Osmosis is the flow of water between two solutions through a semi-permeable membrane and is usually encountered during the study of cells in biology. Osmosis is an often misunderstood topic, and nothing can solidify a student's understanding of a difficult subject better than doing a project on it. Here you will find the basic outlines of three science projects that show osmosis in action.
Osmosis in De-Shelled Eggs
Soaking raw eggs overnight in vinegar will dissolve their shells, leaving a thin membrane in their place. These de-shelled eggs are a great model for an animal cell because water can freely osmose through the membranes. Put one de-shelled egg in a beaker containing pure water, one in a beaker containing some of the vinegar that dissolved the shells, and one in a beaker containing corn syrup. The pure water will be hypotonic to the egg, so water will flow into the egg and it will expand. The vinegar will be isotonic to the egg, so the net flow of water between the egg and the vinegar will be zero and the egg will remain the same size. The corn syrup will be hypertonic to the egg, so water will flow out of the egg and it will shrivel.
Plasmolysis in Onion Skin Cells
Observe the cells in onion skin by placing one layer of the skin on a microscope slide, adding a couple drops of iodine, and looking at it through a light microscope. You should see well defined plant cells with clear nuclei. Add a few drops of saltwater to the slide as you look through the microscope and you will see the cell membranes shrink away from the cell walls. This occurs because the saltwater is hypertonic to the plant cells, causing water to flow out of the cells. Now add a few drops of pure water and you should see the cells expand back to normal size because of the hypotonic water.
Dialysis Tubing in Beakers with Different Sucrose Concentrations
Obtain 6 beakers and fill each one with a different selection from the following solutions: pure water, 0.2 molar sucrose, 0.4 molar sucrose, 0.6 molar sucrose, 0.8 molar sucrose and 1.0 molar sucrose. Obtain 6 pieces of dialysis tubing, each about 6 inches long. Tie off one end of each piece, put 10 ml of 1 molar sucrose solution into each tube, then tie off the other end while making sure that no air gets trapped in the tubing. Each piece of tubing should now look like a small, half-filled bag of water. Measure the mass of each bag. Place each bag into one of the 6 beakers with the different sucrose solutions in them. Let the bags sit for a day and remove them from the solutions. Measure the mass of bags. You should find that mass of the bag that sat in pure water overnight will have increased the most, and the mass of the bag sitting in the 1.0 molar sucrose overnight should not have changed at all. The increase in mass will have diminished among the other bags as the sucrose concentration of the soaking solutions increased.
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