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Date November 2019 Marks available 3 Reference code 19N.3.HL.TZ0.11
Level Higher level Paper Paper 3 Time zone TZ0 / no time zone
Command term Explain Question number 11 Adapted from N/A

Question

Cupriavidus metallidurans CH34 is a heavy metal-resistant bacterium that was genetically modified to be used for bioremediation. The merB gene that controls the conversion of organic mercury into inorganic mercury was introduced in the bacterium. The gel electrophoresis image below shows the presence of the merB gene in two strains after 70 generations.

[Source: Copyright © 2011 Rojas LA, Yáñez C, González M, Lobos S, Smalla K, Seeger M (2011) Characterization of the
Metabolically Modified Heavy Metal-Resistant Cupriavidus metallidurans Strain MSR33 Generated for Mercury Bioremediation.
PLoS ONE 6(3): e17555. https://doi.org/10.1371/journal.pone.0017555]

Outline the aims and methods of bioremediation.

[2]
a.

The generation time of C. metallidurans is a few hours. Two strains of the bacterium were tested for the presence of the merB gene 70 generations after the genetic modification. Suggest one reason for carrying out these tests after 70 generations of the transgenic bacterium.

[1]
b.

Explain the use of Pseudomonas in bioremediation.

[3]
c.

Markscheme

Aims [1 mark]
a. the addition of organisms to remove environmental contaminants
OR
the addition of organisms to convert toxic compounds to non-toxic products ✔

Methods [1 max]
b. physical and chemical procedures can be combined with bioremediation ✔

c. e.g. clean-up of oil spills using bacteria
OR
clean-up of heavy metals using plants and incineration ✔

Accept other valid methods involving living organisms.
Do not accept physical methods alone.

a.

to observe that it was stable
OR
to confirm that change was permanent
OR
to confirm that merB gene still present after many generations ✔

b.

a. used to clean up oil
OR
used to clean up mercury ✔

b. used after other clean-up methods have been used ✔

c. nutrient concentrations have to be sufficient to support the maximal growth rate of the bacteria throughout the clean-up operation ✔

d. converts methylmercury into inorganic mercury «less toxic» ✔

e. converts oil into CO2, water and simpler compounds «non-pollutant» ✔

f. produces extracellular digestive enzymes «lipase» ✔

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.2 Biotechnology in agriculture
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Option B: Biotechnology and bioinformatics » Option B: Biotechnology and bioinformatics (Core topics)
Option B: Biotechnology and bioinformatics

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