GHS Science CAPT Embedded Task Review

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GHS ScienceCAPT Embedded Task Review

• Lab Investigation Yeast Population Dynamics

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Introduction Why Study Yeast Populations?

• Yeast is a good model organism because it is
  simple, but has many of the same processes as
  more complicated cells.
• Yeast use simple sugars to perform cellular
  respiration and make ATP. During cellular
  respiration, they release CO2 as a waste product,
  just like animals and plants. sugar O2 ?
  CO2 H2O ATP (energy)
• Since more yeast cells will release more CO2, we
  can use the amount (or volume) of CO2 volume as a
  measurement of the amount of yeast cells. The
  amount of yeast cells will tell us the size of
  the population.
• Amount of CO2 Population Size
• DID YOU KNOW? Yeast population variations
  produce flavor characteristics in a wide variety
  of food products such wine, beer, and bread.

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Use of Energy, Growth and Reproduction in Yeast

Yeast Cell
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Your Task

• Determine how environmental conditions such as
  pH, temperature, light, etc. can effect the
  growth of a yeast population
• REMEMBER we can use CO2 (carbon dioxide) volume
  as a measurement of the size of the yeast
  population in the test tube.

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Measuring Yeast Population Growth by CO2
Production
Mix the yeast in the solution by putting the
clean palm of your hand over the end and
inverting it 5 times
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CO2 Collection Set-up
This is the double test tube set up for
collection of CO2. To obtain this the lager test
tube is placed over top of the smaller filled
test tube. It is then quickly inverted so that
the larger test tube is open and the smaller one
is upside down. An air bubble will be left at
the top of the tube.
Large Test Tube
Small Test Tube inverted and filled w/ yeast
molasses solution
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Collecting Data
Students Collect CO2 Bubble Height Data for 5 Days
Day 1 Day 3 Day 5
Time in DAYS
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Experimental Design

• You need to choose an environmental variable to
  change during the experiment.
• Environmental variables that you can change pH,
  temperature, light, or concentration of molasses
  (sugar)
• The initial bubble size is subtracted from the
  bubble size each day to calculate the total
  volume of CO2 collected

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Sample Experiment How does changing
temperature affect the yeast population size?
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Sample Experiment The Effect of Temperature
on Yeast Population Size

• Temp 4C (original bubble size 5 mm)

Day 1 Day 2 Day
3 Day 4 Day 5 Bubble Size 5mm
5.5mm 5.5mm 6mm 6mm
Temp 24C (original bubble size 4 mm)
Day 1 Day 2 Day
3 Day 4 Day 5 Bubble Size
14mm 22 mm 33 mm 38 mm 42mm
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Sample Experiment The Effect of Temperature
on Yeast Population Size

• Temp 30C (original bubble size 5 mm)

Day 1 Day 2 Day
3 Day 4 Day 5 Bubble Size
15mm 25mm 40mm 50mm 58mm
Temp 44C (original bubble size 4 mm)
Day 1 Day 2 Day
3 Day 4 Day 5 Bubble Size
12mm 18mm 28mm 32mm 34mm
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Raw Data CO2 Bubble Height from Yeast Grown at
Various Temperatures
Bubble Height measured in mm.
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Analysis Questions

• Directions On a separate sheet of paper, answer
  the following questions in complete sentences.
• Identify the following for this experiment
• Problem statement
• Independent variable
• Dependent variable

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Analysis Questions

• 2. What would you consider the control in this
  experiment? Why?
• 3a. Identify two variables that were held
  constant in this experiment.
• 3b. Explain why it is important to hold these
  variables constant.
• 4. Why do you think the size of the bubble
  doesnt continue to increase at the same rate
  during day 4 and day 5?
• 5. Based on the data, what would your conclusion
  be for this experiment?

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Definitions

• Problem Statement The problem that the
  scientist is trying to solve.
• Hypothesis An educated guess that answers the
  problem statement. Often, an If Then
  statement is used. So, If I change the
  independent variable, Then the dependent variable
  will change in this way.
• Independent Variable The variable in an
  experiment that the scientist purposefully
  changes. This change should affect the dependent
  variable.
• Dependent Variable The variable in an experiment
  that changes and that the scientist measures.
  This variable depends on the independent
  variable.
• Control The baseline that you can compare the
  other groups exposed to the independent variable
  against. Used test how valid the independent
  variable is.
• Controlled Experiment An experiment in which all
  factors are kept constant except for the
  independent variable.