Introduction to Cell & Molecular Biology (BIOL121) - Dr. S.G. Saupe (ssaupe@csbsju.edu); Biology Department, College of St. Benedict/St. John's University, Collegeville, MN 56321

"Spuds" McSaupe Studies Membranes

Setting:  The famous scientist, Spuds McSaupe, Ph.D., will visit our class today to discuss osmosis, diffusion and cell membranes. He will show us an experiment involving potato tubers. Spuds will obtain beakers containing water and a beaker of concentrated salt solution. He will cut cores from a potato, measure the length of each, and then incubate them in either water or a salt solution, respectively.  This "experiment" is diagrammed as follows:

Make some predictions:

1. The length of the core in water will:
a. increase; b. decrease; c. not change
2. The water pressure in the cells of the core incubated in water will:
a. increase; b. decrease; c. not change
3. The turgidity of the core in salt will:
a. increase; b. decrease; c. not change
4. The concentration of water in the cells of the potato core incubated in the salt solution will:
a. increase; b. decrease; c. not change
5. The concentration of salt in the beaker will:
a. increase; b. decrease; c. not change
6. In which core will the cells of the potato be most likely to plasmolyze?
a.  water; b. salt

Results:

 Water Salt Core Length (mm) Initial (mm) Final (mm) Change (mm) % Change ((F - I)/I *100) Turdigity (-, +, ++) Initial Final
• How accurate were your predictions?
• What would the results have been if Spuds had also measured the diameter of the cores?
• Describe the experiment using the following terms: hypertonic, isotonic, hypotonic, water potential, osmotic pressure, osmosis, turdigity, plasmolysis, and  osmotic concentration.  Can you make a concept map for these terms?
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Last updated: July 14, 2009     � Copyright by SG Saupe