Final answer:
The difference in staining between Gram-positive and Gram-negative bacteria is due to their cell wall composition.
Step-by-step explanation:
Prokaryotes stain as Gram-positive or Gram-negative because of differences in the cell wall composition. Gram-positive bacteria have a thick cell wall predominantly made of peptidoglycan and substances called teichoic acids, including lipoteichoic acids that anchor the cell wall to the cell membrane. Conversely, the cell wall of Gram-negative bacteria is thinner, consisting of a few layers of peptidoglycan and is covered by an outer membrane containing lipopolysaccharides (LPS) and lipoproteins, which is distinct from the typical plasma membrane lipid bilayer.