Online Onion Root Tip Lab



The perpetuation of life is based on the reproduction of cells called cell division (…all cells come from preexisting cells; the Cell Theory).   This process is responsible for the growth of an organism from a fertilized egg to its final size and is necessary for the repair and replacement of tissue.  The cell cycle (or cell division) is broken down into three major parts:


During Interphase a cell grows and goes through replication (a copying of the DNA).  Interphase is quickly followed by mitosis.  Mitosis is the division of the nucleus of eukaryotic cells followed by the division of the cytoplasm (Cytokinesis).  If the division proceeds correctly, it produces two cells that are genetically identical to the original cell. 


In plants, the roots continue to grow as they search for water and nutrients.  These regions of growth are good for studying the cell cycle because at any given time, you can find cells that are undergoing mitosis.



In this activity, you will be presented with cells from the tip of an onion root.  You will classify each cell based on what phase it is in.  At the end you will count up the cells found in each phase and use those numbers to predict how much time a dividing cell spends in each phase. 



1.         Log onto a computer and open up Netscape.


2.         Type in the following address exactly as it appears below:


3.         You should be logged onto the University of Arizona’s Biology Project web site.


4.         Read the introductory page. 

·         Look at the upper diagram on the right side of the page.  If you were to make a slide of the tip of an onion root, this is what you would see.  Each somewhat ‘rectangular shaped box’ is an individual onion cell.  Notice that cells do not look exactly alike.  Each cell appears to be somewhat different from the others around it.  The large dark circle you are able to see in some of the cells is the nucleus.  The smaller dark circle in the nucleus is the nucleolus.

·         The lower diagram is an animation of a cell going through the cell cycle.  As you see, one cell divides and becomes two smaller cells.


5.         Click the NEXT button at the bottom of the page.


6.         Read about the 5 major phases of the cell cycle.  Since you will need to refer to this page to complete the lab, a copy of it can be found on page 4 (attached).


7.         Click the NEXT button at the bottom of the page.


8.         Read this page.  You do not actually need to copy the data table.  It has been included in the results section of the lab.


9.         When you click the NEXT button at the bottom of the page you will begin the lab.  You will be shown a picture of a cell.  You must decide which phase of the cell cycle the cell is in (INTERPHASE, PROPHASE, METAPHASE, ANAPHASE or TELOPHASE).   Use the information that you have just read to accurately identify the correct phase.  You may also want to use your notes from in class. 

v     Once you click on the proper phase, you will have to repeat the same process with 35 more cells. 

v     If a mistake is made, you will be given another opportunity to try again.


10.     Once you identified the proper phase for all 36 cells you will see a screen that says “Congratulation!…”  Leave this page on your screen.  You’ll need it for two reasons:

v  to fill in your data table. 

v  to show this screen to your teacher to get credit for the lab.

v TEACHER’S SIGNATURE _______________________


11.     Count up the number of cells in each phase and fill the number in on your data table.


12.     Record the above data on the data table.


13.     Calculate the percent of cells in each phase.  To do this, use the following equation:


Number of cells in the phase   x 100  = percent of cells in the phase

   36 (Total number of cells)


14.     Complete the Questions and Analysis section of the lab.

























1.      What has been done to the onion cells to make them easier to see? __________________________


2.      Use the GLOSSARY in your textbook OR your NOTES to define the following terms:





3.      What are the three major parts of the cell cycle? _______________________________________





4.      Is Interphase part of mitosis? _______________________________________________________


5.      What important process happens to DNA during Interphase? ______________________________


6.      Could a cell go through the cell cycle without the above process taking place? Explain why/why not. ___________________________________________________________________________




7.      Are chromosomes visible during Interphase?  __________________________________________


8.      Approximately what percentage of a cell’s life cycle is spent in Interphase (identify the percentage of cells in interphase at the time the slide of the root was made)?  __________________________


9.      Are chromosomes visible during Prophase?  Explain why/why not? ________________________




10.  What happens to the nuclear membrane during Prophase? _________________________________



11.  Approximately what percentage of a cell’s life cycle is spent in Prophase?  ___________________


12.  Where are the chromosomes normally found during Metaphase?  ___________________________



13.  Why are the chromosomes organized in this way during Metaphase? ________________________



14.  Approximately what percentage of a cell’s life cycle is spent in Metaphase?  __________________


15.  Describe what happens to the chromosomes during Anaphase?  ____________________________



16.  Approximately what percentage of a cell’s life cycle is spent in Anaphase?  __________________


17.  Describe what happens to the chromosomes during Telophase?  ___________________________



18.  Approximately what percentage of a cell’s life cycle is spent in Telophase?  __________________


19.  What process begins during Telophase? _______________________________________________


20.  Which phase does a cell spend most of its time in during its life cycle?  ______________________



Online Onion Root Tips

Determining time spent in different phases of the cell cycle

The life cycle of the cell is typically divided into 5 major phases. The phases are listed below, along with the major events that occur during each phase.

Interphase. The cell is engaged in metabolic activity and performing its duty as part of a tissue. The DNA duplicates during interphase to prepare for mitosis (the next four phases that lead up to and include nuclear division). Chromosomes are not clearly discerned in the nucleus, although a dark spot called the nucleolus may be visible.


Prophase. Chromatin in the nucleus begins to condense and becomes visible in the light microscope as chromosomes. The nuclear membrane dissolves, marking the beginning of prometaphase. Proteins attach to the centromeres creating the kinetochores. Microtubules attach at the kinetochores and the chromosomes begin moving.


Metaphase. Spindle fibers align the chromosomes along the middle of the cell nucleus. This line is referred to as the metaphase plate. This organization helps to ensure that in the next phase, when the chromosomes are separated, each new nucleus will receive one copy of each chromosome.


Anaphase. The paired chromosomes separate at the kinetochores and move to opposite sides of the cell. Motion results from a combination of kinetochore movement along the spindle microtubules and through the physical interaction of polar microtubules.


Telophase. New membranes form around the daughter nuclei while the chromosomes disperse and are no longer visible under the light microscope. Cytokinesis or the partitioning of the cell may also begin during this stage.