# A leaf is adapted for efficient gas exchange. Describe the adaptations of a leaf that allow efficient gas exchange between the leaf and the surrounding air.

> WJEC A-Level Biology (Wales) — 2.2 Adaptations for gas exchange · Describe · 5 marks

> Leaves are the main organs of gas exchange in plants. Carbon dioxide must enter the leaf for photosynthesis, and oxygen and water vapour must be able to leave.

## Mark scheme (5 marks)

1. Stomata are present on the lower epidermis / lower surface of the leaf, which allow gases to diffuse in and out
2. Guard cells control the opening and closing of stomata, regulating gas exchange
3. The spongy mesophyll layer has air spaces which allow fast diffusion of gases through the leaf
4. The large surface area of the leaf / many stomata increases the rate of diffusion / amount of gas exchanged
5. The waxy cuticle reduces water loss but does not prevent gas exchange through the stomata / cells are moist which allows gases to dissolve before diffusing across the membrane

## Related

- [Revision notes for WJEC A-Level Biology (Wales)](https://www.gradenine.co.uk/learn)
- [How to answer "Describe" 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/a-leaf-is-adapted-for-efficient-0e11be33) · Published by Druglandscape Ltd.