Investigating the Effects of Artificial Sweeteners on Yeast CO2 Production
Fundamental Question: Can organisms use artificial sweeteners as an energy source?
Testable Question: Write a “When…, while…, will…?” testable question.
Starting information: Use the information below along with information in your textbook to write a
background section for this lab. Use the CHS lab report format.
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 CO 2 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.
Prediction Graph: Draw a graph of your predicted results.
Protocol: Make an illustrated procedure using the steps 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: Create a data table that allows you to record your CO2 concentration (ppm) for 30 minutes.
Create a second data table for class averages of the data from yeast with Equal and yeast with sugar.
Time (min)
CO2 (ppm)
Yeast + ________
0
1
2
etc…
Time (min)
Initial
Final
Change
Percent change
Average CO2 (ppm)
Yeast + Equal
Average CO2 (ppm)
Yeast + Sugar
Your analysis should include…
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A line graph showing the carbon dioxide levels for each test tube
A written summary of your results (qualitative and quantitative data) and a comparison of your results to your
prediction (hypothesis, graph). Include numbers with your quantitative data.
A discussion of the contents of Equal artificial sweetener packets (look at the ingredients). What is in there and
why?
An explanation of the observed results as they relate to cellular respiration and the contents of Equal.
State likely human errors that could have occurred during the experiment and how the experiment could have
been done better.
Your conclusion should include…
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Restating your hypothesis; determining whether your hypothesis is supported by the data or rejected by the
data. Include actual data (e.g. numbers) in this part.
A brief discussion of whether or not the fundamental question has been addressed.
Based on your results, choose two additional questions that could be investigated to better understand the
fundamental question.