NCERT Solutions for Class 8th Science Chapter 3 Health: The Ultimate Treasure
Updated on 2026-09-19
About this chapter
Health means complete physical, mental and social well-being, not merely the absence of disease. Loneliness, stress and a polluted neighbourhood damage health just as germs do. A symptom is what we feel — pain, tiredness, dizziness. A sign is what can be seen or measured — fever, rash, high blood pressure, swelling. Communicable diseases are caused by pathogens (bacteria, viruses, fungi, worms, protozoa) and spread by air, by contaminated food and water, by direct or indirect contact, and by vectors such as mosquitos and houseflies. Non-communicable diseases — diabetes, heart disease, cancer, asthma, and deficiency diseases such as scurvy, anaemia and goitre — are not caused by pathogens. They are linked to lifestyle, diet and environment, and today cause most deaths in India. Immunity is
- Chapter opener
- Health: Is It More Than Not Falling Sick?
- How Can We Stay Healthy?
- Keep the environment clean
- How are communicable diseases caused and spread?
- How are non-communicable diseases caused?
- How to Prevent and Control Diseases?
- Ability of the body to fight diseases
- Edward Jenner and the smallpox vaccine
- Treatment of diseases
Quick revision
| Term | What it means | Example from the chapter | Key point to remember |
|---|---|---|---|
| Health | Complete physical, mental and social well-being, not merely the absence of disease (WHO) | The Grade 8 boy in Activity 3.1 had no infection, yet he was unwell | All three aspects — body, mind and relationships — must be looked after |
| Symptom | What the patient feels | Pain, tiredness, dizziness | Cannot be measured by anyone else |
| Sign | What can be seen or measured | Fever, rash, high blood pressure, swelling | This is what a doctor records |
| Pathogen | A disease-causing organism | Bacteria, viruses, fungi, worms, protozoa | All communicable diseases are caused by pathogens |
| Vector | An insect that carries a pathogen from one person to another | Mosquitos spread malaria and dengue; houseflies carry germs to food | Control the vector and you stop the disease |
| Communicable disease | A disease caused by a pathogen that can spread from person to person | Typhoid, dengue, flu, chickenpox, COVID-19 | Break the route of spread — air, water, food, contact, vector |
| Non-communicable disease (NCD) | A disease not caused by a pathogen and not passed on to others | Diabetes, heart disease, cancer, asthma | Linked to lifestyle, diet and environment; most deaths in India |
| Deficiency disease | A non-communicable disease caused by lack of a nutrient | Scurvy, anaemia, goitre (learnt in Grade 6) | Cured by correcting the diet, not by medicines alone |
| Chronic disease | A disease that persists for a long time — more than 3 months | Cancer, diabetes, asthma | Needs continuous care, not a one-week course |
| Immunity | The natural ability of the body to fight disease | The immune system recognises and attacks germs | Explains why two people in the same house fall ill differently |
| Vaccine | A preparation of dead, weakened or harmless parts of a germ that trains the immune system | Polio drops, measles, tetanus, hepatitis vaccines | Gives acquired immunity; preventive, not curative |
| Antibiotic | A medicine that kills bacteria | Penicillin, discovered by Alexander Fleming in 1928 | Useless against viruses and protozoa |
| Antibiotic resistance | Bacteria once killed by an antibiotic survive and multiply despite treatment | Caused by taking antibiotics when not required or leaving the dose incomplete | Take antibiotics only on a doctor's prescription, in full dose |
Exercises
- Chapter opener — Probe and ponder Page 28
- In-text Questions — Health: Is It More Than Not Falling Sick? Page 29
- Activity 3.1: Let us read — Health: Is It More Than Not Falling Sick? Page 29
- In-text Questions — How Can We Stay Healthy? Page 30
- Activity 3.2: Let us list — How Can We Stay Healthy? Page 30
- Activity 3.3: Let us compare — Keep the environment clean Page 31
- Activity 3.4: Let us find out — How are communicable diseases caused and spread? Page 33
- In-text Questions — How are non-communicable diseases caused? Page 35
- In-text Questions — How are non-communicable diseases caused? Page 36
- Activity 3.5: Let us survey — How are non-communicable diseases caused? Page 36
- Activity 3.6: Let us read — How to Prevent and Control Diseases? Page 37
- Ability of the body to fight diseases — In-text Questions Page 37
- Edward Jenner and the smallpox vaccine — In-text Questions Page 38
- Activity 3.7: Let us infer — Treatment of diseases Page 41
- End-of-chapter questions — Keep the curiosity alive Page 42–45
- Interdisciplinary projects: Science and Society — Discover, design, and debate Page 45