2cm³ salivary amylase per test; 15cm³ per test; spotting tile; 500ml beaker; 1 test tube per test; spotting tile, 2 pipettes, a water heater with a thermostatically-controlled heating element, measuring cylinder, stopclock, iodine with pipette, thermometer.
I will mix the starch and amylase together, then spot a sample of this on to some iodine every 30 seconds at different temperatures.
This is how I did the experiment:
I added the amylase and starch to the two test tubes, which I labelled. I placed these in a water bath and added hot or cold water to heat them to the correct temperature (I did the experiment at 20, 30, 40, 50 and 60 degrees centigrade).
This was difficult to do exactly, so I recorded the temperature before and after the experiment to see any change in temperature. There was not be a dramatic change, as there was not any sharp increases in temperature, as in from a Bunsen burner.
I set up a spotting tile, with a drop of iodine in each orifice.
Once the two test tubes were at the correct temperature, I poured one into the other, started the stopclock, and spotted a sample of the formed mixture on to the first hole in the spotting tile.
I added a sample of the mixture into a hole of the spotting tile every 30 seconds until the colour of the iodine reached a shade of orange which I picked from my first result, which showed that the mixture had reacted.
I repeated the experiment 3 times at each different temperature.
The experiment was repeated at 10 degree intervals, instead of, for example 5ºC, because I had a limited amount of time and I wished to show what would happen to the results after the enzymes start to denature.
Fair Testing and Control
The test will be fair because:
- Both the solutions will be at the same temperature.
- The same apparatus will be used for each repetition.
- The same colour will be used to compare the others to when the tests finish.
Control:
A control for this experiment would be to repeat it not using amylase and see if the same colour change in the iodine occurs. If it doesn’t, it will prove that it is the amylase that splits up the starch into maltose, not anything else.
Safety
All of our equipment was safe, but we had to be careful with the liquids, i.e. not swallow them, and also be careful with the water in the tank, as it was hot – but not hot enough to scald.
Obtaining Evidence
This is a copy of the raw results I recorded during the experiment:
I then computed the averages for all the temperatures, and put them into the chart on the next page.
I also worked out the rate of the reaction, which is 1 divided by time.
Time is in seconds, and temperature is in ºC.
The time is the time taken for the iodine to reach orange.
Analysing Evidence
The graphs on the next pages show the above results.
The trend shown in my graphs was that the lines in the graph showed a faster rate of reaction up to about 40°C, and then the reaction slowed down again. This is supported by my background knowledge section, which says that the enzymes become denatured after 40ºC, so they cannot aid the reaction anymore. The salivary amylase enzyme becomes denatured after body temperature, which is its optimum working temperature. Other enzymes in the body become denatured at higher temperatures, but the mouth is a cooler place than the rest of the body, so amylase can denature at a lower temperature without having a risk of actually doing so.
The graphs are not in a straight line down to 40°C, and then up again, because of the kinetic theory. As I made the water surrounding the amylase and starch mixture hotter, some molecules would have heated up faster than others, so at any one time, not all the molecules would have been at the same temperature. That is why, after 40°C, not all the enzymes are denatured, and theoretically a smooth curve would be gained for the time taken for the enzyme to react.
This is a picture I got off the Internet that shows how my curve should have looked:
This graph is very similar to my graph for rate of reaction. The values are different, but the curve is the same (if upside down) – it shows the same effect of heat.
My graphs support my prediction. They also show that the temperature rise is proportional to the time. A rise of 10ºC should approximately double the rate of reaction. This did not happen, but apart from 1 anomalous point, the curves are smooth.
Evaluation
The apparatus I used for this experiment was all suitable for my needs; however there are some human errors that could have occurred, and some ways the apparatus could have been improved upon.
- The solution I held in the pipette in between the 30s intervals may have cooled down. I think this factor was the main one in causing anomalous points.
- I should have taken a new pipette full of solution at each reading.
- Several errors may have occurred from me judging the colour changes; it was improbable that I managed to stop the experiment at exactly the same shade of orange each time.
- I could have used a colourimeter to judge the colours.
- A digital stopclock was used, eliminating parallax errors
- The temperature may not at have been exactly what it was supposed to be at.
- I checked the temperature before and after the experiment, but few errors occurred.
- It was difficult to add the solution at precisely the right time.
- Two people could have done the experiment together, eliminating all the tasks you have to do at the start.
- The test tubes may have contained impurities before the experiment started.
- This is unlikely, but I could have washed them in distilled water.
There were some anomalous points in my results, but the results matched my prediction, and the theoretical results obtained from the internet.
The experiment proved that enzymes increase the rate of reaction of substances, and do so with greater efficiency proportional to temperature, until they begin to denature.
The anomalous points in my graph did not quite fit in with the smooth lines of the curves, but the one at 40 centigrade, emphasises the effect of correct heat for the enzymes to work in.