Explain how the structure of arteries and veins is related to their function in the circulatory system.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Arteries carry blood away from the heart at high pressure, while veins return blood to the heart at low pressure.
Model answer (5 marks)
1. Arteries have thick, muscular and elastic walls.
2. The thick walls allow arteries to withstand and cope with the high pressure of blood pumped from the heart.
3. Veins have valves in their walls.
4. The valves prevent back‑flow, ensuring blood moves in one direction toward the heart.
5. Capillaries have walls that are only one cell thick, which allows substances to diffuse between the blood and body cells or tissues.
2. The thick walls allow arteries to withstand and cope with the high pressure of blood pumped from the heart.
3. Veins have valves in their walls.
4. The valves prevent back‑flow, ensuring blood moves in one direction toward the heart.
5. Capillaries have walls that are only one cell thick, which allows substances to diffuse between the blood and body cells or tissues.
Examiner tips
- Use the exact terms "thick muscular/elastic walls" and "valves". Mention the pressure difference for arteries. Explain the one‑cell‑thick wall of capillaries. Keep each point short and to the point.
Common mistakes
- Confusing the function of arteries and veins. Omitting the role of valves. Not stating that capillary walls are one cell thick.
Mark scheme (5 marks)
- Arteries have thick muscular / elastic walls
- Thick walls of arteries withstand / cope with high blood pressure (from the heart)
- Veins have valves
- Valves prevent the backflow of blood (so blood flows in one direction towards the heart)
- Capillaries have walls that are one cell thick, allowing substances to diffuse between the blood and body cells / tissues
Key terms in this question
Related
- All Edexcel A-Level Biology A: Salters-Nuffield (9BN0) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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