Cambridge IGCSE Sciences - Co-ordinated (Double) 0654 — 2011 Oct/Nov Paper 2 · Variant 2

This document consists of 21 printed pages and 3 blank pages. IB11 11_0654_22/3RP © UCLES 2011 [Turn over *6824241612* For Examiner's Use 1 2 3 4 5 6 7 8 9 Total UNIVERSITY OF CAMBRIDGE INTERNATIONAL EXAMINATIONS International General Certificate of Secondary Education CO-ORDINATED SCIENCES 0654/22 Paper 2 (Core) October/November 2011 2 hours Candidates answer on the Question Paper. No Additional Materials are required. READ THESE INSTRUCTIONS FIRST Write your Centre number, candidate number and name on all the work you hand in. Write in dark blue or black pen. You may use a soft pencil for any diagrams, graphs, tables or rough working. Do not use staples, paper clips, highlighters, glue or correction fluid. DO NOT WRITE IN ANY BARCODES. Answer all questions. A copy of the Periodic Table is printed on page 24. At the end of the examination, fasten all your work securely together. The number of marks is given in brackets [ ] at the end of each question or part question. www.XtremePapers.com

2 © UCLES 2011 0654/22/O/N/11 For Examiner's Use 1 Fig. 1.1 shows five insects. A B C D E wing coverings Fig. 1.1 (a) Use the key below to identify each insect. Fill in the table to show how you arrived at your identifications. The first one has been done for you. 1a has wings go to 2 b does not have wings go to 3 2a wings are covered go to 4 b wings are not covered Musca 3a head longer than front leg Termes b head shorter than front leg Formica 4a striped pattern on wing coverings Graphosoma b spots on wing coverings Coccinella 1 2 3 4 insect a b a b a b a b name A ✓ ✓ Musca B C D E [4]

3 © UCLES 2011 0654/22/O/N/11 [Turn over For Examiner's Use (b) The common name for insect A is housefly. The complete binomial of insect A is Musca domestica. Suggest why scientists may prefer to use the binomial of an insect, rather than its common name. [1] (c) Houseflies feed by spitting saliva onto food, such as meat. Enzymes in the saliva turn insoluble substances into soluble ones. The flies can then suck the liquid into their digestive system. (i) Suggest one enzyme in a housefly's saliva that could digest a substance in meat. [1] (ii) State the soluble product or products that this enzyme would produce. [1] (d) Houseflies spread diseases such as typhoid fever. They leave harmful microorganisms on food that will later be eaten by a person. (i) Name the cells in the human body that can help to prevent microorganisms causing infections. [1] (ii) Pesticides are sometimes used to kill houseflies and therefore reduce the risk of spreading disease. Give one reason why pesticides should not be used more than necessary. [1] (e) When a housefly flies, its wings produce a buzzing sound. (i) Suggest how a movement such as that of a fly's wings produces sound. [2]

4 © UCLES 2011 0654/22/O/N/11 For Examiner's Use (ii) A housefly beats its wings about 200 times per second. A midge (a small insect) beats its wings about 1000 times per second. State and explain how the sound produced by a flying midge will differ from the sound produced by a flying housefly. [2]

5 © UCLES 2011 0654/22/O/N/11 [Turn over For Examiner's Use 2 (a) Fig. 2.1 shows an aircraft moving along a runway. (i) Draw and label arrows on Fig. 2.1 to show the directions of the driving and friction forces acting on the aircraft. [1] runway Fig. 2.1 (ii) The driving and friction forces are balanced. Explain what is meant by the phrase forces are balanced. [1] (iii) Describe the movement of the aircraft when these forces are balanced. [1] (b) People who fly frequently have greater exposure to ionising radiation than those who do not fly. (i) Explain why exposure to ionising radiation may be harmful. [2] (ii) This ionising radiation is cosmic radiation from outer space. This is one source of background radiation. State one other natural source of background radiation. [1]

6 © UCLES 2011 0654/22/O/N/11 For Examiner's Use (c) The aircraft is able to navigate using radar. This involves using microwaves. These are part of the electromagnetic spectrum. Name one other wave which is part of the electromagnetic spectrum and give a use for this radiation. name use [2] (d) Potato snacks are packed in airtight packets and filled with nitrogen gas at atmospheric pressure. (i) Suggest why nitrogen gas is used rather than air. [2] (ii) A passenger has a packet of potato snacks in his hand luggage on the aircraft. During the flight, the aircraft cabin is at a pressure less than normal atmospheric pressure. The passenger notices that the packet has expanded. State why this happens. [1]

