Mitosis Onion Root Tip Lab

Analysis Questions:

  1. Explain how mitosis leads to two daughter cells, each of which is diploid and genetically identical to the original cell. What activities are going on in the cell during interphase? During interphase, the cell is undergoing the normal cell processes. For example, if the cell is a muscle cell, the cell is functioning as a muscle cell is intended to function. However, also during interphase, a cell is preparing for future division. This preparation includes duplication cellular structures, such as the genetic material (chromosomes) and the centrosomes. After duplication, each cell contains twice the necessary number of chromosomes, and is therefore able to create two identical daughter cells after cell division. Each daughter cell then has an equal number of chromosomes.
  2. How does mitosis differ in plant and animal cells? How does plant mitosis accommodate a rigid, inflexible cell wall? Mitosis is essentially the same in animal cells and plant cells, with a few important differences. While both plant and animal cells contain a centrosome, plant cells lack the centrioles that are found within the centrosome in animal cells. In addition, plant cells have cell walls, and animal cells do not. This makes plant cells incapable of cleaving the plasma membrane at cytokinesis. Instead, a cell plate forms across the center of the cell where the chromosomes were once aligned, and forms the cell wall between the two daughter cells.
  3. What is the role of the centrosome (the area surrounding the centrioles)? Is it necessary for mitosis? The centrosome is the formation center for the microtubules, or spindle fibers. These spindle fibers attach to the chromosomes, and after the chromosomes align in the middle of the cell, the spindle fibers pull the chromosomes apart during anaphase. Without the centrosome, microtubules would not be formed, and the chromosomes would not be pulled apart. This would mean that the cell could not separate the duplicated DNA, and two daughter cells could not be formed.AP Biology Test Study Help

Data:

Screen Shot 2013-11-08 at 9.26.02 AM

Questions:

  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? If the observations had been taken at a section of the onion root that was higher up than the tip, the cells would not have been actively dividing. This would likely result in a much higher number and percentage of cells spent in interphase, and very few cells in the other phases of mitosis. If the observations had been taken lower on the onion root, on the root cap, the observed cells would be dead or not undergoing mitosis, and so the cells would primarily, if not entirely, be in interphase.
  2. Based on the data, what can you infer about the relative length of time an onion root tip cell spends in each stage of cell division? Interphase is the phase in which cells in the onion root tip spend the majority (91.8%) of the time. Of the phases in  cell division, prophase is the longest, consuming 6.4% of the total cell cycle time. Cells spend the next most amount of time (0.8%) in metaphase, then telophase (0.6%), then anaphase (0.4%). Cells spend a significantly longer period of time in prophase than in the other three cell division phases.
  3. Draw and label a pie chart of the onion root tip cell cycle using the data.

Mitosis Lab Graph

 

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