Answer :
Final answer:
During the first step of the Calvin cycle, carbon fixation, six CO2 molecules react with six RuBP molecules, catalyzed by the enzyme RuBisCO, and produce twelve molecules of PGA. To eventually form a glucose molecule, the cycle runs six times, each round contributing to the formation of two PGA molecules.
Explanation:
In the Calvin cycle, six molecules of CO2 are bound to six molecules of RuBP (Ribulose biphosphate) to produce twelve molecules of PGA (3-phosphoglyceric acid). The enzyme which catalyses this process is called RuBisCO.
This early stage of the cycle is known as carbon fixation. Each CO2 molecule that reacts with one RuBP will form two molecules of PGA. To produce a six-carbon glucose molecule, the cycle needs to be completed six times. Therefore, twelve PGA molecules are generated from the six CO2 molecules fixed into the cycle.
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