Particle theory and bonding — Paper 2 · A Level Marine Science 9693

4 Hunga Tonga is an underwater volcano in the tropical South Pacific Ocean near Tonga. (a) Use the theory of plate tectonics to describe how the Hunga Tonga volcano formed. … … … … … … … … [4] (b) In January 2015 the Hunga Tonga volcano created a new island. It measured 500 m across and 250 m high. Use the Darwin-Dana-Daly theory to suggest what might eventually happen to the new island over time. … … … … … … … … [4] (c) Describe and explain how volcanic activity and other factors can affect the concentration of dissolved gases in sea water. … … … … … … … … … … … … … … [7] [Total: 15]

15 marks

Mark scheme: 4(a) any 4 from: volcano will have formed at plate boundary ; named plate boundary, convergent or divergent ; magma / lava / molten rock, released from below Earth’s crust / from mantle ; (lava) cools AND solidifies ; forms new igneous rock ; ref. to formation in subduction zone ; Question Answer Marks 4(b) any 4 from: 1 colonised / settling, by, reef-building / hermatypic, coral OR colonised / settling, by coral polyps / coral larvae ; 2 so, fringing reef develops ; 3 volcano becomes dormant / extinct ; 4 volcano / island, begins to sink / subside ; 5 so, barrier reef develops ; 6 lagoon / description of, forms between reef and island ; 7 volcano / island, eventually sinks below sea level / disappears ; 4 Question Answer Marks 4(c) any 7 from: 1 gases from volcanic action dissolve ; 2 named volcanic gas ; 3 change in temperature ; 4 higher temperature decreases solubility / ORA ; 5 suggested cause for change e.g. vent / volcano / glacial melt / global warming ; 6 wave action ; 7 (increased turbulence) increases dissolution ; 8 salinity ; 9 increased salinity decreases solubility / ORA ; 10 pressure ; 11 increased pressure increases solubility / ORA ; 12 ref to photosynthesis, increasing O2 / decreasing CO2 ; 13 ref to respiration, decreasing O2 / increasing CO2 ; 7

This question in 9693/22 May/June 2020

4 Hunga Tonga is an underwater volcano in the tropical South Pacific Ocean near Tonga. (a) Use the theory of plate tectonics to describe how the Hunga Tonga volcano formed. … … … … … … … … [4] (b) In January 2015 the Hunga Tonga volcano created a new island. It measured 500 m across and 250 m high. Use the Darwin-Dana-Daly theory to suggest what might eventually happen to the new island over time. … … … … … … … … [4] (c) Describe and explain how volcanic activity and other factors can affect the concentration of dissolved gases in sea water. … … … … … … … … … … … … … … [7] [Total: 15]

15 marks

Mark scheme: 4(a) any 4 from: 4 volcano will have formed at plate boundary ; named plate boundary, convergent or divergent ; magma / lava / molten rock, released from below Earth’s crust / from mantle ; (lava) cools AND solidifies ; forms new igneous rock ; ref. to formation in subduction zone ; 4(b) any 4 from: 4 1 colonised / settling, by, reef-building / hermatypic, coral OR colonised / settling, by coral polyps / coral larvae ; 2 so, fringing reef develops ; 3 volcano becomes dormant / extinct ; 4 volcano / island, begins to sink / subside ; 5 so, barrier reef develops ; 6 lagoon / description of, forms between reef and island ; 7 volcano / island, eventually sinks below sea level / disappears ; 4(c) any 7 from: 7 1 gases from volcanic action dissolve ; 2 named volcanic gas ; 3 change in temperature ; 4 higher temperature decreases solubility / ORA ; 5 suggested cause for change e.g. vent / volcano / glacial melt / global warming ; 6 wave action ; 7 (increased turbulence) increases dissolution ; 8 salinity ; 9 increased salinity decreases solubility / ORA ; 10 pressure ; 11 increased pressure increases solubility / ORA ; 12 ref to photosynthesis, increasing O2 / decreasing CO2 ; 13 ref to respiration, decreasing O2 / increasing CO2 ;

This question in 9693/23 May/June 2020

1 A student was given water samples from three different environments to compare. They tested the pH of the samples. (a) State two ways of measuring pH. 1 … 2 … [2] (b) The student measured the pH using two different methods. Table 1.1 shows the results. Table 1.1 pH water sample method 1 method 2 J 8.2 8.0 K 3.6 4.0 L 7.6 7.0 (i) Suggest why the student did not calculate the mean of the two methods for each sample. … … [1] Dissolved nutrients affect the pH of water. (ii) Identify which sample, J, K, or L, came from near a hydrothermal vent. … [1] (iii) Explain your answer from (ii) for the sample from the hydrothermal vent. … … … … [2] (c) Explain why the dissolved oxygen level in surface open ocean water is higher than in water near a hydrothermal vent. … … … … … … [4] [Total: 10]

