In order to study respiration in yeast we set up an experiment using Bromothymol Blue (an indicator which is sensitive to the pH changes that result when carbon dioxide is dissolved in it), sugar, live yeast cells, and dead yeast cells (yeast were boiled). The students set up three test tubes with 15mL Bromothymol Blue solution and 2 grams of sugar. The first test tube served as a control containing only the Bromothymol Blue solution and sugar. The second tube had live yeast cells added to it, and the third had dead yeast cells added. The samples were then placed in a warm, dark room to incubate over night.
This lab group had an excellent result. From left to right the dead yeast tube, the live yeast tube and the control tube. Some lab groups had tubes that exhibited contamination in the dead yeast tube. Several groups had forgotten to clean their test tubes prior to beginning the lab. Lesson learned, never assume that your glassware is clean even if it looks clean. Of course we are not working under sterile conditions and some contamination is to be expected.
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