Interactions — Paper 2 · A Level Marine Science 9693

3 (a) Explain what is meant by each of the following terms used in ecology. (i) community … … … … [2] (ii) productivity … … … … [2] (b) Explain why sandy shores tend to have a relatively low biodiversity. … … … … … … … … … … [5] (c) Discuss the role of coral reefs in protecting coasts. … … … … … … … … … … … … [6] [Total: 15]

15 marks

Mark scheme: 3(a)(i) all the different, species of organisms / populations ; in a particular, habitat / ecosystem, at the same time ; 2 3(a)(ii) rate ; at which, organic material / biomass, is produced ; 2 3(b) any 5 of: 1 sandy shores are unstable / continuously shifting / longshore drift / AW ; 2 subject to erosion ; 3 sand has a high porosity / dries out quickly / AW ; 4 lack of suitable substrate for attachment ; 5 no / few, producers for food / lack of photosynthesis / low primary productivity ; 6 no shelter / exposure to predators ; 7 only burrowing animals can live there / idea of, only a small number of species are adapted to live there ; 8 few niches available ; 5 Question Answer Marks Guidance 3(c) any 6 of: 1 reefs, dissipate / reduce, wave energy ; 2 slow down / reduce, wave action ; 3 protect shores from flooding ; 4 reduce coastal erosion ; 5 provide protection for (named) coastal habitats ; 6 provide protection for coastal, properties / infrastructure ; 7 idea of providing safe anchorages ; 6

This question in 9693/21 Oct/Nov 2017

3 (a) Mutualism and parasitism are two examples of interrelationships between species. Describe each of these types of interrelationships, with reference to specific marine examples. … … … … … … … … … … … … … … … … [8] (b) (i) Coral reefs are areas with high productivity. Explain the meaning of the term productivity. … … … … [2] (ii) Suggest reasons why coral reefs have a high productivity. … … … … … … … … … … [5] [Total: 15]

15 marks

Mark scheme: 3(a) both are types of a symbiotic relationship ; (mutualism) both species benefit ; (parasitism) 1 species benefits at expense of other ; use term host appropriately ; mutualism named pair of species ; Only credit examples if they are mutualism – if in doubt, look it up. For example, whale and barnacle is NOT mutualism. benefit to species 1 ; benefit to species 2 ; parasitism example of host and parasite ; description of the benefit to parasite ; description of the harm to host ; 8 Question Answer Marks Guidance 3(b)(i) rate ; at which, organic material / biomass is produced / increases ; 2 R idea of energy production 3(b)(ii) Any 5 of: 1 clear water / low turbidity ; 2 for, high light penetration ; 3 shallow water / being near surface ; 4 idea of, suitable temperature ; 5 for, enzymes ; 6 large amounts of sunlight / a lot of energy / high light intensity ; 7 idea of, fast rate of photosynthesis ; 8 by zooxanthellae / producer ; 9 it is, a stable / not extreme, environment ; 10 idea of, rapid / high, nutrient cycling / AW ; 5 I warm unqualified I photosynthesise easily

This question in 9693/21 May/June 2018

2 Coral bleaching, in which coral polyps expel their zooxanthellae, can be caused by increased sea water temperature. (a) State the type of interrelationship between coral and zooxanthellae. … … [1] Some marine biologists suggested the hypothesis that coral reef communities do not recover from coral bleaching. Fig. 2.1 is a graph of the predicted changes following a severe coral bleaching event based on this hypothesis. 1.0 0.5 algae cover proportional 0.0 change number of fish species –0.5 coral cover –1.0 0 1 2 3 4 5 6 7 8 9 10 time after severe severe coral coral bleaching event / years bleaching event Fig. 2.1 (b) (i) Describe how the coral reef communities ten years after a bleaching event are predicted to differ from the communities before the event occurred. … … … … … … [3] (ii) Suggest how the predicted changes in algae cover may result in a reduction in coral cover. … … … … [2] (c) In 1998, a reef in Western Australia suffered a severe coral bleaching event. Fig. 2.2 shows the results of a study of the changes in percentage coral cover and percentage algae cover before and after this event. It also shows the changes in the density of herbivorous fish. 100 75 herbivorous fish 75 50 percentage fish density cover 50 / arbitrary algae cover units 25 25 coral cover 0 0 1996 1998 2000 2002 2004 2006 2008 2010 year severe coral bleaching event Fig. 2.2 (i) Suggest how percentage coral cover may be measured on a coral reef. … … … … [2] (ii) Explain why the hypothesis that coral reef communities do not recover from a bleaching event is not supported by the results shown in Fig. 2.2. … … … … [2] (iii) Use information from Fig. 2.2 to suggest a reason for the changes in density of herbivorous fish. … … [1] [Total: 11]

11 marks

Mark scheme: 2(a) mutualistic / mutualism ; 1 2(b)(i) increase in algae (cover) ; decrease in coral (cover) ; decrease in number of fish (species) ; 3 2(b)(ii) any two of algae block light (to zooxanthellae) ; (which) prevents photosynthesis ; prevent settlement of new coral ; prevent polyps from feeding / blocks mouths of polyps ; 2 2(c)(i) idea of, counting / estimate / calculate (%) cover ; any one of idea of, quadrats ; appropriate sample area (e.g. per m2) ; ref. to how placed – transect / random ; idea of, repeats + calculating mean ; 2 2(c)(ii) idea of, species present is similar to previous levels / AW ; idea of, coral cover returns to (nearly) previous levels / AW ; idea of, fish returns to (nearly) previous levels / AW ; idea of, algae cover returns to previous levels / AW ; 2 2(c)(iii) fish eat algae (so as algae changes, fish density changes) ; 1 A clear description that shows the data of fish and algae are correlated

This question in 9693/22 May/June 2018

3 (a) Describe how a tropical cyclone develops. … … … … … … … … … … [5] (b) Explain the meaning of the terms ecosystem and biodiversity. … … … … … … … … … … [5] (c) Outline how mangroves protect tropical coastlines. … … … … … … … … … … [5] [Total: 15]

15 marks

Mark scheme: 3(a) any five of sea surface (temperature) at least 26.5 °C / 80 °F ; low (air) pressure / low (air) pressure system ; minimum sea depth of 50 m ; idea of, sufficiently far from equator to provide spin or twist / Coriolis effect ; idea of, rotating winds OR winds from different directions ; evaporation ; (gives rise to warm) moist air ; (air) rises and cools OR rises and draws in/up cooler air ; condensation ; release of latent heat ; idea of, this energy perpetuates cyclone further ; low wind-shear ; 5 A sea at least 26.5 °C A warm water at surface warm sea water unqualified is insufficient A circling / spiralling I strong wind unqualified Question Answer Marks Guidance 3(b) any five of ecosystem interaction between ; (community of) living organisms AND non-living components / biotic AND abiotic factors ; linked through, nutrient cycles ; (and) movement of, energy / nutrients, through, food chains / food webs ; biodiversity ref. number of species ; idea of, ref. evenness / relative abundance of each / AW ; (in an) ecosystem / habitat ; 5 3(c) any five of idea of, mangroves live in intertidal regions / delta regions / salt tolerant ; idea of, interlocking / thick / complex, root (system) ; idea of, protect from wave (action) ; energy dissipation ; reduction in, current / flow, speed ; reduce erosion ; increase sedimentation / fine sediment accumulates ; AVP ; 5 e.g. ref. extreme events

This question in 9693/22 May/June 2018

4 The Humboldt Current off the coasts of Chile and Peru causes upwelling. This supports huge shoals of the Peruvian anchoveta, which provide the greatest catches of any fish species. (a) Explain how upwelling supports large numbers of fish. … … … … … … … … … … [5] (b) Discuss the advantages of shoaling in fish such as the Peruvian anchoveta. … … … … … … … … … … [5] (c) Describe the causes of El Niño events. Explain how such an event may result in the collapse of the Peruvian anchoveta population. … … … … … … … … … … [5] [Total: 15]

15 marks

Mark scheme: 4(a) any five of nutrient rich water ; ref. named nutrient ; rise up from depth / upwellings ; idea of, replenishing nutrients in surface ; stimulates growth / reproduction of phytoplankton / producers ; increases productivity ; increase food / energy / (zoo)plankton, for fish (such as anchoveta) ; 5 Question Answer Marks Guidance 4(b) any five of successful strategy for feeding / helps feeding ; by, idea of, more eyes to spot the food ; by, idea of, corralling prey / splitting up schools of prey fish / break-up bait balls ; successful predator avoidance / helps avoid predation / reduces predation ; by, idea of, more eyes to spot the predators ; by, idea of, large numbers will confuse predator ; by, idea of less chance of predation on an individual / forming a bait ball ; successful strategy for reproduction / assists in reproduction / easier reproduction ; due to, proximity of mates / increased chance of finding a mate / easier to find a mate ; increase chance of fertilisation ; (increase) hydrodynamic efficiency / reduce drag ; saves energy / increase swimming speed (for same amount of energy) ; 5 Question Answer Marks Guidance 4(c) any five of winds reverse / change direction ; decreased wind from E / change in trade winds ; less upwelling ; ref. warmer (surface) water (over Humboldt Current) ; lowers thermocline / thermocline found deeper in ocean ; prevents nutrient rich water reaching surface / less nutrients at surface ; reduction in phytoplankton / productivity ; decreased zooplankton / decreased food source (for anchoveta) ; increased rainfall ; (may) alter nutrient availability / salinity ; reduction in light energy ; 5

This question in 9693/22 May/June 2018

2 Coral bleaching, in which coral polyps expel their zooxanthellae, can be caused by increased sea water temperature. (a) State the type of interrelationship between coral and zooxanthellae. … … [1] Some marine biologists suggested the hypothesis that coral reef communities do not recover from coral bleaching. Fig. 2.1 is a graph of the predicted changes following a severe coral bleaching event based on this hypothesis. 1.0 0.5 algae cover proportional 0.0 change number of fish species –0.5 coral cover –1.0 0 1 2 3 4 5 6 7 8 9 10 time after severe severe coral coral bleaching event / years bleaching event Fig. 2.1 (b) (i) Describe how the coral reef communities ten years after a bleaching event are predicted to differ from the communities before the event occurred. … … … … … … [3] (ii) Suggest how the predicted changes in algae cover may result in a reduction in coral cover. … … … … [2] (c) In 1998, a reef in Western Australia suffered a severe coral bleaching event. Fig. 2.2 shows the results of a study of the changes in percentage coral cover and percentage algae cover before and after this event. It also shows the changes in the density of herbivorous fish. 100 75 herbivorous fish 75 50 percentage fish density cover 50 / arbitrary algae cover units 25 25 coral cover 0 0 1996 1998 2000 2002 2004 2006 2008 2010 year severe coral bleaching event Fig. 2.2 (i) Suggest how percentage coral cover may be measured on a coral reef. … … … … [2] (ii) Explain why the hypothesis that coral reef communities do not recover from a bleaching event is not supported by the results shown in Fig. 2.2. … … … … [2] (iii) Use information from Fig. 2.2 to suggest a reason for the changes in density of herbivorous fish. … … [1] [Total: 11]

11 marks

Mark scheme: 2(a) mutualistic / mutualism ; 1 2(b)(i) increase in algae (cover) ; decrease in coral (cover) ; decrease in number of fish (species) ; 3 2(b)(ii) any two of algae block light (to zooxanthellae) ; (which) prevents photosynthesis ; prevent settlement of new coral ; prevent polyps from feeding / blocks mouths of polyps ; 2 2(c)(i) idea of, counting / estimate / calculate (%) cover ; any one of idea of, quadrats ; appropriate sample area (e.g. per m2) ; ref. to how placed – transect / random ; idea of, repeats + calculating mean ; 2 2(c)(ii) idea of, species present is similar to previous levels / AW ; idea of, coral cover returns to (nearly) previous levels / AW ; idea of, fish returns to (nearly) previous levels / AW ; idea of, algae cover returns to previous levels / AW ; 2 2(c)(iii) fish eat algae (so as algae changes, fish density changes) ; 1 A clear description that shows the data of fish and algae are correlated

This question in 9693/23 May/June 2018

3 (a) Describe how a tropical cyclone develops. … … … … … … … … … … [5] (b) Explain the meaning of the terms ecosystem and biodiversity. … … … … … … … … … … [5] (c) Outline how mangroves protect tropical coastlines. … … … … … … … … … … [5] [Total: 15]

15 marks

Mark scheme: 3(a) any five of sea surface (temperature) at least 26.5 °C / 80 °F ; low (air) pressure / low (air) pressure system ; minimum sea depth of 50 m ; idea of, sufficiently far from equator to provide spin or twist / Coriolis effect ; idea of, rotating winds OR winds from different directions ; evaporation ; (gives rise to warm) moist air ; (air) rises and cools OR rises and draws in/up cooler air ; condensation ; release of latent heat ; idea of, this energy perpetuates cyclone further ; low wind-shear ; 5 A sea at least 26.5 °C A warm water at surface warm sea water unqualified is insufficient A circling / spiralling I strong wind unqualified Question Answer Marks Guidance 3(b) any five of ecosystem interaction between ; (community of) living organisms AND non-living components / biotic AND abiotic factors ; linked through, nutrient cycles ; (and) movement of, energy / nutrients, through, food chains / food webs ; biodiversity ref. number of species ; idea of, ref. evenness / relative abundance of each / AW ; (in an) ecosystem / habitat ; 5 3(c) any five of idea of, mangroves live in intertidal regions / delta regions / salt tolerant ; idea of, interlocking / thick / complex, root (system) ; idea of, protect from wave (action) ; energy dissipation ; reduction in, current / flow, speed ; reduce erosion ; increase sedimentation / fine sediment accumulates ; AVP ; 5 e.g. ref. extreme events

This question in 9693/23 May/June 2018

4 The Humboldt Current off the coasts of Chile and Peru causes upwelling. This supports huge shoals of the Peruvian anchoveta, which provide the greatest catches of any fish species. (a) Explain how upwelling supports large numbers of fish. … … … … … … … … … … [5] (b) Discuss the advantages of shoaling in fish such as the Peruvian anchoveta. … … … … … … … … … … [5] (c) Describe the causes of El Niño events. Explain how such an event may result in the collapse of the Peruvian anchoveta population. … … … … … … … … … … [5] [Total: 15]

15 marks

Mark scheme: 4(a) any five of nutrient rich water ; ref. named nutrient ; rise up from depth / upwellings ; idea of, replenishing nutrients in surface ; stimulates growth / reproduction of phytoplankton / producers ; increases productivity ; increase food / energy / (zoo)plankton, for fish (such as anchoveta) ; 5 Question Answer Marks Guidance 4(b) any five of successful strategy for feeding / helps feeding ; by, idea of, more eyes to spot the food ; by, idea of, corralling prey / splitting up schools of prey fish / break-up bait balls ; successful predator avoidance / helps avoid predation / reduces predation ; by, idea of, more eyes to spot the predators ; by, idea of, large numbers will confuse predator ; by, idea of less chance of predation on an individual / forming a bait ball ; successful strategy for reproduction / assists in reproduction / easier reproduction ; due to, proximity of mates / increased chance of finding a mate / easier to find a mate ; increase chance of fertilisation ; (increase) hydrodynamic efficiency / reduce drag ; saves energy / increase swimming speed (for same amount of energy) ; 5 Question Answer Marks Guidance 4(c) any five of winds reverse / change direction ; decreased wind from E / change in trade winds ; less upwelling ; ref. warmer (surface) water (over Humboldt Current) ; lowers thermocline / thermocline found deeper in ocean ; prevents nutrient rich water reaching surface / less nutrients at surface ; reduction in phytoplankton / productivity ; decreased zooplankton / decreased food source (for anchoveta) ; increased rainfall ; (may) alter nutrient availability / salinity ; reduction in light energy ; 5

