool-3-mathematics"
+ ]
+ },
+ {
+ "question_id": "21M.2.SL.TZ2.1",
+ "Question": "
\n
Limestone can be converted into a variety of useful commercial products through the lime cycle. Limestone contains high percentages of calcium carbonate, CaCO3.
\n

\n
\n
The second step of the lime cycle produces calcium hydroxide, Ca(OH)2.
\n
\n
Calcium hydroxide reacts with carbon dioxide to reform calcium carbonate.
\n
Ca(OH)2 (aq) + CO2 (g) → CaCO3 (s) + H2O (l)
\n
\n
Calcium carbonate is heated to produce calcium oxide, CaO.
\n
CaCO3 (s) → CaO (s) + CO2 (g)
\n
Calculate the volume of carbon dioxide produced at STP when 555 g of calcium carbonate decomposes. Use sections 2 and 6 of the data booklet.
\n
[2]
\n
a.
\n
\n
Thermodynamic data for the decomposition of calcium carbonate is given.
\n

\n
Calculate the enthalpy change of reaction, ΔH, in kJ, for the decomposition of calcium carbonate.
\n
[2]
\n
b.
\n
\n
The potential energy profile for a reaction is shown. Sketch a dotted line labelled “Catalysed” to indicate the effect of a catalyst.
\n

\n
[1]
\n
c(i).
\n
\n
Outline why a catalyst has such an effect.
\n
[1]
\n
c(ii).
\n
\n
Write the equation for the reaction of Ca(OH)2 (aq) with hydrochloric acid, HCl (aq).
\n
[1]
\n
d(i).
\n
\n
Determine the volume, in dm3, of 0.015 mol dm−3 calcium hydroxide solution needed to neutralize 35.0 cm3 of 0.025 mol dm−3 HCl (aq).
\n
[2]
\n
d(ii).
\n
\n
Saturated calcium hydroxide solution is used to test for carbon dioxide. Calculate the pH of a 2.33 × 10−2 mol dm−3 solution of calcium hydroxide, a strong base.
\n
[2]
\n
d(iii).
\n
\n
Determine the mass, in g, of CaCO3 (s) produced by reacting 2.41 dm3 of 2.33 × 10−2 mol dm−3 of Ca(OH)2 (aq) with 0.750 dm3 of CO2 (g) at STP.
\n
[2]
\n
e(i).
\n
\n
2.85 g of CaCO3 was collected in the experiment in e(i). Calculate the percentage yield of CaCO3.
\n
(If you did not obtain an answer to e(i), use 4.00 g, but this is not the correct value.)
\n
[1]
\n
e(ii).
\n
\n
Outline how one calcium compound in the lime cycle can reduce a problem caused by acid deposition.
\n
[1]
\n
f.
\n
",
+ "Markscheme": "
\n
«nCaCO3 = =» 5.55 «mol» ✓
\n
«V = 5.55 mol × 22.7 dm3 mol−1 =» 126 «dm3» ✓
\n
Award [2] for correct final answer.
\n
Accept method using pV = nRT to obtain the volume with p as either 100 kPa (126 dm3) or 101.3 kPa (125 dm3).
\n
Do not penalize use of 22.4 dm3 mol–1 to obtain the volume (124 dm3).
\n
a.
\n
\n
«ΔH =» (−635 «kJ» – 393.5 «kJ») – (−1207 «kJ») ✓
\n
«ΔH = + » 179 «kJ» ✓
\n
Award [2] for correct final answer.
\n
Award [1 max] for −179 kJ.
\n
Ignore an extra step to determine total enthalpy change in kJ: 179 kJ mol−1 x 5.55 mol = 993 kJ.
\n
Award [2] for an answer in the range 990 - 993« kJ».
\n
b.
\n
\n

\n
lower activation energy curve between same reactant and product levels ✓
\n
Accept curve with or without an intermediate.
\n
Accept a horizontal straight line below current line with the activation energy with catalyst/Ecat clearly labelled.
\n
c(i).
\n
\n
provides an alternative «reaction» pathway/mechanism ✓
\n
Do not accept “lower activation energy” only.
\n
c(ii).
\n
\n
Ca(OH)2 (aq) + 2HCl (aq) → 2H2O (l) + CaCl2 (aq) ✓
\n
d(i).
\n
\n
«nHCl = 0.0350 dm3 × 0.025 mol dm−3 =» 0.00088 «mol»
OR
nCa(OH)2 = nHCl/0.00044 «mol» ✓
\n
«V = =» 0.029 «dm3» ✓
\n
Award [2] for correct final answer.
\n
Award [1 max] for 0.058 «dm3».
\n
d(ii).
\n
\n
Alternative 1:
\n
[OH−] = « 2 × 2.33 × 10−2 mol dm−3 =» 0.0466 «mol dm−3» ✓
\n
«[H+] = = 2.15 × 10−13 mol dm−3»
pH = « −log(2.15 × 10−13) =» 12.668 ✓
\n
\n
Alternative 2:
\n
[OH−] =« 2 × 2.33 × 10−2 mol dm−3 =» 0.0466 «mol dm−3» ✓
\n
«pOH = −log (0.0466) = 1.332»
\n
pH = «14.000 – pOH = 14.000 – 1.332 =» 12.668 ✓
\n
\n
Award [2] for correct final answer.
\n
Award [1 max] for pH =12.367.
\n
d(iii).
\n
\n
«nCa(OH)2 = 2.41 dm3 × 2.33 × 10−2 mol dm−3 =» 0.0562 «mol» AND
«nCO2 ==» 0.0330 «mol» ✓
\n
«CO2 is the limiting reactant»
\n
«mCaCO3 = 0.0330 mol × 100.09 g mol−1 =» 3.30 «g» ✓
\n
Only award ECF for M2 if limiting reagent is used.
\n
Accept answers in the range 3.30 - 3.35 «g».
\n
e(i).
\n
\n
« × 100 =» 86.4 «%» ✓
\n
Accept answers in the range 86.1-86.4 «%».
\n
Accept “71.3 %” for using the incorrect given value of 4.00 g.
\n
e(ii).
\n
\n
«add» Ca(OH)2/CaCO3/CaO AND to «acidic» water/river/lake/soil
OR
«use» Ca(OH)2/CaCO3/CaO in scrubbers «to prevent release of acidic pollution» ✓
\n
Accept any correct name for any of the calcium compounds listed.
\n
f.
\n
",
+ "Examiners report": "
",
+ "topics": [
+ "reactivity-2-how-much-how-fast-and-how-far",
+ "structure-1-models-of-the-particulate-nature-of-matter",
+ "structure-3-classification-of-matter"
+ ],
+ "subtopics": [
+ "reactivity-2-1-how-much-the-amount-of-chemical-change",
+ "structure-1-5-ideal-gases",
+ "structure-3-1-the-periodic-table-classification-of-elements"
+ ]
+ },
+ {
+ "question_id": "21M.2.SL.TZ2.2",
+ "Question": "
\n
The properties of elements can be predicted from their position in the periodic table.
\n
\n
Explain why Si has a smaller atomic radius than Al.
\n
[2]
\n
a(i).
\n
\n
Explain the decrease in radius from Na to Na+.
\n
[2]
\n
a(ii).
\n
\n
State the condensed electron configurations for Cr and Cr3+.
\n

\n
[2]
\n
b(i).
\n
\n
Describe metallic bonding and how it contributes to electrical conductivity.
\n
[3]
\n
b(ii).
\n
\n
Deduce the Lewis (electron dot) structure and molecular geometry of sulfur dichloride, SCl2.
\n

\n
[2]
\n
c.
\n
\n
Suggest, giving reasons, the relative volatilities of SCl2 and H2O.
\n
[3]
\n
d.
\n
\n
Consider the following equilibrium reaction:
\n
2SO2 (g) + O2 (g) 2SO3 (g)
\n
State and explain how the equilibrium would be affected by increasing the volume of the reaction container at a constant temperature.
\n
[3]
\n
e.
\n
",
+ "Markscheme": "
\n
nuclear charge/number of protons/Z/Zeff increases «causing a stronger pull on the outer electrons» ✓
\n
same number of shells/«outer» energy level/shielding ✓
\n
a(i).
\n
\n
Na+ has one less energy level/shell
OR
Na+ has 2 energy levels/shells AND Na has 3 ✓
\n
less shielding «in Na+ so valence electrons attracted more strongly to nucleus»
OR
effective nuclear charge/Zeff greater «in Na+ so valence electrons attracted more strongly to nucleus» ✓
\n
Accept “more protons than electrons «in Na+»” OR “less electron-electron repulsion «in Na+»” for M2.
\n
a(ii).
\n
\n
Cr:
[Ar] 4s13d5 ✓
\n
Cr3+:
[Ar] 3d3 ✓
\n
Accept “[Ar] 3d54s1”.
\n
Accept “[Ar] 3d34s0”.
\n
Award [1 max] for two correct full electron configurations “1s22s22p63s23p64s13d5 AND 1s22s22p63s23p63d3”.
\n
Award [1 max] for 4s13d5 AND 3d3.
\n
b(i).
\n
\n
electrostatic attraction ✓
\n
between «a lattice of» cations/positive «metal» ions AND «a sea of» delocalized electrons ✓
\n
mobile electrons responsible for conductivity
OR
electrons move when a voltage/potential difference/electric field is applied ✓
\n
\n
Do not accept “nuclei” for “cations/positive ions” in M2.
\n
Accept “mobile/free” for “delocalized” electrons in M2.
\n
Accept “electrons move when connected to a cell/battery/power supply” OR “electrons move when connected in a circuit” for M3.
\n
b(ii).
\n
\n

\n
c.
\n
\n
H2O forms hydrogen bonding «while SCl2 does not» ✓
\n
SCl2 «much» stronger London/dispersion/«instantaneous» induced dipole-induced dipole forces ✓
\n
Alternative 1:
H2O less volatile AND hydrogen bonding stronger «than dipole–dipole and dispersion forces» ✓
\n
Alternative 2:
SCl2 less volatile AND effect of dispersion forces «could be» greater than hydrogen bonding ✓\\
\n
\n
Ignore reference to Van der Waals.
\n
Accept “SCl2 has «much» larger molar mass/electron density” for M2.
\n
d.
\n
\n
pressure decrease «due to larger volume» ✓
\n
reactant side has more moles/molecules «of gas» ✓
\n
reaction shifts left/towards reactants ✓
\n
Award M3 only if M1 OR M2 is awarded.
\n
e.
\n
",
+ "Examiners report": "
",
+ "topics": [
+ "reactivity-2-how-much-how-fast-and-how-far",
+ "structure-1-models-of-the-particulate-nature-of-matter",
+ "structure-2-models-of-bonding-and-structure",
+ "structure-3-classification-of-matter"
+ ],
+ "subtopics": [
+ "reactivity-2-3-how-far-the-extent-of-chemical-change",
+ "structure-1-3-electron-configurations",
+ "structure-2-1-the-ionic-model",
+ "structure-2-2-the-covalent-model",
+ "structure-2-3-the-metallic-model",
+ "structure-3-1-the-periodic-table-classification-of-elements"
+ ]
+ },
+ {
+ "question_id": "21M.2.SL.TZ2.7",
+ "Question": "
\n
\n (a)\n
\n
\n
\n State the equilibrium constant expression,\n \n K\n \n \n c\n \n , for the reaction above.\n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n
\n State and explain how the equilibrium would be affected by increasing the volume of the reaction container at a constant temperature.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n «\n \n K\n \n \n c\n \n =\n \n » ✓\n
\n
\n \n
\n Square brackets required for the mark.\n \n
\n
\n
\n (b)\n
\n
\n pressure decrease «due to larger volume» ✓\n
\n
\n reaction shifts to side with more moles/molecules «of gas» ✓\n
\n
\n reaction shifts left/towards reactants ✓\n
\n
\n \n
\n Award M3 only if M1\n \n OR\n \n M2 awarded.\n \n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "reactivity-2-how-much-how-fast-and-how-far"
+ ],
+ "subtopics": [
+ "reactivity-2-3-how-far-the-extent-of-chemical-change"
+ ]
+ },
+ {
+ "question_id": "21N.2.HL.TZ0.11",
+ "Question": "
\n
50.00 cm3 of 0.75 mol dm−3 sodium hydroxide was added in 1.00 cm3 portions to 22.50 cm3 of 0.50 mol dm−3 chloroethanoic acid.
\n
\n
Calculate the initial pH before any sodium hydroxide was added, using section 21 of the data booklet.
\n
[2]
\n
a.
\n
\n
The concentration of excess sodium hydroxide was 0.362 mol dm−3. Calculate the pH of the solution at the end of the experiment.
\n
[1]
\n
b.
\n
\n
Sketch the neutralisation curve obtained and label the equivalence point.
\n

\n
[3]
\n
c.
\n
",
+ "Markscheme": "
\n
«Ka = 10–2.87 = 1.35 × 10–3 »
\n
«1.35 × 10–3 = »
\n
«x = [H+] ==» 2.6 × 10–2 «mol dm–3» ✔
\n
«pH = –log[H+] = –log(2.6 × 10–2) =» 1.59 ✔
\n
\n
Accept final answer in range 1.58–1.60.
\n
Award [2] for correct final answer.
\n
a.
\n
\n
«pOH = –log(0.362) = 0.441»
\n
«pH = 14.000 – 0.441 =» 13.559 ✔
\n
b.
\n
\n

\n
OR
\n

\n
starts at 1.6 AND finishes at 13.6 ✔
\n
approximately vertical at the correct volume of alkali added ✔
\n
equivalence point labelled AND above pH 7 ✔
\n
\n
Accept any range from 1.1-1.9 AND 13.1-13.9 for M1 or ECF from 11c(i) and 11c(ii).
\n
Award M2 for vertical climb at 28 cm3 OR 15 cm3.
\n
Equivalence point must be labelled for M3.
\n
c.
\n
",
+ "Examiners report": "
",
+ "topics": [
+ "reactivity-3-what-are-the-mechanisms-of-chemical-change"
+ ],
+ "subtopics": [
+ "reactivity-3-1-proton-transfer-reactions"
+ ]
+ },
+ {
+ "question_id": "21N.2.HL.TZ0.2",
+ "Question": "
\n
Electron transitions are related to trends in the periodic table.
\n
\n
Explain the general increase in trend in the first ionization energies of the period 3 elements, Na to Ar.
\n
[2]
\n
a.
\n
\n
Sodium emits yellow light with a frequency of 5.09 × 1014 Hz when electrons transition from 3p to 3s orbitals.
\n
Calculate the energy difference, in J, between these two orbitals using sections 1 and 2 of the data booklet.
\n
\n
Darling, D, n.d. D lines (of sodium). [online] Available at <https://www.daviddarling.info/encyclopedia/D/D_lines.html> [Accessed 6 May 2020].
\n
[1]
\n
b.
\n
",
+ "Markscheme": "
\n
increasing number of protons
OR
increasing nuclear charge ✔
\n
«atomic» radius/size decreases
OR
same number of shells/electrons occupy same shell
OR
similar shielding «by inner electrons» ✔
\n
a.
\n
\n
«ΔE = hν = 6.63 × 10–34 J s × 5.09 × 1014 s–1 =» 3.37 × 10–19 «J» ✔
\n
b.
\n
",
+ "Examiners report": "
",
+ "topics": [
+ "structure-1-models-of-the-particulate-nature-of-matter",
+ "structure-3-classification-of-matter"
+ ],
+ "subtopics": [
+ "structure-1-3-electron-configurations",
+ "structure-3-2-functional-groups-classification-of-organic-compounds"
+ ]
+ },
+ {
+ "question_id": "21N.2.HL.TZ0.3",
+ "Question": "
\n
White phosphorus is an allotrope of phosphorus and exists as P4.
\n
\n
An equilibrium exists between PCl3 and PCl5.
\n
PCl3 (g) + Cl2 (g) PCl5 (g)
\n
\n
Sketch the Lewis (electron dot) structure of the P4 molecule, containing only single bonds.
\n
\n
[1]
\n
a(i).
\n
\n
Write an equation for the reaction of white phosphorus (P4) with chlorine gas to form phosphorus trichloride (PCl3).
\n
[1]
\n
a(ii).
\n
\n
Deduce the electron domain and molecular geometry using VSEPR theory, and estimate the Cl–P–Cl bond angle in PCl3.
\n

\n
[3]
\n
b(i).
\n
\n
Outline the reason why PCl5 is a non-polar molecule, while PCl4F is polar.
\n

\n
[3]
\n
b(ii).
\n
\n
Calculate the standard enthalpy change (ΔH⦵) for the forward reaction in kJ mol−1.
\n
ΔH⦵f PCl3 (g) = −306.4 kJ mol−1
\n
ΔH⦵f PCl5 (g) = −398.9 kJ mol−1
\n
[1]
\n
c(i).
\n
\n
Calculate the entropy change, ΔS, in J K−1 mol−1, for this reaction.
\n

\n
\n
Chemistry 2e, Chpt. 21 Nuclear Chemistry, Appendix G: Standard Thermodynamic Properties for Selected Substances https://openstax.org/books/chemistry-2e/pages/g-standard-thermodynamic-properties-for- selectedsubstances# page_667adccf-f900-4d86-a13d-409c014086ea © 1999-2021, Rice University. Except where otherwise noted, textbooks on this site are licensed under a Creative Commons Attribution 4.0 International License. (CC BY 4.0) https://creativecommons.org/licenses/by/4.0/.
\n
[1]
\n
c(ii).
\n
\n
Calculate the Gibbs free energy change (ΔG), in kJ mol−1, for this reaction at 25 °C. Use section 1 of the data booklet.
\n
If you did not obtain an answer in c(i) or c(ii) use −87.6 kJ mol−1 and −150.5 J mol−1 K−1 respectively, but these are not the correct answers.
\n
[2]
\n
c(iii).
\n
\n
Determine the equilibrium constant, K, for this reaction at 25 °C, referring to section 1 of the data booklet.
\n
If you did not obtain an answer in (c)(iii), use ΔG = –43.5 kJ mol−1, but this is not the correct answer.
\n
[2]
\n
c(iv).
\n
\n
State the equilibrium constant expression, Kc, for this reaction.
\n
[1]
\n
c(v).
\n
\n
State, with a reason, the effect of an increase in temperature on the position of this equilibrium.
\n
[1]
\n
c(vi).
\n
",
+ "Markscheme": "
\n

\n
Accept any diagram with each P joined to the other three.
Accept any combination of dots, crosses and lines.
\n
a(i).
\n
\n
P4 (s) + 6Cl2 (g) → 4PCl3 (l) ✔
\n
a(ii).
\n
\n
Electron domain geometry: tetrahedral ✔
\n
Molecular geometry: trigonal pyramidal ✔
\n
Bond angle: 100«°» ✔
\n
Accept any value or range within the range 91−108«°» for M3.
\n
b(i).
\n
\n
PCl5 is non-polar:
\n
symmetrical
OR
dipoles cancel ✔
\n
\n
PCl4F is polar:
\n
P–Cl has a different bond polarity than P–F ✔
\n
non-symmetrical «dipoles»
OR
dipoles do not cancel ✔
\n
Accept F more electronegative than/different electronegativity to Cl for M2.
\n
b(ii).
\n
\n
«−398.9 kJ mol−1 − (−306.4 kJ mol−1) =» −92.5 «kJ mol−1» ✔
\n
c(i).
\n
\n
«ΔS = 364.5 J K–1 mol–1 – (311.7 J K–1 mol–1 + 223.0 J K–1 mol–1)=» –170.2 «J K–1 mol–1» ✔
\n
c(ii).
\n
\n
«ΔS =» –0.1702 «kJ mol–1 K–1»
OR
298 «K» ✔
\n
«ΔG = –92.5 kJ mol–1 – (298 K × –0.1702 kJ mol–1 K–1) =» –41.8 «kJ mol–1» ✔
\n
\n
Award [2] for correct final answer.
\n
If –87.6 and -150.5 are used then –42.8.
\n
c(iii).
\n
\n
«ΔG = –41.8 kJ mol–1 = × 298 K × lnK»
OR
«ΔG = –41800 J mol–1 = –8.31 J mol–1 K–1 × 298 K × lnK»
«lnK = =» 16.9 ✔
\n
«K = e16.9 =» 2.19 × 107 ✔
\n
\n
Award [2] for correct final answer.
\n
Accept range of 1.80 × 106–2.60 × 107.
\n
If –43.5 is used then 4.25 × 107.
\n
c(iv).
\n
\n
«Kc =» ✔
\n
c(v).
\n
\n
«shifts» left/towards reactants AND «forward reaction is» exothermic/ΔH is negative ✔
\n
c(vi).
\n
",
+ "Examiners report": "
",
+ "topics": [
+ "reactivity-1-what-drives-chemical-reactions",
+ "reactivity-2-how-much-how-fast-and-how-far",
+ "structure-2-models-of-bonding-and-structure"
+ ],
+ "subtopics": [
+ "reactivity-1-2-energy-cycles-in-reactions",
+ "reactivity-1-4-entropy-and-spontaneity",
+ "reactivity-2-1-how-much-the-amount-of-chemical-change",
+ "reactivity-2-3-how-far-the-extent-of-chemical-change",
+ "structure-2-2-the-covalent-model"
+ ]
+ },
+ {
+ "question_id": "21N.2.HL.TZ0.5",
+ "Question": "
\n
Phosphoric acid, H3PO4 can form three different salts depending on the extent of neutralisation by sodium hydroxide.
\n
\n
Formulate an equation for the reaction of one mole of phosphoric acid with one mole of sodium hydroxide.
\n
[1]
\n
a.
\n
\n
Formulate two equations to show the amphiprotic nature of H2PO4−.
\n
[2]
\n
b.
\n
\n
Calculate the concentration of H3PO4 if 25.00 cm3 is completely neutralised by the addition of 28.40 cm3 of 0.5000 mol dm−3 NaOH.
\n
[2]
\n
c.
\n
\n
Outline the reasons that sodium hydroxide is considered a Brønsted–Lowry and Lewis base.
\n

\n
[1]
\n
d.
\n
",
+ "Markscheme": "
\n
H3PO4 (aq) + NaOH (aq) → NaH2PO4 (aq) + H2O (l) ✔
\n
Accept net ionic equation.
\n
a.
\n
\n
H2PO4− (aq) + H+ (aq) → H3PO4 (aq) ✔
\n
H2PO4− (aq) + OH− (aq) → HPO42− (aq) + H2O (l) ✔
\n
Accept reactions of H2PO4− with any acidic, basic or amphiprotic species, such as H3O+, NH3 or H2O.
\n
Accept H2PO4− (aq) → HPO42− (aq) + H+ (aq) for M2.
\n
b.
\n
\n
«»
\n
«» 0.004733 «mol» ✔
\n
«» 0.1893 «mol dm−3» ✔
\n
\n
Award [2] for correct final answer.
\n
c.
\n
\n
Brønsted–Lowry base:
proton acceptor
\n
AND
\n
Lewis Base:
e– pair donor/nucleophile ✔
\n
d.
\n
",
+ "Examiners report": "
",
+ "topics": [
+ "reactivity-2-how-much-how-fast-and-how-far",
+ "reactivity-3-what-are-the-mechanisms-of-chemical-change",
+ "tools"
+ ],
+ "subtopics": [
+ "reactivity-2-3-how-far-the-extent-of-chemical-change",
+ "reactivity-3-1-proton-transfer-reactions",
+ "reactivity-3-4-electron-pair-sharing-reactions",
+ "tool-1-experimental-techniques",
+ "tool-3-mathematics"
+ ]
+ },
+ {
+ "question_id": "21N.2.SL.TZ0.2",
+ "Question": "
\n
Explain the general increase in trend in the first ionization energies of the period 3 elements, Na to Ar.
\n
",
+ "Markscheme": "
\n
increasing number of protons
\n
OR
\n
increasing nuclear charge ✔
\n
\n
«atomic» radius/size decreases
\n
OR
\n
same number of shells/electrons occupy same shell
\n
OR
\n
similar shielding «by inner electrons» ✔
\n
",
+ "Examiners report": "
\n[N/A]\n
",
+ "topics": [
+ "structure-1-models-of-the-particulate-nature-of-matter",
+ "structure-3-classification-of-matter"
+ ],
+ "subtopics": [
+ "structure-1-3-electron-configurations",
+ "structure-3-1-the-periodic-table-classification-of-elements"
+ ]
+ },
+ {
+ "question_id": "21N.2.SL.TZ0.3",
+ "Question": "
\n
White phosphorus is an allotrope of phosphorus and exists as P4.
\n
\n
An equilibrium exists between PCl3 and PCl5.
\n
PCl3 (g) + Cl2 (g) PCl5 (g)
\n
\n
Sketch the Lewis (electron dot) structure of the P4 molecule, containing only single bonds.
\n
\n
[1]
\n
a(i).
\n
\n
Write an equation for the reaction of white phosphorus (P4) with chlorine gas to form phosphorus trichloride (PCl3).
\n
[1]
\n
a(ii).
\n
\n
Deduce the electron domain and molecular geometry using VSEPR theory, and estimate the Cl–P–Cl bond angle in PCl3.
\n

\n
[3]
\n
b(i).
\n
\n
Explain the polarity of PCl3.
\n
[1]
\n
b(ii).
\n
\n
Calculate the standard enthalpy change (ΔH⦵) for the forward reaction in kJ mol−1.
\n
ΔH⦵f PCl3 (g) = −306.4 kJ mol−1
\n
ΔH⦵f PCl5 (g) = −398.9 kJ mol−1
\n
[1]
\n
c(i).
\n
\n
State the equilibrium constant expression, Kc, for this reaction.
\n
[1]
\n
c(ii).
\n
\n
State, with a reason, the effect of an increase in temperature on the position of this equilibrium.
\n
[1]
\n
c(iii).
\n
",
+ "Markscheme": "
\n

\n
Accept any diagram with each P joined to the other three.
\n
Accept any combination of dots, crosses and lines.
\n
a(i).
\n
\n
P4 (s) + 6Cl2 (g) → 4PCl3 (l) ✔
\n
a(ii).
\n
\n
Electron domain geometry: tetrahedral ✔
\n
Molecular geometry: trigonal pyramidal ✔
\n
Bond angle: 100«°» ✔
\n
\n
Accept any value or range within the range 91−108«°» for M3.
\n
b(i).
\n
\n
polar AND unsymmetrical distribution of charge
OR
polar AND dipoles do not cancel
OR
«polar as» dipoles «add to» give a «partial» positive «charge» at P and a «partial» negative «charge» at the opposite/Cl side of the molecule ✔
\n
Accept “polar AND unsymmetrical molecule”.
\n
b(ii).
\n
\n
«−398.9 kJ mol−1 − (−306.4 kJ mol−1) =» −92.5 «kJ mol−1» ✔
\n
c(i).
\n
\n
«Kc =» ✔
\n
c(ii).
\n
\n
«shifts» left/towards reactants AND «forward reaction is» exothermic/ΔH is negative ✔
\n
c(iii).
\n
",
+ "Examiners report": "
",
+ "topics": [
+ "reactivity-1-what-drives-chemical-reactions",
+ "reactivity-2-how-much-how-fast-and-how-far",
+ "structure-2-models-of-bonding-and-structure"
+ ],
+ "subtopics": [
+ "reactivity-1-2-energy-cycles-in-reactions",
+ "reactivity-2-1-how-much-the-amount-of-chemical-change",
+ "reactivity-2-3-how-far-the-extent-of-chemical-change",
+ "structure-2-2-the-covalent-model"
+ ]
+ },
+ {
+ "question_id": "21N.2.SL.TZ0.5",
+ "Question": "
\n
Phosphoric acid, H3PO4, can undergo stepwise neutralization, forming amphiprotic species.
\n
\n
Formulate an equation for the reaction of one mole of phosphoric acid with one mole of sodium hydroxide.
\n
[1]
\n
a.
\n
\n
Formulate two equations to show the amphiprotic nature of H2PO4−.
\n
[2]
\n
b.
\n
\n
Calculate the concentration of H3PO4 if 25.00 cm3 is completely neutralised by the addition of 28.40 cm3 of 0.5000 mol dm−3 NaOH.
\n
[2]
\n
c.
\n
\n
Outline the reason that sodium hydroxide is considered a Brønsted–Lowry base.
\n
[1]
\n
d.
\n
",
+ "Markscheme": "
\n
H3PO4 (aq) + NaOH (aq) → NaH2PO4 (aq) + H2O (l) ✔
\n
Accept net ionic equation.
\n
a.
\n
\n
H2PO4− (aq) + H+ (aq) → H3PO4 (aq) ✔
\n
H2PO4− (aq) + OH− (aq) → HPO42− (aq) + H2O (l) ✔
\n
Accept reactions of H2PO4− with any acidic, basic or amphiprotic species, such as H3O+, NH3 or H2O.
\n
Accept H2PO4− (aq) → HPO42− (aq) + H+ (aq) for M2.
\n
b.
\n
\n
«NaOH »
\n
«» 0.004733 «mol» ✔
\n
«» 0.1893 «mol dm−3» ✔
\n
Award [2] for correct final answer.
\n
c.
\n
\n
«OH− is a» proton acceptor ✔
\n
d.
\n
",
+ "Examiners report": "
",
+ "topics": [
+ "reactivity-2-how-much-how-fast-and-how-far",
+ "reactivity-3-what-are-the-mechanisms-of-chemical-change",
+ "tools"
+ ],
+ "subtopics": [
+ "reactivity-2-3-how-far-the-extent-of-chemical-change",
+ "reactivity-3-1-proton-transfer-reactions",
+ "tool-1-experimental-techniques",
+ "tool-3-mathematics"
+ ]
+ },
+ {
+ "question_id": "21N.2.SL.TZ0.7",
+ "Question": "
\n
Alkanes undergo combustion and substitution.
\n
\n
Determine the molar enthalpy of combustion of an alkane if 8.75 × 10−4 moles are burned, raising the temperature of 20.0 g of water by 57.3 °C.
\n
[2]
\n
a.
\n
\n
Formulate equations for the two propagation steps and one termination step in the formation of chloroethane from ethane.
\n
[3]
\n
b.
\n
",
+ "Markscheme": "
\n
«q = mcΔT = 20.0 g × 4.18 J g−1 °C−1 × 57.3 °C =» 4790 «J» ✔
\n
«» –5470 «kJ mol–1» ✔
\n
\n
Award [2] for correct final answer.
\n
Accept answers in the range –5470 to –5480 «kJ mol−1».
\n
Accept correct answer in any units, e.g. –5.47 «MJ mol−1» or 5.47 x 106 «J mol−1».
\n
a.
\n
\n
Cl· + C2H6 → ·C2H5 + HCl ✔
\n
·C2H5 + Cl2 → Cl· + C2H5Cl ✔
\n
·C2H5 + Cl· → C2H5Cl
OR
Cl· + Cl· → Cl2
OR
·C2H5 + ·C2H5 → C4H10 ✔
\n
Do not penalize incorrectly placed radical sign, eg C2H5·.
\n
b.
\n
",
+ "Examiners report": "
",
+ "topics": [
+ "reactivity-1-what-drives-chemical-reactions",
+ "reactivity-3-what-are-the-mechanisms-of-chemical-change",
+ "tools"
+ ],
+ "subtopics": [
+ "reactivity-1-1-measuring-enthalpy-changes",
+ "reactivity-3-3-electron-sharing-reactions",
+ "tool-1-experimental-techniques"
+ ]
+ },
+ {
+ "question_id": "21N.2.SL.TZ0.8",
+ "Question": "
\n
Fast moving helium nuclei (4He2+) were fired at a thin piece of gold foil with most passing undeflected but a few deviating largely from their path. The diagram illustrates this historic experiment.
\n

\n
Figure from PPLATO / FLAP (Flexible Learning Approach To Physics), http://www.met.reading.ac.uk/pplato2/h-flap/
phys8_1.html#top 1996 The Open University and The University of Reading.
\n
\n
Suggest what can be concluded about the gold atom from this experiment.
\n

\n
[2]
\n
a.
\n
\n
Subsequent experiments showed electrons existing in energy levels occupying various orbital shapes.
\n
Sketch diagrams of 1s, 2s and 2p.
\n

\n
[2]
\n
b(i).
\n
\n
State the electron configuration of copper.
\n
[1]
\n
b(ii).
\n
",
+ "Markscheme": "
\n
Most 4He2+ passing straight through:
\n
most of the atom is empty space
OR
the space between nuclei is much larger than 4He2+ particles
OR
nucleus/centre is «very» small «compared to the size of the atom» ✔
\n
\n
Very few 4He2+ deviating largely from their path:
\n
nucleus/centre is positive «and repels 4He2+ particles»
OR
nucleus/centre is «more» dense/heavy «than 4He2+ particles and deflects them»
OR
nucleus/centre is «very» small «compared to the size of the atom» ✔
\n
\n
Do not accept the same reason for both M1 and M2.
\n
Accept “most of the atom is an electron cloud” for M1.
\n
Do not accept only “nucleus repels 4He2+ particles” for M2.
\n
a.
\n
\n

\n
1s AND 2s as spheres ✔
\n
one or more 2p orbital(s) as figure(s) of 8 shape(s) of any orientation (px, py pz) ✔
\n
b(i).
\n
\n
1s22s22p63s23p64s13d10
\n
OR
\n
[Ar] 4s13d10 ✔
\n
\n
Accept configuration with 3d before 4s.
\n
b(ii).
\n
",
+ "Examiners report": "
",
+ "topics": [
+ "structure-1-models-of-the-particulate-nature-of-matter"
+ ],
+ "subtopics": [
+ "structure-1-2-the-nuclear-atom",
+ "structure-1-3-electron-configurations"
+ ]
+ },
+ {
+ "question_id": "21N.2.SL.TZ0.9",
+ "Question": "
\n
\n (a)\n
\n
\n
\n Suggest what can be concluded about the gold atom from this experiment.\n
\n
\n
\n
\n
\n
\n
\n
\n
\n (b(i))\n
\n
\n
\n Subsequent experiments showed electrons existing in energy levels occupying various orbital shapes.\n
\n
\n Sketch diagrams of 1s, 2s and 2p.\n
\n
\n
\n
\n
\n
\n
\n
\n
\n (b(ii))\n
\n
\n
\n State the electron configuration of copper.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n \n Most\n \n 4\n \n He\n \n 2+\n \n passing straight through:\n \n
\n
\n most of the atom is empty space\n
\n \n \n OR\n \n \n
\n the space between nuclei is much larger than\n \n 4\n \n He\n \n 2+\n \n particles\n
\n \n \n OR\n \n \n
\n nucleus/centre is «very» small «compared to the size of the atom» ✔\n
\n
\n \n
\n Very few\n \n 4\n \n He\n \n 2+\n \n deviating largely from their path:\n \n
\n
\n nucleus/centre is positive «and repels\n \n 4\n \n He\n \n 2+\n \n particles»\n
\n \n \n OR\n \n \n
\n nucleus/centre is «more» dense/heavy «than\n \n 4\n \n He\n \n 2+\n \n particles and deflects them»\n
\n \n \n OR\n \n \n
\n nucleus/centre is «very» small «compared to the size of the atom» ✔\n
\n
\n
\n
\n \n Do\n \n not\n \n accept the same reason for both\n \n M1\n \n and\n \n M2\n \n .\n \n
\n
\n \n Accept “most of the atom is an electron cloud” for\n \n M1\n \n .\n \n
\n
\n \n Do not accept only “nucleus repels\n \n 4\n \n He\n \n 2+\n \n particles” for\n \n M2\n \n .\n \n
\n
\n
\n (b(i))\n
\n
\n
\n
\n
\n 1s\n \n \n AND\n \n \n 2s as spheres ✔\n
\n
\n one or more 2p orbital(s) as figure(s) of 8 shape(s) of any orientation (p\n \n x\n \n , p\n \n y\n \n p\n \n z\n \n ) ✔\n
\n
\n
\n (b(ii))\n
\n
\n 1s\n \n 2\n \n 2s\n \n 2\n \n 2p\n \n 6\n \n 3s\n \n 2\n \n 3p\n \n 6\n \n 4s\n \n 1\n \n 3d\n \n 10\n \n
\n \n \n OR\n \n \n
\n [Ar] 4s\n \n 1\n \n 3d\n \n 10\n \n ✔\n
\n
\n \n
\n Accept configuration with 3d before 4s.\n \n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "structure-1-models-of-the-particulate-nature-of-matter"
+ ],
+ "subtopics": [
+ "structure-1-2-the-nuclear-atom",
+ "structure-1-3-electron-configurations"
+ ]
+ },
+ {
+ "question_id": "22M.2.HL.TZ1.3",
+ "Question": "
\n
Ammonia is produced by the Haber–Bosch process which involves the equilibrium:
\n
N2 (g) + 3 H2 (g) 2 NH3 (g)
\n
The percentage of ammonia at equilibrium under various conditions is shown:
\n

\n
[The Haber Bosch Process [graph] Available at: https://commons.wikimedia.org/wiki/File:Ammonia_yield.png
[Accessed: 16/07/2022].]
\n
\n
One factor affecting the position of equilibrium is the enthalpy change of the reaction.
\n
\n
The standard free energy change, ΔG⦵, for the Haber–Bosch process is –33.0 kJ at 298 K.
\n
\n
Deduce the expression for the equilibrium constant, Kc, for this equation.
\n
[1]
\n
a(i).
\n
\n
State how the use of a catalyst affects the position of the equilibrium.
\n
[1]
\n
a(ii).
\n
\n
With reference to the reaction quotient, Q, explain why the percentage yield increases as the pressure is increased at constant temperature.
\n
[3]
\n
a(iii).
\n
\n
Determine the enthalpy change, ΔH, for the Haber–Bosch process, in kJ. Use Section 11 of the data booklet.
\n
[3]
\n
b(i).
\n
\n
Outline why the value obtained in (b)(i) might differ from a value calculated using ΔHf data.
\n
[1]
\n
b(ii).
\n
\n
Demonstrate that your answer to (b)(i) is consistent with the effect of an increase in temperature on the percentage yield, as shown in the graph.
\n
[2]
\n
b(iii).
\n
\n
State, giving a reason, whether the reaction is spontaneous or not at 298 K.
\n
[1]
\n
c(i).
\n
\n
Calculate the value of the equilibrium constant, K, at 298 K. Use sections 1 and 2 of the data booklet.
\n
[2]
\n
c(ii).
\n
\n
Calculate the entropy change for the Haber–Bosch process, in J mol–1 K–1 at 298 K. Use your answer to (b)(i) and section 1 of the data booklet.
\n
[2]
\n
c(iii).
\n
\n
Outline, with reference to the reaction equation, why this sign for the entropy change is expected.
\n
[1]
\n
c(iv).
\n
",
+ "Markscheme": "
\n
✔
\n
a(i).
\n
\n
same/unaffected/unchanged ✔
\n
a(ii).
\n
\n
increasing pressure increases «all» concentrations
OR
increasing pressure decreases volume ✔
\n
Q becomes less than Kc
OR
affects the lower line/denominator of Q expression more than upper line/numerator ✔
\n
«for Q to once again equal Kc,» ratio of products to reactants increases
OR
«for Q to once again equal Kc,» equilibrium shifts to right/products ✔
\n
\n
Award [2 max] for answers that do not refer to Q.
\n
a(iii).
\n
\n
bonds broken: N≡N + 3(H-H) /«1 mol×»945 «kJ mol–1» + 3«mol»×436 «kJ mol–1» / 945 «kJ» + 1308 «kJ» / 2253 «kJ» ✔
\n
bonds formed: 6(N-H) / 6«mol»×391 «kJ mol–1» / 2346 «kJ» ✔
\n
ΔH = «2253 kJ - 2346 kJ = » -93 «kJ» ✔
\n
\n
Award [2 max] for (+)93 «kJ».
\n
b(i).
\n
\n
«N-H» bond enthalpy is an average «and may not be the precise value in NH3» ✔
\n
\n
Accept ΔHf data are more accurate / are not average values.
\n
b(ii).
\n
\n
increased temperature decreases yield «as shown on graph» ✔
\n
shifts equilibrium in endothermic/reverse direction ✔
\n
b(iii).
\n
\n
spontaneous AND ΔG < 0 ✔
\n
c(i).
\n
\n
✔
\n
✔
\n
\n
Award [2] for correct final answer.
\n
Accept answers in the range 4.4×105 to 6.2×105 (arises from rounding of ln K).
\n
c(ii).
\n
\n
ΔG = «ΔH – TΔS =» –93000 «J» – 298«K» × ΔS = –33000 ✔
\n
ΔS = 〈〈〉〉 = –201 «J mol–1 K–1» ✔
\n
\n
Do not penalize failure to convert kJ to J in both (c)(ii) and (c)(iii).
\n
Award [2] for correct final answer
\n
Award [1 max] for (+) 201 «J mol–1 K–1».
\n
Award [2] for –101 or –100.5 «J mol–1 K–1».
\n
c(iii).
\n
\n
«forward reaction involves» decrease in number of moles «of gas» ✔
\n
c(iv).
\n
",
+ "Examiners report": "
\n
Deducing the equilibrium constant expression for the given equation was done very well.
\n
a(i).
\n
\n
Good performance; however, some misread the question as asking for the effect of a catalyst on equilibrium, rather than on the position of equilibrium.
\n
a(ii).
\n
\n
Mediocre performance; very few identified the effect of increasing pressure on all concentrations. Consequently, Q becomes less than Kc (it affects the denominator of Q expression more than the numerator) was not addressed. Question was often answered with respect to kinetics, namely greater frequency of collisions and speed of reaction rather than from equilibrium perspective based on effect of increase in pressure on concentrations.
\n
a(iii).
\n
\n
Good performance; often the bond energy for single N–N bond instead of using it for the triple bond and not taking into consideration the coefficient of three in calculation of bond enthalpies of ammonia. Also, instead of using BE of bonds broken minus those that were formed, the operation was often reversed. Students should be encouraged to draw the Lewis structures in the equations first to determine the bonds being broken and formed.
\n
b(i).
\n
\n
Outlining why ΔHrxn based on BE values differ due to being average compared to using ΔHf values was generally done well.
\n
b(ii).
\n
\n
Good performance; some did not relate that increased temperature decreases yield «as shown on graph» and others arrived at incorrect shift in equilibrium for the reaction.
\n
b(iii).
\n
\n
Reason for the reaction being spontaneous was generally very done well indeed.
\n
c(i).
\n
\n
Good performance; for lnK calculation in the equation ΔG = RTlnK, ΔG unit had to be converted from kJ to J. This led to an error of 1000 in the value of lnK for some.
\n
c(ii).
\n
\n
Very good performance; since the unit for S is J mol˗1 K˗1, ΔG and ΔH needed to be converted from kJ to J, but that was not done in some cases.
\n
c(iii).
\n
\n
Average performance for sign of the entropy change expected for the reaction. Some answers were based on ΔG value rather than in terms of decrease in number of moles of gas or had no idea how to address the question.
\n
c(iv).
\n
",
+ "topics": [
+ "reactivity-1-what-drives-chemical-reactions",
+ "reactivity-2-how-much-how-fast-and-how-far",
+ "reactivity-3-what-are-the-mechanisms-of-chemical-change"
+ ],
+ "subtopics": [
+ "reactivity-1-2-energy-cycles-in-reactions",
+ "reactivity-1-4-entropy-and-spontaneity",
+ "reactivity-2-1-how-much-the-amount-of-chemical-change",
+ "reactivity-2-3-how-far-the-extent-of-chemical-change",
+ "reactivity-3-4-electron-pair-sharing-reactions"
+ ]
+ },
+ {
+ "question_id": "22M.2.HL.TZ1.5",
+ "Question": "
\n
Organomagnesium compounds can react with carbonyl compounds. One overall equation is:
\n

\n
\n
Compound B can also be prepared by reacting an alkene with water.
\n
\n
Iodomethane is used to prepare CH3Mg. It can also be converted into methanol:
\n
CH3 + HO– → CH3OH + –
\n
\n
State the name of Compound B, applying International Union of Pure and Applied Chemistry (IUPAC) rules.
\n
[1]
\n
a(i).
\n
\n
Compound A and Compound B are both liquids at room temperature and pressure. Identify the strongest intermolecular force between molecules of Compound A.
\n
[1]
\n
a(ii).
\n
\n
State the number of (sigma) and (pi) bonds in Compound A.
\n

\n
[1]
\n
a(iii).
\n
\n
Deduce the hybridization of the central carbon atom in Compound A.
\n
[1]
\n
a(iv).
\n
\n
Identify the isomer of Compound B that exists as optical isomers (enantiomers).
\n
[1]
\n
a(v).
\n
\n
Draw the structural formula of the alkene required.
\n

\n
[1]
\n
b(i).
\n
\n
Explain why the reaction produces more (CH3)3COH than (CH3)2CHCH2OH.
\n
[2]
\n
b(ii).
\n
\n
Deduce the structural formula of the repeating unit of the polymer formed from this alkene.
\n
[1]
\n
b(iii).
\n
\n
Deduce what would be observed when Compound B is warmed with acidified aqueous potassium dichromate (VI).
\n
[1]
\n
c.
\n
\n
Identify the type of reaction.
\n
[1]
\n
d(i).
\n
\n
Outline the requirements for a collision between reactants to yield products.
\n
[2]
\n
d(ii).
\n
\n
Explain the mechanism of the reaction using curly arrows to represent the movement of electron pairs.
\n
[3]
\n
d(iii).
\n
\n
The polarity of the carbon–halogen bond, C–X, facilitates attack by HO–.
\n
Outline, giving a reason, how the bond polarity changes going down group 17.
\n
[1]
\n
d(iv).
\n
",
+ "Markscheme": "
\n
2-methylpropan-2-ol /2-methyl-2-propanol ✔
\n
\n
Accept methylpropan-2-ol/ methyl-2-propanol.
\n
Do not accept 2-methylpropanol.
\n
a(i).
\n
\n
dipole-dipole ✔
\n
\n
Do not accept van der Waals’ forces.
\n
a(ii).
\n
\n
: 9
AND
: 1 ✔
\n
a(iii).
\n
\n
butan-2-ol/CH3CH(OH)C2H5 ✔
\n
a(v).
\n
\n

\n
b(i).
\n
\n
carbocation formed from (CH3)3COH is more stable / (CH3)3C+ is more stable than (CH3)2CHCH2+ ✔
\n
«because carbocation has» greater number of alkyl groups/lower charge on the atom/higher e- density
OR
«greater number of alkyl groups» are more electron releasing
OR
«greater number of alkyl groups creates» greater inductive/+I effect ✔
\n
\n
Do not award any marks for simply quoting Markovnikov’s rule.
\n
b(ii).
\n
\n

\n
Do not penalize missing brackets or n.
\n
Do not award mark if continuation bonds are not shown.
\n
b(iii).
\n
\n
no change «in colour/appearance/solution» ✔
\n
c.
\n
\n
«nucleophilic» substitution
OR
SN2 ✔
\n
Accept “hydrolysis”.
\n
Accept SN1
\n
d(i).
\n
\n
energy/E ≥ activation energy/Ea ✔
\n
correct orientation «of reacting particles»
OR
correct geometry «of reacting particles» ✔
\n
d(ii).
\n
\n

\n
curly arrow going from lone pair/negative charge on O in -OH to C ✔
\n
curly arrow showing I leaving ✔
\n
representation of transition state showing negative charge, square brackets and partial bonds ✔
\n
\n
Accept OH- with or without the lone pair.
\n
Do not allow curly arrows originating on H, rather than the -, in OH-.
\n
Accept curly arrows in the transition state.
\n
Do not penalize if HO and I are not at 180°.
\n
Do not award M3 if OH–C bond is represented.
\n
Award [2 max] if SN1 mechanism shown.
\n
d(iii).
\n
\n
decreases/less polar AND electronegativity «of the halogen» decreases ✔
\n
\n
Accept “decreases” AND a correct comparison of the electronegativity of two halogens.
\n
Accept “decreases” AND “attraction for valence electrons decreases”.
\n
d(iv).
\n
",
+ "Examiners report": "
\n
Naming the organic compound using IUPAC rules was generally done well.
\n
a(i).
\n
\n
Mediocre performance in stating the number of σ (sigma) and π (pi) bonds in propanone; the common answer was 3 σ and 1 π instead of 9 σ and 1 π, suggesting the three C-H σ bonds in each of the two methyl groups were ignored.
\n
a(iii).
\n
\n
sp2 hybridization of the central carbon atom in the ketone was very done well.
\n
a(iv).
\n
\n
Mediocre performance; some identified 2-methylpropan-1-ol or -2-ol, instead butan-2-ol/CH3CH(OH)C2H5 as the isomer that exists as an optical isomer.
\n
a(v).
\n
\n
Good performance; some had a H and CH3 group on each C atom across double bond instead of having two H atoms on one C and two CH3 groups on the other.
\n
b(i).
\n
\n
Poor performance, particularly in light of past feedback provided in similar questions since there was repeated reference simply to Markovnikov's rule, without any explanation.
\n
b(ii).
\n
\n
Mediocre performance; deducing structural formula of repeating unit of the polymer was challenging in which continuation bonds were sometimes missing, or structure included a double bond or one of the CH3 group was missing.
\n
b(iii).
\n
\n
Mediocre performance; deducing whether the tertiary alcohol could be oxidized solicited mixed responses ranging from the correct one, namely no change (in colour, appearance or solution), to tertiary alcohol will be reduced, or oxidized, or colour will change will occur, and such.
\n
c.
\n
\n
Excellent performance on the type of reaction but with some incorrect answers such as alkane substitution, free radical substitution or electrophilic substitution.
\n
d(i).
\n
\n
Good performance. For the requirements for a collision between reactants to yield products, some suggested necessary, sufficient or enough energy or even enough activation energy instead of energy/E ≥ activation energy/Ea.
\n
d(ii).
\n
\n
Mechanism for SN2 not done well. Often the negative charge on OH was missing, the curly arrow was not going from lone pair/negative charge on O in -OH to C, or the curly arrow showing I leaving placed incorrectly and specially the negative charge was missing in the transition state. Formation of a carbocation intermediate indicating SN1 mechanism could score a maximum of 2 marks.
\n
d(iii).
\n
\n
Good performance on how the polarity of C-X bond changes going down group 17.
\n
d(iv).
\n
",
+ "topics": [
+ "reactivity-2-how-much-how-fast-and-how-far",
+ "reactivity-3-what-are-the-mechanisms-of-chemical-change",
+ "structure-2-models-of-bonding-and-structure",
+ "structure-3-classification-of-matter"
+ ],
+ "subtopics": [
+ "reactivity-2-2-how-fast-the-rate-of-chemical-change",
+ "reactivity-3-4-electron-pair-sharing-reactions",
+ "structure-2-2-the-covalent-model",
+ "structure-2-4-from-models-to-materials",
+ "structure-3-1-the-periodic-table-classification-of-elements",
+ "structure-3-2-functional-groups-classification-of-organic-compounds"
+ ]
+ },
+ {
+ "question_id": "22M.2.HL.TZ1.6",
+ "Question": "
\n
Nitric acid is usually produced by the oxidation of ammonia.
\n
\n
A mixture of nitric acid and sulfuric acid can be used to convert benzene to nitrobenzene, C6H5NO2.
\n
\n
Draw arrows in the boxes to represent the electron configuration of a nitrogen atom.
\n

\n
[1]
\n
a(i).
\n
\n
Deduce a Lewis (electron dot) structure of the nitric acid molecule, HNO3, that obeys the octet rule, showing any non-zero formal charges on the atoms.
\n
[2]
\n
a(ii).
\n
\n
Explain the relative lengths of the three bonds between N and O in nitric acid.
\n
[3]
\n
a(iii).
\n
\n
State a technique used to determine the length of the bonds between N and O in solid HNO3.
\n
[1]
\n
a(iv).
\n
\n
Write an equation for the reaction between the acids to produce the electrophile, NO2+.
\n
[1]
\n
b(i).
\n
\n
Draw the structural formula of the carbocation intermediate produced when this electrophile attacks benzene.
\n
[1]
\n
b(ii).
\n
\n
Deduce the number of signals that you would expect in the 1H NMR spectrum of nitrobenzene and the relative areas of these.
\n

\n
[2]
\n
b(iii).
\n
",
+ "Markscheme": "
\n

\n
Accept all 2p electrons pointing downwards.
\n
Accept half arrows instead of full arrows.
\n
a(i).
\n
\n

\n
bonds and non-bonding pairs correct ✔
\n
formal charges correct ✔
\n
\n
Accept dots, crosses or lines to represent electron pairs.
\n
Do not accept resonance structures with delocalised bonds/electrons.
\n
Accept + and – sign respectively.
\n
Do not accept a bond between nitrogen and hydrogen.
\n
For an incorrect Lewis structure, allow ECF for non-zero formal charges.
\n
a(ii).
\n
\n
Any three of:
\n
two N-O same length/order ✔
delocalization/resonance ✔
\n
N-OH longer «than N-O»
OR
N-OH bond order 1 AND N-O bond order 1½ ✔
\n
\n
Award [2 max] if bond strength, rather than bond length discussed.
\n
Accept N-O between single and double bond AND N-OH single bond.
\n
a(iii).
\n
\n
X-ray crystallography ✔
\n
a(iv).
\n
\n
HNO3 + 2H2SO4 NO2+ + H3O+ + 2HSO4- ✔
\n
\n
Accept “HNO3 + H2SO4 NO2+ + H2O + HSO4-”.
\n
Accept “HNO3 + H2SO4 H2NO3+ + HSO4-” AND “H2NO3+ NO2+ + H2O”.
\n
Accept single arrows instead of equilibrium signs.
\n
b(i).
\n
\n

\n
\n
Accept any of the five structures.
\n
Do not accept structures missing the positive charge.
\n
b(ii).
\n
\n
Number of signals: three/3 ✔
\n
Relative areas: 2 : 2 : 1 ✔
\n
b(iii).
\n
",
+ "Examiners report": "
\n
Drawing arrows in the boxes to represent the electron configuration of a nitrogen atom was done extremely well.
\n
a(i).
\n
\n
Drawing the Lewis structure of HNO3 was performed extremely poorly with structures that included H bonded to N, no double bond or a combination of single, double and even a triple bond or incorrect structures with dotted lines to reflect resonance. Many did not calculate non-zero formal charges.
\n
a(ii).
\n
\n
Poorly done; some explained relative bond strengths between N and O in HNO3, not relative lengths; others included generic answers such as triple bond is shortest, double bond is longer, single longest.
\n
a(iii).
\n
\n
A majority could not state the technique to determine length of bonds; answers included NMR, IR, and such instead of X-ray crystallography.
\n
a(iv).
\n
\n
Many had difficulties writing the balanced equation(s) for the formation of the nitronium ion.
\n
b(i).
\n
\n
Again, many had difficulty drawing the structural formula of the carbocation intermediate produced in the reaction.
\n
b(ii).
\n
\n
Deducing the number of signals in the 1H NMR spectrum of nitrobenzene, which depend on the number of different hydrogen environments, was done poorly. Also, instead of relative areas, the common answer included chemical shift (ppm) values.
\n
b(iii).
\n
",
+ "topics": [
+ "reactivity-3-what-are-the-mechanisms-of-chemical-change",
+ "structure-1-models-of-the-particulate-nature-of-matter",
+ "structure-2-models-of-bonding-and-structure",
+ "structure-3-classification-of-matter"
+ ],
+ "subtopics": [
+ "reactivity-3-4-electron-pair-sharing-reactions",
+ "structure-1-3-electron-configurations",
+ "structure-2-2-the-covalent-model",
+ "structure-3-2-functional-groups-classification-of-organic-compounds"
+ ]
+ },
+ {
+ "question_id": "22M.2.HL.TZ2.3",
+ "Question": "
\n
Standard electrode potential values, E⦵, can be used to predict spontaneity.
\n
\n
Iron(II) is oxidized by bromine.
\n
2Fe2+ (aq) + Br2 (l) 2Fe3+ (aq) + 2Br− (aq)
\n
Calculate the E⦵cell, in V, for the reaction using section 24 of the data booklet.
\n
[1]
\n
a(i).
\n
\n
Determine, giving a reason, if iodine will also oxidize iron(II).
\n
[1]
\n
a(ii).
\n
\n
Molten zinc chloride undergoes electrolysis in an electrolytic cell at 450 °C.
\n
Deduce the half-equations for the reaction at each electrode.
\n

\n
\n
[2]
\n
b(i).
\n
\n
Deduce the overall cell reaction including state symbols. Use section 7 of the data booklet.
\n
[2]
\n
b(ii).
\n
",
+ "Markscheme": "
\n
« = 1.09 – 0.77 =» 0.32 «V» ✔
\n
a(i).
\n
\n
«2Fe2+ (aq) + 2 (s) → 2Fe3+ (aq) + 2– (aq) »
\n
no/non-spontaneous AND «= 0.54 – 0.77 »= –0.23 «V»/
OR
no AND reduction potential of 2 lower «than Fe3+ »/ 0.54 <0.77 ✔
\n
\n
Accept “standard electrode potential of 2 lower /less positive than iron”.
\n
a(ii).
\n
\n
Cathode (negative electrode):
\n
Zn2+ + 2e− → Zn (l) ✔
\n
\n
Anode (positive electrode):
\n
2Cl− → Cl2 (g) + 2e−
OR
Cl− → ½ Cl2 (g) + e− ✔
\n
b(i).
\n
\n
ZnCl2 (l) → Zn (l) + Cl2 (g)
\n
balanced equation ✔
\n
correct state symbols ✔
\n
\n
Accept ionic equation.
\n
b(ii).
\n
",
+ "Examiners report": "
\n
Only 50% got this straightforward calculation right, the most common error being to multiply both E0 values by 2, reflecting a lack of practice with this type of exercises.
\n
a(i).
\n
\n
Only 10% were able to correctly justify the feasibility of the reaction with I2; the MS showed the best answer using the E(v) values but also allowed simpler explanations referring to E0 of iron; even then many candidates wrote Fe+2 instead of Fe+3, understandably perhaps as this was mentioned in the question. However, it also revealed some difficulty in using and understanding data from the E0 table in the data booklet.
\n
a(ii).
\n
\n
3(bi)/(bii) Answers to both these questions revealed that many candidates struggle to conceptualize the equations that describe electrolysis. The question asked for products of the easiest case of electrolysis, a molten salt. However, many candidates proposed oxidation or reduction equations at both electrodes, or Zn and Cl2 (with no charge) as the initial species rather than the product; the average mark was 1.2/2 as only 55% answered correctly.
\n
b(i).
\n
\n
3(bi)/(bii) Answers to both these questions revealed that many candidates struggle to conceptualize the equations that describe electrolysis. The question asked for products of the easiest case of electrolysis, a molten salt. However, many candidates proposed oxidation or reduction equations at both electrodes, or Zn and Cl2 (with no charge) as the initial species rather than the product; the average mark was 1.2/2 as only 55% answered correctly.
\n
The determination of the states proved to be even more difficult, with many stating the ions were aqueous in spite of the fact that the question is clearly about molten zinc chloride. Allowing ECF for the overall equation allowed marks for many candidates, but very few realised that both ionic species in ZnCl2 were actually liquid (being a molten salt). As a result, correct answers were below 45% and the average mark was 0.9/2.
\n
b(ii).
\n
",
+ "topics": [
+ "structure-2-models-of-bonding-and-structure"
+ ],
+ "subtopics": [
+ "structure-2-2-the-covalent-model"
+ ]
+ },
+ {
+ "question_id": "22M.2.HL.TZ2.4",
+ "Question": "
\n
Hydrogen and iodine react to form hydrogen iodide.
\n
H2 (g) + 2 (g) 2H (g)
\n
\n
The following experimental data was obtained.
\n

\n
\n
Consider the reaction of hydrogen with solid iodine.
\n
H2 (g) + 2 (s) 2H (g) ΔH⦵ = +53.0 kJ mol−1
\n
\n
Deduce the order of reaction with respect to hydrogen.
\n
[1]
\n
a(i).
\n
\n
Deduce the rate expression for the reaction.
\n
[1]
\n
a(ii).
\n
\n
Calculate the value of the rate constant stating its units.
\n
[2]
\n
a(iii).
\n
\n
State two conditions necessary for a successful collision between reactants.
\n
[1]
\n
b.
\n
\n
State the equilibrium constant expression, Kc, for this reaction.
\n
[1]
\n
c.
\n
\n
Calculate the entropy change of reaction, ΔS⦵, in J K−1 mol−1.
\n

\n
[1]
\n
d(i).
\n
\n
Predict, giving a reason, how the value of the ΔS⦵reaction would be affected if (g) were used as a reactant.
\n
[1]
\n
d(ii).
\n
\n
Calculate the Gibbs free energy change, ΔG⦵, in kJ mol−1, for the reaction at 298 K. Use section 1 of the data booklet.
\n
[1]
\n
d(iii).
\n
\n
Calculate the equilibrium constant, Kc, for this reaction at 298 K. Use your answer to (d)(iii) and sections 1 and 2 of the data booklet.
\n
(If you did not obtain an answer to (d)(iii) use a value of 2.0 kJ mol−1, although this is not the correct answer).
\n
[2]
\n
d(iv).
\n
",
+ "Markscheme": "
\n
Rate=k [H2] [2]
\n
a(ii).
\n
\n
✔
\n
mol–1 dm3 s–1 ✔
\n
a(iii).
\n
\n
E ≥ Ea AND appropriate «collision» geometry/correct orientation ✔
\n
b.
\n
\n
«Δ = 2 × 206.6 – (130.6 + 116.1) =» 166.5 «J K–1 mol–1» ✔
\n
d(i).
\n
\n
Δ lower/less positive AND same number of moles of gas
\n
OR
\n
Δ lower/less positive AND a solid has less entropy than a gas ✔
\n
d(ii).
\n
\n
«ΔG⦵ = 53.0 kJ mol–1 – (298K × 0.1665 kJ K–1 mol–1) =» 3.4 «kJ mol–1» ✔
\n
d(iii).
\n
\n
«ln Kc= – (3.4 × 103 J mol–1 /8.31 J K–1 mol–1 × 298 K)» = –1.37 ✔
\n
«Kc =» 0.25 ✔
\n
Award [2] for “0.45” for the use of 2.0 kJ mol–1 for ΔG⦵.
\n
d(iv).
\n
",
+ "Examiners report": "
\n
4(a)(i)-(iii): Deduction of rate orders and rate expression were very well done overall, with occasional errors in the units of the rate constant, but clearly among the best answered questions.
\n
a(i).
\n
\n
Generally well answered by all but very weak candidates. Some teachers thought this should be a 2-mark question but actually the marks were generally missed when students mentioned both required conditions but failed to refer the necessary energy to Ea.
\n
b.
\n
\n
One of the best answered questions.
\n
c.
\n
\n
ΔS was well calculated in general except for some inverted calculations or failure to consider the ratios of the reactants.
\n
d(i).
\n
\n
Some candidates confused the entropy change in this situation with absolute entropy of a solid and gas, or having realised that entropy would decrease lacked clarity in their explanations and lost the mark.
\n
4(d)(ii)-(d)(iv): marks were lost due to inconsistency of units throughout, i.e., not because answers were given in different units to those required, but because candidates failed to convert all data to the same unit for calculations.
\n
d(ii).
\n
",
+ "topics": [
+ "reactivity-1-what-drives-chemical-reactions",
+ "reactivity-2-how-much-how-fast-and-how-far"
+ ],
+ "subtopics": [
+ "reactivity-1-4-entropy-and-spontaneity",
+ "reactivity-2-2-how-fast-the-rate-of-chemical-change",
+ "reactivity-2-3-how-far-the-extent-of-chemical-change"
+ ]
+ },
+ {
+ "question_id": "22M.2.HL.TZ2.5",
+ "Question": "
\n
Iron(II) disulfide, FeS2, has been mistaken for gold.
\n
\n
State the full electronic configuration of Fe2+.
\n
[1]
\n
a(i).
\n
\n
Explain why there is a large increase from the 8th to the 9th ionization energy of iron.
\n
[2]
\n
a(ii).
\n
\n
Calculate the oxidation state of sulfur in iron(II) disulfide, FeS2.
\n
[1]
\n
b.
\n
\n
Describe the bonding in iron, Fe (s).
\n
[1]
\n
c.
\n
",
+ "Markscheme": "
\n
1s2 2s2 2p6 3s2 3p6 3d6 ✔
\n
a(i).
\n
\n
Any two of:
\n
IE9: electron in lower energy level
OR
IE9: more stable/full electron level ✔
\n
IE9: electron closer to nucleus
OR
IE9: electron more tightly held by nucleus ✔
\n
IE9: less shielding by «complete» inner levels ✔
\n
a(ii).
\n
\n
–1 ✔
\n
\n
Accept “– I”.
\n
b.
\n
\n
electrostatic attraction/hold between «lattice of» positive ions/cations AND delocalized «valence» electrons ✔
\n
c.
\n
",
+ "Examiners report": "
\n
Mostly well done which was a pleasant surprise since this is not overly easy, predictably some gave [Ar] 4s2 3d4.
\n
a(i).
\n
\n
Despite some confusion regarding which sub-level the electrons were being removed from, many candidates were able to make at least one valid point, commonly in terms of lower energy/ full sub level/closer to nucleus.
\n
a(ii).
\n
\n
This was an easy question, yet 30% of the candidates were unable to work it out; some wrote the oxidation state in the conventionally incorrect format, 1- and lost the mark.
\n
b.
\n
\n
Most candidates knew the bonding in Fe is metallic but some did not “describe” it or missed the type of attraction, a minor mistake; others referred to nuclei or protons instead of cations/positive ions. In some cases, candidates referred too ionic bonding, probably still thinking of FeS2 (not reading the question well). Overall, only 30% answered satisfactorily.
\n
c.
\n
",
+ "topics": [
+ "structure-1-models-of-the-particulate-nature-of-matter",
+ "structure-2-models-of-bonding-and-structure",
+ "structure-3-classification-of-matter"
+ ],
+ "subtopics": [
+ "structure-1-3-electron-configurations",
+ "structure-2-3-the-metallic-model",
+ "structure-3-1-the-periodic-table-classification-of-elements"
+ ]
+ },
+ {
+ "question_id": "22M.2.HL.TZ2.6",
+ "Question": "
\n
Sulfur trioxide is produced from sulfur dioxide.
\n
2SO2 (g) + O2 (g) 2SO3 (g) ΔH = −196 kJ mol−1
\n
\n
The reaction between sulfur dioxide and oxygen can be carried out at different temperatures.
\n
\n
Outline, giving a reason, the effect of a catalyst on a reaction.
\n
[2]
\n
a.
\n
\n
On the axes, sketch Maxwell–Boltzmann energy distribution curves for the reacting species at two temperatures T1 and T2, where T2 > T1.
\n

\n
[3]
\n
b(i).
\n
\n
Explain the effect of increasing temperature on the yield of SO3.
\n
[2]
\n
b(ii).
\n
\n
Draw the Lewis structure of SO3.
\n
[1]
\n
c(i).
\n
\n
Explain the electron domain geometry of SO3.
\n
[2]
\n
c(ii).
\n
\n
State the product formed from the reaction of SO3 with water.
\n
[1]
\n
d(i).
\n
\n
State the meaning of a strong Brønsted–Lowry acid.
\n
[2]
\n
d(ii).
\n
",
+ "Markscheme": "
\n
increases rate AND lower Ea ✔
\n
provides alternative pathway «with lower Ea»
OR
more/larger fraction of molecules have the «lower» Ea ✔
\n
\n
Accept description of how catalyst lowers Ea for M2 (e.g. “reactants adsorb on surface «of catalyst»”, “reactant bonds weaken «when adsorbed»”, “helps favorable orientation of molecules”).
\n
a.
\n
\n

\n
both axes correctly labelled ✔
\n
peak of T2 curve lower AND to the right of T1 curve ✔
\n
lines begin at origin AND correct shape of curves AND T2 must finish above T1 ✔
\n
\n
Accept “probability «density» / number of particles / N / fraction” on y-axis.
\n
Accept “kinetic E/KE/Ek” but not just “Energy/E” on x-axis.
\n
b(i).
\n
\n
decrease AND equilibrium shifts left / favours reverse reaction ✔
\n
«forward reaction is» exothermic / ΔH is negative ✔
\n
b(ii).
\n
\n
✔
\n
\n
Note:
\n

\n
Accept any of the above structures as formal charge is not being assessed.
\n
c(i).
\n
\n
three electron domains «attached to the central atom» ✔
\n
repel/as far away as possible /120° «apart» ✔
\n
c(ii).
\n
\n
sulfuric acid/H2SO4 ✔
\n
Accept “disulfuric acid/H2S2O7”.
\n
d(i).
\n
\n
fully ionizes/dissociates ✔
\n
proton/H+ «donor »✔
\n
d(ii).
\n
",
+ "Examiners report": "
\n
Overall well answered though some answers were directed to explain the specific example rather than the simple and standard definition of the effect of a catalyst.
\n
a.
\n
\n
Few got the 3 marks for this standard question (average mark 1.7), the most common error being incomplete/incorrect labelling of axes, curves beginning above 0 on y-axis or inverted curves.
\n
b(i).
\n
\n
Many candidates got one mark at least, sometimes failing to state the effect on the production of SO3 though they knew this quite obviously. This failure to read the question properly also resulted in an incorrect prediction based exclusively on kinetics instead of using the information provided to guide their answers.
\n
b(ii).
\n
\n
Drawing the Lewis structure of SO3 proved to be challenging, with lots of incorrect shapes, lone pair on S, etc.; accepting all resonant structures allowed many candidates to get the mark which was fair considering no formal charge estimation was required.
\n
c(i).
\n
\n
Most were focussed on the shape itself instead of explaining what led them to suggest that shape; number of electron domains allowed most candidates to get one mark and eventually a mention of bond angles resulted in only 35% getting both marks. In general, students were not able to provide clear explanations for the shape (not a language issue) but rather were happy to state the molecular geometry which they knew, but wasn't what was actually required for the mark.
\n
c(ii).
\n
\n
6(d)(i)-(ii): These simple questions could be expected to be answered by all HL candidates. However 20% of the candidates suggested hydroxides or hydrogen as products of an aqueous dissolution of sulphur oxide. In the case of the definition of a strong Brønsted-Lowry acid, only 50% got both marks, often failing to define \"strong\" but in other cases defining them as bases even.
\n
d(i).
\n
",
+ "topics": [
+ "reactivity-2-how-much-how-fast-and-how-far",
+ "reactivity-3-what-are-the-mechanisms-of-chemical-change",
+ "structure-2-models-of-bonding-and-structure",
+ "structure-3-classification-of-matter"
+ ],
+ "subtopics": [
+ "reactivity-2-1-how-much-the-amount-of-chemical-change",
+ "reactivity-2-2-how-fast-the-rate-of-chemical-change",
+ "reactivity-2-3-how-far-the-extent-of-chemical-change",
+ "reactivity-3-1-proton-transfer-reactions",
+ "structure-2-2-the-covalent-model",
+ "structure-3-1-the-periodic-table-classification-of-elements"
+ ]
+ },
+ {
+ "question_id": "22M.2.HL.TZ2.7",
+ "Question": "
\n
The overall equation for the production of hydrogen cyanide, HCN, is shown below.
\n
CH4 (g) + NH3 (g) +O2 (g) → HCN (g) + 3H2O (g)
\n
\n
State why NH3 is a Lewis base.
\n
[1]
\n
a(i).
\n
\n
Calculate the pH of a 1.00 × 10−2 mol dm−3 aqueous solution of ammonia.
\n
pKb = 4.75 at 298 K.
\n
[3]
\n
a(ii).
\n
\n
Justify whether a 1.0 dm3 solution made from 0.10 mol NH3 and 0.20 mol HCl will form a buffer solution.
\n
[1]
\n
a(iii).
\n
\n
Sketch the shape of one sigma () and one pi () bond.
\n

\n
[2]
\n
b(i).
\n
\n
Identify the number of sigma and pi bonds in HCN.
\n

\n
[1]
\n
b(ii).
\n
\n
State the hybridization of the carbon atom in HCN.
\n
[1]
\n
b(iii).
\n
\n
Suggest why hydrogen chloride, HCl, has a lower boiling point than hydrogen cyanide, HCN.
\n

\n
[1]
\n
c.
\n
\n
Explain why transition metal cyanide complexes are coloured.
\n
[3]
\n
d.
\n
",
+ "Markscheme": "
\n
donates «lone/non-bonding» pair of electrons ✔
\n
a(i).
\n
\n
Kb = 10-4.75 /1.78 x 10-5
OR
Kb = ✔
\n
\n
[OH–] = « =» 4.22 × 10–4 «(mol dm–3)» ✔
\n
\n
pOH« = –log10 (4.22 × 10–4)» = 3.37
AND
pH = «14 – 3.37» = 10.6
OR
[H+]« =» = 2.37 × 10–11
AND
pH« = –log10 2.37 × 10–11» = 10.6 ✔
\n
\n
Award [3] for correct final answer.
\n
a(ii).
\n
\n
no AND is not a weak acid conjugate base system
\n
OR
\n
no AND weak base «totally» neutralized/ weak base is not in excess
\n
OR
\n
no AND will not neutralize small amount of acid ✔
\n
\n
Accept “no AND contains 0.10 mol NH4Cl + 0.10 mol HCl”.
\n
a(iii).
\n
\n
Sigma ():
\n

\n
\n
Pi ():
\n

\n
\n
Accept overlapping p-orbital(s) with both lobes of equal size/shape.
\n
Shaded areas are not required in either diagram.
\n
b(i).
\n
\n
Sigma (): 2 AND Pi (): 2 ✔
\n
b(ii).
\n
\n
HCN has stronger dipole–dipole attraction ✔
\n
\n
Do not accept reference to H-bonds.
\n
c.
\n
\n
Any three from:
\n
partially filled d-orbitals ✔
\n
«CN- causes» d-orbitals «to» split ✔
\n
light is absorbed as electrons transit to a higher energy level «in d–d transitions»
OR
light is absorbed as electrons are promoted ✔
\n
energy gap corresponds to light in the visible region of the spectrum ✔
\n
\n
Do not accept “colour observed is the complementary colour” for M4.
\n
d.
\n
",
+ "Examiners report": "
\n
The main error was the omission of lone electron \"pair\", though there was also a worrying amount of very confused answers for a very basic chemistry concept where 40% provided very incorrect answers.
\n
a(i).
\n
\n
Rather surprisingly, many students got full marks for this multi-step calculation; others went straight to the pH/pKa acid/base equation so lost at least one of the marks: students often seem less prepared for base calculations, as opposed to acid calculations.
\n
a(ii).
\n
\n
Poorly answered revealing little understanding of buffering mechanisms, which is admittedly a difficult topic.
\n
a(iii).
\n
\n
This proved to be the most challenging question (10%). It was a good question, where candidates had to explain a huge difference in boiling point of two covalent compounds, requiring solid understanding of change of state where breaking bonds cannot be involved). Yet most considered the triple bonds in HCN as the cause, suggesting covalent bonds break when substance boil, which is very worrying. Others considered H-bonds which at least is an intermolecular force, but shows they are not too familiar with the conditions necessary for H-bonding.
\n
c.
\n
\n
This question appears frequently in exams but with slightly different approaches. In general candidates ignore the specific question and give the same answers, failing in this case to describe why complexes are coloured rather than what colour is seen. These answers appear to reveal that many candidates don't really understand this phenomenon, but learn the answer by heart and make mistakes when repeating it, for example, stating that the ‘d-orbitals of the ligands were split’- an obvious misconception. The average mark was 1.6/3, with a MS providing 4 ideas that would merit a mark
\n
d.
\n
",
+ "topics": [
+ "reactivity-3-what-are-the-mechanisms-of-chemical-change",
+ "structure-2-models-of-bonding-and-structure",
+ "structure-3-classification-of-matter"
+ ],
+ "subtopics": [
+ "reactivity-3-1-proton-transfer-reactions",
+ "reactivity-3-4-electron-pair-sharing-reactions",
+ "structure-2-2-the-covalent-model",
+ "structure-3-1-the-periodic-table-classification-of-elements"
+ ]
+ },
+ {
+ "question_id": "22M.2.HL.TZ2.8",
+ "Question": "
\n
Carbon forms many compounds.
\n
\n
C60 and diamond are allotropes of carbon.
\n
\n
Chlorine reacts with methane.
\n
CH4 (g) + Cl2 (g) → CH3Cl (g) + HCl (g)
\n
\n
Outline two differences between the bonding of carbon atoms in C60 and diamond.
\n
[2]
\n
a(i).
\n
\n
Explain why C60 and diamond sublime at different temperatures and pressures.
\n
[2]
\n
a(ii).
\n
\n
State two features showing that propane and butane are members of the same homologous series.
\n
[2]
\n
b.
\n
\n
Describe a test and the expected result to indicate the presence of carbon–carbon double bonds.
\n

\n
[2]
\n
c.
\n
\n
Draw the full structural formula of (Z)-but-2-ene.
\n
[1]
\n
d(i).
\n
\n
Write the equation for the reaction between but-2-ene and hydrogen bromide.
\n
[1]
\n
d(ii).
\n
\n
State the type of reaction.
\n
[1]
\n
d(iii).
\n
\n
Suggest two differences in the 1H NMR of but-2-ene and the organic product from (d)(ii).
\n
[2]
\n
d(iv).
\n
\n
Predict, giving a reason, the major product of reaction between but-1-ene and steam.
\n
[2]
\n
d(v).
\n
\n
Explain the mechanism of the reaction between 1-bromopropane, CH3CH2CH2Br, and aqueous sodium hydroxide, NaOH (aq), using curly arrows to represent the movement of electron pairs.
\n
[4]
\n
e(i).
\n
\n
Deduce the splitting pattern in the 1H NMR spectrum for 1-bromopropane.
\n
[1]
\n
e(ii).
\n
\n
Calculate the enthalpy change of the reaction, ΔH, using section 11 of the data booklet.
\n
[3]
\n
f(i).
\n
\n
Draw and label an enthalpy level diagram for this reaction.
\n

\n
[2]
\n
f(ii).
\n
",
+ "Markscheme": "
\n
Any two of:
\n
C60 fullerene: bonded to 3 C AND diamond: bonded to 4 C ✔
\n
C60 fullerene: delocalized/resonance AND diamond: not delocalized / no resonance ✔
\n
C60 fullerene: sp2 AND diamond: sp3 ✔
\n
C60 fullerene: bond angles between 109–120° AND diamond: 109° ✔
\n
\n
Accept \"bonds in fullerene are shorter/stronger/have higher bond order OR bonds in diamond longer/weaker/have lower bond order\".
\n
a(i).
\n
\n
diamond giant/network covalent AND sublimes at higher temperature ✔
\n
C60 molecular/London/dispersion/intermolecular «forces» ✔
\n
\n
Accept “diamond has strong covalent bonds AND require more energy to break «than intermolecular forces»” for M1.
\n
a(ii).
\n
\n
same general formula / CnH2n+2 ✔
\n
differ by CH2/common structural unit ✔
\n
\n
Accept \"similar chemical properties\".
\n
Accept “gradation/gradual change in physical properties”.
\n
b.
\n
\n
ALTERNATIVE 1:
\n
Test:
\n
add bromine «water»/Br2 (aq) ✔
\n
Result:
\n
«orange/brown/yellow» to colourless/decolourised ✔
\n
Do not accept “clear” for M2.
\n
ALTERNATIVE 2:
\n
Test:
\n
add «acidified» KMnO4 ✔
\n
Result:
\n
«purple» to colourless/decolourised/brown ✔
\n
Accept “colour change” for M2.
\n
ALTERNATIVE 3:
\n
Test:
\n
add iodine / ✔
\n
Result:
\n
«brown» to colourless/decolourised ✔
\n
c.
\n
\n