10 marks

Mark scheme: Question Answer Marks 1(a) pH meter / probe ; 2 universal indicator ; 1(b)(i) any 1 from: 1 they were measured to different degrees of accuracy ; means should only be calculated when results are measured using the same method / apparatus ; 1(b)(ii) K ; 1 1(b)(iii) any 2 from: 2 water coming from hydrothermal vents has (a high concentration of) dissolved nutrient(s) / minerals / named correct chemical / ions ; which makes the water (very) acidic / pH goes below 7 ; 1(c) any 4 from: 4 light present (in surface water) ; presence of photosynthetic organisms (in surface water) ; (photosynthesis / producers) releasing oxygen (in surface water) ; atmospheric dissolution (in surface water) ; wave action increases oxygen dissolving (in surface water) ; low mixing with higher layers containing oxygen (at hydrothermal vent) ; correct ref. solubility of oxygen at different temps / OWTTE ; organisms respiring oxygen (at hydrothermal vent) ; higher pressure so solubility lower (at hydrothermal vent) ; correct ref. to solubility of oxygen at different salinities / OWTTE ;

This question in 9693/21 Oct/Nov 2022

2 Fig. 2.1 shows a high magnification image of a diatom. pores Fig. 2.1 (a) Make a large drawing of the diatom shown in Fig. 2.1. Include features, but do not include the pores. Do not label the drawing. [4] (b) Diatoms are a possible source of biofuel. Diatoms absorb carbon dioxide from the atmosphere for photosynthesis. With suitable growing conditions and nutrient availability diatoms produce large amounts of lipids. Lipids can form up to 75–80% of their mass. The biomass of a population of diatoms can double in a few hours. Lipids can be removed and turned into biofuel to be used in place of fossil fuels such as oil, coal and natural gas. Diatoms require silicates as an essential nutrient to make parts of their cells. Some land plants also use silicates to make their cells. Other land plants use cellulose to make their cells. Land plants that need silicates only use 8% of the energy to make their cells compared to plants that use cellulose. Scientists believe diatoms may have similar energy requirements to land plants that use silicates. (i) State the word equation for photosynthesis. … … [2] (ii) Describe the chemical structure of lipids. … … … … [2] (iii) Suggest two ways that silicates are replenished into surface waters. 1 … … 2 … … [2] (iv) Evaluate the statement: Scientists believe diatoms may have similar energy requirements to land plants that use silicates. … … … … [2] (v) State two services that diatoms provide to the environment. 1 … 2 … [2] (c) Fig. 2.2 shows a food web containing diatoms. shark 19.0 a.u. tuna 201 a.u. herring anchovy 2110 a.u. crab larvae copepods fish larvae (zooplankton) 19 900 a.u. diatoms 136 000 a.u. Fig. 2.2 (i) State the name of a tertiary consumer found in Fig. 2.2. … [1] (ii) The energy held in each trophic level for one food chain is shown in arbitrary units (a.u.) in the food web. Construct a pyramid of energy for this food chain. Label the pyramid of energy. [3] (iii) The energy transfer efficiency is the percentage of energy held in one trophic level that is passed onto the next. Calculate the energy transfer efficiency from diatoms to fish larvae. Give your answer to an appropriate number of significant figures. Show your working. … % [3] (iv) The energy transfer efficiency from tuna to shark is 9.45%. Explain reasons why the energy transfer efficiency calculated in (c)(iii) differs from the energy transfer efficiency from tuna to shark. … … … … … … [3] (v) Suggest the impact on the pyramid of energy from (c)(ii) if the quantity of silicates in the ocean is reduced. … … [1] [Total: 25]

25 marks

Mark scheme: 2(a) outline is an oval shape (single unbroken line, no sketchy lines) ; 4 size (larger than the diagram) ; detail (central groove running lengthwise, with break in the middle, 2 rows white spots, two outer rows of white structures evenly distributed with clear gap to outer edge of diatom) ; proportions of their included details (relative sizes of groove, spots and / two outer rows of white structures) ; 2(b)(i) carbon dioxide + water ; 2 → glucose + oxygen ; 2(b)(ii) any 2 from: 2 all contain carbon / C + oxygen / O + hydrogen / H ; (many are formed from) fatty acids and glycerol ; AVP ;; 2(b)(iii) any 2 from: 2 decomposition / decay ; upwelling ; run-off ; 2(b)(iv) any 2 from: 2 both types of organisms have silica parts (of cell), so may be justified in statement ; no scientific data / investigations to support this ; land and sea organisms may be from different kingdoms / phyla / domains ; different habitats / temperature differences ; (link to MP3 or 4) so energy requirements may differ ; 2(b)(v) any 2 from: 2 absorb carbon dioxide ; climate control ; release oxygen ; maintain stable, ecosystems / food web ; provide food source ; 2(c)(i) tuna OR shark ; 1 2(c)(ii) 5 rectangular closed bars ; 3 correct relative proportions from base to top + approx. the same height ; correctly labelled with named organisms from food chain ; 2(c)(iii) 19 900 3  100 ; 136 000 14.6 OR 14.63 ;; 2(c)(iv) any 3 from: 3 diatoms to fish larvae more efficient / ORA ; sharks are, more active / faster / longer distance, swimmers than fish larvae / ORA ; (which) increases energy use ; (lost) through heat / movement / respiration ; (lost) through egestion / parts uneaten or undigested ; 2(c)(v) any 1 from: 1 all boxes would (eventually) reduce in size ; size of diatom box would reduce first ;

