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AICE Biology Lab: Preparing a Root Tip Squash to Observe Mitosis Overview You will fix, stain, and make slides of onion root tips. These slides will be studied for the presence of cells in the four stages of mitosis. Objectives At the completion of this laboratory you should be able to Compare the events of mitosis in plant cells with those of animal cells. Demonstrate a procedure to stain tissue for the identification of cells in the various stages of mitosis. Preparing An Onion Root Tip Squash It is possible for you to make your own stained preparations of onion root tips and observe mitotic figures. Onion bulbs have been rooted in water. Growth of new roots is due to the production and elongation of new cells. Mitotic divisions are usually confined to the cells near the tip of the root. Follow the procedure outlined below to make your own root tip preparation. Materials two small cups Sharpie pen forceps metric ruler onion bulb with roots razor blade carnoy fixative 1M HCL clean slide & cover slip transfer pipette crystal violet water paper towels fingernail polish safety glasses Procedure 1. Obtain two small cups, label one “ HCL” and the other “Carnoy.” Pour in enough of each to just cover the bottom of its cup. WEAR GOGGLES!! 2. Obtain an onion bulb that is just beginning to show the emergence of roots. Cut a small piece of root off and use forceps to place it in the cup of 1M HCL for 4 min. 3. Transfer the root into the cup of carony fixative. The root should remain in the carony fixative for 4 minutes. 4. After the 4 minutes, place the root on a slide. Then, cut off the bottom 1 or 2mm of the root tip & discard the rest. 5. Cover the root with a 1drop of Crystal Violet for 2 minutes. After the 2 minutes, blot away the stain; be careful not to touch the root tip. 6. When the stain has been blotted away, cover the root tips with drops of water to remove the stain. Apply water drops until water runs mostly clear. Blot slide without touching root tip. . 7. Gently lower a cover slip over the root tip. Cover the slide with a paper towel and with your thumb (or a pencil eraser), firmly press on the cover slip; Do not twist the cover slip. The pressure will spread the cells into a single layer. 8. Then using the fingernail polish, carefully paint the edges of the cover slip. Make sure not to move the cover slip. Finally allow the slide to dry. Write your name on one side of the slide and hour of biology. 9. Now you are ready to view you slide under low power. Place your prepared slide on the microscope. 10. Use the low power objective on your microscope to look for thin layers of cells and then use the 40X power objective to observe mitotic stages in individual cells. 11. Once your slide is prepared & focused on the microscope, have your instructor sign your lab book to indicate successful completion of the lab. 12. Continue on to the next lab: AP Bio Lab 3.1 Mitosis in Animal and Plant Cells.
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