CBSE – 8th Standard Science

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Reproduction In Animals

Reproduction is essential for the continuation of a species as it ensures the continuation of similar kinds of individuals, generation after generation.

Modes of Reproduction

  • There are two modes by which animals reproduce Sexual and Asexual reproduction.

Sexual Reproduction

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  • In animals males and females have different reproductive parts or organs.
  • Reproductive parts in animals produce gametes that fuse to form a zygote which develops into a new individual.
  • This type of reproduction beginning from the fusion of male and female gametes is called sexual reproduction.

 

Male Reproductive Organs

  • The male reproductive organs include a pair of testes, two sperm ducts and a penis The testes produce the male gametes called sperms.
  • Millions of sperms are produced by a testis, sperms are very small in size, each has a head, a middle piece and a tail.

 

Female Reproductive Organs

  • The female reproductive organs are a pair of ovaries, oviducts (fallopian tubes) and the uterus .
  • Ovary produces female gametes called ova. An egg is also a single cell.
  • In human beings, a single matured egg is released into the oviduct by one of the ovaries every month.
  • Uterus is the part where development of the baby takes place.

 

Fertilization

  • The first step in the process of reproduction is the fusion of a sperm and an ovum. When sperms come in contact with an egg, one of the sperms may fuse with the egg. Such fusion of the egg and the sperm is called fertilization
  • During fertilization, the nuclei of the sperm and the egg fuse to form a single nucleus. This results in the formation of a fertilized egg or zygote
  • Fertilization which takes place inside the female body is called internal fertilization. Internal fertilization occurs in many animals including humans, cows, dogs and hens.
  • Fertilization in which the fusion of a male and a female gamete takes place outside the body of the female is called external fertilization.

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Development of Embryo

  • Fertilization results in the formation of zygote which begins to develop into an embryo The zygote divides repeatedly to give rise to a ball of cells
  •  The embryo gets embedded in the wall of the uterus for further development  It gradually develops the body parts such as hands, legs, head, eyes, ears.
  • The stage of the embryo in which all the body parts can be identified is called a foetus. When the development of the foetus is complete, the mother gives birth to the baby.

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Viviparous and Oviparous Animals

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Young Ones to Adults

  • The new individuals which are born or hatched from the eggs continue to grow till they become adults
  • The transformation of the larva into an adult through drastic changes is called metamorphosis.
  • In human beings, body parts similar to those present in the adults are present from the time of the birth

 

Asexual Reproduction

  • Reproduction in which only a single parent is involved is called asexual reproduction.
  • New individuals develop from the buds this type of asexual reproduction is called budding.

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  • In binary fission an animal reproduces by dividing into two individuals
  • Nucleus divides into two nuclei. This is followed by division of its body into two, each part receiving a nucleus.

 

Cloning

Cloning is the production of an exact copy of a cell, any other living part, or a complete organism. Cloning of an animal was successfully performed for the first time by Ian Wilmut and his colleagues at the Roslin Institute in Edinburgh, Scotland. They cloned successfully a sheep named Dolly . Dolly was born on 5th July 1996 and was the first mammal to be cloned.

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