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Mitosis Lab
In this lab you will use prepared slides of onion root tips to study mitosis in plants. You will be
able to observe each of the stages of mitosis and learn to calculate the length of time the cell
spends in each phase.
Introduction:
All cells come from preexisting cells. New cells are formed by the process of cell division
(mitosis). The formation of an adult organism from a fertilized egg, asexual reproduction,
regeneration of missing body parts or the maintenance and repair of body parts are all
accomplished through mitotic cell division.
Where does mitosis occur? In animals, cell division occurs anywhere new cells are formed or
new cells replace old ones. In plants, mitosis occurs in special growth regions called meristems.
There regions are found at the tips of stems or roots.
Plant roots consist of different regions. The root cap functions as protection for the root as it
digs into the soil. The apical meristem is where the majority of mitosis happens. This is the
area that you will be studying. The region of elongation is where root growth happens. The
region of maturation is where the cells differentiate and become specialized tissues like
phloem and xylem.
Pre-Lab
Each section of the lab data sheet represents one phase of cell division – interphase, prophase,
metaphase, anaphase and telophase. The last two sections are for cytokinesis – one for plants
and one for animals.
For each section; name the phase, then describe what is happening in each stage. Be specific in
your description. This will be your entry ticket to the lab.
Once your pre-lab has been approved, you may begin the lab.
Lab 1: “Observing Mitosis in Plant and Animal Cells”
Lab Procedure
1. Clean both the slide and the objective before beginning the lab.
2. Place the prepared slide on the microscope stage.
3. Scan the side under low power first and locate the apical meristem, directly behind the
protective root cap. Refer to Figures 1 and 2 for guidance.
4. Switch to high power and center your slide in the apical meristem region, so that you
have a field of view that has a wide selection of cells in various stages of mitosis
(including interphase). Be sure to adjust your light for optimum viewing. Refer to
Figure 3 for guidance.
5. Identify one cell that clearly represents each phase. Carefully sketch the cell in the boxes
provided in the pre-lab. Draw only what you can see, but include everything that is
visible. Be sure to label everything you include in your drawing.
6. When you have completed studying all the mitotic phases in the plant cell, sketch and
label an animal cell undergoing cytokinesis.
When all cell phases have been sketched, continue on to Lab 2: “Time for Cell Replication”
Reference Images
Figure 1
Figure 2
Onion tip – Apical Meristem
Interphase
Interphase/
beginning
prophase
Onion tip – Labeled diagram
Early prophase
Mid – prophase Late prophase
Figure 3
Metaphase
Early anaphase
Anaphase
Early telophase Telophase/Cytokinesis
Lab 2: “Time for Cell Replication”
To estimate the relative length of time that the cell spends in each in the various stages of cell
division, you will again examine the meristematic region of the onion root tip.
The length of the cell cycle for onion root tip cells is approximately 12 hours for actively
dividing cells.
Lab Procedure
Because you are working with prepared slides (the cells are dead), you can’t actually observe
cells actively dividing. However, you can still determine how many cells are in each phase.
From this, you can infer the percentage of time each cell spends in each phase.
1. Using the 40X objective, observe every cell in the field of view and determine which
phase of the cell cycle each phase is in. To do this in the most efficient manner, one
person will call out the cell phase while their partner records the information in Table 1.
2. Switch roles and count the cells in a second field of view. If you have not counted at
least 200 cells between both fields of view, count a third.
3. Calculate the percentage of cells in each phase (divide the number of cells counted by
200. Multiply this answer by 100). Record this number in Table 1.
4. Consider that it takes an average of 12 hours (or 720 minutes) for each onion root tip cell
to complete a full cell cycle. Calculate the amount of time spent in each phase by
multiplying the answer from #3 by 720. Record your results in Table 1.
Ex.
180 interphase cells/200 = 0.90 x 100. This is % of Cell Cycle.
0.90 x 720 = 648. This is Time in minutes.
When you have completed all three parts of the lab, answer the summary questions.
Summary Questions
Mitosis Lab 1
1. How does cytokinesis differ in plant and animal cells? (Be specific in your answer).
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2. Why does the cell expend so much energy lining the chromosomes up along the
metaphase plate? In other words, what would the consequences be if the cell didn’t do
this?
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3. In adult humans, where would you expect to find the largest number of cells undergoing
mitosis? Defend your answer.
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4. Genetic variation is essential to life, yet mitosis creates identical daughter cells. Why
would an organism make identical cells rather than ones with variation?
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Mitosis Lab 2
1. Using Excel, create a pie chart of the percentage data you collected. Give the chart a name
and label each of the pie sections.
2. Use the data in Table 1 and your pie chart to describe the relative length of time an onion
root tip cell spends in each stage of cell division.
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3. Your observations of the root tip cells were restricted to the meristem where cells were
actively dividing. How would your data differ if you observed the cells in the regions of
elongation or maturation instead?
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Mitosis Lab 3
Refer to the data and graphs for normal and cancer chicken stomach cells to answer the
following questions.
1. How do the data for each phase in the normal chicken cell compare with that of the onion
root tip cell? Are the percentages of time for the two longest phases similar? What general
conclusions are you able to make based on the information?
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2. How does the timing of the complete cell cycle differ in normal chicken cell vs. cancerous
chicken cells?
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3. Which stage exhibits the most dramatic difference in timing between normal and cancerous
chicken cells? _______________________________________
4. What nuclear and cytoplasmic changes would you expect to find in cancer cells, when
compared to their normal cells? (HINT: What events would be most affected by the change
in timing?)
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