Cell Division in the Onion Root Tip
RS: Ms. Alvarez
CT: Mrs. Rojas
Adapted from M. Arias
The Cell Cycle
• Cells grow and divide.
• As one cell enters Mitosis, two
cells exit which are exact
replicas or clones of the original
“parent” cell.
• Cells that no longer need to
divide exit the cell cycle in
G1(ex. neurons, muscle cells,
fat cells do this).
Purpose: to replenish dead or
dying cells, to allow an
organism to grow and develop
Interphase
• A cell spends the majority of
its lifetime in interphase.
• Cell grows and carries out
normal cell processes
• DNA replicates
• Prepares for cell division
•Plant cell
•Onion root tip
4 Stages of Mitosis: Plants & Animal Cells
Onion root tip
whitefish
•
•
Prophase:
Chromosomes
•
condense and form
visible bodies.
Nuclear
envelope breaks •
down.
Metaphase:
Chromosomes line •
up in the middle of
the cell.
•
Spindle fibers
attach to the
centromeres.
Telophase:
Anaphase:
• Nuclear envelope
Centromeres split.
reappears.
Cytokinesis
Sister chromatids
separate and are• The cytoplasm and
pulled to opposite all its contents
divide
sides of the cell.
What happens when you cut your finger?
3
.
1
.
5.
2
.
4
.
The cells bordering the injury will begin
dividing to fill in the gap in the tissues that
have been torn or broken. This is the process
known as wound healing.
Mitosis in the Onion Root Tip
• Today’s lab activity:
– examine the tip of an
onion root
– Identify and draw the
different stages of
mitosis.
• Root tips are useful to
observe mitosis
because the cells are
frequently dividing as
the root grows.
Examining root tip cells
When you examine a cross section of a root
tip, you will see lots of cells at different growth
stages.
Goals: Today’s activity will help you understand
the phases of the cell cycle and determine what
happens when Mitosis is disrupted.
Hypothesis: If the cells located in the onion root
tip are frequently dividing, then we should be
able to _________________.
Material
• Onions root tips
•Microscope
• Microscope slides and cover slips
• Toluidine blue or aceto-orcein
• 1M hydrochloric acid
• Razor blades
• Safety goggles
• paper towel
• Water
Procedure
1.
Submerge the base of an onion in water at
a constant temperature to grown roots for
48 hours.
2.
Obtain an onion root and cut off the bottom
1 or 2 mm of the root tip and place it on a
Slide.
**Wear proper safety equipment, including
goggles and gloves, for the next steps.
3.
Add a very small drop of 1M HCL acid to
the root tip on the slide and let it sit for 4
min.
4.
Using a paper towel soak the HCL away
from the root tip.
5.
Cover the root tip with a drop staining
solution and let stand for 2 minutes.
Procedure
6.
Blot excess stain and rinse with water until it
runs clear. Add one drop of water and gently lay
a coverslip over the root tip.
7.
Using a pencil eraser, carefully apply pressure
to the coverslip area to squash and spread the
root tip tissue.
8.
Use the low power objective on your
microscope to look for thin layers of cells and
then use the 40X power objective to observe
mitotic stages in individual cells.
9.
Identify chromosomes at the various stages of
mitosis in the water treated root tips. Make
sketches of the stages observed.
Conclusion Questions
1. Summarize the procedure for this lab.
2. The cells in the root of an onion are actively
dividing. How might the numbers of cells found in
this region differ from a different part of the plant?
3. What stage were the majority of the cells in the water
treated root tips?
4. What happens when cell division is interrupted?
•
1.
What process must take place before mitosis can begin?
5. What process must take place before mitosis can
begin?
Conclusion Questions
6. Why is mitosis important? Where does mitosis take
place?
7. Give an example of cells in your body that divide
slowly or do not divide at all.
8. What is cancer? How does cancer affect the rate of
mitosis?
9. How would a slide of cancerous cells look different
from this one?
10. What type of cells in your body do not divide by
mitosis?
Acknowledgements:
• M. Arias
• Images taken from the following sites:
http://www.kabt.org/2008/11/08/onion-roottip-mitosis-lab/
http://www.huntington.org/uploadedFiles/File
s/PDFs/GIB-RootingforMitosis.pdf