Enzymes (Edexcel GCSE Biology: Combined Science)

Exam Questions

2 hours17 questions
1a
Sme Calculator
1 mark

Describe what an enzyme is.

1b
Sme Calculator
1 mark

State what substance enzymes are made from.

1c
Sme Calculator
3 marks

Explain why high temperatures can be detrimental to the function of some enzymes.

Did this page help you?

2a
Sme Calculator
5 marks

Potato cells contain the enzyme catalase.

This enzyme catalyses the breakdown of hydrogen peroxide into oxygen and water.

Figure 1 shows what happened when a student placed a potato disc in a 5% hydrogen peroxide solution.fig-15-1bio-1h-june18-qp-gcse-bio

Figure 1

The student measured the time taken for the potato disc to rise.

The student repeated the investigation using 10%, 15% and 20% concentrations of hydrogen peroxide solution.

(i)
Which term describes the hydrogen peroxide in this reaction?
(1)
  A product
  B substrate
  C active site
  D control

(ii)

The potato discs all had the same mass.

Explain why the student used potato discs with the same mass.

(2)

(iii)
State two other factors that need to be kept the same to improve this investigation.
(2)
2b
Sme Calculator
7 marks

Figure 2 shows the results of this investigation.

The student calculated the rate of reaction using

                        

concentration of
hydrogen peroxide
solution (%)
time taken for disc
to rise (s)
rate (s−1)
5 325 0.003
10 245 0.004
15 132 0.008
20 72  0.014


Figure 2

(i)
State and explain a conclusion based on these results.

(4)

(ii)
The student repeated the investigation with a 25% hydrogen peroxide solution and recorded a time of 75 seconds.

Calculate the rate of reaction for the 25% hydrogen peroxide solution.

(2)

(iii)
The student decided that the rate for the 25% hydrogen peroxide solution was not anomalous.

Give the reason why the result was not anomalous.

(1)

Did this page help you?

3a
Sme Calculator
3 marks

A balanced diet should contain a variety of different biological molecules, each of which is digested by a specific set of enzymes.

Using a straight line, match up the molecule to the specific enzyme involved in its digestion.

enzymes-and-food-groups-sq-1

3b
Sme Calculator
1 mark

The graph below shows the effect of temperature on an enzyme controlled reaction.

enzyme-rate-of-reaction-temp-mcq

Explain the rate of reaction at 41 °C.

Did this page help you?

4a
Sme Calculator
3 marks

Enzyme activity is affected by environmental factors such as pH. Sometimes environmental extremes lead to denaturing of enzymes.

(i)

Name another factor, other than pH which may result in denaturing of enzymes.

(1)

(ii)

Describe what is meant by 'denaturing' of enzymes.

(2)

4b
Sme Calculator
4 marks

Some students carried out an investigation into the effect of pH on the activity of amylase. 

The students used the following method:

  1. Add a drop of iodine to each well of a spotting tile
  2. Set up three test tubes containing solutions as follows:
    • Buffer solution at pH 5, substrate X, amylase solution
    • Buffer solution at pH 7, substrate X, amylase solution
    • Buffer solution at pH 9, substrate X, amylase solution
  3. Start a stopwatch as soon as the amylase is added
  4. Use a pipette to remove a drop of solution every 10 seconds and add it to the spotting tile
  5. Continue this process until the iodine stops changing from brown to black
  6. Note down the time taken

Answer the following questions about the method:

(i)

Identify substrate X.

(1)

(ii)

State the reason for using a buffer solution

(1)

(iii)

Give two safety precautions needed when doing this investigation

(2)

4c
Sme Calculator
4 marks

The table shows the results from the investigation carried out by the students.

pH Time taken until no starch was detected / min
5 7.0
7 1.5
9 3.0

(i)

Give two conclusions that can be made from the results.

(2)

(ii)

The stomach in the digestive system contains strong hydrochloric acid.

Suggest what the amylase activity would be in the stomach. Explain your answer.

(2)
4d
Sme Calculator
2 marks

Amylase is a carbohydrase enzyme.

Identify two other categories of enzymes found in the digestive system.

Did this page help you?

1a
Sme Calculator
4 marks

The 'lock and key hypothesis' is often used as a model to describe the action of enzymes.

Using this model, explain how enzymes work.

1b
Sme Calculator
2 marks

Thousands of unique enzymes exist in nature.

Use your knowledge of proteins and the 'lock and key hypothesis' to suggest how so many unique enzymes can exist in nature.

