Photosynthesis has two main stages: 1) The light-dependent reaction uses chlorophyll and sunlight to produce ATP and NADPH through a series of electron transfers in the thylakoid membranes. 2) The Calvin Cycle uses ATP and NADPH to incorporate CO2 into organic carbohydrates like glucose through enzyme-catalyzed reactions in the chloroplast stroma, producing oxygen as a byproduct. Photosynthesis is essential for converting sunlight into chemical energy that fuels life on Earth.