# Explain how the structure of the alveoli is adapted to allow efficient gas exchange in the lungs.

> AQA A-Level Biology (7402) — 3.3.2 Gas Exchange · Explain · 5 marks

## Mark scheme (5 marks)

1. Alveoli have a large surface area
2. Large surface area allows more gas molecules to diffuse across at once / speeds up rate of diffusion
3. Alveoli have a thin (one cell thick / moist) wall / short diffusion distance
4. Alveoli have a good blood supply / are surrounded by capillaries
5. This maintains a steep concentration gradient (for oxygen and/or carbon dioxide)

## Key terms

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

## 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)

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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-the-structure-of-the-0811c36f) · Published by Druglandscape Ltd.