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Date May 2018 Marks available 1 Reference code 18M.3.HL.TZ1.14
Level Higher level Paper Paper 3 Time zone Time zone 1
Command term Outline Question number 14 Adapted from N/A

Question

The sea star Pisaster ochraceus is identified as a keystone species in the Pacific Ocean.

Outline the characteristics of keystone species in an ecosystem.

[1]
a.

Outline one example of mutualism.

[2]
b.

Markscheme

a. keystone species has a strong/disproportionate effect on a community/food web/ecosystem 

b. absence of keystone species would completely alter the ecosystem

a.

a. example of mutualistic species 

b. description of mutualism

Accept commonplace names for organisms in (a)

Examples:

a. oxpecker (bird) and therhinoceros/zebra 

b. oxpeckers/bird on rhinos/zebras eat parasites getting food while rhino/zebra get pest control

OR

a. hummingbird hawk-moth and Dianthus

b. (hummingbird hawk) moth gets nectar from flower while it pollinates the flower

b.

Examiners report

[N/A]
a.
[N/A]
b.

Syllabus sections

Option C: Ecology and conservation » Option C: Ecology and conservation (Core topics) » C.1 Species and communities
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Option C: Ecology and conservation » Option C: Ecology and conservation (Core topics)
Option C: Ecology and conservation

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