Photosynthesis — Paper 4 · A Level Marine Science 9693

3 Marine organisms are adapted for life in their particular habitat. (a) (i) Explain why large, active animals require specialised gas exchange surfaces and transport systems. … … … … … … … … … [4] (ii) Describe how tuna maximise their rate of gas exchange. … … … … … … … … … … … … … [6] (b) Explain why algal species adapted to live in deeper waters often contain accessory pigments. … … … … … … … … … … … … … [5] [Total: 15]

15 marks

Mark scheme: 3(a)(i) any three of: a low surface area:volume ratio / ORA ; b long diffusion path / distance / ORA ; c high respiration rate / ORA ; d diffusion is insufficient (across body surface) / takes too long / ORA ; e ventilation organs / AW, increase surface area ; and minimum of one of: f blood transports oxygen to respiring tissues / cells ; g returns carbon dioxide to gills / lungs / AW ; 4 Question Answer Marks Guidance 3(a)(ii) any six of: a large gill surface area ; b (due to large numbers of) lamellae ; c thin gill lamellae ; d reducing diffusion distance ; e efficient capillary network / blood supply ; f movement of blood / high heart rate maintains gradient ; g ram ventilation ; h swim with mouth open to force water over gills ; i increases speed of gas exchange / less energy used than in pumped ventilation ; j ram ventilation maintains diffusion gradient ; k swim at surface where there is more oxygen ; l pumped ventilation when stopped / AW ; m buccal cavity / opercular movements to move water over gills / AW ; n ref. to counter-current flow ; 6 Question Answer Marks Guidance 3(b) any five of: a idea of, different light, colours / wavelengths, penetrating different distances ; b red absorbed at surface ; c blue penetrates deepest ; d chlorophyll absorbs blue and red light ; e named accessory pigment / xanthophyll / phycobilin / fucoxanthin ; f absorbs some of green / yellow / other wavelengths ; g maximise photosynthesis / light required for photosynthesis / AW ; h increased primary productivity ; i outcompete other algae ; 5 A long wavelength light for red A short wavelength light for blue

This question in 9693/41 Oct/Nov 2017

1 Scientists carried out an investigation into the composition of water samples taken from an area of the Arctic Ocean. They measured the concentration of dissolved oxygen, and also the quantity of chlorophyll present in a 1 dm3 sample. Sampling was carried out on the first day of each month from late winter, through spring and into early summer. The condition of the surface ice on the water was also determined. It was assessed as increasing in size or melting. The results are shown in Table 1.1. Table 1.1 quantity of oxygen time condition chlorophyll concentration (month) of ice sheet / arbitrary units / mg dm–3 December 1000 8.5 increasing January 500 8.5 increasing February 500 7.8 increasing March 500 6.9 increasing April 2000 7.6 melting May 6000 8.4 melting June 3000 8.6 melting July 1500 8.8 melting (a) Plot a graph to show the changes in quantity of chlorophyll and oxygen concentration over time. [5] (b) (i) Explain the relationship between the quantity of chlorophyll and the oxygen concentration shown in Table 1.1 and your graph. … … … … … [2] (ii) Use the information in Table 1.1 to suggest two explanations, other than the changes in the quantity of chlorophyll, for the changes in oxygen concentration. … … … … … [2] (c) It has been suggested that global warming could affect ocean productivity. Use the information in Table 1.1 and your graph to suggest how ocean productivity could be affected. … … … … … [2] [Total: 11]

11 marks

This question in 9693/40 May/June 2018

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

24 marks

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

This question in 9693/42 May/June 2022

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

24 marks

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

This question in 9693/43 May/June 2022

1 (a) Outline the light-dependent stage of photosynthesis. … … … … … … [3] (b) Fig. 1.1 shows the penetration of different colours of light into water in the open ocean and coastal water. open ocean coastal water violet blue green red violet blue green red 0 50 100 depth / m 150 200 250 Fig. 1.1 (i) Use Fig. 1.1 to compare the depth of penetration of the four colours of light into water in the open ocean and coastal water. … … … … … … [3] (ii) Suggest an explanation for the difference in penetration of light into open ocean water compared with coastal water. … … … … [2] (c) A student investigated two species of seaweed that are found in coastal water. The student collected a sample of one species from a depth of 2 m, and a sample of the other species from a depth of 20 m. They extracted the pigments from the seaweeds and carried out chromatography to identify the pigments. The results are shown in Fig. 1.2. solvent front carotene chlorophyll a chlorophyll b xanthophyll origin species species from 2 m from 20 m Fig. 1.2 (i) Use Fig. 1.2 to calculate the Rf value for xanthophyll. Give your answer to two significant figures. Show your working. distance moved by pigment Rf = distance moved by solvent … [3] (ii) Use Fig. 1.1 and Fig. 1.2 to suggest an explanation for the differences between the pigments found in the two species of seaweed. … … … … … … [3] (d) Light wavelength can be changed by placing coloured, cellophane filters in front of a bench lamp. Plan a laboratory-based investigation into the effect of changing light wavelength on the rate of photosynthesis of a seaweed. You are provided with standard laboratory apparatus and materials. Your plan should: • include a clear statement of the hypothesis • identify the key variables • include full details of the method • describe how you would analyse your results • be safe and ethical. … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … [11] [Total: 25]

25 marks

Mark scheme: Question Answer Marks 1(a) any 3 from: 3 chlorophyll / photosystem (I/II) absorbs light (energy) ; photolysis of water (occurs) / AW ; producing oxygen ; ATP produced ; NADPH / AW, produced ; ref. to movement of electrons / oxidation of chlorophyll / photoactivation / movement along electron transport chain / AW ; 1(b)(i) any 3 from: 3 all colours penetrate further in open ocean / ORA ; blue penetrates furthest in open ocean but green penetrates furthest in coastal water ; violet penetrates least in coastal water but red penetrates the least in open ocean ; red and violet penetrate least for both ; credit correct manipulated comparison ; 1(b)(ii) any 2 from: 2 less sediment / mud / sand ; from outflow of river / less runoff (from land) ; less movement of tide / less wave action, on seabed stirring up sediment ; more algae / phytoplankton in surface water / eutrophication / AW ; deeper water in open ocean so less easy for sediment to be brought to surface / AW ; 1(c)(i) correct measurement of distance from origin to xanthophyll ; 3 correct calculation of Rf value ; correct number of significant figures ; 1(c)(ii) any 3 from: 3 species from 2 m has no xanthophyll / species from 20 m has xanthophyll ; no red / violet, light at 20 m depth ; (xanthophyll) absorbs additional light wavelengths / absorbs, more yellow / green / blue / more colours ; to enable photosynthesis ; credit ref. to idea of competitive advantage of having xanthophyll at depth or disadvantage closer to surface ; 1(d) photosynthesis will be faster in red / blue / orange light / ORA ; 11 any 10 from: independent variable independent variable identified as light wavelength / colour ; place different colours of cellophane in front of lamp / light source ; dependent variable max 2 from: dependent variable identified as rate of photosynthesis / rate of oxygen production / bubble rate / e.g. ; measurement of dependent variable e.g. counting bubbles / collecting volumes of oxygen ; in set time measured with timer ; ref. to minimum 3 replicates and means ; standardised variables max 3 from: constant temperature ; carbon dioxide (concentration) ; volume of water ; mass / species / type, of seaweed ; same distance from lamp / ensure light intensity is constant / same power of bulb ; pH ; method points max 3 from: place seaweed in test tube / beaker / AW, and cover with water ; leave seaweed to adjust to each light colour ; use of water bath / use of heat shield ; addition of sodium hydrogencarbonate (as a source of carbon dioxide) ; (same volume of water) measured with syringe / pipette / measuring cylinder ; switch off all other lights ; risk care with bulb and water / care not to get burnt / low risk experiment statement / care with cutting / do not get wires wet / AW ; 1(d) ethics don’t take seaweed from areas where it is needed / care with disposal of sodium hydrogen carbonate ; analysis max 2 from: calculation of rate as number of bubbles / volume of oxygen divided by time ; bar chart / (line) graph, of light wavelength / colour plotted on x-axis and rate on y-axis ; appropriate statistical test ;

This question in 9693/41 Oct/Nov 2022

1 (a) Outline the light-dependent stage of photosynthesis. … … … … … … [3] (b) Fig. 1.1 shows the penetration of different colours of light into water in the open ocean and coastal water. open ocean coastal water violet blue green red violet blue green red 0 50 100 depth / m 150 200 250 Fig. 1.1 (i) Use Fig. 1.1 to compare the depth of penetration of the four colours of light into water in the open ocean and coastal water. … … … … … … [3] (ii) Suggest an explanation for the difference in penetration of light into open ocean water compared with coastal water. … … … … [2] (c) A student investigated two species of seaweed that are found in coastal water. The student collected a sample of one species from a depth of 2 m, and a sample of the other species from a depth of 20 m. They extracted the pigments from the seaweeds and carried out chromatography to identify the pigments. The results are shown in Fig. 1.2. solvent front carotene chlorophyll a chlorophyll b xanthophyll origin species species from 2 m from 20 m Fig. 1.2 (i) Use Fig. 1.2 to calculate the Rf value for xanthophyll. Give your answer to two significant figures. Show your working. distance moved by pigment Rf = distance moved by solvent … [3] (ii) Use Fig. 1.1 and Fig. 1.2 to suggest an explanation for the differences between the pigments found in the two species of seaweed. … … … … … … [3] (d) Light wavelength can be changed by placing coloured, cellophane filters in front of a bench lamp. Plan a laboratory-based investigation into the effect of changing light wavelength on the rate of photosynthesis of a seaweed. You are provided with standard laboratory apparatus and materials. Your plan should: • include a clear statement of the hypothesis • identify the key variables • include full details of the method • describe how you would analyse your results • be safe and ethical. … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … [11] [Total: 25]

25 marks

Mark scheme: Question Answer Marks 1(a) any 3 from: 3 chlorophyll / photosystem (I/II) absorbs light (energy) ; photolysis of water (occurs) / AW ; producing oxygen ; ATP produced ; NADPH / AW, produced ; ref. to movement of electrons / oxidation of chlorophyll / photoactivation / movement along electron transport chain / AW ; 1(b)(i) any 3 from: 3 all colours penetrate further in open ocean / ORA ; blue penetrates furthest in open ocean but green penetrates furthest in coastal water ; violet penetrates least in coastal water but red penetrates the least in open ocean ; red and violet penetrate least for both ; credit correct manipulated comparison ; 1(b)(ii) any 2 from: 2 less sediment / mud / sand ; from outflow of river / less runoff (from land) ; less movement of tide / less wave action, on seabed stirring up sediment ; more algae / phytoplankton in surface water / eutrophication / AW ; deeper water in open ocean so less easy for sediment to be brought to surface / AW ; 1(c)(i) correct measurement of distance from origin to xanthophyll ; 3 correct calculation of Rf value ; correct number of significant figures ; 1(c)(ii) any 3 from: 3 species from 2 m has no xanthophyll / species from 20 m has xanthophyll ; no red / violet, light at 20 m depth ; (xanthophyll) absorbs additional light wavelengths / absorbs, more yellow / green / blue / more colours ; to enable photosynthesis ; credit ref. to idea of competitive advantage of having xanthophyll at depth or disadvantage closer to surface ; 1(d) photosynthesis will be faster in red / blue / orange light / ORA ; 11 any 10 from: independent variable independent variable identified as light wavelength / colour ; place different colours of cellophane in front of lamp / light source ; dependent variable max 2 from: dependent variable identified as rate of photosynthesis / rate of oxygen production / bubble rate / e.g. ; measurement of dependent variable e.g. counting bubbles / collecting volumes of oxygen ; in set time measured with timer ; ref. to minimum 3 replicates and means ; standardised variables max 3 from: constant temperature ; carbon dioxide (concentration) ; volume of water ; mass / species / type, of seaweed ; same distance from lamp / ensure light intensity is constant / same power of bulb ; pH ; method points max 3 from: place seaweed in test tube / beaker / AW, and cover with water ; leave seaweed to adjust to each light colour ; use of water bath / use of heat shield ; addition of sodium hydrogencarbonate (as a source of carbon dioxide) ; (same volume of water) measured with syringe / pipette / measuring cylinder ; switch off all other lights ; risk care with bulb and water / care not to get burnt / low risk experiment statement / care with cutting / do not get wires wet / AW ; 1(d) ethics don’t take seaweed from areas where it is needed / care with disposal of sodium hydrogen carbonate ; analysis max 2 from: calculation of rate as number of bubbles / volume of oxygen divided by time ; bar chart / (line) graph, of light wavelength / colour plotted on x-axis and rate on y-axis ; appropriate statistical test ;

This question in 9693/42 Oct/Nov 2022

1 (a) Outline the light-dependent stage of photosynthesis. … … … … … … [3] (b) Fig. 1.1 shows the penetration of different colours of light into water in the open ocean and coastal water. open ocean coastal water violet blue green red violet blue green red 0 50 100 depth / m 150 200 250 Fig. 1.1 (i) Use Fig. 1.1 to compare the depth of penetration of the four colours of light into water in the open ocean and coastal water. … … … … … … [3] (ii) Suggest an explanation for the difference in penetration of light into open ocean water compared with coastal water. … … … … [2] (c) A student investigated two species of seaweed that are found in coastal water. The student collected a sample of one species from a depth of 2 m, and a sample of the other species from a depth of 20 m. They extracted the pigments from the seaweeds and carried out chromatography to identify the pigments. The results are shown in Fig. 1.2. solvent front carotene chlorophyll a chlorophyll b xanthophyll origin species species from 2 m from 20 m Fig. 1.2 (i) Use Fig. 1.2 to calculate the Rf value for xanthophyll. Give your answer to two significant figures. Show your working. distance moved by pigment Rf = distance moved by solvent … [3] (ii) Use Fig. 1.1 and Fig. 1.2 to suggest an explanation for the differences between the pigments found in the two species of seaweed. … … … … … … [3] (d) Light wavelength can be changed by placing coloured, cellophane filters in front of a bench lamp. Plan a laboratory-based investigation into the effect of changing light wavelength on the rate of photosynthesis of a seaweed. You are provided with standard laboratory apparatus and materials. Your plan should: • include a clear statement of the hypothesis • identify the key variables • include full details of the method • describe how you would analyse your results • be safe and ethical. … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … [11] [Total: 25]

25 marks

Mark scheme: Question Answer Marks 1(a) any 3 from: 3 chlorophyll / photosystem (I/II) absorbs light (energy) ; photolysis of water (occurs) / AW ; producing oxygen ; ATP produced ; NADPH / AW, produced ; ref. to movement of electrons / oxidation of chlorophyll / photoactivation / movement along electron transport chain / AW ; 1(b)(i) any 3 from: 3 all colours penetrate further in open ocean / ORA ; blue penetrates furthest in open ocean but green penetrates furthest in coastal water ; violet penetrates least in coastal water but red penetrates the least in open ocean ; red and violet penetrate least for both ; credit correct manipulated comparison ; 1(b)(ii) any 2 from: 2 less sediment / mud / sand ; from outflow of river / less runoff (from land) ; less movement of tide / less wave action, on seabed stirring up sediment ; more algae / phytoplankton in surface water / eutrophication / AW ; deeper water in open ocean so less easy for sediment to be brought to surface / AW ; 1(c)(i) correct measurement of distance from origin to xanthophyll ; 3 correct calculation of Rf value ; correct number of significant figures ; 1(c)(ii) any 3 from: 3 species from 2 m has no xanthophyll / species from 20 m has xanthophyll ; no red / violet, light at 20 m depth ; (xanthophyll) absorbs additional light wavelengths / absorbs, more yellow / green / blue / more colours ; to enable photosynthesis ; credit ref. to idea of competitive advantage of having xanthophyll at depth or disadvantage closer to surface ; 1(d) photosynthesis will be faster in red / blue / orange light / ORA ; 11 any 10 from: independent variable independent variable identified as light wavelength / colour ; place different colours of cellophane in front of lamp / light source ; dependent variable max 2 from: dependent variable identified as rate of photosynthesis / rate of oxygen production / bubble rate / e.g. ; measurement of dependent variable e.g. counting bubbles / collecting volumes of oxygen ; in set time measured with timer ; ref. to minimum 3 replicates and means ; standardised variables max 3 from: constant temperature ; carbon dioxide (concentration) ; volume of water ; mass / species / type, of seaweed ; same distance from lamp / ensure light intensity is constant / same power of bulb ; pH ; method points max 3 from: place seaweed in test tube / beaker / AW, and cover with water ; leave seaweed to adjust to each light colour ; use of water bath / use of heat shield ; addition of sodium hydrogencarbonate (as a source of carbon dioxide) ; (same volume of water) measured with syringe / pipette / measuring cylinder ; switch off all other lights ; risk care with bulb and water / care not to get burnt / low risk experiment statement / care with cutting / do not get wires wet / AW ; 1(d) ethics don’t take seaweed from areas where it is needed / care with disposal of sodium hydrogen carbonate ; analysis max 2 from: calculation of rate as number of bubbles / volume of oxygen divided by time ; bar chart / (line) graph, of light wavelength / colour plotted on x-axis and rate on y-axis ; appropriate statistical test ;

This question in 9693/43 Oct/Nov 2022

2 Photosynthesis occurs in chloroplasts. (a) Fig. 2.1 shows an electron micrograph of a chloroplast. Fig. 2.1 (i) On Fig. 2.1, label the part of the chloroplast where the light-independent stage occurs with the letter X and a label line. [1] (ii) Make a large drawing of the part of the chloroplast shown in the circle in Fig. 2.1. Do not label your drawing. [4] (b) A scientist investigated the effect of different colours of light on the rate of photosynthesis of a species of seaweed. Normally, NADP is reduced in the light-dependent stage of photosynthesis. In this experiment, a chemical called DCPIP was reduced instead of NADP. DCPIP is normally blue and becomes colourless when it gains electrons and is reduced. The scientist used the following method. • Chloroplasts were extracted and suspended in a solution of saline. Equal volumes of the chloroplast suspension were placed into five test-tubes. • An equal volume of DCPIP was added to each test-tube. A sixth test-tube containing DCPIP with no chloroplasts was also set up. • One test-tube containing chloroplasts was wrapped in foil to block light. Each of the other tubes containing chloroplasts were wrapped with coloured cellophane to allow different colours of light to pass through. • The test-tubes were all exposed to light and the times taken for the DCPIP to become colourless were recorded. • The experiment was replicated three more times and the mean times taken for the DCPIP to become colourless were calculated. The results are shown in Table 2.1. Table 2.1 conditions mean time taken for the DCPIP to become colourless / s wrapped in foil no change red light 257 blue light 235 green light 758 white light no chloroplasts no change (i) The times taken for each of the replicates exposed to white light were: 175 s, 183 s, 181 s, 174 s Calculate the mean time taken for the DCPIP to become colourless when exposed to white light. Give your answer to three significant figures. … s [2] (ii) Suggest why the scientist included a test-tube wrapped with foil to block light. … … [1] (iii) Suggest why the scientist included a test-tube with no chloroplasts. … … [1] (iv) Explain the effects of red light, blue light and green light on the mean time taken for the DCPIP to become colourless. … … … … … … … … [4] (v) Many deep-water algae contain accessory pigments in their chloroplasts. Name one of these accessory pigments and use the results of the investigation to suggest an explanation for its presence in deep-water algae. … … … … … … [3] [Total: 16]

16 marks

Mark scheme: 2(a)(i) clear labelling of stroma ; 1 2(a)(ii) 1 thin, unbroken, clear lines that do not overlap ; 2 correct proportions and takes up at least two-thirds of space ; (gap between outer membrane and thylakoids of similar size to width of thylakoids  intergrana and grana in same direction, no large spaces between thylakoids) 3 correct detail ; (membrane on outside with two continuous lines, two intergrana on left  start of third intergranum on left + grana drawn on right) 4 no shading and only draw what is inside circle  no additional structures ; (needs to have membrane, grana and intergrana) 4 2(b)(i) correct mean (178.25) ; correct number of significant figures (178) ; 2 2(b)(ii) any 1 of: 1 to show that chloroplasts do not change the colour of DCPIP without light / AW ; 2 to show that light is needed (to change colour of DCPIP) / to show what would happen (to DCPIP) without light ; 3 to show that DCPIP does not change colour without light ; 1 2(b)(iii) any 1 of: 1 to show that light does not change the colour of DCPIP / AW ; 2 to compare the final colours (of other tubes) with ; 3 to show that chloroplasts / chlorophyll (and light) are needed (to change the colour) ; 1 2(b)(iv) any 4 of: 1 fastest rate of decolourisation with red and blue light / blue light / slowest rate with green / AW / ORA ; 2 red / blue, light absorbed ; 3 green is reflected / not absorbed ; 4 (by) chlorophyll / primary pigments / (chloroplasts) contain chlorophyll ; 5 electrons (from chlorophyll) are released ; 6 electrons decolourised / reduced DCPIP ; 4 Question Answer Marks 2(b)(v) any 3 of: 1 xanthophyll / fucoxanthin / carotene / chlorophyll B / phycobilin / phycocyanin / AW ; 2 red / yellow / orange light is absorbed by surface water / does not penetrate far (in water) / AW ; 3 blue / green light available (in deeper water) / blue / green reaches deeper water / penetrates into deeper water ; 4 (accessory pigments) absorb other wavelengths of light / absorb blue / green / AW ; 5 so (algae) can produce glucose / starch / compete (with other algae) ; 3

This question in 9693/41 May/June 2023

5 The rate of photosynthesis of producer organisms can be affected by many abiotic and biotic factors. (a) The light-dependent stage of photosynthesis occurs in the lamellae of chloroplasts. (i) Give the two products of the light-dependent stage that are used in the light-independent stage. 1 … 2 … [2] (ii) Fig. 5.1 shows the absorption spectra for the photosynthetic pigments extracted from two different species of alga, species A and species B. 1 species B species A relative absorption 0 400 450 500 550 600 650 700 750 blue green red wavelength / nm Fig. 5.1 Use Fig. 5.1 to explain which one of the two species of alga is adapted to live in deeper water. … … … … [2] (b) Atrazine is a weedkiller used in agriculture in some parts of the world. Atrazine is a toxic chemical that inhibits the light-dependent stage of photosynthesis. There have been concerns that atrazine can cause pollution due to its being washed into rivers and coastal waters. Plan a laboratory investigation that you could do to investigate the effect of changing the concentration of weedkiller on the rate of photosynthesis of an aquatic plant. You are provided with a 1% stock solution of atrazine. Your plan should: • include a clear statement of the hypothesis • identify the independent, dependent and standardised variables • include full details of the method so that another person can follow it • describe how you would analyse your results • be safe and ethical. … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … [11] [Total: 15] The boundaries and names shown, the designations used and the presentation of material on any maps contained in this question paper/insert do not imply official endorsement or acceptance by Cambridge Assessment International Education concerning the legal status of any country, territory, or area or any of its authorities, or of the delimitation of its frontiers or boundaries.

15 marks

Mark scheme: 5(a)(i) reduced NADP / NADPH / NADPH2 ; 2 ATP ; 5(a)(ii) any 2 of: 2 (species A) because it can absorb more light / green light, between 510 nm and 640 nm ; red light / longer wavelength light, is not available in deeper water / AW / ORA ; so (species A) has, accessory pigments / fucoxanthin, (as well as chlorophyll) (that absorbs in the 510 nm to 640 nm range); 5(b) hypothesis 11 1 photosynthesis (rate) / (rate of) oxygen production, will decrease as weedkiller concentration increases / AW ; and any 10 of: independent variable 2 identified as concentration of atrazine ; 3 use of at least 5 different concentrations in range of up to 1% ; dependent variable 4 identified as rate of photosynthesis / rate of oxygen production / AW ; 5 ref to method of measuring dependent variable in set time ; standardised variables max 3 6 same volume of water / same salinity of water ; 7 constant temperature ; 8 pH ; 9 same size / volume / mass of plant ; 10 light intensity / wavelength / lamp placed at set distance from plant / AW ; 11 same volume / concentration of hydrogencarbonate solution / same carbon dioxide / AW ; 5(b) method max 3 12 method to make dilutions ; 13 ref to placing shoot of plant cut end uppermost in boiling tube / beaker ; 14 ref to using paperclip to weigh down plant / AW ; 15 ref to using 0% or water to replace atrazine as a control experiment ; 16 ref to using a heat shield between lamp and plant / use water bath ; 17 use of pH buffer solutions ; analysis max 3 18 ref to replicating experiment 3 times and calculating means / medians ; 19 method for calculating the rate of photosynthesis ; 20 plot graph of rate of photosynthesis against concentration ; 21 ref to suitable named statistical test e.g. Spearman’s rank ; 22 correct example of results table with headings ; safety and ethics 23 atrazine is toxic so, use eye protection / use gloves / wash spills / pH buffers are irritants so use eye protection / gloves ; 24 do not wash down sink / AW, due to environmental impacts / do not take large amounts of plants from the wild / AW ;

This question in 9693/41 Oct/Nov 2023

5 The rate of photosynthesis of producer organisms can be affected by many abiotic and biotic factors. (a) The light-dependent stage of photosynthesis occurs in the lamellae of chloroplasts. (i) Give the two products of the light-dependent stage that are used in the light-independent stage. 1 … 2 … [2] (ii) Fig. 5.1 shows the absorption spectra for the photosynthetic pigments extracted from two different species of alga, species A and species B. 1 species B species A relative absorption 0 400 450 500 550 600 650 700 750 blue green red wavelength / nm Fig. 5.1 Use Fig. 5.1 to explain which one of the two species of alga is adapted to live in deeper water. … … … … [2] (b) Atrazine is a weedkiller used in agriculture in some parts of the world. Atrazine is a toxic chemical that inhibits the light-dependent stage of photosynthesis. There have been concerns that atrazine can cause pollution due to its being washed into rivers and coastal waters. Plan a laboratory investigation that you could do to investigate the effect of changing the concentration of weedkiller on the rate of photosynthesis of an aquatic plant. You are provided with a 1% stock solution of atrazine. Your plan should: • include a clear statement of the hypothesis • identify the independent, dependent and standardised variables • include full details of the method so that another person can follow it • describe how you would analyse your results • be safe and ethical. … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … [11] [Total: 15] The boundaries and names shown, the designations used and the presentation of material on any maps contained in this question paper/insert do not imply official endorsement or acceptance by Cambridge Assessment International Education concerning the legal status of any country, territory, or area or any of its authorities, or of the delimitation of its frontiers or boundaries.

