Introduction
The cell cycle describes a series of ordered and distinct cellular stages leading to division and replication.
Stages of the cell cycle are called interphase, mitosis, and ctyokinesis.
Interphase includes three parts. The first is the G1 phase or gap phase. This is the phase between the
completion of mitosis and the beginning of DNA synthesis. Then the S phase, or the synthesis phase,
where the cell copies its chromosomes, occurs. The last part of interphase is called G2 and represents
the time between synthesis and the start of mitosis.
The next part of the cell cycle is mitosis and can be divided into four parts. The first is prophase, during
which the chromosomes condense into two chromatids, and the mitotic spindles at the ends of the cell
appear. The nuclear envelope also begins to break down. The next is metaphase where the
chromosomes line up on the metaphase plate. After this, anaphase occurs. During this phase, the
spindle fibers attach to the kinetochores of the chromosomes and pull the chromatids to opposite ends
of the cell. The last part of mitosis is called telophase. During telophase, the mitotic spindles break down
and the chromosomes begin to uncoil. Two new nuclear envelopes appear around both sets of
chromosomes.
After mitosis, the cell forms a contractile ring during a phase called cytokinesis. The ring is made of actin
filaments and surrounds the cell like a belt. The contractile ring cinches the cell and deepens the groove
called a cleavage furrow. This eventually divides the cell in two leaving two new daughter cells.
Purpose
The objective of this exercise is to understand the phenotypic features during phases of the cell cycle
and bean cells used as a model cell type.
Materials and Methods
First, root tips from a bean were prepared by germinating for a week, prior to the experiment. Root tips
were rinsed with tap water, placed in a beaker of 1N HCl, and heated to 60°C using a water bath for 10
minutes. The roots were removed with forceps and allowed to dry. The intensely stained tips were
placed on a slide along with a drop of acetic acid. Root tips were cut using a razor blade and prepared
for microscopic examination by placing a coverslip over the slide and carefully squashed using a thumb
and paper towel. Note: It was carefully done so that cover slip would not move laterally and ruin the
slide. The slide was then examined under a 40X objective and results recorded. The different phases of
mitosis were recorded and drawn. The frequency of cell cycle phase was determined after observation
of 200 individual cells.
Results
Class results were compiled onto one table which described the total number of cells in each phase, the
percent frequency of each phase and the duration of each phase was calculated. The percent frequency
of each phase was:
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
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Interphase 57.91%
Prophase: 21.70%
Metaphase: 6.87%
Anaphase: 6.91%
Telophase: 6.61%
From the percent frequencies, the total time spent in each cycle could also be calculated. The total time
spent in each cycle was:
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


Interphase
Prophase
Metaphase
Anaphase and Telophase combined:
11 hours
4.12 hours
1.31 hours
2.56 hours
Discussion
Each of the phases of the cells were drawn and recorded while looking at them through a 40X objective
(see attached). The first drawing is of a cell in Interphase. The chromosomes are difficult to see because
they are not yet coiled. The next drawing is of a cell during prophase. The chromosomes have
condensed and appear as a disorganized ball of string, and they lack any discernible pattern. The next
drawing is a cell in Metaphase. Here the cells appear more organized because they have aligned on the
metaphasic plate and the chromatids radiate from the center of the chromosomes. The next drawing is
a cell in Anaphase. The spindles have started pulling apart the chromatids towards the cell poles. The
last drawing is a cell in telophase. The separate chromosomes are at opposite end of the cell and
cytokinesis is starting to divide the cell half.
These data demonstrate that Interphase consumes the greatest duration of the cell cycle and suggests
that, the majority of the time, the cells are not reproducing. When they do produce, it is relatively
quickly. The second longest time spent in the cycle is prophase, the first step in mitosis. Metaphase,
anaphase, and telophase all have relatively equal times spent in the cell cycle.