UEN Security Office
Technical Services Support Center (TSSC)
Eccles Broadcast Center
101 Wasatch Drive
Salt Lake City, UT 84112
(801) 585-6105 (fax)
2 class periods of 45 minutes each
Have students design experiments as a class to determine if yeast are autotrophic or heterotrophic. Students will utilize a set of materials to address the above question by growing yeast cultures under conditions containing food, light, both and neither.
Yeast are heterotrohpic organisms (they need food for energy). When placed in an aqueous environment (water) with simple sugars (honey) they ferment (eat) the sugar into ethanol and C02 (this is why bread rises). The CO2 is released in a gaseous state and can be seen bubbling in the bottle as well as when it passes through and airlock or fills a balloon. In order to successfully grow yeast they need to be in room temperature water and have food. Under these conditions a robust fermentation will usually occur within 24 hours. If these conditions aren't met the yeast will not feed and no bubbling will occur.
Students need to be taught Concept of what separates living things from nonliving things. Undergone general introduction to microorganisms and the scientific method.
1. Use Science Process and Thinking Skills
Hydrometers can be used to measure the density of honey solutions before and after fermentation. The resulting change in density can be used to calculate the amount of CO2 released and the ethanol percentage of the fermented solution.
If sugar is added at a rate of more than 3 grams per 4L the yeast are incapable of completely fermenting the solution because they can not continue to grow in ethanol concentrations above 15%. This could be used to teach students about the impacts and definition of pollution.