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Human Health and Disease – Class 12 Biology Chapter 7 Notes & NCERT PDF

Class 12BiologyChapter 7NCERT book: Biology - Class 12

Notes and a simple summary of Chapter 7 of the NCERT Class 12 Biology book, with the official chapter PDF, flashcards, an MCQ quiz and an AI tutor for your doubts.

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Chapter 7: Human Health and Disease

Introduction

Early Greeks (Hippocrates) and Indian Ayurveda saw health as a balance of 'humors'. William Harvey's discovery of blood circulation and thermometer readings disproved this. Today we know the mind influences the immune system through the neural and endocrine systems. Health is affected by genetic disorders, infections and life style. Health is a state of complete physical, mental and social well-being, not merely absence of disease. Healthy people work efficiently, live longer and have lower infant and maternal mortality. Diseases are infectious (easily transmitted) or non-infectious (cancer is the major killer).

Key Concepts

7.1 Common Diseases in Humans

Disease-causing organisms are pathogens (bacteria, viruses, fungi, protozoans, helminths).

  • Typhoid: Salmonella typhi; enters the small intestine through contaminated food and water. Sustained high fever (39° to 40°C), weakness, stomach pain, constipation, headache, loss of appetite; intestinal perforation in severe cases. Confirmed by the Widal test. Mary Mallon ('Typhoid Mary') was a cook who spread typhoid as a carrier.
  • Pneumonia: Streptococcus pneumoniae and Haemophilus influenzae infect lung alveoli, which fill with fluid. Fever, chills, cough, headache; lips and nails may turn grey to bluish. Spread by droplets or shared utensils.
  • Common cold: rhino viruses infect the nose and respiratory passage, not the lungs; nasal congestion, sore throat, cough, lasting 3–7 days; spread by droplets and contaminated objects.
  • Malaria: Plasmodium (P. vivax, P. malaria, P. falciparum); malignant malaria by P. falciparum is most serious.
  • Amoebiasis: Entamoeba histolytica in the large intestine; constipation, cramps, stools with mucus and blood clots. Houseflies are mechanical carriers.
  • Ascariasis: Ascaris (roundworm); internal bleeding, muscular pain, fever, anaemia, intestinal blockage. Eggs in faeces contaminate soil, water and vegetables.
  • Filariasis/elephantiasis: Wuchereria (W. bancrofti, W. malayi); chronic inflammation of lymphatic vessels of lower limbs and genital organs; spread by female mosquito vectors.
  • Ringworm: fungi Microsporum, Trichophyton, Epidermophyton; dry scaly itchy lesions on skin, nails, scalp; thrive in heat and moisture; spread by soil, towels, combs.

    • Life cycle of Plasmodium (step by step):

  • An infected female Anopheles mosquito bites a human and injects sporozoites.
  • Parasites multiply in liver cells.
  • They attack RBCs, which rupture and release haemozoin, causing chill and high fever every three to four days.
  • Gametocytes develop in RBCs; a female Anopheles sucks them with blood.
  • Fertilisation and development occur in the mosquito's stomach wall; sporozoites form and are stored in the salivary glands.

    • The parasite needs two hosts; the mosquito is also the vector.

    Prevention: personal hygiene (clean body, water, food) and public hygiene (waste disposal, disinfecting reservoirs, hygienic catering). For vector-borne diseases, remove stagnant water, clean coolers, use nets, introduce Gambusia fish that eat larvae, spray insecticides, and fit wire mesh. Aedes mosquitoes spread dengue and chikungunya. Vaccines have eradicated smallpox and controlled polio, diphtheria, pneumonia and tetanus.

    7.2 Immunity

    The overall ability of the host to fight pathogens, conferred by the immune system.

    7.2.1 Innate immunity (non-specific, present at birth) has four barriers:

  • Physical: skin; mucus of respiratory, gastrointestinal and urogenital tracts.
  • Physiological: stomach acid, saliva, tears.
  • Cellular: PMNL-neutrophils, monocytes, natural killer cells and tissue macrophages that phagocytose microbes.
  • Cytokine: virus-infected cells secrete interferons that protect non-infected cells.

    • 7.2.2 Acquired immunity is pathogen-specific and has memory. First encounter gives a low-intensity primary response; later encounters give an intensified secondary (anamnestic) response. B-lymphocytes produce antibodies; T-cells help B cells. An antibody has two light and two heavy chains, written H₂L₂; types include IgA, IgM, IgE, IgG. Antibody-mediated response is humoral; T-lymphocytes mediate cell-mediated immunity (CMI), responsible for graft rejection. Hence tissue and blood group matching and lifelong immunosuppressants are needed after transplants.

