C1.1 Enzymes and metabolism
Practice exam-style IB Biology questions for Enzymes and metabolism, aligned with the syllabus and grouped by topic.
Question 1
What is a property of an enzyme acting as a catalyst?
A.
It increases the rate of a reaction without being permanently consumed.
B.
It supplies all the energy released by the reaction.
C.
It changes the final products into substrates at the end of the reaction.
D.
It is used up in the same proportion as substrate molecules.
Question 2
What type of metabolic reaction is protein synthesis from amino acids?
A.
Catabolic condensation
B.
Anabolic condensation
C.
Anabolic hydrolysis
D.
Catabolic oxidation
Question 3
What feature of enzymes allows specific substrates to bind for catalysis?
A.
A large region where all amino acids contact the substrate equally
B.
A permanent covalent bond between enzyme and product
C.
A specific active site formed by the folded globular protein
D.
A linear chain of amino acids that remains unfolded in solution
Question 4
What is required before an enzyme–substrate complex can form in a fluid cell environment?
A.
A collision between the substrate and the active site in a suitable orientation
B.
The permanent immobilization of all substrate molecules
C.
The destruction of the active site by high temperature
D.
The release of water before any molecular contact occurs
Question 5
What is an example of an extracellular enzyme-catalysed process?
A.
Glycolysis occurring in the cytoplasm of a muscle cell
B.
The Krebs cycle occurring inside mitochondria
C.
Hydrolysis of starch by amylase secreted into the gut lumen
D.
DNA replication occurring inside a bacterial cell
Question 6
What correctly classifies glycolysis and the Krebs cycle?
A.
Glycolysis is cyclical and the Krebs cycle is linear.
B.
Both glycolysis and the Krebs cycle are linear pathways.
C.
Glycolysis is linear and the Krebs cycle is cyclical.
D.
Both glycolysis and the Krebs cycle are extracellular pathways.
Question 7
Define enzyme.
[1]
State why cells require enzymes for many metabolic reactions.
[1]
Question 8
What occurs during induced-fit binding?
A.
The active site remains completely rigid as the substrate enters.
B.
The substrate and enzyme both change shape slightly after binding interactions form.
C.
The substrate binds permanently so the enzyme cannot be reused.
D.
The enzyme changes into the product while the substrate remains unchanged.
Question 9
Why does increasing substrate concentration eventually have little effect on the rate of an enzyme-catalysed reaction?
A.
All enzyme molecules are denatured by the extra substrate.
B.
The activation energy becomes greater than without the enzyme.
C.
Most active sites are occupied, so the enzyme is close to its maximum rate.
D.
The substrate molecules stop moving in solution.
Question 10
In an investigation of catalase activity at different hydrogen peroxide concentrations, what is the dependent variable?
A.
The temperature of the water bath kept constant
B.
The concentration of hydrogen peroxide prepared
C.
The volume of oxygen produced per unit time
D.
The source and mass of catalase used in each trial
Question 11
Why do metabolic reactions contribute to body temperature maintenance in birds and mammals?
A.
All metabolic energy is converted into ATP with no loss to surroundings.
B.
Energy transfers in metabolism are not completely efficient, so some energy is dispersed as heat.
C.
Catabolic reactions stop whenever body temperature is constant.
D.
Enzymes store heat permanently in their active sites.
Question 12
What happens when a reversible non-competitive inhibitor binds to an enzyme?
A.
It binds only to the substrate and increases collision frequency.
B.
It binds at an allosteric site and changes the active site enough to reduce catalysis.
C.
It binds reversibly to the active site and is overcome by high substrate concentration.
D.
It permanently forms a covalent bond at the active site.
Question 13
What explains why a fixed concentration of competitive inhibitor has less effect at very high substrate concentration?
A.
The maximum number of enzyme molecules increases.
B.
The inhibitor is forced to bind permanently to an allosteric site.
C.
The enzyme becomes denatured into a different protein.
D.
More substrate molecules compete successfully for active sites.
Question 14
State one example of an anabolic reaction.
[1]
Distinguish between anabolic and catabolic reactions in terms of molecule size and energy.
[1]
Question 15
The diagram shows a globular enzyme with a small labelled active site.
State what is meant by an active site.
[1]
Outline why amino acids outside the active site are important for catalysis.
[1]
Question 16
State the effect of increasing temperature on molecular motion below an enzyme’s optimum temperature.
[1]
Explain why enzyme activity decreases above the optimum temperature.
