Are viruses irritable, as in "capable of responding to a stimuli"?
Viruses are not composed of cells, and are therefore non-living. They have no metabolism to provide energy so they can respond to stimuli.
Viruses are unable to reproduce themselves, another indication that they are non-living. They are composed of either DNA or RNA contained within a protein coat called a capsid.
They must insert their DNA or RNA into the host cell, where it is then replicated, instructing the cell to replicate viral parts and assemble them. Eventually there are so many viruses that the cell undergoes lysis, killing the cell and shedding viruses into the environment.
LYTIC CYCLE: viruses lyse the cell, causing cell death
A bacteriophage is a virus that infects bacterial cells
LYSOGENIC CYCLE: viral DNA/RNA can become part of the host cell's genome, lying dormant until a period of stress