Mitosis is the process by which a single cell divides into two identical “daugter” cells, each with an identical number or chromosomes as the parent cell. The four stages of mitosis follow each other without interruption, and take place in all living cells.
In this lab, you will examine cells from onion root tissue. Root-tips are regions of active cell division. It is very likely to observe every stage of cell division in root tips. You will examine onion root cells under the microscope and identify the different stages of cell division in the tissue sample. You will also determine how much time is spent in each stage of the cell cycle.
To review the cycle of Mitosis, please visit Arizona Biology’s website.
How much time do cells spend in each part of the cell cycle?
- Obtain a slide of onion root cells. Examine the slide under the microscope using the low-power lens, then focus on high power.
- Find examples of cells in each stage of the cell cycle, including interphase and the stages of mitosis. Draw and label 1 cell per stage in the provided table. Label structures the following structures: cell membrane, DNA/Chromosomes, Nuclear membrane, Nucleus on Table 1 of the handout (paper).
- Select a random area of the slide to study using the high-power lens; focus on high power.
- Identify the stage of each cell in the view, and record your data by using the Onion Root Tip Lab Data Table found here.
- To make your counting faster….
- Find the total number of cells by counting the number of cells across (horizontally) and counting the number of cells down (vertically). Multiply these numbers to find the total number of cells.
- To find the number of cells in each stage of mitosis, count them (there won’t be that many).
- To find the number of cells in interphase subtract the number of cells in the different stages of mitosis (prophase, metaphase, anaphase, telophase) from the total number of cells in the field of view. This will give you the number of cells in interphase.
- Repeat steps 4 a second time for a second sample.
- Calculate the percentage of cells in each part of the cell cycle for each sample. Complete Table 2.
- Sample Calculation:
(# of cells in interphase)/(total number of cells) x 100 = % of cells in interphase
Phase Average % Number of Cells
- What patterns exist in your data? In which stage of the cell cycle are most of the cells you examined? How does this data support what you know about the cell cycle?
Some pattern existing in my data were that interphase was a lot more populous than the other mitosis stages. Other patters were that prophase and metaphase cycles were within one percentile of each other within the two trials. The interphase cycle of the cells was the most populous because only 22% of the cells were anything but interphase. This data supports what I know about the cell cycle because most of the cell cycle is spent in interphase and performs most of it’s regular functions in this cycle stage, while the other phases are just a short bit of time. In the cell cycle for the root tip lab, 78% of the following cells were in interphase. Because it takes roughly 24 hours to complete a full cell cycle, that must mean that 18.72 of those hours is spent in interphase; 2.33 hours in prophase, 78 hours in metaphase, .66 hours in anaphase, and .37 hours in telophase. The numbers found in the onion root tip were better dispersed within the phases because the cells in that section in the plant is constantly dividing in order to do a certain function. It might be different in various sections of the onion because not all parts of the onion grow at the same pace as the onion root tip has because that is not their function.
- A chemical company is testing a new product that it believes will increase the growth rate of food plants. Suppose you are able to view the slides of a plant’s root tips that have been treated with the product. If the product is successful, how might the slides look different from the slides you viewed in this lab?
- Design an experiment that would test the product described in question 5. Explain what you could test or do to show that the prodcut really does increase the rate of cell growth and division in plants. Assume the product is a liquid that can be added to the soil in which the plant is growing.