Practical questions
You will complete ten required practical activities if you are studying GCSE Biology and twenty-one if you are studying GCSE Combined Science. You could be asked questions about the methods, safety precautions you might take, results and conclusions of these experiments.
In this Plant Biology section there is one required practical activity:
Investigate the effect of light intensity on the rate of photosynthesis
Edexcel questions courtesy of Pearson Education Ltd.
Sample question 1 - Foundation
Question
A student investigates the effect of light intensity on photosynthesis. They set up the equipment shown in the diagram:
They place the lamp 10 cm from the test tube and record the number of bubbles produced in five minutes.
They then repeat the procedure with the lamp at a distance of 20 cm and 30 cm away from the test tube.
State three variables that should be kept constant during each repeat to improve the results. [3 marks]
- temperature of water (1 mark)
- start each experiment with the same amount of carbon dioxide (1 mark)
- start each experiment with the same amount of water (1 mark)
Sample question 2 - Foundation
Question
The student noticed that the temperature of water near the light increased.
Give one improvement they could make to reduce the effect of this increase in temperature. [1 mark]
Any one improvement from:
- use a lower energy/LED bulb (1 mark)
- use a heat shield (1 mark)
- place the test tube in a beaker of water (1 mark)
Sample question 3 - Higher
Question
A student investigated the effect of light intensity on the rate of photosynthesis of the aquatic Cabomba plant.
A lamp was used as a source of light. The lamp was placed at different distances (d) from the Cabomba plant, and the number of bubbles produced in 60 seconds was counted.
The number of bubbles produced in 60 seconds was used to calculate the rate of photosynthesis. The light intensity was then calculated using the inverse square law \( \frac {1}{d^2}\).
The table shows the student's results.
| Distance (\(d\)) of lamp from Cabomba (cm) | Light intensity (arbitrary units) | Bubbles produced in 60 seconds |
| 5 | 0.0400 | 79 |
| 10 | 0.0100 | 21 |
| 15 | 0.0044 | 12 |
| 20 | 0.0025 | 7 |
| 25 | 0.0016 | 5 |
| 30 | 0.0011 | 4 |
| Distance (\(d\)) of lamp from Cabomba (cm) | 5 |
|---|---|
| Light intensity (arbitrary units) | 0.0400 |
| Bubbles produced in 60 seconds | 79 |
| Distance (\(d\)) of lamp from Cabomba (cm) | 10 |
|---|---|
| Light intensity (arbitrary units) | 0.0100 |
| Bubbles produced in 60 seconds | 21 |
| Distance (\(d\)) of lamp from Cabomba (cm) | 15 |
|---|---|
| Light intensity (arbitrary units) | 0.0044 |
| Bubbles produced in 60 seconds | 12 |
| Distance (\(d\)) of lamp from Cabomba (cm) | 20 |
|---|---|
| Light intensity (arbitrary units) | 0.0025 |
| Bubbles produced in 60 seconds | 7 |
| Distance (\(d\)) of lamp from Cabomba (cm) | 25 |
|---|---|
| Light intensity (arbitrary units) | 0.0016 |
| Bubbles produced in 60 seconds | 5 |
| Distance (\(d\)) of lamp from Cabomba (cm) | 30 |
|---|---|
| Light intensity (arbitrary units) | 0.0011 |
| Bubbles produced in 60 seconds | 4 |
Use information from Question 1 to describe the effect of light intensity on the rate of photosynthesis. [2 marks]
An answer that combines points of interpretation/evaluation to provide a logical description:
- as light intensity decreases the rate of photosynthesis also decreases (1 mark)
- after 20 cm away when light intensity appears to have little effect on the rate of photosynthesis (1 mark)
Sample question 4 - Higher
Question
Explain what would happen to the levels of gas produced if the light intensity decreased to 0.0001 arbitrary units. [2 marks]
An explanation that combines identification via a judgement (1 mark) to reach a conclusion via justification/reasoning (1 mark):
- the volume of gas produced would decrease to below four bubbles (1 mark)
- because light is needed for photosynthesis (1 mark)