Yes, these molecules must enter the cell if the cell is to actually survive for a long period of time. So such molecules can be assisted by integral proteins known also as transfer proteins or carrier proteins. And such a mode of transport is known as facilitated diffusion. Basically, diffusion means we still have a movement down the electrochemical gradient but now we actually need a protein to move that molecule across. So basically, in this case, as in this case, we have the movement of our molecule down the electrochemical gradient. In this case, we don't use any type of protein and we don't use any energy.