Catalase is an enzyme present in living cells. It speeds up the decomposition of hydrogen peroxide into oxygen and water. Some plant cells are a source of catalase.
If plant material is crushed and mixed with water, a suspension containing the cell contents of the plant can be made.
When hydrogen peroxide solution is added to this suspension, the oxygen released appears as gas bubbles. These bubbles gather to make a foam layer at the top of the suspension.
The height of any foam formed can be measured. A greater height shows greater catalase activity.
A student compared catalase activity in the cells of three plant species by measuring the foam height produced in each. Three cell suspensions, one each of celery, apple and potato, were supplied in separate beakers.
The student used these steps:
• stir the celery cell suspension in the beaker with a clean stirring rod
• use a syringe to place $2\ \text{cm}^3$ of celery cell suspension into a clean test-tube
• add $2\ \text{cm}^3$ of hydrogen peroxide solution to this test-tube using a clean syringe
• begin timing at once
• after $60$ seconds, measure the height of any foam formed and write down the result.
Carry out the same steps with the apple cell suspension and then with the potato cell suspension.
Fig. 1.1 shows the combined contents of each of the three test-tubes after $60$ seconds.
(a(i))[7]
Record the height of any foam produced in each test-tube in a table.
(a(ii))[1]
Use your results to arrange the three plant species by catalase activity, starting with the most active and ending with the least active.
(b(i))[1]
Suggest why the three plant tissues were crushed before the hydrogen peroxide solution was added.
(b(ii))[2]
Suggest why the plant suspensions were stirred before the hydrogen peroxide solution was added.
(b(iii))[1]
State one variable that was kept constant in this investigation.
(b(iv))[2]
Suggest two reasons why repeating the investigation would increase the student’s confidence in the results.
(c(i))[4]
Draw a graph of the data in Table 1.1 on the grid below. Join the points you plot with ruled, straight lines.
(c(ii))[3]
Use your graph to estimate the total volume of the contents of the measuring cylinder at $4$ minutes. Show your working on the graph.
(c(iii))[3]
Describe and explain the form of your graph.