15 marks

Mark scheme: 5(a)(i) reduced NADP / NADPH / NADPH2 ; 2 ATP ; 5(a)(ii) any 2 of: 2 (species A) because it can absorb more light / green light, between 510 nm and 640 nm ; red light / longer wavelength light, is not available in deeper water / AW / ORA ; so (species A) has, accessory pigments / fucoxanthin, (as well as chlorophyll) (that absorbs in the 510 nm to 640 nm range); 5(b) hypothesis 11 1 photosynthesis (rate) / (rate of) oxygen production, will decrease as weedkiller concentration increases / AW ; and any 10 of: independent variable 2 identified as concentration of atrazine ; 3 use of at least 5 different concentrations in range of up to 1% ; dependent variable 4 identified as rate of photosynthesis / rate of oxygen production / AW ; 5 ref to method of measuring dependent variable in set time ; standardised variables max 3 6 same volume of water / same salinity of water ; 7 constant temperature ; 8 pH ; 9 same size / volume / mass of plant ; 10 light intensity / wavelength / lamp placed at set distance from plant / AW ; 11 same volume / concentration of hydrogencarbonate solution / same carbon dioxide / AW ; 5(b) method max 3 12 method to make dilutions ; 13 ref to placing shoot of plant cut end uppermost in boiling tube / beaker ; 14 ref to using paperclip to weigh down plant / AW ; 15 ref to using 0% or water to replace atrazine as a control experiment ; 16 ref to using a heat shield between lamp and plant / use water bath ; 17 use of pH buffer solutions ; analysis max 3 18 ref to replicating experiment 3 times and calculating means / medians ; 19 method for calculating the rate of photosynthesis ; 20 plot graph of rate of photosynthesis against concentration ; 21 ref to suitable named statistical test e.g. Spearman’s rank ; 22 correct example of results table with headings ; safety and ethics 23 atrazine is toxic so, use eye protection / use gloves / wash spills / pH buffers are irritants so use eye protection / gloves ; 24 do not wash down sink / AW, due to environmental impacts / do not take large amounts of plants from the wild / AW ;

This question in 9693/42 Oct/Nov 2023

5 The rate of photosynthesis of producer organisms can be affected by many abiotic and biotic factors. (a) The light-dependent stage of photosynthesis occurs in the lamellae of chloroplasts. (i) Give the two products of the light-dependent stage that are used in the light-independent stage. 1 … 2 … [2] (ii) Fig. 5.1 shows the absorption spectra for the photosynthetic pigments extracted from two different species of alga, species A and species B. 1 species B species A relative absorption 0 400 450 500 550 600 650 700 750 blue green red wavelength / nm Fig. 5.1 Use Fig. 5.1 to explain which one of the two species of alga is adapted to live in deeper water. … … … … [2] (b) Atrazine is a weedkiller used in agriculture in some parts of the world. Atrazine is a toxic chemical that inhibits the light-dependent stage of photosynthesis. There have been concerns that atrazine can cause pollution due to its being washed into rivers and coastal waters. Plan a laboratory investigation that you could do to investigate the effect of changing the concentration of weedkiller on the rate of photosynthesis of an aquatic plant. You are provided with a 1% stock solution of atrazine. Your plan should: • include a clear statement of the hypothesis • identify the independent, dependent and standardised variables • include full details of the method so that another person can follow it • describe how you would analyse your results • be safe and ethical. … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … [11] [Total: 15] The boundaries and names shown, the designations used and the presentation of material on any maps contained in this question paper/insert do not imply official endorsement or acceptance by Cambridge Assessment International Education concerning the legal status of any country, territory, or area or any of its authorities, or of the delimitation of its frontiers or boundaries.

15 marks

Mark scheme: 5(a)(i) reduced NADP / NADPH / NADPH2 ; 2 ATP ; 5(a)(ii) any 2 of: 2 (species A) because it can absorb more light / green light, between 510 nm and 640 nm ; red light / longer wavelength light, is not available in deeper water / AW / ORA ; so (species A) has, accessory pigments / fucoxanthin, (as well as chlorophyll) (that absorbs in the 510 nm to 640 nm range); 5(b) hypothesis 11 1 photosynthesis (rate) / (rate of) oxygen production, will decrease as weedkiller concentration increases / AW ; and any 10 of: independent variable 2 identified as concentration of atrazine ; 3 use of at least 5 different concentrations in range of up to 1% ; dependent variable 4 identified as rate of photosynthesis / rate of oxygen production / AW ; 5 ref to method of measuring dependent variable in set time ; standardised variables max 3 6 same volume of water / same salinity of water ; 7 constant temperature ; 8 pH ; 9 same size / volume / mass of plant ; 10 light intensity / wavelength / lamp placed at set distance from plant / AW ; 11 same volume / concentration of hydrogencarbonate solution / same carbon dioxide / AW ; 5(b) method max 3 12 method to make dilutions ; 13 ref to placing shoot of plant cut end uppermost in boiling tube / beaker ; 14 ref to using paperclip to weigh down plant / AW ; 15 ref to using 0% or water to replace atrazine as a control experiment ; 16 ref to using a heat shield between lamp and plant / use water bath ; 17 use of pH buffer solutions ; analysis max 3 18 ref to replicating experiment 3 times and calculating means / medians ; 19 method for calculating the rate of photosynthesis ; 20 plot graph of rate of photosynthesis against concentration ; 21 ref to suitable named statistical test e.g. Spearman’s rank ; 22 correct example of results table with headings ; safety and ethics 23 atrazine is toxic so, use eye protection / use gloves / wash spills / pH buffers are irritants so use eye protection / gloves ; 24 do not wash down sink / AW, due to environmental impacts / do not take large amounts of plants from the wild / AW ;

