Life cycles — Paper 4 · A Level Marine Science 9693

4 (a) With reference to named examples, explain the advantages of internal fertilisation compared to external fertilisation. … … … … … … [3] (b) Oysters use external fertilisation. Outline the life cycle of oysters. … … … … … … … … … … … [4] (c) Oysters are often grown by aquaculture businesses. Discuss how a new aquaculture business could affect other industries in a coastal community. … … … … … … … … … … … … … … … … [8] [Total: 15]

15 marks

This question in 9693/40 Oct/Nov 2019

3 (a) (i) Fig. 3.1 shows a diagram of a piece of Sargassum. thallus air bladder holdfast scale: 10 cm Fig. 3.1 Explain how Sargassum is adapted to live in its habitat. … … … … … … … [3] (ii) Explain why loss of the seagrass Thalassia could negatively impact marine ecosystems. … … … … … … … … … … … … … [6] (b) Discuss how the reproduction of tuna differs from the reproduction of whales. … … … … … … … … … … … … … [6] [Total: 15]

15 marks

This question in 9693/40 May/June 2021

4 Fig. 4.1 shows part of the life cycle of the orca (killer whale). adult calf born juveniles live in groups with adult females Fig. 4.1 (a) Use Fig. 4.1 to explain why the life cycle of an orca is classed as a simple life cycle. … … … … [2] (b) Orcas belong to a group of organisms called cetaceans. In some species of cetaceans, females become infertile at a certain age and stop breeding. This is called a menopause. The time after the menopause until the animal dies is called the post-menopause period. Scientists compared the maximum life expectancy with the maximum length of the post-menopause period of a range of cetacean species. The results are shown in Fig. 4.2. Each plotted point indicates the mean value for one species. 35 30 25 20 maximum length of post-menopause period / years 15 10 5 0 40 50 60 70 80 90 100 maximum life expectancy / years Fig. 4.2 The scientists made a hypothesis that there is a positive correlation between the maximum life expectancy of cetacean species and the maximum length of the post-menopause period. Evaluate how strongly the graph shown in Fig. 4.2 supports the scientists’ hypothesis. … … … … … … [3] (c) The scientists carried out a Spearman’s rank correlation test to determine if there was a significant correlation between the maximum life expectancy and the maximum length of the post-menopause period. Their data and rankings are shown in Table 4.1. Table 4.1 cetacean maximum rank maximum rank D D 2 species life maximum length maximum expectancy life of post- length / years expectancy menopause of post- period menopause / years period fin whale 98 1 2 orca 95 2 30 1 1 1 long-finned 60 6.5 1 8.5 –2 4 pilot whale short-finned 64 4 20 2 2 4 pilot whale false killer 58 8 4 5 3 9 whale North Atlantic 49 9 2 6.5 2.5 6.25 right whale sperm whale 60 6.5 1 8.5 –2 4 beluga whale 62 5 12 4 1 1 narwhal 80 3 18 3 0 0 ∑D 2 = ∑ = sum of (total) D = difference in rank between each pair of measurements (i) Complete Table 4.1 by completing the values for: • fin whale • ∑D 2 [1] (ii) Give a null hypothesis for the statistical test. … … [1] (iii) Use the formula to calculate the Spearman’s rank correlation coefficient, rS, for the data in Table 4.1. 6 × ∑D 2 rS = 1 –  n3 – n  rS = Spearman’s rank correlation coefficient Σ = sum of (total) D = difference in rank between each pair of measurements n = number of pairs of items in the sample … [1] (iv) Table 4.2 is a critical values table for Spearman’s rank correlation coefficient. Table 4.2 number of pairs, n rS (p < 0.05) 5 1.000 6 0.886 7 0.786 8 0.738 9 0.700 10 0.648 11 0.618 Use your calculated value from 4(c)(iii), and Table 4.2, to assess whether there is a significant correlation between maximum life expectancy and maximum length of the post-menopause period. Justify your conclusion. … … … … … … [3] (d) Female orcas live in groups with other females they are related to. Use your knowledge of animal life cycles to suggest an explanation for the extended menopause of female orcas. … … … … … [2] [Total: 13]

13 marks

Mark scheme: 4(a) any 2 from: there is no, intermediate different form / larva / AW ; no metamorphosis ; no form that, occupies different niche / lives in different area / has another habitat / AW ; 4(b) any 3 from: (supported because) the line (of best fit) shows a positive correlation ; so as life expectancy increases, so does post-menopause length ; (not supported because) some / many / several of the points are far from the line of best fit / there are several anomalous values / outliers / points are very scattered ; no idea how large sample size was used ; 3 Question Answer Marks 4(c)(i) species maximum life expectancy rank maximum life expectancy maximum length of post menopause period rank maximum length of post menopause period D D2 fin whale 98 1 2 6.5 (–)5.5 30.25 ∑D2 59.5 ; 1 4(c)(ii) there is no, correlation / relationship / association, between the life expectancy and length of (post-) menopause period ; 1 4(c)(iii) 0.5(04…) ; 1 4(c)(iv) any 3 from: If the calculated number is smaller than the critical value… 1 there is no (significant) correlation / there is no (significant) association between life expectancy and (post) menopause length ; 2 the calculated value is not larger than the critical value ; 3 (identification) of 0.7(00) ; 4 so there is a probability of greater than, 0.05 / 5%, that the correlation / association is due to chance / AW ; 5 the null hypothesis is not rejected / null hypothesis is accepted ; If calculated number is larger, then accept: 1 there is a correlation ; 2 the calculated value is larger than the critical value ; 3 (identification) of 0.7(00) ; 4 so there is a probability of less than 0.05 / 5%, that the association is due to chance / AW ; 5 the null hypothesis is rejected ; 3 Question Answer Marks 4(d) any 2 from: 1 (helping to) feed / protect calves / nurture / protect the group / lots of parental care needed / investment needed / AW ; 2 increase survival of calves ; 3 orcas have few calves / are k-selectors / AW ; 4 (and need) calves stay with group for years / calves stay with mothers / group for a long time / AW ; 2

