Photosynthesis — Paper 2 · A Level Marine Science 9693

3 (a) Mutualism and parasitism are two examples of interrelationships between species. Describe each of these types of interrelationships, with reference to specific marine examples. … … … … … … … … … … … … … … … … [8] (b) (i) Coral reefs are areas with high productivity. Explain the meaning of the term productivity. … … … … [2] (ii) Suggest reasons why coral reefs have a high productivity. … … … … … … … … … … [5] [Total: 15]

15 marks

Mark scheme: 3(a) both are types of a symbiotic relationship ; (mutualism) both species benefit ; (parasitism) 1 species benefits at expense of other ; use term host appropriately ; mutualism named pair of species ; Only credit examples if they are mutualism – if in doubt, look it up. For example, whale and barnacle is NOT mutualism. benefit to species 1 ; benefit to species 2 ; parasitism example of host and parasite ; description of the benefit to parasite ; description of the harm to host ; 8 Question Answer Marks Guidance 3(b)(i) rate ; at which, organic material / biomass is produced / increases ; 2 R idea of energy production 3(b)(ii) Any 5 of: 1 clear water / low turbidity ; 2 for, high light penetration ; 3 shallow water / being near surface ; 4 idea of, suitable temperature ; 5 for, enzymes ; 6 large amounts of sunlight / a lot of energy / high light intensity ; 7 idea of, fast rate of photosynthesis ; 8 by zooxanthellae / producer ; 9 it is, a stable / not extreme, environment ; 10 idea of, rapid / high, nutrient cycling / AW ; 5 I warm unqualified I photosynthesise easily

This question in 9693/21 May/June 2018

2 Tetraselmis is a single-celled phytoplankton, often cultured as a food source for the aquaculture of marine fish larvae. Tetraselmis is grown using a batch culture method. All the required nutrients and a small population of Tetraselmis are placed into a container and grown for several days. Carbon dioxide is continuously bubbled through the water and the light intensity is kept constant. Table 2.1 shows the mean cell density of Tetraselmis grown using a batch culture method over 10 days. Table 2.1 day mean cell density / cells per mm3 0 0 1 70 2 120 3 300 4 5 1400 6 1750 7 1900 8 2000 9 1800 10 1500 To obtain the data in Table 2.1, five samples of the culture were counted daily and a mean value was calculated. Table 2.2 shows the data for day 4. Table 2.2 sample number 1 2 3 4 5 cell density / cells per mm3 681 201 726 654 738 (a) (i) Calculate the mean cell density for day 4, using sample numbers 1, 3, 4 and 5. Give your answer to an appropriate number of significant figures. … cells per mm3 [1] (ii) Suggest why sample 2 was not used to calculate the mean cell density. … … [1] (c) (i) Use the results in Table 2.1 and your graph to suggest the day on which it would be best to harvest Tetraselmis. Give a reason for your answer. … … … … [2] (ii) Predict what would happen to the mean cell density, if the culture was continued to day 15. Explain your prediction. … … … … [2] (d) Name the process which phytoplankton use to transfer light energy to a form available to the rest of the food chain. … … [1] [Total: 11]

11 marks

This question in 9693/20 Oct/Nov 2019

2 Zostera marina is a species of seagrass. Macroalgae are seaweeds. Z. marina and macroalgae are producers that can grow in the same habitat. A scientist noticed that the distribution of Z. marina and macroalgae varied greatly within a single large estuary. Different areas of the estuary varied in their nitrogen input levels. The scientist measured the biomass of each producer and the nitrogen inputs in each area. Table 2.1 shows the biomass of the two producers for different nitrogen input levels. Table 2.1 nitrogen input biomass of biomass of /kg per hectare per year Z. marina macroalgae /g per m2 /g per m2 0 48 53 300 2 116 400 2 174 (a) Plot a bar chart to show the effect of nitrogen input on the biomass of Z. marina and macroalgae. [5] (b) A student developed the following hypothesis. Nitrogen input decreases the growth of Z. marina in the presence of macroalgae. Discuss the extent to which the data in Table 2.1 supports this hypothesis. … … … … … … [3] (c) Macroalgae and Z. marina are photosynthetic. Z. marina can grow to a height of 15 cm. Macroalgae can grow to a height of 175 cm. Use this information to explain why the biomass of Z. marina decreases in conditions of high nitrogen input, when growing in the presence of macroalgae. … … … … [2] [Total: 10]

10 marks

This question in 9693/20 Oct/Nov 2020

2 Fig. 2.1 shows some dinoflagellates, which are small photosynthetic organisms that float in the upper layers of the oceans. They migrate up and down the water column in response to changing environmental conditions. Fig. 2.1 (a) Describe a method for a laboratory-based investigation that tests the following hypothesis: Increasing light intensity causes dinoflagellates to migrate to the surface waters. … … … … … … … … … … … … … [5] (b) Suggest why dinoflagellates may benefit from their ability to migrate to the surface waters. … … … … [2] [Total: 7]

7 marks

Mark scheme: 2(a) any 5 from: (independent variable) description of changing light intensity ; range of three or more light intensity values ; (dependent variable) measuring dinoflagellate numbers near surface ; (control variables) any 2 from: water temperature / water salinity / water pH / nutrient content of water / volume of water / same species / initial distribution or concentration of dinoflagellates ; ; leave for suitable amount of time (at least one hour up to 48 hours) ; tanks of seawater containing dinoflagellates ; idea of repeats ; calculate mean ; 2(b) any 2 from: idea of increased, light intensity / availability of light ; increase their rate of photosynthesis near surface ; increased productivity / biomass production ; allows for increased rate of reproduction ; ref. to increased access to carbon dioxide near surface ; 2

This question in 9693/22 May/June 2021

2 Fig. 2.1 shows some dinoflagellates, which are small photosynthetic organisms that float in the upper layers of the oceans. They migrate up and down the water column in response to changing environmental conditions. Fig. 2.1 (a) Describe a method for a laboratory-based investigation that tests the following hypothesis: Increasing light intensity causes dinoflagellates to migrate to the surface waters. … … … … … … … … … … … … … [5] (b) Suggest why dinoflagellates may benefit from their ability to migrate to the surface waters. … … … … [2] [Total: 7]

7 marks

Mark scheme: 2(a) any 5 from: (independent variable) description of changing light intensity ; range of three or more light intensity values ; (dependent variable) measuring dinoflagellate numbers near surface ; (control variables) any 2 from: water temperature / water salinity / water pH / nutrient content of water / volume of water / same species / initial distribution or concentration of dinoflagellates ; ; leave for suitable amount of time (at least one hour up to 48 hours) ; tanks of seawater containing dinoflagellates ; idea of repeats ; calculate mean ; 2(b) any 2 from: idea of increased, light intensity / availability of light ; increase their rate of photosynthesis near surface ; increased productivity / biomass production ; allows for increased rate of reproduction ; ref. to increased access to carbon dioxide near surface ; 2

This question in 9693/23 May/June 2021

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

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

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 apparatus used to investigate the rate of photosynthesis. The distance of the lamp from the boiling tube can be altered, which changes the intensity of the light falling onto the aquatic plant. Oxygen released by the photosynthesising aquatic plant is collected by the gas syringe and the volume measured. boiling tube gas syringe lamp oxygen bubbles aquatic plant in sea water ruler Fig. 1.1 (a) (i) Identify the independent variable and dependent variable in this investigation. independent variable … … dependent variable … … [2] (ii) The temperature and nutrient content of the water was standardised. Suggest two other variables that should be standardised. 1 … … 2 … … [2] (b) Table 1.1 shows a set of results collected using the apparatus shown in Fig. 1.1. Table 1.1 distance of lamp volume of oxygen produced in 60 minutes / cm3 from boiling trial 1 trial 2 trial 3 mean tube / cm 10 7.0 7.3 7.3 7.2 20 6.2 5.7 5.8 5.9 30 4.6 4.9 4.6 4.7 40 3.5 3.5 3.5 3.5 50 2.8 2.9 3.0 2.9 60 2.5 2.2 2.5 2.4 (i) Name one additional piece of laboratory equipment needed to collect these results. … [1] (ii) Plot a graph showing the relationship between the distance of the lamp from the boiling tube and the mean volume of oxygen produced in 60 minutes. [4] (iii) Explain the relationship shown between the distance of the lamp from the boiling tube and the volume of oxygen produced in 60 minutes. … … … … … … [3] (c) In a further investigation, phytoplankton were placed in tanks containing either sea water that was enriched with nitrate ions, or sea water that was deficient in nitrate ions. Nitrate ions are a source of nitrogen for producers. Scientists measured the rate of photosynthesis in phytoplankton in nitrate-enriched and nitrate-deficient sea water. The investigation was repeated at a range of different temperatures. The results are shown in Fig. 1.2. 25 20 Key rate of 15 nitrate-enriched photosynthesis sea water / arbitrary units nitrate-deficient 10 sea water 5 0 0 5 10 15 20 25 30 temperature / °C Fig. 1.2 (i) Compare the effect of temperature on the rate of photosynthesis in nitrate-enriched and nitrate-deficient sea water. Use data from Fig. 1.2 to support your answer. … … … … … … [3] (ii) Explain why the productivity of the phytoplankton would be higher in nitrate-enriched sea water. … … … … [2] [Total: 17]

17 marks

Mark scheme: 1(a)(i) distance of tube from lamp / distance of the lamp / distance of lamp from the plant ; volume of, gas / oxygen, produced / collected / measured / released ; 2 1(a)(ii) any 2 of: concentration of carbon dioxide / hydrogencarbonate (in water) ; mass / surface area of, aquatic plant / chlorophyll OR number / size of leaves ; pH (of water) ; salinity (of water) ; wavelength of light / colour of light / background light intensity ; time spent / exposed to light / time volume of gas collected for ; volume of water ; 2 1(b)(i) timer / stop clock / stopwatch / watch / clock ; 1 1(b)(ii) both axes labelled with units ; suitable linear scale ; points, plotted correctly  ½ small square ; suitable line ; 4 Question Answer Marks 1(b)(iii) any 3 of: (volume of) oxygen / gas, produced decreases, as, lamp moves further away / there is less light, OR the closer the lamp to the plant is the more oxygen it releases OR negative correlation AW / ORA ; as, light intensity decreases ORA ; rate of photosynthesis decreases (with lower light intensity) ORA ; data manipulation / any data used must be correct ; 3 1(c)(i) 1 both treatments have an, optimum / peak / highest, temperature ; 2 nitrate enriched is, always higher rate / photosynthesis (rate), when photosynthesising than deficient water ; 3 (optimum rate) at 17 °C nitrate-deficient AND 20 °C nitrate-enriched ; 4 (optimum rate) at 13 arbitrary units (a.u.) nitrate-deficient AND 19 arbitrary units (a.u.) nitrate-enriched ; 5 both zero at 2 °C / both zero at 26–27 °C ; 6 correct data manipulation to show a comparison ; 3 1(c)(ii) any 2 of: increased rate of photosynthesis ; (nitrates) allow for increased synthesis of, proteins / DNA / amino acids ; allowing for increased, growth / rate of cell division / population / biomass ; 2

This question in 9693/21 May/June 2023

2 (a) Fig. 2.1 shows apparatus used to investigate the rate of photosynthesis in the laboratory. thermometer gas syringe aquatic plant lamp water glass beaker ruler Fig. 2.1 (i) Describe how the apparatus in Fig. 2.1 could be used to measure the rate of photosynthesis at different light intensities. … … … … … … … … … … [5] (ii) Draw a table that is suitable to record the results of this investigation. Include units where appropriate. Include full headings but do not write in any results. [2] (iii) Describe how the results are used to calculate the rate of photosynthesis. … … [1] (iv) Sketch on the axes the relationship between light intensity and rate of photosynthesis. Include labels for both axes. … … [2] (b) The kite diagram in Fig. 2.2 shows the distribution of three species of seaweed (X, Y, Z) on a rocky shore, from the mean high water mark (MHWM) to the mean low water mark (MLWM). The greater the height of the shaded area, the greater the abundance. MHWM distance down shore / m MLWM 0 10 20 30 40 50 60 70 80 90 100 110 120 species X species Y species Z Fig. 2.2 (i) Use Fig. 2.2 to compare the distribution and abundance of species X, Y and Z. … … … … … … [3] (ii) Suggest which species is best adapted for photosynthesis at lower light intensities. Explain your answer. … … … … [2] (iii) Suggest how species Z may be adapted to survive at the mean high water mark. Explain your answer. … … … … [2] [Total: 17]

17 marks

Mark scheme: 2(a)(i) any 5 of: (independent variable) description of changing distance of light source from beaker ; sensible suggested intervals for lamp e.g. every 10 cm ; (dependent variable) description of measuring volume of gas (in capillary tube) over a set time ; description of any two control variables (pH, temperature, quantity of aquatic plant, CO2 availability) ; ; description of repeats for each light intensity ; calculation of mean ; credit reference to trying to remove heating effect e.g. using Perspex screen ; time spent / exposed to light / time volume of gas collected for ; credit reference to ensuring sufficient CO2 ; credit safety consideration e.g. burn from lamp / electrical kit and water ; 5 2(a)(ii) table with columns headed ‘lamp distance from aquatic plant’ AND ‘volume of gas collected’ ; suitable units for both variables – cm / mm AND cm3 / mm3 / ml respectively ; 2 2(a)(iii) volume of oxygen / gas, divided by time taken ; 1 2(a)(iv) line showing rate increasing with increasing light intensity ; rate increasing and levelling off ; 2 Question Answer Marks 2(b)(i) any 3 of: species X has greatest abundance at / towards MLWM AND species Z has greatest abundance at / towards MHWM ; appropriate use of data from diagram e.g. species X only occurs from 80 m onwards / species Z only occurs down to 70 m ; species Y shows greatest distribution along the shore / only absent for first 10 m below MHWM ; no point on shore where all three species occur together ; comparison of relative abundance in same region of shore e.g. Z more abundant than Y between 10 and 40 m / Y more abundant than Z between 40 and 70 m ; AVP ; 3 2(b)(ii) species X as occurs further down shore ; (so) will spend longer submerged (in reduced light intensity) ; 2 2(b)(iii) spends greater amount of time exposed / uncovered by tide ; so must (be adapted to) prevent desiccation / dehydration ; 2

This question in 9693/22 May/June 2023

2 (a) Fig. 2.1 shows apparatus used to investigate the rate of photosynthesis in the laboratory. thermometer gas syringe aquatic plant lamp water glass beaker ruler Fig. 2.1 (i) Describe how the apparatus in Fig. 2.1 could be used to measure the rate of photosynthesis at different light intensities. … … … … … … … … … … [5] (ii) Draw a table that is suitable to record the results of this investigation. Include units where appropriate. Include full headings but do not write in any results. [2] (iii) Describe how the results are used to calculate the rate of photosynthesis. … … [1] (iv) Sketch on the axes the relationship between light intensity and rate of photosynthesis. Include labels for both axes. … … [2] (b) The kite diagram in Fig. 2.2 shows the distribution of three species of seaweed (X, Y, Z) on a rocky shore, from the mean high water mark (MHWM) to the mean low water mark (MLWM). The greater the height of the shaded area, the greater the abundance. MHWM distance down shore / m MLWM 0 10 20 30 40 50 60 70 80 90 100 110 120 species X species Y species Z Fig. 2.2 (i) Use Fig. 2.2 to compare the distribution and abundance of species X, Y and Z. … … … … … … [3] (ii) Suggest which species is best adapted for photosynthesis at lower light intensities. Explain your answer. … … … … [2] (iii) Suggest how species Z may be adapted to survive at the mean high water mark. Explain your answer. … … … … [2] [Total: 17]

17 marks

Mark scheme: 2(a)(i) any 5 of: (independent variable) description of changing distance of light source from beaker ; sensible suggested intervals for lamp e.g. every 10 cm ; (dependent variable) description of measuring volume of gas (in capillary tube) over a set time ; description of any two control variables (pH, temperature, quantity of aquatic plant, CO2 availability) ; ; description of repeats for each light intensity ; calculation of mean ; credit reference to trying to remove heating effect e.g. using Perspex screen ; time spent / exposed to light / time volume of gas collected for ; credit reference to ensuring sufficient CO2 ; credit safety consideration e.g. burn from lamp / electrical kit and water ; 5 2(a)(ii) table with columns headed ‘lamp distance from aquatic plant’ AND ‘volume of gas collected’ ; suitable units for both variables – cm / mm AND cm3 / mm3 / ml respectively ; 2 2(a)(iii) volume of oxygen / gas, divided by time taken ; 1 2(a)(iv) line showing rate increasing with increasing light intensity ; rate increasing and levelling off ; 2 Question Answer Marks 2(b)(i) any 3 of: species X has greatest abundance at / towards MLWM AND species Z has greatest abundance at / towards MHWM ; appropriate use of data from diagram e.g. species X only occurs from 80 m onwards / species Z only occurs down to 70 m ; species Y shows greatest distribution along the shore / only absent for first 10 m below MHWM ; no point on shore where all three species occur together ; comparison of relative abundance in same region of shore e.g. Z more abundant than Y between 10 and 40 m / Y more abundant than Z between 40 and 70 m ; AVP ; 3 2(b)(ii) species X as occurs further down shore ; (so) will spend longer submerged (in reduced light intensity) ; 2 2(b)(iii) spends greater amount of time exposed / uncovered by tide ; so must (be adapted to) prevent desiccation / dehydration ; 2

