During the biosynthetic phase of photosynthesis in a C₃ plant, if 72 molecules of ATP are consumed, how many molecules of glucose are synthesized?

Step-by-step solution

In C₃ plants, the synthesis of one molecule of glucose requires 6 turns of the Calvin cycle. For each molecule of CO₂ fixed, 3 molecules of ATP and 2 molecules of NADPH are required. Therefore, the synthesis of one molecule of glucose ( 6CO₂ ) requires 6 3 = 18 molecules of ATP. If 72 molecules of ATP are consumed, the number of glucose molecules synthesized is 72 18 = 4 . Students who divide 72 by 3 (ATP per CO₂ ) arrive at 24 , and those who divide by 6 (turns per glucose) arrive at 12 . Answer: 4