# Describe how the structure of arteries, veins and capillaries is adapted to their functions in the human circulatory system.

> WJEC A-Level Biology (Wales) — 2.1 Classification and biodiversity · Describe · 5 marks

## Mark scheme (5 marks)

1. Arteries have thick muscle and elastic layers / thick walls to withstand and maintain high blood pressure (or to prevent bursting).
2. Arteries carry blood away from the heart at high pressure.
3. Veins have thin walls / thin muscle and elastic layer because blood is at low pressure.
4. Veins contain valves to prevent backflow of blood.
5. Capillaries have a thin wall / narrow lumen to decrease diffusion distance, allowing exchange of substances between the blood and tissues.

## 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 "Describe" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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Source: [GradeNine](https://www.gradenine.co.uk/q/describe-how-the-structure-of-arteries-f3b80b58) · Published by Druglandscape Ltd.