# A leaf is a gas exchange surface in plants. Explain how the structure of a leaf is adapted to allow efficient gas exchange.

> OCR A-Level Biology B — Advancing Biology (H422) — 2.4 Gas exchange surfaces · Explain · 5 marks

> Plants need to exchange carbon dioxide and oxygen with their surroundings during photosynthesis and respiration. The leaf is the main gas exchange surface in a plant.

## Mark scheme (5 marks)

1. Stomata are small pores in the epidermis that allow gases to enter and leave the leaf
2. Guard cells control the opening and closing of the stomata, regulating gas exchange
3. The leaf has a large surface area which increases the rate of diffusion of gases
4. The leaf is thin so gases only have a short distance to diffuse to reach the cells
5. Gases (carbon dioxide and oxygen) move by diffusion down a concentration gradient from high to low concentration

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- [Revision notes for OCR A-Level Biology B — Advancing Biology (H422)](https://www.gradenine.co.uk/learn)
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