Cambridge A Level Marine Science 9693 — 2025 Oct/Nov Paper 1 · Variant 3

This document has 16 pages. Any blank pages are indicated. [Turn over Cambridge International AS & A Level * 9 1 9 8 0 0 6 1 3 3 * DC (EV/SG) 347055/4 © UCLES 2025 MARINE SCIENCE 9693/13 Paper 1 AS Level Theory October/November 2025 1 hour 45 minutes You must answer on the question paper. No additional materials are needed. INSTRUCTIONS ● Answer all questions. ● Use a black or dark blue pen. You may use an HB pencil for any diagrams or graphs. ● Write your name, centre number and candidate number in the boxes at the top of the page. ● Write your answer to each question in the space provided. ● Do not use an erasable pen or correction fluid. ● Do not write on any bar codes. ● You may use a calculator. ● You should show all your working and use appropriate units. INFORMATION ● The total mark for this paper is 75. ● The number of marks for each question or part question is shown in brackets [ ]. ,










, * 0000800000001 * ¬OŠ. 4mHuOªEŠ`z6€W ¬ŠXtV¨’pjnƒo§.bn‚ ¥5u•uU Uu E E•EUuU DFD

2 9693/13/O/N/25 © UCLES 2025 Section A Answer all questions in this section. 1 Fig. 1.1 shows diagrams of some of the substances found in sea water. A B CH2OH O OH OH OH OH D E C Fig. 1.1 (a) State the letters from Fig. 1.1 that identify the substance or substances that: are products of respiration … and … are salts … and … can form hydrogen bonds … has the formula CaCO3 … is a product of photosynthesis. … [5] (b) Describe the evidence from Fig. 1.1 which shows that substance B has covalent bonds. … … [1] [Total: 6] * 0000800000002 * ,










, ĬÍĊ®Ġ´íÈõÏĪÅĊÝü¸þ× ĬĊÖó×ĤĖĚÑăõĔåčþĚöĂ ĥĥĥĕµµÅµÅÅĕÅÅÕåĕÕÕ DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DFD

3 9693/13/O/N/25 © UCLES 2025 [Turn over BLANK PAGE * 0000800000003 * ,










, ĬÏĊ®Ġ´íÈõÏĪÅĊÝú¸þ× ĬĊÕôÏĦĚĪèõČÕñĥÚĚĆĂ ĥĥĕÕõÕåÕÕµÅÅŵÅÕÅÕ DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DFD

4 9693/13/O/N/25 © UCLES 2025 2 (a) Fig. 2.1 shows some drawings of different species of crustacean. NOT TO SCALE A D B E C F Fig. 2.1 * 0000800000004 * ,










, ĬÍĊ®Ġ´íÈõÏĪÅĊßü¸Ā× ĬĊÕñÏĠĬğÓûăÎÓÉüĊîĂ ĥÕÅÕµÕåõµĕµÅąµĥÕÕÕ DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DFD

5 9693/13/O/N/25 © UCLES 2025 [Turn over Fig. 2.2 is a dichotomous key. This dichotomous key can be used to identify the different species of crustacean in Fig. 2.1. Species F has been identified. Complete Fig. 2.2 with the correct letter for each species. Letter 1 more than ten legs visible go to 2 ten or fewer legs visible go to 3 2 one pair of antennae longer than the length of its body Penaeus monodon F antennae shorter than the length of its body Bathynomus giganteus … 3 a visible tail-like structure go to 4 no visible tail-like structure go to 5 4 visible claws Homarus gammarus … no visible claws Alacia hettacra … 5 claws of the same size Macrocheira kaempferi … claws of different sizes Minuca pugnax … [3] Fig. 2.2 (b) State three features that are typical of an adult crustacean. 1 … 2 … 3 … [3] [Total: 6] * 0000800000005 * ,










, ĬÏĊ®Ġ´íÈõÏĪÅĊßú¸Ā× ĬĊÖò×ĪĨďæýîěć±àĊþĂ ĥÕµĕõµÅĕåĥĥÅąÕąĕÅÕ DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DFD

6 9693/13/O/N/25 © UCLES 2025 3 (a) Fig. 3.1 shows the view from the side and the view from above of three different types of coral reef, A, B and C. landmass landmass coral coral A lagoon lagoon landmass landmass coral coral B landmass coral coral C lagoon lagoon view from the side view from above Fig. 3.1 Identify the types of coral reef shown in Fig. 3.1. A … B … C … [3] * 0000800000006 * ,










