CAPT STRAND 5CAPT STRAND 5

Yeast Population Dynamics Yeast Population Dynamics LabLab

OverviewOverview

Living organisms have the Living organisms have the capability to produce populations capability to produce populations of unlimited size, but the of unlimited size, but the environment can support only a environment can support only a limited number of individuals from limited number of individuals from each species.each species.

Background infoBackground info

Yeast is a fungus that produces Yeast is a fungus that produces carbon dioxide as a waste product of carbon dioxide as a waste product of cell respiration.cell respiration.

The quantity of waste product is The quantity of waste product is directly related to the size of the directly related to the size of the yeast population.yeast population.

Objective Objective

You will be able to identify the You will be able to identify the relationship between a change in the relationship between a change in the environmental conditions and yeast environmental conditions and yeast population.population.

Possible variables: Changes in pH, Possible variables: Changes in pH, light, temperature and light, temperature and concentrations of food supply concentrations of food supply

Your TaskYour Task

Grow yeast in a sugar solution ( food Grow yeast in a sugar solution ( food for the yeast) and investigate how for the yeast) and investigate how one factor influences the change in one factor influences the change in yeast population growth as yeast population growth as measured by the amount of carbon measured by the amount of carbon dioxide produced.dioxide produced.

Materials

teacher prepared yeast suspension syringeteacher prepared sugar solution collection bottleseveral 1 ml graduated dropping pipettes rubber stopper100 ml graduated cylinder lubrication greaseweak acid/base (provided at teacher’s discretion) Thermometerelectronic balance (optional) safety gogglesrefrigerator/microwave

1. Place 35 ml of 1. Place 35 ml of the 30 % sugar the 30 % sugar solution into the solution into the collection bottle.collection bottle.

2. Place 1 ml of the 2. Place 1 ml of the yeast suspension yeast suspension into the same into the same collection bottlecollection bottle

General procedure for General procedure for growing yeastgrowing yeast

3. Insert plunger 3. Insert plunger into syringe into syringe

4. Place rubber 4. Place rubber stopper onto the stopper onto the syringesyringe

5. Connect the 5. Connect the entire apparatus to entire apparatus to the collection the collection bottle. bottle.

6. Record starting 6. Record starting volume on your volume on your data sheetdata sheet

7.Incubate samples 7.Incubate samples for 24 hours and for 24 hours and record increase in record increase in carbon dioxide carbon dioxide volume .volume .

8. Record data 8. Record data after 48 hours as after 48 hours as well.well.

Possible data tablesPossible data tablesCarbon Dioxide Release

0

10

20

30

40

50

60

1 2 3

Days

mL

Series1

Series2

Series3

You now have a procedure for You now have a procedure for growing yeast and measuring the growing yeast and measuring the amount of carbon dioxide produced amount of carbon dioxide produced as a waste product.as a waste product.

Can you identify a variable you can Can you identify a variable you can change which would also change the change which would also change the amount of carbon dioxide produced?amount of carbon dioxide produced?

Can you identify the independent and Can you identify the independent and dependent variables?dependent variables?

The increase in the The increase in the carbon dioxide volume carbon dioxide volume was Dependent on was Dependent on what variable?what variable?

Possible answers: Possible answers: pH,Temp. amount of pH,Temp. amount of food….. These food….. These represent represent Independent variablesIndependent variables

The next stepThe next step

Design your labDesign your lab The design should match the problemThe design should match the problem Include a control Include a control Identify your variables Identify your variables Review your design with your teacherReview your design with your teacher Follow all safety instructions Follow all safety instructions Begin your labBegin your lab

Items to rememberItems to remember

State the problemState the problem Form a hypothesisForm a hypothesis Describe your experimentDescribe your experiment Organize your dataOrganize your data I.D. independent and dependent I.D. independent and dependent

variablesvariables Support your conclusions Support your conclusions Discuss validityDiscuss validity

EndEnd