Final answer:
A virus gets its envelope during the maturation phase of its life cycle, specifically during the assembly and release phases when new viral particles exit the host cell by budding. The envelope is derived from the host's membrane structures. This process is vital for the completion of viral particle structure and necessary for the virus's ability to infect other cells.
Step-by-step explanation:
A virus obtains its envelope during the maturation phase of its replication cycle. Specifically, the envelope is acquired when the virus particles are assembled inside the host cell and exit the cell by the process known as budding. During this process, the virus snatches a portion of the host cell's plasma membrane to form the envelope around the capsid.
The envelope of a virus comes from the host's membrane structures, which indicates that the correct answer to the reference question is 'B. membrane structures'. The replication cycle of a virus typically follows several steps: attachment, penetration, uncoating, replication, assembly, and release. The critical step of attachment cannot commence without the virus's initial adherence to the host cell's surface receptors. Following attachment, the virus penetrates the host cell membrane, either through endocytosis or membrane fusion, then uncast its genetic material, which later gets replicated and used in the assembly of new viral particles.
Once assembled, new viral particles exit the host cell by budding, which is part of the release phase but can also be considered as part of the assembly and maturation phases since the virus acquires its envelope at this time which completes its structure.