This question in 9693/23 May/June 2023

1 Mangrove forests are important ecosystems. (a) Explain the term ecosystem. … … … … [2] (b) Fig. 1.1 shows the area of mangrove forest in ten countries and the areas of mangrove forest that are protected and unprotected. Key protected mangrove forest unprotected mangrove forest 30 000 25 000 20 000 area of mangrove 15 000 forest / km2 10 000 5000 0 IndonesiaBrazilAustraliaMexicoNigeriaMalaysiaMyanmar GuineaBangladeshCuba New Papua countries Fig. 1.1 (i) State the name of the country which protects the greatest percentage of its mangrove forest. … [1] (ii) Calculate the percentage of mangrove forest in Mexico that is protected. Show your working. … % [2] (iii) State two major threats to mangrove forests. 1 … 2 … [2] (c) Some species of macroalgae grow attached to the roots of mangrove trees. Scientists planned an investigation to compare the rate of photosynthesis at different light intensities in two of these species of macroalgae. (i) State the word equation for photosynthesis. … [1] Fig. 1.2 shows their experimental set-up. This closed system is used to fully contain a standardised volume of water which is circulated. An oxygen sensor recorded oxygen concentration in the water. The whole apparatus was submerged into a much larger tank of sea water for the investigation. circulation pump sealed plastic dome macroalgae grid sealed plastic base dissolved oxygen sensor Fig. 1.2 (ii) Identify the dependent variable. … [1] (iii) Suggest two variables that should be standardised in this investigation. 1 … 2 … [1] (iv) Suggest how the light intensity was changed. … … [1] (v) The scientists allowed the macroalgae to photosynthesise for 8 minutes in the closed system. They then exchanged the water in the closed system with some of the water in the surrounding tank, before beginning to collect results. Suggest one reason the scientists exchanged the water. … … [1] Table 1.1 shows the results from the investigation. Table 1.1 light intensity oxygen production / μmol mm–2 min–1 / arbitrary units macroalgae species A macroalgae species B 50 650 210 350 1750 580 600 2410 1530 900 2950 3090 1200 2910 3310 (vi) Plot a graph of the two sets of data in Table 1.1 on the grid below and draw an appropriate line for each data set. Complete the axes for the graph. oxygen production / … … [5] (vii) The two species of macroalgae used in the investigation are found at different depths on the mangrove tree roots. Use Table 1.1 to explain the expected depth distribution of the two species of macroalgae on the mangrove tree roots. … … … … … … [3] (viii) At a light intensity of zero the oxygen level decreased during the investigation. Explain this observation. … … … … [2] [Total: 22]

22 marks

Mark scheme: Question Answer Marks 1(a) interactions between, different species / community / biotic factors ; 2 and their (physical), environment / habitat / abiotic factors ; 1(b)(i) Bangladesh ; 1 1(b)(ii) correct reading of two figures from graph ; 2 (protected area  total area)  100 = (value between) 61.34%–70.41% ; 1(b)(iii) any 2 from: 2 global warming / climate change / temperature change ; over-harvesting / deforestation ; storm damage ; change in land use or named example e.g. shrimp farms ; 1(c)(i) carbon dioxide + water → glucose + oxygen ; 1 1(c)(ii) oxygen concentration ; 1 1(c)(iii) any 2 from: 1 temperature (of water) / size, mass, length, of algae / salinity / carbon dioxide / water, type or quality / volume of water or water flow or flow rate (through system) / pH / initial oxygen concentration / colour of light or wavelength ; 1(c)(iv) lamp / light source, moved different distances (from the apparatus) ; 1 1(c)(v) any 1 from: 1 add additional carbon dioxide / remove built up oxygen ; to acclimatise the macroalgae to the conditions before collecting results OWTTE ; 1(c)(vi) both axes labelled with units ; 5 (suitable) linear scale ; points plotted  ½ small square with x or dot in circle ; appropriate lines drawn for both sets of data ; key to identify the 2 data sets ; 1(c)(vii) Any 3 from: 3 species B closer to the surface / species A, can extend to greater depth ; (as species B), require a higher light intensity to photosynthesise / higher rate of photosynthesis than A at shallow depths / lower rate of photosynthesis than A at lower light intensities ORA ; correct ref. to data comparison or manipulation (from their graph) ; the lines cross over at stated light intensity (from their graph) OR the same rate (of photosynthesis) at stated light intensity ; species B may be found at a narrower range of depths / ORA ; both species found near the surface / at high light intensities ; 1(c)(viii) no photosynthesis occurring (as no light) ; 2 respiration uses oxygen ;

This question in 9693/21 Oct/Nov 2023

1 Mangrove forests are important ecosystems. (a) Explain the term ecosystem. … … … … [2] (b) Fig. 1.1 shows the area of mangrove forest in ten countries and the areas of mangrove forest that are protected and unprotected. Key protected mangrove forest unprotected mangrove forest 30 000 25 000 20 000 area of mangrove 15 000 forest / km2 10 000 5000 0 IndonesiaBrazilAustraliaMexicoNigeriaMalaysiaMyanmar GuineaBangladeshCuba New Papua countries Fig. 1.1 (i) State the name of the country which protects the greatest percentage of its mangrove forest. … [1] (ii) Calculate the percentage of mangrove forest in Mexico that is protected. Show your working. … % [2] (iii) State two major threats to mangrove forests. 1 … 2 … [2] (c) Some species of macroalgae grow attached to the roots of mangrove trees. Scientists planned an investigation to compare the rate of photosynthesis at different light intensities in two of these species of macroalgae. (i) State the word equation for photosynthesis. … [1] Fig. 1.2 shows their experimental set-up. This closed system is used to fully contain a standardised volume of water which is circulated. An oxygen sensor recorded oxygen concentration in the water. The whole apparatus was submerged into a much larger tank of sea water for the investigation. circulation pump sealed plastic dome macroalgae grid sealed plastic base dissolved oxygen sensor Fig. 1.2 (ii) Identify the dependent variable. … [1] (iii) Suggest two variables that should be standardised in this investigation. 1 … 2 … [1] (iv) Suggest how the light intensity was changed. … … [1] (v) The scientists allowed the macroalgae to photosynthesise for 8 minutes in the closed system. They then exchanged the water in the closed system with some of the water in the surrounding tank, before beginning to collect results. Suggest one reason the scientists exchanged the water. … … [1] Table 1.1 shows the results from the investigation. Table 1.1 light intensity oxygen production / μmol mm–2 min–1 / arbitrary units macroalgae species A macroalgae species B 50 650 210 350 1750 580 600 2410 1530 900 2950 3090 1200 2910 3310 (vi) Plot a graph of the two sets of data in Table 1.1 on the grid below and draw an appropriate line for each data set. Complete the axes for the graph. oxygen production / … … [5] (vii) The two species of macroalgae used in the investigation are found at different depths on the mangrove tree roots. Use Table 1.1 to explain the expected depth distribution of the two species of macroalgae on the mangrove tree roots. … … … … … … [3] (viii) At a light intensity of zero the oxygen level decreased during the investigation. Explain this observation. … … … … [2] [Total: 22]

