Saturday, September 22, 2012
Very Simple Diffusion and Osmosis Experiment
The concept of cellular transport (diffusion, osmosis, hypotonic, hypertonic, active transport, passive transport) is fundamental to a biology class. There are so many great ideas for labs that teach and explore these concepts. Just this week, our biology students completed an activity that is so very simple, but it really illustrates the concept of semipermeable membranes.
Students are given 2 pieces of dialysis tubing. One is filled with a starch solution and the other is filled with a glucose solution. Each is placed into a cup containing tap water. The cup that contains the starch tube also has iodine added to the water in the cup.
Students allow their experiment to sit overnight. Observations are made and results are recorded again after 24 hours. All students quickly determine that: (1) Starch did not leave the bag. (2) Iodine moved into the bag. (3) Glucose moves out of the bag slowly. (This is evidenced by the fact that the initial test for glucose after 20 minutes is negative, but the test is positive after 24 hours.) (4) Much water moves into the bag.
The lab that I use with my students can be found here: Diffusion Through a Non-Living Membrane.
FREEBIE: You might also want to try this lab: The Effect of Concentration on the Rate of Diffusion. This is a free download....Enjoy!