Question

4. Which one of the following is NOT involved in photosynthetic electron transport process?

• A. Plastoquinone(PQ)
• B. Pheophytin (Pheo)
• C. ATP synthase
• D. Photosystem I

Hint:

The electron transport chain (PSI, PSII, Pheophytin, Plastoquinone, Plastocyanin) is responsible for generating a proton gradient across the thylakoid membrane. ATP synthase is the enzyme that harnesses this gradient to make ATP, but it does not transport electrons.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
The light reactions of photosynthesis involve two coupled, sequential processes: the photosynthetic electron transport chain (which moves electrons from water to \(\text{NADP}^+\)) and photophosphorylation (which synthesizes ATP).

Step 2: Detailed Explanation:
Let us analyze the role of each component:
Photosystem I (D), Pheophytin (B), and Plastoquinone (A): These are direct, integral components of the photosynthetic electron transport chain.
- Photoexcitation of Photosystem II transfers an electron to the primary electron acceptor, Pheophytin.
- From Pheophytin, the electron is transferred to the mobile lipid-soluble carrier, Plastoquinone.
- Plastoquinone transfers electrons to the Cytochrome \(b_6f\) complex, which eventually routes them to Photosystem I to reduce \(\text{NADP}^+\).
Each of these components is directly involved in transferring electrons.
ATP Synthase (C): This is a transmembrane protein complex that utilizes the proton motive force (proton gradient across the thylakoid membrane) to synthesize ATP from ADP and inorganic phosphate.
It is involved in photophosphorylation but is not an electron carrier and is not directly involved in the photosynthetic electron transport process itself.
Therefore, ATP synthase is the correct exception.

Step 3: Final Answer:
ATP synthase is not directly involved in the electron transport chain, corresponding to option (C).