Feeding relationships — Paper 2 · A Level Marine Science 9693

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

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

13 marks

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

This question in 9693/22 May/June 2021

5 Fig. 5.1 shows a blue shark. Fig. 5.1 (a) Make a large drawing of part of the blue shark shown in the box in Fig. 5.1. Do not label your diagram. [4] (b) Blue sharks mainly inhabit the epipelagic zone. State what is meant by the epipelagic zone. … … [1] (c) Explain why blue sharks are described as carnivores and predators. … … … … [2] (d) Blue sharks have been extensively fished in many parts of the world, but little is known about their population size. Information about their population size is estimated by studying catch data from blue shark fisheries. Fig. 5.2 shows the global annual blue shark catch and the catch effort from 1980 to 2017. The catch effort is the global number of days that all boats spend fishing for blue shark. global catch effort 160 140 120 100 global global catch effort annual catch / arbitrary units 80/ 1000 tonnes 60 40 20 0 1980 1985 1990 1995 2000 2005 2010 2015 2020 year Fig. 5.2 (i) Compare the catch and catch effort trends shown in Fig. 5.2. … … … … [2] (ii) Evaluate how useful these data are for understanding the population trends of the blue shark. … … … … [2]

11 marks

Mark scheme: 5(a) clear outline ; suitable size ; in proportion ; detail ; 5(b) (upper) part of (open) ocean where light is available (for producers) ; 1 5(c) (all) carnivores eat, meat / do not eat plants / other animals / named animals / consumers ; (predators) hunt animals / prey on animals / catch animals / kill animals ; 2 5(d)(i) any 2 of; both catch effort and catch (generally) increase OR more effort was put into catching blue sharks, global catch (usually) increased ; catch effort and catch rapidly increasing from (1994–1998) onwards / idea that before (1994–1998) there was minimal change / stable ; (global annual) catch, reduces / decreases, in 2015 despite catch effort continuing to increase ; catch effort begins to increase in 1994 OR global annual catch begins to increase more in 1998 ; 2 5(d)(ii) (idea of) most of data of little use as population size unknown ; idea that decreasing catch, from 2015 / despite increased effort, suggests a, decrease in / low population ; 2 Question Answer Marks 5(d)(iii) any 2 of; chance of recapturing marked individuals very low ; due to (large) size of area that individuals exist in ; idea that it is difficult to account for births and deaths ; idea that population is not evenly distributed e.g. move in groups or schools ; 2

This question in 9693/21 May/June 2023

4 (a) Fig. 4.1 shows the mean rate of photosynthesis each month and the water temperature throughout the year in a bay of an ocean in the northern hemisphere. Key mean monthly rate of photosynthesis water temperature 3 30 2 20mean monthly waterrate of temperaturephotosynthesis / °C/ arbitrary units 1 10 0 0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec month Fig. 4.1 (i) Use Fig. 4.1 to describe the relationship between water temperature and the rate of photosynthesis. … … … … [2] (ii) Sketch a line on Fig. 4.2 to suggest what would happen to the primary consumer population over the period of this year. biomass of primary consumers / arbitrary units Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec month Fig. 4.2 [2] (b) Fig. 4.3 shows a flooding river discharging into the bay during winter. J K Fig. 4.3 Discuss how abiotic factors in the water at point J differ to point K. … … … … … … … … … … [5] (c) Table 4.1 shows the mean concentration of some nutrient ions in the bay in January and in August. Table 4.1 mean concentration in mean concentration in percentage change in nutrient bay in January bay in August nutrient ions January / parts per million / parts per million to August CO3 2– 31 26 –16 NO3– 0.92 0.31 –67 Mg2+ 1400 1300 –5.0 PO43– 0.14 0.05 (i) Calculate the percentage change in phosphate ions (PO43–) between January and August. Give your answer to two significant figures. Show your working. … % [3] (ii) Suggest reasons for the increase and decrease in phosphate ion levels in the bay during the year. … … … … … … … … [4] (iii) Discuss the impact of a large decrease in the concentration of nitrate ions (NO3–) on the productivity of food webs in the bay. … … … … … … [3] (d) A scientist took a sample of a small macroalga from the bay. An experiment was set up in a laboratory to investigate the effect of light intensity on the rate of photosynthesis of the alga. (i) State one key variable to standardise. … [1] (ii) Suggest a laboratory method the scientist could use to investigate the effect of light intensity on the rate of photosynthesis of the alga. … … … … … … … … … … [5] (iii) Draw a table to record the results. Include units. Do not write in any results. [3] [Total: 28]

