General cell structure — Paper 4 · A Level Marine Science 9693

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 cell from the leaf of a species of seagrass. B A C Fig. 1.1 (a) (i) Give the names of the structures labelled A and B. A … B … [2] (ii) The magnification of the diagram is × 5000. Calculate the maximum length of the structure labelled C. Show your working. State the unit. … [3] (b) The effect of salinity on the growth of seagrass leaves was investigated. Seagrass plants were placed in different salinities for two weeks. The increase in length of 9 leaves at each of the salinities was measured. The mean rate of leaf growth per day was then calculated. The results are shown in Fig. 1.2. The error bars represent ± 1 standard deviation. 0.40 0.35 0.30 0.25 mean rate of leaf 0.20 growth / cm day–1 0.15 0.10 0.05 0.00 0 5 10 15 20 25 30 35 40 45 50 salinity / ppt Fig. 1.2 (i) Describe the effect of increasing salinity on the mean rate of leaf growth per day. … … … … [2] (ii) A student concluded that the results show that the optimum salinity for growth of the seagrass is 25 ppt. Use the data in Fig. 1.2 to discuss whether their conclusion is correct. … … … … … … [3] (iii) Desalination plants are used to produce fresh water from sea water. Use the information in Fig. 1.2, and your own knowledge, to explain why outflow from a desalination plant might harm seagrass growth. … … … … … … … … [4] [Total: 14]

14 marks

Mark scheme: 1(a)(i) A: Golgi, (body / apparatus) ; B: rough endoplasmic reticulum / RER ; 2 1(a)(ii) 10 (mm) ; 10 / 5000 = 0.002 ; correct unit ; ONLY AWARD UNIT MARK IF ANSWER IS CORRECT (e.g. 2 m, 0.002 mm) 3 1(b)(i) increase and decrease; (increase up to) 25 (ppt) / from 30 (ppt); 2 1(b)(ii) any 3 of: 1 (correct because) the highest / fastest rate of growth is at 25 (ppt) / AW ; 2 carried out with ten / many leaves so reliable ; (incorrect because) 3 no significant difference between 20 / 30 (ppt) and 25 ) ppt) ; 4 (because) standard deviations overlap (between 20 / 30 (ppt) and 25 (ppt)) / AW ; 5 optimum may be between 20 (ppt) and 30 (ppt) ; 6 no measurements taken between 20 (ppt) and 25 (ppt) / 25 (ppt) and 30 (ppt) ; 3 1(b)(iii) any 4 of: 1 reduced photosynthesis ; 2 (because) desalination plants release high salinity water / brine / concentrated brine / increase salinity / return salt to sea / AW ; 3 growth is reduced / lower growth, at high salinities / concentrations / above 25 (ppt) / AW ; 4 osmotic effects harm the seagrass / osmosis will occur / AW ; 5 water leaves cells / plant / seagrass ; 6 cells / plant / seagrass, no longer supported / cells plasmolyse / cells are not turgid / AW ; 7 desalination plants stir up sediment / increase turbidity ; 8 AVP ; 4

This question in 9693/41 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 9693/42 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 9693/42 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

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

1 Fig. 1.1 shows an electron micrograph of part of a marine algal cell, Dunaliella spp. Y nucleus X chloroplast Fig. 1.1 (a) State one function of the cell nucleus. … … [1] (b) (i) The magnification of the electron micrograph is ×40 000. Calculate the actual width, from X to Y, of the nucleus. Give your answer to two significant figures and in micrometres (μm). Show your working. … μm [3] (ii) Make a large drawing of the area of the cell shown in the circle in Fig. 1.1. [4] (c) A student investigated the effect of different colours of light on the growth of Dunaliella spp. The student placed equal masses of algae into different beakers of sea water and exposed each beaker to a different colour of light for one month. This was replicated four times. After one month, the student calculated the mean increase in the dry mass of algae that had been exposed to each colour of light. The experiment was repeated with a second species of alga that lives in surface waters. The results are shown in Table 1.1. Table 1.1 colour of light mean increase in dry mass of algae / g Dunaliella spp. surface water alga purple 2.50 3.15 blue 2.95 2.85 green 1.25 0.12 yellow 0.82 0.10 orange 1.85 1.65 red 2.14 2.95 (i) Compare the effect of different colours of light on the growth of Dunaliella spp. with the growth of the surface water alga. … … … … … … [3] (ii) The student concluded that Dunaliella spp. has additional chloroplast pigments compared with the surface alga and is adapted for living in deeper water. Discuss the student’s conclusion. … … … … … … [3] [Total: 14]

