Name __________________________ Date _______________________ Class ______________
Yeast Alive or Not Lab
Yeast is one of the central ingredients in bread. Yeast is a living organism that uses the sugar in bread dough along
with oxygen for its life processes. As a result, yeast produces carbon dioxide gas. The carbon dioxide makes the
gas bubbles (think about the holes in your bread) that make bread rise and taste fluffy, not flat. These samples of
yeast have been confused with one another and now live samples are mixed with dead ones. These samples need
to be tested to find the live ones in order to ensure that the bakery that receives these will be able to make tasty
bread. Your job is to use information you have about single celled live organisms to correctly identify the live yeast
from the dead yeast.
Question: _____________________________________________________________________
______________________________________________________________________________
Hypothesis: ____________________________________________________________________
______________________________________________________________________________
Procedure:
1. Examine each sample of yeast- the Live Yeast, Sample A, and Sample B. Record your
observations of each including those on odor. (Remember the proper technique for
smelling in science.)
2. Label your test tubes Live Yeast, Sample A, and Sample B.
3. Warm some water to 35-38 C.
4. Add a 1mL scoop of each sample of yeast to the correct tube.
5. Add a 1mL scoop of sugar to each.
6. Add 10 mL of the warm water to each container and stir.
7. Add a 1mL scoop of flour to each. This will make the process more visible.
8. Observe the samples for bubbles. Record your observations in your data table.
9. Make observations at 5 minute intervals for 25 minutes. Continue to write your
observations in your table.
10. Measure the height of your liquid at each time interval.
11. Make a triple line graph to show this data.
12. Finally, after the 25 minutes is up, write your conclusions about the sample in the last
column of the table.
Data: on the back
Live Yeast
Observations
0 minutes
5 minutes
10 minutes
15 minutes
20 minutes
25 minutes
Dead or Alive ?
Sample A
Sample B
Name _________________________ Date ____________________ Class ____________
Yeast Alive or Not Lab Conclusion
Write your conclusion in complete restated sentences in paragraph form on another sheet of paper.
1. What was the name of this lab? (The name of this lab was…….)
2. What was the purpose of this lab? ( The purpose of this lab was….)
3. Why did you add sugar to the yeast samples? ( We added sugar to the yeast samples because…..)
4. Why did you include a yeast sample that you knew was alive in the test? (We included a yeast
sample in the test we knew was alive because…..)
5. How did the two yeast samples (A and B) physically differ from one another during the experiment?
(The yeast samples differed from one another because Sample A……..but Sample B…..)
6. Describe the appearance of all three samples at the end of the experiment. (At the end of the
experiment, the Live Yeast was……Sample A was……….. and Sample B was……….)
7. What did you conclude about Sample A and why? ( Sample A was………. because……..)
8. What did you conclude about Sample B and why? (Sample B was ………… because………)
Name _________________________ Date ____________________ Class ____________
Yeast Alive or Not Lab Conclusion
Write your conclusion in complete restated sentences in paragraph form on another sheet of paper.
1. What was the name of this lab? (The name of this lab was…….)
2. What was the purpose of this lab? ( The purpose of this lab was….)
3. Why did you add sugar to the yeast samples? ( We added sugar to the yeast samples because…..)
4. Why did you include a yeast sample that you knew was alive in the test? (We included a yeast
sample in the test we knew was alive because…..)
5. How did the two yeast samples (A and B) physically differ from one another during the experiment?
(The yeast samples differed from one another because Sample A……..but Sample B…..)
6. Describe the appearance of all three samples at the end of the experiment. (At the end of the
experiment, the Live Yeast was……Sample A was……….. and Sample B was……….)
7. What did you conclude about Sample A and why? ( Sample A was………. because……..)
8. What did you conclude about Sample B and why? (Sample B was ………… because………)