Learning Targets “I Can…” -Focus a slide under a microscope by always starting with the...

Learning Targets“I Can…”

-Focus a slide under a microscope by always starting with the objective (the red) to observe living yeast cells.

-Predict the outcome of yeast growth over a certain time period on a graph.

-Define “exponential growth.”

-Draw/Interpret a graph for a population that is experiencing exponential growth .

Population Dynamics

Examining a Closed Population

Yeast Cells (Microscopic View)

Budding Yeast Cells

Yeast Cells Reproducing

What is a closed population?

Populations normally change in size as individuals reproduce, die, and move in and out of an area.

A closed population is one that does not experience migration, so the population number changes only through births and deaths.

What you will do today…

You will be given yeast cells that have been placed in a closed environment with lots of food (apple cider).

Growth of the yeast cells will be observed under the microscope and by using turbidity over a period of nine days.

Make a prediction . . .

NUMBER OFYEAST CELLS

TIME IN DAYS

What is turbidity?

Turbidity is the cloudiness of a solution.

What is turbidity?

To measure turbidity, we use a Colorimeter.

What is turbidity?

The Colorimeter measures the amount of light absorbed by the yeast cells.

The more yeast cells there are, the cloudier the suspension, the more light that is absorbed.

Make a prediction . . .

ABSORBANCE

TIME IN DAYS

Procedures

1. Prepare a slide for your control. Prepare a slide for your experimental. BE SURE TO USE SEPARATE PIPETTES!

2. Count the number of yeast cells on each slide under the BLUE objective.

3. Fill the labeled cuvettes with the appropriate sample to about ¾ full.

4. Measure the absorbance of each sample using the colorimeter.

5. Record all of your values on the data table on the front table.

6. Discard your sample down the sink, throw away all used pipettes and coverslips, and rinse your test tubes and cuvettes.

7. Return your microscope to the cabinet.

Table 2

Day Absorbance Microscopic count

Team data Class average Team data Class average

Expt Control Expt Control Expt Control Expt Control

0 .23 .20 7 0

1 .30 .20 46.5 0

2 .20 .20 21.5 0

3 .30 .20 40.8 .20

4 .39 .20 48.1 .1

5

6

7 .60 .20 41.3 0

8

Absorbance of Solutions

0

0.2

0.4

0.6

0.8

1

1 2 3 4 5 6 7 8 9

Day

Pe

rce

nta

ge

of

Lig

ht

Ab

so

rbe

d AbsorbanceExperimental

AbsorbanceControl

Microscopic Count of Yeast

0

100

200

300

400

1 2 3 4 5 6 7 8 9

Day

Nu

mb

er

of

Ce

lls

Yeast CountExperimental

Yeast CountControl

References

• http://bugs.bio.usyd.edu.au/learning/resources/CAL/Microconcepts/images/Topics/Diversity/buddingYeastCells.jpg

• http://etc.usf.edu/clipart/15400/15447/grwyeastcell_15447_lg.gif

• http://www.public.asu.edu/~jpbirk/qual/qualanal/WHITE/Ca4ppt.gif

• http://www.copcoinc.com/uploads/col-bta_web-0-0.jpg

• https://www.youtube.com/watch?v=BTHYaf-EuYs