Reaching the age of adolescence class 8 notes

Welcome to Class 8 Science chapter 7 notes. On this page, you will find notes, questions, and answers to class 8 science chapter 7. These Reaching the age of adolescence class 8 notes, explanations, examples, and questions and answers are according to CBSE and the NCERT textbook. If you like the study material, feel free to share the link as much as possible.


  • The word adolescence means to grow into adulthood.
  • Adolescence can be defined as the period of growth during which a child develops into an adult.
  • The period of adolescence begins around the age of 10 -11 years and continues till 18-19 years of age. Growing up is a natural process.
  • It is the period between puberty and adulthood in human development.
  • In this time period, the body undergoes different changes alongside reproductive maturity .
  • Adolescents are also called teenagers because the period covers the teens thirteen to nineteen years of age .
  • In girls, adolescence may begin a year or two earlier than in boys. The period of adolescence varies from person to person. It is a stage of rapid growth and development.

  • When the human body undergoes several changes during the adolescence ,it Mark’s the onset of puberty.
  • Puberty can be defined as the process of physical changes by which a child becomes an adult and is capable of reproduction.
  • The capability of reproduction is the most important change which marks the puberty.

Changes that mark adolescence

  1. Growth Spurt
  2. Change in body shape.
  3. Change in voice
  4. Increased activity of sweat and sebaceous gland
  5. Development of sex organs
  6. Reaching mental, intellectual and emotional maturity.
  7. Development of secondary sexual characters.

The above mentioned changes that mark adolescence are explained below

1. Growth spurt

  • Growth spurt can be defined as a sudden increase in height. At this time bones of the arms and legs elongate and make a person tall.
  • The following chart gives the average rate of growth in height of boys and girls with age .
    <average rate of growth in height of boys and girls with age
  • By the following formulate can calculate the height as follows
    $$\text{Calculation for full height (cm)}=\frac{\text{Present height cm}}{\text{% of full height at this age}}\times 100 $$ % of full height at this age is given in the table.
  • Example A 11- year old girl is 130cm tall.What will be her approximate height at the end of the growth period?
    According to the formula from previous point
    $\frac{130}{88}\times 100 = 147.7\; cm$
    She will most likely to be 147 cm.
    This method gives an approximate estimation of height.

2. Change in body shape

  1. In boys
    • Broader shoulder
    • Wider chests
  2. In girls
    • Region below the waist becomes wider.

3. Changes in voice

  • At the time of puberty the change of voice takes place in girls and boys.In boys the larynx grow larger at the time of puberty and can be seen as protruding part of throat.This protrusion is called Adam's apple.
    <Adam's apple
  • Protruding voice box in boys is called Adam's apple.

4. Increased activity of sweat and sebaceous gland (Oil gland)

  • A temporary condition in which young people get pimples and acne on the face due to increased activity of these glands in the skin but disappears by the time they become adults.

5. Development of sex organs

  • Production of sex hormones that stimulate gamete production.
  • In boys:- Male sex organs like the testes and penis develop completely. Testes begins to produce sperm.
  • In girls:- The ovaries enlarge and egg begins to mature. Ovaries start releasing mature egg.

6. Reaching Mental, Intellectual and Emotional Maturity

  • They become more independent than before.
  • They become self conscious.
  • Develop a way of thinking.
  • This is that time when brain has the greatest capacity for learning.

7. Development of secondary sexual characters

  • Secondary sexual characters can be defined as the characters or features which help to distinguish the male from the female.
  • These characters develop by the secretion of chemical substances called hormones.
  • Testosterone is the male hormone released by testes whereas the oestrogen is the female hormone released by ovaries.
  • Boys develop the following secondary sexual characters
    1. Facial hair.
    2. Body hair, prominently under arm, abdomen, chest, pubic hair.
    3. Deep voice
    4. Beard, Moustaches developed.
  • Girls develop the following secondary sexual characters
    1. Region below the waist becomes wider.
    2. Body hair, prominently in armpits and pubic hair.
    3. Development of mammary glands inside the breast.
    4. Beginning of menstrual cycle.
    5. Shrilled voice


  • Also known as chemical messengers.
  • Hormones are chemicals secreted by specialized gland called endocrine gland.
  • Endocrine glands are also called ductless gland as they pour their secretions directly into the blood stream and reach parts of the body(Target site).
  • The production of hormones is under the control of another hormone secreted from endocrine gland called pituitary gland.
  • Pituitary gland is also called as master gland.
  • Hormones other than sex hormones

    Hormones secreted by the endocrine glands.

