Observing Mitosis in Plant Cells
Student Name: ___________________________________________ Date: ________________ Period: _________
Lab Partner: _____________________________________________ Lab station #: ________________
Purpose/Objective:
To examine the dividing root-tip cells of an onion
To identify the phase of mitosis that different cells in an
onion root-tip are undergoing
To determine the relative length of time each phase of
mitosis takes in onion root-tip cells
Materials:
Compound light microscope
Prepared microscope slide of a longitudinal section of
Allium (onion) root-tip
Background:
Mitosis is divided into four phases: prophase, metaphase,
anaphase, and telophase. Interphase is not considered a
part of mitosis. It is the first stage of the cell cycle. In
many plants, there are growth regions called meristems
where mitosis is ongoing. Meristems are found in the tips
of plant roots and shoots.
Procedure:
1) Examine the meristem carefully. Choose a sample of
about 50 cells. Look for a group of cells that appear to have been actively dividing at the time that the slide was made.
The cells will appear in rows, so it should be easy to keep track of them. The dark staining bodies are the nuclei.
2) For each of the cells in your sample, identify the stage of mitosis and place a mark in the “Tally Marks” column
beside the appropriate phase in Table A.
3) When you have classified each cell in your sample, count the tally marks for each phase and fill in the “Count”
column. In which phase of mitosis were the greatest numbers of cells? In which phase of mitosis did you observe the
fewest number of cells?
4) Calculate the percentage of cells found in each phase. Divide the number of cells in a phase by the total number of
cells in your sample, and multiply by 100. Enter this figure under the “Percentage” column of Table A.
5) The percentage of cells found in each phase is a measure of how long each phase lasts. For example, if 25 percent
of the cells are in prophase, then prophase takes 25 percent of the total time it takes for a cell to undergo mitosis.
Mitosis in onion cells takes about 80 minutes. Calculate the actual time for each phase using this information and the
percentage you have just determined. Use the following equation to find the duration of each phase of mitosis in onion
cells. Enter the time (in minutes) of each phase under the “Time (in minutes)” column of the table.
Duration of phase (in minutes) = percentage/100 x 80 minutes
6) Collect and record the count for each phase of mitosis for the entire class. Fill in the percentage and time
information using the data collected by the entire class in Table B.
7) Find and draw a cell in each phase of mitosis.
Prophase
Metaphase
Anaphase
Telophase
8) Clean up your lab station and put all lab materials back in their proper locations.
Data/Results:
Phase of Mitosis
Prophase
Metaphase
Anaphase
Telophase
Interphase
Phase of Mitosis
Prophase
Metaphase
Anaphase
Telophase
Interphase
Table A: Relative Duration of Each Phase of Mitosis
Tally Marks
Count
Percentage
Table B: Data Collected by the Entire Class
Count
Percentage
Time (in minutes)
Time (in minutes)
Discussion:
1) According to your data table, which phase of mitosis lasts the longest? Why might this phase require more time
than other phases of mitosis?
2) According to your data table, which phase of mitosis takes the least amount of time?
3) How do your results compare with those of the entire class? (Be specific and compare all four (4) phases)
4) In this investigation, you assumed that the percentage of the total time that any given phase takes is equal to the
percentage of cells in that phase at any moment. Why might this not be true for a very small sample of cells? (Why
are the classes totals a more accurate percentage than your totals?)
5) Many of the cells of the root meristem are not undergoing mitosis; rather they are in a stage of the cell cycle called
___________________.
6) Based upon the interpretations made above, interphase appears to be much _______________ (shorter / longer) than
mitosis.
7) What processes occur in interphase of the cell cycle, prior to the onset of mitosis?
8) Why is it incorrect to say that cells in interphase are “resting”?