`C_(4)` plants have carboxylations

Options

A. four
B. three
C. two
D. one

Answer

To solve the question regarding the number of carboxylations that occur in C4 plants, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Basics of Photosynthesis**:
- Photosynthesis is the process by which plants convert light energy into chemical energy, primarily through the conversion of carbon dioxide (CO2) and water into glucose and oxygen.

2. **Differentiate Between C3 and C4 Plants**:
- C3 plants perform photosynthesis using a three-carbon compound (3-phosphoglycerate) as the first stable product of carbon fixation. They have a single type of cell (mesophyll cells) where carboxylation occurs.
- C4 plants, on the other hand, have a more complex structure that includes both mesophyll cells and bundle sheath cells. This adaptation allows them to efficiently fix CO2 even under conditions of high temperature and low water availability.

3. **Identify the Carboxylation Process in C4 Plants**:
- In C4 plants, CO2 is initially fixed into a four-carbon compound (oxaloacetate) through the action of the enzyme phosphoenolpyruvate carboxylase (PEP carboxylase) in the mesophyll cells.
- This four-carbon compound is then transported to the bundle sheath cells, where it is converted back to CO2 for the Calvin cycle.

4. **Count the Number of Carboxylations**:
- In C4 plants, the process involves one primary carboxylation event where CO2 is fixed into a four-carbon compound. This is distinct from C3 plants, which have two carboxylation events.

5. **Conclusion**:
- Therefore, the number of carboxylations that occur in C4 plants is **1**.

### Final Answer:
C4 plants have **1** carboxylation.

---