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

Science Class 8

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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. Adolescents are called teenagers as this period covers the teens (13-18 or 19 years of age). For females, the adolescence begins a year or two earlier than boys. The period of adolescence varies from person to person.
Chapter Notes -2, Reaching Age of Adolescence, Science, Class 8 | EduRev Notes

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

Changes at Puberty:

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

 

1. Increase in HeightThere is sudden increase in height of person during puberty due to elongation of the bones of arms and legs. Even though height of person depends on 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 year.

*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 the girls. For girls, there is widening of the region below the waist and less growth of muscle.

3. Voice change: During puberty, it is being noticed that 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 NotesFig: Adam's Apple

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

5. Development of sex organs: At puberty, male sex organs like testes 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 of insecure when while trying to adjust to the changes in mind and body is prominent. During adolescence, a person’s brain has greatest capacity for learning.


SECONDARY SEXUAL CHARACTERS
Characters which develops prominently during adolescence which helps to distinguish between male and female are known as secondary sexual characters. Some of these characters are as listed below:

Secondary Sexual Characters

Female

Male

Begins to develop breasts
Begins to grow facial hair i.e. moustaches, beard
Hair under arms, pubic region
Hair on chest, arm pit, pubic region


HORMONES
Hormones are chemical substances secreted by endocrine system/ endocrine glands (Ductless gland i.e. endocrine glands release hormone directly into blood stream to reach particular body part/TARGET SITE). Hormones control the changes during adolescence. Pituitary gland (found attached to brain) secretes hormone which in turn control the production of hormone from other endocrine glands. Some endocrine glands,  their secretion and effect are given in the table below;

ENDOCRINE GLAND/ORGAN
SECRETION or HORMONE
FUNCTION
HORMONAL DEFICIENCY DISEASE OF THE HORMONE PRODUCED
SEX HORMONE
Testis in
male
Testosterone

 

Secondary sexual characters like growth of facial hair

 

 
Ovary in
female
Estrogen

 

Develop breasts(*Mammary glands develop inside breasts)

 

 
 
 
HORMONES OTHER THAN SEX HORMONE
Pancreas
Insulin
Control carbohydrate metabolism
Diabetes
Pituitary
gland
Growth hormones

 

Regulate normal growth of person

 

 
Adrenal
glands
Adrenalin Hormone

 

Helps body to adjust to stress resulted by anger, worry etc. Maintains correct salt balance in the blood

 

 
Thyroid
Thyroxine
Controls body metabolism
Goitre(Sufficient Iodine in diet may prevent goitre)

 
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: Egg, Larva, Pupa and Adult.
Metamorphosis: It is the change of insect from larva to an adult.
Hormones in insects control the metamorphosis under the action of thyroxine hormone produced by thyroid.


Reproductive Phase Of Life In Humans:

  • Adolescents become capable of reproduction when their testes and ovaries begin to produce gametes.
  • In females, 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. Fertilized egg develops pregnancy.
  • Unfertilized egg along with the thickened lining of 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 menstrual cycle at 45-50 years of age is called MENOPAUSE.
  • Initially, 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 fertilized egg (zygote). Human have 23 pairs of chromosomes including two sex chromosome (X and Y) in the nucleus of their cells.
  • Females have two X chromosomes and males have one X and one Y chromosome.
  • Unfertilized egg has one X chromosome. Sperm may have one X chromosome or Y chromosome. Therefore, sex chromosomes of the father determine the sex of the unborn baby.

REPRODUCTIVE HEALTH

The physical and mental well being of an individual is regarded as health. 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.

Nutritional needs of the adolescents: Adolescence is a stage of rapid growth and development. So 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 adolescent.
Chapter Notes -2, Reaching Age of Adolescence, Science, Class 8 | EduRev NotesPersonal hygieneTake bath once a day. It is more necessary for adolescents due to increased activity of sweat glands which may lead to smelly body. All parts of body should be washed and cleaned everyday.

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 NotesSay 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
HIV (Human Immunodeficiency Virus)AIDS (Acquired Immunodeficiency Disease) is caused due to this virus. It is incurable disease as yet no medicine can cure it. 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.
Chapter Notes -2, Reaching Age of Adolescence, Science, Class 8 | EduRev Notes

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