Class 8 Science Chapter 10 Notes Pdf Reaching the age of adolescence

In this post we will discuss Class 8 Science Chapter 10 Notes Reaching the age of adolescence

In the previous chapter, we learn how animals reproduce. it is only after “growing up” to a certain age that a human/animal being can produce.

In this chapter Reaching the age of adolescence notes, we learn about changes taking place. In the human body after which a person becomes capable of reproduction. Or we learn about the role hormones play in bringing change that makes a child into an adult. You can also download Class 8 Science Chapter 10 Notes pdf

We also provide Ncert notes of all subjects. You can also check Class 8 Complete Study material.


The period of life when the body undergoes changes leading to reproductive maturity is called adolescence.

  • Adolescence begins around the age of 11 and lasts up to 18/19 years of age.
  • Adolescence is also known as teenagers’ age.
  • In girls, adults may begin a year or 2 years earlier than in boys.
  • The period of adolescence varies from person to person.
  • The body at this stage undergoes important changes and this mark the period of puberty.


  • Puberty is the period during which the human body undergoes certain changes in its body and reproduction organs which lead to sexual maturity.
  • The most important change which mark puberty is that boy and girl become capable of reproduction.

Changes At Puberty

  1. Increasing height:- During poverty there is a sudden increase in height. Girls grow faster than boys but at about 18 years both reach their maximum height.
  2. Change in body shape.
  3. Voice change:- At puberty, the voice box or larynx begins to grow.
  4. Increase activity of sweat and sebaceous glands:- At puberty, many young people get acne and pimples on their face this is because of increased activity of this gland of the skin.
  5. Development of sex organs.
  6. Reaching mental, intellectual and emotional maturity.

Secondary sexual character

There are external, visible characteristics that develop in boys and girls that help to distinguish the two sex and are not directly involved in reproduction.


  • The growth of hair in the face, body including the underarm, abdomen, chest and public region.
  • Chest and Shoulder widen and the body becomes muscular.
  • The male hormone or testosterone begins to be released by the testes at one set of puberty which is responsible for all changes like hair growth, voice change etc.
  • Skin becomes rough and the porous secretion of the sweat glands and sebaceous gland increases.


  • Enlargement of breasts. The milk-secreting gland or mammary gland develops inside the breast.
  • The female hormone or estrogen begin to be released due to this all change occur in female-like enlargement of the breast, hair growth etc.
  • The growth of body hair prominently in the underarm and public areas.
  • Widening of hips and buttocks.

Role of hormones in initiating reproductive function

Class 8 Science Chapter 10 onset of puberty is controlled by
The onset of puberty is controlled by

As we know hormones are responsible for male and female changes.

  • The endocrine gland release hormone into the bloodstream to reach a particular body part called the target site.
  • The target side responds to the hormones.
  • The testes and ovary secret sex hormones are responsible for male and female secondary sexual characters.
  • The sex hormone is under the control of hormones from the pituitary gland.
  • The pituitary gland makes ova mature in ovaries and sperm from in the testes.

The reproductive phase of life in Humans

  • Adolescents become capable of reproduction when their testes and ovaries begin to produce gametes.
  • The capacity of maturation and production of gametes last for a much longer time in males than in females.

Menstrual cycle

  • It is the reproductive cycle of females this start at the age of 10 to 12 year and generally lasts Till the age of 45 to 50.
  • In this cycle, the ova (egg) began to mature after this ovum matures, it is released by one of the ovaries in about 28 to 30 days.
  • During this period, the wall of the uterus becomes thick so as to receive the egg.
  • They release eggs and the thickened lining of the uterus along with its blood vessel and shad off. this cause bleeding in women which are called menstruation.
  • The first menstrual flow is called Menarche.
  • The last menstrual flow is called menopause.
  • In case, the egg gets fertilised and begins to develop this result in pregnancy.

How is the sex of the baby determined

  • All human being has 23 pairs of chromosomes i.e 46 chromosomes in the nucleus of their cell.
  • Out of 46 chromosomes, 2 chromosomes / 1 pair of chromosomes are different in males and females. These are called sex chromosomes.
  • A female has xx i.e 2-x chromosome while the male has XY i.e 1-X and 1-y chromosome.
class 8 Science Chapter 10 notes Sex determination in humans
Sex determination in humans
  • In another word, female gametes i.e egg has one set of sex chromosome while male gametes i.e sperm has x and y chromosome.
  • When a sperm containing an X-chromosome is fertilized the egg develops into a female child.
  • When a sperm containing a y-chromosome fertilize the egg it develops into a male child.

