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6.1.2Inquiry Process

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

5 min read 5 parts Lesson 4 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 5Variables and Their Justification

Every design begins by naming the three kinds of variable and saying how each is handled.

Independent variable
  • Independent variable The one factor you change, stated with its units and the exact values you will use.
Dependent variable
  • Dependent variable The quantity you measure, stated with the method and instrument used to measure it.
Controlled variables
  • Controlled variables Every other factor that could affect the result, each with a stated way of keeping it constant.
Rate measures
  • Rate measures When time to an event is measured, convert it to a rate such as 1 ÷ time so that faster reactions give larger values.

Part 2 of 5Range and Quantity of Data

Range and Quantity of Data
Range
  • Range Use at least five values of the independent variable, spread to cover the expected trend and bracket any optimum.
Justify the range
  • Justify the range Explain why the lowest and highest values were chosen, for example because enzymes denature above a certain temperature.
Repeats
  • Repeats Carry out at least three trials at each value, and more where biological variation is large, so a mean can be found.
Pilot study
  • Pilot study A small trial run shows whether the reaction is too fast or too slow and lets you adjust concentrations before the main experiment.

Part 3 of 5Writing the Method

A good method can be followed and repeated by someone else without any guessing.

1
List the materials with concentrations and the apparatus with sizes and precision, such as a 10 cm³ graduated pipette.
2
Write a short risk assessment that names real hazards, the precautions taken, and how waste will be disposed of.
3
Number each step of the procedure in order and give exact quantities, times and temperatures rather than vague words like some.
4
Explain any clever choice of measurement, such as a colorimeter reading in place of judging a colour change by eye.
5
Consider other approaches when a laboratory test is unsuitable, such as databases, simulations or questionnaires.

Part 4 of 5Worked Example

Question

  • A student has a 1.0 mol dm⁻³ sucrose stock solution and needs 20 cm³ each of 0.2, 0.4, 0.6, 0.8 and 1.0 mol dm⁻³ solutions.
  • How much stock and water is needed for each?

  1. Use C₁V₁ = C₂V₂, so volume of stock = (C₂ × 20 cm³) ÷ 1.0.
  2. 0.2 mol dm⁻³: 0.2 × 20 = 4 cm³ stock plus 16 cm³ water.
  3. 0.4 mol dm⁻³: 8 cm³ stock plus 12 cm³ water; 0.6 mol dm⁻³: 12 cm³ stock plus 8 cm³ water.
  4. 0.8 mol dm⁻³: 16 cm³ stock plus 4 cm³ water; 1.0 mol dm⁻³: 20 cm³ stock and no water.
  5. Add a 0.0 mol dm⁻³ tube of 20 cm³ distilled water as the zero point.

Answer Stock volumes of 4, 8, 12, 16 and 20 cm³, each made up to 20 cm³ with water.

Part 5 of 5Exam Checklist & Tips

6.1.2 – Key Points for the Exam

  • Controlled variable A factor kept constant so that only the independent variable can affect the result.
  • Replicate A repeat of the same treatment, used to calculate a mean and reduce random error.
  • Pilot study A small preliminary trial used to test and improve the planned method.
  • Risk assessment A list of hazards with the precautions taken to reduce harm.
  • Valid method A procedure that measures what it claims to measure by testing only the stated variable.

Common Mistakes

  • Saying that a variable will be kept the same without describing how.
  • Using only two or three values of the independent variable, which cannot show a clear trend.
  • Writing vague steps such as add some solution instead of giving volumes and apparatus.
  • Leaving out safety and waste disposal or giving only general statements about care.

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