Mitosis Lab
Name__________________________________
One of the basic tenets of biology is that all new cells come from living cells. New cells are formed by the process of cell
division which includes both the division of the cell’s nucleus (mitosis) and the division of the cell’s cytoplasm
(cytokinesis). Mitotic nuclear division typically rests in new somatic (body) cells. All of the following processes are
accomplished through mitotic cell divisions:
 Formation of an adult organism from a fertilized egg (zygote)
 Asexual reproduction (as in the reproduction of bacteria)
 Regeneration (as in the re-growth of a starfish arm)
 Repair or maintenance of body parts (as in the healing of awound or the replacement of epithelial tissue)
 Growth (as in growth in height of a tree or growth in size of a maturing animal)
Although, once it has started, mitosis is a continuous process, scientists have divided it into distinct stages for
convenience and ease of study and understanding of the cellular events.
Directions:
1. In this lab, you will be using a compound microscope and a prepared slide of onion root tips to identify the
stages of mitosis.
2. Once you have focused the image, you can begin to identify the stage of each cell in your field of view. Try to
identify at least one cell in every stage of mitosis. Allow all group members to identify the stages.
Stages of mitosis in Onion Root Tip Cells:
Page 1 of 5
Calculating the time for each stage of mitosis:
There is a direct relationship between the number of cells counted in a given stage of mitosis and the time that that
stage takes to complete. This may be calculated if the total time for the cell cycle in onion root tip cells is known. (That
total time is measured from interphase to interphase.) It is generally accepted that the total time for the cell cycle in
onion root tip cells is 720 minutes (12 hours). Therefore, to calculate the time spent in mitosis in these onion cells, set up
a ratio of the number of cells in each phase, compared to the total number of cells counted. Then multiply this fraction
by the total time (720 minutes) needed to complete one mitotic division. In other words, the time for a specific phase is
equal to:
Number of cells in a specific phase
=
Total number of cells counted
x 720 minutes = time for specific phase
Using the sample data provided, calculate the time required for the completion of interphase and mitosis in onion root
tip cells.
Now, calculate the percentage of the cell cycle spent in interphase and mitosis and record it in Data Table 1.
Data Table 1: Count and Timing of Cells in Stages of the Cell Cycle
Stage in the Cell Cycle
# of Cells
Time in Minutes
Interphase
463
Mitosis
59
Totals:
720
Calculations:
Page 2 of 5
% of Cell Cycle
100%
The effects of Environment on Mitosis
Scientists reported that a fungal pathogen may negatively affect the growth of soybeans (Glycine max). Soybean growth
decreased during three years of high rainfall and the soybean roots were poorly developed. A lectin like protein was
found in the soil around the soybean roots. This protein may have been secreted by the fungus. Lectins induce mitosis
in some root tissues. In many instances, rapid cell divisions weaken plant tissues. You have been asked to investigate
whether the fungal pathogen that produces lectin affects the number of cells undergoing mitosis in root tips of plants.
Listed below is the data that your research team collected while viewing 3 onion root tip cells under normal conditions
(control group) and 3 onion root tip cells grown in the presence of lectin (experimental group)
Calculate the % of time spent in mitosis and interphase, mean, and standard deviation for each group. SHOW YOUR
WORK!
Table 1: Onion Root Tip Cell Phase Data; Control Group (Onion root tips grown under normal conditions)
Tip
1
2
3
Number of Cells
Interphase
Mitotic Total
227
28
255
166
18
184
239
25
264
Interphase
Mitotic
Mean
SD
%
Total
Calculations:
Table 2: Onion Root Tip Cell Phase Data; Experimental Group (Onion root tips grown in presence of lectin)
Tip
1
2
3
Number of Cells
Interphase
Mitotic Total
192
9
201
184
11
195
205
9
214
Interphase
Mitotic
Mean
SD
%
Total
Calculations:
Analysis:
Follow the steps below to complete the chi squared analysis for both the lectin treated cells and the untreated cells.
Page 3 of 5
Always begin by writing the Null Hypothesis. Next consult the Critical Values Table for p and df values. Next you
determine the observed and expected values from your experimental data. Once you have your observed and expected
values you can calculate the chi squared values. Finally, you accept or reject the data based on the chi squared result.
1. Write Null Hypothesis:
2. Use the critical values table to determine your 𝑥 2 value. (Make sure to use a p = 0.05 and a 1 degree of freedom)
3. Determine the observed (o) and expected (e) values for both interphase cells and mitotic cells. For OBSERVED
CELLS: this is simply the number of cells you see in interphase and mitosis for the EXPERIMENTAL GROUP. For
EXPECTED CELLS: Calculate the percentage of cells in interphase and mitosis in the CONTROL group and then
multiply these by the OBSERVED cells in your EXPERIMENTAL group. Complete the expected value calculations
and enter your data in Data table 4 below.
Data Table 3: Compiled data from three groups
Control Group
Interphase Cells
Mitotic Cells
Total
Experimental Group
Data Table 4: Chi Squared Test for Lectin Treated Onion Root Tip
Observed Cells (o)
Expected Cells (e)
Interphase Cells
Mitotic Cells
Total Cells
Degrees of Freedom =
Accept of Reject Null Hypothesis?
p=
(𝑜 − 𝑒)2
𝑒
𝑥 2=
Critical Value =
Explanation:
4. Calculate the Chi Squared Value. Show your work. Enter your value in the last column of Data Table 4.
Page 4 of 5
5. Reject or Fail to Reject (accept) your Null Hypothesis. Write the reason for your answer in Data Table 4.
Analysis Questions
1. Which stage of the cell cycle takes the most time? What percentage of the total time is this?
2. Why do you think that this stage (in question 1) takes the most time? What cellular activities are occurring in
this phase?
3. Was there a significant difference between the control group and the experimental (lectin exposed) groups?
Explain using the chi squared test as statistical evidence.
4. Did the fungal pathogen that produces lectin increase the number of root tip cells in mitosis? Explain.
5. Does an increased number of cells in mitosis mean that these cells are dividing faster than the cells in the roots
with a lower number of cells in mitosis? Explain.
Page 5 of 5