NCERT Textbook - Why do we fall ill? Class 9 Notes | EduRev

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Class 9 : NCERT Textbook - Why do we fall ill? Class 9 Notes | EduRev

 Page 1


Activity _____________13.1
• We have all heard of the earthquakes
in Latur, Bhuj, Kashmir etc. or the
cyclones that attack the coastal
regions. Think of as many different
ways as possible in which people’s
health would be affected by such a
disaster if it took place in our
neighbourhood.
• How many of these ways we can think of
are events that would occur when the
disaster is actually happening?
• How many of these health-related events
would happen long after the actual
disaster, but would still be because of the
disaster?
• Why would one effect on health fall into
the first group, and why would another
fall into the second group?
When we do this exercise, we realise that
health and disease in human communities
are very complex issues, with many
interconnected causes. We also realise that
the ideas of what ‘health’ and ‘disease’ mean
are themselves very complicated. When we
ask what causes diseases and how we prevent
them, we have to begin by asking what these
notions mean.
We have seen that cells are the basic units
of living beings. Cells are made of a variety of
chemical substances – proteins, carbo-
hydrates, fats or lipids, and so on. Although
the pictures look quite static, in reality the
living cell is a dynamic place. Something or
the other is always happening. Cells move
from place to place. Even in cells that do not
move, there is repair going on. New cells are
being made. In our organs or tissues, there
are various specialised activities going on –
the heart is beating, the lungs are breathing,
the kidney is filtering urine, the brain is
thinking.
All these activities are interconnected. For
example, if the kidneys are not filtering urine,
poisonous substances will accumulate. Under
such conditions, the brain will not be able to
think properly. For all these interconnected
activities, energy and raw material are needed
from outside the body. In other words, food
is a necessity for cell and tissue functions.
Anything that prevents proper functioning of
cells and tissues will lead to a lack of proper
activity of the body.
It is in this context that we will now look
at the notions of health and disease.
13.1 Health and its Failure
13.1.1 THE SIGNIFICANCE OF ‘HEALTH’
We have heard the word ‘health’ used quite
frequently all around us. We use it ourselves
as well, when we say things like ‘my
grandmother’s health is not good’. Our
teachers use it when they scold us saying ‘this
is not a healthy attitude’. What does the word
‘health’ mean?
If we think about it, we realise that it
always implies the idea of ‘being well’. We can
think of this well-being as effective
functioning. For our grandmothers, being able
to go out to the market or to visit neighbours
is ‘being well’, and not being able to do such
things is ‘poor health’. Being interested in
following the teaching in the classroom so that
we can understand the world is called a
‘healthy attitude’; while not being interested
is called the opposite. ‘Health’ is therefore a
state of being well enough to function well
physically, mentally and socially.
13 13
13 13 13
W W W W WHY HY HY HY HY D D D D DO O O O O W W W W WE E E E E F F F F FALL ALL ALL ALL ALL I I I I ILL LL LL LL LL
Chapter
Page 2


Activity _____________13.1
• We have all heard of the earthquakes
in Latur, Bhuj, Kashmir etc. or the
cyclones that attack the coastal
regions. Think of as many different
ways as possible in which people’s
health would be affected by such a
disaster if it took place in our
neighbourhood.
• How many of these ways we can think of
are events that would occur when the
disaster is actually happening?
• How many of these health-related events
would happen long after the actual
disaster, but would still be because of the
disaster?
• Why would one effect on health fall into
the first group, and why would another
fall into the second group?
When we do this exercise, we realise that
health and disease in human communities
are very complex issues, with many
interconnected causes. We also realise that
the ideas of what ‘health’ and ‘disease’ mean
are themselves very complicated. When we
ask what causes diseases and how we prevent
them, we have to begin by asking what these
notions mean.
We have seen that cells are the basic units
of living beings. Cells are made of a variety of
chemical substances – proteins, carbo-
hydrates, fats or lipids, and so on. Although
the pictures look quite static, in reality the
living cell is a dynamic place. Something or
the other is always happening. Cells move
from place to place. Even in cells that do not
move, there is repair going on. New cells are
being made. In our organs or tissues, there
are various specialised activities going on –
the heart is beating, the lungs are breathing,
the kidney is filtering urine, the brain is
thinking.
All these activities are interconnected. For
example, if the kidneys are not filtering urine,
poisonous substances will accumulate. Under
such conditions, the brain will not be able to
think properly. For all these interconnected
activities, energy and raw material are needed
from outside the body. In other words, food
is a necessity for cell and tissue functions.
Anything that prevents proper functioning of
cells and tissues will lead to a lack of proper
activity of the body.
It is in this context that we will now look
at the notions of health and disease.
13.1 Health and its Failure
13.1.1 THE SIGNIFICANCE OF ‘HEALTH’
We have heard the word ‘health’ used quite
frequently all around us. We use it ourselves
as well, when we say things like ‘my
grandmother’s health is not good’. Our
teachers use it when they scold us saying ‘this
is not a healthy attitude’. What does the word
‘health’ mean?
If we think about it, we realise that it
always implies the idea of ‘being well’. We can
think of this well-being as effective
functioning. For our grandmothers, being able
to go out to the market or to visit neighbours
is ‘being well’, and not being able to do such
things is ‘poor health’. Being interested in
following the teaching in the classroom so that
we can understand the world is called a
‘healthy attitude’; while not being interested
is called the opposite. ‘Health’ is therefore a
state of being well enough to function well
physically, mentally and socially.
