Home/Biology/Chapter 7 — Human Health and Disease
Class 12 Biology

Human Health and Disease

Common infectious diseases, Plasmodium life cycle, innate and acquired immunity, vaccination, allergy, AIDS, cancer, and drug and alcohol abuse — with SVG diagrams, MCQs, A-R and PYQs.

5NCERT Sections
12MCQs
6Assertion–Reason
5PYQs
Section 01

Common Diseases in Humans

7.0Health and Disease

Health

A state of complete physical, mental and social well-being — not merely absence of disease or physical fitness.

  • Health is affected by (i) genetic disorders, (ii) infections, (iii) life style (food, water, rest, exercise, habits).
  • Good health needs a balanced diet, personal hygiene, regular exercise, vaccination, proper waste disposal, vector control and hygienic food and water.
  • Infectious diseases are easily transmitted from person to person; non-infectious diseases include cancer (major cause of death) and drug/alcohol abuse.
  • Pathogens = disease-causing organisms (bacteria, viruses, fungi, protozoans, helminths). Most parasites are pathogens.

7.1Infectious Diseases at a Glance

Disease Pathogen Key points
Typhoid Salmonella typhi (bacterium) Enters small intestine via contaminated food/water, then blood. Sustained fever (39–40°C), weakness, stomach pain, constipation, headache; intestinal perforation in severe cases. Confirmed by Widal test. 'Typhoid Mary' (Mary Mallon) — a cook and carrier.
Pneumonia Streptococcus pneumoniae, Haemophilus influenzae Infects alveoli, which fill with fluid. Fever, chills, cough, headache; lips/nails bluish. Spread by droplets or shared utensils.
Common cold Rhinoviruses Infect nose and respiratory passage, not lungs; lasts 3–7 days; droplets and contaminated objects.
Malaria Plasmodium (P. vivax, P. malariae, P. falciparum) Vector = female Anopheles. Malignant malaria by P. falciparum is most serious. Haemozoin → recurring chill and fever every 3–4 days.
Amoebiasis Entamoeba histolytica (protozoan) Large intestine; constipation, cramps, stools with mucus and blood. Houseflies = mechanical carriers.
Ascariasis Ascaris (roundworm) Intestinal parasite; internal bleeding, muscular pain, fever, anaemia, blocked intestine. Eggs in faeces contaminate soil, water, vegetables.
Filariasis (elephantiasis) Wuchereria bancrofti, W. malayi Chronic inflammation of lymphatic vessels of lower limbs; genital organs may be deformed; spread by female mosquito bite.
Ringworm Fungi: Microsporum, Trichophyton, Epidermophyton Dry, scaly, itching lesions on skin, nails, scalp; thrive in heat and moisture (groin, between toes); spread via soil, towels, clothes, combs.

V1Life Cycle of Plasmodium

The parasite needs two hosts — human and mosquito. Infectious form entering the human = sporozoites.

V1 · Plasmodium: human host and female Anopheles vector HUMAN HOST FEMALE ANOPHELES (VECTOR) ① Sporozoites enter ② Multiply in ③ Attack RBCs ④ Mosquito bites infected ⑤ Development in ⑥ Sporozoites stored in through bite of infected female Anopheles LIVER CELLS (initial multiplication) RBCs rupture → haemozoin chill + high fever every 3–4 days person; parasites enter the mosquito's body mosquito: parasites multiply and form sporozoites SALIVARY GLANDS → next bite infects human

7.1.2Prevention and Control

  • Personal hygiene: clean body, clean drinking water, food, vegetables and fruits. Public hygiene: waste/excreta disposal, periodic cleaning of reservoirs, pools, tanks; hygienic catering (typhoid, amoebiasis, ascariasis).
  • Air-borne (pneumonia, cold): avoid close contact with infected persons or their belongings.
  • Vector-borne (malaria, filariasis): avoid water stagnation, clean coolers, mosquito nets, Gambusia fish in ponds (eat larvae), insecticide spray, wire mesh on doors/windows. Aedes mosquitoes spread dengue and chikungunya.
  • Vaccines: smallpox eradicated; polio, diphtheria, pneumonia, tetanus largely controlled.
Section 02

