Timing the Stages of Cell Division
Objective:
The purpose of this activity is to determine how long an onion cell spends in each phase of the cell
cycle.
Materials:
Colored pencils
Calculator
WARD’s Mitotic Stage Counts Flashcards http://wardsci.com/product.asp_Q_pn_E_IG0015737
Cell division is a dynamic event. Once you know how to identify each phase of the cell cycle and you
know the approximate duration of a particular cell cycle, it is possible to calculate the amount of
time the cell spends in each phase. Follow the steps below:
1.
2.
3.
4.
5.
6.
The approximate duration of the cell cycle for the onion cells being studied is 1440 minutes
(24 hours)
Each flashcard shows many cells captured at various phases of the cell cycle.
Looking at the slide, count at least 50 cells and record, in figure 1, the number of cells that
are in each phase.
Determine the total number of cells counted and record in figure 1.
Determine the percent of cells that are in each phase and record in figure 1.
To calculate the time (in minutes) for each phase, multiply the percent of cells in that phase
by the number of minutes for the whole cycle (refer to equation below). Record your data
in figure 2.
The average time for onion root tip cells to complete the cell cycle is 24 hours = 1440 minutes. To
calculate the time for each stage:
% of cells in the stage X 1440 minutes = number of minutes in the stage
Figure 1: Calculate Percent of Each Phase of the Cell Cycle (18 points)
Interphase
Prophase
Metaphase
Anaphase
[Total % must = 100]
Telophase
TOTAL
# of cells
% of cells
Figure 2: Time in Each Phase (12 points)
Interphase
Prophase
Metaphase
Time in
Phase
[Make sure your time = 1440 minutes]
Anaphase
Telophase
TOTAL
MINUTES
7.
Using the data from figure 2, color the circle graph to illustrate the time spent in each
phase of the cell cycle. Be sure to shade in the key. (5 points)
Figure 3: Time Spent in Each Phase
36 Minutes
36 Minutes
36 Minutes
36 Minutes
Analysis: (5 points each)
1.
Explain the appearance of the chromosomes in each phase of the cell cycle.
2.
It is often difficult to distinguish between interphase and prophase. Explain what changes
occur that distinguish between the two phases. Justify your answer.
3.
Explain why telophase is the reverse of prophase. Justify your answer.