Veins contain valves, whereas arteries do not. Explain why veins need valves to function correctly and why arteries do not require them.

Cambridge International IGCSE Biology (0610) — 9.3 Blood vessels · Explain · 4 marks · View as Markdown

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

Model answer (4 marks)

Veins carry blood at low pressure, so without a mechanism the blood could flow back towards the tissues when the heart relaxes. The valves in veins therefore prevent back‑flow and keep the blood moving in one direction, towards the heart.

Arteries, on the other hand, are under high pressure when the heart contracts. The high pressure keeps the blood moving forward and the thick, elastic and muscular walls of arteries maintain this pressure, so back‑flow does not occur and valves are unnecessary.

Examiner tips

  • Use the word ‘low pressure’ for veins and ‘high pressure’ for arteries to show understanding of the pressure difference.
  • Mention that valves prevent back‑flow in veins and that arterial walls maintain pressure to keep flow unidirectional.
  • Keep the answer concise – 4 marks can be earned with two short sentences per vessel type.
  • Use the exact terminology: ‘valves’, ‘low pressure’, ‘high pressure’, ‘elastic and muscular walls’.

Mark scheme (4 marks)

  1. Blood in veins travels at low pressure, so valves are needed to prevent backflow of blood towards the tissues.
  2. Valves in veins ensure blood flows in one direction, towards the heart.
  3. Blood in arteries is under high pressure, so backflow does not occur.
  4. The thick elastic and muscle walls of arteries maintain this high pressure, so valves are not needed.

Key terms in this question

vein · valve

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