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Date November 2018 Marks available 1 Reference code 18N.3.HL.TZ0.15
Level Higher level Paper Paper 3 Time zone TZ0 / no time zone
Command term Deduce Question number 15 Adapted from N/A

Question

The graph shows a theoretical model that divides species into five ecological groups (I to V) related to the degree of tolerance to an increasing pollution gradient.

[Reprinted from Marine Pollution Bulletin, 40, A. Borja, J. Franco and V. Perez, 'A marine biotic index to establish the ecological quality of soft-bottom benthos within European estuarine and coastal environments', pp. 1100–1114, Copyright (2000), with permission from Elsevier. https://www.sciencedirect.com/journal/marine-pollution-bulletin]

The biotic index is calculated using the formula shown.

BI = Σ ( n i × a i ) N

Identify the group that is most intolerant to pollution.

[1]
a.

Deduce the meaning of ni in this formula.

[1]
b.i.

Deduce the meaning of ai in this formula.

[1]
b.ii.

Outline how organisms in Group V could be used to measure pollution in an environment.

[3]
c.

Markscheme

«group» I ✔

a.

number of individuals of a species ✔

b.i.

tolerance rating of that species ✔

b.ii.

a. group V organisms «could» contain indicator species ✔

b. group V organisms can survive in polluted environments «while others cannot» ✔

c. they have a high tolerance/BI index
OR
«relative number of» indicator species can be used to calculate the value of a biotic index ✔

d. the more group V present could indicate more pollution ✔
OWTTE

e. absence of group V could indicate a cleaner environment ✔

c.

Examiners report

[N/A]
a.
[N/A]
b.i.
[N/A]
b.ii.
[N/A]
c.

Syllabus sections

Option C: Ecology and conservation » Option C: Ecology and conservation (Core topics) » C.4 Conservation of biodiversity
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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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