| Date | November 2014 | Marks available | 2 | Reference code | 14N.1.SL.TZ0.5 |
| Level | Standard Level | Paper | Paper 1 | Time zone | Time zone 0 |
| Command term | Describe | Question number | 5 | Adapted from | N/A |
Question
Figure 3 shows an incomplete model for the nitrogen cycle.
Figure 3
Label the diagram above to complete the processes and flows in the nitrogen cycle.
Distinguish between a transfer and a transformation in the nitrogen cycle.
Describe two ways in which humans may impact the nitrogen cycle.
Markscheme
Must include: clear arrows with processes attached
Award [1 mark] for 2 arrows correctly labelled.
Only credit arrow labelled with process (not storages).
Allow any other reasonable arrow with process.
[3 max]
transfer is the movement/change in location of nitrogen in the cycle;
whereas transformation is chemical conversion/change of state of nitrogen in the cycle;
[1 max] if there is no reference made to the nitrogen cycle but student distinguishes between transfer and transformation process.
Accept examples of each process such as examples given below
Transfer [1 max]:
nitrates from soil to roots of plants;
movement of nitrogen in plants to nitrogen in animals;
Transformations [1 max]:
bacteria convert one form of nitrogen to another;
ammonium to nitrite;
nitrite to nitrate;
denitrification from ammonium/nitrate to N2;
[2 max]
use of Haber process to produce fertilizers / addition of nitrogen fertilizers/manure to soil;
addition/removal of nitrogen fixing plants in agriculture monocultures;
removal of crops without addition of fertilizers (loss of nitrogen in cycle for a particular area) / removal of plants/crops resulting in reduction of nitrogen in the soil;
addition of nitrogen compounds to the atmosphere by combustion of fossil fuels;
[2 max]
Examiners report
Responses were wide ranging achieving form 0 to 3 marks. A significant number of responses were left blank or only had drawn arrows without any labels.
Although a number of candidates confused the two processes, many were able to clearly distinguish between the two and provide appropriate examples.
A number of responses were too vague and ‘stated’ factors rather than ‘describing’ how they impacted on the nitrogen cycle.
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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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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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.
