Human Health and Disease Class 12: Concepts, Diagrams and Board Answers

What Human Health and Disease is about

Weightage: This chapter is part of Unit VIII, Biology and Human Welfare, which carries 12 of the 70 theory marks together with Microbes in Human Welfare.Source: CBSE Biology (044) syllabus 2026-27, course structure, Unit VIII Biology and Human Welfare

In real board papers: asked in 8 of the 8 board papers we hold (2023 to 2026), on average 9 marks per paper. See the questions

Key concepts

Pathogens and common bacterial and viral diseases

NCERT section 7.1 Common Diseases in Humans (typhoid, pneumonia, common cold)

Diseases: infectious (easily transmitted from person to person, e.g. AIDS, which is fatal) and non-infectious (e.g. cancer, the major cause of death among them). Pathogens are disease-causing organisms; most parasites are pathogens. Pathogens must adapt to the host; for example, gut pathogens must survive stomach acid and digestive enzymes.

Typhoid

• Pathogen: bacterium Salmonella typhi.
• Spread: contaminated food and water; enters the small intestine, then other organs through blood.
• Symptoms: sustained high fever (39–40 °C), weakness, stomach pain, constipation, headache, loss of appetite; intestinal perforation and death in severe cases.
• Test: Widal test.
• Typhoid Mary (Mary Mallon), a cook, was a carrier who spread typhoid for years through the food she made.

Pneumonia

• Pathogens: bacteria Streptococcus pneumoniae and Haemophilus influenzae.
• Infects the alveoli of the lungs, which fill with fluid, causing severe breathing problems.
• Symptoms: fever, chills, cough, headache; in severe cases lips and fingernails turn grey to bluish.
• Spread: inhaling droplets/aerosols from an infected person, or sharing glasses and utensils.
• Other bacterial diseases: dysentery, plague, diphtheria.

Common cold

• Pathogen: rhinoviruses; one of the most infectious human ailments.
• Infects the nose and respiratory passage, not the lungs.
• Symptoms: nasal congestion and discharge, sore throat, hoarseness, cough, headache, tiredness; lasts 3–7 days.
• Spread: droplets from coughs or sneezes, inhaled directly or via contaminated objects (pens, books, cups, doorknobs, keyboard, mouse).

Comparison: pneumonia versus common cold: pneumonia is bacterial and reaches the alveoli; common cold is viral and stays in the upper respiratory tract.

Worked example

A patient has sustained fever of 39–40 °C, stomach pain, constipation and loss of appetite. Name the likely disease, its pathogen, the confirmatory test and how it spreads. (2 marks)

Try it first, then show the solutionSolution

1. Typhoid, caused by the bacterium Salmonella typhi. (1)
2. Confirmed by the Widal test; spreads through food and water contaminated with the bacteria. (1)

Answer: Typhoid; Salmonella typhi; Widal test; contaminated food and water.

Malaria and the life cycle of Plasmodium

NCERT section 7.1 Common Diseases in Humans (malaria, life cycle of Plasmodium)

Pathogen: the protozoan Plasmodium; species P. vivax, P. malariae and P. falciparum cause different types. Malignant malaria by P. falciparum is the most serious and can be fatal.

Vector: the female Anopheles mosquito, which also acts as a host.

Life cycle (two hosts: human and mosquito):
1. An infected female Anopheles bites a human and injects sporozoites (the infectious form).
2. Sporozoites reach the liver; the parasites multiply asexually in liver cells, burst them and enter the blood.
3. They attack red blood cells, multiply asexually inside them and rupture them. RBC rupture releases a toxic substance, haemozoin, which causes the chill and high fever recurring every three to four days. Released parasites infect new RBCs.
4. Some parasites in RBCs develop into sexual stages (gametocytes).
5. A female Anopheles biting an infected person takes up gametocytes with the blood meal.
6. Fertilisation and development occur in the mosquito's stomach; parasites multiply to form sporozoites, which move to and are stored in the salivary glands.
7. When this mosquito bites a person, the cycle starts again.

Key points: asexual reproduction in humans (liver, RBCs), sexual reproduction in the mosquito; the mosquito is both the vector and a host.

Dengue and chikungunya are other vector-borne diseases, spread by Aedes mosquitoes, with widespread recent incidence in India; they are controlled by the same vector-control measures.

Worked example

Name the infectious stage of Plasmodium for humans and for the mosquito. Why does a malaria patient get chills and fever every three to four days? (3 marks)

Try it first, then show the solutionSolution

1. Sporozoites, injected by the bite of an infected female Anopheles, infect humans. (1)
2. Gametocytes, taken up with the blood meal, start the cycle in the mosquito (fertilisation in its stomach). (1)
3. Parasites multiply in RBCs and rupture them in cycles; each rupture releases haemozoin, a toxic substance that causes chill and high fever, recurring every 3–4 days. (1)

Answer: Sporozoites (human), gametocytes (mosquito); cyclic RBC rupture releases haemozoin, causing recurring chill and fever.

