How does a virus multiply in a host organism?

A virus multiplies in a host organism primarily by entering a living cell. Once inside the cell, the virus hijacks the cell’s machinery and metabolic pathways to replicate its genetic material and produce new viral particles. This process involves attaching to the cell surface, penetrating the cell membrane, and employing the host's cellular resources to assembly new virus components.

Unlike bacteria, which can reproduce independently through processes like binary fission, viruses cannot replicate on their own and require a living host to propagate. The other options do not accurately reflect the mechanism by which a virus reproduces. For instance, while budding from the host cell might describe a specific way some viruses exit the cell after replication, the initial multiplication process critically depends on entry into a living cell, making it the essential step in the viral life cycle.