Plants transform light energy into chemical energy using photosynthesis.
Photosynthesis is divided into light-dependent reactions and light-independent reactions.
Light-dependent reactions occur in the thylakoids of the chloroplast, where one molecule of chlorophyll absorbs a photon and loses an electron, which is later taken to the molecule of pheophytin and then to a quinone, initiating an electron transport chain that produces NADPH. The movement of electrons also creates a proton gradient, which can be used by the ATP synthase to produce ATP. The electron lost by the chlorophyll is regained from the photolysis, which breaks apart the water and releases oxygen.
The light-independent reactions are the ones where the enzyme RuBisCO transforms CO₂ from the atmosphere and makes carbohydrates, in a process called the Calvin cycle, which uses the NADPH created in the light-dependent reactions. The carbohydrates are later used in cellular respiration to obtain more ATP.