The Biology Behind the Bubbles: Root Beer

As a high school biology teacher, I was always trying to find ways to intrigue my students and get them interested in the reality behind the words in the textbook.  Our cellular respiration unit always seems to approach when students are past the start-of-the-year enthusiasm and are approaching the get-me-out-of-here-for-winter-vacation doldrums.  And it doesn’t help that this is a difficult concept to wrap one’s head around.

Luckily, students seem to catch on to the idea after I show them an episode of one of my favorite videos:  The Magic School Bus!  Yes, I know that I am not an elementary school teacher.  These kids are in high school after all.  But who doesn’t love Mrs. Frizzle and her simple approach to explaining regular topics that we all face every day.

Making Cellular Respiration and Fermentation Simple…

In case you don’t happen to have 20 minutes to watch the show, the basic gist is that Mrs. Frizzle is participating in a rowing competition against a strapping foe.  She gets the hiccups, and a helpful student encourages her to hold her breath.  Unfortunately, her cells need oxygen to perform, and she loses steam…and the race.

In order to learn more about why Mrs. Frizzle is struggling in the race, her students board the Magic School Bus, shrink in size, and enter her blood stream.  Once inside, they learn that in order for cells to perform at their peak performance, they require fuel and oxygen. When there isn’t any oxygen, the process becomes anaerobic (an=without, aerobic=requiring oxygen), and cells form lactic acid, a byproduct that makes her muscles burn and stop working.  This is called Lactic Acid Fermentation, used by muscles and also by bacteria (in the process of making yogurt, kombocha etc.).

Fermentation Lab: Root Beer Biology

In case the cartoon didn’t intrigue my students enough, we decided to do a lab that illustrates another component of cellular respiration: fermentation.  Fermentation happens during the cellular respiration of yeast.  Even though we live close to the wine country, we couldn’t exactly ferment a barrel of the good stuff – so instead we tried to brew a batch of root beer.  As you are aware, alcohol is typically a byproduct of fermentation – a cellular respiration process in which sugar is broken down by yeast in an anaerobic (no oxygen, remember?) environment, and produces (a teensy bit) of alcohol, and carbon dioxide (bubbles!!!!).

When the bottles were finally ready, they were fully pressurized with carbon dioxide bubbles – a sure sign that fermentation had occurred.  Students were impatient to taste the fruits of their labor – and were quite disgusted by the result.  (Clearly, I will not be going into the artisanal root beer brewing business…) But they learned about the topic and couldn’t wait to come to class – both wins, in my book.

Want to try the lab yourself?  Here’s a copy of what I gave to my students.
Root Beer Fermentation Lab

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