Experiment 1 Fermentation by Yeast Experiment Inventory Labware (4) 250 mL Beakers (1) 100 mL Graduated Cylinder (1) Test Tube Rack (5) Fermentation Tubes = (10) Test Tubes (5 plastic and 5 glass; see Figure 4) (1) Measuring Spoon (4) Pipettes (1) Ruler Note: You must provide the materials listed in *red. EXPERIMENT 1: FERMENTATION BY YEAST Yeast cells produce ethanol, C2 H6 O, and carbon dioxide, CO2 , during alcoholic fermentation. In this experiment, you will measure the production of CO2 to determine the rate of fermentation in the presence of different carbohydrates with fermentation tubes. Note: Regular table sugar is sucrose, a disaccharide, which is made up of glucose and fructose. Glucose is a monosaccharide. Figure 4: Fermentation tubes. Note how the smaller, plastic test tube is inverted into the larger glass tube. You will create five fermentation tubes in this experiment. PROCEDURE 1. In this experiment, you will mix yeast with sugar, Equal®, and Splenda®. Before you begin, develop a hypothesis predicting what will happen when the sugar/sweeteners are mixed with yeast. Will fermentation occur? Why or why not? Record your hypothesis in the post-lab questions. 2. Use the permanent marker to label three 250 mL beakers as Equal®, Splenda®, and Sugar. 3. Empty the Equal®, Splenda®, and Sugar packets into the corresponding beakers. 4. Fill the Equal® and Splenda® beakers to the 100 mL mark with warm tap water. 5. Fill the Sugar beaker to the 200 mL mark with warm tap water. 6. Mix each beaker thoroughly by pipetting the solution up and down several times. Use a new pipette to mix each solution. Each beaker now contains a 1% solution. Set these aside for later use. 7. Completely fill one of the smaller plastic tubes with tap water and invert the larger glass tube over it. Push the small tube up into the larger tube until the top connects with the bottom of the inverted tube. Invert the fermentation tube (Figure 4) so that the larger tube is upright (there should be a small bubble at the top of the internal tube). Note: Repeat Step 7 several times as practice. Strive for the smallest bubble possible. When you feel comfortable with this technique, empty the test tube(s) and proceed to Step 8. CAUTION: Do not try to force the plastic test tube into the glass test tube. This might cause your glass test tube to break, causing you injury. If your plastic test tubes do not fit easily, please call eScience Labs for replacement glass tubes. If you are able to set up at least two fermentation tubes, continue with the experiment, but know that you will have to perform steps 12-15 in multiple steps. 8. Use the permanent marker to label the fourth 250 mL beaker as Yeast. 9. Fill this beaker with 175 mL of warm tap water. It should be between 30 and 40o C (warm to the touch). 10.Open the yeast package, and use the measuring spoon to measure and pour 1 tsp. yeast into the beaker. Pipette the solution up and down until all of the yeast is mixed homogenously into the solution. Note: Make sure the yeast solution remains homogenous before each test tube is filled in the proceeding steps. The yeast density is fairly high, and the yeast may settle to the bottom of the beaker if it rests for an extended period of time. 11. Use the permanent marker to label the big glass and small plastic test tubes as 1, 2, 3, 4, and 5. 12.Use the 100 mL graduated cylinder to measure and pour 15 mL of the following solutions into the corresponding small plastic test tubes: Tube 1: 1% Glucose Solution Tube 2: 1% Sucrose Solution Tube 3: 1% Equal® Solution Tube 4: 1% Splenda® Solution Tube 5: 1% Sugar Solution Note: Thoroughly rinse the graduated cylinder between each measurement. 13.Fill the remaining volume in each small tube to the top with the yeast solution. 14.Slide the corresponding larger tube over the small tube and invert it as practiced in Step 7. This will mix the yeast and sugar/sweetener solutions. 15.Place the fermentation tubes in the test tube rack, and use a ruler to measure (in millimeters) the initial air space in the rounded bottom of the internal tube. Record these values in the Table 1. 16.Allow the test tubes to sit in a warm place (approximately 30 °C) for two hours. Placement suggestions include: a sunny window sill, atop (not in!) a warm oven heated to approximately 85 °C (185 °F on an oven setting), or under a very bright (warm) light. 17.At the end of the fermentation period, use your ruler to measure (in millimeters) the final gas height (total air space) in each tube. Record this data in Table 1. 18.Calculate the difference between the initial and final gas height in each tube. Record this data in Table 1.
