When antigens are introduced in the body through vaccination antibodies are produced to fight off infection

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Correct — C, By only B cells. Antibodies are immunoglobulins, and in the human body exactly one cell type secretes them: the plasma cell, which is what a B lymphocyte becomes once an antigen has activated it. A single plasma cell can pour out thousands of identical antibody molecules a second, all of them specific to the one antigen that triggered it. No T lymphocyte, of any subtype, ever secretes an antibody. NCERT Class 12 Biology puts the division of labour in one sentence in the chapter on Human Health and Disease: B-lymphocytes produce an army of proteins in response to pathogens, called antibodies, while the T-lymphocytes themselves do not secrete antibodies but help the B cells produce them. That sentence is the whole question. When a vaccine introduces an antigen — a weakened or killed pathogen, a purified surface protein, a viral vector or an mRNA instruction to make one — the antigen is taken up and displayed, helper T cells recognise the display and release signals, and the B cells whose receptors fit that antigen divide, mature into plasma cells and start manufacturing antibody. Some of them instead become memory B cells, which is why the protection lasts. Every step of that chain except the last needs T cells; only the last step, the manufacture, is what the stem asks about. So (a) and (b) both misattribute production, and since (c) is right, the escape option (d) cannot stand. The response as a whole is a team effort; the antibody factory is not.

Why the other options are wrong — (a) The reverse of the truth. T lymphocytes carry out cell-mediated immunity — cytotoxic T cells kill the body's own cells once a virus has got inside them, and helper T cells coordinate the response — but they secrete cytokines, not immunoglobulins. This is the arm of immunity responsible for rejecting a transplanted organ, which is why tissue matching and immunosuppressants are needed after a graft.  (b) The trap, and a genuinely well-informed candidate's answer. Helper T cells ARE required for the B-cell response to most protein antigens — without their signals the B cell does not switch antibody class or form good memory. But helping is not producing. The stem asks which cells the antibodies are produced BY, and the answer to that is only the B cell line. Read the verb carefully; the option would be correct if the stem asked which cells take part in the response.  (d) Fails because option (c) is exactly right. An escape option can only win when every named alternative can be shown to fail, and here the standard textbook attribution of antibody production to B lymphocytes and their plasma cells is squarely on the list.

Concept: Adaptive immunity has two arms, and telling them apart is the single most examinable idea in this chapter. Humoral, or antibody-mediated, immunity is run by B lymphocytes: on meeting an antigen a matching B cell proliferates and its daughters become plasma cells that secrete antibody into the blood and lymph, where it neutralises toxins, blocks viruses from entering cells and tags bacteria for destruction. It works on pathogens while they are outside cells. Cell-mediated immunity is run by T lymphocytes, which do not secrete antibody at all: cytotoxic T cells destroy the body's own infected cells, and helper T cells release signalling molecules that switch the rest of the response on. It works on pathogens that have already got inside. The letters record where the cells mature — T for the thymus, and B originally for the bursa of Fabricius in birds, the bone marrow in mammals. Both types arise from stem cells in the bone marrow.

State PCS 2025 Q7 — Science & Technology PYQ with Answer

State PCS 2025 Q7 — Science & Technology PYQ with Answer