LABORATORY REPORT
Observing Mitosis in Onion Root
Lecturer:
Dr. Mary Margaret Thomas, M.Sc., Ph.D.
Dr. Lilit Rusyati, S.Pd., M.Pd.
Arranged by:
Rifani Sri Maharani (2200332)
International Program on Science Education (IPSE) Faculty of Mathematics and Science Education
Universitas Pendidikan Indonesia 2024
1. INTRODUCTION
Mitosis means cell division – a process that takes place in all cells of an organism. In order to produce daughter cells, identical to the parent cell, there are a series of steps in the process of cell division/in the cell cycle. During interphase (G1, S and G2 phases) the cell grows and the DNA is copied (replicated). During the M phase, mitosis (chromosomes condense and move to the opposite ends of the cell) and cytokinesis (the cell divides into two daughter cells) takes place. Although all cells undergo mitosis, cells that are actively growing will be more likely to be undergoing mitosis at any given point in time. An onion has a total of 8 pairs of chromosomes which is relatively simple. With fewer chromosomes, it is slightly easier to see them when they are condensed during the phases of mitosis. And roots, especially the tips of roots are growing rapidly. Thus we are likely to have some success in using a microscope to observe different stages of mitosis in onion root tips.
There are four primary phases in mitosis (some of these phases can be subdivided):
- Prophase: chromosomes are condensed and the mitotic spindle begin to form from the centrosomes. The centrosomes begin to move to each end of the cell.
- Metaphase: by this point the spindle fibres have connected to the centromeres on chromatids (chromosomes with replicated DNA are called chromatids). The chromatids align along a central line in the cell.
- Anaphase: the chromatids separate into two chromosomes that are drawn to opposite ends of the cell by the spindle fibres.
- Telophase (not shown in the above diagram): the nuclear membrane reforms around the separated daughter chromosomes.
After telophase, cytokinesis occurs, resulting in separated daughter cells.
2. HYPOTHESIS
If we look at the onion root tip with microscope, then we will see one of the mitosis phase
3. PROCEDURES
a. Growing the onion roots. 4-5 days before the lab class, start to grow onion roots by scraping away any dry/old roots from the bottom of an onion or garlic bulb and then positioning the bulb so the bottom is just touching the water in a glass jar. Here are a couple of diagrams from microscopemaster.com illustrating the what you need to do. Hopefully the roots will be a few centimeters long by the day of the lab
b. On the evening before the lab, cut about half of the growing root tips on your onion bulb ~ 1cm from the tip. Transfer the cut root tips to a bottle containing FAA solution. Put the bottle into a plastic bag to prevent spills and leakage when bringing it to campus on the lab day.
c. On the day of the lab, bring the cut and treated root tips (that have been stored in the FAA solution), as well as your onion bulb with the remaining new root growth to the lab.
d. Work in pairs to prepare the slides for viewing the root tip cells.
e. Using forceps, remove one or two of the FAA treated root tips from the storage bottle and place on your group’s watch glass. Add 10 drops 70% ethanol to the root tips and let stand 2 minutes. Soak up the ethanol with blotting paper and then add 1 drop of 1N HCl and 2-3 drops of the acetocarmine solution to the root tips – make sure the entire tip is covered in staining solution. Allow to sit for 10 minutes.
f. Remove the stained root tips to a glass slide. Cut the very end tips of the roots (~
1mm in length) with the razor blade. Discard the rest of the stained root. You should have 2 or 3 1mm lengths of stained root tip on your slide.
g. Add one drop of distilled water to the root tips on the glass slide. Carefully place a coverslip on top avoiding any air bubbles. Gently tap the coverslip with the end of a pencil or other blunt instrument in order to crush the root tip tissue and spread out the cells into a thin layer under the coverslip.
h. Pass the prepared slide over a lit Bunsen burner briefly in order to set the cells and stain.
i. The cells are ready to be observed under the light microscope. Before moving to observe your preparation under the microscope, clean up your work area.
j. Observe the root cells with a light microscope starting at low power (10X objective lens). Many cells should be visible. Increase magnification to the 40X objective in order to more clearly identify cells in the various stages of mitosis (prophase, metaphase, anaphase and telophase).
4. RESULT
5. QUESTION
a. Why is the stain acetocarmine used in this experiment?
TELOPHASE ANAPHASE
Acetocarmine is a DNA-specific stain, so the supercoiled chromosomes during different stages of mitosis present in the onion root tips cells can be visualized perfectly by treating with the stain
b. About how many cells were visible on your slide at the 10X objective
magnification? How many were in view when you increased the magnification to 40X?
At 10x is not clear how many cells are visible. But, at 40x I see some quite clearly and I can identify them.
c. Where you able to observe cells in each phase of the cell cycle (i.e. the four phases of mitosis as well as interphase)? About how many in each phase?
Using a microscope, there may be at least 1 of each phase
d. What do you think would improve the results if you were to do this experiment again?
Yes, I will improve, when experimenting again the image on the microscope will be much clearer so that it is easier to observe.
e. Other than an onion, can you suggest any other raw material for the study of mitosis?
Ginger root tip, the root tips of any herbaceous plants, or Shoot apex of plants
6. CONCLUSION
Based on the results, the mitotic phase of onion root tips, Anaphase, and Telophase were obtained. At 40x magnification, the image is not clear because the cell has not stained well maybe when treating there are still some that are lacking.
