Enzymes — AS & A Level Biology (9700) questions by topic
Inhibition graphs, enzyme immobilisation and practical enzyme investigations anchor this large topic: interpreting a temperature-activity graph comparing free and immobilised papain, identifying features of a non-competitive inhibitor, and selecting evenly spaced amylase concentrations for a rate investigation. Identify, deduce and explain lead the command words, and deduce wants a graph or data-based inference, not a recalled rule.
This set holds 59 real questions from 2023 to 2025 papers, worth 1 to 22 marks, so single-graph readings sit beside full practical write-ups on reaction rate. Submitting rate calculations and graphs for instant marking is especially useful here, since a non-linear axis scale or an inconsistent end-point sampling time is flagged immediately rather than repeated.
What examiners look for
- A common error assumes end-product inhibition would not reduce the quantity of end-product, when a decrease is the expected outcome.
- Concentration ranges for rate investigations are sometimes too narrow, selecting only two additional values or values outside the range 0.4 to 2.0 percentage concentration.
- Sampling times recorded inconsistently, or exceeding 180 seconds, are a recurring practical error.
- A frequent suggestion proposes a colorimeter for judging an end-point colour, where a colour chart or colour standards would be more appropriate.
- Strong answers select evenly spaced concentrations, organise results with correctly labelled headings and units, and correctly use earlier results to estimate an unknown amylase concentration.
May–June 2025, Paper 11
Which statements about the mode of action of an enzyme are correct? 1 Some enzymes have a region on their surface to which the substrate has a complementary shape. 2 Some enzymes…
Answer this question and get it marked →The graph shows the effect of increasing substrate concentration on the rate of reaction of two enzymes that catalyse reactions with the same substrate. Enzyme P (dashed line)…
Answer this question and get it marked →May–June 2025, Paper 12
Prokaryotes and eukaryotes use extracellular enzymes. Extracellular digestive enzymes are found in the external environments of some prokaryotes. Some prokaryotes are digested by…
Answer this question and get it marked →Amylase breaks down starch molecules. Which substance will have the same number of molecules for the duration of this reaction? A amylase B water C maltose D amylose
Answer this question and get it marked →Which graphs could show the effect of pH on the rate of enzyme-catalysed reactions? Four graphs are shown (1, 2, 3, 4) each with pH on the x-axis (1 to 14) and rate of reaction on…
Answer this question and get it marked →After a heart attack, the enzyme lactate dehydrogenase leaks into the blood plasma from damaged heart muscle. What is required to measure the activity of lactate dehydrogenase…
Answer this question and get it marked →Which graph correctly shows Km and Vmax? Four graphs (A, B, C, D) are shown. Each has 'rate of reaction' on the y-axis with Vmax and Km labelled, and a concentration variable on…
Answer this question and get it marked →May–June 2025, Paper 13
A competitive inhibitor is added to an enzyme-catalysed reaction. What happens to the Michaelis-Menten constant (Km) and maximum rate of reaction (Vmax)? A Km increases; Vmax…
Answer this question and get it marked →May–June 2025, Paper 14
The graph shows the effect of temperature on the activity of compound X. Which row correctly describes compound X? A [enzyme-like, activity decreases above optimum] B [non-enzyme…
Answer this question and get it marked →Enzyme activity was measured at different temperatures. Which statement is correct? A The enzyme has its optimum temperature below 30°C. B The enzyme has its optimum temperature…
Answer this question and get it marked →Inhibitor X is a competitive inhibitor. The graph shows Michaelis-Menten curves with and without the inhibitor. What is the Km value in the presence of inhibitor X? A 0.12 mol…
Answer this question and get it marked →May–June 2025, Paper 21
Scientists investigated the progress of reactions catalysed by two enzymes: dopa oxidase and neutrase. The reactions are shown in Fig. 3.1. Fig. 3.2 shows the progress of the…
Answer this question and get it marked →May–June 2025, Paper 22
Haemoglobin is a globular protein. Explain why haemoglobin is described as a globular protein.
