Energy is required for the existence of life. Energy is used up in the process like growth, reproduction, physical work done by the organisms etc. All the energy needed by organisms is obtained by the process of photosynthesis which occurs in the green plants. All the consumers which are non-photosynthetic organism obtain food from plants. Photosynthesis is an oxygen releasing process. Plants also provide us energy through fossil fuels like coal and petrol which are also obtained.