NCERT Textbook: Reaching the Age of Adolescence | Science Class 8 PDF Download

 Page 1


I
n the previous chapter, you have
learnt how animals reproduce. It is
only after ‘growing up’ to a certain
age that human beings and many other
animals can reproduce. Why can
humans reproduce only after a certain
age?
In this chapter, you will learn about
changes that take place in the human
body after which a person becomes
capable of reproduction.
In Chapter 6, you have learnt about
human reproductive organs. Here, we
shall discuss the role that hormones play
in bringing about changes that make a
child grow into an adult.
7.1 Adolescence and Puberty
Boojho was celebrating his 12th
birthday. After his friends left, Boojho
and Paheli began chatting with their
parents. Paheli studies in an all-girls
school. She started laughing. She
remarked that many of Boojho’s  school
friends, whom she met after a year, had
suddenly shot up in height. Some of
them were looking very funny with a
hairy line above their lips. Her mother
explained that the boys had grown up.
Growth begins from the day one is
born. But upon crossing the age of 10
or 11, there is a sudden spurt in growth
which becomes noticeable. The changes
taking place in the body are part of
growing up. They indicate that you are
I wonder how long this
period marked by changes
in the body will last!
no longer a child but are on the way to
becoming an adult.
It is a strange period of life
when you are neither a child nor
an adult. I wonder whether this
period between childhood and
adulthood had a special name!
Growing up is a natural process. The
period of life, when the body undergoes
changes, leading to reproductive
maturity, is called adolescence.
Adolescence begins around the age of
11 and lasts upto 18 or 19 years of age.
Since this period covers the ‘teens’ (13
to 18 or 19 years of age), adolescents
are also called ‘teenagers’. In girls,
adolescence may begin a year or two
earlier than in boys. Also, the period of
adolescence varies from person to person.
The human body undergoes several
changes during adolescence. These
changes mark the onset of puberty. The
most important change which marks
puberty is that boys and girls become
capable of reproduction. Puberty ends
when an adolescent reaches reproductive
maturity.
REACHING THE AGE OF ADOLESCENCE
REACHING THE AGE OF ADOLESCENCE
2024-25
Page 2


I
n the previous chapter, you have
learnt how animals reproduce. It is
only after ‘growing up’ to a certain
age that human beings and many other
animals can reproduce. Why can
humans reproduce only after a certain
age?
In this chapter, you will learn about
changes that take place in the human
body after which a person becomes
capable of reproduction.
In Chapter 6, you have learnt about
human reproductive organs. Here, we
shall discuss the role that hormones play
in bringing about changes that make a
child grow into an adult.
7.1 Adolescence and Puberty
Boojho was celebrating his 12th
birthday. After his friends left, Boojho
and Paheli began chatting with their
parents. Paheli studies in an all-girls
school. She started laughing. She
remarked that many of Boojho’s  school
friends, whom she met after a year, had
suddenly shot up in height. Some of
them were looking very funny with a
hairy line above their lips. Her mother
explained that the boys had grown up.
Growth begins from the day one is
born. But upon crossing the age of 10
or 11, there is a sudden spurt in growth
which becomes noticeable. The changes
taking place in the body are part of
growing up. They indicate that you are
I wonder how long this
period marked by changes
in the body will last!
no longer a child but are on the way to
becoming an adult.
It is a strange period of life
when you are neither a child nor
an adult. I wonder whether this
period between childhood and
adulthood had a special name!
Growing up is a natural process. The
period of life, when the body undergoes
changes, leading to reproductive
maturity, is called adolescence.
Adolescence begins around the age of
11 and lasts upto 18 or 19 years of age.
Since this period covers the ‘teens’ (13
to 18 or 19 years of age), adolescents
are also called ‘teenagers’. In girls,
adolescence may begin a year or two
earlier than in boys. Also, the period of
adolescence varies from person to person.
