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Transcript of mitosis report
INTERNATIONAL EDUCATION CENTRE (INTEC)UiTM Section 17 Campus 40200 Shah Alam Selangor Darul Ehsan.
TEL: 603-55227000
TITLE: OBSERVING MITOSIS
NAME: NUR AMALINA BT ZOLKEFLEE
SID NUMBER: 2010843164
CLASS: 11M2
DATE OF EXPERIMENT: 24TH JANUARY 2011
LECTURER’S NAME: MISS FATHIAH ABDULLAH
PARTNER’S NAME: FATIN NABILAH BT MOHD NASIR
NUR AIN SOFIA BINTI HARITH
SITI NASHUHA BINTI OSMAN
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OBJECTIVES
Basically, our experiment is done to prepare some slides of actively dividing plant
tissues. The other purpose of this experiment is to observe the stages of the cell cycle in
living tissue and to consider the duration of the stages of mitosis in relation to the whole
cell cycle. Through this experiment also, we can develop certain experimental skills,
namely working safely, the use of microscopes, and producing valid results and recording
results. Not just that, we are also taught to calibrate an eyepiece graticule and use it to
measure the size of the cells.
INTRODUCTION
BACKGROUND INFORMATION Genetic information of human, plants and animals reside in unique structure
called chromosomes. For example, each human cell posses 46 chromosomes while
onion cell posses 8 chromosomes. All cells must replicate their DNA in order to
pass it to the next generation of cells in the whole body. During DNA replication,
two strands of DNA separate and for each strand, new complementary DNA is
produced thus yielding two identical DNA molecules. After DNA replication, the
process followed is mitosis which is important to ensure that each daughter cell
receives one copy of each replicated chromosome. During mitosis, the
chromosomes pass through several stages like prophase, metaphase, anaphase and
telophase. The division is considered as complete once the cell undergo
cytokinesis.
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Figure 1 shows the cell cycle that includes interphase, mitosis and cytokinesis.
Source: http://mysite.cherokee.k12.ga.us/personal/gregg_schumaker/site/Important%20Class%20Documents/1/Growth%20and%20Heredity/Observing%20Mitosis%20Lab.pdf
The first stage in mitosis is prophase. During prophase, chromatin condense to form
highly condensed chromosomes. Chromosomes are visible at high magnification through
light microscope. The two strands of non- sister chromatids are joined at one region
called centromere. The microtubules from cytoplasm form three dimensional structure
called spindle fibre which are formed between two poles. The centrioles move around
nuclear envelope and locate themselves at opposite sides of the cell. Nuclear envelope
and nucleolus break down.
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Figure 2 shows some events that take place during prophase.
Source: http://chuck16.wordpress.com/2009/04/30/phases-of-mitoses/prophase- late__civyrosejpg/
During metaphase, the centromeres of chromosomes line along the metaphase plate or
equatorial plane, an imaginary line that is equidistant from centrosome poles. When this
arrangement has been completed, the cell has reached the end of metaphase.
Figure 3 shows how the chromosomes arrange themselves at metaphase plate during
metaphase.
Source : http://www.sparknotes.com/biology/cellreproduction/mitosis/section2.rhtml
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The third stage in mitotic division is anaphase. During this stage, the centromeres split.
The spindle shorten to pull the two halves of each centromere in opposite directions. One
chromatid of aech chromosome is pulled to each of the poles. Anaphase ends when the
separated chromatids reach the poles and the spindle breaks down.
Figure 4 shows the events occur during anaphase.
Source: http://www.sparknotes.com/biology/cellreproduction/mitosis/section2.rhtml
The last stage in mitotic division is telophase. The events taking place during telophase
is a reverse process of prophase. Chromosomes unravel and nuclear envelope reforms, so
that two sets of genetic information become enclosed in separate nuclei.
Figure 5 shows the events take place during telophase.
Source: http://www.sparknotes.com/biology/cellreproduction/mitosis/section3.rhtml
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Cell cycle consists of three main stages which are interphase, mitosis and
cytokinesis. Cytokinesis is also known as cytoplasmic division. During cytokinesis, plant
cells divide due to formation of walls between two daughter cells. New cell wall material
is brought by microtubule system forming the phragmoplast, a complex organelle
consisting microtubules and actin filaments.
Figure 6 shows the sequence taking place during cytokinesis.
