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Reaching The Age of Adolescence - Class 8 : NCERT Exercise Questions


Q.1 What is the term used for secretions of endocrine glands responsible for changes taking place in the body?
Sol. Hormones which are secretions of endocrine glands are the chemical substances responsible for changes taking place in the body.

Q.2 Define adolescence.
Sol. The period of life, when the body undergoes changes, leading to reproductive maturity, is called adolescence.

Q.3 What is menstruation? Explain.
Sol. In females, the reproductive phase of life begins at puberty .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.

Q.4 List changes in the body that take place at puberty.
Sol. Following is the list of changes that take place in body at puberty:
(i) Increase in height.
(ii) Change in body shape.
(iii) Change in voice.
(iv) Increased Activity of Sweat and Sebaceous Glands
(v) Development of Sex Organs
(vi) Reaching Mental, Intellectual and Emotional Maturity

Q.5 Prepare a Table having two columns depicting names of endocrine glands and hormones secreted by them.
Sol. Following is the table showing endocrine glands and the hormones secreted by them:

Name of Endocrine Gland

Hormone Secreted

Pituitary

Growth Hormones

Adrenal

Adrenalin

Thyroid

Thyroxine

Pancreas

Insulin

Testes

Testosterone

Ovaries

Oestrogen & Progesterone

Q.6 What are sex hormones? Why are they named so? State their function.
Sol. Hormones responsible for the secondary sexual characters are called sex hormones. The sex hormones are responsible for the fundamental change in growth and development. The testes and the ovaries are the reproductive organs and both are stimulated by the pituitary hormone during Puberty. That's the reason these are called sex hormones.
Functions of Sex Hormones:
Testosterone: In male, the testes produce the male sex hormone testosterone. This hormone helps in the development and maintenance of the primary and secondary sexual characters such as growth of beard, development of reproductive organs, production of sperms, etc.
Oestrogen: In female, the ovaries secrete oestrogen and progesterone responsible for the development of primary and secondary sexual characters such as the enlargement of breats, development of female reproductive organs, etc.

Q.7 Choose the correct option.
(a) Adolescents should be careful about what they eat, because
(i) proper diet develops their brains.
(ii) proper diet is needed for the rapid growth taking place in their body.
(iii) adolescents feel hungry all the time.
(iv) taste buds are well developed in teenagers.
(b) Reproductive age in women starts when their
(i) menstruation starts.                   (ii) breasts start developing.
(iii) body weight increases.           (iv) height increases.
(c) The right meal for adolescents consists of
(i) chips, noodles, coke.                 (ii) chapati, dal, vegetables.
(iii) rice, noodles and burger.        (iv) vegetable cutlets, chips and lemon drink.
Sol. (a) (ii) proper diet is needed for the rapid growth taking place in their body.
(b) (i) menstruation starts.
(c) (ii) chapati, dal, vegetables.

Q.8 Write notes on—
(a) Adam’s apple.
(b) Secondary sexual characters.
(c) Sex determination in the unborn baby.
Sol. (a) Adam’s apple:
At puberty, the voice box or the larynx begins to grow. Boys develop larger voice boxes. The increase in the size of voice box in boys is seen as a prominent protrusion in the neck. This protrusion is called Adam’s apple.

(b) Secondary sexual characters:
The characters which distinguish a male from a female are called secondary sexual characters.

(i) In males, growth of hair is seen on face and body.
(ii) Hair growth in the pubic region, under the arms, etc. is seen in both males & females.
(iii) In boys, voice becomes deeper.
(iv) Increase in weight.
(v) Shoulders get broad and chest gets widened in males. The waist gets wide and hips get narrow in females.
(vi) The development of breasts takes place in females.
(vii) Mood swings are seen in males as well as females. Mental and emotional maturity is attained by both sexes. Brain gets more active and has capability of learning more.

(c) Sex determination in the unborn baby:
In human beings, normally a cell has 46 chromosomes, i.e. 23 pairs of chromosomes. Out of these 46 chromosomes, 22 pairs are identical. There are two kinds of chromosomes in 23rd pair. They are known as X and Y chromosomes. The last pair (i.e. 23rd) in a male has XY combination, while in case of female it has XX combination. 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 unfertilized egg always has one X chromosome but sperms may have X or Y. 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. This concludes that the sex chromosomes of the father determine the sex of an unborn baby.

Q.9 Word game: Use the clues to work out the words.
Across:
3. Protruding voice box in boys
4. Glands without ducts
7. Endocrine gland attached to brain
8. Secretion of endocrine glands
9. Pancreatic hormone
10. Female hormone
Down:
1. Male hormone
2. Secretes thyroxine
3. Another term for teenage
5. Hormone reaches here through blood stream
6. Voice box
7. Term for changes at adolescence
Sol. Across:
3. Adam’s Apple
4. Endocrine
7. Pituitary
8. Hormone
9. Insulin
10. Estrogen
Down:
1. Testosterone
2. Thyroid
3. Adolescence
5. Target Site
6. Larynx
7. Puberty

Q.10 The table below shows the data on likely heights of boys and girls as they grow in age. Draw graphs showing height and age for both boys and girls on the same graph paper. What conclusions can be drawn from these graphs?

Age

(Years)

Height (cm)

Boys

Girls

0 53

53

4

96

92

8 114

110

12

129

133

16 150

150

20

173

165

Sol.Following are the conclusions which can be drawn from the graph:
(i) As the age increases, there is an increase in the height of both boys and girls.
(ii) Until 0 – 8 years, girls have less height in comparison to that of boys.
(iii) However from 12 – 16 years, there is sudden increase in the height of girls and becomes more than the boys.
(iv) At age of 20, boys are taller than girls.



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