EXPERIMENT 1: FERMENTATION BY YEAST
Result Tables
Table 1: Yeast Fermentation Data
Tube
Initial Gas Height (mm)
Final Gas Height (mm)
Net Change (mm)
1
2
3
4
5
Post-Lab Questions
Include your hypothesis from Step 1 here. Be sure to include at least one piece of scientific reasoning in your hypothesis to support your predictions.
Did you notice a difference in the rate of respiration between the various sugars? Did the artificial sugar provide a good starting material for fermentation?
Was anaerobic fermentation occurring? How do you know (use scientific reasoning)?
If you observed respiration, identify the gas that was produced. Suggest two methods you could use for positively identifying this gas.
Hypothesize why some of the sugar or sweetener solutions were not metabolized, while others were. Research the chemical formula of Equal® and Splenda® and explain how it would affect yeast respiration.
How do the results of this experiment relate to the role yeast plays in baking?
What would you expect to see if the yeast cell metabolism slowed down? How could this be done?
Indicate sources of error and suggest improvement (for example, what types of controls could be added?).
Experiment 1 Fermentation by Yeast Experiment Inventory Labware (4) 250 mL Beakers (1) 100 mL Graduated Cylinder (1) Test Tube Rack (5) Fermentation Tubes = (10) Test Tubes (5 plastic and 5 glass; see Figure 4) (1) Measuring Spoon (4) Pipettes (1) Ruler Note: You must provide the materials listed in *red. EXPERIMENT 1: FERMENTATION BY YEAST Yeast cells produce ethanol, C2 H6 O, and carbon dioxide, CO2 , during alcoholic fermentation. In this experiment, you will measure the production of CO2 to determine the rate of fermentation in the presence of different carbohydrates with fermentation tubes. Note: Regular table sugar is sucrose, a disaccharide, which is made up of glucose and fructose. Glucose is a monosaccharide. Figure 4: Fermentation tubes. Note how the smaller, plastic test tube is inverted into the larger glass tube. You will create five fermentation tubes in this experiment. PROCEDURE 1. In this experiment, you will mix yeast with sugar, Equal®, and Splenda®. Before you begin, develop a hypothesis predicting what will happen when the sugar/sweeteners are mixed with yeast. Will fermentation occur? Why or why not? Record your hypothesis in the post-lab questions. 2. Use the permanent marker to label three 250 mL beakers as Equal®, Splenda®, and Sugar. 3. Empty the Equal®, Splenda®, and Sugar packets into the corresponding beakers. 4. Fill the Equal® and Splenda® beakers to the 100 mL mark with warm tap water. 5. Fill the Sugar beaker to the 200 mL mark with warm tap water. 6. Mix each beaker thoroughly by pipetting the solution up and down several times. Use a new pipette to mix each solution. Each beaker now contains a 1% solution. Set these aside for later use. 7. Completely fill one of the smaller plastic tubes with tap water and invert the larger glass tube over it. Push the small tube up into the larger tube until the top connects with the bottom of the inverted tube. Invert the fermentation tube (Figure 4) so that the larger tube is upright (there should be a small bubble at the top of the internal tube). Note: Repeat Step 7 several times as practice. Strive for the smallest bubble possible. When you feel comfortable with this technique, empty the test tube(s) and proceed to Step 8. CAUTION: Do not try to force the plastic test tube into the glass test tube. This might cause your glass test tube to break, causing you injury. If your plastic test tubes do not fit easily, please call eScience Labs for replacement glass tubes. If you are able to set up at least two fermentation tubes, continue with the experiment, but know that you will have to perform steps 12-15 in multiple steps. 8. Use the permanent marker to label the fourth 250 mL beaker as Yeast. 9. Fill this beaker with 175 mL of warm tap water. It should be between 30 and 40o C (warm to the touch). 10.Open the yeast package, and use the measuring spoon to measure and pour 1 tsp. yeast into the beaker. Pipette the solution up and down until all of the yeast is mixed homogenously into the solution. Note: Make sure the yeast solution remains homogenous before each test tube is filled in the proceeding steps. The yeast density is fairly high, and the yeast may settle to the bottom of the beaker if it rests for an extended period of time. 11. Use the permanent marker to label the big glass and small plastic test tubes as 1, 2, 3, 4, and 5. 