Biology IA Exemplar: To what extent does the mass of green tea… | RevisionDojo

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IB Biology SL Internal Assessment Example

To what extent does the mass of green tea (Camellia sinensis) leaves (1g, 1.5g, 2g, 2.5g, and 3g), affect the rate of amylase-catalyzed starch hydrolysis, measured by the change in absorbance of starch-iodine complex using a spectrophotometer at 615nm over 10 minutes?SL

Official IB Result

20/24

Criteria A: Research Design

5/6

Criteria StrandsPro

A.1Research question context

Excellent

A.2Methodological considerations

Excellent

A.3Methodology description

Good

Criteria Feedback

The student's research question is focused, specific, and clearly set in a relevant biological context.
The student explains the rationale for the investigation well, including why starch digestion, amylase inhibition, and the starch–iodine assay matter.
The student's method includes several thoughtful controls and enough detail for the investigation to be followed with only minor ambiguity.

Some important validity details are still missing, especially around control matching and how tea colour might affect the assay.
A few procedural details need to be stated more explicitly so the investigation can be reproduced without uncertainty.
The extraction process could be justified more fully as an operational measure of inhibitor concentration.

1.1·Strength

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The introduction places the investigation in a meaningful biomedical context using a relevant statistic. This helps justify why starch hydrolysis and amylase inhibition matter beyond the lab.

1.2·Strength

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The research question is tightly focused and experimentally workable. It specifies the independent-variable range, the enzyme process, the dependent measure, wavelength, and time frame, which makes the investigation clear and reproducible.

1.3·Strength

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The student connects the background to a specific mechanism, not just a general topic. Referring to EGCG as a non-competitive inhibitor gives the research question a biologically appropriate rationale.

1.4·Suggestion

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The link between leaf mass and EGCG concentration is plausible, but it is still an indirect proxy. The student could strengthen the design by explicitly acknowledging extraction efficiency and by explaining why mass is an acceptable operational measure for this investigation.

1.5·Weakness

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This control is important, but the wording is incomplete for reproducibility and validity. The student should state that the control matches the tube volume exactly, including replacing amylase with water in the same amount, so that dilution and iodine conditions remain equivalent.

1.6·Weakness

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This controls brand and particle size well, but it still leaves the extraction yield itself uncertain. The student should explain how consistency of steeping, filtration, and recovery of extract volume will be checked, because those factors also affect the inhibitor concentration reaching the enzyme.

1.7·Suggestion

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The preliminary trial is a strong design choice because it shows the student selected conditions that allow partial hydrolysis rather than complete digestion. The methodology would be even stronger if the selection criteria for the final concentration were briefly stated.

1.8·Suggestion

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The dilution step is understandable, but the student could make the method easier to reproduce by stating the final total volume and final concentration directly in one sentence. That would remove any ambiguity about whether the 0.0625% solution was achieved exactly as intended.

1.9·Weakness

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This is a valid idea, but the method does not clearly state that the control receives the same total volume as the experimental tubes. Without that detail, the control may not isolate enzyme absence from volume effects, which weakens the design.

1.10·Question

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What would happen to the validity of the assay if tea colour also absorbs strongly near 615 nm? The student should consider whether a tea-extract blank would be needed in addition to the water calibration.

Criteria B: Data Analysis

5/6

Criteria StrandsPro

B.1Communication of data recording and processing

Excellent

B.2Consideration of uncertainties

Moderate

B.3Data processing quality

Good

Criteria Feedback

The student presents the raw and processed data clearly, with appropriate units, tables, graphing, and statistical treatment.
The student shows good awareness of uncertainty by including measurement uncertainties, standard deviations, and error bars.
The student's data processing is generally relevant and well chosen for the research question, including calculated rates, regression, and statistical testing.

Some processing steps are not communicated with complete precision, including a mismatch in at least one labelled calculation.
The uncertainty treatment is incomplete because repeat variability and measurement uncertainty are not fully distinguished or propagated through the full analysis.
The way the control and tea colour effects are handled leaves some uncertainty about how fully the processing isolates hydrolysis from other influences.

2.1·Strength

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The student explicitly identifies instrumental uncertainty and attempts to carry it through later calculations. That is good scientific practice because it shows awareness that processed values depend on measurement precision, not just raw numbers.

2.2·Strength

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The note helps explain why one initial reading was used for each mass condition, which improves transparency. This makes the data-recording approach easier to interpret than if the repeated final values were presented without any explanation.

2.3·Strength

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This is a clear and logically structured description of how the change was calculated. Combining the two absorbance-reading uncertainties is appropriate as a first step and makes the processing pathway easy to follow.

2.4·Weakness

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This calculation is not clearly labelled or matched to the values shown in the table. The student should state whether this is the mean final absorbance or the mean change in absorbance, because the current wording creates a mismatch between the formula and the reported result.

2.5·Strength

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The

R^{2}

value is used appropriately to show that the model fits the data well. That strengthens the argument that the pattern is not random and supports the subsequent interpretation.

