Practical questions
You will complete 21 required practical activities if you are studying GCSE combined science: Trilogy. You could be asked questions about the apparatus, methods, safety precautions, results, analysis and evaluation of these experiments.
In this Organisation section, you need to have undertaken two required practical activities:
- Required Practical Activity 4 - Use qualitative reagents to test for a range of carbohydrates, lipids and proteins.
- Required Practical Activity 5 - Investigate the effect of pH on the rate of reaction of amylase enzyme.
There will be a number of different types of practical based questions. Some will be on the set required practicals, some will cover the working scientifically terms and some will be on other science practicals which you might have done in class. Use all the information given in the question particularly any diagrams to help you understand what the question is about.
These questions have been written by Bitesize consultants as suggestions to the types of questions that may appear in an exam paper.
Sample question 1 - Foundation
Question
A student is carrying out food tests.
Her results are shown below.
| Food | Observations with iodine solution | Observations with the biuret test | Observations with the Sudan III test |
| A | Blue-black coloration | Purple coloration | A red layer floating on the surface |
| B | Brown coloration | Blue coloration | No separate layer produced |
| C | Blue-black coloration | The food was coloured so no colour change could be observed | No separate layer produced |
| Food | A |
|---|---|
| Observations with iodine solution | Blue-black coloration |
| Observations with the biuret test | Purple coloration |
| Observations with the Sudan III test | A red layer floating on the surface |
| Food | B |
|---|---|
| Observations with iodine solution | Brown coloration |
| Observations with the biuret test | Blue coloration |
| Observations with the Sudan III test | No separate layer produced |
| Food | C |
|---|---|
| Observations with iodine solution | Blue-black coloration |
| Observations with the biuret test | The food was coloured so no colour change could be observed |
| Observations with the Sudan III test | No separate layer produced |
What conclusions can be drawn about the three foods, A, B and C?
[4 marks]
- A contains starch, protein and lipids [1]
- B does not contain any of these food molecules [1]
- C contains starch [1]
- no conclusion can be drawn about the presence of protein [1]
Sample question 2 - Foundation
Question
Describe how the effect of temperature on the effect of amylase could be investigated. [3 marks]
- add 0.5 cm3 of amylase solution to a test tube
- add 1 cm3 of distilled water to another test tube
- set up a spotting tile, with a drop of iodine solution in the wells corresponding to the measurements to be taken
- set up a series of water baths at different temperatures
- place the tubes in the different water baths and allow them to reach the required temperature
- add 2 cm3 of starch solution to each test tube and start timing
- remove a sample from the tubes immediately and add to the spotting tile to test for the presence of starch
- remove a sample every 30 seconds and test for starch
- record the time at which starch is no longer present for each tube
Do try to specify this level of detail in your answer, rather than be vague, for instance about the volume of enzyme, substrate and distilled water used.
In an exam, you would not be penalised if the method you described was slightly different - for instance, if the volumes and timings were different, provided that they were realistic.
Sample question 3 - Higher
Question
A student was investigating the effect of pH on the rate of an enzyme-controlled reaction.
The breakdown of a sample of lipid by an enzyme was monitored electronically.
The time taken for the lipid to be broken down at different pHs was recorded.
His results are shown below:
| pH | Time taken for breakdown of lipid in seconds | Rate of reaction |
| 4.5 | 31.25 | |
| 5.0 | 12.04 | |
| 6.0 | 7.94 | |
| 7.0 | 7.14 | |
| 8.0 | 9.09 | |
| 8.5 | 13.89 | |
| 9.0 | 35.71 |
| pH | 4.5 |
|---|---|
| Time taken for breakdown of lipid in seconds | 31.25 |
| Rate of reaction |
| pH | 5.0 |
|---|---|
| Time taken for breakdown of lipid in seconds | 12.04 |
| Rate of reaction |
| pH | 6.0 |
|---|---|
| Time taken for breakdown of lipid in seconds | 7.94 |
| Rate of reaction |
| pH | 7.0 |
|---|---|
| Time taken for breakdown of lipid in seconds | 7.14 |
| Rate of reaction |
| pH | 8.0 |
|---|---|
| Time taken for breakdown of lipid in seconds | 9.09 |
| Rate of reaction |
| pH | 8.5 |
|---|---|
| Time taken for breakdown of lipid in seconds | 13.89 |
| Rate of reaction |
| pH | 9.0 |
|---|---|
| Time taken for breakdown of lipid in seconds | 35.71 |
| Rate of reaction |
What is used to produce and maintain a particular pH? [1 mark]
A buffer
Question
Complete the table by calculating the rate of reaction. Write your answer to three decimal places. [2 marks]
Two marks for all calculations correct, or one mark for five or six correct.
| pH | Time taken for breakdown of lipid in seconds | Rate of reaction |
| 4.5 | 31.25 | 0.032 |
| 5.0 | 12.04 | 0.083 |
| 6.0 | 7.94 | 0.126 |
| 7.0 | 7.14 | 0.140 |
| 8.0 | 9.09 | 0.110 |
| 8.5 | 13.89 | 0.072 |
| 9.0 | 35.71 | 0.028 |
| pH | 4.5 |
|---|---|
| Time taken for breakdown of lipid in seconds | 31.25 |
| Rate of reaction | 0.032 |
| pH | 5.0 |
|---|---|
| Time taken for breakdown of lipid in seconds | 12.04 |
| Rate of reaction | 0.083 |
| pH | 6.0 |
|---|---|
| Time taken for breakdown of lipid in seconds | 7.94 |
| Rate of reaction | 0.126 |
| pH | 7.0 |
|---|---|
| Time taken for breakdown of lipid in seconds | 7.14 |
| Rate of reaction | 0.140 |
| pH | 8.0 |
|---|---|
| Time taken for breakdown of lipid in seconds | 9.09 |
| Rate of reaction | 0.110 |
| pH | 8.5 |
|---|---|
| Time taken for breakdown of lipid in seconds | 13.89 |
| Rate of reaction | 0.072 |
| pH | 9.0 |
|---|---|
| Time taken for breakdown of lipid in seconds | 35.71 |
| Rate of reaction | 0.028 |
Example calculation:
At a pH of 4.5:
\( \text{Rate of reaction} = \frac{1}{reaction~time} = \frac{1}{31.25} = {0.032}\)
Sample question 4 - Higher
Question
For the data in question 3, plot a graph of rate of reaction over pH.
Draw a line of best fit. [4 marks]
- axes and scales correct [1]
- all points plotted correctly [2] or two to three points plotted correctly [1]
- appropriate line of best fit [1]
You should have pH on the x-axis and rate of reaction on the y-axis. Your divisions on your scales should be regular. Your axes should be labelled and include units.
All points should be plotted accurately.
In this instance, it's clear that the line of best fit is a curve. Remember that a line of best fit could be linear, or it could be a curve.