This question in 9693/21 Oct/Nov 2022

1 A student was given water samples from three different environments to compare. They tested the pH of the samples. (a) State two ways of measuring pH. 1 … 2 … [2] (b) The student measured the pH using two different methods. Table 1.1 shows the results. Table 1.1 pH water sample method 1 method 2 J 8.2 8.0 K 3.6 4.0 L 7.6 7.0 (i) Suggest why the student did not calculate the mean of the two methods for each sample. … … [1] Dissolved nutrients affect the pH of water. (ii) Identify which sample, J, K, or L, came from near a hydrothermal vent. … [1] (iii) Explain your answer from (ii) for the sample from the hydrothermal vent. … … … … [2] (c) Explain why the dissolved oxygen level in surface open ocean water is higher than in water near a hydrothermal vent. … … … … … … [4] [Total: 10]

10 marks

Mark scheme: Question Answer Marks 1(a) pH meter / probe ; 2 universal indicator ; 1(b)(i) any 1 from: 1 they were measured to different degrees of accuracy ; means should only be calculated when results are measured using the same method / apparatus ; 1(b)(ii) K ; 1 1(b)(iii) any 2 from: 2 water coming from hydrothermal vents has (a high concentration of) dissolved nutrient(s) / minerals / named correct chemical / ions ; which makes the water (very) acidic / pH goes below 7 ; 1(c) any 4 from: 4 light present (in surface water) ; presence of photosynthetic organisms (in surface water) ; (photosynthesis / producers) releasing oxygen (in surface water) ; atmospheric dissolution (in surface water) ; wave action increases oxygen dissolving (in surface water) ; low mixing with higher layers containing oxygen (at hydrothermal vent) ; correct ref. solubility of oxygen at different temps / OWTTE ; organisms respiring oxygen (at hydrothermal vent) ; higher pressure so solubility lower (at hydrothermal vent) ; correct ref. to solubility of oxygen at different salinities / OWTTE ;

This question in 9693/22 Oct/Nov 2022

2 Fig. 2.1 shows a high magnification image of a diatom. pores Fig. 2.1 (a) Make a large drawing of the diatom shown in Fig. 2.1. Include features, but do not include the pores. Do not label the drawing. [4] (b) Diatoms are a possible source of biofuel. Diatoms absorb carbon dioxide from the atmosphere for photosynthesis. With suitable growing conditions and nutrient availability diatoms produce large amounts of lipids. Lipids can form up to 75–80% of their mass. The biomass of a population of diatoms can double in a few hours. Lipids can be removed and turned into biofuel to be used in place of fossil fuels such as oil, coal and natural gas. Diatoms require silicates as an essential nutrient to make parts of their cells. Some land plants also use silicates to make their cells. Other land plants use cellulose to make their cells. Land plants that need silicates only use 8% of the energy to make their cells compared to plants that use cellulose. Scientists believe diatoms may have similar energy requirements to land plants that use silicates. (i) State the word equation for photosynthesis. … … [2] (ii) Describe the chemical structure of lipids. … … … … [2] (iii) Suggest two ways that silicates are replenished into surface waters. 1 … … 2 … … [2] (iv) Evaluate the statement: Scientists believe diatoms may have similar energy requirements to land plants that use silicates. … … … … [2] (v) State two services that diatoms provide to the environment. 1 … 2 … [2] (c) Fig. 2.2 shows a food web containing diatoms. shark 19.0 a.u. tuna 201 a.u. herring anchovy 2110 a.u. crab larvae copepods fish larvae (zooplankton) 19 900 a.u. diatoms 136 000 a.u. Fig. 2.2 (i) State the name of a tertiary consumer found in Fig. 2.2. … [1] (ii) The energy held in each trophic level for one food chain is shown in arbitrary units (a.u.) in the food web. Construct a pyramid of energy for this food chain. Label the pyramid of energy. [3] (iii) The energy transfer efficiency is the percentage of energy held in one trophic level that is passed onto the next. Calculate the energy transfer efficiency from diatoms to fish larvae. Give your answer to an appropriate number of significant figures. Show your working. … % [3] (iv) The energy transfer efficiency from tuna to shark is 9.45%. Explain reasons why the energy transfer efficiency calculated in (c)(iii) differs from the energy transfer efficiency from tuna to shark. … … … … … … [3] (v) Suggest the impact on the pyramid of energy from (c)(ii) if the quantity of silicates in the ocean is reduced. … … [1] [Total: 25]

