Out of _ molecules of G3P, only one leaves the Calvin cycle.

Explanation

Six is the correct option because during the Calvin cycle, six molecules of G3P are formed after three turns of the cycle, using six molecules of carbon dioxide. However, out of these six G3P molecules, only one exits the cycle to be used in the synthesis of glucose or other carbohydrates, while the remaining five are recycled to regenerate RuBP, the molecule that accepts carbon dioxide and keeps the cycle running. Two is incorrect because only one G3P leaves the cycle after three turns, not two. Three is incorrect because that number would not provide enough carbon to regenerate RuBP. Twelve is incorrect because it represents the total number of G3P produced after six turns of the cycle, which is enough to form one glucose molecule, not the number produced in one full cycle sequence.