Are Yeast Alive ?
Target 4c:
3.0
Identify the components and
relationship between respiration
and fermentation.
Name ____________________________
2.5
Identify the components of
respiration and fermentation.
2.0
Describe the purpose of respiration
and fermentation.
In this lab, you will generate evidence to show whether or not yeast can eat sugar. Any and all kinds of cells
require energy to survive. Energy most often comes in the form of sugars. Organisms (cells) can feed directly
on sugars or starches which get broken down into sugars during digestion. If yeast break down sugar (eat it!)
they should expel the gas ______________ ________________ as one of its waste products. Observing or
collecting this waste product can serve as evidence that yeast cells can eat the sugar.
Problem Question: Will yeast produce _____________ ______________ when given 4 types of sweetener?
Independent Variable: ________________________ Dependent Variable: _________________________
Materials
- 5 test tubes in rack
- active dry yeast
- plain sugar
- 3 sugar alternatives: Sweet’N Low / Equal / Splenda
- measuring spoon
- water
- rubber stopper
- 5 balloons
Procedure
BEFORE STARTING, MAKE SURE THE INSIDE OF THE TEST TUBES IS DRY USING THE WIRE
TOOL AT YOUR LAB STATION.
1. Into three test tubes, add a full packet of a different sugar alternative to each using funnel. MAKE SURE
YOU KNOW WHICH TEST TUBE HAS WHICH SWEETNER!!!
2. Into the fourth test tube add one full packet of plain sugar.
3. The 5th and last test tube leave with NO SUGAR!
4. Using the measuring spoon, add 1 ml (level spoon full) yeast to ALL 5 TEST TUBES.
5. Read all of step 6 before you move on.
6. Add warm water to one of the test tubes so it's about even with the mark on the test tube.
Seal the test tube with rubber stopper and shake vigorously 10 seconds until thoroughly mixed.
DO NOT LEAVE STOPPER ON TEST TUBE AFTER SHAKING!
USING 2 PEOPLE, stretch a balloon over the test tube mouth trying to keep the balloon flat as you do it:
ONE PERSON HOLDS TEST TUBE THE OTHER PUTS THE BALLOON ON.
This works much better if the mouth of test tube or balloon is a little wet.
Repeat for the other test tubes – TRY TO GET ALL THE BALLOONS IN PLACE WITH AS LITTLE TIME
BETWEEN EACH ONE.
7. After each minute, swirl to mix the test tubes again. Wait a total of about 10 minutes or so for results.
8. While waiting, make predictions on the back about whether or not the yeast will react to the different
sweeteners and then answer the questions.
What are your predictions about this experiment?
yeast only______________________________ yeast and sugar __________________________________
yeast and Sweet'N low _________________________ yeast and Equal _____________________________
yeast and Splenda ____________________________
QUESTIONS
1. Yeast can, in fact, use respiration OR fermentation when consuming sugar. If yeast can do respiration, that
means they must have ________________________ inside their cells. Considering the conditions of this lab,
which process do you think the yeast are using to break down sugar? ___________________________
Explain your answer: _____________________________________________________________________
______________________________________________________________________________________
2. Based on what you've learned prior to this lab, why would the yeast break down the sugar ie; what do they
get by breaking it down? ____________________________________________________________
3. Use the internet to find the following:
A. The mitochondria found inside cells has drawn a lot of attention from scientists. What have scientists
learned about the origin of mitochondria?
B. What is the importance of the "Endosymbiotic Theory" with regard to the mitochondria found inside cells?
C. What is the relationship between fermentation and respiration in terms of the evolution of cells?
4. Experiment Conclusion: Briefly detail prediction vs. results