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What this skill means
Seeds need three conditions to germinate: water (to activate enzymes and expand cells), oxygen (for aerobic respiration to provide energy), and a suitable temperature (for enzyme activity). Light is NOT required for germination.
This is a common Paper 6 planning question. You need to design a controlled experiment with at least four setups: each removing one condition while providing the others: to prove that all three conditions are necessary for germination.
The Four-Tube Experimental Design
Use four test tubes or containers, each with seeds (e.g. Cress or bean seeds) on damp cotton wool:
Tube
Water
Oxygen
Warmth
Expected result
A (control)
Yes (damp cotton wool)
Yes (open to air)
Yes (room temperature ~20°C)
Seeds germinate
B (no water)
No (dry cotton wool)
Yes
Yes
No germination
C (no oxygen)
Yes
No (layer of oil on water / boiled water / sealed with alkaline pyrogallol)
Yes
No germination
D (no warmth)
Yes
Yes
No (placed in fridge ~4°C)
No germination
Only tube A germinates, proving all three conditions are needed.
Why Each Condition Is Needed
Water: activates enzymes (particularly amylase to break down stored starch into glucose), softens the seed coat allowing the radicle to emerge, and provides the medium for chemical reactions
Oxygen: needed for aerobic respiration to release energy for cell division and growth of the embryo
Suitable temperature: enzymes involved in germination (and respiration) require warmth to function at a sufficient rate. Too cold and enzyme activity is too slow; too hot and enzymes denature
Common Misconceptions
Light is not needed for germination: seeds germinate underground in the dark. Soil is not needed either: seeds contain their own food store (in the cotyledons or endosperm). These are frequently tested misconceptions.
The embryo plant in the seed uses its stored food (starch converted to glucose) and respires aerobically to provide energy for growth until the seedling produces its first leaves and can photosynthesise.
Use this before submitting your answer
A complete answer is specific enough for another person to repeat or assess.
✓Use at least four setups: one control with all conditions, three each removing one condition.
✓Use the same type, number, and size of seeds in each tube.
✓Use identical cotton wool and containers.
✓Only change ONE factor per tube compared to the control.
✓Leave for a set time (e.g. 5–7 days) before observing.
✓Record whether germination has occurred (radicle emergence) and measure seedling length if possible.
✓Repeat with multiple seeds per tube to improve reliability.
Try the skill in a question (4 marks)
Design an experiment to show that seeds need oxygen to germinate. Describe the control setup and the test setup. [4]
Show the answer and marking guidance
Control: seeds on damp cotton wool in an open container at room temperature: all three conditions (water, oxygen, warmth) provided
Test: seeds on damp cotton wool in a sealed container at room temperature, with a layer of oil on the water surface or boiled and cooled water to exclude oxygen
Both setups use the same type, number, and size of seeds and are kept at the same temperature
After 5–7 days, seeds in the control will germinate; seeds in the test setup (no oxygen) will not germinate
Original practice content written for this site. It is not an official Cambridge question.