6.2.3Inquiry Process
Interpreting Results in Biology — IB Biology SL Revision Notes & Topical Questions
5 min read 5 parts Lesson 8 of 10
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
Part 1 of 5A Well-Formed Graph
A graph turns a table of numbers into a pattern that can be interpreted.
Title
- Title State the relationship shown, for example the effect of temperature on the rate of reaction.
Axes
- Axes Plot the independent variable on the x-axis and the dependent variable on the y-axis, with quantity and units.
Scales
- Scales Use even linear scales that fill at least half of the available space on each axis.
Points
- Points Mark each point clearly with a small cross or a dot in a circle, and plot means rather than individual repeats.
Best fit
- Best fit Draw one smooth line or curve that shows the overall trend and need not touch every point.
Error bars
- Error bars Add bars showing the standard deviation so the spread at each value can be seen.
Part 2 of 5Describe, Then Explain
Interpretation has two separate steps, and the second is worth more.
1
Describe the trend with scientific words, such as positive correlation, optimum or plateau, quoting values from the graph.
2
Use the gradient to describe a rate, the x-intercept for a key value, and a peak or trough for an optimum.
3
Explain why the trend occurs using biology, such as enzyme denaturation, osmosis or limiting factors.
4
Identify anomalous points on the graph and justify why they are treated as anomalies.
5
Combine qualitative observations with the numbers to support the explanation.
Part 3 of 5Quality of the Data
Quality of the Data
Accuracy
- Accuracy How close the result is to the accepted value or expected pattern, which is reduced by systematic error.
Precision
- Precision How close repeated measurements are to each other, shown by a small standard deviation and affected by random error.
Reliability
- Reliability The consistency of results when the investigation is repeated, supported by many close replicates.
Validity
- Validity Whether the method tests only the stated variable, which depends on the other variables being controlled.
Part 4 of 5Worked Example
Question
- In an osmosis investigation the mean percentage change in mass is +4.0 % at 0.2 mol dm⁻³ sucrose and −3.0 % at 0.4 mol dm⁻³.
- Estimate the concentration at which there is no change in mass, and say what it means.
- Assume a straight line between the two points, which is reasonable for a short interval.
- Total change in mass over the 0.2 mol dm⁻³ interval = 4.0 − (−3.0) = 7.0 percentage points.
- Fraction of the interval before zero is reached = 4.0 ÷ 7.0 = 0.571.
- Concentration = 0.2 + (0.571 × 0.2) = 0.314 mol dm⁻³, so about 0.31 mol dm⁻³.
- At this x-intercept there is no net movement of water, so the potato tissue and the solution have equal water potential.
Answer The isotonic point is about 0.31 mol dm⁻³ sucrose.
Part 5 of 5Exam Checklist & Tips
6.2.3 – Key Points for the Exam
- Line of best fit A smooth line or curve showing the overall trend of plotted data.
- Error bar A bar showing the spread, such as the standard deviation, of a plotted mean.
- Isotonic point The concentration at which there is no net water movement into or out of tissue.
- Accuracy Closeness of a result to the accepted value.
- Validity Whether the experiment tests only what it claims to test.
Common Mistakes
- Describing the trend but never explaining it using biological principles.
- Joining the points dot-to-dot instead of drawing a smooth line of best fit.
- Plotting error bars but never mentioning them in the interpretation.
- Mixing up precision, which concerns repeats, with accuracy, which concerns the true value.
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