IB Biology 2025 · Theme B · Form and function

B3.2 Transport. Practice questions with markscheme.

75 original IB-style questions on B3.2, written from the 2025 guide: 31 multiple-choice, 24 short-answer, 10 data-based, 4 extended-response parts, 4 drawing, 2 labelling. Below are two ready-made practice papers built from them, one at standard level (20 marks) and one at higher level (22 marks); switch between them above the paper. Hand one out as a class quiz or homework, or sit it yourself and mark against the scheme. Print it, project it, or build a fresh one on the same topic.

What the guide asks for

10 statements at SL and HL, 8 additional higher level.

B3.2.1SL / HL Adaptations of capillaries for exchange of materials between blood and the internal or external environment
B3.2.2SL / HL Structure of arteries and veins
B3.2.3SL / HL Adaptations of arteries for the transport of blood away from the heart
B3.2.4SL / HL Measurement of pulse rates
B3.2.5SL / HL Adaptations of veins for the return of blood to the heart
B3.2.6SL / HL Causes and consequences of occlusion of the coronary arteries
B3.2.7SL / HL Transport of water from roots to leaves during transpiration
B3.2.8SL / HL Adaptations of xylem vessels for transport of water
B3.2.9SL / HL Distribution of tissues in a transverse section of the stem of a dicotyledonous plant
B3.2.10SL / HL Distribution of tissues in a transverse section of the root of a dicotyledonous plant
B3.2.11HL Release and reuptake of tissue fluid in capillaries
B3.2.12HL Exchange of substances between tissue fluid and cells in tissues
B3.2.13HL Drainage of excess tissue fluid into lymph ducts
B3.2.14HL Differences between the single circulation of bony fish and the double circulation of mammals
B3.2.15HL Adaptations of the mammalian heart for delivering pressurized blood to the arteries
B3.2.16HL Stages in the cardiac cycle
B3.2.17HL Generation of root pressure in xylem vessels by active transport of mineral ions
B3.2.18HL Adaptations of phloem sieve tubes and companion cells for translocation of sap

In the bank for B3.2

31 multiple-choice
24 short-answer
10 data-based
4 extended-response parts
4 drawing
2 labelling
39 higher level only

Every question is original and tagged to a guide statement. See the whole bank →

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The practice paper

20 marks at SL · 22 at HL · each has its own code

Take it online → Build a fresh paper Paper code BbB-EAAAgAAAABQAOrN_

Biology · topic quiz

Standard level · topic practice, not an exam format

30 minutes20 marks

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Covers B3.2 Transport · SL

Name:

In a study, 12 000 men aged 40 to 59 with no sign of heart disease were grouped according to whether they smoked and according to the concentration of cholesterol in their blood at the start. The men were then followed for ten years, and every new case of coronary heart disease (CHD) was recorded. The table shows the incidence of CHD in each group.

Blood cholesterol concentration at the start / mmol dm⁻³	Non-smokers: new cases of CHD per 1000 men in ten years	Smokers: new cases of CHD per 1000 men in ten years
low (below 5.2)	30	58
medium (5.2 to 6.2)	48	92
high (above 6.2)	75	140

(a)Calculate how many times greater the incidence of CHD was in smokers with high blood cholesterol than in non-smokers with low blood cholesterol.[1]

(b)Deduce whether the higher incidence of CHD in smokers could be explained by smokers having higher blood cholesterol concentrations.[2]

(c)Discuss whether these data show that smoking causes CHD.[3]

In the early seventeenth century most physicians accepted Galen's model of the blood, in which blood was made continually in the liver from digested food and flowed outwards along the veins to the organs, where it was used up. William Harvey tied a band round a volunteer's upper arm, tight enough to make the veins of the forearm swell, and small swellings could then be seen at intervals along each vein. He pressed one fingertip on a vein at a point P and, with a second finger, pushed the blood along the vein towards the elbow, past a swelling at Q. The length of vein between P and Q then stayed empty and flat for as long as the first finger stayed at P, and filled at once from the hand side when that finger was lifted. When he tried to push blood along a vein from the elbow side of a swelling towards the hand, it would not pass the swelling.

(a)Explain how these observations refute the part of Galen's model in which blood flows outwards along the veins to the organs.[3]

(b)Harvey also argued from quantities. In a resting adult the left ventricle pumps out about 70 cm³ of blood with each beat, the heart rate is about 70 beats min⁻¹, and the body contains about 5.0 dm³ of blood. Calculate the volume of blood pumped out of the left ventricle in one hour, in dm³.[1]

(c)Explain how your answer to (b) supports the model that blood circulates, rather than being made continually and used up.[2]

(d)Harvey could not see how blood passed from the arteries to the veins inside the organs. Outline the prediction his model made about this, and how it was later tested.[2]

Plan diagrams of a transverse section of a dicotyledonous stem are annotated with the main function of each tissue. State the main function of the epidermis and of the cortex.

