 Welcome to passive transport osmosis. In this learning module, you'll explore what passive transport osmosis is and how it moves water through a semi-permeable membrane. Passive transport is the movement of molecules across cell membranes without using any energy. In all cells, osmosis is the movement of water through a semi-permeable membrane. In this process, water moves from a solution of high water potential to one with low water potential. Cells with the lower potential draw water in through the semi-permeable membrane. Cells with the high potential release water through the same membrane. Osmotic pressure generates enough force to move the volume of water on both sides of the membrane. Osmosis forces both sides to find a balance. Water molecules continue to move until both sides reach an equilibrium. Let's examine what this looks like in a lab setup using sides A and B in this beaker. Side A has a lot of large protein molecules and a few water molecules. Side B has fewer protein molecules and more water molecules. The semi-permeable membrane that separates the two sides has small openings that prevent the protein molecules from passing through. In this setup, osmosis allows both sides to reach an equilibrium by only moving the water molecules to the semi-permeable membrane. The water moves from B to A because B has a higher concentration of water molecules than A. This is osmosis in action. Once equilibrium is reached, side A still has more protein molecules, so its volume actually goes up. Osmotic pressure moves the water molecules from side to side regardless of other solutes in the liquid. The final diffusion of water through the membrane from side B to side A is called net osmosis. This process replays itself every day in plant and animal cells. Osmosis moves water in and out of cells without requiring any energy from the plant or animal. Today we've reviewed passive transport osmosis. You've learned that osmosis allows water to move through a semi-permeable membrane to reach equilibrium. You've also explored how passive transport works without using any energy. Congratulations! You have completed passive transport osmosis.