Source of the viral envelope: The membrane envelope present on many animal viruses is typically derived from which host-cell structure during budding?

Introduction / Context:
Enveloped viruses acquire a lipid bilayer as they exit host cells. Identifying the typical origin of this membrane helps explain viral stability, entry pathways, and the composition of viral surface proteins targeted by immunity.

Given Data / Assumptions:

• Many animal viruses bud through a host membrane to acquire their envelope.
• Viral glycoproteins are inserted into the donor membrane before budding.
• The exam-style question asks for the most common, canonical source.

Concept / Approach:
Most classic examples (e.g., orthomyxoviruses, paramyxoviruses, coronaviruses at the plasma membrane or other secretory membranes) obtain their envelope by budding through the host cell (plasma) membrane, incorporating host lipids and viral proteins. While some viruses bud into intracellular membranes (ER/Golgi) and are exocytosed, the standard teaching answer when options are limited is the cell (plasma) membrane.

Step-by-Step Solution:
Identify budding as the mechanism for envelope acquisition.Recall that the plasma membrane is the prototypical donor membrane.Select “the cell membrane” as the best single answer from the provided choices.

Verification / Alternative check:
Examine EM images showing virions budding from the cell surface with continuity of membranes.

Why Other Options Are Wrong:
Mitochondrial membranes are not used for viral envelopes. ER can be used by certain viruses, but the question singles out the typical case; “none of these” is therefore incorrect.

Common Pitfalls:
Overgeneralizing special cases (ER/Golgi budding) as the common rule when a single best answer is expected.

Final Answer:
the cell membrane