Questions: Saved A layer of lipids, proteins and glycoproteins that covers the outer surface of some viruses is the Multiple Choice casing. membrane. envelope. viroid. capsid.

The answer is the third one: envelope.

Explanation for each option:

• Casing: This term is not typically used in virology to describe any part of a virus structure. It is incorrect in this context.

• Membrane: While some viruses do have a lipid bilayer similar to a cell membrane, the specific term used for this structure in viruses is "envelope." Therefore, "membrane" is not the correct term in this context.

• Envelope: This is the correct answer. The envelope is a lipid layer that surrounds the capsid in some viruses, derived from portions of the host cell membranes (phospholipids and proteins), and may include viral glycoproteins.

• Viroid: Viroids are infectious agents composed solely of a short strand of circular, single-stranded RNA without a protein coat. They do not have a lipid layer or any of the structures mentioned in the question.

• Capsid: The capsid is the protein shell that encases the viral genome. It is not the lipid layer described in the question.

In summary, the correct term for the lipid, protein, and glycoprotein layer covering the outer surface of some viruses is the "envelope."