BIOLOGY REPORT MITOSIS
NAME:NOR ALIAH ASHIKIN BINTI RAZAK
GROUP:12 M 8
SID NO: 2011270064
LECTURER NAME: MR.MOHD HAFIZ BIN ROTHI
OBJECTIVE
The objectives of this experiment is to prepare some slides of actively dividing plant
tissue.To observed the stages of the cell cycle in living tissue.Besides that, we want to
consider the duration of the stages of mitosis in relation to the whole cell cycle.Lastly, the
objectives of this experiment is to develop certain experimental skills,namely working
safely,the use of microscopes,producing valid results and recording data.
INTRODUCTION
This laboratory report is all about an experiment on mitosis which is the division of the nucleus
of a cell to form two new daughter cell that are genetically identical to the parent cell. There are a few
stages of mitotic division that are possible to be observed , interphase , prophase , metaphase ,
anaphase and telophase . During interphase , the cell will not be dividing and DNA replication occurs .
Prophase is the first phase of mitotic divison where chromatins will be shorten and thicken , resulting
in visible and condensed chromosomes. Nuclear envelope and and nucleolus will be disappear during
late prophase . During metaphase , spindle fibre are attached to the centromeres and chromosomes will
be aligned at the metaphase plate . During anaphase, the centromers split ans separated sister
chromatids are pulled to the opposite poles . At the final phase , telophase, chromosomes will reach at
the opposite poles and nuclear membrane starts to form around each pole. This will be continued by
cytokinesis whis the divison of the cytoplasm into two cells . For this experiment , onion root tip was
chosen because of rapid growth and easy availability . Therefore, this will result in an easy
opportunity to observe many cell in various stages of mitosis in small sample. Mitosis in plant cells
takes place in the meristems which are normally found at the tips of stems or roots which is absolutely
different in animal cells where mitosis occur . The purpose of this experiment is to observe the stages
of mitosis in root tip as well as estimating the real time spent in each phases of mitosis in onion root
tip cell. It is predicted that most of the cells will be interphase and the shortest stage of mitosis is
telophase. The longest stage is prophase .
HYPOTHESIS
The stages of mitosis in the onion root tip is easily observed under the microscope. When
undergoing mitosis, most of the cell in the onion root tip will be in interphase.More cells will
be in the stage of prophase than metaphase. More cells will be in metaphase than anaphase
and as well as more cells will be in the stage of anaphase than telophase.
MATERIALS/ APPARATUS
Microscope with magnificant x100 and x400,pair or forceps,filter paper,eye
protection,scalpel or sharp knife,2 small sample tubes,onion roots,1M hydrochloric
acid,toluidine purple strain,distilled water,microscope slides and coverslipes.
METHOD
1. Cut off 1-2 cm from several root tips of some growing onion roots.Choosed tips which were
white and have firmed rounded end.(Brown tips will give poor results).
2. Put the root tips into a hollow glass block or small sample tubes contained 2 cm3 1 M
hydrochloric acid for exactly 4 minutes.
3. Transferred the root tips to a watch glass contained approximately 5 cm3 cold water.Left
them for 4 minutes ,then dried them on filter paper.Handle the root tips gently as they will
be very fragiled.
4. Transferred one of the root tips to a clean slide.Cut about 4-5 mm the growed tip.Kept the
rounded tip and discard the rest.The meristem tip is usuallya denser white and more
rounded than the cut end.If u take a wrong end, the presence of xylem will make maceration
more difficult.
5. Gently broke up the root tip with a mounted needle (this is called maceration). Added one
small dropped of toluidine purple and leaved to stain for 2 minutes.
6. Covered with a coverslip,a blot firmly with with severallayers of tissue or filter paper.Press
gently to spred the root tip,or tap gentlyon the coverslip with the end of a pencil.
7. Viewed under the microscope (x400 magnification) and look for the cells with
chromosomes.If cells are overlapped ,squash the slide again between two wads of filter
paper.(Avoid lateral movement of the coverslip)
8. Looked for the regular shape,actively dividing cells.DNA stains dark purple with toluidine
purple stain so you should be able to see purple groups of mosomes against a paler
background.
9. If your preparation is not very successful, repeated with some of the other root tips from
step 3.Tried to adjust your procedure to remedy the problem,for example if your cells are
over or understained,adjusted the time they are lefted in the stain.
RESULTS
NUMBER OF CELLS
TOTAL
PERCENTAGE
SIZE OF CELL
(%)
INTERPHASE
186
93
6/40 = 0.15
PROPHASE
3
1.5
9/40 =0.225
METAPHASE
5
2.5
8/40 = 0.5
ANAPHASE
2
1.0
7/40 = 0.175
TELOPHASE
4
2.0
12/40 =0.3
200
DISCUSSION
Interphase
In this phase , the chromosomes are not condensed yet and individual chromosomes cannot be
distinguished.
