Explain cyclic photosphosphorylation .

Explanation

Cyclic photophosphoryalation refes to the electrons ejected form the pigment system I (Photosystem I) and agin cycled back to the PSI . When the photons activate P 700 reaction centre photosytem II is activated . Eectrons are raised to the high energy level. The primary electron acceptor is Ferredoxin Reducing Substance (FRS) which transfers electrons to Ferredoxin (Fd), Plastquinone (PQ), cytochrome b6 - f complex, Plastocyanin (PC) and finally back to cholorphyll P700 (PS I) . During this movement of electrons Adenosine Di Phosphate (ADP) is phosphorylated , by the addition of inorganic phosphate and generates Adenosine Tri Phosphate (ATP). Cyclic electron transport produces only ATP and there is no `NADPH + H^(+)` formation . At each step of electron transport , lose potential energy and is used by the transport chain to pump `H^(+)` ions across the thylakoid membrance . The proton gradient triggers ATP formation in ATP synthase enzyme situated on the thylakoid membrane . The proton gradient triggers ATP formation in ATP synthase enzyme situated on the thylakoid membrane. Photosystem I need light of longer wave longer `( gt p700nm)` . It operates under low high intensity , less `CO_(2)` and under anaerobic conditions which makes it considered as earlier in evolution .