The cell membrane acts as a semipermeable membrane because it allows some substances, but not others, to pass through its structure.
An example is water and urea, which can pass through the cell membrane. Sodium ions and glucose cannot.
The cell membrane is a lipoprotein structure (which is formed of fat and protein), with a bimolecular layer of lipids (fats), where many protein molecules such as glycoproteins, simple proteins and some enzymes are dispersed.
Performs selective permeability as it controls the entry and exit of molecules and ions.