Question

Arrange the components of photosynthetic machinery of purple bacteria in a sequence followed for flow of electrons :
A. Quinone
B. P870
C. Cyt \(bc_1\) complex
D. Cyt \(c_2\)
E. Pheophytin
Choose the correct answer from the options given below :

• A. \(C, D, A, E, B\)
• B. \(B, E, A, C, D\)
• C. \(A, D, B, C, E\)
• D. \(B, A, E, D, C\)

Hint:

Remember: \[ \text{Purple bacteria perform cyclic photophosphorylation} \] Electron flow: \[ P870 \rightarrow \text{Pheophytin} \rightarrow \text{Quinone} \rightarrow Cyt\,bc_1 \rightarrow Cyt\,c_2 \rightarrow P870 \]
• No oxygen is produced in purple bacterial photosynthesis.

Answer 1

The Correct Option is B

Concept: Purple bacteria perform anoxygenic photosynthesis using a cyclic electron transport system. The reaction center contains: \[ P870 \] which is a special pair of bacteriochlorophyll molecules. During photosynthesis:
• Light excites P870
• Electrons move through a series of carriers
• Electrons eventually return to P870 This cyclic electron flow helps generate: \[ ATP \]

Step 1: Excitation of reaction center P870. The electron flow begins from: \[ P870 \] which becomes photoexcited after absorbing light. Thus, the first component is: \[ \boxed{B} \]

Step 2: Transfer to pheophytin. The excited electron is first transferred to: \[ \text{Pheophytin} \] which acts as the primary electron acceptor. Thus: \[ \boxed{E} \]

Step 3: Transfer to quinone. Electrons next move to: \[ \text{Quinone} \] Thus: \[ \boxed{A} \]

Step 4: Transfer through Cyt \(bc_1\) complex. Electrons are then passed through: \[ \text{Cytochrome } bc_1 \text{ complex} \] which contributes to proton translocation. Thus: \[ \boxed{C} \]

Step 5: Return via Cyt \(c_2\). Finally: \[ \text{Cytochrome } c_2 \] returns electrons back to: \[ P870 \] completing the cyclic electron flow. Thus: \[ \boxed{D} \] Therefore, the correct sequence is: \[ \boxed{P870 \rightarrow \text{Pheophytin} \rightarrow \text{Quinone} \rightarrow Cyt\,bc_1 \rightarrow Cyt\,c_2} \] Hence, the correct answer is: \[ \boxed{(B)\ B, E, A, C, D} \]