My Results
Class results
Possible anomalies could be Dan’s telophase results, compared to the rest of the class, including my results, this number seems to be little too low. It is possible that this has occurred from misidentifying what phase the cell is going through, it can be rather difficult, sometimes, to tell whether the cell is in the late stage of slitting up, or is 2 cells. Although, the number of prophase cells seem to be quite normal. It is possible that the slide was not clear, but as it was provided by the school, I highly doubt that it would be an error from that area, as expect that the slides are checked before the assessed practical begins. Or there could have just been less cells undergoing telophase
In metaphase, 7 seems to be quite a low number, but seeing as how 3 people have the same result, it cannot really be considered as an anomaly. It is possible for 3 people to have unusual results though, and maybe these 3 people had the same problem. This could have occurred from another misidentification of nuclear division stage. Or there could have just been less cells undergoing metaphase.
Rachel’s, prophase result seems a little low, but as it isn’t that much more different than Julia’s, I am not convinced that this is an anomaly
Table of averages
There are no blindingly obvious anomalies, so I will not exclude anybodies results from my table of averages.
All of my averages have been rounded to 1 decimal place
Null hypothesis
i counted 50 cells, in theory there should be around 12 cells in each phase. Thus my null hypothesis being 1:1:1:1 or 12.5:12.5:12.5:12.5.
the equation used to calculate the nul hypothesis is Σ (O-E) ² / E
X²= 5.36
There are 4 classes: prophase, metaphase, anaphase and telophase
4 – 1 = 3 degrees of freedom
For biology, scientists use the 0.05; this is because they are 95% certain that the results are correct every time and that and 5% certain that the results are due to chance alone
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If X² is greater in value than 7.82 then this means it is rejected by the null hypothesis.
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If X² is lower in value than 7.82 then this means it is accepted by the null hypothesis.
My result for x² is lower than 7.82, therefore my null hypothesis is accepted. My null hypothesis is correct. I do not have to change my null hypothesis
Evaluation
As there was a lot of equipment used, and a lot of people were doing the experiment in the same room at the same time, there was a possibility that something could go wrong along the way.
In my practical, nothing really went wrong for me apart from one thing. I made 2 slides, my first slide, wasn’t too good, there were air bubbles and small clumps of the root that hadn’t been mashed up enough. Whereas my second slide was almost perfect, there were no bubbles, and my tissue was perfectly separated into one single layer of cells.
I made sure that I didn’t count the same cell twice by counting in a row, I also used the microscope view finder to help me. On the viewfinder, there is a line, with a sharp point, I moved the slide so that the point was directly on the cell I was counting, this way I knew where I was up to at all times.
Evaluation
Analysis of my results indicates that the stages of nuclear division don’t necessarily last the same length of time, but maybe a similar length of time. By analysing mine and the classes’ results, I can gather that prophase seems to take the longest amount of time; I have come to this conclusion because it would appear that most of the cells in most people’s slides are undergoing prophase. My chi squared results indicate that the amount of cells in each phase aren’t too anomalous, so the amount of time in each phase is indicated as similar, but not completely the same. Prophase is the stage where the cell undergoes a lot of preparation/ processes, far more than for other stages. This would explain why prophase would take longest, and logically my results appear to be correct.
My results could be made more accurate simply by repeating the experiment again. And to make it even more accurate than that, repeat it a few times. Work out the averages. This consumes a lot of time. And the way we did the experiment wasn’t too inaccurate to begin with
Another way to increase the reliability of my results is to work in a more controlled environment. A class lab full of people isn’t exactly ideal. There wasn’t too many distractions but there is more potential for things to go wrong in a room full of people than on my own.
Using completely unused equipment would also increase the reliability of this experiment. The equipment we used was rather old. Although still in good working condition, every time the equipment is used, it becomes slightly less effective.
Prophase
There is a lot going on in this phase, which is why it is understandable that this phase could take longest
“Which condenses into a highly ordered structure called a ” (¹)
“Chromatin condensation, is mediated by the complex. Since the genetic material has been duplicated, there are two identical copies of each chromosome in the cell.” (¹)
Chromosomes are made up of 2 sister chromatids, held together by a centromere. Centromeres are a DNA element, and are present on every chromosome.
“• Chromosomes become more coiled and can be viewed under a light microscope.
• Each duplicated chromosome is seen as a pair of sister chromatids joined by the duplicated but unseparated centromere.
• The nucleolus disappears during prophase.
• In the cytoplasm, the mitotic spindle, consisting of microtubules and other proteins, forms between the two pairs of centrioles as they migrate to opposite poles of the cell.
• The nuclear envelope disappears at the end of prophase. This signals the beginning of the substage called prometaphase.”(²)
Metaphase
Less is going on in this phase, and therefore should be shorter than prophase
This phase is where, in general, the chromasomes line in in the equastor of the cell (in between the 2 centrioles) and spindle fibres begin to form from the centrioles
“• The centrioles are at opposite poles of the cell.
• The pairs of homologous chromosomes (the bivalents), now as tightly coiled and condensed as they will be in meiosis, become arranged on a plane equidistant from the poles called the metaphase plate.
• Spindle fibres from one pole of the cell attach to one chromosome of each pair (seen as sister chromatids), and spindle fibres from the opposite pole attach to the homologous chromosome (again, seen as sister chromatids).”(³)
Anaphase
Where the chromosomes are split at the centromeres and each chromatid is pulled apart, to the centrioles, by the spindle fibres
“Metaphase sets the stage for chromosome separation in the next stage of mitosis: anaphase. Almost immediately after the metaphase chromosomes are aligned at the metaphase plate, the two halves of each chromosome are pulled apart by the spindle apparatus and migrate to the opposite spindle poles. The kinetochore microtubules shorten as the chromosomes are pulled toward the poles, while the polar microtubules elongate to assist in the separation. The photomicrograph above illustrates the early stage of anaphase where the chromosomes are just becoming completely separated. The microtubules are clearly visible in this complex” (4)
Telophase
This is where the nucleolus reforms and nuclear envelope also reforms around the chromatids. Spindle fibres brake away and disappear. The plasma membrane splits between the 2 nucleuses
“-Chromosomes begin to decondense
-Nucleolus and nuclear envelope form
-Spindle begins to dissociate
-Cleavage furrow forms leading to cytokinesis (splitting)” (5)
Bibliography
(¹) = wikipedia (keyword = prophase) paragraph 1 and 2
(²)=http://www.phschool.com/science/biology_place/biocoach/mitosisisg/prophase.html (fist few bullet points after 1st diagram)
(³)=http://www.phschool.com/science/biology_place/biocoach/meiosis/metai.html (first few bullet points)
(4)= http://micro.magnet.fsu.edu/micro/gallery/mitosis/earlyanaphase.html
(5)=
(6)=Cambridge, advanced sciences, Biology1, page 84