Final answer:
Gram-positive bacteria lack an outer membrane and have a thick layer of peptidoglycan in their cell wall, while Gram-negative bacteria have a thin layer of peptidoglycan surrounded by an outer envelope containing lipopolysaccharides (LPS) and lipoproteins.
Step-by-step explanation:
Gram-positive and Gram-negative bacteria differ in their cell wall structure. Gram-positive bacteria lack an outer membrane and have a thick layer of peptidoglycan in their cell wall, which makes up 90% of the cell wall composition. They also have teichoic acids that anchor the cell wall to the cell membrane. On the other hand, Gram-negative bacteria have a thin layer of peptidoglycan surrounded by an outer envelope containing lipopolysaccharides (LPS) and lipoproteins. This outer envelope is chemically different from the lipid bilayer of the cell membrane.