Laboratory 10: Mitosis
Unit Content & Process Targets
VIII. Describe the importance of mitosis in single-celled and multi-cellular organisms in terms of
function, chromosome number of daughter cells, and location
X. Explain the relationship between interphase, mitosis (prophase, metaphase, anaphase, &
telophase), and the G0 phase
B. Use visual representations to explain how DNA in chromosomes is transmitted to the next
generation via mitosis
Introduction
All cells conduct metabolic reactions for growth, perform specialized functions, and undergo
replication to form new cells. All of these activities are part of a repeating set of events called the cell
cycle. A major feature of the cell cycle is cellular replication, and a major feature of cellular replication
is mitosis. Mitosis is nuclear replication in eukaryotic cells. Eukaryotic cells, found in plants, animals,
fungi and protists, contain a membrane-bound nucleus so when a cell replicates the nucleus also
replicates. Prokaryotic cells lack nuclei and do not undergo mitosis. Mitosis is usually followed by
cytokinesis, the cleavage of the cell and cytoplasm into two halves, each containing a nucleus and half
the organelles of the original, parent cell. Mitosis and cytokinesis are important because they provide a
mechanism for orderly growth of living organisms composed of discreet cellular units.
Mitosis and the Cell Cycle
This exercise will emphasize events associated with mitosis. However, mitosis is only part of the
cell cycle. The remainder of the cycle is Interphase and is subdivided further into Cytokinesis (C),
Gap 1 (G1), Synthesis (S) and Gap 2 (G2) phases.
The cell cycle begins with formation of a new cell and ends with replication of that new cell.
The G1 phase of the cell occurs after mitosis and cytokinesis, and includes a variety of growth processes
and synthesis of compounds other that DNA. During the S phase DNA is duplicated and at the end, each
chromosome strand is called a chromatid attached at a centromere. During the G2 phase molecules and
structures necessary for mitosis are synthesized. The Mitosis (M) phase usually occupies less than 10%
of the cycle but the length may vary from ten to thirty hours. The C phase (cytokinesis) may begin
during mitosis but is highly variable in length and time.
Understanding movements of chromosomes is crucial to understanding mitosis, and you can
simulate these movements easily with chromosome bead "models''. This is a simple exercise but a
valuable one. It will be especially helpful when comparing the events of mitosis to the events of meiosis
that will be examined second semester.
Mitosis in animal cells - The two most distinctive features of cell division in animal cells are the
use of centrioles and cytokinesis. In animal cells, organelles called centrioles duplicate prior to mitosis.
The centrioles produce protein polymers called spindle fibers. The spindle fibers attach to the
centromere of chromosomes and assist in the distribution of chromosomes equally between daughter
cells. Cytokinesis involves formation of a cleavage furrow that begins on the periphery of the cell,
pinches inward, and eventually divides the cytoplasm into two cells. Cytokinesis is facilitated by
proteins of the cytoskeleton: microtubules and microfilaments. Cells of a whitefish blastula provide a
good example of the stages of mitosis and cytokinesis. A blastula is an early embryonic stage of a
vertebrate animal and consists of a ball of 25-100 cells.
Mitosis in plant cells - Our model to study cellular division in plants is the root tip of Allium
(onion). Plant root tips, as well as stem tips, contain meristems that are localized areas of rapid cell
division. In plant cells, cytokinesis includes formation of a partition called a cell plate that is
perpendicular to the axis of the spindle apparatus. The emptying of vesicles that originate from the Golgi
1
apparatus forms the cell plate. The cell plate forms in the middle of the parent cell and grows out
towards the periphery. The cell plate will form the boundary between the two new daughter plant cells.
Pre-Lab:
1. Perform an internet image search to locate pictures of whitefish blastula cells in each stage of the cell
cycle and mitosis: interphase, prophase, metaphase, anaphase, and telophase. Print pictures IN
COLOR if possible and cut them out and attach pictures to page 5 of this lab. Be sure to include the
URL of the website from which images were located.
2. Perform an internet image search to locate pictures of onion (Allium) root tip cells in each stage of
the cell cycle and mitosis: interphase, prophase, metaphase, anaphase, and telophase. Print pictures
IN COLOR if possible and cut them out and attach pictures to page 6 of this lab. Be sure to include
the URL of the website from which images were located.
3. Watch the following video: http://tinyurl.com/o8op4kr If this tiny url doesn’t work,
use this full url: http://www.flinnsci.com/teacher-resources/teacher-resourcevideos/combination-minute-videos/chemistry-and-biology-minute-videos-vol5/getting-more-from-your-mitosis-slides/
Answer this question: When you look at the root tip, where is mitosis going on? Sketch
the root tip and point out where mitosis would be going on.
4. Go to the following website and complete the activity. You will be hitting “next” several
times after reading the information.
http://www.biology.arizona.edu/cell_bio/activities/cell_cycle/cell_cycle.html
In the space below, enter your data table as instructed in the activity.
2
Procedure
Chromosome Bead Models
1.
2.
3.
4.
5.
6.
7.
8.
Examine the materials used as chromosome ''models'' provided by your instructor.
Identify the differences in chromosomes represented by various colors, lengths, or shapes of
materials. Also identify materials representing centromeres.
Use a sheet of notebook paper to represent the boundaries of the mitotic cell.
Assemble the chromosomes needed to represent nuclear material in a cell of an organism
with a total of 4 chromosomes. Place the chromosomes in the cell.
Arrange the chromosomes to depict the position and status of chromosomes in interphase
G1. During Gl the chromosomes are usually not condensed as the chromosome models imply, but
the models are an adequate representation.
Depict the status of chromosomes after completing Interphase S.
Depict the chromosomes during prophase, metaphase, anaphase, and telophase.
Draw the results of cytokinesis and the reformation of nuclear membranes.
Whitefish Blastula Examination
1.
2.
3.
4.
5.
Obtain a prepared slide of a cross section through the blastula of a whitefish.
Examine the cells first on low then high magnification and note that some of the cells contain
condensed and stained chromosomes.
Refer to diagrams for a summary of the stages of mitosis, and then identify examples of each
stage on your prepared slide.
Identify cells between stages, or cells that represent early or late condition of a stage.
Examine the whitefish cells for signs of cytokinesis.
Onion Root Tip
1.
2.
3.
4.
5.
6.
7.
Examine a prepared slide of a longitudinal section through an onion root tip.
Search for examples of all stages of mitosis.
Search for signs of cell plate formation.
Examine a prepared slide of an onion root tip and count all the cells in one field of view at
40X magnification. Count the number of cells in each of the stages of mitosis.
Repeat step #4, if necessary, until you’ve counted 100 cells.
Record your results along with the combined results of class the table constructed in your lab
notebook that is similar to Table 10.1.
Now calculate the time spent in each stage based on a 24-hr cell cycle by dividing the number of
cells in each stage by the total number of cells counted. This will give you the percent in each
stage.
3
Results
TABLE 10.1:
Group Data for Number of Cells in Each Phase of Mitosis for Allium Root Meristem
Approximate time
Total #
Field
2
Field
3
PHASE
Field 1
% of Total cell is in each phase
(if necessary) (if necessary)
Cells
(hours) *
Interphase
Prophase
Metaphase
Anaphase
Telophase
TOTALS
*Although your calculations are only a rough approximation of the time spent in each stage, they
clearly illustrate the variation in duration of each stage of mitosis.
TABLE 10.2
Class Data for Number of Cells in Each Phase of Mitosis for Allium Root Meristem
Phase of Mitosis
Group # &
Interphase
Group Total
Members
Prophase
Metaphase
Anaphase
Telophase
1
2
3
4
5
6
7
8
9
10
11
12
Class Total #
of Cells
Class % of
Total # Cells
Time (hours)
4
Analysis: Answer the questions below using complete thoughts and sentences (except for question #6)
on separate paper. Answer all parts of each question.
1. If the chromosome number of a typical onion root tip cell is 16 before mitosis, what is the number of
chromosomes in the nucleus of a daughter cell after nuclear division (mitosis) occurred?
2. Why must the DNA be duplicated during the S phase of the cell cycle, prior to mitosis?
3. In plants, what name is given to the type of tissue in which mitosis occurs most frequently? Name
two places where this tissue is located in plants?
4. Name at least two cellular processes that during each segment of interphase: G1, S, and G2
5. Distinguish between interphase, mitosis, and cytokinesis.
6. Draw the structure of a chromosome during G2 (prior to mitosis) and the structure of a chromosome
after mitosis (G1). Label the centromere and (sister) chromatid in each picture.
7. What would happen if a cell underwent mitosis but not cytokinesis?
8. Provide an explanation for why cytokinesis generally occurs along the cell’s midplane.
5
Whitefish Blastula Images from ______________________________________________
INTERPHASE
PROPHASE
ANAPHASE
METAPHASE
TELOPHASE
6
Onion Root Tip Cell Images from ________________________________________________
INTERPHASE
PROPHASE
ANAPHASE
METAPHASE
TELOPHASE
7