In the early1900’s, scientists discovered that humans have different 4 types of blood: A,B, AB, and O. The distinctionsbetween these blood types are based on different carbohydrates and proteinsthat compose the cell membranes. Each of the different types produces different antibodies and antigens(1). This system of classificationhas proven to be important because different properties make some blood typesincompatible. For example, if aperson with Type B blood needed a blood transfusion or organ transplant, thedonation could not from a person with Type A or Type AB blood because Type Bblood makes antibodies to the antigen of Type A blood.