Objectives

Students should be able to:

1. Differentiate between aerobic and anaerobic processes.

2. Write the overall balanced equation for fermentation.

3. Write the overall balanced equation for cellular respiration.

4. Perform lab exercises that investigate the process of fermentation.

5. Perform lab exercises that investigate the process of cellular respiration.

6. Collect and analyze data from laboratory investigations of cellular respiration and fermentation.

7. Compare and contrast the processes of cellular respiration and fermentation.

Introduction

In this laboratory activity you will investigate the processes of fermentation and cellular respiration. Fermentation is anaerobic while cellular respiration is aerobic. The laboratory procedures for this exercise allow you to create the anaerobic and aerobic conditions. You will be collecting data and analyzing it via graphs and calculations, and drawing some basic conclusions about the respiratory processes carried out by yeast (anaerobic) and peas (aerobic).

Fermentation:

Alcoholic fermentation as carried out by yeasts, is an anaerobic process. In this process, glucose (or other simple sugars) are incompletely degradated and the chemical energy released is captured and used to converted 2 ADP to 2 ATP / glucose molecule. The overall equation for this process is:

C₆H₁₂O₆ + Yeast ---------------> 2 CO₂   + 2 C₂H₅OH  + 2 ATP 

The above process is used in the manufacture of beer, wine, and bread.

Some organisms, such as lactic acid bacteria, carry out lactate fermentation that results in the production of lactate instead of the alcohol, ethanol. This process is used in the production of yogurt, cheese, and chocolate. The overall equation for this process is:

 C₆H₁₂O₆  + Lactic Acid Bacteria ------>   2 CO₂  +  C₃H₆O₃  + 2 ATP

Cellular Respiration:

Cellular respiration, unlike fermentation, is an aerobic process. In cellular respiration glucose is completely degradated and the chemical energy released is captured and used to convert ADP to ATP, and ultimately results in the production of 36 to 38 ATP molecules / glucose molecule. The energy produced in this manner is much greater than that produced in fermentation. The overall equation for this process is:

C₆H₁₂O₆   +   6O₂  ------------>  6CO₂  +  6 H₂O  +  36-38 ATP

Pre-lab Activities

Pre-Lab Activity #1 - Setups for Respiration Exercises

Print out the following pictures of the setups so you may refer to them in lab. Just Click on the Picture

Yeast Respiration:                Pea Respiration:

Respirometer                        Respirometer Content

Pre-Lab Activity #2 - Acquisition of Materials

Download and print out the following:

Pre-lab Questions (html version)    Pre-Lab Questions (Word version)

The Laboratory Activities and Data Collection

Lab Activity #1 - Measuring Yeast Fermentation (Anaerobic) Using Respirometers

Materials:

Procedures:

1. Number four large test tubes 1 - 4. (13 x 150 mm)

2. Number four small test tubes 1 - 4. (10 x 75 mm)

3. Measure up from the bottom of each of the small test tubes a distance of 5 cm (50 mm) and make a mark with the marking pen.

Fill each of the 4 small test tubes up to the 5 cm mark with the sugar solutions as directed in the following chart.

4. Finish filling each of the four small test tubes with a yeast solution and shake the test tube to mix the contents. You may need to add more yeast solution to "top off" the test tube so it is overflowing.

5. Invert a large test tube over the small test tube and with a small dowel rod push the small test tube up into the large test tube until the top of the small test tube contacts the bottom of the large test tube.

6. Quickly invert this tube set up. Make sure you keep the small test tube pushed up into the large one while you do the inversion.

7. A small air bubble may be seen in the bottom of the small test tube once it is inverted. If the bubble is large then repeat until no bubble or a very small one is observed.

8. Repeat Steps 4 - 6 with the remaining respirometers.

9. With the small plastic ruler, measure the height of the air space in the bottom of each of the small test tubes. Record this in your Data Collection Sheet.