12.Use the 100 mL graduated cylinder to measure and pour 15 mL of the following solutions into the corresponding small plastic test tubes: Tube 1: 1% Glucose Solution Tube 2: 1% Sucrose Solution Tube 3: 1% Equal® Solution Tube 4: 1% Splenda® Solution Tube 5: 1% Sugar Solution Note: Thoroughly rinse the graduated cylinder between each measurement. 13.Fill the remaining volume in each small tube to the top with the yeast solution. 14.Slide the corresponding larger tube over the small tube and invert it as practiced in Step 7. This will mix the yeast and sugar/sweetener solutions. 15.Place the fermentation tubes in the test tube rack, and use a ruler to measure (in millimeters) the initial air space in the rounded bottom of the internal tube. Record these values in the Table 1. 16.Allow the test tubes to sit in a warm place (approximately 30 °C) for two hours. Placement suggestions include: a sunny window sill, atop (not in!) a warm oven heated to approximately 85 °C (185 °F on an oven setting), or under a very bright (warm) light. 17.At the end of the fermentation period, use your ruler to measure (in millimeters) the final gas height (total air space) in each tube. Record this data in Table 1. 18.Calculate the difference between the initial and final gas height in each tube. Record this data in Table 1.
EXPERIMENT 1: FERMENTATION BY YEAST
Result Tables
Table 1: Yeast Fermentation Data
| Tube | Initial Gas Height (mm) | Final Gas Height (mm) | Net Change (mm) |
|---|---|---|---|
| 1 | |||
| 2 | |||
| 3 | |||
| 4 | |||
| 5 |
Post-Lab Questions
Include your hypothesis from Step 1 here. Be sure to include at least one piece of scientific reasoning in your hypothesis to support your predictions.
Did you notice a difference in the rate of respiration between the various sugars? Did the artificial sugar provide a good starting material for fermentation?
Was anaerobic fermentation occurring? How do you know (use scientific reasoning)?
If you observed respiration, identify the gas that was produced. Suggest two methods you could use for positively identifying this gas.
Hypothesize why some of the sugar or sweetener solutions were not metabolized, while others were. Research the chemical formula of Equal® and Splenda® and explain how it would affect yeast respiration.
How do the results of this experiment relate to the role yeast plays in baking?
What would you expect to see if the yeast cell metabolism slowed down? How could this be done?
Indicate sources of error and suggest improvement (for example, what types of controls could be added?).
Related textbook solutions
Related questions
Experiment 2: Osmosis - Direction and ConcentrationGradients
In this experiment, we will investigate the effect of soluteconcentration on osmosis. A semi-permeable membrane (dialysistubing) and sucrose will create an osmotic environment similar tothat of a cell. This selective permeability allows us to examinethe net movement of water across the membrane. You will begin theexperiment with a 30% sucrose solution, and perform a set of serialdilutions to create lower concentration solutions. Some of thesucrose concentrations will be membrane permeable; while otherswill not be permeable (can you determine why this is?).
Materials
(3) 250 mL Beakers
(1) 10 mL Graduated Cylinder
(1) 100 mL Graduated Cylinder
Permanent Marker
*8 Rubber Bands (2 blue, 2 green, 2 red, and 2 yellow)
60 g Sucrose (Sugar) Powder, C12H22O11
4 Waste Beakers (any volume)
*Paper Towels
*Scissors
*Stopwatch
*Water
*(4) 15 cm. Pieces of Dialysis Tubing
*Contains latex. Please handle wearing safety gloves if you have alatex allergy.
*You Must Provide
*Be sure to measure and cut only the length you need for thisexperiment. Reserve the remainder for later experiments.
Procedure
1. Use the permanent marker to label the three 250 mL beakers as 1,2, and 3.
2. Cut four strips of dialysis tubing, each 15.0 cm long. FillBeaker 3 with 100 mL of water and submerge the four pieces ofdialysis tubing in the water for at least 10 minutes.
