C1.1.1—Enzymes as catalysts
Enzymes act as reusable biological catalysts, usually proteins, that speed reactions by forming substrate complexes and lowering activation energy in cells.
- Syllabus
- First assessment 2025
- Objective
- C1.1.1
- Level
- SL
Exam analysis
Chance of appearing1%of analysed past papers
Latest appearanceMay 2019
Most common paperPaper2
Typical marks4–8
Common command terms
- Outline
- Explain
Recent exam appearances
May 2019Paper2 ["SL"] · TZ25(c)[ 8 ]C1.1.1—Enzymes as catalysts
May 2016Paper2 ["SL"] · TZ05(a)[ 4 ]C1.1.1—Enzymes as catalysts
Practice this objective
Coverage 2016–2019 · Updated 15 Jul 2026
Concept essentials
- Enzymes speed biological reactions without being used up.
- Substrates bind to active sites to form enzyme-substrate complexes.
- Catalysis lowers activation energy and increases reaction rate.
- Specificity depends on the relationship between substrate and active site.