This is the first lab I run every semester because it can be done with just yeast before fees have been collected to purchase organisms with. This semester, I bought two different kinds of water balloons at Wally World. The ones that come in the large plastic container (kind of like a tennis ball container) were TOO small to even fit over the mouth of the test tubes. The other ones didn't work very well either. I think last semester, I just bought small regular balloons and these seemed to work better.
One change I made to the procedures on Part 1 was to mix the yeast and water in a beaker instead of trying to mix it in a test tube. This cut down on prep time for the kids and worked just as well. They then just evenly distributed the yeast mixture into the four test tubes. I will do this again, so I need to change the procedures before printing them out next semester.
One student asked me how we knew that the production of the gas was an indication of life instead of just an indication of a chemical reaction. I told him that is one reason we are doing Part 2 of the lab also (which will show evidence of growth).
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