Step-by-step explanation:
The cell membrane, also known as the plasma membrane, is a double layer of lipids and proteins that surrounds a cell and separates the cytoplasm (the contents of the cell) from its surrounding environment. It is selectively permeable, which means that it only lets certain molecules enter and exit
The primary function of the plasma membrane is to protect the cell from its surroundings. Composed of a phospholipid bilayer with embedded proteins, the plasma membrane is selectively permeable to ions and organic molecules and regulates the movement of substances in and out of cells.
the cell membrane regulates the flow of any material in or out of the cell. and the substance has to pass through the cell membrane.
it's like a bag containing objects, except that these are much much smaller, and lighter!