Gas from yeast metabolism

This assignment is worth 30 points.
Important note: Do not attempt this activity until after you have completed the lessons on aerobic cellular respiration and fermentation (Lessons 5C-5E). They provide the necessary background. This lab takes approximately 4 hours to complete, including prep time.
Also, please note that you will not receive any credit on this assignment if you do not submit all of the required photos as documentation of your completion of the activity. You will be prompted when it is time to take your first photo.
Learning outcomes
• Using a hands-on approach, measure the amount of alcoholic fermentation of sugar by yeast within a sealed container (an anaerobic environment), by looking at how much carbon dioxide is produced.
• Based on the amount of sugar in an unknown solution, be able to predict whether or not the yeast will succeed in doing enough fermentation to make a balloon stand upright.
Required materials
Figure A5-1: The required materials include large balloons, 16.9 ounce water bottles, sugar, active dry yeast, measuring spoons, and materials for making labels and funnels.
You will need the following:
• Six, empty, 16.9 ounce water bottles and caps (if you use larger or smaller bottles, you will need to adjust your measurements of sugar, yeast, and water; 16.9 ounce work best; all six of your water bottles must be exactly the same size)
• Six, round helium quality balloons (9 inch balloons work best, but if you can’t find those, do not use anything smaller than 6 inches or bigger than 12 inches; color does not matter)
• Measuring spoons and cups (you will need a way to measure a half teaspoon and one quarter cup)
• 3 pack of active dry yeast (it is usually found on the baking aisle near the flour; note: do not buy “rapid rise, highly active yeast” — it does not work for this experiment!)
• Table sugar (one quarter cup; raw sugar will work, too)
• Access to a sink that can provide warm water and microwave to warm your test solutions
• Choice of three of the following to serve as test solutions: flat regular soda (allow it to go flat to remove the bubbles), apple juice, orange juice, milk, lemonade, other fruit juice, energy drink, vitamin water, Gatorade, black coffee, or diet soda; if you use anything with carbonation (“bubbles”) allow it to go flat before using; be sure to choose at least one solution that contains a lot of sugar, so that you can expect at least one bottle to produce carbon dioxide gas
• Paper towels (a few)
• Digital camera for taking photos, and a way to transfer those photos to your computer for uploading with your assignment
• A picture identification card (e.g. Pima school ID or driver’s license) to include in your photo documentation
• A pen, paper, tape, and pair of scissors for creating labels for your photos
• Tape, paper, and a pair of scissors to make funnels; if you have real funnels, feel free to use those instead
Introduction
Yeast cells have a major impact on our lives. Much of this impact has to do with the products that yeast cells make, such as alcohol and carbon dioxide. For example, without the carbon dioxide from this process we would not have bread. Yeast, humans, and other living organisms break down high-energy molecules, such as sugar, to get the energy they need, and give off a gas called carbon dioxide as a by-product of the reaction. You will test whether or not yeast can metabolize the sugar found in various beverages, thus producing a gas which we will presume is carbon dioxide. You will measure gas production by the ability of the gas to inflate a balloon to the point at which it can stand straight up.
YouTube instructional video
The following YouTube video demonstrates what you can expect to see in your experiment when yeast is combined in a bottle with warm water and an adequate amount of sugar. Note that the video is sped up such that you see in one minute what would usually take about an hour to complete. It is clear that the balloon is not inflated at the beginning of the video (it points downward), slowly inflates during the course of the one minute video, and then is inflated enough to point straight up by the end of the video. This indicates that the yeast metabolized the sugar, thus creating the carbon dioxide which inflated the balloon. There is no audio and the description that I have already provided serves as the video transcript.
YouTube Video: A demonstration of a balloon inflating as a result of the carbon dioxide that is created during yeast metabolism of sugar.
Setting up your yeast metabolism experiment
Step 1: Make your funnels.
Figure A5-2: Use a piece of paper, scissors, and tape to create two funnels.
To make a funnel, cut a trapezoid shape out of a piece of paper, fold it into a funnel shape, and tape the sides together. You need to make two funnels. If you have real funnels, feel free to use those instead.
Step 2: Check your balloons for holes.
Figure A5-3: Blow up your balloons to test them for holes or cuts.
Blow up each of 6 to 8 balloons to test them. Do not tie off the balloons. Testing a few extra balloons won’t hurt. You need at least 6 good ones. Make sure that no air escapes from them. Discard any that have a hole or cut.
