Microorganisms the word itself says its meaning.
In nature, many living things such as trees, plants, animals, human, birds are seen by naked eye. But other living things are very small and cannot be seen through naked eye. We need a powerful magnifying lens (microscope) to see them. These organisms are called microorganism. They include single celled organism like bacteria, protozoa, etc.
There are different types of microorganisms are living in   the world and they are grouped in to five types
Before studying the Microorganisms,
We must know what is ‘Cell’