| Date | November 2016 | Marks available | 2 | Reference code | 16N.1.SL.TZ0.4 |
| Level | Standard Level | Paper | Paper 1 | Time zone | Time zone 0 |
| Command term | Describe | 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.2.SL.TZ0.3a:
Distinguish between a pyramid of numbers and a pyramid of productivity.
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17N.2.SL.TZ0.7a:
Outline how soil can be viewed as an ecosystem.
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17N.2.SL.TZ0.4a:
Describe the role of primary producers in ecosystems.
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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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14M.1.SL.TZ0.1a.i:
State the source of energy for this ecosystem.
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16M.1.SL.TZ0.1e.i:
State its trophic level in the ecosystem.
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19M.1.SL.TZ0.7:
Explain two ways in which mangroves improve the water quality for primary producers within marine ecosystems.
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18N.1.SL.TZ0.3a:
With reference to Figure 6, draw a food chain that includes four trophic levels.
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18M.2.SL.TZ0.5b:
Suggest the procedures needed to collect data for the construction of a pyramid of numbers for the following food chain:
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17N.1.SL.TZ0.7:
To what extent might Iceland be viewed as a role model for sustainability by other countries?
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19N.1.SL.TZ0.2d:
With reference to Figure 8, explain why the beluga whale is more at risk from toxic pollutants, such as heavy metals and persistent organic pollutants (POPs), than most other organisms in its food web.
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19M.1.SL.TZ0.8:
With reference to Figure 5, describe how loss of a coral reef ecosystem could impact a neighbouring seagrass community.
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19N.1.SL.TZ0.3b:
With reference to Figure 9(a), outline how the round goby both positively and negatively affects the St Lawrence River ecosystem.
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16M.2.SL.TZ0.1c.iii:
Identify four factors that would affect the primary productivity of forest plantations in the Copperbelt Province.
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18N.1.SL.TZ0.10a:
With reference to Figure 7(a), outline one reason why there are more beaver remains in wolf faeces during summer.
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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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17N.1.SL.TZ0.5c:
Identify two reasons why the future size of the Atlantic puffin population is difficult to predict.
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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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19N.1.SL.TZ0.2a:
Using Figure 6(c), identify a food chain in the St Lawrence River ecosystem that has five trophic levels.
- 17N.1.SL.TZ0.5a.ii: Identify one argument against humans hunting puffins.
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14M.1.SL.TZ0.4d:
Explain how the use of non-biodegradable pesticides on farmland may affect the human food chain.
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19M.2.SL.TZ0.1d:
Outline two ways in which the food web is likely to change as a result of succession.
- 18N.2.SL.TZ0.4c: Using examples, discuss whether habitat conservation is more successful than a species-based...
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17M.2.SL.TZ0.1d:
With reference to the concepts of bioaccumulation and biomagnification, outline how the concentration of DDT has changed along the food chain.
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16M.2.SL.TZ0.1d.i:
With reference to Figure 7, state the most common ecosystem in Zambia.
- 18N.1.SL.TZ0.1: Identify one ecosystem in Algonquin Provincial Park.
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17M.2.SL.TZ0.1b:
State the trophic level labelled X in Figure 1.
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19N.1.SL.TZ0.1d:
Outline why estuaries are highly productive ecosystems.
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17N.1.SL.TZ0.5b:
With reference to Figure 8(c) state the impact that an increase in the mackerel population might have on the Atlantic puffin population.
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14N.1.SL.TZ0.2b:
Elephants eat a variety of vegetation: grasses, shrubs, leaves and small tree seedlings. Describe the impact on a grassland ecosystem of the main large herbivore being removed.
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16N.2.SL.TZ0.4a:
Outline why top carnivores are vulnerable to non-biodegradable toxins.
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14N.2.SL.TZ0.4b:
Explain the transfer of energy through an ecosystem. Support your explanation with a labelled diagram.
- 18M.2.SL.TZ0.3a: Identify one producer in the system illustrated in Figure 3.
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16N.1.SL.TZ0.4d:
Distinguish between a pyramid of numbers and a pyramid of productivity.
