Title: Time Spent in Stages of the Cell Cycle
Purpose: To observe how much time cells spend in each stage of the cell cycle (interphase, Mitosis).
In growing plant roots, the cells at the tip/bottom of the root are always dividing, which allows the root to grow longer. There is a root cap at the very end of the root which is made of dead cells that serve to protect the growing root. Because cells divide independently from other cells, a root tip contains cells at all different stages of the cell life cycle. This makes root tips excellent tissue to study the stages of cell life and cell division in.
When a cell is in interphase, it has not yet begun mitosis and is still performing its normal functions. During this stage, the cell is round and one can clearly see the nucleus/nucleoli. The cell then begins mitosis. During prophase, the nucleolus disappears and chromatin fibers become more tightly coiled. During metaphase, the chromosomes line up at the center of the cell. The next stage is anaphase, during which the sister chromatids separate and are pulled to opposite ends/poles of the cells by spindle fibers and become their own individual chromosomes. Lastly, telophase is where two daughter nuclei form and the cytoplasm splits. This is what cells look like in each stage of the cell cycle:
– Prepared slides of onion root tips
- Get microscope, bring to the lab table. Make sure that low power objective is in position and that the diaphragm is open to the widest setting.
- Get onion root tip slide. Look at the root tips (the pointed ends of the root section), this is where the cells will be actively dividing.
- Place slide on microscope stage with root tips facing away from you. Use the low-power objective to find a root tip, focus with coarse adjust until clearly visible. Just above the root cap is a region with many new small cells, you will be observing these cells. Center the image then switch to higher power magnification and focus the image again.
- When counting, ignore the cells that seem to be empty — these were sliced in a way where they appear to have no genetic material and therefore it can not be determined which stage of the cell cycle they are in.
- Looking at the rows of cells, identify which stage each cell is in…
- Use data table to record number of cells that you see in each stage. Do this by going along each row and looking for and counting cells in telophase and recording that number. Then count number of cells in anaphase. Move on to metaphase, and then prophase. Make sure to record the numbers. Next, count the total number of cells that are in your window of view by counting how many rows and how many columns then multiplying those two numbers. Because there is going to be the most amount of cells in interphase, determine how many there are in this phase by subtracting the added number of cells in prophase, metaphase, anaphase, and telophase from the total number of cells: # of cells in interphase = total # of cells – (# of cells in prophase + # of cells in metaphase + # of cells in anaphase + # of cells in telophase). Record all data in chart.
This data shows how many cells were found in each stage of the cell cycle and what percentage of the cells were in each stage.
Analysis & Conclusions:
- The majority of cells were in interphase.
- Percentage of cells in each stage:
- Mitosis is a continuous process, not a series of separate events. This is known because the stages flow from one to the other and it is sometimes hard to tell apart or differentiate these stages because they are all part of a process. Telophase (and cytokinesis) finalize the two daughter cells, which in turn start the cell cycle all over again — it is all a cycle.
- The onion plant began as a single cell which had X number of chromosomes. Each cell that was observed in this experiment had 4X cells. This is because by the end of interphase, the cells have to have 4X (two copies fo 2X) in order to split into daughter cells with 2X chromosomes in each.
- If this onion were to reproduce sexually, after meiosis each sex cell would have X number of chromosomes.
- If this onion were to complete the process of sexual reproduction, 2X number of chromosomes would be in the zygotes that are produced.
The results show that the majority of cells observed were in the interphase stage of the cell cycle. This means that cells spend the majority of their time in interphase. Looking at the data, it can be concluded that the higher percentage of cells that were in a certain stage means that cells, in general, spend more time in that stage. The data shows that cells spend most of their time in interphase, then prophase, then telophase, metaphase, and anaphase. This order makes logical sense because a cell would want to spend as much time as it can in the phase where it is not duplicating so that it can perform its normal functions — this stage being interphase. Likewise, prophase would take a somewhat longer time because the chromatin has to condense and coil up. Telophase would also take longer time than other phases because the cytoplam has to fully divide and the cells need to become individual. And lastly, metaphase and anaphase would take the least amount of time because the chromosomes just need to line up in the middle of the cell and then are pulled apart.
Errors in this lab may occur for a variety of reasons. The microscopes being used were not able to zoom in a very large amount, so data may be skewed because students were not able to magnify the cells to a size where there was enough detail shown to be absolutely sure about which stage the cell was in. Also, the phases of interphase, prophase, and telophase are difficult to tell apart in most instances. This would lead to miscounting and, in turn, affect the data and results. Additionally, when the cross sections of root tip were being cut, they may have been sliced in a way where the nucleolus was not put in the slide. This could make the cell appear to be in a stage that it is in reality not in, which would affect the data.