Final answer:
Gram-negative bacteria have external structures that include a periplasmic space, which is absent in Gram-positive bacteria, Archaea, and Eukaryotic cells.
Step-by-step explanation:
These bacteria are characterized by a cell wall that is structurally more complex and is composed of three layers: the inner membrane, a thin layer of peptidoglycan, and an outer membrane that includes lipopolysaccharides. This configuration creates a periplasmic space between the inner membrane and the outer membrane. In contrast, Gram-positive bacteria have a thicker peptidoglycan cell wall without an outer membrane, and Archaea have cell walls that do not contain peptidoglycan and thus differ significantly from both types of bacterial cell walls. Eukaryotic cells typically do not have a periplasmic space as part of their cell structure.