The purpose of this lab was to calculate the amount of time that was spent by a cell in each of the phases of mitosis. Also, it is used to be able to compare the process of mitosis between plant and animal cells. Background: •Mitosis: This is the process by which a cell duplicates the chromosomes in its cell nucleus in order to generate two identical daughter nuclei. •Interphase: This particular stage is divided into three phases, G1 (first gap), S (synthesis), and G2 (second gap).
During all three phases, the cell grows by producing proteins and other organelles within the cytoplasm.
However, chromosomes are replicated only during the S phase. In all, a cell grows (G1), continues to grow as it duplicates its chromosomes (S), grows more and prepares for mitosis (G2), and divides (M).
•Prophase: By this point, all the genetic information in the nucleus of the cell is in a loose coil called a chromatin. At the start of prophase, chromatin condenses together into a highly ordered structure called a chromosome. •Metaphase: At this stage, the centromeres of the chromosomes align evenly along the metaphase plate in which they prepare to separate.
This even alignment is due to the counterbalance of the pulling powers generated by the opposing kinetochores; kind of like tug-of-war between humans •Anaphase: Two events occur during this vital stage in mitosis. First, the proteins that bind sister chromatids together are cleaved, allowing them to separate. These sister chromatids turned sister chromosomes are pulled apart by shortening kinetochore microtubules and toward the centrosomes to which they are attached. Next, the nonkinetochore microtubules elongate, pushing the centrosomes apart to opposite ends of the cell. Telophase: In this final stage of Mitosis, the sister chromosomes attach at opposite ends of the cell. A new nuclear envelope, using fragments of the parent cell’s nuclear membrane, forms around each set of separated sister chromosomes. Both sets of chromosomes (which are now surrounded by new nuclei) unfold back into chromatin. Mitosis is complete, but cell division is not yet complete. •Cytokinesis: This is the very last process in the mitotic cycle. It occurs at the very end of telophase because that’s when the actual cell division occurs (pinching in).
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... mitosis the pairs of chromosomes condense and attach to fibers that pull the sister chromatids to opposite sides of the cell. ... periods: interphase—during which the cell grows, accumulating nutrients needed for mitosis preparing it for cell division and duplicating its DNA ... CDKs are constitutively expressed in cells whereas cyclins are synthesised at specific stages of the cell cycle, in response to ...
In animal cells, the formation of the cleavage furrow is what causes them to divide. In plant cells, the cell plate is formed in order to create the final division. Hypothesis: If both plant and animal cells spend more time in interphase, then the amount of time that each cell will spend in the remaining stages of mitosis will decrease. Procedure: Before the actual counting could begin, it was necessary to fully understand what each stage looked like under the microscope. In the first part of the lab, the groups observed prepared slides of plant cells and the whitefish blastula.
In order to get a clear understanding of the cell, it was essential to focus it on the center region of the slide because that’s where the majority of the cells were. Like always, one must first focus in on low power and then move on up to high power as the field of vision gets closer to a reasonable viewing point. Once a cluster of cells was located on the microscope, the next step in the lab was to draw what a cell would look like in the various stages of mitosis. Once this part of the lab was complete, it was then time to move on to the counting procedure.
This was a very tedious process because it was difficult to keep track of which cell was already accounted for on the data sheet. Basically, once a general vicinity was focused in on the microscope, the tallying would commence. Once a person saw a cell in x (x meaning interphase, prophase, metaphase, anaphase, or telophase), then they would simply put a tally on the data sheet in the appropriate section. In order to get a fair trial in regards to the number of cells in each stage, it was estimated that each group should count about 200-300 cells for each type (plant and animal).
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Data: Attached is the tally sheet for the procedure of counting Analysis: Questions from lab manual: 1. ) If your observations had not been restricted to the area of the root tip that is actively dividing, how would your results have been different? In the onion root tip, regions other than the apical (or at top of) meristem contain cells that are not actively dividing. These cells are in interphase. In this case, they would represent the majority because cells spend most of their time in interphase anyway.
They are elongating, differentiating, and performing their functions for the organism. Mitotic stages would not have been found in these areas. 2. ) Based on the data table, what can you infer about the relative length of time an onion root tip cell spends in each stage of cell division? According to the data table, prophase is the longest stage of mitosis. Even though there were more tallies in the interphase section, interphase is not considered a stage of the mitotic cycle; it is more or less considered a stage in the cell cycle.
Telophase is the shortest stage because there were very few cells that showed evidence of them actually being in this stage. Metaphase and anaphase are intermediate stages, with metaphase being longer than anaphase. 3. ) Graphs are attached with key on back Controls- The control in this experiment was very important because if it was not contained, then the data would have been faulty. It was very difficult to keep track and count which cells were doing what under the microscope. For that reason, it was imperative to keep the same person counting during the whole experiment.
Everybody is different, so if there would have been numerous people counting, then there would have been different numbers to each of the stages. In order to help the person that was counting, another person could have stood next to them and tallied on the data sheet. This would have prevented the person from counting to have been constantly taking their eyes away from the microscope Constants- One of the unique facts about this experiment was that all the cells were killed at the same time.
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It was not as if one section of the organism was killed first, and then followed by the remaining. It was necessary to do this because it would provide a still picture of all the cells within the organism and which stage of mitosis they were in. Conclusion: In conclusion, the hypothesis that was made early on in the experiment was proven to be correct. The reason why it was correct was because the more time each cell spent in interphase, the less time it would spend in the other phases of mitosis.
According to the data sheet, the plant cell proved to be more efficient because there were hardly any cells in prophase, metaphase, anaphase, or telophase. There were roughly 254 cells that were counted in interphase and the rest barely average over twenty. It was inferred that the hypothesis was correct because of the data from the whitefish cells. In that case, there were roughly 104 cells in interphase and the rest of the stages averaged about 25 cells per stage. If there would have been more whitefish cells to count from, then maybe the data would have closely resembled the results of the plant.