22 marks

Mark scheme: Question Answer Marks 1(a) interactions between, different species / community / biotic factors ; 2 and their (physical), environment / habitat / abiotic factors ; 1(b)(i) Bangladesh ; 1 1(b)(ii) correct reading of two figures from graph ; 2 (protected area  total area)  100 = (value between) 61.34%–70.41% ; 1(b)(iii) any 2 from: 2 global warming / climate change / temperature change ; over-harvesting / deforestation ; storm damage ; change in land use or named example e.g. shrimp farms ; 1(c)(i) carbon dioxide + water → glucose + oxygen ; 1 1(c)(ii) oxygen concentration ; 1 1(c)(iii) any 2 from: 1 temperature (of water) / size, mass, length, of algae / salinity / carbon dioxide / water, type or quality / volume of water or water flow or flow rate (through system) / pH / initial oxygen concentration / colour of light or wavelength ; 1(c)(iv) lamp / light source, moved different distances (from the apparatus) ; 1 1(c)(v) any 1 from: 1 add additional carbon dioxide / remove built up oxygen ; to acclimatise the macroalgae to the conditions before collecting results OWTTE ; 1(c)(vi) both axes labelled with units ; 5 (suitable) linear scale ; points plotted  ½ small square with x or dot in circle ; appropriate lines drawn for both sets of data ; key to identify the 2 data sets ; 1(c)(vii) Any 3 from: 3 species B closer to the surface / species A, can extend to greater depth ; (as species B), require a higher light intensity to photosynthesise / higher rate of photosynthesis than A at shallow depths / lower rate of photosynthesis than A at lower light intensities ORA ; correct ref. to data comparison or manipulation (from their graph) ; the lines cross over at stated light intensity (from their graph) OR the same rate (of photosynthesis) at stated light intensity ; species B may be found at a narrower range of depths / ORA ; both species found near the surface / at high light intensities ; 1(c)(viii) no photosynthesis occurring (as no light) ; 2 respiration uses oxygen ;

This question in 9693/22 Oct/Nov 2023

1 Mangrove forests are important ecosystems. (a) Explain the term ecosystem. … … … … [2] (b) Fig. 1.1 shows the area of mangrove forest in ten countries and the areas of mangrove forest that are protected and unprotected. Key protected mangrove forest unprotected mangrove forest 30 000 25 000 20 000 area of mangrove 15 000 forest / km2 10 000 5000 0 IndonesiaBrazilAustraliaMexicoNigeriaMalaysiaMyanmar GuineaBangladeshCuba New Papua countries Fig. 1.1 (i) State the name of the country which protects the greatest percentage of its mangrove forest. … [1] (ii) Calculate the percentage of mangrove forest in Mexico that is protected. Show your working. … % [2] (iii) State two major threats to mangrove forests. 1 … 2 … [2] (c) Some species of macroalgae grow attached to the roots of mangrove trees. Scientists planned an investigation to compare the rate of photosynthesis at different light intensities in two of these species of macroalgae. (i) State the word equation for photosynthesis. … [1] Fig. 1.2 shows their experimental set-up. This closed system is used to fully contain a standardised volume of water which is circulated. An oxygen sensor recorded oxygen concentration in the water. The whole apparatus was submerged into a much larger tank of sea water for the investigation. circulation pump sealed plastic dome macroalgae grid sealed plastic base dissolved oxygen sensor Fig. 1.2 (ii) Identify the dependent variable. … [1] (iii) Suggest two variables that should be standardised in this investigation. 1 … 2 … [1] (iv) Suggest how the light intensity was changed. … … [1] (v) The scientists allowed the macroalgae to photosynthesise for 8 minutes in the closed system. They then exchanged the water in the closed system with some of the water in the surrounding tank, before beginning to collect results. Suggest one reason the scientists exchanged the water. … … [1] Table 1.1 shows the results from the investigation. Table 1.1 light intensity oxygen production / μmol mm–2 min–1 / arbitrary units macroalgae species A macroalgae species B 50 650 210 350 1750 580 600 2410 1530 900 2950 3090 1200 2910 3310 (vi) Plot a graph of the two sets of data in Table 1.1 on the grid below and draw an appropriate line for each data set. Complete the axes for the graph. oxygen production / … … [5] (vii) The two species of macroalgae used in the investigation are found at different depths on the mangrove tree roots. Use Table 1.1 to explain the expected depth distribution of the two species of macroalgae on the mangrove tree roots. … … … … … … [3] (viii) At a light intensity of zero the oxygen level decreased during the investigation. Explain this observation. … … … … [2] [Total: 22]

22 marks

Mark scheme: Question Answer Marks 1(a) interactions between, different species / community / biotic factors ; 2 and their (physical), environment / habitat / abiotic factors ; 1(b)(i) Bangladesh ; 1 1(b)(ii) correct reading of two figures from graph ; 2 (protected area  total area)  100 = (value between) 61.34%–70.41% ; 1(b)(iii) any 2 from: 2 global warming / climate change / temperature change ; over-harvesting / deforestation ; storm damage ; change in land use or named example e.g. shrimp farms ; 1(c)(i) carbon dioxide + water → glucose + oxygen ; 1 1(c)(ii) oxygen concentration ; 1 1(c)(iii) any 2 from: 1 temperature (of water) / size, mass, length, of algae / salinity / carbon dioxide / water, type or quality / volume of water or water flow or flow rate (through system) / pH / initial oxygen concentration / colour of light or wavelength ; 1(c)(iv) lamp / light source, moved different distances (from the apparatus) ; 1 1(c)(v) any 1 from: 1 add additional carbon dioxide / remove built up oxygen ; to acclimatise the macroalgae to the conditions before collecting results OWTTE ; 1(c)(vi) both axes labelled with units ; 5 (suitable) linear scale ; points plotted  ½ small square with x or dot in circle ; appropriate lines drawn for both sets of data ; key to identify the 2 data sets ; 1(c)(vii) Any 3 from: 3 species B closer to the surface / species A, can extend to greater depth ; (as species B), require a higher light intensity to photosynthesise / higher rate of photosynthesis than A at shallow depths / lower rate of photosynthesis than A at lower light intensities ORA ; correct ref. to data comparison or manipulation (from their graph) ; the lines cross over at stated light intensity (from their graph) OR the same rate (of photosynthesis) at stated light intensity ; species B may be found at a narrower range of depths / ORA ; both species found near the surface / at high light intensities ; 1(c)(viii) no photosynthesis occurring (as no light) ; 2 respiration uses oxygen ;

This question in 9693/23 Oct/Nov 2023

2 A student investigated photosynthesis in three species of macroalga, P, Q and R. All three species can be found in the littoral zone of a rocky shore. (a) Define the term littoral zone. … … … … [2] (b) The student cut five discs from macroalga species P. The discs were then dropped into a beaker of sea water, as shown in Fig. 2.1, and placed at a low light intensity. The time taken for each disc to rise to the surface was recorded and the mean time calculated. The student repeated this procedure at increasing light intensities. beaker containing sea water disc rising to surface macroalga discs Fig. 2.1 (i) The student used the following table to record the results. light intensity / arbitrary units time taken for discs to rise to surface / s Suggest one improvement that could be made to this table of results. … … [1] (ii) In this investigation, the pH and the salinity of the sea water are examples of standardised variables. Suggest two other variables that need to be standardised during the investigation. 1 … … 2 … … [2] (iii) Suggest why the macroalga discs rise to the surface during this investigation. … … … … [2] (c) The investigation was repeated with macroalga species Q and R. Fig. 2.2 shows the results of the investigation. 240 Key species P species Q species R 180 mean time taken for 120discs to rise to surface / s 60 0 0 10 20 30 40 50 60 light intensity / arbitrary units Fig. 2.2 (i) Use Fig. 2.2 to suggest which species of macroalga is best adapted for living lower down the rocky shore. Explain your answer. … … … … … … [3] (ii) Use Fig. 2.2 to predict the expected mean time for discs to rise to the surface if the investigation was repeated with species Q at a light intensity of 60 arbitrary units. … s [1] [Total: 11]

11 marks

Mark scheme: 2(a) intertidal region of the, shore / shoreline ; idea of highest high tides and lowest low tides e.g. the highest and lowest, spring tides / spring tide marks ; 2 2(b)(i) any 1 from: ref. to repeats / multiple trials / more trials ; record mean (time) / calculation of mean (time) ; use correct units for light intensity (or correct stated example e.g. lumen / lux) ; 1 2(b)(ii) any 2 from: depth / level / volume of the water ; diameter / thickness / mass, (of the discs); concentration of CO2 (in water) ; ensuring discs start at the bottom ; temperature (of the water) ; AVP; e.g. turbidity 2 2(b)(iii) oxygen (bubbles) produced (by photosynthesis) / discs contain oxygen ; (oxygen) reduces density of discs / oxygen (gas) has a lower density than water ; 2 Question Answer Marks 2(c)(i) (species R because)… species R is quickest / takes least time, to rise at lower light intensities ; so must be, producing oxygen / photosynthesising, faster / the most (at lower light intensities) ; light intensity will be, lower / lowest / little, when tide is in / when in deeper water / ; 3 2(c)(ii) (mean time for discs to rise between) 111 (s) ; 1

