# Explain how the structure of a capillary is adapted to allow the exchange of substances between the blood and the body's tissues.

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

## Mark scheme (5 marks)

1. Capillary walls are only one cell thick / very thin walls
2. This decreases the diffusion distance (so substances can move quickly between blood and tissues)
3. Capillaries have a large (total) surface area
4. This allows more molecules to diffuse across at once / increases rate of exchange
5. Blood flow through capillaries is slow, allowing more time for exchange to take place

## Key terms

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

## 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)

---
Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-the-structure-of-a-55792b71) · Published by Druglandscape Ltd.