Osmoregulation — Paper 4 · A Level Marine Science 9693

2 Chinook salmon, blue crabs and marine mussels were placed into water of different salinities. Fig. 2.1 shows the effects of this on the salinity of their internal body fluids. 40 marine mussels blue crabs 30 salinity of internal body fluids / arbitrary units 20 10 Chinook salmon 0 0 10 20 30 40 salinity of water / arbitrary units Fig. 2.1 (a) Describe the effect of increasing water salinity on the salinity of the internal body fluids of the blue crabs. … … … … [2] (b) Explain the effect of increasing water salinity on the salinity of the internal body fluids of the Chinook salmon. … … … … … … … … [3] (c) The blue crab is restricted to estuarine conditions. The mussel is restricted to marine conditions. Use the information in Fig. 2.1 to explain each of these ecological distributions. … … … … … [2] [Total: 7]

7 marks

Mark scheme: 2(a) any 2 of: general trend is (internal body fluid salinity) increase ; low increase / it is level, between 10 (arbitrary units) and 28 (arbitrary units) ; correct numerical manipulation / initial increase less steep than final increase ; 2 A salinity increases except between 10 and 28 for two marks A no increase MUST have 10 and 28 for MP2 2(b) any 3 of: ref. to osmoregulation / osmoregulator ; at low salinities / hypotonic solutions, salmon pumps in / takes salt into, gills OR at low salinity / hypotonic solutions, salmon produces dilute urine ; (in increasing salinity) salmon pumps out / secretes salt from gills OR (in increasing salinity) salmon produces concentrated urine ; ref. to active transport / protein pumps / ATP use / need for energy ; salmon drink water (in high salinities / increasing salinities) ; 3 I any inappropriate named ions I ref. to euryhaline A chloride / sodium chloride / sodium A chloride pumps A excrete 2(c) crab can (osmo)regulate within a range of salinities, so can tolerate, a range of / changing, salinities ; mussel is an osmoconformer / cannot (osmo)regulate, so can only live in specific / stable / high(er) salinities ; 2 ORA

This question in 9693/41 May/June 2017

4 Wild populations of giant clams have decreased since the 1990s. Giant clams are now raised by aquaculture in some Pacific Islands for food, and to help in conservation efforts by releasing cultivated clams into the wild. (a) State what is meant by the term conservation. … … … [1] (b) (i) Outline the process used for the aquaculture of giant clams. … … … … … … … … … … … … … [5] (ii) Explain the risks associated with releasing cultivated giant clams into the wild. … … … … … … … … … … [4] (c) Giant clams are osmoconformers. Explain the meaning of the term osmoconformer and explain the effects on the clams of being placed in water of very high and very low salinities. … … … … … … … … … … … … … … [5]

15 marks

This question in 9693/40 Oct/Nov 2018

3 (a) Explain the meaning of the terms osmoconformer and euryhaline. osmoconformer … … euryhaline … … [2] (b) Many marine organisms regulate their water and ion content. Outline the process of osmoregulation in marine bony fish and explain why this is necessary. … … … … … … … … … … … … … … … [7] (c) Discuss the possible ecological impacts of desalination plants on marine ecology. … … … … … … … … … … … … … [6] [Total: 15]

15 marks

Mark scheme: 3(a) osmoconformer: organisms that have salinity that is same as surrounding water / AW ; euryhaline: organisms that can tolerate a wide range of salinities / live in fresh and salt water / AW ; 2 potential 3(b) any 7 of: how (a) drinking ; (b) remove / excrete , salt / sodium / suitable named ion ; (c) by, gills OR kidney ; (d) active transport / uses energy or ATP / requires respiration ; (e) absorption of water by kidney ; (f) low amount of urine / hypertonic urine / concentrated urine ; why (g) salt water has a higher salinity than body fluids / AW ; (h) water will leave body / dehydration ; (i) due to osmosis ; (j) damaging, cells / tissues / AW OR not enough fluid to transport / AW ; 7 I freshwater I diffuse or any idea of passive process A active pumping / actively pumps sensible impact of the dehydration Question Answer Marks Guidance 3(c) any 6 of: (a) loss of biodiversity / disruption to, food chains / webs ; (b) idea of: benthic / sessile species affected in particular ; (c) releasing (large amounts of) brine / high salt concentration water ; (d) organisms lose water (by osmosis) ; (e) high temperature water is released ; (f) denaturing enzymes ; (g) altering rates of, chemical reactions / photosynthesis / respiration ; (h) lowered oxygen concentration ; (i) stirring up of sediment / increasing turbidity ; (j) (that) reduces photosynthesis / damages coral / damages gills / AW ; (k) release of, toxins / detergents / heavy metals / surfactants / acids / alkalis ; (l) (chemicals may) bioaccumulate / biomagnify / AW OR damage to gills OR other specific appropriate damage to organism ; (m) (killing of), organisms / eggs / larvae / plankton, due to entry (into desalination plant) ; 6 I reducing light intensity I TBT

