Question

what is a differnce between semi permeable and selectively permable membrane

Answer 1

only some specific substances can enter selectively permable membrane
bt if the substances are small enough, they all can enter the semi permeable

Answer 2

a semi permeable membrane allows the transport of nonpolar (uncharged) molecules for eg gases like oxygen , nitrogen ,carbon dioxide etc and small hydrophobic / non polar molecules but not polar (charged) molecules like proteins and ions. For these polar molecules to be transported , the plasma membrane should have specific receptors / ion channels which selectively transport them across it and into the cytoplasm. The plasma membrane of a cell is thus both semi permeable and selectively permeable.