Human Health and Disease

This is the seventh chapter of NCERT's Class 12 Biology textbook (pages 129–148 of the 2026-27 reprint) and the first of Unit VIII, Biology in Human Welfare. It has five parts — common diseases in humans (7.1), immunity (7.2, with seven sub-sections), AIDS (7.3), cancer (7.4) and drugs and alcohol abuse (7.5) — with Figures 7.1–7.11, a summary and 17 exercises. The PDF also carries the unit's opening page and a biography box (pages 127–128). This page uses ten concept sections, splitting NCERT's long first and second parts by pathogen group and by topic.

• Neighbouring chapters: Reproductive Health (this book, Chapter 3) covers sexually transmitted infections including HIV and hepatitis B; Evolution (Chapter 6) explains drug resistance in microbes and in malaria parasites as natural selection; Microbes in Human Welfare (Chapter 8, next) follows with antibiotics. In Psychology, Meeting Life Challenges and Psychological Disorders (Class 12) treat stress and substance-use disorders; Role of the Government in Health (Class 7 social science) gives the public-health setting.
• Prelims — science: UPSC has asked about this chapter's content in nearly every decade — the groups of pathogens (1983, 1998), typhoid's spread (1984), opium (1987), ELISA (1987, 2006), ringworm (1990), malaria fever (1991), antihistamines (1991), antigens (1997, 2001), metastasis (2001), AIDS transmission and symptoms (1986, 1996, 2003, 2010), lymphocytes (2004), Gambusia (2008), the malaria vaccine (2010), hepatitis B (2010, 2013, 2019), smallpox eradication (2014), pneumococcal vaccines (2020), retroviruses (2021) and B and T cells (2022).
• GS3 — Science and Technology: how vaccines work and how Indian manufacturers made COVID-19 vaccines (Mains 2022); biotechnology in health. GS2 — health: immunisation programmes, HIV/AIDS control, tobacco and drug control laws. GS1 — society: adolescence, substance use and its social costs.

• Health = complete physical, mental and social well-being, not just absence of disease. Affected by genetic disorders, infections and lifestyle. Old ‘humours’ idea (Hippocrates, Ayurveda) disproved by experiment (Harvey's circulation; the thermometer). Infectious diseases spread person to person; among non-infectious ones cancer is the major killer.
• Pathogens: Salmonella typhi — typhoid (39–40°C, Widal test, ‘Typhoid Mary’); Streptococcus pneumoniae, Haemophilus influenzae — pneumonia (alveoli fill with fluid); rhinoviruses — common cold (3–7 days, not the lungs); Entamoeba histolytica — amoebiasis (houseflies carry it); Ascaris; Wuchereria — filariasis/elephantiasis; Microsporum, Trichophyton, Epidermophyton — ringworm.
• Malaria: Plasmodium (P. vivax, P. malariae, P. falciparum — malignant, can be fatal). Sporozoites from a female Anopheles → liver (asexual) → RBCs burst, haemozoin → chill and fever every 3–4 days → gametocytes → mosquito gut (fertilisation) → salivary glands. Two hosts; the mosquito is also the vector. Control: no stagnant water, nets, Gambusia fish; Aedes spreads dengue and chikungunya.
• Immunity: innate (from birth, non-specific): physical (skin, mucus), physiological (acid, saliva, tears), cellular (PMNL-neutrophils, monocytes, NK cells, macrophages), cytokine (interferons). Acquired: specific, with memory — primary (weak) vs secondary/anamnestic (strong). B cells → antibodies (H₂L₂; IgA, IgM, IgE, IgG) = humoral; T cells → CMI, graft rejection. Active (own antibodies; vaccines, infection) vs passive (ready-made: colostrum IgA, placenta, antitoxin, snake antivenom). Hepatitis B vaccine made in yeast.
• Allergy: exaggerated response; IgE; mast cells release histamine and serotonin; antihistamines, adrenalin, steroids. Autoimmunity: body attacks self (rheumatoid arthritis). Lymphoid organs: primary = bone marrow, thymus; secondary = spleen, lymph nodes, tonsils, Peyer's patches, appendix, MALT (~50%). AIDS (first reported 1981): HIV, a retrovirus; sex, blood, shared needles, mother to child — not by touch; reverse transcriptase; macrophages = ‘HIV factory’; helper T cells fall; ELISA; NACO.
• Cancer: loss of contact inhibition; benign (stays) vs malignant (invades, metastasis); carcinogens — X-rays, γ-rays, UV, tobacco smoke, oncogenic viruses; proto-oncogenes; detection — biopsy, CT, MRI, antibodies; treatment — surgery, radiotherapy, chemotherapy, α-interferon. Drugs: opioids (heroin = diacetylmorphine, Papaver somniferum), cannabinoids (Cannabis sativa), cocaine (Erythroxylum coca, dopamine); nicotine → adrenaline; adolescence 12–18; addiction (psychological) vs dependence (withdrawal); prevention by support and counselling.