The human body undergoes several
changes during adolescence. These
changes mark the onset of puberty. The
most important change which marks
puberty is that boys and girls become
capable of reproduction. Puberty ends
when an adolescent reaches reproductive
maturity.
REACHING THE AGE OF ADOLESCENCE
REACHING THE AGE OF ADOLESCENCE
2024-25
SCIENCE 80
% of full height
Boys Girls
8 72% 77%
9 75% 81%
10 78% 84%
11 81% 88%
12 84% 91%
13 88% 95%
14 92% 98%
15 95% 99%
16 98% 99.5%
17 99% 100%
18 100% 100%
Age in
Years
Paheli and Boojho
realised that sudden
increase in height and
hairy line above the lips
in boys were signs of
adolescence. They
wanted to know more
about other changes at
puberty.
7.2 Changes at Puberty
Increase in Height
The most conspicuous change during
puberty is the sudden increase in
height. At this time the long bones, that
is, the bones of the arms and the legs
elongate and make a person tall.
Activity 7.1
The following chart gives the
average rate of growth in height of
boys and girls with age. The figures
in columns 2 and 3, give the
percentage of the height a person
has reached at the age given in
column 1. For example, by the age
11, a boy has reached 81% of his
probable full height, while a girl
has reached 88% of her full
height. These figures are only
representative and there may be
individual variations.
Use the Table for your friends
and work out how tall they are likely
to be. Find out who is likely to be
Calculation for full height (cm)
( )
100
Presentheight cm
% of fullheightatthisage
×
    (as given in the chart)
Example:
A boy is 9 years old and 120 cm
tall. At the end of the growth period
he is likely to be
×
120
100
75
 cm = 160 cm tall
the tallest and who might be the
shortest in your class.
2024-25
Page 3


I
n the previous chapter, you have
learnt how animals reproduce. It is
only after ‘growing up’ to a certain
age that human beings and many other
animals can reproduce. Why can
humans reproduce only after a certain
age?
In this chapter, you will learn about
changes that take place in the human
body after which a person becomes
capable of reproduction.
In Chapter 6, you have learnt about
human reproductive organs. Here, we
shall discuss the role that hormones play
in bringing about changes that make a
child grow into an adult.
7.1 Adolescence and Puberty
Boojho was celebrating his 12th
birthday. After his friends left, Boojho
and Paheli began chatting with their
parents. Paheli studies in an all-girls
school. She started laughing. She
remarked that many of Boojho’s  school
friends, whom she met after a year, had
suddenly shot up in height. Some of
them were looking very funny with a
hairy line above their lips. Her mother
explained that the boys had grown up.
Growth begins from the day one is
born. But upon crossing the age of 10
or 11, there is a sudden spurt in growth
which becomes noticeable. The changes
taking place in the body are part of
growing up. They indicate that you are
I wonder how long this
period marked by changes
in the body will last!
no longer a child but are on the way to
becoming an adult.
It is a strange period of life
when you are neither a child nor
an adult. I wonder whether this
period between childhood and
adulthood had a special name!
Growing up is a natural process. The
period of life, when the body undergoes
changes, leading to reproductive
maturity, is called adolescence.
Adolescence begins around the age of
11 and lasts upto 18 or 19 years of age.
Since this period covers the ‘teens’ (13
to 18 or 19 years of age), adolescents
are also called ‘teenagers’. In girls,
adolescence may begin a year or two
earlier than in boys. Also, the period of
adolescence varies from person to person.
The human body undergoes several
changes during adolescence. These
changes mark the onset of puberty. The
most important change which marks
puberty is that boys and girls become
capable of reproduction. Puberty ends
when an adolescent reaches reproductive
maturity.
REACHING THE AGE OF ADOLESCENCE
REACHING THE AGE OF ADOLESCENCE
2024-25
SCIENCE 80
% of full height
Boys Girls
8 72% 77%
9 75% 81%
10 78% 84%
11 81% 88%
12 84% 91%
13 88% 95%
14 92% 98%
15 95% 99%
16 98% 99.5%
17 99% 100%
18 100% 100%
Age in
Years
Paheli and Boojho
realised that sudden
increase in height and
hairy line above the lips
in boys were signs of
adolescence. They
wanted to know more
about other changes at
puberty.
