By the end of this lesson
- Describe the requirements for germination.
- Design controlled germination treatments.
- Evaluate reliability, validity and safety.
BIG QUESTION
How can we prove what a seed needs to begin germinating?
A valid test removes one factor at a time while controlling viability, time and all other conditions.
Seeds require water, oxygen and warmth
Water rehydrates tissues and activates enzymes. Oxygen supports aerobic respiration. A suitable temperature allows enzyme-controlled reactions to proceed sufficiently rapidly.
Light is not a universal requirement for germination, although it affects some species.
Method, variables and the control group
The independent variableThe variable that is deliberately changed in an investigation. is the condition removed; the dependent variableThe variable that is measured in an investigation to see how it is affected by the independent variable. is percentage germination. Place equal numbers of viable seeds on suitable moist support. Compare a control groupA group treated like the others except that it does not receive the change being tested, so each treatment group can be compared with it. given all the normal conditions with: dry conditions, oxygen-poor conditions using cooled boiled water beneath oil, and an unsuitable low temperature.
Keep seed species, number, age, water volume where relevant, container, time and scoring criterion constant as controlled variables.
Data handling and safety
Define germination before collecting data, for example visible radicle emergence. Calculate percentage germination for each treatment and use replicates.
Use clean equipment, wash hands after handling seeds and avoid tasting laboratory material. Do not seal respiring seeds in a way that creates pressure.
Interpretation and limitations
Compare each treatment with the control group. Illustrative result: 18 of 20 control-group seeds germinate but 0 of 20 dry seeds, suggesting water is needed; the conclusion applies to the species and conditions tested.
Limitations include seed viability varying, oil layers not fully excluding oxygen, cold treatments slowing rather than preventing germination and small sample sizes.
Graph skills: SLAPUK and choosing a scaleGermination results: choose the scale before you plot.
Controlled germination treatments
Each treatment tests one factor against a control group with all the normal conditions.
| Treatment | Factor limited | Prediction |
|---|---|---|
| Moist, aerated, suitable temperature | None. | High germination. |
| Dry support | Water. | Little or no germination. |
| Boiled water under oil | Oxygen. | Little or no germination. |
| Moist and refrigerated | Suitable temperature. | Slower/lower germination during test. |
| Replicate control group | Random variation checked. | Similar proportion if reliable. |
Language that earns precision
- germination
- Resumption of growth of the embryo in a seed.
- radicle
- Embryonic root that normally emerges first.
- control group
- Seeds given all the normal conditions, without the change being tested, for comparison with each treatment.
- percentage germination
- Germinated seeds divided by total seeds, multiplied by 100.
Common misconceptions
Claim: Seeds require soil to germinate.
Correction: They require water, oxygen and suitable temperature; support and minerals are needed later for sustained growth.
Claim: Boiling water tests high temperature.
Correction: When cooled and covered with oil, it is used to remove and exclude oxygen.
Claim: One ungerminated seed disproves the conditions.
Correction: Seeds vary in viability, so use groups and replicates.
Match the answer to the command word
Name independent, dependent and controlled variables.
Discuss viability, sample size, repeats and a consistent germination criterion.
Recall, apply, then justify
Describe a controlled investigation showing that seeds require oxygen for germination.
Hint
Control group, oxygen removal, control variables, time and measurement.
Suggested marking points
- Use equal groups of the same viable seed type.
- Place one group in moist aerated conditions as the control group.
- Place another with cooled boiled water covered by oil to exclude oxygen.
- Keep temperature, time and other conditions the same.
- Compare percentage germination using the same radicle criterion.
Explain why water is needed for germination.
Hint
Rehydration, enzymes and transport.
Suggested marking points
- Water rehydrates seed tissues.
- It activates or provides a medium for enzyme-controlled reactions.
- Soluble products can be transported to the growing embryo.
Design an investigation to estimate the optimum germination temperature.
Planning hint
Use a range, replicates and a rate measure.
What a strong design includes
- Use several controlled temperatures across a sensible range.
- Use equal numbers of the same seed batch in each treatment.
- Keep water, oxygen, support, light and observation time constant.
- Use replicates at every temperature.
- Record time to radicle emergence or percentage germinated at fixed intervals.
- Calculate a mean or germination-rate measure.
- Plot response against temperature and identify the best-supported optimum.
- Avoid temperatures likely to cook seeds or create unsafe microbial growth.