Membrane Permeability and Cell Division - Lab Report Example

Name: Instructor: Course: Date: Genetics practical report: Part 1 Title: Membrane permeability and cell division Aims The aims of the experiment are to test on the property of membrane permeability of the onion cells by looking at the effects of different substances on the cells. The experiment looks at the effect of subjecting the cells to hypertonic solutions of different concentrations and observing plasmolysis of the cells brought about by the substances. It also looks at the process of deplasmolysis and the time taken, where the plasmolysed cells are put into distilled water. Introduction In all living organisms, there is a basic fictional unit. This is the cell. Within a cell there are cell organelles and the nucleus which are surrounded by a membrane. This membrane is the cell membrane. The membrane functions in separating the external environment from the interior of the cell. The membrane is made up of a phospholipids layer within which proteins are embedded.1 Among the many properties of cell membrane, it is selectively permeable to what enters or leaves the cell. This way, it controls the movement of molecules and other ions from leaving or entering the cell. Among other function of the cell membrane are its involvement in cell adhesion, and conduction of ions. In plants, and bacteria, it attaches the cell wall and glycocalyx. Membrane permeability of cells thus prevents entry of some substances into the cell and allows others to enter. This permeability depends on the physiological conditions in some cases. There are other factors that also determine the movement of a substance through the semi permeable membrane of the cell. These are the concentration gradient created between the inner cell and the substance passing. This concentration gradient is responsible for the direction of the permeable ion or molecule. It thus dictates if the molecule enters or leaves the cell through the membrane. The property of semi permeability has been given several names such as the differently permeable membrane, partially permeable membrane and selectively permeable. Ions and other molecules pass through it by diffusion, osmosis or facilitated diffusion. Substances pass through this membrane in different rates. The rate at which these ions pass thus depends on the permeability to each particular substance, the pressure, concentration and temperature of the substances or molecules. The size of the solute and its solubility determine the permeability of the membrane. The construct of the membrane also determine the movement rate and the permeability. Substances utilize simple diffusion to get in and out of cells. In diffusion, molecules utilize casual molecular motion to move from highly concentrated region to a lowly concentrated region. All molecules have kinetic energy and collide constantly with each other. The transfer of this energy causes the movement rates of the molecules. When water molecules diffuse into the cell through a semi permeable membrane, the process is osmosis. Just like in diffusion, the movement of the substances depends on the kinetic energy in the inside and outside the cell. Water molecules thus move freely in and out of the membrane depending on the concentration gradient. Water molecules thus move in and out of the cell from a region of high concentration to that of low concentration. In the inside of a cell, there are salts, sugars, and other solutes such as amino acids. When such a cell is surrounded by pure water, the water molecules on the outside get into the cell through osmosis and the cells swell due to increase it its contents. This is because water is more concentrated in the outside and thus moves to the region of low concentration. On the other hand, if the same cell is put in salty water, the water molecules in the cell move from the cell into the salty water because the concentration of water molecules is higher in the cell and lower in the salty water. 2 In plant cells such as the onion cells, plasmolysis occurs when the cell loses water through osmosis and the plasma membrane draws away from the cell wall. Deplasmolysis occurs when the plasmolysed cell draws water molecules by osmosis due to higher osmotic pressure. When plasmolysis and deplsmolysis are keenly observed, the environments of the cell and the rate of passage of molecules is determined. This image shows plasmolysis in onion cells after placing them in high concentration environments where water concentration is low. Osmosis determines the time required for a particular substance to penetrate the cell through the semi permeable membrane. In the case of alcohol penetration to the onion cells, the alcohol is placed in an isotonic solution and then the cells are placed. Penetration of alcohol into the cell is slow than that of water. This means that water may leave the cell rapidly to cause plasmolysis. During the time when alcohol penetrates, the water molecules can again enter the cell and deplamolyse it. This way the time for penetration of alcohol is between the times alcohol was exposed to the cell to deplasmolysis. 