In `C_4` plants , numbers of ATP and NADPH molecules required to fiz 2 molecules of `CO_2` are respectively

Options

A. 6 & 10
B. 10 & 6
C. 4 & 10
D. 10 & 4

Answer

To solve the question regarding the number of ATP and NADPH molecules required to fix 2 molecules of CO2 in C4 plants, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding C4 Photosynthesis**:
- C4 plants utilize a unique pathway for carbon fixation that involves the formation of a 4-carbon compound. This process is different from the C3 pathway and is more efficient in certain environments.

2. **Carbon Fixation Process**:
- In C4 plants, CO2 is initially fixed into a 4-carbon compound (oxaloacetate) by the enzyme phosphoenolpyruvate carboxylase (PEP carboxylase).
- The 4-carbon compound is then converted into malate or aspartate, which is transported to specialized cells where CO2 is released and enters the Calvin cycle.

3. **ATP and NADPH Requirements**:
- For each molecule of CO2 fixed, the process requires:
- **5 ATP** molecules
- **2 NADPH** molecules
- This is because ATP is needed for both the initial fixation and the regeneration of phosphoenolpyruvate (PEP), while NADPH is used in the reduction phase of the Calvin cycle.

4. **Calculating for 2 Molecules of CO2**:
- Since we need to fix 2 molecules of CO2:
- ATP required = 5 ATP/CO2 × 2 CO2 = **10 ATP**
- NADPH required = 2 NADPH/CO2 × 2 CO2 = **4 NADPH**

5. **Final Answer**:
- Therefore, the number of ATP and NADPH molecules required to fix 2 molecules of CO2 in C4 plants are **10 ATP and 4 NADPH**.

### Conclusion:
The correct option is **10 ATP and 4 NADPH**.