Carbon and energy requirement of the autotrophic organisms are fulfilled by photosynthesis. It is a process by which autotrophs take in substance from the outside and convert them into stored form of energy. This material take in the form of carbon dioxide and water which is converted into carbohydrate in the presence of Sunlight and chlorophyll. Carbohydrate are utilised for providing energy to the plants. The carbohydrates which are not used immediately are stored in the form of starch which serve as a internal energy reserve, to be used as and when required by the plant. A somewhat similar situation is seen in US where some of the energy derived from the food we eat store in our body in the form of glycerine. The steps that take place during photosynthesis are
Absorption of light energy by chlorophyll.
Conversion of light energy to chemical energy and splitting of water molecules into hydrogen and oxygen.
Reduction of carbon dioxide to carbohydrates.
After all these steps are completed the oxygen that is a waste material that is released through the the stomata pores and the extra water as well and exchange of gases also take place.