Cambridge IGCSE Science - Combined 0653 — 2025 May/June Paper 6 · Variant 2

1 A student investigates a root vegetable. Fig. 1.1 shows a section cut through the root of a carrot. Fig. 1.1 (a) In the box, make a large pencil drawing of the cut surface of the carrot root. [3] (b) Fig. 1.2 shows a magnified photograph of a section of a lotus root. A B Fig. 1.2 (i) The distance AB represents the diameter of the lotus root section. Measure the distance AB on Fig. 1.2. Record your answer to the nearest mm. distance AB = ...................................................mm [1] (ii) The actual diameter of the lotus root section is 75 mm. Calculate the magnification of the photograph in Fig. 1.2. Use the equation shown. length of line AB magnification = actual diameter of lotus root section Give your answer to two significant figures. magnification = ......................................................... [2] (iii) Distance AB shows the smallest diameter of the lotus root section. Describe how to determine the average diameter of the lotus root section. ........................................................................................................................................... ..................................................................................................................................... [1] (c) (i) Describe one way that the section of lotus root in Fig. 1.2 is similar to the section of carrot root in Fig. 1.1. ........................................................................................................................................... ..................................................................................................................................... [1] (ii) Describe two differences between the section of lotus root in Fig. 1.2 and the section of carrot root in Fig. 1.1. difference 1 ........................................................................................................................ ........................................................................................................................................... ........................................................................................................................................... difference 2 ........................................................................................................................ ........................................................................................................................................... ........................................................................................................................................... [2] (d) A student tests the section of carrot root and a piece of potato for the presence of starch. The student: step 1 places the piece of potato and the section of carrot root onto a white tile step 2 adds a few drops of iodine solution to the surface of the carrot and of the potato step 3 observes the colour of the iodine solution. Fig. 1.3 shows the results the student records. the carrot showed a negative result with iodine the piece of potato gave a positive result Fig. 1.3 Use the results in Fig. 1.3 to complete Table 1.1. Table 1.1 colour with iodine solution conclusion carrot potato [3] [Total: 13]

Mark scheme: Question Answer Marks 1(a) size: drawing fills more than 50% of available space ; 3 quality: clear continuous outline ; detail: minimum of 3 medullary rays and minimum of 3 circular sections shown and no shading ; 1(b)(i) 84 (mm) ; 1 1(b)(ii) 84  75 = 1.12 ; 2 answer to 2 sf = 1.1 ; 1(b)(iii) take additional measurement(s) (of diameter) (using different positions around root) 1 and add together and divide by number of, measurements / diameters ; 1(c)(i) rounded shape / smooth shape / similar shape / skin ; 1 1(c)(ii) any two differences from: 2 lotus root has holes / carrot does not have holes ; carrot is darker / lotus root is lighter ; (radial) lines in carrot / no lines in lotus root ; carrot has more obvious layers / layers not obvious in lotus root ; carrot has less variation in diameter / lotus root has more variation in diameter ; 1(d) brown recorded for carrot ; 3 blue-black recorded for potato ; correct conclusion for starch presence, i.e. (carrot contains) no starch and (potato contains) starch ;

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2 A student investigates the reaction between aluminium and aqueous copper(II) chloride. Aqueous copper(II) chloride is a blue solution. Aluminium is a grey solid. (a) Procedure The student: • assembles the apparatus shown in Fig. 2.1 thermometer plastic cup glass beaker Fig. 2.1 • pours 25 cm3 of aqueous copper(II) chloride into the plastic cup • records in Table 2.1, the initial temperature of the aqueous copper(II) chloride • adds 0.5 g of aluminium to the aqueous copper(II) chloride • stirs the mixture in the plastic cup • records in Table 2.1, the highest temperature reached by the reaction mixture. (i) Fig. 2.2 shows the temperature readings for this experiment. initial temperature highest temperature reached °C °C 30 50 20 40 10 30 Fig. 2.2 Record in Table 2.1, these temperatures to the nearest 0.5 °C. Table 2.1 initial temperature of aqueous copper(II) chloride / °C highest temperature reached by reaction mixture / °C temperature increase / °C [2] (ii) Calculate the temperature increase. Record this value in Table 2.1. [1] (b) At the end of the experiment the plastic cup contains: • a colourless solution • a pink solid • a grey solid. Explain how these observations show that the reaction has finished and that aluminium is in excess in this experiment. ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ............................................................................................................................................. [2] (c) There is an error in the experiment that causes a smaller temperature increase than expected. Identify this error. Suggest one improvement to the experiment to minimise this error. error .......................................................................................................................................... improvement ............................................................................................................................. ................................................................................................................................................... [2] (d) Another student repeats the procedure using six different concentrations of aqueous copper(II) chloride. The unit of concentration is M. Table 2.2 shows the results the student obtains. Table 2.2 concentration of aqueous temperature increase copper(II) chloride / °C / M 0.00 0 0.10 7.5 0.20 16.0 0.30 23.5 0.40 32.5 0.50 39.5 (i) On the grid, plot temperature increase (vertical axis) against the concentration of aqueous copper(II) chloride. [3] (ii) Draw the line of best fit. [1] (e) Estimate using the graph, the concentration of aqueous copper(II) chloride that gives a temperature increase of 20.0 °C. Show your working on the graph. concentration = ......................................................M [2] [Total: 13]

