Photosynthesis revision guide

The reaction

Plants use light energy to make glucose from carbon dioxide and water, releasing oxygen:

carbon dioxide + water → glucose + oxygen, in the presence of light and chlorophyll.

The carbon dioxide comes from the air through the stomata, the water from the soil through the roots. The glucose is used for respiration, converted to starch for storage, or used to build cellulose for cell walls and, with nitrates, proteins.

Why photosynthesis matters

Almost all living things depend on photosynthetic organisms. They make the organic molecules that food chains begin with, and animals get theirs by eating plants or by eating animals that ate plants.

Photosynthesis also removes carbon dioxide from the atmosphere and releases the oxygen that most living things need for respiration.

Adaptations of a leaf

A leaf is built for photosynthesis:

• broad and flat, giving a large surface area to catch light.
• thin, so gases have only a short distance to diffuse.
• packed with chloroplasts in the palisade layer near the top, where the light is strongest.
• with stomata on the underside to let carbon dioxide in and oxygen out.
• with air spaces inside so gases can move around.
• with a network of veins bringing water and carrying sugars away.