An environmental scientist conducted a laboratory experiment to investigate the effects of water acidity on the growth rate of a specific freshwater alga species. Starter cultures in Group A were grown in mildly acidic water (pH 5.5\text{pH } 5.5pH 5.5), while those in Group B were grown in neutral water (pH 7.0\text{pH } 7.0pH 7.0). The scientist used random allocation to assign the starter cultures to the two groups.
Apart from using random allocation, suggest one way in which the scientist might have improved this study by controlling for the effects of extraneous variables. Justify your answer.
Practise AQA A Level Psychology Scientific processes with exam-style questions for A Level Psychology. 689 questions, matched to the AQA A Level Psychology (7182) specification and written in Paper 1, Paper 2 and Paper 3 style. Every question includes a full worked solution and mark scheme, so you can see where marks are awarded rather than just whether you got the answer right.