[1]
Question 17
Catalase produced 18.0 cm³ of oxygen in 45 s during the early part of a reaction.
Calculate the reaction rate in cm³ s⁻¹.
[1]
State why the early part of a product–time graph is usually used to estimate initial rate.
[1]
State one safe handling precaution when using hydrogen peroxide.
[1]
Question 18
State one intracellular enzyme-catalysed pathway.
[1]
Distinguish between intracellular and extracellular enzyme-catalysed reactions.
[1]
Question 19
State why heat is generated during metabolism.
[1]
Explain how shivering can help maintain body temperature in a mammal.
[1]
Question 20
The diagram shows two metabolic pathways, X and Y.
Identify which pathway is linear and which is cyclical.
[1]
Compare linear and cyclical metabolic pathways.
[1]
Question 21
A student measured the rate of a protease-catalysed reaction at different temperatures.
Describe the relationship between temperature and reaction rate shown in the graph.
[1]
Identify the optimum temperature from the graph.
[1]
Explain the decrease in rate at temperatures above the optimum.
[1]
Question 22
Amylase activity was measured at different pH values.
Identify the pH at which amylase activity is greatest.
[1]
Describe the effect of moving away from this pH on enzyme activity.
[1]
Explain why extreme pH reduces enzyme activity.
[1]
Question 23
What effect does an enzyme have on an energy profile for a reaction?
A.
It increases activation energy and makes products less stable.
B.
It lowers activation energy without changing the energy difference between substrates and products.
C.
It makes the product energy level identical to the substrate energy level.
D.
It changes substrates into products without a transition state.
Question 24
In the pathway producing isoleucine, what is the role of isoleucine when its concentration is high?
A.
It binds to every intermediate and converts them into threonine.
B.
It binds allosterically to threonine deaminase and reduces entry into the pathway.
C.
It supplies activation energy to the first committed reaction.
D.
It is hydrolysed by threonine deaminase to form peptidoglycan.
Question 25
How does penicillin inhibit susceptible bacterial transpeptidase?
A.
It digests peptidoglycan directly into amino acid monomers.
B.
It lowers the pH of the cytoplasm until all enzymes denature.
C.
It reversibly binds to an allosteric site and leaves when substrate concentration rises.
D.
It binds at the active site and forms a permanent covalent bond that inactivates the enzyme.
Question 26
Statins reduce cholesterol synthesis by inhibiting HMG-CoA reductase. What type of inhibition is involved?
A.
Reversible competitive inhibition at the active site
B.
Denaturation caused by extreme pH
C.
Irreversible mechanism-based inhibition of transpeptidase
D.
Feedback inhibition by the final product isoleucine
Question 27
State one way induced fit differs from a rigid lock-and-key model.
[1]
Explain how induced fit can increase the rate of an enzyme-catalysed reaction.
[1]
Question 28
A student investigates the effect of pH on amylase activity.
State what a decrease of one pH unit means for hydrogen ion concentration.
[1]
Explain why amylase has an optimum pH.
[1]
State one variable, other than pH, that should be controlled.
[1]
Question 29
The energy profile shows the same reaction with and without an enzyme.
Label the activation energy on the enzyme-catalysed pathway.
[1]
Explain why lowering activation energy increases reaction rate at the same temperature.
[1]
State whether the overall energy difference between substrate and product is changed by the enzyme.
[1]
Question 30
Define allosteric site.
[1]
Explain how a reversible non-competitive inhibitor reduces enzyme activity.
[1]
Question 31
State where a competitive inhibitor binds.
[1]
Distinguish between competitive and non-competitive inhibition in terms of the effect of increasing substrate concentration.
[1]
Name one example of a competitive inhibitor used in medicine.
[1]
Question 32
The pathway from threonine to isoleucine contains several enzyme-catalysed steps.
State what is meant by feedback inhibition.
[1]
Explain how isoleucine regulates this pathway when its concentration is high.
[1]
Question 33
A bacterial strain has transpeptidases with altered active sites.
Suggest why this strain may show resistance to penicillin.
[1]
State whether the altered transpeptidase must still bind its normal substrate for the bacterium to survive.
[1]
Question 34
Catalase activity was investigated by measuring oxygen production from hydrogen peroxide over time.
Use the graph to determine the initial reaction rate.
[1]
Describe how the rate changes as the reaction proceeds.
[1]
Suggest one reason for the change in rate during the reaction.
[1]
State one variable that should be controlled when comparing catalase activity between trials.
