Which term best describes a non-living agent that requires a host cell to replicate?

The term that best describes a non-living agent requiring a host cell to replicate is a virus. Viruses are unique because they cannot reproduce independently; they need to infect a living cell to fulfill their life cycle. Once inside a host cell, a virus hijacks the cell’s machinery to replicate its genetic material and produce new virus particles.

This characteristic distinguishes viruses from other options like bacteria and fungi, which are living organisms capable of independent reproduction and metabolic processes. Pathogens, which can include viruses but also encompass bacteria and other organisms that cause disease, are broader in definition and do not specifically address the requirement for a host cell in the replication process.