For a long time, health was thought to be a balance of body ‘humours’ — the view of early Greeks such as Hippocrates and of the Indian Ayurveda system. People with ‘black bile’ were thought to have a hot personality and fevers. This idea came from reflection alone. William Harvey's experimental discovery of blood circulation, and the thermometer showing normal body temperature in people with ‘black bile’, disproved the ‘good humour’ hypothesis. Later, biology showed that the mind influences the immune system through the neural and endocrine systems, and that the immune system maintains health — so mental state can affect health. Health is affected by (i) genetic disorders (deficiencies a child is born with or inherits), (ii) infections and (iii) lifestyle — food and water, rest and exercise, habits.

Health is not just the absence of disease or physical fitness; it is a state of complete physical, mental and social well-being. Healthy people work more efficiently, which raises productivity and prosperity; health also increases longevity and reduces infant and maternal mortality. A balanced diet, personal hygiene and regular exercise maintain it; yoga has long been practised for physical and mental health. Awareness of diseases, vaccination, proper waste disposal, vector control and hygiene of food and water are needed. When one or more organs or systems are adversely affected, with signs and symptoms, we have a disease.

Disease-causing organisms — pathogens — come from bacteria, viruses, fungi, protozoans and helminths. Most parasites are pathogens, since they harm the host by living in or on it. A pathogen enters, multiplies and interferes with vital activities, causing structural and functional damage. It must also be adapted to the host: one entering the gut must survive the stomach's low pH and resist digestive enzymes.

Typhoid: Salmonella typhi enters the small intestine with contaminated food and water and migrates through the blood to other organs. NCERT recalls the classic case of Mary Mallon, nicknamed ‘Typhoid Mary’, a cook who was a carrier — infected but able to spread the bacterium — and passed typhoid on for years through the food she prepared. Pneumonia attacks the alveoli, the air sacs of the lungs; fluid in them makes breathing very difficult. NCERT names dysentery, plague and diphtheria as other bacterial diseases. Among viruses, rhinoviruses cause the common cold, one of the most infectious human ailments.

Malaria is caused by the protozoan Plasmodium. Different species — P. vivax, P. malariae and P. falciparum — cause different types of malaria; malignant malaria caused by P. falciparum is the most serious and can be fatal. Plasmodium enters the human body as sporozoites, the infectious form, through the bite of an infected female Anopheles mosquito. The parasites first multiply in liver cells, then attack red blood cells, rupturing them. The rupture releases a toxic substance, haemozoin, responsible for the chill and high fever that recur every three to four days. When a female Anopheles bites an infected person, the parasites enter the mosquito, develop and multiply into sporozoites stored in the salivary glands, ready to be injected at the next bite. The parasite needs two hosts — human and mosquito — and the female Anopheles is also the vector.

NCERT's ‘every three to four days’ is the 48-hour and 72-hour rhythms counted inclusively (day 1 then day 3, or day 1 then day 4) — the arithmetic is checked in this page's source file. Amoebiasis (amoebic dysentery) is caused by Entamoeba histolytica, a protozoan of the large intestine. Symptoms are constipation, abdominal pain and cramps, and stools with excess mucus and blood clots. Houseflies act as mechanical carriers, moving the parasite from an infected person's faeces to food; water and food contaminated with faecal matter are the main source.

Helminths. Ascaris, the common roundworm, is an intestinal parasite causing ascariasis; its eggs leave in faeces and contaminate soil, water and plants, and people are infected through contaminated water, vegetables and fruits. Wuchereria (W. bancrofti and W. malayi), the filarial worms, live for many years usually in the lymphatic vessels of the lower limbs, causing slowly developing chronic inflammation — elephantiasis or filariasis; genital organs are often affected, with gross deformities. They are transmitted by the bite of female mosquito vectors.

