Question

why is virus an exception to cell theory

Answer 1

Viruses can be considered to be alive as they depend upon hosts to replicate their DNA from RNA. They are much smaller then cells. But cell theory states that " all living cells are made of cells that are fundamental unit of life". So, a virus is not made up of cells.

Answer 2

viruses are totlly different types of organisms than others. they do not have any proper working system they reproduce inside the cells of living hosts. When infected by a virus, a host cell is forced to produce thousands of identical copies of the original virus