Cambridge IGCSE Biology (9-1) 0970 — 2022 May/June Paper 5 · Variant 1

1 Rice contains starch. Amylase is an enzyme that catalyses the breakdown of starch to form reducing sugars. You are going to investigate the effect of amylase on cooked rice. Read all the instructions but DO NOT CARRY THEM OUT 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 carrying out the practical work. Step 1 Label one empty test-tube W10 and label the other empty test-tube A10. Step 2 Put the test-tubes in the empty beaker labelled 80 °C water-bath. Step 3 Label one of the large test-tubes containing rice W and the other large test-tube containing rice A. Step 4 Put both large test-tubes containing rice in the empty beaker labelled 40 °C water-bath. Step 5 Raise your hand when you are ready for warm water to be added to the 40 °C water-bath. Step 6 Use the measuring cylinder to add 20 cm3 of distilled water to the rice in the test-tube labelled W. Step 7 Use the measuring cylinder to add 20 cm3 of amylase solution to the rice in the test- tube labelled A. Step 8 Start the stop-clock and leave the test-tubes of rice in the 40 °C water-bath for 10 minutes. While you are waiting, carry out step 9. Step 9 Use the syringe to add 2 cm3 of Benedict’s solution to each of the empty test-tubes, W10 and A10. Put the test-tubes back in the empty beaker labelled 80 °C water-bath. Step 10 After 10 minutes (step 8), put the stopper into test-tube W and invert the test-tube three times. Remove the stopper. Step 11 Use a clean pipette to remove 2 cm3 of the liquid surrounding the rice in test-tube W. Put the 2 cm3 of liquid into test-tube W10. Put test-tube W10 back into the beaker labelled 80 °C water-bath. Step 12 Repeat steps 10 and 11 with test-tubes A and A10. Step 13 Raise your hand when you are ready for hot water to be added to the beaker labelled 80 °C water-bath. Step 14 Leave test-tubes W10 and A10 in the 80 °C water-bath for 10 minutes. While you are waiting continue with the other questions. Step 15 After 10 minutes, record the colour of the liquid in test-tubes W10 and A10 in the table you have prepared in 1(a)(i). (a) (i) Prepare a table to record your results. [3] (ii) State a conclusion for your results. ........................................................................................................................................... ........................................................................................................................................... ..................................................................................................................................... [1] (iii) State one variable that was kept constant in this investigation. ..................................................................................................................................... [1] (iv) State the purpose of adding distilled water to the test-tube of cooked rice labelled W. ........................................................................................................................................... ........................................................................................................................................... ..................................................................................................................................... [1] (v) It was important that step 6 was carried out before step 7. Predict the effect on the results if step 7 was carried out before step 6. ........................................................................................................................................... ........................................................................................................................................... ..................................................................................................................................... [1] (vi) The temperature of the 40 °C water-bath will decrease during the investigation. State one piece of equipment that could be used to maintain the temperature at 40 °C. ..................................................................................................................................... [1] (b) State how you could show that cooked rice contains starch. ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ............................................................................................................................................. [2] (c) Some students investigated the effect of temperature on the rate of amylase activity. They measured the mass of reducing sugars produced in five minutes, at different temperatures. The results of this investigation are shown in Fig. 1.1. 60 50 40 mass of reducing sugars produced in five 30 minutes / mg 20 10 0 0 10 20 30 40 50 60 temperature / °C Fig. 1.1 (i) Describe the effect of temperature on the activity of amylase shown in the graph in Fig. 1.1. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ..................................................................................................................................... [2] (ii) Use the graph to estimate the rate of amylase activity, in mg per minute, at a temperature of 42 °C. Space for working. ........................................ mg per minute [2] (iii) The students wanted to obtain a more accurate value for the temperature at which amylase works best. Suggest further investigative work that the students should carry out. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ..................................................................................................................................... [2] (d) Plan an investigation to determine the effect of pH on the activity of amylase. ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ............................................................................................................................................. [6] [Total: 22]

