I will use a pH probe to test the pH of the acid produced. This should reduce the chance of human error as it is computerised and therefore more accurate.
To ensure a fair test, all variables (the amount of lipase and milk used every time) will stay the same, except for the temperature at which the reaction takes place at, which I will be controlling. I will ensure all of these factors are the same as it would be unfair to change the dependant variables and would give me inaccurate and unreliable evidence on which to base a conclusion. I will also ensure that the milk is always the same pH before use and I will do this by using the same milk every time, ensuring it has been stored and treated the same.
To change the temperature variable, I will be using a water-bath and will start at the lowest temperature value (20°C). I have chosen values between 20 and 60°C as this will clearly show me a range of results and therefore make my results more accurate. All measurements collected will be as accurate and reliable as possible because I will strive to conduct a fair test, keeping all variables except the temperature the same. I will also check the temperature of my water bath constantly with a thermometer to make sure it is the correct temperature.
To do my experiment I will need the following equipment:
- pH probe
- 5cm³ lipase
- 25cm³ milk
- Teat pipette
- Test tube rack
- Test tubes
- Water bath
I have chosen this equipment because I feel it is the most suitable for the experiment and that combined with careful variable control, they will produce the best results.
I predict that the lipase will have the optimum reaction rate at around 37°C, as this is human body temperature and therefore the reaction would usually take place at around this temperature. I also predict that at around 45°C, the reaction will slow down as the heat will begin to denature the enzyme.
As acid is being produced, there are general safety considerations to consider and goggles will be worn at all times when acid is present. Also, basic classroom rules will be followed, such as no running, to again ensure the complete safety of all present.
My reason for introducing steps to produce reliable evidence is simple: to be able to write an accurate and concise conclusion, all evident provided has to be reliable and accurate. Human error is unavoidable, but steps can be taken to reduce this as much as possible. I have chosen a pH probe as this is simply more accurate than humans and can do a more precise reading as it is computerised. I have also chosen now to use a temperature probe when checking the temperature of my water bath, as this is computerised and therefore would be expected to be more reliable than using a thermometer. This would also be quicker, as a thermometer would have to adapt from the rooms temperature before being able to reliably use it, whereas a probe would be immediately able to take an accurate temperature reading. Scientifically, I have based my prediction on my previous knowledge of digestive enzymes, which states that all enzymes have an optimum temperature at which to work. Too low, or too high, enzymes will not work or become denatured. This is also why I chose a range of temperatures. As human body temperature is around 37°C, I would expect that the lipase would work better around this, although as it is produced in the pancreas the temperature may vary.
My Results:
Results from my first attempt:
Results from my second attempt:
Results from my third attempt:
I will now collect averages of all my results and then will plot these results onto a graph. A trend should show. I will round my averages up so that they will be easier to read and more clear when plotted.
Table of Averages
Graph to show how the pH of a Lipase & Milk reaction is affected by temperature using how acidic the pH is as a guide
My graph shows me that Lipase worked better at 60°C. After only 30 seconds it had reduced the pH to just above 6, much more quickly than at the other temperatures. It had a final pH of just below 6.6, showing it to be the most acidic of all of the reactions. The lowest acidic reading was when I used a water bath of 20°C and therefore it would be safe to assume that lipase does not work well at lower temperatures.
This contradicts the prediction I earlier made. I expected that the optimum temperature would be around 37°C, and therefore expected the best results when I was using a water bath of 30°C and 40°C. This was clearly not the case and to have made a prediction more scientifically supported, I could have done research into the Pancreas, finding information about temperature and conditions. I would then have used this information in order to predict the results. If I were to do this experiment again, this is what I would do as I would have had more idea scientifically about what to expect.
I found I had no anomalous results and I believe this to be because I followed a strict procedure and was thoroughly conscientious at all times. I controlled variables accurately and checked and double checked readings. I used the same stopwatch throughout when timing and used all the same equipment, such as pH probes and temperature probes. I constantly monitored the temperature of my water baths, ensuring that they were always the exact and same temperature throughout each experiment.
To provide an even firmer conclusion, if I were to perform this experiment again I would do a number of things. I would firstly use more temperatures, for example not just 20, 30, 40, 50 & 60°C but 20, 25, 50, 35, 40, 45, 50, 55, 60°C. This would provide more information as more results are being obtained on which to base a conclusion. I would also research the conditions of the pancreas more thoroughly so that I could predict scientifically what would happen using better knowledge.
