Movement of substances — Paper 4 · A Level Marine Science 9693

2 A student carried out an investigation into the effect of size on the time taken for dye to diffuse to the centre of cubes of agar jelly. Cubes of agar jelly of different side length were placed into a solution of dye, as shown in Fig. 2.1. beaker solution of dye cube of agar jelly Fig. 2.1 The times taken for the dye to reach the centre of the cubes of agar jelly were recorded. The results are shown in Table 2.1. Table 2.1 surface area : time taken for side length of surface area of volume of volume ratio dye to reach cube / mm cube / mm2 cube / mm3 of cube centre / s 5 150 125 1.2 : 1 35 10 600 1000 0.6 : 1 76 15 1350 174 20 2400 8000 0.3 : 1 296 (a) (i) Calculate the surface area : volume ratio for the cube with a side length of 15 mm. Show your working. … [2] (ii) Use the information in Table 2.1 to explain why larger marine organisms require specialised gas exchange organs. … … … … … … … [3] (b) Temperature also affects the time taken for dye to diffuse to the centre of a cube of agar jelly. Describe an experiment that you could do to investigate the effect of temperature on the rate of diffusion of the dye. … … … … … … … … … … … … … … … … [4] [Total: 9]

9 marks

This question in 9693/40 May/June 2018

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

3 A student investigated the rate of respiration of a species of coral. The coral was a species that contained zooxanthellae. A piece of the coral was placed into a tank filled with one cubic decimetre of sea water. The concentration of oxygen dissolved in the water was measured every five minutes for 25 minutes. The coral was kept in darkness throughout the experiment. The results are shown in Fig. 3.1. 10.0 9.5 concentration of oxygen in water 9.0 / mg dm–3 8.5 8.0 0 5 10 15 20 25 time / min Fig. 3.1 (a) (i) Give the balanced chemical (symbol) equation for aerobic respiration. … [2] (ii) Explain why the experiment was carried out in darkness. … … … … [2] (iii) Use Fig. 3.1 to calculate the mean rate of change of oxygen concentration over the first 15 minutes of the experiment. Show your working and state the correct unit. … [3] (b) In a second investigation, a pump was used to circulate the water over the coral polyps. The rate of oxygen uptake by the coral polyps was measured at different speeds of water current. The results are shown in Fig. 3.2. 0.60 0.55 0.50 0.45 0.40 rate of oxygen uptake / mg min–1 0.35 0.30 0.25 0.20 0.15 0.10 0 2 4 6 8 10 12 water current speed / arbitrary units Fig. 3.2 (i) Describe the effect of increasing water current speed on the rate of oxygen uptake. … … … … [2] (ii) Suggest reasons for the effect of increasing water current speed on the rate of oxygen uptake. … … … … … … [3] (c) Coral polyps use simple diffusion for gaseous exchange. Agar cubes that contain alkali and indicator solution can be used as a model for diffusion. The agar cubes can be placed into hydrochloric acid. As the hydrochloric acid diffuses into the agar, it neutralises the alkali and changes the indicator from pink to colourless. This is shown in Fig. 3.3. acid agar cube area of agar that acid has not reached Fig. 3.3 The time taken for the agar to turn colourless when placed into hydrochloric acid is a measure of the rate of diffusion of acid to the centre of the agar cubes. Plan an investigation into the effect of temperature on diffusion of hydrochloric acid into agar cubes. Your plan should: • include a clear statement of the hypothesis • identify the key variables • include full details of the method • describe how you would analyse your results • be safe and ethical. … … … … … … … … … … … … … … … … … … … … … … … … [12] [Total: 24]

24 marks

Mark scheme: 3(a)(i) 6O2 + C6H12O6  6CO2 + 6H2O 2 3(a)(ii) coral / zooxanthellae would not photosynthesise / photosynthesis would not occur ; so no oxygen is released / oxygen levels are not affected (by photosynthesis) ; 2 3(a)(iii) 10 – 8.5 (= 1.5) 8.5 – 10.0 = (1.5) / 15 = 0.1 ; negative gradient (minus) (–0.1) ; mg dm-3 min-1 ; 3 3(b)(i) increase ; level off / decrease from, 7 / 8 / 9 (a.u.) ; 2 3(b)(ii) any 3 from: maintains / steeper, diffusion / concentration gradient ; movement of tentacles (increasing surface area contact with oxygen in water) ; another factor begins to limit rate (at speed of 7) ; such as, surface area of tentacles, rate of oxygen use by coral / temperature / AW ; 3 Question Answer Marks 3(c) hypothesis: increasing temperature increases speed that agar changes colour / increases rate of diffusion / reduces time taken for agar to change colour / AW ; plus any 11 from: variables: independent variable: temperature ; at least five stated temperatures ; dependent variable: time taken for block to change colour / rate of diffusion ; record time taken for block to change colour with stop clock / timer ; controls: max 3 from: cubes have same surface area / volume ; same concentration of acid / pH ; same volume of acid ; same concentration of alkali in block ; same concentration of agar ; method: use of water bath / AW ; left for period of time to reach temperature ; cut agar with scalpel / knife and measure with ruler ; analysis max 3 from: repeats, and means calculated / anomalies identified; rate calculated by inverse of time / AW ; graph of rate / time taken against temperature ; appropriate statistical test ; 12 Question Answer Marks 3(c) safety: max 1 from: safety with cutting away from the body / take care with scalpel correct safety precaution linked with acid, e.g. eye protection care with hot water baths ; ethics max 1 from: do not let acid / indicator / alkali drain into natural water ; no living things involved / affected so few ethical issues ;

