Cell Membranes Investigation

Cell Membranes Investigation
Aim To investigate the influence of a variety of treatments on the permeability of the cell membrane. This experiment aims to discover the effect of 6 different treatments on the permeability of the cell membrane. These will be distilled water, sucrose, sodium hydroxide, hydrochloric acid, ethanol and boiled water. The treatments include immersion in these solutions, and exposure to high temperature. The tissue used is from the taproot of a beetroot, and the effect on the membrane?s permeability assessed by the amount of pigment leakage that occurs. Hypothesis == I predict that the most damage to the membrane will be caused by the acid or the boiling water. I think that this will happen because generally hydrochloric acid causes more damage to things and also it produces more aggressive reactions causing greater effects this I think means that the acid is more likely to effect or disable the proteins in the lipid bi-layer this means that if this happens the membranes selective permeability will be lessened and the restriction of the flow of pigment out of the beetroot will also be lessened so more pigment can and will flow out.
I think that the membranes permeability will also be affected greatly by heat, I think that this is because when the molecules are transported over the membrane they are done so with energy so when the water is heated the molecules will gain more kinetic energy so the transport over the membrane will be quick so more pigment will escape. Planning ==== In this experiment the thing I will be changing, my independent variable, is the solutions that I am testing to find out the permeability or a cell membrane. Also my dependent variable, what will be changing because of my change of solutions is the percentage transmissions giving me the results I need to find out what solutions affect a membranes permeability. My control variables will be:
The size of the beetroot ? 1cm x 0.5cm x 0.5cm
The amount of each solution used ? 10ml
The time the beetroot is immersed ? 15 minutes
4 pieces of beetroot in each tube
I will be keeping these all the same for each test. This will help me ensure a fair test. Equipment =====
Large knife
6 test tubes
Test tube holder
2 test tube racks
100ml beaker
250ml beaker
Chinagraph pencil
Bunsen Burner
Heatproof mat
Distilled water
Dilute hydrochloric acid
Dilute sodium hydroxide
Sucrose solution
Safety -?- Goggles ? hydrochloric acid, sodium hydroxide, ethanol and Bunsen burner. Lab Coat ? corrosive chemicals Procedure -??? ? Cut cubes of beetroot measuring 1cm x 0.5cm x 0.5cm. Put into small beaker and wash thoroughly in tap water until all the pigment set free from damaged cells has been removed. ? Place 4 pieces into each test tube. Label 4 of the tubes with the names of the solutions, one solution to each test tube. The 2 tubes left are to use for temperature effects. ? Using separate graduated pipettes, add 10ml of each solution to its labelled test tube. Note the time when the solution is added. Leave for 15 minutes. During this time begin the temperature treatment as described below. ? After 15 minutes pour the contents of each tube into a labelled curvette for use in the colorimeter. Be sure not to label the curvette below the top 1cm as this could interfere with the light beam. ? Calibrate the colorimeter and read the percentage transmission for each treatment. Record the results as a table. Record the temperature of the laboratory for comparison with the heat effect treatments. ? Make sure that the tube containing ethanol is well away from the Bunsen burner. Light the Bunsen and heat a 250ml beaker of water to boiling point. Add 10ml of distilled water to one of the remaining tubes. Label it 100ºC and place it in the boiling water for 15minutes. Remove, decant to a curvette and leave to cool. Repeat the procedure with the water at 50ºC. When both are cool record the percentage transmission. ? I will be recording my results in a table with the columns Solution, Time Added, Time Removed and Light Transmission. I am now ready to carry out the experiment. Results Solution Time Added Time Removed Light Transmission (%) Distilled water 0.00 15.00 Sucrose 0.30 15.30 Sodium Hydroxide 1.00 16.00 Hydrochloric Acid 1.30 16.30 Ethanol 2.00 17.00 Boiled Water 2.30 17.30 The anomalous result was that of sodium hydroxide this solution went yellow when the beetroot was added to it. Seeing as the colorimeter can only read the light transmission of red solutions we cant rely on the result of sodium hydroxide to be correct. Conclusion My results show that I was right in my prediction water and hydrochloric acid were two of the highest solutions to cause damage to the membranes, however one result that I did not foresee was that of the ethanol it two cause great damage to the cell membrane. There are several different types of solutions that cause a high effect on the permeability of a cell membrane, they do this for different reasons: Temperature The cell membrane consists of a lipid bi-layer with proteins embedded in it which act as carrier channels to molecules. As the cell membrane controls the permeability and therefore the activeness of the proteins it is the effect of temperature on the protein carriers that will alter the permeability of the beetroot cell membrane as they are the ones that will actually do the work. This is why at low temperature the kinetic energy of the pigment molecules and proteins is at a minimum so they are slow to pass through the membrane. When the temperature increases the molecules gain kinetic energy therefore the transport across the membrane is faster and the amount of pigment loss is greatly more noticeable. The maximum rate of energy increased is reached at about 40ºC, at temperatures above this the carriers proteins will begin to lose their specific shape and will no be able to work properly anymore. This normally means that the proteins will lose their ability to control what passes through or allow completely free passage and will also see a greater loss in pigment from the beetroot, as I boiled my water, the temperature of it would have been 100ºC so this would be why the pigment loss in the boiled water solution was so much greater than the others. However from my result I assume this happened because of the great difference however if I had not got this result it would be because of the other effect the destruction of the structure. This is when the proteins? shape distorts and does not allow any passage to any molecules anymore. Alkalis An alkali that I used in this experiment was sodium hydroxide one effect a solution like this can have one the membrane is, if used in high concentrations is that the membrane is disrupted completely and will break apart. Another is, when used in low concentrations the membrane becomes more permeable, this I what I think happened on a small scale in the sodium hydroxide test. In this reaction the solution act on cholesterol and causes water to become soluble. Acids Lipid that make up the cell membrane in a bi-layer are altered by acids, high differences in pH will damage the cell by changing proteins and enzymes, and interfering with the transport of ions across the cell membranes. The hydrogen ions in the solution of the acid react with parts of the membrane and cause its structure to fail, which affects mainly the phospholipids helping it to become more permeable. Alcohol, Ethanol Alcohol damages the weak hydrogen bonds that hold together and in postion the proteins in the cell membrane, the proteins cannot hold together their shape anymore and so therefore denature. Evaluation Generally overall I am pleased that this experiment was carried out effectively and efficiently. However when I first measured my results for water I obtained a result of 108% on the colorimeter and 107% for sucrose I knew that this could not be correct as the result can not be over 100% so I re-calibrated it and re-measured my solutions and got my correct results. This was a technical problem caused by the machine. I received one anomalous result, which was that of sodium hydroxide this solution went yellow when the beetroot was added to it. Seeing as the colorimeter can only read the light transmission of red solutions we cant rely on the result of sodium hydroxide to be correct. I think that I could improve on my results of my experiment and make them more accurate by repeating the experiment by at least once or twice more by doing this I would be able to see if there was any problem with a set of my results or if one set contained any other anomalous results.

Cell Membranes Investigation 7.9 of 10 on the basis of 2382 Review.