Investigation Of Factors That Affect Carbon Dioxide Production In Yeast

Research Questions:

1. What is the optimal temperature for yeast to metabolize sugars?

2. What is the sugar that is most readily metabolized by yeast? Are there any sugars that yeast cannot metabolize?

3. What is the optimal concentration of sugar (in 60 mL of water) for yeast?

Results:

The amount of carbon dioxide (CO2) produced by yeast in various conditions (independent variables: temperature, sugar type, and sucrose concentration) was recorded and is shown in the table below. The table also contains the processed data of the average amount of CO2 produced by yeast under different conditions and the standard deviations for those sets of data.

* Data Point is not included in the calculation of the Mean and Standard Deviation.

(See Evaluation for detail)

1. Processed Data (Mean and Standard Deviation) are highlighted in purple.

2. Some data points were recorded only to the first decimal place (color-coded in brown) depeding on the executing groups.

Data Processing:

1. Mean is calculated by dividing the sum of all the data points by the number of data points.

2. Standard Deviation (S.D.) is calculated by using the formula STDEV in Excel.

Graphs:

Figure 1:

Note for Figure 1:

Through the observation of the error bars of Fructose and Sucrose bar graphs, it is difficult to determine if there is a significant difference between the means of these two sets of data. Therefore, a two-tailed t-test was conducted by using the formula TTEST in Excel . Since the p-value is equal to 0.003, it indicates that there is a lower than 0.05 probability (5% chance) that the two sets of data are from the same population. As a result, it can be concluded that the two sets of data are significantly different.

Figure 2:

Figure 3:

Conclusions:

The immediate conclusions that can be drawn from the results in accordance to the collective data are that the optimal temperature for yeast to metabolize sugars is in the range between 40.00C and 50.00C (Figure 2), fructose is the type of sugar that is most readily metabolized by yeast (Fig. 1), and the optimal concentration of sugar (sucrose, in 60 mL of water) for yeast is indeterminable though it is clearly shown that sugar is necessary for yeast to undergo mentabolism (Fig. 3).

The Type of Sugar factor

The results shown in Figure 1 indicate that yeast most readily metabolize fructose. A two-tailed t-test was conducted the ensure that there is a significant difference between the two sets of data (Fructose and Sucrose). The result of the t-test shows that the two sets of data are significantly different (more detail in Note for Figure 1/Page 3). A conclusion can be drawn that fructose is the type of sugar that yeast metabolize best. There is also a significant different between the lactose set of data and any of the other sets of data. There is not a significant difference between sucrose and glucose (conclusion drawn from the observations of the error bars of the two bar graphs of sucrose and glucose). Therefore, the significance between the two sets of data is not significant enough to make a comparison. Sucrose, as a disaccharide, is harder to be metabolized than Fructose. Similarly, starch, as a polysaccharides, is also harder to be metabolized than Fructose. In addition, strach is degraded by the enzyme amylase, which is found with very limited quantity in yeast. Lactose needs to be broken down by the enzyme lactase only, which is scarcely found in many types of yeast. Therefore, lactose is least metabolized by yeast.

The Temperature factor:

Through the observation of Figure 2, the volume of carbon dioxide produced increases with a steep slope at temperature from 20.00C to 40.00C. At temperatures from 50.00C to 70.00C, the amount of CO2 produced decreases drastically (from 31.68 cm3 to 2.80 cm3). The value for the optimal temperature for yeast to metabolize sugar appears to be in between 40.00C and 50.00C. Because the error bars of the two data points (at 40.00C and 50.00C ) overlap, the two sets of data are not significantly different. Therefore, they can be treated as one whole population of data. In conclusion, the optimal temperature for yeast to metabolize sugars is in the range between 40.00C and 50.00C. However, this conclusion is rather subjective to the limited data collection. (See Evaluation for more details)

With an increasing temperature from 10.00C to 40.00C, the reactions in which yeast respire and produce CO2 are facilitated with more energy that comes from heat, which happen faster and as a result, more CO2 is produced in the same amount of time (20 minutes). However, when the temperature exceeds the thermal tolerance of the yeast, the yeast will disintegrate and therefore, the reactions are slowed down. As a result, the production of carbon dioxide decreases. This result resembles the same trend of the effect of temperature on enzyme activity. Enzyme activity rate increases along as the temperature increases and decreases rapidly when the temperature reaches and exceeds the optimal temperature because denaturation happens. Yeast metabolize sugar with the majority of help coming from enzymes explains the resemblance between the two trends.