Fungi. Fungi of the genera Microsporum, Trichophyton and Epidermophyton cause ringworm, one of the most common infectious diseases. Dry, scaly lesions appear on the skin, nails and scalp with intense itching. Heat and moisture help the fungi grow, so they thrive in skin folds such as the groin or between the toes. Ringworm is acquired from soil or by using an infected person's towels, clothes or comb.

Prevention and control. Personal hygiene — a clean body; clean drinking water, food, vegetables and fruits — and public hygiene — proper disposal of waste and excreta, periodic cleaning and disinfection of water reservoirs, pools, cesspools and tanks, and hygienic public catering — are essential for typhoid, amoebiasis and ascariasis. For air-borne diseases such as pneumonia and the common cold, close contact with infected people and their belongings should also be avoided. For vector-borne diseases such as malaria and filariasis the key is to control vectors and their breeding places: no stagnant water near homes, regular cleaning of household coolers, mosquito nets, wire mesh on doors and windows, insecticide spraying in ditches, drains and swamps, and introducing fish such as Gambusia that eat mosquito larvae. NCERT notes this matters more with the spread of Aedes-borne dengue and chikungunya in India.

Vaccines and immunisation programmes have completely eradicated smallpox and largely controlled polio, diphtheria, pneumonia and tetanus; biotechnology promises newer and safer vaccines; antibiotics and other drugs treat many infections.

We meet huge numbers of infectious agents every day, yet only a few cause disease, because the body defends itself. This overall ability of the host to fight disease-causing organisms, conferred by the immune system, is immunity. It is of two types: innate and acquired. Innate immunity is non-specific and present at birth; it works through four kinds of barriers.

Acquired immunity is pathogen-specific and has memory. At the first encounter with a pathogen the body makes a low-intensity primary response; a later encounter with the same pathogen brings a highly intensified secondary or anamnestic response, as if the body remembers. Both are carried out by two special kinds of lymphocytes in the blood: B-lymphocytes and T-lymphocytes.

B-lymphocytes produce an army of proteins, antibodies, into the blood to fight pathogens. T-cells do not secrete antibodies but help B cells make them. Each antibody has four peptide chains — two small light chains and two longer heavy chains — so it is written H₂L₂. Different antibodies are produced, among them IgA, IgM, IgE and IgG. Because antibodies are in the blood, this is the humoral immune response (antibody-mediated). The second type is the cell-mediated immune response or cell-mediated immunity (CMI), carried out by T-lymphocytes.

Transplants. When organs such as the heart, eye, liver or kidney fail, a transplant may be the only remedy — but grafts from just any source, animal or human, are rejected sooner or later. Tissue matching and blood-group matching are essential, and even then the patient must take immunosuppressants for life. The body distinguishes ‘self’ from ‘non-self’, and the cell-mediated response causes graft rejection.

When a host meets antigens — living or dead microbes or other proteins — its body makes antibodies: active immunity. It is slow and takes time to reach full effect. It follows natural infection, or deliberate injection of microbes in immunisation. When ready-made antibodies are given directly, it is passive immunity. Mother's milk matters for the newborn because colostrum, the yellowish fluid of the first days of lactation, has abundant antibodies (IgA); the foetus also receives some antibodies through the placenta. Both are passive immunity.

Vaccination rests on the immune system's memory. A vaccine — antigenic proteins of a pathogen, or the inactivated or weakened pathogen — is introduced; the antibodies it raises neutralise the real pathogen later, and it creates memory B and T cells that recognise the pathogen quickly and overwhelm it with massive antibody production. For deadly microbes that need a quick response, as in tetanus, preformed antibodies or antitoxin are injected; for snakebite, the injection contains preformed antibodies against the venom — passive immunisation. Recombinant DNA technology lets bacteria or yeast make a pathogen's antigenic polypeptides, allowing large-scale production — for example, hepatitis B vaccine produced from yeast.

