As the students learn the unifying concepts of diffusion and osmosis, they are ready to see the connection to the exchange of nutrients and wastes into and out of a cell. This activity could be used in this unit or used as a transition to a unit on mitosis.

Most cell functions involve chemical reactions. Food molecules taken into cells react to provide the chemical constituents needed to synthesize other molecules. Both breakdown and synthesis are made possible by a large set of protein catalysts, called enzymes. The breakdown of some of the food molecules enables the cell to store energy in specific chemicals that are used to carry out the many functions of the cell.

Potassium permanganate is not recommended for classroom use. I have used methylene blue with success. When the students cut their potatoes in half after removal from the dye, they should see that all potatoes have about the same amount of dye.

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BIOLOGY LAB SURFACE AREA AND CELL DIVISION PURPOSE: To determine how surface area to volume ratios initiate cell division. HYPOTHESIS: Prediction: What will happen when a dye is introduced into cubes of potatoes that vary in size? Will the dye enter the potato cube differently? ALL STUDENTS WHO ARE IN CHARGE OF THE POTASSIUM PERMANGANATE MUST WEAR AN APRON WHILE HANDLING THE POTATOES PROCEDURES: 1. Cut 3 cubes from a potato; one should be each of the following sizes: 0.5 cm on each side 1.5 cm on each side 2.5 cm on each side 2. Put all 3 cubes in a 5% potassium permanganate solution. Leave for 20 - 25 minutes. 3. While you are waiting, prepare a data table. Have a column each for cube size, surface area (sa), volume (v), distance of diffusion, and sa/v ratio. 4. Calculate the surface area, volume, and sa/v ratio for each cube and record on your table. We will do this step together. A = lw (length x width) (area of one side) SA = 6A (a cube has six sides) (total surface area) V = lwh (length x width x height) (volume) SA/V = SA divided by V 5. After the incubation (20 - 25 minutes) carefully remove the cubes with forceps. REMEMBER: THE PERMANGANATE WILL STAIN YOUR HANDS AND CLOTHING! 6. Slice each cube with a razor blade (CAREFUL) down the middle. Dry the razor blade before cutting each cube. 7. Measure the distance in millimeters that the solution diffused into each cube. Record the distance in your table. We will stop here for today and will finish the calculation tomorrow. 8. Calculate the sa/v ratio, record in your table and answer the following questions: a. What happens to the surface area to volume ratio as the cube size changes? b. As the surface area to volume ratio gets closer to 1:1, what happens to the ability of the potassium permanganate to enter the cell? c. What would happen to a cell's ability to absorb adequate nutrients as it increased in size? CONCLUSIONS: Use data collected in this lab to explain why cells cannot exhibit unlimited growth, but must eventually divide.

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