Question

The number of ATP and NADPH molecules required respectively to synthesize one molecule of glucose in C\(_3\) plants is:

• A. 12 ATP and 12 NADPH
• B. 18 ATP and 12 NADPH
• C. 12 ATP and 18 NADPH
• D. 6 ATP and 6 NADPH

Hint:

In C\(_3\) plants: - Glucose formation (6 CO\(_2\)) requires 18 ATP and 12 NADPH. - This energy is supplied by the light-dependent reactions of photosynthesis.

Answer 1

The Correct Option is B

Step 1: Recall the Calvin cycle mechanism. 
The Calvin cycle is the main carbon fixation pathway in C\(_3\) plants. 
It consists of three phases: Carbon fixation, Reduction, and Regeneration of RuBP. 
Step 2: Energy requirement for one CO\(_2\) fixation. 
To fix 1 molecule of CO\(_2\):
3 ATP are used (2 for regeneration of RuBP, 1 in reduction phase) 
2 NADPH are used (during the reduction of 3-phosphoglycerate to G3P) 
Step 3: Glucose synthesis requires 6 CO\(_2\). 
To make one glucose molecule:
6 CO\(_2\) molecules are required 
Therefore, energy requirement: \[ 6 \times 3 = 18 \text{ ATP}, \quad 6 \times 2 = 12 \text{ NADPH} \] 
Step 4: Verify with the options. 
Only option (2) gives the correct numbers: 18 ATP and 12 NADPH.