Regeneration of four molecules of RuBP in `C_3` cycle requires the expenditure of ATP.

Options

A. 1
B. 4
C. 3
D. 2

Answer

To solve the problem regarding the regeneration of four molecules of RuBP in the C3 cycle (also known as the Calvin cycle), we can break down the process step by step:

### Step-by-Step Solution:

1. **Understanding the C3 Cycle**:
The C3 cycle, or Calvin cycle, is a series of biochemical reactions that occur in the chloroplasts of plants during photosynthesis. It consists of three main phases: carboxylation, reduction, and regeneration.

2. **Focus on the Regeneration Phase**:
The regeneration phase is where the RuBP (ribulose bisphosphate) is regenerated from the products of the reduction phase. This is crucial for the cycle to continue.

3. **ATP Requirement for RuBP Regeneration**:
In the regeneration phase, each molecule of RuBP requires one molecule of ATP to regenerate.

4. **Calculating ATP for Four Molecules of RuBP**:
If one RuBP requires one ATP, then for four molecules of RuBP, the total ATP required would be:
\[ \text{ATP needed} = 4 \text{ RuBP} \times 1 \text{ ATP/RuBP} = 4 \text{ ATP} \]

5. **Conclusion**:
Therefore, the regeneration of four molecules of RuBP in the C3 cycle requires the expenditure of **4 ATP**.

### Final Answer:
The correct option is **B) 4 ATP**.

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