Populations and sampling techniques — Paper 2 · A Level Marine Science 9693

1 Fig. 1.1 shows a specimen of Laminaria longicruris. L. longicruris is a species of alga and is a producer in marine ecosystems. magnification × 0.1 Fig. 1.1 Investigations were carried out to study factors affecting L. longicruris. (a) Table 1.1 shows the relationship between the depth of sea water and the population density of L. longicruris. Density is expressed as the number of plants per square metre. Table 1.1 population density depth / m / number m–2 2 3.8 4 5.2 6 3.5 8 2.2 10 1.0 12 1.5 (i) On the grid, plot a graph to show the relationship between depth and the population density of L. longicruris. Join the points on your graph with ruled, straight lines. [4] (ii) Use your graph to estimate the population density at a depth of 5 m. … [2] (b) Table 1.2 shows the mean rate of uptake of nitrate ions (NO3–) by L. longicruris at a range of concentrations of nitrate ions. Concentrations are expressed as micromoles per dm3 (µmol dm–3). Table 1.2 nitrate ion concentration mean rate of uptake per hour / µmol dm–3 / µmol dm–3 hr–1 1.2 2.1 2.9 4.0 6.8 6.7 10.1 8.0 11.7 8.1 14.9 8.2 (i) Use the data in Table 1.2 to describe the relationship between the concentration of nitrate ions and the mean rate of uptake. … … … … … [2] (ii) To determine the mean rate of uptake at a concentration of 1.2 µmol dm–3, seven replicates were used. Explain how the mean rate would be calculated. … … … … [2] (iii) Suggest why nitrate ions are needed for the growth of L. longicruris. … … … … … [2] [Total: 12]

12 marks

Mark scheme: 1(a)(i) appropriate linear scale for both axes ; both axes labelled including units ; all points plotted correctly (±1 mm) ; points joined with ruled lines ; 4 I axis orientation 1(a)(ii) answer is consistent with graph, precise to ±1 mm ; per m2 / m–2 ; 2 ECF from incorrect lines in 1(a)(i) 1(b)(i) any 2 of: uptake increases / simple statement of relationship ; (then) levels off / rate of increase lessens ; credit use of manipulated figures (if units stated, they must be correct) ; 2 e.g. the greater the concentration of nitrate, the higher the mean rate of uptake e.g. an overall increase in uptake of 6.1 ( µmol dm–3 hr–1) ; 1(b)(ii) find the total uptake for all replicates ; divide total by 7 / number of replicates ; 2 1(b)(iii) provide nitrogen for ; synthesis of any 2 of, (named) amino acids / (named) protein / (named) enzyme / chlorophyll / DNA ; ; to produce new cells ; 2

This question in 9693/21 May/June 2017

2 Fig. 2.1 shows a group of nine periwinkles, small molluscs found in the intertidal region of many rocky shores. Periwinkles feed on algae growing on the surface of rocks. Fig. 2.1 (a) State the trophic level occupied by periwinkles. … [1] (b) The mark-release-recapture technique can be used to estimate population densities of animals such as molluscs. In this technique, a sample of animals is collected and each one marked with a small dot of paint. These marked animals are then released. After a suitable time, a second sample is collected from the same area and the number of marked individuals in this sample is counted. The data can then be used to estimate the total number of individuals in the population, using the formula below. N1 × N2 Estimated size of population = N3 where N1 is the number of individuals captured and marked N2 is the total number of individuals in the second sample N3 is the number of marked individuals in the second sample. (i) In an investigation, 204 periwinkles were marked and then returned to their habitat. Two days later, a random sample of 936 periwinkles was collected from the same area. Of these, 72 were marked. Use the formula above to determine the total number of periwinkles in this population. Show your working. … [2] (ii) In this investigation, the area of rocky shore measured 20 m × 20 m. Use your answer from (b)(i) to calculate the mean number of periwinkles per square metre. Show your working. … [2] (iii) Suggest three reasons why the mark-release-recapture technique may not give an accurate measure of the population density of the periwinkles. 1 … … 2 … … 3 … … [3] [Total: 8]

8 marks

Mark scheme: 2(a) second (trophic level) ; 1 2(b)(i) 2652 ; ; 2 If answer incorrect, check working (204 × 936) ÷ 72 = 1 mark 2(b)(ii) 6.63 (per m2) ; ; 2 A 7, 6.6 2(b)(iii) any 3 of: idea of, moving into or out of area ; idea of, marked individuals may not be randomly mixed ; marking may increase likelihood of them being re-captured ; paint may wear off / fade / wash off ; reproduction / death of periwinkles ; marking may increase / change predation (rate) ; marking may harm periwinkles ; 3 I ref. to human error, lack of replicates

This question in 9693/21 May/June 2017

1 A diversity index (D ) can be used to compare the biodiversity of two habitats. One diversity index is calculated using the formula N (N - 1 ) D = - 1 ) /n (n where N is the total number of organisms found n is the number of individuals of each species / means ‘the sum of’. For this diversity index, a higher value of D indicates a higher biodiversity. Researchers carried out an investigation to compare the biodiversity of two rocky shores, shore A and shore B. Ten random samples were taken on each shore, using a quadrat, and the numbers of each species were recorded. Table 1.1 shows the results of this investigation. Table 1.1 number of each species found (n) common name of species shore A shore B beadlet anemone 3 7 dog whelk 12 16 limpet 5 11 mussel 18 23 periwinkle 6 14 shore crab 2 3 topshell 4 5 Table 1.2 shows some of the stages in the calculation of the diversity index, for shore A. Table 1.2 common name of species number (n) on shore A n(n-1) beadlet anemone 3 6 dog whelk 12 132 limpet 5 20 mussel 18 306 periwinkle 6 30 shore crab 2 2 topshell 4 12 Total (N ) = 50 /n(n-1) = 508 (a) Complete Table 1.3, by calculating N, n(n-1) and /n(n-1) for shore B. Write your answers in the spaces in Table 1.3. Table 1.3 common name of species number (n) on shore B n(n-1) beadlet anemone 7 dog whelk 16 limpet 11 mussel 23 periwinkle 14 shore crab 3 topshell 5 Total (N ) = /n(n-1) = [3] (b) The diversity index for shore A is 4.8. Use the information in Table 1.3 to calculate the diversity index for shore B. Show your working. … [2] (c) Compare the biodiversity of shore A with the biodiversity of shore B. … … … … … … [3] (d) Based on the results of this investigation, the researchers proposed the following hypothesis. Dog whelks and mussels are more numerous than other species on rocky shores. State two variables you would need to control in a further investigation to test this hypothesis. 1 … 2 … [2] [Total: 10]

10 marks

Mark scheme: 1(a) number (n) n(n–1) 7 42 16 240 11 110 23 506 14 182 3 6 5 20 ; Total (N) = 79 ; Σn(n–1) = 1106 ; 3 for 1 mark 1(b) figures correctly substituted into formula ; 79 × 78 / 1106 diversity index for shore B = 5.6 ; 2 A ECF from 1(a) 1(c) any 3 of: shore B has a higher biodiversity than shore A ; both shores have the same (7) number of species present / same species richness ; idea that shore B has higher populations of each species than shore A ; total number of organisms greater at shore B / shore B has 29 more organisms ; 3 Question Answer Marks Guidance 1(d) any 2 of: type / location, of shore ; height / position, on shore ; sampling area ; time of year ; state of the tide ; abiotic factor ; 2

This question in 9693/21 Oct/Nov 2017

2 Divers carried out a survey to test the following hypothesis: Each species of coral has an optimum depth where they are found in higher numbers. Table 2.1 shows the results of the survey. Table 2.1 number of coral colonies depth / m species A species B species C species D species E species F 2 67 54 1 0 17 15 4 4 6 0 3 22 13 12 0 0 21 28 18 14 (a) (i) Describe a method the divers could have used to collect reliable data. … … … … … … … … [4] (ii) Draw a bar chart using the data in Table 2.1, to show the number of colonies of each species of coral found at a depth of 4 m. [4] (iii) Use the data in Table 2.1 to compare the depth preferences of the six species of coral. … … … … … … [3] (b) Discuss the extent to which the data in Table 2.1 support the hypothesis. … … … … [2] [Total: 13]

13 marks

Mark scheme: 2(a)(i) Any 4 of: count total number of, each / different, species ; at each depth / 2 m, 4 m and 12 m / idea of, different depths ; idea of, sample every 2 m / smaller intervals of depth ; how to count / estimate (quadrat / belt or line transect) ; control variable ; repeat / find, mean / average ; do not damage coral ; 4 A ‘types’ to mean species A ‘at these depths’ A idea of a grid, take photos (to analyse later) e.g. (suitable) size of area sample / ref. to suitable time period / same reef ; 2(a)(ii) both axes correctly labelled ; linear scale on y axis ; data for 4 m plotted ± ½ square ; bars not touching + of equal width ; 4 plots must take up at least half the grid max 3 for other type of graph – MP4 not available 2(a)(iii) species E + F show even distribution with depth / survive at any depth tested ; species A + B prefer 2 m / shallow water / higher / highest at 2 m; species C + D prefer 12 m / deeper water / higher / highest at 12 m ; 3 R other stated depths / lower/ lowest at 2 m R other stated depths / lower / lowest at 12 m Question Answer Marks Guidance 2(b) species A–D do support (the hypothesis), as narrow range / optimum depth with high numbers AW ; species E and F do not support (the hypothesis), as similar numbers at all depths / E and F can live in both deep and shallow water ; if no other marks awarded, all for 1 mark ‘A to D do support AND E and F do not’ 2 A in terms of just one species A in terms of just one species

This question in 9693/21 May/June 2018

1 When a whale dies, its carcass (body) falls to the deep ocean floor. The carcass creates a complex ecosystem, which supports a variety of deep-sea organisms for decades. At first, scavengers and decomposers feed on the carcass. Later, the community of organisms resembles the community found at a hydrothermal vent. Only the skeleton of the whale remains, and bacteria feeding on it generate hydrogen sulfide. This is used by chemosynthetic bacteria, which support a food web including many diverse and rare species of mussels, worms and snails. (a) State the trophic level of the chemosynthetic bacteria. Explain your answer. … … … … … … [3] Table 1.1 shows the change in the number of species on a newly fallen whale carcass over time. Table 1.1 number of species age of whale carcass / months on the whale carcass 6 15 14 31 24 33 33 38 42 42 57 50 (b) On the grid, plot a graph of the data in Table 1.1. Join the points on your graph with ruled straight lines. [4] (c) Describe the relationship between the age of whale carcass and the number of species present. … … … … [2] [Total: 9]

9 marks

Mark scheme: 1(a) any three of: producers / trophic level 1 ; capture chemical energy (of dissolved minerals) ; idea of, make biomass / organic compounds ; idea of, making energy available (to rest of food chain) ; 3 R idea of energy production 1(b) both axes labelled with units ; linear scale ; all points plotted correctly ; points joined with ruled lines ; 4 plots to cover at least half grid +/– half square R extrapolation beyond +/– half square Max 3 for other types of graph (not MP4) 1(c) any two of general trend increases ; rapid increase at first then levels off / slower after 14 months ; manipulation of data ; 2

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 9693/22 May/June 2018

1 When a whale dies, its carcass (body) falls to the deep ocean floor. The carcass creates a complex ecosystem, which supports a variety of deep-sea organisms for decades. At first, scavengers and decomposers feed on the carcass. Later, the community of organisms resembles the community found at a hydrothermal vent. Only the skeleton of the whale remains, and bacteria feeding on it generate hydrogen sulfide. This is used by chemosynthetic bacteria, which support a food web including many diverse and rare species of mussels, worms and snails. (a) State the trophic level of the chemosynthetic bacteria. Explain your answer. … … … … … … [3] Table 1.1 shows the change in the number of species on a newly fallen whale carcass over time. Table 1.1 number of species age of whale carcass / months on the whale carcass 6 15 14 31 24 33 33 38 42 42 57 50 (b) On the grid, plot a graph of the data in Table 1.1. Join the points on your graph with ruled straight lines. [4] (c) Describe the relationship between the age of whale carcass and the number of species present. … … … … [2] [Total: 9]

9 marks

Mark scheme: 1(a) any three of: producers / trophic level 1 ; capture chemical energy (of dissolved minerals) ; idea of, make biomass / organic compounds ; idea of, making energy available (to rest of food chain) ; 3 R idea of energy production 1(b) both axes labelled with units ; linear scale ; all points plotted correctly ; points joined with ruled lines ; 4 plots to cover at least half grid +/– half square R extrapolation beyond +/– half square Max 3 for other types of graph (not MP4) 1(c) any two of general trend increases ; rapid increase at first then levels off / slower after 14 months ; manipulation of data ; 2

This question in 9693/23 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

2 Fig. 2.1 shows a settlement of acorn barnacles, Semibalanus balanoides, on a rocky shore. 1 cm Fig. 2.1 A student decided to look at the distribution of three different barnacle species on a rocky shore. The results of this investigation are shown in Table 2.1. Table 2.1 distance above number of barnacles per unit area low water spring tide line / m species 1 species 2 species 3 0 0 98 13 2 1 42 49 4 6 3 87 6 49 0 63 8 91 0 15 10 84 0 5 (a) Describe an experimental procedure the student could use to carry out this investigation. … … … … … … … … [4] (b) Use the data in Table 2.1 to determine where the greatest biodiversity of barnacles is found. … m [1] (c) Use the data in Table 2.1 to compare the distribution of the three barnacle species. Suggest reasons for the differences in distribution. … … … … … … … … [4] [Total: 9]

9 marks

This question in 9693/20 Oct/Nov 2018

1 Fig. 1.1 shows the common limpet, Patella vulgata, a mollusc that inhabits rocky shores across Northern Europe. When submerged, limpets feed by moving across the rock surface, scraping off algae. During low tide they attach themselves securely to the rock surface. Repeated use of the same position on the rock by limpets over many years can lead to a home scar forming, also visible in Fig. 1.1. home scar Fig. 1.1 Individual limpets repeatedly return to the same home scar, and are therefore said to have a homing instinct. A researcher investigated this homing instinct to test the following hypothesis. ‘The further a limpet moves from its home scar, the less likely it is to return there.’ At low tide, a sample of similar sized limpets was carefully removed from their home scar and placed 10 cm away, ensuring they reattached securely to the rock surface. The limpets and their original home scars were marked with numbers. The limpets were left until the next low tide. The researcher then counted how many limpets had returned to their home scar. This process was repeated in five different areas, but with limpets moved different distances each time. (a) Suggest two variables that the researcher was unable to control. 1 … … 2 … … [2] Table 1.1 shows the results. Table 1.1 percentage distance moved number of limpets number returning returning / cm moved to home scar to home scar 10 16 15 93.8 20 15 10 66.7 30 14 11 78.6 40 15 11 73.3 50 15 9 (b) (i) Calculate the percentage of limpets returning to their home scar after being moved 50 cm. Show your working. … [2] (ii) Plot a line graph to show the relationship between the distance the limpets were moved and the percentage returning to their home scar. Include a point for your calculated value for limpets that were moved 50 cm. Join the points with ruled, straight lines. [4] (iii) Use the data in Table 1.1 and your graph to discuss the extent to which the data support the hypothesis. … … … … … … [3] (c) Suggest and explain how the homing instinct may increase the chance of survival of limpets. … … … … [2] [Total: 13]

13 marks

Mark scheme: 1(a) any 2 of: age of limpets ; number of limpets in sample ; health of limpets ; impact of predation / death of limpets ; exact morphology of rock / type of rock / nature of rock surface ; (degree of) turbulence (when submerged) / wave action / currents ; length of time exposed / time between tides ; height of tide ; 2 1(b)(i) 60(.0) ; ; 2 1(b)(ii) appropriate linear scale for both axes ; both axes labelled including units ; all points plotted correctly (± 1 mm) ; distance moved / cm percentage returning to home scar 10 93.8 20 66.7 30 78.6 40 73.3 50 60.0 but ECF from 1(b)(i) all points joined correctly with ruled straight lines(± 1 mm) ; 4 Question Answer Marks Guidance 1(b)(iii) any 3 of: data shows the greater the distance, the lower the percentage of limpets returning / AW ; manipulation of figures to support answer ; ref. to (ignoring) anomaly for 20 cm OR reference to it not supporting hypothesis ; ref. to, only 5 data points / lack of repeats ; 3 1(c) any 2 of: home scar allows better surface for attachment to rocks (during low tide) ; so less chance of predation ; so less chance of, desiccation / drying out ; home scar in, more sheltered / less exposed area ; so less chance of being washed off / greater resistance to wave action ; AVP ; ; 2 A tight seal can be formed against rock e.g. allows water to be trapped under shell ; which assists gas exchange ;

