Syllabus Edition
First teaching 2024
First exams 2026
An ecologist collects samples from two different freshwater sources.
Sample A contains stonefly and mayfly nymphs, as well as a few freshwater shrimp, whereas sample B contains a few freshwater shrimp, as well as bloodworms and Tubifex worms.
Both samples are found to have the same species richness and species diversity.
Identify which sample contains the more polluted water.
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Organisms such as mayfly nymphs, freshwater shrimp and bloodworms can help ecologists to assess the quality of a particular environment (in this case a freshwater environment).
State the general term used to describe these types of organisms.
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List three forms of aquatic pollution.
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One parameter that can be measured in order to analyse the quality of a particular aquatic ecosystem is turbidity.
Explain what is meant by the term turbidity.
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Outline how turbidity is measured.
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The boxes below show a number of pollutants and the ways that they affect ecosystems.
Join each pollutant to the effect that it creates.
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The figure below shows the positions of four farms and the concentrations of nitrate at different points in a river.
Identify which farm is likely to have been using too much fertiliser on its land.
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Distinguish between point source and non-point source pollution.
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Identify one potential point source and one potential non-point source of nutrient pollution causing eutrophication in a lake.
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Complete the table below to outline three possible strategies for reducing the impacts of eutrophication (i.e. one strategy for each stage of pollution management).
Stage of Pollution Management | General Description | Strategy for Reducing Impacts of Eutrophication |
|---|---|---|
1 | Change the human activity responsible for the initial production of pollutant(s) | |
2 | Regulate and reduce the quantities of pollutant(s) released at the point of emission | |
3 | Clean up the pollutant(s) and restore the ecosystem after pollution has occurred |
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When raw sewage is released into a waterway it can lead to eutrophication.
The statements below list some of the stages of the process of eutrophication.
Add a number next to statement (from 1 to 6) to put the stages into the correct order.
Stage of Eutrophication | Order |
Algal bloom prevents sunlight from reaching aquatic plants. Water oxygen levels fall. |
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Excessive nutrients from fertilisers run-off from the land into the water. |
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Algae also show rapid growth. |
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Death of organisms requiring dissolved oxygen in water. |
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Decomposition rate increases. Aerobic respiration of decomposers reduces dissolved oxygen further. |
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Aquatic plants flourish, growing rapidly. |
Explain one other potential consequence of the release of raw sewage into a water system.
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The levels of dissolved oxygen were measured in a river
The results were plotted on a graph, which is shown below.
At which point (A, B, C or D) does raw sewage enter the river?
Explain your answer.
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Farmers may add chemical fertilisers to their soil to increase crop yield.
These fertilisers may leak into rivers.
A scientist measures the oxygen content of water in two different locations of the same river during the month of April.
In location A he finds that the mean dissolved oxygen was 6 mg per litre and at location B he finds that the mean dissolved oxygen was 3 mg per litre.
He concludes that the use of fertiliser in the field has affected the oxygen content of the river.
Discuss his conclusion.
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The diagram shows a river and the location of a fertiliser factory.
The arrows indicate the direction of the flow of the river.
A scientist recorded the nitrate concentrations of the water at site A and site B. Her results are shown in the table.
Site | Nitrate concentration / mg per dm3 | |||
Sample 1 | Sample 2 | Sample 3 | Mean | |
A | 17 | 25 | 18 | 20 |
B | 49 | 64 | 58 |
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Calculate the mean nitrate concentration found at site B.
The scientist observed algae and some dead fish in the river at site B. These were not present at site A.
Give an explanation for these observations.
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Define the term biochemical oxygen demand (BOD).
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Describe how biochemical oxygen demand (BOD) is measured.
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Define the term eutrophication.
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Eutrophication is an example of positive feedback.
Explain how.
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Evaluate the uses of indicator species and biotic indices in measuring aquatic pollution.
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Explain how a lake affected by eutrophication can be cleaned and restored.
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Discuss the effectiveness of different strategies used to manage water pollution.
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