Observation of mitosis in garlic root tips
Abstract:
The experiment was conducted to study mitosis in actively growing cells. The source of actively
growing cells in this practical was garlic root tips. Mitosis is an essential process for cells to grow and
develop. The end product of mitotic division is two daughter cells which are genetically identical to
each other as well as to parent cell from which they are produced. The use of light microscope
makes it possible for scientists to study all phases of cell division. Light microscopes have been
widely used to study mitosis. However, in this particular practical not all phases of mitosis were
observed due to some limiting factors such as time.
Introduction:
The experiment carried out consisted of multistep, which were planning and observation. The aim of
the practical was to observe the cell cycle or mitosis in garlic root tips.
Mitosis is also referred to as single nuclear division as compared to meiosis which is double nuclear
division. Mitosis mainly occur in somatic cells. Mitosis in plants mainly occurs in root tips and other
specific parts of them. Before mitosis takes place, DNA and other organelles replication occurs in
interphase. Interphase is then followed by multistep of mitosis. Mitosis consists of prophase,
metaphase, anaphase and telophase. Mitosis is followed by cytokinesis where the cytoplasm of
newly made cells separate. Prophase is the first stage of mitosis in which the chromosome becomes
condensed and visible. You could use light microscope to see chromosomes. This is important in
counting the number of chromosomes present in cells. The structure of chromosome is transparent
which means they need to be stained with particular chemicals before they can be seen.
Mitosis can be easily observed in particular parts of organisms depending upon which organism you
are looking at. For example if you are observing animal cells for mitosis, the major source of animal
cells would be the cells which need growth or repair e.g. early embryonic cells.
In this practical garlic root tips are used to observe mitosis because they are easily obtained and
accessible to everyone. For this practical a garlic clove is soaked in water in a container such as
beaker. Because the garlic root tips have meristem cells which are in the phase of growth, in a few
days’ time the growths could be observed.
Method for preparation:
1. Boiling tube is used as container to heat stained garlic root tips with aceto-orcein at 60
degree Celsius for about 1 hour.
2. It is possible that some of the root tips must have been damaged after heating. Significantly
obtain the roots which are not damaged and apply it onto microscope slide with the help of
forceps.
3. Using cover slip cover the area of the slides where root tip is present.
4. Use small blotting paper and put it on the cover slip and apply pressure from your thumb to
get rid of extra stain.
5. Removing excess stain helps obtaining clear results when looking under microscope. This
also helps chromosome to be clearly seen individually.
6. Once you have made sure that excess stain is removed, you can then put your slide on
microscope’s stage. Using X10 objective lens focus on a particular point of root tips where
the growth is active.
7. After focusing on to specific point and seeing the division, you can now change the objective
lens to X40. Using X40 objective lens you can see chromosomes as well as different stages of
mitosis.
8. Make sure that once you have identified different stages of mitosis; put the stages of mitosis
in the correct order from prophase followed on to the final stage.
9. Specify the number of chromosomes if you possibly can.
Apparatus and materials:
 Aceto-orcein (staining chemical)
 Beaker
 Blotting paper
 Cover slip
 Garlic clove
 Forceps
 Light microscope
 Microscope slide
 Test tube
Results and Discussion:
Interphase, prophase and telophase were observed as the experiment was conducted. Interphase is
not one of the phases of mitosis and it is also known as non-mitotic phase.
Interphase:
During interphase DNA replication and other essential cell organelles growth takes place. The DNA
replication is checked to eliminate any faults and mutations in order to proceed with mitotic division.
The diagram below demonstrate the dark and condensed nucleus surrounded by light cytoplasm,
this is due to the duplication of genetic material.
Prophase:
In this particular stage of mitosis, DNA is condensed hence can easily be seen under the light
microscope. The nuclear envelope starts to disintegrate and the centrioles start to migrate to the
opposite poles of the cell. Microtubules are used to make mitotic spindles as the centrosomes reach
their positions.(Albert et al, 2008). As it is clearly seen in the diagram below that the condensed
chromosomes are no longer inside the nucleus because nucleus disappears in this phase.
Aston Blackboard (2014)
After identifying prophase the next target was to identify metaphase as a sequence because it is the
second stage in mitosis. However, metaphase was not identified efficiently. Instead telophase was
quite remarked as two tiny circles could be clearly seen.
Telophase:
Telophase is the final phase of cell cycle or single nuclear division (also known as mitosis). This
particular stage of mitosis is the end point of mitosis followed by cytokinesis. The formation of two
daughter nuclei and nuclear membrane starts in telophase. The DNA uncoils and at this point it
becomes invisible. (Bailey, 2014). It can be demonstrated from the diagram shown below that two
tiny circles are ready to be separated and divide into two daughter nuclei.
Aston Blackboard (2014)
The practical was conducted to observe all the important stages of mitosis in an order as they are
carried out in actual process of mitosis. All the essential phases of mitosis were expected to be
observed. However, only prophase and telophase were observed in the actual practical. The
observation that was done in the practical did not really meet the aim of the practical. There are a
number of reasons due to which the errors occurred while the practical was conducted. One of the
factors which led to errors in practical was the usage of light microscope. Despite the fact that all
instructions on the usage of light microscope were detailed out and well explained, I did not have
very good experience while using the microscope because I did not have the required skills. The lack
of skills led to obtaining the ambiguous results because I didn’t know when to zoom in and zoom out
to adjust the stage of microscope. The other main factor which led to unexpected errors was the
usage of Aceto-orcein (staining chemical). The staining chemical was used to stain the genetic
material of actively growing and dividing cells so that they are easily seen under the light microscope.
