Revision Notes: Class 8 Science Chapter 3 Health The Ultimate Treasure

Class 8 Science Chapter 3: Health: The Ultimate Treasure — Quick Revision Notes

• Health (WHO definition): a state of complete physical, mental and social well-being — not merely the absence of disease.
• Communicable diseases: caused by pathogens (bacteria, viruses, fungi, protozoa) and transmissible between people — e.g. flu, typhoid, chickenpox, cholera.
• Non-communicable diseases: not transmissible; linked to lifestyle, genetics or environment — e.g. diabetes, asthma, heart disease.
• Spread routes: air/droplets (flu, measles, TB), contaminated water/food/faecal-oral route (cholera, typhoid, Hepatitis A, polio), vectors like mosquitoes (malaria, dengue).
• Immunity: the body’s natural ability to resist pathogens, involving white blood cells and antibodies.
• Primary vs secondary immune response: first exposure to a pathogen triggers a slow, weak response; memory B/T cells formed during this allow a much faster, stronger response on re-exposure.
• Vaccination: trains the immune system in advance (using a weakened/dead/partial pathogen) to build memory cells, enabling a rapid response if the real pathogen is encountered.
• Antibiotics: work only against bacteria, not viruses; misuse for viral infections is ineffective and promotes antibiotic resistance.
• Prevention: combines individual habits (hygiene, diet, exercise, avoiding tobacco/alcohol, sleep) with community measures (vaccination drives, sanitation campaigns, vector control).
• Mental health link: stress and social isolation weaken immunity and contribute to non-communicable disease risk, reflecting the WHO’s broader definition of health.

Frequently Asked Questions

What is the difference between communicable and non-communicable diseases?
Communicable diseases are caused by pathogens like bacteria and viruses and can spread from one person to another, while non-communicable diseases, such as those linked to poor diet or lifestyle, do not spread between individuals.

Last Updated: September 23, 2026

Why is a balanced diet considered essential for maintaining good health?
A balanced diet supplies the body with the right proportions of carbohydrates, proteins, fats, vitamins, and minerals needed for growth, energy, and repair, and its absence can lead to deficiency diseases and weakened immunity.

Written by Satish

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