The most accurate statement comparing cell membranes and cell walls is:
"Cell membranes function mostly as selectively permeable gatekeepers while cell walls function mainly as support systems."
This statement correctly reflects the roles of both structures. The cell membrane regulates the movement of substances in and out of the cell, allowing for selective permeability, while the cell wall provides structural support and protection to the cell, particularly in plant cells. The other statements provided are either incorrect or misleading.