This question in 9693/21 May/June 2019

2 Tetraselmis is a single-celled phytoplankton, often cultured as a food source for the aquaculture of marine fish larvae. Tetraselmis is grown using a batch culture method. All the required nutrients and a small population of Tetraselmis are placed into a container and grown for several days. Carbon dioxide is continuously bubbled through the water and the light intensity is kept constant. Table 2.1 shows the mean cell density of Tetraselmis grown using a batch culture method over 10 days. Table 2.1 day mean cell density / cells per mm3 0 0 1 70 2 120 3 300 4 5 1400 6 1750 7 1900 8 2000 9 1800 10 1500 To obtain the data in Table 2.1, five samples of the culture were counted daily and a mean value was calculated. Table 2.2 shows the data for day 4. Table 2.2 sample number 1 2 3 4 5 cell density / cells per mm3 681 201 726 654 738 (a) (i) Calculate the mean cell density for day 4, using sample numbers 1, 3, 4 and 5. Give your answer to an appropriate number of significant figures. … cells per mm3 [1] (ii) Suggest why sample 2 was not used to calculate the mean cell density. … … [1] (c) (i) Use the results in Table 2.1 and your graph to suggest the day on which it would be best to harvest Tetraselmis. Give a reason for your answer. … … … … [2] (ii) Predict what would happen to the mean cell density, if the culture was continued to day 15. Explain your prediction. … … … … [2] (d) Name the process which phytoplankton use to transfer light energy to a form available to the rest of the food chain. … … [1] [Total: 11]

11 marks

This question in 9693/20 Oct/Nov 2019

1 Fig. 1.1 shows a species of butterfly fish, Chaetodon austriacus, which inhabits coral reefs in the Red Sea. These fish feed primarily by biting live coral. Fig. 1.1 Scientists researched the feeding behaviour of C. austriacus in areas of one coral reef with different percentage cover of coral. They measured: • the feeding rate, as number of bites of live coral per 30 minute period • the size of the territory of the fish, in m2 • the percentage of the area covered by coral. The results are shown in Fig. 1.2 and Fig. 1.3. 600 550 500 feeding rate / bites per 450 30 minutes 400 350 300 0 10 20 30 40 50 percentage cover of coral Fig. 1.2 2500 2000 territory size 1500 / m2 1000 500 0 0 10 20 30 40 50 percentage cover of coral Fig. 1.3 (a) Suggest how the data for percentage cover of coral could be collected. … … … … [2] (b) Suggest a hypothesis that could be formulated, based on the results shown in Fig. 1.2 and Fig. 1.3. … … [1] (c) Suggest explanations for the patterns shown by the data in Fig. 1.2 and Fig. 1.3. … … … … … … [3] (d) The scientists suggested that measuring butterfly fish territory size or feeding rate could be used to assess the health of a coral reef. Discuss the extent to which the data support this suggestion. … … … … … … [3] [Total: 9]

9 marks

Mark scheme: 1(a) any 2 of: use of measured area / use of quadrat ; idea of subdivisions within, area / quadrat ; to record coral coverage (in territory of each fish) ; use of photograph for subsequent analysis ; repeat process ; 2 1(b) any suitable suggestion: increased percentage cover of coral will decrease feeding rate AND / OR territory size ; percentage cover of coral affects feeding rate AND territory size ; there is a (positive) correlation between feeding rate and territory size ; 1 1(c) any 3 of: (territory size will increase with decreased percentage cover) as fish will need to forage further / move around more to find sufficient food ORA ; (feeding rate may increase with decreased percentage cover) as fish will expend more energy seeking food ORA ; (feeding rate may increase with increased cover) as fish can take more bites in one place ; ref. to reasons for increased feeding rate in increased territory size ; AVP ; 3 Question Answer Marks 1(d) any 3 of: (clear) correlation between the variables ; only one species of fish studied ; only one reef studied ; relatively small sample size ; spread of data is high ; credit suitable supporting examples from data ; territory size correlation is stronger ; errors in collection of data e.g. missing a bite ; 3

This question in 9693/21 May/June 2020

2 Phytoplankton are small photosynthetic organisms that float in the upper layers of the oceans. They are eaten by zooplankton. Fig. 2.1 shows the mean number of zooplankton and phytoplankton per m3 in Ticao Pass, a stretch of water between two islands of the Philippines, north of the equator. Data was gathered from September 2010 to April 2011. 120 000 20 000 100 000 15 000 mean number of zooplankton 80 000 / individuals mean number per m3 of phytoplankton / individuals 10 000 per m3 60 000 5000 40 000 20 000 Sept Oct Nov Dec Jan Feb Mar Apr month phytoplankton zooplankton Fig. 2.1 Each data point is the mean from six randomly selected sample sites in Ticao Pass. Table 2.1 shows the numbers of zooplankton from each of the six sample sites in January. Table 2.1 January zooplankton numbers / individuals per m3 site 1 site 2 site 3 site 4 site 5 site 6 mean 3820 4179 4285 3220 4105 3359 (a) (i) Calculate the mean value for the six sample sites in January. … individuals per m3 [1] (ii) Use your answer from part (a)(i) to complete the graph in Fig. 2.1. [2] (b) Explain the relationship between the numbers of phytoplankton and the numbers of zooplankton: (i) from November to December … … … … [2] (ii) from February to March. … … … … [2] (c) (i) State the trophic level of the phytoplankton. … [1] (ii) Suggest reasons for the change in the number of phytoplankton that occurs from March to April. … … … … … … [3] [Total: 11]

11 marks

Mark scheme: 2(a)(i) 3828 ; 1 2(a)(ii) 3828 correctly plotted for January ; lines correctly added joining Dec, Jan and Feb ; 2 2(b)(i) any 2 of: zooplankton numbers low and phytoplankton numbers high ; plenty of food so zooplankton numbers increase ; phytoplankton consumed so numbers decreases ; 2 Question Answer Marks 2(b)(ii) any 2 of: low phytoplankton (numbers) and high zooplankton (numbers) ; so lack of food for zooplankton ; decrease in zooplankton allows phytoplankton numbers to recover ; 2 2(c)(i) first trophic level / trophic level 1 / primary producer / producer ; 1 2(c)(ii) any 3 of: increased water turbidity ; pollution ; decrease in light penetration and photosynthesis ; decrease in nutrient content of water ; increase in numbers of other consumers ; 3

This question in 9693/21 May/June 2020

1 Green shore crabs are predators of the common periwinkle, a herbivorous intertidal snail. A scientist investigated the effect of the presence of a green shore crab on shell length and shell thickness of the common periwinkle. The scientist used ten equal-sized tanks, each filled with the same volume of sea water. The scientist added actively growing brown algae. Each tank was stocked with two common periwinkles as shown in Fig. 1.1. not to scale Fig. 1.1 One male green shore crab, living inside a cage, was placed in each of five of the tanks as shown in Fig. 1.2. The crabs were fed each day. not to scale Fig. 1.2 The length and thickness of the shell of each periwinkle were measured at the start of the investigation, and again after 60 days. (a) (i) Suggest why growing, brown algae were placed in each tank. … … [1] (ii) Suggest one variable that should be controlled when selecting the periwinkles to use in this investigation. … … [1] (iii) Explain why five replicates of the set-up shown in Fig. 1.2 were used. … … [1] (iv) Suggest why the investigation was not continued for more than 60 days. … … … … [2] (b) The results of the investigation are shown in Table 1.1. Table 1.1 predatory mean periwinkle mean periwinkle ratio of mean shell green shore shell length shell thickness length to mean crab / mm / mm shell thickness presence without crab 11.10 1.26 8.81 : 1 with crab 10.20 1.50 … (i) Calculate the percentage difference in shell thickness of the periwinkles in the tanks with a green shore crab, compared to those in tanks without a crab. … % [2] (ii) Suggest one advantage to the periwinkles of the change in shell thickness in the presence of a green shore crab. … … [1] (iii) Complete Table 1.1 by calculating the ratio of mean shell length to mean shell thickness with a green shore crab present. [1] (iv) Referring to Table 1.1, suggest a reason for the difference between the ratios of mean shell length to mean shell thickness in the presence and absence of a green shore crab. … … [1] [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

2 Fig. 2.1 shows a Galapagos penguin, Spheniscus mendiculus, diving for fish. These penguins inhabit several of the Galapagos Islands in the eastern tropical Pacific Ocean. Fig. 2.1 Fig. 2.2 shows the location of the Galapagos Islands in the Pacific Ocean. NorthNorth AmericaAmerica CaribbeanCaribbean SeaSea Atlantic Galapagos Ocean Islands equator South America Pacific Atlantic Ocean Ocean Fig. 2.2 Scientists investigated whether there was a relationship between sea temperature variation and changes in the population size of Galapagos penguins. The sea temperature variation and population size of Galapagos penguins were monitored over 17 years. Sea temperature variation is the difference between the mean sea temperature for a particular year and the long-term sea temperature mean. Fig. 2.3 shows the percentage change in population size of Galapagos penguins plotted against the sea temperature variation for each year. Each plotted point represents a different year. percentage change in Galapagos penguin population 8080 6060 4040 2020 sea temperature –2–2 –1–1 0 11 22 33 44 variation / °C –20–20 –40–40 –60–60 –80–80 Fig. 2.3 (a) Use a ruler to draw one straight line of best fit through the data in Fig. 2.3. [1] (b) Use Fig. 2.3 to describe the effect of sea temperature variation on percentage change in the Galapagos penguin population. … … … … [2] (c) Use your line to predict the percentage change in the Galapagos penguin population when there is a sea temperature variation of +2 °C. … … [1] (d) When the sea temperature variation was +2 °C or higher, an El Niño event had occurred. Explain why this caused the percentage change in Galapagos penguin population observed. … … … … … … … … [4] [Total: 8]

8 marks

Mark scheme: 2(a) line correctly drawn ; 1 2(b) if (sea) temperature (variation) increases, penguin population (change) decreases ORA ; plus any 1 of: majority of data clustered, above population change of –20% / below temperature variation of +0.5°C ; use of data to illustrate relationship ; 2 2(c) value commensurate with plotted line ; 1 2(d) any 4 of; upwelling reduced / ceases ; nutrients / minerals, (in surface waters) not replaced / depleted ; reduced productivity / reduced producer populations ; disruption of food chain / reduced number of primary consumers ; fewer fish / less food available for penguins to eat ; penguins migrate elsewhere ; (idea of) unsuccessful breeding ; 4

This question in 9693/21 May/June 2021

2 Fig. 2.1 shows some dinoflagellates, which are small photosynthetic organisms that float in the upper layers of the oceans. They migrate up and down the water column in response to changing environmental conditions. Fig. 2.1 (a) Describe a method for a laboratory-based investigation that tests the following hypothesis: Increasing light intensity causes dinoflagellates to migrate to the surface waters. … … … … … … … … … … … … … [5] (b) Suggest why dinoflagellates may benefit from their ability to migrate to the surface waters. … … … … [2] [Total: 7]

7 marks

Mark scheme: 2(a) any 5 from: (independent variable) description of changing light intensity ; range of three or more light intensity values ; (dependent variable) measuring dinoflagellate numbers near surface ; (control variables) any 2 from: water temperature / water salinity / water pH / nutrient content of water / volume of water / same species / initial distribution or concentration of dinoflagellates ; ; leave for suitable amount of time (at least one hour up to 48 hours) ; tanks of seawater containing dinoflagellates ; idea of repeats ; calculate mean ; 2(b) any 2 from: idea of increased, light intensity / availability of light ; increase their rate of photosynthesis near surface ; increased productivity / biomass production ; allows for increased rate of reproduction ; ref. to increased access to carbon dioxide near surface ; 2

This question in 9693/22 May/June 2021

2 Fig. 2.1 shows some dinoflagellates, which are small photosynthetic organisms that float in the upper layers of the oceans. They migrate up and down the water column in response to changing environmental conditions. Fig. 2.1 (a) Describe a method for a laboratory-based investigation that tests the following hypothesis: Increasing light intensity causes dinoflagellates to migrate to the surface waters. … … … … … … … … … … … … … [5] (b) Suggest why dinoflagellates may benefit from their ability to migrate to the surface waters. … … … … [2] [Total: 7]

7 marks

Mark scheme: 2(a) any 5 from: (independent variable) description of changing light intensity ; range of three or more light intensity values ; (dependent variable) measuring dinoflagellate numbers near surface ; (control variables) any 2 from: water temperature / water salinity / water pH / nutrient content of water / volume of water / same species / initial distribution or concentration of dinoflagellates ; ; leave for suitable amount of time (at least one hour up to 48 hours) ; tanks of seawater containing dinoflagellates ; idea of repeats ; calculate mean ; 2(b) any 2 from: idea of increased, light intensity / availability of light ; increase their rate of photosynthesis near surface ; increased productivity / biomass production ; allows for increased rate of reproduction ; ref. to increased access to carbon dioxide near surface ; 2

This question in 9693/23 May/June 2021

1 The distribution of seven different species of mangrove tree, A to G, along several Australian estuaries was investigated. In each estuary, locations were classified as upper, middle and lower. This is shown in Fig. 1.1. upper middle X lower ocean Fig. 1.1 The intertidal zones on the shore of each estuary were classified as high, medium and low. This is shown in Fig. 1.2. mean high tide high intertidal zone X medium intertidal zone low intertidal zone mean low tide Fig. 1.2 The researchers counted the number of each species of mangrove tree in the three locations in each estuary. They calculated the mean percentage of each species in each location. They recorded the presence or absence of each species in each intertidal zone. Their results are shown in Table 1.1. Table 1.1 mean percentage of each species at presence of each species at each location in the estuary each intertidal zone species upper middle lower high medium low A 82 14 4   B 70 26 4   C 25 39 36   D 35 46 19  E 30 57 13   F 3 43 54  G 4 4 92  (a) Use Fig. 1.1, Fig. 1.2 and Table 1.1 to state and explain which species, A to G: (i) is most tolerant of the widest range of salinities … … … … [2] (ii) is most tolerant of long periods exposed to air … … … … [2] (iii) is most likely to be found at position X, which is shown in Fig. 1.1 and Fig. 1.2. … … … … [2] (b) (i) Explain why the scientists collected data from more than one estuary. … … … … [2] (ii) Suggest one other variable that may affect the distribution of mangrove tree species, other than salinity or time exposed to air. … [1] [Total: 9]

9 marks

This question in 9693/20 Oct/Nov 2021

1 Artificial reefs are widely used to regenerate coral reef ecosystems. Artificial reefs can be made using 3D printing technology. This technology makes exact copies of the shape and structure of real coral skeletons. Fig. 1.1 shows an artificial coral skeleton made using this technology. Fig. 1.1 (a) Scientists investigated how damselfish (small reef fish) behave when introduced to artificial coral skeletons made of different types of material. Four different types of material were used, A–D, in addition to natural coral as a control. Individual damselfish were introduced to tanks containing all five types of coral skeletons. A total of 44 fish were used. They were able to move freely between the different types of coral skeleton, and the time spent associating with each was recorded. (i) Suggest two variables that the scientists need to control to obtain reliable results. 1 … … 2 … … [2] (ii) Fig. 1.2 shows the percentage of time the damselfish spent associating with each type of coral skeleton. 20 15 percentage of time damselfish 10 associate with coral skeleton 5 0 natural A B C D type of coral material Fig. 1.2 State a conclusion regarding the behaviour of the fish around the coral skeletons. Use the information in Fig. 1.2 to support your answer. … … … … … … [3] (iii) Suggest reasons why small reef fish such as damselfish are dependent on coral for their survival. … … … … [2] (b) Scientists then investigated the settlement and growth of coral polyp larvae on artificial coral skeletons. Equal numbers of coral polyp larvae were introduced into separate tanks containing each type of artificial coral skeleton. The percentage of larvae attached to each type of coral skeleton was recorded over a 14-day period, and the growth rate of those that attached was calculated. Fig. 1.3 shows the percentage of larvae attached to each type of coral skeleton material. 30 Key A B 25 C D 20 percentage of larvae attached 15 10 5 1 2 3 4 5 6 7 8 9 10 11 12 13 14 day Fig. 1.3 Table 1.1 shows the mean growth rate of attached coral polyp larvae. Table 1.1 coral skeleton mean growth rate of material coral polyp larvae / mm2 per week A 0.078 B 0.201 C 0.211 D 0.162 Discuss which of the materials A–D is best to use for the growth of coral polyp larvae. Use the results shown in Fig. 1.3 and Table 1.1 to support your answer. … … … … … … [3] (c) The scientists concluded that 3D-printed coral skeletons can be used for regenerating coral reef ecosystems. Evaluate the extent to which the results from this investigation support this conclusion. … … … … … … [3] (d) Fig. 1.4 shows a damselfish similar to those used in the investigation. Fig. 1.4 (i) Make a large drawing of the damselfish in the space below. [4] (ii) Label the caudal fin and the dorsal fin on your drawing. [1] [Total: 18]

