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Monday, October 3, 2011

Using Potatoes for Osmosis and Diffusion Labs




This lab has two different activities.  In Part A of this lab, the observation of plasmolysis in a living cell is a qualitative measurement.  Students will observe cells under the microscope as plasmolysis takes place.  Cells from an onion or an Elodea leave are subjected to a few drops of salt water and students can instantly view plasmolysis occurring in these cells.

In Part B, the student  will quantitatively measure plasmolysis by measuring the amount of water lost in grams from potato slices.  Students will draw pictures and describe what they see in Part A.  Students will measure and graph their results in Part B.

Purpose:
1. To observe the process of plasmolysis inside living cells.
2. To observe the effect of different types of solutions on living cells.
3. To quantitatively measure the rate of plasmolysis in potato slices.

Materials:  Microscopes, Microscope slides, Cover slips, 5% sodium chloride solution, Medicine droppers, Elodea plant, 10% sodium chloride solution, Distilled water, Potatoes, various sugar solutions, 100 mL beakers, Balances.

In this part of the lab, the student uses a cork borer to make 20 small cores of potato.

The potato cores are massed 4 at a time to determine their initial mass.

The 4 cores of potato are placed in solutions of different sucrose molarities.  The first beaker contains distilled water, the second contains a .2M sucrose solution, the third contains a .4M sucrose solution, the fourth contains a .6M sucrose solution and the last contains a .8M sucrose solution.


The potatoes are allowed to sit in their various solutions overnight.  After 24 hours they are weighed to determine their final mass.  The student will calculate a percent change in mass and place this data on a graph.  From the graph, the student will determine the solute concentration of the potato.  The student will decide if the potato was hypotonic or hypertonic to the solution in which it was placed.



Lab:  Qualitative and Quantitative Plasmolysis

Transport Across the Cell Membrane Worksheet

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