Which one of the following phenomena is represented by Calvin cycle?

Options

A. oxidative carboxylation
B. dark phosphorylation
C. dark respiartion
D. reductive carboxylation

Answer

### Step-by-Step Solution:

1. **Understanding the Calvin Cycle**: The Calvin Cycle is a series of biochemical reactions that take place in the stroma of chloroplasts in photosynthetic organisms. It is primarily responsible for the fixation of carbon dioxide (CO2) into organic molecules.

2. **Identifying the Steps of the Calvin Cycle**:
- **Carboxylation**: This is the first step where CO2 is added to ribulose bisphosphate (RuBP) to form 3-phosphoglycerate (3-PGA).
- **Reduction**: In this step, ATP and NADPH produced in the light-dependent reactions are used to convert 3-PGA into glyceraldehyde-3-phosphate (G3P).
- **Regeneration**: The final step involves the conversion of G3P back into RuBP, allowing the cycle to continue.

3. **Analyzing the Options**:
- **Oxidative Phosphorylation**: This process occurs in cellular respiration, not in the Calvin Cycle.
- **Phosphorylation**: While phosphorylation occurs in various biological processes, it does not specifically represent the Calvin Cycle.
- **Dark Phosphorylation**: This term is not commonly used and does not accurately describe the Calvin Cycle.
- **Dark Respiration**: This refers to the process of respiration that occurs without light, which is not the same as the Calvin Cycle.
- **Reductive Carboxylation**: This term describes the process of fixing CO2 and reducing it, which aligns with the steps of the Calvin Cycle.

4. **Conclusion**: Based on the analysis, the phenomenon represented by the Calvin Cycle is best described as **Reductive Carboxylation**.

### Final Answer:
The phenomenon represented by the Calvin Cycle is **Reductive Carboxylation**.