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Date November 2017 Marks available 3 Reference code 17N.2.SL.TZ0.1
Level Standard Level Paper Paper 2 Time zone Time zone 0
Command term Identify Question number 1 Adapted from N/A

Question

Define the term carrying capacity.

[1]
a.i.

Identify three reasons why carrying capacity can be difficult to estimate.

[3]
a.ii.

Markscheme

the maximum number of individuals/load of a species that can be sustainably supported by a given area/habitat/environment OWTTE;

NB. Definition needs to make clear that cc is associated with a single species. This means that: “The maximum number of a species that can...etc” is acceptable, but “the maximum number of species that can…” is incorrect, and should not be credited.

a.i.

Generally:
there are many different potential limiting factors for natural populations;
populations’ needs may change through time due to genetic changes/evolution;
environmental conditions may change eg climate change/introduced species;
it takes extensive/long-term study to identify a precise relationship between a species and given environmental factor;


For human populations:
human populations exploit/depend upon a far greater range of different resources than most other species;
(human ingenuity) humans are able to substitute one resource/material for another;
variations in lifestyle/culture/economic status between human populations mean different resources/amounts of resources are used/needed;
the importation of resources from other ecosystems/regions can offset a lack of resources in an area;
technological developments cause changes in resources required/available over time;

Award [1] for each correct reason identified, up to [3 max]

Do not credit responses addressing changing population size (has no influence on carrying capacity).

a.ii.

Examiners report

Although, in other contexts, allowances are made for linguistic imperfections, for the purpose of a “define” question, language does need to be precise. For example, in response to this question the phrase “maximum number of a species” means something quite different to “maximum number of species” …and many responses used the latter concept which is incorrect. Similarly, a number of responses omitted the key element of “sustainably” (i.e. as in “…can be sustainably supported”)

a.i.

Candidates often found one valid difficulty in estimating carrying capacity but few went further. A significant minority confused the estimation of carrying capacity, with the estimation of population size.

a.ii.

Syllabus sections

Topic 2: Ecosystems and ecology » 2.1 Species and populations
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Topic 8: Human systems and resource use » 8.4 Human population carrying capacity
Topic 2: Ecosystems and ecology
Topic 8: Human systems and resource use

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