The rocky shore — Paper 2 · A Level Marine Science 9693

4 (a) (i) Explain how the alignment of the Sun and the Moon affects the tidal range. You may use diagrams in your answer. … … … … … … … … … … … … … … … … [6] (ii) Describe other factors that can affect tidal range. … … … … … … [3] (b) Outline how environmental factors affect the formation of communities on a rocky shore. … … … … … … … … … … … … [6] [Total: 15]

15 marks

Mark scheme: 4(a)(i) Any 6 of: 1 ref. to tides due to gravitational, effects / pull / forces, of Sun and Moon ; 2 neap tides have a small(er) range ; 3 spring tides have a large(r) range ; (neap tides) 4 when the Sun, (Earth) and Moon form a right angle / perpendicular ; 5 reduced gravitational effect ; (spring tides) 6 when the Sun, (Earth) and Moon are in a straight line / aligned ; 7 combined / greater, gravitational effect ; 6 tides alone is insufficient for MP2 and 3- idea of tidal range is needed 4(a)(ii) wind direction ; wind speed / strength ; air pressure ; size / depth / area / volume, of water body ; idea of, geomorphology ; 3 A offshore / on shore wind for wind direction I wind unqualified for MP1 and 2 e.g. shape of, coast / shore / seabed, slope of coast Question Answer Marks Guidance 4(b) 1 idea of, organism adapted to survive where they live / environment ; 2 nutrient availability ; 3 ref. to gas concentration / gas availability ; 4 salinity varies ; 5 idea of, large temperature range ; 6 idea of, desiccation / exposure to air OR freezing ; 7 wave action ; 8 topography / slope / shape ; 9 exposed / sheltered, (coastline) ; 10 tidal range ; 11 type of substrate / resistance to, erosion / weathering ; 6 A aspect

This question in 9693/21 May/June 2018

2 Fig. 2.1 shows a settlement of acorn barnacles, Semibalanus balanoides, on a rocky shore. 1 cm Fig. 2.1 A student decided to look at the distribution of three different barnacle species on a rocky shore. The results of this investigation are shown in Table 2.1. Table 2.1 distance above number of barnacles per unit area low water spring tide line / m species 1 species 2 species 3 0 0 98 13 2 1 42 49 4 6 3 87 6 49 0 63 8 91 0 15 10 84 0 5 (a) Describe an experimental procedure the student could use to carry out this investigation. … … … … … … … … [4] (b) Use the data in Table 2.1 to determine where the greatest biodiversity of barnacles is found. … m [1] (c) Use the data in Table 2.1 to compare the distribution of the three barnacle species. Suggest reasons for the differences in distribution. … … … … … … … … [4] [Total: 9]

9 marks

This question in 9693/20 Oct/Nov 2018

1 Fig. 1.1 shows the common limpet, Patella vulgata, a mollusc that inhabits rocky shores across Northern Europe. When submerged, limpets feed by moving across the rock surface, scraping off algae. During low tide they attach themselves securely to the rock surface. Repeated use of the same position on the rock by limpets over many years can lead to a home scar forming, also visible in Fig. 1.1. home scar Fig. 1.1 Individual limpets repeatedly return to the same home scar, and are therefore said to have a homing instinct. A researcher investigated this homing instinct to test the following hypothesis. ‘The further a limpet moves from its home scar, the less likely it is to return there.’ At low tide, a sample of similar sized limpets was carefully removed from their home scar and placed 10 cm away, ensuring they reattached securely to the rock surface. The limpets and their original home scars were marked with numbers. The limpets were left until the next low tide. The researcher then counted how many limpets had returned to their home scar. This process was repeated in five different areas, but with limpets moved different distances each time. (a) Suggest two variables that the researcher was unable to control. 1 … … 2 … … [2] Table 1.1 shows the results. Table 1.1 percentage distance moved number of limpets number returning returning / cm moved to home scar to home scar 10 16 15 93.8 20 15 10 66.7 30 14 11 78.6 40 15 11 73.3 50 15 9 (b) (i) Calculate the percentage of limpets returning to their home scar after being moved 50 cm. Show your working. … [2] (ii) Plot a line graph to show the relationship between the distance the limpets were moved and the percentage returning to their home scar. Include a point for your calculated value for limpets that were moved 50 cm. Join the points with ruled, straight lines. [4] (iii) Use the data in Table 1.1 and your graph to discuss the extent to which the data support the hypothesis. … … … … … … [3] (c) Suggest and explain how the homing instinct may increase the chance of survival of limpets. … … … … [2] [Total: 13]

13 marks

Mark scheme: 1(a) any 2 of: age of limpets ; number of limpets in sample ; health of limpets ; impact of predation / death of limpets ; exact morphology of rock / type of rock / nature of rock surface ; (degree of) turbulence (when submerged) / wave action / currents ; length of time exposed / time between tides ; height of tide ; 2 1(b)(i) 60(.0) ; ; 2 1(b)(ii) appropriate linear scale for both axes ; both axes labelled including units ; all points plotted correctly (± 1 mm) ; distance moved / cm percentage returning to home scar 10 93.8 20 66.7 30 78.6 40 73.3 50 60.0 but ECF from 1(b)(i) all points joined correctly with ruled straight lines(± 1 mm) ; 4 Question Answer Marks Guidance 1(b)(iii) any 3 of: data shows the greater the distance, the lower the percentage of limpets returning / AW ; manipulation of figures to support answer ; ref. to (ignoring) anomaly for 20 cm OR reference to it not supporting hypothesis ; ref. to, only 5 data points / lack of repeats ; 3 1(c) any 2 of: home scar allows better surface for attachment to rocks (during low tide) ; so less chance of predation ; so less chance of, desiccation / drying out ; home scar in, more sheltered / less exposed area ; so less chance of being washed off / greater resistance to wave action ; AVP ; ; 2 A tight seal can be formed against rock e.g. allows water to be trapped under shell ; which assists gas exchange ;

This question in 9693/21 May/June 2019

4 (a) Describe the processes that give rise to the morphology of sandy shores. … … … … … … … … [4] (b) Describe how environmental factors influence the communities of rocky shores. … … … … … … … … … … … … … … [7] (c) Explain, with reference to marine examples, why habitats with high biodiversity tend to contain narrow ecological niches. … … … … … … … … [4] [Total: 15]

15 marks

Mark scheme: 4(a) any four from ref. deposition / sedimentation, greater than erosion ; loose deposit / unconsolidated ; ref. to size range of particles ; shifting substrate / movement / unstable ; ref. shallow slope / how slope allows for deposition ; ref. action of tides / waves / storms / currents, related to erosion and/or movement ; ref. long shore drift ; 4 4(b) any seven from ref. rock / stable substrate ; (idea that substrate isn’t shifting) ref. allows for attachment ; idea of, resistance to erosion ; idea of, shape of rocks creates habitat (e.g. rock pools, overhangs) ; (exposure to) wave action ; tides / tidal cycle, affects length of exposure ; (exposure to) desiccation ; effect of variable temp. / salinity / dissolved oxygen ; idea of, zonation ; (because) length of exposure to air impacts on position up the shore ; ref. competition / predation (sets lower limit) ; (community made up of) organisms with specific adaptation(s) / particular niches available ; 7 A stated hard rock type e.g. granite A differing degrees of tolerance to temp / drying impacts position up shore 4(c) any 4 from: ref. to example of marine ecosystem with high biodiversity(e.g. coral reef) ; (high biodiversity =) many different species (within one ecosystem / habitat); high degree competition ; idea of, narrow niches, prevent overlap OR reduce / avoid competition ; ref. to specialist feeders / only eats coral / may only feed on one type of food ; 4

This question in 9693/22 May/June 2019

4 (a) Describe the processes that give rise to the morphology of sandy shores. … … … … … … … … [4] (b) Describe how environmental factors influence the communities of rocky shores. … … … … … … … … … … … … … … [7] (c) Explain, with reference to marine examples, why habitats with high biodiversity tend to contain narrow ecological niches. … … … … … … … … [4] [Total: 15]

