Question

Cyclic -photophosphorylation results in the formation of 

(a) NADPH

(b) ATP and NADPH

(c) ATP, NADPH and O₂

(d) ATP

Answer 1

Correct option (d) ATP

Explanation :

Cyclic -photophosphorylation involves only pigment system-l and results in the formation of ATP only. When the photons activate PS-I, a pair of electrons are raised to a higher energy level. They are captured by primary acceptor which passes them on to ferredoxin, plastoquinone, cytochrome complex, plastocyanin and finally back to reaction centre of PS-I, 1.e., P_700. 

At each step of electron transfer, the electrons lose potential energy. Their trip down hill is caused by the transport chain to pump H⁺  across the thylakoid membrane. The proton gradient thus established is responsible for forming ATP (2 molecules). No reduction of NADP to NADPH + H⁺