Human Health & Disease Class 12 Exemplar Solutions PDF

Correct option: (c) Health is a state of complete physical, mental and social well-being.

Concept used. The World Health Organisation (WHO) defines health as ``a state of complete physical, mental and social well-being and not merely the absence of disease or infirmity''. This definition is multidimensional: it goes beyond ``not being ill'' and requires that the body, the mind and the social environment of the person are all functioning well together.

1. Read each option as a candidate definition. A correct definition of health must mention all three dimensions: physical, mental, social.
2. Option (a) restricts health to ``body and mind in balance''. This misses the social dimension (relationships, work, community participation). So (a) is incomplete.
3. Option (b) is colloquial. A smiling face is a sign, not a definition; many sick people smile and many healthy people do not.
4. Option (d) confuses health with wealth. Economic prosperity may help maintain health but is not health itself.
5. Option (c) names all three pillars and matches the WHO definition. Hence (c) is correct.

Option (c): Health is a state of complete physical, mental and social well-being.

Correct option: (a) Pathogens.

Concept used. A pathogen is any disease-causing organism. The word comes from Greek pathos (suffering) + genes (producer): a producer of suffering. Pathogens include bacteria (Salmonella), viruses (HIV, rhinovirus), fungi (Trichophyton), protozoans (Plasmodium, Entamoeba) and helminths (Ascaris, Wuchereria). A vector, in contrast, is an organism that transmits a pathogen from one host to another (e.g. female Anopheles carrying Plasmodium); the vector itself is not the disease-causer.

1. Match each option to its biological role. (a) Pathogens cause disease, by definition. (b) Vectors carry pathogens but do not cause the disease themselves. (c) Insects is too narrow: only some insects are pathogens or vectors; most are harmless. (d) Worms is also too narrow: only parasitic worms cause disease.
2. Only (a) is a general term that fits ``organisms which cause diseases''.

Option (a): Pathogens.

Correct option: (d) Widal test.

Concept used. The Widal test is a serological agglutination test used to confirm Salmonella typhi infection (typhoid). The patient's serum is mixed with known Salmonella antigens; if anti-typhoid antibodies are present in the serum, visible clumping (agglutination) occurs, confirming infection. Each of the other options is a real test, but for different conditions: ELISA (Enzyme-Linked Immunosorbent Assay) detects HIV antibodies; ESR (Erythrocyte Sedimentation Rate) is a non-specific marker of inflammation; PCR (Polymerase Chain Reaction) is used to amplify nucleic acids, often for early HIV or COVID detection.

1. Match each test to its primary use. (a) ELISA → HIV / AIDS. (b) ESR → generic inflammation. (c) PCR → DNA / RNA amplification, used in HIV / COVID. (d) Widal → typhoid.
2. Only (d) is specific to typhoid, the disease asked about.

Option (d): Widal test.

Correct option: (d) ii and iv.

Concept used. An infectious disease is one caused by a pathogen (bacterium, virus, fungus, protozoan, helminth) and is transmissible from one person to another. A non-infectious disease is not caused by a pathogen and is not transmissible by direct contact (examples: cancer, hypertension, diabetes, allergies, auto-immune disorders).

1. Classify each listed disease.
   • (i) Cancer → caused by uncontrolled cell division, not by a pathogen. Non-infectious.
   • (ii) Influenza → caused by influenza virus. Infectious.
   • (iii) Allergy → hypersensitive immune response to a harmless antigen. Non-infectious.
   • (iv) Small pox → caused by Variola virus. Infectious.
2. Infectious diseases are therefore (ii) and (iv).

Option (d): ii and iv.

Correct option: (c) Salivary glands of mosquito.

Concept used. The life cycle of Plasmodium (the malaria parasite) is digenetic — it requires two hosts. In the human host, the parasite multiplies asexually in liver cells and then in RBCs. In the mosquito host (female Anopheles), gametocytes ingested with the blood meal fuse in the gut to form a zygote, which migrates to the gut wall, forms an oocyst, and eventually releases sporozoites. These sporozoites migrate to the mosquito's salivary glands, ready to be injected into the next human bitten.

1. Recall the journey of a sporozoite.
   Human bitten → sporozoites injected with mosquito saliva → liver schizogony → merozoites → RBC schizogony → gametocytes
   Mosquito bites infected human → gametocytes ingested → fertilisation in mosquito gut → oocyst → sporozoites → migrate to salivary glands.
2. The question asks where the sporozoites are formed (i.e. where they appear ready-to-inject). They are released from the oocyst on the gut wall and then accumulate in the salivary glands, from which they are injected into the next person bitten.
3. NCERT Section 8.2.4 specifies the salivary glands as the location of the infective sporozoites.

Option (c): Salivary glands of mosquito.

Correct option: (b) Aedes mosquito.

Concept used. Chikungunya is a viral disease caused by the chikungunya virus (CHIKV, a togavirus), transmitted by the Aedes aegypti and Aedes albopictus mosquitoes. The same Aedes species also transmits dengue and Zika viruses. Female Anopheles, by contrast, transmits malaria (Plasmodium).

1. Match each option to the diseases it transmits:
   • House fly → typhoid, cholera (mechanical contamination of food).
   • Aedes mosquito → dengue, chikungunya, yellow fever, Zika.
   • Cockroach → food contamination (passive).
   • Female Anopheles → malaria.
2. Only (b) transmits chikungunya.

Option (b): Aedes mosquito.

Correct option: (a) Difficulty in respiration, fever, chills, cough, headache.

Concept used. Pneumonia is an infection of the alveoli of the lungs, caused most commonly by Streptococcus pneumoniae and Haemophilus influenzae. The alveoli fill with fluid (consolidation), reducing the surface area available for gas exchange. The hallmark symptoms therefore centre on the respiratory system: difficulty in breathing (dyspnea), cough, fever with chills, and headache; in severe cases the lips and nail beds turn grey to bluish (cyanosis) from poor oxygenation.

1. Match each option to the disease whose symptoms it best fits:
   • (a) Respiratory + systemic → pneumonia.
   • (b) Abdominal + blood clots → amoebiasis-like.
   • (c) Upper respiratory + GI mix → common cold variant.
   • (d) High fever + GI symptoms → typhoid.
2. Only (a) is a respiratory cluster, which matches pneumonia.

Option (a).

Correct option: (c) Oncogenes.

Concept used. An oncogene is a gene that, when mutated or expressed at abnormally high levels, contributes to converting a normal cell into a cancer cell. The Greek onkos means ``mass / tumour''. The normal version of such a gene is called a proto-oncogene: it is involved in regulating cell division and differentiation. A mutation, viral insertion, or chromosomal translocation can activate the proto-oncogene into an oncogene that drives uncontrolled proliferation.

1. Reject (a): structural genes code for structural proteins (collagen, actin), not for cell-cycle regulators.
2. Reject (b): ``expressor genes'' is not a standard NCERT term.
3. Reject (d): regulatory genes is a generic term (includes operator/promoter regions) and is not specific to cancer.
4. Accept (c): oncogenes are the textbook cancer-causing genes.

Option (c): Oncogenes.

Correct option: (b) Metastasis.

Concept used. Metastasis is the spread of cancer cells from the primary tumour site to distant organs via blood or lymph, where they seed secondary tumours. It is the defining property of a malignant (cancerous) tumour, contrasting with benign (non-cancerous) tumours, which stay confined to their site of origin.

1. Decode each option:
   • (a) Metagenesis → alternation between sexual and asexual generations (e.g. in Obelia). Not cancer-related.
   • (b) Metastasis → cancer spread. Greek meta- (beyond) + stasis (placement) = ``displaced''.
   • (c) Teratogenesis → formation of birth defects (teratos = monster). Different field.
   • (d) Mitosis → normal cell division. All cells, cancerous or not, divide by mitosis.
2. Only (b) describes cancer spread to distant sites.

Option (b): Metastasis.

Correct option: (c) The patient shows behavioural and social maladjustment.

Concept used. Recall the WHO definition of health (Q1): a state of complete physical, mental and social well-being. A psychiatrist evaluates mental and social well-being. Therefore the cause of an ``unhealthy'' diagnosis from a psychiatrist must lie in either the mental or the social pillar, even if the body looks healthy.

1. Map each option to its dimension. (a) work-efficiency is an outcome, not a health pillar. (b) economic prosperity is not a health pillar. (c) behavioural / social maladjustment → mental + social health. (d) hobbies are not a health pillar.
2. Only (c) names mental-and-social dysfunction, which is exactly what a psychiatrist would diagnose.

