Plants, unlike animals, can make their own food. They do this using a process called photosynthesis.
Photosynthesis requires energy to drive the chemical reaction. Photosynthesis is an endothermic reaction. This means it cannot occur without energy (from the Sun).
Plant leaves are the main photosynthetic organ, but other parts of the plant exposed to the light can develop chlorophyll and photosynthesise.
Oxygen is formed as the waste product. Some is used for respiration by the plant. The excess is released from the leaves, making it available for respiration to animals and many microorganisms. During the light, provided the rate of photosynthesis is sufficiently high, plants, give out oxygen.
The overall reaction for photosynthesis as given above is a simplification. Photosynthesis involves several different chemical reactions, but these can be summarised in two main stages. In the first reaction, energy is used to split water molecules into hydrogen and oxygen. The hydrogen is needed for the second stage of reactions and the oxygen is released by the plant as a waste product. In the reactions of the second stage, the hydrogen is combined with carbon dioxide to make glucose.
Some of the glucose produced by photosynthesis is used for respiration.
Glucose is the starting point for the biosynthesis of materials that plants need to live.
The glucose not used for respiration is used in the following ways: