C1-A NW Connections
What Are the Yeast Cells Doing?
This lab is based on the lab from Prentice Hall Science Explorer book ​Cells and Heredity​ p. 55 and p. 63.1
Problem
How do we know when a cell is dividing and where it is in the process?
Skills
Observation and analysis
Materials
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Whole wheat flour
All Purpose Flour
Room Temperature Water
Sealable container (jar, tupperware, etc.)
Stirrer (spoon, popsicle stick, bread knife, etc.)
Images of Yeast Cells or Onion Cells
Science Book: Cells and Heredity
Overview
This lab will perform one objective in two parts simultaneously. The lab will begin by
creating a ​bread starter​. A bread starter is a technique that many people use to have a
continuous supply of bread at home. It is considered “alive” because the active part of bread is
yeast, ​Saccharomyces cerevisiae,​ and is going about its life in the bread starter. Because yeast
is such a large cell we can see it under a classroom microscope very easily. However, due to
covid restrictions we won’t be able to pull the yeast from the bread and use the microscopes in
class as easily. To remedy this issue, each group will be provided with images of yeast cells and
will have to examine them to complete the lab.
Procedure - ​(Each group member should do every step)
1. Set aside ½ cup of water in a sealable container (like a jar, tupperware, or empty yogurt
container) and let it get to room temperature. This will become your starter.
2. Each group member should read ​Cells and Heredity​ ​Chapter 2: Section 3​ which is the
section that is associated with this lab.
a. Be sure that you know the names of the parts of the Cell Cycle and use the
diagram on page 58 to help understand what the phases look like.
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Photo from Science Direct
i.
Interphase, Prophase, Metaphase, Anaphase, Telophase.
b. Read through this whole lab as well.
3. Using the images provided, each group member should find a cell in interphase. Then
draw what that cell looks like on paper or in drive.
4. Repeat step three by finding a cell in prophase, metaphase, anaphase, and telophase.
5. Next, each group member should create a data table like the one shown below.
Stage
First Sample
Second Sample
Total
Interphase
Mitosis:
Prophase
Metaphase
Anaphase
Telophase
Total number of cells counted -------------->
6. In the picture with the black box, count the number of cells you can find that are in
Interphase.
7. In the same picture as step 6, count the number of cells in the different steps of mitosis.
8. Take a break and add 1 cup of whole wheat flour to your room temperature water. Stir
the water and flour to make a doughy paste to form your “starter.” Leave the starter
uncovered until the end of the lab.
9. Now, repeat steps 6 and 7 for a different picture as your second sample for the data
table.
10. Total your counts for each phase and total the number of cells you counted.
11. Seal your bread starter (the doughy paste) and place it somewhere cool.
Analyze and Conclude
1. How does the bread starter relate to the lab?
2. What stage of the cell cycle did you observe the most in your counts?
3. The cell cycle for yeast, ​Saccharomyces cerevisiae, ​is approximately 180 minutes (3
hours). Use your data and the formula below to find the number of minutes each stage
takes.
a. Time for each stage = ((Number of cells at each stage [s]) divided by (Total cells
counted[t])) times (180 minutes)
…
Time for each stage = (s/t) x 180
4. Use the data to compare the amount of time spent in mitosis with total time for the whole
cell cycle. What could the amount of time a cell spends in each phase of mitosis mean
about that stage of mitosis? Write your answer in paragraph form.
Images for lab steps