Fixation of one `CO_(2)` molecule through calvin cycle requires

Options

A. 1 ATP and 2NADP`H_(2)`
B. 2 ATP and `2NADPH_(2)`
C. 3 ATP and `2NADPH_(2)`
D. 2 ATP and `1NADPH_(2)`

Explanation

To determine the fixation of one CO₂ molecule through the Calvin cycle, we need to analyze the requirements for ATP and NADPH2 in each of the three main steps of the cycle: fixation of carbon, reduction of carbon, and regeneration of RuBP (ribulose bisphosphate).

### Step-by-step Solution:

1. **Understanding the Calvin Cycle**: The Calvin cycle consists of three main phases: carbon fixation, reduction, and regeneration of RuBP. Each phase requires specific energy inputs in the form of ATP and NADPH.

2. **Carbon Fixation**: In the first step, CO₂ is fixed by combining it with RuBP. This reaction is catalyzed by the enzyme RuBisCO. This step does not require ATP or NADPH directly.

3. **Reduction Phase**:
- After carbon fixation, the resulting 3-phosphoglycerate (3-PGA) molecules are converted into glyceraldehyde-3-phosphate (G3P).
- This conversion requires ATP and NADPH. Specifically, it requires:
- 1 ATP for the phosphorylation of 3-PGA to 1,3-bisphosphoglycerate.
- 1 NADPH to reduce 1,3-bisphosphoglycerate to G3P.
- Therefore, for the reduction of one CO₂ molecule, we need 1 ATP and 1 NADPH.

4. **Regeneration of RuBP**:
- The G3P molecules produced can be used to regenerate RuBP. This process requires additional ATP.
- For the regeneration of RuBP, it takes:
- 1 ATP to convert G3P back to RuBP.
- Thus, in total for the regeneration phase, we need 1 ATP.

5. **Total Requirements for Fixing One CO₂**:
- From the reduction phase: 1 ATP + 1 NADPH
- From the regeneration phase: 1 ATP
- Therefore, the total requirement for fixing one CO₂ molecule is:
- **Total ATP = 1 (from reduction) + 1 (from regeneration) = 2 ATP**
- **Total NADPH = 1 (from reduction) = 1 NADPH**

### Final Answer:
To fix one CO₂ molecule through the Calvin cycle, it requires **2 ATP and 1 NADPH**.