Nutrient cycles — 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

4 (a) The mean salinity of sea water is about 35 parts per thousand (‰). The salinity in a tropical lagoon was measured and found to be 37 ‰ and the salinity in an estuary was found to be 20 ‰. Suggest explanations for these differences in salinity. … … … … … … [3] (b) Describe what is meant by the Coriolis effect and how it affects ocean currents. … … … … … [2] (c) Explain how temperature and wind produce ocean currents and upwelling. … … … … … … … … … … [5] (d) The surface layer of the sea contains a reservoir of dissolved nutrients. With reference to named examples, discuss how these nutrients may be lost from the surface layer. … … … … … … … … … … … … [5] [Total: 15]

15 marks

Mark scheme: 4(a) any 3 of: increased evaporation in lagoon ; due to high temperature ; increasing concentration of salt which increases salinity ; idea of, dilution of sea water in an estuary / decrease in concentration of salt ; by fresh water from, rivers / run off, decreases salinity ; 3 4(b) any 2 of: force caused by rotation of the Earth ; idea of deflection of, ocean currents / cyclones / wind direction ; ref. to different direction of spin in northern and southern hemisphere / wind or currents have spiral patterns away from the equator ; 2 Question Answer Marks Guidance 4(c) any 5 of: decrease in temperature of water at surface ; (leads to upwelling) increase in density ; cold / more dense, water sinks ; replaced by water moving up from below / AW ; ref. to convection ; surface currents are driven by the wind ; surface water moved away from coasts ; ref. to (wind driven) currents deflected by underwater ridges causing them to move upwards ; ref. to global conveyer belt / deep water currents, being temperature driven / start at the poles ; 5 Question Answer Marks Guidance 4(d) any 5 of: 1 carbon / carbon dioxide, used to synthesise organic compounds / absorbed by producers / for photosynthesis ; 2 magnesium for chlorophyll ; 3 phosphorus for, DNA / bones ; 4 nitrogen for, amino acids / proteins / DNA ; 5 calcium for, bones / teeth / skeleton ; 6 nutrients are incorporated into food chains ; 7 (loss by) harvesting ; 8 (loss by) dead organisms / faeces, sinking to sea floor ; 9 (loss by) incorporation into coral reefs ; 5

This question in 9693/21 Oct/Nov 2017

3 Ocean currents can distribute nutrients and organisms around the globe. (a) Discuss the factors that cause both surface and deep oceanic currents to form. … … … … … … … … … … … … … … [7] (b) Describe the cycling of calcium within the marine environment. … … … … … … … … … … … … … … … … [8] [Total: 15]

15 marks

This question in 9693/20 Oct/Nov 2021

5 A mid-ocean ridge is a tectonic feature found in the Earth’s crust in the larger oceans. (a) (i) Name the type of plate boundary usually found at a mid-ocean ridge. … … [1] (ii) Explain how the ocean floor forms at this plate boundary. … … … … … … [3] (b) A magnetometer is a scientific instrument that is used to survey the magnetic polarity of rocks on the ocean floor. A survey ship towed a magnetometer in a straight line for 100 km as it passed across a mid-ocean ridge. The direction of travel was perpendicular (at right angles) to the position of the mid-ocean ridge, as shown in Fig. 5.1. aerial view of ship direction of ship travel mid-ocean ridge NOT TO SCALE Fig. 5.1 Fig. 5.2 shows the data that was collected. magnetometer magnetic signal Z positive magnetic + anomaly 0 negative magnetic – anomaly 0 10 20 30 40 50 60 70 80 90 100 distance travelled by survey ship / km Fig. 5.2 (i) Explain the pattern shown by the data in Fig. 5.2. … … … … [2] (ii) Suggest how many kilometres the boat had travelled before it was directly over the centre of the mid-ocean ridge. Explain your answer. … … … … [2] (iii) The ocean floor at this mid-ocean ridge is spreading at a rate of 0.02 m per year. Use this information to estimate the age of rocks at point Z. … [1] (c) Research suggests a link between ocean floor spreading and the carbon cycle, as the formation of rock will act as a sink for carbon. Fig. 5.3 on page 23 shows data for atmospheric carbon dioxide concentration in parts per million (ppm), the total global length of mid-ocean ridge plate boundaries, and the mean rate of ocean floor spreading. Discuss whether the data shown in Fig. 5.3 support the idea that there is a link between ocean floor spreading and the carbon cycle. Explain your answer. … … … … … … … … … … [4] [Total: 13]

