CDS (I) 2024 General Knowledge · Question 23 of 120

Correct — C, 2 and 3 only. NCERT's account of vaccination is the anchor: a preparation of antigenic proteins, or an inactivated or weakened pathogen, is introduced into the body, and 'the antibodies produced in the body against these antigens would neutralise the pathogenic agents during actual infection'. That is statement 2 exactly. The same passage adds that vaccines generate memory B and T cells 'that recognise the pathogen quickly on subsequent exposure and overwhelm the invaders with a massive production of antibodies' — the immune response then destroys the agent once it is inside, which is what statement 3 describes in the exam's looser wording. Statement 1 is the one that fails. Nothing about a vaccine bars a microbe from getting in; entry is resisted by the body's physical barriers, the skin and the mucus lining of the respiratory, gastrointestinal and urogenital tracts. A vaccinated person can still be infected — what changes is what happens next.

• (a)1 only — Picks the one statement that is wrong. Vaccination acts inside the body after exposure; it does not seal the routes by which a pathogen enters.
• (b)2 only — Antibody production is right, but the account is incomplete — the antibodies and the memory cells then act on the pathogen once it is in, which is what statement 3 is getting at.
• (d)1, 2 and 3 — Adds statement 1, and that is the claim vaccination does not support; barring entry is the job of the skin and the mucous membranes, not of a vaccine.

A vaccine works on the immune system's property of memory. Antigenic material from a pathogen — killed or weakened organisms, or just their proteins — is introduced, the body raises antibodies against it, and it retains memory B and T cells. On a real encounter later, those memory cells recognise the pathogen at once and mount a large, fast antibody response, so the infection is cleared before it can cause disease. This is active immunity, in contrast to passive immunity, where preformed antibodies are injected directly, as with anti-tetanus serum.

Two-statement and three-statement immunity items usually hide their trap in a verb. Here the deciding word in statement 1 is 'blocks the entry', which belongs to the innate barriers, not to acquired immunity. Statement 3's verb, 'kills', is loose in the same way but in the direction the key accepts: strictly, antibodies neutralise, agglutinate and mark pathogens for destruction, and cytotoxic T cells kill the body's own infected cells rather than the microbe itself. The examiner is treating that whole clearance process as 'kills', and the card is authored to the official key. If you found yourself hesitating over statement 3 for exactly that reason, your biology was sound — the safer discriminator in the exam hall is statement 1, which is unambiguously wrong, and only one option excludes it while keeping both others.

• NCERT: 'The antibodies produced in the body against these antigens would neutralise the pathogenic agents during actual infection.'
• Vaccines also generate memory B and T cells that recognise the pathogen on later exposure and produce antibodies massively.
• Entry of microbes is resisted by physical barriers — the skin, and the mucus coating of the respiratory, gastrointestinal and urogenital tracts.
• Injecting preformed antibodies or antitoxin, as in tetanus, is passive immunisation, not vaccination.

• Reading 'blocks the entry of the infectious agent' as a description of immunity; that is what skin and mucous membranes do.
• Treating vaccination and immunisation with readymade antibodies as the same thing — one is active, the other passive.
• Assuming a vaccinated person cannot be infected at all, rather than that the infection is cleared faster.

Asked as a statement-set item where one statement quietly swaps an innate barrier's function into the account of vaccination.

• practice — not a real PYQ

  Injecting preformed antibodies into a patient with tetanus is best described as

  • (a)active immunisation
  • (b)passive immunisation
  • (c)vaccination with a live attenuated agent
  • (d)an innate immune barrier

  Answer(b) passive immunisation — readymade antibodies act at once but leave no memory, unlike a vaccine.

• practice — not a real PYQ

  Which one of the following is an example of a physical barrier of innate immunity?

  • (a)Memory B cells
  • (b)Antitoxin
  • (c)Mucus coating of the respiratory tract
  • (d)Antibodies raised by a vaccine

  Answer(c) Mucus coating of the respiratory tract — it traps microbes before they enter, which no vaccine does.