During the Calvin cycle, what happens during the carbon fixation phase?

A. G3P is produced.
B. ATP is produced.
C. The Calvin cycle incorporates each CO2 molecule, one at a time, by attaching it to a five-carbon sugar named ribulose bisphosphate.
D. RuBP (ribulose bisphosphate) is regenerated.
E. Molecular oxygen is produced.
F. NADPH is produced.

In the carbon fixation phase of the Calvin cycle, CO2 is incorporated into the five-carbon molecule RuBP, catalyzed by the enzyme RuBisCO, resulting in the formation of two 3-PGA molecules.

Explanation:

During the carbon fixation phase of the Calvin cycle, the enzyme RuBisCO catalyzes a reaction where carbon dioxide (CO2) is incorporated into a five-carbon molecule named ribulose bisphosphate (RuBP). This is the initial step in the process of carbon fixation, which is the incorporation of CO2 into organic compounds. A molecule of CO2 is attached to RuBP, and this reaction results in the formation of two molecules of the three-carbon compound 3-phosphoglycerate (3-PGA).

In subsequent phases of the Calvin cycle, the 3-PGA is reduced to glyceraldehyde-3-phosphate (GA3P) using energy from ATP and electrons from NADPH, both of which are produced in the light-dependent reactions of photosynthesis. Eventually, GA3P can lead to the production of glucose and other carbohydrates necessary for the plant's energy and structural needs.