25 marks

Mark scheme: 2(a) outline is an oval shape (single unbroken line, no sketchy lines) ; 4 size (larger than the diagram) ; detail (central groove running lengthwise, with break in the middle, 2 rows white spots, two outer rows of white structures evenly distributed with clear gap to outer edge of diatom) ; proportions of their included details (relative sizes of groove, spots and / two outer rows of white structures) ; 2(b)(i) carbon dioxide + water ; 2 → glucose + oxygen ; 2(b)(ii) any 2 from: 2 all contain carbon / C + oxygen / O + hydrogen / H ; (many are formed from) fatty acids and glycerol ; AVP ;; 2(b)(iii) any 2 from: 2 decomposition / decay ; upwelling ; run-off ; 2(b)(iv) any 2 from: 2 both types of organisms have silica parts (of cell), so may be justified in statement ; no scientific data / investigations to support this ; land and sea organisms may be from different kingdoms / phyla / domains ; different habitats / temperature differences ; (link to MP3 or 4) so energy requirements may differ ; 2(b)(v) any 2 from: 2 absorb carbon dioxide ; climate control ; release oxygen ; maintain stable, ecosystems / food web ; provide food source ; 2(c)(i) tuna OR shark ; 1 2(c)(ii) 5 rectangular closed bars ; 3 correct relative proportions from base to top + approx. the same height ; correctly labelled with named organisms from food chain ; 2(c)(iii) 19 900 3  100 ; 136 000 14.6 OR 14.63 ;; 2(c)(iv) any 3 from: 3 diatoms to fish larvae more efficient / ORA ; sharks are, more active / faster / longer distance, swimmers than fish larvae / ORA ; (which) increases energy use ; (lost) through heat / movement / respiration ; (lost) through egestion / parts uneaten or undigested ; 2(c)(v) any 1 from: 1 all boxes would (eventually) reduce in size ; size of diatom box would reduce first ;

This question in 9693/22 Oct/Nov 2022

1 A student was given water samples from three different environments to compare. They tested the pH of the samples. (a) State two ways of measuring pH. 1 … 2 … [2] (b) The student measured the pH using two different methods. Table 1.1 shows the results. Table 1.1 pH water sample method 1 method 2 J 8.2 8.0 K 3.6 4.0 L 7.6 7.0 (i) Suggest why the student did not calculate the mean of the two methods for each sample. … … [1] Dissolved nutrients affect the pH of water. (ii) Identify which sample, J, K, or L, came from near a hydrothermal vent. … [1] (iii) Explain your answer from (ii) for the sample from the hydrothermal vent. … … … … [2] (c) Explain why the dissolved oxygen level in surface open ocean water is higher than in water near a hydrothermal vent. … … … … … … [4] [Total: 10]

10 marks

Mark scheme: Question Answer Marks 1(a) pH meter / probe ; 2 universal indicator ; 1(b)(i) any 1 from: 1 they were measured to different degrees of accuracy ; means should only be calculated when results are measured using the same method / apparatus ; 1(b)(ii) K ; 1 1(b)(iii) any 2 from: 2 water coming from hydrothermal vents has (a high concentration of) dissolved nutrient(s) / minerals / named correct chemical / ions ; which makes the water (very) acidic / pH goes below 7 ; 1(c) any 4 from: 4 light present (in surface water) ; presence of photosynthetic organisms (in surface water) ; (photosynthesis / producers) releasing oxygen (in surface water) ; atmospheric dissolution (in surface water) ; wave action increases oxygen dissolving (in surface water) ; low mixing with higher layers containing oxygen (at hydrothermal vent) ; correct ref. solubility of oxygen at different temps / OWTTE ; organisms respiring oxygen (at hydrothermal vent) ; higher pressure so solubility lower (at hydrothermal vent) ; correct ref. to solubility of oxygen at different salinities / OWTTE ;

This question in 9693/23 Oct/Nov 2022

2 Fig. 2.1 shows a high magnification image of a diatom. pores Fig. 2.1 (a) Make a large drawing of the diatom shown in Fig. 2.1. Include features, but do not include the pores. Do not label the drawing. [4] (b) Diatoms are a possible source of biofuel. Diatoms absorb carbon dioxide from the atmosphere for photosynthesis. With suitable growing conditions and nutrient availability diatoms produce large amounts of lipids. Lipids can form up to 75–80% of their mass. The biomass of a population of diatoms can double in a few hours. Lipids can be removed and turned into biofuel to be used in place of fossil fuels such as oil, coal and natural gas. Diatoms require silicates as an essential nutrient to make parts of their cells. Some land plants also use silicates to make their cells. Other land plants use cellulose to make their cells. Land plants that need silicates only use 8% of the energy to make their cells compared to plants that use cellulose. Scientists believe diatoms may have similar energy requirements to land plants that use silicates. (i) State the word equation for photosynthesis. … … [2] (ii) Describe the chemical structure of lipids. … … … … [2] (iii) Suggest two ways that silicates are replenished into surface waters. 1 … … 2 … … [2] (iv) Evaluate the statement: Scientists believe diatoms may have similar energy requirements to land plants that use silicates. … … … … [2] (v) State two services that diatoms provide to the environment. 1 … 2 … [2] (c) Fig. 2.2 shows a food web containing diatoms. shark 19.0 a.u. tuna 201 a.u. herring anchovy 2110 a.u. crab larvae copepods fish larvae (zooplankton) 19 900 a.u. diatoms 136 000 a.u. Fig. 2.2 (i) State the name of a tertiary consumer found in Fig. 2.2. … [1] (ii) The energy held in each trophic level for one food chain is shown in arbitrary units (a.u.) in the food web. Construct a pyramid of energy for this food chain. Label the pyramid of energy. [3] (iii) The energy transfer efficiency is the percentage of energy held in one trophic level that is passed onto the next. Calculate the energy transfer efficiency from diatoms to fish larvae. Give your answer to an appropriate number of significant figures. Show your working. … % [3] (iv) The energy transfer efficiency from tuna to shark is 9.45%. Explain reasons why the energy transfer efficiency calculated in (c)(iii) differs from the energy transfer efficiency from tuna to shark. … … … … … … [3] (v) Suggest the impact on the pyramid of energy from (c)(ii) if the quantity of silicates in the ocean is reduced. … … [1] [Total: 25]