3 Method A thin layer of onion cells was obtained by cutting the onion through the red layer. To obtain a single layer the onion was peeled. The red pigmented layer was gotten from the onion and pressed against the knife with a thumb to enable peeling away of the red part of the onion as thin as possible. The cells on the thin layer were observed through the microscope and emphasis lay on the cells with the red pigment. To observe plasmolysis and deplasmolysis, two small strips of onion were places at the both ends of a slide of the microscope having drained excess water and distilled water added to one of the strip. On the second strip, 0.6 M of sucrose was added and the two strips cover slipped. Observations of the preparations were done. Plasmolysis was observed and effects of 0.2M, 0.3M, 0.4M and 0.5M of sucrose was determined the same way on the onion cells gotten. To observe deplasmolysis of the cells, two drops of water were put in the slides with plasmolysed cells and allowed for 5 minutes for changes. The time taken for deplasmolysis to occur was observed fro every cell preparations that had plasmolysed. To observe the rate of penetration of a series of alcohols (methanol, 1-propanol, and glycerol), each at a concentration of 4M was put in an isotonic sucrose solution and each sucrose+ alcohol solutions added at a time to the onion strips. Every time two drops of the solution was added, time was recorded. Observation for the duration and extent of plasmolysis was done while examining the cells under the microscope severity of plasmolysis was recorded as slight, moderate and severe. The samples were observed until deplasmolysis appeared and time recorded. This was done for all of the solutions and results recorded. Results Normal onion cells This is an image of the observed normal onion cells Turgid onion cells This is an image of the turgid onion cells Plasmolysed onion cells This image shows plasmolysed onion cells Table showing different concentrations of sucrose and the extent of plasmolysis Sucrose concentration extent of plasmolysis deplasmolysing time 0.6 M sucrose Slight plasmolysis 3 second 0.2 M sucrose Moderate plasmolysis 5 seconds 0.3 M sucrose Moderate plasmolysis 8seconds 0.4 M sucrose Severe plasmolysis 10 seconds 0.5 M sucrose Severe plasmolysis 12 seconds Table showing the alcohol added to the cells, the extent of plasmolysis and the time before deplasmolysis Type of alcohol Extent of plasmolysis Time before deplasmolysis methanol, severe 12 seconds 1-propanol, Moderate 8 seconds glycerol slight 3 seconds Discussion In the movement of particles in and out of the membrane, the concentration of the solutes matters greatly. In the experiment, the more the concentrated the solutes were, the more they caused plasmolysis of the onion cells. For those solutes with low concentrations, plasmolysis occurred slowly and it was faster for the cells to undergo deplasmolysis when put in water. For the more concentrated solutes, plasmolysis occurred faster and it took the cells more time to undergo deplasmolysis. Cell permeability thus related very well with the experiment as the cells allow some of the molecules to pass selectively and prevent others. The fact that osmosis occurs in cells where the water molecules move by diffusion from more concentrated regions to low concentrated region is proved by the experiment. Sucrose being concentrated and there are less water molecules in it, draws water molecules from the cells thereby causing plasmolysis. When the plasmolysed cells are subjected to water molecules on the outer environment, they pass through the semi permeable membrane into the cells where the concentration is low. Alcohol molecules are more concentrated than the onion cells there by causing plasmolysis of the cells. The three alcohols used cause plasmolysis differently because they are in different concentrations. In conclusion, the cell membrane has permeability that allows passage of molecules in and out depending on the concentration gradient created between the inside of the cell and the outside. Cell chemistry and genetics: Part 2 Practical 2: Cell division/ chromosome structure Aims The aims of the experiment was to observe the major changes in cell division using the tip of the root of an onion plant as well as the structure of the chromosomes in a cell and the major abnormalities associated with the chromosomes using different notations in karyotyping. Introduction Parent cells divide through cell division into daughter cells. These daughter cells may be two or more. Cell division where the parent cell divide into two is the mitosis and the daughter cell formed is capable of further divisions. In meiosis, the cell formed is the gamete capable of dividing only in fertilization. Before the parent cell divide, it replicates its DNA where a new DNA molecule is formed. Cell division ensures that the organism grows and cells are repaired. It does this by ensuring that the original genome of the cell is maintained. During replication, the genome is divided and separated between the cells. Chromosomes are the threadlike structures in the nucleus of the cell where DNA is contained. Around the proteinous histones, DNA is coiled to form the chromosome. These chromosomes cannot be seen through the microscope unless division is taking place. This is because in cell division, the chromosomal DNA is packed tightly to make it visible under the microscope. In the structure of the chromosome is the centromere, which is the constriction at the centre, dividing chromosome into two arms. There is the p arm, which is the shortest, and the q arm that is the longest. The shape of the chromosome thus depends on the position of the centromere.4 Cell division has two complicated phases. The first phase has the interphase and prophase while the second phase has the metaphase, anaphase and the telophase. Interphase is the phase during which the cell rests. During this time, the cell gains the required energy and mass as all building of components continues ready for cell division. In prophase, the cell replicates its DNA so that the new cell will have the genome. In metaphase, the nuclear membrane housing the nucleus and its components disappears and chromosomes align themselves at the centre across the cell. In anaphase, the chromosomes have already aligned themselves at the centre and they divide into sister chromatids. The move away from the centre and the cell begins to split into two to form two cells, which can function independently. In telophase, all necessary components of a cell forms and the cells go back to interphase for the process to repeat. The