Enzyme action — practice question

Hydrogen peroxide is a toxic waste product found in living cells. Catalase is the enzyme that breaks hydrogen peroxide down into water and oxygen. Some students investigated catalase in tissues from different plants. They used small filter paper discs. These discs were placed on the cut surface of plant tissues so that they could soak up liquid from the cells. That cell liquid may have contained catalase. Fig. 1.1 shows how the students could determine whether catalase was present in tissues from different plants. Fig. 1.1 text: beaker containing hydrogen peroxide solution; filter paper disc soaked in liquid from plant cells; filter paper disc containing trapped bubbles of oxygen. A filter paper disc soaked in liquid from plant cells was dropped into the hydrogen peroxide solution and sank to the bottom. If catalase was present, bubbles of oxygen formed. The bubbles of oxygen were trapped in the filter paper disc making it float to the surface. The students were supplied with 2 cm \times 2 cm \times 2 cm cubes of tissue from three different plants labelled A, B and C, small filter paper discs and a beaker of hydrogen peroxide solution. The students carried out the following steps. • Cut the piece of plant tissue A in half. • Use forceps to put a filter paper disc onto a cut surface of plant tissue A, so that it could absorb liquid from the cells. • After 1 minute, use forceps to lift the filter paper disc off the cut surface of plant tissue A. • Drop the filter paper disc into the beaker of hydrogen peroxide solution and start timing at once. The filter paper disc will sink to the bottom of the beaker. • Watch the filter paper disc until it reaches the surface of the hydrogen peroxide solution, then stop timing. If a filter paper disc does not float within 4 minutes (240 seconds) stop timing and record the time taken for the filter paper disc to reach the surface as >240. • Record the time taken, to the nearest whole second, for the filter paper disc to reach the surface of the hydrogen peroxide solution. • Use forceps to take the filter paper disc out of the beaker of hydrogen peroxide solution and put it in the waste container provided. • Rinse and dry the forceps. • Repeat the procedure two more times with filter paper discs on the same cut surface of plant tissue A. • Carry out the whole procedure again for filter paper discs on plant tissue B and then once more for plant tissue C. Fig. 1.2 shows a student's notebook. The student has written their results to the nearest whole second. The result for the third filter paper disc on plant tissue A is missing from their notes. Fig. 1.2 text: repeat discs. plant A: 10, 10. plant B: 21, 16, 20. plant C: no disc floated at 4 minutes. Fig. 1.3 shows the time taken for the third filter paper disc on plant tissue A to reach the surface. Fig. 1.3 display: 9.31 SEC.