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Investigate the effect of bile salt concentration on the digestion of milk by the enzyme lipase.

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Biology Coursework Investigation into the effect of bile salt concentration on the digestion of milk by lipase Seham Akkad 13I Skill P - Planning Aim: Investigate the effect of bile salt concentration on the digestion of milk by the enzyme lipase. Background knowledge: Bile: In humans about 1000 cm3 of bile is produced each day. In the body, bile is synthesised in the liver, from cholesterol, by hepatocytes. The bile is then concentrated and stored in the gall bladder ready to be secreted into the bile ducts, travelling into the small intestine making the conditions alkaline. Bile salts have two main roles; emulsification of dietary lipids and transport of lipids in a water soluble environment. The emulsification of lipids involves breaking down the large fat globules into smaller droplets increasing the surface area to volume ratio, as well as allowing lipases to access the lipids inside the droplets. As bile salts are made from cholesterol, the are involved in the transport of lipids around the body in the form of micelles, were the hydrophilic areas point outwards and the hydrophobic areas point inwards encasing lipids such as triglycerides, and allowing them to be transported. Bile salts also allow the transport of lipid soluble vitamins in the bloodstream. http://arbl.cvmbs.colostate.edu/hbooks/pathphys/digestion/smallgut/absorb_lipids.html http://www.piercenet.com/media/Detergent-Micelle.gif Cholesterol in the bile interacts with the bile salts to form water soluble particles. If the bile contains too much cholesterol or not enough water, excess cholesterol can precipitate in the gall bladder forming gallstones. Bile pigments, such as bilirubin and biliverdin, have no known function, however, give bile its distinctive colour. Bile also contains hydrogencarbonate ions, which are alkaline and help neutralise the acidic chyme that has just come from the stomach. I will use sodium hydrogen carbonate instead of sodium carbonate to make the milk alkaline. The reason for this is I am trying to mimic the conditions found in the small intestine in the human body. ...read more.


The graph yielded had a good gradient, however, the amount of bile salts lowered the pH of the reactants too quickly and so this would have had a detrimental affect on the results gained from the experiment. In the fourth trial I decided to make the milk alkaline to pH 8.5, using the sodium hydrogen carbonate in a separate beaker instead of adding 10cm3 separately. This made the environment of the lipase completely constant and always at the same pH. I also increased the volume of lipase to see if the results would be any better. The graph was the best graph so far and had the best gradient. In the fifth trial I was trying to confirm if the fourth trial proportions were the best. I placed double the amount of bile salts as in the fourth trial, but kept the same amount of everything else. The drop in pH was too fast and the gradient was too steep. For the above reason I believe that the fourth trial held the best proportions of each reactant and so this had informed me of what to do in my method. Final Method: 1. Place a clean conical flask into the preheated water bath at 30�C. 2. Place a beaker in the preheated water bath. Measure out 100cm3 of milk using a measuring cylinder and pour in to the beaker. Place the calibrated pH probe into the beaker and monitor the pH. Using a measuring cylinder measure out some sodium hydrogen carbonate and pour it into the beaker. Monitor the change in pH. If the pH is now at 8.2, use a teat pipette to make the milk more alkaline to pH 8.5. When adding the sodium hydrogen carbonate, stir the solution three times clockwise using a stirring rod and leave to settle for 10 seconds before reading the pH. If the pH is slightly greater than 8.5 add some milk using a teat pipette until the pH of the milk is at 8.5. 3. ...read more.


This means that the data values for this are more precise. The box plot for 2% has a similar spread to 1% and so the values have a similar precision. Also the standard deviation and the inter quartile ranges' values are similar. The box plot for 3% has a much larger spread of the data and has a negative skew. This means the data is less precise than the previous two box plots; however the median was still not anomalous due to its position. Additionally, due to the lack of outliers the value of the inter quartile range was much larger than the standard deviation. The box plot for 4% had an inter quartile range that was 0.4, however as the data had a negative skew. This made the median lie in the wrong place and so the value was anomalous. The box plot for 5% has 0.6 inter quartile range and a positive skew. The large spread shows that the data is not very precise. However, the standard deviation is quite small in comparison as it takes into account all data values. The above comparisons of the standard deviation and the inter quartile range imply that the results are actually not precise or accurate due to the large spread in the data. Therefore, the results are not reliable and so only a limited valid conclusion can be drawn for the rate of reaction of lipase. The fact that the results seem to fit the scientific explanation and prediction graphs mean the some valid conclusion scan be drawn, such as that an increase in lipase activity is proportional to the bile salt concentration. However, to draw any more detailed conclusion, such as values for the rate of reaction, is not valid due to the lack of precise, reliable and accurate data that is as a result of the limitations of the method implemented. ?? ?? ?? ?? The effect of bile salt concentration on the digestion of milk by lipase Seham Akkad 13I Mr Hart & Ms Dennis Biology Coursework 1 ...read more.

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