Cambridge A Level Marine Science 9693 — 2021 May/June Paper 4 · Variant 0

1 The area of many tropical coral reefs is decreasing. Scientists think that the reduction in area of living coral is due to global warming. Table 1.1 shows the change in percentage cover of living coral on a reef near Indonesia, and the mean annual global release of carbon dioxide between 2000 and 2016. Table 1.1 year percentage cover of reef with mean annual global release of carbon living coral dioxide / million tonnes 2000 68 24 000 2004 52 26 000 2008 33 32 000 2012 22 35 000 2016 18 37 000 (a) (i) Calculate the mean annual rate of change of percentage cover of the reef with living coral between 2000 and 2016. Space for working. .......................................................... [2] (ii) Draw a line graph to show the change in percentage cover of the reef with living coral and mean annual global release of carbon dioxide between 2000 and 2016. [6] (b) Discuss the extent to which the data in Table 1.1 support the hypothesis that global warming is causing a reduction in area of living coral reefs. ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ............................................................................................................................................. [4] [Total: 12]

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2 Sand that has been contaminated with crude oil can be cleaned by specialised bacteria. These bacteria digest the oil. Algae are naturally present in the sand. Scientists investigated if adding fertiliser to the sand speeds up this digestion process. The investigation is described in the steps below. • Four 5 kg samples of sand were each mixed with 50 g of crude oil. • An equal mass of bacteria which digest oil was added to each sample of sand. • A different mass of fertiliser was added to each sample. • The samples were left for seven weeks. • The percentage reduction of crude oil in each sample was measured. • The mean dry mass of algae that grew in the sand was also measured. • The experiment was repeated five times. • The mean percentage reduction of crude oil, and the mean dry mass of algae, for each mass of fertiliser were calculated. The results are shown in Fig. 2.1. Key ± 1 standard deviation mean percentage reduction of crude oil mean dry mass of algae / g 60 2400 2200 50 2000 1800 40 1600 1400 mean percentage reduction of crude 30 1200 oil mean dry mass 1000 of algae / g 20 800 600 10 400 200 0 0 0 30 60 90 mass of fertiliser / g Fig. 2.1 (a) (i) Use Fig. 2.1 to calculate the percentage increase in mean dry mass of algae when the mass of fertiliser was increased from 0 g to 90 g. Space for working. .......................................................% [2] (ii) Describe the effect of increasing the mass of fertiliser on the mean percentage reduction of crude oil. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ..................................................................................................................................... [2] (b) The scientists concluded that 30 g of fertiliser per 5 kg sand is the ideal quantity to use to digest oil on sandy shores. Use Fig. 2.1 to explain why 30 g of fertiliser was chosen. ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ............................................................................................................................................. [4] [Total: 8]

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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]

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4 (a) (i) Explain why the ecological linkages within a food web must be considered when planning to conserve a species. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ..................................................................................................................................... [3] (ii) Discuss the advantages and disadvantages of replanting mangroves to rehabilitate fish stocks. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ..................................................................................................................................... [5] (b) Explain how negative ecological impacts of an aquaculture venture located in coastal waters can be minimised. ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ............................................................................................................................................. 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