Have you ever wondered why you can’t put fresh pineapple in gelatin? This investigation explores how the enzyme bromelain breaks down gelatin. The lab is easy to set up. You just need to make the Jello according to the package directions. Give students about 12 ml of liquid gelatin. I made it ahead of time and separated them into 50 ml beakers. (I use lime Jello because it looks pretty with pineapple in it.)
The directions call for 3 ml to be added to a test tube, but you can save time by not having them measure precisely. I just tell them to pour the same amount in each test tube, filled up to about an inch. Then, students place a piece of pineapple into the gelatin. One comes from freshly cut pineapple and the other from a can.
Once the pineapple is in the test tube, students place the tubes into an ice water bath. Chilling the gelatin will make it solidify faster, it will take about 10 minutes.
Slushy Results!
Students will discover that the gelatin with the fresh pineapple does not solidify! The canned pineapple will solidify, though many in my class noticed that it took longer. A control test tube with no pineapple is used for comparison. At the end of the lab, you can have a discussion with what is the best way to get the solid Jello out of the test tube. Amazingly, many students in my class proposed using the pineapple juice to liquify it!
Pineapple in Lime Jello
Finally, students will complete an analysis section where they summarize the results of the experiment. I included a CER section (claim, evidence, reasoning), and a place for them to sketch the reaction. The worksheet has questions about enzymes and how they speed reactions. Students in my AP Biology class had no trouble with this lab, and it is probably suitable for beginning biology.
As a follow-up exercise, students do the catalase lab where they use a floating disk technique to estimate rates of reaction. For a more data centered lab, check out the lab simulation on the lactase enzyme. HHMI has great resources on the evolution of lactase!