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NCERT Notes Science for Class 8 Chapter – 7: Reaching The Age of Adolescence

Last Updated : 31 May, 2023
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NCERT Notes for Class 8 Science Chapter – 7: Reaching The Age of Adolescence: Growing up is a natural process. Growth begins from the day one is born. But upon crossing the age of 10 or 11, there is a sudden spurt in growth which becomes noticeable. The changes taking place in the body are part of growing up. They indicate that the individual is no longer a child but is on the way to becoming an adult. The period of life, when the body undergoes changes, leading to reproductive maturity, is called Adolescence.

NCERT Notes on Reaching The Age of Adolescence of Class 8 Science Chapter – 7: Adolescence begins around the age of 11 and lasts up to 18 or 19 years of age. Since this period covers the ‘teens’- 13 to 18 or 19 years of age, adolescents are also called ‘teenagers’. In girls, adolescence may begin a year or two earlier than in boys. Also, the period of adolescence varies from person to person. The human body undergoes several changes during adolescence. These changes mark the onset of Puberty. Puberty ends when an adolescent reaches reproductive maturity.


Puberty is a remarkable journey that every individual undergoes as they enter their teenage years. It is a time of rapid growth and development, both internally and externally, as our body prepares itself for adulthood. These changes are regulated by the hormones released by our endocrine system, which influence various aspects of our physical appearance and emotional well-being.

  1. Increase in Height: The most clearly visible change during puberty is the sudden increase in height. Initially, girls grow faster than boys but by about 18 years of age, both reach their maximum height. The rate of growth in height varies in different individuals. Some may grow suddenly at puberty and then slow down, while others may grow gradually.
  2. Change in Body Shape: At the age of puberty, shoulders generally broaden as a result of growth in boys. In girls, the region below the waist becomes wider. In boys, the muscles of the body grow more prominently than in girls. Thus, changes occurring in adolescent boys and girls are different.
  3. Voice Change: At puberty, the voice box or the larynx begins to grow. Boys develop larger voice boxes. The growing voice box in boys can be seen as a protruding part of the throat called the Adam’s apple. In girls, the larynx is hardly visible from the outside because of its small size.
  4. Increased Activity of Sweat and Sebaceous Glands: During puberty the secretion of sweat glands and sebaceous glands (oil glands) increases. Many young people get acne and pimples on the face at this time because of the increased activity of these glands in the skin.
  5. Development of Sex Organs: At puberty, male sex organs like the testes and penis develop completely. The testes also begin to produce sperm. In girls, the ovaries enlarge and eggs begin to mature. Also, ovaries start releasing mature eggs
  6. Reaching Mental, Intellectual and Emotional Maturity: Adolescents are more independent than before and are also self-conscious. Intellectual development takes place and they tend to spend considerable time thinking.

Secondary Sexual Characters

At puberty, breasts begin to develop in girls and boys begin to grow facial hair, that is, moustaches and beard. Boys also develop hair on their chests. In both, boys and girls, hair grows under the arms and in the region above the thighs or the pubic region. As these features help to distinguish the male from the female they are called secondary sexual characters. The changes which occur in adolescence are controlled by hormones.

Role of Hormones in Initiating Reproductive Function

Endocrine glands release hormones into the bloodstream to reach a particular body part called the target site. The target site responds to the hormone. The pituitary secretes many hormones, one of which makes ova mature in the ovaries and sperm form in the testes. This can be illustrated by the following:

Role of Hormones in Initiating Reproductive Function


Reproductive Phase of Life in Human

At puberty, the released egg (in women), and the thickened lining of the uterus along with its blood vessels get shed off in the form of bleeding known as menstruation. The first menstrual flow begins at puberty and is known as menarche. Menstruation occurs once in about 28 to 30 days. By the age of 45 to 50 years, the menstrual cycle stops, which is known as menopause. The thread-like structures in the fertilized egg are known as chromosomes. All human beings have 23 pairs or 46 chromosomes in the nuclei of their cells. In boys, out of 23 pairs of chromosomes, two chromosomes named X and Y are the sex chromosomes. In girls, out of 23 pairs of chromosomes, two chromosomes named X and X are the sex chromosomes. When a sperm carrying an X chromosome fertilizes with the egg, the zygote would have two X chromosomes that develop into a female child. When a sperm carrying the Y chromosome fertilizes with the egg, the zygote would have two chromosomes i.e. X and Y and such a zygote develops into a male child.

Reproductive phase of life in human

How is the Sex of the Baby Determined?

Sex chromosomes play a crucial role in determining the sex of the unborn baby. Typically, females have two X chromosomes (XX), while males have one X and one Y chromosome (XY). The father’s sperm carries either an X or a Y chromosome, while the mother’s egg always contributes an X chromosome. If the sperm carrying an X chromosome fertilizes the egg, the resulting combination (XX) will develop into a female baby. On the other hand, if the sperm carrying a Y chromosome fertilizes the egg, the combination (XY) will develop into a male baby.

Also Read: Sex Determination

Hormones other than Sex Hormone

Apart from the testes and the ovaries, there are other endocrine glands in the body:

  • Pituitary Gland – Growth Hormone, Prolactin, Thyroid Stimulating Hormone, Adrenocorticotropic hormone, Follicle Stimulating Hormone, Oxytocin, etc.
  • Thyroid Gland – Thyroxine
  • Adrenal Gland – Adrenaline
  • Pancreas – Insulin

Human Endocrine System

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

As we know, the tadpole passes through certain stages to become a frog. This change from larva to adult is called metamorphosis. Metamorphosis in insects is controlled by insect hormones. In a frog, it is controlled by thyroxine, the hormone produced by the thyroid. Thyroxine production requires the presence of iodine in water. If the water in which the tadpoles are growing does not contain sufficient iodine, the tadpoles cannot become adults.

Reproductive Health

To keep the body healthy, every individual, at puberty, needs to have a balanced diet. The person must also observe personal hygiene and undertake adequate physical exercise.

Nutritional Needs of the Adolescents

The diet for an adolescent must include a Balanced Diet. A balanced diet includes proteins, carbohydrates, fats, and vitamins in requisite proportions. Our Indian meal of roti/rice, dal (pulses), and vegetables is a balanced meal. Milk is a balanced food in itself. Fruits also provide nourishment.

Personal Hygiene

Everyone should have a bath at least once every day. All parts of the body should be washed and cleaned every day. If cleanliness is not maintained there are chances of catching the bacterial infection.

Physical Exercise

Walking and playing in fresh air keeps the body fit and healthy. All young boys and girls should take walks, exercise and play outdoor games.

Also Read: Reproductive Health

FAQs on Reaching the Age of Adolescence

Q1: Define adolescence.


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 or 19 years of age. 

Q2: What is Adam’s Apple?


Adam’s apple is the protrusion on the front of the boy’s throat. It’s the cartilage that covers the front of the larynx or voice box. In girls, the larynx is hardly visible from the outside because of its small size.

Q3: What are sex hormones?


Hormones secreted by the testes and ovaries are called sex hormones. They are responsible for the male and female secondary sexual characteristics and hence are named sex hormones.  

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