What is the structural basis for the observation that stroma lamellae membranes perform cyclic photophosphorylation but lack non-cyclic photophosphorylation?

Answer and explanation

Correct answer: A. Stroma lamellae lack Photosystem II and NADP+ reductase enzyme

  1. Step 1: Chloroplast thylakoids are differentiated into appressed granal lamellae and non-appressed stroma lamellae.
  2. Step 2: Grana lamellae are enriched in Photosystem II and the oxygen-evolving complex.
  3. Step 3: Stroma lamellae possess Photosystem I and ATP synthase, but lack Photosystem II and the enzyme ferredoxin-NADP+ reductase (FNR).
  4. Step 4: Without PS II (no photolysis of water) and without FNR, non-cyclic electron transport cannot occur, restricting stroma lamellae to cyclic photophosphorylation.
Answer
Stroma lamellae lack Photosystem II and NADP+ reductase enzyme
Why not the others: 'Stroma lamellae contain only Photosystem II...' is the opposite of reality, as PS II is confined to appressed grana; 'Stroma lamellae lack ATP synthase...' is false because ATP synthase complexes are abundant in non-appressed stroma lamellae; 'Stroma lamellae are completely impermeable to water...' is physiologically impossible in aqueous biological systems.

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