Download Bio. C.10 Onion root tip Mitosis

Biology
C. 10
Unit 3
Whitefish and Onion root tip Mitosis
Name_____________________________
Background Information.
You are studying cell division and the typical processes by which it occurs. In very young organisms, such as a
fertilized fish egg or the root tip of a plant, cell division is occurring at one of the fastest times in the organism’s
life. By slicing these into very thin pieces and staining them properly, one can hunt for cells that are in the
“classic” phases of mitosis. It should be remembered that these preparations have been selected to have a much
higher % of cells undergoing division than would be occurring at normal times in the organism’s life.
In this activity, you will be observing prepared specimens of whitefish eggs shortly after fertilization and very
young root tips of an onion. By systematically searching the slides, you should be able to find cells in each of
the classic phases of mitosis, draw these cells, label their visible structures, and compare them to each other and
the phases as depicted in biology textbooks on the topics.
Procedure.
Your instructor will demonstrate methods to systematically hunt for items on a prepared slide. Use this method
study the slides of both whitefish eggs and onion root tips. Do the drawings on a separate sheet of paper.
A. Onion Root tip cells. Locate the best cell samples you can find and draw as detailed drawing as
possible of a cell in each of the 5 phases of mitosis. Make certain to label each visible structure on each
diagram. Refer to pages 279-285 for examples.
B. Whitefish egg cells. Locate the best cell samples you can find and draw as detailed a drawing as
possible of a cell in each of the 5 phases of mitosis. Make certain to label each visible structure on each
diagram. Refer to pages 279-285 for examples.
Analysis.
1. Contrast the differences you saw between the animal cells (whitefish) and the plant cells (onion root tip).
2. In your observations, were there more of any particular phase? Why might this be so?
3. How does your data compare to the “idealized” diagrams in your text? Be specific, analyzing clarity,
specific structures, etc.
4. What are some factors that control cell division, increasing or decreasing its frequency.
5. Define a mutation.
6. As cells in an organism undergo mitosis, which phase would mutations most likely occur? Why?
7. One mutation can ultimately cause changes in millions of cells or only a few. What circumstances would
result in the former? The later?