How are viruses classified among microorganisms?

Viruses are classified as submicroscopic parasites because they exist at a scale that is smaller than typical microscopic organisms and lack the cellular structure that defines prokaryotic and eukaryotic organisms. Unlike multicellular organisms, viruses do not have the complexity of differentiating tissues and cells; they are essentially composed of genetic material (either DNA or RNA) encased in a protein coat, and in some cases, a lipid envelope. Because viruses cannot reproduce independently and must invade the living cells of a host to replicate, they are considered parasites. This classification as submicroscopic is also crucial, as it highlights that viruses cannot be seen with ordinary light microscopes and require more advanced techniques like electron microscopy for visualization.