A virus is a minute infectious agent that, in general, cannot be seen with a light microscope. It lacks an independent metabolism and is able to replicate only within a living host cell. A free virus particle does not carry out the functions of a living cell, such as respiration and growth, and may be thought of as a packaging device by which viral genetic material can be introduced into appropriate host cells. What are the arguments for and against classifying viruses as living organisms? Discuss