Squeeze the balloons that you have selected to keep to make sure that there is no air remaining in them. We want to start with completely empty balloons.
Step 3: Label your bottles.
Figure A5-4: This bottle is labeled “A”.
Using a piece of paper, scissors, a pen, and tape, create different labels for each of your six water bottles. Label them A, B, C, D, E, and F.
Your hypotheses
Come up with a hypothesis for each of your six test bottles in terms of whether or not they will produce carbon dioxide gas, thus making the balloon inflate and stand straight up:
• Bottle A will contain yeast, sugar, and water. It is what is referred to as a positive controlbecause we know that the yeast will metabolize the sugar and form carbon dioxide gas.
• Bottle B will contain sugar and water only. It is what is referred to as a negative controlbecause we know that in the absence of yeast there will be no metabolism of the sugar to form carbon dioxide gas.
• Bottle C will contain yeast and water only. It is also what is referred to as a negative controlbecause we know with that in the absence of sugar the yeast will not be able to do metabolism and form carbon dioxide gas.
• Bottles D-F are your treatments. They will contain three different test solutions of your choice (see required materials list for choices). Be sure to choose at least one solution that has a lot of sugar, so that you can expect at least one bottle to make gas. Consider what you know about the sugar content of the solutions and take your best, educated guess for each situation.
Here is an example of a properly worded hypothesis for bottle A: (start by saying, “I hypothesize that…”)
• Bottle A: I hypothesize that yeast, sugar, and water will produce carbon dioxide gas, thus making the balloon inflate and stand straight up.
In a computer document, record your 6 different hypotheses for the 6 different bottles (A-F). Be sure to refer to the bottle letters and include the names of the test substance(s) in each bottle. You will be submitting your hypotheses with your assignment in the Assignment 5 dropbox when you are done with the activity.
Fill your bottles and begin the experiment
Open all three of your yeast packets and pour their contents into a small bowl. You will use a half teaspoon to measure out your yeast servings.
If you chose to use smaller water bottles, you will need to adjust the amount of sugar in bottles A and B. For example, if you are using 8 ounce bottles, you will need to cut the amount of sugar in half. Use the same amount of yeast, however. Use a half teaspoon no matter what the size of the bottle, unless you use really large bottles. If you use larger bottles, then you would either need to double the amount of yeast and sugar, or double the amount of time that you run the experiment. If you decide to double the amount of yeast, you would need to buy another 3 pack. There is not enough yeast in a single 3 pack to do 1 teaspoon per bottle. Thus, I highly recommend either using the suggested 16.9 ounce bottles, or doubling the amount of time that you run the experiment if you only have larger bottles available.
Bottle A: Fill your bottle one third full with warm water from your tap. Don’t make it very hot. It just needs to be warm. Using one of your funnels, pour a half teaspoon of yeast into the bottle. Then, using your other funnel, pour one quarter cup sugar into the bottle. Keep track of which funnel is which for future use (you may want to label one of them “yeast”). You will be using each of the funnels again, and we don’t want cross contamination of yeast and sugar.
Put the cap on the bottle and shake vigorously for about 5 seconds. Take off the cap and fill the bottle again with warm water until it is about three quarters full. Don’t fill it all the way to the top because the gas will cause expansion of the liquid. We don’t want the liquid to enter the balloon during the course of the experiment. Shake the bottle again for about 5 seconds. Remove the cap from the bottle.
Figure A5-5: After being filled with the test solution, a balloon is placed on top of the bottle.
After taking off the cap, squeeze out all of the air from a balloon, and then carefully place the balloon over the opening of the top of the bottle. Be sure not to cut into the balloon.
Bottle B: Fill your bottle one third full with warm water from your tap. Don’t make it very hot. It just needs to be warm. Using the sugar funnel, pour one quarter cup sugar into the bottle. Put the cap on the bottle and shake vigorously for about 5 seconds. Take off the cap and fill the water bottle again with warm water until it is about three quarters full. Don’t fill it all the way to the top because the gas will cause expansion of the liquid. We don’t want the liquid to enter the balloon. Shake the bottle again for about 5 seconds. Take off the cap, squeeze out all of the air from a balloon, and then carefully place the balloon over the opening of the top of the bottle. Be sure not to cut into the balloon.
