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Human Health and Disease – Class 12 Biology notes, important questions and MCQs

NCERT Class 12 Biology, chapter 7. Notes, key terms, important questions with answers and MCQs.

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Chapter overview

Health is physical, mental and social well-being. Pathogens cause infectious diseases; the immune system defends the body, and vaccines, hygiene and awareness prevent disease. Cancer and drug abuse are major non-infectious concerns.

Diseases

  • Typhoid (Salmonella typhi, Widal test), pneumonia (Streptococcus), common cold (rhinovirus).
  • Malaria (Plasmodium, Anopheles female; haemozoin causes chills and fever), amoebiasis (Entamoeba), ascariasis, filariasis (Wuchereria), ringworm (fungi).
  • AIDS is caused by HIV, which attacks helper T-cells; diagnosed by ELISA.

Immunity, cancer and drugs

  • Innate immunity (barriers) and acquired immunity (B-cells make antibodies; T-cells cell-mediated).
  • Antibody structure H₂L₂; IgA, IgM, IgE, IgG; active vs passive immunity; vaccines create memory.
  • Cancer cells lose contact inhibition; carcinogens include radiation, tobacco and some viruses; drugs and alcohol damage health and need counselling and help.

Key terms

Antigen
substance that triggers an immune response
Vaccination
introducing weakened or inactivated pathogen to create memory cells
Metastasis
spread of cancer cells to distant sites

Important questions with answers

What is the difference between active and passive immunity?2 marks

Active immunity develops when the body makes its own antibodies after infection or vaccination; it is slow but long-lasting. Passive immunity comes from ready-made antibodies (colostrum, antiserum); it is fast but short-lived.

How does HIV multiply and cause AIDS?3 marks

HIV enters macrophages and helper T-cells. Its RNA is copied into DNA by reverse transcriptase and inserted into the host DNA, so infected cells make new viruses. The number of helper T-cells falls steadily, weakening immunity, so the person suffers from infections like TB and certain cancers (AIDS).

Describe the life cycle of Plasmodium in human and mosquito hosts and explain why malaria causes recurring chills and high fever.5 marks

An infected female Anopheles mosquito injects sporozoites while biting. They multiply asexually in liver cells, then enter red blood cells, multiply again and burst them. The bursting of RBCs releases haemozoin, a toxin that causes chills and high fever recurring every 3–4 days. Some parasites form gametocytes in the blood. When a mosquito bites an infected person, gametocytes enter its gut, fertilisation takes place, and new sporozoites develop and move to the salivary glands, ready to infect another person. Humans are intermediate hosts; the mosquito is the definitive host.

Quick revision

  • HIV attacks helper T-cells.
  • Widal test for typhoid.
  • Colostrum gives IgA (passive immunity).

Exam tips

  • Malaria cycle: sporozoites enter humans via mosquito bite; gametocytes are taken up by the mosquito.
  • Make a table for diseases: pathogen, mode of spread, main symptoms and prevention — this one table answers most questions.

Practice MCQs

  1. Malaria is caused by

    1. a virus
    2. a fungus
    3. a bacterium
    4. Plasmodium
    Show answer

    Answer: (d) Plasmodium. Protozoan.

  2. AIDS is caused by

    1. HPV
    2. rhinovirus
    3. hepatitis B
    4. HIV
    Show answer

    Answer: (d) HIV. Human immunodeficiency virus.

  3. Widal test is used for

    1. typhoid
    2. malaria
    3. AIDS
    4. dengue
    Show answer

    Answer: (a) typhoid. Typhoid.

  4. Antibodies are produced by

    1. T-cells
    2. platelets
    3. RBCs
    4. B-cells
    Show answer

    Answer: (d) B-cells. Humoral immunity.

  5. Elephantiasis is caused by

    1. Ascaris
    2. Entamoeba
    3. Plasmodium
    4. Wuchereria
    Show answer

    Answer: (d) Wuchereria. Filarial worm.

  6. An antibody molecule is represented as

    1. H₂L₂
    2. HL
    3. H₄L₂
    4. H₂L₄
    Show answer

    Answer: (a) H₂L₂. Two heavy, two light chains.

  7. Immunity from antibodies in colostrum is

    1. active natural
    2. innate only
    3. passive
    4. autoimmune
    Show answer

    Answer: (c) passive. Ready-made antibodies.

  8. The drug obtained from the poppy plant that is a strong painkiller is

    1. cocaine
    2. LSD
    3. cannabinoid
    4. morphine
    Show answer

    Answer: (d) morphine. Opioid.

All chapters of Class 12 Biology

Written by Kundali IQ from standard, well-established facts to help with revision. This is not an official NCERT publication; always read your textbook too.