| 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 | Distinguish | 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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19N.1.SL.TZ0.2a:
Using Figure 6(c), identify a food chain in the St Lawrence River ecosystem that has five trophic levels.
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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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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.TZ0.7:
To what extent might Iceland be viewed as a role model for sustainability by other countries?
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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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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:
- 18M.2.SL.TZ0.3a: Identify one producer in the system illustrated in Figure 3.
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16N.2.SL.TZ0.4a:
Outline why top carnivores are vulnerable to non-biodegradable toxins.
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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.
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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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17N.2.SL.TZ0.4a:
Describe the role of primary producers in ecosystems.
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17N.2.SL.TZ0.7a:
Outline how soil can be viewed as an ecosystem.
- 18N.2.SL.TZ0.4c: Using examples, discuss whether habitat conservation is more successful than a species-based...
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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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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.
- 18N.1.SL.TZ0.1: Identify one ecosystem in Algonquin Provincial Park.
- 17N.1.SL.TZ0.5a.ii: Identify one argument against humans hunting puffins.
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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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18M.2.SL.TZ0.4b:
Explain how a community of trees in a woodland may be considered a system.
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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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19N.1.SL.TZ0.1d:
Outline why estuaries are highly productive ecosystems.
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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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17M.2.SL.TZ0.1b:
State the trophic level labelled X in Figure 1.
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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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16N.1.SL.TZ0.4c:
Describe how the second law of thermodynamics operates in relation to the transfer of energy within the Silver Springs ecosystem.
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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.
- 21N.2.SL.TZ0.1a.iii: Explain how the second law of thermodynamics applies to this food chain.
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21M.1.SL.TZ0.7a:
Outline the impact that a reduction in the tiger population may have on other populations in the food web shown in Figure 8(c).
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20N.1.SL.TZ0.2e:
With reference to Figures 2(a) and 2(b), suggest two reasons why the red-necked amazon population has recovered more quickly than the imperial amazon population following Hurricane David in 1979.
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20N.1.SL.TZ0.1a:
Using Figure 1(c), state one ecosystem found at sea level in Dominica.
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21N.1.SL.TZ0.1a:
With reference to Figures 2(b) and 3, identify an ecosystem found in London.
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21N.2.SL.TZ0.5b:
Explain how models of ecosystems might be used in species conservation.
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22M.2.SL.TZ0.7b:
Explain how negative and positive feedback mechanisms may influence the growth of decomposer populations in the soil.
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21N.2.SL.TZ0.4a:
Identify four factors that make the use of the insecticide DDT controversial.
- 21N.2.SL.TZ0.1a.i: State the trophic level of the zebra.
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21N.1.SL.TZ0.1b:
Outline one factor which limits the primary productivity of an ecosystem in London.
