Download Observing the Cell Cycle in Onion Root Tips

Observing the Cell Cycle in Onion Root Tips
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(Mitosis)
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Introduction:
In this lab, you will examine the dividing root-tip cells of an onion. You will examine the specimen to
identify the various phases of the cell cycle, to see which phases cells spend more time in, and you
will answer related analysis questions to further your understanding of the eukaryotic cell cycle.
Pre-lab:
1. What are the three general phases of the cell cycle? List them and describe what happens in each
general phase.
2. What would happen if our cells didn’t go through interphase correctly?
3. What could happen if our cells didn’t go through mitosis correctly?
4. When you look into the microscope, which phase of the cell cycle do you think most cells will be in,
interphase, mitosis, or cytokinesis? Why
5. Why do you think it is easiest to see the nucleus dividing, rather than cell organelles dividing?
6. Just because cells are dividing does not mean that the cell is cancerous- where in our bodies are
cells dividing fast? Why do those cell parts need to divide fast?
Lab:
Look at the onion root tip slides. Choose a sample of about 50 cells. Look for a group of cells that
appear to have been actively dividing at the time that the slide was made. The cells will appear in
rows, so it should be easy to keep track of them. The dark stained bodies are the nuclei.
Stage
Sketch
Description of what’s
happening in each stage
Estimated number or %
of cells in that stage
Interphase
Prophase
Metaphase
Anaphase
Telophase
Cytokinesis
Post lab:
1. Why is the onion root a good specimen for studying mitosis?
2. The majority of the cells in your specimen were in which stage of the cell cycle?
3. Why does it make sense that most cells in your specimen were in that stage?
4. Cancerous tissue is composed of cells undergoing uncontrolled, rapid cell division. How could you
develop a procedure to identify cancerous tissue by counting the number of cells undergoing
mitosis?
Use this image to determine your percentages and to help answer the remaining
questions on page 2 of your lab.