Q.Differentiate between active immunity and passive immunity, giving one example of each.
Concept understanding — Active and Passive Immunity
Active and passive immunity are classified by the origin of protection. Active immunity is generated by the individual's own immune system in response to actual infection or vaccination; it develops memory cells, is durable, shows a booster effect on repeat exposure, but takes time to become effective. Passive immunity, by contrast, involves antibodies transferred into the body from an external source — such as maternal antibodies passed to an infant through colostrum, or injected antiserum — without any active participation by the recipient's own immune system; it acts immediately but is transient, produces no memory, and cannot be boosted by subsequent doses. Both can occur naturally (infection for active; maternal transfer for passive) or artificially (immunization for active; antibody injection for passive).
Active immunity is self-made by the body (after infection or vaccination) and is long-lasting; passive immunity is received ready-made from an outside source (e.g., antitoxin) and is short-lived.
Active immunity example: recovering from chickenpox. Passive immunity example: tetanus antitoxin injection.
Active immunity = body makes its own antibodies (e.g., after vaccination), long-lasting. Passive immunity = ready-made antibodies given from outside (e.g., tetanus antitoxin), short-lived.
Active immunity is immunity the body builds for itself by producing its own antibodies and memory cells in response to an antigen. It can be natural (developed after recovering from an actual infection, such as chickenpox) or artificial (developed after vaccination). Because the body makes its own antibodies, active immunity takes some days to develop but is long-lasting, since memory cells persist.
Passive immunity, in contrast, involves directly receiving ready-made antibodies produced elsewhere, rather than the person's own immune system making them. It can be natural (a mother's antibodies passing to her baby via the placenta or breast milk) or artificial (an antitoxin injection given after a tetanus-prone wound, or antivenom after a snakebite). Passive immunity acts almost immediately, which is why it is used in emergencies, but it fades within weeks because no memory cells are formed.
Active immunity is self-produced by the body (e.g., after vaccination or infection) and is long-lasting due to memory cells. Passive immunity is received ready-made from an outside source (e.g., tetanus antitoxin) and is fast-acting but short-lived, since it forms no memory.
Structure the answer as a clear two-column contrast: source of antibody, speed of action, and duration — covering all three points scores full marks.
Do not give vaccination as an example of passive immunity — vaccination stimulates the body's own antibody production, so it is a form of active (artificial) immunity, not passive.
Showing the 12 most recent of 18 on this concept.
- CBSE 2026Set ANNUAL1 markMCQQ.Which antibody molecule is found to be present in colostrum?(a) IgA(b) IgM(c) IgE(d) IgG
›Reveal solutionSolution
Colostrum, the thick yellowish milk secreted in the first few days after childbirth, is rich in IgA antibodies that protect the newborn.
Of the five antibody (immunoglobulin) classes — IgA, IgD, IgE, IgG and IgM — IgA is secreted at mucosal surfaces and in body secretions such as saliva, tears, and breast milk. Colostrum in particular is especially rich in IgA, giving the newborn infant a dose of passive, ready-made immunity against infections during the vulnerable early days before its own immune system matures.
(b) IgM is the first antibody produced during a primary immune response but is not the hallmark colostrum antibody; (c) IgE is associated with allergic reactions; (d) IgG is the most abundant antibody in blood serum and can cross the placenta, but colostrum's characteristic antibody is IgA.
✓Final answer(a) IgA.
- CBSE 2026Set ANNUAL1 markQ.What is vaccination?
›Reveal solutionSolution
Vaccination stimulates the immune system to produce antibodies and memory cells against a specific pathogen, without causing the actual disease, giving lasting protection.
Vaccination is a preventive medical procedure in which a vaccine — containing a weakened or dead pathogen, or antigenic proteins/toxoids derived from it — is introduced into the body. The immune system responds to these antigens by producing specific antibodies, exactly as it would during a real infection, but without the person developing the actual disease.
Crucially, this process also generates memory B and T cells. If the person is later exposed to the live, virulent pathogen, these memory cells enable a much faster and stronger ('secondary') immune response, neutralising the pathogen before it can cause illness. This principle underlies protection against diseases such as tetanus, polio, measles, and hepatitis, following the strategy pioneered by Edward Jenner with cowpox/smallpox.
✓Final answerVaccination is the process of deliberately introducing a weakened/inactivated pathogen or its antigenic components (a vaccine) into the body to trigger antibody production and immunological memory, providing future protection against that disease.
- CBSE 2025Set 57/5/11 markMCQQ.Colostrum secreted by the mother's mammary glands in a human female during the initial days of lactation is rich in antibody : (A) IgE (B) IgD (C) IgA (D) IgG
›Reveal solutionSolution
Colostrum is the first milk secreted after childbirth, and it is rich in IgA (specifically secretory IgA), which provides passive immunity to the newborn. The correct option is (C).
The Concept: Passive Immunity via Colostrum
When a baby is born, its own immune system is still immature. It cannot yet produce enough antibodies to fight off the many pathogens it will encounter. Nature’s solution is passive immunity — the transfer of ready-made antibodies from mother to child.
