Health: The Ultimate Treasure – Class 8 Science Chapter 3 Notes & NCERT PDF

Probe and Ponder

The chapter opens with a notice board of health news, for example: more than 100 million people in India are diabetic (ICMR report), regular handwashing reduces infection by 50%, air pollution is a leading health risk, the monsoon brings more malaria and dengue, and excessive screen time leads to dry eye disease in children.

Introduction — 3.1 Health: Is It More Than Not Falling Sick?

Activity 3.1: A Grade 8 student who moved to a new city felt lonely, spent more time on his phone and social media, stopped making friends, had headaches, lost weight and could not sleep. A doctor advised less screen time and a counsellor helped him make friends. His habits and surroundings affected his well-being.

WHO definition: Health is a 'state of complete physical, mental, and social well-being, and not merely the absence of disease'.

Our scientific heritage: Ayurveda teaches that true health is a balance of body, mind and surroundings — through dinacharya (daily routine), ritucharya (seasonal routine), fresh food suited to one's prakriti (body constitution), exercise, cleanliness, sleep, and yoga, meditation and mindfulness.

Key Concepts

3.2 How can we stay healthy?

Activity 3.2 lists good habits (personal hygiene, balanced diet, exercise, time to relax) and bad ones (too much screen time, junk food daily, sleeping late, skipping breakfast). Health depends on our lifestyle and our environment.

3.2.1 A healthy lifestyle:

3.2.2 A clean environment (Activity 3.3): a clean playground versus a dirty one full of flies and mosquitoes — people in unhygienic areas fall sick more often. Air pollution from vehicles and factories causes coughing or asthma; the Air Quality Index (AQI) tells us how clean the air is. Friends, family and laughter keep our minds healthy too.

3.3 How do we know we are unwell?

A symptom is what we feel (pain, tiredness, dizziness); a sign can be seen or measured (fever, rash, high blood pressure, swelling).

3.4 Diseases: causes and types

A disease affects the normal working of the body or mind. Disease-causing organisms — bacteria, viruses, fungi, worms, protozoa — are called pathogens.

3.4.1 How communicable diseases spread: through air (coughs, sneezes), direct contact (shaking hands), indirect contact (sharing personal items), contaminated food and water, and insects called vectors (mosquitoes, houseflies).

Activity 3.4 — some communicable diseases (from Table 3.1):

Simple precautions: keep ourselves and surroundings clean; wash hands with soap; cover mouth and nose when coughing or sneezing; wear a mask in crowds; don't share towels or handkerchiefs; keep food and water clean; stay home and rest when ill.

Worms that live inside us and feed on our nutrients are parasites.

3.4.2 Non-communicable diseases: deficiency diseases such as scurvy, anaemia and goitre (lack of specific nutrients) are also non-communicable. Diseases lasting more than 3 months — like cancer, diabetes, asthma — are chronic diseases. Diabetes is rising in adults and children; India has one of the highest numbers of diabetics in the world, due to hormonal imbalance, unhealthy eating, lack of activity, being overweight or obese, and more. Signs of diabetes (Table 3.2): frequent urination, excessive thirst, weight loss, tiredness, slow healing.

Be a scientist: Kamal Ranadive (1917–2001) studied links between hormones, certain viruses and cancer, and showed how tobacco, diet and pollution raise cancer risk.

3.5 How to prevent and control diseases?

'Prevention is better than cure.'

Activity 3.6: a community sanitation campaign in Bhadrak district, Odisha helped people build and use toilets, reducing open defecation and cases of diarrhoea and infection in children.

Immunity: the body's natural ability to fight diseases; the immune system fights against diseases.

Vaccines train the immune system to recognise and attack germs, giving acquired immunity. They are made from weakened or dead pathogens, or inactive/harmless parts of them; some newer vaccines instruct our cells to make a harmless part of the germ. A tetanus shot contains an inactivated bacterial toxin. Vaccines are preventive, not curative, and protect those around you too.

Edward Jenner (late 1700s): people who had cowpox did not get smallpox. Think like a scientist: observation (milkmaids with cowpox escaped smallpox) → hypothesis (pus of cowpox blisters protects) → experiment (injecting cowpox into a boy, who stayed well when exposed to smallpox) → application (mass vaccination; the graph shows a vaccine campaign in 1965 and smallpox eradicated by 1979).

Our scientific heritage: India's traditional variolation — using material from a smallpox sore to scratch the skin and cause a mild infection — was performed by teekedaars.

India is one of the world's largest vaccine producers and helped supply vaccines during COVID-19. Maharaj Kishan Bhan played a key role in developing the Rotavirus vaccine against diarrhoea.

3.5.1 Treatment of diseases

Antibiotics kill bacteria; they work only against bacterial infections, not viruses or protozoa.

Think like a scientist: Penicillin, the first antibiotic, was discovered in 1928 by Alexander Fleming, who noticed a mould on a discarded petri dish stopping bacteria from growing.

Antibiotic resistance: bacteria once killed by an antibiotic survive and multiply — caused by indiscriminate use, taking antibiotics when not needed, or incomplete doses; resistant bacteria spread via animals, crops, hospitals and people. Use antibiotics only when prescribed, in the correct dose, for the right duration.

Traditional systems — Ayurveda, Siddha, Unani — use herbs, oils and minerals and focus on lifestyle; they help with some conditions but may not work for all diseases and all stages. NCDs are managed with medication, lifestyle changes and rehabilitation; early diagnosis and continuous care are key.

Key Terms

Real-life Connections

Common Misconceptions

Keep the Curiosity Alive (exercise hints)