Lesson focus: A fair germination investigation separates the requirements for water, oxygen and suitable temperature from conditions needed for later seedling growth.
Plan and interpret a controlled germination investigation with viableAlive and able to grow, such as a seed that can still germinate. seeds, repeats and an appropriate timescale.
Build on earlier learning
Fertilisation and germinationThe previous lesson identified broad germination requirements. This practical tests those requirements with controlled comparisons.
Planning an investigation?
Design an investigation with CORMMSSA step-by-step Logic Lab guide to planning a fair test, with a worked example and practice.
Practical
Conditions for germination
- Set up dishes of seeds with and without water, warmth and light.
- Change one condition per dish and keep the rest the same.
- Count the germinated seeds after five days.
Record: A table of condition against percentage germinated.
You will be successful when you can…
- State the main germination requirements.
- Design a suitable control group and comparison groups.
- Measure germination consistently.
- Evaluate viability, contamination and sample-size limitations.
Words that carry the science
- viable
- Capable of germinating and developing under suitable conditions.
- dormancy
- A viable state in which growth does not begin despite some apparently suitable conditions.
- germination criterion
- A defined observation used to score a seed as germinated, such as radicle emergence.
- control group
- A comparison group that does not receive the change being tested, such as seeds kept in suitable conditions.
- percentage germination
- Germinated seeds divided by total seeds, multiplied by 100.
- replicate
- An independent repeat of an experimental condition.
Test one germination condition at a time
01Water, oxygen and temperature support metabolism
Water rehydrates tissues and activates metabolic pathways. Oxygen supports aerobic respiration, releasing energy for cell division and growth. Temperature affects enzyme-controlled reactions, so too low slows them and excessive heat can damage tissue.
Some species have additional cues or dormancyWhen a seed is alive but resting, waiting for the right conditions before it starts to grow. mechanisms. The three-factor model describes broad requirements rather than guaranteeing every viableAlive and able to grow, such as a seed that can still germinate. seed germinates immediately.
02Define what counts before observing
Use seeds from the same batch, equal numbers and consistent containers. Define germination as visible radicle emergence by a stated minimum length, then observe at regular times.
Include a control groupA group that does not get the thing being tested, so you have something fair to compare the results with. kept in suitable conditions. To test one factor, change only that factor while controlling the others as far as practical. Use several dishes or tubes per condition, not many seeds in only one container.
03Interpret non-germination cautiously
Failure may reflect the tested condition, non-viable or dormant seeds, fungal growth, insufficient time or uncontrolled differences. The control group shows whether the seed batch can germinate under the experimental period.
Report percentage germinationThe percentage of seeds that start to grow out of all the seeds planted. and spread between replicateA repeat of the same test set up in exactly the same way.. Do not claim that light is required unless a controlled light comparison supports it for the species tested.
What do seeds need to germinate?
Germination is when a seed starts to grow. Set up tubes of cress seeds, changing one condition in each. Seeds need water, warmth and oxygen. They do not need light to germinate: they use their food store.
Tubes A–E. Blue: water. Yellow layer: oil. Pale blue tube: cold. Shaded: in the dark (seedlings grow yellow).
Controls
Percentages are illustrative. Tube A is the control. Cold seeds may germinate very slowly if left for weeks.
Calculate percentage germination
In one dish, 17 of 20 seeds show radicles after five days.
- Use percentage = germinated ÷ total × 100.
- Substitute 17 ÷ 20 × 100.
- Calculate 0.85 × 100.
- Report 85% germination after five days using the stated criterion.
How to make the reasoning visible: The value describes this sample and timescale, not the guaranteed viability of every seed.
Interpret a germination investigation
Each condition used three dishes of 20 seeds. Values are mean percentages after six days.
| Condition | Water | Oxygen | Temperature | Mean germination |
|---|---|---|---|---|
| Control | Available | Available | 22 °C | 88% |
| Dry | Absent | Available | 22 °C | 2% |
| Boiled water with oil layer | Available | Strongly limited | 22 °C | 8% |
| Cold | Available | Available | 4 °C | 25% |
| Hot | Available | Available | 60 °C | 0% |
What conclusion is supported by the dry and low-oxygen comparisons?
Why use three dishes rather than one dish containing 60 seeds?
Check your understanding
Answer from memory, then check against the suggested answer.
What is a viable seed?
Why is oxygen needed?
How is percentage germination calculated?
Both the control group dish (with water) and a dry dish show 0% germination. What can be concluded?
Explain how dormancy can be adaptive even when conditions appear suitable.
Exam Question Practice
Exam Question Practice
Mark points shown after marking
A student plans an investigation into the effect of temperature on seed germination.
Describe the method, including the control variables.
(3)Describe how to record the results and make them reliable and safe.
(3)Total for this question: 6 marks
Command word: For planA description of what you will do in an investigation and why., make the comparison reproducible and distinguish independent dishes from many seeds in one dish.