Which is the most abundant immunoglobulin?
Answer: C
Correct answer: Ig G
IgG makes up roughly 75-80% of the immunoglobulin in serum. It dominates the secondary response, activates complement, opsonises for phagocytosis, and is the only class that crosses the placenta - which is what protects a newborn for its first few months.
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A compound formed in an organism for inhibiting growth of another organism is
Answer: B
Correct answer: Antibiotic
An antibiotic is by definition a substance produced by one organism - classically a mould or a soil bacterium - that inhibits the growth of another. Penicillin from Penicillium is the type case. An antibody is a protein made against a specific antigen, not a growth inhibitor of general use; an antigen provokes a response rather than inhibiting anything.
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Which of the following characteristics are common in lymphocytes, macrophages, and neutrophils?
Answer: D
Correct answer: They are all types of white blood cells
All three are leucocytes. What separates them is which arm they serve: macrophages and neutrophils belong to the non-specific innate response, while lymphocytes carry the specific acquired one. So no statement about one arm can cover all three - only the fact that they are all white blood cells.
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Antibodies are complex
Answer: D
Correct answer: Glycoproteins
Antibodies are glycoproteins: polypeptide chains with carbohydrate attached. They are not lipoproteins, and steroids and prostaglandins are lipid molecules altogether - far too small to carry the two identical binding sites an antibody needs.
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Which of the following immunity is obtained during a lifetime?
Answer: A
Correct answer: Acquired immunity
Acquired (adaptive) immunity is what develops during life, in response to the antigens actually encountered - whether the body makes the response itself (active) or receives antibodies ready-made (passive). Both of those are subdivisions of it, which is why the general term is the answer here.
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A cell which defends against body cells in which viruses are reproducing is
Answer: B
Correct answer: Cytotoxic T cell
A cytotoxic T cell recognises viral peptides displayed on the infected cell’s MHC class I molecules and kills it - by perforin and granzymes, or by triggering apoptosis - before the virus inside can finish replicating. Suppressor (regulatory) T cells damp responses down instead; exotoxins and endotoxins are bacterial poisons, not cells.
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Immunity acquired after an infection is
Answer: A
Correct answer: active immunity
Immunity following an infection is active and naturally acquired: the body met the antigen, mounted its own response, and kept memory cells. Passive immunity is antibody received ready-made; innate immunity is present from birth and is not acquired at all.
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Innate immunity is provided by
Answer: A
Correct answer: Phagocytes
Phagocytes - macrophages and neutrophils - belong to innate immunity: they recognise broad microbial patterns rather than one antigen, and act at once on a first encounter. Antibodies and B and T lymphocytes all belong to the acquired response.
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Which of the following statements is true about the IgM of humans?
Answer: D
Correct answer: IgM is primarily restricted in the circulation
Secreted IgM is a pentamer - five units joined by a J chain, and far too large to cross the capillary wall or the placenta. It therefore stays largely in the bloodstream. IgG is the one that crosses the placenta, IgA protects mucosal surfaces, and IgM is made early in a response by plasma cells before affinity maturation, so its affinity is low - a shortcoming its ten binding sites compensate for.
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Cells involved in innate immunity are_________.
Answer: D
Correct answer: All of the above
All three belong to innate immunity. Phagocytes engulf and digest invaders; macrophages are the long-lived tissue phagocytes and also present antigen to T cells; natural killer cells destroy virus-infected and tumour cells without needing prior exposure. None of them requires a specific receptor for the invader, which is what distinguishes innate from acquired immunity.
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