The Calvin cycle produces G3P, which has the formula C3H7O6P. Inside the chloroplast, this compound combines to form the six-carbon sugar glucose, C6H12O6. How many turns of the Calvin cycle are required to produce a complete glucose molecule?

To produce one molecule of glucose (C6H12O6), which contains six carbon atoms, the Calvin cycle must turn six times. Each turn of the cycle fixes one carbon atom from CO2 into an organic molecule. Since the end product of the cycle is glyceraldehyde-3-phosphate (G3P), which has three carbon atoms (in the formula C3H7O6P), it takes two G3P molecules to form one glucose molecule.

Here's how it works in steps:

1. Each turn of the Calvin cycle incorporates one carbon atom from CO2 into an organic molecule. After three turns, three CO2 molecules have been fixed, producing three-carbon atoms.

2. These three fixed carbon atoms are used to produce one molecule of G3P. However, not every G3P molecule produced can be considered as a net gain, because the Calvin cycle needs to regenerate its starting material, ribulose-1,5-bisphosphate (RuBP).

3. For the cycle to continue, five out of six carbons from two G3P molecules are used to regenerate three molecules of RuBP. Therefore, only one of the two G3Ps can be counted as a net gain toward glucose production.

4. After six turns of the cycle, a total of six carbon atoms have been fixed, resulting in two net G3P molecules (since the others have been recycled).

5. These two G3P molecules (each with three carbon atoms) combine to form one complete glucose molecule with six carbon atoms.

Therefore, six turns of the Calvin cycle are required to produce a complete glucose molecule.