Cambridge A Level Marine Science 9693 — 2025 May/June Paper 1 · Variant 2

[Turn over Cambridge International AS & A Level * 2 9 4 3 1 2 3 0 6 0 * This document has 16 pages. Any blank pages are indicated. DC (WW/CT) 342808/4 © UCLES 2025 MARINE SCIENCE 9693/12 Paper 1 AS Level Theory May/June 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 [ ]. ,










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2 9693/12/M/J/25 © UCLES 2025 Section A Answer all questions in this section. 1 (a) Fig. 1.1 shows part of a red mangrove tree, Rhizophora mangle. propagule Fig. 1.1 (i) Rhizophora mangle reproduces using propagules instead of releasing seeds. Name this type of reproduction. … [1] (ii) Explain the advantage of producing propagules instead of releasing seeds. … … … … [2] * 0000800000002 * ,










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3 9693/12/M/J/25 © UCLES 2025 [Turn over (b) Red mangrove trees have prop roots. Describe how red mangrove prop roots are a benefit for nearby seagrass beds. … … … … … … [3] (c) Worldwide, the area covered by mangrove ecosystems is decreasing. (i) Describe two threats to mangrove ecosystems. 1 … … 2 … … [2] (ii) In one area of the United States of America, over 100 000 people are estimated to be dependent on mangroves for their work. State two ways that mangroves provide work opportunities for people. 1 … … 2 … … [2] [Total: 10] * 0000800000003 * ,










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4 9693/12/M/J/25 © UCLES 2025 2 (a) Sodium chloride is the most abundant salt in sea water. (i) Fig. 2.1 shows the subatomic particles in an atom of sodium. + + + + + + + + + + + Fig. 2.1 Table 2.1 shows information about the structure of a sodium atom. Table 2.1 subatomic particle charge number present in a sodium atom electron … … neutron … 12 proton +1 … Use Fig. 2.1 to complete Table 2.1. [2] (ii) State the particle formed from an atom when electrons are lost or gained. … [1] * 0000800000004 * ,










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5 9693/12/M/J/25 © UCLES 2025 [Turn over (b) Calcium carbonate is found in animals. (i) State the chemical formula of calcium carbonate. … [1] (ii) Describe how calcium carbonate from animals can become part of rocks. … … … … … … [3] (c) Algae require magnesium for growth. Explain why a lack of magnesium can limit the growth of algae. … … … … … … … … [4] [Total: 11] * 0000800000005 * ,










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6 9693/12/M/J/25 © UCLES 2025 3 (a) Name the zone in the open ocean that includes the ocean floor. … [1] (b) Evidence for the theory of plate tectonics has been found in the rocks of the ocean floor. Give two pieces of evidence of plate tectonics that are found in rocks. 1 … … 2 … … [2] (c) Table 3.1 shows three types of plate boundary. Table 3.1 A B C name of plate boundary … … … (i) Complete Table 3.1 with the name of each plate boundary shown. [3] (ii) State the plate boundary, A, B or C, where a mid-ocean ridge could form. … [1] * 0000800000006 * ,










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7 9693/12/M/J/25 © UCLES 2025 [Turn over (d) Hydrothermal vents can form on the ocean floor near to plate boundaries. (i) Describe how a chimney forms at a hydrothermal vent. … … … … … … [3] (ii) Suggest two reasons why photosynthesis would not be expected to occur at a hydrothermal vent. 1 … … 2 … … [2] [Total: 12] * 0000800000007 * ,










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8 9693/12/M/J/25 © UCLES 2025 4 Fig. 4.1 shows a keyhole limpet. shell Fig. 4.1 (a) The keyhole limpet is an animal that attaches to rocks in the littoral zone of a rocky shore. (i) Define the term littoral zone. … … [1] (ii) Rocky shores are formed by weathering and erosion. Contrast the processes of weathering and erosion. … … … … [2] (iii) Many organisms living on rocky shores have shells. Describe one way that a shell is an advantage to living on a rocky shore. … … [1] (iv) The keyhole limpet attaches to rocks. The number of keyhole limpets in an area was investigated. State the name of the equipment used to estimate the number of keyhole limpets in an area. … [1] * 0000800000008 * ,










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9 9693/12/M/J/25 © UCLES 2025 [Turn over (b) The keyhole limpet is an omnivore. Describe why assigning a trophic level to the keyhole limpet is difficult. … … [1] (c) The keyhole limpet produces a protein called keyhole limpet hemocyanin (KLH). (i) Name the four chemical elements found in all proteins. 1 … 2 … 3 … 4 … [1] (ii) KLH is used as an anticancer drug. Patients are given a KLH dose of 0.8 milligrams (mg). An estimated global demand for KLH is 90 000 000 doses per year. One keyhole limpet can produce 1.2 grams (g) of KLH per year. Calculate how many keyhole limpets are needed to meet the yearly global demand of KLH doses. Space for working. … [3] (iii) KLH cannot be made artificially. KLH can only be harvested from keyhole limpets. Describe two ways the over-harvesting of keyhole limpets is a threat to the rocky shore food web. 1 … … 2 … … [2] [Total: 12] * 0000800000009 * ,










