the step at which NADPH is required in Calvin cycle

Options

A. Carboxylation
B. Regeneration
C. Reduction
D. Phosphorylation.

Answer

**Step-by-Step Solution:**

1. **Understanding the Calvin Cycle**: The Calvin cycle is a series of biochemical reactions that take place in the chloroplasts of photosynthetic organisms. It is responsible for converting carbon dioxide and other compounds into glucose.

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 step involves the enzyme Rubisco, which catalyzes the reaction between carbon dioxide and ribulose bisphosphate (RuBP). NADPH is not required in this step.
- **Reduction**: In this phase, ATP and NADPH are used to convert 3-phosphoglycerate (3-PGA) into glyceraldehyde-3-phosphate (G3P). Here, NADPH is essential as it provides the reducing power needed for the conversion.
- **Regeneration**: This step involves the conversion of G3P back into RuBP to continue the cycle. ATP is required for this process, but NADPH is not.

4. **Conclusion**: The step in the Calvin cycle where NADPH is required is the **Reduction** phase.

**Final Answer**: The correct option is **Reduction**.

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