Option (c).

Correct option: (b) ii and iv.

Concept used. Rheumatoid arthritis (RA) is an auto-immune disease: the body's own immune system loses its ability to distinguish ``self'' from ``non-self'' and starts producing antibodies that attack the synovial joints (knees, knuckles, wrists). The fundamental defect is loss of self-tolerance.

1. Evaluate each statement against the auto-immune mechanism.
   • (i) ``Ability to differentiate ... increases'' → False. Increased discrimination would prevent auto-immunity. Reject.
   • (ii) ``Body attacks self cells'' → True. This is the textbook definition of auto-immunity. Accept.
   • (iii) ``More antibodies are produced'' → Misleading. Quantity of antibodies is not the issue; specificity (against self) is. Reject.
   • (iv) ``Ability to differentiate ... is lost'' → True. Loss of self-tolerance is the root cause. Accept.
2. Correct statements: (ii) and (iv). ∴ option (b).

Option (b): ii and iv.

Correct option: (c) Shaking hands with infected persons.

Concept used. HIV is transmitted only through exchange of bodily fluids (blood, semen, vaginal fluid, breast milk). It is not airborne, not transmitted by casual contact (hugging, shaking hands, sharing utensils, mosquito bites), and not transmitted by sweat or tears. Modes of transmission are: unprotected sex, contaminated blood transfusion, sharing of needles, and mother-to-child during pregnancy / delivery / breastfeeding.

1. Check each option:
   • (a) blood transfusion → valid mode of transmission.
   • (b) shared needles → valid mode.
   • (c) shaking hands → NOT a mode. HIV does not survive on dry skin and there is no fluid exchange.
   • (d) unprotected sex → valid mode.
2. The question asks which is not a mode. Hence (c).

Option (c).

Correct option: (a) Latex of Papaver somniferum.

Concept used. Smack is a street name for heroin (diacetylmorphine), an opioid derived from morphine. Morphine and its derivatives are obtained from the dried latex of the unripe seed-capsules of the opium poppy (Papaver somniferum). The other options are also drug sources, but for different drugs:

• Cannabis sativa → marijuana, hashish, ganja (cannabinoids from inflorescence and resin).
• Datura → atropine, scopolamine (tropane alkaloids).
• Erythroxylon coca → cocaine (from leaves, not fruits).

1. Recall the source of heroin: opium poppy latex.
2. Match: only (a) names Papaver somniferum.

Option (a).

Correct option: (c) Interferon.

Concept used. Interferons (IFNs) are antiviral cytokines (small signalling proteins) released by virus-infected cells. They diffuse to neighbouring uninfected cells and bind to specific receptors, triggering those cells to produce antiviral proteins (oligoadenylate synthetase, RNase L, PKR) that block viral replication. Thus interferons set up an antiviral state in the surrounding cells before the virus can reach them.

1. Reject (a) serotonin: a neurotransmitter; not antiviral.
2. Reject (b) colostrum: the first milk after birth, rich in IgA antibodies; protects the infant only.
3. Accept (c) interferon: matches both ``produced by a cell in viral infection'' and ``protects other cells''.
4. Reject (d) histamine: an inflammatory mediator released in allergies.

Option (c): Interferon.

Correct option: (d) Cell-mediated immune response.

Concept used. Acquired immunity has two arms. Humoral immunity is antibody-mediated (B-cells → plasma cells → antibodies in blood) and targets extracellular pathogens. Cell-mediated immunity (CMI) is mediated by T-lymphocytes (cytotoxic T-cells, helper T-cells) and targets intracellular pathogens, tumour cells, and grafted/foreign tissues. Graft rejection is driven by cytotoxic T-cells recognising foreign MHC molecules on the donor tissue.

1. Match the trigger (foreign tissue) to the right arm of immunity. T-cells recognise foreign MHC class I on donor cells. This is cell-mediated.
2. Reject (a) auto-immune: the patient is not attacking self-tissue here, but foreign tissue.
3. Reject (b) humoral: antibodies play a smaller role in graft rejection compared to T-cells.
4. Reject (c) physiological: not a standard immunology term in NCERT.
5. Accept (d) cell-mediated.

Option (d): Cell-mediated immune response.

Correct option: (b) IgA type.

Concept used. Colostrum is the yellowish first milk secreted by the mother in the first 2–3 days after delivery. It is rich in secretory IgA (sIgA) antibodies, which coat the infant's gut mucosa and protect against gastrointestinal pathogens. The other classes have different roles: IgG crosses the placenta during pregnancy (not colostrum-related); IgD is a B-cell receptor; IgE mediates allergic responses.

1. Identify the body fluid: colostrum (breast milk).
2. Identify the antibody class enriched in mucosal secretions: IgA.
3. Hence (b).

Option (b): IgA type.

Correct option: (a) Nicotine.

Concept used. Tobacco contains over 4000 chemicals. The principal psychoactive and cardiovascular agent is nicotine, an alkaloid that binds nicotinic acetylcholine receptors on chromaffin cells of the adrenal medulla, triggering release of adrenaline (epinephrine) and noradrenaline (norepinephrine). These catecholamines raise blood pressure, heart rate and alertness — the rush smokers feel.

1. Reject (b) tannic acid: gives tea / tobacco its astringency but is not the catecholamine-stimulating agent.
2. Reject (c) ``curamin'': curcumin (from turmeric) is unrelated to tobacco.
3. Reject (d) catechin: a flavonoid found in tea; antioxidant, not catecholamine-stimulating.
4. Accept (a) nicotine: directly stimulates adrenal medulla.

Option (a): Nicotine.

Correct option: (c) Antibodies.

Concept used. Antivenom (also called antivenin) is an example of passive immunisation. Horses (or sheep) are first injected with sub-lethal doses of snake venom; their immune systems produce anti-venom antibodies; serum is collected, purified and given to a snake-bite patient. The patient receives ready-made antibodies that neutralise the venom — fast-acting but short-lived.

1. Compare with active immunisation (vaccines): one receives an attenuated antigen and produces one's own antibodies over weeks.
2. In a snake-bite emergency, there is no time to wait for the patient's own antibodies. So the patient is given antibodies directly. This is passive.
3. Antivenom therefore contains preformed antibodies. Hence (c).

Option (c): Antibodies.

Correct option: (c) Pancreas.

Concept used. Lymphoid tissues are organs and tissues where lymphocytes (B-cells, T-cells) are produced, mature, or activated. They are divided into primary lymphoid organs (bone marrow, thymus — sites of lymphocyte production and maturation) and secondary lymphoid organs (spleen, lymph nodes, tonsils, Peyer's patches, appendix — sites where lymphocytes encounter antigens). The pancreas is a digestive and endocrine organ (produces insulin, glucagon, digestive enzymes), not a lymphoid organ.

1. Classify each option:
   • Spleen → secondary lymphoid organ.
   • Tonsils → secondary lymphoid organ.
   • Pancreas → digestive + endocrine. NOT lymphoid.
   • Thymus → primary lymphoid organ (T-cell maturation).
2. The odd one out is pancreas. Hence (c).

Option (c): Pancreas.

Correct option: (c) Thymus.

Concept used. The thymus is a bilobed gland located near the heart and behind the sternum. It is the site of T-cell maturation. It is maximally active at birth and reaches its largest relative size in childhood. With age (especially after puberty) it undergoes thymic involution — its lymphoid tissue is gradually replaced by adipose tissue, and the gland shrinks dramatically. This is one reason elderly individuals mount weaker T-cell responses to new antigens.

1. Reject (a) pineal: small at all ages.
2. Reject (b) pituitary: roughly constant in size through adulthood.
3. Accept (c) thymus: classic involution gland.
4. Reject (d) thyroid: typically grows slightly with age.

Option (c): Thymus.

Correct option: (c) Toxin released from Plasmodium-infected cells.

Concept used. Haemozoin is a dark-brown crystalline pigment produced when Plasmodium (the malarial parasite) digests host haemoglobin inside red blood cells. Haem released from haemoglobin is toxic to the parasite, so the parasite polymerises haem into the inert haemozoin crystal. When the infected RBC ruptures, haemozoin and other parasite products spill into the bloodstream and cause the recurrent cycle of chills, high fever and shivering characteristic of malaria.

