Yeast Respiration Lab Report

What is the Effect of Sugar on Yeast Respiration?

Pre Lab:

1. Yeast is an organism that breaks down molecules like sugar to create energy. It also gives off carbon dioxide as a by-product. This lab observed the relationship between the amount of sugar fed to yeast and the amount of inflation of a balloon attached to the test tube caused by carbon dioxide released as a by-product.

2. In the lab, equal amounts of warm water (⅘ the volume of the test tube) and equal amounts of yeast (2 grams) were placed in three different test tubes. A balloon was placed on each of the test tubes to catch the carbon dioxide that was released. The tubes were observed every two minutes for twenty minutes to check the changes in the balloon diameter and any change within the tubes.

3. The more carbon dioxide that was released caused the balloons to inflate making the diameter larger. This showed how the different amounts of sugar affected the carbon dioxide production of yeast.

4. Independent variable (IV), dependent variable (DV), controlled variables (CV):
IV- time of experiment
IV- amount of sugar
DV- diameter of balloon
CV- brand of test tubes
CV- location of testing
CV- day of testing
CV- amount of warm water
CV- amount of yeast
CV- type of yeast
CV- type of sugar

5. The control

group was test tube one. It received no sugar. Since the test was to see if sugar would affect carbon dioxide production, the control group would have no sugar.

6. Before I started this lab, I believed the tube with the most amount of sugar would produce the most amount of carbon dioxide. I knew that yeast used sugar to create energy, so I thought that the most amount of sugar would yield the most amount of carbon dioxide as a by product.

7. The two characteristics of livings things I knew before this lab were the need for energy and the need to release waste. Anaerobic respiration means it does not need oxygen. Yeast goes through alcoholic fermentation and releases carbon dioxide as waste. In the experiment, this was measured by the diameter of the balloon. Just like yeast, humans also undergo fermentation. We use energy and release waste like carbon dioxide.

Results:

1. Based on the results of the lab, the test tube with 2 grams of sugar, test tube three, produced the most carbon dioxide. All the balloons started at about 11 centimeters. By the end of the twenty minutes, test tube one’s balloon, the tube with no sugar, was still eleven centimeters in diameter, test tube two’s balloon, the tube with 3 grams of sugar, was 13.5 centimeters in diameter, and test tube three’s balloon, the tube with 2 grams of sugar, was 17 centimeters in diameter.

Graphs and Data: (see attached)

The graph shows the results of the three different test tubes and the balloon diameters in centimeters as recorded every four minutes.

Analysis:

1. At the beginning of the experiment, the yeast did not have any bubbles in it, while at the end of the experiment, the yeast in each test tube had bubbles forming and rising to the top of the tube. I did not notice any change in color from the beginning to the end of the experiment. The bubbles were most likely caused by alcoholic fermentation and given off as a by product.

2. The diameter of the experimental groups both increased while the control group balloon did not change. That suggests that the presence of sugar speeds up the process of respiration for yeast.

3. Based on the results, test tubes two and three underwent respiration. They were the only tubes with balloons that inflated. Through respiration, carbon dioxide is released from the yeast. If this process did not happen, then the balloon’s diameter would not increase which was the case for test tube one.

4. When the yeast is added to the mixture to make bread, it consumes the sugar and respires to produces carbon dioxide. The carbon dioxide then rises causing the bread to rise, too.

Conclusion:

From completing this lab, I have learned that in order for yeast to respire, it requires sugar.

The control tube did not have sugar, and it did not produce any carbon dioxide or enough to inflate the balloon at all. On the other hand, the tubes with sugar did inflate the balloons. The lab did not support my hypothesis. I claimed that the tube with the most sugar would produce the most carbon dioxide. The tube with the most carbon dioxide produced was actually tube three with 2 grams of sugar. Test tube two had 3 grams of sugar and ended the twenty minutes with its balloon diameter of 13.5 centimeters. On the other hand, test tube three finished with a balloon diameter of 17

centimeters.

Problems may have arisen during the lab that could have altered the results. Human error like not precise measurements and poor time tracking is a possibility. Although, based on the results of other lab groups and the similarities in results, this is not very likely. I cannot think of any ways that the lab could be improved upon besides the careful watch for human error, but it is always smart to conduct the experiment multiple times to compare results and make sure they are accurate. I learned a great deal about fermentation from this lab. I finally know the importance of east in cooking and how it functions. I also learned that labs can be very fast paced and take a lot of focus to accomplish. It was a good learning experience and interesting experiment.