Maintaining Homeostasis (Part 2/2)

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Students will explore several processes that help a cell maintain homeostasis.

Big Idea

What keeps a cell healthy and happy? Find out in today's exploratorium.

What Students Will Learn in this Lesson

1 minutes

In this lesson, students continue to explore the role of cell membrane has maintaining homeostasis. Students will analyze the results of the gummy worm osmosis lab.  Then they will design an experiment that will determine the internal environment of another cell model.  They will use fruit snacks as the cell for their assessment. Here is an overview of what students will learn today. 

Checking For Understanding/Determining Preconceptions

10 minutes

Students will be presented with the data from yesterday's misconception probe.  In light of the knowledge they acquired yesterday, they will explain the results.

(Note:  Students should recognize that the iodine moved through the dialysis tubing, but the starch did not. They may not understand why that occurs.  To aid students in fully understanding, ask students about the relative size of both molecules. Starch is a huge molecule and is unable to pass through the selectively permeable membrane.)


Maintaining an Osmotic Balance (Part 2)

30 minutes

Students should check the results of the gummy worm osmosis. First, students should carefully remove the gummy worms and weigh the worms.  Students should average the the change in mass for each treatment.  Next, using Logger Pro, students should compare the concentration density (x) with the change in mass (y).  Then they should select Analyze and Curve fit.  Students should choose the function that best fits the graph.  Next, they should select Statistics and determine the standard deviation.  Students should save the graph and print a copy to submit with their lab report.  

They should calculate the change in mass and record their results in the class data table. (Note: We use google docs for this step.)  After all groups have weighed their worms, students should calculate the class mean, std dev, max, and min.  As a class, create a boxplot of the distribution of data for each treatment.

They should explain their individual results of the experiment in light of what they have learned about osmosis and diffusion.  

Using the provided handout from yesterday's lesson, they should write a brief conclusion explaining the results of the experiment.  Students should use the following questions when writing their conclusion.

  • What happened to the change in mass as the concentration density increased?
  • What happened to the change in mass as the concentration density decreased?
  • Using your results, describe what the interior environment in the gummy worm cell model is like.
  • Using your results, explain what type of solution (Gatorade, Distilled Water, and Corn Syrup) is compared to the internal environment of a gummy worm. 

Putting It all Together: Designing Your Own Experiment

30 minutes

Using what they learned about water balance in the cell and movement across a membrane, student groups will design an experiment to determine what the internal environment is like inside a fruit snack.  Students will make at least five solutions of corn syrup and place several fruit snacks in them.  After allowing those fruit snacks to remain in the solution for several hours, they will remove them and determine the change in mass. Students will graph their data and extrapolate the solution that is most like the internal environment of the cell. Students will then summarize that data in a lab report.