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

This document has 16 pages. Any blank pages are indicated. [Turn over Cambridge International AS & A Level * 4 4 7 8 6 2 3 7 4 4 * DC (EV/SG) 347054/4 © UCLES 2025 MARINE SCIENCE 9693/11 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 [ ]. ,










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2 9693/11/O/N/25 © UCLES 2025 Section A Answer all questions in this section. 1 Fig. 1.1 shows part of a food web. Whitemouth croaker Lebranche mullet Guiana dolphin Zooplankton Phytoplankton Shrimp Bay whiff Fig. 1.1 (a) (i) Complete the sentence. Choose one answer from the box. carnivores herbivores omnivores Shrimp are … [1] (ii) State one tertiary consumer in Fig. 1.1. … [1] * 0000800000002 * ,










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3 9693/11/O/N/25 © UCLES 2025 [Turn over (iii) Cutlassfish are predators of whitemouth croakers and lebranche mullets. Cutlassfish are prey of Guiana dolphins. Complete Fig. 1.1 by adding cutlassfish to the food web. [2] (iv) Zooplankton are in the second trophic level. Describe the meaning of the term trophic level. … … … … [2] (b) (i) Barnacles attach to Guiana dolphins in a similar way that they attach to whales. Describe one benefit to the barnacles of being attached to the Guiana dolphin. … … [1] (ii) Suggest two disadvantages to the Guiana dolphin of having barnacles attached. 1 … … 2 … … [2] (iii) State the type of symbiosis where one organism benefits and the other organism is harmed. … … [1] * 0000800000003 * ,










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4 9693/11/O/N/25 © UCLES 2025 (c) (i) Marine organisms require dissolved nutrients for growth. State three ways that dissolved nutrients in the ocean are replenished. 1 … … 2 … … 3 … … [3] (ii) State two elements that are found in chlorophyll. 1 … 2 … [2] [Total: 15] * 0000800000004 * ,










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5 9693/11/O/N/25 © UCLES 2025 [Turn over 2 Hydrothermal vents occur at divergent plate boundaries. (a) (i) Describe the plate movement that occurs at a divergent plate boundary. … … [1] (ii) Describe how a hydrothermal vent chimney forms at a divergent plate boundary. … … … … … … … … [4] (b) (i) A hydrothermal vent is at a depth of 2000 metres. State the type of producer at the hydrothermal vent. … [1] (ii) A chimney at a hydrothermal vent was observed to increase in height by 12.2 metres in 2 years. Calculate the mean monthly growth rate of the chimney. Include the unit. … [3] [Total: 9] * 0000800000005 * ,










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6 9693/11/O/N/25 © UCLES 2025 3 (a) Boxer crabs and anemones have a symbiotic relationship. (i) State the type of symbiotic relationship between boxer crabs and anemones. … [1] (ii) Anemones are in the same phylum as coral. State the name of the phylum of coral. … [1] (b) The size of a boxer crab population on one beach was estimated using the equation: N = n1 × n2 m2 N = estimate of population size n1 = number of individuals captured in first sample n2 = number of individuals (both marked and unmarked) captured in second sample m2 = number of marked individuals recaptured in second sample (i) State the name of the equation used to estimate the population using the mark-release-recapture method. … [1] (ii) 55 boxer crabs were captured in the first sample and marked. 35 boxer crabs were captured in the second sample. 11 boxer crabs in the second sample had a mark. Calculate the boxer crab population size. … [1] * 0000800000006 * ,










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7 9693/11/O/N/25 © UCLES 2025 [Turn over (c) State three limitations of the mark-release-recapture method. 1 … … 2 … … 3 … … [3] (d) Describe three biotic factors that would decrease the size of the boxer crab population. 1 … … 2 … … 3 … … [3] [Total: 10] * 0000800000007 * ,










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8 9693/11/O/N/25 © UCLES 2025 4 (a) Fig. 4.1 shows a diagram of a water molecule. + + + + + + + + + + A … B … Fig. 4.1 (i) Label part A and part B of the oxygen atom in Fig. 4.1. [2] (ii) Name the type of bond between an oxygen atom and a hydrogen atom within one water molecule. … [1] * 0000800000008 * ,










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9 9693/11/O/N/25 © UCLES 2025 [Turn over (b) Explain why hydrogen bonds form between different water molecules. You may include a labelled diagram. … … … … … … … … [4] (c) Explain how hydrogen bonds cause the density of water to decrease when water freezes. … … … … [2] (d) Explain how hydrogen bonds affect the specific heat capacity of water compared with most other liquids. … … … … [2] [Total: 11] * 0000800000009 * ,










