Name: ______________________
Date:_______________
Yeast Cellular Respiration Investigation
Introduction: Yeasts are unicellular microorganisms of the fungi kingdom. They are
facultative anaerobe, which means that they can respire or ferment depending upon
environmental conditions. In the presence of oxygen, respiration takes place
(aerobic respiration). Without oxygen present, fermentation occurs (anaerobic
respiration). Both processes require sugar to produce cellular energy. Here is the
chemical reaction of fermentation, which produces ethanol and carbon dioxide as
metabolic waste products.
For the yeast cell, this chemical reaction is necessary to produce the energy for
life. The alcohol and the carbon dioxide are waste products produced by the yeast.
It is these waste products that we take advantage of. 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.
Objective: In this lab, students will use the respiration powers of yeast to blow
balloons. This activity will reinforce the basic principles of respiration as a
fundamental metabolic process for living organisms using yeast as a model. It will
also explore how humans use this biological knowledge in everyday life.
Material (per group):
· 1 balloon
· narrow funnel
· 2 tbsp. sugar
· 1 cup warm water
· 1 tablespoon active dry yeast
· 1 plastic water bottle
Safety:
 There is NO eating or drinking in the lab.
 Do not attempt to inflate the balloons with their mouths, especially after it is
filled with the reacting agents.
Hypothesis:
What will happen to the balloon? Why do you predict this?
______________________________________________________________
______________________________________________________________
______________________________________________________________
Procedure:
1
1. Stretch out the balloon by pulling from both ends.
2. Fill the water bottle with 1 cup of warm water.
3. Add 2 teaspoonfuls of sugar to the water bottles. (You can use a funnel or
fold a sheet of paper into a cone.)
4. Close the bottle and shake to dissolve the sugar.
5. Add 1 tablespoon of active dry yeast to the bottle, another student quickly
places the mouth of the balloon over the top of the bottle.
6. Check to make sure that the balloon is tight over the top of the bottle. You
may use tape to hold the balloon in place.
7. Gently swirl the contents.
8. Record your observations below.
Observations:
Bottle with Sugar, Water and Yeast
Observations of what is happening in the bottle:
Observations of what is happening in the balloon:
Model: Using diagram(s) and labels, show and explain what happened to the balloon
and its contents and to the contents of the bottle.
Discussion:
1. What are the reactants in fermentation?
2
2. What are the products in fermentation?
3. What is the purpose of warm water?
4. Why is respiration important for living organisms?
5. If you were asked to set up controls for this investigation, what would you
do?
6. How is fermentation different from aerobic respiration?
7. How is fermentation similar to aerobic respiration?
8. How is yeast used in the bread making process?
9. Was your hypothesis correct? Why or why not?
10. What have you learned from this investigation?
3