Biology  by Bradford
IB Biology 2025 · Theme C · Interaction and interdependence

C1.1 Enzymes and metabolism. Practice questions with markscheme.

50 original IB-style questions on C1.1, written from the 2025 guide: 25 multiple-choice, 16 short-answer, 6 data-based, 2 extended-response part, 1 drawing. Below is a 20-mark standard-level practice paper built from them, ready to hand out as a class quiz or homework, or to sit yourself and mark against the scheme. Print it, project it, or build a fresh one on the same topic.

What the guide asks for

10 statements at SL and HL, 7 additional higher level.

  1. C1.1.1SL / HL Enzymes as catalysts
  2. C1.1.2SL / HL Role of enzymes in metabolism
  3. C1.1.3SL / HL Anabolic and catabolic reactions
  4. C1.1.4SL / HL Enzymes as globular proteins with an active site for catalysis
  5. C1.1.5SL / HL Interactions between substrate and active site to allow induced-fit binding
  6. C1.1.6SL / HL Role of molecular motion and substrate-active site collisions in enzyme catalysis
  7. C1.1.7SL / HL Relationships between the structure of the active site, enzyme–substrate specificity and denaturation
  8. C1.1.8SL / HL Effects of temperature, pH and substrate concentration on the rate of enzyme activity
  9. C1.1.9SL / HL Measurements in enzyme-catalysed reactions
  10. C1.1.10SL / HL Effect of enzymes on activation energy
  11. C1.1.11HL Intracellular and extracellular enzyme-catalysed reactions
  12. C1.1.12HL Generation of heat energy by the reactions of metabolism
  13. C1.1.13HL Cyclical and linear pathways in metabolism
  14. C1.1.14HL Allosteric sites and non-competitive inhibition
  15. C1.1.15HL Competitive inhibition as a consequence of an inhibitor binding reversibly to an active site
  16. C1.1.16HL Regulation of metabolic pathways by feedback inhibition
  17. C1.1.17HL Mechanism-based inhibition as a consequence of chemical changes to the active site caused by the irreversible binding of an inhibitor

In the bank for C1.1

  • 25 multiple-choice
  • 16 short-answer
  • 6 data-based
  • 2 extended-response part
  • 1 drawing
  • 18 higher level only

Every question is original and tagged to a guide statement. See the whole bank →

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The practice paper

Take it on screen → Build a fresh paper Paper code BbB-EAAAAAgAABQAOzdd
Biology · topic quiz
Standard level · topic practice, not an exam format
30 minutes20 marks

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Covers C1.1 Enzymes and metabolism
Name:
1.

Amylase digests starch. Samples of a starch–amylase mixture were tested with iodine solution at intervals, and the time taken for the blue-black colour to stop appearing was recorded at several temperatures. How should the rate of reaction be calculated from these results?

[1]
  1. As the time taken to reach the end point, in s
  2. As 1 ÷ time taken, so that a shorter time gives a higher rate
  3. As the concentration of amylase divided by the time taken
  4. As the mass of starch added at the start of the reaction
2.

How do enzymes increase the rate of chemical reactions?

[1]
  1. They lower the activation energy of the reaction
  2. They shift the reaction to produce more product than would otherwise be possible
  3. They supply energy to the substrate
  4. They increase the temperature of the cell
3.

How could the rate of an enzyme-catalysed reaction be measured?
I. Measuring how fast the product accumulates
II. Measuring how fast the substrate disappears
III. Measuring the mass of enzyme at the end

[1]
  1. I and III only
  2. II and III only
  3. I and II only
  4. I, II and III
4.

Which row correctly classifies the metabolic reactions?

[1]
RowProtein synthesis from amino acidsHydrolysis of starch to glucose
A.anabolic (condensation)catabolic (hydrolysis)
B.catabolicanabolic
C.both anabolicboth anabolic
D.both catabolicboth catabolic
  1. Row A
  2. Row B
  3. Row C
  4. Row D
5.

Describe what happens when an enzyme catalyses a reaction, from substrate binding to product release.

[2]
6.

Enzymes from thermophilic bacteria are widely used in industrial processes. Suggest reasons for this.

[2]
7.

A student investigated the activity of catalase, an enzyme found in potato (Solanum tuberosum) tissue that breaks down hydrogen peroxide into water and oxygen. Equal-sized potato discs were added to hydrogen peroxide solutions of different concentrations. The foam produced by the released oxygen was collected in a measuring cylinder and its height recorded after two minutes. Three trials were run at each concentration, at a constant temperature of 25 °C.