13 marks

Mark scheme: 5(a)(i) divergent ; 1 5(a)(ii) any three from: as plate boundaries move apart ; molten magma (from mantle) pushes through crust ; driven by convection currents in mantle ; solidifies due to (cold) sea water ; 3 5(b)(i) any two from: idea of, the polarity of the rocks reverses at different points (on the seabed) ; idea of, polarity of rocks determined when rocks formed ; Earth’s magnetic field reverses over time ; 2 5(b)(ii) 45 km ; pattern either side of ridge will be symmetrical ; 2 5(b)(iii) 1 500 000 years old ; 1 Question Answer Marks 5(c) any four from: (supported as) overall concentration of CO2 has decreased over time AND length of plate boundaries has increased ; (not supported as) concentration of CO2 and length of plate boundaries do not, mirror each other exactly / follow / AW ; between 120 mya and present day, plate boundary length decreased yet concentration of CO2 decreased; rate of seafloor spreading decreased over time but concentration of CO2 decreasing ; idea of correlation not being evidence of causation ; 4

This question in 9693/22 May/June 2022

5 A mid-ocean ridge is a tectonic feature found in the Earth’s crust in the larger oceans. (a) (i) Name the type of plate boundary usually found at a mid-ocean ridge. … … [1] (ii) Explain how the ocean floor forms at this plate boundary. … … … … … … [3] (b) A magnetometer is a scientific instrument that is used to survey the magnetic polarity of rocks on the ocean floor. A survey ship towed a magnetometer in a straight line for 100 km as it passed across a mid-ocean ridge. The direction of travel was perpendicular (at right angles) to the position of the mid-ocean ridge, as shown in Fig. 5.1. aerial view of ship direction of ship travel mid-ocean ridge NOT TO SCALE Fig. 5.1 Fig. 5.2 shows the data that was collected. magnetometer magnetic signal Z positive magnetic + anomaly 0 negative magnetic – anomaly 0 10 20 30 40 50 60 70 80 90 100 distance travelled by survey ship / km Fig. 5.2 (i) Explain the pattern shown by the data in Fig. 5.2. … … … … [2] (ii) Suggest how many kilometres the boat had travelled before it was directly over the centre of the mid-ocean ridge. Explain your answer. … … … … [2] (iii) The ocean floor at this mid-ocean ridge is spreading at a rate of 0.02 m per year. Use this information to estimate the age of rocks at point Z. … [1] (c) Research suggests a link between ocean floor spreading and the carbon cycle, as the formation of rock will act as a sink for carbon. Fig. 5.3 on page 23 shows data for atmospheric carbon dioxide concentration in parts per million (ppm), the total global length of mid-ocean ridge plate boundaries, and the mean rate of ocean floor spreading. Discuss whether the data shown in Fig. 5.3 support the idea that there is a link between ocean floor spreading and the carbon cycle. Explain your answer. … … … … … … … … … … [4] [Total: 13]