Protozoan, helminth and fungal diseases, and prevention

NCERT section 7.1 Common Diseases in Humans (amoebiasis, ascariasis, filariasis, ringworm; prevention and control)

Amoebiasis (amoebic dysentery)

• Pathogen: protozoan Entamoeba histolytica, in the large intestine.
• Symptoms: constipation, abdominal pain and cramps, stools with excess mucus and blood clots.
• Spread: houseflies act as mechanical carriers, carrying the parasite from faeces to food; drinking water and food contaminated by faecal matter.

Ascariasis

• Pathogen: Ascaris, the common roundworm, an intestinal parasite.
• Symptoms: internal bleeding, muscular pain, fever, anaemia, blockage of the intestinal passage.
• Spread: eggs in the faeces of infected people contaminate soil, water and plants; healthy people take them in with contaminated water, vegetables and fruits.

Filariasis (elephantiasis)

• Pathogen: filarial worms Wuchereria (W. bancrofti, W. malayi).
• Effect: slowly developing chronic inflammation of the organs where they live for years, usually the lymphatic vessels of the lower limbs; genital organs often affected, with gross deformities.
• Spread: bite of female mosquito vectors.

Ringworm

• Pathogens: fungi of the genera Microsporum, Trichophyton and Epidermophyton; one of the most common infectious diseases.
• Symptoms: dry, scaly lesions on skin, nails and scalp with intense itching.
• Heat and moisture help the fungi grow, so they thrive in skin folds (groin, between toes).
• Spread: from soil, or using towels, clothes or combs of infected people.

Prevention and control:

• Personal hygiene: keep the body clean; clean drinking water, food, vegetables and fruits.
• Public hygiene: safe disposal of excreta and other wastes; regular disinfection and cleaning of tanks, pools, cesspools and water reservoirs; standard hygiene in public eating places. Essential for food- and water-borne diseases (typhoid, amoebiasis, ascariasis).
• Air-borne diseases (pneumonia, common cold): also avoid close contact with infected persons and their belongings.
• Vector-borne diseases (malaria, filariasis, dengue, chikungunya): control vectors and their breeding places: no stagnant water near homes, clean household coolers regularly, use mosquito nets, introduce Gambusia fish (eats mosquito larvae) in ponds, spray insecticides in ditches, drains and swamps, fit wire mesh on doors and windows.
• Vaccines and drugs: smallpox has been eradicated by vaccination; polio, diphtheria, pneumonia and tetanus are largely controlled; antibiotics and other drugs treat infections.

Worked example

How is each transmitted: (a) amoebiasis, (b) ascariasis, (c) filariasis, (d) ringworm? (2 marks)

Try it first, then show the solutionSolution

1. (a) Food and water contaminated by faeces; houseflies carry the parasite from faeces to food. (½)
2. (b) Water, vegetables and fruits contaminated with eggs of Ascaris from faeces. (½)
3. (c) Bite of female mosquito vectors carrying Wuchereria. (½)
4. (d) From soil, or by using towels, clothes or combs of infected people. (½)

Answer: (a) faecal contamination/houseflies (b) contaminated food and water with eggs (c) mosquito bite (d) soil and shared towels, clothes, combs.

Innate and acquired immunity

NCERT section 7.2 Immunity (7.2.1 Innate Immunity; 7.2.2 Acquired Immunity)

Immunity is the host's overall ability to fight disease-causing organisms, given by the immune system.

Innate immunity: non-specific, present at birth. Four barriers:
1. Physical: skin (main barrier); mucus coating the epithelium of the respiratory, gastrointestinal and urogenital tracts traps microbes.
2. Physiological: stomach acid, saliva, tears prevent microbial growth.
3. Cellular: leukocytes such as neutrophils (PMNL), monocytes and natural killer cells (a type of lymphocyte) in blood, and macrophages in tissues, phagocytose and destroy microbes.
4. Cytokine: virus-infected cells secrete interferons, which protect non-infected cells from further viral infection.

Acquired immunity: pathogen-specific, with memory.

• First encounter → primary response (low intensity).
• Later encounter with the same pathogen → secondary (anamnestic) response (much stronger), because the body 'remembers'.
• Carried out by B-lymphocytes and T-lymphocytes.

Humoral (antibody-mediated) response: B cells produce antibodies into the blood. T cells do not secrete antibodies but help B cells produce them.

• Antibody structure: four polypeptide chains, two light and two heavy, written H₂L₂.
• Types: IgA, IgM, IgE, IgG.

Cell-mediated immunity (CMI): by T-lymphocytes. The body tells 'self' from 'non-self', and CMI causes graft rejection. Before an organ transplant, tissue matching and blood group matching are needed, and patients take immunosuppressants for life.

Comparison:

• Innate: non-specific, from birth, no memory, barriers.
• Acquired: specific, develops after exposure, has memory, B and T cells.

Worked example

A person recovers from measles and is exposed again years later but does not fall ill. Explain using primary and secondary responses. (2 marks)

Try it first, then show the solutionSolution

1. On the first infection, the body mounted a low-intensity primary response and formed memory B and T cells specific to the measles virus. (1)
2. On re-exposure, these memory cells mount a fast, highly intensified secondary (anamnestic) response, destroying the virus before disease develops. (1)

Answer: Memory from the primary response produces a rapid, strong secondary response on re-exposure.