13 13
13 13 13
W W W W WHY HY HY HY HY D D D D DO O O O O W W W W WE E E E E F F F F FALL ALL ALL ALL ALL I I I I ILL LL LL LL LL
Chapter
We need food for health, and this food will
have to be earned by doing work. For this,
the opportunity to do work has to be available.
Good economic conditions and jobs are
therefore needed for individual health.
We need to be happy in order to be truly
healthy, and if we mistreat each other and
are afraid of each other, we cannot be happy
or healthy. Social equality and harmony are
therefore necessary for individual health. We
can think of many other such examples of
connections between community issues and
individual health.
13.1.3 DISTINCTIONS BETWEEN ‘HEALTHY’
AND ‘DISEASE-FREE’
If this is what we mean by ‘health’, what do
we mean by ‘disease’? The word is actually
self-explanatory – we can think of it as
‘disease’ – disturbed ease. Disease, in other
words, literally means being uncomfortable.
However, the word is used in a more limited
meaning. We talk of disease when we can find
a specific and particular cause for discomfort.
This does not mean that we have to know the
absolute final cause;  we can say that
someone is suffering from diarrhoea without
knowing exactly what has caused the loose
motions.
We can now easily see that it is possible
to be in poor health without actually suffering
from a particular disease. Simply not being
diseased is not the same as being healthy.
‘Good health’ for a dancer may mean being
able to stretch his body into difficult but
graceful positions. On the other hand, good
health for a musician may mean having enough
breathing capacity in his/her lungs to control
the notes from his/her flute. To have the
opportunity to realise the unique potential
in all of us is also necessary for real health.
So, we can be in poor health without there
being a simple cause in the form of an
identifiable disease. This is the reason why,
when we think about health, we think about
societies and communities. On the other
hand, when we think about disease, we think
about individual sufferers.
13.1.2 PERSONAL AND COMMUNITY ISSUES
BOTH MATTER FOR HEALTH
If health means a state of physical, mental
and social well-being, it cannot be something
that each one of us can achieve entirely on
our own. The health of all organisms will
depend on their surroundings or their
environment. The environment includes the
physical environment. So, for example, health
is at risk in a cyclone in many ways.
But even more importantly, human beings
live in societies. Our social environment,
therefore, is an important factor in our
individual health. We live in villages, towns
or cities. In such places, even our physical
environment is decided by our social
environment.
Consider what would happen if no agency
is ensuring that garbage is collected and
disposed. What would happen if no one takes
responsibility for clearing the drains and
ensuring that water does not collect in the
streets or open spaces?
So, if there is a great deal of garbage
thrown in our streets, or if there is open drain-
water lying stagnant around where we live,
the possibility of poor health increases.
Therefore, public cleanliness is important for
individual health.
Activity _____________13.2
• Find out what provisions are made by
your local authority (panchayat/
municipal corporation) for the supply
of clean drinking water.
• Are all the people in your locality able
to access this?
Activity _____________13.3
• Find out how your local authority
manages the solid waste generated in
your neighbourhood.
• Are these measures adequate?
• If not, what improvements would you
suggest?
• What could your family do to reduce
the amount of solid waste generated
during a day/week?
WHY DO WE FALL ILL 177
Page 3


Activity _____________13.1
• We have all heard of the earthquakes
in Latur, Bhuj, Kashmir etc. or the
cyclones that attack the coastal
regions. Think of as many different
ways as possible in which people’s
health would be affected by such a
disaster if it took place in our
neighbourhood.
• How many of these ways we can think of
are events that would occur when the
disaster is actually happening?
• How many of these health-related events
would happen long after the actual
disaster, but would still be because of the
disaster?
• Why would one effect on health fall into
the first group, and why would another
fall into the second group?
When we do this exercise, we realise that
health and disease in human communities
are very complex issues, with many
interconnected causes. We also realise that
the ideas of what ‘health’ and ‘disease’ mean
are themselves very complicated. When we
ask what causes diseases and how we prevent
them, we have to begin by asking what these
notions mean.
We have seen that cells are the basic units
of living beings. Cells are made of a variety of
chemical substances – proteins, carbo-
hydrates, fats or lipids, and so on. Although
the pictures look quite static, in reality the
living cell is a dynamic place. Something or
the other is always happening. Cells move
from place to place. Even in cells that do not
move, there is repair going on. New cells are
being made. In our organs or tissues, there
are various specialised activities going on –
the heart is beating, the lungs are breathing,
the kidney is filtering urine, the brain is
thinking.
All these activities are interconnected. For
example, if the kidneys are not filtering urine,
poisonous substances will accumulate. Under
such conditions, the brain will not be able to
think properly. For all these interconnected
activities, energy and raw material are needed
from outside the body. In other words, food
is a necessity for cell and tissue functions.
Anything that prevents proper functioning of
cells and tissues will lead to a lack of proper
activity of the body.
It is in this context that we will now look
at the notions of health and disease.
13.1 Health and its Failure
13.1.1 THE SIGNIFICANCE OF ‘HEALTH’
We have heard the word ‘health’ used quite
frequently all around us. We use it ourselves
as well, when we say things like ‘my
grandmother’s health is not good’. Our
teachers use it when they scold us saying ‘this
is not a healthy attitude’. What does the word
‘health’ mean?
