By InvictaHOG (Own work) [Public domain], via Wikimedia Commons
The ABO blood typing system is dependent on the presence or absence of different antigens on the cell membranes of the erythrocytes. An antigen is a molecule on the surface of a cell that can be recognized by an antibody in the body's immune system. Individuals with A, B, AB, or O blood types have different antibodies, or none at all, in their plasma depending on their blood type. For a successful blood transfusion to occur, the compatibility of the recipient's and the donor's blood must be determined. The ABO blood group has two types of antigens: A and B. The chart shows how each blood type relates to the antigens displayed on that person's erythrocytes.
A person can receive blood only from donors for whom they do not
have the antibody. For example type A blood has type A antigens and type B antibodies, therefore they cannot receive type B or type AB blood. The anti-B antibodies in the plasma of type A will cause clumping of the type B or AB blood cells and can be fatal.
The video belowexplains the difference between each blood type. It also indicates what happens when different blood types mix.
Read "Blood Types" on pages 296 to 297 of your text.