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CBSE Class 8 Biology Notes for Chapter 6 Reaching the Age of Adolescence

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                            CHAPTER 6 REACHING THE AGE OF ADOLESCENCE
 
When the body undergoes changes that lead to reproductive maturity, it is called adolescence. When the human body undergoes these changes, it is called the beginning of puberty and it ends when the adolescent reaches the reproductive maturity.
 
CHANGES AT PUBERTY
Increase in height: Puberty leads to an increase in height as the bones of the arms and the legs elongate to make the person tall.
Change in body shape: For girls, the region below the waist becomes wider and for boys, shoulders broaden and body muscles grow.
Voice change: At puberty, the voice box (or larynx) begins to grow. Boys develop a larger voice box than girls. As a result, the voice box protrudes out and can be seen as Adam’s Apple Girls develop an high pitched voice whereas boys develop a deep voice.
Increased activity of sweat and sebaceous glands: The secretion of sweat glands and oil glands increases during puberty and this causes acne and pimples on the face.
Development of sex organs: In boys, the testes and penis develop completely and testes start to produce sperms. In girls, ovaries enlarge and eggs begin to mature.
Reaching mental, emotional, intellectual maturity: A lot of changes happen in an adolescent’s body and these changes lead to a mental, intellectual and emotional maturity to develop in them.
 
SECONDARY SEXUAL CHARACTERS
The additional features that help to differentiate between the male and female are called secondary sexual characters. For boys, the chest hair, facial hair, etc. are secondary sexual characters. For girls, the development of breasts is secondary sexual characters. The common changes for both genders are hair growth under arms and pubic region.
 
WHY DO THESE CHANGES OCCUR?
An endocrine gland secretes hormones. Hormones are chemical substances which control the physical changes that occur at puberty. The male hormone is called testosterone which is released by the testes. The female hormone is called estrogen and is produced by the ovaries. The estrogen is responsible for the development of the breasts. The milk secreting glands or the mammary glands develop inside the breasts.
All these hormones are controlled by a hormone that is secreted by the pituitary gland.
 
REPRODUCTIVE PHASE OF LIFE IN HUMANS
For females, the reproductive age begins from 10-12 years of age till about 45-50 years of age. The ovum, once matured, is released by one of the ovaries once in about 28 to 30 days. The wall of the uterus thickens so that it can receive the egg. If fertilization occurs, it result in pregnancy but if fertilization does not occur the thickened lining and the blood vessels are shed of and this cause bleeding in women. This is known as menstruation. The beginning of menstrual flow is called menarche and when it stops ate the age of 45-50, it is called menopause. This monthly cycle of bleeding is called menstrual cycle.
 
SEX OF THE CHILD
If the child has the XY set of chromosomes, it is a boy and if the child has XX set of chromosome, it is a girl. The egg has the X and the 2nd chromosome is given by the sperm. It can be X or Y.
 
Adolescence can be a tough time, both physically and mentally. It is important to take care of your body during adolescence. Eating good food, exercising and maintaining personal hygiene is very important.

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