| Date | November 2012 | Marks available | 2 | Reference code | 12N.3.HL.TZ0.4 |
| Level | Higher level | Paper | Paper 3 | Time zone | TZ0 |
| Command term | Distinguish | Question number | 4 | Adapted from | N/A |
Question
In order to investigate the hypothesis that honeybees (Apis mellifera) have an instinct to forage for either nectar or pollen, but not both, researchers installed different feeders containing either nectar alone or pollen alone. They collected four different groups of honeybees (those arriving at the nectar feeders, arriving at the pollen feeders, departing from the nectar feeders and departing from the pollen feeders) and measured the abundance of eight peptides in their brains. The relative difference of these brain peptides was then calculated by subtracting the abundance in nectar foragers from the abundance in pollen foragers and is shown by the bars on the graphs below.
Identify which peptide shows the greatest difference between pollen foragers and nectar foragers departing from the feeders.
Distinguish between the difference in abundance of peptides in nectar and pollen foragers arriving at the feeders.
Evaluate the hypothesis that honeybees have an instinct to forage for either nectar or pollen, but not both.
Discuss how this type of foraging behaviour could optimize food intake.
Markscheme
(peptide) F
(peptides) A, B, C and H more abundant in pollen foragers;
(peptides) D, E, F and G more abundant in nectar foragers;
greater abundance (differences) for nectar foragers;
A and C showed little difference;
Do not accept numerical statements only.
(arguments supporting the hypothesis)
each group of foragers is always associated with the same group of peptides;
trends inverse between nectar (foragers) and pollen (foragers)/arriving and departing / OWTTE;
error bars on the graph show that the differences are likely to be significant;
(arguments not supporting the hypothesis)
no data about nectar/pollen actually collected / sample size;
there is no evidence of causation/that the peptide in the brain is determining the type of foraging itself;
(predisposition/instinct/natural selection) ensures that both pollen and nectar will be collected;
allows the bees to collect whichever food source is in abundance at the time / increases food collection efficiency;
both pollen and nectar are diet requirements;
this behaviour is part of division of labour/specialization;
Examiners report
Many candidates really did not seem to understand the underlying theory relating brain peptides to foraging strategy in bees and this question separated candidates who analysed data as a set and those that searched for details and lost the general picture. Whereas almost all candidates could identify the correct peptide in part (a).
Many candidates really did not seem to understand the underlying theory relating brain peptides to foraging strategy in bees and this question separated candidates who analysed data as a set and those that searched for details and lost the general picture.
Most of them could distinguish the two groups in (b).
Many candidates really did not seem to understand the underlying theory relating brain peptides to foraging strategy in bees and this question separated candidates who analysed data as a set and those that searched for details and lost the general picture.
Many candidates had difficulty evaluating the hypothesis although they could see the inversion of trends in (c).
Many candidates really did not seem to understand the underlying theory relating brain peptides to foraging strategy in bees and this question separated candidates who analysed data as a set and those that searched for details and lost the general picture.
They frequently restated the question in the wording of their answer for (d), but many nevertheless gained the mark about increasing food collection efficiency.
