2. Viruses
• A tiny, non-living particle that enters
and then reproduces inside a living cell
• Needs a host, which provides a source
of energy
• Parasite
– Lives on or in a host and can cause
harm
8. Multiply
• Inside host cell
– Virus’s genetic material takes over many
cell functions
– Instructs cell to produce the virus proteins
and genetic material
– Make new virus’s
9. Bacteria
• Anton van Leeuwenhoek (late 1600s)
– Scrapings from teeth
– Could only see shapes, but not the parts
inside the cells