This question in 9693/41 May/June 2022

5 Copepods are marine zooplankton. They are crustaceans that have a complex life cycle. (a) Explain the advantages of having a complex life cycle. … … … … [2] (b) Algae grow on the surfaces of microplastics when microplastics are left in ocean surface water for over one month. The presence of the algae causes some animals to mistake the microplastic for food. Scientists measured the consumption of microplastic particles by copepod larvae, adult female copepods and adult male copepods. They counted the number of these consumed microplastic particles that were: • new, with no algae growing on them • two months old, with algae growing on them. The results are shown in Fig. 5.1. 16 newnew microplasticmicroplastic 14 two-month-oldtwo-month-old microplasticmicroplastic 12 number of 10 consumed microplastic 8 particles per copepod 6 4 2 0 larvae adult females adult males copepod group Fig. 5.1 (i) Describe the effect of age of the microplastics on their consumption by the different groups of copepod. … … … … … … [3] (ii) Salmon are grown for human consumption, using aquaculture in sea cages. Waste food from the salmon aquaculture is broken down by microorganisms, causing algal blooms. Copepods are small enough to swim into salmon cages and are eaten by salmon. Use this information and the information in Fig. 5.1 to suggest why the presence of microplastics in the waters around salmon aquaculture systems poses a threat to humans. … … … … … … [3] (iii) Plastic sheets placed into sea water gradually break down to form microplastics. As the plastic sheet breaks down, its area decreases. Temperature and wave action are two of the factors that affect the breakdown of plastic sheets into microplastics. Plan a laboratory‑based investigation that you could do to investigate the effect of water temperature on the rate of breakdown of plastic sheets. You are provided with standard laboratory apparatus and materials. 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. … … … … … … … … … … … … … … … …

8 marks

Mark scheme: 5(a) any 2 of: idea of additional stages / larval stage ; for distribution / live in different habitats ; to consume different food source / not compete with adults / AW ; 5(b)(i) any 3 of: 1 more two-month-old / older microplastic (with algal growth) are consumed (by all copepod groups) ; 2 largest increase for male copepods (between new and old) / smallest increase for larvae / AW ; 3 adults consume more than larvae / larvae consume the least / ORA ; 4 correct manipulation of data ; 5 more new microplastics are consumed by the females / least new microplastic consumed by larvae ; 3 5(b)(ii) any 3 of: 1 food breaks down / decomposes, to release mineral ions / named mineral ion ; 2 algae grow due to high mineral ion concentration / AW ; 3 (large amounts of) algae will attach to the microplastics / AW ; 4 microplastics absorb toxins ; 5 copepods eat (large amounts of) microplastic (when covered with algae) / AW ; 6 salmon will consume copepods that contain microplastics / toxins will accumulate in salmon / bioaccumulation / biomagnification / AW ; 3 Question Answer Marks 5(b)(iii) clear statement of hypothesis: increasing temperature will increase rate of / reduce time taken for, breakdown / AW ; AND any 10 of: independent variable 1 independent variable identified as temperature ; 2 using a range of at least five temperatures, stated or range given ; dependent variable 3 dependent variable identified as measuring loss of / change in, mass / length / area, of plastic ; 4 description of how to measure change over a stated time ; standardised variables MAX 4 of: 5 same size / type of plastic / same mass / area, of plastic ; 6 same light intensity / UV / AW ; 7 same movement of water / AW ; 8 same volume of water / AW ; 9 same salinity / AW ; 10 same acidity / carbon dioxide / other correct variable / AW ; 11 Question Answer Marks 5(b)(iii) Safety and ethics 11 safe / ethical disposal of plastic ; 12 eye protection with pH buffers / salinity / care with heating apparatus / statement of low-risk experiment ; Analysis MAX 3 of: 13 repeat at least three times and calculate means / medians / averages ; 14 plot graph of rate / change in mass / AW vs. temperature ; 15 correct named statistical test (e.g. Spearman’s rank) / standard deviation / error bars ; 16 calculate rate as change / time taken ; 17 results table with headings ;

This question in 9693/42 May/June 2023

5 Copepods are marine zooplankton. They are crustaceans that have a complex life cycle. (a) Explain the advantages of having a complex life cycle. … … … … [2] (b) Algae grow on the surfaces of microplastics when microplastics are left in ocean surface water for over one month. The presence of the algae causes some animals to mistake the microplastic for food. Scientists measured the consumption of microplastic particles by copepod larvae, adult female copepods and adult male copepods. They counted the number of these consumed microplastic particles that were: • new, with no algae growing on them • two months old, with algae growing on them. The results are shown in Fig. 5.1. 16 newnew microplasticmicroplastic 14 two-month-oldtwo-month-old microplasticmicroplastic 12 number of 10 consumed microplastic 8 particles per copepod 6 4 2 0 larvae adult females adult males copepod group Fig. 5.1 (i) Describe the effect of age of the microplastics on their consumption by the different groups of copepod. … … … … … … [3] (ii) Salmon are grown for human consumption, using aquaculture in sea cages. Waste food from the salmon aquaculture is broken down by microorganisms, causing algal blooms. Copepods are small enough to swim into salmon cages and are eaten by salmon. Use this information and the information in Fig. 5.1 to suggest why the presence of microplastics in the waters around salmon aquaculture systems poses a threat to humans. … … … … … … [3] (iii) Plastic sheets placed into sea water gradually break down to form microplastics. As the plastic sheet breaks down, its area decreases. Temperature and wave action are two of the factors that affect the breakdown of plastic sheets into microplastics. Plan a laboratory‑based investigation that you could do to investigate the effect of water temperature on the rate of breakdown of plastic sheets. You are provided with standard laboratory apparatus and materials. 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. … … … … … … … … … … … … … … … …

