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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
HL

Exam analysis

Chance of appearing19%of analysed past papers
Latest appearanceNovember 2025
Most common paperPaper1
Typical marks1–2

Common command terms

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

Recent exam appearances

November 2025Paper2 ["HL"] · TZ39(b)[ 7 ]C1.1.8—Effects on enzyme activity
November 2025Paper1A ["HL"] · TZ36[ 1 ]C1.1.8—Effects on enzyme activity
November 2025Paper1A ["HL"] · TZ15[ 1 ]C1.1.8—Effects on enzyme activity
May 2025Paper1A ["HL"] · TZ15[ 1 ]C1.1.8—Effects on enzyme activity
November 2024Paper3 ["HL"] · TZ01(c)[ 2 ]C1.1.8—Effects on enzyme activity
Practice this objective

Coverage 2012–2025 · 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 HL