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 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 combines with CO2 to form a 4-carbon compound, which is why the cycle is referred to as the C4 cycle.

2. **Determine the Location of the CO2 Acceptor**:
- PEP is present in the **mesophyll cells** of the plant, where the initial fixation of CO2 occurs.

3. **Identify the Enzyme Responsible for CO2 Fixation**:
- The enzyme that catalyzes the reaction between PEP and CO2 to form oxaloacetic acid (OAA) is called **PEP carboxylase**.
- This enzyme is specific to the C4 pathway and is responsible for the initial fixation of CO2.

4. **Summarize the Findings**:
- Therefore, the answers to the blanks in the question are:
- (i) PEP (phosphoenolpyruvate)
- (ii) PEP carboxylase

### Final Answer:
In the C4 cycle, the primary CO2 acceptor is a 3C molecule **PEP** and is present in the mesophyll cells. The enzyme responsible for this fixation is **PEP carboxylase**.