During non-cyclic photophosphorylation, electrons are continuously lost from the reaction centre of PS II. Which source is used to replace these electrons?

Options

A. Sunlight
B. `O_(2)`
C. `H_(2)O`
D. `CO_(2)`

Explanation

**Step-by-Step Solution:**

1. **Understanding Non-Cyclic Photophosphorylation**: Non-cyclic photophosphorylation is a process that occurs during photosynthesis in which light energy is used to generate ATP and NADPH. This process involves two photosystems, PS I and PS II.

2. **Role of Photosystem II (PS II)**: In PS II, light energy is absorbed, which excites electrons. These excited electrons are transferred through a series of proteins in the thylakoid membrane, leading to the production of ATP and NADPH.

3. **Electron Loss from PS II**: As the electrons are excited and transferred, they are continuously lost from the reaction center of PS II. This loss needs to be compensated to maintain the function of the photosystem.

4. **Oxygen Evolving Complex (OEC)**: To replace the lost electrons, PS II is associated with an oxygen-evolving complex (OEC). This complex is crucial for the process of photolysis.

5. **Photolysis of Water**: The OEC facilitates the splitting of water molecules (H2O) in a process known as photolysis. During photolysis, water is broken down into protons (H+), electrons (e-), and molecular oxygen (O2).

6. **Replacement of Electrons**: The electrons released from the photolysis of water are the ones that replace the continuously lost electrons from PS II. Specifically, the reaction can be summarized as:
\[ 2 H_2O \rightarrow 4 H^+ + 4 e^- + O_2 \]

7. **Conclusion**: Therefore, the source that replaces the lost electrons in PS II during non-cyclic photophosphorylation is water (H2O).

**Final Answer**: The source used to replace the lost electrons from PS II during non-cyclic photophosphorylation is water (H2O).

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