7.2 Changes at Puberty
Increase in Height
The most conspicuous change during
puberty is the sudden increase in
height. At this time the long bones, that
is, the bones of the arms and the legs
elongate and make a person tall.
Activity 7.1
The following chart gives the
average rate of growth in height of
boys and girls with age. The figures
in columns 2 and 3, give the
percentage of the height a person
has reached at the age given in
column 1. For example, by the age
11, a boy has reached 81% of his
probable full height, while a girl
has reached 88% of her full
height. These figures are only
representative and there may be
individual variations.
Use the Table for your friends
and work out how tall they are likely
to be. Find out who is likely to be
Calculation for full height (cm)
( )
100
Presentheight cm
% of fullheightatthisage
×
    (as given in the chart)
Example:
A boy is 9 years old and 120 cm
tall. At the end of the growth period
he is likely to be
×
120
100
75
 cm = 160 cm tall
the tallest and who might be the
shortest in your class.
2024-25
REACHING THE AGE OF ADOLESCENCE 81
There is no need for Paheli to worry.
All parts of the body do not grow at the
same rate. Sometimes the arms and legs
or hands and feet of adolescents look
oversized and out of proportion with the
body. But soon the other parts catch
up and result in a proportionate body.
You must have noticed that height
of an individual is more or less similar
to that of some family member. This is
because height depends on the genes
inherited from parents. It is, however,
very important to eat the right kind of
food during these growing years. This
helps the bones, muscles and other
parts of the body get adequate
nourishment for growth. You will find
nutritional needs of adolescents
discussed later in the lesson.
Change in Body Shape
Have you noticed that boys in your class
have broader shoulders and wider chests
than boys in  junior classes? This is
because they have entered the age of
puberty when shoulders generally
broaden as a result of growth. In girls,
the region below the waist becomes
wider.
In boys, the muscles of the body grow
more prominently than in the girls.
Thus, changes occurring in adolescent
boys and girls are different.
Voice Change
Did you notice that sometimes the voice
of some of the boys in your class cracks?
At puberty, the voice box or the larynx
begins to grow. Boys develop larger voice
boxes. The growing voice box in boys can
be seen as a protruding part of the throat
Activity 7.2
Use the data given in Activity 7.1 to
draw a graph. Take age on the
X-axis and per cent growth in height
on the Y-axis. Highlight the point
representing your age on the graph.
Find out the percentage of height
you have already reached. Calculate
the height you might eventually
reach. Tally your graph with the one
given here (Fig. 7.1).
Fig. 7.1 : Graph showing percentage of height
with age
I am worried. Though I
have become taller, my
face looks much smaller
compared to my body.
Initially, girls grow faster than boys
but by about 18 years of age, both reach
their maximum height. The rate of
growth in height varies in different
individuals. Some may grow suddenly
at puberty and then slow down, while
others may grow gradually.
2024-25
Page 4


I
n the previous chapter, you have
learnt how animals reproduce. It is
only after ‘growing up’ to a certain
age that human beings and many other
animals can reproduce. Why can
humans reproduce only after a certain
age?
In this chapter, you will learn about
changes that take place in the human
body after which a person becomes
capable of reproduction.
In Chapter 6, you have learnt about
human reproductive organs. Here, we
shall discuss the role that hormones play
in bringing about changes that make a
child grow into an adult.
7.1 Adolescence and Puberty
Boojho was celebrating his 12th
birthday. After his friends left, Boojho
and Paheli began chatting with their
parents. Paheli studies in an all-girls
school. She started laughing. She
remarked that many of Boojho’s  school
friends, whom she met after a year, had
suddenly shot up in height. Some of
them were looking very funny with a
hairy line above their lips. Her mother
explained that the boys had grown up.
