Name: ___________________________________
Date: _____________
Period: ___________
CELLULAR RESPIRATION/FERMENTATION IN YEAST LAB
OBJECTIVES:
 Distinguish between aerobic and anaerobic respiration.
 Calculate the volume of carbon dioxide gas produced under various environmental conditions.
 Graph carbon dioxide production data.
 Determine the ideal growth conditions for yeast and their relation to carbon dioxide production.
BACKGROUND:
“Fermentation” is a chemical process carried out by microorganisms such as bacteria, mold, and yeast. The process
breaks down energy-rich organic materials to help generate energy. Our early ancestors used this process for the
production of food and drink thousands of years before the existence of these microorganisms was established. They
used a combination of yeast cells and nutrients that formed a natural fermentation system in which the microorganisms
consumed the nutrients as food and, in return, produced byproducts such as alcohol and carbon dioxide which are
useful in making wine and bread.
Today, we don’t rely on natural fermentation. We use fermenters, or bioreactors, to manufacture alcoholic beverages,
cheese, bread, and pharmaceutical products. In a bioreactor, living cells are mixed with nutrients grown in a carefully
controlled, sterile environment to make a specific product. The temperature, pH, oxygen, and nutrient content must be
maintained at just the right levels for the process to work correctly.
It wasn’t until 1815 that the process of fermentation was studied in a scientific way. A French chemist, Louis GayLussac, concluded that the production of alcohol and carbon dioxide was due to a physical change in which inert
organic matter decomposed into those two products.
Microorganisms, such as yeast, use sugar in a similar way as animals do. They break sugars down into carbon dioxide
and water while releasing energy for growth, activity, and reproduction. Under proper environmental conditions, the
reaction known as “aerobic respiration” occurs:
C6H12O6 + 6O2

6CO2
+
6H2O
+ energy
Sugar
Oxygen
Carbon dioxide
Water
When oxygen supply is limited, such as in bread dough, the yeast can only partially break down the sugar and it is
forced to undergo “anaerobic respiration” as shown in the following equation:
C6H12O6 + 6O2

2CO2
+
2C2H5OH
+ energy
Sugar
Oxygen
Carbon dioxide
Ethyl alcohol
Carbon dioxide bubbles resulting from the breakdown of sugar molecules provide the fluffy, spongy texture of bread
and the fizz in beer. Although the fermentation process used industrially is much more sophisticated than that of the
early days, it still relies on the same principles of combining living organisms or enzymes, along with nutrients, under
a controlled environment to produce commercially useful products. Today, applications of fermentation have grown
well beyond the traditional manufacture of alcoholic beverages and food products. Newer applications of fermentation
technology cover a vast range of industries and are linked to biotechnology, medicine, and the developing science of
genetic engineering.
In this experiment, you will indirectly measure the release of energy by baker’s yeast, Saccharaomyces cerevisiae.
You will do this by monitoring and measuring the volume of carbon dioxide produced when varying both the type of
sugar it is fed and the temperature of its environment.
Needed equations:
C=2πr
V=4/3πr3
1
1mL=1cm3
Acad Bio
Name: ___________________________________
Date: _____________
Period: ___________
MATERIALS:
Wax Pencil
4 Glass Vials
4 Rubber Bands
4 Balloons
1 Ruler & String
Graduated Cylidner
90 mL of Lukewarm Water
30 mL of Cool Water
8 Grams Dried Yeast
6g Sucrose
2g Lactose
ACTIVITY 1 – WHAT IS YEAST’S FAVORITE FOOD?
An ideal indication of the amount of respiration which yeast is undergoing is the amount of carbon dioxide it releases
as a waste product of the respiration reactions. In this activity, you will feed some yeast sucrose and some yeast
lactose. You will compare the carbon dioxide output from either food source to determine which yeast prefers.
 Step 1: Use a wax pencil to label the vials “#1” and “#2” (#1 will represent sucrose, #2 will represent lactose).
 Step 2: Add 2 grams of dried yeast to each vial.
 Step 3: Add 2 grams of sucrose to vial #1.
 Step 4: Add 2 grams of lactose to vial #2.
