How do viruses reproduce?

Viruses reproduce primarily by invading a living host. This process involves the virus attaching itself to a host cell and inserting its genetic material into the cell. Once inside, the viral DNA or RNA commandeers the host's cellular machinery, directing it to produce new viral components. These components are then assembled into new viruses, which can eventually leave the host cell to infect additional cells. This method is critical because viruses lack the cellular structures necessary for independent reproduction; they rely entirely on the host's biological processes.

While budding off from host cells is a specific mechanism through which some viruses exit and spread to new host cells, it is the initial invasion of a living host that is fundamental to the virus's ability to reproduce. Therefore, the key aspect that makes the invasion of a living host essential is its role in enabling the reproduction cycle of the virus.