Leaf structureSpec 6.11B
In short
A leaf is adapted to absorb light for photosynthesis and to allow gas exchange. It is broad, flat and thin, giving a large surface area and a short diffusion distance. Palisade mesophyll cells near the top have many chloroplasts, air spaces in the spongy mesophyll let gases diffuse, and the waxy cuticle reduces water loss.
A leaf is adapted to absorb light for photosynthesis and to allow gas exchange of carbon dioxide and oxygen.
| Structure | Adaptation | How it helps |
|---|---|---|
| Whole leaf | Broad, flat and thin | Large surface area to absorb light, and a short distance for gases to diffuse |
| Waxy cuticle | A waxy, waterproof layer on the surface | Reduces water loss by evaporation |
| Upper epidermis | A thin layer of transparent cells | Lets light through to the cells underneath |
| Palisade mesophyll | Tightly packed, tall cells near the top of the leaf, with many chloroplasts | Most photosynthesis takes place here, close to the light |
| Spongy mesophyll | Loosely arranged cells with air spaces between them | Carbon dioxide can diffuse through the leaf to the cells, and oxygen can diffuse out |
| Stomata and guard cells | Pores, mostly in the lower epidermis, opened and closed by guard cells | Allow gases to enter and leave, and control water loss |
| Xylem and phloem (veins) | Vascular bundles running through the leaf | Xylem brings water for photosynthesis. Phloem carries sucrose away. |
(opens full size in a new tab)Exam tip:
Always give an adaptation and the reason it helps. For example, 'the air spaces in the spongy mesophyll allow carbon dioxide to diffuse to the photosynthesising cells'.
Written and checked against the Edexcel GCSE Biology (1BI0) specification · Updated October 2026