Active and passive immunity, vaccination, allergy and autoimmunity

NCERT section 7.2.3 Active and Passive Immunity; 7.2.4 Vaccination and Immunisation; 7.2.5 Allergies; 7.2.6 Auto Immunity

Active immunity: the host makes its own antibodies after exposure to antigens (living or dead microbes or other proteins). It is slow to reach full effect but long-lasting. Induced by natural infection or by immunisation (deliberately injecting microbes or antigens).

Passive immunity: ready-made antibodies are given. Fast, but short-lived. Examples:

• Colostrum: the yellowish milk of the first days of lactation, rich in IgA, protects the infant.
• Antibodies from mother to foetus through the placenta.
• Antitoxin for tetanus and anti-venom for snakebite: preformed antibodies injected when a quick response is needed (passive immunisation).

Vaccination: based on the immune system's memory. A vaccine (antigenic proteins of a pathogen, or the inactivated/weakened pathogen) is introduced; the body makes antibodies and memory B and T cells, which recognise the real pathogen quickly later and overwhelm it with massive antibody production.

• Recombinant DNA technology produces antigenic polypeptides in bacteria or yeast, allowing large-scale production, e.g. hepatitis B vaccine from yeast.

Allergy: an exaggerated immune response to certain environmental antigens called allergens (dust mites, pollen, animal dander).

• Antibodies: IgE.
• Cause of symptoms: mast cells release histamine and serotonin.
• Symptoms: sneezing, watery eyes, running nose, difficulty in breathing.
• Diagnosis: expose or inject tiny doses of possible allergens and watch reactions.
• Treatment: antihistamines, adrenalin, steroids.
• More children in metro cities have allergies and asthma, possibly because of the protected environment in early life.

Autoimmunity: due to genetic and unknown reasons, the body attacks its own cells, e.g. rheumatoid arthritis.

Worked example

A child stepped on a rusty nail and was given an anti-tetanus injection of preformed antibodies; his brother received a tetanus vaccine at school. Compare the immunity in the two cases. (3 marks)

Try it first, then show the solutionSolution

1. Injected preformed antibodies (antitoxin) give passive immunity: immediate protection, needed because tetanus requires a quick response. (1)
2. The vaccine gives active immunity: the brother's body makes its own antibodies and memory B and T cells, which takes time. (1)
3. Passive immunity is short-lived with no memory; active immunity is long-lasting because of memory cells. (1)

Answer: Antitoxin: fast but short passive immunity; vaccine: slower but long-lasting active immunity with memory.

Lymphoid organs and the immune system

NCERT section 7.2.7 Immune System in the Body

The immune system consists of lymphoid organs, tissues, cells and soluble molecules (antibodies). It recognises foreign antigens, responds and remembers; it is also involved in allergies, autoimmune diseases and transplantation.

Lymphoid organs: where lymphocytes originate and/or mature and proliferate.

Primary lymphoid organs: bone marrow and thymus, where immature lymphocytes become antigen-sensitive.

• Bone marrow: main lymphoid organ; all blood cells including lymphocytes are made here.
• Thymus: lobed organ near the heart, beneath the breastbone; large at birth, shrinks with age and is very small by puberty.
• Both provide micro-environments for development and maturation of T-lymphocytes.

Secondary lymphoid organs: spleen, lymph nodes, tonsils, Peyer's patches of the small intestine and appendix; sites where lymphocytes meet antigens and proliferate into effector cells.

• Spleen: large, bean-shaped; mainly lymphocytes and phagocytes; filters blood by trapping blood-borne microbes; a large reservoir of erythrocytes.
• Lymph nodes: small solid structures along the lymphatic system; trap microbes and antigens in lymph and tissue fluid, activating lymphocytes there.

MALT (mucosa-associated lymphoid tissue): lymphoid tissue in the lining of the respiratory, digestive and urogenital tracts; about 50% of the body's lymphoid tissue.

Worked example

Name the primary and secondary lymphoid organs. What is the role of each group? Expand MALT and give its share of lymphoid tissue. (3 marks)

Try it first, then show the solutionSolution

1. Primary: bone marrow and thymus, where immature lymphocytes differentiate into antigen-sensitive lymphocytes (T cells mature here). (1)
2. Secondary: spleen, lymph nodes, tonsils, Peyer's patches, appendix, where lymphocytes interact with antigens and proliferate into effector cells. (1)
3. MALT: mucosa-associated lymphoid tissue, about 50% of lymphoid tissue in the body. (1)

Answer: Primary (bone marrow, thymus) produce and mature lymphocytes; secondary (spleen, lymph nodes, tonsils, Peyer's patches, appendix) are where they meet antigens; MALT ≈ 50%.

AIDS

NCERT section 7.3 AIDS

AIDS = Acquired Immuno Deficiency Syndrome: a deficiency of the immune system acquired during life (not congenital); 'syndrome' = a group of symptoms. First reported in 1981; it has killed more than 25 million people worldwide.

Cause: HIV (Human Immunodeficiency Virus), a retrovirus: an envelope enclosing an RNA genome.

