Cambridge A Level Marine Science 9693 — 2024 Oct/Nov Paper 1 · Variant 2

This document has 16 pages. Any blank pages are indicated. [Turn over Cambridge International AS & A Level * 5 8 9 4 3 4 6 2 0 6 * MARINE SCIENCE 9693/12 Paper 1 AS Level Theory October/November 2024 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 [ ]. DC (LK/SG) 326396/4 © UCLES 2024 ,










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2 9693/12/O/N/24 © UCLES 2024 Section A Answer all questions in this section. 1 Sea water consists of many different elements and compounds. (a) Fig. 1.1 shows an atom of chlorine. 17 p 18 n Key p = protons n = neutrons Fig. 1.1 (i) Complete Fig. 1.1 to show the electron arrangement of chlorine. Use a cross (x) to represent each electron. [2] (ii) The compound sodium chloride is a major component of sea water. Chlorine forms chloride ions when it forms an ionic compound with sodium. Explain why the symbol for a chloride ion is Cl –. … … … … [2] (iii) A different ionic compound is used to form the bones and shells of marine organisms. Name this compound and give its chemical formula. name … chemical formula … [2] * 0000800000002 * ,










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3 9693/12/O/N/24 © UCLES 2024 [Turn over (b) Brine is a concentrated solution of sodium chloride in water. A sample was taken from a marine brine pool. The sample had a volume of 300.0 cm3 and a mass of 358.2 g. Calculate the density of the brine sample. Show your working. State the unit. … [3] (c) State two abiotic factors other than sodium chloride concentration that affect the density of sea water. 1 … 2 … [1] [Total: 10] * 0000800000003 * ,










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5 9693/12/O/N/24 © UCLES 2024 [Turn over 2 Fig. 2.1 shows the crown-of-thorns starfish (COTS), Acanthaster planci, an echinoderm. Fig. 2.1 (a) (i) State two features typical of echinoderms. 1 … 2 … [2] (ii) Complete Table 2.1 to show the hierarchy of classification for the crown-of-thorns starfish. Table 2.1 group crown-of-thorns starfish classification domain Eukarya kingdom … … Echinodermata class Asteroidea order Valvatida family Acanthasteridae genus … … … [4] * 0000800000005 * ,










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6 9693/12/O/N/24 © UCLES 2024 (b) Crown-of-thorns starfish (COTS) prey on fast growing branching hard corals, but do not prey on slow growing soft corals as frequently. (i) Explain the effect COTS have on the coral species diversity at a low population density of COTS. … … … … [2] (ii) Explain the effect COTS have on the coral species diversity at a high population density of COTS. … … … … [2] (c) Fig. 2.2 shows the percentage cover of algae and the percentage cover of hard corals on a section of reef between 1993 and 2020. 0 25 1990 1995 2000 2005 year 2010 2015 2020 50 percentage cover 75 100 algae Key hard coral Fig. 2.2 * 0000800000006 * ,










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7 9693/12/O/N/24 © UCLES 2024 [Turn over (i) Use Fig. 2.2 to state the year in which a COTS outbreak started. … [1] (ii) Use Fig. 2.2 to describe the relationship between the percentage cover of algae and the percentage cover of hard corals. … … [1] (iii) Suggest one abiotic factor which reduces percentage cover of coral on a reef. … [1] (iv) Name one method used for estimating the population size of a mobile species such as COTS on a coral reef. … [1] [Total: 14] * 0000800000007 * ,










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8 9693/12/O/N/24 © UCLES 2024 3 Manatees are large, air-breathing, marine mammals that feed on seagrass. Fig. 3.1 shows a seagrass plant. Fig. 3.1 (a) On Fig. 3.1, label four features of a seagrass plant using label lines. [2] (b) There are large seagrass beds around the coastline of Florida in the USA. In 2021, there were many deaths of manatees living in lagoons around Florida. Significant phytoplankton blooms also occurred in the same areas. (i) Suggest one reason why a phytoplankton bloom may have occurred. … … [1] (ii) Suggest how the phytoplankton bloom could have caused the death of the manatees. … … … … … … [3] * 0000800000008 * ,










