IB Biology 2025 · Theme B · Form and function

B3.2 Transport. Practice questions with markscheme.

68 original IB-style questions on B3.2, written from the 2025 guide: 29 multiple-choice, 20 short-answer, 9 data-based, 4 extended-response part, 4 drawing, 2 labelling. Below is a 20-mark standard-level practice paper built from them, ready to hand out as a class quiz or homework, or to sit 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

29 multiple-choice
20 short-answer
9 data-based
4 extended-response part
4 drawing
2 labelling
37 higher level only

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

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The practice paper

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Biology · topic quiz

Standard level · topic practice, not an exam format

30 minutes20 marks

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Covers B3.2 Transport

Name:

The elastic walls of arteries help to move blood along. How?

[1]

They absorb blood and then release it slowly
They stretch with each pulse and then recoil
They contract rhythmically like cardiac muscle
They generate the heartbeat in the vessel wall

Describe the distribution of tissues in a transverse section of the stem of a young dicotyledonous plant.

[3]

A leafy shoot was fitted to a potometer and allowed to equilibrate. The distance moved by the air bubble in 5 minutes was recorded under different conditions, with three trials per condition. Water uptake by the shoot closely tracks transpiration.

Condition	Trial 1 / mm	Trial 2 / mm	Trial 3 / mm	Mean / mm
still air, room temperature	22	26	24	24
fan blowing on leaves	58	61	55	58
leaves enclosed in clear plastic bag	8	7	9	8
bright lamp (still air)	39	42	36	39

(a)Compare the effects of the fan and the plastic bag on water uptake, relative to still air.[2]

(b)Explain the effect of the fan in terms of concentration gradients.[2]

(c)Explain why the plastic bag reduced water uptake.[2]

(d)Outline one assumption made when using water uptake as a measure of transpiration, and one reason repeated trials were performed.[2]

Students made peels of the upper and lower epidermis of leaves from four species. Clear nail varnish was painted onto each surface, allowed to dry and peeled off with sticky tape. Each peel was viewed at ×400 and the stomata were counted in five fields of view of known area, then converted to stomatal density in stomata per mm². The bar chart shows the mean stomatal density of each surface for each species.

(a)Calculate the ratio of stomatal density on the lower surface to that on the upper surface for the bean leaf.[1]

(b)Identify two variables that should have been kept constant when counting the stomata.[2]

(c)The water lily leaf floats with its upper surface exposed to the air. Suggest why water lily leaves have stomata only on the upper surface.[2]

(d)Explain how water is drawn up the xylem to replace the water lost through stomata.[3]

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. B3.2.3 [1]

B: elastic stretch stores energy at systole; recoil between beats maintains flow and smooths pressure; (vessel diameter is adjusted by smooth muscle, not rhythmic contraction);

2. B3.2.9 [3 max]

a single-layered epidermis (with cuticle) forms the outer surface;
cortex (parenchyma) lies beneath the epidermis, and pith (parenchyma) fills the centre;
vascular bundles are arranged in a ring near the outside/periphery;
within each bundle, xylem is on the inner side and phloem on the outer side;
(vascular) cambium lies between the xylem and phloem, OWTTE;

3. B3.2.7

(a) [2]
- fan more than doubles uptake (24 → 58 mm);
- bag reduces it to a third (24 → 8 mm), so moving air raises and humid trapped air lowers transpiration, OWTTE;
(b) [2 max]
- moving air removes the (humid) boundary layer of water vapour at the leaf surface;
- (so) the water-vapour concentration gradient between air spaces and atmosphere stays steep;
- diffusion (through stomata) and hence transpiration is faster, drawing more water up the xylem;
(c) [2]
- vapour accumulates inside the bag, so humidity around the leaves rises (toward saturation);
- the gradient for diffusion out of the leaf is (almost) abolished, so transpiration nearly stops, OWTTE;
(d) [2]
- assumption: (almost) all water taken up is lost by transpiration, little is used (photosynthesis/growth) or stored;
- repeats detect anomalies / allow a (more reliable) mean, since bubble readings vary between runs;

4. B3.2.8

(a) [1]
- 7 : 1 / 7;
Accept 6.5–7.5 from reading the bars.
(b) [2 max]
- magnification / area of the field of view;
- position on the leaf where the peel was taken / distance from the midrib;
- age / size of the leaf sampled;
- number of fields of view counted per peel;
Accept any two. Numbered answer slots.
(c) [2 max]
- the lower surface is in contact with water / stomata on the lower surface would be flooded;
- gas exchange (CO₂ uptake / O₂ release) can only occur across the surface exposed to air;
- water loss is not a limiting problem for an aquatic plant, so stomata on the exposed surface are not a disadvantage, OWTTE;
Accept any two.
(d) [3 max]
- water evaporates from (spongy mesophyll) cell walls into the air spaces and diffuses out through stomata / transpiration;
- this creates tension / negative pressure / a pull in the leaf;
- cohesion between water molecules (hydrogen bonding) transmits the tension down the continuous column of water in the xylem;
- adhesion of water to the xylem wall / capillary action helps to hold the column up;
Content pivot. Accept any three.