Bottle C: Fill your bottle one third full with warm water from your tap. Don’t make it very hot. It just needs to be warm. Using the yeast funnel, pour a half teaspoon of yeast into the bottle. Put the cap on the bottle and shake vigorously for about 5 seconds. Take off the cap and fill the water bottle again with warm water until it is about three quarters full. Don’t fill it all the way to the top because the gas will cause expansion of the liquid. We don’t want the liquid to enter the balloon. Shake the bottle again for about 5 seconds. Take off the cap, squeeze out all of the air from a balloon, and then carefully place the balloon over the opening of the top of the bottle. Be sure not to cut into the balloon.
Bottle D: Using your microwave, warm your solution a little. Don’t do this for too long. You don’t want it to be hot! It should be about as warm as the water that you used for bottles A-C. Fill your bottle one third full with your warm, chosen test solution. Using the yeast funnel, pour a half teaspoon of yeast into the bottle. Put the cap on the bottle and shake vigorously for about 5 seconds.
Take off the cap and fill the bottle again with your test solution until it is about three quarters full. Don’t fill it all the way to the top because the gas will cause expansion of the liquid. We don’t want the liquid to enter the balloon. Shake the bottle again for about 5 seconds. Take off the cap, squeeze out all of the air from a balloon, and then carefully place the balloon over the opening of the top of the bottle. Be sure not to cut into the balloon.
Bottles E and F: Repeat the procedure for Bottle D, using your two other chosen test solutions.
After about 45 minutes or more, watch as some of your balloons begin to inflate! Others should not inflate. Run your experiment for about 3 hours, or more if it seems like some of the balloons just need a little more time to stand straight up. Once it is clear which bottles will make the balloons inflate to a point where they are standing up straight, you can stop. Do not run it over night.
Activity questions
Answer the following questions in your computer document. You will be submitting them with your assignment in the Assignment 5 dropbox when you are done with the activity. You may need to refer back to Lesson 5E to find some of the answers.
1. Consider a favorite food or drink that you think may be a product of fermentation. Using the Internet as your source, research the method by which your food or drink is fermented, including the main steps. Summarize what you found in at least three to five sentences, and give me the URL source that you used to get the information. Don’t just copy their information into your answer. That won’t receive any credit. Put your answer in your own words! Be sure to also include the name of the organism that does the fermentation (e.g. specific name of the bacteria, fungus, or other organism). If you find that your chosen food or drink does not involve fermentation, choose another one that does and start over.
2. During alcoholic fermentation, when is NAD+ converted to NADH — during the conversion of glucose to pyruvate (glycolysis) or during the conversion of pyruvate to alcohol?
3. During alcoholic fermentation, when is NADH converted back into NAD+ — during the conversion of glucose to pyruvate (glycolysis) or during the conversion of pyruvate to alcohol?
4. During alcoholic fermentation, when is the carbon dioxide gas produced — during the conversion of glucose to pyruvate (glycolysis) or during the conversion of pyruvate to alcohol?
5. In what way are alcoholic fermentation and lactic acid fermentation different (hint: look at the end product of each)?
6. If yeast has access to an adequate amount of sugar, and it is in a closed container with a solution at an adequately warm temperature, would you expect the yeast to produce gas? If so, what type of gas? By what process — alcoholic fermentation or lactic acid fermentation?
How are your bottles doing? Do you see any balloons starting to inflate?
If 3 hours have not yet passed since you started your bottles, this might be a good time to take a break.
Document your experimental results
After at least 3 hours have passed, you can stop your experiment. Record in your computer document whether or not each of the six different bottles ended up with balloons that are inflated enough to stand up straight. They must stick straight up to count. Otherwise, consider them uninflated.
It is now time to take a digital photo to document your results for bottles A-C. See example below. The photo must clearly show your three, labeled test bottles (A-C) and balloons at the end of the experiment, and a copy of your photo ID (e.g. Pima school ID or driver’s license) containing both your picture and your name. If you end up using your driver’s license, be sure to cover up your personal information, such as your driver’s license number, address, and signature. You don’t need to include yourself in this initial photo.
Figure A5-6: You need to obtain a picture showing your three labeled, test bottles (A-C) and balloons, along with your photo ID, as documentation of your completion of this part of the activity.
Note that in my example Bottle A has an inflated balloon, indicating that carbon dioxide was produced, whereas Bottle B and Bottle C do not have inflated balloons, indicating that carbon dioxide was not produced.