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9 9693/12/O/N/24 © UCLES 2024 [Turn over (c) Seagrass beds are a food source for many marine species. Explain two other ecological or economic benefits of seagrass beds. 1 … … … … 2 … … … … [4] [Total: 10] * 0000800000009 * ,










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10 9693/12/O/N/24 © UCLES 2024 4 Fig. 4.1 shows a cross-section of a rocky shore. mean low water spring tide R P X Y Z mean high water spring tide Fig. 4.1 (a) (i) Name zones P and R shown on Fig. 4.1. P … R … [2] (ii) Zone P is partly submerged on a few occasions each year. Name one abiotic factor that would cause part of zone P to become submerged. … [1] (b) Describe how abiotic factors in zone Y on Fig. 4.1 change over a tidal cycle on a sunny, warm day. … … … … … … … … [4] * 0000800000010 * ,










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11 9693/12/O/N/24 © UCLES 2024 [Turn over (c) Fig. 4.2 shows two marine organisms, A and B, from a rocky shore. A B 5 cm 5 cm 5 cm Fig. 4.2 On Fig. 4.1, organism A is found in zone X and organism B is found in zone Z. Explain one adaptation each organism has to the zone in which it is found. organism A … … … organism B … … … [4] [Total: 11] * 0000800000011 * ,









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12 9693/12/O/N/24 © UCLES 2024 Section B Answer all questions in this section. 5 (a) Explain the processes involved in the formation of sediment and its deposition in mangrove estuaries. … … … … … … … … … … [5] (b) Discuss the causes and impacts of the loss of mangrove forests. … … … … … … … … … … … … … … [7] [Total: 12] * 0000800000012 * ,









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13 9693/12/O/N/24 © UCLES 2024 [Turn over 6 (a) Describe how hydrogen bonds form between water molecules and how hydrogen bonds are involved in the formation of floating sea ice. You may include labelled diagrams. … … … … … … … … … … … … … … [7] (b) Explain the importance to marine organisms of ice floating on sea water. … … … … … … … … … … [5] [Total: 12] * 0000800000013 * ,









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14 9693/12/O/N/24 © UCLES 2024 7 Explain the processes leading to a vent chimney forming at a hydrothermal vent. … … … … … … … … … … … … [6] * 0000800000014 * ,









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16 9693/12/O/N/24 © UCLES 2024 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 13 printed pages. © Cambridge University Press & Assessment 2024 [Turn over Cambridge International AS & A Level MARINE SCIENCE 9693/12 Paper 1 AS Level Theory Paper October/November 2024 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 2024 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 October/November 2024 © Cambridge University Press & Assessment 2024 Page 2 of 13 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 October/November 2024 © Cambridge University Press & Assessment 2024 Page 3 of 13 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 October/November 2024 © Cambridge University Press & Assessment 2024 Page 4 of 13 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 October/November 2024 © Cambridge University Press & Assessment 2024 Page 5 of 13 Question Answer Marks 1(a)(i) correct number of electrons ; correct arrangement / 2, 8, 7 ; 2 1(a)(ii) gains an electron ; any 1 from: (electron) from sodium ; to complete its outer shell ; 2 1(a)(iii) calcium carbonate ; CaCO3 ; 2 1(b) density = mass ÷ volume OR 358.2 ÷ 300 ; = 1.194 ; g / cm3 OR g cm–3 ; 3 1(c) temperature AND pressure ; 1

