Name: _____________________________________________ Date: _____________ Class: ______________________
Hungry, Hungry Fungi
Introduction
You’ve probably eaten some fungi today. And the fungi you probably ate
are called yeast. People have been eating yeast breads for about 6000 years, but it
was not until the investigations of Louis Pasteur in 1857 that yeast was identified
as a microorganism. Yeasts are single-celled fungi. About 160 different species
are known, with different yeasts useful for
brewing, and baking. Some yeast can cause
human infections and some contribute to food
spoilage. However, yeast is used to transform
many of the foods we eat in important ways.
When bread is made, yeast is an
essential ingredient; it is because of yeast
munching on the grains before we do that
bread rises, becomes soft, and becomes
delicious. When yeast eats the grains found in
bread, it produces carbon dioxide (CO2) and
alcohol (C2H6O). Simple sugars, such as
glucose
and fructose are consumed first, and
Above: Yeast cells. Yeast is a
then
its
metabolism
changes and it consumes
single-celled organism. It
complex
sugars
such
as maltose and sucrose.
benefits us by partially breaking
In
the
presence
of
oxygen,
yeast breaks down
down many of the foods we eat.
sugars into carbon dioxide and water. The
But, some strains of yeast are
production of carbon dioxide is what makes
bad and they can contaminate
bread rise. All of the bubble holes in bread are
our food, or infect humans.
caused by CO2 bubbles being made. When
alcoholic beverages, such as beer, wine, and
whiskey are made, the oxygen is limited, forcing yeast to do fermentation. The
products of this breaking down of sugars without oxygen are carbon dioxide and
alcohol. That is why beer and wine are bubbly, and also alcoholic.
In this experiment, we will provide yeast with several different substances
to “eat.” Which substances do you think yeast can consume the fastest, or easiest?
Which do you think yeast will not be able to consume?
Materials Needed





