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Bio 070 Lab: Mitosis and the cell cycle
Part 1. Modeling mitosis:
Using chromosome models (e.g. pipe cleaners), demonstrate to me and your group what chromosomes
do during the cell cycle, including mitosis, starting with a cell in G1 with a diploid (2n) number of 4. Be
able to use the following words as you demonstrate and explain what the chromosomes are doing.
chromosome chromatid G1 (1st gap phase)
parent cell daughter cell G2 (2nd gap phase)
DNA molecules S (DNA synthesis) phase prophase
centromere spindle fibers metaphase
equational division mitosis anaphase
maternal chromosome paternal chromosome telophase
cell cycle chromatin interphase
Part 2. The steps of mitosis
In plants, a small region of highly active cell division is found at the tips of all roots and shoots. Since
we want to see mitosis and cell division (don’t we!), it is necessary to look at the tips of young, actively
growing roots. Zebrina (wandering jew) roots have been grown by placing stem cuttings in water. After
a week or so, the cuttings form roots, and the roots grow rapidly for a few days. Cells in various stages
of mitosis should therefore be present in the actively dividing region of the root tips.
Method for preparation of a squash mount slide to show cell division in plant root cells
by Connie Roderick [modified from JJ Nickolas]
N.B.: 1. Timing is important. Be as exact as possible.
2. Do on a paper towel all procedures not done on the beaker.
1. Turn on the hot plate so that water in a beaker gently boils. Keep extra distilled water near by to be
added as evaporation occurs. Keep the water about 1 - 2 inches deep.
2. When the water is boiling, remove a Zebrina cutting, and cut off an entire young root with a razor
blade. Place the lower end on a microscope slide, and cut off the lower 1-2 cm of it, discarding the
upper root section - don't throw away the wrong part! Center the root tip on the slide. Add four drops
of 1N HCl (hydrochloric acid).
3. Place the slide on the beaker rack. The acid-heat treatment kills and preserves (fixes) the tissue, as
well as softening it. Treat for exactly 1 1/2 minutes. Timing is important! Use a probe to roll the root
tip to ensure complete treatment. Do not let the preparation dry out, add more acid if needed.
4. Remove slide from beaker and blot off remaining acid from around root tip. Be careful not to loose
the root tip while blotting. Add about 3 drops of TBO stain to the root tip on the slide so it is immersed.
5. Return the slide to the beaker rack and heat treat for exactly 1 1/2 minutes. Use the probe again to
roll the root tip around. Don't let the preparation dry out; add more dye if needed.
6. Remove slide from beaker and blot off excess stain. Quickly add only 1 drop of TBO stain to root
tip. With the probe straighten out and slightly flatten the stained and softened root tip. Add a coverslip.
7. Now to make a "squash mount" - fold the paper towel so the slide/coverslip unit is inside it. Place
your thumb exactly over the coverslip area on the outside of the towel. Without twisting, press down
hard on the coverslip. Gently roll your thumb sideways. Remove the slide from the paper.
8. Lay the slide across the boiling beaker for about 1 minute. This clears excess stain from the mount
and provides contrast between stained and unstained portions of the cells. Remove the slide and dry the
bottom. View with a compound microscope.
Observations:
1) Compare the cells in your field of view. Sketch a typical root tip cell making sure to include and
label the important structures that you can see (e.g. nucleus, cell wall, cytoplasm . . .)
2) Draw a cell that you think is actively dividing. Make sure you include labels of what you think are
important structures.
3) Keep your microscope focused on the cell you just sketched and show it to a neighbor or two. Did
they agree that the cell is dividing?
4) If not, why not? If they did, are their reasons the same as yours?
5) Pick out four (4) different cells and draw and label them, in order, from earliest to latest steps of
mitosis.
#1 #2
#3 #4
Part 3. The cell cycle: what is the timing of the events of mitosis and the cell cycle?
For this part of the lab, use your slide or a prepared slide of onion root tip or whitefish blastula. Using
high power, choose one area of your slide that shows many cells in the process of division. Assign each
cell into one of the five categories listed below and enter these data into the table below. Count all the
cells in the field, then go onto another field and continue this until you have counted 100 cells. If there
are more than 100 cells in the first field of view, choose a contiguous portion of the field and count all
cells in that area until you have categorized 100 cells. Record your data below:
Stage # of Cells % of Total
Cells not in mitosis (Interphase): _______ _______
Mitosis: what are chromosomes doing?
just became visible (Prophase) _______ _______
lined up along middle of cell (Metaphase) _______ _______
separating to opposite sides (Anaphase) _______ _______
arrived at opposite sides of cell (Telophase) _______ _______
TOTALS: 100 100%
Add your data to those collected by others in the lab on the master data sheet
Class Data Stage # of Cells % of Total
Cells not in mitosis: _______ _______
Mitosis: what are chromosomes doing?
just became visible (Prophase) _______ _______
lined up along middle of cell (Metaphase) _______ _______
separating to opposite sides (Anaphase) _______ _______
arrived at opposite sides of cell (Telophase) _______ _______
TOTALS: _______ 100%
Calculations - once all the data have been tabulated:
1. The entire cell cycle (division + growth/synthesis/growth) lasts about 24 hours in these roots.
Using the class data, calculate what part of the cycle is taken up by mitosis and what part is used
for growth and synthesis.
% of 24 hours amount of time
growth / synthesis of DNA (prepare for division) __________ _________
division / mitosis __________ _________
2. Using the class data from above, you calculated how long mitosis lasts. Use that figure, and use
only the cells that are in mitosis, to calculate the relative length of the various stages of mitosis.
Stage: visible (Prophase) __________
middle (Metaphase) __________
separating (Anaphase) __ _
arrived (Telophase) __________
3. What conclusions can you draw about the relative durations of:
a. mitosis vs. interphase?
b. The various stages of mitosis?