, ĬÑĊ®Ġ´íÈõÏĪÅĊÞúµþ× ĬĊÕòÜĤĀĕÞĊÿĢħɽâîĂ ĥąĕĕõĕŵĥąÅÅÅÕåÕĕÕ DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DFD

7 9693/13/O/N/25 © UCLES 2025 [Turn over (b) Fig. 3.2 is a diagram of a coral polyp. (i) On Fig. 3.2 label the: • mouth • stomach • basal plate. Fig. 3.2 [3] (ii) Describe the function of nematocysts. … … [1] (c) State three causes of coral reef erosion. 1 … … 2 … … 3 … … [3] [Total: 10] * 0000800000007 * ,










, ĬÓĊ®Ġ´íÈõÏĪÅĊÞüµþ× ĬĊÖñÔĦĄĥÛðòç³±ęâþĂ ĥąĥÕµõåÕõõĕÅŵÅĕąÕ DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DFD

8 9693/13/O/N/25 © UCLES 2025 4 (a) Fig. 4.1 shows a pyramid of energy for a marine food chain. The energy at each level is shown in arbitrary units (a.u.). The pyramid of energy is not to scale. sea anemone (2 a.u.) small fish (15 a.u.) zooplankton (98 a.u.) phytoplankton (908 a.u.) NOT TO SCALE Fig. 4.1 (i) Identify the tertiary consumer in Fig. 4.1. … [1] (ii) Calculate the percentage decrease in energy between trophic levels 2 and 3 in Fig. 4.1. … % [2] (iii) State three ways energy is lost between trophic levels 3 and 4 in Fig. 4.1. 1 … 2 … 3 … [3] * 0000800000008 * ,










, ĬÑĊ®Ġ´íÈõÏĪÅĊàúµĀ× ĬĊÖôÔĠòĤàòùàđč»²öĂ ĥµµÕõõåõĕÕĥÅąµĥĕĕÕ DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DFD

9 9693/13/O/N/25 © UCLES 2025 [Turn over (b) Consumers gain essential elements from the organisms they eat. Complete Table 4.1 by ticking () the boxes to show all the essential elements that are found in each biological molecule. Table 4.1 essential elements biological molecule chlorophyll protein DNA nitrogen magnesium phosphorus [3] [Total: 9] 5 Rocky shores are an example of a habitat found in the littoral zone and have high levels of biodiversity. (a) Define the term littoral zone. … … [1] (b) State the three levels of biodiversity. 1 … 2 … 3 … [3] (c) Outline the beneficial role of marine organisms in terms of climate control. … … … … … … [3] [Total: 7] * 0000800000009 * ,










, ĬÓĊ®Ġ´íÈõÏĪÅĊàüµĀ× ĬĊÕóÜĪîĔÙĈĈĩÅĥğ²ĆĂ ĥµÅĕµĕÅĕąåµÅąÕąÕąÕ DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DFD

10 9693/13/O/N/25 © UCLES 2025 6 Fig. 6.1 is a diagram showing the direction of movement of some tectonic plates. North American plate North American plate Juan de Fuca plate Caribbean plate Caribbean plate Cocos plate Nazca plate Pacific plate Antarctic plate Philippine plate A B C Fig. 6.1 (a) Identify the type of plate boundary labelled A and the type of plate boundary labelled B in Fig. 6.1. A … B … [2] (b) State one feature that forms on the ocean floor at the plate boundary labelled C in Fig. 6.1. … [1] * 0000800000010 * ,










, ĬÑĊ®Ġ´íÈõÏĪÅĊÝú·þ× ĬĊ×ôÙĞúöâùòĆíďÏĊþĂ ĥĥÕĕõõąõµĥĥąąĕĥĕåÕ DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DFD

11 9693/13/O/N/25 © UCLES 2025 [Turn over (c) Explain how tsunamis form at the plate boundary labelled A in Fig. 6.1. … … … … … … … … [4] [Total: 7] * 0000800000011 * ,









, ĬÓĊ®Ġ´íÈõÏĪÅĊÝü·þ× ĬĊØóÑĬöĆ×ÿÿÃéħċĊîĂ ĥĥåÕµĕĥĕåĕµąąõąÕµÕ DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DFD