Allergy is the exaggerated response of the immune system to certain antigens in the environment, called allergens — mites in dust, pollen, animal dander. The antibodies made are of the IgE type. Symptoms — sneezing, watery eyes, running nose, difficulty in breathing — come from chemicals such as histamine and serotonin released from mast cells. To find the cause, a patient is exposed to or injected with tiny doses of possible allergens and the reactions are studied. Antihistamines, adrenalin and steroids quickly reduce symptoms. NCERT notes that more children in Indian metro cities suffer from allergies and asthma, possibly because of the protected environment provided early in life.

Autoimmunity. Memory-based acquired immunity evolved in higher vertebrates on the ability to tell foreign organisms from self-cells. Two consequences follow: higher vertebrates can distinguish foreign molecules as well as organisms; and sometimes, for genetic and other unknown reasons, the body attacks self-cells — an auto-immune disease. Rheumatoid arthritis is NCERT's example.

The immune system in the body consists of lymphoid organs, tissues, cells and soluble molecules such as antibodies; it recognises, responds to and remembers foreign antigens, and is involved in allergy, autoimmunity and transplantation. Lymphoid organs are where lymphocytes originate and/or mature and multiply. The primary lymphoid organs — bone marrow and thymus — are where immature lymphocytes become antigen-sensitive. Mature lymphocytes migrate to secondary lymphoid organs — spleen, lymph nodes, tonsils, Peyer's patches of the small intestine and the appendix — where they meet antigens and multiply into effector cells. The bone marrow is the main lymphoid organ, producing all blood cells; the thymus, a lobed organ near the heart beneath the breastbone, is large at birth and shrinks to a very small size by puberty; both provide micro-environments for T-lymphocyte development. The spleen, a large bean-shaped organ of lymphocytes and phagocytes, filters blood and holds a reservoir of erythrocytes; lymph nodes trap microbes and antigens in lymph and tissue fluid and activate the lymphocytes there. Mucosa-associated lymphoid tissue (MALT), in the linings of the respiratory, digestive and urogenital tracts, is about 50 per cent of the body's lymphoid tissue.

AIDS stands for Acquired Immuno Deficiency Syndrome: a deficiency of the immune system acquired during life (not congenital), and a syndrome — a group of symptoms. It was first reported in 1981; NCERT says that in ‘the last twenty-five years or so’ it spread worldwide, killing more than 25 million people — a figure from around 2006. It is caused by the Human Immunodeficiency Virus (HIV), a retrovirus: an enveloped virus with an RNA genome.

Transmission generally occurs by (a) sexual contact with an infected person, (b) transfusion of contaminated blood and blood products, (c) sharing infected needles, as among people who inject drugs, and (d) from an infected mother to her child through the placenta. People at higher risk include those with multiple sexual partners, people who inject drugs, people needing repeated transfusions and children born to mothers with HIV. HIV/AIDS does not spread by mere touch or physical contact — only through body fluids — so people living with HIV must not be isolated from family and society. There is always a time-lag between infection and symptoms: a few months to many years, usually 5–10 years.

How HIV damages immunity. HIV enters macrophages, where its RNA genome is copied into viral DNA by the enzyme reverse transcriptase. The viral DNA is incorporated into the host cell's DNA and directs the cell to produce virus particles; macrophages keep releasing virus, acting as an ‘HIV factory’. HIV also enters helper T-lymphocytes (T_H), replicates and releases progeny that attack more helper T cells, so their number falls steadily. Meanwhile the person has bouts of fever, diarrhoea and weight loss, and then infections the body could otherwise overcome — bacteria, especially Mycobacterium, viruses, fungi and parasites such as Toxoplasma.

Diagnosis and treatment. A widely used test is ELISA (enzyme-linked immunosorbent assay). NCERT says anti-retroviral drugs are only partially effective, prolonging life but not preventing death. Prevention: as AIDS has no cure, prevention is best. In India the National AIDS Control Organisation (NACO) and NGOs educate people; WHO runs programmes. Steps include safe blood from blood banks, only disposable needles and syringes in hospitals and clinics, free distribution of condoms, controlling drug abuse, advocating safe sex and regular check-ups in susceptible populations. NCERT stresses that HIV infection should not be hidden, that people with HIV need help and sympathy rather than being shunned, and that society and the medical profession must act together.

