The synthesis of glucose (C₆H₁₂O₆) in photosynthesis occurs through the Calvin cycle, which uses ATP and NADPH produced in the light-dependent reactions. The overall process can be summarized by the following equation:

$6\mathrm{CO}{}_2+18\mathrm{ATP}+12\mathrm{NADPH}+12H^{+}+12H^{2}O\to C{H}_{12}O{}_6+18\mathrm{ADP}+18P{i}_{}+12\mathrm{NADP}{}^{+}+6H^{2}O$

This shows that 18 molecules of ATP are consumed to produce one molecule of glucose. The ATP is used in two main steps:

Step 1: Phosphorylation of 3-phosphoglycerate to 1,3-bisphosphoglycerate requires 6 ATP per turn. Since the cycle turns 6 times for one glucose, this uses 36 ATP? Wait, let's clarify properly.

Actually, per turn of the Calvin cycle (which fixes one CO₂), 3 ATP and 2 NADPH are consumed. To produce one glucose molecule (which requires fixing 6 CO₂ molecules), the cycle must turn 6 times. Therefore:

Total ATP consumed = 6 turns × 3 ATP/turn = 18 ATP

Total NADPH consumed = 6 turns × 2 NADPH/turn = 12 NADPH

Thus, the correct answer is 18 molecules of ATP.

Related Topics

Photosynthesis: The process by which plants convert light energy into chemical energy, storing it in glucose. It consists of light-dependent reactions (producing ATP and NADPH) and light-independent reactions (Calvin cycle, using ATP and NADPH to synthesize glucose).

Calvin Cycle: A series of biochemical reactions that occur in the stroma of chloroplasts, where carbon fixation takes place. Key steps include carbon fixation by RuBisCO, reduction phase (using ATP and NADPH), and regeneration of RuBP (using additional ATP).

Key Formulae

The overall reaction for glucose synthesis in photosynthesis:

$6\mathrm{CO}{}_2+12H^{2}O\to C{H}_{12}O{}_6+6H^{2}O+6O_2$

But the biochemical stoichiometry involving energy carriers is:

$6\mathrm{CO}{}_2+18\mathrm{ATP}+12\mathrm{NADPH}+12H^{+}\to C{H}_{12}O{}_6+18\mathrm{ADP}+18P{i}_{}+12\mathrm{NADP}{}^{+}$