This happens in two ways:
- Across the placenta (before birth): IgG antibodies cross from the mother’s blood into the fetal circulation.
- Through breast milk (after birth): The first milk, called colostrum, is especially rich in a different antibody — IgA.
Why IgA? Because the newborn’s biggest threat is from pathogens that enter through the mouth, nose, and gut. IgA is uniquely suited to protect these mucosal surfaces. In colostrum, it exists as secretory IgA (sIgA) , which is resistant to digestion and can coat the baby’s gut lining, neutralising bacteria and viruses before they cause infection.
Step-by-Step Reasoning
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Identify the unique antibody in colostrum.
Colostrum is yellowish, thick, and produced for the first 2–4 days after birth. It is specifically known for its high concentration of IgA (up to 5–15 g/L), far more than in mature milk. This IgA is secreted by plasma cells in the mammary gland and is transported into the milk as secretory IgA.
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Eliminate the other options based on their roles.
- (A) IgE: Involved in allergic reactions and defence against parasites. Not a major component of colostrum.
- (B) IgD: Functions mainly as a receptor on B cells. Very low concentration in secretions.
- (D) IgG: The most abundant antibody in blood and the one that crosses the placenta. While some IgG is present in colostrum, it is not the dominant antibody there — IgA is.
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Confirm the exam-relevant fact.
This is a well-established, frequently tested point in NEET and board exams: colostrum is rich in IgA antibodies, which protect the newborn’s gut and respiratory tract during the vulnerable early days after birth.
Watch outA common mistake is to pick IgG because it is the most abundant antibody overall. But remember: IgG dominates in blood and crosses the placenta; IgA dominates in secretions like colostrum, saliva, and tears.
TipTo remember: IgA = A for Alimentary canal / Airways (mucosal immunity). Colostrum protects the baby’s gut — so it’s IgA.
✓Final answerThe correct option is (C) IgA.
- CBSE 2025Set ANNUAL1 markQ.Fill in the blank: Readymade antibodies are directly given to protect the body then it is called ___ immunity.
›Reveal solutionSolution
Passive immunity is when ready-made antibodies (not produced by the individual's own immune system) are directly administered to provide immediate protection.
In passive immunisation, pre-formed antibodies are given directly to the individual, for example, antibodies present in mother's milk (colostrum) given to a newborn, or anti-tetanus/anti-snake-venom serum given to a patient after exposure. This provides quick protection but is short-lived because the body did not generate its own memory response, unlike active immunity where the body itself produces antibodies (e.g., after vaccination).
✓Final answerPassive immunity.
- CBSE 2024Set E1 markMCQQ.Which of the following is abundantly found in colostrum?(a) IgA(b) IgG(c) IgM(d) IgD
›Reveal solutionSolution
Colostrum is abundant in IgA antibodies, providing passive immunity to the newborn.
The yellowish first secretion of the mother's mammary glands after childbirth is called colostrum:
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It contains a high concentration of the antibody IgA (immunoglobulin A).
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These maternal IgA antibodies pass to the infant and protect the gut and mucosal surfaces, an example of natural PASSIVE immunity, since the baby's own immune system is not yet developed.
✓Final answer(a) IgA.
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- CBSE 2024Set ANNUAL1 markQ.Define active immunity.
›Reveal solutionSolution
In active immunity, the individual's own immune system produces antibodies against a pathogen/antigen, resulting in lasting immunological memory.
Active immunity is acquired when the body is exposed to an antigen — either through a natural infection by a pathogen, or artificially through vaccination — and the immune system responds by producing its own antibodies (and memory B/T cells) against that antigen. Because memory cells persist, active immunity is generally slower to develop initially but is long-lasting/durable. This is in contrast to passive immunity, in which ready-made antibodies (e.g., from mother to foetus, or via antiserum) are directly given to the body, providing immediate but short-lived protection.
✓Final answerActive immunity: immunity in which the body itself produces antibodies in response to an antigen (infection or vaccine).
- CBSE 2024Set ANNUAL1 markMCQQ.Short lived immunity acquired from mother across placenta is categorized as –(a) Active immunity(b) Passive immunity(c) Innate non-specific immunity(d) Cellular immunity
›Reveal solutionSolution
Maternal antibodies crossing the placenta confer passive immunity, which is short-lived because the antibodies are borrowed, not produced by the infant's own immune system.
Immunity can be active (the body's own immune system produces antibodies/memory cells in response to an antigen — long-lasting) or passive (ready-made antibodies are directly received by the individual — quick but short-lived, since no memory is generated). Before and immediately after birth, an infant receives maternal IgG antibodies across the placenta during pregnancy, and further IgA-rich antibodies through colostrum after birth. Because these antibodies are not actively produced by the infant and gradually degrade, this protection is short-lived — a classic example of natural passive immunity.
Innate non-specific immunity refers to the physical/physiological/cellular barriers present from birth (skin, mucus, phagocytes) acting non-specifically against any pathogen, not to antibody transfer. Cellular immunity refers to responses mediated by T-lymphocytes, not to antibody transfer.
✓Final answer(b) Passive immunity.
