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Date November 2019 Marks available 4 Reference code 19N.3.SL.TZ0.11
Level Standard level Paper Paper 3 Time zone TZ0 / no time zone
Command term Explain Question number 11 Adapted from N/A

Question

Ensuring the delivery of water to homes requires a pressure to be maintained in the pipes. Biofilm formation will reduce the pressure in the pipes. Three experimental water piping systems were set up and the water was treated before entering the system in one of the following three ways:
• untreated water (Control)
• ultrafiltration (UF) filters particles <500 nm
• nanofiltration (NF) filters particles <1 nm.

The drop in pressure of the water coming out of the tap at the end of the system compared to the pressure of water entering the system was measured.

[Source: reprinted from Water Research, 47(8), G. Liu, M.C. Lut, J.Q.J.C. Verberk, J.C. Van Dijk, A comparison of additional
treatment processes to limit particle accumulation and microbial growth during drinking water distribution, pp 2719–2728,
Copyright (2013), with permission from Elsevier ]

Compare and contrast the effect of ultrafiltration and nanofiltration on the drop in pressure.

[3]
a.

State one other way in which the formation of biofilms can be inhibited.

[1]
b.

Some biological systems show emergent properties. Emergent properties arise from the interaction of the component parts of a system that are not predictable from studying the individual components.

Explain how biofilms show emergent properties.

[4]
c.

Markscheme

a. both cause pressure to drop ✔

b. pressure always higher in both compared to control ✔

c. nanofiltration causes least drop in pressure
OR
ultrafiltration causes the most drop in pressure ✔

d. the drop in pressure for ultrafiltration is more irregular than for nanofiltration ✔

a.

using bacteriophages/viruses
OR
adding biocides/bactericides/chlorine
OR
using cell dispersal agents ✔

b.

a. biofilms are composed of different species of bacteria/communities of microbes ✔

b. ‹biofilms› form an extracellular film/slime/EPS/exopolipeptide/exopolysaccharides ✔

c. microbes of biofilms show coordination/cooperation/quorum sensing ✔

d. individual microbes have a greater chance of survival in the biofilm «than on their own» ✔

e. biofilms have antibiotic resistance ✔

f. there are exchanges of nutrients between the microbes which is not possible for individual cells ✔

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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Option B: Biotechnology and bioinformatics » Option B: Biotechnology and bioinformatics (Core topics)
Option B: Biotechnology and bioinformatics

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