8 marks

Mark scheme: 5(a) any 2 of: idea of additional stages / larval stage ; for distribution / live in different habitats ; to consume different food source / not compete with adults / AW ; 5(b)(i) any 3 of: 1 more two-month-old / older microplastic (with algal growth) are consumed (by all copepod groups) ; 2 largest increase for male copepods (between new and old) / smallest increase for larvae / AW ; 3 adults consume more than larvae / larvae consume the least / ORA ; 4 correct manipulation of data ; 5 more new microplastics are consumed by the females / least new microplastic consumed by larvae ; 3 5(b)(ii) any 3 of: 1 food breaks down / decomposes, to release mineral ions / named mineral ion ; 2 algae grow due to high mineral ion concentration / AW ; 3 (large amounts of) algae will attach to the microplastics / AW ; 4 microplastics absorb toxins ; 5 copepods eat (large amounts of) microplastic (when covered with algae) / AW ; 6 salmon will consume copepods that contain microplastics / toxins will accumulate in salmon / bioaccumulation / biomagnification / AW ; 3 Question Answer Marks 5(b)(iii) clear statement of hypothesis: increasing temperature will increase rate of / reduce time taken for, breakdown / AW ; AND any 10 of: independent variable 1 independent variable identified as temperature ; 2 using a range of at least five temperatures, stated or range given ; dependent variable 3 dependent variable identified as measuring loss of / change in, mass / length / area, of plastic ; 4 description of how to measure change over a stated time ; standardised variables MAX 4 of: 5 same size / type of plastic / same mass / area, of plastic ; 6 same light intensity / UV / AW ; 7 same movement of water / AW ; 8 same volume of water / AW ; 9 same salinity / AW ; 10 same acidity / carbon dioxide / other correct variable / AW ; 11 Question Answer Marks 5(b)(iii) Safety and ethics 11 safe / ethical disposal of plastic ; 12 eye protection with pH buffers / salinity / care with heating apparatus / statement of low-risk experiment ; Analysis MAX 3 of: 13 repeat at least three times and calculate means / medians / averages ; 14 plot graph of rate / change in mass / AW vs. temperature ; 15 correct named statistical test (e.g. Spearman’s rank) / standard deviation / error bars ; 16 calculate rate as change / time taken ; 17 results table with headings ;

This question in 9693/43 May/June 2023

5 (a) Explain why international cooperation and legislation are necessary for the effective conservation of many marine species. … … … … [2] (b) Cultivated salmon that have been raised in captivity are often used to rehabilitate wild stocks. Young wild salmon naturally migrate from a river towards its estuary as part of their life cycle. Young salmon that have been raised in captivity often swim in the wrong direction when they are released and do not reach the estuary. Scientists investigated if acclimatising young salmon in rivers before release affects their migration behaviour. This is the method the scientists used. • Young salmon were raised in captivity and then separated into two groups. • One group of the young salmon was placed into cages in the river for two weeks to acclimatise. The other group (non-acclimatised salmon) remained in the fresh-water tanks. • Both groups of salmon were tagged with a unique identifier so they could be detected. Both groups were then released into the river. • Sensors to detect the salmon were placed upstream and downstream of the release site. • The number of salmon that passed each sensor each day were recorded. The results are shown in Fig. 5.1. number of non-acclimatised salmon detected upstream 6 5 number of 4 young salmon 3 detected 2 1 0 0 5 10 15 20 25 30 35 40 45 50 55 60 time / days number of acclimatised salmon detected upstream 6 5 number of 4 young salmon 3 detected 2 1 0 0 5 10 15 20 25 30 35 40 45 50 55 60 time / days number of non-acclimatised salmon detected downstream 12 11 10 9 8 number of 7 young salmon 6 detected 5 4 3 2 1 0 0 5 10 15 20 25 30 35 40 45 50 55 60 time / days number of acclimatised salmon detected downstream 12 11 10 9 8 number of 7 young salmon 6 detected 5 4 3 2 1 0 0 5 10 15 20 25 30 35 40 45 50 55 60 time / days Fig. 5.1 (i) The scientists tagged 150 young salmon in each group. Use Fig. 5.1 to calculate the percentage of acclimatised salmon that moved upstream. Show your working. … % [2] (ii) Discuss the effects of acclimatising the young salmon on their migration behaviour. Use the data in Fig. 5.1 to support your answer. … … … … … … … … [4]

8 marks

Mark scheme: 5(a) any 2 of: 1 to protect, endangered species / species at risk of extinction ; 2 species live across national boundaries / species live in international waters / AW ; 3 species migrate ; 4 need to control import / export / trade (between countries) / AW ; 5 so same rules for all / as different countries may have different views / AW ; 2 5(b)(i) 6.7 / 6.67 / 6.666 recurring / 7% ;; (two marks) one mark for 10 or 6.6 ; 2 5(b)(ii) any 4 of: 1 few(er) acclimatised salmon (compared with non-acclimatised), move upstream / go the wrong way / AW ; 2 more of both types of salmon go downstream (compared with moving upstream) / AW ; 3 acclimatised salmon move upstream earlier / do not stay in area long / AW ; 4 acclimatised salmon move downstream later / stay in area longer / AW ; 5 wider range of times for acclimatised salmon moving downstream / wider range of times non-acclimatised salmon moving upstream / AW ; 6 acclimatised salmon adapt to water conditions / food / currents / temperature / AW ; 7 AVP ; 4 5(c)(i) 25 , 625 , 41.7 ; 1 5(c)(ii) 51.3 ; 1 5(c)(iii) any 3 of: 1 the null hypothesis is rejected ; 2 the calculated value is greater than the critical value ; 3 correct identification of critical value of 3.841 or 6.635 ; 4 there is a significant difference ; 3