25 marks

Mark scheme: 2(a) outline is an oval shape (single unbroken line, no sketchy lines) ; 4 size (larger than the diagram) ; detail (central groove running lengthwise, with break in the middle, 2 rows white spots, two outer rows of white structures evenly distributed with clear gap to outer edge of diatom) ; proportions of their included details (relative sizes of groove, spots and / two outer rows of white structures) ; 2(b)(i) carbon dioxide + water ; 2 → glucose + oxygen ; 2(b)(ii) any 2 from: 2 all contain carbon / C + oxygen / O + hydrogen / H ; (many are formed from) fatty acids and glycerol ; AVP ;; 2(b)(iii) any 2 from: 2 decomposition / decay ; upwelling ; run-off ; 2(b)(iv) any 2 from: 2 both types of organisms have silica parts (of cell), so may be justified in statement ; no scientific data / investigations to support this ; land and sea organisms may be from different kingdoms / phyla / domains ; different habitats / temperature differences ; (link to MP3 or 4) so energy requirements may differ ; 2(b)(v) any 2 from: 2 absorb carbon dioxide ; climate control ; release oxygen ; maintain stable, ecosystems / food web ; provide food source ; 2(c)(i) tuna OR shark ; 1 2(c)(ii) 5 rectangular closed bars ; 3 correct relative proportions from base to top + approx. the same height ; correctly labelled with named organisms from food chain ; 2(c)(iii) 19 900 3  100 ; 136 000 14.6 OR 14.63 ;; 2(c)(iv) any 3 from: 3 diatoms to fish larvae more efficient / ORA ; sharks are, more active / faster / longer distance, swimmers than fish larvae / ORA ; (which) increases energy use ; (lost) through heat / movement / respiration ; (lost) through egestion / parts uneaten or undigested ; 2(c)(v) any 1 from: 1 all boxes would (eventually) reduce in size ; size of diatom box would reduce first ;

This question in 9693/23 Oct/Nov 2022

1 Fig. 1.1 shows the shell of a common dogwhelk, Nucella lapillus, which is adapted to live on rocky shores. Fig. 1.1 (a) State a mineral that is required for the formation of shells. … [1] (b) Make a large drawing of the shell shown in Fig. 1.1. Do not label your drawing. [4] (c) Dogwhelks use a large muscular foot to cling to the rocks on rocky shores. A scientist investigated the shape of dogwhelk shells on different shore types. They analysed dogwhelks from an exposed rocky shore with high wave action, and a sheltered rocky shore with low wave action. 100 dogwhelks from each shore were sampled, and the following measurements were recorded: • total shell length • shell aperture length. Fig. 1.2 shows how these measurements were recorded. total shell length shell aperture length Fig. 1.2 Table 1.1 shows the mean results of the investigation. Table 1.1 shore type mean total shell length / mm mean shell aperture length / mm exposed rocky shore 24.6 12.5 sheltered rocky shore 26.1 11.9 (i) Describe how the mean total shell lengths were calculated. … … [1] (ii) The scientist calculated the ratio of mean total shell length : mean shell aperture length for the dogwhelks on each shore. Complete Table 1.2 by calculating the ratio for the sheltered rocky shore. Table 1.2 shore type ratio of mean total shell length : mean shell aperture length exposed rocky shore 1.97 : 1 sheltered rocky shore [1] (iii) Compare the shapes of dogwhelk shells on each shore type, using data from Table 1.1 and Table 1.2. Suggest reasons for any differences. … … … … … … … … [4] (d) During the investigation the scientist noticed that the dogwhelks showed variation in the colour of their shells, some being darker than others. The scientist also noticed that the darker‑shelled individuals were located in more shaded parts of the rocky shore. They suggested the following hypothesis: ‘Lighter-shelled dogwhelks can tolerate higher exposure to sunlight.’ A further investigation was then carried out. Light and dark dogwhelks on an area of shore were all marked with a small spot of paint on the shell. The paint fades on exposure to sunlight. After three days the degree of fading was recorded, using a score of 1 to 10. Table 1.3 shows the results. Table 1.3 paint fading score number of lighter-shelled number of darker-shelled dogwhelks dogwhelks 1 (least faded) 0 0 2 5 4 3 33 34 4 58 14 5 40 11 6 30 7 7 8 3 8 22 5 9 2 0 10 (most faded) 4 0 Discuss whether the results in Table 1.3 support the scientist’s hypothesis. … … … … … … [3] (e) Suggest one way the scientist ensured their methods were ethical. … … [1] [Total: 15]

