The form of carbon used for carboxylation of phosphoenol pyruvate in `C_(4)` plants is

Options

A. `H_(2)CO_(3)`
B. `C_(2)H_(4)`
C. `CH_(4)`
D. `HCO_(3)^(-)`

Answer

To solve the question regarding the form of carbon used for carboxylation of phosphoenol pyruvate (PEP) in C4 plants, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding C4 Photosynthesis**:
- C4 plants have a unique mechanism of photosynthesis that allows them to efficiently fix carbon dioxide in hot and dry environments.

2. **Identifying the Primary Acceptors**:
- In C4 plants, phosphoenol pyruvate (PEP) acts as the primary carbon dioxide acceptor. This occurs in the mesophyll cells of the plant.

3. **Carboxylation Reaction**:
- The carboxylation of PEP involves the addition of carbon dioxide. However, in C4 plants, carbon dioxide is not directly used; instead, it undergoes a transformation.

4. **Formation of Bicarbonate**:
- Carbon dioxide (CO2) can react with water (H2O) to form carbonic acid (H2CO3), which then dissociates into bicarbonate ions (HCO3^-). This bicarbonate ion is the form of carbon that will participate in the carboxylation of PEP.

5. **Role of Enzyme**:
- The enzyme responsible for this reaction is PEP carboxylase, which catalyzes the reaction between PEP and bicarbonate ions to form oxaloacetic acid, a four-carbon compound.

6. **Conclusion**:
- Therefore, the form of carbon used for the carboxylation of phosphoenol pyruvate in C4 plants is bicarbonate ions (HCO3^-).

### Final Answer:
The correct answer is bicarbonate ions (HCO3^-).

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