1. Reject (a) precursor of haemoglobin: haemozoin is a breakdown product, not a precursor.
2. Reject (b) and (d): no association with Streptococcus or Haemophilus.
3. Accept (c): released by Plasmodium-infected RBCs at rupture.

Option (c).

Correct option: (d) Macrosporum.

Concept used. Ringworm (tinea, dermatophytosis) is a superficial fungal infection of the skin, hair and nails. It is caused by three dermatophyte genera: Microsporum, Trichophyton, and Epidermophyton. ``Macrosporum'' is not a recognised genus of dermatophytes and is a distractor.

1. NCERT lists three causal genera: Microsporum, Trichophyton, Epidermophyton.
2. Match against options. (a), (b), (c) all match. (d) Macrosporum does not.
3. Hence the ``not'' option is (d).

Option (d): Macrosporum.

Correct option: (c) Less prone to malaria.

Concept used. Sickle cell anaemia is a recessive blood disorder caused by a point mutation (Glu → Val at position 6) in the β-globin gene. Heterozygotes (Hb^A Hb^S) carry one copy of the mutant allele; their RBCs sickle slightly under low oxygen. Crucially, the malarial parasite Plasmodium falciparum cannot complete its life cycle inside such RBCs — the deformed cells are cleared too quickly by the spleen. As a result, sickle-cell carriers (and to some extent homozygotes who survive to adulthood) are less susceptible to falciparum malaria. This is a classic example of balanced polymorphism or heterozygote advantage: the sickle allele persists at high frequency in African and Indian populations because it protects against malaria.

1. Recall that the sickle allele's high frequency in Africa overlaps the malarial belt. This is not coincidence.
2. Plasmodium growth is impaired in sickle-shaped (or sickleable) RBCs.
3. Hence sickle-cell carriers are less prone to malaria. Reject (a). Accept (c).
4. No analogous protection exists against typhoid (a bacterial gut infection), so (b) and (d) are irrelevant.

Option (c): Less prone to malaria.

Concept used. Pathogens display tissue tropism — a preference for invading a particular tissue, organ or cell type. This specificity arises because the pathogen requires particular host surface receptors, intracellular machinery, or microenvironmental conditions found only in that tissue.

1. State the claim: many pathogens enter the body through a general route (mouth, lungs, blood) but multiply only in a specific organ.
2. Give worked examples of tropism.
   • Plasmodium (malaria) sporozoites enter through a mosquito bite but multiply only in liver cells and then RBCs, because these cells have the receptors and the haemoglobin the parasite needs.
   • Mycobacterium tuberculosis preferentially infects the lungs (and sometimes lymph nodes, bones, kidneys).
   • Wuchereria (filaria) lodges in lymphatic vessels of the lower limbs.
   • HIV specifically infects CD4⁺ T-helper cells.
   • Salmonella typhi targets the small intestine and then the gallbladder.
3. Conclude: pathogen specificity is the rule, not the exception.

Pathogens are tissue/organ specific because they need particular host receptors and microenvironment; e.g. HIV → CD4 T-cells, Plasmodium → liver & RBC, filaria → lymphatic vessels.

Concept used. ELISA (Enzyme-Linked Immunosorbent Assay) is the standard antibody-based test for HIV diagnosis. A positive ELISA combined with immune suppression points to AIDS (Acquired Immuno-Deficiency Syndrome), caused by the Human Immunodeficiency Virus (HIV). HIV preferentially infects and destroys helper T-lymphocytes (CD4⁺ T-cells), which orchestrate the entire acquired immune response. Their depletion is what produces the immune-suppressed phenotype.

1. (a) The disease is AIDS.
2. (b) The causative organism is HIV (Human Immunodeficiency Virus), a retrovirus of the family Retroviridae.
3. (c) HIV infects helper T-lymphocytes (CD4⁺ T-cells) and, to a lesser extent, macrophages and dendritic cells.

(a) AIDS; (b) HIV (a retrovirus); (c) helper T-lymphocytes (CD4⁺ T-cells).

Concept used. Both B-lymphocytes and T-lymphocytes are formed in the bone marrow from a common haematopoietic stem cell. They diverge by site of maturation: B-cells mature in the bone marrow itself, while T-cells migrate to and mature in the thymus.

1. State formation sites: B-cells → bone marrow (formation + maturation). T-cells → bone marrow (formation) and thymus (maturation).
2. State functional differences:
   • B-cells mediate humoral immunity by secreting antibodies (immunoglobulins) against extracellular pathogens.
   • T-cells mediate cell-mediated immunity by directly killing infected cells (cytotoxic T) or by helping B-cells and macrophages (helper T).

Both formed in bone marrow; B-cells mature in bone marrow and secrete antibodies; T-cells mature in thymus and mediate cell-mediated immunity.

Concept used. Each disease has a specific causative organism. Filariasis is caused by the helminth Wuchereria (or Brugia), not by Microsporum, which is one of the fungi that cause ringworm.

1. Verify each pair.
   • (a) Virus (rhinovirus) → common cold. Correct.
   • (b) Salmonella typhi → typhoid. Correct.
   • (c) Microsporum → ringworm, not filariasis. Wrong pair.
   • (d) Plasmodium → malaria. Correct.
2. The mismatched pair is (c). The correct cause of filariasis is Wuchereria bancrofti / Wuchereria malayi.

Mismatched pair: (c) Microsporum filariasis. Microsporum causes ringworm; filariasis is caused by Wuchereria.

Concept used. The thymus is the primary lymphoid organ where T-lymphocytes mature. Removal of the thymus (thymectomy), especially in early life, prevents the development of mature T-cells.

1. Without thymus → no T-cell maturation → no functional T-cells.
2. Consequences for the immune system:
   • Loss of cell-mediated immunity: cytotoxic T-cells cannot kill infected cells; intracellular pathogens (viruses, Mycobacterium) cannot be cleared.
   • Loss of T-helper signals: B-cells receive no help, so antibody production against most antigens collapses.
   • Severely weakened response to grafts (failure to reject) and to tumour surveillance.
3. The person becomes severely immune-compromised, similar to a SCID phenotype.

Removal of thymus halts T-cell maturation; cell-mediated immunity is lost, and antibody responses (which need T-cell help) are sharply weakened.

Concept used. The body has several layered innate immunity barriers that prevent ingested pathogens from establishing infection. Innate immunity is non-specific, present from birth, and forms the first line of defense.

1. Identify the gut-specific barriers:
   • Saliva in the mouth contains lysozyme that breaks bacterial cell walls.
   • Gastric HCl in the stomach kills most ingested microbes by extreme acidity (pH ≈ 1.5–2).
   • Mucus lining the gut traps microbes.
   • Resident gut microflora competitively exclude pathogens.
   • Peyer's patches and gut-associated lymphoid tissue (GALT) mount localised IgA responses.
2. Classify the immunity. These barriers (saliva, mucus, HCl, normal flora) are innate (non-specific) immunity — specifically the physiological + cellular barriers.

Barriers: saliva (lysozyme), gastric HCl, gut mucus, resident microflora. Type: innate immunity (physiological barriers).

Concept used. Breast milk is uniquely matched to infant nutritional and immune needs. The first secretion (colostrum, in the first 2–3 days) is exceptionally rich in immunoglobulins, especially secretory IgA, which coats the infant's gut.

1. List nutritional benefits: balanced proteins, fats, lactose, vitamins, minerals, water — all at the right concentration and temperature; easy to digest.
2. List immune benefits:
   • Antibodies: colostrum is rich in IgA, which protects against gut infections.
   • Lactoferrin, lysozyme, oligosaccharides provide additional antimicrobial defence.
   • Confers passive natural immunity until the baby's own immune system matures.
3. Other benefits: promotes bonding; sterile and at body temperature.

Mother's milk (especially colostrum) provides complete nutrition plus IgA antibodies that confer passive immunity to the newborn.

Concept used. Interferons (IFNs) are antiviral cytokines — small signalling proteins released by virus-infected cells. They are part of the body's innate immunity response and act in a paracrine (cell-to-cell) manner.

1. Definition: Interferons are glycoproteins secreted by virus-infected cells.
2. Mechanism of protection.
   • IFNs diffuse to neighbouring uninfected cells.
   • They bind IFN receptors on those cells.
   • Receptor signalling activates antiviral genes (encoding 2'-5' OAS, PKR, RNase L).
   • These enzymes degrade viral RNA, inhibit viral protein synthesis, and induce apoptosis if infection occurs.
   • The neighbouring cells are now in an ``antiviral state'' and resist viral replication.
3. Result: viral spread to new cells is sharply slowed, buying time for the adaptive immune response (T-cells, antibodies) to develop.

