A seedling germinates in darkness while attached to a drum that rotates once every two minutes around a horizontal axis. This makes different sides of the root and shoot face downwards in turn.
The drum is stopped when the root and shoot are horizontal. After two hours, a scientist measures the auxin concentration and the mean increase in cell length in their growing regions.
| Organ | Side after the drum stops | Auxin concentration / arbitrary units | Mean increase in cell length / µm |
|---|---|---|---|
| root | upper | 2.1 | 46 |
| root | lower | 6.3 | 18 |
| shoot | upper | 2.1 | 27 |
| shoot | lower | 6.3 | 61 |
Use the data to explain why the root and shoot curve in opposite directions after the drum stops.
The scientist restarts the rotating drum. Explain how the new growth of the root and shoot will change after the drum is restarted.
105 exam-style questions on Edexcel GCSE Biology 6.3 Plant hormones, covering 6.3.1 Plant hormones and tropisms and 6.3.2 Commercial uses of plant hormones. Each one has a worked solution and a mark scheme showing where the marks go.