One key similarity is that both serve as protective barriers for the cell, protecting it from external stresses such as pathogens. Both serve as the primary pathways for molecules to enter and exit the cell. They also contribute to the structure and stability of cells. They do this by providing rigidity to the cell. A fourth similarity is that both form the outermost protective layer of a cell, acting as the first line of defense against external stresses and separating the cell from the environment.