Part C

Effect of Temperature on Heart Rate

13. In this part of the laboratory investigation, you will examine how an earthworm's heart rate changes as its body temperature changes. Add enough tap water to a Petri dish to barely cover the bottom of the dish. Place an earthworm in the dish.

14. Using a hand lens, look for rhythmic contractions of the dorsal blood vessel. Each contraction represents a single heartbeat. Calculate the worm's heart rate by counting the number of contractions that occur in exactly one minute. This is easiest to do if one person counts contractions while another person watches a stopwatch or clock.

15. ^v CAUTION Glassware is fragile. Notify the teacher of broken glass or cuts. Do not clean up broken glass or spills involving broken glass unless the teacher tells you to do so. Place a thermometer next to the worm in the Petri dish, and measure the temperature. Record the worm's heart rate and the temperature in a table on the chalkboard.

16. Float the Petri dish containing the worm on top of either a warm-water bath or a cold-water bath. Place the thermometer next to the worm in the Petri dish, and watch the temperature until it reaches either 30°C (for the warm-water bath) or 10°C (for the cold-water bath).

17. Remove the Petri dish from the water bath, and immediately begin counting heartbeats for exactly one minute. After one minute, measure the temperature in the dish again. Calculate the average temperature to the nearest degree. Record the worm's heart rate and the average temperature in the table on the chalkboard.

18. Using data from the whole class, graph heart rate as a function of temperature. Draw the best-fit curve through the points.

19. Return the earthworm to the container from which you obtained it. Clean up your materials, and wash your hands before leaving the lab.

Analysis and Conclusions

1. State whether your hypotheses in Part B were supported by your observations. Explain.

2. What is the adaptive advantage of the earthworm's responses to light and moisture?

3. List variables that, if not controlled, might have affected the results in Part B.

4. Describe the relationship between the earthworm's heart rate and temperature as shown by your graph.

Further Inquiry

Design an experiment to determine which colors of light an earthworm is sensitive to or which areas on an earthworm are sensitive to light.

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