| Date | November 2016 | Marks available | 1 | Reference code | 16N.1.SL.TZ0.4 |
| Level | Standard Level | Paper | Paper 1 | Time zone | Time zone 0 |
| Command term | State | Question number | 4 | Adapted from | N/A |
Question
Figure 4: The gross and net productivity at different trophic levels within the Silver Springs, Florida, ecosystem.
[Source: Kimball's Biology Pages © John W. Kimball, distributed under a Creative Commons Attribution 3.0 Unported (CC BY 3.0) license]
State the process represented in the box labelled X.
Define net primary productivity.
Describe how the second law of thermodynamics operates in relation to the transfer of energy within the Silver Springs ecosystem.
Distinguish between a pyramid of numbers and a pyramid of productivity.
Markscheme
respiration
[1 max]
the gain by producers in energy or biomass per unit area per unit time remaining after allowing for respiratory losses (R).
[1 max]
the 2nd law of thermodynamics has energy becoming dispersed, in the ecosystem /overtime there is an increase in entropy;
light energy is converted to chemical energy in plants, with some energy being dispersed in less useful forms /with an increase in entropy;
the chemical energy is passed down the food chain through eating/consumption;
the energy is used in respiration which releases some of the energy (in a less useful form) as heat which increases disorder of the system/increases entropy of the system;
90% of energy is lost as heat with each transfer;
the heat goes back to the atmosphere but is removed/lost from the ecosystem.
Accept answers which correctly apply the concepts of entropy / energy/heat sources and sinks.
[2 max]
pyramids of numbers display the number of organisms at each trophic level;
...whereas pyramids of productivity refer to the flow of energy through a trophic level (measured in gm/m2/yr or J/m2/yr);
pyramids of numbers can sometimes display different patterns / e.g. an inverted pyramid when individuals at lower trophic levels are relatively large (e.g. oak tree to aphids to blue tits to sparrow hawk);
...whereas a pyramid of productivity always shows a decrease along the food chain;
the data for pyramids of numbers are relatively easier to collect than for pyramids of productivity
...whereas pyramid of productivity requires rate of biomass production overtime which is more difficult to collect;
pyramid of productivity shows the flow of energy overtime.
BOTH pyramid of numbers and pyramid of productivity must be addressed to achieve maximum 2 marks.
[2 max]
Examiners report
Most candidate correctly responded to this question.
Few students gave a comprehensive definition of net primary productivity. E.g. ‘per unit area per unit time’ was frequently omitted.
Most candidates demonstrated limited understanding of the second law of thermodynamics and responses lacked sufficient detail e.g. marks were lost for not explaining how energy was lost through the trophic levels.
In general this question was well answered by most candidates.
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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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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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.
