Alright — let's do this. Photosynthesis occurs in two main stages: the light-dependent reactions (light phase) and the light-independent reactions (dark phase). The light-dependent reactions take place in the thylakoid membranes of chloroplasts. 1. Light Absorption: Chlorophyll and other pigments absorb light energy. 2. Water Splitting: Water molecules are split (photolysis) to release electrons, protons (H⁺), and oxygen gas (O₂). 3. Electron Transport Chain: The absorbed light energy excites electrons, which move through an electron transport chain. This process generates ATP (adenosine triphosphate), an energy-carrying molecule. 4. NADPH Formation: Electrons and protons are used to reduce NADP⁺ to NADPH, another energy-carrying molecule. Oxygen is released as a byproduct. The main outputs of the light phase are ATP and NADPH, which are used in the next stage. The light-independent reactions (Calvin cycle) occur in the stroma of chloroplasts and do not directly require light, but they depend on the ATP and NADPH produced during the light phase. 1. Carbon Fixation: Carbon dioxide (CO₂) from the atmosphere is incorporated into an organic molecule (RuBP) by the enzyme RuBisCO. 2. Reduction: The ATP and NADPH generated in the light phase are used to convert the fixed carbon molecules into a higher-energy sugar (G3P). 3. Regeneration: Some of the G3P molecules are used to regenerate the starting molecule (RuBP), allowing the cycle to continue. The remaining G3P molecules are used to synthesize glucose and other organic compounds.