5.1 Enzymes

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.  

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.

Fig. 2

Prepare a table for the results from this investigation.

Use information provided in the question to complete your table.

i)

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

[2]

Suggest how you could improve the method that they followed. 

State a conclusion that can be drawn from these results.

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]

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

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.

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.

Table 1

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

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

Fig. 2

Care was taken not to shake 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.

Fig. 3

Prepare a table to record the results.

State a conclusion for the results.

i)

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

[1]

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

[2]

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

[2]

Explain the purpose of test-tube P4.

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. 

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

Fig. 4

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

A student wanted to find out if tomatoes contained starch.

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

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.

Fig. 1

Fig. 2

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

State a conclusion for these results.

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. 

Identify four sources of error in this investigation.

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

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.

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

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.