 Step 5: Add 30mL of lukewarm water (37° C) to each vial. Mix the contents with a stirring stick.
 Step 6: Place a deflated balloon over each vial and secure it by placing a tightly bound rubber band around the neck
of the vial.
 Step 7: Place all vials in the culture incubator set at 37° C to maintain the initial temperature.
 Step 8: Observe your vials every 20 minutes for a total of an hour and 20 minutes and measure the circumference
of each balloon using your string and the ruler. Record your results in Data Table 1.
***As soon as you are done setting up Activity 1,
move on to set up Activity 2 while you wait to take measurements***
Table 1
ACTIVITY 2 – WHAT IS YEAST’S FAVORITE FOOD?
2
Acad Bio
Name: ___________________________________
Date: _____________
Period: ___________
ACTIVITY 2 – DETERMINING THE OPTIMUM GROWING TEMPERATURE FOR YEAST?
An ideal indication of the amount of respiration which yeast is undergoing is the amount of carbon dioxide it releases
as a waste product of the respiration reactions. In this activity, you will feed some yeast in a cool environment and
some yeast in a warm environment. You will compare the carbon dioxide output in either environment to determine
which yeast prefers.
 Step 1: Use a wax pencil to label the vials “#1” and “#2” (#1 will represent sucrose, #2 will represent lactose).
 Step 2: Add 2 grams of dried yeast to each vial.
 Step 3: Add 2 grams of sucrose to each vial.
 Step 4: Add 30mL of cool water (16-18° C) to vial #1.
 Step 5: Add 30mL of lukewarm water (37° C) to vial #2.
 Step 6: Mix the contents of each vial using a stirring stick or by gently swirling.
 Step 7: Place a deflated balloon over each vial and secure it by placing a tightly bound rubber band around the neck
of the vial.
 Step 8: Place vial #1 in a cool waterbath to maintain the temperature. (Create the waterbath by adding cold tap
water to a beaker).
 Step 9: Place vial #2 in a culture incubator to maintain the initial temperature of (37° C).
 Step 10: Observe your vials every 20 minutes for a total of an hour and 20 minutes and measure the
circumference of each balloon using your string and the ruler. Record your results in Data Table 2.
Table 2
3
Acad Bio
Name: ___________________________________
Date: _____________
Period: ___________
RESULTS:
1.
2.
3.
4.
5.
6.
7.
8.
9.
Use some of the space below to show your CO2 volume calculations. Show one for each Data Table.
Draw two graphs: One for Data Table 1 and one for Data Table 2.
Label graph one Sucrose vs. Lactose. Label graph two Optimum Growth Temperature for Yeast.
The dependent variable (x-axis) should be Fermentation Time (in Hours) for each graph.
The independent variable (y-axis) should be Volume of CO2 (in mL) for each graph
Use the  symbol to represent the points for Sucrose.
Use the  symbol to represent the points for Lactose.
Use the  symbol to represent the points for cool water.
Use the  symbol to represent the points for the warm environment.
4
Acad Bio
Name: ___________________________________
Date: _____________
Period: ___________
CONCLUSIONS:
Find each * and answer the question in a way that shows off your scientific knowledge of cellular respiration.
1. *What element did you control by keeping the same in Activity 1? *What element of the experiment did you vary or
manipulate? *What did this setup allow you to determine?
2. *What element did you control by keeping the same in Activity 2? *What element of the experiment did you vary or
manipulate? *What did this setup allow you to determine?
3. *What is yeast’s preferred food? (Which type of sugar was consumed by the yeast?) *How do you know? *Using
the data you have acquired, and what you know about carbohydrates, why was this sugar consumed but not the other?
4. *Why does the balloon expand above any vial?
5. *Based upon your results in Activity 2, what is the ideal temperature to yield the greatest volume of CO2? *Where
does the CO2 come from and what does the CO2 level indicate in terms of the activeness of yeast?
5
Acad Bio
Name: ___________________________________
Date: _____________
Period: ___________
6. *What would happen to the rate of respiration if all of the sugar was used up? *Why?
7. *Why is yeast used to make good bread?
8. *What were you supposed to learn from (why did we conduct) this lab?
6
Acad Bio