This question in 9693/21 May/June 2024

4 (a) Fig. 4.1 shows the mean rate of photosynthesis each month and the water temperature throughout the year in a bay of an ocean in the northern hemisphere. Key mean monthly rate of photosynthesis water temperature 3 30 2 20mean monthly waterrate of temperaturephotosynthesis / °C/ arbitrary units 1 10 0 0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec month Fig. 4.1 (i) Use Fig. 4.1 to describe the relationship between water temperature and the rate of photosynthesis. … … … … [2] (ii) Sketch a line on Fig. 4.2 to suggest what would happen to the primary consumer population over the period of this year. biomass of primary consumers / arbitrary units Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec month Fig. 4.2 [2] (b) Fig. 4.3 shows a flooding river discharging into the bay during winter. J K Fig. 4.3 Discuss how abiotic factors in the water at point J differ to point K. … … … … … … … … … … [5] (c) Table 4.1 shows the mean concentration of some nutrient ions in the bay in January and in August. Table 4.1 mean concentration in mean concentration in percentage change in nutrient bay in January bay in August nutrient ions January / parts per million / parts per million to August CO3 2– 31 26 –16 NO3– 0.92 0.31 –67 Mg2+ 1400 1300 –5.0 PO43– 0.14 0.05 (i) Calculate the percentage change in phosphate ions (PO43–) between January and August. Give your answer to two significant figures. Show your working. … % [3] (ii) Suggest reasons for the increase and decrease in phosphate ion levels in the bay during the year. … … … … … … … … [4] (iii) Discuss the impact of a large decrease in the concentration of nitrate ions (NO3–) on the productivity of food webs in the bay. … … … … … … [3] (d) A scientist took a sample of a small macroalga from the bay. An experiment was set up in a laboratory to investigate the effect of light intensity on the rate of photosynthesis of the alga. (i) State one key variable to standardise. … [1] (ii) Suggest a laboratory method the scientist could use to investigate the effect of light intensity on the rate of photosynthesis of the alga. … … … … … … … … … … [5] (iii) Draw a table to record the results. Include units. Do not write in any results. [3] [Total: 28]

28 marks

Mark scheme: 4(a)(i) any 2 from: increasing water temperature increases rate of photosynthesis ; ref. to (rapid) photosynthesis drop between June / July to August while temperature stays high ; idea of, photosynthesis rate has a second peak (in October) ; ref. to lag period between temperature increase and photosynthesis increase ; 2 4(a)(ii) graph showing similar shape to photosynthesis line 2 peaks and 2 troughs with the peaks up to 1 month after the phytoplankton line ;; (for 2 marks) graph showing similar shape to photosynthesis line 2 peaks and 2 troughs ; (for 1 mark) 2 4(b) any 5 from: 1 J has higher sediment loading / higher turbidity due to high runoff from land carrying sediment ORA ; 2 J has more fine particles of sediment as particles have not been able to settle out ORA ; 3 J has higher, flow rate / speed / velocity, of water due to large volume of water flowing in narrow channel ORA ; 4 J has lower salinity as river water is freshwater (so little salt present) ORA ; 5 J has lower pH as freshwater has a pH of 7 / sea water has a pH of (around) 8.2 ORA ; 6 J is higher in, nutrients/ minerals, due to run-off from land ORA ; 7 J has higher concentration of, oxygen / CO2 ,as gas saturation decreases with increasing salt concentration ORA OR due to increased turbulence at J, ORA ; 8 J will be less dense as it contains fewer salts ORA ; 9 J may carry more, toxins / pollutants / named pollutant, from runoff ; 5 4(c)(i) (0.05 – 0.14) = –0.09 ; 0.09 / 0.14  100 = –64.29… ; –64 (%) ; OR 0.05 ÷ 0.14  100 = MP1 ; 100 – (MP1) ; –64.29 ; 3 Question Answer Marks 4(c)(ii) any 4 from (decrease in summer) 1 (summer) absorbed by phytoplankton / algae / plants ; 2 (uses of phosphate) DNA / RNA / ATP / bone ; 3 to increase productivity ORA ; (increase in winter) 1 flooding occurs in winter / more precipitation in winter ; 2 increase in fertiliser / sewage (from runoff) ; 3 (increased) river run-off / upwelling ; 4 (winter) stormy conditions causes greater mixing of nutrients from the seabed ; 4 4(c)(iii) any 3 from: used to make amino acids / protein / DNA / chlorophyll ; less, (protein / DNA) for growth / repair of cells / cell division / photosynthesis by producers / biomass formed ; (less ) energy to pass along food chain / less food available further up the food chain ; reduces productivity at all levels / a named level ; 3 4(d)(i) temperature / pH / salinity / water volume / carbonate or hydrogen carbonate or carbon dioxide, concentration ; 1 4(d)(ii) any 5 from: changing distance of light source / how light intensity is changed ; ensure ambient light is low ; presence of glass screen / water bath (to ensure not heated by lamp) ; ref. to specimen in beaker / test tube / flask / container ; allowing specimen time to adjust to light intensity ; means of measuring the volume of gas released / count the bubbles ; in a stated time period ; ref. to hydrogen carbonate source in water / maintaining carbon dioxide concentration ; ref. to repeating / 3 sets of data collected, at each light intensity + calculate the mean ; 5 Question Answer Marks 4(d)(iii) distance from light source / cm volume of oxygen collected per minute / cm3 OR number of bubbles / minute 1 2 3 mean column / row, for distance and mm / cm / m ; column / row, for volume of oxygen collected + cm3 / number of bubbles counted + per minute ; column / row, for repeats at least 3 sets of results / mean ; 3

This question in 9693/22 May/June 2024

4 (a) Fig. 4.1 shows the mean rate of photosynthesis each month and the water temperature throughout the year in a bay of an ocean in the northern hemisphere. Key mean monthly rate of photosynthesis water temperature 3 30 2 20mean monthly waterrate of temperaturephotosynthesis / °C/ arbitrary units 1 10 0 0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec month Fig. 4.1 (i) Use Fig. 4.1 to describe the relationship between water temperature and the rate of photosynthesis. … … … … [2] (ii) Sketch a line on Fig. 4.2 to suggest what would happen to the primary consumer population over the period of this year. biomass of primary consumers / arbitrary units Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec month Fig. 4.2 [2] (b) Fig. 4.3 shows a flooding river discharging into the bay during winter. J K Fig. 4.3 Discuss how abiotic factors in the water at point J differ to point K. … … … … … … … … … … [5] (c) Table 4.1 shows the mean concentration of some nutrient ions in the bay in January and in August. Table 4.1 mean concentration in mean concentration in percentage change in nutrient bay in January bay in August nutrient ions January / parts per million / parts per million to August CO32– 31 26 –16 NO3– 0.92 0.31 –67 Mg2+ 1400 1300 –5.0 PO43– 0.14 0.05 (i) Calculate the percentage change in phosphate ions (PO43–) between January and August. Give your answer to two significant figures. Show your working. … % [3] (ii) Suggest reasons for the increase and decrease in phosphate ion levels in the bay during the year. … … … … … … … … [4] (iii) Discuss the impact of a large decrease in the concentration of nitrate ions (NO3–) on the productivity of food webs in the bay. … … … … … … [3] (d) A scientist took a sample of a small macroalga from the bay. An experiment was set up in a laboratory to investigate the effect of light intensity on the rate of photosynthesis of the alga. (i) State one key variable to standardise. … [1] (ii) Suggest a laboratory method the scientist could use to investigate the effect of light intensity on the rate of photosynthesis of the alga. … … … … … … … … … … [5] (iii) Draw a table to record the results. Include units. Do not write in any results. [3] [Total: 28]

