Final answer:
Viruses inject their genetic material into host cells to reproduce and hijack the cell's machinery. They can only enter cells with specific surface receptors. Some viruses enter cells by fusing their envelope with the cell membrane.
Step-by-step explanation:
A virus injects its genetic material into a host cell in order to reproduce. Once inside the host cell, the virus hijacks the cell's machinery to replicate and synthesize proteins. The virus can only enter cells that have specific surface receptors that match the virus's glycoproteins. Some viruses enter cells by fusing their envelope with the cell membrane, while others enter through endocytosis.