Which term describes tiny living organisms only visible with a microscope?

The term that describes tiny living organisms only visible with a microscope is microorganisms. This category encompasses a diverse group of organisms, including bacteria, fungi, protozoa, and some algae. Microorganisms can be unicellular or multicellular, but they are typically so small that they require a microscope for visibility.

Understanding this term is crucial in various fields, particularly in microbiology and medicine, where the role of microorganisms in health, disease, and environmental processes is significant. Pathogens, on the other hand, are a subset of microorganisms that specifically cause disease. While viruses are indeed microorganisms, they are very specific and do not fall within the broader classification that includes other types like bacteria and fungi. Macroorganisms refer to larger living organisms that can be seen without a microscope, such as plants and animals. Thus, microorganisms is the most comprehensive and accurate term for organisms that fit the criteria of being tiny and requiring a microscope for viewing.