Why does one person have type A blood and another type B?
Show answer & explanation
Answer: Their red blood cells carry markers that set the blood type.
Their blood plasma carries antibodies that set the blood type. — Wrong. Antibodies do not set a person's blood type. The immune system makes them against marker molecules the person lacks, so they follow the blood type rather than create it. A and B markers on the red cells are what set the type.
Their red blood cells carry markers that set the blood type. ✓ — Correct! Blood type depends on which marker molecules sit on the red blood cells. Type A has A markers, B has B markers, AB has both, and O has neither. The immune system makes antibodies against markers a person lacks, so a mismatched transfusion can trigger an attack.
Their red blood cells carry oxygen molecules that set the blood type. — Wrong. Oxygen molecules do not set a person's blood type. Red blood cells carry oxygen with hemoglobin, and people of every blood type rely on it. The A, B, AB, and O difference comes from marker molecules on the red cells, not from oxygen capacity.
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