Question

why are virus considered as being at the border line between living and nonliving things

Answer 1

virus do not show any characteristics of a living thing individually, they even lack cellular movements. But when they enter a living host, they use their cell machinery to multiply.
Therefore virus are considered to be at the border line between living and nonliving things.


Hope this helps you

Answer 2

Viruses do not show any characteristic of living organisms when they are freely roaming in environment. But as soon as they hook to a host, they start to reproduce rapidly. They contain DNA like structures and other essential proteins required for reproduction. This viruses act as dead when not hooked to a host. Hence there's still a controversy over the fact whether viruses are dead of alive and hence are kept on the borderline.

Hope this helps!