| Date | May 2011 | Marks available | 1 | Reference code | 11M.3.HL.TZ2.10 |
| Level | Higher level | Paper | Paper 3 | Time zone | Time zone 2 |
| Command term | State | Question number | 10 | Adapted from | N/A |
Question
Cadmium is a heavy metal that can be toxic to many species. In a study, the concentration of cadmium was examined in the tissues of three soil arthropods, Neobisium muscorum, Platynothrus peltifer and Notiophilus biguttatus. The shaded area of each graph indicates the time that the organisms were exposed to cadmium in their environment, while the unshaded area indicates the time when cadmium was not present in their environment.
Identify the highest average concentration of cadmium found in P. peltifer.
Determine, with a reason from the data, which species is unable to eliminate cadmium.
State the species that accumulates the least cadmium.
Suggest, with observations from the data, a reason why the species stated in (c)(i) accumulates the least cadmium.
Describe the possible effects of the presence of cadmium in food chains involving these arthropods.
Markscheme
260 pmol mg−1 (accept answers in the range of 255 pmol mg−1 to 265 pmol mg−1)
Neobisium muscorum;
level of cadmium remains high / does not decrease (when cadmium is removed);
Notiophilus biguttatus
can excrete/remove/eliminate cadmium (from its tissues);
faster reduction/removal / drops to lowest level after cadmium exposure;
cadmium levels stop rising sooner/rise slowing by day ten;
is less tolerant/dies when cadmium reaches a certain concentration;
exposed to cadmium for a shorter time/period;
cadmium accumulates along food chain / biomagnification / bioaccumulation;
heavy metals cause abnormal growth/behaviour/death/failure to reproduce;
Notiophilus biguttatus has less effect on the food chain (as it accumulates less);
cadmium harmful/lethal to organisms at/near the end of the food chain;
(death of arthropods) may change soil quality;
Examiners report
Parts (a) and (c) (i) were answered correctly by most candidates.
Most candidates answered (b) successfully.
Parts (a) and (c) (i) were answered correctly by most candidates. A few candidates abbreviated the genus names to an initial letter, which is not advised when there are two genera starting with the same initial.
(c) (ii) proved more difficult. Where a question asks for reasons for something being least, among three species, it is necessary to give answers comparing the species, rather than just referring to the one that is least. For example, in this case it was better to say that Noteophilus biguttatus eliminates cadmium more rapidly than that it eliminates cadmium rapidly.
Part (d) was well answered by many candidates, who referred to biomagnification or bioaccumulation and then explained that animals at higher trophic levels would be most affected.
