Calcium ions effect on the rate of coagulation of milk
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Practical Examination 1 (Part A - Planning Exercise) Aim The aim of the experiment is to find out if the concentration of calcium ions has any effect on the rate of coagulation of milk. To do this I would vary the concentration of calcium ions and see how it affects coagulation. Prediction Rennin, also known as Chymosin, belongs to a family of enzymes called the aspartic proteinases (the reason that it belongs to this family is because it possesses an aspartic acid residue at the active site of the enzyme) and is a proteolytic enzyme synthesized by chief cells in the stomach. Its role in digestion is to curdle or coagulate milk in the stomach, a process of considerable importance in the very young animal. If milk were not coagulated, it would rapidly flow through the stomach and miss the opportunity for initial digestion of its proteins. Rennin efficiently converts liquid milk to a semisolid like cottage cheese, allowing it to be retained for longer periods in the stomach.
0.00 mol is made up 2cm3 of distilled water with no calcium chloride and would be my control, essential to prove that the reaction would not just happen normally. I would make up different concentrations of calcium chloride by adding water to each amount of calcium chloride (0.00mol would be just water, 0.20mol would combine 0.4cm3 calcium chloride with 1.6cm3 of water and so on with all the solutions) resulting in 6 levels of concentration. I would test each concentration 3 times. I would then take the first 6 test tubes and add 10cm3 of milk. To each of these I would add a solution of 1.0 mol dm-3 of sodium citrate in order to get rid of all calcium ions that are already present. I would then put all the test tubes in a water bath at 37?C to ensure a constant body temperature, before adding 1cm3 of rennin and the calcium chloride solutions. With a pipette, I would immediately put three drops of each concentration onto a slide and, observing under a microscope, log in the results table how long it takes for curd to start to appear.
Results/precision: Results would be measured in seconds to 2 decimal places, as this is fine enough to give an accurate result while being possible to measure. Results chart: Calcium Chloride concentration (mols) Sodium Citrate (cm3) Rennin (cm3) Milk (cm3) Time (s) 0.00 1.00 1.00 10.00 0.20 1.00 1.00 10.00 0.40 1.00 1.00 10.00 0.60 1.00 1.00 10.00 0.80 1.00 1.00 10.00 1.00 1.00 1.00 10.00 I would then plot these results onto a line graph so that I could more easily see if there was a relationship between the concentration of calcium chloride and time taken for flecks of curd to appear. Risk assessment: To conduct the experiment as safely as possible everyone involved would wear goggles at all times to avoid any irritant substance getting into anyone's eyes. In addition, all long hair must be tied back so not to get in the way, any spillages must be wiped up as soon as possible so that they are not later rubbed upon the skin, and any substance that dose make contact must be washed immediatelys.
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