| 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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14N.1.SL.TZ0.5a:
Label the diagram above to complete the processes and flows in the nitrogen cycle.
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17N.2.SL.TZ0.4a:
Describe the role of primary producers in ecosystems.
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18M.2.SL.TZ0.2c.iii:
Identify one other output from the mineral storage in the “A” horizon in Figure 2(b).
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18N.2.SL.TZ0.5c:
Discuss strategies that can be used to improve the sustainability of food production systems.
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14M.2.SL.TZ0.2b:
Explain how the first and second laws of thermodynamics are demonstrated as energy from the sun flows through the primary producers in a food chain.
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16M.2.SL.TZ0.2b:
Describe the similarities and differences between the terms sustainable yield and sustainable development.
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16N.1.SL.TZ0.4a:
State the process represented in the box labelled X.
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18M.2.SL.TZ0.5c:
Quantitative models are frequently constructed to show the flow of energy and cycling of matter in natural systems.
To what extent can these models be useful in assessing the sustainability of named food production systems?
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14M.1.SL.TZ0.4b:
Overgrazing may lead to soil degradation. Identify one impact that overgrazing may have on a named flow and a named storage within the nitrogen cycle.
(i) Impact on flow:
(ii) Impact on storage:
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18N.1.SL.TZ0.3b:
Identify two ways that human activity in Algonquin Provincial Park may affect the food web.
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18M.2.SL.TZ0.4b:
Explain how a community of trees in a woodland may be considered a system.
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14N.1.SL.TZ0.5c:
Describe two ways in which humans may impact the nitrogen cycle.
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16M.1.SL.TZ0.1e.ii:
Describe its role in the carbon cycle of the system.
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14M.2.SL.TZ0.2a.i:
Define net secondary productivity.
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19N.1.SL.TZ0.1d:
Outline why estuaries are highly productive ecosystems.
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17M.2.SL.TZ0.4b:
Suggest a series of procedures that could be used to estimate the net productivity of an insect population in kg m–2 yr–1.
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19N.1.SL.TZ0.1a:
Using Figure 4(a), identify an ecosystem that has an average net primary productivity above 30 000 kJ m–2 a–1.
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14N.1.SL.TZ0.5b:
Distinguish between a transfer and a transformation in the nitrogen cycle.
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18M.2.SL.TZ0.2c.ii:
Identify one other input to the mineral storage in the “A” horizon in Figure 2(b).
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14M.1.SL.TZ0.4a:
Identify in the spaces provided the missing flows and storages labelled 1–4 within the diagram.
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15M.2.SL.TZ0.3b:
Construct a labelled flow diagram to show the processes that link soil with the following three storages:
The atmosphere
The lithosphere
Living organismsAnnotate each labelled flow with an example of the matter involved.
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16M.1.SL.TZ0.2a.iv:
With reference to the cattle in the area, explain how the maximum sustainable yield could be calculated.
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17M.2.SL.TZ0.4a:
Identify four ways in which solar energy reaching vegetation may be lost from an ecosystem before it contributes to the biomass of herbivores.
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14N.2.SL.TZ0.4b:
Explain the transfer of energy through an ecosystem. Support your explanation with a labelled diagram.
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14M.1.SL.TZ0.1a.ii:
Identify one way in which energy may leave this ecosystem.
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17N.2.SL.TZ0.7b:
Compare and contrast the impact of humans on the carbon and nitrogen cycles.
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16N.1.SL.TZ0.4b:
Define net primary productivity.
