Health: The Ultimate Treasure — Class 8 Science (Curiosity)

"A state of complete physical, mental, and social well-being, and not merely the absence of disease." — World Health Organization

1. About the Chapter

This is Chapter 3 of Curiosity (pages 28–45, Reprint 2026-27). It follows directly from Chapter 2, which introduced microorganisms and promised: "We will learn about some of the diseases caused by microbes in the next chapter."

The chapter does two things in order:

1. Redefines health — not as the absence of illness, but as physical, mental and social well-being, and proves the point with a case where loneliness alone caused physical symptoms
2. Sorts every disease by one question — is a pathogen responsible? That single test decides how a disease spreads, what prevents it, and whether an antibiotic or a vaccine could possibly help

2. What Health Actually Means

Activity 3.1 makes the case before any definition is given. A Grade 8 student moved to a new school in another city. With no friends and busy parents, he felt lonely. He coped by spending more time on his phone and social media — which made him feel worse. He stopped trying to make friends, and then came headaches, weight loss, and inability to sleep.

Nothing infected him. Trace the chain:

loneliness (social) → withdrawal and low mood (mental) → more screen time (habit) → headaches, weight loss, poor sleep (physical)

What helped was less screen time, a counsellor, and help making friends. The treatment addressed the cause, not the headaches.

The WHO definition

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

A healthy person can perform tasks more efficiently, cope well in difficult situations, and adjust well with peer groups and society.

Our scientific heritage. Ayurveda teaches that true health is a balance of body, mind and surroundings — the same triad, arrived at far earlier. It recommends dinacharya (daily routine), ritucharya (seasonal routine), and food suited to one's prakriti (body constitution), supported by exercise, cleanliness, restful sleep and a calm mind, through practices like yoga, meditation and mindfulness.

3. Staying Healthy

Activity 3.2 asks you to list habits you are encouraged to follow, and habits that are not good for you.

The conclusion drawn is that health depends on lifestyle (how we live) and environment (our surroundings).

Environment

Activity 3.3 compares two playgrounds. Most people would choose the clean, well-maintained one; the other is polluted, dirty, unhygienic and full of flies and mosquitos. And the consequence is not aesthetic — people living in such areas fall sick more often, because flies and mosquitos are the vectors for diseases you will meet in Table 3.1.

Clean air and water matter. Air pollution from vehicles and factories causes coughing and asthma; the Air Quality Index (AQI) tells us how clean the air is. Contaminated water spreads cholera, typhoid, hepatitis A and ascariasis.

But health is not only about the body. "Even if we eat well and live in a clean place, we may not feel good if we are lonely or upset." Spending time with friends and family — talking, laughing, having fun — keeps the mind healthy too.

4. Signs and Symptoms

The test: could someone else check it without being told? Nobody can measure your headache; anyone can read a thermometer. Doctors need both — signs give objective evidence, symptoms give information no instrument supplies.

5. The One Question That Sorts Every Disease

A disease is a condition that affects the normal working of the body or mind, often when organs or organ systems stop functioning properly.

Pathogens are disease-causing organisms: bacteria, viruses, fungi, worms, protozoa.

Is a pathogen responsible? Yes → communicable — it spreads → prevent by blocking transmission No → non-communicable — it cannot spread → prevent by changing how you live

Why NCDs are rising in India. Three reasons: more processed food, less exercise, and longer lives. Today most deaths in India are caused by NCDs, and India has one of the highest numbers of people with diabetes in the world.

Two more categories. Deficiency diseases — scurvy, anaemia, goitre — are caused by a lack of specific nutrients, and are non-communicable. Chronic diseases persist more than 3 months: cancer, diabetes, asthma.

6. How Communicable Diseases Spread

A vector is an insect that carries a pathogen. The mosquito is not the cause of malaria — a protozoan is. The mosquito merely delivers it.

Table 3.1 — the ten diseases

Spread through the air

Spread through contaminated water and food

Transmitted by insects

Everyday precautions: keep yourself and your surroundings clean; wash hands with soap; cover mouth and nose when coughing; wear a mask in crowds; don't share personal items; keep home, food and water clean; and stay home and rest when unwell — which both helps you recover and stops you infecting others.

Worms live inside the body, especially the digestive system, and feed on our nutrients — which is why ascariasis causes poor growth and anaemia. A parasite is an organism that lives in or on another living being.