\n
\n
Accept
\n

\n
d(i).
\n
\n
CH3CH=CHCH3 + HBr (g) → CH3CH2CHBrCH3
\n
Correct reactants ✔
\n
Correct products ✔
\n
\n
Accept molecular formulas for both reactants and product
\n
d(ii).
\n
\n
«electrophilic» addition/EA ✔
\n
\n
Do not accept nucleophilic or free radical addition.
\n
d(iii).
\n
\n
ALTERNATIVE 1: Any two of:
\n
but-2-ene: 2 signals AND product: 4 signals ✔
\n
but-2-ene: «area ratio» 3:1/6:2 AND product: «area ratio» 3:3:2:1 ✔
\n
product: «has signal at» 3.5-4.4 ppm «and but-2-ene: does not» ✔
\n
but-2-ene: «has signal at» 4.5-6.0 ppm «and product: does not» ✔
\n
\n
ALTERNATIVE 2:
\n
but-2-ene: doublet AND quartet/multiplet/4 ✔
\n
product: doublet AND triplet AND quintet/5/multiplet AND sextet/6/multiplet ✔
\n
\n
Accept “product «has signal at» 1.3–1.4 ppm «and but-2-ene: does not»”.
\n
d(iv).
\n
\n
CH3CH2CH(OH)CH3 ✔
\n
«secondary» carbocation/CH3CH2CH+CH3 more stable ✔
\n
\n
Do not accept “Markovnikov’s rule” without reference to carbocation stability.
\n
d(v).
\n
\n

\n
curly arrow going from lone pair/negative charge on O in HO– to C ✔
\n
curly arrow showing Br breaking ✔
\n
representation of transition state showing negative charge, square brackets and partial bonds ✔
\n
formation of organic product CH3CH2CH2OH AND Br– ✔
\n
\n
Do not allow curly arrow originating on H in HO–.
\n
Accept curly arrow either going from bond between C and Br to Br in 1-bromopropane or in the transition
state.
\n
Do not penalize if HO and Br are not at 180° to each other.
\n
Award [3 max] for SN1 mechanism.
\n
e(i).
\n
\n
triplet/3 AND multiplet/6 AND triplet/3 ✔
\n
e(ii).
\n
\n
bond breaking: C–H + Cl–Cl / 414 «kJ mol–1» + 242 «kJ mol–1»/656 «kJ»
OR
bond breaking: 4C–H + Cl–Cl / 4 × 414 «kJ mol–1» + 242 «kJ mol–1» / 1898 «kJ» ✔
\n
\n
bond forming: «C–Cl + H–Cl / 324 kJ mol–1 + 431 kJ mol–1» / 755 «kJ»
OR
bond forming: «3C–H + C–Cl + H–Cl / 3 × 414 «kJ mol–1» + 324 «kJ mol–1» + 431 kJ mol–1» / 1997 «kJ» ✔
\n
\n
«ΔH = bond breaking – bond forming = 656 kJ – 755 kJ» = –99 «kJ» ✔
\n
\n
Award [3] for correct final answer.
\n
Award [2 max] for 99 «kJ».
\n
f(i).
\n
\n

\n
reactants at higher enthalpy than products ✔
\n
ΔH/-99 «kJ» labelled on arrow from reactants to products
OR
activation energy/Ea labelled on arrow from reactant to top of energy profile ✔
\n
\n
Accept a double headed arrow between reactants and products labelled as ΔH for M2.
\n
f(ii).
\n
",
+ "Examiners report": "
\n
A challenging question, requiring accurate knowledge of the bonding in these allotropes (some referred to graphite, clearly the most familiar allotrope). The most frequent (correct) answer was the difference in number of bonded C atoms and hybridisation in second place. However, only 30% got a mark.
\n
a(i).
\n
\n
Again, this was a struggle between intermolecular forces and covalent bonds and this proved to be even harder than (a)(i) with only 25% of candidates getting full marks. The distinction between giant covalent/covalent network in diamond and molecular in C60 and hence resultant sublimation points, was rarely explained. There were many general and vague answers given, as well as commonly (incorrectly) stating that intermolecular forces are present in diamond. As another example of insufficient attention to the question itself, many candidates failed to say which would sublime at a higher temperature and so missed even one mark.
\n
a(ii).
\n
\n
This easy question was quite well answered; same/similar physical properties and empirical formula were common errors.
\n
Candidates misinterpreted the question and mentioned CH3+, i.e., the lost fragment; the other very common error was -COOH which shows a complete lack of understanding of MS considering the question is about butane so O should never appear.
\n
b.
\n
\n
Well answered by most, but some basic chemistry was missing when reporting results, perhaps as a result of little practical work due to COVID. A significant number suggested IR spectrometry, very likely because the question followed one on H NMR spectroscopy, thus revealing a failure to read the question properly (which asks for a test). Some teachers felt that adding \"chemical\" would have avoided some confusion.
\n
c.
\n
\n
Most were able to draw this isomer correctly, though a noticeable number of students included the Z as an atom in the structural formula, showing they were completely unfamiliar with E/Z notation.
\n
d(i).
\n
\n
Well done in general and most candidates wrote correct reagents, eventually losing a mark when considering H2 to be a product alongside 2-bromobutane.
\n
d(ii).
\n
\n
Very well answered, some mentioned halogenation which is a different reaction.
\n
d(iii).
\n
\n
A considerable number of students (40%) got at least 1 mark here, but marks were low (average mark 0.9/2). Common errors were predicting 3 peaks, rather than 4 for 2 -bromobutane and vague / unspecific answers, such as ‘different shifts’ or ‘different intensities’. It is surprising that more did not use H NMR data from the booklet; they were not directed to the section as is generally done in this type of question to allow for more general answers regarding all information that can be obtained from an H NMR spectrum.
\n
d(iv).
\n
\n
Product was correctly predicted by many, but most used Markovnikov's Rule to justify this, failing to mention the stability of the secondary carbocation, i.e., the chemistry behind the rule.
\n
d(v).
\n
\n
As usual, good to excellent candidates (47.5%) were able to get 3/4 marks for this mechanism, while most lost marks for carelessness in drawing arrows and bond connectivity, issues with the lone pair or negative charge on the nucleophile, no negative charge on transition state, or incorrect haloalkane. The average mark was thus 1.9/4.
\n
e(i).
\n
\n
Another of the very poorly answered questions where most candidates (90%) failed to predict 3 peaks and when they did, considered there would be a quartet instead of multiplet/sextet; other candidates seemed to have no idea at all. This is strange because the compound is relatively simple and while some teachers considered that predicting a sextet may be beyond the current curriculum or just too difficult, they could refer to a multiplet; a quartet is clearly incorrect.
\n
e(ii).
\n
\n
Only the very weak candidates were unable to calculate the enthalpy change correctly, eventually missing 1 mark for inverted calculations.
\n
f(i).
\n
\n
Most candidates drew correct energy profiles, consistent with the sign of the energy change calculated in the previous question. And again, only very weak candidate failed to get at least 1 mark for correct profiles.
\n
f(ii).
\n
",
+ "topics": [
+ "reactivity-1-what-drives-chemical-reactions",
+ "reactivity-2-how-much-how-fast-and-how-far",
+ "reactivity-3-what-are-the-mechanisms-of-chemical-change",
+ "structure-1-models-of-the-particulate-nature-of-matter",
+ "structure-2-models-of-bonding-and-structure",
+ "structure-3-classification-of-matter",
+ "tools"
+ ],
+ "subtopics": [
+ "reactivity-1-2-energy-cycles-in-reactions",
+ "reactivity-2-2-how-fast-the-rate-of-chemical-change",
+ "reactivity-3-4-electron-pair-sharing-reactions",
+ "structure-1-1-introduction-to-the-particulate-nature-of-matter",
+ "structure-2-2-the-covalent-model",
+ "structure-3-2-functional-groups-classification-of-organic-compounds",
+ "tool-1-experimental-techniques"
+ ]
+ },
+ {
+ "question_id": "22M.2.SL.TZ1.1",
+ "Question": "
\n
When heated in air, magnesium ribbon reacts with oxygen to form magnesium oxide.
\n
\n
The reaction in (a)(i) was carried out in a crucible with a lid and the following data was recorded:
\n
Mass of crucible and lid = 47.372 ±0.001 g
\n
Mass of crucible, lid and magnesium ribbon before heating = 53.726 ±0.001 g
\n
Mass of crucible, lid and product after heating = 56.941 ±0.001 g
\n
\n
\n
When magnesium is burnt in air, some of it reacts with nitrogen to form magnesium nitride according to the equation:
\n
3 Mg (s) + N2 (g) → Mg3N2 (s)
\n
\n
The presence of magnesium nitride can be demonstrated by adding water to the product. It is hydrolysed to form magnesium hydroxide and ammonia.
\n
\n
Most nitride ions are 14N3–.
\n
\n
Write a balanced equation for the reaction that occurs.
\n
[1]
\n
a(i).
\n
\n
State the block of the periodic table in which magnesium is located.
\n
[1]
\n
a(ii).
\n
\n
Identify a metal, in the same period as magnesium, that does not form a basic oxide.
\n
[1]
\n
a(iii).
\n
\n
Calculate the amount of magnesium, in mol, that was used.
\n
[1]
\n
b(i).
\n
\n
Determine the percentage uncertainty of the mass of product after heating.
\n
[2]
\n
b(ii).
\n
\n
Assume the reaction in (a)(i) is the only one occurring and it goes to completion, but some product has been lost from the crucible. Deduce the percentage yield of magnesium oxide in the crucible.
\n
\n
[2]
\n
b(iii).
\n
\n
Evaluate whether this, rather than the loss of product, could explain the yield found in (b)(iii).
\n
[1]
\n
c(i).
\n
\n
Suggest an explanation, other than product being lost from the crucible or reacting with nitrogen, that could explain the yield found in (b)(iii).
\n
[1]
\n
c(ii).
\n
\n
Calculate coefficients that balance the equation for the following reaction.
\n
__ Mg3N2 (s) + __ H2O (l) → __ Mg(OH)2 (s) + __ NH3 (aq)
\n
[1]
\n
d(i).
\n
\n
Determine the oxidation state of nitrogen in Mg3N2 and in NH3.
\n

\n
[1]
\n
d(ii).
\n
\n
Deduce, giving reasons, whether the reaction of magnesium nitride with water is an acid–base reaction, a redox reaction, neither or both.
\n

\n
[2]
\n
d(iii).
\n
\n
State the number of subatomic particles in this ion.
\n

\n
[1]
\n
e(i).
\n
\n
Some nitride ions are 15N3–. State the term that describes the relationship between 14N3– and 15N3–.
\n
[1]
\n
e(ii).
\n
\n
The nitride ion and the magnesium ion are isoelectronic (they have the same electron configuration). Determine, giving a reason, which has the greater ionic radius.
\n
[1]
\n
e(iii).
\n
\n
Suggest two reasons why atoms are no longer regarded as the indivisible units of matter.
\n
[2]
\n
f.
\n
\n
State the types of bonding in magnesium, oxygen and magnesium oxide, and how the valence electrons produce these types of bonding.
\n

\n
[4]
\n
g.
\n
",
+ "Markscheme": "
\n
2 Mg(s) + O2(g) → 2 MgO(s) ✔
\n
Do not accept equilibrium arrows. Ignore state symbols
\n
a(i).
\n
\n
s ✔
\n
Do not allow group 2
\n
a(ii).
\n
\n
aluminium/Al ✔
\n
a(iii).
\n
\n
«mol» ✔
\n
b(i).
\n
\n
mass of product ✔
\n
✔
\n
\n
Award [2] for correct final answer
\n
Accept 0.021%
\n
b(ii).
\n
\n
✔
\n
✔
\n
\n
Award «0.2614 mol x 40.31 g mol–1»
\n
Accept alternative methods to arrive at the correct answer.
\n
Accept final answers in the range 91-92%
\n
[2] for correct final answer.
\n
b(iii).
\n
\n
yes
AND
«each Mg combines with N, so» mass increase would be 14x which is less than expected increase of 16x
OR
3 mol Mg would form 101g of Mg3N2 but would form 3 x MgO = 121 g of MgO
OR
0.2614 mol forms 10.536 g of MgO, but would form 8.796 g of Mg3N2 ✔
\n
\n
Accept Yes AND “the mass of N/N2 that combines with each g/mole of Mg is lower than that of O/O2”
\n
Accept YES AND “molar mass of nitrogen less than of oxygen”.
\n
c(i).
\n
\n
incomplete reaction
OR
Mg was partially oxidised already
OR
impurity present that evaporated/did not react ✔
\n
\n
Accept “crucible weighed before fully cooled”.
\n
Accept answers relating to a higher atomic mass impurity consuming less O/O2.
\n
Accept “non-stoichiometric compounds formed”.
\n
Do not accept \"human error\", \"wrongly calibrated balance\" or other non-chemical reasons.
\n
If answer to (b)(iii) is >100%, accept appropriate reasons, such as product absorbed moisture before being weighed.
\n
c(ii).
\n
\n
«1» Mg3N2 (s) + 6 H2O (l) → 3 Mg(OH)2 (s) + 2 NH3 (aq)
\n
d(i).
\n
\n
Mg3N2: -3
AND
NH3: -3 ✔
\n
Do not accept 3 or 3-
\n
d(ii).
\n
\n
Acid–base:
yes AND N3- accepts H+/donates electron pair«s»
OR
yes AND H2O loses H+ «to form OH-»/accepts electron pair«s» ✔
\n
Redox:
no AND no oxidation states change ✔
\n
\n
Accept “yes AND proton transfer takes place”
\n
Accept reference to the oxidation state of specific elements not changing.
\n
Accept “not redox as no electrons gained/lost”.
\n
Award [1 max] for Acid–base: yes AND Redox: no without correct reasons, if no other mark has been awarded
\n
d(iii).
\n
\n
Protons: 7 AND Neutrons: 7 AND Electrons: 10 ✔
\n
e(i).
\n
\n
nitride AND smaller nuclear charge/number of protons/atomic number ✔
\n
e(iii).
\n
\n
Any two of:
subatomic particles «discovered»
OR
particles smaller/with masses less than atoms «discovered»
OR
«existence of» isotopes «same number of protons, different number of neutrons» ✔
\n
charged particles obtained from «neutral» atoms
OR
atoms can gain or lose electrons «and become charged» ✔
\n
atom «discovered» to have structure ✔
\n
fission
OR
atoms can be split ✔
\n
\n
Accept atoms can undergo fusion «to produce heavier atoms»
\n
Accept specific examples of particles.
\n
Award [2] for “atom shown to have a nucleus with electrons around it” as both M1 and M3.
\n
f.
\n
\n

\n
Award [1] for all bonding types correct.
\n
Award [1] for each correct description.
\n
Apply ECF for M2 only once.
\n
g.
\n
",
+ "Examiners report": "
\n
This was not as well done as one might have expected with the most common errors being O instead of O2 oxygen and MgO rather than MgO2.
\n
a(i).
\n
\n
Many students did not know what \"block\" meant, and often guessed group 2 etc.
\n
a(ii).
\n
\n
Many students confused \"period\" and \"group\" and also many did not read metal, so aluminium was not chosen by the majority.
\n
a(iii).
\n
\n
A number of students were not able to interpret the results and hence find the gain in mass and calculate the moles correctly.
\n
b(i).
\n
\n
Only a handful could work out the correct answer. Most had no real idea and quite a lot of blank responses. There also seems to be significant confusion between \"percent uncertainty\" and \"percent error\".
\n
b(ii).
\n
\n
This was not well answered, but definitely better than the previous question with quite a few gaining some credit for correctly determining the theoretical yield.
\n
b(iii).
\n
\n
This proved to be a very difficult question to answer in the quantitative manner required, with hardly any correct responses.
\n
c(i).
\n
\n
Quite a few students realised that incomplete reaction would lead to this, but only 30% of students gave a correct answer rather than a non-specific guess, such as \"misread balance\" or \"impurities\".
\n
c(ii).
\n
\n
This was generally very well done with almost all candidates being able to determine the correct coefficients.
\n
d(i).
\n
\n
About 40% of students managed to correctly determine both the oxidation states, as -3, with errors being about equally divided between the two compounds.
\n
d(ii).
\n
\n
Probably only about 10% could explain why this was an acid-base reaction. Rather more made valid deductions about redox, based on their answer to the previous question.
\n
d(iii).
\n
\n
Most candidates could answer the question about subatomic particles correctly.
\n
e(i).
\n
\n
Identification of isotopes was answered correctly by most students.
\n
e(ii).
\n
\n
In spite of being given the meaning of \"isoelectronic\", many candidates talked about the differing number of electrons and only about 30% could correctly analyse the situation in terms of nuclear charge.
\n
e(iii).
\n
\n
The question was marked quite leniently so that the majority of candidates gained at least one of the marks by mentioning a subatomic particle. A significant number read \"indivisible\" as \"invisible\" however.
\n
f.
\n
\n
About a quarter of the students gained full marks and probably a similar number gained no marks. Metallic bonding was the type that seemed least easily recognised and least easily described. Another common error was to explain ionic bonding in terms of attraction of ions rather than describing electron transfer.
\n
g.
\n
",
+ "topics": [
+ "empty-topic",
+ "reactivity-2-how-much-how-fast-and-how-far",
+ "reactivity-3-what-are-the-mechanisms-of-chemical-change",
+ "structure-1-models-of-the-particulate-nature-of-matter",
+ "structure-2-models-of-bonding-and-structure",
+ "structure-3-classification-of-matter",
+ "tools"
+ ],
+ "subtopics": [
+ "reactivity-2-1-how-much-the-amount-of-chemical-change",
+ "reactivity-3-1-proton-transfer-reactions",
+ "reactivity-3-2-electron-transfer-reactions",
+ "structure-1-2-the-nuclear-atom",
+ "structure-1-3-electron-configurations",
+ "structure-2-1-the-ionic-model",
+ "structure-2-2-the-covalent-model",
+ "structure-2-3-the-metallic-model",
+ "structure-3-1-the-periodic-table-classification-of-elements",
+ "tool-1-experimental-techniques",
+ "tool-3-mathematics"
+ ]
+ },
+ {
+ "question_id": "22M.2.SL.TZ1.3",
+ "Question": "
\n
Magnesium is a reactive metal often found in alloys.
\n
\n
Organomagnesium compounds can react with carbonyl compounds. One overall equation is:
\n

\n
\n
Compound B can also be prepared by reacting an alkene with water.
\n
\n
Iodomethane is used to prepare CH3Mg. It can also be converted into methanol:
\n
CH3 + HO– → CH3OH + –
\n
\n
Magnesium can be produced by the electrolysis of molten magnesium chloride.
\n
Write the half-equation for the formation of magnesium.
\n
[1]
\n
a.
\n
\n
Suggest an experiment that shows that magnesium is more reactive than zinc, giving the observation that would confirm this.
\n
[2]
\n
b.
\n
\n
State the name of Compound A, applying International Union of Pure and Applied Chemistry (IUPAC) rules.
\n
[1]
\n
c(i).
\n
\n
Identify the strongest force between the molecules of Compound B.
\n
[1]
\n
c(ii).
\n
\n
Draw the structural formula of the alkene required.
\n

\n
[1]
\n
d(i).
\n
\n
Deduce the structural formula of the repeating unit of the polymer formed from this alkene.
\n
[1]
\n
d(ii).
\n
\n
Deduce what would be observed when Compound B is warmed with acidified aqueous potassium dichromate (VI).
\n
[1]
\n
e.
\n
\n
Identify the type of reaction.
\n
[1]
\n
f(i).
\n
\n
Outline the requirements for a collision between reactants to yield products.
\n
[2]
\n
f(ii).
\n
\n
The polarity of the carbon–halogen bond, C–X, facilitates attack by HO–.
\n
Outline, giving a reason, how the bond polarity changes going down group 17.
\n
[1]
\n
f(iii).
\n
",
+ "Markscheme": "
\n
Mg2+ + 2 e- → Mg ✔
\n
\n
Do not penalize missing charge on electron.
\n
Accept equation with equilibrium arrows.
\n
a.
\n
\n
Alternative 1
\n
put Mg in Zn2+(aq) ✔
\n
Zn/«black» layer forms «on surface of Mg» ✔
\n
Award [1 max] for “no reaction when Zn placed in Mg2+(aq)”.
\n
\n
Alternative 2
\n
place both metals in acid ✔
\n
bubbles evolve more rapidly from Mg
OR
Mg dissolves faster ✔
\n
\n
Alternative 3
\n
construct a cell with Mg and Zn electrodes ✔
\n
bulb lights up
OR
shows (+) voltage
OR
size/mass of Mg(s) decreases «over time»
OR
size/mass of Zn increases «over time»
\n
Accept “electrons flow from Mg to Zn”.
\n
Accept Mg is negative electrode/anode
OR
Zn is positive electrode/cathode
\n
Accept other correct methods.
\n
b.
\n
\n
propanone ✔
\n
Accept 2-propanone and propan-2-one.
\n
c(i).
\n
\n
hydrogen bonds ✔
\n
c(ii).
\n
\n

\n
d(i).
\n
\n

\n
\n
Do not penalize missing brackets or n.
\n
Do not award mark if continuation bonds are not shown.
\n
d(ii).
\n
\n
no change «in colour/appearance/solution» ✔
\n
e.
\n
\n
«nucleophilic» substitution
OR
SN2 ✔
\n
Accept “hydrolysis”.
\n
Accept SN1
\n
f(i).
\n
\n
energy/E ≥ activation energy/Ea ✔
\n
correct orientation «of reacting particles»
OR
correct geometry «of reacting particles» ✔
\n
f(ii).
\n
\n
decreases/less polar AND electronegativity «of the halogen» decreases ✔
\n
\n
Accept “decreases” AND a correct comparison of the electronegativity of two halogens.
\n
Accept “decreases” AND “attraction for valence electrons decreases”.
\n
f(iii).
\n
",
+ "Examiners report": "
\n
Unfortunately, only 40% of the students could write this quite straightforward half equation.
\n
a.
\n
\n
Many candidates gained some credit by suggesting voltaic cell or a displacement reaction, but most could not gain the second mark and the reason was often a failure to be able to differentiate between \"what occurs\" and \"what is observed\".
\n
b.
\n
\n
Even though superfluous numbers (2-propanone, propan-2-one) were overlooked, only about half of the students could correctly name this simple molecule.
\n
c(i).
\n
\n
Probably just over half the students correctly identified hydrogen bonding, with dipole-dipole being the most common wrong answer, though a significant number identified an intramolecular bond.
\n
c(ii).
\n
\n
Few candidates could correctly eliminate water to deduce the identity of the required reactant.
\n
d(i).
\n
\n
Correct answers to this were very scarce and even when candidates had an incorrect alkene for the previous part, they were unable to score an ECF mark, by deducing the formula of the polymer it would produce.
\n
d(ii).
\n
\n
Some students deduced that, as it was a tertiary alcohol, there would be no reaction, but almost all were lucky that this was accepted as well as the correct observation - \"it would remain orange\".
\n
e.
\n
\n
About a quarter of the students identified this as a substitution reaction, though quite a number then lost the mark by incorrectly stating it was either \"free radical\" or \"electrophilic\". A very common wrong answer was \"displacement\" or \"single displacement\" and this makes one wonder whether this terminology is being taught instead of substitution
\n
f(i).
\n
\n
Generally well done with the vast majority of students correctly citing \"correct orientation\" and many only failed to gain the second mark through failing to equate the energy required to the activation energy.
\n
f(ii).
\n
\n
Another question that was not well answered with probably only a quarter of candidates stating that the polarity would decrease because of decreasing electronegativity down the group.
\n
f(iii).
\n
",
+ "topics": [
+ "reactivity-1-what-drives-chemical-reactions",
+ "reactivity-2-how-much-how-fast-and-how-far",
+ "reactivity-3-what-are-the-mechanisms-of-chemical-change",
+ "structure-2-models-of-bonding-and-structure",
+ "structure-3-classification-of-matter",
+ "tools"
+ ],
+ "subtopics": [
+ "reactivity-1-2-energy-cycles-in-reactions",
+ "reactivity-2-2-how-fast-the-rate-of-chemical-change",
+ "reactivity-2-3-how-far-the-extent-of-chemical-change",
+ "reactivity-3-2-electron-transfer-reactions",
+ "reactivity-3-4-electron-pair-sharing-reactions",
+ "structure-2-2-the-covalent-model",
+ "structure-2-4-from-models-to-materials",
+ "structure-3-1-the-periodic-table-classification-of-elements",
+ "structure-3-2-functional-groups-classification-of-organic-compounds",
+ "tool-1-experimental-techniques"
+ ]
+ },
+ {
+ "question_id": "22M.2.SL.TZ1.5",
+ "Question": "
\n
\n (a(i))\n
\n
\n
\n State the name of Compound B, applying International Union of Pure and Applied Chemistry (IUPAC) rules.\n
\n
\n
\n
\n
\n
\n (a(ii))\n
\n
\n
\n Compound A and Compound B are both liquids at room temperature and pressure. Identify the strongest intermolecular force between molecules of Compound A.\n
\n
\n
\n
\n
\n
\n (b(i))\n
\n
\n
\n Draw the structural formula of the alkene required.\n
\n
\n
\n
\n
\n
\n
\n
\n
\n (b(iii))\n
\n
\n
\n Deduce the structural formula of the repeating unit of the polymer formed from this alkene.\n
\n
\n
\n
\n
\n
\n (d(ii))\n
\n
\n
\n Outline the requirements for a collision between reactants to yield products.\n
\n
\n
\n
\n
\n
\n (d(iv))\n
\n
\n
\n The polarity of the carbon–halogen bond, C–X, facilitates attack by HO\n \n –\n \n .\n
\n
\n Outline, giving a reason, how the bond polarity changes going down group 17.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a(i))\n
\n
\n 2-methylpropan-2-ol /2-methyl-2-propanol ✔\n
\n
\n
\n
\n \n Accept methylpropan-2-ol/ methyl-2-propanol.\n \n
\n
\n \n Do\n \n not\n \n accept 2-methylpropanol.\n \n
\n
\n
\n (a(ii))\n
\n
\n dipole-dipole ✔\n
\n
\n
\n
\n \n Do not accept van der Waals’ forces.\n \n
\n
\n
\n (b(i))\n
\n
\n
\n
\n
\n
\n (b(iii))\n
\n
\n
\n
\n
\n \n Do\n \n not\n \n penalize missing brackets or n.\n \n
\n
\n \n Do\n \n not\n \n award mark if continuation bonds are not shown.\n \n
\n
\n
\n (d(ii))\n
\n
\n energy/E ≥ activation energy/E\n \n a\n \n ✔\n
\n
\n correct orientation «of reacting particles»\n
\n \n \n OR\n \n \n
\n correct geometry «of reacting particles» ✔\n
\n
\n
\n (d(iv))\n
\n
\n decreases/less polar\n \n \n AND\n \n \n electronegativity «of the halogen» decreases ✔\n
\n
\n
\n
\n \n Accept “decreases”\n \n AND\n \n a correct comparison of the electronegativity of two halogens.\n \n
\n
\n \n Accept “decreases”\n \n AND\n \n “attraction for valence electrons decreases”.\n \n
\n
\n",
+ "Examiners report": "
\n (a(i))\n
\n
\n Naming the organic compound using IUPAC rules was generally done well.\n
\n
\n
\n (b(i))\n
\n
\n Good performance; some had a H and CH\n \n 3\n \n group on each C atom across double bond instead of having two H atoms on one C and two CH\n \n 3\n \n groups on the other.\n
\n
\n
\n (b(iii))\n
\n
\n Mediocre performance; deducing structural formula of repeating unit of the polymer was challenging in which continuation bonds were sometimes missing, or structure included a double bond or one of the CH\n \n 3\n \n group was missing.\n
\n
\n
\n (d(ii))\n
\n
\n Good performance. For the requirements for a collision between reactants to yield products, some suggested necessary, sufficient or enough energy or even enough activation energy instead of energy/\n \n E ≥\n \n activation energy/\n \n E\n \n \n a\n \n .\n
\n
\n
\n (d(iv))\n
\n
\n Good performance on how the polarity of C-X bond changes going down group 17.\n
\n
\n",
+ "topics": [
+ "reactivity-2-how-much-how-fast-and-how-far",
+ "reactivity-3-what-are-the-mechanisms-of-chemical-change",
+ "structure-2-models-of-bonding-and-structure",
+ "structure-3-classification-of-matter"
+ ],
+ "subtopics": [
+ "reactivity-2-2-how-fast-the-rate-of-chemical-change",
+ "reactivity-3-4-electron-pair-sharing-reactions",
+ "structure-2-2-the-covalent-model",
+ "structure-2-4-from-models-to-materials",
+ "structure-3-1-the-periodic-table-classification-of-elements",
+ "structure-3-2-functional-groups-classification-of-organic-compounds"
+ ]
+ },
+ {
+ "question_id": "22M.2.SL.TZ1.6",
+ "Question": "
\n
\n (a(i))\n
\n
\n
\n Draw arrows in the boxes to represent the electron configuration of a nitrogen atom.\n
\n
\n
\n
\n
\n
\n
\n
\n
\n (a(iii))\n
\n
\n
\n Explain the relative lengths of the three bonds between N and O in nitric acid.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a(i))\n
\n
\n
\n
\n
\n \n
\n Accept\n \n all\n \n 2p electrons pointing downwards.\n \n
\n
\n \n Accept half arrows instead of full arrows.\n \n
\n
\n
\n (a(iii))\n
\n
\n \n Any three of:\n \n
\n
\n two N-O same length/order ✔\n
\n delocalization/resonance ✔\n
\n
\n N-OH longer «than N-O»\n
\n \n \n OR\n \n \n
\n N-OH bond order 1\n \n \n AND\n \n \n N-O bond order 1½ ✔\n
\n
\n
\n
\n \n Award\n \n [2 max]\n \n if bond strength, rather than bond length discussed.\n \n
\n
\n \n Accept N-O between single and double bond\n \n AND\n \n N-OH single bond.\n \n
\n
\n",
+ "Examiners report": "
\n (a(i))\n
\n
\n Drawing arrows in the boxes to represent the electron configuration of a nitrogen atom was done extremely well.\n
\n
\n
\n (a(iii))\n
\n
\n Poorly done; some explained relative bond strengths between N and O in HNO\n \n 3\n \n , not relative lengths; others included generic answers such as triple bond is shortest, double bond is longer, single longest.\n
\n
\n",
+ "topics": [
+ "reactivity-3-what-are-the-mechanisms-of-chemical-change",
+ "structure-1-models-of-the-particulate-nature-of-matter"
+ ],
+ "subtopics": [
+ "reactivity-3-4-electron-pair-sharing-reactions",
+ "structure-1-3-electron-configurations"
+ ]
+ },
+ {
+ "question_id": "22M.2.SL.TZ2.1",
+ "Question": "
\n
Lithium reacts with water to form an alkaline solution.
\n
\n
A 0.200 g piece of lithium was placed in 500.0 cm3 of water.
\n
\n
Determine the coefficients that balance the equation for the reaction of lithium with water.
\n

\n
[1]
\n
a.
\n
\n
Calculate the molar concentration of the resulting solution of lithium hydroxide.
\n
[2]
\n
b(i).
\n
\n
Calculate the volume of hydrogen gas produced, in cm3, if the temperature was 22.5 °C and the pressure was 103 kPa. Use sections 1 and 2 of the data booklet.
\n
[2]
\n
b(ii).
\n
\n
Suggest a reason why the volume of hydrogen gas collected was smaller than predicted.
\n
[1]
\n
b(iii).
\n
\n
The reaction of lithium with water is a redox reaction. Identify the oxidizing agent in the reaction giving a reason.
\n
[1]
\n
c.
\n
\n
Describe two observations that indicate the reaction of lithium with water is exothermic.
\n
[2]
\n
d.
\n
",
+ "Markscheme": "
\n
2 Li (s) + 2 H2O (l) → 2 LiOH (aq) + H2 (g) ✔
\n
a.
\n
\n
✔
\n
«nLiOH = nLi»
\n
✔
\n
\n
Award [2] for correct final answer.
\n
b(i).
\n
\n
\n
✔
\n
✔
\n
\n
Award [2] for correct final answer.
\n
Accept answers in the range 334 – 344 cm3.
\n
Award [1 max] for 0.343 «cm3/dm3/m3».
\n
Award [1 max] for 26.1 cm3 obtained by using 22.5 K.
\n
Award [1 max] for 687 cm3 obtained by using 0.0288 mol.
\n
b(ii).
\n
\n
lithium was impure/«partially» oxidized
\n
OR
\n
gas leaked/ignited ✔
\n
\n
Accept “gas dissolved”.
\n
b(iii).
\n
\n
H2O AND hydrogen gains electrons «to form H2»
\n
OR
\n
H2O AND H oxidation state changed from +1 to 0 ✔
\n
\n
Accept “H2O AND H/H2O is reduced”.
\n
c.
\n
\n
Any two:
\n
temperature of the water increases ✔
\n
lithium melts ✔
\n
pop sound is heard ✔
\n
\n
Accept “lithium/hydrogen catches fire”.
\n
Do not accept “smoke is observed”.
\n
d.
\n
",
+ "Examiners report": "
\n
This part-question was better answered than part (ii). 50% of the candidates drew a correct arrow between n=2 and n=3. Both absorption and emission transitions were accepted since the question did not specify which type of spectrum was required. Some teachers commented on this in their feedback. Mistakes often included transitions between higher energy levels.
\n
b(iii).
\n
",
+ "topics": [
+ "reactivity-3-what-are-the-mechanisms-of-chemical-change",
+ "structure-1-models-of-the-particulate-nature-of-matter",
+ "tools"
+ ],
+ "subtopics": [
+ "reactivity-3-2-electron-transfer-reactions",
+ "structure-1-4-counting-particles-by-mass-the-mole",
+ "tool-1-experimental-techniques"
+ ]
+ },
+ {
+ "question_id": "22M.2.SL.TZ2.2",
+ "Question": "
\n
Electrons are arranged in energy levels around the nucleus of an atom.
\n
\n
The diagram represents possible electron energy levels in a hydrogen atom.
\n

\n
\n
Explain why the first ionization energy of calcium is greater than that of potassium.
\n
[2]
\n
a.
\n
\n
All models have limitations. Suggest two limitations to this model of the electron energy levels.
\n
[2]
\n
b(i).
\n
\n
Draw an arrow, labelled X, to represent the electron transition for the ionization of a hydrogen atom in the ground state.
\n
[1]
\n
b(ii).
\n
\n
Draw an arrow, labelled Z, to represent the lowest energy electron transition in the visible spectrum.
\n
[1]
\n
b(iii).
\n
",
+ "Markscheme": "
\n
increasing number of protons/nuclear charge/Zeff ✔
\n
«atomic» radius/size decreases
OR
same number of energy levels
OR
similar shielding «by inner electrons» ✔
\n
a.
\n
\n
Any two of:
\n
does not represent sub-levels/orbitals ✔
\n
only applies to atoms with one electron/hydrogen ✔
\n
does not explain why only certain energy levels are allowed ✔
\n
the atom is considered to be isolated ✔
\n
does not take into account the interactions between atoms/molecules/external fields ✔
\n
does not consider the number of electrons the energy level can fit ✔
\n
does not consider probability of finding electron at different positions/OWTTE ✔
\n
\n
Do not accept “does not represent distance «from nucleus»”.
\n
b(i).
\n
\n

\n
upward arrow X AND starting at n = 1 extending to n = ∞ ✔
\n
b(ii).
\n
\n

\n
downward or upward arrow between n = 3 and n = 2 ✔
\n
b(iii).
\n
",
+ "Examiners report": "
\n
It was surprising that this question that appears regularly in IB chemistry papers was not better answered. Many candidates only obtained one of the two marks for identifying one factor (often the larger nuclear charge of calcium or that the number of shells was the same for Ca and K). However, a few candidates did write thorough answers reflecting a good understanding of the factors affecting ionization energy. This question had a strong correlation between candidates who scored well and those who had a high score overall. Some candidates did not score any marks by focusing on trends in the Periodic Table without offering an explanation, or by discussing the number of electrons in Ca and K instead of the number of protons.
\n
a.
\n
\n
Only 30% of the candidates drew the correct arrow on the diagram representing the ionization of hydrogen. A few candidates missed the mark by having the arrow pointing downwards. The most common incorrect answer was a transition between n=1 and n=2.
\n
b(ii).
\n
",
+ "topics": [
+ "empty-topic",
+ "structure-1-models-of-the-particulate-nature-of-matter",
+ "structure-3-classification-of-matter"
+ ],
+ "subtopics": [
+ "structure-1-3-electron-configurations",
+ "structure-3-1-the-periodic-table-classification-of-elements"
+ ]
+ },
+ {
+ "question_id": "22M.2.SL.TZ2.3",
+ "Question": "
\n
Sulfur trioxide is produced from sulfur dioxide.
\n
2SO2 (g) + O2 (g) 2SO3 (g) ΔH = −196 kJ mol−1
\n
\n
The reaction between sulfur dioxide and oxygen can be carried out at different temperatures.
\n
\n
Nitric acid, HNO3, is another strong Brønsted–Lowry acid. Its conjugate base is the nitrate ion, NO3−
\n
\n
Outline, giving a reason, the effect of a catalyst on a reaction.
\n
[2]
\n
a.
\n
\n
On the axes, sketch Maxwell–Boltzmann energy distribution curves for the reacting species at two temperatures T1 and T2, where T2 > T1.
\n

\n
[3]
\n
b(i).
\n
\n
Explain the effect of increasing temperature on the yield of SO3.
\n
[2]
\n
b(ii).
\n
\n
State the product formed from the reaction of SO3 with water.
\n
[1]
\n
c(i).
\n
\n
State the meaning of a strong Brønsted–Lowry acid.
\n
[2]
\n
c(ii).
\n
\n
Draw the Lewis structure of NO3−.
\n
[1]
\n
d(i).
\n
\n
Explain the electron domain geometry of NO3−.
\n
[2]
\n
d(ii).
\n
",
+ "Markscheme": "
\n
increases rate AND lower Ea ✔
\n
provides alternative pathway «with lower Ea»
OR
more/larger fraction of molecules have the «lower» Ea ✔
\n
\n
Accept description of how catalyst lowers Ea for M2 (e.g. “reactants adsorb on surface «of catalyst»”, “reactant bonds weaken «when adsorbed»”, “helps favorable orientation of molecules”).
\n
a.
\n
\n

\n
both axes correctly labelled ✔
\n
peak of T2 curve lower AND to the right of T1 curve ✔
\n
lines begin at origin AND correct shape of curves AND T2 must finish above T1 ✔
\n
\n
Accept “probability «density» / number of particles / N / fraction” on y-axis.
\n
Accept “kinetic E/KE/Ek” but not just “Energy/E” on x-axis.
\n
b(i).
\n
\n
decrease AND equilibrium shifts left / favours reverse reaction ✔
\n
«forward reaction is» exothermic / ΔH is negative ✔
\n
b(ii).
\n
\n
sulfuric acid/H2SO4 ✔
\n
\n
Accept “disulfuric acid/H2S2O7”.
\n
c(i).
\n
\n
fully ionizes/dissociates ✔
\n
proton/H+ «donor » ✔
\n
c(ii).
\n
\n

\n
\n
Do not accept the delocalised structure.
\n
Accept any combination of dots, crosses and lines.
\n
Coordinate/dative bond may be represented by an arrow.
\n
d(i).
\n
\n
three electron domains repel
\n
OR
\n
three electron domains as far away as possible ✔
\n
\n
trigonal planar
\n
OR
\n
«all» angles are 120° ✔
\n
d(ii).
\n
",
+ "Examiners report": "
\n
A generally well-answered question. Most candidates explained the effect of a catalyst on a reaction correctly. A small proportion of candidates thought the catalyst increased the frequency of collisions. Some candidates focussed on the effect of the catalyst on an equilibrium since the equation above the question was that of a reversible reaction. These candidates usually still managed to gain at least the first marking point by stating that both forward and reverse reaction rates were increased due to the lower activation energy. Most candidates mentioned the alternative pathway for the second mark, and some gave a good discussion about the increase in the number of molecules or collisions with E≥Ea. A few candidates lost one of the marks for not explicitly stating the effect of a catalyst (that it increases the rate of the reaction).
\n
a.
\n
\n
The average mark scored for the Maxwell-Boltzmann distribution curves sketch was 1.5 out of 3 marks and the question had a strong correlation with the candidates who did well overall. The majority of candidates were familiar with the shapes of the curves. The most commonly lost mark was missing or incorrect labels on the axes. Sometimes candidates added the labels but did not specify “kinetic” energy for the x-axis. As for the curves, some candidates reversed the labels T1 and T2, some made the two curves meet at high energy or even cross, and some did not have the correct relationship between the peaks of T1 and T2.
\n
b(i).
\n
\n
Another question that showed a strong correlation with the candidates who did well overall. The average mark was 1 out of 2 marks. Many candidates explained the effect of an increase in temperature on the yield of SO3 correctly and thoroughly. One of the common mistakes was to miss the fact that it was an equilibrium and reason that yield would not change due to an increase in the rate of reaction. Unfortunately, a number of candidates also deduced that yield would increase due to the increase in rate. Other candidates recognized that it was an exothermic reaction but deduced the equilibrium would shift to the right giving a higher yield of SO3.
\n
b(ii).
\n
\n
A very well answered question. 70% of the candidates stated H2SO4 as the product from the reaction of SO3 with water.
\n
c(i).
\n
\n
While a straightforward question, many candidates only answered part of the question - either focussing on the “strong” or on the “Brønsted-Lowry acid”. The average mark on this question was 1.2 out of 2 marks.
\n
c(ii).
\n
\n
Only 20% of the candidates scored the mark for the Lewis structure of NO3-. Mistakes included: missing charge, missing lone pairs, 3 single bonds, 2 double bonds.
\n
d(i).
\n
\n
The majority of candidates deduced the correct electron domain geometry scoring the first mark including cases of ECF. Only a small number of candidates satisfied the requirements of the markscheme for the explanation.
\n
d(ii).
\n
",
+ "topics": [
+ "reactivity-2-how-much-how-fast-and-how-far",
+ "reactivity-3-what-are-the-mechanisms-of-chemical-change",
+ "structure-2-models-of-bonding-and-structure",
+ "structure-3-classification-of-matter"
+ ],
+ "subtopics": [
+ "reactivity-2-1-how-much-the-amount-of-chemical-change",
+ "reactivity-2-2-how-fast-the-rate-of-chemical-change",
+ "reactivity-2-3-how-far-the-extent-of-chemical-change",
+ "reactivity-3-1-proton-transfer-reactions",
+ "structure-2-2-the-covalent-model",
+ "structure-3-1-the-periodic-table-classification-of-elements"
+ ]
+ },
+ {
+ "question_id": "22M.2.SL.TZ2.4",
+ "Question": "
\n
Carbon forms many compounds.
\n
\n
C60 and diamond are allotropes of carbon.
\n
\n
But-2-ene reacts with hydrogen bromide.
\n
\n
Chlorine reacts with methane.
\n
CH4 (g) + Cl2 (g) → CH3Cl (g) + HCl (g)
\n
\n
Outline one difference between the bonding of carbon atoms in C60 and diamond.
\n
[1]
\n
a(i).
\n
\n
State two features showing that propane and butane are members of the same homologous series.
\n
[2]
\n
b.
\n
\n
Describe a test and the expected result to indicate the presence of carbon–carbon double bonds.
\n

\n
[2]
\n
c.
\n
\n
Draw the full structural formula of but-2-ene.
\n
[1]
\n
d(i).
\n
\n
Write the equation for the reaction between but-2-ene and hydrogen bromide.
\n
[1]
\n
d(ii).
\n
\n
State the type of reaction.
\n
[1]
\n
d(iii).
\n
\n
Suggest two differences in the 1H NMR of but-2-ene and the organic product from (d)(ii).
\n
[2]
\n
d(iv).
\n
\n
Calculate the enthalpy change of the reaction, ΔH, using section 11 of the data booklet.
\n
[3]
\n
e(i).
\n
\n
Draw and label an enthalpy level diagram for this reaction.
\n

\n
[2]
\n
e(ii).
\n
",
+ "Markscheme": "
\n
C60 fullerene: «each carbon is» bonded to 3 C AND diamond: bonded to 4 C
OR
C60 fullerene: delocalized/resonance AND diamond: not delocalized/no resonance
OR
C60 fullerene: single and double bonds AND diamond: single bonds ✔
\n
\n
Accept “C60 fullerene: sp2 AND diamond: sp3”.
\n
Accept “C60 fullerene: trigonal planar geometry / bond angles between 109.5°/109°/108°–120° AND diamond: tetrahedral geometry / bond angle 109.5°/109°”.
\n
Accept \"bonds in fullerene are shorter/stronger/have higher bond order\".
\n
a(i).
\n
\n
same general formula / CnH2n+2 ✔
\n
differ by CH2/common structural unit ✔
\n
\n
Accept \"similar chemical properties\".
\n
Accept “gradation/gradual change in physical properties”.
\n
b.
\n
\n
ALTERNATIVE 1:
\n
Test:
\n
add bromine «water»/Br2 (aq) ✔
\n
Result:
\n
«orange/brown/yellow» to colourless/decolourised ✔
\n
\n
Do not accept “clear” for M2.
\n
\n
ALTERNATIVE 2:
\n
Test:
\n
add «acidified» KMnO4 ✔
\n
Result:
\n
«purple» to colourless/decolourised/brown ✔
\n
\n
Accept “colour change” for M2.
\n
\n
ALTERNATIVE 3:
\n
Test:
\n
add iodine / ✔
\n
Result:
\n
«brown» to colourless/decolourised ✔
\n
c.
\n
\n

\n
\n
Accept
\n

\n
d(i).
\n
\n
CH3CH=CHCH3 (g) + HBr (g) → CH3CH2CHBrCH3 (l)
\n
OR
\n
C4H8 (g) + HBr (g) → C4H9Br (l) ✔
\n
d(ii).
\n
\n
«electrophilic» addition/EA ✔
\n
Do not accept nucleophilic or free radical addition.
\n
d(iii).
\n
\n
ALTERNATIVE 1: Any two of:
\n
but-2-ene: 2 signals AND product: 4 signals ✔
\n
but-2-ene: «area ratio» 3:1/6:2 AND product: «area ratio» 3:3:2:1 ✔
\n
product: «has signal at» 3.5-4.4 ppm «and but-2-ene: does not» ✔
\n
but-2-ene: «has signal at» 4.5-6.0 ppm «and product: does not» ✔
\n
\n
ALTERNATIVE 2:
\n
but-2-ene: doublet AND quartet/multiplet/4 ✔
\n
product: doublet AND triplet AND quintet/5/multiplet AND sextet/6/multiplet ✔
\n
\n
Accept “product «has signal at» 1.3–1.4 ppm «and but-2-ene: does not»”.
\n
d(iv).
\n
\n
bond breaking: C–H + Cl–Cl / 414 «kJ mol–1» + 242 «kJ mol–1»/656 «kJ»
OR
bond breaking: 4C–H + Cl–Cl / 4 × 414 «kJ mol–1» + 242 «kJ mol–1» / 1898 «kJ» ✔
\n
bond forming: «C–Cl + H–Cl / 324 kJ mol–1 + 431 kJ mol–1» / 755 «kJ»
OR
bond forming: «3C–H + C–Cl + H–Cl / 3 × 414 «kJ mol–1» + 324 «kJ mol–1» + 431 kJ mol–1» / 1997 «kJ» ✔
\n
«ΔH = bond breaking – bond forming = 656 kJ – 755 kJ» = –99 «kJ» ✔
\n
Award [3] for correct final answer.
\n
Award [2 max] for 99 «kJ».
\n
e(i).
\n
\n

\n
reactants at higher enthalpy than products ✔
\n
ΔH/-99 «kJ» labelled on arrow from reactants to products
OR
activation energy/Ea labelled on arrow from reactant to top of energy profile ✔
\n
\n
Accept a double headed arrow between reactants and products labelled as ΔH for M2.
\n
e(ii).
\n
",
+ "Examiners report": "
\n
This was a challenging question that asked about the difference between the bonding of carbon atoms in C60 and diamond. 20% of the candidates gained the mark. The majority of the candidates did not have a specific enough answer for C60 and mentioned the pentagons and hexagons but not the number of bonds or the geometry or the bond order or the electron delocalisation. Diamond was better known to candidates as expected.
\n
a(i).
\n
\n
About two-thirds of the candidates scored one of the two marks and stronger candidates scored both. The most common answers were the same general formula/CnH2n+2, the difference between the compounds was CH2 and similar chemical properties. The same functional group was not accepted since alkanes do not have a functional group. Some candidates only stated that they are saturated hydrocarbons not gaining any marks.
\n
b.
\n
\n
About half of the candidates gave the bromine water test with the correct results. Iodine and KMnO4 were rarely seen in the scripts. There were candidates who used the term “clear” to mean “colourless” which was not accepted. Some candidates referred to the presence of UV light in a correct way and others in an incorrect way which was not penalized in this case. 10% of the candidates left the question blank. The most common incorrect answer was in terms of the IR absorptions. Other candidates referred to enthalpies of combustion and formation.
\n
c.
\n
\n
A well answered question. 70% of the candidates gave the correct structural formula for but-2-ene. Mistakes included too many hydrogens in the structure and an incorrect position of the C=C. Candidates should be reminded that the full structural formula requires all covalent bonds to be shown.
\n
d(i).
\n
\n
Half of the candidates wrote the correct equation for the reaction of but-2-ene with hydrogen bromide. Incorrect answers included hydrogen as a product. As expected, the question correlated well with highly achieving candidates.
\n
d(ii).
\n
\n
Well answered. 60% of candidates identified the type of reaction between but-2-ene and HBr, some of them including the term “electrophilic”. ECF was generously awarded when substitution was stated based on the equation where H2 was produced in part (ii). Candidates lost the mark if they only stated “hydrobromination” without mentioning addition. Some candidates lost the mark for stating “nucleophilic” or “free radical” addition.
\n
d(iii).
\n
\n
The comparison of the 1H NMR spectra of the two organic compounds was more challenging and 10% of the candidates left this question blank. The average mark was 0.7 out of 2 marks. Mistakes included non-specific answers that just stated “more signals” or “higher chemical shift”, and stating 3 signals in 2-bromobutane instead of 4 signals. Standard level candidates were expected to use the number of signals and the ratio of the areas under the signals to answer the question since they do not cover chemical shift, however, many of them did use the 1H NMR section in the data booklet to obtain correct answers in terms of chemical shift.
\n
d(iv).
\n
\n
This was the best answered question on the paper. Candidates identified the bonds and used bond enthalpies to calculate the enthalpy of reaction accurately. The most common mistakes were reversing the signs of bonds broken and bonds formed, assuming two Cl-Cl bonds were broken and using an incorrect value of bond enthalpy for one of the bonds.
\n
e(i).
\n
\n
The majority of candidates drew the enthalpy level diagram and labelled it correctly based on their answer to part (i). Some candidates reversed the products and reactants. A few candidates did not add any labels which prevented the awarding of the second mark. With 2 marks allocated to the question the second mark was awarded for correct labeling of either ΔH or Ea.
\n
e(ii).
\n
",
+ "topics": [
+ "reactivity-2-how-much-how-fast-and-how-far"
+ ],
+ "subtopics": [
+ "reactivity-2-2-how-fast-the-rate-of-chemical-change",
+ "reactivity-2-3-how-far-the-extent-of-chemical-change"
+ ]
+ },
+ {
+ "question_id": "22M.2.SL.TZ2.5",
+ "Question": "
\n
Molten zinc chloride undergoes electrolysis in an electrolytic cell at 450 °C.
\n
\n
Deduce the half-equations for the reaction at each electrode.
\n

