Using a pipette take a drop of the starch and amylase solution. Add this to a drop of iodine in a sample tray and mix with a stirring rod. As the amylase breaks down the starch the amount of starch that is detected by the iodine decreases. When there is no colour change when the starch amylase solution is added to the iodine record the time that it has taken.
After trialling we decided that a ratio of 1:1 was sufficient for the starch and amylase, we decided to use 7.5cm3 of each.
We decided we would test a range of temperatures, at room temperature which is approximately 20ºC and then take readings at each 10ºC rise until we reached 70ºC, as at this temperature the amylase was becoming denatured so this range should be sufficient at producing accurate results.
I predict that the optimum temperature at which the amylase works is about 37ºC as this is the temperature at which the human body maintains. The body has to maintain this temperature otherwise enzymes work at a slow rate, and if the body is too hot the enzymes become denatured.
Obtaining
Whilst obtaining our evidence in our trial we decided to change our procedure slightly to produce more accurate results. We decided to keep the two solutions of starch and amylase, both of which we used 7.5cm3 of, separate and heat them in the water bath until they both reached the correct temperature we then added them together, mixed them and then started the clock.
We kept our water bath and solutions at constant temperature using hot and cold water; this became harder as the temperature increased.
The red reading was our interpolated result.
Analysing
I have produced two graphs. Graph 1 shows the time taken for the starch to be broken down at different temperatures. Graph 2 shows the rate at which the reaction took place at different temperatures; the rate has been worked out next to the graph and multiplied so that it is easier to comprehend.
Graph 1 shows that as the temperature of the starch and the amylase increases the time taken for the amylase to break down decreases. But after a certain temperature the amylase denatures and the time increases.
Our interpolated result helped when drawing a best fit line as there were more points to see where the line joined.
Graph 2 shows the same analysis as Graph 1 but shows that as the temperature increases the rate of reaction increases, on this graph you can also see that the amylase denatures.
The rule of 10ºC rise and a double in rate of reaction does not seem to apply to Graph 2. In chemistry there is a rule that with every 10ºC rise in temperature the rate of reaction doubles, this does not work with this reaction but might work if a different ratio was used.
Amylase is an enzyme these break down large particles into small particles by lowering the energy needed to break bonds.
The amylase locks onto the starch substrate exactly, like a key; this then weakens the active site and makes it easier for the water molecule to break the bonds between the starch molecules. The amylase lowers the activation energy needed for bonds to be broken and so in a time period there are more successful collisions and more bonds are broken. If the temperature of the amylase is increased then it works even more effectively, but there comes a point at which the temperature is so high that the enzyme becomes denatured and cannot work, there is also an optimum temperature at which the enzyme works best.
In my prediction I said that 37ºC would be the optimum temperature as this was the temperature at which the human body is kept so that enzymes can work efficiently. This was not the optimum temperature because the enzyme didn’t come from a human it came from a plant. Amylase was taken from the malt plant, I found that the optimum temperature was around 53ºC, this is a lot higher than my prediction, it is so high because the malt plant has to cope with a huge range of temperatures and make sure that it enzymes still work efficiently. During summer the soil can become very hot a lot higher than air temperature and the plant still needs to do essential things like transpire, if its enzymes are denatured then the plant would soon die, this is why the optimum temperature is so high.
I can conclude that the temperature of enzymes during starch digestions controls the rate at which the enzyme amylase works. The temperature increases the rate of reaction, the enzyme works faster and so the starch is broken down quicker. There is an optimum temperature this is where the amylase is working most efficiently and the water molecules are breaking the starch very quickly. After this optimum temperature the enzyme starts to denature and the rate of reaction becomes less, the enzyme cannot fit to the substrate and the starch takes a long time to be broken down.
Evaluating
Although only a minimum amount of evidence was obtained, this proved to be sufficient in analysing evidence to support a conclusion.
Errors could have occurred during the procedure of obtaining evidence. We could have measured the starch or amylase wrongly leading to unreliable evidence. We could have not had the solutions at a correct constant temperature. We could have contaminated the pipette and not taken a fair sample of solution leading to inaccurate results.
Although some of my results did not fit onto the best fit line I don’t think they were anomalous, but more readings could have proved otherwise.
The key to obtaining accurate and reliable evidence was by making sure that regular samples were taken and that the time was stopped when the sample reached the same colour to show that the starch had been broken down.
This could have been done more accurately using a light sensor, light source and computer. This way you could stop each reading at the same light intensity and the time taken for each temperature would have been more accurate.
For further accuracy an electronic water bath could have been used in which a thermostat controls the temperature of the water and the results would have been not only more accurate but also reliable.
I think the evidence that I obtained is sufficient to conclude that the temperature of enzymes does correspond to the rate at which they work. I found that the optimum temperature for this amylase was at about 53ºC. As the temperature increased up to this point the rate increased. The rate became smaller after this point as the amylase denatured due to the temperature and was unable to fit to the starch substrate.
For further work I would try and find the optimum ratio at which the amylase worked, I would keep the amylase and starch at the optimum temperature but then change the ratios of starch: amylase. I would predict that the optimum ratio was where there was a lot of amylase to little starch, but I cannot support this prediction with evidence.
