Question

We know that cell membrane allows only selectively molecules but which type of molecules and enter and exit and how the cell membrane know which molecule is to be entered and exit ??

Answer 1

The plasma membranes has specialized proteins called receptors that sense each and every molecule. The large molecules bind to these proteins and are transported across the membrane. So the molecule must have affinity with the transport and receptor proteins. Very small molecules can pas across the membrane by osmosis or diffusion by pressure or solute gradient.