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Microorganisms were the first living creatures on earth. It is estimated there are a total of 5 nonillion microorganisms on earth (5x1020). You will find nearly 10 million a millilitre of ocean water and 40 million in a gram of soil. They are also ubiquitous on the human body.
Microorganisms may be unicellular or single-celled, any living thing that has only one cell, the smallest unit of life. Some microor-ganisms are multicellular, having more than one cell. Microorganisms require food, air, water, ways to dispose of waste and an environment in which they can live.Some microorganisms are producers, living things that make their own food from simple substances usually using sunlight, as plants do.ome microor-ganisms are multicellular, having more than one cell. Microorganisms require food, air, water, ways to dispose of waste and an environment in which they can live. Some microorganisms are producers, living things that make their own food from simple substances usually using sunlight, as plants do.