An Aerobic Exercise: Yeast Metabolism with and without Aeration
|Time Required||Average (6-10 days)|
|Material Availability||Readily available|
|Cost||Low ($20 - $50)|
AbstractThis is a straightforward project on glucose metabolism in yeast. You'll grow yeast under aerobic and anaerobic conditions and measure carbon dioxide output to assess metabolic efficiency.
ObjectiveThe objective of this experiment is to investigate yeast metabolism under aerobic and anaerobic conditions by measuring carbon dioxide output.
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Last edit date: 2017-07-28
Yeasts are single-celled fungi. Like the cells in your body, they can derive energy from sugar molecules. They can also break down larger carbohydrate molecules (like starches present in flour) into simple sugar molecules, which are then processed further.
Yeast can extract more energy from sugar when oxygen is present in their environment. In the absence of oxygen, yeast switch to a process called fermentation. With fermentation, yeast can still get energy from sugar, but less energy is derived from each sugar molecule.
In addition to deriving less energy with fermentation, the end products of sugar metabolism are also different. When oxygen is present, the sugar molecules are broken down into carbon dioxide and water (plus the energy that the yeast uses to grow and reproduce). In the absence of oxygen, the fermentation process produces alcohol, carbon dioxide and water (and less energy).
In this experiment, you'll grow yeast in containers with and without aeration, and compare the amount of carbon dioxide in the two conditions.
Terms and Concepts
To do this project, you should do research that enables you to understand the following terms and concepts:
- Cellular respiration
- Decelles, P. (2002, April 25). Cellular Respiration Overview. Retrieved October 22, 2009, from http://staff.jccc.net/pdecell/cellresp/respintro.html
- Thomson Gale, part of the Thomson Corporation. (2006). Respiration. Science of Everyday Things: Real-Life Chemistry, Volume 5. Retrieved October 22, 2009, from http://www.scienceclarified.com/everyday/Real-Life-Chemistry-Vol-5/Respiration.html
- Carter, J.S., 1996. "Cellular Respiration," University of Cincinnati, Clermont College [accessed January 13, 2006] http://biology.clc.uc.edu/courses/bio104/cellresp.htm
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Materials and EquipmentThese items can be purchased from Carolina Biological Supply Company, a Science Buddies Approved Supplier:
- Graduated cylinder (at least 100 mL). Alternatively, an empty 500 mL plastic bottle may be used.
- Plastic tubing, approximately three times as long as the height of the plastic tub or bucket used. (For a 10 inch tall bucket, you will need 30 inches of tubing.)
- Thermometer to measure water temperature
- Aquarium aerator pump
- Air or oxygen stone
- Dry yeast. Alternatively, it can be found in the baking aisle of the grocery store. Tip: Buying a whole jar is probably more economical than individual packets.
- Plastic tub or bucket
- Optional: Plastic wrap
- Packing tape
- Empty plastic bottle, such as a bottled water container (at least 500 mL)
- A cap that fits the bottle
- Drill or a nail and a hammer
- Epoxy or silicone sealant that works with plastics
- Permanent marker
- Measuring spoon
- Measuring cup
- Warm water, typically 43-46°C (about 110-115°F), but consult the recommendations on your yeast package.
- Sugar (at least ¾ C.)
- Lab notebook
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For health and safety reasons, science fairs regulate what kinds of biological materials can be used in science fair projects. You should check with your science fair's Scientific Review Committee before starting this experiment to make sure your science fair project complies with all local rules. Many science fairs follow Intel® International Science and Engineering Fair (ISEF) regulations. For more information, visit these Science Buddies pages: Projects Involving Potentially Hazardous Biological Agents and Scientific Review Committee. You can also visit the webpage ISEF Rules & Guidelines directly.
- Do your background research.
- You will be collecting CO2 from the yeast by displacing water trapped in an inverted graduated cylinder, as shown in Figure 1, below. Here is how to set it up:
- Fill your plastic tub (or bucket) about one-third full with water.
- Fill the graduated cylinder with water.
- If your tub is big enough, fill the graduated cylinder by tipping it on its side inside the tub. Allow any bubbles to escape by tilting the cylinder up slightly, while keeping it under water. Keeping the opening of the cylinder under water, turn it upside down and attach it to the side of the tub with packing tape.
- If your tub is not big enough, fill the graduated cylinder completely and cover the top tightly with plastic wrap. Quickly invert the cylinder and place the opening in the tub, beneath the surface of the water. Remove the plastic wrap. Attach the cylinder to the side of the tub with packing tape.
- The graduated cylinder should now be upside down, full of water and with its opening under the surface of the water in the tub. It is ready to trap CO2 produced by your yeast.
Figure 1. To create your gas collection apparatus, first fill a bucket or tub about one-third full with water. Then fill a graduated cylinder completely full with water and invert it in the bucket, making sure that there is no air inside the graduated cylinder, and then tape it to the bucket's side. Next, feed the empty end of the plastic tubing from the yeast bottle (on the right) into the opening at the bottom of the graduated cylinder.
- Next, you need a way to bring the CO2 from the yeast to your gas collection apparatus.
