Question

what happens during cyclic photophosphorylation State 2 situations in which only cyclic photophosphorylation is seen to occur

Answer 1

In cyclic photophosphorylation (Formation of ATP in presence of light) only one photosystem functions which is P700 (PSI)​. It occurs in stromal lamellae in the chloroplast. In cyclic photophosphorylation​, electrons from P700 (PSI) are returned to it via the cytochrome b6f complex. There is no NADP⁺reduction, but protons are pumped across the membrane and therefore ATP is generated.

Two situations in which only cyclic photophosphorylation occurs

• Cyclic photophosphorylation is favoured in plants when concentration of ATP is low in plants and NADPH is high.
• Cyclic photophosphorylation also occurs when only light of wavelengths beyond 680 nm are available for excitation.