28 marks

Mark scheme: 4(a)(i) any 2 from: increasing water temperature increases rate of photosynthesis ; ref. to (rapid) photosynthesis drop between June / July to August while temperature stays high ; idea of, photosynthesis rate has a second peak (in October) ; ref. to lag period between temperature increase and photosynthesis increase ; 2 4(a)(ii) graph showing similar shape to photosynthesis line 2 peaks and 2 troughs with the peaks up to 1 month after the phytoplankton line ;; (for 2 marks) graph showing similar shape to photosynthesis line 2 peaks and 2 troughs ; (for 1 mark) 2 4(b) any 5 from: 1 J has higher sediment loading / higher turbidity due to high runoff from land carrying sediment ORA ; 2 J has more fine particles of sediment as particles have not been able to settle out ORA ; 3 J has higher, flow rate / speed / velocity, of water due to large volume of water flowing in narrow channel ORA ; 4 J has lower salinity as river water is freshwater (so little salt present) ORA ; 5 J has lower pH as freshwater has a pH of 7 / sea water has a pH of (around) 8.2 ORA ; 6 J is higher in, nutrients/ minerals, due to run-off from land ORA ; 7 J has higher concentration of, oxygen / CO2 ,as gas saturation decreases with increasing salt concentration ORA OR due to increased turbulence at J, ORA ; 8 J will be less dense as it contains fewer salts ORA ; 9 J may carry more, toxins / pollutants / named pollutant, from runoff ; 5 4(c)(i) (0.05 – 0.14) = –0.09 ; 0.09 / 0.14  100 = –64.29… ; –64 (%) ; OR 0.05 ÷ 0.14  100 = MP1 ; 100 – (MP1) ; –64.29 ; 3 Question Answer Marks 4(c)(ii) any 4 from (decrease in summer) 1 (summer) absorbed by phytoplankton / algae / plants ; 2 (uses of phosphate) DNA / RNA / ATP / bone ; 3 to increase productivity ORA ; (increase in winter) 1 flooding occurs in winter / more precipitation in winter ; 2 increase in fertiliser / sewage (from runoff) ; 3 (increased) river run-off / upwelling ; 4 (winter) stormy conditions causes greater mixing of nutrients from the seabed ; 4 4(c)(iii) any 3 from: used to make amino acids / protein / DNA / chlorophyll ; less, (protein / DNA) for growth / repair of cells / cell division / photosynthesis by producers / biomass formed ; (less ) energy to pass along food chain / less food available further up the food chain ; reduces productivity at all levels / a named level ; 3 4(d)(i) temperature / pH / salinity / water volume / carbonate or hydrogen carbonate or carbon dioxide, concentration ; 1 4(d)(ii) any 5 from: changing distance of light source / how light intensity is changed ; ensure ambient light is low ; presence of glass screen / water bath (to ensure not heated by lamp) ; ref. to specimen in beaker / test tube / flask / container ; allowing specimen time to adjust to light intensity ; means of measuring the volume of gas released / count the bubbles ; in a stated time period ; ref. to hydrogen carbonate source in water / maintaining carbon dioxide concentration ; ref. to repeating / 3 sets of data collected, at each light intensity + calculate the mean ; 5 Question Answer Marks 4(d)(iii) distance from light source / cm volume of oxygen collected per minute / cm3 OR number of bubbles / minute 1 2 3 mean column / row, for distance and mm / cm / m ; column / row, for volume of oxygen collected + cm3 / number of bubbles counted + per minute ; column / row, for repeats at least 3 sets of results / mean ; 3