Immunity

7.2.1Innate Immunity — Non-specific, present at birth

Barrier Examples
Physical Skin; mucus coating of epithelium of respiratory, gastrointestinal and urogenital tracts
Physiological Stomach acid, saliva, tears
Cellular Neutrophils (PMNL), monocytes, natural killer cells, macrophages — phagocytose microbes
Cytokine Virus-infected cells secrete interferons that protect non-infected cells

7.2.2Acquired Immunity — Pathogen-specific, with memory

  • Primary response: low intensity at first encounter. Secondary (anamnestic) response: highly intensified on subsequent encounter — due to memory.
  • B-lymphocytes secrete antibodies (humoral/antibody-mediated immunity). T-lymphocytes do not secrete antibodies but help B cells and mediate cell-mediated immunity (CMI).
  • Antibody = H₂L₂: two heavy and two light chains. Types: IgA, IgM, IgE, IgG.
  • CMI is responsible for graft rejection; body differentiates 'self' from 'non-self'. Tissue and blood-group matching plus lifelong immunosuppressants are needed for transplants.
V2 · Antibody molecule (H₂L₂) Heavy chains (2, longer) Light chains (2, shorter) Disulphide bonds Antigen-binding sites Found in blood → humoral (antibody-mediated) immune response
V3 · Primary and secondary immune response 1st exposure 2nd exposure Primary response low intensity Secondary (anamnestic) faster, highly intensified — memory Time → Antibody concentration

7.2.3Active vs Passive Immunity; Vaccination

Point Active Passive
Antibodies Produced by the host after exposure to antigens (living/dead microbes, proteins) Ready-made antibodies given directly
Speed Slow; takes time for full response Immediate
Examples Natural infection, vaccination Colostrum (IgA), antibodies via placenta, antitoxin (tetanus), snake-bite antivenom
  • Vaccination works on the memory of the immune system: weakened/inactivated pathogen or antigenic proteins are introduced; memory B- and T-cells respond rapidly on later exposure.
  • Recombinant DNA technology produces antigenic polypeptides in bacteria/yeast — e.g. hepatitis B vaccine from yeast.

7.2.5Allergy and Auto-immunity

  • Allergy: exaggerated response to environmental antigens (allergens: dust mites, pollen, animal dander). Antibodies are IgE; mast cells release histamine and serotonin → sneezing, watery eyes, running nose, breathing difficulty. Treated with anti-histamine, adrenaline, steroids.
  • Auto-immunity: the body attacks its own cells due to genetic and other reasons — e.g. rheumatoid arthritis.

7.2.7Immune System — Lymphoid Organs

V4 · Primary → secondary lymphoid organs PRIMARY lymphoid organs Bone marrow produces all blood cells Thymus shrinks with age; T-cell maturation SECONDARY lymphoid organs Spleen Lymph nodes Tonsils Peyer's patches Appendix MALT = ~50% of lymphoid tissue migrate Immature lymphocytes mature → antigen-sensitive → meet antigen in secondary organs → effector cells
  • Spleen: lymphocytes + phagocytes; large reservoir of erythrocytes. Lymph nodes: trap antigens in lymph/tissue fluid and activate lymphocytes.
Section 03

AIDS

7.3Acquired Immuno Deficiency Syndrome

  • Acquired = not congenital; syndrome = group of symptoms. First reported in 1981; killed over 25 million people in about 25 years.
  • Caused by HIV — a retrovirus with an envelope enclosing an RNA genome.
  • Transmission: (a) sexual contact, (b) contaminated blood/blood products, (c) shared needles (intravenous drug users), (d) infected mother → child through placenta. Not spread by mere touch or physical contact — only body fluids.
  • Time-lag between infection and symptoms: a few months to many years (usually 5–10 years).
V5 · HIV in the body ① HIV enters ② RNA → viral DNA ③ Viral DNA integrates ④ Virus particles ⑤ HIV enters helper ⑥ TH cells fall in number ⑦ Immuno-deficiency MACROPHAGES (become 'HIV factory') enzyme reverse transcriptase into host cell DNA; directs infected cell produced and released into blood T-lymphocytes (TH): replicates; progeny virus attacks other TH cells progressive decrease; fever, diarrhoea, weight loss Opportunistic infections: Mycobacterium , fungi, Toxoplasma , viruses
  • Diagnosis: ELISA (enzyme linked immuno-sorbent assay). Anti-retroviral drugs only prolong life; they cannot prevent death.
  • Prevention (no cure): safe blood from blood banks; disposable needles and syringes; free distribution of condoms; control of drug abuse; safe sex; regular HIV check-ups. NACO and NGOs educate people; WHO runs prevention programmes.
  • HIV/AIDS patients need help and sympathy, not isolation.
Section 04

