Name
Period
Cell Division – Onion Root Lab
Date
Background:
In a growing plant root, the cells at the tip of the root are constantly dividing to allow the root to grow.
Because each cell divides independently of the others, a root tip contains cells at different stages of the cell
cycle. This makes a root tip an excellent tissue to study the stages of cell division. 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.
Procedure:
1. Obtain a prepared slide of an onion root tip (there will be three root tips on a slide). Hold the slide up to the
light to see the pointed ends of the root sections. This is the root tip where the cells were actively dividing.
(The root tips were freshly sliced into thin sections, then preserved when the slide was prepared.)
2. Place the slide on the microscope stage. Using the low-power objective to find a root tip, and focus it with
the coarse adjust until it is clearly visible. Just above the root “cap” is a region that contains many new small
cells. The larger cells of this region were in the process of dividing when the slide was made. These are the
cells that you will be observing. Sketch what you see and label the magnification.
Next, center the image, then switch to high power. (If you need to change the focus when using high power,
remember to only use the fine adjust!).
Part One:
1. Observe the box-like cells that are arranged in rows. The chromosomes of the cells have been stained to
make them easily visible. Select one cell whose chromosomes are clearly visible.
2. Find a cell in interphase (this should be easy to find) and sketch the cell. Record this information in the
box below. Look around at the cells again. Select four other cells whose internal appearances are different
from each other and the first one that you sketched. Refer to the photos on the next page for help. Record this
information in the appropriate boxes. Note, be patient. The stages can be very hard to find.
______________
Interphase
______________
Prophase
______________
Metaphase
______________
Anaphase
______________
Telophase
Part Two:
1. As you look at the cells of the root tip, you may notice that some cells seem to be empty inside
(there is no dark nucleus or visible chromosomes). This is because these cells are three
dimensional, but we are looking at just thin slices of them. (If you slice a hard boiled egg at random,
would you definitely see the yolk in your slice? No.) We want to continue to look at the cells, but we
will ignore any where we cannot see the genetic material (dark areas).
2. Looking along the rows of cells, identify what stage each cell is in. Use the photos as a guide.
Continue until you have identified 50 cells. (You will probably have to choose more than one row to
view in order to identify 50 cells).
Interphase
Prophase
Metaphase
Anaphase
Telephase
Dark mass
Chromosomes
visible but not
organized
Chromosomes
lining up along the
equator
Chromosomes
pulling apart
Two nuclei in
one cell
3. Use the data table to record the number of cells that you see in each of the stages. The easiest way
to do this is for one person to look through the microscope, going along each row of cells. For each
cell, say out loud what stage the cells appear to be in. Another student can make tally marks for
each stage. Yes, most of them will be in interphase!
Interphase
Prophase
Metaphase
Anaphase
Telephase
Number of
cells
TOTAL
50
Percent of
time in
each stage
100%
(percent of time in each stage = # of cells in stage ÷ total # of cell x 100%)
Part Three:
1. Put back the onion root slide, and pick up a fish mitosis slide. Look at it under low power.
Draw what you see. Write the magnification below.
2.
Switch to high power. Find a cell in each of the following stages of the cell cycle and draw
it below.
INTERPHASE
PROPHASE
METAPHASE
ANAPHASE
Analysis & Conclusions:
1. Why is the onion root a good specimen for studying mitosis? _____________________________________________________
_____________________________________________________________________________________________________________________________
2. Which stage of mitosis is the easiest (in your opinion) to see on the slide? ______________________________________
What about it makes it easy to identify? _______________________________________________________________________________
______________________________________________________________________________________________________________________________
3. The majority of the cells in your specimen were in which stage of the cell cycle? _______________________________
Why? (consider that in onion root cells, mitosis takes approximately 80 minutes and the other parts of the cell
cycle lasts 15 hours) ___________________________________________________________________________________________________
4. Why are individual chromosomes more difficult to see during interphase than during mitosis?
______________________________________________________________________________________________________________________________
5. Define cytokinesis: ____________________________________________________________________________________________________
6. How do the onion root cells differ from the fish mitosis cells?
______________________________________________________________________________________________________________________________