3.1.3Inquiry Process
Enzyme Activity- Skills — IB Biology HL Revision Notes & Topical Questions
5 min read 4 parts Lesson 103 of 160
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 3Variables and Controls
Variables and Controls
Independent variable
- Independent variable The one factor deliberately changed, such as temperature, pH or substrate concentration.
Dependent variable
- Dependent variable The quantity measured to show activity, such as volume of oxygen collected in a fixed time.
Controlled variables
- Controlled variables Factors kept constant, including enzyme concentration, substrate volume, pH when testing temperature, and time of measurement.
Buffer solutions
- Buffer solutions Using buffers fixes the pH, so changes in rate can be linked to temperature or substrate concentration instead.
Pre-incubation
- Pre-incubation Enzyme and substrate are first brought separately to the test temperature before mixing,
- so the reaction starts at the desired temperature.
| Investigating | Independent | Dependent | Key control |
|---|---|---|---|
| Temperature | Water bath temperature | Volume of oxygen per minute | Constant pH using buffer |
| pH | Buffer pH | Time for starch to disappear | Constant temperature |
| Substrate | Substrate concentration | Initial rate | Constant enzyme amount |
Part 2 of 3Reliability and Evaluation
1
Repeat each condition at least three times and calculate a mean so that random errors are averaged out.
2
Look for anomalous results, investigate why they occurred, and exclude them only if a reason is found.
3
Use a range of at least five values of the independent variable so that the optimum can be located and a trend seen.
4
Consider limitations, for example heat produced in the reaction or oxygen dissolving in water instead of being collected.
5
Suggest improvements such as using narrower intervals near the optimum or measuring the rate with a sensor.
Part 3 of 3Exam Checklist & Tips
3.1.3 – Key Points for the Exam
- Catalase An enzyme that breaks down hydrogen peroxide into water and oxygen.
- Buffer A solution that resists changes in pH.
- Dependent variable The variable that is measured in an investigation.
- Control variable A variable kept constant so that it does not affect the results.
- Reliability How consistent repeated measurements are.
Common Mistakes
- Changing more than one variable at a time, so the results cannot be linked to a single cause.
- Mixing enzyme and substrate before they have reached the test temperature.
- Measuring only the final amount of product rather than a rate over time.
- Not using repeats, so a single anomalous result changes the conclusion.
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