# Explain why a leaf is adapted to exchange gases efficiently with the surrounding air.

> AQA A-Level Biology (7402) — 3.3.1 Surface Area to Volume Ratio · Explain · 5 marks

> Leaves are the main site of photosynthesis in plants. They must exchange carbon dioxide and oxygen rapidly with the atmosphere.

## Mark scheme (5 marks)

1. Leaves are thin / flat / have a large surface area
2. Large surface area to volume ratio (allows rapid diffusion / increases rate of exchange)
3. Stomata allow gases to enter and leave the leaf
4. Air spaces / spongy mesophyll layer increase the internal surface area for gas exchange
5. Maintaining a concentration gradient / short diffusion distance means gases diffuse quickly

## 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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