Syllabus Edition

First teaching 2023

First exams 2025

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Enzymes & Metabolism (SL IB Biology)

Exam Questions

3 hours45 questions
1a
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5 marks

Distinguish between anabolic and catabolic reactions. 

Include one example of each reaction.

1b
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2 marks

State the main mode of action of enzymes.

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2a2 marks

The protein Rubisco is an enzyme. 

What is the function of the enzyme Rubisco in living organisms? 

2b1 mark

Enzymes have a specific three-dimensional conformation that enables them to carry out their roles in living organisms. 

Which part of the amino acid determines the conformation of the protein?

2c2 marks

In certain conditions, such as high temperatures, the 3D conformation of proteins can be lost. 

(i)
What is the scientific name given to when a protein loses its 3D conformation? 

[1]

(ii)
State one condition, other than temperature, that can cause the 3D conformation of a protein to be lost. 

[1]

2d2 marks

Sketch a graph to show how the rate of reaction of Rubisco changes over a range of temperatures. 

Use the axes provided below.

e-2d

[2]

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3a1 mark

State the reason why enzymes are referred to as biological catalysts. 

3b3 marks

The image below shows a representation of an enzyme-controlled reaction.

enzyme-substrate-complex

Describe the events taking place in the image.

3c2 marks

State what is meant by the term 'enzyme specificity'?

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4a2 marks

A student wanted to investigate the effect of substrate concentration on the activity of an enzyme called catalase. Catalase is an enzyme that commonly occurs inside living cells where it breaks down toxic hydrogen peroxide into oxygen and water. The image below shows the experimental set up done by the student.

catalase-and-hydrogen-peroxide-investigation-sq

List two control variables that the student would need to be aware of in the experiment shown in the image.

4b
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1 mark

The student decided to make up solutions at five different hydrogen peroxide concentrations. Their measurements for these solutions are shown in the table below.

Concentration of hydrogen peroxide solution (%) Volume of hydrogen peroxide required (cm3) Volume of distilled water required (cm3)
10 10 90
8 B C
6 6 94
A 4 96
2 2 98

Give the measurements needed to fill in gaps A-C in the table. 

4c1 mark

After measuring out the range of hydrogen peroxide concentrations shown in part (b), the student carried out the experiment using the equipment set up in part (a). They recorded the volume of oxygen (the product) produced after one minute, and repeated this measurement three times at each concentration. Their results are shown in the table below.

results-table-for-catalase-experiment

Use the data in the table to calculate the value missing from the square marked X. 

4d2 marks

State the purpose of repeating the experiment three times at each concentration of hydrogen peroxide. 

4e4 marks

Using the data in part (c), draw a graph of hydrogen peroxide concentration against the mean volume of oxygen. 

4f2 marks

Deduce the conclusions that can be drawn from your graph from part (e). 

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5a
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2 marks

A researcher investigated the effect of pH on the activity of stomach enzyme pepsin. 

Their results are shown in the image below. 

pepsin-rate-of-reaction-at-different-ph-sq

The rate of reaction can be calculated by using the following formula:

reaction space rate space equals space fraction numerator Amount space of space product space produced space left parenthesis straight g space dm to the power of negative 3 end exponent right parenthesis over denominator Time space left parenthesis straight s right parenthesis end fraction

Calculate the rate of reaction at pH 4. Give your answer with the correct units.

5b2 marks

Describe the differences between the curves at pH 2 and pH 4.

5c1 mark

State why product production at pH 2 does not continue indefinitely but reaches a plateau at around 14.75 g.

5d3 marks
(i)

Predict the outcome if the pH were increased to pH 10.

[1]

(ii)

Explain your answer at part i).

[2]

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64 marks

Outline the events that occur when enzymes are exposed to high temperatures. 

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71 mark

The graph below shows how enzymes affect biological reactions.

energy-level-diagram-with-and-without-enzyme-sq

Use the graph and your own knowledge of enzyme function to explain how enzymes function as biological catalysts.