28 marks

Mark scheme: 4(a)(i) any 2 from: increasing water temperature increases rate of photosynthesis ; ref. to (rapid) photosynthesis drop between June / July to August while temperature stays high ; idea of, photosynthesis rate has a second peak (in October) ; ref. to lag period between temperature increase and photosynthesis increase ; 2 4(a)(ii) graph showing similar shape to photosynthesis line 2 peaks and 2 troughs with the peaks up to 1 month after the phytoplankton line ;; (for 2 marks) graph showing similar shape to photosynthesis line 2 peaks and 2 troughs ; (for 1 mark) 2 4(b) any 5 from: 1 J has higher sediment loading / higher turbidity due to high runoff from land carrying sediment ORA ; 2 J has more fine particles of sediment as particles have not been able to settle out ORA ; 3 J has higher, flow rate / speed / velocity, of water due to large volume of water flowing in narrow channel ORA ; 4 J has lower salinity as river water is freshwater (so little salt present) ORA ; 5 J has lower pH as freshwater has a pH of 7 / sea water has a pH of (around) 8.2 ORA ; 6 J is higher in, nutrients/ minerals, due to run-off from land ORA ; 7 J has higher concentration of, oxygen / CO2 ,as gas saturation decreases with increasing salt concentration ORA OR due to increased turbulence at J, ORA ; 8 J will be less dense as it contains fewer salts ORA ; 9 J may carry more, toxins / pollutants / named pollutant, from runoff ; 5 4(c)(i) (0.05 – 0.14) = –0.09 ; 0.09 / 0.14  100 = –64.29… ; –64 (%) ; OR 0.05 ÷ 0.14  100 = MP1 ; 100 – (MP1) ; –64.29 ; 3 Question Answer Marks 4(c)(ii) any 4 from (decrease in summer) 1 (summer) absorbed by phytoplankton / algae / plants ; 2 (uses of phosphate) DNA / RNA / ATP / bone ; 3 to increase productivity ORA ; (increase in winter) 1 flooding occurs in winter / more precipitation in winter ; 2 increase in fertiliser / sewage (from runoff) ; 3 (increased) river run-off / upwelling ; 4 (winter) stormy conditions causes greater mixing of nutrients from the seabed ; 4 4(c)(iii) any 3 from: used to make amino acids / protein / DNA / chlorophyll ; less, (protein / DNA) for growth / repair of cells / cell division / photosynthesis by producers / biomass formed ; (less ) energy to pass along food chain / less food available further up the food chain ; reduces productivity at all levels / a named level ; 3 4(d)(i) temperature / pH / salinity / water volume / carbonate or hydrogen carbonate or carbon dioxide, concentration ; 1 4(d)(ii) any 5 from: changing distance of light source / how light intensity is changed ; ensure ambient light is low ; presence of glass screen / water bath (to ensure not heated by lamp) ; ref. to specimen in beaker / test tube / flask / container ; allowing specimen time to adjust to light intensity ; means of measuring the volume of gas released / count the bubbles ; in a stated time period ; ref. to hydrogen carbonate source in water / maintaining carbon dioxide concentration ; ref. to repeating / 3 sets of data collected, at each light intensity + calculate the mean ; 5 Question Answer Marks 4(d)(iii) distance from light source / cm volume of oxygen collected per minute / cm3 OR number of bubbles / minute 1 2 3 mean column / row, for distance and mm / cm / m ; column / row, for volume of oxygen collected + cm3 / number of bubbles counted + per minute ; column / row, for repeats at least 3 sets of results / mean ; 3

This question in 9693/23 May/June 2024

1 Photosynthesis by organisms in the epipelagic zone of the oceans produces carbon-containing substances. Some of this carbon is transported to the mesopelagic zone and bathypelagic zone by the vertical movement of organisms. Fig. 1.1 shows the positions of these zones. NOT TO SCALE epipelagic mesopelagic bathypelagic Fig. 1.1 (a) Sketch a line on the axes in Fig. 1.2 to show the light intensity in the epipelagic, mesopelagic and bathypelagic zones shown in Fig. 1.1. 0 increasing light intensity 0 epipelagic zone mesopelagic zone increasing depth bathypelagic zone Fig. 1.2 [2] (b) Phytoplankton carry out photosynthesis to obtain nutrition. (i) State the word equation for photosynthesis. … [1] (ii) Name one other process used by producers to obtain nutrition. … [1] (c) Scientists investigated the effect of light intensity on the rate of photosynthesis in phytoplankton. Phytoplankton absorb light during photosynthesis. The greater the rate of photosynthesis, the faster the growth of the population. The greater the population of phytoplankton in a container, the less light is transmitted through the container. The percentage of light passing through the container can be measured using a light sensor as shown in Fig. 1.3. light sensor light sea water containing phytoplankton Fig. 1.3 (i) Identify the independent and dependent variables. independent variable … dependent variable … [1] (ii) Complete Table 1.1 to identify two key variables to standardise, and describe how these can be standardised in this investigation. Table 1.1 key variable how to standardise [3] (iii) Using the equipment shown in Fig. 1.3, outline a safe method that can be used to investigate the effect of light intensity on the rate of photosynthesis of the phytoplankton. Do not include how to standardise key variables in your answer. … … … … … … … … [4] [Total: 12]

12 marks

Mark scheme: Question Answer Marks 1(a) line at x axis (anywhere from ‘i’ at start of label to right), continuously getting closer to the y-axis as depth increases ; 2 0 near the top of the bathypelagic zone ; 1(b)(i) carbon dioxide + water → glucose + oxygen ; 1 1(b)(ii) chemosynthesis 1 1(c)(i) (independent variable) (description of variation of) light intensity 1 AND (dependent variable) light transmitted / population or growth of phytoplankton / rate of photosynthesis / AW ; 1(c)(ii) 3 key variable how to standardise any 2 in this column (for 1 1 mark for each correct answer matching a mark) stated key variable (max 2) temperature (of water) use of thermostat or water bath to maintain temp / screen or suitable method to prevent heating ; salinity (of water) idea of start with a stock solution of standard salinity to use for each trial ; volume (of water) use of (suitable) measuring equipment to measure volume ; pH idea of using stock solution / use a (pH) buffer ; turbidity / clarity, (of water) no sediment / particles / anything, that will block light ; (dissolved) CO2 (sodium) hydrogencarbonate added to make this in excess / same amount added ; (concentration of) nutrients e.g. adding same, volume / mass, of nutrients to each experiment ; (starting) description of mixed solution containing volume / mass / number / pop phytoplankton and equal ulation, of phytoplankton volumes / mass / number etc. of phytoplankton used / AW added ; type / species of use the same species / type ; phytoplankton 1(c)(ii) key variable how to standardise background light any valid description to control e.g. turn off any other lights / dark room / close blinds etc ; light sensor make sure set to zero / same initial value each (calibration / initial value) time ; distance of light sensor from using a ruler (or other valid measuring container equipment) ; time the phytoplankton is left stated duration of experiment / use of timer or for / intervals for readings stopwatch ; wavelength / colour of light use the same lamp / bulb / filter ; idea of material the use container made from same material ; container is made from 1(c)(iii) suitable safety precaution e.g. burn from lamp / electrical equipment and water ; 4 plus any 3 from: suitable method for adjusting light intensity ; use of intervals resulting in at least three values ; idea of leaving experiment for a period of time to get results ; idea of repeating at least 3 (sets of) results ; idea of adding nutrients to the vessel ;

This question in 9693/21 Oct/Nov 2024

3 Scientists collected a series of measurements from a ship travelling across the Atlantic Ocean from locations 1 to 12. They recorded the temperature, concentration of nitrate ions (NO3–) and abundance of phytoplankton at five depths from each of the 12 locations shown in Fig. 3.1. 1212 1111 Africa 1010 9 8 7 6 5 4 3 South America 2 1 Fig. 3.1 (a) State the type of sampling used by the scientists, and describe the benefits of this method. … … … … … … [3] (b) Table 3.1 shows the temperatures recorded at location 4. Table 3.1 depth / m temperature / °C 50 28 60 25 75 20 80 15 170 12 Plot the information shown in Table 3.1 as a line graph. [4] (c) Fig. 3.2 shows the analysis of some of the data that the scientists collected at each location. location 1 2 3 4 5 6 7 8 9 10 11 12 0 depth / m 100 200 Key depth of bottom of thermocline / m depth of greatest concentration of nitrate ions / m depth of greatest population of phytoplankton / m Fig. 3.2 Use the information shown in Table 3.1 and Fig. 3.2 and your own knowledge to discuss the reasons for the distribution of phytoplankton. … … … … … … [3] [Total: 10]

