Summary
NCERT Class 12 Biology Chapter 7 covers Human Health and Disease, explaining immunity types, common infectious diseases (typhoid, malaria, pneumonia, AIDS), cancer, and drug/alcohol abuse in adolescents.
Chapter 7 of NCERT Class 12 Biology defines health as a state of complete physical, mental and social well-being, not merely the absence of disease. It covers common human diseases caused by bacteria (typhoid, pneumonia), viruses (common cold), protozoans (malaria caused by Plasmodium falciparum via female Anopheles mosquito), helminths (ascariasis, filariasis) and fungi (ringworm). The chapter explains innate and acquired immunity, B and T lymphocytes, antibodies, vaccination, allergies and auto-immunity. AIDS (caused by HIV, a retrovirus), cancer (benign vs malignant tumours, metastasis, carcinogens) and the harmful effects of drug and alcohol abuse among adolescents are also discussed in detail.
Key points & formulas
- 01Health is defined as complete physical, mental and social well-being; affected by genetic disorders, infections, and lifestyle
- 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)
- 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
- 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
- 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
- 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
Frequently asked questions
01What is the difference between innate and acquired immunity?
Innate immunity is non-specific and present from birth, providing barriers such as skin, stomach acid, phagocytic WBCs and interferons. Acquired immunity is pathogen-specific and develops after exposure; it has memory so that a second encounter with the same pathogen produces a faster, stronger response through B and T lymphocytes.
02How does the malarial parasite complete its life cycle?
Plasmodium enters the human body as sporozoites through the bite of an infected female Anopheles mosquito. It multiplies first in liver cells, then attacks red blood cells, releasing the toxin haemozoin that causes chills and fever every 3-4 days. When a mosquito bites an infected person, the parasite enters the mosquito, develops into sporozoites stored in its salivary glands, and is injected into the next human host — completing the cycle between two hosts.
03Why is AIDS fatal and how can it be prevented?
HIV destroys helper T-lymphocytes progressively, leaving the body unable to fight even minor infections. Anti-retroviral drugs can prolong life but cannot cure AIDS. Prevention includes safe sex, using only disposable needles, screening blood transfusions, and programmes by NACO and WHO to spread awareness.
04Is the NCERT Class 12 Biology Chapter 7 PDF free to download?
Yes, the NCERT Class 12 Biology Chapter 7 PDF is completely free to download on cbseprepmaster.com.
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This is the complete Biology Chapter 7 as published by NCERT — every diagram, solved example, and exercise included, free. Browse all CBSE Class 12 textbooks.
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