Transmission (only through body fluids, not by touch):
1. Sexual contact with an infected person.
2. Transfusion of contaminated blood and blood products.
3. Sharing infected needles (intravenous drug abusers).
4. Infected mother to child through the placenta.
High-risk groups: people with multiple sexual partners, intravenous drug users, people needing repeated transfusions, children of HIV-infected mothers. Infected people should not be isolated from family and society.

Time lag: a few months to many years (usually 5–10 years) between infection and symptoms.

How HIV destroys immunity (flow chart):
1. HIV enters macrophages.
2. Reverse transcriptase makes viral DNA from the viral RNA.
3. Viral DNA is incorporated into the host DNA and directs the cell to make virus particles; macrophages keep producing virus (an 'HIV factory').
4. HIV also enters helper T-lymphocytes (T_H), replicates, and progeny viruses attack more helper T cells.
5. Helper T cell numbers fall progressively; the person has bouts of fever, diarrhoea and weight loss.
6. With few helper T cells, the person suffers opportunistic infections (bacteria, especially Mycobacterium; viruses; fungi; parasites like Toxoplasma) that a healthy immune system would overcome.

Diagnosis: ELISA (enzyme-linked immunosorbent assay). Treatment: anti-retroviral drugs, only partially effective; they prolong life but cannot prevent death.

Prevention (no cure, so prevention is best; 'don't die of ignorance'):

• NACO (National AIDS Control Organisation) and NGOs educate people; WHO programmes.
• Safe blood from blood banks; only disposable needles and syringes; free distribution of condoms; controlling drug abuse; advocating safe sex; regular HIV check-ups for susceptible groups.
• HIV infection should not be hidden; patients need help and sympathy, not rejection.

Worked example

Explain how HIV causes immune deficiency. Why does an AIDS patient die of infections that a healthy person can overcome? (3 marks)

Try it first, then show the solutionSolution

1. HIV enters macrophages; reverse transcriptase copies its RNA into DNA, which joins the host DNA, so macrophages keep producing virus. (1)
2. HIV also enters helper T cells, multiplies, and progeny viruses attack more helper T cells, so their number falls steadily. (1)
3. Helper T cells are needed for antibody production and cell-mediated responses, so the patient cannot fight opportunistic pathogens such as Mycobacterium, fungi or Toxoplasma. (1)

Answer: HIV turns macrophages into virus factories and destroys helper T cells; without them the immune system cannot fight ordinary infections.

Cancer

NCERT section 7.4 Cancer

Cancer is a dreaded disease and a major cause of death worldwide; more than a million Indians suffer from it.

What goes wrong: normal cell growth and differentiation are tightly regulated. Normal cells show contact inhibition: contact with other cells stops their uncontrolled growth. Cancer cells lose contact inhibition, keep dividing and form masses called tumours.

Benign versus malignant tumours:

• Benign: stay confined to their original place; do not spread; cause little damage.
• Malignant: masses of proliferating neoplastic (tumour) cells that grow very rapidly, invade and damage surrounding tissues and starve normal cells by competing for nutrients. Cells shed from them travel through blood and start new tumours elsewhere: metastasis, the most feared property.

Causes (carcinogens):

• Physical: ionising radiation (X-rays, gamma rays) and non-ionising UV damage DNA.
• Chemical: carcinogens in tobacco smoke, a major cause of lung cancer.
• Biological: oncogenic viruses carrying viral oncogenes; normal cells have cellular oncogenes (c-onc) or proto-oncogenes, which, when activated under certain conditions, can cause oncogenic transformation.

Detection and diagnosis (early detection allows successful treatment in many cases):

• Biopsy and histopathology: thin, stained sections of suspected tissue examined by a pathologist.
• Blood and bone marrow tests for raised cell counts in leukaemias.
• Radiography (X-rays), CT (computed tomography: X-rays give a 3-D image), MRI (strong magnetic fields and non-ionising radiation detect pathological and physiological changes).
• Antibodies against cancer-specific antigens.
• Molecular biology to find genes for inherited susceptibility; such people can avoid particular carcinogens (e.g. tobacco smoke for lung cancer).

Treatment: surgery, radiation therapy (tumour cells irradiated lethally, protecting normal tissue), chemotherapy (drugs that kill cancer cells; side effects such as hair loss and anaemia), and immunotherapy. Most cancers are treated by a combination. Tumour cells avoid the immune system, so patients are given biological response modifiers such as α-interferon, which activate the immune system to destroy the tumour.

Worked example

How is a cancer cell different from a normal cell? Explain metastasis and why malignant tumours are dangerous. (3 marks)

Try it first, then show the solutionSolution

1. Normal cells show contact inhibition and stop dividing when they touch other cells; cancer cells have lost contact inhibition and divide uncontrollably, forming tumours. (1)
2. Malignant tumour cells grow rapidly, invade and damage nearby tissue and starve normal cells of nutrients. (1)
3. Metastasis: cells sloughed from the tumour travel through blood to distant sites and start new tumours there. (1)

Answer: Cancer cells lack contact inhibition; malignant tumours invade, starve normal cells and spread by metastasis.

