Method
The apparatus needed was rennin, milk, two syringes, a water bath, test tubes and a stop clock.
First the water bath was set at 37° Celsius because this is body temperature and rennin works best at this temperature. 2cm³ of milk was put into a test tube and 0.1 millilitres of rennin was put into another test tube. The two test tubes were put in to the water bath and left to acclimatize for two minutes and this was timed by a stop clock. After the two minutes the stop clock was reset and the milk was added to the rennin and the stop clock was started again. When the milk had clotted the stop clock was stopped and the reading was converted to seconds and recorded in a result table.
The method was then repeated with 0.2ml, 0.3ml, 0.4ml and 0.5ml of rennin. Each amount of rennin was tested three different times to make sure that the result was correct.
water water
bath 37
rennin milk stop clock
Stephanie Thorpe 10c
To make the experiment a fair test a clean test tube was always used each time so that there was no contamination of the rennin with the milk, clotted milk or some extra rennin.
Also the same temperature was maintained throughout the experiment, which was 37° Celsius. This temperature was chosen because it is body temperature and rennin works fastest and best at this temperature.
Before the experiment was carried out, some preliminary practical work had to be carried out to see approximately how long the rennin took to clot the milk so that I could decide what amounts of rennin to use.
To do the preliminary work I put 0.1 ml of rennin into a test tube and added 2cm³ of milk. It took 340 seconds for the milk to clot and it seemed a reasonable time so the I put 0.5 ml of rennin into a test tube with 2cm³ of milk to see how fast the differences were and to determine whether I should increase the amount of rennin in gaps of 0.1mls or in 0.2mls. It took 65 seconds for the milk to clot with 0.5ml of rennin added to it so I decided to leave a gap of 0.1 ml between each amount of rennin added.
Results
Conclusion
I predicted that if the amount of rennin used on 2cm³ of milk were increased then it would take less time for the milk to clot. My results showed that this prediction was correct because the result for 0.1ml of rennin was two hundred and seventy seconds slower than it was for 0.5ml. On the graph of the results the curve is quite steep from 0.1ml to 0.2 ml and then it evens out a bit and it almost straight between 0.2 ml and 0.4 ml, then between 0.4 ml and 0.5 ml it drops again but not as significantly as at the start of the graph.
I found out from the experiment that the amount of rennin used alters the speed at which milk clots and if there is more rennin it will take a shorter time.
Evaluation
I had a few problems actually getting the rennin to clot the milk at first because it just stayed liquid for ages so then I poured a fresh one and put it in a different water bath and it clotted, so I took all the results from that water bath.
I didn’t really have any anomalous results except that the result for 0.1ml of rennin was quite far apart from the ones for 0.2, 0.3 and 0.4, which were quite close together, and the result for 0.5ml was further away as well. I think that the reason for this may have been because the amounts I was investigating were well spaced out so the results were not really close enough to become out of order and maybe if I had investigated the amount rennin every 0.05mls then some of them may not have been quite in-keeping with the rest.
To improve the experiment I could investigate a wider range of quantities of rennin perhaps from 0.1ml up to 1ml or further so that I could see if the time taken for the milk to clot actually went down after a while. I could also do a more detailed experiment, for example, leaving gaps of 0.05mls between each amount of rennin.
To support my conclusion I could test the different amounts of rennin while the experiment was set up at the pH value of the stomach, which is about pH 2, to improve the speed that was taken for the milk to clot.