NCERT Solutions for Class 8 Science Chapter 3 Health the Ultimate Treasure (PDF) – 2027

The body fights the cold virus with its immune system. The virus enters through the nose or mouth and settles in the respiratory tract. The immune system recognises it and attacks it, and this fight causes what we feel: a blocked and runny nose, a sore throat, sneezing and coughing (which throw the virus out), a mild fever, tiredness and body ache. In a few days the immune system clears the virus and remembers it.

Smallpox and polio are communicable diseases caused by viruses, so vaccines can prevent them. Mass vaccination stopped their spread: smallpox was wiped out worldwide (1979), and polio has been eliminated from India (2014) and most of the world. Diabetes and heart disease are non-communicable. No pathogen causes them, so no vaccine can prevent them. They are rising because of changes in how people live — eating more processed food, getting less exercise, and living longer lives.

Yes. Climate change can bring diseases to places and people that did not have them, and even more surely it changes where and when existing diseases strike.

• Warmer, wetter weather lets mosquitos breed for longer and in new areas such as hills, spreading malaria and dengue.
• Floods and droughts contaminate drinking water, spreading cholera, typhoid and hepatitis A.
• When people and animals are forced to move, pathogens from animals can reach people who have no immunity to them.
• Heat and air pollution make asthma and other breathing problems worse.

Stress and worry affect the body as well as the mind. Long-lasting stress disturbs sleep, changes eating habits (loss of appetite or over-eating), and brings headaches, stomach upset, tiredness and poor concentration. Poor sleep and poor diet weaken the immune system, so we catch infections more easily. That is why health includes mental and social well-being, not only physical well-being — as the story of the lonely boy in Activity 3.1 shows.

Because the pathogen may be the same for everyone, but exposure to it and the ability to resist it are not.

• Environment: crowded housing, no toilets, unsafe drinking water and standing water help diseases spread.
• Immunity: young children, elderly people and people with chronic diseases have weaker defences.
• Nutrition: people who do not get a balanced diet have weaker immunity.
• Access to care: people who miss vaccines or cannot reach a doctor early suffer more.

— questions I would ask:

• If a vaccine cannot cure a disease, why is it given to a healthy person?
• Why does the same cold virus make one member of the family ill and leave another untouched?
• Why do doctors insist that the full course of an antibiotic be finished even after the fever has gone?
• Diabetes is not caused by a germ — so why is it becoming more common in children?
• How does an insect that bites me give me a disease it never suffers from itself?
• Can loneliness really be called a health problem?
• How is the Air Quality Index measured, and what does today’s reading in my town mean for me?

The clippings show that many people in India now suffer from lifestyle-related diseases such as diabetes and obesity, linked to fast food, oily and sugary diets, too much screen time and too little exercise. Loneliness, anxiety and air pollution also harm health, and malaria and dengue cases still rise every monsoon. The clippings also show that simple habits — regular handwashing, yoga, less oil in the diet and staying fit — can prevent much of this.

No. According to the World Health Organization (WHO), health is a state of complete physical, mental, and social well-being, and not merely the absence of disease.

A healthy person takes care of the body, keeps a positive mindset, and enjoys social life with strong relationships.

The cause was loneliness, not any germ. After moving to a new city he had no friends, and his parents were busy. To cope, he spent more time on his phone and social media, which made him feel worse, and he stopped trying to make friends. The loneliness and the long hours on screens led to headaches, weight loss and poor sleep.

His surroundings created the problem and his habits made it worse — and both then damaged all three aspects of his health.

The chapter answers this in two lists — one of habits to build, one of habits to drop.

— the list extended:

— the four printed habits, with more added and the reason for each:

The playground in Fig. 3.3a — because it is clean, well-maintained and looks beautiful, while the one in Fig. 3.3b is polluted, dirty, unhygienic and full of flies and mosquitos.

A dirty playground is also unsafe: mosquitos and flies breeding there carry diseases, so people living in such areas may fall sick more often.

Yes — most of us have, standing near a rubbish fire, a busy road or a dusty construction site. It happens because clean air and water are important for our health.

• In cities, air pollution from vehicles and factories can cause problems like coughing or asthma.
• The Air Quality Index (AQI) helps us know how clean the air is on a given day.
• A cleaner environment helps us stay healthy and feel better.

On checking, the information in Table 3.1 is correct in its main points. Details worth adding:

• Malaria: the parasite enters through the skin with the mosquito bite, but it multiplies in the liver and the red blood cells.
• Tuberculosis: it mostly affects the lungs but can affect other organs too; the BCG vaccine is given to babies soon after birth.
• Cholera: its vaccine is given as drops by mouth, not as an injection.
• Influenza: a vaccine is given every year; there is no vaccine for the common cold.
• Hepatitis A, typhoid, ascariasis: washing hands with soap after using the toilet and before eating, and washing raw fruits and vegetables, also prevent them.
• Dengue: its mosquito breeds in clean, still water and bites mostly in the daytime.

