Some students investigate the effect of the plant growth regulator indole-3-acetic acid (IAA) on the root elongation of radish seedlings. One petri dish contains a buffer solution, which acts as a control, while another contains a test solution of 1.0 × 10-4 mol dm-3 IAA dissolved in the same buffer. After 3 days, the students measure the root lengths of the seedlings.
The mean root lengths recorded are shown in the table below:
| Treatment | Mean root length (mm) |
|---|---|
| Test solution (IAA) | 9.8 |
| Buffer control | 15.6 |
Explain the purpose of using the buffer control instead of the IAA test solution.
Calculate the percentage change in mean root length in the test solution compared with the buffer control. Give your answer to 2 significant figures.
