# Explain how the structure of a leaf is adapted for efficient gas exchange.

> AQA A-Level Biology (7402) — 3.3.2 Gas Exchange · Explain · 5 marks

## Mark scheme (5 marks)

1. Stomata (pores) allow gases to enter and leave the leaf
2. The stomata can open and close to control the rate of gas exchange (and water loss)
3. The spongy mesophyll layer has air spaces which increase the surface area for gas exchange
4. The large surface area of mesophyll cells (in contact with air spaces) maintains a short diffusion distance
5. Leaves are thin / flat, so gases only need to diffuse a short distance to reach all cells

## Related

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