This question in 9693/41 May/June 2024

1 Fig. 1.1 shows some barnacles and a dogwhelk on a rock. Fig. 1.1 Adult barnacles are sessile and are often found attached to rocks on rocky shores. Barnacles have a complex life cycle with planktonic larvae. (a) Explain why a complex life cycle is an advantage for sessile organisms. … … … … [2] (b) The dogwhelk feeds on barnacles on rocky shores. Scientists investigated whether the settlement of barnacles on a rocky shore was affected by: • the presence of dogwhelks • the quantity of phytoplankton in the sea water next to the shore. The scientists placed 0.25 m2 plastic tiles onto four rocky shores: • one shore with a high quantity of phytoplankton in the sea and with dogwhelks present • one shore with a high quantity of phytoplankton in the sea and with no dogwhelks present • one shore with a low quantity of phytoplankton in the sea and with dogwhelks present • one shore with a low quantity of phytoplankton in the sea and with no dogwhelks present. All the tiles had a central area which dogwhelks could not access. Fig. 1.2 shows one of the tiles used. central area covered with mesh to stop dogwhelks getting in plastic tile Fig. 1.2 The plastic tiles were examined after two months. The population densities of the barnacles growing in the central area which dogwhelks could not access were calculated. (i) The central area of one plastic tile had 12 barnacles settled in an area of 0.0225 m2. Calculate the population density of barnacles for this plastic tile as the number of barnacles per m2. Give your answer to three significant figures. … per m2 [2] Fig. 1.3 shows the population density of barnacles that had settled on the plastic tiles on all four rocky shores. Key dogwhelks present dogwhelks not present 800 700 600 500 number of barnacles 400 per square metre 300 200 100 0 low quantities of high quantities of phytoplankton phytoplankton rocky shore Fig. 1.3 (ii) Summarise the results of the investigation shown in Fig. 1.3. … … … … [2] (iii) The scientists concluded that there was a strong probability that the presence of dogwhelks affects the settlement of barnacles onto rocks. Discuss the extent to which the error bars for standard deviation shown in Fig. 1.3 support the scientists’ conclusion. … … … … [2] (iv) Suggest explanations for the effect of dogwhelks and quantities of phytoplankton on the settling of the barnacles. … … … … … … [3] (c) The acorn barnacle has spread all around the world on ships and is now considered to be an invasive species. (i) Explain why invasive species are a risk to ecosystems. … … … … … … [3] (ii) It has been suggested that introducing dogwhelks into new areas colonised by acorn barnacles could be a method of control. Suggest a possible negative consequence of introducing dogwhelks into areas with acorn barnacles. … … [1] [Total: 15]

15 marks

Mark scheme: Question Answer Marks 1(a) any 2 of: 2 allows dispersal to wider area / other areas / moves to different locations / AW ; to reduce competition / larvae have different niches from adults / AW ; allows (larvae to) feed on plankton / AW ; 1(b)(i) 533 (to 3 sig figs) ;; 2 1(b)(ii) more barnacles are found on the shores where there are more phytoplankton / ORA ; 2 more barnacles where there are no dogwhelks / ORA ; 1(b)(iii) any 2 of: 2 supported because no overlap (with and without dogwhelks) on shore with low quantities of phytoplankton / AW ; less support as there is an overlap (with and without dogwhelks) with larger quantities of phytoplankton / AW ; other factors may be affecting result / correlation not causal ; 1(b)(iv) any 3 of: 3 barnacles consume phytoplankton / more food for barnacles (if more phytoplankton) / ORA / AW ; so more survival of larvae ; dogwhelks reduces, attachment / settling, of barnacle larvae ; due to presence of, chemicals / scent, from dogwhelks / AW ; less reproduction of barnacles (to reduce population) (when dogwhelks present / less phytoplankton) / AW ; 1(c)(i) any 3 of: 3 lack predators so increase in population / AW ; overconsume prey / AW ; out compete native species / AW ; AVP ; 1(c)(ii) may become an invasive species itself / may have no predator / consume other native species / AW ; 1

This question in 9693/41 Oct/Nov 2024

2 Plaice is a benthic flatfish caught by commercial fishing ships. Plaice gather in breeding areas during breeding seasons. Scientists investigated the effect of benthic trawling on the fishing mortality of plaice. The scientists determined the fishing mortality of male and female plaice of different ages during the breeding season and outside the breeding season. The results are shown in Fig. 2.1. during breeding season outside breeding season 0.4 0.4 Key male plaice female 0.3 0.3 plaice fishing fishing mortality mortality 0.2 0.2/ arbitrary / arbitrary units units 0.1 0.1 0.0 0.0 0 1 2 3 4 5 6 7 8 9 10 0 1 2 3 4 5 6 7 8 9 10 age of plaice / years age of plaice / years Fig. 2.1 (a) (i) Compare the fishing mortality of plaice during the breeding season and outside the breeding season. … … … … … … [3] (ii) Suggest a reason for the difference in fishing mortality of male and female plaice during the breeding season. … … [1] (iii) Suggest a reason for the difference in the fishing mortality of plaice during the breeding season and outside the breeding season. … … [1] (iv) Use Fig. 2.1 to explain why intensive harvesting of plaice during the breeding season would affect the sustainability of the population. … … … … … … [3] (b) In a further investigation, scientists investigated the gonadosomatic index (GSI) and price of plaice over a period of 48 weeks. Gonad tissues are ovaries and testes. Gonad tissue increases in size during breeding seasons. The gonadosomatic index (GSI) is the mass of gonad tissue divided by the total body mass. The results are shown in Table 2.1. Table 2.1 week mean gonadosomatic index mean price per kilogram (GSI) / USD ($) 1 0.14 1.8 12 0.03 2.5 24 0.02 3.4 36 0.03 3.8 48 0.10 2.1 (i) GSI is calculated using the formula: mass of gonad tissue GSI = total body mass Calculate the mass of gonad tissue in a plaice with a total body mass of 825 g caught during week 1. State the unit. … [2] (ii) Use Table 2.1 to draw a graph to show the GSI and price per kilogram of fish over the 48-week period. Join your points with straight, ruled lines. [6] (iii) Discuss the changes in GSI and the price of plaice over the 48-week period shown in Table 2.1 and the implications for the conservation of plaice. … … … … … … [3] [Total: 19]

