A student counted the number of bubbles released by a piece of pondweed in one minute. The lamp was placed at different distances from the pondweed.
The student repeated the investigation three times.
The Table shows the results.
Table
| Distance from lamp in cm\text{cm}cm | Bubbles per minute (test 1) | Bubbles per minute (test 2) | Bubbles per minute (test 3) | Mean bubbles per minute |
|---|---|---|---|---|
| 10 | 42 | 40 | 44 | 42 |
| 20 | 25 | 23 | 24 | |
| 30 | 12 | 26 | 13 | 12.5 |
| 40 | 7 | 6 | 8 | 7 |
| 50 | 4 | 4 | 4 | 4 |
Calculate the mean number of bubbles per minute at 20 cm.
The student did not use one of the results at 30 cm to calculate the mean.
Identify this result and give a reason why it was not used.
Explain the effect of increasing the distance from the lamp on the rate of photosynthesis.
Counting bubbles is not an accurate way of measuring the volume of gas released.
Suggest one improvement to the method and give a reason for your answer.
87 exam-style questions on Edexcel GCSE Biology 6.1 Photosynthesis, covering 6.1.1 Photosynthetic organisms as producers, 6.1.2a Limiting factors on the rate of photosynthesis, 6.1.2b Interactions of limiting factors on photosynthesis, and 6.1.3 Inverse square law and light intensity. Each one has a worked solution and a mark scheme showing where the marks go.