This question in 9693/23 May/June 2018

4 (a) Hydrothermal vent communities are areas of higher productivity than the surrounding areas. (i) State the meaning of the term community. … … … … [2] (ii) Describe how hydrothermal vents are formed. … … … … … … … … … … [5] (b) At hydrothermal vents, there is a mutualistic relationship between hydrothermal vent bacteria and tubeworms. Tropical coral polyps and zooxanthellae also have a mutualistic relationship. Discuss the similarities and differences between these two relationships. similarities … … … … … … … … differences … … … … … … … … [8] [Total: 15]

15 marks

This question in 9693/20 Oct/Nov 2018

3 (a) (i) Define the term ecological niche. … … … … [2] (ii) With reference to one named example, explain why some marine habitats contain narrow ecological niches. … … … … … … … … [4] (b) (i) Describe two ways in which energy is made available to food chains. … … … … … … … … … … [5] (ii) As energy is passed along a food chain, only about 10% of the energy is transferred to the next trophic level. Explain why energy is lost as it is passed along a food chain. … … … … … … … … [4] [Total: 15]

15 marks

Mark scheme: 3(a)(i) the role of an organism ; in an ecosystem / habitat ; 2 I environment 3(a)(ii) any 4 from: 1 a suitable named marine habitat ; 2 suitable named marine organism e.g. butterfly fish / Tevnia / Riftia / parrot fish / zooxanthellae ; 3 (occur in habitats / ecosystems with) high biodiversity / many different species ; 4 high degree of competition between organisms ; 5 (idea of narrow) niches, prevent overlap / reduce competition ; 6 ref. to specialist feeders / only eats coral / may only feed on one type of food ; 4 3(b)(i) any 5 of: MP2,3,8 could be awarded from correct PS equation 1 photosynthesis / photosynthetic ; 2 use (energy from) (sun)light ; 3 converts carbon dioxide and water ; 4 chemosynthesis / chemosynthetic ; 5 use chemical energy ; 6 (of dissolved) minerals / hydrogen sulfide / methane ; 7 idea of, products (of either process) storing (chemical) energy ; 8 into glucose ; 9 ref. to (primary) production / (named) producers ; 5 Max of 4 if only discussing photosynthesis / chemosynthesis I sun alone R making energy Question Answer Marks Guidance 3(b)(ii) any 4 of: (In organisms being eaten:) some (energy) lost in respiration / as heat ; ref. to use of energy ; (energy) lost in urine / excretion ; (in transfer to consumer:) not all organisms are eaten ; consumer does not eat all parts when feeding ; (energy from undigested / unabsorbed material) lost in faeces / egestion ; (energy) is passed through waste / death, to decomposer / AW ; 4 A any named process that uses energy

This question in 9693/21 May/June 2019

1 Predator-prey relationships are important to maintain a healthy balance of populations within ecosystems. (a) Define the term predator. … … … … [2] (b) Researchers measured the percentage live coral cover in a representative area of the Great Barrier Reef, eastern Australia, each year between 1987 and 2017. They also measured the abundance of the crown-of-thorns starfish (COTS), which feeds on coral. This was done by towing a diver behind a boat over a measured distance. The diver recorded the number of COTS seen per tow. This was not carried out every year. The results are shown in Fig. 1.1. 12 100 10 80 8 percentage COTS live coral per cover 60 6 tow 40 4 20 2 0 1985 1990 1995 2000 2005 2010 2015 2020 year Fig. 1.1 (i) Use Fig. 1.1 to describe the changes in percentage live coral cover between 1996 and 2005. … … … … [2] (ii) Use Fig. 1.1 to explain how populations of coral and COTS are interrelated. … … … … [2] (c) Lionfish are predators that normally live in the Indo-Pacific Ocean. They have recently been introduced to Caribbean coral reefs. Their populations have increased and spread greatly, partly because they have no natural predators in these areas. Lionfish have reduced the number of small reef fish by up to 95% on some reefs. Attempts to eradicate the lionfish have all failed. (i) Suggest the outcomes if there was no attempt to control the number of lionfish. … … … … [2] (ii) A group of biologists have suggested the following hypothesis. Spearfishing of lionfish will reduce their number and therefore prevent the decline in the number of small reef fish. Fig. 1.2 shows the results of lionfish control by spearfishing on the number of small reef fish, on a small experimental area of reef from December 2009 to June 2011. increasing lionfish controlled by spearfishing number of small stable reef fish decreasing no control of lionfish Dec 2009 Jun 2010 Dec 2010 Jun 2011 month Fig. 1.2 Explain how the results of the experiment support the hypothesis. … … … … [2] [Total: 10]

10 marks

Mark scheme: 1(a) (animal) that, hunts / captures / traps / kills ; eats / consumes / feeds on, other, animals / prey / consumers / named animal ; 2 1(b)(i) (rapid) drop / fall ; 80% to 14% / by 66% ; 2 I describing all of the points A 81% to 14% / by 67% A other manipulation of data 1(b)(ii) any two from increase in COTS causes fall in % live coral cover ; (decrease in coral cover) causes decrease in COTS ; (decrease in COTS) which allows increase in % live coral cover ; idea of, COTS population response lagging slightly behind coral ; 2 1(c)(i) any two from small reef fish lost / eradicated ; ref. eventual decline in lionfish ; description of impacts on other species ; 2 I small reef fish decrease / decline 1(c)(ii) removal of lionfish allows increase in small reef fish numbers ; number of small reef fish continue to decline if no control ; 2

This question in 9693/22 May/June 2019

2 Fish in the open ocean ecosystems are dependent on complex plankton-based food webs with many trophic levels. Periodic upwelling of nutrient-rich water leads to plankton blooms, with high productivity. (a) Explain the meaning of the term productivity. … … … … [2] (b) The efficiency of energy transfer between each trophic level in a plankton-based food chain in the Bay of Naples was measured during a plankton bloom and during a normal period. The results are shown in Table 2.1. Table 2.1 percentage efficiency of energy transfer trophic level transfer during plankton bloom during normal period from 1 to 2 22 22 from 2 to 3 20 24 from 3 to 4 20 13 from 4 to 5 21 12 (i) Plot a bar graph of the data shown in Table 2.1. [5] (ii) Use Table 2.1 and your bar graph to describe the changes in efficiency of energy transfer between trophic levels as energy flows along the food chain during a normal period. … … … … [2] (iii) Suggest why there is a lower efficiency of energy transfer from trophic levels 4 to 5 during a normal period compared to during a plankton bloom. … … [1] [Total: 10]

10 marks

Mark scheme: 2(a) ref. new biomass ; ref. rate / quantity ; 2 2(b)(i) both axes labelled ; I axis orientation all bars plotted correctly (± ½ small square) ; bars same width and equidistant between groups ; scale: bars to cover at least half grid, linear scale y-axis ; key to label bars ; 5 within group, bars can touch but between groups bars must not touch if line graph plotted, max 4, MP1, 2, 4 and 5 2(b)(ii) any two from initial increase / (approx.) constant ; then falls (to approx. constant value) ; manipulate figures 22 / 24 to 13 / 12 ; 2 2(b)(iii) any one from food more widespread ; differences in feeding efficiency ; less energy used up in hunting ; AVP ; 1

This question in 9693/22 May/June 2019

1 Predator-prey relationships are important to maintain a healthy balance of populations within ecosystems. (a) Define the term predator. … … … … [2] (b) Researchers measured the percentage live coral cover in a representative area of the Great Barrier Reef, eastern Australia, each year between 1987 and 2017. They also measured the abundance of the crown-of-thorns starfish (COTS), which feeds on coral. This was done by towing a diver behind a boat over a measured distance. The diver recorded the number of COTS seen per tow. This was not carried out every year. The results are shown in Fig. 1.1. 12 100 10 80 8 percentage COTS live coral per cover 60 6 tow 40 4 20 2 0 1985 1990 1995 2000 2005 2010 2015 2020 year Fig. 1.1 (i) Use Fig. 1.1 to describe the changes in percentage live coral cover between 1996 and 2005. … … … … [2] (ii) Use Fig. 1.1 to explain how populations of coral and COTS are interrelated. … … … … [2] (c) Lionfish are predators that normally live in the Indo-Pacific Ocean. They have recently been introduced to Caribbean coral reefs. Their populations have increased and spread greatly, partly because they have no natural predators in these areas. Lionfish have reduced the number of small reef fish by up to 95% on some reefs. Attempts to eradicate the lionfish have all failed. (i) Suggest the outcomes if there was no attempt to control the number of lionfish. … … … … [2] (ii) A group of biologists have suggested the following hypothesis. Spearfishing of lionfish will reduce their number and therefore prevent the decline in the number of small reef fish. Fig. 1.2 shows the results of lionfish control by spearfishing on the number of small reef fish, on a small experimental area of reef from December 2009 to June 2011. increasing lionfish controlled by spearfishing number of small stable reef fish decreasing no control of lionfish Dec 2009 Jun 2010 Dec 2010 Jun 2011 month Fig. 1.2 Explain how the results of the experiment support the hypothesis. … … … … [2] [Total: 10]

10 marks

Mark scheme: 1(a) (animal) that, hunts / captures / traps / kills ; eats / consumes / feeds on, other, animals / prey / consumers / named animal ; 2 1(b)(i) (rapid) drop / fall ; 80% to 14% / by 66% ; 2 I describing all of the points A 81% to 14% / by 67% A other manipulation of data 1(b)(ii) any two from increase in COTS causes fall in % live coral cover ; (decrease in coral cover) causes decrease in COTS ; (decrease in COTS) which allows increase in % live coral cover ; idea of, COTS population response lagging slightly behind coral ; 2 1(c)(i) any two from small reef fish lost / eradicated ; ref. eventual decline in lionfish ; description of impacts on other species ; 2 I small reef fish decrease / decline 1(c)(ii) removal of lionfish allows increase in small reef fish numbers ; number of small reef fish continue to decline if no control ; 2

This question in 9693/23 May/June 2019

2 Fish in the open ocean ecosystems are dependent on complex plankton-based food webs with many trophic levels. Periodic upwelling of nutrient-rich water leads to plankton blooms, with high productivity. (a) Explain the meaning of the term productivity. … … … … [2] (b) The efficiency of energy transfer between each trophic level in a plankton-based food chain in the Bay of Naples was measured during a plankton bloom and during a normal period. The results are shown in Table 2.1. Table 2.1 percentage efficiency of energy transfer trophic level transfer during plankton bloom during normal period from 1 to 2 22 22 from 2 to 3 20 24 from 3 to 4 20 13 from 4 to 5 21 12 (i) Plot a bar graph of the data shown in Table 2.1. [5] (ii) Use Table 2.1 and your bar graph to describe the changes in efficiency of energy transfer between trophic levels as energy flows along the food chain during a normal period. … … … … [2] (iii) Suggest why there is a lower efficiency of energy transfer from trophic levels 4 to 5 during a normal period compared to during a plankton bloom. … … [1] [Total: 10]

10 marks

Mark scheme: 2(a) ref. new biomass ; ref. rate / quantity ; 2 2(b)(i) both axes labelled ; I axis orientation all bars plotted correctly (± ½ small square) ; bars same width and equidistant between groups ; scale: bars to cover at least half grid, linear scale y-axis ; key to label bars ; 5 within group, bars can touch but between groups bars must not touch if line graph plotted, max 4, MP1, 2, 4 and 5 2(b)(ii) any two from initial increase / (approx.) constant ; then falls (to approx. constant value) ; manipulate figures 22 / 24 to 13 / 12 ; 2 2(b)(iii) any one from food more widespread ; differences in feeding efficiency ; less energy used up in hunting ; AVP ; 1

This question in 9693/23 May/June 2019

3 Tuna and sardines are examples of fish that survive in the open ocean. (a) Research has shown that the populations of tuna and sardines have fluctuated greatly over the last 500 years, showing periods of rapid decline and then subsequent recovery. Explain how in some years upwelling may cause the population sizes of tuna and sardines to increase and not in other years. … … … … … … … … [4] (b) Both tuna and sardines use shoaling as a survival strategy in the open ocean. Compare the benefits of shoaling to tuna and to sardines. … … … … … … … … [4] (c) With reference to tuna, explain the meaning of the term parasitism. … … … … … … [3] (d) Tuna occupy a general ecological niche. Explain how a general ecological niche differs from the niche of many coral-eating butterfly fish. … … … … … … … … [4] [Total: 15]

15 marks

Mark scheme: 3(a) upwelling brings nutrient rich water nearer to surface ; increase in primary productivity in surface waters ; increase in animal populations in food chains ; more food for tuna and sardines ; AND / OR: degree of upwelling varies year on year ; reference to impact of El Niño / La Niña ; 4 3(b) any 4 from: 1 both may benefit from increased chance of reproductive success ; 2 idea of, both may benefit from increased hydrodynamic efficiency ; 3 sardines (are prey to various predators so benefit from) safety in numbers ; 4 due to lower probability of predation / ability to respond to each other’s movements ; 5 Tuna may benefit from increased predation efficiency ; 6 due to scattering of prey / increased chance of isolating prey ; 4 3(c) when one organism lives on or in another ; for its non-mutual benefit / benefiting at the expense of the other ; such as nematode worms in tuna ; 3 Question Answer Marks 3(d) any 4 from : 1 tuna live in more than one habitat / described ; 2 tuna feed on a wide range of prey ; 3 butterfly fish have a specialised niche ; 4 eat only, coral / one type of food ; 5 live only on coral reefs ; 6 niche is an organism's role in an ecosystem ; 4

This question in 9693/22 May/June 2020

3 Tuna and sardines are examples of fish that survive in the open ocean. (a) Research has shown that the populations of tuna and sardines have fluctuated greatly over the last 500 years, showing periods of rapid decline and then subsequent recovery. Explain how in some years upwelling may cause the population sizes of tuna and sardines to increase and not in other years. … … … … … … … … [4] (b) Both tuna and sardines use shoaling as a survival strategy in the open ocean. Compare the benefits of shoaling to tuna and to sardines. … … … … … … … … [4] (c) With reference to tuna, explain the meaning of the term parasitism. … … … … … … [3] (d) Tuna occupy a general ecological niche. Explain how a general ecological niche differs from the niche of many coral-eating butterfly fish. … … … … … … … … [4] [Total: 15]

15 marks

Mark scheme: 3(a) any 3 from: upwelling brings nutrient rich water nearer to surface ; 4 increase in primary productivity in surface waters ; increase in animal populations in food chains ; more food for tuna and sardines ; AND / OR: degree of upwelling varies year on year ; reference to impact of El Niño / La Niña ; 3(b) any 4 from: 4 1 both may benefit from increased chance of reproductive success ; 2 idea of, both may benefit from increased hydrodynamic efficiency ; 3 sardines (are prey to various predators so benefit from) safety in numbers ; 4 due to lower probability of predation / ability to respond to each other’s movements ; 5 Tuna may benefit from increased predation efficiency ; 6 due to scattering of prey / increased chance of isolating prey ; 3(c) when one organism lives on or in another ; 3 for its non-mutual benefit / benefiting at the expense of the other ; such as nematode worms in tuna ; 3(d) any 4 from : 4 1 tuna live in more than one habitat / described ; 2 tuna feed on a wide range of prey ; 3 butterfly fish have a specialised niche ; 4 eat only, coral / one type of food ; 5 live only on coral reefs ; 6 niche is an organism's role in an ecosystem ;

