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. **Identify the Dark Reaction**: The dark reaction, also known as the Calvin cycle, is a part of photosynthesis that does not directly require light. It occurs in the stroma of chloroplasts in photosynthetic plants.

2. **Determine the Primary CO2 Acceptor**: In the Calvin cycle, the primary CO2 acceptor is a molecule called ribulose-1,5-bisphosphate, commonly abbreviated as RUBP.

3. **Analyze the Structure of RUBP**: To find out how many carbon atoms are present in RUBP, we can look at its chemical structure. RUBP consists of a five-carbon sugar.

4. **Count the Carbon Atoms**: By examining the structure of RUBP, we can count the number of carbon atoms:
- Carbon 1
- Carbon 2
- Carbon 3
- Carbon 4
- Carbon 5
Thus, there are a total of 5 carbon atoms in RUBP.

5. **Conclude the Answer**: Since RUBP is the primary CO2 acceptor in the dark reaction and 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**.

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