What are some real life examples of a cell membrane?

Cell membrane of a cell is responsible for the substances that goes in and out of the cell’s cytoplasm and organelles. It is transports different materials externally to internally and vice-verse. Hence the cell membrane is like 1.   The wall, window and door of a house. 2.   The security guard of a certain bank 3.   Or the military sector of a country. Like these three real-life examples, they regulate and control the flow of certain entities from outside to inside and vice-versa.