Reaching The Age of Adolescence Question Answers: NCERT Class 8 Science

Endocrine gland secretes a chemical substance called as Hormones. Several changes takes place in the body because of hormones.

This graph shows the relation between the height and age of both boys and girls. During puberty, both boys and girls shows a rapid increase in height. According to graph, girls have less height as compared to the boys at the age of 4 to 8 years. But at the age of 12 to 13 years, a sudden increase appear in the height of girls in compare to boys. Growth becomes stable in both girls and boys in later years.

The time period between the beginning of the puberty and the adulthood is known as adolescence. During adulthood, the several changes undergoes in the body along with the reproductive maturity. It begins at the stage of age 11 to 13 and lasts till 18 or 19 years old. This time period also vary from person to person.

At puberty, in girls the ovaries get enlarged and starts producing eggs (ovum). One egg matures and is released by one of the ovaries at a time or we can say once in about 28 to 30 days. During this period, the wall of the uterus become thick so as to receive the egg. If the egg is fertilized then it begins to develop and results in pregnancy and if this egg is not fertilized then the released egg and thickened lining of the uterus along with its blood vessels are shed off causing bleeding in female which is known as menstruation. 

The process of changes during the adolescence period is known as puberty. Beginning of puberty marks the beginning of adolescence and end of puberty marks the completion of reproductive maturity. Some changes in the body that takes place at the puberty are as follows:

1. Increase in height: There is sudden change in the height of both the sex: girls and boys. They both reach their maximum height at the age of 17-18 years.
2. Change in the body shape: In boys, shoulder grew broader and chest becomes wider. In girls, the region below the waist becomes wider.
3. Voice change: At puberty, the voice box which is larynx, begins to grow. Girls contain high pitched and sharp voice at the puberty and boys have deep and hoarse voice at the stage of puberty.
4. Increased activity of sweat and sebaceous glands: During the puberty, the most of teenagers get acne and pimples on their face, due to increased secretion of sweat and sebaceous gland.
5. Development of sex organs: In males, the testis grows and start producing sperms; and in females, the enlargement of ovary takes place and starts producing matured eggs and menstruation starts as well.
6. Reaching mental and emotional maturity: The adolescent may feel insecure while trying to adjust to the changes in the body and mind. 

There are some endocrine glands and hormones secreted by them, are as follows:

The chemical substances produced by sex organs are called sex hormones. For example:

• Male sex hormone is testosterone produced by testis.
• Female sex hormone is oestrogen produced by the ovary.

Sex hormones affects the sexual features of an organism. So, they named as sex hormones. Sex hormones play a important role in our body. Some of the function of sex hormones are as follows:

Testosterone: It is the male sex hormone. It is responsible for secondary sexual characters in male body like growth of beard, developing of reproductive organs and the voice becomes hoarse etc.

Oestrogen: It is the female sex hormone. It is responsible for the secondary sexual characters in the female body like increase in the size of breast, voice becomes soft, development of reproductive organs etc.

(a) (ii) Proper diet is needed for the rapid growth taking place in their body

At the age of adolescence, they should be careful about their diet because a proper diet is needed for the rapid growth.

(b) (i) Menstruation starts

Reproductive age in women starts at the age of 11 to 12 years. When their menstruation starts.

(c) (ii) Chapati, dal, vegetables

At the age of adolescence, a proper diet is needed like chapatti, dal and vegetables because these helps in the growth and keep them healthy.

(a) Adam’s apple:

During the puberty, the larynx grows larger in male in human beings. It can be seen as a protruding part of the throat. This is called as Adam’s apple. Larynx becomes prominent in boys because of sex hormones. Due to which the vocal cords becomes longer and thicker which leads to a hoarse voice. However, the larynx is of small size in females and it is hardly visible. Girls have a high pitched voice because of the smaller size of the larynx.

(b) Secondary sexual characters:

Sex hormones are responsible for secondary sexual characters in males and females. Males and females are distinguished by the sexual characters. At the time of puberty, the secondary sexual characters are the physical and behavioral changes that appears in humans.

Secondary sexual characters that are appears in boys are as follows:

• Growth of beard
• Appearance of chest hair
• Growth of hair in genital area and other part of the skin as well.

Secondary sexual characters that are appears in females are as follows:

• Increase in the size of breast
• Growth of hair in genital areas and other parts of the skin too.
• Voice becomes soft and high pitched.                                                                                                                                                                                                                                                                                                                                                                                                            (c) Sex determination in an unborn baby:

The sex of the baby is determined by the male gamete that fuses with the female gamete.

23 pairs of chromosomes are present in humans. Out of these pair, the last pair is known as the sex chromosomes.

Male have XY sex chromosome and male gamete can be of two types:

22 + X ; 22 + Y

Whereas female has XX chromosomes and type of female gamete:

22 + X

; X is responsible for a baby girl.

Y is responsible for a baby boy.

Across:

3. Adam’s apple

4. Endocrine

7. Pituitary

8. Hormones

9. Insulin

10. Estrogen

Down:

1. Testosterone

2. Thyroid

3. Adolescence

5. Target site

6. Larynx

7. Puberty