Identify the correct sequence of stages of Calvin cycle.

Options

A. Reduction `rarr` Carboxylation `rarr` Regeneration
B. Carboxylation `rarr` Regeneration `rarr` Reduction
C. Carboxylation `rarr` Reduction `rarr` Regeneration
D. Reduction `rarr` Regeneration `rarr` Carboxylation

Answer

To identify the correct sequence of stages of the Calvin cycle, we need to understand the three main stages involved in this process. The Calvin cycle is crucial for the synthesis of glucose in plants and occurs in the stroma of chloroplasts during the light-independent reactions of photosynthesis.

### Step-by-Step Solution:

1. **Carboxylation**:
- The first stage of the Calvin cycle is carboxylation. In this stage, carbon dioxide (CO2) is fixed into an organic molecule. This process is facilitated by the enzyme ribulose bisphosphate carboxylase/oxygenase (Rubisco).
- CO2 combines with ribulose-1,5-bisphosphate (RuBP) to form 3-phosphoglycerate (3-PGA).

2. **Reduction**:
- The second stage is the reduction phase. Here, the 3-PGA molecules are converted into glyceraldehyde-3-phosphate (G3P) using ATP and NADPH produced during the light reactions of photosynthesis.
- This stage is crucial as it leads to the formation of glucose and other carbohydrates.

3. **Regeneration**:
- The final stage is regeneration. In this phase, some of the G3P molecules are used to regenerate RuBP, allowing the cycle to continue. This regeneration process also requires ATP.
- The regeneration of RuBP is essential for the cycle to repeat and continue fixing CO2.

### Correct Sequence:
Based on the above explanation, the correct sequence of stages in the Calvin cycle is:
1. Carboxylation
2. Reduction
3. Regeneration

Thus, the correct answer is **Option C: Carboxylation, Reduction, and Regeneration**.

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