osmosis is the net movement of a solvent, usually water across a semi permeable membrane. Now this semi permeable membrane is just a material that's allowing solvents and other small molecules to pass across. And we're going to say that these cell membranes are around living that are around living cells are in fact semi criminal themselves. Now these cell membranes, they prevent salutes from passing through and these salutes can be ions or large molecules. Now, if we take a look here at this illustration of a semi permeable membrane here, the membrane is asking if you have an appointment. This larger molecule in red is trying to get through and they can't get past the barrier. But the smaller ones down here do have an appointment are allowed to pass through because they are the right size and they can pass through the semi permeable membrane to the other side. And this is the way that semi permeable membranes work. Osmosis is the movement of water net movement of water. But semi permeable membranes can halt and stop certain molecules from traversing from one side to the other side of a living cell.