Cytochrome `b_(6)` and cytochrome 'f' occur in

Options

A. Ribosomes
B. Mitochondria
C. Chloroplasts
D. Lysosomes.

Answer

To answer the question "Cytochrome b6 and cytochrome f occur in", we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Cytochromes**:
- Cytochromes are redox proteins that play a crucial role in electron transport chains. They contain heme groups with a central iron atom that acts as a cofactor in redox reactions.

2. **Location of Cytochrome b6 and Cytochrome f**:
- Cytochrome b6 and cytochrome f are specifically involved in the photosynthetic process. They are found in the thylakoid membranes of chloroplasts, which are organelles responsible for photosynthesis in plant cells.

3. **Function in Photosynthesis**:
- These cytochromes facilitate the transfer of electrons during the light-dependent reactions of photosynthesis. They help in transferring electrons from plastoquinone (PQ) to plastocyanin (PC).

4. **Comparison with Mitochondria**:
- The cytochrome b6 complex in chloroplasts is analogous to the BC1 complex found in mitochondria, indicating a similar function in energy transfer.

5. **Conclusion**:
- Given that cytochrome b6 and cytochrome f are integral components of the thylakoid membranes in chloroplasts, the correct answer to the question is that they occur in chloroplasts.

### Final Answer:
Cytochrome b6 and cytochrome f occur in **chloroplasts**.

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