A student compares horizontal seedlings kept in darkness with vertical seedlings illuminated from one side. The student concludes that any difference in bending is caused only by light.
Which change would make this conclusion more valid?
keep the lighting different and use different plant species
place both groups vertically and change only the lighting
place both groups horizontally and change their watering
keep the positions different and increase the group sizes
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.