A student tests gibberellin on seeds. Treated seeds are kept at 25∘C25^\circ\mathrm{C}25∘C and untreated seeds at 15∘C15^\circ\mathrm{C}15∘C. More treated seeds germinate.
Which change is needed to determine whether gibberellin caused the difference?
remove gibberellin from both groups and retain the temperature difference
keep both groups at different temperatures and increase the seed numbers
give both groups gibberellin and retain the original temperature difference
keep both groups at the same temperature and vary gibberellin treatment
105 exam-style questions on Edexcel GCSE Biology 6.3 Plant hormones, covering 6.3.1 Plant hormones and tropisms and 6.3.2 Commercial uses of plant hormones. Each one has a worked solution and a mark scheme showing where the marks go.