Answer:
Rubisco is the major enzyme used to catalyse the carbon fixation step during the Calvin cycle in photosynthesis.
During carbon fixation, RUBP undergoes a redox reaction with CO2 to form 3-phosphoglycerate (a 3 carbon compound). 3-phosphoglycerate then undergoes phosphorylation by ATP and reduction by NADPH to form glycerate 3 phosphate molecules (main product), ADP and NADP+ molecules (by product).
Some Glycerate 3 phosphate produced are used to regenerate RUBP for the Calvin cycle to continue while the rest of the Glycerate 3 Phosphate is used to synthesise monosaccharides like glucose.
Without Rubisco, carbon fixation cannot occur and RUBP will not be able to combine with C02 to form a 6 carbon unstable intermediate the breaks down to form 3-phosphoglycerate and eventually undergoing more reactions to form glycerate 3 phosphate which is the basic product of photosynthesis used to synthesise glucose and eventually starch which serves as the world's food.