1c
Sme Calculator
2 marks

State what happens when a substrate with a shape that is not complementary to the enzyme tries to enter the active site.

1d
Sme Calculator
2 marks

Figure 1 below represents the reactants and products in a chemical reaction and four different enzymes (A, B, C or D).

2d

Figure 1

Explain which enzyme (A, B, C or D) is responsible for catalysing this reaction?

Did this page help you?

2a
Sme Calculator
5 marks

Figure 1 shows the effect of temperature on the rate of an enzyme catalysed reaction.

3-4fddyb_3

Figure 1

(i)
Describe the effect of temperature at points A, B and C on the rate of the enzyme catalysed reaction.
(3)

(ii)
Explain why the rise in temperature as shown in Figure 1, initially increases the rate of an enzyme catalysed reaction
(2)

2b
Sme Calculator
1 mark

A student conducted an experiment to investigate how starch is digested by the enzyme amylase. Four identical mixtures of starch and amylase were kept at different temperatures. Figure 2 shows the time taken for the starch to be digested at each temperature. 

c7BGZVVg_4

Figure 2

Identify the temperature which produces the fastest rate of reaction.

2c
Sme Calculator
3 marks
(i)
Starch is the substrate of salivary amylase in humans.

 

State the initial product of the reaction it catalyses.
(1)
(ii)
Amylase is classed as a carbohydrase.

State two other classes of enzymes that are used in human digestion.
(2)

Did this page help you?

3a
Sme Calculator
6 marks

Describe a suitable method to investigate the effect of pH on the time taken for amylase to digest starch.

You don't need to include a risk assessment in your method

3b
Sme Calculator
2 marks

Figure 1 illustrates the results of two enzyme controlled reactions involving two different types of enzymes.

kYBaJdd7_5

Figure 1

From these reactions, what conclusion can be drawn about the function of enzymes?

Did this page help you?

4a
Sme Calculator
2 marks

A student investigated the effect of enzyme concentration on the mass of product formed in one hour.
Figure 1 shows the results of this investigation. 

concentration of
enzyme
in arbitrary units 
mass of product
formed in grams 
5 15
10 22
15 25
20 32
25 38
30 40
35 40
40 40

Figure 1

Complete the graph by plotting the points and drawing a line to show the trend in the data.
The first three points have been plotted for you.

q5a-1bio-1f-june18-qp-gcse-bio
4b
Sme Calculator
2 marks

Describe the effect that enzyme concentration has on the mass of product formed.

4c
Sme Calculator
2 marks

The ratio of enzyme concentration to the mass of product formed, using an enzyme concentration of 40 arbitrary units, is 1:1.

Calculate the ratio of enzyme concentration to product formed when the enzyme concentration is 5 arbitrary units.

ratio............................................
4d
Sme Calculator
4 marks

The investigation used the enzyme pepsin from the stomach, at a temperature of 37°C and at a pH of 7.


(i)

Which statement gives one way to increase the mass of product formed in this investigation?
(1)
  A increase the pH
  B decrease the temperature 
  C decrease the enzyme concentration 
  D increase the substrate concentration

(ii)

Explain why a temperature of 80°C was not used in this investigation.
(3)

Did this page help you?

5
Sme Calculator
5 marks

Female glow-worms have an enzyme called luciferase.
The glow is produced when this enzyme catalyses a reaction between oxygen and a protein.

A scientist devised a plan to investigate the effect of oxygen concentration on this reaction.

The scientist had:

  • five flasks of water each with a different concentration of dissolved oxygen
  • a solution of the protein
  • a solution of the enzyme.
The first step of this plan is:

Step 1. Add some of the protein solution to each of the five flasks.

(i)
Describe the next two steps that should be in this plan to obtain results for this investigation.
(2)

Step 2 ...................................
Step 3 .....................................

(ii)

Which procedure would improve the investigation?
(1)
  A change the concentration of the protein solution in each flask
  B change the volume of the protein solution added to each flask
  C keep the concentration of dissolved oxygen the same in each flask 
  D keep the volume of each solution the same in each flask

(iii)

The enzyme luciferase works best at pH 8.

Explain why the activity of the enzyme decreases at pH 5.
(2)

Did this page help you?

6a
Sme Calculator
6 marks

Lactase is an enzyme that breaks down lactose into glucose and galactose.

A student made some alginate beads containing lactase.

The student added 10 beads to 20cm3 of a solution of lactose, as shown in Figure 1.

