IB DP Biology: Transport: blood vessels, heart, xylem and phloem (DP Biology) – Practice Questions

These are original questions written for Marlbridge, for revision and practice on this content. They are not reproduced past-paper questions, and they do not replicate the exam’s exact structure, question count or mark tariffs – the IB holds copyright in its own papers. Use these alongside the official past papers available through your school or the IB store.

These questions cover IB Diploma Programme Biology section B3.2 (Transport) from the IB Biology guide, first assessment 2025. Questions 10 to 12 and parts of question 7 are HL only, as marked. Read the study guide first and keep the revision notes beside you. Hub: IB DP Biology. Checklist: printable checklist. To find weak areas first, take the free 10-minute diagnostics.

Questions

1. A micrograph of a vessel has a scale bar of 25 mm that represents 50 µm. The lumen is 42 mm across and the wall is 9 mm thick.

(a) Calculate the magnification. [1] (b) Calculate the actual width of the lumen in µm. [1] (c) Calculate wall thickness ÷ lumen diameter and state whether the vessel is an artery or a vein. [2]

2. Explain how the structure of capillaries is adapted for exchange of materials, including fenestrated capillaries. [3]

3. (a) Explain how elastic fibres in artery walls help to maintain blood flow between heartbeats. [2] (b) Explain why veins have valves but arteries do not. [2]

4. A student counts the radial pulse of a rested person for 15 s, three times: 17, 18 and 16 beats. After exercise the count in 15 s is 31.

(a) Calculate the mean resting heart rate in beats per minute. [1] (b) Calculate the percentage increase after exercise. [2] (c) Suggest two ways to improve the reliability of the measurement. [2]

5. (a) Describe how atherosclerosis develops in a coronary artery. [2] (b) Explain how complete blockage of a coronary artery leads to a heart attack. [3]

6. Region M has 450 new cases of coronary heart disease in a population of 360 000. Region N has 150 in a population of 200 000.

(a) Calculate the rate per 100 000 for each region. [2] (b) Calculate how many times greater the rate in M is than in N, to 3 significant figures. [1] (c) A study of 30 countries found a correlation coefficient of +0.78 linking dietary saturated fat with deaths from coronary heart disease. The same study found r = +0.05 between mean annual rainfall and these deaths. Evaluate what these results show. [3]

7. (a) Explain how water is drawn from the roots to the leaves during transpiration. [5] (b) (HL only) A cut stem exudes 4.2 cm³ of sap in 6 hours on a humid night. Calculate the rate in cm³ per hour. [1] (c) (HL only) Explain how root pressure is generated, and state one condition when it is most useful. [3]

8. A dye moves 14.4 mm along a stem in 2 hours.

(a) Calculate the rate in mm per hour, and in µm per second. [2] (b) Explain three adaptations of xylem vessels for transporting water. [3]

9. (a) Describe the positions of xylem and phloem in a transverse section of a dicotyledonous stem and of a root. [3] (b) State what a plan diagram shows, and give one function of the cortex. [2]

10. (HL only) In a capillary, hydrostatic pressure is 4.0 kPa at the arteriole end and 1.4 kPa at the venule end. The pull of plasma proteins keeps fluid in at 3.4 kPa throughout.

(a) Calculate the net outward force at each end. [2] (b) Explain what the results show about fluid movement. [2] (c) Explain how excess tissue fluid is returned to the circulation. [2] (d) State one difference between plasma and tissue fluid. [1]

11. (HL only) The table shows pressures on the left side of a heart in kPa. One cycle lasts 0.75 s.

Time (s)	Atrium	Ventricle	Aorta
0.10	1.3	1.0	10.5
0.15	0.8	3.0	10.4
0.25	0.9	15.2	14.8
0.45	1.0	4.0	11.5
0.60	1.3	0.6	10.8

(a) Explain why both valves are closed at 0.15 s. [2] (b) Explain why blood leaves the ventricle at 0.25 s. [1] (c) Explain why the semilunar valve is closed at 0.45 s. [1] (d) Explain what happens to the atrioventricular valve between 0.45 s and 0.60 s. [2] (e) Calculate the heart rate. [1] (f) State the role of the pacemaker. [1]

12. (HL only) (a) Outline the path of blood in the single circulation of a bony fish. [2] (b) Explain one advantage of double circulation in mammals. [2] (c) Explain how the structure of sieve tube elements and companion cells helps translocation. [4]

Answers

1. (a) 25 mm = 25 000 µm; 25 000 ÷ 50 = ×500 [1] (b) 42 ÷ 500 = 0.084 mm = 84 µm [1] (c) 9 ÷ 42 = 0.21 [1]; the wall is thick relative to the lumen, so it is an artery [1] Examiner insight: Show the unit conversion and the division. Cite the ratio rather than “it looks thick”.

2. Branching networks give a large surface area [1]; a wall one cell thick and a narrow lumen give a short diffusion distance and slow flow that allows time for exchange [1]; fenestrations (pores) in sites such as kidney glomeruli or villi allow rapid passage of substances [1]. [3] Examiner insight: Link each feature to its effect on exchange. A bare list of “thin, narrow, branched” is weaker.

3. (a) The wall stretches when the ventricle contracts [1]; it recoils afterwards, keeping pressure up and pushing blood on between beats [1] (b) Venous pressure is low, so blood could drift backwards, especially when muscles squeeze veins [1]; valves close to give one-way flow, while arterial pressure already drives blood forwards [1] Examiner insight: Part (b) needs the reason arteries differ, not only what valves do. Compare the two vessels directly.