\n
[2]
\n
a.
\n
\n
Deduce the overall cell reaction including state symbols. Use section 7 of the data booklet.
\n
[2]
\n
b.
\n
",
+ "Markscheme": "
\n
Cathode (negative electrode):
\n
Zn2+ + 2e− → Zn (l) ✔
\n
\n
Anode (positive electrode):
\n
2Cl− → Cl2 (g) + 2e−
\n
OR
\n
Cl− → ½ Cl2 (g) + e− ✔
\n
a.
\n
\n
ZnCl2 (l) → Zn (l) + Cl2 (g)
\n
balanced equation ✔
correct state symbols ✔
\n
\n
Accept ionic equation.
\n
b.
\n
",
+ "Examiners report": "
\n
The half-equations were often incorrect. The average mark was 0.8 out of 2, and the correlation to high scoring candidates was strong as expected. Many candidates started the half-equations with the elements and gave the ions as products. We also saw some scripts with Cl instead of Cl2 as the product. Some of the candidates thought the zinc ion was Zn+ instead of Zn2+. Some candidates reversed the anode and cathode equations earning only 1 of the 2 marks.
\n
a.
\n
\n
The performance was weak on this part-question as well. The overall equations did not balance atoms or charges on many of the incorrect answers. For the state symbols, many candidates used the aqueous state symbol, some gave the chloride ion a gaseous state symbol, and some candidates still had a solid zinc product even though they were directed to use the melting point of zinc in the data booklet. 12% of the candidates did not answer the question and the average mark was 0.5 out of 2 marks.
\n
b.
\n
",
+ "topics": [
+ "reactivity-2-how-much-how-fast-and-how-far",
+ "reactivity-3-what-are-the-mechanisms-of-chemical-change",
+ "structure-1-models-of-the-particulate-nature-of-matter",
+ "structure-2-models-of-bonding-and-structure",
+ "structure-3-classification-of-matter"
+ ],
+ "subtopics": [
+ "reactivity-2-1-how-much-the-amount-of-chemical-change",
+ "reactivity-3-2-electron-transfer-reactions",
+ "structure-1-3-electron-configurations",
+ "structure-2-3-the-metallic-model",
+ "structure-3-1-the-periodic-table-classification-of-elements"
+ ]
+ },
+ {
+ "question_id": "22M.2.SL.TZ2.6",
+ "Question": "
\n
\n (a)\n
\n
\n
\n Outline, giving a reason, the effect of a catalyst on a reaction.\n
\n
\n
\n
\n
\n
\n (b(i))\n
\n
\n
\n On the axes, sketch Maxwell–Boltzmann energy distribution curves for the reacting species at two temperatures T\n \n 1\n \n \n and\n \n T\n \n 2\n \n , where T\n \n 2\n \n > T\n \n 1\n \n .\n
\n
\n
\n
\n
\n
\n
\n
\n
\n (b(ii))\n
\n
\n
\n Explain the effect of increasing temperature on the yield of SO\n \n 3\n \n .\n
\n
\n
\n
\n
\n
\n (d(i))\n
\n
\n
\n State the product formed from the reaction of SO\n \n 3\n \n with water.\n
\n
\n
\n
\n
\n
\n (d(ii))\n
\n
\n
\n State the meaning of a strong Brønsted–Lowry acid.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n increases rate\n \n \n AND\n \n \n lower\n \n E\n \n \n a\n \n ✔\n
\n
\n provides alternative pathway «with lower\n \n E\n \n \n a\n \n »\n
\n \n \n OR\n \n \n
\n more/larger fraction of molecules have the «lower»\n \n E\n \n \n a\n \n ✔\n
\n
\n
\n
\n \n Accept description of how catalyst lowers E\n \n a\n \n for M2 (e.g. “reactants adsorb on surface «of catalyst»”, “reactant bonds weaken «when adsorbed»”, “helps favorable orientation of molecules”).\n \n
\n
\n
\n (b(i))\n
\n
\n
\n
\n
\n both axes correctly labelled ✔\n
\n
\n peak of T\n \n 2\n \n curve lower\n \n \n AND\n \n \n to the right of T\n \n 1\n \n curve ✔\n
\n
\n lines begin at origin\n \n \n AND\n \n \n correct shape of curves\n \n \n AND\n \n \n T\n \n 2\n \n must finish above T\n \n 1\n \n ✔\n
\n
\n
\n
\n \n Accept “probability «density» / number of particles / N / fraction” on y-axis.\n \n
\n
\n \n Accept “kinetic E/KE/E\n \n k\n \n ” but not just “Energy/E” on x-axis.\n \n
\n
\n
\n (b(ii))\n
\n
\n decrease\n \n \n AND\n \n \n equilibrium shifts left / favours reverse reaction ✔\n
\n
\n «forward reaction is» exothermic / ΔH is negative ✔\n
\n
\n
\n (d(i))\n
\n
\n sulfuric acid/H\n \n 2\n \n SO\n \n 4\n \n ✔\n
\n
\n \n
\n Accept “disulfuric acid/H\n \n 2\n \n S\n \n 2\n \n O\n \n 7\n \n ”.\n \n
\n
\n
\n (d(ii))\n
\n
\n fully ionizes/dissociates ✔\n
\n
\n proton/H\n \n +\n \n «donor »✔\n
\n
\n",
+ "Examiners report": "
\n (a)\n
\n
\n Overall well answered though some answers were directed to explain the specific example rather than the simple and standard definition of the effect of a catalyst.\n
\n
\n
\n (b(i))\n
\n
\n Few got the 3 marks for this standard question (average mark 1.7), the most common error being incomplete/incorrect labelling of axes, curves beginning above 0 on y-axis or inverted curves.\n
\n
\n
\n (b(ii))\n
\n
\n Many candidates got one mark at least, sometimes failing to state the effect on the production of SO\n \n 3\n \n though they knew this quite obviously. This failure to read the question properly also resulted in an incorrect prediction based exclusively on kinetics instead of using the information provided to guide their answers.\n
\n
\n
\n (d(i))\n
\n
\n 6(d)(i)-(ii): These simple questions could be expected to be answered by all HL candidates. However 20% of the candidates suggested hydroxides or hydrogen as products of an aqueous dissolution of sulphur oxide. In the case of the definition of a strong Brønsted-Lowry acid, only 50% got both marks, often failing to define \"strong\" but in other cases defining them as bases even.\n
\n
\n",
+ "topics": [
+ "reactivity-2-how-much-how-fast-and-how-far",
+ "reactivity-3-what-are-the-mechanisms-of-chemical-change",
+ "structure-3-classification-of-matter"
+ ],
+ "subtopics": [
+ "reactivity-2-1-how-much-the-amount-of-chemical-change",
+ "reactivity-2-2-how-fast-the-rate-of-chemical-change",
+ "reactivity-2-3-how-far-the-extent-of-chemical-change",
+ "reactivity-3-1-proton-transfer-reactions",
+ "structure-3-1-the-periodic-table-classification-of-elements"
+ ]
+ },
+ {
+ "question_id": "22M.2.SL.TZ2.8",
+ "Question": "
\n
\n (a(i))\n
\n
\n
\n Outline\n \n two\n \n differences between the bonding of carbon atoms in C\n \n 60\n \n and diamond.\n
\n
\n
\n
\n
\n
\n (a(ii))\n
\n
\n
\n Explain why C\n \n 60\n \n and diamond sublime at different temperatures and pressures.\n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n
\n State two features showing that propane and butane are members of the same homologous series.\n
\n
\n
\n
\n
\n
\n (c)\n
\n
\n
\n Describe a test and the expected result to indicate the presence of carbon–carbon double bonds.\n
\n
\n
\n
\n
\n
\n
\n
\n
\n (d(ii))\n
\n
\n
\n Write the equation for the reaction between but-2-ene and hydrogen bromide.\n
\n
\n
\n
\n
\n
\n (d(iii))\n
\n
\n
\n State the type of reaction.\n
\n
\n
\n
\n
\n
\n (f(i))\n
\n
\n
\n Calculate the enthalpy change of the reaction, Δ\n \n H\n \n , using section 11 of the data booklet.\n
\n
\n
\n
\n
\n
\n (f(ii))\n
\n
\n
\n Draw and label an enthalpy level diagram for this reaction.\n
\n
\n
\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a(i))\n
\n
\n Any\n \n two\n \n of:\n
\n
\n C\n \n 60\n \n fullerene: bonded to 3 C\n \n \n AND\n \n \n diamond: bonded to 4 C ✔\n
\n
\n C\n \n 60\n \n fullerene: delocalized/resonance\n \n \n AND\n \n \n diamond: not delocalized / no resonance ✔\n
\n
\n C\n \n 60\n \n fullerene:\n \n sp\n \n 2\n \n \n AND\n \n \n diamond:\n \n sp\n \n 3\n \n \n ✔\n
\n
\n C\n \n 60\n \n fullerene: bond angles between 109–120°\n \n \n AND\n \n \n diamond: 109° ✔\n
\n
\n
\n
\n \n Accept \"bonds in fullerene are shorter/stronger/have higher bond order\n \n OR\n \n bonds in diamond longer/weaker/have lower bond order\".\n \n
\n
\n
\n (a(ii))\n
\n
\n diamond giant/network covalent\n \n \n AND\n \n \n sublimes at higher temperature ✔\n
\n
\n C\n \n 60\n \n molecular/London/dispersion/intermolecular «forces» ✔\n
\n
\n
\n
\n \n Accept “diamond has strong covalent bonds\n \n AND\n \n require more energy to break «than intermolecular forces»” for M1.\n \n
\n
\n
\n (b)\n
\n
\n same general formula / C\n \n n\n \n H\n \n 2n+2\n \n ✔\n
\n
\n differ by CH\n \n 2\n \n /common structural unit ✔\n
\n
\n
\n
\n \n Accept \"similar chemical properties\".\n \n
\n
\n \n Accept “gradation/gradual change in physical properties”.\n \n
\n
\n
\n (c)\n
\n
\n \n ALTERNATIVE 1:\n \n
\n
\n \n Test:\n \n
\n
\n add bromine «water»/Br\n \n 2\n \n (aq) ✔\n
\n
\n \n Result:\n \n
\n
\n «orange/brown/yellow» to colourless/decolourised ✔\n
\n
\n \n
\n Do not accept “clear” for M2.\n \n
\n
\n \n
\n ALTERNATIVE 2:\n \n
\n
\n \n Test:\n \n
\n
\n add «acidified» KMnO\n \n 4\n \n ✔\n
\n
\n \n Result:\n \n
\n
\n «purple» to colourless/decolourised/brown ✔\n
\n
\n \n
\n Accept “colour change” for M2.\n \n
\n
\n \n
\n ALTERNATIVE 3:\n \n
\n
\n \n Test:\n \n
\n
\n add iodine /\n \n ✔\n
\n
\n \n Result:\n \n
\n
\n «brown» to colourless/decolourised ✔\n
\n
\n
\n
\n
\n (d(ii))\n
\n
\n CH\n \n 3\n \n CH=CHCH\n \n 3\n \n + HBr (g) → CH\n \n 3\n \n CH\n \n 2\n \n CHBrCH\n \n 3\n \n
\n
\n Correct reactants ✔\n
\n
\n Correct products ✔\n
\n
\n
\n
\n \n Accept molecular formulas for both reactants and product\n \n
\n
\n
\n (d(iii))\n
\n
\n «electrophilic» addition/EA ✔\n
\n
\n
\n
\n \n Do\n \n not\n \n accept nucleophilic or free radical addition.\n \n
\n
\n
\n (f(i))\n
\n
\n bond breaking: C–H + Cl–Cl / 414 «kJ mol\n \n –1\n \n » + 242 «kJ mol\n \n –1\n \n »/656 «kJ»\n
\n \n \n OR\n \n \n
\n bond breaking: 4C–H + Cl–Cl / 4 × 414 «kJ mol\n \n –1\n \n » + 242 «kJ mol\n \n –1\n \n » / 1898 «kJ» ✔\n
\n
\n
\n
\n bond forming: «C–Cl + H–Cl / 324 kJ mol\n \n –1\n \n + 431 kJ mol\n \n –1\n \n » / 755 «kJ»\n
\n \n \n OR\n \n \n
\n bond forming: «3C–H + C–Cl + H–Cl / 3 × 414 «kJ mol\n \n –1\n \n » + 324 «kJ mol\n \n –1\n \n » + 431 kJ mol\n \n –1\n \n » / 1997 «kJ» ✔\n
\n
\n
\n
\n «ΔH = bond breaking – bond forming = 656 kJ – 755 kJ» = –99 «kJ» ✔\n
\n
\n
\n
\n \n Award\n \n [3]\n \n for correct final answer.\n \n
\n
\n \n Award\n \n [2 max]\n \n for 99 «kJ».\n \n
\n
\n
\n (f(ii))\n
\n
\n
\n
\n
\n reactants at higher enthalpy than products ✔\n
\n
\n
\n ΔH/-99 «kJ» labelled on arrow from reactants to products\n
\n \n \n OR\n \n \n
\n activation energy/\n \n E\n \n \n a\n \n labelled on arrow from reactant to top of energy profile ✔\n
\n
\n
\n
\n \n Accept a double headed arrow between reactants and products labelled as ΔH for M2.\n \n
\n
\n",
+ "Examiners report": "
\n (a(i))\n
\n
\n A challenging question, requiring accurate knowledge of the bonding in these allotropes (some referred to graphite, clearly the most familiar allotrope). The most frequent (correct) answer was the difference in number of bonded C atoms and hybridisation in second place. However, only 30% got a mark.\n
\n
\n
\n (a(ii))\n
\n
\n Again, this was a struggle between intermolecular forces and covalent bonds and this proved to be even harder than (a)(i) with only 25% of candidates getting full marks. The distinction between giant covalent/covalent network in diamond and molecular in C60 and hence resultant sublimation points, was rarely explained. There were many general and vague answers given, as well as commonly (incorrectly) stating that intermolecular forces are present in diamond. As another example of insufficient attention to the question itself, many candidates failed to say which would sublime at a higher temperature and so missed even one mark.\n
\n
\n
\n (b)\n
\n
\n This easy question was quite well answered; same/similar physical properties and empirical formula were common errors.\n
\n
\n Candidates misinterpreted the question and mentioned CH3\n \n +\n \n , i.e., the lost fragment; the other very common error was -COOH which shows a complete lack of understanding of MS considering the question is about butane so O should never appear.\n
\n
\n
\n (c)\n
\n
\n Well answered by most, but some basic chemistry was missing when reporting results, perhaps as a result of little practical work due to COVID. A significant number suggested IR spectrometry, very likely because the question followed one on H NMR spectroscopy, thus revealing a failure to read the question properly (which asks for a test). Some teachers felt that adding \"chemical\" would have avoided some confusion.\n
\n
\n
\n (d(ii))\n
\n
\n Well done in general and most candidates wrote correct reagents, eventually losing a mark when considering H\n \n 2\n \n to be a product alongside 2-bromobutane.\n
\n
\n
\n (d(iii))\n
\n
\n Very well answered, some mentioned halogenation which is a different reaction.\n
\n
\n
\n (f(i))\n
\n
\n Only the very weak candidates were unable to calculate the enthalpy change correctly, eventually missing 1 mark for inverted calculations.\n
\n
\n
\n (f(ii))\n
\n
\n Most candidates drew correct energy profiles, consistent with the sign of the energy change calculated in the previous question. And again, only very weak candidate failed to get at least 1 mark for correct profiles.\n
\n
\n",
+ "topics": [
+ "reactivity-1-what-drives-chemical-reactions",
+ "reactivity-2-how-much-how-fast-and-how-far",
+ "reactivity-3-what-are-the-mechanisms-of-chemical-change",
+ "structure-1-models-of-the-particulate-nature-of-matter",
+ "structure-2-models-of-bonding-and-structure",
+ "structure-3-classification-of-matter",
+ "tools"
+ ],
+ "subtopics": [
+ "reactivity-1-2-energy-cycles-in-reactions",
+ "reactivity-2-2-how-fast-the-rate-of-chemical-change",
+ "reactivity-3-4-electron-pair-sharing-reactions",
+ "structure-1-1-introduction-to-the-particulate-nature-of-matter",
+ "structure-2-2-the-covalent-model",
+ "structure-3-2-functional-groups-classification-of-organic-compounds",
+ "tool-1-experimental-techniques"
+ ]
+ },
+ {
+ "question_id": "22N.2.SL.TZ0.4",
+ "Question": "
\n
\n (a.i)\n
\n
\n
\n Deduce the structural and empirical formulas of\n \n B\n \n .\n
\n
\n
\n
\n
\n
\n
\n
\n
\n (a.ii)\n
\n
\n
\n Explain, with reference to Le Châtelier’s principle, the effect of using dilute rather than concentrated sulfuric acid as the catalyst on the yield of the reaction.\n
\n
\n
\n
\n
\n
\n (a.iii)\n
\n
\n
\n Explain, with reference to intermolecular forces, why\n \n B\n \n is more volatile than\n \n A\n \n .\n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n
\n Compound\n \n A\n \n can also react with bromine. Describe the change observed if\n \n A\n \n is reacted with bromine.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a.i)\n
\n
\n \n Structure:\n \n
\n
\n
\n
\n
\n ester functional group ✔\n
\n
\n rest of structure ✔\n
\n
\n
\n \n Empirical Formula:\n \n
\n
\n C\n \n 3\n \n H\n \n 5\n \n O ✔\n
\n
\n
\n
\n \n Accept condensed/skeletal formula.\n \n
\n
\n
\n (a.i)\n
\n
\n \n Structure:\n \n
\n
\n
\n
\n
\n ester functional group ✔\n
\n
\n rest of structure ✔\n
\n
\n
\n \n Empirical Formula:\n \n
\n
\n C\n \n 3\n \n H\n \n 5\n \n O ✔\n
\n
\n
\n
\n \n Accept condensed/skeletal formula.\n \n
\n
\n
\n (a.ii)\n
\n
\n dilute adds «excess» water\n
\n
\n \n \n OR\n \n \n
\n
\n water is a product ✔\n
\n
\n
\n
\n shift left\n \n \n AND\n \n \n decreases yield ✔\n
\n
\n
\n (a.iii)\n
\n
\n \n A\n \n has hydrogen bonding/bonds «and dipole-dipole and London/dispersion forces»\n \n \n AND\n \n B\n \n has dipole-dipole «and London/dispersion forces»\n
\n
\n \n \n OR\n \n \n
\n
\n \n A\n \n has hydrogen bonding/bonds\n \n \n AND\n \n \n \n B\n \n does not ✔\n
\n
\n
\n
\n intermolecular forces are weaker in\n \n B\n \n
\n
\n \n \n OR\n \n \n
\n
\n hydrogen bonding/bonds stronger «than dipole-dipole» ✔\n
\n
\n
\n (b)\n
\n
\n brown/orange/red/yellow to colourless ✔\n
\n
\n
\n \n Do\n \n not\n \n accept clear for colourless.\n \n
\n
\n",
+ "Examiners report": "
\n (a.i)\n
\n
\n A question that discriminated well between high-scoring and low-scoring candidates. The average mark on this three-mark question was 1.3. The majority of candidates did not recognize it as an esterification reaction and the ester functional group was only seen in a small proportion of the scripts. Some candidates earned a mark for the remainder of the structure. Only about half of the candidates earned error carried forward for the mark allocated for the empirical formula. Some candidates had the molecular formula instead, and some candidates miscounted the numbers of atoms in the structure they drew.\n
\n
\n
\n (a.i)\n
\n
\n A question that discriminated well between high-scoring and low-scoring candidates. The average mark on this three-mark question was 1.3. The majority of candidates did not recognize it as an esterification reaction and the ester functional group was only seen in a small proportion of the scripts. Some candidates earned a mark for the remainder of the structure. Only about half of the candidates earned error carried forward for the mark allocated for the empirical formula. Some candidates had the molecular formula instead, and some candidates miscounted the numbers of atoms in the structure they drew.\n
\n
\n
\n (a.ii)\n
\n
\n This was the most challenging question on the paper according to the difficulty index. Many candidates stated that catalysts do not affect the position of an equilibrium and hence the yield is not changed. Some candidates stated that the rate of reaction would be slower and the yield per unit time would be lower. Only a few candidates recognized that the dilute sulfuric acid catalyst would introduce more water, and since water is a product it would shift the equilibrium to the left and lower the yield of the ester. 23% of the candidates did not answer the question. Some teachers commented in their feedback that it was not fair to expect the students to know about the dehydrating property of H\n \n 2\n \n SO\n \n 4\n \n , but this was not intended. The students were expected to deduce the effect.\n
\n
\n
\n (a.iii)\n
\n
\n This question about intermolecular forces discriminated well between high-achieving and low-achieving candidates. Stronger candidates showed excellent understanding of the types of intermolecular forces found between the molecules of each compound and how they compared in strength. They gave more detail than the markscheme required. The average mark on the question was 0.8 out of 2. 21% of the candidates left the question blank. Error carried forward was applied whenever it was possible based on the answer in (a)(i).\n
\n
\n
\n (b)\n
\n
\n Although it was a straightforward organic question, 22% of the candidates left it blank, indicating less confidence in answering the organic chemistry questions. 40% of the candidates gained the mark for the decolourization of bromine. One of the common mistakes was reversing the colour change and another was using the term \"clear\" instead of \"colourless\".\n
\n
\n",
+ "topics": [
+ "reactivity-2-how-much-how-fast-and-how-far",
+ "reactivity-3-what-are-the-mechanisms-of-chemical-change",
+ "structure-2-models-of-bonding-and-structure",
+ "structure-3-classification-of-matter"
+ ],
+ "subtopics": [
+ "reactivity-2-3-how-far-the-extent-of-chemical-change",
+ "reactivity-3-4-electron-pair-sharing-reactions",
+ "structure-2-2-the-covalent-model",
+ "structure-2-4-from-models-to-materials",
+ "structure-3-2-functional-groups-classification-of-organic-compounds"
+ ]
+ },
+ {
+ "question_id": "22N.2.SL.TZ0.5",
+ "Question": "
\n
\n (a)\n
\n
\n
\n Calculate the amount, in mol, of sulfur dioxide produced when 500.0 g of lignite undergoes combustion.\n
\n
\n S (s) + O\n \n 2\n \n (g) → SO\n \n 2\n \n (g)\n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n
\n Write an equation that shows how sulfur dioxide can produce acid rain.\n
\n
\n
\n
\n
\n
\n (c)\n
\n
\n
\n Sodium thiosulfate reacts with hydrochloric acid as shown:\n
\n
\n Na\n \n 2\n \n S\n \n 2\n \n O\n \n 3\n \n (aq) + 2HCl (aq) → S (s) + SO\n \n 2\n \n (aq) + 2NaCl (aq) + H\n \n 2\n \n O (l)\n
\n
\n The precipitate of sulfur makes the mixture cloudy, so a mark underneath the reaction mixture becomes invisible with time.\n
\n
\n
\n
\n
\n Suggest\n \n two\n \n variables, other than concentration, that should be controlled when comparing relative rates at different temperatures.\n
\n
\n
\n
\n
\n
\n (d)\n
\n
\n
\n Discuss\n \n two\n \n different ways to reduce the environmental impact of energy production from coal.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n «\n \n » 2.0 «g» ✔\n
\n
\n «\n \n » = 0.062 «mol of SO\n \n 2\n \n » ✔\n
\n
\n
\n
\n \n Award\n \n [2]\n \n for correct final answer.\n \n
\n
\n \n Accept 0.063 «mol».\n \n
\n
\n
\n (a)\n
\n
\n «\n \n » 2.0 «g» ✔\n
\n
\n «\n \n » = 0.062 «mol of SO\n \n 2\n \n » ✔\n
\n
\n
\n
\n \n Award\n \n [2]\n \n for correct final answer.\n \n
\n
\n \n Accept 0.063 «mol».\n \n
\n
\n
\n (b)\n
\n
\n SO\n \n 2\n \n (g) + H\n \n 2\n \n O (l) → H\n \n 2\n \n SO\n \n 3\n \n (aq)\n
\n
\n \n \n OR\n \n \n
\n
\n SO\n \n 2\n \n (g) + ½O\n \n 2\n \n (g) → SO\n \n 3\n \n (g)\n \n \n AND\n \n \n SO\n \n 3\n \n (g) + H\n \n 2\n \n O (l) → H\n \n 2\n \n SO\n \n 4\n \n (aq)\n
\n
\n \n \n OR\n \n \n
\n
\n SO\n \n 2\n \n (g) + ½O\n \n 2\n \n (g) + H\n \n 2\n \n O (l) → H\n \n 2\n \n SO\n \n 4\n \n (aq) ✔\n
\n
\n
\n
\n \n Accept ionized forms of acids.\n \n
\n
\n
\n (c)\n
\n
\n \n Any two of:\n \n
\n
\n depth/volume «of solution» ✔\n
\n
\n colour/darkness/thickness/size/background of mark ✔\n
\n
\n intensity of lighting in the lab ✔\n
\n
\n
\n
\n \n Accept same size flask.\n \n
\n
\n \n Accept position of observation/person observing.\n \n
\n
\n \n Accept same equipment/apparatus.\n \n
\n
\n \n Do\n \n not\n \n accept catalyst/particle size/pressure/time.\n \n
\n
\n
\n (d)\n
\n
\n \n Any\n \n two\n \n of:\n \n
\n
\n remove sulfur from coal ✔\n
\n
\n add lime during combustion ✔\n
\n
\n not allow sulfur oxides to be released into the environment ✔\n
\n
\n reduce proportion/percentage of energy/power produced by «the combustion of» coal ✔\n
\n
\n
\n
\n \n Accept any valid method to wash coal and remove sulfur content for M1.\n \n
\n
\n \n Accept any valid combustion/post-combustion method to remove sulfur oxides.\n \n
\n
\n \n Accept any suggestion that would reduce the amount of coal that is burnt or would reduce the damage caused.\n \n
\n
\n \n Do\n \n not\n \n accept answers that only reduce production of SO\n \n 2\n \n /CO\n \n 2\n \n from other fuels.\n \n
\n
\n \n Accept “improve efficiency of energy production from coal”.\n \n
\n
\n \n Accept “use coal of lower sulfur content”\n \n OR\n \n “cleaner coal”.\n \n
\n
\n",
+ "Examiners report": "
\n (a)\n
\n
\n A question that discriminated well between high-achieving and low-achieving candidates. The majority of the candidates were able to achieve one mark for determining the number of moles using 500g, while stronger candidates determined 0.40% of 500g to determine the correct number of moles. A number of candidates had a power of ten error in the first step.\n
\n
\n
\n (a)\n
\n
\n A question that discriminated well between high-achieving and low-achieving candidates. The majority of the candidates were able to achieve one mark for determining the number of moles using 500g, while stronger candidates determined 0.40% of 500g to determine the correct number of moles. A number of candidates had a power of ten error in the first step.\n
\n
\n
\n (b)\n
\n
\n This question was poorly answered and only 30% of the candidates wrote a correct equation for the formation of acid rain from SO\n \n 2\n \n . Mistakes included unbalanced equations and hydrogen added as a product.\n
\n
\n
\n (c)\n
\n
\n Most candidates mentioned \"volume\" as a variable that should be controlled gaining one of the two marks, while only a small proportion of candidates seemed to understand how the experiment worked and discussed the lighting in the room and the thickness of the mark. The most common incorrect answer was \"pressure\" which was irrelevant to this experiment.\n
\n
\n
\n (d)\n
\n
\n Some candidates referred to the pre-combustion and post combustion methods of minimizing the release of SO\n \n 2\n \n . Some candidates focused on using cleaner coal, other fuels or renewable energy sources. Some mentioned increasing the efficiency of power stations to reduce the amount of coal burned. Some focused on removing the CO\n \n 2\n \n released by planting trees. All these options were valid with sufficient detail. But answers that were not relevant to coal, such as fitting catalytic converters on cars, were not accepted. 15% of the candidates did not answer the question, and the average mark was 0.8 out of 2 marks.\n
\n
\n",
+ "topics": [
+ "inquiry",
+ "reactivity-1-what-drives-chemical-reactions",
+ "reactivity-2-how-much-how-fast-and-how-far",
+ "structure-3-classification-of-matter"
+ ],
+ "subtopics": [
+ "inquiry-1-exploring-and-designing",
+ "reactivity-1-3-energy-from-fuels",
+ "reactivity-2-1-how-much-the-amount-of-chemical-change",
+ "structure-3-1-the-periodic-table-classification-of-elements"
+ ]
+ },
+ {
+ "question_id": "23M.2.HL.TZ1.1",
+ "Question": "
\n
\n (a.i)\n
\n
\n
\n Deduce the ionic equation, including state symbols, for the reaction of hydrogen chloride gas with water.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a.i)\n
\n
\n H\n \n 2\n \n O\n \n (l)\n \n + HCl\n \n (g)\n \n → Cl\n \n −\n \n \n (aq)\n \n + H\n \n 3\n \n O\n \n +\n \n \n (aq) ✓✓\n \n
\n
\n
\n
\n \n One for the equation and one for the state symbols.\n
\n Do not accept\n \n H\n \n 2\n \n O\n \n (l)\n \n + H\n \n +\n \n \n (g)\n \n →\n \n \n H\n \n 3\n \n O\n \n +\n \n \n (aq)\n \n \n
\n Do not accept equilibrium sign.\n \n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "empty-topic"
+ ],
+ "subtopics": []
+ },
+ {
+ "question_id": "23M.2.HL.TZ1.2",
+ "Question": "
\n
\n (a.i)\n
\n
\n
\n Annotate and label the ground state orbital diagram of boron, using arrows to represent electrons.\n
\n
\n
\n
\n
\n
\n
\n
\n
\n (a)\n
\n
\n
\n The results are given where ✓ = reaction occurred and\n \n = no reaction.\n
\n
\n \n \n \n \n Metal\n \n | \n \n \n ASO\n \n 4\n \n (aq)\n \n | \n \n \n BSO\n \n 4\n \n (aq)\n \n | \n \n \n CSO\n \n 4\n \n (aq)\n \n | \n \n \n DSO\n \n 4\n \n (aq)\n \n | \n \n \n ESO\n \n 4\n \n (aq)\n \n | \n
\n \n \n \n A\n \n | \n \n —\n | \n \n ✓\n | \n \n ✗\n | \n \n ✓\n | \n \n ✓\n | \n
\n \n \n \n B\n \n | \n \n ✗\n | \n \n —\n | \n \n ✗\n | \n \n ✓\n | \n \n ✓\n | \n
\n \n \n \n C\n \n | \n \n ✓\n | \n \n ✓\n | \n \n —\n | \n \n ✓\n | \n \n ✓\n | \n
\n \n \n \n D\n \n | \n \n ✗\n | \n \n ✗\n | \n \n ✗\n | \n \n —\n | \n \n ✓\n | \n
\n \n \n \n E\n \n | \n \n ✗\n | \n \n ✗\n | \n \n ✗\n | \n \n ✗\n | \n \n —\n | \n
\n \n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a.i)\n
\n
\n
\n
\n
\n arrows\n \n \n AND\n \n \n identifies 2s\n \n \n AND\n \n \n 2p sub orbitals ✓\n
\n
\n
\n
\n \n Accept “hooks” to represent the electrons.\n \n
\n
\n
\n (a)\n
\n
\n +2/II ✓\n
\n
\n
\n \n Do\n \n not\n \n accept A\n \n 2+\n \n , A\n \n +2\n \n , 2\n \n OR\n \n 2+.\n \n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "empty-topic"
+ ],
+ "subtopics": []
+ },
+ {
+ "question_id": "23M.2.HL.TZ1.3",
+ "Question": "
\n
\n (a.i)\n
\n
\n
\n Outline the meaning of homologous series.\n
\n
\n
\n
\n
\n
\n (a)\n
\n
\n
\n High-pressure carbon monoxide disproportionation (HiPco) produces carbon atoms that react with nano catalysts to produce carbon nanotubes.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a.i)\n
\n
\n compounds of the same family\n \n \n AND\n \n \n general formula\n
\n \n \n OR\n \n \n
\n compounds of the same family\n \n \n AND\n \n \n differ by a common structural unit/\n \n CH\n \n \n 2\n \n ✓\n
\n
\n
\n
\n \n Accept contains the same functional group for same family.\n \n
\n
\n
\n (a)\n
\n
\n 2CO(g) → C(s) + CO\n \n 2\n \n (g) ✓\n
\n
\n
\n \n Accept reversible arrows.\n \n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "empty-topic"
+ ],
+ "subtopics": []
+ },
+ {
+ "question_id": "23M.2.HL.TZ1.4",
+ "Question": "
\n
\n (a)\n
\n
\n
\n State the oxidation state of sulfur in copper (II) sulfate.\n
\n
\n
\n
\n
\n
\n (a)\n
\n
\n
\n Explain why metals alloyed with another metal are usually harder and stronger but poorer conductors than the pure metal.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n +6/VI ✓\n
\n
\n
\n
\n \n Do\n \n not\n \n accept 6/6\n \n +\n \n .\n \n
\n
\n
\n (a)\n
\n
\n metal ions/atoms have different sizes ✓\n
\n cations/atoms/layers do not slide over each other as easily ✓\n
\n «irregularities» obstruct free movement of electrons ✓\n
\n
\n
\n \n Accept electrons move less easily/less delocalized for M3.\n \n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "empty-topic"
+ ],
+ "subtopics": []
+ },
+ {
+ "question_id": "23M.2.HL.TZ1.5",
+ "Question": "
\n
\n (a.i)\n
\n
\n
\n Draw\n \n one\n \n Lewis (electron dot) structure of the sulfate ion.\n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n
\n The\n \n K\n \n \n sp\n \n of copper (II) hydroxide is 2.2 × 10\n \n −20\n \n . Calculate the molar solubility of Cu\n \n 2+\n \n (aq) ions in a solution of pH 9.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a.i)\n
\n
\n
\n ✓\n
\n
\n
\n
\n \n Accept any combination of dots, crosses and lines.\n
\n Double bonds do not have to be opposite each other.\n
\n Do\n \n not\n \n penalise missing square brackets.\n \n
\n
\n
\n (b)\n
\n
\n \n K\n \n \n sp\n \n =[Cu\n \n 2+\n \n ][OH\n \n −\n \n ]\n \n 2\n \n
\n \n \n OR\n \n \n
\n 2.2 × 10\n \n −20\n \n =[Cu\n \n 2+\n \n ] × (10\n \n −5\n \n )\n \n 2\n \n ✓\n
\n
\n [Cu2+] «= Ksp/[OH−]2 =2.2 x 10−20/(10−5)2»\n
\n = 2.2 ×10\n \n −10\n \n «mol dm\n \n −3\n \n » ✓\n
\n
\n
\n \n Award\n \n [2]\n \n for correct final answer.\n \n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "empty-topic"
+ ],
+ "subtopics": []
+ },
+ {
+ "question_id": "23M.2.HL.TZ1.6",
+ "Question": "
\n
\n (a.i)\n
\n
\n
\n Determine the standard enthalpy of reaction (\n \n ), in kJ mol\n \n −1\n \n , for the oxidation of SO\n \n 2\n \n to SO\n \n 3\n \n .\n
\n
\n \n \n \n \n Substance\n \n | \n \n \n Enthalpy of formation, (\n \n ), in kJ mol\n \n −1\n \n \n | \n
\n \n \n SO\n \n 2\n \n | \n \n −296.8\n | \n
\n \n \n SO\n \n 3\n \n | \n \n −395.8\n | \n
\n \n
\n
\n
\n
\n
\n
\n (a)\n
\n
\n
\n Outline why vitamins usually need to be obtained from food sources.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a.i)\n
\n
\n «Δ\n \n H\n \n °\n \n rxn\n \n = ΣΔ\n \n H\n \n °f (Products) − ΣΔ\n \n H\n \n °f (Reactants) =»\n
\n −395.8 − (−296.8)» = −99.0«kJ mol\n \n −1\n \n » ✓\n
\n
\n
\n (a)\n
\n
\n cannot be synthesized «by the human body» ✓\n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "empty-topic"
+ ],
+ "subtopics": []
+ },
+ {
+ "question_id": "23M.2.HL.TZ1.7",
+ "Question": "
\n
\n (a.i)\n
\n
\n
\n Deduce the number of signals you would expect to find in the\n \n 1\n \n H NMR spectrum of each compound.\n
\n
\n
\n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n
\n Glucose, an isomer of fructose, exists as two isomeric ring forms. Annotate the diagram below to complete the structure of β-glucose. Use section 34 of the data booklet.\n
\n
\n
\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a.i)\n
\n
\n \n \n \n Name\n | \n \n Number of signals\n | \n
\n \n \n Ethyl methanoate\n | \n \n 3\n | \n
\n \n \n Methyl ethanoate\n | \n \n \n \n AND\n \n \n 2\n | \n
\n \n
\n
\n ✓\n
\n
\n
\n (b)\n
\n
\n
\n
\n
\n
\n
\n \n Entire structure must be correct to score the mark.\n \n
\n
\n \n Ignore incorrect connectivity.\n \n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "empty-topic"
+ ],
+ "subtopics": []
+ },
+ {
+ "question_id": "23M.2.HL.TZ1.9",
+ "Question": "
\n
\n (a)\n
\n
\n
\n Explain why a colorimeter set at a wavelength of 500 nm is not suitable to investigate reactions of Zn\n \n 2+\n \n compounds. Use section 3 of the data booklet.\n
\n
\n
\n
\n
\n
\n (a)\n
\n
\n
\n State the\n \n three\n \n components of a monomer of DNA (a nucleotide).\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n Zn\n \n 2+\n \n does not form coloured compounds/ has a complete d subshell/orbital ✓\n
\n
\n 500 nm/«the setting on the colorimeter» in visible region\n \n \n AND\n \n \n no absorbance will be seen ✓\n
\n
\n
\n (a)\n
\n
\n phosphate\n \n \n AND\n \n \n deoxyribose\n \n \n AND\n \n \n nitrogenous base ✓\n
\n
\n
\n \n Accept named base.\n
\n Do\n \n not\n \n accept ‘sugar’ or ‘pentose sugar’ in place of deoxyribose.\n \n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "empty-topic"
+ ],
+ "subtopics": []
+ },
+ {
+ "question_id": "23M.2.HL.TZ2.1",
+ "Question": "
\n
\n (a)\n
\n
\n
\n An unknown organic compound,\n \n X\n \n , comprising of only carbon, hydrogen and oxygen was found to contain 48.6 % of carbon and 43.2 % of oxygen.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n «n(C) =» 4.05 «mol»\n
\n \n \n AND\n \n \n
\n «n(O) =» 2.70 «mol» ✓\n
\n
\n «% H =» 8.2 %\n
\n \n \n OR\n \n \n
\n «n(H) =» 8.12 «mol» ✓\n
\n
\n «empirical formula =» C\n \n 3\n \n H\n \n 6\n \n O\n \n 2\n \n ✓\n
\n
\n \n Award\n \n [2]\n \n for the simplest ratio ″1.5 C: 3 H: 1 O″.\n \n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "empty-topic"
+ ],
+ "subtopics": []
+ },
+ {
+ "question_id": "23M.2.HL.TZ2.2",
+ "Question": "
\n
\n (a)\n
\n
\n
\n Nitrogen (IV) oxide exists in equilibrium with dinitrogen tetroxide, N\n \n 2\n \n O\n \n 4\n \n (g), which is colourless.\n
\n
\n 2NO\n \n 2\n \n (g) ⇌ N\n \n 2\n \n O\n \n 4\n \n (g)\n
\n
\n
\n
\n
\n
\n (a)\n
\n
\n
\n All species are almost colourless except for MnO\n \n 4\n \n \n −\n \n , which has an intense purple colour, though the kale extract is coloured by the chlorophyll present.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n reaction hardly proceeds\n
\n \n \n OR\n \n \n
\n reverse reaction/formation of NO\n \n 2\n \n is favoured\n
\n \n \n OR\n \n \n
\n «concentration of» reactants greater than «concentration of» products «at equilibrium» ✓\n
\n
\n \n Accept equilibrium lies to the left.\n \n
\n
\n
\n (a)\n
\n
\n green to purple\n
\n \n \n OR\n \n \n
\n green to brown\n
\n \n \n OR\n \n \n
\n green to purple-green ✓\n
\n
\n
\n
\n \n Accept “colourless to purple”.\n
\n Accept “green to grey/blueish”.\n
\n Do\n \n not\n \n accept “clear” for “colourless”.\n
\n Do\n \n not\n \n accept “purple to “brown”.\n
\n Do\n \n not\n \n accept blue as final colour.\n \n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "empty-topic"
+ ],
+ "subtopics": []
+ },
+ {
+ "question_id": "23M.2.HL.TZ2.3",
+ "Question": "
\n
\n (a)\n
\n
\n
\n An electrolytic cell was set up using inert electrodes and a dilute aqueous solution of magnesium chloride, MgCl\n \n 2\n \n (aq).\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n
\n
\n
\n electron flow from anode to battery\n \n \n OR\n \n \n from battery to cathode ✓\n
\n
\n Mg\n \n 2+\n \n /H\n \n +\n \n ions to − electrode\n
\n \n \n AND\n \n \n
\n Cl\n \n −\n \n /OH\n \n −\n \n ions to + electrode ✓\n
\n
\n \n Do not award M1 if electrons are shown in electrolyte.\n \n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "empty-topic"
+ ],
+ "subtopics": []
+ },
+ {
+ "question_id": "23M.2.HL.TZ2.4",
+ "Question": "
\n
\n (a)\n
\n
\n
\n Bismuth has atomic number 83. Deduce\n \n two\n \n pieces of information about the electron configuration of bismuth from its position on the periodic table.\n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n
\n Explain how a substance in the same phase as the reactants can reduce the activation energy and act as a catalyst.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n \n Any two of the following:\n \n
\n «group 15 so Bi has» 5 valence electrons ✓\n
\n «period 6 so Bi has» 6 «occupied» electron shells/energy levels ✓\n
\n «in p-block so» p orbitals are highest occupied ✓\n
\n occupied d/f orbitals ✓\n
\n has unpaired electrons ✓\n
\n has incomplete shell(s)/subshell(s) ✓\n
\n
\n \n Award\n \n [1]\n \n for full or condensed electron configuration, [Xe] 4f\n \n 14\n \n 5d\n \n 10\n \n 6s\n \n 2\n \n 6p\n \n 3\n \n .\n
\n \n
\n
\n \n Accept other valid statements about the electron configuration.\n \n
\n
\n
\n (b)\n
\n
\n forms an intermediate/activated complex ✓\n
\n «intermediate/activated complex» dissociates to form product «\n \n \n AND\n \n \n catalyst» ✓\n
\n
\n
\n
\n \n Accept correct annotated energy profile for either mark.\n \n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "empty-topic"
+ ],
+ "subtopics": []
+ },
+ {
+ "question_id": "23M.2.HL.TZ2.5",
+ "Question": "
\n
\n (a)\n
\n
\n
\n The concentration of methanoic acid was found by titration with a 0.200 mol dm\n \n −\n \n 3\n \n \n standard solution of sodium hydroxide, NaOH (aq), using an indicator to determine the end point.\n
\n
\n
\n
\n
\n
\n (a)\n
\n
\n
\n The unit cell of lead (II) sulfide is shown:\n
\n
\n
\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n «[OH\n \n −\n \n ] = 0.200 mol dm\n \n −3\n \n »\n
\n
\n \n \n ALTERNATIVE 1:\n \n \n
\n «pOH = −log\n \n 10\n \n (0.200) =» 0.699 ✓\n
\n «pH = 14.000 − 0.699 =» 13.301 ✓\n
\n
\n \n \n ALTERNATIVE 2:\n \n \n
\n «[H\n \n +\n \n ] =\n \n = » 5.00 × 10\n \n −14\n \n «mol dm\n \n −3\n \n » ✓\n
\n «pH = −log\n \n 10\n \n (5.00 × 10\n \n −14\n \n )» = 13.301 ✓\n
\n
\n \n Award\n \n [2]\n \n for correct final answer.\n \n
\n
\n
\n (a)\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "empty-topic"
+ ],
+ "subtopics": []
+ },
+ {
+ "question_id": "23M.2.HL.TZ2.7",
+ "Question": "
\n
\n (a)\n
\n
\n
\n Identify the type of reaction.\n
\n
\n
\n
\n
\n
\n (a)\n
\n
\n
\n Describe the interactions between amino acids occurring at the primary, secondary and tertiary levels within a protein.\n
\n
\n \n \n \n \n Structure Level\n \n | \n \n \n Interactions between amino acids\n \n | \n
\n \n \n Primary\n | \n \n ...........................................................\n | \n
\n \n \n Secondary\n | \n \n ...........................................................\n | \n
\n \n \n Tertiary\n | \n \n ...........................................................\n | \n
\n \n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n «electrophilic» addition/A\n \n E\n \n ✓\n
\n
\n
\n
\n \n Do\n \n not\n \n accept nucleophilic addition.\n \n
\n
\n
\n (a)\n
\n
\n \n \n \n \n Structure Level\n \n | \n \n \n Interactions between amino acids\n \n | \n
\n \n \n Primary\n | \n \n covalent bonding\n \n \n \n OR\n \n \n \n peptide bond\n \n \n \n OR\n \n \n \n amide bond ✓\n | \n
\n \n \n Secondary\n | \n \n hydrogen bonding ✓\n | \n
\n \n \n Tertiary\n | \n \n interactions between R groups/side chains\n \n \n \n OR\n \n \n \n ionic/electrostatic «attraction»\n \n \n \n OR\n \n \n \n hydrogen bonding\n \n \n \n OR\n \n \n \n hydrophobic interactions\n \n \n \n OR\n \n \n \n disulfide bridges\n \n \n \n OR\n \n \n \n London/dispersion/van der Waals/«instantaneous» induced dipole-induced dipole ✓\n | \n
\n \n
\n
\n
\n
\n \n Do\n \n not\n \n accept “amino acid sequence” for M1.\n
\n \n
\n
\n \n Do\n \n not\n \n accept “alpha helix”\n \n OR\n \n “beta sheets” for M2.\n
\n \n
\n
\n \n Accept “covalent bonding” for M3.\n \n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "empty-topic"
+ ],
+ "subtopics": []
+ },
+ {
+ "question_id": "23M.2.HL.TZ2.8",
+ "Question": "
\n
\n (a)\n
\n
\n
\n Enthalpy of solution, enthalpy of hydration and lattice enthalpy are related in an energy cycle.\n
\n
\n
\n
\n
\n
\n (a)\n
\n
\n
\n Compare the hydrolytic and oxidative rancidity and contrast the site where the chemical changes occur.\n
\n
\n
\n
\n Compare rancidity: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .\n
\n
\n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .\n
\n
\n Contrast reaction site: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .\n
\n
\n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n
\n
\n
\n correct boxes ✓\n
\n A: enthalpy of solution / Δ\n \n H\n \n solution / Δ\n \n H\n \n sol\n
\n \n \n AND\n \n \n
\n B: lattice enthalpy / Δ\n \n H\n \n lattice\n
\n \n \n AND\n \n \n
\n C: enthalpy of hydration / Δ\n \n H\n \n hydration ✓\n
\n
\n
\n (a)\n
\n
\n \n Compare rancidity:\n \n
\n «both produce» disagreeable smell/taste/texture/appearance ✓\n
\n
\n \n Contrast reaction site:\n \n
\n hydrolytic reaction occurs at ester link/COOC link\n \n \n AND\n \n \n oxidative reaction occurs at carbon-carbon double bond/C=C ✓\n
\n
\n
\n
\n \n Do\n \n not\n \n accept “double bond” alone for oxidative reaction site.\n \n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "empty-topic"
+ ],
+ "subtopics": []
+ },
+ {
+ "question_id": "23M.2.SL.TZ1.2",
+ "Question": "
\n
\n (a.i)\n
\n
\n
\n Annotate and label the ground state orbital diagram of boron, using arrows to represent electrons.\n
\n
\n
\n
\n
\n
\n
\n
\n
\n (a)\n
\n
\n
\n The results are given where ✓ = reaction occurred and\n \n = no reaction.\n
\n
\n \n \n \n \n Metal\n \n | \n \n \n ASO\n \n 4\n \n (aq)\n \n | \n \n \n BSO\n \n 4\n \n (aq)\n \n | \n \n \n CSO\n \n 4\n \n (aq)\n \n | \n \n \n DSO\n \n 4\n \n (aq)\n \n | \n \n \n ESO\n \n 4\n \n (aq)\n \n | \n
\n \n \n \n A\n \n | \n \n —\n | \n \n ✓\n | \n \n ✗\n | \n \n ✓\n | \n \n ✓\n | \n
\n \n \n \n B\n \n | \n \n ✗\n | \n \n —\n | \n \n ✗\n | \n \n ✓\n | \n \n ✓\n | \n
\n \n \n \n C\n \n | \n \n ✓\n | \n \n ✓\n | \n \n —\n | \n \n ✓\n | \n \n ✓\n | \n
\n \n \n \n D\n \n | \n \n ✗\n | \n \n ✗\n | \n \n ✗\n | \n \n —\n | \n \n ✓\n | \n
\n \n \n \n E\n \n | \n \n ✗\n | \n \n ✗\n | \n \n ✗\n | \n \n ✗\n | \n \n —\n | \n
\n \n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a.i)\n
\n
\n
\n
\n
\n arrows\n \n \n AND\n \n \n identifies 2s\n \n \n AND\n \n \n 2p sub orbitals ✓\n
\n
\n
\n
\n \n Accept “hooks” to represent the electrons.\n \n
\n
\n
\n (a)\n
\n
\n +2/II ✓\n
\n
\n
\n \n Do\n \n not\n \n accept A\n \n 2+\n \n , A\n \n +2\n \n , 2\n \n OR\n \n 2+.\n \n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "empty-topic"
+ ],
+ "subtopics": []
+ },
+ {
+ "question_id": "23M.2.SL.TZ1.3",
+ "Question": "
\n
\n (a.i)\n
\n
\n
\n Outline the meaning of homologous series.\n
\n
\n
\n
\n
\n
\n (a)\n
\n
\n
\n High-pressure carbon monoxide disproportionation (HiPco) produces carbon atoms that react with nano catalysts to produce carbon nanotubes.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a.i)\n
\n
\n compounds of the same family\n \n \n AND\n \n \n general formula\n
\n \n \n OR\n \n \n
\n compounds of the same family\n \n \n AND\n \n \n differ by a common structural unit/\n \n CH\n \n \n 2\n \n ✓\n
\n
\n
\n
\n \n Accept contains the same functional group for same family.\n \n
\n
\n
\n (a)\n
\n
\n 2CO(g) → C(s) + CO\n \n 2\n \n (g) ✓\n
\n
\n
\n \n Accept reversible arrows.\n \n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "empty-topic"
+ ],
+ "subtopics": []
+ },
+ {
+ "question_id": "23M.2.SL.TZ1.4",
+ "Question": "
\n
\n (a)\n
\n
\n
\n State the oxidation state of sulfur in copper (II) sulfate.\n
\n
\n
\n
\n
\n
\n (a)\n
\n
\n
\n Explain why metals alloyed with another metal are usually harder and stronger but poorer conductors than the pure metal.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n +6/VI ✓\n
\n
\n
\n
\n \n Do\n \n not\n \n accept 6/6\n \n +\n \n .\n \n
\n
\n
\n (a)\n
\n
\n metal ions/atoms have different sizes ✓\n
\n cations/atoms/layers do not slide over each other as easily ✓\n
\n «irregularities» obstruct free movement of electrons ✓\n
\n
\n
\n
\n \n Accept electrons move less easily/less delocalized for M3.\n \n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "empty-topic"
+ ],
+ "subtopics": []
+ },
+ {
+ "question_id": "23M.2.SL.TZ1.5",
+ "Question": "
\n
\n (a.i)\n
\n
\n
\n Calculate the percentage of oxygen present in the double salt.\n
\n
\n
\n
\n
\n
\n (a)\n
\n
\n
\n Outline why vitamins usually need to be obtained from food sources.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a.i)\n
\n
\n «100 − (7.09 + 5.11 + 16.22 + 14.91) =» 56.67 «%» ✓\n
\n
\n
\n (a)\n
\n
\n cannot be synthesized «by the human body» ✓\n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "empty-topic"
+ ],
+ "subtopics": []
+ },
+ {
+ "question_id": "23M.2.SL.TZ2.1",
+ "Question": "
\n
\n (a)\n
\n
\n
\n An unknown organic compound,\n \n X\n \n , comprising of only carbon, hydrogen and oxygen was found to contain 48.6 % of carbon and 43.2 % of oxygen.\n
\n
\n Determine the empirical formula.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n «n(C) =» 4.05 «mol»\n
\n \n \n AND\n \n \n
\n «n(O) =» 2.70 «mol» ✓\n
\n «% H =» 8.2 %\n
\n \n \n OR\n \n \n
\n «n(H) =» 8.12 «mol» ✓\n
\n
\n «empirical formula =» C\n \n 3\n \n H\n \n 6\n \n O\n \n 2\n \n ✓\n
\n
\n
\n
\n \n Award\n \n [2]\n \n for the simplest ratio ″1.5 C: 3 H: 1 O″.\n \n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "empty-topic"
+ ],
+ "subtopics": []
+ },
+ {
+ "question_id": "23M.2.SL.TZ2.2",
+ "Question": "
\n
\n (a)\n
\n
\n
\n Nitrogen (IV) oxide exists in equilibrium with dinitrogen tetroxide, N\n \n 2\n \n O\n \n 4\n \n (g), which is colourless.\n
\n
\n 2NO\n \n 2\n \n (g) ⇌ N\n \n 2\n \n O\n \n 4\n \n (g)\n
\n
\n
\n
\n
\n
\n (a)\n
\n
\n
\n All species are almost colourless except for MnO\n \n 4\n \n \n −\n \n , which has an intense purple colour, though the kale extract is coloured by the chlorophyll present.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n reaction hardly proceeds\n
\n \n \n OR\n \n \n
\n reverse reaction/formation of NO\n \n 2\n \n is favoured\n
\n \n \n OR\n \n \n
\n «concentration of» reactants greater than «concentration of» products «at equilibrium» ✓\n
\n
\n \n Accept equilibrium lies to the left.\n \n
\n
\n
\n (a)\n
\n
\n green to purple\n
\n \n \n OR\n \n \n
\n green to brown\n
\n \n \n OR\n \n \n
\n green to purple-green ✓\n
\n
\n
\n
\n \n Accept “colourless to purple”.\n
\n Accept “green to grey/blueish”.\n
\n Do\n \n not\n \n accept “clear” for “colourless”.\n
\n Do\n \n not\n \n accept “purple to “brown”.\n
\n Do\n \n not\n \n accept blue as final colour.\n \n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "empty-topic"
+ ],
+ "subtopics": []
+ },
+ {
+ "question_id": "23M.2.SL.TZ2.3",
+ "Question": "
\n
\n (a)\n
\n
\n
\n An electrolytic cell was set up using inert electrodes and molten magnesium chloride, MgCl\n \n 2\n \n (l).\n
\n
\n
\n
\n
\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n magnesium/Mg «metal» ✓\n
\n
\n
\n
\n \n Do not accept magnesium ions/Mg\n \n 2+\n \n .\n \n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "empty-topic"
+ ],
+ "subtopics": []
+ },
+ {
+ "question_id": "23M.2.SL.TZ2.4",
+ "Question": "
\n
\n (a)\n
\n
\n
\n Bismuth has atomic number 83. Deduce\n \n two\n \n pieces of information about the electron configuration of bismuth from its position on the periodic table.\n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n
\n Explain how a substance in the same phase as the reactants can reduce the activation energy and act as a catalyst.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n \n Any two of the following:\n \n
\n «group 15 so Bi has» 5 valence electrons ✓\n
\n «period 6 so Bi has» 6 «occupied» electron shells/energy levels ✓\n
\n «in p-block so» p orbitals are highest occupied ✓\n
\n occupied d/f orbitals ✓\n
\n has unpaired electrons ✓\n
\n has incomplete shell(s)/subshell(s) ✓\n
\n
\n \n Award\n \n [1]\n \n for full or condensed electron configuration, [Xe] 4f\n \n 14\n \n 5d\n \n 10\n \n 6s\n \n 2\n \n 6p\n \n 3\n \n .\n
\n \n
\n
\n \n Accept other valid statements about the electron configuration.\n \n
\n
\n
\n (b)\n
\n
\n forms an intermediate/activated complex ✓\n
\n «intermediate/activated complex» dissociates to form product «\n \n \n AND\n \n \n catalyst» ✓\n
\n
\n
\n
\n \n Accept correct annotated energy profile for either mark.\n \n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "empty-topic"
+ ],
+ "subtopics": []
+ },
+ {
+ "question_id": "23M.2.SL.TZ2.6",
+ "Question": "
\n
\n (a)\n
\n
\n
\n Suggest an experimental method that could be used to determine the rate of reaction.\n
\n
\n
\n
\n
\n
\n (a)\n
\n
\n
\n Describe the interactions between amino acids occurring at the primary, secondary and tertiary levels within a protein.\n
\n
\n \n \n \n \n Structure Level\n \n | \n \n \n Interactions between amino acids\n \n | \n
\n \n \n Primary\n | \n \n ...........................................................\n | \n
\n \n \n Secondary\n | \n \n ...........................................................\n | \n
\n \n \n Tertiary\n | \n \n ...........................................................\n | \n
\n \n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n «measure change in»\n
\n mass\n
\n \n \n OR\n \n \n
\n pressure\n
\n \n \n OR\n \n \n
\n volume of gas/CO\n \n 2\n \n produced\n
\n \n \n OR\n \n \n
\n «intensity of» colour\n
\n \n \n OR\n \n \n
\n «electrical» conductivity\n
\n \n \n OR\n \n \n
\n pH ✓\n
\n
\n with time ✓\n
\n
\n
\n
\n \n Accept any of the following for M1:\n
\n perform experiment on balance\n
\n \n OR\n \n
\n use pressure probe\n
\n \n OR\n \n
\n collect gas/gas syringe\n
\n \n OR\n \n
\n use colorimeter\n
\n \n OR\n \n
\n use conductivity meter\n
\n \n OR\n \n
\n use pH meter\n \n
\n
\n \n Do\n \n not\n \n accept “measure rate of change” for M2.\n \n
\n
\n
\n (a)\n
\n
\n \n \n \n \n Structure Level\n \n | \n \n \n Interactions between amino acids\n \n | \n
\n \n \n Primary\n | \n \n covalent bonding\n \n \n \n OR\n \n \n \n peptide bond\n \n \n \n OR\n \n \n \n amide bond ✓\n | \n
\n \n \n Secondary\n | \n \n hydrogen bonding ✓\n | \n
\n \n \n Tertiary\n | \n \n interactions between R groups/side chains\n \n \n \n OR\n \n \n \n ionic/electrostatic «attraction»\n \n \n \n OR\n \n \n \n hydrogen bonding\n \n \n \n OR\n \n \n \n hydrophobic interactions\n \n \n \n OR\n \n \n \n disulfide bridges\n \n \n \n OR\n \n \n \n London/dispersion/van der Waals/«instantaneous» induced dipole-induced dipole ✓\n | \n
\n \n
\n
\n
\n
\n \n Do\n \n not\n \n accept “amino acid sequence” for M1.\n
\n \n
\n
\n \n Do\n \n not\n \n accept “alpha helix”\n \n OR\n \n “beta sheets” for M2.\n
\n \n
\n
\n \n Accept “covalent bonding” for M3.\n \n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "empty-topic"
+ ],
+ "subtopics": []
+ },
+ {
+ "question_id": "EXM.1B.HL.TZ0.1",
+ "Question": "
\n
\n (a)\n
\n
\n
\n The student reported the volumes of titrant used per trial for samples collected each day in the following table:\n
\n
\n
\n
\n
\n
\n
\n
\n
\n (i)\n
\n
\n
\n The candidate used a 25 cm\n \n 3\n \n burette with an uncertainty of ±0.05 cm\n \n 3\n \n . Comment on the uncertainty recorded for the titrant volumes.\n
\n
\n
\n
\n
\n
\n (ii)\n
\n
\n
\n Calculate the initial % content of Fe\n \n 2+\n \n in the raw spinach, showing your working.\n
\n
\n
\n
\n
\n
\n (iii)\n
\n
\n
\n The results calculated for the subsequent days are shown.\n
\n
\n
\n
\n
\n Comment on the significance of the difference in Fe\n \n 2+\n \n content measured for day 4 and 5.\n
\n
\n
\n
\n
\n
\n (i)\n
\n
\n
\n Suggest\n \n two\n \n flaws in the design that could have contributed to the random error in the investigation.\n
\n
\n
\n
\n
\n
\n (ii)\n
\n
\n
\n The student did not standardise the KMnO\n \n 4\n \n solution used for titration. Suggest what type of error this may have caused, giving your reasons.\n
\n
\n
\n
\n
\n
\n (i)\n
\n
\n
\n The titration of Fe(II) with MnO\n \n 4\n \n in acid medium is a redox reaction. State the oxidised and reduced species, including their change in oxidation states.\n
\n
\n
\n Oxidised: ........................................................................................................................................\n
\n
\n
\n Reduced: ........................................................................................................................................\n
\n
\n
\n
\n
\n
\n (ii)\n
\n
\n
\n Spinach contains a large amount of antioxidant compounds, including ascorbic acid and oxalic acid. Predict how this will affect the accuracy of the results, mentioning the type and direction of the error.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n Incorrect\n \n \n AND\n \n \n two readings, uncertainty is ±0.1 ✔\n
\n
\n
\n (i)\n
\n
\n Incorrect\n \n \n AND\n \n \n two readings, uncertainty is ±0.1 ✔\n
\n
\n
\n (ii)\n
\n
\n «mol» MnO\n \n 4−\n \n «=0.00339 × 0.01» = 3.38 × 10\n \n −5\n \n «mol» ✓\n
\n
\n «mol MnO\n \n 4−\n \n : mol Fe\n \n +2\n \n = 1:5»\n
\n
\n «mol» Fe\n \n 2+\n \n = 1.95 × 10\n \n −4\n \n ✓\n
\n
\n % Fe\n \n 2+\n \n «= 1.95 × 10\n \n −4\n \n × 55.8 × 100/2.0»= 0.47«%» ✓\n
\n
\n
\n
\n \n Must show working for the marks.\n \n
\n
\n
\n (iii)\n
\n
\n no difference\n \n \n AND\n \n \n uncertainty larger than difference ✔\n
\n
\n
\n
\n \n Accept other explanations referred to overlapping.\n \n
\n
\n
\n (i)\n
\n
\n dilute the titrant to use larger volumes «of titrant» ✔\n
\n
\n ensure spinach leaf fragments are the same size ✔\n
\n
\n
\n (ii)\n
\n
\n systematic error\n \n \n AND\n \n \n all values «equally» inaccurate ✔\n
\n
\n
\n (i)\n
\n
\n Oxidised: Fe\n \n +2\n \n → Fe\n \n +3\n \n ✔\n
\n
\n Reduced: Mn\n \n 7+\n \n → Mn\n \n 2+\n \n ✔\n
\n
\n
\n (ii)\n
\n
\n systematic error\n \n \n AND\n \n \n lower accuracy ✔\n
\n
\n overestimation of [Fe(II)] ✔\n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "inquiry",
+ "reactivity-3-what-are-the-mechanisms-of-chemical-change",
+ "tools"
+ ],
+ "subtopics": [
+ "inquiry-3-concluding-and-evaluating",
+ "reactivity-3-2-electron-transfer-reactions",
+ "tool-3-mathematics"
+ ]
+ },
+ {
+ "question_id": "EXM.1B.HL.TZ0.2",
+ "Question": "
\n
\n (a)\n
\n
\n
\n A calibration curve with pure ascorbic acid and appropriate amounts of the reagent, R, was prepared by dilutions with water of an initial aqueous solution of\n \n 100\n \n \n μg/cm\n \n −3\n \n \n ascorbic acid in water, AA (aq)\n
\n
\n
\n
\n
\n
\n (i)\n
\n
\n
\n Calculate the volumes of pure ascorbic acid solution required for each point of the calibration curve; point 4 of the curve is shown as an example.\n
\n
\n
\n
\n
\n
\n
\n
\n
\n (ii)\n
\n
\n
\n The resulting calibration curve is shown:\n
\n
\n
\n
\n
\n Suggest a range of absorbance values for which this curve can be used to calculate ascorbic acid of broccoli accurately.\n
\n
\n
\n
\n
\n
\n (iii)\n
\n
\n
\n Suggest what should be used as a blank for spectrophotometric reading.\n
\n
\n
\n
\n
\n
\n (iv)\n
\n
\n
\n Discuss why it is important to obtain a value of R\n \n 2\n \n close to 1 for a calibration curve.\n
\n
\n
\n
\n
\n
\n (i)\n
\n
\n
\n The sample stored at 5 °C showed an absorbance of 0.600. Determine the concentration of ascorbic acid in the sample solution by interpolation and using the line equation.\n
\n
\n
\n interpolation in graph: ..........................................................................................................................\n
\n
\n
\n using line equation: .............................................................................................................................\n
\n
\n
\n
\n
\n
\n (ii)\n
\n
\n
\n Suggest which of the two methods will provide a more accurate value.\n
\n
\n
\n
\n
\n
\n (c)\n
\n
\n
\n Suggest why water was chosen to extract ascorbic acid from the spinach leaves with reference to its structure.\n
\n
\n
\n
\n
\n
\n (i)\n
\n
\n
\n Estimate the % change in ascorbic acid concentration when stored for 3 days storage at 5 °C and 20 °C.\n
\n
\n
\n
\n
\n
\n (ii)\n
\n
\n
\n Estimate how much ascorbic acid will remain after 6 days storage at 20 °C in the same experimental conditions, stating any assumption made for the calculation.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n \n 1-\n \n 1.0 cm\n \n 3\n \n
\n
\n \n 2-\n \n 4.0 cm\n \n 3\n \n \n \n ✔\n
\n
\n \n 3-\n \n 8.0 cm\n \n 3\n \n
\n
\n \n 5-\n \n 4.0 cm\n \n 3\n \n \n \n \n \n ✔\n
\n
\n
\n
\n \n Award [1] for 2 correct answers\n \n
\n
\n
\n (i)\n
\n
\n \n 1-\n \n 1.0 cm\n \n 3\n \n
\n
\n \n 2-\n \n 4.0 cm\n \n 3\n \n \n \n ✔\n
\n
\n \n 3-\n \n 8.0 cm\n \n 3\n \n
\n
\n \n 5-\n \n 4.0 cm\n \n 3\n \n \n \n \n \n ✔\n
\n
\n
\n
\n \n Award [1] for 2 correct answers\n \n
\n
\n
\n (ii)\n
\n
\n (iii)\n
\n
\n water\n \n \n AND\n \n \n all samples dissolved «in water» ✔\n
\n
\n
\n (iv)\n
\n
\n ensures the line is best-fit ✔\n
\n
\n line/equation of the line will be used for quantitation ✔\n
\n
\n
\n
\n \n Accept any other explanations referring to accuracy.\n \n
\n
\n
\n (i)\n
\n
\n \n Interpolation:\n \n 9.8 μg cm\n \n −3\n \n ✔\n
\n
\n \n using equation:\n \n 0.600/0.06283 = 9.55 «μg cm\n \n −3\n \n »\n \n \n ✔\n
\n
\n
\n (ii)\n
\n
\n line equation\n \n \n AND\n \n \n uses the values for 5 determinations ✔\n
\n
\n
\n (c)\n
\n
\n «ascorbic acid» has multiple −OH/hydroxyl groups ✔\n
\n
\n can H-bond with water ✔\n
\n
\n
\n
\n \n Do not accept OH−/hydroxide for M1\n \n
\n
\n
\n (i)\n
\n
\n Δ % = «95.5 - 50.0/95.5 × 100»= 47.6 % ✔\n
\n
\n
\n
\n \n Accept calculations using line equation\n \n
\n
\n
\n (ii)\n
\n
\n assumption: linear decrease ✔\n
\n
\n rate «mg 100 g\n \n −1\n \n day\n \n −1\n \n = 95.5 − 50.0 / 3 » = 15 «mg 100 g\n \n −1\n \n day\n \n −1\n \n » ✔\n
\n
\n «95.5 − 15 × 6 = 5.5 «mg 100 g\n \n −1\n \n day\n \n −1\n \n » ✔\n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "inquiry",
+ "structure-2-models-of-bonding-and-structure",
+ "tools"
+ ],
+ "subtopics": [
+ "inquiry-1-exploring-and-designing",
+ "inquiry-2-collecting-and-processing-data",
+ "structure-2-2-the-covalent-model",
+ "tool-1-experimental-techniques",
+ "tool-3-mathematics"
+ ]
+ },
+ {
+ "question_id": "EXM.1B.SL.TZ0.1",
+ "Question": "
\n
\n (a)\n
\n
\n
\n The student reported the volumes of titrant used per trial for samples collected each day in the following table:\n
\n
\n
\n
\n
\n
\n
\n
\n
\n (i)\n
\n
\n
\n The candidate used a 25 cm\n \n 3\n \n burette with an uncertainty of ±0.05 cm\n \n 3\n \n . Comment on the uncertainty recorded for the titrant volumes.\n
\n
\n
\n
\n
\n
\n (ii)\n
\n
\n
\n Calculate the initial % content of Fe\n \n 2+\n \n in the raw spinach, showing your working.\n
\n
\n
\n
\n
\n
\n (iii)\n
\n
\n
\n The results calculated for the subsequent days are shown.\n
\n
\n
\n
\n
\n Comment on the significance of the difference in Fe\n \n 2+\n \n content measured for day 4 and 5.\n
\n
\n
\n
\n
\n
\n (i)\n
\n
\n
\n Suggest\n \n two\n \n flaws in the design that could have contributed to the random error in the investigation.\n
\n
\n
\n
\n
\n
\n (ii)\n
\n
\n
\n The student did not standardise the KMnO\n \n 4\n \n solution used for titration. Suggest what type of error this may have caused, giving your reasons.\n
\n
\n
\n
\n
\n
\n (i)\n
\n
\n
\n The titration of Fe(II) with MnO\n \n 4\n \n in acid medium is a redox reaction. State the oxidised and reduced species, including their change in oxidation states.\n
\n
\n
\n Oxidised: ........................................................................................................................................\n
\n
\n
\n Reduced: ........................................................................................................................................\n
\n
\n
\n
\n
\n
\n (ii)\n
\n
\n
\n Spinach contains a large amount of antioxidant compounds, including ascorbic acid and oxalic acid. Predict how this will affect the accuracy of the results, mentioning the type and direction of the error.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n Incorrect\n \n \n AND\n \n \n two readings, uncertainty is ±0.1 ✔\n
\n
\n
\n (i)\n
\n
\n Incorrect\n \n \n AND\n \n \n two readings, uncertainty is ±0.1 ✔\n
\n
\n
\n (ii)\n
\n
\n «mol» MnO\n \n 4−\n \n «=0.00339 × 0.01» = 3.38 × 10\n \n −5\n \n «mol» ✓\n
\n
\n «mol MnO\n \n 4−\n \n : mol Fe\n \n +2\n \n = 1:5»\n
\n
\n «mol» Fe\n \n 2+\n \n = 1.95 × 10\n \n −4\n \n ✓\n
\n
\n % Fe\n \n 2+\n \n «= 1.95 × 10\n \n −4\n \n × 55.8 × 100/2.0»= 0.47«%» ✓\n
\n
\n
\n
\n \n Must show working for the marks.\n \n
\n
\n
\n (iii)\n
\n
\n no difference\n \n \n AND\n \n \n uncertainty larger than difference ✔\n
\n
\n
\n
\n \n Accept other explanations referred to overlapping.\n \n
\n
\n
\n (i)\n
\n
\n dilute the titrant to use larger volumes «of titrant» ✔\n
\n
\n ensure spinach leaf fragments are the same size ✔\n
\n
\n
\n (ii)\n
\n
\n systematic error\n \n \n AND\n \n \n all values «equally» inaccurate ✔\n
\n
\n
\n (i)\n
\n
\n Oxidised: Fe\n \n +2\n \n → Fe\n \n +3\n \n ✔\n
\n
\n Reduced: Mn\n \n 7+\n \n → Mn\n \n 2+\n \n ✔\n
\n
\n
\n (ii)\n
\n
\n systematic error\n \n \n AND\n \n \n lower accuracy ✔\n
\n
\n overestimation of [Fe(II)] ✔\n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "inquiry",
+ "reactivity-3-what-are-the-mechanisms-of-chemical-change",
+ "tools"
+ ],
+ "subtopics": [
+ "inquiry-3-concluding-and-evaluating",
+ "reactivity-3-2-electron-transfer-reactions",
+ "tool-3-mathematics"
+ ]
+ },
+ {
+ "question_id": "EXM.1B.SL.TZ0.2",
+ "Question": "
\n
\n (a)\n
\n
\n
\n A calibration curve with pure ascorbic acid and appropriate amounts of the reagent, R, was prepared by dilutions with water of an initial aqueous solution of\n \n 100\n \n \n μg/cm\n \n −3\n \n \n ascorbic acid in water, AA (aq)\n
\n
\n
\n
\n
\n
\n (i)\n
\n
\n
\n Calculate the volumes of pure ascorbic acid solution required for each point of the calibration curve; point 4 of the curve is shown as an example.\n
\n
\n
\n
\n
\n
\n
\n
\n
\n (ii)\n
\n
\n
\n The resulting calibration curve is shown:\n
\n
\n
\n
\n
\n Suggest a range of absorbance values for which this curve can be used to calculate ascorbic acid of broccoli accurately.\n
\n
\n
\n
\n
\n
\n (iii)\n
\n
\n
\n Suggest what should be used as a blank for spectrophotometric reading.\n
\n
\n
\n
\n
\n
\n (iv)\n
\n
\n
\n Discuss why it is important to obtain a value of R\n \n 2\n \n close to 1 for a calibration curve.\n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n
\n After 3 days, the broccoli samples were removed from storage and 1.0 g of each sample was blended with 100.0 cm\n \n 3\n \n of water. The filtered solution was mixed with the reactant in the same proportions as that used for the calibration curve in a cuvette and measured.\n
\n
\n The sample stored at 5 °C showed an absorbance of 0.600. Determine the concentration of ascorbic acid in the sample solution by interpolation and using the line equation.\n
\n
\n
\n interpolation in graph: ..........................................................................................................................\n
\n
\n
\n using line equation: .............................................................................................................................\n
\n
\n
\n
\n
\n
\n
\n
\n
\n
\n (c)\n
\n
\n
\n Suggest why water was chosen to extract ascorbic acid from the spinach leaves with reference to its structure.\n
\n
\n
\n
\n
\n
\n (i)\n
\n
\n
\n Estimate the % change in ascorbic acid concentration when stored for 3 days storage at 5 °C and 20 °C.\n
\n
\n
\n
\n
\n
\n (ii)\n
\n
\n
\n Estimate how much ascorbic acid will remain after 6 days storage at 20 °C in the same experimental conditions, stating any assumption made for the calculation.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n \n 1-\n \n 1.0 cm\n \n 3\n \n
\n
\n \n 2-\n \n 4.0 cm\n \n 3\n \n \n \n ✔\n
\n
\n \n 3-\n \n 8.0 cm\n \n 3\n \n
\n
\n \n 5-\n \n 4.0 cm\n \n 3\n \n \n \n \n \n ✔\n
\n
\n
\n
\n \n Award [1] for 2 correct answers\n \n
\n
\n
\n (i)\n
\n
\n \n 1-\n \n 1.0 cm\n \n 3\n \n
\n
\n \n 2-\n \n 4.0 cm\n \n 3\n \n \n \n ✔\n
\n
\n \n 3-\n \n 8.0 cm\n \n 3\n \n
\n
\n \n 5-\n \n 4.0 cm\n \n 3\n \n \n \n \n \n ✔\n
\n
\n
\n
\n \n Award [1] for 2 correct answers\n \n
\n
\n
\n (ii)\n
\n
\n (iii)\n
\n
\n water\n \n \n AND\n \n \n all samples dissolved «in water» ✔\n
\n
\n
\n (iv)\n
\n
\n ensures the line is best-fit ✔\n
\n
\n line/equation of the line will be used for quantitation ✔\n
\n
\n
\n
\n \n Accept any other explanations referring to accuracy.\n \n
\n
\n
\n (b)\n
\n
\n \n Interpolation:\n \n 9.8\n \n μg\n \n cm\n \n −3\n \n ✔\n
\n
\n \n using equation:\n \n 0.600/0.06283 = 9.55 «\n \n μg\n \n cm\n \n −3\n \n »\n \n \n ✔\n
\n
\n
\n (c)\n
\n
\n «ascorbic acid» has multiple −OH/hydroxyl groups ✔\n
\n
\n can H-bond with water ✔\n
\n
\n
\n
\n \n Do not accept OH−/hydroxide for M1\n \n
\n
\n
\n (i)\n
\n
\n Δ % = «95.5 - 50.0/95.5 × 100»= 47.6 % ✔\n
\n
\n
\n
\n \n Accept calculations using line equation\n \n
\n
\n
\n (ii)\n
\n
\n assumption: linear decrease ✔\n
\n
\n rate «mg 100 g\n \n −1\n \n day\n \n −1\n \n = 95.5 − 50.0 / 3 » = 15 «mg 100 g\n \n −1\n \n day\n \n −1\n \n » ✔\n
\n
\n «95.5 − 15 × 6 = 5.5 «mg 100 g\n \n −1\n \n day\n \n −1\n \n » ✔\n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "inquiry",
+ "structure-2-models-of-bonding-and-structure",
+ "tools"
+ ],
+ "subtopics": [
+ "inquiry-1-exploring-and-designing",
+ "inquiry-2-collecting-and-processing-data",
+ "structure-2-2-the-covalent-model",
+ "tool-1-experimental-techniques",
+ "tool-3-mathematics"
+ ]
+ },
+ {
+ "question_id": "EXM.2.HL.TZ0.2",
+ "Question": "
\n
\n (a)\n
\n
\n
\n Determine the ratio in which 0.1 mol dm\n \n –3\n \n NaH\n \n 2\n \n PO\n \n 4\n \n and 0.1 mol dm\n \n –3\n \n Na\n \n 2\n \n HPO\n \n 4\n \n should be mixed to obtain a buffer with pH= 7.8.\n
\n
\n p\n \n K\n \n \n a\n \n NaH\n \n 2\n \n PO\n \n 4\n \n = 7.20\n
\n
\n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n
\n Suggest, giving your reasons, the effect of diluting the buffer 1/100 with water on its pH and reaction to the addition of acids or bases.\n
\n
\n
\n
\n change in pH:\n
\n
\n .............................................................................................................................................................\n
\n
\n .............................................................................................................................................................\n
\n
\n
\n
\n reaction to addition of bases/acids:\n
\n
\n .............................................................................................................................................................\n
\n
\n .............................................................................................................................................................\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n \n
\n
\n \n «\n \n » 0.6 ✓\n
\n
\n \n «\n \n » 3.98 ✓\n
\n
\n Na\n \n 2\n \n PO\n \n 4\n \n to Na\n \n 2\n \n HPO\n \n 4\n \n = 3.98:1 ✓\n
\n
\n
\n (a)\n
\n
\n \n
\n
\n \n «\n \n » 0.6 ✓\n
\n
\n \n «\n \n » 3.98 ✓\n
\n
\n Na\n \n 2\n \n PO\n \n 4\n \n to Na\n \n 2\n \n HPO\n \n 4\n \n = 3.98:1 ✓\n
\n
\n
\n (b)\n
\n
\n \n change in pH:\n \n
\n
\n no «significant» effect as ratio of salt/acid are unchanged ✓\n
\n
\n
\n
\n \n reaction to addition of bases/acids:\n \n
\n
\n resistance to change/buffering capacity decreases ✓\n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "reactivity-3-what-are-the-mechanisms-of-chemical-change"
+ ],
+ "subtopics": [
+ "reactivity-3-1-proton-transfer-reactions"
+ ]
+ }
+]
\ No newline at end of file
diff --git a/assets/jsonqb/Physics 2025 QB merged.json b/assets/jsonqb/Physics 2025 QB merged.json
new file mode 100644
index 0000000..9fda93e
--- /dev/null
+++ b/assets/jsonqb/Physics 2025 QB merged.json
@@ -0,0 +1,2272 @@
+[
+ {
+ "question_id": "19M.3.SL.TZ1.1",
+ "Question": "
\n
In an experiment to measure the acceleration of free fall a student ties two different blocks of masses m1 and m2 to the ends of a string that passes over a frictionless pulley.
\n

\n
The student calculates the acceleration a of the blocks by measuring the time taken by the heavier mass to fall through a given distance. Their theory predicts that and this can be re-arranged to give .
\n
In a particular experiment the student calculates that a = (0.204 ±0.002) ms–2 using m1 = (0.125 ±0.001) kg and m2 = (0.120 ±0.001) kg.
\n
\n
Calculate the percentage error in the measured value of g.
\n
[3]
\n
a.i.
\n
\n
Deduce the value of g and its absolute uncertainty for this experiment.
\n
[2]
\n
a.ii.
\n
\n
There is an advantage and a disadvantage in using two masses that are almost equal.
\n
State and explain the advantage with reference to the magnitude of the acceleration that is obtained.
\n
[2]
\n
b.i.
\n
\n
There is an advantage and a disadvantage in using two masses that are almost equal.
\n
State and explain the disadvantage with reference to your answer to (a)(ii).
\n
[2]
\n
b.ii.
\n
",
+ "Markscheme": "
\n
error in m1 + m2 is 1 % OR error in m1 − m2 is 40 % OR error in a is 1 % ✔
\n
adds percentage errors ✔
\n
so error in g is 42 % OR 40 % OR 41.8 % ✔
\n
Allow answer 0.42 or 0.4 or 0.418.
\n
Award [0] for comparing the average value with a known value, e.g. 9.81 m s-2.
\n
a.i.
\n
\n
g = 9.996 «m s−2» OR Δg = 4.20 «m s−2» ✔
\n
g = (10 ± 4) «m s−2»
\n
OR
\n
g = (10.0 ± 4.2) «m s−2» ✔
\n
Award [1] max for not proper significant digits or decimals use, such as: 9.996±4.178 or 10±4.2 or 10.0±4 or 10.0±4.18« m s−2 » .
\n
a.ii.
\n
\n
the acceleration would be small/the time of fall would be large ✔
\n
easier to measure /a longer time of fall reduces the % error in the time of fall and «hence acceleration» ✔
\n
Do not accept ideas related to the mass/moment of inertia of the pulley.
\n
b.i.
\n
\n
the percentage error in the difference of the masses is large ✔
\n
leading to a large percentage error/uncertainty in g/of the experiment ✔
\n
Do not accept ideas related to the mass/moment of inertia of the pulley.
\n
b.ii.
\n
",
+ "Examiners report": "
\n
Atwoods machine a) is a quite straightforward question that tests the ability to propagate uncertainties through calculations. Almost all candidates proved the ability to add percentages or relative calculations, however, many weaker candidates failed in the percentage uncertainty when subtracting the two masses.
\n
a.i.
\n
\n
Many average candidates did not use the correct number of significant figures and wrote the answers inappropriately. Only the best candidates rounded out and wrote the proper answer of 10±4 ms−2. Some candidates did not propagate uncertainties and only compared the average calculated value with the known value 9.81 ms−2.
\n
a.ii.
\n
\n
Q 1 b) was quite well answered. Only the weakest candidates presented difficulty in understanding simple mechanics.
\n
b.i.
\n
\n
In part ii) many were able to appreciate that the resultant percentage error in “g” was relatively large however linking this with what caused the large uncertainty (that is, the high % error from the small difference in masses) proved more challenging.
\n
b.ii.
\n
",
+ "topics": [
+ "inquiry",
+ "tools"
+ ],
+ "subtopics": [
+ "i-1-3-controlling-variables",
+ "inquiry-1-exploring-and-designing",
+ "tool-3-mathematics"
+ ]
+ },
+ {
+ "question_id": "19M.3.SL.TZ2.1",
+ "Question": "
\n
A student investigates the electromotive force (emf) ε and internal resistance r of a cell.
\n

\n
The current I and the terminal potential difference V are measured.
\n
For this circuit V = ε - Ir .
\n
The table shows the data collected by the student. The uncertainties for each measurement
are shown.
\n

\n
The graph shows the data plotted.
\n

\n
\n
The student has plotted error bars for the potential difference. Outline why no error bars are shown for the current.
\n
[1]
\n
a.
\n
\n
Determine, using the graph, the emf of the cell including the uncertainty for this value. Give your answer to the correct number of significant figures.
\n
[3]
\n
b.
\n
\n
Outline, without calculation, how the internal resistance can be determined from this graph.
\n
[2]
\n
c.
\n
",
+ "Markscheme": "
\n
ΔI is too small to be shown/seen
\n
OR
\n
Error bar of negligible size compared to error bar in V ✔
\n
a.
\n
\n
evidence that ε can be determined from the y-intercept of the line of best-fit or lines of min and max gradient ✔
\n
states ε=1.59 OR 1.60 OR 1.61V«» ✔
\n
states uncertainty in ε is 0.02 V«» OR 0.03«V» ✔
\n
b.
\n
\n
determine the gradient «of the line of best-fit» ✔
\n
r is the negative of this gradient ✔
\n
c.
\n
",
+ "Examiners report": "
\n
Almost all candidates realised that the uncertainty in I was too small to be shown. A common mistake was to mention that since I is the independent variable the uncertainty is negligible.
\n
a.
\n
\n
The number of candidates who realised that the V intercept was EMF was disappointing. Large numbers of candidates tried to calculate ε using points on the graph, often ending up with unrealistic values. Another common mistake was not giving values of ε and Δε to the correct number of digits - 2 decimal places on this occasion. Very few candidates drew maximum and minimum gradient lines as a way of determining Δε.
\n
b.
\n
",
+ "topics": [
+ "inquiry",
+ "tools"
+ ],
+ "subtopics": [
+ "i-2-1-collecting-data",
+ "inquiry-2-collecting-and-processing-data",
+ "tool-3-mathematics"
+ ]
+ },
+ {
+ "question_id": "19M.3.SL.TZ2.3",
+ "Question": "
\n
A student uses a Young’s double-slit apparatus to determine the wavelength of light emitted by a monochromatic source. A portion of the interference pattern is observed on a screen.
\n

\n
The distance D from the double slits to the screen is measured using a ruler with a smallest scale division of 1 mm.
\n
The fringe separation s is measured with uncertainty ± 0.1 mm.
\n
The slit separation d has negligible uncertainty.
\n
The wavelength is calculated using the relationship .
\n
\n
When d = 0.200 mm, s = 0.9 mm and D = 280 mm, determine the percentage uncertainty in the wavelength.
\n
[2]
\n
a.
\n
\n
Explain how the student could use this apparatus to obtain a more reliable value for λ.
\n
[2]
\n
b.
\n
",
+ "Markscheme": "
\n
Evidence of used ✔
\n
«add fractional/% uncertainties»
\n
obtains 11 % (or 0.11) OR 10 % (or 0.1) ✔
\n
a.
\n
\n
ALTERNATIVE 1:
\n
measure the combined width for several fringes
\n
OR
\n
repeat measurements ✓
\n
take the average
\n
OR
\n
so the «percentage» uncertainties are reduced ✓
\n
ALTERNATIVE 2:
\n
increase D «hence s»
\n
OR
\n
Decrease d ✓
\n
so the «percentage» uncertainties are reduced ✓
\n
Do not accept answers which suggest using different apparatus.
\n
b.
\n
",
+ "Examiners report": "
\n
A very easy question about percentage uncertainty which most candidates got completely correct. Many candidates gave the uncertainty to 4 significant figures or more. The process used to obtain the final answer was often difficult to follow.
\n
a.
\n
\n
The most common correct answer was the readings should be repeated and an average taken. Another common answer was that D could be increased to reduce uncertainties in s. The best candidates knew that it was good practice to measure many fringe spacings and find the mean value. Quite a few candidates incorrectly stated that different apparatus should be used to give more precise results.
\n
b.
\n
",
+ "topics": [
+ "inquiry",
+ "tools"
+ ],
+ "subtopics": [
+ "i-3-2-evaluating",
+ "inquiry-3-concluding-and-evaluating",
+ "tool-3-mathematics"
+ ]
+ },
+ {
+ "question_id": "19M.2.HL.TZ1.2",
+ "Question": "
\n
A beam of electrons each of de Broglie wavelength 2.4 × 10–15 m is incident on a thin film of silicon-30 . The variation in the electron intensity of the beam with scattering angle is shown.
\n

\n
\n
Use the graph to show that the nuclear radius of silicon-30 is about 4 fm.
\n
[3]
\n
a.i.
\n
\n
Estimate, using the result from (a)(i), the nuclear radius of thorium-232 .
\n
[2]
\n
a.ii.
\n
\n
Suggest one reason why a beam of electrons is better for investigating the size of a nucleus than a beam of alpha particles of the same energy.
\n
[1]
\n
a.iii.
\n
\n
Outline why deviations from Rutherford scattering are observed when high-energy alpha particles are incident on nuclei.
\n
[2]
\n
a.iv.
\n
",
+ "Markscheme": "
\n
read off between 17 and 19 «deg» ✔
\n
correct use of d = = 7.8 × 10−15 «m» ✔
\n
so radius = «fm» = 3.9 «fm» ✔
\n
Award ecf for wrong angle in MP1.
\n
Answer for MP3 must show at least 2 sf.
\n
a.i.
\n
\n
RTh = Rsi or substitution ✔
\n
7.4 «fm» ✔
\n
a.ii.
\n
\n
electron wavelength shorter than alpha particles (thus increased resolution)
OR
electron is not subject to strong nuclear force ✔
\n
\n
a.iii.
\n
\n
nuclear forces act ✔
\n
nuclear recoil occurs ✔
\n
significant penetration into nucleus / probing internal structure of individual nucleons ✔
\n
incident particles are relativistic ✔
\n
a.iv.
\n
",
+ "Examiners report": "
\n
This question was left blank by many candidates and many of those who attempted it chose an angle that when used with the correct equation gave an answer close to the given answer of 4 fm. Very few selected the correct angle, calculated the correct diameter, and divided by two to get the correct radius.
\n
a.i.
\n
\n
This question was also left blank by many candidates. Many who did answer simply used the ratio of the of the mass numbers of the two elements and failed to take the cube root of the ratio. It should be noted that the question specifically stated that candidates were expected to use the result from 2ai, and not just simply guess at the new radius.
\n
a.ii.
\n
\n
This question was very poorly answered with the vast majority of candidates simply listing differences between alpha particles and electrons (electrons have less mass, electrons have less charge, etc) rather than considering why high speed electrons would be better for studying the nucleus.
\n
a.iii.
\n
\n
Candidates struggled with this question. The vast majority of responses were descriptions of Rutherford scattering with no connection made to the deviations when high-energy alpha particles are used. Many of the candidates who did appreciate that this was a different situation from the traditional experiment made vague comments about the alpha particles “hitting” the nucleus.
\n
a.iv.
\n
",
+ "topics": [
+ "c-wave-behaviour"
+ ],
+ "subtopics": [
+ "c-3-wave-phenomena"
+ ]
+ },
+ {
+ "question_id": "19M.2.HL.TZ1.3",
+ "Question": "
\n
A beam of microwaves is incident normally on a pair of identical narrow slits S1 and S2.
\n

\n
When a microwave receiver is initially placed at W which is equidistant from the slits, a maximum in intensity is observed. The receiver is then moved towards Z along a line parallel to the slits. Intensity maxima are observed at X and Y with one minimum between them. W, X and Y are consecutive maxima.
\n
\n
Explain why intensity maxima are observed at X and Y.
\n
[2]
\n
a.
\n
\n
The distance from S1 to Y is 1.243 m and the distance from S2 to Y is 1.181 m.
\n
Determine the frequency of the microwaves.
\n
[3]
\n
b.
\n
\n
Outline one reason why the maxima observed at W, X and Y will have different intensities from each other.
\n
[1]
\n
c.
\n
\n
The microwaves emitted by the transmitter are horizontally polarized. The microwave receiver contains a polarizing filter. When the receiver is at position W it detects a maximum intensity.
\n

\n
The receiver is then rotated through 180° about the horizontal dotted line passing through the microwave transmitter. Sketch a graph on the axes provided to show the variation of received intensity with rotation angle.
\n

\n
[2]
\n
d.
\n
",
+ "Markscheme": "
\n
two waves superpose/mention of superposition/mention of «constructive» interference ✔
\n
they arrive in phase/there is a path length difference of an integer number of wavelengths ✔
\n
a.
\n
\n
path difference = 0.062 «m»✔
\n
so wavelength = 0.031 «m»✔
\n
frequency = 9.7 × 109 «Hz»✔
\n
Award [2 max] for 4.8 x 109 Hz.
\n
b.
\n
\n
intensity is modulated by a single slit diffraction envelope OR
\n
intensity varies with distance OR points are different distances from the slits ✔
\n
c.
\n
\n

\n
cos2 variation shown ✔
\n
with zero at 90° (by eye) ✔
\n
Award [1 max] for an inverted curve with maximum at 90°.
\n
d.
\n
",
+ "Examiners report": "
\n
Many candidates were able to discuss the interference that is taking place in this question, but few were able to fully describe the path length difference. That said, the quality of responses on this type of question seems to have improved over the last few examination sessions with very few candidates simply discussing the crests and troughs of waves.
\n
a.
\n
\n
Many candidates struggled with this question. Few were able to calculate a proper path length difference, and then use that to calculate the wavelength and frequency. Many candidates went down blind paths of trying various equations from the data booklet, and some seemed to believe that the wavelength is just the reciprocal of the frequency.
\n
b.
\n
\n
This is one of many questions on this paper where candidates wrote vague answers that did not clearly connect to physics concepts or include key information. There were many overly simplistic answers like “they are farther away” without specifying what they are farther away from. Candidates should be reminded that their responses should go beyond the obvious and include some evidence of deeper understanding.
\n
c.
\n
\n
This question was generally well answered, with many candidates at least recognizing that the intensity would decrease to zero at 90 degrees. Many struggled with the exact shape of the graph, though, and some drew a graph that extended below zero showing a lack of understanding of what was being graphed.
\n
d.
\n
",
+ "topics": [
+ "a--space-time-and-motion",
+ "c-wave-behaviour"
+ ],
+ "subtopics": [
+ "a-5-galilean-and-special-relativity",
+ "c-2-wave-model",
+ "c-3-wave-phenomena"
+ ]
+ },
+ {
+ "question_id": "19M.2.HL.TZ1.5",
+ "Question": "
\n
The moon Phobos moves around the planet Mars in a circular orbit.
\n
\n
Outline the origin of the force that acts on Phobos.
\n
[1]
\n
a.i.
\n
\n
Outline why this force does no work on Phobos.
\n
[1]
\n
a.ii.
\n
\n
The orbital period T of a moon orbiting a planet of mass M is given by
\n
\n
where R is the average distance between the centre of the planet and the centre of the moon.
\n
Show that
\n
[3]
\n
b.i.
\n
\n
The following data for the Mars–Phobos system and the Earth–Moon system are available:
\n
Mass of Earth = 5.97 × 1024 kg
\n
The Earth–Moon distance is 41 times the Mars–Phobos distance.
\n
The orbital period of the Moon is 86 times the orbital period of Phobos.
\n
Calculate, in kg, the mass of Mars.
\n
[2]
\n
b.ii.
\n
\n
The graph shows the variation of the gravitational potential between the Earth and Moon with distance from the centre of the Earth. The distance from the Earth is expressed as a fraction of the total distance between the centre of the Earth and the centre of the Moon.
\n

\n
Determine, using the graph, the mass of the Moon.
\n
[3]
\n
c.
\n
",
+ "Markscheme": "
\n
gravitational attraction/force/field «of the planet/Mars» ✔
\n
Do not accept “gravity”.
\n
a.i.
\n
\n
the force/field and the velocity/displacement are at 90° to each other OR
\n
there is no change in GPE of the moon/Phobos ✔
\n
a.ii.
\n
\n
ALTERNATE 1
\n
«using fundamental equations»
\n
use of Universal gravitational force/acceleration/orbital velocity equations ✔
\n
equating to centripetal force or acceleration. ✔
\n
rearranges to get ✔
\n
ALTERNATE 2
\n
«starting with »
\n
substitution of proper equation for T from orbital motion equations ✔
\n
substitution of proper equation for M OR R from orbital motion equations ✔
\n
rearranges to get ✔
\n
b.i.
\n
\n
or other consistent re-arrangement ✔
\n
6.4 × 1023 «kg» ✔
\n
\n
b.ii.
\n
\n
read off separation at maximum potential 0.9 ✔
\n
equating of gravitational field strength of earth and moon at that location OR
✔
\n
7.4 × 1022 «kg» ✔
\n
Allow ECF from MP1
\n
c.
\n
",
+ "Examiners report": "
\n
This was generally well answered, although some candidates simply used the vague term “gravity” rather than specifying that it is a gravitational force or a gravitational field. Candidates need to be reminded about using proper physics terms and not more general, “every day” terms on the exam.
\n
a.i.
\n
\n
Some candidates connected the idea that the gravitational force is perpendicular to the velocity (and hence the displacement) for the mark. It was also allowed to discuss that there is no change in gravitational potential energy, so therefore no work was being done. It was not acceptable to simply state that the net displacement over one full orbit is zero. Unfortunately, some candidates suggested that there is no net force on the moon so there is no work done, or that the moon is so much smaller so no work could be done on it.
\n
a.ii.
\n
\n
This was another “show that” derivation. Many candidates attempted to work with universal gravitation equations, either from memory or the data booklet, to perform this derivation. The variety of correct solution paths was quite impressive, and many candidates who attempted this question were able to receive some marks. Candidates should be reminded on “show that” questions that it is never allowed to work backwards from the given answer. Some candidates also made up equations (such as T = 2𝝿r) to force the derivation to work out.
\n
b.i.
\n
\n
This question was challenging for candidates. The candidates who started down the correct path of using the given derived value from 5bi often simply forgot that the multiplication factors had to be squared and cubed as well as the variables.
\n
b.ii.
\n
\n
This question was left blank by many candidates, and very few who attempted it were able to successfully recognize that the gravitational fields of the Earth and Moon balance at 0.9r and then use the proper equation to calculate the mass of the Moon.
\n
c.
\n
",
+ "topics": [
+ "a--space-time-and-motion",
+ "d-fields"
+ ],
+ "subtopics": [
+ "a-2-forces-and-momentum",
+ "a-3-work-energy-and-power",
+ "d-1-gravitational-fields"
+ ]
+ },
+ {
+ "question_id": "19M.2.HL.TZ1.6",
+ "Question": "
\n
A small metal pendulum bob is suspended at rest from a fixed point with a length of thread of negligible mass. Air resistance is negligible.
\n
The pendulum begins to oscillate. Assume that the motion of the system is simple harmonic, and in one vertical plane.
\n
The graph shows the variation of kinetic energy of the pendulum bob with time.
\n

\n
\n
When the 75 g bob is moving horizontally at 0.80 m s–1, it collides with a small stationary object also of mass 75 g. The object and the bob stick together.
\n

\n
\n
Calculate, in m, the length of the thread. State your answer to an appropriate number of significant figures.
\n
[3]
\n
a.i.
\n
\n
Label on the graph with the letter X a point where the speed of the pendulum is half that of its initial speed.
\n
[1]
\n
a.ii.
\n
\n
The mass of the pendulum bob is 75 g. Show that the maximum speed of the bob is about 0.7 m s–1.
\n
[2]
\n
a.iii.
\n
\n
Calculate the speed of the combined masses immediately after the collision.
\n
[1]
\n
b.i.
\n
\n
Show that the collision is inelastic.
\n
[3]
\n
b.ii.
\n
\n
Sketch, on the axes, a graph to show the variation of gravitational potential energy with time for the bob and the object after the collision. The data from the graph used in (a) is shown as a dashed line for reference.
\n

\n
[2]
\n
b.iii.
\n
\n
The speed after the collision of the bob and the object was measured using a sensor. This sensor emits a sound of frequency f and this sound is reflected from the moving bob. The sound is then detected by the sensor as frequency f′.
\n
Explain why f and f′ are different.
\n
[3]
\n
b.iv.
\n
",
+ "Markscheme": "
\n
identifies T as 2.25 s ✔
\n
L = 1.26 m ✔
\n
1.3 / 1.26 «m» ✔
\n
Accept any number of s.f. for MP2.
\n
Accept any answer with 2 or 3 s.f. for MP3.
\n
a.i.
\n
\n
X labels any point on the curve where EK of maximum/5 mJ ✔
\n
a.ii.
\n
\n
mv2 = 20 × 10−3 seen OR × 7.5 × 10-2 × v2 = 20 × 10-3 ✔
\n
0.73 «m s−1» ✔
\n
Must see at least 2 s.f. for MP2.
\n
a.iii.
\n
\n
initial energy 24 mJ and final energy 12 mJ ✔
\n
energy is lost/unequal /change in energy is 12 mJ ✔
\n
inelastic collisions occur when energy is lost ✔
\n
b.ii.
\n
\n
graph with same period but inverted ✔
\n
amplitude one half of the original/two boxes throughout (by eye) ✔
\n
b.iii.
\n
\n
mention of Doppler effect ✔
\n
there is a change in the wavelength of the reflected wave ✔
\n
because the wave speed is constant, there is a change in frequency ✔
\n
b.iv.
\n
",
+ "Examiners report": "
\n
This question was well approached by candidates. The noteworthy mistakes were not reading the correct period of the pendulum from the graph, and some simple calculation and mathematical errors. This question also had one mark for writing an answer with the correct number of significant digits. Candidates should be aware to look for significant digit question on the exam and can write any number with correct number of significant digits for the mark.
\n
a.i.
\n
\n
This question was well answered. This is a “show that” question so candidates needed to clearly show the correct calculation and write an answer with at least one significant digit more than the given answer. Many candidates failed to appreciate that the energy was given in mJ and the mass was in grams, and that these values needed to be converted before substitution.
\n
a.iii.
\n
\n
Candidates fell into some broad categories on this question. This was a “show that” question, so there was an expectation of a mathematical argument. Many were able to successfully show that the initial and final kinetic energies were different and connect this to the concept of inelastic collisions. Some candidates tried to connect conservation of momentum unsuccessfully, and some simply wrote an extended response about the nature of inelastic collisions and noted that the bobs stuck together without any calculations. This approach was awarded zero marks.
\n
b.ii.
\n
\n
Many candidates drew graphs that received one mark for either recognizing the phase difference between the gravitational potential energy and the kinetic energy, or for recognizing that the total energy was half the original energy. Few candidates had both features for both marks.
\n
b.iii.
\n
\n
This question was essentially about the Doppler effect, and therefore candidates were expected to give a good explanation for why there is a frequency difference. As with all explain questions, the candidates were required to go beyond the given information. Very few candidates earned marks beyond just recognizing that this was an example of the Doppler effect. Some did discuss the change in wavelength caused by the relative motion of the bob, although some candidates chose very vague descriptions like “the waves are all squished up” rather than using proper physics terms. Some candidates simply wrote and explained the equation from the data booklet, which did not receive marks. It should be noted that this was a three mark question, and yet some candidates attempted to answer it with a single sentence.
\n
b.iv.
\n
",
+ "topics": [
+ "a--space-time-and-motion"
+ ],
+ "subtopics": [
+ "a-4-rigid-body-mechanics"
+ ]
+ },
+ {
+ "question_id": "19M.2.HL.TZ1.7",
+ "Question": "
\n
\n (a)\n
\n
\n
\n Show that during an adiabatic expansion of an ideal monatomic gas the temperature\n \n \n \n \n \n and volume\n \n \n \n \n \n are given by\n
\n
\n \n \n \n \n \n = constant\n
\n
\n
\n
\n
\n
\n (b.i)\n
\n
\n
\n Calculate the efficiency of the cycle.\n
\n
\n
\n
\n
\n
\n (b.ii)\n
\n
\n
\n The work done during the isothermal expansion A → B is 540 J. Calculate the thermal energy that leaves the gas during one cycle.\n
\n
\n
\n
\n
\n
\n (b.iii)\n
\n
\n
\n Calculate the ratio\n \n \n \n \n \n where\n \n V\n \n C\n \n \n is the volume of the gas at C and\n \n V\n \n B\n \n \n is the volume at B.\n
\n
\n
\n
\n
\n
\n (c.i)\n
\n
\n
\n Calculate the change in the entropy of the gas during the change A to B.\n
\n
\n
\n
\n
\n
\n (c.ii)\n
\n
\n
\n Explain, by reference to the second law of thermodynamics, why a real engine operating between the temperatures of 620 K and 340 K cannot have an efficiency greater than the answer to (b)(i).\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n substitution of\n \n \n \n \n in\n \n \n \n \n ✔\n
\n
\n manipulation to get result ✔\n
\n
\n
\n (b.i)\n
\n
\n e « = 1 −\n \n \n \n \n \n = 1 −\n \n \n \n » = 0.45 ✔\n
\n
\n
\n (b.ii)\n
\n
\n heat into gas «is along AB» and equals\n
\n
\n \n Q\n \n in\n \n \n «= Δ\n \n U\n \n +\n \n W\n \n = 0 + 540» = 540 «J» ✔\n
\n
\n heat out is (1−\n \n e\n \n )\n \n Q\n \n in =\n \n \n (1−0.45) × 540 = 297 «J» ≈ 3.0 × 10\n \n 2\n \n «J» ✔\n
\n
\n \n Award\n \n [2]\n \n for bald correct answer.\n \n
\n
\n
\n (b.iii)\n
\n
\n \n \n \n \n \n ✔\n
\n
\n \n \n \n \n \n ✔\n
\n
\n \n Award\n \n [2]\n \n for bald correct answer.\n \n
\n
\n
\n (c.i)\n
\n
\n Δ\n \n S\n \n «=\n \n \n \n =\n \n \n \n »= 0.87 «JK\n \n −1\n \n » ✔\n
\n
\n
\n (c.ii)\n
\n
\n the Carnot cycle has the maximum efficiency «for heat engines operating between two given temperatures »✔\n
\n
\n real engine can not work at Carnot cycle/ideal cycle ✔\n
\n
\n the second law of thermodynamics says that it is impossible to convert all the input heat into mechanical work ✔\n
\n
\n a real engine would have additional losses due to friction\n \n etc\n \n ✔\n
\n
\n",
+ "Examiners report": "
\n (a)\n
\n
\n The algebraic manipulation required for this question was well mastered by only the better-prepared candidates. Many candidates tried to find the required formula via randomly selected equations from the data booklet.\n
\n
\n
\n (b.i)\n
\n
\n The efficiency of the Carnot cycle was well calculated by most of the candidates, but the thermal energy that leaves the gas was well calculated only by the best candidates. Many candidates were able to establish that the heat added to the gas was 540 J - but struggled to then link this with the efficiency to determine the thermal energy leaving the gas. In iii) the better candidates used the formula given at i) to appropriately calculate the ratio but many were not able to manipulate the expressions to achieve the desired outcome. The reciprocal of 2.5 (0.4) was a common error in the final result and so was the incorrect use of the formula for isobaric expansion. The change in the entropy was well calculated by many candidates with ECF being very prominent from part biii). A complete and proper explanation in ii) was well formulated only by the better candidates. However, many were able to recognize that the Carnot engine was ideal and not real. Many answers referred to heat being lost to the environment but not to “additional losses” that make the engine less than its ideal capacity.\n
\n
\n
\n (b.ii)\n
\n
\n The efficiency of the Carnot cycle was well calculated by most of the candidates, but the thermal energy that leaves the gas was well calculated only by the best candidates. Many candidates were able to establish that the heat added to the gas was 540 J - but struggled to then link this with the efficiency to determine the thermal energy leaving the gas. In iii) the better candidates used the formula given at i) to appropriately calculate the ratio but many were not able to manipulate the expressions to achieve the desired outcome. The reciprocal of 2.5 (0.4) was a common error in the final result and so was the incorrect use of the formula for isobaric expansion. The change in the entropy was well calculated by many candidates with ECF being very prominent from part biii). A complete and proper explanation in ii) was well formulated only by the better candidates. However, many were able to recognize that the Carnot engine was ideal and not real. Many answers referred to heat being lost to the environment but not to “additional losses” that make the engine less than its ideal capacity.\n
\n
\n
\n (b.iii)\n
\n
\n The efficiency of the Carnot cycle was well calculated by most of the candidates, but the thermal energy that leaves the gas was well calculated only by the best candidates. Many candidates were able to establish that the heat added to the gas was 540 J - but struggled to then link this with the efficiency to determine the thermal energy leaving the gas. In iii) the better candidates used the formula given at i) to appropriately calculate the ratio but many were not able to manipulate the expressions to achieve the desired outcome. The reciprocal of 2.5 (0.4) was a common error in the final result and so was the incorrect use of the formula for isobaric expansion. The change in the entropy was well calculated by many candidates with ECF being very prominent from part biii). A complete and proper explanation in ii) was well formulated only by the better candidates. However, many were able to recognize that the Carnot engine was ideal and not real. Many answers referred to heat being lost to the environment but not to “additional losses” that make the engine less than its ideal capacity.\n
\n
\n
\n (c.i)\n
\n
\n The efficiency of the Carnot cycle was well calculated by most of the candidates, but the thermal energy that leaves the gas was well calculated only by the best candidates. Many candidates were able to establish that the heat added to the gas was 540 J - but struggled to then link this with the efficiency to determine the thermal energy leaving the gas. In iii) the better candidates used the formula given at i) to appropriately calculate the ratio but many were not able to manipulate the expressions to achieve the desired outcome. The reciprocal of 2.5 (0.4) was a common error in the final result and so was the incorrect use of the formula for isobaric expansion. The change in the entropy was well calculated by many candidates with ECF being very prominent from part biii). A complete and proper explanation in ii) was well formulated only by the better candidates. However, many were able to recognize that the Carnot engine was ideal and not real. Many answers referred to heat being lost to the environment but not to “additional losses” that make the engine less than its ideal capacity.\n
\n
\n
\n (c.ii)\n
\n
\n The efficiency of the Carnot cycle was well calculated by most of the candidates, but the thermal energy that leaves the gas was well calculated only by the best candidates. Many candidates were able to establish that the heat added to the gas was 540 J - but struggled to then link this with the efficiency to determine the thermal energy leaving the gas. In iii) the better candidates used the formula given at i) to appropriately calculate the ratio but many were not able to manipulate the expressions to achieve the desired outcome. The reciprocal of 2.5 (0.4) was a common error in the final result and so was the incorrect use of the formula for isobaric expansion. The change in the entropy was well calculated by many candidates with ECF being very prominent from part biii). A complete and proper explanation in ii) was well formulated only by the better candidates. However, many were able to recognize that the Carnot engine was ideal and not real. Many answers referred to heat being lost to the environment but not to “additional losses” that make the engine less than its ideal capacity.\n
\n
\n",
+ "topics": [
+ "b-the-particulate-nature-of-matter"
+ ],
+ "subtopics": [
+ "b-4-thermodynamics"
+ ]
+ },
+ {
+ "question_id": "19M.2.HL.TZ2.10",
+ "Question": "
\n
A small magnet is dropped from rest above a stationary horizontal conducting ring. The south (S) pole of the magnet is upwards.
\n

