Method
I measured the time taken for the film to become transparent at different temperatures – this demonstrates whether or not the effectiveness of the enzymes increases or decreases with heat.
I first switched on the water bath, setting it to 30ºC. I then measured out 5ml of pepsin into the test tube, placing it upright into the water bath. I then got the photographic strip ready to put into the test tube. Then, when my thermometer told me the water had reached 30ºC, I Immediately put the photographic film into the pepsin, I started my stopwatch, stopping it when the photographic film became transparent and immediately taking the photographic strip out. Using a fresh photographic strip, I repeated this part of the experiment twice, to give me three readings against each temperature, from which I could then take an accurate and meaningful average.
I then turned up the temperature of the water bath at 5-10ºC intervals, recording the results again three times each. I ended my experiment when the temperature reached 55ºC although I carried on doing the experiment to see what temperature the photographic strip denatured at.
Fair Test:
I ensured this was a fair test by doing the following:
§ Doing all the tests on the same day because sometimes there are conditions out of our control that can change
§ Checking that the concentration in the test tube was always the same: 2% pepsin, to ensure balanced results
§ Making sure the temperature on the thermometer was exactly as it should be when recording my stopwatch results
§ Using the same type of photographic film and the same height and length
Safety
Safe Test
As well as the experiment needing to be a fair test, it must also be a safe test for it to be successful. I must make sure that safety goggles are worn at all times in the experiment as trypsin would be very damaging if it got into the eye as it breaks down protein and most of the eye is made of protein. Also as a bunsen burner is to be used in the experiment I must be careful when it is alight.
Results
Results
Conclusion
In order to see the results from my table more easily, I converted them into a graph. From the graph, I could clearly see that, on average, pepsin enzymes work best at temperatures of 30 - 55ºC, because it is then that the film turns transparent fastest, shown on the graph as a flattening-out.
The graph also shows that the enzymes then start to denature at around 65ºC because the line shoots up. Here, the film takes radically longer to become transparent, eventually causing the pepsin to have no effect on the photographic strip.
A curve of best fit would only be appropriate between 30 and 55ºC.
These results fitted in with my predictions because the enzymes did increase their rate of reaction when the temperature increased and did denature at a high temperature.
Evaluation
I thought my experiment worked well because it showed similar readings and I didn’t have any odd-looking figures within the results. I also thought the results were accurate enough, because it gave such a clear pattern of the enzymes’ behaviour.
If I wanted get obtain even more accurate results, I could have tested at an even greater number of temperatures.
I think my method was the best way of carrying out the investigation because I took more than two results to reach my conclusion. I could improve my method by taking even more results.
To provide me with even more evidence for this investigation, I could compare notes with other students who have carried out the same experiment, to see if there are any anomalies.