18 marks

Mark scheme: 1(a)(i) any 2 from: length of time (observed for) ; size of (coral) samples ; spacing of (coral) samples ; any water quality factor, e.g. pH / temperature / salinity / nutrients ;; (idea of) illumination / light intensity / sunlight ; size of tank ; same, size / age / species fish ; colour of coral ; (idea of avoiding bias towards a sample) distance fish introduced / released, to the coral ; 1(a)(ii) any 2 from: samples A, B or C have higher (association) time than natural sample ; sample (B and) C have greatest (increase in association) time / spend largest amount of time with coral C (and B) ; sample D has same, effect / (association) time as natural sample ; AND correct use of data from graph to support answer ; 3 1(a)(iii) any 2 from: food source / eat zooxanthellae ; shelter / protection (from, predators / water movement) ; (idea of) reproductive site / nursery ; 2 Question Answer Marks 1(b) any 3 from: (from day 7) material D has the greatest percentage of larvae attaching… ; …but does not have the highest mean growth rate / relatively high growth rate ; sample(s) (B and) C have the highest growth rate(s) ; sample A has lowest percentage settling and lowest growth rate ; materials B and/or D (greatest percentage of larvae attaching) and are stable / C or D are the lowest percentage of larvae attaching and are decreasing ; insufficient length of time of investigation because percentage of C settling is decreasing ; correct use of manipulated data from table or graph to support answer ; 3 1(c) any 3 from: (supports conclusion) as fish associate with artificial coral at least as much as natural ; (supports conclusion) as some samples allow larvae to, settle / grow ; 44 individual fish used is a high number of repeats ; (however) coral polyps may grow faster / attach better, on natural coral / no data on natural coral growth rate ; (however) larvae survival only monitored for 14 days ; (however) only one species / type of fish studied ; (however) no information on number / type of coral larvae used ; should conduct further research in natural habitat rather than tanks ; (idea of longer time period needed) research for longer than two weeks (idea of) research required on natural (bleached) coral to compare (settlement / growth rates) ; AVP ; 3 Question Answer Marks 1(d)(i) clear outline ; suitable size ; in proportion ; detail – must include all visible fins and outline of three black vertical areas in approximately correct positions and the eye ; 4 1(d)(ii) both fins labelled correctly either on the drawing or photograph ; 1

This question in 9693/21 May/June 2022

5 Bioluminescence occurs when organisms emit light from a chemical reaction in their tissues. It is used by various marine organisms including dinoflagellates, such as those shown in Fig. 5.1. 20 µm Fig. 5.1 An investigation was carried out to test whether bioluminescence in dinoflagellates could help them to avoid predation by zooplankton, such as copepods. Dinoflagellates were kept in tanks of sea water. They were exposed to different concentrations of copepodamide, a chemical released into water by copepods, over a period of 48 hours. The light production was measured after 1 hour, 12 hours and 48 hours. The results were used to calculate the relative increase in light production. (a) (i) Suggest one advantage of using a chemical stimulus such as copepodamide, rather than live copepods. … … [1] (ii) Suggest one other variable that would need to be standardised throughout this investigation. … … [1] (b) The results of the investigation after 48 hours are shown in Table 5.1. Table 5.1 concentration of copepodamide percentage increase in light / arbitrary units production after 48 hours 0 0 2 120 4 165 6 205 8 230 10 250 The results obtained after 1 hour and 12 hours have been plotted on Fig. 5.2. 250 12 hours 1 hour 0 0 2 4 6 8 10 Fig. 5.2 (i) Plot the values from Table 5.1 for percentage increase in light production after 48 hours on Fig. 5.2. Complete the scale for the y-axis and the labels for both axes. Two scale values have been added for you. Draw a line of best fit to indicate the overall trend for the data you have plotted. [4] (ii) Describe the relationship between copepodamide concentration and percentage increase in light production as shown in Fig. 5.2. … … … … … … [3] (iii) Discuss whether the data in Table 5.1 and Fig. 5.2 support the idea that dinoflagellates use bioluminescence to avoid predation. … … … … … … [3]

12 marks

Mark scheme: 5(a)(i) idea of, easier to, manipulate / control the variable / no predation of dinoflagellates / ethical / AW ; 1 5(a)(ii) any 1 from: temperature / pH / salinity / nutrient content / illumination of water / light intensity / dissolved CO2 / dissolved O2 / volume of water / tank size ; number / concentration / species of dinoflagellates ; 1 5(b)(i) correct plots within 1 mm ; correct scale on y-axis ; correct label on both x and y-axis ; suitable line of best fit ; 4 Question Answer Marks 5(b)(ii) any 3 from: higher concentration of copepodamide results in increased light production ; increase is greatest at lower concentrations / ORA ; greatest effect seen after 48 hours / effects are shown more clearly over a longer period of time / the longer the dinoflagellates are exposed the more light they produce / AW ; little effect after 1 hour / ORA ; at 48 hours it is still increasing ; at 0 concentration zero light is emitted ; increases at the start before levelling out ; use of data / manipulation of data e.g. after 1 hour the percentage increase is only 40% ; 3 5(b)(iii) any 3 from: data supports idea + because there is greater bioluminescence in presence of, copepodamide / predator ; (idea of) long time taken for full effect may not help avoid predation ; bioluminescence may be coincidence / for other biochemical reasons; (idea of) not knowing how much copepodamide equates to one copepod ; not tested with actual predators to see if bioluminescence works ; 3 5(c) any 3 from: (supported because…) 1 (in sample A) non-bioluminescent dinoflagellates make up majority (76%) of predator diet ; 2 in sample B or C when bioluminescent dinoflagellates present, majority of diet changes to alternative prey (75%) or (96%) / ORA ; 3 idea that presence of copepodamide increases further the extent to which alternative prey are consumed / copepodamide decreases the extent to which dinoflagellates are being consumed ; 4 manipulation of data e.g. difference of 51% dinoflagellate consumption between samples A and B ; (not supported because…) 5 may be other differences between types of dinoflagellates that affect predation (e.g. chemical cues) ; 6 not clear how many dinoflagellates / alternative prey were available to eat ; 7 (idea that) other predators may not be deterred by bioluminescence ; 8 reference to lack of, repeats / means in the investigation ; 9 repeat investigation with non-bioluminescent dinoflagellates ; 10 AVP, e.g. comment on methodology 3

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

3 Many organisms have a planktonic stage in their development. (a) Define the term plankton. … … [2] (b) Some zooplankton show a vertical swimming response towards light when a light stimulus is applied above them. These zooplankton do not swim in darkness. An investigation is carried out in a laboratory to compare the swimming speeds of zooplankton of different sizes in response to white light. A student makes the hypothesis: The swimming speed of zooplankton is proportional to their size. The maximum speed of any of the zooplankton provided is 10 mm s–1. The size range of the zooplankton is 2–10 mm. distance Speed can be calculated using the equation: speed = time (i) List the equipment required for this investigation. 1 … 2 … 3 … [3] (ii) State three key variables to standardise in this investigation. 1 … 2 … 3 … [3] (iii) Outline a method to compare the swimming speeds of zooplankton of different sizes in response to white light. … … … … … … … … … … … … … [5] (c) Use the space below to draw a suitable table to record the results from the method described in (b)(iii). Include full headings and units in the table. Do not write in any results. [2] [Total: 15]

15 marks

Mark scheme: 3(a) microscopic ; 2 drift in currents / limited motility ; 3(b)(i) any 3 from: 3 stopwatch ; ruler ; light (source) ; water container / measuring cylinder (containing water) ; AVP ; 3(b)(ii) any 3 from: 3 (same) temperature ; (same) pH ; (same) salinity ; (same) oxygen concentration ; (same) time to settle ; (same) species ; (same) volume / height of measuring cylinder / water column ; (same) intensity of light source ; (same) exposure time OR (same) distance travelled ; ref. to background light ; 3(b)(iii) any 5 from: 5 place a zooplankton in measuring cylinder containing sea water and leave in dark (to settle to the bottom) ; (place glass sheet between light source and cylinder) to ensure temperature doesn’t change ; switch on light ; record time to swim (set) distance e.g. 5 cm / analyse a video to find time OR record distance swam in a set time ; repeat 3 times + find mean ; repeat with at least 3 different sized zooplankton / 3 stated sizes ; photograph / measure, size of each zooplankton on ruler / mm scale ; accept reasonable safety precaution ; AVP ; 3(c) a column / row, headed zooplankton size / mm ; 2 PLUS any 1 from: a column / row, headed distance, cm / mm OR a column / row headed time / s OR a column / row headed speed mm / s or mm s–1 ;

This question in 9693/21 Oct/Nov 2022

6 A report was made to scientists that an invasive tree species, Nypa fruticans, had become established within an area of mangrove forest on the west coast of Africa. An invasive species is an organism that is not native to an area and that easily spreads to cause ecological damage in the new habitat. The scientists investigated this using the hypothesis: The presence of an invasive species reduces biodiversity. Scientists studied two areas of mangrove of equal size. The invasive Nypa species was present in area Y, but not in area X. Large mangrove plant species were identified and the number of each species of plant in each transect was recorded. The results are shown in Table 6.1. (a) Calculate the total number of all species in mangrove area X and record it in Table. 6.1. Table 6.1 number of individuals number of individuals species name in mangrove area X in mangrove area Y Acrostichum aureum 24 3 Avicennia germinans 19 14 Drepanocarpus lanatus 24 4 Nypa fruticans 0 53 Rhizophora harrisonii 3 0 Rhizophora racemosa 50 35 Total number of all species 109 … [1] (b) Simpson’s index of diversity is used to calculate the species diversity of each habitat. Table 6.2 shows the data calculated for mangrove area X. The equation for Simpson’s index of diversity is: n D = 1 – (Σ( N) 2) where: D = Simpson’s index of diversity Σ = sum of (total) n = number of individuals of each different species N = the total number of individuals of all species Use the formula and the data from Table 6.1 to complete Table 6.2 and calculate the Simpson’s index of diversity for mangrove area Y. Table 6.2 mangrove mangrove mangrove mangrove species name area X area X area Y area Y n / N (n / N)2 n / N (n / N )2 Acrostichum aureum 0.20 0.0400 0.03 0.0009 Avicennia germinans 0.16 0.0256 0.13 0.0169 Drepanocarpus lanatus 0.20 0.0400 0.04 0.0016 Nypa fruticans 0 0 … … Rhizophora harrisonii 0.03 0.0009 … … Rhizophora racemosa 0.42 0.1764 … … Σ 0.2829 … Simpson’s index of diversity for mangrove area X = 1 – 0.2829 = 0.7171 Simpson’s index of diversity for mangrove area Y = … [5] (c) Discuss the extent to which the hypothesis is proven. … … … … … … [3] [Total: 9] The boundaries and names shown, the designations used and the presentation of material on any maps contained in this question paper/insert do not imply official endorsement or acceptance by Cambridge Assessment International Education concerning the legal status of any country, territory, or area or any of its authorities, or of the delimitation of its frontiers or boundaries.

9 marks

Mark scheme: 6(a) 120 ; 1 6(b) 5 mangrove area Y mangrove area Y n / N (n / N)2 Nypa fruticans 0.49 0.2401 ; / (A range of 0.2334–0.2364) Rhizophora harrisonii 0 0 ; Rhizophora racemosa 0.32 0.1024 ; (A 0.1031)  0.3619 ; (A range 0.3555–0.3589) 1 – 0.3619 = 0.6381 ; (0.6411 – 0.6445) 6(c) any 3 from: 3 inconclusive ; diversity index lower for mangrove area Y by 0.079 (A ECF from 6(b)) / ORA ; (but) not by a large amount / need to do (named) significance test ; but species richness is unchanged ; (looking at raw data) 2 species (Acrosichum aureum and Drepanocarpus lanatus) reduced by a large amount (in area Y) ; one species (Rhizophora harrisonii) disappeared but numbers low in mangrove area X ; dominant species in mangrove area X (Rhizophora racemosa) is no longer the dominant species ; need to test in more areas / more data needs to be collected ; AVP ;

This question in 9693/21 Oct/Nov 2022

3 Many organisms have a planktonic stage in their development. (a) Define the term plankton. … … [2] (b) Some zooplankton show a vertical swimming response towards light when a light stimulus is applied above them. These zooplankton do not swim in darkness. An investigation is carried out in a laboratory to compare the swimming speeds of zooplankton of different sizes in response to white light. A student makes the hypothesis: The swimming speed of zooplankton is proportional to their size. The maximum speed of any of the zooplankton provided is 10 mm s–1. The size range of the zooplankton is 2–10 mm. distance Speed can be calculated using the equation: speed = time (i) List the equipment required for this investigation. 1 … 2 … 3 … [3] (ii) State three key variables to standardise in this investigation. 1 … 2 … 3 … [3] (iii) Outline a method to compare the swimming speeds of zooplankton of different sizes in response to white light. … … … … … … … … … … … … … [5] (c) Use the space below to draw a suitable table to record the results from the method described in (b)(iii). Include full headings and units in the table. Do not write in any results. [2] [Total: 15]

15 marks

Mark scheme: 3(a) microscopic ; 2 drift in currents / limited motility ; 3(b)(i) any 3 from: 3 stopwatch ; ruler ; light (source) ; water container / measuring cylinder (containing water) ; AVP ; 3(b)(ii) any 3 from: 3 (same) temperature ; (same) pH ; (same) salinity ; (same) oxygen concentration ; (same) time to settle ; (same) species ; (same) volume / height of measuring cylinder / water column ; (same) intensity of light source ; (same) exposure time OR (same) distance travelled ; ref. to background light ; 3(b)(iii) any 5 from: 5 place a zooplankton in measuring cylinder containing sea water and leave in dark (to settle to the bottom) ; (place glass sheet between light source and cylinder) to ensure temperature doesn’t change ; switch on light ; record time to swim (set) distance e.g. 5 cm / analyse a video to find time OR record distance swam in a set time ; repeat 3 times + find mean ; repeat with at least 3 different sized zooplankton / 3 stated sizes ; photograph / measure, size of each zooplankton on ruler / mm scale ; accept reasonable safety precaution ; AVP ; 3(c) a column / row, headed zooplankton size / mm ; 2 PLUS any 1 from: a column / row, headed distance, cm / mm OR a column / row headed time / s OR a column / row headed speed mm / s or mm s–1 ;

This question in 9693/22 Oct/Nov 2022

6 A report was made to scientists that an invasive tree species, Nypa fruticans, had become established within an area of mangrove forest on the west coast of Africa. An invasive species is an organism that is not native to an area and that easily spreads to cause ecological damage in the new habitat. The scientists investigated this using the hypothesis: The presence of an invasive species reduces biodiversity. Scientists studied two areas of mangrove of equal size. The invasive Nypa species was present in area Y, but not in area X. Large mangrove plant species were identified and the number of each species of plant in each transect was recorded. The results are shown in Table 6.1. (a) Calculate the total number of all species in mangrove area X and record it in Table. 6.1. Table 6.1 number of individuals number of individuals species name in mangrove area X in mangrove area Y Acrostichum aureum 24 3 Avicennia germinans 19 14 Drepanocarpus lanatus 24 4 Nypa fruticans 0 53 Rhizophora harrisonii 3 0 Rhizophora racemosa 50 35 Total number of all species 109 … [1] (b) Simpson’s index of diversity is used to calculate the species diversity of each habitat. Table 6.2 shows the data calculated for mangrove area X. The equation for Simpson’s index of diversity is: n D = 1 – (Σ( N) 2) where: D = Simpson’s index of diversity Σ = sum of (total) n = number of individuals of each different species N = the total number of individuals of all species Use the formula and the data from Table 6.1 to complete Table 6.2 and calculate the Simpson’s index of diversity for mangrove area Y. Table 6.2 mangrove mangrove mangrove mangrove species name area X area X area Y area Y n / N (n / N)2 n / N (n / N )2 Acrostichum aureum 0.20 0.0400 0.03 0.0009 Avicennia germinans 0.16 0.0256 0.13 0.0169 Drepanocarpus lanatus 0.20 0.0400 0.04 0.0016 Nypa fruticans 0 0 … … Rhizophora harrisonii 0.03 0.0009 … … Rhizophora racemosa 0.42 0.1764 … … Σ 0.2829 … Simpson’s index of diversity for mangrove area X = 1 – 0.2829 = 0.7171 Simpson’s index of diversity for mangrove area Y = … [5] (c) Discuss the extent to which the hypothesis is proven. … … … … … … [3] [Total: 9] The boundaries and names shown, the designations used and the presentation of material on any maps contained in this question paper/insert do not imply official endorsement or acceptance by Cambridge Assessment International Education concerning the legal status of any country, territory, or area or any of its authorities, or of the delimitation of its frontiers or boundaries.

