Permeability of a Membrane

At higher temperatures some water vapour was seen this may have made the pigment less dilute then it would have been had no water escaped. Also at higher temperatures the cubes were seen to float this would increase the surface area because at lower temperatures some faces of the cube were pressed against the sides of the test tube.

Errors

The random errors were:

* Maintaining the temperature of the water bath +/- 10% (this was the most significant)

* Human error in reading the thermometer +/- 2%

* Human error in reading the colorimeter +/- 2%

The systematic errors were:

* Inaccuracies in the thermometer +/- 1%

* Inaccuracies in the colorimeter +/- 5%

Conclusions

The graph shows clear negative correlation (i.e. As the temperature goes up the light transmission falls). This indicates that the membrane becomes more permeable at higher temperatures. The sharp fall between 65°C and 70°C is indicative of a breakdown of the membrane which is in holding with the fluid mosaic model of the membrane whereby at lower temperatures the membrane is tightly packed and gel like but at higher temperatures it becomes less tightly packed and more fluid until eventually it looses its structure and breaks down completely.

Evaluation

The method selected would appear to be sound with most of the errors being quite low with only the temperature of the water bath being really significant. This could have been overcome if an automated water bath could have been used; unfortunately this was not possible due to lack of apparatus. Another related problem was reading off the thermometer as one had to make sure it was not at an angle and that the line of sight was directly at the top of mercury to make sure that it was at the right temperature. The results are all stated to two significant figures, as it is reasonable to assume that the equitment was accurate to this degree of precision. It is therefore reasonable to assume that the conclusions drawn are both reliable and accurate.