Bryan Bishop

Introduction

	Cell theory states that (1) all organisms are composed of one or more cells, (2) cells are the smallest organized living units, and (3) cells arise only from divisions of other cells. This lab and report is focused on #3, and more specifically, the cell cycle, which describes how any cell goes about the process of dividing and the other related important phases. Knowledge of these phases has lead to the development of the concept of the cell cycle, which consists of particular phases that lead to the continuation of those same phases, except executed by other cells (the child-cells). The cell cycle has some mechanisms for controlling how long each phase takes and how the cell continues between the phases.
	
	http://www.bioteach.ubc.ca/CellBiology/TheCellCycle/cellcycle.gif
	
		Although all of the phases in the cell cycle are important, this lab focused on mitosis (the M phase) and the duration of the phases involved. Mitosis is how the cell replicates and further provides supporting evidence to  cell theory.

http://www.bioteach.ubc.ca/CellBiology/TheCellCycle/cellmitosis.gif


Purpose of Lab
		The lab was meant to show the students how to approximate the total number of cells and time needed for each phase of mitosis given a specific specimen. Students approximated the duration of each phase of mitosis based on the number of cells to further any understanding of mitosis and the cell cycle. Knowing how to approximate the number of cells in a certain phase could be important for determining how one should interact with the cell if interaction through cell signaling is available ( http://www.cellsignal.com ). 
		Originally, I predicted that telophase was the longest part of mitosis (prophase, metaphase, anaphase, telophase), and that interphase was the longest part of the cell cycle entirely. I was partially wrong, as I later discovered.
	
Procedures / Materials
		The materials required for the lab were a microscope, colored pencils, a prepared slide of an onion root-tip, and a prepared slide of whitefish cells.
		The directions call for the student to find a group of cells undergoing mitosis on the onion root-tip via the microscope's low powered mode and then the high powered mode. The student was to count and record the number of cells in each phase of the cell cycle. The total number of cells had to also be recorded, which was done by declaring a certain number of cells to be the height, and a certain number to be the length (based on the cells actually seen). Then, the student repeated that process two more times. The student was to total the number of cells counted in each phase and in interphase for the three areas. The student was to add the total number of cells viewed in each phase and interphase together to get the total of all cells counted too.
		After the lab procedures were completed, the student was to determine the time required for each phase based on the collected data. The lab packet claims that the time for a phase is equivelant to the total number of cells in a phase divided by the total number of cells counted all multiplied by 720 minutes. At a first glance, this may seem like a good way to go about estimating the time it takes for each phase to take place, however seems flawed in a few particulars. For example, if this method was accurate, and gave the precise length of time for each phase of mitosis, that would mean that the duration of the phases are dependent on the total number of cells of a particular phase in a 'random' selection. This is not how the duration is decided, and this entire lab seems to be instead a way to go about estimating a generalized view of the duration of the phases of the cell cycle.
		The student was collecting data to bring to mind one method by which one can estimate the time it takes for cells to undergo noticable processes. It is likely that the student was gathering the data to be lead by the lab packet to do the specific calculations, instead of coming up with the student's own way of determining the length of each phase. Perhaps it would be more productive to have a live sample to work off of instead of a static sample as it was. Unfortunately, such resources are not generally available for high school biology students and hence this primitive way of analyzing the given cells was used.
		The microscope was used to examine the cells in whatever phase of the cell cycle they were in. The microscope is a suitable instrument because it sufficiently magnifies the specimens. The slides of the specimens were the only items available for the high school level class. In a lab with more funding it is likely that the student would have had access to a live sample and been able to clock the time it takes for each phase of the cell cycle.
		As it has been mentioned, the student could learn more from data gathered in "real time". A higher power microscope would not lead the way for more data in clocking the duration of each phase of the cell cycle, however a clearer definition as to when one phase starts and when one phase ends, may prove helpful.
		The tools used may have effected the data that was collected. For example, the microscopes or slides could have been dirty, distorting the observable specimen. This could greatly interfere with any cell counting. 
	My hypothesis was that telophase is the longest phase in mitosis and interphase is the longest phase in the cell cycle. My belief of that was because it seemed to me that the cell separation would take the longest time because the warping of the cell membrane and other objects would take more energy, which has to be applied over a finite time, than the other phases. It was later discovered that telophase is not the longest phase, but in fact is about the third longest phase of the cell cycle (when one includes g0, g1, S, and g2 phases in interphase).
	

