The trap: Aspirants consistently confuse active and passive immunity — especially calling vaccination "passive" because the antigen is given from outside. The source of the antibody (your body vs. someone else's) is the deciding criterion, not the source of the antigen.
Innate immunity is the non-specific first line of defence present from birth. It includes physical barriers (skin, mucous membranes), physiological barriers (acid in stomach, lysozyme in tears), cellular barriers (neutrophils, macrophages, natural killer cells), and cytokine barriers (interferons). It does not improve with repeated exposure.
Acquired (adaptive) immunity is specific, has memory, and improves on re-exposure. It operates through two arms:
Active immunity: The body produces its own antibodies in response to an antigen — either through natural infection or vaccination. It is slow to develop but long-lasting (memory cells persist).
Passive immunity: Pre-formed antibodies are transferred from another source — colostrum (IgA from mother to infant), or antiserum injection (e.g., anti-tetanus serum). It provides immediate but short-lived protection (no memory cells formed).
(Reference: NCERT Class 12 Biology Chapter 7, pages 135–136)
Watch-out: If the question says "vaccination," the immunity is ACTIVE — the body builds its own response. If it says "antiserum" or "mother's milk," it is PASSIVE — antibodies are received ready-made.
Select an option to see the explanation. Wrong answers show why your choice was tempting — and name the exact trap it exploits.
A person with a rare genetic defect cannot produce interferons. This person develops unusually frequent and severe viral infections, but handles ordinary bacterial infections normally. Which explanation best accounts for this pattern?
Answer: B. Virus-infected cells secrete interferons, which protect neighbouring non-infected cells from further viral infection (NCERT Class 12 Biology, Chapter 7, page 135). This is a cytokine barrier of innate immunity that is specifically antiviral — it does not act against bacteria. Losing interferon production therefore leaves viral spread unchecked while bacterial defences (phagocytes, physical/physiological barriers, antibodies) are unaffected, matching the selective pattern described.
Why A is wrong: A is wrong because interferons are cytokines of innate immunity, not antibodies of humoral (acquired) immunity — antibodies are produced by plasma cells, not virus-infected cells.
Why C is wrong: C is wrong because interferons are secreted by virus-infected cells as an innate, non-specific response — they are not restricted to memory T-cells, and their absence does not abolish memory against bacterial pathogens (bacterial memory depends on B/T lymphocytes, not interferons).
Why D is wrong: D is wrong because interferons are cytokine barriers, not physical barriers like mucus — and their described antiviral action, not antibacterial trapping, is what explains the selective viral vulnerability.
Innate immunity differs from acquired immunity in that innate immunity:
Answer: D. Innate immunity is non-specific, present from birth, and does not generate immunological memory — it responds identically regardless of prior exposure (NCERT Class 12 Biology Chapter 7, page 134).
Why A is wrong: A is wrong because high specificity is the hallmark of acquired (adaptive) immunity, not innate immunity — innate defences respond broadly to any foreign substance (trap: confusing innate and acquired properties).
Why B is wrong: B is wrong because memory cell production is a feature of acquired immunity (via B and T lymphocytes) — innate immunity lacks this capacity (trap: confusing innate and acquired properties).
Why C is wrong: C is wrong because antibody production by B-lymphocytes is humoral acquired immunity — innate immunity uses non-specific mechanisms like phagocytosis and physical barriers (trap: confusing innate and acquired properties).
A newborn receives IgA antibodies from its mother through colostrum. This is an example of:
Answer: A. The infant receives pre-formed antibodies (IgA) from the mother through a natural process (breastfeeding) — the infant's immune system does not produce these antibodies itself, making this naturally acquired passive immunity (NCERT Class 12 Biology Chapter 7, page 136).
Why B is wrong: B is wrong because (i) no artificial intervention is involved (colostrum is natural) and (ii) the infant does not produce antibodies itself — this fails both the 'artificial' and 'active' criteria (trap: active vs passive confusion).
Why C is wrong: C is wrong because 'active' requires the body to produce its own antibodies — the infant receives ready-made IgA without mounting its own immune response (trap: active vs passive — vaccination confusion extends to colostrum).