12 9693/13/O/N/25 © UCLES 2025 Section B Answer all questions in this section. 7 Explain the factors that change the tidal range in one location. … … … … … … … … … … … … … … … … [8] * 0000800000012 * ,









, ĬÑĊ®Ġ´íÈõÏĪÅĊßú·Ā× ĬĊØòÑĢĈăäāĈÌċËéĚĆĂ ĥÕõÕõĕĥµÅµÅąÅõåÕåÕ DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DFD

13 9693/13/O/N/25 © UCLES 2025 8 (a) Explain the adaptations of the red mangrove tree to its environment. … … … … … … … … … … … … [6] [Turn over * 0000800000013 * ,









, ĬÓĊ®Ġ´íÈõÏĪÅĊßü·Ā× ĬĊ×ñÙĨČóÕ÷ùýϳíĚöĂ ĥÕąĕµõąÕÕÅĕąÅĕÅĕµÕ DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DFD

14 9693/13/O/N/25 © UCLES 2025 (b) Explain the importance of mangrove forests to humans and to the environment. … … … … … … … … … … … … … … [7] [Total: 13] * 0000800000014 * ,









, ĬÍĊ®Ġ´íÈõÏĪÅĊàû¶Ă× ĬĊØóÜĪ÷ċçñîâóĪùêîĂ ĥõąÕõĕÅõµÕĕÅąÕĥÕĥÕ DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DFD

15 9693/13/O/N/25 © UCLES 2025 9 Explain the abiotic factors that affect the chemical composition of sea water with reference to named chemicals. … … … … … … … … … … … … … … … … … … [9] * 0000800000015 * ,









, ĬÏĊ®Ġ´íÈõÏĪÅĊàù¶Ă× ĬĊ×ôÔĠûûÒćăħçĒÝêþĂ ĥõõĕµõåĕååÅÅąµąĕõÕ DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DFD

16 9693/13/O/N/25 © UCLES 2025 The boundaries and names shown, the designations used and the presentation of material on any maps contained in this question paper/insert do not imply official endorsement or acceptance by Cambridge Assessment International Education concerning the legal status of any country, territory, or area or any of its authorities, or of the delimitation of its frontiers or boundaries. 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. To avoid the issue of disclosure of answer-related information to candidates, all copyright acknowledgements are reproduced online in the Cambridge Assessment International Education Copyright Acknowledgements Booklet. This is produced for each series of examinations and is freely available to download at www.cambridgeinternational.org after the live examination series. Cambridge Assessment International Education is part of Cambridge Assessment. Cambridge Assessment is the brand name of the University of Cambridge Local Examinations Syndicate (UCLES), which is a department of the University of Cambridge. BLANK PAGE * 0000800000016 * ,









, ĬÍĊ®Ġ´íÈõÏĪÅĊÞû¶Ą× ĬĊ×ñÔĦĉîåĉČĠą®ÿºöĂ ĥÅåĕõõåµÅąµÅŵåĕĥÕ DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DFD

This document consists of 14 printed pages. © Cambridge University Press & Assessment 2025 [Turn over Cambridge International AS & A Level MARINE SCIENCE 9693/13 Paper 1 AS Level Theory Paper October/November 2025 MARK SCHEME Maximum Mark: 75 Published 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 should be read in conjunction with the question paper and the Principal Examiner Report for Teachers. Cambridge International will not enter into discussions about these mark schemes. Cambridge International is publishing the mark schemes for the October/November 2025 series for most Cambridge IGCSE, Cambridge International A and AS Level components, and some Cambridge O Level components.