3. After 10 minutes, remove one piece of tubing from the beaker.Use your thumb and pointer finger to rub the tubing between yourfingers; this will open the tubing. Close one end of the tubing byfolding over 3.0 cm of one end (this will become the bottom). Foldit again and secure with a yellow rubber band (use
4. Tie a knot in the remaining dialysis tubing just above or justbelow the rubber band. This will create a seal and ensures thatsolution will not leak out of the tube later in theexperiment.
5. To test that no solution can leak out, add a few drops of waterto the tubing and look for water leakage. If any water leaks,tighten the rubber band and/or the knot in the tubing. Make sureyou pour the water out of the tubing before continuing to the nextstep.
6. Repeat Steps 4 - 5 with the three remaining dialysis tubes,using each of the three remaining rubber band colors.
7. Reconstitute the sucrose powder according to the instructionsprovided on the bottle�s label (your kit contains 60 g of sucrosein a chemical bottle) . This will create 200 mL of a 30% stocksucrose solution.
8. Use Table 2 to create additional sucrose solutions that are 30%,15% and 3% concentrated, respectively. Use the graduated cylinderand waste beakers to create these solutions. Set these solutionsaside.
Table 2: Serial Dilution Instructions
Sucrose Solution mL of Stock Sucrose Solution Needed mL of WaterNeeded
30% 10 0
15% 5 5
3% 1 9
3% 1 9
9. Pour 150 mL of the remaining stock sucrose solution into Beaker1.
10. Use some of the remaining stock sucrose solution to create anadditional 200 mL of a 3% sucrose solution into Beaker 2.
Hint: Use your knowledge of serial dilutions to create this final,3% sucrose solution.
11. Measure and pour 10 mL of the remaining 30% sucrose solutioninto the dialysis bag with the yellow rubber band. Seal the top ofthis tubing with the remaining yellow rubber band.
12. Measure and pour 10 mL of the 15% sucrose solution in the bagwith the red rubber band, and seal the top of the dialysis tubingwith the remaining red rubber band. 10 mL of the 3% sucrosesolution in the bag with the blue rubber band, and seal thedialysis tubing with the remaining blue rubber band. The final 10mL of 3% sucrose solution in the bag with the green rubber band.Seal the dialysis tubing with the remaining green rubberband.
13. Verify and record the initial volume of solution from each bagin Table 3.
Figure 8: The dialysis bags are filled with varying concentrationsof sucrose solution and placed in one of two beakers.
14. Place the yellow, red, and blue banded tubing in Beaker 2.Place the green banded tubing in Beaker 1 (Figure 8).
15. Hypothesize whether water will flow in or out of each dialysisbag. Include your hypotheses, along with supporting scientificreasoning in the Hypotheses section at the end of thisprocedure.
16. Allow the bags to sit for one hour. While waiting, pour out thewater in the 250 mL beaker that was used to soak the dialysistubing in Step 1. You will use the beaker in Step 19.
17. After allowing the tubing to sit for one hour, remove them fromthe beakers.
18. Carefully open the tubing. The top of the tubing may need to becut off/removed as they tend to dry out over the course of an hour.Measure the solution volumes of each dialysis bag using the 100 mLgraduated cylinder. Make sure to empty and dry the cylindercompletely between each sample.
19. Record your data in Table 3.
Data Tables and Post-Lab Assessment
Table 3: Sucrose Concentration vs. TubingPermeability
Table 3: Sucrose Concentration vs. TubingPermeability | |||||
Band Color | % Sucrose in Beaker | % Sucrose in Bag | Initial Volume (mL) | Final Volume (mL) | Net Displacement (mL) |
Yellow | |||||
Red | |||||
Blue | |||||
Green | |||||
Hypothesis:
For each of the tubing pieces, identify whether the solutioninside was hypotonic, hypertonic, or isotonic in comparison to thebeaker solution in which it was placed.
Which tubing increased the most in volume? Explain why thishappened.
What do the results of this experiment this tell you about therelative tonicity between the contents of the tubing and thesolution in the beaker?
What would happen if the tubing with the yellow band was placedin a beaker of distilled water?
How are excess salts that accumulate in cells transferred to theblood stream so they can be removed from the body? Be sure toexplain how this process works in terms of tonicity.
If you wanted water to flow out of a tubing piece filled with a50% solution, what would the minimum concentration of the beakersolution need to be? Explain your answer using scientificevidence.
How is this experiment similar to the way a cell membrane worksin the body? How is it different? Be specific with yourresponse.
