The cell wall is a rigid outer layer that surrounds the cell membrane in plant cells, fungi, and some bacteria. It provides structural support, protection, and helps maintain the shape of the cell. Composed mainly of cellulose in plants, the cell wall plays a crucial role in regulating the movement of substances in and out of the cell. In addition to providing support, the cell wall also helps protect against mechanical stress and pathogens. It is involved in processes such as growth and development, allowing cells to expand while maintaining their integrity. The composition and structure of cell walls can vary significantly among different organisms, reflecting their diverse functions.