In `C_4` plants , `CO_2` is first fixed in

Options

A. Bundle sheath
B. Mesophyll
C. Guard cells
D. All epidermal cells

Answer

**Step-by-Step Solution:**

1. **Understanding C4 Photosynthesis:**
- C4 plants have a unique mechanism for photosynthesis that involves two types of cells: mesophyll cells and bundle sheath cells.

2. **Initial Carbon Fixation:**
- In C4 plants, carbon dioxide (CO2) is initially fixed in the mesophyll cells. This process involves the enzyme PEP carboxylase, which catalyzes the reaction to form four-carbon compounds, such as oxaloacetic acid.

3. **Transport of Compounds:**
- The four-carbon compounds produced in the mesophyll cells are then transported to the bundle sheath cells.

4. **Decarboxylation in Bundle Sheath Cells:**
- In the bundle sheath cells, the four-carbon compounds undergo decarboxylation, releasing CO2. This CO2 is then used in the Calvin cycle, facilitated by the enzyme rubisco.

5. **Conclusion:**
- Therefore, the correct answer to the question "In C4 plants, CO2 is first fixed in" is the mesophyll cells.

**Final Answer:**
In C4 plants, CO2 is first fixed in mesophyll cells.

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