15 marks

Mark scheme: 1(a) calcium ; 1 1(b) clear outline ; suitable size ; in proportion ; detail ; 4 1(c)(i) add together all shell lengths (for one / each shore) AND divide by 100 ; 1 1(c)(ii) 2.19 : 1 ; 1 1(c)(iii) any 4 of: length : aperture ratio lower on exposed shore / ORA ; shell aperture is larger (relative to length) on exposed shore / ORA ; larger foot ; stronger attachment to rock ; increases, survival chance / ability to stay attached, with stronger wave action ; (mean) shell length greater on sheltered shore / ORA ; because dogwhelks have higher life expectancy so grow bigger ; feeding efficiency greater on sheltered shore ; 4 Question Answer Marks 1(d) any 3 of: (yes because…) more light-shelled dogwhelks with a higher paint fading score / ORA ; suggesting they spent more time exposed to the Sun / ORA ; (no because) peak numbers are very close together ; sample size of dark-shelled dogwhelks much smaller / less than half ; ref. to limited scope of investigation e.g. one area / small numbers / only ; 3 days ; other factor may affect fading of paint e.g. saltwater ; idea of, correlation not causation / a different factor may be involved ; 3 1(e) any 1 of: taking care not to damage dogwhelks / other shore organisms ; taking care to, replace dogwhelks in same place / allow dogwhelks to reattach properly ; using a paint that does not harm the dogwhelks / environment ; 1

This question in 9693/22 May/June 2023

1 Fig. 1.1 shows the shell of a common dogwhelk, Nucella lapillus, which is adapted to live on rocky shores. Fig. 1.1 (a) State a mineral that is required for the formation of shells. … [1] (b) Make a large drawing of the shell shown in Fig. 1.1. Do not label your drawing. [4] (c) Dogwhelks use a large muscular foot to cling to the rocks on rocky shores. A scientist investigated the shape of dogwhelk shells on different shore types. They analysed dogwhelks from an exposed rocky shore with high wave action, and a sheltered rocky shore with low wave action. 100 dogwhelks from each shore were sampled, and the following measurements were recorded: • total shell length • shell aperture length. Fig. 1.2 shows how these measurements were recorded. total shell length shell aperture length Fig. 1.2 Table 1.1 shows the mean results of the investigation. Table 1.1 shore type mean total shell length / mm mean shell aperture length / mm exposed rocky shore 24.6 12.5 sheltered rocky shore 26.1 11.9 (i) Describe how the mean total shell lengths were calculated. … … [1] (ii) The scientist calculated the ratio of mean total shell length : mean shell aperture length for the dogwhelks on each shore. Complete Table 1.2 by calculating the ratio for the sheltered rocky shore. Table 1.2 shore type ratio of mean total shell length : mean shell aperture length exposed rocky shore 1.97 : 1 sheltered rocky shore [1] (iii) Compare the shapes of dogwhelk shells on each shore type, using data from Table 1.1 and Table 1.2. Suggest reasons for any differences. … … … … … … … … [4] (d) During the investigation the scientist noticed that the dogwhelks showed variation in the colour of their shells, some being darker than others. The scientist also noticed that the darker‑shelled individuals were located in more shaded parts of the rocky shore. They suggested the following hypothesis: ‘Lighter-shelled dogwhelks can tolerate higher exposure to sunlight.’ A further investigation was then carried out. Light and dark dogwhelks on an area of shore were all marked with a small spot of paint on the shell. The paint fades on exposure to sunlight. After three days the degree of fading was recorded, using a score of 1 to 10. Table 1.3 shows the results. Table 1.3 paint fading score number of lighter-shelled number of darker-shelled dogwhelks dogwhelks 1 (least faded) 0 0 2 5 4 3 33 34 4 58 14 5 40 11 6 30 7 7 8 3 8 22 5 9 2 0 10 (most faded) 4 0 Discuss whether the results in Table 1.3 support the scientist’s hypothesis. … … … … … … [3] (e) Suggest one way the scientist ensured their methods were ethical. … … [1] [Total: 15]

15 marks

Mark scheme: 1(a) calcium ; 1 1(b) clear outline ; suitable size ; in proportion ; detail ; 4 1(c)(i) add together all shell lengths (for one / each shore) AND divide by 100 ; 1 1(c)(ii) 2.19 : 1 ; 1 1(c)(iii) any 4 of: length : aperture ratio lower on exposed shore / ORA ; shell aperture is larger (relative to length) on exposed shore / ORA ; larger foot ; stronger attachment to rock ; increases, survival chance / ability to stay attached, with stronger wave action ; (mean) shell length greater on sheltered shore / ORA ; because dogwhelks have higher life expectancy so grow bigger ; feeding efficiency greater on sheltered shore ; 4 Question Answer Marks 1(d) any 3 of: (yes because…) more light-shelled dogwhelks with a higher paint fading score / ORA ; suggesting they spent more time exposed to the Sun / ORA ; (no because) peak numbers are very close together ; sample size of dark-shelled dogwhelks much smaller / less than half ; ref. to limited scope of investigation e.g. one area / small numbers / only ; 3 days ; other factor may affect fading of paint e.g. saltwater ; idea of, correlation not causation / a different factor may be involved ; 3 1(e) any 1 of: taking care not to damage dogwhelks / other shore organisms ; taking care to, replace dogwhelks in same place / allow dogwhelks to reattach properly ; using a paint that does not harm the dogwhelks / environment ; 1

