Human Health and Disease – Class 12 Biology Notes | Complete NCERT Summary

 🧬 Chapter 8: Human Health and Disease – Class 12 Biology

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🔹 What is Health?

A state of complete physical, mental and social well-being.

WHO defines health as not just absence of disease.

Factors affecting health: Nutrition, environment, lifestyle, social conditions.

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🔹 Common Diseases:

A. Infectious Diseases:

Caused by pathogens (bacteria, virus, fungi, protozoa, helminths).

Examples:

Disease Causative Organism Transmission

Typhoid Salmonella typhi Contaminated food/water

Pneumonia Streptococcus pneumoniae Air (droplets)

Common Cold Rhinovirus Direct contact

Malaria Plasmodium (protozoa) Female Anopheles mosquito

Ascariasis Ascaris (worm) Contaminated food/water

Filariasis Wuchereria bancrofti Mosquito bite

📌 Important Diagram: Plasmodium life cycle in humans and mosquito

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B. Non-Infectious Diseases:

Caused by genetic, lifestyle or environmental factors.

Examples: Cancer, Diabetes, Hypertension

📌 Diagram: Difference between benign and malignant tumor cells

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🔹 Immunity

Innate Immunity – Present from birth, non-specific.

Acquired Immunity – Developed after exposure; specific.

Types of Acquired Immunity:

1. Active Immunity – Produced by own body after infection or vaccine.

2. Passive Immunity – Ready-made antibodies (e.g., anti-venom)

📌 Diagram: Chart showing active vs passive immunity

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🔹 Lymphoid Organs

Primary: Bone marrow, Thymus

Secondary: Spleen, Lymph nodes, Tonsils

📌 Diagram: Structure of lymph node and thymus

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🔹 Vaccination and Immunisation

Vaccines stimulate active immunity.

Examples: BCG (TB), DPT, Polio, MMR

📌 Diagram: Table of common vaccines and diseases prevented

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🔹 Allergies

Hypersensitive immune response.

Allergens: Dust, pollen, food items.

Involves IgE antibodies, release of histamine.

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🔹 Autoimmune Diseases

Immune system attacks body’s own cells.

Example: Rheumatoid arthritis, Type 1 diabetes.

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🔹 AIDS (Acquired Immuno Deficiency Syndrome)

Caused by: HIV virus

Transmitted via blood, sexual contact, placenta, syringes.

Targets Helper T-cells, weakens immune system.

📌 Diagram: Structure of HIV and its replication cycle

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🔹 Cancer

Abnormal uncontrolled cell growth.

Benign – Localized | Malignant – Spreads (metastasis)

Causes: Carcinogens, radiation, genetics.

Treatment: Surgery, radiation, chemotherapy.

📌 Diagram: Difference between benign and malignant tumors

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🔹 Drugs and Alcohol Abuse

Drugs: Opioids, cannabinoids, coca alkaloids (e.g., heroin, morphine, marijuana)

Effects: Hallucination, depression, liver damage, cardiac arrest.

Alcohol Abuse: Affects liver (cirrhosis), brain, coordination.

📌 Diagram: Flowchart of drug addiction cycle

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🖼️ Important Diagrams to Include:

1. Life cycle of Plasmodium

2. Structure of HIV

3. Lymphoid organs (thymus, spleen)

4. Chart of immunity types

5. Difference between active and passive immunity

6. Comparison of b

enign vs malignant tumors

7. Vaccines and diseases chart

8. Drug addiction impact cycle

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✍️ Written by: Shahid – Study with Shahid

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