Natural Classification of Micro-Organisms

Source:  Natural Classification of Micro-Organisms    Tag:  reproduction in fungi
You know living beings can be divided into three main groups: Plants, Animals, Microorganisms. Out of them I explained about Plants and Animals classification further in my previous posts. I think you read them too. So today I'm going to explain further about the last category of that main three groups: Microorganisms


  • Micro-Organisms are living organisms that cannot be clearly seen or seen with the naked eye.
  • They are mostly unicellular. An organized nucleus may or may not be present.
  • There may be organisms which may not possible to be classified under that two categories: Animals and plants.
Smile note: Full stop of a sentence in a book could be just covered by about 900 Bacteria kept together.

There 5 main groups of Micro-Organisms when they classified further.
  1. Bacteria.
  2. Algae.
  3. Protozoa.
  4. Fungi.
  5. Virus.

1. Bacteria

  • These are unicellular organisms with body size of about 3 - 5 um( micro meter)
  • The cell consists of protoplasm.
  • The nucleus membrane is absent.
  • The cell wall is made up of protein (Mucopeptide)
  • Some bacteria -especially disease causing, have a gelatinous case around the cell wall.
  • The structure of the cell and reproduction is similar to certain algae.
  • Reproduction is through binary fission or spores.
Bacteria show is a variety of nutritional habits.
  1. Saprophytic - These live on decomposing tree trunks.
  2. Parasitic      - Live on living organisms (tissues) and may cause diseases in the host. (pathogenic)
  3. Autotrophic  - The purple colored bacteria are photosynthetic .
  4. Symbiotic    - The rhizobium bacteria living in the root nodules of the leguminous plants can change the atmospheric nitrogen into an absorb-able form. This is known as nitrogen fixation. This is a symbiotic relationship.
  5. Chemosynthetic - This bacteria make chemical reactions to obtain energy to prepare its food.
Example: Iron bacteria (ferro bacteria) oxidize iron to release energy which is utilized in the preparation of food.

Smile Note: There is a belief that the evolution of life was due to chemotropic bacteria. The fission of bacteria occurs every 18-20 minutes. If a cholera bacterium undergoes binary fission at this rate 4.7 * 1022 bacteria will be reproduced within 24 hours. It'd have a mass of 2000 tons. this does not really happen due to poisoning of excretory products.

2. Algae

  • These consists of unicellular algae  that cannot be seen with naked eye as well as multicellular filamentous algae.
  • They are autotrophic - They prepare their own food by photosynthesis.
  • Most algae are aquatic, both marine and fresh water.
  • Grows as individual cells or in clusters.

3. Protozoa

  • Unicellular organisms.
  • There are about 40,000 aquatic species. 
  • They normally move feed on other organisms.
Paramecium Protozoa organism
Protozoa organism called Paramecium

    4. Fungi

    • Simple non-green plants which are not photosynthetic.
    • Has a heterotrophic type of nutrition : parasitic or saprophytic.
    • Display a symbiotic relationship with algae forming lichens.
    • Some fungi as well as muticellular algae are visible to the naked eye.
    • Some fungi may exist as mushrooms and various moulds. These have a muticellular filamentous structure called mycelium.

    5. Viruses

    • Have a simple structure.
    • Can reproduce.
    • Do not breathe.
    • Have the ability of crystallization.
    • The smallest micro-organism discovered so far.
    • Intrude living cells and start multiplying in them.
    • Some artificial substances resembling viruses that show the characteristics of viruses have been reproduced. Hence some people believe that viruses are in between living and non-living things.
    Ahh this is the last post I write about Natural Classification. And Natural Classification post series is over from here. Now I'll tell you the standard way of identifying same organism in different countries. Now next thing is up to you..!

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