This question in 9693/41 May/June 2019

2 A scientist investigated the effect of changing salinity on a species of estuary crab, Metacarcinus gracilis. They placed crabs into water of different salinities for one hour and then measured the salinity of the body fluid of the crabs. The results are shown in Fig. 2.1. 35 30 25 20 mean salinity of body fluid 15 / parts per thousand 10 5 0 0 5 10 15 20 25 30 35 salinity of water / parts per thousand Fig. 2.1 (a) The scientists concluded that this species of crab is an osmoconformer. Explain whether the results shown in Fig. 2.1 support this conclusion. … … … … [2] (b) In a further experiment, the behavioural response of the crabs to different salinities was investigated. A rectangular tank was divided up into five chambers, each with a different salinity, as shown in Fig. 2.2. A passageway between the chambers was provided for crabs to move between chambers. The salinities used ranged between 60% and 100% of the salinity of normal sea water. Fig. 2.2 shows the chambers as viewed from above. chamber passageway for crabs 60% 70% 80% 90% 100% salinity salinity salinity salinity salinity Fig. 2.2 Crabs of the same age, mass, sex and species were placed randomly into different salinities in the tank and the times spent in each salinity recorded. The mean time that the crabs spent in each salinity was calculated. The results are shown in Fig. 2.3. 120 100 80 mean time spent in each 60 salinity / min 40 20 0 60 70 80 90 100 percentage salinity compared to sea water Fig. 2.3 (i) Describe the effect of increasing salinity on the mean time the crabs spent in each salinity. … … … … [2] (ii) Crabs of the same age, mass, sex and species were used. Suggest two other variables that would need to be kept constant in this experiment. 1 … 2 … [1] (iii) Use your knowledge of marine animal physiology to explain the response of the crabs to the different salinities. … … … … … … [3] [Total: 8]

8 marks

This question in 9693/40 Oct/Nov 2020

2 In Norway, some electricity is generated by using osmotic power stations. This method requires access to sea water and also fresh water from a river. Both types of water are pumped through the power station as shown in Fig. 2.1. The sea water and fresh water are separated by a partially permeable membrane in the osmosis module. As the water flows, pressure increases in the sea water in the osmosis module. The increased pressure drives a turbine to generate electricity. Waste water from the power station is returned to the sea and the river. osmosis module sea water sea water turbine generating electricity fresh water partially fresh water permeable membrane waste water waste water returned to returned to river sea Fig. 2.1 (a) (i) Use Fig. 2.1, and your own knowledge, to explain how the osmotic power station increases the pressure of the sea water in the osmosis module. … … … … … … [3] (ii) Some scientists claim that using this method to generate electricity will help to reduce global warming. Suggest why this method of generating electricity could reduce global warming. … … … … … … [3] (b) Some environmentalists have criticised the use of osmotic power stations. They suggest that the waste water could damage stenohaline marine organisms that are osmoconformers. (i) Give the meaning of the terms stenohaline and osmoconformer. stenohaline … … osmoconformer … … [2] (ii) Salmon are predicted to be unaffected by the waste water outflow as they are able to live in areas with different salinities. Outline how salmon osmoregulate in areas of low salinity. … … … … … … [3] [Total: 11]

11 marks

Mark scheme: 2(a)(i) any 3 from: 1 sea water has high(er) salinity / AW / ORA ; 2 sea water has lower water potential / ORA ; 3 water moves into sea water (from freshwater) ; 4 volume increases ; 3 2(a)(ii) any 3 from: 1 (osmotic power) is a renewable (energy source) ; 2 (idea of) less need for fossil fuel ; 3 (less) carbon (dioxide) (released) / (less) carbon emission / lower carbon footprint ; 4 less greenhouse effect ; 5 less reflection / trapping, of radiation (back to Earth) ; 3 2(b)(i) an organism that can only survive in a narrow range of salinities / AW / ORA ; an organism that has same salinity as its surrounding water / AW ; 2 2(b)(ii) any 3 from: 1 salmon will gain water by osmosis ; 2 excrete / release, (excess) water through, kidney / urine ; 3 take salt (from water) into, blood / body / salmon ; 4 using active transport / active pumping ; 3

This question in 9693/41 May/June 2022

1 Desalination plants are industrial facilities that produce fresh water from sea water. A group of students investigated the effect of a desalination plant on the salinity of sea water and the percentage cover of the seabed with seagrass. They measured the salinity of the sea water and percentage cover of the seabed with seagrass every 5 m from the desalination plant over a total distance of 30 m. The results are shown in Table 1.1. Table 1.1 distance from desalination salinity of sea water / ppt percentage cover of plant / m seabed with seagrass 5 45 25 10 41 27 15 34 58 20 33 85 25 32 95 30 32 95 (a) (i) Draw a graph to show how the salinity of the sea water and percentage cover of the seabed with seagrass change with distance from the desalination plant. Join your points with ruled, straight lines. [5] (ii) Use your graph and Table 1.1 to suggest an explanation for the distribution of the seagrass. … … … … [2] (b) Outline how salmon perform osmoregulation in regions of high salinity. … … … … … … [3] [Total: 10]

10 marks

Mark scheme: 1(a)(i) linear axes that use at least one y axis scale half the grid ; all axes labelled ; plots correct ; points joined by straight lines ; key for both lines / labelled lines; 5 1(a)(ii) any 2 from: seagrass cannot live in areas with high salinity / less seagrass grows in areas with high salinity / seagrass cannot live in areas of concentrated brine / ORA ; high salinity / water near desalination plant, has a low water potential ; water is lost from seagrass cells (by osmosis) / cells lose turgidity / AW ; toxins are released from desalination plant / AW ; 2 1(b) any 3 from: salmon body (cells) have higher water potential than seawater so lose water (by osmosis) ; salmon drink water ; excrete / release, salt / AW ; produce concentrated urine ; active pumping (of salt) into water ; 3

