In Calvin cycle which stage needs ATP?

Options

A. Carboxylation only
B. Only regeneration
C. Both carboxylation and reduction
D. Both reduction and regeneration

Answer

### Step-by-Step Solution:

1. **Understanding the Calvin Cycle**: The Calvin Cycle, also known as the dark reaction of photosynthesis, occurs in the chloroplasts of plant cells and consists of three main stages: fixation, reduction, and regeneration.

2. **Identifying the Stages**:
- **Fixation**: In this stage, carbon dioxide is fixed by the enzyme Rubisco, leading to the formation of a stable product called phosphoglyceric acid (PGA).
- **Reduction**: In this stage, ATP and NADPH are used to convert PGA into glyceraldehyde-3-phosphate (G3P).
- **Regeneration**: In this stage, ATP is used to regenerate ribulose bisphosphate (RuBP) from G3P, allowing the cycle to continue.

3. **Determining ATP Usage**:
- During the **reduction phase**, ATP is utilized to convert PGA into G3P. Specifically, 6 ATP molecules are converted into 6 ADP molecules.
- During the **regeneration phase**, ATP is again utilized to regenerate RuBP from G3P. This also requires ATP.

4. **Conclusion**: In the Calvin Cycle, ATP is needed in both the reduction and regeneration stages. Therefore, the stages that require ATP are the reduction and regeneration phases.

### Final Answer:
The stages in the Calvin Cycle that need ATP are the **reduction and regeneration** phases.

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