Interferons are antiviral proteins secreted by infected cells; they induce an antiviral state in neighbouring cells, blocking viral replication.

Concept used. A typical antibody (immunoglobulin) has the formula H₂ L₂ — two identical heavy (H) chains and two identical light (L) chains, joined together by disulphide bonds into a Y-shape. The arms of the Y have variable regions that form the antigen-binding sites. The labels typically asked in this diagram are: A = antigen, B = light chain, C = heavy chain. Some versions of the figure label A = antigen-binding site, B = light chain, C = heavy chain.

1. Identify the Y-shape: top two arms = Fab regions (variable); base = Fc region (constant).
2. Identify A, B, C from typical NCERT labelling.
   • A = Antigen-binding site (top of each arm).
   • B = Light chain (the shorter polypeptide flanking each arm).
   • C = Heavy chain (the longer polypeptide running through each arm and into the stem).
3. Note: the molecule is held together by inter-chain disulphide (S–S) bridges (visible in the figure).

A = antigen-binding site; B = light chain; C = heavy chain.

Concept used. Addiction produces physical dependence: the body adapts to the constant presence of the drug, and its sudden absence triggers a stereotyped set of withdrawal symptoms (also called abstinence syndrome).

1. Recall the classical withdrawal-symptom list.
   • Anxiety, restlessness and irritability.
   • Shakiness or tremors.
   • Nausea, vomiting and sweating.
   • Strong craving for the drug; depression; insomnia.
2. Any four of the above are acceptable. Severe alcohol withdrawal can also cause seizures and hallucinations.

Four withdrawal symptoms: anxiety, tremors / shaking, nausea & sweating, strong craving for the substance.

Concept used. Many respiratory pathogens (rhinovirus, influenza, Streptococcus pneumoniae, Haemophilus influenzae) spread by airborne droplet transmission. Closed, crowded, air-conditioned spaces re-circulate the same air, increasing pathogen load and increasing person-to-person transmission.

1. During changing weather, body's mucosal defences are stressed (cold air dries mucus), and many pathogens flourish (rhino-, influenza viruses).
2. Closed crowded places concentrate exhaled droplets; air-conditioning recycles them.
3. Result: a single infectious person can infect many others quickly.
4. Avoiding such places reduces exposure and disease incidence.

Closed, crowded, AC spaces concentrate respiratory pathogens in re-circulated air; one infected person spreads to many. Hence avoid them during seasonal transitions.

Concept used. The sickle-cell allele (Hb^S) is maintained in malaria-endemic populations by heterozygote advantage (balanced polymorphism). Heterozygotes (Hb^A Hb^S) are resistant to falciparum malaria because their RBCs sickle when invaded by Plasmodium, leading to rapid clearance of infected cells by the spleen.

1. In malaria-endemic Africa and India, Hb^A Hb^A homozygotes are susceptible to fatal malaria.
2. Hb^S Hb^S homozygotes have severe anaemia and die young, so this genotype is at a disadvantage.
3. Hb^A Hb^S heterozygotes have only mild anaemia but strong malaria resistance; they survive and reproduce best.
4. Natural selection therefore maintains the Hb^S allele at intermediate frequency: the death toll from sickle disease is balanced by the survival advantage during malaria epidemics. This is balanced polymorphism.

Sickle cell allele persists because heterozygotes are protected from falciparum malaria — a classic heterozygote advantage.

Concept used. Lymph nodes are small bean-shaped organs scattered along lymphatic vessels. They serve as filtration stations and meeting points where antigens carried by lymph encounter lymphocytes, triggering specific immune responses.

1. Filtration: lymph from tissues enters the node, where macrophages remove microbes, debris and cancer cells.
2. Antigen presentation: dendritic cells in the node display antigen fragments to lymphocytes.
3. Lymphocyte activation: B-cells and T-cells encounter their cognate antigen, become activated, proliferate (clonal expansion) and differentiate into effector cells.
4. Antibody production: activated B-cells become plasma cells that pour antibodies into the lymph and blood.
5. Memory formation: some activated cells become memory cells, providing rapid recall response on future exposure.

Lymph nodes filter lymph, present antigens, activate B & T-cells, produce antibodies, and generate memory cells — they are the principal sites where adaptive immune responses are mounted.

Concept used. A typical antibody (immunoglobulin) is a tetramer of four polypeptide chains: two identical heavy (H) chains and two identical light (L) chains, linked by disulphide bonds into a Y-shape.

1. Count the chains: 2 heavy + 2 light = 4 polypeptide chains in total.
2. Express stoichiometrically: H_{× 2} + L_{× 2} = H₂ L₂.
3. Therefore the formula representation is H₂ L₂.

An antibody has 2 heavy + 2 light chains, hence the formula H₂ L₂.

Concept used. Immunological memory is the ability of the acquired immune system to mount a faster, larger and more specific response on second (or later) exposure to the same antigen than on the first exposure. The cells responsible are memory B-cells and memory T-cells formed during the primary response.

1. During the first exposure, some activated B and T-cells differentiate not into short-lived effectors but into long-lived memory cells that persist for years to decades.
2. On re-exposure, these memory cells recognise the antigen immediately, proliferate rapidly, and generate plasma cells / cytotoxic cells in days rather than weeks.
3. This secondary response produces high-affinity IgG antibodies in large amounts, often clearing the pathogen before symptoms appear.
4. Vaccination relies on this memory: a vaccine creates memory cells without the danger of the disease.

Immune memory = the ability to recognise a previously-encountered antigen and mount a faster, stronger response, mediated by long-lived memory B and T-cells.

Concept used. Anti-Retroviral Therapy (ART) is a combination drug regimen (typically 3 or more drugs from different classes) that suppresses the replication of retroviruses, especially HIV.

1. Identify infection: ART is the standard treatment for AIDS / HIV infection.
2. Identify pathogen: the causative organism is the Human Immunodeficiency Virus (HIV), a retrovirus belonging to the family Retroviridae.
3. Why ``retroviral''? HIV stores its genome as RNA and uses reverse transcriptase to copy RNA → DNA inside the host cell. Drugs target this enzyme (NRTIs, NNRTIs), the integrase, or the protease.

The patient has HIV / AIDS infection; the causative organism is the Human Immunodeficiency Virus (HIV), a retrovirus.

Concept used. Active immunity is generated when the host's own immune system encounters an antigen (natural infection or vaccine) and produces specific antibodies and memory cells. Passive immunity is conferred when preformed antibodies (from another source) are introduced into the host; the host's immune system does not learn or remember.

1. State origin: active = host's own response; passive = ready-made antibodies given.
2. Onset and duration: active is slow to develop (1–2 weeks) but long-lasting (often life-long) due to memory cells; passive is immediate but short-lived (a few weeks) because the antibodies are not replenished.
3. Examples:
   • Active natural: recovery from chickenpox.
   • Active artificial: vaccination (DPT, MMR).
   • Passive natural: maternal IgG via placenta; IgA via colostrum.
   • Passive artificial: antivenom serum, anti-tetanus serum.
4. Memory: active immunity generates memory; passive does not.

Active immunity: host's own response, slow onset, long-lasting, has memory (e.g. vaccines). Passive immunity: preformed antibodies given, immediate but short-lived, no memory (e.g. antivenom).

Concept used. Tumours are classified by their growth behaviour. A benign tumour is non-cancerous, encapsulated, slow-growing, and confined to the site of origin. A malignant tumour is cancerous: it grows rapidly, invades surrounding tissue, and metastasises to distant organs via blood and lymph.

1. Growth rate: benign = slow; malignant = rapid and uncontrolled.
2. Capsule: benign tumours are usually encapsulated; malignant tumours have ill-defined borders and infiltrate adjacent tissue.
3. Metastasis: benign tumours stay where they form; malignant tumours seed secondary tumours at distant sites.
4. Risk to life: benign tumours rarely kill (unless they compress a vital organ); malignant tumours are often fatal if untreated.
5. Cell appearance: benign cells resemble the tissue of origin (well-differentiated); malignant cells are poorly differentiated and often have abnormal nuclei.

