# Explain how the structure of the alveoli makes them well suited for gas exchange.

> Eduqas GCSE Biology — 1.2.2 The respiratory system · Explain · 4 marks

## Mark scheme (4 marks)

1. Large surface area (of alveoli / many alveoli present) allows more gas to diffuse at once
2. Thin walls (one cell thick) so diffusion distance is short / gases diffuse quickly
3. Good blood supply (dense capillary network) maintains a concentration gradient for 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 Eduqas GCSE Biology](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-the-structure-of-the-def3f977) · Published by Druglandscape Ltd.