13 marks

Mark scheme: 5(a)(i) divergent ; 1 5(a)(ii) any 3 from: as plate boundaries move apart ; molten magma (from mantle) pushes through crust ; driven by convection currents in mantle ; solidifies due to (cold) sea water ; 3 5(b)(i) any 2 from: idea of, the polarity of the rocks reverses at different points (on the seabed) ; idea of, polarity of rocks determined when rocks formed ; Earth’s magnetic field reverses over time ; 2 5(b)(ii) 45 km ; pattern either side of ridge will be symmetrical ; 2 5(b)(iii) 1 500 000 years old ; 1 Question Answer Marks 5(c) any 4 from: (supported as) overall concentration of CO2 has decreased over time AND length of plate boundaries has increased ; (not supported as) concentration of CO2 and length of plate boundaries do not, mirror each other exactly / follow / AW ; between 120 mya and present day, plate boundary length decreased yet concentration of CO2 decreased; rate of seafloor spreading decreased over time but concentration of CO2 decreasing ; idea of correlation not being evidence of causation ; 4

This question in 9693/23 May/June 2022

3 (a) Nitrates are an important source of nitrogen. State the importance of nitrogen for marine organisms. … … [1] (b) In October 2017 researchers recorded the following data in an ocean: • temperature of the sea water • concentration of nitrate ions (NO3–) in the sea water • rate of uptake of nitrate ions from the sea water. They took readings every 40 m down to a depth of 200 m. Table 3.1 shows the recorded temperature of the sea water. Table 3.1 depth / m sea water temperature / °C 0 28.4 40 28.2 80 26.5 120 20.1 160 17.5 200 17.0 (i) Use the data in Table 3.1 to complete the graph. You should: • label the x‑axis • add a scale to the x‑axis • plot the data • draw a line of best fit. (ii) Suggest the range of depths where the thermocline is found. Explain your answer. … … … … [2] (iii) Suggest a reason why the position of the thermocline may change. … … [1] (i) Use your graph in (b)(i) and Fig. 3.1 to determine the temperature of the sea water at the maximum rate of nitrate ion uptake. … °C [1] (ii) Describe and suggest reasons for the changes in nitrate ion uptake shown in Fig. 3.1. … … … … … … [3] (d) An influx of nitrate ions caused an algal bloom, during which the population density of phytoplankton species increased. Fig. 3.2 shows the population density before and during the algal bloom in the first 20 m of sea water. phytoplankton population density 1000 cells / ml 00 2 4 6 8 4 8 depth / m 12 16 20 Key population density before algal bloom population density during algal bloom Fig. 3.2 Predict and explain the impact of the algal bloom on the trend for the rate of uptake of nitrate ions shown in Fig. 3.1. Use information from Fig. 3.1 and Fig. 3.2 in your answer. … … … … … … [3] [Total: 14]

14 marks

Mark scheme: 3(a) used (by producers as nitrogen source) for building amino acids / proteins / DNA ; 1 3(b)(i) x–axis labelled (with units) AND suitable linear scale ; all points plotted correctly  ½ small square ; suitable curved line ; 3 Question Answer Marks 3(b)(ii) within the range of 60–140 m ; (idea of) greatest change in temperature with change in depth / AW ; 2 3(b)(iii) any 1 of: seasonal change in air temperature / radiation input from Sun ; changes in currents / upwelling / mixing ; extreme weather event such as typhoon / hurricane ; 1 3(c)(i) 28.3(C) ; 1 3(c)(ii) any 3 of: rate of uptake lower in surface water due to lower concentration ; increase in uptake with depth due to increased concentration / increased number of producers ; decrease in uptake with increasing depth due to lack of producers / phytoplankton ; decrease in uptake with increasing depth due to decreasing water temperature ; 3 3(d) peak nitrate uptake will be greater ; peak abundance now three times higher… ; at a shallower depth than previous peak ; so trend may show peak at shallower depth than before algal bloom ; algal bloom near surface will reduce light intensity / block light, for algae at greater depth AW ; 3

