What happens during cyclic photophosphorylation?

During cyclic photophosphorylation, photosystem I (PSI) is the primary focus, while photosystem II (PSII) remains inactive. This process involves the transfer of electrons within PSI, where light energy is captured and used to energize electrons. As these energized electrons move through a series of proteins in the electron transport chain, they help pump protons across the thylakoid membrane, creating a proton gradient. This gradient ultimately drives ATP synthesis through ATP synthase.

Cyclic photophosphorylation does not involve the splitting of water, which is a characteristic of non-cyclic photophosphorylation. The splitting of water provides electrons for PSII and leads to the production of oxygen, but this is not part of cyclic photophosphorylation. Additionally, cyclic photophosphorylation does not generate NADPH; this is produced during non-cyclic photophosphorylation when electrons from PSII ultimately reduce NADP+. Therefore, the essence of cyclic photophosphorylation is centered on PSI generating ATP when PSII is not functioning, which aligns perfectly with the noted answer.