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Class 8, Science, Chapter-7, Lecture-1, Puberty (Notes)

ADOLESCENCE:

The period of life, when the body undergoes physical, mental and emotional changes, leading to reproductive maturity, is called adolescence.

Adolescents are also called Teenagers.

The period of adolescence starts around 11 years and lasts upto 18 or 19 years.

Since it covers the ‘teen’ years (13 to 19), adolescents are also called teenagers.

PUBERTY:

The process of physical changes through which a child's body matures into an adult body capable of sexual reproduction.

Puberty starts in Girls at an age of 10 to 13 years
in Boys at an age of 12 to 14 years

Changes at Puberty:

  1. Sudden increase in height
  2. Different changes in body shapes of boys and girls
    1. Boys develop broader shoulders and wider chests
    2. Girls develop broader hips
    3. Boys become muscular
    4. Girls develop breasts
    5. Boys develop Adam’s Apple and voice becomes deep
    6. Girl’s voice becomes shrilling
  3. Boys develop facial hair.
  4. Increased activity of sweat glands and sebaceous glands causes development of acne and pimples on the face.
  5. Development of Sex Organs 
    Testes mature in boys and begin to produce sperms and Testosterone 
    Ovaries enlarge in girls and start releasing mature eggs and Estrogen
  6. Reaching mental, intellectual and emotional maturity

SECONDARY SEXUAL CHARACTERISTICS:

The characteristics controlled by hormones which distinguish between sexually mature males and females but are not directly involved in reproduction are called secondary sexual characteristics.

Secondary Sexual Characteristics in BOYS:

  1. Facial hair (Beard and moustache)
  2. Hair on chest
  3. Broadened shoulder
  4. Low pitched deeper voice
  5. Adams Apple (Protruded voice box)

Secondary Sexual Characteristics in GIRLS:

  1. Developed breasts
  2. Broadened hips
  3. High pitched shrill voice
  4. Adams Apple (Protruded voice box)

Secondary Sexual Characteristics common to Boys and Girls:

  1. Hair in armpits
  2. Pubic hair (hair in the region above the thighs)

OVULATION:

The release of ovum from the ovary into the oviduct is termed as ovulation.

MENSTRUATION:

The breakdown and removal of the inner, thick and soft lining of the uterus along with its blood vessels in the form of vaginal bleeding is called menstrual flow or menstruation.

MENSTRUAL CYCLE:

The cycle of events taking place in the ovaries and uterus every twenty-eight days and marked by the menstrual flow, is called menstrual cycle.

MENARCHE:

The beginning of menstruation at puberty in a female human being is termed menarche.

MENOPAUSE:

The stoppage of menstrual flow around the age of 50 years in a female human being is termed as menopause.

When the egg is not fertilised:

In human females, ovary release on egg every month. The uterus prepares itself by making the inner lining thick and spongy for the nourishment of the fertilised egg. 
If egg is not fertilized, it leaves for about one day after which the lining breaks and moves out through vagina as blood and mucous.

SEX CHROMOSOMES:

The pair of chromosomes which determine the sex of an organism and which differ in males and females are called sex chromosomes.

SEX DETERMINATION IN HUMAN BEING:

In males (XY) — half of the sperms carry X–chromosomes and half of the sperm, carry Y–chromosomes.

In females (XX) — all the eggs carry X–chromosomes.

During fertilisation —

If a sperm carrying y–chromosomes fuses with an egg, the result is a male zygote (XY).

If a sperm carrying x–chromosome fuses with an egg, the result is a female zygote (XX).