cell biology tutorial

1. HCB 1019 Cell Biology Trimester 1, 2012/13
Osama Barayan - 1091105869
HCB 1019 – CELL BIOLOGY
LECTURE : TAN CHAI HONG
Practical 7:
Mitosis of Onion
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2. HCB 1019 Cell Biology Trimester 1, 2012/13
Introduction
Describe mitosis and the processes in mitosis. Additional information eg; its significance
and functions in living cells, differences compared to meiosis.
(Caution: Do not limit your thinking to only discuss mitosis in onion root, discuss mitosis
as a whole)
Objective
• To prepare slides from onion skin and root tip to witness mitotic processes
• To understand the different phases that involve in mitosis
Materials
Two small beakers, tweezers, Onion bulb with roots, razor blade, toluidine blue , slide
and cover slips, fingernail polish, paper toweling, methanol, 1M HCl
Methods
Prior to lab:
1. Cut off last 6 mm of the root tip or get the thin slice of onion skin. Place in a
small beaker.
2. Add methanol and make sure all tips are immersed
During lab:
1. Remove your samples from the beaker and immerse in a new tube filled with 1 ml
HCl. Incubate for 12 min at 60ºC.
2. Remove the sample from HCl.
3. Let the samples stain in toluidine blue for about 10 min or until they shows
distinct dark coloring. Be careful not to touch the root tip.
4. Place the sample on the slide. Use tweezers or blade; cut 1-2 mm of the root tip
and discard the rest of the root tip.
5. Put one drop of methanol on the slide
6. Gently lower a cover slip over the root tip or onion skin. Cover the slide with a
paper towel and with your thumb, firmly press on the cover slip; do not twist the
cover slip. The pressure will spread the cells into a single layer.
7. Finally seal the cover slip with fingernail polish.
8. Now you are ready to view you slide under low power. In a given field of view,
count the number of cells at each of the five stages of mitosis. You will have to
decide where your cut-off point is when considering if cells in prophase and
telophase contain condensed chromosomes before turn the objective lens to higher
power. Record this in the table below.
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3. HCB 1019 Cell Biology Trimester 1, 2012/13
Stage of Mitosis Number of Cells
Percent of time in each
stage =
# of cells in stage X
100%
Total # of Cell
Prophase
5
25%
Metaphase 1 5%
Anaphase 1 5%
Telophase 1 5%
Interphase
(Not a Mitotic
Stage)
12 60%
Total # cells 100%
Questions
1. What is the function of methanol and toluidine blue?
Function of toluidine is a dye, and it is used to stain cells. The function of the
methanol transfer buffer and enhance adsorption.
2. What is the purpose of transferring the onion root tip in HCl? Why is this step
helpful in your experiment?
provides the acidic medium for the chemicalprocesses involved and to soften
the tissue texture so that it is easy to press the root tips and put it on the slide
of microscope.
3. Why is the onion root a good specimen for studying mitosis?
Cells of the onion are growing so it is easy to find cells in various stages of
mitosis.
4. Which stage of mitosis is the easiest (in your opinion) to see on the slide?
metaphase is usually pretty obvious
metaphase is usually pretty obvious.
5. In allium, interphase lasts about 15 hours, and mitosis takes up 80 minutes.
Assuming that each stage of mitosis takes the same amount of time, how many
hours old is a cell that is just starting anaphase.
Well since there are 4 phases in Mitosis then you divide 80 by 4 which is 20
minutes. That means each stage takes 20 minutes. So by the time the cell gets
to Anaphase, which is the third stage, it would have been half way through.
So a cell just starting Anaphase is 15 hours and 40 minutes old.
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4. HCB 1019 Cell Biology Trimester 1, 2012/13
6. What is the main event in every phase of mitosis? Give brief explanation and
attach images that you get from internet.
Stage Distinguishing Characteristics
Interphase single, prominent nucleus
Prophase chromosomes visible
Metaphase chromosomes line up
Anaphase chromatids separate
Telophase two nuclei visible, cell splits
.
7. What phase do cells spend most of their time in? Why?
Most cells spend most of their time in interphase. If cells spent most their
time inmitosis then cells would undergo cell division at higher than normal
rates, which is generally associated with a form of cancer. Cells within the
body do not need to be replaced at a higher than normal pace under normal
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5. HCB 1019 Cell Biology Trimester 1, 2012/13
healthy circumstances. Since the cell is in interphase the longest, the cell is
able to spend more time to carefully proofread the synthesized DNA for any
errors. By having a correct copy of DNA helps ensures to lower the rate of
genetic flaws, as well, The cell line generations down will more likely have a
correct copy of DNA with as little mistakes as possible.
References :
http://www.biologycorner.com
http://schoolworkhelper.net
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6. HCB 1019 Cell Biology Trimester 1, 2012/13
healthy circumstances. Since the cell is in interphase the longest, the cell is
able to spend more time to carefully proofread the synthesized DNA for any
errors. By having a correct copy of DNA helps ensures to lower the rate of
genetic flaws, as well, The cell line generations down will more likely have a
correct copy of DNA with as little mistakes as possible.
References :
http://www.biologycorner.com
http://schoolworkhelper.net
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