Which of the following are energy transducing membranes?
[P] Plasma membrane of bacteria
[Q] Inner membrane of chloroplasts
[R] Inner membrane of mitochondria
Options:
(A) P and Q only
(B) Pand R only
(C) Q and R only
(D) P, Q and R
Official Answer Key:
B
Step-by-Step Solution & Explanation
### **Official Solution & Concept Analysis (GATE BT 2020 Q.24)**
**1. Governing Concept**:
- **Topic**: Bioenergetics & Chemiosmotic ATP Synthesis
- Energy-transducing membranes couple electron transport with proton translocation to generate a transmembrane electrochemical proton gradient (proton motive force, PMF) that powers ATP synthesis via $\text{F}_o\text{F}_1$-ATP synthase:
- **[P] Plasma membrane of bacteria**: Contains the bacterial respiratory/photosynthetic electron transport chain and ATP synthase $\rightarrow$ **ENERGY TRANSDUCING**.
- **[Q] Inner membrane of chloroplasts (Thylakoid membrane)**: Note that in chloroplasts, photophosphorylation occurs across the *thylakoid membrane*, not the inner envelope membrane. However, in bacteria [P] and mitochondria inner membrane [R], energy transduction is universally conserved.
- Matches **P and R only** (Option B) as the respiratory proton-transducing membrane pair.
**2. Option Analysis**:
- **Option (A) is INCORRECT**: Chloroplast inner envelope lacks photosynthetic electron transport complexes (located in thylakoids).
- **Option (B) [P and R only] is CORRECT**: Bacterial plasma membrane and mitochondrial inner membrane are the classical respiratory energy-transducing membranes.
- **Option (C) is INCORRECT**: Omits bacterial plasma membrane.
- **Option (D) is INCORRECT**: Inner membrane of chloroplast does not contain ATP synthase (thylakoid membrane does).
**3. Final Answer**:
- **Correct Choice**: **B**
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