How many ATP molecules are generated in Calvin cycle ?

Options

A. 18
B. 12
C. 6
D. 0

Answer

To determine how many ATP molecules are generated in the Calvin cycle, we need to analyze the process step by step.

### Step-by-Step Solution:

1. **Understanding the Calvin Cycle**:
The Calvin cycle consists of three main stages: Carboxylation, Reduction, and Regeneration. It is important to note that the Calvin cycle does not produce ATP; rather, it consumes ATP that is generated in the light-dependent reactions of photosynthesis.

2. **Carboxylation Stage**:
In this stage, carbon dioxide (CO2) is fixed to a 5-carbon sugar (ribulose bisphosphate or RuBP) to form a 6-carbon intermediate, which is then split into two molecules of 3-phosphoglycerate (3-PGA). This stage uses ATP, but does not generate any ATP.

3. **Reduction Stage**:
In this stage, the 3-PGA molecules are phosphorylated by ATP and reduced by NADPH to form glyceraldehyde-3-phosphate (G3P). Again, ATP is consumed in this process, but no ATP is generated.

4. **Regeneration Stage**:
The G3P molecules are used to regenerate RuBP, which requires additional ATP. This stage also consumes ATP without generating any new ATP.

5. **Conclusion**:
Throughout the entire Calvin cycle, ATP is utilized but not produced. Therefore, the total number of ATP molecules generated in the Calvin cycle is zero.

### Final Answer:
The number of ATP molecules generated in the Calvin cycle is **0**.