When non-cyclic photophosphorylation changes to cyclic photophosphorylation, the excited electrons leaves PSI and goes back to _____to make more______

Options

A. `b_(6)`-f complex, ATP
B. `b_(6)`-f complex, ADP
C. `b_(6)`- f complex, NADPH
D. `b_(6)`-f complex, `NADPH_(2)`

Answer

**Step-by-Step Text Solution:**

1. **Understanding Non-Cyclic Photophosphorylation:**
- In non-cyclic photophosphorylation, the process begins when light energy excites electrons in Photosystem I (PSI). These excited electrons are transferred through a series of proteins in the electron transport chain (ETC).

2. **Electron Flow in Non-Cyclic Photophosphorylation:**
- The excited electrons from PSI move to ferredoxin (Fd) and then to NADP+, reducing it to NADPH. This process also involves the generation of ATP through chemiosmosis.

3. **Transition to Cyclic Photophosphorylation:**
- In cyclic photophosphorylation, instead of moving forward to reduce NADP+, the excited electrons from PSI are redirected back into the electron transport chain.

4. **Electrons Returning to the Electron Transport Chain:**
- The excited electrons leave PSI and return to the cytochrome b6f complex (B6f complex). This is a crucial step in cyclic photophosphorylation.

5. **Production of ATP:**
- As the electrons cycle back through the B6f complex, a proton gradient is established across the thylakoid membrane, which drives ATP synthesis through ATP synthase. This results in the production of more ATP.

6. **Final Answer:**
- Therefore, when non-cyclic photophosphorylation changes to cyclic photophosphorylation, the excited electrons leave PSI and go back to the **B6f complex** to make more **ATP**.

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