Class 12 Biology – Human Health and Disease Notes

Class 12 Biology – Human Health and Disease Notes

1. Health and Disease

  • Health: State of complete physical, mental, and social well-being.
  • Disease: Malfunctioning of body organs or systems.
  • Diseases may be:
    • Infectious (Communicable) – Spread from person to person.
    • Non-infectious (Non-communicable) – Do not spread.

2. Causes of Diseases

A. Infectious Agents (Pathogens)

  • Viruses – e.g., common cold, AIDS
  • Bacteria – e.g., tuberculosis, typhoid
  • Fungi – e.g., ringworm
  • Protozoa – e.g., malaria
  • Helminths (worms) – e.g., ascariasis

Modes of Transmission

  • Air
  • Water and food
  • Direct contact
  • Vectors (e.g., mosquitoes)

3. Immunity

A. Innate Immunity (Non-specific)

  • Present from birth.
  • Includes:
    • Physical barriers (skin)
    • Cellular barriers (WBCs)
    • Physiological barriers (acid in stomach)

B. Acquired Immunity (Specific)

  • Develops after infection or vaccination.
  • Involves B-lymphocytes and T-lymphocytes.
  • Types:
    • Active immunity – Body produces antibodies.
    • Passive immunity – Ready-made antibodies given.

4. Vaccination and Immunization

  • Vaccine: Weakened or killed pathogen used to stimulate immunity.
  • Produces memory cells for long-term protection.
  • Example: Polio vaccine, BCG vaccine.

5. Common Diseases

A. Bacterial Diseases

  • Tuberculosis (TB) – Affects lungs.
  • Typhoid – Caused by contaminated food/water.

B. Viral Diseases

  • AIDS (Acquired Immunodeficiency Syndrome)
    • Caused by HIV.
    • Attacks immune system (T-helper cells).
    • Spread by unprotected sex, blood transfusion, infected needles.

C. Protozoan Disease

  • Malaria
    • Caused by Plasmodium.
    • Spread by female Anopheles mosquito.

6. Cancer

  • Uncontrolled cell division.
  • Caused by mutation in genes controlling cell cycle.
  • Oncogenes – Cancer-causing genes.
  • Treatment: Surgery, chemotherapy, radiation therapy.

7. Drugs and Alcohol Abuse

  • Drug abuse: Excessive use of harmful substances.
  • Effects:
    • Damage to liver, brain, and heart
    • Addiction
    • Social problems
  • Prevention: Education, counseling, awareness.

8. Prevention and Control of Diseases

  • Personal hygiene
  • Balanced diet
  • Regular exercise
  • Vaccination
  • Public awareness programs

Human Health and Disease | MCQs

  1. Health is defined as:
    a) Absence of disease
    b) Physical fitness only
    c) Complete physical, mental and social well-being
    d) Mental stability only
    Answer: c) Complete physical, mental and social well-being
  2. Diseases that spread from one person to another are called:
    a) Genetic diseases
    b) Communicable diseases
    c) Nutritional diseases
    d) Deficiency diseases
    Answer: b) Communicable diseases

2. Pathogens and Transmission

  1. Tuberculosis is caused by:
    a) Virus
    b) Bacteria
    c) Fungi
    d) Protozoa
    Answer: b) Bacteria
  2. Malaria is caused by:
    a) Virus
    b) Bacteria
    c) Protozoa
    d) Helminth
    Answer: c) Protozoa
  3. Female Anopheles mosquito transmits:
    a) Dengue
    b) Malaria
    c) Cholera
    d) Typhoid
    Answer: b) Malaria
  4. AIDS spreads through:
    a) Casual contact
    b) Mosquito bite
    c) Infected blood transfusion
    d) Air
    Answer: c) Infected blood transfusion
  5. Typhoid spreads mainly through:
    a) Air
    b) Contaminated food and water
    c) Mosquito bite
    d) Skin contact
    Answer: b) Contaminated food and water

3. Immunity

  1. Immunity present from birth is called:
    a) Acquired immunity
    b) Passive immunity
    c) Innate immunity
    d) Artificial immunity
    Answer: c) Innate immunity
  2. Antibodies are produced by:
    a) T-lymphocytes
    b) B-lymphocytes
    c) RBCs
    d) Platelets
    Answer: b) B-lymphocytes
  3. Memory cells are formed during:
    a) Innate immunity
    b) Acquired immunity
    c) Mutation
    d) Infection only
    Answer: b) Acquired immunity
  4. Vaccination provides:
    a) Passive immunity
    b) Active immunity
    c) Genetic immunity
    d) Artificial infection
    Answer: b) Active immunity
  5. Skin acts as a:
    a) Chemical barrier
    b) Cellular barrier
    c) Physical barrier
    d) Genetic barrier
    Answer: c) Physical barrier

4. AIDS

  1. AIDS is caused by:
    a) Bacteria
    b) Protozoa
    c) Virus
    d) Fungus
    Answer: c) Virus
  2. HIV attacks:
    a) RBCs
    b) T-helper cells
    c) Platelets
    d) Neurons
    Answer: b) T-helper cells
  3. AIDS stands for:
    a) Acquired Immune Deficiency Syndrome
    b) Auto Immune Disease Syndrome
    c) Acquired Infectious Disease System
    d) Acute Immune Deficiency State
    Answer: a) Acquired Immune Deficiency Syndrome

5. Cancer

  1. Cancer is caused by:
    a) Controlled cell division
    b) Uncontrolled cell division
    c) Lack of oxygen
    d) Nutrient deficiency
    Answer: b) Uncontrolled cell division
  2. Genes that cause cancer are called:
    a) Exons
    b) Introns
    c) Oncogenes
    d) Operons
    Answer: c) Oncogenes
  3. Chemotherapy is used for:
    a) Malaria
    b) Cancer treatment
    c) TB
    d) Typhoid
    Answer: b) Cancer treatment

6. Drugs and Alcohol Abuse

  1. Drug addiction primarily affects the:
    a) Liver only
    b) Heart only
    c) Brain and nervous system
    d) Bones
    Answer: c) Brain and nervous system
  2. Excessive alcohol consumption can damage the:
    a) Kidney
    b) Liver
    c) Skin
    d) Teeth
    Answer: b) Liver