Which group has a lipid monolayer as their cell membrane?

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

Answer: (C)

Archaea can have a lipid monolayer because their membranes can be built from ether-linked, isoprenoid lipids that form tetraether lipids spanning the membrane. When these tetraether lipids connect across the entire membrane, they create a single continuous layer rather than two separate leaflets, giving a monolayer. This design adds rigidity and stability, which is advantageous in extreme conditions like high temperature or acidic environments where many archaea live. Bacteria and Eukarya typically have lipid bilayers with ester linkages, while viruses may have envelopes that are lipid bilayers derived from host membranes, not a true archaeal cell membrane. Hence, the group known for having a lipid monolayer is Archaea.