Chapter Notes -2, Reaching Age of Adolescence, Science, Class 8 | EduRev Notes

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Class 8 : Chapter Notes -2, Reaching Age of Adolescence, Science, Class 8 | EduRev Notes

The document Chapter Notes -2, Reaching Age of Adolescence, Science, Class 8 | EduRev Notes is a part of the Class 8 Course Science Class 8.
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Adolescence

  • The period of life, when the body undergoes changes, leading to reproductive maturity.
  • Adolescence begins around the age of 11 and lasts up to 18 or 19 years of age.

Chapter Notes -2, Reaching Age of Adolescence, Science, Class 8 | EduRev Notes

  • Adolescents are called teenagers as this period covers the teens (13-18 or 19 years of age).
  • For females, adolescence begins a year or two earlier than boys. The period of adolescence varies from person to person.

Try yourself:Adolescence is the period of
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Puberty

The period of adolescence during which an adolescent reaches sexual maturity and becomes able to reproduce.

Chapter Notes -2, Reaching Age of Adolescence, Science, Class 8 | EduRev Notes

Changes at Puberty

Chapter Notes -2, Reaching Age of Adolescence, Science, Class 8 | EduRev NotesChanges at Puberty

1. Increase in Height

  • There is a sudden increase in height of a person during puberty due to the elongation of the bones of arms and legs. Even though the height of a person depends on an inherited gene, eating habits and exercise during adolescence also decides height.
  • Initially, girls grow faster than boys. Both reach maximum height by the age of about 18 years.

Formula for calculating full height(cm) = Present height(cm)/ % of full height at this age X 100

2. Changes in Body Shape

  • In boys, the shoulders broaden and muscles of the body grow more prominently than in girls. 
  • For girls, there is the widening of the region below the waist and less growth of muscle.

3. Voice Change

During puberty, it is being noticed that the voice of boys starts cracking and their voice box or larynx starts to grow

Adam’s Apple:
The increase in the size of voice box in boys is seen as a prominent protrusion in the neck. This protrusion is called Adam’s apple.

Chapter Notes -2, Reaching Age of Adolescence, Science, Class 8 | EduRev Notes

4. Increased Activity of Sweat and Sebaceous Glands

During puberty, there is an increase in the secretion of sweat glands and sebaceous glands which may lead to the appearance of acne and pimples.

5. Development of Sex Organs

  • At puberty, male sex organs like the testis and penis develop completely and begin to produce sperms. 
  • In girls, the ovaries enlarge and start releasing eggs/ova.

6. Reaching Mental, Intellectual, and Emotional Maturity

  • Adolescents are more independent and self-conscious than earlier. They tend to think more. Feeling insecure when while trying to adjust to the changes in mind and body is prominent. 
  • During adolescence, a person’s brain has the greatest capacity for learning.

Try yourself:Adam’s apple is
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Secondary Sexual Characters

  • Characters that develop prominently during adolescence which helps to distinguish between male and female are known as secondary sexual characters. 
  • Some of these characters are listed below:Chapter Notes -2, Reaching Age of Adolescence, Science, Class 8 | EduRev Notes

Hormones other than Sex Hormones

  • Hormones are chemical substances secreted by the endocrine system/ endocrine glands (Ductless glands, i.e. endocrine glands release hormone directly into the bloodstream to reach a particular body part/target site). 
  • Hormones control the changes during adolescence. The pituitary gland (found attached to the brain) secretes hormones which in turn control the production of hormones from other endocrine glands.
  • Some endocrine glands, their secretion, and effect are given in the table below:Chapter Notes -2, Reaching Age of Adolescence, Science, Class 8 | EduRev Notes

Role of Hormones in Initiating Reproductive Function:

Chapter Notes -2, Reaching Age of Adolescence, Science, Class 8 | EduRev Notes

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

  • The life span of insects can be categorized into four stages:
    (i) Egg
    (ii) Larva
    (iii) Pupa
    (iv) Adult
  • Metamorphosis: It is the change of an insect from a larva to an adult.
  • Hormones in insects control the metamorphosis under the action of thyroxine hormone produced by the thyroid.

Reproductive Phase of Life in Humans

  • Adolescents become capable of reproduction when their testes and ovaries begin to produce gametes.
  • In females, the reproductive phase of life begins at puberty (10-12 years of age and generally lasts till the age of approximately 45-50 years).
  • Ova mature and is released by one of the ovaries once in about 28-30 days. During this period, the uterus becomes thick so as to receive the mature ova. A fertilized egg develops pregnancy.
  • Unfertilized egg along with the thickened lining of the uterus and blood vessels are shed off in the form of bleeding in women once in about 28-30 days is termed Menstruation.
  • Initial menstrual flow begins at puberty and is termed Menarche.
  • Stoppage of the menstrual cycle at 45-50 years of age is called Menopause.
  • Initially, the menstrual cycle may be irregular. It takes some time to become regular.

How is the Sex of the Baby Determined?

  • Instruction for determining the sex of a baby is present in the chromosome of the fertilized egg (zygote). Humans have 23 pairs of chromosomes, including two sex chromosomes (X and Y) in the nucleus of their cells.
  • Females have two X chromosomes and males have one X and one Y chromosome.
  • An unfertilized egg has one X chromosome. Sperm may have one X chromosome or Y chromosome. Therefore, the sex chromosomes of the father determine the sex of the unborn baby.

Try yourself:When a sperm having X-chromosome fuses with the ovum, the child born will be
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Reproductive Health

The physical and mental well-being of an individual is regarded as healthy. To keep the body healthy, every human being at any age needs to have a balanced diet, must observe personal hygiene, and undertake adequate physical exercise.

1. Nutritional Needs of the Adolescents

  • Adolescence is a stage of rapid growth and development. So a balanced diet comprising proteins, carbohydrates, fats, minerals, and vitamins in requisite quantity is essential. 
  • Iron builds blood. Iron-rich food such as leafy vegetables, jaggery, meat, citrus, Indian gooseberry is good for adolescents.

Chapter Notes -2, Reaching Age of Adolescence, Science, Class 8 | EduRev NotesBalanced Diet 

2. Personal Hygiene

Take bath once a day. It is more necessary for adolescents due to the increased activity of sweat glands which may lead to a smelly body. All parts of the body should be washed and cleaned every day.

3. Physical Exercise

Adolescents should take walk, exercise, and play outdoor games in fresh air to keep them fit and healthy.

Chapter Notes -2, Reaching Age of Adolescence, Science, Class 8 | EduRev Notes

4. Say No to Drugs

During teenage, anyone might get affected by the negative energies surrounding him. At such times, falling for drugs can ruin your life.

Chapter Notes -2, Reaching Age of Adolescence, Science, Class 8 | EduRev Notes

5. HIV (Human Immunodeficiency Virus)

  • AIDS (Acquired Immunodeficiency Disease) is caused due to this virus. It is an incurable disease as yet no medicine can cure it. Chapter Notes -2, Reaching Age of Adolescence, Science, Class 8 | EduRev Notes
  • It might spread due to sexual contact, because of infected needles, and from an infected mother to her unborn child.
  • Hence, prevention is the only way to keep away from this dangerous disease.
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