23 September 2014

Sexual and Asexual Reproduction in Animals : NCERT / CBSE

Sexual and Asexual Reproduction in Animals: Science Cbse / Ncert Revision Notes

Reproduction is the biological process by which existing organisms give rise to their offspring. Reproduction can be of two types – Sexual mode and Asexual mode

Sexual mode of reproduction: 

This type of reproduction involves two organisms, the male and the female. Reproductive organs in humans produce gametes - eggs and sperms. A zygote, the future individual is formed by the fusion of an egg and a sperm.

Sexual and Asexual Reproduction in Animals, Science Cbse / Ncert Revision Notes, Class 8

Reproductive organs

  • Male reproductive organs include a pair of testes, two sperm ducts, and a penis.Testes produce sperms, the male gametes. Sperms have a head, a middle piece and a tail. Sperms contain cell membrane, cytoplasm and nucleus.
  • The female reproductive organs consist of a pair of ovaries, two oviducts also called fallopian tubes, and the uterus. The ovary produces female gametes called ova or eggs.

Copulation is the act in which a male reproductive organ enters the female reproductive tract to discharge the male gametes.

Fertilisation is the fusion of male and female gametes to give rise to a single cell – zygote. Fertilisation can be external fertilisation or internal fertilisation.
  • When male and female gametes unite outside the body, it is called external fertilisation
  • When fertilisation takes place inside the body, it is called internal fertilisation.
  • When fertilisation takes place in a test tube, the offspring are called test tube babies.
  • Fertilisation that takes place outside the human body is in-vitro fertilisation.

Zygote, the super cell marks the beginning of a new individual. The zygote divides repeatedly to form a ball of cells making an embryo.

Embryo gets embedded in the wall of uterus, part of the female reproductive system. The development of the embryo takes place in the mother’s uterine wall. All parts of the body start developing in an embryo which finally transforms itself into foetus.

Reproduction in plants:

Stamens, the male reproductive organs give rise to male gametes, the pollen grains. Ovary, the female reproductive organ contains  the female gametes, the ovules.

Pollination is the process in which pollen grains fall on to the stigma of the pistil.

Fertilisation is the process in which the male gamete fuses with the female gamete.
The nuclei of the pollen and that of ovule fuse to form a zygote. Fertilised ovules transform into seeds.

Asexual Reproduction in Animals 

Reproduction is the biological process by which existing organisms give rise to their offspring. Reproduction can be of two types – Sexual mode and Asexual mode

Asexual mode of reproduction: 

This type of reproduction involves single parent in giving rise to offspring.

Organisms reproduce asexually by different processes like binary fission, fragmentation, budding, cloning etc.

Binary fission: It involves the splitting of an organism into two. Amoeba is a simple, unicellular organism which reproduces by binary fission. The division begins with the division of the nucleus.

Fragmentation: The parent organism divides into two or many fragments. Each fragment develops into an individual organism.  

Budding: It involves the appearance of protuberances called as buds. These buds separate out as new individuals. Bulges that appear as outgrowths on hydra are called buds.

Cloning: It involves the creation of an exact copy of a biological entity. A clone is created by inserting the complete genetic material of a regular body cell from a donor into a recipient. Dolly was the first cloned mammal, and is genetically identical to its parent sheep. Sir Ian Wilmut from Roslin Institute in Edinburgh, Scotland created Dolly. Cloning involves certain abnormalities. Dolly suffered from arthritis.