Then unbiased observers should perhaps grade the rags as to their cleanliness. This is a simple example of the scientific method, but the principal applies to all research in biology, including cell biology. The scientific method is the basis for all accepted knowledge about cells. A virus is an infectious particle, and is not considered to be a cell . But it is important that you know why they are not cells, in order to better understand what cells are, and how viruses relate to cells.
Viruses can only grow and replicate by infecting living cells .
The virus uses the host cell machinery to cause the host cell to manufacture additional virus particles. For this reason it is questionable as to whether viruses are actually living organisms. Because of this, viruses can only be visualized with the help of electron microscopes. The two cell types found in nature are prokaryotes and eukaryotes . The former constitute many of the single celled life forms found in the microscopic realm.