Why D is wrong: D is wrong because 'artificially acquired' requires deliberate medical intervention (like injecting antiserum) — colostrum transfer is a natural biological process, not a medical procedure (trap: confusing natural vs artificial route).
Which of the following is NOT a component of innate immunity?
Answer: C. Antibodies are produced by plasma cells (differentiated B-lymphocytes) as part of acquired humoral immunity, not innate immunity (NCERT Class 12 Biology Chapter 7, page 135).
Why A is wrong: A is wrong because lysozyme is a physiological barrier of innate immunity — it is present from birth and non-specifically destroys bacterial cell walls (trap: confusing which barriers belong to innate vs acquired).
Why B is wrong: B is wrong because interferons are part of innate immunity's cytokine barrier — they are released non-specifically by virus-infected cells to protect neighbouring cells (trap: assuming all molecular defences are acquired).
Why D is wrong: D is wrong because stomach acid (HCl, pH ~1.5–3.5) is a physiological barrier of innate immunity — it non-specifically destroys ingested pathogens (trap: confusing which barriers belong to innate vs acquired).
Cell-mediated immunity (CMI) is primarily carried out by:
Answer: D. T-lymphocytes (helper T and cytotoxic T cells) are the primary effectors of cell-mediated immunity — they destroy intracellular pathogens, infected cells, and transplanted tissues (NCERT Class 12 Biology Chapter 7, page 135).
Why A is wrong: A is wrong because B-lymphocytes mediate humoral immunity (antibody production), not cell-mediated immunity — confusing B-cell and T-cell roles is a common terminology trap.
Why B is wrong: B is wrong because eosinophils are innate immune cells primarily involved in parasitic infections and allergic reactions — they do not carry out the specific recognition that defines CMI.
Why C is wrong: C is wrong because mast cells participate in allergic/inflammatory responses (releasing histamine) — they are part of innate immunity, not the specific cell-mediated arm of acquired immunity.
A patient bitten by a venomous snake is given anti-venom serum. The type of immunity provided is:
Answer: A. Anti-venom serum contains pre-formed antibodies (produced in horses/other animals) that are artificially injected into the patient — the patient's immune system does not produce these antibodies, making this artificially acquired passive immunity (NCERT Class 12 Biology Chapter 7, pages 136–137).
Why B is wrong: B is wrong because 'active' requires the patient's body to mount its own antibody response — in anti-venom treatment, pre-formed antibodies are directly injected, bypassing the patient's immune response (trap: confusing vaccination with antiserum).
Why C is wrong: C is wrong because 'naturally acquired' means no deliberate medical intervention — anti-venom injection is an artificial medical procedure (trap: confusing the route of administration).
Why D is wrong: D is wrong because (i) there is artificial medical intervention (injection) and (ii) the patient receives ready-made antibodies without producing their own — this fails both 'natural' and 'active' criteria (trap: active vs passive confusion).
Which immunoglobulin class is present in colostrum and provides mucosal immunity to the newborn?
Answer: B. IgA is the predominant immunoglobulin in colostrum and mucosal secretions — it protects the infant's gut mucosal surfaces from pathogens (NCERT Class 12 Biology Chapter 7, pages 135–136).
Why A is wrong: A is wrong because although IgG crosses the placenta (providing prenatal passive immunity), the dominant immunoglobulin in colostrum specifically providing mucosal immunity is IgA, not IgG (trap: confusing placental transfer with colostrum transfer).
Why C is wrong: C is wrong because IgE is associated with allergic responses and parasitic infections — it is not the class transferred in colostrum for mucosal protection (trap: confusing immunoglobulin functions).
Why D is wrong: D is wrong because IgM is the first antibody produced during a primary immune response and is found mainly in blood — it is not the predominant class in colostrum for mucosal immunity (trap: confusing primary response antibody with mucosal protection antibody).
A person recovers from chickenpox and becomes immune to future infections. This immunity is classified as:
Answer: C. Recovery from natural infection means the body mounted its own immune response (produced antibodies and memory cells) without artificial intervention — this is naturally acquired active immunity (NCERT Class 12 Biology Chapter 7, pages 135–136).
Why A is wrong: A is wrong because (i) no artificial intervention occurred (the infection was natural) and (ii) the body produced its own antibodies (active, not passive) — this fails both criteria (trap: active vs passive confusion).
