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Date	May 2022	Marks available	2	Reference code	22M.2.SL.TZ2.1
Level	Standard level	Paper	Paper 2	Time zone	Time zone 2
Command term	Describe	Question number	1	Adapted from	N/A

Question

There is growing evidence of a decrease in bee populations. This decrease is a serious problem because of their valuable role as pollinators in the ecosystems where they live. Neonicotinoid pesticides have been implicated in this decrease because they have been found at trace levels in the nectar and pollen of crop plants and in the bee colonies.

Scientists placed colonies of a species of bumblebee, Bombus terrestris, in the laboratory to test the effects of different levels of a neonicotinoid on their development. They divided the colonies into three groups:

The control colonies were given a solution of water and sugar that resembled nectar produced by flowers.
A second group of colonies was given the same sugar solution containing a neonicotinoid dissolved in it at low concentrations, similar to those found in nature.
A third group of colonies was given the same sugar solution containing a neonicotinoid dissolved in it at high concentrations, similar to those found in nature.

After two weeks, all colonies were placed in the field to allow the bumblebees to feed naturally.

The mass of the colonies, including adult bumblebees, wax, honey and larvae, was recorded every week. The cumulative increase in mass was calculated and is shown on the graph.

[Source: Adapted from Whitehorn, P.R., O’Connor, S., Wackers, F.L. and Goulson, D., 2012.
Bumble Bee Colony Growth and Queen Production. Science, [e-journal] 336(6079), pp. 351–352.
http://dx.doi.org/10.1126/science.1215025.]

The number of queen bumblebees produced in each colony was recorded. New bumblebee colonies are started by a queen.

A similar study compared the effect of a different neonicotinoid on four different species of bumblebees. The queens were exposed to either control conditions (with no pesticide), or low or high doses of neonicotinoid. The scientists then measured the average length of the developing eggs in the ovaries of the queens.

[Source: Baron GL, Raine NE, Brown MJF. 2017 General and species-specific impacts of a neonicotinoid insecticide
on the ovary development and feeding of wild bumblebee queens. Proc. R. Soc. B 284: 20170123.
http://dx.doi.org/10.1098/rspb.2017.0123 Licensed under a Creative Commons Attribution 4.0
International License https://creativecommons.org/licenses/by/4.0/ Source adapted.]

Describe the effect of neonicotinoid pesticides on the nervous system of insects.

[1]

a.i.

State the cumulative increase in the mass of control colonies at 7 weeks.

[1]

a.ii.

Compare and contrast the cumulative increase in mass of the three groups of colonies once they were placed in the field.

[2]

a.iii.

Suggest a reason for the changes in mass in the colonies between weeks 6 and 8.

[1]

a.iv.

Using the data in the graph, predict how the use of neonicotinoid pesticides will affect bumblebee populations.

[3]

Identify the species whose eggs are most affected by a high dose of neonicotinoid.

[1]

c.i.

Describe the overall effects of low and high doses of neonicotinoid on the egg lengths of all four species.

[2]

c.ii.

Deduce, based on the data presented, whether the levels of neonicotinoids used in agriculture cause direct harm to B. terrestris.

[1]

Markscheme

blocks synaptic transmission at (cholinergic synapses);
binds to (acetylcholine) receptors;

a.i.

230 g;

Accept range of 215 – 265. This takes into account the beginning and end of week 7.
Unit required.

a.ii.

all increased in (cumulative) mass gain up to 5–6 weeks
OR
all decreased (in cumulative mass gain) after 6 weeks;
both with neonicotinoids have significantly lower (cumulative) mass than the control colonies (at all periods)
OR
colonies exposed to high concentration always had the lowest (cumulative) mass gain;

Accept vice versa.

a.iii.

less production of honey/wax;
fewer bees/dispersal of bees/queens;
bad weather/environmental change/predators/disease/pests;

a.iv.

number of populations may/will decrease;
both treatments decreased very significantly the number of queens;
low treatment had (almost) the same effect as the high
OR
even low levels have as toxic/lethal effects as high levels;
without new queens, new colonies cannot be founded;
no/less/little reproduction (as only queens lay eggs);
new colonies are essential to maintain bumblebee populations;

B. lucorum;

c.i.

low doses caused (slight) decrease in (average) egg lengths in 3 species/most species
OR
low doses caused a slight increase in 1 species/B. pascuorum;
high doses caused (slightly) lower (average) results in all 4 species (compared to control);
in only one species/B. pratorum, the high doses caused larger lengths than the low doses;

Accept any other valid comparison.

c.ii.

yes, as even low/both doses (of first neonicotinoid) affect the (overall) development of colonies negatively; (From Graph 1)
yes, as decreased numbers of queens (likely) affect reproductive capabilities; (From Graph 2)
the second neonicotinoid (likely) had less/little/no effect on the bees as it had little effect on egg size; (From Graph 3)

OWTTE

Examiners report

A pleasing number were able to correctly describe the effect of the pesticides on the synapses and state the cumulative increase correctly in ai and aii. However, in aiii, many did not see the similarity in pattern for the compare mark. In part b stronger candidates commented on the fact that even at low doses the pesticide had a great effect and that the difference between high and low doses was negligible. Many examiners were bemused by the answers to c(i) where about half of the candidates failed to identify B. lucorum as the most affected species. B. pascuorum and B. terrestris were often incorrectly given. In cii. Better candidates described the overall effects as asked, with weaker candidates just describing each species in turn. In 1d the top candidates looked at all of the data, but those who just stated that the effect was not noticeable as the egg length was not significantly smaller gained the mark.

a.i.

[N/A]

a.ii.

[N/A]

a.iii.

[N/A]

a.iv.

[N/A]

c.i.

[N/A]

c.ii.

[N/A]