18 5 Wollemia is an endangered Australian tree. Catherine is studying the effect of light level on the chlorophyll concentration in the leaves of wollemia seedlings. Catherine planted six wollemia seedlings in her laboratory. She ensured that the seedlings were all of the same age and received the same amounts of water and food during the experiment. Catherine planted half of the seedlings in soil with a pH of 4.5 and the other half in soil with a pH of 6.5 For each soil pH level, one of the seedlings was exposed to a low light level, one to a medium light level and one to a high light level. Allocations to growing conditions were made at random. After 24 months, Catherine took pieces of leaf from seedlings subjected to each combination of light level and soil pH. She measured the chlorophyll concentration in the leaves in micrograms per square centimetre (μg/cm2). Catherine’s results are shown in Figure 5. Light level Low Medium High Row sums Soil pH 4.5 40.5 40.2 49.5 130.2 6.5 25.9 26.3 32.2 84.4 Column sums 66.4 66.5 81.7 214.6 Figure 5 (Data source: https://dx.doi.org/10.1093/aobpla/plu011) (a) Name the type of experimental design used by Catherine. (1) _____________________________________________________________________________________ _____________________________________________________________________________________ _____________________________________________________________________________________ _____________________________________________________________________________________ _____________________________________________________________________________________ _____________________________________________________________________________________ _____________________________________________________________________________________ _____________________________________________________________________________________ _____________________________________________________________________________________