Cell Membranes Of The Beetroot Discs example essay topic

To investigate the effect of detergent on Cell Membranes Cell membranes are composed mainly of phospholipids. A cell membrane is a phospholipid bilayer, which acts as an effective barrier, controlling what substances enter and exit the cell. This property can be explained by the structure of phospholipids. Phospholipids are composed of a hydrophilic head and a hydrophobic tail.

When in water, all of the hydrophilic heads face outwards into the water and the hydrophobic tails face each other, shielded on either side by hydrophilic heads As the hydrophobic tails create a non-polar interior, it is difficult for polar molecules, or ions, to pass through them and so acts as a barrier to most water-soluble substances. The phospholipid bilayer also prevents the contents of the cell from escaping. If detergent is introduced to the phospholipid bilayer it gradually breaks down, allowing the interior contents to vacate the cell, which will inevitably lead to the demise of the cell. Detergents attack lipids (for example in washing powders), which are an integral part of phospholipids, and make them increasingly soluble, thus destroying the cell membrane.

Hypothesis Because of the effect of detergent on cell membranes, it is feasible to assume that the greater the amount of detergent added to the cell membrane, the greater the amount of phospholipids that will be dissolved, and therefore the greater the leakage of cell content Strategy In a previous experiment concerning the effect of heat on channel proteins in cell membranes, beetroot discs were used. Three beetroot discs were placed in each test tube and were then subjected to various temperatures. These proved to work very effectively, releasing a pink / red pigment, Betacyanin, when the channel proteins broke down. The leakage of Betacyanin was easy to see and record, and therefore beetroot discs will be used in this experiment.

In this case, the beetroot discs will be placed in different concentrations of detergent. The effects on the beetroot cell membranes will be measured by observing the varying colour intensity of the samples, produced by leakage of Betacyanin. To ensure that a coherent set of results is obtained, a wide range of concentrations will be used (10% detergent, 1%, 0.1%, 0.01% and 0.001%). These concentrations will be produced in the following way: To ensure that this will be a fair test, three beetroot discs will be placed in each test tube, as was done in the previous experiment involving beetroot discs. The beetroot discs will be cut using a cork borer and a scalpel, ensuring that the size, and therefore surface area of each individual beetroot disc is almost identical. This will help to improve the accuracy and reliability of the results obtained.

To ensure that nothing other than the concentration of the detergent affects the cell membranes of the beetroot discs, the test tubes will be placed in a water bath, which will be maintained at a fairly low temperature to ensure that there is no denaturation of channel proteins within the cell membrane. In a previous experiment concerning the effect of heat on beetroot disc cell membranes, at a temperature of 300 C, no denaturation occurred. Taking this into consideration, the water bath will be maintained at a temperature of precisely 300 C. All 5 test tubes will be left in the water bath for duration of exactly 30 minutes. This will be timed using a stop clock. In order for this to be a fair test, the following variables must be controlled: . Volume of detergent solution.

Duration of exposure. Number of beetroot discs In a previous experiment concerning the effect of heat on beetroot disc cell membranes, the varying colour intensities of the samples of coloured liquid produce by the leakage of Betacyanin were judged using only the human eye. This led to some major errors within the results obtained. In this experiment, to ensure that the results obtained are accurate and reliable, a colorimeter will be used. This will eliminate any possible errors that human judgement can cause, and will also provide highly accurate results. The cuvettes will be filled with samples of the coloured liquid produced by the leakage of Betacyanin.

Care will be taken to ensure that the transparent sides of the cuvettes are correctly aligned. For each particular concentration, the colorimeter will be 'zeroed'. The results will be recorded in an appropriate form, and a graph will be produced using these results. Apparatus.

Beetroot discs. Detergent (100% conc. ). 5 Test tubes. Test tube rack. Water bath.

Thermometer. Beakers (3 approx). Pipettes. Colorimeter. Cuvettes (5).