In addition to the proteins (agglutinogens) existing on your red blood cells, other genes make proteins called agglutinins (a-GLOO-tin-ins) that circulate in your blood plasma. Agglutinins are responsible for ensuring that only the blood cells of your blood type exist in your body.
Older children and teens are unlikely to start calling a stepmom mom or mother partly because of their fear of disloyalty to their biological mom. It is vital for all parties involved -- biological parents and stepmom -- to support their child's choice of what to call the stepmom.
Lets say you have a half-sister. She will have the same mom but her dad is not the same dad as yours... A step-sister is someone who comes with their parent to your family when one of your parents gets married. Lets say that your parents get divorced and your dad decides to get remarried.