Limitless IGCSE Biology Exam
14.5.3 Practical Tropisms Investigation
Paper 6: Alternative to Practical
Exam Instructions
- • Total Time: 60 minutes
- • Total Marks: 45 marks
- • Question Types: Experimental design, analysis, variables, controls, and evaluation
- • Answer Format: Type your answers in the text boxes provided
- • Marking: Click "Reveal Answer" to see model answers and check which keywords you included
- • Note: For drawing questions, sketch on paper and compare with the model answer criteria
A student investigates gravitropism by placing cress seedlings on a clinostat that rotates slowly. After 48 hours, the shoots grow straight upwards rather than showing any curvature.
Explain why the shoots grow straight upwards when the seedling is rotated on a clinostat.
[3 marks]A student sets up two groups of bean seedlings to investigate gravitropism:
• Group A: Seedlings placed horizontally and kept stationary • Group B: Seedlings placed horizontally on a rotating clinostat
Draw and label diagrams showing the expected growth pattern of shoots for BOTH Group A and Group B after 48 hours. Include arrows showing the direction of growth and label the position of auxin accumulation.
[4 marks]Drawing Requirements:
- • Group A shows upward shoot curvature
- • Group B shows straight shoot growth
- • Auxin position labeled on lower side (Group A)
- • Arrows showing growth direction for both groups
A student investigates the effect of rotation speed on gravitropic response using a clinostat.
Identify the independent variable, dependent variable, and state TWO variables that must be kept constant in this investigation.
[3 marks]A student obtains the following results from a clinostat experiment:
Data:
• Stationary seedling: Shoot curves 45° upward after 48 hours • Slow rotation (2 rpm): Shoot curves 20° upward • Fast rotation (10 rpm): Shoot grows straight (0° curvature)
Explain why faster rotation produces straighter growth.
[3 marks]A student wants to investigate whether roots show the same response as shoots when placed on a clinostat.
Describe how the student should set up this investigation, including appropriate controls.
[3 marks]Cambridge Grade Boundaries (Paper 6)
A*
≥41/45
A
≥36/45
B
≥32/45
C
≥27/45
D
≥23/45
E
≥18/45
U
<18/45
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