9 marks

Mark scheme: 6(a) 120 ; 1 6(b) 5 mangrove area Y mangrove area Y n / N (n / N)2 Nypa fruticans 0.49 0.2401 ; / (A range of 0.2334–0.2364) Rhizophora harrisonii 0 0 ; Rhizophora racemosa 0.32 0.1024 ; (A 0.1031)  0.3619 ; (A range 0.3555–0.3589) 1 – 0.3619 = 0.6381 ; (0.6411 – 0.6445) 6(c) any 3 from: 3 inconclusive ; diversity index lower for mangrove area Y by 0.079 (A ECF from 6(b)) / ORA ; (but) not by a large amount / need to do (named) significance test ; but species richness is unchanged ; (looking at raw data) 2 species (Acrosichum aureum and Drepanocarpus lanatus) reduced by a large amount (in area Y) ; one species (Rhizophora harrisonii) disappeared but numbers low in mangrove area X ; dominant species in mangrove area X (Rhizophora racemosa) is no longer the dominant species ; need to test in more areas / more data needs to be collected ; AVP ;

This question in 9693/22 Oct/Nov 2022

3 Many organisms have a planktonic stage in their development. (a) Define the term plankton. … … [2] (b) Some zooplankton show a vertical swimming response towards light when a light stimulus is applied above them. These zooplankton do not swim in darkness. An investigation is carried out in a laboratory to compare the swimming speeds of zooplankton of different sizes in response to white light. A student makes the hypothesis: The swimming speed of zooplankton is proportional to their size. The maximum speed of any of the zooplankton provided is 10 mm s–1. The size range of the zooplankton is 2–10 mm. distance Speed can be calculated using the equation: speed = time (i) List the equipment required for this investigation. 1 … 2 … 3 … [3] (ii) State three key variables to standardise in this investigation. 1 … 2 … 3 … [3] (iii) Outline a method to compare the swimming speeds of zooplankton of different sizes in response to white light. … … … … … … … … … … … … … [5] (c) Use the space below to draw a suitable table to record the results from the method described in (b)(iii). Include full headings and units in the table. Do not write in any results. [2] [Total: 15]

15 marks

Mark scheme: 3(a) microscopic ; 2 drift in currents / limited motility ; 3(b)(i) any 3 from: 3 stopwatch ; ruler ; light (source) ; water container / measuring cylinder (containing water) ; AVP ; 3(b)(ii) any 3 from: 3 (same) temperature ; (same) pH ; (same) salinity ; (same) oxygen concentration ; (same) time to settle ; (same) species ; (same) volume / height of measuring cylinder / water column ; (same) intensity of light source ; (same) exposure time OR (same) distance travelled ; ref. to background light ; 3(b)(iii) any 5 from: 5 place a zooplankton in measuring cylinder containing sea water and leave in dark (to settle to the bottom) ; (place glass sheet between light source and cylinder) to ensure temperature doesn’t change ; switch on light ; record time to swim (set) distance e.g. 5 cm / analyse a video to find time OR record distance swam in a set time ; repeat 3 times + find mean ; repeat with at least 3 different sized zooplankton / 3 stated sizes ; photograph / measure, size of each zooplankton on ruler / mm scale ; accept reasonable safety precaution ; AVP ; 3(c) a column / row, headed zooplankton size / mm ; 2 PLUS any 1 from: a column / row, headed distance, cm / mm OR a column / row headed time / s OR a column / row headed speed mm / s or mm s–1 ;

This question in 9693/23 Oct/Nov 2022

6 A report was made to scientists that an invasive tree species, Nypa fruticans, had become established within an area of mangrove forest on the west coast of Africa. An invasive species is an organism that is not native to an area and that easily spreads to cause ecological damage in the new habitat. The scientists investigated this using the hypothesis: The presence of an invasive species reduces biodiversity. Scientists studied two areas of mangrove of equal size. The invasive Nypa species was present in area Y, but not in area X. Large mangrove plant species were identified and the number of each species of plant in each transect was recorded. The results are shown in Table 6.1. (a) Calculate the total number of all species in mangrove area X and record it in Table. 6.1. Table 6.1 number of individuals number of individuals species name in mangrove area X in mangrove area Y Acrostichum aureum 24 3 Avicennia germinans 19 14 Drepanocarpus lanatus 24 4 Nypa fruticans 0 53 Rhizophora harrisonii 3 0 Rhizophora racemosa 50 35 Total number of all species 109 … [1] (b) Simpson’s index of diversity is used to calculate the species diversity of each habitat. Table 6.2 shows the data calculated for mangrove area X. The equation for Simpson’s index of diversity is: n D = 1 – (Σ( N) 2) where: D = Simpson’s index of diversity Σ = sum of (total) n = number of individuals of each different species N = the total number of individuals of all species Use the formula and the data from Table 6.1 to complete Table 6.2 and calculate the Simpson’s index of diversity for mangrove area Y. Table 6.2 mangrove mangrove mangrove mangrove species name area X area X area Y area Y n / N (n / N)2 n / N (n / N )2 Acrostichum aureum 0.20 0.0400 0.03 0.0009 Avicennia germinans 0.16 0.0256 0.13 0.0169 Drepanocarpus lanatus 0.20 0.0400 0.04 0.0016 Nypa fruticans 0 0 … … Rhizophora harrisonii 0.03 0.0009 … … Rhizophora racemosa 0.42 0.1764 … … Σ 0.2829 … Simpson’s index of diversity for mangrove area X = 1 – 0.2829 = 0.7171 Simpson’s index of diversity for mangrove area Y = … [5] (c) Discuss the extent to which the hypothesis is proven. … … … … … … [3] [Total: 9] The boundaries and names shown, the designations used and the presentation of material on any maps contained in this question paper/insert do not imply official endorsement or acceptance by Cambridge Assessment International Education concerning the legal status of any country, territory, or area or any of its authorities, or of the delimitation of its frontiers or boundaries.

9 marks

Mark scheme: 6(a) 120 ; 1 6(b) 5 mangrove area Y mangrove area Y n / N (n / N)2 Nypa fruticans 0.49 0.2401 ; / (A range of 0.2334–0.2364) Rhizophora harrisonii 0 0 ; Rhizophora racemosa 0.32 0.1024 ; (A 0.1031)  0.3619 ; (A range 0.3555–0.3589) 1 – 0.3619 = 0.6381 ; (0.6411 – 0.6445) 6(c) any 3 from: 3 inconclusive ; diversity index lower for mangrove area Y by 0.079 (A ECF from 6(b)) / ORA ; (but) not by a large amount / need to do (named) significance test ; but species richness is unchanged ; (looking at raw data) 2 species (Acrosichum aureum and Drepanocarpus lanatus) reduced by a large amount (in area Y) ; one species (Rhizophora harrisonii) disappeared but numbers low in mangrove area X ; dominant species in mangrove area X (Rhizophora racemosa) is no longer the dominant species ; need to test in more areas / more data needs to be collected ; AVP ;

This question in 9693/23 Oct/Nov 2022

3 Mangrove forests are globally threatened ecosystems. (a) Describe one adaptation of the red mangrove tree (Rhizophora mangle) for its environment. … … [1] (b) Mangrove forests can be regenerated by growing mangrove seedlings in controlled conditions and planting them into their native forest ecosystems. Scientists investigated the survival of three species of mangrove seedlings (species X, Y and Z) in different salinities of sea water. 50 seedlings of each species were grown in three different salinities: • low salinity (4 ppt) • moderate salinity (16 ppt) • high salinity (34 ppt). The seedlings were kept at these salinities for 30 weeks. The percentage of seedlings surviving was recorded every two weeks. (i) Suggest how the scientists created the different salinity treatments. … … … … [2] (ii) Describe two ways in which this investigation could be improved. 1 … … 2 … … [2] (c) Fig. 3.1 shows the results from this investigation. Key low salinity moderate salinity high salinity 100 80 percentage 60 of seedlings surviving 40 20 species X 0 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 time / weeks 100 80 percentage 60 of seedlings surviving 40 20 species Y 0 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 time / weeks 100 80 percentage 60 of seedlings surviving 40 20 species Z 0 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 time / weeks Fig. 3.1 (i) Describe how the percentage of seedlings surviving in each salinity was calculated. … … [1] (ii) Calculate how many seedlings of species Z survived the first 10 weeks of the investigation in the highest salinity. Show your working. … [2] (d) Fig. 3.2 shows three locations, A, B and C, in a delta. shoreline C A B river water flow delta channels Fig. 3.2 Use the information in Fig. 3.1 and Fig. 3.2 to suggest which species is best adapted to survive at location A. Explain your answer. … … … … … … [3] (e) At the delta, seedlings will be exposed to changes in the tidal cycle. Suggest why the tidal cycle will cause variations in the salinity of the water at location B. … … … … … … [3] (f) The conservation of mangrove ecosystems is important for human populations. State two benefits. 1 … … 2 … … [2] [Total: 16]

16 marks

Mark scheme: 3(a) any 1 of: prop roots ; salt exclusion by roots / roots help filter salt water ; viviparous reproduction / propagules ; 1 3(b)(i) either: known mass of, sodium chloride / salt ; dissolved in, known / stated, volume / mass, of water ; or: use, (stock) solution / sea water, of known concentration / 34 ppt ; and dilute known volume with known volume of water ; or: add salt to, distilled / fresh, water OR (dilute) seawater with distilled / fresh, water + using a, salinometer / refractometer ; until it reaches the correct salinity ; 2 3(b)(ii) any 2 of: (investigate for) longer than 30 weeks ; (investigate) more (than 3) species ; (investigate) a greater range of salinities ; more seedlings ; 2 3(c)(i) surviving number / 50,  100 ; 1 Question Answer Marks 3(c)(ii) 48  100  50 OR 48  is 48 in 100 so 24 in 50 OR 24 / 50  0.48 OR 48  2 ; 24 ; 2 3(d) species X + highest survival rate in most saline water ; Site A highest salinity (closest to sea / shoreline) ; Site A will experience, least mixing with fresh water / fresh water spread out over a wider area / more time mixed with incoming sea water AW ; 3 3(e) (idea of) high tide increasing salinity / water becomes more saline at high tide / as tide comes in more salty water will be at B / as tide goes out more fresh water will be at B / ORA ; (idea of) increased (proportion of) sea water to freshwater / ORA ; (idea of) spring tides cause greater increase in salinity (at high water) / ORA for neap tides ; 3 3(f) any 2 of: tourism ; food sources / nursery grounds for fish / fisheries / provide nutrients ; (source of) timber ; coastal protection / flooding / reduce wave energy / prevent erosion ; (source of) fuel ; (source of) (antifungal) drug / medicines / medical use ; 2

This question in 9693/21 May/June 2023

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

1 Fig. 1.1 shows the shell of a common dogwhelk, Nucella lapillus, which is adapted to live on rocky shores. Fig. 1.1 (a) State a mineral that is required for the formation of shells. … [1] (b) Make a large drawing of the shell shown in Fig. 1.1. Do not label your drawing. [4] (c) Dogwhelks use a large muscular foot to cling to the rocks on rocky shores. A scientist investigated the shape of dogwhelk shells on different shore types. They analysed dogwhelks from an exposed rocky shore with high wave action, and a sheltered rocky shore with low wave action. 100 dogwhelks from each shore were sampled, and the following measurements were recorded: • total shell length • shell aperture length. Fig. 1.2 shows how these measurements were recorded. total shell length shell aperture length Fig. 1.2 Table 1.1 shows the mean results of the investigation. Table 1.1 shore type mean total shell length / mm mean shell aperture length / mm exposed rocky shore 24.6 12.5 sheltered rocky shore 26.1 11.9 (i) Describe how the mean total shell lengths were calculated. … … [1] (ii) The scientist calculated the ratio of mean total shell length : mean shell aperture length for the dogwhelks on each shore. Complete Table 1.2 by calculating the ratio for the sheltered rocky shore. Table 1.2 shore type ratio of mean total shell length : mean shell aperture length exposed rocky shore 1.97 : 1 sheltered rocky shore [1] (iii) Compare the shapes of dogwhelk shells on each shore type, using data from Table 1.1 and Table 1.2. Suggest reasons for any differences. … … … … … … … … [4] (d) During the investigation the scientist noticed that the dogwhelks showed variation in the colour of their shells, some being darker than others. The scientist also noticed that the darker‑shelled individuals were located in more shaded parts of the rocky shore. They suggested the following hypothesis: ‘Lighter-shelled dogwhelks can tolerate higher exposure to sunlight.’ A further investigation was then carried out. Light and dark dogwhelks on an area of shore were all marked with a small spot of paint on the shell. The paint fades on exposure to sunlight. After three days the degree of fading was recorded, using a score of 1 to 10. Table 1.3 shows the results. Table 1.3 paint fading score number of lighter-shelled number of darker-shelled dogwhelks dogwhelks 1 (least faded) 0 0 2 5 4 3 33 34 4 58 14 5 40 11 6 30 7 7 8 3 8 22 5 9 2 0 10 (most faded) 4 0 Discuss whether the results in Table 1.3 support the scientist’s hypothesis. … … … … … … [3] (e) Suggest one way the scientist ensured their methods were ethical. … … [1] [Total: 15]

15 marks

Mark scheme: 1(a) calcium ; 1 1(b) clear outline ; suitable size ; in proportion ; detail ; 4 1(c)(i) add together all shell lengths (for one / each shore) AND divide by 100 ; 1 1(c)(ii) 2.19 : 1 ; 1 1(c)(iii) any 4 of: length : aperture ratio lower on exposed shore / ORA ; shell aperture is larger (relative to length) on exposed shore / ORA ; larger foot ; stronger attachment to rock ; increases, survival chance / ability to stay attached, with stronger wave action ; (mean) shell length greater on sheltered shore / ORA ; because dogwhelks have higher life expectancy so grow bigger ; feeding efficiency greater on sheltered shore ; 4 Question Answer Marks 1(d) any 3 of: (yes because…) more light-shelled dogwhelks with a higher paint fading score / ORA ; suggesting they spent more time exposed to the Sun / ORA ; (no because) peak numbers are very close together ; sample size of dark-shelled dogwhelks much smaller / less than half ; ref. to limited scope of investigation e.g. one area / small numbers / only ; 3 days ; other factor may affect fading of paint e.g. saltwater ; idea of, correlation not causation / a different factor may be involved ; 3 1(e) any 1 of: taking care not to damage dogwhelks / other shore organisms ; taking care to, replace dogwhelks in same place / allow dogwhelks to reattach properly ; using a paint that does not harm the dogwhelks / environment ; 1

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 9693/22 May/June 2023

1 Fig. 1.1 shows the shell of a common dogwhelk, Nucella lapillus, which is adapted to live on rocky shores. Fig. 1.1 (a) State a mineral that is required for the formation of shells. … [1] (b) Make a large drawing of the shell shown in Fig. 1.1. Do not label your drawing. [4] (c) Dogwhelks use a large muscular foot to cling to the rocks on rocky shores. A scientist investigated the shape of dogwhelk shells on different shore types. They analysed dogwhelks from an exposed rocky shore with high wave action, and a sheltered rocky shore with low wave action. 100 dogwhelks from each shore were sampled, and the following measurements were recorded: • total shell length • shell aperture length. Fig. 1.2 shows how these measurements were recorded. total shell length shell aperture length Fig. 1.2 Table 1.1 shows the mean results of the investigation. Table 1.1 shore type mean total shell length / mm mean shell aperture length / mm exposed rocky shore 24.6 12.5 sheltered rocky shore 26.1 11.9 (i) Describe how the mean total shell lengths were calculated. … … [1] (ii) The scientist calculated the ratio of mean total shell length : mean shell aperture length for the dogwhelks on each shore. Complete Table 1.2 by calculating the ratio for the sheltered rocky shore. Table 1.2 shore type ratio of mean total shell length : mean shell aperture length exposed rocky shore 1.97 : 1 sheltered rocky shore [1] (iii) Compare the shapes of dogwhelk shells on each shore type, using data from Table 1.1 and Table 1.2. Suggest reasons for any differences. … … … … … … … … [4] (d) During the investigation the scientist noticed that the dogwhelks showed variation in the colour of their shells, some being darker than others. The scientist also noticed that the darker‑shelled individuals were located in more shaded parts of the rocky shore. They suggested the following hypothesis: ‘Lighter-shelled dogwhelks can tolerate higher exposure to sunlight.’ A further investigation was then carried out. Light and dark dogwhelks on an area of shore were all marked with a small spot of paint on the shell. The paint fades on exposure to sunlight. After three days the degree of fading was recorded, using a score of 1 to 10. Table 1.3 shows the results. Table 1.3 paint fading score number of lighter-shelled number of darker-shelled dogwhelks dogwhelks 1 (least faded) 0 0 2 5 4 3 33 34 4 58 14 5 40 11 6 30 7 7 8 3 8 22 5 9 2 0 10 (most faded) 4 0 Discuss whether the results in Table 1.3 support the scientist’s hypothesis. … … … … … … [3] (e) Suggest one way the scientist ensured their methods were ethical. … … [1] [Total: 15]

