I predict that the higher the concentration of yeast, the less time it would take to change the colour of resazurin because there would be more of the enzyme dehydrogenase for the resazurin to react with and therefore the colour would change quicker. Dehydrogenase is a catalyst that aids the process of reduction by speeding up the oxidation of the yeast. The reason the resazurin seems to disappear when the reaction is finished is because it changes colour when hydrogen is released through the yeasts process of anaerobic respiration. Glucose is gradually broken down in this process and energy is released.
Hydrogen is also released in a process called oxidation, and when hydrogen is released the resazurin gains this hydrogen. The gaining of hydrogen is called reduction and molecules which gain this hydrogen are said to be reduced. I think that this will happen faster in my experiment when there is less distilled water in each yeast suspension. I did not repeat the experiments for 80, 60 and 50 as they were within 2 seconds of each other therefore I thought my results would be reliable enough. 25% yeast suspension was not carried out as it took too long to react. (See attached graph for results as graph form)
The graph has a fairly average negative correlation. The plotted data seems to go in a straight line which is why the line I have drawn is a straight line. The pattern in my graph is the higher the percentage of yeast in suspension in distilled water, the less time it takes for the resazurin to lose its colour. This proves that my prediction was correct. As in my prediction, the more yeast in suspension, the more dehydrogenase which therefore the faster the oxidisation of the yeast, and the faster the reduction of the resazurin, which changes to clear when it is fully reduced.
Evaluation I think that some of my results were a little out due to human error and the fact that I only had my eye to judge on whether the substance had become clear or not. This could be resolved if we had an automated device that measure the amount of light let though the boiling tube. Also, other groups were using out water bath, so the average temperature of the water bath would be slightly skewed by the fact there were so many colder boiling tubes being added to it.
Also, I think that the measuring equipment we used wasnt accurate enough. If we had more mechanical measuring pipettes, the ones that use vacuum to suck up liquids, then the measurements of yeast and resazurin would be a lot more accurate, and therefore lead to a more reliable experiment. If I did the experiment again I would also use a lot more variables of yeast suspension, such as ranging from 10% to 100%, going up in 10s. This would provide me with more valid data. Also if I repeated the experiment the results would be a lot more reliable.