15 marks

Mark scheme: 4(a) any four from ref. deposition / sedimentation, greater than erosion ; loose deposit / unconsolidated ; ref. to size range of particles ; shifting substrate / movement / unstable ; ref. shallow slope / how slope allows for deposition ; ref. action of tides / waves / storms / currents, related to erosion and/or movement ; ref. long shore drift ; 4 4(b) any seven from ref. rock / stable substrate ; (idea that substrate isn’t shifting) ref. allows for attachment ; idea of, resistance to erosion ; idea of, shape of rocks creates habitat (e.g. rock pools, overhangs) ; (exposure to) wave action ; tides / tidal cycle, affects length of exposure ; (exposure to) desiccation ; effect of variable temp. / salinity / dissolved oxygen ; idea of, zonation ; (because) length of exposure to air impacts on position up the shore ; ref. competition / predation (sets lower limit) ; (community made up of) organisms with specific adaptation(s) / particular niches available ; 7 A stated hard rock type e.g. granite A differing degrees of tolerance to temp / drying impacts position up shore 4(c) any 4 from: ref. to example of marine ecosystem with high biodiversity(e.g. coral reef) ; (high biodiversity =) many different species (within one ecosystem / habitat); high degree competition ; idea of, narrow niches, prevent overlap OR reduce / avoid competition ; ref. to specialist feeders / only eats coral / may only feed on one type of food ; 4

This question in 9693/23 May/June 2019

1 A student investigated the substrate (surface) that barnacle larvae preferred to settle on. They chose four substrates: • smooth granite • rough sandstone • loose sand • smooth plastic (from the hull of a boat). (a) State one hypothesis the student could test in this investigation. … … … [1] The student selected two pieces of each substrate, of different sizes, and placed them in four separate tanks, as shown in Fig. 1.1. Sea water was added to the tanks, and barnacle larvae of the same age, of the species Balanus glandula, were placed in the water in each tank. Phytoplankton were added to the water each day to provide food for the barnacle larvae. smooth rough loose sand smooth granite sandstone (in a tray) plastic Fig. 1.1 The student removed the pieces of substrate each day and counted the number of larvae that had settled on each piece. The substrates were then returned to the tanks, in the same position each time. Table 1.1 shows the results after 10 days. Table 1.1 substrate number of larvae settled smooth granite 1 rough sandstone 2 loose sand 0 smooth plastic 1 (b) State one variable that the student controlled in this investigation. … [1] (c) The student could not reach a firm conclusion from the data they had collected. Suggest three reasons why a firm conclusion could not be reached. 1 … … 2 … … 3 … … [3] (d) Suggest how the experimental method could have been improved. … … … … … … … … [4] [Total: 9]

9 marks

This question in 9693/20 Oct/Nov 2019

4 (a) Explain why the biodiversity on sandy shores is usually lower than that of rocky shores. … … … … … … … … [4] (b) Two rocky shores on the same coastline are found to have different levels of biodiversity. Discuss how environmental factors, including the morphology of the shore, could cause this difference. … … … … … … … … … … [5] (c) Explain why hydrothermal vents have very specific communities of organisms, which may change over time. … … … … … … … … … … … … [6] [Total: 15]

15 marks

Mark scheme: 4(a) any 4 from: 1 unstable substrate (inability to attach) / sediments ; 2 prone to erosion / deposition ; 3 reference to burrowing organisms ; 4 limited food sources ; 5 prone to desiccation ; 6 ref. to need for specific adaptation e.g. burrowing ability ; ORA for rocky shores Question Answer Marks 4(b) any 5 from: 1 degree of exposure to wave action ; 2 sheltered shores likely to show higher biodiversity ORA ; 3 slope / relief / incline ; 4 greater incline likely to have lower biodiversity ORA ; 5 topography ; 6 presence of rock/tidepools likely to give higher biodiversity ; 7 nature of substrate / rock type ; 8 sedimentary rock more prone to erosion / less suitable for attachment ; 9 tidal range ; 10 will affect length of time exposed to desiccation ; 11 aspect ; 12 will affect, degree of wave exposure / fetch ; 5 Question Answer Marks 4(c) Max 5 from: 1 ecosystem contends with extreme conditions ; 2 high water pressure ; 3 lack of light / aphotic conditions ; 4 high mineral content / toxicity ; 5 high water temperature (superheated water) ; 6 reliance on chemosynthesis to support ecosystem ; 7 organisms must be adapted to extreme conditions (extremophiles) ; Plus, at least one from: 8 ref to transient nature of vents (providing new habitat) ; 9 ref to succession ; 10 Tevnia replaced by Riftia ; 6

This question in 9693/21 May/June 2020

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

15 marks

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

This question in 9693/22 May/June 2023

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

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

15 marks

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

This question in 9693/23 May/June 2023

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

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