For the synthesis of one molecule of glucose via the Calvin cycle, which one of the following represents the correct requirement?

Correct Option

The correct option is 6 turns and 18 ATP and 12 NADPH.

Explanation

The Calvin cycle (or C₃ cycle) is the light-independent reaction of photosynthesis that takes place in the stroma of chloroplasts. It fixes atmospheric carbon dioxide (CO₂) to synthesize sugars. The cycle consists of three main stages: Carboxylation, Reduction, and Regeneration.

Stoichiometric Analysis

To synthesize one molecule of glucose (C₆H₁₂O₆), which contains 6 carbon atoms, the cycle must fix 6 molecules of CO₂. Since one turn of the Calvin cycle fixes one molecule of CO₂, the cycle must turn 6 times.

The energy requirements for a single turn (fixing 1 CO₂) are as follows:

• Reduction Stage: Requires 2 molecules of ATP and 2 molecules of NADPH for the reduction of 3-phosphoglycerate.
• Regeneration Stage: Requires 1 molecule of ATP for the regeneration of Ribulose-1,5-bisphosphate (RuBP).
• Total per turn: 3 ATP and 2 NADPH.

Therefore, for the synthesis of one glucose molecule (6 turns):

• Total ATP: 6 turns × 3 ATP/turn = 18 ATP
• Total NADPH: 6 turns × 2 NADPH/turn = 12 NADPH

Key Takeaway: The synthesis of one molecule of glucose requires 6 turns of the Calvin cycle, consuming a total of 18 ATP and 12 NADPH molecules.