Human Health and Disease Class 12 Notes मानव स्वास्थ्य तथा रोग — कक्षा 12 जीव विज्ञान अध्याय 7

Revise these first (prerequisites)

• Basic differences between bacteria, viruses, protozoa and fungi (Class 8–9)
• Components of blood — RBC, WBC (Class 11)
• The STI part of Chapter 3 (HIV, hepatitis-B)

1. Health is not just the absence of disease

   Health means being completely well in all three ways — physical, mental and social. Good food, cleanliness, exercise and positive thinking are all part of health.

2. Who spreads the disease?

   Organisms that cause disease are called pathogens (रोगजनक) — bacteria, viruses, fungi, protozoa and some worms (helminths). For example, typhoid is caused by bacteria, the common cold by a virus, malaria by a protozoan (Plasmodium) and ringworm by fungi.

3. How does the disease spread?

   Some diseases spread through contaminated water/food (typhoid, amoebiasis), some through tiny droplets in the air (pneumonia, common cold), and some through mosquito bites (malaria, filariasis, dengue). So clean water, hand-washing and protection from mosquitoes are the simplest 'medicine'.

4. Immunity = the body's security team

   The body's own defence system is called immunity (प्रतिरक्षा). Skin and mucus are the 'boundary wall', WBCs are the 'guards', and antibodies are the special weapons that recognise and capture specific pathogens.

5. How does a vaccine protect?

   A vaccine contains a weakened/killed form of the pathogen or its protein. The body recognises it and forms memory cells, so that when the real pathogen arrives, it can mount a faster and stronger attack. Like a fire drill at school — practise first, then act quickly in a real emergency.

6. AIDS, cancer and drugs

   AIDS is caused by HIV, a virus that weakens the immune system itself. In cancer, cells begin to divide uncontrollably. Drugs and alcohol harm both the body and the mind — accurate information and talking openly with parents/teachers are the first steps towards prevention.

Quick check ✔

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As per NCERT 2026-27 — every point you need for the board exam.

1. Health

   Genetic disorders, infections and lifestyle (food, water, rest, exercise, habits) affect health. William Harvey discovered blood circulation.

2. Typhoid

   Salmonella typhi; spread through contaminated food and water. Sustained high fever (39–40°C), weakness, stomach pain. Confirmed by the Widal test. Typhoid Mary — a cook who remained a carrier for years.

3. Pneumonia

   Streptococcus pneumoniae, Haemophilus influenzae; alveoli get filled with fluid. Fever, chills, cough; in severe cases lips/fingernails turn bluish-grey. Spreads through droplets and shared glasses.

4. Common cold

   Rhino viruses; infect the nose and respiratory passage, but not the lungs. Spread through droplets or contaminated objects. Lasts 3–7 days.

5. Malaria

   Plasmodium (P. vivax, P. malariae, P. falciparum — the most dangerous). Female Anopheles mosquito = vector. Sporozoites → liver → RBCs; when RBCs rupture, haemozoin is released → chills and high fever every 3–4 days. The sexual stage occurs in the mosquito.

6. Amoebiasis, ascariasis, filariasis

   Entamoeba histolytica (amoebic dysentery; housefly is the carrier). Ascaris (roundworm; eggs via soil/water). Wuchereria (bancrofti, malayi) — elephantiasis/filariasis; spread by the bite of Culex/Aedes.

7. Ringworm

   Fungi: Microsporum, Trichophyton, Epidermophyton. Dry, itchy patches on skin, nails and scalp; grows in heat and moisture.

8. Prevention

   Personal hygiene, safe drinking water, proper disposal of sewage. Vector control: no stagnant water, Gambusia fish (eats larvae), insecticides, mosquito nets. Dengue, chikungunya — Aedes mosquito.

9. Innate immunity

   Present from birth, non-specific. 4 barriers: physical (skin, mucus), physiological (stomach acid, saliva, tears), cellular (PMNL-neutrophils, monocytes, NK cells, macrophages), cytokine (interferons — from virus-infected cells).

10. Acquired immunity

    Pathogen-specific, with memory. Primary response is weak; secondary (anamnestic) response is strong. B-cells → antibodies (humoral, HMI); T-cells → CMI (graft rejection). Antibody: H₂L₂ — 2 heavy + 2 light chains; IgA, IgM, IgE, IgG.

