Question

Why are virus form an exception to cell theory

Answer 1

Virus are an exception because viruses are alive only until they are inside their host cell. They are considered to behave dead when outside the host cell.According to wikipedia there are three.Viruses are considered alive by some, yet they are not made up of cells. Viruses have many features of life, but by definition of the cell theory, they are not alive. The first cell did not originate from a pre-existing cell. 

Answer 2

Because they are non cellular. They don't show any molecular movements.
Therefore, they look like dead. They start their molecular movement when they the cell of other organisms