7 © UCLES 2011 0654/22/O/N/11 [Turn over For Examiner's Use 3 Hydrocarbons are compounds which contain only the elements hydrogen and carbon. (a) (i) State the number of electrons in the outer shell of a carbon atom. [1] (ii) Another element, X, has atoms whose nuclei contain 14 protons. Name element X and explain whether or not atoms of X have the same number of outer electrons as a carbon atom. name of element X explanation [2] (iii) Name the least reactive element which is in the same period of the Periodic Table as carbon. [1] (b) The simplest hydrocarbon is methane which is an important gaseous fuel. (i) State two natural sources of methane. 1 2 [2] (ii) A fuel such as methane combines with oxygen in a chemical reaction. When the reaction is occurring, a large amount of heat is given off each second. Suggest and explain which one of the sentences, A to D, accurately describes the reaction between a typical fuel and oxygen. A The reaction is endothermic and has a very high rate. B The reaction is exothermic and has a very high rate. C The reaction is exothermic and has a very low rate. D The reaction is endothermic and has a very low rate. sentence explanation [2]

8 © UCLES 2011 0654/22/O/N/11 For Examiner's Use (c) Some types of oil and grease contain hydrocarbons. Oil and grease stick to clothes and make them look dirty. Washing with water alone does not remove oil and grease from clothes. (i) State the type of substance which could be added to water so that washing does remove oil and grease. [1] (ii) Suggest one possible disadvantage, other than cost, of using large amounts of the substance given in answer (c)(i) over a long period of time. [1]

9 © UCLES 2011 0654/22/O/N/11 [Turn over BLANK PAGE Please turn over for Question 4.

10 © UCLES 2011 0654/22/O/N/11 For Examiner's Use 4 Yaks are animals that live in the cold mountainous region of the Himalayas. Fig. 4.1 shows a yak. Fig. 4.1 (a) Explain how the long hair of the yak keeps it warm during the cold weather. [2] (b) Yaks are used as ‘beasts of burden’. They can be ridden or used to carry or pull heavy objects. A yak of mass 1000 kg is carrying a load of 80 kg. (i) Calculate the combined weight of the yak and load. The Earth’s gravitational field strength is 10 N / kg. N [1]

11 © UCLES 2011 0654/22/O/N/11 [Turn over For Examiner's Use (ii) The yak carries its load up a mountain slope and finishes 100 m higher up the mountain. Calculate the work done in gaining this height. State the formula that you use and show your working. formula used working J [2] (iii) While the yak is carrying the load, it travels at a speed of 0.2 m / s. Calculate the kinetic energy of the yak and its load at this time. State the formula that you use and show your working. formula used working J [2] (iv) The yak then travels 1000 m in 4000 s. Calculate the average speed of the yak. State the formula that you use and show your working. formula used working m/s [2]

12 © UCLES 2011 0654/22/O/N/11 For Examiner's Use (c) Yak dung is commonly burned as a fuel in the Himalayas. However, it is slowly being replaced by kerosene. State and explain one environmental reason why yak dung is a better fuel than kerosene. [1]

13 © UCLES 2011 0654/22/O/N/11 [Turn over BLANK PAGE Please turn over for Question 5.

14 © UCLES 2011 0654/22/O/N/11 For Examiner's Use 5 Fig. 5.1 shows two plants that are grown as crops. many tiny nodules containing nitrogen-fixing bacteria swollen underground stem Fig. 5.1 (a) Plant P reproduces using flowers and also by growing new plants from its underground stem. State the type of reproduction that each of these processes involves. using flowers growing new plants from underground stems [1] (b) The flowers of plant Q are pollinated by insects. (i) State one feature, visible on Fig. 5.1, that would attract insects to the flowers. [1]

15 © UCLES 2011 0654/22/O/N/11 [Turn over For Examiner's Use (ii) After pollination, fertilisation takes place in the flower. Describe what happens during fertilisation. [2] (iii) Name the part of the flower that would develop into a fruit, following fertilisation. [1] (iv) What structures are present inside all fruits? [1] (c) Farmers often add fertilisers containing nitrates to the soil where they grow crops. (i) Explain why this is done. [2] (ii) Explain why fields in which plant Q is growing will require less nitrate fertiliser than fields in which plant P is growing. [2]