This question in 9693/23 May/June 2020

2 Zostera marina is a species of seagrass. Macroalgae are seaweeds. Z. marina and macroalgae are producers that can grow in the same habitat. A scientist noticed that the distribution of Z. marina and macroalgae varied greatly within a single large estuary. Different areas of the estuary varied in their nitrogen input levels. The scientist measured the biomass of each producer and the nitrogen inputs in each area. Table 2.1 shows the biomass of the two producers for different nitrogen input levels. Table 2.1 nitrogen input biomass of biomass of /kg per hectare per year Z. marina macroalgae /g per m2 /g per m2 0 48 53 300 2 116 400 2 174 (a) Plot a bar chart to show the effect of nitrogen input on the biomass of Z. marina and macroalgae. [5] (b) A student developed the following hypothesis. Nitrogen input decreases the growth of Z. marina in the presence of macroalgae. Discuss the extent to which the data in Table 2.1 supports this hypothesis. … … … … … … [3] (c) Macroalgae and Z. marina are photosynthetic. Z. marina can grow to a height of 15 cm. Macroalgae can grow to a height of 175 cm. Use this information to explain why the biomass of Z. marina decreases in conditions of high nitrogen input, when growing in the presence of macroalgae. … … … … [2] [Total: 10]

10 marks

This question in 9693/20 Oct/Nov 2020

1 Cleaner fish feed on parasites attached to other fish. (a) State why this interrelationship is an example of mutualism. … … [1] Sharknose gobies, Elacatinus evelynae, are a species of cleaner fish that are found around tropical coral reefs. Scientists investigated the cleaning behaviour of sharknose gobies on one reef over eight years. Each year they recorded: • the total number of reef fish species present • the number of fish species that were cleaned by sharknose gobies. From the data, they calculated the percentage of species on the reef that were cleaned by sharknose gobies. The results are shown in Fig. 1.1. Key percentage of fish species 80 80 cleaned total number 70 70 of fish species on reef 60 60 50 50 total number percentage of fish of fish species species cleaned by 40 40 present on reef sharknose gobies 30 30 20 20 10 10 0 0 2010 2011 2012 2013 2014 2015 2016 2017 year Fig. 1.1 (b) Describe the changes in the number of fish species on the reef between 2010 and 2017. Use the data shown in Fig. 1.1 to support your answer. … … … … … … [3] (c) (i) In 2016, 24 fish species were cleaned by sharknose gobies on the reef. Use Fig. 1.1 to calculate the percentage of fish species on the reef that were cleaned by sharknose gobies in 2016. … % [3] (ii) Use your answer to (c)(i) to draw a bar on Fig. 1.1 to show the percentage of fish species cleaned in 2016. [1] (d) (i) The scientists were investigating the following hypothesis: When the total number of fish species present on the reef increases, the percentage of fish species cleaned by sharknose gobies increases. Use Fig. 1.1 to explain why this hypothesis was rejected. … … … … [2] (ii) Suggest why there are differences in the percentage of fish species cleaned by sharknose gobies each year. … … … … [2] [Total: 12]

12 marks

Mark scheme: 1(a) both, (species / organisms) benefit ; 1 1(b) any 3 of: (idea of) overall increase (from 2010 to 2016 / 2017) ; slight decrease from 2012–2013 ; (idea of) (sudden) decrease in 2017 / from 2016 AW ; (idea of) greatest increase between 2015–2016 ; correct manipulation of data ; 3 1(c)(i) 31.(1688) correct rounding ;;; 3 1(c)(ii) bar correctly plotted for answer from 1(c)(i), both height and width drawn on Fig. 1.1 ; 1 1(d)(i) any 2 of: (idea of) no apparent / negative, correlation ; correct, description / explanation, of why it is rejected ; correct use of data to support answer ; 2 1(d)(ii) any 2 of: sharknose goby / the cleaner fish, may have species preferences ; other cleaner fish may have relationship with new species appearing ; population (density) of cleaner fish may vary ; so more than enough clients AW ; not all species visit cleaning stations ; the (visiting) number of fish species may have changed ; disease/ decrease, in the number of parasites ; 2

This question in 9693/21 May/June 2021

1 Scientists investigated the effect of red grouper and lionfish on the numbers of juvenile fish in an area of sea bed. Red grouper feed mainly on marine invertebrates. They often live in natural hollows in the sea bed which also act as nurseries for juvenile fish. Lionfish have been introduced into this area by humans and feed mainly on juvenile fish. Red grouper and lionfish do not consume each other. The scientists randomly assigned sixteen natural hollows of equal size to one of four treatments: • no red grouper or lionfish present • one lionfish present • one red grouper present • one red grouper and one lionfish present. The percentage change in the numbers of juvenile fish in each hollow was calculated every week for 6 weeks. Fig. 1.1 shows the results of this investigation. (a) Describe the effect of the following on the percentage change of juvenile fish numbers. Use the data in Fig. 1.1 to support your answer. one lionfish present … … … … one red grouper present … … … … [4] (b) The scientists concluded that the presence of red grouper reduces the effect of lionfish on the numbers of juvenile fish. Explain whether the results in Fig. 1.1 support this conclusion. … … [1] (c) The scientists calculated the percentage of juvenile fish and shrimp in the diet of the lionfish when red grouper were present and absent. Table 1.1 shows the composition of the diet of the lionfish. Table 1.1 percentage composition of lionfish diet red grouper juvenile fish shrimp present 43 57 absent 78 22 (d) Discuss the extent to which the whole investigation supports the idea that red grouper presence increases biodiversity. … … … … … … [3] [Total: 13]

13 marks

Mark scheme: 1(a) one lionfish present causes (large) decrease in juvenile fish number ; decreases by 90% (after 6 weeks) ; one red grouper present causes (large) increase in juvenile fish number ; increases by 110% (after 6 weeks) ; 4 1(b) Yes because… presence of red grouper seems to reduce impact of Lionfish (predation) on juvenile fish ; presence of red grouper may also deter other predators of juvenile fish : 1 1(c)(i) Axes: labels correct for both axes ; Scale : y axis allows bars to cover at least half of grid ; Bars: correctly plotted ±1 / 2 small square ; Bars: equal in width and not touching ; 4 1(c)(ii) generalist / generalised niche ; 1 1(d) any 3 from: supports idea as more juvenile fish present ; idea not supported by decrease in shrimp species ; no information on, other invertebrates / other predators ; no information on relative abundance ; only one study ; results may be different in other habitats ; 3

This question in 9693/22 May/June 2021

4 (a) Describe how abyssal plains form on the sea bed. … … … … … … [3] (b) Marine snow is the remains of dead organisms and faeces that sink to the abyssal plain from above. (i) Explain why most food chains on the abyssal plain depend on marine snow as a source of energy. … … … … … … … … [4] (ii) Marine snow also provides nutrients for organisms living on the abyssal plain. State the roles of different named examples of nutrients in marine organisms. … … … … … … … … … … … … … … … … [8] [Total: 15]

15 marks

Mark scheme: 4(a) any 3 from: between mid-ocean ridges and continental rise ; upwards movement of molten material / magma ; which solidifies and forms new ocean crust ; ref. mantle convection ; uneven rock surface becomes covered by sediments from above ; Question Answer Marks 4(b)(i) any 4 from: absence of light (on deep ocean floor) ; absence of photosynthetic organisms ; lack of primary productivity / synthesis of organic molecules by producers ; cold temperatures ; limited input from chemosynthesis ; 4 4(b)(ii) any 8 from: (source of) nitrogen ; required for protein synthesis / amino acids / DNA / RNA / ATP ; (source of) calcium ; required for bones / shells ; (source of) phosphorus ; required for bone / DNA / RNA / ATP ; (source of) carbon ; (required for) organic molecules ; (source of) magnesium ; required for chlorophyll / bones ; other correct named example ; other correct use ; 8

This question in 9693/22 May/June 2021

1 Scientists investigated the effect of red grouper and lionfish on the numbers of juvenile fish in an area of sea bed. Red grouper feed mainly on marine invertebrates. They often live in natural hollows in the sea bed which also act as nurseries for juvenile fish. Lionfish have been introduced into this area by humans and feed mainly on juvenile fish. Red grouper and lionfish do not consume each other. The scientists randomly assigned sixteen natural hollows of equal size to one of four treatments: • no red grouper or lionfish present • one lionfish present • one red grouper present • one red grouper and one lionfish present. The percentage change in the numbers of juvenile fish in each hollow was calculated every week for 6 weeks. Fig. 1.1 shows the results of this investigation. (a) Describe the effect of the following on the percentage change of juvenile fish numbers. Use the data in Fig. 1.1 to support your answer. one lionfish present … … … … one red grouper present … … … … [4] (b) The scientists concluded that the presence of red grouper reduces the effect of lionfish on the numbers of juvenile fish. Explain whether the results in Fig. 1.1 support this conclusion. … … [1] (c) The scientists calculated the percentage of juvenile fish and shrimp in the diet of the lionfish when red grouper were present and absent. Table 1.1 shows the composition of the diet of the lionfish. Table 1.1 percentage composition of lionfish diet red grouper juvenile fish shrimp present 43 57 absent 78 22 (d) Discuss the extent to which the whole investigation supports the idea that red grouper presence increases biodiversity. … … … … … … [3] [Total: 13]

13 marks

Mark scheme: 1(a) one lionfish present causes (large) decrease in juvenile fish number ; decreases by 90% (after 6 weeks) ; one red grouper present causes (large) increase in juvenile fish number ; increases by 110% (after 6 weeks) ; 4 1(b) Yes because… presence of red grouper seems to reduce impact of Lionfish (predation) on juvenile fish ; presence of red grouper may also deter other predators of juvenile fish : 1 1(c)(i) Axes: labels correct for both axes ; Scale : y axis allows bars to cover at least half of grid ; Bars: correctly plotted ±1 / 2 small square ; Bars: equal in width and not touching ; 4 1(c)(ii) generalist / generalised niche ; 1 1(d) any 3 from: supports idea as more juvenile fish present ; idea not supported by decrease in shrimp species ; no information on, other invertebrates / other predators ; no information on relative abundance ; only one study ; results may be different in other habitats ; 3

This question in 9693/23 May/June 2021

4 (a) Describe how abyssal plains form on the sea bed. … … … … … … [3] (b) Marine snow is the remains of dead organisms and faeces that sink to the abyssal plain from above. (i) Explain why most food chains on the abyssal plain depend on marine snow as a source of energy. … … … … … … … … [4] (ii) Marine snow also provides nutrients for organisms living on the abyssal plain. State the roles of different named examples of nutrients in marine organisms. … … … … … … … … … … … … … … … … [8] [Total: 15]

15 marks

Mark scheme: 4(a) any 3 from: between mid-ocean ridges and continental rise ; upwards movement of molten material / magma ; which solidifies and forms new ocean crust ; ref. mantle convection ; uneven rock surface becomes covered by sediments from above ; Question Answer Marks 4(b)(i) any 4 from: absence of light (on deep ocean floor) ; absence of photosynthetic organisms ; lack of primary productivity / synthesis of organic molecules by producers ; cold temperatures ; limited input from chemosynthesis ; 4 4(b)(ii) any 8 from: (source of) nitrogen ; required for protein synthesis / amino acids / DNA / RNA / ATP ; (source of) calcium ; required for bones / shells ; (source of) phosphorus ; required for bone / DNA / RNA / ATP ; (source of) carbon ; (required for) organic molecules ; (source of) magnesium ; required for chlorophyll / bones ; other correct named example ; other correct use ; 8

This question in 9693/23 May/June 2021

2 An investigation was carried out to compare the effect of cleaner fish on a species of damselfish. The cleaner fish remove external parasites from the damselfish at cleaning stations. Damselfish live in shallow-water fringing reefs. They defend their exclusive territories from other damselfish. A number of damselfish were observed at sites around each of six different islands, H to M. At each island site half of the damselfish had a cleaning station in their territory. The other half of the damselfish had no cleaning station in their territory. This is shown for one island in Fig. 2.1. island Key individual damselfish territories cleaning stations Fig. 2.1 The damselfish were collected for examination and the number of external parasites on each damselfish was counted. The mean number of external parasites per damselfish was calculated. Fig. 2.2 shows the results of the investigation. 4 3 Key (10)(10) = cleaning mean number (8)(8) station in the territoryof external 2 parasites = per no cleaning damselfish station in the (6)(6) territory 1 (10)(10) (11)(11) (13)(13) (number) = (9)(9) (8)(8) number of (10)(10) (9)(9) damselfish collected 0 H I J K L M island Fig. 2.2 (a) The data for island K are shown in Table 2.1. Table 2.1 total number total number of mean number of of damselfish external parasites external parasites collected found per damselfish damselfish with 12 8 cleaning stations … damselfish without 13 22 cleaning stations … (i) Calculate the mean number of external parasites per damselfish for damselfish with cleaning stations and damselfish without cleaning stations. Add this information to Table 2.1. [1] (ii) Use your calculated numbers from (i) to complete the graph for island K in Fig. 2.2. [2] (b) Use Fig. 2.2 to calculate the percentage difference between the mean number of external parasites on damselfish that do not have a cleaning station and those that do, for island M. Show your working. … % [3] (c) Discuss the extent to which these data support the theory that cleaner fish reduce the number of external parasites on damselfish. … … … … … … [3] (d) Suggest two other variables that may affect external parasite numbers on damselfish. 1 … 2 … [2] [Total: 11]

11 marks

This question in 9693/20 Oct/Nov 2021

4 (a) Coral polyps have a symbiotic relationship with zooxanthellae. Name and describe this relationship. … … … … … … … … [4] (b) Productivity is the rate of production of biomass in an ecosystem. Explain why coral reefs typically have a high productivity. … … … … … … … … … … [5] (c) Many fish living on coral reefs are shoaling fish. Explain why shoaling is a successful strategy for fish. … … … … … … … … … … … … [6] [Total: 15]

15 marks

This question in 9693/20 Oct/Nov 2021

4 Fig. 4.1 shows an atoll in the Indian Ocean. Atolls typically consist of a reef enclosing a central lagoon. Fig. 4.1 This atoll is mostly submerged at high tide. As the tide level falls, parts of the reef rim become exposed, largely isolating the central lagoon. Scientists collected data on the tidal height for 15 days, both in the central lagoon, and offshore in the surrounding ocean. The results of this investigation are shown in Fig. 4.2. Key offshore lagoon 2 1 tidal height relative to 0 mean / m – 1 – 2 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 day Fig. 4.2 (a) (i) Use Fig. 4.2 to determine the maximum tidal range recorded during the investigation. … … [1] (ii) Explain why the tidal range changes. Use the data in Fig. 4.2 to support your answer. … … … … … … [3] (b) Fig. 4.3 shows the tidal cycle data over one 18-hour period during the investigation. Key offshore lagoon 2 1 tidal height relative to 0 mean / m – 1 – 2 0 6 12 18 time / hours Fig. 4.3 Compare the tidal cycle of the lagoon with the tidal cycle offshore, explaining any differences. … … … … … … [3] (c) Suggest how changes in the tidal cycle may affect biotic and abiotic factors in the lagoon. … … … … … … … … … … [5] [Total: 12]

12 marks

Mark scheme: 4(a)(i) 3.9 (m) ; 1 4(a)(ii) any 3 from: ref. to gravitational pull of Moon AND Sun ; ref. to alignment of Moon AND Sun ; correct description of spring OR neap tide ; correct use of example days from data ; 3 4(b) MAX 2 from: high tide is the same time for both ; (idea of) low tide is later for lagoon / low tide has a lag time for lagoon / lagoon takes longer to adjust between high and low tides ; high tide is the same depth / height, for both ; low tide is lower for offshore / tidal range is greater offshore ORA ; PLUS at least 1 from: idea that water is trapped inside lagoon / takes time to drain away ; idea that not all water leaves lagoon before tide turns ; rate of water flow into the lagoon (after low tide) is greater than offshore ; rate of change of tide height is greater for the lagoon than offshore ; offshore tide needs to be high enough to re-enter the lagoon ; 3 Question Answer Marks 4(c) any 5 from: abiotic factors: 1 higher tides will allow greater mixing of ocean and lagoon water / ORA ; 2 (may affect) mixing of nutrients ; 3 (may affect) temperature of lagoon water ; 4 (may affect) salinity of lagoon due, to evaporation (at low tide) / influx of sea water at high tide ; 5 (reef) erosion ; 6 change in atoll shape / movement of sand / sediments / morphology of lagoon ; 7 correct ref. to light intensity ; 8 change in oxygen / carbon dioxide, levels / concentration; biotic factors: 9 lower tides will result in reef acting as barrier to organisms ; 10 ability of predators to enter or exit lagoon / prey will need to avoid predators ; 11 (at low tide) food availability changes e.g. may affect ability of zooplankton / phytoplankton to enter lagoon ; 12 (may affect) ability of larvae to enter / leave lagoon ; 13 (idea of) desiccation of corals / organisms ; 14 damage to vegetation ; 15 competition increases as more species enter lagoon at high tide ; 5

