Cambridge IGCSE Sciences - Co-ordinated (Double) 0654 — 2025 May/June Paper 6 · Variant 1

1 A student investigates diffusion in animals. The student uses agar jelly cubes to represent different sized animals. Each cube contains a green coloured indicator that turns red in acid. The acid moves into the cubes by diffusion. (a) Procedure The student: • places a cube of agar jelly with sides of 1 cm into a clean beaker • pours acid into this beaker until the cube is completely covered with acid • starts a stop-watch • records in Table 1.1 for trial 1 the time it takes for the cube to turn from green to completely red • does another trial and records this time in Table 1.1 as trial 2. Repeats the procedure with a cube of side 2 cm. (i) Fig. 1.1 shows the stop-watch reading for trial 1 for the cube of side 2 cm. Record in Table 1.1 this time in seconds to the nearest second. 01:01. 82 trial 1 Fig. 1.1 Table 1.1 surface time taken to turn completely red volume of ratio of surface cube side area of / s cube area to unit / cm cube / cm3 volume / cm2 trial 1 trial 2 average 1 6.0 24 34 29 2 3.0 65 [1] (ii) Calculate the average time for the cubes of side 2 cm. Record this value in Table 1.1 to the nearest whole second. [1] (iii) Use the value of the cube side given in Table 1.1 to calculate the surface area of each cube. Use the equation shown. surface area = length × height × 6 Record these values in Table 1.1. [1] (iv) Use the value of the cube side given in Table 1.1 to calculate the volume of each cube. Use the equation shown. volume = length × height × depth Record these values in Table 1.1. [1] (v) Calculate the rate of diffusion for the cube of side 1 cm in Table 1.1. Use the equation shown. 1000 rate of diffusion = average time taken to turn completely red rate of diffusion = ........................... per 1000 seconds [1] (b) A teacher repeats the procedure in (a) with increasing sizes of cube. They calculate the rate of diffusion for each cube as shown in Table 1.2. Table 1.2 cube side ratio of surface time rate of diffusion / cm area to unit volume / s per 1000 seconds 2 3.0 59 16.9 3 2.0 165 6.1 4 1.5 240 4.2 5 1.2 298 3.4 6 1.0 368 2.7 (i) On the grid, plot rate of diffusion (vertical axis) against ratio of surface area to unit volume. [3] (ii) Draw the curve of best fit. [1] (iii) Estimate the rate of diffusion for a cube with ratio of surface area to unit volume of 2.5. Show your working on the graph. rate of diffusion = ........................... per 1000 seconds [2] (c) The teacher obtains a rate of diffusion for a cube of side 1 cm. This rate of diffusion is 25.0 per 1000 seconds. Compare this rate of diffusion with the rate you calculated in (a)(v). Suggest one reason why the values are different. ................................................................................................................................................... ............................................................................................................................................. [1] (d) The cubes represent different sized animals. The acid moves into the cubes by diffusion. Some small animals rely on diffusion from their body surface to supply all their oxygen. Larger animals use a transport system such as blood to supply oxygen. Use the data in Table 1.2 and your graph to suggest why large animals cannot use diffusion from their body surface to supply oxygen. ................................................................................................................................................... ............................................................................................................................................. [1] [Total: 13]

Mark scheme: Question Answer Marks 1(a)(i) 62 ; 1 1(a)(ii) 64 ; 1 1(a)(iii) 6 and 24 ; 1 1(a)(iv) 1 and 8 ; 1 1(a)(v) 34.5 ; 1 1(b)(i) axes labelled with units ; 3 suitable linear scale, plotted points at least ½ grid, and all points can be plotted ; points plotted correctly to  ½ a small square ; 1(b)(ii) line of best fit ; 1 1(b)(iii) correct reading from graph ; 2 2 lines drawn one from each axis to line  ½ small square ; 1(c) (student) stopped watch too late / cut cube too big / 1 (teacher) stopped watch early / cut cube too small ; 1(d) rate of diffusion too low (to supply needs of larger animal) ; 1

