Enzyme Action (Cambridge O Level Biology)

Exam Questions

2 hours16 questions

5 marks

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

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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

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]

How did you do?

4 marks

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]

How did you do?

1 mark

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

How did you do?

6 marks

A student stated that:

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

Plan an investigation to test this statement.

How did you do?

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.

How did you do?

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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 king and write your answer to one decimal place.

How did you do?

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.

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Fig. 3

Prepare a table to record the results.

How did you do?

2 marks

State a conclusion for the results.

How did you do?

5 marks

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]

How did you do?

2 marks

Explain the purpose of test-tube P4.

How did you do?

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.

How did you do?

4 marks

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

tomato

Fig. 4

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

How did you do?

1 mark

A student wanted to find out if tomatoes contained starch.

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

How did you do?

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