This question in 9693/42 May/June 2022

1 Desalination plants are industrial facilities that produce fresh water from sea water. A group of students investigated the effect of a desalination plant on the salinity of sea water and the percentage cover of the seabed with seagrass. They measured the salinity of the sea water and percentage cover of the seabed with seagrass every 5 m from the desalination plant over a total distance of 30 m. The results are shown in Table 1.1. Table 1.1 distance from desalination salinity of sea water / ppt percentage cover of plant / m seabed with seagrass 5 45 25 10 41 27 15 34 58 20 33 85 25 32 95 30 32 95 (a) (i) Draw a graph to show how the salinity of the sea water and percentage cover of the seabed with seagrass change with distance from the desalination plant. Join your points with ruled, straight lines. [5] (ii) Use your graph and Table 1.1 to suggest an explanation for the distribution of the seagrass. … … … … [2] (b) Outline how salmon perform osmoregulation in regions of high salinity. … … … … … … [3] [Total: 10]

10 marks

Mark scheme: 1(a)(i) linear axes that use at least one y axis scale half the grid ; all axes labelled ; plots correct ; points joined by straight lines ; key for both lines / labelled lines; 5 1(a)(ii) any 2 from: seagrass cannot live in areas with high salinity / less seagrass grows in areas with high salinity / seagrass cannot live in areas of concentrated brine / ORA ; high salinity / water near desalination plant, has a low water potential ; water is lost from seagrass cells (by osmosis) / cells lose turgidity / AW ; toxins are released from desalination plant / AW ; 2 1(b) any 3 from: salmon body (cells) have higher water potential than seawater so lose water (by osmosis) ; salmon drink water ; excrete / release, salt / AW ; produce concentrated urine ; active pumping (of salt) into water ; 3

This question in 9693/43 May/June 2022

4 Killifish are a euryhaline species of fish. (a) State what is meant by the term euryhaline. … … [1] (b) Killifish have cells called ionocytes in their gills that are involved in osmoregulation. Ionocyte cells have large numbers of mitochondria. Fig. 4.1 shows an electron micrograph of a mitochondrion. B A Fig. 4.1 (i) The electron micrograph has a magnification of ×14 000. Calculate the actual length of the mitochondrion in Fig. 4.1 between A and B. Give your answer in micrometres (μm). Show your working. … μm [2] (ii) Make a large drawing of the part of the mitochondrion shown in the circle in Fig. 4.1. Do not label your drawing. [4] (c) Scientists investigated the effect of salinity on the rate of oxygen consumption by killifish. Three tanks of water with salinities of 0 ppt, 11 ppt and 35 ppt were set up. Five killifish were placed into each tank. The fish were left for one week to acclimatise. The scientists then measured: • the mean rate of oxygen consumption by each group of fish • the mean gill surface area of each group of fish • the mean density of the ionocytes in the gills of each group of fish. The results are shown in Fig. 4.2 and Table 4.1. 45 40 35 30 mean rate of 25 oxygen consumption 20 / μmol O2 g–1 hr–1 15 10 5 0 0 11 35 salinity / ppt Fig. 4.2 Table 4.1 salinity / ppt mean gill surface area / μm2 g–1 mean ionocyte density / number of cells per μm2 0 62 000 000 320 11 78 000 000 127 35 82 000 000 235 (i) The scientists first measured the mean gill surface area of each group of fish. Suggest why the scientists then calculated the mean gill surface area per gram of fish. … … [1] (ii) Describe the effect of increasing salinity on the rate of oxygen consumption by the killifish. … … … … [2] (iii) Discuss the effects of increasing salinity on the gill surface area and density of ionocyte cells. Use information in Fig. 4.2 and Table 4.1 in your answer. … … … … … … … … [4] [Total: 14]

14 marks

Mark scheme: 4(a) able to live in / tolerate a range of salinities / can live in fresh and sea water / AW ; 1 4(b)(i) correct length conversion to m from mm or cm (100 000) ; correct division of 100 000 by 14 000 (7.14…) ; 2 4(b)(ii) outline drawn with thin, clear, unbroken lines ; proportions of length and width okay ; at least 1 / 3 of space, not drawn over text of question and fourth crista between half and three quarters length of other cristae ; correct detail ; four cristae and membrane as two lines no shading ; at least three cristae and membrane must be drawn 4 4(c)(i) fish are different masses / different sizes / to make a valid comparison / AW ; 1 4(c)(ii) decrease then increase / AW ; correct quantitative manipulation of data ; 2 Question Answer Marks 4(c)(iii) any 4 of: 1 increased oxygen consumption due to increased (aerobic) respiration / ATP production / AW ; 2 increased (density of) ionocytes when need to transport more, salt / ions / ORA ; 3 ions pumped out in high salinity / 35 / ions pumped in, in low salinity / 0 / no need to osmoregulate at 11 / ORA / AW ; 4 ref to active transport of ions ; 5 high(er) salinity water has lower oxygen concentration ; 6 increasing salinity increases gill SA ; 7 (so) increasing gill area will compensate for lower oxygen concentration / increased gill surface area to increase diffusion of oxygen / AW ; 4

