Yeast Fermentation
Adapted from:
http://www.qacps.k12.md.us/cms/sci/cell/Lab_Yeast.doc
Background Information:
Yeast are tiny single-celled (unicellular) fungi.
The organisms in the Kingdom Fungi are not
capable of making their own food. Fungi, like
any other organism, need food for energy.
They rely on sugar found in their
environment to provide them with this energy
so that they can grow and reproduce.
Yeast, like bacteria grow in or on their food
source. They produce and release digestive
proteins (enzymes) into their environment
where the sugar molecules are found. Sugar
molecules then break down into smaller
molecules that can be absorbed by the yeast
and used for food (energy).
There are many species of yeast, and each has
a particular food source.
• Certain yeast feed on a variety of natural
sources of sugar such as fruits, nectar from
plants, and molasses from the plant crop
called sorghum.
• Others break down wood and corn stalks. In
doing this, a compound called ethanol is
produced. This compound can be used in our
cars like gasoline.
• Another species breaks down sugar from
grain into alcohol. Others break down fruits
into wine, which is another type of alcohol.
• Bread recipes rely on yeast to break down
sugar in our dough.
All of these processes are called fermentation,
a type of anaerobic respiration (respiration
without oxygen). The formula for the yeast
fermentation reaction is:
C6H12O6
Reactant
Products
>>>>>>>
2CH3CH2OH + 2CO2 + energy for 2 ATP molecules
Glucose breaks down into ethyl alcohol +
carbon dioxide + energy for 2 ATP molecules.
For the yeast cell, this chemical reaction is
necessary to produce the energy for life. The
alcohol and the carbon dioxide carbon
dioxide are waste products produced by the
yeast. It is these waste products that we take
advantage of. We use the alcohol and the
carbon dioxide makes a cake rise when
baking.
The chemical reaction, known as
fermentation, can be watched and
measured by the amount of carbon dioxide
gas that is produced from the break down
of glucose.
Do you think that the volume of carbon
dioxide produced during fermentation
would be affected by using different
masses of sugar????
In this exercise you will add the same
amounts of yeast and water to different
amounts of sugar in water bottles and cap
them with a balloon to see how much
carbon dioxide gas is produced. The more
the fermentation, the more that carbon
dioxide will be produced, and the more the
balloon will expand.
You should include the following
components in your lab report:
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Name(s), date of experiment, title
Purpose statement:
Prelab questions
Procedure-to be created as a class
Data table
Graph of class data
Answers to analysis questions
Prelab Questions
1. Write out the equations for aerobic
cellular respiration and anaerobic
fermentation.
2. Create a table to compare the two
equations. List at least 2 differences and
2 similarities between the equations.
3. What is an advantage to cellular
respiration?
4. What is an advantage to fermentation?
Materials
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5 yeast packets
Sugar
Erlenmeyer flask
5 balloons
Warm water
String
Meter stick
Rubber band
Stopwatch
Spoons
Procedure
1. Blow balloon up to circumference of
65cm and release air.
2. Add 100ml of hot tap water to flask.
3. Add grams of sugar to flask (5g, 10g,
15g, 20g, 25g, 30g, 35g)
4. Add 1 complete packet of yeast
5. Place empty balloon over flask opening,
secure with rubberband.
6. Gently shake to mix contents.
7. Measure circumference of balloon every
5 minutes for 25minutes.
Data Table:
Group
1
2
3
4
5
5 min
10min
15min
20min
25min
Analysis Questions
1. Which group’s balloon reached the largest
size?
2. What substance was collected in the
balloon? How do you know?
3. What were the independent and dependent
variables in this experiment?
4. Which group was the control? Why is it
considered the control? What is its purpose?
5. Write a brief summary describing what you
saw happen in this experiment and then give
your explanation of the results. (why)