Growth begins from the day one is
born. But upon crossing the age of 10
or 11, there is a sudden spurt in growth
which becomes noticeable. The changes
taking place in the body are part of
growing up. They indicate that you are
I wonder how long this
period marked by changes
in the body will last!
no longer a child but are on the way to
becoming an adult.
It is a strange period of life
when you are neither a child nor
an adult. I wonder whether this
period between childhood and
adulthood had a special name!
Growing up is a natural process. The
period of life, when the body undergoes
changes, leading to reproductive
maturity, is called adolescence.
Adolescence begins around the age of
11 and lasts upto 18 or 19 years of age.
Since this period covers the ‘teens’ (13
to 18 or 19 years of age), adolescents
are also called ‘teenagers’. In girls,
adolescence may begin a year or two
earlier than in boys. Also, the period of
adolescence varies from person to person.
The human body undergoes several
changes during adolescence. These
changes mark the onset of puberty. The
most important change which marks
puberty is that boys and girls become
capable of reproduction. Puberty ends
when an adolescent reaches reproductive
maturity.
REACHING THE AGE OF ADOLESCENCE
REACHING THE AGE OF ADOLESCENCE
2024-25
SCIENCE 80
% of full height
Boys Girls
8 72% 77%
9 75% 81%
10 78% 84%
11 81% 88%
12 84% 91%
13 88% 95%
14 92% 98%
15 95% 99%
16 98% 99.5%
17 99% 100%
18 100% 100%
Age in
Years
Paheli and Boojho
realised that sudden
increase in height and
hairy line above the lips
in boys were signs of
adolescence. They
wanted to know more
about other changes at
puberty.
7.2 Changes at Puberty
Increase in Height
The most conspicuous change during
puberty is the sudden increase in
height. At this time the long bones, that
is, the bones of the arms and the legs
elongate and make a person tall.
Activity 7.1
The following chart gives the
average rate of growth in height of
boys and girls with age. The figures
in columns 2 and 3, give the
percentage of the height a person
has reached at the age given in
column 1. For example, by the age
11, a boy has reached 81% of his
probable full height, while a girl
has reached 88% of her full
height. These figures are only
representative and there may be
individual variations.
Use the Table for your friends
and work out how tall they are likely
to be. Find out who is likely to be
Calculation for full height (cm)
( )
100
Presentheight cm
% of fullheightatthisage
×
    (as given in the chart)
Example:
A boy is 9 years old and 120 cm
tall. At the end of the growth period
he is likely to be
×
120
100
75
 cm = 160 cm tall
the tallest and who might be the
shortest in your class.
2024-25
REACHING THE AGE OF ADOLESCENCE 81
There is no need for Paheli to worry.
All parts of the body do not grow at the
same rate. Sometimes the arms and legs
or hands and feet of adolescents look
oversized and out of proportion with the
body. But soon the other parts catch
up and result in a proportionate body.
You must have noticed that height
of an individual is more or less similar
to that of some family member. This is
because height depends on the genes
inherited from parents. It is, however,
very important to eat the right kind of
food during these growing years. This
helps the bones, muscles and other
parts of the body get adequate
nourishment for growth. You will find
nutritional needs of adolescents
discussed later in the lesson.
Change in Body Shape
Have you noticed that boys in your class
have broader shoulders and wider chests
than boys in  junior classes? This is
because they have entered the age of
puberty when shoulders generally
broaden as a result of growth. In girls,
the region below the waist becomes
wider.
In boys, the muscles of the body grow
more prominently than in the girls.
Thus, changes occurring in adolescent
boys and girls are different.
Voice Change
Did you notice that sometimes the voice
of some of the boys in your class cracks?
At puberty, the voice box or the larynx
begins to grow. Boys develop larger voice
boxes. The growing voice box in boys can
be seen as a protruding part of the throat
Activity 7.2
Use the data given in Activity 7.1 to
draw a graph. Take age on the
X-axis and per cent growth in height
on the Y-axis. Highlight the point
representing your age on the graph.
