# Explain how the structure of alveoli makes them well adapted as an exchange surface for gases in the lungs.

> Pearson Edexcel A-Level Biology A (9BI0) — Topic 4 Exchange and Transport · Explain · 5 marks

## Mark scheme (5 marks)

1. Alveoli have a large surface area
2. Large surface area increases the rate of diffusion (of oxygen/carbon dioxide)
3. Alveoli have thin walls, which reduces the diffusion distance
4. Alveoli have a good (rich) blood supply / are surrounded by capillaries
5. The good blood supply maintains a steep concentration gradient for oxygen/carbon dioxide, allowing continuous diffusion

## Key terms

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

## 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-alveoli-20a06005) · Published by Druglandscape Ltd.