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

> Pearson Edexcel International GCSE Biology (4BI1) — 2.9 Gas exchange: humans · Explain · 4 marks

## Mark scheme (4 marks)

1. Large surface area (of alveoli) allows more gas molecules to diffuse simultaneously
2. Thin walls (one cell thick) give a short diffusion distance / pathway for gases
3. Rich blood supply / dense capillary network maintains a steep concentration gradient for both oxygen and carbon dioxide
4. Moist lining allows gases to dissolve before diffusing across the membrane

## Key terms

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

## Related

- [Revision notes for Pearson Edexcel International GCSE Biology (4BI1)](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-fcca8c91) · Published by Druglandscape Ltd.