In this TWO DAY biology laboratory activity, students will explore the effect of osmosis on three different food samples: de-shelled eggs, potato slices, and gummy bears. Each food sample will be placed in solutions of varying solute concentrations, and changes in both the mass of the samples and volume of the solutions will be analyzed after 24 hours. While these osmosis demonstrations have been used often in biology classrooms, they are typically used separately, and I have never been able to find any resource that combined all three of these food samples into one activity. This lab is a combination of all of my favorite classroom osmosis activities!
The results of this lab are extremely surprising and memorable for the students, as they do not expect the food samples to grow or shrink as much as they do! This lab includes first a teacher demonstration of osmosis in de-shelled eggs, and then a student-led investigation of osmosis in gummy bears and potato slices. In addition to exploring osmosis, students will practice their metric measurement skills, including using electronic balance scales and graduated cylinders. Finally, they will calculate the percent change in mass for each of the food samples.
To make de-shelled eggs, soak eggs in white vinegar for at least 24 hours before beginning the lab. I always soak a few more than I need because they are delicate and some always end up popping! I also create a 10% saltwater solution for the potato and gummy bear phase of the experiment. Each day of the lab takes approximately 45 minutes.
Students usually expect the gummy bear placed in salt water to lose mass, but in actuality, it gains mass! Although unexpected, it can lead into an interesting discussion as to why this result was obtained. There is more dissolved sugar in the gummy bear than there is dissolved salt in the water, making the salt water hypotonic to the gummy bear.
Included in the Zip File:
1- Osmosis Investigation Student Handout (5 pages)
2- Teacher Answer Key
3- Detailed Teacher Implementation Guide (5 pages)
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