LabBench Activity

Analysis of Results I

Timing the Stages of Cell Division

You've now seen that cell division is a dynamic event. Once you know the approximate duration of a particular cell cycle, it's possible to calculate the amount of time the cell spends in each phase. You can do this even though you are looking at a slide of cells that have been arrested in the process of division. Follow these steps:

  1. Determine the approximate duration of the entire cycle for the cells you are studying. (Your instructor will provide this information.)
  2. Looking at the slide, count and record the number of cells in the field of view that are in each phase.
  3. Determine the total number of cells counted.
  4. Determine the percent of cells that are in each phase.
  5. 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.

We will practice with the slide of onion root cells below. Looking at the cells marked with an X, count the number of cells in each phase. (In lab, you will count at least 200 cells by moving your slide so that you view several fields.)

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 × 1440 minutes = number of minutes in the stage

Calculate the time for each stage and fill in the table below; then check your answer.