Which group has a lipid bilayer as their cell membrane?

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

Answer: (B)

Membranes in cellular life are built from phospholipids that arrange into a lipid bilayer. The typical bacterial cell membrane uses ester-linked phospholipids formed from glycerol with fatty acid tails, creating that familiar two-layer sheet that encloses the cell.

Archaea also have membranes, but their lipids are different: they use ether bonds and often contain isoprenoid chains, and many archaeal membranes form monolayers rather than bilayers in some extreme environments. This chemical difference means their membrane structure isn’t the standard bilayer described in many introductory biology contexts. Eukarya indeed have lipid bilayers as well, so they share the bilayer feature, but the question is asking about the classic, textbook membrane chemistry that distinguishes the bacterial group. Viruses don’t have a true cell membrane; enveloped viruses acquire a lipid envelope from a host, which is not a cellular membrane.

Thus, the group whose cell membrane is classically described as a lipid bilayer with ester-linked phospholipids is the bacteria group.