An Eggsperiment

 

             This lab allows students to learn about properties of the cell, such as diffusion, osmosis, and semi permeable membranes.  It serves as an excellent introductory lab to an animal cell unit, and gives students more experience in partially designing their own lab.  Most the procedure from the lab is obvious from the sheets describing the experiment also provided on this site, but here is more information that will be useful:

            The lab takes a good amount of time to follow through with properly, and so two class periods should be set aside for it.  Students may have some trouble with the questions at first that are on the sheet, but still have them write down all answers.  Check all three of their questions in number 2) on the worksheet before letting them continue on, and do so with number 4) on the worksheet as well, as students often have trouble with quantitative vs. qualitative labels.  Based on the students’ questions, let them come up with their own experimental procedure to work out, and check this before allowing them to start the experiment. 

            The teacher should soak the eggs that are to be used in the lab in vinegar for 3 days to remove the hard outer calcium layer of the egg.  Provide the students with distilled water, corn syrup, salt water, or some other substance to soak the eggs in to notice what happens afterwards.  Make sure the students, in their experimental procedure, include a control of just the normal egg not in any medium.  Remind students to take all possible measurements of what they’re testing, such as circumference of the egg, its weight on a triple beam balance, etc.  These should be included by the students in the “observable results” section of the provided worksheet. 

 

Here is a sample procedure a student may do:

The student’s question may be, “How will the internal environment of the egg be affected by soaking it in a medium of distilled water?”  To test this, the student should have a control of an egg in no medium.  Then, he/she should quantitatively measure this egg as well as another in terms of mass or some other measure.  Before massing, remind the students to rinse the egg under water to get rid of any vinegar that may still be on it.  The student should recognize the variables they are testing, and make sure they are only testing one at a time.  Make sure the students fill out the Predictions section of the worksheet thoroughly; it is in this part that they really have to think about the reasons behind their hypothesis.  Students should conduct most the experiment and all the original measuring on the first day, and then leave it overnight, and then measure all the variables once again the next day, and compile their data with that of the rest of the class and have an open discussion discussing conclusions and what happened. 

 

This lab can get hectic, as students want to play with the eggs and have to treat them delicately.  Groups of 3 or so are ideal.  If the teacher intends on going deeper into eukaryotic cells after this lab, and starting a unit on this, this article and concept map are excellent potential homework assignments within such a unit.