The Sucrose Concentration factor:

Because there is no significant difference between most of the data sets (with the exception of the data set of 0.0g sugar concentration), no definite conclusion can be drawn from this part of the experiment. Though the optimal sugar concentration may exist, it is not possible to be determined through the results shown in Figure 3. The expected trend for the optimal sugar concentration is similar to the trend of substrate concentration in enzyme activity. When the optimal concentration is reached, the reaction rate will not change anymore but stay at a constant rate. This phenomenon can be explained as when the optimal concentration is reached, all the yeast that are working in the sugar solutions are occupied, therefore, exceeding amount of sugar added in does not change the plateau that the reaction rate has reached.

Application of the knowledge gained from this experiment:

Yeast are most used in baking and the process of alcohol making. Knowing the best conditions for yeast to ferment and produced wanted products (ethanol and CO2) can be beneficial in the application of yeast in baking and wine making. For example: setting the right temperature for the dough that has yeast in it can maximize the amount of CO2 produced by yeast and minimize the amount of yeast used.

Evaluation:

Weaknesses, limitations, and further improvements:

The experiment was not conducted in an ideal environment and condition. Therefore, the occurrence of weaknesses and limitations is inevitable in this particular experiment.

The data at some sections did not show consistency and precision. Four data points, which show obvious inaccuracy and imprecision, were excluded from the calculation in order to enhance the precision of the results. The imprecision of these four data points could be the result of the leakiness in the tubes or the contamination of the flasks. There are two sets of data that have relatively high standard deviation (7.0 g sucrose solution and 9.0 sucrose solution with S.D. of 17.53 and 16.45 respectively). Their high S.D. values make the data sets overlap with most of the rest of the data in the same section, resulting in an unclear set of data. Half of the data (3 values for each set) collected on the first day of the experiments show precision to each other but not to the values collected the day after.

Therefore, it is impossible to determine which part of the data set should be excluded from the calculation since it is indeterminable which part of the data is more accurate. An improvement for data precision and accuracy can be made by increasing the numbers of data values collected from 6 to 20 or more data points per condition so that the imprecise data points could be easily identified and excluded from the calculation. Specifically, in the case of this experiment, if there were more data values collected, the imprecise subset of data of the 7.0 g and 9.0 g sucrose solution data sets could be easily identified and excluded.

Another weakness of the experiment lies on the execution of the experiment and the equipment. The amalgam of water, sugar, and yeast was mixed by 3 shakes, which is not considered a valid constant because it was rather difficult to maintain the same shake for more than 3 times. This can be improved by having a designated member to do the shake for all the samples. The glassware was not properly cleaned, which left sugar or yeast in the flask, and therefore, resulted in the inaccurate measurement of yeast and sugar in the following trials. Students could improve by being more cautious about this and prepare the glassware more carefully. The glassware should be thorougly cleaned after an experiment or trial and double-checked before starting a new experiment or trial. There should be no clumps of yeast or sugar left in the flasks or beakers before and after an experiment or trial. During the setting up of equipments, students should be make sure that the rubber stops are carefully fastened to prevent any gas leak.

The limitation of the data collecting process can be improved by shortening the interval between the point of data. For the experiment on the effect of temperature on the gas production by yeast, the interval between tested temperature should be shortened from 10. 00C degrees to 5. 00C degrees and kept constant through out the whole experiment, unlike in this orginial lab, in which the interval is increased from 10. 00C degrees to 20. 00C degrees (40. 00C – 50. 00C – 70. 00C). For the experiment on the effect of sugar concentration on gas production by yeast, the interval between sugar concentration

should also be shortened and kept constant at 0.5 g or 1.0 g through out the entire experiment, depending on the availabity of time and supply. For the experiment on the effect of different types of

sugar on gas production by yeast, more types of sugar from each group of monosaccharides, disaccharides, and polysaccharides can be added, for examples: galactose and glycogen.

The majority of the collected data shows relevance, which indicates that the lab went well overall. However, if the weaknesses and limitations mentioned above are taken into considerations for the next experiments, improvement on the data collecting process and lab design could be made.