CBSE Class 8 Science, Reaching the age of Adolescence

Class VIII Science
Notes for Reaching the age of Adolescence
Facts that Matter
•   Adolescence: The period of life, when the body undergoes changes, leading to reproductive maturity is known as adolescence.
   Generally, adolescence begins at the age of 11 and lasts upto 18 or 19 years of age. Adolescents are also called teenagers because they cover the period of the �teens� i.e. 13 to 18 or 19 years of age.
•   Puberty: The 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. The rate of growth in height varies in different individual.
        Height of an individual (male or female) depends on the genes inherited from parents. However, right kind of food during growing years is also essential.
   Calculation for full height (cm): The average rate of growth in the height of boys and girls with age given in the chart helps in calculating full height of the individuals.
        Calculation for full height (cm)
For example: A girl is 9 years old and 120 cm tall. At the end of the growth period she is likely to be
   Boys develop larger voice boxes (Larynx) to form a protruding part of throat called Adam�s Apple. Boys have deep voice.
        In Girls, larynx is hardly visible (Adam�s apple not visible). They have pitched voice.
•   Change in Body Shape: In boys, at the age of puberty, shoulders generally brooden as a result of growth. In boys, the muscles of the body grow prominently than in the girls.
        In girls, the region below the waist becomes wider. The muscles also comparatively grow less.
Fig. 10.1 Adam�s apple in grown up boy.
   The secretion of sweat glands and sebaceous glands (oil glands) increases during puberty.
•   Development of Sex Organs: In males, testes and penis develop completely. Tests start producing sperms.
        In girls, ovaries enlarge and eggs begin to mature. Ovaries start releasing mature eggs (ova).
   At puberty, individuals reach mental, intellectual and emotional maturity.
•   Secondary Sexual Character: Such as development of breasts in girls, moustaches and beard in boys, begin to develop. These characters that help in distinguishing the males from the females are called secondary sexual characters.
        Boys also develop hair on their chest.
•   Hormones: Hormones are chemical substances secreted in endocrine glands. They also known as ductless glands. These glands release hormones directly into the blood stream to reach a particular body part known as target site.
        Hormones control the changes that occur at adolescence. The male hormone called testosterone is secreted by the testes at the onset of puberty and cause development of facial hair, chest hair etc. At the onset of puberty in girls, ovaries secrete female hormone or estrogen which makes the breast develop. Their secretion is under the pituitary endocrine gland.
   Reproductive phase lasts for a much longer time in males than in females.
   The uterine wall in females prepares itself to receive the developing fertilised egg. In case there is no fertilisation, the thickened lining of the uterine wall breaks down and goes out alongwith blood.
        This bleeding in women is called menstruation which occurs once in about 28 to 30 days.
•   Menarche: The first menstrual flow which begins at puberty is known as menarche.
•   Menopause: At 45 to 50 years of age, the menstruation cycle stops. Stoppage of menstruation is known as menopause.
•   Sex chromosome: The thread structures present inside the nucleus of every cell are called chromosomes. All human beings have 23 pairs of chromosomes in nuceli of their cells. Two chromosomes out of these are the sex chromosomes known as X and Y. A female has two X chromosomes whereas a male has one X and one Y choromosomes.
   Sex of the unborn child depends on whether the zygote has XX or XY chromosome.
Fig. 10.2 Sex determination in humans.
•   Hormones other than Sex Harmones
•   Metamorphosis: The change from larva to adult is called metamorphosis. In insects, metamorphosis is controlled by insect hormones. In frog, metamorphosis from tadpole to adult frog is controlled by thyroxine hormone which is produced by thyroid gland. Thyroxine production requires the presence of iodine in water.
Fig. 10.3 Position of endocrine glands in the human body.
•   Nutritional need of the Adolescents: Adolescence is a stage of rapid growth and development.
        Hence, the balanced diet is very important at this stage. Here, balanced diet means that the meals should include proteins, carbohydrates, fats, minerals and vitamins in requisite proportion.
•   Personal Hygine:
        (a) It is more necessary for teenagers because the increased activity of sweat glands makes the body smelly. So, daily bath is necessary.
        (b) If all body parts are not washed or cleaned everyday, the chances of bacterial infection are more.
        (c) Girls should take special care of cleanliness during the time of menstrual flow.
•   Say �No� to Drugs: Adolescence period is full of much activities, confusion or insecurity. Some people take advantage of this and lead adolescents to had habits. They are addictive, and sexual contact with persons infected with HIV may happen.
        You should be firm to say NO to such activities because they run in your health and happiness.