Benign: slow, encapsulated, non-invasive, no metastasis, rarely fatal. Malignant: rapid, invasive, metastasises, often fatal — true cancer.

Concept used. Passive (second-hand) smoking is inhaling the smoke exhaled by a smoker or smoke from a burning cigarette. Side-stream smoke (from the cigarette tip) is unfiltered and contains higher concentrations of certain carcinogens (carbon monoxide, nicotine, tar, benzopyrene) per gram than the mainstream smoke a smoker inhales through the filter.

1. Composition difference: side-stream smoke from the lit end of a cigarette burns at a lower temperature than the smoker's puff, producing more carcinogens (benzopyrenes, nitrosamines).
2. Lack of filter: smokers' filters trap a fraction of particulates and tar; passive smokers receive un-filtered smoke directly.
3. Vulnerable victims: children and pregnant women are common passive smokers; they cannot choose to leave the environment, magnifying risk.
4. Result: passive smokers can develop the same diseases as active smokers — lung cancer, COPD, cardiovascular disease — without ever choosing to smoke. In that sense, passive smoking is more dangerous or at least as dangerous: the victim has no agency, the smoke is unfiltered, and side-stream smoke is chemically harsher.

Yes, passive smoking can be more dangerous: side-stream smoke is unfiltered and richer in carcinogens, and passive smokers (often children, pregnant women) inhale it involuntarily.

Concept used. The aphorism captures a public-health principle: stopping a disease from occurring is more efficient (in cost, suffering, and outcomes) than treating it after onset. Many infectious and lifestyle diseases lack reliable cures, so prevention is the most powerful intervention.

1. Disease has direct and indirect costs (medication, hospitalisation, lost work, family stress). Prevention avoids all of these.
2. Many diseases have no cure (AIDS, polio, rabies once symptoms appear). Vaccination or hygiene prevents them outright.
3. Even curable diseases (typhoid, malaria) leave long-term complications. Prevention avoids those sequelae.
4. Preventive tools include vaccination, hygiene, clean water, balanced diet, exercise, vector control (mosquito nets, indoor spraying), and screening (Pap smear, mammography).

Prevention is cheaper, more effective and avoids suffering; especially crucial for incurable diseases (AIDS, polio, rabies) and for diseases with long-term sequelae.

Concept used. Microbial infections can be controlled at three points: (i) at the source (pathogen reservoir), (ii) during transmission, and (iii) at the host (immunity). Public-health programmes target all three.

1. Personal and public hygiene. Wash hands before meals; keep food covered; dispose of garbage; provide clean drinking water; treat sewage. This interrupts faecal–oral transmission of typhoid, cholera, hepatitis A, and amoebiasis.
2. Vector control. Eliminate breeding sites of mosquitoes (stagnant water); use insecticides and bed nets; introduce larvivorous fish (Gambusia). This breaks transmission of malaria, dengue, chikungunya, filariasis.
3. Vaccination (immunisation). Routine vaccines (DPT, OPV, MMR, BCG, Hepatitis-B) prime the immune system so the host clears the pathogen before disease develops. This has eradicated smallpox and brought polio and measles to near-elimination.

Three preventive measures: (1) personal & public hygiene; (2) vector control; (3) vaccination.

Concept used. A retrovirus (e.g. HIV) has an RNA genome and the enzyme reverse transcriptase, which copies the viral RNA into double-stranded cDNA (viral DNA) inside the host. The viral DNA integrates into the host chromosome as a provirus. The integrated provirus is later transcribed and translated by the host machinery to produce new viral RNA and proteins, which assemble into new virions that bud out of the host cell.

1. (a) Fill in the blanks.
   • (1) Viral DNA formed by reverse transcription of viral RNA.
   • (2) New viral RNA (and viral proteins) produced from the integrated provirus.
2. (b) The virus is called retrovirus because it reverses the normal direction of genetic information flow. The Central Dogma says DNA → RNA → protein; retroviruses run the first arrow backwards: RNA → DNA, using reverse transcriptase.
3. (c) The infected cell ultimately dies. While viruses are being produced, the cell's resources are consumed, its membrane is breached as new virions bud out, and (for HIV) the host CD4 T-cell is destroyed within days to weeks. Some retroviruses can persist in a latent state, but eventually production of virions kills the host cell.

(1) Viral DNA; (2) new viral RNA and proteins. ``Retro'' = reverse: RNA → DNA via reverse transcriptase. The host cell typically dies as virions are released.

Concept used. Many infectious diseases are transmitted by routes that hygiene directly interrupts: faecal–oral (contaminated food/water), respiratory droplet (coughs, sneezes), and contact (skin, fomites). Good hygiene practices block these routes.

1. Personal hygiene.
   • Hand-washing before meals and after toilet: prevents typhoid, cholera, amoebiasis, hepatitis A.
   • Bathing and clean clothes: prevent ringworm, scabies, lice.
   • Covering nose/mouth while coughing: prevents pneumonia, influenza, TB.
2. Public hygiene.
   • Safe drinking water: prevents typhoid, cholera, hepatitis.
   • Sewage disposal and treatment: prevents amoebiasis, hookworm, cholera.
   • Garbage management and food covering: reduces fly population and food contamination.
   • Eliminating mosquito breeding sites: prevents malaria, dengue, chikungunya, filariasis.
3. Hygiene was the single most impactful public-health intervention before antibiotics and vaccines, and it remains the bedrock today.

Personal hygiene (hand-washing, bathing, droplet cover) prevents typhoid, hepatitis, ringworm, pneumonia. Public hygiene (water, sewage, garbage, vector control) prevents cholera, malaria, dengue. Hygiene blocks transmission at source.

Concept used. Each NCERT-listed infectious disease has a fixed (causative organism, key symptom) tuple. The table tests recall of these tuples.

1. Fill each gap.
   • (i) Ascaris (round worm) causes internal bleeding, muscular pain, fever, anaemia and blockage of intestinal passage.
   • (ii) Trichophyton causes ringworm.
   • (iii) Typhoid is caused by Salmonella typhi (a bacterium).
   • (iv) Pneumonia symptoms: fever, chills, cough, difficulty in breathing, headache; lips and finger-tips may turn grey/blue in severe cases.
   • (v) Rhinoviruses cause the common cold.
   • (vi) Filariasis is caused by Wuchereria (W. bancrofti and W. malayi).

(i) intestinal blockage, anaemia, pain; (ii) Ringworm; (iii) Salmonella typhi; (iv) fever, chills, cough, dyspnea; (v) Common cold; (vi) Wuchereria.

Concept used. The structure shown is that of a cannabinoid (the THC / cannabinol skeleton — a phenolic compound with a long alkyl side chain). Cannabinoids are derived from the inflorescences of Cannabis sativa.

1. (a) The compound represents the cannabinoids group (marijuana, hashish / charas, ganja).
2. (b) Cannabinoids are usually consumed by inhalation (smoking) of dried inflorescences or hashish, and by oral ingestion (in food preparations such as bhang).
3. (c) The principal organs affected are the cardiovascular system (raised heart rate, blood pressure) and the central nervous system / brain (impaired memory, distorted perception, hallucinations).

(a) Cannabinoids; (b) inhalation (smoking) or oral ingestion; (c) cardiovascular system and brain (CNS).

Concept used. CT (Computed Tomography) uses multiple X-ray projections combined by computer reconstruction to produce cross-sectional images of the body. MRI (Magnetic Resonance Imaging) uses a strong magnetic field and radio-frequency pulses to align hydrogen nuclei in the body and detect their relaxation signals, producing soft-tissue images. Both are non-invasive imaging modalities used in cancer detection.

1. Full forms:
   • CT = Computed Tomography
   • MRI = Magnetic Resonance Imaging
2. Differences.
   • CT uses ionising X-rays; MRI uses non-ionising magnetic field + radio waves.
   • CT is faster (seconds), MRI is slower (15–45 minutes).
   • CT excels for bone and acute haemorrhage; MRI excels for soft tissues (brain, spinal cord, ligaments, tumours).
   • CT has some radiation exposure; MRI has no ionising radiation.
3. Uses: both detect tumours and structural abnormalities of internal organs; CT is commonly used for emergency head/chest imaging and cancer staging; MRI for brain, spine, soft-tissue tumours and joints.

CT = Computed Tomography (X-rays); MRI = Magnetic Resonance Imaging (magnetic field + radio waves). CT is fast and good for bone/haemorrhage; MRI is non-ionising and good for soft tissue. Both detect cancers and structural lesions.

