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

Adolescence is the age period of life when the human body undergoes many changes, and this period also will lead to reproductive maturity. This begins from the age of 11 and lasts up to 18 or 19. This age may vary from individual to individual. Adolescents are also called teenagers as this period covers the teens that are 13 to 18 or 19 years of age.

Menstruation occurs in the female after puberty once in about 28 to 30 days. 

Every month, an ovary produces an egg and the uterus is prepared for implantation. During this, the wall of the uterus becomes thick so it receives the egg, just in case it’s fertilized and begins to develop. This results in pregnancy. If fertilization doesn’t occur, this causes bleeding in women which are named menstruation. This happens because of the released egg, and the thickened lining of the uterus along with its blood vessels are shed off. This lasts for 3 to 5 days in a healthy female and this process occurs every month so called as Menstrual cycle. The menstrual cycle is controlled by hormones. Menarche is the first menstrual flow that begins at puberty. The stoppage of menstruation is called menopause this happens at 45 to 50 years of age.

Hormone is that the term used for secretions of endocrine glands responsible for changes happening within the body. The changes which occur in adolescence are controlled by these chemical substances called hormones.

Changes at puberty:

• Increase in height.

• Change in body shape.

• Voice change. Changing the pharynx leads to a slight deepening of voice for girls and much deeper in boys.

• Increased Activity of Sweat and Sebaceous Glands. The appearance of facial and pubic hair in boys, while the development of mammary glands in girls is observed.

• Development of Sex Organs. Testis grows and starts producing mature sperms while ovaries start the menstrual cycle to produce eggs.

• Reaching Mental, Intellectual and Emotional Maturity.

Table showing names of endocrine glands and hormones secreted by them is as below,

• The sex hormones, which are produced by the sex organs. The sex organs in males are the testis and for females, it is the ovaries.

• Testis produces testosterone as a male sex hormone while estrogen is the female sex hormone.

• The function of testosterone: Growth of facial and pubic hairs, deepening of voice, development of reproductive organs etc.

• The function of estrogen: Breast enlargement, change in voice, development of reproductive organs etc.

(i) Adolescents should be careful about what they eat because a proper diet is needed for the rapid growth taking place in their body.

(ii) Reproductive age in women starts when their menstruation starts.

(iii) The right meal for adolescents consists of chapati, dal, vegetables.

(a) The larynx or voice box in males begins to grow at puberty. . Boys develop larger voice boxes than girls so boys will have a deep voice. In males, the growing voice box may be seen as a protruding part of the throat which is called Adam’s apple.

(b) These are those characteristics that help in distinguishing male and female. The characteristics developed during the time of puberty.

In Male:

• The appearance of mustache, beard, chest hair.

• Deepening of voice.

• Hair growth in the pubic and other parts of the skin. 

In Female:

• Increasing the size of the breast and hips

• Growth of hair at pubic and other parts of the skin.

• Sex determination in the unborn baby.

 Sex determination can be done based on the sex chromosome that fuses together to make the zygote. Every individual has 23 pairs (46 individuals) of chromosomes whether male or female. Out of that 23 pairs, 22 pairs are the same for both males and females. The last one is called as sex chromosome. In the male sex, the chromosome is XY while in the female sex chromosome is XX. During gamete formation the male produces two types of gametes X gamete and Y gametes while the female produces two X gametes.

So, during fusion females will always give 22+X always while males can give 22+X or       22+Y.

Depending on which one fuses with 22+X (given by female) the sex of the unborn baby is decided.

22+X (F) + 22+X (M) = girl child 

22+X (F) + 22+Y (M) = boy child

So, X and Y chromosome is the deciding factor for the sex of the unborn kid.

Across

• Adam’s Apple

• Endocrine

• Pituitary

• Hormone

• Insulin

• Estrogen

Down

• Testosterone

• Thyroid

• Adolescence

• Target Site

• Larynx

• Puberty

Image: Graph showing height and age for both boys and girls.

The graph depicts the relation between the age and height for both boys and girls. During puberty, there’s a sudden increase in height of both boys and girls. Based on 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 which is more than boys. In later years, growth in both boys and girls becomes stable. Growth during puberty is under the control of hormones.