You and Your Students!
Vicki Cobb, Education World Science Editor
Discover how (and why) anti-dandruff shampoos inhibit yeast production.
Yeast are one-celled microorganisms related to fungi. The yeast you find dried and packaged in the supermarket (called Saccharomyces cerevisiae) is used for making bread. "Feed it some water and a little sugar, and it springs into action! It uses the sugar as food, and it begins multiplying itself. In this process, which is called fermentation, the yeast gives off two valuable waste products -- alcohol and carbon dioxide. The alcohol is essential to the production of beer and wine. The carbon dioxide is used to make breads and cakes rise. (The alcohol evaporates during baking.)
Human skin is host to a type of yeast (called Pityrosporum ovale) that normally doesnt bother us. However, an outgrowth of this particular yeast causes the skin on the scalp to react, producing dandruff. One treatment is often found in dandruff shampoos, particularly those that contain the antifungal agent ketoconasole. By inhibiting the growth of yeast, the dandruff is reduced.
Does anti-dandruff shampoo inhibit fermentation of bakers yeast? Do this experiment to find out.
This procedure lends itself to a nice hands-on investigation. You can do this as a class demonstration, or students can do it in cooperative groups. The results take several hours, so you want to set it up first thing in the morning.
Watch your experiment over the next 2 to 3 hours. Note the time when each balloon pops into an upright position. After that, you can measure the carbon dioxide production by wrapping a string around the largest part of each balloon. The length of the string will give a measure of the circumference of the balloon and, therefore, a rough measure of how much gas has been produced.
Smell the balloons. Can you smell any alcohol? If you can, that tells you that the alcohol molecules are small enough to pass through the rubber of the balloons. Can you smell anything through the bottle?
Can students discover any other yeast-buster substances? Like anti-dandruff shampoos, some antifungal preparations for feet and antiseptics for cleaning bathrooms are yeast busters too.
The balloon that popped up first was your control. The baby shampoo was a test to see if shampoo alone inhibited fermentation. How good was the anti-dandruff shampoo at inhibiting yeast action?
Use this experiment to stimulate a conversation about advertising.
Article By Vicki Cobb
Copyright © 2007 Education World