Investigating the rate of CO2 production of yeast in various temperatures
Introduction:
Yeast is a eukaryote and can undergo aerobic respiration in the presence of oxygen and produce water and CO2, and it can also undergo anaerobic respiration in the absence of oxygen to produce ethanol and CO2. Some organisms use fermentation as an anaerobic pathway, which is a process that transfers the hydrogen atoms of NADH to certain organic molecules without consumption of oxygen or change in concentrations of NAD+ or NADH (Giuseppe, 2003). Yeast uses ethanol fermentation as an anaerobic way of making ATP. In ethanol fermentation, NADH passes the hydrogen atoms to acetaldehyde which forms ethanol. This process allows NAD+ to be recycled and glycolysis to continue, and produces two ATP. When yeast digests sugar under anaerobic conditions, ethanol (ethyl alcohol) and carbon dioxide are released as shown by the following equation:
C6H12O6 → 2 CH3CH2OH + 2 CO2 + 2 ATP
Hypothesis:
If the yeast is placed in ideal temperature conditions, it will have the highest metabolic rate, and therefore produce the maximum amount of CO2. At temperatures higher or lower than the those of the optimal range, the metabolic rate will be lower.
Procedure:
Five water reservoirs of temperatures 5°C, 15°C, 25°C, 35°C, and 45°C were created by placing one in the freezer for an hour, one in the fridge for an hour, one was left in neutral conditions, one was heated up to 35°C, and the last one was heated up to 45°C. After the desired temperature for each of the reservoirs was reached, a half cup measure was used to measure out half a cup of water from each temperature reservoir into separate identically sized containers. The containers were labelled with their corresponding temperature. In each container, two teaspoons of white table sugar were stirred until dissolved. Then, two teaspoons of active dry yeast were added to the water and sugar solution and stirred for five seconds. A timer was set for five, ten, fifteen, twenty, and twenty-five minutes, and the height of the bubbles formed was measured at these time intervals using a ruler. This procedure was repeated three times.
Results:
Table 1: Height in each container at the 5 minute interval
Height of bubbles produced (mm)
Temperature (°C)
Trial 1
Trial 2
Trial 3
Average
5
0
0
0
0
15
0
0
0
0
25
10
13
09
10.7
35
12
15
14
13.7
45
13
15
10
12.7
Table 2: Height in each container at the 10 minute interval
Height of bubbles produced (mm)
Temperature (C)
Trial 1
Trial 2
Trial 3
Average
5
0
0
0
0
15
5
07
8
6.7
25
12
13
10
8.3
35
27
30
29
28.7
45
35
32
33
33.3
Table 3: Height in each container at the 15 minute interval
Height of bubbles produced (mm)
Temperature (C)
Trial 1
Trial 2
Trial 3
Average
5
3
0
4
2.3
15
10
9
7
8.7
25
14
17
11
14
35
55
57
59
57
45
41
45
48
44.7
Table 4: Height in each container at the 20 minute interval
Height of bubbles produced (mm)
Temperature (C)
Trial 1
Trial 2
Trial 3
Average
5
4
1
4
3
15
11
11
8
10
25
15
17
15
15.7
35
66
70
64
66.7
45
47
50
51
49.3
Table 5: Height in each container at the 25 minute interval
Height of bubbles produced (mm)
Temperature (C)
Trial 1
Trial 2
Trial 3
Average
5
4
2
5
3.7
15
13
11
8
10.7
25
15
17
15
15.7
35
75
79
77
77
45
60
55
59
58
Table 6: Average height of bubble produced in each container at the time intervals
Height of bubbles produced (mm) in each container
Time (minutes)
5°C
15°C
25°C
35°C
45°C
0
0
0
0
0
0
5
0
0
10.7
13.7
12.7
10
0
6.7
8.3
28.7
33.3
15
2.3
8.7
14
57
44.7
20
3
10
15.7
66.7
49.3
25
3.7
10.7
15.7
77
58
Graph 1: height of bubbles produced over time in each temperature reservoir
Discussion:
The results show that the closest temperature out of the ones that were tested is 35°C. This indicates that 35°C is in the optimal range of temperatures that maximize the metabolic rate of enzymes responsible for breaking down sugar in yeast. This is based on the observation that the 35°C environment produced the largest amount of bubbles over time, in comparison to other temperatures on both the higher and lower sides, as seen in the graph. This temperature created the most ideal environment for the enzymes that metabolize the sugar in yeast and therefore resulted in the highest metabolic rate. The higher the metabolic rate, the faster the rate of ethanol fermentation is, which is why the most ideal conditions resulted in the largest production of CO2, since it is a by-product of the process of ethanol fermentation. (Libretexts, 2019)
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The enzymes that catalyze the sugar need specific environments to be able to function. If the conditions are significantly higher in temperature than the accepted range for the enzymes, then the high temperature will denaturize it and prevent it from functioning properly. The yeast in the 45°C environment had a lower metabolic rate than the 35°C one since the temperature was probably too high in this case, and resulted in the denaturing of some of the enzymes. Enzymes will also not function if the conditions are significantly colder than the ideal temperature, since colder temperatures reduce the frequency at which the enzyme-substrate collisions occur and therefore decreasing enzyme activity (Graw, 2019).
