MITOSISMEIOSIS Lab Report Example | Topics and Well Written Essays - 1000 words

MITOSISMEIOSIS - Lab Report Example This is followed by separation of daughter cells. Meiosis is the type of cell division by which germ cells (eggs and sperm) are produced. Meiosis was first observed by the Belgian cytologist Pierre-Joseph van Beneden in 1887. Meiosis involves a reduction in the amount of genetic material. It comprises two successive nuclear divisions with only one round of DNA replication. One parent cell, at the end of one meiotic division, produces four daughter cells. Daughter cells have half the number of chromosomes found in the original parent cell and with crossing over, are genetically different. Meiosis differs from mitosis primarily because there are two cell divisions in meiosis, resulting in cells with a haploid number of chromosomes. Cell division is especially rapid in the growing root tips of sprouting seeds. The chromosomes in dividing root tip cells can be demonstrated if, after sprouting seeds or bulbs,and harvesting the young root tips, and then fix, acid digest, stain, squash, and view them under a microscope. The root tip is the place of intense mitotic activity. This region is three dimensional and individual cells cannot be seen. It is therefore necessary to separate the cells out into a thin layer. Plant cells are glued together by the middle lamella of calcium pectate. Hydrochloric acid will dissolve this calcium pectate but leave the cellulose cell wall unaffected. In addition the acid kills and fixes the cell contents in position. Acetic orcein stains nuclei and not the cytoplasm. 1. The apical 5mm from the tip of a growing lateral root of a broad bean was carefully cut. 2. The root tip was placed in a watch glass containing acetic orcein stain and 1mol dm-3 hydrochloric acid in the approximate proportions 10 parts stain to 1 part acid. 3. Allowed to warm for five minutes by passing repeatedly through a low Bunsen flame. 4. The fixed root tip was placed on a microscope slide and two drops of acetic orcein were added. 5. The root tip was broken up without destroying the arrangement of the cells, and the root tip was spread out as thinly as possible. 6. A cover slip was placed over the root tip, and covered it with blotting paper and squashed gently by pushing down on the cover slip. 7. The slide was warmed gently to intensify the stain, by quickly passing through a low Bunsen burner flame a few times. 8. The slide was examined for identifying any stage of mitosis. Results Mitosis The four phases of mitosis- Prophase, Metaphase, Anaphase and Telophase- were observed under the microscope. The different phases were identified based on the unique chromatin organization features: 1. Interphase: Each chromosome undergoes replication, making an identical copy of itself. At this point, the chromosomes are still long and thin, and are not visible inside the nucleus. Cells spend most of their life in this non-reproductive phase. 2. Prophase: The chromosomes coil and shorten, and become visible. It becomes apparent that the chromosomes have duplicated. Pairs of identical chromosomes remain