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10 9693/11/O/N/25 © UCLES 2025 Section B Answer all questions in this section. 5 Fig. 5.1 shows a map of the Bay of Fundy. Atlantic Ocean Bay of Fundy N S W E 0 100 km Fig. 5.1 (a) Explain the factors that will cause the highest tide each year in the Bay of Fundy. … … … … … … … … … … … … … [5] * 0000800000010 * ,










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11 9693/11/O/N/25 © UCLES 2025 [Turn over (b) Discuss the adaptations of named animals to the abiotic factors on a rocky shore. … … … … … … … … … … … … [6] * 0000800000011 * ,









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12 9693/11/O/N/25 © UCLES 2025 (c) The blades of macroalgae from the littoral zone are harvested by people for food. The macroalgae are cut at the stipe. The holdfast is left attached to rock. The macroalgae can grow from the holdfast. Explain the ecological and economic benefits of not harvesting the holdfast of macroalgae. … … … … … … … … … … … … [6] [Total: 17] * 0000800000012 * ,









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13 9693/11/O/N/25 © UCLES 2025 6 (a) Identify the phylum of bony fish and describe the four common physical features shared by all organisms in this phylum at some point in their development. … … … … … … … … … … [5] (b) Compare the structures of a typical adult bony fish and a typical adult cartilaginous fish. … … … … … … … … … … … … … … [8] [Total: 13] * 0000800000013 * ,









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16 9693/11/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 * ,









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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 9693/11 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.

9693/11 Cambridge International AS & A Level – Mark Scheme PUBLISHED October/November 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 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.

9693/11 Cambridge International AS & A Level – Mark Scheme PUBLISHED October/November 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 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.

9693/11 Cambridge International AS & A Level – Mark Scheme PUBLISHED October/November 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.

9693/11 Cambridge International AS & A Level – Mark Scheme PUBLISHED October/November 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 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 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 incorrect point or mark not awarded point has been noted, but no credit has been given or blank page seen

9693/11 Cambridge International AS & A Level – Mark Scheme PUBLISHED October/November 2025 © Cambridge University Press & Assessment 2025 Page 6 of 15 Annotation Meaning response is too vague or there is insufficient detail in response 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 Highlighted text Highlighting areas of text On-page comment box Allows comments to be entered on the page Off-page comment box Allows comments to be entered at the bottom of the RM Assessor marking window and then displayed when the associated question item is navigated to

9693/11 Cambridge International AS & A Level – Mark Scheme PUBLISHED October/November 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 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

9693/11 Cambridge International AS & A Level – Mark Scheme PUBLISHED October/November 2025 © Cambridge University Press & Assessment 2025 Page 8 of 15 Question Answer Marks 1(a)(i) omnivores ; 1 1(a)(ii) whitemouth croaker / Guiana dolphin / bay whiff ; 1 1(a)(iii) label added with correct links ; arrows on links correct direction ; 2 1(a)(iv) stage / step / position, in a food, web / chain ; compared with the producer ; 2 1(b)(i) any 1 of: move from place to place (attached to dolphin) ; movement (attached to dolphin) moves water over barnacle(s) ; greater availability of food ; 1 1(b)(ii) any 2 of: reduced hydrodynamic efficiency ; decreased camouflage ; damage to skin ; AVP ; 2 1(b)(iii) parasitic ; 1

9693/11 Cambridge International AS & A Level – Mark Scheme PUBLISHED October/November 2025 © Cambridge University Press & Assessment 2025 Page 9 of 15 Question Answer Marks 1(c)(i) any 3 of: upwelling ; run-off ; tectonic activity ; (atmospheric) gases dissolving ; excretion ; decomposition / decay ; AVP ; 3 1(c)(ii) any 2 of: nitrogen ; magnesium ; carbon ; hydrogen ; oxygen ; 2

9693/11 Cambridge International AS & A Level – Mark Scheme PUBLISHED October/November 2025 © Cambridge University Press & Assessment 2025 Page 10 of 15 Question Answer Marks 2(a)(i) plates are moving apart ; 1 2(a)(ii) any 4 of: sea water enters, gaps / cracks / fissures, in crust and is heated by magma / mantle ; minerals dissolve ; hot water rises (from crust) ; (water from fissure) cools due to sea water being colder ; minerals precipitate ; AVP ; 4 2(b)(i) chemosynthetic ; 1 2(b)(ii) 12.2 2 12  ; 0.51 OR 0.508 ; m month–1 OR m / month OR metres / month OR metres per month ; 3

9693/11 Cambridge International AS & A Level – Mark Scheme PUBLISHED October/November 2025 © Cambridge University Press & Assessment 2025 Page 11 of 15 Question Answer Marks 3(a)(i) mutualistic / mutualism ; 1 3(a)(ii) cnidaria ; 1 3(b)(i) Lincoln index ; 1 3(b)(ii) 175 ; 1 3(c) any 3 of: catching / mark, may harm, crab / animal OR make, crab / animal, more / less, likely to be, recaptured / survive / predated ; (organisms may) emigrate / immigrate / migrate ; population may not randomly mix ; time between release and recapture must be long enough to allow mixing ; time between release and recapture must be short enough compared with the life span of the organism / crab ; organisms may, be difficult to catch / hide ; mark / tag, may fall off / rub off ; 3

