Cambridge IGCSE Biology (9-1) 0970 — 2023 Oct/Nov Paper 6 · Variant 2

1 Students investigated the effect of temperature on the activity of amylase. Amylase is an enzyme that catalyses the breakdown of starch to form reducing sugars. The students used this method: Step 1 Use a pen to label a spotting tile as shown in Fig. 1.1. 1 2 1 2 dimple 3 4 3 4 5 6 5 6 W C Fig. 1.1 Step 2 Put one drop of iodine solution into each of the dimples on the spotting tile. Step 3 Put 2 cm3 of 2% amylase solution into two test-tubes. Step 4 Label a third test-tube W and a fourth test-tube C. Step 5 Put 2 cm3 of starch suspension into test-tube W and into test-tube C. Step 6 Label a beaker W and put approximately 200 cm3 of warm water into beaker W. Step 7 Put test-tube W and one of the test-tubes containing 2 cm3 of 2% amylase solution into beaker W. Leave both test-tubes in beaker W for three minutes. Step 8 After three minutes, pour the 2% amylase solution into test-tube W and start the stop-clock. Step 9 Wait for 30 seconds and then use a pipette to remove a sample of the liquid from test-tube W. Put two drops of this sample into the dimple labelled W1 on the spotting tile. Record the colour of the liquid in dimple W1. Step 10 Repeat step 9 using dimple W2. Continue taking and testing samples of liquid from test-tube W at 30-second intervals, using the remaining dimples W3, W4, W5 and W6. Record the colour of the liquid in each dimple. Stop the stop-clock and reset it to zero. Step 11 Label a beaker C and put approximately 200 cm3 of cold water into beaker C. Step 12 Put test-tube C and the other test-tube containing 2 cm3 of 2% amylase solution into beaker C. Leave both test-tubes in beaker C for three minutes. Step 13 After three minutes, pour the 2% amylase solution into test-tube C and start the stop-clock. Step 14 Repeat step 9 and step 10 with test-tube C and the dimples labelled C1, C2, C3, C4, C5 and C6. The results of the investigation are shown in Fig. 1.2. Key: 1 2 1 2 blue-black colour 3 4 3 4 yellow-brown colour 5 6 5 6 W C Fig. 1.2 (a) (i) Prepare a table and record the results shown in Fig. 1.2. [3] (ii) State a conclusion for the results shown in Fig. 1.2. ........................................................................................................................................... ........................................................................................................................................... ..................................................................................................................................... [1] (iii) State the independent variable in this investigation. ..................................................................................................................................... [1] (iv) State three variables that were kept constant in this investigation. 1 ........................................................................................................................................ ........................................................................................................................................... 2 ........................................................................................................................................ ........................................................................................................................................... 3 ........................................................................................................................................ ........................................................................................................................................... [3] (b) (i) Explain why the method used in this investigation does not allow the students to obtain an accurate time for the breakdown of starch. ........................................................................................................................................... ........................................................................................................................................... ..................................................................................................................................... [1] (ii) The temperature of the water in the beakers during the investigation was a source of error. Describe how you could improve the method to reduce this error. ........................................................................................................................................... ........................................................................................................................................... ..................................................................................................................................... [1] (iii) The test-tubes were left in the beakers of warm or cold water for three minutes in step 7 and step 12 before the amylase solution was poured into the starch suspension. Explain why the test-tubes were left in the beakers for three minutes. ........................................................................................................................................... ........................................................................................................................................... ..................................................................................................................................... [1] [Total: 11]

Mark scheme: Question Answer Marks Guidance 1(a)(i) table drawn with minimum three columns and a header line ; 3 appropriate column / row headings ; correct recording of 12, colours / results ; 1(a)(ii) the greater the temperature the greater the, 1 enzyme / amylase, activity / AW / ora ; 1(a)(iii) temperature ; 1 1(a)(iv) any three from: 3 (number of) drops of iodine (solution) ; volume of amylase / 2 cm3 amylase ; concentration of amylase ; same enzyme ; volume of starch (suspension) ; time for equilibration / AW ; sample intervals / time intervals ; number of drops of sample added to iodine (solution) ; 1(b)(i) any one from: 1 idea that colour change might take place between sampling times ; time intervals were too long ; difficult to judge end point / colour change is subjective / it is qualitative ; 1(b)(ii) any one from: 1 insulate the beaker / AW ; use a thermostatically controlled water-bath ; description of using a Bunsen burner and a thermometer to control the temperature ; 1(b)(iii) to equilibrate / to allow the temperature of the test tube 1 contents to become the same as the water in the beaker / AW ;

