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Sally Seashell
Lab Partner: Barn Acle
Nov. 9, 2005
Green 2 Biology
Mitosis in an Onion Root Tip Cell
Introduction: Mitosis and the resulting multiplication of cells are
responsible for the growth of an organism. Cells getting ready for mitosis
are in interphase. This is the phase in which the nucleolous and nucleus are
usually clearly visible. The cell then proceeds through prophase, metaphase,
anaphase and telophase, or the four phases of mitosis. After cytokinesis,
the cells return to interphase. Since mitosis in Allium (onion root tip)
normally takes about 80 minutes at room temperature to complete, the
amount of time each stage takes can be calculated. The percentage of the
cells in a particular stage of mitosis is equal to the percentage of 80 minutes
that the stage takes (geocities website, 2005). This lab was conducted to
see if mitosis occurs in all areas of an onion root tip cell at the same rate,
and to see which phase of mitosis takes the longest time to complete.
Prepared onion root tip cells, microscopes and a calculator were utilized to
find this out.
Hypothesis: Due to the fact that cells may be dividing more frequently near
the edges of the root tip, as seen in area Y on p. 214 in Biology, the Dynamics
of Life, it is believed that cells in this area will be experiencing mitosis at a
faster rate. It is believed that prophase will take the longest amount of
time to complete because of the condensing of chromosomes, the migrating
of the centrioles, and the formation of spindle fibers are assumed to take a
longer time to complete compared to the processes occurring in the other
phases.
Procedure: A prepared slide of an onion root tip cell was placed on the stage
of the microscope and focused under low power to locate area X (p. 214). It
was then focused under high power and the cells in mitosis and those in
interphase were identified. The number of cells in interphase and the
number of cells in each phase of mitosis in area X (see diagram 1) were
recorded in a data table (see data table 1). Cells were counted by column.
The slide was then refocused on area Y (refer to diagram 1) under low and
then high power. The number of cells were counted as being either in phases
of mitosis or interphase and these numbers were recorded in data table 2.
The cells were counted by the column. All cells for both areas were counted
which were within view. To determine the percentage of cells found in each
phase of mitosis, the following equation was used: number in stage/total
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sample number x 100. To determine the time each phase takes the
following equation was used: 80 minutes x (percentage of cells in phase) =
total time in minutes. This was based on the information presented in the
introduction. The percentage values and the time were filled in on the
corresponding data table 1. All equipment was returned and the data was
analyzed.
Diagram 1:
Data Table 1; Area X:
Stage/Phase
Interphase
Prophase
Metaphase
Anaphase
Telophase
Tally Marks
1111111111111
11111
1
11
0
Count
13
5
1
2
0
Percent
62%
24%
5%
10%
0%
Time (min.)
N/A
19.2 min.
4 min.
8 min.
0 min.
Example of calculating percent: Interphase = 13 cells -> divide by 21 (total
number of cells in sample) = .619 x 100 = 62%
Example of calculating for time: 80 min. x % of cells in phase = time in
minutes -> Prophase: 80 min. x .24 = 19.2 minutes
Data Table 2; Area Y:
Stage/Phase
Interphase
Prophase
Metaphase
Anaphase
Telophase
Tally Marks
11111111111
111
1
1
0
Count
11
3
1
1
0
Percent
69%
19%
6%
6%
0%
Time (min.)
N/A
15.2 min.
4.8 min.
4.8 min.
0 min.
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Results: It is evident from the data that area x experienced more cells
undergoing mitosis than area y. In area x the total number of cells
experiencing interphase was 13 while in area y it was only 11. Also, the
number of cells experiencing mitosis in area x was 8, while in area y it was
only 5. The phase that took the longest amount of time in both areas was
prophase, with respective times of 19.2 minutes for area x and 15.2 minutes
for area y. In both areas telophase experienced no cells going through this
phase.
Discussion and Conclusion:
The hypothesis for this lab was that area Y would experience more
cells undergoing mitosis than area X, and that prophase would be the phase
that takes the longest amount of time. One part of this hypothesis, that
prophase would be longest, was supported by the evidence provided from
this lab. However, area X experienced more cell division than area Y, and so
this experiment conflicted with this part of the hypothesis. The data
showed that area X experiences more cell division, and this is indicative of
an area that would have more growth, such as human hair follicles. This
makes sense because the area of x is where roots would be dividing rapidly
in order to expand the roots of the plant into the ground. The fact that
prophase was shown to take the longest amount of time in both areas
supports the hypothesis and the information that it was derived from. To
reiterate, prophase had many processes going on at once, more so than other
phases, and in turn would take the most amount of time.
Sources of error in this lab could have arisen from human error in
counting, and focusing on the wrong areas of the onion root tip. To improve
this experiment, it should be repeated many times to see if the same results
could be obtained. To expand on this lab it would be interesting to compare
mitosis in animal cells to mitosis in plant cells. Also, it would be interesting
to see if better results could be obtained with freshly prepared slides.
This lab demonstrated mitosis in a deceased onion root tip cell. The
phases of mitosis were able to be observed in actual cells, aiding in further
comprehension of this topic. The hypothesis was partly supported by this
lab, but after reviewing the data it was understood why area X would have
more cells undergoing mitosis than area Y. This lab was a helpful
demonstration of the cell division process, and highlighted that not all
phases take the same amount of time and that mitosis will occur at different
rates in various parts of the cell.
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Works Cited
Biggs, A., Hagins, W.C., Kapicka, C., Lundgren, L., Rillero, P., Tallman,
K.G., Zike, D & The National Geographic Society. (2004). Biology:
The Dynamics of Life. Glencoe Science.
Geocities website: http://www.geocities.com/CapeCanaveral/Hall/1410/lab-B21.html?20057. (Nov. 2005)