Name______Period______
ONLINE ONION ROOT TIP LAB (25 points)
Introduction:
The epidermis (skin) of the onion is an ideal subject for cell study because it is composed of a single layer of cells; you are looking into functioning units of living material. Before you can work with the cells you need to identify all the phases of cell division, so we can apply that information to learn more about the process of mitosis itself and how long it takes for the average onion skin cell.
Have you ever calculated what percentage of your life you spend asleep, in the car or watching TV? The results might surprise you. In Part II of this activity you will count and calculate the amount of time cells spend in each stage of their cell cycle. The results may not surprise you because you may have never wondered about thinking about a dividing onion, but it is necessary for scientists to understand how long it takes each cell type to divide so that we can use that information in the production of fertilizers or even herbicides that stop plant growth. Plant and Animal cells have to complete cell division in slightly different ways since plant cells lack centrioles and have to create a new cell wall from vesicles. Scientists believe can even use this information from plant studies to help in understanding animal cell division. Scientists think it may be important because they think our cells will only divide a certain number of times before they quit dividing and we get old. Knowing how to control cell cycle might someday unlock the secret of youth or even help us to control cancers.
Procedure:
PART I
1. Use the website Go to website http://www.biology.arizona.edu/ or use your notes to help you draw detailed pictures of each phase
2. Label the following structures
£ chromatin
£ spindle fibers
£ centrioles
£ centromeres
£ chromosomes
£ chromatids
£ nuclear membrane
£ sister chromatids
Phase Drawings:
INTERPHASE PROPHASE
METAPHASE ANAPHASE
TELOPHASE
PART II
£ Go to website http://www.biology.arizona.edu/
£ On the left of the screen, click on “Onion Root Tips”
£ Read through the information on each phase of mitosis, click “next”. (You will click “next” three times.)
£ Click “next” and classify the cells that appear on the screen for what phase of mitosis they are in.
£ After classifying the 36 cells according to the phase they are in, count the number of cells in each phase and then transfer the data onto your data chart.
£ Calculate the percentages for how long each cell spends in each phase using 36 as your sample size.
QUESTIONS FROM WEB SITE: (Prelab Questions #1-9 )
1. Describe the steps that are used to prepare onion slides in order to view mitosis?
2. Why was the tip of an onion root used to study cells undergoing mitosis?
3. What structure can you see in the cells that tell that the cells are undergoing mitosis and not in interphase?
4. What are the 5 phases of the cell cycle?
a. Which phases are considered mitosis?
5. What is happening during interphase?
6. What is main event that happens during prophase?
7. What is main event that happens during metaphase?
8. What is main event that happens during anaphase?
9. What is the main event that happens during telophase?
10. Assume that the onion root takes 24 hours to complete the entire cell cycle. Show the calculations for how long it will take in minutes?
DATA TABLE:CELLS PER PHASE / PERCENT OF TOTAL / CALCULATIONS / DURATION IN MINUTES
Interphase
Prophase
Metaphase
Anaphase
Telophase
TOTAL / 36 / 100
Calculation example: 10 cells in Metaphase
o Divide 10/36 = .277 then Multiply .277 x 960 min = 267 minutes in Metaphase
DATA ANALYSIS QUESTIONS: give detailed responses using your notes and the background info to this lab
11. What phase of the cell cycle do cells spend most of their time in?
a. Why do they need to spend so much time in this phase (What is happening)?
12. According to the data what stage is most present during mitosis?
13. Give the three (3) reasons why cells undergo mitosis
14. Based on the differences in plants and animal cells, how is plant cell division different from animal cell division.
15. What would happen if plant cells never underwent the process?