Find out the percentage of height
you have already reached. Calculate
the height you might eventually
reach. Tally your graph with the one
given here (Fig. 7.1).
Fig. 7.1 : Graph showing percentage of height
with age
I am worried. Though I
have become taller, my
face looks much smaller
compared to my body.
Initially, girls grow faster than boys
but by about 18 years of age, both reach
their maximum height. The rate of
growth in height varies in different
individuals. Some may grow suddenly
at puberty and then slow down, while
others may grow gradually.
2024-25
SCIENCE 82
and pimples on the face at this time
because of the increased activity of these
glands in the skin.
Development of Sex Organs
Look up Fig. 6.1 and 6.3 of the
previous lesson which show sex
organs of humans. At puberty, male
sex organs like the testes and penis
develop completely. The testes also
begin to produce sperms. In girls, the
ovaries enlarge and eggs begin to
mature. Also ovaries start releasing
mature eggs.
Reaching Mental, Intellectual and
Emotional Maturity
Adolescence is also a period of change
in a person’s way of thinking.
Adolescents are more independent than
before and are also self conscious.
Intellectual development takes place and
they tend to spend considerable time
thinking. In fact, it is often the time in
one’s life when the brain has the
greatest capacity for learning.
Sometimes, however, an adolescent may
feel insecure while trying to adjust to
the changes in the body and mind. But
as adolescent learners, you should know
that there is no reason to feel insecure.
These changes are a natural part of
growing up.
7.3 Secondary Sexual
Characters
You have learnt in Chapter 6, that
testes and ovaries are the reproductive
organs. They produce the gametes,
that is, sperms and ova. In girls,
breasts begin to develop at puberty
Many of my classmates
have a hoarse voice. Now I
know why?
Fig. 7.2 : Adam’s apple in a grown up boy
called Adam’s apple (Fig. 7.2). In girls,
the larynx is hardly visible from the
outside because of its small size.
Generally, girls have a high pitched voice,
whereas boys have a deep voice. In
adolescent boys, sometimes, the muscles
of the growing voice box go out of control
and the voice becomes hoarse. This state
may remain for a few days or weeks after
which the voice becomes normal.
A few glands such as sweat glands,
oil glands and salivary glands release
their secretions through ducts.
Endocrine glands release hormones
directly into the bloodstream. So, they
are also termed ductless glands.
Increased Activity of Sweat and
Sebaceous Glands
During puberty the secretion of sweat
glands and sebaceous glands (oil glands)
increases. Many young people get acne
Adam’s
apple
2024-25
Page 5


I
n the previous chapter, you have
learnt how animals reproduce. It is
only after ‘growing up’ to a certain
age that human beings and many other
animals can reproduce. Why can
humans reproduce only after a certain
age?
In this chapter, you will learn about
changes that take place in the human
body after which a person becomes
capable of reproduction.
In Chapter 6, you have learnt about
human reproductive organs. Here, we
shall discuss the role that hormones play
in bringing about changes that make a
child grow into an adult.
7.1 Adolescence and Puberty
Boojho was celebrating his 12th
birthday. After his friends left, Boojho
and Paheli began chatting with their
parents. Paheli studies in an all-girls
school. She started laughing. She
remarked that many of Boojho’s  school
friends, whom she met after a year, had
suddenly shot up in height. Some of
them were looking very funny with a
hairy line above their lips. Her mother
explained that the boys had grown up.
Growth begins from the day one is
born. But upon crossing the age of 10
or 11, there is a sudden spurt in growth
which becomes noticeable. The changes
taking place in the body are part of
growing up. They indicate that you are
I wonder how long this
period marked by changes
in the body will last!
no longer a child but are on the way to
becoming an adult.
It is a strange period of life
when you are neither a child nor
an adult. I wonder whether this
period between childhood and
adulthood had a special name!
