When light strikes chlorophyll, the energy from the light excites electrons in the chlorophyll molecule. These excited electrons are then transferred to the electron transport chain. To replace the lost electrons, water molecules are split in a process called photolysis, which generates hydrogen ions (H⁺), electrons, and oxygen (O₂).
The electrons released from water ultimately help to replace the excited electrons that were lost from chlorophyll. The H⁺ ions created during photolysis diffuse across the thylakoid membrane through a protein called ATP synthase.
The diffusion of H⁺ ions through ATP synthase generates enough energy to allow ATP synthase to rotate, which facilitates the conversion of ADP and inorganic phosphate (Pi) into ATP.
NADPH (Nicotinamide adenine dinucleotide phosphate) is a carrier molecule that transports energized electrons produced in the light-dependent reactions. It plays a critical role in the Calvin cycle, where it supplies the electrons needed for the reduction of carbon compounds, ultimately leading to the production of glucose.
To summarize:
- Electrons lose their energy when they become excited and are replaced by electrons from water.
- Water is broken down into hydrogen ions and oxygen.
- H⁺ ions diffuse through a protein called ATP synthase.
- This process produces ATP.
- NADPH is an electron carrier.
- NADPH carries the electrons to the Calvin cycle for carbon fixation and the synthesis of glucose.
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