This question in 9693/21 May/June 2022

4 Parma victoriae is a species of fish living on rocky reefs. They are highly territorial, aggressively defending their territory from other fish. Scientists investigated the factors affecting the number of aggressive attacks by P. victoriae. Table 4.1 shows the number of aggressive encounters recorded with various types of other fish. The food source and population density of each species (measured as mean number of fish per 500 m2) is also shown. Table 4.1 species of fish food source population number of density of aggressive species encounters with / mean number P. victoriae per 500 m2 Caesioperca rasor zooplankton 84.0 12 Cheilodactylus nigripes carnivore 6.6 4 Dactylosargus herbivore 0.6 3 arctidens Meuschenia herbivore 16.2 41 flavolineata Meuschenia freycineti herbivore 1.2 2 Meuschenia herbivore 8.4 29 hippocrepis Parma victoriae herbivore 30.4 61 Penicipelta vittiger herbivore 8.6 18 Pseudolabrus tetricus carnivore 27.1 3 Scorpis aequipinnis omnivore 10.8 11 Upeneichthys lineatus carnivore 5.8 2 (a) Use Table 4.1 to state the number of aggressive encounters due to intra-specific competition. Explain your answer. … … … … [2] (i) The scientist decided that a firm conclusion could not be drawn from the data. Use the data in Fig. 4.1 to explain the scientist’s decision. … … … … [2] (ii) To analyse the data further the scientists used Spearman’s rank correlation (rs) to decide if there was a correlation between the two variables. Explain why they chose Spearman’s rank correlation to analyse the data further. … … … … [2] (iii) The calculation for Spearman’s rank correlation (rs) uses the following equation: 2 6 # / D rs = 1 – 3 f n - n p where, / = sum of (total) n = number of pairs of items in the sample D = difference in rank between each pair of measurements Table 4.2 shows the scientists’ calculations of D and D2. Table 4.2 population density aggressive encounters species number per rank number rank D D2 500 m2 Caesioperca rasor 84.0 1 12 5 4 16 Cheilodactylus nigripes 6.60 8 4 7 1 1 Dactylosargus arctidens 0.600 11 3 8.5 2.5 6.25 Meuschenia flavolineata 16.2 4 41 2 2 4 Meuschenia freycineti 1.20 10 2 10.5 0.5 0.25 Meuschenia hippocrepis 8.40 7 29 3 4 16 Parma victoriae 30.4 2 61 1 1 1 Penicipelta vittiger 8.60 6 18 4 2 4 Pseudolabrus tetricus 27.1 3 3 8.5 5.5 30.3 Scorpis aequipinnis 10.8 5 11 6 1 1 Upeneichthys lineatus 5.80 9 2 10.5 1.5 2.25 Use the information in Table 4.2 and the equation to calculate a value for rs. Show your working. Give your answer to 3 significant figures. rs = … [5] (iv) What does your calculated value for rs tell you about the original hypothesis? … … [1] (c) Suggest what other factors, apart from population density, may be affecting the number of aggressive encounters by P. victoriae. … … … … … … [4] [Total: 16]

16 marks

Mark scheme: 4(a) 61 ; involves competition with the same species ; 2 4(b)(i) overall pattern / correlation is not clear ; use of data to illustrate e.g. Caesioperca rasor / outlier / anomaly plot at 12, 84 2 4(b)(ii) provides an (statistical) analysis of strength / degree of correlation / AW ; by comparing rank order of the two variables / AW ; 2 4(b)(iii) sum D2 = 82.05 and n = 11 ; 6  82.05 = 492.3 and 113 – 11 = 1320 ; 492 / 1320 = 0.37295 ; 1 – 0.37295 = 0.62705 ; correct application of 3 sig figs to calculated answer ; 5 Question Answer Marks 4(b)(iv) answer must be marked in the light of their calculated answer to 4(b)(iii) hypothesis can be accepted – calculated answer is closer to 1 than 0 ; weak positive correlation ; 1 4(c) any four from: more encounters may occur with direct feeding competitors ; example used e.g. highest encounters with other (named) herbivores / lower encounters with (named) plankton feeder or carnivore or omnivore ; more encounters may occur due to courtship / breeding relationships ; because highest encounters are intra-specific ; number of encounters may vary with varying territory size ; number of encounters may vary with varying number of adjacent territories ; AVP ; 4

This question in 9693/22 May/June 2022

4 Parma victoriae is a species of fish living on rocky reefs. They are highly territorial, aggressively defending their territory from other fish. Scientists investigated the factors affecting the number of aggressive attacks by P. victoriae. Table 4.1 shows the number of aggressive encounters recorded with various types of other fish. The food source and population density of each species (measured as mean number of fish per 500 m2) is also shown. Table 4.1 species of fish food source population number of density of aggressive species encounters with / mean number P. victoriae per 500 m2 Caesioperca rasor zooplankton 84.0 12 Cheilodactylus nigripes carnivore 6.6 4 Dactylosargus herbivore 0.6 3 arctidens Meuschenia herbivore 16.2 41 flavolineata Meuschenia freycineti herbivore 1.2 2 Meuschenia herbivore 8.4 29 hippocrepis Parma victoriae herbivore 30.4 61 Penicipelta vittiger herbivore 8.6 18 Pseudolabrus tetricus carnivore 27.1 3 Scorpis aequipinnis omnivore 10.8 11 Upeneichthys lineatus carnivore 5.8 2 (a) Use Table 4.1 to state the number of aggressive encounters due to intra-specific competition. Explain your answer. … … … … [2] (i) The scientist decided that a firm conclusion could not be drawn from the data. Use the data in Fig. 4.1 to explain the scientist’s decision. … … … … [2] (ii) To analyse the data further the scientists used Spearman’s rank correlation (rs) to decide if there was a correlation between the two variables. Explain why they chose Spearman’s rank correlation to analyse the data further. … … … … [2] (iii) The calculation for Spearman’s rank correlation (rs) uses the following equation: 2 6 # / D rs = 1 – 3 f n - n p where, / = sum of (total) n = number of pairs of items in the sample D = difference in rank between each pair of measurements Table 4.2 shows the scientists’ calculations of D and D2. Table 4.2 population density aggressive encounters species number per rank number rank D D2 500 m2 Caesioperca rasor 84.0 1 12 5 4 16 Cheilodactylus nigripes 6.60 8 4 7 1 1 Dactylosargus arctidens 0.600 11 3 8.5 2.5 6.25 Meuschenia flavolineata 16.2 4 41 2 2 4 Meuschenia freycineti 1.20 10 2 10.5 0.5 0.25 Meuschenia hippocrepis 8.40 7 29 3 4 16 Parma victoriae 30.4 2 61 1 1 1 Penicipelta vittiger 8.60 6 18 4 2 4 Pseudolabrus tetricus 27.1 3 3 8.5 5.5 30.3 Scorpis aequipinnis 10.8 5 11 6 1 1 Upeneichthys lineatus 5.80 9 2 10.5 1.5 2.25 Use the information in Table 4.2 and the equation to calculate a value for rs. Show your working. Give your answer to 3 significant figures. rs = … [5] (iv) What does your calculated value for rs tell you about the original hypothesis? … … [1] (c) Suggest what other factors, apart from population density, may be affecting the number of aggressive encounters by P. victoriae. … … … … … … [4] [Total: 16]

16 marks

Mark scheme: 4(a) 61 ; involves competition with the same species ; 2 4(b)(i) overall pattern / correlation is not clear ; use of data to illustrate e.g. Caesioperca rasor / outlier / anomaly plot at 12, 84 ; 2 4(b)(ii) provides an (statistical) analysis of strength / degree of correlation / AW ; by comparing rank order of the two variables / AW ; 2 4(b)(iii) sum D2 = 82.05 and n = 11 ; 6  82.05 = 492.3 and 113 – 11 = 1320 ; 492 / 1320 = 0.37295 ; 1 – 0.37295 = 0.62705 ; correct application of 3 sig figs to calculated answer ; 5 Question Answer Marks 4(b)(iv) answer must be marked in the light of their calculated answer to 4(b)(iii) hypothesis can be accepted – calculated answer is closer to 1 than 0 ; weak positive correlation ; 1 4(c) any 4 from: more encounters may occur with direct feeding competitors ; example used e.g. highest encounters with other (named) herbivores / lower encounters with (named) plankton feeder or carnivore or omnivore ; more encounters may occur due to courtship / breeding relationships ; because highest encounters are intra-specific ; number of encounters may vary with varying territory size ; number of encounters may vary with varying number of adjacent territories ; AVP ; 4

This question in 9693/23 May/June 2022

4 Sandy shore ecosystems often have low biodiversity. Scientists investigated abiotic factors that affect biodiversity on sandy shores. (a) State the meaning of the term abiotic factor. … … [1] (b) The scientists investigated the relationship between the gradient of the shore, particle size and biodiversity on 12 sandy shores, A–L, at low tide. The gradient of each shore was recorded as a percentage: the higher the percentage, the steeper the gradient. The mean number of species per m2 on each shore was estimated using sampling techniques. Describe a method that could be used to sample the mean number of species per m2 present on each shore. … … … … … … … … … … [5] (c) Table 4.1 shows the data collected from the investigation. Table 4.1 shore gradient mean particle mean number of shore percentage size / μm species per m2 A 10.7 538 4.5 B 8.8 959 1.2 C 4.2 319 8.0 D 11.4 895 2.9 E 3.5 253 9.4 F 6.5 474 5.7 G 6.2 311 7.5 H 6.4 316 5.3 I 4.5 313 7.9 J 6.9 449 4.7 K 4.2 264 5.6 L 9.6 460 4.6 Fig. 4.1 is a scatter diagram showing the relationship between the mean number of species per m2 and shore gradient percentage. 10 8 mean number 6 of species per m2 4 2 3 4 5 6 7 8 9 10 11 12 shore gradient percentage Fig. 4.1 (i) Scientists used Spearman’s rank correlation (rs) to decide if there was a correlation between the mean number of species per m2 and shore gradient percentage. The calculation for Spearman’s rank correlation (rs) uses the following equation: 6 × ΣD 2 rs = 1 – ( n3 – n ) where, Σ = sum of (total) n = number of pairs of items in the sample D = difference in rank between each pair of measurements A value of 539.5 was calculated for ΣD 2. Use this value and the information in Table 4.1 to calculate the value for rs. Give your answer to two significant figures. Show your working. rs = … [3] (ii) Use your calculated value for rs in (c)(i) to describe the correlation between mean number of species per m2 and shore gradient percentage. Explain your answer. … … … … [2] (iii) Fig. 4.2 is a scatter diagram showing the relationship between mean number of species per m2 and mean particle size. 100 80 60 mean number of species per m2 40 20 0 0 100 200 300 400 500 600 700 800 900 1000 mean particle size / μm Fig. 4.2 Spearman’s rank correlation was performed again for this data and an rs value of – 0.80 was calculated. Use this value and the one calculated in part (c)(i) to discuss the effect of shore gradient percentage and particle size on the biodiversity of sandy shores. … … … … … … [3] (d) Suggest why particle size and shore gradient percentage may have an effect on the number of species per m2 found on each shore. … … … … … … … … [4] (e) Simpson’s index of diversity could be used to assess the biodiversity on each shore. Suggest why this would be a better measure of biodiversity than data used in this investigation. … … [1] [Total: 19]

19 marks

Mark scheme: 4(a) abiotic factors are non-living (factors) ; 1 4(b) any 5 of: 1 correctly linking a described method as systematic or random ; 2 transect or grid ; 3 (use of 1 m2) quadrats ; 4 place quadrat at, stated / even, intervals along the transect OR random distance apart along the transect OR random placement within a grid ; 5 ref. method of generating random locations / coordinates ; 6 remove and examine sediment / sieve sediment to obtain samples / take a core sample to examine for species ; 7 suitable reference to depth of sediment taken ; 8 counting the species / record the number of species, found in each quadrat ; 9 correct description of calculating the mean number of species per m2 ; 10 repeat same method on each, shore / coastline ; 11 reference to ethical treatment of organisms ; 12 ref. to a relevant and sensible health and safety ; 5 4(c)(i) substitution of numbers into equation ; correct answer only to any number of sig. figs. from –0.8863636363636363 to –0.89 (any rounding must be correct) ; reasonable answer expressed to 2 significant figures ; 3 Question Answer Marks 4(c)(ii) it is an, inverse / negative, (correlation) ; as the value is negative ; OR it is a strong correlation ; as value is close to (-)1 ; 2 4(c)(iii) any 3 of: the greater the slope gradient the lower the biodiversity ORA ; the greater the particle size the lower the biodiversity ORA ; awareness of correlation not meaning causation ; ref. to data only showing species number not abundance ; 3 4(d) particle size may affect: 1 ability to burrow / move ; 2 ability to, ingest food / pass food through body ; 3 moisture content of substrate OR risk of (organisms) drying out ; slope may affect: 4 drainage of water / slope affects risk of (sediment / organism) drying out ; 5 how easily, detritus / food sources, deposited ; 6 area of shore in tidal range ; 7 size / impact of wave action ; 4 4(e) takes into account number of individuals / population size (as well as number of species) / takes into account abundance (as well as number of species) ; 1

This question in 9693/21 May/June 2023

4 Fig. 4.1 shows a boxer crab with two anemones attached to its front claws. Fig. 4.1 (a) Boxer crabs and anemones show a mutualistic relationship. Explain why this relationship is an example of mutualism. … … … … [2] (b) Boxer crabs are crustaceans. State one main feature of a typical adult crustacean. … [1] (c) Anemones belong to the same phylum as corals. Name this phylum. … [1] (d) Scientists investigated the relationship between the boxer crabs and the anemones. They measured the size of the anemones on the left and right front claws on 30 crabs. Fig. 4.2 is a scatter diagram showing the results. 3.5 3 2.5 2 right anemone diameter / mm 1.5 1 0.5 0 0 0.5 1 1.5 2 2.5 3 3.5 left anemone diameter / mm Fig. 4.2 (i) Scientists applied Spearman’s rank correlation to the data. Explain why Spearman’s rank correlation is a suitable way to analyse these data. … … … … [2] (ii) Spearman’s rank correlation uses the following equation: 6 × !D 2 rs = 1 – ( n3 – n ) A value for !D 2 was calculated as 509.0 Complete the calculation for the rs value using the equation. Give your answer to two significant figures. Show your working. … [3] (iii) State a conclusion about the correlation between the anemone size on each claw. Use your calculated value for rs from (d)(ii) to support your answer. … … … … [2] (e) Scientists hypothesised that the boxer crabs controlled the size of the anemones on their claws. (i) Suggest a reason why the boxer crabs might need to control the size of the anemones. … … [1] The scientists investigated the growth over a period of 60 days of: • anemones that were attached to crab claws • anemones that had never been attached to crab claws • anemones that had been attached to crab claws but were removed. Fig. 4.3 shows the results. 5 Key day 1 day 30 4 day 60 mean 3 diameter of anemone / mm 2 1 0 anemones anemones never anemones removed attached to claws attached to claws from claws Fig. 4.3 (ii) Discuss whether the data in Fig. 4.3 support the idea that the crabs controlled the size of the anemones. … … … … … … [3] [Total: 15]

