| Date | November 2020 | Marks available | 1 | Reference code | 20N.3.HL.TZ0.15 |
| Level | Higher level | Paper | Paper 3 | Time zone | TZ0 / no time zone |
| Command term | Suggest | Question number | 15 | Adapted from | N/A |
Question
Sea urchins (Strongylocentrotus) are echinoderms that consume large quantities of algae. Sea otters (Enhydra lutris) feed on sea urchins.
The graphs show the biomass of sea urchins in an area of 0.25 m2 plotted against their size. Data were collected in two Aleutian Islands, Amchitka and Shemya. In Amchitka the sea otter population is high while at Shemya there are no sea otters.
[Source: From Estes, J.A. and Palmisano, J.F., 1974. Sea Otters: Their Role in Structuring Nearshore Communities. Science,
185(4156), pp.1058–1060.16. DOI: 10.1126/science.185.4156.1058, https://science.sciencemag.org/content/185/4156/1058.
Reprinted with permission from AAAS. Readers may view, browse, and/or download material for temporary copying purposes
only, provided these uses are for noncommercial personal purposes. Except as provided by law, this material may not be further
reproduced, distributed, transmitted, modified, adapted, performed, displayed, published, or sold in whole or in part, without prior
written permission from the publisher.]
Outline a method that could have been used in this study to measure the numbers of sea urchins per 0.25 m2.
Sea otters are considered keystone species in this environment. Suggest how the presence of sea otters could affect the algae population.
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.
Markscheme
a. with quadrats (of 0.5 m side / 0.25m2);
b. (quadrats) position determined at fixed distance by transects
OR
(quadrats) position determined at random;
c. random sampling / capture-recapture;
d. average number calculated;
a. sea otters (feeding on sea urchins) limit sea urchin population;
b. the largest sea urchins are eaten;
c. shown by low biomass/small size (of sea urchins);
d. fewer/smaller sea urchins allow for increase in algae population;
e. sea otters have a top down effect;
Allow converse reasoning.
the sea urchins’ limiting factors in their original habitat are missing
OR
lack of (natural) predators for sea urchins
Examiners report
Most candidates did well on this question, especially strong ones, although there was evidence that many candidates are not familiar with population evaluation skills. Candidates should be aware that writing "quadrants" (with a "n") is questionable, and that although it may not be assumed that they knew what echinoderms or sea urchins were, the capture-mark-release-recapture method was not really appropriate to evaluate their numbers, given the very limited areas of 0.25 m2.
The majority of candidates could suggest that the sea algae population could be affected by sea otters feeding on sea urchins; most nevertheless did not use the graphs or mention that a top down effect was present.
Many suggested that sea urchins' predators were not present, but too many irrelevant or blank answers were seen.
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.
- 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.
-
17N.3.SL.TZ0.13a:
Compare and contrast the effects of the predators on the population of the mussels.
- 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.
-
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.
