Observing Mitosis in Onion Root Tip Cells

Introduction: Mitosis takes place in both plant and animal cells. In this investigation, you will observe prepared slides of onion root tip cells to identify cells that are dividing. Because prepared slides are used, these cell divisions have been “frozen in time.” You will not be able to watch a single cell divide from prophase to telephase.

Materials: - Microscope

- Prepared microscope slide of an onion root tip

Procedure:

1. Place the onion root tip slide on the microscope stage and observe it under low power. Be sure that your image is centered in the field of view.

2. Use your coarse-focusing knob to move the stage up until you can clearly see the image. At that point, use your fine-focusing knob to sharpen the image.

3. Carefully change to medium power, focus (using the fine-focusing knob only), and go to high power to observe the cells. When at medium and high power, you only use the fine-focusing knob because these lenses are longer and can be easily damaged.

4. Try to find cells in each stage of mitosis and #1 draw a biological drawing of a cell in each phase (four drawings).

5. Return to low power and move the slide to view the root tip. Change to medium power, focus, and go to high power. #2 Note at least two differences from the last area you observed.

6. Change to low power, remove the onion root tip slide, and place it back on the tray.

Assignment and Questions:

1. Draw a biological drawing of a cell in each phase (four drawings) and label the following (note that some objects will only apply to one specific phase):

• Cell wall, cell plate, cytoplasm, sister chromatids, daughter chromosomes, spindle fibers, metaphase plate

2. Note at least two differences in the cells behind the root tip, compared to those in the tip.

3. Why were onion root tip cells used for viewing cell division?

4. If a cell has 10 chromosomes, how many chromosomes will each daughter cell have following cell division?

5. Predict what might happen to each daughter cell if all of the chromosomes moved to only one side of the cell during anaphase.

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How to make a Biological Drawing

o Use unlined white paper and a sharp pencil.

o A drawing should take up approximately one quarter of the page.

o All labeling lines should be horizontal and end at the same point, followed by the label of the object. These lines should never cross. Labels should be to the right of your drawing and be written in lower-case letters.

o Draw and label only what you see! Never draw what you think you’re supposed to see.

o Shading or coloring is not necessary. To indicate darker regions, use stippling (a series of dots). You can use double lines to indicate thick parts of the object.

o Write the title of the drawing and its total magnification at the base of the page (or each picture).