Learning focus
Develop transferable AO3 skills: plan, measure, record, process, interpret and evaluate biological investigations accurately and safely.
Phototropism
Expose similar seedlings to light from one side and measure curvature or angle after a fixed time. Compare with uniform light or darkness. Keep water, temperature, species, age and duration constant.
Gravitropism
Place seedlings horizontally in darkness so light does not confound the response. Record root and shoot curvature. A clinostat, if available, provides a rotating comparison that reduces a constant gravitational direction.
Nervous response
Simple human-response investigations may measure reaction time with a ruler drop or sensory discrimination. Standardise the procedure, repeat several times and consider learning, anticipation and fatigue.
Ethical and measurement issues
Human participants should consent, avoid risk and be allowed to stop. Plant curvature should be photographed against a grid or measured with a protractor to reduce subjective judgement.
Practical or data skill
Plan one tropism and one human reaction-time investigation. Identify the dependent measurement and one major source of variation in each.
Examination tip
Keep gravitropism seedlings in darkness to remove light as a confounding stimulus.
Review questions and suggested answers
Question 1
Why use darkness in a gravitropism test?
Suggested answer
To prevent phototropism affecting growth direction.
Question 2
What can affect repeated ruler-drop results?
Suggested answer
Practice, anticipation, fatigue or inconsistent release.
Question 3
How can shoot curvature be measured objectively?
Suggested answer
Photograph against a grid and measure angle with a protractor.
