OCR GCSE Biology A: Exchange surfaces and the human circulatory system (J247) – 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 – examination boards hold copyright in their own papers. Use these alongside the official past papers from your board or school.

These questions cover statements B2.2a to B2.2e of OCR GCSE (9-1) Gateway Science Biology A (J247), specification Version 4.0 (August 2026), for first assessment in 2018. No statement in this unit is Higher Tier only, so every question suits both tiers. Learn the content first from the study guide or the revision notes. Course pages: OCR GCSE Biology hub, checklist and free diagnostics.

Questions

1. A cube-shaped model organism has sides of 10 mm. Calculate its surface area, its volume and its surface area : volume ratio. [3]

2. A second model organism is a cube with sides of 20 mm. Its surface area is 2400 mm² and its volume is 8000 mm³.

(a) Calculate its surface area : volume ratio. [1] (b) Compare this ratio with your answer to question 1. [1] (c) Explain what this tells you about oxygen supply in a very large organism. [2]

3. Two blocks of tissue each have a volume of 60 mm³. Block X is a flat slab measuring 20 mm by 6 mm by 0.5 mm. Block Y measures 6 mm by 5 mm by 2 mm. Calculate the surface area : volume ratio of each block to 2 significant figures, and state which shape is better suited to gas exchange across its surface. [4]

4. Cubes of agar containing an indicator are left in dilute acid. After a fixed time the acid has reached 3 mm in from every face of each cube. Calculate the percentage of the volume reached by the acid in a 10 mm cube and in a 20 mm cube, then explain what the results show. [5]

5. Name one substance in each case.

(a) A gas that diffuses from the water into the blood in a fish’s gills. [1] (b) A waste substance carried in blood plasma from the liver to the kidneys. [1] (c) A dissolved food molecule absorbed from the human small intestine. [1] (d) A mineral ion taken up by plant roots and used to make amino acids. [1]

6. Blood leaves the right ventricle of the heart. Describe the route it takes until it arrives at the left ventricle. [4]

7. Explain why mammals have a double circulatory system. [4]

8. This question is about the human heart.

(a) Name the vessel that brings oxygenated blood to the left atrium. [1] (b) Name the valve that lets blood pass from the left atrium into the chamber below it. [1] (c) Name the vessel that carries deoxygenated blood away from the heart. [1] (d) Name the vessels that supply the cardiac muscle with oxygen. [1] (e) The muscle in the wall of the left ventricle is much thicker than in the right ventricle. Explain the reason. [2]

9. An artery has a wall 1.5 mm thick and a lumen 3.0 mm across. A vein has a wall 0.2 mm thick and a lumen 5.0 mm across.

(a) Calculate wall thickness ÷ lumen width for each vessel. [2] (b) Explain how the structure of the artery wall suits its function. [2] (c) Explain why the vein contains valves. [1]

10. Data for one body: the aorta has a cross-sectional area of about 4 cm², while all the capillaries together present about 4000 cm².

(a) Calculate how many times larger the capillary area is. [1] (b) Explain why blood moves slowly through the capillaries and why this is useful. [3]

11. (a) Explain how two features of a red blood cell help it to transport oxygen. [4] (b) Name three substances, other than blood cells, carried in blood plasma. [3]

12. A student counts her pulse. At rest she counts 35 beats in 30 seconds. After exercise she counts 29 beats in 15 seconds.

(a) Calculate her heart rate at rest, in beats per minute. [2] (b) Calculate her heart rate after exercise in beats per minute. [2] (c) Explain why her heart rate rises during exercise. [4]

Answers

1. Surface area = 6 × 10 × 10 = 600 mm² [1]. Volume = 10 × 10 × 10 = 1000 mm³ [1]. Ratio = 600 ÷ 1000 = 0.6 : 1 [1]. [3] Examiner insight: Show surface area and volume before dividing. A bare ratio leaves no working to give credit to if there is a slip, and area and volume should carry units.

2. (a) 2400 ÷ 8000 = 0.3 : 1 [1]. (b) The ratio has halved (0.6 to 0.3) when the side doubled [1]. (c) In a large organism the surface area is small compared with the volume [1], and the distance from the surface to inner cells is long, so diffusion alone is too slow to supply them [1]. [4] Examiner insight: A good answer to (c) ties the ratio to diffusion distance. “It is bigger so it needs more oxygen” does not explain the need for exchange surfaces.

3. Block X surface area = 2(120 + 3 + 10) = 266 mm² [1]; ratio = 266 ÷ 60 = 4.4 : 1 [1]. Block Y surface area = 2(30 + 12 + 10) = 104 mm²; ratio = 104 ÷ 60 = 1.7 : 1 [1]. Block X, the flat slab, is better because the larger ratio and short distance from surface to centre give faster diffusion [1]. [4] Examiner insight: Round only at the end, to the figures the question asks for. Giving the final answer without the ratio for both blocks leaves the comparison unsupported.

