Daphnia Heart Rate Inquiry Lab

Part 1:  Forming a Question or Hypothesis

1.  Problem Question:  Does a Daphnia’s heart rate change in different water temperatures?

2.  Purpose:  (what are we trying to find out)

The goal of this lab is to find out:

3.  Background Information:

Daphnia are members of a collection of animals that are broadly termed as “water fleas”.  The daphnia used in this lab feed on particles found floating in the water (phytoplankton or decaying organic material), but the main food are algae and bacteria.

Daphnia tend to be almost kidney shaped, have a single compound eye, two antennae, and leaf-like limbs that produce a current of water which carried food and oxygen to the mouth and gills.  Their bodies are transparent and with a microscope, you can see the heart beating and sometimes even their last meal (their gut is green if they have just eaten algae).

Daphnia are poikilothermic, which means that their body temperature and therefore their metabolic rate are affected directly by the temperature of the environment.  The change in metabolic rate is reflected in the rate at which the heart beats.  

In your own words, name three facts that you learned about Daphnia:

4.  Variables:

Independent Variable (IV): The variable you manipulated or changed

Dependent Variable (DV):  The variable that will respond to the independent variable (what you measure).

DV units

Control Test: What the IV will be compared to in order to know the change was due to your test, and not some random variable.

Constant Variables: What will remain the same during the experiment that the variables can be compared to

5.  Hypothesis

Part 2:  Designing the Investigation

1.  Materials:

2:  Procedure:






Tips:  Don’t overheat your Daphnia under the microscope - keep on LOW power.  The beating of the heart is located on the dorsal side just above the gut and in front of the brood pouch (see diagram).  Make sure that your are counting the heart beats and not just the flapping of the gills or the movement of the gut.

Part 3:  Collecting Data

Table 1:  Heartbeats per minute of Daphnia in various water temps

1st trial

2nd trial

3rd trial


Room Temp

Cold Temp

Warm Temp

Part 4:  Analyzing and Interpreting Results

1.  Results:

Make a graph for the average number of heart beats/minute (y axis = dependant variable) versus temperature (x axis = independent variable). Insert graph below.

2.  Describe what your results are.  Refer to your graph.  Use specific numbers in your answer.

3.  Explain Results.  The above results happened because:

4.  Support or Reject.  Therefore, according to these results, the hypothesis can be:

5.  Review.  There were errors with the design of this experiment.  They were:

6.  Further Question:  A suggestion for a further study would be to: