Stage 1: Light-dependent reactions

During the light-dependent reactions, light energy is absorbed by pigments in the thylakoid membranes of chloroplasts. This energy is used to generate ATP and NADPH, which are essential for the second stage of photosynthesis. The light-dependent reactions can be broken down into several steps:

1. Light absorption: Pigments such as chlorophyll and carotenoids absorb light energy, which excites electrons and creates a high-energy state.

2. Electron transport: These high-energy electrons are passed along a series of electron carriers in the thylakoid membrane, releasing energy that is used to pump protons (H+) across the membrane.

3. ATP production: The buildup of protons creates a concentration gradient that drives the production of ATP through ATP synthase.

4. NADPH production: In a separate pathway, electrons from the electron transport chain are used to reduce NADP+ to NADPH.

Stage 2: Light-independent reactions

The light-independent reactions, also known as the Calvin cycle, take place in the stroma of chloroplasts. This stage does not require light energy directly but uses the ATP and NADPH produced in the first stage. The Calvin cycle can be broken down into several steps:

1. Carbon fixation: CO2 from the atmosphere is fixed into organic molecules using the enzyme Rubisco.

2. Reduction: These organic molecules are then reduced using ATP and NADPH to produce glyceraldehyde-3-phosphate (G3P).

3. Regeneration: Some of the G3P molecules are used to regenerate the starting material, ribulose bisphosphate (RuBP), while others are used to produce glucose or other sugars.

Overall, these two stages of photosynthesis work together to convert light energy into chemical energy that can be used by plants and other organisms.