Concept used. Plants produce many secondary metabolites (alkaloids, terpenes, phenolics) that have powerful pharmacological action. Many become medicines when used in the right dose for the right indication, and become drugs of abuse when misused.

1. Example: opioids from Papaver somniferum.
   • Morphine, extracted from opium poppy latex, is one of the most effective analgesics (pain killers) used in surgery, cancer pain, and palliative care.
   • The same compound, when used recreationally and at higher doses (as heroin / smack), causes addiction, respiratory depression and death.
2. Other examples: cocaine (medical anaesthetic vs. stimulant abuse); cannabinoids (chronic pain relief vs. recreational marijuana); barbiturates (anti-seizure vs. abuse).
3. Conclusion: secondary metabolites are double-edged; medical control of dose and indication separates therapy from abuse.

Plant secondary metabolites (e.g. morphine from opium poppy) are valuable medicines (analgesics) but become addictive drugs (heroin) when misused. Dose and indication control matter.

Concept used. Cannabinoids (marijuana, charas, hashish) are banned by sports regulatory bodies (WADA, IOC) because they impair athletic performance, alter judgement, and are addictive.

1. Cannabinoids affect the central nervous system: they alter perception, slow reaction time, impair coordination and short-term memory.
2. They affect the cardiovascular system: increase heart rate and blood pressure.
3. They can be used to mask pain and fatigue, giving an unfair edge in endurance events.
4. Athletes risk addiction and long-term cognitive and respiratory damage.
5. Hence cannabinoids are on the WADA prohibited list for in-competition use.

Cannabinoids impair CNS function, raise cardiovascular load, mask pain/fatigue, and are addictive — hence banned by sporting bodies.

Concept used. Primary metabolism is the universal set of biochemical pathways needed for growth and survival (glycolysis, TCA cycle, protein synthesis). Secondary metabolism produces compounds (alkaloids, terpenes, phenolics, flavonoids) that are not strictly required for growth but provide ecological functions such as defence against herbivores, antimicrobial activity, attraction of pollinators, or UV protection.

1. Define secondary metabolites: organic compounds produced by plants (and microbes) that are not directly involved in basal growth or reproduction.
2. Give examples: morphine (poppy), nicotine (tobacco), caffeine (coffee), cannabinoids (cannabis), quinine (cinchona), atropine (Datura).
3. Note their importance: many are starting points for medicines and drugs.

Secondary metabolism produces compounds (alkaloids, terpenoids, phenolics) not essential for plant growth but useful for defence and ecological interactions; many are valuable medicines.

Concept used. Most psychoactive drugs and alcohol act on the brain's reward pathway (dopamine release in the nucleus accumbens). This produces a short-term euphoria. With repeated use, the brain adapts (tolerance, dependence), and chronic use damages multiple organ systems.

1. Short-term effects (the ``high''):
   • Euphoria, relaxation, distorted perception.
   • Lowered inhibitions, impaired judgement.
2. Long-term effects (the ``damages''):
   • Brain: addiction, depression, memory loss, psychosis.
   • Liver (especially alcohol): fatty liver, hepatitis, cirrhosis.
   • Heart: hypertension, cardiomyopathy, arrhythmias.
   • Kidney: chronic injury.
   • Reproductive system: impotence, infertility.
   • Social: family breakdown, financial ruin, crime, academic failure.
   • Risk of overdose and death; with shared needles, risk of HIV/Hepatitis B/C.
3. The short-term euphoria is far outweighed by long-term, often irreversible damage.

Brief euphoria masks lasting harm: addiction, brain damage, organ failure, social ruin. The trade-off is sharply negative.

Concept used. These are all faecal–oral transmitted diseases caused by ingestion of food or water contaminated with faecal pathogens. Overcrowding magnifies every link in their transmission chain.

1. Inadequate sanitation in crowded slums leads to open defecation or leaking sewers, contaminating water sources.
2. Limited clean water means people share water sources; one contamination event infects many.
3. Crowding accelerates person-to-person transmission via hand contact and shared utensils.
4. Flies multiply on uncollected garbage and mechanically transfer pathogens to food.
5. Poor nutrition and stress in crowded settings reduce host resistance.
6. Combined, all these factors keep the basic reproductive number R₀ above 1, sustaining the disease.

Overcrowding + poor sanitation + shared water + flies + low nutrition all amplify faecal–oral transmission of dysentery, cholera, typhoid.

Concept used. Cannabinoids are a class of psychoactive compounds extracted from the inflorescences and resin of Cannabis sativa (Indian hemp).

1. Source plant: Cannabis sativa.
2. Two cannabinoids (common preparations): marijuana (from leaves/inflorescences), hashish or charas (from resin), ganja (from female flowering tops), bhang (from leaves, ingested orally). Two examples: marijuana and hashish (charas). The principal active molecule is Δ⁹-tetrahydrocannabinol (THC).
3. Body parts affected: the central nervous system (brain) — distortion of perception, impaired memory, hallucinations — and the cardiovascular system — raised heart rate, blood pressure.

Source: Cannabis sativa; examples: marijuana, hashish; affected systems: CNS (brain) and cardiovascular.

Concept used. Allergy is a hypersensitive response of the immune system to harmless environmental antigens called allergens (dust, pollen, mould, animal dander, pollutants, certain foods, drugs). The response is mediated by IgE antibodies, which bind to mast cells, triggering release of histamine and other mediators.

1. Main causes in metropolitan settings.
   • Air pollution: PM_2.5 and PM₁₀ particulates, NOx, SO2, smoke.
   • Indoor allergens: house-dust mites, pet dander, mould.
   • Pollen from urban trees / weeds.
   • Reduced microbial exposure in childhood (hygiene hypothesis): the immune system, lacking microbial training, over-reacts to harmless antigens.
   • Tobacco smoke (active and passive).
2. Symptoms of allergic reactions.
   • Sneezing, runny nose, nasal congestion.
   • Watery, itchy eyes.
   • Difficulty breathing, wheezing, cough (asthma).
   • Skin rashes, hives, itching.
   • In severe cases, anaphylaxis (drop in blood pressure, swelling of airway, shock).
3. Antihistamines and steroids are used for symptom relief; avoidance of triggers is the long-term management.

Causes: urban air pollution, dust mites, pet dander, pollen, low microbial exposure. Symptoms: sneezing, watery eyes, wheezing, rash, breathing difficulty.

Concept used. Vaccination is the deliberate introduction of an antigen (in a safe form) into the body so that the immune system generates a specific response and memory cells without causing disease. The principle exploits immunological memory.

1. Principle. Expose the immune system to a weakened (attenuated), killed, or sub-unit form of a pathogen. The system mounts a primary response, produces antibodies, and most importantly generates memory B and T-cells.
2. Mechanism of protection. On future natural infection, memory cells recognise the antigen and trigger a fast, large secondary response that clears the pathogen before disease develops.
3. Hepatitis B vaccine source. The recombinant Hepatitis B vaccine is produced by inserting the gene for HBsAg (Hepatitis B surface antigen) into yeast (Saccharomyces cerevisiae). The yeast cell expresses the surface antigen, which is purified and used as the vaccine.

Vaccination principle: prime the immune system with a safe antigen to generate memory cells. Mechanism: rapid secondary response on real infection. Hep-B vaccine: recombinant HBsAg from yeast Saccharomyces cerevisiae.

Concept used. Cancer is a disease characterised by uncontrolled cell division and the ability to invade and spread (metastasise). Normal cells exhibit contact inhibition (stop dividing on contact with neighbours) and obey growth-control checkpoints; cancer cells lose these.

1. Definition of cancer. Uncontrolled, invasive proliferation of cells that can spread (metastasise) to distant organs.
2. How cancer cells differ from normal cells.
   • Normal: contact inhibition; cancer: no contact inhibition.
   • Normal: limited divisions (Hayflick limit); cancer: unlimited (telomerase reactivated).
   • Normal: differentiated, stays in tissue; cancer: poorly differentiated, invades surrounding tissue and metastasises.
   • Normal: dies on damage (apoptosis); cancer: resists apoptosis.
   • Normal: dependent on growth signals; cancer: self-sufficient in growth signals.
3. How normal cells become cancerous. Normal cells contain proto-oncogenes (which promote cell division) and tumour-suppressor genes (which restrain it). Mutations or activations (by chemical carcinogens like tobacco tar; physical carcinogens like UV/X-rays; biological carcinogens like HPV, HBV, EBV) convert proto-oncogenes into oncogenes and inactivate tumour-suppressor genes. Accumulation of multiple such mutations transforms a normal cell into a cancer cell.