If we think about it, we realise that it
always implies the idea of ‘being well’. We can
think of this well-being as effective
functioning. For our grandmothers, being able
to go out to the market or to visit neighbours
is ‘being well’, and not being able to do such
things is ‘poor health’. Being interested in
following the teaching in the classroom so that
we can understand the world is called a
‘healthy attitude’; while not being interested
is called the opposite. ‘Health’ is therefore a
state of being well enough to function well
physically, mentally and socially.
13 13
13 13 13
W W W W WHY HY HY HY HY D D D D DO O O O O W W W W WE E E E E F F F F FALL ALL ALL ALL ALL I I I I ILL LL LL LL LL
Chapter
We need food for health, and this food will
have to be earned by doing work. For this,
the opportunity to do work has to be available.
Good economic conditions and jobs are
therefore needed for individual health.
We need to be happy in order to be truly
healthy, and if we mistreat each other and
are afraid of each other, we cannot be happy
or healthy. Social equality and harmony are
therefore necessary for individual health. We
can think of many other such examples of
connections between community issues and
individual health.
13.1.3 DISTINCTIONS BETWEEN ‘HEALTHY’
AND ‘DISEASE-FREE’
If this is what we mean by ‘health’, what do
we mean by ‘disease’? The word is actually
self-explanatory – we can think of it as
‘disease’ – disturbed ease. Disease, in other
words, literally means being uncomfortable.
However, the word is used in a more limited
meaning. We talk of disease when we can find
a specific and particular cause for discomfort.
This does not mean that we have to know the
absolute final cause;  we can say that
someone is suffering from diarrhoea without
knowing exactly what has caused the loose
motions.
We can now easily see that it is possible
to be in poor health without actually suffering
from a particular disease. Simply not being
diseased is not the same as being healthy.
‘Good health’ for a dancer may mean being
able to stretch his body into difficult but
graceful positions. On the other hand, good
health for a musician may mean having enough
breathing capacity in his/her lungs to control
the notes from his/her flute. To have the
opportunity to realise the unique potential
in all of us is also necessary for real health.
So, we can be in poor health without there
being a simple cause in the form of an
identifiable disease. This is the reason why,
when we think about health, we think about
societies and communities. On the other
hand, when we think about disease, we think
about individual sufferers.
13.1.2 PERSONAL AND COMMUNITY ISSUES
BOTH MATTER FOR HEALTH
If health means a state of physical, mental
and social well-being, it cannot be something
that each one of us can achieve entirely on
our own. The health of all organisms will
depend on their surroundings or their
environment. The environment includes the
physical environment. So, for example, health
is at risk in a cyclone in many ways.
But even more importantly, human beings
live in societies. Our social environment,
therefore, is an important factor in our
individual health. We live in villages, towns
or cities. In such places, even our physical
environment is decided by our social
environment.
Consider what would happen if no agency
is ensuring that garbage is collected and
disposed. What would happen if no one takes
responsibility for clearing the drains and
ensuring that water does not collect in the
streets or open spaces?
So, if there is a great deal of garbage
thrown in our streets, or if there is open drain-
water lying stagnant around where we live,
the possibility of poor health increases.
Therefore, public cleanliness is important for
individual health.
Activity _____________13.2
• Find out what provisions are made by
your local authority (panchayat/
municipal corporation) for the supply
of clean drinking water.
• Are all the people in your locality able
to access this?
Activity _____________13.3
• Find out how your local authority
manages the solid waste generated in
your neighbourhood.
• Are these measures adequate?
• If not, what improvements would you
suggest?
• What could your family do to reduce
the amount of solid waste generated
during a day/week?
WHY DO WE FALL ILL 177 SCIENCE 178
uestions
1. State any two conditions
essential for good health.
2. State any two conditions
essential for being free of disease.
3. Are the answers to the above
questions necessarily the same
or different? Why?
13.2 Disease and Its Causes
13.2.1 WHAT DOES DISEASE LOOK LIKE?
Let us now think a little more about diseases.
In the first place, how do we know that there
is a disease? In other words, how do we know
that there is something wrong with the body?
There are many tissues in the body, as we
have seen in Chapter 6. These tissues make
up physiological systems or organ systems
that carry out body functions. Each of the
organ systems has specific organs as its parts,
and it has particular functions. So, the
digestive system has the stomach and
intestines, and it helps to digest food taken
in from outside the body. The musculoskeletal
system, which is made up of bones and
muscles, holds the body parts together and
helps the body move.
When there is a disease, either the
functioning or the appearance of one or more
systems of the body will change for the worse.
These changes give rise to symptoms and
signs of disease. Symptoms of disease are the
things we feel as being ‘wrong’. So we have a
headache, we have cough, we have loose
motions, we have a wound with pus; these
are all symptoms. These indicate that there
may be a disease, but they don’t indicate what
the disease is. For example, a headache may
mean just examination stress or, very rarely,
it may mean meningitis, or any one of a dozen
different diseases.
Signs of disease are what physicians will
look for on the basis of the symptoms. Signs
will give a little more definite indication of
the presence of a particular disease.
Physicians will also get laboratory tests done
to pinpoint the disease further.
13.2.2 ACUTE AND CHRONIC DISEASES
The manifestations of disease will be different
depending on a number of factors. One of the
most obvious factors that determine how we
perceive the disease is its duration. Some
diseases last for only very short periods of
time, and these are called acute diseases. We
all know from experience that the common
cold lasts only a few days. Other ailments can
last for a long time, even as much as a lifetime,
and are called chronic diseases. An example
is the infection causing elephantiasis, which
is very common in some parts of India.
