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Return to Model Zoom Lesson Plans |
 ZOOMplan
The Effects of Temperature Variations on the Heartbeat Rate of Daphnia
(ZOOMplan developed by Dr. Ken Mechling, Clarion, Pennsylvania) |
The Daphnia—What It Is: Daphnia, popularly known as water fleas, are
small crustaceans that live in fresh water such as ponds, lakes, and
streams. They serve as an important source of food for fish and
other aquatic organisms. Daphnia are excellent organisms to use in
bioassays because they are sensitive to changes in water chemistry
and are simple and inexpensive to raise in an aquarium. They mature
in just a few days, so it does not take long to grow a culture of
test organisms. Because Daphnia are transparent, it is possible to
conduct bioassays using endpoints other than death. For example,
through a microscope you can measure their heart rate or observe
whether they have been eating.
Science: Experimental Investigation
for Middle School Science
Objective: Using DigiScope technology, MAIS
middle school students will design, conduct, and report on an
experiment to determine the effects of varying water temperatures on
the heartbeat rate of Daphnia.
Concepts: Structure and function in
living systems, regulation and behavior, diversity and adaptation of
organisms
Processes: Observation, inquiry, measurement, hypothesis
formulation, experimental design, technological design
Project AERO
Standards: The Living Environment # 16 Students will understand the
structure, functions, and reproduction of living cells and
organisms. Inquiry # 2 Students will communicate scientific ideas
and activities clearly. Technology # 3 Students will gather,
analyze, interpret, synthesize, apply, and communicate information
and designs using technological tools. Mathematics # 7 Students will
estimate and measure to a required degree of accuracy and precision
by selecting and using appropriate units, tools, and
technologies.
Materials: Daphnia, well slides and cover glasses, ice
cubes, cotton filters, droppers, DigiScopes
Procedure:
1. Have the
students observe Daphnia specimens under the DigiScope and discuss
what they see, e.g. intestines, external appendages, heart.
2. Have
the students count the number of heartbeats per unit of time, e.g.
15 seconds. Do 3 trials and have them calculate the average. This
count will serve as a baseline for later comparison.
3. Return the
Daphnia to the specimen jar. Now discuss the heartbeat rate with the
students. Ask them to suggest what factors may affect the heartbeat
rate. Among the suggestions such as activity variations, chemicals
added to the water, light and dark, temperature—select temperature
as the variable to be manipulated. Have them formulate hypotheses,
e.g. If water temperature decreases, then Daphnia heartbeat rates
will (increase, decrease, or stay the same). Next, have students
design, record, and do their own investigations.
4. Have them place a
few cotton strands across the well of the slide (the fibers will
trap the Daphnia and prevent them from swimming out of view). Use
droppers to obtain Daphnia specimens, together with a small amount
of water. Cover the slide with a cover glass.
5. Observe the Daphnia
under different magnifications. Remove the eyepiece from the DigiScope and insert the camera in its place. Now go to the main
menu page of Motic Play and click the capture button. Adjust the
DigiScope until you have a clear image in the window, then click the
Capture button. Print the image by clicking on the Jump to Edit
button. When in the editing window, click the Print button. You can
create a video of the Daphnia for a specific time limit by clicking
on the time setting button on the Capture Menu.
6. To set the time
limit, click on the 15 button on the panel or click and move the
slider to 15 seconds. Next click on the Record Video button on the
Capture Menu. The Name File box will appear at the top of the image
window. After you type in the name for the video, click and drag the
Name File box to the side so that the image window can be
seen.
7. When you are ready to begin the video of the Daphnia’s
heartbeat, click Open and quickly click OK to begin recording. After
15 seconds, the video will automatically stop. Chill the slide of
Daphnia on top of an ice cube for different lengths of time and make
a 15-second video of the heartbeat each time.
8. Using the videos,
count the number of heartbeats. Chart and graph your results. Have
the students complete their written investigation results, noting
the results and whether or not their hypotheses were
supported.
References:
Norden, Beth B. and Lynette Ruschak,
Magnification, Lodestar Books, New York, 1993.
Ross, Michael Elsohn,
The World of Small, Yosemite Association, California, 1993.
Snedden,
Robert, Yuck! A Big Book of Little Horrors, Simon and Schuster, New
York, 1996
Stewart, Kimberlee, K-8 Experiment Manual, Science Kit &
Boreal Laboratories & Motic Incorporation Limited, 2002. |
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