Drugs, alcohol and tobacco

NCERT section 7.5 Drugs and Alcohol Abuse (opioids, cannabinoids, coca alkaloids, tobacco)

Commonly abused drugs are opioids, cannabinoids and coca alkaloids, mostly from flowering plants (some from fungi).

Drug	Source	Acts on	How taken	Effect
Heroin ('smack'), diacetylmorphine (opioid)	Acetylation of morphine, from the latex of poppy, Papaver somniferum	Opioid receptors in CNS and GI tract	Snorting, injection	Depressant: slows body functions
Cannabinoids (marijuana, hashish, charas, ganja)	Inflorescences (flower tops, leaves, resin) of Cannabis sativa	Cannabinoid receptors, mainly in the brain	Inhalation, oral	Effects on the cardiovascular system
Cocaine ('coke', 'crack'), coca alkaloid	Coca plant, Erythroxylum coca (South America)	Interferes with transport of dopamine	Usually snorted	Potent CNS stimulant: euphoria, energy; excess causes hallucinations

• Heroin is a white, odourless, bitter crystalline compound.
• Other hallucinogenic plants: Atropa belladonna, Datura. Some sportspersons abuse cannabinoids.
• Medicines often abused: barbiturates, amphetamines, benzodiazepines (used for depression and insomnia). Morphine is a very effective sedative and painkiller after surgery.
• Drug abuse: use for non-medical purposes, or in amounts/frequency that impair physical, physiological or psychological functions.

Tobacco (used for over 400 years; smoked, chewed or as snuff):

• Contains nicotine, an alkaloid that stimulates the adrenal gland to release adrenaline and noradrenaline, raising blood pressure and heart rate.
• Smoking increases cancers of lung, urinary bladder and throat, bronchitis, emphysema, coronary heart disease and gastric ulcer; chewing raises risk of oral cancer.
• Smoking raises carbon monoxide in blood and lowers haem-bound oxygen, causing oxygen deficiency.
• Smoking paves the way to hard drugs.

Misuse in sports: narcotic analgesics, anabolic steroids, diuretics and certain hormones to increase muscle strength and bulk and aggressiveness.

• In females: masculinisation, aggressiveness, mood swings, depression, abnormal menstrual cycles, excess facial and body hair, enlarged clitoris, deepened voice.
• In males: acne, aggressiveness, mood swings, depression, smaller testes, decreased sperm production, possible kidney and liver dysfunction, breast enlargement, premature baldness, enlarged prostate.
• In adolescents: severe acne and premature closure of growth centres of long bones, causing stunted growth.

Worked example

Name the plant source and the receptor or neurotransmitter affected by (a) heroin and (b) cocaine. Classify each as depressant or stimulant. (2 marks)

Try it first, then show the solutionSolution

1. (a) Heroin: from morphine of Papaver somniferum (poppy latex); binds opioid receptors in the CNS and GI tract; depressant. (1)
2. (b) Cocaine: from Erythroxylum coca; interferes with transport of dopamine; potent CNS stimulant. (1)

Answer: (a) Poppy, opioid receptors, depressant (b) coca plant, dopamine transport, stimulant.

Adolescence, addiction, dependence and prevention

NCERT section 7.5.1 Adolescence and Drug/Alcohol Abuse; 7.5.2 Addiction and Dependence; 7.5.3 Effects; 7.5.4 Prevention and Control

Adolescence: both 'a period' and 'a process' in which a child matures in attitudes and beliefs; roughly 12–18 years; a bridge between childhood and adulthood, with biological and behavioural changes; a very vulnerable phase.

Why adolescents start: curiosity, need for adventure and excitement, experimentation; later, use to escape problems; stress from academic or exam pressure; the perception that it is 'cool' or progressive (promoted by TV, movies, newspapers, internet); unstable or unsupportive families; peer pressure.

Addiction: a psychological attachment to effects such as euphoria and a temporary feeling of well-being. With repeated use, the tolerance level of receptors increases, so they respond only to higher doses, leading to greater intake. Even one use can lead to addiction.

Dependence: the body shows an unpleasant withdrawal syndrome (anxiety, shakiness, nausea, sweating) when regular use stops suddenly; it may be severe and need medical supervision. Dependence makes people ignore social norms to get money for drugs.

Effects of abuse:

• Immediate: reckless behaviour, vandalism, violence; overdose can cause coma and death (respiratory failure, heart failure, cerebral haemorrhage); combining drugs, or drugs with alcohol, often causes overdose.
• Warning signs in youth: drop in academic performance, unexplained absence, poor personal hygiene, withdrawal, isolation, depression, fatigue, aggressive and rebellious behaviour, deteriorating relationships, loss of interest in hobbies, changed sleeping and eating habits, fluctuating weight and appetite.
• Intravenous users risk AIDS and hepatitis B by sharing needles.
• Chronic use damages the nervous system and liver (cirrhosis); alcohol in adolescence can lead to heavy drinking later; drugs and alcohol in pregnancy harm the foetus.
• Social: stealing; mental and financial distress to family and friends.

