Final answer:
In stage 1 of viral replication, the virus attaches to the host cell membrane by binding to specific receptors, which is crucial for initiating the viral infection process.
Step-by-step explanation:
In stage 1 of viral replication, the virus is attaching to the host cell membrane. This initial step is crucial as it involves the virus attaching to specific receptor sites on the membrane of the host cell. This process is governed by the affinity between viral proteins and host cell receptors, which is highly specific. Following a successful attachment, the virus can proceed to the subsequent stages of viral replication, including penetration, where it injects its genetic material into the host cell.