Cancer

7.4Cancer — Features

  • Normal cells show contact inhibition; cancer cells lose it and divide continuously → tumours.
  • Benign tumours: remain in the original location, little damage. Malignant tumours: rapidly proliferating neoplastic cells invading and damaging neighbouring tissue and starving normal cells; cells reaching distant sites via blood start new tumours — metastasis (most feared property).
  • Carcinogens: physical (X-rays, gamma rays, UV — DNA damage), chemical (tobacco smoke → lung cancer), biological (oncogenic viruses with viral oncogenes). Cellular oncogenes (c-onc) / proto-oncogenes in normal cells can turn cancerous when activated.
V6 · Normal growth, benign tumour, malignant tumour with metastasis Normal cells contact inhibition Benign tumour confined; little damage Malignant tumour invades neighbouring tissue METASTASIS — new tumour at distant site Growth stops on contact Remains at original site

7.4.1Detection and Treatment

Aspect Methods
Detection Biopsy and histopathological studies; blood and bone-marrow tests (leukaemia); radiography (X-rays), CT, MRI for internal organs (CT = X-ray 3-D images; MRI = strong magnetic fields and non-ionising radiation); antibodies against cancer-specific antigens; molecular biology to detect genes for inherited susceptibility.
Treatment Surgery, radiation therapy, immunotherapy, chemotherapy (side effects: hair loss, anaemia). Tumour cells evade the immune system, so patients get biological response modifiers such as α-interferon.
Section 05

Drugs and Alcohol Abuse

7.5Commonly Abused Drugs

Group Source Key points
Opioids Latex of poppy Papaver somniferum → morphine → heroin (smack, diacetylmorphine) Bind opioid receptors in CNS and gut. Heroin is a depressant (slows body functions); snorted or injected. Morphine is a sedative and painkiller useful after surgery.
Cannabinoids Cannabis sativa inflorescence — marijuana, hashish, charas, ganja Act on cannabinoid receptors in the brain; affect the cardiovascular system; inhaled or taken orally.
Coca alkaloids Erythroxylum coca (South America) → cocaine (coke, crack) Interferes with transport of dopamine; strong CNS stimulant — euphoria, energy; excess → hallucinations.
Other Atropa belladonna, Datura; barbiturates, amphetamines, benzodiazepines Hallucinogenic plants; medicines for depression and insomnia are often abused.
Tobacco

Nicotine stimulates the adrenal gland to release adrenaline and noradrenaline → raised BP and heart rate. Smoking → cancers of lung, urinary bladder, throat; bronchitis, emphysema, coronary heart disease, gastric ulcer. Chewing → oral cancer. Smoking raises CO in blood and reduces haem-bound O₂ → oxygen deficiency.

7.5.1Adolescence, Addiction and Dependence

  • Adolescence = 12–18 years; a vulnerable phase. Causes of drug use: curiosity, adventure, experimentation, stress (academic pressure), 'cool' image promoted by media, unstable family, peer pressure.
  • Addiction = psychological attachment to effects (euphoria, well-being). With repeated use, tolerance of receptors rises → higher doses needed. Even a single use can be a forerunner to addiction.
  • Dependence = body shows a withdrawal syndrome (anxiety, shakiness, nausea, sweating) if the regular dose is stopped; may be severe and need medical supervision.
V7 · The vicious circle of addiction Curiosity · stress · peer pressure Perceived 'benefit' Tolerance rises Dependence Regular use (abuse) → first use euphoria, temporary well-being receptors need higher doses withdrawal syndrome if stopped cannot easily get out Even one use can be a forerunner to addiction

