Free Specific Defense Mechanism MCQs with Answers

31. A moderate fever helps the body fight infection mainly because

• A. it melts the cell walls of bacteria
• B. it replaces damaged white blood cells
• C. it dissolves antigens directly
• D. the raised temperature speeds defence reactions and slows some pathogens

Explanation: Metabolic and immune reactions run faster at slightly higher temperature while many microbes grow more slowly, so fever is a defence rather than merely a symptom. Only very high fever becomes dangerous.

32. In type 1 diabetes the immune system mistakenly destroys the

• A. red blood cells
• B. cells of the thyroid gland
• C. insulin secreting beta cells of the pancreas
• D. nerve cells of the spinal cord

Explanation: T cells attack the pancreatic islet beta cells, stopping insulin production and causing lifelong dependence on injections. The target organ is what distinguishes one autoimmune disease from another.

33. Transfusing type A blood into a person with type B blood is dangerous because

• A. the donor cells are larger than the recipient's
• B. the recipient's anti A antibodies agglutinate the donor red cells
• C. both blood types destroy the plasma
• D. the mixture becomes hypertonic

Explanation: Type B plasma contains anti A antibodies that clump and lyse A cells, blocking capillaries. Matching blood groups before transfusion prevents this antigen antibody reaction.

34. A person with blood group AB is called a universal recipient because their plasma contains

• A. neither anti A nor anti B antibodies
• B. both anti A and anti B antibodies
• C. only anti A antibodies
• D. no red cell antigens

Explanation: With A and B antigens on their own cells, AB individuals make no antibodies against either, so they can receive cells of any group. Universal donors, group O, sit at the opposite end of the logic.

35. Agglutination refers to

• A. the bursting of white blood cells
• B. the formation of lymph
• C. a rise in platelet count
• D. the clumping of red blood cells when antibodies bind their antigens

Explanation: Cross linking by antibodies ties red cells into visible clumps, the reaction used to type blood groups. Clotted clumps can block vessels, which is why agglutination makes mismatched transfusion lethal.

36. The class of antibody that appears first in the blood during an infection and is the largest in size is

• A. IgG
• B. IgA
• C. IgM
• D. IgE

Explanation: IgM is a pentamer, the first antibody deployed in a primary response, while IgG dominates later and crosses the placenta. Knowing one signature feature per class is enough for most options.

37. Plasma cells, the factories that secrete antibodies, are derived from

• A. B lymphocytes
• B. T lymphocytes
• C. monocytes
• D. eosinophils

Explanation: When a B cell meets its antigen and receives helper T cell signals, it differentiates into antibody secreting plasma cells and memory cells. T cells never become plasma cells; their weapons are cellular.

38. A kidney transplanted from another person is usually rejected because the recipient's immune system recognises foreign

• A. hormones on the organ
• B. self markers, the MHC proteins, on the donor's cells
• C. digestive enzymes
• D. phospholipids of the membranes

Explanation: Every person's MHC proteins are unique identity tags, and cytotoxic T cells attack any tissue carrying unfamiliar ones. Close matching of MHC between donor and recipient reduces this recognition.

39. To reduce the risk of rejection, recipients of organ transplants are given drugs that

• A. stimulate antibody production
• B. raise the white blood cell count
• C. suppress the immune response
• D. dissolve the antigens of the organ

Explanation: Immunosuppressants dampen T cell activation so the graft is tolerated, at the cost of greater susceptibility to infection. This trade off is managed for life in transplant patients.

40. The class of antibody mainly responsible for allergic reactions is

• A. IgG
• B. IgM
• C. IgA
• D. IgE

Explanation: IgE attaches to mast cells, and when allergen cross links it, histamine is released, producing sneezing, itching and swelling. The other classes defend against microbes rather than driving allergy.