# Explain how the alveoli in the lungs are adapted for efficient gas exchange.

> Eduqas A-Level Biology — 2.2 Adaptations for gas exchange · Explain · 5 marks

> The lungs contain millions of tiny air sacs called alveoli. Oxygen must move from the air inside the alveoli into the blood, and carbon dioxide must move from the blood into the alveoli.

## Mark scheme (5 marks)

1. Large surface area (of the alveoli) allows more molecules to diffuse across at once
2. Thin walls / short diffusion distance so gases diffuse across quickly
3. Moist lining so gases can dissolve before diffusing across the membrane
4. Good blood supply / capillaries carry oxygen away, maintaining a large concentration gradient
5. Ventilation maintains a large concentration gradient by replacing air in the alveoli / keeping carbon dioxide concentration low in the alveoli

## Related

- [Revision notes for Eduqas A-Level Biology](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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