15 marks

Mark scheme: 4(a) both organisms benefit ; crab gets protection AND anemone gets food ; 2 4(b) carapace / segmented abdomen / jointed legs / two pairs of antennae ; 1 4(c) Cnidaria ; 1 4(d)(i) any 2 of: scattergram appears to show a (positive) correlation ; allows them to determine if there is a significant / strong correlation ; idea of using data that can be ranked ; 2 4(d)(ii) substitution of numbers into equation ; correct answer only to any number of sig. figs. From 0.8867630701 ; reasonable answer expressed to 2 significant figures ; 3 4(d)(iii) (strong) positive correlation ; as answer is close to 1 ; 2 4(e)(i) to keep anemones a manageable size ; 1 Question Answer Marks 4(e)(ii) any 3 of: supports idea as anemones removed grow at similar rate as anemones never attached ; (whereas) attached anemones change little in size ; however doesn’t prove crabs control this ; correlation is not causation / could be due to another factor (such as area available for attachment) ; idea of larger sample size would give firmer conclusion ; 3

This question in 9693/22 May/June 2023

4 Fig. 4.1 shows a boxer crab with two anemones attached to its front claws. Fig. 4.1 (a) Boxer crabs and anemones show a mutualistic relationship. Explain why this relationship is an example of mutualism. … … … … [2] (b) Boxer crabs are crustaceans. State one main feature of a typical adult crustacean. … [1] (c) Anemones belong to the same phylum as corals. Name this phylum. … [1] (d) Scientists investigated the relationship between the boxer crabs and the anemones. They measured the size of the anemones on the left and right front claws on 30 crabs. Fig. 4.2 is a scatter diagram showing the results. 3.5 3 2.5 2 right anemone diameter / mm 1.5 1 0.5 0 0 0.5 1 1.5 2 2.5 3 3.5 left anemone diameter / mm Fig. 4.2 (i) Scientists applied Spearman’s rank correlation to the data. Explain why Spearman’s rank correlation is a suitable way to analyse these data. … … … … [2] (ii) Spearman’s rank correlation uses the following equation: 6 × !D 2 rs = 1 – ( n3 – n ) A value for !D 2 was calculated as 509.0 Complete the calculation for the rs value using the equation. Give your answer to two significant figures. Show your working. … [3] (iii) State a conclusion about the correlation between the anemone size on each claw. Use your calculated value for rs from (d)(ii) to support your answer. … … … … [2] (e) Scientists hypothesised that the boxer crabs controlled the size of the anemones on their claws. (i) Suggest a reason why the boxer crabs might need to control the size of the anemones. … … [1] The scientists investigated the growth over a period of 60 days of: • anemones that were attached to crab claws • anemones that had never been attached to crab claws • anemones that had been attached to crab claws but were removed. Fig. 4.3 shows the results. 5 Key day 1 day 30 4 day 60 mean 3 diameter of anemone / mm 2 1 0 anemones anemones never anemones removed attached to claws attached to claws from claws Fig. 4.3 (ii) Discuss whether the data in Fig. 4.3 support the idea that the crabs controlled the size of the anemones. … … … … … … [3] [Total: 15]

15 marks

Mark scheme: 4(a) both organisms benefit ; crab gets protection AND anemone gets food ; 2 4(b) carapace / segmented abdomen / jointed legs / two pairs of antennae ; 1 4(c) Cnidaria ; 1 4(d)(i) any 2 of: scattergram appears to show a (positive) correlation ; allows them to determine if there is a significant / strong correlation ; idea of using data that can be ranked ; 2 4(d)(ii) substitution of numbers into equation ; correct answer only to any number of sig. figs. From 0.8867630701 ; reasonable answer expressed to 2 significant figures ; 3 4(d)(iii) (strong) positive correlation ; as answer is close to 1 ; 2 4(e)(i) to keep anemones a manageable size ; 1 Question Answer Marks 4(e)(ii) any 3 of: supports idea as anemones removed grow at similar rate as anemones never attached ; (whereas) attached anemones change little in size ; however doesn’t prove crabs control this ; correlation is not causation / could be due to another factor (such as area available for attachment) ; idea of larger sample size would give firmer conclusion ; 3

This question in 9693/23 May/June 2023

1 Mangrove forests are important ecosystems. (a) Explain the term ecosystem. … … … … [2] (b) Fig. 1.1 shows the area of mangrove forest in ten countries and the areas of mangrove forest that are protected and unprotected. Key protected mangrove forest unprotected mangrove forest 30 000 25 000 20 000 area of mangrove 15 000 forest / km2 10 000 5000 0 IndonesiaBrazilAustraliaMexicoNigeriaMalaysiaMyanmar GuineaBangladeshCuba New Papua countries Fig. 1.1 (i) State the name of the country which protects the greatest percentage of its mangrove forest. … [1] (ii) Calculate the percentage of mangrove forest in Mexico that is protected. Show your working. … % [2] (iii) State two major threats to mangrove forests. 1 … 2 … [2] (c) Some species of macroalgae grow attached to the roots of mangrove trees. Scientists planned an investigation to compare the rate of photosynthesis at different light intensities in two of these species of macroalgae. (i) State the word equation for photosynthesis. … [1] Fig. 1.2 shows their experimental set-up. This closed system is used to fully contain a standardised volume of water which is circulated. An oxygen sensor recorded oxygen concentration in the water. The whole apparatus was submerged into a much larger tank of sea water for the investigation. circulation pump sealed plastic dome macroalgae grid sealed plastic base dissolved oxygen sensor Fig. 1.2 (ii) Identify the dependent variable. … [1] (iii) Suggest two variables that should be standardised in this investigation. 1 … 2 … [1] (iv) Suggest how the light intensity was changed. … … [1] (v) The scientists allowed the macroalgae to photosynthesise for 8 minutes in the closed system. They then exchanged the water in the closed system with some of the water in the surrounding tank, before beginning to collect results. Suggest one reason the scientists exchanged the water. … … [1] Table 1.1 shows the results from the investigation. Table 1.1 light intensity oxygen production / μmol mm–2 min–1 / arbitrary units macroalgae species A macroalgae species B 50 650 210 350 1750 580 600 2410 1530 900 2950 3090 1200 2910 3310 (vi) Plot a graph of the two sets of data in Table 1.1 on the grid below and draw an appropriate line for each data set. Complete the axes for the graph. oxygen production / … … [5] (vii) The two species of macroalgae used in the investigation are found at different depths on the mangrove tree roots. Use Table 1.1 to explain the expected depth distribution of the two species of macroalgae on the mangrove tree roots. … … … … … … [3] (viii) At a light intensity of zero the oxygen level decreased during the investigation. Explain this observation. … … … … [2] [Total: 22]

22 marks

Mark scheme: Question Answer Marks 1(a) interactions between, different species / community / biotic factors ; 2 and their (physical), environment / habitat / abiotic factors ; 1(b)(i) Bangladesh ; 1 1(b)(ii) correct reading of two figures from graph ; 2 (protected area  total area)  100 = (value between) 61.34%–70.41% ; 1(b)(iii) any 2 from: 2 global warming / climate change / temperature change ; over-harvesting / deforestation ; storm damage ; change in land use or named example e.g. shrimp farms ; 1(c)(i) carbon dioxide + water → glucose + oxygen ; 1 1(c)(ii) oxygen concentration ; 1 1(c)(iii) any 2 from: 1 temperature (of water) / size, mass, length, of algae / salinity / carbon dioxide / water, type or quality / volume of water or water flow or flow rate (through system) / pH / initial oxygen concentration / colour of light or wavelength ; 1(c)(iv) lamp / light source, moved different distances (from the apparatus) ; 1 1(c)(v) any 1 from: 1 add additional carbon dioxide / remove built up oxygen ; to acclimatise the macroalgae to the conditions before collecting results OWTTE ; 1(c)(vi) both axes labelled with units ; 5 (suitable) linear scale ; points plotted  ½ small square with x or dot in circle ; appropriate lines drawn for both sets of data ; key to identify the 2 data sets ; 1(c)(vii) Any 3 from: 3 species B closer to the surface / species A, can extend to greater depth ; (as species B), require a higher light intensity to photosynthesise / higher rate of photosynthesis than A at shallow depths / lower rate of photosynthesis than A at lower light intensities ORA ; correct ref. to data comparison or manipulation (from their graph) ; the lines cross over at stated light intensity (from their graph) OR the same rate (of photosynthesis) at stated light intensity ; species B may be found at a narrower range of depths / ORA ; both species found near the surface / at high light intensities ; 1(c)(viii) no photosynthesis occurring (as no light) ; 2 respiration uses oxygen ;

This question in 9693/21 Oct/Nov 2023

4 In 2016 scientists located a previously unknown coral reef near the mouth of the Amazon River. Fig. 4.1 shows the location of the mouth of the Amazon River, the coral reef locations, and the extent of the spread of river water as it enters the ocean. B A FrenchFrench GuianaGuiana N BrazilBrazil mouthmouth ofof Key AmazonAmazon coral reef RiverRiver land 0 180 river water spread km ocean Fig. 4.1 (a) Suggest and explain two reasons why scientists did not expect coral reefs to grow below the river water spread. 1 … … 2 … … [4] (b) Data were collected on temperature, salinity and dissolved oxygen from the surface down to the benthic region at location A and location B, which are shown on Fig. 4.1. Fig. 4.2 shows the data collected from these two locations. location A location B dissolved oxygen 0 2 4 6 8 0 2 4 6 8 / arbitrary units 20 22 24 26 28 30 20 22 24 26 28 30 temperature / … 20 25 30 35 40 20 25 30 35 40 salinity / … 0 0 20 20 40 40 60 60 depth / m 80 80 100 100 120 120 Key salinity temperature 140 140 dissolved oxygen 160 160 Fig. 4.2 (i) Add the units for temperature and salinity to Fig. 4.2. [1] (ii) Use Fig. 4.2 to describe and explain the change in salinity with increasing depth at location A. … … … … … … … … [4] (iii) Use Fig. 4.2 to compare and explain the change in the dissolved oxygen levels between location A and location B. … … … … … … [3] (iv) Suggest why the coral reef was not covered in sediment. … … … … [2] (c) (i) The scientists found zooxanthellae in mutualistic symbiosis with the coral polyps. Explain the terms mutualism and symbiosis. mutualism … … symbiosis … …

16 marks

Mark scheme: 4(a) any 2 pairs from: 4 freshwater input / reduced salinity ; so coral / polyps not able to survive ; increases turbidity / sediment (caried) in river ; coral / polyps, smothered or light intensity too low / prevents photosynthesis (by zooxanthellae) ; temperature change or stated ; may not be suitable range for coral / polyp growth ; (fine) sediment on seabed ; does not allow coral / polyp attachment ; pH of freshwater is closer to 7 / more acidic (than seawater) ; reducing growth of corals / polyps ; named pollution from runoff into river ; may cause eutrophication / toxicity to the corals / polyps ; high current flow rate from river ; may be too fast for corals / polyps to capture food ; 4(b)(i) (temperature) °C and (salinity) ppt / % ; 1 4(b)(ii) (low salinity at surface) salinity rapidly increases (over a small depth) / halocline + then remains steady (with increasing 4 depth) ; PLUS any 3 from: (because) fresh water enters from the river ; with a low salinity ORA ; this causes lower density ORA ; so it floats above the sea water ORA ; freshwater mixes with sea water ; until 35–36 (ppt) ; over 8–10 m (depth) the water is sea water and it does not mix with the (floating) fresh water 4(b)(iii) any 3 from: 3 (at location A) at the surface / top 4–8 m, dissolved oxygen (concentration) is higher (than B) ORA ; (because) fresh water can dissolve more oxygen (than sea water) ORA ; (at location B) below 8 m, dissolved oxygen / oxygen concentrations, are similar to location A; (because) mixing has occurred at location A / salinity and temperature of both similar below 12 m, so will hold similar dissolved oxygen / oxygen concentrations ; 4(b)(iv) Any 2 from: 2 fine particulates / silt / sediment, were not able to, cross / mix with, lower, more saline water ; due to density differences in surface water and sea water ; (idea of) sediment deposited further out than the coral reef due to the strong currents from the Amazon river ; (idea of) movement of water keeping sediment in suspension / fine particulates need low flow rate to settle ; (idea of) sediment deposited between the mouth of the river and the coral reef / mangroves caused sediment to deposit in estuary ; 4(c)(i) (mutualism) both benefit ; 2 (symbiosis) different species living in, close contact / long-term association ; 4(c)(ii) Any 1 from: 1 less light available for, photosynthesis ; increased turbidity ; salinity too low ; temperature out of range ; (presence of) freshwater ; 4(c)(iii) any 3 from: 3 use nematocysts ; to catch passing, zooplankton / small fish ; tentacles draw them into mouth ; pass to stomach (for digestion) ;

This question in 9693/21 Oct/Nov 2023

1 Mangrove forests are important ecosystems. (a) Explain the term ecosystem. … … … … [2] (b) Fig. 1.1 shows the area of mangrove forest in ten countries and the areas of mangrove forest that are protected and unprotected. Key protected mangrove forest unprotected mangrove forest 30 000 25 000 20 000 area of mangrove 15 000 forest / km2 10 000 5000 0 IndonesiaBrazilAustraliaMexicoNigeriaMalaysiaMyanmar GuineaBangladeshCuba New Papua countries Fig. 1.1 (i) State the name of the country which protects the greatest percentage of its mangrove forest. … [1] (ii) Calculate the percentage of mangrove forest in Mexico that is protected. Show your working. … % [2] (iii) State two major threats to mangrove forests. 1 … 2 … [2] (c) Some species of macroalgae grow attached to the roots of mangrove trees. Scientists planned an investigation to compare the rate of photosynthesis at different light intensities in two of these species of macroalgae. (i) State the word equation for photosynthesis. … [1] Fig. 1.2 shows their experimental set-up. This closed system is used to fully contain a standardised volume of water which is circulated. An oxygen sensor recorded oxygen concentration in the water. The whole apparatus was submerged into a much larger tank of sea water for the investigation. circulation pump sealed plastic dome macroalgae grid sealed plastic base dissolved oxygen sensor Fig. 1.2 (ii) Identify the dependent variable. … [1] (iii) Suggest two variables that should be standardised in this investigation. 1 … 2 … [1] (iv) Suggest how the light intensity was changed. … … [1] (v) The scientists allowed the macroalgae to photosynthesise for 8 minutes in the closed system. They then exchanged the water in the closed system with some of the water in the surrounding tank, before beginning to collect results. Suggest one reason the scientists exchanged the water. … … [1] Table 1.1 shows the results from the investigation. Table 1.1 light intensity oxygen production / μmol mm–2 min–1 / arbitrary units macroalgae species A macroalgae species B 50 650 210 350 1750 580 600 2410 1530 900 2950 3090 1200 2910 3310 (vi) Plot a graph of the two sets of data in Table 1.1 on the grid below and draw an appropriate line for each data set. Complete the axes for the graph. oxygen production / … … [5] (vii) The two species of macroalgae used in the investigation are found at different depths on the mangrove tree roots. Use Table 1.1 to explain the expected depth distribution of the two species of macroalgae on the mangrove tree roots. … … … … … … [3] (viii) At a light intensity of zero the oxygen level decreased during the investigation. Explain this observation. … … … … [2] [Total: 22]

