The process of Photosynthesis on plants gives both food and oxygen to every living organisms on the earth.
Every plant make their food by the process of Photosynthesis. In this process leaves of the plant capture the light energy from the sun and use it to make food. Animals that feed on plants get this energy by eating it. They pass it on further when they are eaten by other animals. Human beings also get energy from this by eating plant products such as fruits and vegetables. The energy obtained from food is used by all organism for various activities.
Oxygen is also released by plants during the process of Photosynthesis. If there is absence the process of Photosynthesis, the oxygen level in the atmosphere will decrease and life on the earth will become impossible.