Living organism (such as a bacteria, fungi, viruses) too small to be seen with naked eye but visible under a microscope. Also called microbe.

Microorganisms are microscopic ( cannot be seen with a naked eye ), single celled organisms, for eg.-- Bacteria, Fungus etc. These were the first living organisms on earth and is estimated that at present there are 5 nonillion microorganisms on earth. Almost all the animals and humans are dependent on microorganisms. Microbes protect humans from many allergies and also from malaria. Microorganisms too produce enzymes to perform different tasks.
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