| Date | May 2019 | Marks available | 2 | Reference code | 19M.1.SL.TZ0.5 |
| Level | Standard Level | Paper | Paper 1 | Time zone | Time zone 0 |
| Command term | Suggest | Question number | 5 | Adapted from | N/A |
Question
Figure 4(d): Example of a Coral Triangle marine food web
With reference to Figure 4(d), suggest the impact on the marine food web if tuna numbers were to decline.
Markscheme
reduction in sharks/marlin (predators) of the tuna (due to reduction in food source);
increase in micronekton/predatory fish (prey) of the tuna (due to reduction in predation);
reduction in phytoplankton/mesoplankton/microplankton due to increase in micronekton population;
loss of tuna reduces competition for food (micronekton/predatory fish) resulting in overall increase in sharks/marlin population;
to compensate for loss of tuna, shark/marlin eat more micronekton/predatory fish resulting in overall decline of micronekton/predatory fish population;
to compensate for loss of tuna, shark/marlin eat more micronekton/predatory fish resulting in an increase in phytoplankton/mesozooplankton/microzooplankton population;
Accept other reasonable responses.
Do not credit the same marking point twice eg reduction in sharks and reduction in marlin.
Do not accept only “collapse of marine food web” or “reduction in biodiversity”.
[2 max]
Examiners report
This question was answered well by most candidates. Common errors included: (i) only stating changes in feeding behaviour but not how this affects the population numbers; (ii) misinterpreting the direction of the errors.
Syllabus sections
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15M.2.SL.TZ0.2b.ii:
Explain how predation may lead to long-term population decrease or extinction of the prey species.
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15N.1.SL.TZ0.2b.i:
Identify one abiotic factor which may affect the population of insects in a forest.
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19N.1.SL.TZ0.2e:
Suggest why the St Lawrence River beluga whale population has not recovered despite being given protected status in 1983.
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16M.1.SL.TZ0.1d:
Oystercatchers and avocets both feed on small animals in the mud of the wetlands. State the most likely relationship between these two species.
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19M.2.SL.TZ0.5a:
Identify four impacts on an ecosystem that may result from the introduction of an invasive species of herbivore.
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17M.2.SL.TZ0.1e.ii:
Outline how this relationship may be of benefit to the populations of both species.
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19N.1.SL.TZ0.2b:
Using Figure 7, state the St Lawrence beluga whale population in 1920 and 1940.
1920:
1940:
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15M.2.SL.TZ0.2a:
Outline the similarities and differences between predation and competition.
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18M.2.SL.TZ0.5a:
Distinguish between the terms niche and habitat with reference to a named species.
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14N.2.SL.TZ0.2a:
Distinguish between negative and positive feedback using examples from environmental systems.
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18N.1.SL.TZ0.10c:
With reference to Figure 10(b), explain the threats to the future existence of a small and sustainable population of wolves as a result of their protection in limited area.
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17N.2.SL.TZ0.1a.ii:
Identify three reasons why carrying capacity can be difficult to estimate.
- 17M.2.SL.TZ0.1e.i: State the relationship between large and small fish in Figure 1.
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18N.1.SL.TZ0.5:
With reference to Figures 9(a) and 9(b), describe one abiotic change and one biotic change in a beaver meadow community undergoing succession.
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19N.1.SL.TZ0.2c:
Calculate the percent decrease in beluga whale numbers from 1920 to 1940.
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19N.1.SL.TZ0.3c:
With reference to Figure 9(a), explain why the realized niche of the mottled sculpin has changed in recent years.
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16M.1.SL.TZ0.1a:
Define the term species.
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19M.2.SL.TZ0.5b:
Explain how both positive and negative feedback mechanisms may play a role in producing a typical S population growth curve for a species.
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15M.2.SL.TZ0.2b.i:
Explain how predation may lead to stability in a population of the prey species.
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15M.2.SL.TZ0.1d:
Evaluate the possible use of grass carp in controlling the growth of water hyacinth in Inle Lake.
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15N.1.SL.TZ0.2c:
Distinguish between a mutualistic relationship and a parasitic relationship.
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14N.1.SL.TZ0.2c:
Using Figure 1 below, calculate the annual rate of population increase for elephants in Zimbabwe from 1985 to 2005.
Figure 1 Elephant Population: Kenya compared to Zimbabwe, 1973 – 2011
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16M.2.SL.TZ0.3a:
Outline the role of limiting factors in S and J population curves.
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16N.2.SL.TZ0.1f:
Justify whether or not Mesquite should be cleared from the Swakop River Valley.
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16N.2.SL.TZ0.1e:
With reference to the data in Figure 4(b), suggest two conclusions which can be drawn from the camera trap data.
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15N.1.SL.TZ0.2a.ii:
Identify two possible reasons why species B and C were not present in the litter layer when it was resampled six months later.
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17N.2.SL.TZ0.1a.i:
Define the term carrying capacity.
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14M.1.SL.TZ0.1a.iv:
Identify two possible effects of removing trout on this ecosystem.