Cancer is among the most dreaded diseases and a major cause of death worldwide; NCERT says more than a million Indians suffer from it. In the body, cell growth and differentiation are tightly regulated; in cancer cells these controls break down. Normal cells show contact inhibition: contact with other cells stops their growth. Cancer cells have lost it, so they keep dividing into masses called tumours. Benign tumours stay where they began, do not spread and cause little damage. Malignant tumours are masses of proliferating neoplastic (tumour) cells that grow fast, invade and damage normal tissue, and starve normal cells by competing for nutrients. Cells shed from them travel through the blood and start new tumours wherever they lodge — metastasis, the most feared property of malignant tumours.

Causes. Normal cells can be transformed into cancerous, neoplastic cells by physical, chemical or biological agents called carcinogens. Ionising radiation (X-rays, gamma rays) and non-ionising radiation (UV) damage DNA. Chemical carcinogens in tobacco smoke are a major cause of lung cancer. Oncogenic viruses carry viral oncogenes. Normal cells also carry cellular oncogenes (c-onc) or proto-oncogenes which, when activated under certain conditions, can cause oncogenic transformation.

Detection and diagnosis. Early detection lets many cancers be treated successfully. Detection rests on biopsy and histopathology — a thin, stained section of suspected tissue examined under a microscope by a pathologist — and on blood and bone-marrow tests for raised cell counts in leukaemias. Radiography (X-rays), CT (computed tomography, which uses X-rays to build a three-dimensional image) and MRI (strong magnetic fields and non-ionising radiation) detect cancers of internal organs. Antibodies against cancer-specific antigens detect certain cancers, and molecular biology can find genes for inherited susceptibility, so such people can avoid particular carcinogens (e.g. tobacco smoke for lung cancer).

Treatment. NCERT lists surgery, radiation therapy and immunotherapy. In radiotherapy, tumour cells are irradiated lethally while protecting normal tissue. Chemotherapeutic drugs kill cancer cells — some are specific to particular tumours — and most have side effects such as hair loss and anaemia. Most cancers are treated by a combination of surgery, radiotherapy and chemotherapy. Because tumour cells evade the immune system, patients are also given biological response modifiers such as α-interferon, which activate the immune system to destroy the tumour.

Surveys show rising drug and alcohol use, especially among the young; NCERT argues that education and guidance can protect them. The drugs most commonly abused are opioids, cannabinoids and coca alkaloids, mostly from flowering plants, some from fungi.

When drugs are taken for purposes other than medicine, or in amounts or frequency that impair physical, physiological or psychological functions, it is drug abuse. Tobacco has been used for more than 400 years — smoked, chewed or as snuff. It contains many chemicals including nicotine, an alkaloid, which stimulates the adrenal gland to release adrenaline and nor-adrenaline, raising blood pressure and heart rate. Smoking is associated with cancers of the lung, urinary bladder and throat, bronchitis, emphysema, coronary heart disease and gastric ulcer; chewing tobacco with oral cancer. Smoking raises carbon monoxide in the blood and lowers haem-bound oxygen, causing oxygen deficiency. NCERT also says smoking ‘paves the way to hard drugs’, notes the statutory warning on cigarette packets, and says anyone addicted needs counselling and medical help.

Adolescence — roughly 12–18 years — is both a period and a process of becoming mature in attitudes and beliefs: a bridge between childhood and adulthood, with biological and behavioural changes, and a vulnerable phase. Common reasons young people try drugs and alcohol are curiosity, a need for adventure and excitement, and experimentation; later use can become a way to escape problems. Stress from pressure to excel in studies and examinations, the perception that smoking, drugs or alcohol are ‘cool’ (promoted by television, films, newspapers and the internet), unstable or unsupportive families and peer pressure also contribute.

Addiction is a psychological attachment to certain effects — euphoria, a temporary feeling of well-being — that drives use even when it is not needed or becomes self-destructive. With repeated use, the tolerance of receptors rises, so only higher doses work, increasing intake. NCERT warns that even one use can be a forerunner to addiction. Dependence is the body's tendency to show a characteristic, unpleasant withdrawal syndrome — anxiety, shakiness, nausea, sweating — when regular use stops abruptly; it may be relieved when use resumes, and severe withdrawal can be life-threatening and needs medical supervision. Dependence can push a person to ignore social norms to get money for drugs, causing social adjustment problems.