Activity _____________13.4
• Survey your neighbourhood to find out:
(1) how many people suffered from
acute diseases during the last three
months,
(2) how many people developed chronic
diseases during this same period,
(3) and finally, the total number of
people suffering from chronic
diseases in your neighbourhood.
• Are the answers to questions (1) and
(2) different?
• Are the answers to questions (2) and
(3) different?
• What do you think could be the reason
for these differences? What do you think
would be the effect of these differences
on the general health of the population?
13.2.3 CHRONIC DISEASES AND POOR
HEALTH
As we can imagine, acute and chronic
diseases have different effects on our health.
Any disease that causes poor functioning of
some part of the body will affect our general
health as well. This is because all functions
of the body are necessary for general health.
But an acute disease, which is over very soon,
will not have time to cause major effects on
general health, while a chronic disease will
do so.
As an example, think about a cough and
cold, which all of us have from time to time.
Most of us get better and become well within
a week or so. And there are no bad effects on
Q
Page 4


Activity _____________13.1
• We have all heard of the earthquakes
in Latur, Bhuj, Kashmir etc. or the
cyclones that attack the coastal
regions. Think of as many different
ways as possible in which people’s
health would be affected by such a
disaster if it took place in our
neighbourhood.
• How many of these ways we can think of
are events that would occur when the
disaster is actually happening?
• How many of these health-related events
would happen long after the actual
disaster, but would still be because of the
disaster?
• Why would one effect on health fall into
the first group, and why would another
fall into the second group?
When we do this exercise, we realise that
health and disease in human communities
are very complex issues, with many
interconnected causes. We also realise that
the ideas of what ‘health’ and ‘disease’ mean
are themselves very complicated. When we
ask what causes diseases and how we prevent
them, we have to begin by asking what these
notions mean.
We have seen that cells are the basic units
of living beings. Cells are made of a variety of
chemical substances – proteins, carbo-
hydrates, fats or lipids, and so on. Although
the pictures look quite static, in reality the
living cell is a dynamic place. Something or
the other is always happening. Cells move
from place to place. Even in cells that do not
move, there is repair going on. New cells are
being made. In our organs or tissues, there
are various specialised activities going on –
the heart is beating, the lungs are breathing,
the kidney is filtering urine, the brain is
thinking.
All these activities are interconnected. For
example, if the kidneys are not filtering urine,
poisonous substances will accumulate. Under
such conditions, the brain will not be able to
think properly. For all these interconnected
activities, energy and raw material are needed
from outside the body. In other words, food
is a necessity for cell and tissue functions.
Anything that prevents proper functioning of
cells and tissues will lead to a lack of proper
activity of the body.
It is in this context that we will now look
at the notions of health and disease.
13.1 Health and its Failure
13.1.1 THE SIGNIFICANCE OF ‘HEALTH’
We have heard the word ‘health’ used quite
frequently all around us. We use it ourselves
as well, when we say things like ‘my
grandmother’s health is not good’. Our
teachers use it when they scold us saying ‘this
is not a healthy attitude’. What does the word
‘health’ mean?
If we think about it, we realise that it
always implies the idea of ‘being well’. We can
think of this well-being as effective
functioning. For our grandmothers, being able
to go out to the market or to visit neighbours
is ‘being well’, and not being able to do such
things is ‘poor health’. Being interested in
following the teaching in the classroom so that
we can understand the world is called a
‘healthy attitude’; while not being interested
is called the opposite. ‘Health’ is therefore a
state of being well enough to function well
physically, mentally and socially.
13 13
13 13 13
W W W W WHY HY HY HY HY D D D D DO O O O O W W W W WE E E E E F F F F FALL ALL ALL ALL ALL I I I I ILL LL LL LL LL
Chapter
We need food for health, and this food will
have to be earned by doing work. For this,
the opportunity to do work has to be available.
Good economic conditions and jobs are
therefore needed for individual health.
We need to be happy in order to be truly
healthy, and if we mistreat each other and
are afraid of each other, we cannot be happy
or healthy. Social equality and harmony are
therefore necessary for individual health. We
can think of many other such examples of
connections between community issues and
individual health.
13.1.3 DISTINCTIONS BETWEEN ‘HEALTHY’
AND ‘DISEASE-FREE’
If this is what we mean by ‘health’, what do
we mean by ‘disease’? The word is actually
self-explanatory – we can think of it as
‘disease’ – disturbed ease. Disease, in other
words, literally means being uncomfortable.
However, the word is used in a more limited
meaning. We talk of disease when we can find
a specific and particular cause for discomfort.
This does not mean that we have to know the
absolute final cause;  we can say that
someone is suffering from diarrhoea without
knowing exactly what has caused the loose
motions.
We can now easily see that it is possible
to be in poor health without actually suffering
from a particular disease. Simply not being
diseased is not the same as being healthy.
‘Good health’ for a dancer may mean being
able to stretch his body into difficult but
graceful positions. On the other hand, good
health for a musician may mean having enough
breathing capacity in his/her lungs to control
the notes from his/her flute. To have the
opportunity to realise the unique potential
in all of us is also necessary for real health.
