Explain cyclic photosphosphorylation .

Explanation

1. Cyclic photophosphorylation refers to the electrons ejected from the pigment system I (Photosystem I) and again cycled back to the PS I.
2. When te photons activate P700 reaction centre photosystem II is activated. Electrons are raised to high enery level .
3. During this movement of electrons Adenosine Di Phosphate (ADP) is phosphorylated , by the addition of inorganic phosphate and generates Adenosine Tri Phosphate (ATP).
4. Cyclic electron transport produces only ATP and there is no `NADPH + H^(+)` formation .
5 At each step of electron transport , electron loses potential energy and is used by the transport chain to pump `H^(+)` ions across the thylakoid membrane . The proton gradient triggers ATP formation in ATP synthase enzyme situated on the thylakoid membrane.

6 Photosystem I need light of longer wave length (`gt P700` nm) . It operates under low light intensity , less `CO_(2)` and under anaerobic conditions which makes it considered as earlier in evolution .