My students love to watch passive transport in action as, over the course of 3 days, a gummy bear massively expands and then contracts when placed in different substances.
This activity does not take long. 15 minutes to gather data at the start of days 1, 2 and 3 and a little longer thereafter to answer the follow up questions that ask students to compare their data to that of 3 other class members.
Also included is a link to a gummy bear song that will quickly become an annoying earworm. It is a little fun to torture the kids with this. Even though we NEVER EAT the gummy bears, watch out for the few kids who will still attempt it even after the bear has been out and put through the ringer for three days. Enjoy.