NCERT Solutions Class 8 Science Chapter 3 Health the Ultimate Treasure

F R E E S T U D Y M AT E R I A L F O R E V E R Y S T U D E N T

CLASS 8 · SCIENCE

NCERT Solutions

Chapter 3: Health: The Ultimate
Treasure

NCERT Textbook — Curiosity

BOOK PAGES SECTIONS QUESTIONS MEDIUM

28 – 45 16 45 English

Solutions, notes, sample papers & more at 57 pages

Class 8 Science Chapter 3 Health: The Ultimate Treasure AglaSem · NCERT Solutions

CLASS 8 · SCIENCE · CURIOSITY

NCERT Solutions — Chapter 3: Health: The Ultimate
Treasure
Health is not simply the absence of disease. Following the WHO, this chapter treats health as complete
physical, mental and social well-being, and then asks what actually goes wrong when we fall ill — how
communicable diseases are carried from person to person by pathogens, why non-communicable diseases
such as diabetes and heart disease are now India's biggest killers, and how immunity, vaccines and antibiotics
work.

TEXTBOOK BOOK PAGES

Curiosity (Class 8) 28 – 45

SECTIONS QUESTIONS

16 45

MEDIUM

English

Probe and ponder — Page 28
Chapter opener

PROBE AND PONDER

Q1 How does your body respond to an infection such as common cold?

The body fights back through its immune system, and almost everything we call “having a cold”
is that fight, not the virus itself.
Step by step, this is what happens:

1. The virus enters through the nose or mouth and settles in the lining of the respiratory tract.
2. The immune system recognises it as foreign and rushes blood and defence cells to the nose
and throat. The lining swells and makes extra mucus — this is the nasal congestion and
discharge and the sore throat listed in Table 3.1.
3. Sneezing and coughing throw the virus and the mucus out of the body. They are protective
actions, which is exactly why they also pass the infection on to others.
4. The body may raise its temperature. A mild fever makes conditions less comfortable for the
pathogen and makes the immune response work faster.
5. Body ache and tiredness follow because energy is being spent on the defence rather than on
ordinary work.

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Class 8 Science Chapter 3 Health: The Ultimate Treasure AglaSem · NCERT Solutions

In most people the cold clears in a few days. Afterwards the immune system remembers that
particular virus, so the same one troubles us less next time.

Why it happens: fever, running nose and tiredness are signs and symptoms — the
visible result of the immune system working. They are not the damage done by the
virus.

Tip: a cold is caused by a virus, so an antibiotic does nothing for it. Rest at home,
drink fluids, and cover the mouth and nose while coughing or sneezing so that
others are not infected.

Q2 We rarely see cases of smallpox or polio these days, but diseases like diabetes and
heart problems are more common. Why?

Because the two groups of diseases have completely different causes, and only one of them can
be stopped by a vaccine.

SMALLPOX, POLIO DIABETES, HEART DISEASE

Communicable — caused by a pathogen (a virus) Non-communicable — no pathogen is
involved

Spread from person to person Do not spread from person to person

Can be prevented by vaccination No vaccine is possible

Mass vaccination broke the chain of spread; smallpox was Linked to lifestyle, diet and environment, which
eradicated worldwide in 1979 have changed a great deal

Once enough people were vaccinated, the smallpox and polio viruses could not find new bodies
to move into, and they died out. Diabetes and heart disease work differently. The chapter names
the reasons for their rise in India: more processed food, less physical activity, and longer lives.
None of these is a germ, so no injection can protect against them.

Why it happens: a vaccine works by teaching the immune system to recognise a
pathogen. Where there is no pathogen to recognise, the immune system has
nothing to be trained against — so an NCD has to be prevented by changing how we
live, not by a shot.

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Class 8 Science Chapter 3 Health: The Ultimate Treasure AglaSem · NCERT Solutions

This is why the chapter says that today most deaths in India are caused by non-
communicable diseases, even though a century ago infections were the biggest killers.

Q3 Could climate change lead to new types of diseases?

Yes — and more certainly, it changes where and when existing diseases strike, which is already
visible in India.

Vector-borne diseases spread to new places. Mosquitos breed in warm, wet conditions.
The notice board on page 28 states that the arrival of the monsoon leads to an increase in
malaria and dengue cases. If warm, wet weather lasts longer in the year, or reaches hill areas
that were previously too cold, mosquitos survive there too — and malaria and dengue arrive
with them.
Floods and drought spoil drinking water. Flood water carries excreta into wells and pipes.
That is the route for cholera, typhoid and hepatitis A, all listed in Table 3.1.
Pathogens meet new populations. When people and animals are forced to move because
of drought, floods or changing farmland, a pathogen that lived quietly in one animal
population can reach humans who have never been exposed to it — and who therefore have
no immunity to it.
Heat and air pollution add to the load. The board calls air pollution a public health
emergency and one of the leading risk factors for health; it worsens asthma and other
breathing problems.

Why it happens: a pathogen needs a place to survive and a way to travel. Climate
decides both — the breeding season of the vector, the cleanliness of the water, and
where people and animals live. Change the climate and you change the map of the
disease.

Q4 How do emotions like stress or worry affect us and make us sick?

They act on the body, not only on the mind — which is exactly why the WHO definition of health
includes mental and social well-being alongside physical well-being.
Long-lasting stress or worry usually shows itself in this order:

1. Sleep is disturbed first. A worried mind stays alert at night, so the body does not get the
rest in which it repairs itself.

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Class 8 Science Chapter 3 Health: The Ultimate Treasure
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2. Eating changes. Some people lose their appetite and lose weight; others eat much more
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3. Physical symptoms appear — headaches, stomach upset, tiredness, difficulty in
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Activity 3.1 is exactly this story: the boy had no infection at all, yet he had headaches, lost weight

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and could not sleep. His illness began with loneliness.
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Tip: the chapter names what helps — spending time with family and friends, talking,
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speaking to a counsellor or a trusted adult is a sensible step, not a weakness.
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Environment differs. Where housing is crowded, an airborne disease passes on much

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Fig. 3.3b, mosquitos and houseflies breed and carry disease.
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Did you know? This is why public health work — building toilets, supplying clean
water, running vaccination drives — protects a whole community at once, which no
individual can do alone.

Q6 Share your questions

Frame questions of your own about health, and then find the answers from the chapter, from a
trusted health website, or from a doctor or health worker. Good questions begin with why, how,
when and what if.
Sample questions:

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?

Try this: write your questions on a slip, put them all in a box, and let the class draw
and answer one each. The questions your friends ask are usually the ones you had
not thought of.

In-text Questions — Page 29
Section 3.1 Health: Is It More Than Not Falling Sick?

Q1 What do the news clippings on the notice board tell you about people’s health in
our country?

Read together, the clippings say that the biggest health problems in India today are not
infections but the way we live and the surroundings we live in.

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Class 8 Science Chapter 3 Health: The Ultimate Treasure AglaSem · NCERT Solutions

WHAT THE CLIPPINGS REPORT WHAT IT TELLS US

11.4% of India’s population is diabetic; more than 100 million Indians Non-communicable, lifestyle-
are diabetic (ICMR); 28.6% Indians are obese; diabetes and heart attack linked diseases are now very
are more prevalent in people of South-east Asia (WHO) widespread

Fast food is one of the leading causes of diabetics; diet mantra — What we eat is directly linked to
reduce the amount of oil and sugar in diet these diseases

Increase in screen time in children leads to a rise in obesity, sleep Habits, not germs, are harming
disorders and anxiety; excessive screen watching leads to dry eye children
disease in children

Immersion into social media is spurring rise in loneliness Mental and social well-being
are part of health

Air pollution is a public health emergency; air pollution is one of the The environment decides health
leading risk factors for health too

Arrival of monsoon leads to increase in malaria and dengue cases Communicable diseases have
not disappeared — they are
seasonal

Regular handwashing reduces infection by 50%; yoga reduces anxiety Much of this is preventable by
and increases concentration; FIT INDIA MOVEMENT; reduce oil in diet simple, everyday habits
by 10%

Why it matters: notice that the clippings cover the body (diabetes, obesity), the
mind (loneliness, anxiety) and the surroundings (air pollution). That is the full WHO
idea of health appearing in a newspaper.

Q2 Is being healthy just about not having diseases?

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.

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Class 8 Science Chapter 3 Health: The Ultimate Treasure AglaSem · NCERT Solutions

Physical Mental

HEALTH

Social

Fig. 3.1 in the book: health is the overlap of physical, mental and social well-being — a person is
healthy only where all three meet.

So a healthy person is one who

takes care of the body — nutritious food, hygiene, exercise, proper sleep;
keeps a positive mindset; and
enjoys social life, with strong relationships.

Such a person can generally perform various tasks more efficiently, cope well in different and
difficult situations, and adjust well with peer groups and other members of society.

Why it happens: the three aspects feed each other. Poor sleep (physical) makes
concentration and mood worse (mental); loneliness (social) can bring headaches and
weight loss (physical), as Activity 3.1 shows. You cannot fix one and ignore the other
two.

Activity 3.1: Let us read — Page 29

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Class 8 Science Chapter 3 Health: The Ultimate Treasure AglaSem · NCERT Solutions

Section 3.1 Health: Is It More Than Not Falling Sick?

THINK AND REFLECT

Q1 What was the cause of the boy’s health problems?

The cause was loneliness — not any pathogen.
Trace the chain the passage gives:

1. He moved to a new school in another city, so he had no friends in his new environment.
2. His parents were busy, so he had little company at home either.
3. To cope, he spent more time on his phone and social media — but this made him feel
worse, not better.
4. He then stopped trying to make friends, which cut him off further.
5. The physical symptoms followed: headaches, weight loss and disturbed sleep.

Why it happens: health includes social well-being. When that part is missing, the
mind is affected, and a troubled mind shows up in the body as real physical
symptoms. Screen time did not cause the loneliness, but it replaced the thing that
would have cured it — actual company — so the problem deepened.

Note: feeling lonely after moving to a new place is common and is nothing to be
ashamed of. In the story it was solved not by medicine but by help: the doctor
advised less screen time and a counsellor, and the school counsellor arranged
support so that he could make friends. Asking for help was the step that worked.

Q2 How did his habits and surroundings affect his well-being?

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

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Class 8 Science Chapter 3 Health: The Ultimate Treasure
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Why it happens: social media looks like company but does not provide it — there is
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In-text Questions — Page 30
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Section 3.2 How Can We Stay Healthy?
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The chapter answers this in two lists — one of habits to build, one of habits to drop.

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Class 8 Science Chapter 3 Health: The Ultimate Treasure AglaSem · NCERT Solutions

WHAT WE SHOULD DO WHAT WE SHOULD AVOID

Eat a balanced diet with plenty of fruits, vegetables Processed, fatty or sugary food and drinks;
and whole grains eating fast food and other junk food every day

Stay physically active — playing outdoors, walking, Spending too much time on mobile phones or
running, cycling or exercising other digital screens

Get enough sleep so the body and mind rest and Sleeping very late or not getting enough sleep
recover

Keep yourself clean by maintaining personal hygiene Skipping meals, especially breakfast

Make time to relax or meditate every day; practise —
yoga or simple breathing exercises like pranayama

Limit screen time and spend more time in nature —

Say NO to harmful substances like tobacco, alcohol —
and addictive drugs

Keep the surroundings clean; spend time with family —
and friends

Why it happens: every item on the left strengthens one of the three aspects of
health — food and exercise the body, relaxation and sleep the mind, family and
friends the social side. Every item on the right takes time or nutrition away from one
of them.

Activity 3.2: Let us list — Page 30
Section 3.2 How Can We Stay Healthy?

ACTIVITY

Q1 List some good habits that your parents, teachers, or elders often encourage you to
follow. How many of these are already a part of your daily routine? Which ones
would you like to start following? Add to the list below: Keep yourself clean by
maintaining personal hygiene. Eat a healthy and balanced diet. Exercise regularly.
Make time to relax or meditate every day.

Start from the four habits already printed in the book, then add your own. Against each one,
mark honestly whether it is already in your routine or one you want to start.

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Class 8 Science Chapter 3 Health: The Ultimate Treasure AglaSem · NCERT Solutions

Sample answer — the list extended:

GOOD HABIT WHY ELDERS INSIST ON IT ALREADY / TO
START

Keep yourself clean by Washing hands with soap removes pathogens Already
maintaining personal hygiene before they reach the mouth

Eat a healthy and balanced diet Supplies every nutrient; prevents deficiency Already
diseases and lifestyle diseases

Exercise regularly Keeps the heart and muscles strong and helps To start
sleep

Make time to relax or meditate Reduces stress; the board on page 28 notes To start
every day yoga reduces anxiety and increases
concentration

Drink safe, boiled or filtered Prevents cholera, typhoid, hepatitis A Already
water

Sleep and wake at the same The body repairs itself during sleep To start
time every day

Eat breakfast before leaving Supplies energy for the morning; prevents Already
for school tiredness in class

Cover the mouth and nose Stops airborne diseases reaching classmates Already
while coughing or sneezing

Play outdoors for at least an Exercise plus sunlight plus company — all three To start
hour aspects of health at once

Keep the classroom and home Denies flies and mosquitos a place to breed Already
surroundings clean

Try this: pick just one habit from your “to start” column and follow it for two weeks
before adding the next. A habit kept is worth more than a long list written.

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Class 8 Science Chapter 3 Health: The Ultimate Treasure AglaSem · NCERT Solutions

Q2 Now, think about habits that are not good for your health. Add more to the list
below: Spending too much time on mobile phones or other digital screens. Eating
fast food and other junk food every day. Sleeping very late or not getting enough
sleep. Skipping meals, especially breakfast.

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

HABIT THAT IS NOT GOOD FOR WHAT IT DOES
HEALTH

Spending too much time on mobile Linked to obesity, sleep disorders, anxiety and dry eye disease;
phones or other digital screens takes away time for play and company

Eating fast food and other junk food High in oil, sugar and salt, low in the nutrients the body needs; the
every day notice board names fast food as a leading cause of diabetes

Sleeping very late or not getting The body and mind do not get time to rest and recover;
enough sleep concentration and mood suffer next day

Skipping meals, especially breakfast Leaves the body without energy for the morning; often leads to
over-eating later

Drinking sugary cold drinks instead of Adds a large amount of sugar with no other nutrient
water

Not washing hands before eating Carries pathogens straight from hands to mouth — the route for
typhoid, cholera and roundworm

Sharing towels, handkerchiefs or a Indirect contact — one of the ways communicable diseases spread
water bottle

Sitting for hours without moving Lack of physical activity is one of the reasons the chapter gives for
diabetes

Leaving water standing in pots, coolers Gives mosquitos a place to breed, bringing malaria and dengue
and old tyres home

Taking medicines, especially Breeds antibiotic-resistant bacteria (Section 3.5.1)
antibiotics, without a doctor’s advice

Why it happens: notice that these habits do not make you ill the same day. They act
slowly, which is exactly what makes them easy to ignore and hard to reverse.

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Activity 3.3: Let us compare — Page 31

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Class 8 Science Chapter 3 Health: The Ultimate Treasure
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Section 3.2.2 Keep the environment clean
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a s emat Fig. 3.3a and Fig. 3.3b. Which playground would you like to play in, and why?
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The playground in Fig. 3.3a — because it is clean, well-maintained and looks beautiful, while the
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The reason is not only that the clean one looks nicer. A dirty playground is a health risk, and the
chapter explains why:

Mosquitos breeding in standing water are vectors — they carry malaria and dengue.
Houseflies sitting on waste and then on food carry the pathogens of typhoid, cholera and
other food- and water-borne diseases.
Dust and smoke in such places make breathing difficult and can bring on coughing or
asthma.

That is why the book concludes: people living in such areas may fall sick more often.

Why it happens: keeping ourselves clean protects only us. Keeping the surroundings
clean removes the place where the vector breeds — and that protects everybody
who uses the ground. This is why the chapter puts “keep the environment clean” on
the same footing as personal hygiene.

Q2 Have you ever found it hard to breathe in a place with a lot of smoke or dust?

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.
Smoke and dust are made of tiny solid particles. When we breathe them in, the lining of the
airways is irritated. The body responds by coughing (to throw the particles out) and by
narrowing the airways, which is what makes breathing feel hard.

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.

Check it yourself: look up today’s AQI for your town. A low number means clean air;
a high number means the air carries a heavy load of particles, and outdoor exercise
is better postponed to a cleaner day.

Activity 3.4: Let us find out — Page 33

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Class 8 Science Chapter 3 Health: The Ultimate Treasure AglaSem · NCERT Solutions

Section 3.4.1 How are communicable diseases caused and spread?

ACTIVITY

Q1 Check the information listed by referring to books, trusted websites, or asking your
science teacher. Add any missing details.

Table 3.1 as printed is correct. Checked against the chapter itself, this is the verified table, with
one useful column added — the route by which each disease travels, since that is what decides
how to stop it.

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DISEASE CAUSAL SITE OF MAIN SYMPTOMS HOW IT SPREADS
AGENT INFECTION (ADDED)

Diseases spread through the air

Common cold Virus Respiratory Nasal congestion and Droplets from
and influenza tract discharge, sore throat, coughs and sneezes;
fever, cough, body ache sharing personal
items

Chickenpox Virus Respiratory Mild fever, itchy skin, Droplets in air;
tract, skin rashes, blisters contact with the
blisters

Measles Virus Skin, Fever, sore throat, Droplets in air
respiratory reddish rashes on the
tract neck, ears and other
parts of the skin

Tuberculosis (TB) Bacteria Lungs Cough, fever, fatigue, Droplets from the
loss of appetite, night cough of an infected
sweats person

Diseases spread through contaminated water and food

Hepatitis A Virus Liver Fatigue, fever, loss of Drinking water or
appetite, nausea, food contaminated
vomiting, jaundice, pain with excreta
in the upper right
abdomen

Cholera Bacteria Intestine Diarrhoea and Contaminated
dehydration drinking water and
food; flies

Typhoid Bacteria Intestine Headache, abdominal Contaminated
discomfort, fever and drinking water and
diarrhoea food

Ascariasis Worms Intestine Worms in stool, loss of Contaminated food,
(roundworms) appetite, poor growth, water or soil
diarrhoea, weight loss,
anaemia

Diseases transmitted by insects

Malaria Protozoa Skin, blood High fever, profuse Bite of a mosquito
sweating, periodic chills (vector)

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Class 8 Science Chapter 3 Health: The Ultimate Treasure AglaSem · NCERT Solutions

Dengue fever Virus Skin, blood Fever, headache, muscle Bite of a mosquito
(Break bone and joint pain, nausea that breeds in clean,
fever) still water

Why the added column matters: the causal agent tells you what the disease is; the
route tells you what to do. TB and measles are both stopped by covering the mouth;
cholera and typhoid by boiling water; malaria and dengue by removing standing
water — even though the pathogens are of four different kinds.