This question in 9693/43 Oct/Nov 2023

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

14 marks

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

This question in 9693/41 May/June 2024

3 Agriculture poses a threat to coral reefs in many parts of the world due to the run-off of fertilisers and herbicides into the sea. (a) Explain how fertiliser run-off can pose a threat to coral reefs. … … … … … … [3] (b) Herbicides are chemicals that are used to kill weeds on farmland. Scientists investigated the effect of herbicides on the production of ATP, the production of reduced NADP and the rate of carbon fixation by dinoflagellates. Suspensions of chloroplasts taken from dinoflagellates were placed into a test-tube in bright light. The concentrations of ATP, reduced NADP and glucose were measured at time 0. Herbicide was added to the test-tube and the concentrations of ATP, reduced NADP and glucose were measured after 10 minutes, 20 minutes and 30 minutes. The results are shown in Table 3.1. Table 3.1 time / min concentration of ATP concentration of concentration of / arbitrary units reduced NADP glucose / arbitrary units / arbitrary units 0 25 21 15 10 15 15 15 20 10 5 10 30 10 1 5 (i) Compare the change in concentration of ATP with the change in the concentration of reduced NADP over the 30-minute period. … … … … [2] (ii) The herbicide reduces the concentration of chlorophyll in the chloroplasts of dinoflagellates. Explain the effect of adding herbicide on the changes in concentration of ATP and reduced NADP shown in Table 3.1. … … … … … … [3] (iii) Explain the effect of adding herbicide on the change in concentration of glucose shown in Table 3.1. … … … … … … [3] (c) Marine diatoms are planktonic producers. Fig. 3.1 shows a photograph of some marine diatoms. Fig. 3.1 Make a large drawing of the part of the diatom shown inside the box in Fig. 3.1. Do not label your diagram. [4] [Total: 15]

15 marks

Mark scheme: 3(a) any 3 of: 3 1 release of nitrogen / phosphorus ; 2 (increased) algal growth / algal blooms / eutrophication / AW ; 3 (covering coral so) reducing light intensity / AW ; 4 reducing photosynthesis (of coral) / reducing (primary) productivity / AW ; 5 (increased) decomposition ; 6 loss of oxygen ; 7 AVP ; 3(b)(i) any 2 of: 2 both decrease ; ATP levels off / reduced NADP continues to fall / AW ; greater fall in NADP than ATP / ORA / AW ; 3(b)(ii) any 3 of: 3 less light-dependent stage ; less light trapped by chlorophyll / less photoactivation of chlorophyll / AW ; less transfer of energy from, light / chlorophyll, to ATP / reduced NADP ; some ATP continues to be produced via respiration ; AVP ; 3(b)(iii) any 3 of: 3 glucose concentration falls / AW ; light-independent stage does not occur ; due to loss of ATP / reduced NADP ; less fixation of carbon / AW ; glucose is used in respiration ; glucose is converted to starch / organic molecules / other named substance ; 3(c) lines are thin, clear, unbroken and no shading ; 4 at least one third of space used ; correct proportions of cell width, length and chloroplasts ; correct detail ; correct number of chloroplasts (minimum of 8) + double line for cell wall ;

This question in 9693/41 Oct/Nov 2024

3 Agriculture poses a threat to coral reefs in many parts of the world due to the run-off of fertilisers and herbicides into the sea. (a) Explain how fertiliser run-off can pose a threat to coral reefs. … … … … … … [3] (b) Herbicides are chemicals that are used to kill weeds on farmland. Scientists investigated the effect of herbicides on the production of ATP, the production of reduced NADP and the rate of carbon fixation by dinoflagellates. Suspensions of chloroplasts taken from dinoflagellates were placed into a test-tube in bright light. The concentrations of ATP, reduced NADP and glucose were measured at time 0. Herbicide was added to the test-tube and the concentrations of ATP, reduced NADP and glucose were measured after 10 minutes, 20 minutes and 30 minutes. The results are shown in Table 3.1. Table 3.1 time / min concentration of ATP concentration of concentration of / arbitrary units reduced NADP glucose / arbitrary units / arbitrary units 0 25 21 15 10 15 15 15 20 10 5 10 30 10 1 5 (i) Compare the change in concentration of ATP with the change in the concentration of reduced NADP over the 30-minute period. … … … … [2] (ii) The herbicide reduces the concentration of chlorophyll in the chloroplasts of dinoflagellates. Explain the effect of adding herbicide on the changes in concentration of ATP and reduced NADP shown in Table 3.1. … … … … … … [3] (iii) Explain the effect of adding herbicide on the change in concentration of glucose shown in Table 3.1. … … … … … … [3] (c) Marine diatoms are planktonic producers. Fig. 3.1 shows a photograph of some marine diatoms. Fig. 3.1 Make a large drawing of the part of the diatom shown inside the box in Fig. 3.1. Do not label your diagram. [4] [Total: 15]

15 marks

Mark scheme: 3(a) any 3 of: 3 1 release of nitrogen / phosphorus ; 2 (increased) algal growth / algal blooms / eutrophication / AW ; 3 (covering coral so) reducing light intensity / AW ; 4 reducing photosynthesis (of coral) / reducing (primary) productivity / AW ; 5 (increased) decomposition ; 6 loss of oxygen ; 7 AVP ; 3(b)(i) any 2 of: 2 both decrease ; ATP levels off / reduced NADP continues to fall / AW ; greater fall in NADP than ATP / ORA / AW ; 3(b)(ii) any 3 of: 3 less light-dependent stage ; less light trapped by chlorophyll / less photoactivation of chlorophyll / AW ; less transfer of energy from, light / chlorophyll, to ATP / reduced NADP ; some ATP continues to be produced via respiration ; AVP ; 3(b)(iii) any 3 of: 3 glucose concentration falls / AW ; light-independent stage does not occur ; due to loss of ATP / reduced NADP ; less fixation of carbon / AW ; glucose is used in respiration ; glucose is converted to starch / organic molecules / other named substance ; 3(c) lines are thin, clear, unbroken and no shading ; 4 at least one third of space used ; correct proportions of cell width, length and chloroplasts ; correct detail ; correct number of chloroplasts (minimum of 8) + double line for cell wall ;

