7 (a) Gibberellin is involved in the germination of barley seeds. In an investigation, aleurone layers from barley seeds were extracted. One sample was treated with gibberellin and the other sample was given no gibberellin treatment. The rate of production of amylase enzyme by the aleurone layers was measured over 15 hours. The results are shown in Fig. 7.1. [Figure 7.1] Describe the results shown in Fig. 7.1. (b) Explain why the aleurone layers of barley seeds need to produce amylase during germination. (c) The height of some plants is partly controlled by their genes. Height in pea plants is affected by a gene with two alleles. The dominant allele results in the production of active gibberellin, which stimulates stem elongation. (c)(i) State the symbol that represents the dominant allele. (c)(ii) Explain how this dominant allele results in the production of active gibberellin. (c)(iii) Active gibberellin stimulates stem elongation by causing the breakdown of DELLA protein repressors so that growth genes can be expressed. Suggest the effects of the expression of these growth genes.