The principal chemical process that occurs in chloroplasts is photosynthesis. In this process, chloroplasts convert light energy, usually from the sun, into chemical energy stored in glucose. The process involves two main stages: the light-dependent reactions and the Calvin cycle. During the light-dependent reactions, sunlight is captured and converted into ATP and NADPH, while the Calvin cycle uses these energy carriers to synthesize glucose from carbon dioxide. Photosynthesis is fundamental for life on Earth, as it produces oxygen and forms the basis of most food chains.