Note: the table lists protozoa, bacteria, viruses and worms. All four are pathogens,
and the worms live as parasites — organisms that live in or on another living being.

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Class 8 Science Chapter 3 Health: The Ultimate Treasure
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Study the table and think about what simple steps can help prevent each disease.
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Table 3.1: Some common communicable diseases affecting humans (pages 33–35).

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Class 8 Science Chapter 3 Health: The Ultimate Treasure AglaSem · NCERT Solutions

DISEASES CAUSAL SITE OF SYMPTOMS PREVENTIVE
AGENT INFECTION MEASURES

Diseases spread through the air

Common cold Virus Respiratory Nasal Washing hands
and influenza tract congestion and frequently, not
discharge, sore sharing personal
throat, fever, items, covering the
cough, body mouth and nose
ache using a mask

Chickenpox Virus Respiratory Mild fever, itchy Complete isolation
tract, skin skin, rashes, of the patient,
blisters covering the mouth
and nose,
vaccination

Measles Virus Skin, Fever, sore Isolation of the
respiratory throat, and patient, covering the
tract reddish rashes mouth and nose,
on the neck, maintaining good
ears and other hygiene, vaccination
parts of the skin

Tuberculosis Bacteria Lungs Cough, fever, Avoiding close
(TB) fatigue, loss of contact with TB-
appetite, night infected people,
sweats covering the mouth
and nose,
maintaining good
hygiene, getting
vaccinated

Diseases spread through contaminated water and food

Hepatitis A Virus Liver Fatigue, fever, Drinking boiled
loss of appetite, water, vaccination
nausea,
vomiting,
jaundice, pain in
the upper right
abdomen

Cholera Bacteria Intestine Diarrhoea and Maintain personal
dehydration hygiene and good
sanitary habits,
consumption of

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properly cooked food
and boiled drinking
water, vaccination

Typhoid Bacteria Intestine Headache, Maintain personal
abdominal hygiene and good
discomfort, sanitary habits,
fever, and consumption of
diarrhoea properly cooked food
and boiled drinking
water, vaccination

Ascariasis Worms Intestine Worms in stool, Maintain personal
(roundworms) loss of appetite, hygiene and good
poor growth, sanitary habits,
diarrhoea, consumption of
weight loss, properly cooked food
anaemia and boiled drinking
water

Diseases transmitted by insects

Malaria Protozoa Skin, blood High fever, Use of mosquito nets
profuse and repellents,
sweating, wearing long-sleeved
periodic chills clothes, control of
mosquito breeding
in and around your
home

Dengue fever Virus Skin, blood Fever, headache, Use of mosquito nets
(Break bone muscle and joint and repellents,
fever) pain, nausea wearing long-sleeved
clothes, control of
mosquito breeding
in and around your
home, avoiding
areas with still water

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

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ROUTE DISEASES SIMPLE STEPS THAT STOP THEM

Through air Common cold and Cover the mouth and nose while coughing or sneezing;
influenza, chickenpox, wear a mask in crowded places; do not share personal
measles, tuberculosis items; isolate the patient; wash hands frequently; get
vaccinated (chickenpox, measles, TB)

Through Hepatitis A, cholera, Drink boiled or safe water; eat properly cooked food;
contaminated typhoid, ascariasis maintain personal hygiene and good sanitary habits; use
water and food a toilet; wash hands before eating; get vaccinated
(hepatitis A, cholera, typhoid)

Through insects Malaria, dengue fever Use mosquito nets and repellents; wear long-sleeved
(vectors) clothes; control mosquito breeding in and around the
home; avoid areas with still water

Two steps appear against every group and are therefore the most valuable of all:

Washing hands with soap and water — the notice board records that regular handwashing
reduces infection by 50%.
Keeping ourselves and our surroundings clean.

Why it happens: a pathogen has to complete a journey — leave one body, survive
outside, and enter another. Every preventive step above breaks that journey at one
point: the mask blocks the exit, boiling kills the pathogen on the way, the net blocks
the entry, and the vaccine makes the destination body useless to it.

In-text Questions — Page 35
Section 3.4.2 How are non-communicable diseases caused?

Q1 Are diseases always caused by infections?

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

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CAUSED BY INFECTION NOT CAUSED BY INFECTION

Name Communicable (infectious) Non-communicable diseases
diseases

Cause A pathogen — bacteria, virus, Lifestyle, diet and/or environment; or lack of a
fungus, worm or protozoa nutrient

Spread Pass from one person to another Do not spread from person to person

Examples Typhoid, dengue, flu, chickenpox, Cancer, diabetes, asthma, heart disease; and the
COVID-19 deficiency diseases scurvy, anaemia and goitre

In fact, the chapter points out that in India the non-infectious group is now the larger problem:
non-communicable diseases are the most common cause of death in India.

Why it happens: a disease is any condition that affects the normal working of the
body or mind. A pathogen is one way to disturb that working — but so is a diet short
of vitamin C, or years of breathing polluted air, or a body that can no longer control
its blood sugar. No germ is needed for the working to go wrong.

In-text Questions — Page 36
Section 3.4.2 How are non-communicable diseases caused?

Q1 What will happen if I take excess amount of any of the minerals or vitamins?

Nutrients help only in the right amount. Too little causes a deficiency disease; too much can
itself make a person unwell.

AMOUNT WHAT FOLLOWS EXAMPLES

Too little Deficiency disease — a non- Scurvy (vitamin C), anaemia (iron), goitre (iodine) —
communicable disease learnt in Grade 6

Right Normal growth and normal Supplied by a balanced diet
amount working of the body

Too much The extra is either passed out Excess vitamin A can cause headache and harm the
or stored, and a stored excess liver; excess vitamin D raises calcium in the blood and
can harm can damage the kidneys; excess iron is toxic

Page 23 of 57

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Class 8 Science Chapter 3 Health: The Ultimate Treasure
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co m
m.
Why it happens: vitamins B and C dissolve in water, so a moderate excess leaves the

m l a se
body in the urine. Vitamins A, D, E and K dissolve in fat and, like most minerals, are
o
stored in.the a g amount begins
c body. Anything stored can build up, and a large stored
m
se with the organ that holds it.
l a
ag
to interfere

o m
c ag
Tip: a balanced diet with plenty of fruits, vegetables and whole grains supplies these
.
m Tablets and supplements are medicines —
s e
nutrients in the right amounts on its own.
they are worth taking only when laadoctor says a particular nutrient is short.
ag

co m
em.
comare non-communicable diseases caused?
Activity 3.5: Let us survey — Page 36
g l as
Section 3.4.2.How a
a s em
agl
ACTIVITY

om a s
. c agl
Q1 Find out the three most common lifestyle-related diseases in your neighbourhood.

s e m or even a family member who knows about
Talk to a doctor, nurse, health worker

a gla changes can help prevent or manage these
health and what kind of lifestyle
diseases.

co m
m .
as e

m l
.co a g
How to do the survey. Prepare three questions before you go: Which lifestyle-related diseases do

a s em
you see most often here? At what age do they usually begin? What change do you advise first? Speak

agl to a doctor, nurse, ASHA or anganwadi worker at the nearest health centre, and to family
m
members who manage such a condition. Note the answers without adding names — a person’s

a se
com l
illness is private. Cross-check what you hear with a trusted health website or your science
. a g
teacher.
s e m
g
Sample answer. In most Indian l aneighbourhoods the three named most often are:
a
1. Diabetes — the chapter records that India now has one of the highest numbers of people
with diabetes in the world.
co m
m .
as e
2. High blood pressure (hypertension).
m l
.co a g
3. Obesity — the notice board reports that 28.6% of Indians are obese.

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

e m
g l as
a

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m .
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Class 8 Science Chapter 3 Health: The Ultimate Treasure AglaSem · NCERT Solutions

Why the same advice fits all three: these are not separate accidents. They grow
out of the same combination of diet, activity level and stress, so a change in that
combination acts on all of them at once.

Note: lifestyle is one cause among several — the chapter itself lists hormonal
imbalances and “other reasons” alongside habits. Report what you find as a health
matter, never as anyone’s fault.

Q2 Fill in Table 3.2 and learn more about lifestyle-related diseases.
Table 3.2: Non-communicable diseases, as printed on page 36 — the blank cells are
the ones to fill in.

