The cell wall is a rigid and protective structure that surrounds the cell membrane of plants, algae, and some bacteria. It provides support and protection for the cell, helping it to maintain its shape and integrity. The cell wall is composed of various materials, including cellulose, hemicellulose, and pectin in plants, and peptidoglycan in bacteria. It acts as a barrier, regulating the movement of substances in and out of the cell and protecting it from mechanical damage and environmental stresses.