39. Following are some facts regarding localization of photosynthetic supramolecular complexes on plastid lamellae:
    A. PSII is preferentially localized on granal lamellae
    B. ATP synthase and PSI is preferentially localized in stroma) lamellae
    C. PSI and PSII are located adjacent to each other in stroma) lamellae
    D. Cytochrome bob complex is not a membrane bound complex

Which of the following combinations of the above statements is true?
(1) A and B                    (2) C and D
(3) B and D          (4) B and C

The correct combination is (1) A and B:

• A. PSII is preferentially localized on granal lamellae
  True. Photosystem II is predominantly found in the stacked regions of thylakoid membranes, known as grana lamellae.​

• B. ATP synthase and PSI is preferentially localized in stroma lamellae
  True. Both ATP synthase and Photosystem I are most abundant in non-stacked (stroma) thylakoid regions, which protrude into the stroma of the chloroplast.​

• C. PSI and PSII are located adjacent to each other in stroma lamellae
  False. PSI and PSII are spatially segregated; PSI is in stroma lamellae, while PSII is mostly in granal stacks. They do not usually reside adjacent in stroma lamellae.​

• D. Cytochrome bob complex is not a membrane bound complex
  False. The cytochrome b6f complex (sometimes written as bob in error) is indeed a membrane-bound complex, essential for linking PSII and PSI via electron transport and proton pumping.​

Organization of Photosynthetic Complexes in Thylakoid Membranes

Introduction

Key phrase: thylakoid lamellae photosystem II ATP synthase PSI localization membrane complex chloroplast

Efficient photosynthesis depends on the distinctive localization of supramolecular complexes in the thylakoid membrane—each positioned for optimal electron flow and energy conversion.​

Explanation of Each Statement

• A. Correct. PSII is concentrated in granal lamellae.

• B. Correct. ATP synthase and PSI are enriched in stroma lamellae.

• C. Incorrect. PSI and PSII are usually segregated; no close adjacency in stroma lamellae.​

• D. Incorrect. Cytochrome b6f is a classic membrane-bound complex essential for electron transport and proton gradient generation.​

Key Facts: Thylakoid Protein Complex Localization

• PSII: Stacked/grana thylakoid lamellae.

• PSI and ATP synthase: Non-stacked/stromal thylakoid lamellae.

• Cytochrome b6f: Membrane-bound, present in both grana and stroma lamellae, but not soluble.​