S. NAME OF COMMON SIGNS AND SYMPTOMS SUGGESTED
NO. LIFESTYLE-RELATED LIFESTYLE
DISEASES CHANGE(S)

1. Obesity Eating a balanced
diet and exercising
regularly

2. Diabetes Frequent urination;
Excessive thirst; Weight loss;
Tiredness; Slow healing

3. High blood pressure

4. ………………… ………………… …………………

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.

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Class 8 Science Chapter 3 Health: The Ultimate Treasure AglaSem · NCERT Solutions

S. NAME OF SIGNS AND SYMPTOMS SUGGESTED LIFESTYLE
NO. COMMON CHANGE(S)
LIFESTYLE-
RELATED
DISEASES

1. Obesity Body weight well above the healthy Eating a balanced diet and
range for one’s height and age; exercising regularly
getting breathless or tired quickly
during activity; pain in the knees
and joints; snoring and disturbed
sleep

2. Diabetes Frequent urination; excessive A balanced diet with less sugar and less
thirst; weight loss; tiredness; processed food; regular physical
slow healing activity; enough sleep; keeping body
weight in a healthy range; blood sugar
checked as the doctor advises

3. High blood Often no symptom at all — it is Less salt and less oily or processed
pressure found only when blood pressure is food; regular exercise; managing stress
measured; sometimes headache, through relaxation or yoga; enough
giddiness or breathlessness sleep; no tobacco or alcohol; blood
pressure measured at regular intervals

4. Asthma (sample) Wheezing, repeated coughing, Staying away from smoke and dust;
tightness in the chest, difficulty in keeping the home free of dust; checking
breathing — often worse in dust, the AQI before outdoor exercise;
smoke or cold air breathing exercises such as
pranayama; carrying the medicine the
doctor has prescribed

Why high blood pressure is the dangerous one: it usually gives no symptom, so it
is discovered only if someone measures it. A disease with no symptom is not a mild
disease — it is one that goes untreated. This is exactly why the chapter ends by
saying that early diagnosis and continuous care are key.

Note: obesity is a health condition, like the other three in this table. The chapter
itself explains that such conditions develop from a combination of causes — diet,
physical activity, hormonal imbalances and others — so it is described here, not
judged.

Activity 3.6: Let us read — Page 37

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Class 8 Science Chapter 3 Health: The Ultimate Treasure AglaSem · NCERT Solutions

Section 3.5 How to Prevent and Control Diseases?

ACTIVITY

Q1 What do you infer from this case study?

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:

Community campaign in Bhadrak district, Odisha

→ more people build and use toilets

→ open defecation reduced significantly

→ drinking water and soil no longer contaminated with excreta

→ fewer cases of diarrhoea and infections; child health improved

Why it happens: diseases such as cholera, typhoid, hepatitis A and roundworm all
travel the same way — from the excreta of an infected person into water, soil or
food, and then into someone’s mouth. A toilet cuts that route at the very first step,
so all of these diseases fall at once. No medicine can do that.

The second inference is just as important: one family’s toilet is not enough. Water and soil are
shared, so the campaign had to reach the whole village before the diarrhoea cases dropped.
Health is partly a community matter, not only a personal one.

Q2 Find about such community campaigns held in your location. Share in your class
and discuss with your peers about the impact of such initiatives.

How to find out. Ask at the gram panchayat or municipal ward office, the primary health
centre, or the school office; speak to the ASHA or anganwadi worker; look at the notice boards
in the health centre; and check local newspapers. For each campaign, note four things: who ran
it, what people were asked to do, how long it lasted, and what changed afterwards — the last one is
the real test.
Sample answer — campaigns commonly found across India:

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CAMPAIGN WHAT IT DOES WHICH DISEASES IT ACTS
ON

Swachh Bharat Mission Building and using toilets, clearing Cholera, typhoid, hepatitis A,
waste, cleaning drains roundworm, diarrhoea

Pulse Polio / universal Polio drops and other vaccines for Polio, measles, tetanus, hepatitis
immunisation drives every child, house to house

National Deworming Day A deworming tablet for school Ascariasis and other worm
children infections

Anti-dengue “dry day” Emptying coolers, tyres, pots and Dengue, malaria and other
drives tanks once a week mosquito-borne diseases

Fit India Movement Encouraging daily physical activity, Non-communicable diseases —
yoga and a balanced diet obesity, diabetes, heart disease

Discuss: which of these needed everyone to take part before it could work, and which
helped even the one family that followed it? You will find that the sanitation and
mosquito drives need the whole community, while vaccination and exercise also help
the individual directly.

In-text Questions — Page 37
Ability of the body to fight diseases

Q1 You would have noticed that some people get sick more frequently than others,
although living in a similar environment. Do you know why?

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.
Two people can breathe the same air and drink the same water, and still fall ill differently,
because the immune system is not equally strong or equally prepared in both:

Previous exposure. Someone who has already met that pathogen — or been vaccinated
against it — has acquired immunity and fights it off before it can cause illness.
Age. Very young children and elderly people have weaker defences.
Nutrition. A balanced diet is what the immune system is built from; a body short of
nutrients cannot maintain it.
Sleep, exercise and stress. These decide how well the body repairs itself, as Activity 3.1
showed.

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An existing illness. A person already living with a chronic disease has less in reserve to
co m
spend on a new infection.
em.
m l as
.co a g
s em
Why it happens: falling ill is not decided by the pathogen alone. It is the result of a
a
gl — the number of pathogens that get in, against the strength of the immune
acontest
system that meets them. Change either side and the outcome changes.

co m
em . ag
g l as
In-text Questions — Page 38a

m
Edward Jenner and the smallpox vaccine

co
em.
m l as
.co g
Do you know when the first vaccine was discovered?
a
Q1

a s em
a l
gANSWER
s
In the late 1700s, by the English doctor Edward Jenner.
m a
.co
Smallpox was a deadly disease that caused blisters and killed millions. A milder disease of cows
em agl
a s
called cowpox could also infect humans. Jenner discovered that people who had had cowpox

aglto the invention of the first vaccine.
did not get smallpox, and this led
The way he reached it is a model of scientific work:

c o m
Milkmaids who had cowpox did not catch smallpox — likelym .
Observation
m a s e because the two

. co agl
viruses are related

m
seHypothesis
l a
ag
Content in the pus of cowpox blisters protected people from smallpox

Experimentation He injected cowpox sap into a boy, who later showed no illness when exposed to
se m
smallpox
com g l a
m . a
Results
gl ase
People infected with cowpox sap were now resistant to smallpox

Application
a
Mass vaccination eventually helped eradicate smallpox worldwide

co m
m .
se
The graph on page 38 shows how completely this worked. The number of countries reporting

o m l a
g at 1979.
c The vaccine campaign is marked at 1965 and eradication
smallpox fell from about 80 in 1950 to around 40 by the late 1960s, and then dropped steeply
to.zero. a
se m
a
agl c
Our scientific heritage: long before Jenner, India had a traditional method called
m .
m a s e
agl
variolation. Material from a smallpox sore was used to scratch the skin, creating a
. co
e m
mild infection that built immunity. The people who performed this practice were
known as teekedaars.
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a

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Class 8 Science Chapter 3 Health: The Ultimate Treasure AglaSem · NCERT Solutions

Why it happens: the cowpox virus is closely related to the smallpox virus. The
immune system, trained on the harmless relative, recognises the dangerous one
when it arrives — which is the whole principle on which every vaccine since has been
built.

Activity 3.7: Let us infer — Page 41

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Class 8 Science Chapter 3 Health: The Ultimate Treasure AglaSem · NCERT Solutions

Section 3.5.1 Treatment of diseases

ACTIVITY

Q1 Study the infographic given in Fig. 3.5b. How do you think the antibiotic resistance
has been developed in bacterial pathogens?

HOW BACTERIA BECAME RESISTANT TO ANTIBIOTICS?

When antibiotics kill
bacteria causing Some bacteria transfer
Few bacteria develop The antibiotic
illness, they also antibiotic resistance
resistance to resistant bacteria
kill good bacteria to other bacteria,
antibiotics. grow and take over.
protecting the body causing more problems.
from infection.

I need antibiotic for my mother. Are you giving antibiotics to your No… No. Do not give antibiotic
She has a sore throat and a fever. cattle? injection to your cattle.

You must get a prescription from a No. I am not using any It will develop antibiotic
doctor. antibiotics. resistance otherwise.

Fig. 3.5 (b), page 41 — the infographic, redrawn.

It develops through the four steps shown in Fig. 3.5b, and it begins with something we do:
taking antibiotics when they are not required, or taking an incomplete dose.

1. A few bacteria develop resistance to antibiotics. In any large population of bacteria a
small number happen to be able to survive the medicine.
2. When antibiotics kill the bacteria causing illness, they also kill the good bacteria that
protect the body from infection. The space and food that those bacteria were using is now
free.
3. The antibiotic-resistant bacteria grow and take over. With their competitors removed, the
few survivors multiply into the majority.

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Class 8 Science Chapter 3 Health: The Ultimate Treasure AglaSem · NCERT Solutions

4. Some bacteria transfer antibiotic resistance to other bacteria, causing more problems.
Resistance now spreads sideways, to kinds of bacteria that were never treated at all.