This question in 9693/42 May/June 2023

4 Killifish are a euryhaline species of fish. (a) State what is meant by the term euryhaline. … … [1] (b) Killifish have cells called ionocytes in their gills that are involved in osmoregulation. Ionocyte cells have large numbers of mitochondria. Fig. 4.1 shows an electron micrograph of a mitochondrion. B A Fig. 4.1 (i) The electron micrograph has a magnification of ×14 000. Calculate the actual length of the mitochondrion in Fig. 4.1 between A and B. Give your answer in micrometres (μm). Show your working. … μm [2] (ii) Make a large drawing of the part of the mitochondrion shown in the circle in Fig. 4.1. Do not label your drawing. [4] (c) Scientists investigated the effect of salinity on the rate of oxygen consumption by killifish. Three tanks of water with salinities of 0 ppt, 11 ppt and 35 ppt were set up. Five killifish were placed into each tank. The fish were left for one week to acclimatise. The scientists then measured: • the mean rate of oxygen consumption by each group of fish • the mean gill surface area of each group of fish • the mean density of the ionocytes in the gills of each group of fish. The results are shown in Fig. 4.2 and Table 4.1. 45 40 35 30 mean rate of 25 oxygen consumption 20 / μmol O2 g–1 hr–1 15 10 5 0 0 11 35 salinity / ppt Fig. 4.2 Table 4.1 salinity / ppt mean gill surface area / μm2 g–1 mean ionocyte density / number of cells per μm2 0 62 000 000 320 11 78 000 000 127 35 82 000 000 235 (i) The scientists first measured the mean gill surface area of each group of fish. Suggest why the scientists then calculated the mean gill surface area per gram of fish. … … [1] (ii) Describe the effect of increasing salinity on the rate of oxygen consumption by the killifish. … … … … [2] (iii) Discuss the effects of increasing salinity on the gill surface area and density of ionocyte cells. Use information in Fig. 4.2 and Table 4.1 in your answer. … … … … … … … … [4] [Total: 14]

14 marks

Mark scheme: 4(a) able to live in / tolerate a range of salinities / can live in fresh and sea water / AW ; 1 4(b)(i) correct length conversion to m from mm or cm (100 000) ; correct division of 100 000 by 14 000 (7.14…) ; 2 4(b)(ii) outline drawn with thin, clear, unbroken lines ; proportions of length and width okay ; at least 1 / 3 of space, not drawn over text of question and fourth crista between half and three quarters length of other cristae ; correct detail ; four cristae and membrane as two lines no shading ; at least three cristae and membrane must be drawn 4 4(c)(i) fish are different masses / different sizes / to make a valid comparison / AW ; 1 4(c)(ii) decrease then increase / AW ; correct quantitative manipulation of data ; 2 Question Answer Marks 4(c)(iii) any 4 of: 1 increased oxygen consumption due to increased (aerobic) respiration / ATP production / AW ; 2 increased (density of) ionocytes when need to transport more, salt / ions / ORA ; 3 ions pumped out in high salinity / 35 / ions pumped in, in low salinity / 0 / no need to osmoregulate at 11 / ORA / AW ; 4 ref to active transport of ions ; 5 high(er) salinity water has lower oxygen concentration ; 6 increasing salinity increases gill SA ; 7 (so) increasing gill area will compensate for lower oxygen concentration / increased gill surface area to increase diffusion of oxygen / AW ; 4

This question in 9693/43 May/June 2023

2 Killifish are euryhaline fish that are able to osmoregulate. (a) (i) State what is meant by the term euryhaline. … … [1] Scientists kept killifish in sea water with a salinity of 35 parts per thousand (ppt) for one week. The fish were then placed into fresh water. The scientists measured the rate of breakdown of ATP in gill cells and body skin cells of the killifish over one week. Energy is released when ATP is broken down. The results are shown in Fig. 2.1. 5.0 4.5 gill cells 4.0 3.5 3.0 rate of ATP breakdown 2.5 / mmol ATP g–1 h–1 2.0 body skin cells 1.5 1.0 0.5 0.0 0 1 2 3 4 5 6 7 8 time / days fish placed into fresh water Fig. 2.1 (ii) Describe the change in the rate of breakdown of ATP by the gill cells after placing the fish into fresh water. … … … … [2] (iii) Suggest an explanation for the change in the rate of breakdown of ATP after placing the killifish into fresh water. … … … … … … … … [4] (iv) Suggest why the scientists investigated the response of body skin cells as well as of gill cells. … … [1] (b) The scientists also investigated the effect of placing mussels into sea water of different salinities. Two groups of mussels, group A and group B, were placed into tanks of sea water. • Group A mussels were placed into sea water with a salinity of 35 ppt. • Group B mussels were placed into sea water with a salinity of 15 ppt. • After 24 hours, the mean volume of water per gram of dry mass of mussel was measured for a sample of mussels from both groups. This was the initial mass. • Half of the remaining mussels from each group were then placed into tanks with a salinity of 35 ppt. • The other half of the remaining mussels from each group were placed into tanks with a salinity of 15 ppt. • After 24 hours, the mean volume of water per gram of dry mass of mussel was measured for all the mussels. Fig. 2.2 shows the investigation. group A group B mussels placed into mussels placed into sea water of salinity sea water of salinity 35ppt for 24 hours 15ppt for 24 hours mussels placed into mussels placed into mussels placed into mussels placed into sea water of salinity sea water of salinity sea water of salinity sea water of salinity 35ppt for 24 hours 15ppt for 24 hours 35ppt for 24 hours 15ppt for 24 hours Fig. 2.2 The results of the investigation are shown in Fig. 2.3. 3.5 3.0 2.5 mean volume of 2.0 water per dry mass of mussel 1.5 / cm3 g–1 1.0 0.5 0.0 initial 35 ppt 15 ppt initial 35 ppt 15 ppt mass mass group A group B mussel treatments Fig. 2.3 (i) Use Fig. 2.3 to calculate the percentage change in mean volume of water per gram of dry mass of mussel when mussels in group A were moved from water with a salinity of 35 ppt to water with a salinity of 15 ppt. Show your working. … % [2] (ii) Suggest explanations for the results shown in Fig. 2.3. … … … … … … … … [4] [Total: 14]

