The first step of `CO_(2)` fixation in Hatch and Slack's pathway in plants is

Options

A. Formation of OAA by carboxylation of PEP in bundle sheath cells
B. formation of OAA by the carboxylation of RUBP in mesophyll cells
C. formation of PGA in mesophyll cells
D. formation of OAA by carboxylation of PEP in mesophyll cells

Answer

### Step-by-Step Text Solution:

1. **Understanding the C4 Pathway**: The Hatch and Slack pathway, also known as the C4 pathway, is a method of carbon fixation in certain plants, which allows them to efficiently utilize CO2.

2. **Identifying the First Step**: The first step of CO2 fixation in the C4 pathway involves the carboxylation of phosphoenolpyruvate (PEP).

3. **Location of the Reaction**: This reaction occurs in the mesophyll cells of the plant.

4. **Enzyme Involved**: The enzyme responsible for this reaction is called PEP carboxylase.

5. **Formation of the First Product**: The carboxylation of PEP leads to the formation of oxaloacetate (OAA), which is a four-carbon compound.

6. **Summary of the Process**: To summarize, the first step of CO2 fixation in the Hatch and Slack pathway is the carboxylation of PEP to form oxaloacetate in the mesophyll cells, facilitated by the enzyme PEP carboxylase.

### Final Answer:
The first step of CO2 fixation in Hatch and Slack's pathway in plants is the carboxylation of phosphoenolpyruvate (PEP) to form oxaloacetate (OAA) in the mesophyll cells.

---