What characterizes a virus?

A virus is characterized as a parasitic submicroscopic particle that requires a host for replication. This definition highlights the fundamental nature of viruses; they are not considered living organisms by traditional definitions because they cannot reproduce or carry out metabolic processes on their own. Instead, viruses must invade a host cell, hijacking the host's cellular machinery in order to replicate themselves.

This parasitic relationship is essential to their life cycle, as viruses lack the cellular structure and metabolic capability to thrive independently in the environment. They can only replicate when inside a host organism, which makes them distinctly different from other biological entities like bacteria or larger cells that can sustain themselves and reproduce independently.

Understanding this distinction reinforces the importance of host interaction in the life cycle of a virus, emphasizing its role as a pathogen that depends on living cells for survival and propagation.