Answer this question and get it marked →HRP (horseradish peroxidase) is an enzyme used in the sandwich ELISA test. Fig. 6.1 shows a graph of rate of reaction against substrate concentration for HRP. A non-competitive…
Answer this question and get it marked →May–June 2025, Paper 23
Telomeres are lengths of DNA that consist of repetitive nucleotide sequences. Telomeres are present in eukaryotic chromosomes. Outline the role of telomeres in eukaryotic…
Answer this question and get it marked →May–June 2024, Paper 11
The graph shows the trend from an enzyme-catalysed reaction. The y-axis variable rises to a peak and then falls back towards zero as the x-axis variable increases (a bell-shaped…
Answer this question and get it marked →Which statements about the Michaelis-Menten constant (Km) are correct? (1) The higher the Km, the higher the enzyme affinity for the substrate. (2) Km is a measure of the degree…
Answer this question and get it marked →The diagram shows a simple metabolic pathway: W - X - Y - Z. The letters W, X, Y and Z represent four different substances. At each step the substrate undergoes a chemical…
Answer this question and get it marked →May–June 2024, Paper 12
The diagram shows naturally occurring D-glucose and a form of glucose that can be synthesised in the laboratory, known as L-glucose. The two ring structures are mirror images of…
Answer this question and get it marked →Which row describes the expected effect on Vmax and Km when a competitive reversible inhibitor is added to an enzyme-catalysed reaction? The columns are 'effect on Vmax' and…
Answer this question and get it marked →The graph shows the effect of substrate concentration on the rates of reaction of three enzymes, X, Y and Z. Enzyme X rises steeply and plateaus at about 1500 product per second…
Answer this question and get it marked →May–June 2024, Paper 13
The diagram shows different molecules in a solution. The diagram shows four molecules labelled P, Q, R and S. Molecule P is large with a cleft (active site). Molecule Q is a small…
Answer this question and get it marked →The effect of substrate concentration on an enzyme-catalysed reaction was measured in three different conditions: - without an inhibitor - with a competitive inhibitor - with a…
Answer this question and get it marked →Which aspect of enzyme activity can be compared by the Michaelis-Menten constant? A activation energy of a reaction with or without an enzyme B affinity of different enzymes for…
Answer this question and get it marked →The number of substrate molecules one enzyme molecule can convert to product in a second is called the turnover number. This number is obtained when all conditions are optimum for…
Answer this question and get it marked →May–June 2024, Paper 22
Lysozyme is an antibacterial enzyme that was discovered in 1921 by Alexander Fleming, the scientist who discovered penicillin. Lysozyme catalyses the hydrolysis of glycosidic…
Answer this question and get it marked →May–June 2024, Paper 32
Some fruits contain protease enzymes. These enzymes can denature the proteins in milk, causing the milk to clot. You will investigate the effect of protease concentration on the…
Answer this question and get it marked →October–November 2024, Paper 11
A student carried out investigations at pH 1-8 to look at the effect of pH on an enzyme-catalysed reaction. The optimum condition for this enzyme is the acidic environment of the…
Answer this question and get it marked →Which statement is correct for a non-competitive inhibitor?
Answer this question and get it marked →Pyrophosphatase enzymes catalyse a hydrolysis reaction in which pyrophosphate ions (substrate) are converted to phosphate ions (product). In experiment 1, a scientist studied the…
Answer this question and get it marked →Proteases are a group of enzymes that digest proteins. Which statements about proteases are correct? 1 A bacterial protease that is secreted from a disease-causing bacterium could…
Answer this question and get it marked →October–November 2024, Paper 12
The initial rate of a reaction catalysed by an enzyme was measured at various substrate concentrations. Which graph shows the effect of a low concentration of non-competitive…
Answer this question and get it marked →Gout is a type of arthritis in which small uric acid crystals form inside and around the joints. It causes sudden attacks of severe pain and swelling. The diagram shows how uric…
Answer this question and get it marked →October–November 2024, Paper 13
Two different enzymes, P and Q, are investigated to find the optimum pH for each enzyme. The results show that P works only in acidic conditions. Q has an optimum pH which is…
Answer this question and get it marked →A student investigated the effect of substrate concentration on the rate of an enzyme-catalysed reaction. The student plotted the results in a graph of reaction rate (in…
Answer this question and get it marked →Which description identifies a reversible, non-competitive enzyme inhibitor?
