# Leaves are adapted to allow efficient gaseous exchange for photosynthesis. Explain how the internal structure of a leaf is adapted to allow carbon dioxide to reach the palisade mesophyll cells as efficiently as possible.

> Eduqas A-Level Biology — 2.4 Adaptations for nutrition · Explain · 5 marks

> Leaves must obtain carbon dioxide from the air and deliver it to the cells that carry out photosynthesis. Several structural features of a leaf work together to make this process as efficient as possible.

## Mark scheme (5 marks)

1. Stomata are pores in the lower epidermis that allow carbon dioxide to diffuse into the leaf
2. The spongy mesophyll has air spaces which allow carbon dioxide to diffuse quickly through the leaf
3. A large concentration gradient is maintained because carbon dioxide is continuously used up in photosynthesis in the palisade cells
4. The palisade mesophyll cells are near the top of the leaf, close to where light enters, and contain chloroplasts for photosynthesis
5. The short diffusion distance from the stomata to the palisade cells means carbon dioxide reaches them quickly

## Key terms

- [palisade mesophyll](https://www.gradenine.co.uk/glossary/palisade-mesophyll)

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Source: [GradeNine](https://www.gradenine.co.uk/q/leaves-are-adapted-to-allow-efficient-5ad40e75) · Published by Druglandscape Ltd.