This question in 9693/42 Oct/Nov 2024

3 Agriculture poses a threat to coral reefs in many parts of the world due to the run-off of fertilisers and herbicides into the sea. (a) Explain how fertiliser run-off can pose a threat to coral reefs. … … … … … … [3] (b) Herbicides are chemicals that are used to kill weeds on farmland. Scientists investigated the effect of herbicides on the production of ATP, the production of reduced NADP and the rate of carbon fixation by dinoflagellates. Suspensions of chloroplasts taken from dinoflagellates were placed into a test-tube in bright light. The concentrations of ATP, reduced NADP and glucose were measured at time 0. Herbicide was added to the test-tube and the concentrations of ATP, reduced NADP and glucose were measured after 10 minutes, 20 minutes and 30 minutes. The results are shown in Table 3.1. Table 3.1 time / min concentration of ATP concentration of concentration of / arbitrary units reduced NADP glucose / arbitrary units / arbitrary units 0 25 21 15 10 15 15 15 20 10 5 10 30 10 1 5 (i) Compare the change in concentration of ATP with the change in the concentration of reduced NADP over the 30-minute period. … … … … [2] (ii) The herbicide reduces the concentration of chlorophyll in the chloroplasts of dinoflagellates. Explain the effect of adding herbicide on the changes in concentration of ATP and reduced NADP shown in Table 3.1. … … … … … … [3] (iii) Explain the effect of adding herbicide on the change in concentration of glucose shown in Table 3.1. … … … … … … [3] (c) Marine diatoms are planktonic producers. Fig. 3.1 shows a photograph of some marine diatoms. Fig. 3.1 Make a large drawing of the part of the diatom shown inside the box in Fig. 3.1. Do not label your diagram. [4] [Total: 15]

15 marks

Mark scheme: 3(a) any 3 of: 3 1 release of nitrogen / phosphorus ; 2 (increased) algal growth / algal blooms / eutrophication / AW ; 3 (covering coral so) reducing light intensity / AW ; 4 reducing photosynthesis (of coral) / reducing (primary) productivity / AW ; 5 (increased) decomposition ; 6 loss of oxygen ; 7 AVP ; 3(b)(i) any 2 of: 2 both decrease ; ATP levels off / reduced NADP continues to fall / AW ; greater fall in NADP than ATP / ORA / AW ; 3(b)(ii) any 3 of: 3 less light-dependent stage ; less light trapped by chlorophyll / less photoactivation of chlorophyll / AW ; less transfer of energy from, light / chlorophyll, to ATP / reduced NADP ; some ATP continues to be produced via respiration ; AVP ; 3(b)(iii) any 3 of: 3 glucose concentration falls / AW ; light-independent stage does not occur ; due to loss of ATP / reduced NADP ; less fixation of carbon / AW ; glucose is used in respiration ; glucose is converted to starch / organic molecules / other named substance ; 3(c) lines are thin, clear, unbroken and no shading ; 4 at least one third of space used ; correct proportions of cell width, length and chloroplasts ; correct detail ; correct number of chloroplasts (minimum of 8) + double line for cell wall ;

This question in 9693/43 Oct/Nov 2024

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

14 marks

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

This question in 9693/42 May/June 2025

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

14 marks

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

This question in 9693/43 May/June 2025

2 Scientists investigated the effect of temperature on the rate of photosynthesis and the rate of respiration of phytoplankton. (a) Outline the light-dependent stage of photosynthesis. … … … … … … [3] (b) A species of green alga that normally grows in surface water was grown in a tank. The rate of oxygen release from algae is a measure of the rate of photosynthesis. The algae were illuminated with light of the same intensity and wavelengths (colours) as in the surface water. The rate of oxygen release by the algae was measured at temperatures between 5 °C and 35 °C. The experiment was repeated with light of the same intensity and wavelengths as in water at a depth of 15 m. The effect of temperature on the rate of respiration was also determined by measuring the rate of oxygen uptake when the algae were in the dark. The results are shown in Fig. 2.1. 160 20 140 rate of 120 15rate of oxygen oxygen uptake 100release from by algae respiration / μg of 80 10 by algae oxygen / μg of produced 60 oxygen A B per min absorbed 40 5 per min 20 0 0 0 5 10 15 20 25 30 35 temperature / °C Key rate of oxygen release with light of the same intensity and wavelengths as in surface water rate of oxygen release with light of the same intensity and wavelengths as at 15 m depth rate of oxygen uptake from respiration in darkness Fig. 2.1 (i) Describe how the light intensity and light wavelengths at a depth of 15 m will differ from the light intensity and light wavelengths at the surface. … … … … [2] (ii) State the factors that are limiting the rates of photosynthesis at A and B on Fig. 2.1. Explain your answers. limiting factor at A … explanation … … limiting factor at B … explanation … … [4] (iii) The overall rate of photosynthesis of a producer is the total amount of oxygen produced by photosynthesis. It can be calculated using the equation shown. rate of oxygen release rate of oxygen uptake from respiration overall rate of photosynthesis = + by algae by algae Use the equation and Fig. 2.1 to calculate the overall rate of photosynthesis for the algae at a temperature of 20 °C and a depth of 15 m. Assume the rate of respiration is not affected by depth. State the unit. Show your working. … [3] (iv) Use Fig. 2.1 to discuss how global warming could affect the growth of algae at the surface and at 15 m depth. … … … … … … [3] [Total: 15]

15 marks

Mark scheme: 2(a) any 3 of: 3 1 chlorophyll absorbs light energy / is photoactivated ; 2 in the lamellae / grana / thylakoid, of chloroplasts ; 3 ATP made ; 4 reduced NADP made / NADPH / AW ; 5 photolysis of water occurs / AW ; 6 oxygen released ; 2(b)(i) lower light intensity (at 15 m) / AW / ORA ; 2 less longer wavelength light (at 15 m) / less red light / more blue light / more green light / AW / ORA ; 2(b)(ii) (A) 4 temperature ; because increasing temperature increased the rate / higher temperature increases kinetic energy of substrates / AW ; (B) light intensity / wavelengths ; because increasing light intensity / having more wavelengths available, increases rate / AW ; 2(b)(iii) 73 ;; (2 marks) 3 1 mark for 68 OR 5 in working ; g (O2) min–1 ; 2(b)(iv) any 3 of: 3 1 at surface photosynthesis increases AND, at 15 m / in deeper water, photosynthesis will, not increase (as much) / AW ; 2 light (intensity / wavelength) limits photosynthesis in, deeper water / 15 m / AW / ORA ; 3 respiration increases with temperature (at both depths) / AW ; 4 productivity / growth, at surface, increases / is high, AND in deeper water / 15 m, decreases / drops / AW ; 5 other factors may affect algal growth ;