Prevention and control ('prevention is better than cure'; parents and teachers have a special role; nurturing plus consistent discipline lowers risk):
1. Avoid undue peer pressure: respect each child's choices; do not push beyond limits.
2. Education and counselling: to face problems and accept failure; channel energy into sports, reading, music, yoga.
3. Seek help from parents and peers.
4. Look for danger signs: alert parents, teachers and friends.
5. Seek professional and medical help: psychologists, psychiatrists, de-addiction and rehabilitation programmes.

Worked example

Why is it difficult to give up drugs once a person starts taking them? Distinguish addiction from dependence. (3 marks)

Try it first, then show the solutionSolution

1. Repeated use raises the tolerance level of the body's receptors, so they respond only to higher doses, pulling the user into a vicious circle of greater intake. (1)
2. Addiction is a psychological attachment to effects like euphoria and temporary well-being, which drives use even when it is not needed or is self-destructive. (1)
3. Dependence is the body's tendency to show a withdrawal syndrome (anxiety, shakiness, nausea, sweating) when regular use stops abruptly; it may need medical supervision. (1)

Answer: Rising receptor tolerance drives higher doses; addiction is psychological attachment, dependence is physical withdrawal on stopping.

Human Health and Disease in real life

Each concept, met in an everyday situation. Read the situation, answer the question in your own words, then compare with the model answer. The one-line hook is what to remember.

Topics in this chapter

• Common Diseases in Humans and Malaria
• Immunity: Innate, Acquired, Active and Passive
• Drugs and Alcohol Abuse

Human Health and Disease: key facts

Disease–pathogen key

$\text{typhoid: }\text{Salmonella typhi};\text{pneumonia: }\text{S. pneumoniae},\text{H. influenzae};\text{common cold: rhinovirus}$

Bacterial (typhoid, pneumonia) versus viral (cold).

Protozoan and helminth key

$\text{malaria: }\text{Plasmodium};\text{amoebiasis: }\text{Entamoeba histolytica};\text{ascariasis: }\text{Ascaris};\text{filariasis: }\text{Wuchereria}$

Ringworm: Microsporum, Trichophyton, Epidermophyton (fungi).

Vectors and carriers

$\text{malaria: female }\text{Anopheles};\text{dengue, chikungunya: }\text{Aedes};\text{filariasis: female mosquito};\text{amoebiasis: housefly (mechanical)}$

Gambusia fish eats mosquito larvae.

Antibody

$\text{antibody}=H_2{L}_2;\text{types: IgA, IgM, IgE, IgG}$

IgE in allergy; IgA in colostrum.

HIV replication

$\text{viral RNA}\stackrel{\text{reverse transcriptase}}{\to }\text{viral DNA}\to \text{host DNA}\to \text{new virus}$

Targets macrophages and helper T cells; test: ELISA.

Drug sources

$\text{heroin}\leftarrow \text{morphine}\leftarrow \text{Papaver somniferum};\text{cannabinoids}\leftarrow \text{Cannabis sativa};\text{cocaine}\leftarrow \text{Erythroxylum coca}$

Hallucinogenic: Atropa belladonna, Datura.

Human Health and Disease: diagrams to practise

Practise each one on paper: draw it from the checklist, then tick off every label.

How the board asks Human Health and Disease

The question patterns to expect, and the method that works for each.

Tricks to remember Human Health and Disease

Short memory aids. Say each one aloud once, then use it on a question the same day.

• Malaria: 'S-L-R-G, Stomach-Saliva'

  In humans: Sporozoites → Liver → RBCs → Gametocytes. In mosquito: fertilisation in Stomach → sporozoites to Salivary glands.

  Use it when: Plasmodium life cycle.

• Ringworm fungi: 'My Tiny Epidermis'

  Microsporum, Trichophyton, Epidermophyton.

  Use it when: Pathogens of ringworm.

• Innate barriers: 'People Prefer Clean Clothes'

  Physical (skin, mucus), Physiological (acid, saliva, tears), Cellular (neutrophils, monocytes, NK cells, macrophages), Cytokine (interferons).

  Use it when: Four barriers of innate immunity.

• Antibody classes: 'GAMED'

  IgG, IgA, IgM, IgE (and IgD). A in milk (colostrum), E in allergy.

  Use it when: Antibody types.

• Primary lymphoid = 'Born and Trained' (Bone marrow, Thymus)

  Secondary = 'Spleen, Lymph nodes, Tonsils, Peyer's patches, Appendix'.

  Use it when: Lymphoid organs.

• Drugs: 'Poppy Pulls down, Coca Charges up'

  Heroin (poppy) is a depressant; cocaine (coca) is a stimulant; cannabis hits the heart (cardiovascular).

  Use it when: Drug effects.

Human Health and Disease: board-level solved questions

Ordered from board level to HOTS. Cover the solution, write your own, then compare step by step.

Case-study practice (Section D style)

Read the situation, then answer every part. In the board paper this is a 4-mark question split into 1 + 2 + 1 marks.

Where the marks are

How a typical answer is split into step marks. Show every step: a right final answer alone rarely earns full marks.

Where students lose marks in Human Health and Disease

The slips examiners see most often, and what to write instead.

• ✗Mistake: Saying the common cold infects the lungs

  Wrong working

  Rhinoviruses infect the alveoli of the lungs and fill them with fluid.