10. Place the test tube rack with the respirometers in the incubator, which has been set at 37˚C.

11. Let the respirometers incubate for 15 minutes.

12. At the end of 15 minutes check the progress of the fermentation reaction by observing the size of the bubble in the small test tube. If it is increasing rapidly in size, stop the incubation before the bubble completely fills the small test tube. Check with the instructor if you are not sure when to stop the incubation.

13. When you have stopped the incubation, measure the height of the bubble in each of the four small test tubes and record the data in the Data Collection Sheet.

Lab Activity #2 - Measuring Pea Respiration (Aerobic) Using Respirometers

Materials:

Procedures:

1. Fill tray with water to the mark indicated on the tray.

2. Initial preparation of respirometers:

   1. Number the vials 1, 2 and 3.

   2. Place a wad of absorbent cotton in each of the vials.

   3. Saturate the cotton with 15% KOH (Be careful, KOH is corrosive, see materials). DO NOT get KOH on the sides of the vial. If this happens notify the instructor.

   4. Place a wad of nonabsorbent cotton on top of the absorbent cotton. This protects the peas from the corrosive KOH.
       

3. Preparation of Respirometer Contents:

   1. Obtain a 100 mL graduated cylinder and fill it with water to the 40 mL mark.

   2. Place 15 germinating peas into the graduated cylinder and determine the amount of displacement that has occurred. The difference between this and 40 mL is the volume of the germinating peas. Record this data in your Data Collection Sheet

   3. Remove the germinating peas and place them on paper toweling.

   4. Refill the 100 mL graduated cylinder to the 40 mL mark. Add 15 non-germinating peas and read the new volume. Compare this with the volume of the germinating peas. Now add beads to the non-germinating peas until the volume displaced equals the volume of the germinating peas. Record this data in your Data Collection Sheet.

   5. Remove the non-germinating peas and beads and place them on paper toweling.

   6. Refill the 100 mL graduated cylinder to the 40 mL mark. Now add only beads until the volume displaced equals the volume of the germinating peas. Record this data in your Data Collection Sheet.

   7. Remove the beads and place them on paper toweling.
       

4. Assembly of Respirometers:

   1. Place the germinating peas in Vial #1 and then insert into the top of the vial the stopper containing the pipet. (See photograph from your pre-lab)

   2. Place the non-germinating peas and beads in Vial #2 and then insert into the top of the vial the stopper containing the pipet. (See photograph from your pre-lab)

   3. Place the beads in Vial #3 and then insert into the top of the vial the stopper containing the pipet. (See photograph from your pre-lab)
       

5. Prepare the water filled tray for the respirometers by taking a piece of masking tape and fastening it to one side of the tray one third of the way from the end of the tray. Stretching the tape across the tray and fasten it to the other side. You now have a place to rest the pipets while the vials and there contents are equilibrating.
   
   
           

6. Place the copper collar weights on the vials and place the vials with collars into the tray one at a time. Rest the tip portion of the pipet on the masking tape. DO NOT allow the tip of the pipet to submerge in the water. 
7. Check to respirometers to see if there are any leaks into the vials. Turn the respirometers so the numbers on the pipets can be clearly seen.
8. Allow the submerged respirometers to equilibrate for 10 minutes.
9. Take the temperature of the water in the tray and record it.
10. Immerse the respirometers completely into the water by carefully removing the masking tape. (See photograph printed for Pre-Lab)
11. Allow the submerged respirometers to equilibrate for 3 minutes.
12. At the end of the 3 minute equilibration time read and record on the pea respiration spreadsheet the initial level of water that has entered the pipets.
13. Read and record the level of water in the pipets at 5 minute intervals for 20 minutes. Record your data on the pea respiration spreadsheet. 

Post-lab Activity and Data Analysis

Results and Analysis:

Clean up your lab area and return all materials to their proper location.

Graph the data from the Yeast Fermentation Exercise. The graph parameters are:

Graph the Corrected Difference data from the Pea Respiration Exercise. The graph parameters are:

Answer the Post-Lab Questions

Post-Lab Questions (html version)    Post-Lab Questions (Word version)