active dry yeast
sugar
flour
water, warm
artificial sweetener


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
Above: Beer is bubbly and alcoholic.
This is because yeast breaks down the
carbohydrates without oxygen.
Below: When oxygen is available, yeast
breaks down carbohydrates into carbon
dioxide and water. CO2 bubbles can be
seen is this rising loaf of bread. While
bread bakes, oxygen is easily available
to the yeast, so there is no alcohol made
by the yeast.
measuring spoons
50-mL graduated cylinder or measuring cup.
Zipper-lock type plastic bags, quart size
plastic wash tub or bucket
a marker to write on the plastic bags
Procedure
1. Obtain 5 zip-lock type bags and label them. Your instructor may have your group prepare all 5 bags, or just one
or two. Write your group name on the bag and label it.
a. Bag #1: yeast
b. Bag #2: yeast and water
c. Bag #3: yeast, water and sugar
d. Bag #4: yeast, water and flour
e. Bag #5: yeast, water and artificial sweetener
M. R. Lawton 2013
2. Collect the materials that you will need. Write down observations about the materials in the data table.
3. Add the following materials to the bags that you have labeled:
a. Bag #1: 1 package of yeast
b. Bag #2: 1 package of yeast, 50 mL warm water
c. Bag #3: 1 package of yeast, 1 Tbs. sugar, 50 mL warm water***
d. Bag #4: package of yeast, 1 Tbs. flour, 50 mL warm water***
e. Bag #5: package of yeast, 1 Tbs. artificial sweetener (3 packets), 50 mL warm water
***note: one tablespoon (Tbs.) is one leveled off scoop, not one heaping scoop.
4. Carefully, without spilling any of the contents, squeeze out as much air as possible and seal each bag.
5. Measure the volume of the bag by submerging it in a large beaker and measuring the displacement of water.
Record your data in a data table.
6. Put the bags in a warm place for 25 minutes. Observe the bags periodically. While you wait, work on the other
questions and sections of this lab write up!
7. After the 25 minutes, remove the bags from the warm place and observe them. What changes have occurred?
Record them in your observations.
8. Measure the volume of the bag by submerging it in a large beaker and measuring the displacement of water.
Record your data in a data table.
Question
What could be a question for this lab?
Hypothesis
Write a hypothesis for your experiment. Remember to write it as an “if ___ then ___” statement. In the “if” part, the
experiment is briefly described. The “then” part is a prediction about the outcome of the experiment.
Pre-Lab Questions
1. What is the independent variable in this experiment?
2. What is the dependent variable in this experiment?
3. What is the difference between qualitative data and quantitative data (in general)?
4. What is the control group in this experiment?
5. What are the experimental groups in this experiment?
6. Write out the chemical reactions for photosynthesis and cellular respiration. Which reaction will we observe in this
experiment? How do you know?
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Data Collection
Qualitative Observations of Reactants (before you mix them)
Observations of
yeast powder:
Observations of
sugar:
Observations of
flour:
Observations of
artificial sweetener:
Observations of Reaction Remember to write your units! (record your data here, then add in data from other
groups, if needed)
Bag
number
/
Trial
number
Amount
of yeast
Amount
of
water
Type of “food”
for yeast, and
amount
Volume
of bag
before
Volume
of bag
after
Qualitative observations of reaction
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Data Analysis
Graph your data. Give the graph a title. Also, remember to put the independent variable on the x-axis and the dependent
variable on the y-axis.
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(extra graph paper, just in case you need it)
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Conclusion
Was your hypothesis supported or not supported? Explain why or why not using your data. (this step should be several
complete sentences long: discuss your data and graphs in detail and explain what it means)
Post-Lab Questions
Answer the following questions in complete sentences.
1. What is the purpose of the control in this experiment?
2. Some of the bags puffed up like balloons. What was the gas that filled
these bags? Where did it come from?
3. What is the name of the chemical reaction that occurred in the bags that puffed up? Write out this chemical reaction.
4. Where do you think flour comes from? What kinds of macromolecules could be found in flour?
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5. Where do you think sugar comes from? What kinds of macromolecules could be found in sugar?
6.
Where do you think artificial sweetener comes from? What kind of molecule or macromolecules do you think is
found in the artificial sweetener?
7. Which type of “food” did the yeast consume the fastest (base your answer on your data)? Why do you think that is?
8. Which type of “food” did the yeast consume the slowest (base your answer on your data)?
is?
Why do you think that
9. What could be some sources of scientific error in this experiment? List three sources of error in this experiment.
10. What are some ways that we could make this experiment more accurate? Discuss three possible ways to fix or
address the sources of error that you stated in the previous question.
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11. You baked some bread. You did everything correctly, except that you forgot to
add the yeast! What do you think the resulting bread would be like?
12. Wine is made from primarily from three ingredients: grapes,
yeast, and water. What if a wine maker attempted to make wine,
but forgot to add the yeast. What do you think the resulting
beverage would be like?
13. Artificial sweeteners are chemicals that taste very sweet, yet provide zero calories. They are used in diet soda pop to
make it taste just like soda pop, but without a high amount of sugar.
a. How did the yeast react to artificial sweetener?
b. Why do you think the yeast behaved in this way?
c. What could be some ways that artificial sweeteners are healthier than sugar?
d. What do you think could be some ways that artificial sweeteners might not be healthy?
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PHOTOSYNTHESIS
The production of food from carbon dioxide and water in the presence of chlorophyll utilizing light energy and releasing
oxygen is called photosynthesis. Plants produce food in the form of simple sugars (carbohydrate). In order for
photosynthesis to occur sunlight and chlorophyll must be present. There are different types of chlorophyll, but the one
involved in photosynthesis is called chlorophyll-A. Chlorophyll is a pigment which is stored in chloroplasts. During
autumn and winter chlorophyll is not produced allowing the other pigments of brown and red to predominate giving
plants their autumn colors.
Materials Needed
 Elodea plant
 Light source
 Bromothymol Blue



Straws
Five (5) 25-ml graduated cylinders
Demonstration prepared the night before
Procedure
1. Add 1-2 drops of bromothymol blue to 15mL of water in a 25 ml graduated cylinder.
a. Gently blow into the tube using a straw until it changes color to yellow.
b. Discuss the change.
c. The change occurs because CO2 has been added to the solution, making it more acidic therefore causing
a color change.
d. Remember, humans produce carbon dioxide and utilize oxygen whereas plants utilize carbon dioxide
and produce oxygen.
2. Place a piece of elodea in the 25-mL graduated cylinder with the yellow solution and insert a cork stopper in the
beak of the cylinder. Expose the cylinder to sunlight for 20 minutes.
3. In another cylinder, add 1-2 drops of bromothymol blue to water and gently blow with a straw until the solution
changes color. Plug the top of the cylinder with a stopper and place it in the sunlight for 20 minutes without
elodea.
4. Prepare another cylinder in the same manner as the previous one, but do not expose it to sunlight, wait 20
minutes.
5. A final cylinder containing an elodea plant bromothymol blue and water should have been prepared before this
activity and left in a dark place for 24 hours.
M. R. Lawton 2013