This question in 9693/42 May/June 2022

3 A student investigated the rate of respiration of a species of coral. The coral was a species that contained zooxanthellae. A piece of the coral was placed into a tank filled with one cubic decimetre of sea water. The concentration of oxygen dissolved in the water was measured every five minutes for 25 minutes. The coral was kept in darkness throughout the experiment. The results are shown in Fig. 3.1. 10.0 9.5 concentration of oxygen in water 9.0 / mg dm–3 8.5 8.0 0 5 10 15 20 25 time / min Fig. 3.1 (a) (i) Give the balanced chemical (symbol) equation for aerobic respiration. … [2] (ii) Explain why the experiment was carried out in darkness. … … … … [2] (iii) Use Fig. 3.1 to calculate the mean rate of change of oxygen concentration over the first 15 minutes of the experiment. Show your working and state the correct unit. … [3] (b) In a second investigation, a pump was used to circulate the water over the coral polyps. The rate of oxygen uptake by the coral polyps was measured at different speeds of water current. The results are shown in Fig. 3.2. 0.60 0.55 0.50 0.45 0.40 rate of oxygen uptake / mg min–1 0.35 0.30 0.25 0.20 0.15 0.10 0 2 4 6 8 10 12 water current speed / arbitrary units Fig. 3.2 (i) Describe the effect of increasing water current speed on the rate of oxygen uptake. … … … … [2] (ii) Suggest reasons for the effect of increasing water current speed on the rate of oxygen uptake. … … … … … … [3] (c) Coral polyps use simple diffusion for gaseous exchange. Agar cubes that contain alkali and indicator solution can be used as a model for diffusion. The agar cubes can be placed into hydrochloric acid. As the hydrochloric acid diffuses into the agar, it neutralises the alkali and changes the indicator from pink to colourless. This is shown in Fig. 3.3. acid agar cube area of agar that acid has not reached Fig. 3.3 The time taken for the agar to turn colourless when placed into hydrochloric acid is a measure of the rate of diffusion of acid to the centre of the agar cubes. Plan an investigation into the effect of temperature on diffusion of hydrochloric acid into agar cubes. Your plan should: • include a clear statement of the hypothesis • identify the key variables • include full details of the method • describe how you would analyse your results • be safe and ethical. … … … … … … … … … … … … … … … … … … … … … … … … [12] [Total: 24]

24 marks

Mark scheme: 3(a)(i) 6O2 + C6H12O6  6CO2 + 6H2O ; 2 3(a)(ii) coral / zooxanthellae would not photosynthesise / photosynthesis would not occur ; so no oxygen is released / oxygen levels are not affected (by photosynthesis) ; 2 3(a)(iii) 10 – 8.5 (= 1.5) 8.5 – 10.0 = (1.5) / 15 = 0.1 ; negative gradient (minus) (–0.1) ; mg dm-3 min-1 ; 3 3(b)(i) increase ; level off / decrease from, 7 / 8 / 9 (a.u.) ; 2 3(b)(ii) any 3 from: maintains / steeper, diffusion / concentration gradient ; movement of tentacles (increasing surface area contact with oxygen in water) ; another factor begins to limit rate (at speed of 7) ; such as, surface area of tentacles, rate of oxygen use by coral / temperature / AW ; 3 Question Answer Marks 3(c) hypothesis: increasing temperature increases speed that agar changes colour / increases rate of diffusion / reduces time taken for agar to change colour / AW ; plus any 11 from: variables: independent variable: temperature ; at least five stated temperatures ; dependent variable: time taken for block to change colour / rate of diffusion ; record time taken for block to change colour with stop clock / timer ; controls: max 3 from: cubes have same surface area / volume ; same concentration of acid / pH ; same volume of acid ; same concentration of alkali in block ; same concentration of agar ; method: use of water bath / AW ; left for period of time to reach temperature ; cut agar with scalpel / knife and measure with ruler ; analysis max 3 from: repeats, and means calculated / anomalies identified; rate calculated by inverse of time / AW ; graph of rate / time taken against temperature ; appropriate statistical test ; 12 Question Answer Marks 3(c) safety: MAX 1 from: safety with cutting away from the body / take care with scalpel ; correct safety precaution linked with acid, e.g. eye protection ; care with hot water baths ; ethics MAX 1 from: do not let acid / indicator / alkali drain into natural water ; no living things involved / affected so few ethical issues ;

