Although plants have no immune systems, they do have many chemical and physical methods of defence against pathogens and attacks by insects.
White clover (Trifolium repens) reproduces asexually from a runner that grows along the soil surface. The connected new plants are called ramets. The white clover plant in the diagram below is producing ramets in the direction left to right. The fully grown ramets are numbered 1 to 7, from the youngest ramet to the oldest ramet.
Scientists hypothesised that when T. repens ramets are damaged by caterpillars of Spodoptera exigua, the damaged ramets stimulate other ramets to defend themselves against attack by the caterpillars. The scientists conducted an experiment to test their hypothesis. The experiment used two genetically identical runners, A and B. The method is outlined in the flow chart below.
What was the role of the Runner A ramets?
(1 mark)The experiment was repeated 40 times. The average results obtained after Stage 2 are shown in the graph below.
After the experiments, the contents of the leaves were analysed. Significantly higher quantities of phenolic acid were found in the young ramets from Runner B. Phenolic acid acts as a signalling molecule.
It was noticed that the caterpillars preferred to eat the mature leaves in Runner B.
Suggest an effect of the signalling molecule on the cells of the young leaves that would account for the caterpillars’ preference for eating the mature leaves in Runner B
(1 mark)