- Make a hole in your bottle cap, just big enough to insert the plastic tubing. Use a drill or a nail and a hammer. Get help from an adult if needed.
- Insert a piece of plastic tubing through the hole in the cap so that it sticks out about 2 centimeters (cm), as shown in Figure 2, below. This will be the tube for collecting CO2. It should remain above the surface of the yeast solution.
- Seal the tube to the cap with epoxy or silicone sealant so that it is air-tight. Allow the epoxy or silicone to cure fully before conducting your experiment.
- After the epoxy or silicone has completely cured, which should take approximately one day at most, check to make sure the tube and cap are sealed together with an airtight seal or you may have a leak that could affect your results. If there is a leak, apply more epoxy or silicone sealant and let it completely cure again.
Figure 2. To bring the CO2 from the yeast bottle to your gas collection apparatus, make a hole in the bottle cap and insert the tubing about 2 cm through the top of the cap and into the side that will be inside the bottle. Seal the tubing to the cap airtight with epoxy or silicone sealant and allow it to cure.
- When your gas collection apparatus is ready, you can start the actual experiment.
- Make a data table in your lab notebook to record your data in.
- The conditions you will be testing are with oxygen and without oxygen. You will do at least three trials for each condition.
- Label one bottle "+air" and the other bottle "−air".
- You will be making one solution at a time (unless you decide to set up more than one gas collection apparatus). It is important to use the same water temperature each time you make a solution, since yeast activity is temperature-dependent.
- Test the yeast with a solution that has oxygen.
- Boil 3 cups of water and let the water cool to between 43–46°C (about 110–115°F).
- Dissolve 2 tablespoons (Tbsp.) of sugar in 2 cups of warm water. Stir slowly and gently.
- When the sugar is fully dissolved, aerate the solution with the aquarium aerator pump and airstone, as shown in Figure 3, below. After 5 minutes, stop aerating the solution.
- Next add and mix in 2 teaspoons (tsp.) of yeast (this is about the same amount as 1 packet of yeast).
- Pour the entire solution into the "+air" bottle. Leave space at the top of the bottle, so that your CO2 collection tube remains above the yeast solution. Be sure to note the actual temperature of the water in your lab notebook.
- Cap the bottle tightly with your "tube cap," and place the open end of the collection tube inside your gas collecting cylinder. Note the starting time in your lab notebook.
- There should be water in the tubing as soon as it is submerged in the water. The CO2 gas will push some water out of the tubing before the graduated cylinder starts to fill with CO2 gas.
- Within 5–10 minutes, the yeast solution may start foaming, and you may see bubbles collecting in the graduated cylinder. If you observe them, note the time when you first start seeing bubbles in your lab notebook.
- To promote oxygen circulation in the yeast solution, periodically gently "swirl" the bottle to stir the contents.
- Decide how long to collect CO2 (somewhere between 30–60 minutes is probably good, but you may need to adjust for your particular conditions). Use the same amount of time for all of your tests.
- Note: Do not let the graduated cylinder become completely filled with CO2, but instead stop it before this point. If you let it become completely filled, and the next condition you test makes even more CO2, this could lead to poor and inaccurate results because your graduated cylinder may fill up before your test time is over.
- Tip: If your solution makes a large amount of CO2 very quickly, you can try to make it produce less CO2 by using less sugar and possibly less yeast. For example, you could repeat this step using 1 tsp. sugar (instead of 2 Tbsp.) and 1 or 2 tsp. yeast (instead of 2 tsp.).
- When the time is up, note how much CO2 was collected. Record your results in the data table in your lab notebook.
Figure 3. Aerate 2 cups of warm water with 2 Tbsp. of sugar using the aquarium aerator pump and airstone, as shown here, for 5 minutes.
- Repeat steps 2 and 3 to re-fill your gas collection cylinder and reset your gas collection apparatus. Carefully rinse out the yeast solution from the bottle.
- Repeat steps 8 and 9 at least two more times.
- You should run at least three separate trials for each condition.
- Repeat steps 8–10 but this time test the solution without oxygen by making the following changes:
- Skip step 8c so that you do not aerate the solution.
- Boiling the water should have minimized the dissolved oxygen in the water.
- In step 8e, pour the solution into the "+air" bottle and cap it, placing the open end of the collection tube inside your gas collecting cylinder.
- Skip step 8h, as you do not want to promote oxygen circulation this time.
- Be sure to note the starting time in your lab notebook and, if you observe them, note the time when you first start seeing bubbles in your lab notebook.
- Skip step 8c so that you do not aerate the solution.
- Calculate the average volume of CO2 produced under each condition.
- Analyze your results. Which condition produced more CO2? What is the ratio of CO2 production between the two conditions? Is this consistent with your expectations from your background research?
Communicating Your Results: Start Planning Your Display BoardCreate an award-winning display board with tips and design ideas from the experts at ArtSkills.
- For a more advanced science project, investigate what happens if you double the amount of sugar. You will need to do more background research on yeast metabolism for this science project.
- For other science projects that explore CO2 production in yeast, take a look at:
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