In the `C_4` cycle, the primary `CO_2` acceptor is a 3C molecule ………(i)…………and is present in the mesophyll cells. The enzyme responsible for this fixation is …….(ii)…….

Options

A. (i) PEP (ii) PEP carboxylase
B. (i) PEP (ii) RuBiSCO
C. (i) OAA (ii) PEP carboxylase
D. (i) PGA (ii) RuBisCO

Answer

To solve the question regarding the C4 cycle, we need to identify two key components: the primary CO2 acceptor and the enzyme responsible for this fixation.

### Step-by-Step Solution:

1. **Identify the Primary CO2 Acceptor**:
- In the C4 cycle, the primary CO2 acceptor is a 3-carbon molecule. This molecule is known as **Phosphoenolpyruvate (PEP)**.
- PEP is present in the mesophyll cells of C4 plants, where the initial fixation of CO2 occurs.

2. **Identify the Enzyme Responsible for CO2 Fixation**:
- The enzyme that catalyzes the reaction of CO2 with PEP to form a 4-carbon compound is called **PEP carboxylase**.
- This enzyme is specifically located in the mesophyll cells and is crucial for the initial step of the C4 pathway.

### Final Answer:
(i) Phosphoenolpyruvate (PEP)
(ii) PEP carboxylase

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