22 marks

Mark scheme: Question Answer Marks 1(a) interactions between, different species / community / biotic factors ; 2 and their (physical), environment / habitat / abiotic factors ; 1(b)(i) Bangladesh ; 1 1(b)(ii) correct reading of two figures from graph ; 2 (protected area  total area)  100 = (value between) 61.34%–70.41% ; 1(b)(iii) any 2 from: 2 global warming / climate change / temperature change ; over-harvesting / deforestation ; storm damage ; change in land use or named example e.g. shrimp farms ; 1(c)(i) carbon dioxide + water → glucose + oxygen ; 1 1(c)(ii) oxygen concentration ; 1 1(c)(iii) any 2 from: 1 temperature (of water) / size, mass, length, of algae / salinity / carbon dioxide / water, type or quality / volume of water or water flow or flow rate (through system) / pH / initial oxygen concentration / colour of light or wavelength ; 1(c)(iv) lamp / light source, moved different distances (from the apparatus) ; 1 1(c)(v) any 1 from: 1 add additional carbon dioxide / remove built up oxygen ; to acclimatise the macroalgae to the conditions before collecting results OWTTE ; 1(c)(vi) both axes labelled with units ; 5 (suitable) linear scale ; points plotted  ½ small square with x or dot in circle ; appropriate lines drawn for both sets of data ; key to identify the 2 data sets ; 1(c)(vii) Any 3 from: 3 species B closer to the surface / species A, can extend to greater depth ; (as species B), require a higher light intensity to photosynthesise / higher rate of photosynthesis than A at shallow depths / lower rate of photosynthesis than A at lower light intensities ORA ; correct ref. to data comparison or manipulation (from their graph) ; the lines cross over at stated light intensity (from their graph) OR the same rate (of photosynthesis) at stated light intensity ; species B may be found at a narrower range of depths / ORA ; both species found near the surface / at high light intensities ; 1(c)(viii) no photosynthesis occurring (as no light) ; 2 respiration uses oxygen ;

This question in 9693/22 Oct/Nov 2023

4 In 2016 scientists located a previously unknown coral reef near the mouth of the Amazon River. Fig. 4.1 shows the location of the mouth of the Amazon River, the coral reef locations, and the extent of the spread of river water as it enters the ocean. B A FrenchFrench GuianaGuiana N BrazilBrazil mouthmouth ofof Key AmazonAmazon coral reef RiverRiver land 0 180 river water spread km ocean Fig. 4.1 (a) Suggest and explain two reasons why scientists did not expect coral reefs to grow below the river water spread. 1 … … 2 … … [4] (b) Data were collected on temperature, salinity and dissolved oxygen from the surface down to the benthic region at location A and location B, which are shown on Fig. 4.1. Fig. 4.2 shows the data collected from these two locations. location A location B dissolved oxygen 0 2 4 6 8 0 2 4 6 8 / arbitrary units 20 22 24 26 28 30 20 22 24 26 28 30 temperature / … 20 25 30 35 40 20 25 30 35 40 salinity / … 0 0 20 20 40 40 60 60 depth / m 80 80 100 100 120 120 Key salinity temperature 140 140 dissolved oxygen 160 160 Fig. 4.2 (i) Add the units for temperature and salinity to Fig. 4.2. [1] (ii) Use Fig. 4.2 to describe and explain the change in salinity with increasing depth at location A. … … … … … … … … [4] (iii) Use Fig. 4.2 to compare and explain the change in the dissolved oxygen levels between location A and location B. … … … … … … [3] (iv) Suggest why the coral reef was not covered in sediment. … … … … [2] (c) (i) The scientists found zooxanthellae in mutualistic symbiosis with the coral polyps. Explain the terms mutualism and symbiosis. mutualism … … symbiosis … …

16 marks

Mark scheme: 4(a) any 2 pairs from: 4 freshwater input / reduced salinity ; so coral / polyps not able to survive ; increases turbidity / sediment (caried) in river ; coral / polyps, smothered or light intensity too low / prevents photosynthesis (by zooxanthellae) ; temperature change or stated ; may not be suitable range for coral / polyp growth ; (fine) sediment on seabed ; does not allow coral / polyp attachment ; pH of freshwater is closer to 7 / more acidic (than seawater) ; reducing growth of corals / polyps ; named pollution from runoff into river ; may cause eutrophication / toxicity to the corals / polyps ; high current flow rate from river ; may be too fast for corals / polyps to capture food ; 4(b)(i) (temperature) °C and (salinity) ppt / % ; 1 4(b)(ii) (low salinity at surface) salinity rapidly increases (over a small depth) / halocline + then remains steady (with increasing 4 depth) ; PLUS any 3 from: (because) fresh water enters from the river ; with a low salinity ORA ; this causes lower density ORA ; so it floats above the sea water ORA ; freshwater mixes with sea water ; until 35–36 (ppt) ; over 8–10 m (depth) the water is sea water and it does not mix with the (floating) fresh water 4(b)(iii) any 3 from: 3 (at location A) at the surface / top 4–8 m, dissolved oxygen (concentration) is higher (than B) ORA ; (because) fresh water can dissolve more oxygen (than sea water) ORA ; (at location B) below 8 m, dissolved oxygen / oxygen concentrations, are similar to location A; (because) mixing has occurred at location A / salinity and temperature of both similar below 12 m, so will hold similar dissolved oxygen / oxygen concentrations ; 4(b)(iv) Any 2 from: 2 fine particulates / silt / sediment, were not able to, cross / mix with, lower, more saline water ; due to density differences in surface water and sea water ; (idea of) sediment deposited further out than the coral reef due to the strong currents from the Amazon river ; (idea of) movement of water keeping sediment in suspension / fine particulates need low flow rate to settle ; (idea of) sediment deposited between the mouth of the river and the coral reef / mangroves caused sediment to deposit in estuary ; 4(c)(i) (mutualism) both benefit ; 2 (symbiosis) different species living in, close contact / long-term association ; 4(c)(ii) Any 1 from: 1 less light available for, photosynthesis ; increased turbidity ; salinity too low ; temperature out of range ; (presence of) freshwater ; 4(c)(iii) any 3 from: 3 use nematocysts ; to catch passing, zooplankton / small fish ; tentacles draw them into mouth ; pass to stomach (for digestion) ;

This question in 9693/22 Oct/Nov 2023

1 Mangrove forests are important ecosystems. (a) Explain the term ecosystem. … … … … [2] (b) Fig. 1.1 shows the area of mangrove forest in ten countries and the areas of mangrove forest that are protected and unprotected. Key protected mangrove forest unprotected mangrove forest 30 000 25 000 20 000 area of mangrove 15 000 forest / km2 10 000 5000 0 IndonesiaBrazilAustraliaMexicoNigeriaMalaysiaMyanmar GuineaBangladeshCuba New Papua countries Fig. 1.1 (i) State the name of the country which protects the greatest percentage of its mangrove forest. … [1] (ii) Calculate the percentage of mangrove forest in Mexico that is protected. Show your working. … % [2] (iii) State two major threats to mangrove forests. 1 … 2 … [2] (c) Some species of macroalgae grow attached to the roots of mangrove trees. Scientists planned an investigation to compare the rate of photosynthesis at different light intensities in two of these species of macroalgae. (i) State the word equation for photosynthesis. … [1] Fig. 1.2 shows their experimental set-up. This closed system is used to fully contain a standardised volume of water which is circulated. An oxygen sensor recorded oxygen concentration in the water. The whole apparatus was submerged into a much larger tank of sea water for the investigation. circulation pump sealed plastic dome macroalgae grid sealed plastic base dissolved oxygen sensor Fig. 1.2 (ii) Identify the dependent variable. … [1] (iii) Suggest two variables that should be standardised in this investigation. 1 … 2 … [1] (iv) Suggest how the light intensity was changed. … … [1] (v) The scientists allowed the macroalgae to photosynthesise for 8 minutes in the closed system. They then exchanged the water in the closed system with some of the water in the surrounding tank, before beginning to collect results. Suggest one reason the scientists exchanged the water. … … [1] Table 1.1 shows the results from the investigation. Table 1.1 light intensity oxygen production / μmol mm–2 min–1 / arbitrary units macroalgae species A macroalgae species B 50 650 210 350 1750 580 600 2410 1530 900 2950 3090 1200 2910 3310 (vi) Plot a graph of the two sets of data in Table 1.1 on the grid below and draw an appropriate line for each data set. Complete the axes for the graph. oxygen production / … … [5] (vii) The two species of macroalgae used in the investigation are found at different depths on the mangrove tree roots. Use Table 1.1 to explain the expected depth distribution of the two species of macroalgae on the mangrove tree roots. … … … … … … [3] (viii) At a light intensity of zero the oxygen level decreased during the investigation. Explain this observation. … … … … [2] [Total: 22]

22 marks

Mark scheme: Question Answer Marks 1(a) interactions between, different species / community / biotic factors ; 2 and their (physical), environment / habitat / abiotic factors ; 1(b)(i) Bangladesh ; 1 1(b)(ii) correct reading of two figures from graph ; 2 (protected area  total area)  100 = (value between) 61.34%–70.41% ; 1(b)(iii) any 2 from: 2 global warming / climate change / temperature change ; over-harvesting / deforestation ; storm damage ; change in land use or named example e.g. shrimp farms ; 1(c)(i) carbon dioxide + water → glucose + oxygen ; 1 1(c)(ii) oxygen concentration ; 1 1(c)(iii) any 2 from: 1 temperature (of water) / size, mass, length, of algae / salinity / carbon dioxide / water, type or quality / volume of water or water flow or flow rate (through system) / pH / initial oxygen concentration / colour of light or wavelength ; 1(c)(iv) lamp / light source, moved different distances (from the apparatus) ; 1 1(c)(v) any 1 from: 1 add additional carbon dioxide / remove built up oxygen ; to acclimatise the macroalgae to the conditions before collecting results OWTTE ; 1(c)(vi) both axes labelled with units ; 5 (suitable) linear scale ; points plotted  ½ small square with x or dot in circle ; appropriate lines drawn for both sets of data ; key to identify the 2 data sets ; 1(c)(vii) Any 3 from: 3 species B closer to the surface / species A, can extend to greater depth ; (as species B), require a higher light intensity to photosynthesise / higher rate of photosynthesis than A at shallow depths / lower rate of photosynthesis than A at lower light intensities ORA ; correct ref. to data comparison or manipulation (from their graph) ; the lines cross over at stated light intensity (from their graph) OR the same rate (of photosynthesis) at stated light intensity ; species B may be found at a narrower range of depths / ORA ; both species found near the surface / at high light intensities ; 1(c)(viii) no photosynthesis occurring (as no light) ; 2 respiration uses oxygen ;

This question in 9693/23 Oct/Nov 2023

4 In 2016 scientists located a previously unknown coral reef near the mouth of the Amazon River. Fig. 4.1 shows the location of the mouth of the Amazon River, the coral reef locations, and the extent of the spread of river water as it enters the ocean. B A FrenchFrench GuianaGuiana N BrazilBrazil mouthmouth ofof Key AmazonAmazon coral reef RiverRiver land 0 180 river water spread km ocean Fig. 4.1 (a) Suggest and explain two reasons why scientists did not expect coral reefs to grow below the river water spread. 1 … … 2 … … [4] (b) Data were collected on temperature, salinity and dissolved oxygen from the surface down to the benthic region at location A and location B, which are shown on Fig. 4.1. Fig. 4.2 shows the data collected from these two locations. location A location B dissolved oxygen 0 2 4 6 8 0 2 4 6 8 / arbitrary units 20 22 24 26 28 30 20 22 24 26 28 30 temperature / … 20 25 30 35 40 20 25 30 35 40 salinity / … 0 0 20 20 40 40 60 60 depth / m 80 80 100 100 120 120 Key salinity temperature 140 140 dissolved oxygen 160 160 Fig. 4.2 (i) Add the units for temperature and salinity to Fig. 4.2. [1] (ii) Use Fig. 4.2 to describe and explain the change in salinity with increasing depth at location A. … … … … … … … … [4] (iii) Use Fig. 4.2 to compare and explain the change in the dissolved oxygen levels between location A and location B. … … … … … … [3] (iv) Suggest why the coral reef was not covered in sediment. … … … … [2] (c) (i) The scientists found zooxanthellae in mutualistic symbiosis with the coral polyps. Explain the terms mutualism and symbiosis. mutualism … … symbiosis … …

16 marks

Mark scheme: 4(a) any 2 pairs from: 4 freshwater input / reduced salinity ; so coral / polyps not able to survive ; increases turbidity / sediment (caried) in river ; coral / polyps, smothered or light intensity too low / prevents photosynthesis (by zooxanthellae) ; temperature change or stated ; may not be suitable range for coral / polyp growth ; (fine) sediment on seabed ; does not allow coral / polyp attachment ; pH of freshwater is closer to 7 / more acidic (than seawater) ; reducing growth of corals / polyps ; named pollution from runoff into river ; may cause eutrophication / toxicity to the corals / polyps ; high current flow rate from river ; may be too fast for corals / polyps to capture food ; 4(b)(i) (temperature) °C and (salinity) ppt / % ; 1 4(b)(ii) (low salinity at surface) salinity rapidly increases (over a small depth) / halocline + then remains steady (with increasing 4 depth) ; PLUS any 3 from: (because) fresh water enters from the river ; with a low salinity ORA ; this causes lower density ORA ; so it floats above the sea water ORA ; freshwater mixes with sea water ; until 35–36 (ppt) ; over 8–10 m (depth) the water is sea water and it does not mix with the (floating) fresh water 4(b)(iii) any 3 from: 3 (at location A) at the surface / top 4–8 m, dissolved oxygen (concentration) is higher (than B) ORA ; (because) fresh water can dissolve more oxygen (than sea water) ORA ; (at location B) below 8 m, dissolved oxygen / oxygen concentrations, are similar to location A; (because) mixing has occurred at location A / salinity and temperature of both similar below 12 m, so will hold similar dissolved oxygen / oxygen concentrations ; 4(b)(iv) Any 2 from: 2 fine particulates / silt / sediment, were not able to, cross / mix with, lower, more saline water ; due to density differences in surface water and sea water ; (idea of) sediment deposited further out than the coral reef due to the strong currents from the Amazon river ; (idea of) movement of water keeping sediment in suspension / fine particulates need low flow rate to settle ; (idea of) sediment deposited between the mouth of the river and the coral reef / mangroves caused sediment to deposit in estuary ; 4(c)(i) (mutualism) both benefit ; 2 (symbiosis) different species living in, close contact / long-term association ; 4(c)(ii) Any 1 from: 1 less light available for, photosynthesis ; increased turbidity ; salinity too low ; temperature out of range ; (presence of) freshwater ; 4(c)(iii) any 3 from: 3 use nematocysts ; to catch passing, zooplankton / small fish ; tentacles draw them into mouth ; pass to stomach (for digestion) ;

This question in 9693/23 Oct/Nov 2023

1 Zooplankton is composed of a variety of organisms, including copepods. (a) Fig. 1.1 shows a copepod found in zooplankton. Fig. 1.1 Make a large drawing of the copepod in Fig. 1.1. Do not include the internal structure of the copepod. Do not label your drawing. [4] (b) Describe the roles of zooplankton in marine ecosystems. … … … … [2] (c) Sea water samples were taken from different depths in the Arctic Ocean. Fig. 1.2 shows the percentage composition of eight species of copepod zooplankton found in the samples. Not all species occurred at each depth. Key 100 species A species B 80 species C species D 60 percentage species E composition of copepod species F zooplankton 40 species G species H 20 0 0 – 200 201 – 500 501 – 1000 sampling depth / m Fig. 1.2 (i) State how many of the eight species of copepod zooplankton are found in all three depth ranges. … [1] (ii) Use Fig. 1.2 to compare the changes in percentage composition of species A and species H. … … … … … … [3] (iii) Suggest why the percentage compositions of the copepod zooplankton species change with increasing depth. … … … … … … [3] (d) A student compared the copepod zooplankton communities by calculating the biodiversity at different depths. Table 1.1 shows the number of individuals per dm3 of sea water for the six species present at depths 0 – 200 m. Table 1.1 species of copepod zooplankton number of individuals / dm3 A 58 B 95 E 380 F 133 G 228 H 56 total number of individuals of all 950 the species (N) Simpson’s index of diversity (D) can be used to calculate biodiversity. n 2 D = 1 / N -c ` j m / = sum of (total) n = number of individuals of each different species N = the total number of individuals of all the species (i) Using the data in Table 1.1, complete Table 1.2 for species G. Table 1.2 species of copepod n / N (n / N)2 zooplankton A 0.061 0.004 B 0.100 0.010 E 0.400 0.160 F 0.140 0.020 G … … H 0.059 0.004 [1] (ii) Use Table 1.2 and the equation to calculate D for the biodiversity of copepod zooplankton between 0 – 200 m. State your answer to three significant figures. Show your working. D = … [3] (iii) The student calculated the value for D for the depth range 201 – 500 m to be 0.699. Use this value for D and your answer to (d)(ii) to describe the change in the biodiversity of copepod zooplankton as the depth increases. Justify your answer. … … … … [2] [Total: 19]

