 Why are cells so small? And why are we made of so many? It seems like it would be easier to be made of 100 or even 1,000 cells instead of trillions. One of the reasons we teach students that cells are small is because they need a large surface area to volume ratio. The larger the ratio, the more efficient the cell is at moving materials in and out of the cell. I've seen cell size labs that use different sized agar cubes prepared with a pH indicator. The cubes start pink and lose their color as they soak. (Here is a free version from Flinn if you are feeling ambitious!) Frankly with 3 preps a day this year, I didn't have the time or energy to pour agar cubes. Instead I found a quick and easy way for students to see the same concept- using beets and bleach. In this experiment, cut different sized beet cubes, a small, a medium, and a large. The students soak the cubes in bleach for roughly 30 minutes (I had them doing some practice SA:V calculations while they waited). Tip: if you use tupperware containers with lids you won't have to smell bleach fumes all day, or you can put parafilm over the beakers.   After 30 minutes of soaking, students remove the beets, cut them open, and measure the amount of red pigment remaining. It is an easy way to see that small cells are more efficient at moving materials in and out. If you are interested in seeing the lab write-up I wrote, you can view it here. I hope your students enjoy it!
8 Comments
Cassondra
8/21/2020 07:20:20 pm
Is it possible to do this lab with a solution other than bleach? Bleach isn't permitted in Biology classrooms in my school for safety reasons; the Chemistry teachers have to keep it under lock and key.
Thomas
9/18/2020 12:40:18 pm
Maybe potatoes and iodine? I know iodine comes with its own restrictions, but you can likely buy it at a pharmacy (when I was a kid we used to use it as a disinfectant). Then again, when I was a kid we used to treat a fever with a course of leeches.
shep
9/10/2021 08:46:42 pm
Were you able to do this with potatoes and iodine? I want to do this lab in a few days and don't want to make a bunch of agar.
Lisa
10/2/2020 08:29:50 pm
Same here! Vinegar works great as a substitution for bleach in this lab.
Dominique
10/28/2020 03:29:11 pm
Just an FYI. I tried this with vinegar and it doesn't work. The beet loses pigment and the vinegar changes to a pink color, but no visible change in the beet.
Morgan
11/27/2020 01:29:24 pm
Make a jello with red cabbage. It will be purple; use vinegar as a bleach substitute - will turn the jello hot pink around edges. 1/8/2021 05:02:20 pm
I didn't plan enough time to cut open the beets. Can I store in the freezer for a couple days? or will we have to resoak them all?
Kirsten
9/28/2021 11:53:01 am
Fresh beets or canned beets? What works best? Your comment will be posted after it is approved.
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