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Date May 2018 Marks available 3 Reference code 18M.3.HL.TZ1.11
Level Higher level Paper Paper 3 Time zone Time zone 1
Command term Explain Question number 11 Adapted from N/A

Question

Some microorganisms can form a biofilm on living or non-living surfaces. The image shows a Staphylococcus aureus biofilm inside a medical catheter.

Define biofilm.

[1]
a.i.

Explain the difficulties of treating microorganisms growing in biofilms.

[3]
a.ii.

Explain the use of a named bacterium in bioremediation.

[3]
b.

Markscheme

«a biofilm is» any group of microorganisms in which cells stick to each other on a surface

OR

«a biofilm is» any group of microorganisms in which cells cooperatively produce a polysaccharide matrix

a.i.

a. biofilms show properties that are not shown by the individual cells / biofilms develop emergent properties 

b. quorum sensing changes microbial behaviour/production of matrix 

c. (matrix) hard to remove from a surface 

d. biofilms are tolerant to desiccation and heat shock 

e. biofilms may be very resistant to the action of (many) antibiotics/antimicrobial agents 

f. because cell division in biofilms is slow, antibiotics targeting this will be ineffective 

OR

matrix forms a barrier to antibiotics

a.ii.

a. (bioremediation is the) use of microorganisms to consume/break down pollutants 

b. name of bacterium (genus required) and contaminating substance 

c. outline one action of (this) bacterium to remove environmental contaminants from water or soil 

d. another detail of use of (this) bacterium to remove the contaminant 

e. advantage/disadvantage of using this bacterium

 

b. e.g. some Pseudomonas to remove oil spills 

c. uses crude oil for energy / breaks down crude oil 

d. e.g. bacteria also need other chemicals/process may be speeded up by adding essential inorganic nutrients (phosphates/nitrates) 

OR

b. e.g. Pseudomonas used to remove methyl mercury

c. bacteria (Pseudomonas) degrade methyl mercury into elemental mercury and methane 

d. methyl mercury is very toxic / can be biomagnified in food chain

b.

Examiners report

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

Syllabus sections

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