By Julie-Anne Miskelly
Variables
Controlled variables are the variables, which should be kept constant to ensure a fair test.
Controlled variables are: - The same temperature (37oC)
The same amount of time taken (10mins)
The same volume of lipase
The same volume of milk
The same volume of sodium carbonate
The same variety of milk
The same equipment used
From my preliminary experiment I found that these controlled variables worked well and feel that I should use the same controlled variables in this experiment.
Independent variable is the variable you change in the experiment.
Independent variable is: - The concentration of bile salts. The concentrations of bile salts I will use will be 0%, 1%, 2%, 3%, 4% and 5%.
I decided to pick these as I wanted a wide range of concentrations of bile salts to see what effect the concentrations will have on the rate of reaction.
Dependant variable is the variable you measure in the experiment.
Dependant variable is: - The pH of the mixture
Prediction
I predict that as the concentration of bile salts increases, also the rate of reaction will increase the activity of lipase in the solution. This will in turn make the amount of fats emulsified into smaller droplets increase. Therefore a larger surface area for the enzyme lipase to break down the triglycerides to fatty acids and glycerol. This is because the more surface area the more active sites for the substrate concentration to get to for the enzyme-substrate complex to take place. Therefore the reaction will take place quicker as there is more enzyme –substrate complex taking place.
Preliminary Experiment
I carried out a preliminary experiment, firstly to see what variables I will use and change and also to get to grips with the equipment that I will use in the actual experiment.
In the preliminary experiment the method was:-
- Collect apparatus and set up apparatus.
Wash some apparatus used if appropriate with water and then with distilled water.
- Put the following into four different beakers, mark each one clearly :
1. Milk with bile 2.Milk without bile
20cm3 of milk 20cm3 of milk
10cm3 of sodium carbonate 10cm3 of sodium carbonate
5cm3 of bile salts 5cm3 of distilled water
3. Cream with bile 4. Cream without bile
20cm3 of cream 20cm3 of cream
10cm3 of sodium carbonate 10cm3 of sodium carbonate
5cm3 of bile salts 5cm3 of distilled water
- Place the four beakers, in the water bath, which is set at 37oC. Allow five minutes for temperature equilibration.
- Start recording the pH by using pH probes linked to the laptop via analogue to digital converter and immediately add 5cm3 of lipase solution, into each beaker. Record the pH change by printing off the data.
From carrying out my preliminary experiment I have gained appropriate knowledge and skill of how to use the apparatus correctly. I am going to use milk in my actual experiment instead of cream because milk is a lot cheaper. I am going to stir each solution every 30 seconds in the actual experiment to mix it up more so that it doesn’t settle. Also I will take the measurements of the solutions in the syringes to the bottom of the meniscs level. Overall this will make my results more precise.
Results
The results will be recorded initially by using a tabular format. (see below)
Using the information obtained from above, the results will also be displayed in graphical format. (see below)
pH
Time (mins)
Apparatus
- Water Bath (set at 37oC)
- 100cm3 Beaker *
- 20cm3 plastic syringe *
- 10cm3 plastic syringe *
- 5cm3 plastic syringe *
- full fat milk
- Lipase solution 5%
- Sodium carbonate solution 0.1mol dm
- Stock solution of 5% bile salts
- Distilled water
- pH probe *
- Datalogger
- Laptop
* means wash with water and then distilled water.
Drawing of apparatus
Safety
During the course of the experiment it is imperative that the following safety checks are carried out.
- Standard laboratory safety rules must be observed.
- Take care when working with mains voltage – equipment (laptops etc..) near to water and other aqueous solutions.
METHOD
- Collect all apparatus listed. Set up apparatus as shown in diagram.
- Wash all apparatus stared (*) with water and then distilled water.
- Put 20cm3 of full milk into two beakers, followed by 10cm3 of sodium carbonate solution in each beaker.
- Then for the first concentration of bile salts which is 0% put 5cm3 of distilled water (see page for the other concentrations measurements)
- Place the two beakers in the water bath, which is set at 37oC. Allow 5 minutes for temperature equilibration.
- Start recording the pH by using pH probes linked to the laptop via analogue to digital converter and immediately add 5cm3 of lipase solution, into each beaker. Stir the solution every 30 seconds. Record the pH change by printing off the data.
- Repeat the process for 1%, 2%, 3%, 4% and 5% of bile salts, using fresh mixtures of milk, sodium carbonate (as detailed for the experiment of 0% of bile salts.) To each repeat, add the enzyme lipase as you immediately start recording the pH.
Concentration of bile salts
Each beaker will contain for the different concentrations:-
For 0% of Bile = 20 cm3 of milk
= 10cm3 of sodium carbonate solution
= 5 cm3 of distilled water
= 5 cm3 of lipase
For 1% of Bile = 20 cm3 of milk
= 10cm3 of sodium carbonate solution
= 4 cm3 of distilled water
= 1 cm3 of bile salts
= 5 cm3 of lipase
For 2% of Bile = 20 cm3 of milk
= 10cm3 of sodium carbonate solution
= 3 cm3 of distilled water
