Cyclic photophosphorylation releases

Options

A. ATP and `NADPH_(2)`
B. ATP , `NADPH_(2) ` and oxygen
C. ATP only
D. `NADPH_(2)` only

Answer

To answer the question "Cyclic photophosphorylation releases," we will analyze the process of cyclic photophosphorylation step by step.

### Step-by-Step Solution:

1. **Understanding Cyclic Photophosphorylation**:
- Cyclic photophosphorylation is a process that occurs in the thylakoid membranes of chloroplasts during photosynthesis.
- It primarily involves Photosystem I (PSI), which absorbs light energy.

2. **Role of Photosystem I**:
- In cyclic photophosphorylation, electrons are excited by light absorbed by PSI (specifically at the P700 reaction center).
- These excited electrons are transferred through a series of proteins in the electron transport chain.

3. **Electron Transport Chain**:
- The electrons travel through the chain and return to PSI, which is why it is termed "cyclic."
- As the electrons move through the chain, they release energy.

4. **ATP Synthesis**:
- The energy released during the electron transport is used to pump protons (H+) into the thylakoid lumen, creating a proton gradient.
- This gradient drives ATP synthase, an enzyme that synthesizes ATP from ADP and inorganic phosphate (Pi).

5. **Products of Cyclic Photophosphorylation**:
- The main product of cyclic photophosphorylation is ATP.
- Importantly, this process does not produce NADPH or oxygen, as it does not involve Photosystem II (PSII) or water splitting.

6. **Conclusion**:
- Therefore, the correct answer to the question is that cyclic photophosphorylation releases ATP only.

### Final Answer:
Cyclic photophosphorylation releases **ATP only**.

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