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A2 coursework- The effects of bile salts on digestion of fat

Extracts from this document...


How effective are bile salts in aiding the digestion of fats by Lipase. Preliminary work Aim: To investigate which food stuff (milk, cream and egg) works best with the enzyme lipase. In order to investigate this I will test pH with a pH probe after 2 minute intervals for 30 minutes. Bile salts act as detergents and emulsify fats in the small intestine making it easier for them to be digested by lipase and to be absorbed into the lymphatic capillaries in the villi. In my preliminary work I will be provided with the following food stuffs to test: * Egg: consists of 11.2g/1000ml of fats; 3.2g of which saturated. * Cream: consists of 18g/1000ml monounsaturated; 0.5g/1000ml polyunsaturated * Milk: 4.0g/1000ml of fats; 2.5g/1000ml unsaturated Prediction From looking at the above fat contents for each of the food stuffs, I predict that the pH will decrease the most for cream as it contains the most amount of fat. So there will be more fatty acids and glycerol produced when cream is firstly emulsified by bile salts and then broken down by Lipase as the concentration of Hydrogen ions (H+) will increase and so lower the pH of the solution. Apparatus The following apparatus needs to be collected to conduct the method. * 3 boiling tubes- boiling tubes will be used instead of test tubes because they have a bigger surface area. * Boiling tube rack- boiling tube rack help to keep the experiment organized, as they hold the tubes throughout the experiment. * pH testing equipment- to test the pH of the solutions after every 2 minutes. The pH probe will record by 2 decimal places to ensure precision. * 5 10ml measuring cylinders- 10ml measuring cylinders are used instead of 50ml measuring cylinders because a smaller scale ensures greater precision * Pipette- to transport substances safely so at a lower risk of becoming contaminated. * 6ml of Lipase- 2ml of lipase will be added to each of the 3 different food stuffs. ...read more.


Care should be taken when handling the solutions so that contamination doesn't occur as this could affect the results obtained. Lab coats and goggles should be worn at all times to protect clothing from the equipment and vice versa and to protect eyes. If contact of solution with eyes does occur then eyes should be rinsed out with water and medical attention seeked if necessary. Equipment: Below is a table of the equipment used in my experiment. Quantity Apparatus/ solution name Reason for use 30ml Lipase (concentration 100%) Enzyme contains active sites to form enzyme-substrate complexes with substrate (fat) 30ml Bile (concentration 100%) Used to emulsify fats to create a increased surface area for the lipase to act on 30ml Na2CO3 (0.2 mol) Used to dilute the bile salts down so that I can test different concentrations of bile salts 30ml Cream Contains the fat to be broken so a pH reading can be obtained 5 Boiling tubes To hold the solutions instead of test tubes as they have increased surface area. 30 are needed for repeats 3 Boiling tube rack To hold boiling tubes in the water bath in a organized way 1 Water bath To maintain temperature of 40 degrees as this is approximately optimum temperature for lipase to work at. Enzyme activity is dependent on temperature so it needs to be kept constant. 5 Stopwatch To measure 2 minutes intervals. 5 are needed to time 5 different concentrations of bile salt placed in the water bath at once 1 Thermometer To check water bath temperature, so it is maintained at 40degrees 1 pH probe To read pH reading of solution. It is the most accurate available way to measure pH to me. It records pH readings to 2 decimal places making readings more accurate. 3 Small beaker 3 needed for lipase, bile salts and Na2CO3. it is easier to measure out of small beakers than a bottle. ...read more.


There were limitations in my experiment that were that everyone had to make up their own solutions and so everyone's solutions may have slight changes in concentration of bile salt actually contained and so people could receive different pH results due to this. Another limitation was that there were only 2 water baths for the class to use and so sometimes it was hard to get to the water bath after every 2 minute intervals exactly as there were other people in the way and so this could mean that the pH was not recorded at exactly 2 minute intervals. Another limitation in this experiment was that due to time limitation I had to measure the pH of 5 different concentrations within 30 minutes and so it was impossible to measure the time of the reaction to the nearest 0.1 second after 2 minute intervals as it was such a tight time gap to measure the pH for 5 different concentrations even though the stopwatch showed the measurements to the nearest 0.01 second. Even though there are possible improvements to the investigation I think that the results I obtained were significant enough to use to investigate my aim as I was able to draw up graphs and compare trends to prove my prediction correct that at when a higher concentration of bile salt is used then there is a bigger decrease in pH. So my anomalous results were not that significant enough that I was unable to draw up conclusions. Even though the anomalous results can be seen on my graph they are not a great distance away from the best fit line and so this shows the experiment worked well. Appendix 1 Calculating rate of reactions: For the first 4 minutes of the averaged pH recordings of the different concentrations I have calculated the rate of reaction as I think this will help me to investigate my aim. Below are my results: Concentration of bile salt Working out Rate of reaction (s-1) 0.00% 0.22/4=0.055x60= 3.35 0.25% 0.25/4=0.0625x60= 3.75 0.50% 0.27/4=0.0675x60= 4.05 0.75% 0.80/4=0.2x60= 12.05 100.00% 0.82/4=0.205x60= 12. ...read more.

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