IGCSE Biology 0610 · Common mistakes
Common mistakes in enzyme questions
Updated · by the Fahmazing team
Enzyme questions come up every year, and examiners reject some very common phrases. Swap these wrong answers for the right ones and you will pick up easy marks.
Saying the enzyme is "killed"
What happens to an enzyme at 70 °C?
✗ Wrong: The enzyme is killed.
✓ Right: The enzyme is denatured: its active site changes shape, so the substrate no longer fits.
Tip: Enzymes are proteins, not living things, so they cannot be killed. A denatured enzyme stays the wrong shape even after cooling.
Free lesson: Enzymes
"Same shape" instead of "complementary"
Explain why amylase breaks down starch but not protein
✗ Wrong: The active site is the same shape as starch.
✓ Right: The active site of amylase is complementary in shape to starch, so only starch fits. Protein does not fit.
Free lesson: Enzymes
Confusing cold with denatured
Explain why the rate is low at 10 °C
✗ Wrong: The enzyme is denatured by the cold.
✓ Right: The molecules have less kinetic energy, so there are fewer effective collisions between substrate and active site. The enzyme is not denatured.
Tip: Low temperature: slow collisions. High temperature or the wrong pH: the active site changes shape.
Free lesson: Enzymes
Misreading the optimum and the graph
Describe the effect of temperature on the rate [3]
✗ Wrong: The optimum is the highest temperature. The rate goes up then the enzyme dies.
✓ Right: The rate increases up to 40 °C. The optimum is 40 °C, where the rate is highest. Above 40 °C the rate falls.
Tip: The optimum is where the enzyme works fastest, not the hottest temperature tested. Describe = trend plus a number with its unit.
Free lessons: Enzymes · Reading graphs and tables in biology
Upside-down rates and other slips
- Rate = amount ÷ time. 20 cm³ in 40 s is 0.5 cm³/s, not 2.
- Enzymes are catalysts, so they are not used up. The same molecule works again and again.
- When asked for the substrate, name what goes in, not the product.
- In a temperature experiment, temperature is the variable you change, so it cannot be a control variable.
Free lessons: Enzymes · Fair tests and variables
Questions students ask
Can a denatured enzyme work again if it cools down?
No. Denaturing changes the shape of the active site permanently, so the substrate still does not fit after cooling.
Why is "killed" marked wrong for enzymes?
Enzymes are protein molecules, not living organisms. The correct word is denatured.
Does pH denature enzymes too?
Yes. A pH far from the optimum changes the shape of the active site, so the substrate no longer fits and the rate falls.