Biology 9700/31 — October/November 2014
Cambridge AS Level · Advanced Practical Skills · worked solutions for every part, with the mark scheme
Topics Analysis, Conclusions and Evaluation · Presentation of Data and Observations · Manipulation, Measurement and Observation · Use of the Light Microscope
An enzyme, E, catalyses the hydrolysis (breakdown) of triglycerides into fatty acids and glycerol.
The substrate for E will be the triglycerides present in milk, labelled M.
The end-point of this hydrolysis can be determined by using an indicator, I, which changes colour when the fatty acids are produced, as shown in Fig. 1.1.
You are required to:
- prepare different concentrations of the enzyme solution, E
- investigate the effect of different concentrations of E (independent variable) on the hydrolysis of triglycerides in milk.
You are provided with:
| labelled | contents | hazard | volume / |
|---|---|---|---|
| M | milk | none | 40 |
| W | distilled water | none | 50 |
| I | indicator solution | stains | 30 |
| A | solution of alkali | irritant | 40 |
| E | 5% enzyme solution | irritant | 50 |
You are required to dilute the 5% enzyme solution, E, to provide a range of known concentrations using simple dilution.
Decide on the further concentrations of enzyme solution you will use in your investigation in addition to the 5% solution.
You will need to use of each enzyme solution.
Prepare the space below to show:
- the concentration of each enzyme solution
- the volumes of E
- the volumes of W.
Describe the expected trend in the time taken to reach the end-point as the concentration of enzyme solution increases.
State one reason for the expected trend described in (a)(ii).
As part of this investigation you are required to set up a control using the apparatus provided.
Describe how you will set up this control.
Read step 1 to step 10 before proceeding.
Proceed as follows:
- Prepare all the concentrations of enzyme solutions you have listed in (a)(i) in the containers provided.
You are required to investigate the effect of different concentrations of enzyme solutions on the hydrolysis of triglycerides in milk. The appearance of fatty acids can be detected by using the indicator solution I.
- Put of M into each of six separate test-tubes.
- Put of I into each test-tube containing M and gently shake.
- Put of A into each test-tube containing M and I and gently shake so that all the mixture turns orange.
Note that the mixtures might be different shades of orange.
The reaction will start as soon as you add enzyme solution, so read steps 5 to 10 before proceeding.
- Set up your control as described in (a)(iv).
- Put of the lowest concentration of enzyme solution into one of the test-tubes from step 4 and mix well.
- Repeat step 6 with two other concentrations of enzyme solution.
- Start timing.
- Record the time when each end-point (yellow) is reached, as shown in Fig. 1.1.
- Repeat steps 6, 8 and 9 with the remaining concentrations of enzyme solution.
If the time taken to reach the end-point for any one concentration is longer than 300 seconds (5 minutes) record as 'more than 300'.
Prepare the space below to record your results.
Calculate the rate of hydrolysis for the 5% E.
rate = ______
Identify one significant source of error in measuring the dependent variable in the investigation you have just carried out.
You used a syringe to measure the volumes of M.
State the volume of the smallest division on the syringe ______
State the actual error of the syringe.
actual error = ______
Suggest how you would modify this investigation to obtain an accurate optimum temperature for the activity of E.
The rest of this paper
1 more questions- Q2Use of the Light Microscope · Presentation of Data and Observations · Analysis, Conclusions and Evaluation23M