Membrane Permeability and How Cell Division Takes Place - Lab Report Example

BHS006-1 Cell Chemistry and Genetics Practical Report Practical 1: Practical 1. Membrane Permeability Aims The main aim of this experiment was to provide qualitative information on the Membrane permeability and integrity of onion cells after being subjected to isotonic solutions of a series of alcohols. The main objective was to determine the relative rates of penetration of these alcohols into the onion cell membrane. Introduction This experiment was based model experiments carried out by Overton (1899). A plant cell positioned in a hypertonic solution loses it cell sap and its turgor pressure. This makes the plant cell flaccid and a plant usually wilts. The onion cells were exposed to an isotonic solution of sucrose so that the effect of alcohol alone can be followed to determine their rates of penetration into the cells. When alcohols penetrate the cell rapidly, they immediately create equal concentrations inside and outside the cell with almost no effect seen on the cell. If the alcohol slowly penetrates the cell membrane, there is a high concentration of the alcohol on the outside than on the inside of the cell. This causes the cell to lose water by osmosis and the plasmolysis take place. After a while, the alcohol continues to penetrate the cell making the inside of the cell more concentrated than the outside. Water re-enters the cell by osmosis and deplasmolysis occurs. The time taken from the initial exposure to the alcohol solution until deplasmolysis begins is a measure of the time required for alcohol penetration and is used to measure the rate of penetration of the alcohols. Methodology The peeling method was used to prepare the sample in order to obtain the single layer of cells. A small piece of onion of about (1 cm by 1 cm) was obtained with a thickness of 2mm. with the red side facing up; the onion was cut between half way through beneath the red layer. This produced about 1 mm of onion between knife and the red layer. The onion was pressed firmly and carefully against the knife with the thumb. The red part of the onion was peeled away to make the red layer thin. The thick part of the onion was cut away and discarded. The remaining cells were observed under a microscope with specific consideration of the cells filled only with the red pigment. To investigate plasmolysis and deplasmolysis, two small strips of red onions were placed on the microscope slide and excess water drained. Two drops of distilled water were then added on one of the onion strips. A cover slip was placed on top of it. On the second strip of cells, two drops of 0.6M sucrose was added. A fully labeled diagram of the preparation was drawn and careful observation of the sample under a light microscope.The examination of the samples under a microscope continued for 5 minutes and plasmolysis observed. A fully labeled diagram was also drawn. The same was repeated for effects of different concentrations of sucrose. The occurrence and the extent of plasmolysis was noted and fully labeled diagrams drawn. To observe deplasmolysis, the coverslip was carefully removed from a preparation that had earlier been observed for plasmolysis and two drops of distilled water added. It was observed for approximately one minute and a new cover slip added. It was examined under a microscope for 5 minutes and the results noted. Fully labeled diagrams were also drawn. A table of results was drawn to show the sucrose concentration that was added and the extent of plasmolysis. The measurement for relative rates of penetration of alcohols was done on the well prepared. The following alcohols were tested: Methanol, 1-Propanol and Glycerol. The concentration for each of the alcohols was 4M and placed in a sucrose solution that was almost isotonic. The alcohol+ sucrose were tested one at a time on the onion strips. The time of movement of the plasma membrane and the cell contents to cell wall was recorded. This marked the start of deplasmolysis. A table of results indicating the alcohol added, the extent of plasmolysis and the amount of time in seconds that elapsed before deplasmolysis was drawn. Results and Discussion In this study, chemical and histological techniques were used to obtain information on the permeability of the onion cells. The osmosis is the movement of water from a solution with many water molecules to a solution with low water molecules through a semi permeable membrane. When the cells are placed in a sucrose solution, water starts to move from the cell to the surrounding solution. The cell loses its turgidity and becomes flaccid in the process known as plasmolysis. The Diagram below shows different stages of plasmolysis when the onion cell is placed in a hypertonic solution of sucrose. When two drops of distilled water are added to the flaccid cells, this means that the solution surrounding the cell is less concentrated than the one inside the cell. Therefore, by the process of osmosis, the water moves inside the cell causing the cell to be more rigid and turgid and getting it own shape back. The time between plasmolysis and deplasmolysis was observed to be 5 minutes. The movement of substances from the outside the cell into the cell is directly proportional to their size. The rate of penetration of alcohols across the plasma membrane of the onion cells depends on the number of carbon atoms present in the alcohol. Methanol penetrates the cell membrane faster, followed by propanol and glycerol respectively. This is shown by the results observed for the methanol cell to start deplasmolysis and glycerol penetrates the cell at a very slow rate. The following table shows the arête of penetration of a series of alcohols across the membrane of onion cells. Alcohol Time (Seconds) Methanol (CH3OH) 120 Propanol (CH7OH) 240 Glycerol (CH5(OH)3) 300 Practical 2. Cell Division/Chromosome Structure Aims The main aim of this practical was to examine how cell division takes place and also to determine the structure of the chromosomes during cell division. Introduction The onion root tip contains one of the plant