This question in 9693/22 May/June 2024

4 (a) Fig. 4.1 shows the mean rate of photosynthesis each month and the water temperature throughout the year in a bay of an ocean in the northern hemisphere. Key mean monthly rate of photosynthesis water temperature 3 30 2 20mean monthly waterrate of temperaturephotosynthesis / °C/ arbitrary units 1 10 0 0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec month Fig. 4.1 (i) Use Fig. 4.1 to describe the relationship between water temperature and the rate of photosynthesis. … … … … [2] (ii) Sketch a line on Fig. 4.2 to suggest what would happen to the primary consumer population over the period of this year. biomass of primary consumers / arbitrary units Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec month Fig. 4.2 [2] (b) Fig. 4.3 shows a flooding river discharging into the bay during winter. J K Fig. 4.3 Discuss how abiotic factors in the water at point J differ to point K. … … … … … … … … … … [5] (c) Table 4.1 shows the mean concentration of some nutrient ions in the bay in January and in August. Table 4.1 mean concentration in mean concentration in percentage change in nutrient bay in January bay in August nutrient ions January / parts per million / parts per million to August CO32– 31 26 –16 NO3– 0.92 0.31 –67 Mg2+ 1400 1300 –5.0 PO43– 0.14 0.05 (i) Calculate the percentage change in phosphate ions (PO43–) between January and August. Give your answer to two significant figures. Show your working. … % [3] (ii) Suggest reasons for the increase and decrease in phosphate ion levels in the bay during the year. … … … … … … … … [4] (iii) Discuss the impact of a large decrease in the concentration of nitrate ions (NO3–) on the productivity of food webs in the bay. … … … … … … [3] (d) A scientist took a sample of a small macroalga from the bay. An experiment was set up in a laboratory to investigate the effect of light intensity on the rate of photosynthesis of the alga. (i) State one key variable to standardise. … [1] (ii) Suggest a laboratory method the scientist could use to investigate the effect of light intensity on the rate of photosynthesis of the alga. … … … … … … … … … … [5] (iii) Draw a table to record the results. Include units. Do not write in any results. [3] [Total: 28]

28 marks

Mark scheme: 4(a)(i) any 2 from: increasing water temperature increases rate of photosynthesis ; ref. to (rapid) photosynthesis drop between June / July to August while temperature stays high ; idea of, photosynthesis rate has a second peak (in October) ; ref. to lag period between temperature increase and photosynthesis increase ; 2 4(a)(ii) graph showing similar shape to photosynthesis line 2 peaks and 2 troughs with the peaks up to 1 month after the phytoplankton line ;; (for 2 marks) graph showing similar shape to photosynthesis line 2 peaks and 2 troughs ; (for 1 mark) 2 4(b) any 5 from: 1 J has higher sediment loading / higher turbidity due to high runoff from land carrying sediment ORA ; 2 J has more fine particles of sediment as particles have not been able to settle out ORA ; 3 J has higher, flow rate / speed / velocity, of water due to large volume of water flowing in narrow channel ORA ; 4 J has lower salinity as river water is freshwater (so little salt present) ORA ; 5 J has lower pH as freshwater has a pH of 7 / sea water has a pH of (around) 8.2 ORA ; 6 J is higher in, nutrients/ minerals, due to run-off from land ORA ; 7 J has higher concentration of, oxygen / CO2 ,as gas saturation decreases with increasing salt concentration ORA OR due to increased turbulence at J, ORA ; 8 J will be less dense as it contains fewer salts ORA ; 9 J may carry more, toxins / pollutants / named pollutant, from runoff ; 5 4(c)(i) (0.05 – 0.14) = –0.09 ; 0.09 / 0.14  100 = –64.29… ; –64 (%) ; OR 0.05 ÷ 0.14  100 = MP1 ; 100 – (MP1) ; –64.29 ; 3 Question Answer Marks 4(c)(ii) any 4 from (decrease in summer) 1 (summer) absorbed by phytoplankton / algae / plants ; 2 (uses of phosphate) DNA / RNA / ATP / bone ; 3 to increase productivity ORA ; (increase in winter) 1 flooding occurs in winter / more precipitation in winter ; 2 increase in fertiliser / sewage (from runoff) ; 3 (increased) river run-off / upwelling ; 4 (winter) stormy conditions causes greater mixing of nutrients from the seabed ; 4 4(c)(iii) any 3 from: used to make amino acids / protein / DNA / chlorophyll ; less, (protein / DNA) for growth / repair of cells / cell division / photosynthesis by producers / biomass formed ; (less ) energy to pass along food chain / less food available further up the food chain ; reduces productivity at all levels / a named level ; 3 4(d)(i) temperature / pH / salinity / water volume / carbonate or hydrogen carbonate or carbon dioxide, concentration ; 1 4(d)(ii) any 5 from: changing distance of light source / how light intensity is changed ; ensure ambient light is low ; presence of glass screen / water bath (to ensure not heated by lamp) ; ref. to specimen in beaker / test tube / flask / container ; allowing specimen time to adjust to light intensity ; means of measuring the volume of gas released / count the bubbles ; in a stated time period ; ref. to hydrogen carbonate source in water / maintaining carbon dioxide concentration ; ref. to repeating / 3 sets of data collected, at each light intensity + calculate the mean ; 5 Question Answer Marks 4(d)(iii) distance from light source / cm volume of oxygen collected per minute / cm3 OR number of bubbles / minute 1 2 3 mean column / row, for distance and mm / cm / m ; column / row, for volume of oxygen collected + cm3 / number of bubbles counted + per minute ; column / row, for repeats at least 3 sets of results / mean ; 3

