Identify the incorrect statement with respect to Calvin cycle

Options

A. `NADPH + H^(+)` produced in light reaction is used to reduce diphosphoglycerate
B. First stable intermediate compound is phosphoglycerate
C. Carboxylation of `RuBP` is catalysed by Rubisco
D. 18 molecules of `ATP` are synthesised during carbon fixation.

Answer

To identify the incorrect statement with respect to the Calvin cycle, we will analyze each statement provided in the question.

### Step-by-Step Solution:

1. **Statement Analysis**:
- **Statement 1**: "NADPH + H+ produced in the light reaction is used to reduce diphosphoglycerate."
- This statement is incorrect. The correct term should be phosphoglycerate (PGA), not diphosphoglycerate. The NADPH produced in the light reactions is indeed used to reduce PGA, which is the first stable product of the Calvin cycle.

- **Statement 2**: "The first stable intermediate compound is phosphoglycerate."
- This statement is correct. Phosphoglycerate (PGA) is indeed the first stable product formed after the carboxylation of ribulose bisphosphate (RuBP).

- **Statement 3**: "Carboxylation of RuBP is catalyzed by rubisco."
- This statement is also correct. The enzyme ribulose bisphosphate carboxylase/oxygenase (rubisco) catalyzes the carboxylation of RuBP, leading to the formation of PGA.

- **Statement 4**: "18 molecules of ATP are synthesized during carbon fixation."
- This statement is correct as well. During the Calvin cycle, a total of 18 ATP molecules are consumed in the fixation and reduction phases.

2. **Conclusion**:
- After analyzing all the statements, we find that the first statement is the only incorrect one. Therefore, the answer to the question is that the incorrect statement with respect to the Calvin cycle is the first statement regarding NADPH and diphosphoglycerate.

### Final Answer:
The incorrect statement with respect to the Calvin cycle is: "NADPH + H+ produced in the light reaction is used to reduce diphosphoglycerate."

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