9693/13 Cambridge International AS & A Level – Mark Scheme PUBLISHED October/November 2025 © Cambridge University Press & Assessment 2025 Page 2 of 14 Generic Marking Principles These general marking principles must be applied by all examiners when marking candidate answers. They should be applied alon gside the specific content of the mark scheme or generic level descriptions for a question. Each question paper and mark scheme will also comply with these marking principles. GENERIC MARKING PRINCIPLE 1: Marks must be awarded in line with: • the specific content of the mark scheme or the generic level descriptors for the question • the specific skills defined in the mark scheme or in the generic level descriptors for the question • the standard of response required by a candidate as exemplified by the standardisation scripts. GENERIC MARKING PRINCIPLE 2: Marks awarded are always whole marks (not half marks, or other fractions). GENERIC MARKING PRINCIPLE 3: Marks must be awarded positively: • marks are awarded for correct/valid answers, as defined in the mark scheme. However, credit is given for valid answers which go beyond the scope of the syllabus and mark scheme, referring to your Team Leader as appropriate • marks are awarded when candidates clearly demonstrate what they know and can do • marks are not deducted for errors • marks are not deducted for omissions • answers should only be judged on the quality of spelling, punctuation and grammar when these features are specifically assessed by the question as indicated by the mark scheme. The meaning, however, should be unambiguous. GENERIC MARKING PRINCIPLE 4: Rules must be applied consistently, e.g. in situations where candidates have not followed instructions or in the application of generic level descriptors.

9693/13 Cambridge International AS & A Level – Mark Scheme PUBLISHED October/November 2025 © Cambridge University Press & Assessment 2025 Page 3 of 14 GENERIC MARKING PRINCIPLE 5: Marks should be awarded using the full range of marks defined in the mark scheme for the question (however; the use of the full mark range may be limited according to the quality of the candidate responses seen). GENERIC MARKING PRINCIPLE 6: Marks awarded are based solely on the requirements as defined in the mark scheme. Marks should not be awarded with grade thre sholds or grade descriptors in mind. Science-Specific Marking Principles 1 Examiners should consider the context and scientific use of any keywords when awarding marks. Although keywords may be present, marks should not be awarded if the keywords are used incorrectly. 2 The examiner should not choose between contradictory statements given in the same question part, and credit should not be awarded for any correct statement that is contradicted within the same question part. Wrong science that is irrelevant to the question should be ignored. 3 Although spellings do not have to be correct, spellings of syllabus terms must allow for clear and unambiguous separation fro m other syllabus terms with which they may be confused (e.g. ethane / ethene, glucagon / glycogen, refraction / reflection). 4 The error carried forward (ecf) principle should be applied, where appropriate. If an incorrect answer is subsequently used in a scientifically correct way, the candidate should be awarded these subsequent marking points. Further guidance will be included in the mark scheme where necessary and any exceptions to this general principle will be noted. 5 ‘List rule’ guidance For questions that require n responses (e.g. State two reasons …): • The response should be read as continuous prose, even when numbered answer spaces are provided. • Any response marked ignore in the mark scheme should not count towards n. • Incorrect responses should not be awarded credit but will still count towards n. • Read the entire response to check for any responses that contradict those that would otherwise be credited. Credit should not be awarded for any responses that are contradicted within the rest of the response. Where two responses contradict one another, this should be treated as a single incorrect response. • Non-contradictory responses after the first n responses may be ignored even if they include incorrect science.

9693/13 Cambridge International AS & A Level – Mark Scheme PUBLISHED October/November 2025 © Cambridge University Press & Assessment 2025 Page 4 of 14 6 Calculation specific guidance Correct answers to calculations should be given full credit even if there is no working or incorrect working, unless the question states ‘show your working’. For questions in which the number of significant figures required is not stated, credit should be awarded for correct answers when rounded by the examiner to the number of significant figures given in the mark scheme. This may not apply to measured values. For answers given in standard form (e.g. a  10n) in which the convention of restricting the value of the coefficient (a) to a value between 1 and 10 is not followed, credit may still be awarded if the answer can be converted to the answer given in the mark scheme. Unless a separate mark is given for a unit, a missing or incorrect unit will normally mean that the final calculation mark is not awarded. Exceptions to this general principle will be noted in the mark scheme. 7 Guidance for chemical equations Multiples / fractions of coefficients used in chemical equations are acceptable unless stated otherwise in the mark scheme. State symbols given in an equation should be ignored unless asked for in the question or stated otherwise in the mark scheme.

