Q.Which one of the following statement about virus is correct?

A virus is a sub-microscopic, obligate intracellular parasite made of a nucleic acid core (either DNA or RNA, never both) wrapped in a protein capsid, incapable of replicating outside a living host cell. Viruses are famous for showing genuine traits of both the living world (they contain nucleic acid and protein, mutate, multiply inside a host, cause disease, are host-specific, and show irritability) and the non-living world (they can be crystallised, show no metabolism of their own, are inert outside a host, have no functional autonomy, and carry no energy-producing enzyme system) - which is exactly why they are described as a 'biological puzzle' connecting the two. They range from about 20-300 nm across and take one of three shapes: cuboidal (e.g. Adenovirus), helical (e.g. TMV, Influenza virus) or complex/atypical (e.g. Bacteriophage). David Baltimore's 1971 scheme classifies them into seven classes based on their genome type (DNA/RNA, single/double-stranded) and use of reverse transcriptase. Bacteriophages such as T4 multiply through either a lytic cycle (adsorption, penetration, sy …