Fermentation Lab
Performed: October 23, 2012
Mr. Johns
INTRODUCTION
Purpose: To determine the rates of fermentation by yeast cells during alcoholic
fermentation for different carbohydrates within specific time and temperature
constraints.
All organisms must obtain and use energy. Autotrophic organisms use the sun to
convert carbon dioxide and water into products of oxygen and sugars. The sugars are
used by the plant to make more of its structure and most of the oxygen is expelled
through the stomates into the environment. Heterotrophic organisms use food
produced by other organisms. They must break the food into small enough quantities in
order to make use of the molecules found there. These food molecules will generally
contain four different macromolecules: proteins, lipids, nucleic acids, and
carbohydrates. The macromolecules are transformed through an array of metabolic
pathways into a form of energy that can be used by the organism. This energy is
represented in many of the pathways as adenosine triphosphate, also known as ATP.
ATP is used as an energy source for most cellular functions. Carbohydrates are a
general source of energy for this type of organism, and can break the carbohydrates
down using several pathways. In the presence of oxygen, some cells use aerobic
cellular respiration to make ATP from the processes of glycolysis, Krebs cycle, and
electron transport chain. When oxygen is no longer present, cells can break the
carbohydrates down by glycolysis followed by fermentation. When yeast respire glucose
aerobically, O2 in used up at the same rate that CO2 gas is produced. The net equation
for the reaction involved with the aerobic respiration of glucose is:
C6H12O6 (aq) + 6 O2 (g) → 6 H2O (l) + 6 CO2 (g) + energy (36-38 ATP + Heat)
Lactic acid fermentation and alcoholic fermentation are two types of fermentation used
by heterotrophic organisms in order to obtain additional ATP for cellular functions.
Lactic acid fermentation takes place in animal muscles after vigorous exercise, and
alcoholic fermentation is used by yeasts which can be used to make beer and wine.
In this study, conditions are so that yeast perform the reactions anaerobically through
alcoholic fermentation. When yeast ferments the sugars anaerobically, CO2 production
will cause a change in the pressure of a closed inverted cuvette, since no oxygen is
being consumed. The pressure will cause expansion of the CO 2 into the inverted
cuvette, and the amount of CO2 can then be measured. The equation in which yeast
converts glucose into ethyl alcohol and carbon dioxide is written below:
C6H12O6 (aq) → 2 C2H5OH (aq) + 2 CO2 (g) + energy (2 ATP + Heat)
Hypothesis: Yeasts are able to break down different types of sugars at varying rates.
MATERIALS
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1000 mL beaker with 700 mL tap water
Hot plate set to a level to keep 700 mL tap water at 45°C
Plastic shoebox
4 large test tubes (2.2 cm id X 15 cm long)
4 small cuvettes (1.1 cm id X 5 cm long)
4 small test tubes (1 cm id X 10 cm)
4 disposable plastic pipettes
4 metal nuts (weights)
Thermometer
30 % Glucose solution
30% Sucrose solution
30% Molasses solution
30% Agave nectar solution
Distilled water (negative control in the investigation and used for dilution of
sugars
Timer with second hand
Test tube rack
Metric ruler
PROCEDURE
1.
Fill the plastic shoe box 70% full of warm 35°C tap water.
2.
Fill the 1000 mL beaker with approximately 700 mL of tap water. Turn on the hot
plate to a setting comparable to keep the water in the beaker at 45°C. Use the
thermometer to check the temperature periodically. When the temperature has
been adjusted and is steady, perform the next steps.
3.
Completely fill four plastic pipettes with the assigned sugar-yeast solution at your
station. To fill the pipette., pull as much liquid as possible into the stem by
squeezing the bulb with thumb and index finger and then slowly release it. Turn
the pipette upside down and tap the pipette to move the liquid into the bulb. If
this is not effective, try the “Cartoon Air Brakes Method.” This method is achieved
simply by moving the pipette downward quickly while suddenly stopping the
pipette in mid motion. Centrifugal force also works well. Fill the remaining
portion of the pipette until it is completely filled with yeast-sugar solution.
4.
Slide a metal nut over the stem where it rests above the bulb of each pipette.
5.
Submerge one of the large test tubes in the shoebox. Be sure that all air bubbles
are removed by sloping the open end of the test tube toward the water surface.
Gently place the pipette (bulb end first) with nut applied into the test tube.
Submerge a cuvette to fill it completely with water. Place the submerged cuvette
over the small end of the pipette. Bring the test tube assembly out of the water,
and remove water from the test tube until the water level is approximately 4 cm
from the open end of the test tube. Place this partially completed test tube
assembly in the test tube rack.
6.
Fill one of the small test tubes approximately 50% full of water. Place the small
test tube into the large test tube until it rests against the flat end of the cuvette.
This will keep the cuvette from floating away from the pipette tip.
7.
Repeat Steps 4 and 5 for the remaining sugar-yeast solutions being tested
(independent variables), and the yeast-water solution (negative control).
8.
Allow a minimum of 5 minutes or maximum of 15 minutes to pass (this will be
determined by the amount of available volume of the cuvette. It is important to
capture a measurable amount of CO2, without letting it escape from the open
end of the cuvette.
9.
Collect data from the class and calculate the average volume of CO 2 produced by
each solution. Construct a histogram graph of your class data. Type of YeastSugar will be the horizontal axis label and Volume of CO2 in cm3 the vertical axis
label.
RESULTS
RESULTS
DISCUSSION
During the investigation two different yeast-sugar solutions were used as independent
variables. Each solution including the control solution was tested under the same
temperature and time constraints of 45°C for 10 minutes. A water-yeast solution was
used as a negative control, and yielded the expected results with no CO2 produced.
Sucrose-yeast and water solution produced 19 cm3 of CO2. Dextrose-yeast and water
solution produced 30.4 cm3 of CO2. Dextrose is the name given to right-handed
glucose. Glucose is half the size of sucrose. Sucrose is made of left-handed glucose
attached to a fructose.
CONCLUSION
Yeast was able to break down dextrose (glucose) at a faster rate than sucrose during
reactions of alcoholic fermentation. The faster rate is contributed to the different sizes
of the sugars being digested. Glucose is a monomer containing six carbons, twelve
hydrogens, and six oxygens. Sucrose is larger with twelve carbons, twenty-two
hydrogens, and eleven oxygen atoms.
REFERENCES
http://serendip.brynmawr.edu/sci_edu/waldron/pdf/YeastProtocol.pdf
http://www.instruction.greenriver.edu/kmarr/Biology100/Bio100Lab/B100%20Labs_KM_
2011/5_Lab%205%20Alcoholic%20Fermentation/Lab%205_Alcoholic
%20Fermentation_B100_W2011.pdf