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Science

Photosynthesis

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Leaves enable photosynthesis to occur. Photosynthesis is the process by which leaves absorb light and carbon dioxide to produce carbohydrate (food) for plants to grow. Leaves are adapted to perform their function, eg they have a large surface area to absorb sunlight.

Plants have two different types of 'transport' tissue, xylem and phloem, that move substances in and around the plant. When water evaporates from the leaves, resulting in more water being drawn up from the roots, it is called transpiration.

Structure of a leaf

Functions of leaves

The function of a leaf is photosynthesis – to absorb light and carbon dioxide to produce carbohydrates. The equation for photosynthesis is:

Carbon dioxide and water → glucose and oxygen

Did you know:

  • Leaves are the source of all of food on the planet
  • Leaves recycle all of the world's carbon dioxide in the air
  • Leaves contain the world's most abundant enzyme
Leaf, showing the veins, midrib and blade.

Leaves are adapted in several ways to help them perform their function.

Features of leaves

AdaptionPurpose
Large surface areaTo absorb more light
ThinShort distance for carbon dioxide to diffuse into leaf cells
ChlorophyllAbsorbs sunlight to transfer energy into chemicals
Network of veinsTo support the leaf and transport water and carbohydrates
StomataAllow carbon dioxide to diffuse into the leaf

Inside the leaf

Shows the waxy cuticle on top of the upper epidermis.Under this is the palisade mesophyll layer and spongy mesophyll layer, which has air spaces in it. At the bottom, is the lower epidermis and wax cuticle. Gases are exchanged through the stoma. On each side of the stoma there is a guard cell with chloroplasts.

The internal structure of the leaf is also adapted to promote efficient photosynthesis:

Structure of leaves

AdaptionPurpose
Epidermis is thin and transparentTo allow more light to reach the palisade cells
Thin cuticle made of waxTo protect the leaf without blocking out light
Palisade cell layer at top of leafTo absorb more light
Spongy layerAir spaces allow carbon dioxide to diffuse through the leaf, and increase the surface area
Palisade cells contain many chloroplastsTo absorb all the available light

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