Biotechnology Curriculum
Freshmen Year
Fermentation by Yeast Cells
Course Description:
All living things require energy to survive. This energy is derived from the food that is
eaten, and in the end comes from the sun’s energy. This course is intended to examine the
process of fermentation in yeast cells. It is a step to understand how living things extract
energy from food that is necessary for life. Fermentation is different from respiration
because it does not require oxygen.
Using yeast cells and sugars from different sources, the rate of carbon dioxide gas
production by the cells will be measured under various conditions. Linear graphs will be
drawn representing the relationship between gas production and temperature time, or
sugar used.
Objectives:
Student will be able to write the word reaction that takes place
during fermentation, determine if an organism is able to break down different types
sugars, or various other carbohydrates in media. This will provide information in
classifying unknown microbes.
Skills:
Use of fermentation tubes, drawing of a graph representing CO2 production by yeast +
sugar with time and temperature.
Purpose:
To determine the carbohydrate sources that can be used by yeast for
fermentation.
Materials: Per group of students
6 Fermentation Tubes ( can be obtained from fisher science education)
100 grams of yeast (a block of fresh baker’s yeast is the best source)
7 250 ml beakers
glucose
0.1 M
fructose
0.1 M
galactose 0.1 M
any diet drink
balance
spatula
water bath at 37°C
graph paper or use of excel
Ice
Clock or timer
Procedure:
1. Weigh out 10 grams of fresh baker’s yeast and place into 5 different beakers
2. Mix the baker’s yeast with 20 ml of water and place into beaker 1.
Label the beaker control.
3. Mix the baker’s yeast with 20 ml of 0.1M glucose solution in beaker 2.
Label it 0.1 M glucose.
4. Continue this process, placing the different sugar solutions or unknowns such as
diet coke into each of the other beakers and labeling them accordingly.
Step 1. Testing yeast’s ability to digest sugars:
1. Place 10-20 ml of the yeast + water or sugar mixture into a fermentation tube
and fill closed end of tube.
Note: One end of the tube is closed. This end must be completely filled with the yeastsugar solution. To accomplish this, add your solution to the open ended side until it
fills to the top opening. Place your finger over the opening and invert while turning
the flask. You should be able to fill the closed end of the tube completely with solution
mixture.
2. Label the fermentation tube and keep on an ice bath until all tubes are ready.
3. Continue steps 1-2 until all the sugars and unknown solutions have been placed
into their own fermentation tube.
4. Place fermentation tubes into a 37°C water bath
Fill in Data Table below giving the volume of gas produced for each 10 minutes that the
tubes are incubated.
Note: Sometimes it will take 5-10 minutes before the yeast cells begin to ferment and
produce CO2 gas. Begin measurements when you can see the gas is being produced.
Effect of Sugar Source on CO2 production (ml) VS Time (minutes)
Sugar
O
minutes
15
minutes
30
minutes
45
minutes
60
minutes
Water
0.1M
Glucose
0.1M
Fructose
0.1M
Galactose
Diet
Drink
unknown
Going one step further:
Step 2: The effect of temperature on gas production.
1.
2.
3.
4.
5.
6.
7.
8.
9.
Clean out your beakers and fermentation tubes.
Add 10 grams of baker’s yeast to each of three tubes
Place 20 ml of 0.1 M glucose solution into each beaker, mix well.
Place 60 ml of water into the control beaker containing 30 grams of yeast, mix
well.
Fill fermentation tubes as in previous activity.
Place tube one into an ice bath
Place tube two into a 37°C water bath
Leave tube three at room temperature
Control tubes containing water and yeast are placed into three separate
Tubes and placed into an ice bath, 37°C water bath or left at room temperature.
Results cont’d
Effect of Temperature on Gas Production (ml) VS Time (minutes)
temperature
15 minutes
30 minutes
45 minutes
60 minutes
0oC
21oC
37oC
Questions and Answers:
Sugar + yeast
1.
Carbon dioxide gas + water
Draw a graph of the data from table 1 CO2 production in ml vs time in minutes
using the excel program on your computer or by using graph paper. Make the time
of incubation the x axis and the ml of gas produced the y axis.
a. What does the production of gas tell us is happening inside the yeast cell?
b. Were there any differences in gas production between each of the sugars
used?
c. What happened to the water + yeast sample? Why was it included in the
testing?
d. What can you conclude about the sugar content of the diet drink?
2.
Draw a graph of the data from table 2, Effect of temperature on CO2 production in
ml vs time in minutes using the excel program on your computer or by using
graph paper. Make the time of incubation the x axis and the ml of gas produced
the y axis.
a. What was the effect of temperature on the production of gas ?
b. Why did the temperature affect gas production?
c. If you were going to grow yeast cells to produce a product in
biotechnology, what temperature and sugar would you selectfor the best
outcome? Why?
Teacher Resources:
This activity requires some prior lecture on what is an enzyme and how it works. This
doesn’t have to be extensive, as it will be covered in detail in the sophomore year.
I would not get into chemical equations beyond how to write some simple symbols for
oxygen and carbon dioxide. If your group has not had any chemistry, I would use only
words in the equation.
A discussion of the breakdown of sugar in the absence of oxygen as a way to identify
microbes is also important to mention.
Some students will have difficulty with the concept of the rate of a reaction.
However, by drawing a graph, they should see the correlation between gas
production and different treatments. Try to use other examples. Perhaps the idea of the
speed you are going is directly proportional to the number of miles you cover in a car, or
the amount of food you eat is directly proportional to your weight.
This activity will take the entire day to complete or if broken up into 1 hour laboratories
you might want to do it on sequential days or abbreviate the activity.
If the teacher is doing the preparations and the needed introduction on fermentation
before the activity, and the analysis the following day, it should take
three days in total. The use of excel to draw graphs is easier than having the students use
graph paper. It would be advisable to carry out the M&M grab bag activity before this
unit.
You could use the data from the entire class to present the idea of average values
and statistical methods.