Summary, key terms, extra questions with answers and a practice quiz with AI diagnosis for each.
Chapter 3: Health: The Ultimate TreasureClass 8 Science — summary, notes, extra questions & NCERT solutions
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How does the WHO define health?
Summary
This chapter treats health as far more than the absence of disease. Following the World Health Organization, it defines health as a state of complete physical, mental, and social well-being. Staying healthy depends on lifestyle and environment: eating a balanced diet, exercising, sleeping well, limiting screen time, keeping surroundings clean, and avoiding harmful substances like tobacco and alcohol. The chapter distinguishes symptoms (what we feel, such as pain) from signs (what can be seen or measured, such as fever). Diseases are grouped as non-communicable, which are linked to lifestyle, diet, or environment and do not spread (such as diabetes, asthma, and cancer), and communicable, caused by pathogens and able to spread (such as typhoid, dengue, and influenza). Pathogens spread through air, water, food, direct contact, and vectors like mosquitoes. The body fights disease using its immune system. Vaccines provide acquired immunity by training the immune system with weakened, dead, or harmless parts of a germ; Edward Jenner developed the first vaccine against smallpox, and India long practised variolation. Antibiotics treat bacterial infections only, and their misuse causes antibiotic resistance, so they must be used wisely. Prevention through hygiene, sanitation, balanced diet, and timely vaccination is emphasised.
Meaning of healthCommunicable and non-communicable diseasesSpread and prevention of diseaseImmunity and vaccinesAntibiotics and antibiotic resistance
Key terms
Health
A state of complete physical, mental, and social well-being, not merely the absence of disease.
Pathogen
A disease-causing organism such as a bacterium, virus, fungus, protozoan, or worm.
Communicable disease
A disease caused by pathogens that can spread from one person to another, such as flu or typhoid.
Non-communicable disease
A disease linked to lifestyle, diet, or environment that does not spread between people, such as diabetes.
Vaccine
A preparation that trains the immune system to recognise and fight a germ, giving acquired immunity.
Antibiotic resistance
The ability of bacteria to survive and multiply despite treatment with an antibiotic that once killed them.
Extra questions & answers
Probe and ponder
Activity 3.1: Let us read
Activity 3.2: Let us list
Activity 3.3: Let us compare
Activity 3.4: Let us find out
Activity 3.5: Let us survey
Activity 3.6: Let us read
Activity 3.7: Let us infer
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Key-term flashcards
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A state of complete physical, mental, and social well-being, not merely the absence of disease.
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Practice quiz · Health: The Ultimate Treasure
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Health: The Ultimate Treasure
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