\n
\n
While the magnet is moving towards the ring, state why the magnetic flux in the ring is increasing.
\n
[1]
\n
a.
\n
\n
While the magnet is moving towards the ring, sketch, using an arrow on Diagram 2, the direction of the induced current in the ring.
\n
[1]
\n
b.
\n
\n
While the magnet is moving towards the ring, deduce the direction of the magnetic force on the magnet.
\n
[2]
\n
c.
\n
",
+ "Markscheme": "
\n
the magnetic field at the position of the ring is increasing «because the magnet gets closer to the ring» ✔
\n
a.
\n
\n
the current must be counterclockwise «in diagram 2» ✔
\n
eg:
\n

\n
b.
\n
\n
since the induced magnetic field is upwards
\n
OR
\n
by Lenz law the change «of magnetic field/flux» must be opposed
\n
OR
\n
by conservation of energy the movement of the magnet must be opposed ✔
\n
therefore the force is repulsive/upwards ✔
\n
c.
\n
",
+ "Examiners report": "
\n
This was well-answered.
\n
a.
\n
\n
Answers here were reasonably evenly split between clockwise and anti-clockwise, with the odd few arrows pointing left or right.
\n
b.
\n
\n
The majority of candidates recognised that the magnetic force would be upwards and the most common way of explaining this was via Lenz’s law. Students needed to get across that the force is opposing a change or a motion.
\n
c.
\n
",
+ "topics": [
+ "b-the-particulate-nature-of-matter"
+ ],
+ "subtopics": [
+ "b-4-thermodynamics"
+ ]
+ },
+ {
+ "question_id": "19M.2.HL.TZ2.11",
+ "Question": "
\n
In an experiment to determine the radius of a carbon-12 nucleus, a beam of neutrons is scattered by a thin film of carbon-12. The graph shows the variation of intensity of the scattered neutrons with scattering angle. The de Broglie wavelength of the neutrons is 1.6 × 10-15 m.
\n

\n
\n
A pure sample of copper-64 has a mass of 28 mg. The decay constant of copper-64 is 5.5 × 10-2 hour–1.
\n
\n
Suggest why de Broglie’s hypothesis is not consistent with Bohr’s conclusion that the electron’s orbit in the hydrogen atom has a well defined radius.
\n
[2]
\n
a.
\n
\n
Estimate, using the graph, the radius of a carbon-12 nucleus.
\n
[2]
\n
bi.
\n
\n
The ratio is approximately A.
\n
Comment on this observation by reference to the strong nuclear force.
\n
[2]
\n
bii.
\n
\n
Estimate, in Bq, the initial activity of the sample.
\n
[2]
\n
ci.
\n
\n
Calculate, in hours, the time at which the activity of the sample has decreased to one-third of the initial activity.
\n
[2]
\n
cii.
\n
",
+ "Markscheme": "
\n
«de Broglie’s hypothesis states that the» electron is represented by a wave ✔
\n
therefore it cannot be localized/it is spread out/it does not have a definite position ✔
\n
Award MP1 for any mention of wavelike property of an electron.
\n
a.
\n
\n
«» «m» ✔
\n
«m» ✔
\n
bi.
\n
\n
this implies that the nucleons are very tightly packed/that there is very little space in between the nucleons ✔
\n
because the nuclear force is stronger than the electrostatic force ✔
\n
bii.
\n
\n
number of nuclei is ✔
\n
«» «Bq» ✔
\n
ci.
\n
\n
✔
\n
t = 20«hr» ✔
\n
cii.
\n
",
+ "Examiners report": "",
+ "topics": [
+ "c-wave-behaviour",
+ "e-nuclear-and-quantum-physics"
+ ],
+ "subtopics": [
+ "c-3-wave-phenomena",
+ "e-1-structure-of-the-atom",
+ "e-2-quantum-physics",
+ "e-3-radioactive-decay"
+ ]
+ },
+ {
+ "question_id": "19M.2.HL.TZ2.4",
+ "Question": "
\n
Three identical light bulbs, X, Y and Z, each of resistance 4.0 Ω are connected to a cell of emf 12 V. The cell has negligible internal resistance.
\n

\n
\n
When fully charged the space between the plates of the capacitor is filled with a dielectric with double the permittivity of a vacuum.
\n
\n
The switch S is initially open. Calculate the total power dissipated in the circuit.
\n
[2]
\n
a.
\n
\n
The switch is now closed. State, without calculation, why the current in the cell will increase.
\n
[1]
\n
bi.
\n
\n
The switch is now closed. .
\n
\n
[2]
\n
bii.
\n
\n
The cell is used to charge a parallel-plate capacitor in a vacuum. The fully charged capacitor is then connected to an ideal voltmeter.
\n

\n
The capacitance of the capacitor is 6.0 μF and the reading of the voltmeter is 12 V.
\n
Calculate the energy stored in the capacitor.
\n
[1]
\n
c.
\n
\n
Calculate the change in the energy stored in the capacitor.
\n
[3]
\n
di.
\n
\n
Suggest, in terms of conservation of energy, the cause for the above change.
\n
[1]
\n
dii.
\n
",
+ "Markscheme": "
\n
total resistance of circuit is 8.0 «Ω» ✔
\n
«W» ✔
\n
a.
\n
\n
«a resistor is now connected in parallel» reducing the total resistance
\n
OR
\n
current through YZ unchanged and additional current flows through X ✔
\n
bi.
\n
\n
evidence in calculation or statement that pd across Y/current in Y is the same as before ✔
\n
so ratio is 1 ✔
\n
bii.
\n
\n
«» ✔
\n
c.
\n
\n
ALTERNATIVE 1
\n
capacitance doubles and voltage halves ✔
\n
since energy halves ✔
\n
so change is «–»2.2×10–4 «J» ✔
\n
\n
ALTERNATIVE 2
\n
✔
\n
capacitance doubles and charge unchanged so energy halves ✔
\n
so change is «−»2.2 × 10−4 «J» ✔
\n
di.
\n
\n
it is the work done when inserting the dielectric into the capacitor ✔
\n
dii.
\n
",
+ "Examiners report": "
\n
Most candidates scored both marks. ECF was awarded for those who didn’t calculate the new resistance correctly. Candidates showing clearly that they were attempting to calculate the new total resistance helped examiners to award ECF marks.
\n
a.
\n
\n
Most recognised that this decreased the total resistance of the circuit. Answers scoring via the second alternative were rare as the statements were often far too vague.
\n
bi.
\n
\n
Very few gained any credit for this at both levels. Most performed complicated calculations involving the total circuit and using 12V – they had not realised that the question refers to Y only.
\n
bii.
\n
\n
Most answered this correctly.
\n
c.
\n
\n
By far the most common answer involved doubling the capacitance without considering the change in p.d. Almost all candidates who did this calculated a change in energy that scored 1 mark.
\n
di.
\n
\n
Very few scored on this question.
\n
dii.
\n
",
+ "topics": [
+ "a--space-time-and-motion"
+ ],
+ "subtopics": [
+ "a-5-galilean-and-special-relativity"
+ ]
+ },
+ {
+ "question_id": "19M.2.HL.TZ2.6",
+ "Question": "
\n
\n (a)\n
\n
\n
\n \n Define\n \n proper length\n \n .\n \n
\n
\n
\n
\n
\n
\n (bi)\n
\n
\n
\n \n In the reference frame of the train a ball travels with speed 0.50\n \n c\n \n from the back to the front of the train, as the train passes the platform. Calculate the time taken for the ball to reach the front of the train in the reference frame of the train.\n \n
\n
\n
\n
\n
\n
\n (bii)\n
\n
\n
\n \n In the reference frame of the train a ball travels with speed 0.50\n \n c\n \n from the back to the front of the train, as the train passes the platform. Calculate the time taken for the ball to reach the front of the train in the reference frame of the platform.\n \n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n \n the length measured «in a reference frame» where the object is at rest ✔\n
\n \n
\n
\n
\n (bi)\n
\n
\n
\n \n
\n \n
\n
\n
\n (bii)\n
\n
\n \n \n \n ALTERNATIVE 1:\n \n \n \n \n
\n \n
\n
\n \n
\n \n
\n
\n \n \n \n \n ALTERNATIVE 2:\n \n \n \n \n
\n
\n \n \n \n \n v\n \n of ball is 0.846\n \n c\n \n for platform ✔\n
\n \n \n \n
\n
\n \n \n \n length of train is 68m for platform ✔\n \n \n \n
\n
\n \n \n \n
\n \n \n \n
\n
\n \n \n \n \n \n ALTERNATIVE 3:\n \n \n \n \n \n
\n
\n
\n
\n
\n",
+ "Examiners report": "
\n (a)\n
\n
\n Proper length is quite well understood. A common mistake is to mention that it is the length measured by a reference frame at rest.\n
\n
\n
\n (bi)\n
\n
\n Because there were three frames of reference in this question many candidates struggled to find the simple value for the time of the ball’s travel down the train in the train’s frame of reference.\n
\n
\n
\n (bii)\n
\n
\n Almost no candidates could use a Lorentz transformation to find the time of the ball’s travel in the frame of reference of the platform. Most just applied some form of t=γt’. Elapsed time and instantaneous time in different frames were easily confused. Candidates rarely mention which reference frame is used when making calculations, however this is crucial in relativity.\n
\n
\n",
+ "topics": [
+ "a--space-time-and-motion"
+ ],
+ "subtopics": [
+ "a-5-galilean-and-special-relativity"
+ ]
+ },
+ {
+ "question_id": "19M.2.HL.TZ2.8",
+ "Question": "
\n
Monochromatic coherent light is incident on two parallel slits of negligible width a distance d apart. A screen is placed a distance D from the slits. Point M is directly opposite the midpoint of the slits.
\n

\n
Initially the lower slit is covered and the intensity of light at M due to the upper slit alone is 22 W m-2. The lower slit is now uncovered.
\n
\n
The width of each slit is increased to 0.030 mm. D, d and λ remain the same.
\n
\n
Deduce, in W m-2, the intensity at M.
\n
[3]
\n
a.
\n
\n
P is the first maximum of intensity on one side of M. The following data are available.
\n
d = 0.12 mm
\n
D = 1.5 m
\n
Distance MP = 7.0 mm
\n
Calculate, in nm, the wavelength λ of the light.
\n
[2]
\n
b.
\n
\n
Suggest why, after this change, the intensity at P will be less than that at M.
\n
[1]
\n
ci.
\n
\n
Show that, due to single slit diffraction, the intensity at a point on the screen a distance of 28 mm from M is zero.
\n
[2]
\n
cii.
\n
",
+ "Markscheme": "
\n
there is constructive interference at M
\n
OR
\n
the amplitude doubles at M ✔
\n
intensity is «proportional to» amplitude2 ✔
\n
88 «W m−2» ✔
\n
a.
\n
\n
« ✔
\n
» ✔
\n
\n
b.
\n
\n
«the interference pattern will be modulated by»
\n
single slit diffraction ✔
\n
«envelope and so it will be less»
\n
ci.
\n
\n
ALTERNATIVE 1
\n
the angular position of this point is «rad» ✔
\n
which coincides with the first minimum of the diffraction envelope
\n
«rad» ✔
\n
«so intensity will be zero»
\n
\n
ALTERNATIVE 2
\n
the first minimum of the diffraction envelope is at «rad» ✔
\n
distance on screen is «mm» ✔
\n
«so intensity will be zero»
\n
\n
cii.
\n
",
+ "Examiners report": "
\n
This was generally well answered by those who attempted it but was the question that was most left blank. The most common mistake was the expected one of simply doubling the intensity.
\n
a.
\n
\n
This was very well answered. As the question asks for the answer to be given in nm a bald answer of 560 was acceptable. Candidates could also gain credit for an answer of e.g. 5.6 x 10-7 m provided that the m was included.
\n
b.
\n
\n
Many recognised the significance of the single slit diffraction envelope.
\n
ci.
\n
\n
Credit was often gained here for a calculation of an angle for alternative 2 in the markscheme but often the final substitution 1.50 was omitted to score the second mark. Both marks could be gained if the calculation was done in one step. Incorrect answers often included complicated calculations in an attempt to calculate an integer value.
\n
cii.
\n
",
+ "topics": [
+ "a--space-time-and-motion"
+ ],
+ "subtopics": [
+ "a-2-forces-and-momentum",
+ "a-4-rigid-body-mechanics"
+ ]
+ },
+ {
+ "question_id": "19M.2.HL.TZ2.9",
+ "Question": "
\n
A planet of mass m is in a circular orbit around a star. The gravitational potential due to the star at the position of the planet is V.
\n
\n
Show that the total energy of the planet is given by the equation shown.
\n
\n
[2]
\n
ai.
\n
\n
Suppose the star could contract to half its original radius without any loss of mass. Discuss the effect, if any, this has on the total energy of the planet.
\n
[2]
\n
aii.
\n
\n
The diagram shows some of the electric field lines for two fixed, charged particles X and Y.
\n

\n
The magnitude of the charge on X is and that on Y is . The distance between X and Y is 0.600 m. The distance between P and Y is 0.820 m.
\n
At P the electric field is zero. Determine, to one significant figure, the ratio .
\n
[2]
\n
b.
\n
",
+ "Markscheme": "
\n
✔
\n
comparison with ✔
\n
«to give answer»
\n
\n
ai.
\n
\n
ALTERNATIVE 1
\n
«at the position of the planet» the potential depends only on the mass of the star /does not depend on the radius of the star ✔
\n
the potential will not change and so the energy will not change ✔
\n
ALTERNATIVE 2
\n
r / distance between the centres of the objects / orbital radius remains unchanged ✔
\n
since , energy will not change ✔
\n
\n
aii.
\n
\n
✔
\n
✔
\n
\n
b.
\n
",
+ "Examiners report": "
\n
This was generally well answered but with candidates sometimes getting in to trouble over negative signs but otherwise producing well-presented answers.
\n
ai.
\n
\n
A large number of candidates thought that the total energy of the planet would change, mostly double.
\n
aii.
\n
\n
The majority of candidates had an idea of the basic technique here but it was surprisingly common to see the squared missing from the expression for field strengths.
\n
b.
\n
",
+ "topics": [
+ "a--space-time-and-motion",
+ "d-fields"
+ ],
+ "subtopics": [
+ "a-4-rigid-body-mechanics",
+ "d-1-gravitational-fields",
+ "d-2-electric-and-magnetic-fields"
+ ]
+ },
+ {
+ "question_id": "19M.2.SL.TZ1.3",
+ "Question": "
\n
A beam of microwaves is incident normally on a pair of identical narrow slits S1 and S2.
\n

\n
When a microwave receiver is initially placed at W which is equidistant from the slits, a maximum in intensity is observed. The receiver is then moved towards Z along a line parallel to the slits. Intensity maxima are observed at X and Y with one minimum between them. W, X and Y are consecutive maxima.
\n
\n
Explain why intensity maxima are observed at X and Y.
\n
[2]
\n
a.
\n
\n
The distance from S1 to Y is 1.243 m and the distance from S2 to Y is 1.181 m.
Determine the frequency of the microwaves.
\n
[3]
\n
b.
\n
\n
Outline one reason why the maxima observed at W, X and Y will have different intensities from each other.
\n
[1]
\n
c.
\n
",
+ "Markscheme": "
\n
two waves superpose/mention of superposition/mention of «constructive» interference ✔
\n
they arrive in phase/there is a path length difference of an integer number of wavelengths ✔
\n
Ignore references to nodes/antinodes.
\n
a.
\n
\n
path difference = 0.062 «m» ✔
\n
so wavelength = 0.031 «m» ✔
\n
frequency = 9.7 × 109 «Hz» ✔
\n
If no unit is given, assume the answer is in Hz. Accept other prefixes (eg 9.7 GHz)
\n
Award [2 max] for 4.8 x 109 Hz.
\n
b.
\n
\n
intensity varies with distance OR points are different distances from the slits ✔
\n
Accept “Intensity is modulated by a single slit diffraction envelope”.
\n
c.
\n
",
+ "Examiners report": "
\n
Many candidates were able to discuss the interference that is taking place in this question, but few were able to fully describe the path length difference. That said, the quality of responses on this type of question seems to have improved over the last few examination sessions with very few candidates simply discussing the crests and troughs of waves.
\n
a.
\n
\n
Many candidates struggled with this question. Few were able to calculate a proper path length difference, and then use that to calculate the wavelength and frequency. Many candidates went down blind paths of trying various equations from the data booklet, and some seemed to believe that the wavelength is just the reciprocal of the frequency.
\n
b.
\n
\n
This is one of many questions on this paper where candidates wrote vague answers that did not clearly connect to physics concepts or include key information. There were many overly simplistic answers like “they are farther away” without specifying what they are farther away from. Candidates should be reminded that their responses should go beyond the obvious and include some evidence of deeper understanding.
\n
c.
\n
",
+ "topics": [
+ "c-wave-behaviour"
+ ],
+ "subtopics": [
+ "c-1-simple-harmonic-motion",
+ "c-2-wave-model",
+ "c-3-wave-phenomena"
+ ]
+ },
+ {
+ "question_id": "19M.2.SL.TZ1.5",
+ "Question": "
\n
A small metal pendulum bob of mass 75 g is suspended at rest from a fixed point with a length of thread of negligible mass. Air resistance is negligible. The bob is then displaced to the left.
\n
At time t = 0 the bob is moving horizontally to the right at 0.8 m s–1. It collides with a small stationary object also of mass 75 g. Both objects then move together with motion that is simple harmonic.
\n

\n
\n
Calculate the speed of the combined masses immediately after the collision.
\n
[1]
\n
a.
\n
\n
Show that the collision is inelastic.
\n
[3]
\n
b.
\n
\n
Describe the changes in gravitational potential energy of the oscillating system from t = 0 as it oscillates through one cycle of its motion.
\n
[1]
\n
c.
\n
",
+ "Markscheme": "
\n
initial energy 24 mJ and final energy 12 mJ ✔
\n
energy is lost/unequal /change in energy is 12 mJ ✔
\n
inelastic collisions occur when energy is lost ✔
\n
b.
\n
\n
maximum GPE at extremes, minimum in centre ✔
\n
c.
\n
",
+ "Examiners report": "
\n
Candidates fell into some broad categories on this question. This was a “show that” question, so there was an expectation of a mathematical argument. Many were able to successfully show that the initial and final kinetic energies were different and connect this to the concept of inelastic collisions. Some candidates tried to connect conservation of momentum unsuccessfully, and some simply wrote an extended response about the nature of inelastic collisions and noted that the bobs stuck together without any calculations. This approach was awarded zero marks.
\n
b.
\n
\n
This straightforward question had surprisingly poorly answers. Candidate answers tended to be overly vague, such as “as the bob went higher the GPE increased and as it fell the GPE decreased.” Candidates needed to specify when GPE would be at maximum and minimum values. Some candidates mistakenly assumed that at t=0 the pendulum bob was at maximum height despite being told otherwise in the question stem.
\n
c.
\n
",
+ "topics": [
+ "a--space-time-and-motion",
+ "d-fields"
+ ],
+ "subtopics": [
+ "a-2-forces-and-momentum",
+ "a-3-work-energy-and-power",
+ "d-1-gravitational-fields"
+ ]
+ },
+ {
+ "question_id": "19M.2.SL.TZ1.6",
+ "Question": "
\n
The Moon has no atmosphere and orbits the Earth. The diagram shows the Moon with rays of light from the Sun that are incident at 90° to the axis of rotation of the Moon.
\n

\n
\n
A black body is on the Moon’s surface at point A. Show that the maximum temperature that this body can reach is 400 K. Assume that the Earth and the Moon are the same distance from the Sun.
\n
[2]
\n
a.i.
\n
\n
Another black body is on the Moon’s surface at point B.
\n
Outline, without calculation, why the aximum temperature of the black body at point B is less than at point A.
\n
[2]
\n
a.ii.
\n
\n
The albedo of the Earth’s atmosphere is 0.28. Outline why the maximum temperature of a black body on the Earth when the Sun is overhead is less than that at point A on the Moon.
\n
[1]
\n
b.
\n
\n
Outline why a force acts on the Moon.
\n
[1]
\n
c.i.
\n
\n
Outline why this force does no work on the Moon.
\n
[1]
\n
c.ii.
\n
",
+ "Markscheme": "
\n
T = ✔
\n
390 «K» ✔
\n
Must see 1360 (from data booklet) used for MP1.
\n
Must see at least 2 s.f.
\n
a.i.
\n
\n
energy/Power/Intensity lower at B ✔
\n
connection made between energy/power/intensity and temperature of blackbody ✔
\n
a.ii.
\n
\n
(28 %) of sun’s energy is scattered/reflected by earth’s atmosphere OR only 72 % of incident energy gets absorbed by blackbody ✔
\n
Must be clear that the energy is being scattered by the atmosphere.
\n
Award [0] for simple definition of “albedo”.
\n
b.
\n
\n
gravitational attraction/force/field «of the planet/Moon» ✔
\n
Do not accept “gravity”.
\n
c.i.
\n
\n
the force/field and the velocity/displacement are at 90° to each other OR there is no change in GPE of the moon ✔
\n
Award [0] for any mention of no net force on the satellite.
\n
Do not accept acceleration is perpendicular to velocity.
\n
c.ii.
\n
",
+ "Examiners report": "
\n
Many candidates struggled with this question. A significant portion attempted to apply Wein’s Law and simply stated that a particular wavelength was the peak and then used that to determine the temperature. Some did use the solar constant from the data booklet and were able to calculate the correct temperature. As part of their preparation for the exam candidates should thoroughly review the data booklet and be aware of what constants are given there. As with all “show that” questions candidates should be reminded to include an unrounded answer.
\n
a.i.
\n
\n
This is question is another example of candidates not thinking beyond the obvious in the question. Many simply said that point B is farther away, or that it is at an angle. Some used vague terms like “the sunlight is more spread out” rather than using proper physics terms. Few candidates connected the lower intensity at B with the lower temperature of the blackbody.
\n
a.ii.
\n
\n
This question was assessing the understanding of the concept of albedo. Many candidates were able to connect that an albedo of 0.28 meant that 28 % of the incident energy from the sun was being reflected or scattered by the atmosphere before reaching the black body.
\n
b.
\n
\n
This was generally well answered, although some candidates simply used the vague term “gravity” rather than specifying that it is a gravitational force or a gravitational field. Candidates need to be reminded about using proper physics terms and not more general, “every day” terms on the exam.
\n
c.i.
\n
\n
Some candidates connected the idea that the gravitational force is perpendicular to the velocity (and hence the displacement) for the mark. It was also allowed to discuss that there is no change in gravitational potential energy, so therefore no work was being done. It was not acceptable to simply state that the net displacement over one full orbit is zero. Unfortunately, some candidates suggested that there is no net force on the moon so there is no work done, or that the moon is so much smaller so no work could be done on it.
\n
c.ii.
\n
",
+ "topics": [
+ "a--space-time-and-motion",
+ "b-the-particulate-nature-of-matter",
+ "d-fields"
+ ],
+ "subtopics": [
+ "a-2-forces-and-momentum",
+ "a-3-work-energy-and-power",
+ "b-2-greenhouse-effect",
+ "d-1-gravitational-fields"
+ ]
+ },
+ {
+ "question_id": "19M.2.SL.TZ2.1",
+ "Question": "
\n
A student strikes a tennis ball that is initially at rest so that it leaves the racquet at a speed of 64 m s–1. The ball has a mass of 0.058 kg and the contact between the ball and the racquet lasts for 25 ms.
\n
\n
The student strikes the tennis ball at point P. The tennis ball is initially directed at an angle of 7.00° to the horizontal.
\n

\n
The following data are available.
\n
Height of P = 2.80 m
\n
Distance of student from net = 11.9 m
\n
Height of net = 0.910 m
\n
Initial speed of tennis ball = 64 m s-1
\n
\n
Calculate the average force exerted by the racquet on the ball.
\n
[2]
\n
ai.
\n
\n
Calculate the average power delivered to the ball during the impact.
\n
[2]
\n
aii.
\n
\n
Calculate the time it takes the tennis ball to reach the net.
\n
[2]
\n
bi.
\n
\n
Show that the tennis ball passes over the net.
\n
[3]
\n
bii.
\n
\n
Determine the speed of the tennis ball as it strikes the ground.
\n
[2]
\n
biii.
\n
\n
The student models the bounce of the tennis ball to predict the angle θ at which the ball leaves a surface of clay and a surface of grass.
\n

\n
The model assumes
\n
• during contact with the surface the ball slides.
• the sliding time is the same for both surfaces.
• the sliding frictional force is greater for clay than grass.
• the normal reaction force is the same for both surfaces.
\n
Predict for the student’s model, without calculation, whether θ is greater for a clay surface or for a grass surface.
\n
[3]
\n
c.
\n
",
+ "Markscheme": "
\n
✔
\n
= 148«»≈150«» ✔
\n
\n
ai.
\n
\n
ALTERNATIVE 1
\n
✔
\n
» ✔
\n
\n
ALTERNATIVE 2
\n
✔
\n
» ✔
\n
\n
aii.
\n
\n
horizontal component of velocity is 64.0 × cos7° = 63.52 «ms−1» ✔
\n
» ✔
\n
Do not award BCA. Check working.
\n
Do not award ECF from using 64 m s-1.
\n
bi.
\n
\n
ALTERNATIVE 1
\n
uy = 64 sin7/7.80 «ms−1»✔
\n
decrease in height = 7.80 × 0.187 + × 9.81 × 0.1872/1.63 «m» ✔
\n
final height = «2.80 − 1.63» = 1.1/1.2 «m» ✔
\n
«higher than net so goes over»
\n
ALTERNATIVE 2
\n
vertical distance to fall to net «= 2.80 − 0.91» = 1.89 «m»✔
\n
time to fall this distance found using «=1.89 = 7.8t + × 9.81 ×t2»
\n
t = 0.21 «s»✔
\n
0.21 «s» > 0.187 «s» ✔
\n
«reaches the net before it has fallen far enough so goes over»
\n
Other alternatives are possible
\n
bii.
\n
\n
ALTERNATIVE 1
\n
Initial KE + PE = final KE /
\n
× 0.058 × 642 + 0.058 × 9.81 × 2.80 = × 0.058 × v2 ✔
\n
v = 64.4 «ms−1» ✔
\n
ALTERNATIVE 2
\n
» ✔
\n
« »
\n
» ✔
\n
\n
biii.
\n
\n
so horizontal velocity component at lift off for clay is smaller ✔
\n
normal force is the same so vertical component of velocity is the same ✔
\n
so bounce angle on clay is greater ✔
\n
c.
\n
",
+ "Examiners report": "
\n
At both HL and SL many candidates scored both marks for correctly answering this. A straightforward start to the paper. For those not gaining both marks it was possible to gain some credit for calculating either the change in momentum or the acceleration. At SL some used 64 ms-1 as a value for a and continued to use this value over the next few parts to the question.
\n
ai.
\n
\n
This was well answered although a significant number of candidates approached it using P = Fv but forgot to divide v by 2 to calculated the average velocity. This scored one mark out of 2.
\n
aii.
\n
\n
This question scored well at HL but less so at SL. One common mistake was to calculate the direct distance to the top of the net and assume that the ball travelled that distance with constant speed. At SL particularly, another was to consider the motion only when the ball is in contact with the racquet.
\n
bi.
\n
\n
There were a number of approaches students could take to answer this and examiners saw examples of them all. One approach taken was to calculate the time taken to fall the distance to the top of the net and to compare this with the time calculated in bi) for the ball to reach the net. This approach, which is shown in the mark scheme, required solving a quadratic in t which is beyond the mathematical requirements of the syllabus. This mathematical technique was only required if using this approach and not required if, for example, calculating heights.
\n
A common mistake was to forget that the ball has a vertical acceleration. Examiners were able to award credit/ECF for correct parts of an otherwise flawed method.
\n
bii.
\n
\n
This proved difficult for candidates at both HL and SL. Many managed to calculate the final vertical component of the velocity of the ball.
\n
biii.
\n
\n
As the command term in this question is ‘predict’ a bald answer of clay was acceptable for one mark. This was a testing question that candidates found demanding but there were some very well-reasoned answers. The most common incorrect answer involved suggesting that the greater frictional force on the clay court left the ball with less kinetic energy and so a smaller angle. At SL many gained the answer that the angle on clay would be greater with the argument that frictional force is greater and so the distance the ball slides is less.
\n
c.
\n
",
+ "topics": [
+ "a--space-time-and-motion"
+ ],
+ "subtopics": [
+ "a-1-kinematics",
+ "a-2-forces-and-momentum",
+ "a-3-work-energy-and-power"
+ ]
+ },
+ {
+ "question_id": "19M.2.SL.TZ2.14",
+ "Question": "
\n
\n (a)\n
\n
\n
\n \n Show that, when the speed of the train is 10 m s-1, the frequency of the periodic force is 0.4 Hz.\n \n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n
\n \n \n Outline, with reference to the curve, why it is unsafe to drive a train across the bridge at 30 m s\n \n -1\n \n for this amount of damping.\n \n \n
\n
\n
\n
\n
\n
\n (c)\n
\n
\n
\n \n The damping of the bridge system can be varied. Draw, on the graph, a second curve when the damping is larger.\n \n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n \n time period\n \n
\n
\n \n \n T = «\n \n \n \n »\n \n \n \n = 2.5 s\n \n \n \n \n AND\n \n f =\n \n \n \n \n \n
\n
\n \n \n \n OR\n \n \n \n
\n
\n \n \n evidence of f =\n \n \n \n ✔\n \n \n
\n
\n \n \n \n Answer 0.4 Hz is given, check correct working is shown.\n \n \n \n
\n
\n
\n (b)\n
\n
\n \n 30 m s\n \n –1\n \n corresponds to\n \n f\n \n = 1.2 Hz ✔\n
\n \n
\n
\n \n the amplitude of vibration is a maximum for this speed\n
\n \n
\n
\n \n \n \n OR\n \n \n
\n \n
\n
\n \n corresponds to the resonant frequency ✔\n \n
\n
\n
\n (c)\n
\n
\n \n similar shape with lower amplitude ✔\n
\n \n
\n
\n \n maximum shifted slightly to left of the original curve ✔\n \n
\n
\n \n \n \n Amplitude must be lower than the original, but allow the amplitude to be equal at the extremes.\n \n \n \n
\n
\n",
+ "Examiners report": "
\n (a)\n
\n
\n The question was correctly answered by almost all candidates.\n
\n
\n
\n (b)\n
\n
\n The answers to this question were generally well presented and a correct argument was presented by almost all candidates. Resonance was often correctly referred to.\n
\n
\n
\n (c)\n
\n
\n A correct curve, with lower amplitude and shifted left, was drawn by most candidates.\n
\n
\n",
+ "topics": [
+ "c-wave-behaviour"
+ ],
+ "subtopics": [
+ "c-4-standing-waves-and-resonance"
+ ]
+ },
+ {
+ "question_id": "19M.2.SL.TZ2.15",
+ "Question": "
\n
\n (a)\n
\n
\n
\n \n Identify, on the HR diagram, the position of the Sun. Label the position S.\n \n
\n
\n
\n
\n
\n
\n (d)\n
\n
\n
\n \n During its evolution, the Sun is likely to be a red giant of surface temperature 3000 K and luminosity 10\n \n 4\n \n L\n \n \n \n ☉\n \n . Later it is likely to be a white dwarf of surface temperature 10 000 K and luminosity 10-4 L\n \n \n \n ☉\n \n . Calculate the\n \n \n \n .\n \n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n \n the letter S should be in the region of the shaded area\n \n \n \n ✔\n \n \n
\n
\n \n
\n \n
\n
\n
\n (d)\n
\n
\n
\n
\n
\n",
+ "Examiners report": "
\n (a)\n
\n
\n Locating the Sun’s position on the HR diagram was correctly done by most candidates, although a few were unsure of the surface temperature of the Sun.\n
\n
\n
\n (d)\n
\n
\n Calculating the ratio of the radius of a white dwarf to a red giant star was done quite well by most candidates. However quite a few candidates made POT errors or forgot to take the final square root.\n
\n
\n",
+ "topics": [
+ "e-nuclear-and-quantum-physics"
+ ],
+ "subtopics": [
+ "e-5-fusion-and-stars"
+ ]
+ },
+ {
+ "question_id": "19M.2.SL.TZ2.2",
+ "Question": "
\n
A container of volume 3.2 × 10-6 m3 is filled with helium gas at a pressure of 5.1 × 105 Pa and temperature 320 K. Assume that this sample of helium gas behaves as an ideal gas.
\n
\n
A helium atom has a volume of 4.9 × 10-31 m3.
\n
\n
The molar mass of helium is 4.0 g mol-1. Show that the mass of a helium atom is 6.6 × 10-27 kg.
\n
[1]
\n
a.
\n
\n
Estimate the average speed of the helium atoms in the container.
\n
[2]
\n
b.
\n
\n
Show that the number of helium atoms in the container is about 4 × 1020.
\n
[2]
\n
c.
\n
\n
Calculate the ratio .
\n
[1]
\n
di.
\n
\n
Explain, using your answer to (d)(i) and with reference to the kinetic model, why this sample of helium can be assumed to be an ideal gas.
\n
[2]
\n
dii.
\n
",
+ "Markscheme": "
\n
«kg»
\n
OR
\n
6.64 × 10−27 «kg» ✔
\n
\n
a.
\n
\n
✔
\n
v = 1.4 × 103 «ms−1» ✔
\n
b.
\n
\n
\n
OR
\n
✔
\n
N = 3.7 × 1020 ✔
\n
c.
\n
\n
« ✔
\n
di.
\n
\n
«For an ideal gas» the size of the particles is small compared to the distance between them/size of the container/gas
\n
OR
\n
«For an ideal gas» the volume of the particles is negligible/the volume of the particles is small compared to the volume of the container/gas
\n
OR
\n
«For an ideal gas» particles are assumed to be point objects ✔
\n
calculation/ratio/result in (d)(i) shows that volume of helium atoms is negligible compared to/much smaller than volume of helium gas/container «hence assumption is justified» ✔
\n
dii.
\n
",
+ "Examiners report": "
\n
The mark was awarded for a clear substitution or an answer to at least 3sf. Many gained the mark for a clear substitution with a conversion from g to kg somewhere in their response. Fewer gave the answer to the correct number of sf.
\n
a.
\n
\n
At HL this was very well answered but at SL many just worked out E=3/2kT and left it as a value for KE.
\n
b.
\n
\n
Again at HL this was very well answered with the most common approach being to calculate the number of moles and then multiply by NA to calculate the number of atoms. At SL many candidates calculated n but stopped there. Also at SL there was some evidence of candidates working backwards and magically producing a value for ‘n’ that gave a result very close to that required after multiplying by NA.
\n
c.
\n
\n
This was well answered with the most common mistake being to use the volume of a single atom rather than the total volume of the atoms.
\n
di.
\n
\n
In general this was poorly answered at SL. Many other non-related gas properties given such as no / negligible intermolecular forces, low pressure, high temperature. Some candidates interpreted the ratio as meaning it is a low density gas. At HL candidates seemed more able to focus on the key part feature of the question, which was the nature of the volumes involved. Examiners were looking for an assumption of the kinetic theory related to the volume of the atoms/gas and then a link to the ratio calculated in ci). The command terms were slightly different at SL and HL, giving slightly more guidance at SL.
\n
dii.
\n
",
+ "topics": [
+ "a--space-time-and-motion",
+ "b-the-particulate-nature-of-matter"
+ ],
+ "subtopics": [
+ "a-3-work-energy-and-power",
+ "b-1-thermal-energy-transfers",
+ "b-3-gas-laws"
+ ]
+ },
+ {
+ "question_id": "19M.2.SL.TZ2.7",
+ "Question": "
\n
The average temperature of ocean surface water is 289 K. Oceans behave as black bodies.
\n
\n
Show that the intensity radiated by the oceans is about 400 W m-2.
\n
[1]
\n
a.
\n
\n
Explain why some of this radiation is returned to the oceans from the atmosphere.
\n
[3]
\n
b.
\n
",
+ "Markscheme": "
\n
5.67 × 10−8 × 2894
\n
OR
\n
= 396 «W m−2» ✔
\n
«≈ 400 W m−2»
\n
\n
a.
\n
\n
«most of the radiation emitted by the oceans is in the» infrared ✔
\n
«this radiation is» absorbed by greenhouse gases/named greenhouse gas in the atmosphere ✔
\n
«the gases» reradiate/re-emit ✔
\n
partly back towards oceans/in all directions/awareness that radiation in other directions is also present ✔
\n
b.
\n
",
+ "Examiners report": "
\n
This was well answered with candidates scoring the mark for either a correct substitution or an answer given to at least one more sf than the show that value. Some candidates used 298 rather than 289.
\n
a.
\n
\n
For many this was a well-rehearsed answer which succinctly scored full marks. For others too many vague terms were used. There was much talk about energy being trapped or reflected and the ozone layer was often included. The word ‘albedo’ was often written down with no indication of what it means and ‘the albedo effect also featured.
\n
b.
\n
",
+ "topics": [
+ "b-the-particulate-nature-of-matter"
+ ],
+ "subtopics": [
+ "b-2-greenhouse-effect"
+ ]
+ },
+ {
+ "question_id": "19N.3.SL.TZ0.1",
+ "Question": "
\n
A student investigates how the period T of a simple pendulum varies with the maximum speed v of the pendulum’s bob by releasing the pendulum from rest from different initial angles. A graph of the variation of T with v is plotted.
\n

\n
\n
Suggest, by reference to the graph, why it is unlikely that the relationship between T and v is linear.
\n
[1]
\n
a.
\n
\n
Determine the fractional uncertainty in v when T = 2.115 s, correct to one significant figure.
\n
[2]
\n
b.
\n
\n
The student hypothesizes that the relationship between T and v is T = a + bv2, where a and b are constants. To verify this hypothesis a graph showing the variation of T with v2 is plotted. The graph shows the data and the line of best fit.
\n

\n
Determine b, giving an appropriate unit for b.
\n
[3]
\n
c.
\n
\n
The lines of the minimum and maximum gradient are shown.
\n

\n
Estimate the absolute uncertainty in a.
\n
[2]
\n
d.
\n
",
+ "Markscheme": "
\n
a straight line cannot be drawn through all error bars
OR
the graph/line of best fit is /curved/not straight/parabolic etc.
OR
graph has increasing/variable gradient ✔
\n
NOTE: Do not allow “a line cannot be drawn through all error bars” without specifying “straight”.
\n
a.
\n
\n
AND ✔
\n
«»0.04 ✔
\n
NOTE: Accept 4 %
\n
b.
\n
\n
use of 2 correct points on the line with Δv2 > 2 ✔
\n
b in range 0.012 to 0.013 ✔
\n
s3 m–2 ✔
\n
c.
\n
\n
«s» ±0.001 «s» AND «s» ±0.001 «s» ✔
\n
«» 0.003 «s» ✔
\n
d.
\n
",
+ "Examiners report": "
",
+ "topics": [
+ "tools"
+ ],
+ "subtopics": [
+ "tool-3-mathematics"
+ ]
+ },
+ {
+ "question_id": "19N.2.HL.TZ0.11",
+ "Question": "
\n
Monochromatic light of very low intensity is incident on a metal surface. The light causes the emission of electrons almost instantaneously. Explain how this observation
\n
\n
In an experiment to demonstrate the photoelectric effect, light of wavelength 480 nm is incident on a metal surface.
\n

\n
The graph shows the variation of the current in the ammeter with the potential of the cathode.
\n

\n
\n
does not support the wave nature of light.
\n
[2]
\n
a(i).
\n
\n
does support the photon nature of light.
\n
[2]
\n
a(ii).
\n
\n
Calculate, in eV, the work function of the metal surface.
\n
[3]
\n
b(i).
\n
\n
The intensity of the light incident on the surface is reduced by half without changing the wavelength. Draw, on the graph, the variation of the current with potential after this change.
\n
[2]
\n
b(ii).
\n
",
+ "Markscheme": "
\n
«low intensity light would» transfer energy to the electron at a low rate/slowly ✔
time would be required for the electron «to absorb the required energy» to escape/be emitted ✔
\n
NOTE: OWTTE
\n
a(i).
\n
\n
«in the photon theory of light» the electron interacts with a single photon ✔
and absorbs all the energy OR and can leave the metal immediately ✔
\n
NOTE: Reference to photon-electron collision scores MP1
\n
a(ii).
\n
\n
✔
\n
✔
\n
✔
\n
NOTE: Allow reading from the graph of leading to an answer of 1.2 «eV».
\n
b(i).
\n
\n
similar curve lower than original ✔
\n
with same horizontal intercept ✔
\n

\n
b(ii).
\n
",
+ "Examiners report": "
",
+ "topics": [
+ "e-nuclear-and-quantum-physics"
+ ],
+ "subtopics": [
+ "e-2-quantum-physics"
+ ]
+ },
+ {
+ "question_id": "19N.2.HL.TZ0.6",
+ "Question": "
\n
\n (a(i))\n
\n
\n
\n \n Show that the pressure at B is about 130 kPa.\n \n
\n
\n
\n
\n
\n
\n (a(ii))\n
\n
\n
\n \n Calculate the ratio\n \n .\n \n
\n
\n
\n
\n
\n
\n (b(i))\n
\n
\n
\n \n determine the thermal energy removed from the system.\n \n
\n
\n
\n
\n
\n
\n (b(ii))\n
\n
\n
\n \n explain why the entropy of the gas decreases.\n \n
\n
\n
\n
\n
\n
\n (b(iii))\n
\n
\n
\n \n state and explain whether the second law of thermodynamics is violated.\n \n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a(i))\n
\n
\n \n \n ✔\n \n
\n
\n = 127 kPa\n \n ✔\n \n
\n
\n
\n (a(ii))\n
\n
\n \n
\n
\n \n 1.31 ✔\n \n
\n
\n
\n (b(i))\n
\n
\n \n \n ALTERNATIVE 1\n \n \n
\n
\n work done\n \n \n ✔\n \n
\n
\n change in internal energy\n \n
\n \n \n OR\n
\n \n \n \n \n \n \n \n \n ✔\n \n
\n
\n thermal energy removed\n \n
\n \n \n OR\n
\n \n \n \n \n \n \n \n \n ✔\n \n
\n
\n
\n
\n \n \n ALTERNATIVE 2\n \n \n
\n
\n \n \n ✔\n \n
\n
\n thermal energy removed\n \n \n ✔\n \n
\n
\n \n \n \n \n ✔\n \n
\n
\n
\n (b(ii))\n
\n
\n \n \n ALTERNATIVE 1\n \n \n
\n
\n \n «from b(i)»\n \n is negative\n \n ✔\n \n \n
\n
\n \n \n \n \n AND\n \n \n \n is negative\n \n ✔\n \n \n
\n
\n
\n
\n \n ALTERNATIVE 2\n \n
\n
\n \n T\n \n and/or\n \n V\n \n decreases ✔\n
\n
\n less disorder/more order «so\n \n S\n \n decreases» ✔\n
\n
\n
\n
\n \n ALTERNATIVE 3\n \n
\n
\n \n T\n \n decreases ✔\n
\n
\n \n ✔\n
\n
\n \n \n
\n
\n \n NOTE: Answer given, look for a valid reason that S decreases.\n \n
\n
\n
\n (b(iii))\n
\n
\n \n not violated ✔\n \n
\n
\n \n the entropy of the surroundings must have increased\n
\n \n \n OR\n \n \n
\n the overall entropy of the system and the surroundings is the same or increased ✔\n \n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "a--space-time-and-motion"
+ ],
+ "subtopics": [
+ "a-4-rigid-body-mechanics"
+ ]
+ },
+ {
+ "question_id": "19N.2.SL.TZ0.1",
+ "Question": "
\n
The graph shows the variation with time t of the horizontal force F exerted on a tennis ball by a racket.
\n

\n
The tennis ball was stationary at the instant when it was hit. The mass of the tennis ball is 5.8 × 10–2 kg. The area under the curve is 0.84 N s.
\n
\n
Calculate the speed of the ball as it leaves the racket.
\n
[2]
\n
a.
\n
\n
Show that the average force exerted on the ball by the racket is about 50 N.
\n
[2]
\n
b.
\n
\n
Determine, with reference to the work done by the average force, the horizontal distance travelled by the ball while it was in contact with the racket.
\n
[3]
\n
c.
\n
\n
Draw a graph to show the variation with t of the horizontal speed v of the ball while it was in contact with the racket. Numbers are not required on the axes.
\n

\n
[2]
\n
d.
\n
",
+ "Markscheme": "
\n
links 0.84 to Δp ✔
\n
«» 14.5 «m s–1»✔
\n
NOTE: Award [2] for bald correct answer
\n
a.
\n
\n
use of Δt = «(28 – 12) × 10–3 =» 16 × 10–3 «s» ✔
\n
=«» OR 53 «N» ✔
\n
NOTE: Accept a time interval from 14 to 16 ms
Allow ECF from incorrect time interval
\n
b.
\n
\n
Ek = × 5.8 × 10–2 × 14.52 ✔
\n
Ek = W ✔
\n
s = «» 0.12 « m » ✔
\n
\n
Allow ECF from (a) and (b)
\n
Allow ECF from MP1
\n
Award [2] max for a calculation without reference to work done, eg: average velocity × time
\n
c.
\n
\n

\n
graph must show increasing speed from an initial of zero all the time ✔
overall correct curvature ✔
\n
d.
\n
",
+ "Examiners report": "
",
+ "topics": [
+ "a--space-time-and-motion"
+ ],
+ "subtopics": [
+ "a-1-kinematics",
+ "a-2-forces-and-momentum",
+ "a-3-work-energy-and-power"
+ ]
+ },
+ {
+ "question_id": "19N.2.SL.TZ0.3",
+ "Question": "
\n
The solid line in the graph shows the variation with distance of the displacement of a travelling wave at t = 0. The dotted line shows the wave 0.20 ms later. The period of the wave is longer than 0.20 ms.
\n

\n
\n
One end of a string is attached to an oscillator and the other is fixed to a wall. When the frequency of the oscillator is 360 Hz the standing wave shown is formed on the string.
\n

\n
Point X (not shown) is a point on the string at a distance of 10 cm from the oscillator.
\n
\n
Calculate, in m s–1, the speed for this wave.
\n
[1]
\n
a(i).
\n
\n
Calculate, in Hz, the frequency for this wave.
\n
[2]
\n
a(ii).
\n
\n
The graph also shows the displacement of two particles, P and Q, in the medium at t = 0. State and explain which particle has the larger magnitude of acceleration at t = 0.
\n
[2]
\n
b.
\n
\n
State the number of all other points on the string that have the same amplitude and phase as X.
\n
[1]
\n
c(i).
\n
\n
The frequency of the oscillator is reduced to 120 Hz. On the diagram, draw the standing wave that will be formed on the string.
\n

\n
[1]
\n
c(ii).
\n
",
+ "Markscheme": "
\n
v = «» 250 «m s–1»✔
\n
a(i).
\n
\n
λ = 0.30 «m» ✔
= «» 830 «Hz» ✔
\n
NOTE: Allow ECF from (a)(i)
Allow ECF from wrong wavelength for MP2
\n
a(ii).
\n
\n
Q ✔
acceleration is proportional to displacement «and Q has larger displacement» ✔
\n
b.
\n
\n
first harmonic mode drawn ✔
\n

\n
NOTE: Allow if only one curve drawn, either solid or dashed.
\n
c(ii).
\n
",
+ "Examiners report": "
",
+ "topics": [
+ "c-wave-behaviour"
+ ],
+ "subtopics": [
+ "c-1-simple-harmonic-motion",
+ "c-2-wave-model",
+ "c-4-standing-waves-and-resonance"
+ ]
+ },
+ {
+ "question_id": "19N.2.SL.TZ0.4",
+ "Question": "
\n
A proton is moving in a region of uniform magnetic field. The magnetic field is directed into the plane of the paper. The arrow shows the velocity of the proton at one instant and the dotted circle gives the path followed by the proton.
\n

\n
\n
The speed of the proton is 2.0 × 106 m s–1 and the magnetic field strength B is 0.35 T.
\n
\n
Explain why the path of the proton is a circle.
\n
[2]
\n
a.
\n
\n
Show that the radius of the path is about 6 cm.
\n
[2]
\n
b(i).
\n
\n
Calculate the time for one complete revolution.
\n
[2]
\n
b(ii).
\n
\n
Explain why the kinetic energy of the proton is constant.
\n
[2]
\n
c.
\n
",
+ "Markscheme": "
\n
magnetic force is to the left «at the instant shown»
OR
explains a rule to determine the direction of the magnetic force ✔
\n
force is perpendicular to velocity/«direction of» motion
OR
force is constant in magnitude ✔
\n
force is centripetal/towards the centre ✔
\n
NOTE: Accept reference to acceleration instead of force
\n
a.
\n
\n
✔
\n
OR 0.060 « m »
\n
NOTE: Award MP2 for full replacement or correct answer to at least 2 significant figures
\n
b(i).
\n
\n
✔
\n
« s » ✔
\n
NOTE: Award [2] for bald correct answer
\n
b(ii).
\n
\n
ALTERNATIVE 1
work done by force is change in kinetic energy ✔
work done is zero/force perpendicular to velocity ✔
\n
NOTE: Award [2] for a reference to work done is zero hence Ek remains constant
\n
\n
ALTERNATIVE 2
proton moves at constant speed ✔
kinetic energy depends on speed ✔
\n
NOTE: Accept mention of speed or velocity indistinctly in MP2
\n
\n
c.
\n
",
+ "Examiners report": "
",
+ "topics": [
+ "a--space-time-and-motion",
+ "d-fields"
+ ],
+ "subtopics": [
+ "a-2-forces-and-momentum",
+ "a-3-work-energy-and-power",
+ "d-3-motion-in-electromagnetic-fields"
+ ]
+ },
+ {
+ "question_id": "19N.2.SL.TZ0.5",
+ "Question": "
\n
An electron is placed at a distance of 0.40 m from a fixed point charge of –6.0 mC.
\n
\n

\n
\n
Show that the electric field strength due to the point charge at the position of the electron is 3.4 × 108 N C–1.
\n
[2]
\n
a.
\n
\n
Calculate the magnitude of the initial acceleration of the electron.
\n
[2]
\n
b(i).
\n
\n
Describe the subsequent motion of the electron.
\n
[3]
\n
b(ii).
\n
",
+ "Markscheme": "
\n
✔
\n
OR ✔
\n
NOTE: Ignore any negative sign.
\n
a.
\n
\n
OR ✔
\n
✔
\n
NOTE: Ignore any negative sign.
Award [1] for a calculation leading to
Award [2] for bald correct answer
\n
\n
b(i).
\n
\n
the electron moves away from the point charge/to the right «along the line joining them» ✔
decreasing acceleration ✔
increasing speed ✔
\n
NOTE: Allow ECF from MP1 if a candidate mistakenly evaluates the force as attractive so concludes that the acceleration will increase
\n
b(ii).
\n
",
+ "Examiners report": "
",
+ "topics": [
+ "a--space-time-and-motion",
+ "d-fields"
+ ],
+ "subtopics": [
+ "a-2-forces-and-momentum",
+ "d-2-electric-and-magnetic-fields"
+ ]
+ },
+ {
+ "question_id": "19N.2.SL.TZ0.7",
+ "Question": "
\n
A stationary nucleus of uranium-238 undergoes alpha decay to form thorium-234.
\n
The following data are available.
\n
Energy released in decay 4.27 MeV
Binding energy per nucleon for helium 7.07 MeV
Binding energy per nucleon for thorium 7.60 MeV
\n
\n
Radioactive decay is said to be “random” and “spontaneous”. Outline what is meant by each of these terms.
\n
Random:
\n
Spontaneous:
\n
[2]
\n
a.
\n
\n
Calculate the binding energy per nucleon for uranium-238.
\n
[3]
\n
b(i).
\n
\n
Calculate the ratio .
\n
[2]
\n
b(ii).
\n
",
+ "Markscheme": "
\n
random:
it cannot be predicted which nucleus will decay
OR
it cannot be predicted when a nucleus will decay ✔
\n
NOTE: OWTTE
\n
\n
spontaneous:
the decay cannot be influenced/modified in any way ✔
\n
NOTE: OWTTE
\n
a.
\n
\n
234 × 7.6 OR 4 × 7.07 ✔
\n
BEU =« 234 × 7.6 + 4 × 7.07 – 4.27 =» « MeV » ✔
\n
« MeV » ✔
\n
NOTE: Allow ECF from MP2
Award [3] for bald correct answer
Allow conversion to J, final answer is 1.2 × 10–12
\n
b(i).
\n
\n
states or applies conservation of momentum ✔
\n
ratio is «» 58.5 ✔
\n
NOTE: Award [2] for bald correct answer
\n
b(ii).
\n
",
+ "Examiners report": "
",
+ "topics": [
+ "a--space-time-and-motion",
+ "e-nuclear-and-quantum-physics"
+ ],
+ "subtopics": [
+ "a-3-work-energy-and-power",
+ "e-3-radioactive-decay"
+ ]
+ },
+ {
+ "question_id": "20N.3.SL.TZ0.1",
+ "Question": "
\n
A spherical soap bubble is made of a thin film of soapy water. The bubble has an internal air pressure and is formed in air of constant pressure . The theoretical prediction for the variation of is given by the equation
\n
\n
where is a constant for the thin film and is the radius of the bubble.
\n
Data for and were collected under controlled conditions and plotted as a graph showing the variation of with .
\n

\n
\n
Suggest whether the data are consistent with the theoretical prediction.
\n
[2]
\n
a.
\n
\n
Show that the value of is about 0.03.
\n
[2]
\n
b(i).
\n
\n
Identify the fundamental units of .
\n
[1]
\n
b(ii).
\n
\n
In order to find the uncertainty for , a maximum gradient line would be drawn. On the graph, sketch the maximum gradient line for the data.
\n
[1]
\n
b(iii).
\n
\n
The percentage uncertainty for is . State , with its absolute uncertainty.
\n
[2]
\n
b(iv).
\n
\n
The expected value of is . Comment on your result.
\n
[1]
\n
b(v).
\n
",
+ "Markscheme": "
\n
«theory suggests» is proportional to ✓
\n
graph/line of best fit is straight/linear «so yes»
OR
graph/line of best fit passes through the origin «so yes» ✓
\n
\n
MP1: Accept ‘linear’
\n
MP2 do not award if there is any contradiction
eg: graph not proportional, does not pass through origin.
\n
a.
\n
\n
gradient «»
OR
use of equation with coordinates of a point ✓
\n
✓
\n
\n
MP1 allow gradients in range to
\n
MP2 allow a range to for
\n
\n
b(i).
\n
\n
✓
\n
\n
Accept
\n
\n
b(ii).
\n
\n
straight line, gradient greater than line of best fit, and within the error bars ✓
\n

\n
b(iii).
\n
\n
« of » =
OR
« of » = ✓
\n
rounds uncertainty to 1sf
OR
✓
\n
\n
Allow ECF from (b)(i)
Award [2] marks for a bald correct answer
\n
b(iv).
\n
\n
Experimental value matches this/correct, as expected value within the range ✓
OR
experimental value does not match/incorrect, as it is not within range ✓
\n
b(v).
\n
",
+ "Examiners report": "",
+ "topics": [
+ "tools"
+ ],
+ "subtopics": [
+ "tool-3-mathematics"
+ ]
+ },
+ {
+ "question_id": "20N.3.SL.TZ0.2",
+ "Question": "
\n
A student studies the relationship between the centripetal force applied to an object undergoing circular motion and its period .
\n
The object (mass ) is attached by a light inextensible string, through a tube, to a weight which hangs vertically. The string is free to move through the tube. A student swings the mass in a horizontal, circular path, adjusting the period of the motion until the radius is constant. The radius of the circle and the mass of the object are measured and remain constant for the entire experiment.
\n

\n
© International Baccalaureate Organization 2020.
\n
The student collects the measurements of five times, for weight . The weight is then doubled () and the data collection repeated. Then it is repeated with and . The results are expected to support the relationship
\n
\n
\n
In reality, there is friction in the system, so in this case is less than the total centripetal force in the system. A suitable graph is plotted to determine the value of experimentally. The value of was also calculated directly from the measured values of and .
\n
\n
State why the experiment is repeated with different values of .
\n
[1]
\n
a.
\n
\n
Predict from the equation whether the value of found experimentally will be larger, the same or smaller than the value of calculated directly.
\n
[2]
\n
b.
\n
\n
The measurements of were collected five times. Explain how repeated measurements of reduced the random error in the final experimental value of .
\n
[2]
\n
c(i).
\n
\n
Outline why repeated measurements of would not reduce any systematic error in .
\n
[1]
\n
c(ii).
\n
",
+ "Markscheme": "
\n
In order to draw a graph « of versus »
OR
\n
to confirm proportionality between « and »
\n
OR
\n
to confirm relationship between « and »
\n
OR
\n
because W is the independent variable in the experiment ✓
\n
\n
OWTTE
\n
a.
\n
\n
ALTERNATIVE 1
\n
\n
OR
\n
centripetal force is larger «than » / is smaller «than centripetal» ✓
\n
«so» experimental is smaller «than calculated value» ✓
\n
\n
ALTERNATIVE 2 (refers to graph)
\n
reference to «friction force is» a systematic error «and does not affect gradient» ✓
\n
«so» is the same ✓
\n
\n
MP2 awarded only with correct justification.
Candidates can gain zero, MP1 alone or full marks.
\n
OWTTE
\n
b.
\n
\n
mention of mean/average value «of » ✓
\n
this reduces uncertainty in / result
OR
more accurate/precise ✓
\n
\n
Reference to “random errors average out” scores MP1
\n
Accept “closer to true value”, “more reliable value” OWTTE for MP2
\n
\n
c(i).
\n
\n
systematic errors «usually» constant/always present/ not influenced by repetition ✓
\n
\n
OWTTE
\n
c(ii).
\n
",
+ "Examiners report": "
\n
Most candidates scored. Different wording was used to express the aim of confirming the relationship.
\n
a.
\n
\n
Most successful candidates chose to consider a single point then concluding that the calculated mr would be smaller than the real value as W < centripetal force, or even went into analysing the dependence of the frictional force with W. Many were able to deduce this. Some candidates thought that a graph would still have the same gradient (if friction was constant) and mentioned systematic error, so mr was not changed which was also accepted.
\n
b.
\n
\n
Most candidates stated that the mean of 5 values of T was used to obtain an answer closer to the true value if there were no systematic errors. Some just repeated the question.
\n
c(i).
\n
\n
Usually very well answered acknowledging that systematic errors are constant and present throughout all measurements.
\n
c(ii).
\n
",
+ "topics": [
+ "inquiry"
+ ],
+ "subtopics": [
+ "i-1-2-designing",
+ "i-2-3-interpreting-results",
+ "inquiry-1-exploring-and-designing",
+ "inquiry-2-collecting-and-processing-data"
+ ]
+ },
+ {
+ "question_id": "20N.2.HL.TZ0.10",
+ "Question": "
\n
The de Broglie wavelength of a particle accelerated close to the speed of light is approximately
\n
\n
where is the energy of the particle.
A beam of electrons of energy is produced in an accelerator.
\n
\n
The electron beam is used to study the nuclear radius of carbon-12. The beam is directed from the left at a thin sample of carbon-12. A detector is placed at an angle relative to the direction of the incident beam.
\n

\n
The graph shows the variation of the intensity of electrons with . There is a minimum of intensity for .
\n

\n
\n
Show that the wavelength of an electron in the beam is about .
\n
[1]
\n
a.
\n
\n
Discuss how the results of the experiment provide evidence for matter waves.
\n
[2]
\n
b(i).
\n
\n
The accepted value of the diameter of the carbon-12 nucleus is . Estimate the angle at which the minimum of the intensity is formed.
\n
[2]
\n
b(ii).
\n
\n
Outline why electrons with energy of approximately would be unsuitable for the investigation of nuclear radii.
\n
[2]
\n
b(iii).
\n
\n
Experiments with many nuclides suggest that the radius of a nucleus is proportional to , where is the number of nucleons in the nucleus. Show that the density of a nucleus remains approximately the same for all nuclei.
\n
[2]
\n
c.
\n
",
+ "Markscheme": "
\n
OR ✓
\n
Answer to at least s.f. (i.e. 3.0)
\n
a.
\n
\n
«the shape of the graph suggests that» electrons undergo diffraction «with carbon nuclei» ✓
\n
only waves diffract ✓
\n
b(i).
\n
\n
✓
\n
OR ✓
\n
b(ii).
\n
\n
the de Broglie wavelength of electrons is «much» longer than the size of a nucleus ✓
\n
hence electrons would not undergo diffraction
OR
no diffraction pattern would be observed ✓
\n
b(iii).
\n
\n
volume of a nucleus proportional to AND mass proportional to ✓
\n
the ratio independent of «hence density the same for all nuclei» ✓
\n
\n
Both needed for MP1
\n
c.
\n
",
+ "Examiners report": "
\n
An easy calculation with only one energy conversion to consider and a 'show' answer to help.
\n
a.
\n
\n
This question was challenging for candidates many of whom seemed to have little idea of the experiment. Many answers discussed deflection, with the idea that forces between the electron and the nucleus causing it to deflect at a particular angle. This was often combined with the word interference to suggest evidence of matter waves. A number of answers described a demonstration the candidates remembered seeing so answers talked about fuzzy green rings.
\n
b(i).
\n
\n
This was answered reasonably well with only the odd omission of the sine in the equation.
\n
b(ii).
\n
\n
Candidates generally scored poorly on this question. There was confusion between this experiment and another diffraction one, so often the new wavelength was compared to the spacing between atoms. Also, in line with answers to b(i) there were suggestions that the electrons did not have sufficient energy to reach the nucleus or would be deflected by too great an angle to be seen.
\n
b(iii).
\n
\n
This question proved challenging and it wasn't common to find answers that scored both marks. Of those that had the right approach some missed out on both marks by describing A as the mass of the nucleus rather than proportional to the mass of the nucleus.
\n
c.
\n
",
+ "topics": [
+ "e-nuclear-and-quantum-physics"
+ ],
+ "subtopics": [
+ "e-1-structure-of-the-atom",
+ "e-2-quantum-physics"
+ ]
+ },
+ {
+ "question_id": "20N.2.HL.TZ0.6",
+ "Question": "
\n
One possible fission reaction of uranium-235 (U-235) is
\n
\n
Mass of one atom of U-235
Binding energy per nucleon for U-235
Binding energy per nucleon for Xe-140
Binding energy per nucleon for Sr-94
\n
\n
A nuclear power station uses U-235 as fuel. Assume that every fission reaction of U-235 gives rise to of energy.
\n
\n
A sample of waste produced by the reactor contains of strontium-94 (Sr-94). Sr-94 is radioactive and undergoes beta-minus () decay into a daughter nuclide X. The reaction for this decay is
\n
.
\n
\n
\n
The graph shows the variation with time of the mass of Sr-94 remaining in the sample.
\n

\n
\n
State what is meant by binding energy of a nucleus.
\n
[1]
\n
a(i).
\n
\n
Outline why quantities such as atomic mass and nuclear binding energy are often expressed in non-SI units.
\n
[1]
\n
a(ii).
\n
\n
Show that the energy released in the reaction is about .
\n
[1]
\n
a(iii).
\n
\n
Estimate, in , the specific energy of U-235.
\n
[2]
\n
b(i).
\n
\n
The power station has a useful power output of and an efficiency of . Determine the mass of U-235 that undergoes fission in one day.
\n
[2]
\n
b(ii).
\n
\n
The specific energy of fossil fuel is typically . Suggest, with reference to your answer to (b)(i), one advantage of U-235 compared with fossil fuels in a power station.
\n
[1]
\n
b(iii).
\n
\n
Write down the proton number of nuclide X.
\n
[1]
\n
c(i).
\n
\n
State the half-life of Sr-94.
\n
[1]
\n
c(ii).
\n
\n
Calculate the mass of Sr-94 remaining in the sample after minutes.
\n
[2]
\n
c(iii).
\n
",
+ "Markscheme": "
\n
energy required to «completely» separate the nucleons
OR
energy released when a nucleus is formed from its constituent nucleons ✓
\n
Allow protons AND neutrons.
\n
a(i).
\n
\n
the values «in SI units» would be very small ✓
\n
a(ii).
\n
\n
OR ✓
\n
a(iii).
\n
\n
see AND ✓
\n
✓
\n
b(i).
\n
\n
energy produced in one day ✓
\n
mass ✓
\n
b(ii).
\n
\n
«specific energy of uranium is much greater than that of coal, hence» more energy can be produced from the same mass of fuel / per
OR
less fuel can be used to create the same amount of energy ✓
\n
b(iii).
\n
\n
✓
\n
Do not allow unless the proton number is indicated.
\n
c(i).
\n
\n
ALTERNATIVE 1
\n
✓
\n
mass remaining ✓
\n
\n
ALTERNATIVE 2
\n
decay constant ✓
\n
mass remaining ✓
\n
c(iii).
\n
",
+ "Examiners report": "
\n
Generally, well answered but candidates did miss the mark by discussing the constituents of a nucleus rather than the nucleons, or protons and neutrons. There seemed to be fewer comments than usual about 'the energy required to bind the nucleus together'.
\n
a(i).
\n
\n
Well answered with some candidates describing the values as too large or small.
\n
a(ii).
\n
\n
Well answered.
\n
a(iii).
\n
\n
This caused problems for some with mass often correctly calculated but energy causing more difficulty with the eV conversion either being inaccurate or omitted. Candidates were allowed error carried forward for the second mark as long as they were dividing an energy by a mass.
\n
b(i).
\n
\n
Most candidates had the right idea, but common problems included forgetting the efficiency or not converting to days.
\n
b(ii).
\n
\n
HL only. This was well answered.
\n
b(iii).
\n
\n
Most candidates answered this correctly.
\n
c(i).
\n
\n
Most candidates answered this correctly.
\n
c(ii).
\n
\n
This was answered well with most candidates (even at HL) going down the number of half-lives route rather than the exponential calculation route.
\n
c(iii).
\n
",
+ "topics": [
+ "a--space-time-and-motion"
+ ],
+ "subtopics": [
+ "a-4-rigid-body-mechanics"
+ ]
+ },
+ {
+ "question_id": "20N.2.HL.TZ0.7",
+ "Question": "
\n
A vertical solid cylinder of uniform cross-sectional area floats in water. The cylinder is partially submerged. When the cylinder floats at rest, a mark is aligned with the water surface. The cylinder is pushed vertically downwards so that the mark is a distance below the water surface.
\n

\n
At time the cylinder is released. The resultant vertical force on the cylinder is related to the displacement of the mark by
\n
\n
where is the density of water.
\n
\n
The cylinder was initially pushed down a distance .
\n
\n
Outline why the cylinder performs simple harmonic motion when released.
\n
[1]
\n
a.
\n
\n
The mass of the cylinder is and the cross-sectional area of the cylinder is . The density of water is . Show that the angular frequency of oscillation of the cylinder is about .
\n
[2]
\n
b.
\n
\n
Determine the maximum kinetic energy of the cylinder.
\n
[2]
\n
c(i).
\n
\n
Draw, on the axes, the graph to show how the kinetic energy of the cylinder varies with time during one period of oscillation .
\n

\n
[2]
\n
c(ii).
\n
",
+ "Markscheme": "
\n
the «restoring» force/acceleration is proportional to displacement ✓
\n
Allow use of symbols i.e. or
\n
a.
\n
\n
Evidence of equating «to obtain » ✓
\n
\n
OR ✓
\n
\n
Answer to at least s.f.
\n
b.
\n
\n
« is a maximum when hence» ✓
\n
✓
\n
c(i).
\n
\n
energy never negative ✓
\n
correct shape with two maxima ✓
\n

\n
c(ii).
\n
",
+ "Examiners report": "
\n
This was well answered with candidates gaining credit for answers in words or symbols.
\n
a.
\n
\n
Again, very well answered.
\n
b.
\n
\n
A straightforward calculation with the most common mistake being missing the squared on the omega.
\n
c(i).
\n
\n
Most candidates answered with a graph that was only positive so scored the first mark.
\n
c(ii).
\n
",
+ "topics": [
+ "a--space-time-and-motion",
+ "c-wave-behaviour"
+ ],
+ "subtopics": [
+ "a-4-rigid-body-mechanics",
+ "c-1-simple-harmonic-motion"
+ ]
+ },
+ {
+ "question_id": "20N.2.HL.TZ0.8",
+ "Question": "
\n
The diagram shows the electric field lines of a positively charged conducting sphere of radius and charge .
\n

\n
Points A and B are located on the same field line.
\n
\n
A proton is placed at A and released from rest. The magnitude of the work done by the electric field in moving the proton from A to B is . Point A is at a distance of from the centre of the sphere. Point B is at a distance of from the centre of the sphere.
\n
\n
Explain why the electric potential decreases from A to B.
\n
[2]
\n
a.
\n
\n
Draw, on the axes, the variation of electric potential with distance from the centre of the sphere.
\n

\n
[2]
\n
b.
\n
\n
Calculate the electric potential difference between points A and B.
\n
[1]
\n
c(i).
\n
\n
Determine the charge of the sphere.
\n
[2]
\n
c(ii).
\n
\n
The concept of potential is also used in the context of gravitational fields. Suggest why scientists developed a common terminology to describe different types of fields.
\n
[1]
\n
d.
\n
",
+ "Markscheme": "
\n
ALTERNATIVE 1
work done on moving a positive test charge in any outward direction is negative ✓
potential difference is proportional to this work «so decreases from A to B» ✓
\n
\n
ALTERNATIVE 2
potential gradient is directed opposite to the field so inwards ✓
the gradient indicates the direction of increase of «hence increases towards the centre/decreases from A to B» ✓
\n
\n
ALTERNATIVE 3
so as increases decreases ✓
is positive as is positive ✓
\n
\n
ALTERNATIVE 4
the work done per unit charge in bringing a positive charge from infinity ✓
to point B is less than point A ✓
\n
a.
\n
\n
curve decreasing asymptotically for ✓
\n
non zero constant between and ✓
\n

\n
b.
\n
\n
✓
\n
c(i).
\n
\n
✓
\n
✓
\n
c(ii).
\n
\n
to highlight similarities between «different» fields ✓
\n
d.
\n
",
+ "Examiners report": "
\n
The majority who answered in terms of potential gained one mark. Often the answers were in terms of work done rather than work done per unit charge or missed the fact that the potential is positive.
\n
a.
\n
\n
This was well answered.
\n
b.
\n
\n
Most didn't realise that the key to the answer is the definition of potential or potential difference and tried to answer using one of the formulae in the data booklet, but incorrectly.
\n
c(i).
\n
\n
Even though many were able to choose the appropriate formula from the data booklet they were often hampered in their use of the formula by incorrect techniques when using fractions.
\n
c(ii).
\n
\n
This was generally well answered with only a small number of answers suggesting greater international cooperation.
\n
d.
\n
",
+ "topics": [
+ "a--space-time-and-motion",
+ "d-fields",
+ "nature-of-science"
+ ],
+ "subtopics": [
+ "a-4-rigid-body-mechanics",
+ "d-2-electric-and-magnetic-fields"
+ ]
+ },
+ {
+ "question_id": "20N.2.HL.TZ0.9",
+ "Question": "
\n
The diagram shows an alternating current generator with a rectangular coil rotating at a constant frequency in a uniform magnetic field.
\n

\n
\n
The graph shows how the generator output voltage varies with time .
\n

\n
Electrical power produced by the generator is delivered to a consumer some distance away.
\n
\n
Explain, by reference to Faraday’s law of induction, how an electromotive force (emf) is induced in the coil.
\n
[3]
\n
a.
\n
\n
The average power output of the generator is . Calculate the root mean square (rms) value of the generator output current.
\n
[2]
\n
b(i).
\n
\n
The voltage output from the generator is stepped up before transmission to the consumer. Estimate the factor by which voltage has to be stepped up in order to reduce power loss in the transmission line by a factor of .
\n
[1]
\n
b(ii).
\n
\n
The frequency of the generator is doubled with no other changes being made. Draw, on the axes, the variation with time of the voltage output of the generator.
\n
[2]
\n
b(iii).
\n
",
+ "Markscheme": "
\n
there is a magnetic flux «linkage» in the coil / coil cuts magnetic field ✓
\n
this flux «linkage» changes as the angle varies/coil rotates ✓
\n
«Faraday’s law» connects induced emf with rate of change of flux «linkage» with time ✓
\n
Do not award MP2 or 3 for answers that don’t discuss flux.
\n
a.
\n
\n
✓
\n
\n
✓
\n
b(i).
\n
\n
«power loss proportional to hence the step-up factor is ✓
\n
b(ii).
\n
\n
peak emf doubles ✓
\n
halves ✓
\n
Must show at least 1 cycle.
\n
b(iii).
\n
",
+ "Examiners report": "
\n
This question was well answered with the majority discussing changes in flux rather than wires cutting field lines, which was good to see.
\n
a.
\n
\n
Generally well answered.
\n
b(i).
\n
\n
This was well answered by many, but some candidates left the answer as a surd. The most common guess here involved the use of root 2.
\n
b(ii).
\n
\n
Well answered, with the majority of candidates scoring at least 1 mark.
\n
b(iii).
\n
",
+ "topics": [
+ "b-the-particulate-nature-of-matter",
+ "d-fields"
+ ],
+ "subtopics": [
+ "b-4-thermodynamics",
+ "d-4-induction"
+ ]
+ },
+ {
+ "question_id": "20N.2.SL.TZ0.1",
+ "Question": "
\n
A company delivers packages to customers using a small unmanned aircraft. Rotating horizontal blades exert a force on the surrounding air. The air above the aircraft is initially stationary.
\n

