Investigating the Effects of Artificial Sweeteners on Yeast CO2 Production
Fundamental Question: Can organisms use artificial sweeteners as an energy source?
Testable Question: When 1 mL of yeast solution is combined with 1 mL of either sugar or Equal (artificial
sweetener) and monitored for 30 minutes, will the amount of carbon dioxide released differ between the two
treatments?
Background Information:
Many different artificial sweeteners, labeled as “zero-calorie” additives, are available commercially and
industrially that can sweeten foods without increasing calories. These artificial sweeteners allow people to
enjoy foodstuffs such as diet soda, sweetened coffee and sugar-free gum without having to worry about their
daily caloric intake. Because the artificial molecules are thousands of times sweeter than natural sugars, the
packets of artificial sweeteners are usually augmented with a bulking agent (usually dextrose and maltodextrin
or other similar carbohydrates).
Humans are heterotrophic omnivores that derive their energy from the foods they eat. Most of a
person’s caloric intake consists of simple and complex carbohydrates (as well as lipids and, to some extent,
proteins). These carbohydrates (sugars and starches) are metabolized during the process of cellular
respiration as a means of generating ATP for the cell. As a waste product, carbon dioxide gas is produced in
the cells, transported to the lungs and eventually exhaled out of the nose and mouth.
Yeast is a eukaryotic, single-celled fungus that has been used as a model organism for many different
studies (including cancer research). In this lab, the yeast will be used to perform respiration using two
different energy sources: pure cane sugar and the artificial sweetener Equal. By measuring the CO2 released
from the yeast as a waste product, the metabolic activity of the yeast and therefore the efficacy of the
sweetener can be inferred.
Hypothesis: Write an “If…, then…, because…” hypothesis in the space below:
Prediction Graph: Draw a graph of your predicted results (don’t worry about numbers) for both sweeteners.
Protocol: Highlight the verbs and definite articles (with amounts) of the procedure below.
Materials needed: Yeast solution (0.3 g/mL), sharpie, either pure cane sugar solution (0.25 g/mL) or Equal
solution (0.25 g/mL), 1 test tube, test tube rack, 10 mL graduated cylinders, electronic balance, 1 carbon
dioxide probe and bottle, 1 Vernier LabQuest interface, forceps.
Procedure:
1. Turn on the LabQuest interface. Make sure that the CO2 probe is connected to CH1. Verify that the
CO2 probe is toggled to the “low” setting (0 – 10,000 ppm).
2. Wait at least two minutes after plugging the probe into the interface. Check the reading to verify that
the probe is reading approximately 380 ppm. If your value is very different, call over your teacher for
help calibrating.
3. Using the LabQuest stylus, tap the box on the right side of the screen that says “Mode”, “Rate” and
“Duration.” On the next screen, set the following parameters in this sequence:
Mode = Time-based
Duration = 30 min
Rate = 1 sample/min
When you are finished, double check the parameters and units, then tap “OK.”
4. Label your test tube as either S (for sugar) or E (for Equal) with a sharpie.
5. Measure out 1 mL of yeast solution with a graduated cylinder and pour into the test tube.
6. Measure out 1 mL of your assigned test solution (either sugar or Equal) with a graduated cylinder and
pour into the test tube.
7. Carefully place the test tube into the CO2 probe bottle with forceps and insert CO2 probe (connected to
CH1 of the LabQuest interface) into the neck of the bottle so that it seals.
8. Tap the green arrow at the bottom left of the screen to begin data collection. If you want the graph to
autoscale, tap the word “GRAPH” at the top of the screen then “autoscale once”. You can also go into
graph options and toggle “autoscale”. To see the data table, tap the image that has an “X Y” table; tap
the graph symbol to return to the graph. Record your data in the table below:
Data table: Use the data table to record your CO2 concentration (ppm) for 30 minutes.
Time (min)
0
1
2
3
4
5
6
CO2 (ppm)
7
14
Time
(min)
21
8
15
22
29
9
16
23
30
10
17
24
11
18
25
12
19
26
13
20
27
Time (min)
CO2 (ppm)
Time (min)
CO2 (ppm)
CO2
Time
CO2
(ppm) (min) (ppm)
28
Record the class averages of the data from yeast with Equal and yeast with sugar in the table below. Use this
data to calculate change and percent change.
Time (min)
Average CO2 (ppm)
Yeast + Equal
Average CO2 (ppm)
Yeast + Sugar
Initial
Final
Change
Percent change
Analysis and Conclusion:
1. Complete a line graph for your personal lab data. Don’t forget labels, units, title, etc…
2. Did the yeast use Equal as an energy source? Cite specific data from the lab to support your response.
3.
Cite data to determine which sweetener caused the yeast to produce the most CO2 on average?
4.
Was your hypothesis supported or rejected? Use data from the lab to justify your response.
5.
Identify and describe one validity measure and one reliability measure from this procedure.
6. Describe the energy transfer that occurred in the test tube. In your description, be sure to identify the specific
forms of energy before and after the energy transfer and where in the cell the energy transfer happened.