Free energy is released in cyclic photophosphorylation.

Options

A. by the formation of ATP.
B. during the excitation of chlorophyll
C. during the fluorescence of chlorophyll
D. during each of the redox reactions of the electron transport chain

Answer

**Step-by-Step Solution:**

1. **Understanding Cyclic Photophosphorylation**:
- Cyclic photophosphorylation occurs in the thylakoid membranes of chloroplasts. It involves Photosystem I (PSI), which absorbs light energy and is designated as P700 due to its peak absorption wavelength of 700 nm.

2. **Role of Light Energy**:
- When light strikes PSI, it excites electrons, which are then transferred to an electron acceptor molecule. This process initiates the electron transport chain.

3. **Electron Transport Chain**:
- The excited electrons move through a series of proteins in the electron transport chain. As they move, they release energy, which is harnessed to pump protons (H+) across the thylakoid membrane, creating a proton gradient.

4. **ATP Formation**:
- The energy from the proton gradient is used by ATP synthase to convert ADP and inorganic phosphate (Pi) into ATP. This process is known as chemiosmosis.

5. **Free Energy Release**:
- The free energy released during the electron transport chain's redox reactions is what drives the synthesis of ATP. Therefore, the correct answer to the question is that free energy is released during each of the redox reactions of the electron transport chain.

6. **Conclusion**:
- The correct option is that free energy is released during each of the redox reactions of the electron transport chain, leading to ATP production.