Hypothesis:
If the amount of CO2 produced by yeast is related to temperature, then varying temperatures will result in different rates of cellular respiration.
Materials /Apparatus:
∙ 18g sugar ∙ Graduated Cylinder
∙ 18g yeast ∙ 250 mL conical flask
∙ large water supply ∙ 1000 mL beaker
∙ stopper with glass tubing
∙ plastic hose
∙ hot plate
∙ ring stand with ring clamp
∙ balance
∙ pneumonic trough (basin)
∙ thermometer
Procedure:
- A hot bath was set up by filling a 1000mL beaker with 300mL of water and placing it on the hot plate.
- The basin filled with sufficient water. A graduated cylinder was filled with water and flipped upside-down while partially submerged (so that no water escaped from the graduated cylinder). The graduated cylinder was then held steady by the ring stand with a ring clamp. Rubber tubing was then inserted into the graduated cylinder.
- The thermometer was inserted and the temperature was monitor until it reached 23°C (23° should require no heating).
- 3g of sugar and 3g of yeast were prepared.
- The sugar, yeast, and water were mixed together for 5-10 seconds in a 250mL conical flask with a stirring rod. A stopper with glass tubing was then plugged into the conical flask.
- The conical flask was placed into the hot bath and a temperature of 23°C was maintained.
- The amount of displaced water in the graduated cylinder was recorded.
- Steps 3 to 7 were repeated with the temperatures of 30°C, 40°C, 50°C, 60°C, and 70°C.
Data/Observations:
Discussion:
Yeast ferments (or undergoes anaerobic respiration) when supplied with sugar. As we know, anaerobic respiration utilizes the sugars available to produce, in total, 2 ATP molecules, 2 NADH molecules, and 2 unused pyruvates. The reason temperature is usually a factor on enzyme activity and cellular respiration (which involves many enzymes) is because as temperature increases, the atoms consisting of the enzyme move more rapidly throughout the space available to them. Substrate molecules, looking for a place to dock in these enzymes, have an easy time fitting into the enzyme because the enzyme’s shape is less rigid. However, there is a limit to the amount of temperature that can be applied to enzymes until the point where they can no longer function is reached. If an enzyme is heated beyond it’s tolerable limit, the enzyme shape is permanently altered and the enzyme is rendered useless. Therefore too great a temperature causes enzymes to function improperly or not at all, effectively killing the cells.
Based on our lab results, we were able to come to the conclusion that this is true. Enzymes can only function between certain ranges of temperatures, otherwise they denature. Our lab was designed to gauge the amount of CO2 produced from yeast under different temperatures. The more CO2 produced, the more active the enzymes involved in cellular respiration were. According to our results, 50°C is the peak temperature at which yeast works best. All other temperatures ranging from 23°-40° and 60°-70° resulted in smaller amounts of CO2 production. This is agrees with the theory that subjecting the enzymes to high temperatures will denature them, and render the yeast cells dead.
Sources of Error:
There were very few sources of error that occurred during this lab. The only one we noted was that at 70°C, the water inside the conical flask started to evaporate slightly which may have caused a large displacement of water in the conical flask very quickly. This increase, however, stopped several seconds later and not much more water was displaced.
Conclusion:
Yeast absorbs sugar and warm water to produce energy for itself through anaerobic respiration. In this process yeast releases CO2 molecules. The more CO2 produced, the faster the rate of cellular respiration. The amount of CO2 produced by yeast is, in fact, related to temperature, and varying the temperatures will result in different rates of cellular respiration. Yeast works best at 50°C and begins to die near and above 60°C (which is why the amount of CO2 produced at these temperatures is lower than the amount produced at 50°C).