Materials

■ thermometer

■ U-shaped glass tubing, 30 cm long

■ 2 corks to fit both ends of the tubing

■ distilled or non-chlorinated water

■ culture of paramecia

■ hand lens or dissecting scope

■ stopwatch or clock

■ glass-marking pen or wax pencil

Background

1. Some power plants use water from rivers as a coolant. After the water is used, it is much hotter than the water in the river.

2. What is a pollutant?

3. How can heat be considered a pollutant?

4. How can power plants release nonharmful water?

Procedure

1. Discuss the objectives of this investigation with your partners. Develop a hypothesis concerning the effect of temperature on paramecia.

2. Design an experiment using the given materials to test your hypothesis. In your experiment, the paramecia will be contained in the U-shaped tube. One large beaker will be filled with ice, and the other large beaker will be filled with hot water. Other materials that you can use in your experiment are listed in your materials list.

3. In designing your experiment, decide which factor will be an independent variable. Plan how you will vary your independent variable. In your lab report, list your independent variable and your method of varying it.

4. Decide which factor will be the dependent variable in your experiment. Plan how you will measure your dependent variable. In your lab report, list your dependent variable and your method of measuring it.

5. In most experiments, a control is necessary. Plan your control, and describe it in your lab report.

6. Discuss your planned experiment with your teacher. Proceed with your experiment only after you have received your teacher's permission to do so.

7. CAUTION Water hotter than 60°C can ▼ scald. Be careful handling hot water, and alert your teacher if you burn yourself. Fill a 400 mL beaker with ice and water. Make sure that ice remains in the beaker for the entire experiment. Fill another 400 mL beaker with 60°C tap water.

8. In a 125 mL beaker, gently swirl 20 mL of water and 20 mL of a culture of paramecia. Your teacher will provide aged tap water or distilled water for you to use during this step. (Chlorinated water would kill the paramecia.)

9. While your partner holds the test tube steady, carefully pour the paramecia-and-water mixture into the U-shaped tube. Fill the tube completely, leaving just enough room for a cork at each end of the tube. Make sure there are no large air bubbles in the tube. Place a cork at each end of the tube.

10. Create a table similar to the one shown to record your data. For example, the table shown is designed to record the number of paramecia in three parts of the U-shaped tube over time. Design your data table to fit your own experiment. Remember to allow plenty of space for recording your data.

11. Proceed with your experiment, using the tube, ice water, hot water, and hand lens to observe any response of the paramecia to the environment.

12. As you conduct your experiment, record your results, including the number of paramecia and the time involved, in your data table. Organize your data so that others reading your lab report will be able to understand the results of your experiment.

13. J%\ Jk^ Clean up your materials and wash your

^^ hands before leaving the lab.

Analysis and Conclusions

1. Did the results of your experiment support your hypothesis? Explain your answer.

2. What effect did heat and cold have on the paramecia in your experiment?

3. What evidence do you have that paramecia preferred one temperature range to another?

4. What are some possible sources of error in your experiment?

5. How might a pollutant cause an increase in the number of organisms? Explain.

6. Judging from your experiment, how do you think other organisms might react to a change in water temperature?

7. How could a power plant change the type of organisms that live in the water where it releases its cooling water?

Further Inquiry

Develop a hypothesis about the effects of acid rain on paramecia, and design an experiment to test your hypothesis.

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