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  • Level: GCSE
  • Subject: Science
  • Essay length: 6325 words

The factors affecting the rate of permeability in a cell membrane?

Extracts from this essay...


The factors affecting the rate of permeability in a cell membrane? The plasma membrane is a permeable membrane, and it controls exchanges between the cell inner and outer environment. The rate of membrane permeability is dependent on a many factors. These are: * Molecular size of the solute as the permeability mostly decreases with increasing size * Lipid solubility's permeability usually increases with increasing fat or oil solubility * The degree of ionization as permeability mostly decreases with increased ionization * The pH and temperature also have great effect on the permeability of the plasma membrane and in the experiment I will test how temperature has an effect on the rate of permeability. Roles of the components of cell membranes: My study has shown me that cell membranes contain many different types of molecules and they each have different parts to play in the overall structure and function of the membrane, these molecules are; Phospholipids - these forms a bilayer which is the basic structure of the membrane, they have non - polar tails which means that it is difficult for polar molecules or ions to get passed them it can be said they are a barrier to most water soluble substances. Cholesterol - these molecules will help to get the fluidity of the membrane regular and it will prevent it from becoming too rigid or too fluid. Cholesterol is used also for the mechanical stability of membranes this is very important because without this membranes would break rapidly and cells would burst. Proteins - The transmembrane proteins act as carriers and also channels for ions and glucose. Proteins also act as a receptor for hormones this will detect which hormone it is and what it does. Glycolipids and Glycoprotein's - these are only found on the exterior surface of the cell membrane, they are formed by carbohydrates attaching to lipids to form Glycolipids and to proteins to form glycoproteins, they act as receptors and aid in recognition of cells.


As their shape changes this will create holes in the membrane this will allow the pigment to leak out and change the colour of the outside solution. To control this you must make sure that the pH of the extracted solutions is the same before measuring their colour change. This will be done by using litmus paper and dipping it into the solution, the change in colour will be measure against the pH chart, this will determine the pH of the solution. Prediction: I think that if the temperature does not exceed 40ºC - 50ºC which is the optimum temperature then the permeability of the plasma membrane shouldn't be affected. When the temperature goes over the limits then the water expands the cholesterol, Glycolipids and phospholipids which put pressure on the membranes from inside. The part of the membrane that is lipid will become liquid which would make it open to leakage. The proteins in the membrane will denature and this will increase the permeability in the surface. All of this will mean that compounds could exit the cell because high temperatures will make the molecules shake and vibrate more frequent. All this fast movement will mean that there the organised structure will be disrupted and eventually the structure will be ruined, this is because the higher temperatures break the hydrogen bonds in the structure of the protein and the structure is lost. If the membrane is damaged because then the structure will all fall apart and will not work anymore. As the water molecules will rapidly enter the cell membrane by osmosis and the cells will swell up and burst this will release the pigment and it will spread. Equipment List: * Beetroot * Distilled water * Scalpel * Ruler * White tile * Cork borer for size * Colourimeter * Stop clock * Syringes 10cm³ * Water bath * Thermometer * Test tube * Test tube racket * Measuring cylinder 25cm³ * Pipette * Spatula * Tripod Apparatus What it is used for?


beetroot will be released into the distilled water this would mean that the reading is inaccurate some temperature will have more pigment released then should have been and then leading to a anomaly. * The temperature of the water might have altered after I put the test tubes in if this happens then the water will not be heated to the right temperature and the right amount of pigment might not be released meaning that a lower reading taken rather then the real amount that it should have been. To improve the reliability of the result I repeated the experiment again this would have improved the accuracy if I had maybe changed the apparatus by using a different colourimeter which measures light over a much narrower range of wavelength. the stop clock that I used could have counted down this would have meant that it would have stopped on exactly 5 minutes and I could taken the test tubes out in better time. The apparatus which I used was what was available and so using some different apparatus was not really possible and also I did not have time to find and change the apparatus. When timing I used a stop clock it was timed for 5 minutes but I could have let the clock run a bit over the time or under the time and so the beetroot was not taken out at the exact time each time. This could mean that as the beetroot was left in the heated water for longer more pigment could have leaked out this looks to be the case at 50ºC as it does not follow the trend in the graph it is even with 40ºC on the first transmission and on the second transmission it is above 40 ºC this is an anomaly and the cause seems to be that the beetroot was left in the heated water for too long. Hence more pigment being released then should have been released. - 1 - Mohammed Faisal

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