Notes of chapter: Reaching the Age of Adolescence are presented below. Indepth notes along with worksheets and NCERT Solutions for Class 8.
Adolescence is the age of human when body undergoes many changes like height, voice modulation, facial hair growth etc. and body leads to reproductive maturity. The age of adolescence begins from 11 and lasts up to 18 years.
Adolescents are also called”teenagers” because age of adolescence covers age of teens, ie, from thirteen to eighteen.
The period in which adolescence reaches to sexual maturity and ready to reproduces the young ones, is called puberty.
(3) Changes at puberty-
(i) Increase in height-
(a) Height of every adolescence increases at this age.
(b)Normally, height is similar to one of the family person because height depends on the genes of parents.
(c) Generally girls grow faster than boys. But both reach their maximum height at the age of 18.
(d) All parts of body do not grow at the same rate. But, other parts catche up to proportionate the body.
(e) Full height can be calculated by the formula discussed below:-
Calculation for full height (cm) = (Present height cm / % of full height at this age) ×100
Percentage of full height for different age is provided in chart given below. We can take data from the chart.
|Age in years||% of full height boys||% of full height girls|
Eg:- If a boy is 130 cm tall at the age of 10 year. What will be his height when he full grown up. Percentage of full height at this age 78%.
Present height = 130 cm
Percentage of full height at this age 78%.
Calculation for full height (cm) = (130/78) × 100
= 1.66 × 100
= 166 cm (approx.)
Hence, boy’s height will grow up to 166cm.
(ii)Change in body shape-
Change in body shape begins at the age of adolescence. Boys shoulder and chest broaden and lower portion of girl’s waist becomes wider. Muscles of boys grow more than the muscles of girls. The changes occurring in adolescent boys and girls are different.
(iii) Change in voice-
(a)The change in voice of adolescence is called cracks invoice.
(b)The voice changes because of growth of voice box or the larynx. The voice boxes or larynx can be seen in boys.
(c)The growing voice box which can be seen as a protruding part of the throat is called Adam’s apple. Girls have small Adam’s apple which can not be visible from outside.
(d) Generally girls have high pitched voice and boys have deep voice.
(e) When the muscles of the growing voice box go out of control, the voice is called hoarse voice. The state becomes normal after few day or weeks.
(iv) Increased activity of sweat and sebaceous glands-
(a) The secretion of sweat gland and sebaceous glands (Oil glands) increases which causes acne and pimples on the faces of the adolescence.
(b) Some glands like sweat glands, oil glands and salivary glands release their secretion through ducts.
(c) The gland which releases their secretion direct into blood stream is called ductless glands.
Eg:- Endocrine glands
(v) Development of the sex organs-
(a) Male sex organs fully developed at this age and testes begin to produce sperms.
(b) Female sex organs are also fully developed at this age. Ovaries enlarged and start releasing mature eggs.
(vi) Reaching mental, instinctual and emotional maturity-
(a) Adolescents are more confident and independent in thinking.
(b) Some adolescents feel insecure to adjust with changes their bodies.
(4) Secondary sexual characters-
(a) The characters which can distinguish between male and female are called secondary sexual characters.
Eg:- Hair begin to grow on chest, face in boys.
The breast develops in the girls.
Hair grows in arms pit and in the pubic region in boys and girls.
(b) The hormones are the chemical substance which is secreted by the endocrine gland in blood directly and controls the physical and mental changes of adolescences.
(c) The hormone which is released by the testes and caused changes in the male is called male hormone or testosterone.
(d) The hormone which is released by the ovaries and caused breast development in the female is called female hormone or estrogen.
(e) The gland which secretes milk and develops inside the breast is called mammary gland.
(f) The production of these hormones is under the control of another hormone secreted from an endocrine gland called pituitary gland.
(5) Role of hormones in initiating reproductive function-
(a)Target site is a particular body part where hormones released by the endocrine glands into blood stream reached and target site respond to hormones.
(b) There are many endocrine glands or ductless glands in the body.
