Leaf structure

The structure of a leaf has adaptations so that it can carry out photosynthesis effectively.

A leaf needs:

  • a way to transport water to the leaf, and glucose to other parts of the plant
  • a way to exchange carbon dioxide and oxygen
  • the ability to absorb light energy efficiently

Transport

Xylem tissue delivers water from the roots to the leaf, and phloem tissue transports glucose away from the leaf. These tissues form vascular bundles in the plant.

Cross-section of a plant root, showing a vascular bundle of xylem and phloem in the centre.

Gas exchange

Gas exchange happens in the spongy mesophyll tissue of the leaf. Spongy mesophyll cells are covered by a thin layer of water and loosely packed.

When the plant is photosynthesising during the day, these features allow carbon dioxide to diffuse into the spongy mesophyll cells, and oxygen to diffuse out of it.

To get to the spongy mesophyll cells inside the leaf, gases diffuse through small pores called stomata. They also open or close to control the loss of water from leaf by the process of transpiration.

Absorbing light energy

Light absorption happens in the palisade mesophyll tissue of the leaf. Palisade cells are column shaped and packed with many chloroplasts. They are arranged closely together so that a lot of light energy can be absorbed.

Sunlight hits top level waxy cuticle, below this is upper epidermis, palisade mesophyll, spongy mesophyll, lower epidermis and another waxy cuticle. Guard cells allow exchange of gases through stoma.A cross-section through a leaf

Features of leaves and their functions

FeatureFunction
Large surface areaMaximise light absorption
ThinShort distance for carbon dioxide to diffuse into leaf cells
Thin waxy cuticleThis protects the leaves without blocking out light
Thin transparent epidermis Allows light to reach the palisade cells