| Date | November 2016 | Marks available | 2 | Reference code | 16N.1.SL.TZ0.6 |
| Level | Standard Level | Paper | Paper 1 | Time zone | Time zone 0 |
| Command term | Outline | Question number | 6 | Adapted from | N/A |
Question
Figure 6: The effects of organic pollution (raw sewage discharged from a pipe) on a stream ecosystem.
[Source: Dr. Mel Zimmerman, Professor of Biology and Director of Clean Water Institute at Lycoming College. Adapted from Bartsch and Ingram (1975) ]
Define biochemical oxygen demand (BOD).
Outline how turbidity changes after the raw sewage discharge point in Graph B.
Suggest how the population growth curve for algae in Graph C would appear if the pollutant had been nitrates and phosphates from fertilizer run-off.
Outline why point source pollution is often easier to manage than non-point source pollution.
Markscheme
a measure of the amount of dissolved oxygen required to break down the organic material in a given volume of water through aerobic biological activity.
OWTTE.
[1 max]
after the point of sewage discharge the turbidity levels rise until about 150m (accept 125-175m) downstream where levels peak/plateau and thereafter steadily decline;
turbidity will increase at the point sewage enters the water, as the pollutant is particulate/coloured;
turbidity will increase after the outlet of sewage as bacteria grow rapidly as they consume/decompose the sewage;
turbidity remains high as algae now rapidly grow as there are nutrients from the sewage decomposition available;
turbidity decreases once the nutrients levels fall to the pre-sewage levels and the algae growth declines;
turbidity increases as algae decrease, and then decrease as algae increase.
Award 1 max for a clear description of change in turbidity levels along the stream.
[2 max]
increase in nutrients will lead to rapid algae growth /could cause algal bloom;
algae levels will decline as nutrient levels become more restricted downstream from the source;
algae would look like the microorganisms curve in the diagram/ rapidly go up right after the pollution outlet;
algae would also decline, like the microbe curve, as the nutrients run out and algae start to die;
microbes would grow and they could shade out the light for algae causing a further drop in the curve;
the trend observed would be opposite to the current growth curve for algae (on graph C).
Only credit responses that refer to algae levels in Graph C, do not credit descriptions of eutrophication.
[3 max]
point source can be clearly identified;
so pollution can be more easily monitored;
solutions should be more easily applied / pollution can be stopped directly;
with non-point pollution, source is widespread/dispersed and difficult to identify;
solutions also have to be widespread/dispersed, so there are increased costs/difficulties of monitoring;
compliance is difficult to ensure with non-point pollution because of widespread/dispersed nature of sources.
[2 max]
Examiners report
Very few students were able to provide a comprehensive definition of biochemical oxygen demand.
Most students achieved a mark for describing changes in turbidity level along the stream. Few candidates were able to explain the cause of turbidity or give reasons for the changing levels.
Most candidates achieved some marks for this question but few achieved the full 3 marks. Many responses overly discussed eutrophication without reference to the curve.
This question was answered well by most students.
Syllabus sections
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15N.2.SL.TZ0.2c:
Discuss how different environmental philosophies can affect the choice of pollution management strategies in response to global warming.
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14N.1.SL.TZ0.3c.i:
Define the term pollution.
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17N.2.SL.TZ0.6c:
The management of a resource can impact the production of solid domestic waste.
To what extent have the three levels of the pollution management model been successfully applied to the management of solid domestic waste?
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19N.2.SL.TZ0.5a:
Outline, using examples, the differences between primary and secondary pollution.
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19N.1.SL.TZ0.5:
With reference to information in the resource booklet, evaluate the sustainability of Canada’s management of the Large Ocean Management Area of the St Lawrence River estuary and Gulf of St Lawrence.
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15M.2.SL.TZ0.1c.ii:
Identify one possible pollution management strategy for Inle Lake in each of the categories in the table below.
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15M.2.SL.TZ0.1a.iii:
With reference to Figures 4 and 5, identify three environmental impacts that may occur as a consequence of human activities on and around Inle Lake.
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17M.2.SL.TZ0.6c:
The provision of food resources and assimilation of wastes are two key factors of the environment that determine its carrying capacity for a given species.
To what extent does the human production of food and waste each influence the carrying capacity for human populations?
- 17M.2.SL.TZ0.1c: Identify one use of DDT that has led to its presence in the environment.
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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.TZ0.3b:
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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15M.2.SL.TZ0.5a:
Outline two indirect methods that could be used to measure the impact on the river ecosystem of dead organic matter from the flooded vegetation and soils.
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15M.2.SL.TZ0.1c.i:
With reference to Figures 4 and 5, complete the following table.
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14M.2.SL.TZ0.5c:
Pollution management strategies may be applied at any of the three levels identified in the diagram below:
With reference to acid deposition, evaluate the political and economic advantages of applying management strategies at the levels of production and impact of the pollutant.
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16M.2.SL.TZ0.4b:
A non-governmental organization has been contracted to investigate the impacts of a landfill site on the surrounding terrestrial ecosystem.
Suggest how the investigation should be designed to ensure reliability and validity.
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18M.2.SL.TZ0.6a:
With reference to named examples, distinguish between a primary and secondary pollutant.
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14N.2.SL.TZ0.3b:
Explain how three pollution management strategies may reduce eutrophication in agricultural areas.
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16N.2.SL.TZ0.4b:
Explain two factors which lead to a loss of marine (ocean) biodiversity.
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19M.1.SL.TZ0.15:
With reference to data throughout the resource booklet, to what extent would the establishment of Marine Protected Areas (MPAs) benefit marine ecosystems and human societies within the Coral Triangle?
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16M.1.SL.TZ0.2a.v:
Nitrates and phosphates from nearby farms may drain into the lake. Identify a strategy for managing this pollution at each of the following levels:
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16N.2.SL.TZ0.4c:
Evaluate one possible pollution management strategy for solid domestic waste.
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16N.2.SL.TZ0.1f:
Justify whether or not Mesquite should be cleared from the Swakop River Valley.
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18N.2.SL.TZ0.7b:
Urban air pollution can become a problem as human populations develop. Evaluate urban air pollution management strategies at the three levels of intervention.
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17N.1.SL.TZ0.3c:
With reference to Figures 6(c), 7(a) and 7(b) explain the problems associated with land restoration in Iceland.
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17M.2.SL.TZ0.5c:
Pollution management strategies may be aimed at either preventing the production of pollutants or limiting their release into ecosystems.
With reference to either acid deposition or eutrophication, evaluate the relative efficiency of these two approaches to management.