19 marks

Mark scheme: 1(a) clear outline with thin lines with no shading, no gaps ; suitable size ; in proportion ; detail ; 4 1(b) (primary / secondary) consumers / eat phytoplankton / eat plants ; provide food / make energy available / source of energy OR increase biomass, for higher trophic levels OR zooplankton are prey for / fed on by, other animals / other (marine) organisms OR source of food for other organisms ; 2 1(c)(i) 3 ; 1 1(c)(ii) any 3 from: 1 both species / A and H, have the similar (percentage) composition between 0–200 m ; 2 (percentage composition of) both species increase with depth ORA ; 3 idea of greater increase (in percentage composition) for species H ORA ; 4 ref. to greatest increase for both species between 0–200 m and 201–500 m / ORA ; 5 correct manipulation of data to support answers ; 3 Question Answer Marks 1(c)(iii) 1 idea of (presence or absence of) adaptations to different conditions e.g. different species adapted to different (environmental) conditions / some species lack adaptations to survive (and need sunlight) / composition of species H increases with depth, so H is suited to deeper areas of the ocean ; plus any 2 from: 2 (differing / changing amounts of) predation ; 3 (differing / changing) abundance of food ; 4 (differing / changing) salinity / pH ; 5 (differing / changing) oxygen (concentration) ; 6 (differing / changing) density / pressure ; 7 (differing / changing) competition ; 8 (differing / changing)(water) temperature ; 9 (differing / changing) light intensity / brightness / light penetration ; 3 1(d)(i) 0.24(0) AND 0.058 / 0.0576 ; 1 1(d)(ii)  (n / N)2 = 0.256 or 0.2556 ; 1 – 0.256 = 0.744 or 1 – 0.2556 = 0.744(4) ; calculated answer given to 3 sig figs ; 3 1(d)(iii) links change in biodiversity to change in depth e.g. biodiversity is decreasing OR the deeper, the lower biodiversity of copepod zooplankton there is OR biodiversity declines with depth ORA ; value closer to 1 indicates higher biodiversity ; 2

This question in 9693/21 May/June 2024

3 (a) A scientist used the mark-release-recapture technique to estimate the population size, N, of a species of herbivorous sea urchin on a coral reef. Table 3.1 shows the data the scientist collected. Table 3.1 n1 n2 m2 herbivorous sea urchin 128 97 64 Where: n1 = number of individuals captured and marked in the first sample n2 = number of individuals (both marked and unmarked) captured in the second sample and m2 = the number of marked individuals recaptured in the second sample. Use the formula for the Lincoln index to calculate the population, N, of sea urchins. n1 × n2 N = m2 Show your working. … [2] (b) The scientist investigated factors that allow coral polyps to recolonise an eroded coral reef. The scientist measured coral cover, algae cover, and the population density of herbivorous sea urchins on three recovering coral reefs. (i) Describe a systematic sampling method that the scientist could use to measure the mean population density of juvenile coral polyps. … … … … … … … … … … [5] (ii) Fig. 3.1 shows the relationship between percentage algae cover and the population density of juvenile coral polyps. 10 9 8 juvenile coral polyp 7 population density / number per m2 6 5 4 3 20 30 40 50 60 70 % algae cover Fig. 3.1 Humans harvest herbivorous sea urchins for food. Use evidence from Fig. 3.1 to explain why removal of herbivorous sea urchins from eroded coral reefs is a reason for a decline in coral reef recovery. … … … … … … [3] (c) Many species of sea urchin are herbivores, but some are omnivores. Suggest why a large population of omnivorous sea urchins may not help eroded reefs to recover. … … [1] [Total: 11]

11 marks

Mark scheme: 3(a) 12416 / 64 = 194 ; 2 3(b)(i) any 5 from: grid the area of the reef, with a map / GPS ; use of, line / belt, transect (laid along recovering reef) ; of known or given suitable length (e.g. 10 m) / width (1–2 m) ; use of quadrat OR take photographs over a measured area ; of suitable stated size (e.g. between 25 cm square – 50 cm square) ; place (quadrat) at, stated / every other metre (along the transect) / at regular intervals ; count number of (juvenile) polyps ; idea of, repeat(s) count along each transect / repeat (along different transects) + mean calculation ; ref. to calculation of density number per area of polyps / m2 ; AVP ; 5 3(b)(ii) any 3 from: fewer sea urchins means less grazing of algae / less sea urchins means more algal growth ; greater percentage/ more, of reef / rocks, covered in algae ; (so) polyps cannot find attachment site on bare rocks ; algae (growing over the polyps) may block light from (coral polyps) zooxanthellae ; manipulation of data ; 3 3(c) omnivores may feed on coral polyps as well as algae (reducing recolonisation) ; 1

This question in 9693/22 May/June 2024

3 (a) A scientist used the mark-release-recapture technique to estimate the population size, N, of a species of herbivorous sea urchin on a coral reef. Table 3.1 shows the data the scientist collected. Table 3.1 n1 n2 m2 herbivorous sea urchin 128 97 64 Where: n1 = number of individuals captured and marked in the first sample n2 = number of individuals (both marked and unmarked) captured in the second sample and m2 = the number of marked individuals recaptured in the second sample. Use the formula for the Lincoln index to calculate the population, N, of sea urchins. n1 × n2 N = m2 Show your working. … [2] (b) The scientist investigated factors that allow coral polyps to recolonise an eroded coral reef. The scientist measured coral cover, algae cover, and the population density of herbivorous sea urchins on three recovering coral reefs. (i) Describe a systematic sampling method that the scientist could use to measure the mean population density of juvenile coral polyps. … … … … … … … … … … [5] (ii) Fig. 3.1 shows the relationship between percentage algae cover and the population density of juvenile coral polyps. 10 9 8 juvenile coral polyp 7 population density / number per m2 6 5 4 3 20 30 40 50 60 70 % algae cover Fig. 3.1 Humans harvest herbivorous sea urchins for food. Use evidence from Fig. 3.1 to explain why removal of herbivorous sea urchins from eroded coral reefs is a reason for a decline in coral reef recovery. … … … … … … [3] (c) Many species of sea urchin are herbivores, but some are omnivores. Suggest why a large population of omnivorous sea urchins may not help eroded reefs to recover. … … [1] [Total: 11]

11 marks

Mark scheme: 3(a) 12416 / 64 = 194 ; 2 3(b)(i) any 5 from: grid the area of the reef, with a map / GPS ; use of, line / belt, transect (laid along recovering reef) ; of known or given suitable length (e.g. 10 m) / width (1–2 m) ; use of quadrat OR take photographs over a measured area ; of suitable stated size (e.g. between 25 cm square – 50 cm square) ; place (quadrat) at, stated / every other metre (along the transect) / at regular intervals ; count number of (juvenile) polyps ; idea of, repeat(s) count along each transect / repeat (along different transects) + mean calculation ; ref. to calculation of density number per area of polyps / m2 ; AVP ; 5 3(b)(ii) any 3 from: fewer sea urchins means less grazing of algae / less sea urchins means more algal growth ; greater percentage/ more, of reef / rocks, covered in algae ; (so) polyps cannot find attachment site on bare rocks ; algae (growing over the polyps) may block light from (coral polyps) zooxanthellae ; manipulation of data ; 3 3(c) omnivores may feed on coral polyps as well as algae (reducing recolonisation) ; 1

This question in 9693/23 May/June 2024

5 (a) Fig. 5.1 shows a brittle star which belongs to the echinoderm phylum. Fig. 5.1 Make a large drawing of the brittle star shown in Fig. 5.1. Do not include the markings on the arms. [4] (b) Sea urchins and starfish also belong to the echinoderm phylum. Fig. 5.2 shows five species of echinoderm. A B C D E Fig. 5.2 Use the key below to identify species A and B. disc-shaped body with arms … 2 1 body does not have arms … 3 body has 5 arms … Ophiura albida 2 body has 12–23 arms … Acanthaster planci body has many spines which are longer than diameter of the body … 4 3 body has many spines which are shorter than diameter of the body … Mespilia globulus spines are thin and dark in colour … Diadema setosum 4 spines are thick and light in colour … Echinometra mathaei species A: … species B: … [2] (c) Collector urchins feed on seagrass and macroalgae. Collector urchins are prey for octopus. Pufferfish consume collector urchins. Tiger sharks are predators of octopus and pufferfish. Draw a food web for the organisms described above. [2] (d) Collector urchins are often seen coated with debris such as gravel. Suggest why this may be an advantage to their survival. … … … … [2] [Total: 10]

10 marks

Mark scheme: 5(a) quality of outline (thin and continuous) in pencil ; 4 suitable size (at least as large as the photo) ; proportion (angles, length of arms, centre diameter) ; detail (minimum 2 out of the 3 curls on end of 3 arms circled) ; 5(b) Species A: Acanthaster planci ; 2 Species B: Diadema setosum ; 5(c) either: 2 for all six organisms correctly linked with 6 arrows in right direction ;; OR: food web of six organisms correct organisms with 6 lines / incorrect direction of arrows ; OR: food web of five correct organisms with correct direction of arrows ; OR: food web of six organisms correct organisms with correct direction of five arrows ; 5(d) idea of camouflage from / less likely to be seen ; 2 (so less likely to be seen / eaten) by predators / octopus / puffer fish ;

This question in 9693/21 Oct/Nov 2024

5 (a) Fig. 5.1 shows a brittle star which belongs to the echinoderm phylum. Fig. 5.1 Make a large drawing of the brittle star shown in Fig. 5.1. Do not include the markings on the arms. [4] (b) Sea urchins and starfish also belong to the echinoderm phylum. Fig. 5.2 shows five species of echinoderm. A B C D E Fig. 5.2 Use the key below to identify species A and B. disc-shaped body with arms … 2 1 body does not have arms … 3 body has 5 arms … Ophiura albida 2 body has 12–23 arms … Acanthaster planci body has many spines which are longer than diameter of the body … 4 3 body has many spines which are shorter than diameter of the body … Mespilia globulus spines are thin and dark in colour … Diadema setosum 4 spines are thick and light in colour … Echinometra mathaei species A: … species B: … [2] (c) Collector urchins feed on seagrass and macroalgae. Collector urchins are prey for octopus. Pufferfish consume collector urchins. Tiger sharks are predators of octopus and pufferfish. Draw a food web for the organisms described above. [2] (d) Collector urchins are often seen coated with debris such as gravel. Suggest why this may be an advantage to their survival. … … … … [2] [Total: 10]

10 marks

Mark scheme: 5(a) quality of outline (thin and continuous) in pencil ; 4 suitable size (at least as large as the photo) ; proportion (angles, length of arms, centre diameter) ; detail (minimum 2 out of the 3 curls on end of 3 arms circled) ; 5(b) Species A: Acanthaster planci ; 2 Species B: Diadema setosum ; 5(c) either: 2 for all six organisms correctly linked with 6 arrows in right direction ;; OR: food web of six organisms correct organisms with 6 lines / incorrect direction of arrows ; OR: food web of five correct organisms with correct direction of arrows ; OR: food web of six organisms correct organisms with correct direction of five arrows ; 5(d) idea of camouflage from / less likely to be seen ; 2 (so less likely to be seen / eaten) by predators / octopus / puffer fish ;

This question in 9693/22 Oct/Nov 2024

5 (a) Fig. 5.1 shows a brittle star which belongs to the echinoderm phylum. Fig. 5.1 Make a large drawing of the brittle star shown in Fig. 5.1. Do not include the markings on the arms. [4] (b) Sea urchins and starfish also belong to the echinoderm phylum. Fig. 5.2 shows five species of echinoderm. A B C D E Fig. 5.2 Use the key below to identify species A and B. disc-shaped body with arms … 2 1 body does not have arms … 3 body has 5 arms … Ophiura albida 2 body has 12–23 arms … Acanthaster planci body has many spines which are longer than diameter of the body … 4 3 body has many spines which are shorter than diameter of the body … Mespilia globulus spines are thin and dark in colour … Diadema setosum 4 spines are thick and light in colour … Echinometra mathaei species A: … species B: … [2] (c) Collector urchins feed on seagrass and macroalgae. Collector urchins are prey for octopus. Pufferfish consume collector urchins. Tiger sharks are predators of octopus and pufferfish. Draw a food web for the organisms described above. [2] (d) Collector urchins are often seen coated with debris such as gravel. Suggest why this may be an advantage to their survival. … … … … [2] [Total: 10]

10 marks

Mark scheme: 5(a) quality of outline (thin and continuous) in pencil ; 4 suitable size (at least as large as the photo) ; proportion (angles, length of arms, centre diameter) ; detail (minimum 2 out of the 3 curls on end of 3 arms circled) ; 5(b) Species A: Acanthaster planci ; 2 Species B: Diadema setosum ; 5(c) either: 2 for all six organisms correctly linked with 6 arrows in right direction ;; OR: food web of six organisms correct organisms with 6 lines / incorrect direction of arrows ; OR: food web of five correct organisms with correct direction of arrows ; OR: food web of six organisms correct organisms with correct direction of five arrows ; 5(d) idea of camouflage from / less likely to be seen ; 2 (so less likely to be seen / eaten) by predators / octopus / puffer fish ;

This question in 9693/23 Oct/Nov 2024

2 Nitrate ions (NO3–) are a source of nitrogen for marine producers such as seagrass. (a) Define the term ion. … … [1] (b) A student designed an experiment to investigate the relationship between the concentration of nitrate ions in sea water and the growth of seagrass. The student was provided with a solution of nitrate ions at a concentration of 40 µmol dm–3. Fig. 2.1 shows the equipment the student used. lamp large glass cylinder containing sea water metre ruler seagrass sediment Fig. 2.1 (i) Suggest how the student used the equipment shown in Fig. 2.1 to investigate the growth of seagrass at different concentrations of nitrate ions. … … … … … … … … … … [5] (ii) Draw a table that could be used to record the results from the investigation in (b)(i). Include a suitable unit for the dependent variable. Do not write in any results. [2] (iii) Predict the relationship you would expect to find between nitrate ion concentration and growth rate of seagrass. … … [1] (c) State two uses of nitrogen for producers such as seagrass. 1 … … 2 … … [2] (d) Fig. 2.2 shows a pair of pipefish. Seagrasses provide pipefish with food and are ideal breeding grounds. Fig. 2.2 Many pipefish species are in decline. A scientist investigated whether the survival of newborn pipefish depends on the prey species available. Three tanks containing seagrass were set up in controlled conditions and newborn pipefish were placed into each tank. Each tank contained different prey species: tank 1 – prey species R only tank 2 – prey species S only tank 3 – prey species R and S. The percentage of newborn pipefish surviving each day was monitored for seven days. Fig. 2.3 shows the results. 100 Key tank 3 – prey species R and S 90 tank 1 – prey species R only tank 2 – prey species S only 80 percentage 70of newborn pipefish 60surviving 50 40 0 1 2 3 4 5 6 7 time / days Fig. 2.3 (i) Suggest two biotic factors which would need to be standardised in this investigation. 1 … … 2 … … [2] (ii) The starting number of newborn pipefish in tank 2 was 150. Use Fig. 2.3 to calculate the number of newborn pipefish surviving after seven days. … [2] (iii) Give one conclusion that can be made from the results in Fig. 2.3. … … [1] (iv) Describe two limitations of the data collected in this investigation. 1 … … 2 … … [2] [Total: 18]

