1. Photosynthesis uses energy from sunlight, carbon dioxide, and water to produce oxygen and energy-rich organic molecules like glucose. 2. It occurs in two stages - the light reactions that convert solar energy to chemical energy in ATP and NADPH, and the Calvin cycle that uses this energy to fix carbon from carbon dioxide into organic molecules. 3. The light reactions take place in chloroplasts, where photosystems use chlorophyll to absorb light and drive electron transport and ATP synthesis. The Calvin cycle then fixes carbon in the chloroplast stroma.