You will fix, stain, and make slides of onion root tips. These slides will be studied for the presence of cells in the four stages of mitosis.
At the completion of this laboratory you should be able to
•Stain tissue for the identification of cells in the various stages of mitosis •Identify the stages of mitosis in plant cells
All new cells come from previously existing cells. New cells are formed by the process of cell division which involves both replication of the cell’s nucleus (karyokinesis) and division of the cytoplasm (cytokinesis) to form two genetically identical daughter cells. There are two types of nuclear division: mitosis and meiosis. Mitosis typically results in new somatic (body) cells. Formation of an adult organism from a fertilized egg, asexual reproduction, regeneration,and maintenance or repair of body parts is accomplished through mitotic cell division. Meiosis, on the other hand, results in the formation of either gametes (in animals) or spores (in plants). These cells have half the chromosome number of the parent cell.
To study the stages of mitosis, you need to look for tissues where there are many cells in the process of mitosis. The phases of plant mitosis are:
The nondividing cell is in a stage called interphase. The nucleus may have one or more dark-stained nucleoli and is filled with a fine network of threads, the chromatin. Interphase is essential to cell division because the genetic material (DNA) is duplicated (replicated) during this stage.
The first sign of a division is prophase, in which a thickening of the chromatin threads occurs. Thickening continues until it is evident that the chromatin has condensed into chromosomes. With somewhat higher magnification you may be able to see that each chromosome is composed of two chromatids. As prophase continues, the chromatids continue to shorten and thicken. In late prophase the nuclear envelope and nucleoli are no longer visible, and...