2.6·Strength

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Including a regression equation is a strong analytical choice because it quantifies the relationship rather than merely describing it. This allows the reader to see both the direction and the approximate size of the effect.

2.7·Question

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The trend is strong, but how much of the decrease could be influenced by tea colour or other extract components rather than inhibition alone? The student should think about whether the processing isolates enzyme inhibition as cleanly as the numerical trend suggests.

2.8·Weakness

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Dividing the standard deviation by time gives the spread of the calculated rates, but it does not propagate the stated absorbance uncertainty through the processing chain. The student should distinguish between repeat variability and measurement uncertainty, then calculate each separately if both are needed.

2.9·Weakness

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This interpretation is useful, but it becomes too causal when it says the variation is 'explained by' tea mass without noting assay limitations. The student should be careful to present the regression as a relationship within the tested conditions, not proof of direct causation.

Criteria C: Conclusion

5/6

Criteria StrandsPro

C.1Conclusion relevance and consistency

Excellent

C.2Scientific context comparison

Good

Criteria Feedback

The student's conclusion directly answers the research question and stays closely tied to the results they calculated.
The student uses quantitative evidence effectively, which makes the conclusion feel grounded in the analysis rather than generalised.
The student makes a relevant connection to scientific context by linking their pattern to established ideas about green tea and enzyme inhibition.

At points the student goes beyond what the in-vitro data alone can justify, especially when extending the implication toward human glucose regulation.
Some claims are stated too strongly in causal terms when the evidence mainly supports an association within the tested conditions.
The comparison with scientific context would be stronger if the student compared the limitations and conditions of their investigation more explicitly with published work.

3.1·Strength

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The conclusion is well supported by multiple forms of analysis, which is a strong feature. Bringing together correlation and significance testing shows that the student is using both pattern and statistical evidence to justify the claim.

3.2·Strength

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The conclusion directly answers the research question in the same terms used at the start of the investigation. That makes the final judgment easy to follow and shows strong coherence between aim, analysis, and conclusion.

3.3·Weakness

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This overstates what

R^{2}

means. The student should describe it as the proportion of variation explained by the model, not as proof that tea mass alone caused the variation.

3.4·Strength

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The student uses the processed data quantitatively, which is exactly what a justified conclusion should do. Citing the size of the change helps demonstrate that the conclusion is grounded in the analysis rather than in general impression.

3.5·Question

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How strongly can colour alone support the claim that EGCG concentration increased? The student should consider whether darkening reflects all soluble compounds, not just the inhibitor, and whether that affects the certainty of the conclusion.

3.6·Weakness

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This statement goes beyond what the in-vitro data can justify. The student should moderate the claim and make clear that the results suggest an effect on starch hydrolysis in a controlled assay, rather than demonstrating clinical glucose regulation in humans.

3.7·Strength

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The student links the spread of the repeats to reliability, which is a sensible conclusion-level interpretation. This shows an attempt to distinguish precision from the overall trend, rather than simply restating the graph.

Criteria D: Evaluation

5/6

Criteria StrandsPro

D.1Methodological weaknesses

Good

D.2Improvements

Excellent

Criteria Feedback

The student identifies several specific limitations rather than using vague or generic criticism.
The student explains why those limitations matter, which shows real understanding of how method affects interpretation.
The student's suggested improvements are practical, relevant, and clearly linked to the weaknesses they identified.

The evaluation would be stronger if the student prioritised which limitations had the biggest effect on validity and reliability.
Some limitations are described well but not developed far enough in terms of their practical impact on the results.
A few improvements could be made even more targeted by linking them more directly to the control and measurement issues in the investigation.

4.1·Strength

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This is a specific limitation because it identifies both the proxy variable and the competing chemical explanation. That level of precision is good evaluation practice since it shows why the causal claim is weaker than the trend itself.

4.2·Weakness

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The limitation is identified well, but its relative impact is not fully developed. The student should explain how much uncertainty this proxy introduces compared with other limitations, such as colour interference or control matching, so the evaluation prioritises the most important weaknesses.

4.3·Strength

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The student identifies a measurement limitation that affects the meaning of the dependent variable. This is valuable because it shows awareness that an absorbance-based proxy is less biologically direct than calibrated concentration data.

4.4·Strength

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The evaluation names a concrete procedural weakness rather than a generic 'human error' issue. That specificity helps because it can be directly targeted in a revised method.

4.5·Strength

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The proposed improvement is practical and linked to the stated limitation. That makes it stronger than a generic suggestion because it shows how the problem would actually be reduced.

4.6·Suggestion

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The extension is interesting and scientifically relevant. It would be even stronger if the student briefly explained what result would indicate a processing effect and how the extract concentration would be standardised across tea types.

4.7·Weakness

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This is a relevant limitation, but it remains broad. The student should connect it more directly to the investigation by explaining which missing digestive factors matter most for interpreting the in-vitro starch-iodine assay.

Loading scores...

