Photosynthesis In Higher Plants

Step 1: Recall the Calvin cycle mechanism.
The Calvin cycle is the main carbon fixation pathway in C plants.
It consists of three phases: Carbon fixation, Reduction, and Regeneration of RuBP.
Step 2: Energy requirement for one CO fixation.
To fix 1 molecule of CO :
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 .
To make one glucose molecule:
6 CO molecules are required
Therefore, energy requirement:
Step 4: Verify with the options.
Only option (2) gives the correct numbers: 18 ATP and 12 NADPH.

- The light-dependent reactions occur in the thylakoid membranes, not the stroma, so (A) is incorrect.
- Oxygen is released as a by-product of the light-dependent reactions (photolysis of water), not the Calvin cycle, so (B) is incorrect.
- The light-independent reactions (Calvin cycle) use ATP and NADPH to convert carbon dioxide into glucose, making (C) correct.
- Chlorophyll absorbs blue and red light most efficiently, and reflects green light, so (D) is incorrect.
Answer: