Question

In the light reaction of photosynthesis, $NADP{H}_2$ and ATP are formed during

• A. non-cyclic photophosphorylation
• B. cyclic photophosphorylation
• C. both cyclic and non cyclic photophosphorylation
• D. Calvin cycle

Answer 1

Answer: (A)

Non-cyclic photophosphorylation is the normal process of photophosphorylation in which the electron expelled by the excited photocentre does not return to it. It is carried out in collaboration of both photosystems I and II. Electron released during photolysis of water is picked up by photocentre of PS II called $P_{680}$. It passes through a series of electron carriers-phaeophytin, PQ, cytochrome $b-f$ complex and plastocyanin. While passing over cytochrome complex, the electron loses sufficient energy for the synthesis of ATP. The electron is handed over to photocentre $P_{700}$ of PS I by plastocyanin. The electron passes through X, Fe-S, ferredoxin, and NADP reductase which combines it with NADP ${}^{+}$ for becoming reduced though $H^{+}$ released during photolysis to form NADPH. In cyclic process, $NADP{H}_2$ is not formed.