So, we can be in poor health without there
being a simple cause in the form of an
identifiable disease. This is the reason why,
when we think about health, we think about
societies and communities. On the other
hand, when we think about disease, we think
about individual sufferers.
13.1.2 PERSONAL AND COMMUNITY ISSUES
BOTH MATTER FOR HEALTH
If health means a state of physical, mental
and social well-being, it cannot be something
that each one of us can achieve entirely on
our own. The health of all organisms will
depend on their surroundings or their
environment. The environment includes the
physical environment. So, for example, health
is at risk in a cyclone in many ways.
But even more importantly, human beings
live in societies. Our social environment,
therefore, is an important factor in our
individual health. We live in villages, towns
or cities. In such places, even our physical
environment is decided by our social
environment.
Consider what would happen if no agency
is ensuring that garbage is collected and
disposed. What would happen if no one takes
responsibility for clearing the drains and
ensuring that water does not collect in the
streets or open spaces?
So, if there is a great deal of garbage
thrown in our streets, or if there is open drain-
water lying stagnant around where we live,
the possibility of poor health increases.
Therefore, public cleanliness is important for
individual health.
Activity _____________13.2
• Find out what provisions are made by
your local authority (panchayat/
municipal corporation) for the supply
of clean drinking water.
• Are all the people in your locality able
to access this?
Activity _____________13.3
• Find out how your local authority
manages the solid waste generated in
your neighbourhood.
• Are these measures adequate?
• If not, what improvements would you
suggest?
• What could your family do to reduce
the amount of solid waste generated
during a day/week?
WHY DO WE FALL ILL 177 SCIENCE 178
uestions
1. State any two conditions
essential for good health.
2. State any two conditions
essential for being free of disease.
3. Are the answers to the above
questions necessarily the same
or different? Why?
13.2 Disease and Its Causes
13.2.1 WHAT DOES DISEASE LOOK LIKE?
Let us now think a little more about diseases.
In the first place, how do we know that there
is a disease? In other words, how do we know
that there is something wrong with the body?
There are many tissues in the body, as we
have seen in Chapter 6. These tissues make
up physiological systems or organ systems
that carry out body functions. Each of the
organ systems has specific organs as its parts,
and it has particular functions. So, the
digestive system has the stomach and
intestines, and it helps to digest food taken
in from outside the body. The musculoskeletal
system, which is made up of bones and
muscles, holds the body parts together and
helps the body move.
When there is a disease, either the
functioning or the appearance of one or more
systems of the body will change for the worse.
These changes give rise to symptoms and
signs of disease. Symptoms of disease are the
things we feel as being ‘wrong’. So we have a
headache, we have cough, we have loose
motions, we have a wound with pus; these
are all symptoms. These indicate that there
may be a disease, but they don’t indicate what
the disease is. For example, a headache may
mean just examination stress or, very rarely,
it may mean meningitis, or any one of a dozen
different diseases.
Signs of disease are what physicians will
look for on the basis of the symptoms. Signs
will give a little more definite indication of
the presence of a particular disease.
Physicians will also get laboratory tests done
to pinpoint the disease further.
13.2.2 ACUTE AND CHRONIC DISEASES
The manifestations of disease will be different
depending on a number of factors. One of the
most obvious factors that determine how we
perceive the disease is its duration. Some
diseases last for only very short periods of
time, and these are called acute diseases. We
all know from experience that the common
cold lasts only a few days. Other ailments can
last for a long time, even as much as a lifetime,
and are called chronic diseases. An example
is the infection causing elephantiasis, which
is very common in some parts of India.
Activity _____________13.4
• Survey your neighbourhood to find out:
(1) how many people suffered from
acute diseases during the last three
months,
(2) how many people developed chronic
diseases during this same period,
(3) and finally, the total number of
people suffering from chronic
diseases in your neighbourhood.
• Are the answers to questions (1) and
(2) different?
• Are the answers to questions (2) and
(3) different?
• What do you think could be the reason
for these differences? What do you think
would be the effect of these differences
on the general health of the population?
13.2.3 CHRONIC DISEASES AND POOR
HEALTH
As we can imagine, acute and chronic
diseases have different effects on our health.
Any disease that causes poor functioning of
some part of the body will affect our general
health as well. This is because all functions
of the body are necessary for general health.
But an acute disease, which is over very soon,
will not have time to cause major effects on
general health, while a chronic disease will
do so.
As an example, think about a cough and
cold, which all of us have from time to time.
Most of us get better and become well within
a week or so. And there are no bad effects on
Q
WHY DO WE FALL ILL 179
would not lead to loose motions. But they do
become contributory causes of the disease.
Why was there no clean drinking water
for the baby? Perhaps because the public
services are poor where the baby’s family
lives. So, poverty or lack of public services
become third-level causes of the baby’s
disease.
It will now be obvious that all diseases
will have immediate causes and contributory
causes. Also, most diseases will have many
causes, rather than one single cause.
13.2.5 INFECTIOUS AND NON-INFECTIOUS
CAUSES
As we have seen, it is important to keep public
health and community health factors in mind
when we think about causes of diseases. We
can take that approach a little further. It is
useful to think of the immediate causes of
disease as belonging to two distinct types. One
group of causes is the infectious agents,
mostly microbes or micro-organisms.
Diseases where microbes are the immediate
causes are called infectious diseases. This is
because the microbes can spread in the
community, and the diseases they cause will
spread with them.
