Cambridge IGCSE Science - Combined 0653 — 2019 May/June Paper 4 · Variant 3

1 (a) Fig. 1.1 is a bar chart which shows some differences in the composition of inspired air and expired air. 25 20 15 composition of air / % 10 5 0 gas X gas Y gas X gas Y inspired air expired air source of air Fig. 1.1 Identify gas X and gas Y in Fig. 1.1. Give a reason for each answer using data from Fig. 1.1. gas X ................................................. reason ....................................................................................................................................... ................................................................................................................................................... gas Y ................................................. reason ....................................................................................................................................... ................................................................................................................................................... [2] (b) Gaseous exchange takes place in the alveoli of the lungs. State two features of the alveoli that allow efficient gas exchange. 1. ............................................................................................................................................... 2. ............................................................................................................................................... [2] (c) Fig. 1.2 is a diagram showing some cells which line the trachea. ciliated cell goblet cell Fig. 1.2 Describe how the goblet cells and ciliated cells protect the gas exchange system from pathogens and particles. ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ............................................................................................................................................. [3] (d) State two diseases caused by tobacco smoking. 1. ............................................................................................................................................... 2. ............................................................................................................................................... [2] [Total: 9]

Mark scheme: 1(a) gas X oxygen (no mark) reduces in expired air (so oxygen used in respiration) ; gas Y carbon dioxide (no mark) increases in expired air (so carbon dioxide released in respiration) ; 2 1(b) any two of large surface area ; thin walls ; good blood supply ; good ventilation with air ; max 2 1(c) goblet cells secrete mucus ; mucus traps pathogens and particles ; cilia sweep mucus out of the trachea ; 3 1(d) chronic obstructive pulmonary disease / COPD ; lung cancer ; coronary heart disease ; max 2

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2 (a) A simple example of cracking is the cracking of ethane to produce ethene and hydrogen. C2H6 → C2H4 + H2 The energy level diagram for this reaction is shown in Fig. 2.1. energy C2H4 + H2 C2H6 reaction progress Fig. 2.1 (i) On Fig. 2.1 draw a double headed arrow ( ) to show the activation energy for this reaction. [1] (ii) Use the energy level diagram to explain why the reaction is endothermic. ........................................................................................................................................... ..................................................................................................................................... [1] (iii) State one condition required for the process of cracking. ..................................................................................................................................... [1] (b) Ethane and ethene are not in the same homologous series. Explain what is meant by the term homologous series. ................................................................................................................................................... ................................................................................................................................................... ............................................................................................................................................. [2] (c) Draw a dot-and-cross diagram to show the bonding in a molecule of ethane, C2H6. [3] (d) When fuels are burned, carbon dioxide is released into the atmosphere. State one possible negative effect of an increase in the concentration of carbon dioxide in the atmosphere. ................................................................................................................................................... ............................................................................................................................................. [1] (e) Complete the balanced symbol equation for the complete combustion of ethene, C2H4 , in oxygen. ............................ C2H4 + ................... → .......... CO2 + [2] [Total: 11]

Mark scheme: 2(a)(i) arrow from reactant energy level to the top of the curve ; 1 2(a)(ii) reactants have less chemical energy than products ; 1 2(a)(iii) high temperature / high pressure / catalyst ; 1 2(b) family of compounds with a general formula ; similar chemical properties ; 2 Question Answer Marks 2(c) six hydrogen atoms, three attached to each carbon ; one bonding pair between carbon atoms ; single bonding pairs between each carbon and hydrogen ; 3 2(d) global warming / enhanced greenhouse effect / climate change / named consequence of climate change ; 1 2(e) C2H4 + 3O2  2CO2 + 2H2O all formulae correct ; balanced (dependent on correct formulae) ; 2

