What is a microorganism?

A microorganism is defined as any organism that is so small it can only be seen with the aid of a microscope or is of microscopic to submicroscopic size. This definition encompasses a wide range of entities, including bacteria, viruses, fungi, and protozoa. These organisms are crucial in various ecological roles, including decomposition, nutrient cycling, and even influencing health in humans and other living things.

The choice indicating that any organism visible to the naked eye is not accurate because it excludes a vast number of organisms that are classified as microorganisms but cannot be seen without magnification. Similarly, limiting the definition to only pathogenic organisms disregards the many non-pathogenic microorganisms that play essential roles in the ecosystem and human health. Lastly, defining microorganisms strictly as beneficial organisms neglects the existence of harmful microorganisms, which are also significant in understanding the full diversity and function of microbial life. Therefore, the classification of microorganisms embraces both harmful and beneficial organisms, emphasizing the microscopic size of these entities.