Wednesday, May 26, 2010
A classic demonstration of osmosis using a large cell: an egg.
Place an egg in a beaker filled with vinegar for a day or two (over a weekend works well). The vinegar will remove the shell of the egg, leaving the cell membrane. Additionally the process of osmosis will begin with the water found in the vinegar.
Place the egg in a variety of other substances, for one night each.
Vinegar – water flows into the egg, increasing its size.
Water – water flows into the egg, increasing its size (but not as dramatic after a day in the vinegar)
Colored Water – water and dye particles flow into the egg, increasing its size and changing its color
Corn syrup – water flows out of the egg, decreasing its size
You can make the experiment as complex or simple as you wish. You can present this activity as a demonstration, or have students complete it as a lab experiment. Have students measure and record the egg’s dimensions by wrapping a string around the egg’s circumference. Students could also keep track of the volume of liquid that is placed in the beaker and how much remains the following day. After students have recorded data, they can graph it.
Make sure you have antibacterial cleaning supplies ready and available if you take on this lab, especially if you have students working with the eggs – some will break!