Group the diseases by how they travel, and one set of steps prevents the whole group.

No. Infection is only one of the two ways a disease can arise.

Taking too much of some vitamins or minerals can also harm the body. Nutrients help only in the right amount: too little causes deficiency diseases such as scurvy, anaemia and goitre, and too much of some — for example vitamin A, vitamin D or iron — builds up in the body and can make a person unwell. So we should get them from a balanced diet and take supplements only on a doctor’s advice.

Sample answer. In most Indian neighbourhoods the three named most often are:

1. Diabetes — the chapter records that India now has one of the highest numbers of people with diabetes in the world.
2. High blood pressure (hypertension).
3. Obesity — the notice board reports that 28.6% of Indians are obese.

Health workers usually give the same first advice for all three, because the three are closely linked: a balanced diet with less oil, sugar and salt; regular physical activity; enough sleep; no tobacco or alcohol; and a check-up at regular intervals so that the condition is caught early.

The printed entries are kept and the blanks filled in. Row 4 is left for a disease you find in your own survey — asthma is used here as a sample.

That simple steps like good sanitation can greatly reduce the spread of communicable diseases — and that they work best when a whole community acts together.

Follow the chain in the Bhadrak case study:

— campaigns commonly found across India:

Because they differ in immunity — the natural ability of the body to fight diseases. The work is done by a special system called the immune system.

This ability depends on previous exposure to the pathogen or vaccination (acquired immunity), age, nutrition, sleep and stress, and whether the person already has another illness.

In the late 1700s (his experiment was in 1796), by the English doctor Edward Jenner.

Smallpox was a deadly disease that caused blisters and killed millions. A milder disease of cows called cowpox could also infect humans. Jenner discovered that people who had had cowpox did not get smallpox, and this led to the invention of the first vaccine.

Resistance develops when antibiotics are taken when they are not required, or in an incomplete dose. As Fig. 3.5b shows:

1. A few bacteria develop resistance to the antibiotic.
2. The antibiotic kills the bacteria causing illness, and also the good bacteria that protect the body from infection.
3. The resistant bacteria survive, grow and take over.
4. They transfer resistance to other bacteria, causing more problems.

The chapter states the rule directly: use antibiotics wisely — only when prescribed by a doctor, in the correct dose, and for the right duration.

Communicable: cold and flu, typhoid, chickenpox.   Non-communicable: diabetes, asthma.

(b) (ii) and (iii) — asthma and diabetes.

(i) The school should ask children with fever, cough or cold to stay at home and rest; give masks to those who are coughing and ask everyone to cover the mouth and nose; keep soap and water at every washbasin and fix handwashing times; keep windows open; stop the sharing of bottles, tiffins and towels; and clean desks, taps and door handles often.

(ii) Speak to the benchmate quietly and kindly, offer a mask or tissue, and go along to tell the teacher. Suggest sitting a little apart for now, explaining that it is only to stop the virus and not because of them, and offer to share notes.

(iii) Wash hands often with soap, wear a mask, cover the mouth and nose while coughing or sneezing, do not share personal items, eat well and sleep enough, and stay at home if you fall ill.

(i) Before: consult a doctor; pack mosquito nets, repellent and long-sleeved clothes. During: sleep under a mosquito net, apply repellent, wear long-sleeved clothes, and avoid places with still water. After: watch for high fever with chills and sweating for a few weeks; if it comes, see a doctor at once and mention the trip.

(ii) “Malaria spreads only through the bite of a mosquito. If the mosquito cannot reach your skin, it cannot give you malaria. The net keeps it away while we sleep, and the repellent keeps it away when we are outside.”

(iii) They may get malaria, which can become serious; its diagnosis may be delayed; and they may bring the disease home, where local mosquitos can spread it to others.

(i) Speak to him privately and politely: “Chachaji, I say this because I care about you. Smoking harms the lungs and the heart, and the smoke harms everyone at home too. Your friends will not suffer the illness — you will. Let us see a doctor together; I will help you quit.”

(ii) Say firmly, “No, thanks, I don’t smoke,” then change the topic or move away, and leave the party if they keep pressing. Tell a trusted adult if it happens again.

(iii) Schools can teach the harmful effects of tobacco, invite doctors to speak, keep the campus tobacco-free, run poster and street-play campaigns, provide a counsellor, and involve students in sports and clubs.

Vinita can ask:

• “Do antibiotics work against viruses, such as those that cause cold, flu and dengue, or against the protozoa that cause malaria?”
• “If antibiotics cure every infection, why does the doctor not give them for a cold?”
• “What is antibiotic resistance, and what happens when antibiotics are taken without need?”
• “Can antibiotics treat diseases like diabetes or asthma?”