15 marks

Mark scheme: 1(a) calcium ; 1 1(b) clear outline ; suitable size ; in proportion ; detail ; 4 1(c)(i) add together all shell lengths (for one / each shore) AND divide by 100 ; 1 1(c)(ii) 2.19 : 1 ; 1 1(c)(iii) any 4 of: length : aperture ratio lower on exposed shore / ORA ; shell aperture is larger (relative to length) on exposed shore / ORA ; larger foot ; stronger attachment to rock ; increases, survival chance / ability to stay attached, with stronger wave action ; (mean) shell length greater on sheltered shore / ORA ; because dogwhelks have higher life expectancy so grow bigger ; feeding efficiency greater on sheltered shore ; 4 Question Answer Marks 1(d) any 3 of: (yes because…) more light-shelled dogwhelks with a higher paint fading score / ORA ; suggesting they spent more time exposed to the Sun / ORA ; (no because) peak numbers are very close together ; sample size of dark-shelled dogwhelks much smaller / less than half ; ref. to limited scope of investigation e.g. one area / small numbers / only ; 3 days ; other factor may affect fading of paint e.g. saltwater ; idea of, correlation not causation / a different factor may be involved ; 3 1(e) any 1 of: taking care not to damage dogwhelks / other shore organisms ; taking care to, replace dogwhelks in same place / allow dogwhelks to reattach properly ; using a paint that does not harm the dogwhelks / environment ; 1

This question in 9693/23 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

2 A group of students investigated how the distribution of crabs on a rocky shore varied with macroalgae cover. The students used random sampling to select 10 areas of the shore. They collected data on the percentage cover of macroalgae and the number of crabs in 10 quadrats. (a) (i) Describe how to collect data using random sampling on a shore. … … … … … … [3] (ii) State one advantage and one disadvantage of using random sampling compared to systematic sampling. advantage … … disadvantage … … [2] (b) State the null hypothesis for this investigation. … … [1] (c) The students ranked the percentage cover of macroalgae and the number of crabs in each quadrat. Their results are shown in Table 2.1. Table 2.1 rank of percentage rank of quadrat percentage number of difference cover of number of D2 number cover of crabs (D) macroalgae crabs macroalgae 1 100 10 21 8 2 4 2 15 2 6 3 1 1 3 30 3 1 1 2 4 4 70 … 20 … … … 5 95 … 25 … … … 6 45 4 11 4 0 0 7 80 … 22 … … … 8 10 1 2 2 1 1 9 70 … 19 … … … 10 55 5 12 5 0 0 Complete Table 2.1. [2] (d) The formula for Spearman’s rank correlation is: 6 × ∑ D2 rs = 1 –  n3 – n  where ∑ = sum of (total) n = number of pairs of items in the sample D = difference in rank between pairs of measurements. Use this formula to calculate Spearman’s rank correlation for the data in Table 2.1. Show your working. Give your answer to an appropriate number of significant figures. … [4] (e) Discuss the extent to which these results show that the percentage of algae cover affects the number of crabs present. … … … … [2] [Total: 14]

14 marks

Mark scheme: 2(a)(i) divide study area into sections / setting up grid (with tapes) ; 3 use random number generator to select co-ordinates ; place quadrat in selected area / description of how to calculate percentage cover of macroalgae ; 2(a)(ii) (advantages) any 1 from: 2 equal chance of selection ; reduces (researcher) bias ; PLUS (disadvantages) any 1 from: takes more time (than systematic) ; may not represent entire area ; 2(b) the number of crabs present on an area of shore is not affected by the macroalgae cover OWTTE ; 1 2(c) 2 quadrat percentage cover rank of number of crabs rank of number of crabs difference (D) D2 number of macroalgae macroalgae 4 70 6.5 20 7 0.5 0.25 5 95 9 25 10 1 1 6 45 4 11 4 0 0 7 80 8 22 9 1 1 8 10 1 2 2 1 1 9 70 6.5 19 6 0.5 0.25 10 55 5 12 5 0 0 2(d) D2 = 12.5 and n = 10 ; 4 6  12.5 = 75 and 103 − 10 = 990 ; 75 / 990 = 0.0757(57) and 1 − 0.0757 = 0.9243 ; correct application of 1 or 2 sig figs to calculated answer / 0.92 / 0.9 ; 2(e) any 2 from: 2 results, show a positive correlation / close to 1 ; null hypothesis is rejected ; correlation does not mean causation ;

This question in 9693/21 Oct/Nov 2023

3 Fig. 3.1 shows a red snapper, a fish commonly harvested for human food from coral reefs. Fig. 3.1 (a) Make a large drawing of the red snapper in Fig. 3.1. Do not include the scales. [4] (b) On your diagram label the following features: • operculum • pectoral fin. [2] (c) (i) Describe one method that could be used to estimate the population of red snapper on a coral reef. … … … … … … … … [4] (ii) Scientists investigated the population of red snapper on a coral reef every month for six months. Draw a results table for this investigation. Include full headings in the results table, but do not write in any results. [1] (iii) State two biotic factors that affect the population of red snapper on a coral reef. 1 … 2 … [2] (d) Scientists investigated the effect of an artificial reef on the populations of six fish species. The area did not contain any natural reefs. They collected data using fish traps from an artificial reef and from an area 150 m away from the artificial reef, which had no reef. The number of fish caught in each area over 8 hours was recorded. Table 3.1 shows the results. Table 3.1 number of fish caught fish species artificial reef no reef P 2 1 Q 6 1 R 137 8 S 45 0 T 129 2 U 0 1 The scientists made the statement: ‘The artificial reef has increased the biodiversity of the area.’ (i) Discuss the extent to which the data supports this statement. … … … … … … [3] (ii) The artificial reef was built 750 m offshore. Discuss the possible effects of the artificial reef on the shore. … … … … … … [3] [Total: 19]

19 marks

Mark scheme: 3(a) outline (neat lines, no shading) ; 4 size (larger than the original) ; proportion (operculum positioned at around ⅓ of the body length (not including caudal fin) and correct body shape, pectoral fin reaching to approximately the middle of the body) ; detail (all fins included, eye, mouth, caudal peduncle) ; 3(b) 2 operculum Pectoral fin 3(c)(i) any 4 from: 4 catch (a selection of the species at the reef) AND count / stated number caught AND tag (all fish) and release ; return (stated time) later and catch a sample of the species ; count the number of fish tagged AND the total caught the second time ; apply the Lincoln index ; AVP ; 3(c)(ii) 1 Date / month Total number (of red snapper) caught Number (red snapper) tagged Number (red snapper) untagged 3(c)(iii) any 2 from: 2 competition ; disease / parasites ; predation ; AVP ; 3(d)(i) any 3 from: 3 5 species of fish / same no. of species / five out of six species / same species richness, in each area; (but there may be) other species affected they did not monitor / data not collected on, all species / species other than fish ; (on the reef area) there is a large increase in numbers, of 2 species / R and T, OR there is a small increase in, 2 species / Q and P, OR a new species / S, is attracted to artificial reef ; (but) there is a reduction in numbers of 1 species / U (in the artificial reef) / (the species that reduced / U) had only a small number of fish in the area with no reef ; no data for the areas before the reef was built ; fish may have, moved / migrated, from the area without a reef to the area of reef ; data only includes species biodiversity / data does not include genetic or environmental biodiversity ; data manipulation ; AVP ; 3(d)(ii) any 3 from: 3 reduces storm surges ; as they absorb (some of) the energy (of the waves) ; waves break before the shore ; reduces shoreline erosion ; shore profile may change / sand deposited / deeper substrate ; because currents are lower behind the reef ; protects, seagrass beds / other habitats, between reef and shore ; AVP ;

This question in 9693/21 Oct/Nov 2023

2 A group of students investigated how the distribution of crabs on a rocky shore varied with macroalgae cover. The students used random sampling to select 10 areas of the shore. They collected data on the percentage cover of macroalgae and the number of crabs in 10 quadrats. (a) (i) Describe how to collect data using random sampling on a shore. … … … … … … [3] (ii) State one advantage and one disadvantage of using random sampling compared to systematic sampling. advantage … … disadvantage … … [2] (b) State the null hypothesis for this investigation. … … [1] (c) The students ranked the percentage cover of macroalgae and the number of crabs in each quadrat. Their results are shown in Table 2.1. Table 2.1 rank of percentage rank of quadrat percentage number of difference cover of number of D2 number cover of crabs (D) macroalgae crabs macroalgae 1 100 10 21 8 2 4 2 15 2 6 3 1 1 3 30 3 1 1 2 4 4 70 … 20 … … … 5 95 … 25 … … … 6 45 4 11 4 0 0 7 80 … 22 … … … 8 10 1 2 2 1 1 9 70 … 19 … … … 10 55 5 12 5 0 0 Complete Table 2.1. [2] (d) The formula for Spearman’s rank correlation is: 6 × ∑ D2 rs = 1 –  n3 – n  where ∑ = sum of (total) n = number of pairs of items in the sample D = difference in rank between pairs of measurements. Use this formula to calculate Spearman’s rank correlation for the data in Table 2.1. Show your working. Give your answer to an appropriate number of significant figures. … [4] (e) Discuss the extent to which these results show that the percentage of algae cover affects the number of crabs present. … … … … [2] [Total: 14]

14 marks

Mark scheme: 2(a)(i) divide study area into sections / setting up grid (with tapes) ; 3 use random number generator to select co-ordinates ; place quadrat in selected area / description of how to calculate percentage cover of macroalgae ; 2(a)(ii) (advantages) any 1 from: 2 equal chance of selection ; reduces (researcher) bias ; PLUS (disadvantages) any 1 from: takes more time (than systematic) ; may not represent entire area ; 2(b) the number of crabs present on an area of shore is not affected by the macroalgae cover OWTTE ; 1 2(c) 2 quadrat percentage cover rank of number of crabs rank of number of crabs difference (D) D2 number of macroalgae macroalgae 4 70 6.5 20 7 0.5 0.25 5 95 9 25 10 1 1 6 45 4 11 4 0 0 7 80 8 22 9 1 1 8 10 1 2 2 1 1 9 70 6.5 19 6 0.5 0.25 10 55 5 12 5 0 0 2(d) D2 = 12.5 and n = 10 ; 4 6  12.5 = 75 and 103 − 10 = 990 ; 75 / 990 = 0.0757(57) and 1 − 0.0757 = 0.9243 ; correct application of 1 or 2 sig figs to calculated answer / 0.92 / 0.9 ; 2(e) any 2 from: 2 results, show a positive correlation / close to 1 ; null hypothesis is rejected ; correlation does not mean causation ;

This question in 9693/22 Oct/Nov 2023

3 Fig. 3.1 shows a red snapper, a fish commonly harvested for human food from coral reefs. Fig. 3.1 (a) Make a large drawing of the red snapper in Fig. 3.1. Do not include the scales. [4] (b) On your diagram label the following features: • operculum • pectoral fin. [2] (c) (i) Describe one method that could be used to estimate the population of red snapper on a coral reef. … … … … … … … … [4] (ii) Scientists investigated the population of red snapper on a coral reef every month for six months. Draw a results table for this investigation. Include full headings in the results table, but do not write in any results. [1] (iii) State two biotic factors that affect the population of red snapper on a coral reef. 1 … 2 … [2] (d) Scientists investigated the effect of an artificial reef on the populations of six fish species. The area did not contain any natural reefs. They collected data using fish traps from an artificial reef and from an area 150 m away from the artificial reef, which had no reef. The number of fish caught in each area over 8 hours was recorded. Table 3.1 shows the results. Table 3.1 number of fish caught fish species artificial reef no reef P 2 1 Q 6 1 R 137 8 S 45 0 T 129 2 U 0 1 The scientists made the statement: ‘The artificial reef has increased the biodiversity of the area.’ (i) Discuss the extent to which the data supports this statement. … … … … … … [3] (ii) The artificial reef was built 750 m offshore. Discuss the possible effects of the artificial reef on the shore. … … … … … … [3] [Total: 19]

19 marks

Mark scheme: 3(a) outline (neat lines, no shading) ; 4 size (larger than the original) ; proportion (operculum positioned at around ⅓ of the body length (not including caudal fin) and correct body shape, pectoral fin reaching to approximately the middle of the body) ; detail (all fins included, eye, mouth, caudal peduncle) ; 3(b) 2 operculum Pectoral fin 3(c)(i) any 4 from: 4 catch (a selection of the species at the reef) AND count / stated number caught AND tag (all fish) and release ; return (stated time) later and catch a sample of the species ; count the number of fish tagged AND the total caught the second time ; apply the Lincoln index ; AVP ; 3(c)(ii) 1 Date / month Total number (of red snapper) caught Number (red snapper) tagged Number (red snapper) untagged 3(c)(iii) any 2 from: 2 competition ; disease / parasites ; predation ; AVP ; 3(d)(i) any 3 from: 3 5 species of fish / same no. of species / five out of six species / same species richness, in each area; (but there may be) other species affected they did not monitor / data not collected on, all species / species other than fish ; (on the reef area) there is a large increase in numbers, of 2 species / R and T, OR there is a small increase in, 2 species / Q and P, OR a new species / S, is attracted to artificial reef ; (but) there is a reduction in numbers of 1 species / U (in the artificial reef) / (the species that reduced / U) had only a small number of fish in the area with no reef ; no data for the areas before the reef was built ; fish may have, moved / migrated, from the area without a reef to the area of reef ; data only includes species biodiversity / data does not include genetic or environmental biodiversity ; data manipulation ; AVP ; 3(d)(ii) any 3 from: 3 reduces storm surges ; as they absorb (some of) the energy (of the waves) ; waves break before the shore ; reduces shoreline erosion ; shore profile may change / sand deposited / deeper substrate ; because currents are lower behind the reef ; protects, seagrass beds / other habitats, between reef and shore ; AVP ;

This question in 9693/22 Oct/Nov 2023

2 A group of students investigated how the distribution of crabs on a rocky shore varied with macroalgae cover. The students used random sampling to select 10 areas of the shore. They collected data on the percentage cover of macroalgae and the number of crabs in 10 quadrats. (a) (i) Describe how to collect data using random sampling on a shore. … … … … … … [3] (ii) State one advantage and one disadvantage of using random sampling compared to systematic sampling. advantage … … disadvantage … … [2] (b) State the null hypothesis for this investigation. … … [1] (c) The students ranked the percentage cover of macroalgae and the number of crabs in each quadrat. Their results are shown in Table 2.1. Table 2.1 rank of percentage rank of quadrat percentage number of difference cover of number of D2 number cover of crabs (D) macroalgae crabs macroalgae 1 100 10 21 8 2 4 2 15 2 6 3 1 1 3 30 3 1 1 2 4 4 70 … 20 … … … 5 95 … 25 … … … 6 45 4 11 4 0 0 7 80 … 22 … … … 8 10 1 2 2 1 1 9 70 … 19 … … … 10 55 5 12 5 0 0 Complete Table 2.1. [2] (d) The formula for Spearman’s rank correlation is: 6 × ∑ D2 rs = 1 –  n3 – n  where ∑ = sum of (total) n = number of pairs of items in the sample D = difference in rank between pairs of measurements. Use this formula to calculate Spearman’s rank correlation for the data in Table 2.1. Show your working. Give your answer to an appropriate number of significant figures. … [4] (e) Discuss the extent to which these results show that the percentage of algae cover affects the number of crabs present. … … … … [2] [Total: 14]

14 marks

Mark scheme: 2(a)(i) divide study area into sections / setting up grid (with tapes) ; 3 use random number generator to select co-ordinates ; place quadrat in selected area / description of how to calculate percentage cover of macroalgae ; 2(a)(ii) (advantages) any 1 from: 2 equal chance of selection ; reduces (researcher) bias ; PLUS (disadvantages) any 1 from: takes more time (than systematic) ; may not represent entire area ; 2(b) the number of crabs present on an area of shore is not affected by the macroalgae cover OWTTE ; 1 2(c) 2 quadrat percentage cover rank of number of crabs rank of number of crabs difference (D) D2 number of macroalgae macroalgae 4 70 6.5 20 7 0.5 0.25 5 95 9 25 10 1 1 6 45 4 11 4 0 0 7 80 8 22 9 1 1 8 10 1 2 2 1 1 9 70 6.5 19 6 0.5 0.25 10 55 5 12 5 0 0 2(d) D2 = 12.5 and n = 10 ; 4 6  12.5 = 75 and 103 − 10 = 990 ; 75 / 990 = 0.0757(57) and 1 − 0.0757 = 0.9243 ; correct application of 1 or 2 sig figs to calculated answer / 0.92 / 0.9 ; 2(e) any 2 from: 2 results, show a positive correlation / close to 1 ; null hypothesis is rejected ; correlation does not mean causation ;

