Answer:

In cyclic photophosphorylation, the electron released by the reaction center (P700) is ultimately accepted by the reaction center itself (P700).

Explanation:

Cyclic photophosphorylation is a process that occurs in the light-dependent reactions of photosynthesis. It involves the transfer of electrons in a cyclic manner, resulting in the production of ATP (adenosine triphosphate) without the production of NADPH (nicotinamide adenine dinucleotide phosphate).

Key Points:

- In cyclic photophosphorylation, the primary electron donor is P700, which is found in the photosystem I (PSI).
- When light energy is absorbed by the chlorophyll molecules in PSI, it excites an electron in P700 to a higher energy level.
- The excited electron is transferred to an electron acceptor molecule called ferredoxin (Fd), which acts as an intermediate carrier.
- Ferredoxin then transfers the electron to the cytochrome complex, which pumps protons across the thylakoid membrane, creating a proton gradient.
- The electron is then passed to a protein called plastocyanin (PC), which is located on the lumen side of the thylakoid membrane.
- Plastocyanin transports the electron back to the reaction center (P700) through the thylakoid membrane.
- Once the electron reaches P700, it completes the cyclic pathway by returning to its ground state.
- During this process, ATP is synthesized by the ATP synthase enzyme, utilizing the proton gradient generated by the cytochrome complex.

Conclusion:

In cyclic photophosphorylation, the electron released by the reaction center (P700) is ultimately accepted by the reaction center itself (P700). This cyclic pathway allows for the production of ATP without the generation of NADPH, which is required in the non-cyclic photophosphorylation pathway.