Things to ponder
1. Do all diseases spread to people
coming in contact with a sick person?
2. What are the diseases that are not
spreading?
3. How would a person develop those
diseases that don’t spread by contact
with a sick person?
On the other hand, there are also diseases
that are not caused by infectious agents. Their
causes vary, but they are not external causes
like microbes that can spread in the
community. Instead, these are mostly
internal, non-infectious causes.
For example, some cancers are caused by
genetic abnormalities. High blood pressure
can be caused by excessive weight and lack
of exercise. You can think of many other
diseases where the immediate causes will not
be infectious.
our health. We do not lose weight, we do not
become short of breath, we do not feel tired
all the time because of a few days of cough
and cold. But if we get infected with a chronic
disease such as tuberculosis of the lungs,
then being ill over the years does make us
lose weight and feel tired all the time.
We may not go to school for a few days if
we have an acute disease. But a chronic
disease will make it difficult for us to follow
what is being taught in school and reduce
our ability to learn. In other words, we are
likely to have prolonged general poor health
if we have a chronic disease. Chronic diseases
therefore, have very drastic long-term effects
on people’s health as compared to acute
diseases.
13.2.4 CAUSES OF DISEASES
What causes disease? When we think about
causes of diseases, we must remember that
there are many levels of such causes. Let us
look at an example. If there is a baby suffering
from loose motions, we can say that the cause
of the loose motions is an infection with a
virus. So the immediate cause of the disease
is a virus.
But the next question is – where did the
virus come from? Suppose we find that the
virus came through unclean drinking water.
But many babies must have had this unclean
drinking water. So, why is it that one baby
developed loose motions when the other
babies did not?
One reason might be that this baby is not
healthy. As a result, it might be more likely
to have disease when exposed to risk, whereas
healthier babies would not. Why is the baby
not healthy? Perhaps because it is not well
nourished and does not get enough food. So,
lack of good nourishment becomes a second-
level cause of the disease the baby is suffering
from. Further, why is the baby not well
nourished? Perhaps because it is from a
household which is poor.
It is also possible that the baby has some
genetic difference that makes it more likely
to suffer from loose motions when exposed
to such a virus. Without the virus, the genetic
difference or the poor nourishment alone
Page 5


Activity _____________13.1
• We have all heard of the earthquakes
in Latur, Bhuj, Kashmir etc. or the
cyclones that attack the coastal
regions. Think of as many different
ways as possible in which people’s
health would be affected by such a
disaster if it took place in our
neighbourhood.
• How many of these ways we can think of
are events that would occur when the
disaster is actually happening?
• How many of these health-related events
would happen long after the actual
disaster, but would still be because of the
disaster?
• Why would one effect on health fall into
the first group, and why would another
fall into the second group?
When we do this exercise, we realise that
health and disease in human communities
are very complex issues, with many
interconnected causes. We also realise that
the ideas of what ‘health’ and ‘disease’ mean
are themselves very complicated. When we
ask what causes diseases and how we prevent
them, we have to begin by asking what these
notions mean.
We have seen that cells are the basic units
of living beings. Cells are made of a variety of
chemical substances – proteins, carbo-
hydrates, fats or lipids, and so on. Although
the pictures look quite static, in reality the
living cell is a dynamic place. Something or
the other is always happening. Cells move
from place to place. Even in cells that do not
move, there is repair going on. New cells are
being made. In our organs or tissues, there
are various specialised activities going on –
the heart is beating, the lungs are breathing,
the kidney is filtering urine, the brain is
thinking.
All these activities are interconnected. For
example, if the kidneys are not filtering urine,
poisonous substances will accumulate. Under
such conditions, the brain will not be able to
think properly. For all these interconnected
activities, energy and raw material are needed
from outside the body. In other words, food
is a necessity for cell and tissue functions.
Anything that prevents proper functioning of
cells and tissues will lead to a lack of proper
activity of the body.
It is in this context that we will now look
at the notions of health and disease.
13.1 Health and its Failure
13.1.1 THE SIGNIFICANCE OF ‘HEALTH’
We have heard the word ‘health’ used quite
frequently all around us. We use it ourselves
as well, when we say things like ‘my
grandmother’s health is not good’. Our
teachers use it when they scold us saying ‘this
is not a healthy attitude’. What does the word
‘health’ mean?
If we think about it, we realise that it
always implies the idea of ‘being well’. We can
think of this well-being as effective
functioning. For our grandmothers, being able
to go out to the market or to visit neighbours
is ‘being well’, and not being able to do such
things is ‘poor health’. Being interested in
following the teaching in the classroom so that
we can understand the world is called a
‘healthy attitude’; while not being interested
is called the opposite. ‘Health’ is therefore a
state of being well enough to function well
physically, mentally and socially.
13 13
13 13 13
W W W W WHY HY HY HY HY D D D D DO O O O O W W W W WE E E E E F F F F FALL ALL ALL ALL ALL I I I I ILL LL LL LL LL
Chapter
We need food for health, and this food will
have to be earned by doing work. For this,
the opportunity to do work has to be available.
Good economic conditions and jobs are
therefore needed for individual health.
We need to be happy in order to be truly
healthy, and if we mistreat each other and
are afraid of each other, we cannot be happy
or healthy. Social equality and harmony are
therefore necessary for individual health. We
can think of many other such examples of
connections between community issues and
individual health.
