What Affects Yeast Growth?
Kyle Igou
River Falls High School
Curriculum Activity
7/20/2007
Activity Description
The activity that I selected to fulfill my course requirements for this
Biotechnology for Teachers course came from the Institute of Food Technologists. This
is a scientific experiment to observe how yeast populations are affected by a number of
different factors. The objectives of this activity is to determine which factors affect yeast
activity with the variables of pH, temperature, nutrient availability and the concentration
of available nutrients. This experiment will illustrate to the students how yeast growth is
affected and they will discover a natural by-product of yeast in carbon dioxide.
Prior to this activity, I will spend 1-2 days covering cellular respiration, including
glycolysis and fermentation. There will also have to be some time spent on what yeast
are and they role they can play in the fermentation process. After we have talked about
yeast they will be asked to bring in a product (other than what we will be working with)
that they think will affect yeast growth. I will also be preparing all of the solutions prior
to the activity. I will be having each group of students complete all of the activities,
instead of giving each group one. To save time on the day of the activity, you could
assign each group to one of the activities and have the other groups observe each others
to complete their data.
On the day of the activity, my classroom will serve as small fermenting
laboratory. All of the materials will be set out on the side counter top. The students will
be divided into groups of three’s. Each group will then conduct a temperature
experiment, water activity experiment, pH experiment and nutrient experiment. They
will be instructed to record when they have finished one of the experiment and 15
minutes later they will be asked to start recording their observations for each experiment.
Intended Audience
I am writing this activity to use in an intermediate high school biology class. This
could include a mixture of mostly 10th and 11th grade students. I would use this activity
at the end of the cellular respiration unit and before the cell growth and division unit.
This activity should take one day in the block system. If each group does one experiment
like the lesson protocol states it should only take one day in a 45 minute class.
Outline of Activity
Day 1
Lesson Objectives
Upon completion of today’s lesson the students will be able to:



Explain a yeast cell and where they live
Describe the process of fermentation
Identify what factors could affect yeast growth
Lesson Activities
A. Discussion and notes on yeast
B. Demonstration and discussion of fermentation
C. In groups, brain storm factors that could affect yeast growth
Day 2
Lesson Objectives
Upon completion of today’s lesson the students will be able to:



Determine what factors affect the growth of yeast cells during
fermentation
Observe one by-product of the fermentation process is carbon dioxide
Identify products with sugars in them which will affect the growth of yeast
Lesson Activities
A.
B.
C.
D.
E.
Review fermentation
Temperature Experiment
Water experiment
pH Experiment
Nutrient Experiment
Background
Yeast are unicellular fungi. They are microscopic plants that exist naturally on
the surface of the Earth. They are noted for their ability to ferment carbohydrates to
produce various food products, including bread, beer, wine, and cheese. You may think
of yeast only as lifeless, dry powder used for making breads. This dry powder contains
ascospores which become active in a moist environment. Common yeast used for baking
and brewing are members of the genus Saccharomyces, which means “sugar fungi.”
These yeasts are grown in a rich nutrient mixture containing very little oxygen. Lacking
oxygen, yeasts within the mixture use the process of alcoholic fermentation to obtain
energy. The byproducts of alcoholic fermentation are carbon dioxide and alcohol. The
carbon dioxide gas makes beverages bubble and bread rise (by producing bubbles within
the dough). The alcohol in bread dough evaporates during baking. In brewing, alcohol
remains in the resulting alcoholic beverages. (Biology: Miller/Levine)
Once the students know a little about yeast I will review the process of
fermentation and the equations for both alcoholic fermentation and lactic acid
fermentation and make sure they know the difference between the two.
This activity will then lead into the cellular growth unit, so I will introduce the
concept of cell division and the cell cycle. All of this background information will be
instructed through a variety of visual aids including video clips and CD’s.
The last thing we will talk about are the lab procedures and mistakes that can be
made throughout the lab. One common error, is students will use the tap water even if it
is not a neutral pH and this can change the dynamics of the lab.