meristemic regions. These are regions where the cells divide to produce more cells so that the plant can grow. They are therefore regions in which we can view mitosis taking place – the process of normal cell division. Root tips are three dimensional and individual cells cannot be seen under the microscope in the intact tip. It is hence important to divide the cells into a thin layer. Plant cells are glued together by the middle lamella (the area between the cells), which is made from calcium pectate. Hydrochloric acid will dissolve this, but leave the cellulose cell walls intact. The hydrochloric acid acts to kill cells and fix the cell contents in position. For the nuclei of the cell to be seen, the cells were stained with Toluidine Blue. Methodology Two halves of a petri dish were used for treating and washing the root tips. A few millimeters of root tip were carefully cut using a scalpel. The tips were then placed on the petri dish and a small amount of HCL added. The roots were left for 5-10 minutes to dissolve the calcium pectate and to fix the cell wall. The forceps were used to transfer the tips from the dish having the concentrated acid into another dish. The tips were washed in distilled water. One of the washed tips was then placed on a slide and dried using a tissue. A drop of Toluidine Blue stain was placed on the tip and incubated for 2-3 minutes. The tip was then covered with a cover slip and carefully pressed down on the cover slip crush the tip. This was to make sure that the stain has washed all over the crushed tip to ensure that it is fully stained. Excess stain was removed using a tissue. The tips were then viewed under a microscope using the smallest 4x first to focus the image and then increased to either 10x or 40xobjective lens to view the cells. Results and Discussion Cell growth occurs when a cell undergoes a phase called interphase and then mitosis in the cell cycle. As cells mature, they lose their capacity to divide and they rarely divide. Other cells divide rapidly. A perfect example is the root tips of onion cells. As they grow, the cells at the root tip in the meristem divide continuously to make sure the root tip goes through the soil. The root cap then detects the force of gravity and guides the growth of cells at the rot tip. In this experiment, the properties of the environment surrounding the cell were changed to make the conditions necessary for cell division. The cellulose walls are usually held together by compounds in the middle of the lamella. The root tips were treated with concentrated hydrochloric acid to break these cellulose walls down. This is helpful in the preparation because the process of cell division does not occur on cells have cell walls. Therefore, it is important to break the walls down to ensure that the process of cell division takes place well. To view the chromosomes in the nucleus, the cells were treated with the toluidine Blue stain which is taken up by the nucleus in order for the chromosome structures to be easily studied. The mitotic index of the root tip was determined. From the results shown in the table below, Interphase Prophase Metaphase Anaphase Telophase 0 2 2 1 2 Mitotic Index = number of cells in other stages other than interphase / total number of cells = 7/45 = 0.15555 For cells that seldom complete the cell cycle, a high proportion of cells was expected to be ion the G1 phase (resting stage) of the cell cycle (Darbelley, Driss-Ecole, & Perbal, 1989). As expected, the root tip has rapidly dividing cells and therefore, there were many cells observed in the mitosis stage. Cells in the root tip are used for protecting the root and they are continuously replaced because they usually tear away. The apical meristem has numerous dividing cells. The cells in the root tip often go through the cell cycle and complete it more time than those found in other parts of the root. Part 2: Karyotyping Human Chromosomes This study involved the simulation of human karyotyping making the use of digital images of chromosomes from real human genetic cells. The Chromosomes were arranged into a complete karotype and the findings interpreted. Human karyotyping is a commonly used technique that can help diagnose a number of genetic abnormalities that cause disease. This part of the assessment made use of an online teaching resource, The Biology Project, an interactive online resource for learning biology developed at the University of Arizona. The notation used to characterize Patient A’s karyotype is 47, XX, + 21. The diagnosis that Patient A would be given is Down’s syndrome. Patient B’s karyotype would be characterized using the notation 47, XXY and the diagnosis would be Klinefelter's Syndrome. Patient C’s karyotype would be characterized using the notation 47, XY, +13 and the diagnosis he would be given is Trisomy 13 Syndrome. The frequency of occurrence of Down’s syndrome is said to be 1 per 740 births per year. It is also known to be common in fetuses of older parents than when compared to those of younger parents (McClure, et al, 1969). The Klinefelter's Syndrome is known to occur in about 1 per 850 male births per year. Lastly, the frequency of occurrence of the Trisomy 13 Syndrome is approximately 1 per 2500 live female births per year. Trisomy 13 Syndrome occurs when there is an extra no.13 chromosome. The presence of the 13 more chromosomes leads to many physical and mental abnormalities like heart defects (Beers, et al, 2004). References Darbelley, N., D. Driss-Ecole, and G. Perbal (1989), Elongation and cell division in cortical cells in root tips grown in microgravity. Plant Physiological Biochemistry 27:341-347 Belden, K.H., McClure, H.M., and W.A. Jackson (1969),"Autosomal trisomy in a chimpanzee: resemblance to Down's syndrome". Science 165 (897): 1010–12 Beers, M. H., and Robert, B., (editors), (2004). "Congenital Anomalies." Section 19, Chapter 261. In The Merck Manual of Diagnosis and Therapy. Whitehouse Station, NJ: Merck Research Laboratories. EXAMPLE PICTURES YOUR DIAGRAMS Stage = Interphase Stage = Prophase Stage = Metaphase Stage = Anaphase Stage = Telophase Read More