7.5.3Effects, Warning Signs and Prevention

  • Immediate effects: reckless behaviour, vandalism, violence; overdose → coma and death (respiratory/heart failure, cerebral haemorrhage). Combining drugs with alcohol increases overdose risk.
  • Warning signs: drop in academic performance, unexplained absence, neglect of hygiene, isolation, depression, aggressive behaviour, changes in sleep, appetite and weight.
  • Intravenous drug users share needles → AIDS and Hepatitis B (both chronic and ultimately fatal; spread by blood and sexual contact).
  • Long-term: damage to nervous system and liver (cirrhosis); harm to the foetus during pregnancy; adolescent drinking → heavy drinking in adulthood.
  • Sports misuse: narcotic analgesics, anabolic steroids, diuretics, hormones. In females steroids cause masculinisation and aggression; in males acne, mood swings, reduced testicular size, lower sperm production, kidney/liver dysfunction.
  • Prevention: avoid undue peer pressure; education and counselling; help from parents and peers; recognise danger signs; seek professional medical help (psychologists, psychiatrists, de-addiction and rehabilitation programmes).
Practice

📝 Solved Examples with Step Marking

📋 3 Marks

Q1. Differentiate between active and passive immunity.

Active 1.5 Marks

Host produces its own antibodies on exposure to antigens (infection or vaccination); slow but long-lasting, with memory.

Passive 1.5 Marks

Ready-made antibodies are supplied (colostrum IgA, placental antibodies, antitoxin, antivenom); quick protection.

📋 3 Marks

Q2. Why do malaria patients suffer chill and fever every 3–4 days?

Parasite multiplies 1 Mark

Plasmodium multiplies in liver cells, then in RBCs.

RBC rupture 1 Mark

RBCs rupture releasing the toxic haemozoin.

Result 1 Mark

Haemozoin causes chill and high fever; the cycle repeats every 3–4 days.

📋 3 Marks

Q3. Why does an HIV-infected person become prone to infections that a healthy person overcomes easily?

Entry 1 Mark

HIV enters macrophages; RNA → viral DNA by reverse transcriptase and integrates into host DNA.

Loss of TH cells 1 Mark

HIV replicates in helper T-lymphocytes, destroying them; their number progressively falls.

Outcome 1 Mark

Immuno-deficiency → opportunistic infections (Mycobacterium, fungi, Toxoplasma).

Test Yourself

✍️ MCQ Practice

Score: 0 / 12
New Pattern

🎯 Assertion–Reason

(A) Both true, R explains A. (B) Both true, R does NOT explain A. (C) A true, R false. (D) A false, R true.

Score: 0 / 6
Exam Focus

📖 Important Board Questions

NCERT

Q. Explain the life cycle of Plasmodium briefly.

Answer 3 Marks

Sporozoites enter the human through the bite of an infected female Anopheles → multiply in liver cells → attack RBCs, which rupture releasing haemozoin (fever every 3–4 days) → parasites taken up by a mosquito biting an infected person → multiply, form sporozoites stored in salivary glands → infect the next human.

NCERT

Q. What is the principle of vaccination? Why is a second dose (booster) useful?

Answer 3 Marks

Vaccination is based on immunological memory: weakened/inactivated pathogens or antigenic proteins generate antibodies and memory B and T cells, which give a quick, intense secondary response on actual infection.

NCERT

Q. What is AIDS? Write its causative agent, transmission and prevention.

Answer 3 Marks

Acquired Immuno Deficiency Syndrome, caused by HIV (retrovirus). Transmitted by sexual contact, contaminated blood, shared needles and from infected mother to child. Prevention: safe blood, disposable needles, condoms, safe sex, controlling drug abuse, regular check-ups.

NCERT

Q. What are carcinogens? What is metastasis?

Answer 2 Marks

Carcinogens are physical, chemical or biological agents that transform normal cells into cancerous cells (e.g. X-rays, UV, tobacco smoke, oncogenic viruses). Metastasis is the spread of malignant cells through blood to distant sites, where they form new tumours.

NCERT

Q. List the warning signs of drug and alcohol abuse in youth and how it can be prevented.

Answer 3 Marks

Signs: drop in academic performance, unexplained absence, isolation, aggression, depression, changes in sleep/appetite. Prevention: avoid peer pressure, education and counselling, support from parents and peers, medical help from psychologists and de-addiction centres.