Experimental Procedures
Materials Needed
Safety goggles
125-mL Erlenmeyer flasks or small (8-oz.) glass soft drink bottles ( I have more small
bottles)
Balloons, 7-inch size
Fructose, lactose, and glucose from science supply catalog or store
pH paper
Marker or wax pencil
Masking tape
Large bottle or packages of rapid-rise yeast
Vinegar
Ammonia
Clock or stopwatch
Warm water bath (40oC and 80oC)
Triple beam balances or scales
100-mL graduated cylinders
Eyedropper
Thermometers
Temperature Experiment
Label flasks A through E. Add 80 mL of tap water (neutral pH only) to each flask and
place the flasks in the following conditions:
Flask A – in ice bath.
Flask B – at room temperature.
Flask C – in 40oC water bath.
Flask D – in 80oC water bath.
Flask E – in 40oC water bath.
Dissolve 5 g of sucrose in flasks A - D. Then dissolve 5 g of your product in flask E.
Add 4 g of rapid-rise yeast to each flask and stir. Then place a balloon on each flask and
seal it securely with masking tape. Periodically stir the contents by spinning the flask
slowly.
Water Experiment
Label F through J. Add 80 mL of 40oC water (neutral pH only) to each flask and dissolve
the following amounts of sucrose to flasks F – I and dissolve 30 of your product in flask
J:
Flask F – 0 g (water only)
Flask G – 5 g
Flask H – 30 g
Flask I – 50 g
Flask J – 30 g
Add 4 g of rapid-rise yeast to each solution and stir. Then place balloon on each flask
and seal it securely with masking tape. Periodically stir the contents by spinning the flask
slowly.
pH Experiment
Label flasks K though O. Add 80 mL of tap water (neutral pH only) to each flask and
add vinegar or ammonia to adjust the pH as shown below. Use pH paper to verify the
pH.
Flask K – add vinegar to adjust the pH to 3
Flask L – add vinegar to adjust the pH to 5.
Flask M – add vinegar or ammonia to adjust the pH to 7.
Flask N – add ammonia to adjust the pH to 10.
Flask O - add vinegar or ammonia to adjust the pH to 7.
Dissolve 5 g of sucrose in flasks K through N and 5 g of your product in flask O and
warm the solutions to 40oC. Add 4 g of rapid-rise yeast to each solution and stir. Then
place a balloon on each flask and seal it securely with masking tape. Periodically stir the
contents by spinning the flask slowly.
Nutrient Experiment
Label flasks P – T. Add 80 mL of tap water (neutral pH only) at 40oC to each and
dissolve 5 g of each of the following sugars:
Flask P – fructose
Flask Q – glucose
Flask R – sucrose
Flask S– lactose
Flask T – your product
Add 4 g of rapid rise yeast to each solution and stir. Then place a balloon on each flask
and seal it securely with masking tape. Periodically stir the contents by spinning the flask
slowly.
Observations
1. After 15, of putting the balloons on each experiment, record initial observations in
the table provided for each test. Then make additional observations at 10-minute
intervals, for 20 minutes. These observations should include a description of the
fermentation activity and a measure of the amount of gas produced, by measuring
the circumference of the balloon. To measure the circumference, wrap a string
around the balloon at its widest point, then measure the length of the string.
2. Prepare bar graphs of balloon circumference against each of the following:
Temperature
pH
Type of sugar
Water
Your product
Special Needs
The teacher must be able to adapt to the specific need that an individual student
may present. If any conditions would be present in an individual student the teacher
should instruct one of the other group members to assist the student. The teacher may
also have to adapt the number of experiments or the time constraints of the activity to
meet the student’s needs. In my case this would be an intermediate biology class and
many of these students have some sort of special need.
References
This activity was taken out of the Institute of Food Technologists. It comes out of the
book IFT Experiments in Food Science Series: Microbiology in Food Systems. The
background information and supporting information comes out of the Prentice Hall
Biology textbook by Miller/Levien copyright 2004.
