Identify the reaction for which the `C_(4)` plants require some extra ATP molecules in comparison to `C_(3)` plants

Options

A. Conversion of PEP to OAA
B. Conversion of Pyruvate to PEP
C. Conversion of Malate to Oxaloacetate
D. Conversion of PEP to Malate

Answer

### Step-by-Step Solution:

1. **Understanding C4 Photosynthesis**: C4 plants utilize a specific pathway for photosynthesis that differs from C3 plants. In C4 photosynthesis, carbon fixation occurs in two distinct types of cells: mesophyll cells and bundle sheath cells.

2. **Initial Carbon Fixation**: In the mesophyll cells, the enzyme phosphoenolpyruvate carboxylase (PEP carboxylase) catalyzes the reaction where carbon dioxide (CO2) is fixed to phosphoenolpyruvate (PEP) to form oxaloacetic acid (OAA), which is a four-carbon compound.

3. **Conversion of Pyruvate to PEP**: After the initial fixation, pyruvate, which is produced during the process, must be converted back to PEP to continue the cycle. This conversion requires ATP.

4. **ATP Requirement**: The conversion of pyruvate to PEP consumes ATP. Specifically, C4 plants require more ATP than C3 plants for the same amount of glucose produced. In C4 photosynthesis, the total ATP requirement is about 30 ATP molecules for one glucose molecule, whereas C3 photosynthesis requires about 18 ATP molecules.

5. **Calculating Extra ATP**: The difference in ATP usage between C4 and C3 plants is 30 ATP (C4) - 18 ATP (C3) = 12 ATP. This indicates that C4 plants require 12 additional ATP molecules due to the extra steps involved in their photosynthetic pathway.

6. **Identifying the Reaction**: The specific reaction that requires extra ATP in C4 plants is the conversion of pyruvate to PEP. This is the key step that differentiates the ATP requirements of C4 plants from C3 plants.

### Final Answer:
The reaction for which C4 plants require extra ATP molecules in comparison to C3 plants is the conversion of pyruvate to phosphoenolpyruvate (PEP).

---