Sunday, April 25, 2010

Super Simple Science: Biology and Osmosis

I think most people are familiar with this experiment using white carnations. One need not have carnations though. We demonstrated osmosis and cell stiffness using old celery. I used week-old, pale celery with leaves (left over from making chicken stock, yum). We felt how limp the celery was and paid attention to the color of the leaves.

We filled a glass with water and added a lot of liquid food coloring. We put the celery in the glass and waited over night.


By the next morning, we had evidence that the colored water had moved all the way to the top of the celery stalk through osmosis. The leaves were splotched with blue.





When we cut a cross-section, the main channels were also distinctly blue.


It was even more dramatic to pull the celery apart and see those same channels along their length.


We also noted that the celery was much stiffer, and crisper, and could hold its shape better. I explained that this was why we had a high-humidity drawer in the refrigerator, why the supermarket uses misters in the produce area, why there is water in pre-cut vegetable packages, and why I sometimes soak my older lettuce in water before making a salad.

There's an explanation here: http://www.biologycorner.com/bio1/diffusion.html

-- Post From My iPhone

2 comments:

Shez said...

We did this with celery and carnations a few weeks ago. Great fun.

Kim said...

The carnations are certainly more dramatic! I did not feel like driving to a florist (none are local). Another way to show osmosis is using paper towels, paper, or anything else plant-derived, like fabric. That would really tie in a lot of other situations. I should have put that in the post!