In photophosphorylation, under the circumstances when NADP is not longer available as acceptor the electrons are passed to :

Options

A. Cytochrome f
B. Plastocyanin
C. Cytochrome `B_(6)`
D. Quinone

Answer

**Step-by-Step Solution:**

1. **Understand Photophosphorylation**: Photophosphorylation is the process by which ATP is produced using light energy during photosynthesis. It occurs in the thylakoid membranes of chloroplasts.

2. **Role of NADP**: NADP (Nicotinamide adenine dinucleotide phosphate) is a crucial electron acceptor in the light reactions of photosynthesis. It typically accepts electrons and protons to form NADPH.

3. **Scenario When NADP is Unavailable**: The question specifies a situation where NADP is not available as an electron acceptor. In this case, the electrons need to be transferred to another acceptor.

4. **Evaluate the Options**:
- **Cytochrome F**: This is involved in the electron transport chain but does not accept electrons directly when NADP is unavailable.
- **Plastocyanin**: This is a mobile electron carrier that transfers electrons from cytochrome f to photosystem I, but it does not serve as an electron acceptor when NADP is absent.
- **Cytochrome B6**: This is a part of the electron transport chain and can accept electrons in the absence of NADP.
- **Q0**: This is a part of the electron transport chain but does not function as an electron acceptor in this context.

5. **Conclusion**: When NADP is not available, the electrons are passed to **Cytochrome B6**. Therefore, the correct answer is option 3.

**Final Answer**: The electrons are passed to **Cytochrome B6** when NADP is not available as an acceptor during photophosphorylation.

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