NCERT Class 8 Science Chapter 10 - Reaching the Age of Adolescence Notes

Chapter 10 - Reaching the Age of Adolescence Notes

1. Different stages of human
• Infants
• Toddlers
• Adolescents/Teen age
• Adults
• Old age

2. Adolescence is a period of life, when the body undergoes changes leading to sexual maturity. The period of adolescence usually begins from 11 years to 19 years. Adolescents are also called teenagers. The body at this stage undergoes important changes and these mark the period of puberty. 

3. Puberty is a period, during which, the human body undergoes certain changes in their body and reproductive which leads to sexual maturity. The most important change, which marks puberty is that boys and girls become capable of reproduction. In girls, puberty may begin a year or two earlier than in boys. 

4. Changes during puberty
The important changes taking place during puberty are
• Increase in height
• Change in body shape
• Voice change
• Increased activity of sweat and sebaceous glands
• Development of sex organs
• Reaching mental, intellectual and emotional maturity

5. Increase in height
By the age of 11 a boy reaches about 80% of his height and a girl reaches about 88% of her height. Initially girls grow faster than boys. By about 18 years of age both boys and girls reach their maximum height. Generally the height is similar to the parents because it depends on the genes inherited from the parents.

6. Change in body shape
During puberty boys have broader shoulders and wider chests due to faster growth of muscles. In girls the breast begins to develop and region below the waist becomes wider.

7. Voice change
At puberty, the voice box or the larynx begins to grow. Boys develop larger voice boxes. The growing voice box in boys cam be seen as protruding part of throat called Adam's Apple. In girls, the larynx is hary visible from the outside because of its small size. Generally, girls have a high pitched voice, whereas the boys have a deep voice. In adolescent boys, sometimes the voice box go out of control and the voice gets hoarse. This remains for few days or weeks after which voice becomes normal. 

8. Increased activity of Sweat and Sebaceous glands
During puberty the secretions of the sweat and sebaceous glands (oil glands) increases and many teens get acne and pimples on their face.

9. Development of Sex organs
During puberty in boys the tests and penis develops completely and produces sperms. In girls the ovaries develop completely and produces eggs.

10. Reaching Mental, Intellectual and Emotional maturity
During puberty boys and girls mental, intellectual and emotional development takes place. They become more independent, self-conscious and their way of thinking changes.

11. Secondary Sexual Characters
Secondary sexual characters are the changes which takes place during puberty. In boys hairs begin to grow on the face and they develop beards and moustaches. Hair also grows in the chest, armpits and pubic region. The testes starts to produce sperms. In girls their breast develops and hair grows in the armpits and pubic region. The ovary starts to produce eggs. These changes are controlled by chemical substances called hormones produced by endocrine glands. The male hormone which controls secondary sexual characters is called testosterone. It is produced in the testes. The female hormone which controls secondary sexual characters is called estrogen. It is produced in the ovary. The production of these hormones is controlled by another gland called pituitary gland.

12. Reproductive phase in humans
The capacity for reproduction starts at puberty. It lasts for a longer time in males than in females. In females the capacity for reproduction starts at puberty and less for 40-50 years.

13. Menstruation
In females the ovary produces one egg every month and the uterus prepares to receive the fertilised egg. Its wall becomes thick with blood vessels. If fertilisation does not take place then the uterus wall breaks and comes out of the vagina as blood and mucous. This cycle takes place once every month and is called menstruation. The beginning of menstrual cycle is called menarch. When menstrual cycle stops at 40-50 years it is called menopause.

14. Sex determination in humans
Human beings have 23 pairs of chromosomes in the nucleus of the cell. Out of this two chromosomes are sex chromosomes called X and Y chromosomes. The female has two X chromosomes and male has one X and one Y chromosome. The sperms and eggs have one set of sex chromosomes. Some sperms have X chromosome and some have Y chromosome. All eggs have X chromosome. If a sperm having X chromosome fuses with an egg having X chromosome the child will be a girl. If a sperm having Y chromosome fuses with an egg having X chromosome the child will be a boy.

15. Endocrine glands and their functions
Endocrine glands produce chemical substances called hormones which controls different functions in the body. The main endocrine glands are:
• Pituitary gland
• Thyroid gland
• Adrenal gland
• Pancreas
• Testes
• Ovary
→ Pituitary gland: It controls growth and production of hormones by testes and ovary.
→ Thyroid gland: It produces thyroxine. Its deficiency causes goitre (swelling of throat).
→ Adrenal gland: It produces adrenalin. It helps the body to adjust to stress when we are angry or worried.
→ Pancreas: It produces insulin. Its deficiency causes diabetes.
→ Testes: It produces testosterone which controls production of sperms and secondary sexual characters in males.
→ Ovary: It produces estrogen which controls production of eggs and secondary sexual characters in female.

16. Reproductive health
To keep the body healthy everyone should have
• Balanced diet
• Personal hygiene
• Physical exercise
→ Balanced diet: It is a diet which contains nutrients in the right amounts. Balanced diet should contain cereals, vegetable, fruits, pulses, milk, nuts, meat, eggs, sugar, jaggery etc.
→ Personal hygiene: Everyone should have a bath at least once a day. If cleanliness of the body is not done, there can be bacterial infections and diseases.
→ Physical exercise: Walking, playing outdoor games and exercise keeps the body healthy.

17. Say “No” to drugs
Drugs are additive. If you take them once, you feel like taking it again and again. They ruin health and happiness. AIDS is a dangerous disease caused by virus HIV. AIDS spreads from an infected person to a healthy person by:
• Sexual contact
• Sharing syringes used for injecting drugs
• It is also transferred from the mother to child through her milk

18. Hormones are the chemical substances which are synthesized at one place and travels through the blood stream and act upon a target site.

19. Nutrition is the process of obtaining food and utilization by any organism.

20. The components of food which are necessary for the body are called nutrients.

21. What are secondary sexual characters?
At puberty some changes occur in both male and female that distinguish them from each other. The features that develop in them are called secondary sexual characters.

22. There are 2 types of glands in our body
• Endocrine glands
• Exocrine glands

23. Endocrine gland is a gland which don’t have duct or tube and secretes its product directly into the blood stream. They make chemical substances called hormones. They are also known as ductless glands.

24. Exocrine gland is a gland which secretes its product into duct or tube.

25. The pituitary gland is sometimes called the “master” of all the glands of the endocrine system because it controls the functions of many other endocrine glands.

26. Endocrine glands release hormones into the bloodstream to reach a particular body part called target site.

27. Some disease/disorder caused by deficiency of vitamins and minerals

Table

28. AIDS stand for Acquired Immune Deficiency Syndrome. HIV stands for Human Immunodeficiency Virus Infection.


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