Name ___________________________________
CB
24
Onion Mitosis Lab
Purpose/Objective:
To examine the dividing root-tip cells of an onion.
To identify the stages of mitosis.
To determine how long the stages of the cell cycle
take.
Materials:
Microscope
Colored pencils
Calculator
Prepared slide of onion root tip cells
Procedure:
1) Place the slide on the stage of a microscope.
Use low power to locate and focus on cells
undergoing division.
2) Switch to high power and draw 4 cells (in
your science journal) that you observe. Try to
find cells that each look different.
Include the magnification for each drawing.
Magnification ______
Stage______________
Magnification ______
Stage______________
3) Use the picture on the right to
identify the stage of cell
division for each of the cells
that you drew. Write that
stage below each picture.
Magnification ______
Stage______________
Magnification ______
Stage______________
4) Copy the following data table into your lab notebook.
Date Table:
Stage of the Cell
Cycle
My Sample
Other
Classmate’s
Sample
Total
Number
Time for Each
Stage
(see calculation)
Interphase
Mitosis: Prophase
Mitosis: Metaphase
Mitosis: Anaphase
Mitosis: Telophase
Total Number of cell counted
5) Return to low power and find an area of the slide with many cells undergoing cell division.
Switch to a magnification that lets you see about 50 cells at once (for example, 100x).
6) Examine the cells row by row and count the cells that are in interphase. Record that number in
the data table under My Sample.
7) Examine the cells row by row four more times counting the cells in prophase, metaphase,
anaphase, and telophase. Record the results.
8) Find a classmate that has finished his/her counting and copy that data into the Other Classmate’s
Sample column of your data table.
9) Fill in the Total Number column on your data table by adding the numbers across each row in
your data table.
10) Add the totals for your 5 stages to find the total number of cells counted. This should be close to
100.
Calculation:
The cell cycle for the onion root tip takes about 720 minutes (12 hours). Use your data and the
formula below to calculate the number of minutes that each stage takes.
𝑇𝑖𝑚𝑒 𝑓𝑜𝑟 𝑒𝑎𝑐ℎ 𝑠𝑡𝑎𝑔𝑒 =
𝑇𝑜𝑡𝑎𝑙 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑐𝑒𝑙𝑙𝑠 𝑎𝑡 𝑒𝑎𝑐ℎ 𝑠𝑡𝑎𝑔𝑒
𝑥 720𝑚𝑖𝑛
𝑇𝑜𝑡𝑎𝑙 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑐𝑒𝑙𝑙 𝑐𝑜𝑢𝑛𝑡𝑒𝑑
Example: a student found 27 cells in prophase after observing a total of 103 cells.
𝑇𝑖𝑚𝑒 𝑓𝑜𝑟 𝑒𝑎𝑐ℎ 𝑠𝑡𝑎𝑔𝑒 =
27
𝑥 720 min = 188.7 𝑚𝑖𝑛𝑢𝑡𝑒𝑠
103
Onion Mitosis Lab
Analysis and Conclusion Questions:
*Answer each questions in your science journal. Make sure to answer in complete sentences and
thoughts so that a reader would know what question you are answering.
1) Which stage of the cell cycle did you observe most often?
2) According to your data about how much time does a cell spent preparing for mitosis? Remember
that preparation for mitosis is called interphase.
3) Use your data to compare the amount of time spent in mitosis with the total time spent for the
whole cell cycle. Hint: remember that mitosis includes the 4 stages of prophase, metaphase,
anaphase, and telophase.
4) What evidence did you observe to show that mitosis is a continuous process, not a series of
separate steps or events.
5) Cancerous tissue is composed of cells undergoing uncontrolled, rapid cell division. How could
you develop a procedure to identify cancerous tissue by counting the number of cells undergoing
mitosis?
Onion Mitosis Lab
Analysis and Conclusion Questions:
*Answer each questions in your science journal. Make sure to answer in complete sentences and
thoughts so that a reader would know what question you are answering.
1) Which stage of the cell cycle did you observe most often?
a. Interphase
b. Prophase
c. Metaphase
d. Anaphase
e. Telophase
2) According to my data a cell spends ______________________ minutes preparing for mitosis.
(Remember that preparation for mitosis is called interphase.)
3) According to my data a cell spends ______________________ minutes in mitosis.
(Remember that mitosis includes the 4 stages of prophase, metaphase, anaphase, and telophase.)
4) Use your answers above to compare how much time cells spend dividing versus preparing to
divide.
5) What evidence did you observe to show that mitosis is a continuous process (more like a movie),
not a series of separate steps or events (like a time lapse). Think about how each cell looked and
if all cells in the same stage looked exactly the same. Ask Ms. H for a hint if you need one!
6) Cancerous tissue is made of cells undergoing uncontrolled, rapid cell division. How could
counting the number of cells in mitosis help you find out if the tissue is cancerous or not? If you
compared cancerous tissue to normal tissue, would you expect to find more or fewer cells in
mitosis? Explain.