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OCR AS Biology Planning Exercise 2008

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OCR Biology Planning Exercise 2008 The effect of the Concentration of Calcium ions on the Coagulation of Milk Aim/Problem The aim of this project is to investigate the correlation between the amount of calcium ions in an amount of milk and amount of time it takes for the milk to coagulate. Hypothesis I think that the more calcium ions there are in the milk, the faster the milk will coagulate. Also, I think that milk with no calcium ions in will not coagulate at all. The purpose of milk coagulating is so that when milk is drunk by infant mammals it can coagulate in the stomach so that it is there long enough to be digested. Rennin is a protein-digesting enzyme that curdles milk.[1] Rennin affects milk by breaking peptide bonds. Once these peptide bonds between hydrophobic and hydrophilic groups in the milk are broken, the hydrophobic group would unite together and would form a 3D network to trap the aqueous phase of the milk. The resultant product is calcium phosphocaseinate. [2] Therefore, I think that when there are fewer calcium ions in the milk, the reaction that produces calcium phosphocaseinate (which appears as coagulation) ...read more.


* You will be using glass beakers which could be smashed, so you should be careful not to cut yourself on shards of glass if this happens. Apparatus * Rennin solution * Milk * Sodium citrate * 1.0 mol dm-3 calcium chloride solution * Microscope (and lamp, if necessary) * 5cm3 syringe (for measuring out milk, calcium chloride and water) * 1cm3 syringe (for measuring out sodium citrate and rennin solution) * Boiling tube * Slide and cover slip * Pipette * Electronic stopwatch Method 1. Ensure that your work area is clean and safe 2. Measure out 10cm3 of milk with a syringe and put it into a boiling tube 3. Add 1cm3 of sodium citrate solution to get rid of any calcium ions already present in the milk 4. Next, measure out the correct amounts of water and calcium chloride using the table below to make a solution using different 5cm3 syringes. Concentration Amount of Water (cm3) Amount of Calcium chloride (cm3) 0M 5 0 0.2M 4 1 0.4M 3 2 0.6M 2 3 0.8M 1 4 1M 0 5 5. Add this solution to the milk 6. ...read more.


stopwatch) as these are more accurate. Although, the stopwatch could be a problem as it is impossible to add the rennin and start the stopwatch at the same time which could cause a slight delay and make the results out by a second or two. The fact that human judgment is used to tell when the coagulation starts could be a problem as people have different ideas about when the coagulation has started. A device such as a colorimeter could be used instead as this would give an accurate measurement that everyone could keep to and no room for human error at this stage would be left. I think that the experiment is definitely valid as it shows exactly what has been asked (a comparison between concentration of calcium ions and time of coagulation) and the data can be shown in many ways (e.g. a graph or a table). To make the results reliable you could repeat the experiment more than twice. Overall however, I think my experiment is reliable enough and quite fair. There are variables beyond our control, of course (such as air temperature or pressure) which could affect the rate of coagulation, and the experiment would have to be carried out in a sealed environment such as a laboratory to rectify this. ...read more.

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