Respiration Rates by Yeast with Different Sugar Substrates and Temperatures

Aime Rengel, Travis Vickers

CU Boulder, Fall 2002

In this lab we tested the effects of different types of sugar and temperature on the release of CO2 in yeast. Through research, we learned that yeast uses the carbon in the sugar as a source of energy and produces CO2 through respiration. We hypothesized that adding different sugars would affect the rate of CO2 released, and that colder temperatures will decrease the amount of CO2 released by slowing down the yeast’s metabolism.

To test this hypothesis, we mixed 0.63 grams of yeast with 10ml of warm water in a beaker. We then attached a gas probe to measure CO2 and measured the rate of respiration for five minutes; this was our control group. Next we made three more batches like the control group, but added 0.90 grams of a different sugar in each beaker: Equal, cane sugar, and table sugar. We then measured the amount of CO2 released by the different sugar and yeast solutions. Since table sugar is meant for baking, we predicted this would give us the best results when mixed with yeast (highest CO2 release). Conversely, since Equal is basically a fake sugar, we predicted it would have the worst results when mixed with yeast (lowest CO2 release). We also predicted that when the beakers are submerged in an ice bath, the reactions will slow down, causing less CO2 to be released than at room temperature.

According to the t-test the difference between our control group and our mixtures of yeast with Equal (P=0.0008), yeast with cane sugar (P=0.005), and yeast with table sugar (P=0.0002) at room temperature were all significantly different from the control (P<0.05). Also, the difference between our control group and our mixtures of yeast with Equal (P=0.027), yeast with cane sugar (P=0.018), and yeast with table sugar (P=0.018) when placed in an ice bath were significantly different.

Our results are consistent with our predictions. One potential problem with our experimental design was the water temperature while mixing the yeast. We needed hot water, and while we used hot water from the tap, chances are the same temperature wasn’t used every time; and as the ice bath experiment shows, temperature does make a difference. Next time, using a thermometer could help keep all the water used at the same temperature, helping make things more accurate. We were not able to look at different analyses off the CABLE website because we couldn’t find anyone else who had performed this kind of experiment. Since our results show significant differences, we stick to our original hypothesis, both for sugar and temperature. We think that if we ran our tests for ten minutes, instead of five, we would get even more conclusive results. We think that similar experiments performed in the future that compare only natural sugars, like sucrose and fructose, would have a much smaller difference in results.