14 marks

Mark scheme: 2(a)(i) (organisms) that can live in salt and fresh water / can live in a range of salinities / AW ; 1 2(a)(ii) any 2 of: 1 (steep) increase ; 2 levels off after one day/fluctuates after one day / goes up and down after one day / decrease and increase after one day / AW ; 3 accept correct manipulated data ; 2 2(a)(iii) any 4 of: 1 fish has lower water potential (than water) / (fresh) water has higher water potential than fish / AW ; 2 so water enter fish by osmosis / AW ; 3 (gill cells) move, salt / sodium / chloride / ions, into, body / blood ; 4 by active transport / active process (of salt) ; 5 so more energy (needs to be released) ; 6 as salt is lost from body via urine / diffusion / salt diffuses out of fish ; 7 maximum rate of, salt / sodium / chloride, pumping occurs after one day / AW ; 4 Question Answer Marks 2(a)(iv) any 1 of: 1 as a control experiment ; 2 to compare the effects of different salinity on non-osmoregulatory cells / AW ; 1 2(b)(i) 0.85 ; 0.85/2.1  100 = 40.(476190) (%) ; 2 2(b)(ii) any 4 of: 1 mussels are osmoconformers ; 2 correct ref to overlapping error bars ; 3 correct ref to movement of water by osmosis from high water potential to lower water potential / down a water potential gradient ; Group A (max 2) 4 water enters mussel cells by osmosis ; 5 as mussel (cells) had taken up salt / conformed to 35 ppt ; Group B (max 2) 6 water leaves mussel cells by osmosis ; 7 as mussel (cells) had lost salt / conformed to 15 ppt ; 4

This question in 9693/42 May/June 2024

2 Killifish are euryhaline fish that are able to osmoregulate. (a) (i) State what is meant by the term euryhaline. … … [1] Scientists kept killifish in sea water with a salinity of 35 parts per thousand (ppt) for one week. The fish were then placed into fresh water. The scientists measured the rate of breakdown of ATP in gill cells and body skin cells of the killifish over one week. Energy is released when ATP is broken down. The results are shown in Fig. 2.1. 5.0 4.5 gill cells 4.0 3.5 3.0 rate of ATP breakdown 2.5 / mmol ATP g–1 h–1 2.0 body skin cells 1.5 1.0 0.5 0.0 0 1 2 3 4 5 6 7 8 time / days fish placed into fresh water Fig. 2.1 (ii) Describe the change in the rate of breakdown of ATP by the gill cells after placing the fish into fresh water. … … … … [2] (iii) Suggest an explanation for the change in the rate of breakdown of ATP after placing the killifish into fresh water. … … … … … … … … [4] (iv) Suggest why the scientists investigated the response of body skin cells as well as of gill cells. … … [1] (b) The scientists also investigated the effect of placing mussels into sea water of different salinities. Two groups of mussels, group A and group B, were placed into tanks of sea water. • Group A mussels were placed into sea water with a salinity of 35 ppt. • Group B mussels were placed into sea water with a salinity of 15 ppt. • After 24 hours, the mean volume of water per gram of dry mass of mussel was measured for a sample of mussels from both groups. This was the initial mass. • Half of the remaining mussels from each group were then placed into tanks with a salinity of 35 ppt. • The other half of the remaining mussels from each group were placed into tanks with a salinity of 15 ppt. • After 24 hours, the mean volume of water per gram of dry mass of mussel was measured for all the mussels. Fig. 2.2 shows the investigation. group A group B mussels placed into mussels placed into sea water of salinity sea water of salinity 35ppt for 24 hours 15ppt for 24 hours mussels placed into mussels placed into mussels placed into mussels placed into sea water of salinity sea water of salinity sea water of salinity sea water of salinity 35ppt for 24 hours 15ppt for 24 hours 35ppt for 24 hours 15ppt for 24 hours Fig. 2.2 The results of the investigation are shown in Fig. 2.3. 3.5 3.0 2.5 mean volume of 2.0 water per dry mass of mussel 1.5 / cm3 g–1 1.0 0.5 0.0 initial 35 ppt 15 ppt initial 35 ppt 15 ppt mass mass group A group B mussel treatments Fig. 2.3 (i) Use Fig. 2.3 to calculate the percentage change in mean volume of water per gram of dry mass of mussel when mussels in group A were moved from water with a salinity of 35 ppt to water with a salinity of 15 ppt. Show your working. … % [2] (ii) Suggest explanations for the results shown in Fig. 2.3. … … … … … … … … [4] [Total: 14]

14 marks

Mark scheme: 2(a)(i) (organisms) that can live in salt and fresh water / can live in a range of salinities / AW ; 1 2(a)(ii) any 2 of: 1 (steep) increase ; 2 levels off after one day/fluctuates after one day / goes up and down after one day / decrease and increase after one day / AW ; 3 accept correct manipulated data ; 2 2(a)(iii) any 4 of: 1 fish has lower water potential (than water) / (fresh) water has higher water potential than fish / AW ; 2 so water enter fish by osmosis / AW ; 3 (gill cells) move, salt / sodium / chloride / ions, into, body / blood ; 4 by active transport / active process (of salt) ; 5 so more energy (needs to be released) ; 6 as salt is lost from body via urine / diffusion / salt diffuses out of fish ; 7 maximum rate of, salt / sodium / chloride, pumping occurs after one day / AW ; 4 Question Answer Marks 2(a)(iv) any 1 of: 1 as a control experiment ; 2 to compare the effects of different salinity on non-osmoregulatory cells / AW ; 1 2(b)(i) 0.85 ; 0.85/2.1  100 = 40.(476190) (%) ; 2 2(b)(ii) any 4 of: 1 mussels are osmoconformers ; 2 correct ref to overlapping error bars ; 3 correct ref to movement of water by osmosis from high water potential to lower water potential / down a water potential gradient ; Group A (max 2) 4 water enters mussel cells by osmosis ; 5 as mussel (cells) had taken up salt / conformed to 35 ppt ; Group B (max 2) 6 water leaves mussel cells by osmosis ; 7 as mussel (cells) had lost salt / conformed to 15 ppt ; 4