The student timed how long it took for glucose to be produced.

The experiment was repeated using 15, 20 and 25 beads.fig-9-1bio-1h-june19-qp-gcse-bio

Figure 1

The results are shown in Figure 2.

number of beads
containing lactase
time taken to produce
glucose in seconds
10 240
15 210
20 150
25 120


Figure 2

(i)
What is the rate of reaction for 25 beads?

(1)

  A 0.008s−1
  B 0.04s−1
  C 0.21s−1
  D 4.8s−1 

(ii)

Explain the conclusion that can be made from these results.

(3)

(iii)
Explain why the same volume of lactose solution was used for each test.

(2)

6b
Sme Calculator
3 marks

Devise a method to find the optimum temperature for the enzyme lactase.

Did this page help you?

7a1 mark

Why are enzymes called biological catalysts?

  A because they slow down biological processes
  B because they speed up biological processes
  C because they denature biological processes
  D because they stop biological processes
7b9 marks

Many cells contain an enzyme called catalase.

Catalase breaks down hydrogen peroxide into water and oxygen.

A scientist investigated the effect of hydrogen peroxide concentration on the time taken to produce 20 cm3 of oxygen.

Figure 1 shows the equipment used.

fig-12-1bio-1f-nov2021-qp-gcse-bio

Figure 1

(i)
State how the scientist could control the temperature of the flask.
(1)
(ii)
Explain why the temperature should be controlled in this investigation.
(3)
(iii)
This investigation used five different concentrations of hydrogen peroxide.

Figure 2 shows the results of this investigation.

concentration of hydrogen peroxide in arbitrary units time taken to collect 20 cm3 of oxygen in seconds
4 32
8 14
12 9
16 7
20 6

Figure 2

Complete the graph by plotting the points and drawing a line to show the trend in the data.

The first point has been plotted for you.

(2)

q6biii-1bio-1f-nov2021-qp-gcse-bio

(iv)
Describe the trend shown in the graph.

Use data from the table in Figure 2 to support your answer.
(3)

Did this page help you?

8a
Sme Calculator
7 marks

Figure 1 shows the activity of the enzymes pepsin and trypsin at different pH levels.

fig-7-1bio-1f-june19-qp-gcse-bio

Figure 1

(i)
Describe the trend in the graph for the enzyme trypsin.

Use data from the graph to support your answer.

(4)

(ii)
State the optimum pH for the enzyme pepsin.
(1)
(iii)
Pepsin only works effectively in the stomach.

Describe the conditions in the stomach that allow pepsin to work effectively.
(2)
8b
Sme Calculator
1 mark

At high pH values the active site of the enzyme pepsin changes shape.

When the active site of the enzyme changes shape, the enzyme is

  A specific
  B denatured
  C digested
  D dead
8c
Sme Calculator
1 mark

State what is produced when proteins are digested.

Did this page help you?

9
Sme Calculator
1 mark

Starch is a nutrient in food.
Starch is a source of energy.

Name the enzyme that breaks down starch.

Did this page help you?

1a8 marks

Chymosin is an enzyme that causes milk to curdle.

When milk curdles the proteins in the milk clump together and become solid.

As part of an investigation, milk was heated in test tubes to different temperatures using a Bunsen burner.

Two drops of chymosin solution were added to each test tube and the time taken for the milk to curdle was recorded.

Figure 1 shows the results.

temperature of the milk in °C

time taken for milk to curdle in seconds
25 125
30 105
35 90
40 70
45 75

Figure 1

(i)
Which variables need to be kept constant in this investigation?

(1)

  A the volume of milk and the time
  B the temperature and the time
  C the volume of milk and the concentration of chymosin
  D the temperature and the concentration of chymosin

(ii)
Explain why the time taken for the milk to curdle decreases from 30°C to 40°C.
(2)
(iii)
Explain what the expected result would be if two drops of chymosin were added to the milk at 70°C in the test tube.
(2)
(iv)
As part of this investigation, test tubes containing only milk were heated to each temperature and no chymosin solution was added.
State why these test tubes containing only milk were used.
(1)
(v)
Describe two improvements that could be made to the method of this investigation so that the optimum temperature for chymosin can be found.
(2)
1 .........................................................
2 ..........................................................
1b3 marks

Chymosin can be produced by genetically modified bacteria.

Figure 2 shows a bacterial cell.

fig-12-1bio-1h-nov2021-qp-gcse-bio

Figure 2

Explain how to genetically modify a bacterial cell to produce chymosin.