This question in 9693/43 May/June 2022

2 Fig. 2.1 shows a light micrograph of some blood cells from a salmon. A B C D Fig. 2.1 (a) Draw the blood cells, A, B, C and D. Label one nucleus and one cell membrane on your drawing. [4] (b) Fig. 2.2 shows the structure of the cell membrane of the salmon blood cells. X Y Fig. 2.2 (i) Name molecules X and Y. molecule X … molecule Y … [2] (ii) Explain why the cell membrane structure is described as a fluid mosaic. … … … … [2] (c) Fig. 2.3 shows the effect of increasing the external concentration of sodium ions, Na+, on the rate of movement of sodium ions into cells in a salmon gill. 25 20 15 rate of movement of sodium ions / mg s–1 10 5 0 20 30 40 50 60 70 external concentration of sodium ions / g dm–3 Fig. 2.3 (i) Describe the effect of increasing the external concentration of sodium ions on the rate of movement of sodium ions into the gill cells. … … … … [2] (ii) Use your knowledge of membrane structure to explain the relationship between external concentration of sodium ions and the rate of movement of sodium ions into the gill cells, shown in Fig. 2.3. … … … … … … … … [4] [Total: 14]

14 marks

Mark scheme: 2(a) all four cells drawn with clear membrane, nuclei and touching ; 4 clear thin lines with no shading and suitable size ; correct proportions of width and length ; one nucleus and one membrane labelled ; 2(b)(i) X: phospholipid ; 2 Y: protein ; 2(b)(ii) any 2 from: 2 proteins diffuse / move through phospholipids / phospholipids can move ; proteins are embedded in / surrounded by the phospholipids / AW ; ref. to hydrophilic heads of phospholipids on the outside / hydrophobic tails on inside ; 2(c)(i) increase in rate ; 2 level off / AW, at 55 / 60 ; 2(c)(ii) any 4 of: 4 diffusion / facilitated diffusion ; sodium ions are charged / polar / positive ; so do not pass through the bilayer / AW ; pass through (protein) channels / carriers / AW ; diffusion gradient increases as external concentration increases ; as graph levels off, (number of) (protein) channels / carriers becomes limiting ;

This question in 9693/41 Oct/Nov 2022

2 Fig. 2.1 shows a light micrograph of some blood cells from a salmon. A B C D Fig. 2.1 (a) Draw the blood cells, A, B, C and D. Label one nucleus and one cell membrane on your drawing. [4] (b) Fig. 2.2 shows the structure of the cell membrane of the salmon blood cells. X Y Fig. 2.2 (i) Name molecules X and Y. molecule X … molecule Y … [2] (ii) Explain why the cell membrane structure is described as a fluid mosaic. … … … … [2] (c) Fig. 2.3 shows the effect of increasing the external concentration of sodium ions, Na+, on the rate of movement of sodium ions into cells in a salmon gill. 25 20 15 rate of movement of sodium ions / mg s–1 10 5 0 20 30 40 50 60 70 external concentration of sodium ions / g dm–3 Fig. 2.3 (i) Describe the effect of increasing the external concentration of sodium ions on the rate of movement of sodium ions into the gill cells. … … … … [2] (ii) Use your knowledge of membrane structure to explain the relationship between external concentration of sodium ions and the rate of movement of sodium ions into the gill cells, shown in Fig. 2.3. … … … … … … … … [4] [Total: 14]

14 marks

Mark scheme: 2(a) all four cells drawn with clear membrane, nuclei and touching ; 4 clear thin lines with no shading and suitable size ; correct proportions of width and length ; one nucleus and one membrane labelled ; 2(b)(i) X: phospholipid ; 2 Y: protein ; 2(b)(ii) any 2 from: 2 proteins diffuse / move through phospholipids / phospholipids can move ; proteins are embedded in / surrounded by the phospholipids / AW ; ref. to hydrophilic heads of phospholipids on the outside / hydrophobic tails on inside ; 2(c)(i) increase in rate ; 2 level off / AW, at 55 / 60 ; 2(c)(ii) any 4 of: 4 diffusion / facilitated diffusion ; sodium ions are charged / polar / positive ; so do not pass through the bilayer / AW ; pass through (protein) channels / carriers / AW ; diffusion gradient increases as external concentration increases ; as graph levels off, (number of) (protein) channels / carriers becomes limiting ;

