Which of the following steps of the `C_3`- cycle is crucial step to continue the cycle uninterrupted?

Options

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

Answer

To solve the question regarding which step of the C3 cycle (Calvin cycle) is crucial for the cycle to continue uninterrupted, we can break it down into a step-by-step analysis:

### Step-by-Step Solution:

1. **Understanding the Calvin Cycle**:
- The Calvin cycle, also known as the C3 cycle, is a part of photosynthesis where carbon dioxide is fixed into organic compounds. It occurs in three main stages: carboxylation, reduction, and regeneration.

2. **Identifying the Steps**:
- **Carboxylation (Carbon Fixation)**: This is the first step where ribulose bisphosphate (RuBP) reacts with carbon dioxide (CO2) in the presence of the enzyme RuBisCO.
- **Reduction**: In this step, 3-phosphoglycerate (PGA) is converted into glyceraldehyde-3-phosphate (G3P) using ATP and NADPH.
- **Regeneration**: The final step involves the regeneration of RuBP from G3P, allowing the cycle to continue.

3. **Analyzing the Importance of Each Step**:
- The carboxylation step is critical because it is where CO2 is fixed into an organic molecule. If this step does not occur, the cycle cannot proceed, as there would be no substrate for the subsequent reduction and regeneration steps.
- The reduction and regeneration steps, while important, do not involve the fixation of carbon and thus are not as crucial for the continuation of the cycle.

4. **Conclusion**:
- The crucial step that ensures the Calvin cycle continues uninterrupted is the **carboxylation** step, where RuBP is converted into PGA with the help of RuBisCO.

### Final Answer:
The crucial step to continue the C3 cycle uninterrupted is **carboxylation**.