| Date | May 2021 | Marks available | 3 | Reference code | 21M.1.SL.TZ0.5 |
| Level | Standard Level | Paper | Paper 1 | Time zone | Time zone 0 |
| Command term | Describe | Question number | 5 | Adapted from | N/A |
Question
Figure 6(d): The Nadezhda smelting plant in Norilsk opened in 1979
The plant may be a possible source of the water discolouration.
[Source: NASA Earth Observatory image by Jesse Allen, using Landsat data from the U.S. Geological Survey.]
Figure 6(e): Daldykan River in Norilsk
[Source: © Liza Udilova / Greenpeace.]
Describe a practical strategy using a biotic index to provide evidence that the Daldykan River (Figures 6(d) and 6(e)) is damaged by effluent from the metal processing plant.
When measuring levels of pollution, state one advantage of using a biotic index compared to measuring the pollutants directly.
Advantage:
When measuring levels of pollution, state one disadvantage of using a biotic index compared to measuring the pollutants directly.
Disadvantage:
Markscheme
identify sampling sites upstream and downstream of plant/town / sample before and after effluent is released; sample invertebrate populations / e.g. using kick samples/nets;
identify and count numbers of each species; determine the absence/presence of indicator species;
calculate from this data the biotic index for each site / e.g. use BMWP/Simpson’s Diversity Index/Trent Biotic Index; repeat sampling throughout the year;
Do not accept ‘use of fish’.
Do not accept only ‘measure biodiversity’.
measures actual impact on living organisms/ecosystem;
can see if pollution has occurred in the past/in the lifespan of the indicator species even if the water is clean now;
records seasonal changes in the impact of pollutants;
does not require complex chemical analysis;
does not require expensive equipment / is relatively cheap;
Do not accept ‘using a biotic index is quicker than measuring pollutants directly’.
Do not accept ‘provides a numerical value for the level of pollution’.
Do not accept ‘can be used as a reference for future monitoring’.
does not identify pollutant causing impacts / does not measure the level of the actual pollutant;
does not directly measure the level of pollution;
does not help identify source responsible for impacts;
inaccurate as populations change naturally (during the season) / impacts could be due to natural changes in environment/other factors;
requires knowledge of/ability in identification of organisms for area;
requires existence of identification keys;
Do not accept only ‘it is not exact/precise’.
Do not accept ‘method kills organisms’.
Examiners report
Overall this question was poorly answered. A significant number of candidates did not attempt to answer the question, leaving a blank response. Few candidates were able to fully describe how the river could be sampled when using a biotic index. Some students inappropriately suggested the use of BOD, pH, turbidity, colour, fish, Lincoln's Index or vegetation around the river.
There was a wide range of responses for this question, with many correctly linking their response to the actual impact on living organisms. However, it was clear that a significant number of candidates did not understand what a biotic index was and incorrectly discussed the use of abiotic parameters such as pH.
Many candidates correctly answered this question. A popular response was "it does not measure the level of the actual pollutant". A significant number of responses were too vague, such as "it is not exact or precise".