These questions show Saniya that antibiotics work only against bacteria, and that their misuse makes them less effective.

(i) Highest: July, August and September — 65 cases in each of the three months.

(ii) Lowest: January — 10 cases.

(iii) July to September is the monsoon. Rainwater collects in coolers, tyres, pots, drains and potholes, where dengue mosquitos breed; warm, humid weather helps them multiply faster and live longer.

(iv) Before the monsoon: clean drains and fill potholes; run weekly “dry day” drives to empty coolers, tanks and pots; spray larvicide and carry out fogging; release larva-eating fish in ponds; supply mosquito nets and repellents; and run awareness campaigns.

My key messages, under the slogan “Clean hands, clean surroundings, healthy habits”:

Because antibiotics work only against bacterial infections, and a cold, cough or flu is caused by a virus. The medicine has nothing in the patient it can act on.

Taking antibiotics without need also kills the useful bacteria in the body and adds to antibiotic resistance, so the medicine may not work when it is really needed.

Hepatitis A, poliomyelitis and cholera.

Because after the first encounter the immune system remembers that pathogen. The second response is not a fresh start — it is a trained one.

During the first infection the immune system slowly builds a defence against that particular pathogen, and it keeps some of those defence cells. When the same pathogen enters again, they recognise it at once, so the response is quick and much stronger, and the pathogen is destroyed before it can make us ill. This is acquired immunity; vaccines work on the same principle.

— fill one row every night for at least a month:

At the end of the month, look for patterns — for example, whether days with more screen time had less sleep and a worse mood — and choose one habit to improve.

Sample notes:

• Suniti Solomon — detected the first cases of HIV infection in India (Chennai, 1986) and set up care and counselling for people living with HIV.
• Asima Chatterjee — chemist who studied the medicinal plants of India; her work helped develop medicines for epilepsy and malaria.
• Yellapragada Subbarao — biochemist who played a key role in developing medicines for cancer and filariasis, and the antibiotic aureomycin (a tetracycline).
• Mary Poonen Lukose — doctor who became the first woman Surgeon General in India (in Travancore) and worked for the health of mothers and children.

How it was done: after Jenner’s vaccine, countries ran mass vaccination campaigns; the graph on page 38 marks the vaccine campaign in 1965. Each case was found and the people around it were vaccinated, so the virus could not reach new people. Smallpox was eradicated by 1979.

Why it worked: the vaccine was effective, the disease was easy to recognise by its rash, and the virus infected only humans, so it had nowhere else to survive.

Debate (a sample view): a vaccine protects not only the person but also those who cannot be vaccinated, such as newborn babies. So everyone who can safely be vaccinated should be — with free vaccines, clear information, and exemptions only for genuine medical reasons.

Sequence of CPR for an adult (learn it on a manikin from a doctor or trained instructor):

1. Make sure the place is safe.
2. Tap the person’s shoulders and shout to check for a response.
3. Shout for help; call an ambulance (112) and ask someone to bring an AED if available.
4. Check breathing for up to 10 seconds; gasping is not normal breathing.
5. If there is no normal breathing, push hard and fast at the centre of the chest — 100 to 120 times a minute, about 5 cm deep.
6. If trained, give 2 rescue breaths after every 30 compressions; otherwise give compressions only.
7. Use the AED as soon as it arrives, and continue until trained help takes over or the person breathes normally.

The three terms, so that you can follow the discussion:

Sample questions for the doctor: Can a person be over-nourished and still be short of iron or vitamins? What does a balanced plate for our age look like? How is anaemia detected?

A health card should hold what a doctor would need in a hurry, and what you need in order to keep track over time. Keep it to one page.

Yes, fast food has ill-effects on companion animals. It has too much oil, salt and sugar; for a small animal even a small piece is a lot, and regular feeding causes obesity, digestive problems and dental disease. Some human foods, such as chocolate, onion, garlic and grapes, are even poisonous to dogs. Pets cannot choose their food, so their keepers must give them suitable, simple food.

— questions framed after reading the chapter:

• Why does a mosquito spread malaria without falling ill itself?
• When should a person with fever see a doctor instead of resting at home?
• How long does the protection given by a vaccine last?
• Where in the body do the good bacteria that antibiotics kill live?
• Why not take antibiotics to prevent infections before they happen?

— reflecting on a friend’s question, “Why not take antibiotics to prevent infections before they happen?”

I think antibiotics should not be taken without an infection. But we thought they could stop us from falling ill. Maybe they would kill some harmful bacteria, but they would also kill the good bacteria in our body and help resistant bacteria to grow. Shouldn’t it be vaccines, handwashing and clean water that prevent infections, while antibiotics are kept for treating bacterial infections that a doctor has diagnosed?