Electrons lost by PS `II` are regained from

Options

A. `O_(2)`
B. `CO_(2)`
C. `H_(2)O`
D. None of the above.

Answer

To answer the question "Electrons lost by PS II are regained from," we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Photosystem II (PS II)**:
- Photosystem II is a crucial component of the light-dependent reactions of photosynthesis. It absorbs light energy, which excites electrons.

2. **Electron Loss in PS II**:
- When PS II absorbs light, it loses electrons. These excited electrons are transferred to an electron transport chain, which ultimately leads to the production of ATP.

3. **Need for Electron Replacement**:
- As PS II continuously loses electrons, there is a need to replenish these electrons to maintain its function. If PS II runs out of electrons, it cannot continue to operate effectively.

4. **Source of Replacement Electrons**:
- The electrons lost by PS II are replaced through the process of photolysis of water. This process involves splitting water molecules into oxygen, protons, and electrons.

5. **Photolysis of Water**:
- During photolysis, water (H₂O) is split into:
- 4 electrons (which replace those lost by PS II)
- 4 protons (H⁺ ions)
- 1 molecule of oxygen (O₂)
- This reaction is catalyzed by the oxygen-evolving complex, which requires manganese and chloride ions as cofactors.

6. **Conclusion**:
- Therefore, the electrons lost by PS II are regained from the splitting of water, making it the correct answer to the question.

### Final Answer:
The electrons lost by PS II are regained from the photolysis of water.

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