Biology · Bioenergetics

In the Calvin cycle, 3 molecules of carbon dioxide are fixed by an enzyme called RuBisCO, resulting in 6 molecules of G3P. These are the initial products of carbon fixation. Out of these 6 G3P molecules, 5 are used to regenerate RuBP, the CO₂ acceptor molecule, and 1 is available for synthesis of glucose and other carbohydrates. Therefore, while the Calvin cycle produces 6 G3P molecules for every 3 CO₂ molecules, only one contributes directly to biosynthesis outside the cycle. The incorrect options either underestimate or overestimate the number of G3P molecules produced.

This is the correct answer. In the Calvin cycle, for every 3 molecules of CO₂ fixed, 6 molecules of G3P are produced. However, only one of these G3P molecules exits the cycle for the synthesis of glucose or other carbohydrates, while the remaining 5 are used to regenerate RuBP.

This is incorrect. While 5 molecules of G3P are used to regenerate RuBP, for every 3 CO₂ molecules fixed, 6 molecules of G3P are generated in total.

This is incorrect. 3 molecules of CO₂ result in 6 molecules of G3P, not 3. The cycle produces 6 G3P molecules, not one per CO₂ molecule fixed.

This is incorrect. The Calvin cycle produces exactly 6 G3P molecules from 3 CO₂ molecules, not 8.