IMMUNOLOGY

Detailed explanation-1: -Viruses are too small and simple to collect or use their own energy – they just steal it from the cells they infect. Viruses only need energy when they make copies of themselves, and they don’t need any energy at all when they are outside of a cell.

Detailed explanation-2: -Since viruses are intracellular parasites, they rely on their host cells for the energy, macromolecular synthesis machinery and the work benches for genome replication and particle assembly. Because of this dependence, viruses have evolved a myriad of mechanisms for exploiting normal host cell functions.

Detailed explanation-3: -Incapable of producing their own energy supply, (+)RNA viruses must usurp ATP from the host cells to fuel the energy requirement of viral replication.