Question

Which of the following is correct regarding cyclic photophosphorylation?

• A. It involves both PS-l and PS-ll
• B. The electrons released from PS-I are again cycled back to PS-I
• C. It requires an external electron donor
• D. Both ATP and NADPH are formed

Answer 1

The correct option is B The electrons released from PS-I are again cycled back to PS-I

During cyclic photophosphorylation, only PS-I is involved but not PS-II. The reaction centre of PS-I absorbs light of wavelength 700 nm and releases electrons which pass through the electron transport system and are cycled back to the reaction centre. Hence it does not require an external electron donor. During cyclic photophosphorylation, there is only synthesis of ATP but not NADPH unlike non-cyclic photophosphorylation where both ATP and NADPH are synthesised. This process occurs in the membrane of stromal lamella and usually occurs when light of wavelength beyond 680 nm is available.

In non-cyclic photophosphorylation, the electrons from PS-I are picked up by NADP+ and NADPH is synthesised.

Cyclic photophosphorylation