A scientist germinated seedlings in darkness. At the start of the investigation, the roots and shoots were horizontal.
Half of the seedlings remained stationary. The other half were placed on a clinostat that rotated slowly about a horizontal axis.
The table shows the mean results after 48 hours.
| Treatment | Increase in shoot length in mm | Angle the shoot bent upwards in degrees | Increase in root length in mm | Angle the root bent downwards in degrees |
|---|---|---|---|---|
| Stationary | 18 | 74 | 14 | 69 |
| Rotating | 19 | 3 | 15 | 2 |
A student concluded, ‘The seedlings on the clinostat grew straight because rotation prevented auxin from being made in their tips.’
Evaluate the student's explanation.
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.