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
- Beetroot
- Large knife
- Scalpel
- Forceps
- 6 test tubes
- Test tube holder
- 2 test tube racks
- 100ml beaker
- 250ml beaker
- Thermometer
- Tiles
- Chinagraph pencil
- Bunsen Burner
- Tripod
- Gauze
- Heatproof mat
- Ruler
- Colorimeter
- Curvettes
- Droppers
- Stopclock
- Goggles
- Distilled water
- Dilute hydrochloric acid
- Dilute sodium hydroxide
- Ethanol
- 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
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.