Which is not true about cyclic photophosphorylation

Options

A. It does not involve NADPH formation
B. Only PS-I is involved
C. It involves substrate - level phosphorylation
D. It does not generate oxygen.

Answer

To determine which statement is not true about cyclic photophosphorylation, we will analyze each option step by step.

### Step-by-Step Solution:

1. **Understanding Cyclic Photophosphorylation**:
- Cyclic photophosphorylation is a process that occurs during photosynthesis where ATP is produced using light energy. It primarily involves Photosystem I (PS-I).

2. **Analyzing the Options**:
- **Option 1**: "It does not involve NADPH formation."
- This statement is true. Cyclic photophosphorylation does not produce NADPH; it only generates ATP.

- **Option 2**: "Only PS-1 is involved."
- This statement is also true. Cyclic photophosphorylation involves only Photosystem I (PS-I), which is also referred to as P700 due to its absorption peak at 700 nm.

- **Option 3**: "It involves substrate-level phosphorylation."
- This statement is not true. Cyclic photophosphorylation does not involve substrate-level phosphorylation. Instead, it generates ATP via a proton gradient and chemiosmosis, similar to oxidative phosphorylation in cellular respiration.

- **Option 4**: "It does not generate oxygen."
- This statement is true. Cyclic photophosphorylation does not produce oxygen, as it does not involve the splitting of water molecules (photolysis), which is a characteristic of non-cyclic photophosphorylation.

3. **Conclusion**:
- The statement that is not true about cyclic photophosphorylation is **Option 3**: "It involves substrate-level phosphorylation."

### Final Answer:
The correct answer is **Option 3**: "It involves substrate-level phosphorylation."

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