19 marks

Mark scheme: 2(a)(i) any 3 of: 3 1 mortality is higher (for both) during breeding season / AW ; 2 mortality of males is higher than females during breeding season / AW ; 3 mortality of males and females is similar out of breeding season / AW ; 4 larger increase in mortality of males than females during breeding season (compared with out of season) / AW ; 5 both have low mortality for 0–1 years / mortality increases with age / lower mortality for younger fish / AW ; 6 correct manipulation of data ; 2(a)(ii) any 1 of: 1 female plaice are in deeper water / male plaice swim higher up the water column / males remain in the benthic area / ORA / AW ; males and females move to different, habitats / areas, (after breeding) / AW ; male plaice aggregate in same areas (after breeding) / ORA / AW ; male plaice are easier to catch / are targeted by fishers / females are put back by fishers / AW ; 2(a)(iii) any 1 of: 1 plaice (are aggregated) in one area (so are easier to find) / plaice area less dispersed / AW ; fishing boats target breeding areas / fishing occurs around breeding areas / AW ; 2(a)(iv) any 3 of: 3 1 overfishing will reduce population / less recruitment / reduced sustainability / AW ; 2 fewer older / mature fish / more immature / more younger fish / AW ; 3 imbalanced sex ratio / too few males / AW ; 4 so less breeding / fertilisation / lower fecundity / fewer eggs or sperm released / AW ; 5 AVP ; 2(b)(i) 115.5 ; 2 g ; 2(b)(ii) linear scales for both y axes and uses at least half of grid ; 6 all axes labelled ; accurate plots ;; points joined by straight lines ; key for lines ; 2(b)(iii) any 3 of: 3 1 lower price when GSI is high / ORA / AW ; 2 (may be due to) high catch rates before / during breeding season / price low when high catch / ORA / AW ; 3 (catches in breeding season causes) reduced reproduction / unsustainable fishing / population fall / less breeding / AW ; 4 should, ban / control, fishing during breeding season / AW ; 5 low price may be due to less demand for fish with high GSI / ORA ; 6 fish with high GSI may have lower meat content / poorer meat content / AW / ORA ;

This question in 9693/41 Oct/Nov 2024

1 Fig. 1.1 shows some barnacles and a dogwhelk on a rock. Fig. 1.1 Adult barnacles are sessile and are often found attached to rocks on rocky shores. Barnacles have a complex life cycle with planktonic larvae. (a) Explain why a complex life cycle is an advantage for sessile organisms. … … … … [2] (b) The dogwhelk feeds on barnacles on rocky shores. Scientists investigated whether the settlement of barnacles on a rocky shore was affected by: • the presence of dogwhelks • the quantity of phytoplankton in the sea water next to the shore. The scientists placed 0.25 m2 plastic tiles onto four rocky shores: • one shore with a high quantity of phytoplankton in the sea and with dogwhelks present • one shore with a high quantity of phytoplankton in the sea and with no dogwhelks present • one shore with a low quantity of phytoplankton in the sea and with dogwhelks present • one shore with a low quantity of phytoplankton in the sea and with no dogwhelks present. All the tiles had a central area which dogwhelks could not access. Fig. 1.2 shows one of the tiles used. central area covered with mesh to stop dogwhelks getting in plastic tile Fig. 1.2 The plastic tiles were examined after two months. The population densities of the barnacles growing in the central area which dogwhelks could not access were calculated. (i) The central area of one plastic tile had 12 barnacles settled in an area of 0.0225 m2. Calculate the population density of barnacles for this plastic tile as the number of barnacles per m2. Give your answer to three significant figures. … per m2 [2] Fig. 1.3 shows the population density of barnacles that had settled on the plastic tiles on all four rocky shores. Key dogwhelks present dogwhelks not present 800 700 600 500 number of barnacles 400 per square metre 300 200 100 0 low quantities of high quantities of phytoplankton phytoplankton rocky shore Fig. 1.3 (ii) Summarise the results of the investigation shown in Fig. 1.3. … … … … [2] (iii) The scientists concluded that there was a strong probability that the presence of dogwhelks affects the settlement of barnacles onto rocks. Discuss the extent to which the error bars for standard deviation shown in Fig. 1.3 support the scientists’ conclusion. … … … … [2] (iv) Suggest explanations for the effect of dogwhelks and quantities of phytoplankton on the settling of the barnacles. … … … … … … [3] (c) The acorn barnacle has spread all around the world on ships and is now considered to be an invasive species. (i) Explain why invasive species are a risk to ecosystems. … … … … … … [3] (ii) It has been suggested that introducing dogwhelks into new areas colonised by acorn barnacles could be a method of control. Suggest a possible negative consequence of introducing dogwhelks into areas with acorn barnacles. … … [1] [Total: 15]

15 marks

Mark scheme: Question Answer Marks 1(a) any 2 of: 2 allows dispersal to wider area / other areas / moves to different locations / AW ; to reduce competition / larvae have different niches from adults / AW ; allows (larvae to) feed on plankton / AW ; 1(b)(i) 533 (to 3 sig figs) ;; 2 1(b)(ii) more barnacles are found on the shores where there are more phytoplankton / ORA ; 2 more barnacles where there are no dogwhelks / ORA ; 1(b)(iii) any 2 of: 2 supported because no overlap (with and without dogwhelks) on shore with low quantities of phytoplankton / AW ; less support as there is an overlap (with and without dogwhelks) with larger quantities of phytoplankton / AW ; other factors may be affecting result / correlation not causal ; 1(b)(iv) any 3 of: 3 barnacles consume phytoplankton / more food for barnacles (if more phytoplankton) / ORA / AW ; so more survival of larvae ; dogwhelks reduces, attachment / settling, of barnacle larvae ; due to presence of, chemicals / scent, from dogwhelks / AW ; less reproduction of barnacles (to reduce population) (when dogwhelks present / less phytoplankton) / AW ; 1(c)(i) any 3 of: 3 lack predators so increase in population / AW ; overconsume prey / AW ; out compete native species / AW ; AVP ; 1(c)(ii) may become an invasive species itself / may have no predator / consume other native species / AW ; 1

