Table of Contents
Estimating the Time Spent in Mitosis
Overview
In this activity, you will look at several images of onion root cells as seen through a light microscope. You and your lab group partners will identify the stage of the cell cycle of each of the cells (interphase, prophase, metaphase, anaphase, or telophase). The six lab groups will then pool their data and determine how much time onion root cells spend in each stage of the cell cycle.
Cells in your body reproduce at different rates. Skin cells reproduce frequently (about once per day); liver cells reproduce rarely (about once per year). Some specialized cells like nerve and muscle cells almost never reproduce and are in a special stage called G0. The whole process of mitosis, prophase to telophase, takes approximately 90 minutes in human cells. In plants, an area of rapid growth is the tips of roots. This exercise uses onion root tips to illustrate the amount of time spent in each phase of mitosis. The typical onion root cell completes its cell cycle in about 720 minutes.
Before You Begin
Practice identifying the stage of the cell cycle. Look at the cells outlined in red on the image below:
The dark spot in the center of each cell is the chromosomes. You can identify the stage of the cell cycle using these chromosomes.
Use the following links and image to practice identifying the stage of the cell cycle:
Materials
Each lab group will need the following materials:
- images of onion root tip cells (slide 1, slide 2, slide 3, slide 4, slide 5, slide 6, slide 7)
- paper and pen
- calculator
Method
- Each lab bench will be divided into three groups: front, middle, and back.
- Each group will receive an image of onion root tip cells. Work with your group members to identify the phase of the cell cycle of at least 25 cells.
- Share your results with the other five groups in the lab. Use this information to fill in the table below.
- In an onion root tip, the entire cell cycle takes about 12 hours or 720 minutes.
- Calculate the percentage of time spent in each phase by counting the total number of cells in each phase (total in interphase, in prophase, etc.) and dividing each by the total number of cells you counted.
- Multiply the percentage of time in each phase by the total time of the cell cycle (720 minutes) and this gives you an estimate of the time spent in each phase.
