Final answer:
The lipopolysaccharide (LPS) layer is found only in the cell walls of Gram-negative bacteria, contributing to protection, immune response, and antibiotic resistance.
Step-by-step explanation:
The lipopolysaccharide (LPS) layer is found only in the cell walls of bacteria. Specifically, LPS is a characteristic component of the outer membrane of Gram-negative bacteria. The LPS layer contributes to the structure and function of the bacterial cell wall, which is composed of peptidoglycan, by providing an extra layer of protection, participating in the immune response during infections, and helping the cell resist antibiotics. It is worth noting that not all bacteria have the LPS layer; it is absent in Gram-positive bacteria, which instead have a thick peptidoglycan layer and teichoic acids. Unlike bacterial cell walls, other types of cells such as fungi, plants, and animals have different compositions for their cell walls or do not have cell walls at all.