- CBSE 2024Set ANNUAL1 markMCQQ.Colostrum is rich in :(a) Ig D(b) Ig E(c) Ig M(d) Ig A
›Reveal solutionSolution
Colostrum is rich in secretory IgA, which passively protects the newborn's gut and mucosal surfaces before its own immunity develops.
Colostrum is the first milk produced by the mother's mammary glands in the initial days after delivery, before regular milk secretion begins. It differs from regular breast milk in being especially rich in antibodies, principally secretory IgA (sIgA), along with proteins and minimal fat. Because a newborn's own immune system is immature, this maternally-derived IgA lines the infant's gut mucosa and coats pathogens, preventing them from attaching to and invading the intestinal epithelium -- an important form of passively acquired immunity. IgD, IgE and IgM are other classes of immunoglobulins with different roles (IgD as a B-cell receptor, IgE in allergic/anti-parasitic responses, IgM as the first antibody produced in a primary response) but none is the antibody characteristically concentrated in colostrum.
✓Final answerThe correct option is d) Ig A -- colostrum is rich in secretory IgA, giving the newborn passive immunity.
- CBSE 2023Set ANNUAL1 markMCQQ.Which antibodies are found in abundance in colostrum?(a) IgA(b) IgM(c) IgE(d) IgG
›Reveal solutionSolution
Colostrum, the first milk a mother produces after childbirth, is rich in IgA antibodies that protect the newborn.
Colostrum is secreted by the mammary glands during the first few days after delivery, before regular milk production begins.
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It contains a high concentration of Immunoglobulin A (IgA), an antibody that provides passive immunity to the newborn infant by protecting the mucosal surfaces of the gut and respiratory tract from pathogens.
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This is an example of naturally acquired passive immunity, since the antibodies are transferred ready-made from mother to infant rather than being produced by the infant's own immune system.
✓Final answerIgA (option a) is found in abundance in colostrum.
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- CBSE 2023Set ANNUAL1 markMCQQ.Which one of the following antibodies present in breast milk of humans protect the newborn baby from infections?(a) Ig A(b) Ig D(c) Ig E(d) Ig M
›Reveal solutionSolution
IgA is the antibody class secreted in breast milk (especially colostrum) that provides passive immunity to the newborn's gut and mucosal surfaces.
Humans produce five classes of antibodies (immunoglobulins): IgA, IgD, IgE, IgG and IgM, each with a distinct role:
- IgA: secreted in mucosal secretions — saliva, tears, and importantly, breast milk (especially the first milk, colostrum). It coats the lining of the newborn's gut and respiratory tract, protecting it from bacterial and viral infections before the infant's own immune system matures. This is a key example of passive, naturally-acquired immunity.
- IgD: found on the surface of B-lymphocytes as an antigen receptor.
- IgE: involved in allergic reactions (binds mast cells/basophils).
- IgM: the first antibody produced during a primary immune response (largest antibody, pentameric).
Since the question specifically asks which antibody in breast milk protects the newborn, the answer is IgA.
✓Final answer(a) Ig A.
- CBSE 2022Set ANNUAL1 markMCQQ.Active immunization can be brought about by(a) vaccination(b) injecting specific antibodies(c) injecting many allergens(d) none of these OR Interferon is active against which one of the following?(a) Bacteria(b) Fungi(c) Virus(d) None of these.
›Reveal solutionSolution
Vaccination triggers the body's own immune system to produce antibodies/memory cells — this is active immunity.
Active immunisation involves introducing a vaccine (containing a weakened/inactivated pathogen or its antigenic parts) into the body, which stimulates the individual's own immune system to actively produce specific antibodies and memory cells against that pathogen. This provides long-lasting protection, since memory cells persist and mount a faster, stronger response on future exposure to the actual pathogen.
This is different from passive immunisation, which involves directly injecting ready-made antibodies (option b) into the body — providing immediate but short-lived protection, since the body's own immune system is not stimulated to make memory cells. Injecting allergens (option c) is unrelated to immunisation against pathogens; it is used in allergy testing/desensitisation.
✓Final answer(a) vaccination.
Alternative — Interferon is active against which one of the following?
Interferons are a group of small protective proteins (cytokines) secreted by body cells in response to viral infection. When a cell is infected by a virus, it releases interferons that bind to receptors on neighbouring uninfected cells and induce them to produce antiviral proteins, thereby protecting those cells from becoming infected. Interferons are thus part of the innate (non-specific) defence against viruses, and are not directed against bacteria or fungi.
✓Final answer(c) Virus.
- CBSE 2021Set D1 markMCQQ.Triple antigen vaccine is not used for(a) Diphtheria(b) Pertusis(c) Typhoid(d) Tetanus
›Reveal solutionSolution
The DPT (triple antigen) vaccine covers diphtheria, pertussis and tetanus but not typhoid, so the answer is (C).
The triple antigen vaccine, commonly called DPT, is a combined vaccine given to children to protect them against three diseases at once: Diphtheria, Pertussis (whooping cough) and Tetanus.
Typhoid is not one of these; it is prevented by a separate typhoid vaccine (TAB). Therefore, among the options, the disease for which the triple antigen vaccine is not used is typhoid.
✓Final answer(C) Typhoid.
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