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Observing Mitosis in a Root Tip
Cell Division
T E A C H E R
P A G E S
Observing Mitosis in a Root Tip
Individual cells within an organism go through various stages of growth and division. These stages are
referred to as the cell cycle. The life cycle of a cell, or the cell cycle, can be separated into four main
phases; G1, S, G2, and M as shown in figure 1. The G1, S, and G2 stages, collectively, make up the
Interphase portion of the cell’s life cycle. The first gap stage, or G1 stage, is one in which the cell
experiences most of its growth and metabolic activity. The synthesis, or S stage, follows the G1stage. In
the S stage, the cell’s DNA is replicated in preparation for cell division. After replication is complete,
the cell will contain two connected copies of each chromosome. The third stage, G2, is usually the
shortest of the three stages of interphase. During this second gap stage many of the organelles and
molecules required for cell division are produced. When the cell enters the final stage of the cell cycle,
the M stage, the cell will go through mitosis. Mitosis is the process of dividing the nucleus into two
equal portions. Cytokinesis, the process of dividing the cytoplasm of the cell, will occur after mitosis is
complete. Some cells, like muscle cells, may not go through cytokinesis following each mitotic episode.
Source,
http://www2.mcdaniel.
edu/Biology/PGclass/
mitosis/pg3bd.htm
Figure 1
Plants and animals go through the process of mitosis for growth and replacement of cells. Plants contain
rapidly growing areas called meristems in the tips of the roots and shoots. The cells in these rapidly
growing areas are actively engaged in the process of mitosis. The events of mitosis can be divided into
four phases: prophase, metaphase, anaphase and telophase. The following events occur in each stage.
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Prophase – The long, stringy, unwound chromatin fibers coil and condense into thick threads of visible
genetic material called chromosomes. As the cell enters prophase, the chromosomes have already been
replicated forming sister chromatids. The sister chromatids are connected to each other at the
centromere. The spindle apparatus begins to form. The nuclear membrane breaks down and the
nucleolus disappears.
Metaphase – The centromeres of the sister chromatids line up along the center, or metaphase plate, of
the cell bringing the genetic material to the center of the cell. Microtubules connect the centromere of
each chromosome to the spindle.
Anaphase – The centromere of each chromosome divides, separating the sister chromatids from each
other. The chromatids of each pair will be moved by the spindle fibers toward opposite poles of the cell.
The separated chromatids are called chromosomes. This separation allows one copy of each type of
chromosome to be placed on opposite sides of the dividing cell. The chromosomes continue to move to
the poles of the spindle forming two separate groups.
Telophase – The final stage of mitosis occurs as new nuclear membranes are formed around both
groups of chromosomes. The result is two separate nuclei, each containing the same genetic information
at the original cell’s nucleus. The chromosomes will uncoil and relax to form chromatin threads. The
spindle begins to break apart and the nucleoli are reformed.
The events of mitosis have resulted in the production of two identical nuclei. The cell may now undergo
cytokinesis in which the cytoplasm of the cell is divided. In animal cells, the onset of cytokinesis is
marked by the presence of a cleavage furrow. The cell membrane is drawn inward until the cytoplasm is
split into two separate parts forming two distinct cells. In plant cells cytokinesis results from the
formation of a cell plate between the two newly formed nuclei. As the cell wall grows, it separates the
nuclei into two distinct cells.
PURPOSE
In this activity you will prepare squashes of onion root tips which have been going through the process
of mitosis. Using slides of the onion root tip, you will observe the mitotic stages in actively dividing
cells.
MATERIALS
vial of treated onion root tips
forceps
microscope slide (3)
prepared slide of onion root tip
microscope
paper towel
cover slip (3)
Safety Alert
1. Use proper procedure for carrying and focusing the microscope.
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Observing Mitosis in a Root Tip
PROCEDURE
1. Using forceps carefully remove an onion root tip from the vial and place the tip on a clean
microscope slide.
2. Place the slide on a smooth, flat surface. Add a drop of water and a cover slip to the slide to make a
wet mount. Place the wet mount slide between two pieces of paper towel.
3. Use the eraser end of a pencil to press down on the cover slip. Apply only enough pressure to
squash the root tip into a single cell layer. Be careful not to move the cover slip while you are
pressing down with the eraser. If you press too hard, you might break the glass slide and tear apart
the cells in the onion root tip.
4. Repeat steps 1, 2, and 3 to make two additional root tip squashes.
5. View each slide that you have prepared using a compound light microscope. Begin with the low
power lens and then switch to the high power objective. This wet mount slide will be relatively
thick so you will need to take caution when switching to the high power lens. Once on high power,
use the fine-adjustment knob to bring the image into focus. You will find more mitotic cells in the
lower, tip-end of the root.
6. From your three slides, select the one that contains the greatest number of cells undergoing mitosis.
While viewing the slide under high power, count or estimate the number of cells that you see in the
viewing area. Record this number in the Data Table 1. (If none of your slides contain mitotic cells,
notify your teacher who may provide you with a prepared slide to observe.)
7. Without moving the slide, count the number of cells that are undergoing mitosis. Record the number
that you see that are in prophase, metaphase, anaphase and telophase. Record these numbers in Data
Table 1.
8. Move the slide to a completely new viewing area near the one you just observed. Count the total
number of cells present and then count those that are in prophase, metaphase, anaphase and
telophase. Record these numbers in Data Table 1.
9. In the space provided on the student answer sheet, prepare a sketch of each stage of mitosis that you
observed on your slides. Label each sketch with the appropriate stage name.
10. Dispose of your slides and materials according to your teacher’s instructions. Clean up your work
area before leaving the lab.
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Name _____________________________________
Period _____________________________________
Cell Division
Observing Mitosis in a Root Tip
DATA AND OBSERVATIONS
Data Table 1
Mitotic Stage
Viewing Area
Area 1
Area 2
Total number of cells
per stage
Prophase
Metaphase
Anaphase
Telophase
Non-dividing Interphase
Total cells counted in
viewing area
Data Table 2
Sketch of
mitotic stage
Name of stage
ANALYSIS
1. What percentage of the cells that you observed were undergoing mitosis? Use the formula shown
below to calculate your answer. Show your work in the space provided.
% cellsin mitosis =
total number of cells in all phases of mitosis
×100
total number of cells
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2. Using the data found in Data Table 1, determine the percent of cells in each of the stages listed
below:
%=
number of cells in stage
×100
total number of cells observed
Stages of Mitosis
Percentage of cells observed to be in
this stage
Prophase
Metaphase
Anaphase
Telophase
CONCLUSION QUESTIONS
1. What are the stages of the cell cycle? In which stage of the cell cycle were most of the cells that you
observed?
2. Explain why the tip of the root was observed in this activity.
3. Based on the number of cells observed in each stage of mitosis, which stage do you think takes the
longest amount of time to complete? The least amount of time to complete? Explain your
reasoning.
4. What is the role of mitosis in the distribution of genetic information to new cells?
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