Official IB Result

20/24

Criteria A: Research Design

5/6

Criteria StrandsPro

A.1Research question context

Excellent

A.2Methodological considerations

Excellent

A.3Methodology description

Good

Criteria Feedback

The student's research question is focused, specific, and clearly set in a relevant biological context.
The student explains the rationale for the investigation well, including why starch digestion, amylase inhibition, and the starch–iodine assay matter.
The student's method includes several thoughtful controls and enough detail for the investigation to be followed with only minor ambiguity.

Some important validity details are still missing, especially around control matching and how tea colour might affect the assay.
A few procedural details need to be stated more explicitly so the investigation can be reproduced without uncertainty.
The extraction process could be justified more fully as an operational measure of inhibitor concentration.

1.1·Strength

Page 1• Click to view

The introduction places the investigation in a meaningful biomedical context using a relevant statistic. This helps justify why starch hydrolysis and amylase inhibition matter beyond the lab.

1.2·Strength

Page 1• Click to view

1.3·Strength

Page 1• Click to view

1.4·Suggestion

Page 5• Click to view

1.5·Weakness

Page 6• Click to view

1.6·Weakness

Page 8• Click to view

1.7·Suggestion

Page 9• Click to view

1.8·Suggestion

Page 10• Click to view

1.9·Weakness

Page 11• Click to view

1.10·Question

Page 11• Click to view

Criteria B: Data Analysis

5/6

Criteria StrandsPro

B.1Communication of data recording and processing

Excellent

B.2Consideration of uncertainties

Moderate

B.3Data processing quality

Good

Criteria Feedback

The student presents the raw and processed data clearly, with appropriate units, tables, graphing, and statistical treatment.
The student shows good awareness of uncertainty by including measurement uncertainties, standard deviations, and error bars.
The student's data processing is generally relevant and well chosen for the research question, including calculated rates, regression, and statistical testing.

Some processing steps are not communicated with complete precision, including a mismatch in at least one labelled calculation.
The uncertainty treatment is incomplete because repeat variability and measurement uncertainty are not fully distinguished or propagated through the full analysis.
The way the control and tea colour effects are handled leaves some uncertainty about how fully the processing isolates hydrolysis from other influences.

2.1·Strength

Page 15• Click to view

2.2·Strength

Page 15• Click to view

2.3·Strength

Page 15• Click to view

2.4·Weakness

Page 16• Click to view

2.5·Strength

Page 17• Click to view

The

R^{2}

value is used appropriately to show that the model fits the data well. That strengthens the argument that the pattern is not random and supports the subsequent interpretation.

2.6·Strength

Page 17• Click to view

2.7·Question

Page 17• Click to view

2.8·Weakness

Page 17• Click to view

2.9·Weakness

Page 18• Click to view

Criteria C: Conclusion

5/6

Criteria StrandsPro

C.1Conclusion relevance and consistency

Excellent

C.2Scientific context comparison

Good

Criteria Feedback

The student's conclusion directly answers the research question and stays closely tied to the results they calculated.
The student uses quantitative evidence effectively, which makes the conclusion feel grounded in the analysis rather than generalised.
The student makes a relevant connection to scientific context by linking their pattern to established ideas about green tea and enzyme inhibition.

At points the student goes beyond what the in-vitro data alone can justify, especially when extending the implication toward human glucose regulation.
Some claims are stated too strongly in causal terms when the evidence mainly supports an association within the tested conditions.
The comparison with scientific context would be stronger if the student compared the limitations and conditions of their investigation more explicitly with published work.

3.1·Strength

Page 19• Click to view

3.2·Strength

Page 19• Click to view

3.3·Weakness

Page 19• Click to view

This overstates what

R^{2}

means. The student should describe it as the proportion of variation explained by the model, not as proof that tea mass alone caused the variation.

3.4·Strength

Page 19• Click to view

3.5·Question

Page 20• Click to view

3.6·Weakness

Page 20• Click to view

3.7·Strength

Page 20• Click to view

Criteria D: Evaluation

5/6

Criteria StrandsPro

D.1Methodological weaknesses

Good

D.2Improvements

Excellent

Criteria Feedback

The student identifies several specific limitations rather than using vague or generic criticism.
The student explains why those limitations matter, which shows real understanding of how method affects interpretation.
The student's suggested improvements are practical, relevant, and clearly linked to the weaknesses they identified.

The evaluation would be stronger if the student prioritised which limitations had the biggest effect on validity and reliability.
Some limitations are described well but not developed far enough in terms of their practical impact on the results.
A few improvements could be made even more targeted by linking them more directly to the control and measurement issues in the investigation.

4.1·Strength

Page 21• Click to view

4.2·Weakness

Page 21• Click to view

4.3·Strength

Page 21• Click to view

4.4·Strength

Page 21• Click to view

The evaluation names a concrete procedural weakness rather than a generic 'human error' issue. That specificity helps because it can be directly targeted in a revised method.

4.5·Strength

Page 22• Click to view

The proposed improvement is practical and linked to the stated limitation. That makes it stronger than a generic suggestion because it shows how the problem would actually be reduced.

4.6·Suggestion

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4.7·Weakness

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