9693/13 Cambridge International AS & A Level – Mark Scheme PUBLISHED October/November 2025 © Cambridge University Press & Assessment 2025 Page 5 of 14 Annotations guidance for centres Examiners use a system of annotations as a shorthand for communicating their marking decisions to one another. Examiners are trained during the standardisation process on how and when to use annotations. The purpose of annotations is to inform the standard isation and monitoring processes and guide the supervising examiners when they are checking the work of examiners within their team. The meaning of annotations and how they are used is specific to each component and is understood by all examiners who mark the component. We publish annotations in our mark schemes to help centres understand the annotations they may see on copies of scripts. Note that there may not be a direct correlation between the number of annotations on a script and the mark awarded. Similarly, the use of an annotation may not be an indication of the quality of the response. The annotations listed below were available to examiners marking this component in this series. Annotations Annotation Meaning correct point or mark awarded incorrect point or mark not awarded information missing or insufficient for credit allow or accept incorrect or insufficient point ignored while marking the rest of the response contradiction in response, mark not awarded benefit of the doubt given error carried forward applied maximum mark reached point already given

9693/13 Cambridge International AS & A Level – Mark Scheme PUBLISHED October/November 2025 © Cambridge University Press & Assessment 2025 Page 6 of 14 Annotation Meaning power of ten error incorrect point or mark not awarded rounding error point has been noted, but no credit has been given or blank page seen response is too vague or there is insufficient detail in response , , marking point 1 or marking point a is awarded. Used to mark against a particular marking point from an extended answer MS used to highlight parts of an answer / incorrect idea / irrelevant to question used to highlight parts of an extended response / incorrect idea / irrelevant to question key point attempted / working towards marking point / incomplete answer / response seen but not credited / blank page seen ruler allows lengths to be measured multi-line overlay overlays graphs

9693/13 Cambridge International AS & A Level – Mark Scheme PUBLISHED October/November 2025 © Cambridge University Press & Assessment 2025 Page 7 of 14 This mark scheme will use the following abbreviations: ; separates marking points / alternative responses for the same marking point R reject the response A accept the response I ignore the response ECF error carried forward AVP any valid point /alternative valid point ORA or reverse argument AW alternative wording underline actual word given must be used by candidate (grammatical variants accepted) dashed underline the phrase underlined must be used by the candidate (similar wording accepted) ( ) the word / phrase in brackets is not required but sets the context MAX indicates the maximum number of marks that can be given + AND statements on both sides of the + or AND are needed for that mark OR separates two different routes to a mark point and only one should be awarded

9693/13 Cambridge International AS & A Level – Mark Scheme PUBLISHED October/November 2025 © Cambridge University Press & Assessment 2025 Page 8 of 14 Question Answer Marks 1(a) B and C ; A and D ; B ; D ; E ; 5 1(b) electron pairs are shared between atoms ; 1 Question Answer Marks 2(a) A E C B D ;;; 3 2(b) any 3 from: carapace ; segmented abdomen ; jointed, legs / limbs ; two pairs of antennae ; AVP ; 3 Question Answer Marks 3(a) barrier (reef) ; fringing (reef) ; atoll ; 3 3(b)(i) mouth labelled ; stomach labelled ; basal plate labelled ; 3

9693/13 Cambridge International AS & A Level – Mark Scheme PUBLISHED October/November 2025 © Cambridge University Press & Assessment 2025 Page 9 of 14 Question Answer Marks 3(b)(ii) sting / capture, prey OR for defence against predators ; 1 3(c) Any 3 from: change in pH ; change in temperature ; predation / named predator ; physical damage / named physical damage e.g. trawling boats / blast fishing ; sediment, presence / abrasion / blocking polyp mouth ; named pollution ; disease ; hurricanes / tsunami / severe storm ; AVP ; 3 Question Answer Marks 4(a)(i) sea anemone ; 1 4(a)(ii) 98 – 15 or 83 ; (83 / 98)  100 = 85 (%) ; 2 4(a)(iii) Any 3 from: respiration / heat ; excretion ; movement ; not all organism is eaten ; indigestible parts ; 3

9693/13 Cambridge International AS & A Level – Mark Scheme PUBLISHED October/November 2025 © Cambridge University Press & Assessment 2025 Page 10 of 14 Question Answer Marks 4(b) chlorophyll protein DNA nitrogen ✓ ✓ ✓ magnesium ✓ phosphorus ✓ ;;; 3 Question Answer Marks 5(a) intertidal region between the highest and lowest spring tide marks ; 1 5(b) genetic diversity / variation in the genes of a species ; species diversity / number of species and their relative abundance ; ecological diversity / variation in ecosystems (on a regional and global level) ; 3 5(c) Any 3 from: reference to, (named) producer / phytoplankton / photosynthesis ; absorbing / using, carbon dioxide ; (producers) act as carbon sink ; animals die and sink / ref to marine snow ; buried and compressed (for a long time period) ; forms, fossil fuels / (sedimentary) rocks / rocks containing carbonates ; AVP ; 3

