# Explain how the structure of a vein is adapted to allow blood to flow back to the heart.

> WJEC A-Level Biology (Wales) — 2.4 Adaptations for nutrition · Explain · 5 marks

> Veins carry deoxygenated blood from the body's tissues back to the heart. Unlike arteries, veins carry blood at low pressure.

## Mark scheme (5 marks)

1. Veins have thin walls / thin muscle and elastic layer because blood is at low pressure
2. Veins contain valves
3. Valves prevent backflow of blood (so blood moves in one direction towards the heart)
4. Veins have a large lumen (wide central channel)
5. The large lumen allows blood to flow easily / at low pressure back to the heart

## Key terms

- [vein](https://www.gradenine.co.uk/glossary/vein)

## Related

- [Revision notes for WJEC A-Level Biology (Wales)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-the-structure-of-a-1af15634) · Published by Druglandscape Ltd.