Photosynthesis allows autotrophic organisms like plants to produce their own food by converting sunlight, water and carbon dioxide into oxygen and glucose through a two-step process. Chlorophyll in the chloroplasts absorbs sunlight during the light reactions to split water and release oxygen, while the dark reactions in the Calvin cycle use the energy to fix carbon dioxide and produce glucose using ATP and NADPH produced in the light reactions. Plants take in water through their roots and carbon dioxide enters through stomata on the underside of leaves.