The reaction that is responsible for the primary fixation of `CO_(2)` is catalysed by

Options

A. RuBP carboxylase
B. PEP carboxylase
C. RuBP carboxylase and PEP carboxylase
D. PGA synthase

Answer

To solve the question regarding the reaction responsible for the primary fixation of CO₂, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Carbon Fixation**:
- The primary fixation of carbon dioxide (CO₂) refers to the initial step in the process of photosynthesis where CO₂ is incorporated into organic molecules.

2. **Identifying the Reaction**:
- The specific reaction that incorporates CO₂ into an organic molecule is known as carboxylation. This is a crucial step in the Calvin cycle, which is part of photosynthesis.

3. **Catalyzing Enzyme**:
- The enzyme that catalyzes this carboxylation reaction is known as RuBP carboxylase (also referred to as Rubisco). This enzyme facilitates the reaction between ribulose bisphosphate (RuBP) and CO₂.

4. **Products of the Reaction**:
- The reaction catalyzed by RuBP carboxylase results in the formation of two molecules of 3-phosphoglycerate (3-PGA), which are then used in subsequent steps of the Calvin cycle to produce glucose and other carbohydrates.

5. **Conclusion**:
- Therefore, the correct answer to the question is that the reaction responsible for the primary fixation of CO₂ is catalyzed by RuBP carboxylase.

### Final Answer:
The reaction that is responsible for the primary fixation of CO₂ is catalyzed by RuBP carboxylase.