16.3.10 — Germination Practical: Experimental Design
Cambridge IGCSE Biology 0610 · Past Paper 6 Style · 15 Questions
Section A
Experimental Setup
12 marks
Section B
Controls
12 marks
Section C
Variables
13 marks
In an experiment to investigate whether oxygen is needed for germination, a layer of oil is placed over the water surface in the experimental tube. Explain why the oil layer is used.
Before adding the seeds and oil to the experimental tube, the water is boiled and then cooled. State why the water must be boiled before use.
A student sets up two tubes: Tube A (experimental — seeds in boiled, cooled water with oil layer) and Tube B (control). Describe the full setup of Tube B.
State two safety precautions a student should take when handling seeds and boiling water during this experiment.
After 7 days, the student counts the number of germinated seeds in each tube. State what results would be expected, and explain what conclusion could be drawn.
Explain the purpose of including a control tube in a germination experiment.
A student investigates whether light affects germination. She places one set of seeds in a dark cupboard and another set on a windowsill. Identify one variable she has failed to control and explain how this affects the reliability of her results.
In an experiment on the effect of temperature on germination, a student uses dead (autoclaved) seeds as a control. Suggest why dead seeds are used rather than no seeds at all.
Describe the setup of an ideal control tube for an experiment investigating the effect of moisture on germination. Include all relevant conditions.
A student claims: 'I don't need a control because I already know seeds germinate in normal conditions.' Evaluate this claim.
A student investigates the effect of temperature on the germination of cress seeds. State the independent variable and the dependent variable in this experiment.
If investigating the effect of temperature on germination, state three variables that must be kept constant. For each, state why it must be controlled.
A student records the following data on germination at different temperatures. Sketch the expected shape of the graph: germination rate (y-axis) vs. temperature (x-axis, 0–50°C). Describe and explain the expected pattern.
A student claims that testing germination at only two temperatures (20°C and 40°C) is sufficient to draw a valid conclusion. Evaluate this claim.
A student repeats her germination experiment three times at each temperature and calculates a mean. Explain why repeating the experiment and calculating a mean improves the validity of the results.
Golden Keyword Registry — Paper 6 Germination
The factor deliberately changed by the experimenter
The factor measured/observed as a result of the change
A factor kept constant to ensure a fair test
The setup where the independent variable is at its standard/normal level, used as a baseline for comparison
Seeds that are capable of germinating under optimal conditions
A result that does not fit the overall trend; likely caused by experimental error
Results that are consistent and reproducible across repeated trials
Results that truly measure what the experiment intends to measure
Oxygen gas that has dissolved into water from the surrounding air
Permanent change in the shape of an enzyme's active site due to high temperature or extreme pH, preventing substrate binding
The temperature at which enzyme activity (and thus germination rate) is greatest
The sum of all values divided by the number of values; gives a more representative/reliable result
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