| Date | May 2014 | Marks available | 2 | Reference code | 14M.1.SL.TZ0.4 |
| Level | Standard Level | Paper | Paper 1 | Time zone | Time zone 0 |
| Command term | Identify | Question number | 4 | Adapted from | N/A |
Question
Figure 4 below shows a simplified version of the nitrogen cycle.
Figure 4
© International Baccalaureate Organization 2014
Identify in the spaces provided the missing flows and storages labelled 1–4 within the diagram.
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:
Identify two ways in which humans can restore soils degraded by overgrazing
Explain how the use of non-biodegradable pesticides on farmland may affect the human food chain.
Markscheme
For 3 - do not accept lightning or the Haber process.
Award [1] for two or three correct responses and [2] for four correct responses.
[2 max]
Impact on flow: [1 max]
less plants available for feeding;
reduce of flow into dead organic matter;
Do not accept ‘plants absorb less nitrogen’.
Impact on storage: [1 max]
less nitrogen stored within plants;
less nitrogen within dead organic matter /soil;
less nitrogen within animal store;
more nitrogen in the atmosphere;
[2 max]
addition of fertilizers/soil conditioners;
planting leguminous plants (e.g. clover);
wind reduction techniques/wind breaks/shelter belts/strip cultivation/crop rotation;
cultivation techniques/terracing/contour ploughing;
forestation/re-afforestion;
agroforestry/forest farming;
Do not credit ‘leave land fallow/empty of animals’ or only ‘plant grass’.
Accept any other reasonable response.
[2 max]
movement of non-biodegradable material in food chain;
potential to biomagnify;
potential to bio-accumulate/bio-concentrate;
Accept any other reasonable response.
[2 max]
Examiners report
Few candidates achieved both marks for this question. Most achieved either 0 or 1 mark with a number of students not attempting the question. Popular correct responses included (1) consumers and (4) decomposition and few were able to correctly identify (2) as nitrates/nitrites or (3) as nitrogen fixation.
Many candidates struggled with these two questions. For b(i) responses often focused on nitrogen store instead of impact on flow and for b(ii) often stated ‘an increase in nitrogen within soils’ instead of the converse or ‘nitrogen in plants’ which was too vague.
The majority of candidates gained some marks for this question.
Most candidates performed well on this question with many achieving full marks.
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.
- 17M.2.SL.TZ0.1a: State the main source of energy for the food chain in Figure 1.
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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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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.
