How does a virus primarily differ from other microorganisms?

A virus primarily differs from other microorganisms in that it cannot live without a host. Viruses are unique entities that require a living cell to replicate and propagate. Unlike bacteria and fungi, which can reproduce independently in suitable environments, viruses lack the cellular machinery necessary for metabolism and reproduction; they are incapable of carrying out biological functions on their own.

This dependency on a host cell is crucial for viral propagation, as the virus must infect a host to hijack its cellular processes to produce new virions. Thus, the distinguishing characteristic of viruses is their obligate parasitic nature, making them fundamentally different from other microorganisms that can exist and multiply independently outside of a host organism.