NCERT solutions for class 8 Science Chapter 10 Reaching The Age Of Adolsence

Solution for Exercise

Q.1 What is the term used for secretions of endocrine glands responsible for changes taking place in the body?


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Answer :

Harmons

Q.2 Define adolescence.


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Answer :

The period of life, when the body undergoes changes, leading to reproductive maturity, is called adolescence. The period of adolescence is normally 11 years to 19 years.The period of adolescence may vary from person to person.

Q.3 What is menstruation? Explain.


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Answer :

Menstruation is the process of the shedding of the uterine lining on a regular monthly basis. It begins at puberty and is thereproductive cycle of the female body. Every month, the uterus prepares itself to receive a fertilized egg. Therefore, the inner lining of the uterus becomes thick and is supplied with blood to nourish the embryo. If the egg is not fertilized, then the lining of the uterus breaks down and gets released in the form of blood through the vagina. This lasts for about two to eight days. This cycle occurs every month and is known as the menstrual cycle.

Q.4 List changes in the body that take place at puberty.


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Answer :

Changes at puberty:


(i) Sudden increase in height and weight.
(ii) Broadening of shoulders and widening of chest in boys. In girls, the region below waist becomes wider.
(iii) In boys, under the influence of hormones, the larynx becomes prominent, the vocal cords become longer and thicker. These changes cause the voice to become hoarse.
(iv) Appearance of hair in areas such as underarms, face, hands, and legs.
(v) Appearance of acne as a result of excessive secretion of oil from skin.
(iv) Testis grows and starts producing sperms in males, whereas in females, the ovary enlarges and starts producing matured eggs.

Q.5 Prepare a table having two columns depicting names of endocrine glands and hormones secreted by them.


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Answer :

Q.6 What are sex hormones? Why are they named so? State their function.


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Answer :

Sex hormones are chemical substances produced by sex organs. For example, testosterone is the male sex hormone produced by the testis, and oestrogen is the female sex hormone produced by the ovary. These hormones affect the sexual features of an organism. Hence, they are known as sex hormones.

Functions of sex hormones:

Testosterone

: This hormone brings about secondary sex characters in boys such as the growth of a beard, the voice becoming hoarse, development of reproductive organs, etc.

Oestrogen

: This hormone is responsible for the development of secondary sexual characters in females such as the enlargement of breasts, 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.


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Answer :

(a) (ii)
(b) (i)
(c) (ii)

Q.8 Write notes on:
(a) Adam’s apple
(b) Secondary sexual characters.
(c) Sex determination in the unborn baby.


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Answer :

(a)Adam’s apple

During puberty, a change in the voice of boys and girls takes place due to increase in the size of the voice box or larynx. In boys, the voice box tends to protrude out on the upper part of the neck, below the chin and is often referred to as Adam’s apple.

(b) Secondary sexual characters.

Those characters which are visible more apparently and help in distinguishing a male from a female are called secondary sexual characters. For example, in girls, breasts and in boys, facial hair, i.e., moustache and beard.

(c) Sex determination in the unborn baby.

The sex of a baby is determined by the type of male gamete that fuses with the female gamete.All human beings have 23 pairs of chromosomes in their nuclei. Out of these 23 pairs, the last pair is known as the sex chromosome. The human males have 23 pairs of chromosomes including XY sex chromosomes. Therefore, the male gamete has 22 chromosomes and either an X or Y sex chromosome. Male gametes can be of two types: 22+X or 22+Y. Females have 23 pairs of chromosomes including XX sex chromosomes. Therefore, their gametes can only have 22 chromosomes and one X sex chromosome. Type of female gametes: 22+X
Thus, as the mother provides only X chromosome, the sex of the baby is determined by the type of male gamete (X or Y) that fuses with the X chromosome of the female.

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


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Answer :

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?


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Answer :

From the above graph, we conclude that initially boys grow faster than girls from 0-8 years, and girls grow faster than boys from 8-16 years. But both reach their maximum height at the age of 20. Here boys show a greater increase in height than girls.



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