Diversity of living form is enormous. When you look around yourself, you would find a large variety of living organisms. You would identify them as a sparrow, crow, frong, lizard, neem tree or a rose plant. But, are you aware that three is a whole world of living organisms which cannot be seen by the naked eye? These small organisms are called micro-organisms or microbes and can be seen only under a microscope. Thus, micro-organisms can be defined as tiny organisms that cannot be seen with the naked eye and can be seen under a microscope.
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Occurrence of Micro-Organisms
Micro-organisms can thrive in any kind of environment. They are found in air, water, soil, hot springs, ice caps, marshlands, deserts and also inside bodies of plants and animals. Soil contains a large number of bacteria and other microbes. Several microbes are harmful to us. They cause disease like cholera, typhoid, polio and leprosy in human beings. Some of these microbes are helpful to us. The nitrogen-fixing bacteria found in the root nodules of leguminous plants fix atmospheric nitrogen into nitrates. Some bacteria decompose dead bodies of plants and animals and release the inorganic substances into the soil.
Some microbes are free-living while others are found in or on the body of other organisms called the host. Most micro-organisms can survive under extremes of temperature and dryness by growing a hard covering called cyst around them. When the conditions become favorable the cyst raptures and the microbe emerges.
Classification of Micro-Organisms
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Micro-organisms can be classified into the following groups:
1 Bacteria, 2 Algae, 3 Fungi, 4 Protozoa, 5 Viruses.