Cambridge IGCSE Sciences - Co-ordinated (Double) 0654 — 2023 May/June Paper 6 · Variant 3

1 Fig. 1.1 shows a photograph of a flower. B A Fig. 1.1 (a) In the box, make a large and detailed pencil drawing of the flower. Include the internal parts of the flower. [3] (b) (i) Draw a line to join points A and B on Fig. 1.1. Measure the length of this line AB in millimetres to the nearest millimetre. length of line AB on Fig. 1.1 = .................................................. mm [1] (ii) Draw a line on your drawing in (a) in the same place as AB on Fig. 1.1. Measure the length of this line in millimetres to the nearest millimetre. length of line AB on your drawing = .................................................. mm [1] (iii) Use your measurements in (b)(i) and (b)(ii) to calculate the magnification m of your drawing. Use the equation shown. length of line AB on your drawing m = length of line AB on Fig. 1.1 Record your value to two significant figures. magnification m = ......................................................... [2] (c) Fig. 1.2 shows a flower at the same magnification as the flower in Fig. 1.1. Fig. 1.2 (i) Describe three visible differences between the flower in Fig. 1.1 and the flower in Fig. 1.2. difference 1 ........................................................................................................................ difference 2 ........................................................................................................................ difference 3 ........................................................................................................................ [3] (ii) Add a line labelled anther to identify an anther on Fig. 1.2. [1] [Total: 11]

Mark scheme: 1(a) clear and continuous outlines ; size at least half of the box and all of flower in the box ; 3 petals, stigma and minimum 1 anthers ; 3 1(b)(i) 13 mm (and line drawn) ; 1 1(b)(ii) line drawn and correct measurement ; 1 1(b)(iii) correct calculation ; 2 SF ; 2 1(c)(i) any three from: ref petals larger in 1 / smaller in 2 ; petals pointed at end in 1 / blunt in 2 ; more petals in 1 ; AVP ; 3 1(c)(ii) anther labelled ; 1

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2 A student investigates the action of three different concentrations of an enzyme on milk protein. Milk contains a protein that makes it look white (opaque). When the protein is broken down, the milk becomes clear. (a) Procedure The student: • labels four test-tubes A, B, C and D • adds 5 cm3 of enzyme solution of four different concentrations as shown in Table 2.1 • adds 2 cm3 of milk to each test-tube • uses a glass stirring rod to mix the contents of each test-tube and then starts a stop-watch • measures the time it takes for the milk in each test-tube to become clear • records in Table 2.1 these times to the nearest second; if the milk does not clear after 5 minutes, the result is recorded as >300. (i) State the name of a piece of apparatus suitable for measuring 2 cm3 of milk. ..................................................................................................................................... [1] (ii) Fig. 2.1 shows the reading on the stop-watch for test-tube A. Record this time in Table 2.1. 00:59.23 min s Fig. 2.1 Table 2.1 percentage concentration test-tube time / s of enzyme A 4 B 2 133 C 1 196 D 0 >300 [1] (b) Use Table 2.1 to state the relationship between the concentration of the enzyme and the time it takes for the milk to clear. ................................................................................................................................................... ............................................................................................................................................. [1] (c) (i) Explain why it is important to mix the contents of the test-tubes. ........................................................................................................................................... ..................................................................................................................................... [1] (ii) Suggest how a student alters the procedure to investigate the action of this enzyme on a protein solution which is already clear. ........................................................................................................................................... ..................................................................................................................................... [1] (d) (i) The thermometer in Fig. 2.2 shows the temperature of the room. °C 30 20 Fig. 2.2 Record the temperature of the room. temperature of the room = .................................................... °C [1] (ii) Increasing the temperature increases the rate that an enzyme breaks down a protein. The student repeats the procedure in (a) at 35 °C. Suggest the effect of increasing temperature on the times taken for the milk to become clear in test-tubes A, B and C. ........................................................................................................................................... ..................................................................................................................................... [1] (iii) Suggest why there is no effect on the time taken for the milk to become clear in test-tube D. ........................................................................................................................................... ..................................................................................................................................... [1] (iv) The enzyme in this investigation denatures (stops working) at temperatures above 55 °C. The student repeats the procedure in (a) at 75 °C. Predict the results the student obtains. ........................................................................................................................................... ..................................................................................................................................... [1] [Total: 9]

Mark scheme: 2(a)(i) syringe / measuring cylinder / burette / (volumetric or graduated ) pipette ; 1 2(a)(ii) 59 ; 1 2(b) as enzyme concentration increases time decreases ; 1 2(c)(i) ensure enzyme evenly distributed / AW ; 1 2(c)(ii) biuret solution used ; 1 2(d)(i) 24 ; 1 2(d)(ii) (times are) less / smaller / decreases ; 1 2(d)(iii) no enzyme present ; 1 2(d)(iv) 300 s ; 1

