8 Science Chapter 10 Reaching Age Of Adolescence

Chapter Notes and Summary
Teenagers : Generally adolescence begins at age of 11 and lasts upto 18 or 19 years of age. Adolescents are also called teenagers because they cover period of ‘teens’ i.e., 13 to 18 or 19 years of age.
Puberty : period of adolescence during which a adolescent reaches sexual maturity and becomes able to have children.
Changes at Puberty :
• During puberty sudden increase in height takes place. This happens due to elongation of long bones of legs and arms that make a person tall.
• Girls grow faster than boys by about 18 years of age, both reach their maximum height. rate of growth in height varies in different individuals.
• Height of an individual (male or female) depends on genes inherited from parents. However, right kind of food during growing years is also essential.
Calculation for full height (cm) : average rate of growth in height of boys and girls with age given in chart helps in calculating full height of individuals.
Development of Sex Organs : At age of puberty male sex organs such as penis, testes are completely developed.
Testes begin to produce sperms.
• In girls ovaries enlarge and start releasing mature eggs.
Reaching Mental, Intellectual and Emotional Maturity : Intellectual development takes place and they spend considerable time in thinking.
Secondary Sexual Characters : In boys, testes produce sperms, boys begin to grow facial hair, hair grow under arm, on their chest and in region above thighs and in pubic region. These are called secondary sexual characters. Male sex hormone testosterone is secreted at onset of puberty.
• In girls ova are formed. Breasts begins to develop, hair grows under arms and in region above thighs or pubic region. female sex hormone estrogen is released. Release of sex hormones is controlled by pituitary gland.
• Endocrine glands release hormones into blood stream to reach a particular body part called target site. It responds to hormones.
• In female, reproductive phase of life begins at puberty and generally lasts till age of 45 to 50 years. Ovum matures i.e., and if fertilization does not occur, released egg and thickened lining of uterus, along with blood shed off and is called menstruation. It occurs once in 28 to 30 days. first flow is termed as menarche and stoppage phase is called menopause.
Sex Determination (Boy/Girl) : Sex chromosome present in nucleus of sperm and ova determines sex in human beings. Pair of sex chromosomes in female is XX and in male is XY. When sperm carrying X chromosome fuses with ova child will be a female, whereas when sperm carrying Y chromosomes fuses with ova child will be a male.
Hormones : Hormones are chemical substances secreted by endocrine glands. They are also known as ductless glands.
These glands release hormones directly into blood stream to reach a particular body part known as target site.
Hormones control changes that occur at adolescence. male hormone called testosterone is secreted by testes at onset of puberty in girls, ovaries secrete female hormone or estrogen which makes breast develop. Their secretion is under pituitary endocrine gland.
• Reproductive phase lasts for a much longer time in males than in females. uterine wall in females prepares itself to receive developing fertilized egg.
Hormones other than Sex Hormones :
Name of Endocrine gland Hormone secreted Functions
Pituitary gland (i) Growth hormone
Other Hormones Regulates normal growth of a person to regulate functioning of
Thyroid gland
Adrenal gland
Production of testosterone by testes and estrogen by ovaries.
Thyroid gland Thyroxine Controls body metabolism.
Lack of thyroxine causes Goitre.
Sufficient iodine in diet prevents goitre.
Pancreas Insulin Control carbohydrate metabolism. Lack of insulin secretion causes Diabetes.
Adrenal Gland (i) Adrenaline
Hormone Maintains correct balance of salt-water in blood.
It helps body to adjust to stress due to anger, worry or embarrassment.
Reproductive Health : diet for an adolescent has to be carefully planned. He/she should take a balanced diet.
Personal Hygiene : For teenagers because increased activity of sweat glands sometime makes body smelly. All parts of body should be washed and cleaned properly everyday.
Physical Exercise : Walking and playing in fresh air keeps body fit and healthy.
Say ‘No’ to Drugs : If you take some drugs, just say ‘No’ unless it is prescribed by doctor. Drugs are addictive.
They ruin health and happiness both.

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