In the pathway of dark reaction, which occurs in all photosynthetic plants, the primary `CO_2` acceptor contains how many carbons?

Options

A. Three
B. Four
C. One
D. Five

Answer

To solve the question regarding the primary CO2 acceptor in the dark reaction of photosynthesis, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Dark Reaction**:
- The dark reaction, also known as the Calvin cycle, occurs in the stroma of chloroplasts and does not require light directly. It utilizes the products of the light reactions (ATP and NADPH) along with CO2 to synthesize glucose.

2. **Identifying the Primary CO2 Acceptor**:
- In the dark reaction, the first step involves the fixation of CO2. This is where the primary CO2 acceptor comes into play.

3. **Recognizing the Compound Involved**:
- The primary CO2 acceptor in the dark reaction is Ribulose bisphosphate (RuBP), which is a 5-carbon compound.

4. **Carboxylation Process**:
- During the carboxylation process, one molecule of CO2 combines with RuBP to form 3-phosphoglycerate (3-PGA), which is a 3-carbon compound.

5. **Conclusion**:
- Since RuBP is the primary CO2 acceptor and it contains 5 carbon atoms, the answer to the question is that the primary CO2 acceptor contains **5 carbons**.

### Final Answer:
The primary CO2 acceptor in the dark reaction contains **5 carbons**.

---