This question in 9693/23 May/June 2023

5 (a) Magnesium sulfate and sodium chloride are examples of solutes. (i) Define the term solute. … … [1] (ii) State the chemical formulae for magnesium sulfate and sodium chloride. magnesium sulfate … sodium chloride … [1] A student investigated the solubility of magnesium sulfate and sodium chloride in water at different temperatures. (b) (i) Describe how the student could determine the solubility of each salt in water. … … … … [2] Fig. 5.1 shows the student’s results. 500 magnesium sulfate 400 sodium chloride solubility 300/ g dm–3 200 100 0 5 10 15 20 25 30 35 water temperature / °C Fig. 5.1 Table 5.1 shows the ocean surface temperature at a location in the Atlantic Ocean and at a location in the Indian Ocean. Table 5.1 ocean location ocean surface temperature / °C Atlantic Ocean 8 Indian Ocean 27 (ii) Use the results in Fig. 5.1 and the information in Table 5.1 to compare the solubilities of magnesium sulfate and sodium chloride at the two ocean locations. … … … … … … [3] (c) Hydrothermal vents are usually found along plate boundaries close to mid-ocean ridges. (i) State the type of plate boundary found at mid-ocean ridges. … [1] The water coming out of these hydrothermal vents is usually under pressure, at a high temperature and contains a high concentration of dissolved salts. (ii) Explain how chimneys form at hydrothermal vents. Use the trends shown in Fig. 5.1 and your own knowledge in your answer. … … … … … … [3]

11 marks

Mark scheme: 5(a)(i) a substance / chemical, that dissolves in a solvent ; 1 5(a)(ii) MgSO4 AND NaCl ; 1 5(b)(i) use a known volume of water ; determine mass of salt that dissolves ; 2 Question Answer Marks 5(b)(ii) any 3 from: 1 The Atlantic Ocean is colder than the Indian Ocean ORA ; 2 Magnesium sulphate is more soluble (than sodium chloride), in the Indian Ocean / at 27 °C ORA ; 3 both sodium chloride and magnesium sulphate are more soluble in the Indian ocean / at 27 °C ORA ; 4 Sodium chloride is more soluble than magnesium sulphate, in the Atlantic Ocean / 8 °C ORA ; 5 There is a greater difference in the solubility between magnesium sulphate and sodium chloride in the Atlantic Ocean (compared to the Indian Ocean) ORA ; 6 comparing manipulated data ; ; 3 5(c)(i) divergent / constructive ; 1 5(c)(ii) solubility of, salts / minerals, higher at high temperature / minerals dissolve in the water as it’s heated ; sudden cooling reduces solubility ; idea of cold (water) causing, salts / minerals, deposited / precipitate / build up / settle around the (vent)(to form chimney) ; 3 5(d)(i) 117–55 ; 62 (cm per year) ; 2 5(d)(ii) ppt ; 1 5(d)(iii) 1.8 (ppt) ; 1 5(d)(iv) salinity at 50 °N is lower than 30 °S ORA ; at 50 °N precipitation is (much) greater (than evaporation) ORA for 30 °S OR at 30 °S precipitation is (much) lower (than evaporation) ORA for 50 °N ; 2

This question in 9693/21 May/June 2024

2 Nitrate ions (NO3–) are a source of nitrogen for marine producers such as seagrass. (a) Define the term ion. … … [1] (b) A student designed an experiment to investigate the relationship between the concentration of nitrate ions in sea water and the growth of seagrass. The student was provided with a solution of nitrate ions at a concentration of 40 µmol dm–3. Fig. 2.1 shows the equipment the student used. lamp large glass cylinder containing sea water metre ruler seagrass sediment Fig. 2.1 (i) Suggest how the student used the equipment shown in Fig. 2.1 to investigate the growth of seagrass at different concentrations of nitrate ions. … … … … … … … … … … [5] (ii) Draw a table that could be used to record the results from the investigation in (b)(i). Include a suitable unit for the dependent variable. Do not write in any results. [2] (iii) Predict the relationship you would expect to find between nitrate ion concentration and growth rate of seagrass. … … [1] (c) State two uses of nitrogen for producers such as seagrass. 1 … … 2 … … [2] (d) Fig. 2.2 shows a pair of pipefish. Seagrasses provide pipefish with food and are ideal breeding grounds. Fig. 2.2 Many pipefish species are in decline. A scientist investigated whether the survival of newborn pipefish depends on the prey species available. Three tanks containing seagrass were set up in controlled conditions and newborn pipefish were placed into each tank. Each tank contained different prey species: tank 1 – prey species R only tank 2 – prey species S only tank 3 – prey species R and S. The percentage of newborn pipefish surviving each day was monitored for seven days. Fig. 2.3 shows the results. 100 Key tank 3 – prey species R and S 90 tank 1 – prey species R only tank 2 – prey species S only 80 percentage 70of newborn pipefish 60surviving 50 40 0 1 2 3 4 5 6 7 time / days Fig. 2.3 (i) Suggest two biotic factors which would need to be standardised in this investigation. 1 … … 2 … … [2] (ii) The starting number of newborn pipefish in tank 2 was 150. Use Fig. 2.3 to calculate the number of newborn pipefish surviving after seven days. … [2] (iii) Give one conclusion that can be made from the results in Fig. 2.3. … … [1] (iv) Describe two limitations of the data collected in this investigation. 1 … … 2 … … [2] [Total: 18]