Mark scheme: 2(a)(i) 21.5 ; 2 41.0 ; 2(a)(ii) 19.5 ; 1 2(b) there is no blue copper chloride solution left ; 2 there is grey solid aluminium left behind ; 2(c) error stated ; 2 with improvement suggested ; e.g. idea of heat loss ; use insulation / use a lid on the cup ; e.g. thermometer touches (base of) cup ; clamp / hold in place ; 2(d)(i) vertical axis labelled temperature increase / °C and horizontal axis labelled concentration / M ; 3 linear scales so that plotted points occupy at least half the grid ; plots correct to ½ small square ; 2(d)(ii) thin straight line of best fit drawn with even distribution of points ; 1 2(e) evidence of working out on graph (horizontal line from 20.0 °C and then vertical line down to concentration) ; 2 estimation of concentration to within ½ a small square ;

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3 A student investigates an electrical circuit with two identical resistors in series. Procedure The student: step 1 connects the circuit shown in Fig. 3.1 resistor 1 resistor 2 Fig. 3.1 step 2 connects a voltmeter to measure the voltage across resistor 1 step 3 closes the switch step 4 records the voltmeter reading step 5 opens the switch step 6 moves the voltmeter to measure the voltage across resistor 2 step 7 repeats step 3 to step 5. (a) Draw a voltmeter in Fig. 3.1 to show how the student measures the voltage across resistor 1 in step 2. [2] (b) Fig. 3.2 shows the voltmeter readings V1 and V2. Read and record V1 and V2 to the nearest 0.01 V. 0.4 0.6 0.4 0.6 0.2 0.8 0.2 0.8 0 1.0 0 1.0 V V V1 V2 Fig. 3.2 V1 = ............................................................ V V2 = ............................................................ V [2] (c) A student suggests that if resistor 1 has the same resistance as resistor 2 then V1 = V2. Two values are considered equal within the limits of experimental accuracy if they are within 10% of each other. State if your values of V1 and V2 support the student’s suggestion. Justify your answer with a calculation. ................................................................................................................................................... ............................................................................................................................................. [2] (d) Suggest why the student opens the switch after each reading. ................................................................................................................................................... ............................................................................................................................................. [1] [Total: 7]

Mark scheme: 3(a) correct voltmeter symbol ; 2 drawn correctly connected to the wires across resistor 1 ; 3(b) V1 = 0.65 (V) ; 2 V2 = 0.70 (V) ; 3(c) correct calculation of 10%, e.g. 2 (0.05 / 0.70  100 =) 7.1 / 7 % or e.g. (0.05 / 0.65  100 =) 7.7 / 8 % ; (correct calculation plus statement that) yes / this is within 10% / they are equal (within the limits of experimental accuracy) ; 3(d) prevent (wires or resistors) (over)heating / prevent current being drawn from dry cell ; 1

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4 Fig. 4.1 shows a metal rod placed in a box of sand. mass sand metal rod Fig. 4.1 When a mass is dropped onto the rod, the rod moves further into the sand. A student predicts that the distance the rod moves into the sand is proportional to the mass dropped onto the rod. Plan an investigation to test the student’s prediction. You are provided with: • the apparatus in Fig. 4.1 • a number of different masses. In your plan, include: • any additional apparatus you will use • a brief description of the method • the variables you will control and the measurements you will take • a table to record the results (you are not required to enter any readings in the table) • how you will process your results to form a conclusion about the prediction. .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .................................................................................................................................................... [7]

Mark scheme: 4 One marking point from each section and any two others (if one section is missing max 6 etc.): 7 1 apparatus balance ; ruler / tape measure ; 2 description of method drop 2 or more masses onto the rod ; make markings (e.g. with marker) on rod level with sand ; repeat for 5 different masses ; 3 control variables and measurements measure mass ; measure initial and final length of rod above sand / distance between markings made on rod ; control height of mass / starting point of mass above rod ; control initial length of rod (above sand) / depth of rod (in sand) ; 4 table mass (of masses) in g / kg ; initial and final length of rod above sand in cm / mm ; or distance between markings in cm / mm ; 5 processing calculate initial length of rod – final length of rod ; graph of distance (moved) against mass ; straight line through origin shows proportional relationship / mass ÷ distance moved = constant supports proportional relationship / describe doubling etc. of both variables ORA ; repeat each mass and identify / exclude anomalous results ;

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