# Explain how the structure of a capillary is adapted for the exchange of substances between the blood and body cells.

> AQA A-Level Biology (7402) — 3.3.4 Mass Transport · Explain · 5 marks

## Mark scheme (5 marks)

1. Capillaries have walls that are only one cell thick
2. This gives a short diffusion distance (so substances can move quickly/easily between blood and cells)
3. Capillaries have a large surface area (due to forming an extensive network throughout tissues)
4. This increases the rate of diffusion / exchange of substances
5. Blood flow through capillaries is slow, giving more time for exchange of substances

## Key terms

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

## Related

- [Revision notes for AQA A-Level Biology (7402)](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-125de2ae) · Published by Druglandscape Ltd.