This question in 9693/42 Oct/Nov 2022

2 Fig. 2.1 shows a light micrograph of some blood cells from a salmon. A B C D Fig. 2.1 (a) Draw the blood cells, A, B, C and D. Label one nucleus and one cell membrane on your drawing. [4] (b) Fig. 2.2 shows the structure of the cell membrane of the salmon blood cells. X Y Fig. 2.2 (i) Name molecules X and Y. molecule X … molecule Y … [2] (ii) Explain why the cell membrane structure is described as a fluid mosaic. … … … … [2] (c) Fig. 2.3 shows the effect of increasing the external concentration of sodium ions, Na+, on the rate of movement of sodium ions into cells in a salmon gill. 25 20 15 rate of movement of sodium ions / mg s–1 10 5 0 20 30 40 50 60 70 external concentration of sodium ions / g dm–3 Fig. 2.3 (i) Describe the effect of increasing the external concentration of sodium ions on the rate of movement of sodium ions into the gill cells. … … … … [2] (ii) Use your knowledge of membrane structure to explain the relationship between external concentration of sodium ions and the rate of movement of sodium ions into the gill cells, shown in Fig. 2.3. … … … … … … … … [4] [Total: 14]

14 marks

Mark scheme: 2(a) all four cells drawn with clear membrane, nuclei and touching ; 4 clear thin lines with no shading and suitable size ; correct proportions of width and length ; one nucleus and one membrane labelled ; 2(b)(i) X: phospholipid ; 2 Y: protein ; 2(b)(ii) any 2 from: 2 proteins diffuse / move through phospholipids / phospholipids can move ; proteins are embedded in / surrounded by the phospholipids / AW ; ref. to hydrophilic heads of phospholipids on the outside / hydrophobic tails on inside ; 2(c)(i) increase in rate ; 2 level off / AW, at 55 / 60 ; 2(c)(ii) any 4 of: 4 diffusion / facilitated diffusion ; sodium ions are charged / polar / positive ; so do not pass through the bilayer / AW ; pass through (protein) channels / carriers / AW ; diffusion gradient increases as external concentration increases ; as graph levels off, (number of) (protein) channels / carriers becomes limiting ;

This question in 9693/43 Oct/Nov 2022

1 Fig. 1.1 shows a diagram of a section of a cell surface membrane. A B Fig. 1.1 (a) Name the structures labelled A and B. A … B … [2] (b) Cells taken from a mussel were placed into a potassium chloride solution. The mass of potassium ions absorbed by the mussel cells was measured every five minutes for one hour. The experiment was repeated in the presence of cyanide, a chemical that stops respiration. The results are shown in Fig. 1.2. 45 40 without cyanide 35 30 total mass of 25 potassium ions taken 20 up by cells / μg 15 with cyanide 10 5 0 0 10 20 30 40 50 60 time / min Fig. 1.2 (i) Calculate the mean rate of absorption of potassium ions without cyanide over the first 20 minutes. State the unit. Show your working. … [3] (ii) Compare the uptake of potassium ions by the mussel cells without cyanide with the uptake of potassium ions with cyanide. … … … … [2] (iii) Use the information in Fig. 1.2 to explain how the mussel cells absorb potassium ions. … … … … … … … … [4] [Total: 11]

11 marks

Mark scheme: 1(a) A: phospholipid ; B: (carrier / integral / channel / intrinsic) protein ; 2 1(b)(i) correct reading from graph (16) ; calculation of gradient (16 / 20 = 0.8) ; correct units (g min-1) ; 3 1(b)(ii) both have same (increase) up to 15 (minutes) / both are same rate up to 15 mins ; AND 1 of: with cyanide, the uptake levels off / no more taken up / ORA ; without cyanide the maximum rate is, higher / ORA ; 2 1(b)(iii) any 4 of: 1 (facilitated) diffusion occurs ; 2 because potassium enters the cells when cyanide is present / when no respiration / when no ATP released ; 3 (facilitated diffusion occurs when) concentration of potassium is higher outside the cells compared to inside the cells (over the first 15 mins) / AW ; 4 active transport (also) occurs ; 5 because adding cyanide causes uptake to stop / stops when no respiration / AW ; 6 and active transport requires, energy / ATP / AW ; 7 active transport moves against the gradient ; 4

This question in 9693/42 May/June 2023

1 Fig. 1.1 shows a diagram of a section of a cell surface membrane. A B Fig. 1.1 (a) Name the structures labelled A and B. A … B … [2] (b) Cells taken from a mussel were placed into a potassium chloride solution. The mass of potassium ions absorbed by the mussel cells was measured every five minutes for one hour. The experiment was repeated in the presence of cyanide, a chemical that stops respiration. The results are shown in Fig. 1.2. 45 40 without cyanide 35 30 total mass of 25 potassium ions taken 20 up by cells / μg 15 with cyanide 10 5 0 0 10 20 30 40 50 60 time / min Fig. 1.2 (i) Calculate the mean rate of absorption of potassium ions without cyanide over the first 20 minutes. State the unit. Show your working. … [3] (ii) Compare the uptake of potassium ions by the mussel cells without cyanide with the uptake of potassium ions with cyanide. … … … … [2] (iii) Use the information in Fig. 1.2 to explain how the mussel cells absorb potassium ions. … … … … … … … … [4] [Total: 11]