16 © UCLES 2011 0654/22/O/N/11 For Examiner's Use 6 Nordic gold is an alloy of four metals used to make coins. Table 6.1 shows information about the metals contained in Nordic gold. Table 6.1 metal % by mass in Nordic gold aluminium 5 copper tin 1 zinc 5 (a) (i) Complete Table 6.1 by stating the percentage of copper in Nordic gold. [1] (ii) Suggest how Nordic gold could be made. [1] (iii) Nordic gold has properties which make it suitable for making coins. Suggest one property Nordic gold is likely to have, other than its appearance, that makes it suitable for making coins. Explain briefly why this property is important. property importance [2] (b) (i) Tin may be extracted from tin oxide by heating a mixture of tin oxide and carbon. The other product of this reaction is carbon monoxide. Write a word chemical equation for this reaction. [1]

17 © UCLES 2011 0654/22/O/N/11 [Turn over For Examiner's Use (ii) State and explain which substance is oxidised when tin is extracted from tin oxide. substance which is oxidised explanation [2] (c) Aluminium is extracted from aluminium oxide, Al2O3 , by electrolysis. Aluminium oxide is an ionic compound. (i) Explain the meanings of the following terms. cathode electrolyte [2] (ii) Describe briefly the change in electronic structure which occurs when an aluminium atom becomes an aluminium ion. [1] (iii) Calculate the number of oxide ions which will be combined with 10 aluminium ions in aluminium oxide. [1] (d) Zinc oxide is a white solid used in sunscreen to protect human skin from the harmful effects of ultraviolet light from the sun. (i) In a typical sunscreen, tiny pieces of zinc oxide are dispersed in a liquid. Name the type of mixture in which a solid is dispersed in a liquid. [1] (ii) Suggest why a sunscreen is able to protect human skin from ultraviolet light. [1]

18 © UCLES 2011 0654/22/O/N/11 For Examiner's Use 7 Most cells obtain energy from carbohydrates and other nutrients by aerobic respiration. (a) Describe how a cell in a human muscle obtains the oxygen that it needs for respiration. [2] (b) When a person carries out exercise, muscle cells use energy to contract and produce movement. (i) State two uses of energy in the human body, other than the contraction of muscles. 1 2 [2] (ii) Some of the energy in exercising muscles is released as heat. Sweating helps to prevent the internal body temperature from rising too high. State the correct biological term for the maintenance of a constant internal environment. [1] (iii) Suggest why an athlete running a long race, such as a marathon, needs to drink fluids during the run. [2] (c) Regular exercise can help to reduce the risk of having a heart attack. Describe the events that lead to a heart attack. [3]

19 © UCLES 2011 0654/22/O/N/11 [Turn over BLANK PAGE Please turn over for Question 8.

20 © UCLES 2011 0654/22/O/N/11 For Examiner's Use 8 Fig. 8.1 shows the inside of a refrigerator. The temperature inside the freezing compartment is -20 °C and the temperature in the rest of the refrigerator is +5 °C. freezing compartment Fig. 8.1 (a) (i) Draw arrows on Fig. 8.1 to show what happens to the air cooled by the freezing compartment. [1] (ii) Name this method of heat transfer. [1] (iii) Explain why this happens, using the idea of density. [1] (b) Fig. 8.2 shows an ice cube with sides of 2 cm. The ice cube has a mass of 7.4 g. 2 cm 2 cm 2 cm Fig. 8.2 (i) Calculate the density of the ice. State the formula that you use and show your working. State the units of your answer. formula used working [3]

21 © UCLES 2011 0654/22/O/N/11 [Turn over For Examiner's Use (ii) The ice cube has been made by freezing some water. Draw diagrams to show the arrangement of water molecules in solid ice and in liquid water. One molecule has been drawn for you in each box. solid ice liquid water [2] (c) The refrigerator has a lamp inside. The supply voltage is 250 V and the current passing through the lamp when lit is 0.05 A. (i) Show that the resistance of the lamp when lit is 5000 Ω. State the formula that you use and show your working. formula used working [2] (ii) Two lamps with a resistance of 5000 Ω are connected together in series. Calculate the combined resistance of the two lamps. State the formula that you use and show your working. formula used working Ω [2]

