Class 8 › Science › Chapter 3
Health: The Ultimate Treasure
Meaning of health, healthy habits and environment, communicable and non-communicable diseases, immunity, vaccines, antibiotics and antibiotic resistance.
- A healthy person performs tasks efficiently, copes well in difficult situations, and adjusts well with peers and society.
- Activity 3.1 (lonely student): a student in a new school felt lonely, used his phone and social media more, felt worse, stopped making friends, had headaches, lost weight and slept poorly. A doctor advised less screen time and a counsellor. Lesson: habits and surroundings affect well-being; mental and social health are part of health.
- Our scientific heritage (Ayurveda): true health is a balance of body, mind and surroundings, kept by dinacharya (daily routine), ritucharya (seasonal routine) and fresh wholesome food suited to one's prakriti (body constitution), plus exercise, cleanliness, sleep, yoga, meditation and mindfulness.
- Health and happiness are closely related.
Health depends on lifestyle (how we live) and environment (our surroundings).
Healthy lifestyle
Balanced diet with fruits, vegetables and whole grains · physical activity · enough sleep · limited screen time and more time in nature · yoga and pranayama · time with family and friends · positive attitude · personal hygiene.
Unhealthy habits
Processed, fatty or sugary food and drinks · fast food every day · too much screen time · sleeping very late · skipping meals, especially breakfast · tobacco, alcohol and addictive drugs (say 'NO').
- Clean environment: a dirty, polluted place full of flies and mosquitoes makes people fall sick more often. Clean air and water are essential; air pollution from vehicles and factories causes coughing and asthma. The Air Quality Index (AQI) tells how clean the air is.
- Mental health: even with good food and a clean place we may not feel good if lonely or upset; talking, laughing and spending time with friends and family keep the mind healthy.
| Term | Meaning | Examples |
|---|---|---|
| Symptom | What we feel | Pain, tiredness, dizziness |
| Sign | Something that can be seen or measured | Fever (high temperature), rash, high blood pressure, swelling |
- Symptoms and signs show that something inside the body is not working as it should, and help doctors find the cause.
Caused by pathogens
Spread from person to person. Examples: typhoid, dengue, flu, chickenpox, COVID-19, TB, cholera, malaria.
Not caused by pathogens
Do not spread from one person to another; linked to lifestyle, diet and/or environment. Examples: cancer, diabetes, asthma, heart disease.
- NCDs (diabetes, heart disease, cancer) have become more common in India because of more processed food, less exercise and longer lives. Most deaths in India are now caused by NCDs.
- Diseases may be short-lived (acute) or chronic (lasting more than 3 months, needing regular care).
| Mode of spread | How |
|---|---|
| Air | Cough or sneeze of an infected person |
| Direct contact | Shaking hands, touching the infected person |
| Indirect contact | Sharing personal items (towels, handkerchiefs) |
| Food and water | Contaminated food or drinking water |
| Vectors | Insects such as mosquitoes and houseflies carry pathogens |
| Animals | E.g. a rabid animal |
| Disease | Pathogen | Site | Symptoms | Prevention |
|---|---|---|---|---|
| Spread through the air | ||||
| Common cold, influenza | Virus | Respiratory tract | Nasal congestion, sore throat, fever, cough, body ache | Wash hands, do not share personal items, cover mouth and nose (mask) |
| Chickenpox | Virus | Respiratory tract, skin | Mild fever, itchy skin, rashes, blisters | Isolation, cover mouth and nose, vaccination |
| Measles | Virus | Skin, respiratory tract | Fever, sore throat, reddish rashes | Isolation, cover mouth and nose, hygiene, vaccination |
| Tuberculosis (TB) | Bacteria | Lungs | Cough, fever, fatigue, loss of appetite, night sweats | Avoid close contact, cover mouth and nose, hygiene, vaccination |
| Spread through contaminated water and food | ||||
| Hepatitis A | Virus | Liver | Fatigue, fever, nausea, vomiting, jaundice, pain in upper right abdomen | Drink boiled water, vaccination |
| Cholera | Bacteria | Intestine | Diarrhoea, dehydration | Hygiene, sanitation, cooked food, boiled water, vaccination |
| Typhoid | Bacteria | Intestine | Headache, abdominal discomfort, fever, diarrhoea | Same as cholera |
| Ascariasis (roundworms) | Worms | Intestine | Worms in stool, loss of appetite, poor growth, weight loss, anaemia | Hygiene, sanitation, cooked food, boiled water |
| Transmitted by insects (vectors) | ||||
| Malaria | Protozoa | Skin, blood | High fever, profuse sweating, periodic chills | Mosquito nets and repellents, long sleeves, control mosquito breeding |
| Dengue (break-bone fever) | Virus | Skin, blood | Fever, headache, muscle and joint pain, nausea | Same as malaria; avoid areas with still water |
- General precautions: keep self and surroundings clean; wash hands with soap and water; cover mouth and nose when coughing or sneezing; wear a mask in crowds; do not share towels or handkerchiefs; keep home, food and water clean; stay home and rest when unwell to recover and avoid spreading disease.
