6.2.3Inquiry Process
Interpreting Results in Biology — IB Biology HL Revision Notes & Topical Questions
5 min read 6 parts Lesson 158 of 160
Part 1 of 6Presenting Data as a Graph
A well-built graph makes the pattern in your data visible, so every feature of it should be deliberate.
Title
- A specific title states the relationship plotted, for example the effect of temperature on the rate of an enzyme-catalysed reaction.
Axes
- The independent variable goes on the x-axis and the dependent variable on the y-axis, each labelled with the quantity and its unit.
Scale
- Use a linear scale with even intervals that fills at least half of the grid in each direction, so the trend is easy to read.
Points
- Plot each mean value clearly as a small cross or a circled dot, then draw a line or curve of best fit through the overall trend.
Error bars
- Bars showing standard deviation give a picture of spread;
- overlapping bars between two means suggest the difference may not be significant.
Part 2 of 6Reading Graph Features
Different parts of a graph carry different biological information.
Reading Graph Features
Gradient
- The slope at a point is a rate of change, for example the initial rate of an enzyme reaction taken from a tangent to the curve.
Intercept
- Where a line crosses the x-axis can be a key value;
- in an osmosis experiment it marks the isotonic concentration, where mass change is zero.
Peak or trough
- The highest point of a curve can show an optimum, such as the optimum temperature or pH of an enzyme.
Plateau
- A levelling-off shows that another factor has become limiting, so adding more of the variable no longer increases the response.
| Graph feature | What it may represent | Example |
|---|---|---|
| Positive gradient | Response rises as the variable rises | Rate rising with substrate concentration |
| Maximum | Optimum condition | Peak activity at a particular pH |
| x-intercept | Balance point | Isotonic concentration of plant tissue |
Part 3 of 6Describing, Explaining and Handling Anomalies
1
First describe the trend using precise terms such as positive correlation, reaches an optimum or the rate plateaus, quoting values from the graph.
2
Then explain why the trend occurs using biological principles, for example denaturation of the enzyme's active site above the optimum temperature.
3
Circle any anomalous result, meaning a point that clearly does not fit the pattern, and state why it is judged anomalous rather than simply removing it.
4
Link qualitative notes to the numbers, such as soft, limp potato cylinders at the start that explain a smaller mass gain than expected.
5
Finish by commenting on the quality of the results using the four terms in the next section.
Part 4 of 6Judging Data Quality
These four words have precise meanings and should not be used interchangeably.
Accuracy
- How close a result is to the accepted value or expected pattern;
- it is reduced by systematic errors such as a miscalibrated instrument.
Precision
- How close repeated measurements are to each other;
- a small standard deviation shows high precision and random errors reduce it.
Reliability
- The consistency of results when the work is repeated;
- several precise replicates with small error bars give a reliable mean.
Validity
- Whether the method really tests the research question, which depends on controlling variables so only the independent variable changes.
Part 5 of 6Worked Example
Question
- Potato cylinders were placed in sucrose solutions.
- Mean percentage mass change was +18.0% at 0.0 mol dm⁻³, +8.0% at 0.2, −4.0% at 0.4 and −14.0% at 0.6 mol dm⁻³.
- Estimate the isotonic concentration.
- The sign changes between 0.2 and 0.4 mol dm⁻³, so the x-intercept lies in this interval.
- Gradient between these points = (−4.0 − 8.0) ÷ (0.4 − 0.2) = −12.0 ÷ 0.2 = −60 % per mol dm⁻³.
- Concentration change needed to fall from +8.0% to 0%: 8.0 ÷ 60 = 0.133 mol dm⁻³.
- Isotonic concentration = 0.2 + 0.133 = 0.333 mol dm⁻³.
Answer The isotonic concentration is approximately 0.33 mol dm⁻³, where the tissue neither gains nor loses water overall.
Part 6 of 6Exam Checklist & Tips
6.2.3 – Key Points for the Exam
- Line of best fit A line or smooth curve drawn through the trend of the plotted data that need not touch every point.
- Anomalous result A data point that clearly does not fit the overall pattern and needs a justified explanation.
- Error bar A bar on a graph showing the spread of data, usually standard deviation.
- Precision The closeness of repeated measurements to one another.
- Validity The extent to which the method genuinely tests the research question.
Common Mistakes
- Describing a trend without explaining it;
- the biological explanation is the most important part of interpretation.
- Joining plotted points dot to dot instead of drawing a best-fit line or curve.
- Using accuracy and precision as if they mean the same thing;
- one concerns the true value, the other repeat agreement.
- Deleting an anomalous point silently rather than showing it on the graph and justifying why it is anomalous.
Last updated:
\n