Reproduction in Animals Class 8 Notes - Chapter 9

Introduction to Reproduction

  • Reproduction is the process of giving rise to an offspring.
  • Reproduction is essential for the continuation of a species.
  • There are two modes of reproduction:
  1. Sexual reproduction and
  2. Asexual reproduction

Asexual reproduction

The type of reproduction in which only a single parent is involved is called asexual reproduction.

  • There is no mixing of genetic information.
  • Eg: buds in Hydra

Sexual reproduction

The type of reproduction whcih involves two parents to give rise to an offspring is called as sexual reproduction.

  • The males and females have different reproductive parts or organs.
  • These organs produce the male and female gametes which fuse together to form the offspring.
  • Genetic information from both parents is inherited.
  •  Eg: humans


It is a type of asexual reproduction in which a single-celled organism divides into two.

  • Division of nucleus is followed by division of other cell organelles in the cytoplasm and finally the cytoplasm.
  • Thus two cells are produced from one parent cell.
  • Example: Amoeba.
  • Amoeba reproduces by binary fission, which is dividing into two cells.

If one parent cell gives rise to many daughter cells, this type of fission is called as multiple fission.


  • A bud starts as an outgrowth on the parent body.
  • As this bud grows, it becomes a new individual organism.
  • In some organisms, the buds remain attached to the parent’s body (example: yeast)
  • In some organisms, it detaches from parent body and develops into a complete mature individual (hydra).
  • This type of reproduction is called as budding.


Cell Division

  • Reproduction essentially involves cell division.
  • Without cell division life will not propagate.
  • The two types of reproductive processes involve two different types of cell divisions.

Cell division is the process in which a parent cell divides into two or more daughter cells.

Cell division provides more cells:

  • For growth
  • Regeneration
  • Repair and damage control
  • Gamete formation

There are two types of cell division:

  1. Mitosis
  2. Meiosis


Mitosis is a process where a single cell divides into two identical daughter cells.

  • DNA replication occurs once followed by a single division.
  • The number of chromosomes is maintained in this type of division.
  • This type of division happens in asexual reproduction.
  • It is also used for growth, repair and regeneration of tissues.



This is a cell division in which a single cell divides into four haploid cells.

  • DNA replication occurs once followed by two divisions.
  • The numbers of chromosomes are halved in meiosis.
  • Meiosis takes place in sex organs to produce haploid gametes.
  • Thus, the gametes have only half the number of chromosomes in them.



Sexual Reproduction in Humans

Male reproductive system

  • The male reproductive system consists of a pair of testes, a pair of sperm ducts and a penis.
  • The testes are located outside the male body.
  • Sperms are produced in testes.
  • Sperms are the male gametes.

Male reproductive system


  • Testosterone is the primary male sex hormone and is produced by the testes.
  • Testosterone is responsible for the development of sex organs, production of sperms and also the development of secondary sexual characteristics.


  • Sperms are the male gametes produced by testes in humans.
  • Millions of sperms are produced by the testes in a day.
  •  Each sperm is a single, microscopic cell having a head, a middle piece and a tail as its parts.
  • Head contains a nucleus with a single set of chromosomes.
  • The middle piece contains a large number of mitochondria that provide energy during active movement.
  • Sperm is a motile gamete which moves through the female reproductive tract with the help of the tail.

Female reproductive system

  • The female reproductive system consists of a pair of ovaries, a pair of fallopian tubes (oviducts) and a single uterus.
  • Ova are produced by ovaries.
  • Fallopian tubes (oviducts) carry the ova from ovaries to the uterus.
  • Uterus holds the growing embryo/foetus and thus helps in holding the pregnancy.

Female reproductive system


  • Estrogen or oestrogen is the primary female sex hormone secreted by ovaries.
  • It is responsible for the development of female reproductive organs, secondary sexual characteristics, development of female gamete i.e.ovum and maintenance of menstrual cycle.


  • The ovary produces the female gametes known as ovum or ova (plural).
  • In human beings, a single mature egg or ovum is released into the oviduct/fallopian tube by the respective side ovary every month.
  • The ovum is a single cell and is much larger than the sperm.
  • It is non-motile and is carried to the uterus by the oviduct.


Fertilization is the process of fusion of the male gamete with the female gamete.

  • Both the gametes containing haploid (single) set of chromosomes fuse and thus maintain the diploid (double) number of chromosomes.
  • The fertilized ovum is now called a zygote.
  • In human fertilization takes place in the fallopian tube and then the zygote is carried to the uterus.
  • Inside the uterus, it undergoes repeated divisions and grows and becomes an embryo.

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