1. The Effects of Caffeine on the Heart Rate of Daphnia magna
Laura Haggerty
Academy of Notre Dame

2. Abstract
Caffeine is a part of our everyday lives, but how does it affect other species? The purpose of this experiment was to test the effect of caffeine on the heart rate of Daphnia magna, small water crustaceans.
Four serial dilutions of a 1.00mg/ml solution were made and spring water was used as a control. Daphnia magna were then exposed to each of the five solutions and placed on a depression slide. Because their semi-transparent skin allowed for a clear view of the beating heart, the heart rate could be measured with the use of a microscope and stopwatch. After the heart rate was counted for 10 seconds, the data was then multiplied by six to equal the number of beats per minute.
It was hypothesized that an increase in caffeine concentration would increase the heart rate of the Daphnia. The data collected supported this hypothesis. The data displayed a significant increase in heart rate per minute as the concentration was increased. This demonstrated a direct correlation between the caffeine and the heart rate of the Daphnia. In a practical application one could make the connection that caffeine affects human in a similar manner as it did the Daphnia, in the fact that it has been known to increase their heart rate as well.

3. Question
How does the introduction of caffeine affect the heart rate of Daphnia magna?

4. Background Information
Daphnia magna are minute water crustaceans commonly known as water fleas.
Their skin is transparent making all internal organs visible under microscope
Typical life span is approximately days
Environmental factors and temperature can alter the life span of Daphnia magna.
Caffeine (C8H10N4O2 ) is a stimulant drug
Heart rate is defined as the number of beats per minute

5. Hypothesis
It was hypothesized that as Daphnia magna were introduced to increasing concentrations of caffeine, their heart rate would also increase

6. Variables Independent variable- concentration of caffeine
Dependent variable- heart rate of Daphnia magna
Constants- spring water
Control- spring water with no added caffeine

7. Materials Daphnia magna Transfer pipettes
100 mL graduated cylinders (2)
5 petri dishes
Compound microscope
Depression slides
Small container
250 mL beakers (5)
Caffeine pill (200 mg)
Detain

8. Procedure Serial dilutions were made in five 250 mL beakers
This resulted in a control and four varying concentrations of 1 mg/ml, 0.1 mg/ml, 0.01 mg/ml, and .001 mg/ml
The Daphnia magna were placed in each solution in small petri dishes before being transferred to depression slides.
The depression slides were placed on a compound microscope and observed.
The heart rate of the Daphnia magna was then counted for ten seconds and multiplied by six to calculate the results for heart rate per minute.
Five trials were performed for each of the four concentrations and the control.

9. Data Heartbeats per Minute 180 168 204 210 192 162 216 222 228 238 226
Concentrations
Trial 1
Trial 2
Trial 3
Trial 4
Trial 5
0.00 mg/ml
180
168
204
210
.001 mg/ml
192
162
216
222
.01 mg/ml
228
238
.1 mg/ml
226
234
240
1 mg/ml

10. Heartbeats per minute

11. T-test Results (P values)
Control vs .001 mg/ml
0.6
Control vs .01 mg/ml
0.08
Control vs .1 mg/ml
0.01
Control vs 1 mg/ml
0.002

12. Analysis
The hypothesis was supported. When introduced to higher concentrations of caffeine, the heart rate of Daphnia magna increased.
The two most concentrated solutions proved to be significant exhibiting the fact that caffeine does affect the heart rate of the Daphnia, but the solution must be concentrated to a certain level in order for a distinct variation in heart rate to occur.
For further research, one might extend the experiment to test other small organisms
Another extension could be to perform additional trials with more concentrations to pinpoint the exact concentration at which toxicity occurs.

13. Conclusion
The introduction of caffeine had a substantive effect on the heart rate of Daphnia magna tested thus supporting the hypothesis that an increase in caffeine concentration would instigate an increase in heart rate.
The more concentrated solutions of .1 mg/ml and higher were shown to have had a significant effect on the heart rate.

14. Works Cited