Why B is wrong: B is wrong because 'artificially acquired' requires deliberate medical intervention (like vaccination) — recovering from a natural chickenpox infection involves no artificial introduction of antigen (trap: confusing natural infection with vaccination).
Why D is wrong: D is wrong because 'passive' means receiving pre-formed antibodies — in this case the person's own immune system produced the antibodies in response to the virus, making it active (trap: active vs passive confusion).
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Given
A question states: "Match the following immunity types with their examples."
| Column I | Column II |
|----------|-----------|
| (i) Naturally acquired active | (a) Anti-tetanus serum injection |
| (ii) Artificially acquired active | (b) Recovery from measles |
| (iii) Naturally acquired passive | (c) Polio vaccination |
| (iv) Artificially acquired passive | (d) IgA transfer via colostrum |
Required
Correct matching of immunity types to examples.
Concept
The classification depends on two binary criteria:
1. Natural vs Artificial — did the exposure happen without medical intervention (natural) or through deliberate medical procedure (artificial)?
2. Active vs Passive — did the body produce its own antibodies (active) or receive pre-formed antibodies from another source (passive)?
Framework applied
| Example | Natural/Artificial? | Active/Passive? | Classification |
|---------|-------------------|-----------------|----------------|
| Recovery from measles | Natural (infection occurred naturally) | Active (body made antibodies) | Naturally acquired active |
| Polio vaccination | Artificial (deliberate injection) | Active (body responds to vaccine antigen) | Artificially acquired active |
| Colostrum IgA | Natural (breastfeeding) | Passive (infant receives maternal antibodies) | Naturally acquired passive |
| Anti-tetanus serum | Artificial (injection) | Passive (pre-formed antibodies given) | Artificially acquired passive |
Matching
• (i) → (b) Recovery from measles• (ii) → (c) Polio vaccination• (iii) → (d) IgA transfer via colostrum• (iv) → (a) Anti-tetanus serum injection
Verification
Each match satisfies both binary criteria. No calculation involved — this is a classification problem.
Final answer
(i)–(b), (ii)–(c), (iii)–(d), (iv)–(a)
Common trap
The most frequent error is matching vaccination with passive immunity because "something is injected from outside." The critical distinction: in vaccination, the injected substance is an antigen (weakened/killed pathogen or its parts) that stimulates the body's own immune response. In passive immunity, the injected substance is pre-formed antibodies that bypass the immune response entirely.
Similar NEET-style question
"Assertion (A): Vaccination provides active immunity. Reason (R): Vaccines contain pre-formed antibodies that directly neutralise pathogens."
Answer: A is true, R is false. Vaccines contain antigens (not pre-formed antibodies) that trigger the body's own antibody production.
---
Innate (non-specific): physical (skin), physiological (acid pH), cellular (NK cells, macrophages), cytokine. Acquired (specific): humoral (B cells → antibodies — IgG, IgM, IgA, IgE, IgD), cell-mediated (T cells). Active (own immune response) vs passive (preformed antibodies — colostrum, antiserum).
-- NCERT Class 12 Biology, Ch. 7, p. 134These are the exact patterns that cause wrong answers in NEET. Each trap includes when it triggers and how to avoid it.
Category: Similar Terms
Active: own immune response (vaccination, infection). Passive: pre-formed antibodies received (colostrum, antiserum injection).
Question on immunity type from vaccination, antiserum, mother's milk.
Active = body produces; passive = body receives. Vaccination → active. Mother's milk → passive (IgA).
Root cause: term confusion
Vaccination = ACTIVE (body produces antibodies in response to antigen). Antiserum = passive. Maternal IgA in milk = passive.
More in Biology and Human Welfare: 2 exam traps and mistakes · 1 question pattern from its other lessons.
10 questions from NEET 2020, 2022, 2024, 2025, 2026. Answers verified against NTA official keys.
Identify the statement that is NOT correct.
Select the incorrect statement with respect to acquired immunity.
Identify the wrong statement with reference to immunity.
All 37 past-paper questions from Biology and Human Welfare →
Page numbers are the ones printed in the current NCERT textbook (2023 rationalised edition), unless marked pre-2023. The books are free at ncert.nic.in.
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