C1Mitos
THE CELL CYCLE
INTRODUCTION
When the cell has reached its growth potential it will begin to divide. This division is
referred to as the cell cycle. In plant and animal cells, this cycle is very similar but not
identical.
By observing and counting the numbers of cells in each phase of the cell cycle, you may
estimate the amount of time a cell spends in each stage. If you consider that the slide is a
split second of the cell’s life frozen in time, you will see that if a phase lasts a long time,
there should be many cells in this stage. If a phase is very short, there should be very few
cells caught in this stage.
SAFETY
1. Use good microscope skills.
2. Keep pipe cleaners out of your mouth and away from your eyes and nose.
3. Make sure the electrical cords are properly positioned to prevent tripping or
electrocution.
MATERIALS
2 pipe cleaners of one color and 2 of another color
Pencil
Mitosis cards (optional)
Colored pencils
Drawing paper
Microscope
Onion root tip slide
Calculators
PROCEDURE
PART A. Building chromosomes with pipe cleaners and simulating mitosis
1. Obtain 4 pipe cleaners (two of 2 different colors) and a blank sheet of paper.
2. Using a pencil, draw a circle that takes up most of the space on your paper. This circle
represents the cell membrane. Draw a second circle about the size of a grapefruit in the
center of the cell membrane. This represents the nuclear envelope.
3. Using the description of each stage of the cell cycle listed below, build a model of that
phase and sketch your model on Part A Student data sheet.
Interphase
 Events - The cell increases in size, carries on metabolism, and the chromosomes
duplicate. These events are defined as G1, S and G2
Appearance - The cell will contain a smooth round nucleus. There is a smaller
nucleolus inside the nucleus. The duplicated chromosomes (joined at the centromere)
have not condensed and cannot be seen.
Prophase (Mitosis Begins)
 Events - Nuclear division begins. The nuclear membrane disintegrates. The
chromosomes thicken and the mitotic apparatus (centrioles-only in animal cells-and
spindle) is assembled.
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
Appearance - The duplicated chromosomes have tightly coiled, condensed and
remained joined at the centromere. The nuclear membrane becomes less visible.
Metaphase
 Events - Each sister chromatid is attached to a spindle fiber; the chromosomes are pushed
and pulled by these spindle fibers to line up along the central axis.
 Appearance - The chromosomes appear lined up in the middle of the cell between the
centrioles which are located at the opposite poles of the cell. The spindle fibers attached
to each sister chromatid.
Anaphase
 Events - Separation of sister chromatids occurs as the centromeres split. The
chromosomes (now monads) migrate to opposite sides of the cell.
 Appearance - The sister chromatids migrate to opposite ends of the cells, pulled by
spindle fibers attached to the divided centromere.
Telophase
 Events - The chromosomes reach opposite poles (sides of cells) and the chromosomes
unwind to direct metabolic activities, spindle fiber breakdown, nucleolus reappears and
the nuclear envelope forms around the chromosomes.
 Appearance - The chromosomes are organized in bundles on opposite sides of a cell.
Cytokinesis
 Events - In animal cells, the cellular membrane pinches in along the equator and the cell
separates creating two identical daughter cells. Plant cells have a rigid cell wall and the
cytoplasm is divided by the construction of a cell plate across the equatorial plane.
 Appearance - There will be two dark spots of nuclear material at either end of the cell.
The cell membrane pinches inward to form a cleavage furrow which will appear in the
middle of the cell.
PART B. Drawing and quantifying the phases of the cell cycle
1. Obtain a prepared slide of onion root tip or mitosis cards
2. Start with the scanning objective (4X) and work up to the high power objective (40X) to
locate then sketch an example of each of the five phases on the Student Data Sheet.
3. Observe the number of cells in each stage and predict which stage will be the longest.
Record your prediction on the analysis sheet (Part B, #1).
4. Select a row of cells. Scan down the row and identify the stage of the cell cycle for each
cell. As you identify the stage, report the stage to your partner. Your partner will keep a
record of the stage of each cell by placing a tally mark in the appropriate column on the
data sheet. Count all the cells that are in the row. Do not skip any cell that can be
identified. Continue counting until you have identified the stages of 50 cells.
5. After identifying 50 cells, have your partner identify 50 more while you make the tally
marks.
6. Total the tally marks for each stage. Since you counted 100 cells, this number represents
the percent of cells in each stage.
7. Use the formula on your data sheet to calculate the number of hours the cell spends in
each phase of the cycle.
8. Clean your microscope and slide.
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STUDENT DATA SHEET
THE CELL CYCLE
Name: ___________________________
Date: ___________________________
Part A: Model
Sketch each phase of the animal cell cycle here (based on the model you developed in
part A)
INTERPHASE
PROPHASE
METAPHASE
ANAPHASE
TELOPHASE
Part B: Sketch each phase of the onion cell cycle here.
INTERPHASE
PROPHASE
METAPHASE
ANAPHASE
TELOPHASE
DATA
Place tally marks in the appropriate columns for each cell counted.
INTERPHASE
PROPHASE
Total ________ Total ________
________%
Interphase
________%
Prophase
METAPHASE
ANAPHASE
Total ________ Total ________
________%
Metaphase
_______%
Anaphase
TELOPHASE
Total ________
________%
Telophase
Number of hours in each phase:
Number of hours = 24 hr x Number of Cells Counted
100
Interphase _____ Prophase _____ Metaphase _____ Anaphase _____ Telophase ______
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ANALYSIS
Part A.
1. How are chromosomes different in prophase, metaphase then in anaphase/ telophase?
2. What is the difference between chromatids and chromosomes?
3. Why does mitosis occur?
4. What is the significance of the process of mitosis?
5. What is the final stage of mitotic division?
Part B.
1. Refer to your data to answer the following questions:
a. What is the longest phase of the cell cycle? _____________
b. What is the longest phase of mitosis?
_____________
c. What is the shortest phase of the cell cycle? _____________
d. What is the shortest phase of mitosis?
______________
4. Describe the cell plate that was present during telophase. How would telophase differ in
an animal cell?
5. If the pie chart below represents 24 hours in the life of an onion cell, color in the amount
of time spent in each phase based on your calculations.
Cell Cycle
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