4. (a) Mean = (17 + 18 + 16) ÷ 3 = 17; 17 × 4 = 68 beats per minute [1] (b) After exercise 31 × 4 = 124 [1]; (124 − 68) ÷ 68 × 100 = 82.4% [1] (c) Rest before counting [1]; use fingertips, not the thumb, and count for longer or repeat and average [1] Examiner insight: For percentage change divide by the original value. Reliability points should be specific actions, not “be careful”.

5. (a) Fatty material (plaque) builds up beneath the lining of the artery [1]; this narrows the lumen and reduces blood flow [1] (b) A plaque can rupture and a clot form that blocks the artery [1]; muscle beyond the blockage gets no oxygen and cannot respire aerobically [1]; the cells die, which is a heart attack [1] Examiner insight: Write the chain of events in order. Naming the heart attack without the loss of oxygen supply leaves out the explanation.

6. (a) M: 450 ÷ 360 000 × 100 000 = 125 [1]; N: 150 ÷ 200 000 × 100 000 = 75 per 100 000 [1] (b) 125 ÷ 75 = 1.67 times [1] (c) r = +0.78 shows a fairly strong positive correlation, supporting a link [1]; it does not prove that saturated fat causes the disease, because other factors such as smoking or inactivity may differ between countries [1]; r = +0.05 shows no relationship with rainfall, which is consistent with no link [1]. [3] Examiner insight: Evaluation answers gain credit for stating both what the data support and what they cannot show. Avoid “proves”.

7. (a) Water evaporates from the walls of mesophyll cells into the air spaces [1]; this lowers water potential in the walls, so water is drawn out of the xylem through the walls by capillary action [1]; tension (negative pressure potential) develops in the xylem [1]; cohesion between water molecules, by hydrogen bonds, keeps the column continuous [1]; the tension pulls the column up from the roots [1] (b) 4.2 ÷ 6 = 0.7 cm³ per hour [1] (c) Root cells actively transport mineral ions into the xylem [1]; this lowers water potential there, so water enters by osmosis and positive pressure builds [1]; useful in humid air, or in spring before leaves open [1]. [3] Examiner insight: Say “pulled” for transpiration and “pushed” for root pressure. Mixing the two directions is a common loss of credit.

8. (a) 14.4 ÷ 2 = 7.2 mm per hour [1]; 7200 µm ÷ 3600 s = 2.0 µm per second [1] (b) No cell contents and incomplete or missing end walls, so water flows without obstruction [1]; lignified walls resist collapse under tension [1]; pits allow water to enter or leave sideways [1]. [3] Examiner insight: For “explain”, each adaptation needs its reason. State both parts.

9. (a) Stem: vascular bundles in a ring, xylem towards the inside and phloem towards the outside [1]; root: vascular tissue in a central core [1]; xylem often star-shaped with phloem between its arms [1] (b) It shows the arrangement and proportions of tissues, not individual cells [1]; the cortex stores food or provides a route for water [1] Examiner insight: Position words matter. Write “inside”, “outside” and “centre” rather than only naming tissues.

10. (a) Arteriole end: 4.0 − 3.4 = +0.6 kPa [1]; venule end: 1.4 − 3.4 = −2.0 kPa [1] (b) Net force is outward at the arteriole end, so fluid leaves and forms tissue fluid [1]; it is inward at the venule end, so much fluid returns [1] (c) Lymph capillaries have thin walls with gaps, so excess fluid enters [1]; valves prevent backflow and lymph returns to the blood near the heart [1] (d) Plasma contains more protein than tissue fluid (or: tissue fluid has no red blood cells) [1] Examiner insight: Give the sign of each net value and say what it means.

11. (a) Ventricular pressure (3.0) exceeds atrial pressure (0.8), closing the atrioventricular valve [1]; it is below aortic pressure (10.4), so the semilunar valve stays shut [1] (b) Ventricular pressure (15.2) exceeds aortic pressure (14.8), opening the semilunar valve [1] (c) Aortic pressure (11.5) exceeds ventricular pressure (4.0) [1] (d) By 0.60 s ventricular pressure (0.6) has fallen below atrial pressure (1.3) [1]; the atrioventricular valve opens and the ventricle fills [1] (e) 60 ÷ 0.75 = 80 beats per minute [1] (f) The sinoatrial node starts each heartbeat, triggering atrial contraction [1] Examiner insight: Quote the pressures from the table when explaining valve positions.

12. (a) Heart to gill capillaries, then to the body capillaries [1]; then back to the heart, so blood passes through the heart once per circuit [1] (b) The heart pumps blood again after the lungs, restoring pressure [1]; so blood reaches body tissues faster, supporting high metabolic rates [1] (c) Sieve plates have pores, so sap passes between cells [1]; little cytoplasm, few organelles and no nucleus reduce obstruction to flow [1]; companion cells have many mitochondria that supply ATP for active loading [1]; plasmodesmata connect companion cells to sieve tube elements [1]. [4] Examiner insight: Pair each cell feature with its effect on flow or loading. A list of features without effects is incomplete.

Where marks are usually lost

• Comparing artery and vein wall thickness without the lumen.
• Forgetting units after micrograph calculations.
• Dividing a percentage change by the new value, not the original.
• Comparing case numbers instead of rates per head.
• Stating that a strong correlation proves causation.
• Describing transpiration as pushing.
• Not interpreting the sign of a net pressure.
• Explaining valve positions without citing which pressure is greater.
• Leaving out the reason behind each phloem adaptation.

Next steps

• Re-read the revision notes.
• Review the study guide.
• Course hub: IB DP Biology.
• Tick off topics on the printable checklist.
• Take the free 10-minute diagnostics.
• Book a free trial class.

Official syllabus

This resource follows the IB Diploma Programme Biology guide, first assessment 2025, published by the International Baccalaureate Organization.