\n
The air is propelled vertically downwards with speed . The aircraft hovers motionless above the ground. A package is suspended from the aircraft on a string. The mass of the aircraft is and the combined mass of the package and string is . The mass of air pushed downwards by the blades in one second is .
\n
\n
State the value of the resultant force on the aircraft when hovering.
\n
[1]
\n
a(i).
\n
\n
Outline, by reference to Newton’s third law, how the upward lift force on the aircraft is achieved.
\n
[2]
\n
a(ii).
\n
\n
Determine . State your answer to an appropriate number of significant figures.
\n
[3]
\n
a(iii).
\n
\n
The package and string are now released and fall to the ground. The lift force on the aircraft remains unchanged. Calculate the initial acceleration of the aircraft.
\n
[2]
\n
b.
\n
",
+ "Markscheme": "
\n
Blades exert a downward force on the air ✓
\n
air exerts an equal and opposite force on the blades «by Newton’s third law»
OR
air exerts a reaction force on the blades «by Newton’s third law» ✓
\n
Downward direction required for MP1.
\n
a(ii).
\n
\n
«lift force/change of momentum in one second» ✓
\n
✓
\n
AND answer expressed to sf only ✓
\n
Allow from .
\n
a(iii).
\n
\n
vertical force = lift force – weight OR OR ✓
\n
acceleration✓
\n
b.
\n
",
+ "Examiners report": "
",
+ "topics": [
+ "a--space-time-and-motion"
+ ],
+ "subtopics": [
+ "a-1-kinematics",
+ "a-2-forces-and-momentum",
+ "a-3-work-energy-and-power"
+ ]
+ },
+ {
+ "question_id": "20N.2.SL.TZ0.12",
+ "Question": "
\n
\n (b)\n
\n
\n
\n Determine the terminal velocity of the sphere.\n
\n
\n
\n
\n
\n
\n (c(i))\n
\n
\n
\n Determine the force exerted by the spring on the sphere when the sphere is at rest.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (b)\n
\n
\n radius of sphere\n \n ✓\n
\n
\n
\n
\n weight of sphere\n \n
\n
\n \n \n OR\n \n \n
\n
\n \n ✓\n
\n
\n
\n
\n \n ✓\n
\n
\n
\n
\n \n \n Accept use of\n \n leading to\n \n \n \n
\n
\n \n \n Allow implicit calculation of radius for MP1\n \n \n
\n
\n \n \n Do not allow ECF for MP3 if buoyant force omitted.\n \n \n
\n
\n
\n (c(i))\n
\n
\n \n
\n
\n \n \n OR\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 Accept use of\n \n leading to\n \n \n \n
\n
\n",
+ "Examiners report": "
\n (b)\n
\n
\n Only those candidates who forgot to include the buoyant force missed marks here.\n
\n
\n
\n (c(i))\n
\n
\n Continuing from b, most candidates scored full marks.\n
\n
\n",
+ "topics": [
+ "a--space-time-and-motion"
+ ],
+ "subtopics": [
+ "a-2-forces-and-momentum"
+ ]
+ },
+ {
+ "question_id": "20N.2.SL.TZ0.15",
+ "Question": "
\n
\n (a)\n
\n
\n
\n Show that the apparent brightness\n \n , where\n \n is the distance of the object from Earth,\n \n is the surface temperature of the object and\n \n is the surface area of the object.\n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n
\n Two of the brightest objects in the night sky seen from Earth are the planet Venus and the star Sirius. Explain why the equation\n \n is applicable to Sirius but not to Venus.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n substitution of\n \n into\n \n giving\n \n
\n
\n
\n
\n \n \n Removal of constants\n \n and\n \n is optional\n \n \n
\n
\n
\n (b)\n
\n
\n \n equation applies to Sirius/stars that are luminous/emit light «from fusion»\n \n \n ✓\n \n
\n
\n \n but Venus reflects the Sun’s light/does not emit light\n \n \n «\n \n \n from fusion\n \n \n »\n \n \n ✓\n \n
\n
\n
\n
\n \n \n OWTTE\n \n \n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "e-nuclear-and-quantum-physics"
+ ],
+ "subtopics": [
+ "e-5-fusion-and-stars"
+ ]
+ },
+ {
+ "question_id": "20N.2.SL.TZ0.3",
+ "Question": "
\n
A sample of vegetable oil, initially in the liquid state, is placed in a freezer that transfers thermal energy from the sample at a constant rate. The graph shows how temperature of the sample varies with time .
\n

\n
The following data are available.
\n
Mass of the sample
Specific latent heat of fusion of the oil
Rate of thermal energy transfer
\n
\n
Calculate the thermal energy transferred from the sample during the first minutes.
\n
[1]
\n
a(i).
\n
\n
Estimate the specific heat capacity of the oil in its liquid phase. State an appropriate unit for your answer.
\n
[2]
\n
a(ii).
\n
\n
The sample begins to freeze during the thermal energy transfer. Explain, in terms of the molecular model of matter, why the temperature of the sample remains constant during freezing.
\n
[3]
\n
b.
\n
\n
Calculate the mass of the oil that remains unfrozen after minutes.
\n
[2]
\n
c.
\n
",
+ "Markscheme": "
\n
✓
\n
\n
a(i).
\n
\n
OR ✓
\n
OR ✓
\n
Allow any appropriate unit that is
\n
a(ii).
\n
\n
«intermolecular» bonds are formed during freezing ✓
\n
bond-forming process releases energy
OR
«intermolecular» PE decreases «and the difference is transferred as heat» ✓
\n
«average random» KE of the molecules does not decrease/change ✓
\n
temperature is related to «average» KE of the molecules «hence unchanged» ✓
\n
\n
To award MP3 or MP4 molecules/particles/atoms must be mentioned.
\n
b.
\n
\n
mass of frozen oil ✓
\n
unfrozen mass ✓
\n
c.
\n
",
+ "Examiners report": "
",
+ "topics": [
+ "b-the-particulate-nature-of-matter"
+ ],
+ "subtopics": [
+ "b-1-thermal-energy-transfers"
+ ]
+ },
+ {
+ "question_id": "20N.2.SL.TZ0.5",
+ "Question": "
\n
The graph shows how current varies with potential difference across a component X.
\n

\n
\n
Component X and a cell of negligible internal resistance are placed in a circuit.
\n
A variable resistor R is connected in series with component X. The ammeter reads .
\n

\n
\n
Component X and the cell are now placed in a potential divider circuit.
\n

\n
\n
\n
Outline why component X is considered non-ohmic.
\n
[1]
\n
a.
\n
\n
Determine the resistance of the variable resistor.
\n
[3]
\n
b(i).
\n
\n
Calculate the power dissipated in the circuit.
\n
[1]
\n
b(ii).
\n
\n
State the range of current that the ammeter can measure as the slider S of the potential divider is moved from Q to P.
\n
[1]
\n
c(i).
\n
\n
Describe, by reference to your answer for (c)(i), the advantage of the potential divider arrangement over the arrangement in (b).
\n
[2]
\n
c(ii).
\n
",
+ "Markscheme": "
\n
current is not «directly» proportional to the potential difference
OR
resistance of X is not constant
OR
resistance of X changes «with current/voltage» ✓
\n
a.
\n
\n
ALTERNATIVE 1
\n
voltage across X ✓
\n
voltage across R ✓
\n
resistance of variable resistor ✓
\n
\n
ALTERNATIVE 2
\n
overall resistance ✓
\n
resistance of X ✓
\n
resistance of variable resistor ✓
\n
b(i).
\n
\n
power ✓
\n
b(ii).
\n
\n
from to ✓
\n
c(i).
\n
\n
allows zero current through component X / potential divider arrangement ✓
\n
provides greater range «of current through component X» ✓
\n
c(ii).
\n
",
+ "Examiners report": "
",
+ "topics": [
+ "b-the-particulate-nature-of-matter"
+ ],
+ "subtopics": [
+ "b-5-current-and-circuits"
+ ]
+ },
+ {
+ "question_id": "20N.2.SL.TZ0.7",
+ "Question": "
\n
\n (a)\n
\n
\n
\n Outline why the cylinder performs simple harmonic motion when released.\n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n
\n The mass of the cylinder is\n \n and the cross-sectional area of the cylinder is\n \n . The density of water is\n \n . Show that the angular frequency of oscillation of the cylinder is about\n \n .\n
\n
\n
\n
\n
\n
\n (c(ii))\n
\n
\n
\n Draw, on the axes, the graph to show how the kinetic energy of the cylinder varies with time during\n \n one\n \n period of oscillation\n \n .\n
\n
\n
\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n \n the\n \n \n «\n \n \n restoring\n \n \n »\n \n \n force/acceleration is proportional to displacement\n \n \n ✓\n \n
\n
\n \n \n
\n Allow use of symbols i.e.\n \n \n \n or\n \n \n \n
\n
\n
\n (b)\n
\n
\n \n Evidence of equating\n \n «to obtain\n \n » ✓\n \n
\n
\n
\n
\n \n \n \n \n OR\n \n \n \n ✓\n \n
\n
\n
\n
\n \n \n Answer to at least\n \n s.f.\n \n \n
\n
\n
\n (c(ii))\n
\n
\n \n energy never negative\n \n \n ✓\n \n
\n
\n \n correct shape with two maxima\n \n \n ✓\n \n
\n
\n
\n
\n
\n",
+ "Examiners report": "
\n (a)\n
\n
\n This was well answered with candidates gaining credit for answers in words or symbols.\n
\n
\n
\n (b)\n
\n
\n Again, very well answered.\n
\n
\n
\n (c(ii))\n
\n
\n Most candidates answered with a graph that was only positive so scored the first mark.\n
\n
\n",
+ "topics": [
+ "c-wave-behaviour"
+ ],
+ "subtopics": [
+ "c-1-simple-harmonic-motion"
+ ]
+ },
+ {
+ "question_id": "21M.2.HL.TZ1.10",
+ "Question": "
\n
In an electric circuit used to investigate the photoelectric effect, the voltage is varied until the reading in the ammeter is zero. The stopping voltage that produces this reading is 1.40 V.
\n

\n
\n
Describe the photoelectric effect.
\n
[2]
\n
a.
\n
\n
Show that the maximum velocity of the photoelectrons is .
\n
[2]
\n
b.
\n
\n
The photoelectrons are emitted from a sodium surface. Sodium has a work function of 2.3 eV.
\n
Calculate the wavelength of the radiation incident on the sodium. State an appropriate unit for your answer.
\n
[3]
\n
c.
\n
",
+ "Markscheme": "
\n
electrons are ejected from the surface of a metal ✓
\n
after gaining energy from photons/electromagnetic radiation ✓
\n
there is a minimum «threshold» energy/frequency
OR
maximum «threshold» wavelength ✓
\n
a.
\n
\n
«» and manipulation to get ✓
\n
OR ✓
\n
Must see either complete substitution or calculation to at least 3 s.f. for MP2
\n
b.
\n
\n
✓
\n
✓
\n
✓
\n
Must see an appropriate unit to award MP3.
\n
c.
\n
",
+ "Examiners report": "
",
+ "topics": [
+ "b-the-particulate-nature-of-matter",
+ "e-nuclear-and-quantum-physics"
+ ],
+ "subtopics": [
+ "b-5-current-and-circuits",
+ "e-2-quantum-physics"
+ ]
+ },
+ {
+ "question_id": "21M.2.HL.TZ1.2",
+ "Question": "
\n
A planet is in a circular orbit around a star. The speed of the planet is constant. The following data are given:
\n
Mass of planet kg
Mass of star kg
Distance from the star to the planet R m.
\n
\n
A spacecraft is to be launched from the surface of the planet to escape from the star system. The radius of the planet is 9.1 × 103 km.
\n
\n
Explain why a centripetal force is needed for the planet to be in a circular orbit.
\n
[2]
\n
a.
\n
\n
Calculate the value of the centripetal force.
\n
[1]
\n
b.
\n
\n
Show that the gravitational potential due to the planet and the star at the surface of the planet is about −5 × 109 J kg−1.
\n
[3]
\n
c.i.
\n
\n
Estimate the escape speed of the spacecraft from the planet–star system.
\n
[2]
\n
c.ii.
\n
",
+ "Markscheme": "
\n
«circular motion» involves a changing velocity ✓
\n
«Tangential velocity» is «always» perpendicular to centripetal force/acceleration ✓
\n
there must be a force/acceleration towards centre/star ✓
\n
without a centripetal force the planet will move in a straight line ✓
\n
a.
\n
\n
«N» ✓
\n
b.
\n
\n
Vplanet = «−»«−» 5.9 × 107 «J kg−1» ✓
\n
Vstar = «−»«−» 4.9 × 109 «J kg−1» ✓
\n
Vplanet + Vstar = «−» 4.9 «09» × 109 «J kg−1» ✓
\n
Must see substitutions and not just equations.
\n
c.i.
\n
\n
use of vesc = ✓
\n
v = 9.91 × 104 «m s−1» ✓
\n
\n
\n
c.ii.
\n
",
+ "Examiners report": "
",
+ "topics": [
+ "a--space-time-and-motion",
+ "d-fields"
+ ],
+ "subtopics": [
+ "a-2-forces-and-momentum",
+ "d-1-gravitational-fields"
+ ]
+ },
+ {
+ "question_id": "21M.2.HL.TZ1.8",
+ "Question": "
\n
On a guitar, the strings played vibrate between two fixed points. The frequency of vibration is modified by changing the string length using a finger. The different strings have different wave speeds. When a string is plucked, a standing wave forms between the bridge and the finger.
\n

\n
\n
The string is displaced 0.4 cm at point P to sound the guitar. Point P on the string vibrates with simple harmonic motion (shm) in its first harmonic with a frequency of 195 Hz. The sounding length of the string is 62 cm.
\n
\n
Outline how a standing wave is produced on the string.
\n
[2]
\n
a.
\n
\n
Show that the speed of the wave on the string is about 240 m s−1.
\n
[2]
\n
b.i.
\n
\n
Sketch a graph to show how the acceleration of point P varies with its displacement from the rest position.
\n

\n
[1]
\n
b.ii.
\n
\n
Calculate, in m s−1, the maximum velocity of vibration of point P when it is vibrating with a frequency of 195 Hz.
\n
[2]
\n
b.iii.
\n
\n
Calculate, in terms of g, the maximum acceleration of P.
\n
[2]
\n
b.iv.
\n
\n
Estimate the displacement needed to double the energy of the string.
\n
[2]
\n
b.v.
\n
\n
The string is made to vibrate in its third harmonic. State the distance between consecutive nodes.
\n
[1]
\n
c.
\n
",
+ "Markscheme": "
\n
«travelling» wave moves along the length of the string and reflects «at fixed end» ✓
\n
superposition/interference of incident and reflected waves ✓
\n
the superposition of the reflections is reinforced only for certain wavelengths ✓
\n
a.
\n
\n
✓
\n
✓
\n
Answer must be to 3 or more sf or working shown for MP2.
\n
b.i.
\n
\n
straight line through origin with negative gradient ✓
\n
b.ii.
\n
\n
max velocity occurs at x = 0 ✓
\n
✓
\n
b.iii.
\n
\n
✓
\n
✓
\n
b.iv.
\n
\n
use of ✓
\n
✓
\n
b.v.
\n
",
+ "Examiners report": "
",
+ "topics": [
+ "c-wave-behaviour"
+ ],
+ "subtopics": [
+ "c-1-simple-harmonic-motion",
+ "c-2-wave-model",
+ "c-4-standing-waves-and-resonance"
+ ]
+ },
+ {
+ "question_id": "21M.2.HL.TZ2.10",
+ "Question": "
\n
The table gives data for Jupiter and three of its moons, including the radius r of each object.
\n

\n
\n
A spacecraft is to be sent from to infinity.
\n
\n
Calculate, for the surface of , the gravitational field strength gIo due to the mass of . State an appropriate unit for your answer.
\n
[2]
\n
a.
\n
\n
Show that the is about 80.
\n
[2]
\n
b.i.
\n
\n
Outline, using (b)(i), why it is not correct to use the equation to calculate the speed required for the spacecraft to reach infinity from the surface of .
\n
[1]
\n
b.ii.
\n
\n
An engineer needs to move a space probe of mass 3600 kg from Ganymede to Callisto. Calculate the energy required to move the probe from the orbital radius of Ganymede to the orbital radius of Callisto. Ignore the mass of the moons in your calculation.
\n
[2]
\n
c.
\n
",
+ "Markscheme": "
\n
✓
\n
N kg−1 OR m s−2 ✓
\n
a.
\n
\n
AND seen ✓
\n
✓
\n
For MP1, potentials can be seen individually or as a ratio.
\n
b.i.
\n
\n
«this is the escape speed for alone but» gravitational potential / field of Jupiter must be taken into account ✓
\n
OWTTE
\n
b.ii.
\n
\n
✓
\n
« multiplies by 3600 kg to get » 1.9 × 1011 «J» ✓
\n
Award [2] marks if factor of ½ used, taking into account orbital kinetic energies, leading to a final answer of 9.4 x 1010 «J».
\n
Allow ECF from MP1
\n
Award [2] marks for a bald correct answer.
\n
c.
\n
",
+ "Examiners report": "
",
+ "topics": [
+ "d-fields"
+ ],
+ "subtopics": [
+ "d-1-gravitational-fields"
+ ]
+ },
+ {
+ "question_id": "21M.2.HL.TZ2.8",
+ "Question": "
\n
Monochromatic light of wavelength λ is normally incident on a diffraction grating. The diagram shows adjacent slits of the diffraction grating labelled V, W and X. Light waves are diffracted through an angle θ to form a second-order diffraction maximum. Points Z and Y are labelled.
\n

\n
\n
State the effect on the graph of the variation of sin θ with n of:
\n
\n
State the phase difference between the waves at V and Y.
\n
[1]
\n
a.i.
\n
\n
State, in terms of λ, the path length between points X and Z.
\n
[1]
\n
a.ii.
\n
\n
The separation of adjacent slits is d. Show that for the second-order diffraction maximum .
\n
[1]
\n
a.iii.
\n
\n
Monochromatic light of wavelength 633 nm is normally incident on a diffraction grating. The diffraction maxima incident on a screen are detected and their angle θ to the central beam is determined. The graph shows the variation of sinθ with the order n of the maximum. The central order corresponds to n = 0.
\n

\n
Determine a mean value for the number of slits per millimetre of the grating.
\n
[4]
\n
b.
\n
\n
using a light source with a smaller wavelength.
\n
[1]
\n
c.i.
\n
\n
increasing the distance between the diffraction grating and the screen.
\n
[1]
\n
c.ii.
\n
",
+ "Markscheme": "
\n
0 OR 2π OR 360° ✓
\n
\n
a.i.
\n
\n
✓
\n
Do not award ECF from(a)(ii).
\n
a.iii.
\n
\n
identifies gradient with OR use of ✓
\n
gradient = 0.08 OR correct replacement in equation with coordinates of a point ✓
\n
✓
\n
✓
\n
Allow ECF from MP3
\n
b.
\n
\n
gradient smaller ✓
\n
c.i.
\n
",
+ "Examiners report": "
",
+ "topics": [
+ "c-wave-behaviour"
+ ],
+ "subtopics": [
+ "c-3-wave-phenomena"
+ ]
+ },
+ {
+ "question_id": "21M.2.HL.TZ2.9",
+ "Question": "
\n
In an experiment to demonstrate the photoelectric effect, monochromatic electromagnetic radiation from source A is incident on the surfaces of metal P and metal Q. Observations of the emission of electrons from P and Q are made.
\n
The experiment is then repeated with two other sources of electromagnetic radiation: B and C. The table gives the results for the experiment and the wavelengths of the radiation sources.
\n

\n
\n
Outline the cause of the electron emission for radiation A.
\n
[1]
\n
a.i.
\n
\n
Outline why electrons are never emitted for radiation C.
\n
[1]
\n
a.ii.
\n
\n
Outline why radiation B gives different results.
\n
[1]
\n
a.iii.
\n
\n
Explain why there is no effect on the table of results when the intensity of source B is doubled.
\n
[1]
\n
b.
\n
\n
Photons with energy 1.1 × 10−18 J are incident on a third metal surface. The maximum energy of electrons emitted from the surface of the metal is 5.1 × 10−19 J.
\n
Calculate, in eV, the work function of the metal.
\n
[2]
\n
c.
\n
",
+ "Markscheme": "
\n
photon transfers «all» energy to electron ✓
\n
a.i.
\n
\n
photon energy is less than both work functions
OR
photon energy is insufficient «to remove an electron» ✓
\n
Answer must be in terms of photon energy.
\n
a.ii.
\n
\n
Identifies P work function lower than Q work function ✓
\n
a.iii.
\n
\n
changing/doubling intensity «changes/doubles number of photons arriving but» does not change energy of photon ✓
\n
b.
\n
\n
✓
\n
work function ✓
\n
Award [2] marks for a bald correct answer.
\n
c.
\n
",
+ "Examiners report": "
",
+ "topics": [
+ "e-nuclear-and-quantum-physics"
+ ],
+ "subtopics": [
+ "e-2-quantum-physics"
+ ]
+ },
+ {
+ "question_id": "21M.2.SL.TZ1.1",
+ "Question": "
\n
Two players are playing table tennis. Player A hits the ball at a height of 0.24 m above the edge of the table, measured from the top of the table to the bottom of the ball. The initial speed of the ball is 12.0 m s−1 horizontally. Assume that air resistance is negligible.
\n

\n
\n
The ball bounces and then reaches a peak height of 0.18 m above the table with a horizontal speed of 10.5 m s−1. The mass of the ball is 2.7 g.
\n
\n
Show that the time taken for the ball to reach the surface of the table is about 0.2 s.
\n
[1]
\n
a.
\n
\n
Sketch, on the axes, a graph showing the variation with time of the vertical component of velocity vv of the ball until it reaches the table surface. Take g to be +10 m s−2.
\n

\n
[2]
\n
b.
\n
\n
The net is stretched across the middle of the table. The table has a length of 2.74 m and the net has a height of 15.0 cm.
\n
Show that the ball will go over the net.
\n
[3]
\n
c.
\n
\n
Determine the kinetic energy of the ball immediately after the bounce.
\n
[2]
\n
d.i.
\n
\n
Player B intercepts the ball when it is at its peak height. Player B holds a paddle (racket) stationary and vertical. The ball is in contact with the paddle for 0.010 s. Assume the collision is elastic.
\n

\n
Calculate the average force exerted by the ball on the paddle. State your answer to an appropriate number of significant figures.
\n
[3]
\n
d.ii.
\n
",
+ "Markscheme": "
\n
t = «=» 0.22 «s»
OR
\n
t = ✓
\n
Answer to 2 or more significant figures or formula with variables replaced by correct values.
\n
a.
\n
\n
increasing straight line from zero up to 0.2 s in x-axis ✓
\n
with gradient = 10 ✓
\n
b.
\n
\n
ALTERNATIVE 1
\n
«0.114 s» ✓
\n
m ✓
\n
so (0.24 − 0.065) = 0.175 > 0.15 OR 0.065 < (0.24 − 0.15) «so it goes over the net» ✓
\n
\n
ALTERNATIVE 2
\n
«0.24 − 0.15 = 0.09 = so» t = 0.134 s ✓
\n
0.134 × 12 = 1.6 m ✓
\n
1.6 > 1.37 «so ball passed the net already» ✓
\n
\n
Allow use of g = 9.8.
\n
c.
\n
\n
ALTERNATIVE 1
\n
KE = mv2 + mgh = 0.0027 ×10.52 + 0.0027 × 9.8 × 0.18 ✓
\n
0.15 «J» ✓
\n
\n
ALTERNATIVE 2
\n
Use of vx = 10.5 AND vy = 1.88 to get v = «» = 10.67 «m s−1» ✓
\n
KE = × 0.0027 × 10.672 = 0.15 «J» ✓
\n
d.i.
\n
\n
«m s−1» ✓
\n
\n
OR
\n
5.67 «N» ✓
\n
any answer to 2 significant figures «N» ✓
\n
d.ii.
\n
",
+ "Examiners report": "
",
+ "topics": [
+ "a--space-time-and-motion"
+ ],
+ "subtopics": [
+ "a-1-kinematics",
+ "a-2-forces-and-momentum",
+ "a-3-work-energy-and-power"
+ ]
+ },
+ {
+ "question_id": "21M.2.SL.TZ1.2",
+ "Question": "
\n
A planet is in a circular orbit around a star. The speed of the planet is constant.
\n
\n
Explain why a centripetal force is needed for the planet to be in a circular orbit.
\n
[2]
\n
a.i.
\n
\n
State the nature of this centripetal force.
\n
[1]
\n
a.ii.
\n
\n
Determine the gravitational field of the planet.
\n
The following data are given:
\n
Mass of planet kg
Radius of the planet m.
\n
[2]
\n
b.
\n
",
+ "Markscheme": "
\n
«circular motion» involves a changing velocity ✓
\n
«Tangential velocity» is «always» perpendicular to centripetal force/acceleration ✓
\n
there must be a force/acceleration towards centre/star ✓
\n
without a centripetal force the planet will move in a straight line ✓
\n
a.i.
\n
\n
gravitational force/force of gravity ✓
\n
a.ii.
\n
\n
use of ✓
\n
6.4 «Nkg−1 or ms−2» ✓
\n
b.
\n
",
+ "Examiners report": "
",
+ "topics": [
+ "a--space-time-and-motion"
+ ],
+ "subtopics": [
+ "a-2-forces-and-momentum"
+ ]
+ },
+ {
+ "question_id": "21M.2.SL.TZ1.3",
+ "Question": "
\n
A mass of 1.0 kg of water is brought to its boiling point of 100 °C using an electric heater of power 1.6 kW.
\n
\n
A mass of 0.86 kg of water remains after it has boiled for 200 s.
\n
\n
The electric heater has two identical resistors connected in parallel.
\n

\n
The circuit transfers 1.6 kW when switch A only is closed. The external voltage is 220 V.
\n
\n
The molar mass of water is 18 g mol−1. Estimate the average speed of the water molecules in the vapor produced. Assume the vapor behaves as an ideal gas.
\n
[2]
\n
a.i.
\n
\n
State one assumption of the kinetic model of an ideal gas.
\n
[1]
\n
a.ii.
\n
\n
Estimate the specific latent heat of vaporization of water. State an appropriate unit for your answer.
\n
[2]
\n
b.i.
\n
\n
Explain why the temperature of water remains at 100 °C during this time.
\n
[1]
\n
b.ii.
\n
\n
The heater is removed and a mass of 0.30 kg of pasta at −10 °C is added to the boiling water.
\n
Determine the equilibrium temperature of the pasta and water after the pasta is added. Other heat transfers are negligible.
\n
Specific heat capacity of pasta = 1.8 kJ kg−1 K−1
Specific heat capacity of water = 4.2 kJ kg−1 K−1
\n
[3]
\n
c.
\n
\n
Show that each resistor has a resistance of about 30 Ω.
\n
[1]
\n
d.i.
\n
\n
Calculate the power transferred by the heater when both switches are closed.
\n
[2]
\n
d.ii.
\n
",
+ "Markscheme": "
\n
Ek = « » = «J» ✓
\n
v = «» = 720 «m s−1» ✓
\n
a.i.
\n
\n
particles can be considered points «without dimensions» ✓
\n
no intermolecular forces/no forces between particles «except during collisions»✓
\n
the volume of a particle is negligible compared to volume of gas ✓
\n
collisions between particles are elastic ✓
\n
time between particle collisions are greater than time of collision ✓
\n
no intermolecular PE/no PE between particles ✓
\n
\n
Accept reference to atoms/molecules for “particle”
\n
a.ii.
\n
\n
«mL = P t» so «» = 2.3 x 106 «J kg-1» ✓
\n
J kg−1 ✓
\n
b.i.
\n
\n
«all» of the energy added is used to increase the «intermolecular» potential energy of the particles/break «intermolecular» bonds/OWTTE ✓
\n
Accept reference to atoms/molecules for “particle”
\n
b.ii.
\n
\n
use of mcΔT ✓
\n
0.86 × 4200 × (100 – T) = 0.3 × 1800 × (T +10) ✓
\n
Teq = 85.69«°C» ≅ 86«°C» ✓
\n
Accept Teq in Kelvin (359 K).
\n
c.
\n
\n
«Ω» ✓
\n
Must see either the substituted values OR a value for R to at least three s.f.
\n
\n
d.i.
\n
\n
use of parallel resistors addition so Req = 15 «Ω» ✓
\n
P = 3200 «W» ✓
\n
d.ii.
\n
",
+ "Examiners report": "
",
+ "topics": [
+ "b-the-particulate-nature-of-matter"
+ ],
+ "subtopics": [
+ "b-1-thermal-energy-transfers",
+ "b-3-gas-laws",
+ "b-5-current-and-circuits"
+ ]
+ },
+ {
+ "question_id": "21M.2.SL.TZ1.6",
+ "Question": "
\n
On a guitar, the strings played vibrate between two fixed points. The frequency of vibration is modified by changing the string length using a finger. The different strings have different wave speeds. When a string is plucked, a standing wave forms between the bridge and the finger.
\n

\n
\n
The string is displaced 0.4 cm at point P to sound the guitar. Point P on the string vibrates with simple harmonic motion (shm) in its first harmonic with a frequency of 195 Hz. The sounding length of the string is 62 cm.
\n
\n
Outline how a standing wave is produced on the string.
\n
[2]
\n
a.
\n
\n
Show that the speed of the wave on the string is about 240 m s−1.
\n
[2]
\n
b.i.
\n
\n
Sketch a graph to show how the acceleration of point P varies with its displacement from the rest position.
\n

\n
[1]
\n
b.ii.
\n
",
+ "Markscheme": "
\n
«travelling» wave moves along the length of the string and reflects «at fixed end» ✓
\n
superposition/interference of incident and reflected waves ✓
\n
the superposition of the reflections is reinforced only for certain wavelengths ✓
\n
a.
\n
\n
✓
\n
✓
\n
Answer must be to 3 or more sf or working shown for MP2.
\n
b.i.
\n
\n
straight line through origin with negative gradient ✓
\n
b.ii.
\n
",
+ "Examiners report": "
",
+ "topics": [
+ "c-wave-behaviour"
+ ],
+ "subtopics": [
+ "c-1-simple-harmonic-motion",
+ "c-2-wave-model",
+ "c-4-standing-waves-and-resonance"
+ ]
+ },
+ {
+ "question_id": "21M.2.SL.TZ1.7",
+ "Question": "
\n
Conservation of energy and conservation of momentum are two examples of conservation laws.
\n
\n
Outline the significance of conservation laws for physics.
\n
[1]
\n
a.
\n
\n
When a pi meson π- (du̅) and a proton (uud) collide, a possible outcome is a sigma baryon Σ0 (uds) and a kaon meson Κ0 (ds̅).
\n
Apply three conservation laws to show that this interaction is possible.
\n
[3]
\n
b.
\n
",
+ "Markscheme": "
\n
they express fundamental principles of nature ✓
\n
allow to model situations ✓
\n
allow to calculate unknown variables ✓
\n
allow to predict possible outcomes ✓
\n
allow to predict missing quantities/particles ✓
\n
allow comparison of different system states ✓
\n
a.
\n
\n
three correct conservation laws listed ✓
\n
at least one conservation law correctly demonstrated ✓
\n
all three conservation laws correctly demonstrated ✓
\n
b.
\n
",
+ "Examiners report": "",
+ "topics": [
+ "nature-of-science"
+ ],
+ "subtopics": []
+ },
+ {
+ "question_id": "21M.2.SL.TZ1.8",
+ "Question": "
\n
\n (a)\n
\n
\n
\n Outline how a standing wave is produced on the string.\n
\n
\n
\n
\n
\n
\n (b.i)\n
\n
\n
\n Show that the speed of the wave on the string is about 240 m s\n \n −1\n \n .\n
\n
\n
\n
\n
\n
\n (b.ii)\n
\n
\n
\n Sketch a graph to show how the acceleration of point P varies with its displacement from the rest position.\n
\n
\n
\n
\n
\n
\n
\n
\n
\n (c)\n
\n
\n
\n The string is made to vibrate in its third harmonic. State the distance between consecutive nodes.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n «travelling» wave moves along the length of the string and reflects «at fixed end»\n \n ✓\n \n
\n
\n superposition/interference of incident and reflected waves\n \n ✓\n \n
\n
\n the superposition of the reflections is reinforced only for certain wavelengths\n \n ✓\n \n
\n
\n
\n (b.i)\n
\n
\n \n ✓\n
\n
\n \n ✓\n
\n
\n \n Answer must be to 3 or more sf or working shown for\n \n MP2.\n \n \n
\n
\n
\n (b.ii)\n
\n
\n straight line through origin with negative gradient\n \n ✓\n \n
\n
\n
\n (c)\n
\n
\n \n \n ✓\n \n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "c-wave-behaviour"
+ ],
+ "subtopics": [
+ "c-1-simple-harmonic-motion",
+ "c-2-wave-model",
+ "c-4-standing-waves-and-resonance"
+ ]
+ },
+ {
+ "question_id": "21M.2.SL.TZ2.1",
+ "Question": "
\n
A football player kicks a stationary ball of mass 0.45 kg towards a wall. The initial speed of the ball after the kick is 19 m s−1 and the ball does not rotate. Air resistance is negligible and there is no wind.
\n

\n
\n
The player’s foot is in contact with the ball for 55 ms. Calculate the average force that acts on the ball due to the football player.
\n
[2]
\n
a.
\n
\n
The ball leaves the ground at an angle of 22°. The horizontal distance from the initial position of the edge of the ball to the wall is 11 m. Calculate the time taken for the ball to reach the wall.
\n
[2]
\n
b.i.
\n
\n
The top of the wall is 2.4 m above the ground. Deduce whether the ball will hit the wall.
\n
[3]
\n
b.ii.
\n
\n
In practice, air resistance affects the ball. Outline the effect that air resistance has on the vertical acceleration of the ball. Take the direction of the acceleration due to gravity to be positive.
\n
[2]
\n
c.
\n
\n
The player kicks the ball again. It rolls along the ground without sliding with a horizontal velocity of . The radius of the ball is . Calculate the angular velocity of the ball. State an appropriate SI unit for your answer.
\n
[1]
\n
d.
\n
",
+ "Markscheme": "
\n
✓
\n
✓
\n
Allow [2] marks for a bald correct answer.
\n
Allow ECF for MP2 if 19 sin22 OR 19 cos22 used.
\n
a.
\n
\n
✓
\n
✓
\n
Allow ECF for MP2
\n
b.i.
\n
\n
✓
\n
✓
\n
ball does not hit wall OR 2.5 «m» > 2.4 «m» ✓
\n
Allow ECF from (b)(i) and from MP1
\n
Allow g = 10 m s−2
\n
b.ii.
\n
\n
air resistance opposes «direction of» motion
OR
air resistance opposes velocity ✓
\n
on the way up «vertical» acceleration is increased OR greater than g ✓
\n
on the way down «vertical» acceleration is decreased OR smaller than g ✓
\n
Allow deceleration/acceleration but meaning must be clear
\n
c.
\n
\n
✓
\n
Unit must be seen for mark
\n
Accept Hz
\n
Accept
\n
d.
\n
",
+ "Examiners report": "
",
+ "topics": [
+ "a--space-time-and-motion"
+ ],
+ "subtopics": [
+ "a-1-kinematics",
+ "a-2-forces-and-momentum"
+ ]
+ },
+ {
+ "question_id": "21M.2.SL.TZ2.5",
+ "Question": "
\n
A vertical tube, open at both ends, is completely immersed in a container of water. A loudspeaker above the container connected to a signal generator emits sound. As the tube is raised the loudness of the sound heard reaches a maximum because a standing wave has formed in the tube.
\n

\n
\n
Describe two ways in which standing waves differ from travelling waves.
\n
[2]
\n
a.
\n
\n
Outline how a standing wave forms in the tube.
\n
[2]
\n
b.i.
\n
\n
The tube is raised until the loudness of the sound reaches a maximum for a second time.
\n
Draw, on the following diagram, the position of the nodes in the tube when the second maximum is heard.
\n

\n
[1]
\n
b.ii.
\n
\n
Between the first and second positions of maximum loudness, the tube is raised through 0.37 m. The speed of sound in the air in the tube is 320 m s−1. Determine the frequency of the sound emitted by the loudspeaker.
\n
\n
[2]
\n
b.iii.
\n
",
+ "Markscheme": "
\n
energy is not propagated by standing waves ✓
\n
amplitude constant for travelling waves OR amplitude varies with position for standing waves OR standing waves have nodes/antinodes ✓
\n
phase varies with position for travelling waves OR phase constant inter-node for standing waves ✓
\n
travelling waves can have any wavelength OR standing waves have discrete wavelengths ✓
\n
OWTTE
\n
a.
\n
\n
«sound» wave «travels down tube and» is reflected ✓
\n
incident and reflected wave superpose/combine/interfere ✓
\n
OWTTE
\n
Do not award MP1 if the reflection is quoted at the walls/container
\n
b.i.
\n
\n
nodes shown at water surface AND way up tube (by eye) ✓
\n
Accept drawing of displacement diagram for correct harmonic without nodes specifically identified.
\n
Award [0] if waveform is shown below the water surface
\n
b.ii.
\n
\n
✓
\n
✓
\n
Allow ECF from MP1
\n
b.iii.
\n
",
+ "Examiners report": "
",
+ "topics": [
+ "c-wave-behaviour"
+ ],
+ "subtopics": [
+ "c-4-standing-waves-and-resonance"
+ ]
+ },
+ {
+ "question_id": "21M.2.SL.TZ2.6",
+ "Question": "
\n
A photovoltaic cell is supplying energy to an external circuit. The photovoltaic cell can be modelled as a practical electrical cell with internal resistance.
\n
The intensity of solar radiation incident on the photovoltaic cell at a particular time is at a maximum for the place where the cell is positioned.
\n
The following data are available for this particular time:
\n
Operating current = 0.90 A
Output potential difference to external circuit = 14.5 V
Output emf of photovoltaic cell = 21.0 V
Area of panel = 350 mm × 450 mm
\n
\n
Explain why the output potential difference to the external circuit and the output emf of the photovoltaic cell are different.
\n
\n
[2]
\n
a.
\n
\n
Calculate the internal resistance of the photovoltaic cell for the maximum intensity condition using the model for the cell.
\n
\n
[3]
\n
b.
\n
\n
The maximum intensity of sunlight incident on the photovoltaic cell at the place on the Earth’s surface is 680 W m−2.
\n
A measure of the efficiency of a photovoltaic cell is the ratio
\n
\n
Determine the efficiency of this photovoltaic cell when the intensity incident upon it is at a maximum.
\n
[3]
\n
c.
\n
\n
State two reasons why future energy demands will be increasingly reliant on sources such as photovoltaic cells.
\n

\n
[2]
\n
d.
\n
",
+ "Markscheme": "
\n
there is a potential difference across the internal resistance
OR
there is energy/power dissipated in the internal resistance ✓
\n
when there is current «in the cell»/as charge flows «through the cell» ✓
\n
Allow full credit for answer based on
\n
a.
\n
\n
ALTERNATIVE 1
pd dropped across cell ✓
\n
internal resistance ✓
\n
✓
\n
ALTERNATIVE 2
\n
so ✓
\n
✓
\n
✓
\n
Alternative solutions are possible
\n
Award [3] marks for a bald correct answer
\n
b.
\n
\n
power arriving at cell = 680 x 0.35 x 0.45 = «107 W» ✓
\n
power in external circuit = 14.5 x 0.9 = «13.1 W» ✓
\n
efficiency = 0.12 OR 12 % ✓
\n
Award [3] marks for a bald correct answer
\n
Allow ECF for MP3
\n
c.
\n
\n
«energy from Sun/photovoltaic cells» is renewable
OR
non-renewable are running out ✓
\n
non-polluting/clean ✓
\n
no greenhouse gases
OR
does not contribute to global warming/climate change ✓
\n
OWTTE
\n
Do not allow economic aspects (e.g. free energy)
\n
d.
\n
",
+ "Examiners report": "
",
+ "topics": [
+ "a--space-time-and-motion",
+ "b-the-particulate-nature-of-matter"
+ ],
+ "subtopics": [
+ "a-3-work-energy-and-power",
+ "b-5-current-and-circuits"
+ ]
+ },
+ {
+ "question_id": "21N.2.HL.TZ0.5",
+ "Question": "
\n
A square loop of side 5.0 cm enters a region of uniform magnetic field at t = 0. The loop exits the region of magnetic field at t = 3.5 s. The magnetic field strength is 0.94 T and is directed into the plane of the paper. The magnetic field extends over a length 65 cm. The speed of the loop is constant.
\n

\n
\n
Show that the speed of the loop is 20 cm s−1.
\n
[1]
\n
a.
\n
\n
Sketch, on the axes, a graph to show the variation with time of the magnetic flux linkage in the loop.
\n

\n
[1]
\n
b.i.
\n
\n
Sketch, on the axes, a graph to show the variation with time of the magnitude of the emf induced in the loop.
\n

\n
[1]
\n
b.ii.
\n
\n
There are 85 turns of wire in the loop. Calculate the maximum induced emf in the loop.
\n
[2]
\n
c.i.
\n
\n
The resistance of the loop is 2.4 Ω. Calculate the magnitude of the magnetic force on the loop as it enters the region of magnetic field.
\n
[2]
\n
c.ii.
\n
\n
Show that the energy dissipated in the loop from t = 0 to t = 3.5 s is 0.13 J.
\n
[2]
\n
d.i.
\n
\n
The mass of the wire is 18 g. The specific heat capacity of copper is 385 J kg−1 K−1. Estimate the increase in temperature of the wire.
\n
[2]
\n
d.ii.
\n
",
+ "Markscheme": "
\n

\n
shape as above ✓
\n
b.i.
\n
\n

\n
shape as above ✓
\n
\n
Vertical lines not necessary to score.
\n
Allow ECF from (b)(i).
\n
b.ii.
\n
\n
ALTERNATIVE 1
\n
maximum flux at «» «Wb» ✓
\n
emf = «» «V» ✓
\n
ALTERNATIVE 2
\n
emf induced in one turn = BvL = «V» ✓
\n
emf «V» ✓
\n
\n
Award [2] marks for a bald correct answer.
\n
Allow ECF from MP1.
\n
c.i.
\n
\n
OR «A» ✓
\n
«N» ✓
\n
\n
Allow ECF from (c)(i).
\n
Award [2] marks for a bald correct answer.
\n
c.ii.
\n
\n
Energy is being dissipated for 0.50 s ✓
\n
« J»
\n
OR
\n
« J» ✓
\n
\n
Allow ECF from (b) and (c).
\n
Watch for candidates who do not justify somehow the use of 0.5 s and just divide by 2 their answer.
\n
d.i.
\n
\n
✓
\n
«K» ✓
\n
\n
Allow [2] marks for a bald correct answer.
\n
Award [1] for a POT error in MP1.
\n
d.ii.
\n
",
+ "Examiners report": "
",
+ "topics": [
+ "a--space-time-and-motion",
+ "b-the-particulate-nature-of-matter",
+ "d-fields"
+ ],
+ "subtopics": [
+ "a-3-work-energy-and-power",
+ "b-1-thermal-energy-transfers",
+ "b-5-current-and-circuits",
+ "d-3-motion-in-electromagnetic-fields",
+ "d-4-induction"
+ ]
+ },
+ {
+ "question_id": "21N.2.HL.TZ0.7",
+ "Question": "
\n
A conducting sphere has radius 48 cm. The electric potential on the surface of the sphere is 3.4 × 105 V.
\n
\n
The sphere is connected by a long conducting wire to a second conducting sphere of radius 24 cm. The second sphere is initially uncharged.
\n

\n
\n
Show that the charge on the surface of the sphere is +18 μC.
\n
[1]
\n
a.
\n
\n
Describe, in terms of electron flow, how the smaller sphere becomes charged.
\n
[1]
\n
b.i.
\n
\n
Predict the charge on each sphere.
\n
[3]
\n
b.ii.
\n
",
+ "Markscheme": "
\n
\n
OR
\n
«μC» ✓
\n
a.
\n
\n
electrons leave the small sphere «making it positively charged» ✓
\n
b.i.
\n
\n
✓
\n
✓
\n
so «μC», «μC» ✓
\n
\n
Award [3] marks for a bald correct answer.
\n
b.ii.
\n
",
+ "Examiners report": "
",
+ "topics": [
+ "b-the-particulate-nature-of-matter",
+ "d-fields"
+ ],
+ "subtopics": [
+ "b-5-current-and-circuits",
+ "d-2-electric-and-magnetic-fields"
+ ]
+ },
+ {
+ "question_id": "21N.2.HL.TZ0.8",
+ "Question": "
\n
The graph shows the variation with diffraction angle of the intensity of light after it has passed through four parallel slits.
\n

\n
The number of slits is increased but their separation and width stay the same. All slits are illuminated.
\n
\n
State what is meant by the Doppler effect.
\n
[2]
\n
a.
\n
\n
A plate performs simple harmonic oscillations with a frequency of 39 Hz and an amplitude of 8.0 cm.
\n
Show that the maximum speed of the oscillating plate is about 20 m s−1.
\n
[2]
\n
b.
\n
\n
Sound of frequency 2400 Hz is emitted from a stationary source towards the oscillating plate in (b). The speed of sound is 340 m s−1.
\n

\n
Determine the maximum frequency of the sound that is received back at the source after reflection at the plate.
\n
\n
[2]
\n
c.
\n
\n
State what will happen to the angular position of the primary maxima.
\n
[1]
\n
d.i.
\n
\n
State what will happen to the width of the primary maxima.
\n
[1]
\n
d.ii.
\n
\n
State what will happen to the intensity of the secondary maxima.
\n
[1]
\n
d.iii.
\n
",
+ "Markscheme": "
\n
the change in the observed frequency ✓
\n
when there is relative motion between the source and the observer ✓
\n
\n
Do not award MP1 if they refer to wavelength.
\n
a.
\n
\n
use of ✓
\n
maximum speed is «m s−1» ✓
\n
\n
Award [2] for a bald correct answer.
\n
b.
\n
\n
frequency at plate «Hz»
\n
at source «Hz» ✓
\n
\n
Award [2] marks for a bald correct answer.
\n
Award [1] mark when the effect is only applied once.
\n
c.
\n
\n
stays the same ✓
\n
d.i.
\n
",
+ "Examiners report": "
",
+ "topics": [
+ "c-wave-behaviour"
+ ],
+ "subtopics": [
+ "c-1-simple-harmonic-motion",
+ "c-3-wave-phenomena",
+ "c-5-doppler-effect"
+ ]
+ },
+ {
+ "question_id": "21N.2.SL.TZ0.3",
+ "Question": "
\n
A longitudinal wave travels in a medium with speed 340 m s−1. The graph shows the variation with time t of the displacement x of a particle P in the medium. Positive displacements on the graph correspond to displacements to the right for particle P.
\n

\n
\n
Another wave travels in the medium. The graph shows the variation with time t of the displacement of each wave at the position of P.
\n

\n
\n
A standing sound wave is established in a tube that is closed at one end and open at the other end. The period of the wave is . The diagram represents the standing wave at and at . The wavelength of the wave is 1.20 m. Positive displacements mean displacements to the right.
\n

\n
\n
Calculate the wavelength of the wave.
\n
[2]
\n
a.
\n
\n
State the phase difference between the two waves.
\n
[1]
\n
b.i.
\n
\n
Identify a time at which the displacement of P is zero.
\n
[1]
\n
b.ii.
\n
\n
Estimate the amplitude of the resultant wave.
\n
[1]
\n
b.iii.
\n
\n
Calculate the length of the tube.
\n
[1]
\n
c.i.
\n
\n
A particle in the tube has its equilibrium position at the open end of the tube.
State and explain the direction of the velocity of this particle at time .
\n
[2]
\n
c.ii.
\n
\n
Draw on the diagram the standing wave at time .
\n
[1]
\n
c.iii.
\n
",
+ "Markscheme": "
\n
«s» or «Hz» ✓
\n
«m» ✓
\n
\n
Allow ECF from MP1.
Award [2] for a bald correct answer.
\n
a.
\n
\n
«±» OR ✓
\n
b.i.
\n
\n
8.0 OR 8.5 «μm» ✓
\n
From the graph on the paper, value is 8.0. From the calculated correct trig functions, value is 8.49.
\n
b.iii.
\n
\n
L = «» 0.90 «m» ✓
\n
c.i.
\n
\n
to the right ✓
\n
displacement is getting less negative
\n
OR
\n
change of displacement is positive ✓
\n
c.ii.
\n
\n
horizontal line drawn at the equilibrium position ✓
\n
c.iii.
\n
",
+ "Examiners report": "
",
+ "topics": [
+ "c-wave-behaviour",
+ "d-fields"
+ ],
+ "subtopics": [
+ "c-1-simple-harmonic-motion",
+ "d-2-electric-and-magnetic-fields"
+ ]
+ },
+ {
+ "question_id": "21N.2.SL.TZ0.4",
+ "Question": "
\n
A charged particle, P, of charge +68 μC is fixed in space. A second particle, Q, of charge +0.25 μC is held at a distance of 48 cm from P and is then released.
\n

\n
\n
The diagram shows two parallel wires X and Y that carry equal currents into the page.
\n

\n
Point Q is equidistant from the two wires. The magnetic field at Q due to wire X alone is 15 mT.
\n
\n
The work done to move a particle of charge 0.25 μC from one point in an electric field to another is 4.5 μJ. Calculate the magnitude of the potential difference between the two points.
\n
[1]
\n
a.
\n
\n
Determine the force on Q at the instant it is released.
\n
[2]
\n
b.i.
\n
\n
Describe the motion of Q after release.
\n
[2]
\n
b.ii.
\n
\n
On the diagram draw an arrow to show the direction of the magnetic field at Q due to wire X alone.
\n
[1]
\n
c.i.
\n
\n
Determine the magnitude and direction of the resultant magnetic field at Q.
\n
[2]
\n
c.ii.
\n
",
+ "Markscheme": "
\n
«» 18 «V» ✓
\n
a.
\n
\n
✓
\n
«N» ✓
\n
\n
Award [2] marks for a bald correct answer.
\n
Allow symbolic k in substitutions for MP1.
\n
Do not allow ECF from incorrect or not squared distance.
\n
b.i.
\n
\n
Q moves to the right/away from P «along a straight line»
\n
OR
\n
Q is repelled from P ✓
\n
with increasing speed/Q accelerates ✓
\n
acceleration decreases ✓
\n
b.ii.
\n
\n
\n

\n
arrow of any length as shown ✓
\n
c.i.
\n
\n
«using components or Pythagoras to get» B = 21 «mT» ✓
\n
directed «horizontally» to the right ✓
\n
\n
If no unit seen, assume mT.
\n
c.ii.
\n
",
+ "Examiners report": "
",
+ "topics": [
+ "a--space-time-and-motion",
+ "b-the-particulate-nature-of-matter",
+ "d-fields"
+ ],
+ "subtopics": [
+ "a-2-forces-and-momentum",
+ "b-5-current-and-circuits",
+ "d-2-electric-and-magnetic-fields",
+ "d-3-motion-in-electromagnetic-fields"
+ ]
+ },
+ {
+ "question_id": "21N.2.SL.TZ0.5",
+ "Question": "
\n
Plutonium-238 (Pu) decays by alpha (α) decay into uranium (U).
\n
The following data are available for binding energies per nucleon:
\n
plutonium 7.568 MeV
\n
uranium 7.600 MeV
\n
alpha particle 7.074 MeV
\n
\n
State what is meant by the binding energy of a nucleus.
\n
[1]
\n
a.i.
\n
\n
Draw, on the axes, a graph to show the variation with nucleon number of the binding energy per nucleon, . Numbers are not required on the vertical axis.
\n

\n
[2]
\n
a.ii.
\n
\n
Identify, with a cross, on the graph in (a)(ii), the region of greatest stability.
\n
[1]
\n
a.iii.
\n
\n
Show that the energy released in this decay is about 6 MeV.
\n
[3]
\n
b.i.
\n
\n
The plutonium nucleus is at rest when it decays.
\n
Calculate the ratio .
\n
[2]
\n
b.ii.
\n
",
+ "Markscheme": "
\n
the energy needed to «completely» separate the nucleons of a nucleus
\n
OR
\n
the energy released when a nucleus is assembled from its constituent nucleons ✓
\n
\n
Accept reference to protons AND neutrons.
\n
a.i.
\n
\n
curve rising to a maximum between 50 and 100 ✓
\n
curve continued and decreasing ✓
\n
\n
Ignore starting point.
\n
Ignore maximum at alpha particle
\n
a.ii.
\n
\n
At a point on the peak of their graph ✓
\n
a.iii.
\n
\n
correct mass numbers for uranium (234) and alpha (4) ✓
\n
«MeV» ✓
\n
energy released 5.51 «MeV» ✓
\n
\n
Ignore any negative sign.
\n
b.i.
\n
\n
«» OR ✓
\n
«» ✓
\n
\n
Award [2] marks for a bald correct answer.
\n
Accept for MP2.
\n
b.ii.
\n
",
+ "Examiners report": "
",
+ "topics": [
+ "a--space-time-and-motion",
+ "b-the-particulate-nature-of-matter",
+ "d-fields"
+ ],
+ "subtopics": [
+ "a-3-work-energy-and-power",
+ "b-1-thermal-energy-transfers",
+ "b-5-current-and-circuits",
+ "d-3-motion-in-electromagnetic-fields"
+ ]
+ },
+ {
+ "question_id": "21N.2.SL.TZ0.6",
+ "Question": "
\n
Titan is a moon of Saturn. The Titan-Sun distance is 9.3 times greater than the Earth-Sun distance.
\n
\n
Show that the intensity of the solar radiation at the location of Titan is 16 W m−2
\n
[1]
\n
a.i.
\n
\n
Titan has an atmosphere of nitrogen. The albedo of the atmosphere is 0.22. The surface of Titan may be assumed to be a black body. Explain why the average intensity of solar radiation absorbed by the whole surface of Titan is 3.1 W m−2
\n
[3]
\n
a.ii.
\n
\n
Show that the equilibrium surface temperature of Titan is about 90 K.
\n
[1]
\n
a.iii.
\n
\n
The orbital radius of Titan around Saturn is and the period of revolution is .
\n
Show that where is the mass of Saturn.
\n
[2]
\n
b.i.
\n
\n
The orbital radius of Titan around Saturn is 1.2 × 109 m and the orbital period is 15.9 days. Estimate the mass of Saturn.
\n
[2]
\n
b.ii.
\n
",
+ "Markscheme": "
\n
incident intensity OR «W m−2» ✓
\n
\n
Allow the use of 1400 for the solar constant.
\n
a.i.
\n
\n
exposed surface is ¼ of the total surface ✓
\n
absorbed intensity = (1−0.22) × incident intensity ✓
\n
0.78 × 0.25 × 15.7 OR 3.07 «W m−2» ✓
\n
\n
Allow 3.06 from rounding and 3.12 if they use 16 W m−2.
\n
a.ii.
\n
\n
σT 4 = 3.07
\n
OR
\n
T = 86 «K» ✓
\n
a.iii.
\n
\n
correct equating of gravitational force / acceleration to centripetal force / acceleration ✓
\n
correct rearrangement to reach the expression given ✓
\n
\n
Allow use of for MP1.
\n
b.i.
\n
\n
«s» ✓
\n
«kg» ✓
\n
\n
Award [2] marks for a bald correct answer.
\n
Allow ECF from MP1.
\n
b.ii.
\n
",
+ "Examiners report": "
",
+ "topics": [
+ "b-the-particulate-nature-of-matter",
+ "d-fields"
+ ],
+ "subtopics": [
+ "b-2-greenhouse-effect",
+ "d-1-gravitational-fields"
+ ]
+ },
+ {
+ "question_id": "22M.2.HL.TZ1.3",
+ "Question": "
\n
Two loudspeakers A and B are initially equidistant from a microphone M. The frequency and intensity emitted by A and B are the same. A and B emit sound in phase. A is fixed in position.
\n

\n
B is moved slowly away from M along the line MP. The graph shows the variation with distance travelled by B of the received intensity at M.
\n

\n
\n
Explain why the received intensity varies between maximum and minimum values.
\n
[3]
\n
a.
\n
\n
State and explain the wavelength of the sound measured at M.
\n
[2]
\n
b.
\n
\n
B is placed at the first minimum. The frequency is then changed until the received intensity is again at a maximum.
\n
Show that the lowest frequency at which the intensity maximum can occur is about 3 kHz.
\n
Speed of sound = 340 m s−1
\n
[2]
\n
c.
\n
\n
Loudspeaker A is switched off. Loudspeaker B moves away from M at a speed of 1.5 m s−1 while emitting a frequency of 3.0 kHz.
\n
Determine the difference between the frequency detected at M and that emitted by B.
\n
[2]
\n
d.
\n
",
+ "Markscheme": "
\n
movement of B means that path distance is different « between BM and AM »
OR
movement of B creates a path difference «between BM and AM» ✓
\n
interference
OR
superposition «of waves» ✓
\n
maximum when waves arrive in phase / path difference = n x lambda
OR
minimum when waves arrive «180° or » out of phase / path difference = (n+½) x lambda ✓
\n
a.
\n
\n
wavelength = 26 cm ✓
\n
peak to peak distance is the path difference which is one wavelength
\n
OR
\n
this is the distance B moves to be back in phase «with A» ✓
\n
\n
Allow 25 – 27 cm for MP1.
\n
b.
\n
\n
«» = 13 cm ✓
\n
«» 2.6 «kHz» ✓
\n
\n
Allow ½ of wavelength from (b) or data from graph for MP1.
\n
Allow ECF from MP1.
\n
c.
\n
\n
ALTERNATIVE 1
use of (+ sign must be seen) OR = 2987 «Hz» ✓
« » = 13 «Hz» ✓
\n
\n
ALTERNATIVE 2
Attempted use of ≈
« Δf » = 13 «Hz» ✓
\n
d.
\n
",
+ "Examiners report": "
\n
This was an \"explain\" questions, so examiners were looking for a clear discussion of the movement of speaker B creating a changing path difference between B and the microphone and A and the microphone. This path difference would lead to interference, and the examiners were looking for a connection between specific phase differences or path differences for maxima or minima. Some candidates were able to discuss basic concepts of interference (e.g. \"there is constructive and destructive interference\"), but failed to make clear connections between the physical situation and the given graph. A very common mistake candidates made was to think the question was about intensity and to therefore describe the decrease in peak height of the maxima on the graph. Another common mistake was to approach this as a Doppler question and to attempt to answer it based on the frequency difference of B.
\n
a.
\n
\n
Many candidates recognized that the wavelength was 26 cm, but the explanations were lacking the details about what information the graph was actually providing. Examiners were looking for a connection back to path difference, and not simply a description of peak-to-peak distance on the graph. Some candidates did not state a wavelength at all, and instead simply discussed the concept of wavelength or suggested that the wavelength was constant.
\n
b.
\n
\n
This was a \"show that\" question that had enough information for backwards working. Examiners were looking for evidence of using the wavelength from (b) or information from the graph to determine wavelength followed by a correct substitution and an answer to more significant digits than the given result.
\n
c.
\n
\n
Many candidates were successful in setting up a Doppler calculation and determining the new frequency, although some missed the second step of finding the difference in frequencies.
\n
d.
\n
",
+ "topics": [
+ "c-wave-behaviour"
+ ],
+ "subtopics": [
+ "c-3-wave-phenomena",
+ "c-5-doppler-effect"
+ ]
+ },
+ {
+ "question_id": "22M.2.SL.TZ1.1",
+ "Question": "
\n
A student uses a load to pull a box up a ramp inclined at 30°. A string of constant length and negligible mass connects the box to the load that falls vertically. The string passes over a pulley that runs on a frictionless axle. Friction acts between the base of the box and the ramp. Air resistance is negligible.
\n

\n
The load has a mass of 3.5 kg and is initially 0.95 m above the floor. The mass of the box is 1.5 kg.
\n
The load is released and accelerates downwards.
\n
\n
Outline two differences between the momentum of the box and the momentum of the load at the same instant.
\n
[2]
\n
a.
\n
\n
The vertical acceleration of the load downwards is 2.4 m s−2.
\n
Calculate the tension in the string.
\n
[2]
\n
b.
\n
\n
Show that the speed of the load when it hits the floor is about 2.1 m s−1.
\n
[2]
\n
c.i.
\n
\n
The radius of the pulley is 2.5 cm. Calculate the angular speed of rotation of the pulley as the load hits the floor. State your answer to an appropriate number of significant figures.
\n
[2]
\n
c.ii.
\n
\n
After the load has hit the floor, the box travels a further 0.35 m along the ramp before coming to rest. Determine the average frictional force between the box and the surface of the ramp.
\n
[4]
\n
d.
\n
\n
The student then makes the ramp horizontal and applies a constant horizontal force to the box. The force is just large enough to start the box moving. The force continues to be applied after the box begins to move.
\n

\n
Explain, with reference to the frictional force acting, why the box accelerates once it has started to move.
\n
[3]
\n
e.
\n
",
+ "Markscheme": "
\n
direction of motion is different / OWTTE ✓
\n
mv / magnitude of momentum is different «even though v the same» ✓
\n
a.
\n
\n
use of ma = mg − T «3.5 x 2.4 = 3.5g − T »
\n
OR
\n
T = 3.5(g − 2.4) ✓
\n
26 «N» ✓
\n
\n
Accept 27 N from g = 10 m s−2
\n
b.
\n
\n
proper use of kinematic equation ✓
\n
«m s−1» ✓
\n
\n
Must see either the substituted values OR a value for v to at least three s.f. for MP2.
\n
c.i.
\n
\n
use of to give 84 «rad s−1»
\n
OR
\n
to give 84 «rad s−1» ✓
\n
\n
quoted to 2sf only✓
\n
\n
c.ii.
\n
\n
ALTERNATIVE 1
\n
«» leading to a = 6.3 «m s-2»
\n
OR
\n
« » leading to t = 0.33 « s » ✓
\n
Fnet = « = » 9.45 «N» ✓
\n
Weight down ramp = 1.5 x 9.8 x sin(30) = 7.4 «N» ✓
\n
friction force = net force – weight down ramp = 2.1 «N» ✓
\n
\n
ALTERNATIVE 2
\n
kinetic energy initial = work done to stop 0.5 x 1.5 x (2.1)2 = FNET x 0.35 ✓
\n
Fnet = 9.45 «N» ✓
\n
Weight down ramp = 1.5 x 9.8 x sin(30) = 7.4 «N» ✓
\n
friction force = net force – weight down ramp = 2.1 «N» ✓
\n
\n
Accept 1.95 N from g = 10 m s-2.
Accept 2.42 N from u = 2.14 m s-1.
\n
d.
\n
\n
static coefficient of friction > dynamic/kinetic coefficient of friction / μs > μk ✓
\n
«therefore» force of dynamic/kinetic friction will be less than the force of static friction ✓
\n
there will be a net / unbalanced forward force once in motion «which results in acceleration»
\n
OR
\n
reference to net F = ma ✓
\n
e.
\n
",
+ "Examiners report": "
\n
Many students recognized the vector nature of momentum implied in the question, although some focused on the forces acting on each object rather than discussing the momentum.
\n
a.
\n
\n
Some students simply calculated the net force acting on the load and did not recognize that this was not the tension force. Many set up a net force equation but had the direction of the forces backwards. This generally resulted from sloppy problem solving.
\n
b.
\n
\n
This was a \"show that\" questions, so examiners were looking for a clear equation leading to a clear substitution of values leading to an answer that had more significant digits than the given answer. Most candidates successfully selected the correct equation and showed a proper substitution. Some candidates started with an energy approach that needed modification as it clearly led to an incorrect solution. These responses did not receive full marks.
\n
c.i.
\n
\n
This SL only question was generally well done. Despite some power of 10 errors, many candidates correctly reported final answer to 2 sf.
\n
c.ii.
\n
\n
Candidates struggled with this question. Very few drew a clear free-body diagram and many simply calculated the acceleration of the box from the given information and used this to calculate the net force on the box, confusing this with the frictional force.
\n
d.
\n
\n
This was an \"explain\" question, so examiners were looking for a clear line of discussion starting with a comparison of the coefficients of friction, leading to a comparison of the relative magnitudes of the forces of friction and ultimately the rise of a net force leading to an acceleration. Many candidates recognized that this was a question about the comparison between static and kinetic/dynamic friction but did not clearly specify which they were referring to in their responses. Some candidates clearly did not read the stem carefully as they referred to the mass being on an incline.
\n
e.
\n
",
+ "topics": [
+ "a--space-time-and-motion"
+ ],
+ "subtopics": [
+ "a-1-kinematics",
+ "a-2-forces-and-momentum"
+ ]
+ },
+ {
+ "question_id": "22M.2.SL.TZ1.2",
+ "Question": "
\n
Cold milk enters a small sterilizing unit and flows over an electrical heating element.
\n

\n
The temperature of the milk is raised from 11 °C to 84 °C. A mass of 55 g of milk enters the sterilizing unit every second.
\n
Specific heat capacity of milk = 3.9 kJ kg−1 K−1
\n
\n
The milk flows out through an insulated metal pipe. The pipe is at a temperature of 84 °C. A small section of the insulation has been removed from around the pipe.
\n

\n
\n
Estimate the power input to the heating element. State an appropriate unit for your answer.
\n
[2]
\n
a.
\n
\n
Outline whether your answer to (a) is likely to overestimate or underestimate the power input.
\n
[2]
\n
b.
\n
\n
Discuss, with reference to the molecules in the liquid, the difference between milk at 11 °C and milk at 84 °C.
\n
[2]
\n
c.
\n
\n
State how energy is transferred from the inside of the metal pipe to the outside of the metal pipe.
\n
[1]
\n
d.i.
\n
\n
The missing section of insulation is 0.56 m long and the external radius of the pipe is 0.067 m. The emissivity of the pipe surface is 0.40. Determine the energy lost every second from the pipe surface. Ignore any absorption of radiation by the pipe surface.
\n
[3]
\n
d.ii.
\n
\n
Describe one other method by which significant amounts of energy can be transferred from the pipe to the surroundings.
\n
[2]
\n
d.iii.
\n
",
+ "Markscheme": "
\n
energy required for milk entering in 1 s = mass x specific heat x 73 ✓
\n
16 kW OR 16000 W ✓
\n
\n
MP1 is for substitution into mcΔT regardless of power of ten.
\n
Allow any correct unit of power (such as J s-1 OR kJ s-1) if paired with an answer to the correct power of 10 for MP2.
\n
a.
\n
\n
Underestimate / more energy or power required ✓
\n
because energy transferred as heat / thermal energy is lost «to surroundings or electrical components» ✓
\n
\n
Do not allow general term “energy” or “power” for MP2.
\n
b.
\n
\n
the temperature has increased so the internal energy / « average » KE «of the molecules» has increased OR temperature is proportional to average KE «of the molecules». ✓
\n
«therefore» the «average» speed of the molecules or particles is higher OR more frequent collisions « between molecules » OR spacing between molecules has increased OR average force of collisions is higher OR intermolecular forces are less OR intermolecular bonds break and reform at a higher rate OR molecules are vibrating faster. ✓
\n
c.
\n
\n
conduction/conducting/conductor «through metal» ✓
\n
d.i.
\n
\n
use of where T = 357 K ✓
\n
use of « = 0.236 m2» ✓
\n
P = 87 «W» ✓
\n
\n
Allow 85 – 89 W for MP3.
\n
Allow ECF for MP3.
\n
d.ii.
\n
\n
convection «is likely to be a significant loss» ✓
\n
«due to reduction in density of air near pipe surface» hot air rises «and is replaced by cooler air from elsewhere»
\n
OR
\n
«due to» conduction «of heat or thermal energy» from pipe to air ✓
\n
d.iii.
\n
",
+ "Examiners report": "
\n
Most candidates recognized that this was a specific heat question and set up a proper calculation, but many struggled to match their answer to an appropriate unit. A common mistake was to leave the answer in some form of an energy unit and others did not match the power of ten of the unit to their answer (e.g. 16 W).
\n
a.
\n
\n
Many candidates recognized that this was an underestimate of the total energy but failed to provide an adequate reason. Many gave generic responses (such as \"some power will be lost\"/not 100% efficient) without discussing the specific form of energy lost (e.g. heat energy).
\n
b.
\n
\n
This was generally well answered. Most HL candidates linked the increase in temperature to the increase in the kinetic energy of the molecules and were able to come up with a consequence of this change (such as the molecules moving faster). SL candidates tended to focus more on consequences, often neglecting to mention the change in KE.
\n
c.
\n
\n
Many candidates recognized that heat transfer by conduction was the correct response. This was a \"state\" question, so candidates were not required to go beyond this.
\n
d.i.
\n
\n
Candidates at both levels were able to recognize that this was a blackbody radiation question. One common mistake candidates made was not calculating the area of a cylinder properly. It is important to remind candidates that they are expected to know how to calculate areas and volumes for basic geometric shapes. Other common errors included the use of T in Celsius and neglecting to raise T ^4. Examiners awarded a large number of ECF marks for candidates who clearly showed work but made these fundamental errors.
\n
d.ii.
\n
\n
A few candidates recognized that convection was the third source of heat loss, although few managed to describe the mechanism of convection properly for MP2. Some candidates did not read the question carefully and instead wrote about methods to increase the rate of heat loss (such as removing more insulation or decreasing the temperature of the environment).
\n
d.iii.
\n
",
+ "topics": [
+ "b-the-particulate-nature-of-matter"
+ ],
+ "subtopics": [
+ "b-1-thermal-energy-transfers",
+ "b-2-greenhouse-effect"
+ ]
+ },
+ {
+ "question_id": "22M.2.SL.TZ1.3",
+ "Question": "
\n
Two loudspeakers A and B are initially equidistant from a microphone M. The frequency and intensity emitted by A and B are the same. A and B emit sound in phase. A is fixed in position.
\n

\n
B is moved slowly away from M along the line MP. The graph shows the variation with distance travelled by B of the received intensity at M.
\n

\n
\n
Explain why the received intensity varies between maximum and minimum values.
\n
[3]
\n
a.
\n
\n
State and explain the wavelength of the sound measured at M.
\n
[2]
\n
b.
\n
\n
B is placed at the first minimum. The frequency is then changed until the received intensity is again at a maximum.
\n
Show that the lowest frequency at which the intensity maximum can occur is about 3 kHz.
\n
Speed of sound = 340 m s−1
\n
[2]
\n
c.
\n
",
+ "Markscheme": "
\n
movement of B means that path distance is different « between BM and AM »
OR
movement of B creates a path difference «between BM and AM» ✓
\n
interference
OR
superposition «of waves» ✓
\n
maximum when waves arrive in phase / path difference = n x lambda
OR
minimum when waves arrive «180° or » out of phase / path difference = (n+½) x lambda ✓
\n
a.
\n
\n
wavelength = 26 cm ✓
\n
peak to peak distance is the path difference which is one wavelength
\n
OR
\n
this is the distance B moves to be back in phase «with A» ✓
\n
\n
Allow 25 − 27 cm for MP1.
\n
b.
\n
\n
«» = 13 cm ✓
\n
«» 2.6 «kHz» ✓
\n
\n
Allow ½ of wavelength from (b) or data from graph.
\n
c.
\n
",
+ "Examiners report": "
\n
This was an \"explain\" questions, so examiners were looking for a clear discussion of the movement of speaker B creating a changing path difference between B and the microphone and A and the microphone. This path difference would lead to interference, and the examiners were looking for a connection between specific phase differences or path differences for maxima or minima. Some candidates were able to discuss basic concepts of interference (e.g. \"there is constructive and destructive interference\"), but failed to make clear connections between the physical situation and the given graph. A very common mistake candidates made was to think the question was about intensity and to therefore describe the decrease in peak height of the maxima on the graph. Another common mistake was to approach this as a Doppler question and to attempt to answer it based on the frequency difference of B.
\n
a.
\n
\n
Many candidates recognized that the wavelength was 26 cm, but the explanations were lacking the details about what information the graph was actually providing. Examiners were looking for a connection back to path difference, and not simply a description of peak-to-peak distance on the graph. Some candidates did not state a wavelength at all, and instead simply discussed the concept of wavelength or suggested that the wavelength was constant.
\n
b.
\n
\n
This was a \"show that\" question that had enough information for backwards working. Examiners were looking for evidence of using the wavelength from (b) or information from the graph to determine wavelength followed by a correct substitution and an answer to more significant digits than the given result.
\n
c.
\n
",
+ "topics": [
+ "c-wave-behaviour"
+ ],
+ "subtopics": [
+ "c-2-wave-model",
+ "c-3-wave-phenomena"
+ ]
+ },
+ {
+ "question_id": "22M.2.SL.TZ1.6",
+ "Question": "
\n
\n (a)\n
\n
\n
\n Outline\n \n two\n \n reasons why both models predict that the motion is simple harmonic when\n \n is small.\n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n
\n Determine the time period of the system when\n \n is small.\n
\n
\n
\n
\n
\n
\n (c)\n
\n
\n
\n Outline, without calculation, the change to the time period of the system for the model represented by graph B when\n \n is large.\n
\n
\n
\n
\n
\n
\n (d)\n
\n
\n
\n The graph shows for model A the variation with\n \n of elastic potential energy\n \n E\n \n \n p\n \n stored in the spring.\n
\n
\n
\n
\n
\n Describe the graph for model B.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n \n \n For both models:\n \n \n
\n displacement is ∝ to acceleration/force «because graph is straight and through origin» ✓\n
\n
\n displacement and acceleration / force in opposite directions «because gradient is negative»\n
\n \n \n OR\n \n \n
\n acceleration/«restoring» force is always directed to equilibrium ✓\n
\n
\n
\n (b)\n
\n
\n attempted use of\n \n ✓\n
\n
\n suitable read-offs leading to gradient of line = 28 « s\n \n -2\n \n » ✓\n
\n
\n \n «\n \n » ✓\n
\n
\n \n s ✓\n
\n
\n
\n (c)\n
\n
\n time period increases ✓\n
\n
\n
\n
\n because average ω «for whole cycle» is smaller\n
\n
\n \n \n OR\n \n \n
\n
\n slope / acceleration / force at large x is smaller\n
\n
\n \n \n OR\n \n \n
\n
\n area under graph B is smaller so average speed is smaller. ✓\n
\n
\n
\n (d)\n
\n
\n same curve\n \n \n OR\n \n \n shape for small amplitudes «to about 0.05 m» ✓\n
\n
\n for large amplitudes «outside of 0.05 m»\n \n E\n \n \n p\n \n smaller for model B / values are lower than original / spread will be wider ✓\n \n \n OWTTE\n \n \n
\n
\n
\n
\n \n Accept answers drawn on graph – e.g.\n \n
\n
\n \n
\n \n
\n
\n",
+ "Examiners report": "
\n (a)\n
\n
\n This item was essentially encouraging candidates to connect concepts about simple harmonic motion to a physical situation described by a graph. The marks were awarded for discussing the physical motion (such as \"the acceleration is in the opposite direction of the displacement\") and not just for describing the graph itself (such as \"the slope of the graph is negative\"). Most candidates were successful in recognizing that the acceleration was proportional to displacement for the first marking point, but many simply described the graph for the second marking point.\n
\n
\n
\n (b)\n
\n
\n This question was well done by many candidates. A common mistake was to select an incorrect gradient, but candidates who showed their work clearly still earned the majority of the marks.\n
\n
\n
\n (c)\n
\n
\n Many candidates recognized that the time period would increase for B, and some were able to give a valid reason based on the difference between the motion of B and the motion of A. It should be noted that the prompt specified \"without calculation\", so candidates who simply attempted to calculate the time period of B did not receive marks.\n
\n
\n
\n (d)\n
\n
\n Candidates were generally successful in describing one of the two aspects of the graph of B compared to A, but few were able to describe both. It should be noted that this is a two mark question, so candidates should have considered the fact that there are two distinct statements to be made about the graphs. Examiners did accept clearly drawn graphs as well for full marks.\n
\n
\n",
+ "topics": [
+ "c-wave-behaviour"
+ ],
+ "subtopics": [
+ "c-1-simple-harmonic-motion"
+ ]
+ },
+ {
+ "question_id": "22M.2.SL.TZ2.2",
+ "Question": "
\n
A fixed mass of an ideal gas is contained in a cylinder closed with a frictionless piston. The volume of the gas is 2.5 × 10−3 m3 when the temperature of the gas is 37 °C and the pressure of the gas is 4.0 × 105 Pa.
\n
\n
Energy is now supplied to the gas and the piston moves to allow the gas to expand. The temperature is held constant.
\n
\n
Calculate the number of gas particles in the cylinder.
\n
[2]
\n
a.
\n
\n
Discuss, for this process, the changes that occur in the density of the gas.
\n
[2]
\n
b.i.
\n
\n
Discuss, for this process, the changes that occur in the internal energy of the gas.
\n
[2]
\n
b.ii.
\n
",
+ "Markscheme": "
\n
Correct conversion of T «T = 310 K» seen ✓
\n
« use of = to get » 2.3 × 1023 ✓
\n
\n
Allow ECF from MP1 i.e., T in Celsius (Result is 2.7 x 1024)
\n
Allow use of n, R and NA
\n
a.
\n
\n
density decreases ✓
\n
volume is increased AND mass/number of particles remains constant ✓
\n
b.i.
\n
\n
internal energy is constant ✓
\n
internal energy depends on kinetic energy/temperature «only»
\n
OR
\n
since temperature/kinetic energy is constant ✓
\n
\n
Do not award MP2 for stating that “temperature is constant” unless linked to the correct conclusion, as that is mentioned in the stem.
\n
Award MP2 for stating that kinetic energy remains constant.
\n
b.ii.
\n
",
+ "Examiners report": "
\n
a) This was well answered with the majority converting to K. Quite a few found the number of moles but did not then convert to molecules.
\n
bi) Well answered. It was pleasing to see how many recognised the need to state that the mass/number of molecules stayed the same as well as stating that the volume increased. At SL this recognition was less common so only 1 mark was often awarded.
\n
bii) This was less successfully answered. A surprising number of candidates said that the internal energy of an ideal gas increases during an isothermal expansion. Many recognised that constant temp meant constant KE but then went on to state that the PE must increase and so the internal energy would increase.
\n
a.
\n
",
+ "topics": [
+ "b-the-particulate-nature-of-matter"
+ ],
+ "subtopics": [
+ "b-3-gas-laws"
+ ]
+ },
+ {
+ "question_id": "22M.2.SL.TZ2.3",
+ "Question": "
\n
A loudspeaker emits sound waves of frequency towards a metal plate that reflects the waves. A small microphone is moved along the line from the metal plate to the loudspeaker. The intensity of sound detected at the microphone as it moves varies regularly between maximum and minimum values.
\n

