AQA GCSE · Question 03.3 · Homeostasis and Response
Why did the student set up experiment 2 in this investigation?
How to approach this question
Think about the purpose of a control experiment. A control is used for comparison to show that the factor you are investigating (the independent variable) is the one causing the observed effect. In this case, what is Experiment 2 comparing with Experiment 1?
Full Answer
Experiment 2 acts as a control for the investigation. By placing a seedling in a light-proof box, the student removes the stimulus of one-sided light. This allows them to see how a seedling grows without this stimulus (it grows straight up). By comparing the result of Experiment 1 (bends towards light) with the control, the student can conclude that it was the one-sided light, and not some other factor, that caused the shoot to bend.
Common mistakes
✗ Just saying "to make it a fair test". You need to be more specific about what it controls for.
✗ Stating that it's to see if the plant can grow without light. While true, its primary purpose in this investigation is for comparison.
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