The garlic root tips were stained and the extra stain was removed in order to produce clear results
however, the removal of extra stain was not efficient enough; as a result air bubbles were produced,
which caused artefacts; hence all phases of mitosis were not clearly identified.
Moreover, cover slip was used to apply a small amount of pressure onto garlic root tips in order to
get rid of extra stain to obtain clear results however, this might have slightly damaged the root tips
due to which actively growing cells might have been killed and therefore most of the phases in
general were not clearly identified.
The stain was heated with garlic root tips while preparing for the practical. The fluctuations in
temperature could have led to denaturation of vital proteins required in mitotic division and
therefore mitotic division might have not been observed.
A number of steps could be taken to show improvements in the practical and therefore it could be
made possible to observe each and every single phase of mitosis. The first and easy step which could
improve the practical is usage of another staining chemical instead of Aceto- orcein because this
particular staining chemical was not appropriate enough to visualise mitotic spindle. Polylysine
(staining chemical) could have been used to visualise microtubules and therefore metaphase and
other various stages of mitosis could have been identified because chromosomes are attached to
mitotic spindles. (Mcb.berkeley.edu, 2014).
Furthermore when the staining chemical was heated with garlic root tips, the temperature could
have been slightly above 60 degree Celsius and as a result led to denaturation of enzymes (as
discussed above). The temperature could have been controlled using thermostatically controlled
water bath which is quite accurate as compared to thermometer.
The other important improvement which could have led to obtaining more precise results is the
usage of electron microscope because it would provide higher resolution and magnification however,
using electron microscope; live mitotic division would have not been observed because in order to
use electron microscope, we require dead cells. The other problem with the usage of electron
microscope is that a well-trained technician is needed and a separate accommodation is required to
accommodate electron microscope because it is quite huge.
Other phases of mitosis, not observed:
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Metaphase
Anaphase
Cytokinesis (telophase is followed by cytokinesis however; it is not one of the phases of
mitosis).
Metaphase:
In this particular phase, nuclear membrane disintegrates and the genetic material (chromosomes)
attach to mitotic spindles (microtubules). The points at which chromosomes attach to spindles are
called centromeres. Chromosomes line up on the equator of mitotic spindles as shown in the
diagram below. The red substances in the diagram below represent chromosomes and the green
represents spindles.
Albert, et al (2008)
Anaphase:
In anaphase, the sister chromatids are separated to form two sets of chromosomes as mitotic
spindles pull towards the opposite poles of cells. This is clearly seen in the diagram below that the
chromosomes are pulled apart towards opposite sides of the cell
Albert, et al (2008)
Cytokinesis:
This is the process where cytoplasmic separation takes place and two daughter nuclei are formed.
An actin filament is essential for this particular separation as it is required to pinch the two sets of
chromosomes into two daughter cells. Myosin is used along with actin filaments as it is a motor
protein. It is clearly seen from the diagram below that two daughter nuclei are now completely
separated as their cytoplasm has been separated with the help of actin filaments along with other
motor proteins such as myosin.
Albert, et al (2008)
Conclusion:
To sum up, the practical did not work out as it was expected to give positive outcomes. As discussed
previously; not all the phases were observed however, prophase and telophase were observed. The
aim of the practical was to observe mitosis. However, as the experiment was conducted it did not
achieve the aim of the practical.
However, most of the cells were found to be in the stage of interphase. By conducting this practical
and having done some research, it can be concluded that interphase is the longest phase and
therefore most of the cells were observed to be in the stage of interphase. From what was observed
and found it can be stated that the time taken to observe mitosis was not sufficient enough to
observe all the phases of mitosis. This might have been the case that when mitosis was observed,
most of the cells were in the stage of interphase and therefore most of other phases of mitosis were
not observed due to time limitations.
Although, the experiment did not accomplish the aim of the practical, it has given out one positive
outcome in terms of gaining practical skills and using light microscope.
Bibliography:
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Albert, B. (2008). Molecular biology of the cell. 5th ed. New York: Garland science, p.1072
Bailey, R. (2014). Stages of Mitosis. [online] About education. Available at:
http://biology.about.com/od/mitosis/ss/mitosisstep_5.htm [Accessed 8 Dec. 2014].
Dartmouth.edu, (2014). The Cell. [online] Available at:
https://www.dartmouth.edu/~cbbc/courses/bio4/bio4-1997/02-theCell.html [Accessed 11 Dec.
2014].
Google.co.uk, (2014). interphase - Google Search. [online] Available at:
https://www.google.co.uk/search?
Mcb.berkeley.edu, (2014). Untitled Document. [online] Available at:
http://mcb.berkeley.edu/labs/koshland/Protocols/MICROTUBULE/microtubstain.html
[Accessed 10 Dec. 2014]