11 marks

Mark scheme: 1(a) A: phospholipid ; B: (carrier / integral / channel / intrinsic) protein ; 2 1(b)(i) correct reading from graph (16) ; calculation of gradient (16 / 20 = 0.8) ; correct units (g min-1) ; 3 1(b)(ii) both have same (increase) up to 15 (minutes) / both are same rate up to 15 mins ; AND 1 of: with cyanide, the uptake levels off / no more taken up / ORA ; without cyanide the maximum rate is, higher / ORA ; 2 1(b)(iii) any 4 of: 1 (facilitated) diffusion occurs ; 2 because potassium enters the cells when cyanide is present / when no respiration / when no ATP released ; 3 (facilitated diffusion occurs when) concentration of potassium is higher outside the cells compared to inside the cells (over the first 15 mins) / AW ; 4 active transport (also) occurs ; 5 because adding cyanide causes uptake to stop / stops when no respiration / AW ; 6 and active transport requires, energy / ATP / AW ; 7 active transport moves against the gradient ; 4

This question in 9693/43 May/June 2023

1 Desalination plants are industrial factories that produce fresh water from sea water. Fig. 1.1 shows a photograph of a desalination plant. Fig. 1.1 Desalination plants are thought to be harmful to seagrass beds due to the release of highly saline water into the sea. (a) Fig. 1.2 is a diagram of a cell from a seagrass leaf. cell wall mitochondrion nucleus rough endoplasmic reticulum Golgi body A B chloroplast X smooth endoplasmic reticulum Fig. 1.2 (i) Name the organelle labelled X and state its function. name … function … … [2] (ii) The diagram has a magnification of × 30 000. Calculate the actual width of the seagrass cell between A and B on the diagram. Show your working. State the unit. … [3] (b) Scientists investigated the possible impact of desalination plants on seagrasses. They grew seagrass in water of different salinities and measured: • the percentage water content of the seagrass cells • the water potential of the seagrass cells. The percentage water content of the seagrass cells and the water potential of the seagrass cells were measured at the start, after four weeks and after six weeks. Water potential was measured in kilopascals, kPa. The results are shown in Fig. 1.3 and Fig. 1.4. 90 Key 80 start 70 4 weeks 60 6 weeks percentage water 50 content of cells 40 30 20 10 0 35 37 46 54 salinity of water / ppt Fig. 1.3 0 Key start –1000 4 weeks –2000 6 weeks water potential –3000 / kPa –4000 –5000 –6000 35 37 46 54 salinity of water / ppt Fig. 1.4 (i) Use the data in Fig. 1.3 to describe the effect of growing the seagrass in water of different salinities. … … … … … … [3] (ii) Use the data in Fig. 1.3 and Fig. 1.4 to explain the changes in water potential over time when the seagrass is placed into water of 54 ppt salinity. … … … … … … [3] (c) Desalination plants also release toxic heavy metal ions into the sea water. Explain why the release of heavy metal ions is harmful for top predator organisms in ecosystems. … … … … … … [3] [Total: 14]

14 marks

Mark scheme: Question Answer Marks 1(a)(i) (large) (permanent) vacuole ; 2 store sap / salts / water / sugars / nutrients / AW : 1(a)(ii) length measured ; 3 divide length by 30 000 ; convert to magnitude of units and unit, (m or mm) ; 1(b)(i) any 3 of: 3 1 no change / little change, in percentage water content at 35 (ppt), 37 (ppt) and 46 (ppt) ; 2 decrease at 54 (ppt) ; 3 ref to overlap of error bars ; 4 (at 54 ppt) decrease after four and at six weeks / continues to decrease over time ; 5 credit correct manipulated data ; 1(b)(ii) any 3 of: 3 1 water moves out (of cells) ; 2 by osmosis ; 3 because water potential was higher inside / moves down a water potential gradient / ORA ; 4 concentration of, solute / salts / AW, in cells increases ; 5 so that water potential decreases (in cells) ; 6 more water is removed (at 54 ppt) over time ; 1(c) any 3 of: 3 1 metal ions are taken up by producers / filter feeders / low trophic levels / AW ; 2 metal ions are, not excreted / stored in tissues / bioaccumulation occurs / AW ; 3 concentration of metal ions increases along the food chain / biomagnification occurs / AW ; 4 death of producers / lower trophic level organisms results in less food / less energy in ecosystem / damage to food chains / AW ; 5 ref to how metal ions damage organisms ;