This question in 9693/42 Oct/Nov 2024

2 Plaice is a benthic flatfish caught by commercial fishing ships. Plaice gather in breeding areas during breeding seasons. Scientists investigated the effect of benthic trawling on the fishing mortality of plaice. The scientists determined the fishing mortality of male and female plaice of different ages during the breeding season and outside the breeding season. The results are shown in Fig. 2.1. during breeding season outside breeding season 0.4 0.4 Key male plaice female 0.3 0.3 plaice fishing fishing mortality mortality 0.2 0.2/ arbitrary / arbitrary units units 0.1 0.1 0.0 0.0 0 1 2 3 4 5 6 7 8 9 10 0 1 2 3 4 5 6 7 8 9 10 age of plaice / years age of plaice / years Fig. 2.1 (a) (i) Compare the fishing mortality of plaice during the breeding season and outside the breeding season. … … … … … … [3] (ii) Suggest a reason for the difference in fishing mortality of male and female plaice during the breeding season. … … [1] (iii) Suggest a reason for the difference in the fishing mortality of plaice during the breeding season and outside the breeding season. … … [1] (iv) Use Fig. 2.1 to explain why intensive harvesting of plaice during the breeding season would affect the sustainability of the population. … … … … … … [3] (b) In a further investigation, scientists investigated the gonadosomatic index (GSI) and price of plaice over a period of 48 weeks. Gonad tissues are ovaries and testes. Gonad tissue increases in size during breeding seasons. The gonadosomatic index (GSI) is the mass of gonad tissue divided by the total body mass. The results are shown in Table 2.1. Table 2.1 week mean gonadosomatic index mean price per kilogram (GSI) / USD ($) 1 0.14 1.8 12 0.03 2.5 24 0.02 3.4 36 0.03 3.8 48 0.10 2.1 (i) GSI is calculated using the formula: mass of gonad tissue GSI = total body mass Calculate the mass of gonad tissue in a plaice with a total body mass of 825 g caught during week 1. State the unit. … [2] (ii) Use Table 2.1 to draw a graph to show the GSI and price per kilogram of fish over the 48-week period. Join your points with straight, ruled lines. [6] (iii) Discuss the changes in GSI and the price of plaice over the 48-week period shown in Table 2.1 and the implications for the conservation of plaice. … … … … … … [3] [Total: 19]

19 marks

Mark scheme: 2(a)(i) any 3 of: 3 1 mortality is higher (for both) during breeding season / AW ; 2 mortality of males is higher than females during breeding season / AW ; 3 mortality of males and females is similar out of breeding season / AW ; 4 larger increase in mortality of males than females during breeding season (compared with out of season) / AW ; 5 both have low mortality for 0–1 years / mortality increases with age / lower mortality for younger fish / AW ; 6 correct manipulation of data ; 2(a)(ii) any 1 of: 1 female plaice are in deeper water / male plaice swim higher up the water column / males remain in the benthic area / ORA / AW ; males and females move to different, habitats / areas, (after breeding) / AW ; male plaice aggregate in same areas (after breeding) / ORA / AW ; male plaice are easier to catch / are targeted by fishers / females are put back by fishers / AW ; 2(a)(iii) any 1 of: 1 plaice (are aggregated) in one area (so are easier to find) / plaice area less dispersed / AW ; fishing boats target breeding areas / fishing occurs around breeding areas / AW ; 2(a)(iv) any 3 of: 3 1 overfishing will reduce population / less recruitment / reduced sustainability / AW ; 2 fewer older / mature fish / more immature / more younger fish / AW ; 3 imbalanced sex ratio / too few males / AW ; 4 so less breeding / fertilisation / lower fecundity / fewer eggs or sperm released / AW ; 5 AVP ; 2(b)(i) 115.5 ; 2 g ; 2(b)(ii) linear scales for both y axes and uses at least half of grid ; 6 all axes labelled ; accurate plots ;; points joined by straight lines ; key for lines ; 2(b)(iii) any 3 of: 3 1 lower price when GSI is high / ORA / AW ; 2 (may be due to) high catch rates before / during breeding season / price low when high catch / ORA / AW ; 3 (catches in breeding season causes) reduced reproduction / unsustainable fishing / population fall / less breeding / AW ; 4 should, ban / control, fishing during breeding season / AW ; 5 low price may be due to less demand for fish with high GSI / ORA ; 6 fish with high GSI may have lower meat content / poorer meat content / AW / ORA ;

