Photolysis of water occurs at:

Photolysis of water is a critical part of the light-dependent reactions of photosynthesis. It involves the splitting of water molecules into protons, electrons, and oxygen using light energy: $$2H_2O \xrightarrow{light} 4H^+ + 4e^- + O_2$$ 1. **Location**: This process occurs on the inner side (lumen side) of the thylakoid membrane. 2. **Mechanism**: It is catalyzed by the Oxygen Evolving Complex (OEC), which is physically and functionally associated with **Photosystem II (PSII)**. 3. **Purpose**: The electrons generated from water are used to replace the electrons lost by the reaction center chlorophyll ($P_{680}$) of PSII after it has been excited by photons. Therefore, photolysis occurs at PSII, while PSI is involved in the later stages of the electron transport chain, and NADP+ reductase is responsible for the formation of NADPH.