NCERT Textbook: Human Health & Disease | Biology Class 12 - NEET PDF Download

 Page 1


Chapter 7
Human Health and Disease
Chapter 8
Microbes in Human Welfare
Biology is the youngest of the formalised disciplines of natural
science. Progress in physics and chemistry proceeded much
faster than in Biology. Applications of physics and chemistry in
our daily life also have a higher visibility than those of biology.
However, twentieth century and certainly twenty-first century
has demonstrated the utility of biological knowledge in
furthering human welfare, be it in health sector or agriculture.
The discovery of antibiotics, and synthetic plant-derived drugs,
anaesthetics have changed medical practice on one hand
and human health on the other hand. Life expectancy of
human beings have dramatically changed over the years.
Agricultural practices, food processing and diagnostics have
brought socio-cultural changes in human communities. These
are briefly described in the following three chapters of this unit.
2024-25
Page 2


Chapter 7
Human Health and Disease
Chapter 8
Microbes in Human Welfare
Biology is the youngest of the formalised disciplines of natural
science. Progress in physics and chemistry proceeded much
faster than in Biology. Applications of physics and chemistry in
our daily life also have a higher visibility than those of biology.
However, twentieth century and certainly twenty-first century
has demonstrated the utility of biological knowledge in
furthering human welfare, be it in health sector or agriculture.
The discovery of antibiotics, and synthetic plant-derived drugs,
anaesthetics have changed medical practice on one hand
and human health on the other hand. Life expectancy of
human beings have dramatically changed over the years.
Agricultural practices, food processing and diagnostics have
brought socio-cultural changes in human communities. These
are briefly described in the following three chapters of this unit.
2024-25
Born in August 1925 in Kumbakonam in Tamil Nadu, Monkambu Sambasivan
Swaminathan did his graduation and post-graduation in Botany from
Madras University. He worked in different capacities in large number of
institutions in India and abroad and developed his expertise in genetics
and plant breeding.
The School of Cytogenetics and Radiation Research established at the
Indian Agricultural Research Institute (IARI) enabled Swaminathan and his
team to develop short-duration high-yielding varieties of rice including scented
Basmati. He is also known for the development of the concept of crop
cafeteria, crop scheduling and genetically improving the yield and quality.
Swaminathan initiated collaboration with Norman Borlaug, which
culminated in the ‘Green Revolution’ through introduction of Mexican
varieties of wheat in India. This was highly recognised and appreciated. He
is also the initiator of ‘Lab-to-Land’, food security and several other
environmental programmes. He has been honoured with Padma Bhushan
and several other prestigious awards, medals and fellowships by institutions
of excellence.
M.S. SWAMINATHAN
(1925)
2024-25
Page 3


Chapter 7
Human Health and Disease
Chapter 8
Microbes in Human Welfare
Biology is the youngest of the formalised disciplines of natural
science. Progress in physics and chemistry proceeded much
faster than in Biology. Applications of physics and chemistry in
our daily life also have a higher visibility than those of biology.
However, twentieth century and certainly twenty-first century
has demonstrated the utility of biological knowledge in
furthering human welfare, be it in health sector or agriculture.
The discovery of antibiotics, and synthetic plant-derived drugs,
anaesthetics have changed medical practice on one hand
and human health on the other hand. Life expectancy of
human beings have dramatically changed over the years.
Agricultural practices, food processing and diagnostics have
brought socio-cultural changes in human communities. These
are briefly described in the following three chapters of this unit.
2024-25
Born in August 1925 in Kumbakonam in Tamil Nadu, Monkambu Sambasivan
Swaminathan did his graduation and post-graduation in Botany from
Madras University. He worked in different capacities in large number of
institutions in India and abroad and developed his expertise in genetics
and plant breeding.
The School of Cytogenetics and Radiation Research established at the
Indian Agricultural Research Institute (IARI) enabled Swaminathan and his
team to develop short-duration high-yielding varieties of rice including scented
Basmati. He is also known for the development of the concept of crop
cafeteria, crop scheduling and genetically improving the yield and quality.
Swaminathan initiated collaboration with Norman Borlaug, which
culminated in the ‘Green Revolution’ through introduction of Mexican
varieties of wheat in India. This was highly recognised and appreciated. He
is also the initiator of ‘Lab-to-Land’, food security and several other
environmental programmes. He has been honoured with Padma Bhushan
and several other prestigious awards, medals and fellowships by institutions
of excellence.
M.S. SWAMINATHAN
(1925)
2024-25
Health, for a long time, was considered as a state of body
and mind where there was a balance of certain ‘humors’.