11. Active vs passive; vaccines

    Active: body makes its own antibodies (infection/vaccine), slow. Passive: ready-made antibodies (IgA in colostrum, IgG from mother via placenta, anti-tetanus/snake venom). Vaccination creates memory; Hepatitis-B vaccine is produced from yeast (recombinant DNA). Allergy: IgE, histamine, serotonin. Autoimmunity: rheumatoid arthritis. Lymphoid organs: primary (bone marrow, thymus), secondary (spleen, lymph nodes, tonsils, Peyer's patches, MALT).

12. AIDS

    HIV (retrovirus). Spread: unsafe sex, infected blood, shared needles, mother to child. Virus → macrophage (HIV factory) → helper T-cells (T_H) decrease → immunodeficiency. Test: ELISA. Treatment: anti-retroviral drugs (not a complete cure). NACO.

13. Cancer

    Loss of contact inhibition → uncontrolled division. Benign vs malignant (metastasis). Carcinogens: X-rays, UV, tobacco smoke; oncogenic viruses; c-onc / proto-oncogenes. Detection: biopsy, CT, MRI, X-ray. Treatment: surgery, radiation, chemotherapy, α-interferon (immunotherapy).

14. Drugs & alcohol abuse

    Opioids (heroin/smack — diacetylmorphine, from Papaver somniferum), cannabinoids (Cannabis sativa — charas, ganja, marijuana; affect the cardiovascular system), coca alkaloids (cocaine — interferes with dopamine transport). Tobacco: nicotine raises adrenaline; CO reduces O₂. Adolescence (12–18 years) brings peer pressure; prevention: counselling, help from parents and teachers, recognising warning signs.

The concept in depth — the why and the how. Everything stays within the NCERT syllabus.

1. Two-host life cycle of Plasmodium

   When an infected female Anopheles bites, sporozoites enter the human blood → they first multiply in liver cells → then attack RBCs. When RBCs rupture, haemozoin is released, which causes chills and high fever every 3–4 days. Gametocytes enter the mosquito, where fertilisation and development take place, and new sporozoites are stored in the mosquito's salivary glands. Malignant malaria caused by P. falciparum is the most serious.

2. Primary vs secondary immune response

   On first encounter with a pathogen, the response is slow and of low intensity (primary). If the same pathogen comes again, the response is much faster and stronger due to memory — the secondary / anamnestic response. Vaccination and booster doses work on this logic.

3. Active vs passive — which one when?

   With a vaccine, the body makes its own antibodies → active immunity, slow but long-lasting. When immediate protection is needed — as in tetanus or snakebite — ready-made antibodies/antitoxin are given → passive immunity, immediate but short-lived. IgA antibodies in mother's milk (colostrum) also provide passive immunity. Hepatitis-B vaccine is produced in yeast using recombinant DNA technology — this links to Chapter 10.

4. How does HIV bring down the immune system?

   HIV is a retrovirus. It enters macrophages and uses reverse transcriptase to make DNA from its RNA, which gets incorporated into the host DNA — the macrophage becomes an 'HIV factory'. HIV then enters helper T-lymphocytes (T_H) and reduces their number. With fewer helper T cells, the whole immune system weakens and even minor infections become fatal. The ELISA test is used for diagnosis.

5. Cancer: where does the control break down?

   Normal cells show contact inhibition — they stop dividing when they come in contact with other cells. Cancer cells lose this property. Malignant tumour cells travel through the blood to other sites and form new tumours — metastasis. Carcinogens: ionising radiation (X-rays, gamma rays), non-ionising UV, chemicals in tobacco smoke, and oncogenic viruses (viral oncogenes); proto-oncogenes (cellular oncogenes) in normal cells can also cause cancer when activated. Treatment: surgery, radiation, chemotherapy and biological response modifiers such as α-interferon (immunotherapy).

Common confusions — cleared up

1. Innate vs Acquired immunity

   Innate is present from birth and non-specific (skin, acid, WBCs, interferons). Acquired is pathogen-specific and has memory.

2. Humoral vs Cell-mediated immunity

   Humoral = antibodies of B-lymphocytes in blood/lymph. Cell-mediated = mediated by T-lymphocytes; graft rejection in organ transplants is due to this.

3. Benign vs Malignant tumour

   Benign tumours stay confined to their original location and cause little damage. Malignant tumours grow rapidly, invade surrounding tissues and undergo metastasis.

4. Common cold vs Pneumonia

   Common cold (rhinovirus) affects the nose and respiratory passages, not the lungs. Pneumonia (Streptococcus pneumoniae, Haemophilus influenzae) infects the alveoli of the lungs.

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