\n
The speed of sound in air is 340 m s−1.
\n
\n
Explain the variation in intensity.
\n
[3]
\n
a.i.
\n
\n
Adjacent minima are separated by a distance of 0.12 m. Calculate .
\n
[2]
\n
a.ii.
\n
\n
The metal plate is replaced by a wooden plate that reflects a lower intensity sound wave than the metal plate.
\n
State and explain the differences between the sound intensities detected by the same microphone with the metal plate and the wooden plate.
\n
[3]
\n
b.
\n
",
+ "Markscheme": "
\n
«incident and reflected» waves superpose/interfere/combine ✓
\n
«that leads to» standing waves formed OR nodes and antinodes present ✓
\n
at antinodes / maxima there is maximum intensity / constructive interference / «displacement» addition / louder sound ✓
\n
at nodes / minima there is minimum intensity / destructive interference / «displacement» cancellation / quieter sound ✓
\n
\n
OWTTE
\n
Allow a sketch of a standing wave for MP2
\n
Allow a correct reference to path or phase differences to identify constructive / destructive interference
\n
a.i.
\n
\n
wavelength = 0.24 «m» ✓
\n
= «=» 1.4 «kHz» OR 1400 «Hz» ✓
\n
\n
Allow ECF from MP1
\n
a.ii.
\n
\n
relates intensity to amplitude ✓
\n
antinodes / maximum intensity will be decreased / quieter ✓
\n
nodes / minimum will be increased / louder ✓
\n
difference in intensities will be less ✓
\n
maxima and minima are at the same positions ✓
\n
\n
OWTTE
\n
b.
\n
",
+ "Examiners report": "
\n
ai) On most occasions it looked like students knew more than they could successfully communicate. Lots of answers talked about interference between the 2 waves, or standing waves being produced but did not go on to add detail. Candidates should take note of how many marks the question part is worth and attempt a structure of the answer that accounts for that. At SL there were problems recognizing a standard question requiring the typical explanation of how a standing wave is established.
\n
3aii) By far the most common answer was 2800 Hz, not doubling the value given to get the correct wavelength. That might suggest that some students misinterpreted adjacent minima as two troughs, therefore missing to use the information to correctly determine the wavelength as 0.24 m.
\n
b) A question that turned out to be a good high level discriminator. Most candidates went for an answer that generally had everything at a lower intensity and didn't pick up on the relative amount of superposition. Those that did answer it very well, with very clear explanations, succeeded in recognizing that the nodes would be louder and the anti-nodes would be quieter than before.
\n
a.i.
\n
",
+ "topics": [
+ "c-wave-behaviour"
+ ],
+ "subtopics": [
+ "c-4-standing-waves-and-resonance"
+ ]
+ },
+ {
+ "question_id": "22N.2.HL.TZ0.6",
+ "Question": "
\n
\n (a)\n
\n
\n
\n Outline, by reference to nuclear binding energy, why the mass of a nucleus is less than the sum of the masses of its constituent nucleons.\n
\n
\n
\n
\n
\n
\n (b.i)\n
\n
\n
\n Calculate, in MeV, the energy released in this decay.\n
\n
\n
\n
\n
\n
\n (b.ii)\n
\n
\n
\n The polonium nucleus was stationary before the decay.\n
\n
\n Show, by reference to the momentum of the particles, that the kinetic energy of the alpha particle is much greater than the kinetic energy of the lead nucleus.\n
\n
\n
\n
\n
\n
\n (b.iii)\n
\n
\n
\n In the decay of polonium−210, alpha emissions can be accompanied by the emissions of gamma photons, all of the same wavelength of 1.54 × 10\n \n −12\n \n m.\n
\n
\n Discuss how this observation provides evidence for discrete nuclear energy levels.\n
\n
\n
\n
\n
\n
\n (c)\n
\n
\n
\n A sample contains 5.0 g of pure polonium-210. The decay constant of polonium-210 is 5.8 × 10\n \n −8\n \n s\n \n −1\n \n . Lead-206 is stable.\n
\n
\n Calculate the mass of lead-206 present in the sample after one year.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n according to Δ\n \n E\n \n = Δ\n \n mc\n \n \n 2\n \n / identifies mass energy equivalence ✓\n
\n
\n
\n
\n energy is released when nucleons come together / a nucleus is formed «so nucleus has less mass than individual nucleons»\n
\n
\n \n \n OR\n \n \n
\n
\n energy is required to «completely» separate the nucleons / break apart a nucleus «so individual nucleons have more mass than nucleus» ✓\n
\n
\n
\n
\n \n Accept protons and neutrons.\n \n
\n
\n
\n (a)\n
\n
\n according to Δ\n \n E\n \n = Δ\n \n mc\n \n \n 2\n \n / identifies mass energy equivalence ✓\n
\n
\n
\n
\n energy is released when nucleons come together / a nucleus is formed «so nucleus has less mass than individual nucleons»\n
\n
\n \n \n OR\n \n \n
\n
\n energy is required to «completely» separate the nucleons / break apart a nucleus «so individual nucleons have more mass than nucleus» ✓\n
\n
\n
\n
\n \n Accept protons and neutrons.\n \n
\n
\n
\n (b.i)\n
\n
\n (\n \n m\n \n \n polonium\n \n −\n \n m\n \n \n lead\n \n −\n \n m\n \n α\n \n \n )\n \n c\n \n \n 2\n \n \n \n OR\n \n \n (209.93676 − 205.92945 − 4.00151)\n
\n
\n \n \n OR\n \n \n
\n
\n mass difference = 5.8 × 10\n \n −3\n \n ✓\n
\n
\n
\n
\n conversion to MeV using 931.5 to give 5.4 «MeV» ✓\n
\n
\n
\n
\n \n Allow\n \n ECF\n \n from\n \n MP1\n \n .\n \n
\n
\n \n Award\n \n [2]\n \n for a\n \n BCA\n \n .\n \n
\n
\n \n Award\n \n [1]\n \n for 8.6 x 10\n \n −13\n \n J.\n \n
\n
\n
\n (b.ii)\n
\n
\n \n \n ALTERNATIVE 1\n \n \n
\n
\n energy ratio expressed in terms of momentum, e.g.\n \n ✓\n
\n
\n \n hence\n \n ✓\n
\n
\n
\n
\n \n «so\n \n has a much greater KE»\n
\n
\n \n \n OR\n \n \n
\n
\n \n «much» greater than\n \n «so\n \n has a much greater KE» ✓\n
\n
\n
\n
\n \n \n ALTERNATIVE 2\n \n \n
\n
\n alpha particle and lead particle have equal and opposite momenta ✓\n
\n
\n so their velocities are inversely proportional to mass ✓\n
\n
\n but KE ∝\n \n v\n \n \n 2\n \n «so\n \n has a much greater KE» ✓\n
\n
\n
\n (b.iii)\n
\n
\n photon energy is determined by its wavelength ✓\n
\n
\n
\n photons are emitted when nucleus undergoes transitions between its «nuclear» energy levels\n
\n
\n \n \n OR\n \n \n
\n
\n photon energy equals the difference between «nuclear» energy levels ✓\n
\n
\n
\n photons have the same energy / a fixed value\n
\n
\n \n \n OR\n \n \n
\n
\n energy is quantized / discrete ✓\n
\n
\n
\n (c)\n
\n
\n undecayed mass\n \n «\n \n g» ✓\n
\n
\n mass of decayed polonium «\n \n undecayed mass»\n \n «g» ✓\n
\n
\n mass of lead «\n \n »\n \n «g» ✓\n
\n
\n
\n
\n \n Allow\n \n [2] max\n \n for answers that ignore mass difference between Pb and Po (4.2 g).\n \n
\n
\n \n Allow calculations in number of particles or moles for\n \n MP1\n \n and\n \n MP2\n \n .\n \n
\n
\n \n Allow\n \n ECF\n \n from\n \n MP1\n \n and\n \n MP2\n \n .\n \n
\n
\n",
+ "Examiners report": "
\n (a)\n
\n
\n Still several answers that thought that the nucleus needed to gain energy to bind it together. Most candidates scored at least one for recognising some form of mass/energy equivalence, although few candidates managed to consistently express their ideas here.\n
\n
\n
\n (a)\n
\n
\n Still several answers that thought that the nucleus needed to gain energy to bind it together. Most candidates scored at least one for recognising some form of mass/energy equivalence, although few candidates managed to consistently express their ideas here.\n
\n
\n
\n (b.i)\n
\n
\n Generally, well answered. There were quite a few who fell into the trap of multiplying by an unnecessary c\n \n 2\n \n as they were not sure of the significance of the unit of u.\n
\n
\n
\n (b.ii)\n
\n
\n Those who answered using the mass often did not get MP3 whereas those who converted to the number of particles or moles before the first calculation did, although that could be considered an unnecessary complication.\n
\n
\n
\n (b.iii)\n
\n
\n Many identified conservation of momentum and consequently the relative velocities but it was common to miss MP3 for correctly relating this to KE.\n
\n
\n
\n (c)\n
\n
\n Several answers referred incorrectly to electron energy levels. Successful candidates managed to score full marks, although it was also common to miss the relationship between energy and wavelength.\n
\n
\n",
+ "topics": [
+ "a--space-time-and-motion",
+ "e-nuclear-and-quantum-physics"
+ ],
+ "subtopics": [
+ "a-2-forces-and-momentum",
+ "e-3-radioactive-decay"
+ ]
+ },
+ {
+ "question_id": "22N.2.HL.TZ0.7",
+ "Question": "
\n
\n (a.i)\n
\n
\n
\n The intensity of light at point O is\n \n . The distance OP is\n \n .\n
\n
\n Sketch, on the axes, a graph to show the variation of the intensity of light with distance from point O on the screen. Your graph should cover the distance range from 0 to 2\n \n .\n
\n
\n
\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a.i)\n
\n
\n smooth curve decreasing from\n \n to 0 between 0 and\n \n ✓\n
\n
\n secondary maximum correctly placed\n \n \n AND\n \n \n of intensity less than 0.3\n \n ✓\n
\n
\n \n E.g.\n \n
\n
\n
\n
\n (a.i)\n
\n
\n smooth curve decreasing from\n \n to 0 between 0 and\n \n ✓\n
\n
\n secondary maximum correctly placed\n \n \n AND\n \n \n of intensity less than 0.3\n \n ✓\n
\n
\n \n E.g.\n \n
\n
\n
\n",
+ "Examiners report": "
\n (a.i)\n
\n
\n Most scored MP1. Many candidates scored full marks but it was common to see a maximum at 2x or a secondary maxima too high.\n
\n
\n
\n (a.i)\n
\n
\n Most scored MP1. Many candidates scored full marks but it was common to see a maximum at 2x or a secondary maxima too high.\n
\n
\n",
+ "topics": [
+ "c-wave-behaviour"
+ ],
+ "subtopics": [
+ "c-3-wave-phenomena"
+ ]
+ },
+ {
+ "question_id": "22N.2.HL.TZ0.8",
+ "Question": "
\n
\n (a)\n
\n
\n
\n The diagram shows field lines for an electrostatic field. X and Y are two points on the same field line.\n
\n
\n
\n
\n
\n Outline which of the two points has the larger electric potential.\n
\n
\n
\n
\n
\n
\n (b.i)\n
\n
\n
\n Show that the kinetic energy of the satellite in orbit is about 2 × 10\n \n 10\n \n J.\n
\n
\n
\n
\n
\n
\n (b.ii)\n
\n
\n
\n Determine the minimum energy required to launch the satellite. Ignore the original kinetic energy of the satellite due to Earth’s rotation.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n potential greater at Y ✓\n
\n
\n
\n
\n «from\n \n » the potential increases in the direction opposite to field strength «so from X to Y»\n
\n
\n \n \n OR\n \n \n
\n
\n opposite to the direction of the field lines, «so from X to Y»\n
\n
\n \n \n OR\n \n \n
\n
\n «from\n \n » work done to move a positive charge from X to Y is positive «so the potential increases from X to Y» ✓\n
\n
\n
\n (a)\n
\n
\n potential greater at Y ✓\n
\n
\n
\n
\n «from\n \n » the potential increases in the direction opposite to field strength «so from X to Y»\n
\n
\n \n \n OR\n \n \n
\n
\n opposite to the direction of the field lines, «so from X to Y»\n
\n
\n \n \n OR\n \n \n
\n
\n «from\n \n » work done to move a positive charge from X to Y is positive «so the potential increases from X to Y» ✓\n
\n
\n
\n (b.i)\n
\n
\n orbital radius\n \n «\n \n m» ✓\n
\n
\n \n \n \n OR\n \n \n \n «J» ✓\n
\n
\n
\n
\n \n Award\n \n [1] max\n \n for answers ignoring orbital height (KE = 2.5 × 10\n \n \n \n 10\n \n \n J\n \n ).\n \n
\n
\n
\n (b.ii)\n
\n
\n change in PE\n \n «\n \n J» ✓\n
\n
\n energy needed = KE + ΔPE =\n \n «J» ✓\n
\n
\n
\n
\n \n Allow\n \n ECF\n \n from 8(b)(i).\n \n
\n
\n",
+ "Examiners report": "
\n (a)\n
\n
\n A significant majority guessed at X, probably because the field lines are closer together. Those that identified Y were generally successful in their explanation.\n
\n
\n
\n (a)\n
\n
\n A significant majority guessed at X, probably because the field lines are closer together. Those that identified Y were generally successful in their explanation.\n
\n
\n
\n (b.i)\n
\n
\n This question was well done, with only a few missing the height of the satellite.\n
\n
\n
\n (b.ii)\n
\n
\n Generally, this question was not well done. Most carried out a calculation based on the formula for escape velocity. An opportunity to remind candidates of reading back the stem for the sub-question when answering a second or any subsequent part of it.\n
\n
\n",
+ "topics": [
+ "d-fields"
+ ],
+ "subtopics": [
+ "d-1-gravitational-fields",
+ "d-2-electric-and-magnetic-fields"
+ ]
+ },
+ {
+ "question_id": "22N.2.SL.TZ0.1",
+ "Question": "
\n
\n (a)\n
\n
\n
\n State the initial acceleration of the raindrop.\n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n
\n Explain, by reference to the vertical forces, how the raindrop reaches a constant speed.\n
\n
\n
\n
\n
\n
\n (c.i)\n
\n
\n
\n Determine the energy transferred to the air during the first 3.0 s of motion. State your answer to an appropriate number of significant figures.\n
\n
\n
\n
\n
\n
\n (c.ii)\n
\n
\n
\n Describe the energy change that takes place for\n \n t\n \n > 3.0 s.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n \n g\n \n \n \n OR\n \n \n 9.81 «m s\n \n −2\n \n »\n \n \n OR\n \n \n acceleration of gravity/due to free fall ✓\n
\n
\n
\n
\n \n Accept 10 «\n \n m s\n \n −2\n \n \n ».\n \n
\n
\n \n Ignore sign.\n \n
\n
\n \n Do\n \n not\n \n accept bald “gravity”.\n \n
\n
\n \n Accept answer that indicates tangent of the graph at time t=0.\n \n
\n
\n
\n (a)\n
\n
\n \n g\n \n \n \n OR\n \n \n 9.81 «m s\n \n −2\n \n »\n \n \n OR\n \n \n acceleration of gravity/due to free fall ✓\n
\n
\n
\n
\n \n Accept 10 «\n \n m s\n \n −2\n \n \n ».\n \n
\n
\n \n Ignore sign.\n \n
\n
\n \n Do\n \n not\n \n accept bald “gravity”.\n \n
\n
\n \n Accept answer that indicates tangent of the graph at time t=0.\n \n
\n
\n
\n (b)\n
\n
\n Identification of air resistance/drag force «acting upwards» ✓\n
\n
\n «that» increases with speed ✓\n
\n
\n
\n «until» weight and air resistance cancel out\n
\n
\n \n \n OR\n \n \n
\n
\n net force/acceleration becomes zero ✓\n
\n
\n
\n
\n \n A statement as “air resistance increases with speed” scores\n \n MP1\n \n and\n \n MP2\n \n .\n \n
\n
\n
\n (c.i)\n
\n
\n «loss in» GPE = 3.4 × 10\n \n −5\n \n × 9.81 × 21 «= 7.0 × 10\n \n −3\n \n » «J»\n
\n
\n \n \n OR\n \n \n
\n
\n «gain in» KE = 0.5 × 3.4 × 10\n \n −5\n \n × 9.0\n \n 2\n \n «= 1.4 × 10\n \n −3\n \n » «J» ✓\n
\n
\n
\n energy transferred to air «=7.0 × 10\n \n −3\n \n − 1.4 × 10\n \n −3\n \n » = 5.6 × 10\n \n −3\n \n » «J» ✓\n
\n
\n
\n
\n any calculated answer to 2 sf ✓\n
\n
\n
\n
\n \n Allow\n \n [1]\n \n through the use of kinematics assuming constant acceleration.\n \n
\n
\n \n Allow\n \n ECF\n \n from\n \n MP1\n \n .\n \n
\n
\n
\n (c.ii)\n
\n
\n «gravitational» potential energy «of the raindrop» into thermal/internal energy «of the air» ✓\n
\n
\n
\n
\n \n Accept heat for thermal energy.\n \n
\n
\n \n Accept into kinetic energy of air particles.\n \n
\n
\n \n Ignore sound energy.\n \n
\n
\n",
+ "Examiners report": "
\n (a)\n
\n
\n A nice introductory question answered correctly by most candidates. Most answers quoted the data booklet value, with a few 10's or 9.8's, or the answer in words. Very few lost the mark by just stating gravity, or zero.\n
\n
\n
\n (a)\n
\n
\n A nice introductory question answered correctly by most candidates. Most answers quoted the data booklet value, with a few 10's or 9.8's, or the answer in words. Very few lost the mark by just stating gravity, or zero.\n
\n
\n
\n (b)\n
\n
\n This was very well answered with most candidates scoring 3. The MP usually missed in candidates scoring 2 marks was MP2, to justify the variation of the magnitude of air resistance, although that rarely happened.\n
\n
\n
\n (c.i)\n
\n
\n Generally well answered, although several candidates lost a mark, usually as POT (power of ten) by quoting the value in kg leading to an answer of 5.3 J. Most candidates were able to score MP3 by rounding their calculation to two significant figures.\n
\n
\n
\n (c.ii)\n
\n
\n Of the wrong answers, the most common ones were gravitational potential to kinetic or the idea that because there was no change in velocity there was no energy transfer. A significant number, though, scored by identifying the change into thermal (most of them), kinetic of air particles (a few answers) or internal (very few).\n
\n
\n",
+ "topics": [
+ "a--space-time-and-motion"
+ ],
+ "subtopics": [
+ "a-1-kinematics",
+ "a-2-forces-and-momentum",
+ "a-3-work-energy-and-power"
+ ]
+ },
+ {
+ "question_id": "22N.2.SL.TZ0.2",
+ "Question": "
\n
\n (a.i)\n
\n
\n
\n Determine the minimum area of the solar heating panel required to increase the temperature of all the water in the tank to 30°C during a time of 1.0 hour.\n
\n
\n
\n
\n
\n
\n (a.ii)\n
\n
\n
\n Estimate, in °C, the temperature of the roof tiles.\n
\n
\n
\n
\n
\n
\n (b.i)\n
\n
\n
\n State\n \n one\n \n way in which a real gas differs from an ideal gas.\n
\n
\n
\n
\n
\n
\n (b.ii)\n
\n
\n
\n The water is heated. Explain why the quantity of air in the storage tank decreases.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a.i)\n
\n
\n energy required = 250 × 4200 × (30 − 15) ✓\n
\n
\n energy available = 0.30 × 680 ×\n \n t\n \n ×\n \n A\n \n ✓\n
\n
\n \n A\n \n = «\n \n » 21 «m\n \n 2\n \n »\n \n \n OR\n \n \n 22 «m\n \n 2\n \n » ✓\n
\n
\n
\n
\n \n Allow\n \n ECF\n \n from\n \n MP1\n \n and\n \n MP2\n \n .\n \n
\n
\n \n Accept the correct use of 0.30 in either\n \n MP1\n \n or\n \n MP2\n \n .\n \n
\n
\n
\n (a.ii)\n
\n
\n absorbed intensity = (1 − 0.2) × 680 «= 544» «W m\n \n −2\n \n »\n
\n
\n \n \n OR\n \n \n
\n
\n emitted intensity = 0.97 × 5.67 × 10\n \n −8\n \n × T\n \n 4\n \n ✓\n
\n
\n
\n
\n \n T\n \n \n «K» ✓\n
\n
\n 42 «°C» ✓\n
\n
\n
\n
\n \n Allow\n \n ECF\n \n from\n \n MP1\n \n and\n \n MP2\n \n .\n \n
\n
\n \n Allow\n \n MP1\n \n if absorbed or emitted intensity is multiplied by area.\n \n
\n
\n
\n (b.i)\n
\n
\n can be liquefied ✓\n
\n
\n has intermolecular forces / potential energy ✓\n
\n
\n has atoms/molecules that are not point objects / take up volume ✓\n
\n
\n does not follow the ideal gas law «for all\n \n T\n \n and\n \n p\n \n » ✓\n
\n
\n collisions between particles are non-elastic ✓\n
\n
\n
\n
\n \n Accept the converse argument.\n \n
\n
\n
\n (b.ii)\n
\n
\n \n \n ALTERNATIVE 1\n \n \n
\n
\n «constant\n \n p\n \n and\n \n V\n \n imply»\n \n nT\n \n = const ✓\n
\n
\n \n T\n \n increases hence\n \n n\n \n decreases ✓\n
\n
\n
\n \n \n ALTERNATIVE 2\n \n \n
\n
\n «constant\n \n p\n \n and\n \n n\n \n imply»\n \n V\n \n is proportional to\n \n T\n \n / air expands as it is heated ✓\n
\n
\n «original» air occupies a greater volume\n \n OR\n \n some air leaves through opening ✓\n
\n
\n
\n
\n \n \n MP2\n \n in\n \n ALT 2\n \n must come from expansion of air, not from expansion of water.\n \n
\n
\n \n Award\n \n [0]\n \n for an answer based on expansion of water.\n \n
\n
\n \n Award\n \n [1]\n \n \n max\n \n for an answer based on convection currents.\n \n
\n
\n",
+ "Examiners report": "
\n (a.i)\n
\n
\n Most candidates had a good attempt at this but there were often slight slips. Some missed the efficiency of the process. Some included the albedo of the roof tiles. Some thought that the temperature rise needed to have 273 added to convert to kelvin. However, sometimes scoring through ECF (error carried forward), the average mark was around 2 marks.\n
\n
\n
\n (a.ii)\n
\n
\n This was a bit more hit and miss than the previous question part. One common mistake was not understanding what albedo meant. Some took it as the amount of energy absorbed rather than reflected. Emissivity was often missed. Several candidates, successfully answering the question or not, were able to score MP3 converting the final temperature into Celsius degrees.\n
\n
\n
\n (b.i)\n
\n
\n This was very well answered. Candidates showed an understanding of the differences between ideal and real gases.\n
\n
\n
\n (b.ii)\n
\n
\n It was surprising to see a large number of answers based on the expansion of water, as the stem of the question clearly states that the level of water remains constant. Most successful candidates scored by quoting\n \n pV\n \n constant so concluding with the inverse relationship of n and\n \n T\n \n , others also managed to score by explaining that the volume of air increases and therefore must go out through the opening. Answers based on convection currents were given partial credit.\n
\n
\n",
+ "topics": [
+ "b-the-particulate-nature-of-matter"
+ ],
+ "subtopics": [
+ "b-1-thermal-energy-transfers",
+ "b-2-greenhouse-effect",
+ "b-3-gas-laws"
+ ]
+ },
+ {
+ "question_id": "22N.2.SL.TZ0.3",
+ "Question": "
\n
\n (a.i)\n
\n
\n
\n Draw, on the axes, a graph to show the variation with\n \n t\n \n of the displacement of particle Q.\n
\n
\n
\n
\n
\n
\n (a.ii)\n
\n
\n
\n Calculate the speed of waves on the string.\n
\n
\n
\n
\n
\n
\n (b.i)\n
\n
\n
\n Determine the fundamental SI unit for\n \n a\n \n .\n
\n
\n
\n
\n
\n
\n (b.ii)\n
\n
\n
\n The tension force on the string is doubled. Describe the effect, if any, of this change on the frequency of the standing wave.\n
\n
\n
\n
\n
\n
\n (c)\n
\n
\n
\n The standing wave on the string creates a travelling sound wave in the surrounding air.\n
\n
\n Outline\n \n two\n \n differences between a standing wave and a travelling wave.\n
\n
\n
\n
\n
\n
\n (c.i)\n
\n
\n
\n Outline\n \n one\n \n difference between a standing wave and a travelling wave.\n
\n
\n
\n
\n
\n
\n (c.ii)\n
\n
\n
\n The speed of sound in air is 340 m s\n \n −1\n \n and in water it is 1500 m s\n \n −1\n \n .\n
\n
\n Discuss whether the sound wave can enter the water.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a.i)\n
\n
\n oscillation in antiphase ✓\n
\n
\n smaller amplitude than P ✓\n
\n
\n
\n
\n
\n
\n
\n (a.i)\n
\n
\n oscillation in antiphase ✓\n
\n
\n smaller amplitude than P ✓\n
\n
\n
\n
\n
\n
\n
\n (a.ii)\n
\n
\n wavelength\n \n «m» ✓\n
\n
\n speed\n \n «m s\n \n −1\n \n » ✓\n
\n
\n
\n
\n \n Allow\n \n ECF\n \n from incorrect wavelength.\n \n
\n
\n
\n (b.i)\n
\n
\n kg m s\n \n −2\n \n \n \n OR\n \n \n m\n \n 2\n \n s\n \n −2\n \n seen ✓\n
\n
\n kg m\n \n −1\n \n ✓\n
\n
\n
\n
\n \n Award\n \n [2]\n \n for a\n \n BCA\n \n .\n \n
\n
\n
\n (b.ii)\n
\n
\n speed increases hence frequency increases ✓\n
\n
\n by factor\n \n ✓\n
\n
\n
\n (c)\n
\n
\n travelling waves transfer energy\n \n \n OR\n \n \n standing waves don’t ✓\n
\n
\n amplitude of oscillation varies along a standing wave\n \n \n OR\n \n \n is constant along a travelling wave ✓\n
\n
\n standing waves have nodes and antinodes\n \n \n OR\n \n \n travelling waves don’t ✓\n
\n
\n points in an internodal region have same phase in standing waves\n \n \n OR\n \n \n different phase in travelling waves ✓\n
\n
\n
\n (c.i)\n
\n
\n travelling waves transfer energy\n \n \n OR\n \n \n standing waves don’t ✓\n
\n
\n amplitude of oscillation varies along a standing wave\n \n \n OR\n \n \n is constant along a travelling wave ✓\n
\n
\n standing waves have nodes / antinodes\n \n \n OR\n \n \n travelling waves don’t ✓\n
\n
\n points in an internodal region have same phase in standing waves\n \n \n OR\n \n \n different phase in travelling waves ✓\n
\n
\n
\n (c.ii)\n
\n
\n \n \n ALTERNATIVE 1\n \n \n
\n
\n critical angle\n \n «from\n \n » ✓\n
\n
\n the angle of incidence is greater than\n \n hence the sound can’t enter water ✓\n
\n
\n
\n
\n \n \n ALTERNATIVE 2\n \n \n
\n
\n \n ✓\n
\n
\n sine value greater than one hence the sound can’t enter water ✓\n
\n
\n
\n
\n \n Conclusion must be justified, award\n \n [0]\n \n for\n \n BCA\n \n .\n \n
\n
\n",
+ "Examiners report": "
\n (a.i)\n
\n
\n Although there were good answers which scored full marks, there were a significant number of wrong answers where the amplitude was the same or not consistent throughout, or the wave drawn was not in antiphase of the original sketch.\n
\n
\n
\n (a.i)\n
\n
\n Although there were good answers which scored full marks, there were a significant number of wrong answers where the amplitude was the same or not consistent throughout, or the wave drawn was not in antiphase of the original sketch.\n
\n
\n
\n (a.ii)\n
\n
\n This was well answered, particularly MP1 to determine the wavelength, although several candidates misinterpreted the unit of time and obtained a very small value for the velocity of the wave.\n
\n
\n
\n (b.i)\n
\n
\n Students seem to be well prepared for this sort of question, as it was high-scoring.\n
\n
\n
\n (b.ii)\n
\n
\n This question was answered well, although the numerical aspect was often missing. It is worth highlighting that if there is a term like\n \n '\n \n doubled\n \n '\n \n in the question, it makes sense to expect a numerical answer.\n
\n
\n
\n (c)\n
\n
\n This question was answered well. Students showed to be familiar with the differences between standing and travelling waves. In SL they had to identify two differences, so that proved to be more challenging.\n
\n
\n
\n (c.i)\n
\n
\n This question was answered well. Students showed to be familiar with the differences between standing and travelling waves.\n
\n
\n
\n (c.ii)\n
\n
\n Surprisingly well answered as it was sound from air to water, rather than light from air to glass. A mixture of approaches but probably the most common was to calculate a sine value of over 1. Some went about calculating the critical angle but nowhere near as many.\n
\n
\n",
+ "topics": [
+ "c-wave-behaviour",
+ "tools"
+ ],
+ "subtopics": [
+ "c-2-wave-model",
+ "c-3-wave-phenomena",
+ "c-4-standing-waves-and-resonance",
+ "tool-3-mathematics"
+ ]
+ },
+ {
+ "question_id": "22N.2.SL.TZ0.4",
+ "Question": "
\n
\n (a)\n
\n
\n
\n The scale diagram shows the weight\n \n W\n \n of the mass at an instant when the rod is horizontal.\n
\n
\n Draw, on the scale diagram, an arrow to represent the force exerted on the mass by the rod.\n
\n
\n
\n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n
\n Explain why the magnitude of the force exerted on the mass by the rod is not constant.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n horizontal component of any length to the left ✓\n
\n
\n vertical component two squares long upwards ✓\n
\n
\n E.g.\n
\n
\n
\n
\n
\n
\n
\n \n Ignore point of application.\n \n
\n
\n \n Award\n \n [1]\n \n \n max\n \n if arrowhead not present.\n \n
\n
\n
\n (a)\n
\n
\n horizontal component of any length to the left ✓\n
\n
\n vertical component two squares long upwards ✓\n
\n
\n E.g.\n
\n
\n
\n
\n
\n
\n
\n \n Ignore point of application.\n \n
\n
\n \n Award\n \n [1]\n \n \n max\n \n if arrowhead not present.\n \n
\n
\n
\n (b)\n
\n
\n \n \n ALTERNATIVE 1\n \n \n
\n
\n the net/centripetal force has constant magnitude ✓\n
\n
\n the direction of the net/centripetal force constantly changes ✓\n
\n
\n this is achieved by vector-adding weight and the force from the rod\n
\n
\n \n \n OR\n \n \n
\n
\n the force from the rod is vector difference of the centripetal force and weight ✓\n
\n
\n
\n
\n \n \n ALTERNATIVE 2\n \n \n
\n
\n at the top F\n \n rod\n \n = F\n \n c\n \n − W ✓\n
\n
\n at the bottom, F\n \n rod\n \n = F\n \n c\n \n + W ✓\n
\n
\n net F/F\n \n c\n \n is constant so the force from the rod is different «hence is changing» ✓\n
\n
\n
\n
\n \n Accept reference to centripetal or net force indistinctly.\n \n
\n
\n \n Allow reference to centripetal acceleration.\n \n
\n
\n",
+ "Examiners report": "
\n (a)\n
\n
\n Most just added the horizontal component. Not many centrifugal forces, but still a few. Very few were able to score both marks, so this question proved to be challenging for the candidates.\n
\n
\n
\n (a)\n
\n
\n Most just added the horizontal component. Not many centrifugal forces, but still a few. Very few were able to score both marks, so this question proved to be challenging for the candidates.\n
\n
\n
\n (b)\n
\n
\n Many got into a bit of a mess with this one and it was quite difficult to interpret some of the answers. If they started out with the net/centripetal force being constant, then it was often easy to follow the reasoning. Starting with force on the rod varying often led to confusion. Quite a few did not pick up on the constant speed vertical circle so there were complicated energy/speed arguments to pick through.\n
\n
\n",
+ "topics": [
+ "a--space-time-and-motion",
+ "tools"
+ ],
+ "subtopics": [
+ "a-2-forces-and-momentum",
+ "tool-3-mathematics"
+ ]
+ },
+ {
+ "question_id": "22N.2.SL.TZ0.5",
+ "Question": "
\n
\n (a)\n
\n
\n
\n State what is meant by an ideal voltmeter.\n
\n
\n
\n
\n
\n
\n (b.i)\n
\n
\n
\n Show that the internal resistance of the cell is about 0.7 Ω.\n
\n
\n
\n
\n
\n
\n (b.ii)\n
\n
\n
\n Show that the internal resistance of the cell is about 0.7 Ω.\n
\n
\n
\n
\n
\n
\n (b.iii)\n
\n
\n
\n Calculate the emf of the cell.\n
\n
\n
\n
\n
\n
\n (c.i)\n
\n
\n
\n Explain, by reference to charge carriers in the wire, how the magnetic force on the wire arises.\n
\n
\n
\n
\n
\n
\n (c.ii)\n
\n
\n
\n Identify the direction of the magnetic force on the wire.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n infinite resistance\n
\n
\n \n \n OR\n \n \n
\n
\n no current is flowing through it ✓\n
\n
\n
\n (b.i)\n
\n
\n current\n \n «A» ✓\n
\n
\n \n r\n \n \n \n \n OR\n \n \n \n «Ω» ✓\n
\n
\n
\n
\n \n For\n \n MP2\n \n , allow any other correctly substituted expression for r.\n \n
\n
\n
\n (b.ii)\n
\n
\n 29.4 (50.0 +\n \n r\n \n ) = 139 (10.0 +\n \n r\n \n ) ✓\n
\n
\n
\n attempt to solve for\n \n r\n \n , e.g. 29.4 × 50.0 − 139 × 10.0 =\n \n r\n \n (139 − 29.4)\n
\n
\n \n \n OR\n \n \n
\n
\n 0.73 «Ω» ✓\n
\n
\n
\n
\n \n Do\n \n not\n \n allow working backwards from 0.7 Ω.\n \n
\n
\n
\n (b.iii)\n
\n
\n 139 × 10\n \n −3\n \n (10.0 + 0.73)\n
\n
\n \n \n OR\n \n \n
\n
\n 29.4 × 10\n \n −3\n \n (50.0 + 0.73) ✓\n
\n
\n
\n 1.49 «V» ✓\n
\n
\n
\n
\n \n Watch for\n \n ECF\n \n from 5(b)(i).\n \n
\n
\n
\n (c.i)\n
\n
\n charge/carriers are moving in a magnetic field ✓\n
\n
\n
\n
\n there is a magnetic force on them / quote\n \n F = qvB\n \n
\n
\n \n \n OR\n \n \n
\n
\n this creates a magnetic field that interacts with the external magnetic field ✓\n
\n
\n
\n
\n \n Accept electrons.\n \n
\n
\n \n For\n \n MP2\n \n , the force must be identified as acting on charge / carriers.\n \n
\n
\n
\n (c.ii)\n
\n
\n into the plane «of the paper» ✓\n
\n
\n",
+ "Examiners report": "
\n (a)\n
\n
\n A majority of candidates scored a mark by simply stating infinite resistance. Several answers went the other way round, stating a resistance of zero.\n
\n
\n
\n (b.i)\n
\n
\n Many answers here produced a number that did not round to 0.7 but students claimed it did. The simultaneous equation approach was seen in the best candidates, getting the right answer. It is worthy of reminding about the need of showing one more decimal place when calculating a show that value type of question.\n
\n
\n
\n (b.ii)\n
\n
\n Many answers here produced a number that did not round to 0.7 but students claimed it did. The simultaneous equation approach was seen in the best candidates, getting the right answer. It is worthy of reminding about the need of showing one more decimal place when calculating a show that value type of question.\n
\n
\n
\n (b.iii)\n
\n
\n Usually well answered, regardless of b(ii), by utilising the show that value given.\n
\n
\n
\n (c.i)\n
\n
\n Many scored MP1 here but did not get MP2 as they jumped straight to the wire rather than continuing with the explanation of what was going on with the charge carriers.\n
\n
\n
\n (c.ii)\n
\n
\n Generally, a well answered question although there was some confusion on how to communicate it, with some contradictory answers indicating into or out, and also North or South at the same time.\n
\n
\n",
+ "topics": [
+ "b-the-particulate-nature-of-matter",
+ "d-fields"
+ ],
+ "subtopics": [
+ "b-5-current-and-circuits",
+ "d-3-motion-in-electromagnetic-fields"
+ ]
+ },
+ {
+ "question_id": "22N.2.SL.TZ0.6",
+ "Question": "
\n
\n (a)\n
\n
\n
\n Outline, by reference to nuclear binding energy, why the mass of a nucleus is less than the sum of the masses of its constituent nucleons.\n
\n
\n
\n
\n
\n
\n (b.i)\n
\n
\n
\n Calculate, in MeV, the energy released in this decay.\n
\n
\n
\n
\n
\n
\n (b.ii)\n
\n
\n
\n The polonium nucleus was stationary before the decay.\n
\n
\n Show, by reference to the momentum of the particles, that the kinetic energy of the alpha particle is much greater than the kinetic energy of the lead nucleus.\n
\n
\n
\n
\n
\n
\n (b.iii)\n
\n
\n
\n In the decay of polonium-210, alpha emission can be followed by the emission of a gamma photon.\n
\n
\n State and explain whether the alpha particle or gamma photon will cause greater ionization in the surrounding material.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n according to Δ\n \n E\n \n = Δ\n \n mc\n \n \n 2\n \n / identifies mass energy equivalence ✓\n
\n
\n
\n
\n energy is released when nucleons come together / a nucleus is formed «so nucleus has less mass than individual nucleons»\n
\n
\n \n \n OR\n \n \n
\n
\n energy is required to «completely» separate the nucleons / break apart a nucleus «so individual nucleons have more mass than nucleus» ✓\n
\n
\n
\n
\n \n Accept protons and neutrons.\n \n
\n
\n
\n (a)\n
\n
\n according to Δ\n \n E\n \n = Δ\n \n mc\n \n \n 2\n \n / identifies mass energy equivalence ✓\n
\n
\n
\n
\n energy is released when nucleons come together / a nucleus is formed «so nucleus has less mass than individual nucleons»\n
\n
\n \n \n OR\n \n \n
\n
\n energy is required to «completely» separate the nucleons / break apart a nucleus «so individual nucleons have more mass than nucleus» ✓\n
\n
\n
\n
\n \n Accept protons and neutrons.\n \n
\n
\n
\n (b.i)\n
\n
\n (\n \n m\n \n \n polonium\n \n −\n \n m\n \n \n lead\n \n −\n \n m\n \n α\n \n \n )\n \n c\n \n \n 2\n \n \n \n OR\n \n \n (209.93676 − 205.92945 − 4.00151)\n
\n
\n \n \n OR\n \n \n
\n
\n mass difference = 5.8 × 10\n \n −3\n \n ✓\n
\n
\n
\n
\n conversion to MeV using 931.5 to give 5.4 «MeV» ✓\n
\n
\n
\n
\n \n Allow\n \n ECF\n \n from\n \n MP1\n \n .\n \n
\n
\n \n Award\n \n [2]\n \n for a\n \n BCA\n \n .\n \n
\n
\n \n Award\n \n [1]\n \n for 8.6 x 10\n \n −13\n \n J.\n \n
\n
\n
\n (b.ii)\n
\n
\n \n \n ALTERNATIVE 1\n \n \n
\n
\n energy ratio expressed in terms of momentum, e.g.\n \n ✓\n
\n
\n \n hence\n \n ✓\n
\n
\n
\n
\n \n «so\n \n has a much greater KE»\n
\n
\n \n \n OR\n \n \n
\n
\n \n «much» greater than\n \n «so\n \n has a much greater KE» ✓\n
\n
\n
\n
\n \n \n ALTERNATIVE 2\n \n \n
\n
\n alpha particle and lead particle have equal and opposite momenta ✓\n
\n
\n so their velocities are inversely proportional to mass ✓\n
\n
\n but KE ∝\n \n v\n \n \n 2\n \n «so\n \n has a much greater KE» ✓\n
\n
\n
\n (b.iii)\n
\n
\n alpha particle ✓\n
\n
\n is electrically charged hence more likely to interact with electrons «in the surrounding material» ✓\n
\n
\n",
+ "Examiners report": "
\n (a)\n
\n
\n Still several answers that thought that the nucleus needed to gain energy to bind it together. Most candidates scored at least one for recognising some form of mass/energy equivalence, although few candidates managed to consistently express their ideas here.\n
\n
\n
\n (a)\n
\n
\n Still several answers that thought that the nucleus needed to gain energy to bind it together. Most candidates scored at least one for recognising some form of mass/energy equivalence, although few candidates managed to consistently express their ideas here.\n
\n
\n
\n (b.i)\n
\n
\n Generally, well answered. There were quite a few who fell into the trap of multiplying by an unnecessary c\n \n 2\n \n as they were not sure of the significance of the unit of u.\n
\n
\n
\n (b.ii)\n
\n
\n Those who answered using the mass often did not get MP3 whereas those who converted to the number of particles or moles before the first calculation did, although that could be considered an unnecessary complication.\n
\n
\n
\n (b.iii)\n
\n
\n Many did not interpret the stem correctly and failed to compare the ionisation of alpha particles versus gamma rays.\n
\n
\n",
+ "topics": [
+ "a--space-time-and-motion",
+ "e-nuclear-and-quantum-physics"
+ ],
+ "subtopics": [
+ "a-2-forces-and-momentum",
+ "a-3-work-energy-and-power",
+ "e-3-radioactive-decay"
+ ]
+ },
+ {
+ "question_id": "23M.2.HL.TZ1.3",
+ "Question": "
\n
\n (a)\n
\n
\n
\n A transverse water wave travels to the right. The diagram shows the shape of the surface of the water at time\n \n t\n \n = 0. P and Q show two corks floating on the surface.\n
\n
\n
\n
\n
\n
\n
\n
\n
\n (i)\n
\n
\n
\n State what is meant by a transverse wave.\n
\n
\n
\n
\n
\n
\n (ii)\n
\n
\n
\n The frequency of the wave is 0.50 Hz. Calculate the speed of the wave.\n
\n
\n
\n
\n
\n
\n (iii)\n
\n
\n
\n Sketch on the diagram the position of P at time\n \n t\n \n = 0.50 s.\n
\n
\n
\n
\n
\n
\n (iv)\n
\n
\n
\n Show that the phase difference between the oscillations of the two corks is\n \n radians.\n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n
\n Monochromatic light is incident on two very narrow slits. The light that passes through the slits is observed on a screen. M is directly opposite the midpoint of the slits.\n \n represents the displacement from M in the direction shown.\n
\n
\n
\n
\n
\n A student argues that what will be observed on the screen will be a total of two bright spots opposite the slits. Explain why the student’s argument is incorrect.\n
\n
\n
\n
\n
\n
\n (c)\n
\n
\n
\n The graph shows the actual variation with displacement\n \n from M of the intensity of the light on the screen.\n \n is the intensity of light at the screen from one slit only.\n
\n
\n
\n
\n
\n
\n
\n
\n
\n (i)\n
\n
\n
\n Explain why the intensity of light at\n \n = 0 is 4\n \n .\n
\n
\n
\n
\n
\n
\n (ii)\n
\n
\n
\n The slits are separated by a distance of 0.18 mm and the distance to the screen is 2.2 m. Determine, in m, the wavelength of light.\n
\n
\n
\n
\n
\n
\n (iii)\n
\n
\n
\n The two slits are replaced by many slits of the same separation. State\n \n one\n \n feature of the intensity pattern that will remain the same and\n \n one\n \n that will change.\n
\n
\n Stays the same:\n
\n
\n
\n
\n Changes:\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n «A wave where the» displacement of particles/oscillations of particles/movement of particles/vibrations of particles is perpendicular/normal to the direction of energy transfer/wave travel/wave velocity/wave movement/wave propagation ✓\n
\n
\n \n Allow medium, material, water, molecules, or atoms for particles.\n \n
\n
\n
\n (i)\n
\n
\n «A wave where the» displacement of particles/oscillations of particles/movement of particles/vibrations of particles is perpendicular/normal to the direction of energy transfer/wave travel/wave velocity/wave movement/wave propagation ✓\n
\n
\n \n Allow medium, material, water, molecules, or atoms for particles.\n \n
\n
\n
\n (ii)\n
\n
\n \n v\n \n = «0.50 × 16 =» 8.0 «m s\n \n −1\n \n » ✓\n
\n
\n
\n (iii)\n
\n
\n P at (8, 1.2) ✓\n
\n
\n
\n (iv)\n
\n
\n \n \n ALTERNATIVE 1\n \n \n
\n Phase difference is\n \n ×\n \n ✓\n
\n «=\n \n » ✓\n
\n
\n \n ALTERNATIVE 2\n \n
\n
\n One wavelength/period represents «phase difference» of 2\n \n and «corks» are ½ wavelength/period apart so phase difference is\n \n /\n \n \n OWTTE\n \n \n ✓\n
\n
\n
\n (b)\n
\n
\n light acts as a wave «and not a particle in this situation» ✓\n
\n
\n light at slits will diffract / create a diffraction pattern ✓\n
\n
\n light passing through slits will interfere / create an interference pattern «creating bright and dark spots» ✓\n
\n
\n
\n (c)\n
\n
\n The amplitude «at\n \n x\n \n = 0» will be doubled ✓\n
\n
\n intensity is proportional to amplitude squared /\n \n ∝\n \n A\n \n \n 2\n \n ✓\n
\n
\n
\n (i)\n
\n
\n The amplitude «at\n \n x\n \n = 0» will be doubled ✓\n
\n
\n intensity is proportional to amplitude squared /\n \n ∝\n \n A\n \n \n 2\n \n ✓\n
\n
\n
\n (ii)\n
\n
\n Use of\n \n s\n \n =\n \n =\n \n \n \n OR\n \n \n \n s\n \n =\n \n =\n \n ✓\n
\n
\n \n = «\n \n =» 4.6 × 10\n \n −7\n \n «m» ✓\n
\n
\n
\n (iii)\n
\n
\n Stays the same: Position/location of maxima/distance/separation between maxima «will be the same» /\n \n \n OWTTE\n \n \n ✓\n
\n
\n Changes: Intensity/brightness/width/sharpness «of maxima will change»/\n \n \n OWTTE\n \n \n ✓\n
\n
\n \n Allow other phrasing for maxima (fringes, spots, etc).\n \n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "c-wave-behaviour"
+ ],
+ "subtopics": [
+ "c-1-simple-harmonic-motion",
+ "c-2-wave-model",
+ "c-3-wave-phenomena"
+ ]
+ },
+ {
+ "question_id": "23M.2.HL.TZ1.5",
+ "Question": "
\n
\n (a)\n
\n
\n
\n Identify with ticks [✓] in the table, the forces that can act on electrons and the forces that can act on quarks.\n
\n
\n
\n
\n
\n
\n
\n
\n
\n (i)\n
\n
\n
\n Show that the energy released is about 18 MeV.\n
\n
\n
\n
\n
\n
\n (i)\n
\n
\n
\n \n two\n \n difficulties of energy production by nuclear fusion.\n
\n
\n
\n
\n
\n
\n (ii)\n
\n
\n
\n \n one\n \n advantage of energy production by nuclear fusion compared to nuclear fission.\n
\n
\n
\n
\n
\n
\n (i)\n
\n
\n
\n State the nucleon number of the He isotope that\n \n decays into.\n
\n
\n
\n
\n
\n
\n (iii)\n
\n
\n
\n Estimate the fraction of tritium remaining after one year.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n Weak nuclear: 2 ticks ✓\n
\n Strong nuclear: quarks only ✓\n
\n
\n
\n (i)\n
\n
\n «𝜇» = 2.0141 + 3.0160 − (4.0026 + 1.008665) «= 0.0188 u»\n
\n
\n \n \n OR\n \n \n
\n
\n \n In\n \n MeV: 1876.13415 + 2809.404 − (3728.4219 + 939.5714475) ✓\n
\n
\n = 0.0188 × 931.5\n \n \n OR\n \n \n = 17.512 «MeV» ✓\n
\n
\n \n Must see either clear substitutions or answer to at least 3 s.f. for\n \n MP2\n \n .\n \n
\n
\n
\n (i)\n
\n
\n Requires high temp/pressure ✓\n
\n Must overcome Coulomb/intermolecular repulsion ✓\n
\n Difficult to contain / control «at high temp/pressure» ✓\n
\n Difficult to produce excess energy/often energy input greater than output /\n \n \n OWTTE\n \n \n ✓\n
\n Difficult to capture energy from fusion reactions ✓\n
\n Difficult to maintain/sustain a constant reaction rate ✓\n
\n
\n
\n (ii)\n
\n
\n Plentiful fuel supplies\n \n \n OR\n \n \n larger specific energy\n \n \n OR\n \n \n larger energy density\n \n \n OR\n \n \n little or no «major radioactive» waste products ✓\n
\n
\n \n Allow descriptions such as “more energy per unit mass” or “more energy per unit volume”\n \n
\n
\n
\n (i)\n
\n
\n 3 ✓\n
\n
\n \n Do\n \n not\n \n accept\n \n by itself.\n \n
\n
\n
\n (iii)\n
\n
\n \n = «\n \n »0.056«y\n \n −1\n \n »\n \n \n OR\n \n \n \n \n \n OR\n \n \n \n
\n
\n 0.945\n \n \n OR\n \n \n 94.5% ✓\n
\n
\n \n Allow\n \n ECF\n \n from\n \n MP1\n \n \n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "e-nuclear-and-quantum-physics"
+ ],
+ "subtopics": [
+ "e-3-radioactive-decay",
+ "e-4-fission",
+ "e-5-fusion-and-stars"
+ ]
+ },
+ {
+ "question_id": "23M.2.HL.TZ1.6",
+ "Question": "
\n
\n (a)\n
\n
\n
\n The centres of two identical fixed conducting spheres each of charge +\n \n Q\n \n are separated by a distance\n \n D\n \n . C is the midpoint of the line joining the centres of the spheres.\n
\n
\n
\n
\n
\n
\n
\n
\n
\n (i)\n
\n
\n
\n Sketch, on the axes, how the electric potential V due to the two charges varies with the distance r from the centre of the left charge. No numbers are required. Your graph should extend from r = 0 to r = D.\n
\n
\n
\n
\n
\n
\n
\n
\n
\n (ii)\n
\n
\n
\n Calculate the work done to bring a small charge\n \n q\n \n from infinity to point C.\n
\n
\n Data given:\n
\n
\n \n Q\n \n = 2.0 × 10\n \n −3\n \n C,\n
\n
\n \n q\n \n = 4.0 × 10\n \n −9\n \n C\n
\n
\n \n D\n \n = 1.2 m\n
\n
\n
\n
\n
\n
\n (i)\n
\n
\n
\n The magnitude of the net force on\n \n q\n \n is given by\n \n . Explain why the charge\n \n q\n \n will execute simple harmonic oscillations about C.\n
\n
\n
\n
\n
\n
\n (ii)\n
\n
\n
\n The mass of the charge\n \n q\n \n is 0.025 kg.\n
\n
\n Calculate the angular frequency of the oscillations using the data in (a)(ii) and the expression in (b)(i).\n
\n
\n
\n
\n
\n
\n (c)\n
\n
\n
\n The charges\n \n Q\n \n are replaced by neutral masses\n \n M\n \n and the charge\n \n q\n \n by a neutral mass\n \n m\n \n . The mass\n \n m\n \n is displaced away from C by a small distance\n \n and released. Discuss whether the motion of\n \n m\n \n will be the same as that of\n \n q\n \n .\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n Constant, non-zero within spheres ✓\n
\n
\n A clear, non-zero positive minimum at C ✓\n
\n
\n Symmetric bowl shaped up curved shape in between ✓\n
\n
\n
\n
\n
\n
\n
\n \n Do\n \n not\n \n allow a bowl shaped down curve for\n \n MP3\n \n .\n \n
\n
\n
\n (i)\n
\n
\n Constant, non-zero within spheres ✓\n
\n
\n A clear, non-zero positive minimum at C ✓\n
\n
\n Symmetric bowl shaped up curved shape in between ✓\n
\n
\n
\n
\n
\n
\n
\n \n Do\n \n not\n \n allow a bowl shaped down curve for\n \n MP3\n \n .\n \n
\n
\n
\n (ii)\n
\n
\n \n V\n \n «= 2 ×\n \n » = 6.0 × 10\n \n 7\n \n «V» ✓\n
\n
\n \n W\n \n = «qV = 6.0 × 10\n \n 7\n \n × 4.0 × 10\n \n −9\n \n =» 0.24 «J» ✓\n
\n
\n \n Allow\n \n ECF\n \n from\n \n MP1\n \n \n
\n
\n
\n (i)\n
\n
\n The restoring force/acceleration is opposite to the displacement/towards equilibrium /\n \n \n OWTTE\n \n \n ✓\n
\n
\n and proportional to displacement from equilibrium /\n \n \n OWTTE✓\n \n \n
\n
\n \n Allow discussions based on the diagram (such as towards C for towards equilibrium).\n \n
\n
\n \n Accept F ∝ x\n \n OR\n \n a ∝ x for\n \n MP2\n \n \n
\n
\n
\n (ii)\n
\n
\n \n ω\n \n =\n \n \n \n OR\n \n \n use of\n \n F\n \n =\n \n mω\n \n \n 2\n \n \n r\n \n OR\n \n F\n \n = 1.33\n \n x\n \n \n \n OR\n \n \n \n a\n \n = 53.3\n \n x\n \n ✓\n
\n
\n «\n \n » = 7.299 «s\n \n −1\n \n »\n
\n
\n
\n (c)\n
\n
\n the net force will no longer be a restoring force/directed towards equilibrium\n
\n
\n \n \n OR\n \n \n
\n
\n the gravitational force is attractive/neutral mass would be pulled towards larger masses/\n \n \n OWTTE\n \n \n ✓\n
\n
\n «and so» no, motion will not be the same/no longer be SHM /\n \n \n OWTTE\n \n \n ✓\n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "a--space-time-and-motion",
+ "c-wave-behaviour",
+ "d-fields"
+ ],
+ "subtopics": [
+ "a-2-forces-and-momentum",
+ "c-1-simple-harmonic-motion",
+ "d-1-gravitational-fields",
+ "d-2-electric-and-magnetic-fields"
+ ]
+ },
+ {
+ "question_id": "23M.2.HL.TZ1.7",
+ "Question": "
\n
\n (a)\n
\n
\n
\n Explain, by reference to Faraday’s law of electromagnetic induction, why there is an electromotive force (emf) induced in the loop as it leaves the region of magnetic field.\n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n
\n Just before the loop is about to completely exit the region of magnetic field, the loop moves with constant terminal speed\n \n v\n \n .\n
\n
\n The following data is available:\n
\n
\n \n \n \n Mass of loop\n | \n \n \n m\n \n = 4.0 g\n | \n
\n \n \n Resistance of loop\n | \n \n \n R\n \n = 25 mΩ\n | \n
\n \n \n Width of loop\n | \n \n \n L\n \n = 15 cm\n | \n
\n \n \n Magnetic flux density\n | \n \n \n B\n \n = 0.80 T\n | \n
\n \n
\n
\n Determine, in m s\n \n −1\n \n the terminal speed\n \n v\n \n .\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n The induced emf is equal/proportional/related to the «rate of» change of «magnetic» flux/flux linkage ✓\n
\n
\n Flux is changing because the area pierced/enclosed by magnetic field lines changes «decreases»\n
\n
\n \n \n OR\n \n \n
\n
\n Flux is changing because the loop is leaving/moving out of the «magnetic» field. ✓\n
\n
\n \n Need to see a connection between the EMF and change in flux for\n \n MP1\n \n .\n \n
\n
\n \n Need to see a connection between the area changing or leaving the field and the change in flux for\n \n MP2\n \n \n
\n
\n
\n (a)\n
\n
\n The induced emf is equal/proportional/related to the «rate of» change of «magnetic» flux/flux linkage ✓\n
\n
\n Flux is changing because the area pierced/enclosed by magnetic field lines changes «decreases»\n
\n
\n \n \n OR\n \n \n
\n
\n Flux is changing because the loop is leaving/moving out of the «magnetic» field. ✓\n
\n
\n \n Need to see a connection between the EMF and change in flux for\n \n MP1\n \n .\n \n
\n
\n \n Need to see a connection between the area changing or leaving the field and the change in flux for\n \n MP2\n \n \n
\n
\n
\n (b)\n
\n
\n \n mg\n \n =\n \n BIL\n \n \n \n OR\n \n \n I = 0.33 «A» ✓\n
\n
\n \n BvL\n \n =\n \n IR\n \n OR\n \n \n ℰ = 8.25 × 10\n \n −3\n \n «V»\n \n \n OR\n \n \n ℰ = 0.12\n \n v\n \n ✓\n
\n
\n Combining results to get v =\n \n ✓\n
\n
\n \n v\n \n = «\n \n =» 0.068 «m s\n \n −1\n \n »\n
\n
\n \n Allow\n \n ECF\n \n between steps if clear work is shown.\n \n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "b-the-particulate-nature-of-matter",
+ "d-fields"
+ ],
+ "subtopics": [
+ "b-5-current-and-circuits",
+ "d-3-motion-in-electromagnetic-fields",
+ "d-4-induction"
+ ]
+ },
+ {
+ "question_id": "23M.2.HL.TZ1.8",
+ "Question": "
\n
\n (a)\n
\n
\n
\n Photons of wavelength 468 nm are incident on a metallic surface. The maximum kinetic energy of the emitted electrons is 1.8 eV.\n
\n
\n Calculate\n
\n
\n
\n
\n
\n
\n (i)\n
\n
\n
\n the work function of the surface, in eV.\n
\n
\n
\n
\n
\n
\n (ii)\n
\n
\n
\n the longest wavelength of a photon that will eject an electron from this surface.\n
\n
\n
\n
\n
\n
\n (i)\n
\n
\n
\n In an experiment, alpha particles of initial kinetic energy 5.9 MeV are directed at stationary nuclei of lead (\n \n ). Show that the distance of closest approach is about 4 × 10\n \n −14\n \n m.\n
\n
\n
\n
\n
\n
\n (ii)\n
\n
\n
\n The radius of a nucleus of\n \n is 7.1 × 10\n \n −15\n \n m. Explain why there will be no deviations from Rutherford scattering in the experiment in (b)(i).\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n Use of\n \n E\n \n \n max\n \n =\n \n \n E\n \n \n max\n \n ✓\n
\n
\n \n «\n \n −\n \n E\n \n \n max\n \n =\n \n − 1.81» = 0.85625\n \n 0.86 «eV» ✓\n
\n
\n
\n
\n
\n (i)\n
\n
\n Use of\n \n E\n \n \n max\n \n =\n \n \n E\n \n \n max\n \n ✓\n
\n
\n \n «\n \n −\n \n E\n \n \n max\n \n =\n \n − 1.81» = 0.85625\n \n 0.86 «eV» ✓\n
\n
\n
\n
\n
\n (ii)\n
\n
\n Use of\n \n ✓\n
\n
\n \n «\n \n =» 1.45 × 10\n \n −6\n \n «m»✓\n
\n
\n \n Allow\n \n ECF\n \n from\n \n a(i)\n \n \n
\n
\n
\n (i)\n
\n
\n 2e\n \n \n AND\n \n \n 82e seen\n
\n
\n \n \n OR\n \n \n
\n
\n 3.2 × 10\n \n −19\n \n «C»\n \n \n AND\n \n \n 1.312 × 10\n \n −17\n \n «C» seen ✓\n
\n
\n \n d\n \n =\n \n = 3.998 × 10\n \n −14\n \n ≈ 4 × 10\n \n −14\n \n «m» ✓\n
\n
\n \n Must see either clear substitutions or answer to at least 4 s.f. for\n \n MP2\n \n .\n \n
\n
\n
\n (ii)\n
\n
\n The closest approach is «significantly» larger than the radius of the nucleus / far away from the nucleus/\n \n \n OWTTE\n \n \n . ✓\n
\n
\n «Therefore» the strong nuclear force will not act on the alpha particle.✓\n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "e-nuclear-and-quantum-physics"
+ ],
+ "subtopics": [
+ "e-1-structure-of-the-atom",
+ "e-2-quantum-physics"
+ ]
+ },
+ {
+ "question_id": "23M.2.HL.TZ2.4",
+ "Question": "
\n
\n (a)\n
\n
\n
\n State the value of the maximum distance between the stars that can be measured in any reference frame.\n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n
\n State the speed of shuttle S relative to observer P using Galilean relativity.\n
\n
\n
\n
\n
\n
\n (c)\n
\n
\n
\n Calculate the distance between star A and star B relative to observer P.\n
\n
\n
\n
\n
\n
\n (d)\n
\n
\n
\n Show that the speed of shuttle S relative to observer P is approximately 0.6\n \n c\n \n .\n
\n
\n
\n
\n
\n
\n (e)\n
\n
\n
\n Calculate the time, according to observer P, that the shuttle S takes to travel from star A to star B.\n
\n
\n
\n
\n
\n
\n (f)\n
\n
\n
\n State and explain the reference frame in which the proper time for shuttle S to journey from star A to star B can be measured.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n 4.8 «light years» ✓\n
\n
\n
\n (b)\n
\n
\n «−» 0.48\n \n c\n \n ✓\n
\n
\n
\n
\n \n Ignore sign\n \n
\n
\n
\n (c)\n
\n
\n \n = 1.6 ✓\n
\n
\n \n D\n \n =\n \n = 3 «ly» ✓\n
\n
\n
\n
\n \n Allow\n \n ECF\n \n from\n \n MP1\n \n \n
\n
\n
\n (d)\n
\n
\n \n ✓\n
\n
\n «−» 0.63\n \n c\n \n ✓\n
\n
\n
\n
\n \n \n Award [2]\n \n if\n \n MP1\n \n correct and correct answer given to 1 significant figure.\n \n
\n
\n
\n (e)\n
\n
\n \n
\n
\n \n \n OR\n \n \n
\n
\n \n ✓\n
\n
\n = 19\n \n \n OR\n \n \n 20 «years» ✓\n
\n
\n
\n
\n \n Award\n \n [2]\n \n for\n \n BCA\n \n \n
\n
\n
\n (f)\n
\n
\n shuttle measures proper time ✓\n
\n
\n as the events occur at the same place for the shuttle / shuttle is at both events ✓\n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "a--space-time-and-motion"
+ ],
+ "subtopics": [
+ "a-5-galilean-and-special-relativity"
+ ]
+ },
+ {
+ "question_id": "23M.2.HL.TZ2.5",
+ "Question": "
\n
\n (a)\n
\n
\n
\n Outline what is meant by an isotope.\n
\n
\n
\n
\n
\n
\n (a)\n
\n
\n
\n Determine the speed of the spaceship relative to Earth.\n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n
\n Estimate, using the spacetime diagram, the time in seconds when the flash of light reaches the spaceship according to the Earth observer.\n
\n
\n
\n
\n
\n
\n (c)\n
\n
\n
\n Determine the time coordinate\n \n ct′\n \n when the flash of light reaches the spaceship, according to an observer at rest in the spaceship.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n «An atom with» the same number of protons\n \n \n AND\n \n \n different numbers of neutrons\n
\n \n \n OR\n \n \n
\n Same chemical properties\n \n \n AND\n \n \n different physical properties ✓\n
\n
\n \n Do\n \n not\n \n allow just atomic number and mass number\n \n
\n
\n
\n (a)\n
\n
\n 0.6 c\n
\n
\n \n \n OR\n \n \n
\n
\n = 1.8 × 10\n \n 8\n \n «m s\n \n −1\n \n » ✓\n
\n
\n
\n (b)\n
\n
\n Line drawn at 45° from\n \n ct\n \n = 2 km to hit spaceship world line at\n \n ct\n \n = 5 km\n
\n
\n \n \n OR\n \n \n
\n
\n \n ct\n \n = 1.2/(\n \n c\n \n − 0.6\n \n c\n \n ) + 2 = 5 «km» ✓\n
\n
\n \n t\n \n =\n \n = 1.7 × 10\n \n −5\n \n «s» ✓\n
\n
\n
\n
\n \n Award\n \n [2]\n \n for\n \n BCA\n \n \n
\n
\n
\n (c)\n
\n
\n (\n \n ct\n \n ')\n \n 2\n \n − 0 = 5\n \n 2\n \n − 3\n \n 2\n \n
\n
\n \n \n OR\n \n \n
\n
\n \n = 1.25 ✓\n
\n
\n
\n
\n \n ct\n \n ' = 4 «km»\n
\n
\n \n \n OR\n \n \n
\n
\n \n t\n \n ' = 13 «\n \n µ\n \n s» ✓\n
\n
\n
\n
\n \n Allow\n \n ECF\n \n from\n \n (b)\n \n \n
\n
\n \n Allow\n \n ECF\n \n from\n \n MP1\n \n \n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "a--space-time-and-motion",
+ "e-nuclear-and-quantum-physics"
+ ],
+ "subtopics": [
+ "a-5-galilean-and-special-relativity",
+ "e-3-radioactive-decay"
+ ]
+ },
+ {
+ "question_id": "23M.2.HL.TZ2.6",
+ "Question": "
\n
\n (a)\n
\n
\n
\n Determine\n \n .\n
\n
\n
\n
\n
\n
\n (a)\n
\n
\n
\n Show that the net torque on the system about the central axis is approximately 30 N m.\n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n
\n The system rotates from rest and reaches a maximum angular speed of 20 rad s\n \n −1\n \n in a time of 5.0 s. Calculate the angular acceleration of the system.\n
\n
\n
\n
\n
\n
\n (i)\n
\n
\n
\n State and explain the magnitude of the resultant gravitational field strength at O.\n
\n
\n
\n
\n
\n
\n (ii)\n
\n
\n
\n Outline why the graph between P and O is negative.\n
\n
\n
\n
\n
\n
\n (iii)\n
\n
\n
\n Show that the gravitational potential\n \n V\n \n \n P\n \n at the surface of P due to the mass of P is given by\n \n V\n \n \n P\n \n = −\n \n g\n \n \n P\n \n \n R\n \n \n P\n \n where\n \n R\n \n \n P\n \n is the radius of the planet.\n
\n
\n
\n
\n
\n
\n (iv)\n
\n
\n
\n The gravitational potential due to the mass of M at the surface of P can be assumed to be negligible.\n
\n
\n Estimate, using the graph, the gravitational potential at the surface of M due to the mass of M.\n
\n
\n
\n
\n
\n
\n (v)\n
\n
\n
\n Draw on the axes the variation of gravitational potential between O and M.\n
\n
\n
\n
\n
\n
\n (c)\n
\n
\n
\n Determine the moment of inertia of the system about the central axis.\n
\n
\n
\n
\n
\n
\n (i)\n
\n
\n
\n Outline why the angular speed\n \n ω\n \n decreases when the spheres move outward.\n
\n
\n
\n
\n
\n
\n (ii)\n
\n
\n
\n Show that the rotational kinetic energy is\n \n \n Lω\n \n where\n \n L\n \n is the angular momentum of the system.\n
\n
\n
\n
\n
\n
\n (iii)\n
\n
\n
\n When the spheres move outward, the angular speed decreases from 20 rad s\n \n −1\n \n to 12 rad s\n \n −1\n \n . Calculate the percentage change in rotational kinetic energy that occurs when the spheres move outward.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n Work using\n \n g\n \n ∝\n \n ✓\n
\n
\n \n = 0.75 ✓\n
\n
\n
\n (a)\n
\n
\n \n = 50 × 0.5 + 40 × 0.2\n
\n
\n \n \n OR\n \n \n
\n
\n 33 «Nm» ✓\n
\n
\n
\n
\n \n Accept opposite rotational sign convention\n \n
\n
\n
\n (b)\n
\n
\n «α =\n \n =» 4 «rad s\n \n −2\n \n » ✓\n
\n
\n
\n (i)\n
\n
\n g = 0 ✓\n
\n
\n As g «=\n \n which» is the gradient of the graph\n
\n
\n \n \n OR\n \n \n
\n As the force of attraction/field strength of P and M are equal ✓\n
\n
\n
\n (ii)\n
\n
\n The gravitational field is attractive so that energy is required «to move away from P» ✓\n
\n
\n the gravitational potential is defined as 0 at\n \n , (the potential must be negative) ✓\n
\n
\n
\n (iii)\n
\n
\n \n V\n \n \n P\n \n =\n \n \n \n AND\n \n g\n \n \n P\n \n =\n \n (at surface) ✓\n
\n
\n Suitable working and cancellation of\n \n G\n \n and\n \n M\n \n seen ✓\n
\n
\n \n V\n \n \n P\n \n = −\n \n g\n \n \n P\n \n \n R\n \n \n P\n \n
\n
\n \n Must see negative sign\n \n
\n
\n
\n
\n
\n (iv)\n
\n
\n «\n \n =\n \n = 0.75 × 0.27» = 0.20 ✓\n
\n
\n \n V\n \n \n M\n \n = «−6.4 × 10\n \n 7\n \n × 0.2 =» «−»1.3 × 10\n \n 7\n \n «J kg\n \n −1\n \n »✓\n
\n
\n
\n (v)\n
\n
\n Line always negative, of suitable shape and end point below −8 and above −20 unless awarding\n \n \n ECF\n \n \n from\n \n \n b(iv)\n \n \n ✓\n
\n
\n
\n
\n
\n
\n (c)\n
\n
\n \n
\n
\n \n \n OR\n \n \n
\n
\n 33 =\n \n × 4 ✓\n
\n
\n
\n
\n \n = 8.25 «kg m\n \n 2\n \n » ✓\n
\n
\n
\n
\n \n Allow\n \n ECF\n \n from\n \n (a)\n \n and\n \n (b)\n \n \n
\n
\n \n Award\n \n [2]\n \n for a\n \n BCA\n \n \n
\n
\n
\n (i)\n
\n
\n moment of inertia increases ✓\n
\n
\n Angular momentum is conserved ✓\n
\n
\n \n
\n Allow algebraic expressions e.g. ω =\n \n so ω decreases for\n \n MP2\n \n \n
\n
\n
\n (ii)\n
\n
\n \n E\n \n \n k\n \n «=\n \n \n ω\n \n \n 2\n \n =»\n \n (\n \n \n ω\n \n )\n \n ω\n \n =\n \n \n Lω\n \n ✓\n
\n
\n
\n
\n \n Accept equivalent methods\n \n
\n
\n
\n (iii)\n
\n
\n \n «E\n \n \n k\n \n =»\n \n \n Lω\n \n \n 1\n \n \n =\n \n Lω\n \n 2\n \n \n ✓\n
\n
\n \n \n OR\n \n \n
\n
\n \n
\n
\n \n \n OR\n \n \n
\n
\n «\n \n L\n \n is constant so»\n \n E\n \n \n k\n \n is proportional to\n \n ω\n \n ✓\n
\n
\n 40 % «energy loss» ✓\n
\n
\n
\n
\n \n \n MP1\n \n is for understanding that angular momentum is constant so change in rotational kinetic energy is proportional to change in angular velocity\n \n
\n
\n \n \n Award [0]\n \n if E = 0.5 I ω\n \n 2\n \n is used with the same I value for both values of E\n \n
\n
\n \n Award\n \n [2]\n \n for\n \n BCA\n \n \n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "a--space-time-and-motion",
+ "d-fields"
+ ],
+ "subtopics": [
+ "a-4-rigid-body-mechanics",
+ "d-1-gravitational-fields"
+ ]
+ },
+ {
+ "question_id": "23M.2.HL.TZ2.7",
+ "Question": "
\n
\n (a)\n
\n
\n
\n Calculate the pressure of the gas at B.\n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n
\n Sketch, on the\n \n pV\n \n diagram, the remaining two processes BC and CA that the gas undergoes.\n
\n
\n
\n
\n
\n
\n (c)\n
\n
\n
\n Show that the temperature of the gas at C is approximately 350 °C.\n
\n
\n
\n
\n
\n
\n (d)\n
\n
\n
\n Explain why the change of entropy for the gas during the process BC is equal to zero.\n
\n
\n
\n
\n
\n
\n (e)\n
\n
\n
\n Explain why the work done by the gas during the isothermal expansion AB is less than the work done on the gas during the adiabatic compression BC.\n
\n
\n
\n
\n
\n
\n (f)\n
\n
\n
\n The quantity of trapped gas is 53.2 mol. Calculate the thermal energy removed from the gas during process CA.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n use of\n \n pV\n \n = constant ✓\n
\n
\n \n P\n \n \n B\n \n = 43 «Kpa» ✓\n
\n
\n
\n
\n \n \n Award [2]\n \n for\n \n BCA\n \n \n
\n
\n
\n (b)\n
\n
\n concave curved line from B to locate C with a higher pressure than A ✓\n
\n
\n vertical line joining C to A ✓\n
\n
\n
\n
\n \n Allow\n \n ECF\n \n from\n \n MP1\n \n i.e.,\n \n award [1]\n \n for first process locating C at a lower pressure than A, then vertical line to A.\n \n
\n
\n \n Arrows on the processes are not needed.\n \n
\n
\n \n Point C need not be labelled.\n \n
\n
\n
\n
\n
\n
\n (c)\n
\n
\n \n \n ALTERNATIVE 1\n \n \n
\n
\n use of\n \n = constant «so\n \n » ✓\n
\n
\n \n T\n \n \n C\n \n = 624 «K»\n \n \n OR\n \n \n \n T\n \n \n C\n \n = 351 «°C» ✓\n
\n
\n
\n
\n \n \n ALTERNATIVE 2\n \n \n
\n
\n use of\n \n to get either\n \n p\n \n \n c\n \n =\n \n \n \n OR\n \n \n \n p\n \n \n c\n \n = 268 «kPa» ✓\n
\n
\n «\n \n T\n \n \n C\n \n = 268 × 300/129 = so »\n
\n
\n \n T\n \n \n C\n \n = 624 «K»\n \n \n OR\n \n \n \n T\n \n \n C\n \n = 351 «°C» ✓\n
\n
\n
\n (d)\n
\n
\n \n \n ALTERNATIVE 1\n \n \n
\n
\n «the process is adiabatic so» ΔQ = 0 ✓\n
\n
\n
\n
\n \n \n ALTERNATIVE 2\n \n \n
\n
\n The compression is reversible «so ΔS = 0» ✓\n
\n
\n
\n
\n \n \n OWTTE\n \n \n
\n
\n
\n (e)\n
\n
\n area under curve AB is less than area under curve BC ✓\n
\n
\n
\n
\n \n Do\n \n not\n \n allow\n \n ECF\n \n from part\n \n (b)\n \n \n
\n
\n
\n (f)\n
\n
\n «W = 0 so» Q = ΔU ✓\n
\n
\n «ΔU =\n \n × 53.2 × R × (351 – 27) so » ΔU = 2.15 × 10\n \n 5\n \n «J» ✓\n
\n
\n
\n
\n \n \n Award [2]\n \n for\n \n BCA\n \n \n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "b-the-particulate-nature-of-matter"
+ ],
+ "subtopics": [
+ "b-4-thermodynamics"
+ ]
+ },
+ {
+ "question_id": "23M.2.HL.TZ2.8",
+ "Question": "
\n
\n (a)\n
\n
\n
\n Show that the net torque on the system about the central axis is approximately 30 N m.\n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n
\n The system rotates from rest and reaches a maximum angular speed of 20 rad s\n \n −1\n \n in a time of 5.0 s. Calculate the angular acceleration of the system.\n
\n
\n
\n
\n
\n
\n (c)\n
\n
\n
\n Determine the moment of inertia of the system about the central axis.\n
\n
\n
\n
\n
\n
\n (i)\n
\n
\n
\n Outline why the angular speed\n \n ω\n \n decreases when the spheres move outward.\n
\n
\n
\n
\n
\n
\n (ii)\n
\n
\n
\n Show that the rotational kinetic energy is\n \n \n Lω\n \n where\n \n L\n \n is the angular momentum of the system.\n
\n
\n
\n
\n
\n
\n (iii)\n
\n
\n
\n When the spheres move outward, the angular speed decreases from 20 rad s\n \n −1\n \n to 12 rad s\n \n −1\n \n . Calculate the percentage change in rotational kinetic energy that occurs when the spheres move outward.\n
\n
\n
\n
\n
\n
\n (e)\n
\n
\n
\n Outline one reason why this model of a dancer is unrealistic.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n \n = 50 × 0.5 + 40 × 0.2\n
\n
\n \n \n OR\n \n \n
\n
\n 33 «Nm» ✓\n
\n
\n
\n
\n \n Accept opposite rotational sign convention\n \n
\n
\n
\n (b)\n
\n
\n «α =\n \n =» 4 «rad s\n \n −2\n \n » ✓\n
\n
\n
\n (c)\n
\n
\n \n
\n
\n \n \n OR\n \n \n
\n
\n 33 =\n \n × 4 ✓\n
\n
\n
\n
\n \n = 8.25 «kg m\n \n 2\n \n » ✓\n
\n
\n
\n
\n \n Allow\n \n ECF\n \n from\n \n (a)\n \n and\n \n (b)\n \n \n
\n
\n \n Award\n \n [2]\n \n for a\n \n BCA\n \n \n
\n
\n
\n (i)\n
\n
\n moment of inertia increases ✓\n
\n
\n Angular momentum is conserved ✓\n
\n
\n \n
\n Allow algebraic expressions e.g. ω =\n \n so ω decreases for\n \n MP2\n \n \n
\n
\n
\n (ii)\n
\n
\n \n E\n \n \n k\n \n «=\n \n \n ω\n \n \n 2\n \n =»\n \n (\n \n \n ω\n \n )\n \n ω\n \n =\n \n \n Lω\n \n ✓\n
\n
\n
\n
\n \n Accept equivalent methods\n \n
\n
\n
\n (iii)\n
\n
\n \n «E\n \n \n k\n \n =»\n \n \n Lω\n \n \n 1\n \n \n =\n \n Lω\n \n 2\n \n \n ✓\n
\n
\n \n \n OR\n \n \n
\n
\n \n
\n
\n \n \n OR\n \n \n
\n
\n «\n \n L\n \n is constant so»\n \n E\n \n \n k\n \n is proportional to\n \n ω\n \n ✓\n
\n
\n 40 % «energy loss» ✓\n
\n
\n
\n
\n \n \n MP1\n \n is for understanding that angular momentum is constant so change in rotational kinetic energy is proportional to change in angular velocity\n \n
\n
\n \n \n Award [0]\n \n if E = 0.5 I ω\n \n 2\n \n is used with the same I value for both values of E\n \n
\n
\n \n Award\n \n [2]\n \n for\n \n BCA\n \n \n
\n
\n
\n (e)\n
\n
\n one example specified\n \n eg\n \n friction, air resistance, mass distribution not modelled ✓\n
\n
\n
\n
\n \n \n Award [1]\n \n for any reasonable physical parameter that is not consistent with the model\n \n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "a--space-time-and-motion"
+ ],
+ "subtopics": [
+ "a-4-rigid-body-mechanics"
+ ]
+ },
+ {
+ "question_id": "23M.2.HL.TZ2.9",
+ "Question": "
\n
\n (a)\n
\n
\n
\n Show, using the data, that the energy released in the decay of one magnesium-27 nucleus is about 2.62 MeV.\n
\n
\n Mass of aluminium-27 atom = 26.98153 u\n
\n Mass of magnesium-27 atom = 26.98434 u\n
\n The unified atomic mass unit is 931.5 MeV c\n \n −2\n \n .\n
\n
\n
\n
\n
\n
\n (a)\n
\n
\n
\n Calculate the pressure of the gas at B.\n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n
\n Sketch, on the\n \n pV\n \n diagram, the remaining two processes BC and CA that the gas undergoes.\n
\n
\n
\n
\n
\n
\n (i)\n
\n
\n
\n State the conclusion that can be drawn from the existence of these two routes.\n
