A scientist investigated how light and gravity affect the growth of radish roots.
Each newly germinated seedling was fixed with its root initially pointing horizontally. Some dishes were kept stationary and others were placed on a clinostat. The clinostat slowly rotated each dish so that gravity acted evenly on all sides of the seedlings.
In the light treatments, a lamp was attached to the apparatus above the roots. For a dish on the clinostat, the lamp rotated with the dish so that the light remained on the same side of the seedlings.
After 24 hours, the scientist calculated the mean angle through which the roots had bent downwards from their original horizontal direction.
| Treatment | Mean angle bent downwards in degrees |
|---|---|
| Stationary, in darkness | 46 |
| On clinostat, in darkness | 2 |
| Stationary, with light from above | 71 |
| On clinostat, with light from above | 29 |
Describe what the results show about the effects of light and gravity on the growth of the roots.
The scientist placed another dish on the clinostat but attached the lamp below the roots.
Describe how the roots should grow and explain why.
87 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.