Explain how the structure of arteries and veins makes each vessel suited to its function in the circulatory system.

Pearson Edexcel A-Level Biology A (9BI0) — Topic 4 Exchange and Transport · Explain · 5 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Arteries carry blood away from the heart under high pressure, while veins return blood to the heart under low pressure.

Model answer (5 marks)

Arteries have thick walls made up of several layers of smooth muscle and elastic fibres. The elastic fibres allow the wall to stretch when the heart ejects blood and then recoil, which helps to maintain a high pressure and a continuous flow of blood.

Veins have comparatively thin walls and a wider lumen. The thin wall reduces the resistance to flow, which is useful when the pressure is low. Veins also contain valves that prevent back‑flow and help the blood to move towards the heart against gravity.

Examiner tips

  • Use the terms "thick walls", "smooth muscle", "elastic fibres" for arteries and "thin walls", "wide lumen", "valves" for veins. Show the functional link to pressure and flow. Keep the answer concise and to the point.

Common mistakes

  • Confusing the roles of arteries and veins, e.g. saying arteries are low pressure. Omitting the valve function in veins or the elastic recoil of arteries.

Mark scheme (5 marks)

  1. Arteries have thick walls containing thick layers of smooth muscle and elastic fibres
  2. This allows artery walls to withstand / stretch and recoil with the high pressure of blood pumped from the heart
  3. Veins have thinner walls than arteries / relatively thin walls
  4. Veins have a wider lumen than arteries (of comparable size)
  5. Veins contain valves to prevent the backflow of blood and ensure blood moves towards the heart under low pressure

Key terms in this question

vein

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