\n
\n
\n
\n
\n
\n (ii)\n
\n
\n
\n Calculate the difference between the magnitudes of the total energy transfers in parts (a) and (b).\n
\n
\n
\n
\n
\n
\n (iii)\n
\n
\n
\n Explain how the difference in part (b)(ii) arises.\n
\n
\n
\n
\n
\n
\n (c)\n
\n
\n
\n Show that the temperature of the gas at C is approximately 350 °C.\n
\n
\n
\n
\n
\n
\n (i)\n
\n
\n
\n The smallest mass of magnesium that can be detected with this technique is 1.1 × 10\n \n −8\n \n kg.\n
\n
\n Show that the smallest number of magnesium atoms that can be detected with this technique is about 10\n \n 17\n \n .\n
\n
\n
\n
\n
\n
\n (ii)\n
\n
\n
\n A sample of glass is irradiated with neutrons so that all the magnesium atoms become magnesium-27. The sample contains 9.50 × 10\n \n 15\n \n magnesium atoms.\n
\n
\n The decay constant of magnesium-27 is 1.22 × 10\n \n −3\n \n s\n \n −1\n \n .\n
\n
\n Determine the number of aluminium atoms that form in 10.0 minutes after the irradiation ends.\n
\n
\n
\n
\n
\n
\n (iii)\n
\n
\n
\n Estimate, in W, the average rate at which energy is transferred by the decay of magnesium-27 during the 10.0 minutes after the irradiation ends.\n
\n
\n
\n
\n
\n
\n (d)\n
\n
\n
\n Explain why the change of entropy for the gas during the process BC is equal to zero.\n
\n
\n
\n
\n
\n
\n (e)\n
\n
\n
\n Explain why the work done by the gas during the isothermal expansion AB is less than the work done on the gas during the adiabatic compression BC.\n
\n
\n
\n
\n
\n
\n (f)\n
\n
\n
\n The quantity of trapped gas is 53.2 mol. Calculate the thermal energy removed from the gas during process CA.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n (26.98434 - 26.98153) × 931.5\n
\n
\n \n \n OR\n \n \n
\n
\n 2.6175 «MeV» seen ✓\n
\n
\n
\n (a)\n
\n
\n use of\n \n pV\n \n = constant ✓\n
\n
\n \n P\n \n \n B\n \n = 43 «Kpa» ✓\n
\n
\n
\n
\n \n \n Award [2]\n \n for\n \n BCA\n \n \n
\n
\n
\n (b)\n
\n
\n concave curved line from B to locate C with a higher pressure than A ✓\n
\n
\n vertical line joining C to A ✓\n
\n
\n
\n
\n \n Allow\n \n ECF\n \n from\n \n MP1\n \n i.e.,\n \n award [1]\n \n for first process locating C at a lower pressure than A, then vertical line to A.\n \n
\n
\n \n Arrows on the processes are not needed.\n \n
\n
\n \n Point C need not be labelled.\n \n
\n
\n
\n
\n
\n
\n (i)\n
\n
\n evidence for nuclear energy levels ✓\n
\n
\n
\n (ii)\n
\n
\n Difference = 2.6175 – (1.76656 +0.84376) = 2.6175 – 2.61032 = 0.007195 «MeV»\n
\n
\n \n \n OR\n \n \n
\n
\n Difference = 2.6175 – (1.59587 +1.01445) = 2.61032 = 0.007195 «MeV» ✓\n
\n
\n
\n (iii)\n
\n
\n Another particle/«anti» neutrino is emitted «that accounts for this mass / energy» ✓\n
\n
\n
\n (c)\n
\n
\n \n \n ALTERNATIVE 1\n \n \n
\n
\n use of\n \n = constant «so\n \n » ✓\n
\n
\n \n T\n \n \n C\n \n = 624 «K»\n \n \n OR\n \n \n \n T\n \n \n C\n \n = 351 «°C» ✓\n
\n
\n
\n
\n \n \n ALTERNATIVE 2\n \n \n
\n
\n use of\n \n to get either\n \n p\n \n \n c\n \n =\n \n \n \n OR\n \n \n \n p\n \n \n c\n \n = 268 «kPa» ✓\n
\n
\n «\n \n T\n \n \n C\n \n = 268 × 300/129 = so »\n
\n
\n \n T\n \n \n C\n \n = 624 «K»\n \n \n OR\n \n \n \n T\n \n \n C\n \n = 351 «°C» ✓\n
\n
\n
\n (i)\n
\n
\n So 1.1 × 10\n \n −8\n \n kg ≡\n \n × 10\n \n −8\n \n «mol»\n
\n
\n \n \n OR\n \n \n
\n
\n Mass of atom = 27 × 1.66 × 10\n \n −27\n \n «kg» ✓\n
\n
\n 2.4 − 2.5 x 10\n \n 17\n \n atoms ✓\n
\n
\n
\n (ii)\n
\n
\n \n N\n \n \n 10\n \n = 9.50 × 10\n \n 15\n \n ×\n \n e\n \n \n −0.00122×60\n \n seen ✓\n
\n
\n \n N\n \n \n 10\n \n = 4.57 × 10\n \n 15\n \n ✓\n
\n
\n So number of aluminium-27 nuclei = (9.50 – 4.57) × 10\n \n 15\n \n = 4.9(3) × 10\n \n 15\n \n ✓\n
\n
\n
\n (iii)\n
\n
\n Total energy released = ans\n \n (c)(ii)\n \n × 2.62 × 10\n \n 6\n \n × 1.6 × 10\n \n −19\n \n «= 2100 J» ✓\n
\n
\n «\n \n =» 3.4 −3.5 «W» ✓\n
\n
\n
\n (d)\n
\n
\n \n \n ALTERNATIVE 1\n \n \n
\n
\n «the process is adiabatic so» ΔQ = 0 ✓\n
\n
\n
\n
\n \n \n ALTERNATIVE 2\n \n \n
\n
\n The compression is reversible «so ΔS = 0» ✓\n
\n
\n
\n
\n \n \n OWTTE\n \n \n
\n
\n
\n (e)\n
\n
\n area under curve AB is less than area under curve BC ✓\n
\n
\n
\n
\n \n Do\n \n not\n \n allow\n \n ECF\n \n from part\n \n (b)\n \n \n
\n
\n
\n (f)\n
\n
\n «W = 0 so» Q = ΔU ✓\n
\n
\n «ΔU =\n \n × 53.2 × R × (351 – 27) so » ΔU = 2.15 × 10\n \n 5\n \n «J» ✓\n
\n
\n
\n
\n \n \n Award [2]\n \n for\n \n BCA\n \n \n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "b-the-particulate-nature-of-matter",
+ "e-nuclear-and-quantum-physics"
+ ],
+ "subtopics": [
+ "b-1-thermal-energy-transfers",
+ "b-4-thermodynamics",
+ "e-3-radioactive-decay"
+ ]
+ },
+ {
+ "question_id": "23M.2.SL.TZ1.1",
+ "Question": "
\n
\n (a)\n
\n
\n
\n Deduce the unit of μ in terms of fundamental SI units.\n
\n
\n
\n
\n
\n
\n (i)\n
\n
\n
\n draw a free-body diagram for the ball.\n
\n
\n
\n
\n
\n
\n
\n
\n
\n (ii)\n
\n
\n
\n show that the speed of the ball is about 4.3 m s\n \n −1\n \n .\n
\n
\n
\n
\n
\n
\n (iii)\n
\n
\n
\n determine the tension in the string.\n
\n
\n
\n
\n
\n
\n (i)\n
\n
\n
\n Show that the collision is elastic.\n
\n
\n
\n
\n
\n
\n (ii)\n
\n
\n
\n Calculate the maximum height risen by the centre of the ball.\n
\n
\n
\n
\n
\n
\n (iii)\n
\n
\n
\n Explain a possible reason for the systematic error.\n
\n
\n
\n
\n
\n
\n (iv)\n
\n
\n
\n Calculate the gradient of the graph.\n
\n
\n
\n
\n
\n
\n (c)\n
\n
\n
\n The coefficient of dynamic friction between the block and the rough surface is 0.400.\n
\n
\n Estimate the distance travelled by the block on the rough surface until it stops.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n [μ] = «\n \n » kg × m\n \n −1\n \n
\n
\n
\n
\n \n Accept kg/m.\n \n
\n
\n \n Do\n \n not\n \n accept g m\n \n −1\n \n .\n \n
\n
\n
\n (i)\n
\n
\n Tension upwards, weight downwards ✓\n
\n Tension is clearly longer than weight ✓\n
\n
\n
\n
\n \n Look for:\n \n
\n
\n
\n
\n
\n
\n (ii)\n
\n
\n \n v\n \n =\n \n \n \n OR\n \n \n = 4.32 «m s\n \n −1\n \n » ✓\n
\n
\n
\n
\n \n Must see either full substitution or answer to at least 3 s.f.\n \n
\n
\n
\n (iii)\n
\n
\n \n T − mg = F\n \n net\n \n \n OR\n \n \n \n T − mg =\n \n \n ✓\n
\n
\n \n T\n \n «= 0.800 × 9.81 +\n \n » = 23.5 «N» ✓\n
\n
\n
\n (i)\n
\n
\n Use of conservation of momentum. ✓\n
\n Rebound speed = 2.16 «m s\n \n −1\n \n » ✓\n
\n Calculation of initial KE = «\n \n × 0.800 × 4.317\n \n 2\n \n » = 7.46 « J » ✓\n
\n Calculation of final KE = «\n \n × 0.800 × 2.16\n \n 2\n \n +\n \n × 2.40 × 2.16\n \n 2\n \n » = 7.46 «J» ✓\n
\n «hence elastic»\n
\n
\n
\n (ii)\n
\n
\n \n \n ALTERNATIVE 1\n \n \n
\n Rebound speed is halved so energy less by a factor of 4 ✓\n
\n Hence height is\n \n =23.8 «cm» ✓\n
\n
\n \n \n ALTERNATIVE 2\n
\n \n \n Use of conservation of energy /\n \n × 0.800 × 2.16\n \n 2\n \n = 0.800 × 9.8 ×\n \n h\n
\n \n OR\n \n \n
\n
\n Use of proper kinematics equation (e.g. 0 = 2.16\n \n 2\n \n − 2 × 9.8 ×\n \n h\n \n ) ✓\n
\n
\n \n h\n \n = 23.8 «cm» ✓\n
\n
\n \n
\n Allow\n \n ECF\n \n from\n \n b(i)\n \n \n
\n
\n
\n (iii)\n
\n
\n mass of tray of weights neglected/friction at pulley/friction at slider/thickness of slider/zero off-set error ✓\n
\n
\n
\n
\n \n Do\n \n not\n \n allow vague answers like friction neglected / error in length measurement.\n \n
\n
\n
\n (iv)\n
\n
\n large enough triangle Δ\n \n m\n \n ≥ 50 g✓\n
\n
\n answer in range 0.210 − 0.240 «kg m\n \n −1\n \n » ✓\n
\n
\n
\n
\n \n Accept answers in g m\n \n −2\n \n .\n \n
\n
\n \n Do\n \n not\n \n allow\n \n ECF\n \n from\n \n MP1\n \n .\n \n
\n
\n
\n (c)\n
\n
\n \n \n ALTERNATIVE 1\n \n \n
\n Frictional force is\n \n f\n \n «= 0.400 × 2.40 × 9.81» = 9.42 «N» ✓\n
\n 9.42 ×\n \n d\n \n =\n \n × 2.40 × 2.16\n \n 2\n \n \n \n OR\n \n \n \n d\n \n =\n \n ✓\n
\n \n d\n \n = 0.594 «m» ✓\n
\n
\n
\n
\n \n \n ALTERNATIVE 2\n \n \n
\n \n a\n \n = «\n \n =\n \n µg\n \n = 0.4 × 9.81 =» 3.924 «m s\n \n −2\n \n » ✓\n
\n
\n Proper use of kinematics equation(s) to determine ✓\n
\n
\n \n d\n \n = 0.594 «m» ✓\n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "a--space-time-and-motion",
+ "inquiry",
+ "tools"
+ ],
+ "subtopics": [
+ "a-2-forces-and-momentum",
+ "a-3-work-energy-and-power",
+ "i-3-2-evaluating",
+ "inquiry-3-concluding-and-evaluating",
+ "tool-3-mathematics"
+ ]
+ },
+ {
+ "question_id": "23M.2.SL.TZ1.2",
+ "Question": "
\n
\n (a)\n
\n
\n
\n Show that the average rate at which thermal energy is transferred into the chocolate is about 15 W.\n
\n
\n
\n
\n
\n
\n (i)\n
\n
\n
\n one variable that must be controlled,\n
\n
\n
\n
\n
\n
\n (ii)\n
\n
\n
\n the main source of error in\n \n T\n \n .\n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n
\n To determine\n \n T\n \n more precisely, the student measures the total time for 20 oscillations and divides by 20.\n
\n
\n Explain why this is preferable to measuring the time for just one oscillation.\n
\n
\n
\n
\n
\n
\n (c)\n
\n
\n
\n Compare the internal energy of the chocolate at\n \n t\n \n = 2 minutes with that at\n \n t\n \n = 6 minutes.\n
\n
\n
\n
\n
\n
\n (i)\n
\n
\n
\n The student plots a graph with\n \n L\n \n on the horizontal axis. State the variable that must be plotted on the vertical axis in order to obtain a line of best fit that is straight.\n
\n
\n
\n
\n
\n
\n (ii)\n
\n
\n
\n Calculations using the data of the experiment show that\n \n g\n \n = 9.71622 m s\n \n −2\n \n with a percentage uncertainty of 8 %. Determine the value of\n \n g\n \n that can be obtained from this experiment. Include the absolute uncertainty in\n \n g\n \n to one significant figure.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n Reads change in temperature to be 45 − 31\n \n \n OR\n \n \n 14 °C ✓\n
\n
\n
\n \n Q\n \n = 0.082 × 1.6 × 10\n \n 3\n \n × 14 = 1.84 × 10\n \n 3\n \n «J» ✓\n
\n
\n \n P\n \n =\n \n = 15.3\n \n 15 «W»✓\n
\n
\n
\n
\n \n Must see either full substitution\n \n OR\n \n answer to at least 3 s.f. in\n \n MP3\n \n \n
\n
\n
\n (i)\n
\n
\n mass\n \n \n OR\n \n \n diameter\n \n \n OR\n \n \n material of bob\n \n \n OR\n \n \n « initial » amplitude/angle ✓\n
\n
\n
\n
\n \n Do\n \n not\n \n allow statements about rulers, stopwatches, string, number of oscillations, constant gravity.\n \n
\n
\n
\n (ii)\n
\n
\n student’s reaction time «in starting and stopping stopwatch» / starting/stopping stopwatch ✓\n
\n
\n
\n (b)\n
\n
\n it reduces «the random» error/uncertainty ✓\n
\n
\n by a factor of 20 «compared to that in a single period measurement» ✓\n
\n
\n
\n
\n \n For\n \n MP1\n \n , allow increasing accuracy/precision.\n \n
\n
\n \n \n Award [0]\n \n for answers related to number of trials, 20 measurements of one period.\n \n
\n
\n
\n (c)\n
\n
\n Internal energy is greater at\n \n t\n \n = 6 min\n \n \n OR\n \n \n internal energy is lower at\n \n t\n \n = 2 min\n \n \n OR\n \n \n internal energy increases «as energy is added to the system» ✓\n
\n
\n Because kinetic energy «of the molecules» is the same\n \n \n AND\n \n \n potential energy «of the molecules» has increased /\n \n \n OWTTE\n \n \n ✓\n
\n
\n
\n (i)\n
\n
\n \n T\n \n \n 2\n \n ✓\n
\n
\n
\n (ii)\n
\n
\n \n g\n \n = 9.7 «m s\n \n −2\n \n » ✓\n
\n
\n Δ\n \n g\n \n = 0.8 «m s\n \n −2\n \n » ✓\n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "b-the-particulate-nature-of-matter",
+ "inquiry",
+ "tools"
+ ],
+ "subtopics": [
+ "b-1-thermal-energy-transfers",
+ "i-1-2-designing",
+ "inquiry-1-exploring-and-designing",
+ "tool-1-experimental-techniques",
+ "tool-3-mathematics"
+ ]
+ },
+ {
+ "question_id": "23M.2.SL.TZ1.3",
+ "Question": "
\n
\n (a)\n
\n
\n
\n A transverse water wave travels to the right. The diagram shows the shape of the surface of the water at time\n \n t\n \n = 0. P and Q show two corks floating on the surface.\n
\n
\n
\n
\n
\n
\n
\n
\n
\n (i)\n
\n
\n
\n State what is meant by a transverse wave.\n
\n
\n
\n
\n
\n
\n (ii)\n
\n
\n
\n The frequency of the wave is 0.50 Hz. Calculate the speed of the wave.\n
\n
\n
\n
\n
\n
\n (iii)\n
\n
\n
\n Plot on the diagram the position of P at time\n \n t\n \n = 0.50 s.\n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n
\n Monochromatic light is incident on two very narrow slits. The light that passes through the slits is observed on a screen. M is directly opposite the midpoint of the slits.\n \n represents the displacement from M in the direction shown.\n
\n
\n
\n
\n
\n A student argues that what will be observed on the screen will be a total of two bright spots opposite the slits. Explain why the student’s argument is incorrect.\n
\n
\n
\n
\n
\n
\n (c)\n
\n
\n
\n The graph shows the actual variation with displacement\n \n from M of the intensity of the light on the screen.\n \n is the intensity of light at the screen from one slit only.\n
\n
\n
\n
\n
\n The slits are separated by a distance of 0.18 mm and the distance to the screen is 2.2 m. Determine, in m, the wavelength of light.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n «A wave where the» displacement of particles/oscillations of particles/movement of particles/vibrations of particles is perpendicular/normal to the direction of energy transfer/wave travel/wave velocity/wave movement/wave propagation ✓\n
\n
\n
\n
\n \n Allow medium, material, water, molecules, or atoms for particles.\n \n
\n
\n
\n (i)\n
\n
\n «A wave where the» displacement of particles/oscillations of particles/movement of particles/vibrations of particles is perpendicular/normal to the direction of energy transfer/wave travel/wave velocity/wave movement/wave propagation ✓\n
\n
\n
\n
\n \n Allow medium, material, water, molecules, or atoms for particles.\n \n
\n
\n
\n (ii)\n
\n
\n \n v\n \n = «0.50 × 16 =» 8.0 «m s\n \n −1\n \n » ✓\n
\n
\n
\n (iii)\n
\n
\n P at (8, 1.2) ✓\n
\n
\n
\n (b)\n
\n
\n light acts as a wave «and not a particle in this situation» ✓\n
\n
\n light at slits will diffract / create a diffraction pattern ✓\n
\n
\n light passing through slits will interfere / create an interference pattern «creating bright and dark spots» ✓\n
\n
\n
\n (c)\n
\n
\n Ue of\n \n s\n \n =\n \n =\n \n \n \n OR\n \n \n \n s\n \n =\n \n =\n \n ✓\n
\n
\n \n = «\n \n =» 4.6 × 10\n \n −7\n \n «m» ✓\n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "c-wave-behaviour"
+ ],
+ "subtopics": [
+ "c-1-simple-harmonic-motion",
+ "c-2-wave-model",
+ "c-3-wave-phenomena"
+ ]
+ },
+ {
+ "question_id": "23M.2.SL.TZ1.4",
+ "Question": "
\n
\n (a)\n
\n
\n
\n Show that the speed of the spacecraft is 0.80\n \n c\n \n as measured in S.\n
\n
\n
\n
\n
\n
\n (i)\n
\n
\n
\n Show that the current in Q is 0.45 A.\n
\n
\n
\n
\n
\n
\n (ii)\n
\n
\n
\n Calculate the resistance of R.\n
\n
\n
\n
\n
\n
\n (iii)\n
\n
\n
\n Calculate the total power dissipated in the circuit.\n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n
\n Resistor P is removed. State and explain, without any calculations, the effect of this on the resistance of Q.\n
\n
\n
\n
\n
\n
\n (i)\n
\n
\n
\n An event has coordinates\n \n = 0 and\n \n ct\n \n = 0.60 ly in S. Show, using a Lorentz transformation, that the time coordinate of this event in S′ is\n \n ct\n \n ′ = 1.00 ly .\n
\n
\n
\n
\n
\n
\n (ii)\n
\n
\n
\n Label, on the diagram with the letter P, the point on the\n \n ct\n \n ′ axis whose\n \n ct\n \n ′ coordinate is 1.00 ly.\n
\n
\n
\n
\n
\n
\n (i)\n
\n
\n
\n Draw lines to indicate R on the diagram.\n
\n
\n
\n
\n
\n
\n (ii)\n
\n
\n
\n Determine, using the diagram or otherwise, the space coordinate\n \n ′ of event R in S′.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n moves 4 ly in 5 years\n \n \n OR\n \n \n slope of angle with time axis is 0.8 ✓\n
\n
\n
\n
\n \n Allow evidence for mark on the graph.\n \n
\n
\n
\n (i)\n
\n
\n Voltage across P is 1.4 «V» ✓\n
\n
\n Voltage across Q is 4.6 «V» ✓\n
\n
\n And 6 – 1.4 = 4.6 «V» ✓\n
\n
\n
\n
\n \n Need to see a calculation involving the two voltages and the total voltage in the circuit for\n \n MP3\n \n (e.g. 1.4 + 4.6 = 6).\n \n
\n
\n
\n (ii)\n
\n
\n Current in R is «(0.45 − 0.4)=» 0.05 A ✓\n
\n
\n So resistance is «\n \n » = 28 «Ω»\n
\n
\n
\n
\n \n Allow\n \n ECF\n \n from\n \n a(i)\n \n \n
\n
\n \n Allow\n \n ECF\n \n from\n \n MP1\n \n \n
\n
\n
\n (iii)\n
\n
\n «0.45 × 6.0» = 2.7 «W»✓\n
\n
\n
\n (b)\n
\n
\n Q will have a smaller resistance ✓\n
\n
\n «Because total resistance in the circuit is now larger so» the current «through the\n
\n circuit/Q» is smaller /\n \n \n OWTTE\n \n \n ✓\n \n \n
\n \n \n
\n
\n \n Allow similar argument for\n \n MP2\n \n based on voltage across\n \n Q\n \n becoming smaller.\n \n
\n
\n
\n (i)\n
\n
\n \n γ\n \n = 1.67\n \n \n OR\n \n \n \n \n \n OR\n \n \n \n ✓\n
\n
\n \n ct\n \n ' = «\n \n γ\n \n (\n \n ct\n \n −\n \n )» =\n \n × (0.60 +0) ✓\n
\n
\n «= 1.00 ly»\n
\n
\n
\n
\n \n For\n \n MP2\n \n , working should be seen.\n \n
\n
\n
\n (ii)\n
\n
\n identifies point with coordinates\n \n = 0,\n \n ct\n \n = 0.60 on vertical axis ✓\n
\n
\n draws line parallel to the\n \n prime axis until it intersects the prime\n \n ct\n \n axis ✓\n
\n
\n
\n
\n
\n
\n
\n \n \n Award [2]\n \n for correct position of P without working shown.\n \n
\n
\n
\n (i)\n
\n
\n
\n
\n
\n R located at (4,4) ✓\n
\n
\n «as intersection of» vertical line through 4 ly and photon worldline at 45 degrees✓\n
\n
\n
\n
\n \n Allow\n \n MP2\n \n even if one of the lines is not drawn.\n \n
\n
\n
\n (ii)\n
\n
\n \n \n ALTERNATIVE 1\n \n \n
\n
\n \n Using diagram:\n \n
\n
\n line from R parallel to prime ct axis until it intersects space axis ✓\n
\n
\n use of scale from (b) to estimate coordinate to\n \n ' = (1.3 ± 0.2) ly ✓\n
\n
\n
\n
\n
\n
\n
\n \n \n ALTERNATIVE 2\n \n \n
\n
\n \n Using Lorentz transformation:\n \n
\n
\n event R has coordinates\n \n =\n \n ct\n \n = 4.00 ly in S ✓\n
\n
\n so\n \n ' = «\n \n (\n \n −\n \n vt\n \n ) =\n \n × (4.00 − 0.80 × 4.00)» = 1.33 ly ✓\n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "a--space-time-and-motion",
+ "b-the-particulate-nature-of-matter"
+ ],
+ "subtopics": [
+ "a-5-galilean-and-special-relativity",
+ "b-5-current-and-circuits"
+ ]
+ },
+ {
+ "question_id": "23M.2.SL.TZ1.5",
+ "Question": "
\n
\n (a)\n
\n
\n
\n According to laboratory observers\n \n .\n
\n
\n Calculate\n \n D\n \n .\n
\n
\n
\n
\n
\n
\n (i)\n
\n
\n
\n Show that the energy released is about 18 MeV.\n
\n
\n
\n
\n
\n
\n (ii)\n
\n
\n
\n determine the time taken for the detector to reach the muon source.\n
\n
\n
\n
\n
\n
\n (c)\n
\n
\n
\n Calculate, using the answers to (b)(i) and (b)(ii) the ratio\n \n in S.\n
\n
\n
\n
\n
\n
\n (i)\n
\n
\n
\n \n two\n \n difficulties of energy production by nuclear fusion.\n
\n
\n
\n
\n
\n
\n (ii)\n
\n
\n
\n \n one\n \n advantage of energy production by nuclear fusion compared to nuclear fission.\n
\n
\n
\n
\n
\n
\n (d)\n
\n
\n
\n Discuss the ratios in (a) and (c).\n
\n
\n
\n
\n
\n
\n (i)\n
\n
\n
\n State the nucleon number of the He isotope that\n \n decays into.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n \n = 2.00 × 1.56 × 10\n \n −6\n \n or 3.12 × 10\n \n −6\n \n s ✓\n
\n
\n \n D\n \n = «3.12 × 10\n \n −6\n \n × 0.866 × 3 × 10\n \n 8\n \n =» 811 m\n
\n
\n
\n
\n \n \n Award [2]\n \n for\n \n BCA\n \n \n
\n
\n
\n (i)\n
\n
\n «𝜇» = 2.0141 + 3.0160 − (4.0026 + 1.008665) «= 0.0188 u»\n
\n
\n \n \n OR\n \n \n
\n
\n \n In\n \n MeV: 1876.13415 + 2809.404 − (3728.4219 + 939.5714475) ✓\n
\n
\n
\n
\n = 0.0188 × 931.5\n \n \n OR\n \n \n = 17.512 «MeV» ✓\n
\n
\n
\n
\n \n Must see either clear substitutions or answer to at least 3 s.f. for\n \n MP2\n \n .\n \n
\n
\n
\n (ii)\n
\n
\n transit time =\n \n = 1.56\n \n µs\n \n ✓\n
\n
\n
\n
\n \n \n Award [1]\n \n for\n \n BCA\n \n .\n \n
\n
\n
\n (c)\n
\n
\n transit time is one half life ✓\n
\n
\n so ratio has to be\n \n ✓\n
\n
\n
\n
\n \n \n Award [2]\n \n for\n \n BCA\n \n .\n \n
\n
\n
\n (i)\n
\n
\n Requires high temp/pressure ✓\n
\n Must overcome Coulomb/intermolecular repulsion ✓\n
\n Difficult to contain / control «at high temp/pressure» ✓\n
\n Difficult to produce excess energy/often energy input greater than output /\n \n \n OWTTE\n \n \n ✓\n
\n Difficult to capture energy from fusion reactions ✓\n
\n Difficult to maintain/sustain a constant reaction rate ✓\n
\n
\n
\n (ii)\n
\n
\n Plentiful fuel supplies\n \n \n OR\n \n \n larger specific energy\n \n \n OR\n \n \n larger energy density\n \n \n OR\n \n \n little or no «major radioactive» waste products ✓\n
\n
\n
\n
\n \n Allow descriptions such as “more energy per unit mass” or “more energy per unit volume”\n \n
\n
\n
\n (d)\n
\n
\n the answers are the same ✓\n
\n
\n count rates cannot vary from frame to frame /\n \n \n OWTTE\n \n \n ✓\n
\n
\n
\n
\n \n Do\n \n not\n \n allow\n \n ECF\n \n from\n \n (c)\n \n .\n \n
\n
\n \n \n Award [2]\n \n for “count rates cannot vary” if student made a mistake\n \n OR\n \n no answer in\n \n (c)\n \n and well discussed here.\n \n
\n
\n
\n (i)\n
\n
\n 3 ✓\n
\n
\n
\n
\n \n Do\n \n not\n \n accept\n \n by itself.\n \n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "a--space-time-and-motion",
+ "e-nuclear-and-quantum-physics"
+ ],
+ "subtopics": [
+ "a-5-galilean-and-special-relativity",
+ "e-3-radioactive-decay",
+ "e-4-fission",
+ "e-5-fusion-and-stars"
+ ]
+ },
+ {
+ "question_id": "23M.2.SL.TZ1.6",
+ "Question": "
\n
\n (a)\n
\n
\n
\n The moment of inertia of the rod about the axis is 0.180 kg m\n \n 2\n \n . Show that the moment of inertia of the rod–particle system is about 0.25 kg m\n \n 2\n \n .\n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n
\n Show that the angular speed of the system immediately after the collision is about 5.7 rad s\n \n −1\n \n .\n
\n
\n
\n
\n
\n
\n (c)\n
\n
\n
\n Calculate the energy lost during the collision.\n
\n
\n
\n
\n
\n
\n (i)\n
\n
\n
\n the angular deceleration of the rod.\n
\n
\n
\n
\n
\n
\n (ii)\n
\n
\n
\n the number of revolutions made by the rod until it stops rotating.\n
\n
\n
\n
\n
\n
\n (e)\n
\n
\n
\n In another situation the rod rests on a horizontal frictionless surface with no pivot. Predict, without calculation, the motion of the rod–particle system after the collision.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n 0.180 + 0.200 × 0.60\n \n 2\n \n «= 0.252 kg m\n \n 2\n \n » ✓\n
\n
\n
\n (b)\n
\n
\n angular speed of particle = «12/0.6 = » 20 «rad s\n \n −1\n \n »\n
\n
\n \n \n OR\n \n \n
\n
\n angular momentum of particle «0.200 × 12.0 × 0.60» = 1.44 «Js» ✓\n
\n
\n
\n «angular momentum of rod-particle system 0.252\n \n ω\n \n »\n
\n
\n equating\n \n ω\n \n = «\n \n » = 5.71 rad s\n \n −1\n \n ✓\n
\n
\n
\n
\n \n For\n \n MP2\n \n , working or answer to at least 3 SF should be seen.\n \n
\n
\n
\n (c)\n
\n
\n \n × 0.200 × 12.0\n \n 2\n \n −\n \n (0.252) × 5.71\n \n 2\n \n ✓\n
\n
\n 10.3 J ✓\n
\n
\n
\n
\n \n \n Award [1]\n \n for answer 11.5\n \n J\n \n that neglects moment of inertia of particle but do not penalize this omission in\n \n (d)(i)\n \n .\n \n
\n
\n
\n (i)\n
\n
\n \n =\n \n = 0.603 rads\n \n −2\n \n ✓\n
\n
\n
\n
\n \n Accept negative values.\n \n
\n
\n
\n (ii)\n
\n
\n \n θ\n \n =\n \n = 27.0 rad ✓\n
\n
\n \n N\n \n =\n \n = 4.3 ✓\n
\n
\n
\n (e)\n
\n
\n the rod will rotate «about centre of mass» ✓\n
\n
\n «centre of mass» will move along straight line\n
\n «parallel to the particle’s initial velocity» ✓\n
\n
\n
\n
\n \n For\n \n MP2\n \n , mention of translational motion is not enough.\n \n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "a--space-time-and-motion"
+ ],
+ "subtopics": [
+ "a-3-work-energy-and-power",
+ "a-4-rigid-body-mechanics"
+ ]
+ },
+ {
+ "question_id": "23M.2.SL.TZ1.7",
+ "Question": "
\n
\n (a)\n
\n
\n
\n Suggest why AC is the adiabatic part of the cycle.\n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n
\n Show that the volume at C is 3.33 × 10\n \n −2\n \n m\n \n 3\n \n .\n
\n
\n
\n
\n
\n
\n (c)\n
\n
\n
\n Suggest, for the change A ⇒ B, whether the entropy of the gas is increasing, decreasing or constant.\n
\n
\n
\n
\n
\n
\n (d)\n
\n
\n
\n Calculate the thermal energy (heat) taken out of the gas from B to C.\n
\n
\n
\n
\n
\n
\n (e)\n
\n
\n
\n The highest and lowest temperatures of the gas during the cycle are 602 K and 92 K.\n
\n
\n The efficiency of this engine is about 0.6. Outline how these data are consistent with the second law of thermodynamics.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n \n \n ALTERNATIVE 1\n \n \n
\n
\n «considering expansions from A» an adiabatic process will reduce/change temperature ✓\n
\n
\n and so curve AC must be the steeper ✓\n
\n
\n
\n
\n \n \n ALTERNATIVE 2\n \n \n
\n
\n temperature drop occurs for BC ✓\n
\n
\n therefore CA must increase temperature «via adiabatic process». ✓\n
\n
\n
\n (b)\n
\n
\n \n \n ALTERNATIVE 1\n \n \n
\n
\n Use of adiabatic formula «\n \n »\n \n ✓\n
\n
\n \n × 2.00 × 10\n \n −3\n \n «= 3.333 × 10\n \n −2\n \n m\n \n 3\n \n » ✓\n
\n
\n
\n
\n \n For\n \n MP2\n \n , working or answer to at least 4 SF must be seen.\n \n
\n
\n
\n
\n \n \n ALTERNATIVE 2\n \n \n
\n
\n \n V\n \n \n C\n \n =\n \n V\n \n \n B\n \n \n \n AND\n \n \n \n p\n \n \n A\n \n \n V\n \n \n A\n \n =\n \n p\n \n \n B\n \n \n V\n \n \n B\n \n ✓\n
\n
\n \n ✓\n
\n
\n
\n
\n \n \n ALTERNATIVE 3\n \n \n
\n
\n \n V\n \n \n C\n \n =\n \n V\n \n \n B\n \n \n \n AND\n \n \n \n n\n \n = 0.2 mol ✓\n
\n
\n \n V\n \n \n C\n \n = (0.2 × 8.31 × 602) / 4 × 10\n \n 4\n \n ✓\n
\n
\n
\n (c)\n
\n
\n Increasing ✓\n
\n
\n because thermal energy/heat is being provided to the gas « and temperature is constant,\n \n ✓\n
\n
\n
\n (d)\n
\n
\n \n \n ALTERNATIVE 1\n \n \n
\n
\n \n ✓\n
\n
\n \n «\n \n × 3.33 × 10\n \n −2\n \n × (3.00 × 10\n \n 4\n \n − 4.60 × 10\n \n 3\n \n )» = 1268.7 ≈ 1270 «J» ✓\n
\n
\n
\n
\n \n \n Award [2]\n \n for\n \n BCA\n \n .\n \n
\n
\n \n Accept negative values.\n \n
\n
\n
\n
\n \n \n ALTERNATIVE 2\n \n \n
\n
\n \n \n \n OR\n \n \n \n T\n \n c\n \n \n = 4.6 × 10\n \n 3\n \n × 3.33 × 10\n \n −2\n \n × 1.66 = 92.2 ✓\n
\n
\n \n «J» ✓\n
\n
\n
\n
\n \n Award\n \n MP1\n \n if T\n \n c\n \n = 92 taken from\n \n (e)\n \n \n
\n
\n
\n (e)\n
\n
\n \n e\n \n \n c\n \n = 1 −\n \n = 0.847 ✓\n
\n
\n this engine has\n \n e\n \n <\n \n e\n \n \n c\n \n as it should ✓\n
\n
\n
\n
\n \n \n Award [0]\n \n if no calculation shown.\n \n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "b-the-particulate-nature-of-matter"
+ ],
+ "subtopics": [
+ "b-4-thermodynamics"
+ ]
+ },
+ {
+ "question_id": "23M.2.SL.TZ1.8",
+ "Question": "
\n
\n (a)\n
\n
\n
\n The moment of inertia of the rod about the axis is 0.180 kg m\n \n 2\n \n . Show that the moment of inertia of the rod–particle system is about 0.25 kg m\n \n 2\n \n .\n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n
\n Show that the angular speed of the system immediately after the collision is about 5.7 rad s\n \n −1\n \n .\n
\n
\n
\n
\n
\n
\n (c)\n
\n
\n
\n Calculate the energy lost during the collision.\n
\n
\n
\n
\n
\n
\n (i)\n
\n
\n
\n the angular deceleration of the rod.\n
\n
\n
\n
\n
\n
\n (ii)\n
\n
\n
\n the number of revolutions made by the rod until it stops rotating.\n
\n
\n
\n
\n
\n
\n (e)\n
\n
\n
\n In another situation the rod rests on a horizontal frictionless surface with no pivot. Predict, without calculation, the motion of the rod–particle system after the collision.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n 0.180 + 0.200 × 0.60\n \n 2\n \n «= 0.252 kg m\n \n 2\n \n » ✓\n
\n
\n
\n (b)\n
\n
\n angular speed of particle = «12/0.6 = » 20 «rad s\n \n −1\n \n »\n
\n
\n \n \n OR\n \n \n
\n
\n angular momentum of particle «0.200 × 12.0 × 0.60» = 1.44 «Js» ✓\n
\n
\n
\n «angular momentum of rod-particle system 0.252\n \n ω\n \n »\n
\n
\n equating\n \n ω\n \n = «\n \n » = 5.71 rad s\n \n −1\n \n ✓\n
\n
\n
\n
\n \n For\n \n MP2\n \n , working or answer to at least 3 SF should be seen.\n \n
\n
\n
\n (c)\n
\n
\n \n × 0.200 × 12.0\n \n 2\n \n −\n \n (0.252) × 5.71\n \n 2\n \n ✓\n
\n
\n 10.3 J ✓\n
\n
\n
\n
\n \n \n Award [1]\n \n for answer 11.5\n \n J\n \n that neglects moment of inertia of particle but do not penalize this omission in\n \n (d)(i)\n \n .\n \n
\n
\n
\n (i)\n
\n
\n \n =\n \n = 0.603 rads\n \n −2\n \n ✓\n
\n
\n
\n
\n \n Accept negative values.\n \n
\n
\n
\n (ii)\n
\n
\n \n θ\n \n =\n \n = 27.0 rad ✓\n
\n
\n \n N\n \n =\n \n = 4.3 ✓\n
\n
\n
\n (e)\n
\n
\n the rod will rotate «about centre of mass» ✓\n
\n
\n «centre of mass» will move along straight line\n
\n «parallel to the particle’s initial velocity» ✓\n
\n
\n
\n
\n \n For\n \n MP2\n \n , mention of translational motion is not enough.\n \n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "a--space-time-and-motion"
+ ],
+ "subtopics": [
+ "a-3-work-energy-and-power",
+ "a-4-rigid-body-mechanics"
+ ]
+ },
+ {
+ "question_id": "23M.2.SL.TZ1.9",
+ "Question": "
\n
\n (a)\n
\n
\n
\n Suggest why AC is the adiabatic part of the cycle.\n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n
\n Show that the volume at C is 3.33 × 10\n \n −2\n \n m\n \n 3\n \n .\n
\n
\n
\n
\n
\n
\n (c)\n
\n
\n
\n Suggest, for the change A ⇒ B, whether the entropy of the gas is increasing, decreasing or constant.\n
\n
\n
\n
\n
\n
\n (d)\n
\n
\n
\n Calculate the thermal energy (heat) taken out of the gas from B to C.\n
\n
\n
\n
\n
\n
\n (e)\n
\n
\n
\n The highest and lowest temperatures of the gas during the cycle are 602 K and 92 K.\n
\n
\n The efficiency of this engine is about 0.6. Outline how these data are consistent with the second law of thermodynamics.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n \n \n ALTERNATIVE 1\n \n \n
\n
\n «considering expansions from A» an adiabatic process will reduce/change temperature ✓\n
\n
\n and so curve AC must be the steeper ✓\n
\n
\n
\n
\n \n \n ALTERNATIVE 2\n \n \n
\n
\n temperature drop occurs for BC ✓\n
\n
\n therefore CA must increase temperature «via adiabatic process». ✓\n
\n
\n
\n (b)\n
\n
\n \n \n ALTERNATIVE 1\n \n \n
\n
\n Use of adiabatic formula «\n \n »\n \n ✓\n
\n
\n \n × 2.00 × 10\n \n −3\n \n «= 3.333 × 10\n \n −2\n \n m\n \n 3\n \n » ✓\n
\n
\n
\n
\n \n For\n \n MP2\n \n , working or answer to at least 4 SF must be seen.\n \n
\n
\n
\n
\n \n \n ALTERNATIVE 2\n \n \n
\n
\n \n V\n \n \n C\n \n =\n \n V\n \n \n B\n \n \n \n AND\n \n \n \n p\n \n \n A\n \n \n V\n \n \n A\n \n =\n \n p\n \n \n B\n \n \n V\n \n \n B\n \n ✓\n
\n
\n \n ✓\n
\n
\n
\n
\n \n \n ALTERNATIVE 3\n \n \n
\n
\n \n V\n \n \n C\n \n =\n \n V\n \n \n B\n \n \n \n AND\n \n \n \n n\n \n = 0.2 mol ✓\n
\n
\n \n V\n \n \n C\n \n = (0.2 × 8.31 × 602) / 4 × 10\n \n 4\n \n ✓\n
\n
\n
\n (c)\n
\n
\n Increasing ✓\n
\n
\n because thermal energy/heat is being provided to the gas « and temperature is constant,\n \n ✓\n
\n
\n
\n (d)\n
\n
\n \n \n ALTERNATIVE 1\n \n \n
\n
\n \n ✓\n
\n
\n \n «\n \n × 3.33 × 10\n \n −2\n \n × (3.00 × 10\n \n 4\n \n − 4.60 × 10\n \n 3\n \n )» = 1268.7 ≈ 1270 «J» ✓\n
\n
\n
\n
\n \n \n Award [2]\n \n for\n \n BCA\n \n .\n \n
\n
\n \n Accept negative values.\n \n
\n
\n
\n
\n \n \n ALTERNATIVE 2\n \n \n
\n
\n \n \n \n OR\n \n \n \n T\n \n c\n \n \n = 4.6 × 10\n \n 3\n \n × 3.33 × 10\n \n −2\n \n × 1.66 = 92.2 ✓\n
\n
\n \n «J» ✓\n
\n
\n
\n
\n \n Award\n \n MP1\n \n if T\n \n c\n \n = 92 taken from\n \n (e)\n \n \n
\n
\n
\n (e)\n
\n
\n \n e\n \n \n c\n \n = 1 −\n \n = 0.847 ✓\n
\n
\n this engine has\n \n e\n \n <\n \n e\n \n \n c\n \n as it should ✓\n
\n
\n
\n
\n \n \n Award [0]\n \n if no calculation shown.\n \n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "b-the-particulate-nature-of-matter"
+ ],
+ "subtopics": [
+ "b-4-thermodynamics"
+ ]
+ },
+ {
+ "question_id": "23M.2.SL.TZ2.1",
+ "Question": "
\n
\n (a)\n
\n
\n
\n Estimate, using the graph, the maximum height of the bottle.\n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n
\n Estimate the acceleration of the bottle when it is at its maximum height.\n
\n
\n
\n
\n
\n
\n (i)\n
\n
\n
\n Calculate the fraction of the kinetic energy of the bottle that remains after the bounce.\n
\n
\n
\n
\n
\n
\n (ii)\n
\n
\n
\n The mass of the bottle is 27 g and it is in contact with the ground for 85 ms.\n
\n
\n Determine the average force exerted by the ground on the bottle. Give your answer to an appropriate number of significant figures.\n
\n
\n
\n
\n
\n
\n (d)\n
\n
\n
\n The maximum height reached by the bottle is greater with an air–water mixture than with only high-pressure air in the bottle.\n
\n
\n Assume that the speed at which the propellant leaves the bottle is the same in both cases.\n
\n
\n Explain why the bottle reaches a greater maximum height with an air–water mixture.\n
\n
\n
\n
\n
\n
\n (i)\n
\n
\n
\n Calculate the absolute uncertainty in\n \n for Δ\n \n p\n \n = 30 kPa. State an appropriate number of significant figures for your answer.\n
\n
\n
\n
\n
\n
\n (ii)\n
\n
\n
\n Draw the absolute uncertainty determined in part (d)(i) as an error bar on the graph.\n
\n
\n
\n
\n
\n
\n (iii)\n
\n
\n
\n Explain why the new hypothesis is supported.\n
\n
\n
\n
\n
\n
\n (e)\n
\n
\n
\n The maximum height reached by the bottle is greater with an air–water mixture than with only high-pressure air in the bottle.\n
\n
\n Assume that the speed at which the propellant leaves the bottle is the same in both cases.\n
\n
\n Explain why the bottle reaches a greater maximum height with an air–water mixture.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n \n \n ALTERNATIVE 1\n \n \n
\n
\n Attempt to count squares ✓\n
\n
\n Area of one square found ✓\n
\n
\n 7.2 «m» (accept 6.4 – 7.4 m) ✓\n
\n
\n
\n
\n \n \n ALTERNATIVE 2\n \n \n
\n
\n Uses area equation for either triangle ✓\n
\n
\n Correct read offs for estimate of area of triangle ✓\n
\n
\n 7.2 «m» (accept 6.4 – 7.4) ✓\n
\n
\n
\n (b)\n
\n
\n Attempt to calculate gradient of line at\n \n t\n \n = 1.2 s ✓\n
\n
\n «−» 9.8 «m s\n \n −2\n \n » (accept 9.6 − 10.0) ✓\n
\n
\n
\n (i)\n
\n
\n Attempt to evaluate KE ratio as\n \n ✓\n
\n
\n «\n \n =» 0.20\n \n \n OR\n \n \n 20 %\n \n \n OR\n \n \n \n ✓\n
\n
\n
\n
\n \n Accept ± 0.5 velocity values from graph\n \n
\n
\n
\n (ii)\n
\n
\n Attempt to use force = momentum change ÷ time ✓\n
\n
\n «=\n \n = 4.6»\n
\n
\n Force = «4.6 + 0.3» 4.9 «N» ✓\n
\n
\n Any answer to 2sf ✓\n
\n
\n \n Accept ± 0.5 velocity values from graph\n \n
\n
\n
\n (d)\n
\n
\n Mass «leaving the bottle per second» will be larger for air–water ✓\n
\n
\n the momentum change/force is greater ✓\n
\n
\n \n Allow opposite argument for air only\n \n
\n
\n
\n (i)\n
\n
\n 15 % seen anywhere ✓\n
\n
\n «Δ(\n \n F\n \n \n 3\n \n ) =» 39.4 × 10\n \n 5\n \n × 0.15 = 5.9 × 10\n \n 5\n \n ✓\n
\n
\n ±6 × 10\n \n 5\n \n ✓\n
\n
\n \n \n
\n MP1\n \n is for the propagation of 5 %. It can be shown differently, e.g. 3 × 5% Allow students to use 40 × 10\n \n 5\n \n (from the graph).\n \n
\n
\n \n Award\n \n MP3\n \n for\n \n any\n \n uncertainty rounded to 1 significant digit\n \n
\n
\n \n \n Award [3]\n \n for a\n \n BCA\n \n .\n \n
\n
\n \n Allow\n \n ECF\n \n from\n \n MP1\n \n and\n \n MP2\n \n \n
\n
\n
\n (ii)\n
\n
\n error bar drawn at 30 kPa from 34 × 10\n \n 5\n \n to 46 × 10\n \n 5\n \n N\n \n 3\n \n ✓\n
\n
\n \n
\n Allow ± half square on each side of the bar or one square overall (± 2 × 10\n \n 5\n \n )\n \n
\n
\n \n Allow\n \n ECF\n \n from\n \n d(i)\n \n .\n \n
\n
\n
\n (iii)\n
\n
\n a «straight» line can be drawn that passes through origin ✓\n
\n
\n
\n (e)\n
\n
\n Mass «leaving the bottle per second» will be larger for air–water ✓\n
\n
\n the momentum change/force is greater ✓\n
\n
\n
\n
\n \n Allow opposite argument for air only\n \n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "a--space-time-and-motion",
+ "inquiry",
+ "tools"
+ ],
+ "subtopics": [
+ "a-1-kinematics",
+ "a-2-forces-and-momentum",
+ "a-3-work-energy-and-power",
+ "i-2-3-interpreting-results",
+ "inquiry-2-collecting-and-processing-data",
+ "tool-3-mathematics"
+ ]
+ },
+ {
+ "question_id": "23M.2.SL.TZ2.11",
+ "Question": "
\n
\n (i)\n
\n
\n
\n Determine which star will appear to move more.\n
\n
\n
\n
\n
\n
\n (ii)\n
\n
\n
\n Calculate, in m, the distance to star X.\n
\n
\n
\n
\n
\n
\n (iii)\n
\n
\n
\n Determine the ratio\n \n .\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (i)\n
\n
\n Star Y ✓\n
\n
\n because parallax angle is greater\n \n \n OR\n \n \n star Y is closer «and that means movement relative to distant stars is greater» ✓\n
\n
\n
\n
\n \n Allow reverse argument for star X\n \n
\n
\n
\n (ii)\n
\n
\n «distance =\n \n × 3.26 × 9.46 × 10\n \n 15\n \n »\n
\n
\n 1.6 × 10\n \n 18\n \n «m» ✓\n
\n
\n
\n (iii)\n
\n
\n \n =\n \n ✓\n
\n
\n = 10.8 ≈ 11 ✓\n
\n
\n
\n
\n \n Award\n \n MP1\n \n if ratio shown with distance or parallax angle.\n \n
\n
\n \n Award\n \n MP1\n \n for any correct substitution into ratio expression\n \n
\n
\n \n \n Award [2]\n \n for\n \n BCA\n \n \n
\n
\n \n Allow\n \n ECF\n \n for incorrect distances from\n \n b(i)\n \n or\n \n b(ii)\n \n .\n \n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "b-the-particulate-nature-of-matter",
+ "e-nuclear-and-quantum-physics"
+ ],
+ "subtopics": [
+ "b-1-thermal-energy-transfers",
+ "e-5-fusion-and-stars"
+ ]
+ },
+ {
+ "question_id": "23M.2.SL.TZ2.12",
+ "Question": "
\n
\n (a)\n
\n
\n
\n State the main element that is undergoing nuclear fusion in star C.\n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n
\n Explain why star B has a greater surface area than star A.\n
\n
\n
\n
\n
\n
\n (c)\n
\n
\n
\n White dwarfs with similar volumes to each other are shown on the HR diagram.\n
\n
\n Sketch, on the HR diagram, to show the possible positions of other white dwarf stars with similar volumes to those marked on the HR diagram.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n (b)\n
\n
\n stars have same/similar\n \n L\n \n \n \n AND\n \n \n star B has lower\n \n T\n \n ✓\n
\n
\n correct reference to luminosity formula (\n \n L\n \n α\n \n AT\n \n \n 4\n \n ) ✓\n
\n
\n
\n
\n \n \n MP1\n \n Allow reverse argument i.e., star A has higher T\n \n
\n
\n
\n (c)\n
\n
\n Any evidence of correct identification that three dots bottom left represent white dwarfs ✓\n
\n
\n line passing through all 3 white dwarfs\n \n \n OR\n \n \n line continuing from 3 white dwarfs with approximately same gradient, in either direction ✓\n
\n
\n
\n
\n \n Award\n \n MP2\n \n if no line drawn through the three dots but just beyond them in either direction\n \n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "b-the-particulate-nature-of-matter",
+ "e-nuclear-and-quantum-physics"
+ ],
+ "subtopics": [
+ "b-1-thermal-energy-transfers",
+ "e-5-fusion-and-stars"
+ ]
+ },
+ {
+ "question_id": "23M.2.SL.TZ2.17",
+ "Question": "
\n
\n (a)\n
\n
\n
\n State the main element that is undergoing nuclear fusion in star C.\n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n
\n Explain why star B has a greater surface area than star A.\n
\n
\n
\n
\n
\n
\n (c)\n
\n
\n
\n White dwarfs with similar volumes to each other are shown on the HR diagram.\n
\n
\n Sketch, on the HR diagram, to show the possible positions of other white dwarf stars with similar volumes to those marked on the HR diagram.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n (b)\n
\n
\n stars have same/similar\n \n L\n \n \n \n AND\n \n \n star B has lower\n \n T\n \n ✓\n
\n
\n correct reference to luminosity formula (\n \n L\n \n α\n \n AT\n \n \n 4\n \n ) ✓\n
\n
\n
\n
\n \n \n MP1\n \n Allow reverse argument i.e., star A has higher T\n \n
\n
\n
\n (c)\n
\n
\n Any evidence of correct identification that three dots bottom left represent white dwarfs ✓\n
\n
\n line passing through all 3 white dwarfs\n \n \n OR\n \n \n line continuing from 3 white dwarfs with approximately same gradient, in either direction ✓\n
\n
\n
\n
\n \n Award\n \n MP2\n \n if no line drawn through the three dots but just beyond them in either direction\n \n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "b-the-particulate-nature-of-matter",
+ "e-nuclear-and-quantum-physics"
+ ],
+ "subtopics": [
+ "b-1-thermal-energy-transfers",
+ "e-5-fusion-and-stars"
+ ]
+ },
+ {
+ "question_id": "23M.2.SL.TZ2.2",
+ "Question": "
\n
\n (a)\n
\n
\n
\n State the unit for\n \n pV\n \n in fundamental SI units.\n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n
\n Determine, using the graph, whether the gas acts as an ideal gas.\n
\n
\n
\n
\n
\n
\n (c)\n
\n
\n
\n Calculate, in g, the mass of the gas.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n kg m\n \n 2\n \n s\n \n −2\n \n ✓\n
\n
\n
\n (b)\n
\n
\n \n \n ALTERNATIVE 1\n \n \n
\n
\n Graph shown is a straight line/linear\n
\n \n \n OR\n \n \n
\n expected graph should be a straight line/linear ✓\n
\n
\n If ideal then\n \n T\n \n intercept must be at\n \n T\n \n = −273 °C ✓\n
\n
\n Use of\n \n y\n \n =\n \n mx\n \n +\n \n c\n \n to show that\n \n x\n \n = −273 °C when\n \n y\n \n = 0 ✓\n
\n (hence ideal)\n
\n
\n \n \n ALTERNATIVE 2\n \n \n
\n
\n Calculates\n \n for two different points ✓\n
\n Obtains 1.50 «J K\n \n −1\n \n » for both ✓\n
\n
\n States that for ideal gas\n \n which is constant and concludes that gas is ideal ✓\n
\n
\n
\n (c)\n
\n
\n Use of\n \n \n \n OR\n \n \n \n ✓\n
\n
\n Mass of gas =\n \n n\n \n ×\n \n N\n \n \n A\n \n × mass of molecule\n
\n \n \n OR\n \n \n
\n Mass of gas = N\n \n \n × mass of molecule ✓\n
\n
\n 5.1 «g» ✓\n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "b-the-particulate-nature-of-matter",
+ "tools"
+ ],
+ "subtopics": [
+ "b-3-gas-laws",
+ "tool-3-mathematics"
+ ]
+ },
+ {
+ "question_id": "23M.2.SL.TZ2.3",
+ "Question": "
\n
\n (a)\n
\n
\n
\n Explain the pattern seen on the screen.\n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n
\n Calculate, in nm,\n \n .\n
\n
\n
\n
\n
\n
\n (i)\n
\n
\n
\n Calculate, in nm,\n \n .\n
\n
\n
\n
\n
\n
\n (ii)\n
\n
\n
\n The student moves the screen closer to the double slit and repeats the measurements. The instruments used to make the measurements are unchanged.\n
\n
\n Discuss the effect this movement has on the fractional uncertainty in the value of\n \n .\n
\n
\n
\n
\n
\n
\n (c)\n
\n
\n
\n The student changes the light source to one that emits two colours:\n
\n • blue light of wavelength\n \n , and\n
\n • red light of wavelength 1.5\n \n .\n
\n
\n Predict the pattern that the student will see on the screen.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n Mention of interference / superposition ✓\n
\n
\n Bright fringe occurs when light from the slits arrives in phase ✓\n
\n
\n Dark fringe occurs when light from the slits arrives 180°/\n \n out of phase ✓\n
\n
\n
\n (b)\n
\n
\n \n s\n \n =\n \n \n \n OR\n \n \n = 0.0188 «m» ✓\n
\n
\n use of\n \n ✓\n
\n
\n 450 «nm» ✓\n
\n
\n
\n (i)\n
\n
\n \n s\n \n =\n \n \n \n OR\n \n \n = 0.0188 «m» ✓\n
\n
\n use of\n \n ✓\n
\n
\n 450 «nm» ✓\n
\n
\n
\n (ii)\n
\n
\n «As the measurements decrease» the fractional uncertainty in D/s increases. ✓\n
\n
\n «Fractional uncertainties are additive here» so fractional uncertainty in\n \n increases ✓\n
\n
\n \n Answers can be described in symbols e.g. Δs/s\n \n
\n
\n
\n (c)\n
\n
\n Blue fringe is unchanged ✓\n
\n
\n Red fringes are farther apart than blue ✓\n
\n
\n By a factor of 1.5 ✓\n
\n
\n At some point/s the fringes coincide/are purple ✓\n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "c-wave-behaviour",
+ "tools"
+ ],
+ "subtopics": [
+ "c-3-wave-phenomena",
+ "tool-3-mathematics"
+ ]
+ },
+ {
+ "question_id": "23M.2.SL.TZ2.4",
+ "Question": "
\n
\n (a)\n
\n
\n
\n The designers state that the energy transferred by the resistor every second is 15 J.\n
\n
\n Calculate the current in the resistor.\n
\n
\n
\n
\n
\n
\n (i)\n
\n
\n
\n The resistor has a cross-sectional area of 9.6 × 10\n \n −6\n \n m\n \n 2\n \n .\n
\n
\n Show that a resistor made from carbon fibre will be suitable for the pad.\n
\n
\n
\n
\n
\n
\n (ii)\n
\n
\n
\n The power supply to the pad has a negligible internal resistance.\n
\n
\n State and explain the variation in current in the resistor as the temperature of the pad increases.\n
\n
\n
\n
\n
\n
\n (i)\n
\n
\n
\n outline the magnetic force acting on it due to the current in PQ.\n
\n
\n
\n
\n
\n
\n (ii)\n
\n
\n
\n state and explain the net magnetic force acting on it due to the currents in PQ and TU.\n
\n
\n
\n
\n
\n
\n (d)\n
\n
\n
\n The design of the pad encloses the resistor in a material that traps air. The design also places the resistor close to the top surface of the pad.\n
\n
\n
\n
\n
\n Explain, with reference to thermal energy transfer, why the pad is designed in this way.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n \n I\n \n = «\n \n =» 1.9 «A» ✓\n
\n
\n
\n (i)\n
\n
\n \n \n ALTERNATIVE 1\n \n \n (Calculation of length)\n
\n Read off from graph [2.8 − 3.2 × 10\n \n −5\n \n Ω m]✓\n
\n Use of\n \n ✓\n
\n \n l\n \n = 1.3 − 1.4 «m» ✓\n
\n
\n \n \n ALTERNATIVE 2\n \n \n (Calculation of area)\n
\n Read off from graph [2.8 − 3.2 × 10\n \n −5\n \n Ω m]✓\n
\n Use of\n \n ✓\n
\n
\n \n A\n \n = 8.3 − 9.5 × 10\n \n −6\n \n «m\n \n 2\n \n » ✓\n
\n
\n \n \n ALTERNATIVE 3\n \n \n (Calculation of resistance)\n
\n Read off from graph [2.8 − 3.2 × 10\n \n −5\n \n Ω m]✓\n
\n Use of\n \n ✓\n
\n
\n \n R\n \n = 3.6 − 4.2 «Ω» ✓\n
\n
\n \n \n ALTERNATIVE 4\n \n \n (Calculation of resistivity)\n
\n Use of\n \n ✓\n
\n
\n \n \n \n = 3.2 × 10\n \n −5\n \n «Ω m» ✓\n
\n
\n Read off from graph 260 – 280 K ✓\n
\n
\n
\n (ii)\n
\n
\n «Resistivity and hence» resistance will decrease ✓\n
\n
\n «Pd across pad will not change because internal resistance is negligible»\n
\n Current will increase ✓\n
\n
\n
\n (i)\n
\n
\n «The force is» away from PQ/repulsive/to the right ✓\n
\n
\n
\n (ii)\n
\n
\n The magnetic fields «due to currents in PQ and TU» are in opposite directions\n
\n \n \n OR\n \n \n
\n There are two «repulsive» forces in opposite directions ✓\n
\n
\n Net force is zero ✓\n
\n
\n
\n (d)\n
\n
\n Air is a poor «thermal» conductor ✓\n
\n
\n Lack of convection due to air not being able to move in material ✓\n
\n
\n Appropriate statement about energy transfer between the pet, the resistor and surroundings ✓\n
\n
\n The rate of thermal energy transfer to the top surface is greater than the bottom «due to thinner material» ✓\n
\n
\n
\n
\n \n Accept air is a good insulator\n \n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "b-the-particulate-nature-of-matter",
+ "d-fields"
+ ],
+ "subtopics": [
+ "b-1-thermal-energy-transfers",
+ "b-5-current-and-circuits",
+ "d-3-motion-in-electromagnetic-fields"
+ ]
+ },
+ {
+ "question_id": "23M.2.SL.TZ2.5",
+ "Question": "
\n
\n (a)\n
\n
\n
\n Outline what is meant by an isotope.\n
\n
\n
\n
\n
\n
\n
\n (ii)\n
\n
\n
\n proton number.\n
\n
\n
\n
\n
\n
\n (e)\n
\n
\n
\n A beta-minus particle and an alpha particle have the same initial kinetic energy.\n
\n
\n Outline why the beta-minus particle can travel further in air than the alpha particle.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n «An atom with» the same number of protons\n \n \n AND\n \n \n different numbers of neutrons\n
\n \n \n OR\n \n \n
\n Same chemical properties\n \n \n AND\n \n \n different physical properties ✓\n
\n
\n \n Do\n \n not\n \n allow just atomic number and mass number\n \n
\n
\n
\n (i)\n
\n
\n (ii)\n
\n
\n (e)\n
\n
\n Alphas have double charge «and so are better ionisers »✓\n
\n
\n alphas have more mass and therefore slower «for same energy» ✓\n
\n
\n so longer time/more likely to interact with the «atomic» electrons/atoms «and therefore better ionisers» ✓\n
\n
\n \n Accept reverse argument in terms of betas travelling faster.\n \n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "e-nuclear-and-quantum-physics"
+ ],
+ "subtopics": [
+ "e-3-radioactive-decay"
+ ]
+ },
+ {
+ "question_id": "23M.2.SL.TZ2.6",
+ "Question": "
\n
\n (a)\n
\n
\n
\n Determine\n \n .\n
\n
\n
\n
\n
\n
\n (e)\n
\n
\n
\n Outline one reason why this model of a dancer is unrealistic.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n Work using\n \n g\n \n ∝\n \n ✓\n
\n
\n \n = 0.75 ✓\n
\n
\n
\n (e)\n
\n
\n one example specified\n \n eg\n \n friction, air resistance, mass distribution not modelled ✓\n
\n
\n
\n
\n \n \n Award [1]\n \n for any reasonable physical parameter that is not consistent with the model\n \n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "a--space-time-and-motion",
+ "d-fields"
+ ],
+ "subtopics": [
+ "a-4-rigid-body-mechanics",
+ "d-1-gravitational-fields"
+ ]
+ },
+ {
+ "question_id": "EXE.2.HL.TZ0.1",
+ "Question": "
\n
\n (a.i)\n
\n
\n
\n State the principal energy change in nuclear fission.\n
\n
\n
\n
\n
\n
\n (i)\n
\n
\n
\n State the principal energy change in nuclear fission.\n
\n
\n
\n
\n
\n
\n (ii)\n
\n
\n
\n The energy released in the reaction is about 180 MeV. Estimate, in J, the energy released when 1 kg of\n \n undergoes fission.\n
\n
\n
\n
\n
\n
\n (i)\n
\n
\n
\n State and explain the decay mode of\n \n .\n
\n
\n
\n
\n
\n
\n (ii)\n
\n
\n
\n Calculate, in s\n \n −1\n \n , the initial activity of the sample.\n
\n
\n
\n
\n
\n
\n (iii)\n
\n
\n
\n Show that the decay constant of a nuclide is given by −\n \n m\n \n , where\n \n m\n \n is the slope of the graph of ln\n \n A\n \n against\n \n t\n \n .\n
\n
\n
\n
\n
\n
\n (iv)\n
\n
\n
\n Determine, in days, the half-life of\n \n .\n
\n
\n
\n
\n
\n
\n (i)\n
\n
\n
\n Outline the role of the heat exchanger in a nuclear power station.\n
\n
\n
\n
\n
\n
\n (ii)\n
\n
\n
\n Calculate the maximum temperature of the gas during the cycle.\n
\n
\n
\n
\n
\n
\n (iii)\n
\n
\n
\n Outline why the entropy of the gas remains constant during changes BC and DA.\n
\n
\n
\n
\n
\n
\n (iv)\n
\n
\n
\n Determine the efficiency of the cycle.\n
\n
\n
\n
\n
\n
\n (d)\n
\n
\n
\n Show that the rotational kinetic energy of the turbine decreases at a constant rate.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a.i)\n
\n
\n Mass-energy «of uranium» into kinetic energy of fission products ✓\n
\n
\n
\n (i)\n
\n
\n Mass-energy «of uranium» into kinetic energy of fission products ✓\n
\n
\n
\n (ii)\n
\n
\n Mass of uranium nucleus\n \n ✓\n
\n
\n \n ✓\n
\n
\n \n «J» ✓\n
\n
\n
\n (i)\n
\n
\n beta minus decay ✓\n
\n
\n \n has more neutrons / higher\n \n ratio than stable nuclides of similar\n \n A\n \n «and beta minus reduces\n \n » ✓\n
\n
\n
\n (ii)\n
\n
\n \n «s\n \n −1\n \n » ✓\n
\n
\n
\n (iii)\n
\n
\n Takes ln of both sides of\n \n , leading to\n \n ✓\n
\n
\n «hence slope\n \n » ✓\n
\n
\n
\n (iv)\n
\n
\n Slope =«−»\n \n «s\n \n −1\n \n » ✓\n
\n
\n \n «\n \n » 3.2 «days» ✓\n
\n
\n
\n (i)\n
\n
\n Collects thermal energy from the coolant and delivers it to the gas ✓\n
\n
\n Prevents the «irradiated» coolant from leaving the reactor vessel ✓\n
\n
\n
\n (ii)\n
\n
\n Correct read offs of pressure and volume at B ✓\n
\n
\n \n ✓\n
\n
\n \n «K» ✓\n
\n
\n
\n (iii)\n
\n
\n From\n \n , the change in entropy is zero when\n \n ✓\n
\n
\n
\n (iv)\n
\n
\n Net work done = «\n \n » 9.77 «kJ» ✓\n
\n
\n Efficiency =«\n \n » 0.47 ✓\n
\n
\n
\n (d)\n
\n
\n Rotational KE is proportional to\n \n ✓\n
\n
\n Calculation of\n \n for at least four points, e.g. {96.1, 76.7, 57.6, 38.4, 19.3}×10\n \n 3\n \n
\n
\n Shows that the differences in equal time intervals are approximately the same, e.g. {19.4, 19.1, 19.2, 19.1, 19.3}×10\n \n 3\n \n ✓\n
\n
\n
\n
\n \n Allow a tolerance of ±1×10\n \n 3\n \n s\n \n −2\n \n from the values stated in MP2.\n \n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "a--space-time-and-motion",
+ "b-the-particulate-nature-of-matter",
+ "e-nuclear-and-quantum-physics"
+ ],
+ "subtopics": [
+ "a-4-rigid-body-mechanics",
+ "b-3-gas-laws",
+ "b-4-thermodynamics",
+ "e-3-radioactive-decay",
+ "e-4-fission"
+ ]
+ },
+ {
+ "question_id": "EXE.2.HL.TZ0.10",
+ "Question": "
\n
\n (a)\n
\n
\n
\n Calculate the angular impulse applied to the flywheel.\n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n
\n The angular speed of the flywheel increased by 280 rad s\n \n −1\n \n during the application of the angular impulse.\n
\n
\n Determine the moment of inertia of the flywheel.\n
\n
\n
\n
\n
\n
\n (c)\n
\n
\n
\n The flywheel was rotating at 150 rev per minute before the application of the angular impulse. Determine the change in angular rotational energy of the flywheel during the application of the flywheel.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n Attempt to find area of triangle ✓\n
\n
\n \n «kg m\n \n 2\n \n s\n \n −1\n \n » ✓\n
\n
\n
\n (a)\n
\n
\n Attempt to find area of triangle ✓\n
\n
\n \n «kg m\n \n 2\n \n s\n \n −1\n \n » ✓\n
\n
\n
\n (b)\n
\n
\n Use of\n \n ✓\n
\n
\n 2.6 kg m\n \n 2\n \n ✓\n
\n
\n
\n (c)\n
\n
\n Correct conversions to a consistent set of\n \n units ✓\n
\n
\n \n or correct substitution seen ✓\n
\n
\n 113 kJ ✓\n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "a--space-time-and-motion"
+ ],
+ "subtopics": [
+ "a-4-rigid-body-mechanics"
+ ]
+ },
+ {
+ "question_id": "EXE.2.HL.TZ0.11",
+ "Question": "
\n
\n (a)\n
\n
\n
\n Explain why the gas in configuration B has a greater number of microstates than in A.\n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n
\n Deduce, with reference to entropy, that the expansion of the gas from the initial configuration A is irreversible.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n Configuration A has only one microstate ✓\n
\n
\n In configuration B, pairs of particles can be swapped between the halves ✓\n
\n
\n Every such change gives rise to a new microstate «so there is a large number of microstates in B» ✓\n
\n
\n
\n (a)\n
\n
\n Configuration A has only one microstate ✓\n
\n
\n In configuration B, pairs of particles can be swapped between the halves ✓\n
\n
\n Every such change gives rise to a new microstate «so there is a large number of microstates in B» ✓\n
\n
\n
\n (b)\n
\n
\n The entropy of the gas is related to the number of microstates\n
\n
\n \n OR\n \n
\n
\n \n and\n \n ✓\n
\n
\n
\n Since\n \n , the entropy in configuration B is greater ✓\n
\n
\n A process that results in an increase of entropy in an isolated system is irreversible ✓\n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "b-the-particulate-nature-of-matter"
+ ],
+ "subtopics": [
+ "b-4-thermodynamics"
+ ]
+ },
+ {
+ "question_id": "EXE.2.HL.TZ0.12",
+ "Question": "
\n
\n (a)\n
\n
\n
\n State what is meant by an isolated system.\n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n
\n State and explain the number of microstates of the system in configuration A.\n
\n
\n
\n
\n
\n
\n (c)\n
\n
\n
\n Configuration B has 120 microstates. Calculate the entropy difference between configurations B and A. State the answer in terms of\n \n .\n
\n
\n
\n
\n
\n
\n (d)\n
\n
\n
\n The system is initially in configuration A. Comment, with reference to the second law of thermodynamics and your answer in (c), on the likely evolution of the system.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n Neither mass nor energy is exchanged with the surroundings ✓\n
\n
\n
\n (a)\n
\n
\n Neither mass nor energy is exchanged with the surroundings ✓\n
\n
\n
\n (b)\n
\n
\n 6 microstates ✓\n
\n
\n Any of the six particles can be the one of the highest energy ✓\n
\n
\n
\n (c)\n
\n
\n \n ✓\n
\n
\n \n ✓\n
\n
\n
\n (d)\n
\n
\n The second law predicts that isolated systems spontaneously evolve towards high-entropy states ✓\n
\n
\n From (c), the entropy of B is greater than that of A ✓\n
\n
\n The final state will likely be similar to B / contain relatively many low-energy particles «of different energies» ✓\n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "b-the-particulate-nature-of-matter"
+ ],
+ "subtopics": [
+ "b-4-thermodynamics"
+ ]
+ },
+ {
+ "question_id": "EXE.2.HL.TZ0.14",
+ "Question": "
\n
\n (a)\n
\n
\n
\n Determine the fractional number of throws for which the three most likely macrostates occur.\n
\n
\n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n
\n A throw is made once every minute. Estimate the average time required before a throw occurs where all coins are heads or all coins are tails.\n
\n
\n
\n
\n
\n
\n (c)\n
\n
\n
\n In one throw the coins all land heads upwards. The following throw results in 7 heads and 3 tails. Calculate, in terms of\n \n , the change in entropy between the two throws.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n Recognises that 4 heads and 6 tails also required ✓\n
\n
\n Total number of microstates = 672 ✓\n
\n
\n Fractional number = 672/1024 = 0.66 ✓\n
\n
\n
\n
\n \n Allow ecf for MP3\n \n
\n
\n
\n (a)\n
\n
\n Recognises that 4 heads and 6 tails also required ✓\n
\n
\n Total number of microstates = 672 ✓\n
\n
\n Fractional number = 672/1024 = 0.66 ✓\n
\n
\n
\n
\n \n Allow ecf for MP3\n \n
\n
\n
\n (b)\n
\n
\n Two chances in 1024 so once every 512 throws ✓\n
\n
\n 512 throws take 8.5 h so (a reasonable estimate is half way through) on average 4.3 h ✓\n
\n
\n
\n (c)\n
\n
\n \n ✓\n
\n
\n \n ✓\n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "b-the-particulate-nature-of-matter"
+ ],
+ "subtopics": [
+ "b-4-thermodynamics"
+ ]
+ },
+ {
+ "question_id": "EXE.2.HL.TZ0.15",
+ "Question": "
\n
\n (i)\n
\n
\n
\n orbital speed;\n
\n
\n
\n
\n
\n
\n (ii)\n
\n
\n
\n escape speed from its orbit.\n
\n
\n
\n
\n
\n
\n (i)\n
\n
\n
\n in its initial circular orbit;\n
\n
\n
\n
\n
\n
\n (ii)\n
\n
\n
\n in its final orbit.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (i)\n
\n
\n «\n \n »\n \n «m s\n \n −1\n \n » ✓\n
\n
\n
\n (ii)\n
\n
\n «\n \n = »\n \n ✓\n
\n
\n
\n (i)\n
\n
\n (ii)\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "d-fields"
+ ],
+ "subtopics": [
+ "d-1-gravitational-fields"
+ ]
+ },
+ {
+ "question_id": "EXE.2.HL.TZ0.16",
+ "Question": "
\n
\n (a)\n
\n
\n
\n The radius of the dwarf planet Pluto is 1.19 x 10\n \n 6\n \n m. The acceleration due to gravity at its surface is 0.617 m s\n \n −2\n \n .\n
\n
\n Determine the escape speed for an object at the surface of Pluto.\n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n
\n Pluto rotates about an axis through its centre. Its rotation is in the opposite sense to that of the Earth, i.e. from east to west.\n
\n
\n Explain the advantage of an object launching from the equator of Pluto and travelling to the west.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n \n AND\n \n seen ✓\n
\n
\n \n ✓\n
\n
\n Leading to\n \n ✓\n
\n
\n 1.2 km s\n \n −1\n \n ✓\n \n \n
\n
\n
\n (a)\n
\n
\n \n AND\n \n seen ✓\n
\n
\n \n ✓\n
\n
\n Leading to\n \n ✓\n
\n
\n 1.2 km s\n \n −1\n \n ✓\n \n \n
\n
\n
\n (b)\n
\n
\n Object at equator has the maximum linear/tangential speed possible ✓\n
\n
\n It therefore has maximum kinetic energy before takeoff (and this is not required from the fuel) ✓\n
\n
\n Idea that the object is already moving in direction of planet before takeoff ✓\n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "d-fields"
+ ],
+ "subtopics": [
+ "d-1-gravitational-fields"
+ ]
+ },
+ {
+ "question_id": "EXE.2.HL.TZ0.17",
+ "Question": "
\n
\n (a)\n
\n
\n
\n Show that the energy of the scattered photon is about 16 keV.\n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n
\n Determine the wavelength of the incident photon.\n
\n
\n
\n
\n
\n
\n (c)\n
\n
\n
\n Outline why the results of the experiment are inconsistent with the wave model of electromagnetic radiation.\n
\n
\n
\n
\n
\n
\n (d)\n
\n
\n
\n Calculate the scattering angle of the photon.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n \n «= 15.9 keV» ✓\n
\n
\n
\n (a)\n
\n
\n \n «= 15.9 keV» ✓\n
\n
\n
\n (b)\n
\n
\n Energy of incident photon =«\n \n »\n \n «eV» ✓\n
\n
\n Wavelength of incident photon =«\n \n »\n \n «m» ✓\n
\n
\n
\n (c)\n
\n
\n The wavelength of the X-rays changes ✓\n
\n
\n According to the wave model, the wavelength of the incident and scattered X-rays should be the same ✓\n
\n
\n
\n (d)\n
\n
\n \n ✓\n
\n
\n \n ✓\n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "e-nuclear-and-quantum-physics"
+ ],
+ "subtopics": [
+ "e-2-quantum-physics"
+ ]
+ },
+ {
+ "question_id": "EXE.2.HL.TZ0.18",
+ "Question": "
\n
\n (a)\n
\n
\n
\n Outline why the pattern observed on the screen is an evidence for matter waves.\n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n
\n A typical interatomic distance in the graphite crystal is of the order of\n \n m. Estimate the minimum value of\n \n U\n \n for the pattern in (a) to be formed on the screen.\n
\n
\n
\n
\n
\n
\n (c)\n
\n
\n
\n Protons can also be accelerated by the same potential difference\n \n U\n \n . Compare, without calculation, the de Broglie wavelength of the protons to that of the electrons.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n The pattern is formed when the electrons scattered from adjacent planes in the graphite crystal undergo interference / diffract ✓\n
\n
\n Interference / diffraction is a property of waves only ✓\n
\n
\n
\n (a)\n
\n
\n The pattern is formed when the electrons scattered from adjacent planes in the graphite crystal undergo interference / diffract ✓\n
\n
\n Interference / diffraction is a property of waves only ✓\n
\n
\n
\n (b)\n
\n
\n The de Broglie wavelength of the electrons should be comparable to or shorter than the interatomic distance /\n \n m ✓\n
\n
\n Momentum of electrons\n \n «\n \n N s» ✓\n
\n
\n Kinetic energy of electrons = «\n \n »\n \n «J» ✓\n
\n
\n \n U\n \n = «\n \n »40 «V» ✓\n
\n
\n
\n (c)\n
\n
\n The protons have the same energy but greater mass hence a greater momentum than the electrons ✓\n
\n
\n From\n \n , the protons will have a shorter wavelength ✓\n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "e-nuclear-and-quantum-physics"
+ ],
+ "subtopics": [
+ "e-2-quantum-physics"
+ ]
+ },
+ {
+ "question_id": "EXE.2.HL.TZ0.19",
+ "Question": "
\n
\n (a)\n
\n
\n
\n State the de Broglie hypothesis.\n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n
\n Calculate the maximum speed of the electrons in the beam.\n
\n
\n
\n
\n
\n
\n (c)\n
\n
\n
\n After passing through the circular hole the electrons strike a fluorescent screen.\n
\n
\n Predict whether an apparatus such as this can demonstrate that moving electrons have wave properties.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n a moving particle has wave properties ✓\n
\n
\n de Broglie wavelength = Planck constant÷momentum (must define p if quoted as equation) ✓\n
\n
\n
\n (a)\n
\n
\n a moving particle has wave properties ✓\n
\n
\n de Broglie wavelength = Planck constant÷momentum (must define p if quoted as equation) ✓\n
\n
\n
\n (b)\n
\n
\n use of ½\n \n mv\n \n \n 2\n \n =\n \n eV ✓\n \n
\n
\n 1.33 × 10\n \n 7\n \n m s\n \n −1\n \n ✓\n
\n
\n
\n (c)\n
\n
\n idea that de Broglie wavelength and hole size must be similar ✓\n
\n
\n Use of\n \n ✓\n
\n
\n Leading to\n \n around 5 x 10\n \n −11\n \n m (which is unrealistic for a practical situation) ✓\n
\n
\n It would not be possible to construct this hole\n
\n \n OR\n \n
\n hole must be smaller than an atom so impossible ✓\n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "e-nuclear-and-quantum-physics"
+ ],
+ "subtopics": [
+ "e-2-quantum-physics"
+ ]
+ },
+ {
+ "question_id": "EXE.2.HL.TZ0.2",
+ "Question": "
\n
\n (a.i)\n
\n
\n
\n State the movement direction for which the geophone has its greatest sensitivity.\n
\n
\n
\n
\n
\n
\n (i)\n
\n
\n
\n State the movement direction for which the geophone has its greatest sensitivity.\n
\n
\n
\n
\n
\n
\n (ii)\n
\n
\n
\n Outline how an emf is generated in the coil.\n
\n
\n
\n
\n
\n
\n (iii)\n
\n
\n
\n Explain why the magnitude of the emf is related to the amplitude of the ground movement.\n
\n
\n
\n
\n
\n
\n (iv)\n
\n
\n
\n In one particular event, a maximum emf of 65 mV is generated in the geophone. The geophone coil has 150 turns.\n
\n
\n Calculate the rate of flux change that leads to this emf.\n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n
\n Suggest\n \n two\n \n changes to the system that will make the geophone more sensitive.\n
\n
\n
\n
\n
\n
\n (i)\n
\n
\n
\n Show that, when sound travels from clay to sandstone, the critical angle is approximately 40°.\n
\n
\n
\n
\n
\n
\n (ii)\n
\n
\n
\n The angle between the clay–air surface and\n \n path 1\n \n is 80°.\n
\n
\n Draw, on the diagram, the subsequent path of a sound wave that travels initially in the clay along\n \n path 1\n \n .\n
\n
\n
\n
\n
\n
\n (d)\n
\n
\n
\n Calculate\n \n d\n \n .\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a.i)\n
\n
\n Vertical direction / parallel to springs ✓\n
\n
\n
\n (i)\n
\n
\n Vertical direction / parallel to springs ✓\n
\n
\n
\n (ii)\n
\n
\n The magnetic field moves relative to the coil ✓\n
\n
\n As field lines cut the coil, forces act on (initially stationary) electrons in the wire (and these move producing an emf) ✓\n
\n
\n
\n (iii)\n
\n
\n The springs have a natural time period for the oscillation ✓\n
\n
\n A greater amplitude of movement leads to higher magnet speed (with constant time period) ✓\n
\n
\n So field lines cut coil more quickly leading to greater emf ✓\n
\n
\n
\n (iv)\n
\n
\n Use of\n \n ✓\n
\n
\n \n
\n
\n \n mWb s\n \n −1\n \n ✓\n
\n
\n
\n (b)\n
\n
\n Any two suggestions from:\n
\n
\n Increase number of turns in coil ✓\n
\n Because more flux cutting per cycle ✓\n
\n
\n Increase field strength of magnet ✓\n
\n So that there are more field lines ✓\n
\n
\n Change mass-spring system so that time period decreases ✓\n
\n So magnet will be moving faster for given amplitude of movement ✓\n
\n
\n
\n (i)\n
\n
\n \n \n c\n \n n\n \n s\n \n \n \n ✓\n
\n
\n Critical angle\n \n ✓\n
\n
\n
\n (ii)\n
\n
\n ray shown reflected back into the clay (and then to Z) at (by eye) the incidence angle ✓\n
\n
\n ray shown refracted into the sandstone with angle of refraction greater than angle of incidence (by eye) ✓\n
