What term is used to describe one-cell microorganisms?

The term used to describe one-cell microorganisms is Bacteria. Bacteria are single-celled organisms that can exist independently or form colonies. They can be found in various environments, from soil to human bodies, and play roles in processes like fermentation and natural decomposition. While viruses, fungi, and protozoa also represent types of microorganisms, they differ significantly in structure and characteristics. Viruses, for example, require a host to replicate and are not considered living organisms outside of that context. Fungi can be single-celled or multicellular organisms, with the single-celled type being known as yeasts. Protozoa, on the other hand, are predominantly single-celled eukaryotic microorganisms but fall into a different category structurally since they have more complex cellular structures than bacteria. Therefore, when referring specifically to one-cell organisms, bacteria is the correct and most widely accepted term.