9693/12 Cambridge International AS & A Level – Mark Scheme PUBLISHED October/November 2024 © Cambridge University Press & Assessment 2024 Page 6 of 13 Question Answer Marks 2(a)(i) (penta)radial symmetry ; tube feet ; 2 2(a)(ii) group crown of thorns starfish classification domain Eukarya kingdom Animalia ; phylum ; Echinodermata class Asteroidea order Valvatida family Acanthasteridae genus Acanthaster ; species planci ; 4 2(b)(i) (idea of) controlling / reducing / restricting, population of hard corals OR (idea of) creating space for settlement of, new / slower growing / soft, coral polyps OR (idea of) less competition between soft and hard coral ; which increases, (species/ genetic) diversity / population (of soft corals) ; OR hard coral (species /genetic) population(s) decrease AND no / little, effect on soft corals ; which decreases (species/ genetic) diversity ; 2

9693/12 Cambridge International AS & A Level – Mark Scheme PUBLISHED October/November 2024 © Cambridge University Press & Assessment 2024 Page 7 of 13 Question Answer Marks 2(b)(ii) any 2 from: can destroy, large areas of / all (hard) corals OR rate of being eaten is greater than growth rate ; due to intraspecific competition (between COTS) ; will (start) feeding on, any coral present / soft / slow growing, corals ; reduces diversity ; 2 2(c)(i) 2008 / 2009 ; 1 2(c)(ii) inverse relationship OR hard coral decreases AND algae increases OR negative correlation ORA ; 1 2(c)(iii) any 1 from: change in temperature / change in salinity / (presence of or more) hurricanes ; AVP ; 1 2(c)(iv) mark-release-recapture ; 1 Question Answer Marks 3(a) 4 correct for 2 marks 2 or 3 correct for 1 mark 2 roots rhizome Leaf / leaves flower

9693/12 Cambridge International AS & A Level – Mark Scheme PUBLISHED October/November 2024 © Cambridge University Press & Assessment 2024 Page 8 of 13 Question Answer Marks 3(b)(i) increased, nutrients / fertiliser ; 1 3(b)(ii) (phytoplankton / bloom), blocks (sun)light ; prevents seagrass, photosynthesis / growth ; manatee, has no food (seagrass) supply ; OR (some) phytoplankton contain / produces toxins ; (idea of) ingested with the seagrass ; AVP ; 3 3(c) any 2 pairs from: stabilises sand / substrate ; (stability of substrate) reduces turbidity ; absorbs wave energy / reduces wave height ; (reduced wave energy) protect shorelines / reduce erosion ; climate control ; by absorbing carbon dioxide /carbon sequestration / form a carbon sink ; produce oxygen from photosynthesis ; oxygen used for respiration ; form, nursery / habitat ; for commercially important species OR provides shelter / hiding places from predators OR increases biodiversity ; absorb nutrients from runoff ; reducing damage from eutrophication / algal blooms (on coral reefs / other named habitat) ; seagrass bed attracts tourists ; increased income for local population / nation ; 4

9693/12 Cambridge International AS & A Level – Mark Scheme PUBLISHED October/November 2024 © Cambridge University Press & Assessment 2024 Page 9 of 13 Question Answer Marks 4(a)(i) P = splash (zone) ; R = intertidal / littoral, (zone) ; 2 4(a)(ii) any 1 from : low air pressure ; onshore wind ; 1 4(b) any 4 from: (when submerged) water temperature is stable / (when out of water) temperature changes rapidly ; (when submerged) dissolved oxygen available (for gills) / (when out of water) exposed to, air or oxygen or much higher oxygen concentration ; (out of water) increased light intensity / (submerged) low light intensity ; (when out of water exposure to) wind (causing, dehydration / desiccation) / (when in water exposed to) turbulence / tidal flow / currents ; (when out of water exposure to) increased salinity/salt concentration (as water evaporates) / (submerged) decreased salt concentration / salinity ; (out of water) no/decreased dissolved nutrients ; (when submerged) increased carbon dioxide availability / (when out of water) decreased carbon dioxide availability ; AVP ; 4

