What is a basic characteristic of a virus?

A basic characteristic of a virus is that it requires a living host to reproduce. Viruses are unique among microorganisms as they cannot replicate or carry out metabolic processes on their own; they must invade the cells of a living organism to hijack the host's cellular machinery for their own replication. This dependence on a host distinguishes viruses from other infectious agents, such as bacteria, which can live and reproduce independently in various environments.

In contrast, other statements do not accurately describe the nature of viruses. For example, viruses cannot reproduce on their own, contrary to what is suggested in the second option. Additionally, viruses are generally much smaller than bacteria, making the statement about size misleading. Lastly, antibiotics, which are effective against bacterial infections, do not affect viruses; therefore, the claim that viruses can be treated with antibiotics is incorrect. Understanding these characteristics is crucial for properly addressing viral infections and implementing public health measures.