Which domain is described as unicellular prokaryotes whose cell walls contain peptidoglycan?

• A. Eubacteria
• B. Archaea
• C. Eukaryota
• D. Protists

Answer: (A)

The trait being tested is how to identify the domain of organisms based on cellular organization and cell-wall chemistry. Peptidoglycan in the cell wall is a hallmark of true bacteria, meaning these organisms are unicellular and prokaryotic, with walls built from this peptidoglycan network that provides rigidity. Archaea, while also prokaryotic, have cell walls that typically lack peptidoglycan (they may use pseudopeptidoglycan or other polymers). Eukaryota includes cells with a nucleus and organelles, not prokaryotic, and protists are a diverse group of mostly unicellular eukaryotes without peptidoglycan in their walls. Therefore, the description points to the domain Eubacteria.