6) What's the difference between the cell wall of bacteria, archaea, plants and fungi?
Bacteria: contain peptidoglycan, a network of sugar polymers cross-linked by polypeptides
Archaea: the wall is assembled from surface-layer proteins, which form an S-layer. An S-layer is a rigid array of protein molecules that cover the outside of the cell (like chain mail.) This layer provides both chemical and physical protection, and can prevent macromolecules from contacting the cell membrane. Unlike bacteria, most archaea lack peptidoglycan in their cell walls.
Plants: composed of cellulose and hemicellulose, pectin and in many cases lignin, and secreted by the protoplast on the outside of the cell membrane. This contrasts with the cell walls of fungi (which are made of chitin), and of bacteria, which are made of peptidoglycan.
Fungi: contain chitin, unlike the cell walls of plants, which contain cellulose.