This question in 9693/23 Oct/Nov 2023

3 Fig. 3.1 shows a red snapper, a fish commonly harvested for human food from coral reefs. Fig. 3.1 (a) Make a large drawing of the red snapper in Fig. 3.1. Do not include the scales. [4] (b) On your diagram label the following features: • operculum • pectoral fin. [2] (c) (i) Describe one method that could be used to estimate the population of red snapper on a coral reef. … … … … … … … … [4] (ii) Scientists investigated the population of red snapper on a coral reef every month for six months. Draw a results table for this investigation. Include full headings in the results table, but do not write in any results. [1] (iii) State two biotic factors that affect the population of red snapper on a coral reef. 1 … 2 … [2] (d) Scientists investigated the effect of an artificial reef on the populations of six fish species. The area did not contain any natural reefs. They collected data using fish traps from an artificial reef and from an area 150 m away from the artificial reef, which had no reef. The number of fish caught in each area over 8 hours was recorded. Table 3.1 shows the results. Table 3.1 number of fish caught fish species artificial reef no reef P 2 1 Q 6 1 R 137 8 S 45 0 T 129 2 U 0 1 The scientists made the statement: ‘The artificial reef has increased the biodiversity of the area.’ (i) Discuss the extent to which the data supports this statement. … … … … … … [3] (ii) The artificial reef was built 750 m offshore. Discuss the possible effects of the artificial reef on the shore. … … … … … … [3] [Total: 19]

19 marks

Mark scheme: 3(a) outline (neat lines, no shading) ; 4 size (larger than the original) ; proportion (operculum positioned at around ⅓ of the body length (not including caudal fin) and correct body shape, pectoral fin reaching to approximately the middle of the body) ; detail (all fins included, eye, mouth, caudal peduncle) ; 3(b) 2 operculum Pectoral fin 3(c)(i) any 4 from: 4 catch (a selection of the species at the reef) AND count / stated number caught AND tag (all fish) and release ; return (stated time) later and catch a sample of the species ; count the number of fish tagged AND the total caught the second time ; apply the Lincoln index ; AVP ; 3(c)(ii) 1 Date / month Total number (of red snapper) caught Number (red snapper) tagged Number (red snapper) untagged 3(c)(iii) any 2 from: 2 competition ; disease / parasites ; predation ; AVP ; 3(d)(i) any 3 from: 3 5 species of fish / same no. of species / five out of six species / same species richness, in each area; (but there may be) other species affected they did not monitor / data not collected on, all species / species other than fish ; (on the reef area) there is a large increase in numbers, of 2 species / R and T, OR there is a small increase in, 2 species / Q and P, OR a new species / S, is attracted to artificial reef ; (but) there is a reduction in numbers of 1 species / U (in the artificial reef) / (the species that reduced / U) had only a small number of fish in the area with no reef ; no data for the areas before the reef was built ; fish may have, moved / migrated, from the area without a reef to the area of reef ; data only includes species biodiversity / data does not include genetic or environmental biodiversity ; data manipulation ; AVP ; 3(d)(ii) any 3 from: 3 reduces storm surges ; as they absorb (some of) the energy (of the waves) ; waves break before the shore ; reduces shoreline erosion ; shore profile may change / sand deposited / deeper substrate ; because currents are lower behind the reef ; protects, seagrass beds / other habitats, between reef and shore ; AVP ;

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

4 Lugworms are a species of worm found on sandy and muddy shores. Each lugworm lives in a single burrow where it consumes sediment, digesting any food sources within the sediment. Any undigested material is released by the worm from the end of the burrow, which at low tide forms ‘casts’ on the surface of the shore. Fig. 4.1 shows a lugworm in its burrow with a cast. cast Fig. 4.1 Fig. 4.2 shows a muddy shore with lugworm casts on the surface. Fig. 4.2 (a) A student investigated the population density of the lugworms on three different shores, A, B and C, by counting the casts visible on the surface. The results are shown in Table 4.1. Table 4.1 shore mean number of lugworm casts / casts per m2 A 32.21 B 4.64 C 17.56 (i) Describe a safe method to obtain the data shown in Table 4.1. … … … … … … … … [4] (ii) Suggest two reasons why counting casts may not give an accurate estimate of the lugworm population density. 1 … … 2 … … [2] (b) Sediment analyses were also carried out for each shore. Table 4.2 shows the results, including the percentage of organic matter and the mean particle size. Table 4.2 shore mean number of lugworm percentage organic mean particle casts / casts per m2 matter in sediment size / μm A 32.21 7.73 250 B 4.64 3.25 500 C 17.56 4.12 100 (i) Use Table 4.2 to suggest a hypothesis for a factor affecting the population density of lugworms. … … [1] (ii) Suggest how this investigation could be extended to test your hypothesis in (b)(i). … … … … [2] (c) Research shows that lugworms pump water into their burrows whilst submerged at high tide. Fig. 4.3 shows the mean flow rate of water pumped into the burrow over a period of time for one lugworm at high tide. 6 5 4 mean flow rate into burrow 3/ cm3 min–1 2 1 0 0 30 60 90 120 150 180 210 time / min Fig. 4.3 (i) Use Fig. 4.3 to describe the changes in flow rate used by the lugworm. … … … … … … [3] (ii) Suggest advantages for the lugworm of pumping water into its burrow. … … … … … … [3] [Total: 15]

15 marks

Mark scheme: 4(a)(i) note that ref. to low tide must be linked to safety for MP1 or MP9. 1 appropriate safety measure e.g. checking tide times ; plus any 3 from: 2 use of either line transect / belt transect OR grid ; 3 use of quadrat OR take photographs over a measured area ; 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 count how many (lugworm) casts (accept from a photo) / count the number of holes and divide by 2 ; 7 describes or calculates counts of casts to number per m2 ; 8 idea of repeat(s) / series of trials + mean calculation ; 9 idea of timing, to count at low tide / leaving sufficient time for casts to appear ; 4 4(a)(ii) any 2 from: not every lugworm may have produced a cast (at time of counting) / some casts may not be as visible as others and missed / could be other species that make casts / idea that 2 casts could appear to be one ; casts may be disturbed / removed ; standing water may prevent cast formation ; adjacent casts may overlap ; 2 Question Answer Marks 4(b)(i) either increased (percentage) of organic matter in sediment increases the population density of lugworms / more organic matter leads to an increase in population density of lugworm / does the organic matter in sediment affect lugworm population density / if there is a high % organic matter the population density will be larger ; OR lugworm population density will be highest in medium sediment diameters ; OR valid null hypothesis e.g. the percentage of organic matter in sediment does not affect the population density of lugworms ; 1 4(b)(ii) any 2 from: increase number of shores studied / do this with other shores apart from A, B and C. / more areas on the same shore ; increase variety of mean sediment sizes / change the % organic matter content / measuring organic matter within each quadrat ; idea of use of statistical analysis to, accept hypothesis / reject hypothesis / shows significance of data / determine correlation or relationship ; 2 4(c)(i) description of (rapid) increase, followed by (rapid) decrease ; plus any 2 from: description of the decrease changing rate over its duration (more than it does on the increase) ; idea of same / identical pattern OR idea that each cycle is exactly same duration ; correct use of 2 values of flow rate data to support answer ; 3 Question Answer Marks 4(c)(ii) any 3 from: replenishing oxygen (in the burrow) ; preventing accumulation of / expelling waste (from burrow) ; replenishing, food (sources) / organic matter (in the burrow) ; expelling / remove, sediment (from the burrow) ; AVP ; 3

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

3 Scientists collected a series of measurements from a ship travelling across the Atlantic Ocean from locations 1 to 12. They recorded the temperature, concentration of nitrate ions (NO3–) and abundance of phytoplankton at five depths from each of the 12 locations shown in Fig. 3.1. 1212 1111 Africa 1010 9 8 7 6 5 4 3 South America 2 1 Fig. 3.1 (a) State the type of sampling used by the scientists, and describe the benefits of this method. … … … … … … [3] (b) Table 3.1 shows the temperatures recorded at location 4. Table 3.1 depth / m temperature / °C 50 28 60 25 75 20 80 15 170 12 Plot the information shown in Table 3.1 as a line graph. [4] (c) Fig. 3.2 shows the analysis of some of the data that the scientists collected at each location. location 1 2 3 4 5 6 7 8 9 10 11 12 0 depth / m 100 200 Key depth of bottom of thermocline / m depth of greatest concentration of nitrate ions / m depth of greatest population of phytoplankton / m Fig. 3.2 Use the information shown in Table 3.1 and Fig. 3.2 and your own knowledge to discuss the reasons for the distribution of phytoplankton. … … … … … … [3] [Total: 10]

10 marks

Mark scheme: 3(a) systematic / (line / belt), transect ; 3 plus any 2 from: samples taken at regular intervals ; not affected by bias / ensures samples cover the full range of ocean sampled ; idea of change in conditions / environmental factors ; 3(b) axes labels with units ; 4 suitable linear scale ; plotted correctly ± ½ small square ; ruled lines linking points OR line of best fit drawn ; 3(c) any 3 from: 3 (depth of greatest proportion of) phytoplankton similar to / always (closely) above the depth of bottom of thermocline ; idea of water above thermocline is warmer which allows greater, growth / rate of photosynthesis ORA ; depth of (greatest proportion of) phytoplankton corresponds to depth of (greatest concentration of) nitrate ; nitrate needed for growth / named correct biological molecule requiring nitrate ; AVP ;

This question in 9693/21 Oct/Nov 2024

6 A survey was carried out to estimate the total population of the shark Carcharias taurus in the coastal waters off south-east Australia. Scientists attached numbered tags to a dorsal fin of the sharks. (a) Label one dorsal fin on the diagram of a Carcharias taurus in Fig. 6.1. Fig. 6.1 [1] (b) Carcharias taurus are cartilaginous fish. State two features of cartilaginous fish that are not features of bony fish. 1 … … 2 … … [2] (c) The scientists used the mark–release–recapture method to estimate the population of Carcharias taurus off the south-east coast of Australia. The data collected are shown in Table 6.1. Table 6.1 number sharks captured and marked in first sample (n1) 152 sharks captured in second sample (both marked and unmarked) (n2) 185 marked sharks recaptured in second sample (m2) 44 The equation for the Lincoln index is shown. N = n1 × n2 m2 Use the data in Table 6.1 and the equation to estimate the population of Carcharias taurus in the area surveyed. State your answer to two significant figures. Show your working. … [3] (d) Carcharias taurus is known as the grey nurse shark in Australia, the sand tiger shark in the USA and the spotted ragged-tooth shark in South Africa. Explain the importance of using the binomial system of species nomenclature. … … … … [2] (e) Scientists in the USA studied the growth rate of Carcharias taurus and found that its growth rate decreased over time as shown in Table 6.2. Table 6.2 age in years rate of growth / cm year –1 0 to 2 25 to 30 2 to 4 20 to 25 4 to 6 15 to 20 6 to 8 10 to 15 > 8 5 to 10 When a Carcharias taurus is born, it is around 1 m long. Calculate the approximate length of a 5-year-old Carcharias taurus, using the data in Table 6.2. State the units. Show your working. … [3] [Total: 11]

11 marks

Mark scheme: 6(a) correct label on one of two dorsal fins shown 1 6(b) any 2 from: 2 cartilaginous skeleton ; gill slits ; no swim bladder ; denticles ; 6(c) N = (152  185) / 44 ; 3 N = 639.090909 ; N = 640 ; 6(d) idea of consistent name used in all countries / languages ; 2 plus any 1 from: useful for comparing / sharing, scientific research ; idea it avoids confusion / problems / misunderstandings caused by using different names ; idea of useful for showing, classification / evolutionary relationships, with other organisms ; 6(e) working showing (100 cm +) appropriate gains in length ; 3 answer in range 205–230 (cm) / 2.050–2.30 (m) ; correct units for answer given ;

This question in 9693/21 Oct/Nov 2024

3 Scientists collected a series of measurements from a ship travelling across the Atlantic Ocean from locations 1 to 12. They recorded the temperature, concentration of nitrate ions (NO3–) and abundance of phytoplankton at five depths from each of the 12 locations shown in Fig. 3.1. 1212 1111 Africa 1010 9 8 7 6 5 4 3 South America 2 1 Fig. 3.1 (a) State the type of sampling used by the scientists, and describe the benefits of this method. … … … … … … [3] (b) Table 3.1 shows the temperatures recorded at location 4. Table 3.1 depth / m temperature / °C 50 28 60 25 75 20 80 15 170 12 Plot the information shown in Table 3.1 as a line graph. [4] (c) Fig. 3.2 shows the analysis of some of the data that the scientists collected at each location. location 1 2 3 4 5 6 7 8 9 10 11 12 0 depth / m 100 200 Key depth of bottom of thermocline / m depth of greatest concentration of nitrate ions / m depth of greatest population of phytoplankton / m Fig. 3.2 Use the information shown in Table 3.1 and Fig. 3.2 and your own knowledge to discuss the reasons for the distribution of phytoplankton. … … … … … … [3] [Total: 10]

10 marks

Mark scheme: 3(a) systematic / (line / belt), transect ; 3 plus any 2 from: samples taken at regular intervals ; not affected by bias / ensures samples cover the full range of ocean sampled ; idea of change in conditions / environmental factors ; 3(b) axes labels with units ; 4 suitable linear scale ; plotted correctly ± ½ small square ; ruled lines linking points OR line of best fit drawn ; 3(c) any 3 from: 3 (depth of greatest proportion of) phytoplankton similar to / always (closely) above the depth of bottom of thermocline ; idea of water above thermocline is warmer which allows greater, growth / rate of photosynthesis ORA ; depth of (greatest proportion of) phytoplankton corresponds to depth of (greatest concentration of) nitrate ; nitrate needed for growth / named correct biological molecule requiring nitrate ; AVP ;

This question in 9693/22 Oct/Nov 2024

6 A survey was carried out to estimate the total population of the shark Carcharias taurus in the coastal waters off south-east Australia. Scientists attached numbered tags to a dorsal fin of the sharks. (a) Label one dorsal fin on the diagram of a Carcharias taurus in Fig. 6.1. Fig. 6.1 [1] (b) Carcharias taurus are cartilaginous fish. State two features of cartilaginous fish that are not features of bony fish. 1 … … 2 … … [2] (c) The scientists used the mark–release–recapture method to estimate the population of Carcharias taurus off the south-east coast of Australia. The data collected are shown in Table 6.1. Table 6.1 number sharks captured and marked in first sample (n1) 152 sharks captured in second sample (both marked and unmarked) (n2) 185 marked sharks recaptured in second sample (m2) 44 The equation for the Lincoln index is shown. N = n1 × n2 m2 Use the data in Table 6.1 and the equation to estimate the population of Carcharias taurus in the area surveyed. State your answer to two significant figures. Show your working. … [3] (d) Carcharias taurus is known as the grey nurse shark in Australia, the sand tiger shark in the USA and the spotted ragged-tooth shark in South Africa. Explain the importance of using the binomial system of species nomenclature. … … … … [2] (e) Scientists in the USA studied the growth rate of Carcharias taurus and found that its growth rate decreased over time as shown in Table 6.2. Table 6.2 age in years rate of growth / cm year –1 0 to 2 25 to 30 2 to 4 20 to 25 4 to 6 15 to 20 6 to 8 10 to 15 > 8 5 to 10 When a Carcharias taurus is born, it is around 1 m long. Calculate the approximate length of a 5-year-old Carcharias taurus, using the data in Table 6.2. State the units. Show your working. … [3] [Total: 11]

11 marks

Mark scheme: 6(a) correct label on one of two dorsal fins shown 1 6(b) any 2 from: 2 cartilaginous skeleton ; gill slits ; no swim bladder ; denticles ; 6(c) N = (152  185) / 44 ; 3 N = 639.090909 ; N = 640 ; 6(d) idea of consistent name used in all countries / languages ; 2 plus any 1 from: useful for comparing / sharing, scientific research ; idea it avoids confusion / problems / misunderstandings caused by using different names ; idea of useful for showing, classification / evolutionary relationships, with other organisms ; 6(e) working showing (100 cm +) appropriate gains in length ; 3 answer in range 205–230 (cm) / 2.050–2.30 (m) ; correct units for answer given ;

This question in 9693/22 Oct/Nov 2024

3 Scientists collected a series of measurements from a ship travelling across the Atlantic Ocean from locations 1 to 12. They recorded the temperature, concentration of nitrate ions (NO3–) and abundance of phytoplankton at five depths from each of the 12 locations shown in Fig. 3.1. 1212 1111 Africa 1010 9 8 7 6 5 4 3 South America 2 1 Fig. 3.1 (a) State the type of sampling used by the scientists, and describe the benefits of this method. … … … … … … [3] (b) Table 3.1 shows the temperatures recorded at location 4. Table 3.1 depth / m temperature / °C 50 28 60 25 75 20 80 15 170 12 Plot the information shown in Table 3.1 as a line graph. [4] (c) Fig. 3.2 shows the analysis of some of the data that the scientists collected at each location. location 1 2 3 4 5 6 7 8 9 10 11 12 0 depth / m 100 200 Key depth of bottom of thermocline / m depth of greatest concentration of nitrate ions / m depth of greatest population of phytoplankton / m Fig. 3.2 Use the information shown in Table 3.1 and Fig. 3.2 and your own knowledge to discuss the reasons for the distribution of phytoplankton. … … … … … … [3] [Total: 10]

