Four students investigate the effect of caffeine on reaction time. Which procedure gives the most valid comparison?
Different students drink different volumes, use different hands and complete one test each.
Different students drink equal volumes, choose their own rulers and complete repeated tests once.
The same student drinks increasing volumes, rests equally and completes repeated tests at each volume.
The same student drinks equal volumes, changes the drop height and completes one test each time.
40 exam-style questions on AQA GCSE Biology 5.2 The human nervous system, covering 5.2.1 Structure and function, 5.2.2 The brain, 5.2.3 The eye, and 5.2.4 Control of body temperature. Each one has a worked solution and a mark scheme showing where the marks go.