A Level Biology: Transport in mammals — Practice Questions (Cambridge 9700)

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 — Cambridge International holds copyright in its own papers. Use these alongside the official past papers available from your board.

Each question practises a skill tested in the June 2024 Paper 22. After each answer there is an examiner insight, a mark-scheme insight or a tip and, where one matches, the real question to try next.

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Questions

1. A student uses a light microscope to look at a stained section of heart muscle and sees several blood vessels of different sizes. State two features the student could use to identify one of the vessels as a capillary. [2]

2. A red blood cell has a diameter of 7.5 μm. A capillary in the brain has a lumen 0.0055 mm wide. Using calculated values with units, explain whether the red blood cell can pass through this capillary without changing shape. [2]

3. Cardiac muscle cells in the wall of the left ventricle respire aerobically at a high rate. Explain how the structure of the capillaries in this tissue is related to their function. [3]

4. Some patients who need kidney dialysis have a short operation in which a vein in the forearm is joined directly to a nearby artery, so that blood from the artery flows straight into the vein. Over the next few weeks, the wall of this vein becomes thicker and more muscular. Suggest why this change to the vein wall is an advantage to the patient. [3]

5. Compare the structure of the wall of an artery with the wall of a vein, and give one feature found in veins but not in arteries. [3]

6. Blood contains 15 g of haemoglobin per 100 cm³. Each gram of haemoglobin can carry 1.34 cm³ of oxygen when fully saturated. Blood leaving the lungs is 98% saturated and blood leaving a resting muscle is 70% saturated. Calculate the volume of oxygen released to the muscle from each 100 cm³ of blood. Show your working. [3]

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Answers

1. Any two: the wall is a single layer of endothelial cells (one cell thick) [1]; red blood cells pass in single file / the lumen is about the same width as one red blood cell [1]; there is no smooth muscle or elastic tissue in the wall (no tunica media or tunica externa) [1].

Examiner insight (Cambridge 9700 June 2024 examiner report, Paper 22, Question 1(c)): Red blood cells in single file and a lumen the width of one red blood cell were the most common correct features. “The capillary is one cell thick”, “a thin membrane” or “cell wall” were not precise enough: describe the wall as a single layer of endothelial cells. Examiners also wanted “red blood cells” written in full, not “rbc”.

Source for the examiner insights on this page: Cambridge International AS & A Level Biology 9700 June 2024 Principal Examiner Report for Teachers, Paper 9700/22 section, paraphrased.

Try the real question next: Cambridge International AS & A Level Biology 9700, June 2024, Paper 22, Question 1(c)(i).

2. 0.0055 mm × 1000 = 5.5 μm [1]. The red blood cell (7.5 μm) is 2.0 μm wider than the lumen, so it cannot pass through without changing shape; it must bend or squeeze through [1].

Mark-scheme insight (Cambridge 9700 June 2024 mark scheme, Paper 22, Question 1(b)(ii)): In a similar “explain whether” question, the mark needed the decision backed by numerical values with units (the mark scheme’s examples convert both to the same unit). A plain “yes” or “no” was not enough.

Source for the mark-scheme insights on this page: Cambridge International AS & A Level Biology 9700 June 2024 mark scheme for Paper 22 (9700/22), paraphrased. Cambridge’s 9700 past papers page publishes the Paper 21 mark scheme from this series, not the Paper 22 one.

Try the real question next: Cambridge International AS & A Level Biology 9700, June 2024, Paper 22, Question 1(b)(ii).

3. Any three: the capillaries supply oxygen and glucose and remove carbon dioxide [1]; the wall is one endothelial cell thick, so the diffusion distance is short [1]; gaps between endothelial cells let plasma leak out to form tissue fluid, which bathes the muscle cells [1]; capillaries are narrow and form a dense network, so every muscle cell is close to one [1]; the narrow lumen slows red blood cells and presses them against the wall, giving more time and a shorter distance for oxygen to diffuse to the cells [1].

Examiner insight (Cambridge 9700 June 2024 examiner report, Paper 22, Question 1(c)(ii)): The strongest answers named substances delivered or removed, then linked each feature to its benefit. “Easier” or “faster” was not enough without the idea of a short distance. Small size had to be linked to reaching all the cells, because other vessels also run close to tissues.

Try the real question next: Cambridge International AS & A Level Biology 9700, June 2024, Paper 22, Question 1(c)(ii).

4. Any three: the vein now receives blood directly from an artery, at a much higher pressure than normal venous blood [1]; a thicker wall can withstand this pressure, so it is less likely to burst or swell, and it can be used for dialysis for longer [1]; the wall gains more smooth muscle and elastic fibres, so it can stretch and recoil, keeping blood moving forward and evening out the pressure [1]; more collagen in the outer layer adds strength [1].

Examiner insight (Cambridge 9700 June 2024 examiner report, Paper 22, Question 6(c)(ii)): In a related question about a vein used in a bypass graft, most candidates linked the thickening to higher blood pressure, but “withstand pressure” on its own was not detailed enough. Stronger answers named extra smooth muscle or elastic fibres, and a few went on to explain how these let the vein replace an artery.

Try the real question next: Cambridge International AS & A Level Biology 9700, June 2024, Paper 22, Question 6(c)(ii).

5. An artery has a thicker wall with a thicker layer of smooth muscle and elastic fibres (tunica media) than a vein [1]. An artery has a narrower lumen relative to its wall thickness, while a vein has a wide lumen and thin wall [1]. Veins have valves to prevent backflow, and arteries do not [1].

Tip: In a “compare” question, write each point as a matched pair (“artery … whereas vein …”), not two separate descriptions.

6. Oxygen at full saturation = 15 × 1.34 = 20.1 cm³ per 100 cm³ [1]. Leaving the lungs: 20.1 × 0.98 = 19.7 cm³; leaving the muscle: 20.1 × 0.70 = 14.1 cm³ [1]. Oxygen released = 5.6 cm³ per 100 cm³ of blood (20.1 × 0.28 = 5.628) [1].

Tip: You can take the difference in saturation first (98% − 70% = 28%) and multiply once, which gives fewer rounding errors.

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Where marks are usually lost

• Describing a capillary as “one cell thick” or “a thin membrane” instead of a wall made of a single layer of endothelial cells.
• Giving a yes or no answer to an “explain whether” question without converting units and quoting both values.
• Saying diffusion is “easier” or “faster” instead of naming a short diffusion distance.
• Writing “to withstand pressure” without explaining which tissues increase and why.
• Using abbreviations such as “rbc” instead of writing “red blood cells” in full.