22 © UCLES 2011 0654/22/O/N/11 For Examiner's Use 9 Coral reefs are large rocky structures found in shallow seawater. The reefs are formed from the skeletons of small animals (coral polyps). (a) Seawater is a mixture which contains many dissolved compounds. The coral polyps extract the compound calcium carbonate from seawater and use it to build their skeletons. Choose two statements from the list below that describe compounds but which do not describe mixtures. A They have a chemical formula. B They can contain any amounts of two or more substances. C Their properties are different from those of the substances used to make them. D Their formation does not normally produce a significant change in temperature. statements and [2] (b) Certain algae (microscopic plants) live in the coral polyps, and these organisms help each other to survive. The algae produce oxygen in the presence of sunlight. The coral polyps use oxygen and produce carbon dioxide as a waste product. coral polyp algae (i) Name the processes which are occurring in the algae to produce oxygen, in the coral polyps to produce carbon dioxide. [2] (ii) Name the compound which is produced by the algae in addition to oxygen. [1]

23 © UCLES 2011 0654/22/O/N/11 For Examiner's Use (iii) Suggest one way that the coral polyps and the algae help each other to survive. [1] (c) In recent years, the amount of carbon dioxide in the atmosphere has increased. This has caused a decrease in the average pH of seawater. During this period, many coral reefs have become damaged or have stopped growing. (i) State and explain one example of human activity which has caused the amount of carbon dioxide in the atmosphere to increase in recent years. [2] (ii) Explain why increased levels of carbon dioxide in the atmosphere cause the average pH of seawater to decrease. [2] (iii) Suggest a possible reason why a decrease in the average pH of seawater could damage coral reefs. [1]

24 Permission to reproduce items where third-party owned material protected by copyright is included has been sought and cleared where possible. Every reasonable effort has been made by the publisher (UCLES) to trace copyright holders, but if any items requiring clearance have unwittingly been included, the publisher will be pleased to make amends at the earliest possible opportunity. University of Cambridge International Examinations is part of the Cambridge Assessment Group. Cambridge Assessment is the brand name of University of Cambridge Local Examinations Syndicate (UCLES), which is itself a department of the University of Cambridge. © UCLES 2011 0654/22/O/N/11 Group 140 Ce Cerium 58 141 Pr Praseodymium 59 144 Nd Neodymium 60 Pm Promethium 61 150 Sm Samarium 62 152 Eu Europium 63 157 Gd Gadolinium 64 159 Tb Terbium 65 162 Dy Dysprosium 66 165 Ho Holmium 67 167 Er Erbium 68 169 Tm Thulium 69 173 Yb Ytterbium 70 175 Lu Lutetium 71 232 Th Thorium 90 Pa Protactinium 91 238 U Uranium 92 Np Neptunium 93 Pu Plutonium 94 Am Americium 95 Cm Curium 96 Bk Berkelium 97 Cf Californium 98 Es Einsteinium 99 Fm Fermium 100 Md Mendelevium 101 No Nobelium 102 Lr Lawrencium 103 1 H Hydrogen 1 7 Li Lithium 3 23 Na Sodium 11 24 Mg Magnesium 12 40 Ca Calcium 20 45 Sc Scandium 21 48 Ti Titanium 22 51 V Vanadium 23 52 Cr Chromium 24 55 Mn Manganese 25 56 Fe Iron 26 59 Co Cobalt 27 59 Ni Nickel 28 64 Cu Copper 29 65 Zn Zinc 30 70 Ga Gallium 31 27 Al Aluminium 13 11 B Boron 5 12 C Carbon 6 14 N Nitrogen 7 16 O Oxygen 8 19 F Fluorine 9 28 Si Silicon 14 31 P Phosphorus 15 32 S Sulfur 16 35.5 Cl Chlorine 17 40 Ar Argon 18 20 Ne Neon 10 4 He Helium 2 73 Ge Germanium 32 75 As Arsenic 33 79 Se Selenium 34 80 Br Bromine 35 84 Kr Krypton 36 39 K Potassium 19 88 Sr Strontium 38 89 Y Yttrium 39 91 Zr Zirconium 40 93 Nb Niobium 41 96 Mo Molybdenum 42 Tc Technetium 43 101 Ru Ruthenium 44 103 Rh Rhodium 45 106 Pd Palladium 46 108 Ag Silver 47 112 Cd Cadmium 48 115 In Indium 49 119 Sn Tin 50 122 Sb Antimony 51 128 Te Tellurium 52 127 I Iodine 53 131 Xe Xenon 54 137 Ba Barium 56 139 La Lanthanum 57 * 178 Hf Hafnium 72 181 Ta Tantalum 73 184 W Tungsten 74 186 Re Rhenium 75 190 Os Osmium 76 192 Ir Iridium 77 195 Pt Platinum 78 197 Au Gold 79 201 Hg Mercury 80 204 Tl Thallium 81 207 Pb Lead 82 209 Bi Bismuth 83 Po Polonium 84 At Astatine 85 Rn Radon 86 Fr Francium 87 227 Ac Actinium 89 9 Be Beryllium 4 I II III IV V VI VII 0 85 Rb Rubidium 37 133 Cs Caesium 55 226 Ra Radium 88 The volume of one mole of any gas is 24 dm3 at room temperature and pressure (r.t.p.). a X b a = relative atomic mass X = atomic symbol b = proton (atomic) number Key *58-71 Lanthanoid series 90-103 Actinoid series DATA SHEET The Periodic Table of the Elements