This question in 9693/41 Oct/Nov 2023

1 Desalination plants are industrial factories that produce fresh water from sea water. Fig. 1.1 shows a photograph of a desalination plant. Fig. 1.1 Desalination plants are thought to be harmful to seagrass beds due to the release of highly saline water into the sea. (a) Fig. 1.2 is a diagram of a cell from a seagrass leaf. cell wall mitochondrion nucleus rough endoplasmic reticulum Golgi body A B chloroplast X smooth endoplasmic reticulum Fig. 1.2 (i) Name the organelle labelled X and state its function. name … function … … [2] (ii) The diagram has a magnification of × 30 000. Calculate the actual width of the seagrass cell between A and B on the diagram. Show your working. State the unit. … [3] (b) Scientists investigated the possible impact of desalination plants on seagrasses. They grew seagrass in water of different salinities and measured: • the percentage water content of the seagrass cells • the water potential of the seagrass cells. The percentage water content of the seagrass cells and the water potential of the seagrass cells were measured at the start, after four weeks and after six weeks. Water potential was measured in kilopascals, kPa. The results are shown in Fig. 1.3 and Fig. 1.4. 90 Key 80 start 70 4 weeks 60 6 weeks percentage water 50 content of cells 40 30 20 10 0 35 37 46 54 salinity of water / ppt Fig. 1.3 0 Key start –1000 4 weeks –2000 6 weeks water potential –3000 / kPa –4000 –5000 –6000 35 37 46 54 salinity of water / ppt Fig. 1.4 (i) Use the data in Fig. 1.3 to describe the effect of growing the seagrass in water of different salinities. … … … … … … [3] (ii) Use the data in Fig. 1.3 and Fig. 1.4 to explain the changes in water potential over time when the seagrass is placed into water of 54 ppt salinity. … … … … … … [3] (c) Desalination plants also release toxic heavy metal ions into the sea water. Explain why the release of heavy metal ions is harmful for top predator organisms in ecosystems. … … … … … … [3] [Total: 14]

14 marks

Mark scheme: Question Answer Marks 1(a)(i) (large) (permanent) vacuole ; 2 store sap / salts / water / sugars / nutrients / AW : 1(a)(ii) length measured ; 3 divide length by 30 000 ; convert to magnitude of units and unit, (m or mm) ; 1(b)(i) any 3 of: 3 1 no change / little change, in percentage water content at 35 (ppt), 37 (ppt) and 46 (ppt) ; 2 decrease at 54 (ppt) ; 3 ref to overlap of error bars ; 4 (at 54 ppt) decrease after four and at six weeks / continues to decrease over time ; 5 credit correct manipulated data ; 1(b)(ii) any 3 of: 3 1 water moves out (of cells) ; 2 by osmosis ; 3 because water potential was higher inside / moves down a water potential gradient / ORA ; 4 concentration of, solute / salts / AW, in cells increases ; 5 so that water potential decreases (in cells) ; 6 more water is removed (at 54 ppt) over time ; 1(c) any 3 of: 3 1 metal ions are taken up by producers / filter feeders / low trophic levels / AW ; 2 metal ions are, not excreted / stored in tissues / bioaccumulation occurs / AW ; 3 concentration of metal ions increases along the food chain / biomagnification occurs / AW ; 4 death of producers / lower trophic level organisms results in less food / less energy in ecosystem / damage to food chains / AW ; 5 ref to how metal ions damage organisms ;

This question in 9693/42 Oct/Nov 2023

1 Desalination plants are industrial factories that produce fresh water from sea water. Fig. 1.1 shows a photograph of a desalination plant. Fig. 1.1 Desalination plants are thought to be harmful to seagrass beds due to the release of highly saline water into the sea. (a) Fig. 1.2 is a diagram of a cell from a seagrass leaf. cell wall mitochondrion nucleus rough endoplasmic reticulum Golgi body A B chloroplast X smooth endoplasmic reticulum Fig. 1.2 (i) Name the organelle labelled X and state its function. name … function … … [2] (ii) The diagram has a magnification of × 30 000. Calculate the actual width of the seagrass cell between A and B on the diagram. Show your working. State the unit. … [3] (b) Scientists investigated the possible impact of desalination plants on seagrasses. They grew seagrass in water of different salinities and measured: • the percentage water content of the seagrass cells • the water potential of the seagrass cells. The percentage water content of the seagrass cells and the water potential of the seagrass cells were measured at the start, after four weeks and after six weeks. Water potential was measured in kilopascals, kPa. The results are shown in Fig. 1.3 and Fig. 1.4. 90 Key 80 start 70 4 weeks 60 6 weeks percentage water 50 content of cells 40 30 20 10 0 35 37 46 54 salinity of water / ppt Fig. 1.3 0 Key start –1000 4 weeks –2000 6 weeks water potential –3000 / kPa –4000 –5000 –6000 35 37 46 54 salinity of water / ppt Fig. 1.4 (i) Use the data in Fig. 1.3 to describe the effect of growing the seagrass in water of different salinities. … … … … … … [3] (ii) Use the data in Fig. 1.3 and Fig. 1.4 to explain the changes in water potential over time when the seagrass is placed into water of 54 ppt salinity. … … … … … … [3] (c) Desalination plants also release toxic heavy metal ions into the sea water. Explain why the release of heavy metal ions is harmful for top predator organisms in ecosystems. … … … … … … [3] [Total: 14]