This question in 9693/43 May/June 2024

5 Marine organisms are affected by the salinity of sea water. (a) Explain why tuna need to constantly drink sea water. … … … … … … [3] (b) Some kelp species can adapt the water potential of their cells to match the surrounding sea water. Plan a laboratory investigation that you could do to compare the water potential of cells of kelp collected from an estuary and a rocky shore. You are provided with standard laboratory apparatus and materials. Your plan should: • include a clear statement of the hypothesis • identify the independent, dependent and standardised variables • include full details of the method so that another person can follow it • describe how you would analyse your results • be safe and ethical. … … … … … … … … … … … … … … … … … … … … … … … … … … … [11] [Total: 14]

14 marks

Mark scheme: 5(a) any 3 of: 3 1 tuna is an osmoregulator ; 2 salinity / salt concentration, of sea water is higher than body fluids / ORA / AW ; 3 water potential of sea water is lower than body fluids / ORA / AW ; 4 so water leaves (tuna) / AW ; 5 by osmosis ; 5(b) hypothesis 11 kelp from estuary will have a higher water potential than kelp from a rocky shore / AW ; plus any 10 from: independent variable: estuary compared with rocky shore / concentration of sea water / water potential of sea water / AW ; dependent variable water potential of kelp / AW ; standardised variables max 3 of: same mass / surface area / volume of kelp / same size pieces / AW ; same species of kelp / age of kelp / AW ; collect at same time of year / time of day / same season / AW ; same temperature (to do lab experiment) ; same volumes of solutions (in lab experiment) ; same period of time to leave kelp in solutions / AW ; 5(b) method max 3 of: placing kelp in minimum of five different salt concentrations ; weighing kelp before and after placing into solutions / viewing cells under microscope and counting plasmolysed cells / AW ; use of balance / use of microscope ; ref. to correct range of concentrations ; AVP ; Analysis max 3 of: replicate experiment and calculate, means / standard deviations / AW ; calculate percentage change of mass / percentage of cells plasmolysed ; plot graph of percentage change in mass against salinity / percentage plasmolysis against salinity ; read off salinity where percentage change in mass is 0 / plasmolysis is 50 % / AW ; example of results table ; use of correct statistical test, e.g. confidence limits / t test ; safety and ethics correct safety precaution linked to risk / statement that experiment is low risk / AW ; do not remove large amounts of kelp from sea / do not wash contaminated solutions down sink / ensure no other organisms taken with kelp / AW ;

This question in 9693/41 Oct/Nov 2024

5 Marine organisms are affected by the salinity of sea water. (a) Explain why tuna need to constantly drink sea water. … … … … … … [3] (b) Some kelp species can adapt the water potential of their cells to match the surrounding sea water. Plan a laboratory investigation that you could do to compare the water potential of cells of kelp collected from an estuary and a rocky shore. You are provided with standard laboratory apparatus and materials. Your plan should: • include a clear statement of the hypothesis • identify the independent, dependent and standardised variables • include full details of the method so that another person can follow it • describe how you would analyse your results • be safe and ethical. … … … … … … … … … … … … … … … … … … … … … … … … … … … [11] [Total: 14]

14 marks

Mark scheme: 5(a) any 3 of: 3 1 tuna is an osmoregulator ; 2 salinity / salt concentration, of sea water is higher than body fluids / ORA / AW ; 3 water potential of sea water is lower than body fluids / ORA / AW ; 4 so water leaves (tuna) / AW ; 5 by osmosis ; 5(b) hypothesis 11 kelp from estuary will have a higher water potential than kelp from a rocky shore / AW ; plus any 10 from: independent variable: estuary compared with rocky shore / concentration of sea water / water potential of sea water / AW ; dependent variable water potential of kelp / AW ; standardised variables max 3 of: same mass / surface area / volume of kelp / same size pieces / AW ; same species of kelp / age of kelp / AW ; collect at same time of year / time of day / same season / AW ; same temperature (to do lab experiment) ; same volumes of solutions (in lab experiment) ; same period of time to leave kelp in solutions / AW ; 5(b) method max 3 of: placing kelp in minimum of five different salt concentrations ; weighing kelp before and after placing into solutions / viewing cells under microscope and counting plasmolysed cells / AW ; use of balance / use of microscope ; ref. to correct range of concentrations ; AVP ; Analysis max 3 of: replicate experiment and calculate, means / standard deviations / AW ; calculate percentage change of mass / percentage of cells plasmolysed ; plot graph of percentage change in mass against salinity / percentage plasmolysis against salinity ; read off salinity where percentage change in mass is 0 / plasmolysis is 50 % / AW ; example of results table ; use of correct statistical test, e.g. confidence limits / t test ; safety and ethics correct safety precaution linked to risk / statement that experiment is low risk / AW ; do not remove large amounts of kelp from sea / do not wash contaminated solutions down sink / ensure no other organisms taken with kelp / AW ;

