Photosynthesis is the process autotrophs use to convert solar energy into chemical energy, ultimately building carbohydrates like glucose from carbon dioxide and water. The core steps are divided into light-dependent reactions and the Calvin cycle (also called the light-independent reactions).
- Light-dependent reactions: Occur in the thylakoid membranes of chloroplasts. Chlorophyll and other pigments capture light energy, driving the splitting of water (photolysis), releasing oxygen, and transferring energy to the molecule carriers ATP and NADPH. This stage creates the chemical energy carriers used in the next stage.
- Calvin cycle (carbon fixation): Uses ATP and NADPH produced in the light-dependent reactions to convert carbon dioxide into organic sugars, such as glucose, within the stroma of the chloroplasts. This cycle regenerates the initial carbon acceptor and builds carbohydrate molecules that store chemical energy.
In short: light energy is captured and transformed into chemical energy (ATP and NADPH) during the light-dependent reactions, and that energy, along with carbon dioxide, is then used to synthesize sugars in the Calvin cycle. This is the primary and most common pathway by which autotrophs convert solar energy into chemical energy.
