Number of carboxylations in `C_(4)` cycle is

Options

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

Answer

To determine the number of carboxylations in the C4 cycle, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the C4 Cycle**: The C4 cycle is a photosynthetic pathway that occurs in certain plants (C4 plants) that are adapted to hot and dry environments, such as maize and sugarcane.

2. **Identify the Initial Carbon Fixation**: In the C4 cycle, the initial carbon fixation occurs in the mesophyll cells. This process involves the enzyme phosphoenolpyruvate carboxylase (PEP carboxylase), which combines carbon dioxide (CO2) with phosphoenolpyruvate (PEP) to form oxaloacetate.

3. **Conversion to Malate**: The oxaloacetate is then converted into malate (or aspartate), which is transported to the bundle sheath cells.

4. **Second Carboxylation in Bundle Sheath Cells**: In the bundle sheath cells, malate is decarboxylated to release CO2, which is then fixed by the enzyme ribulose bisphosphate carboxylase/oxygenase (Rubisco) in the Calvin cycle (C3 cycle). This is the second carboxylation step.

5. **Conclusion on Carboxylation**: Since the C4 cycle involves two distinct steps of carbon fixation (one in the mesophyll cells and one in the bundle sheath cells), the total number of carboxylations in the C4 cycle is two.

### Final Answer:
The number of carboxylations in the C4 cycle is **2**.

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