General Biology
Name: ________________________
Daphnia Heart Rate vs. Temperature Lab
Daphnia are small, freshwater crustaceans (crabs, lobster, shrimp, etc…) that are filter feeders in the
aquatic ecosystems they inhabit. Their food is primarily algae, but may include protists and bacteria as
well. They may even be sustained in laboratory situations on granules of yeast.
If you refer to the accompanying diagram you’ll see that daphnia possess a number of interesting
physical features. Of special note are its compound eye, antennae, and simple heart. Observing these
structures under the microscope is made all the more simple by their translucent carapace (exoskeleton)
If you remember, organisms are influenced by two types of factors in their environment. Abiotic (nonliving) and biotic (living) factors which have the ability to affect even the internal processes of the
organism. The structure we are of most interest in is the heart. The heart is basically a pump for moving
a fluid (blood) throughout tubes in the organism. The abiotic factor we are of most interest is water
temperature. These organisms inhabit aquatic ecosystems, and the temperature of the water they inhabit
obviously changes from season to season.
What we are proposing then is that you formulate a hypothesis to test the impact of water temperature
on Daphnia heart rate. As always, background research on the topic should be done prior to the
formulation of this hypothesis. You should be thinking about what the “normal” heart rate of a daphnia
is. Is it possible that individual Daphnia possess different heart rates just as humans do? You should
then design and conduct a lab at your lab station that addresses the following water temperatures: 5°C,
10°C, 15°C, 20°C, 25°C, 30°C, 35°C, 40°C. Temperatures should be done in order from lowest to highest
to minimize the stress on the Daphnia and increase the likelihood of meaningful data.
Once the data has been acquired, an x-y scatter plot with data points connected by smooth lines should be
constructed to observe the trends in the data. As you do so, consider what is causing the effect the data
show and an explanation for it. What would the effect be if it were done on humans? Would there be
any differences and if so why? The final analysis for this assignment will be an official lab report using
the 36pt rubric used in this course.