When two groups start with different numbers of seeds, compare the fraction of each group that germinates. A group can have more germinated seeds overall while having a smaller share germinate. Divide the number that germinated by the number planted in that group.
The MOE Primary Science syllabus covers germination in plant reproduction. This practice uses seed counts to show how a calculation supports a conclusion and how the design of a fair test still matters.
- Record the number of seeds at the start.
- Use the same observation period and criterion.
- Compare each count with its own starting group.
- Use the results to make a conclusion about the groups observed.
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Agree on what will count
For this example, count a seed as germinated when its first root has emerged. Inspect both groups after five days using that same rule. Keep a starting count for each group so the final readings can be compared fairly as proportions.
A question asking which tray had more germinated seeds can be answered from the raw counts. A question asking which tray had the greater fraction of its seeds germinate requires the starting counts too.
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Worked example | Twelve seeds versus nine
Tray A starts with 20 seeds and 12 germinate. Tray B starts with 10 seeds and nine germinate. Tray A has more germinated seeds. The fraction that germinated in Tray A is 12/20 or 60%. In Tray B it is 9/10 or 90%.
A clear conclusion gives both the group and the measure. For example, Tray B had the higher percentage of seeds germinate after five days, with 90% compared with 60% for Tray A.
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Improve the investigation
Suppose Tray A was crowded and Tray B had more space between seeds. The percentages still describe what happened, but the difference alone cannot show whether a water treatment caused the result. In a repeat, use the same kind and number of seeds, comparable spacing and the same observation time. Change only the condition being tested.
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Frequently asked questions
Does a higher percentage after five days show that each seed germinated sooner?
It shows a larger share had germinated by the observation time. To compare how soon germination happened, take readings at several times.
What can a parent ask before showing the solution?
Ask which group had more successful seeds and which had the larger share. Have the child point to the starting count used in each fraction.