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6.3.2Inquiry Process

Evaluating in Biology — IB Biology SL Revision Notes & Topical Questions

5 min read 5 parts Lesson 10 of 10

📚 IB Biology SL Hub / Topical Revision
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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.
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Part 1 of 5Errors in the Investigation

Identify specific errors and say which type each one is.

Systematic error
  • Systematic error A fault in method or apparatus that shifts results in one direction, such as a badly calibrated pH meter.
Random error
  • Random error Unpredictable scatter, often from natural variation between organisms or from judging an end point by eye.
Reducing random error
  • Reducing random error Take more replicates and calculate a mean, since random variation tends to cancel out.
Reducing systematic error
  • Reducing systematic error Calibrate instruments and use a better technique, since repeating does not remove a consistent bias.
Evaporation
  • Evaporation Water lost from tissue before weighing makes the final mass consistently too low.

Part 2 of 5Weaknesses, Limitations, Assumptions

Weaknesses, Limitations, Assumptions
Weakness
  • Weakness A feature of the method that causes significant error, such as measuring a non-circular zone with a ruler.
Limitation
  • Limitation A factor that restricts how far the conclusion can be generalised, such as using only one species or one temperature.
Assumption
  • Assumption A simplification in the experiment, such as assuming mass change is due only to water movement.
Hypothesis
  • Hypothesis Comment again on the hypothesis in light of the errors, which may weaken the support for it.

Part 3 of 5Writing the Evaluation

Each point should follow the same three-step pattern.

1
Name one specific weakness and refer to your own data, graph or observations rather than writing generally.
2
Explain the impact of the weakness on the results, saying which way it affected them or how it raised the spread.
3
Suggest a realistic improvement that a school laboratory could carry out and that directly addresses the weakness.
4
Focus on the one or two sources of error that had the greatest effect on the result.
5
Avoid vague phrases like human error, and give the exact action that caused the problem.

Part 4 of 5Worked Example

Question

  • A balance has an uncertainty of ±0.01 g.
  • A potato cylinder changes in mass by 0.12 g, from an initial mass of 1.80 g.
  • Compare the percentage uncertainty in the mass change with that in the initial mass and suggest an improvement.

  1. The change is found by subtracting two readings, so the absolute uncertainties add: 0.01 + 0.01 = ±0.02 g.
  2. Percentage uncertainty in the change = 0.02 ÷ 0.12 × 100 = 16.7 %.
  3. Percentage uncertainty in the initial mass = 0.01 ÷ 1.80 × 100 = 0.56 %.
  4. The small change is therefore much less certain than the starting mass.
  5. Improvementuse larger or more cylinders, a longer soak, or a balance reading to 0.001 g, so the change is large compared with the uncertainty.

Answer The mass change has about 17 % uncertainty, compared with about 0.6 % for the initial mass.

Part 5 of 5Exam Checklist & Tips

6.3.2 – Key Points for the Exam

  • Systematic error A consistent bias in the same direction, reducing accuracy.
  • Random error Unpredictable variation that reduces precision.
  • Limitation A restriction on how widely a conclusion can be applied.
  • Assumption A simplification made about the system being studied.
  • Improvement A specific, realistic change that addresses an identified weakness.

Common Mistakes

  • Writing a general list of errors that could apply to any experiment instead of this one.
  • Blaming human error without naming the exact action that caused it.
  • Suggesting improvements that are unrealistic in a school laboratory or that do not match the weakness.
  • Naming a weakness but not explaining its effect on the results.

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