# Explain how the structure of alveoli makes them well adapted for efficient gaseous exchange in the lungs.

> OCR GCSE Biology A: Gateway Science (J247) — B2.1 Supplying the cell · Explain · 4 marks

> The lungs are the site of gaseous exchange in mammals. Oxygen must pass from the air into the blood, and carbon dioxide must pass from the blood into the air. This exchange happens across the walls of the alveoli.

## Mark scheme (4 marks)

1. Alveoli provide a large surface area
2. A large surface area increases / speeds up the rate of diffusion
3. Alveoli walls are very thin / one cell thick
4. A steep concentration gradient is maintained (e.g. by the blood supply / continuous blood flow removing oxygen)

## Key terms

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

## Related

- [Revision notes for OCR GCSE Biology A: Gateway Science (J247)](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-5dd1eab2) · Published by Druglandscape Ltd.