Why it happens: the antibiotic does not make bacteria resistant. It removes every
bacterium that is not resistant, and so leaves the field to those that are. An
incomplete dose is the worst case of all — enough medicine to wipe out the sensitive
bacteria, not enough to finish the tougher ones, which then multiply undisturbed.

Fig. 3.5a adds the routes by which these resistant bacteria then reach everyone else: from
antibiotics given to animals into animal food products; from manure and animal faeces into
crop fields and so into our digestive system through crop produce; and from patient to patient
in hospitals through dirty surfaces and healthcare workers, and then out into the community
when patients go home.
The result, as the chapter says, is that bacteria that were earlier killed by a given antibiotic
survive and multiply despite treatment — which makes common infections harder to treat
and increases the risk of complications, prolonged illness and even death.

Q2 What precautions may be taken to reduce antibiotic resistance?

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

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PRECAUTION WHY IT WORKS

Take an antibiotic only when a doctor prescribes it Removes the commonest cause — taking
antibiotics when they are not required

Complete the full course, even after feeling better Kills the tougher bacteria too, instead of leaving
them to multiply

Take the correct dose for the right duration A part-dose selects for resistance rather than
curing the infection

Never take an antibiotic for a cold, cough or flu These are viral — the antibiotic cannot help, and
only breeds resistance

Do not use someone else’s leftover medicine, and do The dose and the medicine were chosen for a
not share your own different infection

Do not give antibiotic injections to cattle without Resistant bacteria from animals reach us through
veterinary advice (Fig. 3.5b) food products and manure

Prevent infection in the first place — handwashing, An infection that never happens needs no
clean water, masks, vaccination antibiotic at all

Keep hospital surfaces and hands clean Blocks the spread of resistant bacteria from
patient to patient

As the chapter puts it, avoiding unnecessary use helps prevent the rise of resistant bacteria
and keeps antibiotics effective for future generations.

Did you know? Penicillin, the first antibiotic, was discovered in 1928 by Alexander
Fleming, a bacteriologist in London, when he noticed that a mould on a discarded
petri dish had stopped bacteria from growing. Antibiotics have saved millions of lives
since — which is exactly why they are worth protecting.

Keep the curiosity alive — Pages 42–45

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End-of-chapter questions
co m
e m.
m as
KEEP THE CURIOSITY ALIVE

.co a g l
a s em the diseases shown in the images as communicable or non-communicable.
gl
Group
a
Q1
Cold and flu, Typhoid, Diabetes, Asthma, Chickenpox

co m
e m . ag
g l as
a

co m
se m.
com l a
Cold and flu Typhoid Diabetes Asthma Chickenpox

. ag
m
ase
agl
Page 42 — the five pictures printed with the question, redrawn sketches.

m a s
m.co agl
se

g l a
DISEASE GROUP a CAUSE DOES IT SPREAD?

co m
.
Cold and Communicable Virus, in the respiratory tract Yes — through air, in droplets
flu
se m
from coughs and sneezes

com l a
m . agYes — through contaminated
ase
Typhoid Communicable Bacteria, in the intestine

agl
water and food

se m
Diabetes Non- Hormonal imbalance together No

com
with lifestyle factors
l a
communicable

. a g
m
ase
agl
Asthma Non- Linked to environment, especially No
communicable smoke, dust and polluted air

m
Chickenpox Communicable Virus, in the respiratory tract and Yes — through air and through
skin
. co
contact with the blisters

e m
m l as
m .co a
Communicable: cold and flu, typhoid, chickenpox. Non-communicable: diabetes, asthma. g
l a se
ag
c
Why it happens: the test is not how serious the disease is or how long it lasts — it is
m .
whether a pathogen causes it. A pathogen can travel to another body, so the
a s e
. com
disease is communicable. Diabetes and asthma have no pathogen to travel, so
agl
a s emno one catches it from them.
however unwell a person is,

agl

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Q2 Diseases can be broadly grouped into communicable and non-communicable
diseases. From the options given below, identify the non-communicable diseases. (i)
Typhoid (ii) Asthma (iii) Diabetes (iv) Measles (a) (i) and (ii) (b) (ii) and (iii) (c) (i) and
(iv) (d) (ii) and (iv)

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

DISEASE CAUSED BY GROUP

(i) Typhoid Bacteria — spread through contaminated water and food Communicable

(ii) Asthma Environment and lifestyle — no pathogen Non-communicable

(iii) Diabetes Hormonal imbalance and lifestyle — no pathogen Non-communicable

(iv) Measles Virus — spread through air Communicable

Why the other options fail: every one of them includes typhoid or measles, and
both of these are caused by pathogens and pass from person to person.

Q3 There is a flu outbreak in your school. Several classmates are absent, while some
are still coming to school coughing and sneezing. (i) What immediate actions should
the school take to prevent further spread? (ii) If your classmate, who shares the
bench with you, starts showing symptoms of the flu, how can you respond in a
considerate way without being rude or hurtful? (iii) How can you protect yourself
and others from getting infected in this situation?

(i) Immediate actions by the school. Flu spreads through air, so every step must block
droplets:

Inform parents at once, and ask that any child with fever, cough or cold stay at home and
rest until well — the chapter notes this both helps recovery and minimises spreading the
disease.
Provide masks for anyone who is coughing or sneezing, and ask everyone to cover the
mouth and nose.
Make soap and water available at every washbasin and set fixed handwashing times —
before the mid-day meal and after games.
Keep classrooms well ventilated, with windows open.
Stop the sharing of water bottles, tiffins, handkerchiefs and towels.

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Clean frequently touched surfaces — door handles, desks, taps, sports equipment.
Move a child who falls ill during the day to a separate room and call the parents; postpone
crowded assemblies and large gatherings.
Inform the local health authority if the number of cases keeps rising.

(ii) Responding to your benchmate considerately. The aim is to protect both of you without
making your friend feel blamed or shunned.

Say it quietly and kindly: “You don’t look well — shall we tell Ma’am?” Do not announce it to
the class.
Offer a tissue or a spare mask, and offer to walk with them to the school nurse or the office.
Suggest sitting a little further apart for the day, and explain why — so that they know it is
about the virus, not about them.
Offer to share your notes and to call them in the evening. Being ill at home is lonely.
Never move away with a face of disgust, never tease, and never call anyone the “source” of
the outbreak. Anyone can catch flu; it says nothing about the person.

(iii) Protecting yourself and others.

Wash hands with soap and water frequently, and avoid touching your eyes, nose and mouth
with unwashed hands.
Wear a mask in the classroom while the outbreak lasts.
Cover your own mouth and nose when you cough or sneeze — with a tissue or your sleeve,
not your palm.
Do not share bottles, tiffins or handkerchiefs.
Keep the windows open; sit in fresh air during breaks.
Eat a balanced diet and get enough sleep, so your immune system is at its strongest.
If you develop symptoms, stay at home. That is the single most effective thing you can do for
the rest of the class.

Why it happens: flu is airborne. Each step above cuts the journey at one point — the
mask and the tissue at the exit, ventilation in the air, handwashing on surfaces, and
staying home at the source.

Q4 Your family is planning to travel to another city where malaria is prevalent. (i) What
precautions should you take before, during, and after the trip? (ii) How can you
explain the importance of mosquito nets or repellents to your sibling? (iii) What
could happen if travellers ignore health advisories in such areas?

Malaria is caused by a protozoa and reaches us only through the bite of a mosquito, which acts
as the vector. Every precaution therefore aims at one thing: do not get bitten.

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(i) Precautions

BEFORE THE TRIP DURING THE TRIP AFTER THE TRIP

Find out whether malaria is Sleep under a mosquito net Watch for high fever, profuse
prevalent there and in which every night sweating and periodic chills
season; consult a doctor about what for the next few weeks
to carry

Pack mosquito nets and repellents, Apply repellent, especially If such fever appears, see a
and long-sleeved clothes and full- around dusk and dawn doctor at once and tell the
length trousers doctor where you travelled

Check that windows of the place you Wear long-sleeved clothes Complete the full course of any
will stay in have screens, or carry a in the evening medicine prescribed
net

— Avoid places with still water; Clear any standing water
do not let water collect around your own home too
around where you stay

(ii) Explaining it to a younger brother or sister. Keep it simple and true:

“Malaria does not spread by sitting next to someone or by breathing the same air. It
comes only from the bite of one particular kind of mosquito. That means if the
mosquito cannot reach your skin, the disease cannot reach you at all. The net is a
wall around your bed and the repellent is a smell the mosquito will not come near —
and there is no third way for it to get in.”

Make it a shared job rather than an order: let the child tuck in the net, and let them be the one
who spots and empties any standing water in pots, coolers or old tyres.
(iii) If travellers ignore health advisories.

They are far more likely to be bitten and to develop malaria — high fever, chills and profuse
sweating — which can become serious enough to need hospital care.
Diagnosis is often delayed, because a doctor back home may not think of malaria unless the
travel is mentioned. Delay makes the illness worse.
They can carry the disease home. If a local mosquito bites an infected traveller, it can pass
the parasite on to others — so one person’s carelessness becomes a risk to a whole
neighbourhood.
The same neglect — drinking unsafe water, ignoring standing water — also invites dengue,
typhoid and cholera on the same trip.