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10 9693/12/M/J/25 © UCLES 2025 Section B Answer all questions in this section. 5 Describe the structures and methods that coral polyps use to obtain their nutrition. … … … … … … … … … … … … … … … … … … [8] * 0000800000010 * ,










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11 9693/12/M/J/25 © UCLES 2025 [Turn over 6 (a) Fig. 6.1 shows two water molecules. X O O H H H H Fig. 6.1 The bond labelled X is between two water molecules. Explain the formation of bond X. … … … … … … … … … … [5] * 0000800000011 * ,









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12 9693/12/M/J/25 © UCLES 2025 (b) Fig. 6.2 shows the arrangement of water molecules in liquid water and in ice. O H H O O O H H H H liquid water ice O O H H H H H H O O O O O O H H H H H H H H H H H H Fig. 6.2 Liquid water and ice have different densities. Explain the different densities of liquid water and ice and how this is important to marine organisms. … … … … … … … … … … … … … … … … [8] * 0000800000012 * ,









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13 9693/12/M/J/25 © UCLES 2025 (c) Explain how the solvent action and specific heat capacity of water are important to marine organisms. … … … … … … … … … … … … … … … … … … [9] [Total: 22] * 0000800000013 * ,









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16 9693/12/M/J/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 * ,









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This document consists of 15 printed pages. © Cambridge University Press & Assessment 2025 [Turn over Cambridge International AS & A Level MARINE SCIENCE 9693/12 Paper 1 AS Level Theory May/June 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 May/June 2025 series for most Cambridge IGCSE, Cambridge International A and AS Level components, and some Cambridge O Level components.

9693/12 Cambridge International AS & A Level – Mark Scheme PUBLISHED May/June 2025 © Cambridge University Press & Assessment 2025 Page 2 of 15 Generic Marking Principles These general marking principles must be applied by all examiners when marking candidate answers. They should be applied alongside 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.

9693/12 Cambridge International AS & A Level – Mark Scheme PUBLISHED May/June 2025 © Cambridge University Press & Assessment 2025 Page 3 of 15 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 thresholds 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 from 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.

9693/12 Cambridge International AS & A Level – Mark Scheme PUBLISHED May/June 2025 © Cambridge University Press & Assessment 2025 Page 4 of 15 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.

9693/12 Cambridge International AS & A Level – Mark Scheme PUBLISHED May/June 2025 © Cambridge University Press & Assessment 2025 Page 5 of 15 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 standardisation 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 benefit of doubt was considered, but the response was decided to not be sufficiently close for benefit of doubt to be applied

9693/12 Cambridge International AS & A Level – Mark Scheme PUBLISHED May/June 2025 © Cambridge University Press & Assessment 2025 Page 6 of 15 Annotation Meaning point already given 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

9693/12 Cambridge International AS & A Level – Mark Scheme PUBLISHED May/June 2025 © Cambridge University Press & Assessment 2025 Page 7 of 15 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 excepted) ( ) 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

9693/12 Cambridge International AS & A Level – Mark Scheme PUBLISHED May/June 2025 © Cambridge University Press & Assessment 2025 Page 8 of 15 Question Answer Marks 1(a)(i) viviparous ; 1 1(a)(ii) any 2 from: propagules are (germinated) seeds that grow attached to the parent plant ; (therefore) grow faster (than seeds) once settled away / separated, from the parent plant ; (therefore propagules are) more likely to survive than seed (stated reason) ; 2 1(b) any 3 from: (prop roots) trap / collect, sediment ; decreases turbidity ; idea of decreased turbidity increases light (penetration) in (other / nearby areas) ; allowing seagrass to photosynthesise ; 3 1(c)(i) any 2 from: temperature / climate, change ; over-harvesting ; storm (damage) ; named change in coastal land use e.g. development of hotels ; AVP ;; 2

9693/12 Cambridge International AS & A Level – Mark Scheme PUBLISHED May/June 2025 © Cambridge University Press & Assessment 2025 Page 9 of 15 Question Answer Marks 1(c)(ii) any 2 from: fisheries ; conservation ; tourism / kayaking / tours ; timber harvesting ; AVP ; 2 Question Answer Marks 2(a)(i) subatomic particle charge number present in a sodium atom electron –1 11 neutron neutral / 0 12 proton +1 11 ;; 2 2(a)(ii) ion ; 1 2(b)(i) CaCO3 ; 1

9693/12 Cambridge International AS & A Level – Mark Scheme PUBLISHED May/June 2025 © Cambridge University Press & Assessment 2025 Page 10 of 15 Question Answer Marks 2(b)(ii) any 3 from: (calcium carbonate) forms part of, shell / teeth / bone / skeleton ; animal, dies / sinks / decays / becomes part of marine snow ; idea of compaction ; AVP ; 3 2(c) any 4 from: (magnesium is) used to make chlorophyll ; chlorophyll is needed for photosynthesis ; photosynthesis is used to produce glucose ; glucose is used to form, starch / cellulose ; which increases biomass ; 4 Question Answer Marks 3(a) benthic (zone) ; 1 3(b) any 2 from: (geological) matching of rock formations on different continents ; distribution of similar fossils on different continents ; paleomagnetic stripes on the, ocean floor / sea bed ; AVP ;; 2

