Discuss the difficulties of classifying organisms into trophic levels.

Explain the cause and consequences of biomagnification, using a named example.

a. consumer may have more than one food source;
b. organisms eaten may be at different trophic levels;
c. may change their trophic level over time;
d. different stages in life cycle might exist in different trophic level (eg frog);
e. example of organism (presenting such a difficulty);

a. a process in which chemical substances become more concentrated at each trophic level;
b. valid named example (for example mercury, organophosphorous pesticides, DDT, TBT);
c. these substances cannot be broken down / are broken down slowly by metabolism;
d. are often stored in (adipose) tissues;
e. each organism consumes large quantities of the trophic level below it;
f. so substance accumulates/increases to reach toxic levels;
If no example is given award [3 max].

This option was attempted by many candidates. The data was more challenging for some than in previous years but candidates on the whole responded well to it.  

Few candidates had any difficulty with this question.

This option was attempted by many candidates. The data was more challenging for some than in previous years but candidates on the whole responded well to it.  

For G3(b) there were many full mark answers. Most candidates were able to give examples of biomagnification and explain the cause and consequences of it.