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Anaerobic Respiration (Fermentation)
by
Farah Masood
1. Introduction
Have you noticed that sometimes when you are running a race, you tend to run out of
breath and cramp up after a while? How will this affect your performance? When you have
trouble breathing it means that not enough oxygen is being delivered to your cells. Aerobic
respiration can only take place when there is oxygen present; therefore your body is not
producing enough usable energy, adenosine triphosphate (ATP), for your muscles to use as you
compete in the race.
How do you feel the day after the race? Most likely, your legs will be very sore. This
happens because in the absence of oxygen, the muscles switch to fermentation in order to
produce energy, and the final product of fermentation in the body is lactic acid. The build up of
lactic acid in the muscles cause the pH level of the body to become more acidic, the muscles to
get tired, and cramps to develop.
In this lab we will be studying anaerobic respiration, or fermentation, which is the
process of breaking down sugar to produce energy in the absence of oxygen. You will be using
yeast as the living organism (enzyme) that breaks down the different sugars to produce energy,
with alcohol as the byproduct of fermentation instead of lactic acid.
2. Background
Cellular Respiration:
Living organisms require energy to function. There is potential energy in the chemical
bonds of all organic molecules such as sugars, and some of the common sugars are: glucose,
sucrose, fructose, and lactose. However, this energy can not be used directly by the cells and so
these bonds need to be broken to release the energy in a form that is useful to the cells. Cellular
respiration is the process where energy that is stored in organic compounds is eventually
converted to a usable form called ATP (adenosine triphosphate). ATP is like money of the body,
cells in different muscles use ATP in order to do their work.
The two phases of cellular respiration is anaerobic and aerobic respiration. Anaerobic
respiration is phase 1 and it takes place in the cytoplasm. At the end of anaerobic respiration 2
molecules of ATP are produced. If there is oxygen, present then aerobic respiration or phase
2 can take place. If there is no oxygen present then phase 2 of cellular respiration cannot take
place.
Fermentation begins by splitting a glucose molecule into 2 molecules with 3 carbon
atoms each. This glucose splitting process is called glycolysis, during which ten individual
2
O
R evitalizing A chievement by using I nstrumentation in S cience E ducation 2004 - 2007
The National Science Foundation
chemical reactions occur, with each reaction controlled by a different enzyme. The end result of
anaerobic respiration, or fermentation, is 2 ATP and an alcohol, or an acid. Anaerobic
respiration can be summarized with the following chemical equation:
Energy + Glucose Ethanol + Carbon Dioxide + Energy
Yeast is used as the enzyme because it contains the enzymes that are needed for fermentation.
Structural Formula of Sugar Molecules:
Figure 1
Glucose is the most fundamental
molecular composition of all the sugars; its
structural formula is shown in Figure 1. That
means that the chemical bonds between its
elements are the easiest to break compared to
the bonds in a fructose molecule. Galactose is
another monosaccharide, or a single sugar, that
has very weak chemical bonds. Galactose is
an isomer of glucose, thus it is obtained by
reorienting the location of one of the hydroxyl
groups, , of the glucose as shown above in
Figure 1.
The “glucosidic” links in the
disaccharides, or double sugars, are more
difficult to break down than the interior bonds
of the monosaccharides. The “glucosidic” link
is the oxygen bond between the two sugar
molecules, as shown to the left in Figure 2.
ATP CH O CHCHOH CO ATP
Enzymes
6 12 6 3 2 2
Yeast
OH
R evitalizing A chievement by using I nstrumentation in S cience E ducation 2004 - 2007
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- Insert the single-holed rubber stopper into the test tube. Firmly twist the stopper for an
airtight fit and then secure the test tube with a utility clamp to the ring-stand. Then connect
the free end of the plastic tubing to the connector in the rubber stopper, shown in Figure 3.
Figure 3 (Masterman, 2003)
- Then incubate the test tube for 10 minutes in the water bath. Make sure to keep the water
bath at a constant temperature (37- 40
0
C) and the test tube completely covered by the water.
Periodically check to ensure that the temperature remains constant. If the temperature falls
below or above acceptable levels, add cold or hot water accordingly. (If water is being
added to the bath, first remove the same amount of water that will be added to the beaker to
prevent overflow.)
- After 10 minutes have elapsed you can begin measuring the gas pressure by clicking on the
Collect Data button,. Disconnect the plastic tubing from the Gas Pressure Sensor if
the pressure exceeds 130 kPa, because the pressure inside the test tube is too great. The file
is set up to collect data for 8 minutes.
- After data collection has finished, remove the rubber stopper from the test tube and discard
the contents in a waste basket.
- Determine the rate of fermentation:
- First change the name of the Header in the Data Collection Window on the left to
the drink that is being tested (Gatorade, Coke, Juice, or Milk). This can be done by
double clicking the cell and then typing in the title into the little window that opens.
- To highlight the data move the mouse pointer to the point where the data values
begin to increase. The data should start increasing around 60 seconds. Drag the
pointer to the end of the data and release the mouse button.
- To obtain the rate of fermentation a best fit line needs to be drawn for the data.
After the data has been highlighted, click on the Linear Fit button,. A floating
box will appear with the formula for a best fit line.
- Record the slope of the line, , as the rate of respiration in Table 1. m
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- Close the linear regression floating box and move your data to a stored run. To do
this, choose Store Latest Run from the Experiment menu.
- Use a notebook or notepad to fan air across the opening of the Gas Pressure Sensor.
- Repeat Steps 6– 12 for the second sample.
- Save all your data by choosing “save as” from the file menu, and save the file as Anaerobic
Respiration (Group #).
- Share your data with the class by recording the fermentation rates you obtained for the two
drinks in the appropriate spot on the board.
- After all the groups have recorded their data on the board, copy down all the values into
Table 2.
6. Results
Table 1: Group Data
Drink Tested Actual Temperature
o
C)
Rate of
Fermentation
(kPa/s)
Gatorade
Coke
Fruit Juice
Milk
Table 2: Class Data
Drink Tested Group 1 – Rate
of Fermentation
(kPa/s)
Group 2 – Rate
of Fermentation
(kPa/s)
Group 3 – Rate
of Fermentation
(kPa/s)
Group 4– Rate of
Fermentation
(kPa/s)
Gatorade
Coke
Fruit Juice
Milk
7. Analysis 1. Calculate the average rate of fermentation for each of the five drinks that were tested.
Record the class averages for the fermentation rates in Table 3.
Table 3: Class Average
Drink Tested Rate of
Fermentation
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- Explain why some of the sugars in the drinks were metabolized and the other sugars were
not metabolized as much.
- Why do you need to incubate the yeast at 37- 40
o
C before you start collecting the data?
- Why does all the from the coke need to be released before the yeast is added?
- Explain some possible sources of error?
Reference
Chang, Raymond, Essential Chemistry: A Core Text for General Chemistry 2
nd
edition, 2000,
McGraw-Hill Higher Education, New York, New York
Hallman, Rick, The Living Environment: Biology, 2000, AMSCO School Publications, Inc.,
New York, New York
2
CO
R evitalizing A chievement by using I nstrumentation in S cience E ducation 2004 - 2007
The National Science Foundation
Johnson, George P., Raven, Peter H., Biology Principles & Explorations, 2001, Holt,
Rinehart and Winston, Austin, Texas
Masterman, David, Holman, Scott, Biology with Computers: Biology Experiments Using
Vernier Sensors 3
rd
edition, 2003, Vernier Software & Technology, Beaverton, Oregon
