Chapter 7 — Human Health and Disease

Chapter 7 of the Class 12 Biology NCERT textbook, "Human Health and Disease", explains immunity types, common infectious diseases such as typhoid, malaria, pneumonia and AIDS, cancer, and drug and alcohol abuse in adolescents.

• Health and infectious disease — The chapter frames health as complete physical, mental and social well-being, then surveys the pathogens — bacteria, viruses, protozoans, helminths and fungi — that cause common human diseases and how they spread.
• How the body defends itself — It explains immunity as the body's defence system, contrasting innate non-specific barriers with acquired, memory-based immunity driven by B and T lymphocytes, antibodies and vaccination.
• AIDS and cancer as cellular failures — The chapter treats AIDS and cancer as breakdowns of normal control — HIV destroying immune cells, and cancer cells losing contact inhibition to divide and metastasise under carcinogenic triggers.
• Adolescence and substance abuse — It addresses drug and alcohol abuse as a health issue especially for adolescents, linking addiction and dependence to lasting physical, mental and social harm.

1. 01Health is defined as complete physical, mental and social well-being; affected by genetic disorders, infections, and lifestyle
2. 02Immunity is of two types: innate (non-specific, present at birth with physical, physiological, cellular and cytokine barriers) and acquired (pathogen-specific, memory-based, involving B and T lymphocytes)
3. 03Malaria is caused by Plasmodium falciparum (most dangerous species) transmitted by the bite of an infected female Anopheles mosquito; the toxic substance haemozoin causes recurring chills and fever
4. 04AIDS is caused by HIV (a retrovirus) that destroys helper T-lymphocytes; it spreads through sexual contact, contaminated blood, shared needles or from infected mother to child — not by touch
5. 05Cancer arises when cells lose contact inhibition and divide uncontrollably; malignant tumours spread to distant sites via blood (metastasis) and are caused by carcinogens including radiation, chemicals and oncogenic viruses
6. 06Drug and alcohol abuse among adolescents leads to addiction, dependence, health damage (liver cirrhosis, nervous system damage) and risk of HIV/Hepatitis B through shared needles