<human>: What is the difference between a virus and bacteria?
<bot>: The main difference between viruses and bacteria is that viruses are much smaller than bacteria, usually around 20-400 nanometers in size. Bacteria are larger, typically 1-10 micrometers in size. Viruses can only replicate themselves by infecting host cells while bacteria can multiply on their own without needing to infect other cells. Additionally, viruses have an outer membrane which protects them from the environment, but bacteria do not.