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3 A student investigates the rate of reaction between solution H and solution K. When solutions H, K and starch are mixed together, a blue-black colour is seen after a period of time. When the concentration of solution H is changed, the time taken for the blue-black colour to appear changes. (a) Procedure The student: • adds 2 cm3 of solution H into a conical flask • adds 8 cm3 of distilled water into the conical flask • adds 5 drops of starch solution into the conical flask • adds 10 cm3 of solution K into the conical flask, swirls the flask and immediately starts a stop-watch • stops the stop-watch when the solution turns blue-black • records in Table 3.1 the time taken t in seconds to the nearest second. The student repeats the procedure using the other volumes shown in Table 3.1. Table 3.1 volume of volume of distilled drops of starch volume of time taken t / s solution H / cm3 water / cm3 solution solution K / cm3 2 8 5 10 118 4 6 5 10 6 4 5 10 34 8 2 5 10 17 10 0 5 10 8 (i) The student uses different measuring cylinders to measure the volumes of solution H and solution K. Explain why the student uses different measuring cylinders. ........................................................................................................................................... ..................................................................................................................................... [1] (ii) The substance made when solution H and solution K react together turns the starch solution blue-black. Identify the substance made. ..................................................................................................................................... [1] (iii) Fig. 3.1 shows the reading on the stop-watch for 4 cm3 of solution H. 01:06.21 min s Fig. 3.1 Record in Table 3.1 this time in seconds to the nearest second. [1] (b) (i) On the grid, plot a graph of time taken t (vertical axis) against the volume of solution H. [3] (ii) Draw the line of best fit. [1] (iii) Use your graph to estimate the time taken for the mixture to turn blue-black when 5.5 cm3 of solution H and 4.5 cm3 of distilled water are used. Show on your graph how you arrived at your answer. time taken t = ...................................................... s [2] (c) When distilled water is added to solution H, the solution becomes less concentrated. (i) State the relationship between the concentration of solution H and the time taken for the reaction. ........................................................................................................................................... ..................................................................................................................................... [1] (ii) State the relationship between the concentration of solution H and the rate of reaction. ........................................................................................................................................... ..................................................................................................................................... [1] (d) Suggest what the student does to have more confidence in their results. ................................................................................................................................................... ............................................................................................................................................. [1] (e) Suggest why the experiment is not done using 10 cm3 of distilled water and 0 cm3 of solution H. ................................................................................................................................................... ............................................................................................................................................. [1] [Total: 13]

Mark scheme: 3(a)(i) avoid contamination ; 1 3(a)(ii) iodine ; 1 3(a)(iii) 66 ; 1 3(b)(i) axes correct orientation and labelled with quantity and unit ; scales linear and plotted points cover at least half of grid ; all points plotted and  ½ small square ; 3 3(b)(ii) curve of best-fit ; 1 Question Answer Marks 3(b)(iii) marking on graph ; correct reading from graph ; 2 3(c)(i) as concentration increases time decreases ; 1 3(c)(ii) as concentration increases rate increases ; 1 3(d) repeat to (identify and) exclude anomalies ; 1 3(e) no reaction ; 1

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4 A student does a series of tests to identify solution L. Solution L gives: • a white precipitate when tested with both a few drops of aqueous sodium hydroxide and with excess aqueous sodium hydroxide • a colourless solution when tested with both a few drops of aqueous ammonia and with excess aqueous ammonia • a white precipitate when carbon dioxide is bubbled into it. The student also adds a liquid that shows that solution L is weakly alkaline. (a) Complete a results table to show all the tests and all the observations made by the student. [6] (b) State the identity of solution L. ............................................................................................................................................. [1] [Total: 7]

Mark scheme: 4(a) headers test and observations / results ; cross in results table drawn ; aq NaOH AND white ppt AND white ppt / doesn’t dissolve ; aq NH3 AND no reaction / no precipitate / colourless solution ; CO2 (bubbled in) AND white ppt ; universal indicator / blue / dark green ; 6 4(b) limewater/calcium hydroxide ; 1