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2 A student investigates an enzyme-controlled reaction. Yeast and some plants contain the enzyme catalase. Catalase speeds up the breakdown of hydrogen peroxide, releasing oxygen gas. The oxygen gas released forms a foam. (a) Procedure The student: • stirs a suspension of yeast cells • places approximately 1 cm depth of the suspension of yeast cells in a test-tube • adds 1 cm3 of aqueous hydrogen peroxide to the test-tube and starts a stop-watch • records in Table 2.1 the total height of the suspension of yeast cells and foam after 60 seconds. The student repeats the procedure using liquidised apple instead of the suspension of yeast cells. Fig. 2.1 shows the test-tube of the suspension of yeast cells actual size. (i) Record in Table 2.1 the total height in mm of the suspension of yeast cells and foam. foam suspension of yeast cells and aqueous hydrogen peroxide Fig. 2.1 Table 2.1 total height sample / mm suspension of yeast cells liquidised apple 11 [1] (ii) Use Table 2.1 to compare how much catalase is present in the samples of yeast cells and liquidised apple. Explain your answer. ........................................................................................................................................... ..................................................................................................................................... [1] (b) (i) Liquidising the apple breaks open the cells. Suggest why the cells need to be broken open. ........................................................................................................................................... ..................................................................................................................................... [1] (ii) Suggest why it is important to stir to mix the suspension of yeast cells in the procedure. ........................................................................................................................................... ..................................................................................................................................... [1] (c) Name one piece of apparatus suitable for measuring 1 cm3 of aqueous hydrogen peroxide. ............................................................................................................................................. [1] (d) Suggest one difficulty of measuring the total height of the suspension of yeast cells and foam in the test-tube. ................................................................................................................................................... ............................................................................................................................................. [1] (e) Explain why repeating the procedure increases confidence in the results. ................................................................................................................................................... ............................................................................................................................................. [1] [Total: 7]

Mark scheme: 2(a)(i) 24 ; 1 2(a)(ii) more (enzyme / catalase) in yeast (than apple) and because more foam ; 1 2(b)(i) to release any catalase / enzyme from the cells ; 1 2(b)(ii) cells evenly distributed ; 1 2(c) 1 cm3 syringe / 5 / 10 cm3 measuring cylinder / burette ; 1 2(d) Top of foam not level / bottom of test-tube rounded ; 1 2(e) Identify / exclude anomalies ; 1

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3 A student investigates the neutralisation of dilute hydrochloric acid by aqueous sodium hydroxide. The student does two experiments, one with aqueous sodium hydroxide J, and the other with aqueous sodium hydroxide K. The titration method is used. Bromothymol blue is an indicator. It turns yellow in acid solutions, blue in alkali solutions and green in neutral solutions. (a) Procedure The student: • fills a burette with dilute hydrochloric acid • records in Table 3.1 the initial burette reading to the nearest 0.05 cm3 • uses a measuring cylinder to add 25 cm3 of aqueous sodium hydroxide J to a conical flask • adds three drops of bromothymol blue indicator to the conical flask; the indicator turns blue • adds dilute hydrochloric acid to the conical flask until the indicator turns green • swirls the flask to mix while the dilute hydrochloric acid is added • records in Table 3.1 the final burette reading to the nearest 0.05 cm3. Fig. 3.1 shows a diagram of the apparatus. burette conical flask dilute hydrochloric acid aqueous sodium hydroxide and bromothymol blue indicator Fig. 3.1 The student repeats the procedure for aqueous sodium hydroxide K instead of J. Fig. 3.2 shows the final burette reading for J. cm3 27 28 29 Fig. 3.2 Record in Table 3.1 this volume to the nearest 0.05 cm3. Table 3.1 J K initial burette reading / cm3 1.20 12.60 final burette reading / cm3 25.65 volume of dilute hydrochloric acid added / cm3 [1] (b) (i) Suggest why the conical flask is swirled to mix the solutions as the dilute hydrochloric acid is added to the aqueous sodium hydroxide. ........................................................................................................................................... ..................................................................................................................................... [1] (ii) Suggest one piece of apparatus suitable for measuring the 25 cm3 of aqueous sodium hydroxide more accurately than a measuring cylinder. ..................................................................................................................................... [1] (iii) Suggest what the student does to have more confidence in the volumes of dilute hydrochloric acid used. ........................................................................................................................................... ..................................................................................................................................... [1] (c) Calculate the volume of dilute hydrochloric acid added for aqueous J and aqueous K. Record your values in Table 3.1. [1] (d) The concentrations of aqueous J and K are different. Suggest the relationship between the concentrations of aqueous J and aqueous K. Include a calculation in your answer. ................................................................................................................................................... ................................................................................................................................................... ............................................................................................................................................. [2] (e) A student repeats the procedure but does not notice the indicator turning green. The student continues adding dilute hydrochloric acid to the flask. Suggest the final colour of the mixture in the flask. ............................................................................................................................................. [1] (f) Aqueous sodium chloride is the product in the conical flask. The aqueous sodium chloride is coloured green with the indicator. Suggest how the procedure in (a) is changed to make colourless aqueous sodium chloride. ................................................................................................................................................... ............................................................................................................................................. [1] (g) (i) The student heats the aqueous sodium chloride to make solid sodium chloride using a Bunsen burner. Draw a labelled diagram of the assembled apparatus the student uses. [2] (ii) The student uses a balance to measure the mass of the solid sodium chloride. The mass is larger than expected. The balance is used correctly. Describe what the student does to confirm they have measured only the mass of solid sodium chloride. ........................................................................................................................................... ..................................................................................................................................... [1] (h) A student has two colourless liquids. One of the liquids is dilute hydrochloric acid, HCl. The other liquid is dilute sulfuric acid, H2SO4. Describe tests to confirm the identity of each acid. Include the observations for the positive result in your answer. hydrochloric acid test ............................................................................................................................................ observation ............................................................................................................................... sulfuric acid test ............................................................................................................................................ observation ............................................................................................................................... [1] [Total: 13]