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Why it happens: a vector-borne disease has exactly one doorway. Health advisories
are simply instructions for keeping that one doorway shut, which is why ignoring
them is so much more costly here than it looks.

Q5 Your uncle has started smoking just to fit in with his friends, even though it is well
known that smoking can seriously harm health and even cause death. (i) What
would you say to him to make him stop, without being rude? (ii) What would you do
if your friend offers you a cigarette at a party? (iii) How can schools help prevent
students from indulging in such harmful habits?

(i) What to say to your uncle. Speak privately, respectfully, and from concern rather than
accusation. An elder who feels attacked stops listening.

Begin with the relationship, not the habit: “Chachaji, I am telling you this only because I want
you with us for a long time.”
Give one or two facts rather than a lecture. Tobacco is named in the chapter among the
harmful substances we should say NO to. Smoking damages the lungs and the heart, and it
makes infections such as tuberculosis harder to fight.
Mention that the smoke reaches whoever is in the room — children and elders at home
breathe it too.
Point to the reason he started. Fitting in with friends is a poor bargain if the price is his
health, and his friends will not be the ones who suffer it.
Offer help instead of judgement: go with him to a doctor, or look up the national tobacco
quitline together. Quitting is hard because tobacco is addictive, so treat every attempt as
progress and never mock a relapse.

(ii) If a friend offers you a cigarette.

Refuse plainly and without drama: “No thanks, I don’t smoke.” A short answer is stronger
than a long explanation, and you owe no one a justification.
Move on — change the topic, take a drink of water, join another group. If the pressure
continues, leave the party.
Decide your answer before you are in the situation. Peer pressure works on hesitation, and a
ready sentence removes it.
Tell a parent, teacher or another trusted adult if this keeps happening, especially if others in
your class are being pushed the same way.

Notice that this is exactly what happened to your uncle. Refusing once, early, is far easier than
stopping later.
(iii) How schools can help.

Teach the facts clearly in class, and invite a doctor to speak and answer questions.

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Class 8 Science Chapter 3 Health: The Ultimate Treasure
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Keep the school and its surroundings tobacco-free, and take up with the authorities any
co m
shop selling tobacco to minors near the gate.
se m.
c o m l a
g than one from a
it .to one another — a message from a classmate carries further
Run poster competitions, debates, street plays and health campaigns so that students
explainm a
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Provide a counsellor whom students can talk to privately and without fear of punishment, as

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Offer sports, music, clubs and NSS-type activity, so that students have a group to belong to

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without needing a harmful habit as the entry ticket.
Involve parents, so that the same

co m
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Why it happens: almost nobody starts smoking for the taste. People start to belong

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somewhere. That is why a school that gives every student a place to belong prevents
more .harm a g
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Saniya claims to her friend Vinita that “Antibiotics can cure any infection, so we
.
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s e m What question(s) can Vinita ask her to help
don’t need to worry about diseases.”
astatement is incorrect?
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Saniya understand that her

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m l
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as that was not needed, or stops the course halfway?”
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their effectiveness. So the sentence is wrong twice over — antibiotics cannot cure any infection,
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and relying on them makes them less useful for everyone.

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Tip: a good counter-question does not tell the other person they are wrong. It hands
them one fact they already accept and lets them see the contradiction themselves.

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Class 8 Science Chapter 3 Health: The Ultimate Treasure AglaSem · NCERT Solutions

Q7 The following table contains information about the number of dengue cases
reported in a hospital over a period of one year: January 10, February 12, March 15,
April 18, May 22, June 40, July 65, August 65, September 65, October 30, November
30, December 20. Make a bar graph of the number of cases on the Y-axis and the
month on the X-axis. Critically analyse your findings and answer the following: (i) In
which three months were the dengue cases highest? (ii) In which month(s) were the
cases lowest? (iii) What natural or environmental factors during the peak months
might contribute to the increase in dengue cases? (iv) Suggest a few preventive
steps that the community or government can take before the peak season to
reduce the spread of dengue.
The table as printed on page 44:

S. NO. 1 2 3 4 5 6

Month January February March April May June

No. of 10 12 15 18 22 40
dengue
cases

S. NO. 7 8 9 10 11 12

Month July August September October November December

No. of 65 65 65 30 30 20
dengue
cases

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Class 8 Science Chapter 3 Health: The Ultimate Treasure AglaSem · NCERT Solutions

70
65 65 65
60
Number of dengue cases

50
40
40
30 30
30
22
20
20 18
15
12
10
10

0
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Month

Dengue cases reported in the hospital, month by month. The three red bars are the peak months.

(i) Highest: July, August and September — 65 cases in each of the three months.
(ii) Lowest: January — 10 cases.

Total cases in the year = 10 + 12 + 15 + 18 + 22 + 40 + 65 + 65 + 65 + 30 + 30 + 20

= 392

Cases in July + August + September = 65 + 65 + 65 = 195

Share of the year in three months = 195 ÷ 392 ≈ 0.50, that is about half the year’s cases in

one quarter of the year

(iii) Natural and environmental factors in the peak months. July to September is the
monsoon and the weeks just after it.

Rainwater collects and stands — in old tyres, pots, coolers, tanks, discarded containers,
blocked drains and potholes. The dengue mosquito breeds in exactly this kind of clean, still
water, and the chapter’s own preventive measure is to avoid areas with still water.
Warm and humid weather lets the mosquito complete its life cycle faster and lets the
adults live longer, so far more of them are biting.
Waterlogging and poor drainage after heavy rain create breeding sites everywhere at
once.
There is a lag between the rain and the cases: eggs must hatch, mosquitos must mature and
bite, and the illness must develop. That is why the count climbs through June (40) and only
peaks from July.

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By October the rain stops, the water dries up and the temperature falls — and the count
halves, from 65 to 30.

(iv) Preventive steps before the peak season. The value of the graph is that it shows the peak
arriving at the same time every year, so it can be prepared for.

Clean and desilt drains, and fill in potholes and low ground, before the monsoon.
Run a weekly “dry day” campaign — every household empties and scrubs coolers, tanks,
pots and tyres once a week, which destroys the larvae before they become adults.
Fogging and larvicide spraying in the localities that reported cases last year.
Release larvivorous fish in ponds, tanks and ornamental pools.
Distribute or subsidise mosquito nets and repellents, and encourage full-sleeved clothing.
Awareness drives through schools, health workers, radio and posters at the start of the
rains.
Ask health centres to report suspected cases early, so that a cluster is spotted before it
becomes an outbreak, and ensure hospitals are stocked and staffed for the peak weeks.

Why prevention must come first: there is no medicine that kills the dengue virus.
The whole defence rests on stopping the mosquito from breeding and from biting —
which is work that has to be done in May and June, not in August.

Q8 Imagine you are in charge of a school health campaign. What key messages would
you use to reduce communicable and non-communicable diseases?

A campaign works when each message is short, specific and something a student can do the
same day. I would run it under one slogan — “Clean hands, clean surroundings, healthy
habits” — with two sets of messages, because the two kinds of disease are stopped in two
different ways.

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co m
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TO REDUCE COMMUNICABLE DISEASES WHY THIS MESSAGE

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Wash your hands with soap before eating and after using
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Regular handwashing reduces infection by

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gl your mouth and nose when you cough or sneeze;
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wear a mask in a crowd measles, TB

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TO REDUCE NON-COMMUNICABLE
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occasion, leading causes of diabetes

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diabetes the chapter lists

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Do not skip breakfast Supplies energy for the school day

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the first time

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How I would run it: a health board updated weekly by students; a two-minute demonstration

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agl monthly count — of absences due to illness — so the school can
corridor and garden for standing
answer questions; and a simple
see whether the campaign is working.

co m
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Tip: end every message with an action, not a warning. “Empty your cooler on
Sunday” changes behaviour; “dengue is dangerous” does not.

Q9 It is recommended that we should not take an antibiotic for a viral infection like a
cold, a cough, or flu. Can you provide the possible reason for this recommendation?

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.

Why it happens: antibiotics work by targeting parts of bacterial cells that are
different from human or other animal cells — that is precisely what makes them
safe for us and deadly for bacteria. A virus has no such parts. It is not even a cell of
its own; it multiplies inside our own cells. So there is simply nothing for the antibiotic
to attack, and no dose can change that.

Taking one anyway is not merely useless — it does harm:

It kills the good bacteria that protect the body from infection (Fig. 3.5b), leaving room for
the resistant ones to grow and take over.
It adds to antibiotic resistance, so that when a real bacterial infection comes later, the
medicine may no longer work — for you or for anyone else.
It can cause side effects, and it delays proper care by giving the false comfort that something
is being done.

For a viral cold or flu the right treatment is what the chapter recommends: rest at home, fluids,
and covering the mouth and nose. The immune system clears the virus itself in a few days.

Note: the same reasoning explains why an antibiotic will not help against malaria
either — that is caused by protozoa, and the chapter states that antibiotics do not
work against them.

