The document discusses the differences between gram positive and gram negative bacterial cell walls. Gram positive bacteria have a thick peptidoglycan layer (20-80 nm) in their cell walls that contains teichoic acids, while gram negative bacteria have a thinner peptidoglycan layer (10 nm) and an outer membrane containing lipopolysaccharides. Gram staining is used to differentiate the two types based on their ability to retain crystal violet dye - gram positive bacteria retain the dye due to their thick peptidoglycan layer and appear violet, while gram negative bacteria's thinner peptidoglycan layer is unable to retain the dye and they appear red after counterstaining.