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

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.

Cross section of a leaf showing Waxy cuticle, Upper epidermis, Palisade mesophyll, Spongy mesophyll containing Air space. The Lower epidermis contains Guard cells with chloroplasts surrounding Stoma.A cross-section through a leaf

Features of leaves and their functions

Large surface areaMaximise light absorption
ThinShort distance for carbon dioxide to diffuse into leaf cells
CuticleA waxy waterproof layer which reduces water loss, it is transparent to allow light through the leaf

The role of stomata

The stomata control gas exchange in the leaf. Each stoma can be open or closed, depending on how turgid its guard cells are.

The stomata can open and close to:

  • regulate transpiration
  • allow gas exchange
Cross section of a leaf. Labelled are the Epidermal cell, Chloroplast, Thin outer wall, Stoma, Thick inner wall, Nucleus, and Guard cells.

Diffusion of carbon dioxide, oxygen and water vapour into (or out of) the leaf is greatest when the stomata are open, during the day.