10 marks

Mark scheme: 3(a) systematic / (line / belt), transect ; 3 plus any 2 from: samples taken at regular intervals ; not affected by bias / ensures samples cover the full range of ocean sampled ; idea of change in conditions / environmental factors ; 3(b) axes labels with units ; 4 suitable linear scale ; plotted correctly ± ½ small square ; ruled lines linking points OR line of best fit drawn ; 3(c) any 3 from: 3 (depth of greatest proportion of) phytoplankton similar to / always (closely) above the depth of bottom of thermocline ; idea of water above thermocline is warmer which allows greater, growth / rate of photosynthesis ORA ; depth of (greatest proportion of) phytoplankton corresponds to depth of (greatest concentration of) nitrate ; nitrate needed for growth / named correct biological molecule requiring nitrate ; AVP ;

This question in 9693/21 Oct/Nov 2024

1 Photosynthesis by organisms in the epipelagic zone of the oceans produces carbon-containing substances. Some of this carbon is transported to the mesopelagic zone and bathypelagic zone by the vertical movement of organisms. Fig. 1.1 shows the positions of these zones. NOT TO SCALE epipelagic mesopelagic bathypelagic Fig. 1.1 (a) Sketch a line on the axes in Fig. 1.2 to show the light intensity in the epipelagic, mesopelagic and bathypelagic zones shown in Fig. 1.1. 0 increasing light intensity 0 epipelagic zone mesopelagic zone increasing depth bathypelagic zone Fig. 1.2 [2] (b) Phytoplankton carry out photosynthesis to obtain nutrition. (i) State the word equation for photosynthesis. … [1] (ii) Name one other process used by producers to obtain nutrition. … [1] (c) Scientists investigated the effect of light intensity on the rate of photosynthesis in phytoplankton. Phytoplankton absorb light during photosynthesis. The greater the rate of photosynthesis, the faster the growth of the population. The greater the population of phytoplankton in a container, the less light is transmitted through the container. The percentage of light passing through the container can be measured using a light sensor as shown in Fig. 1.3. light sensor light sea water containing phytoplankton Fig. 1.3 (i) Identify the independent and dependent variables. independent variable … dependent variable … [1] (ii) Complete Table 1.1 to identify two key variables to standardise, and describe how these can be standardised in this investigation. Table 1.1 key variable how to standardise [3] (iii) Using the equipment shown in Fig. 1.3, outline a safe method that can be used to investigate the effect of light intensity on the rate of photosynthesis of the phytoplankton. Do not include how to standardise key variables in your answer. … … … … … … … … [4] [Total: 12]

12 marks

Mark scheme: Question Answer Marks 1(a) line at x axis (anywhere from ‘i’ at start of label to right), continuously getting closer to the y-axis as depth increases ; 2 0 near the top of the bathypelagic zone ; 1(b)(i) carbon dioxide + water → glucose + oxygen ; 1 1(b)(ii) chemosynthesis 1 1(c)(i) (independent variable) (description of variation of) light intensity 1 AND (dependent variable) light transmitted / population or growth of phytoplankton / rate of photosynthesis / AW ; 1(c)(ii) 3 key variable how to standardise any 2 in this column (for 1 1 mark for each correct answer matching a mark) stated key variable (max 2) temperature (of water) use of thermostat or water bath to maintain temp / screen or suitable method to prevent heating ; salinity (of water) idea of start with a stock solution of standard salinity to use for each trial ; volume (of water) use of (suitable) measuring equipment to measure volume ; pH idea of using stock solution / use a (pH) buffer ; turbidity / clarity, (of water) no sediment / particles / anything, that will block light ; (dissolved) CO2 (sodium) hydrogencarbonate added to make this in excess / same amount added ; (concentration of) nutrients e.g. adding same, volume / mass, of nutrients to each experiment ; (starting) description of mixed solution containing volume / mass / number / pop phytoplankton and equal ulation, of phytoplankton volumes / mass / number etc. of phytoplankton used / AW added ; type / species of use the same species / type ; phytoplankton 1(c)(ii) key variable how to standardise background light any valid description to control e.g. turn off any other lights / dark room / close blinds etc ; light sensor make sure set to zero / same initial value each (calibration / initial value) time ; distance of light sensor from using a ruler (or other valid measuring container equipment) ; time the phytoplankton is left stated duration of experiment / use of timer or for / intervals for readings stopwatch ; wavelength / colour of light use the same lamp / bulb / filter ; idea of material the use container made from same material ; container is made from 1(c)(iii) suitable safety precaution e.g. burn from lamp / electrical equipment and water ; 4 plus any 3 from: suitable method for adjusting light intensity ; use of intervals resulting in at least three values ; idea of leaving experiment for a period of time to get results ; idea of repeating at least 3 (sets of) results ; idea of adding nutrients to the vessel ;

This question in 9693/22 Oct/Nov 2024

3 Scientists collected a series of measurements from a ship travelling across the Atlantic Ocean from locations 1 to 12. They recorded the temperature, concentration of nitrate ions (NO3–) and abundance of phytoplankton at five depths from each of the 12 locations shown in Fig. 3.1. 1212 1111 Africa 1010 9 8 7 6 5 4 3 South America 2 1 Fig. 3.1 (a) State the type of sampling used by the scientists, and describe the benefits of this method. … … … … … … [3] (b) Table 3.1 shows the temperatures recorded at location 4. Table 3.1 depth / m temperature / °C 50 28 60 25 75 20 80 15 170 12 Plot the information shown in Table 3.1 as a line graph. [4] (c) Fig. 3.2 shows the analysis of some of the data that the scientists collected at each location. location 1 2 3 4 5 6 7 8 9 10 11 12 0 depth / m 100 200 Key depth of bottom of thermocline / m depth of greatest concentration of nitrate ions / m depth of greatest population of phytoplankton / m Fig. 3.2 Use the information shown in Table 3.1 and Fig. 3.2 and your own knowledge to discuss the reasons for the distribution of phytoplankton. … … … … … … [3] [Total: 10]

10 marks

Mark scheme: 3(a) systematic / (line / belt), transect ; 3 plus any 2 from: samples taken at regular intervals ; not affected by bias / ensures samples cover the full range of ocean sampled ; idea of change in conditions / environmental factors ; 3(b) axes labels with units ; 4 suitable linear scale ; plotted correctly ± ½ small square ; ruled lines linking points OR line of best fit drawn ; 3(c) any 3 from: 3 (depth of greatest proportion of) phytoplankton similar to / always (closely) above the depth of bottom of thermocline ; idea of water above thermocline is warmer which allows greater, growth / rate of photosynthesis ORA ; depth of (greatest proportion of) phytoplankton corresponds to depth of (greatest concentration of) nitrate ; nitrate needed for growth / named correct biological molecule requiring nitrate ; AVP ;

This question in 9693/22 Oct/Nov 2024

1 Photosynthesis by organisms in the epipelagic zone of the oceans produces carbon-containing substances. Some of this carbon is transported to the mesopelagic zone and bathypelagic zone by the vertical movement of organisms. Fig. 1.1 shows the positions of these zones. NOT TO SCALE epipelagic mesopelagic bathypelagic Fig. 1.1 (a) Sketch a line on the axes in Fig. 1.2 to show the light intensity in the epipelagic, mesopelagic and bathypelagic zones shown in Fig. 1.1. 0 increasing light intensity 0 epipelagic zone mesopelagic zone increasing depth bathypelagic zone Fig. 1.2 [2] (b) Phytoplankton carry out photosynthesis to obtain nutrition. (i) State the word equation for photosynthesis. … [1] (ii) Name one other process used by producers to obtain nutrition. … [1] (c) Scientists investigated the effect of light intensity on the rate of photosynthesis in phytoplankton. Phytoplankton absorb light during photosynthesis. The greater the rate of photosynthesis, the faster the growth of the population. The greater the population of phytoplankton in a container, the less light is transmitted through the container. The percentage of light passing through the container can be measured using a light sensor as shown in Fig. 1.3. light sensor light sea water containing phytoplankton Fig. 1.3 (i) Identify the independent and dependent variables. independent variable … dependent variable … [1] (ii) Complete Table 1.1 to identify two key variables to standardise, and describe how these can be standardised in this investigation. Table 1.1 key variable how to standardise [3] (iii) Using the equipment shown in Fig. 1.3, outline a safe method that can be used to investigate the effect of light intensity on the rate of photosynthesis of the phytoplankton. Do not include how to standardise key variables in your answer. … … … … … … … … [4] [Total: 12]

