1.1. A student investigated the effect of different concentrations of auxin on the growth of root tips.

The student was provided with a stock solution of 1.0 mol dm^-3 auxin and distilled water.

Describe how the student could make 100 cm³ of a 1 × 10⁻² mol dm^-3 auxin solution using the stock solution and distilled water.

1.2. The student germinated identical seeds until the roots were a similar starting length, then placed the seedlings in Petri dishes containing filter paper soaked in solutions of different auxin concentration (including a 0 µM control).

She measured root length at the start and after 2 days, then calculated root growth rate in mm day^-1. The results are shown in Fig 8.

Fig. 8

Calculate the percentage decrease in the root growth between the roots that were exposed to an auxin concentration of 0.1 µM compared to those exposed to 0.01 µM.

1.3. State and explain the relationship between auxin concentration and root growth in Fig 8.