4. 10 mm cube: the unreached core is 10 − 6 = 4 mm across, so its volume is 4 × 4 × 4 = 64 mm³ [1]. Reached = (1000 − 64) ÷ 1000 × 100 = 93.6% [1]. 20 mm cube: core is 14 mm across, so 14 × 14 × 14 = 2744 mm³ [1]. Reached = (8000 − 2744) ÷ 8000 × 100 = 65.7% [1]. The smaller cube is reached more completely in the same time, because its larger surface area : volume ratio and shorter diffusion distance help the acid reach the centre; this models why large organisms need transport systems [1]. [5] Examiner insight: A common slip is to subtract 3 mm, not 6 mm, to find the core, because the acid enters from both faces. Show the core width.

5. (a) Oxygen [1]. (b) Urea [1]. (c) Glucose (or an amino acid) [1]. (d) Nitrate [1]. [4] Examiner insight: Give a named substance. “Food” or “minerals” is too vague to credit, and carbon dioxide would not answer (a).

6. The blood goes from the right ventricle into the pulmonary artery [1]. It passes through capillaries around the alveoli in the lungs, where it picks up oxygen and loses carbon dioxide [1]. It returns in the pulmonary vein [1] to the left atrium, and then passes to the left ventricle [1]. [4] Examiner insight: Name the vessels and chambers in order. Writing that the blood “goes to the lungs and back” does not show the route.

7. Blood loses pressure as it passes through the narrow capillaries of the lungs [1]. Returning it to the heart lets it be pumped again at high pressure [1] so it reaches the body quickly [1]. It also keeps oxygenated blood apart from deoxygenated blood [1]. [4] Examiner insight: The idea of pressure loss in the lung capillaries is the key point. Saying “blood goes round twice” restates the question.

8. (a) Pulmonary vein [1]. (b) Bicuspid valve (mitral valve) [1]. (c) Pulmonary artery [1]. (d) Coronary arteries [1]. (e) The left ventricle sends blood round the whole body [1], needing a higher pressure than the short trip to the lungs, so more muscle is needed [1]. [6] Examiner insight: “Thicker to pump harder” is incomplete. Say where each ventricle sends blood.

9. (a) Artery: 1.5 ÷ 3.0 = 0.5 [1]. Vein: 0.2 ÷ 5.0 = 0.04 [1]. (b) The thick wall contains muscle and elastic fibres which stretch as blood surges through [1] and recoil, so the wall withstands high pressure and helps move blood on [1]. (c) Venous blood is under low pressure, so valves are needed to prevent it flowing backwards [1]. [5] Examiner insight: Do not write that the artery is “stronger” without saying what makes it so. Name the elastic fibres and link them to pressure.

10. (a) 4000 ÷ 4 = 1000 times [1]. (b) The same flow of blood is spread across a very large total area [1], so it moves slowly even though each capillary is narrow [1]. This gives time for oxygen and food molecules to diffuse out and wastes to diffuse in [1]. [4] Examiner insight: Examiners look for total cross-sectional area. A reply based on narrow diameter alone points the wrong way, since narrow tubes by themselves would not slow the blood.

11. (a) Biconcave shape gives a large surface area for fast diffusion of oxygen [1] and flexibility to squeeze through capillaries [1]. No nucleus leaves more room for haemoglobin [1], which binds oxygen at the lungs and gives it up in the tissues [1]. (Any two features with their explanations earn full marks.) (b) Any three from: carbon dioxide, glucose, amino acids, mineral ions, urea, hormones [3]. [7] Examiner insight: For each feature, give the feature and then its effect. Naming a feature alone shows recall, so the explanation is what answers “how does it help”.

12. (a) 35 × 2 = 70 beats per minute [1][1]. (b) 29 × 4 = 116 beats per minute [1][1]. (c) Muscles respire faster during exercise [1] and need more oxygen and glucose [1]. The heart beats faster to pump blood to them more quickly [1] and carry carbon dioxide away to the lungs for removal [1]. [8] Examiner insight: Convert to a full minute first. Comparing 35 and 29 directly gives the wrong impression, because the times differ.

Where marks are usually lost

• Saying the surface area : volume ratio rises as an organism gets bigger.
• Giving a ratio with no surface area or volume shown.
• Mixing up which pulmonary vessel carries oxygenated blood.
• Writing “valve” without naming bicuspid, tricuspid or semilunar.
• Saying the left ventricle is thicker “because it is stronger” with no reference to the body.
• Explaining slow capillary flow by narrowness alone.
• Naming a red blood cell feature with no effect on function.
• Omitting units or the time conversion in rate questions.

Next steps

• Revision notes
• Study guide
• OCR GCSE Biology hub and checklist
• All free 10-minute diagnostics
• Book a free trial class

Official syllabus

These questions follow OCR GCSE (9-1) Gateway Science Biology A (J247) specification, Version 4.0 (August 2026), for first assessment in 2018, published by OCR: statements B2.2a to B2.2e.