Title: Observing the Stages of Mitosis Lab
Purpose: Observe roots tips to determine how long cells spend in each phase of the cell cycle.
Introduction: Mitosis is a type of cell division that goes through the stages of the cell cycle: prophase, metaphase, anaphase, and telophase, in result of two identical daughter cells. The daughter cells produced in Mitosis have the same number and type of chromosomes as their parent cell. Interphase, which occurs in the cell cycle, is when the cell is doing its job and the DNA is replicating. Chromatin is not yet condensed into chromosomes during interphase, chromosomes are also not yet distinctly visible. During prophase, the cell membrane starts to break down and the chromosomes condense, but are not organized. In metaphase, the chromosomes line up along the cell’s equator while the spindle fibers continue to grow. Then in Anaphase, the chromatids are being pulled apart by the spindle fibers and are found on opposite sides of the cell. Finally, the nuclear membrane starts to divide and form around each set of chromosomes. The cell splits and the two daughter cells are formed at the end of Telophase, Cytokinesis. Plants grow at their roots; the root cells are constantly dividing in order to grow. A root tip was chosen to be observed because it contains cells at different stages of the cell cycle, since each cell divides independently from other cells.
- Prepared slides of onion root tip
- Set up microscope. Start with low power objective in position with diaphragm open to the widest setting
- Place side of onion root tip on microscope and focus the microscope to get a clear view of the onion root tip. Focus starting with lowest power objective, then move to higher objectives once focused.
- Observe box-like cells arranged in rows.
- Identify what stage of mitosis each cell is in by appearance. Count how many cells are in Telophase, Anaphase, Metaphase, Prophase, then Interphase.
- Convert into percentages (Total # Cells/# Cells n Stage). Record Data
Analysis: I included Quinlyn’s Data to show how my data differed and should be excluded from the total class average. The data I collected only included data from 1 cross section, whereas other students collected data from 2 or 3 cross sections, making the percentages differ. 2 to 3 cross sections samples provide more accurate data than data from only 1 cross section because more data allows for margin of error. From the class average data, 81% of cells were found in interphase, 12.46% in prophase, 1.65% in in metaphase, 1.37% in anaphase, and 2.03% in telophase. Conclusion:
Conclusion: Most of the cells were found in interphase, which is logical because that is when the cell is doing its specified job. Prophase has the second highest amount of cells in that stage because the cell is condensing long strands of chromatin into small coiled chromosomes, forming the mitotic spindle, and breaking down the nuclear envelope. The stages of Metaphase, Anaphase, and Telophase are completed very quickly so the cell can finally split and continue to be productive and do its job. Within the class data, some errors could have occurred from human error (miscounting the amount of cells) or having cross sections where the chromosomes were cut off and could not provide enough information. For my data particularly, the percentages of 1 cross section differs from the percentage of 3 cross section averages. I had to disclude the observations found from the first cross section I examined because the slide was unclear and the nuclear envelope and chromosomes were not visible. It is unnecessary to include data from unclear onion root tip sample slides because they would not provide enough usable information. Each root tip sample is a cross section, so it is possible that the chromosomes could have been cut and only found in the other cross section half.
Evidence that supports that mitosis is a continuous process rather than a series of events is that each cell is hard to differentiate between each stage because it is constantly changing. The onion cell had 4x chromosomes at the end of interphase because DNA is doubled and is preparing to split later on. At the end of telophase, there are two cells, each with 2x chromosomes.
After meiosis, there would be 1x chromosome in each sex cell because the cells start with 4x, then divides twice throughout the process (4 sex cells with 1x chromosomes). If this onion would complete the process of sexual reproduction, 2x chromosomes would be found in the zygotes that are produced, because of a sperm(1x) and an egg(1x) create a zygote.