Cancer = uncontrolled, invasive cell growth. Cancer cells lack contact inhibition and apoptosis. Normal cells become cancerous through carcinogen-induced mutations that activate oncogenes and inactivate tumour-suppressor genes.

Concept used. The described condition is allergy, an IgE-mediated immediate hypersensitivity. The cells most directly responsible are mast cells (and basophils), which carry IgE on their surface and release histamine on antigen binding.

1. Condition: allergic reaction (Type I hypersensitivity).
2. Cells responsible:
   • B-cells / plasma cells produce specific IgE.
   • IgE binds to mast cells and basophils via Fc receptors.
   • On re-exposure to allergen, mast cells degranulate and release histamine, leukotrienes and prostaglandins.
3. Precautions.
   • Identify and avoid the allergen (pollen, dust, dander, perfumes).
   • Use air filters / masks in polluted or pollen-heavy environments.
   • Keep house clean and dust-free.
   • Use prescribed antihistamines or steroidal inhalers; carry an EpiPen for severe allergies.

Condition: allergy. Cells: mast cells & basophils (loaded with IgE, releasing histamine). Precaution: avoid allergens, use masks/filters, take antihistamines.

Concept used. Graft rejection is driven by the recipient's T-cells recognising foreign MHC molecules on donor cells. Identical (monozygotic) twins share 100% of their DNA, including identical MHC alleles, so the donor's tissue is immunologically indistinguishable from the recipient's own.

1. In an unrelated donor, MHC differences trigger cytotoxic T-cell response → rejection.
2. Identical twins share the same MHC haplotypes → the recipient's T-cells see no foreign MHC.
3. The transplanted organ is recognised as ``self'' → no rejection.
4. The recipient does not need life-long immunosuppression and has the best outcome.

Identical twins share identical MHC; the transplanted organ is treated as self, so no immune rejection occurs.

Concept used. Lifestyle diseases are non-communicable diseases caused largely by the way people live — diet, physical activity, smoking, alcohol use, stress — rather than by infection.

1. Definition: chronic non-infectious diseases linked to modifiable lifestyle factors.
2. Causes:
   • Unhealthy diet (high fat, salt, sugar).
   • Lack of physical activity.
   • Tobacco smoking and alcohol consumption.
   • Chronic stress and poor sleep.
   • Obesity (often a consequence of the above).
3. Examples (any two):
   • Type 2 diabetes mellitus.
   • Hypertension and cardiovascular disease.
   • Obesity.
   • Certain cancers (lung, oral, colorectal).
   • Chronic obstructive pulmonary disease (COPD).

Lifestyle diseases are non-infectious chronic disorders driven by diet, inactivity, smoking, alcohol and stress. Examples: type 2 diabetes, hypertension/heart disease, obesity, certain cancers.

Concept used. Mutation rate depends on the fidelity of the polymerase that copies the viral genome. DNA polymerases generally have a 3'→5' exonuclease proof-reading activity, lowering the error rate to about 10^-8 per base. Most viral RNA polymerases (and reverse transcriptase) lack proof-reading, so errors of about 10^-4 per base are typical — roughly 10000 times more.

1. DNA virus: replicated by DNA polymerase with proof-reading → low error rate.
2. RNA virus: replicated by RNA-dependent RNA polymerase (or by reverse transcriptase for retroviruses) without proof-reading → high error rate.
3. Therefore the RNA virus mutates much faster.
4. Practical consequence: RNA viruses (influenza, HIV, SARS-CoV-2, hepatitis C) evolve rapidly, evade immunity, and need annual or strain-specific vaccines; DNA viruses (smallpox, herpes) are much more stable, so a single vaccine often suffices.

RNA virus mutates faster. RNA polymerase / reverse transcriptase lacks proof-reading, so error rate is 10⁴ times higher than DNA polymerase.

Concept used. The malarial parasite (Plasmodium spp., principally P. falciparum and P. vivax) is digenetic: it requires both a human host and a female Anopheles mosquito to complete its life cycle. Key stages: sporozoites (infective stage in mosquito saliva), schizonts and merozoites (asexual stages in liver and RBCs), and gametocytes (sexual stage taken up by mosquito).

1. Step 1 — Bite & sporozoite injection. A female Anopheles bites a human; sporozoites in her saliva enter the blood.
2. Step 2 — Liver schizogony. Sporozoites travel to the liver and infect hepatocytes; they multiply asexually (schizogony) into thousands of merozoites.
3. Step 3 — RBC schizogony. Liver merozoites burst out and invade RBCs. Inside RBCs they multiply again; the synchronous rupture of RBCs releases merozoites + haemozoin every 48–72 hours, causing the recurrent chills and high fever.
4. Step 4 — Gametocyte formation. Some merozoites differentiate into male and female gametocytes, the sexual stage.
5. Step 5 — Uptake by mosquito. When another mosquito bites the infected human, it ingests gametocytes with the blood meal.
6. Step 6 — Fertilisation in mosquito gut. Male and female gametes fuse to form a zygote (ookinete) in the mosquito gut; this becomes an oocyst on the gut wall.
7. Step 7 — Sporozoite formation. Each oocyst releases thousands of sporozoites that migrate to the mosquito's salivary glands, ready to infect the next person bitten.

Plasmodium life cycle: sporozoites (mosquito saliva) → liver schizogony → RBC schizogony (fever) → gametocytes → mosquito bite → zygote in gut → oocyst → sporozoites. A two-host cycle.

Concept used. Lifestyle determines exposure to risk factors and access to health resources. Urban and rural lifestyles differ in diet, physical activity, sanitation, pollution and stress, leading to characteristic disease patterns.

1. Urban lifestyle.
   • Sedentary work (desk jobs); little walking; reliance on motorised transport.
   • Diet rich in processed food, sugar, salt, fats.
   • High exposure to air pollution, noise pollution, light at night.
   • Higher levels of psychological stress, irregular hours.
   • Easy access to tobacco, alcohol.
   • Better access to hospitals and diagnostics.
2. Rural lifestyle.
   • Physical labour (farming, walking long distances).
   • Diet centred on cereals, vegetables, dairy; lower processed food.
   • Cleaner air but sometimes biomass cooking smoke indoors.
   • Poorer sanitation, drinking water, sewage in many areas.
   • Less access to vaccines, doctors, specialist care.
3. Health impacts.
   • Urban populations: high rates of diabetes, hypertension, obesity, heart disease, lung diseases (pollution, smoking), depression, anxiety, certain cancers.
   • Rural populations: high rates of infectious diseases (diarrhoea, typhoid, malaria, TB), malnutrition, anaemia, maternal and child mortality.
4. Conclusion. Urban lifestyle promotes non-communicable lifestyle diseases; rural lifestyle is dominated by communicable diseases and malnutrition. Both need different public-health responses.

Urban: sedentary, processed food, polluted air, stress → diabetes, hypertension, cancer. Rural: physical work, simpler diet, but poor sanitation → infections, malnutrition. Different lifestyles, different disease loads.

Concept used. Adolescence is a phase of curiosity, identity formation, and peer influence; combined with stress and easy availability of drugs, it is a high-risk window for substance initiation.

1. Reasons adolescents start drugs.
   • Curiosity, thrill-seeking.
   • Peer pressure and the urge to be ``accepted''.
   • Stress: academic pressure, family problems, breakup.
   • Imitation of media (films, glamorised drug use).
   • Easy availability and lack of awareness about long-term harm.
   • Family history of substance use; modelling by parents/siblings.
   • Underlying depression, anxiety, low self-esteem.
2. Prevention strategies.
   • Parental support: open communication, monitoring without coercion.
   • Education: school programmes on the science of addiction, real-life consequences.
   • Peer mentoring: connecting at-risk teens with positive role models.
   • Mental-health support: counselling, treatment of underlying depression/anxiety.
   • Channelling energy: sports, art, music, volunteering.
   • Legal enforcement: limit access of drugs to minors.
   • Seek professional help early at first signs (mood change, isolation, falling grades, money problems).
3. Key message. Prevention is most effective in early adolescence, before the first use. Once dependence sets in, recovery is harder.

