A biological agent that cannot reproduce on its own is called a virus.

Here's why:

* Viruses are not considered living organisms: They lack the necessary cellular machinery (ribosomes, etc.) to replicate independently.

* They require a host cell: Viruses need to invade a living cell to access the resources and machinery needed for replication. They then hijack the host cell's processes to create more copies of themselves.

Examples of viruses:

* Influenza virus

* HIV

* Coronavirus (like SARS-CoV-2)

Let me know if you have any other questions!