The Calvin cycle proceed in three stages:
1. Radiation, during which carbohydrate is formed at the expense of the Photochemically made ATP and NADPH.
2. Regeneration, during which the carbon dioxide acceptor ribulose-1,5-biphate is formed.
3. Carboxylation, during which the carbon dioxide combines with ribulose-1,5-biphosphate.
Identify the correct sequence.

Options

A. `3rarr1rarr2`
B. `3rarr2rarr1`
C. `1rarr2rarr3`
D. `2rarr1rarr3`

Answer

To identify the correct sequence of the Calvin cycle stages, we need to analyze the three stages mentioned in the question: Carboxylation, Reduction (often referred to as Radiation in the question), and Regeneration. Here’s the step-by-step solution:

### Step 1: Understand the Stages of the Calvin Cycle
1. **Carboxylation**: This is the first stage where carbon dioxide (CO2) is fixed. In this process, CO2 combines with ribulose-1,5-bisphosphate (RUBP) to form a stable intermediate, which is 3-phosphoglycerate (3-PGA). The enzyme Rubisco catalyzes this reaction.

2. **Reduction (Radiation)**: In this stage, 3-PGA is converted into glyceraldehyde-3-phosphate (G3P) using ATP and NADPH produced during the light-dependent reactions of photosynthesis. This is where carbohydrates are formed.

3. **Regeneration**: The final stage involves the regeneration of RUBP from G3P, allowing the cycle to continue. This process requires ATP.

### Step 2: Sequence the Stages
Based on the understanding of each stage:
- **First Stage**: Carboxylation (CO2 combines with RUBP)
- **Second Stage**: Reduction (Formation of carbohydrates)
- **Third Stage**: Regeneration (RUBP is regenerated)

### Conclusion: Correct Sequence
Thus, the correct sequence of the Calvin cycle is:
1. Carboxylation
2. Reduction (Radiation)
3. Regeneration

The answer to the question is that the correct option is the first one, which corresponds to the sequence: Carboxylation → Reduction → Regeneration.