Ward's World Activity Guides

+ ward ' s science 2. Label one test tube "A", one "B", one "C", one "D", and one "Control". 3. Label 5 pipettes the same way as your test tubes (A, B, C, D, and Control). Label one more pipette as "T" which will be your transfer pipette. Using the pipette marked T, put 4 ml of pond water into each test tube. 4. Using the pipette marked A, add 1 ml of Salt Solution A to the test tube marked A. 5. Match your pipettes to the salt solutions and samples. Repeat Step 5 for the B, C, and D Salt Solutions. 6. Using a clean pipette, put 5 drops of vital stain into each test tube. Be careful not to touch the pipette to any of the salt solutions. 7. Using the T pipette or another clean pipette, put a sample from your control test tube onto the well slide. 8. Cover the well slide with a cover slip and place it on the microscope stage. 9. Using the 10X objective (100X total magnification) and a stopwatch or timer, count how many protists you can see moving in one field of view for 30 seconds. Write this number into a data table 10. Using the same 10X objective, examine your slide once again and count how many different types of protists you can see in one field of view. Record this number into the data table. 11. Rinse the well slide with clean water, and dry it off. 12. Using a new pipette for each of the four remaining samples, repeat steps 6 through 11 for each sample. Record you results for each sample into the data table. 13. Share your data with the rest of your class and calculate the average number of moving protists, and the average number of different types for each of the five (5) test samples. Record your results in data table A. Expected Results: Results may vary based on materials used, setup, procedure, and other factors, however, here are a few examples on what to expect: • The lowest level of salt concentration (solution D) should produce no noticeable effect on the protist population. Students will suggest that this be the recommended level of use. • Play the role of the town, and explain that this concentration of runoff is unrealistic because the roads would be unsafe. Assume that the safest level would be Solution B, and have students discuss the ramifications of maintaining this level. Follow-up Teaching Notes: • Have each student group prepare a presentation to the "town board" (the rest of the class). The presentation should show their results and include a recommendation that incorporates the environmental impact as well as the factors of safety, expense, and feasibility. Add Inquiry: • Inquiry Idea 1 – If the overall solution concentration cannot be reduced below the level of solution B, are the other chemicals that can be used with the same effects of melting ice and snow, but reducing the impact on the environment? 0 Suggestions for additional trials 0 Potassium Chloride 0 Calcium Chloride 0 Commercially available Products A Slippery Dilemma Demonstration (continued)

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