| Date | May 2013 | Marks available | 2 | Reference code | 13M.3.HL.TZ1.10 |
| Level | Higher level | Paper | Paper 3 | Time zone | Time zone 1 |
| Command term | Compare | Question number | 10 | Adapted from | N/A |
Question
Indigenous human populations living along riverbanks in the Amazon basin often rely heavily on fish as a major part of their diet. The data shown below come from a study that was carried out to investigate levels of mercury contamination in the Rio Negro basin in Brazil. Mercury concentration was measured in fish belonging to four different trophic levels and is shown in parts per billion (ppb).
State the trophic level of the fish that presents the least risk of mercury contamination for human consumers.
Compare the levels of mercury found in herbivores (primary consumers) and detritivores.
Explain the large range of mercury concentrations seen in the piscivores.
Markscheme
herbivores (primary consumers)
a. same range of mercury concentrations/up to 200–250 (ppb);
b. levels above 50 (ppb) are lower/less common in herbivores than in detritivores / vice versa;
c. (0–) 50 (ppb) is most common in herbivores whereas (50–) 100 (ppb) is most common in detritivores;
a. piscivores feed at different trophic levels (within the food chain);
b. piscivores that feed on herbivores / detritivores will have lower levels of contamination;
c. piscivores that feed on carnivores/omnivores/top of food chain will have high levels;
Examiners report
This was also a very popular option but not very high scoring in many cases.
Almost all correctly identified the trophic level as herbivores (primary consumers) and thus were able to get this mark.
This was also a very popular option but not very high scoring in many cases.
Many were able to score 1 mark comparing levels of mercury in herbivores and detritivores with the better candidates scoring full marks.
This was also a very popular option but not very high scoring in many cases.
Many found this section difficult as they did not explain the large ‘range’ of mercury concentrations in piscivores but instead explained why there was a high level, which was not what the question asked. It was thus discriminating with only good candidates receiving the 2 marks.
