The carbon dioxide acceptor in the Calvin cycle is

Options

A. Phosphoenol pyruvate .
B. ribulose 1.5-diphosphate.
C. Phosphoglyceric acid.
D. ribulose monophosphate .

Answer

To determine the carbon dioxide acceptor in the Calvin cycle, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Calvin Cycle**: The Calvin cycle is a series of biochemical reactions that occur in the stroma of chloroplasts in photosynthetic organisms. It is responsible for converting carbon dioxide and other compounds into glucose.

2. **Identify the Main Steps of the Calvin Cycle**: The Calvin cycle consists of three main phases:
- Carboxylation
- Reduction
- Regeneration

3. **Focus on the Carboxylation Step**: The first step of the Calvin cycle is carboxylation, where carbon dioxide is fixed into a stable organic intermediate.

4. **Identify the Carbon Dioxide Acceptor**: During carboxylation, carbon dioxide is combined with a five-carbon sugar called ribulose 1,5-bisphosphate (RUBP). This reaction is catalyzed by the enzyme RuBisCO.

5. **Conclusion**: The carbon dioxide acceptor in the Calvin cycle is ribulose 1,5-bisphosphate (RUBP).

### Final Answer:
The carbon dioxide acceptor in the Calvin cycle is ribulose 1,5-bisphosphate.

---