A student investigated the effect of indole-3-acetic acid (IAA) concentration on the growth of root and hypocotyl segments in cucumber seedlings (Cucumis sativus). The student applied different concentrations of IAA to isolated root and hypocotyl segments and measured the percentage stimulation (+++) or inhibition (−-−) of growth compared to a control (0%).
The results are shown in the graph below:
Use the graph to estimate the IAA concentration at which inhibition of growth in root segments is 100%.
State what the student could do to determine whether a suspected anomalous result at 10−8 mol dm−310^{-8}\text{ mol dm}^{-3}10−8 mol dm−3 for root segments is indeed anomalous.
Compare the effects of different IAA concentrations on the growth of root and hypocotyl segments, citing specific concentrations from the graph.
Another researcher plans to investigate the effect of indole-3-butyric acid (IBA) concentration on the rate of adventitious root elongation in willow cuttings (Salix alba).
Suggest appropriate units for the rate of adventitious root elongation.
State two standard environmental variables that must be controlled in this investigation.
