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.