Which domain uses a lipid bilayer in its cell membrane?

• A. Archaea
• B. Eubacteria
• C. Eukarya
• D. Viruses

Answer: (B)

Cell membranes are lipid bilayers that form the boundary and gatekeeper of a cell. In bacteria, the cell membrane is a classic phospholipid bilayer built from ester-linked fatty acids on glycerol, creating the selective barrier that controls what enters and leaves and hosting many transport proteins. Archaea also have membranes, but their lipids are chemically distinct—ether bonds and often isoprenoid chains—and some extreme species even employ a monolayer form, showing a different membrane chemistry from bacteria. Eukaryotes share the bilayer design with similar phospholipids and additional components like sterols that stabilize the membrane. Viruses, on the other hand, do not have their own cellular membrane; enveloped viruses carry a membrane from a host cell, but that is not a cellular membrane of a domain. Because the question points to the domain with the typical lipid bilayer membrane, bacteria is the best fit.