Which of the following best describes the composition of bacterial cell walls?

Bacterial cell walls are primarily composed of peptidoglycan, which is a unique polymer made up of sugars and amino acids. This structure provides rigidity and strength to the cell wall, allowing bacteria to maintain their shape and protect against osmotic pressure. The peptidoglycan layer consists of long chains of glycan, specifically N-acetylglucosamine and N-acetylmuramic acid, cross-linked by peptide bridges, which is a distinguishing feature of bacterial cells.

This composition is crucial for the classification of bacteria into Gram-positive and Gram-negative categories, based on the thickness of the peptidoglycan layer. Gram-positive bacteria have a thick peptidoglycan layer, while Gram-negative bacteria have a thinner layer located between their inner cytoplasmic membrane and an outer membrane.

The other options do not accurately describe the composition of bacterial cell walls. For instance, cellulose is a polysaccharide found in plant cell walls, phospholipids are essential components of all cell membranes rather than cell walls, and while proteins can be part of the bacterial cell envelope, they are not the primary structural component of the cell wall itself.