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An experiment to investigate the effect of enzyme concentration on the rate of milk lipid digestion by lipase.

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Adam Hussein 6B1 28-12-02 An experiment to investigate the effect of enzyme concentration on the rate of milk lipid digestion by lipase. Biology Coursework Plan: Aim: This investigation aims to find out how enzyme concentration affects the rate of milk fat digestion by lipase enzyme. As a result of the experiment I aim to have quantitative results which I can then use to plot graphs illustrating the effect of lipase. Prediction: I predict that as the concentration of lipase enzyme increases, so to will the rate of reaction. The two will be directly proportional to each other up to the point where the substrate (milk fat) becomes rate limiting. This is the point where there are so many enzyme molecules and not enough substrate molecules for them to catalyse. The rate will therefore remain the same past this point as shown in the below graph. Variables: These are factors that will affect the reaction in some way. In order for the experiment to be successful in supplying reliably accurate results all variables must be kept constant apart from the enzyme concentration will be varied by known amounts to show the effect it has on the rate of lipid digestion by lipase. Below are the variables and explanations on how they will be kept constant in order to keep this experiment a fair test, and what affect them not being kept constant will have on the results. - Bile concentration: ==> What is it: Bile is an alkaline substance due to it containing sodium hydrogen carbonate. It is this that neutralises the stomach acid before entering the duodenum through a sphincter. It is very important because without it the enzymes secreted by the pancreas (in pancreatic juice) would be denatured by such extremes in pH. What assists the digestion of fat are the bile salts contained in bile. These help by emulsifying the large fat droplets into tiny droplets called micelles, thus increasing the surface area that the enzyme lipase has to work on therefore increasing the rate of reaction. ...read more.


This ensures that there is relatively the same surface area of lipid for the lipase molecules to catalyse in each test. This way, after the 2 minutes is finished the lipase will be added, which is when the stop clock is started again, and the colour of the solution is recorded every ten seconds for two minutes. However unexpectedly we found recording the colour change every ten seconds particularly difficult which was more than likely to have caused errors in our results. The colours would never quite match the scale and as the pH change is not massive i.e.; changing from very alkaline to very acidic, we need something more precise to measure the pH to the nearest 0.1. I have instead chosen to use a pH probe which will simply be put into the test tube immediately after the lipase has been added. The reading will then be recorded every ten seconds and plotted in a results table. During the experiment lipase was collected using a graduated pipette. It was simply taken out of the beaker then added to the test tube. This however did not take into account the fact that lipase settles at the bottom of the solution. This would mean that concentrations would have a varied leading to inaccurate results. Realising this, I have now decided to stir the lipase solution each time before removing a sample from the beaker. This will ensure we achieve a lipase concentration as close to our desired concentration as possible. After the bile was added to the solution of milk, universal indicator, and sodium carbonate it was just timed for two minutes before adding the lipase. The bile however may not have completely dispersed throughout the solution in some tests and may have in other tests. This will mean that the extent to which the large lipid droplets have been emulsified will differ in many of the tests therefore altering the surface area the lipase can work on. ...read more.


However, it is possible that even stirring the solutions would not results in a constant concentration throughout the solution. This would results in more or less enzymes, or bile salts in the reaction thus speeding or slowing down the rate. To overcome this problem, an electric mixer could be used to slowly and constantly mix all solutions throughout the experiments duration, so lipase for example will never settle at the bottom of the beaker. By having an electrical devise to do a job which was previously done by me, I would be able to spend more time on reducing other aspects of possible human error in the experiment. Lastly, the accuracy of my timing is also a factor which too must be considered to be a potential error causing inaccuracies in results. Readings from the pH probe should have been taken every 10 seconds, however they may in a lot of cases been taken at 9 seconds or 11 seconds, which is enough time difference for the pH to have changed, therefore making some of my results inaccurate. To overcome this problem of human error, data logging equipment could be used and by connecting it to the pH probe, it can automatically record exact readings at exact time intervals (smaller than every 10 seconds to get a clearer picture of the pH change), resulting in the problem of timing being completely ruled out. However data logging equipment is likely to not be available for the whole class to use, so a much smaller class would be needed. To conclude, I believe the experiment was carried out well and to the best of my ability. The results were not as good as predicted however still show the general trend I was hoping for. This experiment shows just how important enzyme concentration can be when breaking down lipids in the body. If too low, lipids will not be broken down fast enough, so it is essential it is kept just right in the body. ...read more.

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