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Date May 2019 Marks available 1 Reference code 19M.3.HL.TZ1.11
Level Higher level Paper Paper 3 Time zone Time zone 1
Command term Outline Question number 11 Adapted from N/A

Question

Some halophilic bacteria biodegrade benzene, which makes them useful in treating oil spills as benzene is contained in crude oil. Investigators added cultures of the bacteria to benzene solutions at different salinities in containers. The amount of benzene remaining in the container was recorded once a week for two weeks.

[Source: adapted from C A Nicholson and B Z Fathepure, (2004),
Applied and Environmental Microbiology, 70 (2), pages 1222–1225]

Outline what is meant by halophilic when describing the bacteria.

[1]
a.

Identify the salt concentration with the greatest rate of benzene biodegradation.

………………......… mol m–3

[1]
b.

State one genus of halophilic bacteria known to biodegrade benzene.

[1]
c.

Suggest one advantage to the bacteria of breaking down benzene.

[1]
d.

Markscheme

thrive/live in a salt rich environment ✔

a.

1 mol m–3

b.

Marinobacter ✔

Allow other correct responses eg: Dechloromonas, Haloferax, Pseudomonas, Fusarium, Halomonas, Halococcus,
Halobacterium, Haloarcula, Haloarchaea, Fundibacter, Fusarium, Alcanivorax, Dietzia

c.

a. energy gained from the benzene ✔ 

b. benzene acts as a source of carbon ✔

d.

Examiners report

(a) to (c) These three questions were often answered well.

a.

(a) to (c) These three questions were often answered well.

b.

(a) to (c) These three questions were often answered well.

c.

Very few students could state that the breakdown of benzene could be used as a source of carbon or energy.

d.

Syllabus sections

Option B: Biotechnology and bioinformatics » Option B: Biotechnology and bioinformatics (Core topics) » B.3 Environmental protection
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