Question 123 marks
Question
You are going to investigate the effect of hydrogen peroxide concentration on the activity of catalase. Catalase is an enzyme found in yeast cells. The enzyme catalyses the breakdown of hydrogen peroxide to form water and oxygen. The reaction releases heat. You are going to compare the activity of catalase in yeast cells in two different concentrations of hydrogen peroxide solution by measuring the change in temperature during the reaction. Read all the instructions but DO NOT DO THEM until you have drawn a table for your results in the space provided in 1(a)(i). You should use the safety equipment provided while you are doing the practical work. Step 1 Cover the outside of each of the test-tubes with a piece of foil. Do not cover the openings at the top of the test-tubes. Step 2 Attach a sticky label to the foil on each test-tube. Label one test-tube A and the other test-tube B. Put the foil-covered test-tubes into the test-tube rack. Step 3 Use the large syringe to put 10 cm3 of hydrogen peroxide solution into test-tube A. Step 4 Measure the temperature of the hydrogen peroxide solution in test-tube A. Record this measurement as the temperature at 0 minutes in your table in 1(a)(i). Step 5 Use the glass rod to stir the yeast suspension. Use the small syringe to add 1 cm3 of yeast suspension to the hydrogen peroxide solution in test-tube A. Immediately start the stop-clock. Step 6 Measure the temperature of the hydrogen peroxide solution in test-tube A every minute for five minutes. Record the measurements in your table in 1(a)(i). Step 7 Use the large syringe to put 5 cm3 of hydrogen peroxide solution and 5 cm3 of distilled water into test-tube B. Step 8 Repeat steps 4, 5 and 6 using test-tube B. (a) (i) Prepare a table to record your results. [4] (ii) Using your results, identify the highest temperature and the lowest temperature in each test-tube. Use these values to calculate the maximum temperature change in each test-tube. Space for working. maximum temperature change in test-tube A ……°C maximum temperature change in test-tube B ……°C [2] (iii) State a conclusion for your results. …… [1] (iv) State the variable that was measured (dependent variable) in this investigation. …… [1] (b) (i) The test-tubes were covered with foil in step 1. Predict and explain the effect on the results of not covering the test-tubes with foil. …… [2] (ii) State one variable, other than covering both test-tubes with foil, that was kept constant in this investigation. …… [1] (c) (i) In a different experiment, students investigated the effect of pH on the breakdown of hydrogen peroxide by calculating the rate of oxygen production. State the two measurements that the students would need to take to calculate the rate of oxygen production in cm3 per minute. 1 …… 2 …… [2] The results of the investigation are shown in Table 1.1. Table 1.1 rate of oxygen production average rate of oxygen / cm3 per minute pH production trial 1 trial 2 trial 3 / cm3 per minute 5 7 8 8 7.7 6 15 17 14 15.3 7 26 29 27 27.3 8 27 16 28 27.5 9 5 6 4 5.0 (ii) The students decided that the result for trial 2 at pH 8 was anomalous. State what is meant by an anomalous result. …… [1] (iii) Describe how the students calculated the average value for pH 8. …… [1] (iv) Using the data in Table 1.1, plot a line graph on the grid to show the effect of pH on the average rate of oxygen production. [4] (v) Describe the effect of pH on the average rate of oxygen production. Use the data from your graph to support your answer. …… [2] (vi) The students wanted to obtain a more accurate value for the pH at which the average rate of oxygen production was highest. Suggest what further investigative work the students should do. …… [2] [Total: 23]
Mark scheme
1(a)(i) one table drawn with minimum three columns and a header 4 line ; appropriate column / row headings, with units for both time and temperature ; recording of 12 temperatures ; correct trend ; i.e. greater temperature rise for test-tube A check supervisor’s report if results not as expected 1(a)(ii) correct temperature change calculated for test-tube A ; 2 correct temperature change calculated for test-tube B ; 1(a)(iii) the, greater / higher, the concentration of hydrogen peroxide 1 A conclusion consistent with results the greater the activity of catalase / AW / ora ; 1(a)(iv) temperature ; 1 1(b)(i) 1 effect on the results if room temperature is lower: 2 the temperature change would be less / the temperature (in the tubes) would be lower / AW ; 2 explanation (without the foil) there was, no insulation / no heat reflection / (more) heat loss / AW ; OR 1 effect on the results if room temperature is higher: temperature (in the tubes) would be higher ; 2 explanation (without the foil) there was, no insulation / no heat reflection / (more) heat gain / AW ; 1(b)(ii) any one from: 1 1 (total) volume of solution ; 2 volume / concentration / amount / type, of yeast ; 3 time (intervals at which measurements were taken) / total time for reaction ; 4 stirring of yeast ; 5 starting temperature (of solution) ; 1(c)(i) volume (of oxygen produced) ; 2 time (over which the oxygen is produced) ; 1(c)(ii) a result that does not fit the, pattern / trend / AW ; 1 1(c)(iii) they did not use the anomalous result in the calculation / AW ; 1 1(c)(iv) axes labelled with units ; 4 uses a linear scale and plotting area occupies half or more of the grid in both directions ; all five points plotted accurately ± half a small square ; suitable line drawn ; 1(c)(v) any two from: 2 the rate (of oxygen production / enzyme activity) increased then decreased as pH increased ; peak at pH 8 / peak or plateau between pH 7–8 ; use of data with units ; 1(c)(vi) test at smaller intervals of pH ; 2 between, pH 7–9 ;