Osmosis, An Accidental Experiment

Last week we finished our unit study of the world's oceans. We had a surprise or accidental experiment last night when the girls notice that one of those starfish toys that you put in water and it swells to way larger than it was to begin with had shrunk. It had been sitting in a bowl of water for the past week. They couldn't figure it out because a few days ago it had increased to three times the original size. They kept questioning why it had suddenly shrunk. Then McKenna looked at the water. That's when we discovered that little Miss McLarin had added salt to the water. A lot of salt!

We did a little investigating and learned that this was due to osmosis. When the toy had increased in size water was more abundant in the cells or fibers of the toy. Adding salt caused the water to be drawn into the salt water and out of the toy. The toy had more water and less salt and the water outside the toy had way more salt. Apparently the cells of this toy starfish were trying to equalize the amount of water inside and outside of itself.

The girls starfish toy has shrunk a size or two from the size it was a few days ago, but is still larger than when it was put into the water. How's that for a cool accidental experiment?




The picture of me holding the toy starfish
helps show the actual size of the starfish.
When it was put into the water it was about
3" across. It then swelled to about 9" across.
Now after the salt was added to the water

Can you see that big pile of salt under the starfish?

it has shrunk to about 5-6". Sorry I don't
 have a picture of it when it was at it's
 largest size. Hope you enjoyed sharing
in our fun learning experience!