This question in 9693/22 May/June 2023

3 (a) Nitrates are an important source of nitrogen. State the importance of nitrogen for marine organisms. … … [1] (b) In October 2017 researchers recorded the following data in an ocean: • temperature of the sea water • concentration of nitrate ions (NO3–) in the sea water • rate of uptake of nitrate ions from the sea water. They took readings every 40 m down to a depth of 200 m. Table 3.1 shows the recorded temperature of the sea water. Table 3.1 depth / m sea water temperature / °C 0 28.4 40 28.2 80 26.5 120 20.1 160 17.5 200 17.0 (i) Use the data in Table 3.1 to complete the graph. You should: • label the x‑axis • add a scale to the x‑axis • plot the data • draw a line of best fit. (ii) Suggest the range of depths where the thermocline is found. Explain your answer. … … … … [2] (iii) Suggest a reason why the position of the thermocline may change. … … [1] (i) Use your graph in (b)(i) and Fig. 3.1 to determine the temperature of the sea water at the maximum rate of nitrate ion uptake. … °C [1] (ii) Describe and suggest reasons for the changes in nitrate ion uptake shown in Fig. 3.1. … … … … … … [3] (d) An influx of nitrate ions caused an algal bloom, during which the population density of phytoplankton species increased. Fig. 3.2 shows the population density before and during the algal bloom in the first 20 m of sea water. phytoplankton population density 1000 cells / ml 00 2 4 6 8 4 8 depth / m 12 16 20 Key population density before algal bloom population density during algal bloom Fig. 3.2 Predict and explain the impact of the algal bloom on the trend for the rate of uptake of nitrate ions shown in Fig. 3.1. Use information from Fig. 3.1 and Fig. 3.2 in your answer. … … … … … … [3] [Total: 14]

14 marks

Mark scheme: 3(a) used (by producers as nitrogen source) for building amino acids / proteins / DNA ; 1 3(b)(i) x–axis labelled (with units) AND suitable linear scale ; all points plotted correctly  ½ small square ; suitable curved line ; 3 Question Answer Marks 3(b)(ii) within the range of 60–140 m ; (idea of) greatest change in temperature with change in depth / AW ; 2 3(b)(iii) any 1 of: seasonal change in air temperature / radiation input from Sun ; changes in currents / upwelling / mixing ; extreme weather event such as typhoon / hurricane ; 1 3(c)(i) 28.3(C) ; 1 3(c)(ii) any 3 of: rate of uptake lower in surface water due to lower concentration ; increase in uptake with depth due to increased concentration / increased number of producers ; decrease in uptake with increasing depth due to lack of producers / phytoplankton ; decrease in uptake with increasing depth due to decreasing water temperature ; 3 3(d) peak nitrate uptake will be greater ; peak abundance now three times higher… ; at a shallower depth than previous peak ; so trend may show peak at shallower depth than before algal bloom ; algal bloom near surface will reduce light intensity / block light, for algae at greater depth AW ; 3

