Blood type is the classification of human blood based on the presence or absence of antibodies and also based on the presence or absence of inherited antigenic substances on the surface of red blood cells. The antigens may be proteins, carbohydrates, glycoproteins or glycolipids depending on the blood group in question. In this case the cell type represented is type O, type O lacks antigens A and B, but contains both antibodies a and b, a fact that makes it a universal donor to all the other blood types.