Identify the primary methods that a virus can use to gain entry into an animal cell.

Direct Penetration: The virus attaches itself to the host cell and injects its genetic material into it. This method does not involve the fusion of the cellular and viral membranes.

Membrane Fusion: This method is used by enveloped viruses. The viral envelope fuses with the host cell membrane, allowing the capsid and viral genome to enter the host cell.

Endocytosis: In this method, the virus is engulfed by the host cell into a vesicle. Once inside, the virus breaks out of the vesicle and releases its genetic material into the host cell.

Translocation: Some viruses can directly pass through the cell membrane of the host cell. This is less common and is not fully understood.

Use of a Receptor: Some viruses use specific receptors on the host cell to gain entry. The virus binds to the receptor, triggering changes in the cell membrane that allow the virus to enter.