| Date | November 2017 | Marks available | 2 | Reference code | 17N.3.SL.TZ0.13 |
| Level | Standard level | Paper | Paper 3 | Time zone | TZ0 / no time zone |
| Command term | Compare and contrast | Question number | 13 | Adapted from | N/A |
Question
The sea snail Nucella ostrina and the sea star Pisaster ochraceus are predators of the mussel Mytilus trossulus. The mussels live on rocks at the edge of the sea and feed on phytoplankton and zooplankton. The zooplankton feed on the phytoplankton.
Groups of 50 mussels were transplanted to an experimental area and protected from predation until the start of the experiment. Researchers then investigated the effect of the predators on the population of the mussels over a period of 60 days.
[Source: Republished with permission of John Wiley and Sons, from Navarrete, S. A. and Menge, B. A. (1996),
Keystone Predation and Interaction Strength: Interactive Effects of Predators on Their Main Prey. Ecological Monographs, 66: 409–429. doi:10.2307/2963488; permission conveyed through Copyright Clearance Center, Inc.]
Compare and contrast the effects of the predators on the population of the mussels.
The sea star also eats the sea snails. Construct a food web to show the feeding relationships between these five organisms in the ecosystem.
Markscheme
a. both cause the frequency of the mussel to decrease
b. sea star affects the mussel population more than the sea snail
c. when both are together the effect of the sea snail is low
Accept binomial names
Allow numerical answers if expressed as comparisons and the candidates are not simply stating numbers
[Max 2 Marks]
Award [2] for a correct food web
Award [1] for phytoplankton, zooplankton and mussel with correct arrows
Award [1] for mussel, sea snail and sea star with correct arrows
Award [0] if arrows are in wrong direction
Accept binomial or scientific names
Examiners report
Syllabus sections
-
20N.3.SL.TZ0.13b.ii:
Describe how ingested plastics can cause problems to marine birds.
- 18M.3.SL.TZ2.14: Discuss the health consequences and environmental consequences of the use of DDT.
-
20N.3.HL.TZ0.15c:
Sea urchins are destroying the giant kelp alga (Macrocystis pyrifera) marine forests of South East Australia. Suggest a reason that sea urchins might be an invasive species in this environment.
- 17M.3.SL.TZ1.15a: Outline one consequence of introducing an alien species into an ecosystem.
- 18N.3.SL.TZ0.14b: Suggest a reason for not cutting invasive plants at certain times of year.
- 19M.3.HL.TZ1.14b: Phosphate can be lost from agricultural land in several different ways. State one of these.
- 19N.3.HL.TZ0.15b: Outline how plastic ingestion may lead to biomagnification in these marine species.
- 18N.3.SL.TZ0.14c: Outline reasons for controlling invasive plants.
- 19M.3.HL.TZ1.16a.i: Distinguish between levels of predation in marmots born in the wild and those born in captivity.
- 19N.3.HL.TZ0.15a: Compare and contrast the information provided for baleen whales and sea turtles.
- 17M.3.SL.TZ1.15b: State the origin of cane toads.
-
17N.3.HL.TZ0.14a.i:
Identify how the pattern in mammals is different from reptiles and birds.
-
17N.3.HL.TZ0.14a.iii:
Suggest a method to limit the impact of F. silvestris on native species.
- 17M.3.SL.TZ1.15c: Evaluate the use of traps containing toxin as a means of cane toad control.
- 16N.3.HL.TZ0.15b: State two possible effects on organisms of microplastic pollution.
- 16N.3.SL.TZ0.14a: Outline the trend in the number of people with malaria during the period when the use of...
- 18M.3.HL.TZ1.16b: Discuss the global impacts of invasive alien species.
- 19N.3.SL.TZ0.14b: Describe the use of indicator species in monitoring environmental change.
-
16N.3.HL.TZ0.15a:
Predict one example of macroplastic pollution that is likely to be found in this lake.
- 20N.3.SL.TZ0.13b.i: Identify the group with the greatest number of species with problems due to ingestion of...
- 20N.3.SL.TZ0.13a.ii: Suggest how entanglement in plastics can lead to the death of marine birds.
-
18M.3.HL.TZ1.16a:
Define invasive alien species.
-
18M.3.HL.TZ1.16d:
The map shows an area of the Pacific Ocean characterized by exceptionally high concentrations of plastics and other debris that have been trapped by the currents of the North Pacific Gyre.
Outline one consequence of marine plastic pollution.
- 18N.3.SL.TZ0.14a: State which plant can be cut in August.
- 19N.3.SL.TZ0.15b.ii: Outline the impact of alien species on endemic species in ecosystems.
- 20N.3.SL.TZ0.13a.i: Calculate the number of species of grebe with problems due to entanglement.
- 20N.3.SL.TZ0.12b: Outline the principle of competitive exclusion.
- 18N.3.SL.TZ0.14d: Discuss what precautions should be taken before considering biological control of the...
- 19M.3.HL.TZ1.14c: Describe how the changes in world rock phosphate production after 1985 may have affected...
- 19M.3.HL.TZ1.16a.ii: Suggest reasons for the differences in predation.
- 16N.3.SL.TZ0.14b: One pesticide used in killing mosquitoes was DDT. Considering its harmful effects,...
- 18M.3.HL.TZ2.18: Evaluate the impact of the introduction of a named invasive alien species into an environment.
- 19N.3.SL.TZ0.15b.i: State an example of an alien species.
-
17M.3.HL.TZ1.14c:
Indicator species may be affected by biomagnification. Discuss biomagnification using a named example of a pollutant.
-
17N.3.HL.TZ0.14a.ii:
Describe how invasive species such as F. silvestris can have a significant impact on native species.
-
18M.3.HL.TZ1.16c:
Using one example, outline biological control of an invasive alien species.
-
19M.3.SL.TZ1.14:
Explain what is meant by competitive exclusion, with respect to a named example of an invasive species.
- 16N.3.HL.TZ0.15c: Outline the effect of wind on the distribution of plastic pollution in this lake.
-
18M.3.HL.TZ1.16e:
Explain the consequences of biomagnification.
- 19M.3.HL.TZ1.14a: Describe the relationship between rock phosphate production and world population.
-
19N.3.SL.TZ0.14a:
Explain how the levels of the Caesium (Cs) radioisotopes could have accumulated in the tissues of these fish.
- 16N.3.HL.TZ0.15d: Suggest changes in the management of the national park that could reduce the amount of...
-
17N.3.HL.TZ0.16c:
Outline three issues arising from the release of pollutants into the environment.
-
19M.3.SL.TZ1.13:
Outline three ways in which a named environmental disturbance can impact an ecosystem.
-
17N.3.SL.TZ0.12c:
Explain how pesticides may undergo biomagnification in the lake.
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19M.3.SL.TZ2.13:
The diagram shows the copper concentration (μg g–1) in the seaweed Porphyra umbilicalis collected along the shoreline in Arklow, Ireland.
[Source: reprinted by permission from Springer Nature: Helgoländer Meeresuntersuchungen,
Problems in the assessment of heavy-metal levels in estuaries and the formation of a pollution index,
D L Tomlinson, et al., 33, issue 1, pages 566–575. Copyright 1980]Explain how the copper found in these seaweeds could affect the birds living in Arklow town.
