Results and discussion:
The yeast suspension and TTC solution were placed in the water bath before mixing together because the contents of both test tubes need to be at the same temperature as the water bath. This is to ensure that the when the reaction takes place, it is sure that the experiment is taking place at the temperature of the water bath. The contents of both test tubes will be at the same temperature when they are mixed so the reaction will take place as efficiently as possible.
This is a graph to show the relationship between temperature and rate of activity of dehydrogenases:
The results show that the optimum temperature for yeast dehydrogenases is somewhere between 70°C and 100°C.
The effect of a 10°C rise in temperature on the rate of a reaction can be expressed as the Q10 value. This is a ratio of the rate of a reaction between two temperatures. These are the Q10 values for the temperatures used in this experiment.
Between the range 20°C and 30°C = 0.002176 ÷ 0.001147
= 1.897
Between the range 30°C and 40°C = 0.003205 ÷ 0.002176
= 1.473
Between the range 40°C and 50°C = 0.004782 ÷ 0.003205
= 1.492
Between the range 50°C and 60°C = 0.006359 ÷ 0.004782
= 1.330
Between the range 60°C and 70°C = 0.007937 ÷ 0.006359
= 1.248
Between the range 70°C and 80°C = 0.007622 ÷ 0.007937
= 0.960
Between the range 80°C and 90°C = 0.007308 ÷ 0.007622
= 0.959
Between the range 90°C and 100°C = 0.006993 ÷ 0.007308
= 0.957
One source of error in this experiment was that not all the yeast suspension was always transferred into the test tube of TTC solution. This meant that different amounts of yeast suspension could have been actually used for each of the temperatures. This in turn would effect the time taken for the correct concentration of colour to appear. One way of improving the experiment in order to combat this would be by placing a larger amount of yeast suspension in the water bath and drawing the 10cm3 straight from the container into the TTC solution test tube, instead of pouring one test tube into another. A wider range of temperatures would increase the accuracy of the results and lead to a much firmer conclusion and therefore a more accurate optimum temperature. Also, if there could be water baths at all the required temperatures then it would be much fairer. Another source of error could be when the solutions were measured. This source of error was reduced by always measuring from the bottom of the meniscus, however slight differences could have occurred. A control test tube could have been set up to make sure that it was in fact the yeast suspension that caused the alteration in colour of the TTC solution. This control would just be 1cm3 of the TTC solution in a test tube to see if it changed colour. Perhaps the major source of error for this experiment was determining when the colour of the formazans was identical to that of the original test tube. The overall accuracy of the experiment could have been improved if the whole experiment was repeated two or three times and an average for each temperature taken.
In organic molecules oxidation involves the removal of both electrons and protons. This process is called dehydrogenation. Dehydrogenases are enzymes that catalyse these reactions. In cell respiration, dehydrogenases are used in the first part of the breakdown of glucose (glycolysis). The two trioses produced after the splitting of fructose-1,6-biphosphate undergo dehydrogenation. The hydrogen atoms produced by this reaction are taken up by NAD+ to from NADH + H+. The electrons then pass along a series of electron carriers, making up the electron transport system. This electron chain then results in ATP synthesis, which is of course the point of respiration. The role of dehydrogenases is also seen in the Krebs cycle. Four of the steps in the Krebs cycle involve the removal of pairs of hydrogen atoms, which are catalysed by NADH dehydrogenase or succinate dehydrogenase. In the same way, the NADH + H+ goes on to the synthesis of ATP from ADP and Pi.