9693/13 Cambridge International AS & A Level – Mark Scheme PUBLISHED October/November 2025 © Cambridge University Press & Assessment 2025 Page 11 of 14 Question Answer Marks 6(a) A – convergent ; B – transform ; 2 6(b) Any 1 from: mid-ocean ridge ; hydrothermal vent / volcanoes ; 1 6(c) Any 4 from: subducting plates get, caught / stuck, (on each other) ; pressure / force / potential energy / tension, (between the plates) builds up ; sudden, underwater earthquake / displacement of seafloor / release of the plates / plate slippage ; releases large amount of energy (in short time frame) ; displaces large volume of water ; AVP ; 4

9693/13 Cambridge International AS & A Level – Mark Scheme PUBLISHED October/November 2025 © Cambridge University Press & Assessment 2025 Page 12 of 14 Question Answer Marks 7 Any 8 from: 1 reference to gravitational interactions of Moon and Sun relative to Earth ; 2 tidal range is difference in height between low water mark and high water mark ; 3 spring tides, are greatest / have a greater, tidal range ; 4 Earth, Moon and Sun in alignment ; 5 the gravitational effect is additive ; 6 neap tides, are lowest / have a lower, tidal range ; 7 Sun and Moon are at right angles relative to Earth ; 8 pulls water in opposite directions ; 9 low air pressure increases tidal height / ORA ; 10 onshore wind increases tidal height / ORA ; 11 increase in onshore wind speed increases tidal height / ORA ; 12 change in the shape of the seabed after tectonic activity ; 13 AVP ; 8

9693/13 Cambridge International AS & A Level – Mark Scheme PUBLISHED October/November 2025 © Cambridge University Press & Assessment 2025 Page 13 of 14 Question Answer Marks 8(a) Any 6 from: 1 reference to prop roots ; 2 prop roots provide, stability / anchorage, in loose substrates ; 3 roots absorb oxygen from, atmosphere / air ; 4 due to anoxic soil ; 5 salt exclusion through roots ; 6 due to high salt content of water ; 7 viviparous reproduction ; 8 reference to, propagules / seeds, germinating or starting to grow on trees ; 9 idea that roots able to embed when reach suitable location ; 10 propagules able to float in sea / water / estuaries ; 11 floating propagules to, colonise / disperse to, new areas ; 6 8(b) Any 7 from: 1 provides a habitat for many species ; 2 provides nursery area for juveniles of many animal species ; 3 which, maintains / increases, biodiversity ; 4 food source / sustaining fisheries industries ; 5 traps sediment ; 6 prevents sediment build up, on coral reefs / seagrass beds; 7 decreases turbidity to allow more light penetration for photosynthesis ; 8 reference to tourism ; 9 for, timber / fuel ; 10 (potential) source of, medicine / pharmaceutical, products or research ; 11 act as a carbon sink / reference to role in climate control ; 12 photosynthesis, removes carbon dioxide / provides oxygen ; 13 protects coastlines / AW ; 7

9693/13 Cambridge International AS & A Level – Mark Scheme PUBLISHED October/November 2025 © Cambridge University Press & Assessment 2025 Page 14 of 14 Question Answer Marks 9 Any 9 from: 1 atmospheric dissolution of, carbon dioxide / nitrogen / oxygen ; 2 wave action / turbulence, increases dissolution ; 3 cold water increases solubility of gases / ORA ; 4 less saline water increases solubility of gases / ORA ; 5 high, air / water, pressure increases solubility of gases / ORA ; 6 volcanoes / hydrothermal vents, release carbon dioxide / sulfur dioxide / hydrogen sulfide / hydrogen chloride ; 7 these gases dissolve in, atmospheric / sea, water ; 8 reference to precipitation of this atmospheric water ; 9 reference to, named salts / magnesium sulfate / calcium carbonate / sodium chloride ; 10 runoff of fertilisers introduces, nitrates / phosphates / ions / chemicals ; 11 freshwater runoff / precipitation, decreases chemical concentration / salinity ; 12 evaporation increases the salinity ; 13 increase temperature of seawater increases solubility of salts ; 14 AVP ;; 9