<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, ranging from about 20-400 nanometers in size. Bacteria are larger, usually around 0.5-10 micrometers in diameter. Viruses also lack a cell membrane and instead rely on host cells for replication. Bacteria have a cell wall and can replicate on their own.