Growing up is a natural process. The
period of life, when the body undergoes
changes, leading to reproductive
maturity, is called adolescence.
Adolescence begins around the age of
11 and lasts upto 18 or 19 years of age.
Since this period covers the ‘teens’ (13
to 18 or 19 years of age), adolescents
are also called ‘teenagers’. In girls,
adolescence may begin a year or two
earlier than in boys. Also, the period of
adolescence varies from person to person.
The human body undergoes several
changes during adolescence. These
changes mark the onset of puberty. The
most important change which marks
puberty is that boys and girls become
capable of reproduction. Puberty ends
when an adolescent reaches reproductive
maturity.
REACHING THE AGE OF ADOLESCENCE
REACHING THE AGE OF ADOLESCENCE
2024-25
SCIENCE 80
% of full height
Boys Girls
8 72% 77%
9 75% 81%
10 78% 84%
11 81% 88%
12 84% 91%
13 88% 95%
14 92% 98%
15 95% 99%
16 98% 99.5%
17 99% 100%
18 100% 100%
Age in
Years
Paheli and Boojho
realised that sudden
increase in height and
hairy line above the lips
in boys were signs of
adolescence. They
wanted to know more
about other changes at
puberty.
7.2 Changes at Puberty
Increase in Height
The most conspicuous change during
puberty is the sudden increase in
height. At this time the long bones, that
is, the bones of the arms and the legs
elongate and make a person tall.
Activity 7.1
The following chart gives the
average rate of growth in height of
boys and girls with age. The figures
in columns 2 and 3, give the
percentage of the height a person
has reached at the age given in
column 1. For example, by the age
11, a boy has reached 81% of his
probable full height, while a girl
has reached 88% of her full
height. These figures are only
representative and there may be
individual variations.
Use the Table for your friends
and work out how tall they are likely
to be. Find out who is likely to be
Calculation for full height (cm)
( )
100
Presentheight cm
% of fullheightatthisage
×
    (as given in the chart)
Example:
A boy is 9 years old and 120 cm
tall. At the end of the growth period
he is likely to be
×
120
100
75
 cm = 160 cm tall
the tallest and who might be the
shortest in your class.
2024-25
REACHING THE AGE OF ADOLESCENCE 81
There is no need for Paheli to worry.
All parts of the body do not grow at the
same rate. Sometimes the arms and legs
or hands and feet of adolescents look
oversized and out of proportion with the
body. But soon the other parts catch
up and result in a proportionate body.
You must have noticed that height
of an individual is more or less similar
to that of some family member. This is
because height depends on the genes
inherited from parents. It is, however,
very important to eat the right kind of
food during these growing years. This
helps the bones, muscles and other
parts of the body get adequate
nourishment for growth. You will find
nutritional needs of adolescents
discussed later in the lesson.
Change in Body Shape
Have you noticed that boys in your class
have broader shoulders and wider chests
than boys in  junior classes? This is
because they have entered the age of
puberty when shoulders generally
broaden as a result of growth. In girls,
the region below the waist becomes
wider.
In boys, the muscles of the body grow
more prominently than in the girls.
Thus, changes occurring in adolescent
boys and girls are different.
Voice Change
Did you notice that sometimes the voice
of some of the boys in your class cracks?
At puberty, the voice box or the larynx
begins to grow. Boys develop larger voice
boxes. The growing voice box in boys can
be seen as a protruding part of the throat
Activity 7.2
Use the data given in Activity 7.1 to
draw a graph. Take age on the
X-axis and per cent growth in height
on the Y-axis. Highlight the point
representing your age on the graph.
Find out the percentage of height
you have already reached. Calculate
the height you might eventually
reach. Tally your graph with the one
given here (Fig. 7.1).
Fig. 7.1 : Graph showing percentage of height
with age
I am worried. Though I
have become taller, my
face looks much smaller
compared to my body.
