Why rewrite the original answer in an error drill?

Writing it out shows whether the error was conceptual or numerical; reading the right answer alone overstates understanding.

Should I distinguish enzyme from catalyst in answers?

Yes; an enzyme is a biological catalyst, so stating that it is a protein with specificity earns more marks than catalyst alone.

DSE Biology | Enzymes and Factors Practice Paper 4 (Error Drill)

2026-11-04

Tutor Prep Guide · Secondary Biology

Ten items built from the most common misconceptions about enzymes, each with the correct statement and the reasoning behind it.

Attempt first, mark afterwards　Allow about twenty-five minutes; write your original answer first, then compare with the explanation to see which step went wrong.

01　Paper details (check answers afterwards)

Item	Detail
Questions	10 items
Suggested time	About 25 minutes
Difficulty mix	Foundation 4 · Intermediate 3 · Challenge 2 · Error redo 1
Chapter	Chapter: DSE Biology \| Enzymes and Affecting Factors
Level	S4 (Secondary 4) Biology

02　Questions (10 items)

FoundationIs an enzyme used up when it finishes catalysing a reaction, and why does that matter?
FoundationIs it true that every enzyme works best at 37°C?
FoundationDoes an enzyme shift the equilibrium position or raise the final yield?
FoundationDo enzymes only carry out breakdown reactions? Give a counter-example.
IntermediateIs it true that an enzyme merely slows down at extreme pH and recovers fully once returned to pH 7?
IntermediateWith Q10 = 1.8 and a rate of 15 units at 20°C, what is the theoretical rate at 40°C?
IntermediateThe same reaction takes 80 minutes without an enzyme and 4 minutes with it. How many times faster is it?
ChallengeA non-competitive inhibitor lowers Vmax from 120 to 60. At substrate equal to Km (10), what is the rate before and after?
ChallengeEnzyme X has Km 10 mmol/L and enzyme Y has Km 2.5 mmol/L with the same Vmax. Which binds substrate more strongly, and what does Km mean?
Error redoError drill: a student writes that the more enzyme present, the faster the reaction, without limit. What is correct?

03　Answers and one-line notes

#	Answer	One-line note
1	No; it is reused, so a small amount can convert a large amount of substrate	The enzyme is unchanged before and after, giving a high turnover number and saving the cell from constant resynthesis.
2	No; the optimum varies, and Taq polymerase from thermophiles works near 70-80°C	The optimum reflects stability in that organism’s environment: human enzymes sit near 37°C while hot-spring enzymes sit far higher.
3	No; it only speeds up reaching equilibrium, which is set by the reaction itself	An enzyme accelerates the forward and reverse reactions equally, so the equilibrium point is unchanged and only the time to reach it falls.
4	No; synthesis needs enzymes too, such as DNA polymerase and aminoacyl-tRNA synthetase	Both catabolic and anabolic pathways are enzyme-catalysed: the direction differs, the mechanism does not.
5	Not necessarily; extreme pH denatures the enzyme and the tertiary structure may not recover	A mild shift from the optimum only changes charges reversibly, while prolonged or extreme pH damage cannot be undone.
6	48.6 units	Two 10-degree steps from 20 to 40°C: 15 times 1.8 squared = 48.6.
7	20.0 times	80 over 4 = 20.0; the fold change in rate is the inverse ratio of the times.
8	From 60.0 down to 30.0	When S equals Km, v is half of Vmax: 60.0 before and 30.0 after, both consistent with the Michaelis-Menten equation.
9	Enzyme Y (Km 2.5); a smaller Km means higher affinity	Km is the substrate concentration giving half of Vmax, so a smaller value means half-saturation is reached with less substrate.
10	Not necessarily; the rate is also limited by substrate, temperature and pH, so extra enzyme only helps once substrate is saturating	When substrate is saturating, extra enzyme molecules have nothing to bind, and very high enzyme levels may also be limited by diffusion and product inhibition.

04　What to do after marking

After marking, redo only the wrong items and write down which step went wrong (formula, unit, or misread number).
Repeat the same item two days later; move to the next paper only when both attempts are correct.
Parents only need the answer and note columns; there is no need to explain every item.

Need a tutor for this chapter? Register here Tutor Registration →

Questions and answers are written originally by the TutorZone team and are not taken from any school, publisher or examination authority paper. Every value is checked by computer.