Question

In the human blood group AB
(a) Antibodies are present
(b) Antibodies are absent
(c) Antibody 'a' is present
(d) Antibody 'b' is present

Answer 1

Hint: The ABO blood group system is based on the presence and absence of antibodies and inherited antigenic substances on the surface of red blood cells. Antigens are present on the RBC and antibodies in the serum. The human blood group contains A, B, and Rh antigens and a and b antibodies.

Complete step by step answer:
A person with blood group AB would have antigen A and Antigen B on the RBC and no antibodies in the serum. Hence an AB patient doesn’t have any antibodies in the serum. A group contains ‘A’ antigen and b antibody it can receive A and the O group and can be donated to A and AB groups, without any danger. B group contains B antigen and antibody a, it can receive B and O group and can be donated to B and AB groups. AB-group contains antigens A and B and no antibodies. So, it can receive all groups, and at the same time can be donated only to AB groups. Similarly, O- group contains antibodies a & b, but no antigens. So, it can be donated to all groups but can receive only O groups. Since AB-group can receive all groups and O-group can be donated to all groups, they are known respectively as the universal recipient and the universal donor.

Additional Information:
- Landsteiner and Weiner independently discovered a previously unknown antigen in the RBCs of the rhesus monkey.
- Persons possessing the Rh antigen are called Rh- positive (Rh+ve), and those lacking it are called Rh- negative(Rh- ve) persons can always receive Rh- ve blood without any complications. But an Rh- ve person can receive Rh +ve blood with no risk only once.
- Human ABO blood group system provides an excellent example of multiple allelism.
So, the correct answer is, ‘(b) Antibodies are absent’.

Note:
- In 1900, the Austrian physician Karl Landsteiner discovered two kinds of antigens and their antibodies. The antigens were termed A and B, and the antibodies a and b.
- These antibodies are not acquired but are constitutive or natural, present in blood as natural constituents.
- Antigens occur in the plasma membrane of RBCs, and antibodies in blood plasma. He could also realize that a particular type of blood may contain either one or both or none of these antigens and antibodies.