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1a3 marks

Distinguish between anabolic reactions and catabolic reactions.

1b2 marks

Complete the table with tick marks (✓) in the appropriate boxes.

Cellular reaction Anabolic Catabolic
Fats → fatty acids and glycerol    
Accumulation of starch from sugars in plants    
Anaerobic respiration in yeast cells    
Hydrolysis of polypeptides into amino acids    
1c2 marks

The diagram below shows part of a biochemical pathway that takes place commonly in cells.oTEfImL9_q3c-2-1-metabolism-water-medium-ib-hl-biology-sq

 Deduce whether the pathway is anabolic or catabolic and give evidence from the diagram for your answer.

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2a3 marks

Lipase is an enzyme that breaks down lipids. The diagram below shows an experiment set up by a teacher to investigate the effect of lipase concentration on the hydrolysis of lipids.

The pH of beaker B is measured for 3 minutes at the start of the experiment. Beaker A containing lipase solution is added to beaker B. The data logger recorded the change in pH over the next 5 minutes.

q1a-2-4-enzymes-medium-ib-hl-biology-sq

State, with a reason, the predicted change in pH after the lipase has been added. 

2b2 marks

State two variables that must be controlled to carry out the experiment in part (a) accurately and reliably.

2c3 marks

For the experiment in part (a), draw a results table that could be used to record the results of the investigation. Your table should include suggested enzyme concentrations, and units should be stated. 

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3a2 marks

A protease is an enzyme that digests protein. A research scientist isolated protease C from a particular species of bacteria. The researcher investigated the effect of temperature on the rate of hydrolysis of a protein by protease C.  The unprocessed results can be seen in the table below.

Temperature / °C Mass of protein hydrolysed after 4 minutes / mg

Rate of hydrolysis /

10 470  
15 990  
20 1180  
25 1310  
30 1030  
35 420  
40 110  

Calculate (with appropriate units) the missing details in the table above.   

 

3b4 marks

Draw a graph of the results seen in part (a). Your graph should include an accurate scale and correct axis labels. q2b-2-4-enzymes-medium-ib-hl-biology-sq

3c1 mark

Suggest how the research scientist controlled the pH throughout the experiment.

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4a2 marks

Explain the aspect of enzyme and substrate structure that enables successful catalysis of a biochemical reaction.

4b1 mark

The sketch graph below shows how the rate of an enzyme-catalysed reaction varies for two separate independent variables. For curve A the independent variable is the concentration of enzyme.

 q3b-2-4-enzymes-medium-ib-hl-biology-sq

Identify the independent variable for Curve B.

4c3 marks

The sketch graph below shows how the rate of an enzyme-catalysed reaction varies as temperature changes. q3c-2-4-enzymes-medium-ib-hl-biology-sq

Explain the rates of reaction at positions A, B, and C on the curve. 

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5a7 marks

The sketch graph below shows the effects of varying the level of the independent variable, X, on the rate of an enzyme-controlled reaction. Lines A, B, and C represent three different independent variables which could be X.q5a-2-4-enzymes-medium-ib-hl-biology-sq 

(i)
Identify the independent variables that would cause lines A, B, and C.

 

(ii)
Use your knowledge of enzyme activity to explain the changes in reaction rate shown by lines A, B and C.
5b4 marks

An experiment was set up to investigate the effect of temperature on an enzyme-catalysed reaction in which the reaction mixture changes from clear-colourless to clear-dark blue as the reaction progresses.

Describe:

(i)
How the independent variable in the experiment could be controlled.

(ii)
How a colorimeter could be used to measure colour change.

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6a
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2 marks

Trypsin is an enzyme produced by the pancreas that hydrolyses proteins in the small intestine. 

The activity of trypsin was investigated by placing a small amount of the enzyme with a known concentration of protein.

The graph below shows the progress of this reaction when it is carried out at 25 °C.