This is what early Greeks like Hippocrates as well as
Indian Ayurveda system of medicine asserted. It was
thought that persons with ‘blackbile’ belonged to hot
personality and would have fevers. This idea was arrived
at by pure reflective thought. The discovery of blood
circulation by William Harvey using experimental method
and the demonstration of normal body temperature in
persons with blackbile using thermometer disproved the
‘good humor’ hypothesis of health. In later years, biology
stated that mind influences, through neural system and
endocrine system, our immune system and that our
immune system maintains our health. Hence, mind and
mental state can affect our health. Of course, health is
affected by –
(i) genetic disorders – deficiencies with which a child is
born and deficiencies/defects which the child inherits
from parents from birth;
(ii) infections  and
(iii) life style including food and water we take, rest and
exercise we give to our bodies, habits that we have or
lack etc.
CHAPTER 7
HUMAN HEALTH AND DISEASE
7.1 Common Diseases in
Humans
7.2 Immunity
7.3 AIDS
7.4 Cancer
7.5 Drugs and Alcohol Abuse
2024-25
Page 4


Chapter 7
Human Health and Disease
Chapter 8
Microbes in Human Welfare
Biology is the youngest of the formalised disciplines of natural
science. Progress in physics and chemistry proceeded much
faster than in Biology. Applications of physics and chemistry in
our daily life also have a higher visibility than those of biology.
However, twentieth century and certainly twenty-first century
has demonstrated the utility of biological knowledge in
furthering human welfare, be it in health sector or agriculture.
The discovery of antibiotics, and synthetic plant-derived drugs,
anaesthetics have changed medical practice on one hand
and human health on the other hand. Life expectancy of
human beings have dramatically changed over the years.
Agricultural practices, food processing and diagnostics have
brought socio-cultural changes in human communities. These
are briefly described in the following three chapters of this unit.
2024-25
Born in August 1925 in Kumbakonam in Tamil Nadu, Monkambu Sambasivan
Swaminathan did his graduation and post-graduation in Botany from
Madras University. He worked in different capacities in large number of
institutions in India and abroad and developed his expertise in genetics
and plant breeding.
The School of Cytogenetics and Radiation Research established at the
Indian Agricultural Research Institute (IARI) enabled Swaminathan and his
team to develop short-duration high-yielding varieties of rice including scented
Basmati. He is also known for the development of the concept of crop
cafeteria, crop scheduling and genetically improving the yield and quality.
Swaminathan initiated collaboration with Norman Borlaug, which
culminated in the ‘Green Revolution’ through introduction of Mexican
varieties of wheat in India. This was highly recognised and appreciated. He
is also the initiator of ‘Lab-to-Land’, food security and several other
environmental programmes. He has been honoured with Padma Bhushan
and several other prestigious awards, medals and fellowships by institutions
of excellence.
M.S. SWAMINATHAN
(1925)
2024-25
Health, for a long time, was considered as a state of body
and mind where there was a balance of certain ‘humors’.
This is what early Greeks like Hippocrates as well as
Indian Ayurveda system of medicine asserted. It was
thought that persons with ‘blackbile’ belonged to hot
personality and would have fevers. This idea was arrived
at by pure reflective thought. The discovery of blood
circulation by William Harvey using experimental method
and the demonstration of normal body temperature in
persons with blackbile using thermometer disproved the
‘good humor’ hypothesis of health. In later years, biology
stated that mind influences, through neural system and
endocrine system, our immune system and that our
immune system maintains our health. Hence, mind and
mental state can affect our health. Of course, health is
affected by –
(i) genetic disorders – deficiencies with which a child is
born and deficiencies/defects which the child inherits
from parents from birth;
(ii) infections  and
(iii) life style including food and water we take, rest and
exercise we give to our bodies, habits that we have or
lack etc.
CHAPTER 7
HUMAN HEALTH AND DISEASE
7.1 Common Diseases in
Humans
7.2 Immunity
7.3 AIDS
7.4 Cancer
7.5 Drugs and Alcohol Abuse
2024-25
130
BIOLOGY
The term health is very frequently used by everybody. How do we
define it? Health does not simply mean ‘absence of disease’ or ‘physical
fitness’. It could be defined as a state of complete physical, mental and
social well-being. When people are healthy, they are more efficient at
work. This increases productivity and brings economic prosperity. Health
also increases longevity of people and reduces infant and maternal
mortality.
Balanced diet, personal hygiene and regular exercise are very important
to maintain good health. Yoga has been practised since time immemorial
to achieve physical and mental health. Awareness about diseases and
their effect on different bodily functions, vaccination (immunisation)
against infectious diseases, proper disposal of wastes, control of vectors
and maintenance of hygiene in food and water resources are necessary
for achieving good health.