Curiosity, peer pressure, stress, family environment and easy availability drive adolescent drug initiation. Prevention: parental support + education + mental-health care + recreation + early intervention.

Concept used. Chronic alcohol dependence produces predictable behavioural, social and physical changes. Recovery requires medical detoxification combined with long-term psychosocial support.

1. Behavioural changes.
   • Mood swings: irritability, aggression, sudden weeping.
   • Loss of interest in family, hobbies, work.
   • Neglect of personal hygiene and appearance.
   • Decline in work performance, absenteeism.
   • Lying, stealing money to buy alcohol.
   • Withdrawal from social activities; isolation.
   • Tremors, slurred speech, unsteady gait.
   • Aggression and domestic violence; financial problems.
   • Sleep disturbances; anxiety; depression.
2. Measures to overcome.
   • Recognise and admit the problem (the hardest step).
   • Seek professional medical help; supervised detoxification to manage withdrawal.
   • Counselling: individual therapy (CBT) and family counselling.
   • Support groups: Alcoholics Anonymous (AA) and peer-led groups.
   • Pharmacotherapy: disulfiram, naltrexone, acamprosate where indicated.
   • Removing access to alcohol; avoiding triggers and bars.
   • Replacement of social network with sober contacts.
   • Engagement in productive activity: work, hobbies, sports.
   • Family support, patience and absence of stigma.
   • Long-term follow-up to prevent relapse.

Behavioural changes: irritability, isolation, neglect, lying, domestic violence, tremors. Measures: medical detox + counselling + support groups + family support + relapse prevention.

Concept used. Cancer treatment depends on early detection. Detection uses imaging, biopsy and molecular markers; treatment combines surgery, radiation, chemotherapy and immunotherapy.

1. Methods of cancer detection.
   • Biopsy and histopathological studies: take a small tissue sample, fix it, stain it, and examine under microscope; the gold standard.
   • Imaging: CT (X-ray cross-sections) and MRI (magnetic resonance) reveal tumour location and size; ultrasound and PET-CT are also used.
   • Blood tests for tumour markers: PSA (prostate cancer), AFP (liver cancer), CA-125 (ovarian).
   • Molecular techniques: detection of oncogenic mutations and chromosomal translocations.
   • Mammography, Pap smear, colonoscopy for screening of common cancers.
2. Common approaches to treatment.
   • Surgery: removal of the primary tumour and adjacent lymph nodes; effective when the tumour is localised and accessible.
   • Radiotherapy: localised killing of cancer cells using ionising radiation (gamma rays, X-rays); often combined with surgery.
   • Chemotherapy: drugs that kill rapidly dividing cells (alkylating agents, antimetabolites, mitotic inhibitors). Used for systemic disease and metastases. Side effects include hair loss, anaemia, immunosuppression.
   • Immunotherapy: interferon-α (boosts the immune response against tumours), monoclonal antibodies (rituximab, trastuzumab), and modern checkpoint inhibitors.
   • Hormonal therapy: for hormone-sensitive cancers (tamoxifen for breast cancer).
   • Combination therapy: surgery + chemo + radio + immunotherapy together for the best outcomes.

Detection: biopsy + CT/MRI + tumour markers + molecular tests. Treatment: surgery, radiotherapy, chemotherapy, immunotherapy (interferon-α), often combined.

Concept used. LSD (Lysergic Acid Diethylamide) is a hallucinogen. Barbiturates are CNS depressants used as sedatives. Amphetamines are CNS stimulants used in attention disorders. Abuse leads to dependence and serious organ damage.

1. LSD adverse effects.
   • Hallucinations, distortion of perception (lights, colours, sounds).
   • Paranoia, anxiety, panic attacks.
   • Bad ``trips'' can lead to suicide or violent accidents.
   • Flashbacks even weeks after use (HPPD).
   • Persistent psychotic disorders.
2. Barbiturate adverse effects.
   • Excessive sedation, drowsiness, slurred speech.
   • Respiratory depression — can be fatal at overdose.
   • Dependence and severe withdrawal (seizures).
   • Combination with alcohol multiplies the risk of death.
3. Amphetamine adverse effects.
   • Insomnia, restlessness, anxiety.
   • Hypertension, irregular heartbeat, heart attack, stroke.
   • Loss of appetite and weight; malnutrition.
   • Paranoia, hallucinations, ``amphetamine psychosis''.
   • Strong addiction.
4. General adverse effects of misuse (all such drugs):
   • Addiction and tolerance.
   • Risk of overdose and death.
   • Liver and kidney damage from chronic use.
   • Shared needles → HIV / Hepatitis B/C.
   • Social and academic decline; financial ruin.
   • Mental-health deterioration.

LSD: hallucinations, psychosis. Barbiturates: respiratory depression, dependence. Amphetamines: hypertension, heart attack, psychosis. All: addiction, organ damage, overdose risk, social ruin.

Concept used. Pulse Polio Immunisation (PPI) is a mass vaccination campaign launched in India in 1995, aimed at eradicating poliomyelitis. The slogan ``Do Boond Zindagi Ki'' (``Two drops of life'') refers to the drops of Oral Polio Vaccine (OPV) given to every child under 5 on National Immunisation Days.

1. Pulse Polio Programme. A nationwide campaign of giving polio drops to every child under 5, on selected dates each year, in addition to the routine vaccination schedule. The objective is to interrupt person-to-person transmission by saturating the population with immunity.
2. OPV (Oral Polio Vaccine). Developed by Albert Sabin. It is a live attenuated vaccine containing weakened polio virus, given orally as two drops. Advantages:
   • Easy to administer (no needles).
   • Induces both serum (IgG) and mucosal (IgA) immunity.
   • The attenuated virus is shed in stools and can passively immunise close contacts (herd effect).
3. Why eradication has been slow.
   • India was declared polio-free in 2014 by WHO (after the last wild-type case in 2011), but maintaining this status has been challenging.
   • Large, mobile and high-density population; reaching every child is logistically difficult.
   • Pockets of low immunisation coverage (urban slums, migrant communities, religious resistance in some areas).
   • Poor sanitation in some regions sustains faecal–oral transmission.
   • Vaccine-derived poliovirus (VDPV) can rarely emerge in under-immunised communities.
   • Cross-border transmission risk from neighbouring endemic countries (Pakistan, Afghanistan).
   • Hence continued vigilance and pulse campaigns are needed even after technical eradication.

Pulse Polio = mass OPV campaign on national immunisation days. OPV = oral live-attenuated polio vaccine giving mucosal + serum immunity. Slow eradication because of population size, sanitation gaps, vaccine refusal, and cross-border imports.

Concept used. Recombinant DNA vaccines are sub-unit vaccines made by inserting the gene encoding a pathogen's antigenic protein into a harmless host (yeast, bacterium, mammalian cell) which expresses and secretes the antigen. The purified antigen alone is used as the vaccine — without the pathogen itself.

1. Definition. Vaccines whose antigen is produced by recombinant-DNA technology rather than from cultured pathogens.
2. Steps in production.
   • Isolate the gene encoding the antigenic surface protein.
   • Clone it into a vector (plasmid).
   • Transform a host (e.g. yeast Saccharomyces cerevisiae).
   • Grow the host in bioreactors; the host expresses the antigen.
   • Purify the antigen and formulate as vaccine.
3. Two examples.
   • Hepatitis-B vaccine: HBsAg (Hepatitis B surface antigen) gene cloned into yeast Saccharomyces cerevisiae; yeast produces HBsAg, which is purified.
   • Human Papilloma Virus (HPV) vaccine (Cervarix, Gardasil): HPV L1 capsid protein produced in yeast / insect cells, self-assembles into virus-like particles.
4. Advantages.
   • Safety: no live pathogen, so cannot cause disease in the recipient.
   • Purity: a single defined antigen, free of contaminants from the original pathogen.
   • Scalability: yeast bioreactors produce huge quantities cheaply.
   • Stability: protein subunits are stable, easy to store and transport.
   • Designability: the antigen can be engineered for optimal immunogenicity (e.g. adjuvants, fusion proteins).
   • Useful when the pathogen is difficult to culture (Hepatitis B cannot be grown easily in lab).

Recombinant DNA vaccines use cloned antigen genes expressed in safe hosts. Examples: Hepatitis-B vaccine (HBsAg from yeast) and HPV vaccine (L1 from yeast). Advantages: safety, purity, scalability, stability, engineering flexibility.