This question in 9693/23 May/June 2024

2 Scientists investigated food webs in the open ocean. Organisms were captured, and their trophic level was identified. The total biomass of organisms at each trophic level was then calculated. The results are shown in Table 2.1. Table 2.1 trophic level total biomass / arbitrary units 1 3.8 2 4.6 3 3.4 4 2.1 5 0.5 (a) Construct a pyramid of biomass for the data shown in Table 2.1. Draw your pyramid to scale, and label the trophic levels. [4] (b) Suggest an explanation for the difference in total biomass between trophic levels 1 and 2. … … … … [2] (c) The efficiency of biomass transfer is a measure of the proportion of biomass transferred from a lower trophic level to a higher one. The biomass transfer efficiency between trophic levels 3 and 4 is 61.8%. Calculate the percentage biomass transfer efficiency between trophic levels 4 and 5. … % [1] (d) Suggest reasons for the difference in the biomass transfer efficiency between trophic levels 3 and 4 and the biomass transfer efficiency between trophic levels 4 and 5. … … … … [2] (e) Explain how nutrients leave ocean food chains and become available to producers again. … … … … [2] [Total: 11]

11 marks

Mark scheme: 2(a) five horizontal rectangles drawn AND stacked centrally on top of each other AND no gaps ; 4 all five bars in correct order (from bottom to top so smallest at top, largest second from bottom) ; all five bars drawn to scale AND all same, height for horizontal bars / width for vertical bars ; all bars labelled with correct trophic levels ; trophic level total 5 biomass / arbitrary 4 units 3 2 5 0.5 1 4 2.1 3 3.4 2 4.6 (widest) 1 3.8 2(b) any 2 from: 2 idea that producers / trophic level 1 able to reproduce faster (than other trophic levels) ; idea that data is a snapshot / point in time ; idea of differences in percentage water content of different organisms affecting (dry) biomass readings ; 2(c) 24 (%) / 23.8 (%) ; 1 2(d) any 2 from: 2 idea of comparison of more energy used in TL5 / less energy used in TL4 ; reason for more energy being used, e.g. hunting / catching prey / respiration / movement ; idea that (TL4) are carnivores and have more teeth / bones / indigestible parts / more waste (excreted) by TL5 (resulting in biomass that can not be transferred) ; idea of the higher the trophic level the smaller the prey population to support it ; AVP ;; 2(e) any 1 from: 2 harvesting ; idea of excretion / marine snow ; decomposers / bacteria ; break down, waste / detritus OR decomposition ; named example of excreted chemical ; plus any 1 from: upwelling ; uptake of (inorganic) nutrients ; named example of uptaken chemical ;

This question in 9693/21 Oct/Nov 2024

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

10 marks

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

This question in 9693/21 Oct/Nov 2024

2 Scientists investigated food webs in the open ocean. Organisms were captured, and their trophic level was identified. The total biomass of organisms at each trophic level was then calculated. The results are shown in Table 2.1. Table 2.1 trophic level total biomass / arbitrary units 1 3.8 2 4.6 3 3.4 4 2.1 5 0.5 (a) Construct a pyramid of biomass for the data shown in Table 2.1. Draw your pyramid to scale, and label the trophic levels. [4] (b) Suggest an explanation for the difference in total biomass between trophic levels 1 and 2. … … … … [2] (c) The efficiency of biomass transfer is a measure of the proportion of biomass transferred from a lower trophic level to a higher one. The biomass transfer efficiency between trophic levels 3 and 4 is 61.8%. Calculate the percentage biomass transfer efficiency between trophic levels 4 and 5. … % [1] (d) Suggest reasons for the difference in the biomass transfer efficiency between trophic levels 3 and 4 and the biomass transfer efficiency between trophic levels 4 and 5. … … … … [2] (e) Explain how nutrients leave ocean food chains and become available to producers again. … … … … [2] [Total: 11]