Effects. Immediate effects include reckless behaviour, vandalism and violence; overdoses can cause coma and death from respiratory failure, heart failure or cerebral haemorrhage, and combining drugs, or drugs with alcohol, often leads to fatal overdose. Warning signs in the young include falling academic performance, unexplained absence, neglect of hygiene, withdrawal, isolation, depression, fatigue, aggression, worsening relationships, loss of interest in hobbies, and changes in sleep, eating, weight and appetite. A person who cannot afford drugs may turn to stealing, and families suffer mental and financial distress. People who inject drugs with shared needles risk AIDS and hepatitis B; both can also spread through sexual contact or infected blood. Chronic drug and alcohol use damages the nervous system and liver (cirrhosis); use in pregnancy harms the foetus; alcohol use in adolescence may lead to heavy drinking later.

Misuse in sport. Some sportspersons misuse narcotic analgesics, anabolic steroids, diuretics and certain hormones to increase muscle strength and bulk, aggressiveness and performance. NCERT lists side-effects of anabolic steroids: in females, masculinisation, aggressiveness, mood swings, depression, abnormal menstrual cycles, excess facial and body hair, enlargement of the clitoris and a deeper voice; in males, acne, aggressiveness, mood swings, depression, smaller testicles, decreased sperm production, possible kidney and liver dysfunction, breast enlargement, premature baldness and an enlarged prostate — possibly permanent with prolonged use; in adolescents, severe acne and premature closure of the growth centres of long bones, stunting growth.

Prevention and control — ‘prevention is better than cure’, and habits usually begin in adolescence, so parents and teachers have a special role; parenting that combines high nurturance with consistent discipline lowers the risk. NCERT's five measures: (i) avoid undue peer pressure — respect each child's choices and limits; (ii) education and counselling to face problems, stress, disappointment and failure, and channel energy into sport, reading, music, yoga and other activities; (iii) seek help from parents and peers, including trusted friends, to sort out problems and vent anxiety and guilt; (iv) look for danger signs — friends too should tell parents or teachers in the person's interest; (v) seek professional and medical help from psychologists, psychiatrists, and de-addiction and rehabilitation programmes, with which a person can recover completely and lead a normal, healthy life.

These approaches are often combined in practice; the table records what each stresses, not which is right.

The chapter has four questions set in its running text.

Numbers

One-liners

• Health is complete physical, mental and social well-being.
• Salmonella typhi causes typhoid, confirmed by the Widal test.
• Pneumonia infects the alveoli; the common cold spares the lungs.
• Only the female Anopheles transmits malaria.
• Haemozoin released from bursting RBCs causes malarial fever.
• Plasmodium falciparum causes malignant malaria.
• Houseflies are mechanical carriers of amoebiasis.
• Wuchereria causes filariasis in the lymphatic vessels.
• Ringworm is a fungal disease.
• Gambusia fish eat mosquito larvae.
• Innate immunity is non-specific and present at birth.
• Acquired immunity is specific and has memory.
• B cells make antibodies; T cells mediate cell-mediated immunity.
• Graft rejection is a cell-mediated response.
• Colostrum gives the newborn IgA — passive immunity.
• Allergy involves IgE, mast cells and histamine.
• Bone marrow and thymus are primary lymphoid organs.
• HIV is a retrovirus that destroys helper T cells.
• ELISA is the widely used test for HIV.
• Cancer cells have lost contact inhibition.
• Metastasis is the spread of malignant cells through blood.
• Heroin is diacetylmorphine from the opium poppy.
• Cocaine interferes with dopamine transport.
• Nicotine stimulates release of adrenaline.

Traps to avoid

• Ringworm is a fungus, not a worm.
• Widal is for typhoid; ELISA is for HIV.
• Vaccination gives active immunity; antivenom and antitoxin give passive immunity.
• T cells do not secrete antibodies.
• Interferons are an innate barrier; α-interferon is also a cancer therapy.
• Benign tumours do not metastasise.
• CT uses X-rays; MRI does not.
• UV is non-ionising but still damages DNA.
• HIV does not spread by touch or mosquitoes.
• Addiction is psychological; dependence shows withdrawal symptoms.
• NCERT's ‘P. malaria’ is P. malariae; ‘W. malayi’ is now Brugia malayi.
• Anti-retroviral therapy controls HIV but is not a cure; NCERT's ‘death is inevitable’ is dated.
• Hepatitis B has a vaccine; hepatitis C does not.
• Smallpox, not chickenpox, has been eradicated.

