Adaptations of the leaf

The leaf is a plant organ adapted to carry out photosynthesis. The table describes some of its adaptations:

AdaptationFunction
ThinProvides a short distance for carbon dioxide to move by diffusion into the leaf
Contains chlorophyllAbsorbs light
StomataAllows carbon dioxide to move by diffusion into the leaf
Guard cellsTo open and close the stomata depending on the conditions
Network of tubes (xylem and phloem)To transport water (xylem) and food (phloem)

Light

A leaf usually has a large surface area, so that it can absorb a lot of light. Its top surface is protected from water loss, disease and weather damage by a waxy layer.

The upper part of the leaf is where the light falls, and it contains a type of cell called a palisade cell. This is adapted to absorb a lot of light. It has lots of chloroplasts and is shaped like a tall box.

Shows how the leaf is structured: Upper layers, palisade layer, spongy layer, lower layer. Sunlight hits the upper layer. Gases are exchanged through the stoma in the lower layerA cross-section through a leaf showing its main parts

Carbon dioxide

Plants get the carbon dioxide they need from the air through their leaves. It moves by diffusion through small holes in the underside of the leaf called stomata. Guard cells control the size of the stomata so that the leaf does not lose too much water in hot, windy or dry conditions.

The lower part of the leaf is a spongy layer with loose-fitting cells. These let carbon dioxide reach the other cells in the leaf, and also let the oxygen produced in photosynthesis leave the leaf easily.

Water

The water needed for photosynthesis is absorbed through the roots and transported through tubes to the leaf.

The roots have a type of cell called a root hair cell. These project out from the root into the soil, and have a big surface area and thin walls. This lets water pass into them easily.

Note that root cells do not contain chloroplasts, as they are normally in the dark and cannot carry out photosynthesis.

Shows a root hair cell. The water can pass through the thin cell wall of the root hairWater is absorbed from the soil by root hair cells