11 marks

Mark scheme: 2(a) five horizontal rectangles drawn AND stacked centrally on top of each other AND no gaps ; 4 all five bars in correct order (from bottom to top so smallest at top, largest second from bottom) ; all five bars drawn to scale AND all same, height for horizontal bars / width for vertical bars ; all bars labelled with correct trophic levels ; trophic level total 5 biomass / arbitrary 4 units 3 2 5 0.5 1 4 2.1 3 3.4 2 4.6 (widest) 1 3.8 2(b) any 2 from: 2 idea that producers / trophic level 1 able to reproduce faster (than other trophic levels) ; idea that data is a snapshot / point in time ; idea of differences in percentage water content of different organisms affecting (dry) biomass readings ; 2(c) 24 (%) / 23.8 (%) ; 1 2(d) any 2 from: 2 idea of comparison of more energy used in TL5 / less energy used in TL4 ; reason for more energy being used, e.g. hunting / catching prey / respiration / movement ; idea that (TL4) are carnivores and have more teeth / bones / indigestible parts / more waste (excreted) by TL5 (resulting in biomass that can not be transferred) ; idea of the higher the trophic level the smaller the prey population to support it ; AVP ;; 2(e) any 1 from: 2 harvesting ; idea of excretion / marine snow ; decomposers / bacteria ; break down, waste / detritus OR decomposition ; named example of excreted chemical ; plus any 1 from: upwelling ; uptake of (inorganic) nutrients ; named example of uptaken chemical ;

This question in 9693/22 Oct/Nov 2024

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

10 marks

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

This question in 9693/22 Oct/Nov 2024

2 Scientists investigated food webs in the open ocean. Organisms were captured, and their trophic level was identified. The total biomass of organisms at each trophic level was then calculated. The results are shown in Table 2.1. Table 2.1 trophic level total biomass / arbitrary units 1 3.8 2 4.6 3 3.4 4 2.1 5 0.5 (a) Construct a pyramid of biomass for the data shown in Table 2.1. Draw your pyramid to scale, and label the trophic levels. [4] (b) Suggest an explanation for the difference in total biomass between trophic levels 1 and 2. … … … … [2] (c) The efficiency of biomass transfer is a measure of the proportion of biomass transferred from a lower trophic level to a higher one. The biomass transfer efficiency between trophic levels 3 and 4 is 61.8%. Calculate the percentage biomass transfer efficiency between trophic levels 4 and 5. … % [1] (d) Suggest reasons for the difference in the biomass transfer efficiency between trophic levels 3 and 4 and the biomass transfer efficiency between trophic levels 4 and 5. … … … … [2] (e) Explain how nutrients leave ocean food chains and become available to producers again. … … … … [2] [Total: 11]

11 marks

Mark scheme: 2(a) five horizontal rectangles drawn AND stacked centrally on top of each other AND no gaps ; 4 all five bars in correct order (from bottom to top so smallest at top, largest second from bottom) ; all five bars drawn to scale AND all same, height for horizontal bars / width for vertical bars ; all bars labelled with correct trophic levels ; trophic level total 5 biomass / arbitrary 4 units 3 2 5 0.5 1 4 2.1 3 3.4 2 4.6 (widest) 1 3.8 2(b) any 2 from: 2 idea that producers / trophic level 1 able to reproduce faster (than other trophic levels) ; idea that data is a snapshot / point in time ; idea of differences in percentage water content of different organisms affecting (dry) biomass readings ; 2(c) 24 (%) / 23.8 (%) ; 1 2(d) any 2 from: 2 idea of comparison of more energy used in TL5 / less energy used in TL4 ; reason for more energy being used, e.g. hunting / catching prey / respiration / movement ; idea that (TL4) are carnivores and have more teeth / bones / indigestible parts / more waste (excreted) by TL5 (resulting in biomass that can not be transferred) ; idea of the higher the trophic level the smaller the prey population to support it ; AVP ;; 2(e) any 1 from: 2 harvesting ; idea of excretion / marine snow ; decomposers / bacteria ; break down, waste / detritus OR decomposition ; named example of excreted chemical ; plus any 1 from: upwelling ; uptake of (inorganic) nutrients ; named example of uptaken chemical ;

This question in 9693/23 Oct/Nov 2024

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

10 marks

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

This question in 9693/23 Oct/Nov 2024