Prelims — what UPSC asks

• Pathogens and routes: amoeba, malarial parasite and typhoid bacillus as ‘protozoa’ (1983); safest visiting a typhoid patient (1984); ringworm is a fungus (1990); disease–organism match (1998); disease–organ match — malaria and blood cells, filaria and lymph node (1997); unsafe water and sanitation diseases (1993); Gambusia (2008); smallpox eradicated (2014); pneumococcal conjugate vaccines (2020).
• Malaria: fever from bursting red blood cells (1991); why a malaria vaccine is difficult (2010). Immunity: fewer white cells mean fewer antibodies (1979); antigen triggers the immune system / stimulates antibody formation (1997, 2001); lymphocytes formed in long-bone marrow (2004); antihistamines for allergy (1991); B and T cells protect against pathogens (2022); COVID-19 vaccine platforms (2022).
• AIDS and hepatitis B: caused by a virus and carried by body fluids (1986); ELISA (1987); HIV ‘living’ because it reproduces (1990); HIV linked to AIDS (1991); routes (1996); symptoms (2003); transmission facts (2010); hepatitis B more infectious than HIV and a cause of liver cancer (2010); tattooing spreads hepatitis B and HIV (2013); hepatitis B has a vaccine (2019); adenoviruses vs retroviruses (2021). Cancer and drugs: cancer described from a single cell (1995); metastasis (2001); ELISA is not a cancer test (2006); opium from the poppy capsule (1987).
• Key notes: 1983 keyed (b) ‘protozoa’ — flawed question: the typhoid bacillus is a bacterium; amoeba and Plasmodium are protozoans; pick (b) as the only option that fits two of three. 1986 keyed (b), including ‘found mostly in homosexuals’ — disputed and dated: it reflects early-1980s reporting; today the safe statements are only ‘caused by a virus’ and ‘carried by body fluids’. 1987 opium keyed (c) ‘seed capsule’ — disputed: opium is the dried latex of the unripe capsule, so (b) ‘latex juice’ is also defensible; (c) is the expected answer. 1990 HIV keyed (c) ‘auto reproduction’ — flawed wording: viruses reproduce only inside host cells. 1993 keyed (b) — flawed: malaria is mosquito-borne, not spread by drinking water, though stagnant water breeds the vector; (b) is still the only workable option. 1996 prints options (b) and (c) identically. 2010 malaria vaccine keyed (a) ‘several species’ — stands as the best option, though the bigger reason is the parasite's many life stages and changing antigens; (d) is a true fact but not a reason.
• Likely next: innate barrier examples, H₂L₂ and Ig classes, active vs passive pairs (colostrum, antivenom), allergy chemicals, lymphoid organs, retrovirus enzymes, benign vs malignant, CT vs MRI, drug–plant–receptor matches, nicotine and adrenaline, vector–disease pairs (Aedes, Anopheles, Culex), malaria and dengue vaccines, and programmes such as Mission Indradhanush.

Mains — where it appears and how to answer

• GS3 2022 asked the basic principle behind vaccine development, how vaccines work, and the approaches Indian manufacturers used for COVID-19 vaccines. This chapter supplies the core: immune memory (primary vs secondary response), antigens as inactivated or weakened pathogen or antigenic proteins, and recombinant production at scale (hepatitis B in yeast). Frame: principle → mechanism (memory B and T cells) → Indian platforms (inactivated COVAXIN; viral-vector Covishield) → manufacturing scale and cold chain → conclusion on preparedness.
• Use this chapter in GS2 answers on public health (sanitation and vector control as disease prevention; immunisation coverage; HIV policy and the 2017 Act's rights approach; tobacco control under COTPA) and in GS1 answers on youth and society (peer pressure, stress, family support in substance use). Present drug-policy choices as positions — enforcement, treatment and harm reduction — not as verdicts.
• Write about disease and drug use in people-first language (‘people living with HIV’, ‘people who use drugs’); examiners reward balance and accuracy, and NCERT itself argues against isolating people with HIV.

Tap an option. NCERT's own exercise questions come first; the rest test the figures and common confusions.

Open any question to attempt it in the Question bank — your attempt is saved to your progress.