Did this page help you?

2a
Sme Calculator
2 marks

A group of students carried out the following practical to establish the effect of temperature on protein breakdown:

    1. Place a drop of biuret solution into every well in a spotting tile.
    2. Put 4 cm3 of 1 % protein solution into a boiling tube.
    3. Put 4 cm3 of pepsin solution into a second boiling tube.
    4. Put both boiling tubes into a water bath at 20 °C.
    5. After 4 minutes add the pepsin solution to the protein solution together in one boiling tube, mixing together with a stirring rod.
    6. After 20 seconds add a drop of the protein/pepsin mixture to a drop of biuret solution in one well of the spotting tile.
    7. Repeat step 6 until the biuret solution no longer changes colour.
    8. Repeat steps 1–7 at 10 °C (using an ice water bath), 30 °C, 40 °C and 50 °C.

The concentration of protein present in the solution can also be measured using a colorimeter.

In a colorimeter, the amount of light that cannot pass through a solution is measured; giving the ‘absorbance’ of a solution. The darker the colour, the higher the absorbance.

Suggest advantages of using the colorimeter method rather than the method used by the students.

2b
Sme Calculator
1 mark

The graph below shows a calibration curve of concentration of protein versus absorbance.

protein-digestion-graph

An experiment was carried out to investigate the effect of a protease enzyme on a 1 % protein solution.

The absorbance at 30 °C was 0.8 arbitrary units after 20 seconds.

Using the calibration curve, estimate the final concentration of protein in this solution after 20 seconds.

2c
Sme Calculator
3 marks

The students found that the concentration of protein in the solution at 10 °C after 1 minute was different to the concentration at 30 °C after 1 minute.

Explain the observation above.

2d
Sme Calculator
3 marks

The students repeated the experiment while incubating the protease and 1 % protein solution at 80  °C.

The absorbance was measured at approximately 1.14 arbitrary units.

Suggest a reason for this result.

Did this page help you?

3a
Sme Calculator
1 mark

The protein Rubisco is an enzyme. 

Identify where, in a cell, Rubisco would be made.

3b
Sme Calculator
2 marks

Rubisco has a unique 3D shape that enables it to carry out its roles in living organisms. 

Describe how the 3D shape of rubisco is determined.

3c
Sme Calculator
4 marks

Extreme hyperthermia is a condition in which human body temperature rises above the normal body temperature of 37 °C. Body temperatures above 40 °C can be life threatening.

Use your knowledge of proteins to suggest why body temperatures above 40 °C can be life threatening.

3d
Sme Calculator
2 marks

Sketch a graph to show how the rate of reaction of an enzyme such as Rubisco would change over a range of temperatures from 0 to 60 °C.

Use the axes provided below.

e-2d

Did this page help you?

4a
Sme Calculator
1 mark

Catalase is an enzyme found in the liver which catalyses the breakdown of the harmful substrate hydrogen peroxide into the products water and oxygen.

Some students investigated the effect of pH on catalase activity. Each experiment was repeated at a different pH value (pH 2, 4, 7, 9 and 11) and was set up as follows:

  • Five potato cubes of similar dimensions were used as a source of catalase.
  • Each cube was added to 50 cm3 of hydrogen peroxide.
  • The volume of oxygen released from this reaction was collected in a measuring cylinder.
  • This was used to calculate the initial rate of the reaction in dm3s-1

Which of the rows in the following table correctly identifies the variables in this experiment?

  Independent variable Dependent variable Control variable
A pH Initial reaction rate Volume of oxygen released
B Initial reaction rate pH Volume of hydrogen peroxide
C pH Initial reaction rate Volume of hydrogen peroxide
D Volume of oxygen released pH Initial reaction rate
4b
Sme Calculator
3 marks

The results below show the effect of pH 7 and pH 9 on the activity of the enzyme catalase.

dpS~Fe2N_catalase-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 change space in space product space concentration 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 difference in rate of reaction between pH 7 and pH 9 during the first 20 seconds. Give your answers with the correct units.

4c
Sme Calculator
2 marks

Describe the differences between the curves at pH 7 and pH 9 in the graph in part (b).

4d
Sme Calculator
1 mark

Explain the shape of the curve for pH 7 from around 20 s onwards in the graph in part (b).

4e
Sme Calculator
3 marks

Predict the outcome of the experiment described in part (a) if the pH were increased to pH 11.

Explain your answer.

Did this page help you?