    7.2.3 Active and passive immunity: Active immunity arises when the host makes its own antibodies after exposure to antigens (infection or vaccination); it is slow. Passive immunity comes from ready-made antibodies: colostrum rich in IgA, and antibodies crossing the placenta.

    7.2.4 Vaccination: based on immune memory. Antigenic proteins or inactivated/weakened pathogens produce antibodies and memory B and T cells. For quick protection (tetanus, snakebite) preformed antibodies or antitoxin are injected: passive immunisation. Recombinant DNA technology makes antigens in bacteria or yeast, e.g., hepatitis B vaccine from yeast.

    7.2.5 Allergies: exaggerated response to environmental allergens (dust mites, pollen, animal dander) involving IgE antibodies. Mast cells release histamine and serotonin, causing sneezing, watery eyes and breathing difficulty. Treated with anti-histamines, adrenalin and steroids.

    7.2.6 Auto-immunity: the body attacks self-cells, e.g., rheumatoid arthritis.

    7.2.7 Immune system: Primary lymphoid organs are bone marrow and thymus, where lymphocytes mature. Secondary lymphoid organs: spleen, lymph nodes, tonsils, Peyer's patches, appendix. The thymus is large at birth and shrinks by puberty. The spleen filters blood and stores erythrocytes. MALT (mucosa-associated lymphoid tissue) is about 50% of lymphoid tissue.

    7.3 AIDS

    Acquired Immuno Deficiency Syndrome, first reported in 1981; it has killed more than 25 million people. Caused by HIV, a retrovirus with an enveloped RNA genome. Transmission: sexual contact, contaminated blood, shared needles, and mother to child through the placenta. It does not spread by touch. Symptoms appear after a lag of usually 5–10 years.

    How HIV destroys immunity:

  • HIV enters macrophages; reverse transcriptase copies viral RNA into DNA.
  • Viral DNA integrates into host DNA; macrophages become an 'HIV factory'.
  • HIV enters helper T-lymphocytes (T_H), replicates, and progeny attack more T_H cells.
  • T_H numbers fall; fever, diarrhoea, weight loss follow, then infections by Mycobacterium, viruses, fungi and Toxoplasma.

    • Diagnosis: ELISA. Anti-retroviral drugs only prolong life. Prevention: safe blood, disposable needles, condoms, controlling drug abuse and awareness by NACO, NGOs and WHO.

    7.4 Cancer

    Normal cells show contact inhibition; cancer cells lose it and form tumors. Benign tumors stay localised; malignant tumors are neoplastic, invade tissue and spread through blood (metastasis, the most feared property).

  • Carcinogens: ionising radiation (X-rays, gamma rays), non-ionising UV, chemicals in tobacco smoke, and oncogenic viruses (viral oncogenes). Proto-oncogenes (c-onc) in normal cells can be activated.
  • Detection: biopsy and histopathology; blood and bone marrow tests (leukaemia); radiography, CT (3-D image using X-rays) and MRI (strong magnetic fields, non-ionising radiation); antibodies against cancer antigens.
  • Treatment: surgery, radiotherapy, chemotherapy (side effects like hair loss, anaemia) and immunotherapy with biological response modifiers such as α-interferon.

    • 7.5 Drugs and Alcohol Abuse

  • Opioids bind opioid receptors in the CNS and gut. Heroin (smack) is diacetylmorphine from acetylation of morphine from Papaver somniferum; a depressant taken by snorting or injection. Morphine is a useful sedative and painkiller after surgery.
  • Cannabinoids from Cannabis sativa inflorescences (marijuana, hashish, charas, ganja) affect the cardiovascular system.
  • Cocaine (coke, crack) from Erythroxylum coca interferes with dopamine transport; a stimulant causing euphoria and, in excess, hallucinations. Atropa belladona and Datura are hallucinogenic.
  • Tobacco: nicotine stimulates the adrenal gland to release adrenaline and nor-adrenaline, raising blood pressure and heart rate. Smoking raises blood CO, reducing haem-bound oxygen, and causes cancers, bronchitis, emphysema and heart disease.
  • Adolescence (12–18 years): curiosity, stress, peer pressure and the 'cool' image lead to abuse. Addiction is psychological attachment; rising receptor tolerance needs higher doses. Dependence shows as a withdrawal syndrome (anxiety, shakiness, nausea, sweating).
  • Effects: reckless behaviour, coma or death by overdose, AIDS and hepatitis B from shared needles, liver cirrhosis. Anabolic steroids in sports cause masculinisation in females and reduced testes, acne and baldness in males.
  • Prevention: avoid undue peer pressure; education and counselling; help from parents and peers; look for danger signs; seek professional help.

