They are smaller and simpler in structure and are parasitic. Virus particles can't live independently, but must exist in a host cell and use the host cell's metabolic machinery for essential life processes like protein synthesis and replication. Debate about calling viruses living. Discuss Viroids- pieces of RNA that aren't quite virus particles since they lack a complete protective structure. But under some circumstances viroids seem to be able to reproduce themselves .
All microbes are too small to see with the unaided human eye.
Invented by Robert Hooke - Improved by Anton van Leeuwenhoek , Holland not a scientist, amateur lens grinder in 1600's. Leeuwenhoek's microscopes magnified things about 300x - Today the microscopes you will use in lab can magnify things a max. of 1,000x. Dual lenses that magnify things. Made up of curved glass. Slide of flask making things bigger.