- Parasites: organisms that live in or on another living being and feed on it (e.g. intestinal worms), spread through contaminated food, water, soil or contact with infected people or animals.
- Monsoon raises malaria and dengue cases because stagnant water lets mosquitoes breed.
| Type | Description | Examples |
|---|---|---|
| Lifestyle-related | Linked to diet, inactivity, environment | Obesity, diabetes, high blood pressure, heart disease |
| Deficiency diseases | Caused by lack of a specific nutrient in the diet (also non-communicable) | Scurvy, anaemia, goitre |
| Chronic diseases | Persist for more than 3 months | Cancer, diabetes, asthma |
- Diabetes: signs include frequent urination, excessive thirst, weight loss, tiredness and slow healing of wounds. India has one of the highest numbers of diabetics. It develops from a combination of hormonal imbalance, unhealthy eating, lack of physical activity, overweight or obesity, and other reasons.
- Obesity: manage with a balanced diet and regular exercise.
- Kamal Ranadive (1917–2001) studied links between hormones, certain viruses and cancer, and showed how tobacco, diet and pollution raise cancer risk.
- Therapy for NCDs manages symptoms and improves quality of life through medication, lifestyle changes and rehabilitation; early diagnosis and continuous care prevent complications.
- 'Prevention is better than cure.'
- Community sanitation (Bhadrak, Odisha): a community campaign led to more toilets being built and used, less open defecation, fewer cases of diarrhoea and infections: good sanitation greatly reduces spread of communicable diseases.
- Immunity: the natural ability of the body to fight diseases, carried out by the immune system. Some people fall sick more often than others in the same environment.
- Acquired immunity: protection developed after exposure to a pathogen or a vaccine.
- On meeting the same pathogen again, the immune response is stronger and faster because the body 'remembers' it from the first exposure.
- Our scientific heritage: India's traditional variolation used material from a smallpox sore to scratch the skin, causing a mild infection and building immunity; practitioners were called teekedaars.
- Vaccines are preventive, not curative: they protect before disease and do not treat someone already sick. They protect you and the people around you.
- India is one of the world's largest vaccine producers and supplied many countries during COVID-19. Maharaj Kishan Bhan (Secretary, Department of Biotechnology) helped develop the Rotavirus vaccine, which protects children from diarrhoea.
- Penicillin (1928, Alexander Fleming, London): while studying bacteria he noticed a mould on a discarded petri dish stopped bacteria from growing; the mould released a bacteria-killing substance. First antibiotic.
- Traditional medicine (Ayurveda, Siddha, Unani) uses herbs, oils and minerals and a healthy lifestyle and diet; useful for everyday well-being but may not work for all diseases and stages.
| Concept | Key point |
|---|---|
| Health (WHO) | Physical + mental + social well-being |
| Symptom / sign | Felt (pain) / seen or measured (fever, rash) |
| Communicable vs NCD | Pathogen, spreads vs lifestyle/diet/environment, does not spread |
| Vector | Insect that carries a pathogen (mosquito, housefly) |
| Immunity | Body's natural ability to fight disease; acquired immunity after exposure or vaccine |
| Vaccine | Preventive; uses dead, weakened or harmless parts of germ |
| Antibiotic | Kills bacteria only; not for viruses or protozoa |
| Resistance | Caused by misuse of antibiotics |
From 'Keep the curiosity alive'
Q1: communicable: cold and flu, typhoid, chickenpox; non-communicable: diabetes, asthma. Q2: (b) asthma and diabetes. Q7: highest July, August, September (65 each); lowest January (10); causes: monsoon rain, stagnant water, mosquito breeding. Q9: antibiotics act on bacteria, not viruses. Q10: hepatitis A, cholera and poliomyelitis (spread through faecally contaminated water).
Key names and dates
Jenner: late 1700s, smallpox vaccine · Smallpox eradicated 1979 · Fleming: penicillin, 1928 · Kamal Ranadive (cancer research) · M. K. Bhan (Rotavirus vaccine).
• Saying health only means not being ill; it includes mental and social well-being.
• Confusing symptom (felt) and sign (seen or measured).
• Saying NCDs spread from person to person; they do not.
• Saying antibiotics cure viral infections; they work only against bacteria.
• Saying vaccines treat disease; they are preventive.
• Stopping antibiotics midway; incomplete doses promote resistance.
• Calling malaria and dengue contagious by touch; they are spread by mosquito vectors.