the Age of Adolescence
Q52. How does the height of boys and girls change during puberty?
Ans. At the time of puberty the long bones, that is,
the bones of the arms and the legs elongate and make a person tall. 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
Q53. Prepare a Table having two columns depicting names of
endocrine glands and hormones secreted by them.
Q54. What is menstruation? Explain.
Ans. In females, the reproductive phase of life begins
at puberty (10 to 12 years of age) and generally lasts till the age of approximately
45 to 50 years. The ova begin to mature with the onset of puberty. One ovum
matures and is released by one of the ovaries once in about 28 to 30 days.
During this period, the wall of the uterus becomes thick so as to receive the
egg, in case it is fertilised and begins to develop. This results in pregnancy.
If fertilisation does not occur, the released egg, and the thickened lining of the
uterus along with its blood vessels are shed off. This causes bleeding in women
which is called menstruation.
Q55. What are sex hormones? Why are they named so? State their
Ans. Sex hormones are chemical substances produced by
a sex gland or other organ. For example, the testes make male sex hormone
called testosterone and the ovaries make female sex hormone called estrogen.
These hormones affect the sexual features of an organism. Hence they are called
– It produces male secondary sexual characteristics in boys such as deeper
voice, growth of moustache and beard, broad shoulders and chest, adam’s apple,
more muscles, development of reproductive organs etc.
– It produces female secondary sexual characteristics in girls such as
development of breasts, broader hips, development of reproductive organs etc.
Q56. List changes in the body that take place at puberty.
State some of the changes which take place in boys and girls
Ans. Changes at puberty
Sudden increase in height and weight.
Boys develop broader shoulders and wider
chests. In girls, the region below the waist becomes wider.
In boys, the muscles of the body grow more
prominently than in the girls.
Boys develop larger voice boxes. The
growing voice box in boys can be seen as a protruding part of the throat
Development of pimples and acne on the face
due to the increased activity of sebaceous glands and sweat glands present in
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.
In girls, breasts begin to develop at
puberty and boys begin to grow facial hair, that is, moustaches and beard.
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.
Q57. Write notes on—
(a) Adam’s apple.
(b) Secondary sexual characters.
(c) Sex determination in the unborn baby.
Ans. (a) Adam’s apple - 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 called
Secondary sexual characters - In girls, breasts begin to develop at puberty 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
Sex determination in the unborn baby - All human beings have 23 pairs of
chromosomes in the nuclei of their cells. Two chromosomes out of these are the
sex chromosomes, named X and Y. A female has two X chromosomes, while a male
has one X and one Y chromosome. The gametes (egg and sperm) have only one set
of chromosomes. The unfertilised egg always has one X chromosome. But sperms
are of two kinds. One kind has an X chromosome, and the other kind has a Y
chromosome. When a sperm containing X chromosome fertilises the egg, the zygote
would have two X chromosomes and develop into a female child. If the sperm
contributes a Y chromosome to the egg (ovum) at fertilisation, the zygote would
develop into a male child.