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5 A student measures the density of plasticine (modelling clay) by two different methods. Method 1 (a) Procedure The student: • places a piece of plasticine onto a top-pan balance • records the mass m of the plasticine. Fig. 5.1 shows the reading on the balance. plasticine 84.6 g top-pan balance Fig. 5.1 Record the mass of the plasticine to the nearest gram. m = ...................................................... g [1] (b) (i) Procedure The student: • pours water into a measuring cylinder • records in Table 5.1 the volume V1 of water in the measuring cylinder • uses a thread to lower the plasticine into the measuring cylinder until it is completely immersed • records in Table 5.1 the new volume V2. Fig. 5.2 shows the reading V2 on the measuring cylinder. cm3 80 measuring cylinder 70 water Fig. 5.2 Record in Table 5.1 the reading on the measuring cylinder. Table 5.1 V1 / cm3 V2 / cm3 31 [1] (ii) Use the values of V1 and V2 to calculate the volume V of the piece of plasticine. V = .................................................. cm3 [1] (iii) State one precaution that the student takes when reading the volume of water in a measuring cylinder to obtain an accurate reading. ........................................................................................................................................... ..................................................................................................................................... [1] (c) Suggest why the mass of the plasticine is measured before its volume is measured. ................................................................................................................................................... ............................................................................................................................................. [1] (d) Use your answers to (a) and (b)(ii) to calculate the density ρ1 of the plasticine. Use the equation shown. m ρ1 = V Give the unit for your answer. ρ1 = ......................... unit ........................ [2] Method 2 (e) Procedure The student: • removes the plasticine from the measuring cylinder • dries the plasticine with a paper towel • moulds the plasticine into a shape that approximates to a sphere • places the plasticine between two wooden blocks • uses a ruler to measure the diameter d1 of the sphere of plasticine in centimetres to the nearest 0.1 cm. Fig. 5.3 is a full-size diagram that shows how the student arranges the wooden blocks and the sphere. wooden block wooden block plasticine sphere view from above scale: full size Fig. 5.3 (i) Suggest why the wooden blocks must be parallel to one another. ........................................................................................................................................... ..................................................................................................................................... [1] (ii) Use a ruler to measure the horizontal diameter d1 of the sphere of plasticine in centimetres to the nearest 0.1 cm. d1 = ................................................... cm [1] (iii) The student rotates the sphere and measures the diameter d2 of the sphere across a different part of the sphere. d2 = 4.4 cm Use the values of d1 and d2 to calculate the average diameter D of the sphere. D = ................................................... cm [1] (f) Calculate the volume VS of the plasticine sphere. Use the equation shown. VS = 0.52D3 VS = .................................................. cm3 [1] (g) Use your answers to (a) and (f) to calculate the density ρ2 of the plasticine. Use the equation shown. m ρ2 = VS ρ2 = ......................................................... [1] (h) Compare your answers for the density of plasticine from (d) and (g). Suggest one practical reason why the values are different. ................................................................................................................................................... ............................................................................................................................................. [1] [Total: 13]

Mark scheme: 5(a) 85 recorded to nearest gram ; 1 5(b)(i) 76 ; 1 5(b)(ii) 45 ; 1 5(b)(iii) view scale at right angles / at eye level / perpendicular ; 1 5(c) water on the plasticine adds to its mass ; 1 5(d) 1.9 ; g / cm3 ; 2 5(e)(i) so that the distance between them is constant ; 1 5(e)(ii) 4.0 ; 1 5(e)(iii) 4.2 ; 1 5(f) 38.5 ; 1 5(g) 2.2 ; 1 5(h) any one from: difficult to mould a perfect sphere ; water still remaining on plasticine ; measuring cylinder only reads to 1 cm3 ; volume of thread adds to total volume ; difficult to get blocks parallel ; 1

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6 Plan an investigation to find out if the material from which a spring is made affects the extension of the spring when it is stretched by a load. You are provided with: • springs made from aluminium, steel, iron and nickel • a set of 100 g masses, together with a hanger • boss, stand and clamp. You may use any other common laboratory apparatus. In your plan include: • any other apparatus needed • a brief description of the method, including what you will measure and how you will make sure your measurements are accurate • the variables you will control • a results table to record your measurements (you are not required to enter any readings in the table) • how you will process your results to draw a conclusion. You may include a labelled diagram if you wish. .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .................................................................................................................................................... [7]

Mark scheme: 6 additional apparatus: metre rule / ruler ; method and measurements and accuracy: clamp spring and add load(s) and repeat for other materials ; measure unstretched length of spring ; measure length of extended spring ; do each material more than once ; eye level / fiducial aid / ruler close to spring / repeating and averaging results ; table: columns for initial length, final length and material ; units of length for both i and f ; control variables: (unstretched) length of spring ; diameter of spring ; load / range / mass of loads used ; conclusion: calculate extension by stretched spring length – unstretched spring length ; if the extensions are different materials have an effect / if extension changes (within limits of experimental error) as the material is changed then material has an effect / is there a (significant) difference in length for each material used ; plot graph of load / extension / plot a bar chart for each metal if one load used and compare if material makes a difference ;

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