2.4 Enzymes

A student wanted to investigate the effect of substrate concentration on the activity of an enzyme called catalase. Catalase is an enzyme that commonly occurs inside living cells where it breaks down toxic hydrogen peroxide into oxygen and water. The image below shows the experimental set up done by the student.

List two control variables that the student would need to be aware of in the experiment shown in the image.

[2 marks]

The student decided to make up solutions at five different hydrogen peroxide concentrations. Their measurements for these solutions are shown in the table below.

Concentration of hydrogen peroxide solution (%)	Volume of hydrogen peroxide required (cm3)	Volume of distilled water required (cm3)
10	10	90
8	B	C
6	6	94
A	4	96
2	2	98

Give the measurements needed to fill in gaps A-C in the table. 

[1 mark]

After measuring out the range of hydrogen peroxide concentrations shown in part (b), the student carried out the experiment using the equipment set up in part (a). They recorded the volume of oxygen (the product) produced after one minute, and repeated this measurement three times at each concentration. Their results are shown in the table below.

Use the data in the table to calculate the value missing from the square marked X. 

[1 mark]

State the purpose of repeating the experiment three times at each concentration of hydrogen peroxide. 

Using the data in part (c), draw a graph of hydrogen peroxide concentration against the mean volume of oxygen. 

Deduce the conclusions that can be drawn from your graph from part (e). 

A researcher investigated the effect of pH on the activity of stomach enzyme pepsin. 

Their results are shown in the image below. 

The rate of reaction can be calculated by using the following formula:

Calculate the rate of reaction at pH 4. Give your answer with the correct units.

[2 marks]

Describe the differences between the curves at pH 2 and pH 4.

[2 marks]

State why product production at pH 2 does not continue indefinitely but reaches a plateau at around 14.75 g.

[1 mark]

State two benefits of using immobilised enzymes in industrial processes.

When the enzymes are immobilised for this process they are fixed to small alginate beads. The substrate solution is then poured through the beads in order for the substrate to react with the enzyme. 

Describe the processes that occur during an enzyme-catalysed reaction. 

Outline the events that occur when enzymes are exposed to high temperatures.