When the functioning of one or more organs or systems of the body is
adversely affected, characterised by appearance of various signs and
symptoms, we say that we are not healthy, i.e., we have a disease. Diseases
can be broadly grouped into infectious and non-infectious. Diseases
which are easily transmitted from one person to another, are called
infectious diseases.  Infectious diseases are very common and every
one of us suffers from these at sometime or other. Some of the infectious
diseases like AIDS are fatal. Among non-infectious diseases, cancer is the
major cause of death. Drug and alcohol abuse also affect our health adversely.
7.1 COMMON DISEASES IN HUMANS
A wide range of organisms belonging to bacteria, viruses, fungi,
protozoans, helminths, etc., could cause diseases in man. Such disease-
causing organisms are called pathogens. Most parasites are therefore
pathogens as they cause harm to the host by living in (or on) them. The
pathogens can enter our body by various means, multiply  and interfere
with normal vital activities, resulting in morphological and functional
damage. Pathogens have to adapt to life within the environment of the
host. For example, the pathogens that enter the gut must know a way of
surviving in the stomach at low pH and resisting the various digestive
enzymes. A few representative members from different groups of
pathogenic organisms are discussed here alongwith the diseases caused
by them. Preventive and control measures against these diseases in general,
are also briefly described.
Salmonella typhi is a pathogenic bacterium which causes typhoid
fever in human beings. These pathogens generally enter the small intestine
through food and water contaminated with them and migrate to other
organs through blood. Sustained high fever (39° to 40°C), weakness,
stomach pain, constipation, headache and loss of appetite are some of
the  common symptoms of this disease. Intestinal perforation and death
may occur in severe cases. Typhoid fever could be confirmed by
2024-25
Page 5


Chapter 7
Human Health and Disease
Chapter 8
Microbes in Human Welfare
Biology is the youngest of the formalised disciplines of natural
science. Progress in physics and chemistry proceeded much
faster than in Biology. Applications of physics and chemistry in
our daily life also have a higher visibility than those of biology.
However, twentieth century and certainly twenty-first century
has demonstrated the utility of biological knowledge in
furthering human welfare, be it in health sector or agriculture.
The discovery of antibiotics, and synthetic plant-derived drugs,
anaesthetics have changed medical practice on one hand
and human health on the other hand. Life expectancy of
human beings have dramatically changed over the years.
Agricultural practices, food processing and diagnostics have
brought socio-cultural changes in human communities. These
are briefly described in the following three chapters of this unit.
2024-25
Born in August 1925 in Kumbakonam in Tamil Nadu, Monkambu Sambasivan
Swaminathan did his graduation and post-graduation in Botany from
Madras University. He worked in different capacities in large number of
institutions in India and abroad and developed his expertise in genetics
and plant breeding.
The School of Cytogenetics and Radiation Research established at the
Indian Agricultural Research Institute (IARI) enabled Swaminathan and his
team to develop short-duration high-yielding varieties of rice including scented
Basmati. He is also known for the development of the concept of crop
cafeteria, crop scheduling and genetically improving the yield and quality.
Swaminathan initiated collaboration with Norman Borlaug, which
culminated in the ‘Green Revolution’ through introduction of Mexican
varieties of wheat in India. This was highly recognised and appreciated. He
is also the initiator of ‘Lab-to-Land’, food security and several other
environmental programmes. He has been honoured with Padma Bhushan
and several other prestigious awards, medals and fellowships by institutions
of excellence.
M.S. SWAMINATHAN
(1925)
2024-25
Health, for a long time, was considered as a state of body
and mind where there was a balance of certain ‘humors’.
This is what early Greeks like Hippocrates as well as
Indian Ayurveda system of medicine asserted. It was
thought that persons with ‘blackbile’ belonged to hot
personality and would have fevers. This idea was arrived
at by pure reflective thought. The discovery of blood
circulation by William Harvey using experimental method
and the demonstration of normal body temperature in
persons with blackbile using thermometer disproved the
‘good humor’ hypothesis of health. In later years, biology
stated that mind influences, through neural system and
endocrine system, our immune system and that our
immune system maintains our health. Hence, mind and
mental state can affect our health. Of course, health is
affected by –
(i) genetic disorders – deficiencies with which a child is
born and deficiencies/defects which the child inherits
from parents from birth;
(ii) infections  and
(iii) life style including food and water we take, rest and
exercise we give to our bodies, habits that we have or
lack etc.
CHAPTER 7
HUMAN HEALTH AND DISEASE
7.1 Common Diseases in
Humans
7.2 Immunity
7.3 AIDS
7.4 Cancer
7.5 Drugs and Alcohol Abuse
2024-25
130
BIOLOGY
The term health is very frequently used by everybody. How do we
define it? Health does not simply mean ‘absence of disease’ or ‘physical
fitness’. It could be defined as a state of complete physical, mental and
social well-being. When people are healthy, they are more efficient at
work. This increases productivity and brings economic prosperity. Health
also increases longevity of people and reduces infant and maternal
mortality.
