Biological Systems MCAT Practice Exam

Disable ads (and more) with a membership for a one time $2.99 payment

Prepare for the Biological Systems section of the MCAT. Review detailed explanations and interactive questions to understand complex systems. Enhance your exam readiness and aim for a high score!

Each practice test/flash card set has 50 randomly selected questions from a bank of over 500. You'll get a new set of questions each time!

Practice this question and more.

Which blood type is considered a universal donor?

AB+
O-
A+
B-

The correct answer is: O-

The designation of blood types, particularly concerning blood donation, is based on the presence or absence of specific antigens on the surface of red blood cells. Type O blood is recognized as a universal donor because it lacks both A and B antigens. This absence means that it does not provoke an immune response in recipients who have any of the other blood types (A, B, AB, or O), allowing it to be safely transfused to individuals with various blood types. Moreover, O- (O negative) is particularly significant because it not only lacks the A and B antigens but also does not have the Rh factor (the D antigen). This makes O- blood compatible with any Rh type, reinforcing its status as the universal donor. Patients who receive transfusions are at risk of transfusion reactions when their blood contains antigens that interact with the donor’s blood components, which is avoided with O- donations. The other blood types listed (AB+, A+, and B-) each contain specific antigens that could lead to a risk of hemolytic reactions if transfused into incompatible recipients. Thus, O- is essential in emergency situations where blood types need to be matched quickly, as it can be safely given to anyone without immediate compatibility testing.