Enzymes (Cambridge (CIE) IGCSE Biology)

Exam Questions

4 hours34 questions
1a
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5 marks

Catalase is an enzyme found in plant and animal cells. It catalyses the breakdown of hydrogen peroxide to form water and oxygen.

2023specimenq1a

The oxygen produced forms a foam. You can measure the height of the foam to determine catalase activity.

A student investigated catalase activity in cooked and uncooked potato tissue. 

The student: 

Step 1

Cut two potato cylinders so that they were identical in shape and size

Step 2

Put 5 cm3 of 3 % hydrogen peroxide solution into a test-tube labelled cooked potato

Step 3

Put 5 cm3 of 3 % hydrogen peroxide solution into a test-tube labelled uncooked potato

Step 4

Put one of the potato cylinders into a beaker of hot water for five minutes

Step 5

Removed the potato cylinder from the hot water and put it into the test-tube labelled cooked potato

Step 6

Put the uncooked potato cylinder into the test-tube labelled uncooked potato

Step 7

Left the potato cylinders in the 3 % hydrogen peroxide solution for three minutes and then measured the height of the foam produced in each of the test-tubes.

Fig. 1 shows the test-tubes after three minutes. 

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Fig. 1

(i)

Prepare a table to record your results.

Measure the height of the foam in each of the test-tubes in Fig. 1 Record these measurements in your table.

[3]

(ii)

Calculate the difference in the height of the foam produced by the cooked and uncooked potato after three minutes.

[1]

(iii)

State one conclusion for these results.

[1]

1b
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4 marks

(i)

Identify the independent variable in this investigation. 

[1]

(ii)

State why it is important that the two potato cylinders were identical in shape and size.

[1]

(iii)

State two other variables that were kept constant in this investigation. 

[2]

1c
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1 mark

Identify one possible source of error in the method used in this investigation. 

1d
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6 marks

A student stated that:

'Catalase activity is the same in all species of plants'

Plan an investigation to test this statement.

1e
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5 marks

Potatoes contain starch. Starch can be broken down into reducing sugars.

Describe the tests to identify starch and reducing sugars and give the results of the positive tests. 

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2a
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6 marks

Some students investigated the activity of catalase.

Catalase is an enzyme found in plant and animal tissues. It catalyses the breakdown of hydrogen peroxide into water and oxygen. The activity of this enzyme can be measured by collecting the oxygen produced.  

2H2O2                     →          2H2O     +     O2 hydrogen peroxide                   water        oxygen       

The students used the apparatus shown in Fig. 1 to compare the activity of catalase using pieces of sweet potato of different sizes.  

cie-igcse-2020-specimen-p6-q1a-catalase-experiment

Fig. 1

Three cubes of 10 mm × 10 mm × 10 mm of sweet potato were used.

Cube 1 was placed into the test-tube and 5 cm3 of hydrogen peroxide was added. The bung was quickly replaced into the top of the test-tube. The students carefully counted the number of bubbles of oxygen delivered into the water in one minute and then measured the final height of foam in the test-tube. For cube 1, they counted 12 bubbles in one minute. The height of the foam was 42 mm. They then discarded the contents of the test-tube and rinsed it with clean water.

Cube 2 was cut into two pieces of approximately the same size. Both of these pieces were placed into the test-tube and 5 cm3 of hydrogen peroxide was added as before. For cube 2, they counted 23 bubbles in one minute. The height of foam was 63 mm. They then discarded the contents of the test-tube and rinsed it with clean water.

Cube 3 was cut into eight small pieces which were all placed into the test-tube and 5 cm3 of hydrogen peroxide was added as before. For cube 3, they counted 38 bubbles in one minute. The height of foam was 76 mm.

cie-igcse-2020-specimen-p6-q1a-height-of-bubbles

Fig. 2

Prepare a table for the results from this investigation.

Use information provided in the question to complete your table.

2b
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5 marks

(i)

State two variables that the students kept constant in this investigation.

[2]

(ii)

Suggest how you could improve the method that they followed. 

[3]

2c
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1 mark

State a conclusion that can be drawn from these results.

2d
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7 marks

(i)

The students were given a hypothesis that said:

“The activity of catalase increases with increasing temperature”.

 Describe a similar investigation to the one carried out in a) to test this hypothesis.

[6]

(ii)

Outline one safety precaution that you would need to take when performing this experiment.

[1]

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3a
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2 marks

Fruit juice can be produced by crushing and squeezing fresh fruit. The juice produced in this way is often cloudy.

The enzyme pectinase is used to produce clear fruit juice. This process is called clarification.

Fig. 1 shows fruit juice before and after clarification.

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Fig. 1

A student investigated the effect of pectinase concentration on the clarification of apple juice.

The student was provided with freshly prepared apple juice, water and a 5% pectinase solution.

Step 1

Four test-tubes were labelled P1, P2, P3 and P4.

Step 2

Syringes were used to add the volumes of water and 5% pectinase solution shown in Table 1.1 to each of the test-tubes.

Table 1

Test-tube

Volume of water / cm3

Volume of 5% pectinase solution / cm3

Final percentage concentration of pectinase solution

P1

0.00

1.00

5.0

P2

0.50

0.50

2.5

P3

0.75

0.25

 

P4

1.00

0.00

0.0

Calculate the final concentration of the pectinase solution in test-tube P3.

Show your working and write your answer to one decimal place.

3b
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4 marks

Step 3

5cm3 of apple juice was added to each of test-tubes P1, P2, P3 and P4.

Step 4

The contents of each test-tube were carefully mixed using a glass rod.

Step 5

A stop-clock was immediately started.

Step 6

After five minutes, the height of the precipitate formed was measured using a ruler, as shown in Fig. 2 If no precipitate had formed in the test-tube, it was recorded as ‘0’. 

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Fig. 2

Care was taken not to shake the test-tubes.

Step 7

After a further five minutes, the student repeated the measurement of the precipitates in the test-tubes.

Fig.3 shows the test-tubes at 0, 5 and 10 minutes.

Note that the height of the precipitate is given for each test-tube.

ZL~UAXAy_test-pic

Fig. 3

Prepare a table to record the results.

3c
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2 marks

State a conclusion for the results.

3d
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5 marks

(i)

State the variable that was changed (independent variable) in this investigation.

[1]

(ii)

State two variables that should have been kept constant in this investigation.

[2]

(iii)

Identify one possible error in step 6 and suggest an improvement.

[2]

3e
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2 marks

Explain the purpose of test-tube P4.

3f
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6 marks

A student stated the hypothesis: 

“Treating fruit juice with pectinase reduces the vitamin C content of the fruit juice”.

Plan an investigation to test this hypothesis. 

3g
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4 marks

Fig. 4 shows a cross-section of a tomato fruit.

tomato

Fig. 4

Sketch a large drawing of the cross-section of tomato fruit.

3h
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1 mark

A student wanted to find out if tomatoes contained starch.

State the result you would expect for a positive test for starch.

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4a
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3 marks

Young mammals feed on milk containing protein.

Some mammals produce an enzyme called rennin. Rennin changes the protein in milk so that it can be digested by another enzyme.

The action of rennin causes small lumps or clots to form in the milk.

An investigation was carried out to find the effect of pH on the activity of the enzyme rennin.

Step 1

Three test-tubes were labelled P, Q and R.

Step 2

A syringe was used to add 5cm3 of milk to each of these test-tubes.

Step 3

A dropping pipette was used to add two drops of acid to test-tube P.

Step 4

A dropping pipette was used to add two drops of distilled water to test-tube Q.

Step 5

A dropping pipette was used to add two drops of alkali to test-tube R.

Step 6

Another three test-tubes were labelled P1, Q1 and R1

Step 7

A clean syringe was used to add 1cm3 of 0.1% rennin solution to each of test-tubes P1, Q1 and R1.

Step 8

All six test-tubes were placed into a water-bath at 40°C and left for three minutes.

Step 9

The contents of test-tube P1 were added to test-tube P. The contents of test-tube Q1 were added to test-tube Q. The contents of test-tube R1 were added to test-tube R.

Step 10

Test-tubes P, Q and R were kept in the water-bath and a stop-clock was started.

Step 11

After one minute, test-tube P was removed from the water-bath.It was tipped and rotated as shown in Fig.1.The appearance of the milk was observed, and the stage of clotting was decided by comparing it to the diagrams in Fig.1.

 

 

cie-igcse-2018-series-1-p6-q1a-clotting-milk

Fig. 1

Step 12

Test-tube P was returned to the water-bath.

Step 13

Steps 11 and 12 were repeated for test-tubes Q and R.

Step 14

Steps 11, 12 and 13 were repeated every minute for five minutes.

The results are shown in Fig. 2.

Test-tube P had some clotting at one minute and was all clotted at two minutes. Test-tube Q had no clotting at one, two or three minutes but some clotting at four and five minutes. Test-tube R had no clotting throughout the investigation, and remained unchanged after five minutes.

Fig. 2

Prepare a table in which to record these results. Use the information in Fig. 2 to complete this table.

4b
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2 marks

State a conclusion for these results.

4c
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3 marks

(i)

Suggest why, in step 8, all of the test-tubes were placed into a water-bath for three minutes before mixing the contents together in step 9.

[1]

(ii)

State two variables that were kept constant in this investigation. 

[2]

4d
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4 marks

Identify four sources of error in this investigation.

4e
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1 mark

Identify one hazard associated with this procedure that would require the use of eye protection.

4f
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2 marks

Clotting separates milk into a solid part and a liquid part.

Describe how you could find out if there was any protein remaining in the liquid part.

4g
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1 mark

State the name of the test that would be used to test the milk for the presence of fat.

4h
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6 marks

After rennin has changed the protein in milk into a white solid, protease enzymes can be used to digest the protein. The digested protein forms a colourless liquid.

A hypothesis stated:

The optimum temperature for protease enzymes to digest changed milk protein is 37°C.

Describe a method that could be used to test this hypothesis.

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