Source: http://www.bms.ed.ac.uk/research/others/smaciver/Cyto- topics/Plant %20Cytokinesis.htm
Overall, mitosis is very crucial in order to maintain genetic consistency. This is
because the daughter cells are made to be ganetically identical to each other and parent
cell. Can you imagine to have different colours of skin? This probably happen if mitosis
do not occur as our genetic information is not restored in producing new cells. Genetic
consistency is achieved by DNA replication prior to nuclear division and during the
arrangement of the chromosomes on the spindle fibre and the separation of chromatids to
the poles. Mitosis is also important to animals and plants that practice asexual
reproduction. For example starfish can regrow a completely new body from a fragment of
its body. Furthermore, mitosis is also significant in replacing our dead cells sepecially
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our skin cells which are easily rubbed by the friction. So, in order to maintain in good
condition, mitosis will occur to replace those old cells.
In this experiment, we are using onion roots due to several specialities that it owns.
Firstly, the onion roots are easily grewn in large numbers. Therefore, no ethical issues
arise here as it is not an endangerd population and it will be much cheaper to be compared
to other type of plants. Secondly, cells at the tip of roots are actively dividing and thus
many cells will be in stages of mitosis. The tips can be prepared in a way that allows them
to be flattened or microscopes slide(‘squashed’) so that chromosomes of individual cells
can be observed. The chromosomes of onion cells can be stained to make them more
easily observable and as the chromosoes are large and become very dark when stained,
therefore the onion root cells is the most suitable to be used in this experiment. There are
three cellular regions at the tip of onion root. The first one is root cap. It contains cells
that cover and protect the underlying growth region as the root pushed through the soil.
The second region is the region of cell division(meristem). Here, the cells are actively
dividing but not increasing in size while the third region is the region of cell elongation
where the cells increase in size but not dividing.
Figure 7 shows the three regions at the tip of onion root
Source: http://www.excellup.com/InterBiology/morphologyplant.aspx
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In order to get an accurate result, we have to make sure that we know how to use the
microscope correctly because our result is only depending on microscope. What we see
through the microscope indicate how successful our experiment is. Firstly, you have to
put your microscope on flat surface. Then, switch on the microscope’s light source and
then adjust the diaphragm to the largest hole diameter to allow the greatest amount of
light passing through. Use the lowest power objective (usually 4x for 40x magnification).
Place the slide on the stage and adjust the large coarse focus knob until specimen is in
focus. After that, adjust the small fine focus knob until specimen is clearly in focus. Then,
adjust the diaphragm to get the best lighting. Rotate the objective lens to 10x objective for
100x magnification. Refocus and view the specimen carefully. Repeat this step by using
40x objective. It is an optional for you to use the 100x objective for 1000x magnification.
You need to put 1-2 drops of immersion oil over the slide coverslip before viewing it at
highest power.
Figure 9 shows a microscope
Source : http://www.hometrainingtools.com/how-to-use-a-microscope/a/1120/
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In this experiment also, we are using toluidine blue instead of carbol fuschin.
Toluidine blue is a polychromatic dye that absorbs different colours depending on the
nature of its chemical binding with components of the tissues. At pH 4.4, it will bind to
pectins in cell walls and colour them pink. Compounds containing benzene rings such as
lignin will be coloured green. At lower acidic pH, toluidine blue gives only blue or only
green colour. At higher basic pH (11.1) the stained tissue will be coloured dark pink since
most pectins will be charged and hinder the green colour of lignin.
EXPERIMENTAL HYPOTHESIS
Mitosis occurs in onion root tip and it is easily observable. By observing onion
meristem cells under microscope, we can see the interphase, the four stages of mitosis
that is prophase, metaphase, anaphase and telophase and cytokinesis clearly. The most
time spent in a stage is in prophase and the least time spent in a stage is anaphase. All the
stages can be differentiated by observing the chromosomes in nucleus that is the
chromosomes’ position within the nucleus. If only long strand can be seen, it indicates the
cell is undergoing interphase. If the chromosomes scattered in the nucleus, it indicates the
prophase stage while if the chromosomes arrange themselves at the centre which is
known as metaphase plate, it shows metaphase stage. On the other hand, if the spindle
looked shorter and like pulling the chromosomes to the pole, it means that the cell is
undergoing anaphase. The telophase stage can be observed when you can see two sets of
chromosomes in a cell. Cytokinesis is the easiest stage to be detected; that is when you
can see cell plate formed in between the two sets of chromosomes.