14 marks

Mark scheme: Question Answer Marks 1(a)(i) (large) (permanent) vacuole ; 2 store sap / salts / water / sugars / nutrients / AW : 1(a)(ii) length measured ; 3 divide length by 30 000 ; convert to magnitude of units and unit, (m or mm) ; 1(b)(i) any 3 of: 3 1 no change / little change, in percentage water content at 35 (ppt), 37 (ppt) and 46 (ppt) ; 2 decrease at 54 (ppt) ; 3 ref to overlap of error bars ; 4 (at 54 ppt) decrease after four and at six weeks / continues to decrease over time ; 5 credit correct manipulated data ; 1(b)(ii) any 3 of: 3 1 water moves out (of cells) ; 2 by osmosis ; 3 because water potential was higher inside / moves down a water potential gradient / ORA ; 4 concentration of, solute / salts / AW, in cells increases ; 5 so that water potential decreases (in cells) ; 6 more water is removed (at 54 ppt) over time ; 1(c) any 3 of: 3 1 metal ions are taken up by producers / filter feeders / low trophic levels / AW ; 2 metal ions are, not excreted / stored in tissues / bioaccumulation occurs / AW ; 3 concentration of metal ions increases along the food chain / biomagnification occurs / AW ; 4 death of producers / lower trophic level organisms results in less food / less energy in ecosystem / damage to food chains / AW ; 5 ref to how metal ions damage organisms ;

This question in 9693/43 Oct/Nov 2023

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

4 Turgor pressure is the force exerted by the contents of the cytoplasm of a plant cell when the cell membrane presses outwards against the cell wall. Turgor pressure is measured in megapascals (MPa). A student investigated the effect of different concentrations of sucrose on mass and turgor pressure in mangrove roots. Equal-sized pieces of mangrove root were placed into five different sucrose solutions and also placed into pure water. After six hours, the student calculated the percentage change in mass of the roots and the turgor pressure in the root cells. The results are shown in Table 4.1. Table 4.1 sucrose concentration percentage change in turgor pressure / mol dm–3 mass / MPa 0.00 +25 0.42 0.25 +15 0.28 0.50 +10 0.14 0.75 –5 0.00 1.00 –10 0.00 1.25 –25 0.00 (a) (i) Draw a line graph to show the percentage change in mass and the turgor pressure when the roots were placed in the different concentrations of sucrose. Join your points with ruled straight lines. [5] (ii) Explain the effect of increasing sucrose concentration on the percentage change in mass of the roots. … … … … … … [3] (iii) Explain the effect of increasing sucrose concentration on the turgor pressure. … … … … [2] (b) Reverse osmosis is a method that can be used to produce fresh water from sea water. Fig. 4.1 is a diagram to show how reverse osmosis works. pressure from pump A B fresh water dissolved salts in sea water water flow selectively permeable membrane Fig. 4.1 (i) A pump forces sea water under pressure into chamber A. Fresh water is produced in chamber B. Explain why pressure is needed to produce the fresh water in chamber B. … … … … [2] (ii) Chamber A contains a very concentrated solution of salts after the reverse osmosis process has finished. Explain why this solution in chamber A should not be returned to the sea. … … … … … … [3] [Total: 15]