7. Immunity and Vaccination

Immunity is the natural ability of the body to fight diseases, carried out by the immune system. It varies between people — with nutrition, age, existing illness, sleep, stress, and previous exposure — which is why some fall sick more often than others in the same environment.

A vaccine trains the immune system to recognise and attack harmful germs, giving acquired immunity — protection developed after exposure to a pathogen or a vaccine. Vaccines are made from weakened or dead pathogens, inactive or harmless parts of them, or instructions for our own cells to make such a part.

Vaccines are preventive, not curative. They prevent serious disease before it happens; they do not treat someone already sick.

Jenner and the first vaccine

Our scientific heritage. Long before modern vaccines, India used variolation — scratching the skin with material from a smallpox sore to create a mild infection and build immunity. Practitioners were called teekedaars. The principle is the same as vaccination; Jenner's advance was using the far milder cowpox instead, at much lower risk.

India today is one of the world's largest vaccine producers, supplying many countries and playing a key role during COVID-19. Maharaj Kishan Bhan, as Secretary of the Department of Biotechnology, helped develop the rotavirus vaccine protecting children from diarrhoea, and worked for affordable healthcare.

Prevention works without medicine too. In Bhadrak district, Odisha, a community sanitation campaign helped more people build and use toilets, reducing open defecation and improving child health with fewer cases of diarrhoea and infections — breaking the contaminated-water route with no vaccine or drug involved.

8. Antibiotics and Resistance

Antibiotics kill bacteria. They work by targeting parts of bacterial cells that are different from human or other animal cells — which is what makes them safe for us, and also what limits them. They do not work against viruses or protozoa, which have none of those structures.

Penicillin. Discovered in 1928 by Alexander Fleming, a London bacteriologist, who noticed that a mould on a discarded petri dish had stopped bacteria growing and realised it released a bacteria-killing substance. The first antibiotic came from one microorganism killing another.

Antibiotic resistance

Bacteria that were once killed by an antibiotic survive and multiply despite it — making common infections harder to treat, with greater risk of complications, prolonged illness and death.

How it develops:

1. The antibiotic kills the harmful bacteria — and the good bacteria that protect the body
2. A few bacteria develop resistance and survive
3. Those grow and take over, their competitors having been removed
4. Some transfer resistance to other bacteria

What causes it: taking antibiotics when they are not required, or taking an incomplete dose.

How it spreads (Fig. 3.5a): through humans — between patients, via healthcare workers and dirty surfaces, then home into the community — and through animals and crops, via manure and animal faeces into soil and back through food.

The precaution: use antibiotics only when prescribed by a doctor, in the correct dose, for the right duration.

Traditional medicine. Ayurveda, Siddha and Unani use herbs, oils and minerals and stress lifestyle and diet. The chapter's own careful wording: they "can help with some conditions, and are useful for everyday well-being", but "may not be effective for all diseases and at all stages."

Treating NCDs. Since no pathogen is involved, therapy focuses on managing symptoms and improving quality of life through medication, lifestyle changes and rehabilitation. Early diagnosis and continuous care are key.

9. Summary

• Health is physical, mental and social well-being — not merely the absence of disease
• A symptom is what we feel; a sign is what can be seen or measured
• One question sorts every disease: is a pathogen responsible?
• Communicable → spreads → block the route. Non-communicable → cannot spread → change how you live
• NCDs cause most deaths in India — more processed food, less exercise, longer lives
• The route of transmission decides the precaution — a mask does nothing against cholera
• A vector carries a pathogen; the mosquito is not the cause of malaria
• Vaccines are preventive, not curative — they create acquired immunity in advance
• Antibiotics work only on bacteria, and misuse breeds resistance
• Smallpox was eradicated by vaccination in 1979; penicillin was discovered by Fleming in 1928

Appendix — What Belongs to Other Years, Not This Chapter

Notes on this chapter often expand the nutrition section into a full Grade 6 revision and then omit the disease half entirely. The chapter mentions deficiency diseases in one line — recalling scurvy, anaemia and goitre from Grade 6 as examples of non-communicable disease — but does not teach nutrition in detail.

And what such notes leave out is most of the chapter: sections 3.3, 3.4 and 3.5 — signs and symptoms, the ten diseases of Table 3.1, immunity, vaccination, Jenner, antibiotics and antibiotic resistance. That is where the marks are.