9693/12 Cambridge International AS & A Level – Mark Scheme PUBLISHED October/November 2024 © Cambridge University Press & Assessment 2024 Page 10 of 13 Question Answer Marks 4(c) (organism A) any pair from: shell that fits to the rock / traps water in its shell / impermeable shell ; to reduce, desiccation / water loss ; hard shell ; for protection from waves / predators ; conical / grooved (shell) ; to absorb wave energy / to allow water to run off the shell / to prevent shell damage ; strong foot ; for attachment (to rock) / to prevent being washed off the rock / to hold it in place ; (organism B) any pair from: (strong) holdfast ; to prevent being washed away / to hold it in place ; air bladder ; to float (when tide in) / to keep near the surface / for (maximum) photosynthesis/ to absorb maximum light ; flat / long, blades ; to absorb maximal light for photosynthesis ; thick cuticle ; to reduce desiccation ; falls flat / collapses on itself ; reduces desiccation by trapping moisture ; 4

9693/12 Cambridge International AS & A Level – Mark Scheme PUBLISHED October/November 2024 © Cambridge University Press & Assessment 2024 Page 11 of 13 Question Answer Marks 5(a) at least 1 from : rocks are weathered ; by chemical / physical / biological means ; plus MAX. 4 from: the pieces are eroded/ moved, by, water / wind / gravity ; large particles can settle in higher water flow ; (smaller) particles stay suspended until flow rate reduces / (fine) particles sediment out when flow rate slows ; in estuary river widens (flow reduces) ; (mangrove) prop roots (further) slow the water current ; 5 5(b) MAX. 5 from: (causes of mangrove loss) over harvesting / deforestation ; storm damage ; stated change in land use ; temperature change / global warming / climate change ; oil/chemical pollution ; disease ; fire ; plus MAX. 5 from: (impacts of loss) substrate no longer stabilised / roots not present to hold the soil together ; increases (coastal) erosion ; increases turbidity, reducing productivity ; loss of biodiversity ; loss of nursery / breeding grounds ; reduced fish population ; loss of a carbon sink ; 7

9693/12 Cambridge International AS & A Level – Mark Scheme PUBLISHED October/November 2024 © Cambridge University Press & Assessment 2024 Page 12 of 13 Question Answer Marks 6(a) any 7 from: covalent bonds / shared electrons / electron pairs are shared ; higher positive charge on the oxygen has more attraction for the electrons / ORA ; leaving oxygen atom - / hydrogen + / water is a polar molecule / water is a dipole ; ()+ of hydrogen forms (weak) bond with ()- of oxygen atom of another water molecule ; (hydrogen bonds are) weak bonds ; as water cools, kinetic energy (of the molecules) decreases ORA ; fixed hydrogen bonds form (as water cools) ; water molecules held apart by the hydrogen bonds / molecules less densely packed ; density of water is max. at 4 °C ; ice is less dense (than liquid water so it floats) ; 7 6(b) any 5 from: it is a thermal insulator ; stops rest of the water column from freezing / limits the amount of water that freezes ; organisms don’t freeze ; habitat for organisms ; for large mammals / seabirds ; to rest on / breed / escape from predators ; algae present on underside (of ice) ; (algae) is a food source ; glacial ice transfers nutrients to the ocean ; 5

9693/12 Cambridge International AS & A Level – Mark Scheme PUBLISHED October/November 2024 © Cambridge University Press & Assessment 2024 Page 13 of 13 Question Answer Marks 7 MAX. 5 from : cracks form at (divergent / convergent) plate boundaries ; due to, subduction / sea floor spreading / hot spots ; water seeps through cracks in the sea bed ; (water is) superheated ; by the mantle / magma ; large quantities of (named) salts/ minerals, are dissolved into the water ; water forced back into the ocean ; ocean water is cold ; at least 1 of: salts / minerals precipitate (out of solution) ; (salts / minerals) solidify and build up (forming the chimney) ; 6