What strategies do viruses commonly use to enter host cells?

Viruses have evolved specific strategies to effectively enter host cells and establish infection. The correct answer highlights the primary methods that viruses utilize: binding to host cell receptors and employing endocytosis or membrane fusion.

When a virus approaches a host cell, it first attaches to specific receptors on the cell surface. These receptors are often proteins that the host cell naturally uses for its own functions, but the virus hijacks them to gain entry. This interaction is highly specific and is crucial for the virus's ability to infect the cell.

Once the virus binds to the receptor, it can enter the cell through two main mechanisms. Endocytosis is a process where the host cell membrane engulfs the virus, forming a vesicle that brings the virus into the interior of the cell. Alternatively, some viruses can directly fuse their viral membrane with the host cell membrane, allowing their genetic material to enter the cell cytoplasm.

These strategies are fundamental to the viral life cycle, as successful entry into the host cell is the first step toward replication and propagation of the virus. The other suggested strategies, such as creating pores in membranes or producing toxins, do not accurately reflect the primary mechanisms viruses typically use to gain entry into host cells.