Interpreting, concluding and reporting
Interpreting your processed data
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Interpreting means saying what the data show, in terms of the relationship between your variables. It comes before the conclusion, and it is a separate step.
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Describe the trend or pattern:
- Its direction — as the IV increases, does the DV increase, decrease, or both in turn?
- Its shape — linear, curved, plateauing, or peaking at an optimum.
- Where it changes — the IV value at which the direction or gradient alters.
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Quote figures from your data when describing the trend. "The rate increased" is weak; "the mean rate rose from 4.2 to 14.0 cm3 min−1 between 10 and 30 °C, then fell to 6.2 cm3 min−1 at 50 °C" is specific and demonstrably drawn from your results.
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The absence of a pattern is a legitimate finding. The standard explicitly allows for "a trend or pattern (or absence)". If your data show no relationship, report that clearly and consider why — the range may have been too narrow, the effect too small to detect, or there may genuinely be no relationship.
Writing a valid conclusion
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A conclusion answers your purpose, and this is what makes it valid — it must address the hypothesis you actually stated.
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A conclusion has three parts:
- Whether the hypothesis was supported, and to what extent. "Supported" and "not supported" are the correct terms — data do not prove a hypothesis.
- The evidence, quoted from your processed data.
- The biological explanation — why the result occurred, in terms of biological ideas.
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Common failures:
- Concluding something the data do not address — a conclusion about an optimum when the range never reached it.
- Restating the trend without explaining the biology. That is interpretation, not a conclusion.
- Claiming the hypothesis is "proved". A single investigation supports or fails to support; it does not prove.
Using another source
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Achieved requires identifying relevant findings from another source. This is a discrete requirement and is frequently the reason an otherwise complete report falls short.
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Merit requires more: the biological ideas must be explained using both your own findings and those from other sources — the two must be brought together, not presented in separate sections.
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A useful source is one that:
- Addresses the same biological relationship, even if the organism or method differs.
- Comes from a credible origin — a textbook, a scientific publication, a university or government source rather than an unattributed website.
- Is referenced so a reader can locate it.
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How to integrate a source well:
- Where it agrees, say so and say what that adds — agreement with an independent method makes both results more credible, since they are unlikely to share the same errors.
- Where it disagrees, say so and suggest why. Different species, different conditions, different measurement techniques, or a limitation in your own method are all legitimate explanations. A disagreement handled thoughtfully is worth more than an agreement mentioned in passing, because it requires you to reason about both investigations.
Reaching Excellence
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Excellence requires two things beyond Merit, and they are specific.
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Justify the choices you made, by evaluating the validity of the method or the reliability of the data.
- Justify means explain why you chose what you chose — this range, this measurement technique, this number of repeats, this sampling method.
- Evaluate means make a judgement about quality, supported by evidence from your own data. "The repeats at each temperature differed by no more than 1.0 cm3, indicating the data were reliable" is an evaluation; "the results were reliable" is an assertion.
- Justifying a change you made mid-investigation is particularly strong, because it shows the reasoning rather than just the outcome.
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Discuss the biological ideas alongside either the findings of others, scientific principles, theories, or models.
- This means connecting your specific result to the wider biology — the enzyme–substrate model, limiting factor theory, the principles of diffusion — rather than treating your investigation in isolation.
Structuring the report
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A conventional structure, which maps onto the criteria:
- Purpose and hypothesis, with the biological link.
- Method, with variables, range, controls and how each was controlled.
- Results — raw data, processed data, and a graph.
- Interpretation — the trend, with figures.
- Discussion — the biology explained, integrated with other sources.
- Evaluation — validity, reliability, specific limitations and their effects, justified choices.
- Conclusion — the hypothesis addressed, with evidence and explanation.
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Keep interpretation (what the data show) separate from discussion (why, biologically) and evaluation (how good the investigation was). Reports that merge them tend to lose marks because the marker cannot find each requirement.
Selective advantage
- Not applicable — this is a skills standard, assessing investigative process rather than biological content.
Worked Example
Worked Example
A student's processed data for catalase activity (mean volume of oxygen in 60 s):
| Temperature (°C) | Mean volume (cm3) |
|---|---|
| 10 | 4.2 |
| 20 | 8.3 |
| 30 | 14.0 |
| 40 | 18.8 |
| 50 | 6.2 |
A textbook states that catalase from most sources has an optimum of about 45 °C.
Write an interpretation and a conclusion at Excellence standard.
Answer:
Interpretation.
The mean volume of oxygen produced increased with temperature from 4.2 cm3 at 10 °C to 18.8 cm3 at 40 °C, an increase of roughly 4.5 times. Between 40 °C and 50 °C it then fell sharply to 6.2 cm3, a decrease of about 67%.
The relationship is therefore not linear. The rate rises to a maximum somewhere at or above 40 °C and falls steeply beyond it. The rise between 10 and 40 °C is itself slightly curved, with the increase per 10 °C growing from 4.1 cm3 to 5.7 cm3 then falling to 4.8 cm3, which is consistent with the rate approaching a peak within the tested range.
Conclusion.
The hypothesis was supported. The prediction that rate would increase to a maximum and then decrease sharply is consistent with the data: the rate rose steadily to 18.8 cm3 at 40 °C and fell to 6.2 cm3 at 50 °C.
The biological explanation. Below the optimum, increasing temperature gives enzyme and substrate molecules more kinetic energy. They move faster, so collisions between them are more frequent and a greater proportion have sufficient energy to form the enzyme–substrate complex. The rate therefore rises.
Above the optimum, the increasing kinetic energy disrupts the hydrogen and ionic bonds holding the enzyme's tertiary structure. The active site changes shape, so it is no longer complementary to the hydrogen peroxide substrate and cannot bind it. The enzyme is denatured, and because denaturation is essentially irreversible, the rate falls steeply rather than gradually — which is exactly the asymmetry seen in the data, where the fall over 10 °C is far steeper than any rise over 10 °C.
Comparison with the source. The textbook gives an optimum of about 45 °C, while this investigation's highest measured rate was at 40 °C. These are consistent, and the apparent difference is expected rather than contradictory:
- The investigation used levels 10 °C apart, so it can only locate the optimum to within that interval. The true optimum lies somewhere between 30 and 50 °C, and 45 °C sits within that. The data cannot distinguish 40 from 45 °C, so no discrepancy has actually been demonstrated.
- The textbook value is for catalase from a range of sources; potato catalase may differ slightly.
Justifying the choices made. The range of 10–50 °C was chosen after a pilot study confirmed that measurable oxygen was produced at both extremes, and it was set to span the expected optimum so that both the rise and the fall could be observed — which is what allowed the shape of the relationship to be established rather than only its direction. Three repeats at each temperature were used so that anomalies could be identified and random variation reduced by taking means.
Evaluating reliability. The repeats at each temperature differed by no more than 1.0 cm3 except at 40 °C, where one anomalous trial was identified, attributed to a suspected gas leak, excluded from the mean and reported. The close agreement of the remaining repeats indicates that random error was small and the means are trustworthy.
Evaluating validity. The principal limitation is the 10 °C interval between levels, which is too coarse to locate the optimum precisely. This affects the precision of the optimum but not the shape of the relationship, so the conclusion about the pattern stands while any claim about a specific optimum temperature does not. Repeating with 5 °C or 2 °C intervals between 35 and 50 °C would resolve this.
Connecting to wider biology. This result is what the lock-and-key and induced-fit models of enzyme action predict: both depend on the active site being complementary in shape to the substrate, so any change in tertiary structure must reduce activity. The asymmetry of the curve — a gradual rise and a steep fall — follows from the two processes being different in kind: increasing collision frequency is a gradual, reversible effect of temperature, while denaturation is a structural and effectively irreversible one.