During Calvin cycle , the first step in the regeneration of `CO_2` acceptor is

Options

A. Reduction
B. Condensation
C. Dephosphorylation
D. Isomerisation

Answer

**Step-by-Step Solution:**

1. **Understanding the Calvin Cycle**: The Calvin cycle is a crucial process in photosynthesis that occurs in three main stages: carboxylation, reduction, and regeneration.

2. **Identifying the Stages**:
- **Carboxylation**: This is the first step where carbon dioxide (CO2) is fixed. CO2 combines with ribulose bisphosphate (RuBP) to form 3-phosphoglycerate (3-PGA).
- **Reduction**: In this stage, ATP and NADPH (produced in the light reactions) are used to convert 3-PGA into glyceraldehyde-3-phosphate (G3P), a carbohydrate.
- **Regeneration**: This is the final stage where RuBP is regenerated to allow the cycle to continue.

3. **Focusing on Regeneration**: The question specifically asks about the first step in the regeneration of the CO2 acceptor (RuBP).

4. **Determining the First Step in Regeneration**: The first step in the regeneration of RuBP involves the conversion of G3P back into RuBP. This process requires ATP and involves several enzymatic reactions.

5. **Conclusion**: The correct answer to the question is that the first step in the regeneration of the CO2 acceptor (RuBP) is **reduction**.

**Final Answer**: The first step in the regeneration of the CO2 acceptor during the Calvin cycle is **reduction**.

---