12 marks

Mark scheme: Question Answer Marks 1(a) line at x axis (anywhere from ‘i’ at start of label to right), continuously getting closer to the y-axis as depth increases ; 2 0 near the top of the bathypelagic zone ; 1(b)(i) carbon dioxide + water → glucose + oxygen ; 1 1(b)(ii) chemosynthesis 1 1(c)(i) (independent variable) (description of variation of) light intensity 1 AND (dependent variable) light transmitted / population or growth of phytoplankton / rate of photosynthesis / AW ; 1(c)(ii) 3 key variable how to standardise any 2 in this column (for 1 1 mark for each correct answer matching a mark) stated key variable (max 2) temperature (of water) use of thermostat or water bath to maintain temp / screen or suitable method to prevent heating ; salinity (of water) idea of start with a stock solution of standard salinity to use for each trial ; volume (of water) use of (suitable) measuring equipment to measure volume ; pH idea of using stock solution / use a (pH) buffer ; turbidity / clarity, (of water) no sediment / particles / anything, that will block light ; (dissolved) CO2 (sodium) hydrogencarbonate added to make this in excess / same amount added ; (concentration of) nutrients e.g. adding same, volume / mass, of nutrients to each experiment ; (starting) description of mixed solution containing volume / mass / number / pop phytoplankton and equal ulation, of phytoplankton volumes / mass / number etc. of phytoplankton used / AW added ; type / species of use the same species / type ; phytoplankton 1(c)(ii) key variable how to standardise background light any valid description to control e.g. turn off any other lights / dark room / close blinds etc ; light sensor make sure set to zero / same initial value each (calibration / initial value) time ; distance of light sensor from using a ruler (or other valid measuring container equipment) ; time the phytoplankton is left stated duration of experiment / use of timer or for / intervals for readings stopwatch ; wavelength / colour of light use the same lamp / bulb / filter ; idea of material the use container made from same material ; container is made from 1(c)(iii) suitable safety precaution e.g. burn from lamp / electrical equipment and water ; 4 plus any 3 from: suitable method for adjusting light intensity ; use of intervals resulting in at least three values ; idea of leaving experiment for a period of time to get results ; idea of repeating at least 3 (sets of) results ; idea of adding nutrients to the vessel ;

This question in 9693/23 Oct/Nov 2024

3 Scientists collected a series of measurements from a ship travelling across the Atlantic Ocean from locations 1 to 12. They recorded the temperature, concentration of nitrate ions (NO3–) and abundance of phytoplankton at five depths from each of the 12 locations shown in Fig. 3.1. 1212 1111 Africa 1010 9 8 7 6 5 4 3 South America 2 1 Fig. 3.1 (a) State the type of sampling used by the scientists, and describe the benefits of this method. … … … … … … [3] (b) Table 3.1 shows the temperatures recorded at location 4. Table 3.1 depth / m temperature / °C 50 28 60 25 75 20 80 15 170 12 Plot the information shown in Table 3.1 as a line graph. [4] (c) Fig. 3.2 shows the analysis of some of the data that the scientists collected at each location. location 1 2 3 4 5 6 7 8 9 10 11 12 0 depth / m 100 200 Key depth of bottom of thermocline / m depth of greatest concentration of nitrate ions / m depth of greatest population of phytoplankton / m Fig. 3.2 Use the information shown in Table 3.1 and Fig. 3.2 and your own knowledge to discuss the reasons for the distribution of phytoplankton. … … … … … … [3] [Total: 10]

10 marks

Mark scheme: 3(a) systematic / (line / belt), transect ; 3 plus any 2 from: samples taken at regular intervals ; not affected by bias / ensures samples cover the full range of ocean sampled ; idea of change in conditions / environmental factors ; 3(b) axes labels with units ; 4 suitable linear scale ; plotted correctly ± ½ small square ; ruled lines linking points OR line of best fit drawn ; 3(c) any 3 from: 3 (depth of greatest proportion of) phytoplankton similar to / always (closely) above the depth of bottom of thermocline ; idea of water above thermocline is warmer which allows greater, growth / rate of photosynthesis ORA ; depth of (greatest proportion of) phytoplankton corresponds to depth of (greatest concentration of) nitrate ; nitrate needed for growth / named correct biological molecule requiring nitrate ; AVP ;

This question in 9693/23 Oct/Nov 2024

3 A student investigated how light intensity affected the rate of photosynthesis in two species of macroalga, X and Y. Fig. 3.1 shows the apparatus used. stop-clock gas bubbles from photosynthesis lamp 00.00 macroalga metre ruler Fig. 3.1 (a) Name the gas produced by photosynthesis. … [1] (b) (i) Describe a method to compare the rate of photosynthesis at different light intensities in each species of macroalga. Use only the apparatus shown in Fig. 3.1. … … … … … … … … … … [5] (ii) Draw a results table for the investigation in (b)(i). Include full headings and units in the results table. Do not write in any results. [3] (iii) Predict the relationship between light intensity and rate of photosynthesis in macroalga. … … [1] (c) Suggest two improvements that could be made to the apparatus used in this investigation. Give a reason for each suggestion. 1 … … reason … … 2 … … reason … … [4] (d) Explain the importance of photosynthesis to consumers. … … … … … … [3] [Total: 17]

17 marks

Mark scheme: 3(a) oxygen ; 1 3(b)(i) distance between the lamp and the macroalga, varies / is independent variable ; 5 count number of bubbles produced per minute / unit time OR number of bubbles produced per minute / unit time, is dependent variable ; reference to sufficient range (min 3 distances) ; allow time for macroalga to adjust ; reference to control variable e.g. pH / size of macroalga / same macroalga / temperature / ambient light / known volume of sea water ; repeat with species X and Y / with the two different species ; reference to repeats to, identify anomalies / calculating mean ; 3(b)(ii) table with column headings for distance of lamp AND bubbles per minute / number of bubbles ; 3 columns / rows for both species X and Y ; suitable units for independent and dependent variables ; 3(b)(iii) increasing light intensity increases rate of photosynthesis ORA ; 1 3(c) any two pairs from: 4 1 use gas syringe / (inverted) measuring cylinder ; to measure volume of oxygen produced ; 2 use transparent screen ; to prevent heating effect of lamp ; 3 AVP ;; 3(d) any three from: 3 transfers energy from light ; glucose / carbohydrate / organic substances , in producers ; to produce biomass (in consumers) ; provides oxygen for respiration ;

This question in 9693/22 Oct/Nov 2025

3 A student investigated how light intensity affected the rate of photosynthesis in two species of macroalga, X and Y. Fig. 3.1 shows the apparatus used. stop-clock gas bubbles from photosynthesis lamp 00.00 macroalga metre ruler Fig. 3.1 (a) Name the gas produced by photosynthesis. … [1] (b) (i) Describe a method to compare the rate of photosynthesis at different light intensities in each species of macroalga. Use only the apparatus shown in Fig. 3.1. … … … … … … … … … … [5] (ii) Draw a results table for the investigation in (b)(i). Include full headings and units in the results table. Do not write in any results. [3] (iii) Predict the relationship between light intensity and rate of photosynthesis in macroalga. … … [1] (c) Suggest two improvements that could be made to the apparatus used in this investigation. Give a reason for each suggestion. 1 … … reason … … 2 … … reason … … [4] (d) Explain the importance of photosynthesis to consumers. … … … … … … [3] [Total: 17]

17 marks

Mark scheme: 3(a) oxygen ; 1 3(b)(i) distance between the lamp and the macroalga, varies / is independent variable ; 5 count number of bubbles produced per minute / unit time OR number of bubbles produced per minute / unit time, is dependent variable ; reference to sufficient range (min 3 distances) ; allow time for macroalga to adjust ; reference to control variable e.g. pH / size of macroalga / same macroalga / temperature / ambient light / known volume of sea water ; repeat with species X and Y / with the two different species ; reference to repeats to, identify anomalies / calculating mean ; 3(b)(ii) table with column headings for distance of lamp AND bubbles per minute / number of bubbles ; 3 columns / rows for both species X and Y ; suitable units for independent and dependent variables ; 3(b)(iii) increasing light intensity increases rate of photosynthesis ORA ; 1 3(c) any two pairs from: 4 1 use gas syringe / (inverted) measuring cylinder ; to measure volume of oxygen produced ; 2 use transparent screen ; to prevent heating effect of lamp ; 3 AVP ;; 3(d) any three from: 3 transfers energy from light ; glucose / carbohydrate / organic substances , in producers ; to produce biomass (in consumers) ; provides oxygen for respiration ;

This question in 9693/23 Oct/Nov 2025