What is a significant characteristic of viruses regarding their cell entry methods?

A significant characteristic of viruses regarding their methods of cell entry is receptor-mediated endocytosis. This process allows viruses to attach to specific receptors on the surface of host cells, facilitating their entry into those cells. Once bound to the receptor, the cell membrane can engulf the virus in a vesicle, which then allows the virus to release its genetic material into the host cell. This is a critical step for the virus to initiate its replication process and spread within the host.

The other options do not reflect the methods by which viruses typically enter cells. Viruses do not have active metabolism because they rely on host cells for metabolic processes. Fission is a form of asexual reproduction typical of many prokaryotic organisms and does not apply to viral replication or entry. Flagellar movement pertains to motility in some bacteria and eukaryotic cells but is not a mechanism used by viruses to enter host cells, as they do not possess flagella and rely solely on the interaction with host cell receptors for entry.