Chilling Effects 

 Introduction:

Many animals are affected by changes in their environment.  Small animals, such as daphnia, have very dramatic changes that we can observe.  The temperature of their environment readily affects cold-blooded organisms.  Cold-blooded means that their body temperature is dependant upon the temperature of their environment.  Daphnia are cold-blooded animals and this lab will look at the changes they undergo.

National Standard Addressed:

During this lesson unifying concepts and processes such as change, constancy and measurement will be applied.  This will be accomplished when the students measure the heart rate of the daphnia and then observe the change it undergoes when it is submerged in cold water.  During this time they will witness a change in the heart rate and be able to measure the amount of slowdown it experiences. 

The life science standard of regulation and behavior will also be observed when the daphnia slow their heartbeat because the cold water has caused a general shut down of their body processes.  This behavior is a direct result of the daphnia trying to survive the harsh conditions that it has been placed in.

Investigative inquiry can be stressed during this lesson as you urge students to ask questions about what is happening.  They will most likely be inclined to want to know more about what is happening to the daphnia and why.

Objectives and Benchmarks: 

This lab will show the effect the temperature has on the daphnia.  Students will be able to see the heartbeat and witness its reaction to a colder temperature.

Materials:

Live daphnia            Depression Slides                      Vaseline            Paintbrushes            Pipets  

Petri Dishes            Dissecting microscopes            Chilled Fish Tank Water  

Advance Preparation: 

Obtain the live daphnia and chill some tank water in the refrigerator overnight.

Procedure:

Help students prepare a depression slide by placing a small dab of Vaseline in the depression.  This dab should be half the size of a pencil eraser.  Then have them make a bowl shaped depression in the dab of Vaseline.  Using a pipet each student should catch a daphnia and place it in the depression with a drop of water.  With a paintbrush, students can gently push the daphnia on its side so it is stuck in the Vaseline.

Have your students place the daphnia under a dissecting microscope and look for the heartbeat.  The heart is located on the upper part of the back behind the eye.  They should find a partner and count the heart rate for fifteen seconds.  They should do this three times and determine their average.  If the heart rate is too fast to be counted have them write very fast.

Next, have students place their slides with the daphnia in a petri dish that is half filled with the chilled tank water.  After waiting for several minutes they should find the heart again.  Once again have students count the heart rate for fifteen seconds and calculate their average after three trials.

Things to Consider:

What effect did temperature have on the daphnia?

Would warm water have the opposite effect?

What does this tell us about cold-blooded organisms?

Possible Integration:

Math is one way to integrate this lesson into an area other than biology.  This is accomplished by having the students calculate averages of their observed data.

Critical Concepts:

Cold-Blooded            Body Regulation            Daphnia          Heart Rate     Pipet