3-2-fig-3-1

Calculate the initial rate of the reaction in the graph. Show your working.

6b2 marks

The investigation was extended to compare the initial reaction rates of trypsin obtained from different species of animal. 

Suggest two advantages of calculating the initial reaction rates of enzyme catalysed reactions here rather than the reaction rates at another point during the experiment.

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7a2 marks

The Plasmodium falciparum parasite depends on glycolysis for its survival, particularly the uptake of glucose from its host cells which is mediated by hexokinase.

The scientists investigated the action of hexokinase within Plasmodium falciparum.  They tagged hexokinase with two different potential drugs that inhibit its action. Their results are shown in the graph below.

q4c_8-1_metabolism_medium_ib_hl_biology_sq


Describe how to calculate the rate of reaction from the graph.

7b3 marks

The scientists concluded that drug 1 was less effective than drug 2.

Evaluate this conclusion.

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83 marks

Distinguish between an enzyme catalysed reaction and a non enzymatic reaction.

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1a
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2 marks

Washing powders often contain different types of enzymes that break down substances in stains. An investigation was carried out into washing powder that contained enzymes and washing powder that did not contain enzymes. The graph below shows the results of this investigation.

6-1-hard-q1a

Some of the substances that cause food stains are large insoluble proteins. 

Explain how washing powder containing enzymes would be able to remove these stains.

1b
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3 marks

The manufacturers of the washing powder containing enzymes claimed that their washing powder was more effective at removing tough stains compared to the washing powder without enzymes.

Based on the results of the investigation in part a), evaluate the claim of the manufacturers.

1c
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1 mark

The investigation at part a) was carried out at 40 °C.

Suggest a reason for this.

1d
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3 marks

The investigation was repeated at a temperature of 85 °C.

Predict, with a reason, the expected results from this investigation.

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2a1 mark

Certain plants that reproduce sexually contain an enzyme called pyrophosphatase. This enzyme plays a role in ensuring self-incompatibility, which is a mechanism that prevents a plant from fertilising itself. The selective advantage of self-incompatibility is that more cross-breeding can occur within a species, which has long term benefits for evolution and for maintaining a large pool of alleles.

Known volumes of pyrophosphatase and substrate can be mixed in a cuvette with a dye that starts as colourless and develops into a blue colour over time. The rate of colour development can be measured in a colorimeter by measuring the absorbance of light at a wavelength of 620 nm (red light). 

The graph shows the mean rate of reaction of pyrophosphatase measured over five repeats at 20°C.

mean-rate-of-reaction-of-pyrophosphatase-graph-sq

State why the wavelength of 620 nm was selected for this experimental measurement.

2b
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3 marks

Use the graph from part (a) to calculate the rate of the reaction at 100 seconds. Give your answer in suitable units. 

2c2 marks
(i)

Predict the effect that a higher enzyme concentration at the start of the experiment would have on the results calculated in part (b).

[1]

(ii)

Explain your answer in part (i).

[1]

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3a3 marks

Outline how changes in substrate concentration affects the rate of enzyme action. 

3b7 marks

Plan an investigation to determine how changing the temperature of amylase affects the rate of reaction of the digestion of starch to maltose. 

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43 marks

Three rivers in the Scottish Highlands were polluted with copper, which affected the aquatic wildlife. Scientists were provided with one dead brown trout, Salmo trutta, from each of the rivers.

Scientists were unable to take a direct measurement of the copper ion concentration in the river.

Using the information provided in part (b), suggest the dependent, independent and control variables of an experiment using the fish tissue to compare the copper ion pollution in the three rivers.

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53 marks

Scientists were trying to investigate the rate of reaction of alcohol dehydrogenase by measuring the quantity of product, methanoic acid, produced over time, with a fixed quantity of methanol added at the start. 

The graph below shows their results. 

rate-of-reaction-calculation-graph

Use the graph below to calculate the rate of reaction of alcohol dehydrogenase after 3 minutes. 

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