Mark scheme: 3(a) 27.75 ; 1 3(b)(i) ensure complete reaction ; 1 3(b)(ii) volumetric pipette / burette ; 1 3(b)(iii) repeat (the procedure) ; 1 3(c) 26.55 AND 13.05 ; 1 3(d) calculation of J  K or K  J (seen) ; 2 J (approximately) double (concentration of) K ; 3(e) yellow ; 1 3(f) repeat using same volumes of NaOH and HCl as the first but without indicator ; 1 3(g)(i) Bunsen burner and heatproof mat and tripod and gauze and evaporating basin ; 2 any 3 correct labels ; 3(g)(ii) heats AND checks that the mass doesn’t decrease ; 1 3(h) (nitric acid and) silver nitrate and white ppt 1 AND (nitric acid and) barium nitrate and white pp ;

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4 An iron key is electroplated with copper metal using the apparatus shown in Fig. 4.1. battery + – + – copper anode key cathode aqueous copper sulfate Fig. 4.1 When the switch is closed, the copper dissolves from the anode, moves through the aqueous copper sulfate and coats (plates) onto the key at the cathode. Plan an investigation to find the relationship between the number of volts supplied by the batteries and the mass of copper coated onto the key. You are provided with: • several 1.5 V batteries • the apparatus and chemicals shown in Fig. 4.1. You may use any common laboratory apparatus in your plan. In your plan, include: • any other apparatus you will need • a brief description of the method • the measurements you will make and how you make them as valid as possible • the variables you will control • how you will process your results to reach a conclusion. .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .................................................................................................................................................... [7]

Mark scheme: 4 apparatus 7 balance and mass / amount measured in plan ; voltmeter and voltmeter in circuit / measure volts in plan ; timer and time measured in plan ; method 1 battery, measure mass of key repeat with more voltage / batteries ; measurements and validity mass of key at start and mass at end ; measure the number of volts ; use a minimum of 5 different voltages / batteries ; repeat each voltage to identify / exclude anomalies ; control variables time ; concentration / volume of copper sulfate / electrolyte ; size / mass of copper electrode / anode ; size / mass / sa of key ; distance apart of copper and key ; temperature ; processing and conclusion mass increase = mass at end – mass at start ; plot graph of volts / number of batteries against mass change / increase / mass of the copper coating ; describe possible shapes of graph e.g. straight line – linear relationship / straight line through origin – proportional etc. ; if voltage increases does mass increase or decrease (or stay the same) ;

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5 A student does an experiment to find the density of glass using solid glass marbles. (a) Procedure The student: • uses a balance to find the mass m of 6 glass marbles • pours water into a 50 cm3 measuring cylinder and measures the volume • carefully drops the 6 glass marbles into the water and measures the volume again. (i) Fig. 5.1 shows the balance with the 6 glass marbles. marbles 31.66 g Fig. 5.1 Record the mass m of the 6 glass marbles to the nearest 0.1 g. m = ...................................................... g [1] (ii) The student measures the volume V1 of water before adding the glass marbles. Fig. 5.2 shows the measuring cylinder. cm3 30 20 10 V1 Fig. 5.2 Record the volume V1 of water in cm3 to the nearest 0.5 cm3. V1 = .................................................. cm3 [1] (iii) The reading on the measuring cylinder after adding the glass marbles is 39.0 cm3. Calculate the volume Vm of the 6 glass marbles. Use the equation shown. Vm = 39.0 – V1 Vm = .................................................. cm3 [1] (iv) Calculate the density ρ of the glass marbles. Use the equation shown. m ρ = Vm Give your answer to three significant figures. ρ = .............................................. g / cm3 [2] (v) A teacher does the same experiment and calculates the density of the glass marbles as 2.80 g / cm3. Two values are considered to be equal within the limits of experimental error if the difference between them is less than 10%. Explain if the value in (a)(iv) and the teacher’s value are equal within the limits of experimental error. Justify your answer with a calculation. ........................................................................................................................................... ..................................................................................................................................... [2] (b) Describe how the student measures the volume of water accurately using the measuring cylinder. You may draw a diagram to help. ................................................................................................................................................... ............................................................................................................................................. [1] (c) (i) Another student does the experiment and uses a balance to measure the mass of the glass marbles. Fig. 5.3 shows the balance before any glass marbles are added. 0.60 g Fig. 5.3 State why this balance does not give the correct reading for the mass of the glass marbles. Suggest what the student does to obtain an accurate mass of the glass marbles. statement .......................................................................................................................... ........................................................................................................................................... suggestion ......................................................................................................................... ........................................................................................................................................... [1] (ii) The student calculates the volume of one glass marble using its diameter. The student measures the diameter of one glass marble using a 30 cm ruler. The student uses two wooden blocks to make the measurement of the diameter more accurate. Describe how the student uses the blocks. You may draw a diagram to help. ........................................................................................................................................... ..................................................................................................................................... [1] (iii) The student repeats the procedure in (a) but uses different marbles. The 6 marbles used have the same diameter and are made of the same glass as those used in the procedure in (a). These marbles have a large air bubble in the centre as shown in Fig. 5.4. glass air Fig. 5.4 State the effect the air bubble has on the density of the marbles and on the density of the glass. Explain your answers. effect on density of the marbles ........................................................................................ explanation ........................................................................................................................ ........................................................................................................................................... effect on density of the glass ............................................................................................. explanation ........................................................................................................................ ........................................................................................................................................... [2] [Total: 12]