This question in 9693/42 Oct/Nov 2024

1 Fig. 1.1 shows some barnacles and a dogwhelk on a rock. Fig. 1.1 Adult barnacles are sessile and are often found attached to rocks on rocky shores. Barnacles have a complex life cycle with planktonic larvae. (a) Explain why a complex life cycle is an advantage for sessile organisms. … … … … [2] (b) The dogwhelk feeds on barnacles on rocky shores. Scientists investigated whether the settlement of barnacles on a rocky shore was affected by: • the presence of dogwhelks • the quantity of phytoplankton in the sea water next to the shore. The scientists placed 0.25 m2 plastic tiles onto four rocky shores: • one shore with a high quantity of phytoplankton in the sea and with dogwhelks present • one shore with a high quantity of phytoplankton in the sea and with no dogwhelks present • one shore with a low quantity of phytoplankton in the sea and with dogwhelks present • one shore with a low quantity of phytoplankton in the sea and with no dogwhelks present. All the tiles had a central area which dogwhelks could not access. Fig. 1.2 shows one of the tiles used. central area covered with mesh to stop dogwhelks getting in plastic tile Fig. 1.2 The plastic tiles were examined after two months. The population densities of the barnacles growing in the central area which dogwhelks could not access were calculated. (i) The central area of one plastic tile had 12 barnacles settled in an area of 0.0225 m2. Calculate the population density of barnacles for this plastic tile as the number of barnacles per m2. Give your answer to three significant figures. … per m2 [2] Fig. 1.3 shows the population density of barnacles that had settled on the plastic tiles on all four rocky shores. Key dogwhelks present dogwhelks not present 800 700 600 500 number of barnacles 400 per square metre 300 200 100 0 low quantities of high quantities of phytoplankton phytoplankton rocky shore Fig. 1.3 (ii) Summarise the results of the investigation shown in Fig. 1.3. … … … … [2] (iii) The scientists concluded that there was a strong probability that the presence of dogwhelks affects the settlement of barnacles onto rocks. Discuss the extent to which the error bars for standard deviation shown in Fig. 1.3 support the scientists’ conclusion. … … … … [2] (iv) Suggest explanations for the effect of dogwhelks and quantities of phytoplankton on the settling of the barnacles. … … … … … … [3] (c) The acorn barnacle has spread all around the world on ships and is now considered to be an invasive species. (i) Explain why invasive species are a risk to ecosystems. … … … … … … [3] (ii) It has been suggested that introducing dogwhelks into new areas colonised by acorn barnacles could be a method of control. Suggest a possible negative consequence of introducing dogwhelks into areas with acorn barnacles. … … [1] [Total: 15]

15 marks

Mark scheme: Question Answer Marks 1(a) any 2 of: 2 allows dispersal to wider area / other areas / moves to different locations / AW ; to reduce competition / larvae have different niches from adults / AW ; allows (larvae to) feed on plankton / AW ; 1(b)(i) 533 (to 3 sig figs) ;; 2 1(b)(ii) more barnacles are found on the shores where there are more phytoplankton / ORA ; 2 more barnacles where there are no dogwhelks / ORA ; 1(b)(iii) any 2 of: 2 supported because no overlap (with and without dogwhelks) on shore with low quantities of phytoplankton / AW ; less support as there is an overlap (with and without dogwhelks) with larger quantities of phytoplankton / AW ; other factors may be affecting result / correlation not causal ; 1(b)(iv) any 3 of: 3 barnacles consume phytoplankton / more food for barnacles (if more phytoplankton) / ORA / AW ; so more survival of larvae ; dogwhelks reduces, attachment / settling, of barnacle larvae ; due to presence of, chemicals / scent, from dogwhelks / AW ; less reproduction of barnacles (to reduce population) (when dogwhelks present / less phytoplankton) / AW ; 1(c)(i) any 3 of: 3 lack predators so increase in population / AW ; overconsume prey / AW ; out compete native species / AW ; AVP ; 1(c)(ii) may become an invasive species itself / may have no predator / consume other native species / AW ; 1

This question in 9693/43 Oct/Nov 2024

2 Plaice is a benthic flatfish caught by commercial fishing ships. Plaice gather in breeding areas during breeding seasons. Scientists investigated the effect of benthic trawling on the fishing mortality of plaice. The scientists determined the fishing mortality of male and female plaice of different ages during the breeding season and outside the breeding season. The results are shown in Fig. 2.1. during breeding season outside breeding season 0.4 0.4 Key male plaice female 0.3 0.3 plaice fishing fishing mortality mortality 0.2 0.2/ arbitrary / arbitrary units units 0.1 0.1 0.0 0.0 0 1 2 3 4 5 6 7 8 9 10 0 1 2 3 4 5 6 7 8 9 10 age of plaice / years age of plaice / years Fig. 2.1 (a) (i) Compare the fishing mortality of plaice during the breeding season and outside the breeding season. … … … … … … [3] (ii) Suggest a reason for the difference in fishing mortality of male and female plaice during the breeding season. … … [1] (iii) Suggest a reason for the difference in the fishing mortality of plaice during the breeding season and outside the breeding season. … … [1] (iv) Use Fig. 2.1 to explain why intensive harvesting of plaice during the breeding season would affect the sustainability of the population. … … … … … … [3] (b) In a further investigation, scientists investigated the gonadosomatic index (GSI) and price of plaice over a period of 48 weeks. Gonad tissues are ovaries and testes. Gonad tissue increases in size during breeding seasons. The gonadosomatic index (GSI) is the mass of gonad tissue divided by the total body mass. The results are shown in Table 2.1. Table 2.1 week mean gonadosomatic index mean price per kilogram (GSI) / USD ($) 1 0.14 1.8 12 0.03 2.5 24 0.02 3.4 36 0.03 3.8 48 0.10 2.1 (i) GSI is calculated using the formula: mass of gonad tissue GSI = total body mass Calculate the mass of gonad tissue in a plaice with a total body mass of 825 g caught during week 1. State the unit. … [2] (ii) Use Table 2.1 to draw a graph to show the GSI and price per kilogram of fish over the 48-week period. Join your points with straight, ruled lines. [6] (iii) Discuss the changes in GSI and the price of plaice over the 48-week period shown in Table 2.1 and the implications for the conservation of plaice. … … … … … … [3] [Total: 19]

