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Date May 2017 Marks available 2 Reference code 17M.3.HL.TZ2.10
Level Higher level Paper Paper 3 Time zone Time zone 2
Command term Outline Question number 10 Adapted from N/A

Question

Compounds containing the cyanide group (CN) are used to help extract gold from gold-containing rocks called ore. The process results in heaps of rocks that are contaminated with cyanide, a toxin that can inhibit cellular respiration. The bacterium Pseudomonas fluorescens degrades cyanide to ammonia (NH3 ), which is less toxic.

In an effort to explore the conditions that lead to maximum degradation of cyanide, researchers sprayed different samples of cyanide-processed ore with one of three solutions:

• a sterile solution
• a solution containing a culture of P. fluorescens
• a solution containing a culture of P. fluorescens and sucrose.

Outline the evidence that P. fluorescens can degrade the cyanide.

[2]
a.

Suggest how the addition of sucrose promotes the degradation of cyanide. 

[1]
b.

With respect to the degradation of cyanide by P. fluorescens, explain what is meant by bioremediation.

[2]
c.

Markscheme

a. in sterile solution/control there is no degradation of cyanide but there is in the solutions with P. fluorescens 
OWTTE

b. in solution containing P. fluorescens and sucrose degradation of cyanide higher than without sucrose 

c. control with sucrose «only» missing to establish causality OWTTE

a.

«organic» carbon source «necessary for the reaction to degrade cyanide»
OR
sucrose provides the energy source

b.

a. bioremediation is the use of organisms to degrade pollution/toxins in the environment 

b. P. fluorescens necessary to degrade cyanide which is toxic to the environment OWTTE

c. often involves supplementing with nutrients/carbon source/aeration

c.

Examiners report

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

Syllabus sections

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