Investigating Cellular Respiration Under Different Variables

Cellular Respiration in Yeast

Purpose

The purpose of this experiment was to teach the students about the effects different variables have on cellular respiration and also to give the students an opportunity to design their own experiment.

Hypothesis

If the concentration of sugar in the water increases, then the yeast will have a faster rate of respiration and therefore will produce more carbon dioxide.

Procedure

• 1. Label three tubes A, B, and C.
• 2. Put 0.5 teaspoons of sugar into test tube A.
• 3. Put 0.75 teaspoons of sugar into test tube B.
• 4. Put 1 teaspoon of sugar into test tube C.
• 5. Add 2 mL of water into each test tube and gently swirl until sugar is fully dissolved.
• 6. Put 0.5 teaspoons of yeast into each test tube.
• 7. Put a balloon over the top of each test tube and immediately begin timing.
• 8. Every four minutes, measure the circumference of each balloon and record the measurement.
• a. If the balloon cannot stand up on its own, do not measure the circumference.
• 9. Continue to measure the balloons until five intervals have passed.

Analysis Questions

1. What do you think would happen to the reaction rate if you increased the temperature of the water?

a. I think that the reaction rate would be faster, because when baking with yeast, the instructions always say to allow the yeast to activate in warm water.

b. Are there any other factors that could alter the rate?

i. Some other factors that could possibly alter the rate of reaction are pH level, the age of the yeast, the quality of the sugar, and the surface area of the yeast cluster.

2. What would happen in the experiment if yeast utilized lactic acid fermentation instead of alcohol fermentation?

a. If yeast utilized lactic acid fermentation instead of alcohol fermentation, none of the balloons would fill because lactic acid fermentation does not produce carbon dioxide.

3. Were there any sources of error in your experiment?

a. Our main source of error was that we did not fully dissolve the sugar into the water in test tubes B and C, which meant that the sugar mostly sunk to the bottom of the test tube and the water stayed on top of the sugar.

b. How would they affect the outcome of your experiment?

i. Because yeast floats in water, after we added the yeast to the test tubes and swirled them, the yeast was still on separated from the sugar by the water in test tubes B and C and therefore it could not perform alcohol fermentation very well. Test tube A was the only test tube where the yeast produced a significant amount of carbon dioxide, meaning that we did not have enough data to find a trend among the different sugar concentrations.

Conclusion

The main idea of this experiment was to see if yeast’s rate of respiration was affected by the amount of sugar that was available. We were unable to find a trend due to inconclusive results, which were the result of a lab error. Test tube A produced enough carbon dioxide to fill a balloon to a 5cm diameter, but the other two test tubes did not produce a measurable amount of carbon dioxide. Thus, our reports can neither support nor disprove our hypothesis because there is no trend in our results.