In this investigation, I will be finding out which temperature, the enzyme, lipase, works best at. I will do this by looking to see how effective the enzyme is at each of the chosen temperatures.

Variables

 The controlled variable used was the temperature of which each step is done at. The uncontrolled variable was the time it took for the each step of the experiment to finish.

Fair Test

 To ensure my investigation is a fair test, I will need to carry out many checks. The first check I need to carry out is that exactly the same amount of milk, lipase, phenolphthalein and sodium carbonate is used in each experiment. If I were to use unequal amounts it would perhaps take longer for the lipase to break down the milk particles. To ensure all amounts of each substance are equal I will use a syringe or pipette. Another check, which has to be carried out, is that the temperature of the substances in the test tube is the same as the temperature of the water bath before the phenolphthalein and lipase solution are poured into the other test tube. If the temperatures are different then the experiment will not be taking place at the correct temperature.        

Hypothesis

 I believe that the trend of the graph will look like this:

 I believe there will be rise in my graph this is shown at point 1 this will be due to the fact that up until the peak on the graph, as the temperatures rises there will be more energy in each of the fat and lipase particles therefore causing them to move around at a faster rate. The faster the particles will be moving the more collisions there will be. This will lead to more fat particles being broken down in a shorter space of time therefore causing an increasing rate as shown on part 1 of the sketch graph. Part 2 of the sketch is a decline this is through the lipase particles becoming too hot and therefore denaturing into a shape which does not fit into the fat particles therefore not managing to break them down this causes a decreasing rate of the reaction and therefore less fat particles being broken down in a longer period of time. The peak of the graph is where the lipase enzyme will work best. I think this will be a round forty degrees Celsius as this is the closest temperature to the human body temperature. The enzyme will work best at this stage, as they are adapted to working in the human body, which has a temperature of around thirty-seven degrees Celsius. As forty degrees Celsius is the closest temperature to this that I will be testing I believe that the lipase will work best at this temperature.          

Preliminary Work

 To test which volumes of each substance I would be using I carried out some preliminary results. At first I used twenty drops of sodium carbonate, but the solution never went white, as it was too alkaline. I then tried using ten drops of sodium carbonate and this was just about the right amount as the solution went white in a relatively short period. I then tried using two drops of phenolphthalein but the colour was too weak to start with so I then used five drops of phenolphthalein but the colour was too strong. I then tried using three drops of phenolphthalein and this worked perfectly. Next I tried an experiment using five millilitres of milk but the experiment went on for too long so I then tried using five millilitres of lipase but this went too quickly. I then decided to use two millilitres of lipase and two millilitres of milk and this also worked perfectly. So I decided to use two millilitres of milk, ten drops of sodium carbonate, two millilitres of lipase and three drops of phenolphthalein.          

Results

Conclusion

 From my graph I can see there is a rise in rate until a peak at forty degrees Celsius, which is followed by a decline. The rise is caused by the increase in temperature as this gives each of the milk and lipase particles more energy causing them to collide with each other more often. The more collisions made the more the lipase breaks down the fat. The peak is at the temperature where the enzyme is the most effective. The peak is at forty degrees Celsius this is because the enzymes are adapted to human body temperature this is at around thirty-seven degrees Celsius and, as forty degrees Celsius is the closest temperature to the human body temperature it is here where the enzyme is most effective. So therefore we can say that the enzymes ware more effective in between twenty degrees Celsius and sixty degrees Celsius. The decline on the graph comes after the peak and this is because of the high temperatures. The high temperatures cause the enzymes to denature into a shape, which does not fit into the fat particles so they cannot be broken down. This means that it takes a lot longer for the lipase to finally break down the enzymes and so the rate of reaction is lower after the peak temperature. I was correct in my hypothesis because I predicted that in the graph there would be a rise at first, followed by a peak at forty degrees Celsius, and then a decline from there on after.    

Evaluation

 In my results I had no anomalies so therefore my results must be accurate. Each of my repeats was close to another repeat for each temperature also proving my results were accurate. My average result in each case was closest to the median repeat for each temperature therefore proving that my results were accurate. In the graph the accuracy of my results was shown as my graph has a good fit to the expected curve. In the method there are possible sources of error. An example of this is the measurement of the phenolphthalein and the sodium carbonate. These were measured using a pipette and by counting the drops one of the problems that arose is that the drops from the pipette maybe different sizes therefore meaning that a different amount of each substance may have been put in to the test tube each time. Another problem that arose is relating back to an original colour. The end of the reaction was very difficult to differentiate between each time as it was difficult to say whether the original colour had been restored, to defeat this problem in the experiment a control test tube containing just plain milk was used to refer to but it was still difficult to ensure that they were exactly the same colour. To overcome this problem a colorimeter could have been used and this would allow us to match the colours more easily. Another option for the same problem is to use a pH meter, which indicates the exact pH of the solution this could be used by testing the control test tube and the experiment would be over when the control test tube and the test tube containing the experiment have the same pH levels.