Members of which group are primarily characterized by their peptidoglycan cell wall structure?

Bacteria are primarily characterized by their peptidoglycan cell wall structure, which is a critical component of their physical integrity and protection. Peptidoglycan is a polymer consisting of sugars and amino acids, forming a mesh-like structure that surrounds the bacterial cell membrane. This characteristic is fundamental for distinguishing bacteria from other groups of organisms, as it plays a vital role in maintaining the shape of the bacteria and withstanding osmotic pressure.

In contrast, other groups, such as Archaea, have cell walls that do not contain peptidoglycan; instead, they may consist of different materials such as pseudopeptidoglycan or proteinaceous layers. Similarly, Rhizarians and Excavata do not have peptidoglycan in their cell walls; some may have other protective structures but lack this specific component that defines bacterial cell walls. Therefore, the unique presence of peptidoglycan makes bacteria distinct within the tree of life.