Question

Read the following statement and select the correct ones.
(i) PS-I is involved in non-cyclic photophosphorylation only.
(ii) PS-II is involved in both cyclic and non-cyclic photophosphorylation.
(iii) Stroma lamellae membranes possess PS-I only, whereas grana lamellae membranes possess both PS-I and PS-II.
A.(i) only
B.(ii) only
C.(iii) only
D.(i), (ii) and (iii)

Answer 1

Hint: Photosystem is a system of two units known as photosystem-I (PS-I) and photosystem-II (PS-II), They both are located in the thylakoid membrane of chloroplast and they are involved in the photosynthesis of plants.

Complete answer:
1.Both the photosystems have various pigments related to photosynthesis and the chlorophyll-a forms the reaction center in both the photosystems but the peak of absorption is 700 nm in PS-I and 680 nm in PS-II.
2.In Non-cyclic phosphorylation both the photosystems are involved. PS-II absorbs light of wavelength 680 nm due to which electrons are excited which are accepted by the electron acceptors then the electrons travel through the electron transport chain after which electrons are accepted by PS-I.

3.But Cyclic phosphorylation involves only PS-I where the electrons travel through the electron transport chain and return to the PS-I.
4.The stroma lamellae do not have PS-II and NADP reductase enzymes whereas the grana lamellae contain both PS-I and PS-II.

Option C: The PS-I is involved in both the cyclic and noncyclic phosphorylation but the PS-II is only involved in noncyclic phosphorylation and has no role in cyclic phosphorylation. Also, the stroma lamellae have only PS-I and grana lamellae have both the photosystems, Hence only statement (iii) is correct, Therefore, this is the correct option.

All other options are irrelevant.

Hence, the correct answer is option (C)

Note: The reason why stroma lamellae lack NADP reductase enzyme and the PS-II is because only cyclic phosphorylation occurs in the stroma lamellae where only PS-I is required and the electrons are not passed to NADP because electrons return to the PS-I again, hence NADP reductase enzyme is not required. Therefore non-cyclic phosphorylation produces both ATP and NADPH whereas cyclic phosphorylation produces ATP only.