Stages of photosynthesis
Stage one: light reactions
This stage is so-called because it depends on light being available. The reactions of this stage also require specific enzymes to catalyse them.
Light energy absorbed by chlorophyll is converted into chemical energy. Some of this energy is used to split water into hydrogen and oxygen.
Some of the chemical energy is used to make Stands for 'adenosine triphosphate' which is the high-energy chemical that transfers chemical energy in cells. from ADP and phosphate (Pi). This chemical energy is stored as ATP.
Fate of products of the light reactions
Hydrogen and ATP are both transferred to the second stage of photosynthesis.
Some of the oxygen produced can be used by the mitochondria of plant cells for aerobic respiration. Most oxygen diffuses out of plant cells and out of the leaves through the stomata. The overall effect of photosynthesis is to increase the concentration of oxygen in the Earth's atmosphere.
Stage two: carbon fixation
This stage also requires energy, which is supplied by the ATP made by the light reactions. The ATP is broken down to release energy which is used to combine hydrogen (from the light reactions) with carbon dioxide to produce sugar.
The reactions of carbon fixation are controlled by specific enzymes. The overall process of carbon fixation is summarised in the diagram below.