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Reaching the Age of Adolescence Notes for Class 8

Important topics covered:

  • Adolescence
  • Puberty
  • Changes at puberty
  • Secondary sexual characters
  • Role of Hormones in Initiating Reproductive Function
  • Reproductive Phase of Life in Humans
  • How is the Sex of the Baby Determined?
  • Hormones other than Sex Hormones
  • Role of Hormones in Completing the Life History of Insects and Frogs
  • Reproductive Health
  • Say “NO” to Drugs



  • Adolescence is the period of life, when the body undergoes changes, leading to reproductive maturity.
  • The period of adolescence starts at the age of 10 and lasts up to 18 or 19 years of age.
  • Girls attains adolescence year or two earlier than that of boys.
  • Three year period of adolescence ending with teen i.e. thirteen, fourteen, fifteen years are said to be teenagers.



  • The different changes that takes place during adolescence are the sign of puberty.
  • Teenagers when reach sexual maturity, the puberty ends.
  • At this stage, one can bear a child.

Changes that takes place during puberty:

There are several which can be observed in the body of humans during puberty. They are:

Increase in height

increase in height

  • Sudden increase in height is the most conspicuous change during puberty.
  • Growth in long bones of legs and arms causes increase in height.
  • The growth in girls is observed faster than that of boys.
  • Both boys, as well as girls, reach adolescence at the age of 18 years.

Change in body shape

change in body shape

  • During puberty body becomes more muscular.
  • Also, shoulders and chest becomes wide and waist becomes narrow.
  • The body of a girl becomes wider below waist and narrower at shoulder.

Change in voice

change in voice

  • As the children reach the age of adolescence voice box or larynx also grows.
  • The voice of boys becomes horse in place of child voice. Voice at this time cracks.
  • A buldge appears at the throat which is called Adam’s apple.
  • Low-pitched voice is developed in boys whereas girls develop high-pitched voice.

Increased Activity of Sweat and Sebaceous Glands

Increased Activity of Sweat and Sebaceous Glands

  • The secretion of sweat glands and sebaceous glands (oil glands) increases during puberty.
  • The increased activity of these glands in the skin causes acne and pimples.

Development of Sex Organs

  • In boys, testes and penis develop completely.
  • Sperms production in testes begins at this stage.
  • Ovaries starts producing eggs in girls.

Reaching Mental, Intellectual and Emotional Maturity


  • It is also a period of change in a person’s way of thinking.
  • Adolescents also becomes self-conscious.
  • They become more independent than before.
  • They tend to spend considerable time in thinking and also at this stage the brain has the greatest capacity for learning.

Secondary Sexual characteristics

  • In boys, Beards and moustache begin to grow.
  • Hair on the chest and genital area also start to grow.
  • In girls, breasts develop.
  • Those characters which help to distinguish the male and female body are said to be secondary sexual characteristics.
  • Also, hair in pubic region also starts to grow.

Role of Hormones in Initiating Reproductive Function

  • The chemical substances secreted in endocrine glands are known to be hormones.
  • We also call endocrine glands as ductless glands.
  • These glands release hormones directly into the blood stream to reach a particular body part. That particular body part is said to be target site.
  • Hormones control the changes that take place at adolescence.
  • Testes secrets the male hormone called testosterone at the onset of puberty and cause development of facial, chest hair etc.
  • Ovaries secrete female hormone called estrogen which causes the breast to develop.
  • In males, reproductive phase lasts for a much longer time than in females.

Characteristics of Endocrine glands

  • They act as chemical messengers.
  • The secretion of these hormones is in very less amount.
  • Living cells/tissues or glands secrets these hormones.
  • The hormonal action is very slow but is long lasting.
  • Either they accelerate or inhibit a reaction.