  Right working

  Rhinoviruses infect the nose and respiratory passage but not the lungs; it is pneumonia that fills the alveoli with fluid.

  ✓Do this: Cold = upper respiratory tract (virus); pneumonia = alveoli (bacteria).

  Usually costs: 1 mark.

• ✗Mistake: Writing that fertilisation of Plasmodium occurs in human blood

  ✓Do this: Gametocytes form in human RBCs, but fertilisation and development occur in the mosquito's stomach.

  Usually costs: 1 mark.

• ✗Mistake: Calling vaccination passive immunity

  ✓Do this: Vaccines make the body produce its own antibodies and memory cells: active immunity. Injecting preformed antibodies (antitoxin, anti-venom) is passive.

  Usually costs: 1 mark.

• ✗Mistake: Saying T cells secrete antibodies

  ✓Do this: B cells produce antibodies; T cells help B cells and mediate cell-mediated immunity (graft rejection).

  Usually costs: 1 mark.

• ✗Mistake: Saying HIV spreads by touch or sharing food

  ✓Do this: HIV spreads only through body fluids: sexual contact, blood transfusion, shared needles, mother to child.

  Usually costs: 1 mark.

• ✗Mistake: Mixing up benign and malignant

  ✓Do this: Benign tumours stay in one place; malignant tumours invade tissues and spread by metastasis.

  Usually costs: 1 mark.

NCERT exercise guide: Human Health and Disease

What each exercise in the NCERT chapter tests, how to approach it, and a question of the same kind solved step by step. Questions here are written in our own words.

Human Health and Disease: previous year questions

• Asked in 8 of the 8 board papers we hold (2023 to 2026), on average 9 marks per paper; 32 questions in all, counting OR alternatives. In 4 of 4 sample papers.

Counted from the real papers on our previous year papers page, not estimated. Average marks are over every board paper we hold, with an OR pair counted once. Chapter tags are ours.

Solved board questions from Human Health and Disease

Real questions from recent papers. Try each one first, then open our step-by-step solution with marks per step.

Every Human Health and Disease question, by year

Practice questions on Human Health and Disease

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

1. Q1 · 1 mark · MCQBoard level

   Which of these is a cytokine barrier of innate immunity?
   (a) Skin (b) Tears (c) Interferons (d) Neutrophils

   Hint

   Proteins from virus-infected cells.

   Answer

   (c) Interferons

2. Q2 · 1 mark · Assertion-reasonBoard level

   Assertion (A): Cancer cells form tumours.
   Reason (R): Cancer cells show contact inhibition.
   (a) Both A and R are true and R is the correct explanation of A.
   (b) Both A and R are true but R is not the correct explanation of A.
   (c) A is true but R is false.
   (d) A is false but R is true.

   Hint

   What have cancer cells lost?

   Answer

   (c) A is true but R is false: cancer cells have lost contact inhibition.

3. Q3 · 1 mark · MCQHarder board level

   Cocaine interferes with the transport of which neurotransmitter?
   (a) Acetylcholine (b) Dopamine (c) Serotonin (d) Adrenaline

   Hint

   Coca alkaloid.

   Answer

   (b) Dopamine

4. Q4 · 2 marks · Very short answerBoard level

   Name the pathogen and two symptoms of (a) ascariasis and (b) amoebiasis. (2 marks)

   Hint

   Roundworm and protozoan.

   Answer

   (a) Ascaris: internal bleeding, muscular pain, fever, anaemia, intestinal blockage (any two) (1). (b) Entamoeba histolytica: constipation, abdominal pain and cramps, stools with excess mucus and blood clots (any two) (1).

5. Q5 · 2 marks · Very short answerHarder board level

   Why is colostrum important for a newborn, and why is the immunity it gives called passive? (2 marks)

   Hint

   IgA.

   Answer

   Colostrum, the yellowish milk of the first days of lactation, contains abundant IgA antibodies that protect the infant (1). The antibodies are ready-made from the mother, not produced by the baby's own immune system, so the immunity is passive (and short-lived) (1).

6. Q6 · 2 marks · Very short answerHarder board level

   Explain the cause of allergy and how it is treated. Why are allergies rising among children in metro cities? (2 marks)

   Hint

   IgE, mast cells.

   Answer

   Allergy is an exaggerated immune response to allergens (mites, pollen, dander); IgE antibodies are made and mast cells release histamine and serotonin; treated with antihistamines, adrenalin or steroids (1). Modern lifestyle with a protected early environment may lower immunity and raise sensitivity to allergens (1).

7. Q7 · 3 marks · Short answerBoard level

   Describe the role of the spleen, lymph nodes and thymus in immunity. (3 marks)

   Hint

   Filter, trap, mature.

   Answer

   Spleen: bean-shaped secondary organ with lymphocytes and phagocytes; filters blood by trapping blood-borne microbes; reservoir of erythrocytes (1). Lymph nodes: along the lymphatic system; trap microbes and antigens in lymph and tissue fluid, activating lymphocytes there (1). Thymus: primary organ near the heart beneath the breastbone; provides the environment for T-lymphocyte maturation; large at birth, small by puberty (1).