Data / Commentary
	The data is on the attached lab packet. It is worthy of mentioning that the data was collected on each specimen at only three seemingly random locations. This means that the numbers for the total number of cells in each phase in the specimen are only approximations based off of random evidence, and not exactly meant to represent the entire cell cycle in the normal operation. It is also worthy of notice that only a few specific specimen were observed in this experiment and hence it should not be used as a way to represent all cells, however it is perhaps usable to represent all cells of that specific type if one voids the fact that the data is only usable as a rough approximation.
		Interesting comparisons with data found from the Internet can be made. For example, Wikipedia ( http://en.wikipedia.org/wiki/Interphase ) claims that Interphase is 90% of the cell cycle. My data shows that it is about 75%. Another site ( http://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=mboc4.section.3169 ) claims that the S phase requires about 10 to 12 hours, yet, the M phase (wherein mitosis occurs) requires a mere hour. This suggests that S phase, the DNA replication phase, takes up the majority of interphase and hence the cell cycle. The website also claims that the cell cycle could take about 24 hours for complete turn of the cell cycle where interphase takes about 23 hours, close to 95%. It should be pointed out that the information on the previously mentioned website is not for onion-root tip cells, but instead based on human cells. 

Conclusions / Further Contemplation
		Regardless of the precise duration of each phase of mitosis, there is an importance of the knowledge of duration. When we know how long stages of mitosis last, we can better apply our knowledge of cellular biology to change the progress of the dividing cell. For example, perhaps, when nanotechnology becomes more developed, we will over see that no cell lacks control mechanisms in the cell cycle that generate cancers.
	Interphase may be the longest part of the cell cycle because of an immense ammount of energy required for cell division. It is also possible that the length of interphase has been influenced over the generations such that there is an equillibrium in how much an organism reproduces such that the other populations of species do not go to dangerously low levels and hence hurt the first organism's way of life and going about the cell cycle.
	During this lab, a method of approximating the number of cells viewable under the microscope was developed. One simply takes the count of cells in the horizontal direction, then vertical, and multiplies the counts together to get the total number of cells. Granted, the microscope's view is generally circular, perhaps to allow finer adjustment of the light, however counting in a circular manner is harder and perhaps ineffecient when results will be approximations anyway.
	Different cells probably take different amounts of time per each phase in the cell cycle. It is obvious that there is cell specialization in animal bodies, though this is not the limit to where the phases of the cell cycle vary. A cell that is larger may take more time to divide than a smaller cell, for example. Perhaps this is why a bacteria is able to divide at a much faster rate than cells.
	The importance of time in the processes of mitosis seems limited. The cells seem to change shape and loose their nucleus during cellular division, which could be a threat to security. One can approach the length of the phases from an evolutionary standpoint and ask "why?", to which one can answer that the time for each process is either (1) optimized, (2) the best developed thus far, or (3) appropriate given the environment, enemies, food, ... Option two seems more suitable because cancer cells tend to lack the mechanisms for control of the cell cycle, and hence are an evolutionary step ahead of other cells. (It is important to note that cancer cells generally lead to death, showing that the lack of cellular control mechanisms is not entirely good for the cell's purpose.)
	It has been said in class that the events in mitosis are not exactly linear and many things happen at once. It is clear that there is a distinct outline of events, such as the chromatin must condense before the chromosomes can be separated after metaphase, but there are probably parts within each phase that are not so linear. For this reason, viewing a cell undergoing mitosis would be particularly hard to label when it is switching between one phase to the next. This is a minor problem, although important in the sense that it shows that we do not have a "flag" that is activated to say that one phase has stopped and another has begun. One can argue that the cellular control mechanisms are like these flags, however one can go deeper and ask how those cellular mechanisms are set on and off for the cell to continue going through the phases, leading to the same problem yet again.
	The duration of biological processes are important because it helps us understand how a cell might react at a certain time. This could be important, for example, to cell signaling specialists ( http://www.cellsignal.com ). The cell cycle is a suitable example to study for showing how to go about approximating the time required for cellular (and also chemical) processes to complete because the cell cycle has observable, specific patterns in time duration between the cell types.