More questions on Enzymes

2 (a) Milk contains fats. The enzyme lipase catalyses the breakdown of fats to form fatty acids and glycerol. The fatty acids cause the pH of the milk to decrease. Plan an investigation to determine the effect of lipase concentration on the breakdown of fats in milk. ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ............................................................................................................................................. [6] (b) The emulsion test is used to test a sample of food for fat. Describe the method you would use to do the emulsion test. ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ............................................................................................................................................. [2] [Total: 8]

Mark scheme: 2(a) independent variable: 6 1 (at least) two different, enzyme / lipase, concentrations ; dependent variable: 2 measuring pH after a set time OR measuring time to reach a certain pH ; detail of method: 3 use of pH meter / pH paper / (named) indicator ; 4 measure / same, initial pH / initial colour ; 5 control and description of the control e.g. using boiled enzyme / water instead of enzyme ; 6 & 7 variables kept constant – max two from ;; • volume of milk • type of milk / same milk / fat content of milk • volume of, lipase / enzyme • temperature • volume of indicator 8 two or more repeats / total of three or more trials ; 9 relevant safety precaution e.g. use of goggles / gloves ; 2(b) add ethanol and (then) water ; 2 shake ;

More questions on Enzymes

3 Fig. 3.1 is a photograph of a type of seaweed called bladder wrack. The bladders help the seaweed float in water. P Q bladder Fig. 3.1 (a) (i) Draw a large diagram of the bladder wrack seaweed shown in Fig. 3.1. [4] (ii) Line PQ on Fig. 3.1 represents the length of one bladder on the bladder wrack seaweed. The actual length of the bladder is 19 mm. Measure the length of line PQ on Fig. 3.1. length of line PQ ............................ mm Calculate the magnification of the photograph using the formula and your measurement. length of line PQ magnification = actual length of the bladder Give your answer to two decimal places. Space for working. ................................................................ [3] (iii) Seaweeds are species of algae that live in the sea. Fig. 3.2 shows photographs of bladder wrack seaweed and a different species of seaweed called egg wrack. The photographs are the same magnification. bladder wrack egg wrack Fig. 3.2 State two ways, visible in Fig. 3.2, that bladder wrack is different from egg wrack. 1 ........................................................................................................................................ ........................................................................................................................................... 2 ........................................................................................................................................ ........................................................................................................................................... [2] (b) Bladder wrack is found on the seashore and is exposed to the air when it is not covered by water at certain times of day. Students investigated how rapidly bladder wrack lost water. They used this method: • Three samples of bladder wrack were collected. • The samples were blotted with tissue to remove any water on the surface of the seaweed. • The initial mass of each sample was recorded. • The samples were hung from a piece of string stretched between two stands. • The mass of each sample was recorded every 30 minutes for the first two hours and then every hour for a further three hours.

Mark scheme: 3(a)(i) outline – single clear line no shading ; 4 size – frond length at least 114 mm ; detail 1: 7 bladders drawn ; detail 2: central midrib shown as a double line at least up to the point at which the midrib branches ; 3(a)(ii) line PQ = 12 ± 1 mm ; 3 MP1 correct measurement 0.63 ;; MP2 dividing their measurement by 19, R if incorrect unit given with the answer MP3 correct rounding to two decimal places A 0.58 / 0.68 if measured as 11 or 13 mm ecf MP2 / MP3 from error in previous step 3(a)(iii) any two from: 2 bladder wrack has more bladders ; bladders are closer together ; bladder wrack, has bladders in pairs / either side of mid rib, or egg wrack has single bladders ; bladder wrack has a central mid rib ; bladder wrack, divides into two at the end / more branched ; bladder wrack is, wider / thicker / AW, (all the way along) ; bladder wrack is, lighter / brighter, (in colour) ; bladder wrack (fronds) are all in the same direction ; bladder wrack has smaller bladders ; bladder wrack has rounded ends / smoother ; AVP ; 3(b)(i) any two from: 2 temperature ; wind(speed) ; humidity ; species / type, of seaweed ; age of seaweed ; size / length / surface area ; idea of how long the bladder wrack has been out of the water ; measuring time / interval time (between measuring mass) / sampling times ; spacing while hung up ; amount of blotting / blotting time / blotting method / type of blotting paper ; 3(b)(ii) a result that does not fit the pattern / trend / AW ; 1 3(b)(iii) did not include sample 2 in the calculation / AW ; 1 3(b)(iv) 57 (%) ;; 2 MP1 correct calculation MP2 correct rounding to two significant figures ecf MP2 from incorrect MP1 3(c) axes labelled with units ; 4 suitable size with a linear scale and data that occupies at least half of the grid in both directions ; all seven points plotted accurately ± half a small square ; suitable line drawn ; 3(d) biuret ; 2 DCPIP ;

More questions on Features of organisms