Download Counting Phases of Mitosis–Time for the Cell Cycle

Counting Phases of Mitosis–Time for the Cell Cycle
Onion root tips are regions of rapid growth, so cells in all phases of
the cell cycle can be observed. Cells in interphase have an intact
nucleus. The nucleus is evenly stained, and individual chromosomes
cannot be distinguished. In prophase, the nucleus appears enlarged.
Darklyu stained chromosomes are visible. In metaphase, the
chromosomes are lined up at the equator (equatorial plane) of the
spindle. During anaphase, the chromosomes are found at both sides
of the equator, the centromeres leading and the arms of the
chromosomes trailing behind. In telophase, two dark, compact nuclei
are visible, one at each pole of the cell. A cell plate may be visible
between the nuclei at the site of the old equatorial plane.
PREPARATION:
Problem How long do onion root tip cells spend in each phase of the
cell cycle?
Objectives: Identify the phases of the cell cycle, and Determine the
time a cell spends in each part of the cell cycle.
Materials: Microscope, Prepared Onion root tip slide, compass,
protractor, pencil and paper.
Safety: Always use care when handling mircroscopes and glass slides.
PROCEDURE:
1. Examine a prepared onion root tip slide. Using the low power of
your microscope, find an onion root tip. Then find the area just
behind the tip of the root. This is where the cells are dividing
most rapidly.
2. Now, switch your microscope to high power, and start looking at
individual cells, You’ll learn to recognize each phase of the cell
cycle.
3. Copy the data table. Working with a partner, examine each cell in
your field of view, and identify the phase of the cell cycle that
each cell is in. Have your partner record in the data table the
phase of each cell you examine.
4. Now switch with your partner. Have your partner examine a
different field of view while you record the phase of each cell.
5. Continue in this manner until you have counted at least 100 cells.
6. Add the number of cells in each phase, and record these numbers
in the row marked TOTAL. Total the number of cells you counted.
7. Calculate the fraction of cells in each phase by dividing the
number of cells in that phase by the total number of cells you
counted. Express your answer as a decimal, then as a percentage.
8. Calculate the number of degrees in a circle graph for each phase
by multiplying the fraction of time the cell spends in each phase
by 360o (the total number of degrees in a circle).
9. Make a pie chart showing the percentage of time a cell spends in
each phase of the cell cycle. Label each portion of the circle with
the phase it represents.
INTERPHASE
PROPHASE
METAPHASE
ANAPHASE
TELOPHASE
# of cells 1st field
# of cells 2nd field
Total
Fraction of cells in
this phase
Percent of time in
this phase
Number of degrees
in a circle graph for
this phase
ANALYSIS:
In your analysis make sure you answer the following questions. 1) In
which phase of the cell cycle does a cell spend most of its time? The
least time? 2) Explain why a slide of stained cells can be used to
estimate how much time a living cell spends in each phase of the cell
cycle. 3) Describe the appearance of the cell plate in the telophase
cells you observed. How would the division of the cytoplasm appear
in an animal cell?
BIBLIOGRAPHY:
Biggs, A., M.S., Kapicka, C., Ph.D., & Lundgren, L., M.S. (1998). Biolab.
In Biology, the Dynamics of LIfe (pp. 274-275). New York:
Glencoe/McGraw-Hill.
You might also cite YOUR textbook or other sources you used. Remember Noodletools.com!