It seems to me that the ability to distinguish viruses from plasmids,
i.e. whether both or neither are organisms, is a bit thornier than I had
heretofore considered. Both plasmids and viruses are capable of self-
duplication and their distinction is further muddled by the fact that,
positive-sense viruses (except retroviruses) contain nucleic acids that are
infectious. Well, you might say, viruses exhibit a life cycle by (passively)
transferring themselves from one cell or host to another. But plasmids
clearly do that as well, albeit presumably with lesser efficiency. Remember
RTFs- one of the early concepts associated with plasmids. And the fact is
that both plasmids and viruses depend on pre-existing cellular processes
in order to replicate. It may be an academic discussion, we all can
distinguish plasmids from viruses, but providing a definition of viruses
to students that distinguishes them from plasmids, should one care to do
that, is more difficult than I had formerly conceived.
