2nd, 3rd, & 5th
“What’s for lunch?” YEAST LAB
In this lab you will learn about the effects of two substances on the activity of yeast. Yeast produce
carbon dioxide gas when they break down a food source. Carbon dioxide can be measured to
determine whether yeast are feeding.
Purpose: Does the presence of sugar or salt increase the activity of yeast?
Research: What are the 4 things a living thing needs to survive (look back in your notes)
Hypothesis: Write out an answer for the purpose and explain why you think that
****BEFORE GOING ANY FURTHER***** Write out research and hypothesis
in your notebook and write down necessary information!
__________________________________________________________________________
Materials:
4 glass beakers
1 glass measuring cup – you will use this to come get 200 mL of water
Yeast, Salt, & Sugar - are in bowls at supply table
4 plastic spoons
Paper towels
Procedures:
1. Read all instructions before beginning.
2. Make sure your beakers are labeled A, B, C, & D
3. Go get 200 ml of warm water (105-120 degrees F) from the designated area
4. Beaker A: Go to the supply table and add ½ teaspoon of yeast to the beaker, then go back to
your work area and add 50 ml of water to the beaker. Stir well. Cover with a warm, wet
brown paper towel as tightly as possible – secure with a rubber band. This is your control to
your experiment.
Mrs. Lutes will make the sugar and salt controls for you.
5. Beaker B: Add ½ teaspoon of yeast and a ½ teaspoon of sugar to the beaker, then add 50 ml of
water to the beaker. Stir well. Cover with a warm, wet brown paper towel as tightly as
possible – secure with a rubber band.
6. Beaker C: Add ½ teaspoon of yeast and a 1 teaspoon of sugar to the beaker, then add 50 ml of
water to the beaker. Stir well. Cover with a warm, wet brown paper towel as tightly as
possible – secure with a rubber band.
7. Beaker D: Add ½ teaspoon of yeast and a ½ teaspoon of salt to the beaker, then add 50 ml of
water to the beaker. Stir well. Cover with a warm, wet brown paper towel as tightly as
possible – secure with a rubber band.
8. Look at the clock and write down what time it is: ____________Wait for 10 minutes then make
observations and measure with a ruler how many cm of bubbles there are!
ANALYSIS – make a chart like this in your notebook – BUT MAKE IT BIGGER!
Beaker
Contents
A
Yeast and water only
B
Yeast and ½ teaspoon sugar
C
Yeast and 1 teaspoon sugar
Observations AND Measurement of gas
D
SALT
Yeast and ½ teaspoon salt
Salt and water only (Mrs.
Lutes did this one)
SUGAR Sugar and water only (Mrs.
Lutes did this one)
Conclusions: ( In your notebook, answer these questions with complete sentences, but no paragraph
needed)
1. Which beakers showed a change in this lab? What did that tell you?
2. Why did some beakers show a change and others no change?
3. Do yeast cells use sugar as a food source?_____How do you know?
4. How did beaker B differ from beaker C? Why do you think there was a difference?
TECHNICAL DRAWING
Take EITHER beaker B or C (whichever one produced the most bubbles), and make a wet mount
slide. You will use an eyedropper to get a little bit of where the foam meets the water level in the
beaker. A LITTLE BIT – is all it takes. Put it in your well slide. You may or may not need to add 1-2
drops of water, depending on how thin it is. Cover with a coverslip and look at it under the
microscope.
MAKE A TECHNICAL DRAWING of your observation!
Self Evaluation: Please circle the description that best (and honestly) describes how you worked in
your group.
Never works
toward group
goals or contributes.
Is not sensitive
to the feelings
of others.
Sometimes works
toward group goals
and contributes. Is
not often sensitive
to the feelings of
others.
Usually works
toward group
goals and contributes.
Is usually
sensitive to the
feelings of others.
Works toward
group goals and
contributes.
Sensitive to feelings
of others.
Helps identify
needed changes
and action.
Consistently works
toward group goals; is
sensitive to feelings of
others and values all
members. Encourages
group action for
change.