(c) The onset of puberty is controlled by hormones is discussed with the diagram below:-
(6) Reproductive phase of life in humans-
(a) The capacity for maturation and production of gametes lasts for a much longer time in males and females.
(b) In female reproductive phase of the life begins at puberty (10 to 12 years) when mensuration cycle begins and lasts till the age (45 to 50 years) when menopause begins.
(c) Mensuration is a process of bleeding which occur in females after every 28 – 30 days when a matured ovum is released by one of the ovaries and received by the uterus whose wall become thick to receive egg. If this egg does not fertilised, the released egg and thickened lining of the uterus with its blood vessels shed off and caused bleeding in women.
(d) If released egg fertilised, the woman become pregnant.
(e) Menarche is a first menstrual flow begins at puberty.
(f) Mensuration is the stoppage of the menstrual cycle at the age of 45 – 50 years.
(7) Sex determination of the Baby-
(a) Chromosomes are thread like structure which are responsible for the sex determination.
(b) All human beings have 23 pairs of chromosomes in the nuclei of their cell.
(c) 2 chromosomes out of 23 chromosomes are the sex chromosomes. These are X and Y.
(d) A female has two X chromosomes.
(e) A male has asset of X and Y chromosomes.
(f) The gametes (egg and sperm) have only one set of chromosomes. It means the unfertilized egg has only X chromosomes but the sperm can have either X chromosomes or Y chromosomes.
(g) If sperm containing X chromosomes fertilised egg then, a zygote will have two X Chromosomes. It will result in the development of female child.
(h) If sperm containing Y chromosomes fertilised egg then, a zygote will have one X Chromosomes and one Y chromosomes. It will result in the development of male child.
(8) Hormones other than sex hormones-
(a) There are other endocrine glands in the body such as thyroid, pancreas and adrenals apart from the pituitary gland.
(b)Thyroid gland produces thyroxine harmone. Insufficient secretion of thyroxine hormones can cause ‘Goitre”.
(c) Pancreas produces insulin. Insufficient secretion of insulin caused diabetes.
(d) Adrenal gland produces hormones which keep balance of salt in blood.
(e) Adrenals also produce hormone adrenalin which helps the body to adjust to stress when one is very angry, embarrassed or worried.
(f) Thyroid and adrenal secrets their hormones when they receive orders from the pituitary through hormones.
(g) Pituitary also secrets growth hormone which is very necessary for a normal person.
(9) Role of hormones in completing the life history of insects and frogs-
(a) Metamorphosis in insects is controlled by insect hormones.
(b) Metamorphosis is controlled by thyroxine produced by thyroid in the frogs. Thyroxine production needs iodine in water. If water in which tadpoles are growing does not have sufficient iodine tadpole will not grow or become adult.
(10) Reproductive health-
(i) Nutritional needs of the adolescence-
(a) Adolescent needs balanced diet which has adequate quantity of protein, carbohydrate, fats, vitamin, minerals and other nutrients.
(b) Dal, roti, rice, vegetables are Indian meal which is balanced diet.
(c) Fruits are also full of nutrients.
(d) Iron is good for building blood. All leafy vegetables, jiggery, meat, citrus have iron.
(e) Mother’s milk is good for infants.
(ii) Personal hygiene-
(a) Adolescence should take bath everyday because the increased activity of the sweat glands sometimes makes the body smelly. Therefore all parts of the body should be washed and cleaned to prevent the bacterial growth.
(b) Girls should take care of personal hygiene during the flow of menstruation. They should note date of the menstrual cycle.
(iii) Physical exercise-
(a)Walking, playing outdoor, going to gym, dong yoga are some type of physical exercise which keep our body fit.
(b) All teenagers should do physical exercise daily to keep themselves fit.
(iv) Teenagers should keep themselves away from the drug and alcohol because it is not good for health.
(v) AIDS is caused by a virus HIV which is passed from one person to other by sharing of infected syringes and by sexual contact with a person infected with HIV. Infants can catch AIDS by their mother through breast feeding.