Hormones other than sex hormones or Some other hormones

Harmons are chemical messengers secreted by the endocrine gland. The below image Position of endocrine glands in the human body is shown.

Class 8 Science Chapter 10 Position of endocrine glands in the
human body
Position of endocrine glands in the
human body

Pituitary gland

  • The pituitary gland is situated in the brain and is called the master endocrine gland.
  • It produces hormones that instruct another gland to secret its hormones.
  • The pituitary gland secret growth hormone which controls the overall growth of a person.
  • Secretion of growth hormone is maximum in adolescence period.
  • Apart from the pituitary gland, the testes and ovaries, there are other endocrine glands in the body such as the thyroid, pancreas and adrenals.

Thyroid gland

  • It is situated in the throat.
  • It secretes hormones called thyroxine.
  • The deficiency of thyroxine can cause goitre due to this thyroid gland getting swelling.


  • The pancreas secretary hormone called insulin, which regulates the blood sugar level in the body.
  • The deficiency of insulin leads to diabetes.

Adrenal glands

  • The adrenal gland secretes hormones which maintain the correct salt balance and pH balance in the blood.
  • The adrenal gland produces adrenalin hormone.
  • It helps the body to adjust to stress.

Reproductive Health

To keep the body healthy comma every human being needs,

  1. Balance diet
  2. personal hygiene
  3. physical exercise

Balance diet

  • A balanced diet means that include protein, carbohydrates, fat and vitamin in requisite proportions.
  • Adolescence is a stage of rapid growth and development so it needs a properly balanced diet.
  • All teenagers should consume a balanced diet and not junk food.

Personal hygiene

  • Personal hygiene is very important, especially during the teenage years because increases the activity of sweat glands and sometimes makes the body smelly.
  • All parts of the body should be washed and cleaned every day.
  • If cleanliness is not maintained there are chances of catching a bacterial and fungal infection.
  • Girls should take special care of cleanliness during the time of menstrual flow.

Physical exercise

Walking and playing in fresh air keeps the body fit and healthy.

Say no to drugs

  • Drugs are addictive and harm the body in long term.
  • All teenagers should say no to drugs.
  • People who are addicted to drugs have more chance of having HIV infection.

What we learn in Class 8 Science Chapter 10 Notes Pdf

In Class 8th Science Ch 10 Notes pdf / Reaching the Age of Adolescence pdf we learn-

  • Humans become capable of reproduction after puberty sets in between the ages of 11 years and 19 years children are called adolescents.
  • The onset of puberty brings about the growth of the reproductive organs. Hair grows at various places on the body. Breasts develop in girls and facial hair (moustache and beard) appear in boys. The Voice of boys becomes hoarse as the voice box enlarges during adolescence.
  • Children gain height during adolescence.
  • The onset of puberty and maturity of reproductive parts are controlled by hormones.
  • Hormones are secretions of endocrine glands which pour them directly into the bloodstream.
  • The pituitary gland secretes hormones which include growth hormones and hormones that
  • make other glands such as the testes, ovaries, thyroids and adrenals, secrete hormones. The pancreas secretes insulin, the thyroid produces thyroxine and the adrenals produce adrenalin.
  • Testosterone is the male hormone and estrogen, is the female hormone. The uterine wall in females prepares itself to receive the developing fertilised egg. In case there is no fertilisation, the thickened lining of the uterine wall breaks down and goes out of the body along with blood. This is called menstruation.
  • The sex of the unborn child depends on whether the zygote has XX or XY chromosomes.
  • It is important to eat balanced food and maintain personal hygiene during adolescence.

We hope you like the NCERT notes for Class 8 Science Chapter 10 pdf | Reaching the Age of Adolescence notes class 8 pdf you

what is adolescence?

The period of life when the body undergoes changes leading to reproductive maturity is called adolescence.

what is Oestrogen?

Oestrogen is the hormone responsible for the development of secondary sexual characters in females like enlargement of breasts, development of female reproductive organs, etc.

what is Testosterone

Testosterone is the hormone that brings the secondary sex character in boys such as the growth of a beard, the voice becoming hoarse, development of the reproductive organs etc.

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