13.1.3 DISTINCTIONS BETWEEN ‘HEALTHY’
AND ‘DISEASE-FREE’
If this is what we mean by ‘health’, what do
we mean by ‘disease’? The word is actually
self-explanatory – we can think of it as
‘disease’ – disturbed ease. Disease, in other
words, literally means being uncomfortable.
However, the word is used in a more limited
meaning. We talk of disease when we can find
a specific and particular cause for discomfort.
This does not mean that we have to know the
absolute final cause;  we can say that
someone is suffering from diarrhoea without
knowing exactly what has caused the loose
motions.
We can now easily see that it is possible
to be in poor health without actually suffering
from a particular disease. Simply not being
diseased is not the same as being healthy.
‘Good health’ for a dancer may mean being
able to stretch his body into difficult but
graceful positions. On the other hand, good
health for a musician may mean having enough
breathing capacity in his/her lungs to control
the notes from his/her flute. To have the
opportunity to realise the unique potential
in all of us is also necessary for real health.
So, we can be in poor health without there
being a simple cause in the form of an
identifiable disease. This is the reason why,
when we think about health, we think about
societies and communities. On the other
hand, when we think about disease, we think
about individual sufferers.
13.1.2 PERSONAL AND COMMUNITY ISSUES
BOTH MATTER FOR HEALTH
If health means a state of physical, mental
and social well-being, it cannot be something
that each one of us can achieve entirely on
our own. The health of all organisms will
depend on their surroundings or their
environment. The environment includes the
physical environment. So, for example, health
is at risk in a cyclone in many ways.
But even more importantly, human beings
live in societies. Our social environment,
therefore, is an important factor in our
individual health. We live in villages, towns
or cities. In such places, even our physical
environment is decided by our social
environment.
Consider what would happen if no agency
is ensuring that garbage is collected and
disposed. What would happen if no one takes
responsibility for clearing the drains and
ensuring that water does not collect in the
streets or open spaces?
So, if there is a great deal of garbage
thrown in our streets, or if there is open drain-
water lying stagnant around where we live,
the possibility of poor health increases.
Therefore, public cleanliness is important for
individual health.
Activity _____________13.2
• Find out what provisions are made by
your local authority (panchayat/
municipal corporation) for the supply
of clean drinking water.
• Are all the people in your locality able
to access this?
Activity _____________13.3
• Find out how your local authority
manages the solid waste generated in
your neighbourhood.
• Are these measures adequate?
• If not, what improvements would you
suggest?
• What could your family do to reduce
the amount of solid waste generated
during a day/week?
WHY DO WE FALL ILL 177 SCIENCE 178
uestions
1. State any two conditions
essential for good health.
2. State any two conditions
essential for being free of disease.
3. Are the answers to the above
questions necessarily the same
or different? Why?
13.2 Disease and Its Causes
13.2.1 WHAT DOES DISEASE LOOK LIKE?
Let us now think a little more about diseases.
In the first place, how do we know that there
is a disease? In other words, how do we know
that there is something wrong with the body?
There are many tissues in the body, as we
have seen in Chapter 6. These tissues make
up physiological systems or organ systems
that carry out body functions. Each of the
organ systems has specific organs as its parts,
and it has particular functions. So, the
digestive system has the stomach and
intestines, and it helps to digest food taken
in from outside the body. The musculoskeletal
system, which is made up of bones and
muscles, holds the body parts together and
helps the body move.
When there is a disease, either the
functioning or the appearance of one or more
systems of the body will change for the worse.
These changes give rise to symptoms and
signs of disease. Symptoms of disease are the
things we feel as being ‘wrong’. So we have a
headache, we have cough, we have loose
motions, we have a wound with pus; these
are all symptoms. These indicate that there
may be a disease, but they don’t indicate what
the disease is. For example, a headache may
mean just examination stress or, very rarely,
it may mean meningitis, or any one of a dozen
different diseases.
Signs of disease are what physicians will
look for on the basis of the symptoms. Signs
will give a little more definite indication of
the presence of a particular disease.
Physicians will also get laboratory tests done
to pinpoint the disease further.
13.2.2 ACUTE AND CHRONIC DISEASES
The manifestations of disease will be different
depending on a number of factors. One of the
most obvious factors that determine how we
perceive the disease is its duration. Some
diseases last for only very short periods of
time, and these are called acute diseases. We
all know from experience that the common
cold lasts only a few days. Other ailments can
last for a long time, even as much as a lifetime,
and are called chronic diseases. An example
is the infection causing elephantiasis, which
is very common in some parts of India.
Activity _____________13.4
• Survey your neighbourhood to find out:
(1) how many people suffered from
acute diseases during the last three
months,
(2) how many people developed chronic
diseases during this same period,
(3) and finally, the total number of
people suffering from chronic
diseases in your neighbourhood.
• Are the answers to questions (1) and
(2) different?
• Are the answers to questions (2) and
(3) different?
• What do you think could be the reason
for these differences? What do you think
would be the effect of these differences
on the general health of the population?
13.2.3 CHRONIC DISEASES AND POOR
HEALTH
As we can imagine, acute and chronic
diseases have different effects on our health.
Any disease that causes poor functioning of
some part of the body will affect our general
health as well. This is because all functions
of the body are necessary for general health.
But an acute disease, which is over very soon,
will not have time to cause major effects on
general health, while a chronic disease will
do so.
As an example, think about a cough and
cold, which all of us have from time to time.
