CBSE Class 10 Answered

• They are composed of a single strand of genetic information encased within a protein capsule.
• On entering the appropriate host, the virus becomes active and displays properties typified by living organisms, such as reacting to its environment and directing its efforts toward self-replication 
• They are thus able to pass on genetic information to future generations.

Non-living features:

• Viruses lack most of the internal structure and machinery which characterize 'life', including the biosynthetic machinery that is necessary for reproduction.
• Without a suitable host cell, the virus is unable to replicate and behaves like a non-living structure. During this time there are no internal biological activities occurring within the virus, and in essence the virus is no more than a static organic particle. In order for a virus to replicate it must infect a suitable host cell.
• They may even be purified and crystallized like chemical substances.

Hence viruses are said to be intermediate between living and non-living organisms.