Hydrogen peroxide is a poisonous waste substance present in cells. The enzyme catalase, which is found in cells, decomposes hydrogen peroxide to form water and oxygen.
hydrogen peroxide catalase water + oxygen
If potato tissue is placed into a hydrogen peroxide solution in a test-tube, the catalase in the potato cells makes oxygen bubbles form. When detergent is added to the hydrogen peroxide solution, the oxygen bubbles become trapped and build up as a bubble layer that moves up the test-tube. The height of this layer shows how much catalase activity has taken place.
A student used this method to investigate the activity of the catalase in potato tissue by following these instructions:
• Label three large test-tubes A, B and C.
• Add $5\text{ cm}^3$ of hydrogen peroxide solution to each test-tube. Hydrogen peroxide is an irritant that may damage eyes and skin.
• Add $1\text{ cm}^3$ of detergent to the hydrogen peroxide solution in each test-tube.
• Cut three pieces of potato measuring $10\text{ mm} \times 10\text{ mm} \times 10\text{ mm}$.
• Put one of the pieces of potato into test-tube A.
• Start the timer immediately and watch the potato piece. Oxygen bubbles will rise to the surface and make a layer at the top of the hydrogen peroxide solution.
• Measure the height of this layer at 2, 4 and 6 minutes from the start and record these values. The height of the bubble layer should be measured from the top of the hydrogen peroxide solution to the top of the bubble layer, as shown in Fig. 1.1.
(a(i))[1]
State a safety precaution that the student should follow when carrying out the investigation with hydrogen peroxide solution.
(a(ii))[2]
Fill in the headings in Table 1.1.
(a(iii))[3]
Complete Table 1.1 by entering the student's results.
(a(iv))[3]
Describe the effect of increasing the surface area of the potato and explain what causes this effect.
(a(v))[1]
Suggest what they could do to make the readings taken every two minutes comparable.
(a(vi))[2]
The student noticed two unexpected problems during the investigation. Suggest how each may have affected the results.
1. bubbles sometimes stuck to the potato
2. some of the eight parts of potato in test-tube C stuck together
(a(vii))[1]
Suggest how the student can show that the activity of the enzyme catalase is responsible for producing the bubbles.
(b(i))[1]
Name the piece of apparatus marked D.
(b(ii))[6]
Design an investigation to determine how temperature affects the activity of catalase in potato. Use the apparatus shown in Fig. 1.3.
Worked solution & mark scheme
This 20-mark question has a full step-by-step worked solution and mark scheme. One marking point: “Wear safety spectacles / goggles / eye protection / gloves” …