Concentration of hydrogen peroxide / %Foam height, trial 1 / mmTrial 2 / mmTrial 3 / mm
0.5454
1.09810
2.0171816
3.0242223
4.0252425
(a)Calculate the mean foam height at a hydrogen peroxide concentration of 2.0 %.[1]
(b)State the relationship between hydrogen peroxide concentration and catalase activity shown by the data.[1]
(c)Suggest a reason for the very similar foam heights at 3.0 % and 4.0 % hydrogen peroxide.[2]
(d)Identify two variables, other than temperature, that were kept constant in this investigation.[2]
1.
2.
(e)Outline the roles of enzymes in metabolism.[2]
8.

A student heated a solution of an enzyme to 60 °C, cooled it back to 30 °C, added substrate, and found no activity. They concluded: "the enzyme has been denatured." Evaluate this conclusion and the evidence needed to support it.

[4]

Original practice questions © Biology by Bradford · CC BY-NC-SA 4.0 · Not affiliated with or endorsed by the International Baccalaureate Organization.
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Markscheme BbB-EAAAAAgAABQAOzdd

One mark per point; / separates alternative wording within a point, OR separates alternative answers, words in brackets are not required, underlined words are essential. OWTTE = or words to that effect.

1. C1.1.9 [1]
  • B: rate is inversely related to the time taken to reach the end point, so 1/time gives a value that increases as the reaction speeds up;
2. C1.1.10 [1]
  • A: enzymes lower the activation energy needed for the reaction to proceed; they do not supply energy or change the end point of the reaction;
3. C1.1.7-C1.1.8 [1]
  • C: rate = change of product or substrate per unit time; enzyme quantity does not change during the reaction;
4. C1.1.3 [1]
  • A: anabolism builds larger molecules (condensation); catabolism breaks them down (hydrolysis/oxidation);
5. C1.1.4-C1.1.5 [2 max]
  • substrate collides with / binds to the active site, forming an enzyme–substrate complex;
  • the active site changes shape (slightly) to fit the substrate more closely / induced fit;
  • the reaction occurs and products are released, leaving the enzyme unchanged (and reusable);
6. C1.1.7 [2 max]
  • they remain active / are not denatured at high temperatures;
  • reactions can run faster at higher temperatures (more collisions) without loss of enzyme;
  • less cooling of reaction vessels needed / lower contamination risk at high temperature / longer working life, OWTTE;

Any 2. Accept a named example such as Taq polymerase.

7. C1.1.2, C1.1.8
  • (a) [1]
    • 17 mm;

    ECF not applicable; units not required if consistent.

  • (b) [1]
    • activity/foam height increases with (substrate) concentration, levelling off / plateauing at higher concentrations;

    Do not accept "positive correlation" alone without reference to the plateau.

  • (c) [2]
    • (nearly) all active sites are occupied / enzyme is saturated (with substrate);
    • enzyme concentration / number of active sites becomes the limiting factor, OWTTE;
  • (d) [2]
    • size/mass/surface area of potato discs;
    • time for which foam was collected / number of discs / volume of hydrogen peroxide solution / source (age/variety) of potato;

    Mark the first two answers only.

  • (e) [2 max]
    • enzymes catalyse/speed up the (specific) reactions of metabolic pathways;
    • each reaction/step is catalysed by a different/specific enzyme;
    • (so) cells can control which reactions occur / regulate pathways (by controlling enzymes), OWTTE;

    Content pivot from the data into taught content.

8. C1.1.8 [4 max]
  • the loss of activity after heating and cooling is consistent with denaturation (an irreversible change to tertiary structure), so the conclusion is plausible;
  • however a single result is weak evidence / the loss could have other causes (substrate or product broke down, evaporation, pH change, contamination);
  • a valid conclusion needs a control kept at 30 °C throughout to show the assay can detect activity, plus repeats;
  • testing whether activity returns on cooling (reversibility) distinguishes true denaturation from reversible inactivation;
  • measurements at several temperatures would locate the optimum and show the fall above it, strengthening the claim;
  • overall the conclusion is reasonable but under-supported by one observation, OWTTE;

NOS: evaluating method + evidence. Evaluate requires strengths, limitations and a judgement.

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