Balanced diet, personal hygiene and regular exercise are very important
to maintain good health. Yoga has been practised since time immemorial
to achieve physical and mental health. Awareness about diseases and
their effect on different bodily functions, vaccination (immunisation)
against infectious diseases, proper disposal of wastes, control of vectors
and maintenance of hygiene in food and water resources are necessary
for achieving good health.
When the functioning of one or more organs or systems of the body is
adversely affected, characterised by appearance of various signs and
symptoms, we say that we are not healthy, i.e., we have a disease. Diseases
can be broadly grouped into infectious and non-infectious. Diseases
which are easily transmitted from one person to another, are called
infectious diseases.  Infectious diseases are very common and every
one of us suffers from these at sometime or other. Some of the infectious
diseases like AIDS are fatal. Among non-infectious diseases, cancer is the
major cause of death. Drug and alcohol abuse also affect our health adversely.
7.1 COMMON DISEASES IN HUMANS
A wide range of organisms belonging to bacteria, viruses, fungi,
protozoans, helminths, etc., could cause diseases in man. Such disease-
causing organisms are called pathogens. Most parasites are therefore
pathogens as they cause harm to the host by living in (or on) them. The
pathogens can enter our body by various means, multiply  and interfere
with normal vital activities, resulting in morphological and functional
damage. Pathogens have to adapt to life within the environment of the
host. For example, the pathogens that enter the gut must know a way of
surviving in the stomach at low pH and resisting the various digestive
enzymes. A few representative members from different groups of
pathogenic organisms are discussed here alongwith the diseases caused
by them. Preventive and control measures against these diseases in general,
are also briefly described.
Salmonella typhi is a pathogenic bacterium which causes typhoid
fever in human beings. These pathogens generally enter the small intestine
through food and water contaminated with them and migrate to other
organs through blood. Sustained high fever (39° to 40°C), weakness,
stomach pain, constipation, headache and loss of appetite are some of
the  common symptoms of this disease. Intestinal perforation and death
may occur in severe cases. Typhoid fever could be confirmed by
2024-25
HUMAN HEALTH AND DISEASE
131
Widal test : A classic case in medicine, that of Mary Mallon nicknamed
Typhoid Mary, is worth mentioning here. She was a cook by profession
and  was a typhoid carrier who continued to spread typhoid for several
years through the food she prepared.
Bacteria like Streptococcus pneumoniae and Haemophilus influenzae
are responsible for the disease pneumonia in humans which infects the
alveoli (air filled sacs) of the lungs. As a result of the infection, the alveoli
get filled with fluid leading to severe problems in respiration. The symptoms
of pneumonia include fever, chills, cough and headache. In severe cases,
the lips and finger nails may turn gray to bluish in colour.  A healthy
person acquires the infection by inhaling the droplets/aerosols released
by an infected person or even by sharing glasses and utensils with an
infected person.  Dysentery, plague, diphtheria, etc., are some of the other
bacterial diseases in man.
Many viruses also cause diseases in human beings. Rhino viruses
represent one such group of viruses which cause one of the most infectious
human ailments – the common cold.  They infect the nose and respiratory
passage but not the lungs. The common cold is characterised by nasal
congestion and discharge, sore throat, hoarseness, cough, headache,
tiredness, etc., which usually last for 3-7 days. Droplets resulting from
cough or sneezes of an infected person are either inhaled directly or
transmitted through contaminated objects such as pens, books, cups,
doorknobs, computer keyboard or mouse, etc., and cause infection in a
healthy person.
Some of the human diseases are caused by protozoans too. You might
have heard about malaria, a disease man has been fighting since many
years. Plasmodium, a tiny protozoan is responsible for this disease. Different
species of Plasmodium (P. vivax, P. malaria and P. falciparum) are
responsible for different types of malaria. Of these, malignant malaria caused
by Plasmodium falciparum is the most serious one and can even be fatal.
Let us take a glance at the life cycle of Plasmodium (Figure 7.1).
Plasmodium enters the human body as sporozoites (infectious form)
through the bite of infected female Anopheles mosquito. The parasites
initially multiply within the liver cells and then attack the red blood cells
(RBCs) resulting in their rupture. The rupture of RBCs is associated with
release of a toxic substance, haemozoin, which is responsible for the chill
and high fever recurring every three to four days. When a female Anopheles
mosquito bites an infected person, these parasites enter the mosquito’s
body and undergo further development. The parasites multiply within
them to form sporozoites that are stored in their salivary glands. When
these mosquitoes bite a human, the sporozoites are introduced into his/
her body, thereby initiating the events mentioned above. It is interesting
to note that the malarial parasite requires two hosts – human and
mosquitoes – to complete its life cycle (Figure 7.1); the female Anopheles
mosquito is the vector (transmitting agent) too.
2024-25