`CO_(2) NADPH_(2)` ATP ratio in `C_(3)` plants is

Options

A. 1:2:3
B. 1:2:4
C. 1:3:6
D. 1:5:10

Answer

To determine the CO₂, NADPH₂, and ATP ratio in C₃ plants, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the C₃ Cycle**:
- In C₃ plants, photosynthesis occurs primarily in the mesophyll cells where the Calvin cycle (also known as the C₃ cycle) takes place.

2. **Role of Rubisco**:
- The enzyme Rubisco is crucial in the Calvin cycle for the fixation of carbon dioxide (CO₂).

3. **Calvin Cycle Steps**:
- The Calvin cycle consists of three main steps:
1. Carbon fixation
2. Reduction phase
3. Regeneration of RuBP (ribulose bisphosphate)

4. **Energy Requirements**:
- For the fixation of one molecule of CO₂, specific amounts of ATP and NADPH are required:
- **ATP**: 3 molecules
- **NADPH**: 2 molecules

5. **Glucose Formation**:
- To synthesize one glucose molecule (C₆H₁₂O₆), six molecules of CO₂ need to be fixed. This means:
- Total ATP used: 6 CO₂ x 3 ATP = 18 ATP
- Total NADPH used: 6 CO₂ x 2 NADPH = 12 NADPH

6. **Final Ratio Calculation**:
- From the above calculations, for the fixation of one CO₂:
- The ratio of CO₂ : NADPH : ATP is 1 : 2 : 3.

7. **Conclusion**:
- Therefore, the correct ratio of CO₂ to NADPH₂ to ATP in C₃ plants is 1 : 2 : 3.

### Final Answer:
The CO₂ : NADPH₂ : ATP ratio in C₃ plants is **1 : 2 : 3**.

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