Photosynthesis converts sunlight, water and carbon dioxide into oxygen and sugars such as glucose. It occurs in plant leaves within organelles called chloroplasts. Chloroplasts contain chlorophyll and other pigments that absorb sunlight, which drives a pair of reactions - the light reactions that capture energy from sunlight, and the dark reactions that use that energy to produce sugars from carbon dioxide. Photosynthesis provides organic molecules that plants use for food and that other organisms rely on as a food source.