10 marks

Mark scheme: 3(a) systematic / (line / belt), transect ; 3 plus any 2 from: samples taken at regular intervals ; not affected by bias / ensures samples cover the full range of ocean sampled ; idea of change in conditions / environmental factors ; 3(b) axes labels with units ; 4 suitable linear scale ; plotted correctly ± ½ small square ; ruled lines linking points OR line of best fit drawn ; 3(c) any 3 from: 3 (depth of greatest proportion of) phytoplankton similar to / always (closely) above the depth of bottom of thermocline ; idea of water above thermocline is warmer which allows greater, growth / rate of photosynthesis ORA ; depth of (greatest proportion of) phytoplankton corresponds to depth of (greatest concentration of) nitrate ; nitrate needed for growth / named correct biological molecule requiring nitrate ; AVP ;

This question in 9693/23 Oct/Nov 2024

6 A survey was carried out to estimate the total population of the shark Carcharias taurus in the coastal waters off south-east Australia. Scientists attached numbered tags to a dorsal fin of the sharks. (a) Label one dorsal fin on the diagram of a Carcharias taurus in Fig. 6.1. Fig. 6.1 [1] (b) Carcharias taurus are cartilaginous fish. State two features of cartilaginous fish that are not features of bony fish. 1 … … 2 … … [2] (c) The scientists used the mark–release–recapture method to estimate the population of Carcharias taurus off the south-east coast of Australia. The data collected are shown in Table 6.1. Table 6.1 number sharks captured and marked in first sample (n1) 152 sharks captured in second sample (both marked and unmarked) (n2) 185 marked sharks recaptured in second sample (m2) 44 The equation for the Lincoln index is shown. N = n1 × n2 m2 Use the data in Table 6.1 and the equation to estimate the population of Carcharias taurus in the area surveyed. State your answer to two significant figures. Show your working. … [3] (d) Carcharias taurus is known as the grey nurse shark in Australia, the sand tiger shark in the USA and the spotted ragged-tooth shark in South Africa. Explain the importance of using the binomial system of species nomenclature. … … … … [2] (e) Scientists in the USA studied the growth rate of Carcharias taurus and found that its growth rate decreased over time as shown in Table 6.2. Table 6.2 age in years rate of growth / cm year –1 0 to 2 25 to 30 2 to 4 20 to 25 4 to 6 15 to 20 6 to 8 10 to 15 > 8 5 to 10 When a Carcharias taurus is born, it is around 1 m long. Calculate the approximate length of a 5-year-old Carcharias taurus, using the data in Table 6.2. State the units. Show your working. … [3] [Total: 11]

11 marks

Mark scheme: 6(a) correct label on one of two dorsal fins shown 1 6(b) any 2 from: 2 cartilaginous skeleton ; gill slits ; no swim bladder ; denticles ; 6(c) N = (152  185) / 44 ; 3 N = 639.090909 ; N = 640 ; 6(d) idea of consistent name used in all countries / languages ; 2 plus any 1 from: useful for comparing / sharing, scientific research ; idea it avoids confusion / problems / misunderstandings caused by using different names ; idea of useful for showing, classification / evolutionary relationships, with other organisms ; 6(e) working showing (100 cm +) appropriate gains in length ; 3 answer in range 205–230 (cm) / 2.050–2.30 (m) ; correct units for answer given ;

This question in 9693/23 Oct/Nov 2024

1 Blue crabs are crustaceans. Fig. 1.1 shows a blue crab. Fig. 1.1 (a) (i) On Fig. 1.1, label the carapace on the blue crab. [1] (ii) State two other features of a typical adult crustacean. 1 … … 2 … … [2] (iii) Fig. 1.2 shows the right claw of the blue crab. Fig. 1.2 Make a large drawing of the crab claw shown in Fig. 1.2. Do not include markings. [4] (b) Blue crabs are harvested by humans in Chesapeake Bay, USA. A scientist used the Lincoln index to estimate the population of blue crabs in one area of Chesapeake Bay. The scientist collected the data shown in Table 1.1. Table 1.1 data collected number blue crabs captured in first sample (n1) 147 blue crabs (both marked and unmarked) captured in 139 second sample (n2) blue crabs (marked) recaptured in second sample (m2) 45 The equation for the Lincoln index is: n1 × n2 N = m2 where, N = estimate of population size n1 = number of individuals captured in first sample n2 = number of individuals (both marked and unmarked) captured in second sample m2 = number of marked individuals recaptured in second sample. (i) Use the data in Table 1.1 and the equation to estimate the population of blue crabs in the area surveyed. Give your answer to three significant figures. Space for working. … [3] (ii) State two limitations of using the mark-release-recapture method to estimate the blue crab population. 1 … … 2 … … [2] (c) Since 1990, scientists have used the mark-release-recapture method and the Lincoln index to monitor the blue crab population in Chesapeake Bay. In 2008, new rules were introduced to limit the harvesting of blue crabs. Fig. 1.3 shows the estimated population of blue crabs in Chesapeake Bay from 1990 to 2020. 300 280 260 240 220 200 180 160 population / millions 140 120 100 80 60 40 20 0 1990 1995 2000 2005 2010 2015 2020 years Fig. 1.3 Use Fig. 1.3 to evaluate the effect of the new harvesting rules on the population of blue crabs. … … … … … … … … [4] [Total: 16]

16 marks

Mark scheme: Question Answer Marks 1(a)(i) 1 carapace ; 1(a)(ii) any two from: 2 segmented, abdomen / body ; jointed legs ; two pairs of antennae ; AVP ; 1(a)(iii) outline: unbroken pencil lines and no shading ; 4 size: most of the space provided and at least as big as original picture ; in proportion ; detail any number of nodules in the pincers AND 3 spines on top edge ; 1(b)(i) (147  139) / 45 ; 3 = 454.067 ; 454 ; 1(b)(ii) any two from: 2 idea of reproduction or death of individuals ; idea of migration in to or out from area ; marked individuals are not randomly distributed ; sample size may be too small ; AVP ; 1(c) any four from: MAX 3 marks for supports and 1 from the ‘however’ 4 supports idea (MAX 3 marks) 1 positive impact on the population / increased numbers (from 2008 / 2009) ; 2 the increase was sudden / significant / large / alot (for following 2 years) ; 3 increase n population, in most years / overall, compared to 2008 ; 4 higher mean 2008–2020 compared to 1990–2007 ; 5 (one or two) highest peak(s) (in 2010 and 2017) post 2008 higher than previous peaks ; however 6 some years post-2008 had very low population / accept a specific year ; 7 other factors may be having more impact on population size ; 8 manipulation of data ;

This question in 9693/21 May/June 2025

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

3 Hydrothermal vents occur close to plate boundaries. (a) State the type of plate boundary where ocean floor spreading occurs. … … [1] (b) Scientists investigated whether the rate of ocean floor spreading affects the number of hydrothermal vents along the length of an ocean ridge. Table 3.1 shows the data collected by the scientists. Table 3.1 rate of ocean floor spreading mean number of hydrothermal / mm per year vents per 100 km 39 1.8 55 2.5 67 3.1 88 3.6 100 4.0 115 4.8 140 6.2 (i) Plot a line graph showing the relationship between the rate of ocean floor spreading and the mean number of hydrothermal vents. [4] (ii) Name the statistical test that could be used to test if there is a correlation between the two variables. … … [1] (c) A probe was moved at a fixed depth into the vent plume over a total distance of 6 km, as shown in Fig. 3.1. vent plume horizontal movement of probe through plume hydrothermal vent Fig. 3.1 Fig. 3.2 shows the concentration of hydrogen sulfide and the turbidity of the water recorded by the probe across the hydrothermal vent plume. 1.50 3.0 Key turbidity concentration of 1.25 2.5 hydrogen sulfide 1.00 2.0 concentration of hydrogen turbidity 0.75 1.5 sulfide / a.u. / nmol dm–3 0.50 1.0 0.25 0.5 0 0.0 0 2 4 6 distance moved by probe / km start of vent plume Fig. 3.2 (i) Compare the trends for the concentration of hydrogen sulfide and the turbidity of the water shown in Fig. 3.2. … … … … … … [3] (ii) Use Fig. 3.2 to calculate the range in turbidity recorded by the probe. … a.u. [1] (iii) State two other conditions in the sea water that are affected by the hydrothermal vent plume. 1 … 2 … [2] (iv) Suggest how conditions caused by the hydrothermal vent plume affect the organisms in the surrounding water. … … … … … … [3] [Total: 15]

15 marks

Mark scheme: 3(a) divergent (plate boundary) ; 1 3(b)(i) both axes labelled with units ; 4 suitable linear scale ; points, plotted correctly  ½ small square ; suitable line ; rate of ocean floor spreading / mm mean number of hydrothermal per year vents per 100 km 39 1.8 55 2.5 67 3.1 88 3.6 100 4.0 115 4.8 140 6.2 3(b)(ii) Spearman’s (rank); 1 3(c)(i) any three from: 3 both factors start low; both factors show increase AND decrease (thereafter) ; both factors increase more rapidly than they decrease ; decrease in hydrogen sulfide concentration more rapid than turbidity / ORA ; both peak at (around) the same distance / both reach their highest point at the same distance / both peak at 2 km ; concentration of hydrogen sulfide has a larger range than the turbidity ; 3(c)(ii) 2.2 / 2.20 (a.u) ; 1 3(c)(iii) any two from: 2 temperature ; pH ; (dissolved) oxygen concentration ; salinity ; density ; 3(c)(iv) any three from: 3 organisms cannot tolerate extreme conditions in the plume / temperature of water is beyond that suitable for organisms to survive / ORA ; dissolved, minerals / ions AND affect / lower pH / more acidic, (of) water which organisms cannot tolerate ; temperature change AND affects solubility of gases so there is less O2 available (for organisms) ; temperature change AND could affect growth rates (of organisms) ; increased turbidity AND affects bioluminescent organisms ; increases biodiversity / productivity ; (availability of) hydrogen sulfide for, chemosynthetic organisms / Endoriftia* producers / chemosynthesis ; AVP ;

This question in 9693/21 May/June 2025

4 Fig. 4.1 shows a Southern flounder, a species of fish that lives and reproduces in estuaries. Fig. 4.1 (a) Scientists investigated the effect of the size of sediment in an estuary on the distribution of Southern flounder. Samples of sediment were taken from three locations, A, B and C, in the estuary. Each sediment sample was then analysed. The sediment types found were: clay (smallest particle size) silt sand stones (largest particle size). The percentage of the different sediment types in each location was calculated. The results are shown in Fig. 4.2. 100 Key clay 80 silt sand percentage 60 stones sediment type 40 20 0 A B C location Fig. 4.2 (i) Use Fig. 4.2 to compare the permeability of samples from locations A, B and C. … … … … [2] (ii) Suggest why particle size affects the permeability of sediment types found in locations A, B and C. … … … … [2] (b) Southern flounders were caught using nets dragged along the bottom of the estuary at each location. The mean population density of Southern flounder was recorded. Fig. 4.3 shows these results. 0.07 0.06 0.05 mean population 0.04 density / number per m2 0.03 0.02 0.01 0.00 A B C location Fig. 4.3 (i) Compare the effect of sediment type on the distribution of Southern flounder at locations A, B and C. Use the bar charts in Fig. 4.2 and Fig. 4.3 to support your answer. … … … … … … … … [4] (ii) Suggest three reasons why the type of sediment found in locations A, B and C may affect the distribution of Southern flounder. 1 … … 2 … … 3 … … [3] (c) Particle size affects the permeability of sediments. Fig. 4.4 shows apparatus that could be used to find the permeability of sediment samples. tube containing sediment porous material keeping sediment in tube vessel to catch water passing through Fig. 4.4 Describe how the apparatus in Fig. 4.4 can be used to determine the permeability of sediment samples from locations A, B and C. Include any additional laboratory equipment that may be needed. … … … … … … [3] [Total: 14]

14 marks

Mark scheme: 4(a)(i) any two from: 2 location C would have lowest (permeability) ; B will have slightly higher (permeability) than A / location A and B has more (permeability) than C / A and B are the highest ; samples from location A and B would have similar (permeability) / A is almost as permeable as B ; 4(a)(ii) larger particles have larger spaces in between / ORA ; 2 idea of permeability as, space for / flow of, water through material e.g. allowing greater permeability for water / increased movement of water / ORA ; 4(b)(i) any four from: 4 1 flounder have greatest density on substrates with large particles ORA ; 2 (mean) population / density, of flounder is higher when (percentage of) sand in sediment is higher / ORA ; 3 (mean) population / density, of flounder is lower when (percentage of) clay in sediment is higher / ORA ; 4 (mean) population / density, of flounder is lower when (percentage of) silt in sediment is higher / ORA ; 5 comparison of correct data e.g. location A and B both have population density of 0.05 AND have percentage of sand close to 80% ; 6 (idea that) similar percentage of stones at all three locations has no / little / unknown effect on the (mean) density of flounder ; 4(b)(ii) any three from: 3 (may affect) ability of flounder to, avoid / hide from / camouflaged from, predators ; (may affect) ability of flounder to, hide from / camouflaged from, prey ; (may affect) species / abundance, of, prey / predators, present ; (may affect) ability of flounder to reproduce / better nursery conditions ; (may affect) presence of competitor species ; AVP ; 4(c) any three from: 3 idea of same, mass / volume, of sediment from each sample (placed in tube) ; water poured in at constant rate / equal, mass / volume, of water passed through each sample ; measure, volume / mass / depth, of water passing through in set time OR time taken for set, volume / mass / depth, of water to be collected ; relevant measuring equipment suggested ; e.g. stop clock / timer / measuring cylinder / balance / graduated cylinder. idea of repeats for each sample and mean calculate ;

This question in 9693/21 May/June 2025

1 Scientists in Australia monitored the population of the Green Turtle for five years. They used the mark-release-recapture method to estimate the population of the turtles in the southern Great Barrier Reef. (a) Describe an ethical method of mark-release-recapture that could be used by the scientists. … … … … … … [3] (b) This mark-release-recapture method was carried out each year from 2000 to 2004. The results are shown in Table 1.1. Table 1.1 year 2000 2001 2002 2003 2004 turtles captured in first 247 253 292 230 309 sample (n1) turtles captured in second sample (both marked and 355 345 392 326 418 unmarked) (n2) marked turtles recaptured 108 92 100 115 109 in second sample (m2) estimated turtle 812 949 1145 1185 population (N) … Use Table 1.1 and the Lincoln index to estimate the population of turtles in 2003. The equation for the Lincoln index is shown. n1 × n2 N = m2 Where: N = estimated turtle population n1 = number of individuals captured in first sample n2 = number of individuals captured in second sample (both marked and unmarked) m2 = number of marked individuals recaptured in second sample. Write your answer in Table 1.1. [1] (c) Plot a graph of the estimated turtle population (N) from 2000 to 2004. [4] (d) Use the data in Table 1.1 to describe the trend shown for the population of turtles. … … … … [2] (e) Turtles were not counted as being previously marked if it was not clear that the marks on their body were from the previous capture. Evaluate the population estimates shown in Table 1.1 based on this observation. … … … … [2] [Total: 12]

12 marks

Mark scheme: Question Answer Marks 1(a) idea of attaching tags in a way that does not cause pain / harm to the turtles ; 3 plus any two from: capturing / trapping turtles (from sea or on beach) AND attach tags AND releasing turtles back to, sea / beach ; idea of revisiting (same site), a year later / after suitable time period ; explanation of a suitable time period e.g. allowing tagged population to mix with untagged ; recording no. of turtles with a tag AND total no. of turtles without tags ; 1(b) 1 2003 652 1(c) both axes labelled (no units) ; 4 suitable linear scale ; point OR bars plotted correctly ± ½ small square ; plots joined by ruled lines OR appropriate line of best fit OR bars labelled, equal width, equidistant, with gaps ; 652 1(d) population increases (overall) ; 2 decrease in population in 2003 / idea of anomaly in 2003 ; 1(e) estimates may be inaccurate as not all the marked turtles may have been counted as marked previously ; 2 idea that this would give a higher estimate of population (than those that have been calculated) ;

This question in 9693/22 May/June 2025

4 Fig. 4.1 shows a barrel jellyfish. Fig. 4.1 (a) Make a large drawing of the jellyfish shown in Fig. 4.1. Do not label your drawing. [4] (b) Citizen science projects encourage people to make observations in their environment and submit their observations to a research team. Scientists sometimes use citizen science projects to collect data from many people. Citizen science projects can be used to collect data on jellyfish washed up on beaches. (i) Suggest three advantages of collecting data from many people about jellyfish found on beaches instead of scientists collecting their own data. 1 … … 2 … … 3 … … [3] (ii) Suggest one disadvantage of collecting data from many people about jellyfish found on beaches instead of scientists collecting their own data. … … [1] (iii) Describe how the disadvantage you have given in 4(b)(ii) could be limited. … … [1] (iv) Jellyfish are in the phylum Cnidaria and have nematocysts. State the risk that jellyfish cause to people taking part in the study. … … [1] (v) Suggest two ways scientists can reduce the risk you have given in 4(b)(iv). 1 … … 2 … … [2] (c) Scientists investigated the relationship between nitrate ion (NO3–) and phosphate ion (PO43–) concentration in the ocean and the number of jellyfish found on beaches. (i) Explain why an increase in nitrate ion and phosphate ion concentration in the ocean can cause an increase in the jellyfish population. … … … … [2] (ii) State why the number of jellyfish found on beaches increases when the population of jellyfish increases. … … [1]

