| Date | May 2013 | Marks available | 2 | Reference code | 13M.3.SL.TZ2.19 |
| Level | Standard level | Paper | Paper 3 | Time zone | Time zone 2 |
| Command term | Compare | Question number | 19 | Adapted from | N/A |
Question
A grassland food web was studied to understand how climate warming affects the interaction of different animal and plant species. Grasshoppers (Melanoplus femurrubrum) feed on grasses growing amongst taller bushes. Spiders (Pisaurina mira) feed on the grasshoppers. For 75 days, the feeding behaviour of the grasshoppers was observed with and without predators, in temperatures that were cool or warm. During the study period, the grasshoppers progressed through stages of larval development (instars) to adulthood.
Identify the primary food for all grasshoppers without predators.
Deduce, using the data, how the feeding behaviour of instar larvae changes if without predators, conditions change from cool to warm.
Deduce, using the data, how the feeding behaviour of instar larvae changes if in warm conditions, predators are introduced.
Compare adult feeding to instar larval feeding.
Suggest why adult feeding differs from instar larval feeding when predators are present.
Markscheme
grasses
feeding time on grasses (slightly) reduces / feeding time on bushes increases
feeding time on grasses (greatly) reduces / feeding time on bushes increases
feeding is similar without predators;
more feeding on grass by adults with predators;
a. instars are more protected from predators/camouflaged when feeding in bushes;
b. adults can escape predator attacks more easily/camouflaged when feeding in grasses;
c. adults are bigger and less easily captured;
Accept other reasonable responses.
Examiners report
There were some comments on the G2 forms that said that these graphs were confusing. In fact the vast majority of candidates gained all three marks on parts a and b.
There were some comments on the G2 forms that said that these graphs were confusing. In fact the vast majority of candidates gained all three marks on parts a and b.
There were some comments on the G2 forms that said that these graphs were confusing. In fact the vast majority of candidates gained all three marks on parts a and b.
In c there were often very wordy answers that did not get to the point, not being proper comparisons. Only the better candidates were able to narrow it down to the fact that the feeding in adults and instars is similar without predators, but there is more feeding on grass by adults with predators.
Many could correctly suggest a reason why the feeding differs.