This question in 9693/42 Oct/Nov 2024

5 Marine organisms are affected by the salinity of sea water. (a) Explain why tuna need to constantly drink sea water. … … … … … … [3] (b) Some kelp species can adapt the water potential of their cells to match the surrounding sea water. Plan a laboratory investigation that you could do to compare the water potential of cells of kelp collected from an estuary and a rocky shore. You are provided with standard laboratory apparatus and materials. Your plan should: • include a clear statement of the hypothesis • identify the independent, dependent and standardised variables • include full details of the method so that another person can follow it • describe how you would analyse your results • be safe and ethical. … … … … … … … … … … … … … … … … … … … … … … … … … … … [11] [Total: 14]

14 marks

Mark scheme: 5(a) any 3 of: 3 1 tuna is an osmoregulator ; 2 salinity / salt concentration, of sea water is higher than body fluids / ORA / AW ; 3 water potential of sea water is lower than body fluids / ORA / AW ; 4 so water leaves (tuna) / AW ; 5 by osmosis ; 5(b) hypothesis 11 kelp from estuary will have a higher water potential than kelp from a rocky shore / AW ; plus any 10 from: independent variable: estuary compared with rocky shore / concentration of sea water / water potential of sea water / AW ; dependent variable water potential of kelp / AW ; standardised variables max 3 of: same mass / surface area / volume of kelp / same size pieces / AW ; same species of kelp / age of kelp / AW ; collect at same time of year / time of day / same season / AW ; same temperature (to do lab experiment) ; same volumes of solutions (in lab experiment) ; same period of time to leave kelp in solutions / AW ; 5(b) method max 3 of: placing kelp in minimum of five different salt concentrations ; weighing kelp before and after placing into solutions / viewing cells under microscope and counting plasmolysed cells / AW ; use of balance / use of microscope ; ref. to correct range of concentrations ; AVP ; Analysis max 3 of: replicate experiment and calculate, means / standard deviations / AW ; calculate percentage change of mass / percentage of cells plasmolysed ; plot graph of percentage change in mass against salinity / percentage plasmolysis against salinity ; read off salinity where percentage change in mass is 0 / plasmolysis is 50 % / AW ; example of results table ; use of correct statistical test, e.g. confidence limits / t test ; safety and ethics correct safety precaution linked to risk / statement that experiment is low risk / AW ; do not remove large amounts of kelp from sea / do not wash contaminated solutions down sink / ensure no other organisms taken with kelp / AW ;

This question in 9693/43 Oct/Nov 2024

5 Pacific salmon are euryhaline fish that spend part of their life cycle in the sea and part of their life cycle in rivers. (a) State what is meant by the term euryhaline. … … [1] (b) Scientists investigated the effect of placing salmon into water of different salinities. Salmon were first kept in water with a salinity of 35 ppt for two weeks. Five of these salmon were selected and each one was placed into a separate tank of water with a salinity of 15 ppt. The decrease in oxygen concentration of the water in each of the tanks was determined over a period of one hour. This was repeated twice. In the first repeat, five different salmon were selected and each one placed into separate tanks with a salinity of 35 ppt. In the second repeat, five different salmon were selected and each one placed into separate tanks with a salinity of 47 ppt. Table 5.1 shows the results. Table 5.1 salinity number of mean decrease standard standard 2 × / ppt salmon (n) in oxygen deviation error standard concentration / mg dm–3 kg–1 error / mg dm–3 kg–1 15 5 2.3 0.50 0.22 0.44 35 5 2.1 0.20 0.09 0.18 47 5 3.8 0.40 (i) Calculate the standard error for the mean decrease in oxygen concentration of the water with a salinity of 47 ppt. Use the equation: s standard error, SE = n s = standard deviation n = sample size (number of observations) … [1] (ii) Use your answer to (b)(i) to calculate the 95% confidence interval for the mean decrease in oxygen concentration of the water with a salinity of 47 ppt. Use the equation: 95% confidence interval (95% CI) = x ± (2 × SE) x = mean SE = standard error … to … [1] (iii) Assess whether placing the salmon into water with salinities of 15 ppt and 47 ppt resulted in significant differences in the mean decrease in oxygen concentration of the water compared with the results at 35 ppt. Use the information in Table 5.1 and your answer to (b)(ii) to support your answer. … … … … … … [3] (iv) Explain why placing the salmon into the water with a salinity of 47 ppt caused a decrease in the oxygen concentration. … … … … … … [3] [Total: 9]

9 marks

Mark scheme: 5(a) can live in a range of salinities / can tolerate a wide range of salinity / AW ; 1 5(b)(i) 0.18 ; 1 5(b)(ii) 3.44 to 4.16 ; 1 5(b)(iii) there is a significant, decrease / difference, in oxygen when in 47 ppt ; 3 there is not a significant, decrease / difference, in oxygen when in 15 ppt ; because the ranges for 47 ppt do not overlap with 35 ppt / because the ranges when in 15 ppt the ranges do overlap with 35 ppt ; 5(b)(iv) any 3 of: 3 1 water potential of, body fluids / AW, is higher than solution ; 2 so water loss occurs / AW ; 3 osmoregulation occurs ; 4 active transport of salt / ions / AW ; 5 (more) respiration (using oxygen) ; 6 correct reference to ATP use ;

