DSE Biology | Enzymes and Limiting Factors Lesson-Prep Guide (Tutor Edition) | Q10 of 2, an Optimum at 40 C and 9 mg per Minute

2026-11-03

Tutor lesson-prep guides · Secondary Biology

Students can recite that enzymes are biological catalysts, yet freeze at a curve that collapses after 50 C. Six temperatures and one set of readings turn the curve into evidence they can read.

Objectives — Students can: (1) find the optimum temperature from activity data and use the doubling between 20 and 30 C to explain Q10; (2) describe the shape of the temperature, pH and enzyme-concentration curves and say why denaturation is irreversible; (3) compute an average rate as product divided by time and distinguish it from an instantaneous rate.

01 Prerequisites (3-minute check)

If any of these fails, fix it before the lesson starts.

Skill	Quick check	Pass mark
Catalysts	What happens to a catalyst during a reaction	It is not used up and can work again
Protein structure	Which bonds hold an enzyme in shape	Peptide bonds plus hydrogen and ionic bonds
Rates	What unit expresses a rate	Amount of product divided by time

02 Lesson flow (60 minutes)

Time	Stage	Tutor does	Student does
0-8 min	What an enzyme is	Activation energy, active site, specificity	Say lowering activation energy
8-20 min	Six temperatures	Read the table, find the peak	Optimum 40 C, activity 90
20-32 min	Curve shape	Rising and falling have different causes	Only 50% left at 50 C
32-42 min	pH and concentration	Optimum pH, saturation curve	Add enzyme, not substrate
42-52 min	Rate arithmetic	Product over time	45 mg over 5 minutes
52-60 min	Exit check	Three questions marked live	All three right

03 Teaching script (read it out)

Scene 1: An enzyme lowers activation energy

The substrate binds at the active site to form an enzyme-substrate complex, which lowers the activation energy so the reaction can run at body temperature.
Specificity comes from shape: only a complementary substrate fits, which is the lock-and-key idea. Heat or the wrong pH breaks the hydrogen bonds holding that shape, the site distorts and the substrate no longer fits. That is denaturation, and it is not the enzyme dying but its structure failing.
Keep the two cases apart: low temperature slows the enzyme down and is reversible; high temperature denatures it and is not. The rising and falling limbs of the curve therefore have completely different explanations, and answers must separate them.

Students must say: why an enzyme chilled to 0 C recovers on warming but one held at 60 C does not.

Scene 2: Six readings give one curve

One enzyme extract reads 15 at 10 C, 30 at 20 C, 60 at 30 C, 90 at 40 C, 45 at 50 C and 0 at 60 C (arbitrary units).
From 20 C to 30 C the activity goes 30 to 60, exactly double, so Q10 = 2: a ten-degree rise roughly doubles the rate because molecules move faster. The peak of 90 at 40 C is the optimum. At 50 C the reading halves to 45 because some enzyme molecules have already denatured, and at 60 C it reaches zero because all of them have.
Answers must name the segment they are describing. Writing that higher temperature always means faster activity loses marks the moment the curve turns down. The pH curve has the same shape, but its peak sits at a pH value.

Students must say: why 50 C leaves half the activity rather than none (only part of the enzyme has denatured).

Scene 3: Rates are calculated, not felt

Forty-five milligrams of maltose in five minutes is an average rate of 45 / 5 = 9 mg per minute. That is an average over the whole period, not the rate at any one instant.
If the curve flattens later, substrate is running out or product is inhibiting, so the instantaneous rate falls while the average stays inflated by the fast start. Comparisons therefore need the same time window and the same initial rate, or two different quantities are being compared.
Doubling enzyme concentration doubles the rate while substrate is plentiful. Once substrate is saturating, more substrate does nothing and only more enzyme helps, which is the saturation curve examiners like to test.

Students must say: what 45 mg divided by 5 minutes gives and in what unit (9 mg per minute, an average).

04 Question types and worked steps

Type	Example	Steps	Answer
Graph reading	Optimum temperature from a curve	Find the peak and read the axis	40 C, activity 90
Explanation	Why the curve rises and falls	Kinetic energy versus denaturation	Kept separate
Calculation	Average rate of reaction	Product divided by time	9 mg per minute
Design	A controlled experiment	Change one variable, fix the rest	Same volume, concentration, time

Sanity check (teach this): There is one optimum: of the six readings 90 at 40 C is the peak, so never write that hotter is always faster.
Q10 is a ratio: 60 divided by 30 is 2, not a difference of 30.
Rate units follow the time: 45 mg over 5 minutes is 9 mg per minute, not 9 mg.
Denaturation cannot be reversed by cooling, whereas inhibition usually can.

05 Independent practice (3 questions)

Question	Answer	What to watch
Activity ratio from 20 C to 30 C	2 (Q10 = 2)	60 divided by 30
Activity at 50 C as a share of the optimum	50%	45 divided by 90
Average rate for 45 mg in 5 minutes	9 mg per minute	Product divided by time

06 Common mistakes and what to say

Mistake	Student writes	Say this
Calling the falling limb faster	Writing that hotter is always faster	Past 40 C the enzyme denatures, so activity falls rather than rises.
Treating denaturation as reversible	Claiming cooling restores the enzyme	Heat has destroyed the three-dimensional shape, and cooling does not rebuild it.
Rate without a unit	Answering a bare 9	Nine milligrams per minute; without the unit the number means nothing.
Confusing enzyme and substrate	Adding substrate after saturation	Once saturated only more enzyme helps; extra substrate changes nothing.

07 Homework (paper, section and question numbers)

Secondary biology chapter index — Enzymes and metabolism practice
All lesson-prep guides — Compare other subjects

08 Exit check (last 5 minutes)

Question	Answer	Decision
Optimum temperature	40 C	All three right: move to respiration
Activity share at 50 C	50%	One wrong: reteach denaturation
Average rate	9 mg per minute	Two wrong: return to act three

09 Tutor FAQ

Are all enzymes proteins?

Almost all are; a few RNA molecules catalyse reactions, and school biology treats proteins as the rule.

Why does cold not destroy an enzyme?

Cold only slows molecular motion, so activity drops while the structure survives and warming restores it.

Why use a water bath?

A water bath holds temperature steady, which matters when temperature is the independent variable.

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A TutorZone lesson-prep guide. Written by the TutorZone team; questions and lesson flow are original and are not taken from any school or publisher material.