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90
18/20 × 100 = 90.
Class 9 · Bangla Version · Biology
Biological investigation and data interpretation
Interpret biological data with controls, replication and cautious conclusions.
Shared cross-level core and stretch unit. Start with the core questions, then use the stretch example for deeper work. The same unit is available in related class and board pathways; it is not a full grade-specific or examination-specification course. A teacher should select the appropriate depth and further topics.
Learn the idea
A biological investigation must define its variables, sampling method and ethical limits. A control provides a useful comparison; repeats help assess variability. Biological variation means group averages can differ by chance or because of confounding factors. A conclusion should describe what was measured, in which organisms and under which conditions.
Worked example
Fictional germination results: group A 18 of 20 seeds, group B 15 of 20. These are 90% and 75% in those samples. The difference alone does not prove the treatment caused it; seed quality, allocation and repeats matter.
- Define the comparison and outcome.
- Calculate proportions with denominators.
- Consider alternative explanations and further evidence.
Stretch example
A quadrat sample estimates density in the sampled area. Extrapolating to a habitat assumes the placement and sample represent that habitat. Clumped organisms can make a few convenient quadrats misleading.
Your written practice
Show your working on paper and enter your answer here. If it does not match, compare the model and try again.
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5
20−15 = 5.
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no
The same exclusion can remain in every repeat.
Write in your own words. A guardian or teacher should review this response.
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It reduces systematic differences in seed characteristics between the groups.
Explain the purpose rather than promising identical groups.
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More seeds germinated in A than B in this trial, but further controlled repeats are needed to assess whether the treatment explains the difference.
Keep denominators and limitations visible.
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24
12/0.5 = 24 per square metre.
Write in your own words. A guardian or teacher should review this response.
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Choosing rich patches deliberately overrepresents high-density areas.
Describe how placement changes the estimate.
Seed investigation plan
Plan a seed comparison on paper with no requirement to experiment.
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- State allocation and controls.
- Specify the germination rule and observation time.
- Explain how uncertainty limits a conclusion.
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