The graph shows that temperatures above or below 35°C by 10°C do not lie in the optimal range of temperatures that allow the enzymes to catalyze the sugar at the maximum rate. These results support the hypothesis since the temperature closest to the optimal range of the enzymes’ resulted in the highest metabolic rate.
Around the fifteen minute point, the temperature in the 35°C container had decreased by 3°C and the temperature in the 45°C container had decreased by 5°C. The temperatures in the 5°C and 15°C containers both increased by 4°C at the ten minute mark, and the 5°C container proceeded to increase in temperature by 1°C at the twenty minute mark. This trend was prevalent in all trials, and lead to inaccurate results since the temperature of the water in each container is supposed to be constant and not changing. The constant measuring of the temperature resulted in the agitation of the contents of the containers which resulted in the carbon dioxide collapsing in some trials. This error may have caused skewed results by resulting in an unintended change in the height of bubbles.
To further investigate the exact temperatures that may lie in the optimal range, temperatures ranging from 30°C to 40°C can be tested to see how close their effect on the metabolic rate is to the 35°C container, since any number too far from 35°C appears to have a significantly lower rate of bubble production and therefore lower metabolism. To ensure that the water temperature in each container stays consistent throughout the entire experiment, a water bath can be created with each of the temperatures to minimize temperature changes and also allow temperature measuring in the trial that will not disrupt or agitate the contents since the water bath temperature ca be measured instead.
Yeast uses ethanol fermentation as an anaerobic respiration pathway to make ATP when there is no access to oxygen. In ethanol fermentation, NADH passes its hydrogen atoms to acetaldehyde, a compound formed when a carbon dioxide molecule is removed from pyruvate by the enzyme pyruvate decarboxylase. This forms ethanol. The two ATP molecules produced satisfy the yeast’s energy needs, and the ethanol and carbon dioxide are released as waste products.
Under normal conditions, animals such as humans catabolize glucose by aerobic respiration. However, during strenuous exercise, muscle cells use up glucose faster than oxygen can be supplied. To allow the recycling of NAD+ and glycolysis to continue when oxygen is not available, homo sapiens use a form of fermentation called lactic acid (lactate) fermentation. In lactate fermentation, lactic acid is produced from glucose, and NADH is oxidized to NAD+ in the process, allowing glycolysis to continue. (Giuseppe, 2003)
Lactic acid is a by-product of fermentation. The build-up of lactate in the cells will eventually limit the amount of fermentation that can occur. The only way to get rid of lactic acid is through a pathway that requires oxygen. Which is why after a quick sprint a runner might go through period of heavy breathing to deliver enough oxygen to cells in order to clear the lactic acid build up (Giuseppe, 2003). Human muscle cells make ATP through lactic acid fermentation since alcohol fermentation produces ethanol that is a potential toxin and might kill the cells (Yavorski, 2019).
In aerobic respiration, oxygen is used to oxidize glucose molecules, and occurs in four stages: glycolysis, pyruvate oxidation, the Krebs cycle, and the electron transport chain and chemiosmosis. This process yields a net of 36 ATP and also produces carbon dioxide and water as shown by the following equation:
C6H12O6 + 6O2 6CO2 + 6H2O + 36 ATP
Anaerobic respiration stops producing ATP after breaking the 6-carbon glucose into two pyruvate molecules, releasing only two ATP which is significantly lower than the amount produced by aerobic respiration. Cellular respiration produces ATP at a slower rate by breaking the glucose down to CO2 and producing a net of 36 ATP, which is 34 more ATP than fermentation Therefore, aerobic respiration is much more effective at making energy. (Britannica, 2018)
Works Cited
Britannica, T. E. (2018, February 08). Cellular respiration. Retrieved from https://www.britannica.com/science/cellular-respiration
Giuseppe, M. D. (2003). Nelson biology 12. Toronto: Nelson Education.
Graw, M. (2019, March 02). What Are the Effects of Boiling & Freezing on Enzyme Activity? Retrieved June 14, 2019, from https://sciencing.com/effects-boiling-freezing-enzyme-activity-23207.html
Libretexts. (2019, June 05). 18.5: Fermentation. Retrieved June 14, 2019, from https://bio.libretexts.org/Bookshelves/Microbiology/Book:_Microbiology_(Kaiser)/Unit_7:_Microbial_Genetics_and_Microbial_Metabolism/18:_Microbial_Metabolism/18.5:_Fermentation
Yavorski, K. (2019, March 25). What Is Alcoholic & Lactic Acid Fermentation? Retrieved from https://sciencing.com/alcoholic-lactic-acid-fermentation-5635612.html
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