Photosynthesis consists of two steps :
(1) Photochemical phase or light reaction in which solar energy is trapped by chlorophyll and stored in the form of chemical energy of ATP and as reducing power in NADPH2. Oxygen is involved in the light reaction by splitting of water (photolysis of water).
(2) Biosynthetic phase or dark reaction in which the
reducing capacity of NADPH and the energy of ATP are utilized in the conversion of carbon dioxide to carbohydrates.