Calvin cycle or dark reaction of photosynthesis is a light-independent reaction in which products of the light reaction are consumed . In which step of the Calvin cycle these products are not consumed ?

Options

A. Carboxylation
B. Reduction
C. Regeneration
D. Both (B) and (C)

Answer

**Step-by-Step Solution:**

1. **Understanding the Calvin Cycle**: The Calvin cycle, also known as the dark reaction, is a series of biochemical reactions that occur in the stroma of chloroplasts. It does not require light directly but utilizes the products of the light-dependent reactions (ATP and NADPH).

2. **Identifying the Steps of the Calvin Cycle**: The Calvin cycle consists of three main phases:
- Carboxylation
- Reduction
- Regeneration

3. **Analyzing Each Step**:
- **Carboxylation**: This is the first step where carbon dioxide is fixed into an organic molecule. During this step, ATP and NADPH are not consumed.
- **Reduction**: In this step, ATP and NADPH are used to convert 3-phosphoglycerate (3-PGA) into glyceraldehyde-3-phosphate (G3P). Therefore, ATP and NADPH are consumed in this step.
- **Regeneration**: This step involves converting G3P back into ribulose bisphosphate (RuBP) to continue the cycle. ATP is consumed in this process as well.

4. **Conclusion**: The only step in the Calvin cycle where the products of the light reaction (ATP and NADPH) are not consumed is the **Carboxylation** step.

5. **Final Answer**: The correct answer is **Carboxylation** (Option 1).

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