Onion Cell Mitosis Lab IMPORTANT: YOU MUST FOLLOW ALL DIRECTIONS CAREFULLY! Procedure: 1. Trim the tip of each root to 1 cm; use only the tapered end of the root tip. 2. Use forceps to place 2–3 root tips (use only the 1-cm tips) on a dish 3. Using a clean, graduated pipet, add 2–3 drops of 1 M hydrochloric acid to cover the root tips 4. Allow the root tips to soak in the acid for 4 minutes. 5. After 4 minutes, use a paper towel and carefully blot away excess hydrochloric acid from the dish. Caution: Avoid contact of the acid with skin. 6. Using a clean, graduated pipet, add 2–3 drops of deionized water to the root tips. 7. Use a paper towel to blot away excess water. 8. Repeat steps 6 and 7. 9. Your teacher will come around and add 2-3 drops of Methylene Blue Stain to your root tips. Caution: this is a permanent stain. 10. Allow the root tips to soak in the stain for 3 minutes. 11. Use a paper towel to blot away excess methylene blue stain. 12. Add 1 drop of deionized water to the root tips. 13. Use forceps to move one root tip to a clean microscope slide. 14. Place a cover slip on the root tissue. Using the eraser end of a pencil, gently apply pressure on the cover slip to squash the root tissue. Apply an even downward pressure on the root tips and cover slip but not so hard as to break the cover slip. Do not twist or grind the cover slip. Microscope Time! AT THIS STEP, PAUSE AND WAIT FOR THE TEACHER TO GUIDE YOU THROUGH THE MICROSCOPY. 15. Using low magnification on the microscope, focus on the root cells. Switch to medium power or high power as necessary to easily visualize the inside of the onion root cells. 17. Study all of the squashed tissue to locate cells in each stage of the cell cycle. Note: All stages of mitosis may not be present within a single field of view. 18. Repeat steps 14–17 using the remaining two root tips. Analysis Questions: 1. Focus your microscope. Draw what you initially see in your field of view. 2. Try to find an actively dividing cell (going through Mitosis). Focus on that. Draw it below. 3. How can you tell a cell is going through mitosis? 4. What do you think the purpose of the Hydrochloric Acid was in this experiment? 5. What was the purpose of the Methylene Blue Stain in this experiment? 6. Roughly how many onion cells fit across the field of view of the microscope? 7. Carefully switch to the High Power magnification on the microscope. Now how many onion cells fit across the field of view? 8. Carefully switch back to Medium magnification. The diameter of the field of view at Medium magnification is 4mm. Knowing this, roughly how big is one onion cell? This means that the distance from the left side of what you see to the right side of what you see is 4mm.