15 marks

Mark scheme: 4(a)(i) 1 two linear y-axes and linear x-axis labelled with units ; 5 2 both plotted lines taken up at least three large squares ; 3 correct plots for percentage change in mass (+/– ½ square) ; 4 correct plots for turgor pressure (+/– ½ square) ; 5 plots joined with straight lines and lines have a key or are labelled ; 4(a)(ii) any 3 of: 3 1 at low concentrations / below 0.5, mass increases / water enters cells, / AW ; 2 at high concentrations / above 0.75 / value from graph, decrease in mass / water leaves cells ; 3 (water moves in / out) by osmosis ; 4 (water moves) from a higher water potential to a lower water potential ; 5 solute concentration of cells is equivalent to value from graph where line intersects x-axis ; 4(a)(iii) any 2 of: 2 1 turgor pressure decreases up to concentration of 0.75 and then levels off (at zero) / AW ; 2 because as concentration increases, water content of cells is less / AW ; 3 below 0.75, membrane presses / touches cell wall / AW ; 4 over 0.75, cell membrane peels away from cell wall / cells has become plasmolysed / AW ; 4(b)(i) any 2 of: 2 1 water would (naturally) move into chamber A / from chamber B / from freshwater to sea water / AW ; 2 as the water potential of B is higher than A / water would down the water potential gradient / water is being forced against the water potential gradient / AW ; 3 so pressure needs to be greater than osmotic force / pressure / AW ; 4 salts cannot pass through the membrane / only water can pass through the membrane / AW ; 4(b)(ii) any 3 of: 3 1 salinity of the sea increases / water potential decreases ; 2 affects osmoconformer species / AW ; 3 water would be lost (from organisms) / cause dehydration / AW ; 4 alters density of water / salinity gradients / haloclines / AW ; 5 (high salinity) would reduce oxygen content of water / AW ; 6 causing organisms to suffocate / reduces respiration / AW ; 7 (the salt solution) may also contain high concentrations of toxins / AW ; 8 AVP ;

This question in 9693/42 May/June 2025

4 Turgor pressure is the force exerted by the contents of the cytoplasm of a plant cell when the cell membrane presses outwards against the cell wall. Turgor pressure is measured in megapascals (MPa). A student investigated the effect of different concentrations of sucrose on mass and turgor pressure in mangrove roots. Equal-sized pieces of mangrove root were placed into five different sucrose solutions and also placed into pure water. After six hours, the student calculated the percentage change in mass of the roots and the turgor pressure in the root cells. The results are shown in Table 4.1. Table 4.1 sucrose concentration percentage change in turgor pressure / mol dm–3 mass / MPa 0.00 +25 0.42 0.25 +15 0.28 0.50 +10 0.14 0.75 –5 0.00 1.00 –10 0.00 1.25 –25 0.00 (a) (i) Draw a line graph to show the percentage change in mass and the turgor pressure when the roots were placed in the different concentrations of sucrose. Join your points with ruled straight lines. [5] (ii) Explain the effect of increasing sucrose concentration on the percentage change in mass of the roots. … … … … … … [3] (iii) Explain the effect of increasing sucrose concentration on the turgor pressure. … … … … [2] (b) Reverse osmosis is a method that can be used to produce fresh water from sea water. Fig. 4.1 is a diagram to show how reverse osmosis works. pressure from pump A B fresh water dissolved salts in sea water water flow selectively permeable membrane Fig. 4.1 (i) A pump forces sea water under pressure into chamber A. Fresh water is produced in chamber B. Explain why pressure is needed to produce the fresh water in chamber B. … … … … [2] (ii) Chamber A contains a very concentrated solution of salts after the reverse osmosis process has finished. Explain why this solution in chamber A should not be returned to the sea. … … … … … … [3] [Total: 15]

15 marks

Mark scheme: 4(a)(i) 1 two linear y-axes and linear x-axis labelled with units ; 5 2 both plotted lines taken up at least three large squares ; 3 correct plots for percentage change in mass (+/– ½ square) ; 4 correct plots for turgor pressure (+/– ½ square) ; 5 plots joined with straight lines and lines have a key or are labelled ; 4(a)(ii) any 3 of: 3 1 at low concentrations / below 0.5, mass increases / water enters cells, / AW ; 2 at high concentrations / above 0.75 / value from graph, decrease in mass / water leaves cells ; 3 (water moves in / out) by osmosis ; 4 (water moves) from a higher water potential to a lower water potential ; 5 solute concentration of cells is equivalent to value from graph where line intersects x-axis ; 4(a)(iii) any 2 of: 2 1 turgor pressure decreases up to concentration of 0.75 and then levels off (at zero) / AW ; 2 because as concentration increases, water content of cells is less / AW ; 3 below 0.75, membrane presses / touches cell wall / AW ; 4 over 0.75, cell membrane peels away from cell wall / cells has become plasmolysed / AW ; 4(b)(i) any 2 of: 2 1 water would (naturally) move into chamber A / from chamber B / from freshwater to sea water / AW ; 2 as the water potential of B is higher than A / water would down the water potential gradient / water is being forced against the water potential gradient / AW ; 3 so pressure needs to be greater than osmotic force / pressure / AW ; 4 salts cannot pass through the membrane / only water can pass through the membrane / AW ; 4(b)(ii) any 3 of: 3 1 salinity of the sea increases / water potential decreases ; 2 affects osmoconformer species / AW ; 3 water would be lost (from organisms) / cause dehydration / AW ; 4 alters density of water / salinity gradients / haloclines / AW ; 5 (high salinity) would reduce oxygen content of water / AW ; 6 causing organisms to suffocate / reduces respiration / AW ; 7 (the salt solution) may also contain high concentrations of toxins / AW ; 8 AVP ;

This question in 9693/43 May/June 2025