Are plasma membranes the outer boundaries of all cells? - Cuntorio

No, in many cells the plasma membrane is encased within an extraneous coat of nonliving material that usually confers some rigidity on the cell it surrounds. Although not affecting permeability, this rigid coat affords considerable protection to the underlying cell, especially in dilute solutions in which the cell might take in water and tend to swell. The coat is known as a cell wall in plant