Total energy requirement for fixing one `CO_(2)` by combined `C_(4)` and `C_(3)` cycle is -

Options

A. 5 ATP+4 NADPH
B. 3 ATP+4 NADPH
C. 5 ATP+2 NADPH
D. 8 ATP+2 NADPH

Answer

To determine the total energy requirement for fixing one CO₂ molecule by combining the C₄ and C₃ cycles, we will analyze the energy requirements for both cycles step by step.

### Step-by-Step Solution:

1. **Understanding the C₄ Cycle:**
- The C₄ cycle is primarily found in plants adapted to hot and dry climates, such as maize.
- In the C₄ cycle, CO₂ is initially fixed into a 4-carbon compound, oxaloacetic acid.

2. **Energy Requirement for C₄ Cycle:**
- For the fixation of one CO₂ molecule in the C₄ cycle, **2 ATP** molecules are required.
- Additionally, **2 NADPH** molecules are produced during the C₄ cycle.

3. **Understanding the C₃ Cycle:**
- The C₃ cycle, also known as the Calvin cycle, is the process that occurs in all plants for the synthesis of glucose.
- It involves the fixation of CO₂ into a 3-carbon compound.

4. **Energy Requirement for C₃ Cycle:**
- For the fixation of one CO₂ molecule in the C₃ cycle, **3 ATP** molecules are required.

5. **Combining the Energy Requirements:**
- To find the total energy requirement for fixing one CO₂ molecule when combining both cycles:
- From the C₄ cycle: **2 ATP**
- From the C₃ cycle: **3 ATP**
- Total ATP = 2 ATP (C₄) + 3 ATP (C₃) = **5 ATP**
- Additionally, from the C₄ cycle, we have **2 NADPH**.

6. **Final Calculation:**
- Therefore, the total energy requirement for fixing one CO₂ molecule by combining the C₄ and C₃ cycles is:
- **5 ATP + 2 NADPH**

### Conclusion:
The total energy requirement for fixing one CO₂ by combining the C₄ and C₃ cycles is **5 ATP + 2 NADPH**.