Daphnia Heart Rate
Carolina Labsheets™
In this introductory physiology lab, students determine the heart rate of Daphnia magna and then test the effect of changing temperature on the heart rate.
Needed Materials
Daphnia magna Culture (142330)
stopwatches
thermometers or temperature probes
beakers or cups of two different sizes
ice
hot pot, or other means of heating water
insulated containers
stereomicroscopes or compound microscopes with a 4x scanning objective (for 40x viewing)
Safety
Ensure that students understand and adhere to safe laboratory practices when performing any activity in the classroom or lab. Demonstrate the protocol for correctly using the instruments and materials necessary to complete the activities, and emphasize the importance of proper usage. Use personal protective equipment such as safety glasses or goggles, gloves, and aprons when appropriate. Model proper laboratory safety practices for your students and require them to adhere to all laboratory safety rules. This activity requires the use of hot water. To avoid the possibility of scalding, at no point should the water temperature exceed 49°C (120°F). Cultures remaining after the completion of the activities may be added to a classroom aquarium or discarded by flushing them down a sink with tapwater. The chlorine and chloramine in most tap water will kill Daphnia. If your tap water is not chlorinated, pipet 1 mL of household bleach (sodium hypochlorite solution) or isopropanol (rubbing alcohol) into the culture and wait 15 minutes before flushing down the sink.
Procedures
Students may work in pairs. You may have all groups make counts at three temperatures (room temperature, above, and below), or you may divide the class into three groups and have each group test at a different temperature.
Use only springwater with Daphnia. Even after treatment to eliminate chlorine and chloramine, tap water often contains metal ions that are toxic to Daphnia. Refer to the Daphnia Care Guide for more information about the care of this organism. Also avoid distilled water. See our video Measuring Heart Rate Using Daphnia for a demonstration of the setup and procedure.
Although you may use other Daphnia species in this activity, we recommend Daphnia magna because of its larger size. The openings of many pipets are too small for D. magna. If needed, use scissors to cut the tips of the plastic pipets at a 45° angle to accommodate D. magna.
The two beakers or cups must be sized such that the smaller will nest inside the larger.
Tungsten or halogen lamps will heat the water. It is best if the illuminators on your microscopes are fluorescent or LED.
Each student group will need at least one Daphnia and the Student LabSheet.
Set up four workstations as follows.
| Daphnia station Daphnia culture dropping pipet concavity slide |
Materials station stopwatches thermometers |
| Warm-water station insulated container of warm water (35–40°C) beakers of two sizes springwater sink |
Cold-water station insulated container of ice beakers of two sizes springwater sink |
Optional
Students may compare their data for Daphnia heart rate with those for Lumbriculus. See our LabSheet Lumbriculus: Contraction Rate of the Dorsal Blood Vessel for details. That sheet contains suggestions for testing the effects of caffeine and other substances, which may also be done with Daphnia.
Answer Key to Questions Asked on the Student LabSheet
Students’ data will vary but should show the following pattern.
| Temperature, °C | Heartbeats/15 sec | Heart Rate, beats/min |
| 21 | 91 | 364 |
| 10 | 57 | 228 |
| 25 | 108 | 432 |
You will now find the heart rate of Daphnia in water that is either warmer than room temperature or colder than room temperature. Do you think the heart rate will respond to differences in temperature? If so, how?
Yes. As temperature increases, so will the heart rate.
Give a reason for your answer.
Answers will reflect the student’s background knowledge. Acceptable answers include but are not limited to the following: The body temperature of ectothermic organisms increases as environmental temperature increases. As body temperature increases, the rate of chemical reactions and physiological activities within the organism increase. The rate of cellular respiration increases, requiring more oxygen and producing more carbon dioxide. This requires an increased flow of blood, which is pumped by the heart.
Are the results of testing at different temperatures what you expected?
Yes. (Answers may vary according to the data recorded.)
