<Table> <Tr> <Td> </Td> <Td> This scientific article needs additional citations to secondary or tertiary sources such as review articles, monographs, or textbooks . Please add such references to provide context and establish the relevance of any primary research articles cited . Unsourced material may be challenged and removed . (January 2016) </Td> </Tr> </Table> <Tr> <Td> </Td> <Td> This scientific article needs additional citations to secondary or tertiary sources such as review articles, monographs, or textbooks . Please add such references to provide context and establish the relevance of any primary research articles cited . Unsourced material may be challenged and removed . (January 2016) </Td> </Tr> <P> A semipermeable membrane is a type of biological or synthetic, polymeric membrane that will allow certain molecules or ions to pass through it by diffusion--or occasionally by more specialized processes of facilitated diffusion, passive transport or active transport . The rate of passage depends on the pressure, concentration, and temperature of the molecules or solutes on either side, as well as the permeability of the membrane to each solute . Depending on the membrane and the solute, permeability may depend on solute size, solubility, properties, or chemistry . How the membrane is constructed to be selective in its permeability will determine the rate and the permeability . Many natural and synthetic materials thicker than a membrane are also semipermeable . One example of this is the thin film on the inside of the egg . </P> <P> Note that a semipermeable membrane is not the same as a selectively permeable membrane . Semipermeable membrane describes a membrane that allows some particles to pass through (by size), whereas the selectively permeable membrane "chooses" what passes through (size is not a factor). </P>

The selective permeability of a cell membrane to different substances depends on