This question in 9693/23 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

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

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

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

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

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

2 Scientists investigated the relationship between corals and their symbionts. They investigated if nitrogen and phosphorus are provided by the symbiont to the coral. (a) (i) State and explain the type of symbiotic relationship between coral polyps and zooxanthellae. type of symbiotic relationship … explanation … … … … [3] (ii) State one function of phosphorus in corals. … [1] (iii) Describe how the structure of coral polyps enables them to obtain nutrients from fish larvae. … … … … … [2] (b) The scientists investigated the growth of one species of coral in sea water with different concentrations of nitrate ions (NO3–) and phosphate ions (PO43–). Two tanks of sea water were used: • tank one was maintained at a normal concentration of nitrate and phosphate ions • tank two was maintained at a low concentration of nitrate and phosphate ions. Ten samples of the coral were placed into each tank. The tanks contained no other organisms. The sea water was constantly filtered to remove any small particles and food sources. The scientists measured the growth of coral in both tanks for six months. (i) Identify the independent variable and the dependent variable in this investigation. independent variable … … dependent variable … … [2] (ii) Use the information given above to identify one variable that was standardised. … … [1] (iii) Suggest two other variables not described above that need to be standardised to ensure the data collected is valid. 1 … 2 … [2] (c) Table 2.1 shows the mean data the scientists collected. Table 2.1 mean percentage change in mass of the corals time / months normal concentration of low concentration of nitrate and phosphate nitrate and phosphate ions ions 0 0 0 1 15 24 2 33 32 3 54 35 4 91 41 5 158 62 6 212 80 (i) The graph in Fig. 2.1 shows the mean percentage change in mass of the corals in the normal concentration of nitrate and phosphate ions. A line of best fit has been drawn to show the trend. Complete the scale and the labels for both axes. One scale value has already been added. Plot the values from Table 2.1 for the mean percentage change in mass of the corals in the low concentration of nitrate and phosphate ions on Fig. 2.1. Draw a line of best fit to indicate the overall trend for the data you have plotted. (ii) Compare the growth rates of the corals in normal concentrations and in low concentrations of nitrate and phosphate ions shown in Table 2.1. … … … … [2] (d) In further investigations, the scientists found that the growth of the coral was linked to digestion of some of the symbionts hosted in the coral tissues. The number of zooxanthellae per cm2 in the coral tissue: • remained constant in the tank with the normal concentration of nitrate and phosphate ions • decreased in the tank with the low concentration of nitrate and phosphate ions. The colour of the coral is due to the presence of zooxanthellae. The coral in the sea water with the low concentration of nitrate and phosphate ions gradually changed to white during the investigation. Suggest reasons for the change in appearance and growth of the coral in the sea water with the low concentration of nitrate and phosphate ions. … … … … … … … … … … [5] (e) A student formed the following conclusion based on the results. ‘Zooxanthellae are essential for all corals to obtain nutrients and grow faster.’ Use the information provided throughout Question 2 to evaluate this conclusion. … … … … … … [3] [Total: 25]

25 marks

Mark scheme: 2(a)(i) type of symbiotic relationship 3 mutualism ; explanation coral / host, gains energy / carbohydrate / glucose (from zooxanthellae) ORA ; zooxanthellae / symbiont, gains shelter / protection / carbon dioxide (from coral) ORA ; 2(a)(ii) (to make) DNA 1 2(a)(iii) any two from: 2 nematocysts, sting / stun / kill, larvae ; tentacles move larvae, into/through, the mouth ; stomach digests larvae ; 2(b)(i) independent variable: 2 idea of concentration of nitrate (NO3-) AND phosphate (PO43-) dependent variable: idea of growth of coral 2(b)(ii) any one from: 1 no other organisms were present in the tanks ; water filtered (to remove particles) ; no additional food provided ; time results recorded for (six months) ; coral species used ; 2(b)(iii) any two from: 2 temperature ; pH ; salinity ; concentration of other nutrients ; light availability ; starting, mass / volume, of coral ; volume of tank / volume of water ; 2(c)(i) both axes labelled with units 4 scale added correctly ; points, plotted correctly  ½ small square ; suitable line of best fit ; 2(c)(ii) any two from: 2 corals grow, faster, in low phosphate and nitrate in first 1 (to 2) months ; (from 2 months) the corals grow, faster, in normal concentration of phosphate and nitrate ; increase (in mass) in normal concentration increases at greater rate with time ; 2(d) any five from: 5 1 idea of greater number of zooxanthellae the more intense the colour / ORA ; 2 nitrate / nitrogen stated use e.g. protein, amino acids, etc. ; 3 reduced, nitrate / phosphate, reduces availability of, nitrogen / phosphorus, to zooxanthellae / ORA ; 4 zooxanthellae, rate of reproduction / growth, is reduced (in low conc. water) / ORA ; 5 digested zooxanthellae cannot be replaced (as quickly) / ORA ; 6 less nutrients passed on to the corals ; 7 organic nutrient example stated e.g. glucose ; 2(e) any three from: 3 1 data shows clear difference after first two months ; 2 data only for 6 months / no longer term data ; 3 data only for the 1 species / many other species not investigated / limited range of species ; 4 no indication of the range in the results ; 5 not all species host zooxanthallae ; 6 coral polyps also consume animals / obtain nutrients from other sources ; AVP ; ;

This question in 9693/21 Oct/Nov 2025