    Reaching the age of adolescence class 8 notes (Science Chapter 10)
    Position of various glands in Human Body
    Position of various glands in Human Body

    Reproductive phase of life in humans

    Hormones from pituitary gland stimulate testes and ovaries to release testosterone in males and Oestrogen in females and released in the blood stream and reach the parts of body (Target site).It stimulate the changes in the body at onset of puberty.

    In the female body, the reproductive phase of life starts at puberty. The process can be explained as follows

    • The ova begin to mature with the onset of puberty. One ovum matures and is released by one of the ovaries in 28 or 30 days .This is called ovulation. This cycle repeats every month and is known as menstrual cycle. The whole process is known as menstruation.
    • Menstruation can be defined as shedding of the unfertilized egg along with the thickened lining of the uterus and its blood vessels from a female body on a monthly basis and commonly called periods.
    • The first menstruation occurs at the onset of puberty and beginning of the menstrual cycle is called menarche.
    • Whereas, pause of the menstrual cycle in females at the age of 45 – 50 years is called menopause .

    Sex determination of a baby

    • In human beings, each cell of the body contain 46 chromosomes or 23 pairs of chromosomes. Out of these,22 pairs of chromosomes are common to both males and females and are called autosomes. Only one pair is different which is called sex chromosome.
    • The sex of a human is determined by the sex chromosome.
      1. In females – XX chromosomes is present.
      2. In males – X chromosomes and Y chromosomes is present.
    • So, in the process of fertilization, if a sperm containing the X chromosomes fertilizes the egg containing X chromosomes, the zygote is formed which consists of two X chromosomes and will develop into a female child.
    • Similarly, If a sperm containing the Y chromosome fertilizes the egg containing the X chromosomes, the zygote formed will have one X and one Y chromosomes which will develop into a male child.
    • It’s clear from the above that sex of a unborn child depends on the type of chromosomes their father posses.
    • Determination of Sex in Humans | Reaching the age of adolescence class 8 notes (Science Chapter 7)

    Reproductive health of adolescents

    • Health can be defined as a state of physical, mental well being of an individual.
    • During adolescence, nutritional health is very important for supporting the body as it is growing.
    • Adolescence is a stage of rapid growth and development. Hence the diet should be balanced.

    Nutritional needs of adolescence

    • Balanced diet is a diet which contains all the nutrients like carbohydrates, proteins, vitamins, fats and minerals in a right proportion. Apart from healthy diet ,personal hygiene and physical exercise is considered most important.
    • Personal hygiene refers to the practice of keeping yourself clean as by taking bath regularly. Bathing is essential due to body odour which is caused by sweat glands. Poor hygiene can lead to a microbial infection. Girls should also take special care of cleanliness during the time of period.
    • Doing regular physical exercise, can keep the bod healthy and mind calm. It control body weight as well as control the feeling of anxiety and depression. Physical exercise includes walking, cycling, doing yoga and playing outdoor games.

    Things to avoid during adolescence

    Say no to drugs

    During adolescence, always stay away from bad habits like smoking, or using narcotic drugs. Taking drugs can spoil the life .Sometimes per pressure can lead to bad habits. Peer pressure may have positive side but also have negative consequences for mental or physical health.

    AIDS- Acquired Immuno deficiency syndrome

    AIDS is caused by the Human Immunodeficiency Syndrome (HIV).

    It is a diseases f the immune system. It is transmitted by unprotected sex, through contaminated syringes, blood transfusions and from infected pregnant mother to child.


    Here is reaching the age of adolescence class 8 notes summary
    • The phase of development during which a kid transforms into an adult is known as adolescence. This is a time of fast growth and development.
    • Both girls and boys experience a change in voice during puberty. In boys, the larynx enlarges during puberty and can be seen as a protruding portion of the throat; this protrusion is known as the Adam's apple.
    • Hormones are secretions of endocrine glands, which are also known as ductless glands because they pour their secretions directly into the blood stream and reach regions of the body. Hormones influence the beginning of puberty and the maturity of reproductive parts
    • It is important to eat balanced food and maintain personal hygiene during adolescence.Taking drugs can spoil the life .Sometimes per pressure can lead to bad habits.

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