[2]

Draw a plan diagram of a transverse section of the root of a dicotyledonous plant to show the distribution of tissues. A plan diagram shows the outlines of the tissues but not individual cells.

[4]

Original practice questions © Biology by Bradford · CC BY-NC-SA 4.0 · Not affiliated with or endorsed by the International Baccalaureate Organization.
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Show the markscheme

Markscheme BbB-EAAAgAAAABQAOrN_

One mark per point; / separates alternative wording within a point, OR separates alternative answers, words in brackets are not required, underlined words are essential. OWTTE = or words to that effect.

1. B3.2.6

(a) [1]
- 140 ÷ 30 = 4.7 (times);
Accept 4.67 or 4.7.
(b) [2 max]
- no: within each cholesterol group, smokers have a higher incidence of CHD than non-smokers;
- the incidence in smokers is about twice / 1.9 times that in non-smokers at every cholesterol level (58 against 30, 92 against 48, 140 against 75);
- (so) the difference remains when cholesterol is the same, and smoking is associated with CHD independently of blood cholesterol, OWTTE;
Do not award the first mark for 'no' alone, without a comparison made within a cholesterol group.
(c) [3 max]
- the incidence of CHD is higher in smokers in every cholesterol group, so the association is consistent;
- blood cholesterol, which might otherwise explain the difference, has been allowed for by grouping the men;
- smoking was recorded before any CHD developed, so the disease cannot have caused the smoking;
- but this is an observational study, and a correlation/association does not prove causation;
- other variables that may differ between smokers and non-smokers were not controlled, e.g. diet / exercise / alcohol intake / blood pressure / stress / income, and could cause the difference;
- the number of men in each group and any statistical test are not given, so it is not known whether the differences could be due to chance;
- only men aged 40 to 59 were studied, so the findings may not apply to women or to other age groups;
For full marks the answer must include at least one point supporting and one point against a causal link.

2. B3.2.5

(a) [3 max]
- the length of vein between P and Q stays empty, so no blood flows back into it from the elbow/heart side, past Q;
- blood cannot be pushed past a swelling towards the hand, so the swellings are valves that let blood pass in one direction only;
- the vein refills only from the hand side, so the blood in it arrives from the tissues of the hand;
- the veins swell below the band, which blocks flow towards the heart, so blood in them is moving towards the heart;
- (so) blood in the veins flows from the organs towards the heart, the opposite of Galen's model, OWTTE;
Each observation must be linked to the direction of flow it shows.
(b) [1]
- 70 × 70 × 60 = 294 000 cm³ = 294 dm³ (per hour);
Accept 290 dm³. Unit required.
(c) [2 max]
- about 59 times the volume of blood in the body is pumped out each hour / all the blood is pumped out about once a minute;
- far more than could be made from the food eaten, or used up by the organs, in that time;
- (so) the same blood must return to the heart and be pumped round again / must circulate, OWTTE;
Award ECF from (b).
(d) [2 max]
- the model predicted vessels linking the arteries to the veins within the tissues/organs;
- these vessels must be too narrow to be seen with the naked eye;
- capillaries were later seen with (improved) microscopes, confirming the prediction / the test needed new apparatus, OWTTE;
Nature of science: a model making a testable prediction, confirmed when technology improved.

3. B3.2.9 [2]

epidermis: protects the stem / reduces water loss (with its waxy cuticle) / barrier to pathogens;
cortex: support (turgid cells) / storage (of starch/food) / photosynthesis (in young green stems);

4. B3.2.10 [4 max]

epidermis drawn as a single outer outline, with root hairs shown as extensions from it, labelled;
wide cortex drawn between the epidermis and the central vascular tissue, labelled;
vascular tissue drawn as a single central cylinder, not a ring of bundles and with no pith;
xylem drawn as a central star/cross shape, labelled;
phloem drawn in the separate regions between the arms of the xylem, labelled;
endodermis drawn as a ring around the central vascular cylinder (stele), labelled;

Individual cells must not be drawn. Do not accept vascular bundles in a ring or a central pith (stem arrangement).

Take it online → Build a fresh paper Paper code BbB-EAEAgAAAABQAaHdt

Biology · topic quiz

Higher level · topic practice, not an exam format

35 minutes22 marks

Paper code: this paper was generated, so the code is its recipe. Enter it at biologybybradford.com/exam-maker to rebuild this exact paper and its markscheme.

Covers B3.2 Transport · HL

Name:

The figure shows drawings made from light micrographs of transverse sections of two blood vessels, R and S, taken from different parts of the body of the same mammal. One vessel is an artery and the other is a vein. The two drawings are at different magnifications, so each has its own scale bar.

(a)Using the scale bars, calculate the actual thickness of the wall of each vessel.[2]

(b)A student argued that the vessel with the thicker wall must be the artery. Using your answers to (a), evaluate this argument.[3]

Draw a plan diagram of a transverse section of the root of a dicotyledonous plant to show the distribution of tissues. A plan diagram shows the outlines of the tissues but not individual cells.

