What are the main stages of photosynthesis, including the light-dependent reactions and the Calvin cycle?

Photosynthesis is the process by which plants, algae, and some bacteria convert light energy from the sun into chemical energy in the form of organic compounds, such as glucose. It occurs in two main stages: the light-dependent reactions and the Calvin cycle.

Light-Dependent Reactions

The light-dependent reactions occur in the thylakoid membranes of the chloroplasts and convert light energy into chemical energy in the form of ATP and NADPH, which are used in the Calvin cycle. The main steps in the light-dependent reactions are:

• 1. Absorption of light energy by chlorophyll and other pigments in photosystem II.
• 2. Conversion of light energy into chemical energy in the form of ATP and NADPH through the electron transport chain and chemiosmosis.
• 3. Photolysis of water to produce oxygen gas and protons that contribute to a proton gradient across the thylakoid membrane.
• 4. Absorption of light energy by chlorophyll and other pigments in photosystem I.
• 5. Production of NADPH through the electron transport chain.

Calvin Cycle

The Calvin cycle, also known as the light-independent reactions, occur in the stroma of the chloroplasts and use the ATP and NADPH produced in the light-dependent reactions to fix carbon dioxide into organic compounds, such as glucose. The main steps in the Calvin cycle are:

• 1. Fixation of carbon dioxide into an organic molecule using the enzyme Rubisco.
• 2. Reduction of the fixed carbon dioxide into a three-carbon sugar using the ATP and NADPH produced in the light-dependent reactions.
• 3. Regeneration of the organic molecule that accepts the carbon dioxide using ATP.