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What Do I Need to Make an Osmosis Model?

Osmosis is the process by which some molecules pass through a membrane while others are blocked. In nature, water molecules will naturally move from an area of high concentration to one of lower concentration; your finished model will demonstrate this tendency. The membrane is semi-permeable, so it allows water molecules to pass while it blocks larger molecules. An effective osmosis model does not need to accurately depict the appearance of molecules or the membrane. It only needs to illustrate the mechanism by which osmosis occurs.

Container
- Build your model in a container larger enough to hold all the necessary components. A box about 12 inches long by 6 inches to 8 inches wide provides ample room, but you may make your container a little larger or smaller, depending on available materials. A shoe box, walled plastic tray or similarly shaped box makes a good container. If none of these are available, construct your own out of wood, cardboard, plastic or tag board. Once you have your container, imagine an invisible line through its center that divides it into two equal sections. One section represents the inside cell and the other represents the outside cell.
Membrane
- Place a barrier along the imaginary line between your inside cell and your outside cell. Construct your barrier from any material hard enough to withstand the coming impacts, yet thin or malleable enough that you can easily cut openings into it. Create a series of openings along the barrier's bottom edge. These openings should be flush with the container's floor once the barrier is in place. Make the openings large enough to allow only your small molecules through. The barrier should still block the larger ones. Cut several of these openings, make them a uniform size and space them as evenly and as frequently as you can.
Small Molecules
- Use small, smooth spheres to represent water molecules. Ball bearings or small marbles are good for this purpose, although any suitably smooth and small spheres will work. These spheres are small enough to pass through the openings in your barrier and will do so when you shake the container. Place all, or most, of your small molecules in the inside cell area before you begin. When you begin shaking the container, these molecules will pass back and forth through the membrane until both sections begin to exhibit a roughly equal number of small molecules.
Larger Molecules
- Use shooter marbles, large ball bearings or rubber balls for your large molecules. Their only requirement is that their diameter exceeds the size of the openings in your membrane. As you shake the container, these molecules will bounce against all four walls of the inside cell. Unlike the small molecules, they will not pass through the membrane.

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