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3 Fig. 3.1 shows a boy swimming in a swimming pool. Fig. 3.1 He swims at a constant speed. (a) (i) On Fig. 3.1 draw a force arrow to show the force pushing the swimmer through the water. [1] (ii) A gravitational force of 600 N acts on the boy. Suggest why the boy does not sink to the bottom of the pool as a result of this force. ........................................................................................................................................... ..................................................................................................................................... [1] (b) The boy dives into the pool and swims. Fig. 3.2 shows a speed–time graph for the boy. 1.2 speed 1.0 m / s 0.8 0.6 0.4 0.2 0 0 10 20 30 time / s Fig. 3.2 (i) The boy dives from the side of the pool at time = 0 s on the graph and hits the water at time = 2 s. Describe the motion of the boy during the dive. ........................................................................................................................................... ..................................................................................................................................... [2] (ii) Suggest why the boy’s speed slowed down between time = 2 s and time = 3 s. ........................................................................................................................................... ..................................................................................................................................... [1] (iii) The mass of the boy is 60 kg. Use data from Fig. 3.2 to calculate the kinetic energy of the swimmer at time = 20 s. Show your working. kinetic energy = ...................................................... J [2] (iv) The boy takes 30 s to swim 25 m. Calculate the average speed of the swimmer. Show your working. average speed = ................................................. m / s [2] [Total: 9]

Mark scheme: 3(a)(i) arrow pointing from right to left ; 1 3(a)(ii) has to be an (equal and) opposite upward force / owtte ; 1 3(b)(i) acceleration ; constant ; 2 3(b)(ii) water friction / resistance (much higher than air resistance) ; 1 3(b)(iii) working mark from one or more of : speed at 20 s = 0.88 m/s (KE =) ½ mv2 (KE =) ½ x 60 × 0.882 ; = 23.2(3) (J) ; 2 Question Answer Marks 3(b)(iv) (average speed =) distance ÷ time or 25 ÷ 30 ; = 0.83 (m/s) ; 2

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4 Plants need a supply of mineral ions which they get from water in the soil. (a) (i) State why plants need magnesium ions. ..................................................................................................................................... [1] (ii) Describe the effect on plants if they are deficient in magnesium ions. ..................................................................................................................................... [1] (b) Farmers add fertilisers containing nitrate ions to their land. Some of these nitrate ions enter lakes. This can lead to eutrophication. Use words from the list to complete the flow diagram about eutrophication. Each word may be used once, more than once or not at all. consumers death decomposition decrease growth increase producers increase in availability of nitrate ions increase in ........................................................ of producers increase in decomposition after death of ........................................................ ........................................................ in aerobic respiration by decomposers ........................................................ in dissolved oxygen death of organisms in the water. [4] (c) A student investigates transpiration in leaves. He attaches a piece of blue cobalt chloride paper to the upper surface of a leaf. Another piece is attached to the lower surface. Cobalt chloride paper changes colour from blue to pink when water is present. The cobalt chloride paper on the lower surface of the leaf turns pink before the cobalt chloride paper on the upper surface. (i) Explain the result in terms of leaf structure. ........................................................................................................................................... ........................................................................................................................................... ..................................................................................................................................... [2] (ii) The experiment is repeated in a warmer environment. The cobalt chloride paper on the lower surface turns pink more quickly than before. Explain in detail why this happens. ........................................................................................................................................... ........................................................................................................................................... ..................................................................................................................................... [2] [Total: 10]

Mark scheme: 4(a)(i) to make chlorophyll ; 1 4(a)(ii) leaves turn yellow ; 1 4(b) growth ; producers ; increase ; decrease ; 4 4(c)(i) faster rate of transpiration / water loss from lower surface / cell surfaces ; more stomata on lower surface ; 2 4(c)(ii) transpiration rate increases / increased evaporation from stomata / mesophyll cell surfaces ; water molecules have more kinetic energy due to higher temperature ; correct reference to diffusion of water molecules / vapour from air spaces in the leaf ; max 2

