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C1.1.8—Effects on enzyme activity

Temperature, pH, substrate concentration, enzyme concentration and inhibitors alter activity by changing collisions, active sites or saturation during reactions in cells.

Syllabus
First assessment 2025
Objective
C1.1.8
Level
SL

Exam analysis

Chance of appearing28%of analysed past papers
Latest appearanceMay 2025
Most common paperPaper1
Typical marks1–2

Common command terms

  • Explain
  • Outline
  • Describe
  • Determine
  • Compare
  • Evaluate
  • Suggest
  • Sketch
  • Label

Recent exam appearances

May 2025Paper1B ["SL"] · TZ34(c)[ 2 ]C1.1.8—Effects on enzyme activity
November 2024Paper3 ["SL"] · TZ28(a)[ 2 ]C1.1.8—Effects on enzyme activity
November 2024Paper1 ["SL"] · TZ110[ 1 ]C1.1.8—Effects on enzyme activity
May 2024Paper1 ["SL"] · TZ29[ 1 ]C1.1.8—Effects on enzyme activity
May 2024Paper2 ["SL"] · TZ13(a)(ii)[ 1 ]C1.1.8—Effects on enzyme activity
Practice this objective

Coverage 2010–2025 · Updated 15 Jul 2026

Concept essentials

  • Temperature increases collision frequency up to an optimum before denaturation lowers activity.
  • pH changes can alter charges, tertiary structure and active-site shape.
  • Substrate concentration raises rate until active sites become saturated.
  • Graphs of enzyme activity must be interpreted using enzyme structure and reaction conditions.
ConceptIB Biology SL