NAME
Yeast Respiration: lots of gas!
Objective
The purpose of this activity is to visualize aerobic respiration. For today’s activity, we will use
the unicellular eukaryote baker’s yeast (Saccaromyces cerevisiae) as the model organism for
observing respiration. Yeast are members of the Fungi Kingdom. These small, single-cell
organisms are important in food production because of the way they break down their food to
make energy. Yeast use their own digestive enzymes to break down their food. The chemical
formula for respiration is:
C6H12O6 (glucose) + 6 O2
2 CO2 (gas) + 6 H2O + ATP (energy)
Yeast also are able to undergo respiration in environments without oxygen. Anaerobic respiration
is called fermentation. Fermentation is a process many organisms use to make energy when
oxygen is not available. There are two types of fermentation: alcohol and lactic acid. Alcohol
fermentation occurs when yeast breaks down sugar and produces alcohol, carbon dioxide (gas)
and energy.
Lactic acid fermentation occurs in us when our muscles are working harder and faster than when
oxygen can reach all our cells. Lactic acid is a product when fermentation occurs within our
cells. When lactic acid builds up in our cells, our muscles feel sore.
Materials
water bottle
glasses
balloon
dry active baker’s yeast
writing utensil
water
string
clock
sugar
ruler
Procedures & Data Collection
1.
Make a hypothesis about which bottle/balloon will produce the most gas.
2.
You will work in groups of 4
3.
Label each water bottle ‘A’ through ‘D’
a. Add 25 mL water and yeast to bottle ‘A’
b. Add 25 mL water only to bottle ‘B’
c. Add 25 mL water, yeast, corn starch to bottle ‘C’
d. Add 25 mL water, yeast, 2 sugar cubes to bottle ‘D’
4.
Tightly cover each flask with a balloon
5.
Use a clock/watch to take measurements every 5 minutes for 20 minutes
safety
NAME
a. Use the sting and ruler to measure the circumference of each balloon at each time point
b. Record this data in your chart
Flask
Circumference at 5
minutes (cm)
Circumference at 10
minutes (cm)
Circumference at 15
minutes (cm)
Circumference at
20 minutes (cm)
A
B
C
D
Balloon Circumference (cm)
c. Make a graph showing the balloon circumference (y-axis) over time (x-axis)
Time (minutes)
NAME
6.
Describe any observations you see happening inside the bottles during the experiment.
7.
Clean up your work space
Questions/Assessment
1.
What was causing the balloon to inflate?
2.
Eventually, the balloons will stop inflating. What do you think is happening to stop the
balloon from inflating?
3.
What do you think the balloon circumference would look like if cold water was used
instead?
4.
What are some foods that require fermentation?
5.
What cup(s) were the control samples?