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5 (a) Magnesium is an element in Group II of the Periodic Table, shown on page 20. (i) An atom of magnesium has a nucleon number of 24. Deduce the number of protons and the number of neutrons in this atom. number of protons ..................................... number of neutrons ..................................... [1] (ii) Complete Fig. 5.1 to show the electronic structure of a magnesium atom. nucleus Fig. 5.1 [2] (b) Magnesium is produced by the electrolysis of magnesium chloride. (i) Before magnesium chloride is electrolysed it must be melted. Explain, in terms of particles and energy changes, what happens to a solid as it is melting. ........................................................................................................................................... ........................................................................................................................................... ..................................................................................................................................... [1] (ii) Magnesium chloride consists of magnesium ions, Mg2+, and chloride ions, Cl –. Name the electrode at which magnesium forms when molten magnesium chloride is electrolysed. ..................................................................................................................................... [1] (iii) Describe how magnesium ions are changed into magnesium atoms during electrolysis. ........................................................................................................................................... ........................................................................................................................................... ..................................................................................................................................... [2] (c) A student investigates the reaction between dilute hydrochloric acid and excess magnesium carbonate powder. Fig. 5.2 shows the apparatus she uses. gas syringe bubbles of gas excess magnesium carbonate powder dilute hydrochloric acid Fig. 5.2 (i) Name the salt formed during this reaction. ..................................................................................................................................... [1] (ii) Carbon dioxide is released during this reaction. State the chemical test and the positive result for carbon dioxide. test .................................................................................................................................... positive result .................................................................................................................... ........................................................................................................................................... [2] [Total: 10]

Mark scheme: 5(a)(i) number of protons = 12 and number of neutrons = 12 ; 1 5(a)(ii) 12 electrons shown ; 2,8,2 configuration shown ; 2 5(b)(i) (thermal) energy absorbed which decreases inter-particle forces / allows particles to separate / move around freely ; 1 5(b)(ii) cathode ; 1 5(b)(iii) gain electrons ; (gain) two (electrons) ; 2 Question Answer Marks 5(c)(i) magnesium chloride ; 1 5(c)(ii) limewater ; goes cloudy / milky ; 2

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6 (a) Fig. 6.1 shows a cylinder of compressed air (air at high pressure) used by a scuba diver in the sea. compressed air Fig. 6.1 The diver opens a valve on the cylinder to let the compressed air escape into her face mask. (i) Describe how the forces and distances between the molecules in the air change as the air leaves the cylinder. forces ................................................................................................................................ ........................................................................................................................................... distances ........................................................................................................................... ........................................................................................................................................... [2] (ii) As the air leaves the cylinder, the temperature of the air decreases slightly. Describe what happens to the motion of the molecules in the air. ..................................................................................................................................... [1] (b) The diver returns to her boat after a dive. On the boat, she hangs up her wet diving suit to dry. Describe how the weather conditions will affect evaporation from the wet diving suit. Explain your answer in terms of water molecules escaping from the surface of the diving suit. ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ............................................................................................................................................. [3] (c) The wind causes waves on the sea. Fig. 6.2 shows a boat anchored and going up and down as the waves pass. wave direction boat moves up and down Fig. 6.2 Between each wave the boat moves a vertical distance of 2 m from the top of a wave to the bottom of a wave. The speed of the waves is 3 m / s. The time taken for the boat to go from the top of one wave to the top of the next wave is 5 s. (i) Determine the amplitude of these waves. amplitude = ..................................................... m [1] (ii) Determine the frequency of the waves. frequency = .................................................... Hz [1] (iii) Calculate the wavelength of these waves. Show your working. wavelength = ............................................... m [2] [Total: 10]

Mark scheme: 6(a)(i) forces decrease ; distances increase ; 2 6(a)(ii) (average) speed (of molecules) decreases ; 1 6(b) the higher the wind speed the higher the rate of evaporation / drying ; increased wind speed increases the rate at which molecules move away from suit / decreases the chances that escaped molecules return / owtte ; the higher the temperature the higher the rate of evaporation / drying ; increased temperature increases the energy / speed of molecules so they leave the surface at a higher rate / owtte ; max 3 6(c)(i) 1 (m) 1 6(c)(ii) f = (1 ÷ time between waves = 1 ÷ 5 ) = 0.2 (Hz) ; 1 6(c)(iii) v = f λ or λ = v / f or λ = 3 / 0.2 ; = 15 (m) ; 2

