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The smallest organism, capable of autonomous growth and reproduction, is
1. Virus
2. Bacteria
3. Mycoplasma
4. Bacteriophage

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Correct Answer - Option 3 : Mycoplasma

The correct answer is Mycoplasma.

  • The smallest organism, capable of autonomous growth and reproduction, is Mycoplasma.
  • Mycoplasma:
    • Mycoplasmas are spherical to filamentous cells with no cell walls.
    • There is an attachment organelle at the tip of filamentous M pneumonia and several other pathogenic mycoplasmas.
    • Fried-egg-shaped colonies are seen on agar.
    • The mycoplasmas presumably evolved by degenerative evolution from Gram-positive bacteria and are phylogenetically most closely related to some clostridia.
    • Mycoplasmas are the smallest self-replicating organisms with the smallest genomes.
    • They are low in guanine and cytosine.

  • Virus:
    • The virus is an infectious agent of small size and simple composition that can multiply only in living cells of animals, plants, or bacteria.
    • The name is from a Latin word meaning “slimy liquid” or “poison.”
    • The earliest indications of the biological nature of viruses came from studies in 1892 by the Russian scientist Dmitry I. Ivanovsky and in 1898 by the Dutch scientist Martinus W. Beijerinck.
    • Beijerinck first surmised that the virus under study was a new kind of infectious agent, which he designated contagium vivum fluidum, meaning that it was an alive, reproducing organism that differed from other organisms.
  • Bacteria:
    • Bacteria, singular bacterium, any of a group of microscopic single-celled organisms that live in enormous numbers in almost every environment on Earth, from deep-sea vents to deep below Earth’s surface to the digestive tracts of humans.
    • Bacteria lack a membrane-bound nucleus and other internal structures and are therefore ranked among the unicellular life-forms called prokaryotes.
    • Prokaryotes are the dominant living creatures on Earth, having been present for perhaps three-quarters of Earth history and having adapted to almost all available ecological habitats.
    • As a group, they display exceedingly diverse metabolic capabilities and can use almost any organic compound, and some inorganic compounds, as a food source.
    • Some bacteria can cause diseases in humans, animals, or plants, but most are harmless and are beneficial ecological agents whose metabolic activities sustain higher life-forms.
  • Bacteriophage:
    • Bacteriophage is also called phage or bacterial virus, any of a group of viruses that infect bacteria.
    • Bacteriophages were discovered independently by Frederick W. Twort in Great Britain (1915) and Félix d’Hérelle in France (1917).
    • D’Hérelle coined the term bacteriophage, meaning “bacteria eater,” to describe the agent’s bacteriocidal ability. Bacteriophages also infect the single-celled prokaryotic organisms known as archaea.

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