Learn NCERT Exercise 10 with Free Lessons & Tips

Hormones are chemical substances which are secreted by endocrine glands. They are responsible for changes taking place in the body.

Adolescence is the time period between the beginning of puberty and adulthood. During this period, the body undergoes several changes alongside 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.

Menstruation is the process of the shedding of the uterine lining on a regular monthly basis. It begins at puberty and is the reproductive 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 Female urine tract. This lasts for about two to eight days. This cycle occurs every month and is known as the menstrual cycle.

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.

(vi) Testis grows and starts producing sperms in males, whereas in females, the ovary enlarges and starts producing matured eggs.

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

(b) (i) Reproductive age in women starts when their menstruation starts.

(c) (ii) The right meal for adolescents consists of chapatti, dal, vegetables.

(a) Adam's apple:

In human males, the larynx grows larger during puberty and can be seen as a protruding part of the throat. This protrusion is known as Adam's apple. In boys, under the influence of hormones, the larynx becomes prominent. As a result, the vocal cords become longer and thicker, causing the voice to become hoarse. However, in females, the larynx is of small size and is hardly visible. Therefore, girls have a high pitched voice, while the sound of boys is low pitched.

(b) Secondary characters are those 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 characters in boys:

(i) The appearance of moustache and beard.

(ii) The appearance of chest hair.

(iii) Growth of hair in the genital area and other parts of the skin.

A secondary character in girls:

(i) Growth of hair in the genital area and other body parts.

(c) Gender determination in an unborn baby:

The gender 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 couple is known as the sex chromosome.

The human males have 23 pairs of chromosomes, including XY chromosomes. Therefore, the male gamete has 22 chromosomes and either an X or Y chromosome.

Male gametes can be of two types: 22+X or 22+Y

Females have 23 pairs of chromosomes, including XX chromosomes. Therefore, their gametes can only have 22 chromosomes and one X chromosome.

Thus, as the mother provides only X chromosome, the gender of the baby is determined by the type of male gamete (X or Y) that fuses with the X chromosome of the female.