<human>: Can you explain the difference between a virus and a bacterium?
<bot>: A virus is an infectious agent that replicates only within the living cells of other organisms. Bacteria, on the other hand, are single-celled organisms that can reproduce independently of other cells. Viruses are much smaller than bacteria and contain either DNA or RNA as their genetic material. Bacteria have cell walls made up of peptidoglycan, while viruses do not.