| Date | May 2017 | Marks available | 1 | Reference code | 17M.2.SL.TZ0.1 |
| Level | Standard Level | Paper | Paper 2 | Time zone | Time zone 0 |
| Command term | State | Question number | 1 | Adapted from | N/A |
Question
The concentration of DDT at different trophic levels of the food chain.
Figure 1: Levels of concentration of DDT in food chain
[Source: © International Baccalaureate Organization, 2017]
State the main source of energy for the food chain in Figure 1.
State the trophic level labelled X in Figure 1.
Identify one use of DDT that has led to its presence in the environment.
With reference to the concepts of bioaccumulation and biomagnification, outline how the concentration of DDT has changed along the food chain.
State the relationship between large and small fish in Figure 1.
Outline how this relationship may be of benefit to the populations of both species.
Markscheme
Sun/sunlight/insolation/solar energy
(primary) producer / autotrophs / phototrophs / phytoplankton / green plants
The command term “State” requires a “specific name” so do not credit “trophic level 1”.
insecticide/pesticide / kill pests/insects / control malarial mosquitoes / plague / OWTTE
bioaccumulation: DDT absorbed by a given trophic level is not broken down/excreted / is non-biodegradable so accumulates in tissues [1 mark]
biomagnification: the concentration of DDT will increase as it’s passed along/up food chain (because other biomass is lost) [1 mark]
Do not allow simply “organisms at higher levels eat/consume more”. Higher trophic levels do not consume more biomass in a given time than lower trophic levels.
predator-prey / carnivory / predation / OWTTE
Do not credit “small fish are eaten/consumed by large fish”.
the predator benefits by gaining food from prey / its population is limited/stabilized by amount of prey available [1 mark]
they prey benefits by predators limiting/stabilizing its population / selecting out weaker/diseased individuals / maintaining healthy gene pool in prey / reducing competition in prey for available food/resources [1 mark]
Award full marks is response describes negative feedback between both populations, or indicates that each group regulates population of the other.
Examiners report
Only around half the candidates were able to identify solar energy as the energy source for food chains.
Great majority were able to identify plants/primary producers as base of food chain.
Most were able to identify DDT as a pesticide … students should be advised that where question specifies a single response it is not a wise strategy to offer a selection of responses.
Very few candidates were able to apply these terms of “bioaccumulation” & “biomagnification” appropriately …some confused the two; some made no reference to them as required by the question. More were able to identify biomagnification correctly than bioaccumulation.
Most were able to identify predation but a surprisingly large number failed to do so.
The great majority were able to identify benefits to both populations.
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.
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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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19M.1.SL.TZ0.5:
With reference to Figure 4(d), suggest the impact on the marine food web if tuna numbers were to decline.
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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.