This question in 9693/41 Oct/Nov 2025

5 Pacific salmon are euryhaline fish that spend part of their life cycle in the sea and part of their life cycle in rivers. (a) State what is meant by the term euryhaline. … … [1] (b) Scientists investigated the effect of placing salmon into water of different salinities. Salmon were first kept in water with a salinity of 35 ppt for two weeks. Five of these salmon were selected and each one was placed into a separate tank of water with a salinity of 15 ppt. The decrease in oxygen concentration of the water in each of the tanks was determined over a period of one hour. This was repeated twice. In the first repeat, five different salmon were selected and each one placed into separate tanks with a salinity of 35 ppt. In the second repeat, five different salmon were selected and each one placed into separate tanks with a salinity of 47 ppt. Table 5.1 shows the results. Table 5.1 salinity number of mean decrease standard standard 2 × / ppt salmon (n) in oxygen deviation error standard concentration / mg dm–3 kg–1 error / mg dm–3 kg–1 15 5 2.3 0.50 0.22 0.44 35 5 2.1 0.20 0.09 0.18 47 5 3.8 0.40 (i) Calculate the standard error for the mean decrease in oxygen concentration of the water with a salinity of 47 ppt. Use the equation: s standard error, SE = n s = standard deviation n = sample size (number of observations) … [1] (ii) Use your answer to (b)(i) to calculate the 95% confidence interval for the mean decrease in oxygen concentration of the water with a salinity of 47 ppt. Use the equation: 95% confidence interval (95% CI) = x ± (2 × SE) x = mean SE = standard error … to … [1] (iii) Assess whether placing the salmon into water with salinities of 15 ppt and 47 ppt resulted in significant differences in the mean decrease in oxygen concentration of the water compared with the results at 35 ppt. Use the information in Table 5.1 and your answer to (b)(ii) to support your answer. … … … … … … [3] (iv) Explain why placing the salmon into the water with a salinity of 47 ppt caused a decrease in the oxygen concentration. … … … … … … [3] [Total: 9]

9 marks

Mark scheme: 5(a) can live in a range of salinities / can tolerate a wide range of salinity / AW ; 1 5(b)(i) 0.18 ; 1 5(b)(ii) 3.44 to 4.16 ; 1 5(b)(iii) there is a significant, decrease / difference, in oxygen when in 47 ppt ; 3 there is not a significant, decrease / difference, in oxygen when in 15 ppt ; because the ranges for 47 ppt do not overlap with 35 ppt / because the ranges when in 15 ppt the ranges do overlap with 35 ppt ; 5(b)(iv) any 3 of: 3 1 water potential of, body fluids / AW, is higher than solution ; 2 so water loss occurs / AW ; 3 osmoregulation occurs ; 4 active transport of salt / ions / AW ; 5 (more) respiration (using oxygen) ; 6 correct reference to ATP use ;

This question in 9693/42 Oct/Nov 2025

5 Pacific salmon are euryhaline fish that spend part of their life cycle in the sea and part of their life cycle in rivers. (a) State what is meant by the term euryhaline. … … [1] (b) Scientists investigated the effect of placing salmon into water of different salinities. Salmon were first kept in water with a salinity of 35 ppt for two weeks. Five of these salmon were selected and each one was placed into a separate tank of water with a salinity of 15 ppt. The decrease in oxygen concentration of the water in each of the tanks was determined over a period of one hour. This was repeated twice. In the first repeat, five different salmon were selected and each one placed into separate tanks with a salinity of 35 ppt. In the second repeat, five different salmon were selected and each one placed into separate tanks with a salinity of 47 ppt. Table 5.1 shows the results. Table 5.1 salinity number of mean decrease standard standard 2 × / ppt salmon (n) in oxygen deviation error standard concentration / mg dm–3 kg–1 error / mg dm–3 kg–1 15 5 2.3 0.50 0.22 0.44 35 5 2.1 0.20 0.09 0.18 47 5 3.8 0.40 (i) Calculate the standard error for the mean decrease in oxygen concentration of the water with a salinity of 47 ppt. Use the equation: s standard error, SE = n s = standard deviation n = sample size (number of observations) … [1] (ii) Use your answer to (b)(i) to calculate the 95% confidence interval for the mean decrease in oxygen concentration of the water with a salinity of 47 ppt. Use the equation: 95% confidence interval (95% CI) = x ± (2 × SE) x = mean SE = standard error … to … [1] (iii) Assess whether placing the salmon into water with salinities of 15 ppt and 47 ppt resulted in significant differences in the mean decrease in oxygen concentration of the water compared with the results at 35 ppt. Use the information in Table 5.1 and your answer to (b)(ii) to support your answer. … … … … … … [3] (iv) Explain why placing the salmon into the water with a salinity of 47 ppt caused a decrease in the oxygen concentration. … … … … … … [3] [Total: 9]

9 marks

Mark scheme: 5(a) can live in a range of salinities / can tolerate a wide range of salinity / AW ; 1 5(b)(i) 0.18 ; 1 5(b)(ii) 3.44 to 4.16 ; 1 5(b)(iii) there is a significant, decrease / difference, in oxygen when in 47 ppt ; 3 there is not a significant, decrease / difference, in oxygen when in 15 ppt ; because the ranges for 47 ppt do not overlap with 35 ppt / because the ranges when in 15 ppt the ranges do overlap with 35 ppt ; 5(b)(iv) any 3 of: 3 1 water potential of, body fluids / AW, is higher than solution ; 2 so water loss occurs / AW ; 3 osmoregulation occurs ; 4 active transport of salt / ions / AW ; 5 (more) respiration (using oxygen) ; 6 correct reference to ATP use ;

This question in 9693/43 Oct/Nov 2025