The Significance of Time and Mitosis
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Mitosis is a process in which new cells are formed. The formation of new cells allows growth and
repair of multicellular organisms. In unicellular organisms, mitosis is essentially reproduction.
Two new organisms are produced from mitosis of one organism. Mitosis is sometimes called cell
division. However, it is really only nuclear division. The nucleus and its contents are replicated,
followed by the division of the cytoplasm to form two daughter cells. By mitosis, each daughter
cell obtains a set of chromosomes identical to the parent cell.
The time it takes for a cell to complete mitosis, from prophase to telophase, varies with each type
of tissue and with the surrounding environmental or metabolic temperature. Usually mitosis
time for most cells ranges from 20 minutes to just over an hour depending on the cell type.
Dividing cells respond to a biological clock mechanism. That is, cells in some phase of mitosis are
more numerous at specific times during a 24 hour cycle than are cells in other phases.
During this lab, you are to be guided by two assumptions concerning the amount of time for each
phase of cell division. Assume that (1) the total time it takes for mitosis to occur in onion root
tips is the maximum for all phases, and (2) all cells counted came from root tips grown under the
same conditions and were cut and preserved at the same time. From these assumptions, you are
to test the following hypothesis: the amount of cells in a given phase of mitosis is equal to the
length of time required for completion of the phase. For example at 10°C, if 45 minutes are
required to complete prophase, then 45 out of 110 cells observed should be in prophase.
Procedure:
Study the physical features of each stage of mitosis as shown in this lab. Place a prepared slide of
a longitudinal section of an Allium root tip on the stage of a microscope. Locate the meristematic
area of the root on low power. Change to high power and observe the cells. Record the number of
cells in each stage of mitosis out of the first 110 cells. Do not count the cells in interphase. Record
your observations in the data table. Record your data in the computer along with the rest of the
class. Record the average of the class data for each phase of mitosis in your lab report.
Data:
Phase of Mitosis
Number of minutes needed to
complete each phase at 10°C
Number of cells expected
in slides
Prophase
45
45
Metaphase
10
10
Anaphase
20
20
Telophase
35
35
Total
110
110
Number of cells observed
Your Data
Class Data
Use the graph to plot the numbers of cells in each stage of mitosis. Plot the number of cells
expected, the cells you observed, and the class average.
Conclusion:
1. List three changes that take place in the cell during prophase.
2. What happens to the chromosomes in a cell during metaphase
3. What happens to each chromosome and centromere during anaphase?
4. Using the class data, which stage of mitosis had the most cells present?
Explain why these cells were present in the greatest amount.
5. Using the class data, which stage of mitosis had the least amount of cells present?
Explain why these cells were present in the least amount.
6. Which stage of mitosis takes the greatest amount of time?
7. Does the class data support this hypothesis?
The Significance of Time and Mitosis
Explain.
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