Human: What is the difference between a bacterium, a virus, and a fungus? Assistant: 
A bacterium is an organism that is not a fungus or a virus. Bacteria are prokaryotic cells that have no nucleus. They are usually single-celled organisms that can move around and feed on other organisms. Viruses are small infectious agents that replicate only inside living cells. Fungi are multicellular organisms that can produce spores and reproduce by spore division.