During the dark reaction, 3 - PGA is derived from

Options

A. RuBP only
B. `CO_2` only
C. RuBP + `CO_2`
D. RuBP + `CO_2` + PEP

Answer

To solve the question "During the dark reaction, 3-PGA is derived from:", we can break it down step by step.

### Step-by-Step Solution:

1. **Understanding Dark Reactions**:
- Dark reactions, also known as the Calvin cycle, occur in the stroma of chloroplasts and do not require light directly. They utilize the products of the light reactions (ATP and NADPH) to synthesize glucose.

2. **Key Components**:
- The main components involved in the dark reactions are ribulose bisphosphate (RUBP) and carbon dioxide (CO2).

3. **Carboxylation Step**:
- The first step of the dark reaction is carboxylation. In this step, CO2 is fixed by RUBP.
- The enzyme that catalyzes this reaction is called Rubisco (ribulose-1,5-bisphosphate carboxylase/oxygenase).

4. **Formation of 3-PGA**:
- When RUBP combines with CO2, it forms a 6-carbon intermediate that quickly splits into two molecules of 3-phosphoglycerate (3-PGA).
- Therefore, 3-PGA is derived from the combination of RUBP and CO2.

5. **Conclusion**:
- The correct answer to the question is that 3-PGA is derived from RUBP plus CO2.

### Final Answer:
3-PGA is derived from RUBP plus CO2.