18 marks

Mark scheme: 2(a) particle that has gained or lost electron(s) /negative and positive charge ; 1 2(b)(i) any five from: 5 (independent variable) – idea of how to change nitrate concentration ; (suitable range) – at least 3 concentrations used ; (dependent variable) – idea of measuring change in height of seagrass ; idea of replicates / repeat at least twice and calculate, means / medians / control experiment (using only sea water) ; description of calculation of growth rate ; standardised variables ;; (MAX two marks from this list) • leave to grow for, suitable / fixed time • temperature of water • all other mineral ions in equal concentration • concentration of CO2 • from lamp OR position / distance of the lamp / light intensity • pH • similar starting height of seagrass • same species of seagrass • volume of water • depth / type / mass, of sediment 2(b)(ii) suitable column / row headings e.g. (nitrate) concentration AND growth (rate) / change in length of seagrass / change in 2 height of seagrass ; appropriate units for dependent variable in heading only ; 2(b)(iii) Idea of increase in nitrate concentration increases growth (rate) / ORA ; 1 2(c) any two from: 2 proteins or amino acids ; chlorophyll ; DNA ; AVP ; 2(d)(i) any two from: 2 species / sex, of pipefish used ; health of pipefish ; number of pipefish (in the tank) ; reference to the, number / age / size / density / population, of prey ; quantity / mass / species / age, of seagrass in each tank ; 2(d)(ii) 150 / 100  62 2 OR 62  150 / 100 OR 150  0.62 OR 62 / 100  150 93 ;; 1 mark for incorrect values of 61 or 63 but correct calculation 150 / 100  61 OR 61  150 / 100 = 92 150 / 100  63 OR 63  150 / 100 = 95 2(d)(iii) any one from: 1 highest survival rate seen with diet of both R and S together / pipefish survive the most when both prey species R and S are present / ORA ; prey species S cause the percentage to decrease most / species S has the lowest survival rate ; all survived for at least one day ; juvenile pipefish have greater survival rate with prey species R rather than prey species S ; idea of those with R in diet have higher survival ; 2(d)(iv) any two from: 2 only 1 species of pipefish investigated /only two prey species investigated ; only one tank (of pipefish) investigated for each diet / no repeats / only 1 trial ; differences in survival may be for other (unknown) reasons ; 7 days is too short a duration / not enough time for investigation / records only 7 days ; idea of tank environment is not representative of conditions in the sea ;

This question in 9693/21 May/June 2025

2 A student investigated the effect of salinity on the freezing point of water. They made a stock solution of water with a salinity of 40 ppt. The stock solution was used to make a range of solutions of lower salinity from 10 to 30 ppt. Distilled water was also used with a salinity of 0 ppt. Each solution and the distilled water were placed in a freezer with a temperature probe as shown in Fig. 2.1. The temperature probes were all connected to a data logger and the freezing point recorded. A data logger automatically records the temperature at regular intervals. data logger freezer temperature probe plastic container and lid 0 ppt 10 ppt 20 ppt 30 ppt 40 ppt Fig. 2.1 (a) (i) Explain why the student used plastic containers rather than glass. … … … … [2] (ii) State a method to make the stock solution with a salinity of 40 ppt. … … … … [2] (iii) Describe how to use the stock solution to make 500 cm3 of solution with a salinity of 20 ppt. … … … … [2] (b) Table 2.1 shows the results from the investigation. Table 2.1 salinity of solution / ppt freezing point / °C 0 0.00 10 –0.56 20 –1.18 30 –1.80 40 –2.35 (i) Use the data in Table 2.1 to plot a line graph showing the relationship between the salinity of solution and the freezing point. … 0 0 … [4] (ii) Use the graph to predict the freezing point of water with a salinity of 35 ppt. … [1] (c) Explain why the salinity of sea water may decrease. … … … … [2] (d) The student investigated how salinity affected the pH of the five salinities of water. Explain the advantage of using a pH probe rather than Universal Indicator to obtain the results. … … … … [2] [Total: 15]

15 marks

Mark scheme: 2(a)(i) water expanding as it freezes (due to hydrogen bonding) ; 2 reference to hazard of broken glass / plastic is flexible ; 2(a)(ii) stated mass of salt / sodium chloride ; 2 dissolved in stated volume of water ; 2(a)(iii) add known volume of stock solution to measuring cylinder ; 2 top up with distilled water to correct stated volume ; 2(b)(i) both axes labelled with units ; 4 suitable linear scale ; points, plotted correctly  ½ small square (including 0,0) ; suitable line ; 2(b)(ii) correct reading from their plotted graph ; 1 2(c) addition of fresh water ; 2 plus any one from: from precipitation / rain ; from run-off ; 2(d)(i) Universal Indicator is not sensitive enough to distinguish differences ; 2 pH probe is more precise ;

This question in 9693/23 Oct/Nov 2025