\n
\n
\n (d)\n
\n
\n distance difference\n \n m ✓\n
\n
\n ½ distance difference\n \n m so YZ\n \n m ✓\n
\n
\n \n ✓\n
\n
\n
\n 29.8 m ✓\n
\n
\n \n OR\n \n
\n
\n Recognises situation as (almost) 3:4:5 triangle ✓\n
\n
\n
\n 30 m (\n \n 1 sf answer only accepted in this route\n \n ) ✓\n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "a--space-time-and-motion",
+ "c-wave-behaviour",
+ "d-fields"
+ ],
+ "subtopics": [
+ "a-1-kinematics",
+ "c-1-simple-harmonic-motion",
+ "c-3-wave-phenomena",
+ "d-4-induction"
+ ]
+ },
+ {
+ "question_id": "EXE.2.HL.TZ0.20",
+ "Question": "
\n
\n (a)\n
\n
\n
\n The quantity\n \n is known as the Compton wavelength.\n
\n
\n Show that the Compton wavelength is about 2.4 pm.\n
\n
\n
\n
\n
\n
\n (i)\n
\n
\n
\n State the wavelength of the photon after the interaction.\n
\n
\n
\n
\n
\n
\n (ii)\n
\n
\n
\n Outline why the wavelength of the photon has changed.\n
\n
\n
\n
\n
\n
\n (iii)\n
\n
\n
\n Deduce the scattering angle for the photon.\n
\n
\n
\n
\n
\n
\n (iv)\n
\n
\n
\n Determine, in J, the kinetic energy of the electron after the interaction.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n (a)\n
\n
\n (i)\n
\n
\n (ii)\n
\n
\n (Energy of photon inversely prop to wavelength)\n
\n
\n
\n
\n photon transfers some of its energy to the electron. ✓\n
\n
\n If its energy decreases so its wavelength increases. ✓\n
\n
\n
\n (iii)\n
\n
\n (for this interaction)\n
\n
\n \n and therefore\n \n must equal 1 ✓\n
\n
\n so cos theta = 0 and theta = 90 deg ✓\n
\n
\n
\n (iv)\n
\n
\n (Because energy is conserved)\n
\n
\n
\n \n
\n
\n \n ✓\n
\n
\n 9.6 fJ ✓\n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "e-nuclear-and-quantum-physics"
+ ],
+ "subtopics": [
+ "e-2-quantum-physics"
+ ]
+ },
+ {
+ "question_id": "EXE.2.HL.TZ0.21",
+ "Question": "
\n
\n (a)\n
\n
\n
\n Suggest one problem that is faced in dealing with the waste from nuclear fission reactors. Go on to outline how this problem is overcome.\n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n
\n Strontium-90 is a waste product from nuclear reactors that has a decay constant of 7.63 x 10\n \n −10\n \n s\n \n −1\n \n . Determine, in s, the time that it takes for the activity of strontium-90 to decay to 2% of its original activity.\n
\n
\n
\n
\n
\n
\n (i)\n
\n
\n
\n Calculate the energy released when one mole of strontium-90 decays to 2% of its original activity forming the stable daughter product.\n
\n
\n
\n
\n
\n
\n (ii)\n
\n
\n
\n Strontium-90 decays to Zirconium-90 via two successive beta emissions. Discuss whether all the energy released when strontium-90 decays to Zirconium-90 can be transferred to a thermal form.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n Waste is very hot …\n
\n
\n … So has to be placed in cooling ponds to transfer the (thermal) energy away ✓\n
\n
\n
\n
\n \n OR\n \n
\n
\n Waste is very radioactive … ✓\n
\n
\n … So has to be placed in cooling ponds to absorb this radiation\n
\n
\n \n OR\n \n
\n
\n … So has to be handled remotely\n
\n
\n \n OR\n \n
\n
\n … So has to be transported in crash resistant casings / stored on site ✓\n
\n
\n
\n
\n \n OR\n \n
\n
\n Waste will be radioactive for thousands of years … ✓\n
\n
\n … So storage needs to be (eventually) in geologically stable areas ✓\n
\n
\n
\n (a)\n
\n
\n Waste is very hot …\n
\n
\n … So has to be placed in cooling ponds to transfer the (thermal) energy away ✓\n
\n
\n
\n
\n \n OR\n \n
\n
\n Waste is very radioactive … ✓\n
\n
\n … So has to be placed in cooling ponds to absorb this radiation\n
\n
\n \n OR\n \n
\n
\n … So has to be handled remotely\n
\n
\n \n OR\n \n
\n
\n … So has to be transported in crash resistant casings / stored on site ✓\n
\n
\n
\n
\n \n OR\n \n
\n
\n Waste will be radioactive for thousands of years … ✓\n
\n
\n … So storage needs to be (eventually) in geologically stable areas ✓\n
\n
\n
\n (b)\n
\n
\n \n or equivalent seen ✓\n
\n
\n \n Gs ✓\n
\n
\n
\n (i)\n
\n
\n Idea that the Yttrium half life is much less than Strontium so can assume all Yttrium energy is included. ✓\n
\n
\n \n seen ✓\n
\n
\n \n
\n
\n Answer\n \n GJ ✓\n
\n
\n
\n (ii)\n
\n
\n (No)\n
\n (anti-)neutrinos are released in (both) decays ✓\n
\n
\n Carrying away energy because they interact poorly with matter ✓\n
\n
\n
\n
\n \n Ignore arguments relating to energy transferred to nucleus as this appears eventually as thermal energy.\n \n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "e-nuclear-and-quantum-physics"
+ ],
+ "subtopics": [
+ "e-4-fission"
+ ]
+ },
+ {
+ "question_id": "EXE.2.HL.TZ0.3",
+ "Question": "
\n
\n (a.i)\n
\n
\n
\n State the vertical component of the total momentum of the balls after the collision.\n
\n
\n
\n
\n
\n
\n (i)\n
\n
\n
\n State the vertical component of the total momentum of the balls after the collision.\n
\n
\n
\n
\n
\n
\n (ii)\n
\n
\n
\n Hence, calculate the vertical component of the velocity of ball B after the collision.\n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n
\n Determine the angle\n \n θ\n \n that the velocity of ball B makes with the initial direction of motion of ball A.\n
\n
\n
\n
\n
\n
\n (c)\n
\n
\n
\n Predict whether the collision is elastic.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a.i)\n
\n
\n (i)\n
\n
\n (ii)\n
\n
\n \n ✓\n
\n
\n \n = «−»0.71 «m s\n \n −1\n \n » ✓\n
\n
\n
\n (b)\n
\n
\n The use of conservation of momentum in the horizontal direction, e.g.\n \n ✓\n
\n
\n \n «\n \n »\n \n «m s\n \n −1\n \n » ✓\n
\n
\n \n ✓\n
\n
\n
\n (c)\n
\n
\n Initial kinetic energy\n \n
\n
\n Final kinetic energy\n \n ✓\n
\n
\n \n ✓\n
\n
\n Final energy is less than the initial energy hence inelastic ✓\n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "a--space-time-and-motion"
+ ],
+ "subtopics": [
+ "a-2-forces-and-momentum"
+ ]
+ },
+ {
+ "question_id": "EXE.2.HL.TZ0.4",
+ "Question": "
\n
\n (a.i)\n
\n
\n
\n State what is meant by an elastic collision.\n
\n
\n
\n
\n
\n
\n (i)\n
\n
\n
\n State what is meant by an elastic collision.\n
\n
\n
\n
\n
\n
\n (ii)\n
\n
\n
\n No unbalanced external forces act on the system of the curling stones. Outline why the momentum of the system does not change during the collision.\n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n
\n Show that\n \n .\n
\n
\n
\n
\n
\n
\n (c)\n
\n
\n
\n Determine\n \n v\n \n \n A\n \n . State the answer in terms of\n \n v\n \n .\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a.i)\n
\n
\n No change in the kinetic energy of the system ✓\n
\n
\n
\n (i)\n
\n
\n No change in the kinetic energy of the system ✓\n
\n
\n
\n (ii)\n
\n
\n From\n \n , zero net force on the system implies that\n \n
\n
\n \n OR\n \n
\n
\n From Newton’s third law, the impulse delivered to A is equal but opposite to the impulse delivered to B, hence\n \n for the system ✓\n
\n
\n
\n (b)\n
\n
\n The vertical momentum is zero hence\n \n ✓\n
\n
\n «leading to the expected result» ✓\n
\n
\n
\n (c)\n
\n
\n Energy is conserved hence\n \n ✓\n
\n
\n Eliminate\n \n using the result of part (a), e.g.,\n \n ✓\n
\n
\n \n ✓\n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "a--space-time-and-motion"
+ ],
+ "subtopics": [
+ "a-2-forces-and-momentum"
+ ]
+ },
+ {
+ "question_id": "EXE.2.HL.TZ0.5",
+ "Question": "
\n
\n (a.i)\n
\n
\n
\n Calculate the component of momentum of the first curling stone perpendicular to the initial direction.\n
\n
\n
\n
\n
\n
\n (i)\n
\n
\n
\n Calculate the component of momentum of the first curling stone perpendicular to the initial direction.\n
\n
\n
\n
\n
\n
\n (ii)\n
\n
\n
\n Calculate the velocity component of the first curling stone in the initial direction.\n
\n
\n
\n
\n
\n
\n (iii)\n
\n
\n
\n Determine the velocity of the first curling stone.\n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n
\n Deduce whether this collision is elastic.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a.i)\n
\n
\n \n ✓\n
\n
\n
\n (i)\n
\n
\n \n ✓\n
\n
\n
\n (ii)\n
\n
\n \n ✓\n
\n
\n \n ✓\n
\n
\n
\n (iii)\n
\n
\n 2.04 m s\n \n −1\n \n ✓\n
\n
\n At 7.9° to initial direction ✓\n
\n
\n
\n (b)\n
\n
\n Total angle between stones is 38°, angle will be 90° when elastic\n
\n
\n \n OR\n \n
\n
\n Compares kinetic energies in a correct calculation (initial ke = 53 J, final ke = 34 J +2.4 J) ✓\n
\n
\n
\n Collision is not elastic ✓\n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "a--space-time-and-motion"
+ ],
+ "subtopics": [
+ "a-2-forces-and-momentum"
+ ]
+ },
+ {
+ "question_id": "EXE.2.HL.TZ0.6",
+ "Question": "
\n
\n (a)\n
\n
\n
\n Determine the recoil velocity of the cannon.\n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n
\n Calculate the initial kinetic energy of the cannon.\n
\n
\n
\n
\n
\n
\n (c)\n
\n
\n
\n Suggest what happens to the vertical component of momentum of the cannon when the shell is fired.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n Momentum must be conserved in initial direction of shell (20° above horizontal) ✓\n
\n
\n Recoil velocity is 4.2 m s\n \n −1\n \n at 20° below horizontal ✓\n
\n
\n 3.95 m s\n \n −1\n \n ✓\n
\n
\n
\n (a)\n
\n
\n Momentum must be conserved in initial direction of shell (20° above horizontal) ✓\n
\n
\n Recoil velocity is 4.2 m s\n \n −1\n \n at 20° below horizontal ✓\n
\n
\n 3.95 m s\n \n −1\n \n ✓\n
\n
\n
\n (b)\n
\n
\n \n ✓\n
\n
\n
\n (c)\n
\n
\n Must be transferred into the ground beneath the cannon\n \n OR\n \n into the suspension system ✓\n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "a--space-time-and-motion"
+ ],
+ "subtopics": [
+ "a-2-forces-and-momentum"
+ ]
+ },
+ {
+ "question_id": "EXE.2.HL.TZ0.7",
+ "Question": "
\n
\n (a)\n
\n
\n
\n Calculate the angular impulse delivered to the flywheel during the acceleration.\n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n
\n Determine the average magnitude of\n \n \n \n .\n
\n
\n
\n
\n
\n
\n (c)\n
\n
\n
\n State\n \n two\n \n assumptions of your calculation in part (b).\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n \n ✓\n
\n
\n \n «N m s» ✓\n
\n
\n
\n (a)\n
\n
\n \n ✓\n
\n
\n \n «N m s» ✓\n
\n
\n
\n (b)\n
\n
\n Average torque\n \n «N m» ✓\n
\n
\n Average force\n \n «N» ✓\n
\n
\n
\n (c)\n
\n
\n No other forces than\n \n F\n \n provide the torque ✓\n
\n
\n The thread unwinds without slipping ✓\n
\n
\n The thread is weightless ✓\n
\n
\n \n F\n \n is always tangent to the flywheel ✓\n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "a--space-time-and-motion"
+ ],
+ "subtopics": [
+ "a-4-rigid-body-mechanics"
+ ]
+ },
+ {
+ "question_id": "EXE.2.HL.TZ0.8",
+ "Question": "
\n
\n
\n (i)\n
\n
\n
\n the angular acceleration of the ring;\n
\n
\n
\n
\n
\n
\n (ii)\n
\n
\n
\n the angular velocity of the ring after a time of 5.0 s.\n
\n
\n
\n
\n
\n
\n (i)\n
\n
\n
\n the angular impulse delivered to the disc and to the ring during the first 5.0 s.\n
\n
\n
\n
\n
\n
\n (ii)\n
\n
\n
\n the final kinetic energy of the disc and the ring.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n \n ✓\n
\n
\n \n «rad s\n \n −2\n \n » ✓\n
\n
\n
\n (i)\n
\n
\n \n ✓\n
\n
\n \n «rad s\n \n −2\n \n » ✓\n
\n
\n
\n (ii)\n
\n
\n \n «rad s\n \n −1\n \n » ✓\n
\n
\n
\n (i)\n
\n
\n The angular impulse is the product of torque and time ✓\n
\n
\n Both factors are the same so the angular impulse is the same ✓\n
\n
\n
\n (ii)\n
\n
\n The disc has a smaller moment of inertia «because its mass is distributed closer to the axis of rotation» ✓\n
\n
\n From\n \n , the disc will achieve a greater kinetic energy «because\n \n \n \n is the same for both» ✓\n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "a--space-time-and-motion"
+ ],
+ "subtopics": [
+ "a-4-rigid-body-mechanics"
+ ]
+ },
+ {
+ "question_id": "EXE.2.HL.TZ0.9",
+ "Question": "
\n
\n (a)\n
\n
\n
\n For the propellor,\n \n and\n \n .\n
\n
\n Calculate the moment of inertia of the propellor.\n
\n
\n
\n
\n
\n
\n (i)\n
\n
\n
\n Calculate the angular impulse that acts on the propellor.\n
\n
\n
\n
\n
\n
\n (ii)\n
\n
\n
\n Calculate, using your answer to (b)(i), the time taken by the propellor to attain this rotational speed.\n
\n
\n
\n
\n
\n
\n (iii)\n
\n
\n
\n State and explain the effect of the angular impulse on the body of the aeroplane.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n \n ✓\n
\n
\n
\n (a)\n
\n
\n \n ✓\n
\n
\n
\n (i)\n
\n
\n 190 rev s\n \n −1\n \n = 1190 rad s\n \n −1\n \n ✓\n
\n
\n \n ✓\n
\n
\n
\n (ii)\n
\n
\n \n used ✓\n
\n
\n 0.25 s ✓\n
\n
\n
\n (iii)\n
\n
\n As the motor is internal, angular momentum is conserved (ignoring the torques due to resistive forces) ✓\n
\n
\n The body of the plane will (try to) rotate in the opposite direction to the propellor ✓\n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "a--space-time-and-motion"
+ ],
+ "subtopics": [
+ "a-4-rigid-body-mechanics"
+ ]
+ },
+ {
+ "question_id": "EXE.2.SL.TZ0.10",
+ "Question": "
\n
\n (a)\n
\n
\n
\n Calculate the pressure of the gas in the container.\n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n
\n Determine the mass of the gas in the container.\n
\n
\n
\n
\n
\n
\n (c)\n
\n
\n
\n Calculate the average translational speed of the gas particles.\n
\n
\n
\n
\n
\n
\n (d)\n
\n
\n
\n The temperature of the gas in the container is increased.\n
\n
\n Explain, using the kinetic theory, how this change leads to a change in pressure in the container.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n \n seen\n \n ✓\n
\n
\n
\n (a)\n
\n
\n \n seen\n \n ✓\n
\n
\n
\n (b)\n
\n
\n \n ✓\n
\n
\n
\n (c)\n
\n
\n \n ✓\n
\n
\n
\n (d)\n
\n
\n increased temperature means increased average KE and hence increased average translational speed ✓\n
\n
\n This increases the momentum transfer at the walls for each collision /\n \n mv\n \n is greater per collision ✓\n
\n
\n This increases the frequency of collisions at the walls / particles cover the distance between walls more quickly ✓\n
\n
\n Ideas that\n \n AND\n \n (can be in words) so that force increases and pressure\n \n increases\n \n ✓\n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "b-the-particulate-nature-of-matter"
+ ],
+ "subtopics": [
+ "b-3-gas-laws"
+ ]
+ },
+ {
+ "question_id": "EXE.2.SL.TZ0.11",
+ "Question": "
\n
\n (a)\n
\n
\n
\n A comet orbits the Sun in an elliptical orbit. A and B are two positions of the comet.\n
\n
\n
\n
\n
\n Explain, with reference to Kepler’s second law of planetary motion, the change in the kinetic energy of the comet as it moves from A to B.\n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n
\n An asteroid (minor planet) orbits the Sun in a circular orbit of radius 4.5 × 10\n \n 8\n \n km. The radius of Earth’s orbit is 1.5 × 10\n \n 8\n \n km. Calculate, in years, the orbital period of the asteroid.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n The areas swept out in unit time by the Sun-comet line are the same at A and B ✓\n
\n
\n At B, the distance is greater hence the orbital speed/distance moved in unit time is lower «so that the area remains the same» ✓\n
\n
\n A decrease in speed means that the kinetic energy also decreases ✓\n
\n
\n
\n (a)\n
\n
\n The areas swept out in unit time by the Sun-comet line are the same at A and B ✓\n
\n
\n At B, the distance is greater hence the orbital speed/distance moved in unit time is lower «so that the area remains the same» ✓\n
\n
\n A decrease in speed means that the kinetic energy also decreases ✓\n
\n
\n
\n (b)\n
\n
\n An attempt to use Kepler’s 3\n \n rd\n \n law, e.g.,\n \n ✓\n
\n
\n \n «\n \n » 5.2 «years» ✓\n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "d-fields"
+ ],
+ "subtopics": [
+ "d-1-gravitational-fields"
+ ]
+ },
+ {
+ "question_id": "EXE.2.SL.TZ0.12",
+ "Question": "
\n
\n (a)\n
\n
\n
\n Show that\n \n .\n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n
\n The table gives data relating to the two moons of Mars.\n
\n
\n
\n
\n \n \n \n Moon\n | \n \n \n T\n \n / hour\n | \n \n \n r\n \n / Mm\n | \n
\n \n \n Phobos\n | \n \n 7.66\n | \n \n 9.38\n | \n
\n \n \n Deimos\n | \n \n 30.4\n | \n \n -\n | \n
\n \n
\n
\n
\n
\n Determine\n \n r\n \n for Deimos.\n
\n
\n
\n
\n
\n
\n (c)\n
\n
\n
\n Determine the mass of Mars.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n Equates centripetal force (with Newton’s law of gravitation\n \n )\n
\n
\n \n \n OR\n \n \n
\n
\n \n ✓\n
\n
\n
\n Uses both equation correctly with clear re-arrangement ✓\n
\n
\n
\n (a)\n
\n
\n Equates centripetal force (with Newton’s law of gravitation\n \n )\n
\n
\n \n \n OR\n \n \n
\n
\n \n ✓\n
\n
\n
\n Uses both equation correctly with clear re-arrangement ✓\n
\n
\n
\n (b)\n
\n
\n \n seen or correct substitution ✓\n
\n
\n 23.5 Mm ✓\n
\n
\n
\n (c)\n
\n
\n Converts\n \n T\n \n to 27.6 ks\n \n and\n \n converts to m from Mm ✓\n
\n
\n \n «s\n \n 2\n \n m\n \n −3\n \n » ✓\n
\n
\n «\n \n »\n \n «kg» ✓\n
\n
\n
\n
\n \n MP1 can be implicit\n \n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "d-fields"
+ ],
+ "subtopics": [
+ "d-1-gravitational-fields"
+ ]
+ },
+ {
+ "question_id": "EXE.2.SL.TZ0.13",
+ "Question": "
\n
\n (a)\n
\n
\n
\n Show that\n \n for the planets in a solar system where\n \n \n \n is the orbital period of a planet and\n \n \n \n is the radius of circular orbit of planet about its sun.\n
\n
\n
\n
\n
\n
\n (i)\n
\n
\n
\n Outline what is meant by one astronomical unit (1 AU)\n
\n
\n
\n
\n
\n
\n (ii)\n
\n
\n
\n Pluto is a dwarf planet of the Sun that orbits at a distance of 5.9 × 10\n \n 9\n \n km from the Sun. Determine, in years, the orbital period of Pluto.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n Equates centripetal force (with Newton’s law gravitation\n \n )\n
\n
\n AND\n
\n
\n \n ✓\n
\n
\n leads to\n \n hence result ✓\n
\n
\n
\n (a)\n
\n
\n Equates centripetal force (with Newton’s law gravitation\n \n )\n
\n
\n AND\n
\n
\n \n ✓\n
\n
\n leads to\n \n hence result ✓\n
\n
\n
\n (i)\n
\n
\n «mean» Distance from centre of Sun to centre of Earth ✓\n
\n
\n \n \n OR\n \n \n
\n
\n Suitable ratio in terms of parsec and arcsecond ✓\n
\n
\n
\n (ii)\n
\n
\n \n used ✓\n
\n
\n Earth orbital radius = 1.5 × 10\n \n 11\n \n m (from AU)\n \n AND\n \n uses 1 earth year (in any units) ✓\n
\n
\n 247 years ✓\n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "d-fields"
+ ],
+ "subtopics": [
+ "d-1-gravitational-fields"
+ ]
+ },
+ {
+ "question_id": "EXE.2.SL.TZ0.14",
+ "Question": "
\n
\n (a)\n
\n
\n
\n State and explain the magnitude of the force on a length of 0.50 m of wire Q due to the current in P.\n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n
\n Calculate the current in wire Q.\n
\n
\n
\n
\n
\n
\n (i)\n
\n
\n
\n State the direction of the current in R, relative to the current in P.\n
\n
\n
\n
\n
\n
\n (ii)\n
\n
\n
\n Deduce the current in R.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n From Newton’s third law, the force on a length of Q is equal but opposite to the force on the same length of P ✓\n
\n
\n \n ✓\n
\n
\n
\n (a)\n
\n
\n From Newton’s third law, the force on a length of Q is equal but opposite to the force on the same length of P ✓\n
\n
\n \n ✓\n
\n
\n
\n (b)\n
\n
\n \n ✓\n
\n
\n \n «A» ✓\n
\n
\n
\n (i)\n
\n
\n (ii)\n
\n
\n The force on Q due to R must have the same magnitude «but opposite direction» as the force on Q due to P ✓\n
\n
\n The distance is halved therefore one half of the current is needed to produce the same force, so 2.5 A ✓\n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "d-fields"
+ ],
+ "subtopics": [
+ "d-3-motion-in-electromagnetic-fields"
+ ]
+ },
+ {
+ "question_id": "EXE.2.SL.TZ0.15",
+ "Question": "
\n
\n (a)\n
\n
\n
\n State the fundamental SI units for permeability of free space,\n \n .\n
\n
\n
\n
\n
\n
\n (i)\n
\n
\n
\n magnetic field at A;\n
\n
\n
\n
\n
\n
\n (ii)\n
\n
\n
\n magnetic force on section AB of the loop.\n
\n
\n
\n
\n
\n
\n (i)\n
\n
\n
\n magnitude of the net force acting on the loop;\n
\n
\n
\n
\n
\n
\n (ii)\n
\n
\n
\n direction of the net force acting on the loop.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n kg m s\n \n −2\n \n A\n \n −2\n \n ✓\n
\n
\n
\n (a)\n
\n
\n kg m s\n \n −2\n \n A\n \n −2\n \n ✓\n
\n
\n
\n (i)\n
\n
\n Into the page ✓\n
\n
\n
\n (ii)\n
\n
\n Repulsive / to the right ✓\n
\n
\n
\n (i)\n
\n
\n \n ✓\n
\n
\n \n «N» ✓\n
\n
\n
\n (ii)\n
\n
\n Repulsive / to the right ✓\n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "d-fields"
+ ],
+ "subtopics": [
+ "d-3-motion-in-electromagnetic-fields"
+ ]
+ },
+ {
+ "question_id": "EXE.2.SL.TZ0.16",
+ "Question": "
\n
\n (a)\n
\n
\n
\n Determine the magnetic force acting on the 15 Ω wire due to the current in the 30 Ω wire.\n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n
\n The magnetic field strength of Earth’s field at the location of the wires is 45 μT.\n
\n
\n Discuss the assumption made in this question.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n Use of combination of resistors OR\n \n ✓\n
\n
\n To show that current in 30 Ω wire is 5.0 A ✓\n
\n
\n \n ✓\n
\n
\n \n N ✓\n
\n
\n
\n (a)\n
\n
\n Use of combination of resistors OR\n \n ✓\n
\n
\n To show that current in 30 Ω wire is 5.0 A ✓\n
\n
\n \n ✓\n
\n
\n \n N ✓\n
\n
\n
\n (b)\n
\n
\n Use of\n \n ✓\n
\n
\n \n ✓\n
\n
\n Concludes that the assumption is not valid ✓\n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "d-fields"
+ ],
+ "subtopics": [
+ "d-3-motion-in-electromagnetic-fields"
+ ]
+ },
+ {
+ "question_id": "EXE.2.SL.TZ0.17",
+ "Question": "
\n
\n (a.i)\n
\n
\n
\n Draw the magnetic field lines due to A.\n
\n
\n
\n
\n
\n
\n (i)\n
\n
\n
\n Draw the magnetic field lines due to A.\n
\n
\n
\n
\n
\n
\n (ii)\n
\n
\n
\n State and explain, using your diagram, why a force acts on B due to A in the plane of the paper.\n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n
\n Both wires are 7.5 m long and are 0.25 m apart. The current in both wires is 12 A. Determine the force that acts on one wire due to the other.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a.i)\n
\n
\n At least one circle centred on centre of wire A\n
\n \n \n AND\n
\n \n \n indication of clockwise direction ✓\n
\n
\n More than 2 circles with increasing separation between circles from centre outwards (by eye) ✓\n
\n
\n
\n (i)\n
\n
\n At least one circle centred on centre of wire A\n
\n \n \n AND\n
\n \n \n indication of clockwise direction ✓\n
\n
\n More than 2 circles with increasing separation between circles from centre outwards (by eye) ✓\n
\n
\n
\n (ii)\n
\n
\n B lies in magnetic field of A OWTTE ✓\n
\n
\n Explained use of appropriate rule together with drawn indication of rule operating in this case ✓\n
\n
\n To show that force on B is to left and in plane of paper ✓\n
\n \n \n OR\n
\n \n \n Magnetic field lines of B merge with those of A to give combined field line pattern ✓\n
\n
\n Sketch of combined pattern to show null point somewhere on line between wires. ✓\n
\n
\n Wires will move to reduce stored energy and this is achieved by moving together so force on B is to left ✓\n
\n
\n
\n (b)\n
\n
\n \n ✓\n
\n
\n \n ✓\n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "d-fields"
+ ],
+ "subtopics": [
+ "d-3-motion-in-electromagnetic-fields"
+ ]
+ },
+ {
+ "question_id": "EXE.2.SL.TZ0.18",
+ "Question": "
\n
\n (a)\n
\n
\n
\n Outline, with reference to the decay equation above, the role of chain reactions in the operation of a nuclear power station.\n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n
\n Calculate, in MeV, the energy released in the reaction.\n
\n
\n
\n
\n
\n
\n (c)\n
\n
\n
\n Two nuclides present in spent nuclear fuel\n \n are and cerium-144 (\n \n ). The initial activity of a sample of pure\n \n is about 40 times greater than the activity of the same amount of pure\n \n .\n
\n
\n Discuss which of the two nuclides is more likely to require long-term storage once removed from the reactor.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n The four neutrons released in the reaction may initiate further fissions ✓\n
\n
\n «If sufficient U-235 is available,» the reaction is self-sustained ✓\n
\n
\n Allowing for the continuous production of energy ✓\n
\n
\n The number of neutrons available is controlled with control rods «to maintain the desired reaction rate» ✓\n
\n
\n
\n (a)\n
\n
\n The four neutrons released in the reaction may initiate further fissions ✓\n
\n
\n «If sufficient U-235 is available,» the reaction is self-sustained ✓\n
\n
\n Allowing for the continuous production of energy ✓\n
\n
\n The number of neutrons available is controlled with control rods «to maintain the desired reaction rate» ✓\n
\n
\n
\n (b)\n
\n
\n \n ✓\n
\n
\n 169 «MeV» ✓\n
\n
\n
\n (c)\n
\n
\n «For the same number of nuclei,» the activity is inversely related to half-life ✓\n
\n
\n Thus\n \n has a longer half-life and will likely require longer storage ✓\n
\n
\n Half-lives of their decay products need also be considered when planning storage ✓\n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "e-nuclear-and-quantum-physics"
+ ],
+ "subtopics": [
+ "e-3-radioactive-decay",
+ "e-4-fission"
+ ]
+ },
+ {
+ "question_id": "EXE.2.SL.TZ0.19",
+ "Question": "
\n
\n (a)\n
\n
\n
\n Compare and contrast spontaneous and neutron-induced nuclear fission.\n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n
\n Every neutron-induced fission reaction of uranium-235 releases an energy of about 200 MeV. A nuclear power station transfers an energy of about 2.4 GJ per second.\n
\n
\n Determine the mass of uranium-235 that undergoes fission in one day in this power station.\n
\n
\n
\n
\n
\n
\n (c)\n
\n
\n
\n State\n \n two\n \n properties of the products of nuclear fission due to which the spent nuclear fuel needs to be kept safe.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n Spontaneous fission occurs with no external influence, neutron-induced fission requires an interaction with a neutron «of appropriate energy» ✓\n
\n
\n Both result in the release of energy\n
\n \n \n OR\n \n \n
\n both have a large number of possible pairs of products ✓\n
\n
\n
\n (a)\n
\n
\n Spontaneous fission occurs with no external influence, neutron-induced fission requires an interaction with a neutron «of appropriate energy» ✓\n
\n
\n Both result in the release of energy\n
\n \n \n OR\n \n \n
\n both have a large number of possible pairs of products ✓\n
\n
\n
\n (b)\n
\n
\n Fissions per day\n \n «\n \n » ✓\n
\n
\n Mass of uranium\n \n ✓\n
\n
\n 2.5 «kg» ✓\n
\n
\n
\n (c)\n
\n
\n Have relatively short half-lives / high activity ✓\n
\n
\n Their decay products are «usually» also radioactive ✓\n
\n
\n Volatile / chemically active ✓\n
\n
\n Biologically active / easily absorbed by living matter ✓\n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "e-nuclear-and-quantum-physics"
+ ],
+ "subtopics": [
+ "e-3-radioactive-decay",
+ "e-4-fission"
+ ]
+ },
+ {
+ "question_id": "EXE.2.SL.TZ0.2",
+ "Question": "
\n
\n (a)\n
\n
\n
\n A tram is just leaving the lower railway station.\n
\n
\n Determine, as the train leaves the lower station,\n
\n
\n
\n
\n
\n
\n (i)\n
\n
\n
\n the pd across the motor of the tram,\n
\n
\n
\n
\n
\n
\n (ii)\n
\n
\n
\n the mechanical power output of the motor.\n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n
\n Discuss the variation in the power output of the motor with distance from the lower station.\n
\n
\n
\n
\n
\n
\n (c)\n
\n
\n
\n The total friction in the system acting on the tram is equivalent to an opposing force of 750 N.\n
\n
\n For one particular journey, the tram is full of passengers.\n
\n
\n Estimate the maximum speed\n \n v\n \n of the tram as it leaves the lower station.\n
\n
\n
\n
\n
\n
\n (d)\n
\n
\n
\n The tram travels at\n \n v\n \n throughout the journey. Two trams are available so that one is returning to the lower station on another line while the other is travelling to the village. The journeys take the same time.\n
\n
\n It takes 1.5 minutes to unload and 1.5 minutes to load each tram. Ignore the time taken to accelerate the tram at the beginning and end of the journey.\n
\n
\n Estimate the maximum number of passengers that can be carried up to the village in one hour.\n
\n
\n
\n
\n
\n
\n (e)\n
\n
\n
\n There are eight wheels on each tram with a brake system for each wheel. A pair of brake pads clamp firmly onto an annulus made of steel.\n
\n
\n The train comes to rest from speed\n \n v\n \n . Ignore the energy transferred to the brake pads and the change in the gravitational potential energy of the tram during the braking.\n
\n
\n Calculate the temperature change in each steel annulus as the tram comes to rest.\n
\n
\n Data for this question\n
\n
\n The inner radius of the annulus is 0.40 m and the outer radius is 0.50 m.\n
\n
\n The thickness of the annulus is 25 mm.\n
\n
\n The density of the steel is 7860 kg m\n \n −3\n \n
\n
\n The specific heat capacity of the steel is 420 J kg\n \n −1\n \n K\n \n −1\n \n
\n
\n
\n
\n
\n
\n (f)\n
\n
\n
\n The speed of the tram is measured by detecting a beam of microwaves of wavelength 2.8 cm reflected from the rear of the tram as it moves away from the station. Predict the change in wavelength of the microwaves at the stationary microwave detector in the station.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n Resistance of cable = 0.072 Ω ✓\n
\n
\n Pd is (500 − 0.072 × 600) = 457 V ✓\n
\n
\n
\n (i)\n
\n
\n Resistance of cable = 0.072 Ω ✓\n
\n
\n Pd is (500 − 0.072 × 600) = 457 V ✓\n
\n
\n
\n (ii)\n
\n
\n Power input = 457 × 600 = 274 kW ✓\n
\n
\n Power output = 0.9 × 274 = 247 kW ✓\n
\n
\n
\n (b)\n
\n
\n The pd across the motor increases as the tram travels up the track ✓\n
\n
\n (As the current is constant), the power output also rises ✓\n
\n
\n
\n (c)\n
\n
\n Total weight of tram = 75 × 710 + 5 × 10\n \n 4\n \n = 1.03 × 10\n \n 5\n \n N ✓\n
\n
\n Total force down track = 750 + 1.03 × 10\n \n 5\n \n sin (10) = 1.87 × 10\n \n 4\n \n N ✓\n
\n
\n Use of\n \n P\n \n =\n \n F ×\n \n \n v ✓\n \n
\n
\n (\n \n v\n \n = 247 000 ÷ 1.87 × 10\n \n 4\n \n )= 13 m s\n \n −1\n \n ✓\n
\n
\n
\n (d)\n
\n
\n Time for run =\n \n s/v\n \n = 3000 ÷ 13.2 = 227 s ✓\n
\n
\n 3 minutes loading = 180 s\n
\n
\n So one trip = 407 s ✓\n
\n
\n And there are 3600/407 trips per hour = 8.84 ✓\n
\n
\n So 8\n \n complete\n \n trips with 75 = 600 passengers ✓\n
\n
\n
\n (e)\n
\n
\n Work leading to volume = 7.1 x 10\n \n −3\n \n m\n \n 3\n \n ✓\n
\n
\n Work leading to mass of steel = 55 .8 kg ✓\n
\n
\n Kinetic Energy transferred per annulus =\n \n
\n
\n = 110 kJ ✓\n
\n
\n \n K ✓\n
\n
\n
\n (f)\n
\n
\n Use of\n \n ✓\n
\n
\n 1.2 nm ✓\n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "a--space-time-and-motion",
+ "b-the-particulate-nature-of-matter",
+ "c-wave-behaviour"
+ ],
+ "subtopics": [
+ "a-1-kinematics",
+ "a-2-forces-and-momentum",
+ "a-3-work-energy-and-power",
+ "b-1-thermal-energy-transfers",
+ "b-5-current-and-circuits",
+ "c-5-doppler-effect"
+ ]
+ },
+ {
+ "question_id": "EXE.2.SL.TZ0.20",
+ "Question": "
\n
\n (a)\n
\n
\n
\n State\n \n one\n \n source of the radioactive waste products from nuclear fission reactions.\n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n
\n Outline how this waste is treated after it has been removed from the fission reactor.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n Fission fragments from the fuel rods\n
\n
\n \n OR\n \n activated materials in (e.g.) fuel rod casings\n
\n
\n \n OR\n \n nuclei formed by neutron activation from U-235\n
\n
\n \n OR\n \n stated products, e.g. Pu, U-236 etc. ✓\n
\n
\n
\n (a)\n
\n
\n Fission fragments from the fuel rods\n
\n
\n \n OR\n \n activated materials in (e.g.) fuel rod casings\n
\n
\n \n OR\n \n nuclei formed by neutron activation from U-235\n
\n
\n \n OR\n \n stated products, e.g. Pu, U-236 etc. ✓\n
\n
\n
\n (b)\n
\n
\n Waste (fuel rod) is placed in cooling ponds for a number of years ✓\n
\n
\n After most active products have decayed the uranium is separated to be recycled/reprocessed ✓\n
\n
\n The remaining highly active waste is vitrified / made into a solid form ✓\n
\n
\n And stored (deep) underground ✓\n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "e-nuclear-and-quantum-physics"
+ ],
+ "subtopics": [
+ "e-4-fission"
+ ]
+ },
+ {
+ "question_id": "EXE.2.SL.TZ0.3",
+ "Question": "
\n
\n
\n (i)\n
\n
\n
\n the initial temperature gradient through the base of the pot. State an appropriate unit for your answer.\n
\n
\n
\n
\n
\n
\n (ii)\n
\n
\n
\n the initial rate, in kW, of thermal energy transfer by conduction through the base of the pot.\n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n
\n The electrical power rating of the hot plate is 1 kW. Comment, with reference to this value, on your answer in (a)(ii).\n
\n
\n
\n
\n
\n
\n (c)\n
\n
\n
\n Describe how thermal energy is distributed throughout the volume of the water in the pot.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n \n ✓\n
\n
\n K m\n \n −1\n \n ✓\n
\n
\n
\n (i)\n
\n
\n \n ✓\n
\n
\n K m\n \n −1\n \n ✓\n
\n
\n
\n (ii)\n
\n
\n 45 × 0.15 × 3.4 × 10\n \n 4\n \n = 230 «kW» ✓\n
\n
\n
\n (b)\n
\n
\n The answer is unrealistically large / impossible to sustain ✓\n
\n
\n Due to much lower actual power, a lower temperature gradient through the base of the pot is quickly established ✓\n
\n
\n The surface of the hot plate becomes colder from contact with pot\n
\n \n \n OR\n \n \n
\n there is a temperature gradient also through the hot plate ✓\n
\n
\n
\n (c)\n
\n
\n By means of convection currents ✓\n
\n
\n That arise due to density difference between hot and cold water ✓\n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "b-the-particulate-nature-of-matter"
+ ],
+ "subtopics": [
+ "b-1-thermal-energy-transfers"
+ ]
+ },
+ {
+ "question_id": "EXE.2.SL.TZ0.4",
+ "Question": "
\n
\n (a)\n
\n
\n
\n The temperature of the air outside of the bottle is 20 °C. The surface area of the bottle is 4.0 × 10\n \n −2\n \n m\n \n 2\n \n . Calculate the initial rate of thermal energy transfer by conduction through the bottle.\n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n
\n Explain why the rate calculated in part (a) is decreasing.\n
\n
\n
\n
\n
\n
\n (c)\n
\n
\n
\n Estimate the initial rate of the change of the temperature of the water in the bottle. State your answer in K s\n \n −1\n \n . The specific heat capacity of water is 4200 J kg\n \n −1\n \n K\n \n −1\n \n .\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n \n ✓\n
\n
\n 480 «W» ✓\n
\n
\n
\n (a)\n
\n
\n \n ✓\n
\n
\n 480 «W» ✓\n
\n
\n
\n (b)\n
\n
\n The temperature gradient decreases as the water cools down ✓\n
\n
\n The rate of energy transfer is proportional to the temperature gradient ✓\n
\n
\n
\n (c)\n
\n
\n \n ✓\n
\n
\n \n «K s\n \n −1\n \n » ✓\n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "b-the-particulate-nature-of-matter"
+ ],
+ "subtopics": [
+ "b-1-thermal-energy-transfers"
+ ]
+ },
+ {
+ "question_id": "EXE.2.SL.TZ0.5",
+ "Question": "
\n
\n (a)\n
\n
\n
\n Discuss the mechanism that accounts for the greatest rate of energy transfer when:\n
\n
\n
\n
\n
\n
\n (i)\n
\n
\n
\n \n T\n \n \n t\n \n >\n \n T\n \n \n b\n \n
\n
\n
\n
\n
\n
\n (ii)\n
\n
\n
\n \n T\n \n \n b\n \n >\n \n T\n \n \n t\n \n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n
\n The liquid now freezes so that the vertical column is entirely of ice. Suggest how your answer to (a)(ii) will change.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n Conduction identified ✓\n
\n
\n energy transfer through interaction of particles in liquid at atomic scale ✓\n
\n
\n
\n (i)\n
\n
\n Conduction identified ✓\n
\n
\n energy transfer through interaction of particles in liquid at atomic scale ✓\n
\n
\n
\n (ii)\n
\n
\n Convection identified ✓\n
\n
\n energy transfer through movement of bodies of liquid at different densities ✓\n
\n
\n
\n (b)\n
\n
\n the solid cannot now move relative to material above it ✓\n
\n
\n so conduction only ✓\n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "b-the-particulate-nature-of-matter"
+ ],
+ "subtopics": [
+ "b-1-thermal-energy-transfers"
+ ]
+ },
+ {
+ "question_id": "EXE.2.SL.TZ0.6",
+ "Question": "
\n
\n (a)\n
\n
\n
\n The side of the rod can be unlagged or ideally lagged. Explain the difference in energy transfer for these two cases.\n
\n
\n
\n
\n
\n
\n (i)\n
\n
\n
\n Calculate the temperature at Y.\n
\n
\n
\n
\n
\n
\n (ii)\n
\n
\n
\n The temperatures are now reversed so that X is at 45 °C and Z is at 90 °C. Show that the rate of energy transfer is unchanged.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n When ideally lagged, no energy transfer can occur through the sides of the bar. ✓\n
\n
\n All the power input/ energy input per second at one end will emerge at the other end. ✓\n
\n
\n When unlagged, energy transfer occurs from the sides of the bar and the power /energy input per second at input > the energy output per second at the other end. ✓\n
\n
\n
\n
\n \n Max 1 if answer does not refer to rate of energy transfer in MP2 and MP3.\n \n
\n
\n
\n (a)\n
\n
\n When ideally lagged, no energy transfer can occur through the sides of the bar. ✓\n
\n
\n All the power input/ energy input per second at one end will emerge at the other end. ✓\n
\n
\n When unlagged, energy transfer occurs from the sides of the bar and the power /energy input per second at input > the energy output per second at the other end. ✓\n
\n
\n
\n
\n \n Max 1 if answer does not refer to rate of energy transfer in MP2 and MP3.\n \n
\n
\n
\n (i)\n
\n
\n idea that\n \n is same in both bars because lagged ✓\n
\n
\n work to show that\n \n
\n \n \n OR\n \n \n
\n Temperature difference across XY is twice temperature difference across YZ ✓\n
\n
\n solves to show that\n \n ✓\n
\n
\n
\n (ii)\n
\n
\n repeats calculation to show that\n \n θ\n \n = 75 °C ✓\n
\n
\n temperature difference across YZ is still 15 K which gives the same rate of energy transfer (but in opposite direction) ✓\n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "b-the-particulate-nature-of-matter"
+ ],
+ "subtopics": [
+ "b-1-thermal-energy-transfers"
+ ]
+ },
+ {
+ "question_id": "EXE.2.SL.TZ0.7",
+ "Question": "
\n
\n (a)\n
\n
\n
\n State\n \n two\n \n assumptions of the kinetic model of an ideal gas that refer to intermolecular collisions.\n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n
\n Discuss how the motion of the molecules of a gas gives rise to pressure in the gas.\n
\n
\n
\n
\n
\n
\n (c)\n
\n
\n
\n The average speed of the molecules of a gas is 500 m s\n \n −1\n \n . The density of the gas is 1.2 kg m\n \n −3\n \n . Calculate, in kPa, the pressure of the gas.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n The collisions are elastic ✓\n
\n
\n The time for a collision is much shorter than the time between collisions ✓\n
\n
\n The intermolecular forces are only present during collisions ✓\n
\n
\n
\n (a)\n
\n
\n The collisions are elastic ✓\n
\n
\n The time for a collision is much shorter than the time between collisions ✓\n
\n
\n The intermolecular forces are only present during collisions ✓\n
\n
\n
\n (b)\n
\n
\n The momentum of a molecule changes when it collides with a container wall ✓\n
\n
\n From\n \n and Newton’s third law, this leads to a force exerted on the wall by the molecule ✓\n
\n
\n The average force exerted by all the molecules on a unit area of the wall is equivalent to pressure ✓\n
\n
\n
\n
\n
\n (c)\n
\n
\n \n ✓\n
\n
\n 100 «kPa» ✓\n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "b-the-particulate-nature-of-matter"
+ ],
+ "subtopics": [
+ "b-3-gas-laws"
+ ]
+ },
+ {
+ "question_id": "EXE.2.SL.TZ0.8",
+ "Question": "
\n
\n (a)\n
\n
\n
\n Calculate the average translational speed of air molecules.\n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n
\n The air is a mixture of nitrogen, oxygen and other gases. Explain why the component gases of air in the container have different average translational speeds.\n
\n
\n
\n
\n
\n
\n (c)\n
\n
\n
\n The temperature of the sample is increased without a change in pressure. Outline the effect it has on the density of the gas.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n \n ✓\n
\n
\n \n «m s\n \n −1\n \n » ✓\n
\n
\n
\n (a)\n
\n
\n \n ✓\n
\n
\n \n «m s\n \n −1\n \n » ✓\n
\n
\n
\n (b)\n
\n
\n Average kinetic energy of the molecules is determined by the temperature only ✓\n
\n
\n The mass of a molecule is different for each component gas ✓\n
\n
\n From\n \n , the same\n \n and different mass implies a different average velocity ✓\n
\n
\n
\n (c)\n
\n
\n \n \n ALTERNATIVE 1\n \n \n
\n
\n The average translational speed increases «because\n \n T\n \n increases» ✓\n
\n
\n From\n \n , the density decreases «to keep\n \n \n \n constant» ✓\n
\n
\n
\n \n \n ALTERNATIVE 2\n \n \n
\n
\n From the ideal gas law, the volume of the gas increases ✓\n
\n
\n Since\n \n and\n \n \n \n is constant, the density decreases ✓\n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "b-the-particulate-nature-of-matter"
+ ],
+ "subtopics": [
+ "b-3-gas-laws"
+ ]
+ },
+ {
+ "question_id": "EXE.2.SL.TZ0.9",
+ "Question": "
\n
\n (a)\n
\n
\n
\n Outline how the concept of absolute zero of temperature is interpreted in terms of:\n
\n
\n
\n
\n
\n
\n (i)\n
\n
\n
\n the ideal gas law,\n
\n
\n
\n
\n
\n
\n (ii)\n
\n
\n
\n the kinetic energy of particles in an ideal gas.\n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n
\n A container holds a mixture of argon and helium atoms at a temperature of 37 °C.\n
\n
\n Calculate the average translational speed of the argon atoms.\n
\n
\n The molar mass of argon is 4.0 × 10\n \n −2\n \n kg mol\n \n −1\n \n .\n
\n
\n
\n
\n
\n
\n (c)\n
\n
\n
\n Discuss how the mean kinetic energy of the argon atoms in the mixture compares with that of the helium atoms.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n it is the temperature at which the volume\n
\n
\n \n \n OR\n \n \n
\n
\n the pressure extrapolates to zero (can be shown by sketch) ✓\n
\n
\n
\n (i)\n
\n
\n it is the temperature at which the volume\n
\n
\n \n \n OR\n \n \n
\n
\n the pressure extrapolates to zero (can be shown by sketch) ✓\n
\n
\n
\n (ii)\n
\n
\n it is the temperature at which all the (random) motion stops\n
\n
\n \n \n OR\n \n \n
\n
\n at which all the motion can be extrapolated to stop\n
\n
\n \n \n OR\n \n \n
\n
\n at which the kinetic energy of all particles is zero ✓\n
\n
\n
\n (b)\n
\n
\n Use of\n \n ✓\n
\n
\n Work showing that\n \n ✓\n
\n
\n Correct substitution AND conversion to K (310 K) ✓\n
\n
\n 430/440 «m s\n \n −1\n \n » ✓\n
\n
\n
\n (c)\n
\n
\n the gases are in the same container at the same temperature so are\n \n in equilibrium\n \n ✓\n
\n
\n they must have the same mean/average kinetic energy ✓\n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "b-the-particulate-nature-of-matter"
+ ],
+ "subtopics": [
+ "b-3-gas-laws"
+ ]
+ },
+ {
+ "question_id": "SPM.1B.HL.TZ0.1",
+ "Question": "
\n
\n (a)\n
\n
\n
\n The students vary\n \n V\n \n and measure the time\n \n T\n \n for the ball to move\n \n once\n \n from one plate to the other. The table shows some of the data.\n
\n
\n
\n
\n
\n
\n
\n
\n
\n (i)\n
\n
\n
\n \n V\n \n is provided by two identical power supplies connected in series. The potential difference of each of the power supplies is known with an uncertainty of 0.01 kV.\n
\n
\n State the uncertainty in the potential difference\n \n V\n \n .\n
\n
\n
\n
\n
\n
\n (ii)\n
\n
\n
\n \n T\n \n is measured with an electronic stopwatch that measures to the nearest 0.1 s.\n
\n
\n Describe how an uncertainty in\n \n T\n \n of less than 0.1 s can be achieved using this stopwatch.\n
\n
\n
\n
\n
\n
\n (iii)\n
\n
\n
\n Outline why it is unlikely that the relationship between\n \n T\n \n and\n \n V\n \n is linear.\n
\n
\n
\n
\n
\n
\n (iv)\n
\n
\n
\n Calculate the largest fractional uncertainty in\n \n T\n \n for these data.\n
\n
\n
\n
\n
\n
\n (i)\n
\n
\n
\n Determine\n \n A\n \n by drawing the line of best fit.\n
\n
\n
\n
\n
\n
\n (ii)\n
\n
\n
\n State the units of\n \n A\n \n .\n
\n
\n
\n
\n
\n
\n (iii)\n
\n
\n
\n The theoretical relationship assumes that the ball is only affected by the electric force.\n
\n
\n Suggest why, in order to test the relationship, the length of the string should be much greater than the distance between the plates.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n (i)\n
\n
\n (ii)\n
\n
\n by measuring the time for many bounces ✓\n
\n
\n and dividing the result by the number of bounces ✓\n
\n
\n
\n (iii)\n
\n
\n it is not possible to draw a straight line through all the error bars ✓\n
\n
\n
\n (iv)\n
\n
\n \n T\n \n = 0.5 s ✓\n
\n
\n «\n \n » 0.2 ✓\n
\n
\n
\n (i)\n
\n
\n a best-fit line drawn through the entire range of the data ✓\n
\n
\n large triangle greater than half a line or two data points on the line greater than half a line apart ✓\n
\n
\n correct read offs consistent with the line,\n \n eg\n \n \n ✓\n
\n
\n \n Accept answer in the range 3.8–4.2\n \n
\n
\n
\n (ii)\n
\n
\n (iii)\n
\n
\n the angle between the string and the vertical should be very small «for any position of the ball» ✓\n
\n
\n
\n
\n so that the tension in the string is «almost» balanced by the ball’s weight\n
\n
\n \n \n OR\n \n \n
\n
\n restoring force from the string / horizontal component of tension negligibly small «compared with electric force» ✓\n
\n
\n
\n
\n \n OWTTE\n \n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "inquiry",
+ "tools"
+ ],
+ "subtopics": [
+ "i-1-2-designing",
+ "inquiry-1-exploring-and-designing",
+ "tool-1-experimental-techniques",
+ "tool-3-mathematics"
+ ]
+ },
+ {
+ "question_id": "SPM.1B.HL.TZ0.2",
+ "Question": "
\n
\n (a)\n
\n
\n
\n The group obtains the following repeated readings for\n \n d\n \n for\n \n one\n \n value of\n \n W\n \n .\n
\n
\n
\n
\n
\n The group divides into two subgroups, A and B, to analyse the data.\n
\n
\n Group A quotes the mean value of\n \n d\n \n as 2.93 cm.\n
\n
\n Group B quotes the mean value of\n \n d\n \n as 2.8 cm.\n
\n
\n Discuss the values that the groups have quoted.\n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n
\n The variation of\n \n d\n \n with\n \n W\n \n is shown.\n
\n
\n
\n
\n
\n Outline\n \n one\n \n experimental reason why the graph does not go through the origin.\n
\n
\n
\n
\n
\n
\n (c)\n
\n
\n
\n Theory predicts that\n
\n
\n \n
\n
\n where\n \n \n \n and\n \n are constants. The fundamental units of\n \n are m\n \n 4\n \n and those of\n \n E\n \n are kg m\n \n −1\n \n s\n \n −2\n \n .\n
\n
\n Calculate\n \n and\n \n .\n
\n
\n
\n
\n
\n
\n (i)\n
\n
\n
\n Suggest an appropriate measuring instrument for determining\n \n b\n \n .\n
\n
\n
\n
\n
\n
\n (ii)\n
\n
\n
\n Calculate the percentage uncertainty in the value of\n \n A\n \n .\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n 3 sf is inappropriate for\n \n A\n \n ✓\n
\n
\n rejects trial 3 as outlier for\n \n B\n \n ✓\n
\n
\n
\n (a)\n
\n
\n 3 sf is inappropriate for\n \n A\n \n ✓\n
\n
\n rejects trial 3 as outlier for\n \n B\n \n ✓\n
\n
\n
\n (b)\n
\n
\n beam bends under its own weight / weight of pan\n
\n
\n \n \n OR\n \n \n
\n
\n specified systematic error in\n \n d\n \n ✓\n
\n
\n
\n (c)\n
\n
\n units of\n \n \n \n : kg m s\n \n −2\n \n ✓\n
\n
\n work leading to\n \n and\n \n ✓\n
\n
\n
\n (i)\n
\n
\n instrument (capable of reading to 0.05 mm) with reason related to resolution of instrument ✓\n
\n
\n \n eg micrometer screw gauge, Vernier caliper, travelling microscope\n \n
\n
\n
\n (ii)\n
\n
\n attempt to calculate fractional uncertainty in either\n \n a\n \n or\n \n b\n \n [0.0357, 0.0167] ✓\n
\n
\n 0.0357 + 0.0167 = 0.05 = 5% ✓\n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "inquiry",
+ "tools"
+ ],
+ "subtopics": [
+ "i-2-3-interpreting-results",
+ "inquiry-2-collecting-and-processing-data",
+ "tool-1-experimental-techniques",
+ "tool-3-mathematics"
+ ]
+ },
+ {
+ "question_id": "SPM.1B.SL.TZ0.1",
+ "Question": "
\n
\n (a)\n
\n
\n
\n The students vary\n \n V\n \n and measure the time\n \n T\n \n for the ball to move\n \n once\n \n from one plate to the other. The table shows some of the data.\n
\n
\n
\n
\n
\n
\n
\n
\n
\n (i)\n
\n
\n
\n \n V\n \n is provided by two identical power supplies connected in series. The potential difference of each of the power supplies is known with an uncertainty of 0.01 kV.\n
\n
\n State the uncertainty in the potential difference\n \n V\n \n .\n
\n
\n
\n
\n
\n
\n (ii)\n
\n
\n
\n \n T\n \n is measured with an electronic stopwatch that measures to the nearest 0.1 s.\n
\n
\n Describe how an uncertainty in\n \n T\n \n of less than 0.1 s can be achieved using this stopwatch.\n
\n
\n
\n
\n
\n
\n (iii)\n
\n
\n
\n Outline why it is unlikely that the relationship between\n \n T\n \n and\n \n V\n \n is linear.\n
\n
\n
\n
\n
\n
\n (iv)\n
\n
\n
\n Calculate the largest fractional uncertainty in\n \n T\n \n for these data.\n
\n
\n
\n
\n
\n
\n (i)\n
\n
\n
\n Determine\n \n A\n \n by drawing the line of best fit.\n
\n
\n
\n
\n
\n
\n (ii)\n
\n
\n
\n State the units of\n \n A\n \n .\n
\n
\n
\n
\n
\n
\n (iii)\n
\n
\n
\n The theoretical relationship assumes that the ball is only affected by the electric force.\n
\n
\n Suggest why, in order to test the relationship, the length of the string should be much greater than the distance between the plates.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n (i)\n
\n
\n (ii)\n
\n
\n by measuring the time for many bounces ✓\n
\n
\n and dividing the result by the number of bounces ✓\n
\n
\n
\n (iii)\n
\n
\n it is not possible to draw a straight line through all the error bars ✓\n
\n
\n
\n (iv)\n
\n
\n \n T\n \n = 0.5 s ✓\n
\n
\n «\n \n » 0.2 ✓\n
\n
\n
\n (i)\n
\n
\n a best-fit line drawn through the entire range of the data ✓\n
\n
\n large triangle greater than half a line or two data points on the line greater than half a line apart ✓\n
\n
\n correct read offs consistent with the line,\n \n eg\n \n \n ✓\n
\n
\n \n Accept answer in the range 3.8–4.2\n \n
\n
\n
\n (ii)\n
\n
\n (iii)\n
\n
\n the angle between the string and the vertical should be very small «for any position of the ball» ✓\n
\n
\n so that the tension in the string is «almost» balanced by the ball’s weight\n
\n
\n \n \n OR\n \n \n
\n
\n restoring force from the string / horizontal component of tension negligibly small «compared with electric force» ✓\n
\n
\n \n OWTTE\n \n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "inquiry",
+ "tools"
+ ],
+ "subtopics": [
+ "i-1-1-exploring",
+ "i-1-2-designing",
+ "i-1-3-controlling-variables",
+ "inquiry-1-exploring-and-designing",
+ "tool-1-experimental-techniques",
+ "tool-3-mathematics"
+ ]
+ },
+ {
+ "question_id": "SPM.1B.SL.TZ0.2",
+ "Question": "
\n
\n (a)\n
\n
\n
\n The group obtains the following repeated readings for\n \n d\n \n for\n \n one\n \n value of\n \n W\n \n .\n
\n
\n
\n
\n
\n The group divides into two subgroups, A and B, to analyse the data.\n
\n
\n Group A quotes the mean value of\n \n d\n \n as 2.93 cm.\n
\n
\n Group B quotes the mean value of\n \n d\n \n as 2.8 cm.\n
\n
\n Discuss the values that the groups have quoted.\n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n
\n The variation of\n \n d\n \n with\n \n W\n \n is shown.\n
\n
\n
\n
\n
\n Outline\n \n one\n \n experimental reason why the graph does not go through the origin.\n
\n
\n
\n
\n
\n
\n (c)\n
\n
\n
\n Theory predicts that\n
\n
\n \n
\n
\n where\n \n and\n \n are constants. The fundamental units of\n \n are m\n \n 4\n \n and those of\n \n are kg m\n \n −1\n \n s\n \n −2\n \n .\n
\n
\n Calculate\n \n and\n \n .\n
\n
\n
\n
\n
\n
\n (i)\n
\n
\n
\n Suggest an appropriate measuring instrument for determining\n \n b\n \n .\n
\n
\n
\n
\n
\n
\n (ii)\n
\n
\n
\n Calculate the percentage uncertainty in the value of\n \n A\n \n .\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n 3 sf is inappropriate for\n \n A\n \n ✓\n
\n
\n rejects trial 3 as outlier for\n \n B\n \n ✓\n
\n
\n
\n (a)\n
\n
\n 3 sf is inappropriate for\n \n A\n \n ✓\n
\n
\n rejects trial 3 as outlier for\n \n B\n \n ✓\n
\n
\n
\n (b)\n
\n
\n beam bends under its own weight / weight of pan\n
\n
\n \n \n OR\n \n \n
\n
\n specified systematic error in\n \n d\n \n ✓\n
\n
\n
\n (c)\n
\n
\n units of\n \n W\n \n : kg m s\n \n −2\n \n ✓\n
\n
\n work leading to\n \n and\n \n ✓\n
\n
\n
\n (i)\n
\n
\n instrument (capable of reading to 0.05 mm) with reason related to resolution of instrument ✓\n
\n
\n \n eg micrometer screw gauge, Vernier caliper, travelling microscope\n \n
\n
\n
\n (ii)\n
\n
\n attempt to calculate fractional uncertainty in either\n \n a\n \n or\n \n b\n \n [0.0357, 0.0167] ✓\n
\n
\n 0.0357 + 0.0167 = 0.05 = 5 % ✓\n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "inquiry",
+ "tools"
+ ],
+ "subtopics": [
+ "i-2-3-interpreting-results",
+ "inquiry-2-collecting-and-processing-data",
+ "tool-1-experimental-techniques",
+ "tool-3-mathematics"
+ ]
+ },
+ {
+ "question_id": "SPM.2.HL.TZ0.1",
+ "Question": "
\n
\n (a)\n
\n
\n
\n State the nature and direction of the force that accelerates the 15 kg object.\n
\n
\n
\n
\n
\n
\n (b)\n
\n
\n
\n Determine the largest magnitude of\n \n F\n \n for which the block and the object do not move relative to each other.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n static friction force «between blocks»\n
\n
\n \n \n AND\n \n \n
\n
\n directed to the right ✓\n
\n
\n
\n (a)\n
\n
\n static friction force «between blocks»\n
\n
\n \n \n AND\n \n \n
\n
\n directed to the right ✓\n
\n
\n
\n (b)\n
\n
\n \n F\n \n = 60\n \n a ✓\n \n
\n
\n \n F\n \n \n f\n \n = 0.6 × 15 × 9.8 «= 88.2 N» ✓\n
\n
\n \n «N» ✓\n
\n
\n
\n
\n \n Allow use of a =\n \n 0.6\n \n g leading to 353 N.\n \n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "a--space-time-and-motion"
+ ],
+ "subtopics": [
+ "a-2-forces-and-momentum"
+ ]
+ },
+ {
+ "question_id": "SPM.2.HL.TZ0.2",
+ "Question": "
\n
\n (a)\n
\n
\n
\n Calculate\n \n for a speed of 0.80\n \n c\n \n .\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n \n ✓\n
\n
\n
\n (a)\n
\n
\n \n ✓\n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "a--space-time-and-motion"
+ ],
+ "subtopics": [
+ "a-5-galilean-and-special-relativity"
+ ]
+ },
+ {
+ "question_id": "SPM.2.HL.TZ0.3",
+ "Question": "
\n
\n (a)\n
\n
\n
\n Outline how this standing wave pattern of melted spots is formed.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n standing waves form «in the oven» by superposition / constructive interference ✓\n
\n
\n energy transfer is greatest at the antinodes «of the standing wave pattern» ✓\n
\n
\n
\n (a)\n
\n
\n standing waves form «in the oven» by superposition / constructive interference ✓\n
\n
\n energy transfer is greatest at the antinodes «of the standing wave pattern» ✓\n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "c-wave-behaviour"
+ ],
+ "subtopics": [
+ "c-4-standing-waves-and-resonance"
+ ]
+ },
+ {
+ "question_id": "SPM.2.HL.TZ0.4",
+ "Question": "
\n
\n (a)\n
\n
\n
\n Draw an arrow on the diagram to represent the direction of the acceleration of the satellite.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n arrow normal to the orbit towards the Earth ✓\n
\n
\n
\n (a)\n
\n
\n arrow normal to the orbit towards the Earth ✓\n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "a--space-time-and-motion",
+ "d-fields"
+ ],
+ "subtopics": [
+ "a-2-forces-and-momentum",
+ "d-1-gravitational-fields"
+ ]
+ },
+ {
+ "question_id": "SPM.2.HL.TZ0.5",
+ "Question": "
\n
\n (a)\n
\n
\n
\n Outline why the magnetic flux in ring B increases.\n
\n
\n
\n
\n
\n
\n (d)\n
\n
\n
\n Outline why work must be done on ring B as it moves towards ring A at a constant speed.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n ring B cuts an increasing number of magnetic field lines ✓\n
\n
\n \n OR\n \n
\n
\n magnetic field from current in A increases at the position of B ✓\n
\n
\n
\n (a)\n
\n
\n ring B cuts an increasing number of magnetic field lines ✓\n
\n
\n \n OR\n \n
\n
\n magnetic field from current in A increases at the position of B ✓\n
\n
\n
\n (d)\n
\n
\n the current induced in B gives rise to a magnetic field opposing that of A\n
\n
\n \n OR\n \n
\n
\n there will be a magnetic force opposing the motion ✓\n
\n
\n work must be done to move B in the opposite direction to this force ✓\n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "a--space-time-and-motion",
+ "d-fields"
+ ],
+ "subtopics": [
+ "a-3-work-energy-and-power",
+ "d-4-induction"
+ ]
+ },
+ {
+ "question_id": "SPM.2.HL.TZ0.6",
+ "Question": "
\n
\n (a)\n
\n
\n
\n A nucleus of americium-241 has 146 neutrons. This nuclide decays to neptunium through alpha emission.\n
\n
\n Complete the nuclear equation for this decay.\n
\n
\n
\n
\n
\n
\n
\n
\n
\n (d)\n
\n
\n
\n Calculate the maximum current in the chamber due to the electrons when there is no smoke in the chamber.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n \n ✓\n
\n
\n \n ✓\n
\n
\n
\n (d)\n
\n
\n Each alpha gives rise to\n \n ion pairs ✓\n
\n
\n So\n \n ion pairs per second ✓\n
\n
\n current\n \n «A» ✓\n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "b-the-particulate-nature-of-matter",
+ "e-nuclear-and-quantum-physics"
+ ],
+ "subtopics": [
+ "b-5-current-and-circuits",
+ "e-3-radioactive-decay"
+ ]
+ },
+ {
+ "question_id": "SPM.2.HL.TZ0.7",
+ "Question": "
\n
\n (a)\n
\n
\n
\n Show that the surface temperature of\n \n δ\n \n Vel A is about 9000 K.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n correct substitution into\n \n OR 9350 K ✓\n
\n
\n
\n (a)\n
\n
\n correct substitution into\n \n OR 9350 K ✓\n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "b-the-particulate-nature-of-matter"
+ ],
+ "subtopics": [
+ "b-1-thermal-energy-transfers"
+ ]
+ },
+ {
+ "question_id": "SPM.2.HL.TZ0.8",
+ "Question": "
\n
\n (a)\n
\n
\n
\n Calculate the theoretical equilibrium temperature of the mixture.\n
\n
\n
\n
\n
\n
\n (ii)\n
\n
\n
\n The mixture was held in a large metal container during the mixing.\n
\n
\n Explain\n \n one\n \n change to the procedure that will reduce the difference in (b)(i).\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n \n
\n
\n \n
\n
\n One heat capacity term correctly substituted ✓\n
\n
\n latent heat correctly substituted\n \n ✓\n
\n
\n \n «°C» ✓\n
\n
\n
\n (a)\n
\n
\n \n
\n
\n \n
\n
\n One heat capacity term correctly substituted ✓\n
\n
\n latent heat correctly substituted\n \n ✓\n
\n
\n \n «°C» ✓\n
\n
\n
\n (ii)\n
\n
\n Insulate the container\n
\n
\n \n OR\n \n
\n
\n Carry out experiment quicker\n
\n
\n \n OR\n \n
\n
\n Use larger volumes of substances ✓\n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "b-the-particulate-nature-of-matter",
+ "inquiry"
+ ],
+ "subtopics": [
+ "b-1-thermal-energy-transfers",
+ "i-1-3-controlling-variables",
+ "inquiry-1-exploring-and-designing"
+ ]
+ },
+ {
+ "question_id": "SPM.2.HL.TZ0.9",
+ "Question": "
\n
\n (a.i)\n
\n
\n
\n Draw the electric field lines due to the charged plates.\n
\n
\n
\n
\n
\n
\n (i)\n
\n
\n
\n Draw the electric field lines due to the charged plates.\n
\n
\n
\n
\n
\n
\n (ii)\n
\n
\n
\n Draw the forces acting on the oil drop, ignoring the buoyancy force.\n
\n
\n
\n
\n
\n
\n
\n
\n
\n (iii)\n
\n
\n
\n Show that the electric charge on the oil drop is given by\n
\n
\n \n
\n
\n where\n \n is the density of oil and\n \n is the volume of the oil drop.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a.i)\n
\n
\n equally spaced arrows «by eye» all pointing down ✓\n
\n
\n edge effects also shown with arrows ✓\n
\n
\n
\n (i)\n
\n
\n equally spaced arrows «by eye» all pointing down ✓\n
\n
\n edge effects also shown with arrows ✓\n
\n
\n
\n (ii)\n
\n
\n Weight vertically down\n \n \n AND\n \n \n electric force vertically up ✓\n
\n
\n Of equal length «by eye» ✓\n
\n
\n
\n (iii)\n
\n
\n Mass of drop is\n \n ✓\n
\n
\n \n ✓\n
\n
\n «hence answer»\n
\n
\n
\n \n MP1 must be shown implicitly for credit.\n \n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "a--space-time-and-motion",
+ "d-fields",
+ "tools"
+ ],
+ "subtopics": [
+ "a-2-forces-and-momentum",
+ "d-2-electric-and-magnetic-fields",
+ "tool-3-mathematics"
+ ]
+ },
+ {
+ "question_id": "SPM.2.SL.TZ0.1",
+ "Question": "
\n
\n (a)\n
\n
\n
\n State the nature and direction of the force that accelerates the 15 kg object.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n static friction force «between blocks»\n
\n
\n \n AND\n \n
\n
\n directed to the right ✓\n
\n
\n
\n (a)\n
\n
\n static friction force «between blocks»\n
\n
\n \n AND\n \n
\n
\n directed to the right ✓\n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "a--space-time-and-motion"
+ ],
+ "subtopics": [
+ "a-2-forces-and-momentum"
+ ]
+ },
+ {
+ "question_id": "SPM.2.SL.TZ0.2",
+ "Question": "
\n
\n (a)\n
\n
\n
\n Outline how this standing wave pattern of melted spots is formed.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n standing waves form «in the oven» by superposition / constructive interference ✓\n
\n
\n energy transfer is greatest at the antinodes «of the standing wave pattern» ✓\n
\n
\n
\n (a)\n
\n
\n standing waves form «in the oven» by superposition / constructive interference ✓\n
\n
\n energy transfer is greatest at the antinodes «of the standing wave pattern» ✓\n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "c-wave-behaviour"
+ ],
+ "subtopics": [
+ "c-4-standing-waves-and-resonance"
+ ]
+ },
+ {
+ "question_id": "SPM.2.SL.TZ0.3",
+ "Question": "
\n
\n (a)\n
\n
\n
\n Draw an arrow on the diagram to represent the direction of the acceleration of the satellite.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n arrow normal to the orbit towards the Earth ✓\n
\n
\n
\n (a)\n
\n
\n arrow normal to the orbit towards the Earth ✓\n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "a--space-time-and-motion",
+ "d-fields"
+ ],
+ "subtopics": [
+ "a-2-forces-and-momentum",
+ "d-1-gravitational-fields"
+ ]
+ },
+ {
+ "question_id": "SPM.2.SL.TZ0.4",
+ "Question": "
\n
\n (a)\n
\n
\n
\n A nucleus of americium-241 has 146 neutrons. This nuclide decays to neptunium through alpha emission.\n
\n
\n Complete the nuclear equation for this decay.\n
\n
\n
\n
\n
\n
\n
\n
\n
\n (c)\n
\n
\n
\n Calculate the maximum current in the chamber due to the electrons when there is no smoke in the chamber.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n \n ✓\n
\n
\n \n ✓\n
\n
\n
\n (c)\n
\n
\n Each alpha gives rise to\n \n ion pairs ✓\n
\n
\n So\n \n ion pairs per second ✓\n
\n
\n current\n \n «A» ✓\n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "b-the-particulate-nature-of-matter",
+ "e-nuclear-and-quantum-physics"
+ ],
+ "subtopics": [
+ "b-5-current-and-circuits",
+ "e-3-radioactive-decay"
+ ]
+ },
+ {
+ "question_id": "SPM.2.SL.TZ0.5",
+ "Question": "
\n
\n (a)\n
\n
\n
\n Show that the surface temperature of\n \n δ\n \n Vel A is about 9000 K.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n correct substitution into\n \n OR 9350 K ✓\n
\n
\n
\n (a)\n
\n
\n correct substitution into\n \n OR 9350 K ✓\n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "b-the-particulate-nature-of-matter"
+ ],
+ "subtopics": [
+ "b-1-thermal-energy-transfers"
+ ]
+ },
+ {
+ "question_id": "SPM.2.SL.TZ0.6",
+ "Question": "
\n
\n (a)\n
\n
\n
\n Calculate the theoretical equilibrium temperature of the mixture.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a)\n
\n
\n \n
\n
\n \n
\n
\n One heat capacity term correctly substituted ✓\n
\n
\n latent heat correctly substituted\n \n ✓\n
\n
\n \n «°C» ✓\n
\n
\n
\n (a)\n
\n
\n \n
\n
\n \n
\n
\n One heat capacity term correctly substituted ✓\n
\n
\n latent heat correctly substituted\n \n ✓\n
\n
\n \n «°C» ✓\n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "b-the-particulate-nature-of-matter"
+ ],
+ "subtopics": [
+ "b-1-thermal-energy-transfers"
+ ]
+ },
+ {
+ "question_id": "SPM.2.SL.TZ0.7",
+ "Question": "
\n
\n (a.i)\n
\n
\n
\n Draw the electric field lines due to the charged plates.\n
\n
\n
\n
\n
\n
\n (i)\n
\n
\n
\n Draw the electric field lines due to the charged plates.\n
\n
\n
\n
\n",
+ "Markscheme": "
\n (a.i)\n
\n
\n equally spaced arrows «by eye» all pointing down ✓\n
\n
\n edge effects also shown with arrows ✓\n
\n
\n
\n (i)\n
\n
\n equally spaced arrows «by eye» all pointing down ✓\n
\n
\n edge effects also shown with arrows ✓\n
\n
\n",
+ "Examiners report": "None",
+ "topics": [
+ "d-fields"
+ ],
+ "subtopics": [
+ "d-2-electric-and-magnetic-fields"
+ ]
+ }
+]
\ No newline at end of file
diff --git a/assets/style.css b/assets/style.css
index feb26e3..b4d11bd 100644
--- a/assets/style.css
+++ b/assets/style.css
@@ -46,9 +46,8 @@ body {
}
hr {
- height: 0;
- color: #000;
- border-top-width: 1px
+ height: 2px;
+ background-color: #000;
}
abbr:where([title]) {
@@ -334,13 +333,66 @@ h4 {
word-break: break-word;
}
-#right-col {
+#right-wrapper {
flex: 4;
+ display: flex;
+ flex-direction: column;
width: 80%;
+ height: 100%;
+}
+
+#upper-right-col {
+ flex: 1;
+ /*overflow: hidden;*/
+ word-break: break-word;
+}
+
+#right-col {
+ flex: 9;
+ /*height: 90%;
+ width: 80%;*/
overflow-y: auto;
word-break: break-word;
}
+.toolbar {
+ display: flex;
+ justify-content: flex-end;
+ flex-wrap: wrap;
+ gap: 0.5rem;
+}
+
+.selectables {
+ display: flex;
+ justify-content: left;
+ flex-wrap: wrap;
+ gap: 2rem;
+}
+
+@media (max-width: 480px) {
+ .selectables {
+ flex-direction: column;
+ align-items: stretch;
+ gap: 0;
+ }
+}
+
+select {
+ min-width: 60px;
+}
+
+#subtopic-select, #topic-select {
+ max-width: 100px;
+}
+
+#topic-list, .topic-label {
+ display: block;
+}
+
+#topic-list label {
+ padding-bottom: 0.5rem;
+}
+
#appContainer{
display: flex;
height: 100%;