Thursday, June 18, 2020

REPRODUCTION IN ORGANISMS

  • Life span is the period from birth to the natural death of an organism.
  • After the death of living organisms also, the population is maintained by the process of reproduction.
  • Reproduction is the biological process by which an organism produces its offspring similar to itself.
  • The offspring grows, matures and in turn produces new offspring.
  • By the process of reproduction, all living organisms maintain their population and ensure the continuity of species.
  • Reproduction is of two types- 1) asexual reproduction 2) sexual reproduction.

ASEXUAL REPRODUCTION
  • The offspring is produced by single parent without the fusion of gametes.

  • A single parent produces offspring and the off springs are exact copies of their parents.
  • The off springs are genetically and morphologically similar - clones.
  • Common in unicellular organisms, and plants and animals of relatively simple organisation.

Characteristics of asexual reproduction

  • A single parent is involved and so no fusion of gametes.
  • Only mitosis takes place.
  • Rapid multiplication.
  • Modes of asexual reproduction

    • fission- the parent body divides in to two equal halves and each half grows in to an adult -- binary fission

    Example- Amoeba.


    Dividing plane- 

    Transverse, eg paramoecium, planaria


    Longitudinal, euglena


    When nucleus divides multiple times and forms multiple cells - multiple fission



    • Budding- small bud is produced due to the cell division at one particular site -- remains attached initially to the parent cell --grows -- gets separated -- matures into a new individual.

    Example- yeast


    Fragmentation

    Body divides into several parts -- each part develop into a independent complete organism.

    Eg. Planaria, hydra, starfish, spirogyra (green algae), fungus.




    Asexual reproductive structures-

    • Members of kingdom fungi and simple plants reproduce through special reproductive microscopic motile structures called as zoospores.
    • Example- chlamydomonas

    • Other common structures are conidia in Penicillium,

    •  buds in Hydra

    • gemmules in sponge



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