Photosynthesis

Photosynthesisphotosynthesis: The chemical change that occurs in the leaves of green plants. It uses light energy to convert carbon dioxide and water into glucose. Oxygen is produced as a by-product of photosynthesis. is the chemical change which happens in the leaves of green plants. It is the first step towards making food - not just for plants but ultimately every animal on the planet.

During this reaction, carbon dioxidecarbon dioxide: A gaseous compound of carbon and oxygen, which is a by-product of respiration, and which is needed by plants for photosynthesis. and water are converted into glucose and oxygenoxygen: Gaseous element making up about 20 per cent of the air, which is needed by living organisms for respiration. The reaction requires light energylight energy: Visible electromagnetic radiation., which is absorbed by a green substance called chlorophyll.

Photosynthesis takes place in leaf cells. These contain chloroplasts, which are tiny objects containing chlorophyll.

Cross-section through a leaf cell

Here is the equation for photosynthesis:

carbon dioxide + water (+ light energy)    →    glucose + oxygen

'Light energy' is shown in brackets because it is not a substance. You will also see the equation written like this:

Plants absorb water through their roots, and carbon dioxide through their leaves. Some glucose is used for respiration, while some is converted into insoluble starchstarch: A type of carbohydrate. Plants can turn the glucose produced in photosynthesis into starch for storage, and turn it back into glucose when it is needed for respiration. for storage. The stored starch can later be turned back into glucose and used in respiration. Oxygen is released as a by-product of photosynthesis.