Q10 Which disease(s) among the following may spread if drinking water gets
contaminated by the excreta from an infected person? Hepatitis A, Tuberculosis,
Poliomyelitis, Cholera, Chickenpox.

Hepatitis A, poliomyelitis and cholera.

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Class 8 Science Chapter 3 Health: The Ultimate Treasure AglaSem · NCERT Solutions

DISEASE SPREADS THROUGH REASON
CONTAMINATED DRINKING
WATER?

Hepatitis A Yes A water- and food-borne virus; Table 3.1 gives
its preventive measure as drinking boiled water

Tuberculosis No A bacterial disease of the lungs, spread
through air from the cough of an infected
person

Poliomyelitis Yes The polio virus leaves the body in the excreta
and enters a new person through
contaminated water or food

Cholera Yes A bacterial disease of the intestine; Table 3.1
prevents it by boiled drinking water and good
sanitary habits

Chickenpox No A virus of the respiratory tract and skin, spread
through air and contact with blisters

Why it happens: for a disease to travel by this route, the pathogen must be able to
leave the body in the excreta and survive in water. Hepatitis A, polio and cholera all
infect the digestive system or pass out through it. Tuberculosis lives in the lungs and
chickenpox in the airways and skin, so neither reaches the water in the first place.

Did you know? All three of these are exactly what the Bhadrak sanitation campaign
in Activity 3.6 acted upon. Building and using toilets keeps excreta out of water —
which is why one campaign reduced several different diseases at once.

Q11 When our body encounters a pathogen for the first time, the immune response is
generally low but on exposure to the same pathogen again, the immune response
by the body is much more compared to the first exposure. Why is it so?

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

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Class 8 Science Chapter 3 Health: The Ultimate Treasure AglaSem · NCERT Solutions

FIRST EXPOSURE SECOND EXPOSURE TO THE SAME
PATHOGEN

Recognition The pathogen is unknown; the immune Recognised at once by the cells kept from
system must first identify it last time

Speed Slow — several days pass before the Fast — the defence begins almost
specific defence is ready immediately

Size of Low Much greater
response

Result The person usually falls ill while the The pathogen is destroyed before it can
defence is being built multiply enough to cause illness

Why it happens: during the first infection the immune system builds a defence
specific to that one pathogen, and it keeps some of those cells afterwards. When the
same pathogen returns, these cells recognise it instantly and multiply, so the full
response arrives in hours instead of days. The chapter calls this acquired immunity
— protection developed after exposure to a pathogen or a vaccine.

This is the entire principle of vaccination. A vaccine gives the immune system a safe first
exposure — using dead or weakened pathogens, or an inactive or harmless part of the
pathogen — so that the memory is built without the illness. When the real pathogen arrives, the
body treats it as a second exposure and defeats it quickly.

Did you know? This is also why we usually get chickenpox or measles only once, but
a cold many times: there are hundreds of different cold viruses, and remembering
one does not help against the next.

Discover, design, and debate — Page 45

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Class 8 Science Chapter 3 Health: The Ultimate Treasure AglaSem · NCERT Solutions

Interdisciplinary projects: Science and Society

DISCOVER, DESIGN, AND DEBATE PROJECTS

Q1 Students maintain a health diary for at least a month to track food, hygiene,
exercise, sleep, screen time, and emotional state.

Method. Rule a page for each week with the six columns below and fill it in at a fixed time each
night — the entry must take under two minutes, or it will not be kept up for a month. Record
what actually happened, not what you meant to do; a diary you edit is a diary that teaches you
nothing. Keep it private, and at the end of the month look for patterns rather than judging single
days.

DATE FOOD HYGIENE EXERCISE SLEEP SCREEN HOW I
TIME FELT

1 Aug Breakfast yes; 1 Handwash 45 min 10:30 pm – 1 h 20 min Good
fruit; 1 packet before meals: cricket 6:30 am (8
of chips yes h)

2 Aug Breakfast Bath, nails cut None 12:15 am – 3h Tired,
skipped; 2 cold 6:30 am (6 irritable
drinks h)

What to look for at the end of the month. Count, do not guess:

How many days did you get 8 hours of sleep? Compare your mood entries on those days
with the rest.
On days with the most screen time, what was the sleeping time and the mood? This is the
link the notice board reports between screen time, sleep disorders and anxiety.
How many days did you skip breakfast, and how did you feel in school on those mornings?
How many days had at least an hour of physical activity?
Draw a simple bar graph of screen time (or sleep) across the month, exactly as you did for
Q7. A graph makes a pattern visible that a list of numbers hides.

Tip: the diary is for you, not for marks. Its only purpose is to let you find one habit
worth changing, backed by your own evidence rather than by advice.

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co m
m.
Read about Indian scientists like Suniti Solomon, Asima Chatterjee, Yellapragada
e
Q2

com
Subbarao, Mary Poonen Lukose for their contributions in the field of health and
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diseases.

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a gl

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Here is a short note on each, to start you off. Check and add to it from a library book or a
. co ag
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trusted website, exactly as Activity 3.4 asked you to do with Table 3.1.

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SCIENTIST FIELD agCONTRIBUTION TO HEALTH AND DISEASE
Suniti Microbiology,
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Detected the first documented cases of HIV infection in India, in

se m.
Solomon medicine Chennai in the mid-1980s, when many refused to believe the disease had

m l a
.co ag and worked to remove the
reached the country. She went on to build care, counselling and

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research services for people living with HIV,

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stigma attached to them.
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a Asima Organic Studied the chemistry of medicinal plants of India and the alkaloids

om a s
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Chatterjee chemistry they contain. Her work contributed to the development of drugs against

. c
m a Doctor of Science.
epilepsy and malaria, and she was among the first Indian women to be

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awarded

Yellapragada Biochemistry a Worked out how the body stores and uses energy through phosphorus

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Subbarao compounds such as ATP, and helped develop medicines for cancer and

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for filariasis, as well as work leading to the antibiotic tetracycline.

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Mary Poonen Medicine, The first woman doctor of Travancore and the first woman to be

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Lukose public health Surgeon General in India. She organised

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treatment of tuberculosis, and for the health of mothers and children.

se m
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You may add Kamal Ranadive and Maharaj Kishan Bhan from this chapter itself — she
studied how hormones and certain viruses
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pollution raise the risk of it; he played

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s
Each took up a problem that was harming people around them
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Q3 The deadly disease smallpox was eradicated by vaccination. Discover how this was
done and why it worked. Debate whether everyone should be required to get
vaccinated to protect others.

How it was done. After Jenner’s discovery, a worldwide campaign was organised. The graph on
page 38 records the result: about 80 countries were reporting smallpox in 1950; the intensified
vaccine campaign began in 1965; the number fell steeply through the 1970s; and by 1979
smallpox was eradicated. It remains the only human disease ever wiped out.
Why it worked. Smallpox happened to have every feature that makes eradication possible:

The vaccine was effective and could be stored and carried to remote places.
The disease produced an unmistakable rash, so every case could be found and reported
quickly.
The virus infected only human beings — it had nowhere else to hide and wait.
Health workers used ring vaccination: when a case was found, everyone around the patient
was vaccinated, so the virus could not reach a new body.
Countries cooperated and kept it up for more than a decade, including in India.

Why it happens: a pathogen survives only by moving to a new body. Vaccinate
enough of the people around each case and every route is closed at once — the
chain snaps, and the virus dies out with its last patient.

The debate: should vaccination be compulsory?

FOR REQUIRING IT AGAINST REQUIRING IT

A vaccine protects not only you but the people Medical decisions about one’s own body are
around you, as the chapter states normally a matter of choice

Some people cannot be vaccinated — newborns, A few people genuinely cannot take a particular
the seriously ill. They are safe only if those vaccine, so no rule can be absolute
around them are

Eradication needs very high coverage; a few Compulsion can increase suspicion; persuasion
unprotected pockets let the disease return may achieve more coverage than a rule

Some fear or doubt vaccines, but scientists and Information and access must come first — many
doctors carefully test them for safety miss vaccines because no centre is nearby, not
because they refuse

A defensible position: free access, clear information and active outreach should come first,
because most gaps are gaps in access rather than in willingness; requirements for entry to
school or hospital work are reasonable where a disease is dangerous and spreads easily, with

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genuine medical exemptions allowed. Argue your own side, but argue it with the graph and the
figures, not with opinion alone.

Q4 According to current guidelines, learn the correct sequence of steps for performing
cardiopulmonary resuscitation (CPR) on an adult in case of sudden stoppage of
breathing. School may invite a doctor or a professional to demonstrate a mock drill.

Read this as an outline of the sequence, not as training. CPR is a physical skill. Learn it by
practising on a manikin under a doctor or a certified trainer, exactly as the book suggests — a
mock drill in school is the right way.
The current sequence for an adult, in order:

1. Check that the scene is safe — for you and for the person. You cannot help anyone if you
are hurt too.
2. Check for response. Tap the shoulders firmly and ask loudly, “Are you all right?”
3. Shout for help and call for an ambulance at once (112 in India), or ask a specific person by
name to call and to bring an AED if one is available. Put the phone on speaker so you can
keep your hands free.
4. Check breathing for no more than about 10 seconds. Gasping is not normal breathing.
5. If there is no normal breathing, begin chest compressions. Place the heel of one hand at
the centre of the chest, the other hand on top, keep your arms straight and your shoulders
above your hands, and push hard and fast — about 100 to 120 compressions a minute,
about 5 cm deep, letting the chest come back fully between compressions.
6. If you are trained and willing, give 2 rescue breaths after every 30 compressions. If you
are not trained, give compressions only and do not stop.
7. Use the AED as soon as it arrives, and follow its spoken instructions exactly.
8. Continue without stopping until the person starts breathing normally, a trained responder
takes over, or you are physically unable to continue. If someone else is present, change over
every two minutes so that neither of you tires.

