Explain how the structure of a vein is related to its function in returning blood to the heart.

Pearson Edexcel A-Level Biology A (9BI0) — 1.3 Mass transport in animals · Explain · 5 marks · View as Markdown

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

Veins carry blood from the body's organs back towards the heart. The blood in veins is at a lower pressure than the blood in arteries.

Model answer (5 marks)

Veins have a wide lumen, which reduces resistance to flow and allows blood to return to the heart easily even at low pressure.
The walls of veins are thin and contain less muscle and elastic tissue than arteries, which is adequate because the blood pressure in veins is low.
Veins also contain valves that prevent backflow, ensuring that blood moves in one direction towards the heart.

Examiner tips

  • Use the word "wide lumen" and explain its effect on resistance. Mention the thin walls and low pressure. Include the role of valves in preventing backflow.
  • Use correct terminology: lumen, resistance, valves, low pressure, thin walls.

Mark scheme (5 marks)

  1. Veins have a wide lumen / large internal diameter
  2. Wide lumen reduces resistance to flow / allows blood to flow easily back to the heart at low pressure
  3. Veins have thin walls / less muscle / less elastic tissue than arteries
  4. Thin walls are sufficient because the blood is at low pressure / there is no need to withstand high pressure
  5. Veins contain valves to prevent the backflow of blood / to ensure blood travels in one direction towards the heart

Key terms in this question

vein

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