This question in 9693/41 Oct/Nov 2025

2 Scientists investigated the effect of temperature on the rate of photosynthesis and the rate of respiration of phytoplankton. (a) Outline the light-dependent stage of photosynthesis. … … … … … … [3] (b) A species of green alga that normally grows in surface water was grown in a tank. The rate of oxygen release from algae is a measure of the rate of photosynthesis. The algae were illuminated with light of the same intensity and wavelengths (colours) as in the surface water. The rate of oxygen release by the algae was measured at temperatures between 5 °C and 35 °C. The experiment was repeated with light of the same intensity and wavelengths as in water at a depth of 15 m. The effect of temperature on the rate of respiration was also determined by measuring the rate of oxygen uptake when the algae were in the dark. The results are shown in Fig. 2.1. 160 20 140 rate of 120 15rate of oxygen oxygen uptake 100release from by algae respiration / μg of 80 10 by algae oxygen / μg of produced 60 oxygen A B per min absorbed 40 5 per min 20 0 0 0 5 10 15 20 25 30 35 temperature / °C Key rate of oxygen release with light of the same intensity and wavelengths as in surface water rate of oxygen release with light of the same intensity and wavelengths as at 15 m depth rate of oxygen uptake from respiration in darkness Fig. 2.1 (i) Describe how the light intensity and light wavelengths at a depth of 15 m will differ from the light intensity and light wavelengths at the surface. … … … … [2] (ii) State the factors that are limiting the rates of photosynthesis at A and B on Fig. 2.1. Explain your answers. limiting factor at A … explanation … … limiting factor at B … explanation … … [4] (iii) The overall rate of photosynthesis of a producer is the total amount of oxygen produced by photosynthesis. It can be calculated using the equation shown. rate of oxygen release rate of oxygen uptake from respiration overall rate of photosynthesis = + by algae by algae Use the equation and Fig. 2.1 to calculate the overall rate of photosynthesis for the algae at a temperature of 20 °C and a depth of 15 m. Assume the rate of respiration is not affected by depth. State the unit. Show your working. … [3] (iv) Use Fig. 2.1 to discuss how global warming could affect the growth of algae at the surface and at 15 m depth. … … … … … … [3] [Total: 15]

15 marks

Mark scheme: 2(a) any 3 of: 3 1 chlorophyll absorbs light energy / is photoactivated ; 2 in the lamellae / grana / thylakoid, of chloroplasts ; 3 ATP made ; 4 reduced NADP made / NADPH / AW ; 5 photolysis of water occurs / AW ; 6 oxygen released ; 2(b)(i) lower light intensity (at 15 m) / AW / ORA ; 2 less longer wavelength light (at 15 m) / less red light / more blue light / more green light / AW / ORA ; 2(b)(ii) (A) 4 temperature ; because increasing temperature increased the rate / higher temperature increases kinetic energy of substrates / AW ; (B) light intensity / wavelengths ; because increasing light intensity / having more wavelengths available, increases rate / AW ; 2(b)(iii) 73 ;; (2 marks) 3 1 mark for 68 OR 5 in working ; g (O2) min–1 ; 2(b)(iv) any 3 of: 3 1 at surface photosynthesis increases AND, at 15 m / in deeper water, photosynthesis will, not increase (as much) / AW ; 2 light (intensity / wavelength) limits photosynthesis in, deeper water / 15 m / AW / ORA ; 3 respiration increases with temperature (at both depths) / AW ; 4 productivity / growth, at surface, increases / is high, AND in deeper water / 15 m, decreases / drops / AW ; 5 other factors may affect algal growth ;

This question in 9693/42 Oct/Nov 2025

2 Scientists investigated the effect of temperature on the rate of photosynthesis and the rate of respiration of phytoplankton. (a) Outline the light-dependent stage of photosynthesis. … … … … … … [3] (b) A species of green alga that normally grows in surface water was grown in a tank. The rate of oxygen release from algae is a measure of the rate of photosynthesis. The algae were illuminated with light of the same intensity and wavelengths (colours) as in the surface water. The rate of oxygen release by the algae was measured at temperatures between 5 °C and 35 °C. The experiment was repeated with light of the same intensity and wavelengths as in water at a depth of 15 m. The effect of temperature on the rate of respiration was also determined by measuring the rate of oxygen uptake when the algae were in the dark. The results are shown in Fig. 2.1. 160 20 140 rate of 120 15rate of oxygen oxygen uptake 100release from by algae respiration / μg of 80 10 by algae oxygen / μg of produced 60 oxygen A B per min absorbed 40 5 per min 20 0 0 0 5 10 15 20 25 30 35 temperature / °C Key rate of oxygen release with light of the same intensity and wavelengths as in surface water rate of oxygen release with light of the same intensity and wavelengths as at 15 m depth rate of oxygen uptake from respiration in darkness Fig. 2.1 (i) Describe how the light intensity and light wavelengths at a depth of 15 m will differ from the light intensity and light wavelengths at the surface. … … … … [2] (ii) State the factors that are limiting the rates of photosynthesis at A and B on Fig. 2.1. Explain your answers. limiting factor at A … explanation … … limiting factor at B … explanation … … [4] (iii) The overall rate of photosynthesis of a producer is the total amount of oxygen produced by photosynthesis. It can be calculated using the equation shown. rate of oxygen release rate of oxygen uptake from respiration overall rate of photosynthesis = + by algae by algae Use the equation and Fig. 2.1 to calculate the overall rate of photosynthesis for the algae at a temperature of 20 °C and a depth of 15 m. Assume the rate of respiration is not affected by depth. State the unit. Show your working. … [3] (iv) Use Fig. 2.1 to discuss how global warming could affect the growth of algae at the surface and at 15 m depth. … … … … … … [3] [Total: 15]

15 marks

Mark scheme: 2(a) any 3 of: 3 1 chlorophyll absorbs light energy / is photoactivated ; 2 in the lamellae / grana / thylakoid, of chloroplasts ; 3 ATP made ; 4 reduced NADP made / NADPH / AW ; 5 photolysis of water occurs / AW ; 6 oxygen released ; 2(b)(i) lower light intensity (at 15 m) / AW / ORA ; 2 less longer wavelength light (at 15 m) / less red light / more blue light / more green light / AW / ORA ; 2(b)(ii) (A) 4 temperature ; because increasing temperature increased the rate / higher temperature increases kinetic energy of substrates / AW ; (B) light intensity / wavelengths ; because increasing light intensity / having more wavelengths available, increases rate / AW ; 2(b)(iii) 73 ;; (2 marks) 3 1 mark for 68 OR 5 in working ; g (O2) min–1 ; 2(b)(iv) any 3 of: 3 1 at surface photosynthesis increases AND, at 15 m / in deeper water, photosynthesis will, not increase (as much) / AW ; 2 light (intensity / wavelength) limits photosynthesis in, deeper water / 15 m / AW / ORA ; 3 respiration increases with temperature (at both depths) / AW ; 4 productivity / growth, at surface, increases / is high, AND in deeper water / 15 m, decreases / drops / AW ; 5 other factors may affect algal growth ;

This question in 9693/43 Oct/Nov 2025