Flexi Says: Photosynthesis occurs in two stages. Stage I is called the light reactions because it requires sunlight or artificial light. This stage uses water and changes light energy from the sun into chemical energy stored in ATP and NADPH (another energy-carrying molecule). This stage also releases oxygen as a waste product. Stage II is called the Calvin cycle or the light-independent reactions because they can take place in the absence of light. This stage combines carbon from carbon dioxide in the air and uses the chemical energy in ATP and NADPH to make glucose.
