In the mesophyll cells of CAM plants, `CO_(2)` fixation during the night day occurs through

Options

A. RuBP oxygenase
B. PEP carboxylase
C. RuBP carboxylase
D. Both RuBP carboxylase and PEP carboxylase

Answer

To solve the question regarding CO2 fixation in the mesophyll cells of CAM (Crassulacean Acid Metabolism) plants during the night, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding CAM Plants**:
- CAM plants are adapted to arid conditions and have a unique photosynthetic pathway that allows them to conserve water. They typically open their stomata at night to take in carbon dioxide (CO2) when temperatures are cooler and humidity is higher.

2. **CO2 Fixation Timing**:
- In CAM plants, CO2 fixation occurs at night. This is crucial for minimizing water loss through transpiration, which would occur if the stomata were open during the hotter daytime.

3. **Process of CO2 Fixation**:
- During the night, the CO2 that enters the plant is fixed into an intermediate compound. In CAM plants, this is primarily done through a process that converts CO2 into malic acid.

4. **Enzyme Involved**:
- The enzyme responsible for this fixation of CO2 into malic acid is called **PEP carboxylase**. This enzyme catalyzes the reaction that combines CO2 with phosphoenolpyruvate (PEP) to form oxaloacetate, which is then converted into malic acid.

5. **Daytime Utilization**:
- During the day, the malic acid that was produced at night is decarboxylated to release CO2 for the Calvin cycle, which ultimately leads to the production of glucose and other carbohydrates.

### Final Answer:
In the mesophyll cells of CAM plants, CO2 fixation during the night occurs through **PEP carboxylase**.

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