Evaluation Methods
Group Evaluation
Grading Rubric for Group Evaluation of Yeast Growth
Temperature
Experiment
Water
Experiment
pH Experiment
Nutrient
Experiment
Group Product
Data
3
All procedures are
followed with
complete accuracy –
Data table filled out
completely with no
mistakes
All procedures are
followed with
complete accuracy –
Data table filled out
completely with no
mistakes
All procedures are
followed with
complete accuracy –
Data table filled out
completely with no
mistakes
All procedures are
followed with
complete accuracy –
Data table filled out
completely with no
mistakes
All data sections are
complete for your
groups product
2
One mistake is
identified in
procedure or data
table
1
More than one
mistake is identified
in the lab
procedures or data
table
One mistake is
identified in
procedure or data
table
More than one
mistake is identified
in the lab
procedures or data
table
One mistake is
identified in
procedure or data
table
More than one
mistake is identified
in the lab
procedures or data
table
One mistake is
identified in
procedure or data
table
More than one
mistake is identified
in the lab
procedures or data
table
One section of data is
incomplete for your
groups product
More than one
section of data is
incomplete for your
groups product
Data Table 1
Test/Flask
Temperature
A
Conditions
Sucrose + Ice Bath
B
Sucrose + Room
Temperature
C
Sucrose + 40oC
D
Sucrose + 80oC
E
Your product +
40oC
Water activity
F
40oC + No sucrose
G
40oC + 5 g sucrose
H
40oC + 30 g sucrose
I
40oC + 50 g sucrose
J
40oC + 30 g of your
product
*Balloon Circumference in cm
Fermentation observed
Gas Produced*
Data Table 2
Test/Flask
pH
K
Conditions
40oC + pH 3
L
40oC + pH 5
M
40oC + pH 7
N
40oC + pH10
O
40oC + pH 7
Nutrient
P
40oC + Fructose
Q
40oC + Glucose
R
40oC + Sucrose
S
40oC + Lactose
T
40oC + your
product
*Balloon Circumference in cm
Fermentation observed
Gas Produced*
Individual Evaluation
Worksheet Questions (To be completed by each student individually)
Name ________________________
Lab Report: What Affects Yeast Growth?
1. What observations were you able to make about the flasks, prior to the addition of
yeast?
2. Which flasks showed the greatest yeast growth (most production of CO2 gas)?
3. Did the contents of the flasks look the same at the end of the test time? Explain.
4. Knowing what you have learned about yeast “food,” do you think yeast will
ferment gelatin or fat?
5. Which were the most favorable conditions for growth?
6. Which were the least favorable conditions for growth?
7. Did the product you brought in encourage yeast growth? Why or why not?
8. What were the main ingredients of your product?
9. What types of things do yeast need to grow on?
10. What are some ways we might have been able to improve this experiment?
Alignment with Standards
These are the National Science Teaching Standards that are met by this
activity.
Science as Inquiry
CONTENT STANDARD A: As a result of activities in grades 9-12, all students
should develop


Abilities necessary to do scientific inquiry
Understandings about scientific inquiry
Students also need to learn how to analyze evidence and data. The evidence they analyze
may be from their investigations, other students' investigations, or databases. Data
manipulation and analysis strategies need to be modeled by teachers of science and
practiced by students. Determining the range of the data, the mean and mode values of
the data, plotting the data, developing mathematical functions from the data, and looking
for anomalous data are all examples of analyses students can perform. Teachers of
science can ask questions, such as "What explanation did you expect to develop from the
data?" "Were there any surprises in the data?" "How confident do you feel about the
accuracy of the data?" Students should answer questions such as these during full and
partial inquiries.
These are the Wisconsin State Standards met by this activity.
C. Science Inquiry
Content Standard
Students in Wisconsin will investigate questions using scientific methods and tools,
revise their personal understanding to accommodate knowledge, and communicate these
understandings to others.
Performance Standard
C.12.3 Evaluate* the data collected during an investigation*, critique the data-collection
procedures and results, and suggest ways to make any needed improvements
F. Life and Environmental Science
Content Standard
Students in Wisconsin will demonstrate an understanding of the characteristics and
structures of living things, the processes of life, and how living things interact with one
another and their environment.
Performance Standards
F.12.1 Evaluate the normal structures and the general and special functions of cells in
single-celled and multiple-celled organisms
F.12.9 Using the science themes, investigate energy systems (related to food chains) to
show how energy is stored in food (plants and animals) and how energy is released by
digestion and metabolism