Observing Mitosis Through Onion Root Tips
In class, we recently conducted this lab to take what we have been learning about the cell life cycle, Mitosis, and study it even further and deepen our level of understanding of this topic! This lab required the class to break out the microscopes, work individually, and observe mitosis at work in the root slides of an everyday vegetable, an onion.
- To determine cells at different stages of the Cell Cycle (Mitosis)
- To compare cross sections of onion root cells to determine phase percentages
- To study the stages of cell division in a real plant cell
In the Cell Cycle, cells divide to allow growth of new cells (in this case the growth of an onion root). The onion root tip contains these cells at different phases of the cell cycle (which can be seen at a microscopic level). These phases are Interphase, Prophase, Metaphase, Anaphase, and Telophase. First, Interphase can be seen as a dark mass with a nucleus as the main component. Prophase can be seen as visible chromosomes that are beginning to separate, but are yet to become organized in the cell. Metaphase can be seen as chromosomes that have lined up along the center of the cell. Anaphase can be seen as the pulling apart of chromosomes to opposite sides of the cell. Lastly, Telophase can be seen as two nuclei that have formed in the cell.
- Place onion root tip slide under microscope stage
- Observe the box-like plant cells and how they are organized in rows
- Determine each phase of the Cell Cycle in the cells
- In a data table, record the approximate number of cells seen in each stage (Interphase, Prophase, Metaphase, Anaphase, & Telophase)
- Repeat data for each cross section
- Average data and write percentages to show time spent by each phase during the Cell Cycle
|Stage of Cell Cycle||Percentage of Cells in Stage (%)|
What stages were the majority of the cells in?
What percentage of the cells were in each stage?
Interphase – 81%
Prophase – 12.46%
Metaphase – 1.65%
Anaphase – 1.37%
Telophase – 2.03%
What evidence shows that mitosis is a continuous process not a series of separate events?
Mitosis is a continuous process, not a series of separate events because this cycle is a cell life cycle that is always at work. Each phase is dependent upon the completion of the previous phase.
The onion plant began as a single cell. That cell had X number of chromosomes. (The exact number does not matter, we will just call that number “X”.) How many chromosomes are in each of the cells that you observed? (Give the answer in terms of X.) How do you know?
4X chromosomes are in each of the cells that were observed because cells have to double themselves so that they can split later on (DNA is double).
If this onion would reproduce sexually, it would need to produce sperm and/or eggs by the process of meiosis. After meiosis, how many chromosomes would be in each sex cell (in terms of X)?
- (4X → 2X + 2X → X + X + X + X)
If this onion would complete the process of sexual reproduction (fertilizing and egg cell), how many chromosomes would be in the zygotes that are produced (in terms of X)?
Sperm + Egg = X + X = 2X.
Observing Mitosis Through Onion Root Tips was a rather challenging lab, but the knowledge gained from it was extensive. Some of the challenges faced during this lab were one’s inability to determine the different phases given the microscope equipment and their failure to zoom past a certain point, as well as counting error shown in the percentages. For example, in my lab when I was counting the phases, I did not account for the presence of Anaphase in my data, which offset the normal balance of each percentage that is usually present in the data. However, as a class average, we were able to combine our percentages to become very close to accurately representing the length of each stage at work in the cell cycle. Interphase takes up about 81% , with Prophase at 12.46%, and the rest of the phases (Metaphase at 1.65%, Anaphase at 1.37%, and 2.03%) fulfilling the small remainder of the cell cycle. It was obvious that cell division had taken place in these root tips, emphasizing that the cell cycle is constantly at work in everyday living things.