9693/11 Cambridge International AS & A Level – Mark Scheme PUBLISHED October/November 2025 © Cambridge University Press & Assessment 2025 Page 12 of 15 Question Answer Marks 3(d) any 3 of: increase in, predation / predator, population ; decrease in, prey / food supply ; increase in, interspecific competition ; increase in, intraspecific competition ; (new) disease / pathogen ; new / increased, parasitism ; decrease in, (mutualistic) anemone population ; 3 Question Answer Marks 4(a)(i) (A) electron ; (B) neutron ; 2 4(a)(ii) covalent ; 1 4(b) any 4 of: hydrogen (atoms in water molecule) are slightly positive(ly charged) ; oxygen (atoms in water molecule) are slightly negative(ly charged) ; due to oxygen attracting the electrons more strongly than hydrogen ; oxygen (from one water molecule) is attracted to hydrogen (in another water molecule) ; reference to dipole ; 4

9693/11 Cambridge International AS & A Level – Mark Scheme PUBLISHED October/November 2025 © Cambridge University Press & Assessment 2025 Page 13 of 15 Question Answer Marks 4(c) more (hydrogen bonds) form between water molecules (when water freezes) ; so water molecules are held further apart ; 2 4(d) water has a high(er) specific heat (capacity) ; because (more) energy is required to break hydrogen bonds ; 2 Question Answer Marks 5(a) any 5 of: 1 (highest predicted will be) Spring tide ; 2 alignment of Earth, Sun and Moon ; 3 due to (force of) gravity (on water) from Sun and Moon ; 4 the (gravitational) effect is additive ; 5 wind direction from South-West ; 6 high wind speed (into bay) ; 7 low (air) pressure ; 8 shape of bay funnels the water into a narrower channel (so tide height is increased) ; 9 flow of water into bay due to Coriolis effect ; 10 AVP ;; 5

9693/11 Cambridge International AS & A Level – Mark Scheme PUBLISHED October/November 2025 © Cambridge University Press & Assessment 2025 Page 14 of 15 Question Answer Marks 5(b) any 6 of: 1 named example of animal (linked to its correct adaptation) ;; 2 firm substrate for attachment ; 3 animals form tight closure / muscular foot to attach, to substrate ; 4 (attachment / shell to) withstand (high) wave impact ; 5 (animals have) shell to reduce / prevent desiccation ; 6 migrate with the changing tide / live in rock pools ; 7 move / hide, under macroalgae / seaweed / rocks, to avoid desiccation ; 8 move / hide in, crevices to reduce wave impact or to avoid desiccation ; 9 description of how abiotic factors vary in the different zones ;; 10 description of how abiotic factors vary in rock pools ;; 11 AVP ;; 6 5(c) any 6 of: ecological 1 macroalgae is a producer ; 2 carbon dioxide removed from, water / air ; 3 providing habitat ; 4 oxygenating (water) ; 5 (algae regrow quickly) so primary productivity is maintained ; economic (a) (macroalgae will grow again from holdfast) ensuring future harvest(s) ; (b) (macroalgae) grows back faster, so more to sell OR so less time between harvest ; (c) blades may be worth more money without holdfast ; (d) (as algae regrow) fish stocks for harvesting are not affected as food chains are not disrupted ; either ecological or economic (i) reduce wave, height / speed / energy ; (ii) (which) protects coastlines ; 6

9693/11 Cambridge International AS & A Level – Mark Scheme PUBLISHED October/November 2025 © Cambridge University Press & Assessment 2025 Page 15 of 15 Question Answer Marks 6(a) (phylum) chordata / chordate(s) ; max 4 (features) notochord ; dorsal neural tube ; pharyngeal slits ; post-anal tail ; AVP ;; 5 6(b) any 8 of: (similarities) 1 skeleton ; 2 gills ; 3 lateral line ; 4 pectoral, caudal, pelvic, anal and dorsal fins ; (differences) (cartilaginous fish) (a) has gill slits ORA ; (b) cartilaginous skeleton / non-calcified or non-ossified, skeleton ; (c) buoyancy created by fatty liver ORA ; (d) denticles present / placoid scales ; (bony fish) (e) skeleton is calcified / ossified ; (f) operculum present ORA ; (g) scales present ; (h) swim bladder (present in many) ORA (absent in all cartilaginous fish) ; (i) visible lateral line ORA ; (j) AVP;; 8