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Investigating the effects of temperature on the rate of clotting milk and Rennet

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GSCE Biology Coursework: Investigating the effects of temperature on the rate of clotting milk and Rennet Introduction The following experiment investigates the effects of different temperatures on a mixture of rennet and whole milk. On having the choice between testing the mixtures reactions at various temperatures, or testing the mixture with various amounts of concentration of rennet, my partner and I decided upon the first option. We made this decision as we felt it would be valuable to our scientific knowledge if we had a better understanding of how different temperatures can effect the behaviour of an enzyme, such as Rennin, which is also known as Chymosin. Our scientific knowledge tells us that enzymes work most efficiently at specific temperatures, and this experiment helps us to discover exactly which temperatures they are. It is important to remember that the Rennet was mixed with milk, which is perhaps one of the most important sources of nutrition in the world, and drunk by billions of people everyday. It is particularly important to babies and growing children. It provides: * Calcium, to build strong bones and teeth * Protein, to build and repair muscle tissue * Potassium, to help regulate our body's fluid balance * Vitamin A And many other useful vitamins and nutrients which help to maintain a healthy body. As wonderful a necessity that milk is, it is also an extremely perishable food. Milk is usually stored in the fridge, because it preserves better at a low temperature, but even so, once it has passed its sell by date, it is no longer suitable for consumption. Although the milk itself does not have a very long life, other foods and some dairy products can be made using it. Cheese would be the main example of this, which can be produced simply by the curdling of milk. Rennin, found in the substance rennet, is a milk-coagulating enzyme capable of assisting in the production of cheese. ...read more.


Another reason to be as quick as possible is that the stopwatch will continue to time the reaction, even whilst the tubes are removed from the bath. If the tubes are out of the bath for any reasonable length of time then the times we have recorded for the tubes being inside the bath would be incorrect. It is just as important that we are careful as well as quick. Rushing to check the mixtures could mean that some splashes out of the tube. As it was believed that there would be no or little reaction at certain temperatures, there has to be a limit as to how long their progress should be monitored. If there was no reaction occurring after fifteen minutes, then the stopwatch will be stopped and the test confirmed as to have given "no reaction". The pilot test itself proved to be quite successful and a good practice for the real thing. . There was a reaction for all of the mixtures maintained at thirty, forty, and fifty degrees Celsius. However no reaction occurred at room temperature, or at sixty degrees Celsius. It came as a surprise to me that there was such a good reaction at 30oC seeing as it was quite close to the room temperature of 24oC which had no reaction whatsoever. I did find it quite challenging to complete all of tests in the given time, and perhaps some of the times I recorded weren't as accurate as they could have been because there were several tests taking place at the same time in different water baths. For the main experiment, the water baths will be situated closer together so that it is easier to move from one to the other to check on the reactions. I know now that either my partner or myself must check all of the tubes at least every minute. If not then the milk in one tube may have clotted whilst we are attending to another, and the times that we record will be wrong. ...read more.


I was unsure before the experiment whether the two repeats would be enough to show exactly which results were correct and which ones may have been incorrect. There was no real need to worry about this as the curve for temperature against time shows that there are no particular results that stand out, they are all in a similar position. This is a good result because it shows that all the repeats took approximately the same amount of time to react and were therefore quite accurate. The curve for the rate of reaction also turned out quite well and showed a good positive correlation which is what I had hoped for. Using the graduated pipettes did make the measuring of the milk and rennet easier than just pouring into a measuring beaker. However, the difficult was squeezing all of its contents into the tube. The milk in particular would stick to the sides, and when the pipette was pinched at the top to try and force out the last drops, bubbles of air appeared, and the milk remained on the sides. There was no way of getting every last bit of the milk out of the pipette, but my partner and I tried our best to persevere for as long as we could just waiting for it to drip out on its own accord. Next time I need to use the graduated pipette, I'll practice beforehand and try to find a way of removing as much of the liquid as possible. My hypothesis turned out to be reasonably accurate, and in the main practical the milk clotted at the same temperatures as I predicted it would. I did think that there would be no reaction at 30oC because I assumed it would be too low a temperature. This was a correct prediction in as much as it matched the final results, but it did not match the results of the pilot test, which had a higher concentration of rennet. ...read more.

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