Photosynthesis is the process of converting carbon dixoide and an electron donor into a carbohydrate that the plant uses for energy. This process also takes place in humans, called chemeosynthesis. In humans, carbohydrates are the energy source used to covert the hydrogen in water, the carbon in carbon dioxide, and the oxygen in water and carbon dioxide, into glucose. In plants, the energy source is light instead of carbohydrates. The chemical reaction for photosynthesis is:
Where D denotes the electron donor. In oxygenic photosnythesis, the electron donor is water.