[1]
Question 35
The graph shows the effect of substrate concentration on the rate of an enzyme-catalysed reaction.
Describe the relationship shown by the graph.
[1]
Explain the shape of the curve at low substrate concentration.
[1]
Explain why the curve levels off at high substrate concentration.
[1]
Question 36
The graph shows reaction rate at different substrate concentrations for an uninhibited enzyme and the same enzyme with a fixed concentration of inhibitor X.
Identify whether inhibitor X is more likely to be competitive or non-competitive.
[1]
Use the graph to justify your answer.
[1]
Explain why increasing substrate concentration has this effect on inhibitor X.
[1]
Question 37
An enzyme was tested with no inhibitor, inhibitor A and inhibitor B at different substrate concentrations.
Identify which inhibitor is non-competitive.
[1]
Give one piece of evidence from the graph for this identification.
[1]
Distinguish the binding site of the non-competitive inhibitor from that of a competitive inhibitor.
[1]
Question 38
Define mechanism-based inhibition.
[1]
Explain how penicillin can cause susceptible bacterial cells to burst.
[1]
Question 39
A generalized model predicts that enzyme activity increases to an optimum temperature and then decreases. Experimental data for an enzyme are shown.
State one feature of the data that supports the model.
[1]
State one feature of the data that does not fit a smooth sketch model perfectly.
[1]
Suggest one experimental reason for scatter in the data.
[1]
Evaluate the use of the generalized sketch model for predicting enzyme activity in this investigation.
[1]
Question 40
The table shows concentrations of threonine, isoleucine and an intermediate in bacterial cells before and after isoleucine was added to the growth medium.
| Metabolite | Before / µmol g^-1 | After / µmol g^-1 |
|---|---|---|
| Threonine | 2.1 | 6.8 |
| Intermediate X | 4.5 | 0.9 |
| Isoleucine | 1.3 | 8.7 |
Describe the change in intermediate concentration after isoleucine was added.
[1]
Suggest why threonine concentration changes after isoleucine was added.
[1]
Explain how the data support feedback inhibition.
[1]
Question 41
A culture of bacteria was exposed to penicillin. Transpeptidase activity and viable cell number were measured over time.
Describe the change in transpeptidase activity after penicillin exposure.
[1]
Explain why viable cell number changes after transpeptidase activity decreases.
[1]
Suggest why a second strain with altered transpeptidase shows a different response.
[1]
Question 42
Outline how the active site of an enzyme is formed.
[1]
Explain the relationship between active-site structure, enzyme–substrate specificity and denaturation.
[1]
Question 43
Define metabolism and state why many enzymes are required in metabolism.
[1]
Compare and contrast anabolic and catabolic reactions, using named examples.
[1]
Question 44
Outline two methods for measuring the rate of an enzyme-catalysed reaction.
[1]
Evaluate the design of an investigation testing the effect of substrate concentration on catalase activity.
[1]
Question 45
Distinguish between intracellular and extracellular enzyme-catalysed reactions, giving one example of each.
[1]
Explain how metabolic reactions contribute to temperature regulation in birds and mammals.
[1]
Question 46
Oxygen consumption and heat output were measured in small mammals at different environmental temperatures.
| Temperature / °C | O₂ consumption / µmol kg⁻¹ s⁻¹ | Heat output / W kg⁻¹ |
|---|---|---|
| 5 | 95 | 45 |
| 10 | 80 | 38 |
| 20 | 55 | 26 |
| 30 | 35 | 16 |
| 35 | 30 | 14 |
Identify the environmental condition associated with the highest heat output.
[1]
Describe the relationship between oxygen consumption and heat output.
[1]
Explain why increased metabolic activity can increase heat output.
[1]
Suggest why this response helps maintain a constant body temperature.
[1]
Question 47
Describe the effect of increasing substrate concentration on enzyme activity.
[1]
Discuss how temperature and pH affect enzyme activity, including collision theory and denaturation.
[1]
Question 48
Outline how a competitive inhibitor reduces enzyme activity.
[1]
Compare and contrast competitive and non-competitive inhibition, including the effect of substrate concentration.
[1]
Question 49
Describe the organization of the threonine to isoleucine pathway.
[1]
Explain feedback inhibition in this pathway and its importance to the cell.
[1]
Question 50
Outline the difference between reversible inhibition and irreversible mechanism-based inhibition.
[1]
Discuss penicillin action and the basis of resistance involving altered transpeptidase.
[1]
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