The scientific investigation

📚What is not in the word count

Six things are excluded: charts and diagrams, data tables, equations, formulas and calculations, citations and references of any style, the bibliography, and headers.

So a well-annotated table or a clearly labelled graph costs nothing, while a paragraph describing what the table shows costs words. Put information into tables and figures wherever you legitimately can.

State at the start of the report: the title, your IB candidate code, the candidate codes of any group members, and the word count. No cover page or contents page is needed.

📈The four criteria, and where the marks really are

Research design (6 marks)

This assesses how well you communicate the purpose and practice of your methodology. The top band (5–6) needs three things:

• the research question described within a specific and appropriate context — naming the independent and dependent variables (or two correlated variables, for a field or database study), describing the system concisely, and giving background theory of direct relevance. “How does temperature affect enzymes?” is not a research question; “How does temperature (20–60 °C) affect the initial rate of hydrogen peroxide breakdown by catalase from potato, measured as the volume of oxygen released in 30 s?” is;
• methodological considerations explained, not merely stated — why that method of measuring the dependent variable, why that range and interval, how many repeats and why, which control variables and how each was controlled, how samples were chosen, and the safety, ethical and environmental issues;
• a description detailed enough that the investigation could be reproduced — specific materials, concentrations, sample sizes and steps — without repetitive detail.

The verb hierarchy across the bands is stated → described → explained. Most mid-band scripts fail on that one word: they say what was controlled without saying why it mattered.

Data analysis (6 marks)

The top band needs all three strands:

• recording and processing communicated both clearly and precisely — clear means the method of processing can be followed; precise means conventions are right: units in column headings, consistent decimal places, appropriate significant figures, properly annotated graphs;
• evidence of an appropriate consideration of uncertainties — in biology this usually means recording instrument uncertainties and, more importantly, dealing with biological variation: calculating the standard deviation of repeats, showing error bars (SD or standard error), and discussing overlap;
• processing carried out appropriately and accurately — which often includes a statistical test suited to the data: a t-test to compare two means, chi-squared for frequencies or associations, or a correlation coefficient with \( R^{2} \) for a relationship between two variables.

Show one worked example of each type of calculation and tabulate the rest — calculations are excluded from the word count.

Conclusion (6 marks)

The top band requires a conclusion that is justified, relevant to the research question, fully consistent with the analysis — interpreting your processed data including its uncertainties and the result of any statistical test — and justified through relevant comparison to the accepted scientific context.

That last phrase is where marks are routinely dropped. Compare your findings with published results, accepted theory or textbook values, and cite the source in enough detail to be traceable. In biology, published values are often a trend or an optimum rather than a single number: explain whether your pattern agrees with it, and why it might not.

Evaluation (6 marks)

The top band asks you to explain the relative impact of specific methodological weaknesses or limitations, and to explain realistic improvements that address them.

• Generic against specific. “Human error” and “the equipment was not accurate” score in the lowest band. “Leaf discs were cut from different leaves of different ages, which varied in chlorophyll content; this probably caused the large standard deviations at the two highest light intensities” is specific.
• Weakness against limitation. A weakness concerns control of variables, precision of measurement or variation in the data. A limitation concerns how far the conclusion can be extended — the range of data, the confines of the system (one species, one site, one season), or the assumptions made.

Relative impact means ranking: say which weakness mattered most and why, using your data. Large, overlapping error bars at particular values of the independent variable are evidence you can point to.

🔧Choosing a research question

The research question need not go beyond the syllabus, but it must allow enough extent and depth for every criterion to be addressed. The guide allows several approaches, alone or combined: hands-on laboratory work, fieldwork, use of a spreadsheet for analysis and modelling, extraction and analysis of data from a database, and use of a simulation. A database investigation is legitimate, but the methodology must then focus on how the data were selected, filtered and sampled.

Biology topics that work well because they give quantitative data with controllable variables:

⚖️Ethics, safety and academic integrity

Ethics and safety come before any data collection, and your teacher must be satisfied that you have considered them. The IB’s animal experimentation and sciences experimentation guidelines apply. In practice:

• No investigation may cause pain, harm or distress to animals, including invertebrates. Behavioural studies of small invertebrates are acceptable if the animals are returned unharmed to their habitat; experiments that deprive animals of food or expose them to extremes are not.
• Investigations involving human participants (for example heart rate or reaction time) need informed consent, must not put anyone at risk, must respect the right to withdraw, and must keep data anonymous. Body fluids such as blood should not be used.
• Microorganisms must be handled with aseptic technique, cultures sealed and incubated at temperatures that do not favour human pathogens, and disposed of safely.
• Fieldwork should minimize disturbance to habitats, and collected organisms or samples should be returned where possible.

The report must be your own work. Your teacher may comment on one draft, and the next version submitted is final. Reference everything you use; omitted or improper referencing is academic malpractice.

Collaborative work is optional and limited to groups of up to three. Each student must have their own research question, investigated by manipulating a different independent variable, or the same one with a different dependent variable, or different data selected from a larger shared data set. No two students may present the same set of raw data, and all authoring, including the methodology, must be done individually.

✅Before you submit — a checklist

• Title, candidate code, group members’ codes and word count at the start.
• Research question naming the independent and dependent variables (or correlated variables), with ranges and the biological system.
• Relevant background theory, cited.
• Every control variable listed with how it was controlled and why it matters.
• Safety, ethical and environmental considerations addressed.
• Sample size and number of repeats justified, ideally from a pilot.
• Raw data tables with units and uncertainties in column headings, and qualitative observations.
• Means with standard deviations, and graphs with error bars.
• An appropriate statistical test, with the null hypothesis, the result and its interpretation stated.
• Conclusion compared with cited scientific context, consistent with the statistics.
• Evaluation naming specific weaknesses and limitations, ranked by impact, each with a realistic improvement.
• Full bibliography in one consistent style.