Prediction:
After carrying out a preliminary experiment I can now make a connection between the ph and the time that it takes for the gelatine substance on the photographic film to disappear. I noticed that as the ph was higher or more alkaline then it took less time for the black substance to disappear. As the ph was lower or more acidic then it took less time for the black substance or it did not disappear at all. I can safely predict that as the ph gets higher then the less time it will take for the black substance to disappear from the film. Another reason why I think this is because the thing that the ph is representing is the pancreatic juice. The juice that the pancreas secretes is alkaline so the ph that works best should also be alkaline. The temperature won’t affect the reaction as I am going to keep it as the same temperature throughout the experiment.
This is what I think will happen as the ph increases the rate of reaction should decrease
Variables:
The variables that I am going to have to consider are ones such as what temperature I am going to use. I will keep the temperature at about 37 degrees at all times during the experiment as this will keep the experiment fair and this is about the temperature that the pancreatic juices work in. to keep the temperature constant at 37 degrees I am going to put it into a water bath this will ensure that the temperature will remain the same and make it a fair test. There are quite a few variables that I am going to have to consider such as how does the concentration of the pancreatic solution effect the reaction and how does the concentration of the substrate affect the reaction. The results will have to be reliable and the reliability of the results means that they have to be repeatable. The substrate is the gelatine on the film so the concentration of this is going to be kept the same through out the whole experiment.
Method:
- Get out 5cm3 boiling tubes and add 5cm3 of trypsin then add 5cm3 of the chosen ph. The ph is there to act as the concentration and the trypsin is the substrate
- Place the boiling tubes on to a boiling tube rack
- Cut up 5 pieces of photographic film all being the same size at of 1.5 cm by 1.5cm
- Place the boiling tubes in the heater and leave them for a few minutes so that they can get to the right temperature
- Drop the photographic film into the boiling tube and start the stop clock
- Keep shaking the boiling tube until the gelatine has disappeared and record the time. You know when the gelatine has been digested because the black part of the film will have disappeared
- Once one time has been recorded keep the stop clock going and just write down the time keep this process going until all 5 times have been recorded
Safety:
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.
Fair Test:
The experiment must be a fair test or I will be getting a lot of anomalous results and there may not be a clear pattern in the results. To make the experiment a fair test I am going to make sure that volumes of trypsin and pH buffer are the same in each experiment and the size of the photographic film is the same. I must also make sure that the temperature of the water and the trypsin and pH buffer remains at 37°C to keep the experiment accurate.
I will also need to make sure that the photographic film is completely clear before I stop the timer. When I think it is clear I will press the red button on the timer and if the film goes no clearer I will take the time that I paused the timer at. If it does go clearer I will continue the timer and stop it when it goes clearer.
Apparatus:
- 5 boiling tubes
- boiling tube rack
- pipette
- stopwatch
- measuring cylinder
- water bath
- stirrer
Conclusion:
From my results I can conclude that the ph that the gelatine gets dissolved quicker in is between ph 8 and ph 9. I thought these 2 ph’s would be the best because these are the ph’s of the conditions that the pancreas has to work under. As you can see from my graph as the ph gets towards ph 8 and 9 it is at its peak and this proves my prediction correct. If the ph value becomes either too acidic or too alkaline the enzyme will not work as well. This occurs because when the ph is too high or too low this will denature the enzyme by changing its shape therefore not fitting in like when the shape of a key is altered it will no longer fit into the door.The rough graph that I drew which I thought that’s what the results would look like is similar to the proper one. The results are not entirely accurate as there has been many things that will have contributed to the unreliability of them. Such as you could not tell whether the gelatine had dissolved and when it did dissolve you were unable to get the time exact.
Evaluation:
There appears to be no clear anomalous results in my experiment. As my method and plan was to make the experiment a fair test and if I had made sure that the results were exactly accurate, the results should have been near perfect. But because I could not ensure exact measurement was used, this could be a possible reason for the slight inaccuracy in the results.
I tried to keep accurate measurements in my experiment and I kept the temperature of the beaker within a couple of degrees of 40°C. There is an inaccuracy that cannot be ruled out of my experiment, unless there is another way of performing the experiment, and that is human error. It is not perfectly clear in many cases if the acetate is clear or not, and it is hard to tell. This will be a problem unless another way of is found to stop the clock. One way which would make the stopping of the clock at the right time would be to use a light on one side of the test tube and a light sensor on the other side of the tube connected to a stopclock. When the light sensor detects light through the acetate when it is clear, it would stop the clock. This would eliminate the problem of human error in stopping the clock at an incorrect time.
Although there will be slight inaccuracies in my results, the basic shape of the graph is definitely quite clear. The graph shows that as the pH increases from 6 to 9 the rate of reaction increases and as the pH increases from 9 to ten the rate of reaction decreases. I could make my results even more clear by using more pH values, I could use from 3 to 12. I could try mixing an even quantity of two consecutive pH values to gain a midway pH value. This would give me much more accurate results and any anomalous results would become much clearer and I could re-do them and hopefully gain a more accurate result.