19 marks

Mark scheme: 2(a)(i) any 3 of: 3 1 mortality is higher (for both) during breeding season / AW ; 2 mortality of males is higher than females during breeding season / AW ; 3 mortality of males and females is similar out of breeding season / AW ; 4 larger increase in mortality of males than females during breeding season (compared with out of season) / AW ; 5 both have low mortality for 0–1 years / mortality increases with age / lower mortality for younger fish / AW ; 6 correct manipulation of data ; 2(a)(ii) any 1 of: 1 female plaice are in deeper water / male plaice swim higher up the water column / males remain in the benthic area / ORA / AW ; males and females move to different, habitats / areas, (after breeding) / AW ; male plaice aggregate in same areas (after breeding) / ORA / AW ; male plaice are easier to catch / are targeted by fishers / females are put back by fishers / AW ; 2(a)(iii) any 1 of: 1 plaice (are aggregated) in one area (so are easier to find) / plaice area less dispersed / AW ; fishing boats target breeding areas / fishing occurs around breeding areas / AW ; 2(a)(iv) any 3 of: 3 1 overfishing will reduce population / less recruitment / reduced sustainability / AW ; 2 fewer older / mature fish / more immature / more younger fish / AW ; 3 imbalanced sex ratio / too few males / AW ; 4 so less breeding / fertilisation / lower fecundity / fewer eggs or sperm released / AW ; 5 AVP ; 2(b)(i) 115.5 ; 2 g ; 2(b)(ii) linear scales for both y axes and uses at least half of grid ; 6 all axes labelled ; accurate plots ;; points joined by straight lines ; key for lines ; 2(b)(iii) any 3 of: 3 1 lower price when GSI is high / ORA / AW ; 2 (may be due to) high catch rates before / during breeding season / price low when high catch / ORA / AW ; 3 (catches in breeding season causes) reduced reproduction / unsustainable fishing / population fall / less breeding / AW ; 4 should, ban / control, fishing during breeding season / AW ; 5 low price may be due to less demand for fish with high GSI / ORA ; 6 fish with high GSI may have lower meat content / poorer meat content / AW / ORA ;

This question in 9693/43 Oct/Nov 2024

3 Oysters are shelled molluscs that have a complex life cycle. The adults are sessile organisms that anchor to a substrate. Fig. 3.1 shows some adult oysters. Fig. 3.1 (a) Outline the importance of having a complex life cycle for organisms such as oysters. … … … … … … [3] (b) Scientists investigated the effects of temperature and pH on the survival of oyster larvae. Oyster larvae were placed into tanks of water at different temperatures and pHs. The percentages of larvae surviving were calculated after two days and then again after 15 days. Fig. 3.2 and Fig. 3.3 show the results. 100 Key 90 day 2 day 15 80 70 60 percentage of 50 larvae surviving 40 30 20 10 0 20 25 27 30 35 temperature / °C Fig. 3.2 100 Key 90 day 2 day 15 80 70 60 percentage of 50 larvae surviving 40 30 20 10 0 6.5 7.0 7.5 8.0 8.2 8.5 pH Fig. 3.3 (i) The scientists placed 500 larvae in each condition. Calculate the number of larvae that did not survive from day 2 to day 15 when placed at a temperature of 30 °C. … [2] (ii) Use Fig. 3.2 and Fig. 3.3 to state the optimum temperature and optimum pH for the survival of oyster larvae. optimum temperature … °C optimum pH … [1] (c) Fishers in India reported declining harvests of adult oysters from an area of coastal water after 2011. (i) Table 3.1 shows the temperature and pH of the water during 2009 in this area. Table 3.1 month temperature / °C pH February 25 8.0 April 27 7.9 June 34 8.2 August 30 7.0 October 32 6.5 December 28 7.0 Use Table 3.1 to plot a line graph to show the temperature and the pH from February to December. [5] (ii) Around the coasts of India, oysters spawn throughout the year but have two peak periods of breeding, in April and August. Discuss the reasons for the reduction in the number of oysters that the fishers harvested after 2011. Use information in Table 3.1, Fig. 3.2 and Fig. 3.3 to support your answer. … … … … … … … … [4] (d) Explain why the use of fossil fuels places future oyster populations at risk. … … … … … … [3] [Total: 18]

18 marks

Mark scheme: 3(a) any 3 from: 3 1 larvae can move to other areas / larvae allow distribution to other areas / AW ; 2 reduced competition / AW ; 3 (reduced competition for) food / nutrients / AW ; 4 idea that larvae and adults occupy different niches / AW ; 5 increased genetic diversity (if oysters spread to other areas) / AW ; 6 reduces spread of disease (as population density is lower) ; 3(b)(i) 180 = 2 marks 2 36 (%) = 1 mark OR 320 survived = 1 mark 3(b)(ii) (optimum temperature) = 27 (°C) 1 optimum pH = 8(.0) ; 3(c)(i) 1. linear y axes for both temperature and pH, labelled with units, and horizontal axis as month ; 5 2. all three scales enable plots to cover at least half grid ; 3. plots correct +/- ½ square for temperature ; 4. plots correct +/- ½ square for pH ; 5. points joined with straight lines and key ; 3(c)(ii) any 4 from: 4 1 in April, conditions enable survival / there are optimal conditions / oysters can breed / conditions are ideal for breeding / AW ; 2 August has a temperature of 30 oC and pH of 7(.0) / April has a temperature of 27 oC and pH of 7.9 / AW ; 3 in August, conditions reduce larvae settling / kill larvae / few larvae survive / will not settle in August / too acidic for survival / AW ; 4 there is only one successful breeding season (per year) / AW ; 5 idea that few oyster larvae become adults / it takes time to produce adults (so effects are only seen in 2011) / AW ; 6 few other months have ideal conditions for larvae / AW ; 7 overfishing / pollution / AW, may be causing the fall ; 3(d) any 3 from: 3 1 release of carbon dioxide / AW ; 2 causes (enhanced) greenhouse effect / increased temperature / global warming / AW ; 3 acidification of water / AW ; 4 (acid) reduces oyster shell formation / erodes shells / dissolves shells / AW ; 5 larvae do not survive / larvae cannot settle / fewer adult oysters to breed (in future) / AW ;

This question in 9693/41 May/June 2025