How many turns of the Calvin cycle are necessary for one molecule of $G_{3}P$ (glyceraldehyde-3-phosphate) to exit the cycle?

• A. $3$ turns
• B. $6$ turns
• C. $1$ turn
• D. $2$ turns

Answer: (A)

Verified step by step guidance

1. Understand that the Calvin cycle is a series of biochemical reactions that occur in the chloroplasts of photosynthetic organisms. It is responsible for converting carbon dioxide and other compounds into glucose.
2. Recognize that G3P (glyceraldehyde-3-phosphate) is a three-carbon sugar phosphate molecule that is a product of the Calvin cycle. It is an intermediate in the synthesis of glucose.
3. Recall that the Calvin cycle must fix carbon dioxide molecules to produce G3P. Each turn of the cycle fixes one carbon dioxide molecule.
4. To produce one G3P molecule, the cycle must incorporate three carbon dioxide molecules, as G3P is a three-carbon compound. Therefore, it takes three turns of the Calvin cycle to produce one G3P molecule.
5. Conclude that the correct answer is 3 turns, as each turn of the Calvin cycle fixes one carbon dioxide molecule, and three are needed to form one G3P molecule.