10. Reaching the age of adolescence Science class 8 in English Medium ncert book solutions Chapter Review

Chapter Review:

• Growing up is a natural process. The period of life, when the body undergoes changes, leading to reproductive maturity, is called adolescence.

• The human body undergoes several changes during adolescence. These changes mark the onset of puberty.

• The period covers the ‘teens’ (13 to 18 or 19 years of age), adolescents are also called ‘teenagers’.

• Height depends on the genes inherited from parents.

• During puberty the secretion of sweat glands and sebaceous glands (oil glands) increases.

• Endocrine glands release hormones directly into the bloodstream. So, they are also termed ductless glands.

• In girls, breasts begin to develop at puberty and boys begin to grow facial hair, that is, moustaches and beard.

• The changes which occur at adolescence are controlled by
  hormones. 

• The male hormone is testosterone and the female
  hormone is estrogen.

• Development of sexual organ as well as they produce sperm and ovum. In girls, breasts begin to develop at puberty and boys begin to grow facial hair, that is, moustaches and beard. Hair grows under the arms and in the region above the thighs or the pubic region.

• The ovary releases eggs for fertilization. If fertilisation does not occur, the released egg, and the thickened lining of the uterus along with its blood vessels are shed off. This causes bleeding in women which is called menstruation.

• Testes and ovary are even exocrine glands, which secrete sex hormone. These are responsible for secondary sexual characters  so these are called sex hormones. The sex hormones are under the control of hormones from pituitary gland.

• The chromosomes which determine the sex in the human beings are called sex- chromosomes. These are two ane is ‘X’ and another ‘Y’. A female has two X chromosomes, while a male has one X and one Y chromosome.     

• First The first menstrual flow begins at puberty and is termed menarch .

• At 45 to 50 years of age, the menstrual cycle stops. Stoppage of menstruation is termed menopause.

• The reproduction period in lady Starts in age of 10 – 12^th  years and ends in age of 40 – 45^th . 

• Endocrine glands release hormones into the bloodstream to reach a
  particular body part called target site.

• The growing voice box in boys can be seen as a protruding part of the throat called Adam’s apple.

• Pituitary also secretes growth hormone which is necessary for the normal growth of a person.

• All human beings have 23 pairs of chromosomes in the nuclei of their cells.

• A female has two X chromosomes, while a male has one X and one Y chromosome.

• This change from larva to adult is called metamorphosis.

• Metamorphosis in insects is controlled by insect hormones. In a frog, it is controlled by thyroxine, the hormone produced by thyroid.

• A balanced diet means that the meals includs proteins,carbohydrates,fats and vitamins in requisite proportions.