Mark scheme: 5(a)(i) 31.7 ; 1 5(a)(ii) 21.5 ; 1 5(a)(iii) 17.5 ; 1 5(a)(iv) 1.81142….. ; 2 1.81; 5(a)(v) Any suitable method and statement ;; 2 e.g. 10% of 1.8 is 0.18 ; 0.18 + 1.8 = 1.98 which is below 2.8 so no ; or 10% of 2.8 is 0.28 ; 2.8 – 0.28 = 2.52 which is above 1.8 so no ; or find 90% and 110% of one of the values; show that other value either is or is not in that range so is / is not equal ; 5(b) measured from bottom of meniscus / at eye level to the reading (on the scale) / at 90° / perpendicularly to the reading (on 1 the scale) ; 5(c)(i) there is a zero error / the balance does not read 0 1 and subtract 0.6 g from the reading ; 5(c)(ii) trap the marble between (parallel) blocks and measure the distance between the blocks ; 1 5(c)(iii) Marbles 2 decrease and air has a lower density than glass (so average density is less) ; Glass no change and same glass so density is a fixed value / a constant ;

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6 A student does an experiment to find a value for the acceleration of free fall g using a pendulum. (a) Procedure The student: • sets up a pendulum as shown in Fig. 6.1 l bob Fig. 6.1 • uses a stop-watch to measure the time t for the pendulum to complete 20 swings. (i) The length l is the distance from the bottom of the clamp to the centre of the pendulum bob. The student uses a ruler to measure the length l . Fig. 6.2 shows the reading of l on the ruler. cm 33 34 Fig. 6.2 Record this reading of length l in cm to the nearest 0.1 cm. l = ................................................... cm [1] (ii) The stop-watch in Fig. 6.3 shows the time t for 20 swings. min s Fig. 6.3 Record t in seconds to the nearest 0.1 s. t = ...................................................... s [1] (iii) Calculate the time T for one swing. T = ...................................................... s [1] (iv) Calculate T 2. T 2 = ..................................................... s2 [1] (v) Calculate the acceleration of free fall g. Use your answers from (a)(i) and (a)(iv) and the equation shown. 0.395 × l g = T 2 g = ................................................ m / s2 [1] (b) (i) A student is given ruler A and ruler B to measure the length of the pendulum. Parts of the rulers are shown in Fig. 6.4. cm 1 2 cm 1 2 ruler A ruler B Fig. 6.4 State which ruler the student uses. Explain your answer. ruler ....................... explanation ........................................................................................................................ ........................................................................................................................................... [1] (ii) The student does the experiment and uses a fan to keep the room cool. The wind from the fan changes the time taken for one swing of the pendulum. Suggest what the student does to minimise the effect of the wind on the pendulum. The student does not adjust the fan. ........................................................................................................................................... ..................................................................................................................................... [1] (c) Explain why it is more accurate to time 20 swings of the pendulum instead of just one swing. ................................................................................................................................................... ............................................................................................................................................. [1] [Total: 8]

Mark scheme: 6(a)(i) 33.8 ; 1 6(a)(ii) 23.5 ; 1 6(a)(iii) 1.175 ; 1 6(a)(iv) 1.38(0625) ; 1 6(a)(v) 9.67 ; 1 6(b)(i) ruler A 1 and has smaller graduations / has mm ; 6(b)(ii) shield the pendulum ; 1 6(c) one swing is too short a time to measure / pendulum moves too quickly ; 1

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