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CBSE Board NCERT Solutions for Class 8th Science Chapter10:Reaching the Age of Adolescence

NCERT Solutions for Class 8th Science Chapter 10 : Reaching the Age of Adolescence

Page No: 124
Excercise

1. What is the term used for secretions of endocrine glands responsible for changes taking place in the body?
Answer:
Hormones are chemical substances which are secreted by endocrine glands. They are responsible for changes taking place in the body.

2. Define adolescence.
Answer:
Adolescence is the period of life, when the body undergoes changes, leading to reproductive maturity. It begins around the age of 11 and lasts till 18 or 19 years of age. The period of adolescence may vary from person to person.

3. What is menstruation? Explain.
Answer:
Menstruation is the process of the shedding of the uterine lining on a regular monthly basis in woman. During menstruation the uterus wall along with blood vessels break off. This causes blood to come out and a new wall of uterus is formed. Menstruation lasts generally lasts for 4 to 5 days.

4. List changes in the body that take place at puberty.
Answer:
Changes at puberty:
→ Sudden increase in height and weight.
→ Broadening of shoulders and widening of chest in boys. In girls, the region below waist becomes wider.
→ 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.
→ Appearance of hair in areas such as underarms, face, hands, and legs.
→ Appearance of acne as a result of excessive secretion of oil from skin.
→ Testis grows and starts producing sperms in males, whereas in females, the ovary enlarges and starts producing matured eggs.

5. Prepare a table having two columns depicting names of endocrine glands and hormones secreted by them.
Answer:
Endocrine gland    Hormones
Testis    Testosterone
Ovary    Oestrogen
Thyroid    Thyroxin
Adrenal    Adrenalin
Pancreas    Insulin
Pituitary    Growth hormone

6. What are sex hormones? Why are they named so? State their function.
Answer:
Sex hormones are the hormones that control the development of secondary sexual characteristics and also regulate the proper functioning of the sex organs. They are named so because they are produced in both males and females by the respective sex organs under the influence of the pituitary gland.
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.

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.
Answer:
(ii) proper diet is needed for the rapid growth taking place in their body.
(b) Reproductive age in women starts when their
(i) menstruation starts.
(ii) breasts start developing.
(iii) body weight increases.
(iv) height increases.

► (i) menstruation starts.

(c) The right meal for adolescents consists of
(i) chips, noodles, coke.
(ii) chapatti, dal, vegetables.
(iii) rice, noodles and burger.
(iv) vegetable cutlets, chips and lemon drink.

► (ii) chapatti, dal, vegetables.

8. Write notes on –
(a) Adam’s apple: The protruding part of the throat is called Adam’s apple. It is the enlarged voice box or larynx which gets enlarged and visible from outside in boys at the onset of puberty. This makes the voice of boys hoarse.
(b) Secondary sexual characters: These are features features that help in distinguishing the male and the female body from each other. They are physical or behavioural characteristics that appear in humans at the time of puberty.
Secondary sexual characters in boys:
→ Appearance of moustache and beard.
→ Appearance of chest hair.
→ Growth of hair in genital area and other parts of the skin.
Secondary sexual character in girls:
→ Increase in breast size and darkening of the skin of nipples present at the tip of the breasts.
→ Growth of hair in genital area and other body parts.
→ Sex determination in the unborn baby.

(c) Sex determination in an unborn baby: Sex of a unborn baby depends upon the pair of sex chromosomes that are present in the cells of the baby. The two sex chromosomes are X and Y. 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.
If both the chromosmes are X then the baby is girl.
If one of the chromosomes are X and the other is Y then the baby is boy.

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 thyroxin
3. Another term for teenage
5. Hormone reaches here through blood stream
6. Voice box
7. Term for changes at adolescence

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

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?

Answer:
The graph depicts the relation between the age and height of both boys and girls. During puberty, there is a sudden increase in height of both boys and girls. On the basis of the above graph, it can be observed that during the age of 4-8 years, girls have less height as compared to boys. However, as soon as girls reach 12- 13 years, their height shows a sudden increase and becomes more than boys. In later years, growth in both sexes becomes stable. Growth during puberty is under the control of hormones.

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