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It's February ... And That Means Daphnia Love is in the Air!

This is the PERFECT lab for a high school biology class on Valentine's Day!

I soooo look forward to this lab each and every year.  Measuring the heart rate in Daphnia is FUN, is fairly easy to do, allows our biology students to work with living organisms in the lab, and perhaps most importantly, it provides an outstanding situation for having our students design and implement their own experiment.

Are you nervous about "student-designed experiments"?  Don't be!  If properly trained and instructed on the front end, the students will surprise you with their creativity and passion for designing an experiment.  But I am getting ahead of myself.  Let me go back to the beginning....

Daphnia are tiny crustaceans, closely related to a shrimp. They are often called "water fleas." They are small, but not microscopic.  They can be seen with the naked eye, but you will need a dissecting microscope to view the beating heart. Daphnia can be purchased from any of the companies that sell lab supplies and equipment. Since Daphnia are arthropods, they demonstrate the three major arthropod characteristics: exoskeleton, jointed appendages, and segmented body. The exoskeleton is clear, allowing the student to easily view the heart. Daphnia are ectotherms and their body temperature changes with the surrounding environment.  This further means that there is a direct relationship between the internal body activities and the external temperature of the water in which it lives.

This sets the stage for the first part of our experiment.  I have my students carry out an experiment where they measure the change in heart rate when Daphnia are exposed to different temperatures.  I provide the procedure, and the student simply follows the instructions and carries out the lab.  The Daphnia are exposed to three different temperatures, and the student counts the number of heart beat per minute in each environmental condition.


Students carry out my procedure, graph their results, and answer my questions.  On Day 2, the fun begins!  It is time for the students to design their own experiment!  They are asked to design an experiment to test the effect of caffeine on the heart rate of Daphnia.  The students must state a hypothesis, describe their experimental and control groups, carry out the experiment, collect their data, graph their data, and come to a conclusion based on their data. 

The student-designed experiment will take some time.  I require my students to write their experiment and submit it to me for approval before they begin. Once approved, they carry out their experiment and write a formal lab report. The best learning occurs as the student is carrying out their experiment.  They invariably realize that their procedure is flawed, and they must revise, revise, and revise until they get it right.

For my honors and AP students I require that they also complete a worksheet on how to calculate the Q10 temperature coefficient.

And this is what we do to celebrate Valentine's Day in my biology classroom.  Happy Valentine's Day everyone!

In my TpT Store: "Measuring the Heart Rate of Daphnia" contains handouts for all parts of this experiment, including the student designed experiment and the Q10 worksheet.  Teacher Guide included. 


1 comment:

EllenWeber said...

Where were you when I sat in secondary science classes -- love the ways you hook science onto life! Thanks for sharing! Ellen