18 marks

Mark scheme: 2(a) particle that has gained or lost electron(s) /negative and positive charge ; 1 2(b)(i) any five from: 5 (independent variable) – idea of how to change nitrate concentration ; (suitable range) – at least 3 concentrations used ; (dependent variable) – idea of measuring change in height of seagrass ; idea of replicates / repeat at least twice and calculate, means / medians / control experiment (using only sea water) ; description of calculation of growth rate ; standardised variables ;; (MAX two marks from this list) • leave to grow for, suitable / fixed time • temperature of water • all other mineral ions in equal concentration • concentration of CO2 • from lamp OR position / distance of the lamp / light intensity • pH • similar starting height of seagrass • same species of seagrass • volume of water • depth / type / mass, of sediment 2(b)(ii) suitable column / row headings e.g. (nitrate) concentration AND growth (rate) / change in length of seagrass / change in 2 height of seagrass ; appropriate units for dependent variable in heading only ; 2(b)(iii) Idea of increase in nitrate concentration increases growth (rate) / ORA ; 1 2(c) any two from: 2 proteins or amino acids ; chlorophyll ; DNA ; AVP ; 2(d)(i) any two from: 2 species / sex, of pipefish used ; health of pipefish ; number of pipefish (in the tank) ; reference to the, number / age / size / density / population, of prey ; quantity / mass / species / age, of seagrass in each tank ; 2(d)(ii) 150 / 100  62 2 OR 62  150 / 100 OR 150  0.62 OR 62 / 100  150 93 ;; 1 mark for incorrect values of 61 or 63 but correct calculation 150 / 100  61 OR 61  150 / 100 = 92 150 / 100  63 OR 63  150 / 100 = 95 2(d)(iii) any one from: 1 highest survival rate seen with diet of both R and S together / pipefish survive the most when both prey species R and S are present / ORA ; prey species S cause the percentage to decrease most / species S has the lowest survival rate ; all survived for at least one day ; juvenile pipefish have greater survival rate with prey species R rather than prey species S ; idea of those with R in diet have higher survival ; 2(d)(iv) any two from: 2 only 1 species of pipefish investigated /only two prey species investigated ; only one tank (of pipefish) investigated for each diet / no repeats / only 1 trial ; differences in survival may be for other (unknown) reasons ; 7 days is too short a duration / not enough time for investigation / records only 7 days ; idea of tank environment is not representative of conditions in the sea ;

This question in 9693/21 May/June 2025

5 Some copepods are parasites of marine fish. (a) Describe the meaning of the term parasitism. … … … … [2] (b) Gobies are small fish that compete with each other for hiding spaces in coral reefs. These spaces provide shelter from predators. Fig. 5.1 shows two gobies on a coral reef. Fig. 5.1 Scientists investigated whether the presence of copepod parasites affected the behaviour of gobies. Observations were made of goby behaviour with and without copepod parasites. Fig. 5.2 shows the relationship between the mean number of gobies competing for each hiding space and the maximum distance travelled by gobies from the hiding space. Key with copepod parasite without copepod parasite maximum distance travelled by gobies from the hiding space / cm mean number of gobies competing for each hiding space Fig. 5.2 (i) Use Fig. 5.2 to compare the behaviour of gobies with and without copepod parasites. … … … … [2] (ii) Some copepod parasites have different stages of their life cycle in different organisms. The parasite changes the behaviour of the goby. Use Fig. 5.2 and your own knowledge to suggest ways that copepod parasites could affect gobies. … … … … [2] (c) In another investigation, scientists observed the symbiotic relationship between two species of manta ray and each of two species of remora. Each individual manta ray only associates with one remora species. Each time a manta ray was seen, the number of remora associating with it were counted and the mean number of remora per manta ray calculated. Table 5.1 shows the results. Table 5.1 manta ray remora total number of number of manta mean number of species species remora observed ray observed remora per manta ray Echeneis 1815 825 2.2 naucrates Mobula alfredi Remora 52 40 1.3 remora Echeneis 81 45 1.8 naucrates Mobula birostris Remora 612 3.6 remora … (i) Use Table 5.1 to state the total number of genus groups observed. … [1] (ii) Use the data in Table 5.1 to calculate the number of Mobula birostris observed with Remora remora. Write your answer in Table 5.1. [1]

8 marks

Mark scheme: 5(a) one organism lives, in / on, another organism ; 2 (parasite) gains benefit AND (host) organism is, harmed / disadvantaged ; 5(b)(i) any two from: 2 idea that gobies with parasites travelled further ORA ; idea that as (mean no of) gobies competing for each hiding space increases the distance travelled increases (both with and without parasites) ORA ; idea that difference in maximum distance travelled by gobies (with parasite) increases with increasing mean number competing per hiding place ORA ; 5(b)(ii) any two from: 2 1 reduces energy available, for growth / reproduction / disrupts physiological processes ; 2 (behaviour changes) to travel further to find, an (alternative) hiding space / food / need to eat more / to reach more favourable conditions for the copepod ; 3 resulting in smaller gobies ; 4 increases chance of (goby) predation ; 5(c)(i) 3 ; 1 5(c)(ii) (612 / 3.6) = 170 ; 1 5(c)(iii) correct manipulation of data ;; 4 plus MAX three from: Echeneis naucrates (EN) associated more with Mobula alfredi (MA) OR Mobula alfredi (MA) associated more with Echeneis naucrates (EN) ; Remora remora (RR) associated more with Mobula birostris (MB) OR Mobula birostris (MB) associated more with Remora remora (RR) ; Mobula birostris (MB) has more remora (in total) compared to Mobula alfredi (MA) ; sample sizes vary considerably ;

This question in 9693/21 May/June 2025

1 (a) Fig. 1.1 shows a species of starfish. Fig. 1.1 (i) Make a large drawing of the starfish shown in Fig. 1.1. Do not include markings. Do not label your drawing. [4] (ii) State why this starfish species is not a typical echinoderm. … … [1] (b) Starfish regrow their arms if they become damaged. Fig. 1.2 shows a different starfish species with a damaged arm. Fig. 1.2 Starfish arms can be damaged by the impact of humans. Suggest one other way a starfish arm can become damaged. … … [1] (c) Scientists investigated if the number of arms damaged affected the rate at which the arms can regrow. Starfish with damaged arms were collected from one shoreline. The starfish were placed in a tank of sea water in a laboratory and fed daily. The scientists measured the length of the damaged arms every 50 days over a period of 300 days. Fig. 1.3 shows the results. Key one arm regrowing two arms regrowing 160 140 120 100 mean length of regrowing 80 arm / mm 60 40 20 0 0 50 100 150 200 250 300 time / days Fig. 1.3 (i) Suggest one abiotic factor the scientists should keep the same as the natural environment of the starfish. … … [1] (ii) Use the line of best fit on Fig.1.3 to calculate the mean rate of growth of the damaged arm for starfish with one arm regrowing. Give your answer to two significant figures. growth rate = … mm per day [3] (iii) The scientists predicted that the mean rate of growth of damaged arms would be greater for starfish with only one damaged arm. Discuss the extent to which the results support this prediction. … … … … [2] (iv) Describe one safety and one ethical consideration for this investigation. safety … … ethical … … [2] [Total: 14]

14 marks

Mark scheme: Question Answer Marks 1(a)(i) outline: unbroken lines and no shading ; 4 size: most of the space provided and at least as big as original picture ; in proportion ; detail ; 1(a)(ii) reference to more than 5 arms OR has 7 arms ; 1 1(b) any one from: 1 lost to predator ; lost due to wave action ; lost during reproduction ; AVP ; 1(c)(i) any one from: 1 (water) temperature ; dissolved oxygen concentration ; salinity ; pH ; AVP ; 1(c)(ii) correct numbers for mm and time read from line of best fit ; 3 correct calculation of mm / time ; answer correctly rounded to 2 sig figs ; 1(c)(iii) Yes + as gradient for 1 arm re-growing is steeper than gradient for 2 arms ; 2 and one from: however, sample size not known / mean starting lengths different ; reference to significant difference / need for statistical analysis ; may have collected different species / ages / genders ; calculated difference of 0.1 mm per day ; difference in feeding ability ; no control group (growth of starfish with all limbs intact) AW ; AVP ; 1(c)(iv) safety – any one from: 2 reference to safety when collecting starfish on shoreline e.g. don’t go alone / awareness of tides / suitable footwear / using gloves to avoid stings or infection or cuts ; ethical – any one from: reference to avoidance of further damage to starfish ; provide hiding places for the starfish ; provide a rock for starfish to pull themselves out of the water ; starfish released at same shoreline they were collected from ; AVP ;

This question in 9693/22 Oct/Nov 2025

3 A student investigated how light intensity affected the rate of photosynthesis in two species of macroalga, X and Y. Fig. 3.1 shows the apparatus used. stop-clock gas bubbles from photosynthesis lamp 00.00 macroalga metre ruler Fig. 3.1 (a) Name the gas produced by photosynthesis. … [1] (b) (i) Describe a method to compare the rate of photosynthesis at different light intensities in each species of macroalga. Use only the apparatus shown in Fig. 3.1. … … … … … … … … … … [5] (ii) Draw a results table for the investigation in (b)(i). Include full headings and units in the results table. Do not write in any results. [3] (iii) Predict the relationship between light intensity and rate of photosynthesis in macroalga. … … [1] (c) Suggest two improvements that could be made to the apparatus used in this investigation. Give a reason for each suggestion. 1 … … reason … … 2 … … reason … … [4] (d) Explain the importance of photosynthesis to consumers. … … … … … … [3] [Total: 17]

17 marks

Mark scheme: 3(a) oxygen ; 1 3(b)(i) distance between the lamp and the macroalga, varies / is independent variable ; 5 count number of bubbles produced per minute / unit time OR number of bubbles produced per minute / unit time, is dependent variable ; reference to sufficient range (min 3 distances) ; allow time for macroalga to adjust ; reference to control variable e.g. pH / size of macroalga / same macroalga / temperature / ambient light / known volume of sea water ; repeat with species X and Y / with the two different species ; reference to repeats to, identify anomalies / calculating mean ; 3(b)(ii) table with column headings for distance of lamp AND bubbles per minute / number of bubbles ; 3 columns / rows for both species X and Y ; suitable units for independent and dependent variables ; 3(b)(iii) increasing light intensity increases rate of photosynthesis ORA ; 1 3(c) any two pairs from: 4 1 use gas syringe / (inverted) measuring cylinder ; to measure volume of oxygen produced ; 2 use transparent screen ; to prevent heating effect of lamp ; 3 AVP ;; 3(d) any three from: 3 transfers energy from light ; glucose / carbohydrate / organic substances , in producers ; to produce biomass (in consumers) ; provides oxygen for respiration ;

This question in 9693/22 Oct/Nov 2025

1 (a) Fig. 1.1 shows a species of starfish. Fig. 1.1 (i) Make a large drawing of the starfish shown in Fig. 1.1. Do not include markings. Do not label your drawing. [4] (ii) State why this starfish species is not a typical echinoderm. … … [1] (b) Starfish regrow their arms if they become damaged. Fig. 1.2 shows a different starfish species with a damaged arm. Fig. 1.2 Starfish arms can be damaged by the impact of humans. Suggest one other way a starfish arm can become damaged. … … [1] (c) Scientists investigated if the number of arms damaged affected the rate at which the arms can regrow. Starfish with damaged arms were collected from one shoreline. The starfish were placed in a tank of sea water in a laboratory and fed daily. The scientists measured the length of the damaged arms every 50 days over a period of 300 days. Fig. 1.3 shows the results. Key one arm regrowing two arms regrowing 160 140 120 100 mean length of regrowing 80 arm / mm 60 40 20 0 0 50 100 150 200 250 300 time / days Fig. 1.3 (i) Suggest one abiotic factor the scientists should keep the same as the natural environment of the starfish. … … [1] (ii) Use the line of best fit on Fig.1.3 to calculate the mean rate of growth of the damaged arm for starfish with one arm regrowing. Give your answer to two significant figures. growth rate = … mm per day [3] (iii) The scientists predicted that the mean rate of growth of damaged arms would be greater for starfish with only one damaged arm. Discuss the extent to which the results support this prediction. … … … … [2] (iv) Describe one safety and one ethical consideration for this investigation. safety … … ethical … … [2] [Total: 14]

14 marks

Mark scheme: Question Answer Marks 1(a)(i) outline: unbroken lines and no shading ; 4 size: most of the space provided and at least as big as original picture ; in proportion ; detail ; 1(a)(ii) reference to more than 5 arms OR has 7 arms ; 1 1(b) any one from: 1 lost to predator ; lost due to wave action ; lost during reproduction ; AVP ; 1(c)(i) any one from: 1 (water) temperature ; dissolved oxygen concentration ; salinity ; pH ; AVP ; 1(c)(ii) correct numbers for mm and time read from line of best fit ; 3 correct calculation of mm / time ; answer correctly rounded to 2 sig figs ; 1(c)(iii) Yes + as gradient for 1 arm re-growing is steeper than gradient for 2 arms ; 2 and one from: however, sample size not known / mean starting lengths different ; reference to significant difference / need for statistical analysis ; may have collected different species / ages / genders ; calculated difference of 0.1 mm per day ; difference in feeding ability ; no control group (growth of starfish with all limbs intact) AW ; AVP ; 1(c)(iv) safety – any one from: 2 reference to safety when collecting starfish on shoreline e.g. don’t go alone / awareness of tides / suitable footwear / using gloves to avoid stings or infection or cuts ; ethical – any one from: reference to avoidance of further damage to starfish ; provide hiding places for the starfish ; provide a rock for starfish to pull themselves out of the water ; starfish released at same shoreline they were collected from ; AVP ;

This question in 9693/23 Oct/Nov 2025

3 A student investigated how light intensity affected the rate of photosynthesis in two species of macroalga, X and Y. Fig. 3.1 shows the apparatus used. stop-clock gas bubbles from photosynthesis lamp 00.00 macroalga metre ruler Fig. 3.1 (a) Name the gas produced by photosynthesis. … [1] (b) (i) Describe a method to compare the rate of photosynthesis at different light intensities in each species of macroalga. Use only the apparatus shown in Fig. 3.1. … … … … … … … … … … [5] (ii) Draw a results table for the investigation in (b)(i). Include full headings and units in the results table. Do not write in any results. [3] (iii) Predict the relationship between light intensity and rate of photosynthesis in macroalga. … … [1] (c) Suggest two improvements that could be made to the apparatus used in this investigation. Give a reason for each suggestion. 1 … … reason … … 2 … … reason … … [4] (d) Explain the importance of photosynthesis to consumers. … … … … … … [3] [Total: 17]

17 marks

Mark scheme: 3(a) oxygen ; 1 3(b)(i) distance between the lamp and the macroalga, varies / is independent variable ; 5 count number of bubbles produced per minute / unit time OR number of bubbles produced per minute / unit time, is dependent variable ; reference to sufficient range (min 3 distances) ; allow time for macroalga to adjust ; reference to control variable e.g. pH / size of macroalga / same macroalga / temperature / ambient light / known volume of sea water ; repeat with species X and Y / with the two different species ; reference to repeats to, identify anomalies / calculating mean ; 3(b)(ii) table with column headings for distance of lamp AND bubbles per minute / number of bubbles ; 3 columns / rows for both species X and Y ; suitable units for independent and dependent variables ; 3(b)(iii) increasing light intensity increases rate of photosynthesis ORA ; 1 3(c) any two pairs from: 4 1 use gas syringe / (inverted) measuring cylinder ; to measure volume of oxygen produced ; 2 use transparent screen ; to prevent heating effect of lamp ; 3 AVP ;; 3(d) any three from: 3 transfers energy from light ; glucose / carbohydrate / organic substances , in producers ; to produce biomass (in consumers) ; provides oxygen for respiration ;

This question in 9693/23 Oct/Nov 2025