| Date | November 2016 | Marks available | 1 | Reference code | 16N.3.SL.TZ0.14 |
| Level | Standard level | Paper | Paper 3 | Time zone | TZ0 |
| Command term | Outline | Question number | 14 | Adapted from | N/A |
Question
In 1997 in South Africa, a decision was made to decrease the use of mosquito-killing pesticides due to their negative effect on the environment. Mosquitoes are known to be responsible for the spread of malaria. In 2001 the decision was reversed and the use of pesticides was increased. The graph shows the estimated numbers of people with malaria in each year.
Outline the trend in the number of people with malaria during the period when the use of pesticides was decreased in South Africa.
One pesticide used in killing mosquitoes was DDT. Considering its harmful effects, discuss whether the decision to reintroduce it was justified.
Markscheme
the number of people with malaria increased
a. choice has to be made between damage to environment or increase in malaria
b. DT may lead to biomagnification/bioaccumulation in food chains
OR
taken up by species in lower trophic levels becoming more concentrated at higher trophic levels
c. causes harm to consumers at end of food chain
OR
example «eg: thin egg shells of falcons»
d. DDT is shown to be effective in reducing malaria
e. possible partial solution to be selective in areas sprayed with DDT
f. may kill insects that are not pests
| Date | May 2015 | Marks available | 1 | Reference code | 15M.3.SL.TZ2.19 |
| Level | Standard level | Paper | Paper 3 | Time zone | Time zone 2 |
| Command term | Outline | Question number | 19 | Adapted from | N/A |
Question
Limpets (Helcion pectunculus) are marine molluscs that live in rock crevices (cracks and holes) in South Africa. In order to see whether the crevices protected the limpets from wave action, the force required to detach limpets in their natural habitat was measured. Once detached from the rocks, the area of the foot of each limpet was also measured.
State the force required to detach a limpet with an area of foot of 2 cm2 .
State the smallest area of foot necessary to resist a force of 50 N.
……………….cm2
Outline the relationship between area of foot and the force required to detach the limpet.
Smaller limpets can only be found at the back of crevices. Discuss the reasons for this.
Limpets tend to live towards the high tide zone. State the method used to determine the distribution of limpets between the low and high tide lines.
Markscheme
42 (N) (allow answers in the range of 41 (N) to 43 (N))
2.6 (cm2) (allow answers in the range of 2.5 (cm2) to 2.7 (cm2))
Positive correlation / as area of foot increases so does force required.
a. back of crevice less subjected to action of waves;
b. (hypothesis supported as) small area of foot requires less force;
c. amount of predators/food could be affecting the distribution;
d. larger limpets may not fit in the back of the crevice;
e. less competition with larger limpets at the back of the crevice;
transect line / quadrat with transect line
Do not accept quadrat alone.
| Date | May 2015 | Marks available | 1 | Reference code | 15M.3.SL.TZ1.19 |
| Level | Standard level | Paper | Paper 3 | Time zone | Time zone 1 |
| Command term | Identify | Question number | 19 | Adapted from | N/A |
Question
The brown alga Sargassum muticum is a successful invasive species around the world. It grows attached to rocks in the intertidal zone and has large fronds that float in the water. It has recently become established in intertidal communities on the west coast of Scotland. The impact of this invasive species was investigated by measuring the composition of the animal community in the intertidal zone in an affected area. The data were compared to a control site with no invasive S. muticum which was located close by.
Identify the most abundant animal type at
the S. muticum site:
the control site:
Describe the impact of invasive S. muticum on the shoreline animal community.
Discuss possible reasons for the differences in the animal communities seen at the two sites.
Markscheme
S.muticum site: Corophiidae sp.
control site: S. squamata
Both needed for [1].
a. fewer different types of organism / smaller diversity at S. muticum site;
b. mean abundance at S. muticum site is higher for those organisms present;
c. Rissoidea sp. and P. maculata found at control site but not at S. muticum site;
d. C. pagurus only found at S. muticum site;
Comparisons are required but the control site does not need to be mentioned in each response.
a. S. muticum provide habitat/shelter/protection from predators for some species;
b. S. muticum change the environment to suit some species/example of a change;
c. some organisms more successful because less (inter-specific) competition;
d. more food may be available (for herbivores);
e. some herbivores may rely on native algae that have been displaced;
f. (other) conditions at the control site may not be identical to the test site;
| Date | November 2015 | Marks available | 1 | Reference code | 15N.3.SL.TZ0.19 |
| Level | Standard level | Paper | Paper 3 | Time zone | TZ0 |
| Command term | State | Question number | 19 | Adapted from | N/A |
Question
The distributions of many terrestrial organisms are currently shifting in latitude in response to changing climate. The graph shows the latitudinal shifts of the northern range boundaries of species within two taxonomic groups that were observed over 25 years in Britain. Positive latitudinal shifts indicate that a species now inhabits areas further to the north than it did before and negative shifts indicate that the northern edge of the range has moved south.
State which taxonomic group shows the greatest median shift.
Calculate the percentage of ground beetles that are below the zero shift.
Compare the changes in the range of ground beetles with the changes in the range of spiders.
Spiders and ground beetles are both predators. Discuss possible effects on other species resulting from the latitudinal shift of the predators.
Markscheme
spider
16.75(%)
Accept answer in the range of 16.5 (%) to 17(%).
a. both taxonomic groups showed movement to the north;
b. slightly more spiders moved north;
c. spiders shows the furthest northern shift;
d. range of ground beetles extends further south (than spiders);
e. the spiders’ biggest movement is 75 to 100 km to the north and the ground beetles’ biggest movement is 50 to 75 km to the north;
f. overall spiders have a broader range;
a. competition for resources/food/space/other resource;
b. change in predation/number of other species;
c. change/decrease/increase in biodiversity;
d. food webs may change;
| 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.
| Date | November 2009 | Marks available | 2 | Reference code | 09N.3.SL.TZ0.20 |
| Level | Standard level | Paper | Paper 3 | Time zone | TZ0 |
| Command term | Outline | Question number | 20 | Adapted from | N/A |
Question
Outline one example of herbivory.
State the units used in a pyramid of energy.
Explain the small biomass of organisms in higher trophic levels.
Markscheme
named example of herbivore;
named example of plant;
e.g. aphid
rose
kJ m-2 yr-1 / kilojoules per meter squared per year / example of energy per unit area per time unit (must be metric units)
much loss of energy / 10/20 % retained / 80/90 % loss of energy;
respiration;
egestion;
less valuable as a food source than primary producers;