Download AP Biology Core Lab: Mitosis

AP Biology Lab #3: Mitosis
Name __________________________
Date ______________ Period _____
Introduction and Overview
All new cells come from preexisting cells. New cells are formed by the process of cell division which involves
both replication of the cell’s nucleus (karyokinesis) and division of the cytoplasm (cytokinesis). There are two
types of cell division, mitosis and meiosis. Mitosis typically results in new somatic (body) cells which are diploid
in chromosome number. Formation of an adult organism from a fertilized egg, asexual reproduction,
regeneration, and maintenance or repair of body parts are accomplished through mitotic cell division.
Where does one find cells undergoing mitosis? Plants and animals differ in this respect. In higher plants, the
process of forming new cells is restricted to special growth regions called meristems. These regions usually
occur at the tips of stems or roots. In animals, cell division occurs anywhere new cells are formed or as new
cells replace old ones. However some tissues in both plants and animals rarely divide once an organism is
mature.
In this lab you will observe onion root tips and whitefish blastula under the microscope to observe the stages of
mitosis (3A). You will also calculate the relative duration of the phases of the cell cycle in the meristem tissue of
the onion root (3B).
Exercise 3A-1: Observing Mitosis in Plant and Animal Cells using Prepared Slides.
Roots consist of different regions (figure 1). The root cap functions in protection. The apical meristem is the
region that contains the highest percentage of cells undergoing mitosis. The zone of elongation is the area in
which growth occurs. The zone of maturation is where the cells differentiate to become xylem, phloem, and
other tissues.
Whitefish blastula (figure 2) is often used for the study of cell division. As soon as the egg is fertilized it begins
to divide, and nuclear division after nuclear division follows.
Procedure
Examine the prepared slides of both the onion root tip and the whitefish blastula. First locate the meristematic
region of the onion or blastula of the whitefish with the scanning objective (4x). Then focus on the image using
the low power (10x) objective and then finally the high power (40x) to view individual cells.
Find a field of view in which the cells are clearly in focus, many nuclei are visible and the cells seem to be in
various stages of the cycle. Identify a cell that is representative of each phase and draw the image in Table 1.
You must draw a cell in each stage for both the plant cell and the animal cell. Then list the major events that are
characteristic of that stage.
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Table 1. Microscope Observations of Cells undergoing Cell Division
Labeled Drawing
Stage of Cell
Plant Cell
Animal Cell
Cycle
(onion root tip)
(whitefish blastula)
Major Events Occuring
Interphase
Magnification:
Magnification:
Magnification:
Magnification:
Magnification:
Magnification:
Magnification:
Magnification:
Magnification:
Magnification:
Magnification:
Magnification:
Mitosis
Prophase
Metaphase
Anaphase
Telophase
Cytokinesis
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Analysis Questions:
1. How does mitosis differ in plant and animal cells? How does plant mitosis accommodate a rigid, inflexible
cell wall?
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2. What is the role of the centrosome? Is it necessary for mitosis? Defend you answer.
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3. What is the restriction point in mammalian cells? ________________________________________
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4. What is the G0 phase of the cell cycle? How and why do cells enter this phase?
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5. What are MPFs, Cdks and cyclins? What is the relationship among these molecules in controlling the cell
cycle?
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6. Can a cell that is normally non-dividing be stimulated to divide? When does this happen and how is it
accomplished in an organism?
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7. Cancer cells do not respect their neighbors. Describe what this means in more technical terminology. How
is this different than normal cell functioning?
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3A-2: Time for Cell Replication.
To estimate the relative length of time that a cell spends in the various stages of cell division, you will examine
the meristematic region of a prepared slide of the onion root tip. The length of the cell cycle is approximately 24
hours for cells in actively dividing onion root tips.
Procedure:
1. Observe every cell in one high-power field of view and determine which phase of the cell cycle it is in. This
is best done in pairs. The partner observing the slide calls out the phase of each cell while the other partner
records. Then switch so the recorder becomes the observer and vise versa. Count 3 full fields of view.
2. Record your data in Table 1.
3. Calculate the percentage of cells in each phase, and record in Table 1.
Consider that it takes, on average, 24 hours for onion root tip cells to complete the cell cycle. You can
calculate the amount of time spent in each phase of the cell cycle from the percentage of cells in that stage.
Percentage of cells in stage x 1,440 minutes = ________ minutes of cell cycle spent in stage
Results:
Table 1: Mitosis in Onion Root Tip Cells
Percent of
Total Cells
Counted
Number of Cells
Mitosis
Phase
Field 1
Field 2
Field 3
Field 4
Time in Each
Phase
Total
Interphase
Prophase
Metaphase
Anaphase
Telophase
Total
Cells
Counted
Draw and label a pie chart of the onion root tip cell cycle using the date in Table 1.
Title: ______________________________________________________________
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Analysis Questions:
1. If your observations had not been restricted to the area of the root tip that is actively dividing, how would
your results have been different?
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2. Based on your data in table 1, what can you infer about the relative length of time an onion root tip spends
in each stage of cell division?
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Review the data below and answer the questions that follow.
Table 2. Time spent in stages of the cell cycle in normal and cancerous chicken stomach cells.
Interphase
Prophase
Metaphase
Anaphase
Telophase
Total time
Normal Chicken
540 mins
60 mins
10 mins
3 mins
12 mins
Stomach Cells
Cancerous
Chicken
75 mins
15 mins
2 mins
1 minute
3 mins
Stomach Cells
3. Determine the time of the cell cycle for both normal and cancerous cells. How does it differ?
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4. What percent of time does a normal cell spend in interphase? (Show your work!)
5. What percent of time does a cancerous cell spend in interphase? (Show your work!)
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