These DAV Class 8 Science Notes and DAV Class 8 Science Chapter 15 Notes – Reaching the Age of Adolescence act as excellent revision resources, particularly in preparation for board exams.
Reaching the Age of Adolescence Class 8 DAV Notes
→ Adolescence: Adolescence is the transitional stage of physical and mental human development which occurs between childhood and adulthood. The period between 12 to 18 years of age is called adolescence.
→ Puberty: The phase when physical changes in the body start to take place is called puberty.
The phase of puberty lasts between 12 to 15 years of age. This phase marks the onset of sexual maturity in human beings.
→ Changes at Puberty:
→ Increase in height: This is the most dramatic and apparent change. There is a sudden increase in height and weight. The long bones in the body grow at a faster rate and the person becomes awkward in appearance.
→ Changes in the size of heart and lungs: The diameter of the heart increases by half and the weight almost becomes double. The size and the capacity of lungs also increase.
→ Change in body shape: Boys generally develop larger bones, more muscles, larger head and lungs; as compared to girls. Boys also develop broad shoulders and narrow hip, while the girls develop a curvaceous body and broader hips due to enlargement of pelvic bones.
→ Change in voice: The larynx becomes bigger in boys and the voice becomes low pitched. A protuberance; called Adam’s apple develops in the neck in boys.
→ Increased activity of sweat and sebaceous glands: Increased activity of sweat and sebaceous glands leads to increased sweat secretion. Acne and pimples are common problems among adolescents, due to increased activity of sebaceous glands.
→ Sexual Development:
→ Development of sex organs: The testes mature in boys and begin producing sperms. Ovaries; in girls; enlarge and begin the production of ova. Menstruation begins in girls.
→ Development of secondary sexual characters: Facial hairs develop in boys. Pubic hairs and hairs under armpits develop in both; boys and girls. Breasts enlarge in girls.
→ Changes in hormonal balance: Secretion of male hormone, i.e. testosterone; increases in boys. Secretion of female hormone, i.e. oestrogen; increases in girls. These hormones facilitate maturation of sex organs (gonads).
→ The Reproductive Phase In Human Beings:
→ After the onset of puberty, human beings become capable of reproduction. The ovaries become active in women around 11 to 13 years of age. The reproductive phase in women lasts till . about 45 to 50 years of age. The reproductive phase in men lasts longer and it can be up to 70 years of age.
→ Menstrual cycle: The sequence of events which start with the release of an ovum and culminates in discarding the ovum if no pregnancy takes place is called menstrual cycle. A menstrual cycle is of about 28 days. When an ovum is released from the ovary, it is trapped by filmbriae of the fallopian tube and remains in the fallopian tube in anticipation of pregnancy. The uterine wall thickens so that it can provide support to the developing embryo.
→ Developments in case of fertilization: The fertilization occurs in the fallopian tube. After fertilization, zygote undergoes several rounds of cell division till it becomes a ball of cells. This is called embryo. The embryo then enters the uterus and gets implanted in the uterine wall. This is called conception and marks the beginning of pregnancy. The embryo develops further to resemble a human being. At this stage, it is called a foetus.
→ Development in case of no fertilization: The additional layers in the uterine wall get broken and shed in fragments. The ovum; along with fragments of the extra layer of the uterine wall; is shed along with blood through vagina. This is called menstruation.
→ Menstruation: The discharge of dead cells and ovum; along with blood; is called menstruation. The menstruation lasts for 3 to 7 days and marks the end of a menstrual cycle.
→ Menarche: The first menstrual flow is called menarche. It happens at the beginning of puberty.
→ Menopause: The last menstrual flow is called menopause. It marks the end of reproductive phase in women.
→ Sex Determination In Human Beings:
In a somatic cell of human beings, there are 46 chromosomes or 23 pairs of chromosomes. The last pair of chromosomes can have similar or dissimilar chromosomes. In case of similar chromosomes (XX), the chromosomes in the last pair are called autosomes. In case of dissimilar chromosomes (XY), the chromosomes in the last pair are called heterosomes. Autosomes are present in females, while heterosomes are present in males.
When sperm is formed, the 23rd chromosome in it can be either an X chromosome or a Y chromosome. When ovum is formed, the 23rd chromosome in it will be an X chromosome.
During fertilization, if a sperm with X chromosome fertilises the egg; the zygote shall have XX chromosomes. This will result in the birth of a girl child. On the other hand, if a sperm with Y chromosome fertilises the egg; the zygote shall have XY chromosome and this will result in the birth of a male child.
→ Role of Hormone in Life Cycle of Insects and Frogs; A hormone released by thyroid gland signals the beginning of metamorphosis in frogs. Similarly, a hormone controls the metamorphosis in insects.
→ Reproductive Health:
→ Nutritional Needs of Adolescents: Adolescence is a period of high growth rate so nutrition needs of adolescents are special. One should take vitamin and mineral rich diet. Calcium rich diet promotes proper development of bones. Girls experience lot of blood loss during menstruation and hence they should take iron rich diet. Oily food should be avoided as it can increase the chances of pimples and acne.
→ Personal Hygiene: Increased activity of sweat and sebaceous glands creates many problems. Sweat accumulated under armpits and in pubic area can promote growth of bacteria. This can create the problem of body odour. Too much oil on the skin can clog the pores and can result in pimples. So an adolescent should take good care of personal hygiene. Girls should specially take care of cleanliness during menstruation.
→Physical Exercise: Exercise is important for people of all age groups, but is more important for adolescents. Exercise helps in increasing blood circulation and strengthens the respiratory system. Physical activity also helps in combating stress and strain which usually happen as a part of the growing up process.
→ Say ‘NO’ to Drugs: Adolescence is a period when one is more influenced by peer group than by family members. Peer pressure can mislead someone to develop some bad habits; like use of tobacco, alcohol and even drugs. These substances are addictive in nature and have highly crippling effect on the psychological and physical health. You should say a big ‘NO’ to drugs so that you can lead a highly productive life.
→ Adolescence: The phase which marks the onset and completion of sexual maturity.
→ Puberty: The onset of adolescence is called puberty.
→ Menstrual cycle: The sequence of events which begin with ovulation and end in menstruation.
→ Menstruation : The discharge of dead cells, ovum and blood at the end of menstrual cycle.
→ Menarche : The first menstrual flow.
→ Menopause : The last menstwal flow.
→ Endocrine gland : A ductless gland.
→ Hormone : A special chemical which is released by endocrine glands.
→ Osteoporosis : Weakening of bones due to decreased bone density.
→ The endocrine system: The endocrine system is a system of endocrine glands. The ductless glands in the body are called endocrine glands. These glands release special chemicals which are called hormone. A hormone is directly released in the blood stream and through that it is sent to a target organ.
| Endocrine Gland | Hormone | Function |
| Pituitary Gland | Growth Hormone | Growth and development of body |
| Thyroid Gland | Thyroxine | Controls general metabolism |
| Pancreas | Insulin | Glucose metabolism |
| Adrenal Gland | Adrenaline | Prepares the body during emergency |
| Testis (male) | Testosterone | Facilitates sperm production and development of secondary sexual characters in male. |
| Ovaries (female) | Oestrogen | Facilitates ovulation and development of secondary sexual characters in female. |