BPSC 70th CCE Re-exam Prelims General Studies · Question 70 of 142

Correct — D, None of the above. Blood group is determined by antigens — glycoproteins and glycolipids — sitting on the surface membrane of the red blood cells, and by the matching antibodies present in the plasma. In the ABO system the antigens are called agglutinogens A and B and the plasma antibodies agglutinins anti-A and anti-B, and the four groups follow mechanically from which of each are present. Group A carries the A antigen and anti-B antibody; group B carries the B antigen and anti-A; group AB carries both antigens and neither antibody, which is why an AB person is a universal recipient; group O carries neither antigen and both antibodies, which with a negative Rh makes O the universal donor. The Rh system runs alongside it on the same cells, its key marker being the D antigen. That mechanism is the answer to the stem, and it is not among the three options — none of them so much as mentions an antigen — so the escape option is correct. Karl Landsteiner, who worked this out at the turn of the twentieth century, received the Nobel Prize in Physiology or Medicine in 1930 'for his discovery of human blood groups'. Each of the three named options fails for its own reason, and each failure is a fact worth holding: shape is identical across groups, haemoglobin is present in everyone's red cells, and white cells play no part in ABO typing at all.

• (a)Shape of RBC — Every healthy human red blood cell is the same biconcave disc regardless of blood group — the shape is an adaptation for surface area and flexibility, not a marker of identity. When red cells do change shape it signals disease, not group: the crescent cells of sickle cell anaemia, the spheres of hereditary spherocytosis. A person with sickle cell disease can belong to any of the four ABO groups.
• (b)Presence of Haemoglobin — Haemoglobin is the oxygen-carrying protein packed inside every red cell of every human being, so it cannot distinguish one person's blood from another's — a property shared by all four groups discriminates none of them. Haemoglobin level is what a blood test measures for anaemia, and it changes with iron status and altitude, not with blood group.
• (c)Combination of WBC and RBC — ABO and Rh typing involves red cells only; white blood cells are not part of it. There is a genuine white-cell typing system, and knowing it is what makes this option a trap worth understanding — the human leukocyte antigen system, used to match donors and recipients for organ and bone-marrow transplants. HLA matching and blood grouping answer different clinical questions on different cells.

The reason blood groups exist at all is immunological. The body tolerates the antigens on its own red cells and manufactures antibodies against the ones it lacks, so transfusing incompatible blood causes the recipient's antibodies to clump the donor's cells — agglutination — with results that can be fatal. That is why the ABO system had to be discovered before transfusion could become safe medicine, and why Landsteiner's work earned a Nobel Prize. The Rh system, identified later, adds a second dimension and a second danger: an Rh-negative mother carrying an Rh-positive foetus can be sensitised to the D antigen and attack the red cells of a subsequent Rh-positive pregnancy, a condition called haemolytic disease of the newborn, which is why anti-D immunoglobulin is given prophylactically. Groups are inherited, with the A and B alleles co-dominant and O recessive, which is why parentage questions can be built on them: an AB parent and an O parent can have A or B children but never an O child.

This question is solved by a single test applied to each option: could this property tell two people's blood apart? Shape cannot — all healthy red cells are the same disc. Haemoglobin cannot — everyone has it. White cells cannot — they are not involved in ABO typing. When all three named options fail that test and you can name the property that would pass it, the escape option is not a guess but a conclusion. That is the disciplined way to use a 'None of the above' option anywhere on this paper: identify the missing answer first, then take the escape. It is worth noticing what the question is really rewarding, which is knowing that a blood group is a surface marker rather than a bulk property of blood. Once that is fixed, the rest of the topic follows — why AB is the universal recipient, why O negative is the universal donor, and why an organ transplant needs a different kind of matching altogether.

• ABO blood group is determined by antigens (agglutinogens) A and B on the surface of red blood cells, with the corresponding antibodies (agglutinins) anti-A and anti-B in the plasma.
• Group A: A antigen with anti-B; group B: B antigen with anti-A; group AB: both antigens, no antibodies — the universal recipient; group O: no antigens, both antibodies — with Rh negative, the universal donor.
• Karl Landsteiner received the Nobel Prize in Physiology or Medicine in 1930 'for his discovery of human blood groups'.
• The Rh system's principal marker is the D antigen; an Rh-negative mother carrying an Rh-positive foetus may be sensitised, causing haemolytic disease of the newborn in a later pregnancy.
• White blood cells carry the human leukocyte antigen (HLA) system, used for tissue matching in organ and bone-marrow transplantation — a different system from ABO typing, on a different cell.

• Assuming a property everybody shares can classify anybody. Haemoglobin is in every red cell of every group, so it discriminates nothing.
• Confusing red-cell shape with red-cell antigens. Abnormal shapes indicate disease — sickle cell, spherocytosis — and are unrelated to ABO group.
• Bringing white blood cells into blood grouping. They carry the HLA system used for transplant matching, which is a separate question on a separate cell.

BPSC asks the definition head-on and keeps the true mechanism off the option list, so the item turns on whether the candidate can name the missing answer and then commit to the escape. UPSC works the same system through its consequences — why AB is the universal recipient, which group is safe to transfuse into an unknown patient, or which child in a family cannot be the biological one — testing the mechanism by making the student use it.

• practice — not a real PYQ

  The Nobel Prize in Physiology or Medicine for the discovery of human blood groups was awarded in 1930 to

  • (a)Alexander Fleming
  • (b)Karl Landsteiner
  • (c)Robert Koch
  • (d)Paul Ehrlich

  Answer(b) Karl Landsteiner — cited 'for his discovery of human blood groups', the work that made transfusion safe.

• practice — not a real PYQ

  The human leukocyte antigen (HLA) system is chiefly used for

  • (a)Determining the ABO blood group
  • (b)Measuring haemoglobin concentration
  • (c)Matching donors and recipients for organ and bone-marrow transplants
  • (d)Detecting the Rh factor in pregnancy

  Answer(c) Matching donors and recipients for organ and bone-marrow transplants — HLA markers sit on white blood cells and other nucleated cells, and are a different system from ABO typing on red cells.