8. Q8 · 3 marks · Short answerHarder board level

   List the four routes of HIV transmission and four steps taken to prevent the spread of AIDS. (3 marks)

   Hint

   Body fluids only.

   Answer

   Routes: sexual contact with an infected person; transfusion of contaminated blood; sharing infected needles; infected mother to child through the placenta (1½). Prevention: safe blood from blood banks; disposable needles and syringes; free condoms and safe sex; controlling drug abuse; regular check-ups in susceptible groups; education by NACO and NGOs (any four) (1½).

9. Q9 · 5 marks · Long answerHarder board level

   (a) Name the three main groups of abused drugs, giving one example, its source and effect for each. (3)
   (b) Distinguish addiction from dependence. (2) (5 marks)

   Hint

   Opioids, cannabinoids, coca alkaloids.

   Answer

   (a) Opioids: heroin (smack), by acetylation of morphine from Papaver somniferum latex; binds opioid receptors in the CNS and gut; depressant (1). Cannabinoids: marijuana, hashish, charas, ganja from Cannabis sativa inflorescences; act on cannabinoid receptors in the brain; affect the cardiovascular system (1). Coca alkaloid: cocaine from Erythroxylum coca; interferes with dopamine transport; CNS stimulant causing euphoria, hallucinations in excess (1). (b) Addiction: psychological attachment to effects like euphoria, driving use even when harmful; receptor tolerance rises, so larger doses are needed (1). Dependence: the body shows withdrawal symptoms (anxiety, shakiness, nausea, sweating) when regular use stops suddenly (1).

10. Q10 · 3 marks · Short answerHOTS / competency

    Suppose a town sees cases of typhoid, amoebiasis and ascariasis after a flood contaminates drinking water. What do these diseases have in common, and what public hygiene steps would you recommend? (3 marks)

    Hint

    Faecal–oral route.

    Answer

    All three spread through food and water contaminated with faecal matter (Salmonella typhi, Entamoeba histolytica, Ascaris eggs) (1). Steps: proper disposal of waste and excreta; periodic cleaning and disinfection of water reservoirs and tanks; safe drinking water (boiled or treated) (1). Hygiene in public catering, washing vegetables and fruits, and controlling houseflies that carry Entamoeba to food (1).

11. Q11 · 2 marks · Very short answerHOTS / competency

    A kidney transplant from an unrelated donor is rejected after a few weeks despite blood group matching. Explain why, and what could reduce the chance of rejection. (2 marks)

    Hint

    Self versus non-self.

    Answer

    The recipient's cell-mediated immunity (T-lymphocytes) recognised the graft tissue as non-self and attacked it; blood group matching alone is not enough (1). Tissue matching before the transplant and lifelong immunosuppressant drugs reduce rejection (1).

12. Q12 · 2 marks · Very short answerHarder board level

    Why is the hepatitis B vaccine produced in yeast considered an advance over older vaccines? (2 marks)

    Hint

    Recombinant DNA.

    Answer

    Recombinant DNA technology lets the antigenic polypeptide of the pathogen be made in yeast, without using the whole pathogen (1). This allows large-scale production and hence greater availability for immunisation (1).

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1. 1.Which test confirms typhoid?Show answer

   The Widal test.

2. 2.Which toxic substance causes the chill and fever of malaria?Show answer

   Haemozoin, released when infected RBCs rupture.

3. 3.Which species of Plasmodium causes malignant malaria?Show answer

   Plasmodium falciparum.

4. 4.Name the vector of dengue and chikungunya.Show answer

   Aedes mosquitoes.

5. 5.What do interferons do?Show answer

   Secreted by virus-infected cells, they protect non-infected cells from further viral infection.

6. 6.Why is an antibody written H₂L₂?Show answer

   It has two heavy and two light polypeptide chains.

7. 7.Which antibody is abundant in colostrum?Show answer

   IgA.

8. 8.Give an example of a vaccine made by recombinant DNA technology.Show answer

   Hepatitis B vaccine produced from yeast.

9. 9.Name an autoimmune disease.Show answer

   Rheumatoid arthritis.

10. 10.What is the diagnostic test for AIDS?Show answer

    ELISA (enzyme-linked immunosorbent assay).

11. 11.What are proto-oncogenes?Show answer

    Cellular oncogenes (c-onc) in normal cells that, when activated under certain conditions, can cause cancer.

12. 12.What does nicotine do in the body?Show answer

    Stimulates the adrenal gland to release adrenaline and noradrenaline, raising blood pressure and heart rate.

Quick revision checklist

The night before the exam: can you do each of these without looking?

• ☐Can you name the pathogen, symptoms and spread of each of the ten syllabus diseases?
• ☐Can you draw and explain the life cycle of Plasmodium?
• ☐Can you list the four innate barriers with examples?
• ☐Can you draw a labelled antibody and name four classes?
• ☐Can you give two examples each of active and passive immunity?
• ☐Can you name the primary and secondary lymphoid organs and explain MALT?
• ☐Can you explain how HIV destroys helper T cells, and list four preventive steps?
• ☐Can you contrast benign and malignant tumours and name the source and effect of heroin, cannabinoids and cocaine?

Human Health and Disease: frequently asked questions