Answer :
The Calvin cycle begins with carbon fixation using the enzyme rubisco, which is the first stage where CO2 is incorporated into an organic molecule.
The Calvin cycle begins with carbon fixation using rubisco. This is stage 1 of the Calvin cycle, where the enzyme RuBisCO incorporates carbon dioxide into an organic molecule, 3-PGA. This process transforms the inorganic CO2 into an organic form that is then utilized in the subsequent steps of the cycle. The fixation is the initial stage before the cycle proceeds to the reduction of PGA to G3P and the regeneration of RuBP. The Calvin cycle begins with the regeneration of ribulose bisphosphate. This is the last stage of the cycle where ribulose bisphosphate is reformed to continue the cycle.