Why it works: when the heart stops, the blood stops moving, and the brain begins
to be damaged within minutes. Chest compressions push the heart from outside
and keep some blood — and therefore some oxygen — moving to the brain until the
heart can be restarted. Every minute without compressions makes survival less
likely, which is why starting quickly matters more than starting perfectly.

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Ask the doctor at the drill: how do I know it is cardiac arrest and not fainting? How
deep is 5 cm really? What do I do if I hear a rib crack? What is different for a child or
an infant?

Q5 Invite a doctor to the school. Students may be encouraged to interact with the
doctor on the issues of malnutrition, under-nutrition, and over-nutrition.

Prepare before the visit. Send the doctor the topic in advance, collect written questions from
every class so that shy students are also heard, and appoint two students to take notes and one
to thank the guest. Keep the discussion about the conditions, never about any individual in the
room.
The three terms, so that you can follow the discussion:

TERM WHAT IT MEANS WHAT IT CAN LEAD TO

Malnutrition The diet does not supply nutrients in the The body cannot work or grow normally
right amounts — the general term that
covers both of the others

Under- Too little food, or too little of some Poor growth, tiredness, low resistance to
nutrition nutrient infection, and the deficiency diseases learnt
in Grade 6 — scurvy, anaemia, goitre

Over- More energy taken in than the body Obesity, and a higher chance of diabetes and
nutrition uses, often with too much oil, sugar and heart disease later
salt but still short of some nutrients

Questions worth asking the doctor:

Can a person be over-nourished and still be short of iron or vitamins at the same time?
What does a genuinely balanced plate look like for a student of our age, using foods
available in our market?
Which deficiency do you see most often in children here, and what is the cheapest way to
correct it?
Why does the same diet affect two people differently?
How is anaemia detected, and what should a student do if they are always tired?
What should we not do — which popular diet advice do you wish students would ignore?

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Class 8 Science Chapter 3 Health: The Ultimate Treasure AglaSem · NCERT Solutions

Note: discuss all three as health conditions with many causes — the food available
at home, family income, illness, hormones and activity all play a part. The chapter
itself lists several causes side by side. Nobody’s body should be discussed as a
personal failure.

Q6 If you are given an opportunity to create a health card, what all would you like to
include in it. Create your own health card and have discussion about it.

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.

SECTION WHAT TO INCLUDE WHY IT IS NEEDED

Identity Name, age, date of birth, class, address, Blood group is the first thing asked in
blood group an emergency

Emergency Parent or guardian, family doctor, nearest Saves minutes when minutes matter
contacts hospital, ambulance number

Growth record Height and weight, measured on the A single reading says little; the trend
same date each term says a lot

Vaccination record Every vaccine taken, with the date; the Vaccines are preventive — a missed
next one due date is the whole problem

Allergies and long- Allergies to any medicine or food; Prevents a dangerous mistake in
term conditions asthma, diabetes or other chronic treatment
condition; medicines taken regularly

Illness history Major illnesses, hospital stays, surgeries, Helps a new doctor understand the
with dates pattern

Check-ups Dates of eye test, dental check-up, Problems such as weak eyesight are
general check-up and their findings found only if looked for

Daily habits Usual sleeping hours, physical activity, These are the causes behind most non-
screen time communicable diseases

Well-being A place to note if you have been feeling Health is physical, mental and social
low, anxious or lonely, and whom you can — Activity 3.1 showed why this
talk to belongs on the card

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co m
m.
Discuss in class: who should be allowed to see this card? Most classes conclude that

m l a se
the student, the parents, the doctor and the school nurse should — and no one else.
o
m .c is private information, and that principle is worthagagreeing on before
A health record
se are made.
theacards
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Have a debate on ‘Are there ill-effects
a
Q7

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The motion is a question, so the debate should be settled by evidence rather than by feeling.

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The honest answer is yes — fast food does harm companion animals, and
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for two separate
reasons. o
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a s em1: too much of the wrong nutrients. Fast food is high in oil, salt and sugar. A dog or a
l is far smaller than an adult human, so the same piece of pizza or samosa is a very large
Reason
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share of its daily energy. Regularly fed such food, pets become overweight, which brings on the
m a s
. c o agl
same kind of trouble the chapter describes in people — breathlessness, joint pain and a shorter,
less comfortable life. Sudden fatty mealsmcan also inflame the pancreas, and soft, sugary food
l a se
ag
damages teeth and gums.
Reason 2: some human foods are actively poisonous to animals. This is the part many
people do not know. Chocolate, onion and garlic, grapes and raisins, and the sweetener xylitol
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e
are all dangerous to dogs — not merely unhealthy. A pet cannot read a label, so the

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responsibility is entirely ours.

m THE MOTION
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AGAINST THE REPLY
a (THERE ARE ILL-EFFECTS) MOTION

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Excess oil, salt and sugar “A small piece now True for a rare treat of safe food; the harm comes

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cause obesity and digestive and then does no from a routine, and from the fact that “small” for

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illness in pets harm” us is large for a 10 kg animal

Several common human “Street animals eat Surviving is not being healthy — and it is exactly
foods are toxic to dogs and leftovers and survive”
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these animals that are seen at shelters with

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cats digestive disease

comcannot choose or g l as
.Pets a
sem refuse; the keeper decides
“Pet food is Plain cooked rice, dal, curd, boiled vegetables and

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expensive” clean water cost little and are safer than fast food

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How to run the debate well: ask each side to bring one source — a veterinary
a s e
m . co
doctor’s advice, a pet-care book, or a trusted website — and to name it while
agl
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speaking. Invite the local veterinarian to judge. A debate in which both sides quote a
agthan one in which both sides only feel strongly.
source teaches more

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.co


a g l Page 54 of 57

Class 8 Science Chapter 3 Health: The Ultimate Treasure AglaSem · NCERT Solutions

Chapter at a glance
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 the body's natural ability to fight disease. A vaccine trains the immune system
using dead, weakened or harmless parts of a germ, giving acquired immunity. Vaccines
are preventive, never curative.
Antibiotics kill bacteria only, because they attack parts of bacterial cells that human cells do
not have. Using them when they are not needed, or stopping the dose halfway, breeds
antibiotic resistance.

Page 55 of 57

Class 8 Science Chapter 3 Health: The Ultimate Treasure AglaSem · NCERT Solutions

Quick revision

TERM WHAT IT MEANS EXAMPLE FROM THE KEY POINT TO
CHAPTER REMEMBER

Health Complete physical, mental and The Grade 8 boy in All three aspects — body,
social well-being, not merely Activity 3.1 had no mind and relationships —
the absence of disease (WHO) infection, yet he was must be looked after
unwell

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 This is what a doctor
pressure, swelling records

Pathogen A disease-causing organism Bacteria, viruses, fungi, All communicable diseases
worms, protozoa are caused by pathogens

Vector An insect that carries a Mosquitos spread malaria Control the vector and you
pathogen from one person to and dengue; houseflies stop the disease
another carry germs to food

Communicable A disease caused by a Typhoid, dengue, flu, Break the route of spread
disease pathogen that can spread from chickenpox, COVID-19 — air, water, food, contact,
person to person vector

Non- A disease not caused by a Diabetes, heart disease, Linked to lifestyle, diet and
communicable pathogen and not passed on to cancer, asthma environment; most deaths
disease (NCD) others in India

Deficiency disease A non-communicable disease Scurvy, anaemia, goitre Cured by correcting the
caused by lack of a nutrient (learnt in Grade 6) diet, not by medicines
alone

Chronic disease A disease that persists for a Cancer, diabetes, asthma Needs continuous care,
long time — more than 3 not a one-week course
months

Immunity The natural ability of the body The immune system Explains why two people in
to fight disease recognises and attacks the same house fall ill
germs differently

Vaccine A preparation of dead, Polio drops, measles, Gives acquired immunity;
weakened or harmless parts of tetanus, hepatitis preventive, not curative
a germ that trains the immune vaccines
system

Page 56 of 57

Class 8 Science Chapter 3 Health: The Ultimate Treasure AglaSem · NCERT Solutions

TERM WHAT IT MEANS EXAMPLE FROM THE KEY POINT TO
CHAPTER REMEMBER

Antibiotic A medicine that kills bacteria Penicillin, discovered by Useless against viruses
Alexander Fleming in and protozoa
1928

Antibiotic Bacteria once killed by an Caused by taking Take antibiotics only on a
resistance antibiotic survive and multiply antibiotics when not doctor's prescription, in
despite treatment required or leaving the full dose
dose incomplete

Page 57 of 57