The light-independent reactions of photosynthesis, also known as the Calvin cycle, must repeat three times in order for a cell to have enough material to construct half a glucose molecule. A variety of molecules are used and produced during this process. Identify the molecules into three categories: molecules brought in and used in three turns of the Calvin cycle, molecules produced during three turns of the Calvin cycle that leave the cycle, and molecules used and regenerated within the Calvin cycle during three turns.

- molecules brought in and used in three turns of the Calvin cycle = carbon dioxide (CO2)

- molecules produced during three turns of the Calvin cycle that leave the cycle = Glyceraldehyde-3-phosphate (G3P)

- molecules used and regenerated within the Calvin cycle during three turns = Ribulose bi phosphate (RUBP)

Explanation:

The second stage of photosynthesis, called CALVIN CYCLE, occurs in the stroma of the chloroplast. The processes that occur in this stage can be divided into three stages namely: carbon fixation, reduction and regeneration.

As rightly stated in this question, the calvin cycle must repeat three times in order for a cell to have enough material to construct half a glucose molecule. Hence;

- In carbon fixation, molecules of carbon dioxide (CO2) are brought in and used in three turns of the Calvin cycle. The CO2 combines with a CO2 acceptor called RUBP (ribulosebiphosphate) to produce PGA (3-phosphoglycerate).

- In the reduction stage, PGA is reduced to Glyceraldehyde-3-phosphate (G3P). This G3P molecule is produced during three turns of the Calvin cycle and leaves the cycle to be used to form glucose.

- In the regeneration stage, remaining molecules of G3P are used to regenerate RUBP in order for the cycle to continue. Hence, RUBP molecules are used and regenerated within the Calvin cycle during three turns.