CBSE Class 8 Science, Reaching the age of Adolescence

•   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

        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

        

Fig. 10.1 Adam�s apple in grown up boy.

•   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.

        

•   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.

        (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.