Virons do not generate metabolic energy. They are obligate intracellular parasites, meaning that they require a host cell to reproduce. Viruses can be harmful. Virulent - disease causing. Temperate - not immediately disease causing.
Viruses play a role in causing some cancers.
Viruses may be helpful. A temperate virus introduces nucleic acid from its former host into a new host, thus changing the genetic code of the host. By this process of transduction, viruses cause genetic variation within a host population. Certain varieties of flowers have been developed using viruses to alter the genetic code. Characteristics used to classify viruses.