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NCERT Solutions for Class 8 Science chapter 10 – Reaching the Age of Adolescence

Back Exercise

Question 1:
What is the term used for chemical secretions of endocrine glands responsible for changes taking place in the body?

Answers
The chemical substance secreted by the endocrine glands is called Hormones. Hormones are responsible for the changes taking place in the body.

Question 2:
Define adolescence.

Answers
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.

Question 3:
What is menstruation? Explain.

The process of shedding of the uterine lining on a regular monthly basis in female body is called menstruation. It starts at puberty and in the reproductive cycle of the female body. The uterus prepares itself to receive a fertilized egg on every month. Due to this the inner lining of the uterus become 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 get released in the form of blood through the vagina. The time period for this is about 2 to 8 days every month. This monthly cycle is known as the menstrual cycle.

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

Answers
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.
→ In boys, the larynx becomes prominent under the influence of hormones, the vocal cord becomes longer and thicker resulting in hoarse voice.

Question 5:
Prepare a Table having two columns depicting names of endocrine glands and hormones secreted by them.

Answers

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

Answers
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.

Question 7:
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.

Answers
(a) (ii) proper diet is needed for the rapid growth taking place in their body.
(b) (i) menstruation starts.
(c) (ii) chapati, dal, vegetables.

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

Answers
(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 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.

Question 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

Answers

Question 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?

Answers
➢ The graph depicts the relation between the age and 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.
➢ Girls are taller than boys till they reach the age of 12.
➢ Till the age of 16, the height of both boys and girls remain the same.
➢ After 16, both boys and girls gain increase in height. In genetal, the boys are taller than girls.