14 marks

Mark scheme: 1(a) controls the cell / contains genes / contains chromosomes / contains DNA / stores DNA / synthesis DNA / AW ; 1 1(b)(i) 2.0 up to 2.1 (three marks) ;;; correct answer to wrong number of significant figures (two marks) ;; 82 000 up to 85 000 (mm) OR division by 40 000 OR 0.00205 / 0.002125 (one mark) ; 3 1(b)(ii) lines are thin, clear, unbroken and no shading ; size takes up most of the space provided ; correct proportions of gaps between membrane groups ; correct detail ; nuclear envelope drawn as two close lines, circle structure present and at least four lines for bottom right membranes 4 1(c)(i) any 3 of: 1 surface water alga has high(est) / best, growth with purple / AW ; 2 Dunaliella has high(est) / best, growth with blue / AW ; 3 both species grow least with yellow / AW ; 4 surface water alga has highest overall growth (with purple) (compared with Dunaliella) / AW ; 5 Dunaliella is higher than surface alga with blue / green / yellow / orange / ORA 6 wider range of growth for surface water alga / ORA / AW ; 7 comparison with manipulated data ; 3 1(c)(ii) any 3 of: 1 Dunaliella grows more with green / yellow (compared with surface alga) / is better at absorbing (all) colours / AW ; 2 red light does not penetrate into deeper water / AW ; 3 surface alga has (mainly) chlorophyll (a) / primary pigment ; 4 chlorophyll absorbs red and blue / chlorophyll does not absorb green / yellow ; 5 Dunaliella has (more) accessory pigments ; 6 Dunaliella is adapted for deep water because has high growth with blue / increase with blue / AW ; 7 but there is no proof for presence of accessory pigments ; 8 surface alga can absorb some of all colours / may just have different proportions of pigments ; 3

This question in 9693/41 May/June 2024

1 The gills of most fish have cells on their surfaces that secrete a thick, slippery fluid called mucus. The cells that secrete mucus are known as goblet cells. Fig. 1.1 is a diagram of a goblet cell from the gill of a salmon. A B ×8500 Fig. 1.1 (a) (i) The diagram has a magnification of ×8500. Calculate the actual length of the goblet cell between A and B on Fig. 1.1. Give your answer to three significant figures and in micrometres (μm). Show your working. … μm [3] (ii) Name two cell structures not present in the goblet cell that would be present in a plant cell. 1 … 2 … [2] (b) Fig. 1.2 shows an electron micrograph of a mitochondrion. Make a large drawing of the mitochondrion. Do not label your drawing. Fig. 1.2 [4] [Total: 9]

9 marks

Mark scheme: 1(a)(i) correct conversion to µm ; image length divided by 8500 ; given to three significant figures ; 3 1(a)(ii) any 2 of: 1 chloroplast ; 2 cell wall ; 3 vacuole ; 4 starch granule ; 2 1(b) clear thin lines with no shading and suitable size ; drawing at least size of micrograph mitochondrion ; width of mitochondrion in proportion to length and cristate thickness in proportion ; double membrane, minimum of 4 cristae and two circles ; 4

This question in 9693/42 May/June 2024

1 The gills of most fish have cells on their surfaces that secrete a thick, slippery fluid called mucus. The cells that secrete mucus are known as goblet cells. Fig. 1.1 is a diagram of a goblet cell from the gill of a salmon. A B ×8500 Fig. 1.1 (a) (i) The diagram has a magnification of ×8500. Calculate the actual length of the goblet cell between A and B on Fig. 1.1. Give your answer to three significant figures and in micrometres (μm). Show your working. … μm [3] (ii) Name two cell structures not present in the goblet cell that would be present in a plant cell. 1 … 2 … [2] (b) Fig. 1.2 shows an electron micrograph of a mitochondrion. Make a large drawing of the mitochondrion. Do not label your drawing. Fig. 1.2 [4] [Total: 9]

9 marks

Mark scheme: 1(a)(i) correct conversion to µm ; image length divided by 8500 ; given to three significant figures ; 3 1(a)(ii) any 2 of: 1 chloroplast ; 2 cell wall ; 3 vacuole ; 4 starch granule ; 2 1(b) clear thin lines with no shading and suitable size ; drawing at least size of micrograph mitochondrion ; width of mitochondrion in proportion to length and cristate thickness in proportion ; double membrane, minimum of 4 cristae and two circles ; 4