The reproductive phase begins at the onset of puberty

  • With the onset of puberty the reproductive phase begins.
  • Reproductive phase in men lasts much longer than in females.
  • In men, reproductive phase lasts even beyond 60 years of age whereas in females it lasts till about 50 years of age.
  • Menstruation: Each month ovaries in female releases egg. To support a foetus to prepare for a possible pregnancy the uterus develops a thickening layer. If fertilization does not happen; egg and thickening in uterus are broken in small fragments which results in bleeding through the vagina for some days. The bleeding through vagina at the end of menstrual cycle is called menstruation.
  • Menstrual Cycle: The repetition of events from time from the releasing of egg to breaking of uterus lining which is of 28 to 30 days are called menstrual cycle.
  • Menarche: The first menstrual bleeding in a girl when she attains puberty are said to be menarche.
  • Menopause: The end of menstrual cycle (reproductive phase) when women are around 40 to 50 years of age are said to be menopause.

How is the Sex of the Baby Determined?

how sex of a baby determined

  • The sex of a baby depends upon the chromosome.
  • These chromosomes are a thread like structure and always present in pairs.
  • There are 23 pairs of chromosomes in baby.
  • Two chromosomes X and Y are said to be sex hormones.
  • A female body contains two X chromosomes whereas a male child has one X and one Y chromosome.
  • There are only one set of chromosomes in the male and female gametes.
  • There is “X” chromosome in unfertilized egg while different sperms carry different chromosomes i.e. one having X while the other have Y
  • If a sperm containing “X” chromosome fertilizes the egg then it will give birth to a girl child as the pair forms “XX”.
  • If a sperm containing Y chromosome fertilizes the egg then it will give birth to a baby boy with “XY” chromosome.

Hormones other than Sex Hormones

The major endocrine gland s in human beings are given below. The action of hormones are regulated by a feedback mechanism. Take a look at the different glands:

Pituitary gland

  • It secrets growth hormone.
  • It is present at the base of brain and is pea sized.

Thyroid gland

  • It secrets thyroxine hormone.
  • It is present near the trachea in the neck.
  • Thyroid gland regulates the metabolism of the body.

Parathyroid gland

  • Four parathyroid glands are present at the back side of the thyroid glands.
  • This hormone is responsible for regulating the presence of calcium ions in bloodstreams.


  • It releases insulin and glucagon.
  • These hormones maintain blood sugar level and its deficiency can cause diabetes.

Adrenal gland

  • On the upper part of each kidney, two adrenal glands are present.
  • It also controls the rate of metabolism and prepares our body to face stressful conditions.

Role of Hormones in Completing the Life History of Insects and Frogs

  • The caterpillar passes through various stages to become an adult moth. Similarly, to become a frog, the tadpole passes through certain stages.
  • Metamorphosis: This change from larva to adult is called metamorphosis.
  • Insect hormones controls metamorphosis in insects. In frog, it is controlled by thyroxine. Thyroid produces it.
  • Thyroxine can only be produced in the presence of iodine in water. The tadpoles cannot become mature/adults if the water in which the tadpoles are growing does not contain sufficient iodine.

Reproductive Health

  • The physical and mental well-being of an individual is said to be as an individual’s health.
  • To keep the body healthy, every human being needs to have a balanced diet.
  • Balanced diet means that the meals include proteins, carbohydrates, fats and vitamins in requisite proportions.
  • Everyone must also observe personal hygiene and undertake adequate physical exercise.
  • During adolescence, however, these become even more essential as the body is growing.

Say “NO” to Drugs:

say no to drugs

  • The body and mind of Adolescent are filled with much activity which is a normal part of growing up. So don’t feel insecure about these conditions.
  • If someone suggests you to take drugs for relief, don’t take it unless it is prescribed by a doctor.
  • These are addictive and it will feel you to take it again and again.



  • AIDS stands for Acquired Immuno Deficiency Syndrome.
  • It is caused by a dangerous virus of HIV (Human Immunodeficiency Virus).
  • When one shares the syringes used for injecting drugs it can transfer HIV too from normal person to infected person.
  • Sometimes mother’s milk is also responsible for transmission of HIV to infants.
  • Sexual contact is also responsible for the transfer of virus from a person infected with HIV to a cure person.
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