Answer this question and get it marked →October–November 2024, Paper 21
Trypsin is an enzyme which catalyses the hydrolysis of casein, a protein found in milk. Milk that contains casein has a cloudy, white appearance. As the casein is hydrolysed by…
Answer this question and get it marked →October–November 2024, Paper 23
Biofuels contain alcohols that are produced by the fermentation of sugars derived from crop waste. This waste contains cellulose and other organic compounds in cell walls.…
Answer this question and get it marked →May–June 2023, Paper 11
The graph shows the energy of molecules in a reaction against time, with one curve 'with enzyme' and one curve 'without enzyme'. Several regions of the graph are labelled A, B, C…
Answer this question and get it marked →The graph shows the effect of an increasing substrate concentration on the rate of an enzyme-catalysed reaction, with rate of reaction on the y-axis and substrate concentration on…
Answer this question and get it marked →May–June 2023, Paper 12
CYP3A4 is an important enzyme in the human digestive system where it is needed to break down a range of different toxins. The activity of CYP3A4 has been shown to be reduced by…
Answer this question and get it marked →A fixed volume and concentration of substrate and enzyme were mixed. All other variables were kept constant. The enzyme-catalysed reaction was left until it was complete. Four…
Answer this question and get it marked →May–June 2023, Paper 13
Some animals produce antimicrobial proteins which protect them from pathogens. These proteins could be used to kill human pathogens, however when used as a medicine they are…
Answer this question and get it marked →A student investigated the effect of substrate concentration on the rate of an enzyme-catalysed reaction. A graph was plotted to show the relationship between these two variables.…
Answer this question and get it marked →The end-product of a metabolic pathway can act as a competitive inhibitor. This is called end-product inhibition and allows a cell to control a metabolic pathway. The diagram…
Answer this question and get it marked →May–June 2023, Paper 31
Yeast cells contain the enzyme catalase which catalyses the breakdown of hydrogen peroxide, releasing oxygen. You will investigate the effect of pH on the activity of catalase in…
Answer this question and get it marked →October–November 2023, Paper 11
The specific heat capacity of different substances is shown. substance specific heat capacity / J g^-1 deg C --- --- air 1.0 hydrogen gas 14.3 water (liquid) 4.2 water (steam) 2.1…
Answer this question and get it marked →The solid line on the graph represents the product formed over time for a reaction in a cell, plotted as total product formed against time. Curve A rises steeply then plateaus…
Answer this question and get it marked →The graph shows how the rate of an enzyme-controlled reaction is affected by the change in temperature, with all other variables standardised. Region X is the rising portion of…
Answer this question and get it marked →How will the removal of a reversible non-competitive enzyme inhibitor affect an enzyme-catalysed reaction? A The Km will decrease and the Vmax will increase. B The Km will…
Answer this question and get it marked →October–November 2023, Paper 12
The graph shows the effect of an enzyme on a reaction, with energy of system plotted against time. The substrate energy level is higher than the product energy level. Curve X…
Answer this question and get it marked →The graph shows the results of two experiments on the effect of increasing substrate concentration on the rate of an enzyme-catalysed reaction. One experiment was at a high…
Answer this question and get it marked →Which statements about the Michaelis-Menten constant (Km) of an enzyme are correct? 1 At the Km value, half the active sites of the enzyme should be occupied by the substrate. 2…
Answer this question and get it marked →October–November 2023, Paper 13
Which statements describe some enzyme actions? 1 Enzymes hold reacting molecules so that their reactive groups are close together. 2 In an enzyme-catalysed reaction, more…
Answer this question and get it marked →Influenza virus has an enzyme called neuraminidase which breaks down glycoproteins in the surface membrane of the cell that the virus will infect. The glycoprotein binds to the…
Answer this question and get it marked →The graph compares the effect of temperature on the activity of the protease enzyme, papain, when in solution (free) and when immobilised in alginate beads. Which statement about…
Answer this question and get it marked →October–November 2023, Paper 23
Glucose is used in the synthesis of amylose. Glucose is first converted to glucose 1-phosphate (G 1-P). Starch phosphorylase is an intracellular enzyme that can catalyse the…
Answer this question and get it marked →October–November 2023, Paper 33
Yeast cells contain enzymes that hydrolyse sucrose into reducing sugars. You will investigate the activity of the enzymes in yeast cells, with the yeast cells immobilised in…
Answer this question and get it marked →October–November 2023, Paper 34
The enzyme amylase catalyses the hydrolysis of starch to maltose. You will investigate the effect of different concentrations of amylase on the hydrolysis of starch. You are…
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