15 marks

Mark scheme: 4(a) outline: unbroken lines and no shading ; 4 size: most of the space provided and at least as big as original picture ; in proportion ; detail – bell section and three oral arms section ; 4(b)(i) any three from: 3 1 enables collection of more, data / information ; 2 (data collected from) a larger / greater, area ; 3 free / cheaper, to collect ; 4 increased awareness in conservation ; 5 idea of more effective use of scientists time ; 4(b)(ii) any one from: 1 disadvantage: 1 identification may be incorrect ; 2 could be duplication from different members of public ; 3 inaccurate estimates of numbers ; 4 variation in ease of submission due to connectivity to internet 4(b)(iii) any one from: 1 how to limit disadvantage: 1 provision of key to help public make correct identification ; ask public to provide photos so some or all of sightings can be checked 2 use of location data to identify reportings from a location (e.g. per day or week) ; 3 offer citizens training on estimating numbers ; 4 ability to save and submit reporting later ; 4(b)(iv) any one from: 1 (jellyfish) stings ; AVP ; 4(b)(v) any two from: 2 warning of risk to participants ; identification of (very) dangerous species ; advice on how to treat stings ; 4(c)(i) any two from: 2 increase in nutrients will increase productivity / rate of photosynthesis ORA ; (idea of) greater availability of food in food chains ORA ; (idea of) jellyfish are animals / consumers ; 4(c)(ii) any one from: 1 limited motility / swept in by strong currents / wave action ; competition for food / insufficient food ; the greater the population, the greater the chance of jellyfish being washed up ; 4(c)(iii) line showing similar trend to phytoplankton mass ; 2 time delay for both peaks ; 4(d)(i) increases AND decreases ; 2 peaks in 2013 ; 4(d)(ii) 300 (%) ; 1 4(d)(iii) any three from: 3 no information about nitrate and phosphate availability in graph ; idea that information is only annual / time intervals are too large ; different species peak at different times ; different species show different trends / patterns ; AVP ;

This question in 9693/22 May/June 2025

1 Scientists in Australia monitored the population of the Green Turtle for five years. They used the mark-release-recapture method to estimate the population of the turtles in the southern Great Barrier Reef. (a) Describe an ethical method of mark-release-recapture that could be used by the scientists. … … … … … … [3] (b) This mark-release-recapture method was carried out each year from 2000 to 2004. The results are shown in Table 1.1. Table 1.1 year 2000 2001 2002 2003 2004 turtles captured in first 247 253 292 230 309 sample (n1) turtles captured in second sample (both marked and 355 345 392 326 418 unmarked) (n2) marked turtles recaptured 108 92 100 115 109 in second sample (m2) estimated turtle 812 949 1145 1185 population (N) … Use Table 1.1 and the Lincoln index to estimate the population of turtles in 2003. The equation for the Lincoln index is shown. n1 × n2 N = m2 Where: N = estimated turtle population n1 = number of individuals captured in first sample n2 = number of individuals captured in second sample (both marked and unmarked) m2 = number of marked individuals recaptured in second sample. Write your answer in Table 1.1. [1] (c) Plot a graph of the estimated turtle population (N) from 2000 to 2004. [4] (d) Use the data in Table 1.1 to describe the trend shown for the population of turtles. … … … … [2] (e) Turtles were not counted as being previously marked if it was not clear that the marks on their body were from the previous capture. Evaluate the population estimates shown in Table 1.1 based on this observation. … … … … [2] [Total: 12]

12 marks

Mark scheme: Question Answer Marks 1(a) idea of attaching tags in a way that does not cause pain / harm to the turtles ; 3 plus any two from: capturing / trapping turtles (from sea or on beach) AND attach tags AND releasing turtles back to, sea / beach ; idea of revisiting (same site), a year later / after suitable time period ; explanation of a suitable time period e.g. allowing tagged population to mix with untagged ; recording no. of turtles with a tag AND total no. of turtles without tags ; 1(b) 1 2003 652 1(c) both axes labelled (no units) ; 4 suitable linear scale ; point OR bars plotted correctly ± ½ small square ; plots joined by ruled lines OR appropriate line of best fit OR bars labelled, equal width, equidistant, with gaps ; 652 1(d) population increases (overall) ; 2 decrease in population in 2003 / idea of anomaly in 2003 ; 1(e) estimates may be inaccurate as not all the marked turtles may have been counted as marked previously ; 2 idea that this would give a higher estimate of population (than those that have been calculated) ;

This question in 9693/23 May/June 2025

4 Fig. 4.1 shows a barrel jellyfish. Fig. 4.1 (a) Make a large drawing of the jellyfish shown in Fig. 4.1. Do not label your drawing. [4] (b) Citizen science projects encourage people to make observations in their environment and submit their observations to a research team. Scientists sometimes use citizen science projects to collect data from many people. Citizen science projects can be used to collect data on jellyfish washed up on beaches. (i) Suggest three advantages of collecting data from many people about jellyfish found on beaches instead of scientists collecting their own data. 1 … … 2 … … 3 … … [3] (ii) Suggest one disadvantage of collecting data from many people about jellyfish found on beaches instead of scientists collecting their own data. … … [1] (iii) Describe how the disadvantage you have given in 4(b)(ii) could be limited. … … [1] (iv) Jellyfish are in the phylum Cnidaria and have nematocysts. State the risk that jellyfish cause to people taking part in the study. … … [1] (v) Suggest two ways scientists can reduce the risk you have given in 4(b)(iv). 1 … … 2 … … [2] (c) Scientists investigated the relationship between nitrate ion (NO3–) and phosphate ion (PO43–) concentration in the ocean and the number of jellyfish found on beaches. (i) Explain why an increase in nitrate ion and phosphate ion concentration in the ocean can cause an increase in the jellyfish population. … … … … [2] (ii) State why the number of jellyfish found on beaches increases when the population of jellyfish increases. … … [1]

15 marks

Mark scheme: 4(a) outline: unbroken lines and no shading ; 4 size: most of the space provided and at least as big as original picture ; in proportion ; detail – bell section and three oral arms section ; 4(b)(i) any three from: 3 1 enables collection of more, data / information ; 2 (data collected from) a larger / greater, area ; 3 free / cheaper, to collect ; 4 increased awareness in conservation ; 5 idea of more effective use of scientists time ; 4(b)(ii) any one from: 1 disadvantage: 1 identification may be incorrect ; 2 could be duplication from different members of public ; 3 inaccurate estimates of numbers ; 4 variation in ease of submission due to connectivity to internet 4(b)(iii) any one from: 1 how to limit disadvantage: 1 provision of key to help public make correct identification ; ask public to provide photos so some or all of sightings can be checked 2 use of location data to identify reportings from a location (e.g. per day or week) ; 3 offer citizens training on estimating numbers ; 4 ability to save and submit reporting later ; 4(b)(iv) any one from: 1 (jellyfish) stings ; AVP ; 4(b)(v) any two from: 2 warning of risk to participants ; identification of (very) dangerous species ; advice on how to treat stings ; 4(c)(i) any two from: 2 increase in nutrients will increase productivity / rate of photosynthesis ORA ; (idea of) greater availability of food in food chains ORA ; (idea of) jellyfish are animals / consumers ; 4(c)(ii) any one from: 1 limited motility / swept in by strong currents / wave action ; competition for food / insufficient food ; the greater the population, the greater the chance of jellyfish being washed up ; 4(c)(iii) line showing similar trend to phytoplankton mass ; 2 time delay for both peaks ; 4(d)(i) increases AND decreases ; 2 peaks in 2013 ; 4(d)(ii) 300 (%) ; 1 4(d)(iii) any three from: 3 no information about nitrate and phosphate availability in graph ; idea that information is only annual / time intervals are too large ; different species peak at different times ; different species show different trends / patterns ; AVP ;

This question in 9693/23 May/June 2025

5 Scientists studied the biodiversity at eight locations in the Arabian Sea. The scientists used a net to catch species in the benthic zone. (a) Describe what is meant by the benthic zone. … … [1] At each location the nets were pulled at a constant speed for one hour. Four of the locations sampled were at a depth of 200 m. The other four locations sampled were at a depth of 1000 m. Table 5.1 shows the depth and total catch at each location. Table 5.1 location depth / m total catch / kg number 1 200 169 2 200 122 3 200 34 4 200 582 5 1000 75 6 1000 453 7 1000 256 8 1000 120 (b) Use the data shown in Table 5.1 to describe if there is a relationship between depth and total catch. … … … … [2] (c) The scientists identified the species present in each catch and the number of individuals of each species. They used this data to calculate Simpson’s index of diversity using the equation: 2 D = 1 – (Σ(nN) ) = sum of (total) Σ n = number of individuals of each different species N = the total number of individuals of all the species (i) Use the data provided to complete Table 5.2 for location 1. Give your answers to three significant figures. Table 5.2 location 1 species 2 n n n N ( N) P 27 0.278 0.077 Q 23 … … R 18 0.186 0.034 S 16 0.165 0.027 T 13 0.134 0.018 N 97 Σ … [4] (ii) Use your answer to (c)(i) to calculate Simpson’s index of diversity for location 1. … [1] (d) Table 5.3 shows the Simpson’s index of diversity calculated for each other location sampled. Table 5.3 Simpson’s location depth / m total catch / kg index of number diversity 1 200 169 2 200 122 0.88 3 200 34 0.92 4 200 582 0.68 5 1000 75 0.91 6 1000 453 0.71 7 1000 256 0.78 8 1000 120 0.91 Compare the biodiversity for the catches shown in Table 5.3. … … … … … … [3] [Total: 11]

11 marks

Mark scheme: 5(a) the lowest part of the ocean (sediments / water) ; 1 5(b) any two from: 2 no, correlation / relationship, + no, trend / pattern / consistency, in results ; more data required to establish a relationship ; possible anomalies at site 3 / 4 and 5 ; relevant use of data to support ; 5(c)(i) 4 location 1 species 2 n n  n    N  N  Q 23 0.237 ; 0.056(0) ; N 97  0.212 ; n values for AND  to 3 sig. fig ; N 5(c)(ii) 0.788 ; 1 5(d) any three from: 3 higher Simpson’s index, value / number, indicates a, greater / higher, biodiversity ORA ; results suggest smaller catches have a higher biodiversity ORA ; results suggest no significant difference between biodiversity at different depths ; use of at least 2 data to support answer ;

This question in 9693/21 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 9693/22 Oct/Nov 2025

4 Living walls are used to help increase diversity on human made structures. Fig. 4.1 shows several different designs used to create living walls. Fig. 4.1 Scientists investigated how three different designs of living wall, design A, design B and design C, affect diversity. Ten of each design were attached to a sea wall at the mean low water mark. The scientists recorded the total number of individuals of all species found on each design and on a control area after 12 months. Simpson’s index of diversity was used to calculate the diversity of each design. The equation for Simpson’s index of diversity is given below: n 2 D = 1 -c / ` j m N ∑ = sum of (total) n = number of individuals of each different species N = the total number of individuals of all species The results for design C are shown in Table 4.1. Table 4.1 number of individuals of n n 2 species ` j each different species (n) N N 1 34 0.168 0.028 2 7 0.035 0.001 3 21 0.104 0.011 4 6 0.030 0.001 5 37 0.183 0.033 6 12 0.059 0.003 7 59 0.292 0.085 8 19 0.094 0.009 9 7 0.035 0.001 total number of individuals 202 of all species (N) (a) Suggest what the scientists used for the control area. … … … … [2] (b) (i) Use the information in Table 4.1 to calculate D for design C. D = … [2] (ii) Table 4.2 shows the values for Simpson’s index of diversity (D) in design A, design B and in the control area. Table 4.2 design A design B control area Simpson’s index of diversity (D) 0.674 0.818 0.143 Compare the effectiveness of designs A and B for increasing diversity. Use the values for D from Table 4.2 to support your answer. … … … … … … [3] (iii) Evaluate the extent to which the results from this investigation support the idea that living walls increase diversity on human made structures. … … … … … … [3] (c) Suggest reasons why the different designs shown in Fig. 4.1 affect the diversity of the sea wall. … … … … … … [3] (d) State three examples of the benefits that marine biodiversity provides. 1 … … 2 … … 3 … … [3] [Total: 16]

16 marks

Mark scheme: 4(a) bare, sea wall / human-made surface ; 2 of same size area / at same depth ; 4(b)(i) 0.172 ; 2 1 – 0.172 = 0.828 ; 4(b)(ii) reference to value closer to 1 indicating greater biodiversity ; 3 both designs have greater biodiversity than control area ; design B has greater biodiversity than A ; 4(b)(iii) any three from: 3 supported as all designs show increased diversity compared to control ; (however) only one human-made structure investigated ; (however) only one, sea area / coast investigated ; (however) relatively small sample size ; (however) investigation only lasted 12 months ; investigation only performed once ; AVP ; 4(c) any three from: 3 may provide different surface for secure attachment by organisms ; different shapes may have different degrees of shading at low tide ; different shapes may hold different volumes of water at low tide ; may be made of different materials ; size of hollows / crevices may affect how many, individuals / species, can occupy them ; larger surface area ; idea of not being a uniform habitat ; AVP ; 4(d) any three from: 3 maintaining stable ecosystems ; protection of the physical environment ; providing food sources / increased opportunity for harvesting ; as a source of pharmaceuticals /medicines ; climate control / reduces global warming ;

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

4 Living walls are used to help increase diversity on human made structures. Fig. 4.1 shows several different designs used to create living walls. Fig. 4.1 Scientists investigated how three different designs of living wall, design A, design B and design C, affect diversity. Ten of each design were attached to a sea wall at the mean low water mark. The scientists recorded the total number of individuals of all species found on each design and on a control area after 12 months. Simpson’s index of diversity was used to calculate the diversity of each design. The equation for Simpson’s index of diversity is given below: n 2 D = 1 -c / ` j m N ∑ = sum of (total) n = number of individuals of each different species N = the total number of individuals of all species The results for design C are shown in Table 4.1. Table 4.1 number of individuals of n n 2 species ` j each different species (n) N N 1 34 0.168 0.028 2 7 0.035 0.001 3 21 0.104 0.011 4 6 0.030 0.001 5 37 0.183 0.033 6 12 0.059 0.003 7 59 0.292 0.085 8 19 0.094 0.009 9 7 0.035 0.001 total number of individuals 202 of all species (N) (a) Suggest what the scientists used for the control area. … … … … [2] (b) (i) Use the information in Table 4.1 to calculate D for design C. D = … [2] (ii) Table 4.2 shows the values for Simpson’s index of diversity (D) in design A, design B and in the control area. Table 4.2 design A design B control area Simpson’s index of diversity (D) 0.674 0.818 0.143 Compare the effectiveness of designs A and B for increasing diversity. Use the values for D from Table 4.2 to support your answer. … … … … … … [3] (iii) Evaluate the extent to which the results from this investigation support the idea that living walls increase diversity on human made structures. … … … … … … [3] (c) Suggest reasons why the different designs shown in Fig. 4.1 affect the diversity of the sea wall. … … … … … … [3] (d) State three examples of the benefits that marine biodiversity provides. 1 … … 2 … … 3 … … [3] [Total: 16]

16 marks

Mark scheme: 4(a) bare, sea wall / human-made surface ; 2 of same size area / at same depth ; 4(b)(i) 0.172 ; 2 1 – 0.172 = 0.828 ; 4(b)(ii) reference to value closer to 1 indicating greater biodiversity ; 3 both designs have greater biodiversity than control area ; design B has greater biodiversity than A ; 4(b)(iii) any three from: 3 supported as all designs show increased diversity compared to control ; (however) only one human-made structure investigated ; (however) only one, sea area / coast investigated ; (however) relatively small sample size ; (however) investigation only lasted 12 months ; investigation only performed once ; AVP ; 4(c) any three from: 3 may provide different surface for secure attachment by organisms ; different shapes may have different degrees of shading at low tide ; different shapes may hold different volumes of water at low tide ; may be made of different materials ; size of hollows / crevices may affect how many, individuals / species, can occupy them ; larger surface area ; idea of not being a uniform habitat ; AVP ; 4(d) any three from: 3 maintaining stable ecosystems ; protection of the physical environment ; providing food sources / increased opportunity for harvesting ; as a source of pharmaceuticals /medicines ; climate control / reduces global warming ;

This question in 9693/23 Oct/Nov 2025