UNIVERSITY OF CAMBRIDGE INTERNATIONAL EXAMINATIONS International General Certificate of Secondary Education MARK SCHEME for the October/November 2011 question paper for the guidance of teachers 0654 CO-ORDINATED SCIENCES 0654/22 Paper 2 (Core Theory), maximum raw mark 100 This mark scheme is published as an aid to teachers and candidates, to indicate the requirements of the examination. It shows the basis on which Examiners were instructed to award marks. It does not indicate the details of the discussions that took place at an Examiners’ meeting before marking began, which would have considered the acceptability of alternative answers. Mark schemes must be read in conjunction with the question papers and the report on the examination. • Cambridge will not enter into discussions or correspondence in connection with these mark schemes. Cambridge is publishing the mark schemes for the October/November 2011 question papers for most IGCSE, GCE Advanced Level and Advanced Subsidiary Level syllabuses and some Ordinary Level syllabuses. www.XtremePapers.com

Page 2 Mark Scheme: Teachers’ version Syllabus Paper IGCSE – October/November 2011 0654 22 © University of Cambridge International Examinations 2011 1 (a) 1 2 3 4 insect a b a b a b a b name A

Musca B

Formica ; C

Termes ; D


Graphosoma ; E


Coccinella ; one mark per correct row (if no ticks, or if all ticks are wrong, allow one mark for getting all four names correct) [4] (b) idea of universal understanding / to identify its genus and species ; [1] (c) (i) protease / trypsin / pepsin OR lipase ; [1] (ii) amino acids OR fatty acids and glycerol ; [1] (d) (i) white (blood) cells ; [1] (ii) they can kill other organisms ; cause disruption to food chains ; they could harm human health ; pests can become resistant to the pesticides ; [max 1] (e) (i) vibrations ; ref. to air particles / compressions and rarefactions ; [2] (ii) (midge buzz) higher pitch ; because higher frequency ; [2] [Total: 13] 2 (a) (i) arrows correctly drawn and labelled ; [1] (ii) equal and opposite ; [1] (iii) constant speed ; [1]

Page 3 Mark Scheme: Teachers’ version Syllabus Paper IGCSE – October/November 2011 0654 22 © University of Cambridge International Examinations 2011 (b) (i) cause cancer / kills cells / radiation burns / radiation sickness ; mutation / change DNA ; [2] (ii) (granite) rocks / radon ; [1] (c) electromagnetic wave ; use ; [2] (d) (i) to stop snacks spoiling / oxidising ; stops microbes respiring ; nitrogen is unreactive ; [max 2] (ii) pressure inside packet is greater than airplane pressure ; [1] [Total: 11] 3 (a) (i) 4 ; [1] (ii) silicon ; (does have same outer electrons) because in same group ; [2] (iii) neon ; [1] (b) (i) formed as fossil fuel ; decomposition of organic matter ; from digestive systems of ruminants ; ref. volcanism ; [max 2] (ii) B ; exothermic means heat given off ; much heat per second means rate is high ; [max 2] (c) (i) detergent / soap ; [1] (ii) suitable example of water pollution ; [1] [Total: 10]

