Download Class Sheet 1 - Dr. Thornton`s Courses

Name:
Observing and Calculating the Amount of Time Cells Spend in
Interphase and each of the Mitotic Phases
Introduction
The cell cycle is the life cycle of a eukaryotic cell. For most eukaryotic cells, the cell cycle includes
interphase, a time when the cell is not dividing, and a mitotic phase, when the chromosomes and
cytoplasm are dividing.
•
Interphase consists of three phases – G1, S, and G2.



The cell is growing and performing its normal functions (doing its “job”) during G1.
During the S phase, the DNA is replicated, refer to your text on DNA Replication. At
this point, the cell is committed to dividing.
During the G2 phase, the cell prepares for division.
During all phases of interphase the nucleus in intact with the nuclear membrane and
nucleolus clearly visible. The chromosomes still in the form of chromatin (not visible).
Though different activities are occurring in the cell during each of the phases of
interphase, the cells will look the same under the compound light microscope.
•
The mitotic phase consists of four phases of mitosis and cytokinesis. During all phases of
mitosis, the chromosomes are condensed (“bunched up”) and visible. The arrangement of the
visible chromosomes and spindle fibers allow you to identify each mitotic phase.

During prophase, chromosomes condense and become visible, the nucleolus
disappears, and the nuclear membrane dissolves. The spindle fibers form, attach to
the chromosomes, and move to opposite poles (ends) of the cell.

During metaphase, the spindles line the chromosomes up at the equator (middle)
of the cell.

During anaphase, the spindles pull the (replicated) chromosomes apart, moving
sister chromatids toward opposite poles of the cell.

During telophase, the chromosomes unwind back into chromatin, the nuclear
membrane reforms, and the nucleolus reappears.

Cytokinesis then occurs, during which the cytoplasm divides equally between the
two daughter cells and the cell membranes will pinch off between them (in animals)
or a cell plate forms between them from which a new cell wall will form (in plants).
By the end of the mitotic phase there are two identical daughter cells.
In this lab, you will be observing and identifying whitefish blastula and onion root tip cells in
interphase and various phases of mitosis. (A blastula is the first embryonic stage formed after a
fertilized egg starts to divide.) You will sketch plant and animal cells in interphase and each of the
mitotic phases. You will then count and record the number of cells in each phase in your field of
vision at high power (100x). You will use that data to determine the duration those cells spend in
interphase and each of the mitotic phases.
Materials
Prepared slide of whitefish
Compound light microscope (1 per pair)
Colored pencils
EXCEL
Pre-Lab Questions
1.
2.
Why did we use whitefish to observe the phases of mitosis?
What is the relationship between the process of mitosis and cytokinesis?
Procedure
Hypothesis: Predict which phase of mitosis has the greatest duration.
Part A: Identifying and sketching plant and animal cells in interphase and each mitotic phase
1. Obtain your microscope, slide, and colored pencils.
2. Using low power, examine your slide and then move to medium and high power. Find cells in
each of the phases of mitosis as well as in interphase.
3. Sketch a cell in each phase of mitosis (prophase, metaphase, anaphase, and telophase) on the
sheet provided using colored pencils. Label the chromosomes and spindles. One sheet is for
sketches of animal cells the other is for plant cells.
4. Sketch a cell in interphase on the sheet provided using colored pencils. Label the nucleus and
nuclear membrane. One sheet is for sketches of animal cells the other is for plant cells.
5. Adhere the labeled sketches into your lab notebook on opposite pages, so they are juxtaposed
for easy comparison.
Part B: Calculating and comparing the duration cells spend in each mitotic phase and in
interphase in plant and animal cells.
1. You need to count the number of cells in your field of vision at high magnification (100x) in
interphase and each mitotic phase (prophase, metaphase, anaphase, and telophase). This will
likely be many cells – 100 or more.
2. Create a table in which to record your count as well as the counts of at least three other lab
members. Record your data then collaborate with at least three other lab members to record
their data as well. The table should include space for the calculation of total cells counted, the
average of each and a conversion to actual time (see below).
3. Add up the total number of cells in interphase and each mitotic phase and enter that on your
lab notebook. Then calculate the percent of the total cells counted in each phase by dividing
the total number of cells in each phase by the number of counts you have and record that
number in your lab notebook.
4. To calculate the time (number of minutes) cells spend in interphase and each of the mitotic
phases, consider that it takes on average 24 hours (1440 minutes) for cells to complete this
cycle. So, you will need to multiply the percent of cells in each phase by 1440 minutes to get
the number of minutes the cells spend in interphase and each of the mitotic phases. Complete
these calculations in your lab notebook.
5. Using your data from your table, create a pie chart/graph of the durations of each part of the
cell cycle for both animal and plant cells. Similar to the cell sketches, the graph’s should be
created adjacently so that they may be easily compared. Each graph should show the amount
of time (in minutes) the cells spend in interphase as well as each of the mitotic phases
(prophase, metaphase, anaphase, and telophase). This should reflect the percent of time each
phase takes in a 24 hour period. Use a different colored pencil for each phase on both graphs.
6. Use the same colored pencil for each phase to make an easy to read Key for both graphs.
Analysis and Conclusion Questions (Answer in complete sentences on a separate sheet and
turn in with your sketches and cell cycle calculations).
1. Is your hypothesis supported by the data you collected? Why or why not?
2. a. In which stage of the cell cycle does a eukaryotic cell spend the most time?
b. Which mitotic phase takes the longest? What occurred during this phase? Why do you
think the cell spent the most time in this phase?
c. Which mitotic phase takes the least amount of time? Why?
3. Why is collaboration of data important for this lab? Other labs?
4. What is the purpose of mitosis?
5. If you start with one diploid cell in which 2N = 10 chromosomes, what will you have at the end
of cell division?
6. Discuss your results for animal cell division. How do your results compare? Why might your
data compare the way it does? Were you surprised in any way by your data?
7. How might plant mitosis differ? (google it!)