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7 (a) Enzymes are proteins that function as biological catalysts. Fig. 7.1 shows a representation of an enzyme molecule and some possible substrate molecules. active site A B C D enzyme molecule possible substrate molecules Fig. 7.1 State the letter of the correct substrate for the enzyme shown in Fig. 7.1. Explain your answer. letter .............................................. explanation ............................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... [2] (b) Fig. 7.2 shows the effect of temperature on enzyme activity for an enzyme. enzyme activity 0 10 20 30 40 50 60 temperature / °C Fig. 7.2 (i) State the optimum temperature of the enzyme. optimum temperature = ............................................... °C [1] (ii) Explain in detail why the enzyme activity decreases at higher temperatures. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ..................................................................................................................................... [3] (c) The enzymes secreted by the human digestive system are responsible for the chemical digestion of food. Define the term chemical digestion. ................................................................................................................................................... ................................................................................................................................................... ............................................................................................................................................. [2] [Total: 8]

Mark scheme: 7(a) C ; shape of C is complementary to the active site ; 2 7(b)(i) 40 °C ; 1 7(b)(ii) enzyme is denatured ; shape of active site changes ; substrate no longer fits the enzyme ; 3 7(c) the breakdown of large / insoluble molecules ; into small / soluble molecules ; 2

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8 (a) Complete the sentence: An electric current in a metal is a flow of ........................................................ , which carry negative ........................................................ . [2] (b) A battery has an e.m.f. of 24 V. (i) Use the formula E = IVt to calculate the energy E transferred from the battery when a current of 50 A flows for 1 hour. Show your working. energy = ...................................................... J [2] (ii) Calculate the electric charge that flows when a current of 25 A flows for 60 s. Show your working and state the unit of your answer. charge = ...................................... unit ......................... [3] (c) The battery is used to operate the starter motor on a truck. The battery is also used to operate the lights on the truck. The starter motor must have its own switch and operate independently from the lights. Fig. 8.1 shows part of the electrical circuit of the truck. Fig. 8.1 The symbol for the starter motor is M On Fig. 8.1, complete the circuit diagram to show how the starter motor and a switch should be included in this circuit. [1] [Total: 8]

Mark scheme: 8(a) electrons ; charges ; 2 8(b)(i) 1 hour = 3600 s / (E =) 50 × 24 × 3600 ; 4 320 000 (J) ; 2 8(b)(ii) (Q=) I × t or (Q =) 25 × 60 ; = 1500 ; coulombs / C ; 3 8(c) motor symbol with switch connected in parallel with lamps ; 1

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9 (a) Rubidium and caesium are Group I metals. In the Periodic Table, there is a trend in the properties of the Group I metals. Rubidium melts at 39 °C. Caesium is a solid at 20 °C. (i) Suggest the melting point of caesium. ..................................................... °C [1] (ii) Describe the trend in the reaction of Group I metals with water. ........................................................................................................................................... ..................................................................................................................................... [1] (b) Iron is extracted from its ore in a blast furnace. Explain why Group I metals cannot be extracted from their ores by reduction with carbon in a blast furnace. ................................................................................................................................................... ............................................................................................................................................. [1] (c) Table 9.1 shows the elements in Period 2 of the Periodic Table and their electronic structures. Table 9.1 group I II III IV V VI VII VIII element Li Be B C N O F Ne lithium beryllium boron carbon nitrogen oxygen fluorine neon electronic 2,1 2,2 2,3 2,4 2,5 2,6 2,7 2,8 structure (i) Describe the relationship between group number and the number of outer shell electrons. ........................................................................................................................................... ..................................................................................................................................... [1] (ii) Describe the trend in the metallic character of the elements within Period 2. ........................................................................................................................................... ..................................................................................................................................... [1] [Total: 5]

Mark scheme: 9(a)(i) in range 21 °C to 38 °C ; 1 9(a)(ii) increases as group is descended ; 1 9(b) metals are too reactive / more reactive than carbon ; 1 9(c)(i) The group number is equal to the number of outer shell electrons ; 1 9(c)(ii) metallic character decreases going from left to right ; 1

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