This question in 9693/43 May/June 2024

1 Fig. 1.1 is an electron micrograph of part of a cell from a salmon. B mitochondrion A X Fig. 1.1 (a) (i) Name the organelle labelled X in Fig. 1.1. … [1] (ii) Outline the function of the organelle labelled X in Fig. 1.1. … … … … [2] (b) (i) Make a large drawing of the part of the mitochondrion in the circle in Fig. 1.1. [4] (ii) The electron micrograph has a magnification of ×65 000. Calculate the length of the mitochondrion in nanometres (nm) between lines A and B. Give your answer to two significant figures. Show your working. … nm [3] (iii) Muscle is a type of tissue that is specialised for movement. Salmon have two types of muscle tissue: red muscle and white muscle. Scientists measured the mean percentage of muscle tissue volume that is composed of mitochondria in both types of salmon muscle tissue. The results are shown in Fig. 1.2. 8 7 6 mean percentage of 5 tissue volume composed of 4 mitochondria 3 2 1 0 red white muscle type Fig. 1.2 Salmon use red muscle tissue for long-distance swimming. Salmon use white muscle tissue for short periods of quick swimming. Describe and explain the results shown in Fig. 1.2. … … … … … … … … [4] [Total: 14]

14 marks

Mark scheme: Question Answer Marks 1(a)(i) rough endoplasmic reticulum / RER / rough ER ; 1 1(a)(ii) any 2 from: 2 1 translation / joining of amino acids / AW ; 2 protein synthesis / polypeptide synthesis ; 3 (proteins) leave in vesicles / sends (proteins) to Golgi / AW ; 4 AVP ; 1(b)(i) 1 outline: unbroken lines and no shading ; 4 must be the area in the circle on the diagram 2 size: most of the space provided ; minimum 70 mm high x 70 mm wide 3 proportion: cristae are correct lengths and spacing ; • lengths of cristae in proportion (two bottom left crista needs to be longer than top) • horizontal spaces and space between upper and lower cristae in proportion • glycogen granule in scale 4 detail: at least 7 cristae and the glycogen granule and outer membrane ; 1(b)(ii) 1700 OR 1800 = 3 marks 3 An answer between 1700 and 1800 that is not to two significant figures = 2 marks One mark for: ÷ 65 000 in working OR mm measurement × 1 000 000 in working OR cm measurement × 10 000 000 in working 1(b)(iii) any 4 from: 4 1 more mitochondria present in red muscle cells / higher (mean percentage) in red muscle / ORA ; 2 5.4(%) more mitochondria in red muscle / 5.4(%) less in white muscle / 3.3 × more mitochondria in red muscle ; 3 mitochondria are used for aerobic respiration ; 4 more ATP / energy needed for long distance swimming / for swimming for long times / ORA ; 5 for (more) muscle contraction ; 6 red muscle (does mainly) aerobic respiration / white muscle (does mainly) anaerobic respiration / AW ;

This question in 9693/41 May/June 2025

1 (a) Fig. 1.1 shows a light micrograph of some leaf cells from an aquatic plant. chloroplast X Fig. 1.1 (i) Name the structure labelled X in Fig. 1.1. … [1] (ii) Make a large drawing of the part of the micrograph shown in the box in Fig. 1.1. [4] (b) Hydrogencarbonate indicator solution is a substance that changes colour depending on the concentration of dissolved carbon dioxide. Fig. 1.2 shows the colour changes. increasing concentration of carbon dioxide indicator colour: RED ORANGE YELLOW Fig. 1.2 A student compared the effects of changing the colour of light on the rates of photosynthesis of an aquatic plant and a deep-sea macroalga, using the method described. • Pieces of aquatic plant and macroalga were placed into separate boiling tubes. • The aquatic plant and macroalga were covered with orange hydrogencarbonate indicator. • The boiling tubes were placed in front of a lamp producing red light. • The time taken for the indicator colour to change from orange to red was recorded. • The experiment was repeated 10 times and the mean times taken were calculated. • The experiment was repeated with green light, yellow light and blue light. The results are shown in Fig. 1.3. For the aquatic plant exposed to green light there was no colour change, with the colour remaining orange throughout the experiment. 80 70 Key red light 60 green light mean time 50 yellow light taken for blue light indicator to 40 change colour / min 30 20 10 0 aquatic plant macroalga organism Fig. 1.3 (i) Explain why the indicator solution changed colour from orange to red when the aquatic plant was exposed to blue light. … … … … [2] (ii) Explain how the results show that the macroalga is better adapted to live in deep water than the aquatic plant. Use Fig. 1.2 and Fig. 1.3 to support your answer. … … … … … … … … [4] (iii) When the aquatic plant was placed in front of the green light for more than two hours, the indicator solution changed to a yellow colour. Explain why the indicator solution changed to a yellow colour. … … … … [2] (iv) Suggest why the experiment does not give an accurate measurement of the rates of photosynthesis. … … [1] [Total: 14]

