An experiment was conducted to test the following two hypotheses about the effect of the plant growth regulator indoleacetic acid (IAA): - Hypothesis 1 - Low concentrations of IAA stimulate root growth and have no effect on shoot growth - VCE - SSCE Biology - Question 15 - 2016 - Paper 1

Based on the data presented in the table, we can analyze the effects of varying concentrations of IAA on shoot and root growth:

1. Analysis of Hypothesis 1:

   • Hypothesis 1 states that low concentrations of IAA stimulate root growth and have no effect on shoot growth. The data shows that at 0.00001 parts per million, there is a slight stimulation of shoot growth (+10%), but root growth is negatively impacted (–30%). At 0.0001 parts per million, shoot growth is neutral (+0%), while root growth is again negatively impacted (–50%). As concentrations increase, both shoot and root growth are inhibited. Thus, Hypothesis 1 is either unsupported or at best very weakly supported.

2. Analysis of Hypothesis 2:

   • Hypothesis 2 claims that concentrations of IAA above 0.01 parts per million stimulate shoot growth but inhibit root growth. However, the data indicates that at 0.01 parts per million, shoot growth is inhibited (–60%) and root growth is also inhibited (–100%). At concentrations of 0.1 and 100 parts per million, both shoot and root growth continue to be inhibited. Therefore, Hypothesis 2 is also unsupported.

3. Conclusion: Given that neither hypothesis is supported by the experimental results, the reasonable conclusion is option D: Hypotheses 1 and 2 are not both supported.