Yeast Habitat Carrying Capacity Lab by C. Kohn
Name:
Hour
Date Assignment is due: On Wed Nov 23rd
Day of Week
Date
Date:
Why late?
If your project was late, describe why
Directions: In this lab you will be working in groups of two to create two different “habitats” for yeast and then
measuring their population growth. To create your yeast habitat, you will be preparing two different molasses solutions.
Step 1: Prepare the molasses solutions. Using a graduated cylinder or a measuring cup, prepare a 25% molasses
solution and a 50% molasses solution.
-
To prepare the 25% solution, mix 5 ml of molasses with tap water until you get 20 ml of solution. Pour into a
test tube and with a grease pen, write “25” on the tube.
Rinse your measuring cup or graduated cylinder well and add 10 ml of molasses. Add another 10 ml of water to
make 20 ml. Add to a second test tube and with a grease pen write “50” on the tube.
Add your initials to each tube.
Step 2: Prepare the yeast solutions. With the group next to you, mix a packet (7 grams) of yeast into 200 ml of warm tap
water. You will be using this same 200 ml yeast solution between both groups.
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Stir the yeast into the warm tap water until it is evenly suspended in the solution.
Add 25 ml of the yeast solution to your 25% molasses test tube; then add another 25 ml to your 50% molasses
solution.
Immediately place a balloon over each test tube and secure each balloon with 1 or 2 rubber bands. With your
thumb over the top of the tube and balloon, shake each tube gently for 2 minutes.
Place each tube in the rack in the warm water bath. As the yeast eats the molasses, they will produce CO2 (just
like you do when you breathe out). The yeast will also grow and reproduce. The amount of CO2 produced is an
indirect way to measure the population growth of your yeast populations.
1. What differences do you think you will see between the 25% molasses solution and the 50% molasses solution?
Write your expectations for what will happen below:
2. Why do you think this will happen? Write a justification for why you think what you wrote in #1 will happen:
Step 3: Record your data. Using a ruler, record the diameter of the balloon in centimeters using the time intervals listed
on the chart on the back of this page.
Diam. of
balloons
(cm)
25%
solution
50%
solution
Diam. of
balloons
(cm)
1 minute
15
minutes
3 minutes
17
minutes
5 minutes
19
minutes
7 minutes
21
minutes
9 minutes
23
minutes
11
minutes
25
minutes
13
minutes
Final
25%
solution
50%
solution
3. Which balloon inflated the most from CO2?
4. Why do you think this occurred?
5. Graph the rate of both balloons’ inflation below (use a separate line for each balloon; note which is which)
cm of
inflation
6. How do you think shaking the tubes affected the growth of the yeast and the production of CO2? Explain:
7. The solutions of molasses were models of carrying capacities of a habitat. Explain how the availability of
molasses to yeast in a test tube is similar to availability of resources in a habitat:
8. What happened to the yeast population when we doubled the carrying capacity of the test tube?
9. How might doubling the carrying capacity of a habitat affect the population of wildlife in that habitat?
10. Could doubling the carrying capacity of a habitat have any negative effects to that habitat and the wildlife that
live within it? Explain: