Biology IA Exemplar: Ethanol Concentration and α-Amylase Inhibition | RevisionDojo

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IB Biology HL Internal Assessment Example

What is the effect of varying ethanol concentration (0%, 5%, 10%, 15%, 20%, 25%) on the inhibition of α-amylase enzyme activity on starch in a solution, as measured by the time taken for the iodine-starch complex to disappear caused by an iodine-starch complex at room temperature (25°C)?HL

Official IB Result

20/24

Criteria A: Research Design

6/6

Criteria StrandsPro

A.1Research question context

Excellent

A.2Methodological considerations

Good

A.3Methodology description

Poor

Criteria Feedback

The student's research question is focused and clearly identifies the variable, the biological system, the response being measured, and the temperature context.
The student situates the investigation in a relevant biochemical context, showing that they understand why the question matters beyond the experiment itself.
The student includes several important controls and methodological considerations that show awareness of factors affecting enzyme activity.

Some scientific wording is imprecise, especially in how the iodine–starch colour change is explained.
A few methodological choices are not fully justified or chemically valid, such as the way the buffer is described.
The procedure is not fully reproducible because some key preparation details are missing or inconsistent.

1.1·Strength

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The research question is sharply focused: it names the independent variable, the biological system, the dependent variable, and the temperature. That level of specificity gives the investigation a clear scope and makes the planned comparison across concentrations easy to follow.

1.2·Strength

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This gives the investigation a relevant biochemical context by linking ethanol, amylase, starch hydrolysis, and the iodine indicator. The student is not just naming variables; they are explaining why the reaction is worth studying in a broader metabolic setting.

1.3·Weakness

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This mechanistic claim is too confidently stated for the evidence presented, especially because the cited source in the bibliography is not an amylase paper. The student should either support this claim with more relevant evidence or qualify it as a hypothesis rather than a settled fact.

1.4·Weakness

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The wording is scientifically imprecise here: iodine does not cause the complex to disappear, and the endpoint is better described as starch hydrolysis causing loss of the iodine–starch colour. Tightening that phrasing would make the question more accurate and technically stronger.

1.5·Suggestion

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This hypothesis would be stronger if it stated a measurable expected outcome in operational terms, such as longer reaction times or lower calculated rates. That would make it easier to judge whether the data support the prediction.

1.6·Question

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How could the student justify a claim of mixed inhibition from this design alone, when the investigation does not vary substrate concentration or measure

K_{m}

and

V_{ma x}

? Reflecting on that mismatch would help separate what is observed from what is inferred.

1.7·Weakness

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The control is only partly reproducible because "5 drops" is not a precise concentration or volume measure. To make the method reproducible, the student should specify the exact prepared concentration, the stock solution, and the calibrated volume delivered per trial.

1.8·Weakness

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This method does not convincingly produce a pH 7 buffer. Because pH control is central to enzyme activity, the student needs a chemically valid buffering system and should specify exactly how the target pH is verified.

1.9·Weakness

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This step is too vague to reproduce the investigation. The student should state the starting concentration of the amylase stock, the exact dilution ratio, and the final volume prepared, otherwise another researcher cannot independently repeat the method.

1.10·Weakness

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This conflicts with the reported data set, which later contains fifteen trials per concentration. That inconsistency weakens confidence in the method and should be resolved so the planned procedure matches the recorded analysis.

Criteria B: Data Analysis

4/6

Criteria StrandsPro

B.1Communication of data recording and processing

Moderate

B.2Consideration of uncertainties

Poor

B.3Data processing quality

Moderate

Criteria Feedback

The student's data are recorded in an organized way with repeated trials, units, and summary statistics, so the overall pattern is easy to inspect.
The student applies relevant processing such as means, standard deviations, reciprocal-time calculations, and statistical testing.
The student makes a serious attempt to consider uncertainty and to present the results in a more analytical way than simple raw data reporting.

There are inconsistencies between the raw data, sample calculations, procedure, and the data set used later in the report.
Some units, labels, and formulae are incorrect or mismatched to the quantities being shown.
The treatment of uncertainty is incomplete, especially for volume preparation, drop size, and visual endpoint judgement.

2.1·Weakness

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The main table is incomplete, which makes the recorded dataset difficult to evaluate on its own. The student should either include all trials in the main body or clearly signal where the full dataset sits so the analysis can be checked without ambiguity.

2.2·Question

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How was the spreadsheet formula checked for correctness, and were the same settings used consistently across all groups? Verifying that calculation method would strengthen confidence in the precision claims made later.

2.3·Strength

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The raw data are presented in a clear table with units and repeated trials, which makes the trend across ethanol concentrations easy to inspect. That structure supports transparent recording and allows the reader to trace later processing back to the original measurements.

2.4·Weakness

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The unit is incorrect here:

\frac{1}{45.5}

should be reported as approximately

0.022 s^{- 1}

, not seconds. Correct units are essential because they determine whether the processed quantity is interpretable as a rate.

2.5·Weakness

Page 10• Click to view

The rate formula is incorrect as written and the notation is inconsistent. Reciprocal rate should be expressed as

\frac{1}{t}

s^{- 1}

, so the student needs to correct both the formula and the units used in later processing.

2.6·Weakness

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This label is not consistent with the plotted quantities if the graph shows reaction time values rather than rates. The student should match the axis label to the actual data being graphed, because clear variable naming is essential for accurate interpretation.

2.7·Weakness

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The interpretation goes beyond the graph if it claims a reduction in rate while the plotted values appear to be reaction times. The student should make the relationship explicit and keep the wording aligned with the processed variable being displayed.

2.8·Weakness

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The inequality is mathematically wrong:

4.98 \times 1 0^{- 193}

is far less than

0.05

, not greater. This matters because statistical interpretation depends on correct comparison of the p-value to the significance threshold.

2.9·Strength

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Using a post hoc test after ANOVA is a sensible next step because it allows the student to identify which ethanol groups differ from each other. This shows more than simple trend reporting and indicates an attempt at structured statistical analysis.

2.10·Weakness

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This is overstated and too absolute. A statistically significant pairwise comparison does not mean the groups are "different" in every meaningful sense; the student should report which comparisons are significant and what the mean differences imply biologically.

Criteria C: Conclusion

4/6

Criteria StrandsPro

C.1Conclusion relevance and consistency

Moderate

C.2Scientific context comparison

Moderate

Criteria Feedback

The student's conclusion answers the research question directly and is consistent with the overall direction of the results.
The student makes some relevant links to broader scientific context and shows awareness that the investigation relates to enzyme function in digestion.
The student also shows some self-awareness by recognizing that their interpretation has limits.

The conclusion sometimes claims a specific inhibition mechanism that the investigation does not actually establish.
Several mechanistic explanations go beyond what the data directly show, especially where denaturation or plateau behavior is inferred.
The link to broader physiological claims is too ambitious compared with what a single amylase assay can support.

3.1·Question

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What evidence from this investigation specifically supports claims about insulin resistance or carbohydrate uptake in the body? The student should think about whether those physiological outcomes extend beyond what a test-tube amylase assay can show.

3.2·Weakness

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This is a valid limitation, but it comes very late and is not tied back to the core conclusion. The student should explain which of these factors most likely affected the result and how strongly each one could have changed the reaction times.

3.3·Weakness

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The plateau claim is not securely justified from the presented values, and neither denaturation nor starch solubility was directly measured. The student should distinguish clearly between observed trends and mechanistic explanations.

3.4·Strength

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The conclusion does address the research question directly and links the direction of the effect to the collected results. That makes the final statement easy to connect back to the investigation's central aim.

3.5·Weakness

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This interpretation overreads the standard deviation. A slightly larger spread does not by itself demonstrate denaturation or a different inhibition mechanism, so the student should avoid causal claims that are not directly supported by the data.

3.6·Strength

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This is a useful sign of self-awareness because it opens the door to a more balanced conclusion. Acknowledging limitations helps the student avoid overstating the certainty of the findings.

3.7·Weakness

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The conclusion claims a specific inhibition type that the investigation cannot establish because it did not measure

K_{m}

V_{ma x}

or vary substrate concentration. The student should limit the conclusion to what the data actually show: a concentration-dependent change in reaction time.

Criteria D: Evaluation

6/6

Criteria StrandsPro

D.1Methodological weaknesses

Good

D.2Improvements

Good

Criteria Feedback

The student identifies several specific limitations rather than staying at a generic level.
The student proposes improvements that are realistic and clearly linked to the issues they noticed.
The student shows good understanding that stronger mechanistic claims would require more appropriate measurements.

Some limitations are identified well but are not prioritized by their impact on the validity of the main conclusion.
A few improvements read more like extensions than direct fixes to the problems in the method.
The relative importance of the biggest methodological weaknesses is not always explained clearly enough.

4.1·Strength

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This is a strong, specific limitation because it identifies a genuine source of measurement error in the endpoint. Recognizing subjectivity shows the student understands why the data may be less precise than the numerical tables suggest.

4.2·Weakness

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The student identifies the variability, but does not explain its relative importance compared with other limitations such as the visual endpoint and inconsistent methodology. Prioritising the most serious weaknesses would make the evaluation more analytical.

4.3·Weakness

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This limitation is accurately identified, but the student should go further and explain how it may have skewed the timing results, especially at mid-range concentrations where the endpoint is less obvious. That would show the limitation's actual effect on validity.

4.4·Weakness

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This is a relevant limitation, but its impact on the central conclusion is not fully explained. The student should say whether the limited range prevents identification of a maximum effect, a plateau, or a threshold concentration.

4.5·Strength

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This is a relevant and well-matched improvement because it directly addresses the subjective endpoint problem. It would also strengthen the link between the raw measurements and the claimed effect of ethanol on starch hydrolysis.

4.6·Strength

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This is a highly appropriate improvement because it directly follows from the stated limitation. It shows the student understands that mechanism claims require kinetic evidence, not just endpoint timing data.

4.7·Weakness

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This is a sound limitation, but it should be linked more explicitly to why the student cannot claim a specific inhibition model. Explaining that missing kinetics data prevents mechanism identification would make the evaluation much stronger.

4.8·Strength

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This is a thoughtful evaluation point because it moves beyond describing the result to questioning the nature of the inhibition. That kind of analysis shows deeper understanding of how to test mechanism in a follow-up study.

4.9·Strength

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This is a realistic and targeted improvement, and it follows logically from the limitation just identified. It would make the investigation more mechanistically informative rather than simply expanding the dataset.

Loading scores...

Official IB Result

20/24

Criteria A: Research Design

6/6

Criteria StrandsPro

A.1Research question context

Excellent

A.2Methodological considerations

Good

A.3Methodology description

Poor

Criteria Feedback

The student's research question is focused and clearly identifies the variable, the biological system, the response being measured, and the temperature context.
The student situates the investigation in a relevant biochemical context, showing that they understand why the question matters beyond the experiment itself.
The student includes several important controls and methodological considerations that show awareness of factors affecting enzyme activity.

Some scientific wording is imprecise, especially in how the iodine–starch colour change is explained.
A few methodological choices are not fully justified or chemically valid, such as the way the buffer is described.
The procedure is not fully reproducible because some key preparation details are missing or inconsistent.

1.1·Strength

Page 1• Click to view

1.2·Strength

Page 1• Click to view

1.3·Weakness

Page 1• Click to view

1.4·Weakness

Page 1• Click to view

1.5·Suggestion

Page 2• Click to view

1.6·Question

Page 2• Click to view

How could the student justify a claim of mixed inhibition from this design alone, when the investigation does not vary substrate concentration or measure

K_{m}

and

V_{ma x}

? Reflecting on that mismatch would help separate what is observed from what is inferred.

1.7·Weakness

Page 4• Click to view

1.8·Weakness

Page 4• Click to view

1.9·Weakness

Page 7• Click to view

1.10·Weakness

Page 8• Click to view

Criteria B: Data Analysis

4/6

Criteria StrandsPro

B.1Communication of data recording and processing

Moderate

B.2Consideration of uncertainties

Poor

B.3Data processing quality

Moderate

Criteria Feedback

The student's data are recorded in an organized way with repeated trials, units, and summary statistics, so the overall pattern is easy to inspect.
The student applies relevant processing such as means, standard deviations, reciprocal-time calculations, and statistical testing.
The student makes a serious attempt to consider uncertainty and to present the results in a more analytical way than simple raw data reporting.

There are inconsistencies between the raw data, sample calculations, procedure, and the data set used later in the report.
Some units, labels, and formulae are incorrect or mismatched to the quantities being shown.
The treatment of uncertainty is incomplete, especially for volume preparation, drop size, and visual endpoint judgement.

2.1·Weakness

Page 9• Click to view

2.2·Question

Page 9• Click to view

2.3·Strength

Page 9• Click to view

2.4·Weakness

Page 10• Click to view

The unit is incorrect here:

\frac{1}{45.5}

should be reported as approximately

0.022 s^{- 1}

, not seconds. Correct units are essential because they determine whether the processed quantity is interpretable as a rate.

2.5·Weakness

Page 10• Click to view

The rate formula is incorrect as written and the notation is inconsistent. Reciprocal rate should be expressed as

\frac{1}{t}

s^{- 1}

, so the student needs to correct both the formula and the units used in later processing.

2.6·Weakness

Page 11• Click to view

2.7·Weakness

Page 11• Click to view

2.8·Weakness

Page 12• Click to view

The inequality is mathematically wrong:

4.98 \times 1 0^{- 193}

is far less than

0.05

, not greater. This matters because statistical interpretation depends on correct comparison of the p-value to the significance threshold.

2.9·Strength

Page 13• Click to view

2.10·Weakness

Page 13• Click to view

Criteria C: Conclusion

4/6

Criteria StrandsPro

C.1Conclusion relevance and consistency

Moderate

C.2Scientific context comparison

Moderate

Criteria Feedback

The student's conclusion answers the research question directly and is consistent with the overall direction of the results.
The student makes some relevant links to broader scientific context and shows awareness that the investigation relates to enzyme function in digestion.
The student also shows some self-awareness by recognizing that their interpretation has limits.

The conclusion sometimes claims a specific inhibition mechanism that the investigation does not actually establish.
Several mechanistic explanations go beyond what the data directly show, especially where denaturation or plateau behavior is inferred.
The link to broader physiological claims is too ambitious compared with what a single amylase assay can support.

3.1·Question

Page 15• Click to view

3.2·Weakness

Page 15• Click to view

3.3·Weakness

Page 15• Click to view

3.4·Strength

Page 15• Click to view

3.5·Weakness

Page 15• Click to view

3.6·Strength

Page 15• Click to view

This is a useful sign of self-awareness because it opens the door to a more balanced conclusion. Acknowledging limitations helps the student avoid overstating the certainty of the findings.

3.7·Weakness

Page 15• Click to view

The conclusion claims a specific inhibition type that the investigation cannot establish because it did not measure

K_{m}

V_{ma x}

or vary substrate concentration. The student should limit the conclusion to what the data actually show: a concentration-dependent change in reaction time.

Criteria D: Evaluation

6/6

Criteria StrandsPro

D.1Methodological weaknesses

Good

D.2Improvements

Good

Criteria Feedback

The student identifies several specific limitations rather than staying at a generic level.
The student proposes improvements that are realistic and clearly linked to the issues they noticed.
The student shows good understanding that stronger mechanistic claims would require more appropriate measurements.

Some limitations are identified well but are not prioritized by their impact on the validity of the main conclusion.
A few improvements read more like extensions than direct fixes to the problems in the method.
The relative importance of the biggest methodological weaknesses is not always explained clearly enough.

4.1·Strength

Page 16• Click to view

4.2·Weakness

Page 16• Click to view

4.3·Weakness

Page 16• Click to view

4.4·Weakness

Page 16• Click to view

4.5·Strength

Page 16• Click to view

4.6·Strength

Page 17• Click to view

4.7·Weakness

Page 17• Click to view

4.8·Strength

Page 17• Click to view

4.9·Strength

Page 17• Click to view