A scientist investigated the effect of a directional light stimulus on the distribution of IAA in plants - AQA - A-Level Biology - Question 6 - 2021 - Paper 1

To compare the IAA concentration in shoots from two different plant species using the given method, follow these steps:

1. Sample Preparation: Ensure shoots from both plant species are of equal size and age to minimize variability caused by growth conditions. Cut the shoots using a standardized method, as indicated in Figure 2.

2. Use of Controls: Establish control samples alongside experimental ones to account for any external factors that might affect IAA concentration. Keep the environmental conditions constant for both sets, such as light intensity, temperature, and humidity.

3. Calibration Process: Utilize the calibration curve depicted in Figure 3 to establish IAA concentrations accurately. This necessitates measuring the degree of curvature in the biosassy and correlating it with the concentration of IAA.

4. Consistent Measurement Techniques: Apply the same measurement approach for both plant species when determining curvature to ensure comparability of results. Any differences in measurement techniques can lead to biased data.

5. Replications: Perform multiple replicates for both species to ensure that the results are consistent and statistically significant.

By following these steps diligently, the comparison of IAA concentrations in shoots from two different plant species will be valid.