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MATERIALS AND APPARATUS
MATERIALS: carnoy fixative, holding solution(70% ethanol), HCl acid( 18%), toluidine
blue.
APPARATUS : microscope slides, coverslips, small beakers, watch glasses, blades,
Forceps, filter paper, compound microscope.
METHOD
Preparing the sample
1. Sample of onion root cells is obtained from the holding solution.
2. Two cups of solutions are prepared. The first cup contains HCl acid while the
second one contains carnoy solution.
3. By using a forcep, an onion root tip is transferred into HCl acid solution for four
minutes.
4. Then, the root tip is transferred into carnoy solution for four minutes.
5. By using a blade, 1 mm of the root tip is cut and is put on microscope slide.
6. A few drops of toluidine blue is dropped into the root tip and is left for two
minutes. Then, a few drops of water is put onto the root tip to dilute the
concentrated toluidine blue.
7. By using a filter paper, the stain surround the root tip is blotted away.
8. Then, a cover slip is put over the specimen.
9. The slide is covered with a paper tissue and the cover slip is pressed with the
thumb.
10. Then, the slide is observed under microscope.
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Preparing the microscope
1. A stage micrometer is slide on the stage of microscope. The smallest division on
the stage micrometer is measured.
2. By using low power objective, the microscope is focused on stage micrometer.
The eyepiece is rotated and the slide is moved.
3. The number of divisions on eyepiece graticule is counted and is made equivalent
to the smallest division on stage micrometer and hence the length that one
eyepiece division is calculated.
4. Step 3 is repeated for medium and high power objectives. The cell size can be
measured.
RESULTS AND DATA
Figure 10 shows the drawing of overlapping cell walls.
What we can see from the microscope is only overlapping cell walls.
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Figure 11 shows Nucleus is hardly seen due to compact cell wall.
Source: http://mrswolfgang.wikispaces.com/Animal+and+Plant+Cells+-+Bizousky,+Byerly
Table 1 shows number of cells in each stage
DISCUSSION
Based on our result, we found that our result is not valid at all due to some errors
that we encounter that we will discuss in detail in sources of error. After discussing with
other groups that manage to conduct their experiment successfully, we found that each
stage in cell cycle can been observed clearly under microscope. Here is some pictures
showing how chromosomes behave in each stage of mitotic division and interphase.
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Stage of cell cycle Number of cells in each stage
Interphase Cannot be observed
Prophase Cannot be observed
Metaphase Cannot be observed
Anaphase Cannot be observed
Telophase Cannot be observed
Figure 12 shows all the cells that can be observed under microscope using low power
objective.
Figure 13 shows the chromosomes behaviour using higher power objective.
Source: http://www.practicalbiology.org/areas/advanced/cells-to-systems/cell-division/investigating-mitosis-in-allium-root-tip-squash,121,EXP.html
Through our discussion too, we found that our hypothesis made is accepted. That is
most of the time in mitotic division is spent in prophase while the least time spent is in
anaphase.
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Table 2 shows number of cells in each stage.
Source: http://www.practicalbiology.org/areas/advanced/cells-to-systems/cell-division/ investigating-mitosis-in-allium-root-tip-squash,121,EXP.html
In calibrating the eyepiece graticule, we found that the smallest division on the stage
micrometer equals to 100 micrometer. The eyepiece is rotated and the slide is moved to
superimpose the scales of eyepiece graticule and stage micrometer. Number of division
on eyepiece graticule is found to be three divisions equal to 1 smallest division of the
stage micrometer. Therefore, each division on eyepiece graticule is equal to 33.33
micrometer.
Figure 14 shows the stage micrometer and eyepiece graticule scale.
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VALIDITY AND RELIABILITY
It is obvious that our experimental result is not valid. This is because we could not see
any stages in the cells. Our group only manage to see the overlapping cell walls. But then,
our experimental result is quite reliable because we have been repeated this experiment
for three times but unfortunately, we obtained the same results. So, we come into
conclusion that there might be errors due to apparatus because our experimental result is
constantly the same.Not just that, this experiment is a time critical experiment. This is
because a few steps in this experiment is constraint with time. As we have been repeated
this experiment three times, our result obtained can be considered as quite reliable but not
valid.
SOURCE OF ERROR
There are lots of errors that we have analysed. The first one comes from microscope.