9693/12 Cambridge International AS & A Level – Mark Scheme PUBLISHED May/June 2025 © Cambridge University Press & Assessment 2025 Page 11 of 15 Question Answer Marks 3(c)(i) A – convergent ; B – divergent ; C – transform ; 3 3(c)(ii) B ; 1 3(d)(i) any 2 from: sea water seeps into cracks in crust and is heated ; solubility of, salts / minerals, increases at higher temperatures ; higher temperature water is less dense, therefore rises, mixing with colder water above ; PLUS salts precipitate (forming chimney) ; 3 3(d)(ii) any 2 from: high temperature ; lack of light / no light ; high pressure ; AVP ; 2

9693/12 Cambridge International AS & A Level – Mark Scheme PUBLISHED May/June 2025 © Cambridge University Press & Assessment 2025 Page 12 of 15 Question Answer Marks 4(a)(i) the (intertidal) region (on a shoreline) between the highest and lowest spring tide marks ; 1 4(a)(ii) weathering is the breakdown of rock ; erosion is the transport of rock (by the eroding agent) ; 2 4(a)(iii) any 1 from: helps withstand desiccation ; helps withstand wave action ; (shells) protect from (land) predators (when exposed to air) ; 1 4(a)(iv) (frame) quadrat ; 1 4(b) (keyhole limpet) can feed on consumers and producers ; 1 4(c)(i) carbon + hydrogen + oxygen + nitrogen ; 1 4(c)(ii) 1.2 (g)  1000 = 1200 mg 1200 / 0.8 = 1500 (doses per limpet) (90 000 000 / 1500 =) 60 000 ;;; 3 4(c)(iii) any 2 from: the population of (keyhole limpet) predators may decrease ; the population of (keyhole limpet) prey may increase ; predators compete for other food sources ; AVP ; 2

9693/12 Cambridge International AS & A Level – Mark Scheme PUBLISHED May/June 2025 © Cambridge University Press & Assessment 2025 Page 13 of 15 Question Answer Marks 5 any 8 from: 1 nematocyst ; 2 on tentacles ; 3 (nematocyst) fire out barb (into prey) ; 4 (barb) contains toxin ; 5 (toxin) which paralyses prey ; 6 (prey) passed through the mouth / into stomach for digestion ; 7 ref to zooxanthellae ; 8 symbiotic / (zooxanthellae) live in the coral tissues ; 9 (zooxanthellae) are photosynthetic ; 10 produce glucose (and oxygen) ; 11 excess glucose used by, coral / polyp ; 8

9693/12 Cambridge International AS & A Level – Mark Scheme PUBLISHED May/June 2025 © Cambridge University Press & Assessment 2025 Page 14 of 15 Question Answer Marks 6(a) any 5 from: 1 (X is a) hydrogen bond ; 2 to lone pair of electrons on oxygen ; 3 hydrogen atoms (in water molecule) are slightly positive(ly charged) ; 4 oxygen atoms (in water molecule) are slightly negative(ly charged) ; 5 oxygen attracts electrons more strongly than hydrogen (causing differences in charge) ; 6 oxygen (from one water molecule) is attracted to hydrogen in another water molecule ; 7 reference to dipole ; 5 6(b) any 8 from: different densities 1 water has hydrogen bonds that break and reform often OR ice has, more permanent / fixed, hydrogen bonds ; 2 water molecules can be closer OR ice molecules can be further apart ; 3 more water molecules per unit volume OR fewer ice molecules per unit volume ; 4 ice floats ; importance 5 (thermal) insulator ; 6 so whole water column doesn’t freeze / maintains warmer temperature in sea below / organisms don’t freeze in the water ; 7 habitat, for (named) organism(s) / algae OR algae / bacteria / protists, live / grow, in the ice / attached to bottom / sides of ice / on the underside of the ice ; 8 platform / place / surface, for / organisms, to rest / hide from predators OR a platform to hunt from / organisms hide below the ice / protection from predators ; 9 water at different temperatures has different densities ; 10 ref to idea of thermal stratification ; 11 ref to nutrient cycling (between the layers) ; 12 AVP ; 8

9693/12 Cambridge International AS & A Level – Mark Scheme PUBLISHED May/June 2025 © Cambridge University Press & Assessment 2025 Page 15 of 15 Question Answer Marks 6(c) any 9 from: (solvent action) 1 water is a polar molecule ; 2 therefore able to dissolve many substances ; 3 named example of substance that dissolves ; 4 oxygen required for respiration ; 5 carbon dioxide required for photosynthesis ; 6 example of name nutrient use in organisms ; 7 transport of nutrients / nutrient cycling / upwelling ; 8 AVP ; (specific heat capacity) 9 specific heat capacity of water is (relatively) high ; 10 it takes more energy to increase the temperature of water (compared to other substances) ; 11 as lots of energy is required to break hydrogen bonds (between water molecules) ; 12 temperature buffer ; 13 importance in climate control ; 14 AVP ; 9