The Time for the Cell Cycle
Growth in an organism is carefully controlled by regulating the cell cycle. In plants, the
roots continue to grow as they search for water and nutrients. These regions of growth
are good for studying the cell cycle because at any given time, you can find cells that are
undergoing mitosis. The length of the cycle is about 24 hours (1440 minutes).
It is hard to imagine that you can estimate how much time a cell spends in each phase of
cell division from a slide of dead cells, yet it is precisely what you will do in this lab.
Since you are working with a prepared slide, you cannot get any information about how
long it takes a cell to divide. What you can find is how many cells are in a phase and
infer the amount of time each cell spends in each phase.
1. Set up a compound light microscope.
2. Place a slide containing a stained preparation of the Allium (onion root tip).
3. Locate the meristematic or growth zone, which is just above the root cap at the very
end of the tip.
4. Focus on low power, and then switch to medium or high power. Below find
micrographs of four stages of the cell cycle. Use them to help you identify the stages on
the microscope slide.
Interphase Prophase Metaphase Anaphase Telophase
5. Observe 100 cells and determine the phase of the cell cycle. This is best done by the
person observing the cells calling out the phases of each cell while another person
records. Record your data in the chart below.
6. Determine the percentage of time each cell will spend in each stage of the cell cycle.
Divide the number of each cell by the total number of cells and multiply by 100 to
determine the percentage. Place these values in the chart below.
Data and Analysis
Phase of Cell Cycle Number of Cells Percentage of Time Spent in Phase
Time Spent in (minutes)
7. On the basis of a 24-hr cycle, calculate the approximate time in minutes that is spent
in each stage. Include this information in your data table.
8. Make a circle graph showing the amount of time (minutes) a cell spends in each
phase of the cell cycle. Label each phase and give the graph a title.
Complete the following questions on the back of your circle graph and attach to this worksheet.
1. Based on the data you collected, what can you infer about the relative length of
time an onion root-tip cell spends in each stage of the cell cycle?
2. In which stage of the cell cycle do the cells spend the most time? Approximately
how much time?
3. In which stage of the cell cycle do the cells spend the least time? Approximately
how much time?
4. Why do you think there were no cells found in cytokinesis? What can you infer
about the length of time cells spend in cytokinesis?
5. What is the importance of the cell cycle to multi-cellular organisms?