Final answer:
Blood types A, B, and AB have enzymes that add carbohydrate components to the protein receptors on red blood cells, while blood type O lacks these enzymes, resulting in the absence of carbohydrates on the red blood cells.
Step-by-step explanation:
The ABO blood group system is determined by the addition of specific carbohydrates to the protein receptors on red blood cells (RBCs). Individuals with blood types A, B, and AB have enzymes that add the carbohydrate component to the protein receptors, while individuals with blood type O lack these enzymes. Consequently, the absence of carbohydrates on the RBCs in blood type O results in the classification of blood group O.