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

> WJEC A-Level Biology (Wales) — 2.3 Adaptations for transport in plants and animals · Describe · 5 marks

## Mark scheme (5 marks)

1. Arteries have thick muscle and elastic layers / thick walls to withstand or maintain high blood pressure / prevent bursting
2. Arteries carry blood away from the heart (under high pressure)
3. Veins have thin muscle and elastic layers / thin walls because blood is at low pressure
4. Veins contain valves to prevent backflow of blood
5. Capillaries have a thin wall / small diameter / thin lumen to decrease diffusion distance, allowing exchange of substances between 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)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

---
Source: [GradeNine](https://www.gradenine.co.uk/q/describe-how-the-structure-of-arteries-606b79fe) · Published by Druglandscape Ltd.