Mark scheme: 1(a)(i) table drawn with two, columns / rows with line separating headings from body of table ; suitable headings test-tube and colour ; recording of blue / no change, in W(10) and orange in A(10) ; 3 check supervisor’s report if results not as expected 1(a)(ii) rice contains starch / starch is broken down to form (reducing) sugar / starch is broken down by amylase / (reducing) sugar is produced when amylase is present ora ; 1 ecf from their data – answer must be consistent with the data in the table in 1(a)(i) 1(a)(iii) any one from: mass of rice ; type of rice ; temperature (of the water-bath) ; time (in water-bath after adding rice) ; volume of water and, amylase / solution / liquid, added ; sample size (removed) ; volume of Benedict’s solution (used) ; concentration of Benedict’s solution ; 1 1(a)(iv) as a control (investigation) / for comparison / to show what would happen if no amylase were present / to show the (colour) change was due to amylase / AW ; 1 1(a)(v) any one from: W(10), will change colour / turn, yellow / green / orange / red ; a positive result in (test-tube) W(10) ; (reducing) sugar present in (test-tube) W(10) ; both test-tubes show a positive result with Benedict’s solution ; 1 1(a)(vi) any one from: thermostatically controlled water-bath ; thermo-isolated container / insulated jacket / (foam) insulation / AW ; lid (used on water bath) ; 1 1(b) (test rice with) iodine (solution / reagent) / iodine in potassium iodide solution ; (observe) blue-black colour (if starch present) ; 2 Question Answer Marks Guidance 1(c)(i) (the activity of amylase / mass of (reducing) sugar produced), increased and then decreased (as the temperature increased) ; peak / optimum / AW, temperature is 35 °C ± 1 °C ; 2 1(c)(ii) 6 (mg per minute) ;; 2 MP1 correct reading 30 mg from graph MP2 correct answer calculated ecf from incorrect MP1 reading divided by five 1(c)(iii) test at smaller intervals of temperature ; select a narrower range of temperatures around 35 °C ; 2 Question Answer Marks Guidance 1(d) either – reducing sugar method independent variable: 1 at least two pH values tested / two pH values stated ; dependent variable: 2 time to (first) colour change / colour of Benedict’s solution after a set period of time (at 80 °C) of time / mass, of (reducing) sugars ; 3,4 variables kept constant, max. two from ;;  volume of pH solution  concentration of amylase (solution)  volume / quantity, of amylase (solution)  type of amylase solution  temperature  volume of starch suspension / mass of (starch source) / AW  concentration of starch solution (if used)  source of starch suspension  volume of Benedict’s (solution) 5, 6 given method, max. two from ;;  take (fixed volume of) samples  (testing with) Benedict’s (solution)  heat / incubate at 80 °C 7, 8 new method, max. two from ;;  use of buffer  use of colorimeter (for Benedict’s) / colour chart  use of balance to measure mass (of reducing sugars / precipitate) 9 repeat investigation twice / at least two replicates ; 10 relevant safety precaution: gloves / goggles / tongs / test-tube holder ; 11 AVP ; e. g., equilibration time (in the water bath before mixing) 6 Question Answer Marks Guidance 1(d) (cont./…) OR disappearance of starch method independent variable: 1 at least two pH values tested / two pH values stated ; dependent variable: 2 time for iodine solution to stay yellow-brown / disappearance of starch ; 3, 4 variables kept constant, max. two from ;;  volume of pH solution  concentration of amylase  volume / quantity, of amylase solution  type of amylase solution  temperature  volume of starch suspension / mass of rice / mass of plant tissue / AW  concentration of starch suspension (if used)  same source of starch 5, 6 given method take (fixed volume of) samples ; samples taken at regular intervals ; 7, 8 new method, max. two from ;;  use of buffer  (testing with), iodine solution  use of spotting / white, tile 9 repeat investigation twice / at least two replicates ; 10 relevant safety precaution: gloves / goggles ; 11 AVP ; e.g. equilibration time (in the water bath before mixing)

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2 Fig. 2.1 is a photomicrograph of a section through part of a marram grass leaf, Ammophila arenaria. Fig. 2.1 (a) (i) Draw a large diagram of the section of marram grass leaf shown in Fig. 2.1. Do not draw individual cells. [4] (ii) Fig. 2.2 shows a cross-section of a whole marram grass leaf. Q P magnification ×120 Fig. 2.2 Measure the length of line PQ on Fig. 2.2. length of line PQ ............................................. mm Calculate the actual diameter of the marram grass leaf using the formula and your measurement. length of line PQ on Fig. 2.2 magnification = actual diameter of the marram grass leaf Give your answer to one decimal place. Space for working. ......................................................... mm [3] (b) Scientists investigated the effect of different concentrations of sodium chloride solution on the germination and growth of marram grass. Marram grass seeds were germinated in Petri dishes on filter paper which had been soaked in one of the different sodium chloride solutions. Each Petri dish contained 15 seeds and the investigation was repeated four times. After 20 days, the lengths of the seedling roots were measured with a ruler. (i) State the variable that was changed (independent variable) and the variable that was measured (dependent variable) in this investigation. independent variable ......................................................................................................... ........................................................................................................................................... dependent variable ............................................................................................................ ........................................................................................................................................... [2] (ii) State two ways the scientists designed the investigation to produce valid and reliable results. 1 ........................................................................................................................................ ........................................................................................................................................... 2 ........................................................................................................................................ ........................................................................................................................................... [2] (c) The results of the investigation described in 2(b) are shown in Table 2.1. Table 2.1 concentration of average root length sodium chloride / mm solution / g per dm3

Mark scheme: 2(a)(i) outline - single clear unbroken line ; size - greater than 90 mm diagonally (top left to bottom right) ; detail 1: (at least) four projections ; detail 2: either four vascular bundles shown OR presence of hairs on at least two projections ; 4 R if individual cells drawn R shading 2(a)(ii) measuring line PQ = 112 (mm) ±1 (mm) ; 0.9 (mm) ;; 3 MP1 correct measurement MP2 correct answer calculated MP3 correct rounding of answer to one decimal place ecf MP2 and MP3 from incorrect measurement / calculation 2(b)(i) independent variable: concentration of sodium chloride solution ; dependent variable: length of roots ; 2 2(b)(ii) any two from: (four) repeats ; large number / AW / 15, seeds (grown at each sodium chloride concentration) ; measured, at same time / (after) 20 days (of growth) ; same species / all marram grass seeds / AW ; 2 2(c)(i) 31.6(%) ;;; 3 MP1 correct selection of data from Table 2.1, i.e., 19 mm and 13 mm MP2 correct answer calculated MP3 correct rounding of answer to three significant figures ecf MP2 and MP3 from incorrect data / calculation 2(c)(ii) axes labelled with units ; suitable even scale and plotting area occupies at least half the grid in both directions ; six points plotted accurately ± half a small square ; suitable line drawn ; 4

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