Prophase
Chromosomes in prophase are visible , shortened and condensed but are not organized in a
line.
Metaphase
Cell in metaphase has distinct chromosome that align along the middle of the cell
Anaphase
Cells in anaphase have two clusters of distinct chromosomes that are being pulled away towards opposite
poles .
Telophase / Cytokinesis
Two distinct chromosomes are observed with the nuclear membrane is forming around each
cluster.
After observing various phases of mitotic division , the number of cells in each stage of mitosis is
calculated. The number of cells are divided by the total number of cells in the sample , 400 and times by
100 to get the percentage.
Based on the table above , interphase has the highest percentage of cells followed by metaphase
and telophase , anaphase and the lowest percentage of cells is in the stage of metaphase .From this
results, we can conclude that the least time is spent in metaphase while prophase and telophase are the
longest stage of mitosis in the onion root tip. In order to identify the stage of mitosis , carnoy fixative is
used to instantaneously stop mitosis in the root tip cell or in other words to fix the movement of
chromosome . Thus , when we eventually see the chromosomes, we are looking at one moment of
mitosis frozen in time. In addition , Toluidine Blue is used to stain the cell , making a better view under
the microscope . Before starting the experiment , the root tip is immersed in holding solution, an
antimicrobial liquid which is used to place the root tip temporarily while awaiting sterilization.
Hydrochloric acid is used to break the middle lamella in the cell wall and soften the roots so that later
they can be spread on a microscope slide .There is only few dividing cells in the root tip as it is
underground and does not contact with sunlight, resulting in no photosynthesis occurred . Therefore , the
root tip does not grow as fast as the part above ground . Besides that , the root tip that have been observed
might comes from a bad section of the tip or the magnification is not proper enough to see more dividing
cells in the root tip. The size of interphase cells is smaller than cells that are undergoing cytoplasmic
divison
In order to compare the size of cells during interphase and cytoplasmic division , we use eyepiece
graticule to measure the size of the cells as below .
1 scale of micro stage
= 10 μm
100 scales of micro stage
= 1000 μm
40 division of eyepiece
= 1000 μm
1 division
= 25 μm
From the measurements taken , we can say that the size of interphase cell is smaller than size of
mitosis cells. This is because chromosomes in interphase cell are still in the nuclear envelope which
control and maintain the size of the cell. During mitosis, nuclear envelope will disintegrates . Thus,
movement of chromosomes will cause a big change and increase the size of the cell.
VALIDITY AND REALIBILITY
To provide more valid and reliable result , the experiment is held using large number of cells which is
200. Besides that , the observation through microscope should be done in pairs so one can person observe
the cells and the other person can record which phase the cell is in. The counting should be done at least
three times to get more accurate results. With all the results collected an average should have been
calculated to give a more concise number of cells in each phase . The use of eyepiece graticule also
provide more appropriate measurements of the cells. However , an inaccurate results are received. There
should have been fewer cells in telophase than any of the other phases and it should have been the
shortest stage in mitosis The results received are inaccurate because the number of cells that were in
telophase were improperly counted. We received results that more cells were in telophase and spent more
time in telophase than anaphase.
SOURCE OF ERROR
There is very small chance of error in this kind of lab experiment as it is only involved observations and
sketching .There also might be a misidentification of the mitotic phases due to overdyed and grays areas
which causing the miscounting of cells in particular stages .Besides that , too much water and too little
water added to the sample also cause some errors to the observation of the mitotic phases.
SAFETY AND PRECAUTIONS
During the experiment , glassware that are used should be handled with care to avoid any injuries as well
as the microscope . Besides that , be more careful not to get hydrochloric acid on skin or clothing . The
sample of cell should not be twisted to avoid any breaking of cell wall. The observation through
microscope should be done in pairs so one can person observe the cells and the other person can record
which phase the cell is in. The counting should be done at least three times to get more accurate results.
With all the results collected an average should have been calculated to give a more concise number of
cells in each phase .
LIMITATION
During the experiment , the overdyed and grays areas cause some difficulties to detect certain phases of
mitosis. The time constraint also prevent us from observing other sample of cells away from root tip. The
experiment is conducted for only 2hours. Therefore , no comparison can be made between the mitotic
index of two different areas. Besides that , most of the cells in the onion root tip is in interphase which is
the longest phase before mitosis. Thus , there is very little chance to observe the 4 major phases in
mitotic division .
CONCLUSION
From these experiments we can conclude that the mitotic stages of onion root tip cells is observable
under a microscope. Thus , we can say that most of the cells cycle in an onion root tip is spent in
interphase. There is four stages of mitosis which is prophase , metapahase , anaphase and telophase
Prophase is after interphase in time spent in each cycle.
REFERENCES
1. Biology edexcel
2. Biology Campbell
3. Biology Form 4
4. Biology junction , Mitosis. Available from :
http://www.biologyjunction.com/lab_3__ap_sample2_mitosis_.htm. Accesses on 2nd February 2011