Virus – replicates only inside of the living cell of an organism, infect all life forms, animals, plants, microorganisms, including bacteria and archaea. Virion – complete virus particle that consists of an RNA or DNA core, outer protein shell called a capsid and an inner core of nucleic acid host specificity – capability of living solely on or in one species of host, number and identity of host species that are used by a parasite population. lytic cycle - attachment, entry, replication, assembly, lysis. Viral reproductive cycle, virus takes over all metabolic activities of a cell and causes the host cell to die.