A wall is a tough protective boundary around a structure but it can have some door like opening to pass through. As wall is around a cell that's why it is called cell wall. In this way a tough...
The Cell Wall would be the wall surrounding the city (no equivalent in modern cities). In comparison, the membrane would be the city border patrol. Nobody is going to get past the cell wall, but once...
The Cell Wall basically compares to a very strong board of wood. Because the cell wall's job is to provide structural support. A board of wood can to. (if its strong enough)