Which one of the following category of electron carriers is not common in ETS of both photosynthesis and respiration ?

Options

A. Quinone
B. plastocyanin
C. Fe-S
D. Cytochrome

Answer

To determine which category of electron carriers is not common in the electron transport systems (ETS) of both photosynthesis and respiration, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Electron Transport System (ETS)**:
- The ETS is a series of protein complexes and other molecules that transfer electrons from electron donors to electron acceptors via redox reactions. This process is crucial in both photosynthesis and cellular respiration.

2. **Identify Electron Carriers in Photosynthesis**:
- In photosynthesis, the main electron carriers involved in the ETS are plastoquinone, plastocyanin, and ferredoxin. These carriers facilitate the transfer of electrons during the light-dependent reactions in the thylakoid membranes of chloroplasts.

3. **Identify Electron Carriers in Respiration**:
- In cellular respiration, the electron carriers include NADH, FADH2, and cytochromes. These carriers play a significant role in the mitochondrial electron transport chain, transferring electrons derived from glucose breakdown.

4. **Compare the Carriers**:
- Upon comparison, we note that while both processes utilize electron carriers, the specific types of carriers differ. For instance, plastoquinone and plastocyanin are unique to photosynthesis, while NADH and FADH2 are unique to respiration.

5. **Determine the Answer**:
- The category of electron carriers that is not common in both processes is plastoquinone and plastocyanin, as they are specific to the photosynthetic electron transport chain.

### Final Answer:
The category of electron carriers that is not common in the electron transport systems of both photosynthesis and respiration is **plastoquinone and plastocyanin**.

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