    • Diagrams to Know

  • Plasmodium life cycle: human liver and RBC stages, mosquito stomach and salivary gland stages.
  • Antibody (H₂L₂): Y-shaped with two heavy and two light chains and antigen-binding sites at the tips.
  • HIV replication: RNA → DNA by reverse transcriptase, integration, new virus release.

    • Key-Facts Sheet

  • Widal test: typhoid. ELISA: AIDS.
  • Colostrum: IgA. Allergy: IgE.
  • MALT ≈ 50% of lymphoid tissue.

    • Board Exam Focus

  • Transmission of amoebiasis, malaria, ascariasis and pneumonia.
  • Expand MALT, CMI, AIDS, NACO, HIV.
  • Differentiate innate/acquired and active/passive immunity; draw an antibody.
  • Mechanism of immune deficiency in AIDS; metastasis; harmful effects of drugs.

    • Key Terms

  • Pathogen (रोगजनक)
  • Immunity (प्रतिरक्षा)
  • Antibody (प्रतिरक्षी)
  • Antigen (प्रतिजन)
  • Vaccination (टीकाकरण)
  • Allergy (एलर्जी / प्रत्यूर्जता)
  • Auto-immunity (स्वप्रतिरक्षा)
  • Interferon (इंटरफेरॉन)
  • Metastasis (मेटास्टेसिस / दूरस्थ प्रसार)
  • Carcinogen (कैंसरजन)
  • Vector (रोगवाहक)
  • Addiction (व्यसन)
  • Withdrawal syndrome (प्रत्याहार लक्षण)

    • Common Mistakes

  • Saying common cold infects the lungs; rhino viruses affect only the nose and respiratory passage.
  • Saying HIV spreads by touch; it spreads only through body fluids.
  • Calling colostrum active immunity; it gives passive immunity.
  • Linking allergy to IgA; allergy involves IgE.
  • Confusing benign and malignant tumors; only malignant tumors metastasise.

    • 💡 Key Learning Points

    • ✓Health is complete physical, mental and social well-being; pathogens such as Salmonella, Plasmodium, Entamoeba, Ascaris, Wuchereria and ringworm fungi cause common diseases.
    • ✓Innate immunity uses physical, physiological, cellular and cytokine barriers; acquired immunity is specific, has memory, and works through B-cell antibodies (H₂L₂) and T-cell mediated responses.
    • ✓Vaccination exploits immune memory; passive immunity uses ready-made antibodies (colostrum, antitoxin); allergy (IgE) and auto-immunity are faulty immune responses.
    • ✓HIV, a retrovirus, destroys helper T cells, causing AIDS; it is diagnosed by ELISA and prevented through safe practices and awareness.
    • ✓Cancer involves loss of contact inhibition and metastasis; opioids, cannabinoids, cocaine, tobacco and alcohol cause addiction, dependence and serious health damage.

    👨‍🏫 Teaching Tips

    • →Make a disease card for each pathogen (organism, organ affected, symptoms, transmission, prevention) and have students quiz each other.
    • →Draw the Plasmodium life cycle as two linked circles (human and mosquito) and ask students to mark where fever begins.
    • →Compare the immune system to a country's defence: borders (physical barriers), police (phagocytes), trained army with records (lymphocytes and memory).
    • →Use a graph of primary versus secondary antibody response to explain why booster doses are given.
    • →Show a flow chart of HIV entering macrophages and helper T cells and ask why infections by Mycobacterium follow.
    • →Discuss drug abuse through case stories and role-play refusing peer pressure rather than lecturing.
    • →Run a quick abbreviation drill: MALT, CMI, AIDS, NACO, HIV, ELISA, PMNL, CT, MRI.

    📋 Assessment Questions

    1. Can the student name the pathogen, symptoms and mode of transmission of typhoid, malaria, amoebiasis, ascariasis and pneumonia?
    2. Can the student differentiate innate and acquired, and active and passive immunity with examples?
    3. Can the student explain how HIV causes immune deficiency?
    4. Can the student distinguish benign and malignant tumours and describe causes and detection of cancer?
    5. Can the student list effects of drug and alcohol abuse and ways to prevent it among adolescents?

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    Keep learning

    All chapters in Biology - Class 12

    1. 1. Sexual Reproduction in Flowering Plants
    2. 2. Human Reproduction
    3. 3. Reproductive Health
    4. 4. Principles of Inheritance and Variation
    5. 5. Molecular Basis of Inheritance
    6. 6. Evolution
    7. 7. Human Health and Disease
    8. 8. Microbes in Human Welfare
    9. 9. Biotechnology: Principles and Processes
    10. 10. Biotechnology and its Applications
    11. 11. Organisms and Populations
    12. 12. Ecosystem
    13. 13. Biodiversity and Conservation