It takes place in the stroma lamellae membrane of chloroplasts. The process of cyclic photophosphorylation involves only photosystem I.

Cyclic photophosphorylation is a process that occurs in the light reactions of photosynthesis. It takes place in both photosystem I (PSI) and photosystem II (PSII), but it is more commonly associated with PSI.

**Photosynthesis Reaction:**
Photosynthesis is the process by which green plants, algae, and some bacteria convert light energy into chemical energy in the form of glucose. It consists of two main stages: the light-dependent reactions and the light-independent reactions (also known as the Calvin cycle).

The light-dependent reactions take place in the thylakoid membrane of the chloroplasts and involve the absorption of light energy by chlorophyll molecules. This energy is used to generate ATP (adenosine triphosphate) and NADPH (nicotinamide adenine dinucleotide phosphate), which are then used in the light-independent reactions to produce glucose.

**Cyclic Photophosphorylation:**
Cyclic photophosphorylation is an alternative pathway of electron flow during the light-dependent reactions. It occurs when there is a shortage of NADPH compared to the requirement for ATP. This can happen when the light intensity is high, or when the Calvin cycle is unable to utilize all the NADPH produced.

During cyclic photophosphorylation, only PSI is involved. Here is a detailed explanation of the process:

1. Absorption of Light: PSI contains a pigment called chlorophyll a, which absorbs light energy. When light energy is absorbed by the chlorophyll molecules, it excites electrons in the pigment to a higher energy state.

2. Electron Transport: The excited electrons are transferred from chlorophyll a to a primary electron acceptor molecule in PSI. From there, they are passed along a series of electron carriers, including iron-sulfur proteins and cytochromes, in a process called the electron transport chain.

3. ATP Synthesis: As the electrons move through the electron transport chain, their energy is used to pump protons (H+) from the stroma into the thylakoid lumen, creating a proton gradient. This gradient is then used by ATP synthase to produce ATP through chemiosmosis.

4. Return of Electrons: Once the electrons have passed through the electron transport chain, they return to the chlorophyll a molecules in PSI. This completes the cyclic pathway.

**Conclusion:**
In conclusion, cyclic photophosphorylation is a process that occurs in both PSI and PSII during the light-dependent reactions of photosynthesis. However, it is more commonly associated with PSI. It involves the absorption of light energy, the transfer of excited electrons through an electron transport chain, the synthesis of ATP, and the return of electrons to the chlorophyll a molecules. This process helps to generate ATP when there is a shortage of NADPH, ensuring that the energy needs of the cell are met.