Most of us get better and become well within
a week or so. And there are no bad effects on
Q
WHY DO WE FALL ILL 179
would not lead to loose motions. But they do
become contributory causes of the disease.
Why was there no clean drinking water
for the baby? Perhaps because the public
services are poor where the baby’s family
lives. So, poverty or lack of public services
become third-level causes of the baby’s
disease.
It will now be obvious that all diseases
will have immediate causes and contributory
causes. Also, most diseases will have many
causes, rather than one single cause.
13.2.5 INFECTIOUS AND NON-INFECTIOUS
CAUSES
As we have seen, it is important to keep public
health and community health factors in mind
when we think about causes of diseases. We
can take that approach a little further. It is
useful to think of the immediate causes of
disease as belonging to two distinct types. One
group of causes is the infectious agents,
mostly microbes or micro-organisms.
Diseases where microbes are the immediate
causes are called infectious diseases. This is
because the microbes can spread in the
community, and the diseases they cause will
spread with them.
Things to ponder
1. Do all diseases spread to people
coming in contact with a sick person?
2. What are the diseases that are not
spreading?
3. How would a person develop those
diseases that don’t spread by contact
with a sick person?
On the other hand, there are also diseases
that are not caused by infectious agents. Their
causes vary, but they are not external causes
like microbes that can spread in the
community. Instead, these are mostly
internal, non-infectious causes.
For example, some cancers are caused by
genetic abnormalities. High blood pressure
can be caused by excessive weight and lack
of exercise. You can think of many other
diseases where the immediate causes will not
be infectious.
our health. We do not lose weight, we do not
become short of breath, we do not feel tired
all the time because of a few days of cough
and cold. But if we get infected with a chronic
disease such as tuberculosis of the lungs,
then being ill over the years does make us
lose weight and feel tired all the time.
We may not go to school for a few days if
we have an acute disease. But a chronic
disease will make it difficult for us to follow
what is being taught in school and reduce
our ability to learn. In other words, we are
likely to have prolonged general poor health
if we have a chronic disease. Chronic diseases
therefore, have very drastic long-term effects
on people’s health as compared to acute
diseases.
13.2.4 CAUSES OF DISEASES
What causes disease? When we think about
causes of diseases, we must remember that
there are many levels of such causes. Let us
look at an example. If there is a baby suffering
from loose motions, we can say that the cause
of the loose motions is an infection with a
virus. So the immediate cause of the disease
is a virus.
But the next question is – where did the
virus come from? Suppose we find that the
virus came through unclean drinking water.
But many babies must have had this unclean
drinking water. So, why is it that one baby
developed loose motions when the other
babies did not?
One reason might be that this baby is not
healthy. As a result, it might be more likely
to have disease when exposed to risk, whereas
healthier babies would not. Why is the baby
not healthy? Perhaps because it is not well
nourished and does not get enough food. So,
lack of good nourishment becomes a second-
level cause of the disease the baby is suffering
from. Further, why is the baby not well
nourished? Perhaps because it is from a
household which is poor.
It is also possible that the baby has some
genetic difference that makes it more likely
to suffer from loose motions when exposed
to such a virus. Without the virus, the genetic
difference or the poor nourishment alone
SCIENCE 180
The ways in which diseases spread, and
the ways in which they can be treated and
prevented at the community level would be
different for different diseases. This would
depend a lot on whether the immediate
causes are infectious or non-infectious.
uestions
1. List any three reasons why you
would think that you are sick and
ought to see a doctor. If only one
of these symptoms were present,
would you still go to the doctor?
Why or why not?
2. In which of the following case do
you think the long-term effects on
your health are likely to be most
unpleasant?
• if you get jaundice,
• if you get lice,
• if you get acne.
Why?
13.3 Infectious Diseases
13.3.1 INFECTIOUS AGENTS
We have seen that the entire diversity seen in
the living world can be classified into a few
groups. This classification is based on
common characteristics between different
organisms. Organisms that can cause disease
are found in a wide range of such categories
of classification. Some of them are viruses,
some are bacteria, some are fungi, some are
single-celled animals or protozoans. Some
diseases are also caused by multicellular
organisms, such as worms of different kinds.
Peptic ulcers and the Nobel prize
For many years, everybody used to think
that peptic ulcers, which cause acidity–
related pain and bleeding in the stomach
and duodenum, were because of lifestyle
reasons. Everybody thought that a
stressful life led to a lot of acid secretion
in the stomach, and eventually caused
peptic ulcers.
Then two Australians made a discovery
that a bacterium, Helicobacter pylori, was
responsible for peptic ulcers. Robin Warren
(born 1937), a pathologist from Perth,
Australia, saw these small curved bacteria
in the lower part of the stomach in many
patients. He noticed that signs of
inflammation were always present around
these bacteria. Barry Marshall (born 1951),
a young clinical fellow, became interested
in Warren’s findings and succeeded in
cultivating the bacteria from these sources.
In treatment studies, Marshall and
Warren showed that patients could be
cured of peptic ulcer only when the
bacteria were killed off from the stomach.
Thanks to this pioneering discovery by
Marshall and Warren, peptic ulcer disease
is no longer a chronic, frequently disabling
condition, but a disease that can be cured
by a short period of treatment with
antibiotics.
Q
For this achievement, Marshall and
Warren (seen in the picture) received the
Nobel prize for physiology and medicine
in 2005.
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