Some students investigated phototropism in oat coleoptiles using two different setups over 48 hours. In both setups, a single directional light source was positioned to the right of the plants:
The results of the angle of curvature towards the light source (measured in degrees, where 0∘ 0^\circ\,0∘ represents straight vertical growth) are shown in the table below:
| Coleoptile number | Setup A (Stationary) angle of curvature (∘^\circ∘) | Setup B (Rotating) angle of curvature (∘^\circ∘) |
|---|---|---|
| 1 | 24 | 2 |
| 2 | 26 | 1 |
| 3 | 8 | 3 |
| 4 | 28 | 0 |
| 5 | 25 | 2 |
Explain how the rotating clinostat in Setup B acts as a control.
Identify the anomalous coleoptile in Setup A and suggest why including its measurement in the mean calculation reduces the validity of the results.
Calculate a more valid mean angle of curvature for the coleoptiles in Setup A by omitting the anomalous result. Give your answer to 1 decimal place.
59 exam-style questions on AQA GCSE Biology 5.4 Plant hormones, covering 5.4.1 Control and coordination and 5.4.2 Use of plant hormones (HT only). Each one has a worked solution and a mark scheme showing where the marks go.