IMMUNOLOGY

Detailed explanation-1: -For instance, viruses can reproduce inside a host just like any other living organism, but this ability to reproduce is lost when the virus is outside the host cell. This is because viruses do not have the cellular machinery that is required to multiply, hence they hijack a living cell.

Detailed explanation-2: -Once inside a host, viruses invade the organism’s cells and “hijack” them, causing them to stop performing their normal functions and to start making more copies of the virus. Viruses are really, really, small (even 100x smaller than bacteria!) pathogens that can only replicate within a living organism, called a host.