This can be done by adding 1cm³ sodium citrate solutions to the milk. If I want to increase the increase the concentration of calcium ions then I can simply add calcium chloride solution into the milk which shall provide me with the calcium ions.
In this investigation my independent variable will be the calcium ion, whose concentration I shall change.
The dependant variable will the rate of coagulation, or the time it takes for the flecks of
curd to appear. I shall keep the rennin solution constant, i.e., use the same volume of it each time.
Factors
Temperature; If the temperature is increased then the rate of reaction will also increase. At low temperatures, enzymes work slowly .Substrate molecules will not often collide with an active site and so binding between the substrate and the enzyme is a rare event.
The enzyme rennin is found in the stomach, where the likely temperature is 37°C. This means that this is the enzymes optimum temperature, so I shall set the hot water bath at 37°C throughout the experiment.(ref2)
PH level; Enzymes are specific in their optimal pH. Calcium chloride is likely to be a weak acid because of the chlorine molecule, in which case it can have an affect on the enzyme. Rennin is accustomed to working in extremely acidic conditions and to tamper with that may damage the enzymes active site temporarily or permanently resulting in it not working, so I shall have to maintain pH, as close to being acidic as possible.
During the conduction of this experiment I shall have to try and keep these factors the same.
Prediction
I predict that the higher the concentration of the calcium ions is the quicker the rate of coagulation of milk. This will happen because the more calcium ions there are, the higher the production of casein protein precipitation taking place at a time.
Method
The first step in this experiment is to add around 20cm³ milk to the test tubes using a syringe to each of the five test tubes.
I shall also have 5 different concentrations of sodium citrate solution to remove either all or some of the calcium ions that are present in the milk. A concentration of 2cm³ will remove all the calcium ions. Gradually I shall decrease the concentration of the solution each time.
Then I shall make 5 different concentrations of calcium chloride. Then I shall add one of these concentrations to the milk solution and label the concentration that I have added.
I shall then place the test tubes in a pre heated water bath which is set at 37°C in which the rennin solutions would have already been put in.
The next step is to work out the coagulation time.
As soon as the rennin solution has been poured into the milk I shall start the stop watch and record what I observe every 30 seconds.
Also I shall have with me microscope slides and dip them in to the sample of milk and stop the watch until the first sign of the flecks of the curds appear.
I shall then repeat this procedure for the rest of my calcium chloride concentrations.
Finally to a get a good idea, I shall plot a graph of concentration vs. coagulation time, and finding the gradient at different points, which is in effect the rate of reaction.
I shall work out the rate of coagulation by doing.
1 / Time taken.
This I what my table of results will look like, with time taken for coagulation on the side and the concentrations of calcium chloride on the side.
Precision and Reliability
In order to get the most accurate of results I shall have to perform the experiment with the highest precision and reliability.
For precision my measured values of calcium chloride and rennin solutions should be as close as possible to their actual values. The equipment that I will use for maximum precision are measuring cylinders, pipettes and rulers that measure to the nearest millimeter.
For reliability I shall repeat the experiment that I have conducted at least 6 times and use the average of the results.
Safety
As I will constantly be in contact with irritant chemicals, I shall have to handle them with the utmost caution and also remember to wash my hands thoroughly after direct contact.
I shall also be wearing safety goggles as rennin is a protein digesting enzyme, any contact with the eye can be extremely dangerous.
Sources
. (ref1)
(ref2)