CAPT STRAND 5
Yeast Population Dynamics Lab
Overview
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Living organisms have the capability to
produce populations of unlimited size,
but the environment can support only a
limited number of individuals from each
species.
Background info
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Yeast is a fungus that produces carbon
dioxide as a waste product of cell
respiration.
The quantity of waste product is directly
related to the size of the yeast population.
Objective
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You will be able to identify the relationship
between a change in the environmental
conditions and yeast population.
Possible variables: Changes in pH, light,
temperature and concentrations of food
supply
Your Task
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Grow yeast in a sugar solution ( food for
the yeast) and investigate how one factor
influences the change in yeast population
growth as measured by the amount of
carbon dioxide produced.
Materials
teacher prepared yeast suspension
teacher prepared sugar solution
several 1 ml graduated dropping pipettes
100 ml graduated cylinder
weak acid/base (provided at teacherÕs discretion)
electronic balance (optional)
refrigerator/microwave
syringe
collection bottle
rubber stopper
lubrication grease
Thermometer
safety goggles
General procedure for
growing yeast
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1. Place 35 ml of the
30 % sugar solution
into the collection
bottle.
2. Place 1 ml of the
yeast suspension into
the same collection
bottle
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3. Insert plunger into
syringe
4. Place rubber
stopper onto the
syringe
5. Connect the entire
apparatus to the
collection bottle.
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6. Record starting
volume on your data
sheet
7.Incubate samples
for 24 hours and
record increase in
carbon dioxide
volume .
8. Record data after
48 hours as well.
Possible data tables
Carbon Dioxide Release
60
50
mL
40
Series1
Series2
Series3
30
20
10
0
1
2
Days
3
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You now have a procedure for growing
yeast and measuring the amount of
carbon dioxide produced as a waste
product.
Can you identify a variable you can
change which would also change the
amount of carbon dioxide produced?
Can you identify the independent and
dependent variables?


The increase in the
carbon dioxide volume
was Dependent on what
variable?
Possible answers:
pH,Temp. amount of
food….. These represent
Independent variables
The next step
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Design your lab
The design should match the problem
Include a control
Identify your variables
Review your design with your teacher
Follow all safety instructions
Begin your lab
Items to remember
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State the problem
Form a hypothesis
Describe your experiment
Organize your data
I.D. independent and dependent variables
Support your conclusions
Discuss validity
End