A group of students investigated the effect of indole-3-acetic acid (IAA), a plant growth hormone, on the elongation of decapitated Avena (oat) coleoptile segments. One group of coleoptile segments was incubated in a control solution of distilled water, while another group was incubated in a test solution of IAA.
After 24 hours, the mean length of the coleoptile segments in each treatment was measured. The results are shown in the table below:
| Treatment | Mean coleoptile segment length (mm) |
|---|---|
| Test solution (IAA) | 22.1 |
| Distilled water control | 15.4 |
Explain the purpose of incubating a group of coleoptile segments in distilled water instead of the IAA solution.
Calculate the percentage change in the mean length of the coleoptile segments in the IAA test solution compared with the distilled water control. Give your answer to 2 significant figures.
