Proton translocation is observed through a membrane complex present on thylakoid membranes namely

Options

A. PS-II complex
B. PS-I complex
C. Cytochrome `b_(6)` f complex
D. `CF_(0) - CF_(1)` complex

Answer

To answer the question regarding proton translocation through a membrane complex present on thylakoid membranes, we will follow these steps:

### Step-by-Step Solution:

1. **Understanding the Context**: The question asks about proton translocation, which is a key process in photosynthesis occurring in chloroplasts, specifically on the thylakoid membranes.

2. **Identifying the Complex**: The options provided are:
- PS2 complex
- PS1 complex
- Cytochrome B6F complex
- CF0, CF1 complex

3. **Analyzing the Functions**:
- **PS1 and PS2**: These are photosystems involved in capturing light energy and converting it into chemical energy but are not primarily responsible for proton translocation.
- **CF0, CF1 complex**: This is associated with ATP synthesis but does not directly mediate proton translocation.
- **Cytochrome B6F complex**: This complex is known for its role in the electron transport chain and is specifically involved in proton translocation across the thylakoid membrane.

4. **Mechanism of Proton Translocation**: The cytochrome B6F complex facilitates the movement of protons into the thylakoid lumen during the process of water oxidation. This process occurs when water molecules are split, releasing protons and oxygen. The protons are then translocated into the thylakoid lumen, creating a proton gradient that is crucial for ATP synthesis.

5. **Conclusion**: Based on the analysis, the correct answer to the question is the **Cytochrome B6F complex**. This complex is responsible for proton translocation observed on the thylakoid membranes.

### Final Answer:
The membrane complex present on thylakoid membranes that facilitates proton translocation is the **Cytochrome B6F complex**.

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