Question

Read the following four statements, A, B, C, and D and select the right option having both correct statements.
Statement:
(A) Z scheme of light reaction takes place in presence of PS-I only.
(B) Only PS-1 is functional in cyclic photophosphorylation.
(C) Cyclic photophosphorylation results in the synthesis of ATP and NADPH2
(D) Stroma lamellae lack PS-II as well as NADP.
I. C and D
II. B and D
III. A and B
IV. B and C

Answer 1

Hint: The term PS stands for Photo System. Photophosphorylation can be defined as the process of formation of ATP from ADP in photosynthesis using sunlight. It includes cyclic photophosphorylation and non- photophosphorylation. The high energy electron P700 of PS1 flows down in a cyclic pathway during cyclic photophosphorylation.

Complete step by step answer: Phosphorylation of ADP to form ATP using the energy of sunlight during photosynthesis is called photophosphorylation. It is further classified as cyclic photophosphorylation and non-cyclic photophosphorylation. During photophosphorylation, a high-energy electron donor and a lower-energy electron acceptor are produced using light energy and thus it is transferred through an electron transport chain (ETC). During cyclic photophosphorylation PS-I is active and it produces electron carrier NADPH. It occurs in the stromal lamellae which are also called fret channels. During cyclic photophosphorylation, only ATP is generated and not NADPH2. The non-cyclic flow of electrons from PS-II through quinone, cytochrome b6f complex, and plastocyanin to NADPH through PS-I is called the Z scheme of light reaction. PS-I and PS-II are both included in the Z scheme reaction. Photosystem I is a protein complex that uses the light energy photon to accelerate the transfer of electrons. Transfer of electrons takes place across the thylakoid membrane from plastocyanin to ferredoxin. So, from the above context, it is clear that PS-1 is active only during cyclic photophosphorylation and stromal lamellae lack PS-II and NADP.
So, option II is the correct option.

Note: In both aerobic and anaerobic conditions cyclic photophosphorylation can take place. PS-I and PS-II both are present in grana lamellae. Stromal lamellae consist of only PS-I. Enzyme ATP synthase is used for the formation of ATP during cyclic photophosphorylation.