Explain3 marksBGCSE
A digestive enzyme works fastest at 37 °C. Explain why its activity falls sharply at 60 °C.
Show the mark scheme and the examiner note
Answer: The high temperature changes the shape of the enzyme active site (denaturation), so the substrate is no longer complementary and fewer enzyme–substrate complexes form.
- Heat changes the shape of the active site
- The substrate no longer fits (the enzyme is denatured)
- Fewer enzyme–substrate complexes form, so the rate falls
Examiner technique: Denaturation is a shape answer. Writing "the enzyme is killed" is a common phrasing and it is wrong: enzymes are molecules, not organisms.