number of the chromosomes in a cell and their appearance is called karytype. This thus describes an individuals complete set of chromosomes. The physical characteristics of the chromosome are looked at during karyotyping. These characteristics are the length of the chromosomes, centromere position, sex chromosomes differences and the pattern of their banding.5 The root tip of an onion plant is a meristemic part where cell divide rapidly for the growth of the plant. Using these regions, one is able to view mitosis where the cells divide normally. To view the cells properly is important to get thin layers. In plants, the cells are glued together lamella at the middle of the cells. Therefore, it is important to dissolve the calcium pectate that makes the lamella to obtain separate cells. The acid does not have any effects on the cell walls. Other than separating the cells, it kills them as it also glues in position the contents of cells. Toluidine blue stains the cells to allow for proper viewing of the nucleus. Method To examine chromosomes during cell division, the end of the root is cut and placed in a Petri dish where 1M hydrochloric acid has been added for 5 minutes to allow it fully dissolve calcium pectate as it fixes the cell. The tip is then washed with distilled water from a bottle. The tip is then dried using a tissue and put on a slide where toluene blue is added and left for 2-3 minutes to incubate. A cover slip is laid on top of the tip and pressed to crush it. This preparation was later viewed under the microscope and the cells were viewed. To karytype human chromosomes, an online teaching resource was used developed by university of Arizona through the link: http://www.biology.arizona.edu/human_bio/activities/karyotyping/karyotyping.html. Digital images are used where completed karyotypes were completed by arranging chromosomes and results analyzed. The instructions on the website were followed; karyotypes for three patients completed and diagnosed any extra or missing chromosome. Results EXAMPLE PICTURES YOUR DIAGRAMS Stage = anaphase Stage = _______metaphase ________________________ Stage = prophase_______ Stage = ______________interphase_________________ Stage = _________telophase_____________________ Table showing the mitotic index in the different stages Interphase Prophase Metaphase Anaphase Telophase 19/20 =0.99 18/21 =0.98 19/22 =0.99 18/20=0.98 Conclusion Some compounds in the lamella hold the cells in a plant together. When the onion tips were treated with hydrochloric acid, the compounds were dissolved and to break the cells apart so that each cell was viewed separately. The Toluene blue stain was also used to stain the nucleus of the cell where cell division occurs. This enabled the viewer to see clearly, what happens during cell division. The presence of cells where chromosomes had not condensed means that the cell is not undergoing any cell division. However, most of the cells viewed had their chromosomes condensed. The mitotic index of the cells dividing against the total cells in the view indicates the rate at which the cells are dividing in the root tissue. This index was very high in all stages since the root is a meristemic tissue and cells actively divide to facilitate growth. This thus shows that almost every cell in the root was actively dividing. When three copies of chromosome arise, the situation is called trisomy. In normal situations, the copies should be two. This thus means that the person has number of chromosomes that are abnormal. It is the work of the lab technician to look at the karyotypes, compile them, and characterize them through a specific notation. Here, the number of the chromosomes and other additions or subtractions of the chromosomes are looked at keenly. Both the three patients A, B, and C chromosomes are abnormal where there is addition, subtraction or a change in other features and other sex chromosomes. A patient can be male with 47chromosomes. Since the normal numbers of chromosomes are 46, an extra chromosome 18 is autonomic. It could also be a female with the right 46 chromosomes or a patient with a sex chromosome extra. It takes the technician to diagnose the patient or find normality in the chromosomes. If the fetus in A had an extra or less chromosome then it could not grow. If the fetus were to term, then other clinical problems would arise. To diagnose, if the patient has the normal number of chromosomes then the problem is due to something else other than the chromosomes number. Klinefelter syndrome results when there sex chromosomes extra. Downs syndrome results when there are three copies of chromosome such as the extra chromosomes are 21. This is called trisomy 21. Trisomy 13 syndrome arises when there is extra chromosome 13. To characterize patient A karytype, the notation used is the number of chromosomes. The patient has Downs’s syndrome. For patient B, the sex chromosome notation and chromosome number are used. The patient was diagnosed with Klinefelter syndrome. Lastly patient C used extra or less autosomal chromosomes to characterize the karyotypes. He is diagnosed with trisomy 13 syndromes.6 References and bibliography DO Morgan, The Cell Cycle: Principles of Control London, New Science Press, 2007. The University of Arizona, Karyotyping Activity, 1996, retrieved 12 March 2011 ‹http://www.biology.arizona.edu/human_bio/activities/karyotyping/karyotyping.html › F Borg, What is osmosis? Explanation and understanding of a physical phenomenon, Chydenius Institute: Karleby, Finland, 2003, retrieved 12 March 2011 ‹http://arxiv.org/abs/physics/0305011v1› G Jesse, G Shana, L Tony, G Zara, Membrane Structure" (SWF). Davidson College, 2002, retrieved 12 March 2011 ‹http://www.bio.davidson.edu/people/macampbell/111/memb-swf/membranes.swf›. A Maton, JJ Hopkins, L Susan et al, Cells: Building Blocks of Life. New Jersey: Prentice Hall, 2007. Read More