Across the three domains of life, which two domains have the most chemically similar membrane lipids?

Introduction / Context:
Membrane lipid chemistry is a classic comparative feature distinguishing Archaea from Bacteria and Eukarya. The linkage type, backbone stereochemistry, and hydrocarbon chains differ markedly across domains.

Given Data / Assumptions:

• Bacteria and Eukarya: ester-linked fatty acids on glycerol-3-phosphate backbones.
• Archaea: ether-linked isoprenoid chains on glycerol-1-phosphate backbones; can form monolayers.
• We compare overall chemical similarity.

Concept / Approach:
Eukaryotes inherited membrane lipid biochemistry more closely resembling bacteria than archaea. Archaea are distinct in both linkage (ether vs ester) and backbone stereochemistry (G1P vs G3P), reflecting deep evolutionary divergence.

Step-by-Step Solution:

Verification / Alternative check:
Biochemistry references consistently group eukaryotic membranes with bacterial-type lipids; archaeal membranes remain unique.

Why Other Options Are Wrong:
A/C: Both pairings include Archaea, which are most distinct. D: Incorrect; the domains are not chemically identical.

Common Pitfalls:
Assuming eukaryotes are intermediate; in lipid chemistry, they align closely with bacteria.

Final Answer:
Bacteria and Eukarya