In `C_4` pathway, `CO_(2)` fixation in mesophyll cells is carried out by the enzyme

Options

A. PEP carboxylase
B. Pyruvate dehydrogenase
C. Rubisco
D. Pyruvate decarboxylase.

Answer

To solve the question regarding which enzyme is responsible for CO₂ fixation in the mesophyll cells during the C₄ pathway, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the C₄ Pathway**: The C₄ pathway is a photosynthetic process that occurs in certain plants (C₄ plants) that have adapted to high light intensities and temperatures. It involves two types of cells: mesophyll cells and bundle sheath cells.

2. **Identify the Role of Mesophyll Cells**: In the C₄ pathway, the initial fixation of carbon dioxide (CO₂) occurs in the mesophyll cells. This is different from the C₃ pathway, where CO₂ fixation occurs in the same cells as the Calvin cycle.

3. **Know the Enzymes Involved**: The key enzyme that facilitates the fixation of CO₂ in the mesophyll cells of C₄ plants is called PEP carboxylase. This enzyme catalyzes the reaction where phosphoenolpyruvate (PEP) combines with CO₂ to form oxaloacetic acid (OAA).

4. **Differentiate Between C₄ and C₃ Pathways**: In the C₃ pathway, the enzyme RuBisCO is responsible for CO₂ fixation, but it is located in the bundle sheath cells and is not the enzyme of interest in the C₄ pathway.

5. **Conclusion**: Based on the understanding of the C₄ pathway and the role of PEP carboxylase, we conclude that the enzyme responsible for CO₂ fixation in mesophyll cells during the C₄ pathway is PEP carboxylase.

### Final Answer:
The enzyme responsible for CO₂ fixation in mesophyll cells in the C₄ pathway is **PEP carboxylase**.

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