The first virus to be discovered was the Tobacco mosaic virus in 1892 and the controversy surrounding their
classification as living or not living has been debated ever since.
The debate centres around the fact that viruses cannot survive without a host and they are unable to carry out even the most simple of biological processes alone. However, with a host they are able to function and reproduce like any
other life form. This is because a virus is essentially an isolated free roaming string of DNA without its own cell or metabolic processes, so it has no cell of its own or the enzymes that are needed for chemical reactions such as the
steps required to gain energy.
The string of nucleic acid is generally only between three to 400 genes long, and to survive it needs a host to produce and carry out the chemical reactions required to live. Once a virus reaches a cell it is able to get inside and hitch a ride with the DNA of the host.
It then combines with the DNA of the host and use it to sustain itself. Viruses can reproduce here using the cells’ code for building new copies. It will then burst out of the cell when it becomes packed with replicated viruses.
For now, most scientists support the theory that viruses cannot constitute as being alive.
However, it is agreed that if they are classified as life then they are the simplest form of it that we are yet to discover.