Question

what on the blood determine a person’s blood type.

Answer 1

Blood types are determined by the presence or absence of certain antigens – substances that can trigger an immune response if they are foreign to the body. Since some antigens can trigger a patient's immune system to attack the transfused blood, safe blood transfusions depend on careful blood typing and cross-matching.

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Answer 2

A blood type or blood group of a person is determined by the antigen present on the surface of blood cell of that person. The antigen present on the cell surface may a carbohydrate, glycolipid, protein, or glycoprotein molecule. Humans show four blood groups, which are A, B, AB, and O on the basis of antigen present in their red blood cells.
Thus, the blank can be filled as
antigens.