class 8th science solutions
9

Reaching the age of Adolescence

AGE OF ADOLESCENCE

Adolescence:

Adolescence Adolescence may be defined as that period within the life span when most of a person’s characteristics are changing from what is typically considered childlike to what is typically considered adultlike. Changes in the body are the most readily observed, but other, less definitive attributes such as thoughts, behaviour, and social relations also change radically during this period. The rate of such changes varies with the individual as well as with the particular characteristic. Typically describes the years between ages 13 and 19 and can be considered the transitional stage from childhood to adulthood. However, the physical and psychological changes that occur in adolescence can start earlier, during the preteen or “tween” years (ages 9 through 12).
Teenage: Denoting a person between 13 and 19 years old.
Puberty: Puberty refers to the process of physical changes by which a child’s body becomes an adult body capable of reproduction. Growth accelerates in the first half of puberty and reaches completion by the end.

Changes at Puberty

  1. Increase in Height: The most apparent change during puberty is the sudden increase in height. Long bones grow rapidly and hence height of a person increases rapidly during this period. Initially, girls grow faster than boys but ultimately boys are usually taller than girls. The maximum height is attained by 18 years of age.
  2. Change in Body Shape: The body of a boy becomes more muscular. His shoulders become wide and waist becomes narrow. The body of a girl becomes wider below waist and narrower at shoulder.
  3. Voice Change: A boy’s voice becomes deep, and the child like voice is first replaced by a hoarse voice. This happens because the voice is said to crack. Gradually, the voice becomes deep. The change in voice happens because voice box in a boy becomes larger. Girl’s voice is usually high pitched.
  4. Increased Activity of Sweat and Sebaceous Glands: Secretion from sweat and sebaceous glands increases during adolescence. Due to this, some teenagers may suffer from acne and pimples.
  5. Development of Sex Organs: In boys, testes begin to produce sperms. Testis and penis develop completely. In girls, ovaries enlarge and eggs begin to mature. Ovaries start releasing mature egg.
  6. Reaching Mental, Intellectual and Emotional Maturity: These changes also have a profound effect on a person’s way of thinking. Teenagers spend more time on thinking than earlier. So many rapid changes in the body may create a sense of insecurity in most of the teenagers. But teenagers should not worry because these are natural changes.

 

Adam’s Apple: A projection at the front of the neck formed by the thyroid cartilage of the larynx, often prominent in men is called Adam’s apple.

Secondary Sexual Characters

The change in physical characters which help in distinguishing a male from a female are called secondary sexual characters. Marked difference between male and female of a species because of apparent physical traits is called sexual dimorphism.

  • Secondary Sexual Characters in Boys: Facial hairs, deep voice and hair on chest.
  • Secondary Sexual Characters in Girls: Enlargement of breasts and high pitched voice.
  • Some common characters in girls and boys: Hair under armpits, hair in pubic region.

Hormonal Control

The changes during this period are controlled by hormones. Hormones are substances secreted by endocrine glands. Hormones play important role in various metabolic activities.

In boys, testis secretes the hormone testosterone. This hormone is responsible for many changes in boys. In girls, ovaries secrete the hormone estrogen. This is responsible for development of breasts.

Action of these hormones is under the control a hormone secreted by pituitary gland. Another hormone from pituitary gland stimulates the maturation of eggs and production of sperms. Endocrine glands are ductless glands; which means that a hormone reaches the target site through bloodstream.

Reproductive Phase of Life in Humans

The reproductive phase begins with the onset of puberty and it happens at around the same age in boys and girls. But reproductive phase in men lasts much longer than in females. Reproductive phase in women lasts till about 50 years of age. Reproductive phase in men lasts even beyond 60 years of age.

Menstruation: Menstruation is the 2 to 7 days that a girl or woman has her menstrual flow, which is when blood and tissue leave her body through her vagina. … Each month, blood and tissue build up in the uterus to prepare for a fertilized egg in case a woman becomes pregnant.

Menstrual Cycle: The cycle of events which begin from release of an egg and end in shedding off egg is called menstrual cycle. A menstrual cycle is usually of 28 to 30 days.

Menarche: The first menstrual bleeding in a girl’s life is called menarche. Menarche marks the beginning of puberty in girl.

Menopause: Cessation of menstrual cycle is called menopause. This happens at around 45 – 50 years of age. Menopause marks the end of reproductive phase.

EXERCISES

  1. Hormones
  2. Adolescense is the period of life, when the body undergoes changes, leading to reproductive maturity .
  3. When the egg produced by ovary does not get fertilised, the released egg and the thickened lining of the uterus along with its blood vessels are shed off. This causes bleeding in women which is called menstruation.Menstruation occurs once in about 28 to 30 days.
  1. The changes in the body of puberty are:

(i) Sudden increase in height.

(ii) The bones of arms and legs elongate and make a person tall.

(iii) Growing of hair at different parts of body.

(iv) The voice of a boy gets hoarsed.

(v) Development of sex organs.

(vi)Growth of moustaches and beards in the boys.

(vii) The breast in girls develops and hips become wider whereas in boys shoulders generally broaden.

5.

  1. The hormones which help and control the formation of secondary sexual characters are called sex hormones. They are called sex hormones because they control the sexual activities and help us to distinguish boys from girls.The sex hormones help to develop the secondary sexual characters. Such as, in boys they control formation of sperms by testes and growth of facial hair. In girls they help to develop breasts, milk secreting glands or mammary glands.
  1. (a) (ii) proper diet is needed for the rapid growth taking place in their body.

(b) (i) menstruation starts.

(c) (ii) chapati, dal, vegetable.

  1. (a) Adam’s apple: The protruding part in the throat is called Adam’s apple. It is the enlarged voice box or larynx. It makes the voice of boys coarse.

(b) Secondary sexual characters: The characters which help to distinguish the male from female are called secondary sexual characters. The characters like hair on chest under arms, development of breast, beard and moustaches are called secondary sexual characters.

(c) Sex determination in unborn baby:

The sex 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 pair is known as the sex chromosome.
The human males have 23 pairs of chromosomes including XY sex chromosomes, Therefore, the male gamete has 22 chromosomes and either an X or Y sex chromosome.
Male gametes can be of two types: 22+X or 22+Y
Females have 23 pairs of chromosomes including XX sex chromosomes. Therefore, their gametes can only have 22 chromosomes and one X sex chromosome,
Type of female gametes: 22+X
Thus, as the mother provides only X chromosome, the sex of the baby is determined by the type of male gamete (X or Y) that fuses with the X chromosome of the female.
  1. Across
  1. Adam’s apple
  2. Endocrine
  3. Pituitary
  4. Hormone
  5. Insulin
  6. Estrogen

Down

  1. Testosterone
  2. Thyroid
  3. Adolescence
  4. Target site
  5. Larynx
  6. Puberty

 

9.We conclude that intially, girls grow faster than boys but by about 18 years of age both reach about their maximum height. The rate of growth in height varies in different individuals.

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