| Date | May 2016 | Marks available | 2 | Reference code | 16M.3.SL.TZ0.15 |
| Level | Standard level | Paper | Paper 3 | Time zone | TZ0 |
| Command term | Identify and Suggest | Question number | 15 | Adapted from | N/A |
Question
The images show three predator–prey relationships.
Biomagnification of two groups of organic pollutants was investigated in three predator–prey relationships. BDEs and PCBs are broadly used in industry. The biomagnification factor is a ratio of the amount of pollutant in predator tissue compared to the amount of pollutant in prey tissue.
Outline how biomagnification occurs.
(i) Identify the predator with the least biomagnification of pollutants.
(ii) Suggest a reason for the species identified in (b)(i) having the lowest biomagnification factor.
Deduce two conclusions about PCBs that are supported by the data.
Markscheme
Toxin at lowest concentrations in organisms at lowest trophic level
Toxin concentration builds/is magnified in organisms at each successively higher trophic level
Toxins often fat-soluble
OR
can accumulate in body tissues
Toxin/chemical is not metabolized/excreted
(i) Fox
(ii) Unlike the other two predators, it is a mammal
OR
has other sources of food
OR
different biochemistry/metabolism
PCBs biomagnify in all three predator–prey relationships
PCBs biomagnify most in rodent–buzzard/least in rodent–fox relationship
Greatest range of PCB biomagnification occurs in rodent–buzzard
Biomagnification in birds is higher than in mammals
Examiners report
N/A
(ii) Candidates struggled to find reasons the fox had lower PCB levels and restated that they had lower levels.
Only the better candidates could deduce conclusions about PCB's.
