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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
 cell membrane
 centromeres
 nuclear
 sister
 spindle fibers
 chromosomes
membrane
chromatids
 centrioles
 chromatids
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.
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Period________________
ONLINE ONION ROOT TIP LAB (25 POINTS)
PART I
PHASE DRAWINGS:
INTERPHASE
PROPHASE
METAPHASE
ANAPHASE
TELOPHASE
PART II
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:
PHASES
CELLS PER
PHASE
PERCENT OF TOTAL
36
100
CALCULATIONS
DURATION
IN MINUTES
INTERPHASE
PROPHASE
METAPHASE
ANAPHASE
TELOPHASE
TOTAL
Calculation example: 10 cells in Metaphase
 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?