And because they don't use any energy molecules, for instance, ATP molecules, to carry out the process, this type of transport is known as passive transport. So it doesn't use any ATP. So let's summarize our results. So we have certain ions which contain full, positive or negative charges and molecules which are very polar or large. These cannot move across the cell membrane because they cannot dissolve inside the hydrophobic nonpolar region of that membrane. Now, channels are essentially these pathogeways that allow these ions or molecules to move and bypass the non polar core of that membrane, so they can cross that cell membrane without ever interacting with that hydrophobic core of the membrane.