Page 4 Mark Scheme: Teachers’ version Syllabus Paper IGCSE – October/November 2011 0654 22 © University of Cambridge International Examinations 2011 4 (a) traps layer of air ; ref. good insulator ; [2] (b) (i) (weight =) 10 800 (N) ; [1] (ii) (work =) force × distance ; = 10 800 × 100 = 1 080 000 (J) ; [2] (iii) (kinetic energy =) ½ mv2 ; = ½ × 1080 × 0.2 × 0.2 = 21.6 (J) ; [2] (iv) (average speed = ) distance / time ; =1000 / 4000 = 0.25 (m / s) ; [2] (c) does not deplete fossil fuel reserves / carbon neutral / kerosene is a hydrocarbon fuel ; [1] [Total: 10] 5 (a) sexual and asexual ; (both needed) [1] (b) (i) (large) petals / large flowers / nectar guides / landing platform ; [1] (ii) male gamete fuses with female gamete ; zygote produced ; (allow 'sex cell' or 'nucleus' instead of 'gamete') [2] (iii) ovary ; [1] (iv) seeds ; [1] (c) (i) increase growth of plants ; (plants need nitrates) to produce proteins ; proteins needed to produce new cells ; [max 2] (ii) Q has nitrogen-fixing bacteria in its roots ; provide plants with, nitrogen-containing compounds / ammonium ions ; [2] [Total: 10]

Page 5 Mark Scheme: Teachers’ version Syllabus Paper IGCSE – October/November 2011 0654 22 © University of Cambridge International Examinations 2011 6 (a) (i) 89 ; [1] (ii) melt the component metals together ; [1] (iii) strong / hard / low malleability ; coins must not easily be damaged / must be easily recognised over long periods / owtte ; OR (chemically) unreactive ; coins must not easily corrode ; OR malleable ; can be shaped (for coin manufacture) ; [max 2] (b) (i) tin oxide + carbon → tin + carbon monoxide ; [1] (ii) carbon ; joins with oxygen ; [2] (c) (i) negative electrode ; liquid which conducts a current / contains mobile ions ; [2] (ii) (atom) loses electrons ; [1] (iii) 15 ; [1] (d) (i) sol / colloid ; [1] (ii) (sols are) not transparent so light does not reach skin / (sol) reflects light ; [1] (allow sunscreen absorbs light / acts as a light filter) [Total: 13] 7 (a) from blood ; (ignore ‘ref to bleeding’) from red blood cells ; from haemoglobin ; by diffusion ; [max 2] (b) (i) keeping warm ; making new cells ; transmitting nerve impulses ; [max 2] (ii) homeostasis ; [1] (iii) water lost in sweat ; ref. to need to maintain water content of body ; [max 2]

Page 6 Mark Scheme: Teachers’ version Syllabus Paper IGCSE – October/November 2011 0654 22 © University of Cambridge International Examinations 2011 (c) ref. to coronary artery ; supplies heart muscle with, blood / oxygen ; blockage (in blood vessel) ; cause of blockage (e.g. plaque, cholesterol, blood clot) ; heart, muscle / cells, die / cannot contract, because of lack of oxygen ; [max 3] [Total: 10] 8 (a) (i) arrows go down ; [1] (ii) convection ; [1] (iii) cold air becomes more dense and sinks ; [1] (b) (i) (density =) mass / volume ; = 7.4 / 8; = 0.925 (g / cm3) ; [3] (ii) solid – regular arrangement and all particles touching ; liquid – irregular arrangement and most particles touching ; [2] (c) (i) (resistance = ) voltage / current ; = 250 / 0.05 = 5000 (Ω) ; [2] (ii) RT = R1 + R2; = 5000 + 5000 = 10 000 (Ω) ; [2] [Total: 12] 9 (a) (i) A ; C ; [2] (b) (i) photosynthesis ; respiration ; [2] (ii) glucose / carbohydrate / sugar / starch ; [1] (iii) algae produce oxygen which coral uses / coral produces carbon dioxide which algae uses ; [1]

Page 7 Mark Scheme: Teachers’ version Syllabus Paper IGCSE – October/November 2011 0654 22 © University of Cambridge International Examinations 2011 (c) (i) increased use of fossil fuel / example which implies this ; carbon dioxide produced when fuel burns ; [2] (ii) carbon dioxide dissolves in / reacts with (sea) water ; makes water more acidic / less alkaline ; non-metal oxides are acidic ; [max 2] (iii) accept any reasonable science based idea: e.g. calcium carbonate may react with more acidic water / lower pH makes it more difficult for coral to extract ions from sea / coral (polyps) / algae do not survive in more acidic water ; [max 1] [Total: 11]