Effects of Temperature & pH (Cambridge O Level Biology)

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. 

Extended Tier Only

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.