NCERT Curiosity · Class 8 · Science
Health: The Ultimate Treasure
Smallpox and polio have nearly vanished, but diabetes and heart disease are far more common now — health means more than the absence of illness.
Disease Immunity Vaccines Antibiotics
Key idea
Health is complete physical, mental, and social well-being.
According to the WHO, it's not merely the absence of disease. A healthy person can perform tasks efficiently, cope with difficulty, and adjust well with others.
Key idea
How Can We Stay Healthy

Healthy habits

A balanced diet, staying active, enough sleep, yoga, avoiding tobacco and alcohol.

A clean environment

The Air Quality Index tells us how clean the air is. Time with friends and family matters too.

Key idea
Symptoms and Signs
Symptom

What a person feels — pain, dizziness, or tiredness.

Sign

What can be seen or measured — fever, a rash, or high blood pressure.

Key idea
Communicable and Non-communicable Disease
Communicable

Caused by a pathogen, spreads person to person — typhoid, dengue, chickenpox.

Non-communicable

From lifestyle, diet, or environment, not contagious — diabetes, asthma, cancer.

Key idea
How Diseases Spread

Air

Coughing, sneezing — cold, flu, TB.

Contact

Direct or indirect touch.

Food & water

Contamination — typhoid, cholera.

Vectors

Mosquitoes — malaria, dengue.

Key idea
Immunity and Vaccines
Immunity

The body's natural ability to fight disease, carried out by the immune system.

Vaccines

Train the immune system to recognise a pathogen — preventive, not curative.

Key idea
Edward Jenner found that cowpox protected people against smallpox.
This became the world's first vaccine. India historically used variolation, carried out by teekedaars, against smallpox even before modern vaccines.
Key idea
Antibiotics, and Resistance
A lucky accident

Alexander Fleming discovered penicillin in 1928 after noticing a mould killing bacteria in a dish.

Resistance

Bacteria surviving despite treatment, often from indiscriminate use, makes infections harder to treat.

Chapter · key terms to remember
Key Terms

Health

Complete physical, mental, and social well-being.

Symptom / Sign

What's felt / what's seen or measured.

Pathogen

A disease-causing organism.

Chapter · key terms to remember
More Key Terms

Communicable disease

Caused by a pathogen, spreads person to person.

Non-communicable disease

Not caused by a pathogen; not contagious.

Immunity

The body's natural ability to fight disease.

Chapter · key terms to remember
More Key Terms

Vaccine

Trains the immune system to fight a pathogen.

Antibiotic resistance

Bacteria surviving despite antibiotic treatment.

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