What is the primary distinguishing feature of viruses?

The primary distinguishing feature of viruses is that they are acellular and require a host cell for replication. Unlike living organisms, which are composed of cells and capable of independent reproduction and metabolism, viruses do not have a cellular structure. They consist of genetic material (either DNA or RNA) enclosed in a protein coat, and sometimes an additional lipid envelope.

To reproduce, viruses must invade a host cell and hijack the host's cellular machinery to replicate themselves. This dependency on a host for reproduction is a fundamental characteristic that sets viruses apart from other types of microorganisms, such as bacteria and fungi, which can reproduce independently. Understanding this distinction is essential in microbiology, as it also informs treatment strategies for viral infections, which differ significantly from those aimed at bacterial infections.