Question

why are some organisms called microorganisms?

Answer 1

If some organisms have only one cell is called as microorganisms because they are very very very small for the naked eye

Answer 2

Here is your answer
Some organisms are called microorganisms because they are very small in size and are not visible to naked eyes. They can only be seen by microscope. Thus, their extremely small size is the reason they are called microorganisms. For ex- bacteria viruses protozoa some fungi etc