Our group’s microscope has been contaminated by the emulsion oil. The emulsion oil can
damage the structure of the cell. The lens of the microscope are not being wiped out first
before we are using it. Secondly, the intensity of toluidine solution used is too low until
the nucleus of the specimen cannot be observed under microscope. It makes us difficult to
trace the stage easily. Thirdly, we assumed that the root tip has not been fully immersed
in HCl and carnoy solution which later interrupt the image observed under microscope.
Next, the duration for the root tip to be immersed in HCl acid and carnoy solution is not
exactly four minutes. As the root tip has been cut in a large size and not exactly 1 mm, it
cause the specimen to overlap each other. Not just that, the specimen might be damaged
due to high pressure exerted by the thumb on it.
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SAFETY MEASURES AND PRECAUTION
There are a few safety measures that must be taken into consideration in order to make
sure that the experiment is going on smoothly without any accidents. First, we must wear
the lab coat to prevent any stain onto our cloth. For example, toluidine blue can stain your
cloth if you do not wear lab coat. We have to make sure the concentration of HCl acid
used is not too concentrated because it might be dangerous to be handled. Do not eat and
drink throughout the experiment because the biology lab still keep the hazardous
chemical substances even we are not using it. We must also be very careful when
handling the lab apparatus like beakers and cavity slide which tend to break easily and
will harm our safety. The microscope is fragile and light bulbs can get so hot, so we have
to be careful. Ethanoic ethanol is corrosive, so wear eye protection (goggles). Not just
that, take care with scalpels and always carry them on a white tile to prevent any injury
occur during lab session. And always keep the laboratory in clean state.
LIMITATIONS
There are a few limitations that prevent us from getting a very acurate and precise
result. This is due to lack in time. Each step takes at least 2-3 minutes to be done. As there
are many steps of them; overall, it takes about 30 minutes to prepare each specimen.
Furthermore, it is not easy to observe the specimen under microscope. It takes about 10
minutes for us to actually see the specimen. Basically, this experiment consume a lot of
time. Next, the microscopes provided are not enough to accommodate all of us. For
example, as our microscope is not in good condition, we have to use other group’s
microscope as there is no extra microscope provided. We have to wait to use a particular
microscope. This consume more and more time. Furthermore, this is our first experience
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in conducting mitosis experiment. We are lacking in skill especially the skill to cut the
root tip.
MEDICATION AND FURTHER WORKS
In order to get a more accurate result, a few suggestions had came across. The first one
is we have to wipe the lens before we are using it to prevent any immersion oil that might
be used by the previous group. We have to make sure that the concentration of toluidine
blue is just fine( neither too dilute nor too concentrated) so that we can see the nucleus
clearly. We have also to make sure that the root tip is fully immersed in HCl acid and
carnoy fixative so that the structure of the cell can be clearly observed. Moreover, we
have to increase our alertness in recording time so that the duration taken for the root tip
to be immersed is actually as required. From what I have read some tips from example
reports, they are suggesting us to squash the root tip using blunt pencils. This could be a
good alternative.
CONCLUSION
After we have done this experiment, finally we came into conclusion that our
experiment is not success to prove what had been stated in hypothesis that is the most
time spent is in prophase and the least time spent is in anaphase. Therefore hypothesis is
rejected and in order to verify this statement, we must undergo this experiment one more
time by using different microscope, slides and other apparatus and material to overcome
any lacking during conducting this experiment. However through long discussion with
other group members, we can conclude that mitotic stages of onion root tip can be
observed with a light microscope and the most time spent is in prophase while the least
time spent is in anaphase.
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REFERENCES AND BIBLIOGRAPHY
FROM INTERNET 2011. Available from: http://www.practicalbiology.org/areas/advanced/cells-to-
systems/cell-division/investigating-mitosis-in-allium-root-tip-squash,121,EXP.html. Accessed on 1st February 2011
2011. Available from : http://en.wikipedia.org/wiki/Mitosis. Accessed on 1st February 2011
2011. Available from : http://www.123helpme.com/preview.asp?id=156102. Accessed on 1st February 2011
2011. Available from : http://www.experiment-resources.com/validity-and-reliability.html. Accessed on 1st February 2011
2011. Available from: http://staff.jccc.net/pdecell/celldivision/oniontip.html. Accessed on 1st February 2011
FROM BOOK Angela,H. et al . 2008. Voice of Genome. In Salters-Nuffield Advanced Biology
or Edexcel AS Biolog, p.116-117. London. Edexcel Pearson.
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