14 marks

Mark scheme: Question Answer Marks 1(a)(i) nucleus ; 1 1(a)(ii) 1 unbroken lines with no shading ; 4 2 at least same size as photograph ; 3 proportions of drawing correct ; {nucleus and chloroplasts in proportion, gap between nucleus and cell wall in proportion} 4 nucleolus, cell wall and minimum of nine chloroplasts drawn ; 1(b)(i) any 2 of: 2 1 blue light is, absorbed / trapped, by chlorophyll (a / b) / pigments / AW ; 2 photosynthesis (occurs) ; 3 carbon dioxide, taken in / absorbed / used / AW ; 1(b)(ii) any 4 of: 4 1 blue / green light, penetrates deeper / AW / ORA ; 2 macroalga can use all colours / absorbs all colours / AW ; 3 macroalga has faster colour change (than aquatic plant) with, green / yellow / ORA ; 4 macroalga has slower colour change (than aquatic plant) with blue / red light / ORA ; 5 macroalga has, accessory / additional, pigments / fucoxanthin / AW ; 6 macroalga can photosynthesise / make glucose, in deep water / when no red light present / AW ; 1(b)(iii) any 2 of: 2 1 green light is not absorbed ; 2 no photosynthesis occurs ; 3 respiration occurs ; 4 so rate of production of carbon dioxide is higher than uptake of carbon dioxide / AW ; 1(b)(iv) any 1 of: 1 1 colour change is subjective ; 2 difficult to see differences between colours ; 3 the experiment measures photosynthesis minus respiration ;

This question in 9693/42 May/June 2025

1 (a) Fig. 1.1 shows a light micrograph of some leaf cells from an aquatic plant. chloroplast X Fig. 1.1 (i) Name the structure labelled X in Fig. 1.1. … [1] (ii) Make a large drawing of the part of the micrograph shown in the box in Fig. 1.1. [4] (b) Hydrogencarbonate indicator solution is a substance that changes colour depending on the concentration of dissolved carbon dioxide. Fig. 1.2 shows the colour changes. increasing concentration of carbon dioxide indicator colour: RED ORANGE YELLOW Fig. 1.2 A student compared the effects of changing the colour of light on the rates of photosynthesis of an aquatic plant and a deep-sea macroalga, using the method described. • Pieces of aquatic plant and macroalga were placed into separate boiling tubes. • The aquatic plant and macroalga were covered with orange hydrogencarbonate indicator. • The boiling tubes were placed in front of a lamp producing red light. • The time taken for the indicator colour to change from orange to red was recorded. • The experiment was repeated 10 times and the mean times taken were calculated. • The experiment was repeated with green light, yellow light and blue light. The results are shown in Fig. 1.3. For the aquatic plant exposed to green light there was no colour change, with the colour remaining orange throughout the experiment. 80 70 Key red light 60 green light mean time 50 yellow light taken for blue light indicator to 40 change colour / min 30 20 10 0 aquatic plant macroalga organism Fig. 1.3 (i) Explain why the indicator solution changed colour from orange to red when the aquatic plant was exposed to blue light. … … … … [2] (ii) Explain how the results show that the macroalga is better adapted to live in deep water than the aquatic plant. Use Fig. 1.2 and Fig. 1.3 to support your answer. … … … … … … … … [4] (iii) When the aquatic plant was placed in front of the green light for more than two hours, the indicator solution changed to a yellow colour. Explain why the indicator solution changed to a yellow colour. … … … … [2] (iv) Suggest why the experiment does not give an accurate measurement of the rates of photosynthesis. … … [1] [Total: 14]

14 marks

Mark scheme: Question Answer Marks 1(a)(i) nucleus ; 1 1(a)(ii) 1 unbroken lines with no shading ; 4 2 at least same size as photograph ; 3 proportions of drawing correct ; {nucleus and chloroplasts in proportion, gap between nucleus and cell wall in proportion} 4 nucleolus, cell wall and minimum of nine chloroplasts drawn ; 1(b)(i) any 2 of: 2 1 blue light is, absorbed / trapped, by chlorophyll (a / b) / pigments / AW ; 2 photosynthesis (occurs) ; 3 carbon dioxide, taken in / absorbed / used / AW ; 1(b)(ii) any 4 of: 4 1 blue / green light, penetrates deeper / AW / ORA ; 2 macroalga can use all colours / absorbs all colours / AW ; 3 macroalga has faster colour change (than aquatic plant) with, green / yellow / ORA ; 4 macroalga has slower colour change (than aquatic plant) with blue / red light / ORA ; 5 macroalga has, accessory / additional, pigments / fucoxanthin / AW ; 6 macroalga can photosynthesise / make glucose, in deep water / when no red light present / AW ; 1(b)(iii) any 2 of: 2 1 green light is not absorbed ; 2 no photosynthesis occurs ; 3 respiration occurs ; 4 so rate of production of carbon dioxide is higher than uptake of carbon dioxide / AW ; 1(b)(iv) any 1 of: 1 1 colour change is subjective ; 2 difficult to see differences between colours ; 3 the experiment measures photosynthesis minus respiration ;

This question in 9693/43 May/June 2025