It is now time to take a digital photo to document your results for bottles D-F. See example below. The photo must clearly show your three, labeled test bottles (D-F) and balloons at the end of the experiment, and a copy of your photo ID (e.g. Pima school ID or driver’s license) containing both your picture and your name. If you end up using your driver’s license, be sure to cover up your personal information, such as your driver’s license number, address, and signature. You don’t need to include yourself in this initial photo.
Figure A5-7: You need to obtain a picture showing your three labeled, test bottles (D-F) and balloons, along with your photo ID, as documentation of your completion of this part of the activity.
Note that in my example Bottle D and Bottle E have inflated balloons, indicating that carbon dioxide was produced in both cases, whereas Bottle F does not have an inflated balloon, indicating that carbon dioxide was not produced.
Take one more photo that includes yourself in the picture. This photo must clearly show your results and YOU. Do the best that you can to get as many of the bottles as possible in the picture with you. Feel free to either take the picture yourself or have someone else take the photo.
Figure A5-8: You need to also obtain a picture of yourself with your experimental results (bottles and balloons after 3 hours) as documentation of your completion of this part of the activity.
A note about replication
I would like to take the time now to mention something about replication. This relates to what you learned about the scientific method in Module 1. One major problem with the way that you conducted this experiment is your lack of repetition or replication (this was also an issue for Assignments 3 and 4). For example, in this experiment your sample size was equal to only one because you only had one bottle to represent each situation. This is bad because you don’t know the extent of variation for each of the test solutions. Perhaps what happened in your Bottle D sample is different than what might happen in another Bottle D sample.
The way to avoid this potential problem is to have replication in your data, or increase your sample size, so that you account for possible variation. This helps to lower sampling error, or the effect of chance on our experimental results. It is always best to keep sampling error as low as possible, and the best way to do so is to have a large sample size!
In order to avoid confusion, save time, and get good results, we used sample sizes of one in our experiments. In a real scientific experiment you would need to have much larger sample sizes. For example, in this yeast metabolism activity you would probably want to run at least 10 different treatments or controls for each bottle type (e.g. 10 control bottles of the Bottle A ingredients, 10 treatment bottles of the Bottle B ingredients, etc.). Thus, what you did was more a “demonstration” than an actual scientific “experiment.”
End of the activity questions
Answer the following questions in your computer document. You will be submitting them with your assignment in the Assignment 5 dropbox when you are done with the activity.
7. Based on your results, did you support or reject your hypothesis for Bottle A? Explain.
8. Based on your results, did you support or reject your hypothesis for Bottle B? Explain.
9. Based on your results, did you support or reject your hypothesis for Bottle C? Explain.
10. Based on your results, did you support or reject your hypothesis for Bottle D? Explain.
11. Based on your results, did you support or reject your hypothesis for Bottle E? Explain.
12. Based on your results, did you support or reject your hypothesis for Bottle F? Explain.
13. Based on the known sugar content, did any of your chosen test solutions (D-F) turn out differently than you expected? Why did you think that it (they) should or should not have produced gas? Can you think of anything that might have gone wrong in your experiment (e.g. not measuring correctly, not warming the solution enough, not running the experiment for long enough, a hole in the balloon, etc.)?
If you used fruit juice, soda, or another sugary beverage for one or more of your chosen test solutions (D-F), you probably noticed that the yeast reacted just as well with your treatment as it it did with the positive control, which contained yeast and a quarter cup of sugar. That gives you an idea of how much sugar is actually in these beverages. Many of these drinks contain a lot of sugar!
Dump the contents of your bottles down your sink and rinse out your bottles thoroughly. Note the “yeasty” smell. It will remind you of sourdough. So that your home does not start to smell, dispose of the bottles promptly.
Your evaluation of the activity
1. Did the activity help you to understand the concept of yeast metabolism and fermentation?
2. Are the directions for the activity clear?
3. What part of the activity was confusing?
4. Include any suggestions you have to improve this activity.
Thanks for your input.
It is now time to upload your computer document containing your six hypotheses, your documentation photos (3), and your answers to the activity questions (#1-13) in the Assignment 5 dropbox.
Feel free to include the documentation photos in your computer document, or you can send them as separate file(s).
Congratulations! You are now done with this activity!
You will not receive any credit for this assignment if you do not submit all of the required photos
Grading criteria