Final answer:
Viruses construct their viral envelope using the endoplasmic reticulum of the host cell, which provides the lipid bilayer necessary for the protective envelope. This envelope includes glycoproteins that facilitate attachment to new host cells.
Step-by-step explanation:
The cellular location that viruses use to construct a viral envelope is the endoplasmic reticulum (ER). When enveloped viruses infect a host cell, they often utilize the host's own cellular machinery to assemble and escape. The viral envelope is derived from portions of the host's membranes, particularly the plasma membrane, nuclear membrane, or internal membranes like the ER. This envelope is embedded with glycoproteins and other viral proteins that play crucial roles in the virus's life cycle, including attachment and entry into host cells. Hence, the correct answer to the question is (A) Endoplasmic reticulum.
Furthermore, this envelope is created when the virus buds through the membrane, trapping a piece of it and using it as a protective layer. The lipid membrane and any carbohydrates present in the viral envelope come entirely from the host cell. While glycoproteins are coded by the viral genome, the lipid bilayer is entirely of cellular origin. Proteins embedded in the viral envelope facilitate the virus's attachment to new host cells, which is essential for the viral infection process to continue.