Initially, girls grow faster than boys
but by about 18 years of age, both reach
their maximum height. The rate of
growth in height varies in different
individuals. Some may grow suddenly
at puberty and then slow down, while
others may grow gradually.
2024-25
SCIENCE 82
and pimples on the face at this time
because of the increased activity of these
glands in the skin.
Development of Sex Organs
Look up Fig. 6.1 and 6.3 of the
previous lesson which show sex
organs of humans. At puberty, male
sex organs like the testes and penis
develop completely. The testes also
begin to produce sperms. In girls, the
ovaries enlarge and eggs begin to
mature. Also ovaries start releasing
mature eggs.
Reaching Mental, Intellectual and
Emotional Maturity
Adolescence is also a period of change
in a person’s way of thinking.
Adolescents are more independent than
before and are also self conscious.
Intellectual development takes place and
they tend to spend considerable time
thinking. In fact, it is often the time in
one’s life when the brain has the
greatest capacity for learning.
Sometimes, however, an adolescent may
feel insecure while trying to adjust to
the changes in the body and mind. But
as adolescent learners, you should know
that there is no reason to feel insecure.
These changes are a natural part of
growing up.
7.3 Secondary Sexual
Characters
You have learnt in Chapter 6, that
testes and ovaries are the reproductive
organs. They produce the gametes,
that is, sperms and ova. In girls,
breasts begin to develop at puberty
Many of my classmates
have a hoarse voice. Now I
know why?
Fig. 7.2 : Adam’s apple in a grown up boy
called Adam’s apple (Fig. 7.2). In girls,
the larynx is hardly visible from the
outside because of its small size.
Generally, girls have a high pitched voice,
whereas boys have a deep voice. In
adolescent boys, sometimes, the muscles
of the growing voice box go out of control
and the voice becomes hoarse. This state
may remain for a few days or weeks after
which the voice becomes normal.
A few glands such as sweat glands,
oil glands and salivary glands release
their secretions through ducts.
Endocrine glands release hormones
directly into the bloodstream. So, they
are also termed ductless glands.
Increased Activity of Sweat and
Sebaceous Glands
During puberty the secretion of sweat
glands and sebaceous glands (oil glands)
increases. Many young people get acne
Adam’s
apple
2024-25
REACHING THE AGE OF ADOLESCENCE 83
and boys begin to grow facial hair, that
is, moustaches and beard. As these
features help to distinguish the male
from the female they are called
secondary sexual characters. Boys
also develop hair on their chest. In
both, boys and girls, hair grows under
the arms and in the region above the
thighs or the pubic region.
Paheli and Boojho have now
understood that puberty marks the
beginning of the reproductive period
when one becomes capable of
reproduction. But they want to know
if reproductive life, once begun,
continues, or it ends some time.
The testes and ovaries secrete sex
hormones. You have just learnt that
these hormones are responsible for the
male and female secondary sexual
characters. Further, the sex hormones
are under the control of hormones from
the pituitary gland (Fig. 7.3). The
pituitary secretes many hormones, one
of which makes ova mature in the
ovaries and sperms form in the testes.
Both Boojho and Paheli wish to know
what initiates changes at puberty.
Fig. 7.3 : The onset of puberty is controlled by
hormones
The changes which occur at
adolescence are controlled by
hormones. Hormones are chemical
substances. These are secretions from
endocrine glands, or endocrine system.
The male hormone or testosterone
begins to be released by the testes at
the onset of puberty. This causes
changes in boys about which you have
just learnt, for example, the growth of
facial hair. Once puberty is reached in
girls, ovaries begin to produce the female
hormone or estrogen which makes the
breasts develop. Milk secreting glands
or mammary glands develop inside the
breasts. The production of these
hormones is under the control of
another hormone secreted from an
endocrine gland called pituitary gland.
7.4 Role of Hormones in
Initiating Reproductive
Function
Endocrine glands release hormones
into the bloodstream to reach a
particular body part called target site.
The target site responds to the
hormone. There are many endocrine
glands or ductless glands in the body.
2024-25