Free Specific Defense Mechanism MCQs with Answers

• A. bone marrow
• B. thymus
• C. tonsils
• D. spleen only

Explanation: B cells develop and mature in the bone marrow before settling in lymphoid tissue, while T cells migrate to the thymus to mature.

• A. cell mediated immunity
• B. humoral immunity
• C. innate immunity only
• D. autoimmunity

Explanation: Humoral immunity works through soluble antibodies produced by B cells, while cell mediated immunity relies on T cells attacking directly.

• A. phagocytes
• B. red blood cells
• C. memory cells
• D. platelets

Explanation: Memory B and T cells are the biological basis of lasting immunity and of the booster effect.

• A. all antibody molecules are identical
• B. antigens destroy competing antibodies
• C. the blood filters out mismatched antibodies
• D. the shape of its binding site matches a specific epitope of that antigen

Explanation: Antibody arms carry binding sites shaped for one epitope, like a lock for one key, which is why each clone makes only one specificity.

• A. phagocytes
• B. lymphocytes
• C. platelets
• D. mast cells

Explanation: Phagocytes flow around a particle, internalise it in a vacuole and digest it with lysosomal enzymes.

• A. artificially active immunity
• B. naturally active immunity
• C. naturally passive immunity
• D. artificially passive immunity

Explanation: The person's own immune system met the real pathogen and built memory, so the immunity is active and natural.

• A. active immunity lasting many years
• B. a vaccination effect
• C. immediate but temporary passive immunity
• D. permanent genetic resistance

Explanation: Borrowed antibodies neutralise the venom at once but are gradually broken down over weeks, giving no memory.

• A. constant region of the heavy chains
• B. Fc tail
• C. carbohydrate side chains
• D. variable region at the tips of the two arms

Explanation: The amino acid sequence of the variable region changes from one antibody to another, shaping the binding site, while the constant tail…

• A. reduce the side effects of the first dose
• B. raise the antibody level and strengthen immunological memory
• C. replace antibodies that have expired
• D. treat an existing infection

Explanation: Each booster re-stimulates memory cells, driving antibody concentration higher and memory longer, the classic secondary response curve.

• A. vasodilation and increased capillary permeability, producing inflammation
• B. clotting of the lymph
• C. a fall in body temperature
• D. immediate antibody production

Explanation: Histamine opens the local vessels so plasma and phagocytes reach the injured site, causing the redness, heat and swelling of inflammation.

• 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…

• 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.

• 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.

• 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.

• 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.

• 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.

• 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…

• 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.

• 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.

• 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.