# Explain how the structure of capillaries is adapted to allow efficient exchange of substances between the blood and body cells.

> Pearson Edexcel A-Level Biology A (9BI0) — 1.2 Heart, blood and blood vessels · Explain · 5 marks

> Capillaries are the smallest blood vessels in the body and form extensive networks within tissues. They are the site of exchange between the blood and the surrounding cells.

## Mark scheme (5 marks)

1. Capillaries have walls that are only one cell thick
2. This short diffusion distance allows substances to diffuse quickly / efficiently between blood and cells
3. Capillaries have a large surface area (due to forming extensive networks / large number of capillaries)
4. A large surface area increases the rate of diffusion / allows more substances to be exchanged at once
5. Substances such as glucose and oxygen diffuse out of the capillaries into cells, and waste products such as carbon dioxide diffuse in

## Key terms

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

## Related

- [Revision notes for Pearson Edexcel A-Level Biology A (9BI0)](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-capillaries-06be1a8c) · Published by Druglandscape Ltd.