[4]

The diameter of the trunk of a tree was measured every three hours through one sunny summer day with a sensitive gauge (a dendrometer) fixed around the trunk. The rate of transpiration from the leaves was measured at the same times. At 06:00 the trunk diameter was 250 mm; the table gives the change in diameter from that value.

Time of day	Transpiration rate / g water per m² of leaf per hour	Change in trunk diameter / µm
06:00	10	0
09:00	90	−40
12:00	180	−95
15:00	160	−85
18:00	60	−30
21:00	5	−5

(a)Describe the relationship between the rate of transpiration and the change in trunk diameter.[2]

(b)Calculate the percentage decrease in trunk diameter at 12:00.[2]

(c)Explain why the trunk becomes narrower when the rate of transpiration is high.[3]

(d)Suggest, using evidence from the data, why the walls of xylem vessels are strengthened with lignin.[1]

Fish have a single circulation, in which blood passes through the heart once for each complete circuit of the body. Mammals and birds have a double circulation. Compare and contrast these two arrangements, and explain the advantage of a double circulation.

[5]

Show the markscheme

Markscheme BbB-EAEAgAAAABQAaHdt

1. B3.2.2

(a) [2]
- R: 1.0 mm;
- S: 0.4 mm;
Accept 0.8 to 1.2 mm for R and 0.35 to 0.45 mm for S. Units required. Award [1 max] if both are correct in proportion to each other but the unit is missing or wrong.
(b) [3 max]
- the argument would identify R as the artery, because R has the thicker wall in real size (1.0 mm against 0.4 mm);
- but the vessels differ greatly in size, so comparing absolute wall thickness is not a valid way to tell them apart, OWTTE;
- the wall must be judged relative to the diameter of the lumen;
- the wall of S is about half the diameter of its lumen (0.4 mm to about 0.8 mm), whereas the wall of R is only about a tenth of its lumen (1.0 mm to about 10 mm);
- (so) S is the artery and R is the vein, and the student's argument is wrong;
- S also has a round lumen with a wavy (folded) lining and a thick middle layer, whereas R has a wide, oval lumen, supporting this identification, OWTTE;
Allow ECF from the values in (a). The identification of S as the artery earns credit only with a relative-thickness reason.

2. B3.2.10 [4 max]

epidermis drawn as a single outer outline, with root hairs shown as extensions from it, labelled;
wide cortex drawn between the epidermis and the central vascular tissue, labelled;
vascular tissue drawn as a single central cylinder, not a ring of bundles and with no pith;
xylem drawn as a central star/cross shape, labelled;
phloem drawn in the separate regions between the arms of the xylem, labelled;
endodermis drawn as a ring around the central vascular cylinder (stele), labelled;

Individual cells must not be drawn. Do not accept vascular bundles in a ring or a central pith (stem arrangement).

3. B3.2.7

(a) [2 max]
- as the transpiration rate increases the trunk diameter decreases / negative correlation;
- the greatest decrease (95 µm) is at 12:00, when the transpiration rate is highest (180 g m⁻² h⁻¹);
- the trunk returns almost to its 06:00 diameter by 21:00, as transpiration falls (to 5 g m⁻² h⁻¹), OWTTE;
(b) [2]
- 95 µm = 0.095 mm;
- 0.095 ÷ 250 × 100 = 0.038 %;
Award [1] for a correct method with a unit-conversion error (e.g. 38 %).
(c) [3 max]
- evaporation of water from the walls of leaf cells draws water out of the xylem, generating tension / negative pressure in the xylem;
- cohesion between water molecules (hydrogen bonding) transmits the tension down the continuous column of water to the trunk;
- adhesion of water to the xylem walls means the tension pulls the walls inward, so the trunk contracts slightly;
- the faster the transpiration, the greater the tension and the greater the narrowing (hence largest at midday), OWTTE;
(d) [1]
- the tension in the xylem is great enough to pull the trunk inward, so lignified walls are needed to stop the vessels collapsing (under negative pressure), OWTTE;

4. B3.2.14 [5 max]

both are closed circulations driven by a muscular heart, with blood kept within vessels;
in a single circulation blood passes through the heart once per circuit (heart → gills → body → heart), whereas in a double circulation it passes through the heart twice (a pulmonary and a systemic circuit);
in a single circulation blood loses much of its pressure at the gill capillaries before reaching the body, so delivery to the tissues is slower;
in a double circulation blood returns to the heart to be re-pressurised before the systemic circuit, giving higher pressure and faster delivery to the tissues;
a double circulation (with a four-chambered heart) keeps oxygenated and deoxygenated blood separate, and lets lung and body pressures be controlled separately;
(so) a double circulation can support the higher metabolic rate of endothermic birds and mammals, OWTTE;

Comparative points required; award converse statements.